EPA 625/1-77-008
(COE EM1110-1-501)
PROCESS DESIGN MANUAL
FOR
LAND TREATMENT OF
MUNICIPAL WASTEWATER
U.S. ENVIRONMENTAL PROTECTION AGENCY
Environmental Research Information Center
Technology Transfer
Office of Water Program Operations
U.S. ARMY CORPS OF ENGINEERS
U.S. DEPARTMENT OF AGRICULTURE
October 1977
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ACKNOWLEDGMENTS
There were three groups of participants involved in the preparation of
this manual: (1) the contractor-authors, (2) an interagency workgroup,
and (3) the group of experts and invited reviewers. The interagency
workgroup defined the scope of the effort, guided the work of the
contractor, and was responsible for manual review. The membership of
each group is listed below.
CONTRACTOR: Metcalf & Eddy, Inc., Palo Alto, California
Supervision: C. Pound, Vice President
Senior Author: R. Crites, Project Manager
Staff Authors: J. Esmay, D. Griffes, J. Olson, J. Powers, R. Shedden, R.
Smith, A. Uiga
Consultant Authors: Dr. F. Broadbent, University of California, Davis
Dr. P. Pratt, University of California, Riverside
Dr. A. Wallace, University of Idaho
Dr. J. Melnick, Dr. C. Gerba, Dr. S. Goyal,
Baylor University
Dr. R. Burau, University of California, Davis
INTERAGENCY WORKGROUP
Chairmen: B. Seabrook, OWPO, EPA
N. Urban, COE
Deputy Chairmen: R. Bastian, OWPO, EPA
S. Reed, CRREL, COE
Project Officer: Dr. J.E. Smith, Jr.,
ERIC, EPA
Members: W. Whittington, OWPO, EPA
R. Thomas, RSKERL, EPA
R. Dean, Region VIII, EPA
H. Thacker, OALWU, EPA
C. Rose, FHA, USDA
G. Loomis, USDA
R. Duesterhaus, USDA
Dr. J. Parr, ARS, USDA
Dr. P. Hunt, ARS, USDA
Dr. W. Larson, ARS, USDA
Col. T. Bishop, COE
D. Knudson, COE
Dr. H. McKim, CRREL, COE
EXPERTS AND INVITED REVIEWERS
Dr. H. Bouwer, Director, WCL,
USDA/ARS
Dr. C. Lance, ARS, USDA
Dr. R. Loehr, Cornell
University
Dr. W. Jewell, Cornell
University
Dr. T. Hinesly, University
of Illinois
Dr. M. Kirkham, Oklahoma
State University
Dr. E. Lennette, M.D.,
California Health Department
E. Sepp, California Health
Department
Lt. Col. V. Ciccone, USAMD
Capt. J. Glennon, USAMD
H. Pahren, HERL, EPA
Dr. C. Enfield, RSKERL, EPA
Dr. L. Carpenter, M.D., Former
Director, Oklahoma State
Health Department
R. Sletten; A. Palazzo;
J. Bouzon; CRREL, COE
Dr. R. Lee, USAE, WES, COE
R. Madancy, OWRT, USD I
J. Dyer, OWRT, USD I
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ABSTRACT
This manual presents a rational procedure for the design of land
treatment systems. Slow rate, rapid infiltration, and overland flow
processes for the treatment of municipal wastewaters are given emphasis.
The basic unit operations and unit processes are discussed in detail, and
the design concepts and criteria are presented.
The manual includes design examples as well as actual case study
descriptions of operational systems. Information on planning and field
investigations is presented along with the process design criteria for
both large and small scale systems.
m
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CONTENTS
Chapter Page
ACKNOWLEDGMENTS i i
ABSTRACT 11i
CONTENTS iv
FIGURES viii
TABLES xii
FOREWORD xviii
1 INTRODUCTION
1.1 Background and Purpose 1-1
1.2 Objectives 1-3
1.3 Scope of the Manual" 1-3
1.4 Guide to Intended Use 1-4
1.5 References 1-5
2 TREATMENT PROCESS CAPABILITIES AND OBJECTIVES
2.1 Introduction 2-1
2.2 Slow Rate Process 2-1
2.3 Rapid Infiltration 2-9
2.4 Overland Flow 2-11
2.5 Other Processes 2-14
2.6 References 2-19
3 TECHNICAL PLANNING AND FEASIBILITY ASSESSMENT
3.1 Purpose and Scope 3-1
3.2 Approach to Development of Alternatives 3-2
3.3 Evaluation of Unit Processes 3-4
3.4 Wastewater Quality 3-12
3.5 Regional Site Characteristics 3-15
3.6 Other Planning Considerations 3-31
3.7 Evaluation of Alternative Systems 3-44
3.8 References 3-57
4 FIELD INVESTIGATIONS
4.1 Introduction 4-1
4.2 Wastewater Characteristics 4-2
4.3 Soil Physical and Hydraulic Properties 4-2
4.4 Soil Chemical Properties 4-2
4.5 Other Field Investigations 4-4
4.6 References 4-9
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CONTENTS (Continued)
Chapter Page
5 PROCESS DESIGN
5-1
5-26
5-30
5-38
5-70
5-77
5-94
5-99
5-102
6-1
6-1
6-14
6-22
6-28
7-1
7-2
7-10
7-18
7-26
7-32
7-41
7-44
7-53
7-60
7-67
7-71
7-76
7-77
8
5.1
5.2
5.3
5.4
5.5
5.6
5.7
5.8
5.9
SMALL
6.1
6.2
6.3
6.4
6.5
CASE
7.1
7.2
7.3
7.4
7.5
7.6
7.7
7.8
7.9
7.10
7.11
7.12
7.13
7.14
Land Treatment Process Design
Preappli cation Treatment
Storage
Distribution
Management of Renovated Water
Vegetation
System Monitoring
Facilities Design Guidance
References
SYSTEMS
General Considerations
Design Procedures
Facilities Design
Small System Design
References
STUDIES
Introduction
Pleasanton, California
Walla Walla, Washington
Bakersfield, California
San Angelo, Texas
Muskegon, Michigan
St. Charles, Maryland
Phoenix, Arizona
Lake George, New York
Fort Devens, Massachusetts
Pauls Valley, Oklahoma
Paris, Texas
Other Case Studies
References
DESIGN EXAMPLE
8.1
8.2
8.3
8.4
8.5
8.6
8.7
8.8
Introduction
Statement of Problem
Design Data
Process Alternatives
Preliminary Performance Estimate
Cost Comparison
Process. Design
References
8-1
8-1
8-1
8-8
8-12
8-15
8-16
8-25
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CONTENTS (Continued)
Appendix Page
A NITROGEN
A.I Introduction A-l
A.2 Nitrogen Transformations A-l
A.3 Nitrogen Removal from the Soil System A-9
A.4 Nitrogen Removal with Various Application Systems A-21
A.5 Summary A-28
A.6 References A-29
B PHOSPHORUS
B.I Introduction B-l
B.2 Removal Mechanisms B-2
B.3 Phosphorus Removal by Land Treatment Systems B-10
B.4 Models B-19
B.5 References B-27
C HYDRAULIC CAPACITY
C.I Introduction C-l
C.2 Hydraulic Properties C-l
C.3 Soil Infiltration Rate and
Permeability Measurements C-l2
C.4 Groundwater Flow Investigations C-31
C.5 Groundwater Mound Height Analysis C-35
C.6 Control of the Groundwater Table C-44
C.7 Relationship Between Measured Hydraulic
Capacity and Actual Operating Capacity C-46
C.8 References C-47
D PATHOGENS
D.I Introduction D-l
D.2 Relative Public Health Risk D-l
D.3 Pathogens Present in Wastewater D-l
D.4 Bacterial Survival D-6
D.5 Virus Survival D-9
D.6 Movement and Retention of Bacteria in Soil D-ll
D.7 Movement and Retention of Viruses in Soil D-14
D.8 Potential Disease Transmission Through
Crop Irrigation D-20
D.9 Potential Disease Transmission by Aerosols D-22
D.10 References D-25
E METALS
E.I Introduction E-l
E.2 Metals in Wastewater E-l
E.3 Receiving Soils E-6
E.4 Chemistry of Metals in Soil E-10
E.5 Environmental Benefits from Metal
Addition to Soil E-19
VI
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CONTENTS (Concluded)
Appendixes
E.6 Environmental Impact from Metal
Addition to Soil
E.7 References
FIELD INVESTIGATION PROCEDURES
F.I Introduction
F.2 Crop Water Requirements
F.3 Soil Investigations
F.4 References
Page
E-22
E-35
F-l
F-l
F-4
F-21
GLOSSARY. CONVERSION FACTORS, AUTHOR INDEX,
SUBJECT INDEX
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FIGURES
No. Page
2-1 Slow Rate Land Treatment 2-5
2-2 Rapid Infiltration 2-10
2-3 Overland Flow 2-13
2-4 Subsurface Application to Soil Mound Over Creviced Bedrock 2-18
3-1 Planning Sequence for the Development of Land Treatment
Alternatives 3-3
3-2 Potential Evapotranspiration Versus Mean Annual
Precipitation 3-6
3-3 Soil Permeability Versus Ranges of Application Rates for
Slow Rate and Rapid Infiltration Treatment 3-7
3-4 Examples of Combined Systems 3-9
3-5 Total Land Requirement (Includes Land for Application,
Roads, Storage, and Buildings) 3-11
3-6 Estimated Wastewater Storage Days Based Only on Climatic
Factors 3-13
3-7 Proportions of Sand, Silt, and Clay in the Basic Soil-
Textural Classes 3-22
3-8 Dominant Water Rights Doctrines and Areas of Water
Surplus or Deficiency 3-33
3-9 Public Acceptability of Renovated Water Reuse 3-43
4-1 Closed and Open Barrel Augers and Tiling Spade 4-6
4-2 Soil Profile With Two Horizons 4-7
4-3 Typical Drill Rig Used for Soil Borings 4-8
5-1 Slow Rate Design Procedure 5-5
5-2 Rapid Infiltration Design Procedure 5-11
5-3 Effect of Infiltration Rate on Nitrogen Removal for
Rapid Infiltration, Phoenix, Arizona 5-15
5-4 Overland Flow Design Procedure 5-18
5-5 Principal Nitrogen Transformations in Wetlands 5-24
5-6 Wetland System at Brillion Marsh, Wisconsin 5-25
5-7 Determination of Storage by EPA Computer Programs and
Water Balance According to Climatic Constraints 5-32
5-8 Surface Distribution Methods . 5-40
5-9 Plastic Siphon Tube for Furrow Irrigation 5-45
5-10 Aluminum Hydrant and Gated Pipe for Furrow Irrigation 5-46
5-11 Outlet Valve for Border Strip Application 5-49
5-12 Natural Drainage of Renovated Water Into Surface Water 5-50
5-13 Rapid Infiltration Basin Influent Structure 5-51
5-14 Overland Flow Slope (8%) at Utica, Mississippi 5-52
5-15 Alfalfa Valve Characteristics 5-54
5-16 Orchard Valve Characteristics 5-55
5-17 Hand Moved Sprinkler Systems 5-57
5-18 Mechanically Moved Sprinkler System 5-58
5-19 Permanent Solid Set Sprinkler System 5-59
5-20 Stationary Gun Sprinkler Mounted on a Tractor Trailer 5-61
5-21 Traveling Gun Sprinkler 5-62
5-22 Side Wheel Roll Sprinkler System 5-63
5-23 Center Pivot Rig 5-64
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FIGURES (Continued)
No. Page
5-24 Center Pivot Irrigation System 5-64
5-25 Rotating Boom, Fan Sprinkler, Ada, Oklahoma 5-66
5-26 Collection of Renovated Water by Drain 5-73
5-27 Trenching Machine for Installation of Drain Tile 5-74
5-28 Plan and Cross Section of Two Parallel Recharge Basins
With Wells Midway Between Basins 5-75
5-29 Effect of Selected Vegetation on Soil Infiltration Rates 5-78
5-30 Infiltration Rates for Various Crops 5-79
5-31 Crop Growth and Nitrogen Uptake Versus Days From Planting
for Forage Crops Under Effluent Irrigation 5-84
5-32 Schematic of Groundwater Flow Lines and Alternative
Monitoring Well Locations 5-97
6-1 Small System Design Procedure 6-3
6-2 Estimated Wastewater Storage Days Based Only on Climatic 6-4
Factors
6-3 Schematic for Typical Slow Rate System 6-15
6-4 Schematic for Typical Rapid Infiltration System 6-19
6-5 Schematic for Typical Overland Flow System 6-21
6-6 Bubbling Orifice Distribution for Overland Flow 6-22
7-1 Land Treatment System, City of Pleasanton 7-4
7-2 Irrigated Pasturelarid, Pleasanton, California 7-6
7-3 Portable Sprinkler System, Pleasanton, California 7-6
7-4 Schematic Flow Diagram, Wastewater Treatment Plant,
Walla Walla, Washington 7-13
7-5 Large Diameter Sprinkler Gun for Industrial Wastewater
Application Used at Walla Walla, Washington 7-16
7-6 Alfalfa Harvesting Equipment, Sprinkler Riser, and
Impact Head at City Irrigation Site, Walla Walla,
Washington 7-16
7-7 Existing Wastewater Irrigation System, Bakersfield,
California 7-21
7-8 Proposed Wastewater Irrigation System, Bakersfield,
California 7-25
7-9 Slow Rate Land Treatment System at San Angelo, Texas 7-28
7-10 Coastal Bermuda Grass Hay at San Angelo, Texas 7-29
7-11 Border Strip Irrigation of Pasture at San Angelo, Texas 7-29
7-12 Muskegon Project Land Treatment Site Plan 7-34
7-13 Center Pivot Boom With Low Pressure Nozzle, Muskegon
Project 7-35
7-14 Installation of Drainage Tiles, Muskegon Project 7-37
7-15 Layout of the 23rd Avenue Rapid Infiltration and Recovery
Project 7-47
7-16 Inlet Structure, 23rd Avenue Project, Phoenix, Arizona 7-48
7-17 Schematic of the 23rd Avenue Rapid Infiltration and
Recovery System 7-50
7-18 Rapid Infiltration Basin, Lake George, New York 7-55
7-19 Operational Basin Covered With Ice, Lake George,
New York 7-55
7-20 Lake George Village Wastewater Treatment Plant and
Sampling Locations 7-56
IX
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FIGURES (Continued)
No.
7-21 Land Treatment System, Fort Devens, Massachusetts 7-63
7-22 Distribution Channel Into Rapid Infiltration Basin,
Fort Devens, Massachusetts 7-64
7-23 Grass Covered Infiltration Basins, Fort Devens,
Massachusetts 7-64
7-24 Fixed Fan Nozzle, Pauls Valley, Oklahoma 7-69
7-25 Bubbling Orifice for Wastewater Application, Pauls Valley,
Oklahoma 7-70
7-26 Overland Flow Terraces at Paris, Texas 7-75
8-1 General Topography 8-5
8-2 Agricultural Soil Map 8-6
8-3 Existing Vegetative Cover 8-9
A-l Nitrate in Effluent From a Column of Salado Subsoil
Receiving 3 in./wk of Wastewater Containing 42 mg/L
NH|-N, Showing High-Nitrate Wave A-4
A-2 Effect of Input NHJ-N Concentration on N Removal From
Wastewater Applied to Panoche Sandy Loam at the Rate
of 3 in./wk for 6 Months A-l3
A-3 Yield, Crop Uptake of N, and Potentially Leachable
Nitrate in Relation to Fertilizer Application Rate on
Corn Grown on Hanford Sandy Loam • A-16
A-4 Clay Fixed NHt in Three Soils Resulting From Five
Applications of a Solution Containing 100 mg/L NH^-N,
Without Intervening Drying A-l8
A-5 Exchangeable NH^ in the Profile of a Sandy Soil Beneath
a Sludge Pond as Compared to an Untreaited Area A-20
A-6 Effect of 36 Years of Wastewater Application on
Organic N in a Soil at Bakersfield, California A-22
B-l Relationships Between Phosphorus Concentration and Soil
Depth for Abrupt and Diffuse Boundaries Between
Enriched and Nonenriched Soil B-4
B-2 Net Phosphorus Application to the Soil B-l2
B-3 Relationship Among Phosphorus Concentration, Drainage
Flow, and the Amount of Phosphorus Transfer From
Land to Streams B-14
B-4 Illustration of a Simple Phosphorus Balance -
Phosphorus Reaction Model for a Slow Rate System B-24
C-l Soil-Water Characteristic Curves for Several Soils C-3
C-2 Field Capacity Relationship C-4
C-3 Schematic Showing Relationship of Total Head (H),
Pressure Head (h), and Gravitation Head (Z) for
Saturation Flow C-7
C-4 Permeability as a Function of the Matric Potential
for Several Soils C-9
C-5 Infiltration Rate as a Function of Time for
Several Soils C-10
C-6 Porosity, Specific Retention, and Specific Yield
Variations with Grains Size, South Coastal Basin,
California C-ll
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FIGURES (Concluded)
No. Page
C-7 Infiltration Rate Curves Showing the Influence of Initial
Water Content, 0 (Fraction by Volume), on Infiltration
Rate Computed for Yolo Light Clay C-13
C-8 Cumulative Intake Curves Showing the Infiltration of
Water Into.Soil From Single Ring Infiltrometers C-15
C-9 Typical Pattern of the Changing Moisture Profile
During Drying and Drainage C-16
C-10 Flooding Basin Used for Measuring Infiltration C-20
C-ll Layout of Sprinkler Infiltrometer C-21
C-12 Cylinder Infiltrometer in Use C-23
C-13 Variability of Infiltrometer Test Results on
Relatively Homogeneous Site C-26
C-14 Number of Tests Required for 90% Confidence That the
Calculated Mean is Within Stated Percent of the True Mean C-28
C-15 Number of Tests Required for 95% Confidence That the
Calculated Mean is Within Stated Percent of the True Mean C-28
C-16 Lysimeter Cross-Section C-29
C-17 Mound Development for Strip Recharge C-36
C-18 Mound Development for Circular Recharge Area C-36
C-19 Definition Sketch for Auger-Hole Technique C-41
C-20 Experimental Setup for Auger-Hole Technique C-41
C-21 Definition Sketch for Drain Spacing Formula C-45
D-l Virus Adsorption by Various Soils as a Function of pH D-16
E-l Patterns of Distribution of Trace Elements With
Depth in Soil Profiles E-9
E-2 Effect of pH on Adsorption of Metal by Oxides
and Silicates E-16
E-3 Typical Adsorption Isotherm for Metal Salt Addition
to a Soil- or Sediment-Water System E-17
E-4 Schematic Response of a Typical Plant Species to
Increasing Zinc Addition to a Soil E-21
E-5 Calculated Accumulation of Cadmium in Soil at
Constant Annual Input • E-26
E-6 Log-Log Plot of Dry Matter Production of Sweet Corn as
a Function of Zinc (Zinc Acetate) Additions to Soil E-29
F-l Nomograph for Determining the SAR Value of Irrigation
Water and For Estimating the Corresponding ESP Value
of a Soil That is at Equilibrium with the Water F-15
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TABLES
No. Page
1-1 Selected Early Land Application Systems 1-2
1-2 U.S. Municipalities Using Land Treatment 1-2
2-1 Comparison of Design Features for Land Treatment Processes 2-2
2-2 Comparison of Site Characteristics for Land
Treatment Processes 2-3
2-3 Expected Quality of Treated Water from Land
Treatment Processes 2-4
2-4 Treatment Performance for Two Artificial Wetland
Systems on Long Island 2-15
2-5 Treatment Capability of Water Hyacinths Fed
Oxidation Pond Effluent 2-16
2-6 Treatment Performance of Peatland in Minnesota 2-17
2-7 Treatment Performance of an Experimental Soil
Mound System in Wisconsin 2-19
3-1 Applicability of Recovery Systems for
Renovated Water 3-14
3-2 Important Constituents in Typical Domestic Wastewater 3-14
3-3 Typical BOD Loading Rates 3-15
3-4 Concentration of Trace Elements in Various U.S.
Wastewaters 3-16
3-5 Site Selection Guidelines 3-18
3-6 Soil Textural Classes and General Terminology Used
in Soil Descriptions 3-23
3-7 Permeability Classes for Saturated Soil 3-24
3-8 Typical Soil Permeabilities and Textural Classes
for Land Treatment Processes 3-24
3-9 Summary of Climatic Analyses 3-27
3-10 Average Values of Nitrogen and Phosphorus Measured in
Agricultural Stormwater Runoff Studies 3-29
3-11 Summary of Agricultural Nonpoint Sources Characteristics 3-30
3-12 Potential Water Rights Problems for Land
Treatment Alternatives 3-34
3-13 Checklist of Capital Costs for Alternative
Land Treatment Systems 3-46
3-14 Suggested Service Life for Components of an
Irrigation System 3-47
3-15 Checklist of Annual Operation and Maintenance Costs
for Alternative Land Treatment Systems 3-49
3-16 Requirements for Land Leasing for PL 92-500
Grant Funding 3-51
3-17 Cost Tradeoff Considerations for Land Treatment Systems 3-53
3-18 Nonmonetary Factors for Evaluation of Alternatives 3-53
3-19 Comparison of Effluent Quality for Conventional, Land
Treatment,.and Advanced Wastewater Treatment Systems 3-55
4-1 Summary of Field Tests for Land Treatment Processes 4-1
4-2 Relationship of Potential Problems to Concentrations of
Major Inorganic Constituents in Irrigation Waters
for Arid and Semi arid Climates 4-3
4-3 Interpretation of Soil Physical and Hydraulic Properties 4-4
xn
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TABLES (Continued)
No. Page
4-4 Interpreptation of Soil Chemical Tests 4-5
4-5 Probable Soil Characteristics Indicated by Plants . 4-9
5-1 EPA-Proposed Regulations on Interim Primary
Drinking Water Standards, 1975 5-3
5-2 Typical Values of Crop Uptake of Nitrogen 5-6
5-3 Factors Favoring Denitrification in the Soil 5-7
5-4 Suggested Maximum Applications of Trace Elements
to Soils Without Further Investigation 5-10
5-5 Typical Hydraulic Loading Rates for RI Systems 5-12
5-6 Typical Hydrualic Loading Cycles 5-13
5-7 BOD and Suspended Solids Data for Selected Rapid
Infiltration Systems 5-16
5-8 Fecal Coliform Removal in Selected Rapid
Infiltration Systems 5-17
5-9 Selected Hydraulic Loading Rates for Overland Flow Systems 5-19
5-10 Nitrogen Concentrations in Treated Runoff From Overland
Flow When Using Untreated Wastewater 5-20
5-11 Phosphorus Concentrations in Treated Runoff From
Overland Flow, Ada, Oklahoma 5-21
5-12 Hydraulic Loadings and General Performance Criteria -
Research and Demonstration Wetland Systems 5-22
5-13 Need for Preapplication Treatment 5-27
5-14 Summary of Computer Programs for Determining Storage
From Climatic Variables 5-31
5-15 Threshold Values for the EPA-1 Storage Program 5-33
5-16 Example of Storage Determination From a Water Balance
for Irrigation 5-36
5-17 Irrigation and Consumptive Use Requirements for Selected
Crops at Bakersfield, California 5-37
5-18 Surface Irrigation Methods and Conditions of Use 5-41
5-19 Nonirrigating Surface Application Methods and
Conditions of Use 5-43
5-20 Suggested Maximum Lengths of Cultivated Furrows for
Different Soils, Slopes, and Depths of Water to be Applied 5-44
5-21 Optimum Furrow or Corrugation Spacing 5-44
5-22 Recommended Maximum Border Strip Width 5-47
5-23 Design Standards for Border Strip Irrigation, Deep
Rooted Crops 5-47
5-24 Design Standards for Border Strip Irrigation, Shallow
Rooted Crops 5-48
5-25 Discharge Capacities of Surface Gated Pipe Outlets 5-56
5-26 Sprinkler System Characteristics 5-59
5-27 Classification of Sprinklers and Their Adaptability 5-68
5-28 Factor (F) by Which Pipe Friction Loss is Multiplied to
Obtain Actual Loss in a Line with Multiple Outlets 5-70
5-29 Depth and Spacing of Underdrains for Slow Rate Systems 5-72
5-30 Recommended ASAE Runoff Design Factors for Surface
Flood Distribution 5-75
5-31 Peak Consumptive Water Use and Rooting Depth 5-80
xm
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TABLES (Continued)
No. Page
5-32 Nutrient Uptake Rates for Selected Crops 5-82
5-33 Electrical Conductivity Values Resulting in Reductions
in Crop Yield 5-85
5-34 Crop Boron Tolerance 5-86
5-35 Crop Acidity Tolerance 5-86
5-36 Evapotranspiration of Woodland and Forest Crops 5-88
5-37 Recommended Irrigation Rates of Forest Crops 5-89
5-38 Effect of Lime on Element Availability in Soil 5-91
5-39 Example Monitoring Program for a Large Slow Rate System 5-95
5-40 A Comparison of Chemicals to Gypsum 5-98
5-41 Allowable Soil Contact Pressure 5-101
6-1 Types and Sources of Data Required for Land
Treatment Designs 6-2
6-2 Important Components of Domestic Wastewater 6-4
6-3 Design Unit Wastewater Flows for Recreational Facilities,
Yellowstone National Park 6-5
6-4 Average Wastewater Flows from Institutional Facilities 6-5
6-5 Total Land Area Guidelines for Preliminary
Site Identification 6-6
6-6 Preliminary Selection of Land Treatment Systems 6-8
6-7 Summary of Application Periods for Land Treatment Systems 6-9
6-8 Design Application Rates for Small Systems 6-9
6-9 Minimum Preapplication Treatment Practice 6-13
6-10 Guidelines for Storage Volumes 6-13
6-11 Factors Affecting the Design of Surface Irrigation Systems 6-16
6-12 Factors Affecting the Design of Sprinkler
Irrigation Systems 6-18
6-13 Potential Land Treatment Sites for Angus, Washington 6-24
6-14 Required Acreages for Angus Land Treatment Systems 6-25
6-15 Land Treatment Alternatives for Angus, Washington 6-27
6-16 Summary of Feasible Land Treatment Systems for
Angus, Washington 6-29
7-1 Summary of Case Studies 7-1
7-2 Design Factors, Pleasanton, California 7-3
7-3 Characteristics of Holding Pond Effluent and Groundwater
Quality, Pleasanton, California 7-7
7-4 Trace Wastewater Constituents of Holding Pond Effluent,
Pleasanton, California, September 1975 7-8
7-5 Approximate Operation and Maintenance Costs, Land
Treatment System, Pleasanton, California 7-9
7-6 Design Factors, Walla Walla, Washington 7-11
7-7 Average Daily Flow of Wastewater, Walla Walla, Washington 7-14
7-8 Average Estimated Operations Costs, Walla Walla, Washington 7-18
7-9 Design Factors, Bakersfield, California 7-19
7-10 Composite Wastewater Characteristics for City Plants Nos. 1
and 2, Bakersfield, California 7-22
7-11 Loading Rates in 1973 and Typical Nitrogen Uptake
Requirements, Bakersfield Land Treatment System 7-22
7-12 Existing Crop Yields and Economic Return, Bakersfield
Land Treatment System 7-23
xiv
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TABLES (Continued)
No. Page
7-13 Estimated Construction Costs, Proposed Wastewater
Irrigation System, Bakersfield, California 7-26
7-14 Design Factors, San Agnelo, Texas . 7-27
7-15 Treatment Performance, San Angelo, Texas 7-30
7-16 Sample of Groundwater Quality, San Angelo, Texas 7-31
7-17 Design Factors, Muskegon Project, Muskegon, Michigan 7-33
7-18 Distribution System Data, Muskegon Project 7-36
7-19 Representative Yields of Corn Grain, for Various Soil
Types, Muskegon Land Treatment Site, 1975 7-38
7-20 Increased Agricultural Productivity, Muskegon Land
Treatment Site 7-39
7-21 Summary of Treatment Performance, 1975 Average
Results, Muskegon Project 7-40
7-22 Operating Costs, Muskegon Wastewater System, 1975 7-41
7-23 Design Factors, St. Charles, Maryland 7-42
7-24 Design Factors, Phoenix, Arizona 7-45
7-25 Renovated Water Quality, The 23rd Avenue Project in
Phoenix, Arizona 7-49
7-26 Characteristics of System Influent and Renovated
Water, Flushing Meadows, Phoenix, Arizona 7-52
7-27 Design Factors, Lake George, New York 7-54
7-28 Water Quality Data, Seasonal Means, Lake George, New York 7-59
7-29 Design Factors, Fort Devens, Massachusetts 7-61
7-30 Chemical and Bacteriological Characteristics of Primary
Effluent and Groundwater in Selected Observation Wells,
Fort Devens Land Treatment Site 7-66
7-31 Design Factors, Pauls Valley, Oklahoma 7-68
7-32 Unit Costs of Overland Flow Application, Pauls
Valley, Oklahoma . 7-71
7-33 Design Factors, Paris, Texas 7-72
7-34 Treatment Performance During 1968 Compared to Effluent
Quality in 1976, Paris, Texas 7-73
7-35 Seasonal Quality of Treated Effluent, Paris, Texas 7-74
7-36 Construction and Operating Costs, Paris, Texas, 7-75
8-1 Climatic Data for the Worst Year in 10 8-2
8-2 Water Quality Characteristics 8-3
8-3 Available Land Areas by Soil Type 8-7
8-4 Determination of Overland Flow Application Schedule
Based on Climatic Data 8-11
8-5 Summary of Design Information for Treatment Alternatives 8-15
8-6 Relative Cost Comparisons, Design Example Alternatives 8-16
8-7 Monthly Design Nitrogen Balance, Slow Rate System 8-20
8-8 Trace Metals in Slow Rate Design Example 8-22
8-9 Design Factors, Slow Rate Treatment with
Center Pivot Distribution 8-24
A-l Nitrogen Uptake Efficiencies of Corn in Relation to
Quantities of Nitrogen and Water Applied A-10
A-2 Three Year Balance Sheet for Isotopically Labelled Nitrogen
Fertilizer Applied tc Corn Plots on Hanford Sandy Loam A-l2
xv
-------
TABLES (Continued)
No. Page
A-3 Nitrate-N Concentrations in Soil Solution Samples Obtained
by Means of Suction Probes at Four Depths on Two Dates
in a Corn Field on Yolo Fine Sandy Loam A-17
A-4 Recovery of Total and Tagged N in Effluent From Three
Soils Receiving l^N-Labelled Wastewater at the
Rate of 3 in./wk A-23
B-l Removal of Phosphorus by the Usual Harvested Portion
of Selected Crops B-5
C-l Relation of Saturation Percentage to Soil Texture C-6
C-2 Comparison of Infiltration Measurement Using Flooding
and Sprinkling Techniques C-18
C-3 Comparison of Infiltration Measurement Using Standard
USPHS Percolation Test and Double-Cylinder Infiltrometer C-19
C-4 Subsurface Logging Information Obtained by Various Methods C-34
C-5 Approximate Drainable Voids for Major Soil Classifications C-38
C-6 Statistical Variability of Several Physical
Properties of Soil C-39
C-7 Measured Ratios of Horizontal to Vertical Permeability C-40
C-8 Summary of Measured Infiltration Rates and Operating
Rates for Selected Land Application Systems C-46
D-l Estimated Concentrations of Wastewater Pathogens D-4
D-2 Factors That Affect the Survival of Enteric Bacteria
and Viruses in Soil D-8
D-3 Factors That Influence the Movement of Viruses in Soil D-l9
D-4 Factors That Affect the Survival and Dispersion of
Bacteria and Viruses in Wastewater Aerosols D-23
E-l Classification of Substances with Which Metals May Form
Chemical and/or Physical Associations in Fresh Waters
and Wastewaters E-3
E-2 Average and Ranges of Soil Concentrations of
Selected Elements E-7
E-3 Classification of States of Metals in Soils E-ll
E-4 Assumptions and Selected Performance Values Used to
Calculate Crop Removal Coefficients k2 and Yearly
Application of Metal in Wastewater k] for Evaluation
of Cadmium E-24
E-5 Concentration of Zinc in Plant Tissues and Interpolated
Applied Zinc Concentration in Soil at the 20% Yield
Decrement E-32
F-l Types of Data Needed for Various Evapotranspiration
Predicition Methods F-2
F-2 Typical Properties Determined When Formulating Soil Maps F-6
F-3 Effects of Various pH Ranges on Crops F-ll
F-4 Typical Ranges of Cation Exchange Capacity of Various
Types of Soils F-l3
F-5 Satisfactory Balance of Exchangeable Cations Occupying
the Cation Exchange Capacity F-13
F-6 Factors for Computing the Adjusted SAR F-16
xvi
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TABLES (Concluded)
No. Page
F-7 Salinity Levels at Which Crop Growth is Restricted F-17
F-8 Approximate Critical Levels of Nutrients for Selected
Crops in California F-19
F-9 Critical Phytotoxic Levels of Boron in Soils F-20
xvn
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FOREWORD
Land treatment is a reliable engineering process for wastewater
management. Land application of wastewaters has been practiced in a
number of modes, including crop and landscape irrigation; as a treatment
process with collection and discharge of treated water; as indirect
discharge to surface water; and as application to the soil surface for
groundwater recharge. It is possible to modify any of these modes to
meet project objectives, including the combination of several in a single
management system.
The benefits of land treatment systems can go beyond the treatment of
wastewater. Land treatment processes involve the recovery and beneficial
reuse of wastewater nutrients and other elements through good
agriculture, silviculture, and aquaculture practices. These practices
permit the achievement of advanced levels of wastewater treatment as well
as water reclamation and resource recovery objectives of recent
environmental legislation. The production of revenues through the sale
of byproducts (e.g., crops) can be realized. Land treatment systems can
aid in the reclamation and reuse of water resources, recharge of
groundwater aquifers, reclamation of marginal land, and the preservation
of open spaces for future greenbelts.
It is the purpose of this manual to describe the basic principles of land
treatment and to present a rational procedure for design of land
treatment systems. Information contained in this manual can be used in
identifying alternatives during planning, in selecting a process
alternative or site, in determining necessary field investigations, and
in conducting the process design.
This manual is unique in the Technology Transfer Process Design Manual
series because its preparation was jointly sponsored by the U. S.
Environmental Protection Agency (EPA) and the U.S. Army Corps of
Engineers. The U.S. Department of Agriculture (USDA) provided technical
assistance during the review process. In recognition of these
contributions, the cover and title page were designed to clearly indicate
the endorsement of these three agencies. The review process included
over thirty individuals contributing significantly to the preparation of
this manual. They provided a broad range of technical expertise and
represented a wide variety of agencies and institutions. This extensive
review ensured the accuracy and the authority of the product.
The manual represents the current state-of-the-art with respect to
criteria, data, and procedures for the design of land treatment processes
for municipal wastewaters. Much of the information is also applicable
for design of systems managing industrial wastewaters. Revisions and
improvements will be made as results of current and future research and
development become available.
xvm
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CHAPTER 1
INTRODUCTION
1.1 Background and History
Land treatment of municipal wastewater involves the use of plants, the
soil surface, and the soil matrix to remove many wastewater consti-
tuents. A wide variety of processes can be used to achieve many differ-
ent objectives of treatment, water reuse, nutrient recycling, and crop
production.
The concept of land application of wastewater certainly is not new to
the field of sanitary engineering. Evidence of such systems in western
civilization extends back as far as ancient Athens [1]. A wastewater
irrigation system in Bunzlaw, Germany, is reported to have been in oper-
ation for over 300 years beginning in 1559 [2].
The greatest proliferation of land treatment systems occurred in Europe
in the second half of the nineteenth century. Pollution of many rivers
had reached unacceptable levels, and disposal of sewage on the land was
the only feasible means of treatment available at the time. "Sewage
farming," the practice of transporting sewage into rural areas for irri-
gation and disposal, was commonly used by many European cities, inclu-
ding some of those shown in Table 1-1. In the 1870s, the practice was
recognized in England as treatment, with many underdrained systems ex-
hibiting sparkling clear effluents [3]. As urban areas expanded and in-
plant treatment processes became available, many of these older systems
were abandoned because of land development pressures.
Early experiences in the United States also date back to the 1870s [4].
As in Europe, sewage farming became relatively common as a first attempt
to control water pollution. In the first half of the twentieth century,
these early systems were generally replaced either by in-plant treatment
or by (1) managed farms where treated wastewater was used for crop
production, (2) landscape irrigation sites, or (3) groundwater recharge
sites [1]. These newer land treatment systems tended to predominate in
the West where the resource value of wastewater was an added advantage.
In addition, experience with land application of food processing and
pulp and paper industrial wastewaters has been drawn upon in developing
the technology of land treatment [1, 5].
The increasing use of land treatment over the last 40 years is shown in
Table 1-2, which was compiled from periodic inventories of municipal
wastewater treatment facilities [2]. While it is evident that the
number of systems has steadily grown, it still represents only a small
percentage of the estimated 15 000 total municipal treatment facilities
[2].
1-1
-------
TABLE 1-1
SELECTED EARLY LAND APPLICATION SYSTEMS
[1, 2, 5, 6, 7, 8]
Location
International
Croydon-Beddington, England
Paris, France
Leamington, England
Berlin, Germany
Wroclaw, Poland
Melbourne, Australia
Braunschweig, Germany
Mexico City, Mexico
United States
Calumet City, Michigan
Woodland, California
Fresno, California
San Antonio, Texas
Vineland, New Jersey
Ely, Nevada
Date
started
1860
1869
1870
1874
1882
1893
1896
1900
1888
1889
1891
1895
1901
1908
Type of
system
Sewage farm
SRa
Sewage farm
Sewage farm
Sewage farm
SR
OFb
Sewage farm
SR
RIC
SR
SR
SR
RI
SR
Area,
acres
630
16 000
400
68 000
2 000
10 400
3 500
11 000
112 000
12
240
4 000
4 000
14
1 400
Flow,
Mgal/d
5.6
79
1
28
50
70
16
570
1.2
4.2
26
20
0.8
1.5
a. SR = slow rate.
b. OF = overland flow.
c. RI = rapid infiltration.
1 acre = 0.405 ha
1 Mgal/d = 43.8 L/s
TABLE 1-2
U.S. MUNICIPALITIES
USING LAND TREATMENT [2]
Year
1940
1945
1957
1962
1968
1972
No. of
systems
304
422
461
401
512
571
Population
served, millions
0.9
1.3
2.0
2.7
4.2
6.6
1-2
-------
In recent years, much effort has been spent on developing land treatment
technology and improving methods of control. The various types of land
treatment systems have become accepted as viable wastewater management
techniques that should be considered equally with any others. The regu-
lations developed pursuant to the Federal Water Pollution Control Act
Amendments of 1972 (Public Law 92-500) require that such consideration
be given for federally funded municipal wastewater projects. In the
Act, the Environmental Protection Agency administrator is directed to
encourage waste treatment management that results in facilities for
(1) the recycling of potential pollutants through the production of
agricultural, silvicultural, and aquacultural products; (2) the
reclamation of wastewater; and (3) the elimination of the discharge of
pollutants.
1.2 Objectives
The primary objective of this manual is to provide a comprehensive
source of information to be used in the planning and design of land
treatment systems. It is not intended to serve as a definition of
policy on land treatment, but rather to set forth and extend the present
state-of-the-art technology. Recommended procedures, case studies, and
several examples are presented which are intended to serve as planning
and design aids.
Throughout the manual, emphasis is given to the wide range of design
possibilities available for land treatment systems. The user is
encouraged to adapt the techniques and procedures described to suit
local needs and conditions.
1.3 Scope of the Manual
Planning and technical information for each of the following major
wastewater treatment processes involving land application are presented:
• Slow rate (SR), also referred to as^crop irrigation
• Rapid infiltration (RI)
• Overland flow (OF)
Other types of systems, such as wetland and subsurface systems, which
are uncommon or new, are also described but in less detail. Systems
specifically involving the land application of sludge, injection wells,
sealed evaporation ponds, and conventional septic tank leach fields are
not covered.
The scope of most of the information in the manual is directed to
medium-to-large systems. For small.systems, say 0.1 million gallons per
1-3
-------
day (Mgal/d) [4.4 L/s], or less, many of the design procedures presented
in the manual must be realistically simplified. Special considerations
for small systems are discussed separately in Chapter 6.
To minimize the amount of theoretical and background information in the
manual, papers on six topics of special interest are included as
appendixes. These papers were written by recognized experts in their
particular fields and cover the following topics: (1) nitrogen,
(2) phosphorus, (3) hydraulic capacity, (4) pathogens, (5) metals, and
(6) field investigation procedures. These appendixes form the technical
foundation for the body of the report. Research results reported in
this manual are current through 1976. Detailed procedures for deter-
mining capital and operation and maintenance costs are not included in
this manual. Sources for such information are given in Chapter 3 along
with general summaries.
1.4 Guide to Intended Use
The contents of the manual should be helpful to a variety of different
users, including those seeking to gain a general perspective on land
treatment and those looking for specific design information. Conse-
quently, the manual is organized to allow the user to locate particular
information and to concentrate on specific areas of interest as easily
as possible. Subject, location, and author indexes are provided to al-
low easy access to specific information. A glossary is also provided to
give definitions of terms germane to land treatment which might not be
familiar to the traditional civil/sanitary engineer. The following
brief chapter descriptions are provided as an introduction to the organ-
ization of the manual.
Chapter 2 - Treatment Process Capabilities and Objectives.
The basic concepts of each process of land treatment are described.
Standard terminology and ranges of important design criteria that are
encountered throughout the rest of the manual are presented.
Chapter 3 - Technical Planning and Feasibility Assessment.
Information for those users involved in both regional and facilities
planning efforts is provided. Most of the technical information and
guidance contained in the manual is presented here and in Chapter 5.
Procedures are described for investigating sites and for developing and
evaluating land treatment alternatives. Wherever possible, desirable
ranges of criteria associated with physical characteristics are given.
Chapter 4 - Field Investigations.
Field investigations are outlined for each land treatment process.
Reasons for field tests are given along with guidance on possible inter-
pretation of test results.
1-4
-------
Chapter 5 - Process Design.
Design guidelines are presented for projects in which the site and
process have been determined. In the first part of the chapter, each of
the major treatment processes is discussed separately with respect to
application rates and removals of various wastewater constituents. Sub-
sequent sections are devoted to design components of land treatment
systems. These include preapplication treatment, storage, distribution,
and management of renovated water. Discussions are then provided on
vegetation and agricultural management, system monitoring, and facili-
ties design guidance.
Chapter 6 - Small Systems.
Simplified designs that are possible for small community systems are
described. Shortcuts for the planning and design procedures described
in Chapters 3 and 5 are given along with special considerations. A
design example is also included.
Chapter 7 - Case Studies.
Brief descriptions of the design criteria and operational characteris-
tics of 11 successful land treatment systems are presented. The systems
were chosen to represent as broad a cross-section as possible with res-
pect to type of system, size, and location.
Chapter 8 - Design Example.
An example that illustrates the principles described in Chapters 3 and 5
is presented. For a flow of 10 Mgal/d (0.44 m3/s), in a humid eastern
climate, alternatives are developed and compared for slow rate and a
combination of the overland flow and rapid infiltration processes.
1.5 References
1. Pound, C.E. and R.W. Crites. Wastewater Treatment and Reuse by
Land Application. Volumes I and II. Environmental Protection
Agency, Office of Research and Development. August 1973.
2. Thomas. R.E. Land Disposal II: An Overview of Treatment Methods.
Jour. WPCF 45:1476-1484. July 1973.
3. Kirkwood, J.P. The Pollution of River Waters. Seventh Annual
Report of the Massachusetts State Board of Health. Wright &
Potter, Boston. 1876. Reprint Edition 1970 by Arno Press Inc.
4. Rafter, G.W. Sewage Irrigation, Part II. USGS Water Supply and
Irrigation. Paper No. 22. 1899.
5. Sullivan, R.H., et al. Survey of Facilities Using Land Application
of Wastewater. Environmental Protection Agency, Office of Water
Program Operations. EPA-430/9-73-006. July 1973.
1-5
-------
6. Hartman, W.J. Jr. An Evaluation of Land Treatment of Municipal
Wastewater and Physical Siting of Facility Installations. May
1975.
7. Baillod, C.R., et al. Preliminary Evaluation of 88 Years Rapid
Infiltration of Raw Municipal Sewage at Calumet, Michigan.
(Presented at the 8th Annual Cornell Waste Management Conference.
Rochester. April 1976.)
8. Bocko, J. and J. Paluch. The Effect of Irrigation with Municipal
Sewage on the Sanitary Condition of Ground Waters. Zesz. Nauk.
(Poland) WSR Wroclaw, Melioracja: 14(90):49-59. 1970.
1-6
-------
CHAPTER 2
TREATMENT PROCESS CAPABILITIES AND OBJECTIVES
2.1 Introduction
Land treatment of municipal wastewater encompasses a wide variety of
processes or methods. The three principal processes, as referred to in
this manual, are:
1. Slow rate
2. Rapid infiltration
3. Overland flow
Other processes, which are less widely used and generally less adaptable
to large-scale use than the three principal ones, include:
1. Wetlands
2. Subsurface
The major concepts involved in these processes are introduced in this
chapter. Descriptions are given of system objectives and treatment
mechanisms.
Typical design features for the various land treatment processes are
compared in Table 2-1, with more detail provided in Chapter 5. The
major site characteristics are compared for each process in Table 2-2,
with more detail provided in Chapter 3. The expected quality of treated
water from the three principal land treatment processes is shown in
Table 2-3. The major removal mechanisms responsible for the quality
improvement are described for each land treatment process in the follow-
ing sections.
2.2 Slow Rate Process
In several previous EPA reports, including Evaluation of Land Applica-
tion Systems [1], slow rate land treatment was referred to as irriga-
tion. The term slow rate land treatment is used to focus attention on
wastewater treatment rather than on irrigation of crops. However, in
slow rate systems, vegetation is a critical component for managing water
and nutrients.
2-1
-------
TABLE 2-1
COMPARISON OF DESIGN FEATURES FOR LAND TREATMENT PROCESSES
ro
i
ro
Feature
Application techniques
Annual application
rate, ft
Field area required,
acresb
Typical weekly appli-
cation rate, in.
Minimum preappli cation
treatment provided
in United States
Disposition of
applied wastewater
Need for vegetation
Slow rate
Sprinkler or
surface9
2 to 20
56 to 560
0.5 to 4
Primary
sedimentation^
Evapotranspi ration
and percolation
Required
Principal processes
Rapid Infiltration
Usually surface
20 to 560
2 to 56
4 to 120
Primary
sedimentation
Mainly
percolation
Optional
Other processes
Overland flow
Sprinkler, or
surface
10 to 70
16 to 110
2.5 to 6C
6 to 16d
Screening and
grit removal
Surface runoff and
evapotranspi rati on
with some
percolation
Required
Wetlands
Sprinkler or
surface
4 to 100
11 to. 280
1 to 25
Primary
sedimentation
Evapotranspi ration ,
percolation,
and runoff
Required
Subsurface
Subsurface piping
8 to 87
13 to 140
2 to 20
Primary
sedimentation
Percolation
with some
evapotranspi ration
Optional
a. Includes ridge-and-furrow and border strip.
b. Field area in acres not including buffer area, roads, or ditches for 1 Mgal/d (43.8 L/s) flow.
c. Range for application of screened wastewater.
d. Range for application of lagoon and secondary effluent.
e. Depends on the use of the effluent and the type of crop.
1 in. = 2.54 cm
1 ft = 0.305 m
1 acre" = 0.405 ha
-------
TABLE 2-2
COMPARISON OF SITE CHARACTERISTICS FOR LAND TREATMENT PROCESSES
PO
I
co
Characteristics
Slope
Soil permeability
Depth to
groundwater
Climatic
restrictions
Slow rate
Less than 20% on culti-
vated land; less than
40% on noncultivated
land
Moderately slow to
moderately rapid
2 to 3 ft (minimum)
Storage often needed
for cold weather and
precipitation
Principal processes
Rapid infiltration
Not critical; excessive
slopes require much
earthwork
Rapid (sands, loamy
sands)
10 ft (lesser depths
are acceptable where
underdrainage is
provided)
None (possibly modify
operation in cold -
weather)
Other processes
Overland flow
Finish slopes
2 to 8%
Slow (clays,
silts, and
soils with
impermeable
barriers)
Not critical
Storage often
needed for
cold weather
Wetlands
Usually less
than 5%
Slow to
moderate
Not critical
Storage may
be needed
for cold
weather
Subsurface
Not critical
Slow to rapid
Not critical
None
1 ft = 0.305 m
-------
TABLE 2-3
EXPECTED QUALITY OF TREATED WATER FROM LAND TREATMENT PROCESSES
mg/L
Slow rate3
Rapid
infiltration15 Overland flowc
Constituent
BOD
Suspended solids
Ammonia nitrogen as N
Total nitrogen as N
Total phosphorus as P
Average
<2
<1
<0.5
3
<0.1
Maximum
<5
<5
<2
<8
<0.3
Average
2
2
0.5
10
1
Maximum
<5
<5
<2
<20
<5
Average
10
10
0.8
3
4
Maximum
<15
<20
<2
<5
<6
a. Percolation of primary or secondary effluent through 5 ft (1.5 m)
of soil.
b. Percolation of primary or secondary effluent through 15 ft (4.5 m)
of soil.
c. Runoff of comminuted municipal wastewater over about 150 ft (45 m)
of slope.
The applied wastewater is treated as it flows through the soil matrix,
and a portion of the flow percolates to the groundwater. Surface runoff
of the applied water is generally not allowed. A schematic view of the
typical hydraulic pathway for slow rate treatment is shown in Figure 2-
l(a). Typical views of slow rate land treatment systems, using both
surface and sprinkler application techniques, are also shown in Figure
2-1(b, c). Surface application includes ridge-and-furrow and border
strip flooding techniques. The term sprinkler application is correctly
applied to impact sprinklers and the term spray application should only
be used to refer to fixed spray heads.
The case studies in Chapter 7 include six slow rate systems that are
fairly representative of those found throughout the United States:
Pleasanton, California; Walla Walla, Washington; Bakersfield, Califor-
nia; San Angelo, Texas; Muskegon, Michigan; and St. Charles, Maryland.
These case studies provide an insight into actual experiences with slow
rate systems.
2-4
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FIGURE 2-1
SLOW RATE LAND TREATMENT
EVAPOTRANSPIRATION
PERCOLATION
(a) HYDRAULIC PATHWAY
(b) SURFACE DISTRIBUTION
(c) SPRINKLER DISTRIBUTION
2-5
-------
2.2.1 System Objectives
Slow rate systems can be operated to achieve a number of objectives
including:
1. Treatment of applied wastewater
2. Economic return from use of water and nutrients to produce
marketable crops (irrigation)
3. Water conservation, by replacing potable water with treated
effluent, for irrigating landscaped areas, such as golf
courses
4. Preservation and enlargement of greenbelts and open space
When requirements for surface discharge are very stringent for nitrogen,
phosphorus, and biochemical oxygen demand (BOD), they can be met with
slow rate land treatment. If the percolating water must meet EPA
drinking water standards, reduction in nitrogen below the 10 mg/L
standard for nitrate-nitrogen is often the limiting criterion. In arid
regions, however, increases in chlorides and toial dissolved salts in
the groundwater may be limiting. Management approaches to meet the
above objectives within the slow rate process are discussed under the
topics (1) wastewater treatment, (2) crop irrigation, (3) turf
irrigation, and (4) silviculture. , '
2.2.1.1 Wastewater Treatment
When the primary objective of the slow rate process is treatment, the
hydraulic loading is limited either by the infilration capacity of the
soil or the nitrogen removal capacity of the soil-vegetation complex.
If the hydraulic capacity of the site is limited by a relatively
impermeable subsurface layer or by a high groundwater table, underdrains
can be installed to increase the allowable loading. Grasses are usually
chosen for the vegetation because of their high nitrogen uptake
capacities.
2.2.1.2 Crop Irrigation
When the crop yields and economic returns from slow rate systems are
emphasized, crops of higher values than grasses are usually selected.
In the West, application rates are generally between 1 and 3 ip./wk (2.5
to 7.6 cm/wk), which reflect the consumptive use of crops. Consumptive
use rates are those required to replace the water lost to evaporation,
plant transpiration, and stored in: plant tissue, in areas where water
2-6
-------
does not limit plant growth, the nitrogen and phosphorus in wastewater
can be recycled in crops. These nutrients can increase yields of corn,
grain sorghum, and similar crops and provide an economic return.
2.2.1.3 Turf Irrigation
Golf courses, parks, and other turfed areas can be irrigated with
wastewater, thus, conserving potable water supplies. These areas
generally have considerable public access and this usually requires that
a disinfected effluent be applied.
2.2.1.4. Silviculture
Silviculture, the growing of trees, is being conducted with wastewater
effluent in at least 11 existing sites in Oregon, Michigan, Maryland,
and Florida [2]. In addition, experimental systems at Pennsylvania
State University [3], Michigan State University [4], and the University
of Washington [5] are being studied extensively to determine permissible
loading rates, responses of various tree species, and environmental
effects.
Forests offer several advantages as potential sites for land treatment:
1. Large forested areas exist near many sources of wastewater.
2. Forest soils often exhibit better infiltration properties than
agricultural soils.
3. Site acquisition costs for forestland are usually lower than
site acquisition costs for agricultural land because of lower
land values for forestlands.
4. During cold weather, soil temperatures are often higher in
forestlands than in comparable agricultural lands.
The principal limitations on the use of wastewater for silviculture are
that:
1. Water tolerances of the existing trees may be low.
2. Nitrogen removals are relatively low.
3. Fixed sprinklers, which are expensive, must generally be used.
2-7
-------
Existing forests are adapted to the water supply from natural
precipitation. Unless soils are well drained, the increase in hydraulic
loading from wastewater application will drown existing trees. At
Seabrook Farms, New Jersey, the types of vegetation have changed from
predominantly oak trees to wild berries, marsh grass, and other grasses
[6].
2.2.2 Treatment Performance
Slow rate treatment is generally capable of producing the best results
of all the land treatment systems. The quality values shown in Table
2-3 can be expected for most well-designed and well-operated slow rate
systems.
Organics are reduced substantially by slow rate land treatment by bio-
logical oxidation within the top few inches of soil. At Muskegon, Mich-
igan, the BOD of renovated water from the drain tiles has ranged from
1.2 to 2.2 mg/L, and the BOD of renovated water intercepted by two
nearby creeks has ranged from 2 to 3.3 mg/L [7]. Preliminary results
for six test cells at a research project in Hanover, New Hampshire, show
average annual BOD concentrations in the percolate ranging from 0.6 to
2.1 mg/L [8]. These results were consistently achieved with application
rates ranging up to 6 in./wk (15 cm/wk) with both primary and secondary
effluents applied. Filtration and adsorption are the initial mechanisms
in BOD removal, but biological oxidation is the ultimate treatment
mechanism.
Suspended solids removals are not as well documented as BOD removals,
but concentrations of 1 mg/L or less can generally be expected in the
renovated water. Filtration is the major removal mechanism for suspen-
ded solids. Volatile solids are biologically oxidized, and fixed or
mineral solids become part of the soil matrix.
Nitrogen is removed primarily by crop uptake, which varies with the type
of crop grown and the crop yield. To remove the nitrogen effectively,
the portion of the crop that contains the nitrogen must be physically
removed from the field. Denitrification can also be significant, even
if the soil is in an aerobic condition most of the time. In a labora-
tory study using radioactive tracer materials, Broadbent reported deni-
trification losses of up to 32% of the applied nitrogen [9]. In the
test cells at Hanover, denitrification losses were found to be 5 to 28%
[8]. In both of these cases, the soils were considered to be
essentially aerobic.
Phosphorus is removed from solution by fixation processes in the soil,
such as adsorption and chemical precipitation. Removal efficiencies are
generally very high for slow rate systems and are usually more dependent
2-8
-------
on the soil properties than on the concentration of the phosphorus ap-
plied. A small but significant portion of the phosphorus applied (15 to
30% depending on the soil and the crop) is taken up and removed with the
crop.
2.3 Rapid Infiltration
In rapid infiltration land treatment (referred to in previous EPA re-
ports as infiltration-percolation), most of the applied wastewater per-
colates through the soil, and the treated effluent eventually reaches
the groundwater. The wastewater is applied to rapidly permeable soils,
such as sands and loamy sands, by spreading in basins or by sprinkling,
and is treated as it travels through the soil matrix. Vegetation is not
usually used, but there are some exceptions.
The schematic view in Figure 2-2(a) shows the typical hydraulic
pathway for rapid infiltration. A much greater portion of the applied
wastewater percolates to the groundwater than with slow rate land
treatment. There is little or no consumptive use by plants and less
evaporation in proportion to a reduced surface area.
In many cases, recovery of renovated water is an integral part of the
system. This can be accomplished using underdrains or wells, as shown
in Figure 2-2(b, c).
Among the case studies in Chapter 7 are three that serve as representa-
tive examples of rapid infiltration systems: Phoenix, Arizona; Lake
George, New York; and Fort Devens, Massachusetts.
2.3.1 System Objectives
The principal objective of rapid infiltration is wastewater treatment.
Objectives for the treated water can include:
1. Groundwater recharge
2. Recovery of renovated water by wells or underdrains with sub-
sequent reuse or discharge
3. Recharge of surface streams by interception of groundwater
4. Temporary storage of renovated water in the aquifer
2-9
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FIGURE 2-2
RAPID INFILTRATION
APPLIED
•ASTEWATER
EVAPORATION
PERCOLATION
(a) HYDRAULIC PATHWAY
FLOODING BASINS
-G R OU NOW A T E R
PERCOLATION
(UNSATURATED ZONE)
(b) RECOVERY OF RENOVATED WATER BY UNDERDRAINS
PERCOLATION
(UNSATURATED ZONE)
(c) RECOVERY OF RENOVATED WATER BY WELLS
2-10
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If groundwater quality is being degraded by salinity intrusion, ground-
water recharge by rapid infiltration can help to reverse the hydraulic
gradient and protect the existing groundwater.
Return of the renovated water to the surface by wells, underdrains, or
groundwater interception may be necessary or advantageous when discharge
to a particular surface water body is dictated by senior water rights,
or when existing groundwater quality is not compatible with expected re-
novated water quality. At Phoenix, for example, treated .water is with-
drawn immediately by wells to prevent spreading into the groundwater and
to allow reuse of the water for irrigation [10],
2.3.2 Treatment Performance
Removals of wastewater constituents by the filtering and straining ac-
tion of the soil are excellent. Suspended solids, BOD, and fecal coli-
forms are almost completely removed in most cases [10, 11] .
Nitrogen removals are generally poor unless specific operating proce-
dures are established to maximize denitrification. At Flushing Meadows,
total nitrogen removals of 30% were obtained consistently. In labora-
tory studies it was shown, however, that increased denitrification could
have been obtained by: (1) adjusting application cycles, (2) supplying
an additional carbon source, (3) using vegetated basins, (4) recycling
the portions of the renovated water containing high nitrate concentra-
tions, and (5) reducing application rates [12]. Applying some of these
practices in the field increased nitrogen removal, resulting from deni-
trification, to about 50%. Although total nitrogen removals may be
poor, rapid infiltration is an excellent method for achieving a
nitrified effluent.
Phosphorus removals can range from 70 to 99%, depending on the physical
and chemical characteristics of the soil. As with slow rate systems,
the primary removal mechanism is adsorption with some chemical precipi-
tation, so the long-term capacity is limited by the mass of soil in con-
tact with the wastewater. Removals are related also to the residence
time of the wastewater in the soil and the travel distance (see Section
5.1.3).
2.4 Overland Flow
In overland flow land treatment, wastewater is applied over the upper
reaches of sloped terraces and allowed to flow across the vegetated sur-
face to runoff collection ditches. The wastewater is renovated by phy-
sical, chemical, and biological means as it flows in a thin film down
the relatively impermeable slope. A schematic view of overland flow
2-11
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treatment is shown in Figure 2-3(a), and a pictorial view of a
typical system is shown in Figure 2-3(b). As shown in Figure 2-3(a),
there is relatively little percolation involved either because of an
impermeable soil or a subsurface barrier to percolation.
Overland flow is a relatively new treatment process for municipal waste-
water in the United States. As of August 1976, only three relatively
small, full-scale municipal systems have been constructed. These are
located in Oklahoma, Mississippi, and South Carolina. The earliest of
these systems, at Pauls Valley, Oklahoma, is described as a case study
in Chapter 7. In Melbourne, Australia, overland flow has been used to
treat settled wastewater for several decades [13, 14]. The Campbell
Soup Company treatment plant at Paris, Texas, which is perhaps the best
known of approximately 10 industrial systems in the county, is also des-
cribed as.a case study in Chapter 7. Besides these full-scale examples,
extensive reference is made throughout this manual to the pilot scale
municipal studies sponsored by the EPA at Ada, Oklahoma, and the bench-
scale greenhouse studies sponsored by the Corps of Engineers at Vicks-
burg, Mississippi.
2.4.1 System Objectives
The objectives of overland flow are wastewater treatment and, to a minor
extent, crop production. Treatment objectives may be either (1) to
achieve secondary or better effluent quality from screened primary
treated, or lagoon treated wastewater, or (2) to achieve high levels of
nitrogen and BOD removals comparable to conventional advanced wastewater
treatment from secondary treated wastewater. Treated water is collected
at the toe of the overland flow slopes and can be either reused or dis-
charged to surface water. Overland flow can also be used for production
of forage grasses and the preservation of greenbelts and open space.
2.4.2 Treatment Performance
Biological oxidation, sedimentation, and grass filtration are the pri-
mary removal mechanisms for organics and suspended solids. At Ada,
using raw comminuted wastewater, Thomas reported total suspended solids
concentrations of 6 to 8 mg/L in the runoff during the summer and 8 to
12 mg/L in the winter [15]. BOD concentrations during the same period
were 7 to 11 mg/L in the summer and 8 to 12 mg/L in the winter. An
acclimation or seasoning period of about 3 months was required before
optimum removals were achieved.
Nitrogen removal is attributed primarily to denitrification. Hunt has
reasoned that an aerobic-anaerobic double layer exists at the surface of
the soil and allows both nitrification and denitrification to occur [16,
17]. Because this process depends on two stages of microbial activity,
it is sensitive to environmental conditions. Plant uptake of nitrogen
2-12
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APPLIED
WASTEWATER
SLOPE 2-8»
FIGURE 2-3
OVERLAND FLOW
GRASS AND
VEGETATIVE LITTER
EVAPOTRANSPIRATION
RUNOFF
COLLECTION
PERCOLATION
(a) HYDRAULIC PATHWAY
SPRINKLER CIRCLES
RUNOFF
COLLECTION
DITCH
(b) PICTORIAL VIEW OF SPRINKLER APPLICATION
2-13
-------
can also be a significant removal mechanism. Permanent nitrogen removal
by plant uptake is only possible if the crop is harvested and removed
from the field. Ammonia volatilization can be significant if the pH of
the water is above 7. Nitrogen removals usually range from 75 to 90%
with runoff nitrogen being mostly in the nitrate form. Higher levels of
nitrate and ammonium may occur during cold weather as a result of re-
duced biological activity and limited plant uptake.
Phosphorus is removed by adsorption and precipitation in essentially the
same manner as with the slow rate and rapid infiltration methods.
Treatment efficiencies are somewhat limited because of the incomplete
contact between the wastewater and the adsorption sites within the soil.
Phosphorus removals usually range from 30 to 60% on a concentration
basis. Increased removals may be obtained by adding alum or ferric
chloride prior to application (see Section 5.1.4).
2.5 Other Processes
The three principal land treatment processes, when implemented, repre-
sent planned and engineered changes to the existing environment. Re-
cently, the concept of using natural ecosystems, such as wetlands, for
wastewater treatment has received considerable attention. Applications
of wastewater (1) to wetlands for treatment, and (2) to the soil by sub-
surface techniques are described in this section.
2.5.1 Wetlands
Wetlands, which constitute 3% of the land area of the continental United
States [18], are intermediate areas in a hydrological sense: they have
too many plants and too little water to be called lakes, yet they have
enough water to prevent most agricultural or silvicultural uses. The
term wetlands is used in this manual to encompass areas also known as
marshes, bogs, wet meadows, peatlands, and swamps. The ability of wet-
lands to influence water quality is the reason for much current research
on their use for wastewater management.
Three categories of wetlands are currently used for municipal wastewater
treatment:
• Artificial wetlands
• Existing wetlands
• Peatlands
2-14
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Wetlands are discussed in more detail in Section 5.1.5. Peatlands are
discussed separately because these highly organic soils can be drained
and managed in a manner similar to that used in slow rate land
treatment.
2.5.1.1 Artificial Wetlands
Two artificial wetlands treatment systems have been developed at the
Brookhaven National Laboratory on Long Island, New York [19]. Both are
wetlands-pond systems. In the first, the wetlands consist of wet mead-
ows merging into a marsh followed by a pond (meadow-marsh). In the
second system, the wet meadows are deleted. Both systems are being
loaded at an application rate of about 25 in./wk (63 cm/wk). Aerated
wastewater is applied and recycling is no longer employed.
These artificial wetlands were formed in sandy soil by installing an im-
pervious plastic liner under the soil. They were placed in operation in
June 1973. Operating modes have evolved from the original recycling to
the present once-through approach with increasing loading rates until
April 1976, when the present rates were established. Typical averaged
results for July through September 1975 for operation with a one-to-one
recycling of pond effluent are presented in Table 2-4.
TABLE 2-4
TREATMENT PERFORMANCE FOR TWO
ARTIFICIAL WETLAND SYSTEMS ON LONG ISLAND [19]
mg/L
Constituent
Meadow-marsh Wetlands
Influent effluent effluent
BOD 520 15 16
Suspended solids 860 43a 57a
Total nitrogen 36 3 4
Fecal coliforms,
count/100 mL 3,000 17b 21°
a. Principally algae.
b. Geometric mean.
2-15
-------
The wetlands area occupies 0.2 acre (0.08 ha) and is flooded to a depth
of about 0.5 ft (0.15 m). Small recommends a 1 ft (0.3 m) depth or more
to prevent volunteer weed growth and to prevent washout during storms
[20]. Cattails were planted and duckweed (Lemna minor) is prevalent.
Regular harvest of cattails is not practiced but weeds, grasses, and
cattails were thinned out in March 1976.
2.5.1.2 Existing Wetlands
The application of secondary effluent to existing freshwater and salt
water wetlands is being studied in Mississippi, as well as in Califor-
nia, Michigan, Louisiana, Florida, and Wisconsin. In Mississippi, Wol-
verton has studied the use of water hyacinths in secondary wastewater
lagoons to effect removals of BOD, suspended solids, and nutrients [21].
A surface area of 0.7 acre (0.28 ha) was used, and detention times
ranged from 14 to 21 days. The treatment performance of this system is
compared to that of a control lagoon free of water hyacinths for Septem-
ber 1975 as shown in Table 2-5.
TABLE 2-5
TREATMENT CAPABILITY OF WATER HYACINTHS FED
OXIDATION POND EFFLUENT [21]
mg/L
Hyacinth pond
Control pond
Constituent
Influent Effluent Influent Effluent
BOD
Suspended solids
Total Kjeldahl
nitrogen
Total phosphorus
TDS
22
43
4.4
5.0
187
7
6
1.1
3.8
183
27
42
4.5
4.8
390
30
46
4.5
4.6
380
Hyacinths must be harvested for effective nutrient removal. Wolverton
suggests harvesting every 5 weeks during the warm growing season. The
harvested plants may be processed into high-protein feed products, or-
ganic fertilizer and soil conditioner, or methane gas [22].
The use of existing wetlands appears to hold promise as an emerging
technology for wastewater management. Management techniques for nutri-
ent removal, loading rates, climatic constraints and suitable site
characteristics need further study.
2-16
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2.5.1.3 Peatlands
The use of peatlands or organic soils for land application has been
studied by Farnham in Minnesota [23] and by Kadlec in Michigan [24]. A
system has been designed by Stanlick [25] on the basis of Farnham1s re-
search.
Although sprinkler or surface application techniques can be used on
peatlands, the North Star Campground system in Minnesota uses
sprinklers [25]. It was designed for 13.3 in./wk (33.8 cm/wk) and is
underdrained at a depth of about 3 ft (1 m). Treatment efficiency for
1975 is summarized in Table 2-6. Secondary effluent was applied.
TABLE 2-6
TREATMENT PERFORMANCE OF PEATLAND IN MINNESOTA [25]
mg/L
Constituent Influent Effluent
ROD
Suspended solids
Total nitrogen 20-40
Total phosphorus 10
Fecal col i forms, , j-
c
5
1-10
0.1
count/100 mL 10-10 0-4
Because of the high loading rate, the nitrogen uptake of the grass
planted on the peat surface was surpassed. Although the peat pH was 4,
the effluent pH was consistently between 6.5 and 7.5.
2.5.2 Subsurface Application
Two systems that are quite similar to the peatland system are the soil
mound and the subsurface filter systems. The subsurface filter is des-
cribed in the Manual of Septic-Tank Practice [26]. The soil mound
system used by Bouma [27] and others is similar to the peatland system
in Minnesota, except that the application is by subsurface pipe.
The soil mound system for a shallow soil over creviced rock is shown in
Figure 2-4. Such systems are alternatives to treatment and discharge to
2-17
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surface waters where adverse soil conditions exist. The soil mound can
be used for [28]:
1. Shallow soils (<3 ft or 1 m) over creviced or otherwise ra-
pidly permeable bedrock
2. Sites with slowly permeable soils
3. Sites with seasonally high groundwater
FIGURE 2-4
SUBSURFACE APPLICATION TO SOIL MOUND OVER CREVICED BEDROCK
EVAPOTRANSPIRATION
(GROWING SEASON)
VEGETATION
TOPSOIL
•••>;••' • ••• ; • * '"I
I I i I j SOIL-FI
APPLIED
WASTEWATER
^^
Mill
2 ft (0.6m)
ORIGINAL SOIL
CREVICED BEDROCK
Bouma has reported on an experimental soil mound system at Sturgeon Bay,
Wisconsin [27], The work is part of the Small Scale Waste Management
Project at the University of Wisconsin. The mound, shown in Figure
2-4, was designed for 2 in./d (5 cm/d) but was actually dosed at about
half of that rate. Septic tank effluent was dosed four times a day
through a network of 1 in. (2.5 cm) PVC pipes. The actual loading was
6.4 in./wk (16.3 crn/wk). Treatment performance of this mound system is
given in Table 2-7.
2-18
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TABLE 2-7
TREATMENT PERFORMANCE OF AN EXPERIMENTAL
SOIL MOUND SYSTEM IN WISCONSIN [27]
mg/L
Constituent
Influent Effluent
BOD
COD
Ammonia nitrogen
Total nitrogen
Total phosphorus
Fecal col i forms,
count/mL
Total col i forms,
count/raL
90
256
56
62
15
2,500
37,000
0
42
2
56
8
5
54
2.6 References
1. Evaluation of Land Application Systems. Office of Water Program
Operations, Environmental Protection Agency. EPA-430/9-75-001.
March 1975.
2. Sullivan, R.H., et al. Survey of Facilities Using Land Application
of Wastewater. Environmental Protection Agency, Office of Water
Program Operations. EPA-430/9-73-006. July 1973.
3. Kardos, L.T., W.E. Sopper, E.A. Myers, R.R. Parizek, and J.B.
Nesbitt. Renovation of Secondary Effluent for Reuse as a Water
Resource. Environmental Protection Agency, Office of Research and
Development. EPA-660/2-74-016. February 1974.
4. Michigan State University, Institute of Water Research. Utilization
of Natural Ecosystems for Wastewater Renovation. Final Report for
Region V Office, Environmental Protection Agency. East Lansing,
Mich. March 1976.
5. Cole.D.W. University of Washington. Personal Communication. May 1977.
6. Jackson, W.G. , R.K. Bastian and J.R. Marks. Effluent Disposal in an
Oak Woods During Two Decades. Publications in Climatology. 25(3):
20-36. 1972.
7. Uemirjian, Y.A. Land Treatment of Municipal Wastewater Effluents,
Muskegon County Wastewater System. Environmental Protection Agency,
Technology Transfer. 1975.
2-19
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8. Iskandar, I.K., R.S. Sletten, D.C. Leggett, and T.F. Jenkins.
Wastewater Renovation by a Prototype Slow Infiltration Land
Treatment System. Corps of Engineers, U.S. Army Cold Regions
Research and Engineering Laboratory. CRREL Report 76-19. Hanover,
N.H. June 1976.
9. biroadbent, F.E. Nitrification and Denitrification of Municipal
Wastewater Effluents Disposed to Land. Prepared for the California
Water Resources Control Board. University of California, Davis.
February 1976.
10. Bouwer, H., R.C. Rice, and E.D. Escarcega. High-Rate Land
Treatment I: Infiltration and Hydraulic Aspects of the Flushing
Meadow Project. Jour. WPCF. 46:834-843, May 1974.
11. McMichael, F.C. and J.E. McKee. Wastewater Reclamation at
Whittier Narrows. California State Water Quality Control Board.
Publication No. 33. 1966.
12. Bouwer, H., J.C. Lance, and M.S. Riggs. High-Rate Land Treatment
II: Water Quality and Economic Aspects of the Flushing Meadows
Project. Jour. WPCF. 46:844-859, May 1974.
13. Seabrook, B.L. Land Application of Wastewater in Australia.
Environmental Protection Agency, Office of Water Programs.
EPA-430/9-75-017. May 1975.
14. Melbourne and Metropolitan Board of Works. Waste into Wealth
(Wastewater Treatment by Irrigation). Melbourne, Australia. 1971.
15. Thomas, R.E., K. Jackson, and L. Penrod. Feasibility of Overland
Flow for Treatment of Raw Domestic Wastewater. Environmental
Protection Agency, Office of Research and Development. EPH-66Q/2-
74-087.' July 1974.
16. Hunt P.G. and C.R. Lee. Overland Flow Treatment of Wastewater - A
Feasible Approach. In: Land Application of Wastewater.
Proceedings of a Research Symposium Sponsored by the USEPA, Region
III, Newark, Del. November 1974.
17. Carlson, C.A., P.G. Hunt, and T.B. Delaney, Jr. Overland Flow
Treatment of Wastewater. Army Engineer Waterways Experiment Station.
Miscellaneous Paper Y-74-3. August 1974.
18. Witter, J.A. and S. Croson. Insects and Wetlands. In: Proceedings
of the National Symposium on Freshwater Wetlands and Sewage Effluent
Disposal. University of Michigan. Ann Arbor, May 1976. pp
269-295.
19. Small, M.M. Meadow/Marsh Systems as Sewage Treatment Plants.
brookhaven National Laboratory. BNL20757. Upton, N.Y. November
1975.
2-20
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20. Small, M.M. Marsh/Pond Sewage Treatment Plants. In: Proceedings
of the National Symposium on Freshwater Wetlands and Sewage Effluent
Disposal. University of Michigan. Ann Arbor, May 1976. pp
197-214.
21. wolverton, B.C. and R.C. McDonald. Water Hyacinths for Upgrading
Sewage Lagoons to Meet Advanced Wastewater Treatment Standards, Part
1. NASA Technical Memorandum TM-X-72729. Bay St. Louis, Miss.
October 1975.
22. Wolverton, B.C. et al. Bio-conversion of Water Hyacinths into
Methane Gas: Part 1. NASA Technical Memorandum TM-X-72725. Bay
St. Louis, Miss. July 1975.
23. Farnham, R.S. and D.H. Boelter. Minnesota's Peat Resources:
Their Characteristics and Use in Sewage Treatment, Agriculture, and
Energy. In: Proceedings of the National Symposium on Freshwater
Wetlands and Sewage Effluent Disposal. University of Michigan. Ann
Arbor, May 1976. pp 241-256.
24. Kadlec, J.A. Dissolved Nutrients in a Peatland near Houghton Lake,
Michigan. In: Proceedings of the National Symposium on Freshwater
Wetlands and Sewage Effluent Disposal. University of Michigan. Ann
Arbor, May 1976. pp 25-50.
25. Stanlick, H.T. Treatment of Secondary Effluent Using a Peat Bed.
In: Proceedings of the National Symposium on Freshwater Wetlands
and Sewage Effluent Disposal. University of Michigan. Ann Arbor,
May 1976. pp 257-268.
26. Manual of Septic-Tank Practice. U.S. Department of Health,
Education, and Welfare. Public Health Service Publication No. 526.
Revised 1967.
27. Bouma, J., et al. An Experimental Mound System for Disposal of
Septic Tank Effluent in Shallow Soils Over Creviced Bedrock. In:
Proceedings of the International Conference on Land for Waste
Management, Ottawa, Canada, October 1973. pp 367-377.
28. Bouma, J. Use of Soil for Disposal and Treatment of Septic Tank
Effluent. In: Water Pollution Control in Low Density Areas,
Proceedings of a Rural Environmental Engineering Conference,
Jewell, W.J. and R. Swan, (ed.). Hanover, The University Press of
New England, 1975. pp 89-94.
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CHAPTER 3
TECHNICAL PLANNING AND FEASIBILITY ASSESSMENT
3.1 Purpose and Scope
The purpose of this chapter is to describe those aspects of land
treatment that are important to a technical and economic feasibility
assessment. The major divisions of this chapter are:
• Approach to development of alternatives
• Evaluation of unit processes
• Wastewater quality
• Regional site characteristics
• Other planning considerations
t Evaluation of alternatives
The scope of the chapter is directed at those factors that are unique to
the formulation and evaluation of land treatment alternatives. Planning
and feasibility considerations that are common to conventional
wastewater management systems are adequately discussed elsewhere.
It is important to be aware of the distinction made between "alternative
land treatment processes" (described in Chapter 2) and "system
alternatives." The term "land treatment process" .refers to the unit
process only (e.g., slow rate, overland flow) whereas the term "system
alternatives" includes the entire wastewater management facility
(transmission, treatment processes, storage, collection, and discharge
facilities).
This chapter presents planning level information related to unit process
selection, the wastewater characteristics important to land treatment
systems, and the significant regional characteristics involved in
developing land treatment system alternatives. It is expected that the
user will also refer to Chapter 5, or for small systems Chapter 6,
during the feasibility assessment to obtain more technical details for
the development of alternative systems. The evaluation of the resulting
systems is then discussed in Section 3.7.
3-1
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3.2 Approach to Development of Alternatives
Three major factors combine to determine the type of land treatment
process that can be used on a given site:
1. Soil permeability
2. Wastewater quality
3. Discharge quality criteria
For a given site, the soil permeability can be determined. The other
two factors, however, must be considered as variables. The wastewater
quality to be applied depends on the preapplication treatment. The
discharge criteria are also variable because there is a choice between
surface water and groundwater discharge. There is also the possibility
of collecting the treated water for other uses in agriculture or
industry.
The many variables and options associated with land treatment processes
and systems require the use of an organized, systematic approach to
selecting alternatives. Many approaches have been considered but only
three have been commonly used. The three most common approaches to
developing land treatment alternatives are:
1. No constraints approach—There are no prior constraints placed
on the study. The entire study area is investigated for
potential sites while considering the whole spectrum of land
treatment processes and combinations to develop alternatives.
2. Process constrained approach—The study begins with some prior
constraints that limit consideration of alternatives to
certain land treatment processes. Potential sites are
identified within the reduced spectrum of land treatment
processes created by the constraints.
3. Site-constrained approach—A predetermined site (or sites) is
available, and treatment processes are evaluated to match the
site(s) and the project objectives.
The approach to the development of land treatment alternatives is
iterative in nature, as illustrated in Figure 3-1. This iterative
process is best achieved in the no-constraints approach. Within the
iterative cycle of site identification, site evaluation, process
assessment, and planning implications assessment, there are so many
degrees of freedom available that several cycles or iterations may be
necessary to define and develop an alternative. When the number of
sites or processes is predetermined, as in the process-constrained or
site-constrained approach, fewer alternative systems can be developed.
A variation of the no-constraints approach is the use of an inductive
analytical planning process. Regional goals and objectives are
3-2
-------
FIGURE 3-1
PLANNING SEQUENCE FOR THE DEVELOPMENT OF LAND TREATMENT ALTERNATIVES
IDENTIFY STUDY
AREA GOALS
AND
OBJECTIVES
IDENTIFY
POTENTIAL
LAND TREATMENT
AREAS OR SITES
DETERMINE
WASTEWATER
TREATMENT
NEEDS
oo
i
OJ
EVALUATE
SITE
CHARACTERISTICS
DEVELOP
LAND TREATMENT
ALTERNATIVES
\
ASSESS
PLANNING
IMPLICATIONS
EVALUATE
LAND TREATMENT
ALTERNATIVES
ASSESS
LARD TREATMENT
PROCESSES
-------
initially identified and the ability of land treatment to help achieve
these and other benefits is assessed. Included are the possibilities
for reclamation and resource recovery such as recycling of nutrients
through the production of cash crops, preservation of agriculture and
open space, and the implementation of other land use planning
objectives. Thus, land treatment may be viewed as a means to an end
rather than an end in itself.
3.3 Evaluation of Unit Processes
To evaluate the applicability of land treatment processes, the treatment
objectives and wastewater quality must be known. The preliminary design
of land treatment processes can then be accomplished using average
flowrates and hydraulic loading rates. In this section, hydraulic
loading rates are discussed for each land treatment process. Guidance
is then provided for preliminary planning purposes on land area
requirements, preapplication treatment, storage, and recovery of
renovated water.
3.3.1 Land Treatment Processes
The first step in evaluating land treatment unit processes is to
identify the processes that may be suitable for the requirements and
conditions of the study area. The description of treatment process
capabilities and objectives in Chapter 2 will provide a useful
background for this purpose. The types of factors that should generally
be considered at this stage include:
• The ability of each process to meet treatment requirements
• The disposition of applied wastewater in relation to water
needs
• The predominant characteristics of the study area that may
dictate certain land treatment processes
• The desired secondary objectives, such as increased irrigation
water supply
3.3.1.1 Slow Rate Process
For the slow rate process, the hydraulic loading rate can be determined
initially from the use of the water balance:
Precipitation + Wastewater applied = Evapotranspiration + Percolation + Runoff (3-1)
3-4
-------
Effluent runoff is usually not desirable for the slow rate process. For
planning, the relationship between precipitation and evapotranspiration
on a mean annual basis can be taken from Figure 3-2. If the
precipitation and evapotranspiration balance, an estimate of wastewater
application rates can be made from the soil permeability rates as
presented in Figure 3-3. For example, a slow permeability soil could be
loaded at 1.0 to 3 in./wk (2.5 to 7.6 cm/wk) from Figure 3-3. If
evapotranspiration exceeds precipitation, the effluent applied can be
increased to equal the sum of net evapotranspiration and soil
permeability. For example, in central Texas, where net evapotranspira-
tion is 36 in./yr (90 cm/yr), the application rate could be increased by
0.7 in./wk (1.8 cm/wk) on an annual average to a total of 1.7 to 3.7
in./wk (4.3 to 9.4 cm/wk). Application rates beyond 4 in./wk (10 cm/wk)
are normally defined as rapid infiltration and involve different
considerations.
The shaded area in Figure 3-3 represents the range of average, long-term
infiltration rates when considering only soil permeability derived from
clear water. The range of values shown in Figure 3-3 as "Range of
Application Rates in Practice" is indicative of the many factors that
must be considered in selecting the final application rate. Such
considerations include crop water needs and tolerances, nutrient
balance, and reductions in application rates for crop harvesting or to
account for algae in the wastewater.
The hydraulic loading is also affected by the climate and crop
selection. The climate will affect the growing season and will dictate
the period of application and the amount of storage required. Crop
water tolerances and nutrient requirements can directly affect hydraulic
loading rates. The following factors affect the selection of crops:
1= Suitability to local climate and soil conditions
2. Consumptive water use and water tolerance
3. Nutrient uptake and sensitivity to wastewater constituents
4. Economic value and marketability
5. Length of growing season
6. Ease of management
7. Public health regulations
3.3.1.2 Rapid Infiltration Process
Rapid infiltration systems are designed on the basis of hydraulic
capacity of the soil and the underlying geology. The relationship shown
in Figure 3-3 can be used for approximation of hydraulic loading rates,
3-5
-------
FIGURE 3-2
POTENTIAL EVAPOTRANSPIRATION VERSUS MEAN ANNUAL PRECIPITATION [1]
Inches
CT)
+ 30
+ 50
1 \ n. = 2. 54 cm
-5
+ 50
+ 30
f POTENTIAL EVAPOTRANSPIRATION MORE THAN
MEAN ANNUAL PRECIPITATION
- POTENTIAL EVAPOTRANSPIRATION LESS THAN
MEAN ANNUAL PRECIPITATION
-------
1000
0.1
FIGURE 3-3
SOIL PERMEABILITY VERSUS RANGES OF APPLICATION RATES
FOR SLOW RATE AND RAPID INFILTRATION TREATMENT
PROBABLE
LONG TERM
FOR
INFILTRATION
OF APPLICA
IN PRACTrC
ARBITRA
BETWEEN
AND RAP
SYSTEMS
SLOV RATE
SYSTEMS
Y DlVISIOi
SLOV RATE
D INFILTR
PERMEABILITY RATES OF MOST RESTRICTIVE LAYER IN SOIL PROFILE, in./h
PERMEABILITY* SOIL CONSERVATION SERVICE DESCRIPTIVE TERMS
VERY SLOV
< 0.06
SLOV
0.06-0. 20
MODERATE-
LY SLOV
0.20-0.60
MODERATE
0. 60-2. 0
MODERATE-
LY RAPID
2.0-6.0
RAPID
6.0-20. 0
VERY RAPID
> 20.0
* MEASURED VITH CLEAR VATER
1 in./«ik- 2.54 cn/wk
3-7
-------
if the permeability of the most restrictive layer in the soil profile is
known. Application rates in the low end of the range should be chosen
if any of a number of conditions exist which may be adverse. These
include: (1) wide variations in soil types and permeability,
(2) shallow soil profiles, and (3) shallow or perched water tables.
Reductions in application rates may also be necessary if the system is
to be managed to optimize denitification. The cycle of wastewater
application and resting must be defined.
3.3.1.3 Overland Flow Process
For overland flow, the application rate depends primarily on the
expected treatment performance and the level of preapplication
treatment. If primary effluent is used, an application rate in the
range of 2.5 to 6 in./wk (6.4 to 15 cm/wk) is usually necessary to
produce the effluent quality shown in Table 2-2. The lower end of this
range should be considered where: (1) terrace slopes will be greater
than about 6%, (2) terraces are less than 150 ft (45 m) long,
or (3) climatic conditions are poor. The upper end of the scale can be
used when evapotranspiration rates are high, or when a moderate amount
of percolation can be expected to take place. In cases where overland
flow is to be used as a polishing process or for advanced treatment
following preapplication treatment, application rates as high as 6 to 16
in./wk (15 to 40 cm/wk) may be used. These rates have been used in
demonstration systems with slopes of 2 to 3% that are 120 ft (36 m)
long.
3.3.1.4 Combinations
Combinations of land treatment processes in series can be considered.
Examples of two such systems are shown schematically in Figure 3-4. In
the first example, rapid infiltration is used after overland flow to
further reduce concentrations of BOD, suspended solids, and phosphorus.
Because of the increased reliability and overall treatment capability,
the application rates for the overland flow process could be higher than
normal.
In the second example, the rapid infiltration process precedes slow rate
treatment. The recovered renovated water should meet even the most
restrictive requirements for use on food crops. The unsaturated zone
can be used for storage of renovated water to be withdrawn on a schedule
consistent with crop needs.
3-8
-------
FIGURE 3-4
EXAMPLES OF COMBINED SYSTEMS
PREAPPLICATION
TREATMENT
STORAGE
OVERLAND
FLOW
RAPID
INFILTRATION
OPTIONAL
RECOVERY
WELLS
DISCHARGE
CO
vo
a) OVERLAND FLOW FOLLOWED BY RAPID INFILTRATION
\ ' / S
1
MM, y^ s-~*J>-^J>-^J>-
^M^
PREAPPLICATION RAPID RECOVERY SLOW RATE
TREATMENT INFILTRATION WELLS TREATMENT
b) RAPID INFILTRATION FOLLOWED BY SLOW RATE TREATMENT
-------
3.3.2 Land Area Requirements
The total land area required for a land treatment system consists of the
actual land to which wastewater is applied and the additional area
required for buffer zones, storage reservoirs, access roads, pumping
stations, preapplication treatment, and maintenance and administration
buildings. In addition, it may be necessary to set aside some land for
future expansion or emergencies.
The total land area requirement can be estimated for preliminary
planning using the nomograph in Figure 3-5. To use the nomograph, first
draw a line through appropriate points on the design-flow and
application-rate axes to the pivot line. Draw a second line from the
intersection of the first line with the pivot line through the
appropriate point on the nonoperating time axis. (Nonoperating time is
the period during the year when the system is shut down for weather or
other reasons.) The calculated total area is then noted at the
intersection of that axis with the second line. This total area
includes land for application, roads, storage, and buildings. The total
area with a 200 ft (61 m) wide buffer zone allowance is read from the
right-hand side of the axis; the total area with no allowance for buffer
zones is read from the left-hand side.
3.3.3 Preapplication Treatment
Preapplication treatment of wastewater may be necessary for a variety of
reasons, including (1) maintaining a reliable distribution system,
(2) allowing storage of wastewater without creating nuisance conditions,
(3) obtaining a higher level of wastewater constituent removal,
(4) reducing soil clogging, and (5) reducing possible health risks. A
summary of preapplication treatment practice is presented in Table 2-1.
3.3.4 Storage
Storage is provided primarily for nonoperating periods and periods of
reduced application rates resulting from climatic constraints. In most
situations, however, where this requirement is small, storage may still
be necessary for system backup, flow equalization, and proper
agricultural management including periods for harvesting. In the
planning stage, it will usually be important to determine the
approximate volume required for each land treatment alternative so that
storage costs can be estimated.
It has been shown that slow rate and overland flow irrigation systems
can usually operate successfully below 32°F (0°C), and 25°F (-4°C) is
3-10
-------
20 -=>
15 —
10
9
8
7
6
3 -^
9 ——
s
FIGURE 3-5
TOTAL LAND REQUIREMENT (INCLUDES LAND FOR APPLICATION, ROADS, STORAGE, AND BUILDINGS)
100 —
50 -
- 10 —
a
5 H
0.5 -
0.1 —
1 in./ 1 wk = 2.54 cm/ wk
1 Mgal/ d = 43.8 L/S
1 ACRE = 0.405 ha
30000 —|
20000 —
10000
5000
— 30000
— 20000
— 10000
5000
. 1000
oe
= 500
50 -
10 —
5 —'
ut
Ul
ec.
u
. 1000 u.,
0
500 J[
SAMPLE PLOT
25
* 20
Ul
^ 15-^
CO
5 -10 •
cc
Ul
o 5 —
z
o -
o —
— 100
- 50
— 10
SAMPLE PLOT
DES I GN FLOt 3 M ga I /d
APPL. RATE 1.5 IN. /WK
NONOPER. TIME 10 WK
READ: goo ACRES «ITH BUFFER
750 ACRES WITHOUT BUFFER
-------
sometimes used as a lower limit. A conservative method for predicting
the number of days that are too cold for operation is to assume that
application is suspended on all days in which the mean temperature is
below 32°F (0°C). This method has the advantage of using readily
accessible data.
The National Climatic Center in Asheville, North Carolina, has conducted
an extensive study of climate and weather variations throughout the
United States. A computer program has been developed to use weather
station data in estimating the amount of wastewater storage required at
a location because of climatic constraints [2]. For planning and
preliminary feasibility assessment, a value for storage days can be
found using Figure 3-6. The map gives the number of nonapplication days
for which storage would normally be required for a 20 year return period
on the basis of climatic factors alone. Additional storage time may be
required if reduced winter loading rates are used for overland flow (see
5.1.4.1).
Rapid infiltration basins which are intermittently flooded can often be
operated year-round regardless of climatic conditions. The only storage
that might be required is that for system backup or extremely severe
climatic conditions. During extended periods of cold weather, an ice
layer may form on the surface of the bed. However, at Lake George, New
York, and at Fort Devens, Massachusetts, this has not proved to be a
problem. The application of the wastewater merely floats the ice and
infiltration continues. This condition should prevail whenever the soil
is porous and well drained; otherwise, precautions are advised.
3.3.5 Recovery of Renovated Water
Recovery of the applied wastewater after renovation for reuse or further
treatment is often a part of the overall land treatment process. The
means to recover renovated water include (1) surface runoff collection,
(2) underdrains, (3) recovery wells, and (4) tailwater return. The
applicability of these systems to the treatment processes is summarized
in Table 3-1. These recovery methods are described in various
situations in Chapter 5.
3.4 Wastewater Quality
Knowledge of the quality of the wastewater to be treated is needed in
planning to properly assess preapplication treatment needs or special
management needs. The major constituents in typical untreated domestic
wastewater are presented in Table 3-2. Preapplication treatment using
primary sedimentation will reduce BOD and suspended solids (SS),
but will not greatly affect nitrogen or phosphorus concentrations.
Treatment in oxidation ponds, aerated lagoons, or other biological
3-12
-------
FIGURE 3-6
ESTIMATED WASTEWATER STORAGE DAYS BASED
ONLY ON CLIMATIC FACTORS [2]
J 20
GO
I
u>
SHADING DENOTES REGIONS WHERE
THE PRINCIPAL CLIMATIC CONSTRAINT
TO APPLICATION OF WASTEWATER
IS PROLONGED WET SPELLS
I 60
BASED ON 32°'F (0°C)
MEAN TEMPERATURE
0.5 in./d PRECIPITATION,
1 in. OF SNOWCQVER
1 in.= 2.54 en
-------
treatment processes further reduces the
nitrogen or phosphorus.
BOD and SS, and may reduce
TABLE 3-1
APPLICABILITY OF RECOVERY SYSTEMS
FOR RENOVATED WATER
Recovery system
Slow rate
Rapid infiltration Overland flow
Surface runoff collection
Effluent
Stormwater
Underd rains
Recovery wells
Tail water
Sprinkler application
Surface application
NA NA
Sediment control NA
Groundwater control Groundwater control
and effluent recovery and effluent recovery
Usual ly NA
NA
25-50% of applied
flow
Groundwater control
and effluent recovery
NA
NA
Collect3
Erosion control
NA
NA
NA
NA
NA = not applicable.
a. Disinfect if required before discharge; provide for short-term recycling of waste-
water after extended periods of shutdown, if effluent requirements are stringent.
TABLE 3-2
IMPORTANT CONSTITUENTS IN TYPICAL
DOMESTIC WASTEWATER [3]
mg/L
Type of wastewater
Constituent
BOD
Suspended solids
Nitrogen (total as N)
Organic
Ammonia
Nitrate
Phosphorus (total as P)
Organic
Inorganic
Strong
300
350
85
35
50
0
20
5
15
Medium
200
200
40
15
25
0
10
3
7
weak
100
100
20
8
12
0
6
2
4
Land treatment processes are capable of removing large amounts of BOD
and SS as well as nutrients, trace elements, and microorganisms.
3-14
-------
Hydraulic loading rates were discussed in the previous section and will
usually govern site area. However, in some cases constituent loading
rates may dictate land area needs. For preliminary planning purposes,
the BOD loading rate guidelines in Table 3-3 can be used to determine
whether hydraulic or constituent loadings will control the design.
Using hydraulic application rates appropriate for the process and the
BOD concentrations of the wastewater, BOD loadings can be computed and
compared with the values in Table 3-3.
TABLE 3-3
TYPICAL BOD LOADING RATES
lb/acre-d
Slow rate Rapid infiltration Overland flow
Typical range
for municipal
wastewater^ 0.2-5 20-160 5-50
a. Loading rates represent total annual loading divided by
the number of days in the operating season.
Exceeding the typical values in Table 3-3 will not necessarily be
detrimental to the system. The planner or engineer should be aware that
special management may be required above these values and provide
appropriate safeguards. Loading rates are discussed in detail for each
process in Section 5.1.
For trace elements, the concentrations in wastewater vary tremendously
with location and percentage of industrial flows. Ranges of values in
untreated wastewater, primary effluent, and secondary effluent are
presented in Table 3-4. Also included in Table 3-4 are the EPA drinking
water standards for these constituents for comparison. Concentrations
of trace elements in the wastewater after preapplication treatment which
are equal to or less than those recommended for drinking water should
represent no management concern. If one or more values is expected to
exceed these recommendations, the more detailed discussion of trace
element loadings should be consulted in Section 5.1.
3.5 Regional Site Characteristics
Compared to other forms of wastewater treatment, land treatment systems
and processes are very site specific. The objective of characterizing
physical features of the region is to provide the basic information
necessary to make a preliminary assessment of land treatment processes
and systems within the study area. The physical regional features that
are considered important include: topography, soils, geology, climate,
3-15
-------
surface water hydrology and quality, and groundwater hydrology and
quality. In this section, these topics, along with sources of data, are
discussed as they relate to the land treatment processes described in
Chapter 2.
TABLE 3-4
CONCENTRATION OF TRACE ELEMENTS IN VARIOUS
U.S. WASTEWATERS
mg/L
Element
Arsenic
Cadmium
Chromium
Copper
Iron
Lead
Manganese
Mercury.
Nickel
Zinc
Untreated
wastewatera
0.003
0.004-0.14
0.02-0.700
0.02-3.36
0.9-3.54
0.05-1.27
0.11-0.14
0.002-0.044
0.002-0.105
0.030-8.31
Primary
effluents3
0.002
0.004-0.028
<0. 001 -0.30
0.024-0.13
0.41-0.83
0.016-0.11
0.032-0.16
0.009-0.035
0.063-0.20
0.015-0.75
Secondary
effluents3
<0. 005-0. 01
0.0002-<0.02
<0. 010-0. 17
0.05-0.22
0.04-3.89
0.0005-<0.20
0.021-0.38
0.0005-0.0015
<0. 10-0. 149
0.047-0.35
EPA recoircnended
drinking
water standards'3
0.05
0.01
0.05
1.0
0.3
0.05
0.05
0.002
No standard
5.0
a. The concentrations presented encompass the range of values reported in
references [4, 5, 6, 7, 8, 9, 10, 11].
b. Reference [12].
