EPA 625/1-81-013
(COE EM1110-1-501)
PROCESS DESIGN MANUAL
FOR
LAND TREATMENT OF
MUNICIPAL WASTEWATER
U. S. ENVIRONMENTAL PROTECTION AGENCY
U. S. ARMY CORPS OF ENGINEERS
U. S. DEPARTMENT OF INTERIOR
U. S. DEPARTMENT OF AGRICULTURE
October 1981
Published by
U. S. Environmental Protection Agency
Center for Environmental Research Information
Cincinnati, Ohio 45268
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ACKNOWLEDGMENTS
This manual presents the state-of-the-art on process design
for land treatment systems.; It replaces the process design
manual with the same title, published in October 1977.
Preparation of this manual was sponsored by the U.S.
Environmental Protection Agency (EPA), Office of Research
and Development, and Office of Water; the U.S. Army Corps of
Engineers; the U.S. Department of the Interior (USDI), Office
of Water Research and Technology; and the U.S. Department,
Of Agriculture (USDA), Office of Environmental Quality and
Farmers Home Administration. An interagency,coordinating
committee representing these sponsors was established; this
committee then selected a team of contract authors. Contract
administration was provided' by EPA CERI, Cincinnati, Ohio.
PROJECT OFFICER; Dr. James;E. Smith Jr., EPA, CERI.
Dr. Smith was also chairman'of the interagency coordinating
committee. Assistance in contract administration was
provided by Enviro Control, Inc., under the direction of
Mr. Torsten Rothman. j
CONTRACTOR; Metcalf & Eddyi, Inc. , Sacramento, California.
Supervision and Principal Authors;
Ronald W. Crites, Project!Manager,
E.L. Meyer and R.G. Smith!
Staff Authors; »
M. Walker, K. Alston, M. Alpert, C. Stein
Editing and Review; | .-. , ,
F. Burton, J. Miller, C. Pound
Consultant Authors; ' .-••.. • •. •.
Dr. A. Wallace, University of Idaho; Dr. W. Nutter,
University of Georgia; Mr^. D. Hinrichs, Culp/Wesner/
Gulp; Mr. B. Whitson, Mr. ; D. Deemer, Dr. Q-. Aly, arid
Mr. L. Gilde, Campbell SoUp Company; Dr. E. Myers,
Williams & Works, Inc.; Mr. D. Hirschbrunner and
Ms. D. Parkes, Bruce Gilmore & Associates, Inc.
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ACKNOWLEDGMENTS
II
A technical workgroup composed of members from the spon-
soring agencies, as well as other invited experts, was
formed. In addition, a rnultidisciplinary group of engineers
and scientists also furnished technical review. Under the
direction of its chairman, the workgroup defined the scope
of the effort, supervised the work of the contractor, re-
viewed the manual, and provided technical editing and input
to the manual.
CHAIRMAN; Sherwood C. Reed, USA CRREL '
WORKGROUP;
EPA:
U.S. Army:
US DA:
USDI:
USDOE:
NSF:
Mr.
Dr.
Mr.
Dr.
Dr.
Mr.
Mr.
Mr.
Dr.
Mr.
Mr.
Dr.
Mr.
Dr.
Mr.
Mr.
Ms.
Dr.
R
C
R
N
C
W
N
W
I
J
M
S
P
H
R
.R
B
E
E. Thomas, Dr. J.E. Smith Jr.,
Harlin, Mr. W. Whittington,
Bastian, Dr. H. Thacker,
Kowal, Mr. R. Dean, Mr. J. Ariail,
Enfield, Mr. J. Roesler,
Huang, Mr. J. Smith
Urban, Mr. D. Lament,
Medding, Mr. P. Carmichael,
Iskandar, Mr. J. Martel,
Bouzoun, Dr. R. Lee,
Cullinane, Mr. J. Bauer,
Schaub, Dr. H. McKim
Smith, Mr. C. Rose, Mr. G. Deal,
Bouwer, Mr. W. Opfer, Dr. D. Urie,
Phillips, Dr. D. Clapp
Madancy
Broomfield
Bryan
Academic Institutions and Stalbe Agencies:
Dr. M. Kirkham, Dr. E., Lennette, Dr. W. Sopper,
Dr. R. Smith, Dr. A. Overman, Dr. R. Abernathy,
Dr. M. Overcash, Dr. A. Erickson, Mr. D. Kendrick
Invited Technical Reviewers;
Mr. B. Seabrook, Mr. T. Jenkins, Mr. J. Kreissl,
Mr. A. Palazzo, Dr. E.. Smith, Ms. H. Farquhar,
Dr. R. Lewis, Dr. T. Asano, Mr. T. Rothman,
Mr. R. Sletten, Mr. G, Abele
111
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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 discussed in detail, and the design concepts
and criteria are presented;, A two-phased planning approach
to site investigation and selection is also presented.
The manual includes examples of each process design.
Information on field investigations is presented along with
special considerations for small scale systems. Equations
and procedures are included to allow calculations of energy
requirements for land treatment systems. Potential health
and environmental effects and corresponding mitigation
measures are discussed.
IV
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CONTENTS
Chapter
ACKNOWLEDGMENTS I
ACKNOWLEDGMENTS II .
ABSTRACT , •
CONTENTS , . .,.
FIGURES
TABLES
INTRODUCTION AND PROCESS CAPABILITIES
1.1 Purpose ....,.*.•.•,
1.2 Scope
1. 3 Treatment Processes
1.4 Slow Rate Process
1.4.1 Process Objectives
1.4.2 Treatment Performance
1.5 Rapid Infiltration
1.5.1 Process Objectives
1.5.2 Treatment Performance
1.6 Overland Flow
1.6.1 Process Objectives
1.6.2 Treatment Performance
1.7 Combination Systems
1.8 Guide to Intended Use of the Manual
1.9 References
PLANNING AND TECHNICAL ASSESSMENT
2.1 Planning Procedure
2.2 Phase 1 Planning
2.2.1 Preliminary Data
2.2.2 Land Treatment System Suitability
2.2.3 Land Area Requirements
2.2.4 Site Identification
2.2.5 Site Screening
2.3 Phase 2 Planning
2.3.1 Field Investigations
2.3.2 Selection of Preliminary
Design Criteria
2.3.3 Evaluation of Alternatives
2.3.4 Plan Selection
2.4 Water Rights and Potential Water
Rights Conflicts
2.4.1 Natural Watercourses
2.4.2 Surface Waters
2.4.3 Percolating Waters (Ground Waters)
2.4.4 Sources of Information
2.5 References
Page
ii
iii
iv
v
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xviii
1-1
1-1
1-2
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1-8
1-8
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1-13
1-13
1-14
1-14
1-17
2-1
2-1
2-1
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2-16
2-22
2-27
2-27
2-27
2-29
2-34
2-34
2-35
2-37
2-37
2-38
2-38
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CONTENTS (Continued)
Chapter , Page
3 FIELD INVESTIGATIONS 3-1
3.1 Introduction 3-1
3.2 Physical Properties 3-1
3.2.1 Shallow Profile Evaluation 3-3
3.2.2 Profile Evaluation to
Greater Depths 3-4
3.3 Hydraulic Properties 3-4
3.3.1 Saturated Hydraulic Conductivity 3-5
3.3.2 Infiltration Capacity 3-6
3.3.3 Specific Yield 3-8
3.3.4 Unsaturated Hydraulic Conductivity 3-8
3.3.5 Profile Drainage 3-10
3.4 Infiltration Rate Measurements 3-10
3.4.1 Flooding Basin Techniques 3-13
3.4.2 Cylinder Infiltrometers 3-17
3.4.3 Sprinkler Infiltrometers 3-20
3.5 Measurement qf Vertical Hydraulic
Conductivity ( 3-22
3.5.1 Double-Tube Method 3-24
3.5.2 Air Entry Permeameter 3-24
3.6 Ground Water 3-27
3.6.1 Depth/Hydrostatic Head 3-28
3.6.2 , Flow 3-30
3.6.3 Ground Water Quality 3-36
3.7 Soil Chemical Properties 3-36
3.7.1 Interpretation of Soil
Chemical Tests 3-37
3.7.2 Phosphorus Adsorption Test • 3-38
3.8 References i 3-39
i
t
4 SLOW RATE PROCESS bESIGN
4.1 Introduction 4-1
4.2 Process Perfqrinance 4-1
4.2.1 BOD and Suspended Solids Removal 4-1
4.2.2 Nitrogen 4-3
4.2.3 Phosphorus 4-5
4.2.4 Trace ;Elements 4-7
4.2.5 Microorganisms 4-7
4.2.6 Trace Organics 4-10
4.3 Crop Selection 4-11
4.3.1 Guidelines for Crop Selection 4-11
4.3.2 Crop Characteristics 4-15
4.4 Preapplication Treatment 4-24
4.4.1 Preapplication Treatment for
Storage and During Storage 4-25
4.4.2 Preapplication Treatment to
Protect Distribution Systems 4-27
VI
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CONTENTS (Continued)
Chapter Page
4.4.3 Industrial Pretreatment 4-28
4.5 Loading Rates and Land Area Requirements 4-28
4.5.1 Hydraulic Loading Rate Based
on Soil Permeability 4-28
4.5.2 Hydraulic Loading Rate Based
on Nitrogen Limits 4-30
4.5.3 Hydraulic Loading Rate Based
on Irrigation Requirements 4-34
4.5.4 Land Area Requirements 4-35
4.6 Storage Requirements 4-37
4.6.1 Estimation of Volume Requirements
Using Storage Water Balance
Calculations 4-37
4.6.2 Estimated Storage Volume
Requirements Using Computer
Programs 4-39
4.6.3 Final Design Storage Volume
Calculations ' 4-41
4.6.4 Storage Pond Design Considerations 4-43
4.7 Distribution System 4-44
4.7.1 Surface Distribution Systems 4-44
4.7.2 Sprinkler Distribution Systems 4-45
4.7.3 Service Life of.Distribution
System Components 4-53
4.8 Drainage and Runoff Control 4-53
4,. 8.1 Subsurface Drainage Systems 4-53
4.8.2 Surface Drainage and Runoff Control 4-56
4.9 System Management 4-58
4.9.1 Soil Management 4-58
4.9.2 Crop Management 4-61
4.10 System Monitoring • 4-64
4.10.1 Water Quality Monitoring 4-65
4.10.2 Soils Monitoring 4-65
4.10.3 Vegetation Monitoring 4-66
4.11 Facilities Design Guidance ', 4-66
4.12 References 4-68
5 RAPID INFILTRATION PROCESS DESIGN
5.1 Introduction 5-1
5.1.1 RI Hydraulic Pathway 5-1
5.1.2 Site Work ' . ' 5-1
5.2 Process Performance 5-3
5.2.1 BOD and Suspended Solids 5-3
5.2.2 Nitrogen .' 5-3
5.2.3 Phosphorus 5-5
5.2.4 Trace Elements 5-6
5.2.5 Microorganisms 5-8
5,2.6 Trace Organics 5-9
VII
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CONTENTS (Continued)
Chapter
5.3 Determination of Preapplication
Treatment Level
5.3.1 EPA Guidance
5.3.2 Water! Quality Requirements
and Treatment Goals
5.4 Determination; of Hydraulic
Loading Rate j
5.4.1 Measured Hydraulic Capacity
5.4.2 Selection of Hydraulic Loading
Cycle and Application Rate
5.4.3 Other;Considerations
5.5 Land Requirements
5.5.1 Infiltration Basin Area
5.5.2 Preapplication Treatment
Facilities
5.5.3 Other:Land Requirements
5.6 Infiltration System Design
5.6.1 Distribution and Basin Layout
5.6.2 Storage and Flow Equalization
5.6.3 • Cold Weather Modifications
5.7 Drainage i , .
5.7.1 Subsurface Drainage to
Surface Waters
, 5.7.2 Ground Water Mounding
5.7.3 Underdrains
5.7.4 Wells1
5.8 Monitoring and Maintenance Requirements
5.8.1 Monitoring
5.8.2 Maintenance
5.9 Design and Construction Guidance
5.10 References i . .
[
OVERLAND FLOW PROCESS DESIGN
6.1 Introduction !
6.1.1 Site Characteristics and
Evaluation"
6.1.2 Water Quality Requirements
6.1.3 Design and Operating Parameters
6.2 Process Performance
6.2.1 BOD Removal
6.2.2 Suspended Solids Removal
6.2.3 Nitrogen Removal
6.2.4 Phosphorus Removal
6.2.5 Trace Element Removal
6.2.6 Mircroorganism Removal
6.2.7 Trace Organics Removal
6.2.8 Effect of Rainfall
Page
5-10
5-10
5-10
5-12
5-12
5-14
5-17
5-22
5-22
5-22
5-22
5-23
5-23
5-27
5-27
5-28
5-28
5-30
5-38
5-42
5-42
5-42
5-44
5-45
5-46
6-1
6-1
6-1
6-3
6-3
6-3
6-6
6-6
6-8
6-8
6-8
6-9
6-9
Vlll
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CONTENTS (Continued)
Chapter Page
6.2.9 Effect of Slope Grade 6-10
6.2.10 Performance During Startup 6-10
6.3 Preapplication Treatment, 6-10
6.4 Design Criteria Selection . 6-11
6.4.1 Hydraulic, Loading Rate 6-12
6.4.2 Application Rate 6-12
6.4.3 Application Period 6-13
6.4.4 Application Frequency 6-14
6.4.5 Constituent Loading Rates 6-14
6.4.6 Slope Length 6-14
6.4.7 Slope Grade 6-15
6.4.8 Land Requirements 6-15
6.5 Storage Requirements 6-18
6.5.1 Storage Requirements for
Cold Weather 6-18
6.5.2 Storage for Stormwater Runoff 6-19
6.5.3 Storage for Equalization 6-21
6.6 Distribution 6-22
6.6.1 Surface Methods 6-22
6.6.2 Low Pressure Sprays 6-24
6.6.3 High Pressure Sprinklers 6-25
6.6.4 Buried Versus Aboveground Systems 6-27
6.6.5 Automation . • 6-27
6.7 Vegetative Cover 6-27
6.7.1 Vegetative Cover Function 6-27
6.7.2 Vegetative Cover Selection 6-28
6.8 Slope Construction 6-28
6.8.1 System Layout 6-28
6.8.2 , Grading Operations 6-29
6.8.3 Seeding and Crop.Establishment 6-29
6.9 Runoff Collection 6-31
6.10 System Monitoring and Management 6-32
6.10.1 Monitoring 6-32
6.10.2 System Management . : :/ , 6-32
6.11 Alternative Design Methods 6-34
6.11.1 CRREL Method 6-34
6.11.2 University of California,
Davis, (UCD) Method ' 6-36
6.11.3 Comparison of Alternative Methods 6-38
6.12 References 6-39
7 SMALL SYSTEMS
7.1 Introduction . 7-1
7.2 Facility Planning 7-1
7.2.1 Process Considerations 7-1
7.2.2 Site Selection 7-5
7.2.3 Site Investigations 7-8
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CONTENTS! (Continued)
i •
Chapter j Page
i
7.3 Facility Design 7-9
7.3.1 Preapplication Treatment
and Storage 7-9
7.3.2 Hydraulic Loading Rates 7-10
7.3.3 Land Area Requirements 7-15
7.3.4 Distribution Systems 7-16
7.4 Typical Small Community Systems 7-17
7.4.1 Slow Rate Forage System 7-17
7.4.2 Slow Rate Forest System 7-22
7.4.3 Rapid; Infiltration 7-26
7.4.4 Overland Flow 7-30
7.5 References 7-31
8 ENERGY REQUIREMENTS! AND CONSERVATION
8.1 Introduction 8-1
8.2 Transmission Pumping 8-2
8.3 General Process Energy Requirements 8-4
8.3.1 Slow Rate 8-4
8.3.2 Rapid; Infiltration 8-4
8.3.3 Overland Flow 8-5
8.4 Energy Conseryation 8-6
- 8.4.1 Areas of Potential Energy Savings 8-6
8.4.2 Example: Energy Savings in
Slow Rate Design 8-8
8.4.3 Summary 8-10
8.5 Procedures for Energy Evaluations 8-10
8.5.1 Slow Rate 8-11
8.5.2 Rapid Infiltration 8-12
8.5.3 Overland Flow 8-13
8.5.4 Examples 8-13
8.6 Equations for Energy Requirements 8-16
8.6.1 Preapplication Treatment 8-17
8.6.2 Land Treatment Processes 8-18
8.7 References \ 8-18
HEALTH AND ENVIRONMENTAL EFFECTS
9.1 Introduction
9.2 Nitrogen
9.2.1 Crops!
9.2.2 Ground Water
9.2.3 Surface Water
9.3 Phosphorus
9.3.1 Soils
9.3.2 Crops;
9.3.3 Ground Water
9.3.4 Surface Water
9-1
9-3
9-4
9-4
9-4
9-5
9-5
9-5
9-5
9-5
x
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CONTENTS (Continued)
Chapter
Appendix
B
9.4 Dissolved Solids
9.4.1 Soils
9.4.2 Crops
9.4.3 Ground Water
9.5 Trace Elements
9.5.1 Soils
9.5.2 .Crops
9.5.3 Ground Water
9.6 Microorganisms
9.6.1 Soils
9.6.2 Crops
9.6.3 Ground Water
9.6.4 Surface Water
9.6.5 Aerosols
9.7 Trace Organics
9.7.1 Soils,
9.7.2 Crops
9.7.3 Ground Water
9.7.4 Surface Water
9.8 References
SLOW RATE DESIGN EXAMPLE
A.I Introduction
A.2 Statement of Problem
A. 2.1 Background
A.2.2 Population and Wastewater
Characteristics
A.2.3 Discharge Requirements
A.2.4 Site Characteristics
A.2.5 Climate
A.3 Slow Rate System Selection
A.3.1 Preapplication Treatment
A.3.2 Crop Selection
A.4 System Design
A.4.1 Forage Crop Alternative
A.4.2 Deciduous Forest Crop Alternative
A.4.3 Selected SR Design
A.4.4 Energy Requirements
RAPID INFILTRATION DESIGN EXAMPLE
B.I Introduction
B.2 Design Considerations
B.2.1 Design Community
B.2.2 Wastewater Quality and Quantity
B.2.3 Existing Wastewater
Treatment Facilities
Page
9-5
9-5
9-6
9-6
9-8
9-8
9-9
9-11
9-12
9-13
9-14
9-16
9-16
9-17
9-21
9-21
9-22
9-22
9-23
9-24
A-l
A-l
A-l
A-l
A-l
A-2
A-2
A-4
A-4
A-5
A-5
A-5
A-22
A-28
A-28
B-l
B-l
B-l
B-l
B-2
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CONTENTS (Continued)
Appendix Page
B.2.4 Climate B-2
B.3 Site and Process Selection B-3
B.4 Site Investigations B-6
B.4.1 Soil I Characteristics B-6
B.4.2 Ground Water Characteristics B-8
B.4.3 Hydraulic Capacity B-8
B.5 Determination of Wastewater Loading Rate B-10
B.5.1 Preapplication Treatment Level B-10
B.5.2 Hydraulic Loading Rate B-10
B.5.3 Hydraulic Loading Cycle B-ll
B.5.4 Effect of Precipitation on
Wastewater Loading Rate • B-ll
B.5.5 Underdrainage B-ll
B.5.6 Nitrification B-13
B.6 Land Requirements B-13
B.6.1 Preapplication Treatment - '
Facilities i B-13
B.6.2 Infiltration Basins ! B-14
B.7 System Design B-14
B.7.1 General Requirements B-14
B.7.2 Underdrainage B-18
B.8 Maintenance and Monitoring B-18
B.8.1 Maintenance , ' B-18
B.8.2 Monitoring B-20
B.9 System Costs : • B-20
B.10 Energy Budget B-20
B.ll References . B-22
C OVERLAND FLOW DESIGN EXAMPLE
C.I Introduction C-l
C.2 Statement of ,the Problem C-l
C.3 Design Considerations C-l
C.3.1 Wastewater Characteristics
and Discharge Requirements C-l
C.3.2 Climate C-2
C.4 Site Evaluation and Process Selection C-2
C.4.1 General Site Characteristics C-2
C.4.2 Soil Characteristics C-4
C.4.3 Process Selection : C-4
C.5 Distribution^Method C-4
C.6 Preapplication Treatment C-4
C.7 Wastewater Storage C-5
C.7.1 Storage Requirement C-5
C.7.2 Storage Facility Description C-5
C.8 Selection of Design Parameters C-6
C.8.1 Hydraulic Loading Rate C-6
C.8.2 Application Period and Frequency C-6
Xll
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Appendix
D
E
CONTENTS (Continued)
; Page
C.8.3 Slope Length and Grade C-6
C.8.4 Application Rate C-7
C.8.5 Land Requirements C-7
C.9 Distribution System C-7
C.10 Preliminary System Layout C-9
C.ll System Design C-9
C.ll.l Treatment Slopes C-9
C.ll.2 Runoff Channel Design , C-9
C.ll.3 Collection Waterways C-12
C.ll.4 Pumping System C-12
C.ll.5 Monitoring and Collection System C-13
C.12 Land Requirements C-13
C.13 Cover Crop Selection C-14
C.14 System Costs C-14
C.15 Energy Budget C-15
C.16 Alternative Design Methods -
Design Example C-15
C.16.1 CRREL Method C-15
C.16.2 University of California,
Davis, Method C-17
C.16.3 Comparison of Methods C-19
C.17 References , C-19
LOCATION OF LAND TREATMENT SYSTEMS
D.I Slow Rate Systems D-l
D.2 Rapid Infiltration Systems ' D-5
D.3 Overland Flow Systems D-7
DISTRIBUTION SYSTEM DESIGN FOR SLOW RATE
E.I Introduction E-l
E.2 General Design Considerations E-l
E.2.1 Depth of Water Applied E-l
E.2.2 Application Frequency E-l
E.2.3 Application Rate E-2
E.2.4 Application Period E-2
E.2.5 Application Zone E-2
E.2.6 System Capacity E-3
E.3 Surface Distribution System1 E-4
E.3.1 Ridge and Furrow Distribution E-4
E.3.2 Graded Border Distribution E-10
E.4 Sprinkler Distribution Systems E-15
E.4.1 Application Rates E-15
E.4.2 Solid Set Sprinkler Systems E-15
E.4.3 Move-Stop Sprinkler Systems E-20
E.4.4 Continuous Move Systems E-24
E.5 References E-31
Xlll
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Appendix
CONTENTS (Concluded)
ESTIMATED STORAGE DAYS FOR LAND TREATMENT
USING EPA COMPUTER |PROGRAMS
GLOSSARY OF TERMS
CONVERSION FACTORS
Page
F-l
G-l
G-3
xiv,
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FIGURES
No. Page
1-1 Slow Rate Hydraulic Pathways , : 1-5
1-2 Rapid Infiltration Hydraulic Pathways 1-10
1-3 Overland Flow .1-12
1-4 Examples of Combined Systems 1-15
2-1 Two-Phase Planning Process 2-2
2-2 Potential Evapotranspiration Versus Mean
Annual Precipitation 2-11
2-3 Estimated Design Percolation Rate as a
Function of Soil Permeability for SR and
RI Land Treatment 2-12
2-4 Winter Operation of Rapid Infiltration
at Lake George, New York 2-14
2-5 Estimated Wastewater Storage Days Based
only on Climatic Factors 2-15
2-6 Total Land Required (Includes Land for
Application, Roads, Storage, and Buildings) 2-17
2-7 Example Area of Soil .Map to be Evaluated 2-25
2-8 Example Suitability Map for Soils
in Figure 2-7 2-26
2-9 Staffing Requirements for Land Treatment
Components (not Including Sewer System or
Preapplication Treatment) for Municipally
Owned and Operated Systems 2-33
2-10 Dominant Water Rights Doctrines and Areas
of Water Surplus or Deficiency 2-36
3-1 Flow Chart of Field Investigations 3-2
3-2 Infiltration Rate as a Function of
Time for Several Soils 3-7
3-3 Porosity, Specific Retention, and Specific
Yield Variations with Grain Size,
South Coastal Basin, California 3-9
3-4 General Relationship Between Specific Yield
and Hydraulic Conductivity 3-9
3-5 Typical Pattern of the Changing Moisture
Profile During Drying and Drainage 3-11
3-6 Flooding Basin Used for Measuring Infiltration 3-13
3-7 Groove Preparation for Flashing (Berm) 3-14
3-8 Schematic of Finished Installation 3-14
3-9 Infiltration Rate and Cumulative Intake Data Plot 3-16
3-10 Cylinder Infiltrometer in Use 3-18
3-11 Layout of Sprinkler Infiltrometer 3-21
3-12 Schematic of Double-Tube Apparatus 3-25
3-13 Schematic of Air-Entry Permeameter 3-25
3-14 Well and Piezometer Installation 3-29
3-15 Vertical Flows Indicated by Piezometers 3-30
3-16 Definition Sketch for Auger-Hole Technique 3-33
xv
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FIGURES ! (Continued)
No.
3-17
4-1
4-2
4-3
4-4
4-5
4-6
5-1
5-2
5-3
5-4
5-5
5-6
5-7
5-8
5-9
5-10
5-11
5-12
5-13
5-14
5-15
6-1
6-2
6-3
6-4
6-5
7-1
7-2
Experimental Setup for! Auger-Hole Technique
Slow Rate Design Procedure
Nitrogen Uptake Versus! Growing Days for
Annual and Perennial Crops
Determination of Storage by EPA Computer
Programs According to! Climatic Constraints
Surface Distribution Methods
Fan Nozzle Used for Spray Application at
West Dover, Vermont !
Solid Set Sprinklers with Surface Pipe
in a Forest System [
Rapid Infiltration Design Procedure
Effect of Infiltration'Rate on Nitrogen Removal
Infiltration Basin Outlet and Splash Pad
Interbasin Transfer Structure with
Adjustable Weir j
Natural Drainage of Renovated Water
Into Surface Water i
Example Design for Subsurface Flow to Surface Water
Schematic of Ground Water Mound
Mounding Curve for Center of a Square
Recharge Area |
Mounding Curve for Center of a Rectangular
Recharge Area at Different Ratios of
Length (L) to Width (W)
Rise and Horizontal Spread of Mound Below a
Square Recharge Area |
Rise and Horizontal Spread of Mound Below a
Rectangular Recharge Area Whose Length
is Twice its Width j
Centrally Located Undeirdrain
Underdrain System Using Alternating ;
Infiltration and Drying Strips
Parameters Used in Drain Design
Well Configurations
Overland Flow Design Procedure
Surface Distribution Using Gated Pipe for OF
Distribution for OF Using Low Pressure
Fan Spray Nozzles |
Alternative Sprinkler Configurations for
Overland Flow Distribution
Land Plane Used for Final Grading
Land Area Estimates for Preliminary Planning
Process (Including Land for Preapplication
Treatment)
Typical Annual Hydraulic Loading Rate of
Small SR and OF Systems
Page
3-33
4-2
4-17
4-40
4-46
4-51
4-52
5-2
5-19
5-24
5-24
5-29
5-31
5-32
5-34
5-34
5-36
5-37
5-39
5-40
5-41
5-43
6-2
6-23
6-24
6-26
6-30
7-7
7-12
xvi
-------
FIGURES (Concluded)
No.
7-3
7-4
7-5
7-6
8-1
8-2
A-l
A-2
A-3
B-l
B-2
B-3
B-4
B-5
B-6
C-l
C-2
C-3
C-4
E-l
E-2
E-3
E-4
E-5
E-6
E-7
E-8
E-9
E-10
Typical Annual Hydraulic Loading Rate of
Small SR Systems
Overflow Control Structure for Pond Discharge
to SR System
Treatment Facility Layout - Kennett Square,
Pennsylvania, SR System
SR Facilities at Kennett Square, Pennsylvania
Center Pivot System
Automatic Surface Irrigation System
Soils Map
System Layout: Forage Crop Alternative
System Layout: Forest Crop Alternative
Soils Map, Sites 1 and 2
Ground Water Contours
Intake Curves - Infiltration Basin 1
Community B Rapid Infiltration System Flowsheet
Community B Site Layout
Underdrain Location
Proposed Overland Flow Treatment Site
Typical Overland Flow Slope
Contour Map of Proposed Overland Flow
Treatment System
Overland Flow System Layout
Surface Distribution Methods
Aluminum Hydrant and Gated Pipe at
Sweetwater, Texas
Outlet Valve for Border Strip Application
Solid Set Sprinkler System
Move-Stop Sprinkler Systems
Side Wheel Roll Sprinkler System
Continuous Move Sprinkler Systems
Hose-Drag Traveling Gun Sprinkler
Center Pivot Rig
Center Pivot Irrigation System
Page
7-13
7-21
7-23
7-24
8-7
8-8
A-3
A-18
A-26
B-4
B-7
B-9
B-15
B-l 6
B-19
C-3
C-8
C-10
C-ll
E-5
E_ Q
O
E-13
E-16
E-22
E-23
E-25
E-26
E-30
E-30
ixvii
-------
TABLES
i
No. [ Page
1-1 Comparison of Typical Design Features for
Land Treatment Processes 1-3
1-2 Comparison of Site Characteristics for
Land Treatment Processes 1-3
1-3 Expected Quality of Treated Water from
Land Treatment Processes 1-4
2-1 Important Constituents; in Typical
Domestic Wastewater 2-3
2-2 Comparison of Trace Elements in Water
and Wastewaters j 2-4
2-3 Typical BOD Loading Rates 2-4
2-4 National Interim Primary Drinking
Water Standards, 197?! 2-6
2-5 Summary of Climatic Analyses 2-8
2-6 Land Use Suitability Factors for
Identifying Land Treatment Sites 2-19
2-7 Grade Suitability Factors for
Identifying Land Treatment Sites 2-19
2-8 Soil Textural Classes and General
Terminology Used in Soil Descriptions 2-21
2-9 Typical Soil Permeabilities and Textural
Classes for Land Treatment Processes 2-22
2-10 Site Selection Guidelines 2-23
2-11 Rating Factors for Site Selection 2-24
2-12 Characteristics of Soil Series
Mapped in Figure 2-7 j 2-25
2-13 Example Use of Rating Factors for Site Selection 2-26
2-14 Applicability of Recovery Systems for
Renovated Water 2-29
2-15 Lease/Easement Requirements for Construction
Grants Program Funding 2-31
2-16 Potential Water Rights'Problems for
Land Treatment Alternatives 2-37
3-1 Summary of Field Tests ifor Land
Treatment Processes 3-3
3-2 Comparison of Infiltration -Measurement Techniques 3-12
3-3 Sample Comparison of Infiltration
Measurement Using Flooding and
Sprinkling Techniques 3-12
3-4 Suggested Vertical Placement of
Tensiometers in BasiniInfiltrometer Tests 3-15
3-5 Measured Ratios of Horizontal to
Vertical Conductivity! 3-32
3-6 Interpretation of SoiliChemical Tests 3-39
4-1 BOD Removal Data for Selected SR Systems 4-3
4-2 Nitrogen Removal Data for Selected SR Systems 4-4
xvan
-------
TABLES (Continued)
No. Page
4-3 Phosphorus Removal Data for Typical SR Systems 4-6
4-4 Trace Element Behavior During SR Land Treatment 4-8
4-5 Suggested Maximum Applications of
Trace Elements to Soils Without
Further Investigations 4-9
4-6 Coliform Data for Several SR Systems 4-10
4-7 Benzene, Chloroform, and Trichloroethylene
in Muskegon Wastewater Treatment System 4-11
4-8 Relative Comparison of Crop Characteristics 4-13
4-9 Summary of Operational Forest Land Treatment
Systems in the United States Receiving
Municipal Wastewater 4-15
4-10 Height Growth Response of Selected Tree Species 4-15
4-11 Nutrient Uptake Rates for Selected Crops 4-16
4-12 Estimated Net Annual Nitrogen Uptake in the
Overstory and Understory Vegetation of Fully
Stocked and Vigorously Growing Forest
Ecosystems in Selected Regions of the
. United States 4-19
4-13 Biomass and Nitrogen Distribution by Tree
Component for Stands in Temperate Regions 4-20
4-14 Examples of Estimated Monthly Potential
Evapotranspiration for Humid and
Subhumid Climates 4-21
4-15 Consumptive Water Use and Irrigation Requirements
for Selected Crops at San Joaquin Valley,
California 4-22
4-16 Summary of Wastewater Constituents Having
Potential Adverse Effects 4-24
4-17 Water Balance to Determine Hydraulic Loading
Rates Based on Soil Permeability 4-31
4-18 Estimating of Storage Volume Requirements
Using Water Balance Calculations 4-38
4-19 Summary of Computer Programs for Determining
Storage from Climatic Variables 4-39
4-20 Final Storage Volume Requirement Calculations 4-42
4-21 Surface Distribution Methods' and
Conditions of Use 4-47
4-22 Advantages and Disadvantages of Sprinkler
Distribution Systems Relative to
Surface Distribution Systems 4-49
4-23 Sprinkler System Characteristics 4-49
4-24 Suggested Service Life for Components of
Distribution System . 4-54
4-25 Recommended Design Factors for
Tailwater Return Systems 4-57
xxx
-------
TABLES (Continued)
No. Page
4-26 Approximate Critical!Levels of Nutrients
in Soils for Selected Crops in California , 4-59
4-27 Grazing Rotation Cycles for Different
Numbers of Pasture Areas 4-62
4-28 Recommended Soil Contact Pressure 4-67
5-1 BOD Removal for Selected RI Systems 5-4
5-2 Nitrogen Removal Data for Selected RI Systems 5-5
5-3 Phosphorus Removal Data for Selected RI Systems 5-6
5-4 Comparison of Trace Element Levels to
Irrigation and Drinking Water Limits 5-7
5-5 Heavy Metal Retention in an Infiltration Basin 5-7
5-6 Fecal Coliform Removal Data for Selected
RI Systems 5-8
5-7 Reported Isolations of Virus at RI Sites 5-9
5-8 ' Recorded Trace Organic Concentrations at
Selected RI Sites ( 5-10
5-9 Suggested Preapplication Treatment Levels 5-11
5-10 Typical Hydraulic Loading Rates for RI Systems 5-13
5-11 Suggested Annual Hydraulic Loading Rates 5-14
5-12 Typical Hydraulic Loading Cycles 5-16
5-13 Suggested Loading Cycles 5-17
5-14 Minimum Number of Basins Required for
Continuous Wastewater Application 5-25
6-1 OF Design and Operating Parameters 6-3
6-2 Summary of Process Operating Parameters,
BOD and SS Performance at OF Systems 6-4
6-3 Summary of Nitrogen and Phosphorus
Performance at OF Systems 6-5
6-4 Removal Efficiencies^ Heavy Metals at
Different Hydraulic Rates at Utica, Mississippi 6-9
6-5 Overland Flow Design Guidelines 6-12
7-1 Types and Sources of Data Required for Design
of Small Land Treatment Systems 7-2
7-2 General Characteristics of Small
Land Treatment Systems 7-3
7-3 Typical Staffing Requirements at Small Systems 7-6
7-4 Recommended Level of ; Preapplication Treatment 7-9
7-5 Typical Design Parameters for Several
Types of Ponds ,7-10
7-6 Nitrogen Uptake Rates for Selected Crops 7-14
7-7 Design Information for SR System 7-19
7-8 Design Information for Chapman RI System 7-27
7-9 Wastewater Flows to Chapman RI System 7-29
7-10 Treatment Performance of Carbondale OF System 7-31
8-1 Energy Requirements for Crop Production 8-4
8-2 Most Common Unit Energy Requirements for
Land Treatment of Municipal Wastewater 8-5
xx
-------
TABLES (Continued)
No. Page
8-3 Example System Characteristics 8-8
8-4 Comparison of Conventional and Automated Ridge
and Furrow Systems for 38,000 m3/d 8-9
8-5 Comparison of Impact and Drop-Type Center Pivot
System Nozzle Designs on Energy Requirements 8-10
8-6 Total Annual Energy for Typical 3,785 m3/d System 8-11
9-1 Land Treatment Methods and Concerns 9-2
9-2 Relationship of Pollutants to Health Effects 9-2
9-3 EPA Long-Term Effects Studies 9-3
9-4 Tolerance of Selected Crops to Salinity in
Irrigation Water • 9-7
9-5 Mass Balance of Trace Elements in OF System
at Utica, Mississippi 9-9
9-6 Trace Element Content of Forage Grasses at
Selected SR Systems 9-11
9-7 Trace Element Drinking and Irrigation
Water Standards 9-12
9-8 Virus Transmission Through Soil at RI Systems 9-15
9-9 Aerosol Bacteria at Land Treatment Sites 9-18
9-10 Aerosol Enteroviruses at Land Treatment Sites 9-19
9-11 Comparison of Coliform Levels in Aerosols at
Activated Sludge and Slow Rate Land
Treatment Facilities 9-20
9-12 Trace Organics Removals During Sand Filtration 9-21
9-13 Trace Organics Removals at Selected SR Sites 9-23
9-14 Removal of Refractory Volatile Organics by
Class at Phoenix RI Site 9-23
9-15 Chloroform and Toluene Removal During OF 9-24
A-l Population and Wastewater Characteristics A-2
A-2 Climatic Data for the Worst Year in 5 A-4
A-3 Hydraulic Loading Rates .Based on Soil
Permeability: Forage Crop Alternative A-7
A-4 Design Hydraulic Loading Rate A-9
A-5 Storage Volume Determination: Forage
Crop Alternative A-11
A-6 Final Determination of Storage Volume ' A-14
A-7 Design Criteria for Storage Lagoons:
Forage Crop Alternative A-15
A-8 Slow Rate System Design Data: Forage
Crop Alternative A-19
A-9 Cost Estimate Criteria: Forage Crop Alternative A-19
A-10 Cost Estimate Calculations:
Forage Crop Alternative A-20
A-ll Summary of Costs: Forage Crop Alternative A-21
A-12 Initial Determination of Storage Volume:
Forage Crop Alternative A-23
xxi
-------
TABLES (Concluded)
i
No. Page
I
A-13 Design Data for Storage Pond: Forest
Crop Alternative A-24
A-14 Design Data: Forest JGrop Alternative A-25
A-15 Summary of Cost: Deciduous Forests A-27
B-l Projected Wastewater [Characteristics B-l
B-2 Surface Water Discharge Requirements B-2
B-3 Average Meteorological Conditions B-3
B-4 General Soil Characteristics: Sites 1 and 2 B-5
B-5 Typical Log of Test Hole B-6
B-6 Ground Water Quality B-8
B-7 Cost of Community B R± System B-21
C-l Raw Wastewater Characteristics C-l
C-2 Average Meteorological Conditions C-2
C-3 Storage Requirements ; C-5
C-4 Land Requirements | C-13
C-5 Cost of Community C OF System C-l4
E-l Optimum Furrow Spacing E-6
E-2 Suggested Maximum Lengths of Cultivated Furrows
for Different Soils,; Grades, and Depths of
Water to be Applied E-6
E-3 Design Guidelines for Graded Border Distribution,
Deep Ro'oted Crops E-ll
E-4 Design Guidelines for Graded Border Distribution,
Shallow Rooted Crops E-ll
E-5 Recommended Reductions in Application Rates
Due to Grade E-l5
E-6 Recommended Spacing o|f Sprinklers E-18
E-7 Factor (F) by Which Pipe Friction Loss is
Multiplied to Obtain Actual Loss in a Line
with Multiple Outlets E-l9
E-8 Recommended Maximum Lane Spacing for
Traveling Gun Sprinklers E-28
F-l Storage Days Using EPA-1 for 20 Year (5%)
and 10 Year (10%) Return Intervals F-l
F-2 Storage Days Using EPA-2 for 20 Year (5%)
and 10 Year (10%) Return Intervals F-2
F-3 Storage Days Using EPA-3 for 20 Year (5%)
and 10 Year (10%) Return Intervals F-3
xxiz
-------
CHAPTER 1
INTRODUCTION AND PROCESS CAPABILITIES
1.1 Purpose
The purpose of this manual is to provide criteria and
supporting information for planning and process design of
land treatment systems. Recommended procedures for planning
and design are presented along with state-of-the-art
information on treatment performance, energy considerations,
and health and environmental effects.
Cost curves are not included in this manual, although some
cost information is . included in Chapter 2. Costs for
planning may be obtained from cost curves in references [1,
2] , or through the CAPDET computer system developed by the
Corps of Engineers for EPA. CAPDET computer terminals are
available in EPA regional offices.
This document is a revision of the Process Design Manual
for Land Treatment of Municipal Wastewater sponsored by the
U.S. Environmental protection Agency, U.S. Army Corps of
Engineers, and U.S. Department of Agriculture, and published
in 1977. The revision is necessary because of the large
amount of research data, criteria, and operating experience,
that has become available in recent years. As a result of
PL 92-500 and PL 95-217, the interest in and use of land
treatment concepts has increased significantly and is
expected to continue to increase.
1.2 Scope
Land treatment is defined as the controlled application of
wastewater onto the land surface to achieve a designed de-
gree of treatment through natural physical, chemical, and
biological processes within the plant-soil-water matrix.
The scope of this manual is limited to the three major land
treatment processes:
• Slow rate (SR)
• Rapid infiltration (RI)
• Overland flow (OF)
These processes are defined later in this chapter and dis-
cussed in detail in the design chapters. The titles were
adopted for the original 1977 manual to reflect the rate of
1-1
-------
wastewater application a'nd the flow path within the
process. Prior to the 19j?7 manual, the term "irrigation"
was often used to describe the slow rate process. The pre-
sent term was chosen to focus attention on wastewater treat-
ment rather than on irrigation of crops.
Subsurface systems, wetlands, and aquaculture were discussed
briefly in the 1977 manual but are deleted here since they
are now covered in detail in other documents [3, 4]. Land
application of sludge, injection wells, evaporation ponds,
and other forms of treatment or disposal that involve the
soil matrix are also excluded.
I
Most of the information in this manual is applicable to
medium-to-large systems. | For small systems, up to
1,000 m^/d (250,000 .gal/d) , many of the design procedures
can be simplified. Special considerations for these small
systems and a number of typical examples are discussed in
Chapter 7. Case studies for larger systems are available in
other publications [5-9]. This manual addresses land
treatment of municipal wastewater, not industrial wastes.
Under controlled conditions, however, land treatment of many
types of industrial wastewaters and even hazardous materials
can be both technically and economically feasible.
Although the principal focus in the manual is on the three
basic processes (SR, RI, OF), the possibility of combining
two or more of the concepts in a continuous system should
not be overlooked. Overland flow could be a preapplication
step for either SR or RI, or different processes could be
used in cold and warm weather.
1.3 Treatment Processes ;
Typical design features for the three land treatment
processes are compared in Table 1-1. The major site charac-
teristics are compared for each process in Table 1-2. These
are desirable characteristics and not limits to be adhered
to rigorously, as discussed in Chapter 2.
The expected quality of treated water for biochemical oxygen
demand (BOD), suspended solids (SS), nitrogen, phosphorus,
and fecal coliforms is presented for each process in
Table 1-3. The average and expected upper range values are
valid fpr the travel distances and applied wastewater as
indicated. The fate off these materials (plus metals,
viruses, and trace organics) is discussed in the chapters
that follow.
1-2
-------
TABLE 1-1
COMPARISON OF TYPICAL DESIGN FEATURES
FOR LAND TREATMENT PROCESSES
Feature
Slow rate
Rapid infiltration Overland flow
Application techniques
Annual loading
rate, m
Field area
required, hab
Typical weekly
Sprinkler
or surfacea
0.5-6
23-280
1.3-10
Usually surface
6-125
3-23
10-240
Sprinkler or
surface
3-20
6.5-44
6-40°
loading rate, cm
Minimum preapplication
treatment provided in
the United States
Disposition of
applied wastewater
Need for vegetation
Primary
sedimentation0
Primary
sedimentation6
Evapotranspiration Mainly
and percolation percolation
Required
Optional
Grit removal and
comminution6
Surface runoff and.
evapotranspiration
with some
percolation
Required
a. . Includes ridge-and-furrow and border strip.
b. Field area in hectares not including buffer area, roads, or ditches for
3,785 m3/d (1 Mgal/d) flow.
c. Range includes raw wastewater to secondary effluent, higher rates for higher
level of preapplication treatment.
d. With restricted public access; crops not for direct human consumption.
e. With restricted .public access.
Note: See Appendix G for metric conversions.
TABLE 1-2
COMPARISON OF SITE CHARACTERISTICS
FOR LAND TREATMENT PROCESSES
Slow rate
Rapid infiltration
Overland flow
Grade
Soil
permeability
Depth to
ground water
Climatic
restrictions
Not critical; excessive
grades require much
earthwork
Less than 20% on-
cultivated land;
less than 40% on '
noncultivated land
Moderately slow to Rapid (sands, sandy loams)
moderately rapid
0.6-1 m (minimum)13 .1 m during flood cycleb;
1.5-3 m during drying cycle
Storage often
needed for cold
weather and during
heavy precipitation
None (possibly modify
operation in cold weather)
Finish slopes 2-8%°
Slow (clays, silts,
and soils with
impermeable barriers)
Not critical0
Storage usually needed
for cold weather
a. Steeper grades might be feasible at reduced hydraulic loadings.
b. Underdrains can be used to maintain this level at sites with high ground
water table.
c. Impact on ground water should be considered for more permeable soils.