3.5.1 Site Identification
The complexity of site identification depends on the size of the study
area and the nature of the land use. One approach is to start with land
use plans and identify undeveloped land. A tool that can be used is the
map overlay technique. Map overlays can help the planner or engineer to
organize and study the combined effects of land use, slope, relief, and
soil permeability. Criteria can be set on these four factors, and areas
that satisfy the criteria can then be located. If this procedure is
used as a preliminary step in site identification, the criteria should
be reassessed, during each successive iteration. Otherwise, strict
adherence to such criteria may result in overlooking either sites or
land treatment opportunities.
3-16
-------
Information required to make a map overlay includes:
Source Information
USGS quad sheets Base map with topography
Land use maps Existing and future land use
Soil maps Soil permeability and slope
3.5.2 Site Selection
The process of characterizing, evaluating, and selecting sites is
usually iterative in nature. The first screening of sites may be done
using overlays or considering only land use and soil permeability.
Subsequent evaluations include factors such as those presented in
Table 3-5.
Once the full array of site characteristics is assembled, and sites have
been screened for acceptability, the selection process can include
numerical rating systems. The relative effect of each characteristic
can be determined by assigning weighting values. The resulting ratings
should include input from as many qualified planners and engineers as
possible to reduce bias.
3.5.3 Topography
Three main topographic features that affect the suitability of a site
for land treatment of wastewater are: slope, relief, and susceptibility
to flooding. These features play a major role in the preliminary
identification and evaluation of potential sites. A less important
topographic feature--aspect--may also affect site suitability. The
amount of solar radiation a site receives is related to the aspect, or
direction, of the slope. This will affect the consumptive water use of
crops, vegetation, or woodland being considered. The type of climate
will determine the impact that aspect has on site suitability.
The USGS publishes topographic maps for most areas in the United States.
These maps usually have scales of 1:24 000 (7.5 minute series) or
1:62 500 (15 minute series), and they are suitable for determining the
slope and elevation of a region for a project in the planning stage.
Examination of topographic features should not be limited to the
potential site. Adjacent topography should be evaluated for its effects
on the site, particularly with respect to drainage and areas of
potential erosion. Adjacent land characteristics to be identified are
3-17
-------
those that may potentially (1) add stormwater runoff to the site,
(2) back up water onto the site, (3) provide relief drainage, or
(4) cause the appearance of groundwater seeps.
TABLE 3-5
SITE SELECTION GUIDELINES
Characteristic
Land treatment
process affected
Effect
Soil permeability Overland flow
High permeability soils are more suitable to
other processes.
Rapid infiltration Application rates increase with permeability.
and slow rate
Potential ground-
water pollution
Groundwater storage
and recovery
Rapid infiltration
and slow rate
Rapid infiltration
Existing land uses All processes
Future land use
Size of site
Flooding hazard
Slope
All processes
All processes
All processes
All processes
Rapid infiltration
Overland flow
Affected by the (1) proximity of the site to a
potential potable aquifer, (2) presence of an
aquiclude, (3) direction of groundwater flow,
and (4) degree of groundwater recovery by wells
or underdrains.
Capability for storing percolated water and
recovery by wells or underdrains is based on
aquifer depth, permeability, aquiclude con-
tinuity, effective treatment depth, and ability
to contain the recharge mound within the
desired area.
Involves the occurrence and nature of
conflicting land use.
Future urban development may affect the ability
to expand the system.
If there are a number of small parcels, it is
often difficult to control the needed area and
implement the plan.
May exclude or limit site use.
Steep slopes may (1) increase capital expenditures
for earthwork, and (2) increase the erosion hazard
during wet weather.
Steep slopes often affect groundwater flow pattern.
Steep slopes reduce the travel time over the
treatment area and treatment efficiency. Flat
land may require extensive earthwork to create
slopes.
3.5.3.1 Slope
Excessive slope is an undesirable characteristic for land application
because (1) it increases the amount of runoff and erosion that will
occur, (2) it may lead to unstable soil conditions when the soil is
saturated, and (3) it makes crop cultivation difficult or, in some
3-18
-------
cases, impossible. Criteria for maximum slope will depend, in part, on
both the amount of land with moderate slopes (less than 10%) that is
available and the land treatment process. Successful agriculturally
related systems using slopes of 15% or more and silviculture type
systems on wooded slopes of up to 40% have been reported L13J.
The system configuration and earthwork requirements, particularly for
overland flow and rapid infiltration treatment, are important factors
that will determine the maximum slopes permissible for a potential site.
If rolling terrain is to be used for cultivated agriculture, the slope
should not exceed about 15%. Grass and forage crops can be adapted to
steeper slopes. Relatively flat land is normally required for surface
irrigation, although contour furrows have been used on slopes as steep
as 5,%.
For rapid infiltration, the primary topographic concern is that lateral
water movement be controlled so that percolation rates of lower basins
are not affected. At Westby, Wisconsin, basins have been terraced into
a 5% sloping hillside, but there are no underdrains, and the lateral
movement of water from the upper basins reportedly affects the
percolation rates in the lower basins.
For overland flow, the primary requirement is that the existing
topography be such that terrace slopes of 2 to 8% can be formed
economically. The cost and impact of the earthwork required are the
major constraints.
3.5.3.2 Relief
Relief is the relative elevation or elevation difference between one
part of the land treatment system and another. Relief and terrain are
interrelated as they affect the economics of pumping wastewater. The
pumping cost is the principal annual operation cost when large elevation
differences exist between the wastewater source and the land treatment
site, reuse location, or discharge point. This cost must be weighed
against the cost of constructing gravity conveyance to sites that may
have greater distances between system components but favorable relief
characteristics.
For silviculture (where sprinkler irrigation of forest land is
considered), more liberal relief and slope tolerances are possible
because the nature of the root system, forest litter, and vegetation
offer resistance to direct surface runoff and resulting erosion.
3-19
-------
3.5=3.3 Susceptibility to Flooding
Location of land treatment systems within a flood plain can be either an
asset or a liability, depending on the approach taken to planning and
design. Flood prone areas may be undesirable because of the highly
variable drainage characteristics usually encountered and potential
flood damage to the physical components of the treatment system. On the
other hand, flood plains, alluvial deposits, and delta formations may be
the only deep soils available in the area. With careful design and
choice of application techniques, a land treatment system can be an
integral part of a flood plain management plan. The flooding hazard of
a potential site should be evaluated with respect to both the severity
of floods that could occur and the extent of the area flooded.
The extent of flood protection built into a land treatment system will
depend on local conditions. In some cases, it may be preferred to allow
the site to flood as needed and provide the protection through offsite
storage. Further, flood plains are generally unacceptable for
construction of dwellings or commercial buildings, offering an
opportunity for imaginative uses of land treatment systems. It should
be noted that crops can be grown in flood plains if the infrequency of
floods makes it economical to farm.
Descriptions of severe floods that have occurred in the United States,
and summaries of all notable floods of each year, are published as USGS
Water Supply Papers. Maps of certain localities showing the area
inundated in past floods are published as Hydrologic Investigation
Atlases by the USGS. More recent maps of flood prone areas have been
produced by the USGS in many areas of the country as part of the
"Uniform National Program for Managing Flood Losses." The maps are
based on standard 7.5 minute (1:24 000) topographic sheets; and, by
means of overprint in black and white, they identify those areas that
have a 1 in 100 chance of being inundated in any given year.
Additionally, other detailed flood information is usually available from
local offices of the U.S. Corps of Engineers and the flood control
districts that deal with such problems firsthand.
3.5.4 Soils
The soil at a potential site should be identified in terms of its
hydraulic, physical, and chemical characteristics. Important physical
characteristics include texture, structure, and soil depth. Important
hydraulic characteristics are infiltration rate and permeability.
Chemical characteristics that may be important include pH, cation
exchange capacity, nutrient levels, and the adsorption and filtration
capabilities for various inorganic ions.
3-20
-------
Information on soil properties can be obtained from several sources, but
the SCS soil surveys are the primary source. Well logs can also offer
additional data on soils and geology. Soil surveys will normally
provide soil maps delineating the apparent boundaries of soil series
with their surface texture. A written description of each soil series
provides limited information on chemical properties, engineering
applications, interpretive and management information, slopes, drainage,
erosion potentials, and general suitability for most kinds of crops
grown in the particular area. Additional information on soil
characteristics and information regarding the availability of soil
surveys can be obtained directly from the SCS. The SCS serves as the
coordinating agency for the National Cooperative Soil Survey, and as
such, cooperates with other government agencies, universities, and
agricultural extension services in obtaining and distributing soil
survey information.
3.5.4.1 Soil Physical Characteristics
The physical properties of texture and structure are important because
of their effect on hydraulic properties. Soil textural classes are
defined on the basis of the relative percentage of the three classes of
particle size—sand, silt, and clay. Sand particles range in size from
2.0 mm to 0.05 mm; silt particles range from 0.05 mm to 0.002 mm; and
particles smaller than 0.002 mm are clay. From the particle size
distribution, the textural class can be determined using the textural
triangle shown in Figure 3-7. Terms commonly used to describe soil
texture and the relationship to textural class names as established by
the SCS are listed in Table 3-6.
Fine-textured soils do not drain well and retain large percentages of
water for long periods of time. As a result, crop management is more
difficult than with more freely drained soils such as loamy soils.
Fine-textured soils are generally best suited to overland flow systems.
Medium-textured soils exhibit the best balance for wastewater renovation
and drainage. Loamy (medium texture) soils are generally best suited
for slow rate systems (crop irrigation).
Coarse-textured soils (sandy soils) can accept large quantities of water
and do not retain moisture very long. This feature is important for
crops that cannot withstand prolonged submergence or saturated root
zones. Soil structure refers to the aggregation of individual soil
particles. If these aggregates resist disintegration when the soil is
wetted or tilled, it is well structured. The large pores in well-
structured soils conduct water and air, making well-structured soils
desirable for infiltration.
Adequate soil depth is important for root development, for retention of
wastewater components on soil particles, and for bacterial action.
3-21
-------
FIGURE 3-7
PROPORTIONS OF SAND, SILT, AND CLAY IN
THE BASIC SOIL-TEXTURAL CLASSES [14]
too
10
PERCENT SAND
U.S STANDARD SIEVE NUMBERS
10 2040 60 200
I
\
L
1 1 i i i in M i
SAHD
er oc
UJ ^
>• 0
CJ
UJ
CO
QC
^
0
o
i i
z
a
UJ
Z
UJ
at •*.
UJ —
> u.
SILT
CLAY
1 III III II
^ — in in
o o
GRA IN SIZE, mm
3-22
-------
Plant roots can extract water from depths ranging from 1 to 9 ft (0.3 to
2.7 m) or more. Retention of wastewater components, such as phosphorus,
heavy metals, and viruses, is a function of residence time of wastewater
in the soil and the degree of contact between soil colloids and the
wastewater components.
TABLE 3-6
SOIL TEXTURAL CLASSES AND GENERAL TERMINOLOGY
USED IN SOIL DESCRIPTIONS [15]
General terms
Basic soil textural
Common name Texture class names
Sandy soils Coarse {Samy sand
Moderately coarse ]oam
Loamy soils Medium
Very fine sandy loam
Loam
Silt loam
Silt
!Clay loam
Sandy clay loam
Silty clay loam
iSandy clay
Clayey soils Fine {Silty clay
'Clay
The type of land treatment system being considered will determine
whether soil depth is adequate. The minimum soil depth for most systems
that rely on infiltration (rapid infiltration and slow rate) is
about 3 to 5 ft (1.0 to 1.5 m). Soil depths of 1 to 2 ft (0.3 to 0.6 m)
can support grass or turf. Overland flow systems require sufficient
soil depth to form slopes that are uniform and to maintain a vegetative
cover.
3.5.4.2 Soil Hydraulic Properties
Drainage of water within the soil depends on texture, structure, and the
absence of subsurface constraints to the flow of water. An example of a
vertical constraint would be an impermeable clay, hardpan, or rock
strata underlaying a sandy soil. The lateral transmissibility and
percolation rates may limit the application rate unless they are equal
to or higher than the infiltration rate. For high rate systems that
depend largely on vertical water movement, the permeability of the most
3-23
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restricting layer in the upper several feet of soil will usually
determine the maximum hydraulic loading.
The most recent permeability class definitions developed by the SCS are
shown in Table 3-7. Soil permeabilities other than the values shown
in Table 3-7 (for the respective permeability class) may appear in
soil literature depending on the age of the document and local
variations in interpretation. The soil permeability ranges normally
associated with each land treatment process are compared along with the
corresponding permeability and textural class in Table 3-8.
TABLE 3-7
PERMEABILITY CLASSES FOR SATURATED SOIL [15]
Soil permeability,
in./h Class
<0.06
0.06 to 0.2
0.2 to 0.6
0.6 to 2.0
2.0 to 6.0
6.0 to 20
>20
Very slow
Slow
Moderately slow
Moderate
Moderately rapid
Rapid
Very rapid
1 in./h = 2.54 cm/h
TABLE 3-8
TYPICAL SOIL PERMEABILITIES AND TEXTURAL
CLASSES FOR LAND TREATMENT PROCESSES
Soil permeability
range, in./h
Permeability
class range
Textural
class range
Unified Soil
Classification [16]
Principal
Slow rate
0.06-20
Moderately slow to
moderately rapid
Clay loams to
sandy loams
GM-d, SM-d, ML,
OL, MH, PT
processes
Rapid
infiltration
2.0
Rapid
Sapds and
sandy loams
GW, GP, SW,
SP
Overland
flow'
0.2
Slow
Clays and
clay loams
GM-u, GC,
SM-u, SC,
CL, OL, CH, OH
Other pr
Wetlands
0.06-2.0
Slow to
moderate
Clay loams
to silt loams
ocesses
Subsurface
0.2-20.0
Moderately
slow to rapid
Clay loams
to sands
3-24
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3.5.4.3 Soil Chemical Characteristics
The balance of chemical constituents in soil is important to plant
growth and wastewater renovation. The mechanisms of retention of
certain constituents by the soil are discussed in Appendixes A through
E. Chemical properties of the soil should be known by the engineer
prior to design for the purpose of determining changes in soil chemistry
that could occur during operation. Some of the indicators of soil
conditions are pH, salinity, cation exchange capacity (CEC),
exchangeable sodium percentage (ESP), percent base saturation,
nutrients, and metals. Detailed discussion of these chemical
characteristics is deferred to Appendix F.
3.5.5 Geology
Geologic formations and discontinuities that might cause unexpected flow
patterns of applied wastwater to the groundwater should be identified in
the planning stages of a land treatment system. If the underlying rock
is fractured or crevassed like limestone, percolating wastewater may
shortcircuit to the groundwater, thus receiving less than proper
treatment because of reduced residence time in the soil. Similarly,
perched water tables above the normal groundwater can result from
impermeable or semi permeable layers of rock, clay, or hardpan, thus
reducing the effective renovative depth. Permanent groundwater should
be distinguished from localized perched groundwater conditions. Both
the reason for and the direction of movement of a perched groundwater
are important geohydrologic factors of a site.
Geologic discontinuities, such as faults and intrusions, should be
evaluated for their effect on groundwater occurrence, influence on
quantity, and direction of movement. The USGS and many state geological
surveys have completed studies and maps indicating the effects of
geologic formations on groundwater occurrence and movement. Water well
logs can also provide local, detailed information. A groundwater
geologist familiar with local conditions can provide valuable
information by identifying geologic features that may affect groundwater
movement at a particular site.
3.5.6 Climate
An evaluation of climatic factors, such as precipitation, evapo-
transpiration, temperature, and wind, is used in the determination of
the (1) water balance, (2) length of the growing season, (3) number of
days when the system cannot be operated, (4) the storage capacity
requirement, and (5) the amount of stormwater runoff to be expected.
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3.5.6.1 Climatic Data and Its Use
Sufficient climatic data are generally available for most locations from
three publications of the National Oceanic and Atmospheric Administra-
tion (NOAA - formerly the U.S. Weather Bureau).
The Monthly Summary of Climatic Data provides basic data, such as total
precipitation, maximum and minimum temperatures, and relative humidity,
for each day of the month for every weather station in a given area.
Evaporation data are also given where available.
The Climatic Summary of the United States provides 10 year summaries of
data for the same stations in the same given areas. This form of the
data is convenient for use in most of the evaluations that must be made
and includes:
• Total precipitation for each month of the 10 year period
• Total snowfall for each month of the period
• Mean number of days with precipitation exceeding 0.10 and 0.50
in. (0.25 and 1.3 cm) for each month
• Mean temperature for each month of the period
• Mean daily maximum and minimum temperatures for each month
• Mean number of days per month with temperature less than or
equal to 32°F (0°C), and greater than or equal to 90°F
(32.5UC)
Local Climatological Data, an annual summary with comparative data, is
published for a relatively small number of major weather stations.
Among the most useful data contained in the publication are the normals,
means, and extremes which are based on all data for that station, on
record to date. To use such data, correlation may be required with a
station reasonably close to the site.
Climatic data should be subjected to a frequency analysis to determine
the expected worst conditions for a given return period. The data
analyses are summarized in Table 3-9.
3.5.6.2 Climatic Considerations for Crops
The consumptive use by plants is in direct relation to the climate of
the area. Consumptive use or evapotranspiration is the total water used
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in transpiration, stored in plant tissue, and evaporated from adjacent
soil [17]. The consumptive use varies with the type of crop, humidity,
air temperature, length of growing season, and wind velocity. The
amount of water lost by evapotranspiration can be estimated from the pan
evaporation data supplied by NOAA in the vicinity of the site or from
theoretical methods (see Appendix F).
TABLE 3-9
SUMMARY OF CLIMATIC ANALYSES
Factor Data required
Precipitation Annual average.
Analysis
Frequency
analysis.
in.
/yr
Water
Use
balance
maximum, minimum
Rainfall storm Intensity, duration Frequency analysis, in./d Runoff estimate
Frost free period, d
Temperature
Wind
Days with average
below freezing
Velocity and
direction
Storage, treatment efficiency,
crop growing season
Cessation of sprinkling
1 in. = 2.54 cm
The length of the growing season affects the amount of water used by the
crop. The length of the growing season for perennial crops is generally
the period beginning when the maximum daily temperature stays above the
freezing point for an extended period of days, and continues throughout
the season despite later freezes LI7]. This period is related to
latitude and hours of sunlight as well as to the net flow of energy or
radiation into and out of the soil. A limited growing season will
require long periods of storage or alternative methods of disposal in
winter.
3.5.7 Surface Water Hydrology and Quality
3.5.7.1 Hydrology
Surface water hydrology is of interest in land treatment processes
mostly because of the runoff of stormwater. Considerations relating to
surface runoff control apply to both slow rate and overland flow. Rapid
infiltration processes are designed for no runoff.
The control of stormwater runoff both onto and off a land treatment site
must be considered. First, the facilities constructed as part of the
treatment system must be protected against erosion and washout from
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extreme storm events. For example, where earthen ditches and/or
terraces are used, erosion control from stormwater runoff must be
provided. The degree of control of runoff to prevent the destruction of
the physical system should be based on the economics of replacing
equipment and structures. There is no standard extreme storm event in
the design of drainage and runoff collection systems, although a 10 year
return event is suggested as a minimum.
3.5.7.2 Quality
The need to control surface runoff resulting from stormwater depends
mainly on the expected quality of the runoff relative to the normal
discharge requirements to a local body of water. Runoff quality
resulting from storms at land treatment sites is essentially unknown for
most constituents. However, to give some perspective to the magnitude
of nitrogen and phosphorus concentrations in runoff from various
agricultural and rural areas, and as an approach to solving the problem,
selected data from agricultural stormwater runoff studies are given in
Table 3-10.
It is important to note that the research work reported in Table 3-10
was aimed primarily at fertilizing practice and cultivation versus
noncultivation as related to nutrient losses. Nevertheless, these data
suggest that it is advisable to provide some form of sediment removal at
land treatment sites before allowing the remaining runoff water to
escape. Based on the experimental work in Wisconsin 121J, this would
greatly reduce the nutrient losses from the site. Methods used to
minimize sediment and nutrient loss include (1) contour planting versus
straight-row planting, and (2) incorporation of plant residues to
increase organic matter in the soil. In each research study, many
additional factors that affect erosion losses were presented, and the
interested reader should consult the literature.
More recently, Loehr [22] has compiled runoff quality data from various
nonpoint sources. Ranges of values for concentrations of constituents
in agricultural runoff resulting from precipitation and the potential
yield per unit area of these constituents are listed in Table 3-11.
Runoff quality estimates derived from data in Table 3-11 are to be
considered preliminary in nature because of variations in sampling
methods, analytical methods, field conditions, and meteorological
constraints. The order of magnitude of the characteristics and the
differences between sources are more significant than the values.
Adherence to established agricultural practices for erosion control and
environmental protection will limit adverse runoff impacts.
3-28
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TABLE 3-10
AVERAGE VALUES OF NITROGEN AND PHOSPHORUS MEASURED
IN AGRICULTURAL STORMWATER RUNOFF STUDIES
Location
•'ind si te
description Management practice
North Carolina Heavily fertilized,
[18] uncultivated
Lightly fertilized,
uncultivated
Ithaca, H.Y. Highly fertilized
(corn, beans, „ , ^ , . . ., . .
wheat) [19] Moderately fertilnzed
Ontario (marsh) Fertilized and cultivated
Unfertilized and uncultivated
Wisconsin Fertilized plowed surface
(pilot plots, l. in sediment
oat stubble) 2. In water
[21]
Unfertilized plowed surface
1 . In sediment
2. In water
a. Ammonia plus nitrate nitrogen only.
b. Inorganic phosphorus only.
c. Nitrate plus nitrite nitrogen only.
d. Organic nitrogen from soil sediment accounted
nitrogen. Runoff occurred from 1 h of rain at
after a similar rain event.
Total
nitrogen ,
mg/L
4.60
4.60
1.60
6.17a
1.70a
1.88C
0.05C
81. 8d
2.8
84.6
75.2
0.7
75.9
for 90+% of
2.5 in./h,
Total
phosphorus,
mg/L
0.10
0.10
0.08
0.26b
0.12
0.67
0.17
0.88
0.49
T737
0.33
0.1
0.43
all
24 h
1 in./h = 2.54 cm/h
3.5.8 Groundwater Hydrology and Quality
Collection and analysis of available data on groundwater hydrology and
quality are essential to planning and feasibility studies. Desirable
information includes soil surveys, geologic and groundwater resources
surveys, well drilling logs, groundwater level measurements, and
chemical analysis of the groundwater. Numerous federal, state, county,
and city agencies have this type of information as well as universities,
professional and technical societies, and private concerns with
groundwater-related interests. Particularly good sources are the USGS
at the federal level, state water resources departments, and county
water conservation and flood control districts.
3-29
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TABLE 3-11
SUMMARY OF AGRICULTURAL NONPOINT SOURCES CHARACTERISTICS [22J
Source
Preciptation
Forested land
Rangeland
Agricultural
cropland
Land receiving
manure
Irrigation tile
drainage, western
United States
Surface flow
Subsurface
drainage
Cropland tile
drainage
Seepage from
stacked manure
Feedlot runoff
Concentration, mg/L
BOD NOs-N Total N
12-13 0.14-1.1 1.2-0.04
0.1-1 .3 0.3-1 8
7 0.4 9
04-1.5 0.6-2.2
1 8-19 2.1-19
10-25
10 300-13 800 1 800-2 350
1 000-11 000 10-23 920-2 100
Area yield rate, lb/acre-yr
Total P
0.02-0.04
0.01-0.11
0.02-1.7
0.2-0.4
0.1-0.3
0.02-0.7
190-280
290-360
BOD N03-N Total N
1.3-3.7 5-9
0.6-7.9 3-12
06
0 1-12
3.6-12
3-24
.... 74 38-166
0.3-12
1 390 . 890-1 430
Total P
0.04-0.05
0.03-0.8
0.07
0.05-2.6
0.7-2.6
0.9-4.0
3-9
0.009-0.3
9-550
Note: Data do not reflect the extreme ranges caused by improper waste management or extreme stonoi
conditions.
1 lb/acre-yr = 1.12 kg/ha-yr
3.5.8.1 Hydrology
A knowledge of the regional groundwater conditions is particularly
important for potential rapid infiltration and slow rate sites.
Overland flow will not usually require an extensive hydrogeologic
investigation. Sufficient removal of pollutants in the applied
wastewater before reaching a permanent groundwater resource is the
primary concern. The depth to groundwater and its seasonal fluctuation
are a measure of the aeration zone and the degree of renovation that
will take place.
When several layers of stratified groundwater underlie a particular
site, the occurrence of the vertical leakage between layers should be
evaluated. Direction and rate of groundwater flow and aquifer
permeability together with groundwater depth are useful in predicting
the effect of applied wastewater on the groundwater regime. The extent
of recharge mounding, interconnection of aquifers, perched water tables,
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the potential for surfacing groundwater, and the design of monitoring
and withdrawal wells are dependent on groundwater flow data.
Much of the data required for groundwater evaluation may be determined
through use of existing wells. Wells that could be used for monitoring
should be listed and their relative location described. Historical data
on quality, water levels, and quantities pumped from the operation of
existing wells may be of value. Such data include seasonal groundwater-
level variations, as well as variations over a period of years. The
USGS maintains a network of about 15 800 observation wells to monitor
water levels nationwide. Records of about 3 500 of these wells are
published in Water-Supply Paper Series, "Groundwater - Levels in the
United States." Many local, regional, and state agencies compile
drillers' boring logs that are also valuable for defining groundwater
hydrology.
3.5.8.2 Groundwater Quality
Land treatment of wastewater can provide an alternative to discharge of
conventionally treated wastewater. However, the adverse impact of
percolated wastewater on the quality of the groundwater must also be
considered. Existing groundwater quality should be determined and
compared to quality standards for its current or intended use.
Groundwater classifications are discussed in Section 5.1.1. The
expected quality of the renovated wastewater can then be compared to
determine which constituents in the renovated water might be limiting.
The USGS "Groundwater Data Network" monitors water quality in
observation wells across the country. In addition, the USGS undertakes
project investigations or areal groundwater studies in cooperation with
local, state, or other federal agencies to appraise groundwater quality.
Such reports may provide a large part of the needed groundwater data.
3.6 Other Planning Considerations
Land treatment systems make use of existing natural conditions;
therefore, a thorough knowledge of all aspects of any given site is
necessary for a successful design. Most features common to all sites or
projects have been discussed briefly in the preceding sections. There
are also governmental features or planning factors that may be
indirectly related to land treatment studies. Some of these factors are
presented in this section, including:
• Water rights
• Governmental programs
• Land use
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• Environmental setting
t Social and economic aspects
3.6.1 Water Rights
On the basis of water rights considerations, the implementation of a
land treatment system may involve a change in water use from
nonconsumptive (passing flow through a treatment plant with subsequent
discharge) to consumptive. This change can interfere with the water
rights of downstream or senior claims to the water as the source of flow
is depleted when the discharge is not returned to its original channel
[23J.
Water rights problems tend to arise in water-short or fully allocated
areas, yet the existence of a market for reclaimed water in these areas
will aid in the cost effectiveness and acceptability of land treatment.
On a national level, these areas are shown in Figure 3-8.
Most riparian (land ownership) rights are in effect east of the
Mississippi River, and most appropriative (permit system) rights are in
effect west of the Mississippi River, as shown in Figure 3-8 [24], A
legal distinction is made between discharges to a receiving water in a
well-defined channel or basin (natural watercourse), superficial waters
not in a channel or basin (surface waters), and underground waters not
in a well-defined channel or basin (percolating or groundwaters) [24].
A guide in determining whether certain land treatment alternatives may
involve water rights problems is presented in Table 3-12. The intention
here is not to imply that some alternatives will have problems and
others will no~t, but merely to guide the planner or engineer through the
preliminary screening of alternatives.
3.6.1.1 Riparian Rights
According to the Riparian Doctrine, anyone owning land adjacent to, or
underlying, a natural watercourse has the right to use, but not consume,
the water. Within this theory have arisen two subtheories ("natural
flow allocation" and "reasonable use") that affect the manner in which a
riparian right can be executed. In natural flow, the landowner can
diminish neither the quantity nor the quality of the water before
returning it to the watercourse. Beyond minimum consumptive uses, such
as drinking, bathing, or cooking, this right is very restrictive, and it
gave rise to the reasonable use theory. Water under natural flow can be
withdrawn for a "natural," riparian, or nonriparian use. Reasonable use
requires that the water be used for a legal and beneficial purpose.
Because the water right under riparian theory is closely aligned with
the concept of land ownership, the rights to water ownership pass with
sale of the land [25].
3-32
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FIGURE 3-8
DOMINANT WATER RIGHTS DOCTRINES AND AREAS OF WATER SURPLUS OR DEFICIENCY [24]
GO
I
CO
to
APPROPRIATE AND
LAND OWNERSHIP
ss&isJisssssfiss?
RIGHTS
DOMINANTLY
APPROPRIATE
, RIGHTS
LAND OWNERSHIP
RIGHT
APPROPRIATE
AND LAND
OWNERSHI
RIGHTS
AREAS OF WATER SURPLUS
AREAS OF WATER DEFICIENCY
-------
TABLE 3-12
POTENTIAL WATER RIGHTS PROBLEMS FOR LAND
TREATMENT ALTERNATIVES
Land treatment process
Water definition and
water rights theory
Slow rate
Rapid
infiltration
Overland flow
Natural watercourses
Riparian Unlikely Unlikely
Appropriative Likely'5 Likely'5
Combination
Likelyb Likely5
Unlikely
Depends on location of discharge
from collection ditch
Depends on location of discharge
from collection ditch
Surface waters
Riparian
Appropriative
Combination
Percolating
or groundwaters
Riparian
Appropriative
Combination
Unlikely
Unlikely
Unlikely
Unlikely
Likely
Likely
Unlikely
Unlikely
Unlikely
Possible
Likely
Likely
Likely0
Likely^
Likelyc
Unlikely
Unlikely
Unlikely
a. For existing conditions and alternatives formulation stage of the planning
process only. It is also assumed that the appropriative situations are
water-short or over-appropriated.
b. If effluent was formerly discharged to stream.
c.
If collection/discharge ditch crosses other properties to
natural watercourse.
3.6.1.2 Appropriative Rights
Appropriative rights tended to be enacted by statute and defined in the
courts on a case-by-case basis. As a result, wide variations exist
among the 19 western states that recognize such rights. In general, the
basic principles of appropriative rights theory are: (1) first in time,
first in right for the water, and (2) subsequent appropriations cannot
diminish the quantity or quality of a senior right. Usually, permits
are required to establish the right to appropriative water, and the
water thus appropriated must also be put to a beneficial use. Rights to
appropriated water are not connected with land ownership. They may be
bought, sold, exchanged, or transferred wholly or in part [26],
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3.6.1.3 Combination Rights
Many states recognize a combination of riparian and appropriative
rights. This dual-rights system has developed in states that have
water-short and water-surplus areas within their borders. In such
cases, the appropriative theory is usually the predominant one L24J.
3.6.1.4 Types of Waters
For legal purposes, states have divided waters into three types:
natural watercourses, surface water, and percolating (groundwaters).
These classifications are arbitrary and are not based on any scientific
or empirical rating system but their definition does affect the type of
legal problems that may be encountered in land treatment.
3.6.1.4.1 Natural Watercourse
A natural watercourse is one in which water flows in a defined channel
either on or below the earth's surface. This definition includes lakes
and estuaries and intermittent as well as perennial streams.
The major legal problem that could be expected in both riparian and
appropriative states would involve the diversion of what was a direct
discharge with the subsequent reduction in flow to the natural
watercourse. If the watercourse in question is near or at over-
appropriation, junior water users who feel that a reduction in flow may
impair their reasonable use of the water may seek administrative or
judicial relief.
In a riparian state, the diversion of a discharge that was not
originally a part of a stream should not be cause for legal action by
downstream users under natural flow theory.
For appropriative rights states, the risk of legal action against the
diversion is easier to analyze. If the conditions of the stream are
such that the diversion would threaten the quantity or quality of the
appropriated water of a downstream user, the damaged party has cause for
legal action against the diverter. This action may be injunctive, in
which the diverter is prevented from affecting the diversion, or
monetary, in which the diverter would be required to compensate for
damages caused by his diversion. If the stream in dispute is not
already over-appropriated (as is the case in many western streams), or
if the area is not water short, it is unlikely that damages could be
proved as a result of the diversion.
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3.6.1.4.2 Surface Water
A surface water is the legal term for water not contained in a well-
defined basin or channel, i.e., rainfall or snowmelt directly on a
parcel of land. Such waters belong to the landowner, but he cannot
collect and discharge them across adjoining properties without the
consent of the owners of those lands. For surface water rights, there
is little difference between riparian and appropriative states.
If any of the land treatment alternatives being considered by the
planner or engineer require that the renovated water cross another's
property, the granting of a drainage or utility easement across the land
to the natural watercourse or final user is a necessity in all cases.
The cost of such an easement must be considered in the cost-
effectiveness analysis.
3.6.1.4.3 Percolating Waters (Groundwaters)
Problems with water rights could arise from two areas: (1) the rise in
groundwater caused by the land treatment method may damage adjoining
lands, or there may be some interference with the subsurface flow
patterns; and (2) if trace contaminants appear in wells of other water
rights holders, they may perceive a damage as a result of altered water
quality.
In riparian states, the claim of damages would require that a landowner
prove that he overlies the same source of the groundwater as the
owner/operator. If the alleged damages are not caused by negligent
operation of the treatment site, or in a way that is deliberately
harmful to the adjoining landowners, it is doubtful that they have
sufficient cause for legal action.
For appropriative theory states, the question of an increase in the
level or volume of a groundwater should cause no problems because no
one's appropriative right would be threatened.
3.6.1.5 Other Water Rights Considerations
In some states, basin authorities or water/irrigation districts have
regulations against the transfer of water outside their jurisdictional
boundaries. In the western states particularly, the right to divert or
use water does not carry with it the right to store such water.
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The right to water salvaged from imported water that has run off
irrigated lands is also not automatic. The rights in both cases must be
specifically obtained or at least must be assured by precedent legal
action.
3.6.1.6 Sources of Information
The data contained in this section may be sufficient for a small system,
but for larger systems and in problem areas, the watermaster or water
rights engineer at the state or local level should be consulted. Some
states either have no records or carry unenforceable rights in their
records L27], so that further investigation will be necessary if doubt
remains. An excellent reference is the National Water Commission
publication, A Summary-Digest of State Water Laws available from the
Commission L28]. Although summaries of precedent rulings are not
guarantees, they may clarify the situation if similar cases can be found
L23, 24, 27, 29, 30]. Lastly, if problems arise, the assistance of a
water rights attorney is warranted.
3.6.1.7 Resolving Water Rights Problems
To resolve water rights problems, the planner should first attempt to
define the water rights setting that could affect the fate of any
renovated water and then be aware,of the quantity and priority of all
rights in the district or basin. The next step is to define the water
rights constraints for all alternatives. Once the candidate systems
have been selected, the point of discharge, availability and quantity of
discharge, and modifications to existing practices should be examined.
If problems are likely with any of the feasible alternatives, a water
rights attorney should be consulted to define more closely the legal
constraints on the alternatives and to define the owner/operator's
rights and responsibilities. If the owner's rights to the renovated
water can be established, he can now trade those rights with any
potentially damaged senior rights or use the revenues from sale of the
water to offset possible damage claims.
3.6.2 Governmental Programs
The most important federal programs that should be considered in land
treatment, in addition to the EPA Construction Grants Program, are the
Soil Conservation Service, Bureau of Reclamation, and U.S. Army Corps of
Engineers with their reclamation/irrigation programs being of greatest
interest. However, despite the national policy of wastewater
reclamation [31J and the National Water Commission's recommendation to
exchange sewage effluent with potable water now being used for
irrigation, previously subsidized water resources programs often result
in such low water prices that renovated wastewater cannot be
competitively marketed [27].
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In western states, reclamation/irrigation projects are presently
financed by interest-free loans to fanners or irrigation districts and
can be repaid in 40 years with the first payment due 10 years from
project completion for a 50 year total payback period. In eastern
states, up to 50% of the cost of supplying irrigation water is borne by
the federal government; the remainder is repaid over 40 years at low
interest (currently around 5%) L27].
In cases where treated wastewater reuse and sale is desired, the
potential markets for irrigation sales and industrial cooling or process
water should be evaluated. If the irrigation reuse is not able to
compete with existing federal programs, potential industrial users
should be contacted. They may be interested because they are not
eligible for federally subsidized water projects, and may be prevented
from expanding or relocating because of a lack of usable water.
3.6.3 Land Use
The planner should be cognizant of the full spectrum of land uses in the
study area. Further, he must be aware of the community goals and
objectives expressed by the proposed distribution of land use in the
area's general plan. With this knowledge, the planner can develop the
opportunities for land treatment sites that will help achieve these land
use goals and objectives. Further, the site location, type of system,
and related facilities can be planned to optimize conformance to the
proposed environmental and social setting.
As a general guide, the type of land uses that are encountered are
residential, commercial, industrial, recreational, urban open space,
agricultural, wilderness, and greenbelt preserves. In urban areas,
residential, commercial, and industrial uses are the most difficult to
develop compatible plans for, whereas recreational and urban open space
uses are the easiest. Agricultural, wilderness, and greenbelt preserve
uses are most easily incorporated into land treatment site planning
L32J.
A variety of data sources may be used to evaluate present and planned
land uses for the study area. Most city, county, and regional planning
agencies have land use plans that indicate present land use policy.
Often, the plans for future land use are current, but actual land use is
out of date. In this case, satellite earth-imagery photographs may be
helpful. By using LANDSAT (Land Satellite) or ERTS (Earth Resources
Technology Satellite) photographs, not only present land uses but also a
number of very useful physical phenomena, such as the extent of the
flood plain, location of unmapped faults, and point sources of
pollution, can often be determined [33J. Although the techniques for
photointerpretation are a subject beyond the scope of this manual, true
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color, false color infrared, and color infrared prints of the study area
as obtained from the USGS, can provide valuable, up-to-date information
L33J.
When completed, the Land Use Data and Analysis (LUDA) Program of the
USGS will be an invaluable planning tool. LUDA will provide a
comprehensive collection and analysis of land use and land cover data on
a nationwide basis. Individual land use/cover maps will be released
following compilation. Periodic revision of the data is planned.
Once the land uses have been identified, the study area should be
divided into population density areas for comparison with the land uses.
The preferred sites tend to lie in areas that have the lowest population
densities (5 persons per acre or less) L32J. This will have the
positive side effect of minimizing the number of relocations (with their
attendant costs and legal problems) that may be required. Those sites
with the lowest population density and with compatible land use should
be ranked high in the evaluation process for preliminary screening.
The zoning for each candidate site should be checked. Zoning laws are
the means by which a community maintains local control over what kinds
of land uses are allowed. They are also the means by which the tax
assessment rates are set L34]. If a site appears to be excellent in all
other respects but zoning conflicts exist, use permits or waivers may be
obtained through the agency having zoning authority.
In addition to minimum population density, the size of land parcels in
the study area will strongly affect the final site selection. The
fewest number of land parcels needed to develop a site will result in
the least number of property acquisitions or lease contracts and the
relocation of the least number of families. Assessors plats are the
usual source of this type of information.
3.6.4 Environmental Setting
Most public projects require an assessment of their impacts to the
environment. Although the environmental impact statement (EIS)
procedure is lengthy and described in numerous sources, a brief
description of certain key topics is presented.
3.6.4.1 Vegetation and Wildlife
The important relationships are between the ecological communities.
Once these are defined as closely as possible, the task of evaluating
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how the overall ecosystem may adjust to project-created stress becomes
easier to accomplish, and the results are easier to relate to decision-
makers L35].
If the interrelationships of the various plant and animal ecosystems
cannot be defined sufficiently to evaluate the stress, the following
information, as a minimum, should be obtained:
• The habitats of rare or endangered species [36]
• Locations of unique or rare native ecological communities [36]
• Preferred routes of migratory animals or birds
• Locations of feeding, watering, nesting, and mating areas—
especially of those animals that have a low tolerance for
human activity
t Areas whose ecosystems would be substantially altered by
periodically applied water or a raised groundwater table
• Plant communities with high water tolerance to the land
treatment alternatives
Some of the needed data may be available in the community or regional
land use or comprehensive plans. Other excellent sources are state fish
and game departments or the U.S. Bureau of Sports Fisheries and
Wildlife. Colleges and universities usually have data on the flora and
fauna of a region in their biology and zoology departments.
Conservation groups, such as the Sierra Club, Audubon Society, Isaac
Walton League, and Ducks Unlimited, either have access to these data or
know where they can be obtained. Many communities have a naturalist who
has intimate knowledge of unrecorded data. If possible, these people
should be consulted before and during the definition of the vegetation
and wildlife setting.
In the evaluation of the sites for the initial and final screenings,
vegetation and wildlife considerations can be significant. Encroachment
on the habitats of rare, endangered, or threatened species could
eliminate the site from further consideration. If an entire' study area
has been designated as a potential habitat, a field survey is required
for direct observations by qualified biologists/zoologists. In the
absence of direct observations, these professionals can usually render
judgments on the possibility of the species being found at the various
sites.
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3.6.4.2 Historical and Archaeological Sites
Because land treatment systems involve large areas of land, the
possibility of encountering an historical or archaeological site within
the project study area must be carefully considered. Pursuant to the
National Historic Preservation Act (PL 89-655) of 1966, many states have
begun programs of indentifying historic or archaeologic features or
structures. Some states have also developed purchase and preservation
programs L37]. Reports on the plans are excellent sources of data for
regional considerations. Other data can be found in local universities
or college history or geology departments. Aid should be solicited from
the local historical or archaeological organizations and their
individual members.
3.6.5 Social and Economic Aspects
The social and economic aspects, including relocation, aesthetics, and
general public acceptability, are the most difficult for the project
planner/engineer to define and evaluate. Gathering factual and
statistical data about the study area will be one of the first tasks.
One excellent source is the Census Bureau. Also, the Economic
Development Administration may provide community economic profile
reports. Regional and local planning authorities have generally
compiled data for land use, recreation, and employment/population
projections. The best sources, however, will be the public advisory
group and the feedback obtained at the public participation workshops
and the required public hearings [35, 36, 38, 39, 40].
If substantial purchase of land is proposed, relocation may be required
of residences, farm buildings, and possibly commercial buildings.
Relocation has both social and economic impacts and the magnitude must
be fully assessed. An additional consideration is the proximity of
schools, churches, and cemeteries, for which relocation may not be
socially acceptable L41J.
What will be the public reaction to land treatment and reuse of
renovated water alternatives? Although the recycling of animal wastes
is encouraged and accepted, . people are more concerned about the
application of human wastes to the land. They generally have misgivings
about potential public health, odor, property values, and nuisance
problems in connection with land treatment, yet these problems should
not arise in a well-planned, well-engineered, and well-managed system
L34J. The aesthetic effects can be enhanced by proper planning and the
use of buffer zones, trees, shrubs, and careful operation to minimize
odor potential, uncontrolled growth of weeds, and standing water.
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The other aspect of the public acceptability evaluation—reaction to
reuse of renovated water—may depend on the contemplated use of that
resource. A recent study conducted in 10 southern California
communities indicates that the public is ready for large-scale reuse of
renovated water for purposes that do not involve body contact uses of
renovated water. In this same study, government officials were surveyed
nationally, and they rated "public acceptability" lower than the general
public rated it in 12 of the 13 potential reuse categories. These
officials were generally the most conservative of the four groups
surveyed (general public, water resources experts, industry, and
government officials). The results are summarized in Figure 3-9 [42J.
These poll results should not be considered indicative of the kind of
acceptance that may be encountered elsewhere as Southern California has
had positive experiences with wastewater reclamation. It was noteworthy
that local officials, who deal with the public on a daily basis, rated
public acceptability lower than other government officials. However, as
reclamation, conservation of resources, and water shortages become more
prevalent, public acceptance to wastewater renovation and reuse should
improve.
The project planner or engineer should realize that if land treatment
and water renovation is unknown in the study area, it may represent a
major change in considering wastewater management and a public education
program may be necessary. Unless people understand what is proposed and
how it can benefit them, any change will be resisted [43J. A public
advisory board can aid in the acceptance of the land treatment
alternatives. The problem of "representative" members in the advisory
board is not a new one. A typical range of interests for the group
might include the following:
• Farmers representing irrigation districts
• Property owners in areas that have a high potential for system
siting
• Civic groups interested in community development
• Conservation groups
There are essentially two types of public participation programs:
reactive and participative. In reactive programs, the major events in
the planning process (e.g., alternative sites for consideration) are
presented to the public. The reactions to the information presented and
the remarks of the participants are incoporated into the final screening
and selection process [44J.
Participative planning differs in the number of meetings and the
alternative selection process. A number of public hearings are held in
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FIGURE 3-9
PUBLIC ACCEPTABILITY OF RENOVATED WATER REUSE [42]
LEGEND
100 r-
6ENERAL PUBLIC ACCEPTANCE
GOVERNMENT OFFICIAL'S ACCEPTANCE
GOVERNMENT OFFICIAL'S ESTIMATE OF
PUBLIC ACCEPTANCE
BO -
40 -
20 -
C9 C9 Cfl
POTENTIAL REUSE
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which the alternatives are presented, and the advantages and
disadvantages are listed. The next meeting presents any new
alternatives or advantages/disadvantages from the previous meetings.
Any rejected alternatives are shown and the reasons for their rejection
are outlined. This process is repeated until a final selection is made
L38]. The unique involvement of the public at all stages of the
alternative development will generate more useful informed feedback and
public support L44].
The definition of the social and economic setting and the evaluation of
public acceptance will be the result of working within the study area
framework and constant interaction between the participants.
3.7 Evaluation of Alternative Systems
The number of alternatives to be evaluated in detail will depend on
factors specific to each project, and may involve one or more choices of
the treatment process, the site location, or the recovery/reuse options
for the renovated water. On the other hand, the topography and soil
conditions within a given project area may restrict land treatment to
one feasible process, or a very limited number of potential sites may be
available. A careful preliminary investigation and screening process is
necessary to identify a number of alternatives without sacrificing an
objective approach.
For the purposes of this manual, the EPA cost-effectiveness analysis
procedures documented in 40 CFR 35, Appendix A, are closely followed
[45], These procedures must be used in selecting municipal wastewater
management systems submitted for construction grant funding under PL 92-
500. For other planning situations, the EPA document provides a
complete evaluation procedure that can be adapted to fit particular
objectives. General references on engineering economic evaluations [46]
and benefit/cost analysis in water resources planning [47] can provide
additional background information for methods of evaluating alterna-
tives. The EPA procedures require an evaluation of both monetary and
nonmonetary factors. The most cost-effective alternative is described
as follows [45]:
The most cost-effective alternative shall be the waste treatment
management system determined from the analysis to have the lowest
present worth and/or equivalent annual value without overriding
adverse nonmonetary costs and to realize at least identical minimum
benefits in terms of applicable Federal, State, and local standards
for effluent quality, water quality, water reuse and/or land and
subsurface disposal.
In the following sections, both monetary cost factors and nonmonetary
aspects of land treatment systems are discussed. Detailed cost
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evaluation procedures are not described, but methods of comparing
overall costs and nonmonetary factors for land treatment and
conventional systems are discussed.
3.7.1 Cost Estimating
Factors that influence both capital and operation and maintenance costs
are discussed in the following paragraphs. Only a few cost figures are
actually presented, but references are made to specific sources of cost
information. Because the cost effectiveness of land treatment is
sensitive to land cost, a separate discussion for estimating this item
is included. Methods of evaluating revenues and a discussion of
tradeoffs that are unique to land treatment cost analysis are also
discussed.
3.7.1.1 Capital Costs
Curves for capital costs are available in Costs of Wastewater Treatment
by Land Application [48]. The Stage II curves are recommended in
conducting cost estimates. Although the base date for these curves was
February 1973, they should not be arbitrarily updated by conventional
cost indexes. A comparison of unit costs for key items, such as
earthwork and continuous-move sprinkling equipment, may provide a more
reasonable estimate of the increase in current local prices over the
prices of February 1973 [49].
Components that might be used for preapplication treatment include
primary sedimentation and aerated lagoons. Their capital costs can be
determined from published cost curves for conventional treatment systems
[50, 51], recent construction bids, and current price quotations, as
necessary. Additional cost estimating data have been published for
aerated lagoons because they are commonly used in conjunction with land
treatment systems [48, 52]. Costs should include sludge handling as
well as liquid processing components.
A checklist of the items requiring a capital cost estimate is provided
in Table 3-13. These should be completed for each alternative system.
Salvage values at the end of the planning period for structures and
equipment should be based on expected service life. Appendix A of 40
CFR 35 [45] specifies service lives to be used in Section 201 facilities
planning (under PL 92-500) as follows:
Land Permanent
Structures 30 to 50 years
Process equipment 15 to 30 years
Auxiliary equipment 10 to 15 years
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TABLE 3-13
CHECKLIST OF CAPITAL COSTS FOR ALTERNATIVE
LAND TREATMENT SYSTEMS [48]
Alternative No.
Type of system
Average flow mgd
Analysis date
Total
cost, $
Amortized
cost, S/yra
Preapplication treatment
Transmission
Storage
Field preparation
Recovery
Additional costs
Service and
interest factor at
Landb at
Mgal
SUBTOTAL
SUBTOTAL
/acre
TOTAL
a. Check salvage values, Table 3-14 and preceding text.
b. Section 3.7.1.3.
Additional guidelines for service life of irrigation system components
are given in Table 3-14.
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TABLE 3-14
SUGGESTED SERVICE LIFE FOR COMPONENTS OF
AN IRRIGATION SYSTEM |_53Ja
Service life
Hours Years
Well can casing 20
Pump plant housing • 20
Pump, turbine
Bowl (about 50% of cost of pump unit) 16,000 8
Column, etc. 32,000 16
Pump, centrifugal 32,000 16
Power transmission
Gear head 30,000 15
V-belt 6,000 3
Flat belt, rubber and fabric 10,000 5
Flat belt, leather 20,000 10
Power units
Electric motor 50,000 25
Diesel engine 28,000 14
Gasoline or distillate
Air cooled 8,000 4
Water cooled 18,000 9
Propane engine 28,000 14
Open farm ditches (permanent) 20
Concrete structures 20
Concrete pipe systems 20
Wood flumes 8
Pipe, surface, gated 10
Pipe, water works class 40
Pipe, steel, coated, underground 20
Pipe, aluminum, sprinkler use 15
Pipe, steel, coated, surface use only 10
Pipe, steel galvanized, surface only 15
Pipe, wood buried 20
Sprinkler heads 8
Solid set sprinkler system 20
Center pivot sprinkler system 10-14
Side roll traveling system 15-20
Traveling gun sprinkler system 10
Traveling gun hose system 4
Land grading0 none
Reservoirs'1 None
a. Certain irrigation equipment may have a lesser life
when used in a wastewater treatment system.
b. These hours may be used for year-round operation.
The comparable period in years was based on a
seasonal use of 2 000 h/yr.
c. Some sources depreciate land leveling in 7 to 15
years. However, if proper annual maintenance is
practiced, figure only interest on the leveling
costs. Use interest on capital invested in water
right purchase.
d. Except where silting from watershed above will fill
reservoir in an estimated period of years.
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3.7.1.2 Annual Operation and Maintenance Costs
Operation and maintenance costs include labor, materials and supplies,
and power costs. They may be assumed constant for the planning period
though many of the costs will vary throughout the period, particularly
those which are flow-dependent, such as power costs for aeration and
pumping, and chemical costs. If flows are expected to increase
substantially during the planning period, varying operation and
maintenance costs should be analyzed on a year-by-year basis (life-cycle
cost) or by reducing the total future value of "the increasing annual
costs to an equivalent annuity amount.
Preapplication treatment will require operation and maintenance labor,
materials including chemicals, and power costs. These costs can be
determined from cost estimating sources for conventional treatment
processes [50, 51, 54]. Additional operation cost data on aerated
lagoons can be obtained from other sources [48]. Operation and
maintenance costs for the remaining categories can be found in reference
[48]. A checklist has also been prepared for operation and maintenance
cost estimating purposes and is shown in Table 3-15.
3.7.1.3 Land Costs
3.7.1.3.1 Fee-Simple Purchase
The land category includes the cost of acquiring land for application
sites, buffer zones, service roads, storage reservoirs, preapplication
treatment facilities, administrative and laboratory buildings, and other
miscellaneous facilities. Easements for transmission pipelines may also
be included in this category.
Land for preapplication treatment facilities and other permanent
structures is usually purchased outright if it is not already under
control of the wastewater management agency. Several options are
potentially available for acquisition or control of the land used for
the treatment process. These include outright purchase (fee-simple
acquisition), long-term lease or easement, and purchase with leaseback
of the land with no direct involvement in the management of the land. A
separate option of simply negotiating contracts with private landowners
to sell or deliver wastewater for application would eliminate land
acquisition as a capital cost. According to a recent survey, fee-simple
land acquisition is preferred by most states, communities, and federal
agencies [55].
Purchase of the land provides the highest degree of control over the
application sites and ensures uninterrupted land availability for both
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TABLE 3-15
CHECKLIST OF ANNUAL OPERATION AND MAINTENANCE COSTS
FOR ALTERNATIVE LAND TREATMENT SYSTEMS [48]
Alternative No.
Type of system
Average flow
Analysis date
Mgal/d
Annual cost, $
Labor Power Material Total
Preapplication treatment
Transmission
Storage
Distribution
Recovery
Additional costs
Mgal
Revenues
L&nd lease
SUBTOTAL
TOTAL
a. Section 3.7.1.4.
short-term and long-term planning. In many cases, purchase will be more
economical than leasing or easements. For this option, land acquisition
is treated as a simple capital expenditure.
For projects eligible for PL 92-500 construction grant funding, purchase
of land to be used as an integral part of the treatment process is
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eligible. Purchase and leaseback of land for agricultural or other use
involving application of wastewater would require an initial capital
expenditure and annual revenues, or negative operation costs, as
discussed in a later section.
Assuming that land is purchased, the capital cost is determined simply
by multiplying the total area required by the prevailing market value.
Methods of estimating the total area required have been discussed in
Section 3.3. Because the final alternatives usually include specific
sites, the prevailing market value can be estimated from information
supplied by a local source, such as the tax assessor's office. In a few
cases, the wastewater management agency may already control sufficient
land and acquisition is therefore eliminated as a capital cost factor.
The costs of relocating residences and other buildings must be included
in the estimate of initial costs and are highly dependent on the
location. Agencies such as the U.S. Army Corps of Engineers, U.S.
Bureau of Reclamation, and state highway departments can assist in the
estimates. For federally funded projects, the acquisition of land and
relocation of residents must be conducted in accordance with the Uniform
Relocation Assistance and Land Acquisition Policies Act of 1970. In one
case, relocation costs for moving approximately 200 familes averaged
about $5000 per family, plus about $300 000 for administration of the
program [42].
EPA guidelines require that the salvage value of land be assumed equal
to the initial purchase price. Land values may, in fact, appreciate
considerably during the planning period, particularly if relatively
undeveloped land is purchased initially.
3.7.1.3.2 Leasing
The cost of leasing land for application purposes is included as an
operation cost for those alternatives in which fee-simple acquisition is
not a viable or an economic option. However, long-term leases are
eligible for PL 92-500 construction grant financing, if they can be
shown to be more cost-effective.
It has been estimated that leasing/easements will be cost-effective only
for several hundred projects nationwide. Most of these projects would
be in arid or semiarid areas where effluent has a high value and land
has a low value. In these areas, some landowners may be willing to
either pay for wastewater effluents, accept wastewater effluents free of
charge, or make leasing arrangements at a nominal charge. To be
eligible for grant funding, the lease or easement should include the
conditions shown in Table 3-16.
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TABLE 3-16
REQUIREMENTS FOR LAND LEASING FOR PL 92-500 GRANT FUNDING [56]
• Limit the purpose of the lease or easement to land application and activities
incident to land application.
• Describe explicitly the property use desired.
• Waive the landowner's right to restoration of the property at the termination
of the lease/easement.
• Recognizing the serious risk of premature lease termination, provide for full
recovery of damages by the grantee in such an event with recovery of the paid
federal share or, alternatively, retention of the federal share to be used
solely for the eligible costs of the expansion or modification of the treatment
works associated with the project. The damages would include the difference
between the total present worth of treatment works changes resulting from
premature termination and the costs resulting from expiration of the lease.
The damages would also include any additional losses or costs due to unplanned
disruption of wastewater treatment.
• Provide for payment of the lease/easement in a lump sum for the full value of
the entire term.
• Provide for leases/easements for a minimum of twenty (20) years, or the useful
life of the treatment plant, whichever is longer, with an option of renewal for
an additional term, as deemed appropriate.
3.7.1.4 Revenues
Revenues can accrue from crop sales, sale of renovated water, sale of
treated effluent for land application, or leaseback of purchased land
for farming or other purposes. In the evaluation and comparison of
alternatives, revenue estimates can be viewed as offsetting or negative
annual costs, but with a higher degree of uncertainty than with
estimating capital and operating costs. Crop returns may be anticipated
from slow rate processes in which the wastewater management agency
controls the land and manages the farming, while overland flow and rapid
infiltration processes generally will not produce significant crop
revenues. In either case, revenues can be expected to offset only a
portion of the total operating cost. Prevailing market values for crops
can usually be obtained from state university cooperative extension
services, but yield estimates must be made for the proposed conditions
of application. These estimates are preliminary and can be based on
typical yields for the local area. In a few cases, however,
optimization of proposed application rates based on crop yield,
revenues, and costs may be investigated during the development of
alternatives. Economic models for such a procedure have been published
[57, 58].
Relatively little information on crop revenues is available from
agencies that actually manage their own farming operations. The most
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widely reported operation is the one at Muskegon, Michigan {Section
7.6). During 1975, the first full year of operation, total crop
revenues amounted to about 44% of the total operating expenses,
including a farming management contract fee [59]. The revenues
increased an estimated 60% in 1976. The farm operated by San Angelo,
Texas, where slow rate application of wastewater is used (Section 7.5),
is also reported to be profitable.
For alternatives that propose purchase of land by the wastewater agency
and subsequent leaseback to farmers with an agreement to use wastewater
for application, a second source of income, is the estimated lease
payment. In Bakersfield, California, this type of arrangement brings
revenues to the city that are approximately 2Q% of total treatment
operating expenses [60].
Another major source of income may be the renovated water recovered from
land treatment systems, particularly runoff from overland flow systems
or pumped withdrawal following rapid infiltration systems. Possible
markets for the renovated water must be investigated on a case-by-case
basis. Methods of assessing the relative value of renovated wastewater
for various uses and levels of effluent quality are discussed in
reference L61J. Potential reuse categories and possible user costs that
would have to be borne as a result of using renovated wastewater rather
than normal supplies are discussed in a separate study [62J.
For some projects, the quality and quantity of renovated water from all
alternatives may not be sufficiently different to affect the
marketability of the effluent. For those situations, revenues from the
sale of renovated water may not be a meaningful evaluative factor for
comparison purposes.
3.7.1.5 Cost Tradeoffs
There are many considerations that can improve the cost-effectiveness of
an alternative without changing overall treatment performance. Some of
the more important tradeoffs that should be considered in analyzing the
alternatives are summarized in Table 3-17.
3.7.2 Nonmonetary Considerations
To complete the cost-effective analysis as previously defined, a range
of nonmonetary factors should be evaluated for each alternative. This
evaluation also serves as a basis for unavoidable adverse impacts of the
selected plan and for outlining mitigation measures for these impacts.
Nonmonetary factors, as listed in Table 3-18, may be divided into four
categories: (1) treatment performance and reliability, (2) environmen-
tal impacts, (3) resource commitments, and (4) implementation and legal
constraints.
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TABLE 3-17
COST TRADEOFF CONSIDERATIONS FOR
LAND TREATMENT SYSTEMS3
Option A versus Option B
• Land leveling for surface flooding Sprinkler systems
• Cash crop revenues and operating costs Forage and cover (requires less land)
• High drawdown rates from storage Low dradown rates requiring smaller
requiring high volume pumps pumps and distribution facilities
(minimizes storage volume) (requires more land)
• Existing vegetation Land preparation for high-nitrogen
uptake vegetation
• Double cropping Perennial crops
• One 8 hour daily shift, no weekend Round-the-clock and weekend operation
application (requires larger (higher operating cost)
pumps, pipes)
• Automatic systems (high capital) Nonautomatic systems (high operation
and maintenance)
a. The list is intended to show some of the more obvious options. Many other
.possibilities will arise in the alternative development process.
TABLE 3-18
NONMONETARY FACTORS FOR
EVALUATION OF ALTERNATIVES
1. Treatment performance and reliability
• Ability to meet effluent quality/water quality goals
• Process reliability and control
• Process flexibility
2. Environmental impacts
• Archaeological, historical, geological sites
• Plant and animal communities
• Surface and groundwaters
• Soils
• Air quality and odors
• Noise and traffic
• Public health
• Land use
• Social issues
• Economic issues
• Secondary (induced-growth) effects
3. Resource commitments
• Land
• Energy
• Chemicals
4. Implementation and legal constraints
• Implementation authority
• Water rights
• Existing regulations and plans
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Table 3-18 can serve as a comprehensive guideline for comparing
alternatives, but it must be recognized that each planning situation is
unique. Some factors may be relatively insignificant in one situation,
while others may be critical. The approach used to compare each factor
for various alternatives may be selected by the planner/engineer or may
be dictated by requirements of the study. For example, the Urban
Studies Program specifically discourages the use of numerical ratings in
the Impact Assessment and Evaluation Appendix of its reports [35J. The
planner/engineer must be aware of particular requirements for evaluating
environmental or other factors for a specific type of project.
3.7.2.1 Treatment Performance and Reliability
Alternatives that are not capable of meeting minimum effluent quality or
water quality criteria, and those that provide significantly higher
quality but at unacceptable cost, will normally be eliminated during the
preliminary screening process. Thus, the expected effluent Quality from
all alternatives may be relatively similar and may not provide a basis
for comparison. However, there are some differences in effluent quality
from the various land treatment processes, as pointed out in Chapter 2.
These differences should be noted when two or more processes of land
treatment are being compared. There may also be differences in
performance when conventional and land treatment alternatives are
compared. For example, a comparison of expected effluent quality from
two conventional systems, three land treatment systems, and four
advanced wastewater treatment systems is presented in Table 3-19.
Well planned and operated land treatment systems are reliable [64].
Factors that affect the reliability of land treatment systems include
climatic conditions, natural disasters, and equipment breakdown. Future
resource availability should also be evaluated, particularly when
comparing land treatment systems with systems that consume a higher
quantity of power and/or chemicals.
The flexibility of any treatment system, and all its components, to
adapt to changing conditions should be evaluated. Conditions that might
change include effluent quality standards, wastewater characteristics,
growth rate or growth beyond the planning period, surrounding land use,
and technological advances. Of particular concern in land treatment
systems is the future availability of land. Prudent design will avoid
situations on which no land is available for future expansion.
3.7.2.2 Environmental Impacts
Information on characterizing various aspects of the environmental
setting was presented in Section 3.6. With this background, the primary
and secondary impacts of each of the alternative plans may be assessed.
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TABLE 3-19
COMPARISON OF EFFLUENT QUALITY FOR
CONVENTIONAL, LAND TREATMENT, AND
ADVANCED WASTEWATER TREATMENT SYSTEMS [63]
Effluent constituent, mg/L
System BOD SS NHa-N NOa-N Total N P
Conventional treatment
Aerated lagoon 35 40 10 20 30 8
Activated sludge 20 25 20 10 30 8
Land treatment
Slow rate 1 1 0.5 2.5 3 0.1
Overland flow 5 5 0.5 2.5 3 5
Rapid infiltration 5 1 10 10 2
Advanced wastewater
treatment3
1
2
3
4
12
15
5
5
15
16
5
5
1
....
26"
29
....
io"
—
30
3
30
3
8
8
0.5
0.5
a. The advanced wastewater treatment systems are as follows:
1 = biological nitrification
2 = biological nitrification-denitrification
3 * tertiary, two-stage lime coagulation,
and fil-tration
4 « tertiary, two-stage lime coagulation, filtration,
and selective ion exchange
3.7.2.3 Resource Commitments
The use and conservation of resources—land, energy, and chemicals—will
be indirectly included in the cost analysis, but the noneconomic impacts
should be evaluated as well. The amount of land committed to wastewater
treatment and renovation will be larger for land treatment systems than
for conventional treatment systems. The extent to which this is a
negative or positive impact involves evaluation of several factors
discussed in the preceding section, including project land use, and
social and economic issues. It must be recognized that the use of the
land is necessarily a long-term commitment. However, the land used for
an application site is not destroyed or irrevocably altered. When
operations cease, it again becomes available for other land uses.
should be compared independently of the cost
Energy requirements should be compared independently or tne cost
analysis. Land treatment energy requirements will depend significantly
on the distance and elevation required for transmission, as well as on
other pumping requirements. Conventional or advanced wastewater
3-55
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treatment processes may require relatively high energy inputs, in part
because of the energy required for additional sludge handling and
disposal. Relative comparisons of energy requirements for a number of
treatment strategies have been published [54, 64J.
Chemical requirements should be evaluated primarily on the basis of
future availability, which will depend, in part, on the location of the
project. If disinfection or supplemental fertilization is needed,
chemicals may be needed for a land treatment system. In advanced
wastewater treatment, there are many additional processes that require
chemicals. Land treatment alternatives involving cultivation and
harvesting of crops can be viewed as conserving nutrients, whereas most
advanced wastewater treatment methods for nutrient removal tie up or
release nutrients in a relatively unusable form.
3.7.3 Plan Selection
The approach taken to summarize and present the results of the
evaluation will depend on the specific planning situation. Monetary
costs for each alternative should be expressed on the basis of total
present worth or equivalent annual cost. Nonmonetary factors should be
presented on a numerical scale or expressed in qualitative terms. To
the greatest extent possible, the summary should permit comparison of
land treatment and conventional treatment systems on an equivalent
basis.
The actual selection process may involve the wastewater management
agency, the engineer/planner, technical or nontechnical advisory groups,
input from citizens or special interest groups, and other interested
governmental bodies. The selected alternative is the most cost
effective, reliably meets all water quality goals, and does not have
overriding nonmonetary impacts.
Once a plan has been selected tentatively, the final step should be to
address any adverse impacts associated with the plan that are
unavoidable. Mitigating measures should be outlined to ensure at the
planning stage that such impacts can be minimized.
3-56
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3.8 References
1. Flach, K.W. Land Resources. In: Recycling Municipal Sludges and
Effluents on Land. Champaign, University of Illinois. July 1973.
2. Whiting, D.M. Use of Climatic Data in Estimating Storage Days for
Soil Treatment Systems. Environmental Protection Agency, Office
of Research and Development. EPA-IAG-D5-F694. 1976.
3. Metcalf & Eddy, Inc. Wastewater Engineering. New York, McGraw-Hill
Book Co. 1972.
4. Pound, C.E. and R.W. Crites. Characteristics of Municipal
Effluents. In: Proceedings of the Joint Conference on Recycling
Municipal Sludges and Effluents on Land, Champaign, University of
Illinois, July 1973.
5. Blakeslee, P.A. Monitoring Considerations for Municipal Wastewater
Effluent and Sludge Application to the Land. In: Proceedings of
the Joint Conference on Recycling Municipal Sludges and Effluents on
Land, Champaign, University of Illinois, July 1973. pp 183-198.
6. Davis, J.A., III and J. Jacknow. Heavy Metals in Wastewater in
Three Urban Areas. Journal WPCF, 47:2292-2297, September 1975.
7. Hodain, R.H. The Best Way to Remove Heavy Metals Might Turn Out to
Be Activated Sludge. California Water Pollution Control Association
Bulletin, 12:54-55. April 1976.
8. Pound, C.E., R.W. Crites, and J.V. Olson. Long-Term Effects of
the Rapid Infiltration of Municipal Wastewater. (Presented at the
8th International Conference of the International Association on
water Pollution Research, Sydney, Australia. October 1976.)
9. Ketchum, B.H. and R.F. Vaccaro. The Removal of Nutrients and
Trace Metals by Spray Irrigation and in a Sand Filter Bed. In:
Land as a Waste Management Alternative. Loehr, R.C. (ed.) Ann
Arbor, Ann Arbor Science. 1977. pp 413-434.
10. Thomas, R.E. Personal Communication. January 1977.
11. Chen, K.Y., C.S. Young, T.K. Jan, and M. Rohatgi. Trace Metals
in Waste Water Effluents. Jour. WPCF. 46:2663-2675, December
1974.
12. National Interim Primary Drinking Water Regulations. US
Environmental Protection Agency. 40 CFR 141. December 24, 1975.
13. Sepp, E. Disposal of Domestic Wastewater by Hillside Sprays.
Journal of the Environmental Engineering Division, Proceedings of
the ASCE. 99(2):109-121, April 1973.
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14. Soil-PIant-Water Relationship. Irrigation, Chapter 1. SCS National
Engineering Handbook, Section 15. U.S. Department of Agriculture,
Soil Conservation Service. March 1964.
15. Stone, J.E. Soil As a Treatment Medium. In: Land Application of
Wastes - An Educational Program, Cornell University. May 1976.
16. Reed, S.C. et al. Wastewater Management by Disposal on the Land.
Corps of Engineers, US Army Cold Regions Research and Engineering
Laboratory. Hanover, NH. May 1972. 183 p.
17. Blaney, H.F. and W.D. Criddle. Determining Consumptive Use and
Irrigation Water Requirements. US Department of Agriculture,
Washington, D.C. Technical Bulletin No. 1275. December 1962.
18. Kilmer, V.J., et al. Nutrient Losses From Fertilized Grassed
Watersheds in Western North Carolina. Journal of Environmental
Quality, 3, No. 3, 1974. pp 214-319.
19. Klausner, S.D., et al. Surface Runoff Losses of Soluble Nitrogen
and Phosphorus Under Two Systems of Soil Management. Journal of
Environmental Quality, 3, No. 1. 1974. pp 42-46.
20. Nicholls, K.H. and H.R. MacCrimmon. Nutrients in Subsurface and
Runoff Waters of the Holland Marsh, Ontario. Journal of
Enviromental Quality, 3, No. 1, 1974. pp 31-35.
21. Timmons, D.E., R.E. Burwell, and R.F. Holt. Nitrogen and
Phosphorus Losses in Surface Runoff From Agricultural Land as
Influenced by Placement of Broadcast Fertilizer. Water Resources
Research, Vol. 9, No. 3. June 1973. p 658.
22. Loehr, R.C. Agricultural Waste Management—Problems, Processes and
Approaches. New York, Academic Press. 1974.
23. Walker, W.R. and W.E. Cox. Wastewater Irrigation: Its Legal
Impact. Water Sprectrum. 6(2):15-22, 1974.
24. Large, D.W. Legal Constraints Imposed on Land Application of
Wastewater by Private Water Rights Law.
25. Reid, G.W., E.E. Pritchett, and S. Pritchett. Can Engineering
Forecasters Affect Water Law? Journal of the Sanitary Engineering
Division, Proceedings of the ASCE. 97(4):479-484, August 1971.
26. Powell, G.M. Design Seminar for Land Treatment of Municipal
Wastewater Effluents. EPA Technology Transfer Program. (Presented
at Technology Transfer Seminar. 1975.) 75 p.
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27. National Water Commission. Water Policies for the Future.
Washington, D.C. US Government Printing Office. June 1973. 579 p.
28. Dewsnup, R.L. and D.W. Jensen (eds.). A Summary-Digest of State
Water Laws. National Water Commission. Washington, D.C. May,
1973. 826 p.
29. duff, C.B., K.J. DeCood, and W.G. Matlock. Technical Economic
and Legal Aspects Involved in the Exchange of Sewage Effluent for
Irrigation Water for Municipal Use: Case Study - City of Tucson.
University of Arizona, Office of Water Resources Research. Tucson.
Project A-022-ARIZ. December 1972. 74 p.
30. Hutchins, W.A. Irrigation Water Rights in California. University
of California, Division of Agricultural Sciences. Sacramento,
Circular 452 (Rev.), February 1967. 55 p.
31. 92 USC, Public Law 92-500, An Act to Amend the Federal Water
Pollution Control Act, 86 Stat. 816 (October 18, 1972) 89 p.
32. Markland, R.E., L.D. Smith, and J.D. Becker. A Benefit-Cost
Analysis of Alternative Land Disposal Waste Water Methods in an
Urban Environment. University of Missouri at St. Louis, School of
Business Administration. Washington, D.C. USDI 14-31-0001-4221.
US Department of the Interior, Office of Water Resources Research.
January 1, 1974. 234 p.
33. Godfrey, K.A. (ed.). Satellites Help Solve Down-to-Earth
Engineering Problems. Civil Engineering. 45:49-53, August 1975.
34. Morris, C.E. Societal and Legal Constraints. In: Land Appl ication
of Wastes - An Educational Program, Cornell University. May 1976.
35. Department of Defense, Department of the Army, Corps of Engineers,
Urban Studies Program, Federal Register, 39 No. 130 part III (July
5, 1974) 19 p.
'36. State of California Water Resources Control Board. Environmental
Impact Report and Public Participation Guidelines for Wastewater
Agencies, Sacramento CA. State of California. July 1973. 17 p.
37. McHarg, I.L. Design with Nature. Garden City, Doubleday & Company,
Inc., 1971. 197 p.
38. Sargent, H.L., Jr. Fishbowl Planning Immerses Pacific Northwest
Citizens in Corps Projects. Civil Engineering. 42:54-56, September
1972.
39. Guidance for Preparing a Facility Plan. Environmental Protection
Agency, Municipal Wastewater Treatment Works Construction Grants
Program. (Revised) May 1975.
3-59
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40. Guidelines for Areawide Waste Treatment Management Planning.
Environmental Protection Agency. Washington, D.C. August 1975.
145 p.
41. Postlewait, J.C. Some Experiences in Land Acquisition for a Land
Disposal System for Sewage Effluent. In: Proceedings of the Joint
Conference on Recycling Municiple Sludges and Effluents on Land,
Champaign, University of Illinois, July 1973. pp 25-38.
42. Stone, R. Water Reclamation: Technology and Public Acceptance.
Journal of the Environmental Engineering Division, Proceedings of
the ASCE. 102(EE3):581-594, June 1976.
43. Dunbar, J.O. Educational and Informational Needs for Achieving
Public Acceptance. In: Land Application of Wastewater.
Proceedings of a Research Symposium Sponsored by the USEPA, Region
III, Newark, Del a. November 1974. pp 35-38.
44. Warner, K.P. A State of the Art Study of Public Participation in
the Water Resources Planning Process. University of Michigan,
School of Natural Resources, Environmental Simulation Laboratory.
Washington, D.C. NWC-SBS-71-013. National Water Commission. July
1971. 233 p.
45. US Code of Federal Regulations, 40 CFR 35, Appendix A, Cost-
Effectiveness Analysis.
46. Grant, E.L. and W.G. Ireson. Principles of Engineering Economy.
New York, Ronald Press. 1970.
47. James, L.O. and R.R. Lee. Economics of Water Resources Planning.
New York, McGraw-Hill Book Company, 1971. 615 p.
48. Pound, C.E., R.W. Crites, and D.A. Griffes. Costs of Wastewater
Treatment By Land Application. Environmental Protection Agency,
Office of Water Program Operations. EPA-430/9-75-003. June 1975.
49. Crites, R.W. Use of Land Application Cost Curves. In: Proceedings
of the Sprinkler Irrigation Association, Annual Technical
Conference, Technology for a Changing World, Kansas City. February
22-24, 1976. pp 126-130.
50. VanNote, R.H., et al. A Guide to the Selection of Cost-Effective
Wastewater Treatment Systems. Environmental Protection Agency,
Office of Water Program Operations. EPA-430/9-7-002. July 1975.
51. Patterson, W.L. and R.F. Banker. Estimating Costs and Manpower
Requirements for Conventional Wastewater Treatment Facilities. EPA
17090 DAN. October 1971.
52. Sanks, R.L., T. Asano, and A.H. Ferguson. Engineering
Investigations for Land Treatment and Disposal. In: Land Treatment
and Disposal of Municipal and Industrial Wastewater. Sanks, R.L.
and T. Asano (eds.). Ann Arbor, Ann Arbor Science. 1976. pp
213-250.
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53. Evaluation of Land Application Systems. Office of Water Program
Operations, Environmental Protection Agency. EPA-430/9-75-001.
March 1975.
54. Battelle-Pacific Northwest Laboratories. Evaluation of Municipal
Sewage Treatment Alternatives. (Prepared for Council of
Environmental Quality. February 1974.)
55. Don Sowle Associates, Inc. An Assessment of the Impact of Long-Term
Leases and Easements on the Construction Grants Program. Final
Report to the Environmental Protection Agency. Arlington, Va. July
ly?6.
56. Environmental Protection Agency. Grant Eligibility of Land Acquisi-
tion for Use in Land Treatment and Ultimate Disposal of Residues.
Program Requirements Memorandum No. 77-5. December 15, 1976.
57. Christensen, L.A., L.J. Conner, and L.W. Liddy. An Economic
Analysis of the Utilization of Municipal Waste Water for Crop
Production. Department of Agricultural Economics, Michigan State
University, East Lansing. Report No. 292. US Department of
Agriculture, Economic Research Service, Natural Resource Economics
Division. November 1975. 40 p.
58. Seitz, W.D. and E.R. Swanson. Economic Aspects of the Application
of Municipal Wastes to Agricultural Land. In: Proceedings of the
Joint Conference on Recycling Municipal Sludges and Effluents on
Land, Champaign, University of Illinois, July 1973. pp 175-182.
59. Walker, J.M. Wastewater: Is Muskegon County's Solution Your
Solution? U.S. Environmental Protection Agency, Region V, Office
of Research and Development. September 1976.
60. Crites, R.W. Wastewater Irrigation: This City Can Show You How.
Water and Wastes Engineering. 12:49-5U, July 1975.
61. Schmidt, C.J. and E.V. Clements, III. Demonstrated Technology and
Research Needs for Reuse of Municipal Wastewater. Environmental
Protection Agency. EPA-670/2-75-038. May 1975.
62. Banks, H.O. et al. Economic and Institutional Analysis of
Wastewater Reclamation and Re-Use Projects. Leeds, Hill & Jewett,
Inc. Washington, D.C. OWRR C-1912. US Department of the Interior,
Office of Water Resources Research. December 1971. 171 p.
63. Pound, C.E., R.W. Crites, and R.G. Smith. Cost-Effective
Comparison of Land Application and Advanced Wastewater Treatment.
Environmental Protection Agency, Office of Water Program
Operations. EPA-430/9-75-016. November 1975.
64. Metcalf & Eddy, Inc. Report to National Commission on Water Quality
on Assessment of Technologies and Costs for Publicly Owned Treatment
Works. September 1976.
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CHAPTER 4
FIELD INVESTIGATIONS
4.1 Introduction
The primary information for a specific site can usually be found in a
USDA-SCS county soil survey. Detailed field investigations are often
needed, however, to assess the suitability of a site for land treatment.
The intent of this chapter is to outline those tests normally conducted
for each type of land treatment process, the reasons for their use, and
the conclusions that can be reached from the results. The procedures
for conducting these tests are discussed elsewhere: infiltration,
permeability, and aquifer tests are discussed in Appendix C; and
physical and chemical soil tests are discussed in Appendix F. The
significance of various wastewater characteristics to land treatment is
also presented. The field tests normally associated with land treatment
processes are summarized in Table 4-1.
TABLE 4-1
SUMMARY OF FIELD TESTS FOR LAND TREATMENT PROCESSES
Properties
Wastewater
constituents
Soil physical
properties
Soil hydraulic
properties
-
Slow rate (SR)
Nitrogen, phosphorus,
SARa, ECa, boron
Depth of profile
Texture and structure
Infiltration rate
Subsurface
permeability
Aquifer tests
(optional )
Processes
Rapid
infiltration (RI)
BOD, SS, nitrogen,
phosphorus
Depth of profile
Texture and structure
Infiltration rate
Subsurface
permeability
Aquifer tests
Overland
flow (OF)
BOD, SS, nitrogen,
phosphorus
Depth of profile
Texture and structure
Infiltration rate
Soil chemical
properties
pH, CEC, exchange-
cations (% of CEC),
ECa, metalsb,
phosphorus adsorp-
tion (optional)
pH, CEC, phosphorus
adsorption
pH, CEC, exchange-
able cations (* of CEC)
a. May be applicable to arid and semiarid areas.
b. Background levels of metals such as cadmium, copper, or zinc in the
soil should be determined if food chain crops are planned.
4-1
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4.2 Wastewater Characteristics
The wastewater constituents to be characterized for the various land
treatment processes will vary with the climate and the discharge quality
requirements. For example, for slow rate systems in humid areas the
sodium adsorption ratio (SAR) and electrical conductivity (EC) will be
less important than they are in arid areas. The discharge quality
requirements for surface water will be provided in the discharge permit.
The discharge quality requirements for groundwater can include nitrate
nitrogen and trace elements, as presented in Section 5.1.1.
For constituents such as BOD, suspended solids, nitrogen, and
phosphorus, the concentrations are used to compute the loading rates.
These rates can be compared to soil treatment mechanisms as discussed in
Section 5.1. For trace elements, the allowable loadings are also
discussed in Section 5.1. For inorganic constituents of importance to
slow rate systems, guidelines are presented in Table 4-2.
4.3 Soil Physical and Hydraulic Properties
The physical and hydraulic properties of soils are interrelated. For
example, a major reason for establishing the depth of the profile and
the texture and .structure is to determine the hydraulic capacity. Depth
of the soil profile above bedrock is" also important in assessing
wastewater renovation (slow rate and rapid infiltration processes) and
in assessing practical limits on earth moving. Interpretation of soil
physical and hydraulic properties is presented in Table 4-3.
4.4 Soil Chemical Properties
Chemical properties are of importance in assessing (1) potential
treatment efficiency for infiltration systems, (2) need for soil
amendments, and (3) baseline levels of any constituents expected to
accumulate in the profile and cause long-term problems.
Both chemical and biological treatment mechanisms are affected by soil
pH. Chemical removal mechanisms for phosphorus change with pH (Appen-
dix B). Biological activity is reduced as the pH drops below about 5.
The effects on plants are presented in Table 4-4.
The cation exchange capacity (CEC) is a measurable indicator of the
potential adsorption capacity for trace elements. The percentage of the
CEC occupied by exchangeable sodium (ESP) is important to maintenance of
soil permeability.
4-2
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TABLE 4-2
RELATIONSHIP OF POTENTIAL PROBLEMS TO CONCENTRATIONS OF
MAJOR INORGANIC CONSTITUENTS IN IRRIGATION WATERS
FOR ARID AND SEMIARID CLIMATES [1]
Problem and related constituent
No problem
Increasing
problems
Severe
Salinity3
EC of irrigation water, mmhos/cm
Permeability
EC of irrigation water, mmhos/cm
SAR (sodium adsorption ratio)*5
Specific ion toxicityc
From root absorption
Sodium (evaluate by SAR)
Chloride, meq/L
Chloride, mg/L
Boron, mg/L
From foliar absorption (sprinklers)"1
Sodium, meq/L
Sodium, mg/L
Chloride, meq/L
Chloride, mg/L
Miscellaneous6
meq/L
HC03, mg/L
<0.75 0.75-3.0
>0.5
<6.0
<3
<4
<142
<0.5
<3.0
<69
<3.0
<106
3.0-9.0
4.0-10
142-355
0.5-2.0
>3.0
>69
>3.0
>106
>3.0
<0.5 <0.2
6.0-9.0 >9.0
>9.0
>355
2.0-10.0
PH
<1.5 1.5-8.5 >8.5
<90 90-520 >520
Normal range = 6.5-8.4
Note: Interpretations are based on possible effects of constituents on
crops and/or soils. Suggested values are flexible and should be
modified when warranted by local experience or special conditions
of crop, soil, and method of irrigation.
a. Assuming water for crop plus water needed for leaching requirement
will be applied. Crops vary in tolerance to salinity. Electrical
conductivity (EC) mmhos/cm x 640 = approximate total dissolved
solids (TDS) in mg/L or ppm; mmhos x 1,000 = micromhos.
Na
b.
where Na = sodium; Ca = calcium; Mg = magnesium, in all meg/L.
Most tree crops and woody ornamentals are sensitive to sodium and
chloride (use values shown). Most annual crops are not sensitive.
Leaf areas wet by sprinklers (rotating heads) may show a leaf burn
due to sodium or chloride absorption under low-humidity, high-
evaporation conditions. (Evaporation increases ion concentration
in water films on leaves between rotations of sprinkler heads.)
HCO, with overhead sprinkler irrigation may cause a white carbonate
deposit to form on fruit and leaves.
4-3
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TABLE 4-3
INTERPRETATION OF SOIL PHYSICAL AND HYDRAULIC PROPERTIES
Depth of soil profile, ft
2-5
5-10
Texture and structure
Fine texture, poor structure
Fine texture, well-structured
Coarse texture, well-structured
Infiltration rate, in./h
0.2-6
>2.0
<0.2
Subsurface permeability
Exceeds or equals infiltration rate
Less than infiltration rate
Suitable for OF0
Suitable for SR and OF
Suitable for all processes
Suitable for OF
Suitable for SR and possibly OF
Suitable for SR and RI
Suitable for SR
Suitable for RI
Suitable for OF
Infiltration rate limiting
May limit application rate
a. Suitable soil depth must be available for shaping of overland flow
slopes. Slow rate process using a grass crop may also be suitable.
1 ft = 0.305 m
1 in. = 2.54 cm
For slow rate systems that emphasize agricultural crop production, soil
tests will be conducted for the major nutrients—nitrogen, phosphorus,
and potassium; boron; gypsum content; and insoluble calcium (CaC03).
While the latter three are most applicable on arid climates, the
remainder are applicable to all locations. These tests should be
conducted and the results interpreted for both crop production and land
application aspects under the supervision of a qualified soil scientist.
4.5 Other Field Investigations
4.5.1 Soil Borings
When field investigations are conducted during the facilities planning
stage for assessing the suitability of the site, it may be necessary to
conduct soil borings. Existing well logs can provide additional
information if the wells are located within a similar geologic
formation. Generally the shallow (up to 10 ft [3 m] deep) soils work
4-4
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can be performed using a soil auger (Figure 4-1) or a backhoe. The soil
horizons exposed by a backhoe are illustrated in Figure 4-2. For deeper
investigations of soils and groundwater, drill rigs can be used (Figure
4-3). The drill holes can be small diameter with 2 to 4 in. (5 to 10
cm) being typical. The soil removed should be logged and notations made
for depths at which groundwater and restricting layers to hydraulic
movement are encountered.
TABLE 4-4
INTERPRETATION OF SOIL CHEMICAL TESTS
Test result
Interpretation
pH of saturated soil paste
<4.2
4.2-5.5
5.5-8.4
>8.4
CEC, meq/100 g
1-10
12-20
>20
Exchangeable cations,
% of CEC (desirable range)
Sodium
Calcium
Potassium
ESP, % of CEC
<5
>10
>20
ECe, mmhos/cm at 25"
of saturation extract
<2
2-4
4-8
8-16
Too acid for most crops to do well
Suitable for acid-tolerant crops
Suitable for most crops
Too alkaline for most crops, indicates a possible
sodium problem
Sandy soils (limited adsorption)
Silt loam (moderate adsorption)
Clay and organic soils (high adsorption)
60-70
5-10
Satisfactory
Reduced permeability in fine-textured soils
Reduced permeability in coarse-textured soils
No salinity problems
Restricts growth of very salt-sensitive crops
Restricts growth of many crops
Restricts growth of all but salt-tolerant crops
Only a few very salt-tolerant crops make
satisfactory yields
4.5.2 Groundwater
Knowledge of the existing groundwater quality beneath a site can provide
information on quality objectives of treated water. As indicated in
Section 5.1.1 the determination of the groundwater case (1, 2, or 3)
4-5
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depends on the use and quality of the groundwater. Wells on adjacent
land should have similar quality if located within the same aquifer.
Some soil borings can also be used as observation wells for system
monitoring.
FIGURE 4-1
CLOSED AND OPEN BARREL AUGERS AND TILING SPADE
. -Or?'-;
4.5.3 Vegetation and Topography
Site inspections are necessary to assess the existing vegetation and
topography. The plant species growing in an area can be used as an
indication of soil characteristics relating to plant growth. They
should not be used as the only means of problem assessment. However, if
their occurrence is noted, detailed soil investigations should be
conducted to assess the extent of the problem. Some plant species and
the probable indication of soil characteristics are given in Table 4-5.
The topography should be mapped prior to final design to allow accurate
earthwork computations. Both the existing vegetation and topography
should be assessed for costs of clearing and field preparation.
4-6
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FIGURE 4-2
SOIL PROFILE WITH TWO HORIZONS
• • f
4-7
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FIGURE 4-3
TYPICAL DRILL RIG USED FOR SOIL BORINGS
4-8
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TABLE 4-5
PROBABLE SOIL CHARACTERISTICS
INDICATED BY PLANTS [2]a
Plant species
Probably indicates
Alpine fir
Spruce
Cattails
Sedges
Willow
Dogwood
Needle and thread grass
Western wheat grass
Salt grass
Mexican fireweed
Grease wood
Foxtail
Ponderosa pine
Good sage brush
high water table
high water table
high water table
high water table
Poorly drained soil, high water table
Poorly drained soil, high water table
Poorly drained soil.
Poorly drained soil:
Poorly drained soil,
Poorly drained soil.
Light textured, sandy soil
Heavy textured, poorly drained soil
Highly saline soil
Highly saline soil
Highly saline soil, sodium problems
Salt, sodium, high water table
Dry soil
Good and deep soil
a. Primarily for western states. Similar information for
other locations can be found in county soil surveys.
4.6 References
1. Ayers, R.S. and R.L.
Water Quality for
Cooperative Extention.
Branson. Guidelines for Interpretation of
Agriculture. University of California
1975.
2. Sanks, R.L., T. Asano, and A. H. Ferguson. Engineering
Investigations for Land Treatment and Disposal. In: Land
Treatment and Disposal of Municipal and Industrial Wastewater.
Sanks, R.L. and T. Asano (eds.). Ann Arbor, Ann Arbor Science.
1976. pp 213-250.
4-9
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CHAPTER 5
PROCESS DESIGN
5.1 Land Treatment Process Design
The design of a land treatment process does not lend itself to a step-
by-step procedure. The two most important determinations in design are:
(1) selection of the site and treatment process, and (2) calculation of
the required field area. The iterative nature of site and process
selection is described in Chapter 3 and the decisions reached there are
assumed to be inputs to this chapter. In this chapter, the process
design discussion centers on determining the critical loading rates
required to calculate the field area.
This chapter is organized into discussions of (1) the process design for
slow rate, rapid infiltration, overland flow, and wetlands application;
(2) system components such as preapplication treatment (5.2), storage
(5.3), distribution (5.4), and effluent recovery (5.5); (3) vegetation
selection and agricultural management; (4) system monitoring, and
(5) facilities design guidance. The purpose of the chapter is to focus
on design aspects unique to land treatment.
Much background detail is provided to familiarize the environmental
engineer with land treatment. Practices common to most engineers will
not be discussed. Detailed cost data are not provided, but sources for
such information are described in Chapter 3.
The process design procedure for land treatment starts with the required
final effluent quality. For each process, the critical loading rate
(usually hydraulic or nitrogen) is then determined. The loadings and
removals of BOD, SS, phosphorus, trace elements, and microorganisms are
also discussed as they may be important in estimating effluent quality
or the expected life of the selected site. Extensive discussions of the
chemistry and microbiology of nitrogen, phosphorus, pathogens, and
metals are presented in the appendixes.
5.1.1 Effluent Quality Criteria
As in conventional process design, it is first necessary to determine
the quality required for the treated effluent produced by the system as
well as the influent wastewater quality. The wastewater quality is
discussed in Chapters 3 and 4. The expected treated water quality from
slow rate, rapid infiltration, and overland flow was presented in Table
2-3.
5-1
-------
Surface discharge of treated water is expected from overland flow and
wetlands systems. Surface discharge from slow rate and rapid
infiltration systems can result from the installation of underdrains or
wells. The quality criteria for surface discharges are established for
the particular watercourse by state and federal agencies.
Subsurface discharge consists of percolate from slow and rapid
infiltration systems. Because of the clay soils associated with
overland flow and wetland systems, little percolating (usually 5 to 20%)
of the applied wastewater occurs. There is little concern for this
percolate quality because of the reduction in wastewater constituents
after passing through fine textured soils.
The EPA criteria for best practicable waste treatment for alternatives
using land application include three cases for groundwater discharge
[2].- In each case, the constituent concentration is assumed to be
measured in the groundwater at the perimeter of the site.
Case 1 - The groundwater can potentially be used for drinking
water supply.
The chemical and pesticide levels in Table 5-1 should
not be exceeded in the groundwater. If the existing
concentration of an individual parameter exceeds the
standards, there should be no further increase in the
concentration of that parameter resulting from land
application of wastewater.
Case 2 - The groundwater is used for drinking water supply.
The same criteria as Case 1 apply and the bacteriological
quality criteria from Table 5-1 also apply in cases
where the groundwater is used without disinfection.
Case 3 - Uses other than drinking water supply.
1. Groundwater criteria should be established by the
Regional Administrator based on the present or
potential use of the groundwater.
The Regional Administrator in conjunction with the appropriate
state officials and the grantee shall determine on a site-by-site
basis the areas in the vicinity of a specific land application site
where the criteria in Case 1, 2, and 3 shall apply. Specifically
determined shall be the monitoring requirements appropriate for the
project site. This determination shall be made with the objective
of protecting the groundwater for use as a drinking water supply
and/or other designated uses as appropriate and preventing
irrevocable damage to groundwater. Requirements shall include
provisions for monitoring the effect on the native groundwater.
5-2
-------
Having established the effluent quality requirements for a surface
discharge and for the appropriate class of groundwater, the process
selection can be made or confirmed. The next step is to determine the
needed loading rates to achieve the requirements.
TABLE 5-1
ERA-PROPOSED REGULATIONS ON INTERIM PRIMARY
DRINKING WATER STANDARDS, 1975 [2]
Constituent
or characteristic
Value
Reason
for standard
Physical
Turbidity, units
Chemical, mg/L
Arsenic
Barium
Cadmium
Chromium
• Fluoride
Lead
Mercury
Nitrates as N
Selenium
Silver
Aesthetic
0.05
1.0
0.01
0.05
.4-2.4c
0.05
0.002
10
0.01
0.05
Health
Health
Health
Health
Health
Health
Health
Health
Health'
Cosmetic
Bacteriological
Total col i form, per 100 mi
Pesticides, mg/L
Endrin
Lindane
Methoxychlor
Toxaphene
2,4-0
2,4,5-TP
1
0.0002
0.004
0.1
0.005
0.1
0.01
Disease
Health
Health
Health
Health
Health
Health
a. The latest revisions to the constituents
and concentrations should be used.
b. Five mg/L of suspended solids may be substituted
if it can be demonstrated that it does not
interfere with disinfection.
c. Dependent on temperature; higher limits for
lower temperatures.
5-3
-------
5.1.2 Slow Rate Process
The design procedure for the slow rate process is iterative (see Figure
5-1). The field area is first calculated based on hydraulic loading
rates and the wastewater flow to be treated. The area is then
calculated from the nitrogen loading rate which is determined using a
nitrogen balance. The larger area is used in design. Both the
acceptable hydraulic and nitrogen loadings depend in part on the
vegetation selected (see Section 5.6.1). The discussion of hydraulic
and nitrogen loading rates is followed by discussions of removals of BOD
and suspended solids, phosphorus, trace elements, and microorganisms.
5.1.2.1 Hydraulic Loading Rates
The hydraulic loading will be limiting in situations where slow
permeability soils are used, or nitrogen limits are not critical. The
hydraulic loading rates for the design must be within the soil
capabilities, as estimated (Figure 3-3) or measured (Chapter 4 and
Appendix C).
The hydraulic loading is based on a water balance that includes
precipitation, infiltration rate, evapotranspiration (or consumptive use
by plants), soil storage capabilities, and subsoil permeability.
Generally, the total monthly application should be distributed
uniformly, but considerations must be made for planting, harvesting,
drying, and other nonapplication periods. The application rate must
then be balanced as shown in Equation 5-1.
Lw + Pr = ET + Wp + R (5-1)
where LW = wastewater hydraulic loading rate, in./wk (cm/wk)
Pr = design precipitation, in./wk (cm/wk)
ET = evapotranspiration (or crop consumptive use of water),
in./wk (cm/wk)
Wn = percolating water, in./wk (cm/wk)
R = net runoff, in./wk (cm/wk)
The relationship in Equation 5-1 can be used for a weekly balance, as
shown, or for monthly or annual balances. Design precipitation is
calculated from a 10 year return frequency analysis of wetter-than-
normal conditions using all the available data (Section 3.5.4.1).
Evapotranspiration estimates can be obtained from extension specialists,
land grant universities, or irrigation specialists. Peak rates for
selected crops that affect maximum hydraulic loadings are presented in
Section 5.6.1. Expected percolating water can be estimated from soil
characteristics and verified with field investigations (Appendix C).
For slow rate systems, wastewater is assumed to percolate, so net
runoff, R , can be assumed to be negligible.
5-4
-------
FIGURE 5-1
SLOW RATE DESIGN PROCEDURE
NASTEVATER
CHARACTERISTICS
EFFLUENT
REQUIREMENTS
(SECTION 5.1.1)
4
SITE
CHARACTERISTICS
(SECTIONS 3.2, 3.5
AND 4.1)
HYDRAULIC
LOADING
(SECTION 5.1.2.1)
STORAGE
(SECTION 5.3)
MONITORING
(SECTION 5.7)
I
FIELD AREA
(SECTION 5.1.2)
REMOVALS OF
N, P, BOD, ETC.
PR E A PPL I CAT I ON
TREATMENT
(SECTION 5.2)
I
DISTRIBUTION
(SECTION 5.4)
I
GROUNDWATER
NITROGEN
LOADING RATES
(SECTION 5.1.2.2)
CROP SELECTION
(SECTION 5.6.1)
AGRICULTURAL
MANAGEMENT
(SECTION 5.6.2)
UNDERDRA
(SECTION 5
INS
.5.2) I
SURFACE WATER
5-5
-------
5.1.2.2 Nitrogen Loading Rates
Nitrogen management for the slow rate process is principally crop uptake
with some denitrification. The annual nitrogen balance is:
Lp = U + D + 2.7 WC "
where Ln = wastewater nitrogen loading, lb/acre-yr (kg/ha-yr)
U = crop nitrogen uptake, lb/acre-yr (kg/ha-yr)
D = denitrification, lb/acre-yr (kg/ha-yr)
Wp = percolating water, ft/yr (cm/yr)
Cp = percolate nitrogen concentration, mg/L
Crop nitrogen uptake values are presented in Table 5-2. . These values
are based on typical yields under commercial fertilization and may
increase where conditions of excess nitrogen prevail. Crop nitrogen
uptake values in design depend on actual crop yields and local
agricultural agents should be contacted. Double cropping of field crops
such as corn and barley can increase the total annual nitrogen uptake.
TABLE 5-2
TYPICAL VALUES OF CROP UPTAKE OF NITROGEN3
[3, 4, 5, 6]
Nitrogen uptake,
Crop lb/acre-yr
Forage crops
Alfalfa6 • 200-480
Coastal bermuda grass 350-600
Kentucky bluegrass 180-240
Bromegrass 116-200
Reed canary grass 300-400
Sweet clover 158
Tall fescue 135-290
Quackgrass 210-250
Field crops
Barley 63
Corn 155-172
Cotton 66-100
Milo maize 81
Soybeans'3 94-128
Forest crops
Young deciduous 100
Young evergreen 60
Medium and mature deciduous 30-50
Medium and mature evergreen 20-30
a. For choice of suitable crop and uptake
value, contact the local agricultural
agent.
b. Legumes will also take nitrogen from
the atmosphere.
1 lb/acre-yr = 1.12 kg/ha-yr
5-6
-------
Denitrification is difficult to determine under field conditions, but
losses generally range from 15 to 25% of the applied nitrogen.
Conditions favorable to increased denitrification are summarized in
Table 5-3. Volatilization is known to occur (see Appendix A) but is
difficult to quantify.
TABLE 5-3
FACTORS FAVORING DENITRIFICATION
IN THE SOIL
High organic matter
Fine textured soils
Frequent wetting
High groundwater table
Neutral to slightly alkaline pH
Vegetative cover
Warm temperature
The percolate nitrogen will be limited in concentration to 10 mg/L for
design purposes if the flow is to Case 1 or Case 2 groundwater. An
alternative approach is to conduct a geohydrologic study (Appendix C) to
quantify groundwater flow. If it can then be shown that groundwater
quality leaving the site meets Case 1 or Case 2 requirements, then a
higher design percolate nitrogen concentration should be allowed. The
percolating water is determined from the water balance. It affects the
allowable loading of nitrogen considerably, as illustrated in the
following example for both arid and humid climates.
EXAMPLE 5-1: ANNUAL NITROGEN BALANCE FOR DESIGN PERCOLATE
NITROGEN CONCENTRATION OF 10 mg/L
Conditions
Humid climate Arid climate
1. Applied nitrogen concentration, Cn , mg/L 25 25
2. Crop nitrogen uptake, U , lb/acre-yr 300 300
3. Denitrification, as % of applied nitrogen 20 20
4. Precipitation minus evapotranspiration, Pr - ET , ft/yr 1.7 -1.7
The annual water balance, using Equation 5-1, is:
Lw + Pr = ET + Up
or Wp = Lw + Pr
Wp = Lw + 1.7 (humid)
Wp = Lw - 1.7 (arid)
The amount of percolating water, Wp , resulting from the applied effluent, Lw , has a
significant effect on the allowable nitrogen loading, Ln .
The annual nitrogen balance, using Equation 5-2, is:
Ln = U + D + 2.7 WpCp (5'2'
Ln = 300 + 0.2 Ln + (2.7)(LW + 1.7)00) (humid)
Ln = 300 + 0.2 Ln + (2.7)(LW - 1.7)00) (arid)
5-7
-------
The relationship between the nitrogen loading and the hydraulic loading is:
Ln = 2.7 CnLw (U.S. customary)
ln = 0.1 CnLw (SI units)
where Ln = wastewater nitrogen loading, Ib/acre-yr (kg/ha-yr)
Cn = applied nitrogen concentration, mg/L
LW = wastewater hydraulic loading, ft/yr (cm/yr)
Therefore, for this example,
Ln = (2.7)(25) Lw
= 67.5 Lw
or Lw = 0.015 Ln
With two equations and two unknowns, the nitrogen balance can now be solved:
(5-3)
(5-3a)
Humid climate
Ln = 300
Ln = 300
0.2 Ln
0.2 Ln
(2.7)(LW +
(2.7)(0.015 Ln
Ln = 300 + 0.2 Ln + 0.405 Ln + 45.9
0.395 Ln = 345.9
Ln = 875 lb/acre-yr
Arid cl imate
Ln = 300 + 0.2 L
n
Ln = 300
Ln
(2.7)(LW -
0.2 Ln + (2.7)(0.015 Ln -
Ln = 300 4 0.2 Ln + 0.405 Ln - 45.9
0.395 Ln = 254.1
Ln = 643 lb/acre-yr
Humid climate
1.
2.
3.
4.
5.
Wastewater nitrogen loading, Ln ,
Wastewater hydraulic loading, Lw
Percolating water, Wp , ft/yr
Denitrification, D , Ib/acre-yr
Percolate nitrogen loading, Pn =
, Ib/acre-yr
, ft/yr
2.7 CpWp , lb/acre-yr
875
13.1
14.8
175
400
Arid climate
643
9.6
7.9
129
213
1 Ib/acre-yr =1.12 kg/ha
1 ft/yr = 0.305 m/yr
5.1.2.3 BOD and SS Removal
As indicated in Table 2-3, the expected BOD concentration of treated
water after 5 ft (1.5 m) of percolation is less than 2 mg/L. At
Hanover, New Hampshire, percolate BOD ranged from 0.6 to 2.1 mg/L after
passage through 5 ft (1.5 m). For a primary effluent with a BOD
concentration of about 100 mg/L at a loading rate of 5 Ib/acre-d (5.6
kg/ha'd), the average percolate concentration was 1.5 mg/L [7]. For
industrial wastewaters, BOD loadings have exceeded 200 ib/acre-d (224
kg/ha-d). Suspended solids removals are expected to be similar to BOD
removals although few data are available for existing systems.
5.1.2.4 Phosphorus Removal
Phosphorus retention is extremely effective in slow rate systems as a
result of adsorption and chemical precipitation. Phosphorus retention
for sites can be enhanced by use of crops such as grass with large
5-8
-------
phosphorus uptake. Grass also minimizes soil erosion and surface runoff
losses. Field determination of levels of free iron oxides, calcium, and
aluminum, and soil pH will provide information on the type of chemical
reactions that will occur. Determination of the phosphorus sorption
capacity of the soils requires laboratory testing with field samples
from the proposed areas (see Appendix F).
The estimated phosphorus retention from the empirical model (Appendix
B.4.4) can be computed for the loading and soil sorption properties.
Systems with strict phosphorus control for recovered water should
include routine soil phosphorus monitoring to verify retention in the
soil and system performance.
5.1.2.5 Trace Element Removal
An evaluation of the annual applications of trace metals should be made
on the basis of wastewater applications and an estimate of wastewater
concentrations from field testing or existing data (see Table 3-4). The
assessment of trace metal concentrations is especially important in
cases where industrial sources are present. The potential toxicity to
plants can be assessed by comparing loadings computed to the recommended
application values for sensitive crops (Table 5-4). In cases where
annual total application, or applied concentrations approach levels shown
in Table 5-4, system management to maintain soil pH at 6.5 or above by
liming may be needed.
5.1.2.6 Microorganism Removal
The minimizing of public health risks is a basic goal for any wastewater
treatment system. The potential for public health risks resulting from
land application of wastewater varies greatly depending upon specific
site details such as:
1. Type of application
2. Public access to the site
3. Preapplication treatment
4. Population density and adjacent land use
5. Type of disposition of vegetative cover
6. Natural occurring and artificial onsite buffer zones
7. Climate
The U.S. Army Medical Department and the EPA have conducted and are
continuing to conduct studies at operational land application sites to
document microorganism removal and transport mechanisms. These
locations include Fort Devens, Massachusetts, Deer Creek, Ohio; Fort
Huachuca, Arizona; and Pleasanton, California. In addition, the
5-9
-------
development of a mathematical
underway by the U.S. Army.
model describing aerosol transport is
TABLE 5-4
SUGGESTED MAXIMUM APPLICATIONS OF TRACE ELEMENTS
TO SOILS WITHOUT FURTHER INVESTIGATION3
Element
Mass application Typical
to soil, Ib/acre concentration, mg/L"
Aluminum
Arsenic
Beryl i urn
Boron
Cadmium
Chromium
Cobalt
Copper
Fluoride
Iron
Lead
Lithium
Manganese
Molybdenum
Nickel
Selenium
Zinc
4 080
82
82
610
8
82
41
164
820
4 080
4 080
164
8
164
16
1 640
10
0.2
0.2
1.4C
0.02
0.2
0.1
0.4
1.8
10
10
2.5d
0:4
0.02
0.4
0.04
4
a. Values were developed for sensitive crops on
soils with low capacities to retain elements in
available forms [8, 9].
b. Based on reaching maximum mass application in
20 years at an annual application rate of
8 ft/yr.
c. Boron exhibits toxicity to sensitive plants at
values of 0.75 to 1.0 mg/L.
d. Lithium toxicity limit is suggested at 2.5 mg/L
concentration for all crops, except citrus which
uses a 0.075 mg/L limit. Soil retention is
extremely limited.
1 Ib/acre = 1.12 kg/ha
1 ft =0.305 m
5.1.3 Rapid Infiltration
The design procedure for rapid infiltration is presented in Figure 5-2.
The principal differences from slow rate systems are (1) hydraulic
applications are greater, so greater reliability of permeability
measurements is required; (2) nitrogen removal mechanisms rely less on
crop uptake and more on nitrification-denitrification; (3) solids
applications are greater; and (4) systems can be adapted to severe
climates.
5-10
-------
FIGURE 5-2
RAPID INFILTRATION DESIGN PROCEDURE
r ~
WASTEWATER
CHARACTERISTICS
(SECTIONS 3.3
AND 4.2)
EFFLUENT
REQUIREMENTS
(SECTION 5.1.1)
I
SITE
CHARACTERISTICS
(SECTIONS 3.2, 3.5
AND 4.1)
PREAPPLICATION
TREATMENT
(SECTION 5.2)
HYDRAULIC
LOADINGS
(SECTION 5.1.3.1)
BOD AND SS
LOADINGS
(SECTION 5.1.3)
STORAGE
~l
(SECTION 5.3)
I
FIELD AREA
(SECTION 5.1.3)
—H VEGETATIVE COVER
REMOVALS OF
N, P, BOD, ETC.
SYSTEM
MONITORING
(SECTION 5.7)
I
DISTRIBUTION
(SECTION 5.4)
I
DISCHARGE
T
RECOVERY
T
GROUNDWATER
SURFACE WATER
5-11
-------
5.1.3.1 Hydraulic Loading Rates
Hydraulic loadings and subsequent liquid movement through the soil
depend on soil permeability, subsurface geological conditions, and
constituent loadings. Annual hydraulic loading rates can range from 20
to 400 ft/yr (6 to 120 m/yr). Typical loading rates are shown in Table
5-5.
TABLE 5-5
TYPICAL HYDRAULIC LOADING RATES FOR RI SYSTEMS
1
Location .
Flushing Meadows, Arizona
Santee, California
Lake George, New York
Calumet, Michigan
Hemet, California
Hollister, California
Fort Devens , Massachusetts
Westby, Wisconsin
Hydraulic
loading rat
ft/yr
364
265
140
no
108
97
94
36
e,
Soil type
Sand
Gravel
Sand
Sand
Sand
Sandy loam
Sand and gravel
Silt loam
Type of
wastewater
Secondary
Secondary
Secondary
Untreated
Secondary
Primary
Primary
Secondary
1 ft/yr = 0.305 m/yr
System design for a rapid infiltration process includes the interrelated
factors of hydraulic loading rate per application cycle, soil
infiltration capacity, application and resting cycle, solids applied in
the wastewater, and subsoil permeability. Although site investigations
may show that the infiltration rate is greater than the soil
permeability, the infiltration rate, under design conditions with solids
applications, will usually decrease and control liquid applications.
Figure 3-3 can be used for an initial estimate of the average
infiltration rate. For final design values, soil infiltration tests
(described in Appendix C) should be conducted. The most limiting layer
in the soil profile should be evaluated and that permeability should be
used in design.
The operating infiltration rate will vary between two values: one being
the initial rate for clean soil and clear water, and the other being a
decreased rate for wastewater, with a surface accumulation of organics
and other suspended solids. The cycle of application and resting is
designed to restore the infiltration rate to nearly its initial value by
the end of the resting period. For a specific rapid infiltration site,
a design decision has to be made that balances suspended solids
application, land area requirements, and resting requirements.
5-12
-------
5.1.3.2 Hydraulic Loading Cycles
The existing hydraulic loading and resting cycles of rapid infiltration
systems, as given in Table 5-6, demonstrate several design concepts.
Most systems are intended to maximize infiltration rates, although
Flushing Meadows, Arizona, and Fort Devens, Massachusetts, experimented
with the cycle to promote denitrification.
TABLE 5-6
TYPICAL HYDRAULIC LOADING CYCLES [11]
Location
Calumet, Michigan
Flushing Meadows, Arizona
Maximum infiltration
Summer
Winter
Fort Devens, Massachusetts
Fort Devens, Massachusetts
Lake George, New York
Summer
Winter-
Tel Aviv, Israel
Vineland, New Jersey
Westby, Wisconsin
Whittier Narrows, California
Loading objective
Maximize infil-
tration rates
Increase ammonium
adsorption capacity
Maximize nitrogen
removal
Maximize nitrogen
removal
Maximize infil-
tration rates
Maximize nitrogen
removal
Maximize infil-
tration rates
• Maximize infil-
tration rates
Maximize
renovation
Maximize infil-
tration rates
Maximize infil-
tration rates
Maximize infil-
tration rates
Application
period
1-2 d
2 d
2 wk .
2 wk
2 d
7 d
9 h
9 h
5-6 d
1-2 d
2 wk
9 h
Resting
period
7-14 d
5 d
10 d
20 d
14 d
14 d
4-5 d
5-10 d
10-12 d
7-10 d
2 wk
15 h
Bed surface
Sand (not cleaned)
Sand (cleaned) and
grass cover3
Sand (cleaned) and
grass cover3
Sand (cleaned) and
grass cover3
Grass (not cleaned)
Grass (not cleaned)
Sand (cleaned)3
Sand (cleaned)3
Sandb
Sand (disked), solids
turned into soilc
Grassed
Pea gravel
a. Cleaning usually involved physical removal of surface solids.
b. Maintenance of sand cover is unknown.
c. Solids are incorporated into surface sand.
For basin surfaces with grass or vegetation, the need for maintenance is
less strict than for bare surfaces. Based on operations at Fort Devens,
the grass should be allowed to grow and die without placing heavy
5-13
-------
mechanical equipment, which compacts the surface, on the infiltration
beds. Periodic harrowing of the soil surface or mowing of the grass may
be considered depending on aesthetic demands.
In summary, system design-for maximum infiltration rates should include
adequate drying time based on local climate and solids loadings to
restore infiltration rates. If the soil surface is maintained bare of
vegetation, the surface should be periodically raked, harrowed, or
disked. Nitrogen removal by denitrification will require additional
considerations for lesser soil aeration and the effect of lessened
opportunity for solids degradation.
5.1.3.3 Nitrogen Loading Rates
Because nitrogen loading rates can exceed crop uptake by an order of
magnitude, crop uptake (if a crop is planted) is relatively minor and
nitrification, denitrification, and ammonium sorption are generally of
greatest importance.
The retention of ammonium by the cation exchange capacity can be
excellent. The conversion of ammonium to nitrate occurs rapidly when
short, frequent applications are used to promote aerobic conditions in
the soil. Longer application cycles, which restrict soil reaeration,
favor nitrogen loss by denitrification. Available organic matter in the
soil profile as a result of applied BOD also increases the amount of
denitrification. The most comprehensive work on nitrogen has been
conducted at the Flushing Meadows Project (described in Section 7.8).
At the Flushing Meadows Project, at a 365 ft/yr (111 m/yr) application,
the sustained removal of nitrogen was 30% [12]. For lower application
rates Lance found that the nitrogen removal increased to over 80% (see
Figure 5-3). Although the relationship is strictly valid only for the
sandy soil and secondary effluent used at Flushing Meadows, similar
relationships should exist for other soils and wastewaters.
Infiltration rates in the field can be changed by modifying the depth of
flooding, compacting the soil surface, or by applying wastewater
containing higher BOD and suspended solids [10].
When nitrification is the objective of rapid infiltration, short
application periods followed by relatively long resting periods are
used. Rapid infiltration systems will produce a nitrified effluent at
nitrogen loadings up to 60 lb/acre-d (67.2 kg/ha-d). Nitrification
below 36°F (2°C) and below pH 4.5 is minimal (Appendix A).
5-14
-------
FIGURE 5-3
EFFECT OF INFILTRATION RATE ON NITROGEN REMOVAL
FOR RAPID INFILTRATION, PHOENIX, ARIZONA [10]
UJ
C9
90
eo
70
60
50
40
30
20
1 0
1 in./d = 2.54 cm/d
I
10 20 30 40
INFILTRATION RATE, cm/d
5060
5.1.3.4 BOD and SS Removal
Removals of BOD and suspended solids depend on the soil type and travel
distance in the soil. Removal of BOD is primarily accomplished by
aerobic bacteria that depend on resting periods to reaerate the soil.
Loading rates have some effect on removals but too many other variables
such as temperature, resting period, and soil type are involved to allow
estimation of removals from loading rates alone. Selected loading rates
and concentrations in the treated water are presented in Table 5-7.
5.1.3.5 Phosphorus Removal
The basic mechanisms for phosphorus removal are similar to those
described for slow rate systems (Section 5.1.2.4). The coarser textured
soils used for rapid infiltration may have less retention capacity for
phosphorus. Soil capabilities can be estimated from specific testing
(Appendix F; Section F.3.3.2).
5-15
-------
TABLE 5-7
BOD AND SUSPENDED SOLIDS DATA FOR SELECTED
RAPID INFILTRATION SYSTEMS [13-16]
Location
Phoenix,
Arizona
Lake George,
New York
Calumet,
Michigan
Hollister,
California
Fort Devens,
Massachusetts
BOD
Average
loading
rate,
Ib/acre-d9
40
47
71
158
78
Suspended solids
Treated water
concentration,
mg/L
0-1
1.2
lib
8
12
Average
loading
rate,
lb/acre-d
54
43
197
...
Treated water
concentration,
mg/L
0.8
...
...
...
Sampling
depths,
ft
100
10
11
25
64
a. Total lb/acre-yr applied divided by the number of days in the operating
season (365 days for these cases).
b. Soluble TOC.
1 lb/acre-d = 1.12 kg/ha-d
5.1.3.6 Trace Element Removal
As indicated in Section 5.1.2.5, heavy metals are removed from solution
by the adsorptive process and by precipitation and ion exchange in the
soil. The concerns about heavy metals in rapid infiltration systems
are: (1) the high rates of application, and (2) the potentially low
adsorptive potential of the coarse soils. The heavy metal application
criteria (Table 5-4), recommended to ensure protection of sensitive
plants in slow rate systems, can be safely exceeded for rapid
infiltration systems because sensitive agricultural crops are not grown.
5.1.3.7 Microorganism Removal
The mechanisms of microorganism removal include straining, sedimenta-
tion, predation and desiccation during preapplication treatment; des-
iccation and radiation during application; and straining, desiccation,
radiation, predation, and hostile environmental factors upon application
to the land. Removals of fecal col i forms for selected rapid
infiltration systems are presented in Table 5-8.
5-16
-------
TABLE 5-8
FECAL COLIFORM REMOVAL IN SELECTED
RAPID INFILTRATION SYSTEMS
Fecal col i forms, MPN/100 ml
£•„,' 1
Location
Phoenix
Hemet,
Calumet
, Arizona
California
, Michigan
type Effluent applied
Sand 1 000 000
Sand 60 000
Sand — a
Renovated water
0-30
11
1-10
- Sampling
• depth, ft
100
8
10
a. Untreated wastewater.
1 ft = 0.305 m
5.1.4 Overland Flow
Overland flow systems use the land surface as the treatment medium over
which a thin sheet of wastewater moves and upon which the biological and
chemical processes occur. The design procedure is typically to select a
hydraulic loading based on the required treatment performance for BOD in
the wastewater. Nitrogen removals or transformations are then assessed
based on comparison with existing systems. The design procedure is
presented in Figure 5-4.
5.1.4.1 Hydraulic Loading Rates
Hydraulic loading rates, when untreated or primary effluent is applied,
can range from 2.5 to 8 in./wk (6.4 to 20 cm/wk) depending on the
climate, required treatment performance, and detention time on the
slope. Lower values of 3 to 4 in./wk (7.5 to 10 cm/wk) should be
considered (1) for slopes greater than 6%, (2) for terraces less than
150 ft (45 m), or (3) because of reduced biological activity during very
cold weather. Thomas has reported excellent results using untreated
wastewater at about 4 in./wk (10 cm/wk) on 2 to 4% slopes 120 ft (36 m)
long [17]. Recently, Thomas has experimented with loadings of 6 and 8
in./wk (15 and 20 cm/wk) with untreated wastewater and primary effluent
and has indicated continued excellent removals of BOD, suspended solids,
and nitrogen [18].
For lagoon or secondary effluent, loadings of 6 to 16 in./wk (15 to 40
cm/wk) can be considered. Lower values of 7 to 10 in./wk (17.5 to 25
cm/wk) should be considered when the factors (1) through (3) described
above, apply. Loading rates and design conditions for four
demonstration projects are presented in Table 5-9.
5-17
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FIGURE 5-4
OVERLAND FLOW DESIGN PROCEDURE
WASTENATER
CHARACTERISTICS
(SECTIONS 3.3
AND 4.2)
EFFLUENT
REQUIREMENTS
(SECTION 5.1.1)
SITE
CHARACTERISTICS
(SECTIONS 3.2. 3.5
AND 4.1)
I
HYDRAULIC
1 nin 1 UP? .*
LUAUINua *
(SECTION 5.1.4.1)
1
PREAPPLICATION
TREATMENT
(SECTION 5.2)
1
STORAGE
(SECTION 5.3)
FIELD
(SECTION
r
BOD AND SS
fc. i ni n i ucc
^ LIMU 1 iluo
(SECTION 5.1.4)
1
AREA
5.1.4)
REMOVALS OF
N, P, BOD, ETC.
I
I
AGRICULTURAL
MANAGEMENT
DISTRIBUTION
(SECTION 5.4)
RUNOFF
COLLECTION
(SECTION 5.5)
I
DISCHARGE
T
SURFACE WATER
5-18
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TABLE 5-9
SELECTED HYDRAULIC LOADING RATES FOR OVERLAND FLOW SYSTEMS
Hydraulic
Type of loading Degree of Slope
effluent applied rates, in./wk 'slope, % length, ft
Ada, Oklahoma
Ada, Oklahoma
Pauls Valley, Oklahoma
Utica, Mississippi
Raw comminuted
Trickling filter
Oxidation pond
Oxidation pond
4-8
10-16
10.3
2.5-5
2-4
2-4
2-3
2-8
120
120
150
150
1 in./wk =2.54 cm/wk
1 ft = 0.305 m
Loading rates and cycles for an overland flow system are designed to
maintain active microorganism growth on the soil surface. The operating
principles are similar to a conventional trickling filter with
intermittent dosing. The rate and length of application should be
controlled; anaerobic conditions can result from overstressing the
system. The resting period should be long enough to allow the soil
surface layer to reaerate, yet short enough to keep the microorganisms
in an active state. Experience with existing systems indicates that
optimum cycles range from 6 to 8 hours on and 16 to 18 hours off, for 5
to 6 d/wk depending on the time of year. Application periods may be
extended during the summer months to allow portions of the system to be
taken out of service for crop harvesting.
5.1.4.2 Nitrogen Removal
Nitrogen removal in overland flow systems is excellent. Two important
mechanisms responsible for these removals are biological nitrifi-
cation/denitrification and crop uptake. The overlying water film and
organic matter, and the underlying saturated soil form an aerobic-
anaerobic double layer necessary for nitrification followed by
devitrification. These conditions are similar to those found in rice
fields or marshes. The treated runoff quality for nitrogen at Ada,
Oklahoma, is shown in Table 5-10.
5.1.4.3 BOD and SS Removal
Removals of BOD, both at Ada, Oklahoma and at Paris, Texas, have
improved with system age. At Ada, after about 100 days of operation,
the BOD concentration in the runoff stabilized at an average of 8 mg/L
for the 4 in./wk (10 cm/wk) rate [17]. At Paris, Texas (described in
5-19
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Section 7.12), the BOD in the treated runoff improved from an average of
9 mg/L in 1968 to an average of 3.3 mg/L in 1976.
Suspended solids removals are generally less than those for BOD. At
Ada, removals averaged 95% and concentrations ranged from 8 to 16 mg/L
for the 4 in./wk (10 cm/wk) rate [17]. At Paris, Texas, 245 mg/L of
suspended solids is applied and the treated runoff typically contains 25
to 30 mg/L of suspended solids [11].
TABLE 5-10
NITROGEN CONCENTRATIONS IN TREATED RUNOFF
FROM OVERLAND FLOW WHEN USING UNTREATED WASTEWATER [17, 18]
mg/L
Loading rate, in./wk
Nitrogen forms 4 8
Total
Organic
Ammonia
Nitrate and nitrite
2.9
1.6
0.8
0.5
3
a
a
a
a. Not measured, but assumed to be
similar to 4 in./wk loading rate.
•1 in./wk = 2.54 cm/wk
5.1.4.4 Phosphorus Removal
Of the three major land treatment processes, overland flow systems have
the most limited potential for phosphorus removal. Because there is
very limited percolation of wastewater in overland flow systems, the
soil-water contact is limited to the soil surface area. The wastewater
flowing over the soil surface does not have extensive contact with the
components of the soil that normally fix large amounts of phosphorus.
In addition, the residence time on the slope is usually less than 24
hours. However, some phosphorus appears to be removed by the organic
layer on the surface of overland flow slopes [19] and the grass will
take up 30 to 40 lb/acre-yr (33 to 44 kg/ha-yr).
At Ada, Oklahoma, alum was added to the wastewater prior to application.
For an application rate of 4 in./wk (10 cin/wk), the removals of
phosphorus are presented in Table 5-11. Similar results were obtained
at Vicksburg, Mississippi [20].
5-20
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TABLE 5-11
PHOSPHORUS CONCENTRATIONS IN TREATED RUNOFF FROM
OVERLAND FLOW, ADA, OKLAHOMA [17]
Sample
Concentration of total Phosphorus
phosphorus, mg/L removal, %
Untreated wastewater
Runoff
No alum
14 mg/L alum
20 mg/L alum
9.8
3.7
1.6
1.5
62
84
85
Carlson et al. reported 75% phosphorus removal
in greenhouse studies at 0.5 in./d (1.3 cm/d)
Melbourne, Australia, phosphorus removals of 35%
reported (Appendix B).
from secondary effluent
applications [21]. At
from raw wastewater are
5.1.4.5 Trace Element Removal
Trace element removal by overland flow is relatively good. Hunt and Lee
[19] report that .rates of removal are greater than 90% for all, and
greater than 98% for some heavy metals. It is believed that most of the
heavy metals are removed in the surface organic mat.
5.1.4.6 Microorganism Removal
The mechanisms involved in the removal of bacteria by the soil in
overland flow systems are similar to those for removal of metals. At
the pilot study at Ada, Oklahoma, the overall reduction for total
coliforms was about 95%, while fecal coliform reduction was about 90%
[17].
5.1.5 Wetlands Application
The designed use of wetlands to receive and satisfactorily treat
wastewater effluents is a relatively new concept. At present, the use
of wetlands has not been incorporated into large, full-scale treatment
systems; however, the potential treatment capacity has been confirmed at
many pilot systems and research sites. Hydraulic loadings and general
performance criteria are given in Table 5-12.
5-21
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ro
no
TABLE 5-12
HYDRAULIC LOADINGS AND GENERAL PERFORMANCE CRITERIA -
RESEARCH AND DEMONSTRATION WETLAND SYSTEMS
Location
System type
Final concentrations, mg/L
Preapplication Length of Application Suspended Total Total
treatment application rate, in./d BOD solids nitrogen phosphorus
New York Constructed
[22] marsh/pond
Aerated
Year-round
1.8
16
43
Wisconsin Constructed marsh Primary and Year-round
[23] secondary
Natural marsh Primary and Year-round
secondary
5-18 14-80
5-27 90-154 0.5-2
a. Application varies to give detention times of 5 hours to 10 days.
b. At point in swamp 2.26 mi (3 640 m) downstream from outfall.
2.2
10-12
1-3 •
California
[24]
New Jersey
[25]
Canadian
Northwest
[26]
Minnesota
[27]
Florida
[28, 29].
Constructed marsh
Natural tidal
marsh
Natural swamp
Constructed
peat bed
Natural cypress
dome
Secondary
Secondary
Lagoon and
raw septage
Secondary
Secondary
Year-round ... .... <7 2.8
Year-round 2.0-5.0 ....
Year-round <10D <40b <8b
-------
5.1.5.1 Process Description
There are several types of wetlands (as mentioned in Chapter 2) with
varying amounts of organic substrate and vegetative growth and varying
degrees of soil moisture. They require low-lying, usually level,
saturated land, sometimes partially or intermittently covered with
standing water. In wetland application systems, wastewater is renovated
by the soil, plants, and microogranisms as it moves through and over the
soil profile. Wetland systems are somewhat similar to overland flow
systems in that most of the water flows over a relatively impermeable
soil surface and the renovation action is more dependent on rnicrobial
and plant activity than soil chemistry.
5.1.5.2 Hydraulic Loadings
Items to be considered in selecting the hydraulic loading include:
1. Detention time of applied wastewater
2. Rate of water loss from system by planned overflow or slow
seepage
3. System upsets due to washouts by precipitation or wastewater
applications
5.1.5.3 Nitrogen Management
For a wetland system, the following mechanisms should be considered as
factors having an influence on nitrogen balance:
1. Denitrifi cation
2. Above ground and below ground plant uptake
3. Dilution
4. Sorption with living or dead material
The biomass productivity of wetland systems has been reported to be 4 to
5 tons/acre (8 to 10 Mg/ha) in Wisconsin marshes, with other reported
values up to 6.7 to 8 tons/acre (15 to 18 Mg/ha) [30]. The total plant
nitrogen uptake is extremely high since nitrogen content of the plants
may be from 2.0 to 2.5%; however, the below ground portion of the plant
may contain 4 to 6 times as much biomass as the above ground portion.
Thus, the majority of the nitrogen content in the system is released and
recycled rather than being available for removal by harvest. The
seasonal uptake and release by perennial and annual vegetation is
5-23
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influenced by the nitrogen cycling. In general, natural wetlands can be
classified as low in nitrogen availability, because their high organic
content can serve as a nitrogen sink. Managed wetlands can facilitate
biomass production and harvesting to provide an effective nitrogen
removal mechanism.
The schematic diagram presented in Figure 5-5 illustrates the principal
nitrogen transformations occurring in a wetland system. The overlying
water and underlying organic soil form an aerobic-anaerobic double-
layer, thus providing ideal conditions for biological nitrification-
denitrifi cation reactions to occur.
FIGURE 5-5
PRINCIPAL NITROGEN TRANSFORMATIONS
IN WETLANDS [20]
APPLIED NITROGEN
(MOSTLY NH4)
ORGANIC
MATTER
SOIL
OXIDIZED
£~ NH -NO. 2\\r.'NITRIFICATION.;
4
^"^-.^
REDUCED
5.1.5.4 Climatic Considerations
Climatic considerations for wetland systems are not well defined.
Although wetland systems have been utilized in locations from Florida
[28] to the Canadian Northwest Territories [26], the mechanisms involved
5-24
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in retention or removal of each wastewater component are uncertain. A
wetland system in Wisconsin used for wastewater application is shown in
Figure 5-fa.
FIGURE 5-6
WETLAND SYSTEM AT BRILLION MARSH, WISCONSIN
b.1.5.5 Phosphorus Management
Within the range of wetland system types, the phosphorus removals can
vary considerably. For peatlands, Stanlick reports 99X removal of
phosphorus [27]. In Wisconsin, using man-made and natural marshes,
Spangler et al. report 30 to 40% removal on a year-round oasis [23].
capabilities are generally high during the growing season,
soils have a high cation exchange capacity (about lOb
and wetland plants account for luxury uptake of phosphorus.
the above ground plant portions will remove some phosphorus
from the system; however, release from the below ground portion will
occur during the nongrowing season.
The removal
because the
meq/100 g)
Harvest of
5-25
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5.1.5.6 Trace Elements Removal
Although extensive research has not been done with wetlands, the results
of research from metal accumulation in lake and river sediments are
generally applicable. Organic soils may have high cation exchange
capacities so retention should be excellent; however, the effects of pH
on retention must be considered.
5.1.5.7 Microorganism Removal
The removal of pathogenic microorganisms depends on the pathway for
water leaving the site. Systems that have no overflow and function by
water seepage through a slightly permeable soil will have excellent
removal of all microorganisms, due to physical entrapment and die-off
mechanisms. Surface overflow systems offer a less positive removal, so
natural die-off as a function of detention time, climate, and other
environmental factors must be assessed.
5.2 Preapplication Treatment
The design of preapplication treatment facilities involves three steps:
1. Determine the level of treatment required for the selected
land treatment process and site conditions
2. Select a treatment system capable of meeting this level
3. Establish design criteria and perform detailed design of the
selected treatment system
Only the level of treatment required will be discussed, because the
second and third items are standard engineering procedures that are not
unique to land treatment.
5.2.1 Determination of Level Required
In general, the level of preapplication treatment required is an
internal process decision made by the designer to ensure optimum
performance of the land treatment process. Preapplication treatment may
be necessary for a variety of reasons including (1) improving
distribution system reliability, (2) reducing the potential for nuisance
conditions, (3) obtaining a higher overall level of wastewater
treatment, (4) reducing soil clogging, and (5) reducing the risk of
public health impacts. The need for preappl ication treatment to reduce
impacts on various system components is summarized in Table 5-13.
5-26
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TABLE 5-13
NEED FOR PREAPPLICATION TREATMENT
System
component
Storage
Distribution
system
Crops
Hydraulic
loading
Public access
Potential problems
Odors and solids
accumulation
Solids deposition
orifice clogging
Limited selection
Reduced loading
rate for rapid
infiltration
Health risk due
to contact
Level of treatment and mitigating measures
Screened3 - add aerators
Primary - add aerators'3
Biological
Screened - velocity control and larger orifice
Primary - velocity control
Biological
Screened - limit to high tolerance crops (i.e.,
Primary - limit to feed, seed, and fiber crops
Biological - disinfect to suit individual needs
Screened - increased basin maintenance
Primary - increased basin maintenance or use of
Biological
nozzles
grass)
vegetation
Screened - posting and fencing or buffer zones or disinfection
Primary - posting and fencing or buffer zones or disinfection
Biological - disinfect for public access areas
a. Bar screens and comminution.
b. Only for short-term (less than a month) storage.
5.2.1.1 Impacts During Storage
The primary consideration for preapplication treatment prior to storage
is reduction of the potential for nuisance conditions. This may require
reduction in the settleable solids and organic content of the wastewater
to levels achievable with primary treatment. This will minimize the
possibility of nuisance conditions developing in the storage lagoon.
Such factors as climate, length of storage, and reservoir design will
determine the necessary level of BOD reduction. Storage reservoirs
provide additional treatment through further biological action,
deposition of solids, and long-term pathogen die-off [31]. Supplemental
aeration could be provided in the reservoir to meet excessive oxygen
demand. An alternative concept would be to design the storage lagoon to
double as a deep facultative lagoon. Disinfection prior to storage
should not be necessary as long as public access to the storage lagoon
is restricted.
5-27
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5.2.1.2 Impacts on Transmission
Although transmission of wastewater to the application site will usually
not govern the level of preapplication treatment, the method of
transmission should be taken into consideration. For systems in which
wastewater is to be pumped to the application site and no other
preapplication treatment is required, coarse screening, degritting, and
comminution should be included to avoid excessive wear on the equipment.
5.2.1.3 Impacts on Distribution Systems
Preapplication treatment considerations for surface distribution
techniques include coarse and settleable solids removal to avoid solids
deposition in ditches and laterals. The need for disinfection will
depend on the possibility of public contact with the distribution
system.
Different criteria apply to sprinkler distribution systems. To avoid
plugging of nozzles, it has been recommended that the size of the
largest particle in the applied wastewater be less than one-third the
diameter of sprinkler nozzles [11]. Removal of coarse and settleable
solids as well as grit and any oil and grease should be a minimum
preapplication treatment level to maintain reliability in systems using
sprinkler distribution.
5.2.1.4 Impacts on Slow Rate Application
For slow rate systems, hydraulic or nitrogen loadings will generally
govern the system performance. Thus, from the standpoint of process
performance and soil matrix impacts, preapplication treatment for
reduction of organics and suspended solids is not necessary. Industrial
wastewaters with high organic strength have been applied to land
successfully, and data are available to indicate that no significant
difference in overall performance was obtained when both primary and
secondary effluent were applied under similar conditions [32].
Where the method of application is by sprinkling, limits on aerosol and
mist drift should be considered. Preapplication treatment such as
primary settling, secondary treatment, and disinfection all serve to
reduce the bacterial content of the effluent and hence reduce the
numbers of aerosolized bacteria. The need for secondary treatment or
disinfection must be evaluated on a case-by-case basis taking into
account (1) the population density of the area, (2) the degree of public
access to the site, (3) the relative size of the application area,
(4) the feasibility of providing buffer zones or plantings of trees or
shrubs, and (5) the prevailing climatic conditions.
5-28
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For forage crop irrigation, the need for disinfection can be balanced
against the exposure risk to the public or grazing animals from
pathogens in municipal wastewater. On the basis of a limited comparison
of land treatment with conventional treatment and discharge, it was
concluded that the relative risks to the public were essentially the
same [33]. Primary treatment followed by surface application to land
that is fenced has been considered adequate to minimize health risks.
For application to parks, golf courses, and areas of public access,
biological treatment followed by disinfection is often practiced.
5.2.1.5 Impacts on Rapid Infiltration Application
The potential for soil clogging is higher for rapid infiltration systems
than for slow rate systems due to greater hydraulic loading rates. As a
minimum, primary treatment to remove coarse and settleable solids should
be included as preapplication treatment. Reduction of solids to
secondary levels will increase-the allowable hydraulic loading rates for
rapid infiltration systems and a balance can be achieved between the
degree of preappl ication treatment and the hydraulic loading rate.
Algae carryover from holding ponds or lagoons will increase the
potential for soil clogging. The use of in situ pilot studies may be
required to develop soil response relationships between hydraulic
loading and wastewater solids and organic levels [11].
5.2.1.6 Impacts on Overland Flow Application
Because overland flow treatment is basically a surface phenomenon, soil
clogging is not a problem, and high BOD and suspended solids removals
have been achieved with systems applying raw comminuted municipal
wastewater [34] and industrial wastewater with 616 mg/L BOD and 263 mg/L
of suspended solids [35]. Thus, preappl ication treatment for removal of
organics and solids would be necessary only to the extent required by
other system components. The need for predisinfection would be governed
by consideration of the method of distribution. Low-pressure, large-
droplet, downward sprinkling nozzles and bubbling orifices or gated pipe
distribution should not require predisinfection if public access is
controlled. Postdisinfection of the wastewater runoff may be required.
Because overland flow systems are less effective for removal of
phosphorus than other land treatment methods, preapplication treatment
to enhance overall phosphorus removal may be necessary if a low level is
required in the collected runoff.
5.2.2 Industrial Pretreatment
Pretreatment of industrial wastewaters discharged into municipal systems
may be required for several reasons, including (1) protection of the
collection system; and (2) removal of constituents that would have an
5-29
-------
adverse impact on the treatment system or would pass through the
treatment process relatively unchanged, causing unacceptable effluent
quality. General guidelines for pretreatment of industrial wastes
discharged to municipal systems using conventional secondary treatment
have been published by the EPA [36].
Pollutants that are compatible with conventional secondary treatment
systems would generally be compatible with land treatment systems. As
with conventional systems, pretreatment requirements will be necessary
for such constituents as fats, grease, and oils, and sulfides to
protect collection systems and treatment components. Pretreatment
requirements for conventional biological treatment will also protect
land treatment processes.
High levels of sodium decrease the soil permeability. Pretreatment
requirements may be necessary for industrial wastes high in sodium, if
the SAR of the total wastewater might be increased to unacceptable
level s.
Plant toxicity from metals is discussed in Appendix E and recommended
maximum concentrations of trace elements in irrigation water have been
previously presented in Table 5-4. Concern over accumulation in the
food chain is greatest for cadmium, as discussed in Appendix E. The
potential for groundwater contamination from trace elements is greatest
for rapid infiltration systems, although the ability of soils to remove
and accumulate heavy metals from such systems has been demonstrated [13,
37].
5.3 Storage
There is a need for storage in many land treatment systems because of
the effect of climate on treatment or an imbalance between wastewater
supply and application. Slow rate and overland flow systems may cease
operation during adverse climatic conditions whereas rapid infiltration
systems can usually continue operation year-round. An alternative to
storage may be seasonal discharge to surface waters.
5.3.1 Determining Storage Needs
The National Climatic Center in Asheville, North Carolina, has conducted
an extensive study of climatic variations throughout the United States
and the effect of these variations on storage requirements for soil
treatment systems [38]. Three computer programs, as presented in Table
5-14, have been developed to estimate the storage days required when
inclement weather conditions preclude land treatment system operation.
5-30
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TABLE 5-14
SUMMARY OF COMPUTER PROGRAMS FOR DETERMINING
STORAGE FROM CLIMATIC VARIABLES
EPA
program Applicability
EPA-1 Cold climates
Variables
Mean temperature,
Remarks
Uses freeze index
EPA-2
EPA-3
Wet climates
rainfall, snow depth
Rainfall
Storage to avoid
surface runoff
Moderate climates Maximum and minimum Variation of EPA-1
temperature, rainfall, for partly favor-
snow depth able conditions
Depending on the dominant climatic conditions of a region, one of the
three computer programs will be most suitable. The program best suited
to a particular region is shown in Figure 5-7. The maximum storage days
over the period of record is calculated as well as storage days for
recurrence intervals of 5, 10, and 50 years.
The validity of any one of the computer storage programs will depend on
the presence of adequate data. The quality, completeness, and length of
record are all important. Assigning threshold values and the confidence
level of the output must be considered carefully in order to provide a
realistic estimate of required storage. To use these programs, contact
the National Climatic Center of the National Oceanic and Atmospheric
Administration in Asheville, North Carolina 28801; a fee is required.
5.3.1.1 Determining Storage in Cold Climates
The operation of a slow rate or overland flow system is likely to be
affected adversely if severe cold weather prevails for long periods (2
to 4 months). If annual crops are being irrigated, then the growing
season will determine the storage requirement. However, if perennials,
such as grasses and woodlands, are irrigated, then wastewater
application will normally be stopped only by frozen soil conditions.
The EPA-1 program computes a "freezing index" which provides a measure
of the intensity and duration of cold periods that are likely to occur
in the Northeast, the northern half of the Midwest, and parts of the
Rocky Mountain area (see Figure 5-7). When the index reaches 200 to
300, the ground is assumed to be frozen and wastewater application is
not recommended [39]. Limitations to the use of the freezing index
include: lack of soil temperature data, yearly winter temperature
variations, and differences in design and operating practices for
existing land treatment systems.
5-31
-------
FIGURE 5-7
DETERMINATION OF STORAGE BY EPA COMPUTER PROGRAMS AND WATER BALANCE
ACCORDING TO CLIMATIC CONSTRAINTS [11, 38]
en
i
to
IND
WATER BALANCE
&/
EPA-3
-------
EPA-1 also computes storage based on the favorable/unfavorable day
analysis by assigning threshold values to (1) mean daily temperature,
(2) daily precipitation, and (3) snow cover. The storage requirement is
increased by one day's flow on days designated as unfavorable according
to the threshold values. On a favorable day, storage is reduced by a
fraction of one day's flow—the drawdown rate. A range of common
threshold values used as input to the EPA-1 program is listed in
Table 5-15.
TABLE 5-15
THRESHOLD VALUES FOR THE EPA-1 STORAGE PROGRAM
Favorable day
Parameter threshold values
Mean daily temperature, °F >25-32
Daily precipitation, in. <0.5-1.0
Snow cover, in. <1.0
Drawdown rate, % of average
flow " 50-25
1°F = 1.8°C + 32
1 in. = 2.54 cm
5.3.1.2 Determining Storage in Moderate Climates
To estimate storage for moderate climatic zones where winter conditions
are less severe such as the mid-Atlantic states (see Figure 5-7), EPA-3
is recommended. This program is more flexible than EPA-1 in that
minimum and maximum daily temperatures are examined instead of the mean
daily temperature. Both temperature thresholds must be reached for a
day to be favorable. However, if the maximum daily temperature is
exceeded, but the minimum temperature is below the lower threshold, the
program assumes that it is warm enough to permit operation during a
portion of the day, i.e., a partly favorable day. EPA-3 is organized so
that on partly favorable days, storage is automatically increased by
some fraction of the daily flow. The precipitation and snow cover
thresholds and the drawdown rate act as they do for EPA-1. Weather
station data for the above parameters are examined during the months of
November through April for the available period of record (20 years
minimum).
The drawdown rate, as used in EPA-3, is the amount of water applied on
favorable days in addition to the average daily flow. In moderate
climates, this parameter can significantly reduce storage requirements
5-33
-------
but at the expense of increasing land requirements. Availability and
cost of the additional land will determine how much wastewater can be
applied from storage.
5.3.1.3 Determining Storage in Wet Climates
In wet regions where a high percentage of the annual precipitation is in
the form of rain and the mean daily temperature seldom drops below 32°F
(0°C), the EPA-2 storage program should be used. EPA-2 accounts for
prolonged wet periods where rain can occur almost daily between the
months of November and April. Regions where prolonged wet spells limit
the application of wastewater are at locations along the Gulf states and
the Pacific Northwest Coastal Region. Daily climatological data are
examined in an attempt to identify days when the soil is saturated and
an application of wastewater would result in unwanted runoff. Any day
where runoff occurs is defined as unfavorable and considered a storage
day.
The EPA-2 program is an outgrowth of work by Palmer to determine
conditions of meteorological drought for agricultural purposes [4U].
The rate at which excess soil moisture is depleted from the soil (the
soil drying rate) is approximated by the EPA-2 program to account for
the long-term effects of extremely heavy rainfall. The program can be
modified to suit different soil conditions.
5.3.1.4 Determining Storage in Warm Climates
In warm climates, such as the semiarid and arid southwest United States,
the climatic constraints to application of wastewater are usually very
small (1 to 5 days). In these situations total storage may depend on
the balance between water supply and application rate and the amount of
certain wastewater constituents, e.g., nitrogen that can be applied to
the soil without exceeding groundwater quality restrictions.
An irrigation water balance, which also considers nitrogen loading, can
be used to estimate cumulated storage in warm climates for slow rate
systems. The water balance consists of the elements in the following
equation:
Design + W"tewfer = Evapotranspiration + Percolation + Runoff (5-4)
precipitation applied r r \~> -r/
A monthly evaluation of water balance is suggested due to seasonal
variations in component factors. Of all the factors, precipitation is
the most unpredictable. A range of values that might be encountered can
be established on the basis of a frequency analysis of wetter-than-
normal years (the wettest in 10, 20, or 25 years may be reasonable).
5-34
-------
When using the water balance to estimate storage, the recurrence
interval for precipitation and evapotranspiration should be the same.
An example of a monthly irrigation water balance to determine storage
requirements for a 1 Mgal/d (43.8 L/s) slow rate system is shown in
Table 5-16. This water balance assumed (1) precipitation and
evapotranspiration data for the wettest year in 25, (2) nitrogen is
limiting and separate calculations show that 120 acres (48 ha) are
required, (3) a perennial grass is grown and irrigated year-round,
(4) tailwater runoff from surface application is contained and
reapplied, and (5) the storage reservoir is empty at the beginning of
the water year.
The maximum storage would be 22.7 in. (58 cm) in the month of March,
calculated for an application area of 120 acres (48 ha), yielding the
required storage volume of 227 acre-ft (280 000 m3) or 74 days flow at
1 Mgal/d (43.8 L/s).
5.3.1.5 Irrigation and Consumptive Use Requirements
In mild climates, storage requirements could be governed by the
management of crops that are to be grown. The irrigation and
consumptive use requirements shown in Table 5-17 for the Bakersfield,
California, slow rate system illustrate how storage is affected by crop
selection. It should be pointed out that only a portion of the applied
wastewater is actually consumed by the crops (or lost by
evapotranspiration). Some of the wastewater will be lost by seepage
from irrigation ditches, from surface runoff, and by deep percolation
below the root zone in the field. This is reflected in Table 5-17,
where irrigation requirements are shown to be greater than consumptive
use values. The U.S. Department of Agriculture has estimated that on
the average about 47% of the irrigation water enters the soil and is
held in the root zone where it is available to crops. It also points
out that it is possible to attain irrigation efficiencies of 70 to 75%
by proper selection, design, and operation of the irrigation system,
including provision for tailwater return [42].
There are several months listed in Table 5-17 when there is no
irrigation requirement although consumptive use is indicated. In these
cases, it is assumed that crop water needs are being supplied by
effective growing season precipitation and carryover soil moisture from
winter rains, or pre-irrigation.
5-35
-------
TABLE 5-16
EXAMPLE OF STORAGE DETERMINATION FROM A WATER
BALANCE FOR IRRIGATION [41]
Inches
Month
(1)
Oct
Nov
Dec
Jan
Feb
Mar
Apr
May
Jun
Jul
Aug
Sep
Evapotrans-
pi ration3
(2)
2.3
1.0
0.5
0.2
0.3
1.1
3.0
3.5
4.8
6.0
5.7
3.9
Allowable
percolation'5
(3)
10.0
10.0
5.0
5.0
5.0
10.0
10.0
10.0
10.0
10.0.
10.0
10.0
Water
losses0
(2M3)
= (4)
12.3
11.0
5.5
5.2
5.3
11.1
13.0
13.5
14.8
16.0
15.7
13.9
Precipitation3
(5)
1.6
2.4
2.7
3.0
2.8
3.4
3.0
2.1
1.0
0.5
1.1
2.0
Water
deficitd
(4)-(5)
= (6)
10.7
8.6
2.8
2.2
2.5
7.7
10.0
11.4
13.8
15.5
14.6
11.9
Wastewater
available6
(7)
9.3
9.3
9.3
9.3
9.3
9.3
9.3
9.3
9.3
9.3
9.3
9.3
Change in
storage^
(7)-(6)
= (8)
-1.4
0.7
6.5
7.1
6.8
1.6
-0.7
-2.1
-4.5
-6.2
-5.3
-2.6
Total
storage
(9)
0
0.7 ,
7.2
14.3
21.1
22.7
22.0
19.9
15.4
9.2
3.9
1.3
Total
annual
32.3
105.0
137.3
25.6
111.7
111.8
a. Precipitation and evapotranspiration data are entered into columns 5 and 2, respectively.
b. On the basis of the nutrient balance to satisfy groundwater quality standards, the design
allowable percolation rate is 10 in./month from March through November and 5 in./month for the
remaining months (column 3).
c. The water losses (column 4) are found by summing evapotranspiration and percolation.
d. The water deficit (column 6) is the difference between the water losses and the precipitation.
e. The wastewater available per month (column 7) is
. Wastewater _ 1 Mgal/d x 30.4 d/month x 36.3 acre-in./Mgal
available 120 acres
f. The monthly change in storage (column 8) is the difference between the wastewater available
(column 7) and the monthly water deficit (column 6).
1 in. - 2.54 cm
1 Mgal/d = 43.8 L/s
1 acre = 0.405 ha
5-36
-------
TABLE 5-17
IRRIGATION AND CONSUMPTIVE USE REQUIREMENTS FOR SELECTED CROPS
AT BAKERSFIELD, CALIFORNIA [43, 44]
Depth of Water in Inches
Double crop
Pastures or alfalfa3 barley and grain sorghum Cotton0 Sugar beets"
Month
Jan
Feb
Mar
Apr
May
Jun
Jul
Aug
Sep
Oct
Nov
Dec
Consumptive
use
0.9
2.0
3.8
5.2
7.0
8.6
9.4
8.7
5.8
4.3
2.0
1.0
Irrigation
requirements
1.2
2.7
5.1
7.0
9.4
11.5
12.6
11.7
7.8
5.8
2.7
1.3
Consumptive
use
1.0
2.0
3.8
5.2
2.6
4.5
8.0
6.0
3.0
1.0
Irrigation
requirements
....
6.0
6.0
10.0
7.0
12.0
9.0
10.0
Consumptive
use
....
0.6
1.2
3.6
7.2
8.4
6.0
2.5
....
Irrigation
requirements
15e
5
12
12
Consumptive
use
1.0
2.5
5.0
7.0
8.0
Irrigation
requirements
5.0
9.0
5.0
9.0
7.5
4.5
6.0f
Total 58.7 78.8 37.1 60.0 29.5 44 23.5 46.0
a. Estimated maximum consumptive use (evapotranspiration) of water by mature crops with nearly complete ground-
cover throughout the year.
b. Barley planted in November-December, harvested in June. Grain sorghum planted June 20-July 10, harvested
in November-December.
c. Rooting depth of mature cotton: 6 ft. Planting dates: March 15 to April 20. Harvest: October, November,
and December.
d. Rooting depth: 5 to 6 ft. Planting date: January. Harvest: July 15 to September 10.
e. Pre-irrigation should wet soil to 5 to 6 ft depth prior to planting.
f. Pre-irrigation is used to ensure germination and emergence. First crop irrigations are heavy in order to
provide deep moisture.
1 in. = 2.54 cm
1 ft = 0.305 m
5-37
-------
5.3.2 Storage Reservoir Design
Most agricultural reservoirs are constructed of simple homogeneous
(uniform materials) earth embankments, the design of which conforms to
the principles of small dam design. Depending on the magnitude of the
project, state regulations may govern the design. In California for
example, any reservoir with embankments higher than 6 ft (1.8 m) and a
capacity in excess of 50 acre-ft (61 800 m3) is subject to state
regulations on design and construction of dams, and plans must be
reviewed and approved by the appropriate agency [45]. Design criteria
and information sources are included in the U.S. Bureau of Reclamation
publication, Design of Small Dams [46]. In many cases, it will be
necessary that a competent soils engineer be consulted for proper soils
analyses and structural design of foundations and embankments.
5.4 Distribution
The most common distribution techniques for land application fall within
two major categories—surface and sprinkler--the selection of which
depends on the objectives of the project and the limitations imposed by
physical conditions such as topography, type of soil, crop requirements,
and level of preapplication treatment.
Surface distribution employs gravity flow from piping systems or open
ditches to flood the application area with several inches of water.
Surface distribution is more suited to soils with moderate to low intake
rates. Control of runoff is usually more of a consideration for surface
distribution than for sprinkling, as applications of 2 in. (5 cm) or
less by surface methods are difficult to apply uniformly. Graded land
is essential to proper performance of a surface system.
Sprinkler distribution simulates rainfall and is less susceptible to
topographic constraints than surface methods. It is particularly suited
to irrigation of both highly permeable and highly impermeable soils.
Sprinkler distribution may be used to irrigate most crops and, when
properly designed, provides a more uniform distribution of water and
greater flexibility in range of application rates than is available with
surface distribution. Limitations to sprinkling include adverse wind
conditions, clogging of nozzles with solids, and preapplication
treatment requirements. Sprinkling also involves a significant
utilization of equipment and its capital costs are significantly higher
than those for surface distribution.
5-38
-------
For all types of distribution systems, the maximum flow requirement of a
given system and field area is referred to as the system capacity, which
is computed by the formula:
(5-5)
where Q = discharge capacity, gal/min (L/s)
C = constant, 453 (28.1)
A = field area, acres (ha)
D = gross depth of application, in. (cm)
F = number of days to complete one cycle
H = number of operating hours
The system capacity is useful for determining mainline sizes, pump
capacities, storage requirements, and operating time requirements. If
several sites are involved with different loading requirements, system
capacities must be computed separately within the same period of time to
determine total system capacity.
5.4.1 Surface Systems
Surface distribution methods include ridge and furrow irrigation,
surface flooding (border strip) irrigation, infiltration basins, and,
overland flow. The distinguishing physical features of these methods
are illustrated in Figure 5-8. Variations of methods employed in crop
irrigation and the suitability of each to conditions of use are
summarized in Table 5-18. Similar criteria for the surface application
methods not normally associated with crop irrigation are summarized in
Table 5-19.
5.4.1.1 Ridge and Furrow Irrigation
Ridge and furrow irrigation consists of running irrigation streams along
small channels (furrows) bordered by raised beds (ridges) upon which
crops are grown. Furrows may be level or graded, straight or contoured.
A similar method is corrugation irrigation, which consists of furrows
excavated from the surface without creating raised beds. To simplify
this presentation, only straight, graded ridge and furrow irrigation
will be referred to hereafter, as its design considerations are
applicable to all these methods.
Intake characteristics for furrow irrigation are distinguished from
those for border and sprinkler irrigation because the water only
partially covers a given field area, and moves both downward and
outward. Intake characteristics are best determined by inflow-outflow
5-39
-------
FIGURE 5-8
SURFACE DISTRIBUTION METHODS
(a)RIDGE AND FURROW IRRIGATION
COMPLETELY FLOODED-
rrr^fiTfWTtTTTi^m
(b) FLOODING (BORDER STRIP) IRRIGATION
EVAPORATION
SURFACE A PPLICATION
ZONE OF AE
AND THE ATM
RECHA!
WATER TABLE
SURFACE
APPLICATION
OLD WATER TABLE
(c) RAPID INFILTRATION
EVAPORA Tl ON
RASS AND VEGETATIVE LITTER
SHEET FLOW
(d) OVERLAND FLOW
5-40
-------
TABLE 5-18
SURFACE IRRIGATION METHODS AND CONDITIONS OF USE [47]
Suitabilities and conditions of use
Irrigation
method
Crops
Topography
Water quantity
Soils
.Remarks.
Small
rectangular
basins
Grain, field crops,
orchards, rice
Relatively flat land;
area within each basin -
should be leve-led.
Can be adapted
to streams' of
various.sizes
en
i
Large
rectangular
basins
Contour
checks
Marrow
borders up to
16 ft wide
Wide borders
up to 100 ft
wide
Grain, field crops,
rice
Orchards, grain,
rice, forage crops
Pasture, grain,
alfalfa, vineyards,
orchards
Grain, alfalfa,
orchards
Flat land; must be
graded to uniform
plane
Irregular land,
slopes less than 2%
Uniform slopes less
than 7%
Land graded to uniform
plane wi th maximum
slope less than 0.5%
Large flows of
water
Flows greater
than 1 ft3/s
Moderately large
flows
Large flows, up
to 20 ft3/s
Suitable for soils
of high or low in-
. take rates; should
not be used on
soils that.tend to
puddle
Soils of fine tex-
ture with low
intake rates
Soils of medium to
•heavy texture that
do not crack on
drying
Soils of medium to
heavy texture
Deep soils of
. medium to fine
texture
High installation costs.
Considerable labor
required for irrigating.
When used for close-
spaced crops, a high
percentage of land is
used for levees and
distribution ditches.
High efficiencies of
water use possible.
Lower installation costs
and less labor, required
for irrigation than small
basins. Substantial
levees needed.
Little land grading
required. Checks can be
continuously flooded
(rice), water ponded
(orchards), or inter-
mittently flooded
(pastures).
Borders should be in
direction of maximum
slope. Accurate cross-
leveling required between
guide levees.
Very careful land grading
necessary. Minimum of
labor required for irri-
gation. Little inter-
ference with use of farm
machinery.
-------
TABLE 5-18
(Concluded)
Suitabilities and conditions of use
ro
Irrigation
method Crops Topography
Benched Grain, field crops, Slope up to 20%
terraces
Water quantity Soils
Streams of small Soils must be suf-
to medium size ficiently deep that
grading operations
will not impair
crop growth
Remarks
Care must be taken in
constructing benches and
providing adequate drainage
channel for excess water.
Irrigation water must be
properly managed. Misuse
of water can result in
serious soil erosion.
Furrow
Straight
furrows
Graded
contour
furrows
Corrugations
Basin
furrows
Zizag
furrows
Vegetables, row
crops, orchards,
vineyards
Vegetables, field
crops, orchards,
vineyards
Close-spaced crops
such as grain,
pasture, alfalfa
Vegetables, cotton,
maize, and other
row crops
Vineyards, bush
.berries, orchards
Uniform slopes not ex-
ceeding 2% for cuti-
vated crops
Undulating land with
slopes up to 8%
Uniform slopes of up
to 10";
Relatively flat land
Land graded to uniform
slopes of less than }%
Flows up to
12 ft3/s
Flows up to
3 ft3/s
Flows up to
1 ft3/s
Flows up to
5 ft3/s
Flows required
are usually less
than for straight
furrows
Can be used on all
soils if length of
furrows is adjusted
to type of soil
Soils of medium to
fine texture that
do not crack on
drying
Best on soils of
medium to fine
textura
Can be used with
most soil types
Used on soils with
low intake rates
Best suited for crops that
cannot be flooded. High
irrigation efficiency
possible. Well adapted to
mechanized farming.
Rodent control is essential.
Erosion hazard from heavy
rains or water breaking out
of furrows. High labor
requirement for irrigation.
High water losses possible
from deep percolation or
surface runoff. Care must
be used in limiting size of
flow in corrugations to
reduce soil erosion. Little
land grading required.
Similar to small rectangular
basins, except crops are
planted on ridges.
This method is used to slow
the flow of water in furrows
to increase water penetra-
tion into soil .
1 ft3/s = 0.028 m3/s
1 ft = 0.305 m
-------
TABLE 5-19
NONIRRIGATING SURFACE APPLICATION METHODS AND CONDITIONS OF USE
tn
co
Application
method
Rapid
infiltration
Overland
flow
Vegetation
Perennial
grasses
Perennial
grasses9
Suitabilities
Topography
Relatively flat
to irregular
Uniformly graded
with slopes from
and conditions of
Water supply
May be relatively
large, soils
permitting
Moderately large
flows with high
percentage of
runoff
use
Soils
Coarse texture
and high infil-
tration rates
Limited
permeabi li ty
Remarks
Water applied on inter-
mittent basis to maintain
permeability. Often less
land preparation than
most irrigation systems.
Land must be smooth to
achieve sheet flow
without ponding .
a. Suitable for continuously wet-root conditions.
-------
measurements in the field. Design application rates are then based on
these results. Furrow intake rates are usually expressed as flowrate
(gal/min, L/s) per unit length (100 ft, 100 m) of furrow. Application
rates are usually expressed as flowrate per furrow, or furrow stream
size.
Other factors of critical importance for design of ridge and furrow
irrigation are: furrow stream size [48, 49, 50], furrow length (Table
5-20), furrow slope [47], and furrow spacing (Table 5-21).
TABLE 5-20
SUGGESTED MAXIMUM LENGTHS OF CULTIVATED FURROWS FOR DIFFERENT
SOILS, SLOPES, AND DEPTHS OF WATER TO BE APPLIED [47]
Feet
Furro1
slope,
0.05
0.1
0.2
0.3
0.5
1.0
1.5
2.0
1 ft =
1 in.
% 3
1 000
1 100
1 200
1 300
1 300
900
800
700
0.305 m
= 2.54 cm
Avg
depth of water applied, in.
Clays
6
1 300
1 400
1 500
1 600
1 600
1 300
1 100
900
9
1 300
1 500
1 700
2 000
1 800
1 600
1 400
1 100
12
1 300
1 600
2 000
2 600
2 400
1 900
1 600
1 300
2
400
600
700
900
900
800
700
600
Loams
4
900
1 100
1 200
1 300
1 200
1 000
900
800
6
1 300
1 400
1 500
1 600
1 500
1 200
1 100
1 000
8
1 300
1 500
1 700
1 900
1 700
1 500
1 300
1 100
2
200
300
400
500
400
300
250
200
Sands
3
300
400
600
700
600
500
400
300
4
500
600
800
900
800
700
600
500
5
600
700
1 000
1 300
1 000
80.0
700
600
TABLE 5-21
OPTIMUM FURROW OR CORRUGATION SPACING [49]
Optimum
Soil condition spacing, in.
Coarse sands - uniform profile 12
Coarse sands - over compact subsoils 18
Fine sands to sandy loams - uniform 24
Fine sands to sandy loams - over
more compact subsoils 30
Medium sandy-silt loam - uniform 36
Medium sandy-silt loam - over
more compact subsoils 40
Silty clay loam - uniform 43
Very heavy clay soils - uniform 36
1 in. = 2.54 cm
5-44
-------
The distribution systems most commonly used for ridge and furrow
irrigation consist of open ditches with siphon pipes (see Figure 5-9),
or gated surface piping system (see Figure 5-10). The open ditch system
may be supplied by distribution ditches or canals with turnouts, or by
buried pipelines with valved risers. Gated surface piping systems
generally consist of aluminum pipe with multiple gated outlets, one per
furrow. The pipe is connected to hydrants which are secured to valved
risers from underground piping systems.
FIGURE 5-9
PLASTIC SIPHON TUBE FOR FURROW IRRIGATION
5.4.1.2 Surface Flooding Irrigation
Surface flooding irrigation consists of directing a sheet flow of water
along border strips, or cultivated strips of lana bordered by small
levees. This method is particularly suited to close-growing crops such
as grasses that can tolerate periodic inundation at the ground surface.
The border strips usually have slight, if any, cross slopes, and nay be
level or graded in the direction of flow. Border strips may also be
straight or contoured. For purposes of illustration, only straight,
graded border irrigation will be included in the design considerations
that follow. Detailed design procedures developed by the SCS for the
various types of borders are given in Chapter 4, Section 15 of the SCS
Engineering Handbook [51].
5-45
-------
FIGURE 5-10
ALUMINUM HYDRANT AND GATED PIPE FOR FURROW IRRIGATION
£ • "* - -
Application rate for border irrigation is dependent on the soil intake
rate and physical features of the strip. Water is applied in the same
manner as in ridge and furrow irrigation. However, the stream is
normally shut off when it has advanced about 75% of the length of the
border. The objective is to have sufficient water remaining on the
border after shutoff to irrigate the remaining length of border to the
proper depth with very little runoff. Theoretically, it is possible to
apply the water nearly uniformly along the border using this technique.
However, actually achieving uniform distribution with minimal runoff
requires a good deal of skill and experience on the part of the
operator. Minimization of runoff is somewhat less critical when
tailwater return systems are used.
The widths of border strips are often selected for compatibility with
farm implements, but they also depend to a certain extent upon slope,
which affects the uniformity of distribution across the strip. A guide
for estimating strip widths based on grades in the direction of flow is
presented in Table 5-22.
Other design factors for a border strip system are similar to those of
ridge and furrow irrigation. These factors include intake character-
istics [51], border strip lengths and slopes (Table 5-23 and 5-24).
Another factor influencing design is surface roughness, which is a
measure of resistance to flow caused by soil and vegetation.
5-46
-------
TABLE .5-22
RECOMMENDED MAXIMUM BORDER STRIP WIDTH [51]
Irrigation
grade, %
0
0.0-0.1
0.1-0.5
0.5-1.0
1.0-2.0
2.0-4.0
4.0-6.0
Maximum strip
width, ft
200
120
60
50
40
30
20
1 ft = 0.305 m
TABLE 5-23
DESIGN STANDARDS FOR BORDER STRIP IRRIGATION,
DEEP ROOTED CROPS [47]
Soil type and
infiltration rate
Sandy
Loamy
1 in.
Sandy
0.75
Clay
, 1+ in./h
sand, 0.75-
/h
loam, 0.5-
in./h
loam, 0.25-
0.5 in./h
Clay,
0.25
0. 10-
in. /h
Slope, *
0.
0.
0.
0.
0.
0.
0.
0.
0.
0.
0.
0.
0.
2-0.
4-0.
6-1.
2-0.
4-0.
6-1.
2-0.
4-0.
6-1.
2-0.
4-0.
6-1.
2-0.
4
6
0
4
6
0
4
6
0
4
6
0
3
Unit flow
per foot, of
strip width,
ft3/s
0
.11-0.
0.09-0.
0
0
0
.06rO.
.07-0.
.06-0.
0.03-0.
0
0
0
0
0
0
0
.06-0.
.04-0.
.02-0.
.03-0.
.02-0.
.01-0.
.02-0.
16
11
09
11
09
06
08
07
04
04
03
02
04
Avg deptf
of water
applied, •
4
4
4
5
5
5
6
6
6
7
7
7
8
i Border
in. Width,
40-100
30-40
20-30
40-100
25-40
25
40-100
20-40
20
40-100
20-40
20
40-100
strip, ft
„ Length
200-300
200-300
250
250-500
250-500
250
300-800
300-600
300
600-1 000
300-600
300
1 200+
1 ft3/s = 28.3 L/s
1 in. = 2.54 cm
1 ft = 0.305 m
The distribution systems for surface flooding irrigation are basically
the same as for ridge and furrow irrigation. A common practice in
system layouts is to locate the vertical risers from buried lines at
spacings equal to the border strip widths. Thus, one valve supplies
5-47
-------
TABLE 5-24
DESIGN STANDARDS FOR BORDER STRIP IRRIGATION,
SHALLOW ROOTED CROPS [47]
Soil profile
Clay loam, 24 in.
deep over per-
meable subsoil
Clay, 24-in.
deep over per-
meable subsoil
Loam, 6-18 in.
deep over
hardpan
Slope, %
0.15-0.6
0.6-1.5
. 1.5-4.0
0.15-0.6
0.6-1.5
1.5-4.0
1.0-4.0
Unit flow
per foot of
strip width,
ft3/s
0.06-0.08
0.04-0.07
0.02-0.04
0.03-0.04
0.02-0.03
0.01-0.02
0.01-4.0
Avg depth
of water
applied, in.
2-4
2-4
2-4
4-6
4-6
4-6
1-3
Border
Width
15-60
15-20
15-20
15-60
15-20
15-20
15-20
strip, ft
Length
300-600
300-600
300
600-1 000
600-1 000
600
300-1 000
1 ft3/s = 28.3 L/s
1 in. = 2.54 cm
1 ft = 0.305 m
each strip, and is preferably located midway between the borders to
provide uniform distribution across the strip (see Figure 5-11). For
strips having widths greater than 30 ft (9.1 m), at least two outlets
per strip will ensure good distribution uniformity. Use of gated pipe
provides much more uniform distribution at the head of border strips and
allows the flexibility of easily changing to ridge and furrow irrigation
if crop changes are desired.
5.4.1.3 Rapid Infiltration Basins
The design of rapid infiltration basins depends on topography; when
subsurface flow is to a surface water body, the basin shape and the
elevation difference between the basins and the surface water are
important. The basins are usually formed by constructing earthen dikes
or by excavation.
Control of subsurface flow and recovery of renovated water are essential
considerations for proper design of a rapid infiltration systems. If
discharge to permanent groundwater is not feasible, a recovery system
should be planned to withdraw the renovated water and reuse it for
irrigation or recreation or discharge it to surface waters. Methods of
recovery include underdrainage systems, pumped withdrawal, and natural
drainage to surface waters.
5-48
-------
FIGURE 5-11
OUTLET VALVE FOR BORDER STRIP APPLICATION
Where natural subsurface drainage to surface water is planned, the
groundwater table must be controlled to prevent groundwater mounding.
The aquifer should be able to readily transmit the renovated water away
from the infiltration site. Bouwer [52] suggests the following equation
for determining the required elevation difference between the water
course and the spreading basin.
WI = KDh/L
5-b)
where W = width of infiltration area, ft (m)
I = hydraulic loading rate, ft/a (m/d)
K = permeability of aquifer, ft/d (m/d)
D = average thickness of aquifer below water table perpendicular
to flow direction, ft (m)
H = elevation difference between water level in stream or lake and
maximum allowable water table level below infiltration area,
ft (m)
L = distance of lateral flow, ft (m)
The relationships of these parameters are indicated in Figure 5-12. The
product WI defines the amount of the applied water for a given section
and thereby controls the infiltration basin sizing. Thus, if the amount
of applied water is controlled by groundwater considerations, relatively
5-49
-------
large hydraulic loading rates (I) may be employed by utilizing
relatively narrow (W) basins.
FIGURE 5-12
NATURAL DRAINAGE OF RENOVATED WATER
INTO SURFACE WATER [52]
IMPERMEABLE
LAYER
Basin sizing includes consideration of the amount of usable land
available, the hydraulic loading rate, topography, and management
flexibility. Sizing may also be influenced by groundwater considera-
tions as discussed in the previous paragraph. In order to operate a
system on a continuous basis, at least two basins will be required, one
for flooding and one for drying, unless sufficient storage is available
elsewhere in the system. Multiple basins are desirable to provide
flexibility in the management of the system.
Basins should be relatively flat to allow uniform distribution of
applied water over the surface. Thus, where sloping lands are to be
utilized, terraced basins may be required. Cross slopes and
longitudinal slopes should be on the order of those used for border
irrigation. Basin widths and lengths are controlled by slopes, number
of basins desired for management, distribution system hydraulics, and as
previously discussed, water table restrictions.
The type of basin surface has been the subject of considerable debate
and the relative advantages and disadvantages should be weighed on a
case-by-case basis. The surface may consist of bare soil, or it may be
covered with vegetation. The advantages of a vegetative cover include
5-50
-------
maintenance of infiltration rates, removal of suspended solids by
filtration, additional nutrient removal if the vegetation is harvested,
and possible promotion of denitrification. Among the disadvantages are
increased basin maintenance, lower depth of application to avoid
drowning the vegetation, and shorter periods of inundation to promote
growth. At Flushing Meadows, it was found that a gravel covered surface
reduced the infiltration capacity of a basin [53]. This was attributed
to the mulching effect of the gravel, which prevented the drying of the
underlying soil.
The distribution system for infiltration basins is often similar to that
tor surface irrigation, although sprinklers have been used. The purpose
of the distribution system is to apply water at a rate which will
constantly flood the basin throughout the application period at a
relatively uniform depth. Effluent weirs may be used to regulate the
depth of applied water. The discharge from the weirs is collected and
distributed to holding ponds for recirculation, or to other infiltration
basins. Water may be conveyed to the basins by pipeline or open channel
systems. If equal flow distribution is intended for each basin, the
distribution line or channel supplying the outlets to parallel basins
should be sized so that hydraulic losses between the outlets will be
insignificant. Outlets may be turnout gates from open channels or
valved risers from underground piping systems. A basin outlet and
splash pad are shown in Figure 5-13.
FIGURE 5-13
RAPID INFILTRATION BASIN INFLUENT STRUCTURE
5-51
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5.4.1.4 Overland Flow
Overland flow distribution is accomplished by applying wastewater
uniformly over relatively impermeable sloped surfaces which are
vegetated. Although the most common method of distribution is with
sprinklers, surface methods such as gated pipe or bubbling orifice may
be used (Section 7.1.1). Gravel may oe necessary to dissipate energy
and ensure uniform distribution of water from these surface methods.
Slopes must be steep enough to prevent ponding of the runoff, yet im'ld
enough to prevent erosion and provide sufficient detention time for the
wastewater on the slopes. Experience at Paris, Texas, has indicated
that best results are obtained with slopes oetween 2 and 6% [54]. A
slope of o«, used at Utica, Mississippi, is shown in Figure 5-14.
Slopes must have a uniform cross slope and be free from gullies to
prevent channeling and allow uniform distrioution over the surface. The
network of slopes and terraces that make up an overland flow system may
be adapted to natural rolling terrain, as has been done at Napoleon,
Ohio [11]. The use of this type of terrain will minimize land
preparation costs.
FIGURE 5-14
OVERLAND FLOU SLOPE (8%) AT UTICA, MISSISSIPPI
5-52
-------
5.4.1.5 Distribution System Design
r ••'-.'.
Water is, normally conveyed to surface distribution systems by canals
(lined and unlihed) or pipelines whose design standards are published by
the American Society of Agricultural Engineers (ASAE). Design standards
for flow, control and measurement techniques are also included in the
ASAE standards.
The methods of flow,distribution to the fields include turnouts, siphon
pipes',;•• valved risers, gated surface pipe, and bubbling orifices.
Turhbuts are; circular or rectangular openings which discharge flow
directly from open ditches, canals, or open concrete pipe risers. Flow
is control led by slide gates, and discharge capacities are normally
restricted to velocities of 3 ft/s (1 m/s) or less.
Siphon pipes are steel, aluminum, or plastic tubes (shown previously in
Figure 5-9) used to siphon water from open ditches to supply furrows
with irrigation water. Flow control is accomplished by combinations of
pipe sizes or varying the number of pipes used. Although siphon pipes
often require the least capital expenditure for distribution, operating
demands., are significant due to the amount of handling and the
requiremerit for maintaining minimum water levels in the supply ditch to
ensure continuity of flow.
Valved .risers are, vertical concrete pipe risers attached to buried
concrete pipelines, and are used for surface flooding irrigation or
discharge to gated, pipe hydrants; Flow is controlled by a simple wafer-
shaped valve, which is adjusted by a threaded stem. The more common
valves are, the alfalfa valve (mounted on top of the riser) and the
orchard valve (mounted inside the riser). Typical cross-sections and
capacities of these valves are shown in Figures 5-15 and 5-16.
Gated surface pipe, which is attached to aluminum hydrants, is aluminum
pipe with multiple outlets. The pipe and hydrants are portable so that
they may be moved for each irrigation. As described in the preceding
paragraph, the hydrants are mounted on valved risers. Operating handles
extend through the hydrants to control the alfalfa or orchard valves
located in the risers. Control of flow is accomplished with slide gates
or screw adjustable orifices at each outlet. The outlets are spaced to
match furrow spacings ano are usually fabricated to order. Gated outlet
capacities vary with the available head at the gate, the velocity of
flow passing the gate, and the gate opening. Typical gate capacities of
standard gated pipe for various flow velocities are shown in Table 5-25.
Hydrant spacings (and valved riser spacings) are controlled either by
the losses in the gated pipe or by widths of boraer strips when border
and .furrow methods are alternated.
5-53
-------
FIGURE 5-15
ALFALFA VALVE CHARACTERISTICS
CONCRETE RISER
FROM LATERAL
CROSS SECTIONAL VIEW
1 i n. = 2.54 cm
SIZES AND RECOMMENDED MAXIMUM DESIGN CAPACITIES
Inside
diameter
of riser,
in.
6
8
10
12
14
16
18
20
Diameter
of port,
in.
6
8
10
12
14
16
18
20
Maximum design capacity
Usual
low head,
ft3/sa
0.8
1.4
2.2
3.1
4.3
5.6
7.1
8.7
High head,
ft3/sb
1.6
2.8
4.4
6.3
8.6
11.2
14.2
17.5
a. Recommended for minimum erosion with
hydraulic gradient 1 ft above ground.
Assumed 0.5 ft ponding over valve.
b. Can be used where higher pressures
are available (hydraulic gradient
2.5 ft above ground) and pre-
cautions are taken to prevent
erosion (ponding =0.5 ft).
1 in. = 2.54 cm
1 ft3/s = 0.284 m3/s
1 ft = 0.305 m
5-54
-------
FIGURE 5-16
ORCHARD VALVE CHARACTERISTICS [55]
AT GROUND SURFACE-
CONCRETE RISER
FROM LATERAL
CROSS SECTIONAL VIEW
1 ft = 0.305 m
SIZES AND RECOMMENDED MAXIMUM CAPACITIES
Inside diameter
of riser, in.
6
6
6
6
8
8
10
10
10
12
12
Diameter of
valve outlet, in.
1.5
2.5
3.5
6
5
8
6
6.5
10
8
12
Approximate design
capacities, ft3/s
Low head3
0.04
0.12
0.23
0.67
0.46
1.18
0.67
0.78
1.85
1.18
2.67
Higher headb
0.08
0.23
0.45
1.34
0.93
2.37
1.34
1.57
3.71
2.37
5.35
a. Usual design with hydraulic gradient 1 ft above ground.
b. Higher head design with hydraulic gradient 2.5 ft
above ground.
1 in. = 2.54 cm
1 ft3/s = 0.0284 m3/s
1 ft = 0.305 m
5-55
-------
TABLE 5-25
DISCHARGE CAPACITIES OF SURFACE GATED PIPE OUTLETS [56]
Gallons per Minute
Velocity
in pipe,
ft/s
0
1
3
Head,
ft
1
2
3
4
5
1
2
3
4
5
1
2
3
4
5
Gate opening
Full
48.
67.
80.
87.
94.
45.
63.
76.
84.
90.
40.
56.
69.
76.
83.
8
2
1
7
2
3
7
6
2
7
0
4
3
9
4
3/4
35.7
50.0
60.8
69.5
77.1
32.8
47.1
57.9
66.6
74.2
26.7
41.0
51.8
60.5
68.1
1/2
22
32
39
45
50
21
.8
.3
.1
.3
.6
.3
30.8
37
43
49
18
27
34
40
46
.6
.8
.1
.2
.7
.5
.7
.0
1/4
10.
15.
18.
21.
23.
10.
14.
17.
21.
23.
8.
13.
16.
19.
21.
6
3
3
4
7
2
9
9
0
3
8
5
5
6
9
1/8
5.
7.
8.
9.
10.
4.
6.
8.
9.
10.
4.
6.
7.
9.
10.
0
0
5
7
7
9
9
4
7
7
3
3
8
0
0
1/16
2.3
3.2
3.8
4.3
4.8
2.2
3.1
3.7
4.2
4.7
2.1
3.0
3.5
4.1
4.6
i
1 gal/min = 0.063 L/s
1 ft/s = 0.305 m/s
Bubbling orifices are small diameter outlets from laterals used to
introduce flow to overland flow systems or checks at'low operating
pressures. Such outlets may consist of orifices in the laterals or
small diameter pipe stubs attached to the laterals. Outlets may range
from O.b to 2 in. (1.3 to 5 cm) in diameter, the capacities of which are
regulated by the available head. , • ,. ' : "'
5.4.2 Sprinkler Systems
Sprinklers can be for all types of land treatment systems. The most
common types of sprinklers may be cat'egorized as hand moved,
mechanically moved,, and permanent set. The basic layout features of the
various types of systems are depicted in Figures 5^17,'5-18, and 5-19.
The more significant design considerations for sprinkler system
selection include field conditions (shape, slope, vegetation, and soil
type), climate, operating conditions (system management) ;• and ecpnornics.
These considerations are summarized in Table 5-26. '
5-56
-------
FIGURE 5-17
HAND MOVED SPRINKLER SYSTEMS
PREVIOUSLY
IRRIGATED
AREA
LATERAL WITH MULTIPLE
SPRINKLERS
_ MAIN
PUMP
(a) PORTABLE PIPE
PREVIOUSLY
IRRIGATED
AREA
PUMP
LATERAL WITH SPRINKLER
CONNECTIONS
MAIN
GUN-TYPE
SPRINKLER
(b) STATIONARY BIG GUN
5-57
-------
FIGURE 5-18
MECHANICALLY MOVED SPRINKLER SYSTEMS
LATERAL WITH MULTIPLE
SPRINKLERS
PREVIOUSLY
IRRIGATED
AREA
DISASSEMBLED
MAIN LENGTHS
ANCHOR
SELF-PROPELLED
DRIVE UNIT WITH
GUN-TYPE SPRINKLER
MAIN
PUMP
CABLE
(a) END TOW
(b) BIG GUN TRAVELER
PREVIOUSLY
-IRRIGATED
AREA
MAIN
WHEEL-SUPPORTED LATERAL
WITH MULTIPLE SPRINKLER
PREVIOUSLY
IRRIGATED
AREA
POWER
DRIVE
UNITS
LATERAL
WITH
MULTIPLE
SPRINKLER
PREVIOUSLY
IRRIGATED
AREA
(c) SIDE WHEEL ROLL
(d) CENTER PIVOT
5-58
-------
FIGURE 5-19
PERMANENT SOLID SET SPRINKLER SYSTEM
BURIED LATERALS
WITH MULTIPLE
SPRINKLER
PUMP
f
— BURIED MAIN
PREVIOUSLY IRRIGATED
AREA
TABLE 5-26
SPRINKLER SYSTEM CHARACTERISTICS [57, 58]
Typical
application
rate, in./h
Hand moved
Portable pipe
Stationary gun
Mechanically
moved
End tow
Traveling gun
Side wheel roll
Center pivot
Permanent
Solid set
0.1-2.0
0.25-2
0.1-2.
0.25-1.
0.1-0-2.
0.20-1.
0.05-2.
.0
.0
.0
.0
.0
.0
Outlets
per lateral
Multiple
Single
Multiple
Single
Multiple
Multiple
Multiple
Nozzle
pressure
range,
lb/in.2
30-60
50-100
30-60
50-100
30-60
15-60
30-60
Size of
single
system,
acres
1-40
20-40
20-40
40-100
20-80
40-160
Unlimited
Shape of
field
Any shape
Any shape
Rectangular
Rectangular
Rectangular
Circular3
Any shape
Maximum
slope, %
20
20
5-10
Unlimited
5-10
5-15
Unlimited
Maximum
crop
height,
ft
....
3-4
8-10
a. Travelers are available to allow irrigation of any shape field.
1 in./h = 2.54 cm/h
1 lb/in.2 = 0.69 N/cm2
1 acre = 0.405 ha
1 ft = 0.305 m
5-59
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5.4.2.1 Hand Moved Systems
Hand moved sprinkler systems include portable pipe and stationary gun
systems. As the name implies, each is placed and removed manually for
each irrigation set or period.
Portable pipe systems are surface pipe systems consisting of lateral
lines which are moved between sets (piping position for one application)
and a main line which may also be moved, or it may be permanent. The
laterals are usually constructed of aluminum pipe in 30 or 40 ft (9 or
12 in) lengths with sprinklers mounted on risers extending from the
laterals. Riser heights are determined by crop heights and angle of
spray. In general, lateral spacings and sprinkler spacings are located
at approximately equal intervals, usually ranging from 40 to 90 ft (12
to 27 m). Sprinklers may operate at a wide range of pressures and
application. If sufficient pipe is available so that movement between
sets is not required, the system is referred to as solid set.
The major advantages of portable systems include low capital costs and
adaptability to most field conditions and climates. They may also be
removed from the fields to avoid interferences with farm machinery. The
principal disadvantage is the extensive labor requirement to operate
the system.
Stationary gun systems are wheel-mounted or skid-mounted single
sprinkler units(seeFigure 5-20), which are moved manually between
hydrants located along the laterals. Since the sprinkler operates at
greater pressures and flowrates than multiple sprinkler systems, the
irrigation time is usually shorter. After a set has been completed for
the lateral, the entire lateral is moved to the next point along the
main. In some cases a number of laterals and sprinklers may be provided
to minimize movement of laterals.
The advantages of a stationary gun are similar to those of portable pipe
systems with respect to capital costs and versatility. In addition, the
larger nozzle of the gun-type sprinkler is relatively free from
clogging. The drawbacks to this system are also similar to those for
portable pipe systems in that labor requirements are high due to
frequent sprinkler moves. Power requirements are relatively high due to
high pressures at the nozzle, and windy conditions adversely affect
distribution of the fine droplets created by the higher pressures.
5.4.2.2 Mechanically Moved Systems
The most common types of mechanically moved systems are end tow,
traveling gun, side wheel roll, and center pivot. These systems may be
5-60
-------
moved after each irrigation by external drive mechanisms (tractors or
winches) or integral drive units, or they may be self-propelled,
continuous-moving systems.
FIGURE 5-20
STATIONARY GUN SPRINKLER MOUNTED ON A TRACTOR TRAILER
End tow systems are multiple-sprinkler laterals mounted on skids or
wheel assemblies to allow a tractor to pull the lateral intact from one
setting to the next. As indicated in Figure b-18, the lateral is guided
by capstans to control its alignment. The pipe and sprinkler design
considerations are identical to those for portable pipe systems with the
exception that pipe joints are stronger to accommodate the pulling
requirements.
The primary advantages of an end tow system are relatively low labor
requirements and overall system costs, and the capability to be readily
removed from the field to allow farm implements to operate.
Disadvantages include crop restrictions to movement of laterals and
cautious operation to avoid crop and equipment damage.
Traveling gun systems are self-propelled, single sprinkler units which
are connected to the supply source by a flexible hose (see Figure 5-21).
The traveler is driven by a hydraulic or gas-driven winch located
within the unit, or a gas-driven winch located at the end of the run.
In both cases, a cable anchored at the end of the run guides the unit in
5-61
-------
a straight path. Variable speed drives are used to control application
rates. Typical lengths of run are 660 or 1 320 ft (201 or 403 in), ana
spacings between travel lanes are commonly 33U ft (100 in). The rubber
hose, which may be 2.5 to b in. (6.4 to 12.7 cm) is a specially-
constructed item and may constitute a considerable portion of the total
cost of the system.
FIGURE 5-21
TRAVELING GUN SPRINKLER
The more important advantages of a traveling gun system are low labor
requirements and relatively clog-free nozzles. They may also be
adapted to fields of somewhat irregular shape and topography.
Disadvantages are high initial costs and power requirements, hose travel
lanes required for most crops, and drifting of sprays in windy
conditions.
Side wheel roll systems consist of aluminum or galvanized steel pipe
laterals 4 to 5 in. (10.2 to 12.7 cm) in diameter, which act as axles
for 5 to 7 ft (1.5 to 2.1 m) diameter wheels (see Figure 5-22). The end
of the lateral, which is typically 1 320 ft (403 m) long, is connected
to hydrants located along the main line. The system is moved between
sets by an integral drive unit located at the center of the lateral.
The unit is a gas-driven engine operated by the irrigator. The
sprinklers, which have the same general characteristics as those for
5-62
-------
portable pipe systems, are mounted on swivel connections to ensure
upright positions at all times. Sprinkler spacings are typically 3D or
40 ft (9.2 to 12.b m) ana wheel spacings may range from 30 to 10U ft
(9.2 to 30.b m). Side wheel laterals may be equipped with trail lines
up to 90 ft (27 in) in length located at each sprinkler connection on the
axle lateral. Each trail line has sprinklers mounted on risers spaced
typically at 30 to 40 ft (9 to 12 m). Use of trail lines allows several
lateral settings to be irrigatea simultaneously and reduces the number
of moves required to irrigate a field.
FIGURE b-22
SIDE WHEEL ROLL SPRINKLER SYSTEM
*>4
The principal advantages of side wheel roll systems are relatively low
labor requirements and overall costs, and freedom from interference with
farm implements. Disadvantages include restrictions to crop height and
field shape, and misalignment of the lateral caused by uneven terrain.
A center pivot system is a lateral with multiple sprinklers which is
mounted on self-propelled, continuously moving tower units (see Figure
b-23) rotating about a fixed pivot in the center of the field. Water is
supplied Dy a well or a buried main to the pivot, where power is also
furnished. The lateral is usually constructed of 6 to 8 in. (15 to 20
cm) steel pipe 200 to 2 600 ft (61 to 793 m) in length. A typical
system irrigates a 160 acre (64 ha) parcel (see Figure 5-24) with
a 1 288 ft (393 m) lateral. The circular pattern reduces coverage to
about 130 acres (52 ha), although systems with traveling end sprinklers
are available to irrigate the corners.
5-63
-------
FIGURE b-23
CENTER PIVOT RIG
FIGURE 5-24
CENTER PIVOT IRRIGATION SYSTEM
_.
5-64
-------
The tower units are driven electrically or hydraulically and may be
spaced from 80 to 250 ft (24 to 76 m) apart. The lateral is supported
between the towers by cables or trusses. Control of the application
rate is achieved by varying the running time of the tower motors.
Variations in sprinkler sizes or spacings must be provided along the
lateral for uniform distribution, since the area of coverage per
sprinkler increases with the distance from the center. The relatively
low application rates shown in Table 5-26 account for the fact that
center pivot systems irrigate more frequently and at lower rates than
other systems.
Another type of center pivot system is the rotating boom. This system
eliminates the need for wheel-mounted power units by supporting the
lateral with cables extending from a tower at the pivot. These systems
have limited applications, as the area of coverage is small, up to 40
acres (16 ha), relative to conventional center pivot systems, and the
corresponding per acre costs are high when multiple systems are
required.
The main advantage of a center pivot system is the high degree of
automation and a corresponding low requirement for labor. Limitations
include restricted area of coverage (dead spaces in corners of fields),
crop heights, and potential maintenance problems related to the numerous
mechanical components.
5.4.2.3 Permanent Solid Set Systems
Permanent solid set systems are distinguished from portable solid set
systems only in that the laterals are buried and constructed of plastic
pipe instead of aluminum. Sprinkler selection and spacing criteria are
identical. Risers may be fixed or removable to accommodate farm
equipment. The primary advantages of solid set systems are low labor
requirements and maintenance costs, and adaptability to all types of
terrain, field shapes, and crops. They are also the most adaptable
systems for climate control requirements. The major disadvantages are
high installation costs and obstruction of fixed risers to farming
equipment.
5.4.2.4 Overland Flow Systems
Sprinkler application for overland flow consists either of permanent
solid set systems or rotating booms. These systems are distinguished
from those for slow rate by their layout arrangements (single row of
sprinklers) and application rates (designed for runoff). Sprinkler
5-65
-------
spacing is normally equal to the radius of the wetted circle,
sprinkler discharge rate, Q , may be computed as follows:
The
Q =
I x R x L
t x C
(5-7)
where Q = nozzle discharge, gal/min (L/s)
I = total depth of water applied, in.
t = period of time to apply water, h
R = spacing between sprinklers, ft (rn)
L = length of overland slope, ft (m)
C - constant = 96.3 (360)
(cm)
Sprinkler heads may be arranged to avoid drifting of sprays at the
expense of reducing the area of coverage. The primary objective of the
distribution system is to concentrate the applied water at the upper
ends of the slopes to produce runoff.
Fan nozzles may be used for overland flow distribution to minimize
pumping pressure head and minimize aerosol formation. At Pauls Valley,
Oklahoma (Section 7.11), fixed nozzles are being used. At Ada,
Oklahoma, rotating booms are being used with fan nozzles on both ends as
shown in Figure 5-25.
FIGURE 5-25
ROTATING BOOM, FAN SPRINKLER,
ADA, OKLAHOMA
5-66
-------
5.4.2.5 System Design
The procedure for sprinkler system design involves the determination of
the optimum rate of application, sprinkler selection, sprinkler spacings
and performance characteristics, lateral design, and miscellaneous
requirements. Although the following discussions are limited to
stationary systems, the general theory applies to moving systems as
well. Detailed design requirements for specific systems may be obtained
from equipment suppliers.
The optimum rate of application for a sprinkler system is the rate that
ensures uniform distribution under prevailing climatic conditions
without exceeding the basic intake rate of the soil (except for overland
flow systems).
Sprinkler selection is primarily based on conditions of service, such as
type of distribution system, pressure limitations, application rate,
clogging potential, and effects of winds. Sprinklers used for
application of wastewater are usually of the rotating head type with one
or two nozzles. Special attention should be given to sprinkler design
for low temperature winter operation. A general classification of
sprinklers and their adaptabilities to various service conditions is
presented in Table 5-27. More specific performance characteristics for
the many types of sprinklers are available from the sprinkler
manufacturers.
Sprinkler spacings and performance characteristics are jointly analyzed
to determine the most uniform distribution pattern at the optimum rate
of application. Distribution patterns of individual sprinklers are
affected primarily by pressure—low pressures cause large drops which
are concentrated in a ring a certain distance away from the sprinkler,
whereas high pressures result in fine drops which fall near the
sprinkler. These finer sprays are easily distorted by winds.
Since the amount of water applied by a sprinkler decreases with the
distance from the nozzle and the distribution pattern is circular,
sprinklers and laterals are spaced to provide overlapping of the wetted
diameters. Spacings are normally related to the wetted diameters
specified by the sprinkler manufacturers. These spacings may be
determined empirically or by using published guidelines. The SCS
recommends limiting sprinkler spacinys along the lateral (S[_) to 50%
or less of the wetted diameter, and lateral spacings along the main
(S^) to less than 65%. In windy areas, S^ should be reduced to 50%
for velocities of 5 to 10 mi/h (2.2 to 4.4 m/s) and to 30% for
velocities greater than 10 mi/h (4.4 m/s) [59]. For high pressure
sprinklers, the SCS recommends a maximum diagonal distance between
sprinklers of two-thirds the wetted diameter with similar deductions for
wind as discussed for lower pressure sprinklers.
5-67
-------
TABLE 5-27
CLASSIFICATION OF SPRINKLERS AND
THEIR ADAPTABILITY [58]
Type of
sprinkler
Low pressure,
5-15 lb/in.2
Moderate
pressure,
15-30 lb/in.2
Intermediate
pressure,
30-60 lb/in. z
High pressure.