1-3
-------
TABLE 1-3
EXPECTED QUALITY OF TREATED WATER
FROM LAND TREATMENT PROCESSES3
mg/L Unless Otherwise Noted
Constituent
BOD
Suspended solids
Ammonia nitrogen as N
Total nitrogen as N
Total phosphorus as P
Fecal coliforms, No./lOO mL
Slow rateb
Upper
Average ; range
<2 <5
<1 l<5
<0. 5 <2
3e !<8e
<0.1 K0.3
0 ^10
Rapid infiltration0 Overland
Average
5
2
0.5
10
1
10
Upper
range
' <10
<5
<2
<20
<5
<200
Average
10
10
<4
5f
4
200
flowd
Upper
range
<15
<20
<8
<10f
<6
<2,000
a. Quality expected with loading rates at the mid to low end of the range
shown in Table 1-1. |
b. Percolation of primary or secondary effluent through 1.5 m (5 ft) of
unsaturated soil. |
c. Percolation of primary or secondary effluent through 4.5 m (15 ft) of
unsaturated soil; phosphorus and fecal coliform removals increase with
distance (see Tables 5-3 and 5-6).
d. Treating comminuted, screened wastewater using a slope length of 30-36 m
(100-120 ft). |
e. Concentration depends on loading rate and crop.
f. Higher values expected when operating through a moderately cold winter or when
using secondary effluent at high rates.
1.4 Slow Rate Process
Slow rate land treatment is| the application of wastewater to
a vegetated land surface with the applied wastewater being
treated as it flows through the plant-soil matrix. A
portion of the flow percolates to the ground water and some
is used by the vegetation., Offsite surface runoff of the
applied water is generally avoided in design. Schematic
views of the typical hydraulic pathways for SR treatment, are
shown in Figure l-l(a)(b)(c). Surface application tech-
niques include ridge-and-furrow and border strip flooding.
Application by sprinklers can be from fixed risers or from
moving systems, such as cen;ter pivots.
1.4.1 Process Objectives
Slow rate processes can bej operated to achieve a number of
objectives including: [
i
1. Treatment of applied wastewater
2. Economic return from use of water and nutrients to
produce marketable crops (irrigation)
-------
EVAPOTRANSPIRATION
PERCOLATION
(a) APPLICATION PATHWAY
UNOERDRAINS
(b) RECOVERY PATHWAYS
WELLS
(c) SUBSURFACE PATHWAY
FIGURE 1-1
SLOW RATE HYDRAULIC PATHWAYS
1-5
-------
3. Water conservation, by replacing potable water with
treated effluent, for irrigation
4. Preservation and enlargement of greenbelts and open
space
When requirements are very stringent for nitrogen,
phosphorus, BOD, SS, pathogiens, metals, and trace organics,
they can be met usually w|ith SR treatment. Nitrogen is
often the limiting factor for SR design because of EPA
drinking water limits on ground water quality. In arid
regions, however, maintaining chlorides and total dissolved
salts at acceptable levels for crop production may be
limiting. Management apprpaches to meet these objectives
within the SR process are discussed under the topics
(1) wastewater treatment, (2) agricultural systems, (3) turf
systems, and (4) forest systems.
1.4.1.1
Wastewater Treatment
When the primary objective of the SR process is treatment,
the hydraulic loading is usually limited either by the hy-
draulic capacity of the !soil or the nitrogen removal
capacity of the soil-vegetation matrix. Underdrains are
sometimes needed for development of sites with high ground
water tables, or where perched water tables or impermeable
layers prevent deep percolation. Perennial grasses are
often chosen for the vegetation because of their high
nitrogen uptake, a longer wastewater application season, and
the avoidance of annual planting and cultivation. Corn and
other crops with higher market values are also grown on
systems where treatment is the major objective. Muskegon,
Michigan [10] is a noted example in the United States with
over 2,000 hectares (5,000 acres) of corn under cultivation.
i
i
1.4.1.2 Agricultural Systems
In the more arid western portions of the United States, the
water itself (not the nutrient content) is the most valuable
component of the wastewater. Crops are selected for their
maximum market potential and the least possible amount of
wastewater needed for irrigation. Application rates between
2 to 8 cm/wk (0.8 to 3.1 in./wk) are common. This is enough
water to satisfy crop needs, plus a leaching requirement to
maintain a desired salt balance in the root zone.
In the more humid east, the water component may be critical
at certain times of the year and during extended drought
periods, but the nutrients j in the wastewater are the most
valuable component. Systems are designed to promote the
1-6
-------
nutrient uptake by the crop and increase yields. At
Muskegon, Michigan, for example, corn yields in 1977 were
6.5 m3/ha (75 bushels per acre) compared to 5.2 m3/ha (60
bushels per acre) for the nonwastewater farming in the same
area [10]. Regardless of geographical location, wastewater
irrigation can benefit crop production by providing
nutrients and moisture.
1.4.1.3 Turf Systems
Golf courses, parks, and other turfed areas are used in many
parts of the United States for SR systems, thus conserving
potable water supplies. These areas have considerable
public access and this requires strict control of pathogenic
organisms. This control can be achieved by disinfection or
by natural processes in biological treatment ponds or
storage ponds.
1.4.1.4 Forest Systems
Slow rate forest systems exist in many states including
Oregon, Washington, Michigan, Maryland, Florida, Georgia,
Vermont, and New Hampshire. In addition, experimental
systems in a variety of locations are being studied
extensively to determine permissible loading rates,
responses of various tree species, and environmental effects
(see Chapter 4).
Forests offer several advantages that make them desirable
sites for land treatment:
1. Forest soils often exhibit higher infiltration
rates than agricultural soils.
2. Site acquisition costs for forestland are usually
lower than site acquisition costs for prime agri-
cultural land.
3. During cold weather, soil temperatures are often
higher in forestlands than in agricultural lands.
4. Systems can be developed on steeper grades in the
forest as compared to agricultural sites.
The principal limitations to the use of wastewater for
forested SR systems are:
1. Water needs and tolerances of some existing trees
may be low.
1-7
-------
2. Nitrogen removals are relatively low unless young,
developing forests are used or conditions conducive
to denitrif ication are present.
3. Fixed sprinklers, vj/hich are expensive, are usually
necessary. I
i
4. Forest soils may be; rocky or very shallow.
1.4.2
Treatment Performance
The SR process is capable of producing the highest degree of
wastewater treatment of all the land treatment systems. The
quality values shown in Table 1-3 can be expected for most
well-designed and well-opera|ted systems.
i
Organics are reduced substantially by SR land treatment
within the top 1 to 2 cm (0.4 to 0.8 in.) of soil.
Filtration and adsorption are the initial steps in BOD
removal, but biological oxidation is the ultimate treatment
mechanism. Filtration is the major removal mechanism for
suspended solids. Residues remaining after oxidation and
the inert solids become part of the soil matrix.
i
Nitrogen is removed primarily by crop uptake, which varies
with the type of crop grown and the crop yield. To remove
the nitrogen effectively, i the crop must be harvested.
Denitrif ication can also be significant, even if the soil is
in an aerobic condition mo?t of the time. Other nitrogen
removal mechanisms include ammonia volatilization and
storage in the soil. i
Phosphorus is removed from solution by fixation processes in
the soil, such as adsorption and chemical precipitation.
Removal efficiencies are generally very high for SR systems
and are more dependent on the soil properties than on the
concentration of the phosphorus applied. Residual phos-
phorus concentrations in the, percolate will generally be
less than 0.1 mg/L [11]. AjSinall but significant portion of
the phosphorus applied is j taken up and removed with the
crop. i
1.5 Rapid Infiltration Process
In RI land treatment, most of the applied wastewater per-
colates through the soil, and the treated effluent drains
naturally to surface waters or joins the ground water. The
wastewater is applied to moderately and highly permeable
soils (such as sands and i loamy sands), by spreading in'
basins or by sprinkling, 'and is treated as it travels
1-E
-------
through the soil matrix. Vegetation is not usually planned,
but there are some exceptions, and emergence of weeds and
grasses usually does not cause problems.
The schematic view in Figure 1-2(a) shows the typical
hydraulic pathway for rapid infiltration. A much greater
portion of the applied wastewater percolates to the ground
water than with SR land treatment. There is little or no
consumptive use by plants. Evaporation ranges from about
0.6 m/yr (2 ft/yr) for cool regions to 2 m/yr (6 ft/yr) for
hot arid regions. This is usually a small percentage of the
hydraulic loading rates.
In many cases, recovery of renovated water is an integral
part of the system. This can be accomplished using under-
drains or wells, as shown in Figure l-2(b). In some cases,
the water drains naturally to an adjacent surface water
(Figure l-2(c)). Such systems can provide a,higher level of
treatment than most mechanical systems discharging: to the
same surface water.
1.5.1
Process Objectives
The objective of RI is wastewater treatment.
treated water can include:
Uses for the
1.
2.
3.
Ground water recharge
Recovery of renovated water by wells or underdrains
with subsequent reuse or discharge
Recharge of
ground water
surface streams by interception of
4. Temporary storage of renovated water in the aquifer
If .ground water quality is being degraded by saltwater.
intrusion, ground water recharge by RI can help to create a
barrier and protect the existing fresh ground water. In
many cases, the major treatment goal is conversion of
ammonia nitrogen to nitrate nitrogen prior to discharge to
surface waters. The RI process offers a cost-effective
method for achieving this goal with recovery or recharge as
described in items 2 and 3 above. Return of the renovated
water to the surface by wells, underdrains, or ground water
interception may be necessary or advantageous when, discharge
to. a particular surface water body is controlled by water
rights, or when existing ground water quality is not compat-
ible with expected renovated water quality. At Phoenix,
Arizona, for example, renovated water is being withdrawn by
wells to allow reuse of the water for irrigation.
1-9
-------
APPLIED
WASTEWATER
EVAPORATION
PERCOLATION
(a) HYDRAULIC PATHWAY
FLOODING BASINS
RECOVERED WATER
PERCOLATION
(UNSATURATED ZONE)
WELL
UNDERDRAINS HELLS
(b) RECOVERY PATHWAYS
FLOODING BASIN
(c) NATURAL DRAINAGE INTO SURFACE WATERS
FIGURE 1-2
RAPID INFILTRATION HYDRAULIC PATHWAYS
1-10
-------
1.5.2
Treatment Performance
Removals of wastewater constituents by the filtering and
straining action of the soil are excellent. Suspended
solids, BOD, and fecal coliforms are almost completely
removed.
Nitrification of the applied wastewater is essentially com-
plete when appropriate hydraulic loading cycles are used.
Thus, for communities that have ammonia standards in their
discharge requirements, RI can provide an effective way to
meet such standards.
Generally, nitrogen removal averages 50% unless specific
operating procedures are established to maximize denitrifi-
cation. These procedures include optimizing the application
cycle, recycling the portions of the renovated water that
contain high nitrate concentrations, reducing the
infiltration rate, and supplying an additional carbon
source. Using these procedures in soil column studies,
average nitrogen removals of 80% have been achieved.
Nitrogen removal by denitrification can be significant if
the hydraulic loading rate is at the mid range or below the
values in Table 1-1 and the BOD to nitrogen ratio is 3 or
more.
Phosphorus removals can range from 70 to 99%, depending on
the physical and chemical characteristics of the soil. As
with SR systems, the primary removal mechanism is adsorption
with some chemical precipitation, so the long-term capacity
is limited by the mass and the characteristics of soil in
contact with the wastewater. Removals are related also to
the residence time of the wastewater in the soil, the travel
distance, and other climatic and operating conditions.
1.6 Overland Flow Process
In OF land treatment, wastewater is applied at the upper
reaches of grass covered slopes and allowed to flow over the
vegetated surface to runoff collection ditches. The OF
process is best suited to sites having relatively imper-
meable soils. However, the process has been used with
success on moderately permeable soils with relatively
impermeable subsoils. The wastewater is renovated by
physical, chemical, and biological means as it flows in a
thin film down the length of the slope. A schematic view of
OF treatment is shown in Figure 1-3(a), and a pictorial view
of a typical system is shown in Figure 1-3(b). As shown in
Figure 1-3(a), there is relatively little percolation
involved either because of an impermeable soil or a
subsurface barrier to percolation.
1-11
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1ASTEWATER
SLOPE 2-8«
r
GRASS AND
VEGETATIVE LITTER
EVAPOTRANSPIRATION
RUNOFF
COLLECTION
PERCOLATION
(a) HYDRAULIC PATHWAY
SPRINKLER CIRCLES
RUNOFF
COLLECTION
DITCH
(b) PICTORIAL VIEW OF SPRINKLER APPLICATION
FtCURE 1-3
OVERLAND FLOW
1-12
-------
Interest by municipalities and design engineers has spurred
research and demonstration projects in South Carolina, New
Hampshire, Mississippi, Oklahoma, Illinois, and
California. Cold-weather operation has been demonstrated
through several winters at Hanover, New Hampshire. Rational
design equations have been developed based on research at
Hanover and at Davis, California.
1.6.1
Process Objectives
The
objectives of OF are wastewater treatment and, to a
minor extent, crop production. Treatment objectives may be
either:
1.
2.
To achieve secondary effluent quality
screened raw wastewater, primary
treatment pond effluent.
when applying
effluent, or
To achieve high levels of nitrogen, BOD, and SS
removals.
Treated water is collected at the toe of the OF slopes and
can be either reused or discharged to surface water. Over-
land flow can also be used for the preservation of
greenbelts.
1.6.2
Treatment Performance
Biological oxidation, sedimentation, and filtration are the
primary removal mechanisms for organics and suspended
solids.
Nitrogen removals are a combination of plant uptake,
denitrification, and volatilization of ammonia nitrogen.
The dominant mechanism in a particular situation will depend
on the forms of nitrogen present in the wastewater, the
amount of carbon available, the temperature, and the rates
and schedules of wastewater application. Permanent nitrogen
removal by the plants is only possible if the crop is har-
vested and removed from the field. Ammonia volatilization
can be significant if the pH of the wastewater is above 7.
Nitrogen removals usually range from 75 to 90% with the form
of runoff nitrogen dependent on temperature and on
application rates and schedule. Less removal of nitrate and
ammonium may occur during cold weather as a result of
reduced biological activity and limited plant uptake.
Phosphorus is removed by adsorption and precipitation in
essentially the same manner as with the SR and RI methods.
Treatment efficiencies are somewhat limited because of the
limited contact between the wastewater and the adsorption
1-13
-------
sites within the soil. Pho'sphorus removals usually range
from 50 to 70% on a mass basis. Increased removals may be
obtained by adding alum or fe'rric chloride to the wastewater
just prior to application on the slope.
1.7 Combination Systems ;
In areas where effluent quality must be very good, or where
a high degree of treatment Reliability must be maintained,
combinations of land treatment processes may be desirable.
For example, either an SR, RI, or a wetlands treatment
system could follow an OF system and would result in better
overall treatment than the QF alone. In particular, these
combinations could be used tb improve BOD, suspended solids,
nitrogen, and phosphorus removals.
Similarly, OF could be used prior to RI to reduce nitrogen
levels to acceptable levels. This combination was
demonstrated successfully in a pilot scale study at. Ada,
Oklahoma, using screened raw! wastewater for the OF portion
[12]. :
Rapid infiltration may also precede SR land treatment. In
this combination, renovated |water quality following RI is
expected to be high enough that even the most restrictive
requirements regarding the use of renovated water on food
crops can be met. Also, the ground water aquifer can be
used to store renovated water to correspond with crop
irrigation schedules. Some of these combinations are shown
schematically in Figure 1-4.
1.8 Guide to Intended Use of the Manual
This manual is organized similarly to the original 1977
edition except that the design examples are included as
appendixes. Completely nev^ features in this manual are
chapters on energy, and health and environmental effects.
Chapters 2 through 6 follow, in sequence, a logical pro-
cedure for planning and design of land treatment systems.
The procedure commences (Chapter 2) with screening of the
entire study area to identify potential land treatment
sites. The Phase 1 planning is based on existing infor-
mation and data on land use, water rights, topography,
soils, and geohydrology. If potentially suitable sites
exist, the Phase 2 planninjg then involves detailed site
investigations (Chapter 3) to determine process suitability
and preliminary design criteria (Chapters 4, 5, and 6).
Process selection for a particular situation is' influenced
by health and environmental issues (Chapter 9) and by energy
1-1H
-------
CO
LU
H-
CO
CO
a
LLJ
'" co
LU S
CC O
=30
CD
— U_
11 f—\
CO
LU
__l
a.
X
UJ
1-15
-------
needs (Chapter 8). Thus, Phase 2 planning requires the use
of all the technical chapters in the manual.
i
Small communities (up to 13,500 population) do not usually
need the same level of planning and investigation that is
essential for large systems. Nor do they always need the
level of sophistication that is normally provided, in terms
of equipment and management procedures, for large systems.
Procedures and shortcuts ;that are unique to small land
treatment systems are described in Chapter 7. Typical
examples are included to | illustrate the level of effort
needed in field work and de'sign.
The final design of a land treatment system needs only to
draw on the pertinent chapter (4, 5, or 6) for the intended
process. Some additional| field investigation (Chapter 3)
may be necessary to optimize hydraulic loading rates and
ensure proper subsurface • flow conditions. The design
chapters do not present complete detail on the hardware
(i.e., pumps, pipe materials, sprinkler rigs, etc.)
involved. Other sources will be needed for these design
details. The cost information in reference [1] or in the
CAPDET program is suitable for planning, comparison of
alternatives, and preliminary design only. The final
construction cost estimate should be derived ,in the
conventional way (by material take-off, etc.) from the final
plans.
Appendixes A, B, and C provide design examples of SR, RI,
and OF and are intended to demonstrate the design
procedure. Energy budgets knd costs are provided along with
the process design. Apperidix D contains a representative
list of currently operating municipal (also federal
government and selected industrial) land treatment systems
in the United States.
Appendix E provides information on designing irrigation
systems for SR facilities. The level of detail in this
appendix is sufficient to develop preliminary layouts and
sizing for distribution system components. Appendix F con-
tains a list of communities for which the EPA programs that
determine storage requirements based on climate
(Section 4.6.2) have been , run. The final appendix, G,
provides a glossary of terms and conversion factors from
metric to U.S. customary units for all figures and tables.
The design approach for land treatment has been essentially
empirical, i.e., observation of successful performance
followed by derivation of criteria and mathematical
expressions that describe overall performance. Essentially
the same approach was used; to develop design criteria for
1-16
-------
activated sludge and other biological treatment processes.
The physical, chemical, and biological reactions and
interactions occurring in all treatment processes are quite
complex and are difficult to define mathematically. Such
definition is still evolving for activated sludge as well as
land treatment. As a result, the design procedures
presented in this manual are still conservative and are
based on successful operating experience.
More rational design procedures however, are becoming
available (see Section 6.11). In addition, there are
mathematical models available that may be used to evaluate
the response to a particular constituent (nitrogen,
phosphorus, etc.) or used in combination to describe the
entire system performance. A brief summary of models, that
are currently available is included in reference [13] . A
more detailed discussion of specific models for land
treatment can be found in reference [14].
1.9 References
1. Reed, S.C. , et al. Cost of Land Treatment Systems.
U.S. Environmental Protection Agency. EPA-430/9-75-003,
MCD 10. September 1979.
Culp/Wesner/Culp. Water Reuse and Recycling.
U.S.D.I. OWRT/RU-79/2. 1979.
Vol. 2.
3. U.S. Environmental Protection Agency. Aquaculture
Systems for Wastewater Treatment: Seminar Proceedings
and Engineering Assessment. Office of Water Program
Operations. EPA-430/9-80-006, MCD 67. September
1979.
4. U.S. Environmental Protection Agency. Design Manual for
Onsite Wastewater Treatmept and Disposal Systems.
Center of Environmental Research Information. EPA-
645/1-80-012. October 1980.
5. U.S. Environmental Protection Agency. Slow Rate Land
Treatment: A Recycle Technology. Office of Water Pro-
gram Operations. EPA-430/9-80-011a, MCD 70. October
1980.
6. U.S. Environmental Protection Agency. Rapid Infiltra-
tion Land Treatment: A Recycle Technology. Office of
Water Program Operations. EPA-430/9-80-011b, MCD 71.
(In Press) 1981.
1-17
-------
7. Proceedings of the International Symposium on Land
Treatment of Wastewater. Volumes 1 and 2. Hanover, New
Hampshire. August 20-25, 1978.
I
8. Hinrichs, D.J., et al.j Assessment of Current Informa-
tion on Overland Flow, Treatment. U.S. Environmental
Protection Agency. ' Office of Water Program
Operations. EPA-430/9^80-002, MCD 66. September 1980.
9. Leach, L.E., C.G. Enfi<=ld, and C.C. Harlin, jr. Summary
of Long-Term Rapid Infiltration System Studies. U.S.
Environmental Protection Agency. Office of Research and
Development. Ada, Oklahoma. EPA-600/2-80-165. July
1980.
10. Walker, J.M. Wastewater; Is Muskegon County's Solution
Your Solution? U.S. Environmental Protection Agency.
EPA-905/2-76-004, MCD-3'4. August 1979.
11. Jenkins, T.F. and A.J. Palazzo. Wastewater Treatment by
a Slow Rate Land Treatment System. U.S. Army Corps of
Engineers, Cold Regions Research and Engineering
Laboratory. CRREL Report 81-14. Hanover, New
Hampshire. August 1981.
12. Thomas, R.E., et al. feasibility of Overland Flow for
Treatment of Raw Domestic Wastewater. U.S.
Environmental Protection Agency. EPA-66/2-74-087.
1974. '
13. Iskandar, I.K. Overview on Modeling Wastewater
Renovation by Land Treatment. USACRREL, Special Report.
USACRREL, Hanover, New Hampshire. 1981.
14. Iskandar, I.K. (ed.). iModeling Wastewater Renovation:
Land Treatment. Wiley Unterscience, New York. 1981.
1-18
-------
CHAPTER 2
PLANNING AND TECHNICAL ASSESSMENT
2.1 Planning Procedure
Adequate planning must precede any wastewater treatment
system design to ensure selection of the most cost-effective
process that is feasible for the situation under consider-
ation. In many cases, guidelines or specifications for the
planning procedure are provided by the agency responsible
for the project. The purpose of this chapter is to present
those aspects of the planning procedure that are either
unique or require special emphasis because of land
treatment.
Process selection for land treatment systems is more depen-
dent on site conditions than are mechanical treatment alter-
natives. This can mean that there is a need for extensive
and, in some cases, expensive site investigation and field
testing programs. To avoid unnecessary effort and expense,
a two-phase planning approach has been developed and adopted
by most agencies concerned. As shown in Figure 2-1, Phase 1
involves identification of potential sites via screening of
available information and experience. If potential sites
for any of the land treatment processes are identified, the
study moves into Phase 2. This phase includes field inves-
tigations and an evaluation of the alternatives.
2.2 Phase 1 Planning
Early during Phase 1, basic data that are common to all
wastewater treatment alternatives must be collected and
analyzed along with land treatment system requirements to
determine whether land treatment is a feasible concept. If
no limiting factors are identified that would eliminate land
treatment from further consideration, the next steps are to
identify potential land treatment sites and to evaluate the
feasibility of each site.
2.2.1 Preliminary Data
Service area definition, population forecasts, wastewater
quality and quantity projections, and water quality require-
ments are usually either specified or determined using
procedures established by the responsible authority. With
the exception of water quality requirements, the dati=> are
generally the same for all forms of wastewater treatmeuc. A
few aspects are specific to land treatment and are discussed
in this section.
2-1
-------
WASTE
CHARACTERIZATION
LAND TREATMENT
SYSTEM SUITABILITY
ESTIMATION OF LAND
REQUIREMENTS
PHASE 1
SITE IDENTIFICATION
SITE SGREENIN6
- SELECTION OF
POTENTIAL SITES
LAND TREATMENT
.NOT FEASIBLE BECAUSE
OF LIMITING FACTORS OR
PROJECT REOUIREMENTS
LAND APPLICATION
NOT FEASIBLE IF
THERE ARE NO
POTENTIAL SITES
FIELD INVESTIGATIONS
PHASE 2
DEVELOPMENT OF
PRELIMINARY DESIGN
CRITERIA AND COSTS
EVALUATION OF
ALTERNATIVES
PLAN SELECTION
LAND APPLICATION
NOT FEASIBLE FOR
OTHEfl REASONS OR OTHER
ALTERNATIVES MORI-
COST EFFECTIVE
INITIATION OF LAND
TREATMENT DESIGN
FIGURE 2-1
TWO-PHASE PLANNING PROCESS
2-2
-------
2.2.1.1 Wastewater Quality and Loadings
Major constituents in domestic wastewater are presented in
Table 2-1. Trace element concentration ranges are shown in
Table 2-2. The values in these tables may be used for plan-
ning purposes when a community's water quality has not been
determined. Other important parameters in land treatment
design can include total dissolved solids, pH, potassium,
sodium, calcium, magnesium, boron, barium, selenium, fluor-
ide, and silver.
TABLE 2-1
IMPORTANT CONSTITUENTS IN TYPICAL
DOMESTIC WASTEWATER [1]
mg/L
Type of wastewater
Constituent
BOD
Suspended solids
Nitrogen (total as N)
Organic
Ammonia
Nitrate
Phosphorus (total as P)
Organic
Inorganic
Total organic carbon
Strong
400
350
85
35
50
0
15
5
10
290
Medium
220
220
40
15
25
0
8
3
5
160
Weak
110
100
20
8
12
0
4
1
3
80
For municipal land treatment systems, BOD and suspended
solids loadings seldom limit system capacity. Typical BOD
loading rates at municipal systems are shown in Table 2-3
and are much lower than rates used successfully in land
treatment of food processing wastewaters. Suspended solids
loadings at these industrial systems would be similar to the
BOD loadings shown in Table 2-3.
In contrast, if nitrogen removal is required, nitrogen load-
ing may limit the system capacity. Nitrogen removal
capacity depends on the crop grown, if any, and on system
management practices. The engineer should consult Sections
4.5 and 5.4.3.1 to determine whether nitrogen loading will
govern system capacity and, therefore, land area
requirements.
2-3
-------
TABLE 2-2
COMPARISON OF1TRACE ELEMENTS IN
WATER AND WASTEWATERS
I mg/L
Maximum recommended
Untreated
Element wastewater3
Arsenic 0.003
Boron 0.3-1.8
Cadmium 0.004-0.14
Chromium 0.02-0.700
Copper 0.02-3.36
Iron 0.9-3.54
Lead 0:05-1.27
Manganese 0.11-0.14
Mercury 0.002-0.044
Nickel 0.002-0.105
Zinc 0.030-8.31
concentrations for
irrigation water"
0.1
0.5-2.0
0.01
0.1
0.2
5.0
5.0
0.2
No standard
0.2
2.0
a. The concentrations presented encompass the
reported in references
[2-6] .
b. Based on unlimited irrigation .at 1.0 m/yr(3
c. Reference [7] :
EPA recommended
drinking
water standards'3
0.05
No standard
0.01
0.05
1.0
0.3
0.05
0.05
0.002
No standard
5.0
range of values
f t/yr) .
TABLE 2-3
TYPICAL BOD LOADING RATES
kg/ha-yr
Slow rate Rapid infiltration Overland" flow
Range for
municipal
wastewater 370-1/830 8,000-46,000
2,000-7,500
Note: See Appendix Gifor metric conversions.
In some cases, other wastewater constituents such as phos-
phorus or trace elements may control design. For example,
if wastewater trace element concentrations exceed the maxi-
mum recommended concentrations for irrigation water (Table
2-2), SR systems may be infeasible or may require special
precautions. This is rare, however, and most municipal
systems will be limited either by hydraulic capacity or
nitrogen loading.
2.2.1.2 Water Quality Requirements
Land treatment systems ;have somewhat unique discharge
requirements because many of these systems do not have
2-4
-------
conventional point discharges to receiving surface waters.
In the past, the ability of the soil to treat wastewater was
not well recognized. As a result, discharge standards were
often imposed on a wastewater prior to its application on
land, thereby increasing treatment costs and energy require-
ments without significantly improving overall treatment
performance. More recently, land has been recognized as an
important component in the treatment process. For this
reason, discharge requirements now apply to water quality
following land treatment.
For systems that discharge to receiving waters, such as OF
systems and some underdrained or naturally draining SR and
RI systems, renovated water quality must meet surface dis-
charge requirements. For systems where the renovated water
remains underground, EPA has established guidance for three
categories of ground water discharge that meet the criteria
for best practicable waste treatment. These three
categories are as follows:
Case 1 - The ground water can potentially be used for
drinking water supply.
The chemical and pesticide levels in Table 2-4
should not be exceeded in the ground water. If the
existing concentration in the ground water 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 ground water is used for drinking water supply.
The same criteria as Case 1 apply and the bacterio-
logical quality criterion from Table 2-4 also
applies in cases where the ground water is used
without disinfection.
Case 3 T Uses other than drinking water supply.
•E
Ground water criteria should be established by the
Regional Administrator in conjunction with appro-
priate .state agencies based on the present or
potential use of the ground water.
For each ground water category, discharge requirements must
be met at the boundary of the land treatment project.
2-5
-------
TABLE 2-4
NATIONAL INTERIM PRIMARY
DRINKING WATER STANDARDS, 1977 [7,8]
Constituent
or characteristic
Physical
Turbidity, units
Chemical, mg/L
Arsenic
Barium
Cadmium
Chromium
Fluoride
Lead
Mercury
Nitrates as N
Selenium
Silver
Sodium"
Value3
lb
1 0.05
1.0
0.01
0.05
i 1.4-2.4
0.05
0.002
10
0.01
0.05
Reason
for standard
Aesthetic
Health
Health
Health
Health
Health
Health
Health
Health
Health
Cosmetic
Health
Bacteriological
Total coliforms,
MPN/100 mL
Pesticides, mg/L
Endrin
Lindane
Methoxychlor
Toxaphene
2,4-D
2,4,5-TP
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 ambient air temperature;
higher limits for lower temperatures.
d. Ground water drinking supplies must be
monitored at least once every 3 years;
surface water supplies must be monitored
at least annually.
For SR systems, individual states often have additional,
crop-specific preapplication treatment requirements. These
requirements are usually based on the method of wastewater
application, the degree of public contact with the site, and
the disposition of the crop. For example, crops for human
consumption generally require higher levels of preappli-
cation treatment than forage crops.
i
Local and state water quality requirements may also apply to
site runoff. Generally, all wastewater runoff must be con-
tained onsite and reapplied or treated. Stormwater runoff
requirements will vary from site to site and will depend on
2-6
-------
the expected quality of the runoff and the quality of local
surface waters. State and local water quality agencies
should be contacted for more specific requirements.
2.2.1.3 Regional Characteristics
Critical regional parameters include climate, surface water
hydrology and quality, and ground water quality.
Climate
Local climate may affect (1) the water balance (and thus the
acceptable wastewater hydraulic loading rate), (2) the
length of the growing season, (3) the number of days per
year that a land treatment system cannot be operated,
(4) the storage capacity requirement, (5) the loading cycle
of RI systems, and (6) the amount of stormwater runoff. For
this reason, local precipitation, evapotranspiration,
temperature, and wind values must be determined before
design criteria can be established. Whenever possible, at
least 10 years of data should be used to obtain these
values.
Three publications of The National Oceanic and Atmospheric
Administration (NOAA) provide sufficient data for most com-
munities. The Monthly Summary of Climatic Data provides
basic information, includingtotalprecipitation, tem-
perature maxima and minima, and relative humidity, for each
day of the month and every weather station in a given
area. Whenever available, evaporation data are included.
An annual summary of climatic data, entitled Local Climato-
logical Data, is published for a small number of major
weatherstations. Included in this publication are the
normals, means, and extremes of all the data on record to
date for each station. The Climate ' Summary of the United
States provides 10 year summariesolthemonthlyclimatic
data.Other data included are:
• Total precipitation for each month of the 10 year
period.
• Mean number of days that precipitation exceeded
0.25 and 1.3 cm (0.10 and 0.50 in.) during each
month
• Total snowfall for each month of the period
• Mean temperature for each month of the period
• Mean daily temperature maxima and minima for each
month —
2-7
-------
• Mean number of days per month that the temperature
was less than or equal to 0 °C (32 °F) or greater
than or equal to 32.5 °C (90 °F)
A fourth reference that can be helpful is EPA's Annual and
Seasonal Precipitation Probabilities [9]. This publication
includes precipitation probabilities for 93 stations
throughout the United States.
Data requirements for planning purposes are summarized in
Table 2-5. The amount of water lost by evapotranspiration
should also be estimated, either by using pan evaporation
data supplied by NOAA or by using theoretical methods
(Section 4.3.2.3). The length of the growing season for
perennial crops is usually assumed to be the number of con-
tinuous days per year that the maximum daily temperature is
above freezing. Specific information on growing seasons can
also be obtained from the local county agent. ,
TABLE 2-5
SUMMARY OF QLIMAT1C ANALYSES
Factor
Precipitation
Rainfall storm
Temperature
Wind
Evapotran-
spiration
Data required
Annual average,
maximum, minimum
Intensity, duration
Days with average
below freezing
Velocity, direction
Annual, monthly
average
Analysis
Frequency
Frequency
Frost free
period
--
Annual
dis tr ibution
Use
Water balance
Runoff estimate
Storage, treatment efficiency,
crop growing season
Cessation of sprinkling
Water balance
Surface Water Hydrology
For SR systems (see Chapter 4 for details) best management
practices for control of stormwater should be used. Contour
planting (instead of straight-row planting) and incorpo-
rating plant residues into the soil to increase the soil
organic content will also minimize sediment and nutrient
losses. When designing drainage and runoff collection sys-
tems, a 10 year return event should be the minimum interval
considered.
Ground Water Hydrology
Information that should be obtained includes soil surveys,
geologic and ground water resources surveys, well drilling
logs, ground water level measurements, and chemical analyses
of the ground water. Numerous federal, state, county,, and
city agencies have this type of information as well as uni-
versities, professional and technical societies, and private
2-8
-------
concerns with ground water related interests. Particularly
good sources are the U.S. Geological Survey (USGS), state
water resources departments, and county water conservation
and flood control districts. Much of the information col-
lected from these agencies and entities will also be useful
during the site identification step. (Figure 2-1).
2.2.2 Land Treatment System Suitability
Factors that should be considered in determining suitability
of a particular land treatment process are:
• Process ability to meet treatment requirements
(refer to Chapter 1)
Study area characteristics that may dictate
eliminate certain land treatment processes
or
• Secondary project objectives, such as a desire for
increased water supplies for irrigation or recrea-
tion
Once a preliminary decision regarding process suitability
has been made, typical hydraulic and nutrient loading rates
can be used to estimate land area. Minimum preapplication
treatment, storage, and other requirements are then deter-
mined, and the feasibility of each type of land treatment
process is evaluated.
2.2.2.1 Process Loading Rates
Slow Rate Process
The amount of wastewater that can be applied to a given SR
site per unit area and per unit time is the wastewater hy-
draulic loading rate, which can be estimated by using the
following water balance equation:
Precipitation + applied wastewater (2-1)
= evapotranspiration + percolation
Runoff is not included in the equation since SR design is
based on having no runoff of applied wastewater. The perco-
lation rate is the volume of water that must travel through
the soil, per unit application area and unit time, and is
established during system design. To ensure that there is
no runoff, the design percolation rate should never exceed
the saturated hydraulic conductivity, or permeability, of
the most restrictive layer in the soil profile (i.e., the
minimum soil permeability). Potential evapotranspiration
values have been calculated for various locations in the
2-9
-------
United States. These evapotranspiration values have been
used along with local precipitation records to plot the
difference between potential! evapotranspiration and precipi-
tation as a function of location [10]. This plot, included
as Figure 2-2, can be used jto determine rough estimates of
the difference between evapotranspiration and precipitation
at any site in the mainland United States.
Experience has shown that the maximum design percolation
rate should equal no more than a fraction of the minimum
soil permeability or hydraulic conductivity measured with
clear water and using typical field and laboratory proce-
dures (Sections 3.4 and 3.5). For planning purposes, the
fraction ranges from about 4| to 10% of the minimum (hydraulic
conductivity depending on the uniformity of the soil and the
degree of conservativeness (Sections 4.5.1, 5.4.1). Based
on this relationship, the recommended maximum percolation
rate is plotted in Figure 2-3 as a function of minimum soil
permeability as measured with clear water. To use the plot
during Phase 1, soil permeability must be estimated from
soil survey information. Then, the range of recommended
maximum percolation rates is read from the graph. The
recommended range of annual wastewater hydraulic loading
rates is estimated using Equation 2-1, by adding the-differ-
ence between evapotranspiration and precipitation (taken
from Figure 2-2) to the range of percolation rates identi-
fied in Figure 2-3. During Phase 2, hydraulic conductivity
measurements should be conducted at selected sites and used
to estimate maximum percolation rates.
The range of percolation rates that have been used in prac-
tice is broader than the maximum recommended range shown in
Figure 2-3. The. range is greater because parameters other
than soil hydraulic capacity, such as nitrogen loading, crop
requirements, and climate, often limit the allowable perco-
lation rate of SR systems. For preliminary planning
purposes, loading rates and!land requirements are estimated
by assuming that corn or sorghum or forage grasses will be
grown. Nitrogen requirements for these crops are discussed
in Section 4.3.
Rapid Infiltration Process
Wastewater hydraulic loading rates for RI systems are based
on the hydraulic capacity of the soil and on the underlying
soil geology. During Phase 1, hydraulic capacity is esti-
mated from soil survey data and other published sources.
Then, the range of percolation rates to use during prelim-'
inary planning is read from Figure 2-3. This figure (2-3)
should not be used for desigjn.
2-10
-------
o
LU
DC
0.
CM LU
1 3E
CM
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C9LU
•*«» 2° —
S^ ^^ Q.
*••« !t* CO
Ul_l U<-J
o
a.
>.<»-« ~«-
o ui o u< —
2-11
-------
200 —
I I
TYPICAL'SR
UNITS
In./h
cn/h
CLEAR RATER PEIWEARILITY, MIL CWMRWIM SERVICE »E»C»lfTI»E TEWS
VERT SLM
< 0.01
•* 0.15
JL»I
t.M-t.2*
0.1 5-1. J1
•MERftTE-
LY SLItf
0.20-D.fO
0.51-1.5
MIERATE
l.lt-2.t
1.5-5.1
MIERATE-
LY RAPID
2 «-f .»
5.I-1S.2
»*f 1*
8.1-M.I
1S.2-M.8
VERY »»Clll
» It.t
> 51.1
PERMEABILITY OF MOST RESTRICTIVE LAYER IN SOIL PROFILE
FIGURE 2-3
ESTIMATED DESIGN PERCOLATION RATE AS A FUNCTION
OF SOIL PERMEABILITY FOR SR AND Rl LAND TREATMENT
2-12
-------
During Phase 2, design percolation rates are determined by
measuring at least one of the following parameters:
• Infiltration rate using appropriate tests (Section
3.4)
* Hydraulic conductivity (permeability) of the soil,
usually in vertical direction
As described in Section 5.4.1, the design percolation rate
will always be a fraction of the test results. Considera-
tions of nutrient removal and cold weather operation may
require adjustments in the design percolation rate.
Overland Flow Process
During Phase 1 and Phase 2 planning, the engineer can as-
sume a hydraulic loading rate of 6.3 to 20 cm/wk (2.5 to
8 in./wk) for screened raw wastewater and a rate of 10 to
25 cm/wk (4 to 10 in./wk) for primary effluent (Section
6.4). Often, OF is used to polish wastewater effluent from
biological treatment processes. In such cases, assumed
wastewater loading rates may be as high as 20 to 40 cm/wk (8
to 16 in./wk).
2.2.2.2 Storage Needs
For SR and OF systems, adequate storage must be provided
when climatic conditions halt operations or require reduced
hydraulic loading rates. Most RI basins are operated year-
round, even in areas that experience cold winter weather
(Figure 2-4). Rapid infiltration systems may require cold
weather storage during periods when the temperature of the
wastewater to be applied is near freezing and the ambient
air temperature at the site is below freezing. Generally,
the problem occurs only when ponds are used for preapplica-
tion treatment. Land treatment systems also may need
storage for flow equalization, system backup and
reliability, and system management, including crop harvest-
ing (SR and OF) and spreading basin maintenance (RI).
Reserve application areas can be used instead of storage for
these system management requirements.
During the planning process, Figure 2-5 may be used to ob-
tain a preliminary estimate of storage needs for SR and OF
systems. This figure was developed from data collected and
analyzed by the National Climatic Center in Asheville, North
Carolina. The data were used to develop computer programs
that estimate site specific wastewater storage requirements
based on climate [11] , which, in turn, were used to plot
Figure 2-5. The map is based on the number of freezing days
2-13
-------
per year corresponding to a 20 year return period. If
application rates are reduced during cold weather,
additional storage may be required. Should there be a need
for more detailed data, the engineer should contact:
Director j
National Climatic Center
Federal Building
Asheville, North Carolina 28801
(704) 258-2850
Any communications should refer to computer programs EPA-1,
2, and 3 (Section 4.6.2 and Appendix F). Each of these
programs costs $225 for an initial computer run (January
1981).
FIGURE 2-4
WINTER OPERATION OF RAPID INFILTRATION
AT LAKE GEORGE, NEW YORK
Alternatively, for OF and SR systems, -4 °C (25 °F) can be
assumed as the minimum temperature at which a system will
successfully operate. Readily available temperature data
2-14
-------
CO
cc
CD
o
H-
«t
_l
CD
O
O
in
I a
CM UJ
CO
UJ -
U. *c
a
cr
o
»—
CO
QC
CO
UJ
CO
2-15
-------
may be used by assuming' that systems do not operate below
-4 °C. Then, the required |Storage volume is estimated from
the average cold weather flow and the number of days in
which the mean temperature is less than -4 °C.
i
2.2.3 Land Area Requirements
The amount of land required for a land treatment system
includes the area needed for buffer zones, preapplication
treatment, storage, access roads, pumping stations, and
maintenance and administration buildings, in addition to the
land actually required for ; treatment. Depending on growth
patterns in the study area, and on the accessibility of the
land treatment site, additional land may be required for
future expansion or for plant emergencies.
During planning, the total jamount of land required, exclud-
ing any buffer zones that may be required by state agencies,
can be roughly approximate^ from Figure 2-6. To use the
nomograph shown in this figure, the design wastewater flow
must be known. First, the wastewater hydraulic loading rate
is estimated (Section 2.2.2). Then, the wastewater flow and
hydraulic loading rate are located on the appropriate axes
and a line is drawn passing through them to the pivot
line. Next, the number of weeks per year that the system
will not operate, due to weather, crop harvesting, or other
reasons, is estimated. A: second line is drawn from the
pivot point to the number of no.noperating weeks. The point
at which this second line crosses the axis labeled "total
area" corresponds to the estimated required area.
2.2.4 Site Identification
Potential land treatment sites are identified using existing
soils, topography, hydrogeology, and land use data, shown by
parameter on individual study area maps. Eventually, the
data are combined into composite study area maps that
indicate areas of high, moderate, and low land treatment
suitability.
Potential land treatment sites are identified using a deduc-
tive approach [13]. First, 'any constraints that might limit
site suitability are identified. In most study areas, all
land within the area should be evaluated for each land
treatment process. The next step is to classify broad areas
of land near the area where wastewater is generated
according to their land treatment suitability. Factors that
should be considered include current and planned land use,
topography, and soils.
2-16
-------
GO
CD
|l 1 I! I I ! I 1 I I I I I I I I 1 1 I I ! I I |
in o in o in CD
e-i 04 »— •*-
>!« '3NI1 [aimVHSclONON
CD Q-09
o:
s°-
O
I—
0
CD u_
-------
2.2.4.1 Land Use!
Land use in most communities is regulated by local, county,
and regional zoning laws'. Land treatment systems must
comply with the appropriate zoning regulations. For this
reason, the planner should be fully aware of the actual land
uses and proposed land uses in the study area. The planner
should attempt to develop land treatment alternatives that
conform to local land use goals and objectives.
Land treatment systems can conform with the following land
use objectives:
• Protection of open space that is used for land
treatment
* Production of agricultural or forest products using
renovated water on the land treatment site
* Reclamation of land by using renovated water to
establish vegetation on scarred land
* Augmentation of parklands by irrigating such lands
with renovated water
« Management of flood plains by using flood plain
areas for land treatment, thus precluding land
development on such sites
<» Formation of buffer areas around major public
facilities, such as airports
To evaluate present and planned land uses, city, county, and
regional land use plans should be consulted. Because such
plans often do not reflect actual current land use, site
visits are recommended tp determine existing land use.
Aerial photographic maps may be obtained from the Soil Con-
servation Service (SCS) or the local assessor's office.
Other useful information may be available from the USGS and
the EPA, including true color, false color infrared, and
color infrared aerial photos of the study area.
Once the current and planned land uses have been determined,
they should be plotted on a study area map. Then, land use
suitability may be plotted using the factors shown in
Table 2-6.
Both land acquisition procedures and treatment system opera-
tion are simplified when few land parcels are involved and
contiguous parcels are used. Therefore, parcel size is an
important parameter. Usually, information on parcel size
2-18
-------
can be obtained from county assessor or county recorder
maps. Again, the information should be plotted on a map of
the study area.
TABLE 2-6
LAND USE SUITABILITY FACTORS FOR
IDENTIFYING LAND TREATMENT SITES [14]
Type of system
Agricultural Forest Overland
Land use factor slow rate slow 'rate flow
Open or cropland High
Partially forested Moderate
Heavily forested Low
Built upon Low
(residential,
commercial, or
industrial)
Moderate High
Moderately Moderate
high
High Low
Very low Very low
Rapid
infiltration
High
Moderate
Low
Very low
2.2.4.2 Topography
Steep grades limit a site's potential because the amount of
runoff and erosion that will occur is increased, crop culti-
vation is made "more difficult, if not impossible, and satur-
ation of steep slopes may lead to unstable soil
conditions. The maximum acceptable grade depends on soil
characteristics and the land treatment process used
(Table 1-2).