50-100 lb/in. 2
General
characteristics
Special thrust
springs or reaction-
type arms
Usually single-nozzle
oscillating or long-
arm dual-nozzle
design
Either single or
dual-nozzle design
Either single of
dual-nozzle design
Range of
wetted
diameters,
'ft
20-50
60-80
75-120
110-230
Recommended
minimum
application
rate, in./h
0.40
0.20
0.25
0.50
Moisture
distribution
pattern3
Fair
Fair to "good at
upper limits of
pressure range
Very good
Good except
where wind
velocities ex-
Adaptations and limitations
Small acreages; confined to soils
with intake rates exceeding 0.50 in./h
and to good ground cover on medium-
to coarse-textured soils
Primarily for undertree sprinkling
in orchards; can be used for field
crops and vegetables
For all field crops and most irrigable
soils; well -adapted to overtree
sprinkling in orchards and groves and
to tobacco shades
Same as for intermediate pressure
sprinklers except where wind is
excessive
Hydraulic or One large nozzle with 200-400 0.65
giant, 80- smaller supplemental
120 lb/in.2 nozzles to fill in
pattern gaps; small
nozzle rotating
sprinkler
Undertree low- Designed to keep 40-90 0.33
angle, 10- stream trajectories
50 lb/in.2' below fruit and
foliage by lowering
the nozzle angle
Perforated pipe, Portable irrigation lO-Sff5 0.50
4-20 lb/in.2 pipe with lines of
small perforations
in upper third of
pipe perimeter
Acceptable in Adaptable to close-growing crops that
calm air; provide good ground cover; for rapid
severely dis- coverage and for odd shaped areas;
torted by wind limited to soils with high intake rates
Fairly good; For all orchards or citrus groves; in
diamond pattern orchards where wind will distort over-
recommended tree sprinkler patterns; .in orchards
where laterals were available pressure is not suffi-
spaced more cient for operation of overtree
than one tree sprinklers
interspace
Good pattern is For low growing crops only; unsuitable
rectangular for tall crops; limited to soils with
relatively high intake rates; best
adapted to small acreages of high value
crops; low oeprating pressure permits
use of gravity or municipal supply
a. Assuming proper spacing and pressure nozzle size relationships.
b. Rectangular strips.
1 ft = 0.305 m
1 in. = 2.54 cm
1 lb/in.2 = 0.69 N/cm2
1 mi/h = 0.44 m/s
5-68
-------
Once the preliminary spacing has been determined, the nozzle discharge
capacity to supply the optimum application rate is found by the equation
Q =
SL x SM x
(5-8)
in which Q = flow rate from nozzle, gal/min (L/s)
SL = sprinkler spacing along lateral, ft (m)
SM = sprinkler spacing along main, ft (m)
I = optimum application rate, in./h (cm/h)
C = constant = 96.3 (360)
This establishes the basis for final sprinkler selection, which is a
trial and adjustment procedure to match given conditions with
performance characteristics of available sprinklers. The normal
selection procedure
discharge capacity.
the nozzle sizes,
sprinklers operating
diameters are then
with the established
is to a-ssume a spacing and determine the nozzle
Manufacturers' data are then reviewed to determine
operating pressures, and wetted diameters of
at the desired discharge rate. The wetted
checked with the assumed spacings for conformance
spacing criteria.
Lateral design consists of selecting lateral sizes to deliver the total
flow requirement of the lateral with friction losses limited to a
predetermined amount. A general practice is to limit all hydraulic
losses (static and dynamic) in a lateral to 2U% of the operating
pressure of the sprinklers. This will result in sprinkler discharge
variations of about 10% along the lateral [58]. Since flow is being
discharged from a number of sprinklers, the effect of multiple outlets
on friction loss in the lateral must be considered. A simplified
approach developed by Christiansen is to multiply the friction loss in
the entire lateral at full flow (discharge at the distal end) by a
factor based on the number of outlets. The factors for selected numbers
of outlets are presented in Table 5-28. For long lateral lines, capital
costs may be reduced by using two or more lateral sizes which will
satisfy the head loss requirements.
System
automation is receiving greater attention as labor costs
All of the systems described herein may be automatically
to some degree. The most common control devices are remote
increase.
controlled
control valves energized electrically or pneumatically to start or stop
flow in a lateral or main. The energy source for operating these valves
may be activated manually at a push-button station or automatically by a
time-controlled switch. In order to determine the economics of a
control system, the designer must compare the costs of labor with the
costs of controls at the desired level of operating flexibility.
5-69
-------
TABLE 5-28
FACTOR (F) BY WHICH PIPE FRICTION LOSS
IS MULTIPLIED TO OBTAIN ACTUAL LOSS IN
A LINE WITH MULTIPLE OUTLETS [49]
No. of outlets Value of F
1
2
3
4
5
6
7
8
9
10
15
20
25
30
40
50
100
1.000
0.634
0.528
0.480
0.451
0.433
0.419
0.410
0.402
0.396
0.379
0.370
0.365
0.362
0.357
0.355
0.350
5.5 Management of Renovated Water
5.5.1 General Considerations
5.5.1.1 Flow to Groundwaters
For rapid infiltration, an unsaturated soil zone is necessary to
maintain desired infiltration rates since oxygen is usually depleted
when inundation periods exceed 48 hours. However, good internal
drainage must be present to reinstate an aerobic zone during the dry-up
period. Bouwer reports that only 5 ft (1.5 m) of unsaturated soil need
be maintained [52]. A deeper water table does not materially increase
the depth of the aerobic zone since oxygen diffusion is slowed
considerably below about 3 ft (1 m).
5-70
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5.5.1.2 Stormwater Runoff Considerations
The quality of stonnwater runoff is essentially unknown, but the
nitrogen and phosphorus values given in Table 3-11, measured in rural
stonnwater runoff studies, should give perspective to the magnitude of
the problem. The principal considerations are to minimize the quantity
of runoff and to minimize the sediment load in the runoff. This can be
accomplished for the most part by sound farm management practices.
Overland flow systems are designed to shed water and must be capable of
handling storm runoff flows. It has been shown at Paris, Texas [54],
that the effect of precipitation is to improve the quality of overland
flow runoff as measured by electrical conductivity.
5.5.2 Underdrainage Systems
Underdrains are mainly associated with slow rate treatment but can also
be used with rapid infiltration treatment. The underdrainage system
must control the water table to provide sufficient soil detention time
and underground travel distance if the desired quality of renovated
water is to be achieved. In the case of slow rate treatment, the
ability to plant, grow, and harvest a crop properly also depends on the
drainage conditions. Skaggs has developed a model to manage water in
soils with high groundwater [60, 61].
In arid regions, drains are usually placed at much greater depths and
farther apart than in humid regions to ensure that salt-laden water
cannot move upward to the root zone by capillary action. Since there is
no real agreement on proper depth and spacing, the designer is forced to
rely on local experience. Examples of drain depth and spacing in humid
and arid climates, for slow rate systems, are shown in Table 5-29.
Control of the groundwater table is discussed in Appendix C, Section
C.4. An equation for spacing and depth underdrains is presented.
Additional discussion of the theoretical aspects of drain spacing is
contained in references [60, 61, 62]. Procedures for planning and
design of underdrainage systems are also described in Drainage of
Agricultural Land by the U.S. Department of Agriculture, Soil
Conservation Service [63].
5-71
-------
TABLE 5-29
DEPTH AND SPACING OF UNDERDRAINS FOR SLOW RATE SYSTEMS
Feet
Avg depth Spacing
Arid climate
Imperial Valley, California [62] 6-9 200-400
Delta, Utah [62] ...a 1 000-1 320
Humid climate
Malheur Valley, Oregon [62] 8-9 660
Muskegon, Michigan, loamy to
sandy soils [31] 5-8 500-1 000
Skaggs Water Management Model
Sandy loam [60] 3.2 265
Sandy loam [61] 3.3 140
Clay loam [61] 3.3 40-65b
a. Referred to as deep drains.
b. Good surface drainage increases spacing.
1 ft = 0.305 m
Proper placement of underdrains to recover renovated water from rapid
infiltration treatment is more critical than for slow rate treatment.
Bouwer [52] has developed an equation to determine the distance
underdrains should be placed away from the infiltration area. The
height, H , of the water table below the outer edge of the infiltration
area (see Figure 5-26) can be calculated:
Hc2 = Hd2 + IW (W + 2D/K (5-9)
where Hd = drain height above impermeable layer, ft (m)
I = infiltration rate, in./h (cm/h)
W = width of infiltration basin, ft (m)
L = distance to underdrain, ft (m)
K = permeability of the soil, in./h (cm/h)
The location of the drain is selected and HC is calculated with Equation
5-9. By adjusting variables (L, W, and I), a satisfactory value of Hc
is obtained. An L-value less than the most desirable distance of under-
ground travel may have to be accepted to obtain a workable system.
Plastic, concrete, and clay tile lines are used for underdrains. The
choice usually depends on price and availability of materials. Where
sul fates are present in the groundwater, it is necessary to use a
sul fate-resistant cement pipe, if concrete is chosen, to prevent excess
5-72
-------
internal stress from crystal formation. Most tile drains are
mechanically laid in a machine dug trench (see Figure 5-27) or by direct
plowing. In organic soils and loam and clay-loam soils, a filter is not
needed. The value of a filter is also dependent on the cost of cleaning
a plugged tile line versus the cost of the filter material.
FIGURE 5-26
COLLECTION OF RENOVATED WATER BY DRAIN [52]
WATER TABLE
^ IMPERMEABLE LAYER
5.5.3 Pumped Withdrawal
Pumped withdrawal of percolated water is generally only considered for
rapid infiltration systems. It can be the economical recovery method
when the aquifer is deep enough (more than 15 ft or 4.5 m usually) and
permeable enough to allow pumping. Evaluation of the permeability of an
aquifer to properly locate recovery wells is based on the principles of
groundwater flow presented in Appendix C.
Procedures for obtaining the necessary information on the permeability
for rapid infiltration systems have been developed by Bouwer [64]. Two
procedures, (1) an analog technique and (2) field permeability
measurements, predict water table positions for a system of parallel,
rectangular infiltration basins, with wells located midway between the
basins as shown in Figure 5-28. The shape of the water table system can
be calculated with dimensionless graphs developed with Bouwer's
electrical analog technique [64] and summarized in reference [52]. The
evaluation ,of the permeability components by the analog technique
requires a knowledge of the infiltration rates and the response of water
levels in the recovery (or observation) wells at different depths
located between the basins.
5-73
-------
FIGURE 5-27
TRENCHING MACHINE FOR INSTALLATION
OF DRAIN TILE
5.5.4 Tailwater Return
It is standard design practice to include a tailwater return system for
wastewater runoff from excess surface application in slow rate systems.
Typically, tailwater systems consist of a small pond, a pump, and return
pipeline. The system is usually sized for 25 to 50% of the applied
surficial flow. Suggested guidelines, recommended by the ASAE, for
determining runoff as a percentage of the application rate have been
summarized by Hart [56] and are included here.
5-74
-------
FIGURE 5-28
PLAN AND CROSS SECTION OF TWO PARALLEL RECHARGE
BASINS WITH WELLS MIDWAY BETWEEN BASINS [64]
RECHARGE BASINS
RECOVERY
WELL
PLAN
J
1
1
1
1
•X'!
**r
*+*
J
I
1
j
1
/<
/— »
A
T
ER TABLE
N N N \ X \\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\ V\
CROSS SECTION
Total application time should be long enough to properly wet the lower
end of a field. The time that applied wastewater is allowed to enter
the tailwater runoff system before the supply source is cut off and the
runoff volume depend on the intake rate of the soil. For slow rate land
treatment, the practical guidelines shown in Table 5-30 provide the
simplest procedure for estimating runoff factors.
TABLE 5-30
RECOMMENDED ASAE RUNOFF DESIGN FACTORS
FOR SURFACE FLOOD DISTRIBUTION [56]
Pnrmcnhil1ty Maximum runoff Estimated runoff
duration, % of volume, % of
Class Rate, in./h Texture range application time application volume
Slow to
moderate
Moderate to
moderately
rapid
0.06 to 0.6 Clay to silt 33
0.6 to 6.0 Clay loams to 75
sandy loams
15
35
1 in./h =2.54 cm/h
5-75
-------
The rate of runoff increases with time and tends to reach a constant
value as cutoff time is approached. A runoff duration of one-half the
application time and a maximum runoff rate of two-thirds application
rate results in a runoff volume of about 25% of application for slowly
permeable soils [56]. Permeable soils, with intake rates greater than
0.8 in./h (2 cm/h), require rapid advance rates and shorter irrigation
times if deep percolation is to be minimized. If deep percolation is
not a problem, longer application periods can be used.
Design factors on sumps, pumps, and storage reservoirs for continuous
pumping systems and cycling sump systems are beyond the scope of this
manual but can be obtained from references [56, 65].
5.5.5 Overland Flow Runoff
Runoff will range from 40 to 80% of the applied liquid depending on:
(1) soil infiltration capacity, (2) prior moisture condition of the
soil, (3) slope, and (4) type of vegetation. Percent runoff will vary
over the year depending on the rainfall and evaporation. A water
balance should be performed to estimate the runoff volume.
At the Campbell Soup overland flow system in Paris, Texas, Thomas et al.
determined that direct evaporation from sprinklers ranged from 2 to 8%;
evapotranspiration ranged from 7 to 27% of the applied liquid
(wastewater ana rainfall); while runoff ranged from a midsummer low of
42% to a high of 71% in midwinter [66]. Similar studies at Ada,
Oklahoma, indicated that overall recovery was about 50% of the applied
wastewater, and ranged from 25% in summer to 80% in winter [17].
Runoff collection systems are commonly open, grass-lined channels at the
toe of the overland flow slopes. They must be graded to prevent erosion
(typically 0.3 to 1%) and have sufficient slope to prevent ponding in
low spots. Channel slopes greater than 1% will begin to influence the
distribution of the sheet flow on the overland flow slopes. Gravity
pipe systems may be required when unstable soil conditions are
encountered, or when flow velocities are prohibitively erosive. The
collection system must be designed to accept a realistic amount of storm
runoff—design storms of 2 to 10 years may not be unreasonable.
5.5.6 Stormwater Runoff Provisions
For slow rate systems, control of stormwater runoff to prevent erosion
is necessary. Terracing of steep slopes is a well known agricultural
practice to prevent excessive erosion. In general, the management
techniques recommended in 208 planning for nonpoint discharges are
applicable. Sediment control basins and other nonstructural control
5-76
-------
measures, such as contour plowing, no-till fanning, grass border strips,
and stream buffer zones can be used. As wastewater application will
usually be stopped during storm runoff conditions, recirculation of
storm runoff for further treatment is usually unnecessary.
For overland flow systems, even the "first flush" of a high intensity
storm should meet water quality standards. Where the treated runoff is
to be disinfected or collected for other uses, the quantity of
stormwater will require that provisions for maximum treatment capacity
be made. Stormwater in excess of this capacity should be allowed to
overflow to a planned stormwater runoff system or to natural drainage.
When more than 2 or 3 terraces discharge to the same collection main,
provisions should be made to dampen the peak runoff from storms to
minimize erosion and channel maintenance problems.
5.6 Vegetation
Vegetation in land treatment serves three major functions:
1. As a nutrient extractor, vegetation concentrates nitrogen and
phosphorus above the ground and thus makes these nutrients
available for removal through harvest.
2. Plants effectively reduce erosion by reducing surface runoff
velocity. The extension of root growth maintains and
increases soil permeability, and the leaf shelter protects the
soil against the compacting effect of falling water. The
overall effect of various ground covers on soil infiltration
rates for one soil is shown in Figures 5-29 and 5-30.
3. For overland flow and wetlands, the vegetation, in addition to
taking up nutrients, provides a matrix for the growth of
microorganisms that decompose the organic matter in the
wastewater.
5.6.1 Selection of Vegetation
For slow rate systems, the important considerations for agricultural
crops are:
1. Rate of water uptake
2. Rate of nitrogen and phosphorus uptake
3. Tolerance to potentially harmful wastewater constituents
4. Ease of cultivation
5-77
-------
5. Production of a marketable crop
6. Minimum net cost of production, after deducting the current
market value of the crop
FIGURE 5-29
EFFECT OF SELECTED VEGETATION ON
SOIL INFILTRATION RATES [67]
2 . 4
2. 0
I . 6
1 . 2
0. 8
0 . 4
BARE
SOIL
CORN
WHEAT
HAY
PERMANENT
PASTURE
1 in/h - 2.54 cm/h
For rapid infiltration systems, the primary requirement is for a water-
tolerant species that will help to maintain high infiltration rates.
For overland flow systems, the need is for a vegetative cover that is
well rooted in impermeable soils, is water tolerant (withstands
flooding), and has a high rate of nitrogen uptake.
In general, the forage and fodder crops are preferred because they:
(1) treat large amounts of wastewater, (2) are tolerant of variations in
wastewater quality, and (3) require less maintenance and skill to grow.
However, they have a lower market value. Successful forage crops used
to date include: Reed canary grass, fescue, perennial rye, orchard
grass, and Bermuda grass.
5-78
-------
FIGURE 5-30
INFILTRATION RATES FOR VARIOUS CROPS [68] .
2 . 8
2 . 4
1 . 6
- 1.2
0 . i
0. 4
0.0
OLD PERMANENT
PASTURE OR HEAVY
MULCH
4-8 YEAR OLD
PERMANENT PASTURE
3-4 YEA R OLD
PERMANENT PASTURE
LIGHTLY BRAZED
PERMANENT PASTURE
MODERATELY GRAZED
HA YS
PERMANENT PASTURE
HEAVILY GRAZED
STRIP CROPPED OR
MIXED COVER
WEEDS OR GRAIN
CLEAN TILLED
BARE GROUND
CRUSTED
1 i n. - 2. 54 cm
5.6.1.1 Hydraulic Considerations
Peak consumptive water use and rooting depth for various crops and
regional areas are presented in Table 5-31 as an aid in system design.
The tolerance of individual species to flooding is based on the rooting
depth and the duration of flooding. Rooting depths for various crops
are also listed in Table 5-31. The soil should drain and become
unsaturated to these depths during the irrigation resting cycle to
obtain optimal growth. Some saturation of the root zone by groundwater
may be tolerated, but the usual result is decreased plant performance.
In general, grain crops such as wheat, oats, and barley will suffer high
yield losses if subjected to soil saturation. Vegetable and row crops
are slightly more tolerant, but they are still susceptible to damage.
5-79
-------
TABLE 5-31
PEAK CONSUMPTIVE WATER USE AND ROOTING DEPTH [69]
Washington, California, Texas, Arkansas, Nebraska, Colorado,
Columbia San Joaquin southern Mississippi eastern western
Basin Valley high plains bottoms part part
Use
Depth, rate,
Crop in. in./d
Corn 42 0.27
Alfalfa 60 0.25
Pasture 24 0.29
Grain 48 0.21
Sugar
beets 36 0.26
Cotton • •
Potatoes 24 0.29
Deciduous
orchards • •
Citrus
orchards • •
Grapes . . ....
Annual
legumes ..
Soybeans . . ....
Shallow-
rooted
truck crops . .
Medium-
rooted . .
truck crops
Deep-
rooted
truck crops . . ....
Tomatoes . . ....
Tobacco ..
Rice ..
Depth,
in.
60
72
24
48
72
72
48
96
72
72
••
••
Use
rate,
in./d
0.26
0.25
0.32
0.17
0.22
0.22
0.24
0.21
0.19
0.18
Use
Depth, rate,
in. in./d
72 0.30
72 0.30
42b 0.25
72C 0.30
72 0.15
72 0.25
* • » •
48 0.18
'.'. '.I
Depth,
in.
30
42
36C
24
36
•
18
36
18d
18e
•• .
24
rate, Depth, rate, Depth, rate,
in./d in. in./d in. in./d
0.23 72 0.28 48 0.23
0.24 96 0.27 72 0.23
0.13 48 0.29 36 0.23
0.22
0.15 48 0.26 36 0.22
48 0.26 48 0.20
0.18
36 0.26 36 0.22
72 0.18
0.28
0.19 60 0.27 ..
0.20
0.12
36 0.22
0.17 ..
5-80
-------
TABLE 5-31
(Concluded)
State of
Wisconsin
Crop
Corn
Alfalfa
Pasture
Grain
Sugar
beets
Cotton
Potatoes
Deciduous
orchards
Citrus
orchards
Grapes
Annual
legumes
Soybeans
Shallow-
rooted
truck crops
Medium-
rooted
truck crops
Deep-
rooted
truck crops
Tomatoes
Tobacco
Rice
Depth,
in.
24
36
24
18
18
18
36
18
12
18
24
18
••
Use
, rate.
in./d
0.30
0.30
0.20
0.25
0.25
....
0.20
0.30
0.25
0.20
0.20
0.20
0.20
....
State of
Indiana
Depth,
in.
24
36
30
12
24
24
9
12
18
18
24
••
Use
, rate,
in./d
0.30
0.30
0.30
....
0.25
....
0.25
0.30
0.20
0.20
0.20
0.20
0.25
Piedmont Virginia, State of
Plateau"^ coastal plain New York
Depth,
in.
24
36
24
24
24
24
36
30
24
12
18
24
24
18
Use Use
rate. Depth, rate, Di.'pl.ti
in./d in. in./d in.
0.22 24 0.18 24
0.25 36 0.22 30
0.25 20 0.22
0.16
.... . . ....
0.21
0.18 18 0.18 18
0.25 36 0.22 36
0.20
0.18
0.14 12
0.14 18 0.16 18
0.18 24
0.21 24 0.18 24
0.18 18 0.17
Use
, riilo.
in./d
0.20
0.20
....
....
....
0.18
0.20
....
....
0.18
0.18
0.18
0.18
....
a. Average daily water use rate during the 6 to 10 days of the highest consumptive
use of the season.
b. Cool season pasture.
c. Warm season pasture.
d. Summer.
e. Fall.
f. Parts of Georgia, Alabama, North Carolina,.and South Carolina.
1 in. = 2.54 cm
5-81
-------
Corn and potatoes will tolerate some flooding, possibly up to a few
days, without suffering damage; clover, timothy, and rye are also
somewhat resistant. Grasses (such as coastal Bermuda, meadow, fescue,
brome, orchard, or Reed canary) are the most tolerant species and can
sustain several weeks of flooding without injury. Reed canary grass, a
tall cool-season perennial with a rhizomatous root system, will grow in
a very wet, marshy area, and reportedly has withstood flooding for as
long as 49 days without permanent injury [70].
5.6.1.2 Nutrient Uptake
The major nutrients essential to plant growth are nitrogen, phosphorus,
potassium, calcium, magnesium, and sulfur. Of these, the prominent
constituents in wastewater are nitrogen, phosphorus, and potassium.
Typical uptake rates of these elements for various crops are listed in
Table 5-32. Variations noted in the amount of nutrient uptake from the
soil can arise from changes in either (1) the amount and form of the
nutrient present, or (2) the net yield of the crop.
TABLE 5-32
NUTRIENT UPTAKE RATES FOR SELECTED CROPS
[3, 4, 5, 6, 70, 71]
Uptake, lb/acre-yr
Nitrogen Phosphorus Potassium
Forage crops
Alfalfa3
Bromegrass
Coastal Bermuda grass
Kentucky bluegrass
Quackgrass
Reed canary grass
Ryegrass
Sweet clover^
Tall fescue
Field crops
Barley
Corn
Cotton
Milomaize
Potatoes
Soybeans3
Wheat
200-480
116-200
350-600
180-240
210-250
300-400
180-250
158
135-290
63
155-172
66-100
81
205
94-128
50-81
20-30
35-50
30-40
40
27-41
36-40
55-75
16
26
15
17-25
12
14
20
11-18
15
155-200
220
200
180
245
280
240-290
90
267
20
96
34
64
220-288
29-4R
18-42
a. Legumes will also take nitrogen from the atmosphere
and will not withstand wet conditions.
1 lb/acre-yr = 1.12 kg/ha-yr
5-82
-------
Nutrient content of a plant depends, in part, on the amounts of
nutrients available to the plant. The minimum cellular amounts required
are about 2% nitrogen, 0.2% phosphorus, and 1+% potassium, but when
sufficient quantities are available, these amounts can easily double
[71, 72]. For forage crops in general, the percent composition for
nitrogen can range from 1.2 to 2.8% and averages around 1.8% (dry weight
of the plant); but with wastewater irrigation it can range from 3.0 to
4.5% [72].
The total uptake of nutrients from applied wastewater increases as crop
yield increases (see Figure A-3, Appendix A). Crop yield increases
ranging up to twofold to fourfold have been achieved when wastewater
effluent irrigation is used instead of ordinary irrigation water [73].
Although nutrient uptake continues to increase with yield, the
relationship is not linear.
A factor that affects both percent nitrogen composition and yield of
forage crops is stage of growth. In general, grasses contain the
highest percentage of nitrogen during the green, fast growth stage. The
nitrogen uptake decreases with maturity. These effects are demonstrated
in Figure 5-31. For corn and grasses, nitrogen uptake is very low
during early growth (the first 30 to 40 days) and thereafter climbs
sharply. For corn, this rise is maintained until harvest. For grasses,
nitrogen uptake reaches a peak around the 50th day and thereafter
declines. This suggests that harvesting these grasses every 8 to 9
weeks (for a total of two to three harvests per season) will result in
maximum nitrogen uptake.
The amounts of phosphorus in applied wastewaters are usually much higher
than plant requirements. Fortunately, many soils have a high sorption
capacity for phosphorus and very little of the excess is passed on to
the groundwater. Instead, it is held in the soil and serves to enrich
the soil [74].
Potassium is used in large amounts by many crops, but typical wastewater
is relatively deficient in this element. In some cases fertilizer
potassium may be needed to provide for optimal plant growth, depending
on the soil and crop grown.
The micronutrients important to plant growth (in descending order) are:
iron, manganese, zinc, boron, copper, molybdenum, and occasionally,
sodium, silicon, chloride, and cobalt. Most wastewaters contain an
ample supply of these elements, and in some cases, phytotoxicity may be
a consideration.
5-83
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FIGURE 5-31
CROP GROWTH AND NITROGEN UPTAKE VERSUS DAYS FROM
PLANTING FOR FORAGE CROPS UNDER EFFLUENT IRRIGATION [75]
4
3
2
1
0
4
3
2
I
0
7 5
50
25
0
60
60
40
20
0
n—i—I—I—I i r
_ SORGHUII-SUDANGRASS
O 5 cm/wk
- B20 cm/wK
I
20
40 80
AGE. d
80
100
V
a
4
2
0
4
3
2
1
0
200
t 50
1 00
50
0
80
60
40
20
0
O 5 cm/»k
Q 20 cm/wK
20
J I
40
AGE
60
80
1 00
» i n ./«k - 2*. 54 cm/wk
1 I b/ac re = 1. 1 2 k g/h a
1 t on/ac re =2. 24 Mg/ha
5.6.1.3 Sensitivity to Wastewater Constituents
Plant growth can be adversely affected by excess salts (generally
chloride and sodium), excess acidity, or excess concentrations of any of
a large number of microelements, including the micronutrients.
Tolerances of selected crops to salinity, boron, and acidity are
presented in Tables 5-33, 5-34, and 5-35, respectively. In general,
forage crops are the most tolerant, field crops are less tolerant, and
5-84
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vegetable and row crops are least tolerant. There are many exceptions
to this rule, however, and wide differences can be found even between
two varieties of the same crop. Data on crops not listed in these
tables are available in references [76-78], and the local Agricultural
Extension Service can give details on crops suitable for a proposed
site.
TABLE 5-33
ELECTRICAL CONDUCTIVITY VALUES RESULTING
IN REDUCTIONS IN CROP YIELD [77]
mmhos/cm
ECe values (saturated
paste extract) for
a reduction in
crop yield of
Forage crops
Alfalfa
Bermuda grass
Clover
Corn (forage)
Orchard grass
Perennial rye grass
Tall fescue
Vetch
Tall wheat grass
Field crops
Barley
Corn
Cotton
Potato
Soybeans
Sugarbeets
Wheat
0%
2.0
6.9
1.5
1.8
1.5
5.6
3.9
3.0
7.5
8.0a
1.7
7.7
1.7
5.0
7.0
6.0
25%
5.4
10.8
3.6
5.2
5.5
8.9
8.6
5.3
13.3
13
3.8
13
3.8
6.2
11.0
9.5
100%
15.5
22.5
10
15.5
17.5
19
23
12
31.5
28
10
27
10
10
24
20
a. Barley and wheat are less tolerant during
germination and seedling stage.
not exceed 4 or 5 mmhos/cm.
ECB should
When evaporation is high, problems can arise from the use of sprinklers.
When water is applied to vegetative surfaces, excess quantities of
sodium and chloride can be absorbed through the wet leaves and cause
leaf burn. Nighttime applications can alleviate foliar absorption and
leaf burn due to chlorides or bicarbonates.
5-85
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TABLE 5-34
CROP BORON TOLERANCE [77]
mg/L
Tolerant, Semitolerant Sensitive,
1-3 mg/L boron 0.67-2 mg/L boron <1 mg/L boron
Alfalfa Barley Citrus
Cotton Corn American elm
Sugarbeet Kentucky bluegrass Berries
Sweetclover Potato
Tomato
Wheat
TABLE 5-35
CROP ACIDITY TOLERANCE [78]
Will tolerate
mild acidity,
pH 5.8 to 6.5
Will tolerate
slight acidity,
pH 6.2 to 7.0
Very sensitive
to acidity,
pH 6.8 to 7.5
Cotton
Buckwheat
Bentgrass
Millet
Potato
Poverty grass
Oats
Rye
Sudan grass
Vetch
Corn
Beans
Kentucky bluegrass
Clovers: alsike
crimson,
white
Kale
Tomato
Soybean
Wheat
red,
Alfalfa
Barley
Carrot
Sweet clover
Sugarbeet
There are two considerations in trace element accumulation in the soil:
(1) phytotoxicity, and (2) translocation into the food chain. Copper,
zinc, and nickel are the prime examples of elements that can be toxic to
some plants at relatively high levels. At present there is little
definitive evidence that these elements have accumulated to phytotoxic
levels in any land treatment system [79]. The principal element of
concern for potential translocation into the food chain is cadmium.
This is discussed in detail in Appendix A.
When selecting
should be made
resistant species to prevent toxicity, a distinction
between accumulators and excluders. Accumulators will
5-86
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tolerate high levels of an element while transferring large quantities
of it into the harvestable portions of the plant, making it available
for removal. Excluders will also tolerate high levels, but prohibit
passage of the toxifying element into the fruit, root, or leaf tissue
that is to be consumed. For example, corn may take up cadmium but it is
mostly excluded from the grain. In general, grain crops are superior to
vegetables in excluding heavy metals [79].
5.6.1.4 Selection of Overland Flow Vegetation
Perennial grasses with long growing seasons, high moisture tolerance
(hydrophytic), and extensive root formation are best suited to the
process. The grass should form a sod and not grow in bunches. While
common Bermuda, red top, fescue, and rye grass all form sod, none of
these is always suitable for all weather conditions. Bermuda goes
dormant in winter while red top, fescue, and rye grass are cool season
grasses. Reed canary grass is the most versatile but it is a bunch
grass. It should therefore be planted with a mixture of other grasses
such as red top, fescue, and rye grass.
Comparative field studies at Paris, Texas, indicated that Reed canary
grass was the superior grass at that location. It demonstrated a very
high nutrient uptake capacity and yielded a high quality hay upon
harvest [54]. Hauling the crop away during harvest provides permanent
removal of the nutrients taken up during plant growth. The harvested
grass is suitable for feeding to cattle.
5.6.1.5 Other Vegetation
Sod, landscape vegetation, trees, and wetlands vegetation are discussed
separately because of their unique features. Much of the previous
discussion will apply.
5.6.1.5.1 Sod
Sod farming is the controlled growth of turf grasses for transplanting
to lawns, golf courses, and parks. Usually, public access to the
growing site is restricted so that bacteriological quality of the
wastewater is not a major concern. Because the sod is ranoved
periodically, the nitrogen loadings can exceed crop uptake as well as
soil nitrogen accumulation.
5-87
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5.6.1.5.2 Landscape Irrigation
Application of wastewater on landscape areas such as highway median and
border strips, airport strips, golf courses, parks and recreational
areas, and nature-wildlife areas has several advantages. The areas
irrigated are already publicly owned, saving acquisition cost, and
problems associated with crops for consumption are avoided.
Additionally, the maintenance of landscape projects generally requires
less water than other vegetation (since watering in these cases is based
on vegetative maintenance rather than production); hence, the wastewater
can be spread over a greater area.
Although sufficient areas to accept available effluent are usually
available, wastewater distribution, especially for roadside rights-of-
way, can be a problem. For roadside application, sprinkler trucks are
commonly used; for application to golf courses, playgrounds, and nature
areas, fixed sprinklers are most commonly used.
5.6.1.5.3 Woodlands Irrigation
Approximate average water consumption rates for native stands of
different tree species are given in Table 5-36.
TABLE 5-36
EVAPOTRANSPIRATION OF WOODLAND AND FOREST CROPS [80]
Evapotranspiration, in./yr
M« ~f
Pines
Mixed coniferous
and deciduous
Deciduous
Mixed hardwoods
studies
32
6
58
2
Average
15
25
17
31
Range
5-34
18-34
8.5-34
27-35
1 in./yr = 2.54 cm/yr
Recommended irrigation rates for maintaining desired forest crops,
determined from studies using wastewater irrigation, are shown in Table
5-37. These rates, which generally agree with those in Table 5-36,
suggest that where water consumption is a primary consideration, pines
are at a disadvantage.
5-88
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TABLE 5-37
RECOMMENDED IRRIGATION RATES OF FOREST CROPS
Species
Maximum recommended
irrigation rate, in./wk
Reason for limit
Pines [75, 76, 77]
Hardwoods
[81]
[82, 83]
Douglas firs
cottonwoods [84]
Conifers [85]
1
2-4
1 (winter)
4 (summer)
(104 in./yr)
Satisfactory tree growth rate
and nitrogen removal
Satisfactory nitrogen removal
Satisfactory tree growth rate
Trees grow well and consume
all available water at
this rate
Satisfactory tree growth rate
1 in./wk =2.54 cm/wk
Pines and other conifers, however, have an advantage in that they
maintain their water uptake rates year-round, if freezing temperatures
do not make the water unavailable. Deciduous species exhibit cyclical
water needs with a very active growing season during the summer,
followed by a dormant phase in the winter. Water consumption then drops
to a level of one-half to one-fourth the summer rates, generally less
than 1 in./wk (2.54 cm/wk). A major objective in silviculture is to
maintain an adequate unsaturated soil zone for the proper development of
the tree root system.
Wood quality associated with effluent-irrigated stands, as studied by
Murphey et al. [86], indicates that the pulpwood characteristics of pine
and oak are improved via an increase in fibre length and cell wall
thickness. Structural strength, however, appears to suffer a decrease,
rendering the wood less suitable for construction purposes.
For harvesting purposes, cottonwood seems to show the greatest growth
response to effluent irrigation [82, 83], and tree harvests every 6 to
10 years may be possible. Eucalyptus is also a fast grower, but is
limited to areas without hard frosts. Studies at Stanford Research
Institute have suggested the creation'of eucalyptus biomass plantations
to be harvested and burned for the production of electricity [87].
A major limitation to the use of woodlands and forests is the relatively
low rates of nutrient uptake. Typical rates of nitrogen uptake for
different forest crops were listed in Table 5-2. These rates will
usually be maintained through the growing phase (20 to 40 years) and
5-89
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will taper off as maturity is reached. Conifers as Christmas trees
should be abandoned. The extra water and nutrients cause the trees to
grow upward, rather than outward, resulting in spindly, unattractive
trees.
5.6.1.5.4 Wetlands
Experience has shown that duckweed (Lemna minor) and various species of
bulrush (Scirpus acustus, Scirpus lacustris, Scirpus validus) are the
most desirable species, based on treatment capabilities, growth rates,
and harvest response for marshes [22, 23, 88]. Cattails seem to have
trouble competing with the bulrushes and duckweed under harvest
conditions [22].
Marsh studies by the National Aeronautics and Space Administration
concluded that water hyacinths (Eichornia crassipes), and to a lesser
extent alligator weed (Alternanthera philovernides) are effective in
removal of both organics and some metals [89, 90].
Experiments have been conducted in Florida with cypress domes as
nutrient sinks, and they appear to be quite efficient [27]. Artificial
peat beds also appear to be effective, removing 85% of the nitrogen,
99.3% of the phosphorus, and 99.99% of the coliform bacteria when grown
with a quackgrass or bluegrass cover [27, 91].
5.6.1.6 Regulatory Constraints
Many states regulate the type of wastewater that can be used to irrigate
some crops. In addition, several states require that a suitable crop be
planted before land application begins [92]. In some cases the type of
crop proposed affects the slope of the site that is acceptable.
5.6.1.7 Crop Utilization
Of crops historically grown with wastewater, under present cost
conditions, corn appears to provide the greatest (net) profit [93, 94].
At the Muskegon Project, the 1976 revenue from their corn harvest was
approximately $1 000 000 (see Section 7.6). There are no restrictions
placed on the sale of this corn.
Among the trees, maples (and certain other hardwoods), cotton woods, and
pines grown under wastewater irrigation are suitable for sale as pulp,
but not for structural wood [86], Cotton wood and eucalyptus are
suitable for sale as fuel [87].
5-90
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5.6.2 Site Preparation and Management
It is critical to maintain the soil-vegetation system in a healthy,
productive, and renovative state. A successful agricultural system
requires knowledge of fanning operations, which are described briefly in
this section. Assistance in design and planning can be provided by
local farm advisers and land grant college extension specialists.
5.6.2.1 Field Preparation
Procedures for preparing fields for slow rate systems may include
clearing the fields of vegetative growth (bulldozing of heavy vegetation
into piles followed by burning, or heavy stubble disking on lighter
vegetation); planing and grading, if required, and ripping, disking, and
tilling of the soil to loosen and aerate it. Undeveloped soils may
require chemical soil amendments, including gypsum to reclaim sodic
soils and increase permeability, and lime to reduce acidity and metals
toxicity. Determination of amendment needs is discussed in Section
5.7.3. The effects of lime on element availability are indicated in
Table 5-38. Fertilizers may also be added for nutrient-deficient
soils, although nutrient-rich,wastewaters often make this unnecessary.
TABLE 5-38
EFFECT OF LIME ON ELEMENT
AVAILABILITY IN SOIL [76, 78]
Elements for which liming
Reduces
availabi lity
Aluminum
Barium
Beryllium
Boron3
Cadmium
Cobalt
Copper3
Fluoride
Iron
Li thium
Manganese
Nickel
Zinc
Increases
avai labi lity
Calcium
Magnesium
Molybdenum
Nitrogen3
Phosphorus
Potassium
Sulfur3
a. Minor effect on availability.
5-91
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5.6.2.2 Maintenance of Infiltration for Slow Rate Systems
Soil-water infiltration rates can be reduced by surface sealing and
clogging. The sealing is the result of: (1) compaction of the surface
from machine working, (2) compaction from raindrops and sprinkler drops,
(3) a clay crust caused by water flowing over the surface (fine
particles are fitted around larger particles to form a relatively
impervious seal), or (4) clogging due to suspended particles, buildup of
organic matter, or trapped gases. This surface layer can be broken up
by plowing, cultivation, or any other stirring of the soil that will
result in increased water intake. Tillage beyond the point of breaking
up an impermeable layer is generally harmful in that it results in
further soil compaction. The effect of surface sealing on intake can be
greatly reduced, and possibly eliminated, by cultivating grass or other
close-growing vegetation. Maintenance of soil organic matter through
the use of high residual crops, such as barley, and plowing under of
stubble is another step that helps maintain soil permeability.
5.6.2.3 Salinity Control
If the soil is saline (EC >4 mmhos/cm) for most crops, control measures
must be taken. The average salt concentration of the soil solution of
the rooting depth is usually three times the concentration of the salts
in the applied water (in arid climates) and is believed to be
representative of the salinity to which the crop responds [77]. If
excessive salts build up, the method of control is leaching by adding
enough irrigation water so that water in excess of crop needs percolates
below the root zone, lowering the overall salinity. The most important
zone for leaching is the upper quarter of the root zone where the
primary (40%) water use by the plant occurs. As a rule-of-thumb,
about a 12 in. (30 cm) depth of water leached through a 12 in. (30 cm)
depth of soil should remove about 80% of the soluble salts.
5.6.2.4 Crop Management
5.6.2.4.1 Planting
'Local extension services or similar experts should be consulted
regarding planting technique and schedules.
5.6.2.4.2 Harvesting
Harvesting for grass crops and alfalfa involves regular cuttings, and a
decision regarding the trade-off between yield and quality must be made.
Crop yield will usually increase up to and beyond the flowering stage,
5-92
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but quality (amount of stems versus leaves and the amount of digestible
material) is highest in the younger growth stages and falls off very
rapidly once the flowering stage is reached. ^Advice can be obtained
from local extension services.
5.6.2.4.3 Double Cropping
Double cropping can extend the operating period for slow rate systems,
increase the economic return for the system, and increase the nitrogen
uptake capacity.
A growing practice in the East and Midwest is to provide a continuous
vegetative cover with grass and corn. This "no-till" corn management
consists of planting grass in the fall and then applying a herbicide in
the spring before planting the corn. When the corn completes its growth
cycle, grass is reseeded. Thus, cultivation is avoided, water rates are
maximized, and nutrient uptake is enhanced.
5.6.2.4.4 Grazing
Grazing of pasture by beef cattle or sheep can provide an economic
return for slow rate systems (see Pleasanton, California, and San
Angelo, Texas, in Chapter 7). This approach has also been successsfuly
pursued at the land treatment farm in Melbourne, Australia, for the past
65 years [95], Grazing cattle and sheep keep the vegetative cover short
for maximum wastewater renovation efficiency. No health hazard has been
associated with the sale of the animals for human consumption.
Grazing animals do return nutrients to the ground in their waste
products. The chemical state (organic and ammonia nitrogen) and rate of
release of the nitrogen reduces the threat of nitrate pollution of the
groundwater. Much of the ammonia-nitrogen volatilizes. The organic
nitrogen is held in the soil and is slowly mineralized. As a result,
only a portion of the nitrogen is slowly recycled.
One precaution that must be taken is not allowing the cattle and sheep
to graze on wet fields. This would compress the ground and reduce the
permeability of the soil. As described in Chapter 7, Pleasanton,
California, and San Angelo, Texas, solve the problem by using a series
of fields in rotation. Wastewater irrigation proceeds on a field as
soon as the cattle are moved off. In this mariner, by the time the
cattle are moved back onto a field to graze, it has had several weeks to
dry out and firm up.
5-93
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Another concern is the physical contact between the udders of milking
animals (cows, goats) and pastures irrigated with wastewater. This
could represent a direct vector to human food supplies and should be
avoided.
5.7 System Monitoring
Monitoring
significant
monitoring
determine
environment
components
wastewater,
i n some
wastewater.
of land treatment systems involves the observation of
changes resulting from the application of wastewater. The
data are used to confirm environmental predictions and to
if any corrective action is necessary to protect the
or maintain the renovative capacity of the system. The
of the environment that need to be observed include
groundwater, and soils upon which wastewater is applied and,
cases, vegetation growing in soils that are receiving
5.7.1 Water Quality
Monitoring of water quality for land application systems is generally
more involved than for conventional treatment systems because nonpoint
discharges of system effluent into the environment are involved.
Monitoring of water quality at several stages of a land treatment
process may be needed for process control. These stages may be:
(1) applied wastewater, (2) renovated water, and (3) receiving waters--
surface water or groundwater.
5.7.1.1 Applied Wastewater
The water quality parameters and the frequency of analyses will vary
from site to site depending on the regulatory agencies involved and the
nature of the applied wastewater. The measured parameters may include
(1) those that may adversely affect receiving water quality either as a
drinking water supply or an irrigation water supply, (2) those required
by regulatory agencies, and (3) those necessary for system control. An
example of a suggested water quality monitoring program for a large
scale slow rate system is presented in Table 5-39.
5.7.1.2 Renovated Water
Renovated water may be recovered as runoff in an overland flow system,
or as drainage from underdrains or groundwater from recovery wells in
slow rate and rapid infiltration systems. Point discharge to surface
waters must satisfy the NPDES permit.
5-94
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TABLE 5-39
EXAMPLE MONITORING PROGRAM FOR
A LARGE SLOW RATE SYSTEM
Frequency of analysis
Groundwater
Applied Onsite Perimeter Background
Parameter wastewater
Flow
BOD or TOC
COO
Suspended solids
Nitrogen, total
Nitrogen, nitrate
Phosphorus, total
Col i forms, total
PH
Total dissolved
solids
Alkalinity
SAR
Static water
level
Note: C = Continuously
D = Daily
Q = Quarterly
W = Weekly
C
W
W
W
W
••
M
W
D
M
M
M
••
Soil Plants wells
..
Q
Q
..
2A A 0
0
2A A Q
0
Q .. 0
0
0
Q .. Q
M
2A = Two samples per
A = Annually
M = Monthly
wells
..
Q
Q
••
0
Q
0
Q
0
0
Q
Q
M
year
wells
• •
Q
Q
••
0
0
Q
0
0
Q
Q
Q
M
a. Wastewater applied and groundwater should be tested initially
and periodically thereafter, as appropriate, for heavy metals,
trace organics, or other constituents of environmental concern.
5.7.1.3 Groundwaters
In groundwaters, travel time of constituents is slow and mixing is not
significant compared with surface waters. Surface inputs near a
sampling well will move vertically and arrive at the well much sooner
than inputs several hundred feet away from the well. Thus, the
groundwater sample represents contributions from all parts of the
surface area with each contribution arriving at the well at a different
time. A sample may reflect surface inputs from several years before
sampling and have no association with the land application system.
Consequently, it is imperative to obtain adequate background quality
data and to locate sampling wells so that response times are minimized.
5-95
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If possible, existing background data should be obtained from wells in
the same aquifer both beyond and within the anticipated area of
influence of the land application system. Wells with the longest
history of data are preferable. Monitoring of background wells should
continue after the system is in operation to provide a base for
comparison.
In addition to background sampling, samples should be taken from
groundwater at perimeter points in each direction of groundwater
movement from the site. In locating the sampling wells, consideration
must be given to the position of the groundwater flow lines resulting
from the application [96, 97]. Perimeter wells should be located
sufficiently deep to intersect flow lines emanated from below the
application area but not so deep as to prolong response times.
A schematic showing correct and incorrect groundwater sampling locations
is given in Figure 5-32; monitoring points for a hypothetical
application site are also shown. If samples are taken at A and B, the
groundwater flow lines from the application area indicate that treated
effluent would reach these points. It may require several years for
treated effluent to reach point C because the flow lines are a long
distance from the application surface. If samples were taken from point
D, mixing with surface water could make results invalid for groundwater
characterization.
A groundwater flow model that predicts groundwater movement in the area
of influence of the site will be helpful in locating sampling wells.
Guidelines for sampling well construction and sampling procedures are
given by Blakeslee [98].
In addition to quality, the depth to groundwater should be measured at
the sampling wells to determine if the hydraulic response of the aquifer
is consistent with what was anticipated. For slow rate systems, a rise
in water table levels to the root zone would necessitate corrective
action such as reduced hydraulic loading or adding underdrainage. The
appearance of seeps or perched groundwater tables might also indicate
the need for corrective action.
5.7.2 Soils Management
In some cases, application of wastewater to the land will result in
changes in soil properties. Results of soil sampling and testing will
serve as the basis for deciding whether or not soil properties should be
adjusted by the application of chemical amendments. Soil properties
that are important to management include: (1) ph, (2) exchangeable
sodium percentage, (3) salinity, (4) nutrient status, and (5) metals.
5-96
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FIGURE 5-32
SCHEMATIC OF GROUNDWATER FLOW LINES AND
ALTERNATIVE MONITORING WELL LOCATIONS [95]
LAND TREATMENT
CREEK
RIVER
LECENB
IMPERVIOUS
LAYER
C-0
GROUNDWATER TABLE
UNSATURATED FLOW
SATURATED FLOW
INCORRECT MONITORING
LOCATIONS
A-B CORRECT MONITORING
LOCATIONS
5.7.2.1 pH
Soil pH below 5.5 or above 8.5 generally is harmful to most plants (see
Table 5-35). Below pH 6.5 the capacity of soils to retain metals is
reduced significantly, the soil above pH 8.5 generally indicates a high
sodium content and possible permeability problems. If wastewaters
contain high concentrations of sodium, the soil pH may rise in the long
term. A pH adjustment program should be based on the recommendations of
a professional agricultural consultant or county or state farm advisor.
5-97
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5.7.2.2 Exchangeable Sodium Percentage
When the percentage of sodium on the soil exchange complex (ESP) exceeds
10 to 15%, problems with reduced soil permeability can occur. Sodic
soil conditions may be corrected by adding soluble calcium to the soil
to displace the sodium on the exchange and removing the displaced sodium
by leaching. Calcium may be applied in the form of gypsum (CaSCK)
either as a dry powder or dissolved in the applied wastewater. The
amount of gypsum to apply may be determined by a laboratory gypsum
requirement test as described in the standard references. If a soil is
calcareous, that is, containing calcium in the form of insoluble salts
such as carbonates, sul fates, or phosphates, the calcium may be
solubilized and made available for sodium displacement by the addition
of acidulating chemical s--sul fur, sulfuric acid, or iron and aluminum
sulfate. A comparison of these chemicals to gypsum is presented in
Table 5-40.
TABLE 5-40
A COMPARISON OF CHEMICALS TO GYPSUM [99]
Tons equivalent to
Amendment 1 ton of gypsum
Sulfur, S 0.19
Nitrosol, 20% N, 40% S 0.47
Sulfuric acid, H2S04 0.57
Limestone, CaCOj 0.58
Lime-sulfur, 24% S 0.79
Gypsum, CaS04 • 2H20 1.00
Alum, A12(S04)3 • 17 H20 1.29
Ferrous sulfate, FeS04 • 7 H20 1.61
1 ton = 0.907 Mg
5.7.2.3 Salinity
The levels at which salinity becomes harmful to plant growth depend on
the type of crop. Salinity in the root zone is controlled by leaching
soluble salts to the subsoil or drainage system (see Section 5.6.2.3).
5-98
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5.7.2.4 Nutrient and Trace Element Status
The nutrient status of the soil and the need for supplemental
fertilizers should be periodically assessed. The levels of metals in
the soil may be the factor determining the ultimate useful life of the
system. University agricultural extension services may provide the
service or recommend competent laboratories.
5.7.3 Vegetation
Plant tissue analysis is probably more revealing than soil analysis with
regard to deficient or toxic levels of elements. All of the
environmental factors that affect the uptake of an element are
integrated by the plant, thus eliminating much of the complexity
associated with interpretation of soil test results. If a regular plant
tissue monitoring program is established, deficiencies and toxicities
can be determined and corrective action can be taken. Detailed
information on plant sampling and testing may be found in Walsh and
Beaton [100] and Melsted [101].
5.8 Facilities Design Guidance
The purpose of this section is to provide guidance on aspects of
facilities design . that may be unfamiliar to some environmental
engineers.
• Standard surface irrigation practice is to produce longitudi-
nal slopes of 0.1 to 0.2% with transverse slopes not exceeding
0.3%.
Step 1. Rough grade to + 0.15 ft (5 cm) at 100 ft (30 m)
grid stations.
Step 2. Finish grade to + 0.10 ft (3 cm) at 100 ft (30 m)
grid stations with no reversals in slope between
stations.
Step 3. Land plane with a 60 ft (18 m) minimum wheel base,
land plane to a "near perfect" finished grade.
• Specifications are available from the SCS for agricultural
land leveling [102].
• Overland flow slopes should be graded to specification twice
and checked for bulk density and degree of compaction to en-
sure relatively uniform conditions and prevent settlement
during initial operation.
• If the site is large and intense rainfall is likely to occur,
a minimum amount of finished slope should be prepared at any
one time.
5-99
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• Access to sprinklers or distribution piping should be provided
every 1 300 ft (390 m) for convenient maintenance.
• Both asbestos-cement and PVC irrigation pipe are rather
fragile and require care in handling and installation.
• Topsoil should be stripped and preserved during initial
overland flow site grading, then replaced on the slope.
• Reed canary grass requires about 1 year to become established.
A companion crop of orchard or rye grass is recommended for
the first year.
• Tail water return systems should be designed to distribute
collected water to all parts of the field, not consistently to
the same area.
• Screening should be provided for distribution pumping on the
suction side to help prevent nozzle plugging.
• Diaphragm-operated globe valves should be used for controlling
flow to laterals.
• All electric equipment should be grounded, especially when
associated with center pivot systems.
• Automatic controls can be electrically, hydraulically, or
pneumatically operated. Solenoid actuated, hydraulically
operated (by the wastewater) valves with small orifices will
clog from the solids.
• Use 36 in. (1 m) or larger valve boxes made of corrugated
metal, concrete, fiberglass, or pipe material. Valve boxes
should extend 6 in. (15 cm) above grade to exclude stormwater.
• Low pressure shutoff valves should be used to avoid continuous
draining of the lowest sprinkler on the lateral.
• Automatic operation can be controlled by timer clocks. It is
important that when the timer shuts the system down for any
reason that the field valves close automatically and that the
sprinkling cycles resume as scheduled when sprinkling
commences. The clock should not reset to time zero when an
interruption occurs.
• High flotation tires are recommended for land treatment
systems. Allowable soil contact pressures for center pivot
machines are presented in Table 5-41.
• Underdrains are only effective in saturated soil. If they
are placed in a well to moderately-well drained soil above the
water table, they will not recover any water.
5-100
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TABLE 5-41
ALLOWABLE SOIL CONTACT PRESSURE
% fines Contact pressure, lb/in.2
20 25
40 16
50 12
Note: To illustrate the use of this
table, if 20% of the soil fines
pass through a 200-mesh screen, the
contact pressure of the supporting
structure to the ground should be no
more than 25 lb/in.2. If this is
exceeded, one can expect wheel
tracking problems to occur.
Perforated continuous plastic pipe is generally more econo-
mical than clay tile or bell spigot pipe for underdrains.
A filter sock placed over plastic drain pipe will help pre-
vent clogging--a gravel envelope is unnecessary. Encrusting
by iron, etc., can prove to be a problem over time.
Plastic drainage pipe with cut or preformed openings is less
likely to plug than pipe with punched openings.
Maximum depth of placement for standard agricultural
continuous drain-tile trenches is 5.5 ft (1.6 m). Bucket-type
trenches are needed to place tile deeper.
Intensive shallow drainage may be more economical than deep
widely-spaced drains.
Disking or harrowing soil surface about once per year can help
maintain infiltration capacity.
Plowing in "heavy" soils will develop a plowpan layer at the
tip depth of the plow. Ripping or deep plowing at 2 to 4 year
intervals may be necessary.
5-101
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5.9 References
1. Alternative Waste Management Techniques for Best Practicable Waste
Treatment. US Environmental Protection Agency, Office of Water
Program Operations. EPA-430/9-75-013. October 1975.
2. National Interim Primary Drinking Water Regulations. US
Environmental Protection Agency. 40 CFR 141. December 24, 1975.
3. Evaluation of Land Appl ication Systems. Office of Water Program
Operations, Environmental Protection Agency. EPA-430/9-75-001.
March 1975.
4. Powell, G.M. Design Seminar for Land Treatment of Municipal
Wastewater Effluents. EPA Technology Transfer Program. (Presented
at Technology Transfer Seminar. 1975.) 75 p.
5. Clapp, C.E. et al. Nitrogen Removal from Municipal Wastewater
Effluent by a Crop Irrigation System. Minnesota Agricultural
Experiment Station Paper No. 9576. 1976.
6. Larson, W.E. Personal Communication. 1976.
7. Iskandar, I.K., R.S. Sletten, D.C. Leggett, and T.F. Jenkins.
Wastewater Renovation by a Prototype Slow Infiltration Land
Treatment System. Corps of Engineers, U.S. Army Cold Regions
Research and Engineering Laboratory. CRREL Report 76-19. Hanover,
N.H. June 1976.
8. Pratt, P.P. Quality Criteria for Trace Elements in Irrigation
Waters. University of California, Department of Soil Science and
Agricultural Engineering, Riverside. 1972.
9. National Academy of Science. Water Quality Criteria 1972.
Ecological Research Series. US Environmental Protection Agency.
Washington, D.C. Report No. R3-73-033. March 1973.
10. Lance, J.C. and C.P. Gerba. Nitrogen, Phosphate and Virus Removal
from Sewage Water During Land Filtration. In: Progress in Water
Technology. Vol. 9, Pergamon Press. Great Britain. 1977. pp.
157-166.
11. Pound, C.E. and R.W. Crites. Wastewater Treatment and Reuse by
Land Application. Volumes I and II. Environmental Protection
Agency, Office of Research and Development. August 1973.
12. Bouwer, H., R.C. Rice, E.D. Escarcega, and M.S. Riggs.
Renovating Secondary Sewage by Ground Water Recharge With
Infiltration Basins. Environmental Protection Agency, Office of
Research and Monitoring. Project No. 16060 DRV. March 1972. 102 p.
13. Baillod, C.R., et al. Preliminary Evaluation of 88 Years Rapid
Infiltration of Raw Municipal Sewage at Calumet, Michigan.
In: Land as a Waste Management Alternative. Loehr, R.C. (ed.) Ann
Arbor, Ann Arbor Science. 1977. pp 435-45U.
5-102
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14. Aulenbach, D.B., T.P. Glavin, and J.A. Romero Rojas. Protracted
Recharge of Treated Sewage into Sand, Part I - Quality Changes in
Vertical Transport Through the Sand. Ground Water. 12(3) :161-169,
May-June 1974.
15. Pound, C.E., R.W. Crites, and J.V. Olson. Long-Term Effects of
the Rapid Infiltration of Municipal Wastewater. (Presented at the
8th International Conference of the International Association on
Water Pollution Research, Sydney, Australia. October 1976.)
16. Satterwhite, M.B. and G.L. Stewart. Evaluation of an
Infiltration-Percolation System for Final Treatment of Primary
Sewage Effluent in a New England Environment. In: Land as a Waste
Management Alternative. Loehr, R.C. (ed.) Ann Arbor, Ann Arbor
Science. 1977. pp 435-450.
17. Thomas, R.E., B. Bledsoe, and K. Jackson. Overland Flow Treatment
of Raw Wastewater with Enhanced Phosphorus Removal.
EPA-600/2-76-131. Environmental Protection Agency, Office of
Research and Development. June 1976.
18. Thomas, R.E. Personal Communication. March 1977.
19. Hunt, P.G. and Lee, C.R. Land Treatment of Wastewater by Overland
Flow for Improved Water Quality. Biological Control of Water
Pollution. University of Pennsylvania. 1976. pp 151-160.
20. Lee, C.R., et al. Highlights of Research on Overland Flow for
Advanced Treatment of Wastewater. U.S. Army Engineer Waterways
Experiment Station. Miscellaneous Paper Y-76-6. November 1976.
21. 'Carlson, C.A., P.G. Hunt, and T.B. Delaney, Jr. Overland Flow
Treatment of Wastewater. Army Engineer Waterways Experiment Station.
Miscellaneous Paper Y-74-3. August 1974.
22. Small, M.M. Marsh/Pond Sewage Treatment Plants. In: Proceedings
of the National Symposium on Freshwater Wetlands and Sewage Effluent
Disposal. University of Michigan. Ann Arbor, May 1976. pp
197-214.
23. Spangler, F.L. et al. Artificial and Natural Marshes as Wastewater
Treatment Systems in Wisconsin. In: Proceedings of the National
Symposium on Freshwater Wetlands and Sewage Effluent Disposal.
University of Michigan. Ann Arbor, May 1976. pp 215-240.
24. U.S. Department of the Interior, Bureau of Reclamation. Wastewater
Reclamation and Reuse Pilot Demonstration for the Suisun Marsh.
Progress Report. August 1975.
25. Whigham, D.F. and R.L. Simpson. Sewage Spray Irrigation in a
Delaware River Freshwater Tidal Marsh. In: Proceedings of the
National Symposium on Freshwater Wetlands and Sewage Effluent
Disposal. University of Michigan. Ann Arbor, May 1976. pp
119-144.
5-103
-------
26. Hartland-Rowe, R.C.B. and P.B. Wright. Swamplands for Sewage
Effluents, Final Report. Environmental-Social Committee, Northern
Pipelines, Task Force on Northern Oil Development. Report No.
74-4. May 1974.
27. Stanlick, H.T. Treatment of Secondary Effluent Using a Peat Bed.
In: Proceedings of the National Symposium on Freshwater Wetlands
and Sewage Effluent Disposal. University of Michigan. Ann Arbor,
May 1976. pp 257-268.
28 Ewel, K.C. Effects of Sewage Effluent on Ecosystem Dynamics in
Cypress Domes. In: Proceedings of the National Symposium on
Freshwater Wetlands and Sewage Effluent Disposal. University of
Michigan. Ann Arbor, May 1976. pp 169-198.
29. Odum, H.T. et al. Recycling Treated Sewage through Cypress
Wetlands in Florida. University of Florida, Center for Wetlands,
Gainesville. December 1975.
30. Lindsley, D., T. Schuck, and F. Stearns. Productivity and
Nutrient Content of Emergent Macrophytes in Two Wisconsin Marshes.
In: Proceedings of the National Symposium on Freshwater Wetlands
and Sewage Effluent Disposal, University of Michigan, Ann Arbor.
May 1976. pp 51-77.
31. Demirjian, Y.A. Land Treatment of Municipal Wastewater Effluents,
Muskegon County Wastewater System. Environmental Protection Agency,
Technology Transfer. 1975.
32. Reed, S.C., et al. Pretreatment Requirements for Land Application
of Wastewaters. Extended Abstract for ASCE 2nd National Conference
on Environmental Engineering Research, Development and Design,
University of Florida. 1975.
33. Crites, R.W. and A. Uiga. Evaluation of Relative Health Factors
for Wastewater Treatment Processes. Environmental Protection
Agency. Office of Water Program Operations. EPA 430/9-77-003.
June 1977.
34. Thomas, R.E., K. Jackson, and L. Penrod. Feasibility of Overland
Flow for Treatment of Raw Domestic Wastewater. Environmental
Protection Agency, Office of Research and Development. EPA-660/2-
74-087. July 1974.
35. Gilde, L.C. Land Application Systems of Food Processing Waters.
In: Proceedings of the Sprinkler Irrigation Association, Annual
Technical Conference, Atlanta, February 23-25, 1975. pp 176-195.
36. Pretreatment of Pollutants Introduced Into Publicly Owned Treatment
Works. Environmental Protection Agency, Office of Water Program
Operations. October 1973.
5-104
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37. Schaub, S.A., et al. Land Application of Wastewater: The Fate of
Viruses, Bacteria, and Heavy Metals at a Rapid Infiltration Site.
U.S. Army Medical Bioengineering Research and Development
Laboratory. Fort Detrick, Md. May 1975.
38. Whiting, D.M. Use of Climatic Data in Estimating Storage Days for
Soil Treatment Systems. Environmental Protection Agency, Office
of Research and Development. EPA-IAG-D5-F694. 1976.
39. Whiting, D.M. Use of Climatic Data in Design of Soil Treatment
Systems. EPA-660/2-75-018. Environmental Protection Agency,
Office of Research and Development. July 1975.
40. Palmer, W.C. Meteorological Drought, Research Paper No. 45. U.S.
Department of Commerce, Weather Bureau, Washington, D.C. February
1965. 58p.
41. Pound, C.E., R.W. Crites, and D.A. Griffes. Land Treatment of
Municipal Wastewater Effluents, Design Factors-I. Environmental
Protection Agency, Technology Transfer. October 1975.
42. Hagan, R.M., H.R. Haise, and T.W. Edminster. Irrigation of
Agricultural Lands. Agronomy Series No. 11. Madison, American
Society of Agronomy. 1967.
43, Vegetative Water Use in California, 1974. Bulletin No. 113-3,
State of California Department of Water Resources. April 1975.
44. Booher, L.J. ana G.V. Ferry. Estimated Consumptive Use and
Irrigation Requirements of Various Crops. University of California
Agricultural Extension Service, Bakersfield, Ca. March 10, 1970.
45. Statutes ana Regulations Pertaining to Supervision of Dams and
Reservoirs. State of California Department of Water Resources,
Division of Safety of Dams, Rev. 1974.
46, U.S. Department of the Interior, Bureau of Reclamation. Design of
Small Dams. Second Edition, 1973. U.S. Government Printing
Office.
47. Booher, L.J. Surface Irrigation. FAO Agricultural Development
Paper No. 95. Food and Agricultural Organization of the United
Nations. Rome. 1974.
48. Lawrence, G.A. Furrow Irrigation. Leaflet No. 344. U.S.
Department of Agriculture, Soil Conservation Service. December
1953.
49. McCulloch, A.W. et al. Lockwood-Ames Irrigation Handbook. W.R.
Ames Company, Gering, 1973.
5-105
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50. Merriam, J.L. Irrigation System Evaluation and Improvement.
California State Polytechnic College. Blake Printery, San Luis
Obispo, August 1968.
51. Border Irrigation. Irrigation, Chapter 4. SCS National Engineering
Handbook, Section 15. US Department of Agriculture, Soil
Conservation Service. August 1974.
52. Bouwer, H. Infiltration-Percolation Systems. In: Land Application
of Wastewater. Proceedings of a Research Symposium Sponsored by the
USEPA, Region III, Newark, Delaware, November 1974. pp 85-92.
53. Bouwer, H., R.C. Rice, and E.D. Escarcega. High-Rate Land
Treatment I: Infiltration and Hydraulic Aspects of the Flushing
Meadow Project. Jour. WPCF. 46:834-843, May 1974.
54. C.W. Thornthwaite Associates. An Evaluation of Cannery Waste
Disposal of Overland Flow Spray Irrigation. Publications in
Climatology, 22, No. 2. September 1969.
55. Pillsburg, A.F. Concrete Pipe for Irrigation. Circular 418,
University of California College of Agriculture. November 1952.
56. Hart, W.E. Irrigation System Design. Colorado State University,
Department of Agricultural Engineering. Fort Collins, Colorado.
November 10, 1975.
57. Turner, J.H. and C.L. Anderson, Planning for an Irrigation System.
American Association for Vocational Instructional Materials in
Cooperation with the U.S. Department of Agriculture, Soil
Conservation Service. Athens, June 1971.
58. Norum, E.M. Design and Operation of Spray Irrigation Facilities.
In: Land Treatment and Disposal of Municipal and Industrial
Wastewater, Sanks, R.L. and T. Asano (ed.). Ann Arbor, Ann Arbor
Science. 1976. pp 251-288.
59. Sprinkler Irrigation. Irrigation, Chapter 11. SCS National
Engineering Handbook, Section 15. U.S. Department of Agriculture,
Soil Conservation Service. July 1968.
60. Skaggs, R.W. A Water Management Model for High Water Table Soils.
(Presented at the 1975 Winter Meeting, American Society of
Agricultural Engineers, Chicago, 111. December 15-18, 1975.)
61. Skaggs, R.W. Evaluation of Drainage-Water Table Control Systems
Using a Water Management Model (Presented at the Third National
Drainage Symposium, Chicago, 111. December 13-13, 1976.)
62. Luthin, J.N. (ed.). Drainage of Agricultural Lands. Madison,
American Society of Agronomy. 1957.
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63. Drainage of Agricultural Land. A Practical Handbook for the
Planning, Design, Construction, and Maintenance of Agricultural
Drainage Systems. U. S. Department of Agriculture, Soil
Conservation Service. October 1972.
64. Bouwer, H. Ground Water Recharge Design for Renovating Waste Water.
J. San. Eng., ASCE, 96:No.(1):59-73. February 1970.
65. Houston, C.E. and R.O. Schade. Irrigation Return-Water Systems.
Circular No. 542, University of California Division of Agricultural
Sciences. November 1966.
66. Thomas, R.E., J.P. Law, Jr., and C.C. Harlin, Jr. Hydrology of
Spray-Runoff Wastewater Treatment. Journal of the Irrigation and
Drainage Division, Proceedings of the ASCE. 96(3):289-298,
September 1970.
67. Stone, J.E. Role of Vegetative Cover. In: Land Application of
Wastes - An Educational Program, Cornell University, May 1976.
68. Hart, R.H. Crop Selection and Management. In: Factors Involved in
Land Application of Agricultural and Municipal Wastes. US
Department of Agriculture, Agricultural Research Service,
Beltsville, MD. July 1974. pp 178-200.
69. Soil-PIant-Water Relationship. Irrigation, Chapter 1. SCS National
Engineering Handbook, Section 15. U.S. Department of Agriculture,
Soil Conservation Service. March 1964.
70. , A Guide to Planning and Designing Effluent Irrigation Disposal
i Systems in Missouri. University of Missouri Extension Division.
March 1973.
71. Palazzo, A.J. Land Application of Wastewater - Forage Growth and
Utilization of Applied N,P,K. Corps of Engineers, U.S. Army Cold
Regions Research and Engineering Laboratory. Hanover, N.H. April
1976. 15 p.
72. Johnson, R.D., R.L. Jones, T.D. Hinesly, and D.J. David.
Selected Chemical Characteristics of Soils, Forages, and Drainage
Water from the Sewage Farm Serving Melbourne, Australia. US Army
Corps of Engineers, January 1974.
73. Sopper, W.E. and L.T. Kardos. Vegetation Responses to Irrigation
with Treated Municipal Wastewater. In: Recycling Treated Municipal
Wastewater and Sludge through Forest and Cropland. Sopper, W.E.
and L.T. Kardos, (ed.). University Park, The Pennsylvania State
University Press. 1973. pp 271-294.
74.
Kardos, L.T. ana J.E. Hook. Phosphorus Balance in Sewage Effluent
Treated Soils. Journal of Environmental Quality. 5(1):87-90,
January-March 1976.
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75.
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Overman, A.R., and A. Ngu. Growth Response and Nutrient Uptake by
Forage Crops Under Effluent Irrigation. Commun. Soil Science and
Plant Analysis. 6:81-93, 1975.
Chapman, H.D. and P.P. Pratt. Methods of Analysis for Soils,
Plants, and Waters. University of California, Division of
Agricultural Sciences. 1961.
Ayers, R.S. and D.W. Westcot. Water
Food and Agriculture Organization of the
Drainage Paper No. 29. Rome. 1976.
Quality for Agriculture.
United Nations. Irrigation
Western Fertilizer Handbook. Soil
Fertilizer Assoc. The Interstate
Danville, 111. 1975. 250 p.
Sutton, D.L. and W.H. Ornes.
Sewage Effluent Using Duckweed.
4(3):367-370, July-September 1975.
Improvement Committee, California
Printers and Publishers, Inc.
Phosphorus Removal from Static
Journal of Environmental Quality.
Kozlowski, T.
Plant water
1968.
T. (ed). Water Deficit and Plant Growth, Vol. II:
Consumption and Response. New York, Academic Press.
Kardos, L.T., W.E. Sopper, E.A. Myers, R.R. Parizek, and J.B.
Nesbitt. Renovation of Secondary Effluent for Reuse as a Water
Resource. Environmental Protection Agency, Office of Research and
Development. EPA-660/2-74-016. February 1974.
Sutherland, J.C. et al. Irrigation of Trees and Crops with Sewage
Stabilization Pond Effluent in Southern Michigan. In: Wastewater
Use in the Prediction of Food and Fiber, EPA-660/2-74-041. June
1974. pp 295-315.
Sopper, W.E. and L.T. Kardos. Vegetation Responses to Irrigation
with Treated Municipal Wastewater. In: Recycling Treated Municipal
Wastewater and Sludge through Forest and Cropland. Sopper, W.E.
and L.T. Kardos, (ed.). University Park, The Pennsylvania State
University Press. 1973. pp 271-294.
Cole, D.W., et al. A Study of the Interaction of Wastewater With
Terrestial Ecosystems. Second Annual Report to the U.S. Army Corps
of Engineers. Draft. 1976.
Alverson, J.E. Wastewater Irrigation and Forests.
6, No. 4:29-36, 1975.
Water Spectrum,
Murphey, W.K., R.L. Brisbin, W.J. Young,
Anatomical and Physical Properties of Red Oak
Irrigated with Municipal Wastewater.
Municipal Wastewater and Sludge through
Sopper, W.E. and L.T. Kardos, (ed.).
Pennsylvania State University Press. 1973.
and B.E. Cutter.
and ana Red Pine
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Forest and Cropland.
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87. Alich, J.A., Jr. and R.E. Inman. Effective Utilization of Solar
Energy to Produce a Clean Fuel. Stanford Research Institute, Menlo
Park, Calif. Project 2643. Final Report. June 1974.
88. Spangler, F.L., W.E. Sloey, and C.W. Fetter, Jr. Wastewater
Treatment by Natural and Artificial Marshes, University of
Wisconsin. Oshkosh, Wisconsin. EPA-600/2-76-207. September 1976.
89. Wolverton, B.C. Water Hyacinths for Removal of Cadmium and Nickel
from Polluted Waters. NASA Technical Memorandum, TM-X-72721. Bay
St. Louis, MI February 1975.
90. Wolverton, B.C. and R.C. McDonald. Water Hyacinths for Upgrading
Sewage Lagoons to Meet Advanced Wastewater Treatment Standards, Part
1. NASA Technical Memorandum TM-X-72729. Bay St. Louis, Miss.
October 1975.
91. Farnham, R.S. and D.H. Boelter. Minnesota's Peat Resources:
Their Characteristics and Use in Sewage Treatment, Agriculture, and
Energy. In: Proceedings of the National Symposium on Freshwater
Wetlands and Sewage Effluent Disposal. University of Michigan. Ann
Arbor, May 1976. pp 241-256.
92. Morris, C.E. and W.J. Jewell. Regulations and Guidelines for Land
Application of Wastes. In: Land as a Waste Management Alternative.
Loehr, R.C. (ed.) Ann Arbor, Ann Arbor Science. 1977. pp 63-78.
93. Klausner, S.D. Crop Selection and Management. In: Land
Application of Wastes - An Educational Program, Cornell University,
May 1976.
94. Christensen, L.A., L.J. Conner, and L.W. Liddy. An Economic
Analysis of the Utilization of Municipal Waste Water for Crop
Production. Department of Agricultural Economics, Michigan State
University, East Lansing. Report No. 292. US Department of
Agriculture, Economic Research Service, Natural Resource Economics
Division. November 1975. 40 p.
95. Seabrook, B.L. Land Application of Wastewater in Australia.
Environmental Protection Agency, Office of Water Programs.
EPA-430/9-75-017. May 1975.
96. Parizek, R.R. Site Selection Criteria for Wastewater Disposal
Soils and Hydrogeologic Considerations. In: Recycling Treated
Municipal Wastewater and Sludge through Forest and Cropland.
Sopper, W.E. and L.T. Kardos, (ed.). University Park, The
Pennsylvania State University Press. 1973. pp 95-147.
97. Powell, G.M. Design Seminar for Land Treatment of Municipal
Wastewater Effluents. EPA Technology Transfer Program. (Presented
at Technology Transfer Seminar. 1975.) 75 p.-
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93. Blakeslee, P.A. Monitoring Considerations for Municipal Wastewater
Effluent and Sludge Application to the Land. In: Proceedings of
the Joint Conference on Recycling Municipal Sludges and Effluents on
Land, Champaign, University of Illinois, July 1973. pp 183-198.
99. Branson, R. L. Soluble Salts, Exchangeable Sodium, and Boron in
Soils. In: Soil and Plant-Tissue Testing in California.
University of California, Division of Agricultural Sciences.
Bulletin 1879. April 1976. pp 42-48.
100. Walsh, L.M. and J.D. Beaton, (eds.). Soil Testing and Plant
Analysis. Madison, Soil Science Society of America. 1973.
101. Melsted, S.W. Soil-Plant Relationships (Some Practical
Considerations in Waste Management). In: Proceedings of the Joint
Conference on Recycling Municipal Sludges and Effluents on Land,
Champaign, Univeristy of Illinois, July 1973. pp 121-128.
102. Land Leveling. Irrigation, Chapter 11. SCS National Engineering
Handbook, Section 15. U.S. Department of Agriculture, Soil
Conservation Service. November 1961.
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CHAPTER 6
SMALL SYSTEMS
6.1 General Considerations
According to a 1973 survey, 54%, of the land treatment systems were less
than 1.0 Mgal/d (43.8 L/s) LU. While the design principles of land
treatment are the same for all sizes of systems, the approach should
consider a system that is compatible with community resources, design
and operational complexity, and possible environmental impact. The
criteria presented 'in this chapter are principally intended for systems
with a daily wastewater flow of 0.2 Mgal/d (8.8 L/s) or less but in some
cases may be used for intermediate systems with flows from 0.2 to 1.0
Mgal/d (8.8 to 43.8 L/s). For treatment systems with flows greater than
1.0 Mgal/d (43.8 L/s), the additional design details presented in
Chapter 5 should be considered. Sources for cost data are described in
Chapter 3.
Small systems generally do not have full-time operators, so a design
that requires a few days of field operator time per week or a few hours
each day is desirable. In recognition of this, a small system may be
designed somewhat conservatively, and hence should be less affected by
climatic and wastewater variations than larger systems. Further, a
conservative approach to design is often necessary because actual field
data can be quite limited. If, for example, there is a range of soil
permeabilities, the lower values should be selected for design. The
capabilities of the system or the operators will generally not be
sufficient to take advantage of varying site conditions to minimize
costs. The type of information typically required for the design of a
small system and sources of information are presented in Table 6-1.
6.2 Design Procedures
The design procedure for small systems follows a sequence of events as
presented in Figure 6-1. The necessary information to complete each
step is presented in the following sections.
6.2.1 Wastewater Characteristics and Flows
The determination of wastewater characteristics and flows is the initial
design step. For existing treatment systems, the preferred method is to
measure actual flows and.wastewater characteristics. For systems under
planning or construction, an estimate of important wastewater
characteristics can be made with the aid of Table 6-2, using medium
strength values for average domestic/commercial conditions. The strong
6-1
-------
values would apply for new systems with low water use and some minor
industrial wastewater contributions. Weak values would be more
applicable to systems where an older collection system with little or no
industrial wastewaters and where infiltrating water results in dilution
of the wastewater strength.
TABLE 6-1
TYPES AND SOURCES OF DATA REQUIRED FOR
LAND TREATMENT DESIGNS
Type of data
Principal source
Wastewater data
Soil type and permeability
Temperature (mean monthly
and growing season)
Precipitation (mean
monthly, maximum monthly)
Evapotranspiration and
evaporation (mean monthly)
Land use
Zoning
Agricultural practices
Surface and groundwater
discharge requirements
Groundwater (depth
and quality)
Local wastewater authorities
SCS soil survey
SCS soil survey, NOAA, local
airports, newspapers
SCS soil survey, NOAA, local
airports, newspapers
SCS soil survey, NOAA, local
airports, newspapers, agricultural
extension service
SCS soil survey, aerial photos from
the Agricultural Stabilization and
Conservation Service, and county
assessors' plats
Community planning agency, city or
county zoning maps
SCS soil survey, agricultural
extension service, county agents
State or EPA
State water agency, USGS, driller's
logs of nearby wells
Another source of dilution may be cooling waters and other low strength
discharges from local industries. Special attention should be given to
wastewater from nonhousehold sources that may contain constituents
significantly different than those in Table 6-2. Characterization of
nonhousehold wastewater should be made from field sampling, measurements
at existing facilities, at some other similar facility, or from
published values L.2]. Significant amounts of nonhousehold wastewater
may require additional design consideration from that given in this
chapter.
6-2
-------
FIGURE 6-1
SMALL SYSTEM DESIGN PROCEDURE
I
co
CHARACTERIZE
WASTEWATER
QUALITY &
QUANTITY
6.2.1
DETERMINE
SURFACE AND
GROUNDWATER
DISCHARGE
REQUIREMENTS
LOCATE
AVAILABLE
SITES
6.2.2.
CHARACTERIZE
SITES BASED
ON SOILS AND
OTHER FEATURES
6.2.3
EVALUATE AND
SELECT UNIT
PROCESS AND
CORRESPONDING
APPLICATION
AREA
6.2.4
DETERMINE
PREAPPLICATIQN
TREATMENT
STORAGE AND
METHOD OF
APPLICATION
6.2.5
6.2.6
6.2.7
FACILITIES
DESIGN
6.3
-------
TABLE 6-2
IMPORTANT COMPONENTS OF DOMESTIC WASTEWATER [3J
mg/L
Concentration
Strong Medium Weak
BOD5, 20°C 300 200 TOO
Suspended solids 350 200 TOO
Nitrogen as N
Organic 35 15 8
Free ammonia 50 25 12
Nitrates _0 _0 _0
Total 85 40 20
Phosphorus as P
Organic 532
Inorganic 15 7 4
Total 20 10 6
The annual volume of wastewater will be used to estimate the application
area. Due to the extremely variable nature, wastewater flows are best
determined from field measurement. In cases where this is not possible,
an estimate can be made from available data using a per capita or
fixture basis |_4]. The per capita basis is generally preferred.
Typical flows from recreational facilities and institutional facilities
are presented in Tables 6-3 and 6-4. A common value used to estimate
daily wastewater flows is 75 gal/capita (284 L/capita) with a peaking
factor of 4.0 for the peak flow L5J. Seasonal variations in flow should
be considered in the estimate of annual wastewater volume and in
discharge requirements.
6.2.2 Locate Available Sites
Identification of sites for small systems is usually much less
complicated than that for larger systems. The search begins at the
point of wastewater collection and radiates outward until one or more
potentially suitable sites have been located. These sites may be
identified by the following desirable features:
1. Fairly large tracts of undeveloped land or farms under a
single ownership.
2. Land that is now or has been farmed, or is forested.
6-4
-------
TABLE 6-3
DESIGN UNIT WASTEWATER FLOWS FOR RECREATIONAL
FACILITIES, YELLOWSTONE NATIONAL PARK [3]
Establishment
Campground (developed)
Lodge or cabins
Hotel
Trailer village
Dormitory, bunkhouse
Residence homes, apartments
Mess hall
Offices and stores
Visitor centers
Cafeteria
Dining room
Coffee shop
Cocktail lounge
Laundromat
Gas station
Fish-cleaning station
Unit
Person
Person
Person
Person
Person
Person
Person
Employee
Visitor
Table seat
Table seat
Counter seat
Seat
Washing machine
Station
Station
Unit flow, gal/d
25
50
75
35
50
75
15
25
5
150
150
250
20
500
2 000-5 000
7 500
TABLE 6-4
AVERAGE WASTEWATER FLOWS FROM
INSTITUTIONAL FACILITIES L3J
Institution
Medical hospital
Mental hospital
Prisons
High schools
Elementary schools
Avg flow, gal /capita
175
125
175
20
10
1 gal/capita = 3.78 L/capita
3. Location is relatively near point of wastewater collection.
4. Groundwater is more than 10 ft (3 m) deep or there is a nearby
water body that could be used to receive the underdrainage
needed to lower the water table and to receive the percolated
effluent.
6-5
-------
5. Land that is already for sale or that can be bought with
reasonable negotiations.
6. Zoning that is compatible with land treatment facilities
requirements, such as areas zoned for greenbelts.
7. Existing irrigated lands (e.g., golf courses, parks, highway
landscaping).
8. Access from developed roads and power supply.
At this point in the site investigations neither the land treatment
process nor the total land area is known. In order to make some initial
assessment of the sites, some preliminary estimate of area is needed.
Guidelines to land area needs for preliminary site identification are
provided in Table 6-5. These values are for screening purposes only and
must be refined as the study progresses.
TABLE 6-5
TOTAL LAND AREA GUIDELINES FOR
PRELIMINARY SITE IDENTIFICATION
Land area, acres
Slow rate
Rapid infiltration Overland flow
flow, gal/d
100 000
200 000
300 000
500 000
750 000
1 000.000
6 mo/yr
15-30
30-50
40-80
60-150
100-200
150-300
12 mo/yr
7.5-20
15-40
20-60
30-100
50-150
75-200
12 mo/yr
0.5-6
1-12
1.5-20
2.5-30
4-45
5-60
10.5 mo/yr
3-10
5-20
10-30
15-50
25-75
35-100
100 000 gal/d = 4.38 L/s
1 acre = 0.405 ha
6.2.3 Site Characterization
Having identified the potential sites, the next step is to
systematically describe the site characteristics. These characteristics
and the required effluent quality requirements will combine to suggest
the type of land treatment process that should be.used.
6-6
-------
Site characteristics that should be noted Include the following:
1 Soils—type, distribution^ permeability of most restrictive
layers, physical and chemical characteristics, and depth to
groundwater
2. Available land area, both gross and net areas (i.e., excluding
roads, rights-of-way encroachments, stream channels, and
unusable soils)
3. Distance from source of wastewater to site, including
elevation differential
4. Topography, including relief and slopes
5. Proximity of site to industrial, commercial, residential
developments; surface water streams; potable water wells;
public use areas such as parks, cemeteries, or wildlife
sanctuaries
6. Present and future land uses
7. Present vegetative cover
6.2.4 Select Land Treatment Process
The selection of the appropriate unit process depends primarily on the
following two conditions:
1. Soil characteristics at the prospective site
2. The requirements of the discharge permit or groundwater
quality
Obviously, other conditions such as other site features, total land
area, operating personnel, and related economic and environmental
factors, combine to help form the final conclusion. A decision matrix
for forming preliminary conclusions on the land treatment process based
on technical considerations only is presented in Table 6-6. Other
related conditions can then be used to finalize the decision.
The preferred land treatment options for small systems are, in order:
slow rate, rapid infiltration, and overland flow. Other treatment
processes have been used to treat wastewater in research and
demonstration projects but applicable design criteria are not generally
available. Slow rate systems are the first design choice because of the
similarity to normal agricultural practices, and their performance is
the least sensitive to operational changes so that treatment reliability
under variable conditions is greatest. Rapid infiltration systems are
6-7
-------
TABLE 6-6
PRELIMINARY SELECTION OF LAND
TREATMENT SYSTEMS
Levels of effluent
quality (NPDES
permit), mg/L
Range of soil permeability, in./h
iBOD = 10
*SS = 10
*N =3
£P =5
No surface
discharge3
<0.06
0.06-0.2 0.2-0.6 0.6-2.0 2.0-6.0
6.0-20.0
>20.0
SBOD = 4
*ss = 2
iN 4
SP 0.1
SBOD 5
SSS 5
iN 15
iP 1
Slow rate Slow rate Slow rate Slow rate
Rapid
infiltration
Rapid Rapid
infiltration infiltration
Overland Overland
flow flow
Slow rate Slow rate Slow rate Slow rate
Slow rate
Slow rate
Rapid Rapid Rapid
Infiltration Infiltration Infiltration
a. Discharge to groundwater or indirect discharge to surface water.
1 in./h = 2.54 cm/h
the second choice in small scale systems because removals of most
wastewater components are excellent with low operation and maintenance
requirements. A consistent level of nitrogen removal, however, is more
difficult to obtain than with other systems. In some groundwater
aquifers nitrogen content is of little concern, greatly enhancing the
use of rapid infiltration systems. Overland flow systems require the
greatest level of on-site management to maintain high levels of
treatment so extra operator training is required, particularly for
proper maintenance of the terraces.
After selecting the unit process, the required "wetted" or application
land area can be computed. In general, this calculation requires
development of the hydraulic application rate and the duration of
application during the year. It also requires consideration of
additional applied water in the form of precipitation and the lost water
due to percolation and evapotranspiration. This computation is usually
combined with a water balance computation for determining storage
requirements. For each treatment system this procedure is somewhat
different. Therefore, computations of wetted land area are discussed
separately for each process and summarized in Table 6-7.
6-8
-------
TABLE 6-7
SUMMARY OF APPLICATION PERIODS FOR LAND TREATMENT SYSTEMS
Unit process
management
Appl ication
Description Estimated period
Slow rate Annual crop Growing season only 3-5 months
Double crop All year unless restricted 6-12 months3 (also
or perennials by weather or planting • see Figure 6-2)
and harvesting
Rapid NA
infiltration
Overland
flow
Perennial
grasses
All year-round, if in free 12 months
draining materials
All year unless restricted See Figure 6-2
by weather
NA = not applicable.
a. This period is maximum in semiarid areas. The lower values should
be used where winters are severe.
6.2.4.1 Application Area For Slow Rate Systems
The application area
application rate and
permeability
determine a
requirements
Table 6-8.
for slow rate systems is based on a weekly
the length of the application season. The
of the predominant soil types combined with crop water use
weekly application rate, as shown in Table 6-8. Water use
of most crops will be met using the rates presented in
TABLE 6-8
DESIGN APPLICATION RATES FOR SMALL SYSTEMS
Application rate, in./wk
SCS permeability
class
Very slow
Slow
Moderately slow
Moderate
Moderately rapid
Rapid
Very rapid
SCS permeability
range, in./h
<0.06
0.06-0.2
0.2-0.6
0.6-2.0
2.0-6.0
6.0-20
>20
Slow rate3
0.5-1.0
1.0-1.5
1.5-3.0
3.0-4.0
4.0
a. Application during growing season.
b. Year-round application
c. Volume applied equally during 5 to. 7 days pe
Rapid Overland
infiltration'' flowc
4-20
8-30
12-40
r week; low value
4-8
4-8
for
screened effluent and higher rates for primary and biological treat-
ment effluent.
1 in./wk = 2.54 cm/wk
6-9
-------
The length of the application season should be computed on the basis of
intended management. Two management techniques are commonly practiced:
1. Grow a single, annual crop
2. Grow perennial forage grasses, practice double-cropping, or
use the no- till management system
For a single annual crop, the application period will be the growing
season plus any preplanting or after harvest irrigation and could result
in an application period as short as 3 months. For this reason, the
second management technique is generally used.
For the second case, the application season is determined from climatic
data given in a county soil survey or other local source, for the
proposed vegetation. The mean growing season, i.e., the number of weeks
between the last 32UF (0"C) occurrence in the spring and the first 32°F
(0UC) occurrence in the fall, is used for all annual crops. Typical
annual crops used in the United States with land treatment systems are
corn, wheat, barley, cotton, and soybeans. To extend the application
period for annual crops, they may be double-cropped, or winter or spring
cover crops may be planted after harvesting. Perennial crops are
typically forage grasses such as Bermuda grass, orchard grass, tall
fescue, Reed canary grass, and alfalfa. Wastewater can be applied
between occurrences of 26°F (-3.3°C) temperatures in the spring and
fall. The application period should be reduced by 30 to 45 days to
allow for planting (annual crops only) and harvesting periods. The
annual application volume is determined by multiplying the weekly rates
from Table 6-8 by the length of the application season in weeks. The
annual application rate determines the required application area
according to the following equation:
where F = field area, acres (ha) 3
Q = annual flow, Mgal/yr (m /yr)
L = period of application wk/yr
R = rate of application, in./wk (cm/wk)
36.8 (0.01) = conversion factor = 3.06 a^re7ft x 12 in'
Mgal n ft
6-10
-------
6.2.4.2 Application Area For Rapid Infiltration Systems
Where application of wastewater to an infiltration basin is by flooding,
the period of application is the entire year. An exception may occur
under one of the following conditions:
1. The soil is fine textured or not free draining so freezing of
water within the soil pores renders it impermeable.
2. The water is applied by sprinkler methods, and the droplets
freeze and coat the surface with ice.
3. There is a severe low temperature resulting in freezing of
water in the distribution piping or as it exits.
Although some provision is recommended for storage to account for one of
the above events, the application period can be assumed as 12 months.
The application rate can be selected from Table 6-8 based on soil
permeability. Then, using Equation 6-1 and an application period of 52
weeks, the application area can be computed.
6.2.4.3 Application Area For Overland Flow Systems
This process requires an effluent discharge to either a surface water
body or another unit process. Consequently, application rates are not
dependent on soil permeability but rather on biological activity.
Experience has indicated that an application rate of 4 in./wk (10 cm/wk)
will easily match biological activity on the prepared slopes.
The application period is usually.determined by climatic conditions.
These conditions are similar to those for perennial grasses with slow
rate systems. In general, Figure 6-2 can be used to estimate the number
of days that overland flow cannot operate. Subtracting this period in
weeks from 52 wk/yr will result in the application period. Using
Equation 6-1, the wetted area can be computed.
6.2.5 Preapplication Treatment
Preapplication treatment is desirable for small scale systems to control
nuisance and odor conditions during storage with slow rate and overland
flow systems, and to lessen bed maintenance on rapid infiltration
systems. Biological treatment is often employed with many forms of land
treatment but may be avoided with overland flow. Also, rapid
infiltration may be used with only primary level treatment but the
application rate must be reduced somewhat over that of secondary level
because of the clogging effect of suspended solids. The use of primary
6-11
-------
FIGURE 6-2
ESTIMATED WASTEWATER STORAGE DAYS BASED ONLY ON CLIMATIC FACTORS [6]
SHADING DENOTES REGIONS WHERE
THE PRINCIPAL CLIMATIC CONSTRAINT
TO APPLICATION OF WASTEWATER
IS PROLONGED WET SPELLS
i eo
BASED ON 32°F (0°C)
MEAN TEMPERATURE
0.5 in./d PRECIPITATION,
t in. OF SNOWCOVER
1 i n.= 2.54 en
-------
effluent is recommended, but if land area is limited it may be necessary
to provide a higher level of preapplication treatment. A suggested
guide to the selection of preapplication treatment levels for each land
treatment process is presented in Table 6-9.
TABLE 6-9
MINIMUM PREAPPLICATION TREATMENT PRACTICE
Process
Preapplication treatment
Slow rate
Surface application
Sprinkler application
Rapid infiltration
Overland flow
Primary sedimentation
Primary or biological3
Primary
Bar screens and
comminution
a. Typically oxidation ponds or aerated lagoons.
6.2.6 Storage Requirements
Storage volume estimates must include consideration of the total water
balance for the year. However, the designer can approximate this
storage by referring to Figure 6-2 and selecting the proper values for
the geographical location in question. The values taken from the figure
represent days of storage for the worst year in 20, based on severity of
winter conditions. Storage requirements may be further reduced by sea-
sonal discharges to surface waters if permitted by the state. Storage
volume guidelines are summarized in Table 6-10.
TABLE 6-10
GUIDELINES FOR STORAGE VOLUMES
Land treatment
process
Storage volume guidelines
Slow rate
Annual crops
Perennial crops
Rapid infiltration
Overland flow
Up to 9 months of flow
0.5-6 months of flow, see Figure 6-2
7-30 days of flow
See Figure 6-2
6-13
-------
6.2.7 Selection of Application Systems
In preliminary design for slow rate, the method of applying the water
must be decided. Surface application is preferred where the site
topography is quite flat or is suitable for application with a minimum
amount of leveling. This method of application offers the least capital
cost and the least operation and maintenance cost for most systems.
Also, there should be no problems with aerosol transport or need for
buffer zones.
Sprinkler application may be used for almost any topography, but
preferably one having slopes of less than 15% to minimize difficulties
with effluent runoff and erosion control. For small systems, the use of
surface application systems is preferred for both rapid infiltration and
overland flow treatment.
6.2.8 Postapplication Treatment
In those cases where effluent is collected for discharge to surface
waters, discharge requirements must be met. Systems with overland flow
may require postdisinfection: Disinfection may be accomplished using
hypochlorinators or, in some cases, an erosion feeder type of
chlorinator may be used. The latter units have not been widely accepted
but may offer suitable reliability for very small systems.
6.3 Facilities Design
As in other parts of this manual, no attempt will be made to discuss the
detailed design of preapplication treatment and storage facilities. The
discussion is limited to the distribution and application systems. In
addition to the comments contained in this chapter, the reader is
directed to Section 5.8 for detailed design guidance. Distribution and
application systems will be discussed for each land treatment process in
the following section.
6.3.1 Slow Rate System
A schematic diagram showing the typical elements of a slow rate system
is presented in Figure 6-3.
6.3.1.1 Surface Application Systems
Surface application systems require site-specific design, while
sprinkler system design should be based on consultation with the
6-14
-------
FIGURE 6-3
SCHEMATIC FOR TYPICAL SLOW RATE SYSTEM
0>
I
PRELIMINARY
SCREENING
PREAPPLI-
CATION
TREATMENT
STORAGE
SURFACE APPLICATION
TO GROUNDWATER OR RECOVERY
I
ALTE.RNATIVE
DISTRIBUTION
r SYSTEMS
DISINFECTION
I
SPRINKLER APPLICATION
L .
&%
A
\ rtK/F|I
I I I
TO GROUNDWATER OR RECOVERY
-------
equipment manufacturers. The general factors involved in the final
layout and design of a surface application system are presented in Table
6-11. Most of the common surface irrigation systems are included in
this table.
TABLE 6-11
FACTORS AFFECTING THE DESIGN OF SURFACE
IRRIGATION SYSTEMS [7]
Maximum
Level
Level border
Contour levee
Level furrow
Graded
Graded border
Contour ditch
Graded furrow
Corrugation
Contour furrow
Humi d
Nonsod
crops
Nearly
0.1
Nearly
0.5
NA
0.5
NA
areas
crops
level
0.1
level
2.0
4.0
NA
NA
Cross slope
3.0
3.0
slope.
Arid
Nonsod
crops
Nearly
0.1
Nearly
2.0
4.0
3.0
4.0
Cross
6.0
u.»__ . — I*..*; —
a reas
crops
level
0.1
level
4.0
15.0
NA
8.0
slope
6.0
ouc OHplllal.luH
family •- /k3
Mi n i mum
0.1
0.1
0.1
0.3
0.1
0.1
0.1
0.1
T ^
Maximum
2
0
2
2.
3.
3
1
2,
.0
.5
.0
.0
.0
.0
.5
.0
Shape of field
Any shape
Any shape
Rows should be
of equal length
Rectangular
Any shape
Rows should be
of equal length
Rectangular
Rows should be
of equal length
\ 1 uw Ul
bedded)
Yes
Yes
Yes
No
No
Yes
No
Yes
p tab e
. .
i o ,, urcnaras
or sodded ~~
crops
Yes
Yes
Yes
Yes
Yes
Yes
Yes
No
fliiu
vineyards
Yes
Yes
Yes
Yes
Yes
Yes
Yes
Yes
NA = not applicable.
a. Intake family is a grouping of soil by the SCS. It is based on the ability of the soil to take in the required
amount of water during the time 1t takes to irrigate.
1 in./h = 2.54 cm/h
The most desirable design is one in which the furrows or border checks
are so flat that failure to rotate the flow to the next field in the
system would not result in wastewater escaping the property.- In other
words, the field would be flat enough to permit an enclosing or
containment levee around the field. Alternative choices are tailwater
control systems or a gravity return to the lagoon at the lower end of
the site. If this is not possible, closer supervision of the operation
will be necessary to minimize the risk of nuisance conditions occurring.
Any of the common low head or gravity design pipe materials should be
suitable for transporting the wastewater to the field. Gated aluminum
pipe is an effective means of distributing the water uniformly to border
checks or furrows. Open concrete lined ditches with turnouts have been
used effectively with small systems.
6-16
-------
6.3.1.2 Sprinkler Application Systems
If a sprinkler irrigation system has been selected, the designer should
work closely with one or more sprinkler manufacturer's vendors who will
aid the designer in the use of their respective equipment. The
availability of a knowledgeable local representative may weigh heavily
in the final selection of equipment.
A list of most of the common types of sprinkler systems, guidelines for
their application, and limitations is presented in Table 6-12.
Additionally, some states have published regulations regarding
preapplication disinfection, minimum buffer areas, and control of public
access for sprinkler systems. These criteria should be reviewed for
applicability.
Distribution systems may consist of any of the common pressure pipe
materials, such as plastic, aluminum, asbestos-cement, tlined and coated
steel, or ductile iron.
The final design analysis should consider the following points:
1. Provision of adequate thrust blocks
2. Consideration of water hammer and surge conditions
3. Winter operation criteria
4. Provisions of sufficient valves and manifolding to permit
proper agricultural management of the field
5. Automatic timers to limit the application in any one area
6. Alarms to signal system failures
7. Protection against plugging by algae
6.3.2 Rapid Infiltration Systems
Small scale rapid infiltration systems typically apply an annual
application of 17 to 173 ft (5 to 53 m) of wastewater at rates of 4.0 to
40.0 in./wk (10 to 100 cm/wk). The application rate is determined from
soil permeability data. It is preferable to dig at least one test pit
(see Appendix F) and conduct three infiltration tests (see Appendix C).
Multiple infiltration basins are required to permit intermittent
application. A desirable basin design should provide sufficient
flexibility to permit a 1 to 4 day application period followed by a 7 to
14 day drying period.
6-17
-------
en
«l
CO
TABLE 6-12
FACTORS AFFECTING THE DESIGN OF SPRINKLER IRRIGATION SYSTEMS [7]
System
Multisprinkler
Hand moved
Portable set '
Solid set
Tractor moved
Skid mounted
Wheel mounted
Sel f moved
Side wheel roll
Side move
Self propelled
Center pivot
Side move
Single sprinkler
Hand moved
Tractor moved
.Skid mounted
Wheel mounted
Self propelled
Boom sprinkler
Tractor moved
Self propelled
Permanent
Maximum
slope, %
20
2.0
5-10
5-10
5-10
5-10
5-15
5-15
20
5-15
5-15
No limit
5
5
No limit
Water application
rate, in./h
Minimum
0.10
0.05
0.10
0.10
0.10
0.10
0.20
0.20
0.25
0.25
0.25
0.25
0.25
0.25
0.05
Maximum
2.0
2.0
2.0
2.0
2.0
2.0
1.0
1.0
2.0
2.0
2.0
1.0
1.0
1.0
2.0
Shape of field
Rectangular
Any shape
Rectangular
Rectangular
Rectangular
Rectangular
Circular
Square or
rectangular
Any shape
Any shape
Any shape
Rectangular
Any shape
Rectangular
Any shape
Field surface
conditions
No limit
No limit
Smooth enough for
safe tractor operation
Reasonably
smooth
Clear of obstructions,
path for towers
No limit
Safe operation
of tractor
Land for winch
and hose
Safe operation
of tractor
Lane for boom and hose
No limit
Maximum
height of
crop, ft
No limit
No limit
No limit
No limit
4
4-6
8-10
8-10
No limit
No limit
No limit
No limit
8-10
8-10
No limit
Size of
single
system, acres
1-40
1 +
20-40
20-40
20-80
20-80
40-160
80-160
20-40
20-40
20-40
40-100
20-40
40-100
1+
1 in./h = 2.54 cm/h
1 ft = 0.305 m
1 acre = 0.405 ha
-------
A typical rapid infiltration system is illustrated in Figure 6-4. The
layout is based on a relatively level land surface. Sloping lands
should utilize gravity flow to minimize pumping costs. Site layout
should locate the maximum bed dimension perpendicular to probable
groundwater flow. Steeper land would require smaller basins to minimize
cut and fill and to avoid cross-basin subflows according to the
following schedule: for 0 to 1% average cross-slope--! basin; 2%—Z
basins; 3%--4 basins. Slopes in excess of 3% should be graded to a 3%
average before final basin construction.
FIGURE 6-4
SCHEMATIC FOR TYPICAL
RAPID INFILTRATION SYSTEM
CONTAINMENT BERN
PREAPPLICATION
TREATMENT
EMERGENCY
STORAGE
SPLASH APRONS
#4
INFILTRATION
BASINS
Surface design details related to infiltration basins are similar to
those for sludge drying beds with care being taken to minimize severe
erosion at the point of application. Provision for access to the basin
should be included to permit entry of a tractor with a disk, harrow, or
other scarifying equipment. The need for underdrains should be
determined based on Appendix C and details for design are presented in
Chapter 5 (Sections 5.5.2 and 5.8).
6-19
-------
6.3.3 Overland Flow System
Although the preferred method of applying wastewater to the field is by
surface method, many industrial installations now exist with sprinkler
systems. The typical overland flow system, with alternative application
systems is illustrated in Figure 6-5. To provide the maximum treatment
efficiency, wastewater must be applied at least once a day and in
sufficient quantity to wet the entire terrace area.
A suggested method of supporting distribution piping is shown in Figure
6-6. In this case, the stone serves as a support, but it also serves as
a means to convert a point discharge into sheet flow, minimizing erosion
and maximizing treatment efficiency.
Where sprinklers are used, they should be placed downslope from the
highest point on the terrace a distance equal to the radius of the
sprinkler, unless one-half circle sprinklers are used.
Probably the most important feature of the overland flow system is the
sloped terrace. This slope must be as nearly equal to a plane surface
as possible and sloped in such a way as to prevent short-circuiting of
the wastewater and standing water in the collection ditches. No swales,
depressions, or gullies can be permitted; otherwise, water will pond and
permit propagation of mosquitos or the production of odors.
The second factor is the cover crop. Grasses must be selected for their
resistance to continuously wet root conditions. Also, their growth
should not be in clumps as this will result in the formation of rivulets
of flow rather than a uniform sheet flow. Common grasses for this
purpose have been Reed canary grass, Italian rye, red top, tall fescue,
and Bermuda grass.
The distribution system should be designed to permit application on each
portion of the field for from 6 to 12 h/d. This application period is
based on convenience rather than for treatment reasons. The system must
be valved and manifolded to permit a portion of the field to be taken
out of service for grass mowing and/or harvesting. During that period,
the remainder of the field must take the total flow or else it must be
diverted to temporary storage. Following prolonged shutdown, the
wastewater collected in the drainage ditches may have to be recirculated
through the treatment system until discharge requirements are again
being met. This would only be required where stringent discharge
requirements are imposed.
Site access requires special equipment with broad tires having low
pressure (less than 10 lb/in.2 or 7 N/cm2) to avoid creating ruts
6-20
-------
FIGURE 6-5
SCHEMATIC FOR TYPICAL OVERLAND FLOW SYSTEM
PROVIDE FOR RECIRCUUTION OF EFFLUENT
PRELIMINARY
SCREENING
PREAPPLI-
CATION
TREATMENT
FOLLOWING PROLONGED SHUTDOWN
STORAGE
SURFACE APPLICATION
J™kJUU1^^
DISTRI-
BUTION
PUMPING
ALTERNATIVE
DISTRIBUTION
SYSTEMS
COLLECTION.
DISINFECTION
(IF REQUIRED)
AND DISCHARGE
LOW PRESSURE
SPRINKLER APPLICATION
COLLECTION.
DISINFECTION
(IF REQUIRED)
AND DISCHARGE
-------
that would short-circuit the flow and the treatment process. Vegetation
harvest and removal is not always necessary, since the vegetation can be
cut with a chopping mower just prior to maturity (every 4 to 6 weeks)
and allowed to decompose on the terrace [8]. Applications should be re-
duced for 3 or 4 days after winter shutdowns.
FIGURE 6-6
BUBBLING ORIFICE DISTRIBUTION
FOR OVERLAND FLOW
3/4 in. OUTLETS AT 4 FOOT SPACING
ROTATE OR TWIST PIPE TO ADJUST FLOW DISTRIBUTION)
in. DIAMETER PIPE
LOCALLY AVAILABLE CRUSHED STONE
5/8 in. TO 1 1/2 in. GRADATION
DO«H SLOPE
SHEET FLOW
NOTE: 1
1
i n.= 2.54cm
ft =0.305 m
6.4 Small System Design Example*
6.4.1 Setting
The community of Angus, Washington, has decided to construct a land
treatment system to meet its wastewater discharge specifications. The
following information is known:
Present (1977) population - 2 234
Projected 1997 population - 3 400
Annual rainfall - 48 in. (120 cm), evenly distributed throughout the year
Warm season evaporation - 24 in. (60 cm), May 1 to October 1
Seasonal flow variations -
Maximum month (August) - 1.5 of average
Minimum month (January) - 0.8 of average
*Note: This is an example; it is intended for illustration only.
6-22
-------
There is an elementary school of about 200 pupils and 15 staff. The
high school is located in Hereford, about 10 miles (16 km) to the south.
There are some small commercial establishments such as service stations
and restaurants but the town's only industry, a sawmill, treats and
recycles its own wastewater. As the town is presently sewered by
individual systems, mostly septic tanks, a new collection system will be
constructed. Water service is unmetered and estimated consumption is
100 gal/capita-d (378 L/capita-d).
6.4.2 Wastewater Quality and Quantity
Assume: 1. Design for 1997 population
2. Projected pupil and staff population will be 325
3. Due to unmetered water system, waste is relatively high
and the wastewater will be of medium strength through the
planning period (BOD = 200 mg/L).
Wastewater quality can be found in Table 6-2, second column. The
flowrate for average design conditions, using an estimated daily
wastewater flow of 75 gal/capita (284 L/capita), is calculated to be:
325 (10) gal/capita-d + 3 400 (75) gal/capita-d
= 258 250 say 260 000 gal/d
6.4.3 Locate Available Sites
By interpolation of the values in Table 6-5 for a flowrate of 260 000
gal/d the following preliminary site areas were determined:
• Slow rate, 26 to 52 acres (10.5 to 21 ha)
• Rapid infiltration, 3 to 13 acres (1.2 to 5.3 ha)
• Overland flow, 9 to 27 acres (3.6 to 10.9 ha)
As there is sufficient open space and farmland in the immediate area, it
was decided to limit the search for available sites to a radius of 1
mile (1.6 km) from the lowest point in the collection system to minimize
transmission costs.
6.4.4 Site Characterization
After the search, four potential tracts were located, all about 0.5 mile
(0.8 km) from the designated point. The characteristics of the sites
are summarized in Table~~-6-13.
6-23
-------
TABLE 6-13
POTENTIAL LAND TREATMENT SITES FOR ANGUS, WASHINGTON
Range of soil Slope,
Site No. of Size, Minimum depth to permeabilities, average-
No, owners Current use3 acresb groundwater, ftc in./hd maximum, %d
Remarks
A
B
C
D
5 Agriculture
1 Undeveloped
land
1 Nonirrigated
pasture
2 Low density
housing
200
95
300
30
15
10
20
10
0.6-20
0.2-2.0
0.06-0.5
0.2-0.6
2-10
Flat
5-15
4-5
15 acres at
5-10 in./h
Potential
greenbelt
Low permeability
results in local
wet spots
One house zoned
residential
Sources: a. Local planning agency and site visit.
b. County assessor.
c. Well logs.
d. SCS report.
1 acre = 0.405 ha
1 ft = 0.305 m
1 in. = 2.54 cm
On the basis of acreage requirements, all sites except Site D would have
sufficient acreage for all systems. Site D would be marginal for a slow
rate system and would require additional soil testing if it is found to
be the most desirable location.
Sites A, B, and C appear to have area in excess of the anticipated
needs. The treatment site and facilities could be located in the most
desirable location within the site and not all of the land would have to
be purchased.
6.4.5 Select Land Treatment Process
Discharge would have to be either to the groundwater or to nearby White
River, downstream of the water supply intake line. The groundwater is
being used for some small irrigation wells near the sites and some
individual domestic wells 1 to 2 miles {1.6 to 3.2 km) away. It is
anticipated that Angus may some day use groundwater as well as the
surface supply to meet future water demands. Therefore, discharges to
the groundwater would have to meet existing requirements.
For discharge to White River, the Department of Ecology, State of
Washington, has stipulated the following effluent quality limitations:
BOD - 10 mg/L
SS - 10 mg/L
Total N - 15 mg/L
Total P - 5 mg/L
Fecal col i forms -
200/100 nt
Maximum residual chlorine - 0.5 mg/L
6-24
-------
Using Table 6-6, a slow rate or rapid infiltration system is applicable
to Site A. Sites B and C could have either a slow rate or overland flow
system, while a slow rate system appears to be the only choice for
Site D. As all systems are capable of meeting or exceeding the dis-
charge requirements, system selection (except for rapid infiltration)
will be based on the soil permeability ranges.
For rapid infiltration rates on Site A, limited field tests are needed.
Using the guidelines in Appendix F one test pit was dug down to 10 ft (3
m) to verify lack of restrictive layers in the soil profile. Using the
procedures from Appendix C (Section C.3.1.4.3) three double ring
infiltrometer tests were conducted. The resulting infiltration minimum
rate was determined to be 5.0 in./hr (12.7 cm/h). Using Figure 3-3, the
wastewater application rate is determined to be 42.0 in./wk (1.1 m/wk)
which is 5% of the clear water rate (the range in Figure 3-3 is 3 to
10%). However, an upper limit of 40.0 in./wk (1.0 m/wk) is recommended
for small rapid infiltration system design. Based on 52 wk/yr operation
the annual rate is 173 ft/yr (52.7 m/yr).
To compute the area required to treat the wastewater, Equation 6-1 is
used. In keeping with the conservative approach to small system design,
the lower permeability values are used to obtain the equivalent
application rate, R, from Table 6-8. Also, the average annual rainfall,
including a reduction for evapotranspiration (assuming a colder month),
is added to the rate of application R. As an example, a calculation to
derive the area required for a slow rate system at Site A is shown:
L = 46 weeks (52 for rapid infiltration - Figure 6-2)
R = SCS permeability range plus (precipitation-evapotranspiration)
= (1.5 + 0.5) in./wk = 2.0 in./wk (5.0 cm/wk)
Q = 0.26 Mgal/d x 365 = 94.9 Mgal/yr
F = 36* x '9 - 38 acres (15.4 ha)
The acreages calculated for each site and treatment process are shown in
Table 6-14.
TABLE 6-14
REQUIRED ACREAGES FOR ANGUS LAND TREATMENT SYSTEMS
Soil Application Treatment site
Site permeability, in./h rate, in./wk requirement, acres
A
B
C
Slow rate
Rapid infiltration
Slow rate
Overland flow
Slow rate
Overland flow
0.6
5.0
0.6
0.2
0.2
0.06
2.0
40.0
2.0
8.0
1.5
4.0
38
1.7
38
10
51
19
D Slow rate 0.2 1.5 51
1 in. = 2.54 cm
1 acre = 0.405 ha
6-25
-------
In comparing the required acreages with Table 6-13, Site D is eliminated
on the basis of insufficient area.
6.4.6 Preapplication Treatment, Storage, and Application Methods
Preapplication treatment practices for various systems are indicated in
Table 6-9. Unless surface application is selected for one of the slow
rate systems, biological treatment with a minimum of 7 days detention
time is normally practiced. This would most likely be an aerated lagoon
designed to reduce BOD,, to 60 mg/L or less.
From Figure 6-2, a storage of 40 days of flow is advised. The required
storage volume is as follows:
260 000 gal/d x 40 days = 10.4 Mgal = 32 acre-ft (39 500 m3)
Storage pond size, assuming 10 ft working depth (3 ft freeboard)
= 3.2 acres + 25% for levees, road = 4 acres (1.J5 ha)
This will be required for either the slow rate or overland flow systems.
The rapid infiltration system should not require any storage capacity
because of the moderate climate and permeable soils. The methods of
application for surface irrigation systems are summarized in Table 6-11
for various land conditions. By comparing the application rates from
the third column of Table 6-14 and the average to maximum slopes from
Table 6-13 to the values given in Table 6-11, the following surface
application methods are chosen:
Site A - Graded border with any crop (minimum slope)
- Graded contour levee with sod crops (for maximum slopes)
Site B - Level border checks with any crop
Site C - Graded contour levee with sod crops
As the land preparation costs for Sites A and C would raise the
development cost beyond that required for Site B, the use of sprinkler
application should be investigated. Using the procedure outlined above,
the remaining ' sites are screened using the values given in Table 6-12
for sprinkler systems. The preferred methods from this process are:
Site A - Hand or tractor moved solid set
Site C - Hand moved solid set, self propelled, and permanent set
The land at Site A, already in agricultural use, contains some uniform,
rectangular fields. Site C would require grading and preparation (i.e.,
more cost) to enable the use of the more flexible, less expensive
sprinkler systems.
6-26
-------
The rapid infiltration system for Site A and the overland flow system
for Site C are still feasible alternatives according to the criteria in
Sections 6.3.2 and 6.3.3. The need to construct the 2 to 4% sloped
terraces at Site B for effective overland flow would favor the less
expensive grading required to prepare Site C.
A number of other considerations should be included in the cost-
effectiveness analysis for small systems that are discussed in other
sections of this manual. Recovery of renovated water from beneath rapid
infiltration basins or slow rate sites to either provide relief drainage
from perched groundwater or to recover water for sale is discussed in
Section 5.5. For vegetation selection, and revenue generation by
management of a cash crop, Section 5.6 should be reviewed. The systems
that remain to be analyzed for cost effectiveness are summarized in
Table 6-15.
TABLE 6-15
LAND TREATMENT ALTERNATIVES FOR ANGUS, WASHINGTON
Land treatment
Site system Major feature
A Slow rate Tractor moved solid set sprinklers
Rapid infiltration Prepare the 15 acre-site
B Slow rate Level border strips
C Slow rate Hand moved solid set sprinklers
Overland flow Grade terraces and ditches
6.4.7 Other Considerations
On the basis of nonmonetary criteria, Site B holds a clear advantage--!'t
is already owned by the city and would provide needed irrigation water
for the future greenbelt.
If rapid infiltration is shown to be more cost effective than irrigation
at Site A, the purchase or lease of the site would be necessary. For
the irrigation system at Site A, purchase would not be necessary if a
long-range contract could be negotiated with the owner. Since the land
at Site A is presently being irrigated, the renovated water could be
offered at an equal cost and the farmer would have the added advantage
of the wastewater nutrients.
6-27
-------
Site C would require the purchase or lease of a suitable area if the
overland flow alternative were shown to be more cost effective.
Sprinkler irrigation would convert nonirrigated pasture into more
valuable land and should make a long-term lease more attractive to the
owner than was the case, at Site A.
If some alternatives appear to be very close to each other for cost
effectiveness, the consideration of these nonmonetary items may be the
basis for the final site selection.
6.4.8 Summary of Design Example
The total land requirement will be the sum of the acreage needed for
pretreatment facilities, the actual area to be wetted, buffer zones (if
required), access and service roads, and storage ponds. The major
elements of each alternative and the total land requirement are
summarized in Table 6-16.
6.5 References
1. Sullivan, R.H., et al. Survey of Facilities Using Land
Application of Wastewater. Environmental Protection Agency, Office
of Water Program Operations. EPA-430/9-73-006. July 1973.
2. Loehr, R.C. Agricultural Waste Management—Problems, Processes and
Approaches. New York, Academic Press. 1974.
3. Metcalf & Eddy, Inc. Wastewater Engineering. New York, McGraw-
Hill Book Co. 1972.
4. Francingues, N.R., Jr. and A.J. Green, Jr. Water Usage and
Wastewater Characterization at a Corps of Engineers Recreation
Area. U.S. Army Engineer Waterways Experiment Station, Environmen-
tal Effects Laboratory. Miscellaneous Paper Y-76-1. January 1976.
5. Minimum Design Standards for Community Sewerage Systems. U.S.
Department of Housing and Urban Development. FHA G 4518.1. May
1968.
6. Whiting, D.M. Use of Climatic Data in Estimating Storage Days for
Soil Treatment Systems. Environmental Protection Agency, Office of
Research and Development. EPA-IAG-D5-F694. 1976.
7. Turner, J.H. Planning for an Irrigation System. American
Association for Vocational Instructional Materials. Athens, Ga.
1971.
8. Parmelee, D.M. Personal Communication. May 1977.
6-28
-------
cn
i
rvs
10
TABLE 6-16
SUMMARY OF FEASIBLE LAND TREATMENT SYSTEMS FOR ANGUS, WASHINGTON
Preapplication
treatment
Site
A
B
C
Land treatment
system
Slow rate,
sprinkler
Rapid infil-
tration
Slow rate,
surface
Overland flow
Slow rate,
sprinkler
Overland flow
Level3
S
P
Se
P
S
P
Area,
acres
3
2
3
2
3
2
Wetted
Application
area
Area,
rate, in./wk acres
2.0
40.0
2.0
8.0
1.5
4.0
38
1.7
38
10
51
19
Buffer
Needed
Yes
No
No
No
Yes
No
zones'3
Area,
acres
8
0.2
4
1
10
2
Storage
Days
of flow
40
Od
40
40
40
40
Area,
acres
4
.
4
4
4
•4
Total area
Disinfection Discharge0 required, acres
Yes Groundwater
No Groundwater
Yes Groundwater
Nof White River
Yes Groundwater
Nof white River
53
4
49
17
68
27
a. S = Secondary; P = primary.
b. May be required in some states. Average requirement based on 20% of wetted area and includes 10% for service roads.
c. If the discharge is to a groundwater, the nitrogen balance of the system should be checked using methods outlined in
Chapter 5. Nitrate (NOj) measured as nitrogen, should not exceed 10 mg/L in this case.
d. Includes extra freeboard for storage within basins.
e. Because of public contact. Under controlled conditions, primary treatment without disinfection would be sufficient.
f. Unless discharge coliform standard cannot be met—then post-treatment disinfection is necessary
1 acre = 0.405 ha
1 in./wk = 2.54 cm/wk
-------
CHAPTER 7
CASE STUDIES
7.1 Introduction
Eleven case studies are presented in this chapter to illustrate the
variety of existing land treatment systems. Six of the case studies are
slow rate systems; three are rapid infiltration systems; and two are
overland flow systems. Locations of the case studies and some system
characteristics are presented for comparative purposes in Table 7-1.
TABLE 7-1
SUMMARY OF CASE STUDIES
Location
Avg Avg annual
flow, application
Mgal/d rate, ft/yr
Degree of
preapplication
treatment
Application technique
No. of years
in operation
S1 ow ro to
Pleasanton, California 1.4 8.5
Walla Walla, Washington
Industrial 2.1 1.7
Municipal 6.8
Bakersfield, California 14.7 6.9
(existing system)
San Angelo, Texas 5.8 10.3
Huske'gon, Michigan 28.5 6.0
St. Charles, Maryland 0.6 10
Rapid infiltration
Phoenix, Arizona 13 364
Lake George, New York 0.7 140
Fort Devens,
Massachusetts 1.3 94
Overland flow
Pauls Valley, Oklahoma 0.2 19-45
Paris, Texas 4.2 5.2
(industrial)
Secondary (plus
aerated holding ponds)
Aeration
Secondary
Primary
Primary
Aerated lagoons
Aerated lagoons
Secondary
Secondary
Primary
Raw (screened)
and oxidation lagoon
Raw (degreased and
screened)
Sprinkler (portable pipe) 20
Sprinkler (buried pipe) 5
Sprinkler and surface 78
(ridge and furrow)
Surface (border strip and 38
ridge and furrow)
Surface (border strip) 18
Sprinkler (center pivot) 3
Sprinkler (surface pipe) 12
Surface (basin flooding) 3
Surface (basin flooding) 38
Surface (basin flooding) 35
Surface (bubbling orifice) 2
and sprinkler (fixed and
rotating nozzles)
Sprinkler (buried pipe) 13
1 Mgal/d = 43.8 L/s
1 ft/yr = 0.305 m/yr
7-1
-------
In addition to the mix of design flows and climates represented, the
ages of the systems vary from several decades (Walla, Walla, Washington;
Bakersfield, California; and Lake George, New York) to relatively new
(Muskegon, Michigan; Pauls Valley, Oklahoma; and Phoenix, Arizona). The
last two systems are principally demonstration projects with process
optimization the major objective. Nearly all the cases have attracted
some research interests and the ongoing research is discussed separately
from the normal operation.
Capital and operating costs are included when reliable data are
available. Costs for research projects are not comparable to design and
construction costs for normal municipal systems.
7.2 Pleasanton, California
7.2.1 History
Pleasanton, California, with a population of approximately 35 000 is
located 40 miles east of San Francisco. Wastewater irrigation has been
practiced here since 1911, when the population was 2 000 and only 8
acres (3.2 ha) of land was utilized [1]. The agricultural land
apparently has been in continuous use, although historical records are
absent. The present system has been in operation since 1957, and
consists of the sprinkler irrigation of 1.4 Mgal/d (61 L/s) of secondary
effluent on pastureland for the grazing of beef cattle (see Table 7-2)
[2]. Only 17 000 of the total population is served by the land
treatment system. The remaining population is served by a separate
treatment plant. The city is experiencing rapid growth; as a result,
plans are underway to provide a regionalized sewer system, which calls
for abandonment of the irrigation system in 5 years. It should be noted
that abandonment in 5 years was also predicted in 1972 [3].
7.2.2 Project Description and Purpose
There are two primary objectives to be met in this land treatment
system: (1) to provide proper management of wastewater, and (2) to
produce a high quality forage crop for beef cattle grazing on the
wastewater-irrigated fields. This system has proved to be successful in
meeting both of these objectives.
The pastureland receiving wastewater is essentially level and sprinklers
apply water consecutively to all parts. Soils range from gravelly loam
to clay loam and are moderately to slowly permeable. There is a
nonirrigated hill of 19 acres (7.7 ha) adjacent to the field area where
cattle can be quartered when the fields become somewhat soggy during
inclement weather. This is done to protect the soil from excessive
7-2
-------
compaction by the cattle during wet weather and to prevent the cattle
from contracting hoof diseases as a result of the wetness.
TABLE 7-2
DESIGN FACTORS,
PLEASANTON, CALIFORNIA
Type of system
Avg flow, Mgal/d
Type of wastewater
Preapplication treatment
Disinfection
Storage
Field area, acres
Crops
Application technique
Routine monitoring
Buffer zones
Application cycle
Time on, h
Time off, wk
Annual application rate, ft
Weekly application rate, in.
Avg annual precipitation, in.
Avg annual evaporation, in.
Annual nitrogen loading, Ib/acre
Capital costs, $/acre
Operation and maintenance costs, 4/1000 gal
Slow rate
1.4
Primarily domestic; some winery,
cheese, and metal wastes
Secondary (plus aerated holding ponds)
Not required
Not required
184
Forage grass
Sprinkler, portable
Yes
No
12-16
5
8.5
2.2
18
71
325
845
10.4
1 Mgal/d = 43.8 L/s
1 acre - 0.405 ha
1 ft = 0.305 m
1 in. = 2.54 cm
1 Ib/acre = 1.12 kg/ha
1 $/acre = S2.47/ha
1 4/1000 gal = 0.264 c/m3
7.2.3 Design Factors
The land treatment site is schematically depicted in Figure 7-1.
Two holding ponds receive unchlorinated effluent from the undersized
secondary treatment plant. The two ponds are aerated to prevent
septicity prior to application and to provide further biological
treatment. The two ponds total 4 acres (1.6 ha) and provide 5 Mgal
(18 925 m3) storage capacity, which equalizes the diurnal flow to the
sprinkler irrigation system [1].
7-3
-------
FIGURE 7-1
LAND TREATMENT SYSTEM,
CITY OF PLEASANTON
©
vvv .
XXSH
kvxxH
VSNN
6ROUNDIATER SAMPLING
STATIONS
IRRIGATED FIELDS
NONIRRIGATED FIELDS
STORAGE FACILITIES
SECONDARY
TREATMENT
PLANT
4 acres
AERATED
HOLDING PONDS
19 acres
NONIRRIGATED
HILL
EMERGENCY
STORAGE
VAPORATION AREA
1 acre = 0.405 ha
7-4
-------
A 75 hp (56 kW) pump, with an identical standby unit located at the end
of the holding ponds, delivers wastewater to the field area via a 10 in.
(25 cm) aluminum main line. A portion of the irrigated pastureland and
the main line is shown in Figure 7-2. The portable lateral system
consists of 30 ft (9 m) sections of 3 in. (7.5 cm) aluminum pipe, each
containing a riser with an impact-type sprinkler head as shown in Figure
7-3. Each nozzle delivers 10 to 11 gal/min (0.7 L/s) and has a wetting
radius of 30 ft (9 m) [2].
Tail water and stormwater control is provided by peripheral drainage
ditches that discharge into 18 in. (45 cm) and 10 in. (25 cm) steel lines
and thence to a runoff collection pond. This 10 acre (4 ha) pond has a
26 Mgal (98 400 m3) storage capacity and is provided with an overflow to
an emergency storage evaporation area. The 40 acre (16 ha) emergency
storage area is designed to handle the increased flows from a 50 year
storm. Normal runoff water, occurring from about November to March, is
recycled within the system by a 100 hp (75 kW) pump.
7.2.4 Operating Characteristics and Performance
The irrigation system is operated 7 days a week, year-round. A normal
pumping schedule of 12 to 16 hours per day maintains the holding ponds at
a fairly constant elevation. Pumping is by manual control with an
automatic shutoff if the ponds drop to a certain level.
The irrigated pastureland supports a herd of 600 beef cattle. The cattle
are rotated to fenced plots ahead of irrigation. The laterals containing
the sprinklers are moved 60 ft (18.3 m) each day, which results in an
application cycle of 5 weeks. The cattle are provided with a separate
supply of drinking water at one end of the pasture. The cattle have
experienced no ill effects from consumption of the grass; the marketing
and sale of the beef occurs in a normal manner.
The pasture grass seed consisted of 44% tall fescue, 32% Italian rye
grass, 20% orchard grass, and 4% mixed grasses [2], Sudan grass is grown
on the emergency storage field and is used as supplemental feed. The
grasses are cut twice a year with a rotary mower in order to induce
better growth and to control weeds such as star thistle. Fertilizers and
pesticides have not been used.
Values for various wastewater constituents found in the irrigation water
prior to application are presented in Tables 7-3 and 7-4. Although
influent total suspended solids to the irrigation system are
approximately 25 mg/L, no nozzle-plugging- problems have been
experienced; the nozzle diameter is 0.44 in. (1.1 cm).
7-5
-------
FIGURE 7-2
IRRIGATED PASTURELAND, PLEASANTON, CALIFORNIA
FIGURE 7-3
PORTABLE SPRINKLER SYSTEM, PLEASANTON, CALIFORNIA
7-6
-------
TABLE 7-3
CHARACTERISTICS OF HOLDING POND EFFLUENT AND
GROUNDWATER QUALITY, PLEASANTON, CALIFORNIA
Concentration, mg/La
Constituent
BOD
COD (low level)
Total suspended solids (TSS)
Total dissolved solids (TDS)
Total organic carbon (TOC)
Nitrogen
Organic
Ammonium (NH4-N)
Nitrate (N03-N)
Nitrite (N02-N)
Total phosphorus
PH
Temperature, °C
Boron (B)
Chloride (Cl)
Fluoride (F)
Sodium {Na+)
Calcium (Ca^)
Magnesium (Mg++)
Potassium (K+)
Bicarbonate (HCOa)
Carbonate (COs)
Hardness (Ca, Mg)
Non-carbonate hardness
Alkalinity as CaCOs
Specific conductance, pmhos/cm
Sulfate (S04)
Silica (Si02)
Iron (Fe)
Sodium adsorption ratio (SAR)
Sodium, %
Depth of groundwater below land .surface, ft
Holding pond
effluent^
22
25
702
39
3.0
24.6
<0.02
0.01
4.8
8.4
0.73
97
0.17
130
78
23
520
3.6
972
3.3
Groundwater quality0
G-7
30
980
4.3
0.13
0.02
0.02
6.8
17.4
0.0008
125
0.7
150
92
90
0.8
897
600
0
736
1 640
53
16
0.0006
2.7
35
7.5
G-9
5
708
8.2
4.9
0.01
0.02
6.9
16.8
0.0007
111
0.1
no
93
55
3.0
491
460
56
403
1 190
120
23
0.00001
2.2
34
37.3
a. Unless indicated otherwise.
b. Data for September 1975 [4].
c. Data for November 1975 to August 1976 [5].
wells G-7 and G-9.
1 ft = 0.305 m
See Figure 7-1 for location of
Industrial inputs to the system include small flows from a highly acidic
but seasonal waste from a winery, a pretreated cheese factory effluent,
a pretreated metal waste, and a seasonal loading from the Alameda County
Fair. There is no odor in the areas irrigated with wastewater and no
odor from the holding ponds. Odors have been a problem at the treatment
plant in the past, and as a result the trickling filter and settling
tanks have been covered.
7-7
-------
TABLE 7-4
TRACE WASTEWATER CONSTITUENTS OF HOLDING POND EFFLUENT,
PLEASANTON, CALIFORNIA, SEPTEMBER 1975 [4]
Constituent
Arsenic (As)
Barium (Ba)
Cadmium (Cd)
Chromium (Cr+6)
Cyanide (Cn)
Lead (Pb)
Mercury (Hg)
Selenium (Se)
MBAS
ATdrin
Chlordane
DDT
Dieldrin
Endrin
Heptachlor epoxide
Lindane
Methoxychlor
Toxaphene
2,4-D
2,4,5-TP
Carbon chloroform extract (CCE)
Carbon alcohol extract (CAE)
Holding pond
effluent, mg/L
<0.006
<0.1
<0.005
<0.005
<0.05
0.05
0.0003
<0.005
2.6
<0. 00005
<0. 00005
<0. 00005
<0. 00005
<0. 00005
<0. 00005
<0. 00005
<0. 00005
<0. 00005
<0.1
0.001
2.52
17.24
7.2.5 Costs
The City of Pleasanton leases most of the farmland from the City of San
Francisco which owns it as an underground water reserve. Grazing
permits for the 184 acre (74 ha) irrigated pastureland are then
allocated to local farmers by auction. This land is sublet at an annual
rental fee of $100 to $110/acre ($247 to $272/ha) with a 2 year lease.
The city furnishes the irrigation system and the labor to move the
portable pipe. The farmer manages the cattle and the pasture grass.
Labor requirements to move the
hours per day, 7 days a week,
pipes, nozzles, and fencing
consists of about 27 000 kW'h
22 000 kW-h per month for the
kW;h per month. A breakdown
for this land treatment system
irrigation system involve 3 men at 2-1/2
Maintenance costs for repairs to pumps,
are about $5 000/year. Power consumption
per month for the 100 hp (75 kW) pump and
75 hp (56 kW) pump, for a total of 49 000
of the approximate annual operating costs
is shown in Table 7-5.
7-8
-------
TABLE 7-5
APPROXIMATE OPERATION AND MAINTENANCE COSTS,
LAND TREATMENT SYSTEM,
PLEASANTON, CALIFORNIA [2]
Expenditure" Annual cost
Labor3
Taxesb
Power0
Material
Administration
Other
Subtotal
$22 000
21 000
19 000
5 000
500
5 000
$72 500
Revenue from grazing rightsd -19 3QQ
Total ' $53 200
Operation and maintenance
costs,
-------
7.2.6 Monitoring Programs
Since the land treatment operation is conducted over an important
underground aquifer, careful monitoring of groundwater quality is
mandatory. The California Regional Water Quality Control Board, San
Francisco Bay Region, requires regular groundwater sampling at
Pleasanton, and to meet this requirement a number of groundwater
monitoring wells have been installed. These wells serve to ensure
compliance with state regulations and are providing research data to
assess overall groundwater impacts in the adjacent area. The location
of these wells was shown in Figure 7-1. Groundwater quality data for
two representative wells were presented in Table 7-3, covering the
period from November 1975 through August 1976.
The Pleasanton land treatment site is located within a mile of a city
development of more than 10 000 people. There are essentially no buffer
zones; however, the site is 'totally enclosed by fences to limit public
access. A health effects study is being conducted by the Southwest
Research Institute. Scientists are performing measurements to determine
the extent of aerosol dispersal and are analyzing irrigation water and
aerosols for the presence of pathogenic microorganisms and chemicals.
The results and conclusions of this study are not available at the time
of this report.
7.3 Walla Walla, Washington
7.3.1 History
The use of wastewater as a source for irrigation water began in 1899
when the City of Walla Walla installed its first sanitary sewage
collection system and discharged directly to Mill Creek without
treatment. Irrigators still withdraw water from the creek for their
truck crops. As the population increased and the system expanded, the
wastewater became a larger portion of total stream flow, especially
during the summer months.
In 1929, the city constructed a 7.5 Mgal/d (328 L/s) secondary treatment
plant to treat domestic and industrial flows. In 1953, the industrial
(food processing) wastes of about 3 Mgal/d (131 L/s) were separated from
the plant and from 1953 to 1962, industrial wastewaters were treated at
the source by the food processors. In 1962, industrial wastewaters
began to receive treatment in an 8 Mgal/d (350 L/s) separate plant
operated by the city. The industrial wastewater was screened, pH
adjusted to 7.0, and directly discharged to Mill Creek.
In 1972, the domestic plant was upgraded to provide a higher quality
effluent and now has an average treatment capability of 9.12 Mgal/d
7-10
-------
(400 L/s) and a maximum hydraulic capacity of 13 Mgal/d (569 L/s). This
same year, a sprinkler system for application of industrial wastewater
was completed for all industrial effluent not required for stream flow
augmentation. Stream flow., augmentation is required to maintain., a
minimum flow of 11.25 ft /s (318 L/s) in Mill Creek and 1.77 ft /s
(50 L/s) in the irrigation ditches. This source of irrigation water
becomes essential in the summer, when upstream users divert all of the
normal Mill Creek flow. Design factors for the industrial wastewaters
(city operated) and municipal wastewaters (privately operated) slow rate
systems are presented in Table 7-6.
TABLE 7-6
DESIGN FACTORS,
WALLA WALLA, WASHINGTON
Type of system
Avg flow, Mgal/d
Type of wastewater
Preapplication treatment
Disinfection
Storage
Field area, acres
Crops
Application technique
Routine monitoring
Buffer zones
Application cycle, wk
Time on
Time off
Annual application rate, ft
Weekly application rate, in.
Avg annual precipitation, in.
Avg annual evaporation, in.
Capital cost, $/acre
Operation and maintenance
costs, 4/1 000 gal
a. City operated system.
b. Irrigation districts, privately
1 Mgal/d = 43.8 L/s
1 acre = 0.405 ha
1 ft = 0.305 m
1 in. -- 2.54 cm
1 Ib/acre =1.12 kg/ha
1 $/acre = $2.47/ha
1 4/1 000 gal = 0.264 t/m3
Industrial
Slow rate
2.1
Food processing
Aeration
No
Not required
700
Alfalfa
Sprinkler (buried pipe)
No
No
1-2
6-8
1.7
0.7
15.5
41
2 500
4.0
operated.
Municipal
Slow rate
6.8 (municipal effluent to creek in winter)
Domestic
Secondary
Yes
Not required
940
Vegetables
Sprinkler and surface (ridge and furrow)
Yes
No
Varies with crop
Varies with crop
Varies with crop
Varies with crop
15.5
41
--
4.3
7-11
-------
7.3.2 Project Description and Purpose
The treatment plants for all of the city's industrial and domestic
wastewaters are located on an approximately 40 acre (16.3 ha) site 2
miles (3 km) east of the city. Additionally, the city owns
approximately 1 000 acres (405 ha) of land 0.6 mile (1 km) north of this
area for the sprinkler irrigation of effluent from the industrial
treatment plant. Of the 1 000 acres, about 700 acres (285 ha) are
presently being used with the remainder being held in reserve for future
expansion.
7.3.2.1 Municipal System
Incoming domestic wastewaters are received in an aerated grit chamber,
sent to the primary clarifiers, then to the three high-rate trickling
filters. Next is intermediate clarification followed by a standard rate
trickling filter and two final clarifiers. Sufficient chlorine is
injected upstream of the final clarifiers to maintain a 0.1 to 0.5 mg/L
residual in the final clarifier effluent. The final clarifiers double as
chlorine contact tanks. The effluent is then discharged to a holding pond
from which it flows to either the irrigation districts or Mill Creek.
The city normally does not apply domestic effluent to its own land.
7.3.2.2 Industrial System
During the canning season (April through November) wastewater from the
area's food processors (mostly locally grown vegetables) is pretreated at
the packers. All solids above a #20 mesh (0.833 mm diameter) are
screened from the waste stream before discharge to a separate collection
system. The influent is then received at the plant in an aeration basin,
aerated, and pumped to the city's sprinkler irrigation field.
7.3.2.3. Municipal/Industrial Interconnections
To maintain treatment flexibility, there are three operable intercon-
nections between the two normally separated treatment systems. A
schematic flow diagram for the municipal and industrial treatment systems
is shown in Figure 7-4. During low industrial waste flow periods, when
there is insufficient flow to operate the city (industrial) sprinkler
system or when makeup water is needed to meet the irrigation commitment,
a line from the industrial aeration basin connects directly to the end of
the municipal primary clarifier. This has caused some problems with
excessive vegetable oils at certain times of the year so this line will
be rerouted to ahead of the aerated grit chamber, allowing complete
primary treatment of these oils. Another line allows diversion of the
raw industrial wastewater directly to the standard rate trickling filter
7-12
-------
FIGURE 7-4
SCHEMATIC FLOW DIAGRAM, WASTEWATER TREATMENT
PLANT, WALLA WALLA, WASHINGTON
INDUSTRIAL
INFLUENT
2. 6 Mgal/t)
FUTURE;
INDUSTRIAL AERATION r
BASIN AND PUMPING STATION!
DOMESTIC
INFLUENT
6.8 Hgal/d
GRIT
CHAMBER
MIXING
CHAMBER
ALTERNATE DISPOSAL
IN MILL CREEK
(WINTER) 6.8 Mgal/d
PRIMARY
CLARIFICATION
STANDARD RATE
TRICKLING FILTER
I. 2 iga l/d
TO GOSE
IRRIGATION
DISTRICT
INTERMEDIATE
PUMPING STATION
FINAL
CLARIFICATION
TANKS
6.3 Mgal/d TO BLALOCK IRRIGATION DISTRICT
•*•
I Mgal/d= 43.8 L/s
7-13
-------
if the industrial flow is extremely low relative to municipal influent.
A third line, which is normally not used, allows municipal effluent in
the final effluent holding pond to be pumped to the city sprinkler
system. A fourth line, diverting raw industrial wastewater to the
aerated grit chamber, is in place but inoperable due to leakage problems.
7.3.3 Design Factors
Operation of the city sprinkler
November each year for the food
irrigation water by the districts
that a part of the industrial flow
being used for makeup to meet the
patterns for the sprinkler operation
system normally occurs from May to
processing wastewater. Demand for
occurs from May through September so
goes to the city tract with the rest
irrigation demand. The monthly flow
are presented in Table 7-7.
TABLE 7-7
AVERAGE DAILY FLOW OF WASTEWATER,
WALLA WALLA, WASHINGTON
Mgal/d
May Jun Jul Aug Sep Oct Avg
Municipal wastewater3
Industrial wastewater
Total
Irrigation district demand
7.1 7.3
1.2 3.7
7.0
4.0
7.0
3.1
8.3 11.0 11.0 10.1
7.5 7.5 7.5 7.5
6.4 6.0
2.0 2.9
8.4 8.9
7.5 7.5
6.8
2.8
9.6
7.5
Net flow to city owned
sprinkler irrigation fields 0.8 3.5 3.5 2.6
0.9 1.4 2.1
a. From wastewater treatment plant operations monthly report
1 Mgal/d = 43.8 L/s
The city's 700 acre (285 ha) irrigation site is divided into 8 separate
subareas, the largest being 145 acres (69 ha); the smallest 60 acres (24
ha); with an average size of about 87 acres (36 ha).
There is no formal plan for operating the city sprinkler system. Each of
the subareas is irrigated for a period of 1 to 2 weeks. The lack of an
operational schedule and flow records for each plot means that
application rates can only be estimated. The calculated average
application rate based on 6 months flow to the field was presented in
Table 7-6. Soils are principally well drained silt loams with slopes
ranging from 2 to over 20%.
7-14
-------
7.3.4 Operating Characteristics and Performance of City's
Irrigation System
The industrial effluent for city operated sprinkler application is pumped
against a maximum static head of 50 ft (15.2 m). At the farm, it is
distributed to 8 separate fields through 187 laterals and 6 500 sprinkler
heads. A gage pressure as high as 140 lb/in.2 (96 N/cm2) is main-
tained in the main distribution line with pressure at the heads in the 95
to 100 lb/in.2 (67-70 N/cm2) range. Even with some slopes on the site
exceeding 20%, there is evidence of only minor erosion. The city
sprinkle'r system employs two types of heads, the impact nozzle and the
large diameter gun. The latter type, shown in Figure 7-5, distributes
325 gal/min (1 260 L/min) at 100 lb/in.2 (70 N/cm2) with 410 ft (125 m)
diameter of coverage.
At the high operating pressures, there is a problem of breakage of joints
between the risers and the lines and between the risers and the impact
heads. There is also a problem of breakage of the heads and risers by
the mower because of lack of visibility of the heads when the crops are
highest prior to mowing. The type of mower used and an impact sprinkler
are shown in Figure 7-6.
The principal crop being grown on the city's irrigated plot is alfalfa
for hay. The fanning operation is contracted with a local farmer who is
paid on an acreage, bale, or weight basis according to the task being
performed. For example, mowing and windrowing is paid for by the acre.
The city stores the bales and sells them when markets are strong.
Protein quality of the hay is good, averaging 14.5% by weight with a high
of 21.0% and a low of 9.4%.
Although the BOD of the industrial effluent could be considered high
(average = 965 mg/L),° there were no indications of nuisance conditions at
the application site nor have complaints been noted from the surrounding
residents.
7.3.5 Irrigation of Municipal Effluent by Private Districts
Application rates of the municipal effluent used by the irrigation
districts are difficult to estimate as no records are kept. The Blalock
irrigation district consists of 840 acres (339 ha) and the Gose
irrigation district is approximately 100 acres (40 ha) in size. District
farmers withdraw water directly from the ditches or Mill Creek for
sprinkler or flood irrigation, depending upon the time of year or the
crop. On the average, sprinklers are of the 6 to 7 gal/min (23 to 26
L/min) type covering an area 40 ft by 60 ft (12 m by 18 m). Sprinklers
are allowed to run 3 to 6 hours before being rotated to a different
parcel. This gives application rates ranging from a potential minimum of
0.7 in./d (1.8 cm/d) to a maximum of 1.7 in./d (4.3 cm/d).
7-15
-------
FIGURE 7-5
LARGE DIAMETER SPRINKLER GUN FOR INDUSTRIAL
WASTEWATER APPLICATION USED AT WALLA WALLA, WASHINGTON
FIGURE 7-6
ALFALFA HARVESTING EQUIPMENT, SPRINKLER RISER, AND
IMPACT HEAD AT CITY IRRIGATION SITE, WALLA WALLA, WASHINGTON
7-16
-------
No distinction is made between water that is primarily or partly effluent
and welV or reservoir waters-in terms of crop selection. Local fanners
grow whatever has an attractive market price without regard to the
water's source. Effluent irrigated crops sell for as high a price as
noneffluent grown crops and there has been no case of market
discrimination. This was confirmed by a representative of one of the
area's food processing plants who purchases large amounts of both
effluent and noneffluent irrigated vegetables.
Supplemental nitrogen (350 Ib/acre [390 kg/ha] of 48% urea) and
phosphorus are added to the wastewater to increase crop yields. Crops
grown on domestic effluent irrigated land are (in decreasing order of
acreage): onions, carrots, spinach, alfalfa (both for grazing and for
harvesting), radishes, and tomatoes. Local farmers have not noted any
decrease in yields nor deterioration of croplands over the years of
effluent use. Nuisance conditions caused by slime buildup have occurred
in the past, but separation of the industrial wastewater in 1972 appears
to have solved the problem.
7.3.6 Costs
Cost data are difficult to compare between the municipal and industrial
systems. For example, treatment costs for the municipal wastewater are
borne by the irrigation districts and neither these costs nor the revenue
from the farming are included in the treatment plant accounts. Likewise,
much of the time required to maintain the city farm and to administer its
agreement with the contracting farmer is not accounted for separately.
Neither are records kept on the portion of industrial effluent used for
makeup water in meeting the district's contracted irrigation demands.
Last, credit for crops sold does not accrue to the cost of operating the
farm but is returned to the revenue bond payers (the area's two food
processing plants) to help them retire the debt for the sprinkler sys-
tem construction. The estimated operation costs are summarized in
Table 7-8.
The capital cost for construction of the pumping station, transmission
lines, distribution system, and control system for the 700 acre (286 ha)
sprinkler irrigation field was $1.7 million in 1971. This amounts to
about $2 500 per acre ($6 000 per ha) construction cost.
7.3,7 Monitoring Programs
The only continuing monitoring program is carried out by the City of
Walla Walla for the treatment plant operating records [6]. A specific
soils monitoring program was conducted in 1974 and repeated in 1976. The
soils in the city's sprinkler irrigation operation were sampled to
determine the effects of irrigation. The adjacent 500 acre (204 ha) city
7-17
-------
tract is a nonirrigated dry land farming area on which wheat and barley
are grown. Soils tests taken in 1974 of the nonirrigated and irrigated
parcels provide little indication of any differences in conditions after
2 years of wastewater irrigation.
TABLE 7-8
AVERAGE ESTIMATED OPERATIONS COSTS,
WALLA WALLA, WASHINGTON
000 gal
Municipal system3 Industrial system*5
1973 3.4
1975 3.7
1976C 4.3
a. Treatment costs only.
b. Operates May-November,
distribution costs.
7.6
4.0
treatment and
c. To July 1976.
1
-------
surface distribution methods.
because of the warm arid climate.
Year-round irrigation is possible
Although the fanning operation has been successful in containing all
wastewater within the boundaries of the site and producing crop yields
consistent with local averages, certain deficiencies have developed, and
upgrading and expansion of existing facilities are needed. A summary of
principal design factors for both the existing and proposed land
treatment systems is presented in Table 7-9.
TABLE 7-9
DESIGN FACTORS,
BAKERSFIELD, CALIFORNIA
Existing system
Proposed system
Type of system
Avg flow, Mgal/d
Type of wastewater
Preapplication treatment
Disinfection
Storage
Time, d
Capacity, Mgal
Slow rate
14.7
Primarily domestic, some
poultry processing waste
Primary
Not required
4
60
Slow rate
19.0
Primarily domestic
poultry processing
Aerated lagoons
Not required
90
1 710
, some
waste
Field area, acres
Crops
Application technique
Routine monitoring
Buffer zones
Application cycle, d
Time on
Time off
Annual application rate, ft
Maximum weekly application rate, in.
Avg annual precipitation, in.
Avg annual evaporation, in.
Annual nitrogen loading, Ib/acre
Capital cost of proposed system,
$/acrea
2 400
Forage, fiber, and seed
4 800
Forage, fiber, and seed
Surface (border strip and Surface (border strip and
ridge and furrow
Yes
ridge and furrow)
No
No
1-2
7-15
6.9
4
6.4
60
466
No
0.5-1
10-15
4.5
4
6.4
60
280
2 960
a. Not including preapplication treatment or storage.
1 Mgal/d = 43.8 L/s
1 acre = 0.405 ha
1 ft = 0.305
1 in. = 2.54 cm
1 Ib/acre =1.12 kg/ha
1 $/acre = $2.47/ha
7-19
-------
7.4.2 Existing System Characteristics, Design Factors, and
Performance
The existing land treatment system, depicted in Figure 7-7, consists of
a network of ditches and equalizing reservoirs supplying the fields with
wastewater for border strip and ridge and furrow methods of irrigation.
Although the topography is very flat, the drainage is from north to
south with sump pumps along the southern end to return tail water to
stora.ge ponds (see Figure 7-7). Soils range from fine sandy loam to
clay loam. The soils are generally alkaline and poorly drained with
dense clay lenses at depths ranging from 10 to 15 ft (3 to 4.5 m) below
the surface. This clay barrier produces perched water in areas where it
is continuous and reduced percolation in areas where it is not.
Two permanent groundwater aquifers exist at approximate depths of 100 to
200 ft (30 to 60 m) and at 300 ft (90 m). They are separated by a clay
barrier, and the confined lower aquifer is used for water supply. The
deep wells on the farm, as shown in Figure 7-7, produce water for
supplemental irrigation water. The quality in this region, however, is
inadequate for potable uses as a result of naturally occurring high
total dissolved solids and nitrates.
The wastewater is primarily domestic in nature, with only a few poultry-
processing plants discharging high-BOD wastes to plant No. 1. The
characteristics of effluents from plant No. 1 (3.8 Mgal/d [166 L/s]) and
plant No. 2 (10.9 Mgal/d [477 L/s]) have been combined and a typ-
ical blend of constituents found in the irrigation water is given in
Table 7-10.
The quality of the combined primary effluent is quite suitable for
irrigation. The sodium adsorption ratio is relatively high at 7.5;
however, it is not critical. The total dissolved solids concentration is
not a problem for any of the crops grown.
Liquid and nitrogen loading rates, and nitrogen requirements for the
principal crops grown on the farm are shown in Table 7-11. As can be
seen, the nitrogen applied meets the nitrogen uptake of all crops. For
cotton, the nitrogen loading is more than twice that which can be
utilized. Applying excess nitrogen to cotton promotes excess vegetative
growth at the expense of fruitive growth, resulting in decreased yields.
Yields for all other crops are approximately equal to, and in some cases
higher than, the countywide averages. Crop yields resulting from
irrigation with primary effluent and the economic return per acre are
presented in Table 7-12.
7-20
-------
FIGURE 7-7
EXISTING WASTEWATER IRRIGATION SYSTEM,
BAKERSFIELD, CALIFORNIA
PLANT NO. 1
RESERVOIR
PLANT NO. 2
•LTH
n
• RESERVOIR
N
DISTRIBUTION
DITCH-
D
D
STORAGE PONDS
PASTURE
O
0 1000 2000 3BOO
SCALE FEET
LEGEND
• WELL
A TA I HATER
RETURN
STATION
7-21
-------
TABLE 7-10
COMPOSITE WASTEWATER CHARACTERISTICS FOR
CITY PLANTS NOS. 1 AND 2,
BAKERSFIELD, CALIFORNIA9
BOD, rag/Lb 150
Suspended solids, mg/L 48
pH, units 7.0
EC, mmhos/cm 0.88
TDS, mg/L 477
SAR 4.1
SAR(adj) 7.5
Calcium, meq/L 2.30
Magnesium, meq/L 0.41
Sodium, meq/L 4.74
Potassium, mg/L 26
Carbonate, meq/L 0
Bicarbonate, meq/L 3.57
Chloride, meq/L 3.01
Sulfate, meq/L 1.54
Boron, mg/L 0.38
Cadmium, mg/L <0.01
Total nitrogen as N, mg/L 20-25
Phosphorus as P, mg/L'3 6.2
a. Based on 1976 tests, except as
noted.
b. Based on 1973 tests.
TABLE 7-11
LOADING RATES IN 1973 AND TYPICAL NITROGEN UPTAKE REQUIREMENTS,
BAKERSFIELD LAND TREATMENT SYSTEM [7]
Crop
Alfalfa
Barley
Corn
Cotton
Pasture grass
Liquid loading
rate, ft/yr
4.9
1.8
3.3
3.7
4.9
Nitrogen loading
rate, Ib/acre-yr
371
139
252
277
371
Typical
nltroqen uptake,
Ib/acro-yr
360-480
75
150
100
150-250
1 ft = 0.305 m
1 Ib/acre = 1.12 kg/ha
7-22
-------
TABLE 7-12
EXISTING CROP YIELDS AND ECONOMIC RETURN,
BAKERSFIELD, LAND TREATMENT SYSTEM
Typical Economic
Crop Yield, Ib/acre price, $/lba return, $/acre
Alfalfa
Barley
Corn
Cotton
16 000
3 000-5 000
36 000-60 000
600-800
0.025
0.045
0.0075
0.35
400
135-225
270-450
210-280
a. Based on 1973 prices.
1 Ib/acre =1.12 kg/ha
1 $/lb = $2.2/kg
1 $/acre = $2.47/ha
Management of water has become a problem due to lack of storage and
increasing flows. Ponding of excess water has occurred on some areas of
the pastureland in winter. Although flies and mosquitos are attracted to
the stagnant water, no diseases have been traced to effluent use. The
equalizing reservoirs and the storage pond for tail water are periodically
sprayed to control mosquito propagation.
Public health regulations for
are such that the quality of
of primary effluent. No di
none is provided at the two
barley are green chopped (
Dairy cows are not all
nondisinfected effluent so
cattle are allowed to both
and hay.
irrigation of fodder, fiber,
reclaimed water shall not be
sinfection of the effluent i
treatment plants. Normally
not harvested for grain) for
owed to graze pastures
they are fed with green chop
graze pastures and be fed on
and seed crops
less than that
s required, and
both corn and
cattle fodder.
irrigated with
and hay. Beef
the green chop
7.4.3 Proposed System Characteristics and Design Factors
Although primary effluent is suitable according to the California
Department of Health, the Central Valley Regional Water Quality Control
Board has set limits of 40 mg/L on BOD and suspended solids prior to
forage crop irrigation. Their rationale is that such an effluent can be
stored without causing a nuisance and will reduce the potential for odors
in system management.
7-23
-------
The proposed system consists of an upgrading of the existing
preapplication facilities and inclusion of a concrete pipe distribution
system for continued surface irrigation of crops. City plant No. 1 will
be abandoned and its flow redirected to-city plant No. 2, where new
primary clarifiers and aerated lagoons will be constructed. Chlorination
will not be provided since surface application to forage, fiber, and
seed crops does not require disinfection.
The 4 800 acre (1 944 ha) land area of the proposed system will be twice
that of the existing system because the principal objective of the
proposed system is crop production rather than land treatment. Thus,
double cropping with corn and barley is proposed and this combination
requires less water than is presently applied. A schematic of the
portion of the system located within the limits of the existing city
farm and an additional 320 acre (129 ha) parcel northeast of the farm is
presented in Figure 7-8. The remainder of the system (not shown in
the figure) is located to the south, including 960 acres (389 ha) of
undeveloped land which will be reclaimed for irrigation.
7.4.4 Proposed System Operation
Flexibility of operation will be provided by storage reservoirs, which
will hold flows during periods of low irrigation demand. In addition,
automatically operated tail water return stations will control runoff
from irrigated fields. Outlets from the distribution laterals will
consist of orchard-type valves which are adaptable to gated surface
pipe, open ditches with siphon pipe, or direct flooding of border
strips. Telemetered alarms will continuously scan the operation of the
system to alert the operator of malfunctions at any of the pumping
stations.
7.4.5 Costs
City revenues from the lease of the existing farm amount to about 20% of
the operating and maintenance costs for the two treatment plants [7].
Detailed operating and maintenance costs for the existing farm were not
available.
The estimated construction costs for the proposed system on the basis of
summer 1977 construction startup are summarized in. Table 7-13. These
costs do not include land acquisition costs or engineering,
administration, and legal expenses. The City of Bakersfield will lease
the property to the highest responsible bidder for management of the
system, and the city will be responsible only for maintenance of the
main pipeline and all pumping equipment.
7-24
-------
FIGURE 7-8
PROPOSED WASTEWATER IRRIGATION SYSTEM,
BAKERSFIELD, CALIFORNIA
DISTRIBUTION DITCH
^^^F
0 1 000 2000 3000
SCALE FEET
LEGEND
MAIN DISTRIBUTION LINE
AND OVERFLOW STRUCTURE
LATERAL
TA ILWATER RETURN STATION
AND PIPELINE
PUMPING STATION
, , TO ADDITIONAL PROPERTIES (2100ACRES)
7-25
-------
TABLE 7-13
ESTIMATED CONSTRUCTION COSTS,
PROPOSED WASTEWATER IRRIGATION SYSTEM,
BAKERSFIELD, CALIFORNIA3
Land reclamation and site development $ 1 126 000
Storage and equalizing reservoirs 5 385 000
Distribution pipelines 4 697 000
Distribution pumping stations 621 000
Tailwater return systems 513 000
Bonds and insurance 154 OOP
Total $12 496 000
Construction costs, $/gal of capacity15 0.66
a. Based on summer 1977 construction startup.
b. Based on 19 Mgal/d average flow.
1 $/gal = $3.785/L
1 Mgal/d = 43.8 L/s
7.5 San Angelo, Texas
7.5.1 History
San Angelo, a city of about 65 000 in west central Texas, has treated
its wastewater by primary sedimentation followed by land application
since 1928. The system was operated at one site for the first 30 years
and has been operated at the present site for 18 years. Pressure from
development around the first site led to its abandonment in 1958. The
present slow rate system consists of 630 acres (255 ha) of city-
owned pasture and cropland irrigated by the border strip method (see
Table 7-14). Preapplication treatment will soon be upgraded from
primary to secondary to meet state requirements for wastewater irriga-
tion of areas accessible to the public.
7.5.2 Project Description
Wastewater is currently given primary treatment prior to land
application. The effluent can be used directly to irrigate the
pastureland, shown in Figure 7-9, or it can be directed through four
holding ponds. The detention time in the ponds at an average flow of
5.8 Mgal/d (254 L/s) is about 30 days. The 330 acres (134 ha) of
pasture receive somewhat more effluent annually than the 300 acres (121
ha) of cropland, which is rotated between oats, rye, and grain sorghum.
7-26
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TABLE 7-14
DESIGN FACTORS,
SAN ANGELO, TEXAS
Type of system
Avg flow, Mgal/d
Type of wastewater
Preapplication treatment
Disinfection
Storage
Capacity, Mgal
Time, d
Field area, acres
Crops
Application technique
Routine monitoring
Buffer zones
Application cycle, d
Time on
Time off
Annual application rate, ft
Avg weekly application rate, in.
Avg annual precipitation, in.
Avg annual evaporation, in.
Annual nitrogen loading, Ib/acre
Operation and maintenance
costs, 4/1 000 gal
Slow rate
5.8
Domestic and industrial
Primary
No
174
30
630
Coastal Bermuda grass, fescue,
oats, rye, and grain sorghum
Surface (border strip)
Yes
No
1
10-14
10.3
2.4
18.6
60
800
0.9
1 Mgal/d = 43.8 L/s
1 acre = 0.405 ha
1 ft = 0.305 m
1 in. = 2.54 cm
1 Ib/acre =1.13 kg/ha
1 4/1 000 gal = 0.264
-------
FIGURE 7-9
SLOW RATE LAND TREATMENT SYSTEM
AT SAN ANGELO, TEXAS
SEEPAGE
CREEK
NO. 1
HOLDING
PONDS
xxxxxxx
XXXXXXXXXXXXXXXXXX
XXXXXXXXXXXXXXXXXX
XXXXXXXXXXXXXXXXXX
XXXXXXXXXXXXXXXXXX
XXXXXXXXXXXXXXXXXX
XXXXXXXXXXXXXXX
XXXXXXXXXXXXXX
XXXXXXXXXXXXXX
XXXXX
XXXXXXXN\S
XX
XXXXXXXXXX
XXXXX
xxxxxxxxxx
xxxxxxxxxx
xxxxxxxxxx
xxxxxxxxx
xxxx
xxxxxxxxx
xxxxxxxxx
xxxxxxxxxx
xxxxxxxxxx
SEEPAGE
CREEK
NO. 2
xxxxxxxxxx^
xxxxxxxxx
STORAGE POND
WELL NO. 2
IRRIGATED AREAS
STORAGE FACILITIES
7.5.4 Operating Characteristics and Treatment Performance
The pasture!and is planted in coastal Bermuda grass that is both grazed
by beef cattle and harvested as hay. Grazing rights are sold to
cattlemen and the hay, shown in Figure 7-10, is sold to the public by
the bale. The oats, rye, and sorghum are used for cattle feed.
The wastewater is applied by the border strip method as shown in Figure
7-11. The borders vary in width and follow the slope of the land. The
principal soils are Angelo and Rio Concho clay loams.
The treatment performance can be estimated by comparing the quality of
the applied wastewater to the quality of groundwater that emerges out of
7-28
-------
FIGURE 7-10
COASTAL BERMUDA GRASS HAY AT SAM ANGELO, TEXAS
FIGURE 7-11
BORDER STRIP IRRIGATION OF PASTURE AT SAN ANGELO, TEXAS
7-29
-------
seepage creek No. 1. The treatment performance data presented in Table
7-15 are for October 1973 [8]. The apparent nitrogen removal of 52% is
for an area currently in pasture that receives over 800 lb/acre-yr (900
kg/ha-yr). The crops grown in that area in 1973 are unknown.
TABLE 7-15
TREATMENT PERFORMANCE,
SAN ANGELO, TEXAS [8]
mg/L
Constituent
BOO
Ammonia nitrogen
Nitrate nitrogen
Total nitrogen
Total phosphorus
Total dissolved solids
Pond
effluent
54.2
28.0
0.8
28.8
5.9
1 704
Seepage
creek No. 1
1.0
0.2
13.0
13.7
0.09
1 900
The high total dissolved solids value apparently does not adversely
affect crop growth. The pasture that is grazed supports 10 head of
cattle per acre (25 head/ha) which is an order of magnitude greater than
comparable densities for conventional irrigated pasture in central
Texas.
7.5.5 Costs
Capital costs for the construction of the system in 1955 and purchase of
the land are not available. In 1972, the value of the land was
estimated to be $500/acre ($1 250/ha) [3]. The new activated sludge
plant, which will have a capacity of 8.5 Mgal/d (372 L/s), will cost
$4 million (April 1977). This plant will be capable of supplying efflu-
ent as irrigation water to nearby farmers. The present land treatment
system may be expanded when the city can purchase additional land in the
area.
Operations require three farm employees and a manager at a budget of
about $60 000 to $70 000/yr. Grazing rights are sold at $5.50/month for
each head of cattle. The baled hay is sold at $1.50 to $2.00 per bale.
In all, the revenue from the farm amounts to $80 000 to $90 000/yr for a
net profit of around $20 000/yr. Revenues amount to 3.8tf/l 000 gal
7-30
-------
7.5.6 Monitoring
Normal monitoring includes periodic analyses of groundwater in several
wells. In October 1973, an intensive monitoring survey was conducted to
determine the effects of the land treatment system on the Concho River
[8]. The findings were that while seepage from the system was
significantly increasing the flow of the river, it was having a
negligible effect on the water quality. A sample groundwater analysis
from the normal monitoring program is presented in Table 7-16.
TABLE 7-16
SAMPLE OF GROUNDWATER QUALITY,
SAN ANGELO, TEXAS [9, 10]
mg/L
Constituent Well No. 1 Well No. 2
Total dissolved solids
Total alkalinity as CaCOs
Total hardness as CaCOj
pH, units
Calcium
Magnesium
Sodium
Sulfate
Chloride
Bicarbonate
Iron
Phosphorus
Ammonia nitrogen
Nitrate nitrogen
Total nitrogen
- 1,659
352
1,080
7.3
192
146
130
• 140
596
429
2.7
0.015
0.0
9.0
9.1
1,628
394
676
7.3
162
66
265
120
500
481
0.1
0.025
0.0
22.3
22.4
7.5.7 Long-Term Effects Research
Research on the chemical and microbiological effects of 18 years of
operation is being conducted by researchers at Texas A & M University.
The 2 year effort is expected to be finished in 1977. Sampling will
include soil, plant tissue, wastewater, groundwater, and water emerging
as seeps. The heavy metals, nutrients, and organics will be measured in
the water and soil samples. Crops within specially fenced areas will be
checked for yields and tested for nutrients and accumulation of metals.
7-31
-------
7.6 Muskegon, Michigan
7.6.1 History and Objectives
The need for an alternative wastewater management program for the
Muskegon County area became apparent in the late 1960s because of
deterioration in the water quality of local surface waters. Fourteen
municipalities and five major industries were required to achieve an 80%
phosphorus reduction and produce effluent that would not result in the
degradation of the water quality of Lake Michigan.
Areawide solutions were explored and the most cost-effective solution
was to divert all the wastewater discharges from surface waters and make
use of undeveloped land as a major component of an areawide treatment
system. The decision to undertake such a plan was based in part on
economics and in part on a commitment to recycle nutrients as resources
rather than discharge them to the environment in a nonbeneficial manner.
Construction of the facilities commenced in 1972 and operation was begun
in stages starting in May 1974. The first full year of operation was
1975.
7.6.2 Project Description and Design Factors
The Muskegon County Wastewater Project consists of two independent
systems: the Muskegon Project and the smaller Whitehall Project. Both
systems make use of the slow rate process of land treatment. Because of
the much larger size and quantity of information available for the
Muskegon Project, this section will be limited to a discussion of that
system. A summary of the principal design factors for the Muskegon
Project is presented in Table 7-17.
Industrial wastewaters discharged to the system constitute over 60% of
the present flow. The largest single discharger, S.D. Warren Company, a
Kraft papermill, contributes approximately 15 Mgal/d (0.7 m3/s) [11].
The treatment system consists of biological treatment in aerated lagoons
followed by sprinkler irrigation of land on which corn is presently
grown. While there are many interesting features of the system, its
uniqueness lies primarily in^the size of the facility. With a design
capacity of 42 Mgal/d (1.8 m /s) and over 5 000 acres (2 025 ha) of
land under irrigation, it is the largest operating facility in the
United States designed specifically for land treatment of wastewater.
Other features include the low overall operation costs. During 1976,
crop revenues offset 60% of the total operating costs of the system.
7-32
-------
TABLE 7-17
DESIGN FACTORS, MUSKEGON PROJECT,
MUSKEGON, MICHIGAN
Type of system
Avg flow, Mgal/d
Type of wastewater
Preapplication treatment
Disinfection
Storage
Slow rate
28.5
Domestic and industrial (papermilli
Aerated lagoons
As required
Capacity, Mgal
Time, d
Field area, acres
Crops
Application technique
Routine monitoring
Buffer zones
Application cycle
Time on
Time off
Annual application rate, ft
Avg weekly application rate, in.
Avg annual precipitation, in.
Avg annual evaporation, in.
Annual nitrogen loading, Ib/acre
Capital costs, $/gal of capacity^
Operation and maintenance costs, 4/1 000 gal
5 323
187
5 350
Corn and rye grass
Sprinkler (center pivot)
Yes
Yes
Varies
Varies
Varies; 1-9, avg 6
3.0
32
30
130
1.01
12.5
a. Includes transmission, preapplication treatment, storage, distribution
system, and underdrainage.
1 Mgal/d = 43.8 L/s
1 acre = 0.405 ha
1 ft = 0.305 m
1 in. = 2.54 cm
1 Ib/acre =1.13 kg/ha
1 $/gal = 3.785/L
1 4/1 000 gal = 0.264 «/m3
A plan of the facilities is shown in Figure 7-12. Incoming wastewater
first enters one of three 8 acre (3.2 ha) aerated lagoons, which may be
operated in parallel or series. From the treatment cells, wastewater
enters the two 850 acre (344 ha) storage lagoons shown. A separate
settling pond is also provided which can serve as a bypass to the
storage lagoons. During the irrigation season (April through November),
water for irrigation is drawn from either the storage lagoons or from
the settling pond into a 14 acre (5.6 ha) outlet lagoon. The treated
effluent released from the outlet lagoon can be chlorinated in a mixing
chamber prior to delivery via open channels to the two main distribution
7-33
-------
FIGURE 7-12
MUSKEGON PROJECT LAND TREATMENT SITE PLAN
APPLICATION
AREAS
AERATED LAGOONS
SETTLING POND
OUTLET LAGOON
CHLORINATION FA Cl I LTY
DISTRIBUTION PUMPING STATIONS
DRAINAGE PUMPING STATIONS
• DRAINAGE WELLS
*._ — MAIN DRAINAGE TILES
to- DRAINAGE DITCHES
7-34
-------
pumping stations. These pumping stations deliver the wastewater through
a series of buried pipes to the irrigation equipment. Because of
bacteria die-off during the long storage period, chlorination is not
required at all times to meet discharge requirements.
Wastewater is applied to the land by 54 center pivot irrigation machines
which utilize low pressure nozzles and roll on pneumatic tires (see
Figure 7-13). Vertical turbine pumps at two main pumping stations dis-
charge to an asbestos-cement pipeline distribution network. Major design
data for the distribution system are presented in Table 7-18.
Soil types at the application site include sandy soils with infiltration
rates from 5 to more than 10 in./h (12.7 to 25.4 cm/h), loamy soils with
rates from 2.5 to 10 in./hr (6.4 to 25.4 cm/h), and clay soils with
rates ranging from 0.02 to 2.5 in./h (0.05 to 6.4 cm/h). The majority
of the soils, however, are sands and sandy loams. The maximum design
application rate is 4 in./wk (10 cm/wk), which includes an allowance for
0.74 in./wk (1.9 cm/wk) of precipitation.
A combination of drainage tiles, drainage wells, and natural drainage
collects the subsurface water and discharges it to adjacent receiving
surface waters. The majority of the site is underlain with drainage
tiles at approximately 500 ft (153 m) intervals and from 5 to 8 ft
(1.5 to 2.4m) deep. The laterals, constructed of perforated
FIGURE 7-13
CENTER PIVOT BOOM WITH LOW PRESSURE NOZZLE,
MUSKEGON PROJECT
7-35
-------
polyethylene filtered by fiberglass socks, conduct the water to main
concrete drainage pipes. The concrete pipes carry the water to open
ditches which in turn discharge to two receiving streams. Drainage
tiles were largely installed using a continuous plow machine as shown in
Figure 7-14.
TABLE 7-18
DISTRIBUTION SYSTEM DATA [12]
MUSKEGON PROJECT
Pumping
No. of vertical turbine pumps 17
Peak capacity, Mgal/d 91.7
Piping size range, in. 8-36
Center pivot irrigation rigs
No. of rigs 54
Radius, ft 700-1 400
Coverage range, acres 35-141
Operating pressure, Ib/in.2 35-84
2
Nozzle pressure, Ib/in. 3-10
Application rate (continuous operation)
in./h 0.0239
in./wk 4.0
Application season, months 8
1 Mgal/d = 43.8 L/s
1 in. = 2.54 cm
1 ft = 0.305 m
1 acre = 0.405 ha
1 lb/in.2 = 0.69 N/cm2
7.6.3 Operating Characteristics and Performance
Irrigation with wastewater at Muskegon commenced in May 1974, and
numerous temporary startup problems were encountered. Most of the
problems, such as dike damage, breaks in irrigation pressure pipes, and
electrical cable failures, have been resolved. A persistent,
significant odor problem occurred at the treatment site and was
attributed to the high volume of papermill waste. The inlet structure
has been modified to reduce the release of odor.
An operational problem was the plugging of the irrigation rig nozzles
with a mixture of sand and weeds, which are blown into the storage
lagoons and main irrigation ditches. During the first two irrigation
seasons, ten full-time "nozzle cleaners" were hired in an attempt to
minimize plugged nozzles. Even with this effort, the degree of uniform
7-36
-------
water application was not acceptable. To alleviate this problem,
settling basins and screening systems have been installed ahead of both
irrigation pumping stations.
FIGURE 7-14
INSTALLATION OF DRAINAGE TILES,
MUSKEGON PROJECT
Another operational problem during the first season was downtime due to
the irrigation rigs becoming stuck in soft, wet soil in one area. This
problem has been greatly alleviated by increasing tire size from 11 by
24 in. to 14.9 by 24 in. (28 by 60 cm to 38 by 60 cm). To further alle-
viate the problems of stuck rigs, machine speed has been doubled [12].
In 1975, 4 700 acres (1 900
was planted in corn and
wastewater. The remaining
grass. Total wastewater
(254 cm/yr) per field, with
to 75 in./yr (127 to 190
grain from various fields
1975 season are presented in
ha) of the 5 400 acres (2 182 ha) irrigated
irrigated with up to 4 in./wk (10 cm/wk) of
700 acres (283 ha) was fallow or in rye
applied ranged from zero to over 100 in./yr
the majority of the fields receiving from 50
cm/yr) [13], Representative yields of corn
at the Muskegon land treatment site for the
Table 7-19.
7-37
-------
TABLE 7-19
REPRESENTATIVE YIELDS OF CORN GRAIN,
FOR VARIOUS SOIL TYPES,
MUSKEGON LAND TREATMENT SITE, 1975 [13]
Wastewater
application,
Field soil type in./yr
Rosconnton sand
Rubicon sand
AuGres sand
Roscommon sand
Granby loamy sand
Rubicon sand
AuGres sand
Roscommon sand
Project average
57
106
59
69
14
93
14
14
54
Supplemental
nitrogen
fertilizer,
lb/acre-yr
65
63
70
40
27
44
10
0
44
Corn grain
yield,
bu/acre-yr
90
83
71
69
61
53
36
31
60
1 in./yr =2.54 cm/yr
1 Ib/acre-yr = 1.12 kg/ha-yr
1 bu/acre-yr = 2.47 bu/ha-yr
The wastewater provides an adequate amount of phosphorus and potassium
for the corn crop [13]. However, the low levels of nitrogen in the
wastewater would not be adequate without supplemental additions. In the
sandy soil, there is little organic nitrogen and even less in a soluble
form usable by plants, as sandy soils do not retain much nitrogen.
Therefore, during the 2 months of the 6 month irrigation period in which
the corn is actively growing, it is necessary to inject nitrogen
fertilizer into the wastewater on a daily basis. It is important that
the application rate of the soluble nitrogen be adjusted so that the
corn plants absorb and use all of the available nutrients as fast as
their metabolism permits. From 0 to 89 Ib/acre-yr (0 to 100 kg/ha-yr)
of nitrogen fertilizer was added to the different irrigated fields,
depending upon the amount of wastewater applied and crop requirement
needs.
Corn planted in 1976 yielded an average of 81 bu/acre-yr (200 bu/ha-yr),
significantly greater than the 45 to 50 bu/acre-yr (111 to 123 bu/ha-yr)
average corn grain yield on operating farmland in Muskegon County. This
is quite remarkable in light of the fact that most soils at the
treatment site are very poor and that wastewater renovation is the
primary purpose of the system. The agricultural productivity of the
Muskegon land treatment system has steadily increased over its first 3
years of existence, as shown in Table 7-20. Sale of the corn has
proceeded with the grain commanding full market value.
7-38
-------
TABLE 7-20
INCREASED AGRICULTURAL PRODUCTIVITY,
MUSKEGON LAND TREATMENT SITE [13]
1974 1975 1976
Corn yield, bu/acre-yr
Land treatment site
Muskegon County average
Gross crop revenue, $ millions
28
55
0.35
60
65
0.7
81
45-50
1.0a
a. Estimated.
1 bu/acre-yr = 2.47 bu/ha-yr
The entire Muskegon wastewater treatment operation is being handled by
40 full-time people and an additional part-time labor force of up to 10
workers. A part of this work activity is associated with the Muskegon
EPA Research and Development Grant. The normal staffing of the
treatment operation during the day shift is 2 people on the northern
irrigation rigs and 2 people on the southern irrigation rigs with
another 2 people providing maintenance as needed [11]. The other 2
shifts are staffed with 1 person per shift.
The average treatment results for 1975 are presented in Table 7-21.
BOD, suspended solids, and phosphorus levels are well below the
discharge permit requirements, which are 4 mg/L for BOD, 10 mg/L for
suspended solids, and 0.5 mg/L for phosphorus.
7.6.4 Costs
The construction cost for the Muskegon wastewater treatment system was
$42.7 million, of which $12.0 million was for collection (force mains
and sewer lines) and transmission (pumping and lift stations) [13]. The
net operating costs for the total wastewater treatment system (Muskegon
and Whitehall sites) incurred during the 1975 season was $1 232 000.
Gross operating costs by system component and revenues gained are
presented in Table 7-22.
Operating experience based on observations of storage lagoon treatment
performance has shown that the actual biological treatment system was
overdesigned. It has been demonstrated that proper treatment can be
obtained by running a smaller percentage of the aerators [12]. This
has resulted in reduced operating costs for aeration. As additional
7-39
-------
cost-effectiveness measures of this nature become apparent.
reduction in net operating costs can be expected.
further
TABLE 7-21
SUMMARY OF TREATMENT PERFORMANCE,
1975 AVERAGE RESULTS,
MUSKEGON PROJECT [ll]a
Parameter
BOD
pH, units
Specific conductance, ymhos
Total solids
Suspended solids
COD
TOC
Ammonia-N
Total Kjeldahl nitrogen
Nitrate-N
Total P
Chloride
Sodium
Calcium
Magnesium
Potassium
Iron
Zinc
Manganese
Total col i forms,
Fecal col i forms,
colonies/100 nt
Fecal streptococci,
colonies/100 ml
Influent
205
7.3
1 049
1 093
249
545
107
6.1
8.2
Trace
2.4
182
166
73
14
n
0.8
0.6
0.28
Average storage
lagoon effluent
13
7.8
825
691
20
118
38
2.4
4.5
1.1
1.4
154
144
58
16
9
1.0
0.11
0.16
100-1 2xl08
4-1 2xl06
2-3 8x10^
Drain tiles
1.2
599
11.6
0.29
2.2
60
42
72
23
2.6
7.7
0.01
0.20
-------
crop characteristics. Samples are taken for chemical and biological
analyses once or twice daily at each step of the treatment process. On
a weekly basis, a total of 2 883 samples are analyzed for one of 25
wastewater constituents [11]. In addition, groundwater is sampled
monthly to twice yearly from over 300 wells for analysis [13]. This
massive monitoring program requires the services of nine laboratory
personnel and the results, thus far, have been that no significant
effects on the groundwater or surface water of the area have occurred.
TABLE 7-22
OPERATING COSTS
MUSKEGON WASTEWATER SYSTEM, 1975 [13]
Operating costs by component
Collection and transmission $ 431 000
Aeration and storage 191 000
Irrigation and drainage 475 000
Farming 474 000
Laboratory and monitoring 236 000
Other 77 OOP
Subtotal, Muskegon $1 884 000
Total, Whitehall 62 OOP
Total, gross operating , $1 946 000
Revenues
Crop
Corn (4 500 acres x 60 bu x $2.58/bu) $ 698 000
Wheat (270 acres x 10 bu x $3.10/bu) 8 000
Laboratory services 8 OOP
Total $ 714 000
Net operating cost $1 232 000
Unit operating cost,
-------
lagoons, storage, and sprinkler application of approximately 0.6 Mgal/d
(26 L/s) in a wooded area (see Table 7-23). The land application
portion of the system has been operated primarily as a means of disposal
with little attention given to either treatment performance or crop
production benefits.
TABLE 7-23
DESIGN FACTORS,
ST. CHARLES, MARYLAND [3, 14]
Type of system
Avg flow, Mgal/d
Type of wastewater
Preapplication treatment
Disinfection
Storage
Capacity, Mgal
Time, d
Field area, acres
Crops
Application technique
Routine monitoring
Buffer zones
Application cycle
Time on, h
Time off, d
Annual application rate, ft
Avg weekly application rate, in.
Avg annual precipitation, in.
Avg annual evaporation, in.
Capital costs, $/acrea
Unit operation and maintenance
costs, tf/1 000 gal
Slow rate
0.6
Domestic
Aerated lagoons
Yes
90
150
67
Wooded field (oak-pine)
Sprinkler (surface pipe)
No
Provided but not required
8-15
4-7
10
2-3.5
40
27
1 100
a. 1966.
1 Mgal/d = 43.8 L/s
1 acre = 0.405 ha
1 ft = 0.305 m
1 in. = 2.54 cm
1 $/acre = $2.47/ha
1
-------
surface discharge to nearby Zekiah Swamp, which was declared
environmentally unacceptable [3].
At this time, the Charles County Sanitary Commission and neighboring
Prince George's County are constructing an interceptor and regional
treatment plant in the Mattawoman Creek basin. Plans (1976) call for
St. Charles to join this system when completed, abandoning this site.
7.7.2 Design Factors
The preapplication treatment originally consisted of an oxidation pond
system covering approximately 10 acres (4 ha). The combination of
preapplication treatment and storage lagoons now totals 40 acres (16
ha), and six floating aerators have been added to the influent cells.
Effluent quality from the lagoons averages about 40 mg/L BOD and 75 mg/L
suspended solids [15]. The effluent is then chlorinated to 20 MPN/100 ml
fecal coliforms (maximum allowable by State of Maryland).
The land application system consists of 11 woodland plots which are
sprinkled independently. Because wastewater disposal has been
emphasized over treatment or tree production, only enough field area has
been developed to preclude ponding and runoff. The plots receive
differing application rates, depending on their ability to take the
water.
Aboveground aluminum pipe is used for the distribution system. The 6
in. (15 cm) diameter distribution mains are designed to discharge the
effluent when pressure is released, thus providing cold weather
protection. The 2 in. (5 cm) laterals are supported above ground so
that they will drain back into the mains; this appears to have caused
problems in that they are easily knocked over by deer. Sprinkler
spacing is mostly 90 by 80 ft (27 by 24 m), which seems to produce
adequate distribution coverage at 40 lb/in.2 (28 N/cm2). The
sprinklers are primarily the impact type, although it has been found
that the stationary umbrella-type sprinklers reduce tree icing.
Buffer zones were not specifically required for the system, although
adequate buffering is provided by the secluded nature of the site. The
nearest structure is approximately 0.5 mile (0.8 km) and the nearest
well is approximately 1.5 miles (2.4 km) [3].
7.7.3 Operating Characteristics
The system has continued to perform adequately for the purposes
originally intended. Operation is straightforward and requires a
7-43
-------
minimum of control. A crew of two workers and a supervisor operate the
system in addition to their other duties, and usually visit the site 3
to 5 times per day. Pumps and distribution lines are manually
controlled. Decisions regarding application periods and cycles are
based on visual appearances of the fields.
The groundwater table has risen significantly throughout most of the
site and is at or near the surface in many areas [15]. In many of these
areas, the original tree species have been replaced by pokeweed as a
result of the high groundwater.
7.7.4 Monitoring Program
Operational monitoring of the lagoon systems at St. Charles has been
reported, but the land application portion of the system has not been
closely monitored. A research project is currently being conducted
through a combined effort by the Departments of Agricultural
Engineering, Agronomy, Botany, and Civil Engineering at the University
of Maryland [15]. The study program hopes to provide information on the
fluctuation of groundwater levels, the effects on water quality in
groundwater and nearby water courses, the fate of materials applied, and
the effects of vegetation.
7.8 Phoenix, Arizona
7.8.1 History
Rapid infiltration of municipal wastewater at Phoenix, Arizona, started
in 1967 when the U.S. Water Conservation Laboratory, in cooperation with
the Salt River Project and the City of Phoenix, constructed the Flushing
Meadows experimental pilot project. The Flushing Meadows project
demonstrated the feasibility of renovating secondary effluent for
unrestricted use for irrigation and recreational purposes. Uastewater
was applied to the rapid infiltration basins to evaluate the quality
improvement of the effluent as it moved through the soil and the
hydraulics of the groundwater recharge system. The effect of basin
management on infiltration rates was examined by altering surface
conditions and flooding schedules. The results for the first 5 years
are well documented [16, 17]. Operation of the project is continuing
and reports on the second 5 year study period will be prepared in 1978.
The 23rd Avenue Project, a large scale rapid infiltration system, was
designed based on engineering criteria developed at Flushing Meadows.
This project, constructed in 1974, is described in the sections which
follow. Design factors for both the Flushing Meadows and the 23rd
Avenue Project are presented in Table 7-24.
7-44
-------
TABLE 7-24
DESIGN FACTORS,
PHOENIX, ARIZONA
23rd Avenue Project
Flushing Meadows
Type of system
Avg flow, Mgal/d
Type of wastewater
Preapplication treatment
Disinfection
Storage
Field area, acres
Crops
Application technique
Routine monitoring
Buffer zones
Application cycle, d
Time on
Time off
Annual application rate, ft
Avg annual precipitation, in.
Avg annual evaporation, in.
Annual nitrogen loading,
Ib/acre
Rapid infiltration
13
Municipal
Secondary
Yes
Not required
40
None
Surface (basin flooding)
Yes
No
3-21
3-21
364
7
70
35 400
Rapid infiltration
0.6
Municipal
Secondary
Yes
Not required
1.9
None3
Surface (basin flooding)
Yes
No
4
10-20
365
7
70
35 400
a. Several vegetated basins were experimented with, but results
were inconclusive.
1 Mgal/d = 43.8 L/s
1 acre = 0.405 ha
1 ft = 0.305 m
1 in. = 2.54 cm
1 Ib/acre =1.12 kg/ha
7.8.2 Purpose
A need to supplement the present water resources in the Phoenix area
exists. The purpose of the 23rd Avenue Project is to demonstrate the
feasibility of rapid infiltration on a scale that could partially meet
this water need. If the initial demonstration project shows that
wastewater can be economically renovated, the system could be expanded
to reclaim all of the effluent discharged in the Phoenix area. A
significant portion of the treated flow would be used for nuclear power
plant cooling water. The rest could be made available for irrigation
and an extensive aquatic park development (Rio Salado Project) proposed
along the Salt River channel.
7-45
-------
7.8.3 Project Description
The rapid infiltration site is located on the north side of the bed of
the Salt River and east of 35th Avenue. The layout of the 23rd Avenue
Project is shown in Figure 7-15. Secondary effluent from the 23rd
Avenue wastewater treatment plant flows through a concrete channel to
the site. The soil profile at the site is similar to the Flushing
Meadows site, consisting of loamy sands, sand, gravel, and boulders to a
depth of over 200 ft (60 m) [16]. On the basis of results learned at
that project, infiltration rates of at least 2.5 ft/d (76 cm/d) were
expected [16]. Initially, the effluent was routed through an 80 acre
(32 ha) oxidation pond before application to the infiltration basins.
However, the extra detention time in the oxidation pond (approximately 4
days) stimulated dense algae growths in the effluent applied to the
basins and reduced the average infiltration rate to about 0.5 ft/d (15
cm/d). The algae remain in suspension and accumulate on the basin
bottom as a cake. The algae cake does not decompose or shrink during
drying and, consequently, the infiltration rate is not restored
significantly when flooding is resumed. Pilot studies have shown that
the infiltration rate can be expected to at least double when the
oxidation pond is bypassed, as shown in Figure 7-15, and secondary
effluent is applied directly to the basins.
At the time of the site visit (1976), there was no reuse of the
renovated water taking place. The electric rate for pumping the
renovated water initially was higher than that of the local irrigation
district, thus economically prohibiting its use. The City of Phoenix
has negotiated with the local power company to lease the wells to the
irrigation district so that it can take advantage of the lower electric
rate. Resolution of this problem has made the costs of renovated water
competitive with those of native groundwater sources.
7.8.4 Design Factors
At the time when the 23rd Avenue project is in full operation, about 13
Mgal/d (0.57 m^/s) of secondary effluent will be applied to the four
rapid infiltration basins. The renovated water will be recovered by a
series of three 24 in. (60 cm) diameter wells (1 existing and 2 future)
equipped with electric driven pumps of 3 000 gal/min (189 L/s) capacity.
The static water table depth is about 80 ft (24 m). The first well is
200 ft (60 m) deep and perforated from 100 to 120 ft~(30 to 36 m). A
pump discharge and collection piping system will be constructed to the
point of reuse. Two 6 in. (15 cm) diameter observation and sampling
wells have been constructed, one each on the north and south side of the
rapid infiltration basin. The wells will be used to sample renovated
water quality and monitor the groundwater level. The project will be
operated so that the groundwater level will be the same as that in the
aquifer adjacent to the project to preclude the movement of renovated
water away from the site.
7-46
-------
.FIGURE 7-15
LAYOUT OF THE 23RD AVENUE
RAPID INFILTRATION AND RECOVERY PROJECT
PREAPPLICATION TREATMENT
20 Mgal/d SECONDARY
EFFLUENT FROM 23rd AVE
STP
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13 Mgal/d
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/INFILTRATION BASINS
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.300 ,
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T nnn osl/niin^' — ^^ MHA •»•>««» •
1 acre = 0.405 ha
1 ft = 0.305 m
1 Mgal/d = 0.043 m3/s
1 gal/min = 0.063 L/s
RECOVERY WELLS AND
COLLECTION PIPING
PROPERTY LIMITS
7-47
-------
7.8.5 Operating Characteristics and Performance
When the 23rd Avenue Project becomes fully operational,
various wastewater cycling schedules will be studied.
dry-up periods ranging from several days each to several
be employed. During inundation, a constant depth of 1
1.0m) will be maintained. Inflow and outflow will
evaluate infiltration rates in each basin. Basins wil
the end of inundation periods into the next basin to be
the dry-up period can start immediately. One of
structures to the infiltration basins is shown in Figure
the effects of
Inundation and
weeks each will
to 3 ft (0.3 to
be measured to
1 be drained at
flooded so that
the four inlet
7-16.
FIGURE /-16
INLET STRUCTURE, 23RD AVENUE PROJECT, PHOENIX, ARIZONA
The unconfined groundwater table occurs at a depth of 60 to 80 ft (18 to
24 m) beneath the site and is continuous to a depth of 230 ft (69 m)
where a clay layer may be located. The percolated wastewater will move
toward the recovery wells at the center of the basins. The two outer
basins will be inundated while the two inner basins are drying, and
vice-versa. This will provide travel distances in the range of 100 to.
500 ft (30 to 150 m) and 400 to 900 ft (120 to 300 m) which may yield
two different qualities of reclaimed water.
7-48
-------
By pumping only as much reclaimed water as has been infiltrated,
equilibrium should be established so that no flow between the recharge
system and the native groundwater takes place. The equilibrium will be
checked by measuring the water levels in the observation wells. A
schematic of the infiltration and the recovery process is shown
in Figure 7-17.
The renovated water from the one existing recovery well has been sampled
and analyzed to determine the performance of the system. Measured
levels of BOD, SS, and fecal coliforms have always been far below the
specified limit for unrestricted irrigation and recreation use and the
state health department has certified the renovated water for these
purposes. Data on the quality of renovated water at the 23rd Avenue
Project are presented in Table 7-25 [18].
TABLE 7-25
RENOVATED WATER QUALITY
THE 23rd AVENUE PROJECT IN PHOENIX, ARIZONA [18]
a
Constituent Average3
Suspended solids 0.8
Nitrate nitrogen 6.7
Ammonia nitrogen 0.1
Phosphorus 0.16
Fluoride 0.7
Boron 0.5
Total dissolved solids 910.0
Fecal coliforms, colonies/100 mL 0-30
a. mg/L unless otherwise noted.
7.8.6 Monitoring Program
In addition to the quality and level of groundwater, the direction of
groundwater movement will also be checked by monitoring the total
dissolved solids concentration in the observation wells. If no native
groundwater enters the project, the total dissolved solids of the
reclaimed water should be approximately the same as that of the
wastewater effluent.
Continuous 24 hour samples will be taken of the effluent entering the
infiltration basins. Characteristics of the secondary effluent of the
23rd Avenue Project were not available at the time of the site visit.
However, the secondary effluent from the 91st Avenue activated sludge
7-49
-------
--J
I
in
o
FIGURE 7-17
SCHEMATIC OF THE 23RD AVENUE RAPID INFILTRATION AND RECOVERY SYSTEM
DISCHARGE PIPELINE
GROUNDWATER
FLOW LINES
-------
renovated water from the Flushing Meadows project are shown in
Table 7-26.
7.8.7 Other Research at the 23rd Avenue Project
A special objective of the 23rd Avenue Project is to determine how air
pressure buildup in the soil beneath large infiltration basins affects
the infiltration rate. The effect of basin size on air pressure buildup
beneath the advancing wet front in the soil will be studied by comparing
infiltration rates measured by two methods. Measurements will be made
with cylinder infiltrometers or by comparing small inundated areas
within the recharge basin to the infiltration rate when the entire basin
is inundated. Piezometers have been installed to measure air pressures
down to a depth of 40 ft (12 m). Reductions in infiltration rates from
air pressure buildup have proved to be insignificant for small basins.
Additionally, the depth of water during inundation of the basins will be
varied to reduce or increase hydraulic head to determine what effect
these factors have on infiltration rates.
The effects of the high algae loading on surface clogging are also being
studied before the oxidation pond bypass channel is completed. Also,
research is being conducted to determine whether inundation depth can be
used to limit algae growth. Tensiometers have been installed to measure
the increase in hydraulic impedance of the surface layer over time in
the infiltration basins.
7.8.8 Other Research at Flushing Meadows
Research at Flushing Meadows has dealt with the fate of viruses in
wastewater as they enter the soil. Secondary effluent and renovated
water from four observation wells were assayed every 2 months in 1974
for viruses during flooding periods. The number of viruses detected in
the sewage effluent averaged 2 118 per 100 litres. However, no viruses
were detected in any well samples. These results indicate that viruses
are reduced by a factor of at least 104 (99.99%) during percolation of
the wastewater through 10 to 30 ft (3 to 9 m) of the basin soil [19].
The emphasis of the most recent research at Flushing Meadows is aimed at
maximizing nitrogen removal. Increased nitrogen removal has been
realized by reducing the hydraulic loading rate to the basins and using
optimum flooding and drying periods. Preliminary results indicate that
by reducing the annual hydraulic loading to the basins from 300 ft
(100 m) to 173 ft (52 m), nitrogen removal increased to about 60% (from
30%) and phosphate removal increased to 90% (from 70%). These values
are from samples taken from a well in the center of the spreading basins
at a depth of 30 ft (10 m). The application schedule was 9 days
flooding and 12 days drying.