Grade and elevation information can be obtained from USGS
topographic maps, which usually have scales of 1:24,000
(7.5 minute series) or 1:62,500 (15 minute series). Grade
suitability may be plotted using the criteria listed in
Table 2-7.
TABLE 2-7
GRADE SUITABILITY FACTORS FOR IDENTIFYING
LAND TREATMENT SITES [14]
Slow rate systems
Grade factor Agricultural Forest
Overland Rapid
flow infiltration
0 to 12%
12 to 20%
>20%
High
Low
Very low
High
High
Moderate
High
Moderate
Eliminate
High
Low
Eliminate
2-19
-------
Relief is another important itopographical consideration and
is the difference in elevation between one part of a land
treatment system and another. The primary impact of relief
is its effect on the cost ;of conveying wastewater to the
land application site. Often, the economics of pumping
wastewater to a nearby sites must be compared with the cost
of constructing gravity conveyance to more distant sites.
A site's susceptibility to, flooding also can affect its
desirability. The flooding hazard of each potential site
should be evaluated in termjs of both the possible severity
and frequency of flooding as well as the areal extent of
flooding. In some areas, lit may be preferable to allow
flooding of the application |site provided offsite storage is
available. Further, crops ban be grown in flood plains if
flooding is infrequent enough to make farming economical.
Overland flow sites can be located in flood plains provided
they are protected from direct flooding which could erode
the slopes. Backwater from flooding, if it does not last
more than a few days, should not be a problem. Flood plain
sites for RI basins should be protected from flooding by the
use of levees.
Summaries of notable floods and descriptions of severe
floods are published each year as the USGS Water Supply
Papers. Maps of certain areas inundated in past floods are
published as Hydrologic Investigation Atlases by the USGS.
The USGS also has produced more recent maps of flood prone
areas for many regions of the county as part of the Uniform
National Program for Managing Flood Losses. These- maps are
based on standard 7.5 minute (1:24,000) topographic sheets
and identify areas that lie within the 100 year flood
plain. Additional information on flooding susceptibility is
available from local offices of the U.S. Army Corps of Engi-
neers and local flood control districts.
2.2.4.3 Soils
Common soil-texture terms and their relationship to the SCS
textural class names are listed in Table 2-8. ":
Fine-textured soils do not drain well and retain water for
long periods of time. Thus, infiltration is slower and crop
management is more difficult than for freely drained soils
such as loamy soils. Fine-textured soils are best suited
for the OF process. Loamy or medium-textured soils are
desirable for the SR process, although sandy soils may be
used with certain crops that grow well in rapidly draining
soils. Soil structure and soil texture are important char-
acteristics that relate to j permeability and acceptability
'2-20
-------
for land treatment. Structure refers to the degree of soil
particle aggregation, .ft well structured soil is generally
more permeable than unstructured material of the same
type. The RI process is suited for sandy or loamy soils.
TABLE 2-8
SOIL TEXTURAL CLASSES AND GENERAL TERMINOLOGY
USED IN SOIL DESCRIPTIONS
General terms
Common name Texture
Basic soil textural
class names
Sandy soils Coarse
Moderately coarse
Loamy soils Medium
Moderately fine
Clayey soils Fine
Sand
Loamy sand
Sandy loam
Fine sandy loam
Very fine sandy loam
Loam
Silt loam
Silt
Clay loam
Sandy clay loam
Silty clay loam
Sandy clay
Silty clay
Clay'
Soil surveys are usually available from the SCS. Soil sur-
veys normally contain maps showing soil series boundaries
and textures to a depth of about 1.5 m (5 ft). The scale of
these maps ranges from 1:31,680 to 1:15,840 and even 1:7,920
in some locations. In a survey, limited information on
chemical properties, grades, drainage, erosion potential,
general suitability for locally grown crops, and interpre-
tive and management information is provided. In some areas,
published surveys are not available or exist only as
detailed reports with maps ranging in scale from 1:100,000
to 1:250,000. Additional information on soil character-
istics and on soil survey availability can be obtained from
the SCS, through the local county agent.
Although soil depth, permeability, and chemical character-
istics significantly affect site suitability, data on these
parameters are often not available before the site investi-
gation phase. If these data are available, they should be
plotted on a study area map along with soil texture. In
identifying potential sites, the planner should keep in mind
that adequate soil depth is needed for root development and
for thorough wastewater treatment. Further, permeability
requirements vary among the land treatment processes.
Desirable permeability ranges .are shown by process in Table
2-9 together with desired soil texture. The SCS permeabil-
ity class definitions are presented in Figure 2-3.
2-21
-------
Certain geological formations are of interest during
Phase 1. Discontinuities and fractures in bedrock may cause
shortcircuiting or other unexpected ground water flow
patterns. Impermeable or semipermeable layers of rock,
clay, or hardpan can result in perched ground water
tables. The USGS and many state geological surveys have
maps indicating the presence and effects of geological
formations. These maps and other USGS studies may be used
to plot locations within^ the study area where geological
formations may limit the suitability for land treatment.
TABLE 2-9
TYPICAL SOIL PERMEABILITIES AND TEXTURAL
CLASSES FOR LAND TREATMENT PROCESSES
Principal processes
Slow rate
Rapid
infiltration
Overland
flow
Soil permeability
range, cm/h
>0.15
>5.0
<0.5
Permeability
class range
Textural
class range
Unified Soil
Classification
Moderately slow to
moderately rapid
Clay loams to
sandy loams
GM-d, s'M-d, ML,
OL, MH, PT
i
Rapid
Sand and
sandy loams
GW, GP, SW,
SP
Slow
Clays and
clay loams
GM-u, GC,
SM-u, SC,
CL, OL, CH, OH
Once each of the parameters discussed in the preceding para-
graphs have been mapped, the maps are merged into a
composite map that indicates areas with high, moderate, and
low suitability. Map overlays may be useful during this
process.
2.2.5 Site Screening '
During the latter half of Phase lf each part of the study
area that appears to be suitable for land treatment must be
evaluated and rated in terms of technical suitability and
feasibility. Rating is often accomplished by weighting each
of the site selection factors and using a numerical
system. The resulting ratings are used to identify sites
that have high overall suitability and that should be inves-
tigated more thoroughly. If suitable sites are not
available, no further consideration is given to land
treatment.
2-22
-------
Site selection factors and weightings should vary to suit
the needs and characteristics of the community. Several
factors that should be considered are listed in Table 2-10.
A sample rating system is shown in Table 2-11. This system
may be varied by the planner to reflect available
information.
TABLE 2-10
SITE SELECTION GUIDELINES
Characteris tic
Process
Remarks
Soil permeability
Potential ground
water pollution
Ground water storage
and recovery
Existing land uses
Future land use
Size of site
Flooding hazard
Slope
Water rights
Overland flow
Rapid infiltration
and slow rate
Rapid infiltration
and slow rate
Rapid infiltration
All processes
Al 1 procpssi=>s
All processes
All processes
All processes
Rapid infiltration
Overland flow
All processes
High permeability soils are more suitable
to other processes.
Hydraulic loading rates increase with
permeability.
Affected by the (1) proximity of the site to
a potential potable aquifer, (2) presence of
an aquiclude, (3) direction of ground water
flow, and (4) degree of ground water recovery
bv wells or underdrains.
Capability for storing percolated water and
recovery by wells or underdrains is based
on aquifer depth, permeability, aquiclude
continuity, effective treatment depth, and
ability to contain the recharge mound within
the defined area.
Involves the occurrence and nature of con-
flicting land use.
Future urban develooment may affect the ability
to expand the system.
If there are a number of small parcels, it is
often difficult to purchase or lease the
needed area.
May exclude or limit site use.
Steep grades may (1) increase capital expen-
ditures for earthwork, and (2) increase the
erosion hazard during wet weather.
Steep grades often affect ground water
flow pattern.
Steep grades reduce the travel time over the
treatment area and treatment efficiency. • Flat
land requires extensive earthwork to create
grades.
May require disposal of renovated water in a
particular watershed within a particular
stretch of surface water.
2-23
-------
RATING FACTORS
TABLE 2-11
FOR SITE SELECTION [14, 15]
Slow rate systems
Characteristic
Soil depth, ma
0.3-0.6
0.6-1.5
1.5-3.0
>3.0
Minimum depth to
ground water, m
<1. 2
1.2-3.0
>3.0
Permeability, cm/h°
<0.15
0.15-0.5
0.5-1.5
1.5-5.0
>5.0
Grade, %
0-5
5-10
10-15
15-20
20-30
30-35
>35
Existing or planned land use
Industrial
High density residential/urban
Low density residential/urban
Forested
Agricultural or open space
Overall suitability rating3
Low
Moderate
High
Agricultural
: Eb
3
8
9
0
4
6
1
: ' 3
5
8
8
6
4
' 0
Q
E
E
0
0
1
1
4
•
15-25
25-35
Forest
E
3
8
9
0
4
6
1
3
5
8
8
8
g
2
0
o
0
1
4
3
15-25
25-35
Overland
flow
o
4
7
7
2
4
6
10
g
g
E
8
2
E
E
g
E
0
1
4
16-25
25-35
Rapid
infiltration
£'
4
8
2
6
E
E
9
8
1
E
E
E
E
i
0 '
0
1
1
4
16-25
25-35
The higher the maximum number in each characteristic, the more important
the characteristic; the higher!the ranking, the greater the suitability.
a. Depth of the profile to bedrock.
b. Excluded; rated as poor.
c. Permeability of most restrictive layer in soil profile.
d. Sum of values.
2-24 .
-------
EXAMPLE 2-1:
USE OF RATING FACTORS TO DETERMINE
SITE SUITABILITY
An example of the use of rating factors is presented in the following two
figures and tables. Example soil types are shown in Figure 2-7 as presented
in a portion of a county SCS soil survey. Characteristics of the three soil
types and existing land uses are presented in Table 2-12. The characteristics
are then compared to the rating factors in Table 2-11 to obtain the numerical
values in Table 2-13. For example, the Bibb silt loam in Table 2-12 has'a
depth of soil above bedrock of 1.5 to 3 m (5 to 10 ft). From Table 2-11,
this would correspond to values of 8 for SR, 7 for OF, and 4 for RI. These
values are entered into Table 2-13.
When all factors are evaluated, the numerical values are added together to
obtain a total and to determine the suitability rating. The high suitability
areas are presented in the soils map in Figure 2-8. By applying this procedure
to all soils within a given radius of the community, the most suitable sites
(generally 3 to 5) are identified for further field investigation and cost-
effectiveness evaluation.
FIGURE 2-7
EXAMPLE AREA OF SOIL MAP TO BE EVALUATED
TABLE 2-12
CHARACTERISTICS OF SOIL SERIES MAPPED IN FIGURE 2-7
Map symbol
Soil depth, m
Depth to ground water, m
Permeability, cm/h
Grade, %
Land use
Bibb silt loam
Bm
1.5-3.0
<1.2
<0.15
0-5
Agricultural
Sassafras fine
sandy loam
SaB
0.6-1.5
1.2-3.0
1. 5-5.0
0-5
Forested
Evesboro
loamy sand
EoB
>3.0
1.2-3
>5.0
0-5
Industrial
2-25
-------
TABLE 2-13
EXAMPLE USE OF RATING1FACTORS FOR SITE SELECTION
System Ground ;Perme- Land
Spil type type Depth water .ability Grade use Total Suitability
Bibb
silt loam
(Em)
Sassafras
fine sandy
loam (SaB)
Evesboro
loamy sand
(EoB)
SR
OF
RI
SR
OF
RI
SR
OF
RI
8
7
4
2
4
E
9
7
8
0
2
E
4
4
2
4
4
2
1
10
1 E
8
1
6
8
E
9
8
8
8
8
8
8
8
8
8
4
4
4
1
1
1
0
0
0
21
31
— a
24
18
__a
29
__a
27
Moderate
High
Eliminate
Moderate
Moderate
Eliminate
High
Eliminate
High
a. Total not determined because site was clearly eliminated (E) for this
type of land treatment based on one or more site factors.
[7j SR or RI HIGH SUITABILITY
[V| OF HIGH SUITABILITY
^ SR MODERATE SUITABILITY
SR or OF MODERATE SUITABILITY
FIGURE 2-8
EXAMPLE SUITABILITY MAP FOR SOILS IN FIGURE 2-7
2-26
-------
2.3 Phase 2 Planning
Phase 2, the site investigation phase, occurs only if sites
with potential have been identified in Phase 1. During
Phase 2, field investigations are conducted at the selected
sites to determine whether land treatment is technically
feasible. When sufficient data have been collected, prelim-
inary design criteria are calculated for each potential
site. Using these criteria, capital and operation and main-
tenance costs are estimated. These cost estimates and other
nonmonetary factors are used to evaluate the sites selected
during Phase 1 for cost effectiveness. On the basis of this
evaluation, a land treatment alternative is selected for
design.
2.3.1 Field Investigations
Field investigations that should be performed during Phase 2
include:
• Characterization of the soil profile to an approxi-
mate depth of 1.5 m (5 ft) for SR, 3 m (10 ft) for
RI, and 1m (3 ft) for OF
• Measurements of ground water depth, flow, and
quality
• Infiltration rate and soil hydraulic conductivity
measurements
• Determination of soil chemical properties
Methods for these analyses are detailed in Chapter 3.
2.3.2 Selection of Preliminary Design Criteria
From information collected during the field investigations,
the engineer can confirm the suitability of the sites for
the identified land treatment process(es). Using the load-
ing rates described previously (Figure 2-3, Section 2.2.2),
the engineer should then select the appropriate hydraulic
loading rate for each land treatment process that is suit-
able for each site under consideration. Based on the
loading rate estimates, land area, preapplication treatment,
storage, and other system requirements can be estimated.
Reuse/recovery options should also be outlined at this time.
2-27
-------
2.3.2.1 Preapplication Treatment
Some degree of wastewater treatment prior to land applica-
tion is usually necessary, for one or more of the following
reasons: ;
I • ,.'
• To avoid unnecessary wear on the distribution
system, and in particular, pumps in the system
I
• To allow wastewater storage prior to land treatment
without creating nuisance conditions
• To minimize potential public health risks
I
• To reduce soil clogging in RI land treatment
• To obtain a higher overall level of wastewater
treatment . > • ,
i
Industrial pretreatment should be considered when industrial
waste contains materials that (1) could hinder the treatment
processes; (2) could accumulate in quantities that would be
detrimental to the soil-plant system; or (3) could pass
through a land treatment system and restrict the beneficial
uses of the renovated water or the native ground water.
Industrial contaminants of concern include trace organics
and trace elements. General guidelines and time schedules
for implementation of industrial waste pretreatment programs
can be obtained from the EPA regional offices.
2.3.2.2 Recovery of Renovated Water
The collection of renovated iwastewater following land treat-
ment may be either necessary or desirable. If the renovated
wastewater can be reclaimed for beneficial uses, recovery
may even be profitable. In many locations, water rights may
necessitate recovery of renovated water for disposal at a
specific location in a given watershed. In some locations,
underdrainage may be needed to control ground water eleva-
tions and allow site development.
Methods used to recover renovated wastewater include under-
drains, recovery wells, surface runoff collection, and tail-
water return. Wastewater can also be recovered through
springs and seeps that result from land treatment or by
subsurface flow from the land treatment site to the surface
water. These methods and their applicability to each of the
three major types of land treatment are summarised in
Table 2-14. Design of recovery systems is discussed in more
detail in Chapters 4,5, and1 6.
12-28
-------
TABLE 2-14
APPLICABILITY OF RECOVERY SYSTEMS FOR RENOVATED WATER
Recovery system
Slow rate
Rapid infiltration
Overland flow
Springs, seeps, or
natural drainage
Underdrains
Recovery wells
Often used to
maintain water
rights
Ground water control
and effluent reuse
Usually NA
Often used to NA
maintain water rights
Ground water control NA
and effluent reuse
Ground water control NA
and effluent reuse
Surface runoff
Effluent
Stormwater
Tailwater
Sprinkler application
Surface application
NA
Sediment control
NA
25-50% of applied
flow
NA
NA
NA
NA
Collect,
Collect,
NA
NA
discharge3
discharge3
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.
2.3.3 Evaluation of Alternatives
Land treatment alternatives should be evaluated on the basis
of capital costs, operation and maintenance costs (including
energy consumption), and other nonmonetary factors, such as
public acceptability, ease of implementation, environmental
impact, water rights, and treatment consistency and relia-
bility.
2.3.3.1 Costs
For cost analyses, the EPA cost-effectiveness analysis pro-
cedures described in 40CFR 35, Appendix A, must be used in
selecting any municipal wastewater management system that
will be funded under PL 92-500 [16]. For nongrant funded
projects, the EPA analysis may be modified to fit a
community's specific objectives. The most cost-effective
alternative is defined as follows [16]:
The most cost-effective alternative shall be the waste
treatment management system which the analysis deter-
mines to have the lowest present worth or equivalent
annual value unless nonmonetary costs are overriding.
The most cost-effective alternative must also, meet the
minimum requirements of applicable effluent
limitations, groundwater protection, or other
applicable standards established under the Act.
2-29
-------
Curves for estimating capital and operation and maintenance
costs may be found in reference [17] , or' the CAPDET system
can be used for a preliminary estimate.
Cost comparisons should include the cost of preapplication
treatment and sludge handling as well as land treatment
process components, including transmission, storage, field
preparation, renovated water recovery, and land. The costs
of resolving any water rights problems also raust be
included. The EPA cost-effectiveness guidelines require
that grant-funded projects use the following general service
lives:
Land
Structures
Process equipment
Auxiliary equipment
Permanent
30 to 50 years
15 to 30 years
10 to 15 years
Capital costs for land will vary from site to site. Land
treatment systems must have adequate land for preapplication
treatment facilities, storage reservoirs, wastewater appli-
cation, buffer zones, administrative and laboratory build-
ings, transmission pipe easement, and other facilities.
Costs of relocating residences and other buildings depend on
the location but also should be included in capital cost
estimates. The local offices of the U.S. Army Corps of
Engineers, U.S. Bureau of Reclamation, and state highway
departments can provide information on relocation cost
estimates.
Several options are available for acquisition or control of
the land used for wastewater application, including:
• Outright purchase (fee-simple acquisition)
• Long-term lease or easement
• Purchase and leaseback of land (usually to farmer
for irrigation) with no direct municipal involve-
ment i'n land management.
2-30
-------
For larger projects, fee-simple land acquisition is favored
by most federal agencies, states, and communities. Further,
outright purchase provides the highest degree of control
over the land application site and ensures uninterrupted
land availability. Estimates indicate that land leasing has
been cost effective for several hundred projects
nationwide. Generally, these projects are in arid or semi-
arid areas where renovated water has a high value and land a
relatively low value. Leasing or easement arrangements also
can be very attractive for smaller communities.
Capital costs of land for both land treatment processes and
storage prior to land application are eligible for federal
Construction Grants Program funding as specified in1 EPA
guidance [18]. During the cost effectiveness analyses, the
engineer must keep in mind that, unlike many other treatment
components, land has a salvage value. In addition, current
EPA guidance allows the land value to appreciate 3% per
year. Thus, the salvage value after 20 years is:
9 n
(1 + 0.03)zu x present price = (1.806)(present price)
The present worth of this salvage value is calculated using
the prevailing interest rate, not the 3% appreciation
rate. Long-term easements or leases of land for land appli-
cation processes also are eligible for Construction Grants
Program funding, provided that the conditions summarized in
Table 2-15 are met.
TABLE 2-15
LEASE/EASEMENT REQUIREMENTS FOR CONSTRUCTION
GRANTS PROGRAM FUNDING [18]
• 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. The grantee must insure
the capability to operate and meet permit requirements for the useful life of
the project.
• Provide for payment of the lease/easement in a lump sum for the full value of
the entire term.
• Provide for leases/easements for the useful life of the treatment plant,
with an option of renewal for additional terms, as deemed appropriate.
Operation and maintenance costs include labor, materials,
and supplies (including chemicals), and power costs. For
cost comparison purposes, they are assumed to be constant
2-31
-------
during the planning period. However, if average wastewater
flows are expected to increase significantly during the
planning period, operation and maintenance costs should be
developed for each year of the planning process. Operation
and maintenance cost curves may be found in references
[17, 19]. '-
To estimate labor costs, staffing requirements for both
preapplication treatment and land treatment must be deter-
mined. Staffing requirements for preapplication treatment
can be found in reference [19]. Staffing requirements at
municipally owned and operated land treatment systems have
been plotted as a function of flow in Figure 2-9. Land
treatment systems that are !owned and/or operated by farmers
will have lower municipal staffing requirements.
Annual costs should include the cost of leasing land for
wastewater application, when appropriate. Annual cost esti-
mates also should take into consideration revenues from crop
sales, sale of renovated water, sale of effluent for land
application, or leaseback of purchased land for farming or
other purposes. Because of the uncertainty in estimating
these revenues, they should be used to offset only a portion
of the operating costs in the cost-effectiveness analysis.
Prevailing market values for crops usually can be obtained
from state university cooperative extension services. Pre-
liminary yield estimates should be based on the proposed
application conditions and on typical yields in the local
area.
Another source of revenue may be the sale of recovered ren-
ovated water, particularly runoff from OF systems or
renovated water from RI system recovery wells. Markets for
renovated water must be investigated on a community by com-
munity basis. Methods of assessing the relative value of
renovated wastewater for various uses and potential reuse
categories are discussed in reference [20].
2.3.3.2 Energy
Basic energy requirements for unit processes and operations
have been described and quantified in reference [21]. The
data in the report were used to compare land treatment
energy requirements with mechanical system requirements and
to develop equations for calculating the energy requirements
of each unit process [22] . Equations in Chapter 8 can be
used to generate accurate power cost estimates for the cost-
effectiveness analysis.
2-32
-------
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2.3.3.3 Nonmonetary Considerations
l
According to the EPA guidelines, a cost-effectiveness
analysis must also consider nonmonetary factors such as
environmental impacts [23, 24], ease of implementation
(magnitude of potential water rights conflicts, public
acceptability), and treatment consistency and reliability.
Potential water rights conflicts are discussed briefly in
Section 2.4. Public acceptability will be greatly aided by
an effective public participation program, particularly if
there is any chance that local farmers will be involved in
an SR system. Public participation regulations in the
federal Construction Grants Program are given in 40 CFR
Part 35. These regulations implement the public participa-
tion requirements of 40 CFR Part 25.
Changing discharge requirements, wastewater characteristics,
growth rates, and land uses for areas surrounding and con-
tributing to the treatment system require treatment flex-
ibility. The ability of each alternative to adapt to
changes should be evaluated.
2.3.4 Plan Selection
To select an alternative, each of the factors considered
during the evaluation process should be compared on an
equivalent basis. Monetary factors should be expressed in
terms of total present worth or equivalent annual cost.
Nonmonetary factors should' be weighted according to their
local importance, and reasons cited for abandoning any
alternative for nonmonetary reasons. If there are no over-
riding nonmonetary factors, the alternative selected should
be the plan with the lowest total present worth or equiv-
alent annual cost.
Actual alternative selection should involve the wastewater
management agency, the planner/engineer, advisory groups,
citizen and special interest groups, and other interested
governmental agencies. Once an alternative is tentatively
selected, and before design; begins, mitigation measures for
minimizing any identified adverse impacts should be
outlined.
2.4 Water Rights and Potential Water Rights Conflicts
Land application of wastewaters may cause several changes in
drainage and flow patterns [25]:
1. Site drainage may be affected by land preparation,
soil characteristics, slope, method of wastewater
application, cover crops, climate, buffer zones,
and spacing of irrigation equipment.
2-34
-------
2. Land application may alter the pattern of flow in
the body of water that would have received the
wastewater discharge. Although this may diminish
the flow in the body of water, it also may increase
the quality. The change may be continuous or
seasonal.
3. Land application, may cause surface water diversion,
because wastewaters that previously would have been
carried away by surface waters are now applied to
land and often diverted to a different watershed.
Two basic types of water rights laws exist in the United
States: riparian laws, which emphasize the right of
riparian landowners along a watercourse to use of the water,
and appropriative laws, which emphasize the right of prior
users of the water [25] ,, Most riparian or land ownership
rights are in effect east of the Mississippi River, whereas
most appropriative rights are in effect west of the
Mississippi River. Specific areas where these two doctrines
dominate are shown in Figure 2-10.
Most states divide their water laws into three categories:
(1) waters in well-defined channels or basins (natural
watercourses), (2) superficial waters not in channels or
basins (surface waters), and (3) underground waters not in
well-defined channels or basins (percolating waters or
ground waters). Potential water rights problems involving
each type of water and each of the three primary types of
land treatment are summarized in Table 2-16. This table is
intended to aid during planning and preliminary screening of
alternatives, but is not to be used as the basis for elim-
inating any alternatives.
2.4.1 Natural Watercourses
Most legal problems regarding natural watercourses involve
the diversion of a discharge with the subsequent reduction
in flow through the watercourse. In riparian states, diver-
sion of discharges that were not originally part of a stream
should not be cause for legal action. In appropriative
states, if the diversion would threaten the quantity or
quality of a downstream appropriation, the downstream user
has cause for legal action. Legal action may be either
injunctive, preventing the diverter from affecting the
diversion, or monetary, requiring the diverter to compensate
for the damages. If the area is not water-short and if the
watercourse is not already overappropriated, damages would
be difficult if not impossible to prove.
2-35
-------
2-36
-------
TABLE 2-16
POTENTIAL WATER RIGHTS PROBLEMS FOR LAND
TREATMENT ALTERNATIVES3
Land treatment process
Water definition and
water rights theory
Slow rate
Rapid
infiltration
Overland flow
Natural watercourses
Riparian
Appropriative
Combination
Unlikely
Likelyb
Unlikely
Likelyb
Likelyb Likelyb
Unlikely
Depends on location of
discharge from collection ditch
Depends on location of
discharge from collection ditch
Surface waters
Riparian
Appropriative
Combination
Percolating or
ground waters
Riparian
Appropriative
Combination
Unlikely
Unlikely
Unlikely
Unlikely
Likely
Likely
Unlikely
Unlikely
Unlikely
Possible
Likely
Likely
Likely
Likely0
Likely0
Unlikely
Unlikely
Unlikely
a. For existing conditions and alternative formulation stage of the planning
process only. It is also assumed that the appropriative situations are
water-short or overappropriated.
b. If effluent was formerly discharged to stream.
c. If collection/discharge ditch crosses other properties to the
natural watercourse.
2.4.2 Surface Waters
For surface waters, riparian and appropriative rights are
very similar. If renovated water from a land treatment
system crosses private property, a drainage or utility ease-
ment will be necessary.
2.4.3 Percolating Waters (Ground Waters)
Water rights conflicts may be caused either by a rise in the
ground water table that damages lands adjoining a land
treatment system or by the appearance of trace contaminants
in nearby wells. In riparian states, the landowner must
prove that his ground water is continuous with and down-
gradient from ground water underlying the land treatment
site. If the alleged damages are not the result of negli-
gent treatment site operation, cause for legal action will
be difficult to show. In appropriative states, increases in
ground water table elevations would not usually threaten
anyone's appropriative right. Thus, there would be no cause
for legal action.
2-37
-------
2.4.4 Sources of Information
For larger systems and in problem areas, the state or local
water master or water rights engineer should be consulted.
Other references to consider are the publications, _A
Summary-Digest of State Water Laws, available from the
National Water Commission [25] , and Land Application of
Wastewater and State Water Law, Volumes I and II [26, 27].
If problems develop or are likely with any of the feasible
alternatives, a water rights attorney should be consulted.
2.5 References ;
1.
2.
3.
4.
6.
7.
8.
Metcalf & Eddy Inc. Wastewater Engineering, Treatment,
Disposal, Reuse. Second Edition. McGraw Hill Book
Company. New York, N.Y. 1979.
Thomas, R.E. and J.P. Law. Properties of Waste
Waters. In: Soils for Management of Organic Wastes
and Waste Waters. American Society of Agronomy,
Madison, Wisconsin. 1977. p.47-72.
Davis, J.A. , III, and J. Jacknow.
Wastewater in Three Urban Areas.
47:2292-2297. September 1975.
Heavy Metals in
journal WPCF,
Pound, C.E., R.W. Crites, and J.V. Olson. Long-Term
Effects of Land Application of Domestic Wastewater:
Hollister, California, Rapid Infiltration Site. Envi-
ronmental Protection Agency, Office of Resecirch and
Development. EPA-600/2-78-084. April 1978.
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.
Chen, K.Y., et al. Trace Metals in Wastewater
Effluents. journal WPCF, 46:2663-2675. December
1975.
National Interim Primary Drinking Water Regulations.
U.S. Environmental Protection Agency. EPA-570/9-76-
003. 1976.
Interim Primary .Drinking Water Regulations;
Amendments. Federal Register. 45(168):57332-57357.
August 27, 1980. j
2-38
-------
9. Thomas, R. E. and D.M. Whiting. Annual and Seasonal
Precipitation Probabilities. U.S. Environmental
Protection Agency. EPA-600/2-77-182. August 1977.
10. Flach, K.W. Land Resources. In: Recycling Municipal
Sludges and Effluents on Land. Champaign, University
of Illinois. July 1973.
11. Whiting, D.M. Use of Climatic Data in Estimating
Storage Days for Soil Treatment Systems. Environmental
Protection Agency, Office of Research and
Development. EPA-600/2-76-250. November 1976.
12. Thomas, R.E., et al. Feasibility of Overland Flow for
Treatment of Raw Domestic Wastewater. U.S. Environ-
mental Protection Agency. EPA-66/2-74-087. 1974.
13. Sills, M.A. , et al. Two Phase Evaluation of Land
Treatment as a Wastewater Treatment Alternative - A
Rational Approach to Federal and State Planning and
Design Requirements. Proceedings of the Symposium on
Land Treatment of Wastewater, Hanover, New Hampshire.
August 20-25, 1978.
14. Moser, M.A. A Method for Preliminary Evaluation of
Soil Series Characteristics to Determine the Potential
for Land Treatment Processes. Proceedings of the
Symposium on Land Treatment of Wastewater. Hanover,
New Hampshire. August 20-25, 1978.
15. Taylor, G.L. A Preliminary Site Evaluation Method for
Treatment of Municipal Wastewater by Spray Irrigation
of Forest Land. Proceedings of the Conference of
Applied Research and Practice on Municipal and
Industrial Waste. Madison, Wisconsin. September 10-
12, 1980.
16. U.S. Environmental Protection Agency. 40 CFR 35,
, Appendix A, Cost-Effectiveness Analysis. September 27,
1978.
17. Reed, S.C., et al. Cost of Land Treatment Systems.
U.S. Environmental Protection Agency. EPA 430/9-75-
003. September 1979.
18. ,U. S. Environmental
Planning, 1982.
September 1981.
Protection Agency.
EPA-430/9-81-012.
Facilities
FRD-25.
2-39
-------
19
20
21
22
23
24
25
26
27
Patterson, W.L. and R.'F. Banker. Estimating Costs and
Manpower Requirements for Conventional Wastewater
Treatment Facilities. EPA 17090 DAN. October 1971.
Schmidt, C.J. and E.V. Clements, III. Demonstrated
Technology and Research Needs for Reuse of Municipal
Wastewater. U.S. Environmental Protection Agency. EPA
670/2-75-038. May 1975.
Wesner, E.M., et al. Energy Conservation in Municipal
Wastewater Treatment. U.S. Environmental Protection
Agency. EPA-430/9-77-011. March 1978.
Middlebrooks, E.J. and C.H. Middlebrooks. Energy
Requirements for Small Flow Wastewater Treatment
Systems. U.S. Army Corps of Engineers, Cold Regions
Research and Engineering Laboratory. May 1979.
Canter, L. Environmental Impact Assessment.
Hill Book Co. New York, New York. 1977.
McGraw-
U.S. Environmental Protection Agency. Regulations for
Preparation of Environmental Impact Statements « 40 CFR
Part 6, Section 6.512.
Dewsnup, R. L. and D.W, Jensen, eds. A Summary Digest
of State Water Laws. National Water Commission.
Washington, D.C. May 1973.
Large, D.W. Land Application of Wastewater and State
Water Law: An Overview (Volume I). U.S. Environmental
Protection Agency. EPA-600/2-77-232. November 1977.
Large, D.W. Land Application of Wastewater and State
Water Law: State Analyses (Volume II). U.S. Environ-
mental Protection Agency. EPA-600/2-78-175 . August
1978.
2-40
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Chapter 3
FIELD INVESTIGATIONS
3.1 Introduction
In contrast to conventional technologies, the analysis and
design of land treatment systems requires specific informa-
tion on the properties of the proposed site or sites. Too
little field data may lead to erroneous conclusions while
too much will result in unnecessarily high costs with little
refinement in the design concept. Experience indicates that
where uncertainty exists, it is prudent to adopt a
conservative posture relative to data gathering
requirements.
Figure 3-1 is a flow chart which presents a logical sequence
of field testing for a land treatment project. At several
points, available data are used for calculations or
decisions that may then necessitate additional field
tests. These additional tests are usually directed toward
estimation of new parameters, required for extending the
analysis. However, in some cases, additional field tests
may also be required simply to refine preliminary estimates.
Guidance on testing for wastewater constituents and soil
properties is provided for each land treatment process in
Table 3-1. Normally, relatively modest programs of field
testing and data analysis will be satisfactory. In certain
instances, however, more complex investigations and analyses
are required with higher levels of expertise in soil testing
and evaluation procedures. Firms specializing in these
areas are . available for assistance if expertise does not
exist within the firm having general design responsibility.
3.2 Physical Properties
Preliminary screening, as described in Chapter 2, of a
potential site (or sites) will ordinarily be based on exist-
ing field data available from a SCS county soil survey and
other sources. The next step involves some physical
exploration on the site. This preliminary exploration is of
critical importance to subsequent phases of the project.
Its two purposes are: (1) verification of existing data and
(2) identification of probable, or possible, site limita-
tions; and it should be performed with reasonable care. For
example, the presence of wet areas, water-loving plant
species, or surficial salt crusts should alert the designer
to the need for detailed field studies directed toward the
problem of drainage. The presence of rock outcroppings
3-1
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would signify the need for more detailed subsurface
investigations than might normally b,e required. If a stream
were located near the site, there would need to be
additional study of the surface and near-surface hydrology;
wells would create a concern about details of the ground
water flow, and so on. These points may seem obvious.
However, there are examples of systems that have failed
because of just such obvious conditions: limitations that
were not recognized until after design and construction were
complete.
TABLE 3-1
SUMMARY OF FIELD TESTS FOR
LAND TREATMENT PROCESSES
Processes
Properties
Slow rate (SR)
Rapid
infiltration (RI)
Overland flow (OF)
Wastewater
constituents
Soil physical
properties
Soil hydraulic
properties
Soil chemical
properties
Nitrogen, phosphorus,
SARa, ECa, boron
Depth of profile
Texture and structure
Infiltration rate
Subsurface
permeability
pH, CEC, exchangeable
cations (% of CEC),
ECa, metalsb, phos-
phorus adsorption
(optional)
BOD, SS, nitrogen,
phosphorus
Depth of profile
Texture and structure
Infiltration rate
Subsurface
permeability
pH, CEC, phosphorus
adsorption
BOD, SS, nitrogen,
phosphorus
Depth of profile
Texture and structure
Infiltration rate
(optional)
pH, CEC, exchangeable
cations (% of CEC)
a. May be more significant for 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.
3.2.1 Shallow Profile Evaluation
Following the initial field reconnaissance, some subsurface
exploration will be needed. In the preliminary stages, this
consists of digging pits, usually with a backhoe, at several
carefully selected locations. Besides exposing the soil
profile for inspection and sampling, the purpose is to
identify subsurface features that could develop into site
limitations, or that point to potential adverse features.
Conditions such as fractured, near-surface rock, hardpan
layers, evidence of mottling in the profile, lenses of open-
work gravel and other anomalies should be carefully noted.
For OF site evaluations, the depth of soil profile
evaluation can be the top 1m (3 ft) or so. The evaluation
should extend to 1.5 m (5 ft) for SR and 3m (10 ft) or more
for RI systems.
3-3
-------
3.2.2
Profile Evaluation to Greater Depths
In some site evaluations, the 2.5 to 3.7 m (about 8 to
12 ft) deep pits that can be excavated by a backhoe will not
yield sufficient information on the profile to allow all the
desired analyses to be made. For example, it may be
necessary to locate both the ground water table and the
depth to the closest impermeable layer. These depths
together with horizontal conductivity values and certain
other data are required to make mounding analyses,; design
drainage facilities, and for contaminant mass balance
calculations.
Auger holes or bore holes are frequently used to explore
soil deposits below the limits of pit excavation. Augers
are useful to relatively shallow depths compared to other
boring techniques. Depth limitation for augering varies
with soil type and conditions, as well as hole diameter. In
unconsolidated materials above water tables, 12.7 cm (5 in.)
diameter holes have been augered beyond 35 m (115 ft).
Cuttings that are continuously brought to the surface during
augering are not suitable for logging the soil materials.
Withdrawal of the auger flights for removal of the cuttings
near the tip represents an improvement as a logging
technique. The best method is to withdraw the flights and
obtain a sample with a Shelby tube or split-spoon1sampler.
Boring methods, which can be used to probe deeper than
augering, include churn drilling, jetting, and rotary
drilling. When using any of these methods it is preferable
to clean out the hole and secure a sample from the bottom of
the hole with a Shelby tube or split-spoon sampler. ,
3.3 Hydraulic Properties
The planning and design work relative to land treatment
systems cannot be accomplished without estimates of several
hydraulic properties of the site. The capacity of the soil
to accept and transmit water is crucial to the design of RI
systems and may be limiting in the design of some SR systems
as well. In addition, tracking the movement and impacts of
the wastewater and its constituents after application will
always be an important part of design.
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.
3-4
-------
3.3.1
Saturated Hydraulic Conductivity
A material is considered permeable if it contains intercon-
nected pores, cracks, or other passageways through which
water or gas can flow. Hydraulic conductivity (synonymous
with the term permeability in this manual) is a measure of
the ease with which liquids and gases pass through soil.
The term is more easily understood if a few basic concepts
of water flow in soils are introduced first.
In general, water moves through soils or porous media in
accordance with Darcy's equation:
(3-1)
where q = flux of water, the flow, Q per unit cross
sectional area, A, cm/h (in./h)
K = hydraulic conductivity (permeability), cm/h
(in./h)
dH/dl = hydraulic gradient, m/m (ft/ft)
The total head (H) can be assumed to be 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).
The hydraulic conductivity is defined as the proportionality
constant, K. The conductivity (K) is not a true constant
but a rapidly changing function of water content. Even
under conditions of constant water content, such as satura-
tion, 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 soil-water. However, for most purposes, saturated
conductivity (K) can be considered constant for a given
soil. The K value for flow in the vertical direction will
not necessarily be equal to K in the horizontal direction.'
ThisconditionTsknownasanisotropic.ItTsespecially
apparent in layered soils and those with large structural
units.
The conductivity of soils at saturation is an important
parameter because it is used in Darcy's equation to estimate
ground water flow patterns (see Section 3.6.2) and is useful
in estimating soil infiltration rates. Conductivity is
frequently estimated from other physical properties but much
experience is required and results are not sufficiently
3-5
-------
accurate for design purposes [1-5]. For example, hydraulic
conductivity is largely controlled by soil texture: coarser
materials having higher conductivities. However, in some
cases the soil structure may be equally important: well
structured fine soils having higher conductivities than
coarser unstructured soils.
In addition, hydraulic conductivity for a specific soil may
be affected by variables other than those relating to grain
size, structure, and pore distribution. Temperature, ionic
composition of the water, and the presence of entrapped air
can alter conductivity values [1].
3.3.2
Infiltration Capacity
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 with negligible ponding above the
surface, the infiltration rate is equal to the effective
saturated conductivity of the soil profile.
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 3-2
for several different soils. The effect of both texture and
structure on infiltration rate is illustrated by the curves
in Figure 3-2. The Aikeri clay loam has good structural
stability and actually has I a higher final infiltration rate
than the sandy loam soil. The Houston black clay, however,
has very poor structure and infiltration drops to near zero.
For a given soil, 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 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. Thus,
adequate time must be allowed when running field tests to
achieve a steady intake ratja.
Infiltration rates are affected by the ionic composition of
the soil-water, the type o£ vegetation, and tillage of the
soil surface. Factors that have a tendency to reduce
infiltration rates include clogging by suspended solids in
wastewater, classification of fine soil particles, clogging
due to biological growths, gases produced by soil microbes,
swelling of soil colloids, and air entrapped during a
3-6
-------
wetting event [6, 7]. These influences are all likely to be
experienced when a site is developed into a land treatment
system. The net result is to restrict the hydraulic
loadings of land treatment systems to values substantially
less than those predicted from the steady state intake rates
(see Figure 3-2), requiring reliance on field-developed
correlations between clean water infiltration rates and
satisfactory operating rates for full-scale systems. It
should be recognized that good soil management practices can
maintain or even increase operating rates, whereas
practices can lead to substantial decreases.
poor
0. 50
0 45
0-40
0. 35
0. 30
0. 25
0. 20
0. 1 5
0. .1 0
0. 05
0
"«e" CUr
-° .
CROWN SANOY LOAM
SILT
HOUSTON BLACK CLAY
20 40 60 80 1001 20 140
TIME, min
FIGURE 3-2
INFILTRATION RATE AS A FUNCTION
OF TIME FOR SEVERAL SOILS [3]
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 beneath the clogged layers
tends to be unsaturated and at unit hydraulic gradient.
3-7
-------
The short-term change in infiltration rate as a function of
time is of interest in the design and operation of SR
systems. A knowledge of how cumulative water intake varies
with time is necessary to determine the time of application
necessary to infiltrate the design hydraulic load. The
design application rate [of sprinkler systems should be
selected on the basis of the infiltration rate expected at
the end of the application iperiod.
3.3.3
Specific Yield
The term specific yield is most often used in connection
with unconfined aquifers and has also been called the
storage coefficient and drainable voids. It is usually
understood to be the volume of water released from a unit
volume of unsaturated aquifer material drained by a falling
water table. Although the term fillable porosity has occa-
sionally been used as a synonym for the above three terms,
it is actually a somewhat smaller quantity because of the
effect of entrapped air. The primary use of specific yield
values is in computing aquifer properties, for example, to
perform ground water mound height analysesTFor relatively
coarse-grained soils and deep water tables, it is usually
satisfactory to consider the specific yield a constant
value. As computations are not extremely sensitive to small
changes in the value of specific yield, it is usually satis-
factory to estimate it from knowledge of other soil
properties, either physical as in Figure 3-3 [8], or
hydraulic as in Figure 3-4 [9]. To clarify Figure 3-3,
specific retention is equal to the porosity . minus the
specific yield.
A note of caution, however. For fine-textured soils, espe-
cially as the water table ^oves higher in the profile, the
specific yield may not have a constant value because of
capillarity. Discussion of this complication may be found
in references [10, 11]. The effect of decreasing specific
yield with increasing water table height can lead to serious
difficulties with mound height analysis (Section 5.7.2).
3.3.4
Unsaturated Hydraulic Conductivity
The conductivity of soil varies dramatically as water
content is reduced below saturation. As an air phase is now
present, the flow channel is changed radically and now
consists of an irregular solid boundary and the air-water
interface. The flow path becomes more and more tortuous
with decreasing water content as the larger pores empty and
3-8
-------
50
45
40
S 35
3
o 30
;»
s; 25
- 20
UJ
£ 1'
111
°- 10
5
0
1 T
1 1 T
POROSITY
1/1B 1/8 1/4 1/21 2 4 8 16 32 64 128 256
MAXIMUM 10'/, GRAIN SIZE, mm
FIGURE 3-3
POROSITY, SPECIFIC RETENTION, AND
SPECIFIC YIELD VARIATIONS WITH GRAIN SIZE
SOUTH COASTAL BASIN, CALIFORNIA [8]
40
£ 30
=3
5 20
>•
m
i—
u 10
S 8
Ul
' 6
o 5
u 4
: 3
u.
Z 2
UJ
0.
V)
1
i n . /h C
cn/h 0.
/
/
>
/
/
~s
/
/
.1 0.2 0.3 0.4 0.6 0.8
25 0-5 0.8 1 1.5 2
^
,—
«-*"^
^—
***
( ^
— - -^
— -
,,
\ 2 34 6810 20 30 40 60 80 100
2.5 5 8 10 152025 50 80 100 1 50 200250
HYDRAULIC CONDUCTIVITY
FIGURE 3-4
GENERAL RELATIONSHIP BETWEEN SPECIFIC YIELD
AND HYDRAULIC CONDUCTIVITY [9]
3-9
-------
flow becomes confined to ^he smaller pores. Compounding the
effect of decreasing cross-sectional area for flow is the
effect of added friction as the flow takes place closer and
closer to solid particle surfaces. The conductivity of
sandy soils, although much higher at saturation than loamy
soils, decreases more rapidly as the soil becomes less
saturated. In most cases, the conductivities of sandy soils
eventually become lower than finer 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 is complex. A
discussion of such calculations is outside the scope of this
manual. The user is referred to references [1, 10, 12, 13]
for further details and solution of special cases.
3.3.5
Profile Drainage
For SR 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 know-
ledge, together with knowledge of the limiting infiltration
rate of the soil and the ground water movement and buildup,
allows the designer to make a reasonable estimate of the
maximum volume of water that can be applied to a site and
still produce adequate crops. A typical moisture profile
and its change with time following an irrigation is illus-
trated in Figure 3-5 for an initially saturated profile.