7-51
-------
TABLE 7-26
CHARACTERISTICS OF SYSTEM INFLUENT AND
RENOVATED WATER, FLUSHING MEADOWS, PHOENIX, ARIZONA [17]
Concentration, mg/L
Constituent
BOD
COD
Suspended solids
Total dissolved solids
Total organic carbon
Total nitrogen3
Ammonium nitrogen (NH/i'N)
Nitrate nitrogen (NOs'N)
Nitrite nitrogen (N02"N)
Organic nitrogen
Phosphate (P04)-phosphorus
Fecal coliforms per 100 itl
Vi ruses per 100 mL
PH
Boron (B)
Fluoride (F)
Sodium (Na+)
Calcium (Ca++)
Magnesium (Mg"1"1")
Potassium (K+)
Bicarbonate (HCO3)
Chloride (CT)
Sulfate ($04)
Carbonate (CDs)
Cadmium (Cd)
Copper (Cu)
Lead (Pb)
Mercury (Hg)
Zinc (Zn)
System
influent
15
45
20-100
1 100
20
36
30
1
2
3
10
106
2 118
7.6-8.1
0.75
4.1
200
82
36
8
381
213
107
0
0.008
0.12
0.082
0.002
0-19
Flushing Meadows
renovated water
0-1
15
0
1 100
5
25
5-20
0.1-71&
1
1
0.1-3C
Od
0
7.0
0.75
2.6
200
82
36
8
381
213
107
0
0.007
0.017
0.066
0.001
0. 035-0. 108e
a. Overall nitrogen removal during sequences of long
flooding and drying periods was about 30%.
b. Nitrate peaks occurred when flooding was resumed after
long dry-up periods as a result of incomplete
denitrification.
c. Phosphate removal increased with the underground
travel time.
d. Fecal coliforms were between 0 and 200 per 100 mL
in water sampled at 30 ft below the basins.
Renovated wastewater from a well 200 ft away from
the basins had-a zero fecal coliform count.
e. High zinc level may have been the results of using
galvanized plumbing in sampling wells.
7-52
-------
7.9 Lake George, New York
7.9.1 History
Lake George, located in the eastern part of the State of New York, is a
recreational lake 32 mi (52 km) long and from 1 to 3 mi (1.6 to 4.8 km)
wide. The discharge of any wastewaters, treated or untreated, directly
into the lake or into any tributary thereof has been strictly prohibited
for at least 90 years. This has preserved the pristine quality of the
lake which is still used as a public drinking water supply with no
treatment other than chlorination.
By the late 1930s, Lake George Village, located at the southern end of
the lake, had grown large enough to require a wastewater treatment
plant. Since septic tank systems had been allowed, the regulation
restricting the discharge of wastewater into the drainage basin area was
interpreted to mean surface discharges. Thus, it was decided that
discharge into the soil would be a satisfactory means of disposal of the
treated effluent from the proposed wastewater treatment plant.
Although most of the Lake George watershed is underlain by rock
consisting of pre-Cambrian gneisses, a small natural delta sand deposit
created by outwash from the receding glaciers was discovered at the
southwest corner of the Lake George Village area. Advantage was taken
of this mass of delta sand and the wastewater treatment pi ant was
constructed at this location to utilize this sand as a rapid
infiltration area for the secondary effluent. The original treatment
plant was completed and put into operation in 1939 and has been in
continuous operation ever since. Design factors for the rapid
infiltration system are presented in Table 7-27. A view of a rapid
infiltration basin is shown in Figure 7-18. During the winter ice forms
on the basin surface (Figure 7-19) and the applied wastewater floats the
ice and infiltrates into the sandy soil.
7.9.2 Project Description
The Lake George Village wastewater treatment plant receives wastewater
from two force mains, one from the Village and one from the Town of Lake
George. There are five pumping stations, including two located in town
which lift the wastewater approximately 200 ft (60 m) from the
collection point at the lake to the treatment plant. Primary treatment
is provided by one circular Imhoff tank and two mechanically cleaned
circular Clarigesters (similar to Imhoff tanks), all operating in
parallel. Secondary treatment consists of two high-rate rotating arm
trickling filters and one covered standard-rate fixed nozzle trickling
filter. The latter is used exclusively in the winter and is covered to
prevent icing of the sprayed wastewater. Secondary sedimentation is
accomplished by two rectangular and two circular settling tanks. After
7-53
-------
secondary sedimentation, the unchlorinated effluent is passed onto the
natural delta sand beds for infiltration into the soil. At present,
there are 14 north and 7 south sand beds. Sludge from the secondary
settling tanks is returned to the Clarigesters, and digested sludge is
applied to 3 sludge drying beds. The general layout of the treatment
plant and the location of the sand beds and sampling wells are shown in
Figure 7-20.
TABLE 7-27
DESIGN FACTORS,
LAKE GEORGE, NEW YORK
Type of system
Avg flow, Mgal/d
Type of wastewater
Preapplication treatment
Disinfection
Storage
Field area, acres
Crops
Application technique
Routine monitoring
.Buffer zones
Application cycle
Time on, h
Time off, d
Avg annual application rate, ft
Avg annual precipitation, in.
Avg annual evaporation, in.
Avg nitrogen loading, Ib/acre
Rapid infiltration
1.1 (summer)
0.4 (winter)
Domestic
Secondary
No
None
5.4
None
Surface (basin flooding)
No
No
8-24
4-5 (summer); 5-10 (winter)
140
34
26
6 700
1 Mgal/d = 43.8 L/s
1 acre = 0.405 ha
1 ft = 0.305 m
1 in. = 2.54 cm
1 Ib/acre = 1.12 kg/ha
7.9.3 Design Factors
It is estimated that the Lake George Village wastewater treatment plant,
with a design capacity of 1.75 Mgal/d (76.7 L/s), presently serves a
population of approximately 2 100 in the winter and 12 300 in the summer
[20]. In 1965, the plant underwent major expansion with the addition of
eight sand beds, and in 1970 one additional bed was put on line to bring
the total to 21. The material in the beds ranges from coarse to fine
sand, with a few beds having some clay content. Depth to water table
and bedrock varies, but is generally deeper in the old north sand beds
7-54
-------
FIGURE 7-18
RAPID INFILTRATION BASIN, LAKE GEORGE, NEW YORK
FIGURE 7-19
OPERATIONAL BASIN COVERED WITH ICE,
LAKE GEORGE, NEW YORK
7-55
-------
FIGURE 7-20
LAKE GEORGE VILLAGE WASTEWATER TREATMENT
PLANT AND SAMPLING LOCATIONS
GENERAL
6ROUNOWATER
MOVEMENT
PREAPPLICAT
TREATMENT
FACIL
7-56
-------
than in the new south sand beds. Well points driven in bed 11 of the
north sand beds have found the water table to be at a depth of
approximately 65 ft (20 m) below the surface, and bedrock to be
approximately 90 ft (27 m) below the surface. The sand beds vary in
size, ranging from 0.16 acre to 0.42 acre (0.06 to 0.17 ha), and combine
for a total surface area of 5.4 acres (2.2 ha) [21].
The unchlorinated secondary effluent is discharged onto the natural
delta sand beds by surface flooding. In order to prevent erosion of the
sand at the point of discharge, concrete splash pads with brick baffles
are provided. Individual sand beds are dosed by adjusting the gates
within the distribution chambers. The beds have 3 to 5 ft (1 to 1.5 m)
dikes around them, and each bed has a control valve for individual
flooding. The 14 lower (north) beds are fed by gravity, while effluent
from the secondary settling tank must be pumped up to the 7 upper
(south) beds. A float control in the wet well automatically operates
the intermittent pump.
Vertical movement of the infiltrated effluent through the sand ranges
from 15 to 75 ft (4.5 to 20 m), depending on the sand bed and the
season. Horizontal underground movement is approximately 2 000 ft
(600 m) before the renovated effluent emerges as seepage near West
Brook, a tributary to Lake George.
7.9.4 Operating Characteristics and Performance
Normal weekday operation of the sand beds is to dose one north and one
south bed with 8 to 10 in. (20.4 to 25.4 cm) of effluent over an 8 hour
period during the day. A similar pair of beds are flooded throughout
the remaining 16 hours. On weekends, two north and two south beds are
dosed for a period of 24 hours each. During the high flow months of the
summer, more than 2 beds are flooded at a time.
There is no set schedule as to which rapid infiltration bed will be used
on any one day. Plant personnel make daily decisions based on visual
inspection of the status of the beds. Most of the sand beds dry in 1 to
3 days. Generally, the beds are rested for 5 to 10 days prior to the
next application. The frequency of application increases with the
increase in flow due to the influx of tourists during the summer months.
During the peak flows of August, it is often necessary to flood the sand
beds before they have fully dried. This practice is avoided if at all
possible, as the surface of the beds must remain aerobic in order to
restore the renovative capacity of the system.
It has been found that the rapid infiltration basins perform well and
clog slowly under conditions of 1 day dosing followed by several days of
drying. The rest period, providing complete or partial drying, has a
renewing effect on the infiltration capacity of the sand beds. In
7-57
-------
addition, the sand beds are occasionally reconditioned by raking or
scraping the surface. The top few centimetres of sand are removed,
which include a mat of algae and other organic material, and the sand
bed is regraded. This cleaning operation is generally restricted to
spring or autumn, when weather is mild and flows are not at a peak.
Weeds are removed for aesthetic purposes. There have been no serious
problems with the operation of the sand beds.
Application continues year-round without storage, regardless of severe
winter weather. In winter, part of the water freezes and forms an ice
layer which may attain 1 ft (0.3 m) in thickness. This does not
interfere with the operation. The warm effluent flows under the ice,
simultaneously melting the ice above it and the ground below it, and in
effect, floats the ice layer. The ice is actually beneficial to the
process, as it serves as an insulating layer for the soil surface.
7.9.5 Environmental Studies
In an effort to evaluate the environmental effects of the Lake George
Village wastewater treatment plant, numerous studies have been conducted
by Rensselaer Polytechnic Institute, the New York State Health
Department, and the New York State Department of Environmental
Conservation. The Rensselaer Fresh Water Institute was organized and
studies were begun in 1968. A number of well points were placed in the
sand beds and at the periphery of the treatment plant grounds, as shown
in Figure 7-20. Two additional well sites are located between the sand
beds and West Brook and one is located across West Brook.
Analysis of water samples from the wells has shown that there is almost
complete removal of BOD, coliforms, ammonia nitrogen, and organic
nitrogen in the top 10 ft (3 m) of passage through the sand beds [22].
Ammonia and organic nitrogen are converted to nitrate-nitrogen and, at
least partly, the nitrate is reduced to nitrogen gas by denitrification.
Phosphorus removal is a function of the frequency of sand bed use, with
a bed in constant use having considerably less phosphate removal than an
infrequently used bed for the same distance of downward percolation.
A resistivity survey has indicated that the most probable direction of
flow of the wastewater discharged onto the sand beds is northerly along
Gage Road toward West Brook [23]. The seepage which occurs above and
below Gage Road is tributary to West Brook and has been estimated to be
approximately 0.6 Mgal/d (26 L/s), or 10% of the total flow of
West Brook [24].
Water quality data of the plant effluent and seepage above Gage Road and
West Brook are given in Table 7-28. The water which emerges from the
ground in the area of West Brook contains considerably higher
concentrations of dissolved solids, alkalinity, and chloride than the
7-58
-------
TABLE 7-28
WATER QUALITY DATA, SEASONAL MEANS,
LAKE GEORGE, NEW YORK [25]
--J
01
Plant effluent
applied to
sand beds
Spring
Summer
Fall
Winter
Seepage above
Gage Road
Spring
Summer
Fall
Winter
West Brook
downstream
of seepage
Spring
Summer
Fall
Winter
Temper-
ature,
°C
13.0
22.4
10.0
4.5
10.8
14.3
8.9
4.8
10.7
12.6
8.0
2.0
Dissolved
oxygen ,
mg/L
5.3
2.1
4.5
6.8
10.3
8.2
10.1
11.3
11.0
10.2
11.5
13.0
Dissolve
solids ,
mg/L
177
224
197
234
160
173
220
212
85
120
93
79
d /
pH
7.2
6.9
7.0
7.0
7.9
7.8
7.9
7.8
7.4
7.8
7.5
7.3
Ukal inity,
mg/L as
CaCOa
96
218
93
109
106
99
111
118
35
€8
56
39
Chloride,
mg/L
44
46
32
52
37
49
42
40
15
29
25
14
Nitrate-
nitrogen ,
mg/L
1.8
1.6
3.5
1.1
2.3
1.6
3.5
3.8
0.7
1.8
1.5
0.6
Ammonia
nitrogen ,
mg/L
3.8
15.9
3.0
5.1
0.0
0.0
0.1
0.0
0.0
0.1
0.0
0.0
Total
Kjeldahl
nitrogen ,
mg/L
8.0
18.4
9.1
12.5
0.2
0.1
o!i
0.2
0.1
0.0
0.1
Soluble
phosphate,
ug/L
750
2 950
700
488
8
14
<2
10
1
3
1
2
Total
phosphorus,
pg/L
1 555
3 950
1 650
1 425
16
16
10
6
3
2
6
-------
natural groundwater in the area. This is evidence that the seepage does
in fact originate from wastewater effluent. From the data, it can be
seen that the total phosphorus content of the applied wastewater is
reduced by greater than 99% in its passage through the approximately
2 000 ft (600 m) of sand before it emerges and runs off into West Brook
and ultimately into Lake George. It also can be seen that the applied
nitrogen is oxidized to nitrate prior to its emergence from the ground.
The nitrate content of the seepage is about 1.6 to 3.8 mg/L and
increases the nitrate content of West Brook. However, the nitrate-
nitrogen concentration in West Brook downstream of the seepage is about
0.6 to 1.8 mg/L, which is well below the EPA drinking water standard of
10 mg/L.
Based on numerous studies and extensive sampling and analyses, the land
treatment system at Lake George is doing an adequate job of purifying
the wastewater to a drinking water quality [22]. The soil system is
satisfactorily removing essentially all of the phosphorus and is
providing a nitrified effluent which appears to have no deleterious
effect upon the quality of Lake George.
7.10 Fort Devens, Massachusetts
7.10.1 History
Fort Devens is a U.S. Army military installation located in the Nashua
River basin about 32 mi (52 km) northwest of Boston, Massachusetts. A
rapid infiltration system at Fort Devens has received an unchlorinated
primary sewage effluent for over 35 years. The total population and
wastewater flows have fluctuated over the years, but are presently on
the decline. In 1973, the daytime population was about 15 000 of which
10 400 were permanent residents [26]; whereas the 1976 population has
been estimated to be 10 000 and 7 000, respectively. The present
wastewater treatment facility has been providing continuous service
since its construction in 1942. Selected design factors are presented
in Table 7-29.
7.10.2 Project Description and Design Factors
The Fort Devens wastewater treatment facility has a design capacity of
3.0 Mgal/d (131 L/s), but has been receiving from 1.0 to 1.3 Mgal/d (43
to 57 L/s) for the last several years. Comminuted, degreased wastewater
is pumped from a central pumping station to three Imhoff tanks which
provide primary treatment. Settlcable solids accumulate on the bottom
of the Imhoff tanks and are withdrawn to sludge drying beds in April and
in November of each year. These dewatering beds are underdrained and
discharge to an adjacent wetland area [27].
7-60
-------
TABLE 7-29
DESIGN FACTORS,
FORT DEVENS, MASSACHUSETTS
Type of system
Avg flow, Mgal/d
Type of wastewater
Preapplication treatment
Disinfection
Storage
Field area, acres
Crops
Application technique
Routine monitoring
Buffer zones
Application cycle, d
Time on
Time off
Avg annual application rate,
1960 to 1973, ft
Avg annual precipitation, in.
Avg annual evaporation, in.
Annual nitrogen loading, Ib/acre
Rapid infiltration
1.3
Domestic
Primary (Imhoff tank)
No
Not required
16.6
None (weeds)
Surface (basin flooding)
No
No
2
14
94
44
26
11 200
1 Mgal/d = 43.8 L/s
1 acre = 0.405 ha
1 ft = 0.305 m
1 in. = 2.54 cm
1 Ib/acre = 1.12 kg/ha
Final treatment of the unchlorinated primary effluent is achieved by
discharging to 22 rapid infiltration basins. These 22 basins provide a
total field area of 16.6 acres (6.7 ha) or an average of 0.76 acre (0.31
ha) per basin [28]. They are situated on the top of a steep-sided hill
composed of a 200 ft (60 m) thick layer of unconsolidated stratified
sand and gravel deposited by receding glaciers. This flat, oval-shaped
hilltop rises approximately 70 ft (21 m) above the floodplain of the
Nashua River [26]. The soil formation in which the treatment beds were
constructed is primarily poorly graded sands or gravelly sands with
interspersed lenses of silty sand and sandy gravels. Particle size
distribution differs appreciably between the various soil horizons in
the beds. The layout of the Fort Devens land treatment facility is
schematically depicted in Figure 7-21.
7.10.3 Operating Characteristics
Effluent is distributed within each treatment bed by discharging onto a
tapered concrete trough with slotted wooden splashboards, as shown in
7-61
-------
Figures 7-21 and 7-22. A view of several grass-covered basins with
accumulated organic material on the surface is shown in Figure 7-23.
Under normal operating conditions, the application cycle consists of
flooding three treatment beds concurrently with effluent for a 2 day
period, then allowing a 14 day recovery or dry-up period. On a yearly
basis, each bed receives effluent for a total of 52 days [27].
After the 2 days of flooding, effluent has normally accumulated on the
surface of the beds to a depth of 0.5 to 1.6 ft (15 to 50 cm). This
standing water infiltrates the beds within the initial 2 or 3 days of
the recovery period, restoring aerobic conditions to the surface of the
beds. Winter conditions, while reducing infiltration rates somewhat, do
not interfere with normal operations. The effluent is sufficiently
warm, 46 to 54°F (8 to 12°C) during the winter to melt any accumulated
ice and snow cover and to infiltrate and move through the sand beds.
Operation of the Fort Devens rapid infiltration basins normally involves
no routine maintenance. Solids build up on the surface, dry and crack
during the recovery period, and are degraded under the prevailing
aerobic conditions. During the summer, the sand beds have a good stand
of naturally occurring annual grasses and weeds (see Figure 7-22 and
7-23). No attempt is made to remove this vegetation as there is no
apparent detrimental effect. However, renovation of the bed surface has
been performed. This renovation consists of excavation to a depth of 1 ft
(0.3 m) depth to 1.5 to 4.0 ft (0.45 to 1.22 m) in order to remove a
an area adjacent to the treatment beds. The exposed surface is
scarified or raked prior to replacement of the excavated material. It
should be pointed out that this renovation procedure is not required
very often. The only cleaning operation was completed in October 1968
[26]. At this time it was necessary to excavate below the specific
1 ft (0.3 m) depth to 1.5 to 4.0 ft (0.45 to 1.22 m) in order to remove a
tarlike layer about 1.5 ft (0.45 m) thick which had formed below the
surface of the beds. Since the discovery of this tarlike layer, there
has been more surveillance of the dumping of oils and grease into the
system. Grease traps, installed at various locations in the collection
system to remove kitchen grease and fats and various oils from the
wastewater, are cleaned more frequently, and the materials collected are
deposited in sanitary landfills [27].
Normal operation and maintenance of the Fort Devens treatment facility
is carried out by two full-time employees. The application of daily
flows to various combinations of treatment beds is based on the
continued capacity of the beds to accept the effluent and from
operational experience developed over the years.
7-62
-------
FIGURE 7-21
LAND TREATMENT SYSTEM, FORT DEVENS, MASSACHUSETTS
01
OJ
WELL*1
CONCRETE TROUGH
WlTH WOODEN
SPLASHBOARDS
SAND
FILTER
BED
20
DISTRI-
BUTION
GA TE BOX '
OPERATOR'S
\ BUILDING
IMH 0 F F TANK \
\
SLUDGE DRYING BEDS
SROUNDWATER
MONI TOR ING WELLS
-------
FIGURE 7-22
DISTRIBUTION CHANNEL INTO RAPID INFILTRATION BASIN,
FORT DEVENS, MASSACHUSETTS
FIGURE 7-23
GRASS COVERED INFILTRATION BASINS,
FORT DEVENS, MASSACHUSETTS
7-64
-------
7.10.4 Treatment Performance
During 1973 and 1974, the U.S. Army Cold Regions Research and
Engineering Laboratory (CRREL) conducted extensive studies to determine
the effectiveness of the rapid infiltration basins at Fort Devens to
renovate unchlorinated primary sewage effluent. Groundwater quality
beneath the application site and the surrounding area was monitored by
collecting and analyzing bi-weekly samples from 21 observation wells
(Figure 7-21). Results of the chemical and bacteriological analyses of
the primary effluent and selected observation wells are summarized in
Table 7-30.
Analysis of the data has proved that the rapid infiltration system
serving Fort Devens is treating unchlorinated primary sewage effluent to
a quality comparable to that achieved by conventional tertiary
wastewater treatment facilities. The treatment basins were found to
greatly reduce the levels of BODg, COD, organic and ammonia nitrogen,
phosphorus, and total coliform bacteria in the applied effluent.
Although most wastewater constituents were increased in the native
groundwater, the quality of the groundwater peripheral to the treatment
sites continues to meet EPA drinking water standards, with the exception
of nitrate-nitrogen and coliform bacteria. While fecal coliform
determinations proved negative, total coliforms showed a mean value of
200 per 100 mL in the peripheral groundwater wells [26].
7.10.5 Research Studies
In 1974, further studies by CRREL were undertaken in an attempt to
optimize nitrogen removal. The objectives were to remove greater
amounts of nitrogen by management of the treatment system to enhance the
nitrification-denitrification processes. In an effort to achieve this,
the application cycle was modified from inundating 3 beds for 2 days,
followed by a 14 day recovery period, to inundating 9 beds for 7 days,
followed by a 14 day recovery period. Results of this study have shown
that an increase in inundation period continued to renovate the primary
effluent to a degree comparable to before. The total nitrogen levels of
the groundwater continued to be 20 mg/L. However,'when the treatment
basins were inundated for 7 days, the percentage of total nitrogen
removal was greater than when the basins were inundated for 2 days. By
increasing the inundation period, total nitrogen additions were
increased by 54% from about 32 to 50 lb/acre-d (36 to 55 kg/ha-d).
Although total nitrogen additions were larger during the 1974 study, a
proportional increase in groundwater nitrogen levels was not observed,
indicating a greater percentage of nitrogen removal. However, after 6
months of increased inundation period, the infiltration capacity had
been reduced so much that the basin surfaces were still wet at the
beginning of the next cycle of inundation and recovery. This gradual
decline in the basin infiltration capacity over several months was
attributed to clogging of the surfaces of the basins by accumulating
7-65
-------
organic matter. It was found that an occasional extended recovery
period of 60 consecutive days will rejuvenate the infiltration capacity
of the treatment basins so that the 7 day application/14 day recovery
cycle can once again be used. The restoration of infiltration capacity
during the extended recovery period is attributed to the aeration of the
surface and the subsequent oxidation of accumulated organics [29].
TABLE 7-30
CHEMICAL AND BACTERIOLOGICAL CHARACTERISTICS OF PRIMARY
EFFLUENT AND GROUNDWATER IN SELECTED OBSERVATION WELLS,
FORT DEVENS LAND TREATMENT SITE (1973, Average Values) [27]
Well3
Constituent6
BOD5
COD
Total nitrogen
Organic nitrogen
Ammonium nitrogen (NH.-N)
Nitrate nitrogen (N03-N)
Nitrite nitrogen (N02-N)
Total phosphate (P04-P)
Ortho phosphate (P04-P)
Chloride
Sulfate
Total col i forms, MPN/100 ml
ph, units
Conductivity, umhos
Alkalinity (as CaCOg)
Hardness (as CaCO,)
Depth of well below
ground level, ft
Primary effluent
112
192
47
23
21
1.3
0.02
11
9
150
42
3.2 x 107
6.2 - 8.0
511
155
41
--
1C
3.5
42
1.3
0.5
0.6
0.2
0.01
0.4
0.1
20
9
335
7.3
133
29
12
40
2
12
26
14.5
8.3
5.3
0.9
0.03
5.9
5.6
85
48
3 900
6.8
371
120
23
64
3
2.5
19
19.5
2.3
1.3
15.6
0.3
0.9
0.2
230
39
210
6.3
360
28
44
9.5
10
0.9
10
20.3
1.2
0.5
18.6
0.02
1.3
0.1
257
35
620
6.1
333
14
30
23
a. Well locations are shown in Figure 7-20.
b. mg/L unless otherwise noted.
c. Indicative of native groundwater quality.
1 ft = 0.305 m
7-66
-------
A tracer study conducted by the U.S. Army Medical Bioengineering
Research and Development Laboratory has demonstrated that viruses are
capable of movement past the upper soil layers [28]. The wastewater was
artificially spiked to provide a continuous virus concentration of
105 PFU/mL of wastewater applied to the treatment beds. This is a much
greater virus concentration than that normally found in domestic
wastewaters. The field studies at Fort Devens have shown that viruses
at this concentration are not impeded in the local soil strata and can
readily penetrate to the groundwater. In addition to poor adsorption,
other removal mechanisms such as filtration or straining were not a
factor, mainly because of the size of the sandy, silty, and gravelly
soils in relation to the extremely small virus particles. The virus
stabilized in the groundwater beneath the treatment basins at almost 50%
of the artificially high applied virus concentration.
The bacteriological indicator organisms were reported to behave
differently than the viruses at the rapid infiltration site. Total
coliform, fecal coliform, and fecal streptococcus organisms were readily
concentrated on the soil surface. Unlike the viruses, the bacteria were
filtered or strained at the soil surface. However, it was reported that
significant numbers of bacteria are capable of migration into the
groundwater [28].
7.11 Pauls Valley, Oklahoma
7.11.1 History
Pauls Valley is a community of 6 000 in south central Oklahoma. In
1962, a 4 cell, 33 acre (13 ha) lagoon was constructed to treat 0.7
Mgal/d (31 L/s) of wastewater, with some effluent used for irrigation.
In 1975, an experimental overland flow system was constructed to treat a
portion of the flow. Much of the experimental system was patterned
after the EPA research project at nearby Ada, Oklahoma [30, 31]. The
principal design factors are summarized in Table 7-31.
7.11.2 Project Description and Objectives
The purpose of the experimental system is to demonstrate the treatment
of both oxidation lagoon effluent and untreated municipal wastewater by
overland flow. The system consists of 32 terraces, each 0.25 (0.1 ha),
for a total of 8 acres (3.2 ha). Lagoon effluent is supplied to 8
terraces and screened untreated wastewater is supplied to the remaining
24 terraces. Lagoon effluent is taken from the second cell where it has
received approximately 30 days of detention.
Half the terraces are sloped at 2% and half at 3%. A typical terrace is
75 ft wide by 150 ft long (23 m by 45 m). Three distributor mechanisms
7-67
-------
TABLE 7-31
DESIGN FACTORS,
PAULS VALLEY, OKLAHOMA
Type of system
Avg flow, Mgal/d
Type of wastewater
Preapplication treatment
Disinfection
Storage
Field area, acres
Crops
Application technique
Routine monitoring
Buffer zones
Application cycle, h
Time on
Time off
Annual application rate, ft
Screened untreated wastewater
Oxidation lagoon effluent
Avg weekly application rate, in.
Screened untreated wastewater
Oxidation lagoon effluent
Avg annual precipitation, in.
Avg annual evaporation, in.
Capital costs, $/acrea
Overland flow
0.2
Domestic
Raw (screened) and oxidation lagoon
No
Not required
8
Fescue, annual rye, and Bermuda grass
Surface (bubbling orifice) and
sprinkler (fixed and rotating nozzle)
Yes
No
8-12
12-16
19
45
4'. 3
10.3
36
58.5
8 500
a. Includes construction costs of preapplication treatment and
engineering, 1975.
1 Mgal/d = 43.8 L/s
1 acre = 0.405 ha
1 ft = 0.305 m
1 in. = 2.54 cm
1 Ib/acre =1.12 kg/ha
1 $/acre =$2.47/ha
are used: (1) rotating booms with fan nozzles, (2) fixed fan nozzles at
the top of the slope as shown in Figure 7-24, and (3) the bubbling
orifice method as shown in Figure 7-25. The rotating boom is patterned
after those used at the Ada, Oklahoma research project [30].
The purpose of the multiple terraces is to compare the treatment
efficiencies and the operating conditions for: (1) screened untreated
wastewater versus oxidation lagoon effluent, (2) slopes at 2% versus
slopes at 3%, and (3) the three types of distributors.
7-68
-------
FIGURE 7-24
FIXED FAN NOZZLE, PAULS VALLEY, OKLAHOMA
7.11.3 Design Factors
The original seeding was 30 Ib/acre (34 kg/ha) fescue and 15 Ib/acre (17
kg/ha) annual rye. During the summer the annual rye dies out and
subsequent seeding with Bermuda grass has begun to grow. The
application is year-round; however, the oxidation
backup system and would provide storage if needed. The
permeable red clay.
lagoon acts as a
soil is a slowly
The bubbling orifice consists of a 6 in. (15 cm) PVC manifold with 0.75
in. (1.9 cm) outlets. The manifold is cradled in readily available
crushed limestone that is 0.6 in. to 1.50 in. (1.6 to 3.8 cm) in
diameter. The flow of wastewater spreads out and slows down as it
contacts the limestone and begins to travel down the slope.
7-69
-------
FIGURE 7-25
BUBBLING ORIFICE FOR WASTEWATER APPLICATION,
PAULS VALLEY, OKLAHOMA
7.11.4 Operation and Performance
Two related operating problems have taken much of the first year to
solve. The screening device used was not successful initially and large
solids were pumped into the system. This has resulted in frequent
clogging of the sprinkler nozzles. Improved screening has reduced the
clogging. Second, the grasses suffered from the heat and the
occasional dry periods of the first summer. Bermuda grass may become
the principal vegetation because of its tolerance for heat and water.
7.11.5 Costs
The construction cost for the research system in 1975 was approximately
$68 000, including roads, fencing, seeding, preappl ication treatment,
7-70
-------
earthwork, distribution, runoff piping, and engineering. Unit costs of
the three distributor systems are presented in Table 7-32. Each unit
supplies wastewater to a 0.25 acre (0.1 ha) terrace along the top of the
slopes.
TABLE 7-32
UNIT COSTS OF OVERLAND FLOW APPLICATION,
PAULS VALLEY, OKLAHOMA
Unit cost, Cost, $
Item Unit Number $ per acre
Fixed nozzle systems each 8 200 800
Rotating boom systems each 16 375 1,500
Bubbling orifice systems each 8 140 560
7.12 Paris, Texas
7.12.1 History
In 1960, the Campbell Soup Company began to construct an overland flow
system at Paris, Texas. When the food processing plant began operating
at the end of 1964, there were 300 acres (120 ha) of prepared slopes
with a vegetative cover of mixed grasses ready for wastewater treatment.
The system has been expanded in three increments to the present 900
acres (360 ha). In 1968, a 12 month intensive monitoring program was
conducted and the results have been widely published [32, 33, 34, 35].
The principal design factors are presented in Table 7-33.
7.12.2 Objectives and Description
The objective of the overland flow system is to treat the food
processing wastewater in an efficient and cost-effective manner [36].
The construction of the overland flow system also resulted in the
reclamation of the heavily eroded rolling terrain.
Wastewater from the heat processing of soups, beans, and spaghetti-type
products is collected in two drainage systems. The first, containing
grease from cooking, is routed through a gravity grease separator before
it joins the second waste stream from the vegetable trimming area. The
combined stream passes through revolving drum-type #10-mesh screens
prior to being pumped to the sprinklers [34].
7-71
-------
TABLE 7-33
DESIGN FACTORS,
PARIS, TEXAS
Type of system
Avg flow, Mgal/d
Type "of wastewater
Preapplication treatment
Disinfection
Storage
Field area, acres
Crops
Application technique
Routine monitoring
Buffer zones
Application cycle, h
Time on
Time off
Annual application rate, ft
Avg weekly application rate, in.
Avg annual precipitation, in.
Avg annual evaporation, in.
Annual nitrogen loading, Ib/acre
Capital costs, $/acrea
Unit operation and maintenance
cost, £/l 000 galb
Overland flow
4.2
Food processing
Grease removal and screens
No
Not required
900
Reed canary, tall fescue, redtop,
and perennial rye
Sprinkler (buried pipe)
Yes
No
6-8
16-18
5.2
2-3
45
36
240
1 500
4.8
a. Excluding land, 1976.
b. 1971.
1 Mgal/d = 43.8 L/s
1 acre = 0.405 ha
1 ft = 0.305 m
1 in. = 2.54 cm
1 Ib/acre =1.12 kg/ha
1 $/acre = $2.47/ha
1 4/1 000 gal = 0.264
Wastewater is applied to the overland flow terrace by impact-type
sprinklers. The original sprinkler system consisted of 4 in. (10 cm)
aluminum irrigation pipe as laterals laid on the surface
recently constructed terraces have buried laterals.
wastewater is collected as runoff in grassed waterways and is discharged
into a creek.
but the more
The treated
7-72
-------
7.12.3 Design Features
While the current hydraulic loading is 5.2 ft/yr (1.6 m/yr), the system
has operated effectively at higher rates. In the 1968 research program,
the total annual application was measured at 11 ft (3.4 m) for the 11.4
acres (4.6 ha) monitored and rainfall was 4.7 ft (1.4 m). Of this total
amount of water, 18% was accounted for as evapotranspiration, 61% as
runoff, and 21% assumed as percolation [34].
The rolling terrain was graded into terraces with slopes ranging from 1
to 12%. In the more recently added fields, slopes of from 2 to 6% are
used. Slope lengths range from 200 to 300 ft (61 to 92 m). The slopes
are seeded to a mixture of Reed canary grass, tall fescue, red top, and
perennial rye grass [36]. Reed canary grass has become the predominant
grass on the mature slopes.
7.12.4 Operation and Performance
The treatment performance documented in 1968 is compared to recent
effluent quality in Table 7-34. BOD and COD removals on a concentration
basis have improved and are relatively consistent throughout the year,
as shown in Table 7-35. The suspended solids removals are not as
high as BOD removals and are not as consistent. Despite the wide range
in pH of the wastewater, the runoff is consistently between 6.6 and 7.5.
TABLE 7-34
TREATMENT PERFORMANCE DURING 1968
COMPARED TO EFFLUENT QUALITY IN 1976, PARIS, TEXAS [35, 37]
1968 values
June
1976
Constituent
BOD, mg/L
COD, mg/L
Suspended sol Ids, mg/L
Total nitrogen, mg/L
Total phosphorus, mg/L
Chloride, mg/L
Influent
572
806
245
17.2
7.4
44
effluent
9
67
16
2.8
4.3
47
effluent
1.9
45
34
• * * •
• • * •
43
Electrical
conductivity, j/mhos/cm 449
pH, unit
4.4-9.3
490
6.2-8.1
6.6
7-73
-------
TABLE 7-35
SEASONAL QUALITY OF TREATED EFFLUENT
PARIS, TEXAS
mg/L
Month
1975
Jul
Aug
Sep
Oct
Nov
Dec
1976
Jan
Feb
Mar
Apr
May
Jim
Average
BOO
3.1
3.4
1.9
2.7
2.7
3.1
6.5
3.6
3.4
4.6
2.3
1.9
3.3
COD Suspended solids
44
43
38
32
36
34
38
40
44
50
43
45
41
34
17
15
15
23
15
15
19
37
76
38
34
28
The grass was cut but not removed in 1965 and 1966. In 1967, the hay
was harvested and in 1968 three cuttings were made for a total yield of
3.65 tons/acre (8.2 Mg/ha) [32]. Currently, the grass is cut once a
year and it is harvested green, dried in a hay dryer, and converted to
pellets for animal feed [36], The grassed terraces are shown in Figure
7-26. Because the slopes are nearly always wet, access is restricted to
vehicles with high-flotation tires.
7.12.5 Costs
Construction and operating costs reported in 1971 are shown in Table
7-36. It is estimated that the $1 007/acre ($2 483/ha) construction cost
{excluding land) has increased to about $1 500/acre ($3 700/ha) by 1976
[36].
In 1976, 10 men (3/shift) and a supervisor were required to operate the
system. Maintenance includes checking and replacing sprinkler heads
(which have a service life of 4 to 5 years).
7-74
-------
FIGURE 7-26
OVERLAND FLOW TERRACES AT PARIS, TEXAS
TABLE 7-36
CONSTRUCTION AND OPERATING COSTS,
PARIS, TEXAS [34], 1971
Construction costs, $/acre
Site clearing, grading,
and drainage ditches 362
Planting and fertilizing 108
Pipeline and
sprinkler system 348
Engineering, surveying,
and equipment 188
Total 1 007
Operating costs, c/1 000 gal
Labor
Maintenance
Power
Miscel laneous
Subtotal
Revenue
Total
3.2
1.4
0.2
0.4
5.2
0.4
4.8
1 S/acre = S2.47/ha
1 */l 000 qal = 0.264
7-75
-------
7.12.6 Monitoring
In addition to the constituents listed in Table 7-35, the regular
monitoring program includes analyses of temperature, pH, total residue,
chlorides, sulfates, oil and grease, color, and dissolved oxygen. The
total runoff flow is monitored continuously and samples are taken every
3 days for analyses.
7.12.7 Microbiology
Research on the soil microbiology at Paris has been reported by Vela
[38] and Vela and Eubanks [391. Populations of heterotrophic soil
bacteria ranged from 106 to 1Q8 organisms/gram of soil [39]. Large
populations (1.5 X 105 to 7.4 x 105 organisms/gram of soil) of
psychrophilic bacteria that are capable of actively growing at 2°C were
also found, although the soil reaches this low temperature only a few
days of the year [38]. This large microbial population sustains a high
level of treatment even when low temperatures occur.
7.13 Other Case Studies
Many existing case studies of land treatment were necessarily excluded
in this chapter. Lubbock, Texas, is an example of a slow rate system
where a farmer is contracting for municipal effluent for irrigation on
his land [40, 41]. At Tallahassee, Florida, research on nutrient
removal has preceded full scale plans for treatment [42]. Case studies
of operations at Quincy,Washington; and Manteca, California [43]; and
Livermore, California [44], have also been reported.
For rapid infiltration the studies at Santee [45] and Whitter Narrows,
California, [46] are ° available. The Calumet, Michigan, rapid
infiltration system, probably the oldest rapid infiltration system in
the United States, is being studied. Untreated, undisinfected
wastewater at a flow of 1.2 Mgal/d (53 L/s) has been treated on 12 acres
(4.8 ha) since 1887 [47, 48].
The most prominent overland flow system that is not included as a case
study is at Melbourne, Australia. It has been operating successfully
for several decades [49].
7-76
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7.14 References
1. Hartman, W.J., Jr. An Evaluation of Land Treatment of Municipal
Wastewater and Physical Siting of Facility Installations. May
1975.
2. Monaco, A.N. Personal Communication. Public Works Field
Superintendent, City of Pleasanton, Calif. October 1976.
3. Sullivan, R.H., et al. Survey of Facilities Using Land Application
of Wastewater. Environmental Protection Agency, Office of Water
Program Operations. EPA-430/9-73-006. July 1973.
4. Erler, T. Personal Communication. Kennedy Engineers. San
Francisco, Calif. October 1976.
5. Sorenson, S. Personal Communication. USGS. Menlo Park, Calif.
November 1976.
6. Anderson, E.W. Twentieth Annual Report of the Sewage Treatment
Works for Walla Walla, Washington; 1973. Walla Walla, Washington.
December 1974. 27 p.
7. Crites, R.W. Irrigation With Wastewater at Bakersfield,
California. In: Wastewater Use in the Production of Food and
Fiber, EPA-660/2-74-041. June 1974. pp 229-239.
8. Texas Water Quality Board. Intensive Surface Water Monitoring
Survey for Segment No. 1421 (Concho River). Report No. 1MS-2.
1974.
9. Koederitz, T.L. Personal Communication. Water Superintendent,
City of San Angelo, Tex. January 1977.
10. Weaver, R.W. Personal Communication. Texas A&M. April 1977.
11. Culp, G.L. and D.H. Hinrichs. A Review of the Operation and
Maintenance of the Muskegon County Wastewater Management System.
Muskegon County Board of Works. Muskegon, Mich. June 1976.
12. Demirjian, Y.A. Land Treatment of Municipal Wastewater Effluents,
Muskegon County Wastewater System. Environmental Protection
Agency, Technology Transfer. 1975.
13. Walker, J.M. Wastewater: Is Muskegon County's Solution Your
Solution? Environmental Protection Agency, Region V, Office of
Research and Development. September 1976.
14. Corn, P. Personal Communication. Interstate Development Corpora-
tion. 1976.
15. Lehtola, C. and J. Ayars. Personal Communication. Department of
Agricultural Engineering, University of Maryland. 1976.
7-77
-------
16. Bouwer, H., R.C. Rice, and E.D. Escarcega. High-Rate Land
Treatment I: Infiltration and Hydraulic Aspects of the Flushing
Meadows Project. Jour. WPCF. 46:834-843, May 1974.
17. Bouwer, H., J.C. Lance, and M.S. Riggs. High-Rate Land Treatment
II: Water Quality and Economic Aspects of the Flushing Meadows
Project. Jour. WPCF. 46:844-859, May 1974.
18. Bouwer, H. Personal Communication. Director, U.S. Water
Conservation Laboratory, USDA, Phoenix, Ariz. March 1977.
19. Gilbert, R.G., et al. Wastewater Renovation and Reuse: Virus
Removal by Soil Filtration. Science. (Reprint). 192:1004-1005,
June 1976.
20. Aulenbach, D.B. and T.J. Tofflemire. Thirty-Five Years of
Continuous Discharge of Secondary Treated Effluent Onto Sand Beds.
Ground Water. 13(2):161-166, March-April 1975.
21. Beyer, S.M. Flow Dynamics in the Infiltration-Percolation Method
of Land Treatment. M.S. Thesis, Rensselaer Polytechnic Institute,
Troy, N.Y. May 1976.
22. Aulenbach, D.B., N.L. Clesceri, T.J. Tofflemire, S. Beyer, and L.
Hajas. Water Renovation Using Deep Natural Sand Beds. Jour. AWWA.
67:510-515, September 1975.
23. Fink, W.B., Jr. and D.B. Aulenbach. Protracted Recharge of Treated
Sewage Into Sand, Part II - Tracing the Flow of Contaminated Ground
Water With a Resistivity Survey. Ground Water. 12(4):219-223,
July-August 1974.
24. Aulenbach, D.B., et al. Protracted Recharge of Treated Sewage Into
Sand. Part III - Nutrient Transport Through the Sand.
Groundwater. 12(5):301-309, September-October 1974.
25. Hajas, L. Purification of Land Applied Sewage Within the Ground
Water. Thesis, Rensselaer Polytechnic Institute, Troy, N.Y.
December 1975.
26. Satterwhite, M.B. and G.L. Stewart. Evaluation of an Infiltration-
Percolation System for Final Treatment of Primary Sewage Effluent
in a New England Environment. In: Land as a Waste Management
Alternative. Loehr, R.C. (ed.). Ann Arbor, Ann Arbor Science.
1977. pp 435-450.
27. Satterwhite, M.B., et al. Rapid Infiltration of Primary Sewage
Effluent at Fort Devens, Massachusetts. U.S. Army Cold Regions
Research and Engineering Laboratory. Hanover, N.H. 1976.
28. Schaub, S.A., et al. Land Application of Wastewater: The Fate of
Viruses, Bacteria, and Heavy Metals at a Rapid Infiltration Site.
U.S. Army Medical Bioengineering Research and Development
Laboratory. Fort Detrick, Md. May 1975.
7-78
-------
29. Satterwhite, M.B., et al. Treatment of Primary Sewage Effluent by
Rapid Infiltration. U.S. Army Cold Regions Research and
Engineering Laboratory. Hanover, N.H. 1976.
30. Thomas, R.E., K. Jackson, and L. Penrod. Feasibility of Overland
Flow for Treatment of Raw Domestic Wastewater. Environmental
Protection Agency, Office of Research and Development. EPA-660/2-
74-087. July 1974.
31. Thomas, R.E., B. Bledsoe, and K. Jackson. Overland Flow Treatment
of Raw Wastewater With Enhanced Phosphorus Removal. Environmental
Protection Agency, Office of Research and Development. EPA-600/2-
76-131. June 1976.
32. C.W. Thornthwaite Associates. An Evaluation of Cannery Waste
Disposal of Overland Flow Spray Irrigation. Publications in
Climatology, 22, No. 2. September 1969.
33. Thomas, R.E., J.P. Law, Jr., and C.C. Harlin, Jr. Hydrology of
Spray-Runoff Wastewater Treatment. Journal of the Irrigation and
Drainage Division, Proceedings of the ASCE. 96(3):289-298,
September 1970.
34. Gilde, L.C., et al. A Spray Irrigation System for Treatment of
Cannery Wastes. Jour. WPCF. 43:2011-2015, October 1971.
35. Law, J.P., Jr., R.E. Thomas, and L.H. Myers. Cannery Wastewater
Treatment by High-Rate Spray on Grassland. Jour. WPCF, 42:1621-
1631, 1970.
36. Neeley, C.H. The Overland Flow Method of Disposing of Wastewater
at Campbell Soup Company's Paris, Texas, Plant. (Presented at the
Mid-Atlantic Industrial Waste Conference. University of Delaware.
January 1976.)
37. Neeley, C.H. Personal Communication. Plant Service Manager,
Campbell Soup Co., Paris, Tex. 1976.
38. Vela, G.R. Effect of Temperature on Cannery Waste Oxidation.
Jour. WPCF. 46:198-202, January 1974.
39. Vela, G.R. and E.R. Eubanks. Soil Microorganism Metabolism in
Spray Irrigation. Jour. WPCF. 45:1789-1794, August 1973.
40. Gray, J.F. Practical Irrigation With Sewage Effluent. In:
Proceedings of the Symposium on Municipal Sewage Effluent for
Irrigation. Louisiana Polytechnic Institution. July 1968. pp 49-
59.
41. Wells, D.M., et al. Effluent Reuse in Lubbock. In: Land as a
Waste Management Alternative. Loehr, R.C. (ed.). Ann Arbor, Ann
Arbor Science. 1977. pp 451-466.
7-79
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42. Overman, A.R and A. Ngu. Growth Response and Nutrient Uptake by
Forage Crops Under Effluent Irrigation. Commun. Soil Science and
Plant Analysis. 6:81-93, 1975.
43. Murrman, R.P. and I.K. Iskandar. Land Treatment of Wastewater.
(Presented at the 8th Annual Waste Management Conference,
Rochester, N.Y. April 1976.) Corps of Engineers, U.S. Army Cold
Regions Research and Engineering Laboratory. Hanover, N.H.
44. Uiga, A., I.K. Iskandar, and H.L. McKim. Wastewater Reuse at
Livermore, California. (Presented at the 8th Annual Cornell Waste
Management Conference, Rochester, N.Y. April 1976.) Corps of
Engineers, U.S. Army Cold Regions Research and Engineering
Laboratory. Hanover, N.H.
45. Merrell, J.C., et al. The Santee Recreation Project, Santee,
California, Final Report. FWPCA, U.S. Dept. of the Interior,
Cincinnati. 1967.
46. McMichael, F.D. and J.E. McKee. Wastewater Reclamation at Whittier
Narrows. California State Water Quality Control Board. Publica-
. No. 33. 1966.
47. Baillod, C.R., et al. Preliminary Evaluation of 88 Years Rapid
Infiltration of Raw Municipal Sewage at Calumet, Michigan. In:
Land as a Waste Management Alternative. Loehr, R.C. (ed.). Ann
Arbor, Ann Arbor Science. 1977. pp 435-450.
48. Uiga, A. and R. Sletten. An Overview of Land Treatment From Case
Studies of Existing Systems. (Presented at the 49th Annual Water
Pollution Control Federation Conference, Minneapolis, Minn.
October 1976.) Corps of Engineers, U.S. Army Cold Regions Research
and Enginering Laboratory. Hanover, N.H.
49. Seabrook, B.L. Land Application of Wastewater in Australia.
Environmental Protection Agency, Office of Water Programs. EPA-
430/9-75-017. May 1975.
7-80
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Chapter 8
DESIGN EXAMPLE
8.1 Introduction
The design of a land treatment system is highly dependent on conditions,
such as climate, soil, topography, and many others. As a cofisequence,
no design example can be universal; however, the example should be
illustrative of a design procedure in which the feasible alternatives
are developed and assessed according to the methods in this design
manual.
This presentation is adapted from a design example prepared by Mr.
Sherwood Reed of USA CRREL for use in Corps of Engineers training
courses. It is intended to present the development and evaluation of
land treatment alternatives. As such, the design is not intended to be
complete, since many components of a complete system, such as a
transmission system and pumping stations, are omitted. The elimination
of these components from this example will not allow a complete cost-
effective comparison between land treatment and conventional treatment
alternatives. Cost data used in this example were taken from sources
described in Chapter 3.
The approach here is to present a statement of the problem and the data
from which preliminary design alternatives, based on annual loadings,
and process performance estimates are developed. A relative cost
comparison between the developed process alternatives is presented from
which the most cost-effective alternative can be chosen for final
design. The final process design is based on more detailed analyses,
including monthly loading distributions.
b.2 Statement of Problem
The problem is to provide adequate wastewater treatment tor a community
that has an existing primary treatment plant and surface water
discharge. The recommended design must be the most cost-effective
alternative and adapted to local conditions.
8.3 Design Data
8.3.1 Location
The problem area
existing community
is located in the northeastern United States. The
has a present population of 70 000, with a 20 year
8-1
-------
design population of 90 000. The design wastewater flow is 10 Mgal/d
(438 L/s). The existing treatment facilities for the community consist
of a primary treatment plant with disinfection and sludge digestion. At
present, the effluent is discharged to a river, and the digested sludge
is applied to the land. The system was constructed in the early 1940s
and is in very poor structural and mechanical condition, so it will be
abandoned.
8.3.2 Climate
The climatic influences on land treatment are an important aspect in
determining storage and length of the application season for slow rate
and overland flow systems. The climatic data for the site was obtained
from the National Oceanic and Atmospheric Administration's Climatic
Summary of the United States for 20 years of record, and are presented
Tn Table 8-1. For the worst year in 10, there are 142 days (mostly
between November and March) in which the mean air temperature is less
than 32°F (0°C). As indicated in Section 5.3, this necessitates storage
for slow rate and overland flow systems. The annual precipitation of
50.2 in. (128 cm) occurs fairly uniformly throughout each month of the
year. A total evapotranspiration of 25.1 in. (64 cm) occurs from late
March to early November. The difference between precipitation and
evapotranspiration, as given in Table 8-1,
monthly nitrogen and hydraulic balances.
is used in computing
TABLE 8-1
CLIMATIC DATA FOR THE WORST YEAR IN 10
Temperature, °F
Month
Nov
Dec
Jan
Feb
Mar
Apr
May
Jun
Jul
Aug
Sep
Oct
Annual
Mean
41.6
29.4
26.0
28.4
34.3
47.3
57.5
66.3
72.0
69.8
62.2
51.8
48.9
Mean daily
minimum
31.0
20.8
16.7
16.0
25.0
35.7
46.2
55.3
60.7
58.3
51.4
40.4
38.1
Days with
mean
temperature
±32°F
16
28
30
26
26
7
1
0
0
0
1
7
142
Precipitation (Pr)
Total,
in.
4.8
4.2
4.3
3.5
5.0
4.6
3.9
3.3
3.8
4.0
4.2
4.6
50.2
Days with
mean £0.5 in.
4
3
3
2
4
3
3
2
2
3
2
3
34
(ET)
Evapo-
transpi ration,
in.
0.8
0
0
0
0.2
1.4
3.2
4.6
5.4
4.3
3.3
1.9
25.1
Monthly net
water excess
(Pr - ET), .
in.
4.0
4.2
4.3
3.5
4.8
3.2
0.7
-1.3
-1.6
-0.3
0.9
2.7
25.1
1 °F = 1.8 x °C + 32
1 in. = 2.54 cm
8-2
-------
8.3.3 Wastewater Characteristics
The characteristics of the wastewater are important in determining
hydraulic and wastewater component application rates. To avoid nuisance
conditions during winter storage, biological treatment in lagoons will
be provided. The characteristics of the mostly domestic wastewater are
presented in Table 8-2 along with the anticipated quality of the
wastewater applied to the land after storage. Limited information on
the quality of the Susanna River and native groundwater is also
presented. The concentrations of trace metals are low, and mass
application criteria for them are presented in Section 8.7.1.3.
TABLE 8-2
WATER QUALITY CHARACTERISTICS3
Parameter
BODs, mg/L
Suspended solids, mg/L
Total dissolved solids, mg/L
Total nitrogen as N, mg/L
Ammonia as N, mg/L
Organic as N, mg/L
Nitrate as N, mg/L
Total phosphorus as P, mg/L
Chloride, mg/L
Dissolved oxygen, mg/L
CCE
Total coliforms, MPN/100 mL
Raw
wastewaterb
240
240
500
40
20
20
0
10
40
Wastewater to
be applied to
landc
40
45
470
28
10
4
14
8
37
2 000
Susanna
Riverd
3.9
250
6.0
20
5.0
0.16
Groundwater6
...
400
. . .
6
35
a. Trace metal concentrations are within the typical range for municipal
wastewaters. Discussion is included in Section 8.7.1.3.
b. Data obtained from existing wastewater treatment plant records.
c. Assumed preapplication treatment by aerated lagoon plus storage.
d. Data obtained from State Water Quality Control Board.
e. Data obtained from USGS.
b.3.4 Discharge Limitations
The Susanna River, which is used as a public drinking water supply, has
an average flow of 60 ft3/s (1.7 m3/s), a low flow of 44 ft3/s (1.2
m3/s), and a minimum dissolved oxygen concentration of 5.0 mg/L. Five
miles (8 km) downstream from the existing wastewater treatment plant,
the Susanna River flows into an estuary which is widely used for
8-3
-------
recreation. The State Water Quality Regulatory Agency has imposed the
following limits on surface discharges (expressed as mg/L, 30 day
averages):
BOD5 4.0
Suspended solids 1
Phosphorus as P 0.1
Total Kjeldahl nitrogen 1
Nitrate-nitrogen 5
Total nitrogen as N 6
Maximum total chlorine residual 0.1
Total coliforms, organisms/100 nl 3
The groundwater aquifer is a potential drinking water source and fits
Case I (see Section 5.1.1) so the EPA drinking water criteria for
chemical and pesticide levels would therefore apply to discharges to
groundwater. The most critical groundwater criterion would be a nitrate-
nitrogen concentration not to exceed 10 mg/L (at site boundary).
8.3.5 Site Investigation
A preliminary investigation (see Section 3.5) of the lands adjacent to
the community has determined that about 11 000 acres (4 450 ha) is
available. The general topography of the area is shown in Figure 8-1.
The area is bounded on the south by the Susanna River, which flows
westerly. The existing water treatment plant and intake, and wastewater
treatment plant and outfall are in the southwestern corner. The land
increases in elevation from about 100 ft (30 m) above mean sea level
near the Susanna River to a maximum elevation of 450 ft (136 m) at
Clyde's Saddle. The surface slopes in the range of 1 to 4%, although a
relatively flat area of 0 to 2% occurs in the eastern portion.
8.3.5.1 Soil Description
The type and location of agricultural soils as described in the SCS
report for the study area include Hunt clay (HpG), Hanover loamy sand
(Hn), and Bomoseen sandy clay loam (BsN), as shown in Figure 8-2.
The Hunt clay is a red-brown clay with a thin surface mantle of silt
loam. Drainage is very poor with permeability of less than 0.2 in./h
(0.5 cm/h). It is fair to good for grasses and legumes; poor for grain
and seed crops and hardwood trees; and not suited for coniferous trees.
The Hanover loamy sand is a well-drained soil with a distance of 10 ft
(3 m) or more to the water table. The permeability is at least 3 in./h
8-4
-------
00
i
in
FIGURE 8-1
GENERAL TOPOGRAPHY
WATER
TREATMENT PLANT
WASTEWATER
TREATMENT
OUTFALLOO PLAN
1 in.= 2.54 cm
1 ft = 0.305 m
-------
oo
CTl
FIGURE 8-2
AGRICULTURAL SOIL MAP
0 2000 4000
•
SCALE IN FEET
= SOI L BORINGS, BsN
BOMOSEEN SANDY CLAY LOAM, Hn- HANOVER LOAMY SAND, HP6-HUNT CLAY,
-------
(8 cm/h). It is fair to good for grain, seed crops, grasses, and
legumes; good for hardwoods, and fair for coniferous trees.
The Bomoseen sandy clay loam is well drained, underlain by fine sands
with 10 ft (3 m) or more to groundwater^ The permeability is 0.6 in./h
(1.5 cm/h). It is good for grain, seed, grass, legumes, and hardwoods;
and fair for conifers. A descriptive summary of the soil types,
including system suitability and available area, is presented in
Table 8-3.
TABLE 8-3
AVAILABLE LAND AREAS BY SOIL TYPE'
Soil
type
BsN-1
BsN-2
Hn
HpG-lb
HpG-2c
Soil
description
Sandy clay loam
Sandy clay loam
Loamy sand
Clay
Clay
Maximum
slope, %
2
3-4
3
2
3-4
Permeability,
in./h
0.6
0.6
3
<0.2
<0.2
System suitability
jSlow rate
Slow rate
Rapid infiltration
and slow rate
Overland flow
Overland flow
Total
Available
acres
4 240
330
1 340
1 230
4 020
11 160
a. Data from SCS report.
b. Area between 100 and 200 ft contours (half clear, half brush, and woodland).
c. Area above 200 ft contour (all brush and woodland).
1 acre = 0.405 ha
1 ft = 0.305 m
The general soils evaluation shows that within the study area, there
exist soil types that appear to be suitable for all three land treatment
processes. Further assessment of their suitability requires additional
information on the subsurface geology.
8.3.5.2 Soil Borings
Well logs or other information on the soil profile were not available.
Consequently, twelve preliminary soil borings were made as shown in
Figure 8-2 to confirm the SCS soil map. The results from the boring logs
show that groundwater was encountered at the single drill hole (No. 1)
and that the depth to bedrock varied from a minimum of 20 ft (6 m) at
borings Nos. 4 and 5 to a maximum of 70 to 80 ft (21 to 24 m) at borings
Nos. 1 and 8. The underlying geology is a mixture of sands and gravels
with clay and fine sand occurring at various depths without hardpan
layers. The borings at the lowest elevations have the greatest depth to
8-7
-------
bedrock, with decreasing soil depth as the elevation increases. The
subsoil geology has equal to or greater permeability than the upper soil
horizons.
8.3.5.3 Vegetative Cover
The vegetative cover is important as an indicator of the growth con-
ditions for a soil type and as a factor in determining costs of clearing
and other site preparation. As shown in Figure 8-3, in the eastern
part of the study area, there are open lands and native grasses on the
Bomoseen sandy clay loam. In the southwest corner of the study area,
there is previously cleared land on Hanover loamy sand and Hunt clay.
In the rest of the study area (proceeding northward towards Clyde's
Saddle), there is a wooded area of brush and trees, mostly underlain
with Hunt clay.
8.4 Process Alternatives
8.4.1 Slow Rate System
The initial determination of the required field area is made using the
annual water balance:
Pr + Lw = ET + Wp + R (8-1)
where Pr = precipitation, ft/yr (cm/yr)
Lw = wastewater hydraulic loading, ft/yr (cm/yr)
ET = evapotranspiration, ft/yr (cm/yr)
Wp = percolating water, ft/yr (cm/yr)
R = runoff, ft/yr (cm/yr)
In this case, runoff of applied water will be retained and thus will be
considered negligible. The relationship between precipitation and
evapotranspiration is given in Table 8-1. Precipitation exceeds
evapotranspiration by 2.1 ft/yr (64 cm/yr). Wastewater applications are
scheduled for periods when the mean air temperature is above 32°F (0°C),
approximately from March 25 to November 3 (Table 8-1). This 32 week
application season will avoid extreme temperatures and frozen ground
conditions, will ensure some crop response, and necessitate 20 weeks of
storage within the design year. The percolating water can be estimated
from Figure 3-3 using the permeability value of 0.6 in./h (1.5 cm/h)
for the Bomoseen sandy clay loam. A conservative rate of about 3.5
in./wk (8.9 cm/wk) is chosen because crop production is planned. This
value is multiplied by the 32 week season to determine the annual
loading.
(3.5 in./wk) (32 wk/yr) * 12 in./ft = 9.3 ft/yr
8-8
-------
CO
l
FIGURE 8-3
EXISTING VEGETATIVE COVER
0 2000 4000
ml ^
SCALE IN FEET
OPEN LAND
NATIVE GRASSES
-------
The total liquid loading would be reduced by the 2.1 ft/yr (64 cm/yr) of
excess precipitation (Table 8-1) for a resultant loading of 7.2 ft/yr
(216 cm/yr). The required field area is then calculated to be:
F = 3-06 Q (8-2)
I
Lw
where F = field area, acres
Q = annual wastewater flow, Mgal/yr
Lw = wastewater loading, ft/yr
F = 3.06 (10H365)
7.2
F = 1 551 acres
say = 1 600 acres
An examination of the soil classification data and soil boring logs
shows that the soils classified as BsN and Hn would be hydraulically
suitable for slow rate systems. These soils, as located along the
Susanna River and east of Clyde's Saddle (Figure 8-2), comprise 5 910
acres (2 387 ha) (Table 8-3) of suitable land. Thus, it appears that
the slow rate process would be potentially feasible for this location
and should be investigated further using a nitrogen balance (see Section
8.7.1) to determine if groundwater criteria can be satisfied.
8.4.2 Rapid Infiltration System
The determining factor in hydraulic application is the soil
permeability. The Hanover loamy sand has a permeability of at least
3 in./h (8 cm/h), so a wastewater application rate of 25 in./wk (64
cm/wk) is estimated from Figure 3-3. Based on a 52 wk/yr operation,
this results in an annual application rate of 110 ft/yr (33.5 m/yr).
The wetted field area can be estimated in the same manner as a slow rate
system, giving a required wetted field area of 100 acres (45 ha) as
follows:
F = (3.06M3 650)/110 = 100 acres
The alternate flooding and drying cycle can be accomplished by having
multiple basins, with a set of basins being flooded for 4 days to
promote good denitrification followed by an 8 day drying period. This
operational schedule results in approximately one-third of the field
area (8 or 9 basins) being flooded and two-thirds (16 or 17 basins)
being rested at any given time. Approximately 1 350 acres (614 ha) of
suitable soil exists, so this alternative should be investigated further
to determine if it can satisfy water quality requirements.
8-10
-------
8.4.3 Overland Flow System
Overland flow systems require slopes from 2 to 8% on relatively
impermeable soils. The almost continuously wet field conditions are not
conducive to normal forest or agricultural cover, but usually require
special grasses. Nitrogen removal is dependent on complex biochemical
responses in addition to crop uptake. These biochemical responses are
temperature dependent so there are climatic constraints on overland flow
systems.
Since terraces having appropriate slopes and dimensions can be formed
and proper soils are available, it should be possible to apply
approximately 8 in./wk (20.3 cm/wk) of lagoon effluent during the summer
growing season and approximately half that amount, 4 in./wk (10.2
cm/wk), in the spring and fall (Section 5.1.4.1). Since winter storage
requires some form of treatment oxidized wastewater will be applied to
the slopes. Operational experience will dictate the degree of oxidation
required; it may be possible to shut down all of the aerators during the
summer. The application schedule and storage requirements are presented
in Table 8-4, using the number of days with mean temperature less than
32°F (0°C). The results give a design application of 17.8 ft/yr (5.4 m)
and a storage requirement of approximately 142 days.
TABLE 8-4
DETERMINATION OF OVERLAND FLOW APPLICATION SCHEDULE
BASED ON CLIMATIC DATA3
Total No.
of days in
Time period time period
Nov 16 -
Apr 21 -
May 1 -
Oct 1 -
Total
Apr 20
Apr 30
Sep 30
Nov 15
156
10
153
46
365
No. of days
with mean
temperature Applicatio
532°F period, d
133
0
2
7
142
23
10
151
39
223
Application schedule
No. of wks
3.3
1.4
21.6
5.6
31.9
in./wk applied, in.
4 13.2
4 5.6
8 172.8
4 22.4
214.0
a. Based on worst year in 10, from Table 8-1.
1 in. = 2.54 cm
The required field area is 627 acres (254 ha), as computed by the same
method used for the slow rate system:
F = (3.06H3 650) = 627 acres
17.8 ft/yr
8-11
-------
An examination of the soils data indicates that the area north of the
water treatment plant on the lower slopes of Clyde's Saddle will
probably be suitable. Between elevation 100 ft (30 m) and elevation 200
ft (61 m) there is at least 1 230 acres (497 ha) of soils suitable for
constructing an overland flow system, hence'overland flow should also be
considered further.
8.5 Preliminary Performance Estimate
8.5.1 Slow Rate System
The capability of the slow rate system to meet Case 1 groundwater
standards was determined by assuming a 10 mg/L aesign concentration for
nitrate-nitrogen. Removal of phosphorus is excellent, with expected
removals greater than 99%, even though a phosphorus limit does not exist
for drinking water. The concentrations of BOD and suspended solids in
the percolate should be less than 1 to 2 mg/L, and pathogenic organism
removal by the Bomoseen sandy clay loam should be complete within the
upper 2 ft (0.6 m) of the soil.
The limiting design criteria is nitrogen. Based on existing system
performance (see Chapter 7), the concentration of nitrate-nitrogen in
the slow rate system percolate will be better than the 10 mg/L design
value. In addition, the design for 10 mg/L percolate nitrate-nitrogen
concentration is conservative, because significant dilution of the
percolate nitrate-nitrogen will most likely occur as the percolate water
mixes with the underlying native groundwater. Also, design flows are
assumed for 1990, so initial applications will be less, and subsequent
nitrogen performance better. Seasonal variations in performance should
be satisfied by variable monthly applications. The monthly application
criteria will be developed if slow rate systems are most cost effective.
8.5.2 Rapid Infiltration System
The treatment performance of a rapid infiltration system should be
assessed because design applications are usually determined by hydraulic
considerations rather than wastewater constituent applications. For
this example, the performance should be evaluated for groundwater
discharge, as well as surface discharge. The soil permeability and
subsurface geology are both suitable for groundwater discharge.
The total nitrogen applied to the land in a rapid infiltration system
can be estimated from Equation 5-3:
Ln = 2.7 Cn Lw
= (2.7)(28 mg/L)(110 ft/yr) = 8 316 lb/acre-yr
say = 8 400 lb/acre-yr (9 410 kg/ha-yr)
8-12
-------
The nitrogen is rapidly converted from the applied organics and ammonium
form to nitrate-nitrogen. The principal removal mechanism is biological
denitrification of nitrate-nitrogen, although volatilization and crop
uptake (if vegetation is used) can add to the estimated 50% total
removal. The estimated percolate nitrogen amounts to 4 ZOO lb/acre-yr
(4 700 kg/ha-yr) and will move with a percolate volume of 112 ft/yr (34
m/yr) [110 ft (33.5 m) applied wastewater and 2 ft (0.6 m) net
precipitation]. The average concentration of nitrate-nitrogen would be
approximately 4 200/(2.7)(112) = 14 mg/L. This concentration is greater
than the assumed design criteria of 10 mg/L total nitrogen for percolate
and greater than the 6 mg/L total nitrogen criteria for river discharge.
Although the other discharge criteria, i.e., phosphorus, BOD, suspended
solids, and pathogens, would be adequately satisfied, rapid
infiltration, by itself, will not satisfy the nitrogen design criteria.
.Further investigation would be necessary to determine the degree of
mixing and dispersion that would occur in the groundwater under the
site. For this example, rapid infiltration is not discussed further,
except in combination with overland flow.
8.5.3 Overland Flow System
The average total nitrogen concentration of an overland flow runoff is
expected to be about 3 mg/L (see Table 2-3). Existing overland flow
systems have shown that total nitrogen removals (mass basis) have varied
from 75 to 90% for systems operating with an application period of b2
wk/yr. The principal nitrogen removal mechanisms are crop uptake and
nitrification-denitrification on the soil surface; these mechanisms are
adversely affected by low winter temperatures. Therefore, it would be
reasonable to expect a 90% nitrogen removal for a system operating witH
an application period of 32 wk/yr. For the estimated hydraulic appli-
cation of 17.8 ft/yr (5.4 m), the total applied nitrogen (from Equation
5-3) is (2.7)(28)(17.8) = 1 346 lb/acre-yr (1 509 kg/ha-yr). With a 90%
removal, 135 lb/acre-yr (151 kg/ha-yr) is collected in the runoff. The
final concentration is dependent upon the water balance, so inputs and
outputs are given:
Applied wastewater 17.8 (5.4)
Percolate loss3 -1.4 (0.4)
Precipitation-evapotranspirationb +1.7 (Q.5)
Net runoff ia.1 (5.5)
a. Assume 8% loss for HpG soil.
b. Estimate for application period.
The design runoff nitrogen is estimated to be all in the nitrate form.
From a mass of 135 lb/acre-yr (151 kg/ha-yr) and a volume of 18.1 ft/yr
8-13
-------
(4,4 m/yr), the concentration is determined as follows: 135/(2.7)(18.1)
= 2.8 mg/L. This concentration meets both surface and subsurface
nitrogen criteria.
Phosphorus removal, however, is usually 50% since the wastewater
contact with the soil is relatively limited (see Section
5.1.4.5). At the design application rate of 17.8 ft/yr (5.4 m/yr), the
applied phosphorus is P = 2.7 CL = (2.7)(8)(17.8) = 385 lb/acre-yr
(431 kg/ha-yr), of which 192 lb/ac?e-yr (215 kg/ha-yr) can be expected
to run off. This would correspond to a runoff concentration of
192/(2.7){18.1) = 3.9 mg/L. The phosphorus concentration is greater
than the river discharge standard of 0.1 mg/L, so overland flow alone
would not be allowed for surface discharge. In addition, overland flow
alone would not meet discharge criteria for suspended solids.
To make overland flow a feasible alternative for this example, it will
be combined in series with rapid infiltration. The combined system
would depend on the former for nitrogen and BOD removal and on the
latter for suspended solids, microorganisms, and phosphorus removal.
The rapid infiltration basins would be designed for the 18.1 ft/yr
seasonal net runoff from the overland flow slopes:
Net overland flow runoff = (18.1 ft/yr)(627 acres) = 11 350 acre-ft/season
RI application =11 350 acre-ft/season * 32 wk/season = 355 acre-ft/wk
For a 100 acre basin area,
weekly application rate = 355 * 100 x 12 = 42.6 in./wk
From Figure 3-3, the maximum .
weekly application = 50-70 in./wk; thus, 42.6 in./wk is satisfactory.
The hydraulic capacity of the soil would govern design rather than the
loadings of wastewater constituents. Discharge would be to groundwater,
and would eventually appear as a seep to the river (nonpoint discharge).
A summary of the preliminary assessments is presented in Table 8-5. The
slow rate and the combined overland flow and rapid infiltration
processes are capaole of providing satisfactory wastewater treatment
with the tabulated application rates and land areas. A cost estimate
should be determined at this time to decide which option provides the
most cost-effective treatment and should be considered for detailed
design. In addition, slow rate systems have three distribution options
that should be evaluated on a cost-effectiveness basis.
8-14
-------
TABLE 8-5
SUMMARY OF DESIGN INFORMATION
FOR TREATMENT ALTERNATIVES
Treatment
Alternatives
Slow rate (flood,
center pivot or
solid set)
Overland flow
followed by rapid
infiltration
Overland flow
Rapid infiltration
Design
flow,
Mgal/d
10
10
10
Annual Wastewater
application
Period
wk
32
32
32
, Total ,
ft
7.2
17.8
113.5
Avg weekly
application
rate, in.
2.7
6.7
42.6
Application
area, acres
1 600
627
100
Length of
storage,
d
140
140
Storage
area,
acres3
360
36U
Treatment
lagoon,
acresb
15
15
Total
area
acresc
2 170 •
1 100
110
a. Based on 10 Mgal/d flow and 12 ft working depth (see Section b.7.1.5).
b. Based on 7 days detention at 10 Mgal/d, 15 ft working depth.
c. Includes 10% for roads, buildings, and miscellaneous.
1 Mgal/d = 43.8 L/s
1 ft = 0.305 m
1 in. = 2.54 cm
1 acre = 0.405 ha
8.6 Cost Comparison
The procedures to calculate capital, and operation and maintenance costs
have 'been published [1]. Tabulations of the results are presented in
Table 8-6 to show differences due to type of treatment system and
distribution system. The cost comparison is made solely to compare land
treatment systems. Each system will usually contain a collection
system,^collection pumping, preapplication treatment, and administrative
facilities; these are not included in the comparison since the added
capital and operation and maintenance costs should be identical.
Additional comparison to a conventional treatment alternative would
require inclusion of all costs before comparisons with total treatment
system would be made. ";
The total costs in Table 8-6 include unlined storage, site clearing,
site leveling, distribution system, distribution pumping (Alternatives
1-4); tailwater return (Alternative 1); overland flow terrace con-
struction, runoff collection, and open channel transmission from the
overland flow to the rapid infiltration site (Alternative 4).
A slow rate system, utilizing center pivot distribution, has the lowest
relative cost for this design example. The costs generated are not
discussed further since their purpose was only to provide a relative
8-15
-------
cost effectiveness for the general conditions as described in Table 8-6,
and as developed in the text (Sections 8.4 and 8.5). The slow rate,
center pivot alternative will be further developed to provide the
preliminary system design.
TABLE 8-6
RELATIVE COST COMPARISON, DESIGN EXAMPLE ALTERNATIVES'
Land Total Amortized Operation and
area, capital capital maintenance Total Municipal.
Alternative System type acresb cost, $ cost, $/yr cost, $/yr cost, $/yr cost, $/yrc
1
2
3
4
Slow rate,
flood
Slow rate,
center pivot
Slow rate,
solid set
Overland flow
and rapid
infiltration
2 170
2 170
2 170
1 210
8 583 770
8 232 770
10 624 120
8 495 500
756 230
725 310
935 990
748 450
202 750
205 720
186 520
214 000
958 980
931 030
1 122 510
962 450
391 810
387 050
420 520
401 110
a. Based on unique or variable land treatment components. Items that are common to and have
equal costs in all alternatives are not included.
b. Actual area is determined in the final layout.
c. Computed as 25% capital and 100% operation and maintenance costs.
1 acre = 0.405 ha
8.7 Process Design
In this particular example, the slow rate, center pivot alternative was
found to be more cost effective than the treatment system alternative of
overland flow followed by rapid infiltration; under other circumstances
the reverse may be true. For purposes of illustrating the required
design procedures, both treatment system alternatives will be described.
8.7.1 Slow Rate
The development of the slow rate process design includes an assessment
of (1) the hydraulic loading criteria, (2) the annual and monthly
nitrogen loadings, and (3) phosphorus and trace metal loading criteria.
Also included is a discussion of (4) preapplication treatment,
(5) storage design criteria, and (6) distribution system criteria.
8-16
-------
8.7.1.1 Hydraulic Loading
For slow rate systems, net runoff can be assumed to be negligible. From
Table 8-1, the total annual precipitation (Pr) of 50.2 in./yr (128
cm/yr) minus the total annual evapotranspiration (ET) of 25.1 in./yr (64
cm/yr) yields an annual net water excess of 25.1 in./yr (64 cm/yr) or
2.1 ft/yr (0.6 m/yr). Thus Equation 8-1 becomes:
Wn = Lw + Pr - ET
or
WD = Lw + 2.1 ft/yr
The amount of percolating water (Wp) resulting from the applied
effluent (Lw) has a significant effect on the allowable nitrogen loading
(Ln)> as is illustrated in the following section.
8.7.1.2 Nitrogen Loading
The annual nitrogen loading can be estimated from procedures in Section
5.1.2.2, as described below:
The annual nitrogen balance, using Equation 5-2, is:
Ln = U + D + 2.7 Wp Cp (5-2)
where Ln = wastewater nitrogen loading, Ib/acre-yr (kg/ha-yr)
U = crop N uptake = 325 lb/acre-yr (364 kg/ha-yr) for Reed
canary grass (Table 5-2)
D = denitrification = 0.2 Ln (assume denitrification to be
20% of applied nitrogen)
Wp = percolating water = Lw + 2.1 ft/yr
C = design percolate N concentration = 10.0 mg/L
8-17
-------
Therefore,
Ln = 325 + 0.2 Lp + (2.7)(LW + 2.1M10),
and the relationship between the nitrogen loading and the hydraulic
loading (from Equation 5-3) is:
Ln ' 2'7 Cn
where Cn = applied nitrogen concentration, mg/L
L = wastewater hydraulic loading, ft/yr
W
Therefore, at Cn = 28 mg/L (from Table 8-2),
Ln - 75'6 Lw
or .
13 Ln
Now with two equations and two unknowns, the nitrogen balance equation
can be solved:
L = 325 + 0.2 Ln + (2.7)(LW + 2.
Ln = 325 + 0.2 Ln + (2.7)[(0.013 Lnj
Ln = 325 + 0.2 Ln + 0.351 Ln + 56.7
0.45 Ln = 381.7
Ln = 848 lb/acre-yr
The complete solution for a design percolate nitrogen concentration of
10 mg/L is as follows:
1. Wastewater nitrogen loading = Ln = 848 lb/acre-yr
2. Wastewater hydraulic loading = Lw = 0.013 Ln = 0.013 (848) =11.0 ft/yr
3. Percolating water = Wp = Lw + 2.1 = 13.1 ft/yr
4. Denitrification = D = 0.2 Ln = 170 lb/acre-yr
5. Percolate nitrogen loading = Pn = 2.7 CpWp = 2.7(10)(13.1)
= 354 lb/acre-yr
6. Required field area = F = 3.06(365) Q = ] ]j8 (10) = 1 015 acres
Lw 11.0
8-18
-------
The slow rate system design is based on maximum nitrogen uptake by the
vegetation. For this design, a cool season forage grass, such as Reed
canary grass, is chosen since it will provide an estimated nitrogen
removal of 325 lb/acre-yr (364 kg/ha-yr) and provide a year-round cover
for maximum infiltration, minimal soil erosion after 'harvest (in
contrast to an annual crop), and nitrogen response at the beginning and
end of the growing season as a result of an established root system.
The procedure to determine the monthly nitrogen balance accounts for
monthly climatic influences. Thus, greater wastewater applications
occur when more nitrogen is needed by the vegetation and greater
microbial activity occurs.
In order to determine the optimal system design loadings, monthly
wastewater applications (values for L ) were chosen (by trial and
error) to the nearest inch, so that the percolate nitrogen concentration
(C ) was less than, or equal to 10.0 mg/L. For the first cut estimate
or monthly values for L , divide the annual wastewater hydraulic
loading (from above) by the number of months in the application season.
For this example, the first trial value for Lw for the months of April
through October would be 11 ft/yr x 12 in./ft * 7 mo/yr = 19 in./mo.
For the cool weather months of March and November (at the beginning and
end of the growing season), a wastewater hydraulic loading of
1 in./month was assumed.
The monthly nitrogen loading may be calculated using the following
equation:
Ln = 0.227 CnLw (8-3)
where L = wastewater nitrogen loading, lb/acre-month (kg/ha-month)
C = applied nitrogen concentration, mg/L
L = wastewater hydraulic loading, in./month (cm/month)
w
The estimated denitrification is calculated as 20% of the total nitrogen
applied resulting in an annual loss of 147 lb/acre-yr (165 kg/ha-yr).
Crop nitrogen uptake was estimated at 325 Ib/acre-yr (364 kg/ha'yr) and
distributed monthly by the monthly fraction of the total evapotranspira-
tion occurring during the growing season, which can be estimated to be
the months of April through October. This assumes that plants utilize
nitrogen and water at similar rates. Whenever possible, estimation of
the monthly variation of crop nitrogen uptake should be refined by
consulting the local agricultural extension service. Percolate nitrogen
(P ) was computed as the difference between application and
denitrification plus crop nitrogen uptake. The percolate nitrogen
concentration (C ) was computed from monthly percolate nitrogen
(P )(lb/acre) andp total percolate volume (W ). To calculate the
8-19
-------
monthly percolate nitrogen concentration (C ), the following equation
can be used:
Pn =0.227 CpWp
(8-4)
where Pn = percolate nitrogen loading, lb/acre'month (kg/ha-month)
percolate nitrogen concentration, mg/L (10 mg/L limit)
percolating water, in./month (cm/month)
WP =
The result of the monthly nitrogen balance are presented in Table 8-7.
TABLE 8-7
MONTHLY DESIGN NITROGEN BALANCE, SLOW RATE SYSTEM
ii \
(Pr - ET) "-w1 Wastewater
Net monthly Applied nitrogen ^°
excess
Month water, in.a
Nov
Dec
Jan
Feb
Mar
Apr
May
Jun
Jul
Aug
Sep
Oct
4.
4.
4.
3.
4.
3.
0.
-1.
-1.
-0.
0.
2.
Annual 25.
a.
b.
c.
d.
e.
f.
g.
h.
i.
From Table
0
2
3
5
8
2
7
3
6
3
9
7
1
8-1.
Highest possible
of trials)
Lp = 0.227
CnLw'
Leaching
(U)
' Crop N
(Wp)
Percolate
wastewater, loading., Denitrification, uptake, water,
in.b Ib/acreC lb/acred Ib/acre in.e
1
0
0
0
1
9
15
20
24
20
16
11
117
volume
Cn = 28
h 6
h 6
57
95
127
153
127
102
70
743
(to nearest in.) without
mg/L.
1
1
11
19
25
31
25
20
14
147
exceeding 10
• • .
19
43
62
73
58
44
26
325
mg/L
5
4
4
3
5
12
15
18
22
19
16
13
142
.0
.2
.3
.5
.8
.2
.7
.7
.4
.7
.9
.7
.1
1n percolate
(Pn) (Cp)
Percolate Percolate nitrogen
nitrogen. concentration,
lb/acref mg/L9
5
5
27
33
40
49
44
38
30
271
(found
4
3
9
9
9
9
9
9
9
8
.4
.8
.7
.3
.4
.6
.8
.9
.6
.41
after a series
D = 0.2 Ln.
WP ' Lw +
pn = Ln -
Pn = 0.227
Pr - ET.
D - U.
cpwp;
Assume 1 in./wk
Computed as the
CP = P
n/(0.227)(Wp)
application at beginning and end
average
of the monthly values.
of growing season.
Conservative
since
nonapplication season rainwater
percolation and groundwater dilution will reduce yearly average total percolate nitrogen.
1 in. =2.54 cm
1 Ib/acre =1.12 kg/ha
8-20
-------
The monthly design nitrogen balance results in an annual wastewater
application of 117 in./yr or 9.7 ft/yr (3.0 m/yr), which is slightly
less than 11.0 ft/yr (3.3 m/yr) in the previous annual assessment. The
wetted field area should be adjusted to account for the lesser
application, so the required application area is:
P _ 3.06(365) Q
Lw
118 (10)
9.7
rather than 1 015 acres (410 ha).
The permeability for the soil surface (infiltration rate) and subsoil
can be evaluated on the basis of the maximum monthly liquid application
to the soil surface. During July, the wastewater application of 24 in.
(60 cm) and mean precipitation of 3.8 in. (10 cm) and evapotranspiration
of 5;4 in. (14 crn) add up to a monthly infiltration of 22.4 in./mo (57
cm/mo). On a weekly basis, the maximum hydraulic loading would be about
5.6 in./wk (14 cm/wk). For the Bomoseen sandy clay loam with a soil
permeability of 0.6 in./h (1.5 cm/h) and a perennial forage cover, the
total application could be infiltrated within about 9 hours. This
represents less than 6% of the total time in a week, so an application
schedule based on equipment capacity can be determined.
8.7.1.3 Other Mass Loadings
The mass application of phosphorus and trace metals to the site can be
assessed to determine if they would limit total wastewater applications
over the 20 year design life of the project. The phosphorus criterion
is based
vegetation,
trace metal
project for
for elements
on the total mass application, phosphorus removal in
and soil retention by adsorption and precipitation. The
criterion is based on mass application over the life of the
elements retained in the soil, and applied concentrations
that are not retained.
At the annual application rate of 9.7 ft/yr (3.0 m/yr) and the total
phosphorus concentration of 8 mg/L (as P), the annual application is:
(2.7)(8)(9.7) = 210 lb/acre-yr (235 kg/ha-yr). The Reed canary grass
will remove 40 lb/acre-yr (45 kg/ha-yr) (Table B-l) during harvest, so
the net application to the soil is 170 Ib/acre-yr (190 kg/ha'yr). The
sandy clay loam soil will have excellent removal of phosphorus as a
result of the clay content. The 3 400 Ib/acre (3 811 kg/ha) phosphorus
application over 20 years can be completely adsorbed in the top 22 in.
(56 cm) of the soil with a 5 day adsorption capacity of 50 mg of
phosphorus per 100 g of soil and a bulk density of 1.3 g/cm3. This is a
conservative estimate since it has been estimated that the phosphorus
retention (including chemical precipitation) may be at least double that
measured by the 5 day adsorption test.
8-21
-------
The mass application of trace metals should not pose any further
limitations at the proposed site. For the applied concentrations, the
mass applications are below the recommended maximum for use on
agricultural soils (Table 8-8).
TABLE 8-8
TRACE METALS IN SLOW RATE DESIGN EXAMPLE
Concentration in Concentration Mass
raw wastewater, applied to application
Element mg/L land, mg/L lb/acrea
Cadmium
Chromium
Copper
Lead
Mercury
Nickel
Silver
Zinc
0.01
0.03
0.22
0.01
0.001
0.03
0.001
0.31
0.008
0.02
0.10
0.005
0.001
0.02
0.001
0.20
4
10
52
2.6
0.5
10
0.5
105
Maximum
loading
, criteria,
lb/acreb
8
82
164
4 080
d
164
e
1 640
EPA
Drinking Water
Standard, mg/l_c
0.01
0.05
1.0
0.05
0.002
No standard
0.05
5.0
a. On the basis of 9.7 ft/yr and 20 yr life. Example; Cd
= (2.7)(0.008)(9.7)(20) = 4.
b. From Table b-4.
c. From Table 3-4.
d. No suggested limit since retention is very high and applied concentrations are
below drinking water standard.
e. No limit since most applications are too small in comparison with drinking
water standard.
1 lb/acre= 1.13 kg/ha
8.7.1.4 Preapplication Treatment
Preapplication treatment is included as a unit process in this design
example as a means of odor control for the 20 week winter storage period
and for a reduction of suspended solids to minimize clogging in the
distribution system. The treatment removals of nitrogen, phosphorus,
and other wastewater organic and inorganic constituents are not
dependent on a specified level of treatment before application to the
land, so partial oxidation of wastewater organics should be adequate.
The long-term storage pond should provide for additional wastewater
treatment during the retention time of up to 20 weeks, so preapplication
treatment by aerated lagoons to reduce BOD down to a concentration of 60
mg/L should be adequate. Other processes exist to oxidize wastewater
organics before application to the land, but for the purposes of this
example, aerated lagoons are considered the most cost-effective
alternative. A further reduction in BOD will occur during the 20 week
storage period.
8-22
-------
Detailed design procedures for aerated lagoons are covered elsewhere [2]
and will not be repeated herein. Experience with lagoons indicates that
multiple cells offer operating and maintenance advantages. Since the
site is in a northern climate, extra time must be provided to compensate
for the slower reaction rates in the winter. A 4 cell system, with
parallel units, designed for a total detention of 6 days should provide
the desired level of treatment during the winter months at this site.
8.7.1.5 Storage Lagoons
The required volume, area, and depth for the storage lagoon can be
calculated in a manner similar to that used for the aerated lagoon. The
climatic data were used to calculate a 20 week storage, which resulted
in a total storage capacity of 1.4 XH 109 gal (5.3 x 109 L). This is
equivalent to a volume of 1.87 x 10 ft3 (5.3 x 106 m3); so 360
surface acres (164 ha) is required for storage at a depth of 12 ft
(3.7 m). The final design should allow an additional 3 ft (0.9 m) for
freeboard, for a 15 ft (4.6 m) total depth in storage. Further, the
storage lagoon should be divided into multiple cells to reduce wind
fetch and wave generation. The final design would consist of 4 basins
at 90 acres each or 3 basins at 120 acres each, depending on final
topography available for siting and construction.
8.7.1.6 Location of Treatment and Storage Lagoons
The open land to the east of the tree line in Figure 8-3 was identified
as potentially feasible for a slow rate system. There is sufficient
land for location of the treatment and storage lagoons, as well as the
advantage of having all components of the system in proximity. However,
the soil characteristics would require lining of the lagoons to control
seepage.
Further examination of the topography and soils data indicates
significant advantages exist for a location in the general vicinity of
borings No. 2 and No. 7, as shown in Figure 8-2. Such a location would
permit gravity flow of the raw wastewater to the highest possible
elevation shown on the map, and the impermeable surface soils in this
area could be stripped and used to line the treatment and storage
lagoons. It would require clearing of approximately 375 acres (170 ha)
of brush and trees from the site.
8.7.1.7 Slow Rate Distribution System
The design of a mechanical distribution system is usually determined by
the equipment available from various manufacturers. However, it is
desirable to know the number and size of units so that an estimate of
8-23
-------
unsprayed areas between wetted circles can be made. The costs (Table
8-6) were estimated on the basis of a maximum sprayed area of 134 acres
(61 ha) per sprinkler unit, with the rotating booms typically available
as multiples of 100 foot lengths.
To cover the required field area of 1 150 acres (466 ha), 9 units of
134 acres (61 ha) each will be used. Each unit has a rotating boom
radius of about 1 300 ft (397 m). The total area required would be 15
to 20% greater, depending on geometric layout of the circles and degree
of end area coverage from manufacturer's specifications; 2U% should be
assumed, so the required area for application is 1 380 acres (560 ha).
The application frequency should be as high as possible, again depending
on manufacturer's specifications, but at least 2 to 3 rotations per week
are desirable to minimize the high instantaneous rates needed to apply
all the wastewater to soil.
8.7.1.8 Summary for Slow Rate System Design
A summary of the principal design factors for the most cost-effective
alternative, slow rate treatment by center pivot distribution, is
presented in Table 8-9.
TABLE 8-9
DESIGN FACTORS, SLOW RATE TREATMENT WITH
CENTER PIVOT DISTRIBUTION
Total annual wastewater application, ft 9-7
Length of application season, wk 32
Length of storage, wk 20
Nitrogen balance
Applied, lb/acre-yr 74J
Uenitrification, lb/acre-yr 1*7
Crop uptake, lb/acre-yr 32b
cercolate, lb/acre-yr 271
Avg monthly percolate nitrogen concentration, mg/L b.4
Preapplication treatment detention time, d
Aerated lagoons &
Storage lagoons (maximum) 110
Land required, acres
Wetted area 1 IbO
Total field area (center pivot only) 1 38U
Aerated lagoons 15
Storage lagoons 3bU
lotal (including lu* for miscellaneous) 1 98U
Additional application criteria
Maximum monthly infiltration volume (July), in./no 22.4
fhosphorus retention (required soil volume), in.
Conservative 22
Realistic 11
Trace metals Not restricting
1 ft = U.JUb m
1 Ib/acre =1.12 kg/ha
1 acre = 0.405 ha
1 in. = 2.b4 cm
8-24
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b.7.2 Combined Overland Flow and Rapid Infiltration
The process design for the combined system of overland flow followed by
rapid infiltration is presented here. Hydraulic -loading rates and
cycles and distribution systems are discussed. Preapplication treatment
and storage requirements will be the same as for a slow rate system.
is.7.2.1 Hydraulic Loadings and Cycles
The overland flow system will be loaded at 8 in./wk (20 cm/wk) for
approximately 22 of the 32 week application period. Applications will
be for 6 h/d on a 6 d/wk schedule. This allows Iti h/d of resting plus a
full day of resting once a week. This cycle is typical of operating
systems (see Section b.1.4, 7.11, and 7.12).
During the period from October to May, there will be days when the
temperature will be below freezing and storage will be provided. When
conditions are favorable in this time period, the overland flow system
will be loaded at 4 in./wk (10 cm/wk) by operating 6 h/d for
approximately 3 d/wk.
The rapid infiltration system will receive the treated runoff from the
overland flow slopes. Nitrogen removal is nearly complete in overland
flow, so the rapid infiltration system can be managed to maximize
hydraulic loading rates (rather than to optimize denitrification, as is
the case when rapid infiltration receives a primary or secondary
effluent). Thus, application will be for 2 days to a set of basins with
a 6 day drying period. Therefore, 42.6 in. (108 cm) of water will be
applied over 2 days followed by resting. The water should infiltrate
within a day after application ceases. Using the procedure in Appendix
C, field testing should be conducted prior to final design to verify
adequate infiltration rates. The flooding basin technique, as shown in
Figure C-l, should be used for the determination of infiltration rates.
It is recommended that several 20 ft? basins, located in repre-
sentative areas of the site, be employed. The resulting infiltration
rate data should be analyzed according to the procedure discussed in
Appendix C (Section C.3.1).
Soil borings at the proposed rapid infiltration site should also be
examined to verify the lack of restrictive layers in the soil profile.
8.7.2.2 Distribution System
For overland flow, the aerated lagoon effluent would be applied using
the bubbling orifice (surface application technique used at Pauls
Valley, Section 7.11). The application would be at the top of the
8-25
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150 ft (45 m) long slopes. The slopes would be between 3 and 4%. The
runoff would be collected in a series of ditches and conveyed to the
rapid infiltration basins. Overland flow effluent would be applied to
the rapid infiltration basins on a cycle of 2 days wet and 6 days dry.
The 100 acres of basins would be divided into basins ranging in size
from 3 to 10 acres each. Four sets of basins (A through D) with each
set containing about 25 acres would be established. For 2 days the
application would be to set A, followed by sets B, C, and D in rotation.
In actual practice some basins will have higher and some lower infil-
tration rates and the length of flooding and drying can be modified
accordingly.
b.8 References
1. Pound, C.E., R.W. Crites, and D.A. Griffes. Costs of Wastewater
Treatment By Land Application. Environmental Protection Agency,
Office of Water Program Operations. EPA-430/9-75-003. June 1975.
2. Meteal f & Eddy, Inc. Wastewater Engineering. Mew York, McGraw-
Hill Book Co. 1972.
8-26
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APPENDIX A
NITROGEN
A.I Introduction
Application of wastewater on land, as compared to the more common prac-
tice of discharge to surface waters, has a number of advantages to
recommend it. One of these is conservation of valuable resources in the
form of contained nutrient elements. Only one of these nutrient
elements—nitrogen—is considered here. Where it is feasible to do so,
it is much more logical to use nitrogen, the production cost of which is
continually increasing, in the production of essential food and fiber
rather than to treat it entirely as a waste. Nearly all soils respond
to additions of nitrogen by increasing production; however, the require-
ments of nitrogen for optimum crop production and the need to treat
large volumes of nitrogen-containing wastewater may not be in balance.
Nitrogen,applied to soils in amounts greatly in excess of crop needs and
allowed to percolate to the groundwater may result in contamination of
the groundwater through leaching of nitrates below the root zone.
Nitrogen transformations, removal mechanisms, and overall removals by
the land treatment methods are described in this appendix.
A.2 Nitrogen Transformations
A.2.1 Nitrification
In discussing removal of nitrogen from applied wastewater, it is impor-
tant to understand something about the complex and interrelated series
of nitrogen transformations that may occur in soils. The predominant
form of nitrogen in wastewater is usually ammonium, although some ni-
trate is also likely to be present if the preapplication treatment pro-
cesses have included one or more aerobic stages. A small quantity of
organic nitrogen, of which a part is soluble and readily convertible to
ammonium through microbial action, is also usually present. Insoluble
organic nitrogen associated with the particulate matter is also convert-
ible to ammonium, although somewhat more slowly. When wastewater is
applied to soil, a variety of reactions are initiated, some biological
and some nonbiological. Of the biological reactions, nitrification and
denitrification are very important. Nitrification is important because
it converts a form of nitrogen not readily subject to leaching to one
that moves readily with percolating water. Denitrification is important
because it is the principal process by means of which nitrogen as
nitrite or nitrate is lost from the soil system through conversion to
gases that may escape to the atmosphere.
A-l
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A.2.1.1 Nitrifying Bacteria
The conversion of ammonium to nitrate in soil and water systems is due
primarily to activities of a few genera of autotrophic bacteria of which
Nitrosomonas and Nitrobacter are the most important. These bacteria are
normal soil inhabitants and are usually present in sufficient numbers to
convert added ammonium to nitrate rapidly and completely, if environmen-
tal conditions are suitable. Schloesing and Muntz first discovered the
biological nature of the nitrification process by pouring sewage
containing ammonium onto columns of soil mixed with limestone and found
that, after the elapse of a few days, nitrate appeared in the effluent
at the bottom [1].
The nitrifying bacteria are obligate aerobes that derive their energy
from the biochemical reactions involved in oxidation of ammonium or
nitrite. The principal reactions may be written as follows:
NH* + 3/2 U2 ^N0~ + H20 + 2 H+ (A-l)
N0~ + 1/2 0,, -N0~ (A-2)
The first reaction is carried out by bacteria of the genera Nitrosomo-.
nas, Nitrosococcus, Nitrosocystis, and Nitrospira; the second is accom-
plished by Nitrobacter and related species. These bacteria require no
organic matter as a source of energy. A number of heterotrophic nitri-
fiers are known to occur, but their activity appears to be slight com-
pared to that of the autotrophic forms [2]. Although nitrifying bac-
teria are abundant in most soils, populations may be initially low in
subsoils or in coarse-textured soils that are prone to be dry much of
the time. In such soils, several weeks may be required for nitrifiers
to attain maximum numbers after application of wastewater is begun.
A.2.1.2 Rates of Nitrification
Rate constants based on the assumption of steady state conditions and
first order kinetics have been published [3]; but these may have little
value in relation to field situations where soil properties, population
size, and other variables are subject to considerable fluctuation. Rate
constants that have been normalized to take into consideration the size
of the nitrifying population are more comparable from one soil to
another, but are impractical for application to field conditions owing
to the difficulty of obtaining reliable counts. Under favorable mois-
ture and temperature conditions, measured values of ammonium converted
A-2
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to nitrate ranging from 5 to 50 ppm nitrogen per day (soil basis) have
been reported [4, 5]. For purposes of calculation, if one assumes a
depth of only 4 in. (10 cm) of soil implicated in the nitrification
process owing to ammonium adsorption near the surface, it can be deter-
mined that these rates are equivalent to 6 to 60 lb/acre'd (6.7 to 67
kg/ha*d) of nitrogen. The lower rate would be sufficient to nitrify the
ammonium in 1.2 an. (3 cm) of wastewater per day containing 20 mg/L of
NH|; and at the upper end of the range, 12 in./d (30 cm/d) could be
accommodated. Even higher nitrification rates in soil columns have been
reported [6, 7]. These calculations are consistent with observations
that complete conversion of input nitrogen to the nitrate form occurs if
wastewater application periods are short enough to prevent development
of anaerobic conditions [b, 9].
The tendency of soils to adsorb ammonium near the surface may result in
temporary buildup of ammonium in a shallow layer, particularly if the
nitrifying population has not been increased by previous inputs of ammo-
nium. This situation results subsequently in a wave of nitrate at a
high concentration following the increase in the number of nitrifiers to
a level that permits rapid oxidation of the adsorbed ammonium. This is
illustrated in Figure A-l, where wastewater containing 42 mg/L of
NHj-N applied to a soil column at the rate of 3 in./wk (7.5 cm/wk)
produced an effluent containing up to 107 mg/L of N03-N [10]. Following
the period of population buildup (about 5 weeks in this soil), ammonium
was nitrified as rapidly as it was applied, and nitrate concentrations
fell to the input level. A recurring nitrate wave phenomenon is readily
observed in systems of alternate flooding and drying [11]. Here it is
due to the intermittent nature of nitrification, which occurs only during
the drying cycle when oxygen is available.
The rate of nitrification is much more likely to be inhibited by lack of
oxygen or low temperature than by an inadequate population of nitri-
fiers. The usual situation in soils is that nitrite rarely accumulates,
indicating that the activities of Nitrdbacter proceed more rapidly than
does the oxidation of ammonium. Nitrite oxidation is inhibited by free
ammonia in liquid systems, particularly when the pri is alkaline; but in
soils, adsorption of ammonium prevents this inhibition from becoming a
practical consideration in most circumstances.
Prolonged application of high ammonia content wastes, such as sludge,
may result in loading that exceeds the ammonium adsorption capacity in
which case free ammonia may reach concentrations sufficiently high to
retard nitrite oxidation.
A-3
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FIGURE A-l
NITRATE IN EFFLUENT FROM A COLUMN OF SALADO SUBSOIL
RECEIVINGS IN./WK OF WASTEWATER CONTAINING 42 mg/L
NHJ-N, SHOWING HIGH-NITRATE WAVE [10]
ioor
80 -
1 in./wk . 2.54 ci/wk
WEEKS
A.2.1.3 Effects of Soil Properties on Nitrification
A.2.1.3.1 Aeration
The theoretical oxygen requirement in nitrification is for about 4.6 mg
oxygen per milligram of ammonium-N. Although the nitrifiers are obli-
gate aerobes, they will continue to function at oxygen concentrations
well below that of the atmosphere [12, 13].
The rate at which oxygen diffuses to the sites where nitrifying bacteria
are located in relation to the rate of oxygen utilization is of critical
importance. Studies in wastewater treatment systems indicate that the
minimum level of dissolved oxygen that will permit ammonium oxidation is
around 0.5 mg/L [14]. In soils, it is impossible to measure the
dissolved oxygen in the microsites inhabited by bacteria, and in any
A-4
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event the situation is complicated by the presence of large numbers of
heterotrophes which may use a greater proportion of the available oxygen
than do the nitrifiers, if oxidizable carbon is available. Thus,
anaerobic conditions may readily develop in the smaller pores of
unsaturated soils. Lance et al. found that both diffusion and mass flow
of oxygen were important as transport mechanisms between periods of
intermittent flooding in rapid infiltration [6]. Continuous application
of wastewater to soils stops nitrification below the immediate surface
by filling soil pores and preventing diffusion of oxygen downward. In
overland flow systems, nitrification can proceed as a result of aeration
of surface water as it moves over the land via sheet flow [15].
Carbon dioxide is required by nitrifying bacteria as a source of carbon,
but since wastewaters usually contain considerably more bicarbonate than
ammonium, there is little likelihood that nitrification is ever limited
by lack of CCL in land application.
A.2.1.3.2 Temperature
Like all biological processes, nitrification is affected by temperature.
There is evidence that nitrifiers can adapt to the temperature of their
environment to some extent [16], but the optimum usually falls between
75 and 95°F (24 and 35°C). Minimum temperatures as low as 36°F (2°C)
have been reported [5, 17]. As a rule of thumb, the activity of
nitrifiers increases by a factor of 2 for every la°F (10°C) rise in
temperature. Obviously, nitrification is stopped altogether when soils
are frozen.
A.2.1.3.3 pH
The optimum pri for nitrification is in the neutral-to-slightly-alkaline
range corresponding closely to the ph of most wastewater. However, when
wastewater is applied to soil, the controlling factor is usually the ph
of the soil because of the much higher buffer capacity of soils
containing any appreciable amount of clay and organic matter. The pH of
very coarse textured soils may be altered somewhat by addition of
wastewater, particularly with high-rate applications. Nitrification
falls off sharply in acid soils, with a limiting value in the
neighborhood of pH 4.5 [4].
Nitrification is an acid-forming process, with the liberation of two
protons for each ammonium ion oxidized; out the presence of bicarbonate
and other buffering substances in wastewater is usually sufficient to
neutralize the acid as it is formed [18]. With prolonged application of
wastewater, even strong acidic soils may be made neutral or alkaline
[19], indicating that acid produced during nitrification does not play a
dominant role.
A-5
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A.2.2 Denitrification
A.2.2.1 Microorganisms
The important bacteria in denitrification are heterotrophes belonging to
the genera Hseudomonas, Bacillus. Micrococcus. and Achromobacter. une
of the autotrophic sulfur-oxidizing bacteria, Thiobacillus dem'trifi-
cans, may also play a significant role in denitrification where reduced
forms of sulfur are present. The denitrifiers are facultative anaerobes
that preferentially use gaseous oxygen, but can use nitrite and nitrate
as electron acceptors in place of oxygen when concentrations of oxygen
become very low. Denitrifying bacteria, like the nitrifiers, are common
soil organisms of widespread distribution. Focht and Joseph reported
very little correlation between denitrification rates and numbers of
denitrifying bacteria in soils, indicating that factors other than popu-
lation size are likely to be rate-limiting [20].
A.2.2.2 Energy Sources
The denitrification reaction may be written
C6H1206 + 4 NO^ ^6 C02 + 6 H20 + 2 N2 (A-3)
where glucose is used as an example of an organic energy source. In
this example, 3.2 g of glucose is required for each gram of nitrogen
denitrified. The decomposable organic matter required for denitrifi-
cation may be present in the soil , may be carried in the wastewater, or
may be produced by plants growing on the soil. For municipal wastewaters
that are applied after having been stabilized to the degree that most of
the BOD has been removed, the organic matter status of the soil to which
the water is applied is likely to be more important than that of the
wastewater itself for slow rate applications. Cannery wastewater with
its high BOD is an exception, as are certain other types of industrial
wastewater. The typical distribution of organic matter in soils is such
that the high concentrations occur at or near the surface and decline
progressively with depth. Moreover, the availability of organic matter
near the soil surface as a source of energy for microorganisms is often
greater than that at lower depths. Gilmour et al. showed that a flooded
surface soil containing O.yi% total carbon denitrified added nitrate
readily without organic amendments, out the subsoil containing 0.48%
total organic carbon tailed to denitrify unless an available organic
substrate was supplied [21]. This means that the zone of most active
denitrification is likely to be near the soil surface in spite of its
proximity to the atmosphere. This has been demonstrated in field
experiments by Rolston et al. who observed maximum rates of production
of NLO and N- within the top 4 in. (1U cm) [22]. Nitrous oxide is
A-6
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an intermediate in denitrification and may be evolved from soil before
it has an opportunity for further reduction to N£ , particularly when
it is produced near the surface. McGarity and Myers observed a close
correlation' between denitrifying activity and total carbon in some
soils, whereas in others there was little or no correlation with organic
matter parameters [23]. They suggested that this was due to localized
accumulation of small quantities of energy-rich available organic
matter. With continued input of wastewater, any such accumulations
would disappear.
Stanford et al. found a highly significant correlation between total
soil carbon and denitrification rate constants for a group of 30 soils
of diverse properties. A still better correlation was obtained with
extractable glucose carbon [24]. Still riot answered, however, is the
question of whether such rate constants based on the assumption of first
order kinetics would hold up over longer periods than the 10 days used
for their determination. Since rate constants are related to available
carbon, it is likely that they would decrease over time.
Elemental sulfur or sulfides can also be used as an energy source for
denitrification, as has been shown by Mann et al. [25]. Sulfides may
play a role in denitrification in marshland, or where anaerobic sludge
is disposed to land.
In application of high BOL) wastewater, such as cannery wastes, rapid
denitrification is very probable. Law et al. reported 83 to 90% removal
of total nitrogen from overland flow treatment of cannery wastes [26].
A.2.2.3 Aeration
The threshold oxygen concentration which inhibits denitrification has
been shown by Skerman and MacRae to be very low, in the vicinity of 0.2
mg/L [27, 28]. Temporally or spatially restricted anaerobism is a
feature of virtually all soils. Temporary saturation may occur during
wastewater application, with exclusion of oxygen from the soil pores, or
oxygen deficiency may develop in an unsaturated soil if the rate of
consumption exceeds the rate of replenishment. The latter circumstance
is especially likely in the smaller soil pores. Thus, denitrification
may take place in a soil considered to be well aerated. Prolonged
exclusion of oxygen from the soil, as in continuous flooding, causes
denitrification to cease from lack of nitrate, unless this is present in
the input water. Lance et al. reported that, in columns of a loamy sand
soil, both mass flow and diffusion were important mechanisms of oxygen
transport during intermittent flooding with secondary effluent [6].
They noted that enough oxygen entered the soil during a 5 day drying
period to oxidize all the ammonium applied during 6 days of high-rate
A-7
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application of wastewater containing 20 mg/L of NHj-N. Application of
ammonium in excess of that which could be oxidized during the drying
period resulted in an increase of NH^[ in the reclaimed water.
Klausner and Kardos reported little effect of secondary sewage effluent
on oxygen diffusion rates in silt loam and clay loam soils over the
application range of 0 to 2 in./wk (0 to 5 cm/wk) [29].
In overland flow, a sharp gradient in oxygen concentration can develop
between the thin layer of water in contact with the atmosphere and the
underlying soil where an anaerobic zone may develop just below the soil-
water interface. Nitrates formed in the aerated flowing water can
diffuse into the reducing zone of soil and undergo denitrification [15].
The development of this reducing zone is favored by the high BUD of
wastewaters and the relatively impermeable soils to which the overland
flow system of treatment is adapted.
A.2.2.4 Temperature
The optimum temperature for denitrification in soils is very high, 140
to 150°F (60 to 65°C), but Stensel et al. reported little temperature
effect in the 68 to 86°F (20 to 30°C) range [30]. Of greater practical
importance is the minimum temperature. Bremner and Shaw observed very
slow denitrification at 36 and 41°F (2 and 5°C), but the rate increased
very rapidly up to 77°F (25°C) [31].
A.2.2.5 pH
Denitrification is very slow in acid soils, increasing rapidly with
increasing pH up to the neutral-to-slightly-alkaline range [32, 33].
Denitrification affects soil pH according to the reaction
NO^ + organic matter —^2 + H20 + C02 + OH" (A-4)
and has the effect of neutralizing a part of the acid produced in
nitrification. The relative balance between nitrification and
denitrification will therefore have an influence on changes in soil pH
resulting from wastewater application, although other factors are of
greater importance in regulating pH, as has been indicated previously.
A.2.2.6 Nitrate Concentration
The denitrification rate is independent of nitrate concentration over a
fairly wide range [32, 34]. Recently, Volz et al. reported
A-8
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denitrification to be a zero order reaction, but with the possibility of
some dependence on nitrate concentration at very low nitrate levels
[35]. Over the range of nitrate concentrations that commonly occur in
wastewater, there is little effect on denitrification rates.
A.2.2.7 Effects of Living Plants
The presence of living plants has been shown to stimulate
denitrification [36, 37, 3b]. Woldendorp attributed this to two
effects: (1) low oxygen concentrations in the rhizosphere produced by
respiration of roots and microorganisms, and (2) root excretions serving
as a source of decomposable organic matter [36], Similar conclusions
were reached by Stefanson, who reported that in the presence of plants,
N2 was evolved preferentially, while in their absence, N£0 accounted
for most of the nitrogen loss [37]. Woldendorp also suggests the
possibility of stimulation of denitrification by specific amino acids
secreted by plant roots [38]. The role of living plants in the denitri-
fication process is particularly important in slow rate and overland
flow systems.
A.3 Nitrogen Removal from the Soil System
A.3.1 Crop Uptake
A major advantage of applying wastewater to land is the possibility of
recycling part of the plant nutrient content. The important
consideration from the standpoint of nitrogen content is the
relationship between the crop requirement and the quantity applied in
the wastewater. It should be recognized that a crop does not utilize
all of the mineralized nitrogen in the root zone. The fraction of total
nitrate in the soil that is assimilated by the roots of growing plants
varies tremendously, depending on the nature of the plant, depth and
distribution of rooting, nitrogen loading rate, rate of moisture flux
through the root zone, and other factors; but in general, the efficiency
of uptake is not high. Grasses, particularly perennials, tend to be
somewhat more efficient than row crops. It is obviously advantageous to
have the crop growing actively during all or most of the year in order
to maximize nitrogen removal in wastewater application, but climatic
restraints make this impossible in many locations. Terman and Brown
[39] calculated by means of a regression procedure that average nitrogen
recovery at all rates by Bermuda grass in the experiments of burton and
Jackson [40] was 59%.
The most accurate estimates of nitrogen uptake efficiencies are those
obtained by use of isotopically labelled input nitrogen, but few of
these are available. Apparent uptake values are often computed by
dividing the quantity of N found in the crop by the quantity applied.
Where the amount of indigenous soil nitrogen is large, the discrepancy
A-9
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between actual and apparent uptake may be enormous. Some comparisons
for corn, where actual N uptake was determined by the isotope
procedure, and apparent uptake by the conventional procedure, are given
in Table A-l [41].
TABLE A-l
NITROGEN UPTAKE EFFICIENCIES OF CORN IN RELATION TO
QUANTITIES OF NITROGEN AND WATER APPLIED [41]
Percent
Irrigation water applied
7.9 in. 23.6 in. 39.4 in.
N applied,
Ib/acre Actual Apparent Actual Apparent Actual Apparent
80
160 .
320
57.1
54.3
42.3
173
122
68.6
55.4
63.2
43.8
182
139
75.5
55.7
64.7
48.0
172
123
78.6
1 Ib/acre =1.12 kg/ha
1 in. = 2.54 cm
Sopper and Kardos in Pennsylvania computed apparent removal efficiency
values of 242 and 334% of total applied nitrogen by two varieties of
corn silage receiving 1 in./wk (2.5 cm/wk) of wastewater during a single
year [42]. At 2 in./wk (5 crn/wk) the nitrogen removal efficiency
dropped to 145%. Over a 6 year period, Reed canary grass removed 97.5%
of the nitrogen applied in 536 in. (13.6 m) of wastewater. In a
hardwood ,forest, the nitrogen removal efficiency at 2 in./wk (5 cm/wk)
was only 39%. It is clear that the apparent removal values in excess of
100% include a great deal of nitrogen resulting from decomposition of
soil organic matter and could not be maintained over a long period of
time. Much lower values for nitrogen recovery by crop uptake have been
reported by McKim et al. [43] and by Karlen et al. [44].
Total quantities of nitrogen removed by harvested crops generally fall
in the range 50 to 400 lb/acre-yr (56 to 450 kg/ha-yr), depending on the
nature of the crop, fertility of the soil, and a number of management
parameters [45]. These amounts may account for a major part of the
input nitrogen in slow rate and overland flow systems, and in the
former, application rates are primarily limited by plant uptake.
However, plant uptake is of relatively little consequence in rapid
infiltration systems where input levels as high as 15 tons/acre-yr (33.6
Mg/ha-yr) of nitrogen have been reported [a].
A. 3. 2 Volatilization of Ammonia
The equilibrium between NHj and NHa is regulated by pH, and the
proportion of free NHa is sma" 1 at the pH value of most wastewater.
A-10
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Application of water through sprinkler systems increases evaporation and
with it the quantity of ammonia volatilized. Scott states that the net
loss of water during sprinkler irrigation may vary from as low as 5% to
as much as 40% of the water applied [46]. Henderson et al. measured
ammonia losses as a function of pH of fertilizer solutions applied by
sprinkler irrigation and found that, in general, these were less than
10% between pH 7 and 8, but the curve increased sharply above pH 7.8
[47]. Their data would include evaporative losses between the sprinkler
head and the soil surface.
With any type of wastewater application, ammonia losses from the soil
surface may occur during drying. The magnitude of such losses is highly
variable, depending on rate of application, extent of drying, clay
content of the soil, pH of the surface soil, temperature, and type of
plant cover, if any [48, 49, 50]. The coarse-textured soils favored for
wastewater application are prone to ammonia loss because of their low
clay content and tendency to dry quickly, although because of their low
retention capacity the proportion of total ammonia retained near the
surface is unlikely to be large. In a greenhouse study Mills et al.
reported that at pH values above 7.2 at least half the nitrogen applied
to a fine sandy loam soil was volatilized as ammonia, most of it within
2 days of application [49]. In a laboratory study, Ryan and Keeney
measured ammonia volatilized from surface-applied wastewater sludge
containing 950 mg/L of NH^-N and obtained values ranging from 11 to
60% of the applied NH|-N, depending on the nature of the soil and
loading rate [51]. Losses decreased as clay content of the soil
increased, but were directly related to the loading rate. Repeated
applications of sludge produced greater percentage losses than a single
appli cation.
A.3.3 Denitrification
A.3.3.1 Slow Rate Process
The slow rate process, usually on land which is vegetated at least part
of the year, is basically an irrigation procedure. In arid regions the
wastewater is used to meet the evapotranspiration requirements of the
growing plants, and in humid regions the quantity of wastewater applied
is limited to levels which do not greatly exceed plant requirements for
water. The soil is thus maintained primarily in an aerobic condition,
and nitrification is the dominant process. Nevertheless, in
agricultural practice, carefully controlled nitrogen balance experiments
usually reveal an unaccounted-for deficit which is attributed to
denitrification [52]. The magnitude of this deficit typically falls in
the range of 15 to 25% of the applied nitrogen. A balance sheet from a
field experiment is presented in Table A-2 [41]. Isotopically labelled
nitrogen fertilizer was used which made it possible to distinguish
A-11
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between the applied nitrogen and that present in soil or added from
ctner sources. The losses over a 3 year period were a remarkably
constant fraction of tfte input nitrogen, and consistent in magnitude
witfl ocner reported values [52].
TABLE A-2
THREE YEAR BALANCE SHEET FOR ISOTOPICALLY LABELLED NITROGEN
FERTILIZER APPLIED TO CORN PLOTS ON HANFORD SANDY LOAM [41]
Total N adaed. Removed in grain, Remaining in soil, Unaccounted for, Loss,
Tb/acre Ib/acre Ib/acre Ib/acre %
1
'
300
600
SOO
200
500
135
274
312
317
321
118
196
384
539
930
47
129
204
294
248
16
22
23
25
17
1 Ib/acre - 1.12 kg/ha
In wastewater application, the fraction of input nitrogen which is
denitrified is strongly dependent on available carbon in the soil. This
is illustrated in Figure A-2 which shows data from a column of Panoche
sandy learn receiving 3 in./wk (7.5 cm/wk) of wastewater at two different
NHl-N levels over a 6 month period. The chloride curve shows the
behavior of a nonreactive ion, with no holdup in the soil. At the 21.4
mg/L NH|-N level, there was complete removal cf the first 22% of input,
followed by several months of nearly complete removal. Over the entire
period there was 16% recovery, or 84% removal of input nitrogen.
However, at the 61 mg/L NHt-N level, once the supply of available
carbon was exhausted, there was very little denitrification. Overall
recovery in the latter case was 83%, corresponding to only 17% removal.
It should be possible to adjust the loading rate for most soils so as to
maximize denitrification in cases where nitrogen removal is the
principal consideration.
Agricultural wastes, such as straw residues and manures, are effective
in stimulating denitrifieation, but these pose problems of handling and
availability at land treatment sites. Olson et al. applied manure to
Plainfield sand at rates varying from 10 to 27U tons/acre (22.4 to 605
Mg/ha) [53], Under aerobic conditions, nitrate accumulated to 25 to 180
mg/L, but when the soil was maintained in a saturated condition, as
might be done by ponding during wastewater application, virtually no
nitrates were found. Meek et al. observed that redox potentials in
A-12
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calcareous Holtville clay receiving IbO tons/acre (4U3 Mg/ha) of manure
in each of two successive years did not fall below 400 mV with the
normal irrigation schedule, whereas the potential dropped to zero when
the number of irrigations was doubled [54]. These authors suggest that
it is possible to adjust manure application rates and irrigation
schedules for fine-textured soils to achieve maximum denitrification.
The principle is applicable to other kinds of wastes as well.
FIGURE A-2
EFFECT ON INPUT NH4-N CONCENTRATION ON N REMOVAL
FROM WASTEWATER APPLIED TO PANOCHE SANDY LOAM
AT THE RATE OF 3 IN./WK FOR 6 MONTHS [41]
100 i-
(INPUT OF 61mg/L NHi-N)
NITRATE.
(INPUT OF 21mg/L NH^-N)
20 -
40 60
INPUT, % OF TOTAL
1 in./wk = 2.54 cra/wk
A-13
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A.3.3.2 Rapid Infiltration
In the intermittent application ofewastewater to soil, it can be safely
assumed that all of the input ammonium not volatilized will eventually
be nitrified if the adsorption capacity of the soil is not exceeded and
if the periods of application are interspersed with drying periods of
sufficient length and frequency to replenish soil oxygen. Bouwer et al.
reported essentially quantitative conversion of ammonium to nitrate in
rapid infiltration systems having 2 to 3 days of flooding alternated
with 5 days of drying [8], Robeck et al. obtained about 74% ammonia
removal in Ottawa sand with shorter and more frequent applications of
wastewater at a rate of 8 in./d (20 cm/d) containing nitrogen equivalent
to 50 lb/acre-d (55 kg/ha-d) [9J. This removal was attributed primarily
to nitrification. Thus, in rapid infiltration systems, nitrification is
the dominant process unless specific steps are taken to promote
denitrification.
In rapid infiltration experiments with soil columns, Lance and Whisler
found no net removal of nitrogen with 2 days of flooding followed by 5
days of drying, but net removal was 30% with longer cycles involving 9
to 23 days of flooding and 5 days of drying [7]. Lance et al. developed
two successful methods for maximizing denitrification in high rate
applications which achieved 75 to bO% removal of nitrogen [55]. On the
basis of their finding that the percentage of nitrogen removal increased
exponentially as the infiltration rate decreased, they reduced
infiltration rates by soil compaction to a level that allowed nitrate
formed during the dry period to mix with the wastewater subsequently
applied in order to provide a favorable ratio of carbon to nitrate. The
second method involved recycling water of high nitrate content that had
passed through the column as a nitrate peak. This was mixed with two
parts of secondary effluent and recycled throughout the remainder of the
flooding period, both methods encounter practical difficulties in field
application. Adjusting depth of ponding, compacting the surface of the
soil, and altering the solids content of applied wastewater have been
suggested as means of changing infiltration rates [55]. Recycling high
nitrate water in the field would require interceptor drains below the
water table, the effluent from which would be pumped to a holding pond
and mixed with wastewater prior to reapplication.
An alternative method of increasing nitrate removal by denitrification
is to add an energy source. Methanol has been used for this purpose in
reducing the nitrate content of drainage water [56]. The theoretical
methanol requirement in this process for wastewater containing 20 mg/L
of NO§-N would be 45.7 mg/L, or the equivalent of 1.6 gal of methanol
per acre-inch (5.9 L/ha-cm) of water, assuming that all the methanol is
used by denitrifying bacteria. Experiments with drainage water showed
that up to 90% removal of nitrate could be achieved with water initially
containing 20 mg/L of NO^-N by addition of 70 mg/L of methanol, or
A-14
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about 150% of the theoretical requirement [56]. It is unlikely that
methanol added to municipal wastewater and then applied to soil would be
used as efficiently, owing to the presence of large numbers of
heterotrophic microorganisms in addition to the denitrifiers. An
inherent difficulty is that the period of aerobic microbial activity
required for nitrification of input ammonium permits rapid depletion of
available carbon, leaving little for use of denitrifiers when the soil
is again flooded.
A.3.3.3 Overland Flow
In overland flow treatment, a thin film of wastewater passing over the
surface of soils of relatively low permeability serves as a barrier to
oxygen movement below the soil surface. This permits the development of
anaerobic conditions in the soil near the soil-water interface with
attendant denitrification. Other aspects of this type of treatment
which favor denitrification are the close proximity of an oxidizing zone
in the flowing water, and the high BOD of wastewaters to which this
method is applicable. This allows nitrification in the water film,
followed by movement of nitrate into the reducing zone below the soil
surface where energy for denitrifying bacteria is supplied by soluble
organic matter from the wastewater. Quantitative data showing the
relative importance of denitrification in relation to other nitrogen
removal mechanisms such as plant uptake and ammonia volatilization are
lacking, but reported high removal efficiencies of 75 to 90% suggest
that denitrification is the dominant process [57, bb, 59],
A.3.4 Leaching
Nitrogen applied in excess of crop removal is potentially subject to
leaching, but in practice, losses by volatilization of ammonia and by
denitrification diminish the actual quantities of nitrogen leached. In
arid regions, some leaching is essential to prevent excessive
accumulations of salt. In most situations, some movement of nitrate
from the root zone to the groundwater is unavoidable.
In land treatment systems, it is desirable to have an estimate of the
amount of nitrate leached, but reliable estimates are difficult and
expensive to obtain. In considering nitrate as a pollutant, it is
important to bear in mind that total mass flow is of greater
significance than concentration per se. In applications on cropland at
rates not greatly in excess of the consumptive use requirement for
water, fairly high concentrations of nitrate in the subsoil would not
represent a high pollution hazard because of the low leaching fraction.
On the other hand, in high rate application with a large leaching
fraction, a much greater mass of nitrogen may move into an aquifer even
A-15
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though the nitrate concentration is relatively low. In crop irrigation
systems, the quantity of nitrogen that is potentially leachable (nitrate
form) increases sharply above the input level required to achieve
maximum crop production, as is illustrated in Figure A-3. The applied
nitrogen cannot be balanced by the leachable nitrogen plus crop nitrogen
because incorporation of nitrogen into soil organic matter and
denitrification amounts in Figure A-3 are unknown.
FIGURE A-3
YIELD, CROP UPTAKE OF N, AND POTENTIALLY LEACHABLE
NITRATE IN RELATION TO FERTILIZER APPLICATION RATE
ON CORN GROWN ON HANFORD SANDY LOAM [41]
500 I-
400 -
300 -
LEACHABLE N IN SOIL
200 -
100 -
ID
h_
O
3 >
2 _•
0 100 200 300
N APPLIED,Ib/acre
1 lb/acre=1.12 kg/ha
1 ton/4 ere = 2.24 Kg/ha
400
500
Monitoring nitrate flux in a field situation is not a simple matter.
Porous ceramic probes, sometimes referred to as suction lysimeters, are
often used to obtain samples of soil solution at various depths and
locations without disturbing the soil after the initial installation. A
rather dense network of such probes is required to obtain reliable
estimates of soil nitrate concentrations. Even in soils considered to
be uniform, these concentrations are subject to wide variations both in
time and in space. This is illustrated by the data of Table A-3,
obtained from probes located in a corn field on Yolo fine sandy loam.
It will be noted that individual samples vary by an order of magnitude
or more from replicate samples in several instances, and standard
deviations from the mean ranged from 32 to 114% of the mean.
A-16
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TABLE A-3
NITRATE-N CONCENTRATIONS IN SOIL SOLUTION SAMPLES
OBTAINED BY MEANS OF SUCTION PROBES AT FOUR DEPTHS ON
TWO DATES IN A CORN FIELD ON YOLO FINE SANDY LOAM [41]
No. of samples and depth
4 at 4 ft 4 at 6 ft 8 at 8 ft 8 at 10 ft
Jul 28, 1975
Mean NO^-N, mg/L 31.9 25.8 30.3 32.0
Range, mg/L 15.2-60.0 18.9-35.6 6.8-58.9 7.8-55.4
Standard deviation,
% of mean 61 32 58 45
Aug 28. 1975
Mean NO;j-N, mg/L 19.5 12.3 26.3 32.4
Range, mg/L 1.8-50.4 2.3-22.4 1.8-47.2 5.1-58.9
Standard deviation,
% of mean 114 67 66 54
1 ft * 30 cm
It is clear that estimations of nitrogen removal based on a few suction
lysimeter samples may be in serious error. It should be further
realized that measurements of moisture flux in unsaturated soils are
subject to the same kind of variation, making calculations of mass
balance even more hazardous. This variability is inherent in sampling
natural bodies for virtually any parameter. The conclusion is that it
is not generally practical to attempt to estimate nitrate removal from
wastewater in slow rate applications by monitoring composition of the
soil solution. In rapid infiltration applications, where the amount of
water applied is much greater than consumptive use and where applied
nitrogen greatly exceeds any soil contribution, measurements made on
samples from the zone of saturated flow obtained by means of suction
cups, wells, or tile lines are somewhat more reliable.
A.3.5 Storage of Nitrogen in Soil
In a theoretical equilibrium situation over the long term, where
additions and removals of nitrogen are in balance, the storage capacity
of the soil is of little consequence from the standpoint of management
practice, even though the residence time in the soil may be quite long.
In actual wastewater application practice, particularly with slow rate
systems, the storage of nitrogen is very important because equilibrium
A-17
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is not quickly attained. The principal storage mechanisms are fixation
of ammonium by clay minerals and organic matter, retention of ammonium
as an exchangeable cation, and incorporation into soil organic matter.
A.3.5.1 Ammonium Fixation
Certain clays that commonly occur in soils, particularly those of the
vermiculite group, have the ability to trap ammonium ions within the
crystal lattice. Ammonium ions thus fixed do not exchange readily with
other cations and are not accessible to nitrifying bacteria [60].
Fixation of NH| by clays is enhanced by wetting and drying cycles but
may occur without drying. The quantities so fixed depend on the kinds
and amounts of clay present. Quantities of NHj fixed by three
different soils receiving five consecutive applications of a solution
containing 100 mg/L of NH|-N without intervening drying periods are
shown in Figure A-4. The Aiken clay, containing predominantly
kaolinite, fixed no NHt . The Columbia fine sandy loam, typical of
coarse textured soils tnat might be used for wastewater disposal, fixed
22 ppm NHt (soil basis), equivalent to about 275 Ib/acre (308
kg/ha) of " nitrogen in the top 3 ft (1 m) of soil. This soil and the
Sacramento clay contain vermiculite and montmorillonite capable of
NHj fixation.
FIGURE A-4
CLAY-FIXED NHt IN THREE SOILS RESULTING FROM FIVE
APPLICATIONS OF A SOLUTION CONTAINING 100 mg/L
NHj-N, WITHOUT INTERVENING DRYING [41]
40 r
COLUMBIA FINE SANDY LOAM
NUMBER OF APPLICATIONS
A-18
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Another mechanism of NH| fixation involves reaction with soil
organic matter to form stable complexes. The amounts fixed depend
strongly on pH and quantity of organic matter present [61]. It is
unlikely that this mechanism is of much importance at the low
NHj concentrations and near-neutral pH of wastewaters normally applied
to soils of low organic matter content, but'it may assume considerable
importance in sludge applications where NHj concentrations are at
least an order of magnitude higher and where organic matter is supplied
by the sludge.
A.3.5.2 Exchangeable Ammonium
Like other cations in wastewater, NHt can be adsorbed by the
negatively charged clay and organic colloids in soil. Lance discussed a
method of estimating the quantity of NH^ that might be adsorbed from
a particular wastewater based on the ammonium adsorption ratio
calculated from the concentrations of NH| , Ca++ , and Mg++
in the water [62]. In slow rate systems, the ammonium adsorption
capacity of soils is usually sufficient to retain the applied ammonium
near the surface. Continuous flooding in rapid infiltration systems
will in time saturate the ammonium adsorption capacity and permit
downward movement of ammonium. Retention of ammonium in the
exchangeable form is temporary in any case, since'the adsorbed ammonium
is nitrified when oxygen becomes available; but exchangeable NH|
plays a very important role in the nitrification-denitrification sequence
by holding nitrogen near the soil surface until the environment becomes
aerobic during drying.
Even in sandy soils of low cation exchange capacity the quantity of
exchangeable ammonium is of consequence. A profile of exchangeable
NH| beneath a sludge drying pond as compared to untreated soil is shown
in Figure A-5. This represents a situation where high NH| con-
centrations combined with a low infiltration rate have resulted in domi-
nance of the cation exchange complex by NHt . The total quantity of
exchangeable NHt in this soil to a depth of 6 ft (1.8 m) is 10 530 lb/
acre (11 800 kg/ha). The»same profile also contained 1 250 Ib/acre
(1 400 kg/ha) of NO^-N . In a somewhat different situation, Lance
cites calculated values of exchangeable NHt equivalent to 1 554 lb/
acre (1 740 kg/ha) for a wastewater applied to a soil with an exchange
capacity of only 5 meq/100 g [62].
A.3.5.3 Incorporation into Organic Matter
Ammonium may be incorporated into organic matter by the fixation mecha-
nism previously discussed, through assimilation by microorganisms, and
by plant uptake. Net immobilization by microorganisms requires the pre-
sence of decomposable organic matter having a nitrogen content less than
A-19
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about 1.2%. Except for cannery wastes and certain types of industrial
wastes, these conditions are not met for land treatment systems. The
presence of mature crop residues on land receiving wastewater may result
in immobilization of a small amount of nitrogen, though probably not
more than 40 to 60 Ib/acre (45 to 65 kg/ha).
EXCHANGEABLE NHJ
BENEATH A SLUDGE PONt
FIGURE A-5
IN THE PROFILE OF A SANDY SOIL
AS COMPARED TO AN UNTREATED AREA [41]
UNTREATED
1 ft= 0.305 n
A-20
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The most important mechanism of storage is through plant uptake and
subsequent conversion of root and other residues into soil humus. Large
quantities of input nitrogen can be stored in soil for long periods of
time in this way, particularly in soils of initially low organic
nitrogen content. This is illustrated by the profiles of organic
nitrogen shown in Figure A-6 for a cropped area near Bakersfield,
California, where wastewater had been used to irrigate crops for a
periods of 36 years at the time of sampling, compared to an adjacent
area of untreated soil that had never been cropped or irrigated. Total
nitrogen down to a depth of 5 ft (1.5 m) increased by 7 400 Ib/acre
(8 290 kg/ha) as a result of wastewater application, representing an
average annual increment of 2U5 Ib/acre (230 kg/ha) over the 3b year
period.
Lesser quantities of nitrogen would be stored in the organic form in
soils of initially higher organic nitrogen content; and in some
instances, such as those reported by Sopper and Kardos where apparent
crop removals of nitrogen greatly exceeded the quantity applied with the
wastewater, net mineralization of soil organic nitrogen will actually
decrease the quantity stored [42]. Net immobilization is common on
soils of arid regions where there has been little previous input of
organic matter. Net mineralization is more likely in soils of more
humid regions where the native level of organic matter is usually higher
because of more abundant vegetation. Soils of arid regions which have
been irrigated for many years would be unlikely to accumulate much
additional N during wastewater application.
A.4 Nitrogen Removal with Various Application Systems
A.4.1 Slow Rate Systems for Irrigation of Crops
Wastewater used for crop irrigation is commonly applied by sprinklers or
ridge-and-furrow distribution systems, with the rate of application
geared to the needs of the crop for water and nutrients. Nearly all
data on efficiency of nitrogen removal have been obtained at
experimental sites. In an EPA survey of facilities using land
application of wastewater, nitrate concentrations in groundwater were
reported at only ID of 155 locations using municipal wastewater and at
only '
-------
FIGURE A-fa
EFFECT OF 36 YEARS OF WASTEWATER APPLICATION ON
ORGANIC N IN A SOIL AT BAKERSFIELD, CALIFORNIA [41]
ORGANIC N,X
1
0.04
1
0.08
1 1
O.t2
1 1
0.16
I 1
51-
1 ft = 0.305 m
Mineralization of organic nitrogen in soils may also contribute
appreciably to nitrate that eventually reaches groundwater. This is
illustrated by the data of Table A-4 which give total and tagged
nitrogen in the effluent from soil columns treated with wastewater in
which the input water, applied at 3 in./wk (7.5 cm/wk) contained
NHj-N labelled with the 15N isotope. This made it possible to
identify the nitrogen in the effluent which was derived from the applied
wastewater. The difference in percent recovery of total and tagged
nitrogen is due to the contribution of soil nitrogen, most of which was
converted from organic forms to nitrate during the period of treatment.
Thus, net removal from the Sal ado fine sandy loam after application of
137 in. (34b cm) of wastewater would be calculated at only 6%, whereas
the true removal was 48%. Total N added to this soil in wastewater was
equivalent to 1 315 Ib/acre (1 473 kg/ha), and the effluent contained
A-22
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1 236 Ib/acre (1 3b4 kg/ha) of nitrogen; however, only 684 Ib (766 kg)
was derived from wastewater, the other 552 Ib (618 kg/ha) of nitrogen in
the effluent being produced by decomposition of soil organic matter. In
soils of low organic content, such as the Sal ado subsoil, this factor is
of minor importance, as shown by the close correspondence in the figures
for total and tagged nitrogen. At low application rates, nitrogen
removal can be completely masked by mineralization of organic nitrogen
in the soil, as is illustrated by the Panoche sandy loam. A comparison
of nitrogen input versus output shows a net gain, or no removal, whereas
in fact 97% of the input nitrogen did not appear in the effluent.
TABLE A-4
RECOVERY OF TOTAL AND TAGGED N IN EFFLUENT
FROM THREE SOILS RECEIVING 15N-LABELLED
WASTEWATER AT THE RATE OF 3 IN./WK [41]
Wastewater
applied
Soil
Sal ado fine
sandy loam
Salado
subsoil
Panoche
sandy loam
in.
48
137
48
137
87
Ib N/acre
459
1 315
459
1 315
429
N recovered
in effluent, %
Total
24
94
20
78
141
Tagged
1.3
52
17
75
2.7
1 in. * 2.54 cm
1 Ib/acre - 1.12 kg/ha
If total nitrogen input does not greatly exceed crop requirements for
nitrogen, removals of 35 to 60% can be expected as a result of crop
uptake. Depending on soil properties and irrigation schedules,
denitrification may account for 15 to 7U% of the input nitrogen, or even
more at low loading rates. In agricultural practice where attempts are
made to minimize denitrification, losses of 15 to 30% are common [64,
65]. Lienitrification losses with sprinkler irrigation are likely to be
lower than with furrow application because the soil is less likely to
reach the saturated condition, but this may be balanced out by higher
ammonia loss in sprinkler application. Ammonia loss from the soil
surface during periods of drying may be a more important consideration
than is commonly realized [50].
Normally, in wastewater application to crops, it is desirable to rely
primarily on crop uptake as a means of nitrogen removal, and a number of
years of field experience indicates that the procedure is effective in
A-23
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both forest and cropland when rates of application are adjusted to soil
and crop capacity [42, 66]. The capacity of soil to receive nitrogen
may be greatly enhanced by long-term storage in those soils where
substantial buildup of organic nitrogen may occur. The Werribee farm in
Australia is a case in point [67], Soil nitrogen increased from 1 200
to 2 620 ppm after 12 years of irrigation with wastewater. Even if it
is conservatively assumed that the increase was restricted to the
surface 6 in. (15 cm), the additional nitrogen stored is equivalent to
about 2 500 Ib/acre (2 800 kg/ha) averaging a little over 200 Ib/acre-yr
(225 kg/ha-yr)., which is of the same order-of-magnitude as crop removal.
This value is almost identical to the previously cited value maintained
over a 36 year period at Bakersfield, California. In the latter
instance, however, a much greater depth of soil was implicated in the
storage. After 26 years of wastewater application, the Werribee farm
showed a surprising drop in nitrogen content, the reason for which is
not apparent. Adriano et al. estimated total nitrogen immobilization
during 20 years of cannery waste application to sand and loamy sand
soils to be as much as 2 700 Ib/acre (3 000 kg/ha), accounting for
approximately one-third of the total nitrogen applied it>«]. The
quantity of nitrogen immobilized in a given situation depends somewhat
on wastewater composition, being greater with wastewater of high BOD and
low nitrogen content, but it is also affected by climatic variables and
nature of the soil. With constant management, an equilibrium level of
organic nitrogen will eventually be attained, but this may require many
years.
Slow rate land treatment provides sufficient nitrogen removal in several
reported instances to produce a soil percolate below 10 mg/L of NOjj-N
[42]. Karlen et al. reported reduction of nitrogen content from 15
to 7 mg/L with an annual application rate of 79 in. (200 cm) of
wastewater containing 26b Ib/acre (300 kg/ha) of nitrogen on corn
growing on a loam soil with tile drainage [44]. The maximum weekly rate
was 5.3 in. (13.4 cm). McKim et al. in New Hampshire reported total
removals of nitrogen ranging from 73 to 91% with primary or secondary
effluents applied to grass at 2 and 4 in./wk (5 and 10 cm/wic) [43].
Total nitrogen applications varied from 212 to 426 Ib/acre (238 to 478
kg/ha), and the average concentration of nitrogen in the wastewater of
about 35 mg/L was reduced to 3 to 10 mg/L in the percolate. In the
well-known long-term experiments at Pennsylvania State University, soil
solution samples at the 4 ft (1.2 m) depth in Reed canary grass plots
receiving 2 in./wk of wastewater consistently showed less than 4 mg/L of
NO^-N. Application of 2 in./wk to red pine and hardwood plots resulted
in soil nitrate concentrations at the 4 ft (1.2 m) depth substantially
in excess of 10 mg/L of nitrogen, although with 1 in./wk (2.5 cm/wk)
they remained below this value. Kardos and Sopper conclude that, with
appropriate management of nitrogen loading rates to maximize crop uptake
ana with hydraulic loadings adjusted to maximize denitrification, it
should be possible to recharge water that meets drinking quality
standards for nitrogen into the aquifer belowaland treatment site [19].
A-24
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A.4.2 Rapid Infiltration Systems
Rapid infiltration systems use application rates as high as 360 ft/yr
(110 m/yr) and annual nitrogen loading up to 36 000 Ib/acre (40 300
kg/ha) on highly permeable soils. Although grass is sometimes grown on
the receiving areas, the quantity of nitrogen removed by the crop is
only a small fraction of the total applied and exerts little influence
on the quality of the percolating water. Much of the quantitative data
on rapid infiltration systems is derived from the Flushing Meadows
project at Phoenix, Arizona. Lance and Whisler concluded that the only
feasible mechanism for removing the large quantities of nitrogen in
high-rate applications is denitrification [7]. Bouwer et al. reported
that overall nitrogen removal during sequences of long flooding and
drying periods was about 30% [8]. Reducing the infiltration rate 50%
had the effect of increasing nitrate removal to 80%. Lance published a
table showing calculated percentages of nitrogen removal ranging between
75 and 80% using different management systems [62]. The systems involved
reduction of the infiltration rate or recycling high-nitrate percolate
and mixing it with secondary effluent prior to reapplication. These
techniques for achieving high nitrogen removal, although promising,
require testing on a field scale before widespread adoption.
In the Santee, California, project, municipal effluent applied to the
alluvium of a shallow stream channel undergoes about 10 ft (3 m) of
vertical percolation followed by considerable lateral movement
underground [69]. Total nitrogen in the renovated water was reduced to
l.b mg/L, compared to about 25 mg/L in the spreading basins. At Detroit
Lakes in Minnesota where about 98 ft/yr (30 m/yr) of effluent was
applied by sprinkling on a schedule of 20 hours on and 4 hours off,
input nitrogen was converted to nitrate, but little denitrification
occurred and nitrate appeared in the groundwater at concentrations equal
to the influent [70]. In another system with a loading rate of 45 ft/yr
(14 m/yr) where 2 weeks of wetting was followed by 2 weeks of drying,
70% removal of total nitrogen was achieved [71]. At Fort Devens,
Massachusetts, where rapid infiltration of primary effluent has been
used since 1942, recent data show that where 91 ft/yr (28 m/yr) of
wastewater was applied on a scnedule of 2 days of flooding followed by
14 days of drying, nitrate-nitrogen concentrations in the groundwater
were 20 to 40% of the average total nitrogen input level of 47 mg/L
[72].
A.4.3 Overland Flow Systems
Land application of wastewater on fine-textured soils of low
permeability has been made possible by development of the overland flow
treatment method. The relatively high clay content of such soils is
A-25
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advantageous in nitrogen removal because of their increased capacity for
adsorption of ammonium and slow diffusion rates of gases through them,
thereby permitting development of an anaerobic zone near the surface.
Hoeppel et al. have shown that concentrations of NH+ and NO^ in
surface runoff are linearly correlated with flowrate, indicating that
efficiency of nitrogen removal depends on time of contact between water
and the soil surface [57].
In this mode of treatment a ground cover is required, usually a species
of grass that is tolerant of wet conditions, such as Reed canary grass.
The rates of application in some overland flow systems exceed plant
uptake by a substantial margin, but plant uptake undoubtedly plays an
important role in nitrogen removal. Carlson et al. reported a
pronounced gradient in the growth of grass between the lower and upper
ends of the slope in their model, with nitrogen deficiency evident at
the lower end, which shows that much of the inorganic nitrogen present
was assimilated by the grass, lost to denitrification, or both [bb].
In addition to crop uptake, the important processes involved in nitrogen
removal during overland flow may include ammonia volatilization,
adsorption of ammonium by clays and organic matter, immobilization, and
denitrification. Insufficient data are available to evaluate the
relative importance of these processes under a particular set of
circumstances. Law et al. reported the maximum pH of cannery waste at
the Paris, Texas, site was 9.3, while the value in the runoff was b.l
[26]. At these values, ammonia volatilization could be appreciable.
Ammonium adsorption is probably involved in development of a slope
gradient in nitrogen available to the grass.
The overland flow system is ideally adapted to the nitrification-
denitrification sequence, which requires aerobic and anaerobic zones in
close proximity. Applied wastewater is aerated as it contacts the
atmosphere as a thin film flowing over the surface, thereby permitting
nitrification to occur. Nitrate thus formed diffuses into the soil,
encountering reducing conditions in which denitrification can proceed.
The presence of living plants provides a mat of organic debris and root
excretions which can be used as a substrate by denitrifying bacteria.
Conditions are even more favorable for denitrification with wastewater
of high BOu, such as cannery effluents. Thomas states that
denitrification is the major mechanism of nitrogen removal in overland
flow systems [5y]. Another aspect of the role of plants is their
influence on the loss of nitrogen through the nitrification-
denitrification processes in the root zone. Plants capable of surviving
in wet environments have a mechanism for translocating oxygen from the
tops to the roots, and may even excrete oxygen from the roots. For
example, healthy rice roots grown in flooded soil often have a reddish
coating due to hydrous oxides of ferric iron, clearly denoting an
oxidizing micro-environment even though negative, or strongly reducing
A-26
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oxidation-reduction potentials exist in the soil proper. In the
immediate root zone, or rhizosphere, nitrification may occur, after
which the nitrate so formed will diffuse away from the site of formation
and be denitrified. In support of this view is the observation that
nitrogen losses occur in rice soils even when ammonia sources are placed
directly in the reducing zone [73]. ;
/
The overland flow systems for which data are available show high
nitrogen removal efficiencies. Law et al. reported 83 to 90% removal of
total nitrogen from cannery wastes applied on grassland at the rate of
515 lb/acre-yr (578 kg/ha-yr) of nitrogen [26]. In this case where most
of the input nitrogen was organic and the wastewater had a high BOD, it
is possible that much of the applied nitrogen was incorporated into the
soil organic fraction. Johnson et al. cite bO% removal of total
nitrogen from raw sewage at Melbourne, Australia [67]. Hoeppel et al.
reported nearly complete removal of NH| or NOo by a model over-
land flow system using municipal wastewater on a kaolinitic clay soil
[57],
A.4.4. Wetlands
Very little information is available on the use of marshes and wetlands
for wastewater treatment, but a consideration of the foregoing
discussion on the factors that favor the denitrification process will
make it evident that such areas have the requisite characteristics of a
nitrogen sink. In marshes and swarnps, the rate of plant growth is
greater than the rate of decomposition of plant residues as a result of
exclusion of oxygen from the surface soil by excess water, since in an
anaerobic environment decomposition of plant residues is neither rapid
nor extensive. Hence, soils formed under these conditions typically
have high organic matter levels, some falling in the peat and muck
categories. Abundant organic matter and an aerobic-anaerobic zone at
the mud-water interface provide excellent conditions for denitrification.
The potential for nitrogen removal is illustrated by consideration of
the area of peat and muck soils in the Sacramento-San Joaquin delta area
of California. When these soils are drained, aerobic decomposition of
the soil above the water tableisso rapid that subsidence up to 3 in./yr
(7.5 cm/yr) is observed. The organic nitrogen in the soil is mineralized
and converted to nitrate, which appears in the drained soil at high con-
centrations. A subsidence of 2 in./yr (5 cm/yr) represents the release
of nitrogen in the inorganic form of about 4 500 Ib/acre (5 050 kg/ha).
Notwithstanding this enormous input, the drainage waters and ground-
water in the area maintain low concentrations of nitrate as a result
of denitrification in the saturated zone.
A-27
-------
Raveh and Avnimelech have reported substantial enhancement of nitrate
removal by sprinkling or flooding soils in the Hula valley in Israel, an
area previously covered by a lake and marshes [74]. When the water
level in a field was raised to the surface by flooding, the redox
potential dropped to about -100 mV throughout the profile, and the
nitrate concentration in the top layer dropped rapidly from 1 250 to 250
ppm '(soil basis). The quantity of nitrate reduced was 1 650 Ib/acre
(1 850 kg/ha) of nitrogen, or about 70% of the amount initially present
in the top 3 ft (1 m). In another experiment, the soil was wetted by
sprinkling for about 20 hours at a rate lower than the infiltration rate
so that the surface soil remained unsaturated. In this case, nitrate
disappearance from the top 3 ft (1m) was about 980 Ib/acre (1 100
kg/ha). These authors emphasized the importance of surface drying in
releasing readily available organic matter, which stimulates oxygen
consumption and provides a substrate for denitrifying bacteria. In
layers that remained permanently wet, even though the redox potentials
were very low, nitrate reduction was negligible.
Engler and Patrick investigated nitrate removal from floodwater in
relatively undisturbed cores of a fresh water swamp soil and a saltwater
marsh soil in Louisiana [75]. The latter was more effective in nitrogen
removal, with an average rate of a.2 Ib/acre-d (9.2 kg/ha-d), while the
fresh water swamp soil removed 2.9 Ib/acre-d (3.3 kg/ha-d). Addition of
organic matter to a rice soil was shown in other experiments to have the
effect of decreasing the depth of soil through which nitrate had to
diffuse before being reduced, and this drastically increased the rate of
nitrate removal.
A. 5 Summary
The important processes involved in nitrogen removal from wastewater
applied to land are ammonia volatilization, crop removal, soil
adsorption of ammonium, incorporation into the soil organic fraction,
and denitrification. The relative contribution of individual processes
to overall nitrogen removal is dependent on a large number of soil,
climatic, and management parameters. While it is not yet possible to
predict nitrogen removal in a particular situation with a high degree of
confidence, enough is known about the influence of management factors,
such as loading rates, flooding and drying periods, and type of plant
cover, to design systems that will remove the major part of input
nitrogen for a wide variety of disposal requirements and local
circumstances.
A-28
-------
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A-29
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A-30
-------
25. Mann, L.D., et al. Increased Oenitrification in Soils by Addition
of Sulfur as an Energy Source. Journal of Environmental Quality.
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30. Stensel, H.D., R.C. Loehr, and A.W. Lawrence. Biological Kinetics
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40-52, 1958.
32. Nommik, ri. Investigations on Denitrification in Soil. Acta Agric.
Scand. VI. 2:195-226, 1956.
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Process in Soil. Plant and Soil. 5:155-169, 1954.
34. Cooper, G.S. and R.L. Smith. Sequence of Products Formed During
Denitrification in Some Diverse Western Soils. Soil Sci. Soc.
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35. Volz, M.G., et al. Nitrate Reduction and Associated Microbial*
Populations in a Ponded Hanford Sandy Loam. Journal of
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36. Woldendorp, J.W. The Quantitative Influence of the Rhizosphere on
Denitrification. Plant and Soil. 17:267-270,1962.
37. Stefanson, R.C. Soil Denitrification in Sealed Soil- Plant Systems
I. Effect of Plants, Soil Water Content and Soil Organic Matter
Content Plant anu Soil. 33:113-127, 1972.
38. Woldendorp, J.W. The Influence of Living Plants on Denitrification.
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39. Terman, G.L. and M.A. brown. Crop Recovery of Applied Fertilizer
Nitrogen. Plant and Soil. 29:48-65, 1968.
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41. Broadbent, F.E. Unpublished Data, 1976.
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With Treated Municipal Wastewater. In: Recycling Treated
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Simulated Municipal Sewage Effluent. Journal of Environmental
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45. Parizek, R.R., et al. Pennsylvania State Studies Wastewater
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Experimental Station Extension Service Circular. Publication
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47. Henderson, D.W., C. Bianchi, and L.D. Doneen. Ammonia Loss From
Sprinkler Jets. Agricultral Engineering 36:398-399, 1955.
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Fertilized Nebraska Soils. Agronomy Journal. 53:241-244, 1961.
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Volatilization From Soils. Agronomy Journal. 66:355-358, 1974.
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Surface Fertilized Soils. Soil Science. 71:25-34, 1951.
51. Ryan, J.A. and L).R. Keeney. Ammonia Volatilization From Surface-
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359.
53. Olson, R.J., R.F. Hensler, and O.J. Attoe. Effect of Manure
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on Certain Soil Test Values. Soil Sci. Soc. Amer. Proc. 34:222-
225, 1970.
A-32
-------
54. Meek, B.D., et al. The Effect of Large Applications of Manure on
Movement of Nitrate and Carbon in an Irrigated Desert Soil.
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55. Lance, J.C., F.D. Whisler, and R.C. Rice. Maximizing Denitrifica-
tion During Soil Filtration of Sewage Water. Journal of Environ-
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56. Field Evaluation of Anaerobic Denitrificatipn in Simulated Deep
Ponds. California Department Water Resources Bulletin, pp. 174-
179, 1969.
57. Hoeppel, R.E., P.G. Hunt, and T.B. Delaney, Jr. Wastewater
Treatment on Soils on Low Permeability. U.S. Army Engineering
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Treatment of Wastewater. U.S. Army Engineering Waterways
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3. 1974.
«
59. Thomas, R.E., et al. Feasibility of Overland Flow for Treatment of
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61. Burge, W.D. and F.E. Broadbent. Fixation of Ammonia by Organic
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63. Sullivan, R.H., M.M. Conn, and S.S. Baxter. Survey of Facilities
Using Land Application of Wastewater. EPA 430/9-73-006. 1973.
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66. Sopper, W.E. A Decade of Experience in Land Disposal of Municipal
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p. 19-61.
A-33
-------
67. Johnson, R.D., et al. Selected Chemical Characteristics of Soils,
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the Soil and Subsurface Water. Journal of Environmental Quality.
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69. Merrell, J.C., Jr., A. Katko, and H.E. Pintler. The Santee
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70. Larson, W.C. Spray Irrigation for the Removal of Nutrients in
Sewage Treatment Plant Effluent as Practiced at Detroit Lake,
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71. Bendixen, T.W., et al. Ridge and Furrow Liquid Waste Disposal in a
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75. Engler, R.M., and W.H. Patrick, Jr. Nitrate Removal From
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A-34
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APPENDIX B
PHOSPHORUS
B.I Introduction
Phosphorus (P), in the element form, is a highly reactive material and
is thus usually found in nature in an oxidized state in combination with
oxygen and a number of mineral elements. It is also found in many
organic compounds in naturally occurring materials. Because phos-
phorus is essential for all forms of life, it must be present in avail-
able forms in all soils and waters if these are to be biologically pro-
ductive. The production of large amounts of biological materials on
land surfaces is usually considered desirable because these can be used
for food, fiber, fuel, and building materials. In waters, however, the
production of large amounts of biological materials usually causes un-
desirable effects. Thus, on agricultural land, materials containing
phosphorus are added to increase biological production; whereas in most
waters, attempts are made to keep the phosphorus concentration within
low limits to avoid undesirable production of organic materials that
cause problems in the use of water for municipal, industrial, agri-
cultural, and recreational purposes.
Concentrations of phosphorus in municipal wastewaters usually range from
about 1.0 to 40 mg/L, depending on the phosphorus concentration of the
input water and removal during treatment [1-3]. Thomas used 10 mg/L as
a typical phosphorus concentration [4]. Most concentrations are usually
less than 20 mg/L.
On the other hand, the concentration of phosphorus in the soil solution
in most soils is usually between 3 and 0.03 mg/L [5], but typical con-
centrations are a few tenths mg/L [6]. Because of these differences in
ranges of phosphorus concentrations between wastewaters and soil solu-
tions, a reduction in phosphorus concentration as the wastewater enters
the soil is to be expected. As a result of various adsorption and
precipitation reactions, the concentration of phosphorus will decrease
as the wastewater enters the soil, depending on the intensity of these
reactions, the capacity of the soil materials to maintain them, and the
time allowed for them to proceed. Harvested crops also serve as a sink
for the added phosphorus and a certain amount returns to the soil annu-
ally in plant materials (roots, stems, and leaves) that are not har-
vested.
The objectives of this appendix are to discuss the reactions of phos-
phorus with soils, to show their applications to the removal of phos-
phorus from wastewaters applied to soils, and to assess the present
status of our abilities to predict the capacities of soils to remove
phosphorus from such waters. The chemistry of phosphorus in soils,
B-l
-------
plants, and waters is complex, and the literature is voluminous. Con-
sequently, no attempt has been made to provide a complete literature
review. Reports and textbooks that do review the literature are avail-
able, including Russell [5], Tisdale and Nelson [7], Larson [6], Holt et
al. [8], and Ryden et al. [9].
B.2 Removal Mechanisms
The phosphorus that enters a soil in fertilizers, wastes, or wastewaters
is (1) removed in harvested crops; (2) accumulated in the soli a phase of
the soil as organic compounds, adsorbed ions, or precipitated inorganic
compounds; (3) removed by soil erosion as soluble phosphorus or phos-
phorus adsorbed or precipitated on soil particles; or (4) leached from
the root zone in percolating water. The chemical reactions between
added soluble phosphorus and soil materials or sediments influence the
availability of phosphorus to crops and the desorption or solubility of
phosphorus when the soil materials become sediments in streams and
lakes, and control the leaching of phosphorus through soil profiles.
The amount of phosphorus in soils is usually between 0.01 and 0.2%, but
heavily fertilized surface soils can contain greater amounts. Usually
much less than 0.1% of the total phosphorus in soils is soluble in
water. Solid phase phosphorus consists of (1) organic phosphorus, the
quantities of which are highly dependent on the amount of organic matter
in the soil; (2) inorganic compounds; and (3) phosphorus adsorbed on
various types of surfaces in the soil. The orthophosphate form, in
which one phosphorus atom is combined with four atoms of oxygen, is the
most stable configuration in the soil environment.
In discussing the reactions of phosphorus with soils and sediments, it
is assumed that the phosphorus is in the orthophosphate form and that
other forms convert to this form in the soil system [10-13]. The main
soil constituents that react with phosphorus at concentrations usually
found in wastewaters are (1) iron and aluminum as soluble ions, oxides
and hydroxides, and silicates; and (2) calcium as a soluble ion and as
carbonate.
Soluble inorganic phosphorus introduced into a soil is chemically ad-
sorbed on surfaces and can also be precipitated. In the adsorption
processs, the reaction is with iron, aluminum, or calcium ions exposed
on solid surfaces. Reactive iron and aluminum surfaces can occur at the
broken edges of crystalline clay minerals, as surface coatings of oxides
or hydroxides on crystalline clays, and.at the surfaces of particles of
oxides and hydroxides and of amorphous silicates. Aluminum in the form
of positively charged hydroxide polymers and as an exchangeable ion in
acid soils can also adsorb phosphorus. Reactive calcium surfaces are
mainly found on solid calcium carbonates and calcium-magnesium car-
bonates. Precipitation reactions occur with soluble iron, aluminum, and
B-2
-------
calcium. Particles of phosphate compounds can also form by separation
of adsorbed phosphorus along with iron, aluminum, or calcium from solid
surfaces.
The reactions of phosphorus with soils are complex, and the soil system
is complex. Consequently, the uncertainty whether phosphorus is being
adsorbed or precipitated leads to the use of the term "sorption," which
covers both processes and means only that the phosphorus has been re-
moved from solution.
A given soil material does not have a fixed capacity to sorb the phos-
phorus added in wastewaters. Sorption is dependent not only on the
concentration of phosphorus in solution, but also on a number of
factors, including soil ph, temperature, time, the total amount of phos-
phorus added, and the concentrations of various constituents in the
wastewater that directly react with phosphorus or that influence such
soil properties as pH and oxidation-reduction cycles. Another basic
factor is that the downward movement of phosphorus in a soil profile is
diffuse. Because the capacity for sorption of phosphorus is con-
centration-dependent, there is a large transition zone between highly
enriched and nonenriched soil, which is described as a diffuse rather
than as an abrupt boundary as illustrated in Figure B-l. That is, a
given depth interval gradually accumulates sorbed and soluble phos-
phorus, and the breakthrough curve at the bottom of a soil column
extends over considerable time and/or volume of effluent.
B.2.1 Crop Removal
In most cropped soils, the application of phosphorus increases growth of
plants. However, as more phosphorus is accumulated (i.e., excesses are
added), negative effects are sometimes found. These decreased yields
that result from excess available phosphorus in the soil are indirect
effects of phosphorus on the availability of copper, iron, and zinc and
are referred to as nutrient imbalances [14-17]. Corrections of these
imbalances can be made by soil or foliar applications of the needed
elements.
The removal of phosphorus in harvested crops depends on the yield and
the phosphorus concentration in the harvested material, which in turn
are dependent on the crop, soil, climate, and management factors, in-
cluding the amount of phosphorus added to the soil. Typically, the
harvested portions of annual crops contain only 10% or less of the fer-
tilizer phosphorus added during the season in which the crop is grown,
but recoveries as high as 50 to 60% are possible [5]. However, recovery
is low not only because the soil reacts with the added phosphorus to
make it less available, but also because plants absorb considerable
amounts of phosphorus from soil supplies, including the residues from
applications in previous years. Thus, the total removal per year as a
B-3
-------
fraction of the total added per year is more important than the recovery
of that added during the year the crop is grown.
FIGURE B-l
RELATIONSHIPS BETWEEN PHOSPHORUS CONCENTRATION AND
SOIL DEPTH FOR ABRUPT AND DIFFUSE BOUNDARIES
BETWEEN ENRICHED AND NONENRICHED SOIL
PHOSPHORUS IN SOLUTION, mg/L
INCREASING
CONCENTRATION
SOIL
SURFACE
APPLIED
CONCENTRATION
10
-••• 'vrr~ A
\ £ - t
on \.-__
":::::::::: "i :r "
:::::::::::::: .YE :
"::::::::: :~ :: : :\
E \
« 60 — l;
?
H-
0.
UJ
a
U"
i ' U»^
so - y
W\-u
f El*
r
r
1 20- /
i sn
::::::::::::::::::::::::::::::::: --jd
============================================
BRUPT BOUNDARY BETWEEN ,
NKIOHtU ANU NUNtNKIbHtU 5UIL ;K
" • , i " .. . , r
t **
1 ^~^^
y
FFUSE BOUNDARY BETWEEN
RICHED AND NONENRICHED SOIL
B-4
-------
Data for amounts of phosphorus removed by the usual harvested portions
of selected agronomic, vegetable, and fruit crops are presented in Table
B-l. Variations range from as low as 10 lb/acre-yr (11 kg/ha-yr) to as
high as 85 .lb/acre-yr (95 kg/ha-yr).
TABLE B-l
REMOVAL OF PHOSPHORUS BY THE USUAL HARVESTED
PORTION OF SELECTED CROPS
Crop
.Annual crop Phosphorus
yield, uptake,
per acre lb/acre-yr
Corn [18]
Cotton [18]
Lint and
seed
Wheat [18]
Rice [18]
Soybeans [18]
Grapes [18]
Tomatoes [18]
Cabbage [18]
Oranges [18]
Small grain, corn-
hay rotation [19]
Reed canary grass [19]
Corn silage [19]
Poplar trees [20]
Barley-sudan grass
rotation for forages3
Johnson grass [18]
Guinea grass [18]
Tall fescue [18]
180 bu
3 700 Ib
80 bu
7 000 Ib
60 bu
12 tons
40 tons
35 tons
600 boxes
(90 Ib/box)
12 tons
11.5 tons
3.5 tons
31
17
20
20
22
10
30
16
10
29
40
27-36
23-62
75-85
84
45
29
a. Unpublished data for barley in the winter
followed by sudan grass in the summer.
P.P. Pratt and S. Davis, University of
California, and USDA-ARS, Riverside,
California.
1 Ib = 2.2 kg
1 acre = 0.405 ha
B-5
-------
Amounts of phosphorus removed by crops can range by an order of mag-
nitude and are higher with forage crops than with most other crops.
Removal in harvested materials, as a fraction of that added, decreases
as the amount of phosphorus added increases. Where double cropping
during a long season is possible, removal can be nearly double that
where only one crop can be grown.
B.2.2 Adsorption
When solutions containing soluble phosphorus at concentrations usually
found in reclaimed waters (20 mg/L or less) are added to soils, the
initial (and more rapid) reaction can be described by the Freundlich or
Langmuir equations. Slow reactions, such as precipitation, are not
modeled by these equations so that their use will yield conservative
results. 01 sen and Watanabe found that, up to an equilibrating con-
centration of nearly 20 mg/L, using a reaction time of 24 hours, the
reaction was described by the Langmuir equation [21]. TKut is, if a
water containing any specific concentration of phosphorus within the
range of a few to 20 mg/L is added to a soil and allowed to equilibrate
for 24 hours, phosphorus will be sorbed by the soil and the con-
centration in solution will decrease. If a number of waters containing
various phosphorus concentrations are added to samples of the same soil,
a relationship between phosphorus sorption and final phosphorus con-
'centration can be described by the Langmuir equation. From this equa-
tion the decrease in phosphorus concentration and the sorption of phos-
phorus can be predicted for any other initial concentration using the
same soil and reaction time. But at equilibrating concentrations
greater than 20 rng/L, the reactions in most soils are not described by
this equation.
Larson concluded that, in dilute solutions, adsorption generally follows
the Langmuir equation where a plot of C/V against C (where C is con-
centration and V is phosphorus adsorbed per unit weight of soil) gives a
straight line [6]. Larson reported that a study of 120 soils showed
straight line relationships of C/V to C up to concentrations of about 19
mg/L of phosphorus. Above this concentration the C/V-C line curved,
indicating that the adsorption equation was no longer valid. At higher
concentrations, the concentration was assumed to be limited by the for-
mation of sparingly soluble compounds, and the value V increased as more
of these compounds were formed.
Ellis [13] and Ellis and Erickson [22] used the Langmuir equation to
calculate relative capacities of soil profiles to retain phosphorus.
The retention of phosphorus at a solution concentration of 10 mg/L
ranged from 71 to 95% of the adsorption maximum calculated from the
Langmuir equation for a number of soil materials. Amounts retained from
a solution concentration of 10 mg/L ranged from 77 to 1 898 Ib/acre (86
to 2 126 kg/ha) for 12 in. (30 cm) depth intervals, respectively, for a
dune sand to a clay loam. The reaction time in these studies was 24
hours.
B-6
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Even though the original or initial capacity to retain phosphorus can be
described by adsorption equations, the retention increases as a function
of time so that the initial retention is only useful if the ratio of tne
slow reaction to the initial reaction is known for each soil. The slow
reaction involves the formation of precipitates of limited solubilities
and the regeneration of adsorptive surfaces. Crystallization of pre-
cipitates also reduces their solubilities. Thus, there is small prob-
ability that Langmuir adsorption equations will be generally useful in
predicting quantities of phosphorus that will react with soils over
periods of months or years.
B.2.3 Precipitation
The dominant precipitation reactions in soils are with calcium, iron,
and aluminum ions. Reactions of phosphates with iron and aluminum are
not completely identical, but they are sufficiently similar that for
some parts of this discussion they are considered together.
Qualitative and quantitative detenninations of definite compounds or
minerals of phosphorus in soils are difficult. Empirical extraction
techniques, such as that of Chang and Jackson [23], have been used to
semiquantitatively differentiate among calcium, aluminum, iron, and
organic phosphates. More definite determinations of specific compounds
have been made [24-28], but these are qualitative determinations of
reaction products formed from high concentrations of soluble phosphorus
usually near simulated fertilizer bands. Another approach is to study
the formation and stability of phosphorus compounds in solutions and
then assume that the same compounds form in soils under similar chemical'
conditions, or to study phosphorus reactions with relatively pure solids
and assume that the same reactions occur in soils. These various
approaches lead to the same generalities concerning phosphorus compounds
in soils.
The dominant factor that determines whether calcium phosphates or iron
and aluminum phosphates form in soils is the pH. The phase diagrams
presented by Lindsay and Moreno for a number of phosphorus compounds
suggest that calcium compounds predominate above pH 6 to 7, and iron and
aluminum compounds predominate below pH 6 to 7 [29]. The exact pH
cannot be specified without knowing the calcium ion activity and the
calcium phosphate species that is controlling the solubility of phos-
phorus. Larson stated that, as the pH decreases, a level of acidity is
found at which calcium phosphates can no longer control phosphorus solu-
bility, and he suggested that this lower limit might be pH 5 [6]. This
limit might be found if fluoroapatite is the calcium phosphate con-
trolling the phosphorus concentration in solution, whereas when hydro-
xyapatite or octocalcium phosphate is the controlling compound, the pH
limit would be near 6. When dicalcium phosphate dihydrate is the con-
trolling calcium compound, the pH limit would be near 7. For these
limits, it is assumed that iron and aluminum are present in the soil and
compete with calcium for control of the phosphorus solubility. The
B-7
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partial pressure of carbon dioxide in the soil can influence the acti-
vity of calcium ions ana thus exert an effect on a calcareous system.
The usual concentrations of iron and aluminum ions in solution, in the
acid pH range where iron and aluminum phosphates may form, are so low
that the direct precipitation of iron and aluminum phosphates is un-
likely. Concentrations of iron and aluminum in the soil solution of
moderately acid to slightly alkaline soils, pH 5.5 to 8.0, are in the
range of a few fiq/L or in the parts per billion range. An exception to
this statement can be found in highly acid soils containing exchangeable
aluminum in sufficient quantities that direct precipitation of aluminum
phosphate might occur. Exchangeable aluminum, measured by extraction
with a potassium chloride solution, in excess of about 20 ppm in the
soil can be expected to cause a direct precipitation of phosphorus as
amorphous aluminum phosphate. A more general pathway for formation of
iron and aluminum compounds, when dilute solutions of phosphorus are
added, is that the phosphorus first reacts by adsorption on surfaces
containing reactive iron and aluminum, followed by a breaking away from
the surface to form amorphous forms of strengite (iron phosphate) or
variscite (alluminum phosphate), which then slowly crystallize into more
ordered and less soluble forms of these compounds.
There is thermodynamic evidence that the phosphorus adsorbed on iron
surfaces is stable in the well-aerated soils, whereas surface films of
phosphate on aluminum surfaces are not [5]. This suggestion is that
aluminum phosphates break away from surfaces, exposing a new surface to
continue the adsorption process, whereas iron phosphates do not follow
this pattern. Thus, well-aerated soils containing dominantly aluminum
materials would have much higher capacities to retain phosphorus than
soils containing dominantly iron materials. Taylor et al. found that
iron materials were much less important than aluminum materials in the
initial reactions of ammonium phosphate with soils [30, 31]. If soils
undergo alternate cycles of oxidation and reduction, surface iron phos-
phates are more unstable than those of aluminum because of cycles of
reduction of iron to the ferrous form and oxidation to the ferric form.
In contrast to the situation with iron and aluminum, for which con-
centrations in the soil solution are usually in the pg/L range, calcium
concentrations are in the mg/L range. Concentrations of 10 to 200 mg/L
are common. In neutral and alkaline soils irrigated with wastewaters,
calcium concentrations are likely to be sufficiently large that calcium
phosphates will precipitate directly. Under alkaline conditions and
calcium concentrations of 20 to 200 mg/L in the soil solution, dicalcium
phosphate dehydrate can precipitate directly from solution, depending on
the pH and the phosphorus concentration. This compound then redissolves
and the less soluble octocalcium phosphate forms. With more time the
octocalcium phosphate is converted to the less soluble hydroxyapatite«
Another significant difference between the iron and aluminum phosphate
system and the calcium phosphate system, relative to the application of
B-8
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wastewaters to soils, is that these waters may have only traces of iron
and aluminum, but they usually have substantial amounts of calcium. The
reactions with iron and aluminum are thus limited to the supplies of
these in the soil or sediment, whereas the water may supply its own
calcium, setting up a system that can precipitate calcium phosphates
indefinitely. In calcareous soils the calcium from calcium carbonate
can also be a highly significant source for precipitation of phosphorus
over an extended period of time.
The reactions of phosphorus with organic soil are qualitatively the same
as in mineral soils, but the capacities for sorption are usually much
smaller. Many organic soils have small quantities of iron and/or alu-
minum and calcium and thus are not highly suitable for removal of phos-
phorus from wastewaters. There are organic soils that have accumulated
iron and aluminum materials that have relatively large capacities to
sorb phosphorus and there are calcareous organic soils that will retain
phosphorus. However, as a general rule, mineral soils will be more
suitable for removal of phosphorus from wastewaters.
B.2.4 Reaction Rates
The initial adsorption of phosphorus from dilute solutions is rapid. An
apparent equilibrium is attained in a few days [32-35]. But, following
this apparent equilibrium, there are slow reactions that continue for
months 'or years [10, 36-47]. Ellis and Erickson found that most soils
recovered their sorptive capacities in about 3 months [22]. Kao and
Blanchar found that the adsorptive capacity of the Mexico soil of the
Sanborn field at Columbia, Missouri, had changed little after 82 years
of phosphate fertilization [48]. Barrow and Shaw found that the rate of
the slow reaction decreased dramatically as the temperature decreased
[35].
This slow reaction is perhaps mostly the result of the precipitation and
crystallization of highly insoluble compounds, such as the conversion of
dicalcium phosphate dehydrate to octocalcium phosphate or hydro-
xyapatite, and the exposure of fresh adsorptive surfaces where pre-
viously adsorbed phosphates slough off from surfaces of soil particles.
The relationship between adsorption and precipitation can be illustrated
by the equilibrium reaction [6]:
P adsorbed^J> in solution-^? precipitated (B-l)
If soluble phosphorus is added or removed, the immediate reaction is
with the phosphorus adsorbed, but at equilibrium; the precipitated forms
control the phosphorus in solution. Equilibrium is attained very
slowly, however, and under conditions of irrigation with wastewaters
where phosphorus is added periodically if not continuously, the reaction
will be to the right, and the system will be continuously in a state of
B-9
-------
disequilibrium. DeHaan reported that the adsorptive capacity of a soil
was too small to account for the large amount retained and suggested
that adsorption occurred during the application stage and that pre-
cipitation took place during the resting stage with a regeneration of
the adsorptive capacity [49].
B.2.5 Leaching
The leaching of phosphorus from the root zone of a cropped land area or
from the surface soil material in any wastewater treatment project
depends on the amount of water that moves across the boundary being
considered and the phosphorus concentration in that volume. The amount
leached may be calculated as follows:
Amount leached = 0.225 WC (U.S. customary units) (B-2)
Amount leached = 0.1 WC P(SI units) (B-2a)
where amount leached is in Ib/acre-yr (kg/ha-yr)
W = water that moves across the boundary, in./yr (cm/yr)
C = concentration of phosphorus, mg/L
Because volumes of percolating water are small and concentrations are
low, the downward movement of phosphorus in croplands is usually a very
slow process. If 12 in. (30 cm) of water percolates past a given
boundary in the soil profile and the concentration of phosphorus in this
water is 0.2 mg/L, as might be the case in well-fertilized fertile
soils, the amount of phosphorus leached is 0.54 Ib/acre (U.6 kg/ha).
The amounts of phosphorus absorbed by plant roots from soil depths
beneath the zone, of incorporation of added phosphorus more than balance
this amount. Thus, under usual fertilizer practices in agricultural
lands, the net leaching of phosphorus is usually very small.
However, in rapid infiltration systems where large volumes of water move
through the soil per year, the quantities of phosphorus that leach can
be orders of magnitude higher than, is usual for croplands. Under these
conditions of high rates, the limiting factor is the solubility of phos-
phorus, which is controlled by the capacity of the soil to retain phos-
phorus (i.e., adsorption, precipitation, and reaction rates).
B.3 Phosphorus Removal by Land Treatment Systems
Land application has been used for centuries, and there are hundreds of
systems in use in the United States today. Although soil phosphorus,
the reactions of fertilizer phosphorus with soils, and the movement of
phosphorus with surface flows and with leaching waters have been the
subject of many reports during the past few decades, studies of the
behavior of phosphorus in land application systems have been initiated
only in the past few years. Thomas reported in 1973 that historically
B-10
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the effects of land treatment approaches on plant life, soils, and
groundwater had not received much attention [50]. Thus, because tech-
nical questions dealing with the behavior of phosphorus during waste-
water applications to lands have been asked only recently, there are
very few reports on phosphorus retention by soils in land application
systems.
B.3.1 Slow Rate Systems
Slow rate systems, as defined in Chapter 2, are those in which total
wastewater applications range from 2 to 20 ft/yr (0.6 to 6.1 m/yr) at
weekly rates of 0.5 to 4 in. (1.2 to 10 cm). A vegetative cover is an
integral component of the system anu can utilize phosphorus for crop
growth in accordance with typical values given in Table B-l. because
the application rates are similar to those studied in agricultural
systems, much of the information gained from agricultural study is
applicable to slow rate treatment systems. Even though phosphorus is
removed from solution rapidly in slow rate systems by adsorption and
precipitation, it is useful to quantify these numbers for engineering
design purposes. Wastewater applications are usually limited by
nitrogen or hydraulic considerations on a short-term basis, but phos-
phorus application may be a limiting factor over the life of the system.
For the purposes of this design manual, it is useful to know the net
phosphorus application to the soil, i.e., the quantity of phosphorus
applied in the wastewater after the removal by crops is considered.
This value is useful in estimating the life of system in accordance with
the empirical model presented in Section B.4.4.
Crop removal as a factor in predicting a net application of phosphorus
on land is illustrated graphically in Figure B-2, which shows the rela-
tionships among crop removals in pounds per acre per year, total phos-
phorus applications, and the net application to soil.
The net application to the soil is important in estimating phosphorus
sorption as a prediction of the life of the system to retain phosphorus.
An empirical model uses Figure B-2 as input into computing an estimate
of long-term phosphorus retention.
Because of the similarity of slow rate systems to usual practices on
croplands, much of the information obtained on the behavior of phos-
phorus in crop production is applicable. A number of studies have shown
that the retention of phosphorus near the place of its incorporation
into soils is high, i.e., the movement is slow, except in acid sandy
soils and in acid organic soils containing only small amounts of iron
and aluminum [5, 19, 51-56]. In addition, the transfer of phosphorus
from land areas to streams, for lands protected from excessive soil
B-ll
-------
500
400
CD
O
ea
300
200
1 00
FIGURE B-2
NET PHOSPHORUS APPLICATION
TO THE SOIL
PHOSPHORUS REIOVED BY CROP,
Ib/acre-yr
(TABLE B-1)
100
200
300
400
500
PHOSPHORUS APPLIED IN NASTEWATER, Ib/acre.yr
1 lb/acre= 1.12 kg/ha
B-12
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erosion, is usually less than 1.0 lb/acre-yr (1.1 kg/ha-yr) [8, 9, 57-
61]. These small amounts are insignificant in terms of the efficiency
of use of phosphorus by plants and they are small when expressed as a
percent of the phosphorus sorbed by the soil. In terms of the quality
of the drainage water, however, these small amounts of phosphorus can be
signficant, as illustrated in Figure B-3. If phosphorus concentrations
greater than 0.030 rng/L are conducive to algal blooms in lakes and
streams, some streams that contain mainly drainage, including both
surface runoff and subsurface drainage, should have sufficient phos-
phorus to support algal blooms [8]. Of course, in many streams, runoff
from forested areas containing very low concentrations of phosphorus
dilutes the drainage water from croplands [8], and in some cases, sedi-
ments eroded from stream banks and nonfertilized soils act as phosphorus
sorbing agents to reduce the soluble inorganic phosphorus in the stream
[61, 62].
The optimal plans for a slow rate system should involve (Da forage
crop that removes large amounts of phosphorus, (2) erosion prevention to
eliminate surface runoff, and (3) a long pathway consisting of sorptive
materials between the surface soil and the point of discharge of the
water so that concentrations of phosphorus are reduced to low levels,
depending on the intended use of the water. A sufficient pathway length
might be 6 ft (2 in) in clayey soils, but greater lengths should be re-
quired for sandy or silty soils.
B.3.2 Rapid Infiltration Systems
Rapid infiltration systems, as describee in Section 2.3, are those in
which the wastewater is applied at annual rates of 20 to 560 ft (6 to
170 m), and weekly rates of 4 to 120 in. (10 to 300 cm). Vegetation may
be grown on the surface of the basins, but since the typical applica-
tions range from 550 to 15 000 Ib/acre (616 to 16 800 kg/ha) of phos-
phorus, at a concentration of 10 mg/L, the crop uptake is not a signifi-
cant part of the phosphorus budget. The removal mechanisms of interest
are based on the sorption capacities of the soil. The chemical composi-
tion of the wastewater is also important because the compounds of iron,
calcium, and aluminum, and pH are important in precipitating the phos-
phorus from soil solution.
breenberg and Thomas reported phosphorus retention by a Hanford sandy
loam during a rapid infiltration system in which water application was
about 0.5 ft/d (0.6 m/d) [63]. The phosphorus concentration was about 2
to 3 mg/L in the final effluent added to the infiltration basins.
During about 2 years of operation, all of the phosphorus added was re-
tained in the surface foot of soil. The calcium and bicarbonate concen-
trations in the water were sufficiently high that the soil would have
become alkaline, and phosphorus sorbed could have been largely converted
to calcium phosphates.
B-13
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FIGURE B-3
RELATIONSHIP AMONG PHOSPHORUS CONCENTRATION,
DRAINAGE FLOW, AND THE AMOUNT OF PHOSPHORUS
TRANSFER FROM LAND TO STREAMS
1.2 i-
i.o h
0.8
0.6
0.4
0,2
0 5 10 15
DRAINAGE, in./yr
1 Ib/acre • yr- 1.12 kg/ha yr
1 in./yr- 2.54 cm/y r
PHOSPHORUS TRANSFER
TO STREAMS,
Ib/acre-yr
1.0
B-14
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Perhaps the most definitive report on phosphorus in rapid infiltration
systems has been done in the Flushing Meadows project [1, 64]. The
phosphorus concentration in the wastewater averaged 15 mg/L in 1969 but
decreased to about 10 mg/L for the 1970 to 1972 period. Phosphorus
removal was increased with an increase in travel distance which was
related to time. A travel distance of 30 ft (9 m) removed about 70% of
the phosphorus in 1969. The removal was reduced to about 30% in 1970
because of a substantial increase in flowrate, and it was increased to
50% in 1972. With a flow distance of 330 ft (100 m), the phosphorus
ranoval was about 90%. The effluent at this distance had a phosphorus
concentration less than 1 to 3 mg/L in the 1971 to 1972 period, and the
reduction was greater with an even longer travel distance. After 5
years of operation of this system and phosphorus additions of nearly
43 000 Ib/acre (48 000 kg/ha), the removal efficiency was rather stable.
The phosphorus removal mechanism in this coarse gravelly soil was pre-
cipitation of calcium phosphates.
The phosphorus removal in the Flushing Meadows project is entirely
satisfactory for reuse of water for irrigating crops even at short
travel distances. The removal to the level (less than 0.03 mg/L) where
phosphorus would limit biological production in lakes is not definite
in this rapid infiltration system at the high rates with this soil
material. Perhaps, with time for attainment of an equilibration with
hydroxyapatite at high calcium concentrations and alkaline pH values,
this concentration would be obtained, but the required time is not
known.
Rapid infiltration systems naturally require coarse gravelly soils that
can sustain high infiltration rates at the surface and also high trans-
mi ssivity from the point of infiltration to the point of discharge into
surface waters or into wells. This means that no layers with high
sorptive capacity for phosphorus are likely to be encountered. What
little capacity there is will soon be saturated, and the retention will
then depend on precipitation reactions. The most logical precipitant is
the calcium supply in the wastewater. If that supply is insufficient,
application of a calcium supply may be considered if removal of phos-
phorus is deemed to be necessary for future uses of the waters.
Rapid infiltration systems naturally use a cycle of flooding and drying
to maintain the infiltration capacity of the soil material, and in some
cases, to control insect pests in surface applied waters. Therefore,
these rapid infiltration systems can be considered to use flooded soils.
These cycles of reduction and oxidation can increase the phosphorus
retention capacity of the soil if considerable iron is present in the
soil or in the wastewater. Reduction during flooding and oxidation
during drying increase the reactivity of the sesquioxide fraction of the
soil, increase the phosphorus sorbed, and decrease the phosphorus solu-
oility [65]. Of course, most rapid infiltration systems will use coarse
gravelly soils for which the calcium phosphate chemistry will be the
B-15
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critical factor; iron and aluminum will have minor effects because of
the very low surface area of the soil material and the limited number of
sorption sites on iron and aluminum surfaces will soon become saturated.
B.3.3 Overland Flow Systems
Overland flow systems are used where the soil is slightly permeable and
treatment occurs by biological, chemical, and physical reactions on the
soil surface (Section 2.4). A large portion of the applied wastewater
is collected as treated runoff at the toe of the slope. Since the
wastewater flow is predominately on the soil surface, the soil contact
is less than for slow rate and rapid infiltration systems. As such, the
phosphorus removal may be less for overland flow systems, although com-
binations can be used to achieve treatment alternatives (Section 3.3).
The usual reductions in phosphorus concentrations in the wastewater have
been 35 to 60% with overland flow systems [67-69]. Thomas et al. found
that the phosphorus concentration was reduced from 10 to about 5 mg/L of
total phosphorus in an overland flow system [69]. However, applications
of aluminum sulfate at a concentration of 20 mg/L to the wastewater
reduced the phosphorus concentration of the treated water to about
1 mg/L for a 90% removal of the total phosphorus input.
Data from Carlson et al. show that the phosphorus concentration de-
creased at a fairly uniform rate as wastewater ran over overland flow
plots [70]. The phosphorus concentration in the effluent water was 40
to 60% of that in the applied water. However, water that percolated
through the soil had only traces of phosphorus for nearly complete re-
moval. The harvested grasses removed less than 10% of the applied phos-
phorus. The recommendation for more effective removal of phosphorus in
the overland flow effluent was to obtain more contact between the water
and soil surfaces by increased soil roughness or by increased flow path.
B.3.4 Wetland Systems
Although wetland systems have only been studied recently as a means of
wastewater treatment, the principles behind phosphorus behavior under
such conditions are known. Sufficient research has been completed on
flooded rice culture that the behavior of phosphorus in flooded soils is
fairly well understood. Also, recent reports have added considerable
information on the chemistry of phosphorus in lake sediments.
When soils are flooded with a few feet of water, biological activities
in the soil deplete the available oxygen, and the soil becomes anaerobic
or, more specifically, anoxic (lack of oxygen). The water usually
remains aerobic, and a transition zone between aerobic and anaerobic
conditions develops in the immediate surface of the soil. The surface
ot this transition zone is aerobic and oxidized, whereas the bottom is
B-16
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anaerobic and reduced. The thickness of the oxidized part of this tran-
sition layer can vary from about 0.1 to 1 in. (0.25 to 2.5 cm) or more,
depending, on the rate of supply of oxygen to the surface of the soil and
the rate of consumption of oxygen in the lower soil depths [65], In
wetland situations where there is seasonal flooding followed by drying,
such as in rice production, the soil goes through seasonal or yearly
cycles of reduction and oxidation that result from cycles of anoxic and
oxic conditions. Even in wetlands that are not seasonally flooded but
are wet because of cycles of inputs of water, alternate periods of re-
duction and oxidation occur to some degree. Thus, one feature asso-
ciated with all types of wetlands is the occurrence of reduced con-
ditions or cycles of reduction and oxidation.
When soils and sediments become anoxic, most show an increase in soluble
phosphorus [65, 71-73]. This increase in soluble phosphorus was found
to be greatest with alkaline soils and with soils that have low iron
contents, and it was found to be lowest with acid soils with high iron
contents [71]. Some acid soils with high iron contents show no increase
or decrease in soluble phosphorus as reducing conditions develop.
Patrick and Mahapatra stated that the possible mechanisms for release of
soluble phosphorus principally involved the reduction of iron from the
ferric to the ferrous state with a release of phosphorus from ferric
phosphates and the hydrolysis of iron and aluminum phosphates [65]. In
soils with large amounts of iron oxide and iron hydroxide surfaces or
aluminum oxides, the net result of reduction is a decrease in phosphorus
solubility because of secondary precipitation of the dissolved phos-
phorus" on surfaces that become more reactive when the soil is reduced.
When phosphorus is added to soils and sediments, the effect of reduction
is to increase phosphorus sorption as compared to the oxidized state
[65, 73]. Khalid et al. found a significant correlation between phos-
phorus sorbed under reduced conditions and the iron extracted by
oxalate, also under reduced conditions. They postulated that poorly
crystallized and amorphous oxides and hydroxides of iron play a primary
role in phosphorus retention in flooded soils and sediments [73].
Bortelson and Lee concluded from studies of lake sediments that iron,
manganese, and phosphorus are closely related in their deposition pat-
terns and that iron content appeared to be the dominant factor in phos-
phorus retention [74]. Williams et al. [75] and Shukla et al. [76]
found that noncalcareous sediments sorbed more phosphorus than cal-
careous sediments. Shukla et al. reported that the oxalate treatment of
lake sediments to remove iron and aluminum almost completely eliminated
the ability of sediments to retain phosphorus [76]. The amounts of iron
removed were much greater than the amounts of aluminum removed by
oxalate. They suggested that a gel complex of hydrated iron containing
small amounts of aluminum oxide, silicon hydroxide, and organic matter
was the major phosphorus-sorbing component in sediments under reduced
conditions. Norvell found that sediments, maintained under reducing
conditions, sorbed phosphorus at temperatures of 39 to 41°F (4 to 5°C)
and that calcium, iron, and manganese were lost from both exchangeable
and soluble forms during phosphorus sorption [77].
B-17
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The retention of phosphorus by sediments in aqueous suspension has been
demonstrated adequately. Thus, the problem of getting phosphorus
retention by soils and sediments is no greater than in aerated soils.
But the problem of getting contact between the sediments and soils and
the wastewater represents a serious limitation. Pomeroy et al. found
evidence of significant exchange of phosphorus between sediments and
water when the sediments were suspended in the water, but when they were
separated the exchange was trivial [78]. Where the sediments are not
suspended, only a thin layer at the boundary between the water and the
sediments is active in phosphorus retention. When wastewaters are added
to wetlands, the sediments can play a significant part in removal of
phosphorus from the water only if the water moves in and out of the
sediments, or if wind or wave action keeps the sediments suspended.
Running wastewater slowly over flooded soils in which plants are growing
might be expected to remove phosphorus in a similar manner, and to about
the same extent as found in overland flow systems, but in both cases the
capacity of soil and sediments to reduce phosphorus concentrations is
not fully used.
Spangler et al., after a 4 year study of natural and artificial marshes,
concluded that these had potential for wastewater treatment [79]. In
relation to phosphorus in a natural marsh, they found that (1) the marsh
ranoved phosphorus during the summer and released it during other
seasons, thus acting as a buffer; (2) harvesting of marsh vegetation was
not a potential for removing a large portion of the phosphorus input;
and (3) passage of wastewater through 6 232 ft (1 900 m) of the marsh
reduced the orthophosphate and total phosphorus by 13% or less. Some of
this reduction was probably a result of dilution with other water. A
mass balance, using estimated water flows and concentrations, showed the
same order of magnitude of phosphorus leaving the marsh as entering it.
In other words, the marsh acted as a buffer for phosphorus concentration
but was not effective in reducing the output.
However, Spangler et al. found that, in contrast to the natural marsh,
artificial marshes removed 84% of the phosphorus input into greenhouse
installations and 64% of the input into marshes constructed in the field
[79]. They predicted that the removal in the field would be 80% under
optimum conditions. Recommendations were for a system in which water
would flow through, rather than over, the soil in the artificial marsh,
which would be highly significant in removal of phosphorus as
demonstrated by the work of Pomeroy et al. [78].
B-18
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B.4 Models
B.4.1 Background
In a model that would be adequate for predicting the life of a waste-
water treatment system, based on phosphorus retention in soils and sedi-
ments, many factors should be considered, including:
1. The rate of application of phosphorus
2. The amounts of calcium, iron, and aluminum in the wastewater
and the influence of these constituents on the sorption of
phosphorus in the soil
3. The removal of phosphorus by plant roots if the model deals
with time intervals of days or weeks, or annual removal of
phosphorus in harvested crops if the time intervals are years
or decades
4. The travel distance and transit time of water flow
5. The transit time for water to move through the system relative
to the kinetics of phosphorus sorption in soils and sediments
6. The rate of phosphorus application to the land relative to tne
kinetics of phosphorus reactions with soils (rapid infil-
tration systems might move phosphorus through before the slow
reactions have an effect oh phosphorus concentration in the
flowing water)
7. Capacities and kinetics of sorption of phosphorus in soils and
sediments from land surface to the point of discharge into
ground or surface waters
Such a model would obviously be a three-dimensional model that would
require information on water flow and phosphorus reactions that is
usually not available and not easily obtained. Most water flow and
proposed models for phosphorus retention deal only with flow in one
direction, although some work, such as that reported by Jury [80, 81]
deals with two-dimensional water flow. Thus, the discussion here will
deal with flow downward through soils and to a depth that can be sampled
and studied at reasonable cost. This depth is perhaps 6 to 10 ft (1.8
to 3 m) in most cases but might be much deeper in cases of deep alluvial
material s.
All models are based on a materials balance, i.e., the phosphorus that
goes into a volume of soil must be sorbed into the solid phase, must be
B-19
-------
removed by plants, or must move through the soil volume in percolating
water. This means that all models have a water flow component and a
phosphorus reaction component, and, of course, in systems involving
crops, plant removal is a third component for both water and phosphorus.
Models can consist of simple bookkeeping for water and phosphorus
balances or of mathematical equations of various degrees of sophis-
tication.
B.4.2 Limitations of Models
Although progress has been made during the past few years in the
development of models of phosphorus movement in soils, a number of
problems need to be solved before mathematical models or any other pre-
dictive models can be used with any degree of accuracy [10, 39, 40, 46,
82-84]. Large spatial and temporal variability in the hydraulic con-
ductivity of soils in the field is tremendous and brings up the
questions of how many and what kinds of samples or measurements are
needed to characterize the water flow over an area for a given time.
After the data are obtained, there are some problems of averaging and
interpreting such large variations [85, 86],
There have been no studies of the numbers of samples needed to char-
acterize the phosphorus sorption properties of a field to a given depth.
Most sampling studies have dealt with problems of estimating the level
of nutrients in the plow layer of soils. Recent studies of soil
sampling for estimating the concentrations of soluble salts and nitrate
in the unsaturated zone (to depths of lb to 20 ft or 4.5 to 6 m) suggest
that large numbers of samples are required and that adequate sampling of
a field cannot be planned until some knowledge of the variability is
obtained [87, 88]. Similar information on phosphorus sorption is needed
before models can be accurately applied to fields, even if other limita-
tions to the models are removed.
The composition of the wastewater (i.e., concentration of iron,
aluminum, and calcium) will have an influence on the phosphorus
reactions in the soil and the reactions of wastewaters that acidify or
alkalinize the soil; for example, the influence of bicarbonate on
neutralizing soil acidity will have effects on phosphorus reactions.
Until these effects become inputs into a reliable model, the proper
procedure would be to test each possible soil with the wastewater, or a
reasonable simulation of the wastewater, being considered.
Perhaps the most serious limitation to all models is that the reaction
of phosphorus with the soil cannot be predicted from measurements of
simple soil properties that can be mapped in the field or measured
quickly in the laboratory [46, 89]. Methods of characterizing soil that
might correlate with phosphorus retention are likely to be more time-
consuming than direct measurements of phosphorus sorption.