Moisture profile changes may be determined in the field with
tensiometers [4].
3.4 Infiltration Rate Measurements
The value that is required in land treatment design 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.
There are many potential techniques for measuring infiltra-
tion including flooding basin, cylinder infiltrometers,
sprinkler infiltrometers and air-entry permeameters. A
comparison of these four techniques is presented in
Table 3-2. In general, the test area and the volume of
water used should be as large as practical. The two main
categories of measurement techniques are those involving
3-10
-------
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 inf iltrometer provides an ••"* impact
similar to that of natural rain. Flooding infiltrometers
are easier to operate than sprinkling infiltrometers, but
they almost always give higher equilibrium infiltration
rates. In some cases, the difference is very significant,
as shown in Table 3-3. Nevertheless, the flooding
measurement techniques are generally preferred because of
their simplicity. Relationships between infiltration rates
as obtained by various flooding techniques and the loading
rates of RI systems are discussed in Section 5.4.1. The air
entry permeameter is described in Section 3.5.2.
0 ->-WER CONTENTS SATURATION
FIGURE 3-5
TYPICAL PATTERN OF THE
CHANGING MOISTURE PROFILE DURING DRYING AND DRAINAGE
If a sprinkler or flood application is planned, the test
should be conducted in surficial materials. If RI is
planned, pits must be excavated to expose lower horizons
that will constitute the bottoms of the basins. 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 test should be conducted at this
layer to ensure a conservative estimate.
3-11
-------
TABLE 3-2
COMPARISON,OF INFILTRATION
MEASUREMENT TECHNIQUES
Measurement
technique
Flooding
basin
Cylinder
infiltrometer
Sprinkler
infiltrometer
Air entry
perraeameter
(AEP)
Water Time
use per per test,
test, L h
2,000-10,000 4-12
400-700 1-6
1,000-1,200 1.5-3
10 0.5-1
Equipment
needed
Backhoe
or blade
Cylinder
or earthen
berm
Pump, pres-
sure tank,
sprinkler.
cans
AEP
apparatus,
standpipe
with resevoir
Comments
Tensiometers
may be used
Should use large diameter
cylinders (1 m diameter)
For sprinkler applications,
soil should be at field
capacity before test
Measures vertical hydraulic
conductivity. If used to
measure rates of several
different soil layers, rate
is harmonic mean of conducti-
vities from all soil layers.
Note: See Appendix G for metric conversions.
TABLE 3-3
SAMPLE COMPARISON OF( INFILTRATION MEASUREMENT
USING FLOODING AND SPRINKLING TECHNIQUES [14]
Measurement
technique
Equilibrium infiltration
rate, cm/h
Overgrazed Pasture, grazed but
', pasture having good cover
Double-cylinder ;
infiltroraeter (flooding) 2.82
Type F rainfall
simulator (sprinkling) 2.90
5.97
2.87
Infiltration test results are typically plotted as shown in
Figures 3-2 and B-3. The derivation of design values from
these test results is presented in Appendix B.
Before discussing the infiltration measurement techniques,
it should be pointed out that the U.S. Public Health Service
(USPHS) percolation test used for establishing the size of
septic tank drain fields [15] is definitely not recommended
as a method for estimating infiltration.
3-12
-------
3.4.1
Flooding Basin Techniques
Pilot-scale infiltration basins represent an excelle-nt tech-
nique for determining vertical infiltration rates. The
larger the test area is, the less the relative error due to
lateral moisture movement will be and the better the
estimate. Where such basins have been used, the plots have
generally ranged from about 0.9 m (10 ft ) to 0.1 ha
(0.25 acre). In some cases, pilot basins of large scale (2
to 3.2 ha or 5 to 8 acres) have been used to determine
infiltration rates and demonstrate feasibility with the
thought of incorporating the test basins into a subsequent
full-scale system [16]. Figure 3-6 is a photograph of a
pilot basin.
FLOODING BAS
FIGURE 3-6
USED FOR MEASURING INFILTRATION
The Corps of Engineers has used flooding basin tests to
determine infiltration rates on thr'ee existing land
treatment sites [17]. Basins of 6.1 m (20 ft) and 3 m
(10 ft) diameter were used and it was concluded that the 3 m
(10 ft) diameter basin was large enough to provide reliable
infiltration data. About 4 man-hours were required for
completing an installation and less than 1,000 L (265 gal)
of water would probably be adequate to complete a test. As
this testing procedure will undoubtedly become more widely
adopted, Figures 3-7 and 3-8 are included to show the
details of installation [18].
3-13
-------
GROOVE CUTTING TOOL-
CENTER ROD
HANDLE
METAL PIPE-
FOOT STOP
STEEL PLATE
7
15cm
t
FIGURE 3-7
GROOVE PREPARATION FOR FLASHING (BERM) [18]
20c« ABOVt SURFACE
15 cm BEL ill (f SURFACE
ALUMINUM FLASHING
FIGURE 3-8
SCHEMATIC OF FINISHED INSTALLATION [18]
3-14
-------
An important assumption in any flooding type infiltration
test is a saturated (or nearly so) condition in the upper
soil profile. Thus, an essential part of this method is the
installation of a number of tensiometers within the test
area at various depths to verify saturation by their
approach to a zero value of the matric potential, before
obtaining any head drop (water level) measurements. In the
Corps of Engineers studies, six tensiometers were installed
in a 1 m (3.3 ft) diameter circle concentric with the center
of the 3m (10 ft) diameter test basin as shown in
Figure 3-8. Table 3-4 gives their suggested- depths of
placement in a soil of well-developed horizons; however, any
reasonable spacing above strata of lower conductivity, if
such exist, should be adequate. In soils lacking well-
developed horizons, a uniform spacing down to about 60 cm
(24 in.) should suffice. A seventh tensiometer installed at
a depth of about 150 cm (60 in.) is also suggested, but is
not critical.
TABLE 3-4
SUGGESTED VERTICAL PLACEMENT OF
TENSIOMETERS IN BASIN INFILTROMETER TESTS [18]
No.
1
2
3
4
5
6
Soil
horizon
A
B
B
B
B
C
Placement
Midpoint of A
1/5
2/5
3/5
4/5
15
distance
distance
distance
distance
cm below
between
between
between
between
A/B
A/B
A/B
A/B
and
and
and
and
B/C
B/C
B/C
B/C
interfaces
interfaces
interfaces
interfaces
B/C interface
Following installation and calibration of the tensiometers,
a few preliminary flooding events are executed to achieve
saturation. Evidence of saturation is the reduction of
tensiometer readings to near zero through the upper soil
profile. Then a final flooding event is monitored to derive
a cumulative intake versus time curve. A best fit to the
data plotted on log-log paper allows calculation of the
infiltration parameters, as shown in Figure 3-9. Subsequent
observation of tensiometers can then provide data on profile
drainage.
3-15
-------
CD
0>
CO
LLJ
CO
cc
>3 '31VU 3IV1MI 'I HO
•3 'amm 3Aiivin»no 'A
3-16
-------
3.4.2
Cylinder Infiltrometers
The equipment and basic methodology for this popular mea-
surement technique are described in references [9, 19, 20].
The equipment setup for a test is shown in Figure 3-10.
To run a test, a metal cylinder is carefully driven or
pushed into the soil to a depth of about 10 to 15 cm (4 to
6 in.). Measurement cylinders of from 15 to 35 cm (6 to
14 in.) diameter have generally been used in practice, with
lengths of about 25 to 30.5 cm (10 to 12 in.). Divergent
flow, partially obstructed by the portion of the cylinder
beneath the soil surface, is further minimized by means of a
"buffer zone" surrounding the central ring. The buffer zone
is commonly provided by another cylinder 40 to 70 cm (16 to
30 in.) diameter, driven to a depth of 5 to 10 cm (2 to
4 in.) and kept partially full of water during the time of
infiltration. This particular mode of making measurements
has come to be known as the double-cylinder or double-ring
infiltrometer method. Care must be taken to maintain the
water levels in the inner and outer cylinders at the same
level during the measurements. Alternately, buffer zones
are provided by diking the area around the intake cylinder
with low (7.5 to 10 cm or 3 to 4 in.) earthen dikes.
If the cylinder is installed properly and the test carefully
performed, the technique should produce data that at least
approximate the vertical component of flow. In most soils,
as the wetting front advances downward through the profile,
the infiltration rate will decrease with time and approach a
steady-state value asymptotically. This may require as
little as 20 to 30 minutes in some soils and many hours in
others. Certainly, one could not terminate a test until the
steady-state condition was attained or the results would be
totally meaningless (see Figure 3-2).
Anyone contemplating the use of this measurement technique
because of its apparent simplicity should also be aware of
its limitations. Discussions dealing specifically with the
problem of separating the desired vertical component from
the total moisture flux, which may include a large lateral
component, can be found in references [21, 22].
A more promising direction is suggested in reference [19] in
which the main conclusion is applicable: to minimize errors
in the use of the cylinder infiltrometer technique; use only
large-diameter cylinders
and
careful
installation
techniques.Thespecificrecommendation
diameterTs a minimum of 1 m (3.3 ft).
as to cylinder
3-17
-------
BUFFER POND
LEVEL —j
GROUND LEVEL
GAGE INDEX
ENGINEER'S SCALE
WELDING ROD
HOOK
WATER SURFACE
— INTAKE CYLINDER —
FIGURE 3-10
CYLINDER INFILTROMETER IN USE
3-18
-------
Installation should disturb the soil as little as possible.
This generally requires thin-walled cylinders with a
beveled edge and very careful driving techniques. In soft
soils, cylinders may be pushed or jacked in. In harder
soils, they must be driven in. The cylinders must be kept
straight during this process, especially avoiding a
"rocking" or tilting motion to advance them downward. In
cohesionless coarse sands and gravels, a poor bond between
the soil and the metal cylinder often results, allowing
seepage around the edge of the cylinder. Such conditions
may call for special methods to be devised. One such method
is to construct the test area by forming low dikes and
covering the inside walls with plastic sheet to prevent
lateral seepage [19]. This begins to approach the basin
flooding method described in Section 3.4.1.
Measurements of infiltration capacity of soils 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. Problem areas can be anticipated
more readily by field study following spring thaws or
extended periods of heavy rainfall and recharge [23].
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.
Although far too few extensive tests have been made to
gather meaningful statistical data on the cylinder infiltro-
meter technique, one very comprehensive study is available
from which tentative conclusions can be drawn.
Test results from three plots (357 individual tests) 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
inf iltrometers. The inside cylinders had a 15 cm (6 in.)
diameter; the outside cylinders, where used, had a 30 cm
(12 in.) diameter. For this particular soil, the presence
of a buffer zone did not have a significant effect on the
measured rates. These data, although very carefully taken,
overestimate the field average by about 40%, indicating that
small diameter cylinders will consistently overestimate the
true vertical infiltration rate [14].
3-19
-------
3.4.3
Sprinkler Infiltrometers
Sprinkler infiltrometers ar£ used primarily to determine the
limiting application rate for systems using sprinklers. To
measure the soil intake rate for sprinkler application/ the
method presented in reference [24] can be used. The equip-
ment 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 infiltrometer is
presented in Figure 3-11. A 1,814 kg (2 ton) capacity
trailer houses a 1,135 L (300 gal) water supply tank and 2
self-priming centrifugal pumps. The sprinkler pump should
have sufficient capacity to deliver at least 6.3 L/s
(100 gal/min) at 34.5 N/cm2 (50 lb/in.2) 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 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 1.5 m (5 ft) 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
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 calcu-
lated. The calculated rate of infiltration is equal to the
limiting application rate that the soil system can accept
without runoff.
Disadvantages of the technique are the time and expense
involved in determining intake rates using a sprinkler
infiltrometer. There is, in fact, little reason to try to
measure maximum intake rates on soils that are going to be
loaded far below these maximum rates, as is the case for
most SR system designs. However, where economics dictate
the use of application : rates far in excess of the
consumptive use (CU) of the proposed crop on soils of known
or suspected hydraulic limitation, a test such as described
3-20
-------
Ul
CD
.a.
IU
O
CO —
111 cd.
rr- LU
Q-
CO
3-21
-------
above should be given careful consideration. Local SCS
field personnel or irrigation specialists should be
consulted for opinions on ithe advisability of making such
tests.
3.5 Measurement of Vertical Hydraulic Conductivity
The rate at which water percolates through the soil profile
during application depends on the "average" saturated
conductivity (K ) of the prbfile. If the soil is uniform, K
is assumed to Be constant ;with depth. Any differences in
measured values of K are linen due to normal variations in
the measurement technique. ' Thus, average K may be computed
as the arithmetic mean of n samples:
K
K
(3-2)
where K
am
arithmetic mean vertical conductivity
Many soil profiles, approximate a layered series of uniform
soils with distinctly different K values, generally de-
creasing 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] ;
K
hm
K.
D
K.
+ d
K~
n
n
(3-3)
where
D = soil profile depth
n
K
hm
depth of nth layer
harmonic mean conductivity
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 qases, it has been shown that the
geometric mean provides the;best estimate of the true K [25,
26, 27]:
K
where K
gm
K
K
Kn)
1/n
(3-4)
gm
geometric mean conductivity
3-22
-------
The relationships between vertical hydraulic conductivity
and the loading rates for RI systems are discussed in
Section 5.4.1.
There are many in situ methods available to measure vertical
saturated conductivity. For convenience, these may be
divided into methods in the presence of and in the absence
of a water table. In addition, there are several laboratory
techniques which are used to estimate saturated conductivity
in soil samples taken from pits or bore holes. Either
constant-head or falling-head permeameters can be used for
these estimates. Detailed test procedures may be found in
any good soil mechanics text. The main criticisms of the
use of laboratory techniques are the disturbance of the
sample during collection by pushing or driving a sampler
into it and the small size of sample tested. These
criticisms are entirely valid. Nonetheless, when estimates
of conductivity are needed from deep lying strata that
physically cannot be examined in situ, then sampling and
laboratory measurement may be the only feasible technique.
The only important test used below a water table is the pipe
cavity, or piezometer tube method [28], described in
practical terms in reference [29]. This test is especially
helpful when the -soils below the water table are layered,
with substantially different vertical conductivities in each
strata. In such cases, a separate test should be run in
each of the layers of interest in order to apply
Equation 3-3. The most important application occurs when
there is evidence of vertical gradients that could transport
percolate downward to lower lying aquifers.
Methods available to measure vertical saturated conductivity
in a soil region above, or in the absence of a water table,
include the ring permeameter [9, 30], the gradient-intake
[1, 31], the double-tube [1, 30] and the air-entry
permeameter [1, 32, 33]. With the development of the newer
techniques, the ring permeameter method, which requires an
elaborate setup and uses a lot of water per test, is no
longer in widespread use. The gradient-intake technique is
primarily used as a site screening method, for ranking the
relative conductivities of different soils. Conductivity
values obtained by this method are considered conservative
as they often prove to be lower than those produced by other
methods.
In practice, the double-tube and air-entry permeameters have
found favor and are used more frequently than the other
techniques. Therefore, only these two methods will be
discussed. Enough information will be given here to enable
the user to understand the basic measurement concepts.
3-23
-------
Procedural details are covered more completely in the refer-
ences supplied.
3.5.1
Double-Tube Method
The test is run in a hole augered to the depth of the soil
layer whose vertical conductivity is desired. Certainly
that of the most restrictive layer is needed as a minimum.
Additional layers in the profile should be investigated to
ensure proper characterization. The value of K which is
computed from double-tube includes a small horizontal
component but primarily reflects vertical flow. The appara-
tus (commercially available*) is shown in Figure 3-12. To
perform a test, it is first necessary to create a saturated
zone of soil beneath the embedded tubes. This is
accomplished by applying water through both tubes for
several hours. Then two sets of measurements are required:
1. Water level versus time readings for the inner tube
with the supply to this tube stopped while
maintaining the supply to the outer tube.
2. Water level versus time readings for the inner tube
with the supply to this tube and to the outer tube
stopped. The level in this outer tube is held
(closely) the same as that in the inner tube during
this second set of readings by manipulating a valve
(C in Figure 3-12).
The curves of water level , decreases versus time are then
plotted to the same scale and K is calculated. Details of
the calculation and curves needed to obtain a dimensionless
factor for the calculation are to be found in references [1,
30] and are supplied by the[manufacturer of the equipment.
3.5.2
Air-Entry Permeameter
The air-entry permeameter was devised to investigctte the
significance of flows in the capillary zone [32]. Using the
device as shown in Figure 3-13, the soil-water pressure at
which air entered the saturated voids was approximated.
*Soiltest,Inc.,Evanston, Illinois 60202. Mention of prop-
rietary equipment does not constitute endorsement by the
U.S. Government.
3-2M-
-------
VALVE (TYPICAL)-
WATER SUPPLY
=£
]
FIGURE 3-12
SCHEMATIC OF DOUBLE-TUBE APPARATUS [l]
RESERVOIR
SUPPLY VALVE
DISK
AIR ESCAPE
VALVE
WET FRONT
FIGURE 3-13
SCHEMATIC OF THE AIR-ENTRY PERMEAMETER [1,32]
3-25
-------
Assuming a relationship between this value and the pressure
just above the advancing front of a wetted zone, the
conductivity of a mass of soil absorbing water to the point
of saturation can be calculated. Because of the
availability of research data to indicate that this conduc-
tivity value is closely equal to one-half the saturated
hydraulic conductivity, a new method of determining vertical
hydraulic conductivity at saturation became available.
Although the method may appear to have the limitation of
requiring several assumptions, it compares favorably with
other accepted methods and has some distinct advantages.
The equipment is relatively simple; the test does not. take
much time; and, perhaps most important, not much water is
required. A few liters of water will generally suffice for
a single test.
In operation, water is added through the supply valve with
the air valve open until the embedded cylinder becomes full
(the function of the disk is to act as a splash plate). On
filling the cylinder, the|air valve is closed and water is
allowed to infiltrate downward, the reservoir being kept
full.
When the wet front, Lf, has reached the desired depth,
dependent on soil texture and structure (see subsequent
remarks), no more water is added to the reservoir. The drop
in water level with time is measured in order to calculate
an intake rate. Now the supply valve is closed and the
pressure on the vacuum gage is noted periodically. ! At some
point it will reach a maximum (minimum pressure) and then
begin to decrease again. This minimum pressure corresponds
closely to the air-entry pressure, Pa, of the wetted zone
when corrected for gage -height, G, and depth of wetted
zone, Lf.
When the air-entry permeameter is employed at the soil
surface, it is essentially an infiltrometer and as such
could readily be listed with the method of Section 3.4.2.
Several investigators [32, 33] have used the method to
develop vertical conductivity profiles. It has been
suggested that digging a trench with an inclined bottom,
then moving the air-entry permeameter to selected points
along the trench bottom is a good method of accomplishing
this.
A criticism of the original technique [32] was based on the
suggested methods of defining the depth of the wetted zone
beneath the cylinder. These called for digging around the
bottom of the cylinder after completion of the measurements
to locate the wet front qr using a metal rod to probe the
soil, attempting to detect the depth at which penetration
3-26
-------
resistance increases. However, the air-entry permeameter
was modified by adding a fine tensiometer probe through the
lid of the device. By setting the probe to correspond to
the desired depth of wetted zone, Lf (about 15 cm or 6 in.
in sand and 5 cm or 2 in. in massive clay) , it was possible
to detect the arrival of the wetted front during, rather
than after operation of the permeameter. This modification
also allows the method to be used in somewhat wetter soils
than those previously required.
Referring to Figure 3-13, the vertical hydraulic
conductivity of the "rewet" zone, i.e., the zone being
saturated, is calculated from Equation 3-5.
K _ Q
K ~ A TIT
(3-5)
where:
Q = volumetric intake rate through area, A, of
the permeameter
H-, =
lr ~» ~~
•mm
G =
Lf =
the matric potential of the soil just below
the wetting zone, assumed to be 0.5 Pa. It
is less than atmospheric pressure and there-
fore a negative quantity in Equation 3-5
air-entry value, calculated as Pm^n + Lf
+ G; also a negative pressure
minimum pressure (maximum vacuum) read from
the vacuum gage after stopping the water
supply
height of the vacuum gage above the soil
surface
depth of the wetted zone
Hr = height of the water level in the reservoir
above the soil surface
Then, as stated previously, the vertical hydraulic conduc-
tivity at saturation is assumed to be two times the value oT
K as calculated from Equation 3-5.
3.6 Ground Water
In most land treatment systems, and especially for the
higher rate systems, .interaction with the ground water is
important and must be considered carefully in the
3-27
-------
preliminary analysis phase,. Problems with mounding,
drainage, offsite travel and ultimate fate of contaminants
in the percolate will have to be addressed during both the
analysis and design phases. Early recognition of potential
problems and analysis of mitigating measures are necessary
for successful operation of the system. This cannot be
accomplished without competent field investigation. Some
key questions to be answered are:
1. How deep beneath the surface is the (undisturbed)
water table?
2. How does the natural water table depth fluctuate
seasonally? . ;
3. How will the ground water table respond to the
proposed wastewater loadings?
4. In what direction and how fast will the mixture of
percolate and groui-id water move from beneath the
area of application? Is there any possibility of
transport of contaminants to deeper potable
aquifers?
5. What will be the quality of this mixture as it
flows away from the site boundaries?
6. If any of the conditions measured or predicted
above are found to ;be unacceptable, what steps can
be taken to correct;the situation?
3.6.1 Depth/Hydrostatic Head
A ground water table is defined as the contact zone between
the free ground water and the capillary zone. It is the
level assumed by the water in a hole extended a short
distance below the capillary zone. Ground water conditions
are regular when there is only one ground water surface and
when the hydrostatic pressure increases linearly with
depth. Under this condition^ the piezometric pressure level
is the same as the free ground water level regardless of the
depth below the ground ^ater table at which it is
measured. Referring to Figure 3-14, the water level in the
"piezometer" would stand at the same level as the "well" in
this condition.
In contrast to a well, a piezometer is a small diameter open
pipe driven into the soil such that (theoretically) there
can be no leakage around the pipe. As the piezometer is not
slotted or perforated, it can respond only to the
hydrostatic head at the point where its lower open end is
3-28
-------
located. The basic difference between water level measure-
ment with a well and hydrostatic head measurement with a
piezometer is shown in Figure 3-14.
WELL
PIEZOMETER
GROUND SURFACE
.'.'•..'••'. ' GROUND WATER TABLE
FIGURE 3-14
WELL AND PIEZOMETER INSTALLATIONS
Occasionally there may be one or more isolated bodies of
water "perched" above the main water table because of lenses
of impervious strata that inhibit or even prevent seepage
past them to the main body of ground water below. Other
"irregular" conditions are described by Figure 3-15.
Reliable determination of either ground water levels or
pressures requires that the hydrostatic pressures in the
bore hole and the surrounding soil be equalized. Attainment
of stable levels may require considerable time in
impermeable materials. This is called hydrostatic time-lag
and may be froni hours to days in materials of practical
interest (K > 107 cm/s).
Two or more piezometers located together, but terminating at
different depths, can indicate the presence, direction and
magnitude (gradient) of components of vertical flow if such
exists. Their use is indicated whenever there is concern
about- movement of contaminants downward to lower lying
aquifers. Figure 3-15, taken from reference [34], shows
several observable patterns with explanations. Descriptions
of the proper methods of installation of both observation
wells and piezometers may be found in references [9, 34].
,3-29
-------
I
.'i> ' f
i
'.v .•
"A v '. A
• :
THE PIEZOMETERS IN-
DICATE THAT THE
GROUND WATER IS GO-
ING DOWN AND THAT
THERE IS SOME NATU-
RAL DRAINAGE.
I
". A /\ - V •
^>.'!VA:*.
• -i •. j> • A • v • •
'.••.V . v . . . A .
THE PIEZOMETERS IN-
DICATE A HYDROSTATIC
PRESSURE OR THAT
THERE IS WATER COM-
ING UP FROM A DEEP-
ER STRATA.
THE PIEZOMETERS IN-
DICATE A HYDROSTATIC
PRESSURE IN A STRAT-
UM AND THAT WATER IS
BEING FORCED BOTH UP
AND DOWN FROM THE
STRATUM
'.'• I- •
THE PIEZOMETERS IN -
DICATE THAT GROUND
WATER IS MOVING INTO
A STRATUM AND GOING
OUT OF THE AREA.
FIGURE 3-15
VERTICAL FLOWS INDICATED BY PIEZOMETERS [34]
3.6.2
Flow
Exact mathematical description of flows in the saturated
zones beneath and adjacent to (usually downgradient) land
treatment systems is a practical impossibility. However,
for the majority of cases the possession of sufficient field
data will allow an application of Darcy's equation
(Equation 3-1). Answers can thus be obtained which are
satisfactory for making design decisions. In particular,
there are questions which recur for each proposed project,
and which may be approachedi in the manner suggested.
1. What volume of native ground water flows beneath
the proposed site for dilution of percolate? This
is a direct application of Equation 3-1. The width
of the site measured normal to the ground water
flow lines times the aquifer thickness equals the
cross-sectional area used to compute the total
flow.
2. What is the mean travel time between points of
entry of percolate into the ground water and poten-
tial points of discharge or withdrawal? Again,
Equation 3-1 is ;used to compute the flux, q.
Dividing the flux by the aquifer porosity
(Figure 3-3) gives an average ground water
velocity. Travel time is computed as the distance
between the two points of interest (they must both
lie on the same flow line) divided by the average
velocity.
3-30
-------
3. What changes in hydraulic gradient (mound
configuration) will be required to convey the
proposed quantity of percolate away from beneath
the area of application? Methods of answering this
question are presented in Section 5.7.2.
The ' field data and hydrogeologic estimates required to
answer these questions include:
1. Geometry of the flow system, including but not
limited to
a. Depth to ground water
b. Depth to impermeable barrier; generally taken
to be .any layer which has a hydraulic
conductivity less than 10% of that of the
overlying deposits [35].
c. Geometry of the recharge (application) area.
2. Hydraulic gradient - computed from water levels in
several observation wells (assuming only horizontal
flow), knowing distances between wells.
3. Specific yield (see Section 3.3.3). In some areas
of the United States, the SCS has investigated the
soil profiles sufficiently to provide an estimate
of specific yield for a particular site [5].
4. Hydraulic conductivity in the horizontal
direction. Field measurement of this parameter by
the auger-hole method is covered in the following
section.
3.6.2.1 Horizontal Hydraulic Conductivity
Horizontal conductivity cannot be assumed from a knowledge
of vertical conductivity (Section 3.5). In field soils,
isotropic conditions are rarely encountered, although they
are frequently assumed for the sake of convenience.
"Apparent" anisotropic conductivity often occurs in
unconsolidated media because of interbedding of fine-grained
and coarse-grained materials within the profile. Such
interbedding restricts vertical flow much more than it does
lateral flow [25]. Although the interbedding represents
nonhomogeneity, rather than anisotropy, its effects on the
conductivity 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
3-31
-------
and horizontal permeability for specific sites. The
possible spread of ratios is indicated in Table 3-5, which
is based on field measurement^ in glacial outwash deposits
(Sites 1-5) [36] and in a ' river bed (Site 6)' [37],, 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 3-5
MEASURED RATIOS OF HORIZONTAL TO
VERTICAL CONDUCTIVITY [36, 37]
Effective
horizontal
permeability,
Site Kh, m/d Kh/Kv
Remarks
1
2
3
4
5
6
42
75
56
100
72
72,
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 measurements in
field)
86 16.0 (From analysis of
recharge flow system)
It is apparent that if accurate information regarding hori-
zontal conductivity is required for an analysis, field
measurements will be necessary. Of the many field measure-
ment techniques available, the most useful is the auger hole
technique [38] . Details of the test technique may also be
found in [1, 9, 30, 34]. Although auger hole measurements
are certainly influenced by the vertical component of flow,
studies have demonstrated that the technique primarily
measures the horizontal component [39]. A definition sketch
of the measurement system is shown in Figure 3-16 and the
experimental setup is shown in Figure 3-17. The technique
is based on the fact that if the hole extends below the
water table and water is quickly removed from the hole (by
bailing or pumping), the; hole will refill at a rate
determined by the conductivity 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 conductivity is calcu-
lated 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 conduc-
tivity based on an "average" hydraulic head. This is
usually the case.
3-32
-------
SOIL SURFACE
2a
WATER TABU
Ay in
FIGURE 3-16
DEFINITION SKETCH FOR AUGER-HOLE TECHNIQUE
DOUBLE-ACTING
DIAPHRAGM PUMP
EXHAUST HOSE
MEASURING POINT
-STANDARD
///////////////////// ^
/
>
SUC-TION HOSE _/f
^Tn »
/
/
TAPE AND /
5cm FLOAT ^
/:
y
/"
/
/
\
^.
"S
i
r1
,
\
^v
\
\
\
V
r
\
*-
\
\
\
\h-\\\\\\\
II
V
^^ — STATIC
^
^ FINISH
^ START T
FIGURE 3-17
EXPERIMENTAL SETUP FOR AUGER-HOLE TECHNIQUE
3-33
-------
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 [39] allows
determination of the horizontal and vertical components (Kh
and KV in anisotropic soils by combining auger hole measure-
ments with piezometer measurements at the same depth. If
the auger hole terminates at (or in) an impermeable;layer,
the following equation applies (refer to' Figure 3-16 for
symbols):
= 523,000a2
At
(3-6)
where a = auger hole radius, m
At = time for water to rise y, s
K^ = horizontal conductivity, m/d
y0/yj_ = depths defined in Figure 3-16, any units,
usually cm l
If an impermeable layer is encountered at a great, depth
below the bottom of the auger hole, the equation becomes:
_/i,o45,ooo da2
- (2d + a)
(3-7)
where d = depth of auger hole, m
Charts for both cases are available in references [29,
34], An alternative formula, claimed to be slightly more
accurate, has been developed [40]. This 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
conductivity in the presence of a water table. Slug tests,
such as described in reference [41] can be used to calculate
Ktj from the Thiem equation after observing the rate of rise
or water in a well following an instantaneous removal of a
volume of water to create a hydraulic gradient. Pumping
tests, which are already familiar to many engineers, would
certainly provide a meaningful estimate. A comprehensive
discussion of pumping tests> as well as other ground water
problems is presented in reference [42] ; example problems
3-34.
-------
and tables of the mathematical functions needed to evaluate
conductivity from drawdown measurements are also presented.
There are some 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.
Measurement of horizontal conductivity 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. If the layer was
restrictive enough to vertical flow, a perched water table
would result upon application of wastewater. In such cases,
the mound height analysis described in Section 5.7.2 should
be used to determine whether perching would be a problem.
Although mounding calculations are p'resented in Chapter 5
(dealing with RI), it is quite possible that mounding may
occur beneath SR systems as well. The user of this manual
should be aware of this possibility. The analysis requires
an estimate of the horizontal conductivity. Either a
modified version of the double-tube technique described in
Section 3.5.1 [31] or the shallow well pump-in test [1, 9,
30] can be used to estimate K^. The latter of these two
testing methods is, in principle, the reverse of the auger-
hole test.
3.6.2.2 Percolate/Ground Water Mixing
An analysis of the mixing of percolate with native ground
water is needed for SR or RI systems that discharge to
ground water if the quality of this mixture as it flows away
from the site boundaries is to be determined. The
concentration of any constituent in this mixture can be
calculated as follows:
(3-8)
where Cmix = concentration of constituent in mixture
CD = concentration of constituent in percolate
3-35
-------
Q = flow of percolate
tr >
Cgw = concentration of constituent in ground water
QqW = flow of ground water
The flow of ground water can be calculated from Darcy's Law
(Equation 3-1) if the gradient and horizontal hydraulic
conductivity are known. Thi^s is not the entire ground water
flow, but only the flow within the mixing depth.
Relationships of the percolate flow and concentrations of
constituents are discussed in Chapters 4 and 5. Equation 3-8
is valid if there is complete mixing between the percolate
and the _ native ground water. This is usually not the
case. Mixing in the vertical direction may be substantially
less than mixing in the horizontal direction.
An alternative approach to estimating the initial dilution
is to relate the diameter of the mound developed by the
percolate to the diameter ;of the application area. This
ratio has been estimated to be 2.5 to 3.0 [43, 44]. This
ratio indicates the relative1 spread of the percolate and can
be used to relate the mixing of percolate with ground
water. Thus, an upper limit of 3 for the dilution ratio can
be used when ground water If low is substantially (5 to 10
times) more than the percolate flow. If the ground water
flow is less than 3 times the percolate flow, the actual
ground water flow should be used in Equation 3-8.
3.6.3
Ground Water Quality
It is recommended that where a water table is known to exist
that could possibly be impacted by the project, that
baseline ground water quality data be collected. The
details of number, location, depth, etc. of sampling wells
are best left until after a preliminary hydrogeologic study
of the site has been completed. Then following reasonably
well established guidelines [23, 45, 46, 47], sampling wells
may be designed in something approaching an optimum manner.
The parameters that should be measured in samples taken from
the ground water are those specified under the "National
Interim Primary Drinking Water Regulations" [48] ., An
exception is made for nondrinking water aquifers or where
more stringent state regulations apply.
3.7 Soil Chemical Properties
The chemical composition of the soil is the major factor
affecting plant growth and a significant determining factor
3-36
-------
in the capacity of the soil to renovate wastewater. There
are 16 elements known to be essential for crop growth.
Three of these—nitrogen, phosphorus, and potassium—are
deficient in many soils. Secondary and micronutrient
deficiencies are found less often with sulfur, zinc, and
boron being the most common. Soil pH and salinity can limit
crop growth and sodium can reduce soil permeability.
Chemical properties should be determined prior to design to
evaluate the capacity of the soil to support plant growth
and to renovate wastewater. Soils should be monitored
during operation to avoid detrimental changes in soil
chemistry.
3.7.1
Interpretation of Soil Chemical Tests
Several chemical properties, having nothing directly to do
with nutrient status, are nonetheless important. Soil pH
has a significant influence on the solubility of various
compounds, the activities of various microorganisms, and the
bonding of ions to exchange sites. Relative to this last
phenomenon, soil clays and organic matter (known
collectively as the soil colloids), are 'negatively
charged. Thus, they are able to adsorb cations from the
soil solution. Cations adsorbed in this way are called
exchangeable cations. They can be replaced by other cations
from the soil solution without appreciably altering the
structure of the soil colloids. The quantity of
exchangeable cations that a particular soil can adsorb is
known as cation exchange capacity (CEC) and is measured in
terms of milliequivalents per 100 grams (meq/100 g) of
soil. The percentage of the CEC that is occupied by a
particular cation is called the percent saturation for that
cation. The sum of the exchangeable Na, K, Ca and Mg
expressed as a percentage of the CEC is called percent base
saturation.
There are optimum ranges for percent base saturation for
various crop and soil type combinations. Also, for a given
percent base saturation, it is desirable that Ca and Mg be
the dominant cations rather than K and (especially) Na.
High percentages of the alkali metals, in particular Na,
will create severe problems in many fine-texture soils. The
exchangeable sodium percentage (ESP) should be kept below
15% (Section 4.9.1.4). It is important to realize that
regardless of the cation distribution in a natural soil, it
can be altered readily as a result of agricultural
practices. Both the quality of the irrigation water and the
use of soil amendments, such as lime or gypsum, can change
the distribution of exchangeable cations.
3-37
-------
Another chemical property affecting plant growth is
salinity/ the concentration pf soluble ionic substances. It
is salinity in the soil solution in the root zone that is of
primary interest. Unfortunately, there is no simple
relation between this quantity and the salinity of the irri-
gation water, the salt balance being complicated by moisture
transfers through evapotranspiration and deep percolation.
The diagnostic tool usually employed is a check on the elec-
trical conductivity (EC) of the irrigation water and the
soil solution. Guidelines exist for various types of crops
according to their salt tolerance. Procedures for computing
the deep percolation (leaching requirement) needed to
control root zone salinity are given in references [9, 29].
Because of the variable nature of the soil, few standard
procedures for chemical analysis of soil have been
developed. Several references that describe analytical
methods are available [49, 50, 51]. A complete discussion
of analytical methods and interpretation of results for the
purpose of evaluating the soil nutrient status is presented
in reference [52]. The significance of the major chemical
properties is summarized in Table 3-6.
3.7.2
Phosphorus Adsorption Test
Adsorption isotherms for phosphorus can be developed to
predict the removal of phosphorus by the soil. Samples of
soil are taken into the laboratory and are added to
solutions containing known concentrations of phosphorus.
Concentrations normally range from 1 to 30 mg/L. After the
soil is mixed into the solutions and allowed to come into
equilibrium for a period of'time (up to several days), the
solution is filtered and the filtrate is tested for
phosphorus. The difference1 between the initial and final
solution concentrations is the amount adsorbed for a given
time. Details of the test are available in reference [53].
A procedure for using adsorption isotherm data to estimate
phosphorus retention by soils is suggested in reference
[47] . An important consideration discussed is the
possibility of slow reactions between phosphorus and cations
present in the soil which |may "free 'up" previously used
adsorption sites for additional phosphorus retention. Cal-
culations involving adsorption isotherm data, which ignore
these reactions, greatly underestimate phosphorus retention.
3-38
-------
TABLE 3-6
INTERPRETATION OF SOIL CHEMICAL TESTS
Test result
Interpretation
pH of saturated soil paste
<4.2
5.2-5.5
5.5-8.4
>8.4
CEC, meq/100 g
1-10
12-20
>20
Exchangeable cations,
% of CEC
Sodium
Calcium
Potassium
ESP, % of CEC
<5
>10
>20
EC, 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 ai
possible sodium problem
Sandy soils (limited adsorption)
Silt loam (moderate adsorption)
Clay and organic soils (high adsorption)
Desirable range
±5
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 .
3.8 References
1. Bouwer, H. Groundwater Hydrology. McGraw-Hill Book
Co. New York. 1978.
2. Freeze, R.A., and J.A. Cherry. Groundwater. Prentice-
Hall. Englewood Cliffs, N.J. 1979.
3. Taylor, S.A. and Q.L. Ashcroft. Physical Edaphology.
W.H. Freeman & Co. San Francisco. 1972.
4. Richards, L.A. Physical Condition of Water in Soil.
In: Methods of Soil Analysis. Part 1, Agronomy 9.
Black, C.A. (ed.). Madison, Wisconsin. American
Society of Agronomy, Inc. 1965. pp. 131-136.
3-39
-------
5. O'Neal, A.M. A Key fop Evaluating Soil Permeability by
Means of Certain Field Clues. In: Proceedings Soil
Science Society of America. 16:312-315. 1952.
6. Jarrett, A.R. and D.Di, Fritton. Effect of Entrapped
Soil Air on Infiltration. Transcripts of American
Society of Agricultural Engineers. 21:901-906. 1978.
7. Parr, J.F. and A.R. Be'rtrand. Water Infiltration into
Soils. In: Advances in Agronomy. Norman, A.G., (ed.).
New York, Academic Press. 1960. pp. 311-363.
8. Todd, O.K. Groundwater. In: Handbook of Applied
Hydrology. Chow, V.T. (ed.). McGraw-Hill Book Co. New
York. 1964.
9. Drainage Manual. U.S. Department of the Interior,
Bureau of Reclamation. 1st Edition. 1978.
10. Childs, E.G. An Introduction to the Physical Basis of
Soil Water Phenomena.; John Wiley and Sons, Ltd.
London. 1969.
11. Duke, H.R. Capillary Properties of Soils - Influence
upon Specific Yield. Transcripts of the American
Society of Agricultural Engineers. 15:688-691. 1972.
12. Klute, A. Soil Water Flow Theory and its Application in
Field Situations. In: Field Soil Water Regime. Special
Publication, Series No. 5. Madison, Wise., Soil Science
Society of America. 1973. pp. 9-35.
13. Kirkham, D. and W.L. Powers. Advanced Soil Physics.
New York, Wiley-Interscience. 1972. 534 p.
14. Burgy, R.H. and J.N. Luthin. A Test of the Single - and
Double - Ring Types of1 Infiltrometers. Transcripts of
American Geophysical Union. 37:189-191. 1956.
15. Manual of Septic Tank! Practice. U.S. Public Health
Service. Publication No. 526. U.S. Government Printing
Office. 1969. 85 p.
16. Wallace, A.T., et al. Rapid Infiltration Disposal of
Kraft Mill Effluent. In: Proceedings of the 30th Indus-
trial Waste Conference, Purdue University, Indiana.
1975.
3-40
-------
17. Abele, G., et al. Infiltration Characteristics of Soils
at Apple Valley, Minn.; Clarence Cannon Dam, Mo.; and
Deer Creek Lake, Ohio, Land Treatment Sites. Special
Report 80-36. U.S. Army Cold Regions Research and Engi-
neering Laboratory, Hanover, N.H. 1980. 52 p.
18. U.S. Army Corps of Engineers. Simplified Field
Procedures for Determining Vertical Moisture Flow Rates
in Medium to Fine Textured Soils. Engineer Technical
Letter. 1980. 21 p.
19. Bouwer, H. Cylinder Infiltrometers. In: Monograph on
Methods of Soil Analysis. American Society of Agronomy.
(In press). 1981.
20. Haise, H.R., et al. The Use of Cylinder Infiltrometers
to Determine the Intake Characteristics of Irrigated
Soils. U.S. Dept. of Agriculture, Agric. Research
Service. Public No. 41-7. 1956.
21. Hills, R.C. Lateral Flow Under Cylinder
Infiltrometers. A Graphical Correction Procedure.
journal of Hydrology. 13:153-162. 1971.
22. Youngs, E.G. Two- and Three-Dimensional Infiltration:
Seepage from Irrigation Channels and Infiltrometer
Rings. Journal of Hydrology. 15:301-315. 1972.
23. 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.
Kardo (eds.). Pennsylvania State University press.
1973. pp. 95-147.
24. Tovey, R. and C.H. Pair. A Method for Measuring Water
Intake Rate Into Soil for Sprinkler Design. in:
Proceedings of the Sprinkler Irrigation Assoc. Open
Technical Conference. 1963. pp. 109-118.
25. Bouwer, H. Planning and Interpreting Soil Permeability
Measurements. In: Proceedings American Society of
Civil Engineers. Journal of the Irrigation and Drainage
Division. 28:IRS:391-402. 1969.
26. Rogowski, A.S. Watershed Physics: Soil Variability
Criteria. Water Resources Research. 8:1015-1023.
1972.
27. Nielson, D.R., J.W. Biggar and K.T. Erb. Spatial Varia-
bility of Field-Measured Soil-Water Properties.
Hilgardia. 42:215-259. 1973.
-------
28. Frevert, R.K. and D. Kirkham. A Field Method for
Measuring the Permeability of Soil Below a Water
Table. In: Proceedings of Highway Research Board.
48:433-422. 1948.
29. Luthin, J.N. Drainage Engineering, Huntington, New
York, R.E. Krieger Publ. Co. First edition - reprinted
with corrections. 1973. 250 p.
30. Boersma, L. Field Measurement of Hydraulic Conductivity
Above a Water Table. In: Methods of Soil Analysis. Part
1, Agronomy 9. Black, C.A. (ed). Madison, Wisconsin.
American Society of Agronomy, Inc. 1965. pp. 234-252.
31. Bouwer, H. and R.C. Rice. Modified Tube Diameters for
the Double-Tube Apparatus. in: Proceedings Soil
Science Society of America. 31:437-439. 1967
32. Bouwer, H. Rapid Field Measurement of Air Entry Value
and Hydraulic Conductivity of Soil as Significant Para-
meters in Flow System Analysis. Water Resources
Research. 2:729-738. 1966.
33. Topp, G.C. and M.R. Binns. Field Measurements of
Hydraulic Conductivity with a Modified Air-Entry Permea-
meter. Canadian Journal Soil Science. 56:139-147
1976.
34. Drainage of Agricultural Land. U.S. Dept. of
Agriculture - Soil Conservation Service National
Engineering Handbook. Section 16. May 1971.
35. Van Beers, W.F.J. The Auger Hole Method - A Field
Measurement of the Hydraulic Conductivity of Soil Below
a Water Table. ;Wageningen, The Netherlands.
International Inst. for Land Reclamation and
Improvement, Bulletin 1. 1958.
36. Weeks, E.P. Determining the Ratio of Horizontal to
Vertical Permeability by Aquifer-Test Analysis. Water
Resources Research. 5:196-214. 1969.
37. Bouwer, H. Ground Water Recharge Design for Renovating
Waste Water. in: Proceedings of American Society of
Civil Engineers, journal of the Sanitary Engineering
Division. 96:SA 1:59-73. 1970.
38. Van Bavel, C.H.M. and D. Kirkham. Field Measurement of
Soil Permeability Using Auger Holes. In: Proceedings
Soil Science Society of America. 13:90-96. 1948.
3-42
-------
39. Maasland, M. Measurement of Hydraulic Conductivity by
the Auger Hole Method in Anisotropic Soil. In:
Proceedings Soil Science Society of America. 19:379-
388. 1955.
40. Boast, C.W. and D. Kirkham. Auger Hole Seepage
Theory. In: Proceedings Soil Science Society of
America. 35:365-373. 1971.
41. Bouwer, H. and R.C. Rice. A Slug Test for Determining
Hydraulic Conductivity of Unconfined Aquifers with Com-
pletely or Partially Penetrating Wells. Water Resources
Research. 12:423-428. 1976.
42. Glover, R.E. Ground-Water Movement. U.S. Bureau of
Reclamation, Water Resources. Technical Publication
Engineering Monograph No. 31. 1964.
43. Singh, R. Prediction of Mound Geometry Under Recharge
Basins. Water Resources Research. 12:775-780. 1976.
44. Marino, M.A. Artificial Groundwater Recharge, I.
Circular-Recharging Area. journal of Hydrology.
25:201-208. 1975.
45. Smith, J.L. et al. Mass Balance Monitoring of Land
Application Sites for Wastewater Residuals. Transcript
of American Society of Agricultural Engineers. 20:309-
312. 1977.
46. Blakeslee, P. 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, Illinois. 1973. pp. 183-198.
47. Loehr, R.C., et al. Land Application of Wastes, Vols. I
& II. New York. Van Nostrand Reinhold Co. 1979.
48. National Interim Primary Drinking Water Regulations.
U.S. Environmental Protection Agency, Office of Water
Supply. EPA-570/9-76-003. 1976. 159 p.
49. Black, C.A. (ed.). Methods of Soil Analysis, Part 2:
Chemical and Microbiological Properties. Agronomy 9,
American Society of Agronomy. Madison. 1965.
50. Richards, L.A. (ed.). Diagnosis and Improvement of
Saline and Alkali Soil. Agricultural Handbook 60. U.S.
Department of Agriculture. 1954.
3-143
-------
51. Jackson, M.L. Soil Chemical Analysis
Cliffs, N.J. Prentice-Hall, Inc. 1958.
Englewood
52. Walsh, L.M. and. J.D. Beaton, (eds.). Soil Testing and
Plant Analysis. Madison, Soil Science Society of
America. 1973.
53. Fox, R. L. and E.J. Kamprath. Phosphate Sorption
Isotherms for Evaluating the Phosphate Requirements of
Soil. in: Proceedings Soil Science Society of
America. 34:902-906. 1970.
-------
CHAPTER 4
SLOW RATE PROCESS DESIGN
4.1 Introduction
The key elements in the design of slow rate (SR) systems are
indicated in Figure 4-1. Important features are: (1) the
iterative nature of the procedure, and (2) the input
information that must be obtained for detailed design.
Determining the design hydraulic loading rate is the most
important step in process design because this parameter is
used to determine the land area required for the SR
system. The design hydraulic loading rate is controlled by
either soil permeability or nitrogen limits for typical
municipal wastewater. Crop selection is usually the first
design step because preapplication treatment, hydraulic and
nitrogen loading rates, and storage depend to some extent on
the crop. preapplication treatment selection usually
precedes determination of hydraulic loading rate 'because it
can affect the wastewater nitrogen concentration, and,
therefore, the nitrogen loading.
4.2 Process Performance
The mechanisms responsible for treatment and removal of
wastewater constituents such as BOD, suspended solids (SS),
nitrogen, phosphorus, trace elements, microorganisms, and
trace organics are discussed briefly. Levels of removal
achieved at various SR sites are included to show how
removals are affected by loading rates, crop, and soil
characteristics. Chapter 9 contains discussion on the
health and environmental effects of these constituents.
4.2.1
BOD and Suspended Solids Removal
BOD and SS are removed by filtration and bacterial action as
the applied wastewater percolates through the soil. BOD and
SS are normally reduced to concentrations of less than 2
mg/L and less than 1 mg/L, respectively, following 1.5 m
(5 ft) of percolation. Typical loading rates of BOD and SS
for municipal wastewater SR systems, regardless of the
degree of preapplication treatment, are far below the
loading rates at which performance is affected (see
Section 2.2.1.1). Thus, loading rates for BOD and SS are
normally not a concerninthedesignof SR systems^
RemovalsolBODachieved
presented in Table 4-1.
at five selected sites a/re
-------
WASTEWATER
CHAHACTERISTICS
(Section 2.2.1 ,1)
SITE CHARACTERISTICS
(Sections 2.2.1.3,
2.3.1. t Chapttr 3)
WATER OUALITY
REQUIBEiENTS
(Section 2.2.1.2)
PROCESS
PERFORMANCE
(Suction 4.2)
PREAPPL I CATION
TREATMENT
(Section 4.4)
CROP SELECTION
(Sic.tion 4.3)
LOADING RATES
•SOIL; PERMEABILITY
•NITROGEN LIMITS
(Section 4.3)
STORAGE
(Section 4.B)
FIELD AREA
(Section 4.5)
1
'
DRAINAGE AND
RUNOFF CONTROL
DISTRIBUTION
(Section 4.7)
f
4 1 DISCHARGE
I
1 SURFACE WATER M 1 SUBSURFACE
h.
w-
I
SYSTEM MONITORING
, (Section 4.10)
CROP MANAGEMENT
(Section 4.9)
FIGURE 4-1
SLOW RATE DESIGN PROCEDURE
4-2
-------
TABLE 4-1
BOD REMOVAL DATA
FOR SELECTED SR SYSTEMS [1-5]
Location
Dickinson,
North Dakota
Hanover,
New Hampshire
Muskegon,
Michigan
Ro swell,
New Mexico
San Angelo,
Texas
Annual
waste-
water
loading
rate ,
cm/yr
140
130-780
130-260
80
290
BOD
Concentration Concentration
in applied in treated Sampling
Surface wastewater, water, Removal, depth,
soil mg/L mg/L % m
Sandy loams 42 <1 >98 <5
and loamy
sands
Sandy loam 40-92 0.9-1.7 96-98 • 1.5
and silt
loam
Sands and 24 1.3 94 4
loamy sands
Silty clay 42 <1 >98 <30
loams
Clay and 89 0.7 99 2.1
clay loam
Note: See Appendix G for metric conversions.
4.2.2
Nitrogen
For SR systems located above potable aquifers, nitrogen
concentration in percolate must be low enough that ground
water quality at the project boundary * can meet drinking
water nitrate standards. Nitrogen removal mechanisms at SR
systems include crop uptake, nitrification-denitrification,
ammonia volatilization, and storage in the soil. Percolate
nitrogen concentrations less than 10 mg/L can be achieved
with SR systems if the nitrogen loading rate is maintained
within the combined removal rates of these mechanisms. The
nitrogen removal rates and loading rate are, therefore,
important design parameters. Percolate nitrogen levels
achieved at selected SR sites are given in Table 4-2.
Crop uptake is normally the primary nitrogen removal
mechanism operating in SR systems. The amount of nitrogen
removed by crop harvest depends on the nitrogen content of
the crop and the crop yield. Annual nitrogen uptake rates
for specific crops are given in Section 4.3.2.1. Maximum
nitrogen removal can be achieved by selecting crops or crop
combinations with the highest nitrogen uptake potential.
-------
TABLE 4-2
NITROGEN REMOVAL DATA FOR SELECTED
SR SYSTEMS [1, 3-8]
Total nitrogen
Total nitrogen concentration
concentration in percolate
in applied or;affected
Total nitrogen
concentration
Sampling in background
Location
Dickinson,
North Dakota
Hanover,
New Hampshire
Helen,
Georgia3
Roswell,
New Mexico
San Angelo,
Texas
wastewater,
mg/L as N
11.8
27-28
18.0
66.2
35.4
ground water, Removal,
mg/L as N %
3.
7.
3.
10.
6.
9
3
5
7
1
67
72
80
84
83
depth, ground water,
m mg/L as N
11 . 1.9
1.5 —
1.2 . 0..17
30 2.2 ' "
10 —
a. Forest system. All others are agricultural systems.
Nitrogen loss by denitrification depends on several
environmental factors including the oxygen level in the
soil. Assuming that most of the applied nitrogen is in the
organic or ammonium form, increased nitrogen removal due to
denitrification can be expected under the following
conditions:
• High levels of organic matter in the soil and/or
wastewater, such as the concentrations found in
primary effluent
• High soil cation exchange capacity—a character-
istic of f ine-text|ured and organic soils.
• Neutral to slightly alkaline soil pH
• Alternating saturated and unsaturated soil moisture
conditions
• Warm temperatures
Denitrification losses typically are in the range of 15 to
25% of the applied, nitrogen, although measured losses have
ranged from 3 to 70% [4, 9]. The range of 15 to 25% should
be used for conservative; design.Whenconditions are
be
favorable, the maximum ra^e may be used. Lower
should be used when conditibns are less favorable.
values
Ammonia volatilization lossfes can be significant (about 10%)
if the soil pH is above 7.8'and the cation exchange capacity
-------
For design.
is low (sandy, low organic soils).
volatilization losses may be considered included in the 15
to 25% used for denitrification.
Storage of nitrogen in the soil through plant uptake and
subsequent conversion of roots and unharvested residues into
spil humus 'can account for nitrogen retention rates up
to 225 kg/ha'yr (200 Ib/acre-yr) in soils of arid regions
initially low in organic matter (less than 2%). In
contrast, nitrogen storage will be near zero for soils rich
in organic matter. In either case, if nitrogen input
remains constant, the rate of nitrogen storage will decrease
with time because the rate of decay and release of nitrogen
increases with the concentration of soil organic nitrogen.
Eventually, an equilibrium level of organic nitrogen may be
obtained and net storage then ceases. Therefore, for design
purposes, the most conservative approach is to assume net
storage will be zero.
4.2.3
Phosphorus
Phosphorus is removed primarily by adsorption and pre-
cipitation (together referred to as sorption) reactions in
the soil. Crop uptake can account for phosphorus removals
in the range of 20 to 60 kg/ha-yr (18 to 53 Ib/acre-yr),
depending on the crop and yield (Section 4.3.2.1).
Percolate phosphorus concentrations at several Sk sites are
presented in Table 4-3.
The phosphorus sorption capacity of a soil profile depends
on the amounts of clay, aluminum, iron, and calcium
compounds present and the soi'l pH. In general, fine
textured mineral soils have the highest phosphorus sorption
capacities and coarse textured acidic or organic soils have
the lowest.
For systems with coarse textured soils and limits on the
concentration of percolate phosphorus, a phosphorus
adsorption test should be conducted using soil from the
selected site. This test, described in Section 3.7.2,
determines the amount of phosphorus that the soil can remove
during short application periods. Actual phosphorus
retention at an operating system will be at least 2 to ~5~
times the value obtained during a 5~day adsorption
test [13].
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For purposes of design and operation, the soil profile can
be considered to have a finite phosphorus sorption capacity
associated with each layer. Eventually, the sorption
capacity of the entire soil profile may reach saturation and
soluble phosphorus will appear in the percolate. In cases
where .effluent quality requirements limit the concentration
of phosphorus in the percolate, the useful life of the SR
system may be limited by the phosphorus sorption capacity of
the soil profile. An empirical model to predict the useful
life of an SR system has been developed [9].
4.2.4
Trace Elements
Trace element removal in the soil is a complex process
involving the mechanisms of adsorption, precipitation, ion
exchange, and complexation. Because adsorption of most
trace elements occurs on the surfaces of clay minerals,
metal oxides, and organic matter, fine textured and organic
soils have a greater adsorption capacity for trace elements
than sandy soils.
Removal of trace elements from solution is nearly complete
in soils suitable for SR systems. Consequently, trace
element removal is not a concern in the design procedureT
Performance data from selected SR systems are presented in
Table 4-4.
Although some trace elements can be toxic to plants and
consumers of plants, no universally accepted toxic threshold
values for trace element concentrations in the soil or for
mass additions to the soil have been established. Maximum
loadings over the life of a system for several trace
elements have been suggested for soils having low trace
element retention capacities and are presented in Table 4-5.
Toxicity hazards can be minimized by maintaining the soil pH
above 6.5. Most trace elements are retained as unavailable
insoluble compounds above pH 6.5. Methods for adjusting
soil pH are discussed in Section 4.9.1.3.
4.2.5
Microorganisms
Removal of microorganisms, including bacteria, viruses, and
parasitic protozoa and helminths (worms), is accomplished by
filtration, adsorption, desiccation, radiation, predation,
and exposure to other adverse conditions. Because of their
large size, protozoa and helminths are removed primarily by
filtration at the soil surface. Bacteria also are removed
by filtration at the soil surface, although adsorption may
be important. Viruses are removed almost entirely by
adsorption.
4-7
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-------
TABLE 4-5
SUGGESTED MAXIMUM APPLICATIONS OF
TRACE ELEMENTS TO SOILS WITHOUT
FURTHER INVESTIGATION21
Element
Aluminum
Arsenic
Berylium
Boron
Cadmium
Chromium
Cobalt
Copper
Fluoride
Iron
Lead
Lithium
Manganese
Molybdenum
Nickel
Selenium
Zinc
Mass application
to soil, kg/ha
4,570
92
92
680
9
92
46
184
920
4,570
4,570
184
9
184
18
1,840
Typical .
concentration, mg/L
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
Values were based on the tolerances of
sensitive crops, mostly fruits and vegetables,
grown on soils with low capacities for
retaining elements in unavailable forms
[15, 16]. .
Based on reaching maximum mass application in
20 years at an annual application rate of
2.4 m/yr (8 ft/yr).
Boron exhibits toxicity to sensitive plants at
values of 0.75 to 1.0 mg/L.
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.
As noted in Table 1-3, fecal coliforms are normally absent
after wastewater percolates through 1.5 m (5 ft) of soil.
Coliform removals at several operating SR systems are shown
in Table 4-6. Coliform removal in the soil profile is
approximately the same when primary or secondary
preapplication treatment is provided [4] . Virus removals
are not as well documented. State agencies may require
secondary treatment if edible crops are grown or if public
contact is unlimited. Microorganism removal is not a
limiting factor jn the SR design procedure.
4-9
-------
TABLE 4-6
COLIFORM DATA FOR SEVERAL
SR SYSTEMS [1,4,5,8,12]
Location
Camarillo,
California
Dickinson,
North Dakota
Preapplication
treatment
Activated
sludge and
disinfection
Aerated ponds
and disin-
Coliforms
Total
Fecal
Total
Fecal
Concentration
in applied
wastewater ,
MPN/100 mL
57 x 103
220
TNTCa
TNTC
Concentration
in percolate
or ground water,
MPN/100 mL
7
29
<2
<2
12
0
Distance
of
travel,
m
0.5
1.0
0.5
1.0
30-150
30-150
Concentration
in background
ground waiter,
MPN/100 mL
4
27
<2
4
1
0
fection
Hanover,
New Hampshire
Mesa,
Arizona
Roswell,
New Mexico
Primary
Trickling
filters
Trickling
filters and
disinfection
Fecal
Total
Fecal
Total
Fecal
1.2 X 104-
3.1 x 105
3.09 x lb6
1.05 x 105
TNTC3
TNTCa
0-1
<2
9
<2
9
TNTCa
52
1.5
0.5
1.0
0.5
1.0
<6
<6
—
20
60
<2
25
~
a. At least one sample too numerous to count.
4.2.6
Trace Organics
Trace organics are removed by several mechanisms, including
sorption, degradation, and volatilization. One study at
Muskegon, Michigan, evaluated the effectiveness of trace
organics removal during preapplication treatment (aerated
ponds) and SR treatment. Although 59 organic pollutants
were identified in the raw wastewater, renovated water from
drainage tiles underlying the irrigation site contained only
low levels of 10 organic compounds, including two from non-
wastewater sources. Benzene, chloroform, and trichloro-
ethylene were monitored for several days; results are shown
in Table 4-7. ;
Results from pilot SR studies at Hanover, New Hampshire,
indicate that significant levels of volatile trace organics
are removed during sprinkler application [4]. Measurements
of chloroform, toluene, methylene chloride, 1,1 dichloro-
ethane, bromodichloromethane, and tetrachloroethylene showed
that an average of 65% of these six compounds were
volatilized during the sprinkling process, with individual
removals ranging from 57% for toluene to 70% for methylene
chloride.
4-10
-------
TABLE 4-7
BENZENE, CHLOROFORM, AND TRICHLOROETHYLENE
IN MUSKEGON WASTEWATER TREATMENT SYSTEM [17]
Pollutant
Benzene
Chloroform
Trichloroethylene
Sampling
point*3
1
2
3
4
1
2
3
4
1
2
3
4
Concentration, jig/La
8/10/76
6
7
<1
<1
425
105
12
3
13
16 •
7
6
8/11/76
53
2
<1
<1
440
61
9
3
6
3
4
3
8/12/76
6
<1
<1
<1
480
81
4
1
10
5
1
2
9/7/76
41
8
3,
<1
360
365
100 ,
13 .
110
35
11
10
9/8/76
32
5
2
8
2,645
610
75
10
120
33
6
8
a. Average for duplicate samples.
b. Sampling Point 1 - influent
Sampling Point 2 - aerated lagoon effluent
Sampling Point 3 - storage lagoon effluent
Sampling Point 4 - renovated water from drainage tiles
Based on these results, it appears that a typical SR system
is quite effective in removing trace organics. However, if
a community's wastewater contains large concentrations of
trace organics from industrial contributions, industrial
pretreatment should be considered. If hazardous chlorinated
trace organics result from wastewater chlorination, the
engineer must decide in consultation with regulatory
authorities whether it is more important to remove pathogens
or to reduce trace organic levels. This decision should
take into consideration the type of crop and the method of
distribution.
4.3 Crop Selection
The crop is a critical component in the SR process. It
removes nutrients, reduces erosion, maintains or increases
infiltration rates, and can produce revenue where markets
exist.
4.3.1
Guidelines for Crop Selection
Important characteristics or properties of crops that should
be considered when selecting a crop for SR systems
include: (1) nutrient uptake capacity, (2) tolerance to
high, soil moisture conditions, (3) consumptive use of water
and irrigation requirements, and (4) revenue potential. A
relative comparison of these characteristics for several
types of crops is presented in Table 4-8 as a general guide
-------
to selection. Characteristics of secondary importance
include (1) effect on soil infiltration rate, (2) crop
water quality requirements and toxicity concerns, and
(3) management requirements;.
Most SR systems are designed to minimize land area by using
maximum hydraulic loading rates. Crops that are compatible
with high hydraulic loading rates are those having high
nitrogen uptake capacity, high consumptive water use, and
high tolerance to moist soil conditions. Other desirable
crop characteristics for this situation are low sensitivity
to wastewater constituents, and minimum management
requirements. Crops grown for revenue must have a ready
local market and be compatible with wastewater treatment
objectives.
4.3.1.1 Agricultural Crops
Agricultural crops most compatible with the objective of
maximum hydraulic loading are the forage and turf grasses.
Forage crops that have been used successfully includes Reed
canarygrass, tall fescue, perennial ryegrass, Italian
ryegrass, orchardgrass, and bermudagrass. If forage
utilization and value are not a consideration, Reed
canarygrass is often a first choice in its area of
adaptation because of high nitrogen uptake rate, winter
hardiness, and persistence. However, Reed canarygrass is
slow to establish and should be planted initially with a
companion grass (ryegrass, orchardgrass, or tall fescue) to
provide good initial cover.
Of the perennial grasses grown for forage utilization and
revenue under high wastewater loading rates, orchardgrass is
generally considered to be more acceptable as animal feed
than tall fescue or Reed canarygrass. However, orchardgrass
is prone to leaf diseases in the southern and eastern
states. Tall fescue is generally preferred as a feed over
Reed canarygrass but is not! suitable for use in the northern
tier of states due to lapk of winter-hardiness. Again,
other crops may be more suitable for local conditions and
advice of local farm advisers or extension specialists will
be helpful in making the crop selection.
Corn will grow satisfactorily where the water table depth is
about 1.5 to 2 m, (5 to 7 ft) but alfalfa requires neiiturally
well-drained soils and water table depths of at least 3 m
(10 ft) for persistence. The alfalfa cultivar selected
should be high yielding with resistance to root rot and
bacterial wilt in the growing region, especially, when high
hydraulic loading rates (>?!.5 cm/wk or 3 in./wk) are used.
4-12
-------
TABLE 4-8
RELATIVE COMPARISON OF CROP
CHARACTERISTICS [Adapted from 18]
Potential
as revenue
producer3
Potential
as water
userb
Potential
as nitrogen
user0
Moisture
tolerance^
Field crops
Barley Marg
Corn, grain Exc
Corn, silage Exc
Cotton (lint) Good
Grain, sorghum Good
Oats Marg
Rice -Exc
Safflower Exc
Soybeans JGood
Wheat Good
Forage crops
Kentucky bluegrass Good
Reed canarygrass Poor
Alfalfa Exc
Bromegrass Poor
Clover Exc
Orchardgrass Good
Sorghum-sudan Good
Timothy Marg
Vetch Marg
Tall fescue Good
Turf crops
Bentgrass Exc
Bermudagrass Good
Forest crops
Hardwoods Exc
Pine - Exc
Douglas-fir Exc
Mod
Mod
Mod
Mod
Low
Mod
High
Mod
Mod
Mod
High
High
High
High
High
High
High
High
High
High
High
High
High
High
High
Marg
Good
Exc
Marg
Marg
Poor
Poor
Exc
Good-exce
Good
Exc
Exc
Good-exce
Good
Good-exce
Good-exce
Exc
Good
Exc
Good-exc
Exc
Exc
Good-exc1
Goodf
Low
Mod
Mod
Low
Mod
Low
High
Mod
Mod
Low
Mod
High
Low
High
Mod-high
Mod
Mod
High
High
High
High
High
Highg
Mod-low9
Mod
Potential as revenue producers is a judgmental estimate based on
nationwide demand. Local market differences may be substantial
enough to change a marginal revenue producer to a good or
excellent revenue producer and vice versa. Some of the forages
are extremely difficult to market due to their coarse nature
and poor feed values.
Water user definitions expressed as a fraction of alfalfa
consumptive-use.
High 0.8-1.0
Moderate (Mod) 0.6-0.79
Low -< 0. 6
Nitrogen user ratings (kg/ha):
Excellent (Exc}
Good
Marginal (Marg}
Poor
2>200
150-200
100-150
<100
Moisture tolerance ratings:
High - withstands prolonged soil saturation >3 days.
Moderate - withstands soil saturation 2-3 days.
Low - withstands no soil saturation.
Legumes will also take nitrogen from the atmosphere.
Higher nitrogen uptake during juvenile growth stage after crowning.
Species dependent, check with the State Extension Forester.
4-13
-------
A mixture of alfalfa and a persistent forage grass, such as
orchardgrass, can be used on soils that are not naturally
well drained. At high hydraulic loading rates, the alfalfa
may not persist over 2 years, but the forage grass will fill
in the areas in the thinned alfalfa stand.
The most common agricultural crops grown for revenue using
wastewater are corn (silage), alfalfa (silage, hay, or
pasture), forage" grass (silage, hay, or pasture), grain
sorghum, cotton, and grains [18].. However, any crop,
including food crops, may b^ grown with reclaimed wastewater
after suitable preapplicatipn treatment.
In areas with a long growing season, such as California,
selection of a double crop is an excellent means of
increasing the revenue potential as well as the annual
consumptive water use and nitrogen uptake of the crop
system. Double crop combinations that are commonly used
include (1) short season varieties of soybeans, silage corn,
or sorghum as a summer crop; and (2) barley, oats, wheat,
vetch, or annual forage grass as a winter crop.
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 reduced; water use is
maximized; nutrient uptake is enhanced; and revenue
potential is increased.
4.3.1.2 Forest Crops
The most common forest croups used in SR systems have been
mixed hardwoods and pines. A summary of representative
operational systems and types of forest crops used is
presented in Table 4-9.
The growth responses of a number of tree species to a range
of wastewater loadings are identified in Table 4-10. The
high growth response column is most suitable for wastewater
application because of nitrogen uptake and productivity.
The growth response will vary in accordance with a number of
factors; one of the most important is the adaptability of
the selected species to the local climate. Local foresters
should be consulted for specific judgments on the likely
response of selected species. .
4-14
-------
TABLE 4-9
SUMMARY OF OPERATIONAL FOREST LAND TREATMENT
SYSTEMS IN THE UNITED STATES RECEIVING
MUNICIPAL WASTEWATER
Location
Clayton County,
Georgia
Flow,
m3/d
73,800
Forest type
Loblolly pine
plantation and
natural hardwood
Date
started
1981
Hydraulic
loading,
cm/wk
6.3
Other conditions
Ground water to be
recycled as drinking
water
Helen, Georgia
Kings Bay
Submarine Support
Base, St. Marys,
Georgia
Mackinaw City,
Michigan
Mt. Sunapee State
Park, Newbury,
New Hampshire
State College,
Pennsylvania
(Penn State
University)
West Dover,
Vermont
76 Mixed hardwood
and pine
1,250 Slash pine
plantation
760 Aspen, white
pine birch
26 Mixed hardwood
11,350 Mixed hardwood;
red pine plantation;
spruce, old field
2,080 Northern hardwoods;
balsam, hemlock,
spruce in understory
1973
1981
1976
1971
1963
1976
7.6
1.3
11.3
5.0
2.0-
7.5
<6.3
Site drainage with
open ditches
Frost free, seasonal
application
Water stored and
applied in June and
July only
Ground water to be
recycled as drinking
water
Operates at air
temperatures above
-18 °C
4.3.2
TABLE 4-10
HEIGHT GROWTH RESPONSE OF SELECTED
TREE SPECIES [Adapted from 19]
Height growth response class
Low
Intermediate
High
Slash pine
Cherry-laurel
Arizona cypress
Live oak
Holly
Hawthorne
Northern white cedar
Red pine
Tulip poplar
Bald cypress
Saw-tooth oak
Red cedar
Laurel oak
Magnolia
Nuttall oak
Cherry bark oak
Loblolly pine
Shortleaf pine
Virginia pine
Douglas- fir
Cottonwood
Sycamore
Green ash
Black cherry
Sweetgum
Black locust
Red bud
Catalpa
Chinese elm
White pine
Crop Characteristics
Reference data and information on the crop characteristics
of (1) nutrient uptake, water quality requirements, and
toxicity concerns; (2) water tolerance; (3) consumptive
water use; and (4) effect on soil hydraulic properties are
presented in this section for both agricultural crops and
forest crops.
4-15
-------
4.3.2.1 Nutrient Uptake
Agricultural Crops
In general, the largest nutrient removals can be achieved
with perennial grasses and legumes that are cut frequently
at early stages of growth. it should be recognized that
legumes can fix -nitrogen from the air, but they are active
scavengers for nitrate if it is present. The potential for
harvesting nutrients with annual crops is generally less
than with perennials because annuals use only part of the
available growing season for growth and active uptake.
Typical annual uptake rates of the major plant nutrients—
nitrogen, phosphorus, and potassium—are listed in
Table 4-11 for several commonly selected crops.
The nutrient removal capacity of a crop is not a fixed
characteristic but- depends on the crop yield and the
nutrient content of the plant at the time of harvest.
Design estimates of harvest removals should be based on
yield goals and nutrient compositions that local experience
indicates can be achieved with good management on similar
soils. :
TABLE 4-11
NUTRIENT UPTAKE RATES FOR
SELECTED CROPS
kg/ha-yr
Forage crops
Alfalfa3
Bromegrass
Coastal bermudagrass
Kentucky bluegrass
Quackgrass
Reed canarygrass
Ryegrass
Sweet clovera
Tall fescue
Orchardgrass
Field crops
Barley
Corn
Cotton
Grain sorghum
Potatoes
Soybeans2
Wheat
Nitrogen
225-540
130-225
400-675
200-270
235-280
335-450
200-280
175
150-325
250-350
125
175-200
75-110
135
230
250
160
Phosphorus
22-35
40-55
35-45
45
30-45
40-45
60-85
20
30
20-50
15
20-30
15
15
20
10-20
15
Potassium
175-225
245
225
200
275
315
270-325
100
300
225-315
20
110
40
70
245-325
30-55
20-45
a. Legumes will also take nitrogen from the atmosphere.
4-16
-------
The rate of nitrogen uptake by crops changes during the
growing season and is a function of the rate of dry matter
accumulation and the nitrogen content of the plant.
Consequently, the pattern of nitrogen uptake is subject to
many environmental and management variables and is crop
specific. Examples of measured nitrogen uptake rates versus
time are shown in Figure 4-2 for annual crops and perennial
forage'grasses receiving wastewater.
The amounts of phosphorus in applied wastewaters are usually
much higher than plant requirements. Fortunately, most
soils have a high sorption capacity for phosphorus and very
little of the excess passes through the soil (see
Section 4.2.3).
Potassium is used in large amounts by many crops,
but
typical wastewater is relatively deficient in this ele-
ment. In most cases, fertilizer potassium may be needed to
provide for optimal plant growth, depending on the soil and
crop grown (see Section 4.9.1.2). Other macronutrients
taken up by crops include magnesium, calcium and sulfur;
deficiencies of these nutrients are possible in some areas.
s
400 i-
300 -
200 -
100 -
REED CANARY6RASS
AND CORN
APR
FIGURE 4-2
NITROGEN UPTAKE VERSUS GROWING DAYS
FOR ANNUAL AND PERENNIAL CROPS [20,21]
4-17
-------
The micronutrients important to plant growth (in descending
order) are: iron, manganese, zinc, boron, copper, molyb-
denum, and, occasionally, sodium, silicon, chloride, and
cobalt. Most wastewaters contain an ample supply of these
elements; in some cases, phytotoxicity may be a
consideration.
Forest Crops
Vegetative uptake and storage of nutrients depend on the
species and forest stand density, structure, age, length of
season, and temperature. In addition to the trees, there is
also nutrient uptake and storage by the understory tree and
herbaceous vegetation. -The role of the understory
vegetation is particularly important in the early stages of
tree establishment.
Forests take up and store nutrients and return a portion of
those nutrients back to the soil in the form of leaf fall
and other debris such as dead trees. Upon decomposition,
the nutrients are released and the trees take them back
up. During the initial stages of growth (1 to 2 years),
tree seedlings are establishing a root system; biomass
production and nutrient uptake are relatively slow. To
prevent leaching of nitrogen to ground water during this
period, nitrogen loading must be limited or understory
vegetation must be established that will take up and store
applied nitrogen that is in excess of the tree crop needs.
Management of understory vegetation is discussed in
Section 4.9.
Following the initial growth stage, the rates of growth and
nutrient uptake increase and remain relatively constant
until maturity is approached and the rates decrease. When
growth rates and nutrient uptake rates begin to decrease,
the stand should be harvested or the nutrient loading
decreased. Maturity may be reached at 20 to 25 years for
southern pines, 50 to 60 years for hardwoods, and 60 to 80
years for some of the western conifers such as Douglas-
fir. Of course, harvesting may be practiced well in advance
of maturity as with short-term rotation management (see
Section 4.9.2.5).
Estimates of the net annual nitrogen storage for a number of
fully stocked forest ecosystems are presented in
Table 4-12. These estimates are maximum rates of net
nitrogen uptake considering both the understory and
overstory vegetation during the period of active tree
growth.
4-18
-------
TABLE 4-12
ESTIMATED NET ANNUAL NITROGEN UPTAKE IN THE
OVERSTORY AND UNDERSTORY VEGETATION OF FULLY
STOCKED AND VIGOROUSLY GROWING FOREST
ECOSYSTEMS IN SELECTED REGIONS OF THE UNITED STATES [22]
Average annual
Tree nitrogen uptake,
age, yr kg/ha-yr
Eastern forests
Mixed hardwoods 40-60
Red pine , 25
Old field with white 15
spruce plantation
Pioneer succession
Southern forests
Mixed hardwoods 40-60
Southern pine with 20
no understory
Southern pine 20
with understory
Lake states forests
Mixed hardwoods 50
Hybrid poplar'3 5
Western forests
Hybrid poplarb 4-5
Douglas-fir 15-25
plantation
270
110
280
280
340
220a
320
110
155
300-400
150-250
a. Principal southern pine included in these
estimates is loblolly pine.
b. Short-term rotation with harvesting at 4-5 yr;
represents first growth cycle from planted
seedlings (see Section 4.9.2.4).
Because nitrogen stored within the biomass of trees is not
uniformly distributed among the tree components, the amount
of nitrogen that can actually be removed with a forest crop
system will be substantially less than the storage estimates
given in Table 4-12 unless 100% of the aboveground biomass
is harvested (whole-tree harvesting). If only the
merchantable stems are removed from the system, the ne~t
amount of nitrogen removed by the system will be less than
30% of the amount stored in the biomass.The distributions
"51biomassandnitrogenfornaturally growing hardwood and
conifer (pines, Douglas-fir, fir, larch, etc.) stands in
temperate regions are shown in Table 4-13.' For deciduous
species, whole-tree harvesting must take place in the summer
when the leaves are on the trees if maximum nitrogen removal
is to be achieved.
4-19
-------
TABLE 4-13
BIOMASS AND NITROGEN DISTRIBUTIONS BY TREE
COMPONENT FOR STANDS IN TEMPERATE REGIONS [23]
Percent
Conifers
Hardwoods
Tree component Biomass Nitrogen Biomass Nitrogen
Roots
Stems
Branches
Leaves
10
80
8
2
17
50
12
20
12
65
22
1
18
32
42
8
The assimilative capacity for both phosphorus and trace
metals is controlled more by soil properties than plant
uptake. The relatively low pH (4.2 to 5.5) of most forest
soils is favorable to the retention of phosphorus but not
trace metals. However, the high level of organic matter in
forest soil improves the metal removal capacity. The amount
of phosphorus in trees is small, usually less than 30 kg/ha
(27 Ib/acre); therefore, the amount of annual phosphorus
accumulation is quite small.
4.3.2.2
Moisture Tolerance
Crops that can be exposed to prolonged periods of high soil
moisture without suffering damage or yield reduction are
said to have a high moisture or water tolerance. This
characteristic is desirable in situations (1) where
hydraulic loading rates must be maximized, (2) where the
root zone contains a slowly permeable soil, or (3) in humid
areas where sufficient moisture already exists for plant
growth. Refer to Table 4-8 for a comparison of crop
moisture tolerances. Alfalfa and red pine, for example,
have low moisture tolerances.
4.3.2.3 Consumptive Water Use
Consumptive water use by plants is also termed
evapotranspiration (ET). Consumptive water use varies with
the physical characteristics and the growth stage of the
crop, the soil moisture level, and the local climate. In
some states, estimates of maximum monthly consumptive water
use for many crops can be obtained from local agricultural
extension offices or research stations or the SCS. Where
this information is not available, it will be necessary to
make estimates of evapotranspiration using temperature and
4-20
-------
other climatic data. Several methods qf estimating
evapotranspiration are available and are detailed in
publications by the American Society of Civil Engineers
(ASCE) [24] , the Food and Agriculture Organization (FAO) of
the United Nations [25], and the SCS [26].
Agricultural Crops
In humid regions estimates'of potential evapotranspiration
(PET) are usually sufficient for perennial, full-cover'
crops.ExamplesofestimatedPETfor humidandsubhumid
climates are shown in Table 4-14'. Examples . of monthly
consumptive use in arid regions are shown in Table 4-15 for
several California crops. These table values are specific
for the location given and are intended to illustrate
variation in ET due to crop and climate. The designer
should obtain or estimate ET values that are specific to the
site under design.
TABLE 4-14
EXAMPLES OF ESTIMATED MONTHLY POTENTIAL
EVAPOTRANSPIRATION FOR HUMID AND SUBHUMID CLIMATES
cm
Month
Jan
Feb
Mar
Apr
May
Jun
Jul
Aug
Sep
Oct
Nov
Dec
Annual
Paris,
Texas
1.5
1.5
3.6
6.8
9.9
14.7
16.0
16.2
9.7
6.4
2.7
1.4
90.4
Central
Missouri
0.7
1.3
3.0
6.6
10.8
14.5
16.9
15.2
10.3
6.3
2.6
1.1
89.3
Brevard ,
North Carolina
0.2
0.3
2.1
4.6
7.6
10'. 2
11.4
10.4
7.4
4.6
1.6
0.3 ,
60.7
Jonesboro,
Georgia
1.3
1.3
3.0
5.8
10.9
14.7
15.7
15.0
10.9
5.8
2.5
1.3
88.2
Hanover,
New Hampshire
0.0
,0.0
0.1
2.9
8.2
12.9
13..7
11.9
7.4
4.0
0.3
0.0 •
61.4
Seabrook,
New Jersey
0.2
0.3
2.0
4.0
7.4
11.4
13.9
13.6
9.9
4.9
2.1
0.3
70.0
In arid or semiarid regions, water in excess of consumptive
use must be applied to (1) ensure proper soil moisture
conditions for seed germination, plant emergence, and root
development; (2) flush salts from the root, zone; and
(3) account for nonuniformity of water application by the
distribution system (see Section1 4.7). This requirement is
the irrigation requirement and examples are shown in
Table 4-15. Local irrigation specialists should be
consulted for specific values.
4-2-1
-------
TABLE 4-15
CONSUMPTIVE WATER USE AND IRRIGATION REQUIREMENTS FOR
SELECTED CROPS AT SAN JOAQUIN VALLEY, CALIFORNIAa [27, 28]
Depth of Water in cm
Pastures or alfalfa*5
Double crop
barley and grain (sorghumc
Sugar beets e
Month
Jan
Fob
Mar
Apr
•Hay
Jun
Jul
Aug
Sop
Oct
Nov
Dae
Total
Consumptive
use
2.3
S.I
9.7
13.2
17.8
21.8
23.9
22.1
14.7
10.9
S.I
2.5
149.1
Irrigation
requirements
3.0
6.9
13.0
17.8
23.9
29.2
32.0
29.7
19.8
14.7
6.9
3.3
200.2
Consumptive
use
2.5
5.1
9.7
13.2
6.6
—
11.4
20.3
15.2
7.6
~
2.5
94.1
Irrigation
requirements
__
-'-
15.2
15.2
—
125.49
17.8
,30.1
'22.9
—
—
25.4
152.0
Consumptive
use
„
—
—
1.5
3.0
9.1
18.3
21.3
15.2
6.4
—
74.8
Irrigation
requirements
„
38.1£
~
—
—
12.7
30.5
30.5
—
—
—
111.8
Consumptive
use
—
—
2.5
6.4
12.7
17.8
20.3
—
—
—
59.7
Irrigation
requirements
—
12.7
22.9
12.7
22.9
19.1
"' 11.4
1
—
15.29
__
116.9
«. Other cropa having similar growing seasons and ground cover will have similar consumptive use.
b. Estimated maximum consumptive use (evapotranspiration) of water by mature crops with nearly complete ground
cover throughout the year.
o. Barley planted in November-December, harvested in June. Grain sorghum planted June 20-July 10, harvested
in November-December.
d. Rooting depth of mature cotton: 1.8 m. Planting dates! March 15 to April 20. Harvest: October, November,
and December.
o. Rooting depth: 1.5 to 1.8 m. Planting date: January. Harvest: July 15 to September 10.
f. Preirrigation should wet soil to 1.5 to 1.8 m depth prior to planting.
9, Preirrigation is used to ensure germination and emergence. First crop irrigations are heavy in order to
provide deep moisture.
Forest Crops
The consumptive water use of forest crops under high soil
moisture conditions may exceed that of forage crops in the
same area by as much as 30%. For design purposes, however,
the potential ET is used because there is little information
on water use of different forest species. The seasonal
pattern of water use for conifers is more uniform than for
deciduous trees.
4.3.2.4 Effect on Soil Hydraulic Properties
In general, plants tend to increase both the infiltration
rate of the soil surface and the effective hydraulic
conductivity of the soil in the root zone as a result of
root penetration and addition of organic matter. The
magnitude of this effect varies among different crops.
Thus, the crop selected can affect the design application
rate of sprinkler distribution systems, which is based on
-------
the steady state infiltration rate of the soil surface.
Steady state infiltration rate is equivalent to the
saturated permeability of surface soil. Design sprinkler
application rates can be increased by 50% over the
permeability value for most full-cover crops and by 100% for
mature (>4 years old), well-managed permanent pastures (see
Appendix E). The design application rate (cm/h or in./h)
should not be confused with hydraulic loading rate (cm/wk or
cm/mo) which is based on the permeability of the most
restrictive layer in the soil profile. This layer, in many
cases, is below the root zone and is unaffected by the crop.
Forest surface soils are generally characterized by high
infiltration capacities and high porosities due to the
presence of high levels of organic matter. The infiltration
rates of most forest surface soils exceed all but the most
extreme rainfall intensities. Therefore, surface
infiltration rate is not usually a limiting factor in
establishing the design application rate for sprinkler
distribution in forest systems.
In addition, the permeability of subsurface forest soil
horizons is generally improved over that found under other
vegetation systems because there is: (1) no tillage,
(2) minimum compaction from vehicular traffic, (3) decompo-
sition of deep pentrating roots, and (4) a well-developed
structure due to the increased organic matter content and
microbial activity. Where subfreezing temperatures are
encountered, the forest floor serves to insulate the soil so
that soil freezing, if it does occur, occurs slowly and does
not penetrate deeply. Consequently, wastewater application
can often continue through the winter at forest systems.
4.3.2.5 Crop Water Quality Requirements and
Toxicity Concerns
Wastewaters may have constituents that: (1) are harmful to
plants (phytotoxic), (2) reduce the quality of the crop for
marketing, or (3) can be taken up by plants and result in a
toxic concern in the food chain. Thus, the effect of
wastewater constituents on the crop itself and the potential
for toxicity to plant consumers must be considered during
the crop selection process. Agricultural crops are of
primary concern.
A summary of common wastewater constituents that can
adversely affect certain crops either through a direct toxic
effect or through degradation of crop quality is given in
Table 4-16. Also indicated in the table are the constituent
concentrations at which problems occur. These effect are
discussed in further detail in Chapter 9.
4-23
-------
TABLE 4-16
SUMMARY OF WASTEWATER CONSTITUENTS
HAVING POTENTIAL ADVERSE EFFECTS
ON CROPS [29]
Constituent level
Problem and
related constituent
No Increasing Severe
problem problems problems
Crops affected
Salinity (ECW) , <0.75 0.75-3.0 >3.0
nunho/cm
Specific ion toxicity
from root absorption
Boron, mg/L <0.5 0.5-2' 2.0-10.0
Crops in arid climates only
(see Table 9-4)
Fruit and citrus trees -
0.5-1.0 mg/L; field crops
1.0-2.0 mg/L; grasses -
2.0-10.0 mg/L
Sodium, adj-SARa
Chloride, mg/L
Specific ion toxicity
from foliar absorption
Sodium, mg/L
Chloride, mg/L
Miscellaneous
NH4-N + N03-N, mg/L
HC03 , mg/L
pH, units
<3
<142
<69
<106
<5
<90
6.5-8.4
3.0-9.0
142-355
>69
>106
5-30
90-520
4.2-5.5
>9.0
>355
30
>520
<4.2 and
>8.5
Tree crops
Tree crops
Field and vegetable
crops under sprinkler
application
Sugarbeets, potatoes,
cotton, grains
Fruit
Most crops
a. Adjusted sodium adsorption ratio.
Trace elements, particularly zinc, copper, and nickel are of
concern for phytotoxicity. However, the concentration of
these elements in wastewaters,is well below the toxic level
of all crops and phytotoxicity could only occur as a result
of long-term accumulation of these elements in the soil.
4.4 Preapplication Treatment
Preapplication treatment is provided for three reasons:
1. Protection of public health as it relates to human
consumption of crops or crop byproducts or to
direct exposure to applied wastewater
2.
3.
Prevention of nuisance conditions during storage
Prevention of operating problems in distribution
systems
Preapplication treatment is not necessary for the SR process
to achieve maximum treatment, except in the case of harmful
4-24
-------
or ' toxic constituents from industrial sources (see
Section 4.4.3). The SR process is capable of removing high
levels of most constituents present in municipal
wastewaters, and maximum use should be made of this
renovative capacity in a complete treatment system.
Therefore, the level of preapplication treatment provided
should be the minimum necessary to achieve the three stated
objectives. In general, any additional preapplication
treatment will result in higher costs and energy use.
The EPA has issued general guidelines for assessing the
level of preapplication treatment necessary for SR systems
[30] . The guidelines are intended to provide adequate
protection for public health:
A. Primary treatment - acceptable for isolated
locations with restricted public access and when
limited to crops not for direct human consumption.
B. Biological treatment by ponds or inplant processes
plus control of fecal coliform count to less than
1,000 MPN/100 mL - acceptable for controlled
agricultural irrigation except for human food crops
to be eaten raw.
C. Biological treatment by ponds or inplant processes
with additional BOD or SS control as needed for
aesthetics plus disinfection to log mean of 200/100
mL (EPA fecal coliform criteria for bathing waters)
- acceptable for application in public access areas
such as parks and golf courses.
In most cases, state or local public health or water quality
control agencies regulate the quality of municipal
wastewater that can be used for SR. The appropriate state
and local agencies should be contacted early in the design
process to determine specific restrictions on the quality of
applied wastewater.
4.4.1 Preapplication Treatment for Storage and
During Storage
Objectionable odors and nuisance conditions can occur if
anaerobic conditions develop near the surface in a storage
pond. Two preapplication treatment options are available to
prevent odors:
1. Reduce the oxygen demand of the wastewater prior to
storage.
4-25
-------
2. Design the storage pond as a deep facultative pond,
using appropriate•BOD loading.
Complete biological treatment and disinfection are
unnecessary prior to storage. The level of treatment
provided should not exceed that necessary to control
odors. For storage ponds with short detention times (less
than 10 to 15 days), a reduction in the BOD of the
wastewater to a range of 40 to 75 mg/L should be sufficient
to prevent odors. An aerated cell is are normally used for
BOD reduction in such cases. For storage ponds with longer
detention times, BOD reduction before storage is normally
not required because the storage pond is serving as a
stabilization pond.