B-20
-------
To allow near maximum application rates, rapid infiltration systems will
require coarse gravelly or sandy soils having generally low sorptive
capacities. These may soon be saturated, and the retention by the soil
system ,wil.l depend mostly on the iron, aluminum, and calcium in the
wastewater and not on the original soil material. Exceptions to this
general statement might include the use of calcareous sands and gravels
for rapid infiltration systems. Plant removal is usually too small to
be significant in rapid infiltration systems. Thus, the need is for a
model that considers the constituents in the wastewater and how these
will react during flow through the soil and sediments as a function of
distance of flow and rate of flow.
B.4.3 Models of Kinetics of Phosphorus Reactions
The mathematical model for one-dimensional phosphorus movement in soils
has been expressed in a number of ways. Enfield et al . [46] expressed
it as
where C = concentration of phosphorus in solution, mg/L
D = dispersion coefficient at velocity V, cm/h
t = time, h
V = average pore-water velocity, cm/h
X = distance from beginning of 3 flow path, cm
P = bulk density of soil, g/cm
0 = volumetric water content in the soil
S = sorbed phosphorus in solid phase, fig/g
The first two expressions in the equation deal with water flow, and the
third deals with the retention of phosphorus by the soil (i.e., the
kinetics of phosphorus reactions), before this equation becomes a use-
ful model, the kinetics of phosphorus reactions must be known.
The kinetics of phosphorus reactions in soils has been studied by a
number of researchers [10, 33-36, 40, 47, 82, 90, 91]. Perhaps the most
definitive study was that of Enfield et al. who measured the reactions
of phosphorus in 25 soils for a period of 2 to 18 weeks, depending on
the soil, and then used the data to test five kinetic models [46]. All
kinetic models agreed adequately with the experimental models. Corre-
lation coefficients between predicted values and experimental values
averaged 0.81 to 0.88, but these were averages of values for individual
soils. That is, coefficients for each kinetic model were calculated for
and unique to individual' soils, so that to use the models, the phos-
phorus reactions must be measured to supply the coefficients for the
model for any individal soil material.
B-21
-------
However, Enfield and Shew [40], using two of the models tested by
Enfield et al. [45], found good agreement between the predicted movement
of phosphorus and values experimentally determined in small laboratory
columns which were fed a solution containing 10 mg/L of phosphorus. The
first model was
= a (KC - S)
(B-4)
where C = concentration of phosphorus, mg/L
S = concentration of sorbed phosphorus, /xg P/g of soil
t = time, h
and, a, K = constants that depend on the soil
The second model was
f
(B-5)
where the symbols have the same meaning as before and a, b, and d are
constants that depend on the soil. Solutions to these equations were
provided, and constants were calculated for two soils. Combinations of
these with water flow data predicted phosphorus breakthrough curves for
the two soils studied over a period of several days. Breakthrough
curves indicated that the boundary between saturated and unsaturated
soil (enriched versus nonenriched) was diffuse as illustrated in Figure
B-l , so that the concentration of phosphorus in the effluent increased
very slowly as the effluent volume increased.
Novak et al . developed a theoretical model for movement of phosphorus in
soils in which the phosphorus sorption factor of Equation B-3 was cal-
culated from existing adsorption-desorption models developed for chro-
matography and ion-exchange processes [82]. This model predicts an
abrupt boundary for breakthrough of soluble phosphorus into any given
layer of soil .
Harter and Foster developed an empirical model which describes the move-
ment of phosphorus in soils [83]. In this approach, a soil sample is
repeatedly treated with a solution of known phosphorus concentration,
and the sorbed phosphorus is determined. The relationship between
B-22
-------
phosphorus sorbed and the volume of solution that has contacted the soil
is then expressed as a polynomial adsorption equation
Y = A + BX + CX2 + DX3 . (B-6)
where Y is the phosphorus adsorbed, X is the amount of phosphorus
added, and A, B, C, D are constants that depend on the soil. From this
relationship, the phosphorus breakthrough curves, or the phosphorus
leaching front, can be plotted against depth or volume of wastewater
added. The model is simple and might be adequate for most purposes, but
there are no data available showing the effectiveness of the approach
in predicting field data.
Shah et al. developed a materials balance mathematical model which
agreed well with field data obtained from the barriered landscape water
renovation system used to treat liquid swine manure [84]. The kinetic
equation in this model was based on the Langmuir adsorption equation.
B.4.4 Empirical Model for a Slow Rate System
There are no models that adequately describe all factors in water and
phosphorus movement in field soils receiving municipal wastewaters.
Also, there is not sufficient knowledge of phosphorus reaction kinetics
to predict the sorption of phosphorus in a field over periods of
decades. Thus, the model presented here as Figure B-4 provides only an
empirical assessment of relative phosphorus retentions by soil profiles.
In .this simple model, the phosphorus added minus the phosphorus removed
in harvested crops (Figure B-l) is assumed to react progressively with
successive depth increments in the soil. The first depth increment
becomes "saturated" before phosphorus moves to the next depth increment,
and the boundary between the phosphorus-enriched soil and the non-
enriched soil is assumed to be rather abrupt, as in the theoretical
model of Novak et al. [82]. The term "saturated" is defined for the
purposes of this model as the soil in which enrichment with phosphorus
has been sufficient that movement with percolating water is signifi-
cantly above background for the original soil material. Also, in this
model, (1) water movement is considered to be so unimportant relative to
phosphorus reactions that it can be disregarded, (2) there is sufficient
time for slow phosphorus reactions to have a large impact, and (3) the
phosphorus sorption capacities for the depth increments include the slow
reactions.
The sorption capacities for the soil horizons used in Figure B-4 were
taken from a study by Enfield and Bledsoe [10] in which 10 grams of soil
were treated with 100 ml of solution containing a phosphorus con-
centration of 10 mg/L. The reaction time in this study was only
B-23
-------
FIGURE B-4
ILLUSTRATION OF A SIMPLE PHOSPHORUS BALANCE-
PHOSPHORUS REACTION MODEL FOR A SLOW RATE SYSTEM
PHOSPHORUS
APPLIED IN
WASTEWATER,
150 Ib/aere-yr
PHOSPHORUS
REMOVAL IN
HARVESTED
CROPS,
50 Ib/aere-yr
PHOSPHORUS
SORPTION CAPACITY,
lb/acre-6 in.
NOTE: THE PHOSPHORUS SORPTION CAPACITIES USED
•ERE DOUBLE THE SORPTION MEASURED IN A
125 DAY REACTION PERIOD IN THE LABORATORY.
1 lb/acre>yr= 1.12 kg/ha>yr
B-24
-------
125 days; consequently, the sorption capacities in the Enfield and
Bledsoe study were doubled to adjust for slow reactions that continue
for indefinite periods in most soils.
This model, expressed mathematically, is
T - $P (B-7)
'p - HP
where T = time for the phosphorus front to reach a given depth in
the soil, yr
S = the sorption capacity of the volume of soil above that
p depth, Ib/acre (kg/ha)
the input phosphorus, lb/acre-yr (kg/ha-yr)
the phosphorus removed in harvested crops, lb/acre-yr
(kg/ha-yr)
The uncertainties in the model are in the measurements of the phosphorus
sorptive capacity and the assumed abrupt boundary between enriched and
nonenriched soil. There is reason to believe that the phosphorus reten-
tion characteristics of a soil cannot be adequately characterized in the
laboratory in a fixed period of time. Also, there is ample evidence
from fields that have received large amounts of phosphorus as fer-
tilizers or as wastes that the soluble phosphorus gradually decreases as
a function of depth with a diffuse rather than an abrupt boundary
between the highly enriched and the nonenriched soil horizons [5, 19,
49, 51, 52, 93]. But, perhaps even considering these uncertainties, the
model can be useful as a preliminary estimate of the phosphorus reten-
tion characteristics of various soils and sediments. This type of model
is implied in the rate classes proposed by Schneider and Erickson for
phosphorus sorption measurements in soils as a limitation for the use of
the soil for treating municipal wastewaters [94]. Their limitation
classes ranged from very high to very low, respectively, as the phos-
phorus sorption increased from less than 1 QUO to more than 2 000
Ib/acre (1 120 to 2 240 kg/ha) in 3 ft (0.9 m) of soil.
If a model such as presented in Figure B-4 is used to classify the
desirability of various potential areas for a given wastewater,
monitoring of the phosphorus movement in the site selected can be used
to revise estimates of the longevity of the site as it is being used.
B.4.5 Model for Rapid Infiltration Systems
At the present time, there is no accepted model that can predict the
movement of phosphorus through soil profiles. But, one promising
approach which considers the rate of reaction of phosphorus with soils
is that of Enfield and Bledsoe [10]; Enfield and Shew [40], and Enfield
[39, 95]. In this approach, solutions containing phosphorus at various
B-25
-------
concentrations were reacted with soils for up to 125 days, using batch
techniques. The sorption aata thus obtained were compared with phos-
phorus breakthrough curves using small 1.9 in. (5 cm) long soil columns.
As might be expected from discussions of reaction kinetics of phosphorus
in soils, the sorption of phosphorus obtained from a 10 hour reaction
period seriously underestimated the amount of phosphorus sorbed by the
columns in 55 days. However, sorption curves had been obtained at time
intervals from 1 to 3 000 hours, approximating a geometric progression,
so that sorption surfaces as a function of (1) equilibrium solution con-
centration, (2) amount of phosphorus sorbed by the soil, and (3) time,
were produced for each soil. When these sorption surfaces were used to
adjust the ratio of phosphorus sorbed to equilibrium solution
concentration for time corresponding to time intervals in the break-
through curves, there was a markea increase in the agreement between the
batch and column techniques.
The sorption surfaces were used to calculate the sink term 8S/3t in the
equation
9C _ TT 8C e 8S /R p\
--V- (B'8)
where £ = solution phase concentration of phosphorus, mg/L
V" = average pore-water velocity, in./h (cm/h)
X = distance from the beginning of^tne flow path, in. (cm)
e = bulk density of the soil, g/cm
6 - volumetric water content of the soil
S = solid phase concentration of sorbed phosphorus, M9/9
t = time, h
and the sink term was calculated from
|| - a CbSd (B-9)
where a, b, and d are constants and C, S and t are as defined for
Equation B-B. Using these equations, the breakthrough curves agreed
well with predicted curves in three of four soils.
Enfielu recognized that this approach was not satisfactory for all soils
and that it did not predict the effects of rest periods and desorption
of phosphorus during rains and the resultant leaching with rainwater
[95]. Nevertheless, this approach gives an adequate first approximation
to the transport of phosphorus through soils and can provide a basis for
design of wastewater treatment systems. Enfield recommended that an
average phosphorus concentration or application rate adjusted for rest
periods, plant removals, and rainwater, be used [95].
B-26
-------
There are some serious questions about this approach that must be added
as words of caution. The spatial variability in phosphorus reactions
and in water flow can be much smaller in the laboratory columns *than in
the field. Temperature effects on the kinetics of phosphorus reactions
are not built into the laboratory studies but will be encountered in the
field. In the field, a given volume of soil will react with increasing
concentrations of phosphorus as a function of time of treatment with
wastewater; whereas, in the sorption measurements presented by Enfield
and Bledsoe [1U], the soil reacted with decreasing concentrations of
phosphorus. Solutions of phosphorus at 10, 40, and 100 mg/L were added
to soils and the decrease in concentration was measured as a function of
time which is an approach to equilibrium from the opposite direction as
in the field. The sink term, 9S/3t, of Equation B-8 might be sub-
stantially different under these two conditions in some soils.
Another aspect concerning this approach is more pragmatic. Considering
the status of such models, it may be no more expensive to set up columns
of soils in the laboratory and treat them with the wastewater for a
period of 4 to 6 months and directly measure the movement of phosphorus.
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Operations. EPA-430/9-75-017. 1975.
67. Kirby, C.F. Sewage Treatment Farms. (Postgraduate course in
Public Health Engineering). University of Melbourne, Australia.
Session No. 12, Department of Civil Engineering. 1971. 14 p.
68. Law, J.P., Jr., R.E. Thomas, and L.H. Myers. Cannery Wastewater
Treatment by High-Rate Spray on Grassland. Jour. WPCF. 42:1621-
1631,.1970.
69. Thomas, R.E., B. Bledsoe, and K. Jackson. Overland Flow Treatment
of Raw Wastewater With Enhanced Phosphorus Removal. EPA-600/2-76-
131. June 1976.
70. Carlson, C.A., P.G. Hunt, and T.B. Delaney, Jr. Overland Flow
Treatment of Wastewater. U.S. Army Engineering Waterways
Experiment Station, Vicksburg, Miss. Miscellaneous Paper Y-74-3.
August 1974.
71. Pannamperuma, F.N. The Chemistry of Submerged Soils. Advances in
Agronomy. 24:29-96, 1972.
72. Patrick, W.H., Jr., and R.A. Khalid. Phosphate Release and
Sorption by Soils and Sediments: Effect of Aerobic and Anaerobic
Conditions. Science. 186:53-55, 1974.
73. Khalid, R.A., W.H. Patrick, Jr., and R.D. Delaune. Phosphorus
Sorption Characteristics of Flooded Soils. Soil Sci. Soc. Amer. J.
(submitted). 1976.
74. Bortelson, G.C. and G.F. Lee. Phosphorus, Iron, and Manganese
Distribution in Sediment Cores of Six Wisconsin Lakes. Limnol.
Oceanog. 19:794-801, 1974.
B-32
-------
75. Williams, J.D.H., J.K. Syers, R.F. Harris, and D.E. Armstrong.
Adsorption and Desorption of Inorganic Phosphorus by Lake Sediments
in a 0.1 M NaCl System. Environmental Science and Technology.
4:517-519, 1970.
76. Shukla, S.S., J.K. Syers, J.D.H. Williams, D.E. Armstrong, and R.F.
Harris. Sorption of Inorganic Phosphate by Lake Sediments. Soil
Sci. Soc. Amer. Proc. 35:244-249, 1971.
77. Norvell, W.A. Insolubil ization of Inorganic Phosphate by Anoxic
Lake Sediments. Soil Sci. Soc. Amer. Proc. 38:441-445, 1972.
7b. Pomeroy, L.R., E.E. Smith, and G.M. Grant. The Exchange of
Phosphate Between Estuarine Waters and Sediments. Limnol. Oceanog.
10:167-172, 1965.
79. Spangler, F.C., W.E. Sloey, and C.W. Fetter, Jr. Wastewater
Treatment by Natural and Artificial Marshes. EPA-600/2-76-207.
September 1976.
80. Jury, W.A. Solute Travel-Time Estimates for Tile-Drained Fields.
I. Theory. Soil Sci. Soc. Amer. Proc. 39:1020-1024, 1975.
81. Jury, W.A. . Solute Travel-Time Estimates for Tile-Drained Fields.
II. Application to Experimental Fields. Soil Sci. Soc. Amer.
Proc. 39:1024-1028, 1975.
82. Novak, L.T., D.C. Adriano, G.A. Coulman, and D.B. Shah. Phosphorus
Movement in Soils: Theoretical Aspects. Journal of Environmental
Quality. 4:93-99, 1975.
83. Harter, R.D. and B.B. Foster. Computer Simulation of Phosphorus
Movement Through Soils. Soil Sci. Soc. Amer. J. 40:239-242, 1976.
84. Shah, D.B., G.A. Coulman, L.T. Novak, and B.G. Ellis. A
Mathematical Model for Phosphorus Movement in Soils. Journal of
Environmental Quality. 4:87-92, 1975.
85. Nielsen, D.R., J.W. Biggar, and K.T. Erh. Spatial Variability of
Field-Measured Soil Water Properties. Hilgardia. 42:215-259,
1973.
86. Jury, W.A., W.R. Gardner, P.G. Saffigna, and C.B. Tanner. Model
for Predicting Simultaneous Movement of Nitrate and Water Through a
Loarny Sand. Soil Science. 122:36-43, 1976.
87. Pratt, P.F., J.E. Warneke, and P.A. Nash. Sampling the Unsaturated
Zone in Irrigated Field Plots. Soil Sci. Soc. Amer. J. 40:277-
279, 1976.
88. Rible, J.M., P.A. Nash, P.F. Pratt, and L.J. Lund. Sampling the
Unsaturated Zone of Irrigated Lands for Reliable Estimates of
Nitrate. Soil Sci. Soc. Amer. J. 40:566-570, 1976.
B-33
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89. Pratt, P.F., F.F. Peterson, and C.S. Holzhey. Qualitative
Mineralogy and Chemical Properties of a Few Soils from Sao Paulo,
Brazil. Turrialba. 19:491-496, 1969.
90. Kuo, S. and E.G. Lotse. Kinetics of Phosphate Adsorption by
Calcium Carbonate and Ca-Kaolinite. Soil Sci. Soc. Amer. Proc.
36:725-729, 1972.
91. Griffin, R.A. and J.J. Jurinak. Kinetics of the Phosphate
Interaction With Calcite. Soil Sci. Soc. Amer. Proc. 38:75-79,
1974.
92. Adriano, D.C., L.T. Novak, A.E. Erickson, A.R. Wolcott, and B.G.
Ellis. Effect of Long Term Land Disposal by Spray Irrigation of
Food Processing Wastes on Some Chemical Properties of the Soil and
Subsurface Waters. Journal of Environmental Quality. 4:244-248,
1975.,
93. Taylor, A.W. and H.M. Kunishi. Soil Adsorption of Phosphates From
Waste Water. In: Factors Involved in Land Application of
Agricultural and Municipal Wastes. ARS-USDA National Program
Staff, Soil, Water, and Air Sciences, Beltsville, Md. 1974. pp.
66-96.
94. Schneider, I.F. and A.E. Erickson. Soil Limitations for Disposal
of Municipal Wastewaters. Michigan Agricultural Experiment
Station. Research Report No. 195. 1972.
95. Enfield, C.G. Phosphate Transport Through Soil. In: Proceedings
of the National Conference on Disposal of Residues on Land, St.
Louis, Mo. 1976.
B-34
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APPENDIX C
HYDRAULIC CAPACITY
C.I Introduction
The hydraulic capacity of the soil to accept and transmit water is
crucial to the design of rapid infiltration systems and important in the
design of most slow rate systems. The important hydraulic parameters
are infiltration, vertical permeability (percolation), and horizontal
permeability. In this appendix, the basic hydraulic properties are
defined and techniques for measurement and estimation of the more
important parameters are presented. Both vertical and horizontal flow
of groundwater are discussed, and an analysis of groundwater mounding is
presented. The relationship between predicted hydraulic capacity and
actual operating rates is also discussed.
C.2 Hydraulic Properties
For purposes of this manual, hydraulic properties of soil are considered
to be those properties whose measurement involves the flow or retention
of water within the soil profile. These properties include soil-water
characteristic curve, percent moisture at saturation, permeability,
infiltration rate, specific yield, specific retention, and trans-
mi ssivity. In addition, the terms of field capacity, permanent wilting
point, and drainability are commonly used in irrigation practice. How-
ever, these terms describe qualitative relationships—not unique, meas-
urable properties. The concepts of field capacity and permanent wilt-
ing point are discussed in conjunction with soil-water characteristic
curves.
Soil permeability and infiltration rate are especially important to
system design. They should be determined by field testing; however,
they may be estimated from other physical properties (mentioned in
Section F.3.3.1). An in-depth discussion of the more common methods of
estimating or measuring both soil and aquifer properties is presented in
this appendix. Field testing procedures for determining soil
infiltration rates and permeability are outlined in Section C.3, along
with methods of analyzing and interpreting test results. Methods of
measuring or estimating properties of groundwater aquifers are outlined
in Section C.4.
C.2.1 Soil-Water Characteristic Curve
Water in the soil below the saturation level is held in the soil against
the force of gravity primarily by forces that result from the surface
C-l
-------
tension of water, the cohesion of water molecules, the adhesion of water
molecules to soil surfaces, and other electrical attractive forces at
the molecular level. The energy required to remove water from
unsaturated soil when expressed on a per unit mass of water basis is
termed the soil-water pressure potential or matric potential. Soil-
water pressure potential is expressed as J/kg or erg/g. The energy is
sometimes expressed on a unit volume basis in which case it is termed
soil-water pressure. 2 The resulting units (erg/cm?) convert,, to those
of pressure, dyne/cm , or more commonly, bar (10 dyne/cm ). The
most common method of expressing the energy is on a unit weight basis in
which case it is termed soil-water pressure head or simply head. The
resulting units, erg/dyne, convert to centimetres. Soil tension and
suction are terms that also have been used to describe the energy of
soil-water retention, but these terms make no distinction among units.
They are also considered positive quantities, while the above terms are
negative quantities.
The force by which water is held in the soil is approximately inversely
proportional to the pore diameter. Thus, the larger the pore the less
energy is required to remove water. As soil dries or drains, water is
removed from the larger pores first. The water remains in the smaller
pores because it is held more tightly. Thus, as soil-water content
decreases, soil matric potential increases. The graphical relationship
between soil-water content and matric potential is the soil-water
characteristic curve. Examples of such curves for several different
types of soil are shown in Figure C-l. It should be mentioned that
different curves will be obtained depending on whether the soil-water
content is changed by drying or by wetting. This hysteresis phenomenon
is due primarily to soil pore configurations. In most cases we are
interested in the soil-water characteristic curve resulting from drying
or drainage.
It is apparent from Figure C-l and the previous discussion that°the
shape of the soil-water characteristic curve is strongly dependent on
soil texture and soil structure. For example, sandy soils have mostly
large pores of nearly equal size. Consequently, nearly all water is
removed from sands at a very small matric potential. On the other hand,
medium-textured, loamy soils have a greater porosity than sands and a
wide pore size distribution. Thus, more water is held at saturation in
soils than in sands and it is removed much more gradually as matric
potential becomes larger.
Some important aspects of soil-water plant relations may be explained by
the shape of the soil-water characteristic curve. In irrigation
practice, it has been common to describe the maximum amount of water in
soil that is available for plant uptake as the difference in water
content at field capacity (the upper limit) and that at permanent
wilting point (the lower limit). A soil is said to be at field capacity
when the rate of water removal from the soil, due to drainage following
an irrigation or heavy rain, begins to be reduced. As such, field
capacity is not a unique value, but represents a general region of water
C-2
-------
percentages as illustrated in Figure C-2. Using the soil-water
characteristic curve, field capacity then may be expressed as a range of
soil-water pressure potentials. The range of potentials in the region
of field capacity varies with soil texture. For sands, the range of
field capacity is about 10 to 15 J/kg or 0.1 to 0.15 bar. For medium-
to fine-textured soils, the range is about 0.3 to 0.5 bar. A value of
0.3 bar is commonly used as a rough approximation in these soils.
FIGURE C-l
SOIL-WATER CHARACTERISTIC
CURVES FOR SEVERAL SOILS [1]
SOIL WATER CONTENT, Qm
(MASS OF WATER/MASS OF DRY SOIL)
0 0.1 0.2
0. 3
FIELD C» PACI TY
(0.3 ba r )
-200 -
-400 -
-600 -
-BOO -
- I 000 -
-1200 -
-1600 I—I' ' —
The time required for a thoroughly wetted soil to drain to the field
capacity region is also dependent on texture and structure. In the
absence of significant evaporation or transpiration, field capacity in
pure sands may be reached in a few hours; for coarse soils about 2 to 3
days; for medium- to fine-textured soils, a week or more; and for poorly
structured clays, much longer.
There are a few misconceptions associated with the concept of field
capacity that should be pointed out. The first is that field capacity
is a unique property of a soil. It is apparent from the previous
discussion that field capacity expresses only a crude qualitative
relation. The second misconception is that no drainage occurs in soils
at or below field capacity. In fact, drainage does not cease at field
capacity but continues at a reduced rate for a long time, as illustrated
C-3
-------
in Figure C-2. The third misconception is that field capacity
represents the upper limit of water that is available to plants and any
*.i•* ^ AM« •* n n 1 ^ yvst ^m s\\t f~* s\ e* r* f\f f ^ £\l rl *^ar\a/*i^\* i.n 1 1 r\A I /%«* 4* <£w« ssm + L*SN *• s\ ^ 1
water applied in excess of field capacity will be lost from the soil
profile as deep percolation. However, water in excess of field capacity
is available to plants while it remains in contact with plant roots.
FIGURE C-2
FIELD CAPACITY RELATIONSHIP
0.4
0. 3
0. 2
REGION OF
'FIELD CAPACITY
2 4 6 8 1012
DAYS AFTER IRRIGATION
The lower limit of water availability, the permanent wilting point, like
field capacity, is not a unique value but a range of water percentages
over which the rate of water taken up by the plant is not sufficient to
prevent wilting. The ability of the plant to take up water is directly
related to the matric potential of the soil-water rather than the actual
water content. It has been found that most plants exhibit permanent
wilting when the soil-water matric potential is in the range of 1 500
J/kg (15 bars).
If it is assumed that the so called available reservoir of water is the
water content between field capacity and permanent wilting point, some
general observations can be made regarding the effect of texture on
irrigation scheduling. From the shapes of the various soil-water
characteristic curves shown in Figure C-l, it is apparent that sandy
soils have a relatively small difference in water content between the
regions of field capacity and permanent wilting. Medium- to fine-
textured soils, on the other hand, exhibit a rather large difference in
water content between field capacity and permanent wilting point.
Another generalization that can be made is that coarse soils approach
the permanent wilting point very rapidly with small changes in water
content. Thus, plants grown in such soils would be expected to exhibit
C-4
-------
wilting symptoms quite suddenly. Medium- to fine-textured soils
approach permanently wilting point more gradually and plants grown on
these soils will likely show very gradual signs of wilting.
Soil-water characteristic curves generally must be determined in the
laboratory using techniques described in Taylor and Ashcroft [1].
Published soil moisture versus matric potential data are available for
selected typical soils. The USDA Agricultural Research Service
Publication 41-144 [2] provides such data for 200 typical soils in 23
states. In addition, bulk density, total porosity, and saturated
vertical permeability data are presented in this compendium.
C.2.2 Percent Moisture at Saturation
The percent moisture at saturation or saturation percentage is defined
as the number of grams of water required to saturate 100 grams of air-
dry soil. It is a convenient parameter to measure since a saturated
paste is normally prepared for other analyses. Saturation is reached
when the soil surface glistens but no free moisture is present. A
saturated paste will not flow from a container unless shaken. Due to
the subjective nature of the test, large variations in test results from
different sources are common. Thus, saturation percentage data should
be used with caution.
Saturation percentage is a useful parameter because it provides a quick,
rough estimate of the available water-holding capacity of the soil. The
field capacity is approximately one-half the saturation percentage, and
about one-half the field capacity of the soil can be considered
available to plants. Of course, a better estimate of available water-
holding capacity can be obtained from soil-water characteristic curves
as previously 'described.
The value of saturation percentage is related to soil texture. Typical
ranges for various soil textures are presented in Table C-l.
C.2.3 Permeability
Soil permeability is a term that has been used rather loosely to
describe the ease with which liquids and gases pass through soil. In
this manual, the term permeability will be synonymous with hydraulic
conductivity. Hydraulic conductivity is the more descriptive and the
preferred term, but, for the sake of consistency with much of the
literature, permeability will be used in this manual. These terms are
most easily defined if a few basic concepts of water flow in soils are
introduced first.
C-5
-------
TABLE C-l
RELATION OF SATURATION .PERCENTAGE
TO SOIL TEXTURE
Soil texture Saturation % range
Sand or loamy sand Below 20
Sandy loam 20-35
Loam or silt loam 35-50
Clay loam 50-65
Clay 65-135
Peat or muck Above 135
In general, water moves through soils or porous media in accordance with
Darcy's law:
q = K dH/dl (C-l)
where q = flux (flow) of water per unit cross sectional areas, in/h
(cm/h)
K = permeability (or hydraulic conductivity), in./h (cm/h)
dH/dl = total head (hydraulic) gradient, ft/ft (m/m)
Q
The total head (H) is the sum of the soil-water pressure head (h), and
the head due to gravity (Z), or H = h + Z. The hydraulic gradient is
the change in total head (dH) over the path length (dl). These
relationships are illustrated schematically for saturated and
unsaturated conditions in Figure C-3.
The permeability is defined as the proportionality constant, K .
Permeability (K) is not a true constant but a rapidly changing function
of water content. Even under conditions of constant water content, such
as saturation, K may vary over time due to increased swelling of clay
particles, change in pore size distribution due to classification of
particles, and change in the chemical nature of the soil-water.
However, for most purposes saturated permeability (K ) values can be
C-6
-------
considered constant for a given soil. In general, the K value for
flow in the vertical direction will not be equal to Kin the
horizontal direction. This condition is known as anisotropic.
FIGURE C-3
SCHEMATIC SHOWING RELATIONSHIP OF TOTAL HEAD (H),
PRESSURE HEAD (h), AND GRAVITATION HEAD (Z)
FOR SATURATION FLOW
V V,
AH =
SATURATED FLOW
The permeability of soils at saturation is an important parameter
because it is used in Darcy's equation to estimate groundwater flow
patterns (see Section C.4) and is useful in estimating soil infiltration
rates. Permeability can be estimated from other physical properties but
much experience is required and results are not sufficiently accurate
for design purposes.
As suggested by the inclusion of textural classification in Tables 3-7
and 3-9, soil permeability is determined to a large extent by soil
texture with coarse materials generally having higher conductivities.
However, in some cases the soil structure may be equally as important.
A well structured clay with good stability can have a greater
permeability than a much coarser soil.
Permeability of soils is also affected by the ionic nature of the soil
water. A simplified explanation of this effect is given. Clay
particles in the soil are negatively charged due to substitution of
lower valence atoms for higher valence atoms (e.g., Al3+ for Si 4+) in
C-7
-------
the crystal structure. Because of the charge, the clay particles repel
each other and remain dispersed in the soil unless the charge is
neutralized by positively charged cations in the soil-water. Thus,
waters high in salts will contain sufficient cations to neutralize the
clay particles and allow them to come close enough together so that
short-range molecular attractive forces will unite, or flocculate the
particles. Flocculation of particles will result in larger soil pores
and increased permeability. Thus, waters low in salts may result in low
permeability problems.
The type of ion in the soil-water also affects permeability. Water with
larger sodium percentages can cause reduced permeability. This occurs
because the sodium ion in its hydrated state is much larger than other
ions, calcium and magnesium in particular. Thus, the layer of sodium
ions necessary to neutralize clay particles is thicker and the clay
particles are restricted from coming together and remain dispersed. As
a result, the permeability of the soil is low. If sufficient salt is
present in the soil-water, the layer of sodium ions will be suppressed
to the point that clay particles will flocculate and permeability will
be adequate. However, the salt concentration may be so high that the
growth of plants may be restricted (see Section 5.6.2.3).
The type of vegetation will also affect the permeability of soil within
the root zone. The effects of ions and vegetation on permeability are
not of concern for groundwater aquifers because they are below the root
zones and contain little, if any, clay.
As previously discussed, the permeability of soil varies dramatically as
water content is reduced below saturation. Since matric potential also
varies as a function of water content in accordance with the soil-water
characteristic curve, permeability may be described as a function of
matric potential. The inverse relationship between permeability and
matric potential is illustrated for soils of several different textures
in Figure C-4. The significant relationship to note is that the
permeability of sandy soils, although much higher at saturation (matric
potential = 0) than loamy soils, decreases more rapidly as the matric
potential becomes more negative. In most cases, the permeabilities of
sandy soils eventually become lower than the medium soils. This
relationship explains why a wetting front moves more slowly in sandy
soils than medium or fine soils after irrigation has stopped and why
there is little horizontal spreading of moisture in sandy soils after
irrigation.
Estimating water movement under unsaturated conditions using Darcy's
equation and unsaturated K values involves relatively complex
mathematical techniques. A discussion of such techniques is not within
the scope of this manual. The user is referred to Kirkham and Powers
[3] or Klute [4] for further details on the subject of unsaturated flow.
C-8
-------
FIGURE C-4
PERMEABILITY AS A FUNCTION OF THE
MATRIC POTENTIAL FOR SEVERAL SOILS [1]
COACHELL* LOAMY
FINE SAND
_ 0 . 01
o. ooi 2
/~*~~^- CH I NO uj
,.-(lOH SAND• *' SILTY _0.0001 °-
U?tR*ll-.«i ~^^* CL*Y
0 —«^ LOAM
0.00001
-50 -40 -30 -20 -10
MATRIC POTENTIAL, I/kg
C.2.4 Infiltration Rate
The infiltration rate of a soil is defined as the rate at which water
enters the soil from the surface. When the soil profile is saturated,
the infiltration rate is equal to the effective saturated permeability
of the soil profile. This occurs because at saturation the matric
potential (h) is zero at all depths and the total head gradient
(d[h + z]/dz) is equal to unity. Thus, the flux q is equal to k ac-
cording to Darcy's law (Equation C-l).
When the soil profile is relatively dry, the infiltration rate is higher
because water is entering large pores and cracks. With time, these
large pores fill and clay particles swell reducing the infiltration rate
rather rapidly until a near steady-state value is approached. This
change in infiltration rate with time is shown in Figure C-5 for
several different soils. The effect of both texture and structure on
infiltration rate is illustrated by the curves in Figure C-5. The
Aiken clay loam has good structural stability and actually has a higher
final infiltration rate than the sandy soil. The Houston black clay,
however, has very poor structure and infiltration drops to near zero.
As with permeability, infiltration rates are affected by the ionic
composition of the soil-water and the type of vegetation. Of course,
any tillage of the soil surface will affect infiltration rates. Factors
which have a tendency to reduce infiltration rates include clogging by
organic solids in wastewater, classification of fine soil particles,
clogging due to biological growths, and gases produced by soil microbes.
C-9
-------
FIGURE C-5
INFILTRATION RATE AS A FUNCTION
OF TIME FOR SEVERAL SOILS [1]
o.
0.
c
e 0-
.f 0.
-' o.
<
tt
0.
z
o
^ 0.
•<
cr
± °-
u.
z o.
0.
20
1 8
I 6
1 4
1 2
1 0
08
06
04
02
0
104*
— -.
CROWN SANDY LOAM
SILT
HOUSTON BLACK CLAY
20 40 60 80 100120 140
TIME, min
The steady-state infiltration rate is extremely important and generally
serves as the basis for selection of the design hydraulic loading rate
for slow rate and rapid infiltration systems. A more detailed
discussion of soil infiltration, including field measurement techniques,
is presented in Section C.3.
C.2.5 Drainability
Drainability is a qualitative term that is commonly used in soil surveys
and elsewhere to describe the relative rapidity and extent of the
removal of water from the root zone by flowing through the soil to
subsoils or aquifers. A soil is considered well-drained if, upon
saturation, water is removed readily, but not rapidly. A poorly-drained
soil is one in which the root zone remains waterlogged for long periods
of time following saturation and insufficient oxygen supply to roots
becomes growth limiting to most .plants. An excessively-drained soil is
one from which the water is removed so completely that most crop plants
suffer from lack of water.
In general, loamy soils are well-drained and provide the best balance
between drainage and water holding capacity for crop production. Poorly
structured, fine, or moderately fine textured soils normally are poorly-
drained and are best suited to overland flow systems. Sandy soils are
often excessively-drained and best suited to rapid infiltration systems.
C-10
-------
It should be recognized that the drainability of a soil profile.will be
determined by the most restrictive layer in the profile. Thus, a
shallow sandy surface layer underlain by a poorly-drained clay layer
will be poorly-drained.
C.2.6 Specific Yield and Specific Retention
Specific yield and specific retention are related properties that are a
measure of the amount o.f groundwater an aquifer will yield upon pumping.
Specific yield is the amount of water that will drain by gravity from a
saturated aquifer divided by the bulk volume of the aquifer. This value
is typically 10 to 20% for unconfined aquifers [5]. Specific retention
is equal to the porosity (subsurface void space) minus the specific
yield, under saturated conditions. The relationship among specific
yield, specific retention, and porosity is shown in Figure C-6.
FIGURE C-6
POROSITY, SPECIFIC RETENTION, AND
SPECIFIC YIELD VARIATIONS WITH GRAINS SIZE,
SOUTH COASTAL BASIN, CALIFORNIA [5]
50
45
40
35
30
25
20
1 5
1 0
5
0
I I I
1/16 1/8 1/4 1/2 1 2 4 8 16 32 64 128 256
MAXIMUM 10% GRAIN SIZE, mm
C-ll
-------
C.2.7 Transmissivity
Transmissivity is a parameter that is sometimes measured in the field as
part of a method to determine horizontal permeability of aquifers [6].
Transmissivity T is the rate at which water is transmitted through a
unit width of the aquifer under a unit hydraulic gradient. It is equal
to the permeability K multiplied by the aquifer thickness.
C.3 Soil Infiltration Rate and Permeability Measurements
Field measurements of soil infiltration rates and permeability are an
essential part of the design of rapid infiltration systems and most slow
rate systems. These hydraulic parameters serve as the basis for the
designer's selection of an application rate that will be within the
hydraulic capacity of the soil at the proposed site. In this section,
the principal methods for measuring infiltration rates and vertical
permeability are reviewed along with procedures for using the field test
results to obtain infiltration equations that are useful in the design
of irrigation systems. The relation between infiltration and vertical
permeability is discussed. Measurement of soil moisture profiles is
also addressed.
C.3.1 Infiltration
Infiltration refers to the entry of the water into the soil. Hydraulic
or liquid loading is infiltration over a long term (a year, for example)
and includes resting or drying periods. The factors that affect
infiltration have been thoroughly discussed in the literature [7] and
must be firmly kept in mind when planning and making field measurements.
Otherwise, the measurements, which are relatively easy to make, may be
meaningless for the intended purposes.
C.3.1.1 Interpretation and Use of Infiltration Data
As previously mentioned, (Section C.2.4), when water is applied to a
soil that is below field capacity, the rate of infiltration generally
decreases with time, approaching a nearly constant or steady state value
after several minutes or hours of application. However, initial
infiltration rates may vary considerably, depending on the initial soil
moisture level. Dry soil has a higher initial rate than wet soil
because there is more empty pore space for water to enter. The effect
of soil moisture level on initial infiltration rates and the change in
infiltration rate as a function of time is illustrated in Figure C-7.
The short-term decrease in infiltration rate is primarily due to the
change in soil structure and the filling of large pores as clay
particles absorb water and swell.
C-12
-------
FIGURE C-7
INFILTRATION RATE CURVES SHOWING THE INFLUENCE OF INITIAL
WATER CONTENT, Q (FRACTION BY VOLUME), ON INFILTRATION
RATE COMPUTED FOR YOLO LIGHT CLAY [1]
0.4 i—
0.3
0.2
0. 1
5 10
TIME, h
Long-term decreases
place over several
in the steady state infiltration rates that take
months of application are also observed. These
decreases are the result of several factors, including (1) the migration
and concentration of fine soil particles in the soil profile, (2) the
buildup of organic and biological solids in the soil pores, and (3) the
blockage of soil pores by gases produced by soil microbes. The steady
state infiltration rate may be improved or maintained by soil tilling
and other management practices.
The short-term change in infiltration rate as a function of time is of
interest in the design and operation of irrigation systems. A knowledge
of how cumulative water intake varies with time is necessary to
determine the time of application necessary to infiltrate the quantity
of water required to irrigate a crop. The design application rate of
sprinkler systems is selected on the basis of the infiltration rate
C-13
-------
expected at the end of the application period. The short-term change
in infiltration rate can be closely approximated by the simple equation:
I = Atn (C-2)
where I = infiltration rate, in./min
A = a constant, representing the instantaneous intake rate at
time = 1 (usually minutes)
n = an exponent which for most soils is negative with values
between 0 and -1
Integration of the rate equation yields an equation for the cumulative
intake Y at any time t . The equation has the following form:
Y = __L_tn + 1 (C-3)
Data from infiltrometer studies can be plotted to yield cumulative
intake curves from which the coefficients for Equations C-2 and C-3 may
be obtained. Alternatively, the cumulative intake may be computed as a
function of time using the Green-Ampt infiltration model. Knowledge of
the vertical permeability profile and the initial soil moisture profile
is needed to apply this technique. The K profile may be determined by
the methods described in Section C.3.3. The soil moisture may be
determined by using a neutron moisture probe or gravimetric sampling
[1]. The calculation procedures are described by Bouwer for various K
and moisture profiles [8, 9], The advantage of the calculation method
over infiltrometer measurements in generating Y versus t data is
that the uncertainty associated with lateral seepage under infnitro-
meters is avoided, and the Y versus t relationship can be computed
easily ,for any soil moisture profile. Data obtained from the Green-
Ampt model can be plotted in the same manner as infiltrometer data to
yield infiltration rate versus time curves.
The most direct method to determine coefficients for Equation C-3 is to
plot the data points on log-log paper with time on the abscissa and
cumulative intake on the ordinate, and to fit the best straight line
through the points. An example of such a plot for several different
soils is shown in Figure C-8 [1]. The intercept of the curve at t = 1
is equal to A/n + 1 (not shown in Figure C-8), and the slope of the
line is equal to n + 1.
The most important application for the cumulative intake curves is in
the design and evaluation of border irrigation systems. The curves may
be compared with a set of intake family curves developed by SCS for
border irrigation design, and the appropriate intake family can then be
selected. Cumulative intake curves may also be developed for furrow
C-14
-------
irrigation system design and evaluation. However, infil
are not directly applicable to furrow irrigation because
the land is in contact with the water, and lateral seepage
large part'of the total intake. Consequently, actual field
furrows are required to develop infiltration rate versus
Infiltration rate curves may be obtained by applying the
and n to Equation C-2. Infiltration rate curves may
selecting sprinkler application rates.
trometer data
only part of
represents a
trials using
time curves.
constants A
be useful in
FIGURE C-8
CUMULATIVE INTAKE CURVES SHOWING THE INFILTRATION OF
WATER INTO SOIL FROM SINGLE RING INFILTROMETERS [1]
(«= n + 1)
30 i-
20 30 40 5060 80 100 200 300
C.3.1.2 Soil Profile Drainage Studies
For slow rate systems that are operated at application rates
considerably in excess of crop irrigation requirements, it is often
desirable to know how rapidly the soil profile will drain and/or dry
after application has stopped. This knowledge, together with knowledge
of the limiting infiltration rate of the soil and the groundwater
movement and buildup, allows the designer to make a
of the maximum volume of water that can be applied
produce adequate crops. A typical moisture profile
time following an irrigation is illustrated in
initially saturated profile.
reasonable estimate
to a site and still
and its change with
Figure C-9 for an
C-15
-------
FIGURE C-9
TYPICAL PATTERN OF THE CHANGING MOISTURE
PROFILE DURING DRYING AND DRAINAGE
0 —^WATER CONTENT SATURATION
Moisture profile changes may be determined in the field by measuring the
soil-water tension at various times and at various depths in the profile
with tensiometers. Soil tension data can then be converted to moisture
content values by use of the soil-water characteristic curve of the soil
at each measured depth. Soil-water characteristic curves are determined
by laboratory methods. A discussion of these methods and the use of
tensiometers is presented in Taylor and Ashcroft [1].
C.3.1.3 Estimates of Infiltration From Soil Properties
Estimation of infiltration and percolation rates without benefit of
actual onsite testing is an undesirable practice, but the general
relationships that have been established between hydraulic capacity and
soil properties through experience are certainly reliable enough to
permit preliminary screening of several available sites. Soil
scientists generally agree that when a large number of widely different
soils are considered, no single factor can serve as an index for
determining the infiltration rate or permeability of an individual soil
profile.
In a comprehensive study by O'Neal, it was concluded that structure is
probably the most important single soil characteristic in evaluating
hydraulic characteristics, but it was impossible to estimate these on
the basis of structural factors alone [10]. The approach suggested in
C-16
-------
the basis of structural factors alone [10]. The approach suggested in
the study resulted in only fair precision using four principal factors:
(1) relative dimension (both horizontal and vertical) of structural
aggregates, (2) amount and direction of overlap of aggregates (3) num-
ber of visible pores, and (4) texture. None of these factors, when
considered singly, was a reliable indicator of permeability, and each
one had to be considered with reference to all the others. The seven
soil permeability classes used by the SCS are as follows:
Class Soil permeability, in./h
Very slow <0.06
Slow 0.06-0.2
Moderately slow 0.2-0.6
Moderate 0.6-2.0
Moderately rapid - 2.0-6.0
Rapid 6.0-20.0
Very rapid >20.0
1 in./h = 2.54 cm/h
Using these classes, the soils experts who participated in O'Neal's work
were able to estimate the correct permeability class for 68% of the 271
horizons examined, and they were within one class ranking for an
additional 24%. Note particularly, however, that these results were
achieved by trained persons. Moveover, it must be remembered that even
within a particular class there is room for an error of up to 400%.
The difficulty is that even if permeability could be accurately
determined from a particular property (such as particle size
distribution), it would still be influenced by factors which that
particular measurement could not account for. These might include grain
orientation, colloid migration or swelling, bulk density changes by
compaction, and chemical or biological effects. Thus, it would seem
reasonable for reviewing agencies to insist on at least some field
measurements, of the type recommended in Chapter 4, for all land
treatment systems where the intended application rates are well in
excess of the known evapotranspiration rates.
C.3.1.4 Infiltration Measurement Techniques
The value that is required in land treatment is the long-term acceptance
rate of the entire soil surface on the proposed site for the actual
wastewater effluent to be applied. The value that can be measured is
only a short-term equilibrium acceptance rate for a number of particular
areas within the overall site. It is strongly recommended that
hydraulic tests of any type be conducted with the actual wastewater
whenever possible. Such practice will provide valuable information
C-17
-------
relative to possible soil-wastewater interactions which might create
future operating problems. If suitable wastewater is not available at
the site, the ionic composition of the water used should be adjusted to
correspond to that of the wastewater. Even this simple step may provide
useful data on the swelling of expansive clay minerals due to sodium
exchange.
The theory of infiltration, in which great strides have been made in the
past decade, has simply not yet found practical application in the land
treatment of wastewater. Modeling the physics of unsaturated flow,
while important, has not answered the present need for simple and
economical assessment of soil hydraulic capacity. Measurements have
been made by numerous different techniques without follow-up studies to
relate operating results to the original measurements. Research is
needed in this area to improve existing design techniques.
There are many potential techniques for measuring infiltration including
basin flooding, sprinkler infiltrometers, cylinder infiltrometers, and
lysimeters. The technique selected should reflect the actual method of
application being considered. The area of land and the volume of
wastewater used should be as large as practical. The two main
categories of measurement techniques are those involving flooding
(ponding over the soil surface) and rainfall simulators (sprinkling
infiltrometer). The flooding type of infiltrometer supplies water to
the soil without impact, whereas the sprinkler infiltrometer provides
impact similar to that of natural rain. Flooding infiltrometers are
easier to operate than spinkling infiltrometers, but they almost always
give higher equilibrium infiltration rates. In some cases, the
difference is very significant, as shown in Table C-2. Nevertheless,
the flooding measurement techniques are generally preferred because of
their simplicity.
TABLE C-2
COMPARISON OF INFILTRATION MEASUREMENT USING FLOODING
AND SPRINKLING TECHNIQUES [11]
Equilibria infiltration
rate, in./h
Measurement Overgrazed Pasture, grazed but
technique pasture having good cover
Double-cylinder
infiltrometer (flooding) 1.11 2.35
Type F rainfall
simulator (sprinkling) O.K 1.13
in./h =2.54 cm/h
C-18
-------
Before discussing these four techniques, it should be pointed out that
the standard U.S. Public Health Service (USPHS) percolation test used
for establishing the size of septic tank drain fields [12] is not
recommended .except for very small subsurface disposal fields or beds.
Comparative field studies have shown that the percolation rate from the
test hole is always significantly higher than the infiltration rate as
determined from the double-cylinder (also called double ring)
infiltrometer test. The difference between the two techniques is of
course related* to the much higher percentage of lateral flow experienced
with the standard percolation test. The final rates measured at four
locations on a 30 acre (12 ha) site using the two techniques are
compared in Table C-3. The lower coefficient of variation (defined as
the standard deviation divided by the mean value, Cv = O/M) for the
double-cylinder technique is especially significant. A plausible
interpretation is that the measurement technique involved is inherently
more precise than the standard percolation test.
TABLE C-3
COMPARISON OF INFILTRATION MEASUREMENT USING STANDARD
USPHS PERCOLATION TEST AND DOUBLE-CYLINDER INFILTROMETER3
Equilibrium infiltration
rate, in./h
Standard USPHS Double-cylinder
Location percolation test infiltrometer
1
2
3
4
Mean
Standard
deviation
Coefficient
of variation
48.0
84.0
60.0
138.0
82.5
40.0
0.48
9.0
10.3
14.4
12.0
11.6
2.3
0.20
a. Using sandy soil free of clay.
1 in/h = 2.54 cm/h
C.3.1.4.1 Flooding Basin Techniques
Where pilot basins have been used for determination of infiltration, the
plots have generally ranged from 10 ft2 (0.9 m2) to 0.25 acre (0.1
ha). Larger plots are provided with a border arrangement for
application of the water. If the plots are filled by hose, a canvas or
burlap sack over the end of the hose will minimize disturbance of the
soil [7]. Although basin tests are desirable, and should be used
whenever possible, there probably will not arise many opportunities to
C-19
-------
do so because of the large volumes of water needed for measurements. A
sample basin is shown in Figure C-10. In at least one known instance,
pilot basins of large scale (5 to 8 acres or 2 to 3.2 ha) were used to
demonstrate feasibility and then were incorporated into the larger full-
scale system [13].
FIGURE C-10
FLOODING BASIN USED FOR MEASURING INFILTRATION
C.3.1.4.2 Sprinkler Infiltrometers
Sprinkler infiltrometers are used primarily to determine the limiting
application rate for systems using sprinklers. To measure the soil
intake rate for sprinkler application, the method presented by Tovey and
Pair can be used [14]. The equipment needed includes a trailer-mounted
water recirculating unit, a sprinkler head operating inside a circular
shield with a small side opening, and approximately 50 rain gages. A
schematic diagram of a typical sprinkler infnitrometer is presented in
Figure C-ll. A 2 ton (1 814 kg) capacity trailer houses a 300 gallon
tank and 2 self-priming centrifugal pumps. The
have sufficient capacity to deliver at least 100
50 lb/in.2 (34.5 N/cm?) to the sprinkler
nozzle, and the return flow pump should be capable of recycling all
excess water from the shield to the supply tank. The circular sprinkler
shield is designed to permit a revolving head sprinkler to operate
normally inside the shield. The opening in the side of the shield
(1 135 L) water supply
sprinkler pump should
gal/min (6.3 L/s) at
C-20
-------
FIGURE C-ll
LAYOUT OF SPRINKLER INFILTROMETER [14]
2 ton TRAILER
o
ro
300. gal
WATER SUPPLY
TANK
AUXILIARY
WATER SUPPLY
PRESSURE
GAGE
— SPRINKLER
HEAD
ooooootfo
o o o o o o o
o o o o o o o
RAIN GAGES
5 ft
SPRINKLER
SHIELD
• j
VALVES
1 ton = 907.2 Kg
1 ft =0.305 m
1 gal =3.785 L
-------
restricts the wetted area to about one-eighth of a circle. Prior to
testing, the soil in the wetted area is brought up to field capacity.
Rain gages are then set out in rows of three spaced at 5 ft (1.5 m)
intervals outward from the sprinkler in the center of the area to be
wetted. The sprinkler is operated for about 1 hour. The intake of
water in the soil at various places between gages is observed to
determine whether the application rate is less than, greater than, or
equal to the infiltration rate. The area selected for measurement of
the application rate is that where the application is equal to the
infiltration rate, i.e., where the applied water just disappears from
the soil surface as the sprinkler jet returns to the spot. At the end
of the test (after 1 hour), the amount of water caught in the gages is
measured and the intake rate is calculated. This calculated rate of
infiltration is equal to the limiting application rate that the soil
system can accept without runoff.
C.3.1.4.3 Cylinder Infiltrometers
A useful reference on cylinder infiltrometers is Haise et al. [15]. The
basic technique, as currently practiced, is to drive or jack a metal
cylinder into the soil to a depth of about 6 in. (15 cm) to prevent
lateral or divergent flow of water from the ring. The cylinder should
be 6 to 14 in. (15 to 35 cm) in diameter and approximately 10 in. (25
cm) in length. Divergent flow is further minimized by means of a
"buffer zone" surrounding the central ring. The buffer zone is commonly
provided by another cylinder 16 to 30 in. (40 to 75 cm) in diameter
driven to a depth of 2 to 4 in. (5 to 10 cm) and kept partially full of
water during the time of infiltration measurements from the inner ring.
Alternatively, a buffer zone may be provided by diking the area around
the intake cylinder with low (3 to 4 in. or 7.5 to 10 cm) earthen dikes.
The quantity of water that might have to be supplied to the double-
cylinder system during a test can be substantial and might be considered
a limitation of the technique. For highly permeable soil, a 1 500 gal
(5 680 L) tank truck might be needed to hold a day's water supply for a
series of tests. The basic configuration of the equipment during a test
is shown in Figure C-12.
This technique is thought to produce data that are at least
representative of the vertical component of flow. In most soils, the
infiltration rate will decrease throughout the test and approach a
steady state value asymptotically. This may require as little as 20 to
30 minutes in some soils and several hours in others. The test cannot
be terminated until the steady state is attained or else the results are
meaningless (see Figure C-7).
C-22
-------
FIGURE C-12
»
CYLINDER INFILTROMETER IN USE
BUFFER POND
LEVEL
7
GAGE INDEX
ENGINEER'S SCALE
WELDING ROD
HOOK
WATER SURFACE
— INTAKE CYLINDER —
GROUND LEVEL —^
C-23
-------
The following precautions concerning the cylinder infiltrometer test are
noted.
1. If a sprinkler or flood application is planned, the cylinders
should obviously be placed in surficial materials. If rapid
infiltration is planned, pits must be excavated to expose
lower horizons that will constitute the bottoms of the basins.
2. If a more restrictive layer is present below the intended
plane of infiltration and this layer is close enough to the
intended plane to interfere, the infiltration cylinders should
be embedded into this layer to ensure a conservative estimate.
The method of placement into the soil may be a serious
limitation. Disturbance of natural structural conditions
(shattering or compaction) may cause a large variation in
infiltration rates between replicated runs. Also the
interface between the soil and the metal cylinder may become a
seepage plane, resulting in abnormally high rates. In
cohesionless soils (sands and gravels), the poor bond between
the soil and the cylinder may allow seepage around the
cylinder and cause "piping." This can be observed easily and
corrected, usually by moving a short distance to a new
location and trying again. Variability of data caused by
cylinder placement can largely be overcome by leaving the
cylinders in place over an extended period during a series of
measurements [7].
Knowledge of the ratio of the total quantity of water infiltrated to the
quantity of water remaining directly beneath the cylinder is essential
if one is interested only in vertical water movements. If no correction
is made for lateral seepage, the measured infiltration rate in the
cylinder will be well in excess of the "real" rate [16]. Several
investigators have studied this problem of lateral seepage and have
offered suggestions for handling it [16, 17, 18].
As pointed out by Van Schilfgaarde [19], measurements of hydraulic
conductivity on soil samples often show wide variations within a
relatively small area. Hundred-fold differences are common on some
sites. Assessing hydraulic capacity for a project site is especially
difficult because test plots may have adequate capacity when tested as
isolated portions, but may prove to have inadequate capacity after water
is applied to the total area for prolonged periods. Parizek has
observed that problem areas can be anticipated more readily by field
study following spring thaws or prolonged periods of heavy rainfall and
recharge [20]. Runoff, ponding, and near saturation conditions may be
observed for brief periods at sites where drainage problems are likely
to occur after extensive application begins.
C-24
-------
Although far too few extensive tests have been made to gather meaningful
statistical data on the cylinder infiltrometer technique, one very
comprehensive study is available from which tentative conclusions can be
drawn. Burgy and Luthin reported on studies of three 40 by 90 ft
(12.2 x 27.4 m) plots of Yolo silt loam characterized by the absence of
horizon development in the upper profile [11]. The plots were diked
with levees 2 ft (0.6 m) high. Each plot was flooded to a depth of 1.5
ft (0.5 m), and the time for the water to subside to a depth of 0.5 ft
(0.15 m) was noted. The plots were then allowed to drain to the
approximate field capacity and a series of cylinder infiltrometer tests--
357 total--were made.
Test results from the three basins located on the same homogeneous field
were compared. In addition, test results from single-cylinder
infiltrometers with no buffer zone were compared with those from double-
cylinder infiltrometers. The inside cylinders had a 6 in. (15 cm)
diameter; the outside cylinders, where used, had a 12 in. (30 cm)
diameter.
For this particular soil, the presence of a buffer zone did not have a
significant effect on the measured rates. Consequently, all of the data
are summarized on one histogram in Figure C-13. The calculated mean of
the distribution shown is 6.2 in./h (15.7 cm/h). The standard deviation
is 5.1 in./h (12.9 cm/h).
Burgy and Luthin suggest that the extreme high values, while not
erroneous, should be rejected in calculating the hydraulic capacity of
the site. Physical inspection revealed that these values were obtained
when the cylinders intersected gopher burrows or root tubes. Although
these phenomena had an effect on the infiltration rate, they should not
be included in the averaging process as they carried too much weight.
As a criterion for rejection, Burgy and Luthin suggest omitting all
values greater than three standard deviations from the mean value. They
further suggest an arbitrary selection of the mean and standard
deviation for this procedure based on one's best estimate of the
corrected values rather than the original calculations. From inspection
of the histogram, these values might be selected as about 5 in./h (12.7
cm/h) and 3.5 in./h (8.9 cm/h), respectively. Thus, all values greater
than 5.0 + 3(3.5), or 15.5 in./h (39.4 cm/h) are arbitrarily rejected:
a total of 12 of the 357 tests made (3.4%).
Because it is important to provide conservative design parameters for
this work, however, it is recommended that all values greater than two
standard deviations from the mean be rejected. For the example, this
results in the rejection of all values greater than 5.0 + 2(3.5), or 12
in./h (30.5 cm/h) from the average. A recomputation using this
C-25
-------
FIGURE C-13
VARIABILITY OF INFILTROMETER TEST RESULTS ON RELATIVELY
HOMOGENEOUS SITE [20]
o
I
ro
13
12
11
10
9
8
7
6
5
4
3
2
1
0
_L
J_
_L
_L
J_
6 8 10 12 14 16 18 20 22 24 26 28 30 32 34 36 38 40 42 4445
AVERAGE INFILTRATION RATE, in./h
1 in./h - 2.54 cm/h
-------
criterion provides a mean of 5.1 in./h (12.5 cm/h) and a standard
deviation of 2.8 in./h (7.1 cm/h). This average value is within 16% of
the "true" mean value of 4.4 in./h (11.2 cm/h) .as measured during
flooding tests of the entire plot.
The main question to be answered now is, how many individual tests must
be made to obtain an average that is within some given percent of the
true mean, say at the 90% confidence interval? The answer has been
provided by statisticians using the Student "T" distribution. Details
of the derivation are omitted here but can be found in most standard
texts on statistics.
The results of two typical sets of computations are summarized in
Figures C-14 and C-15. The two sets of curves are for 90% and 95%
confidence intervals. The confidence interval and the desired precision
are, of course, basic choices that the engineer must make. A 90%
confidence in the measured mean, which is within 30% of the true mean,
may be sufficient for small sites where neighboring property is
available for expansion if necessary. On the other hand, 95% confidence
that the measured value -is within 10% of the true mean may be more
appropriate for larger sites or for sites where expansion will not be
easily accomplished once the project is constructed.
The coefficient of variation will have to be estimated from a few
preliminary tests because it is the main plotting parameter in these
figures. As an example, for the adjusted distribution of Burgy and
Luthin's data with a coefficient of variation estimated at 0.55, at
least 23 separate tests would be required to have 90% confidence that
the computed mean would be within 20% of the true mean value of
infiltration. Obviously, time and budget constraints must be considered
in making the confidence and accuracy determinations; 3 to 4 man-days of
work might be required to make 23 cylinder infiltrometer tests.
C.3.1.4.4 Lysimeters
Lysimeter studies, using either undisturbed cores (cohesive soils) or
disturbed samples compacted carefully to, or near, the field bulk
density of the undisturbed sample, may have potential for bridging the
very large gap between short-term field tests with clean water and long-
term pilot scale field studies with the actual wastewater. The
configuration of a typical lysimeter is shown in Figure C-16. Smaller
diameters, down to 3 or 4 in. (7.6 or 10.2 cm), have been used with
success, especially for relatively undisturbed cores. The gravel layer
shown in the figure is artificial and was provided only to prevent
clogging at the outlet. Screens and perforated or porous plates have
been used for the same purpose in other lysimeter designs.
C-27
-------
FIGURE C-14
NUMBER OF TESTS REQUIRED FOR 90% CONFIDENCE
THAT THE CALCULATED MEAN IS WITHIN STATED
PERCENT OF THE TRUE MEAN
100
10$
0.1 0.2 0.3 0.4 0.5 0.6
COEFFICIENT OF VARIATION
0.7
0.8
FIGURE C-15
NUMBER OF TESTS REQUIRED FOR 95% CONFIDENCE
THAT THE CALCULATED MEAN IS WITHIN STATED
PERCENT OF THE TRUE MEAN
100
80
o 60
Ul
oe
= 40
a
UJ
O£
2 20
CO
UJ
I—
Z 10
-------
FIGURE C-16
LYSIMETER CROSS-SECTION
4 ft
(APPROX)
6 in.
•"*•••
SOIL
GRADED GRAVEL
UNDERDRAIN
VENT PIPE
ADJUSTABLE
OUTLET
1 ft =0.305 m
1 in.= 2. 54 cm
If clean water is used in lysimeter tests, close agreement with the
results of cylinder infiltrometer results should be obtained, provided
that the infiltrometer tests were made carefully and with sufficient
replicates (usually 6 to 12) [21]. With actual wastewater, however, the
results will not match. In a study by Ongerth and Bhagat, the 18-inch
(45.7 cm) diameter lysimeter, loaded at somewhat less than 100 Ib of
BOD/acre-d (112 kg/ha-d), averaged about 5 to 10% of the infiltration
rates observed on the undisturbed soils using cylinder infiltrometers
and clean water [22]. Follow-up studies on a pilot basin of
approximately 0.25 acre (0.10 ha) showed that rates significantly higher
than those observed in the lysimeters could be sustained [23]. After 1
year of operation the infiltration rate from the pilot basin has
averaged about 25% of those measured by the original cylinder
infiltrometer testing on this site. This is almost three times the rate
predicted from the lysimeter tests. Exact reasons for these differences
are not known, but the packing of the disturbed soil into the lysimeters
is probably a major factor. This problem will be more critical for fine
textured soils. Much more information from studies like the one by
Ongerth and Bhagat is necessary before general conclusions can be drawn.
C-29
-------
C.3.2 Relation Between Infiltration and Vertical Permeability
Percolation, the movement of water through the soil, is a distinctly
different property from infiltration, the movement of water through the
soil surface into the soil. The measurement of the vertical component
of percolation is called the vertical permeability. In a study by
Bouwer [24] it has been shown that the steady state value of
infiltration of secondary wastewater effluents containing approximately
2b mg/L suspended solids is about one-half of the potential saturated
vertical permeability.
Although the measured infiltration rate on the particular site may
decrease in time due to surface clogging phenomena, the subsurface
vertical permeability at saturation will generally remain constant.
That is, clogging in depth does not generally occur. Thus, the short-
term measurement of infiltration serves reasonably well as an estimate
of the long-term saturated vertical permeability if infiltration is
measured over a large area. Once the infiltration surface begins to
clog, however, the flow beneth the clogged layers tends to be
unsaturated and at unit hydraulic gradient.
C.3.3 Measurement of Soil Vertical Permeability
The rate at which water percolates through the soil profile during
application depends on the average saturated permeability (1C) of the
profile. If the soil is uniform, K is constant with depth, and any
differences in measured values of K are due to errors in the
measurement technique. Average K then may be computed as the
arithmetic mean:
(XT ' «^O 1^ O • • • 1^ —
K = J 2 3_ n (c_4)
am n v '
where K,_ = arithmetic mean permeability
GUI
Many soil profiles approximate a layered series of uniform soils with
distinctly different K values, generally decreasing with depth. For
such cases, it can be shown that average K is represented by the
harmonic mean of the K values from each layer [25]:
Khm = d7—dT r (C-5)
1 j. 2 , . n
K2 '"Kn
where D = soil profile depth
d = depth of nth layer
n
K. = harmonic mean permeability
C-30
-------
If a bias or preference for a certain K value is not indicated by
statistical analysis of field test results, a random distribution of K
for a certain layer or soil region must be assumed. In such cases, it
has been shown that the geometric mean provides the best estimate of the
true K [25]:
v - iv . v . v ... v \ (C-6)
Kgm ' (K1 K2 K3 V
where K = geometric mean permeability
Methods available to measure vertical saturated permeability in the soil
region above a water table, or in the absence of a water table, include
the double tube [26, 27], the gradient intake [27, 28], and the air
entry .permeameter [29].
Each method requires wetting of the soil to obtain K values. During
wetting, air is often trapped in the soil pores, and long periods of
infiltration are necessary to achieve true saturation. Thus, the
measured K value (K ) is usually less than the saturated
permeability (Ks). The air entry permeameter measures K in the wetted
zone during wetting, and the measured K is about 0.5 Ks [29]. The
double tube and gradient intake methods required longer periods of
infiltration, and the soil becomes more nearly saturated. Thus, the K
value determined with these two methods may be somewhere between 0.5
K. and K..
In the gradient intake and double tube methods, permeability is measured
at the bottom of an auger hole, so these methods can be used for
measuring K at different depths in a profile. The air entry
permeameter is a surface device, and pits or trenches must be dug if it
is to be used for measuring K at greater depths.
C.4 Groundwater Flow Investigations
Groundwater movement through soil and rock is important to the design
and operation of land treatment systems, especially rapid infiltration
systems. Quantities and qualities of subsurface water will likely be
altered by rapid infiltration. Estimating subsurface water flow by
indirect surface methods and by more direct subsurface methods is
described in this section. The use of hydraulic models to predict
groundwater movement also is described briefly.
C-31
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C.4.1 Groundwater Elevation Maps
Groundwater elevation maps are constructed by interpolating between
measured elevations in wells and drawing contour lines of equal
elevation. The movement of the groundwater is in a direction
perpendicular to the contours from the higher to the lower elevations.
The flowrate can be estimated using Darcy's law, by measuring the length
dl between groundwater elevation contours dH .
Groundwater maps are used to identify zones of discharge and recharge.
Since groundwater flows downgradient, domes, hills, and ridges represent
recharge zones; and basins, troughs, and valleys represent discharge
zones. Recharge and discharge zones are likely to occur where aquifers
are exposed at the earth surface, where lakes and streams intersect
shallow water tables, and where there is concentrated agricultural,
industrial, or municipal land use. Groundwater discharge can occur
because of vertical leakage along faults or other boundaries.
C.4.2 Surface Methods of Estimating Hydrologic Properties
Indirect surface methods can often be used to provide qualitative data
on subsurface hydrologic properties. These methods include: (1) earth
resistivity, (2) remote sensing, and (3) soil and geologic surveys.
C.4.2.1 Earth Resistivity
Earth resistivity surveys are useful in determining shallow water
tables. These and other geophysical, geochemical, and geological
surveys are reviewed by Maxey [30]. Resistivity surveys are inexpensive
and yield qualitative subsurface data.
C.4.2.2 Remote Sensing
Remote sensing by aerial and satellite photography can be used to
estimate subsurface hydrologic properties from interpretation of
differences in vegetation, soil associations, and surface drainage.
Aerial photographs are usually available from the SCS soil surveys or
from land use surveys. Satellite photography, a more recent technique,
and computer-generated maps can be used to estimate subsurface hydrology
from interpretation of surface features, such as soil moisture.
C-32
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C.4.2.3 Soil and Geologic Surveys
Existing soil surveys often include information on geologic features,
depth to groundwater, and areas of poor drainage. Geologic surveys, as
developed by USGS, include discussions of climate, land use, geography,
ohysical geology, mineralogy, petrology, structural geology, historical
geology, paleontology, and economic geology of an area. Methods of
making geologic surveys are discussed by Lahee [31] and Compton [32].
Geologic surveys often include numerous measurements of rock thickness,
texture, structure, attitude (dip, strike, plunge), and statistical
analysis of the data may be given.
Published geologic surveys are useful in describing location, physical
make-up, thickness, attitude, and boundaries of geologic units which may
be aquifers. They are useful in identifying recharge and discharge
areas, subsurface flow directions, surface drainage patterns, water
quality problems, and potential hazards for land use. Surveys are
produced by federal and state geological surveys and bureaus of mines.
They are also available as reports for special engineering, scientific,
and educational studies at universities and research centers.
C.4.3 Subsurface Methods of Estimating Hydrologic Properties
Logging methods, aquifer tests, and laboratory tests are among the
subsurface methods used to estimate hydrologic properties. They require
physical access to the subsurface through wells, pits, or drill holes.
C.4.3.1 Logging Methods
Logging methods are used to estimate texture, porosity, and groundwater
circulation and quality. A log is a description of material properties
with depth as determined by observations or measurements through a hole
or with samples from a hole. Drillers' logs and electrical resistance
and potential logs are most common. Changes in soils or soil materials
can be correlated with spikes or peaks on the electric log printouts.
Various logging methods are reviewed by Jones and Skibitzke [33] and
Todd [34]. Professional logging companies publish detailed manuals and
research papers. A summary of subsurface logging information obtained
by various methods is provided in Table C-4.
C.4.3.2 Aquifer Tests
Aquifer tests by the pumped-well method are performed using a series of
wells in the field. The approach is to discharge (purnp) or recharge one
well at a known rate and to measure the response of water levels in the
C-33
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other wells. Water level responses are then mathematically related to
permeability ( K ) or transmissivity [6].
TABLE C-4
SUBSURFACE LOGGING INFORMATION
OBTAINED BY VARIOUS METHODS [34]
Method
Operation
Information
Drillers' log
Observe well cuttings
during drilling
Drilling-time log Observe drilling time
Resistivity log Measure electrical
resistivity of madia
surrounding encased hole
Potential log
Temperature log
Caliper log
Current log
Measure natural
electric potentia, or
self-potential
Measure temperature
Measure hole diameter
Measure current
Radioactive log Measure attenuation of
gamma and neutron rays
Rock contacts, thickness, description,
or type texture. Samples for laboratory
tests. Common method.
Rock texture, porosity.
Specific resistivity of rocks, porosity,
packing, water resistivity, moisture content,
temperature, groundwater quality. Correlate
with samples for best results. Common method.
Permeable or impermeable,groundwater quality.
Common method.
Groundwater circulation, leakage.
Hole diameter, rock consolidation, caving
zones, casing location.
Groundwater flow velocity, circulation,
leakage.
Consolidation, porosity, moisture content.
Common in soil studies, clay or nonclay materials.
Bouwer summarized other variations including the auger-hole,
piezometer, and tube methods [35]. In the tube method, the resultant K
is for the vertical direction [25, 35]. For the piezometer method, the
direction of measured K depends on the ratio of the piezometer height
to its diameter. The auger-hole test, which measures principally
horizontal permeability, is discussed further in Section C.5.2.2.
C.4.3.3 Laboratory Tests
Laboratory tests of subsurface flow properties are generally not as
reliable as field methods because of the errors introduced in sampling
and the change in properties due to disturbance in sampling. Laboratory
determinations of soil-water characteristics and unsaturated conduc-
tivity curves are presented in Taylor and Ashcroft [1], Kirkham and
Powers [3], Black [36], and Bouwer and Jackson [37]. Because of the
tremendous variability of actual hydrologic properties, a great many
laboratory tests must be conducted to provide statistical validity.
C-34
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C.5 Groundwater Mound Height Analysis
C.5.1 • Introduction
If water that infiltrates the soil and percolates vertically through the
zone of aeration encounters a water table or an impermeable (or less
permeable) layer, a groundwater "mound" will begin to grow. If the
mound height continues to grow, it may eventually encroach on the zone
of aeration to the point where renovation capacity is affected. Further
growth may result in intersection of the mound with the soil surface,
which will reduce infiltration rates. This problem can usually be
identified and analyzed before the system is designed and built if the
proper geologic and hydrologic information is available for analysis.
Parizek [20] and Spiegel [38] support the concept of hydrogeologic
systems analysis to define the probable effects of a project on local
and regional water table configurations. Modeling may be expected to
delineate areas likely to be flooded, demonstrating the need for
drainage facilities and their location. Thus, contingency plans to
eliminate potential drainage problems can be formulated at the time
projects are designed.
Practically all analyses of drainage problems have been limited to the
behavior of the water table, which of course responds to a wetting event
as shown in Figures C-17 and C-18. Irrigation experts recognize that
water table position alone is not a satisfactory criterion in their
work. If the present state of knowledge would permit, they might well
redirect their attentions to the moisture content of the root zone. The
situation is similar with respect to land application of wastewater.
One is really less interested in the position of the water table at any
time than in the onset of anaerobiosis in the soil voids and the
breakdown of renovation capacity. Analysis of the latter is so complex,
however, that we will have to be content for the present to simply be
able to control the water table, or to know how high it will rise under
given loading conditions.
Analysis of the growth and decay characteristics of groundwater mounds
induced by percolating waters is a complex, mathematically sophisticated
process. The problem has been attacked in several ways, including
analytical, analog, and digital modeling. Several empirical equations
representing gross approximations have also appeared. A complete review
of all the work in this area is well beyond the scope of this appendix.
Rather, the input data generally required for the analysis will be
discussed, and a short review will be provided of published studies that
should prove useful to the user searching for a method to suit a
particular problem. Only simple geometries, known to recur frequently
in practical applications, are covered by these references.
C-.35
-------
FIGURE C-17
MOUND DEVELOPMENT FOR STRIP RECHARGE [33]
AXIS OF SYMMETRY
SURFACE OF SPREADING BASIN
•'•:^-V-V-'V:'"^''"'V..r/.'."'";-'* -'• \V*-V^'^I^<^*^'*O^* v'->^7-:'^^^
.%>'•»'. r.•.••'••'•'••*.•" ••-!.:*!- *:: C^^-":-!•:•.'t ^;xv.^-C'L"V».\ta>C*-i'-."""-X*.*i-i-:."r>.••••"•: .«••^l'*,vr:--.".-v\-'-..'.;-;-,:;>/.V%''.-.'.•..'{:
IMPERVIOUS STRATUM
FIGURE C-18
MOUND DEVELOPMENT FOR CIRCULAR RECHARGE AREA
RADIUS OF CIRCULAR
SPREADING GROUNDS
SURFACE OF SPREADING BASIN
UNDISTURBED GROUNDWATER
SURFACE
IMPERVIOUS STRATUM
~ W ^r
C-36
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C.5.2 Data Requirements
Before proceeding with any analysis, a good deal of data must be
collected. The following list of input information requirements is
abstracted from the work of Baumann [39] and Parizek [20]. Pertinent
comments by other investigators are included where appropriate to
provide additional insight or clarification.
1. Coefficients of vertical and horizontal permeability. If the
site is large and/or its soils heterogeneous, a spatial
distribution of these values will be needed. Klute [40] and
Papadopulos et al. [41] both stress the need for extensive
rather than intensive methods of characterization, and
meaningful average conductivity functions, together with
probability statements as to deviations from the mean value.
2. Specific yield (drainable porosity) of deposits saturated or
dewatered by water table fluctuations.
3. Vertical distances between initial groundwater surface and
ground surface, and between initial groundwater surface and
impervious stratum.
4. Slope of impervious strata.
5. Horizontal distance to a control or discharge surface.
6. Geometry of recharge area.
7. Rate and duration of spreading (infiltration). Although most,
if not all, of the analytic expressions assume a steady supply
(constant vertical percolation), Childs has shown that seepage
of a series of intermittent recharges is equivalent to that of
a single steady application [42].
8. Estimates of the evapotranspiration losses for the areas where
groundwater tables will be near the surface.
C.5.2.1 Drainable Voids
The term drainable voids is synonymous with the term "specific yield"
used in water well technology. It is the ratio of water that will drain
freely from the materials to the total volume of the materials. It may
be estimated from data on similar soils (Table C-5), or more preferably,
it may be evaluated in the laboratory from soil moisture data at
saturation and 0.3 bar tension on undisturbed soil fragments.
C-37
-------
TABLE C-5
APPROXIMATE DRAINABLE VOIDS FOR MAJOR SOIL
CLASSIFICATIONS
Material Porosity, %
Clay
Sand
Gravelly sand
Gravel
45
35
20
25
Drainable
voids, %
3
25
16
22
In some areas of the United States, the SCS has investigated the soil
profile sufficiently to provide a reasonable estimate of drainable voids
on a particular site. An outstanding reference, covering 200 typical
soils in 23 states, is the USDA Agricultural Research Service
Publication 41-144 [2]. This compendium of soil-moisture tension data
gives bulk density, total porosity, and saturated vertical permeability
values. It also gives soil moisture at 0.1, 0.3, 0.6, 3.0, and 15 bars
tension for several depths in the soil profile (down to about 4 ft or
1.2 m in many cases).
Drainable voids can be calculated as the difference between total
porosity and the volume percent of moisture at 0.3 bar tension. Other
important hydrologic computations can be made as well, using the
relationships in Holtan et al. [43]. One important factor that was not
discussed in either Reference [2] or [43] was the inherent spatial
variability of the basic measurements reported. Nielsen et al.
conducted a set of experiments on a 370 acre (150 ha) site to determine
the statistical variability of many soil properties affecting its
hydrologic behavior [44]. A few of their results, shown in Table C-6,
should be of value in developing a sensitivity for this variability.
C.5.2.2 Lateral (Horizontal) Flow
Horizontal permeability is a more difficult parameter to obtain. In
field soils, isotropic conditions are rarely encountered, although they
are frequently assumed for the sake of convenience. "Apparent"
anisotropic permeability often occurs in unconsolidated media because of
interbedding of fine-grained and coarse-grained materials within the
profile. Such interbedding restricts permeability to vertical flow much
more than it does lateral flow [25]. Although the interbedding
represents nonhomogeneity, rather than anisotropy, its effects on the
C-38
-------
permeability of a large sample of aquifer material may be approximated
by treating the "aquifer" as homogeneous but anisotropic. A
considerable amount of data is available on the calculated or measured
relationships between vertical and horizontal permeability for specific
sites. The possible spread of ratios is indicated in Table C-7, which
is based on field measurements in glacial outwash deposits (Sites 1-5)
by Weeks [45] and in a river bed (Site 6) by Bouwer [46]. Both authors
claim, with justification, that the reported values would not likely be
observed in any laboratory tests with small quantities of disturbed
aquifer material.
TABLE C-6
STATISTICAL VARIABILITY OF SEVERAL
PHYSICAL PROPERTIES OF SOIL [44]
Standard Coefficient of
Property No. of samples Mean deviation variation, %
Bulk density 720 1.356 g/cm3 0.104 g/cm3 7.7
Moisture at
saturation,
volume fraction
Moisture at
.200 cm tension
120
120
0.469
0.346
0.035
0.072
7.5
20.8
It is apparent, then, that if accurate information regarding horizontal
permeability is required for an analysis, field measurements will be
necessary. Of the many field measurement techniques available, the most
useful is the auger hole technique of Van Bavel and Kirkham [47].
Although auger hole measurements are certainly affected by the vertical
component of flow, studies have demonstrated that the technique
primarily measures the horizontal component [48]. A definition sketch
of the measurement system is shown in Figure C-19 and the experimental
setup is shown in Figure C-20. The technique is based on the fact that
if the hole extends below the water table and-water is removed from the
hole (by bailing or pumping), the hole will refill at a rate determined
by the permeability of the soil, the dimensions of the hole, and the
height of water in the hole. With the aid of either formulas or graphs,
the permeability is calculated from measured rates of rise in the hole.
The total inflow into the hole should be sufficiently small during the
period of measurement to permit calculation of the permeability based on
an "average" hydraulic head. This is usually the case.
In the formulas and graphs that have been derived, the soil is assumed
to be homogeneous and isotropic. However, a modification of the basic
technique by Maasland allows determination of the horizontal and
C-39
-------
vertical components (Kn and KV) in anisotropic soils by combining auger
hole measurements with piezometer measurements at the same depth [48].
If the auger hole terminates at (or in) an impermeable layer, the
following equation applies (refer to Figure C-19 for symbols):
Kh = 523 000 a2 (C-7)
where a = auger hold radius, m
At = time for water to rise y, s
Kh = horizontal permeability, m/d
yQ, y1.= depths defined in Figure C-19, any units, usually cm
If an impermeable layer is encountered at a great depth below the bottom
of the auger hole, the equation becomes
K _ 1 045 OOP da2 ^g^W
h " (2d + a) At(C"b)
where d = depth of auger hole, m
TABLE C-7
MEASURED RATIOS OF HORIZONTAL TO
VERTICAL PERMEABILITY
Effective horizontal
Site permeability, Kh , ft/d Kh/Kv Remarks
1
2
3
4
5
6
138
247
183
329
237
236
2.0
2.0
4.4
7.0
20.0
10.0
Silty
Gravelly
Near terminal moraine
Irregular succession of sand
and
gravel layers (from K measure-
ments in field)
282 16.0 (From analysis of recharge
flow system)
a. Sources: Data on Sites 1 through 5 [45]; data on Site 6 [46].
1 ft/d = 0.305 m/d
C-40
-------
FIGURE C-19
DEFINITION SKETCH FOR AUGER-HOLE TECHNIQUE
SOIL SURFACE
:".v'W--!v"
I
• K:''-.-:-'.!_
y
!*•".•*
1
y
0
i
;h
•*.'*•*'.
[
i
«, 2a »
^"^
WATER TABLE
_!_
^y in. At
t
1
1 in. = 2.54 cm
FIGURE C-20
EXPERIMENTAL SETUP FOR AUGER-HOLE TECHNIQUE
DOUBLE-ACTING
DIAPHRAGM PUMP
MEASURING POINT
STANDARD
EXHAUST HOSE
TAPE AND
2 in.FLOAT
STATIC WATER LEVEL
FINISH TEST
START TEST
1 in.= 2.54 cm
C-41
-------
Charts for both cases were prepared by Ernst and are available in the
text by Luthin [49]. An alternate formula, claimed to be slightly more
accurate, has been developed by Boast and Kirkham [50];. Their equation
employs a table of coefficients to account for depth of impermeable or
of very permeable material below the bottom of the hole.
There are several other techniques for evaluating horizontal
permeability in the presence of a water table. Slug tests, such as
described by Bouwer and Rice, can be used to calculate K^ from the
Thiem equation after observing the rate of rise of water in a well
following an instantaneous removal of a volume of water to create a
hydraulic gradient [51]. Certainly pumping tests, which are already
familiar to many engineers, would provide a meaningful estimate. Glover
presents a comprehensive discussion of pumping tests, as well as other
groundwater problems. He also presents example problems and tables of
the mathematical functions needed to evaluate permeability from drawdown
measurements [52].
There are two limitations to full-scale pumping tests. The first is the
expense involved in drilling and installation. Thus, if a well is not
already located on the site, the pumping test technique would probably
not be considered. If an existing production well fulfills the
conditions needed for the technique to be valid, it should probably be
used to obtain an estimate. However, this estimate may still require
modification through the use of supplementary "point" determinations,
especially if the site is very large or if the soils are quite
heterogeneous. The possibility that the pumping test will not give
results representative of the larger area is the second limitation.
Donnan and Aronovici developed a technique using a small well screen,
carefully manufactured to a set of standard specifications [53].
Because these screens have a constant and reproducible flow geometry
when inserted below the water table and pumped, standard curves prepared
by the authors could be used to compute K. from flowrate and
pressure drop data.
Measurement of horizontal and vertical permeabil ity may occasionally be
necessary in the absence of a water table. A typical case might involve
the presence of a caliche layer, or other hardpan formation near the
surface, which is restrictive enough to vertical flow to result in a
perched water table upon application of effluent. In this case,
equipment and techniques developed by Bouwer will permit the
determination [54], The required equipment is known as the Tempe Double
Tube Hydraulic Permeability Device. Water levels in the inner and outer
tube are manipulated to give as estimate of the overall permeability
which is some resultant of Kn and Kv (more of Kv ). The true
value of Kh can be evaluated by inserting piezometers in the double
tube system to measure the true Kv . Kn can then be computed.
Other methods for measuring K in absence of water table are: shallow
well pump-in method ( Kh ), air entry permeameter (Kv ) and in-
filtration gradient method ( Kv ) [4].
C-42
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C.5.3 Models for Two Geometries of Practical Concern
Two recharge area geometries can be expected to recur frequently in
practice. The first involves a rectangular area lying roughly
perpendicular to the initial direction of groundwater flow. If the
length is large relative to the width, the area can be considered a
strip and the resulting mound will be two-dimensional, as shown in
Figure C-17.
The growth and decay of the two-dimensional mound is given analytically
by both Baumann [39] and Marino [55]. Baumann based his solution on the
analogy of the flow of heat through a prismatic, nonradiating bar of
length L. with a constant heat source v at the origin (X = 0) and
constant temperature at X = Lj. The exact solution for the stable
mound at t = °o is a Fourier-series expansion; however, an approximate
solution for the mound coordinates can be obtained more simply from the
expression
(Ld -
X)
(C-9)
where v = the average infiltration rate
i = the slope of the impermeable strata, usually zero
This expression allows calculation of the mound height at either edge of
the spreading basin. The maximum height H , at the center of the
strip, would have to be estimated from the geometry and the shape of the
curve near X = 0.
If the spreading area can be readily approximated by a circle, the mound
will be three-dimensional. The absence of a circular control for
lateral flow makes the problem of defining a stable mound difficult, but
solutions are available [39, 56, 57]. Referring to the definition
sketch shown in Figure C-18, one solution for the maximum mound height
(from reference [57]) is
H=^
y
-u
1
1 - e
+ u
du
(C-10)
where u
= R2/4«t
a = Kd/y
.y = drainable
void volume
C-43
-------
and the integral above is the well-known exponential integral, values of
which are tabulated in reference [52]. Graphical solutions to the
equations of groundwater mound height analysis for several important
geometries may be found in reference [58], a publication of the USDA -
Agricultural Research Service.
C.6 Control of the Groundwater Table
The need for drainage will be established through some method of
groundwater mound height analysis or when the natural fluctuations in
the groundwater table are thought to bring it too close to the surface,
the latter being a judgment of the designer. For some large projects
that do not require a complete system of underdrainage, drainage at a
few selected locations may be required. For other projects, drainage
may be required only to prevent trespass of wastewater onto adjoining
property by subsurface flow.
The drainage design consists of selecting the depth and spacing for
placement of the drain pipes or tiles. As a frame of reference,
practical drainage systems for wastewater applications will be at depths
of 4 to 8 ft (1.2 to 2.4 m), at or in the water table, and spaced 200 ft
(60 m) or more apart. Spacing may approach 500 ft (150 m) in sandy
soils. Although closer spacings result in better control of the water
table, the cost of moving the drains closer together soon becomes
prohibitive except for a very few cases.
A definition sketch-for the use of the Hooghoudt drain spacing method is
shown in Figure C-21. The assumptions of this method are as follows
[49]:
1. The soil is homogeneous and of permeability K (horizontal
conductivity).
2. The drains are evenly spaced a distance S apart.
3. The hydraulic gradient at any point is equal to the slope of
the water table above that point.
4. Darcy's law is valid.
5. An impermeable layer underlies the drain at a depth d .
6. The rate of replenishment (wastewater application plus natural
precipitation) is v .
C-44
-------
FIGURE C-21
DEFINITION SKETCH FOR DRAIN SPACING FORMULA
APPLICATION RATE V, in./h
11111111111
SOIL SURFACE
WATER TABLE
IMPERMEABLE LAYER
1 in./h = 2.54 cm/h
Omitting all details of the derivation, the final spacing formula is
given as
S2 =
(2d + H)
(C-ll)
where H is the maximum height of water table allowable above the drains.
This equation is approximate, and several modifications are possible
and/or necessary for particular field situations. In particular, the
value of d in Equation C-ll is only equal to the actual depth when the
depth • is small. Hooghoudt developed a table of "equivalent" depths for
large values of d which are to be substituted for the actual value of d
in Equation C-ll. Curves based on Hooghoudt1s analysis are available
in Luthin's text [49]. Additional details of drainage design may be
found in Luthin and other references (see Section C.8). On occasion,
pumped wells have been used for drainage and/or recovery of renovated
effluent when the water table is too deep for the use of horizontal
drains [46].
C-45
-------
C.7 Relationship Between Measured Hydraulic Capacity and Actual
Operating Capacity
The relationship between measured hydraulic capacity and actual
operating capacity is an extremely important subject which is
complicated by the fact that meaningful data are not generally available
for analysis. In addition, not every site is hydraulically limited; in
fact, most sites probably are not. In many cases, loadings are
controlled by management approaches, nitrogen loadings, or other
factors. However, for sites that receive relatively low organic
loadings (say less than 200 lb/acre-d [224 kg/ha-d] of BOD) and that
have no other limiting factors, it would be significant to know the
relationship between the highest hydraulic loadings that did not cause
problems and the original infiltration rates measured on the soils
before the initial applications of wastewater began. Data from several
systems are summarized in Table C-8, but they are from a very limited
cross-section of soil types and wastewater characteristics, so it would
be inappropriate to draw general conclusions from them. More data of
this type are required before a meaningful pattern can emerge. As can
be seen from the footnotes, only two of the systems are being loaded at
or near their maximum acceptance rate in the absence of any other known
constraints. Such situations make data interpretation very difficult.
At present, it appears that loadings in the range of 5 to 25% of the
measured infiltration rate will generally produce a satisfactory result
in terms of system hydraulics, no other constraints existing. Operating
rates reported in Table C-8 are calculated using total cycle times,
including the time allowed for resting and drying. One further point of
interest is the hydraulic loading for the Flushing Meadows project which
averages about 25% of potential infiltration. It is believed that this
may be the peak value (as a percentage) attainable anywhere because of
the nearly ideal conditions at the Phoenix test site [24],
TABLE C-8
SUMMARY OF MEASURED INFILTRATION RATES AND OPERATING
RATES FOR SELECTED LAND APPLICATION SYSTEMS [59]
System Soil texture
type class' Type of wastewater
Slow rate Silt loam Steam peel potato
Slow rate Loam Secondary effluent meat packing
Slow rate Silt loam Secondary municipal
Rapid infiltration Sand Oily cooling water
Rapid infiltration Gravelly sand Secondary kraft mill
Rapid infiltration Loamy sand Secondary kraft mill
Rapid infiltration Sand gravel Secondary municipal
a. Limited by poor drainage (high water table).
b. Limited arbitrarily to irrigate larger acreage for hay production
c. Limited by nitrogen loading considerations.
d. Limited by organic loading (biological clogging problems).
Infiltration
rate I, in./h
0.8-0.9
0.8-2.10
0.2-0.3
9.0-14.4
28.0-55.0
1.5-9.7
8.8-11.8
Operating
rate v , in./h
0.03a
0.03b
0.01C
2.8
0.29d
0.1 9d
0.55
v/I, %
03.4
1.4-3.8
4.0
19.0-31.0
0.5-1.0
2.0-12.7
4.6-6.2
1 in./h = 2.54 cm/h
C-46
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C.8 References
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C-51
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APPENDIX D
PATHOGENS
D.I Introduction
Because land treatment must be compared equitably to conventional
wastewater discharge systems in facilities planning, a need exists to
evaluate the relative health risks associated with land treatment versus
conventional systems. Unfortunately, there are few data on this aspect.
Since the level of enteric disease in the United States is relatively
low, wastewater in the United States would be expected to contain low
levels of pathogens compared with that in many regions of Asia, Africa,
and South America. However, the continual occurrence of waterborne
disease caused by wastewater-contaminated water in the United States [1]
indicates that sufficient numbers of pathogens are present to be a
public health concern.
D.2 Relative Public Health Risk
Sufficient data are not available to show whether or not land treatment
is a greater health risk than conventional treatment and discharge
systems. The paucity of information available on disease caused by
wastewater treatment processes may reflect either the absence of a
problem, lack of intensive surveillance, or the insensitivity of present
epidemiological tools to detect recurrent small-scale incidents of
disease. It should be emphasized, however, that no incidents of disease
have been documented from a planned and properly operated land treatment
system. Comparative epidemiological studies on human populations
associated with conventional as well as land treatment systems are
needed to provide sufficient and reliable data on which regulations
could be based. Thus, evaluation of potential health hazards must rest
on our knowledge of the occurrence of pathogens in wastewater and their
fate during land treatment.
D.3 Pathogens Present in Wastewater
A large variety of disease-causing microorganisms and parasites are
present in domestic wastewater. These include pathogenic bacteria,
viruses, protozoa, and parasitic worms. The number of individual
species of pathogens is high. For example, over 100 different types of
viruses are known to be excreted in human feces. The relative
concentrations of these pathogens are highly variable, being dependent
on a number of complex factors, but pathogens are almost always present
in untreated wastewater in sufficient numbers to be a public health
concern. Thus, it is necessary to identify and put into perspective any
potential routes of disease transmission involved in land treatment as
D-l
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well as conventional treatment of wastewater so that appropriate
safeguards can be assured. It is also necessary to identify the
relative risk of infection for humans and animals from these and other
sources.
Most of the studies reported in this appendix involve applications of
untreated wastewater (often simply referred to as wastewater) to the
land in an unplanned manner, or deliberate artificial seeding of
bacteria or viruses in high concentrations to the soil to determine
their survival or movement under various conditions. Because each study
had different objectives, types of soil, climatic factors, types of
organisms, and methods of detection, the results must be interpreted
accordingly. In citing a particular study for purposes of establishing
safeguards or standards, all of the conditions relevant to that study
should be defined. In general, safeguards should be established on a
case-by-case basis so that the relative risk of disease transmission in
each situation can be evaluated individually.
D.3.1 Bacteria
The most common bacterial pathogens found in wastewater include strains
of Salmonella, Shigella, enteropathogenic Escherichia coli (E. coli),
Vibrio, and Mycobacterium. The genus Salmonella includes over 1 200
different strains, many of which are pathogenic for both man and
animals. Members of this group are commonly isolated from wastewater
and polluted receiving waters. Salmonella typhi has been responsible
for incidents of typhoid fever associated with wastewater-contaminated
drinking water [1] and with the eating of raw vegetables grown on soil
fertilized with untreated wastewater [2]. Other members of the group
are associated with paratyphoid fever and acute gastroenteritis.
Shigella organisms are the most commonly identified cause of acute
bacterial diarrhea! disease in the United States [3]. Waterborne spread
of the organisms can cause outbreaks of shigellosis, commonly known as
bacillary dysentery, which occur frequently in undeveloped countries and
occasionally in developed countries. Unlike Salmonella. Shi gel!a
organisms are rarely found in animals other than man.
Cholera is caused by the organism Vibrio cholerae. In Israel in 1970
cases of cholera were attributed to the practice of irrigating vegetable
crops with untreated wastewater. This practice is contrary to
regulations of the Ministry of Health [4], There were no reported cases
of cholera in the United States between 1911 and 1973, until a single
case occurred in Texas with no known source. Though individual cases of
cholera may arise in international travelers, the likelihood of cholera
being transmitted by wastewater land application projects is minimal.
D-2
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D.3.2 Viruses [5]
Viruses, the smallest wastewater pathogens, consist of a nucleic acid
genome enclosed in a protective protein coat. Viruses that are shed in
fecal matter, referred to as enteric viruses, are characterized by their
ability to infect tissues in the throat and gastrointestinal tract, but
they are also capable of replicating in other organs of the body. They
include the true enteroviruses (polio-, echo-, and coxsackieviruses),
reoviruses, adenoviruses, and rotaviruses, as well as the agent of
infectious hepatitis. These viruses can cause a wide variety of
diseases, such as paralysis, meningitis, respiratory illness,
myocarditis, congenital heart anomalies, diarrhea, eye infections, rash,
liver disease, and gastroenteritis. Almost all of these viruses also
produce inapparent or latent infections. This makes it difficult to
recognize them as being waterborne. Documented cases of waterborne
viral disease have largely been limited to infectious hepatitis, mainly
because of the explosive nature of the cases and the characteristic
nature of the disease.
Knowledge of the actual number and concentration of human pathogenic
viruses in wastewater is inadequate, due to lack of adequate and
standardized sampling and analytical procedures. Furthermore, the
methodology for detecting and monitoring many of these agents has not
yet been developed. This probably accounts for the fact that almost 60%
of all documented cases of disease attributable to drinking water in the
United States has been reported to be caused by agents as yet not
isolated in the laboratory. The lack of documentation reflects the
difficulty in sampling an infectious agent in the carrier at the time of
reported illness. It must be borne in mind that viruses as a group are
generally more resistant to environmental stresses and chlorination than
pathogenic bacteria.
Also present in wastewater are large numbers of bacterial viruses known
as bacteriophages. These viruses are not pathogenic for man, but they
have been studied as models for animal virus behavior because of the
ease with which they can be detected. However, it should not be assumed
that all studies using bacteriophages can be directly applied to human
pathogenic viruses.
D.3.3 Other Pathogens
Protozoans pathogenic to man and capable of transmission in wastewater
are Entamoeba histolytica, the agent of amoebic dysentery; Naegleria
gruberi, which may cause fatal meningoencephalitis; and Giardia Iambi a,
which produces a variety of intestinal symptoms. Waterborne cases of
Giardia lamblia have increased in the United States in recent years [1].
D-3
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The eggs of several intestinal parasitic worms have been found in
wastewater and have been shown to be a potential health problem to
wastewater treatment plant operators and laborers employed on farms in
India and East Germany where untreated wastewater is used for irrigation
[6]. Modern water treatment methods have proved a very effective
barrier against the waterborne spread of disease caused by protozoa and
parasitic worms in developed countries, like the United States.
D.3.4 Concentrations of Pathogens in Wastewater
Evaluation of the relative risk of disease transmission associated with
land application of wastewater requires knowledge of the number of
pathogens in untreated and treated wastewater, as well as the number
necessary to cause an infection in man or other animals. Unfortunately,
data on the removal efficiency of all wastewater treatment methods for
many pathogens are either nonexistent or largely based on laboratory
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