Wastewater undergoes treatment during storage. Suspended
solids, oxygen demand, nitrogen, and microorganisms are
reduced. In general, the extent of reduction depends on the
length of the storage period. In the case of nitrogen,
removal during storage can affect the design and operation
of the SR process because the allowable hydraulic loading
rate may be governed by the nitrogen concentration of the
applied wastewater. Nitrogen removal in storage reservoirs
can be substantial and depends on several factors including
detention time, temperature, pH, and pond depth. A
preliminary model to estimate nitrogen removals in ponds
during ice-free periods has been developed [31]:
where Nt =
No -
Nt = N0 e-
nitrogen concentration in pond effluent
(total N), mg/L
nitrogen concentration entering pond
(total N), mg/L
(4-1)
t = detention time, d
A more precise model for predicting ammonia nitrogen
removals in ponds is presented in the Process Design Manual
on Wastewater Treatment Ponds [32].
Nitrogen in pond effluent is predominantly in the ammonia or
organic form. In most cases, it is desirable to apply
nitrogen in these forms to SR systems because they are held
at least temporarily in the soil profile and are available
for plant uptake for longer periods than nitrate, which is
mobile in the soil profile. Ammonia and organic nitrogen
which is converted to ammonia, are particularly desirable in
4-26
-------
forest systems because many tree species do not take up
nitrate as efficiently as ammonia.
A model describing the removal of fecal coliforms in pond
systems has also been developed [33]:
Cf =
,-Kte
(4-2)
where Cf = effluent fecal coliform concentration,
No./lOO mL
C- = entering fecal coliform concentration,
1 No./lOO mL
K = 0.5 warm months;
0.03 cold months
t = "actual" detention time, d
9 = 1.072
T = liquid temperature, °C.
Based on this model, actual detention times of about 17 days
and 21 days would be necessary at 20 °C (68 °F) to reduce
the coliform level of a typical domestic wastewater to
1,000/100 mL and 200/100 mL, respectively. Thus, effluent
from storage reservoirs, in many cases, may meet the EPA
coliform recommendations for SR systems without
disinfection.
Removal of viruses in ponds is also quite rapid at warm
temperatures. Essentially complete removal of Coxsackie and
polio viruses was observed after 20 days at 20 °C [34].
4.4.2 Preapplication Treatment to Protect
Distribution Systems
Deposition of settleable solids and grease in distribution
laterals or ditches can cause reduction in the flow capacity
of the distribution network and odors at the point of
application. Coarse solids can cause severe clogging
problems in sprinkler distribution systems. Removal of
settleable solids and oil and grease (i.e., primary
sedimentation or equivalent) is therefore recommended as a
minimum level of preapplication treatment.Forsprinkler
systems, It has been recommended that the size of the
largest particle in the applied wastewater be less than one-
4-27
-------
third the diameter of the sprinkler nozzle, to avoid
plugging.
4.4.3
Industrial Pretreatment
Pollutants that are compatible with conventional secondary
treatment systems would generally be compatible with land
treatment systems. As with conventional systems, pre-
treatment requirements will be necessary for such constit-
uents as fats, grease and oils, and sulfides to protect
collection systems and treatment components. Pretreatment
requirements for conventional biological treatment will also
be sufficient for land treatment processes.
4.5 Loading Rates and Land Area Requirements
The hydraulic loading rate is the volume of wastewater
applied per unit area of , land over at least one loading
cycle. Hydraulic loading rate is commonly expressed in
cm/wk or m/yr (in./wk or ft/yr) and is used to compute the
land area required for the SR process. The hydraulic
loading rate used for design is based on the more
restrictive of two limiting conditions—the capacity of the
soil profile to transmit water (soil permeability) or the
nitrogen concentration in water percolating beyond the root
zone.
A separate case is considered for those systems in arid
regions where crop revenue is important and the wastewater
is used as a valuable source of irrigation water. For such
systems, the design hydraulic loading rate is usually based
on the irrigation requirements of the crop.
4.5.1
Hydraulic Loading Rate Based on Soil
Permeability
The general water balance equation with rates based on a
monthly time period is the basis of this procedure*. The
equation, with runoff of applied water assumed to be zero,
is:
- Pr + P
w
(4-3)
where
ET =
Pr =
pw =
wastewater hydraulic loading rate
evapotranspiration rate
precipitation rate
percolation rate
4-28
-------
The basic steps in the procedure are:
1. Determine the design precipitation for each month
based on a 5 year return period frequency analysis
for monthly precipitation. Alternatively, use a 10
year return period for annual precipitation and
distribute it monthly based on the ratio of average
monthly to average annual precipitation.
2. Estimate the monthly ET rate of the selected crop
(see Section 4.3.2.3).
3. Determine by field test the minimum clear water
permeability of the soil profile. If the minimum
soil permeability is variable over the site,
determine an average minimum permeability based on
areas of different soil types.
4. Establish a maximum daily design percolation rate
that does not exceed 4 to 10% of minimum soil
permeability (see Figure 2-3). Percentages on the
lower end of the scale are recommended for variable
or poorly defined soil conditions. The percentage
to use is a judgment decision to be made 'by the
designer. The daily percolation rate is determined
as follows:
pw(daily) = Permeability, cm/h (24 h/d)(4 to 10%)
5. Calculate the monthly percolation rate with
adjustments for those months having periods of
nonoperation. Nonoperation may.be due to:
• Crop management. Downtime must be allowed for harvesting,
planting, and cultivation as applicable.
• Precipitation. Downtime for precipitation is already
factored into the water balance computation. No adjust-
ments are necessary.
• Freezing temperatures. Subfreezing temperatures cause
soil frost that reduces surface infiltration rate. Oper-
ation is usually stopped when this occurs. The most con-
servative approach to adjusting the monthly percolation
rate for freezing conditions is to allow no operation for
days during the month when the mean temperature is less
than 0 °C (32 °F). A less conservative approach is to use
a lower minimum temperature. The recommended lowest mean
temperature for operation is -4 °C (25 °F). Data sources
and procedures for determining the number of subfreezing
days during a month are presented in Sections 2.2.1.3,
4-29
-------
2.2.2.2, and 4.6. Nonoperating days due to freezing con-
ditions may also be estimated using the EPA-1 computer
program without precipitation constraints .(see Section
4.6.2). For forest crops, operation can often continue
during subfreezing^ conditions.
Seasonal crops. When single annual crops are grown,
wastewater is not normally applied during the winter
season, although applications may occur after harvest
and before the next planting. The design monthly per-
colation rate may be calculated as follows:
pw(monthly) = [Pw(daily)] x (No. of operating d/mo)
6.
Calculate the monthly hydraulic loading rate using
Equation 4-3. The monthly hydraulic loadings are
summed to yield the allowable annual hydraulic
loading rate based on soil permeability [L w/p\].
The computation procedure is illustrated by an
example for both arid and humid climates in
Table 4-17. The example is based on systems
growing permanent pasture and having similar winter
weather and soil conditions. Downtime is allowed
for freezing conditions, but pasture management
does not require harvesting downtime.
The allowable hydraulic .loading rate based on soil
permeability calculated by the above procedure L^/pN is the
maximum rate for a particular site and operating conditions,
and this rate will be used for design if there are no other
constraints or limitations. If other limitations exist,
such as percolate nitrogen concentration, it is necessary to
calculate the allowable hydraulic loading rate based on
these limitations and compare that rate with the L ,m. The
lower of the two rates is used for design. ( '•
4.5.2 Hydraulic Loading Rate Based on
Nitrogen Limits
In municipal wastewaters applied to SR systems, nitrogen is
usually the limiting constituent when protection of potable
ground water aquifers is a concern. If percolating water
from an SR system will enter 'a potable ground water aquifer,
then the system should be designed such that the
concentration of nitrate nitrogen in the receiving ground
water at the project boundary does not exceed 10 mg/L.
4-30
-------
TABLE 4-17
WATER BALANCE TO DETERMINE HYDRAULIC LOADING
RATES BASED ON SOIL PERMEABILITY
cm
,-Ionth
Arid
(2) (3)
ET, Pr,
Evapotrans- precip-
piration itation
(4) = (2)-(3)
Net ET
(5)
PW a
Percolation
(6) = (4) + (5)
Lw(p) '
wastewater
hydraulic loading
climates
Jan
Feb
Mar
Apr
May
Jun
Jul
Aug
Sep
Oct
Nov
Dec
Annual
2.3
5.1
9.7
13.2
17.7
21.8
23.9
22.1
14.7
10.9
5.1
2.5
149.0
3.0
2.8
2.8
2.0
0.5
0.3
—
—
0.3
0.8
1.3
2.5
16.3
-0.7
2.3
6.9
11.2
17.2
21.5
23.9
22.1
14.4
10.1
3.8
0.0
132.7
5.1
12.6
16.3
18.0
18.0
18.0
18.0
18.0
18.0
18.0
17.0
14.1
191.1
4.4
14.9
23.2
29.2
35.2
39.5
41.9
40.2
32.4
28.1
20.8
14.1
323.8
Humid
climates
Jan
Feb
Mar
Apr
May
Jun
Jul
Aug
Sep
Oct
Nov
Dec
Annual
1.3
1.3
3.0
5.8
10.9
14.7
15.7
15.0
10.9
5.8
2.5
1.3
88.2
13.5
13.0
15.5
11.3
11.1
11.7
13.3
11.1
9.1
8.0
8.0
12.8
138.4
-12.2
-11.7
-12.5
- 5.5
- 0.2
3.0
2.4
3.9
1.8
- 2.2
- 5.5
-11.5
-50.2
5.1
12.6
16.3
18.0
18.0
18.0
18.0
18.0
18.0
18.0
17.0
14.1
191.1
0.0b
0.9
3.8
12.5
17.8
21.0
20.4
21.9
19.8
15.8
11.5
2.6
148.0
a. Based on a soil profile with a moderately slow permeability
(0.5 to 1.5 cm/h) , Pw(inax) = (0.5 cm/h) (24 h/d) (30 d/mo) (0.05) = 18.0
b. 1 cannot be less than zero.
The approach to meeting this requirement involves first
estimating an allowable hydraulic loading rate based on an
annual nitrogen balance (Lw/n\)f and comparing that to the
previously calculated Lw(p) to determine which value
controls. The detailed stepis in this procedure are:
1. Calculate the allowable annual hydraulic loading
rate based on nitrogen limits using the following
equation:
T , x _ (C )(Pr - ET)
•Lw(n) -- &
(4-4)
- C
4-31
-------
where Lw(n) =
CP =
Pr =
ET =
u =
cn =
allowable annual hydraulic loading rate
based on nitrogen limits, cm/yr
nitrogen concentration in percolating water,
mg/L
precipitation rate, cm/yr
evapotranspiration rate, cm/yr
nitrogen uptake by crop, kg/ha•yr
(Tables 4-2, 4-11, 4-12)
nitrogen concentration in applied
wastewater, mg/L (after losses in
preapplication treatment)
fraction of applied nitrogen removed by
denitrification and volatilization (4.2.2).
Compare the value of. Lw/n) with the value of
calculated previously (Section 4.5.1). If L
greater than L , x,i do not continue the procedure
for design. If
is less than or
e'based on
and use
equal to "£J/p\ > design should uc uaocu un u , *.
The value or i^(n) calculated in Step 1 above may
be used to estimate land requirements for purposes
of Phase 2 planning, but for final design the
procedure outlined in Steps 3 and 4 should be used.
Calculate an allowable monthly hydraulic loading
rate based on nitrogen limits using Equation 4-4
with monthly values for Pr, ET, and U. Monthly
values for Pr and ET will have been determined
previously for the water balance table (see
Section 4.5.1). Monthly values for crop uptake (U)
can be estimated by assuming that annual crop
uptake is distributed monthly according to the same
ratio as monthly to total growing season ET.
If data on nitrogen uptake versus time, such as
that shown in Figure 4-2, are available for the
crops and climatic region specific to the project
under design, then such information may be used to
develop a more accurate estimate of monthly
nitrogen uptake values.
Compare each monthly value of I\,(n) with the
corresponding monthly value of LW/P) calculated
previously (Section 4.5.1). The lower of the two
4-32
-------
values should be used for design. The design
monthly hydraulic loading rates are summed to yield
the design annual hydraulic loading rate.
The above procedure is illustrated in Example 4-1
for an arid climate and a humid climate using the
climatic and operating conditions given in
Table 4-17.
EXAMPLE 4-1:
LOADING RATE
CALCULATION TO ESTIMATE DESIGN HYDRAULIC
Conditions
Applied wastewater nitrogen concentration (Cn)» mg/L
Crop nitrogen uptake (U), kg/ha-yr
Denitrification + volatilization
(as a fraction of applied nitrogen)
Limiting percolate nitrogen concentration (Cp), mg/L
Precipitation (Pr) and evapotranspiration (ET) (see
Table 4-17).
Humid
climate
25
336
0.2
10
Arid
climate
25
336
0.2
10
Calculations
1.
Calculate allowable annual 1^ (nj using Equation 4-4.
(Cp) (Pr - ET) + (U) (10)
(1 - f) (Cn) - Cp
Humid climate
Arid climate
Lw(n)
(10)(138.4 - 88.2) + (336)(10)
(1 - 0.2) (25) - 10
386.2 cm/yr
Lw(n)
2. Compare LW (n) with
Humid climate
Lw(n) = 386.2 cm/yr
Lw(p) = 148.0 cm/yr
.•.Lw(p) controls. Use Lytpi for
design (see Table 4-17)
(10)(16.3 - 149) + (336)(10)
(1 - 0.2) (25) - 10
203.3 cm/yr
Arid climate
Lw(n) = 203.3 cm/yr
Lw(p) = 323.8 cm/yr
controls.
Step'3.
Continue to
3.
Compute allowable monthly Lw(n) using Equation 4-4 and estimated monthly nitrogen
uptake and monthly (Pr - ET) values. Compare with monthly LW(P) and use lower
value for design. Tabulate results. (Arid climate only)
Month
Jan
Feb
Mar
Apr
May
Jun
Jul
Aug
Sep
Oct
Nov
Dec
Annual
(Pr - ET), cm (U), kg/ha Lw(nl> cm Lw(p), cm Design
0.
-2.
-6.
-11.
-17,
-21
-23.
-22,
-14
-10,
-3,
0.0
-132.7
5.2
11.5
21.9
29.8
39.9
49.2
53.9
49.8
33.1
24.6
11.5
5.6
336
5.
9.
15.
18.
22.
27.
30.
27.
18.
14.
7.7
5.6
203.3
4.4
17.5
23.
29.
35.
39.
41.
40.
32.4
28.
20.
4.
9.
15.
18.
22.
27.
30.
27.
18.
14.
7.
14.1
323.8
5.6
201.8
4-33
-------
The above procedure for calculating allowable hydraulic
loading rate based on, nitrogen limits is based on the
following assumptions:
1
2
3
All percolate nitrogen is in the nitrate form.
No storage of -nitrogen occurs in the soil profile.
No mixing and dilution of the percolate with in
situ ground water occurs.
Use of these assumptions results in a very conservative
estimate of percolate nitrogen. This procedure should
ensure that the nitrogen concentration in the ground water
at the project boundaries will be less than the specified
value of Cp.
As indicated by the example, nitrogen loading is more likely
to govern the design hydraulic loading rate for systems in
arid climates than in humid climates. The reason for this
is that the net positive ET rate in arid climates Cciuses an
increase in the concentration of the nitrogen level in the
percolating water.
For systems in arid climates, it is possible that the design
monthly hydraulic loading rates based on nitrogen limits
will be less than the irrigation requirements (IR) of the
crop. The designer should compare the design Lw with the
irrigation requirement to determine if this situation
exists. If it does exist, the designer has three options
available to increase LWn sufficiently to meet the IR.
1.
2.
Reduce the concentration of applied nitrogen (Cn)
through preapplication treatment. ' ' ,
Demonstrate that sufficient mixing and dilution
(see Section 3.6.2) will occur with the existing
ground water to permit higher values of percolate
nitrogen concentration (C^) to be used in
Equation 4-4.
3.
Select a different crop with a higher nitrogen
uptake (U).
4.5.3 Hydraulic Loading Rate Based on
Irrigation Requirements
For SR systems in arid regions that have crop production for
revenue as the objective, the design hydraulic loading rate
can be determined on the basis of the crop irrigation
-------
requirement (see Section 4.3.2.1)
balance equation:
using a modified water
Lw = IR - Pr
(4-5)
where LW = hydraulic loading rate
IR = crop irrigation requirement
Pr = precipitation
The annual hydraulic loading rate is determined by summing
the monthly hydraulic loading rates computed using
Equation 4-5. The computational procedure is similar to
that outlined in Section 4.5.1.
The monthly hydraulic loading rate based on IR should be
checked against the allowable rate based on nitrogen limits
(Lw/n\) as discussed in Section 4.5.2.
4.5.4
Land Area Requirements
The land area to which wastewater is actually applied is
termed a field. In addition to the field area, the total
land area required for an SR system includes land for
preapplication treatment facilities, administration and
maintenance buildings, service roads, buffer zones, and
storage reservoir. Field area requirements and buffer zone
requirements are discussed in this section. Storage area
requirements are discussed in Section 4.6 and area
requirements for preapplication treatment facilities,
buildings, and service roads are determined by standard
engineering practice not included in this manual.
4.5.4.1 Field Area Requirements
The required field area is determined from the design
hydraulic loading rate according to the following equation:
(Q)(365)(d/yr) + AV
Aw =
(4-6)
where Aw = field area, ha (acre)
Q = average daily community wastewater flow
(annual basis), m3/d (ft3/d)
4-35
-------
AVS =
C =
net loss or gain in stored wastewater volume
due to precipitation, evaporation and seepage
at storage pond, m3/yr (ft3/yr)
constant, 100 (3,630)
design hydraulic loading rate, cm/yr (in./yr)
The first calculation of field area must be made without
considering net gain or los? from storage. After storage
pond area is computed, the value of AV can be computed from
precipitation and evaporation data. Field area then must be
recalculated to account for AV_.
o - ,
Using the design hydraulic loading rate for the arid climate
in Example 4-1, the field area for a daily wastewater f.low
of 1,000 m3/d, neglecting AV^f is:
(1,000)(365)
(104)(201.8)(0.01)
= 18.1 ha
4.5.4.2 Buffer Zone Requirements
The objectives of buffer zones around land treatment sites
are to control public access, and in some cases, improve
project aesthetics. There are no universally accepted
criteria for determining the width of buffer zones around SR
treatment systems. In practice, the widths of buffer -zones
range from zero for remote systems to 60 m (200 ft) or more
for systems using sprinklers near populated areas. In many
states, the width of buffer zones is prescribed by
regulatory agencies, and the designer should determine if
such requirements exist.
The requirements for buffer zones in forest systems are
generally less than those of other vegetation systems
because forests reduce wind speeds and, therefore, the
potential movement of aerosols. Forests also provide a
visual screen for the publip. A minimum buffer zone width
of 15 m (50 ft) that is managed as a multistoried forest
canopy will be sufficient ,to meet all objectives. The
multistoried effect is achieved by maintaining mature trees
on the inside edge of the buffer next to the irrigated area
and filling beneath the canopy and out to the outside edge
of the buffer with trees that grow to a moderate height and
have full, dense canopies. Evergreen species are the best
selection if year-round operation is planned. If existing
natural forests are used for the buffer, a minimum width of
4-36
-------
15 m may be sufficient to meet the objectives, if there is
an adequate vegetation density.
4.6 Storage Requirements
In almost all cases, SR systems require some storage for
periods when the amount of available wastewater flow exceeds
the design hydraulic loading rate. The approach used to
determine storage requirements is to first estimate a
storage volume requirement using a water balance computation
or computer programs developed to estimate storage needs
based on observed climatic variations throughout the United
States. The final design volume then is determined by
adjusting the estimated volume for net gain or loss due to
precipitation and evaporation using a monthly water balance
on the storage pond. These estimating and adjustment
procedures are described in the following sections.
Some states prescribe a minimum storage volume (e.g., 10
days storage). The designer should determine if such
storage requirements exist.
All applied wastewater does not need to pass through the
storage reservoir. In cases where primary effluent is
suitable for application, only the water that must be stored
need receive prestorage treatment. Stored and fresh
wastewater is then blended for application.
4.6.1 Estimation of Volume Requirements Using
Storage Water Balance Calculations
An initial estimate of the storage volume requirements may
be determined using a water balance calculation procedure.
The basic steps in the procedure are illustrated using the
arid climate example from Example 4-1:
1. Tabulate the design monthly hydraulic loading rate
as indicated in Table 4-17.
2. Convert the actual volume of wastewater available
each month to units of depth (cm) using the
following relationship.
W = (Qm)dO"2)
(4-7)
where Wa - depth of available wastewater, cm1
Q_ = volume of available wastewater for the
month, m^
4-37
-------
Aw = field area, ha
Insert the results for each month into a water
balance table, as illustrated by the example in
Table 4-18. In some communities,. influent
wastewater flow varies significantly with the time
of year. The values used for Qm should reflect
monthly flow variation based on historical
records. In this example, no monthly flow
variation is assumed.
TABLE 4-18
ESTIMATION OF STORAGE VOLUME REQUIREMENTS
USING WATER BALANCE CALCULATIONS
cm
(1)
Month
Oct
Nov
Dec
Jan
Feb
Mar
Apr
May
Jun
Jul
Aug
Sep
(2)
wastewater
hydraulic
loading
14.5
7.7
5.6
4.4
9.2
15.0
18.6
22.6
27.6
30.0
27.9
18.7
(3)
Wa,
available
wastewater3
16.8
16.8
16.8
: 16.8
16.8
16.8
16.8
16.8
16.8
16.8
16.8
16.8
(4)
Change
in
storage
2.3
9.1
11.2
12.4
7.6
1.8
- 1.8
- 5.8
-10.8
-13.2
-11.1
- 1.9
(5)
Cumulative
storage
-0.2b
2.3
11.4
22.6
35.0
42.6
44.4°
42.6
36.8
26.0
12.8
1.7
Annual
201.8
201.6
a. Based on a field area of 18.1 ha and 30,438 m^/mo
of wastewater.
b. Rounding error. Assume zero.
c. Maximum storage month.
Compute the net change in storage each month by
subtracting the monthly hydraulic loading from the
available wastewater in the same month.
Compute the cumulative storage at the end of each
month by adding the change in storage during one
month to the accumulated quantity from the previous
month. The computation should begin with the
reservoir empty at the beginning of the largest
storage period. This month is usually October or
November, but in some humid areas it may be
February or March.
M--38
-------
5. Compute the required storage volume using the
maximum cumulative storage and the field area as
indicated below.
Required storage volume '
= (44.4 cm)(18,1 ha)(10~2 m/cm)(104 m2/ha)
= 8.04 x 104 m3
The advantage of using this water balance procedure to
estimate storage volume requirements is that all factors
that affect storage, including (1) seasonal changes in
precipitation, evapotranspiration, and wastewater flow; and
(2) downtime for precipitation or crop management are
accounted for in the design hydraulic loading rate. The
disadvantage of this procedure is that downtime for cold
weather has to be determined separately and added in by
reducing allowed monthly percolation.
4.6.2 Estimated Storage Volume Requirements
Using Computer Programs
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 [35]. Based on this study, three computer programs,
as presented in Table 4-19, have been developed to estimate
the storage days required when inclement weather conditions
preclude land treatment system operation.
TABLE 4-19
SUMMARY OF COMPUTER PROGRAMS FOR DETERMINING
STORAGE FROM CLIMATIC VARIABLES [36]
EPA
program Applicability
Variables
Remarks
EPA-1
EPA- 2
EPA- 3
Cold climates
Wet climates
Moderate climates
Mean temperature,
rainfall , snow depth
Rainfall
Maximum and minimum
temperature, rainfall,
'snow depth
Uses freeze index
Storage to avoid
surface runoff
Variation of EPA-1
for more temperate
regions
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 4-3. The storage days are calculated for recurrence
intervals of 2, 4, 10, and 20 years. A list of stations
4-39
-------
co
CD
O
a:
Q_
2EI
CO
Q_ ac
3£ I—
CD CO
O Z
O
«C O
IJJ CJ
C9«C O
— CC
CO
C3
U- Z
CD —
a
z a:
oo
— o
»—o
4-40
-------
with storage days for 10 and 20 year recurrence intervals
from EPA computer programs is presented in Appendix F. A
list of 244 stations for which EPA-1 has been run is
included in reference [35]. 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.
Storage days required for crop management activities
(harvesting, planting, etc.) must be added to the computer
estimated storage days due to weather to obtain the total
storage days required in each month. The estimated required
storage volume is then calculated by multiplying the
estimated number of storage days in each month times the
average daily flow for the corresponding month.
4.6.3 Final Design Storage Volume Calculations
The estimated storage volume requirement obtained by water
balance calculation or computer programs must be adjusted to
account for net gain or loss in volume due to precipitation
or evaporation. The mass balance procedure is Illustrated
by Example 4-2 using arid climate data from Example 4-1 and
the estimated storage volume from Table 4-18. .An example
for a system in a more humid climate is given in Appendix E.
EXAMPLE 4-2: CALCULATIONS TO DETERMINE FINAL STORAGE VOLUME
REQUIREMENTS
1. Using the initial estimated storage volume and an assumed storage pond depth
compatible with local conditions, calculate a required surface area for the
storage pond:
AS = Vs^St) (4-8)
where As = area of storage pond, m2
vs{est) = estimated storage volume, m3
ds = assumed pond depth, m
For the example, assume ds = 4 m ,
. (8.02 x 104 m3)
AS j-j;
= 2 x 104 m2
2. Calculate the monthly net volume of water gained or lost from storage due to
precipitation, evaporation, and seepage: '
AVS = (Pr - E - seepage) (As) (10~2 m/cm) (4-9)
where AVS = net gain or loss in storage volume, m3
Pr = design monthly precipitation, cm
E = monthly evaporation, cm
As = storage pond area
Estimated lake evaporation in the local area should be used for E, if available.
Potential ET values may be used if no other data are available. Tabulate monthly
values and sum to determine the net annual AVS.
For example, assume:
E = ET
Seepage = 0
Results are tabulated in Column (2) of Table 4-20.
-------
TABLE 4-20
FINAL STORAGE VOLUME REQUIREMENT CALCULATIONS
m3 x 103
Month
Oot
Nov
Dec
Jan
Feb
Mar
Apr
May
Jun
Jul
Aug
Sep
(2)
AVS
Net
gain/loss
-2.0
-0.7
0.0
0.1
-0.5
-1.4
-2.2
-3.4
-4.3
-4.8
-4.4
-2.9
(3)
Available
wastewater
30.4
30.4
30.4
30.4
30.4
30.4
30.4
30.4
30.4
30.4
30.4
30.4
(4)
Vw
Applied
wastewater
24.3
12.9
9.4
7.4
15.4
25.2
31.2
37.9
46.3
50.3
46.8
31.4
(5) = (2) + (3) - (4)
AVs
Change in storage
4.1
16.8
21.0
23.1
14.5
3.8
-3.0
-10.9
-20.2
-24.7
-20.8
-3.9
Cumulative
storage
-0.2a
4.1
20.9'
41.9
65.0
79.5
83. Jb
' 80.3
69.4
49.2
24. 5
3.7
Annual
-26.5
365
338.5
a. Rounding error (assume zero).
b. Maximum design storage volume.
Tabulate the volume of wastewater available each month (Qm) accounting for any
expected monthly flow variations. For the example, monthly flow is constant.
(1,000 m3/d)(365 d/yr)
12 mo/yr
30.4 x 1Q3 m3/mo :
Qm
Calculate an adjusted field area to account for annual net gain/loss in storage
volume.
Aw1 =
m/cm)
(1CP mVha) U<>-
where AW' » adjusted field area, ha
EAVs = annual net storage gain/loss, m3
£Qm = annual available wastewater, m3
Ly, - design annual hydraulic loading rate, cm
For the example:
AW- =
(4-1.0)
365 X 103 - 26.5 x 103
(201.8) (10.4) (io-
= 16.8 ha
Mote:
The final design calculation reduced the field area
from 18.1 ha to 16.8 ha.
5.
Calculate the monthly volume of applied wastewater using the design monthly
hydraulic loading rate and adjusted field area:
(Lw>
™2/ha) (10~2 m/cm)
(4-111
where Vw = monthly volume of applied wastewater, m3
LW z design monthly hydraulic loading rate, cm
Aw' = adjusted field area, ha
Results are tabulated in Column (4) of Table 4-20.
6. Calculate the net change in storage each month by subtracting the monthly
applied wastewater (Vw) from the sura of available wastewater (Qra) and net
storage gain/loss (AVS) in the same month. Results are tabulated in
Column (5) of Table 4-20.
7. Calculate the cumulative storage volume at the end of each month by adding '
the change in storage during one month to the accumulated total from the
previous month. The computation should begin with the cumulative storage
equal to zero at the beginning of the largest storage period. The maximum
monthly cumulative volume is the storage volume requirement used for design.
Results are tabulated in Column (6) of Table 4-20.
Design Vs = 83.3 x 103 ra3
-------
8. Adjust the assumed value of storage pond depth (ds) to yield the required
design storage volume using Equation 4-12.
For the example
(4-12;
83.3 x 103 m3
2 x 10« mi
= 4. 16 m
If the pone depth cannot be adjusted due to subsurface constraints, then the
surface area must be adjusted to obtain the required design volume. However,
if the surface area is changed, another iteration of the above procedure will
be necessary because the value of net storage gain/loss 'iVs)will be different
for a new pone area.
4.6.4
Storage Pond Design Considerations
Most agricultural storage ponds are constructed of
homogeneous 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 1.8 m (6 ft) and a capacity in
excess of 61,800 mj (50 acre-ft) is subject to state
regulations on design and construction of dams, and plans
must be reviewed and approved by the appropriate agency.
Design criteria and information sources are included in the
U.S. Bureau of Reclamation publication, Des i gn of Small Dams
[37]. 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.
In addition to storage volume, the principal design
parameters are depth and area. The design depth and area
depend on the function of the pond and the topography at the
pond site. If the storage pond is to also serve as a
facultative pond, then a minimum water depth of at least 0.5
to 1 m (1.5 to 3 ft) should be maintained in the pond when
the stored volume is at a minimum. The area must also be
sufficient to meet the BOD pond loading criteria for the
local climate. The use of aerators can reduce area
requirements. The maximum depth depends on .whether the
reservoir is constructed with dikes or embankments on level
ground or is constructed by damming a natural water course
or ravine. Maximum depths of diked ponds typically range
from 3 to 6 m (9 to 18 ft). Other design considerations
include wind fetch, and the need for riprap and lining.
These aspects of design are covered in standard engineering
references and assistance is also available from local SCS
offices.
4-43
-------
4.7 Distribution System
Design of the distribution system involves two steps:
(1) selection of the type of distribution system, and
(2) detailed design of system components. Emphasis in this
section is placed on criteria for selection of the type of
distribution system. Design procedures for SR distribution
systems are presented in Appendix E. Only basic design
principles for each type of distribution system are pre-
sented in the manual, and the designer is referred to
several standard agricultural engineering references for
further design details. Certain design requirements of
distribution systems for forest crop systems do not conform
to standard agricultural irrigation practice and are dis-
cussed under a separate heading.
4.7.1
Surface Distribution Systems
With surface distribution systems, water is applied to the
ground surface at one end of a field and allowed to spread
over the field by gravity. Conditions favoring the
selection of a surface distribution system include the
following:
1. Capital is not available for the initial investment
required for more sophisticated systems.
2. Skilled labor is available at reasonable rates to
operate a surface system.
3. Surface topography of land requires little
additional preparation to make uniform grades for
surface distribution.
The principal limitations or
systems include the following:
disadvantages of surface
Land leveling costs
terrain.
may be excessive on uneven
Uniform distribution cannot be achieved with highly
permeable soils.
Runoff control and a return system must be provided
when applying wastewater.
Skilled labor is usually required to achieve proper
performance.
Periodic maintenance of leveled surface is required
to maintain uniform grades.
4-44
-------
Surface distribution systems may be classified into two
general types: ridge and furrow and graded border (also
termed bermed cell). The distinguishing physical features
of these methods are illustrated in Figure 4-4. A summary
of variations of the basic surface methods and conditions
for their use is presented in Table 4-21. Details of
preliminary design are presented in Appendix E.
4.7.2
Sprinkler Distribution Systems
Sprinkler distribution systems simulate rainfall by creating
a rotating jet of water that breaks up into small droplets
that fall to the field surface. The advantages and
disadvantages of sprinkler distribution systems relative to
surface distribution systems are summarized in Table 4-22.
4.7.2.1 Types of Sprinkler Systems
In this manual, sprinkler systems are classified according
to their movement during and between applications because
this characteristic determines the procedure for design.
There are three major categories of sprinkler systems based
on movement: (1) solid set, (2) move-stop, and
(3) continuous move. A summary of the various types of
sprinkler systems under each category is given in Table 4-23
along with respective operating characteristics.
4.7.2.2 Sprinkler Distribution Systems for Forest
The requirements of distribution systems for forests are
somewhat different from those for agricultural and turf
crops.
Solid-set irrigation systems are the most commonly used
systems in forests. Buried systems are less susceptible to
damage from ice and snow and do not interfere with forest
management activities (thinning, harvesting, and
regeneration). A center pivot irrigation system has been
used in Michigan for irrigation of Christmas trees because
their growth height would not exceed the height of the pivot
arms. Traveling guns have also been used to irrigate short-
term rotation hardwood plantations.
As discussed in Section 4.3.2.4, the design sprinkler
application rate is usually not limited by the infiltration
capacity of most forest soils.. Steep grades (up to 35%), in
general, do not limit the design hydraulic loading rate per
application for forest systems. In fact, hydraulic loadings
per application may be increased up to 10% on grades greater
than 15% because of the higher drainage rate. Precautions
must be taken to make sure that water draining through the
surface soil does not appear as runoff further down the
slope.
4--U5
-------
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(a) RIDGE AND FURROW METHOD
USING GATED PIPE
^SS-^^&S^^
(b) GRADED BORDER METHOD
FIGURE 4-4
SURFACE DISTRIBUTION METHODS
4-4-6
-------
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4-48
-------
TABLE 4-22
ADVANTAGES AND DISADVANTAGES OF SPRINKLER
DISTRIBUTION SYSTEMS RELATIVE TO SURFACE
DISTRIBUTION SYSTEMS
Advantages
Disadvantages
1. Can be used on porous and variable soils.
2. Can be used on shallow soil profiles.L-
3. Can be used on rolling terrain.
4. Can be used on easily eroded soils.
5. Can be used with small flows.
6. Skilled labor not required.
7. Can be used where high water tables exist.
8. Can be used for light, frequent
applications.
9. Control and measurement of applied water
is easier.
10. Interference with cultivation is minimized.
11. Higher application efficiencies are
usually possible.
12. Tailwater control and reapplication
not usually required.
1. Initial capital cost can be high.
• 2. Energy costs are higher than for surface
systems.
3. Higher humidity levels can increase
disease potential, for some crops.
4. Sprinkler application of high salinity
water can cause leaf burn.
5. Water droplets can cause blossom damage to
fruit crops or reduce the quality of some
fruit and vegetable crops.
6. Portable or moving systems can get stuck
in some clay soils.
7. Higher levels of preapplication treatment
generally are required for sprinkler systems
than for surface systems to prevent operating
problems (clogging).
8. Distribution is subject to wind distortion.
9. Wind drift of sprays increases,the potential
for public exposure to wastewater.
SPRINKLER
Typical
application
rate , cm/h
Solid set
Permanent
Portable
Move- stop
Hand move
End tow
Side wheel roll
Stationary gun
Continuous move
Traveling gun
Center pivot
Linear move
0
0
0
0
0
0
0
0
0
.13-5.
.13-5.
.O3-5.
.03-5.
.25-5.
.64-5.
.64-2.
.51-2.
.51-2.
08
08
08
08
08
08
54
54
54
TABLE 4-23
SYSTEM CHARACTERISTICS
Labor
required
per
application,
h/ha
0.
0.
0
0.
0.
0.
0.
0.
0.
02-0.
08-0.
.2-0.
O8-0.
04-0.
08-0.
04-0.
02-0.
02-0.
04
10
6
16
12
16
12
06
06
Nozzle Size of
pressure single
range, system,
N/cm2 ha
21-69
21-41
21-41
21-41
21-41
35-69
35-69
10-41
10-41
Unlimited
Unlimited
8-16
8-32
8-16
16-41
16-65
16-130
Maximum
crop
Shape of Maximum height,
field grade, % m
Any shape ~-
Any shape — —
Any shape 20 —
Rectangular 5-10 —
Rectangular 5-10 1-1.2
Any shape 20 —
Any shape
Circular3 5-15 2.4-3
Rectangular 5-15 2.4-3
a. Travelers are available to allow irrigation of any shape field.
-------
Solid set sprinkler systems for forest crops have some
special design requirements. Spacing of sprinkler heads
must be closer and operating pressures lower in forests than
other vegetation systems because of the interference from
tree trunks and leaves and possible damage to bark. An 18 m
(60 ft) spacing between, sprinklers and a 24 m (80 ft)
spacing between laterals has proven to be an acceptable
spacing for forested areas [39]. This spacing, with
sprinkler overlap, provides good wastewater distribution at
a reasonable cost. Operating pressures at the nozzle should
not exceed 38 N/cm2 (55 lb/in.2), although pressures up to
59 N/cm2 (85 lb/in.) may be used with mature or thick-
barked hardwood species. The sprinkler risers should be
high enough to raise the sprinkler above most of the
understory vegetation, but generally not exceeding 1.5 m
(5 ft). Low-trajectory sprinklers should be used so that
water is not thrown into the tree canopies, particularly in
the winter when ice buildup on pines and other evergreen
trees can cause the trees to be broken or uprooted.
A number of different methods of applying wastewater during
subfreezing temperatures in the winter have been
attempted. These range from various modifications of
rotating and nonrotating sprinklers to furrow and
subterranean applications. General practice is to use low-
trajectory, single nozzle impact-type sprinklers, or low
trajectory, double nozzle hydraulic driven sprinklers. A
spray nozzle used at West Dover, Vermont, is shown in
Figure 4-5.
Installation of a buried solid-set irrigation system in
existing forests must be done with care to avoid excessive
damage to the trees or soil. Alternatively, solid-set
systems can be placed on the surface if adequate line
drainage is provided (see Figure 4-6). For buried systems,
sufficient vegetation must be removed during construction to
ensure ease of installation while minimizing site
disturbance so that site productivity is not decreased or
erosion hazard increased. A 3 m wide (10 ft) path cleared
for each lateral meets these objectives. Following
construction, the disturbed area must be mulched or seeded
to restore infiltration and prevent- erosion. During
operation of the land treatment system, a 1.5 mi (3 ft)
radius should be kept clear around each sprinkler,, This
practice allows better distribution and more convenient
observation of sprinkler operation. Spray distribution
patterns will still not meet agricultural standards, but
this is not as important in forests because the roots are
quite extensive.
4-50
-------
a .
SPRAYING
b. DRAINING
BRASS TUBE IN LEFT HALF DRAINS QUICKLY,
UNTIL LIQUID LEVEL IS BELOW ITS TOP.
THEN ONLY RIGHT HALF CONTINUES TO DRAIN.
c. LINE DRAINED
SMALL AMOUNT OF ICE HAS FORMED TO BLOCK
RIGHT HALF OF NOZZLE. BRASS TUBE LEFT
HALF IS OPEN AND READY FOR NEXT SPRAY
CYCLE.
d. NEXT SPRAY CYCLE
•WATER INITIALLY SPRAYS THROUGH THE BRASS
TUBE ON THE LEFT SIDE. THE HEAT FROM
THE LIQUID MELTS THE ICE PLUG BLOCKING
THE RIGHT HALF OF THE NOZZLE AND SPRAY-
ING RESUMES IN THE NORMAL MANNER AS
SHOWN IN a .
FIGURE 4-5
FAN NOZZLE USED FOR SPRAY APPLICATION AT WEST DOVER, VERMONT
4-51
-------
FIGURE 4-6
SOLID SET SPRINKLERS WITH
SURFACE PIPE IN A FOREST SYSTEM
14-52
-------
4.7.3 Service Life of Distribution System
Components
The expected service life of the distribution system
components is a design consideration and 'must be used to
develop detailed cost comparison. The suggested service
lives of common distribution system components are listed in
Table 4-24.
4.8 Drainage and Runoff Control
Provisions to improve or control subsurface drainage are
sometimes necessary with SR systems to remove excess water
from the root zone or to remove salts from the root zone
when these conditions adversely affect crop growth. Control
of surface runoff is necessary for^SR systems"using surface
distribution methods. In humid areas with intense rain-
falls, control of surface drainage is necessary to prevent
erosion and may be helpful in reducing the amount of water
entering the soil profile and thereby reducing or elimin-
ating the need for subsurface drainage. Design
considerations for drainage and runoff control 'provisions
are discussed in the following sections.
4.8.1 •-
Subsurface Drainage Systems
Subsurface drainage systems are used in .situations where the
natural rate of subsurface drainage is restricted by
relatively impermeable layers in the' soil profile near the
surface or by high ground water. As a result of the
restrictive layer, shallow ground water tables can form that
extend into the root zone and even to the soil surface.
The major consideration for wastewater treatment is the
maintenance of an aerobic zone in the upper soil profile.
Many of the wastewater removal mechanisms require an aerobic
environment to function most effectively. A travel distance
of 0.6 to 1m (2 to 3 ft) through aerobic soil is considered
the minimum distance to achieve treatment by the SR
process. Therefore, a water table depth of 1 m (3 ft) or
more is desirable from a wastewater treatment standpoint.
4-53
-------
TABLE 4-24
SUGGESTED SERVICE LIFE FOR COMPONENTS OF
DISTRIBUTION SYSTEM [40]
Service life3
Well and casing
Puir.p plane housing
Pump, turbine
Bowl (about 50* of cost of pump unit)
Column, etc.
Pump, centrifugal
Power transmission
Gear head
V-belt
Flat belt, rubber and fabric
Flat belt, leather
Power units
Electric motor
Diesel engine
Gasoline or distillate
Air cooled
Water cooled
Propane engine
Open farm ditches (permanent)
Concrete structures
Concrete pipe systems
Wood flumes
Pipe, surface, gated
Pipe, water works class ,
Pipe, steel, coated, underground
Pipe, aluminum, sprinkler use
Pipe, steel, coated, surface use only
Pipe, steel galvanized, surface only
Pipe, wood buried
Sprinkler heads
Solid set sprinkler system
Center pivot sprinkler system
Side roll traveling system
Traveling gun sprinkler system
Traveling gun hose system
Land grading0
Reservoirsd
Hoursb
--
16,000
32,000
32,000
30,000
6,000
10,000
20,000
50,000
28,000
8,000
18,000
28,000
—
—
—
—
--
—
—
—
--
__
—
—
—
—
—
—
years
20
20
s
16
16
15
3
5
10
25
14
4
9
14
20
20
20
8
10
40
20
15
10
15
20
8
20
10-14
15-20
10
4
None
None
a. Certain irrigation equipment may have a shorter life
when used in a wastewater treatment system.
b.
d.
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.
Some sources depreciate land leveling in 1 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.
Except where silting'from watershed above will fill
reservoir in an estimated period of years.
-------
For SR systems where wastewater treatment and maximum
hydraulic loading rate are the design objectives, the
presence of excess moisture in the root zone is of limited
concern for crops because water tolerant crops are generally
selected for such systems. However, restrictive subsurface
layers and resulting high water tables limit the allowable
percolation rate and, therefore, the design hydraulic
loading rate. Subsurface drains placed above the
restrictive layer eliminate the effect of that layer on
percolation and allow the design percolation rate to be
based on more permeable overlying soil horizons. The design
hydraulic loading rate is thereby increased.
In arid regions, the additional problem of salinity control
is encountered. With such systems, excess water is applied
to remove salts that concentrate in the root zone
(Section 4.3.2.3). Where the natural drainage rate is
insufficient to remove salty leaching water from the root
zone within 2 to 3 days, crop damage due to salinity may
occur depending on the tolerance of the crop and the
salinity of the applied water (see Section 4.3.2.5). In
such cases, the objectives of a subsurface drainage system
are to (1) prevent the persistence of high water tables when
leaching is practiced, and (2) to keep the water table
sufficiently low between growing seasons to minimize evapor-
ation from the water table and resulting salt accumulation
in the root zone. As a rule of thumb, the water table
should not be permitted to come closer than about 125 cm (49
in.) from the surface to prevent salt accumulation. This
minimum depth is greater than those generally used in humid
areas. Any drainage water from crop revenue systems that is
discharged to surface waters must meet applicable discharge
requirements.
The decision to use subsurface drains must be based on the
economic benefit to be gained from their use. For example,
the cost of installing and maintaining a subsurface drain
system should be compared to the value of developing an
otherwise unsuitable site or to the cost of a larger land
area that will be required if subsurface drains are not
used.
Buried plastic, concrete, and clay tile lines are normally
used for underdrains. The choice usually depends on price
and availability of materials. Where sulfates are present
in the ground water, it is necessary to use a sulfate-
resistant cement, if concrete- pipe is chosen, to prevent
excess internal stress from crystal formation. Most tile
drains are mechanically laid in a machine dug trench or by
direct plowing. Open trenches can be used for subsurface
drainage, but if closely spaced, they can interfere with
farming operations and consume usable land.
4-55
-------
Underdrains are normally buried 1.8 to 2.4 m (6 to 8 ft)
deep but can be as deep as 3 m (10 ft) or as shallow as 1 m
(3 ft). Drains are normally 10 to 15 cm (4 to 6 in.) in
diameter. Spacings as small as 15 to 30 m (50 to 100 ft)
may be required for clayey soils. For sandy soils, 120 m
(400. ft) is typical with the range being from 60 to 300 m
(200 to 1,000 ft).
Procedures for determining the proper depth and spacing of
drain lines to maintain the water table below a minimum
depth are discussed in Section 5.7. Additional detailed
design procedures and engineering aspects of subsurface
drainage systems are described in references [41, 42, 43].
4.8.2
Surface Drainage and Runoff Control
Drainage and control of surface runoff is a design
consideration for SR systems as it relates to tailwater from
surface distribution systems and stormwater runoff from all
systems.
4.8.2.1 Tailwater Return Systems
Most surface distribution systems
which is referred to as tailwater
wastewater is applied, tailwater
the treatment site and reapplied.
system is an integral part of an
distribution methods. A typical
consists of a sump or reservoir
pipeline.
will produce some
When partially
must be contained
Thus a tailwater
SR system using
tailwater return
, a pump(s), and
runoff,
treated
within
return
surface
system
return
The simplest and most flexible type of system is a storage
reservoir system in which all or a portion of the tailwater
flow from a given application is stored and either
transferred to a main reservoir for later reapplication or
reapplied from the tailwater reservoir to other portions of
the field. Tailwater return systems should be designed to
distribute collected water to all parts of the field, not
consistently to the same area. If all the tailwater is
stored, pumping can be continuous and can commence at the
convenience of the operator. Pumps can be any convenient
size, but a minimum capacity of 25% of the distribution
system capacity is recommended [44]. If a portion of the
tailwater flow is stored, the reservoir capacity can be
reduced but pumping must begin during tailwater collection.
Cycling pump systems and continuous pumping systems can be
designed to minimize the storage volume requirements, but
these systems are much less flexible than storage -systems.
The designer is directed to reference [44] for design
procedures.
4-56
-------
The principal design variables for tailwater return systems
are the volume of tailwater and the duration of tailwater
flow. The expected values of these parameters for a well-
operated system depend on the infiltration rate of the
soil. Guidelines for estimating tailwater volume, the
duration of tailwater flow, and suggested maximum design
tailwater volume are presented in Table 4-25.
TABLE 4-25
RECOMMENDED DESIGN FACTORS
FOR TAILWATER RETURN SYSTEMS [44]
Permeability
Maximum'duration Estimated Suggested maximum
of tailwater tailwater volume, design tailwater
% of application volume, % of appli-
Class
Very slow
to slow
Slow to
moderate
Moderate to
moderately
rapid
Rate, cm/h Texture range application time volume
0.15-0.5 Clay to clay 33 15
loam
0.5-1.5 Clay loam to 33 25
silt loam
1.5-15 Silt loams to 75 35
sandy loams
cation volume
30
50
70 '
Runoff of applied wastewater from sites with sprinkler
distribution systems should not occur because the design
application rate of the sprinkler system is less than the
infiltration rate of the soil-vegetation surface. However,
some runoff from systems on steep (10 to 30%) hillsides
should be anticipated. In these cases, runoff can be
temporarily stored behind small check dams located in
natural drainage courses. The stored runoff can be
reapplied with portable sprinkling equipment.
4.8.2.2 Stormwater Runoff Provisions
For SR systems, control of stormwater runoff to prevent
erosion is necessary. Terracing of steep slopes is a well
known agricultural practice to prevent excessive erosion.
Sediment control basins and other nonstructural control
measures, such as contour plowing, no-till farming, grass
border strips, and stream buffer zones can be used. Since
wastewater application will usually be stopped during storm
runoff conditions, recirculation of storm runoff for further
treatment is usually unnecessary. Channels or waterways
that carry stormwater runoff . to discharge points should be
designed with a capacity to carry runoff from a storm of a
specified return frequency (10 year minimum).
-------
4.9 System Management
4.9.1
Soil Management
Management of the soil involves tillage operations and
maintenance of the proper so,!! chemical properties including
plant nutrient levels, pH, sodium levels, and salinity
levels. Much of what is discussed under soil management
refers to agricultural crop systems, since most forest crop
systems require very little soil management.
4.9.1.1 Tillage Operations
One of the principal objectives of tillage operations is to
maintain or enhance the infiltration capacity of the soil
surface and the permeability of the entire soil profile. In
general, tillage operations that expose bare soil should be
kept to a minimum. Minimum tillage and no-till methods
conserve fuel, reduce labor' costs, and minimize compaction
of soils by heavy equipment. Conventional plowing (20 to 25
cm or 8 to 10 in.) arid preparation of a seedbed free of
weeds and trash are necessary for most vegetables and root
crops. Many field crops, however, can be planted directly
in sod or residues from a previous crop or after partial
incorporation of residues by shallow disking. Crop residues
left on the surface or partially incorporated to a depth of
8 or 10 cm (3 or 4 in.) provide protection against runoff
and erosion during intervals between crops. The
decomposition of residues on or near the soil surface helps
to maintain a friable, open condition conducive to good
aeration and rapid infiltration of water. Actively
decomposing organic matter also helps to reduce the
concentration of other soluble pollutants and can hasten the
conversion of toxic organics, like pesticides, to less toxic
products.
At sites where clay pans have formed and reduce the
effective permeability of the soil profile, it may be
necessary to plow very deeply (60 to 180 cm or 2 to 6 ft) to
mix impermeable subsoil strata with more permeable surface
materials. Impermeable pans formed by vehicular traffic
(plow pans) or by cementation of fine particles (hard pans)
can be broken up by subsoiling equipment that leaves the
surface protected by vegetation or stubble. To be
effective, however, the subsoiling equipment must completely
break through the pan layers. This is difficult if the pan
layers are more than 30 cm (1 ft) thick. Local soil
conservation district personnel should be consulted
regarding tillage practices appropriate for specific crops,
soils, and terrain.
4-58
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4.9.1.2
Nutrient Status
During design, it is recommended that the nutrient status of
the soil be evaluated. Periodic evaluation is recommended
as part of the system monitoring program (Section 4.10).
Sufficient nitrogen, phosphorus, and most other essential
nutrients for plant growth are generally supplied by most
wastewaters. Potassium is the nutrient most likely to be
deficient since it is usually present in low concentrations
in wastewater. For soils having low levels of natural
potassium, the following relationship has been developed to
estimate potassium fertilizer requirements?
where Kf =
U =
Kww =
Kf = 0.9U - Kww (4-1.3)
annual fertilizer potassium needed, kg/ha
estimated annual crop uptake of nitrogen,
kg/ha
amount of potassium applied in wastewater,
kg/ha
On the basis of commonly used test methods for available
nutrients, the University of California Agricultural
Extension Service has developed a summary of adequate
available levels in the soil of the nutrients most commonly
deficient for some selected crops. This summary is
presented in Table 4-26. Critical values for nitrogen are
not included because there are no well accepted methods for
determining available nitrogen.
Table 4-26
APPROXIMATE CRITICAL LEVELS OF NUTRIENTS
IN SOILS FOR SELECTED CROPS IN CALIFORNIA
Nutrient
Approximate
critical range, ppm
Test method
Phosphorus
Range and pasture
Field crops and warm
season vegetables
Cool season vegetables
Potassium
Grain and alfalfa
Cotton
Potatoes
10
5-9
12-20
45-55
55-65
90-110
0.5 M NaHCC>3 extraction
at pH 8.5
1.0 N ammonium acetate
extraction at pH 7.0
Zinc
0.4-0.6
DPTA extraction
-------
4.9.1.3 Soil pH Adjustment
In general, a pH less than 4.2 is too acid for most crops
and above 8.4 is too alkaline for most crops. The optimum
PH range for crop growth depends on the type of crop.
Extremes in the soil pH also can affect the performance of
an SR system or indicate problem conditions. Below pH 6.5,
the capacity of the soil to retain metal is reduced. A soil
PH above 8.5 generally indicates a high sodium content and
possible permeability problems.
The pH of soils can be adjusted by the addition of liming
materials or acidulating chemicals. A pH adjustment program
should be based on the recommendations of a professional
agricultural consultant or county or state farm adviser.
4.9.1.4 Exchangeable Sodium Control
Soils containing excessive exchangeable sodium are termed
"sodic" soils. A soil is considered sodic when the
percentage of the total cation exchange capacity (CEC)
occupied by sodium, the exchangeable sodium percentage
(ESP), exceeds 15%. High levels of sodium cause low soil
permeability, poor soil aeration, and difficulty in seedling
emergence. Fine-textured soil may be affected at an ESP
above 10%, but coarse-textured soil may not be damaged until
the ESP reaches about 20%. The ESP should be determined by
laboratory analysis before design if sodic soils are known
to exist in the area of the site. 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. Advice on correcting"sodic
soils should be obtained from agricultural consultants or
farm advisers.
4.9.1.5 Salinity Control
Salinity control may be necessary in arid climates where
natural rainfall is insufficient to flush salts from the
root zone. The salinity leve^L of a soil is usually measured
on the basis of the electrical conductivity of an extract
solution from a saturated soil (ECe). Saline soils are
defined as those yielding an EC value greater than 4,000
micromhos/cm at 25 °C (77 °F).
Soils that are initially saline may be reclaimed by
leaching; however, management of the leachate is often
required to protect ground water quality. The U.S.
Department of Agriculture's Handbook 60 [45] deals with the
diagnosis and improvement of such soils for agricultural
purposes. This reference can be used as a practical guide
-------
for managing saline and saline-sodic soil conditions in arid
and semiarid regions.
4.9.2
Crop Management
Because of their substantially different requirements, the
management of agricultural crops and forest crops are
discussed separately.
4.9.2.1 Agricultural Crop Planting and Harvesting
Local extension services or similar experts should be
consulted regarding planting techniques and schedules. Most
crops require a period of dry weather before harvest to
mature and reach a moisture content compatible with
harvesting equipment. Soil moisture at harvest time should
be low enough to minimize compaction by harvesting
equipment. For these reasons, application should be discon-
tinued well in advance of harvest. The time required for
drying will depend on the soil drainage and the weather. A
drying time of 1 to 2 weeks is usually sufficient if there
is no precipitation. However, advice on this should be
obtained from local agricultural experts.
Harvesting of grass crops and alfalfa involves regular
cuttings, and a decision regarding the trade-off between
yield and quality must be made. Advice can be obtained from
local agricultural experts. In the northeast and north
central states, three cuttings per season have been
successful with grass crops.
4.9.2.2 Grazing
Grazing of pasture by beef cattle or sheep can provide an
economic return for SR systems. No health hazard has been
associated with the sale of the animals for human
consumption.
Grazing animals 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 ground water. Much of
the ammonia-nitrogen volatilizes and the organic nitrogen is
held in the soil where it is slowly mineralized to ammonium
and nitrate forms. Steer and sheep manure contain
approximately 20% nitrogen after volatile losses, of which
about 40% is mineralized in the first year, 25% in the
second, and 6% in successive years [41].
In terms of pasture management, cattle or sheep must not be
allowed on wet fields to avoid severe soil compaction and
4-61
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reduced soil infiltration rates. Wet grazing conditions can
also lead to animal hoof diseases. Pasture rotation should
be practiced so that wastewater can be applied immediately
after the livestock are remdved. In general, a pasture area
should not be grazed longer than 7 days. Typical regrowth
periods between grazings range from 14 to 35 days.
Depending on the period of regrowth provided, one to three
water applications can be made during the regrowth period.
Rotation grazing cycles for 3 to 8 pasture areas are given
in Table 4-27. At least 3 to 4 days drying time following
an application should be allowed before livestock are
returned to the pasture.
Table 4-27
GRAZING ROTATION CYCLES FOR
DIFFERENT NUMBERS OF PASTURE AREAS
No. of Rotation Regrowth Grazing
pasture areas cycle, days period, days period, days
3
4
5
6
7
8
21
28
35
36
35
32
14
21
28
30
28
28
7
7
7
6
7
4
4.9.2.3 Agricultural Pest Control
Problems with weeds, insects, and plant diseases are
aggravated under conditions of frequent water application,
particularly when a single crop is grown year after year or
when no-till practices are used. Most pests can be
controlled by selecting resistant or tolerant crop varieties
and by using pesticides in combination with appropriate
cultural practices. State and local experts should be
consulted in developing an overall pest control program for
a given situation.
4.9.2.4 Forest Crops
The type of forest crop management practice selected is
determined by the species mix grown, the age and structure
of the stand, the method of reproduction best suited and/or
desired for the favored species, terrain, and type of
equipment and technique used by local harvesters. The most
typical forest management situations encountered in land
treatment are management of existing forest stands,
reforestation, and short-term rotation.
-------
Existing Forest Ecosystems
The general objective of the forest management program is to
maximize biomass production. The compromise between fully
attaining a forest's growth potential and the need to
operate equipment efficiently (distribution and harvesting
equipment) requires fewer trees per unit area. These
operations will assure maintenance of a high nutrient
uptake, particularly nitrogen, by the forest.
For uneven-aged forests, the desired forest composition,
structure, and vigor can be best achieved through thinning
and selective harvest. However, excessive thinning can make
trees susceptible to wind throw and caution is advised in
windy areas. The objective of these operations would be to
maintain an age class distribution in accordance with the
concept of optimum nutrient storage (see Section 4.3). The
maintenance of fewer trees than normal would permit adequate
sunlight to reach the understory to promote reproduction and
growth of the understory. Thinning should be done initially
prior to construction of the distribution system and only
once every 10 years or so to minimize soil and site damage.
In even-aged forests, trees will all reach harvest age at
the same time. The usual practice is to clear-cut these
forests at harvest age and regenerate a stand by either
planting seedlings, natural seeding, sprouting from stumps
(called coppice), or a combination of several of the
methods. Even-aged stands may require a thinning at an
intermediate age to maintain maximum biomass production.
Coniferous forests, in general, must be replanted, whereas
hardwood forests can be reproduced by coppice or natural
seeding.
The concept of "whole-tree harvesting" should be considered
for all harvesting operations, whether it be thinning,
selection harvest, or clear-cut harvest. Whole-tree
harvesting removes the entire standing tree: stem,
branches, and leaves. Thus, 100% of the nitrogen
accumulated in the aboveground biomass would be removed (see
Section 4.3.2.1).
Prescribed fire is a common management practice in many
forests to reduce the debris or slash left on the site
during conventional harvesting methods. During the
operation, a portion of the forest floor is burned and
nitrogen is volatilized. Although this represents an
immediate benefit in terms of nitrogen removal from the
site, the buffering capacity that the forest floor offers is
reduced and the likelihood of a nitrate leaching to the
ground water is increased when application of wastewater is
resumed.
-------
Reforestation
Wastewater nutrients often stimulate the growth of the
herbaceous vegetation to such an extent that they compete
with and shade out the desirable forest species. Herbaceous
vegetation is necessary to act as a nitrogen sink while the
trees are becoming established, and therefore, cultural
practices must be designed to control but not eliminate the
herbaceous vegetation. As the tree crowns begin to close,
the herbaceous vegetation will be shaded and its role in the
renovation cycle reduced. Another alternative to control of
the herbaceous vegetation is to eliminate it completely and
reduce the hydraulic and nutrient loading during the
establishment period.
Short-Term Rotation
Short-term rotation forests are plantations of closely
spaced hardwood trees that are harvested repeatedly on
cycles of less than 10 years^ The key to rapid growth rates
and biomass development is the rootstock that remains in the
soil after harvest and then resprouts. Short-term rotation
harvesting systems are readily mechanized because the crop
is uniform and relatively small.
Using conventional tree spacings of 2,5 to 4 m (8 to 12 ft),
research on systems where wastewater has been applied to
short-term rotation plantations has shown that high growth
rates and high nitrogen removal are possible [16]. Planted
stock will produce only 50% to 70% of the biomass produced
following cutting and resprouting [47, 48]. If nitrogen and
other nutrient uptake is proportional to biomass, the first
rotation from planted stock will not remove as much as
subsequent rotations from coppice. Therefore, the initial
rotation must receive a reduced nutrient load or other
herbaceous vegetation must be employed for nutrient
storage. Alternatively, closer tree spacings may be used to
achieve desired nutrient uptake rates during initial'
rotation.
4.10 System Monitoring
The broad objectives of a monitoring program', for an SR
system are to determine if the effluent quality requirements
are being met, to determine if any corrective action is
necessary to protect the environment or maintain the
renovative capacity of the system, and to aid in system
operation. The components of the environment that need to
be observed include water quality, the soils receiving
wastewater, and in some cases, vegetation growing in: soils
that are receiving wastewater.
4-64
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4.10.1
Water Quality Monitoring
Monitoring of water quality for land application systems can
be more complex than for conventional treatment systems
because nonpoint discharges of system effluent are
involved. Monitoring of applied wastewater and renovated
water quality is useful for process control. For SR
systems, renovated water would only be monitored in. cases
where underdrains are used. Monitoring of receiving waters,
surface or ground water, may be required by regulatory
authorities.
In most cases, a water quality monitoring program, including
constituents to be analyzed and frequency of analysis, will
be prescribed by local regulatory agencies. It may be
desired to monitor additional constituents or parameters for
purposes of crop and soil management.
Ground water monitoring data are difficult to interpret
unless sampling wells are located properly and correct
sampling procedures are followed. In addition to quality,
the depth to ground water should be measured at the sampling
wells to determine if the hydraulic response of the aquifer
is consistent with what was anticipated. For SR 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 ground water tables might also indicate the need for
corrective action.
4.10.2
Soils Monitoring
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. Annual monitoring of
the soil properties described in Section 4.9.1 is sufficient
for most systems.
It is recommended that the level of trace elements of
concern (see Chapter 9) in the soil be monitored every few
years so that the rate of accumulation can be observed and
toxic levels avoided. Total metal analysis by hot acid
digestion is recommended for monitoring and comparison
purposes.
4-65
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4.10.3
Vegetation Monitoring
Plant tissue analysis is more revealing than soil analysis
with regard to deficient or toxic levels of elements. If
visual symptoms of nutrient deficiencies or toxicities
appear, plant tissue testing can be used for confirmation,
and corrective action can be taken. A regular plant, tissue
monitoring program can often detect deficiencies or toxicity
before visual symptoms and damage to the plant occurs.
Nitrate should be determined in forages or leafy vegetables
if there is reason to suspect concentrations which might be
toxic to livestock. Detailed information on plant sampling
and testing may be found in references [49, 50]. Extension
specialists or local farm advisers should be consulted
regarding plant tissue testing.
4.11 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
longitudinal slopes of 0.1 to 0.2% with transverse
slopes not exceeding 0.3%.
Step 1. Rough grade to 5 cm (0.15 ft) at
30 m (100 ft) grid stations.
Step 2. Finish grade to ±3 cm (0.10 ft) at
30 m (100 ft) grid stations with no
reversals in slope between stations.
Step 3. Land plane with a 18 m (60 ft) minimum
wheel base, land plane
perfect" finished grade.
to
'near
Access to sprinklers or distribution piping should
be provided every 390 m (1,300 ft) for convenient
maintenance.
Both asbestos-cement and PVC irrigation pipe' are
rather fragile and require care in handling and
installation.
Diaphragm-operated globe valves are recommended for
controlling flow to laterals.
All electric equipment should be grounded,
expecially when associated with center pivot
systems.
4-66
-------
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.
Valve boxes, 1 m (36 in.) or larger, should be made
of corrugated metal, concrete, fiber glass, or pipe
material. Valve boxes should extend 15 cm (6 in.)
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 system vehicles. Recommended soil
contact pressures for center pivot machines are
presented in Table 4-28.
TABLE 4-28
RECOMMEDED SOIL CONTACT PRESSURE
% fines
20
40
50
17
11
8
25
16
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 17 N/cm2 (25 lb/in.^). If this
is exceeded, one can expect wheel tracking
problems to occur.
4-67
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4.12 References
1. Benham-Blair and Affiliates, Inc. and Engineering
Enterprises, Inc. Long-term Effects of Land Application
of Domestic Wastewater: Dickinson, North Dakota, Slow
Rate Irrigation Site. U.S. Environmental Protection
Agency. EPA-600/2-79-144. August 1979.
2. Demirjian, Y.A. et al. Muskegon County Wastewater
Management •System. U.S. Environmental Protection
Agency. EPA-905/2-80-004. February 1980.
3. Hossner, L.R., et al. Sewage Disposal on Agricultural
Soils: Chemical and Microbiological Implications (San
Angelo, Texas). U.S. Environmental Protection Agency.
EPA-600/2-78-131a,b. June 1978.
4. Jenkins, T.F. and A.J. Palazzo. Wastewater Treatment by
a Slow Rate Land Treatment System. U.S. Army Corps of
Engineers, Cold Regions Research and Engineering
Laboratory. CRREL Report 81-14. Hanover,, New
Hampshire. August 1981.
5. Koerner, E.L. and D.A. Haws. Long-Term Effects of Land
Application of Domestic Wastewater: Roswell, New
Mexico, Slow Rate Irrigation Site. U.S. Environmental
Protection Agency. EPA-600/2-79-647. February 1979.
6. Iskandar, I.K., R.P. Murrmann, and D.C. Leggett.
Evaluation of Existing ISystems for Land Treatment of
Wastewater at Manteca, California and Quincy,
Washington. U.S. Army Cold Regions Research and
Engineering Laboratory. CRREL Report 77-24. September
1977.
7. Nutter, W.L., R.C. Schultz, and G.H. Bristeir. Land
Treatment of Municipal Wastewater on Steep Forest Slopes
in the Humid Southeastern United States. Proceedings of
Symposium on Land Treatment of Wastewater. Hanover, New
Hampshire. August 20-25, 1978.
8. Stone, R. and J. Rowlands. Long-Term Effects of Land
Application of Domestic Wastewater: Mesa, Arizona,
Irrigation Site. U.S. Environmental protection
Agency. EPA-600/2-80-061. April 1980.
9. Enfield, C.G. and B.E. Bledsoe. Kinetic Model for
Orthophosphate Reactions in Mineral Soils. EPA-S60/2-
75-002. U.S. Government Printing Office. June 1975.
4-68
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10. Land as a Waste Management Alternative. R.C. Loehr,
ed. Ann Arbor Science. Ann Arbor, Michigan. 1977.
11. Overman, A.R. Wastewater Irrigation at Tallahassee,
Florida. U.S. Environmental Protection Agency. EPA-
600/2-79-151. August 1979.
12. Stone, R. and J. Rowlands. Long-Term Effects of Land
Application of Domestic Wastewater: Camarillo,
California, Irrigation Site. U.S. Environmental
Protection Agency. EPA-600/2-80-080. May 1980.
13. Tofflemire, T.J. and M. Chen. Phosphate Removal by
Sands and Soils. In: Land as a Waste Management
Alternative. Loehr, R.C. (ed). Ann Arbor, Ann Arbor
Science. 1977.
14. Uiga, A. and R.W. Crites. Relative Health Risks of
Activated Sludge Treatment and Slow Rate Land
Treatment. Journal WPCF, 52(12):2865-2874. December
1980.
15. Pratt, P.F. Quality Criteria for Trace Elements in
Irrigation Waters. University of California, Riverside,
Department of Soil Science and Agricultural
Engineering. 1972.
16. National Academy of Science. Water Quality Criteria
1972. Ecological Research Series. U.S. Environmental
Protection Agency. Report No. R3-73-033. March 1973.
17. U.S. Environmental Protection Agency. Preliminary
Survey of Toxic pollutants at the Muskegon Wastewater
Management System. Robert S. Kerr Environmental
Research Laboratory, Groundwater Research Branch. Ada,
Oklahoma. 1977.
18. Hinrichs, D.J. Design of Irrigation Systems for
Agricultural Utilization of Effluent. Presented at the
California Water Pollution Control Association Annual
Conference,' Monterey, Calif. May 1, 1980.
19. Smith, W.H. and J.O. Evans. Special Opportunities and
Problems in Using Forest Soils for Organic Waste
Application. In: Soils for Management of Organic
Wastes and Waste Waters.. ASA, CSSA, SSSA, Madison,
Wisconsin. pp. 429-451. 1977.
20.' Palazzo, A. J. , and J.M. Graham. Seasonal Growth and
Uptake of Nutrients by Orchardgrass irrigated with
Wastewater. U.S. Army Cold Regions Research and
Engineering Laboratory. CRREL Report 81-8. June 1981.
4-69
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21. Duscha, L.A. Dual, Cropping Procedure for Slow
Infiltration of Land Treatment of Municipal
Wastewater. Department of the Army, Engineering
Technical Letter No. 1110-2-260. March 12, 1981.
22. McKim, H.L., et al. Wastewater .Application in Forest
Ecosystems. CRREL Report 119, Corps of Engineers, U.S.
Army. May 1980.
23. USDA Forest Service. Impact of Intensive Harvesting on
Forest Nutrient Cycling. Northeast Forest Experiment
Station. Broomall, Pa. 1979.
24. Jensen, M.E. (ed.). Consumptive Use of Water and
Irrigation Water Requirements. ASCE. ASCE Committee on
Irrigation Water Requirements. 1973. :
25. Doorenbos, J. and W.O. Pruitt. Guidelines for
Predicting Crop Water Requirements. Irrigation and
Drainage Paper 24. Presented at United Nations Food and
Agriculture Organization. Rome. 1975.
26. Irrigation Water Requirements. Technical Release No.
21, U.S. Department of Agriculture, Soil Conservation
Service. September 1970.
27. Vegetative Water Use in California, 1974. Bulletin No.
113-3, State of California Department of Water
Resources. April 1975.
28. Booher, L.J. and G.V. Ferry. Estimated Consumptive Use
and Irrigation • Requirements of Various Crops.
University of California Agricultural Extension Service,
Bakersfield, Calif. March 10, 1970.
29. Ayers, R.S. Quality of Water for Irrigation, Jour, of
the Irrigation and Drainage Division, ASCE, Vol. 1O3,
No. IR2. June 1977. pp. 135-154.
30. U.S. Environmental Protection Agency. Facilities
Planning, 1982. EPA-430/9-81-012. FRD-25. September
1981.
31. Reed, S.C. Treatment/Storage Ponds for Land Application
Systems. CRREL Special Report. December 1981.
32. Environmental Protection Agency. Process Design Manual
for Wastewater Treatment Ponds (In Preparation),
33. Bowles, D.S., et al. Coliform Decay Rates in Waste
Stabilization Ponds, Journal WPCF, 51(l):87-99, January
1979.
4-70
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34. Sagik, B.P. et al. The Survival of Human Enteric
Viruses in Holding Ponds. Contract Report DAMD 17-75-C-
5062. U.S. Army Medical Research and Development
Command. 1978.
35. Whiting, D.M. Use of Climatic Data in Estimating
Storage Days for Soil Treatment Systems. Environmental
Protection Agency, Office of Research and Development.
EPA-600/2-76-250. November 1976.
36. 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.
37. U.S. Department of the Interior, Bureau of
Reclamationo Design of Small Dams. Second Edition.
U.S. Government Printing Office. 1973.
38. Booher, L.J. Surface Irrigation. FAO Agricultural
Development Paper No. 95. Food and Agricultural
Organization of the United Nations. Rome. 1974.
t •
39. Myers, E.A. Design and Operational Criteria for Forest
Irrigation Systems. In: Utilization of Municipal
Sewage Effluent and Sludge on Forest and Disturbed
Land. The Pennsylvania State University Press,
University Park, Pa. p. 265-272. 1979.
Systems. U.S.
EPA-430/9-75-001.
40. Evaluation of Land Application
Environmental Protection Agency.
March 1975.
41. Luthin, J.N. (ed.). Drainage of Agricultural Lands
Madison, American Society of Agronomy. 1957.
42. Van Schilfgaarde, J, ed. Drainage for Agriculture.
American Society of Agronomy, Madison, Wisconsin. 1974.
43. 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,
44. Hart, W.E. Irrigation System Design, Colorado State
University, Department of Agricultural Engineering,.
Fort Collins, Colorado. November 10, 1975.
45. Richards, L.A. (ed.). Diagnosis and Improvement of
Saline and Alkali Soil. Agricultural Handbook 60. U.S.
Department of Agriculture. 1954.
4-71
-------
46. California Fertilizer Assn. Western Fertilizer Handbook
Sixth Ed. The Interstate Printers and Publishers.
1980.
47. Saucier, J.R. Estimation of Biomass Production and
Removal. In: Impact of Intensive Harvesting on Forest
Nutrient Cycling. College of Environmental Science and
Forestry, State University of New York, Syracuse, New
York, p. 172-189. 1979.
48. Steinbeck, K. and C.L. Brown. Yield and Utilization of
Hardwood Fiber Grown on Short Rotations. Applied
Polymer Symposium 28: 393-401. 1976.
49. Walsh, L.M. and J.D. Beaton, (eds.). Soil Testing and
Plant Analysis. Madison, Soil Science Society of
America. 1973.
50. 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, University of
Illinois. July 1973. pp. 121-128.
4-72
-------
CHAPTER 5
RAPID INFILTRATION PROCESS DESIGN
5.1 Introduction
The design procedure for rapid infiltration (RI) is
diagrammed in Figure 5-1. As indicated by this figure,
there are several major elements in the design process and
the design approach is somewhat iterative. For example, the
amount of land required for an RI system is a function of
the loading rate, which is affected by the loading cycle and
the level of preapplication treatment. If the engineer
initially assumes a level of preapplication treatment and a
loading cycle that result in a loading rate requiring more
land than is available at the selected site, the level of
preapplication treatment and loading cycle can be
reevaluated to reduce the land area required.
5.1.1 RI Hydraulic Pathway
The engineer and the community must decide which hydraulic
pathway (see Figure 1-2) is appropriate for their
situation. This decision is based on the hydrogeologic
characteristics of the selected site and regulatory agency
decisions.
5.1.2 Site Work
For RI design, the results of the field investigations
(Chapter 3) must be analyzed and interpreted. Backhoe pits
and drill holes are needed to establish the depth and
hydraulic conductivity of the permeable material and the
depth to ground water. Sufficient subsurface information
must be obtained in the Phase ,2 planning process (Chapter 2)
to allow the engineer to calculate:
1. Infiltration rate (Section 5.4)
2. Subsurface flow (Section 5.7)
• Potential for mounding
• Drainage (if needed)
• Natural seepage (if adequate)
3. Mixing of percolate with ground water (if
critical to meet performance requirements)
5-1
-------
WASTEWATER
CHARACTERISTICS
(SECTION 2.2.1)
WATER QUALITY
REQUIREMENTS
(SECTION 2.2.1)
SITE
CHARACTERISTICS
(SECTIONS 2.2.1,
2.3.1 )
RI
HYDRAULIC PATHWAY
(SECTION 5.1.1)
PREAPPLICATION
TREATMENT LEVEL
(SECTION 5.3)
LOADING RATE
(SECTION 5.4.)
LOADING CYCLE
(SECTION 5.4.2)
LAND
REQUIREMENTS
(SECTION 5.5)
BASIN DESI6N
AND LAYOUT
(SECTION 5.6)
DRAINA6E AND/OR
RECOVERY
(SECTION 5.7)
MONITORING AND
MAINTENANCE
REQUIREMENTS
(SECTION 5.8)
FIGURE 5-1
RAPID INFILTRATION DESIGN PROCEDURE
5-2
-------
5.2 Process Performance ;
The RI mechanisms ' for removal of wastewater constituents
such as BOD, suspended solids, nitrogen, phosphorus, trace
elements, microorganisms, and trace organics are discussed
briefly along with typical results from various operating
systems. Chapter 9 contains discussions of the health and
environmental effects of these constituents.
5.2.1 BOD and Suspended Solids
Particulate BOD and suspended solids are removed by
filtration at or near the soil surface. Soluble BOD may be
adsorbed by the soil or may be removed from the percolating
wastewater by soil bacteria. Eventually, most BOD and
suspended solids that are removed initially by filtration
are degraded and consumed by soil bacteria. BOD and
suspended solids removals are generally not affected by the
level of preapplication treatment. However, high hydraulic
loadings of wastewaters with high concentrations of BOD and
suspended solids can cause clogging of the soil. Typical
BOD loadings (Table 2-3) are less than 130 kg/ha«d
(115 lb/acre-d) for municipal wastewaters^Removals
achievedatselectedRIsystemsarepresented in
Table 5-1. Some systems have been operated successfully at
higher loadings.
5.2.2 Nitrogen
The primary nitrogen removal mechanism in RI systems is
nitrification-denitrification. This mechanism involves two
separate steps: the oxidation of ammonia nitrogen to
nitrate (nitrification) and the subsequent conversion of
nitrate to nitrogen gas (denitrification). Ammonium adsorp-
tion also plays an important intermediate role in nitrogen
removal.
Both nitrification and denitrification are accomplished by
soil bacteria. The optimum temperature for nitrogen removal
is 30 °C to 35 °C (86 °F to 95 °F). Both processes proceed
slowly between 2 °C and 5 °C (36 °F and 41 °F) and stop near
the freezing point of/water. Nitrification rates decline
sharply in acid conditions and reach a limiting value at
approximately pH 4.5. The denitrification reaction rate is
reduced substantially at pH values below 5.5. Thus, both
soil temperature and pH must be considered if nitrogen
removal is important (Section 5.4.3.1). Furthermore,
alternating aerobic and anaerobic conditions must be
provided for significant nitrogen removal (Section 5.4.2).
Because aerobic bacteria deplete soil oxygen during flooding
periods, resting and flooding periods must be alternated to
result in alternating aerobic and anaerobic soil conditions.
5-3
-------
TABLE 5-1
BOD REMOVAL DATA FOR
SELECTED RI SYSTEMS [1-6]
Location
Calumet,
Michigan
Fort Devens,
Massachusetts
Hollister,
California
Lake George,
New York
Milton,
Wisconsin
Phoenix,
Arizona
Vineland,
New Jersey
Preapplication
treatment
Untreated
Primary
Primary
Trickling
filters '
Activated
sludge
Activated
sludge
Primary
Sampling
depth, m
3.3
20
8
3
8-29
6-9
2-14
Average
loading
rate,
kg/ha -da
80
87
177
53
155
45
48
BOD
Treated
water concen- Removal,
tration, mg/L %
llb 86
12 86
8C 95
1.2 98
1.0-19.0 88-99
0-1 98-100
6.5° 86
•
a. Total kg/ha-yr applied divided by the number of days in the operating
season (365 days for these cases).
b. Soluble total organic carbon.
c. Average value from several wells.
Note: See Appendix G for metric conversions.
Organic carbon is needed in the applied wastewater to 'supply
energy for the denitrification reaction. Approximately
2 mg/L of total organic carbon (TOG) is needed to denitrify
1 mg/L of nitrogen. Because the BOD concentration decreases
as the level of preapplication treatment increases,
preapplication treatment must be limited if denitrification
is to occur in the soil. Thus, if the goal of RI is
nitrogen removal, primary preapplication treatment is
preferred.
Nitrogen removal efficiencies at various operating RI
systems are shown in Table 5-2. As shown in this table,
nitrogen removals of approximately 50% are typical"! Greater
amounts can Be removed using special management proced ure s
(Section 5.4.3.1).
5-4
-------
TABLE 5-2
NITROGEN REMOVAL DATA FOR SELECTED RI
SYSTEMS [1,2,4,6-9]
Concentration Concentration in
in applied Loading Flooding renovated water, mg/L Removal,
wastewater: rate, BOD:N to drying % of
Location total N, mg/L m/yr ratio time ratio NO-.-N Total N total N
N03-N
Boulder,
Colorado
Brookings,
South Dakota
Calumet,
Michigan
Disney World,
Florida
Fort Devens,
Massachusetts
Hollister,
California
Lake George,
New York
Phoenix,
Arizona
16.5
10.9
24.4
—
50
40.2
11.5
12.0
27.4
48
12
17
54
30
15
58
58
61
.8
.2
.1
.9
.5
.2
.0
.0
.0
2.3:
2:
3.6:
0.3:
2.4:
5.5:
2:
2:
1:
1
1
1
1
1
1
1
1
1
1:
1:
1:
150:
2:
1:
1:
1:
9:
3 6-16
2 5.3
2 3.4
14
12 13.6
14 0.9
4
4
12 6.2
9-16 10-20
6.2 43
7.1 71
12
19.6 61
2.8 93
7.70 33
7.50 38
9.6. 65
At some sites the goal of RI may be only nitrification (for
example, Boulder, Colorado). Generally, nitrification
occurs if wastewater application periods are short enough
that the upper soil layers remain aerobic. For this reason,
if nitrification is the objective of RI , short application
periods followed by somewhat longer drying periods are
used. Because the nitrification rate decreases during
winter months, reduced loading rates may be required in cold
climates. Under favorable temperature and moisture
conditions, up to 50 ppm ammonia nitrogen (as nitrogen) per
day (soil basis) may be converted to nitrate [10]. Assuming
that nitrification only occurs TH the top 10 cm (4 in. ) of
soil, this corresponds to nitrification rates of up to
67 kg/ha-d (60 Ib/acre -d) . At the Boulder, Colorado, RI
system, the percolate ammonia concentration remained below
1 mg/L on a year-round basis.
5.2.3 Phosphorus
The primary phosphorus removal mechanisms in RI systems are
the same as described in Section 4.2.3 for SR. Phosphorus
removals achieved at typical RI systems are provided in
Table 5-3.
5-5
-------
TABLE 5-3
PHOSPHORUS REMOVAL DATA FOR SELECTED
RI SYSTEMS [1, 2, 4-9]
Average
concentration
in applied
wastewater ,
Location mg/L
Boulder,
Colorado
Brookings, .
South Dakota
Calumet,
Michigan
Fort Devens, .
Massachusetts
Hollister,
California13
Lake George,
New Yorkb
Phoenix,
Arizona3
Vineland, .
New Jersey
6.2
3.0
3.5
3.5
9.0
10.5
2.1
2.1
8-11
7.9
4.8
4.8
c
Distance of travel, m
Vertical
2.4-3.0
0.8
3-9
c
15
6.8
3
c
9.1
6
2-18
4-16
Horizontal
0
0
0-125
1,700C
30
0
0
600C
0
30
0
26O-530
Average
oncentration
in renovated
wastewater,
mg/L
0.2-4.5
0.45
0.1-0.4
0.03
0.1
7.4
<1
0.014
2-5
0.51
1 . 54
0.27
Removal,
%
40-97
85
89-97
99
99
29
>52
' 99
40-80
94
68
94
a. Total phosphate measured.
b. Soluble phosphate measured.
c. Seepage.
5.2.4 Trace Elements
Trace element removal involves essentially the same
mechanisms discussed in Section 4.2.4 for SR systems. The
results presented in Table 5-4 compare trace element
concentrations in wastewater at Hollister, California, to
drinking water and irrigation requirements.
At RI sites, trace elements accumulate in the upper soil
layers. Data from Cape Cod, Massachusetts, reflect this
phenomenon and are presented in Table 5-5. As indicated in
this table, the percent retention of most of the metals is
quite high. For example, 85% of the copper applied over
33 years was retained in the top 0.52 m (1.7 ft). The
distribution of the retained metals is also shown in
Table 5-5.
5r-6
-------
TABLE 5-4
COMPARISON OF TRACE ELEMENT LEVELS TO
IRRIGATION AND DRINKING WATER LIMITS [6]
mg/L
Maximum
Recommended maximum concentration
in irrigation in drinking
Element waters waters
Ag
As
Ba
Cd
Co
Cr
Cu
Fe
Hg
Mn
Ni
Pb
Se
Zn
(silver)
(arsenic)
(barium)
(cadmium)
(cobalt)
(chromium)
(copper)
( iron )
(mercury)
(manganese)
(nickel)
(lead)
(selenium)
(zinc)
~«
0.1
— a
0.01
0.1
0.05
0.2
5.0
a
0.2
0.2
5.0
0.02
2.0
0.05
0.05
1.0
0.010
a
0.05
a
— a
0.002
a
a
0.05
0.01
a
Hollister,
California,
average
wastewater
concentration
<0.008
<0.01
<0.13
<0.004
<0.008
<0.014
0.034
0.39
<0.001
0.070
0.051
0.054
<0.001
0.048
a. None set.
TABLE 5-5
HEAVY METAL RETENTION IN AN
INFILTRATION BASIN a
Percent
Depth, m
0-0.04
0.04-0.06
0.14-0.16
0.24-0.26
0.29-0. 31
0.44-0.46
0.50-0.52
Total .
Percent
retention
of 33 year
loads
0-0.52
Cadmium
84
12
1
1
1
0.5
0.5
100
113
Chromium Copper
87
10
0
2
0
1
0
100
62
76
23
0.4
0.4
0.1
0.1
0.0
100
85
Lead
88
12
0
0
0
0
0
100
129
Zinc
82
13
1
2
0.8
1.2
0
100
49
a. Adapted from reference [11].
5-7
-------
5.2.5 Microorganisms
Removal mechanisms for microorganisms are discussed in
Section 4.2.5.
Fecal coliform removal efficiencies obtained at selected RI
sites are given in Table t 5-6. As shown in this table,
effective removal of fecal coliforms can be achieved with
adequate travel distance.
TABLE 5-6
FECAL COLIFORM REMOVAL DATA FOR
SELECTED RI SYSTEMS [1, 3-6, 12]
Fecal coliforms, MPN/100 mL
Distance; of
Location Soil type Applied wastewater Renovated water travel, ra
Hercet ,
California
Hoi lister,
California
Lake George,
New York
Landis,
New Jersey
Milton,
Wisconsin
Phoenix,
Arizona
Santee,
California
Vineland,
New Jersey
Sand
Sandy
loam
Sand
Sand and
gravel
Gravelly
sands
Sand
Gravelly
sands
Sand and
gravel
60,000
12,400,000
359,000
359,000
TNTC3
TNTCa
244,071
244,071
130,000
130,000
TNTC3
11
171,000
72
0
16
0
104
0
580
<2
0
2
7 ,
2
7
1-2
8-17
30
90
61
762
. 6-7
a. At least one sample too numerous to count.
The primary removal mechanism for viruses is adsorption.
Because of their small, size, viruses are not removed by
filtration at the soil surface, but instead, travel into the
soil profile. Only a limited number of studies have been
conducted to determine the efficiency of virus removal. At
Phoenix, Arizona, results indicate that 90 to 99% of the
applied virus is removed within 10 cm (4 in.) of travel when
either primary or secondary effluent is applied [13, 14] and
that 99.99% removal is achieved during travel through 9 m
(30 ft) of soil following the application of secondary
effluent [15].
The only RI sites at which viruses have been detected in
ground water, and the distances traveled by the virus prior
to detection are listed in Table 5-7. As noted in the
5-8
-------
table, all four of these sites are located on coarse sand
and gravel type soils. Infiltration rates on these soils
are relatively high, allowing constituents in the applied
wastewater to travel greater distances than normally
expected. Thus, the coarser the soil is, the higher the
loading rate, and the higher the virus concentration, the
greater the risk of virus migration.
TABLE 5-7
REPORTED ISOLATIONS OF VIRUS AT RI SITES [16]
Location
Soil type
Distance of migration, m
Vertical Horizontal
East Meadows,
New York
Fort Devens,
Massachusetts
Holbrook,
New York
Vineland,
New Jersey
Sands and
gravel
Sands and
gravel
Sands and
gravel
Sands and
gravel
11
18
6
16
.3
.3
.1
.8
3
183
45.7
250
a. Application of unchlorinated primary effluent.
5.2.6 Trace Organics
Trace organics can be removed by volatilization, sorption,
and degradation. Degradation may be either chemical or
biological; trace organic removal from the soil is primarily
the result of biological degradation.
Studies to determine trace organic removal efficiencies
during RI were conducted at the Vineland and Milton sites
[3, 5]. At these two systems, applied effluent and ground
water were analyzed for six pesticides and the results of
the studies are summarized in Table 5-8. At both locations,
the concentrations of 2,4-D, 2,4,5-TP silvex, and lindane
were well below the maximum concentrations for domestic
water supplies established in the National Primary Drinking
Water Regulations.
If local industries contribute large concentrations of
synthetic organic chemicals and the RI system overlies a
potable aquifer, industrial pretreatment should be
considered. Further, since chlorination prior to land
application causes formation of chlorinated trace organics
that may be more difficult to remove, chlorination before
application should be avoided whenever possible.
5-9
-------
TABLE 5-8
RECORDED TRACE ORGANIC CONCENTRATIONS
AT SELECTED RI SITES [3,5]
ng/L
Vineland, New Jersey3
Pesticide
Endrin
Lindane
Methoxychlor
Toxaphene
2,4-D
2,4,5-TP
ailvex
Applied
<0.03
2,830-
1,227
<0.01
<0.1
9.5-
10.5
72
Shallow
ground
water
<0.03
453-
1,172
<0.01
<0.1
16.4-
13.0
26.8-
120
Control
ground
water
<0.03
21.3
<0.01
<0.1
10.4
185
Applied
<0.03
41
<0.01
<0.1
53.8
16.2
Milton,
Shallow
ground
water"
<0.03
157.6
<0.01
<0.1
92.4
41.2
Wisconsin
Down-
gradient0
<0.03
3.9
<0.01
<0.1
23.6
38.7
1
Control
ground
water
<0.03
7.4
<0.01
<0. 1
31.0
76.8
b.
c.
If two values are listed, the first is for the Vineland site and the second
is for the Landis site (see reference [5]). If one value is listed, results
were the same at both sites.
Shallow ground water was sampled directly below infiltration basins.
Ground water sampled approximately 45 m (148 ft) downgradient from the infil-
tration basins.
5.3 Determination of Preapplication Treatment Level
The first step in designing an RI system is to determine the
appropriate level of preapplication treatment. This section
describes the factors that should be considered as well as
the levels of preapplication treatment that should be used
to meet various treatment objectives.
5.3.1 EPA Guidance
EPA has issued guidelines suggesting the following levels of
preapplication treatment for RI systems [17]:
• Primary treatment in isolated locations that
have restricted public access
• Biological treatment by lagoons or in-plant
processes at urban sites that have controlled
public access
5.3.2 Water Quality Requirements and Treatment Goals
Preapplication treatment is used to reduce soil clogging and
to reduce the potential for nuisance conditions
(particularly odors) developing during temporary storage at
the application site. If surface discharge is required and
ammonia discharge requirements are stringent, the treatment
5-10
-------
objective should be to maximize nitrification. In all other
cases, system design is based on achieving the maximum,
cost-effective loading rate that provides the required level
of overall treatment.
For all systems, the equivalent of primary treatment is the
minimum recommended preapplication treatment. This level of
treatment reduces wear on the distribution system, prevents
unmanageable soils clogging, reduces the potential for
nuisance conditions, and allows the potential for maximum
nitrogen removal.
Nitrification may be achieved using either primary or
secondary preapplication treatment. For this reason, the
selection of a preapplication treatment level to maximize
nitrification at a specific site is based on the same
factors that influence the selection of a preapplication
treatment level for maximizing infiltration rates.
In mild climates, ponds can be used if land is relatively
plentiful and not expensive,. In areas that experience cold
winter weather, it may not be possible to operate RI systems
that use ponds for preapplication treatment. Also, if ponds
are used prior to infiltration, algae carryover may increase
the potential for soil clogging. Ponds can also be used to
reduce the nitrogen loading (Section 4.4.1).
Recommended levels of preapplication treatment are
summarized in Table 5-9. This table should t be used only as
a guide; the designer should select preapplication treatment
facilities that reflect local conditions, including local
preapplication treatment requirements and existing
wastewater treatment facilities.
TABLE 5-9
SUGGESTED PREAPPLICATION TREATMENT LEVELS
RI system objective
Preapplication
treatment level
Maximize infiltration
rates or nitrification
General case
Limited land
High quality effluent
polishing
Maximize nitrogen
removal
General case
Primary
Secondary
Secondary or
higher
Primary
5-11
-------
5.4 Determination of Hydraulic Loading Rate
Selection of a hydraulic loading rate is the most important
and, at the same time, the most difficult step in the design
procedure. The loading rate is a function of the site-
specific hydraulic capacity, the loading cycle, the quality
of the applied wastewater, and the treatment requirements.
5.4.1 Measured Hydraulic Capacity
Hydraulic capacity varies from site to site and is a
difficult parameter to measure. For design purposes,
infiltration tests are usually used to estimate hydraulic
capacity. The most commonly employed measurement for RI
design is the basin infiltration test; cylinder
inf iltrometers are used when basin testing is not
feasible. Both methods are described in Section 3.4»
Saturated vertical hydraulic conductivity (also called
permeability) is sometimes measured. However, saturated
vertical hydraulic conductivity is a constant with time,
whereas infiltration rates decrease as wastewater solids
clog the soil surface. Thus, vertical , conductivity
measurements overestimate the wastewater infiltration rates
that can be maintained over long periods of time. For this
reason, and to allow adequate time for drying periods and
for proper basin management, annual hydraulic loading rates
should be limited to between 4 and 10% of the measured clear
water permeability of the most restrictive soil layer.
Although basin infiltration tests are more accurate than
soil hydraulic conductivity measurements and are the
preferred method, the small areas usually used allow a
larger fraction of the wastewater to flow horizontally
through the soil from the test site than from an operating
basin. The result is that infiltration rates at the test
sites are higher than rates . operating systems would
achieve. Thus, design annual hydraulic loading rates should
be no greater than 10 to 15% of measured basin infiltration
rates.
Cylinder infiltrometers greatly overestimate operating
infiltration rates. When cylinder infiltrometer measure-
ments are used, annual hydraulic loading rates should be no
greater than 2 to 4% of the minimum measured infiltration
rates. Annual hydraulic loading rates based on air entry
permeameter test results ! should be in the same range.
Annual loading rates and corresponding infiltration rates
RI systems are presented in
loading rates are summarized in
for several
Table 5-10.
Table 5-11.
operating
Suggested
5-12
-------
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-------
TABLE 5-11
SUGGESTED ANNUAL HYDRAULIC LOADING RATES
Field measurement
Annual loading rate
Basin infiltration test
Cylinder infiltrometer •
and air entry permeameter
measurements
Vertical hydraulic
conductivity measurements
10-15% of minimum measured
infiltration rate
2-4% of minimum measured
infiltration rate
4-10% of conductivity of most
restricting soil layer
The total hydraulic load includes both precipitation and
wastewater. If the local precipitation is significant,
wastewater loading rates should be adjusted accordingly.
Once the hydraulic capacity has been measured, the engineer
must calculate an annual hydraulic loading rate. Experience
in the United States with treatment systems using RI has
been limited to annual loading rates of about 120 m (400 ft)
or less.
For example, if the basin test infiltration rate is 3.6 cm/h
(1.4 in./h)f the annual hydraulic loading rate is calculated
to equal:
3.6 cm/h x 24 h/d x 365 d/yr x 1 m/100 cm x (0.1 to 0.15)
= 31.5 to 47.3 m/yr (103 to 155 ft/yr)
It is necessary to ensure that BOD and suspended solids are
within typical ranges (Sections 2.2.1.1 and 5.2.1) at the
calculated annual loading rate. If the applied wastewater
contains 150 mg/L BOD and 100 mg/L suspended solids „ at a
loading rate of 31 m/yr (102 ft/yr), the BOD and SS loadings
would average 127 kg/ha-d (114 lb/acre-d) and 85 kg/ha-d
(76 lb/acre-d), respectively. These quantities are within
the typical BOD range given in Table 2-3 and the suspended
solids range discussed in Section 2.2.1.1.
5.4.2 Selection of Hydraulic Loading Cycle
and Application Rate
Wastewater application is not continuous in RI , instead,
application periods are alternated with drying periods.
This improves wastewater treatment efficiency, maximizes
long-term infiltration rates, and allows for periodic basin
maintenance.
-------
Loading cycles are selected to maximize either the infil-
tration rate, nitrogen removal, or nitrification. To
maximize infiltration rates, the engineer should include
drying periods that are long enough for soil reaeration and
for drying and oxidation of filtered solids.
Loading cycles used to maximize nitrogen removal vary with
the level of preapplication treatment and with the climate
and season. In general, application periods , must be long
enough for soil bacteria to deplete soil oxygen, resulting
in anaerobic conditions.
Nitrification requires short application periods followed by
longer drying periods. Thus, hydraulic loading cycles used
to achieve nitrification are essentially the same as the
cycles used to maximize infiltration rates.
Hydraulic loading cycles at selected RI sites are presented
in Table 5-12. Recommended cycles are summarized in
Table 5-13. Generally, the shorter drying periods shown in
Table 5-13 should be used only in mild climates; RI systems
in cooler climates should use the longer drying periods. In
areas that experience extremely cold weather, even longer
drying periods than those presented in Table 5-13 may be
necessary. The cycles suggested in Table 5-13 are presented
only as guidelines; the actual cycle selected should be
suitable and flexible enough for the community's climate,
flow, and treatment site characteristics.
Application rates can be calculated from the annual loading
rate and the loading cycle. For example, the annual loading
rate is 31 m/yr (102 ft/yr) and the loading cycle is 3 days
of application followed by 11 days of drying.
• Total cycle time = 3 + 11 = 14 d
• Number of cycles per year = 365/14 = 26
• Loading per cycle = 31/26 = 1.19 m/cycle
• Application rate = (1.19 m/cycle)/(3 d)
=0.4 m/d
The application rate can then be used to calculate the
maximum depth of applied wastewater. For example, if 'the
basin infiltration test rate of 3.6 cm/h (1.4 in./h) is
maintained over the 3 day application period, the appli-
cation rate of 0.4 m/d (1.3 ft/d) should not result in
standing water at the end of 3 days:
(0.4 m/d x 100 cm/m) - (3.6 cm/h x 24 h/d)
= -46.4 cm (-18.3 in.)
5-15
-------
TABLE 5-12
TYPICAL HYDRAULIC LOADING CYCLES [6, 9, 18, 19]
Location
Boulder,
Colorado
Calumet,
Michigan
Flushing Meadows,
Arizona
Year-round
Stunner
Winter
Year-round
Fort Devens,
Massachusetts
year-round
Year-round
Hollister,
California
Summer
Winter
Lake George,
New York
Summer
Winter
Tel Aviv,
Israel
Vineland,
New Jersey
Westby,
Wisconsin
Whittier Narrows,
California
Preapplication
treatment
Trickling filters
Untreated
Activated sludge
Primary
Primary
Trickling filters
Ponds, lime preci-
pitation, and
ammonia stripping
Primary
Trickling filters
Activated sludge
with filtration d
Cycle objective
Maximize nitrifi-
cation and infil-
tration rates
Maximize infil-
tration rates
Maximize nitrifi-
cation
Maximize infil-
tration rates
Maximize infil-
tration rates
Maximize nitrogen
removal
Maximize infil-
tration rates
Maximize nitrogen
removal
Maximize infil-
tration rates
Maximize infil-
tration rates
Maximize infil-
tration rates
Maximize infil-
tration rates
Maximize
polishing
Maximize infil-
tration rates
Maximize infil-
tration rates
Maximize infil-
tration rates
Application Resting
period period
<1 d <3 1/2 d
1-2 d 7-14 d-
2 d 5 d
2 wk 10 d
2 wk 20 d
9 d 12 d
2 d 14 d
7 db 14 d
1 d 14-21 d
1 d 10-16 d
9 h 4-5 d
9 h 5-10 d
5-6 d 10-12 d
1-2 d 7-10 d
2 wk 2 wk
9 h 15 h •
Bed surface
Sand (disked) ,
solids turned
into soil
Sard (not
cleaned)
Sand (cleaned)3
Sand (cleaned)3
Sand (cleaned)3
Sand (cleaned)3
Weeds (not
cleaned)
Weeds (not
cleaned)
Sand
Sand
Sand (cleaned)3
Sand • (cleaned) a
Sand c
Sand (disked)
solids turned
into soil
Grassed
Pea gravel
a. Cleaning usually involved physical removal of surface solids.
b. Caused clogging and reduced long-term hydraulic capacity.
c. Maintenance of sand cover is unknown.
d. Treated wnstewater blended with surface waters before application..
5-16
-------
TABLE 5-13
SUGGESTED LOADING CYCLES
Loading cycle
objective
Applied Application Drying
wastewater Season period, da period, d
Maximize
infiltration
rates
Maximize
nitrogen
removal
Maximize
nitrification
Primary
Secondary
Primary
Secondary
Primary
Secondary
Summer
Winter
Summer
Winter
Summer
Winter
Summer
Winter
Summer
Winter
Summer
Winter
1-2
1-2
1-3
1-3
1-2
1-2
7-9
9-12
1-2
1-2
1-3
1-3
5-7
7-12
4-5
5-10
10-14
12-16
10-15
12-16
5-7
7-12
4-5
5-10
a. Regardless of season or cycle objective, application
periods for primary effluent should be limited to
1-2 days to prevent excessive soil clogging.
If the calculated depth is a positive number, the maximum
design wastewater depth should not exceed 46 cm (18 in.); a
maximum depth of 30 cm (12 in.) is preferable because soil
clogging and algae growth decrease as the loading depth and
detention time decrease. If the calculated depth exceeds 46
cm (18 in.) either the application period must be lengthened
or the loading rate decreased. From this example, it is
clear that infiltration rates must be determined as
accurately as possible. If the infiltration rate is over-
estimated, basin depth will be underestimated and diffi-
culties will arise when system operation begins.
5.4.3 Other Considerations
The following three subsections describe other factors that
can affect the loading cycle and loading rate and must be
considered by the designer.
5.4.3.1
Nitrogen Removal
The amount of nitrogen that theoretically (under optimal
conditions) can be removed by denitrification can be
described by the equation [19].
AN - TOC - K
(5-1)
5-17
-------
where AN =
TOC =
K =
change in total nitrogen concentration, mg/L
total organic carbon concentration in the
applied wastewater, mg/L (see Table 2-1)
TOC remaining in percolate, assumed to
equal 5 mg/L
The equation is based on experimental data that indicated
2 grams of wastewater carbon are needed to denitrify 1 gram
of wastewater nitrogen [19] .
Equation 5-1 can be used tp determine whether a wastewater
contains enough carbon to remove the desired amount of
nitrogen. For example, if the applied wastewater contains
42 mg/L TOC and 25.8 mg/L total nitrogen, it is only
possible to remove (42-5)/3> mg/L or 18.5 mg/L of nitrogen
and to reduce the total nitrogen concentration from
25.8 mg/L to 7.3 mg/L. Thus, using this wastewater,
complete nitrogen removal could not be achieved. If the
applied wastewater contains,248 mg/L TOC and 40.2 mg/L total
nitrogen, there is sufficient carbon to remove 121 :mg/L of
nitrogen. This means that, theoretically, under proper
management, all of the nitrogen could be removed during RI
(although total removal might never be achieved in
practice). If nitrogen removal is important, the engineer
should use Equation 5-1 to determine whether nitrogen
removal is feasible using RI. If so, a loading cycle should
be selected that maximizes nitrogen removal.
Nitrogen removal from secondary effluent is more difficult
than nitrogen removal from a wastewater that contains high
concentrations of organic carbon. Nitrogen removal is
especially difficult when infiltration rates are high,
because nitrates tend to pass through the soil profile
before they can be converted to nitrogen gas. In fact,
nitrogen removal from secondary effluent increases
exponentially as the infiltration rate decreases [20]. This
relationship is shown in Figure 5-2. ;
Although Figure 5-2 is based on data from soil column
studies using loamy sand, data from operating systems in
warm climates indicate that the figure can be used to obtain
conservative estimates of a similar soil's nitrogen removal
potential. Thus, if secondary effluent infiltrates at a
rate of 30 cm/d (12 in./d), using a loading cycle that
promotes nitrogen removal, it should be possible to remove
at least 30% of the applied nitrogen. To achieve 80%
5-18
-------
nitrogen removal, the soil column studies indicated maximum
infiltration rates are:
• 20 cm/d (8 in./d) for primary preapplication
treatment
• 15 cm/d (6 in./d) for secondary preapplication
treatment
If nitrogen removal is important and these suggested rates
are exceeded, soil column studies or pilot testing should be
conducted to determine how much nitrogen can be removed.
Also, infiltration rates can be reduced somewhat by
decreasing the depth of the applied wastewater, or by
compacting the soil surface.
90
80
70
60
50
^
i 40
o
X -
UJ
<>= 30
20
1 0
10 20 30 40 50 60
INFILTRATION RATE, cm/d
FIGURE 5-2
EFFECT OF INFILTRATION RATE ON NITROGEN REMOVAL [20j
5-19
-------
5.4.3.2
Phosphorus Removal
The amount of phosphorus that is removed during Ri at
neutral pH can be estimated from the following equation [19,
e,J. J J
CX ~ G06
-kt
(5-2)
where Cx = total phosphorus concentration at a distance ,
x along the percolate flow path, mg/L
C0 = total phosphorus concentration in the applied
.wastewater, mg/L
k = instantaneous rate constant and equals
0.002 h ••• at neutral pH
t = detention time = X0/I, h
where x = distance along the flow path, cm
9 = volumetric water content, cm3/cm3,
use 0.4
I = infiltration rate during system
operation, cm/h (use basin test results,
20% of cylinder infiltration results, or
horizontal conductivity for horizontal
flow)
Because the minimum phosphorus precipitation rate occurs at
neutral pH, this equation can be used to conservatively
estimate phosphorus removal. if the calculated phosphorus
concentration is an acceptable value, phosphorus con-
centrations from an operating Ri system should 'be well
within limits. However, if the calculated phosphorus
concentration at a distance x exceeds acceptable values, a
phosphorus adsorption test should be performed. This test
measures the ability of a specific soil to remove phosphorus
and is described in Section 3.7.2.
For example, consider a site where wastewater percolates
through the soil to the ground water table, which is 15 m
(49 ft) below the soil surface. The initial phosphorus
concentration is 10 mg/L and the basin infiltration test
rate is 40 cm/d (16 in./d). By the time the water reaches
5-20
-------
the ground water table, the phosphorus concentration should
be less than:
Q Q02h-
(10 mg/L)e-°-002h \ 0.4
15
m/d
- 4.9 mg/L
If the movement is then predominantly horizontal, with the
renovated water seeping into a creek 200 m (650 ft) from the
infiltration site, and the horizontal hydraulic conductivity
is 120 cm/d (47 in./d), the phosphorus concentration in the
seepage should be less than:
-200
Q 002h-
(4.9 mg/L)e-°-002h V 1.2 m/d
0.2 mg/L
5.4.3.3
Climate
In regions that experience cold weather, longer loading
cycles may be necess'ary during winter months
(Section 5.4.2). Nitrification, denitrification, ox-idation
(of accumulated organics), and drying rates all decrease
during cold weather, particularly as the temperature of the
applied wastewater decreases. Longer application periods
are needed for denitrification so that the application rate
can be reduced as the rate of nitrogen removal decreases.
Similarly, longer resting periods are needed to compensate
for reduced nitrification and drying rates.
Combined with the reduced hydraulic capacity experienced
during cold weather, the need for longer loading cycles
changes the allowable wastewater loading rate. Cold weather
loading rates are somewhat lower than warm weather rates;
therefore, more land is required during cold weather as long
as winter and summer wastewater flows are equal. If loading
rates must be reduced during cold weather, either the cold
weather loading rate should be used to determine land
requirements or. cold weather storage should be included.
In communities that use ponds as preapplication treatment
and experience cold winter weather, winter storage may be
required. This is because the temperature of the wastewater
becomes quite low prior to land treatment and makes the
applied wastewater susceptible to long-term freezing in the
basin. Alternatively, RI may be continued through cold
weather if warmer wastewater from the first cell of the pond
system (if possible) is applied. In such communities, the
engineer must keep in mind that the annual loading rate
5-21
-------
actually applies only to the portion of the year when RI is
used.
5.5
Land Requirements
An RI site must have adequate land for infiltration basins,
buffer zones, and access roads. At some systems, land is
also needed for preapplication treatment facilities,
storage, or future expansion.
5.5.1 Infiltration Basin Area
If wastewater flow equalization is provided (including
treatment ponds), the land area required for infiltration
only (ignoring land required between and around basins) is
simply the average annual wastewater flow divided by the
annual wastewater loading rate. For example, if the annual
average daily flow is 0.3 mj/s (6.8 Mgal/d ) and the
wastewater loading rate is 25 m/yr (82 ft/yr), the area
required for infiltration is:
(0.3 m3/s) (86,400 s/d ) (365 d/yr ) =
(25 m/yr) (101 mVha)
If the wastewater flow varies with season and seasonal flows
are not equalized, the highest average seasonal flow should
be used. An RI site must either have enough basins so that
at least one basin can be dosed at all times or have
adequate storage for equalization between application
periods.
5.5.2 Preapplication Treatment Facilities
The communities that already have preapplication treatment
facilities will, in general, only need additional land for
facilities to convey wastewater to the RI site. In
communities that are constructing a completely 'new treatment
facility, land requirements for preapplication trecitment
will vary with the level and method of preapplication
treatment.
5.5.3 Other Land Requirements
Additional land may be needed for buffer zones, access
roads, storage or flow equalization (when provided), and
future expansion. Buffer zones can be used to screen RI
sites from public view. Preapplication treatment facili-
ties, access roads, and storage or flow equalization may be
included in the buffer area.
5-22
-------
Access roads must be provided so that equipment and labor
can reach the infiltration basins. Maintenance equipment
must be able to enter each basin (for scarification or
surface maintenance).
Typically/ access roads should be 3 to 3.7 m (10 to 12 ft)
wide. In any case, access roads should be wide enough for
the selected maintenance equipment and curves should have
large enough radii to allow maintenance equipment to turn
safely.
Land requirements for flow equalization or storage vary with
the type and amount of storage provided. This subject is
discussed in greater detail in Section 5.6.2.
5.6 Infiltration System Design
Items that must be addressed during RI system design include
wastewater distribution, basin layout and dimensions, basin
surfaces, and flow equalization or storage. In areas that
experience cold winter weather, cold weather system
modifications should also be considered.
5.6.1 Distribution and Basin Layout
Although sprinklers may be used, wastewater distribution is
usually by surface spreading. This distribution technique
employs gravity flow from piping systems or ditches to flood
the application area. To ensure uniform basin application,
basin surfaces should be reasonably flat.
Overflow weirs may be used to regulate basin water depth.
Water that flows over the weirs is either collected and
conveyed to holding ponds for recirculation or distributed
to other infiltration basins. If each basin is to receive
equal flow, the distribution piping channels should be sized
so that hydraulic losses between outlets to basins are
insignificant. Design standards for distribution systems
and for flow control and measurement techniques are
published by the American Society of Agricultural Engineers
(ASAE). Outlets used at currently operating systems include
valved risers for underground piping systems and turnout
gates from distribution ditches. An infiltration basin
outlet and splash pad are shown in Figure 5-3. An
adjustable weir used as an interbasin transfer structure is
shown in Figure 5-4.
Basin layout and dimensions are controlled by topography,
distribution system hydraulics, and loading rate. The
number of basins is also affected by the selected loading
cycle. As a minimum, the system should have enough basins
5-23
-------
FIGURE 5-3
INFILTRATION BASIN OUTLET AND
SPLASH PAD
150 cm
CONCRETE FILL
REMOVABLE RINGS
(WOOD. PLASTIC. OR NCNCORRODING
METAL ALL SUITABLE)
(15 cm INCREMENTS)
FIGURE 5-4
INTERBASIN TRANSFER STRUCTURE WITH ADJUSTABLE WEIR
S-24
-------
so that at least one basin can be loaded at all times,
unless storage is provided. The minimum number of basins
required for continuous wastewater application is presented
as a function of loading cycle in Table 5-14. The engineer
should keep in mind that if the minimum number of basins is
used, the resulting loading cycle may not be exactly as
planned. For example, if the selected loading cycle is 2
application days followed by 6 days of drying and 4 basins
are constructed, the resulting loading cycle will be the
same as the selected loading cycle. However, if a cycle of
2 days of application followed by 9 days of drying is
selected initially and 6 basins are constructed, the
resulting loading cycle wll actually be 2 days of
application followed by 10 days of drying.
TABLE 5-14
MINIMUM NUMBER OF BASINS REQUIRED FOR
CONTINUOUS WASTEWATER APPLICATION
Loading Cycle Minimum
application drying number of
period, period, infiltration
d d basins
1
2
1
2
1
2
3
1
2
3
1
2
1
2
7
8
9
7
8
9
5-7
5-7
7-12
7-12
4-5
4-5
4-5
5-10
5-10
5-10
10-14
10-14
12-16
12-16
10-15
10-15
•10-15
12-16
12-16
12-16
6-8
4-5
8-13
5-7
5-6
3-4
3
6-11
4-6
3-5
11-15
6-8
13-17
7-9
3-4
3
3
3-4
3
3
The number of basins also depends on the total area required
for infiltration. Optimum basin size can range from 0.2 to
2 ha (0.5 to 5 acres) for small to medium sized systems to 2
to 8 ha (5 to 20 acres) for large systems. For a 25 ha
(62 acre) system, if the selected loading cycle is 1 day of
wastewater application alternated with 10 days of drying, a
5-25
-------
typical design would include 22 basins of 1.14 ha (2.8
acres) each. Using 22 basins, 2 basins would be flooded at
a time and there would be ample time for basin maintenance
before each flooding period.
At many sites, topography makes equal-sized basins
impractical. Instead, basin size is limited to what will
fit into areas having suitable slope and soil type (Section
2.3.1). Relatively uniform loading rates and loading cycles
can be maintained if multiple basins are constructed.
However, some sites will require that loading rates or
cycles vary with individual basins.
In flat areas, basins should be adjoining and should be
square or rectangular to maximize land use. In areas where
ground water mounding is a potential problem (Section
5.7.2), less mounding occurs when long, narrow basins with
their length normal to the prevailing ground water flow are
used than when square or round basins are constructed.
Basins should be at least 30 cm (12 in.) deeper than the
maximum design wastewater depth, in case initial
infiltration is slower than expected and for emergencies.
Basin walls are normally compacted soil with slopes ranging
from 1:1 to Is 2 (vertical distance to horizontal
distance). In areas that experience severe winds or heavy
rains, basin walls should be planted with grass or covered
with riprap to prevent erosion.
If basin maintenance will be conducted from within the
basins, entry ramps should be provided. These ramps are
formed of compacted soil atj grades of 10 to 20% and cire from
3.0 to 3.7 m (10 to 12 ft) wide. Basin surface area for
these ramps and for wall slopes should not be considered as
part of the necessary infiltration area.
The basin surface may be bare or covered with vegetation.
Vegetative covers tend to remove suspended solids by filtra-
tion and maintain infiltration rates. However, vegetation
also limits the application depth to a value that avoids
drowning of vegetation, increases basin maintenance needs,
requires an increased application frequency to promote
growth, and reduces the soil drying rate. At Lake George,
New York, allowing grass to grow in the basins improved the
infiltration rate when flooding depths exceeded 0.3 m (1 ft)
but decreased the rate at shallower wastewater depths [1] .
Gravel covered basins are not recommended. The long-term
infiltration capacity of gravel covered basins is lower than
the capacity of sand covered basins, because sluclge-like
solids collect in the voids between gravel particles and
because gravel prevents the underlying soil from drying [4].
5-26
-------
5.6.2 Storage and Flow Equalization
Although RI systems usually are capable of operating during
adverse climatic conditions, storage may be needed to
regulate wastewater application rates or for emergencies.
Flow equalization may be required if significant daily or
seasonal flow peaking occurs. Equalization also may be
necessary to store wastewater between application periods,
particularly when only one or two infiltration basins are
used and drying periods are much longer than application
periods.
One example of flow equalization at an RI site occurs at the
Milton, Wisconsin, system. Milton discharges secondary
effluent to three lagoons. One of these lagoons is used as
an infiltration basin; the other two lagoons are used for
storage. In this way, Milton is able , to maintain a
continuous flow into the infiltration basin [3].
In contrast, the City of Hollister formerly equalized flow
with an earthen reservoir that was ahead of the treatment
plant headworks. In addition, one infiltration basin was
kept in reserve for primary effluent during periods when
wastewater flows were excessive [6].
Winter storage may be needed if the soil permeability is on
the low end for RI. In such cases, the water may not drain
from the profile fast enough to avoid freezing.
5.6.3 Cold Weather Modifications
Rapid infiltration systems that operate successfully during
cold winter weather without any cold weather modifications
can be found in Victor, Montana; Calumet, Michigan; and Fort
Devens, Massachusetts. However, a few different basin
modifications have been used to improve cold weather
treatment in other communities. First, basin surfaces that
are covered with grass or weeds should be mowed during
fall. Mowing followed by disking should prevent ice from
freezing to vegetation near the soil surface. Floating ice
helps insulate the applied wastewater, whereas ice that
freezes at the soil surface prevents infiltration. Problems
with ice freezing to vegetation have been reported at
Brookings, South Dakota, where basins were not mowed and
ponds are used for preapplication treatment [7].
Another cold weather modification involves digging a ridge
and furrow system in the basin surface. Following
wastewater application, ice forms on the surface of the
water and forms bridges between the ridges as the water
level drops. Subsequent loadings are applied beneath the
5-27
-------
surface of the ice, which insulates the wastewater and the
soil surface. For bridging to occur, a thick layer of ice
must form before the wastewater surface drops below the top
of the ridges. This modification has been used successfully
in Boulder, Colorado, and Westby, Wisconsin.
The third type df basin modification involves the use of
snow fencing or other materials to keep a snow cover over
the infiltration basins. The snow insulates both applied
wastewater and soil.
5.7 Drainage
Rapid infiltration systems require adequate drainage to
maintain infiltration rates and treatment efficiencies. The
infiltration rate may be limited by the horizontal hydraulic
conductivity of the underlying aquifer. Also, if there is
insufficient drainage, the soil will remain saturated with
water and reaeration will be inadequate for oxidation of
ammonia nitrogen to occur.
Renovated water may be isolated to protect either or both
the ground water or the renovated water. In both cases,
there must be some method of engineered drainage to keep
renovated water from mixing with native ground water,,
Natural drainage often involves subsurface flow to ,surface
waters. If water rights are important, the engineer must
determine whether the renovated water will drain to
the correct watershed or whether wells or underdrains will
be needed to convey the renovated water to the required
surface water. In all cases, the engineer needs to
determine the direction of subsurface flow due to drainage
from RI basins'! ~~
5.7.1 Subsurface Drainage to Surface Waters
If natural subsurface drainage to surface water is planned,
soil characteristics can be analyzed to determine if the
renovated water will flow from the recharge site to the
surface water. For subsurface discharge to a surface water
to occur, the width of the infiltration area must be limited
to values equal to or less than the width calculated in the
following equation [22] :
W = KDH/dL
(5-3)
where W = total width of infiltration area in direction of
ground water flow, m (ft)
5-28
-------
K = permeability of aquifer in direction of
groundwater flow, m/d (ft/d)
D = average thickness of aquifer below the water
table and perpendicular to the direction of
flow, m (ft)
H = elevation difference between the water level
of the water course and the maximum allowable
water table below the spreading area, m (ft)
d = lateral flow distance from infiltration area
to surface water, m (ft)
L = annual hydraulic loading rate (expressed as
daily rate), m/d (ft/d)
Examples of these parameters are shown in Figure 5-5.
IMPERMEABLE LAYER
FIGURE 5-5
NATURAL DRAINAGE OF RENOVATED WATER
INTO SURFACE WATER [22]
5-29
-------
As an example, consider an infiltration site located above
an aquifer whose permeability is 1.1 m/d (3.6 ft/d) and
whose average thickness is 9 m (30 ft). The annual
hydraulic loading rate is 30 m/yr or 0.082 m/d (98 ft/yr or
0.27 ft/d). The surface water elevation is 6 'm (20 ft)
below the infiltration site, and the water table should
remain at least 1.5 m (5 ft) below the soil surface. The
infiltration site is 25 m (82 ft) from the surface water.
Thus,
W -
W ~
m/d)(9 m)(6 m - 1.5 m)
(25 m)(0.082 m/d)
^
22 m (72 ftj
Under these conditions, either a single basin 22 m (72 ft)
wide or multiple basins having a combined width of 22 m
could be constructed. If more infiltration area is needed,
additional basins could be built in the two directions
perpendicular to the direction of ground water flow. Four
basins oriented in this manner are illustrated in
Figure 5-6.
If the calculated width is quite small (less than about 10 m
or 33 ft) , natural subsurface drainage to surface waters is
not feasible and engineered drainage should be provided.
5.7.2 Ground Water Mounding
During RI , the applied wastewater travels initially downward
to the ground water, resulting in a temporary ground water
mound beneath the infiltration site. This condition is
shown schematically in Figure 5-7. Mounds continue to rise
during the flooding period and only recede during the
resting period.
Excessive mounding will inhibit infiltration and reduce the
effectiveness of treatment. For this reason, the capillary
fringe above the ground water mound should never be closer
than 0.6 m (2 ft) to the bottom of the infiltration basin
[23] . This distance corresponds to a water table depth of
about 1 to 2 m (3 to 7 ft), depending on the soil texture.
The distance to ground water should be 1.5 to 3 m (5 to
10 ft) below the soil surface within 2 to 3 days following a
wastewater application. The following paragraphs describe
an analysis that can be used to estimate the mound height
that will occur at various loading conditions. This method
can be used to estimate whether a site has adequate natural
drainage or whether mounding will exceed the recommended
values without constructed drainage.
5-3Q
-------
SURFACE WATER
LENGTH BASED ON NECESSARY
INFILTRATION AREA
DIRECTION OF
GROUND HATER FLOW
FIGURE 5-6
EXAMPLE DESIGN FOR SUBSURFACE FLOt TO SURFACE WATER
5-31
-------
SOIL SURFACE
WASTEWATER APPLICATION
llllillll
FIGURE 5-7
SCHEMATIC OF GROUND WATER MOUND
5-32
-------
Ground water mounding can be estimated by applying heat-flow
theory and the Dupuit-Forchheimer assumptions [24]. These
assumptions are as follows:
1. Flow within ground water occurs along horizontal
flow lines whose velocity is independent of
depth.
2. The velocity along these horizontal streamlines
is proportional to the slope of the free water
surface.
Using these assumptions, heat-flow theory has been
successfully compared to actual ground water depths at
several existing RI sites.
To compute the height at the center of the ground water
mound, one must calculate the values of W//4at and Rt,
where W = width of the recharge basin, m (ft)
ct = KD/V, m2/d (ft2/d)
where K = aquifer (horizontal) hydraulic
conductivity, m/d (ft/d)
D = saturated thickness,of the
aquifer, m (ft) ,
V = specific yield or fillable pore space
of the soil, m3/m3 (ft3/ft3)
(Figures 3-5 and 3-6)
t = length of wastewater application, d
R = I/V, m/d (ft/d)
where I = infiltration rate or volume of water per
unit area of soil surface, m EUO/m -d
(ft3H20/ft2-d)
The parameters that can be shown schematically are illustra-
ted in Figure 5-5.
Once the value of W//4at is obtained, one can use dimension-
less plots of W//4at versus ho/Rt, provided as Figures 5-8
(for square recharge areas) and 5-9 (for rectangular recharge
areas), to obtain the value of ho/Rt, where ho is the rise at
the center of the mound. Using the calculated value of Rt,
one can solve for ho.
5-33
-------
1.0
0.8
0.6
0.4
0.2
1 . 0
2. 0
3.0
1 .0 r-
0.8
0.6
0.4
0.2
0.0
FIGURE 5-8
MOUNDING CURVE FOR CENTER OF A SQUARE
RECHARGE AREA L24J
1.0
2.0
3.0
FIGURE 5-9
MOUNDING CURVE FOR CENTER OF A RECTANGULAR RECHARGE AREA AT
DIFFERENT RATIOS OF LENGTH (L) TO WIDTH (W) [241
5-34
-------
For example, an RI system is planned above an aquifer that is
4 m (13 ft) thick.. Auger hole measurements (Section 3 . 6 . 2 .1)
have indicated that the hydraulic conductivity is (5 m3/d)/
4 m or 1.25 m/d (4.1 ft/d). Using Figure 3-6 with this hy-
raulic conductivity, the specific yield is 15%. ;. The basins
are to be 12 m (39 ft) wide and square; the basin infiltra-
tion rate is 0.20 m/d (7.9 in./d); and the application per-
iod will be 1 day long. Using these data, the following
calculations are performed.
a
= (1.25 m/d)(4m)
0.15
= 33.3 m2/d (360 ft2/d)
R =
0.20 m/d
0.15
=1.3 m/d (4.3 ft/d)
Rt = (1.3 m/d)(Id)
=1.3 m (4.3 ft)
12 m
[4(33.3 m2/d)(l d) ] V2
= 1.0
Using Figure 5-8, hQ/Rt equals 0.53.
Thus, h0 equals (0.53)(1.3 m) or 0.7 m (2.3 ft). If the
initial ground water depth is 6.0 m (20 ft), the depth after
wastewater application is still 5.3 m (17 ft) and engineered
drainage is unnecessary. Should the calculations indicate
that the ground water table will rise to within less than 1
to 2m (3.3 to 6.6 ft) below the basin, additional drainage
will be needed. '
Figures 5-10 (for square recharge areas) and 5-11 (for
recharge areas that are twice as long as they are wide) can
be used to estimate the depth to the mound at various
distances from the center of the recharge basin. Again
the values of W//4at and Rt must be determined first.. Then,
for a given value of x/W, where x equals the horizontal
distance from the center of the recharge basin, one can
obtain the value of hQ/Rt from the correct plot.
Multiplying this number by the calculated value of Rt
results in the rise of the mound, h , at a distance x from
the center of the recharge site. The depth to the mound
from the soil surface is simply the difference between the
distance to the ground water before recharge and the rise
due to the mound.
5-35
-------
1. 0
0. 0
EDGE OF PLOT
1. 0
FIGURE 5-10
RISE AND HORIZONTAL SPREAD OF MOUND BELOW
A SQUARE RECHARGE AREA [24]
5-36
-------
1.0 r-
•3. 0
0.3 -
0.2 -
0.1 1
0.0
EDGE OF PLOT
1. 0
(f)
FIGURE 5-11
RISE AND HORIZONTAL SPREAD OF MOUND BELOW A
RECTANGULAR RECHARGE AREA WHOSE LENGTH
IS TWICE ITS WIDTH [24]
5-37
-------
To evaluate -mounding beneath adjacent basins, Figures 5-10
and 5-11 should be used to plot ground water table mounds as
functions of distance from the center of the pldt and time
elapsed since initiation of wastewater application. Then,
critical mounding times should be determined, such as when
adjacent or relatively close basins are being flooded,, and
the mounding curves of each basin at these times should be
superimposed. At sites where drainage is critical because
of severe land limitations, or extremely high ground water
tables, the engineer should use the approach described in
reference [25] to evaluate mounding.
In areas where both the water table and the impermeable
layer underneath the aquifer are relatively close to the
soil surface, it may be possible to avoid the complicated
mounding analysis by using the following procedure:
1. Assume underdrains are needed and calculate the
underdrain spacing (Section 5.7.3).
2. If the calculated underdrain spacing is
relatively narrow, between 15 and 50 m (50 and
160 ft), underdrains will be required and there
is no need to verify that the mound will reach
the soil surface.
3. if the calculated spacing is less than about
10 m (30 ft), the loading rate may have to be
reduced for the project to be economically
feasible.
4. If the calculated spacing is greater than about
50 m (160 ft), mounding should be evaluated to
determine if any underdrains will be necessary.
This procedure is not appropriate for unconfined or
relatively deep aquifers. For such aquifers, mounding
should always be evaluated.
5.7.3 Underdrains
For RI systems located in areas where both the water table
and the impermeable layer underneath the aquifer' are
relatively close to the soil surface, renovated water can be
collected by open or closed drains. In such areas, when
drains can be installed at depths of 5 m (16 ft) or less,
underdrains are more effective and less costly than wells
for removing renovated water from the aquifer. Horizontal
drains have been used to collect renovated river water from
RI systems in western Holland, where polluted Rhine water is
treated, and at Dortmund, Germany, where water from the Ruhr
5-38
-------
River is pretreated for a municipal water supply [23]. At
Santee, California, an open ditch was used to intercept
reclaimed water [23].
Rapid infiltration systems using underdrains may consist of
two parallel infiltration strips with a drain midway between
the strips or a series of strips and drains. These two
types of configurations are shown in Figures 5-12 and
5-13. In the first system, the drains are left open at all
times during the loading cycle. If the second system is
used, the drains below the strips receiving wastewater are
closed and renovated water is collected from drains beneath
the resting strips. When infiltration beds are rotated, the
drains that were closed before are opened and those that
were open are closed. This procedure allows maximum
underground detention times and travel distance.
To determine drain placement, the following equation is
useful [27]:
S =
f4KH
•^
-(2d + H)
1/2
(5-4)
where S = drain spacing, m (ft)
K = horizontal hydraulic conductivity of the soil,
m/d (ft/d)
H = height of the ground water mound above the drains,
m (ft)
1^ = annual wastewater loading rate, expressed as a
daily rate, m/d (ft/d)
P = average annual precipitation rate, expressed as a
daily rate, m/d (ft/d)
d = distance from drains to underlying impermeable
layer, m (ft)
INPERNEAIIE
FIGURE 5-12
CENTRALLY LOCATED UNDERDRAIN [260
5-39
-------
IMPERMEABLE
IMPERMEABLE
O DRAIN OPEN
& DRAIN CLOSED
FIGURE 5-13
UNDERDRAW SYSTEM USING ALTERNATING
INFILTRATION AND DRYING STRIPS [26]
For clarification, these parameters are shown in
Figure 5-14. When L, P, K, and the maximum acceptable value
of H are known, this equation can be used to determine S for
various values of d. For example, consider an RI system
loaded at an average rate of 44 m/yr or 0.12 m/d (144 ft/yr
or 0.40 ft/d). Using Equation 5-4, the drain spacing can be
calculated using the following data:
K = 12 m/d (39 ft/d)
H = 1 m (3.28 ft)
d = 0.6 m (2 ft)
5-JtO
-------
HYDRAULIC LOADING RATE LW + P
I I 1 i I 1 1 1 1 1 1
SOIL SURFACE
WATER TABLE
IMPERMEABLE LAYER
FIGURE 5-14
PARAMETERS USED IN DRAIN DESIGN [26]
The application rate must include precipitation as well as
wastewater. Therefore, a design storm of 0.03 m/d
(0.10 ft/d) is added to the 0.12 m/d (0.40 f t/d ) wastewater
load for a total of 0.15 m/d (0.50 ft/d). The drain spacing
is calculated as:
S2 =
+ P)] (2d + H)
= 4(12 m/d) (1 m)
0.12 m/d +0.03 m/d
= 704 m2
[2(0.6 m) + 1 m]
S = 26 m (85 ft)
Generally, drains are spaced 15 m (50 ft) or more apart and
are at depths of 2.5 to 5.0 m (8 to 16 ft). In soils with
high lateral permeability, spacing may approach 150 m
(500 ft). Although closer drain spacing allows more control
over the depth of the ground water table, as drain spacing
decreases the cost of providing underdrains increases. When
designing a drainage system, different values of d should be
-------
selected and used to calculate S, so that the optimum
combination of d, H, and S can be determined. Detailed
information on drainage may be found in the U.S. Bureau of
Reclamation Drainage Manual [28] and in the American Society
of Agronomy manual, Drainage for Agriculture [29].
Once the drain spacing has been calculated, drain sizing
should be determined. Usually, 15 or 20 cm (6 in. or 8 in.)
drainage laterals are used. The laterals connect to a
collector main that must be sized to convey the expected
drainage flows. Drainage laterals should be placed so that
they will be free flowing; the engineer should check
drainage hydraulics to determine necessary drain slopes.
5.7.4 Wells
Rapid infiltration systems that utilize unconfirmed and
relatively deep aquifers should use wells to improve
drainage or to remove renovated water. Wells are used to
collect renovated water directly from the RI sites at both
Phoenix, Arizona, and Fresno, California. Wells are also
involved in the reuse of recharged wastewater at Whittier
Narrows, California; however, the wells pump ground water
that happens to contain reclaimed water, rather than pumping
specifically for renovated water.
The arrangement of wells and recharge areas varies; wells
may be located midway between two recharge areas, may be
placed on either side of a single recharge strip, or may
surround a central infiltration area. These three
configurations are illustrated in Figure 5-15. Well design
is beyond the scope of this manual but is described in
detail in reference [30] .
5.8 Monitoring and Maintenance Requirements
The purpose of discussing monitoring and maintenance
requirements is to enable the engineer to determine labor
and equipment needs. The engineer must know these needs to
complete a thorough cost estimate and to ensure that the
necessary labor and equipment are available.
5.8.1 Monitoring
There are two distinct reasons for monitoring RI systems:
1. To document that the system meets any
requirements established by appropriate
regulatory agencies and to confirm that the
design provides adequate treatment
5-42
-------
IMPERMEABLE
LAYER
WASTEWATER
APPLICATION
WATER TABLE
(a)
a. VELLS MIDWAY BETWEEN TWO APPLICATION STRIPS
1
(b)
•
(c)
b. and c. WELLS (DOTS) SURROUNDIN6 APPLICATION AREAS
(HATCHED AREAS)
FIGURE 5-15
WELL CONFIGURATIONS [26]
5-43
-------
2. To provide data needed to make management
decisions
A monitoring program may include measurements of ground
water quality, soil characteristics applied water quality,
and, when appropriate, the quality of water removed from the
aquifer for reuse. Representative measurements of ground
water quality are difficult to obtain. Because constituent
movement is slower than in surface water, a ground water
sample can contain contributions from several years past
that do not accurately reflect treatment occurring at the RI
site. For this reason, it is important to place sampling
wells in positions that minimize the time period between
wastewater application and appearance of wastewater
constituents in the observation wells. Techniques for
monitoring well design and sampling procedures are included
in references [31, 32]. Guidance in determining what
parameters and site conditions to monitor can be obtained
from federal, state, and local agencies.
Although soil monitoring is not required at many sites, it
is periodically desirable. Below pH 6.5, soil retention of
metals decreases substantially and the possiblity of ground
water contamination by heavy metals increases. Potential
soil permeability problems may be indicated by either a high
pH (above 8.5) or a high percent of sodium on the soil
exchange complex (over 10 to 15%). High soil pH can
indicate a high sodium content. This condition may be
corrected by displacing the sodium with soluble calcium.
Both applied wastewater and any renovated water collected
from the aquifer for reuse or discharge should be
monitored. Applied wastewater analyses are necessary for
process control to ensure that the design hydraulic loading
is maintained. Renovated water that is recovered for any
purpose must meet whatever water quality criteria have been
established for those purposes.
5.8.2 Maintenance
Basic maintenance requirements are as follows:
• Periodic scarification or scraping of RI basin
surfaces .
• Periodic mowing of vegetated surfaces
As a result of bacterial activity and solids deposition, a
mat forms on the surfaces of infiltration areas and reduces
infiltration rates. Furthermore, wastewater applications
may cause classification of the underlying soils, allowing
5-44
-------
the fines to migrate to the top and to seal the soil
surface. Periodically, basin surfaces must be scarified
(raked, harrowed, or disked) to break up the mat and loosen
the soil surface. Alternatively, the mat may be scraped
from the soil surface with a front-end loader [4] and
landfilled or buried. These operations should be performed
whenever regular drying fails to restore infiltration rates
to acceptable levels. If scraping alone does not restore
the initial infiltration rate, the soi.l surface should be
loosened by disking or harrowing. Basin surfaces may be
scarified following each drying period if time, labor, and
equipment are available; basin scarification or scraping
should be done at least once every 6 months to 1 year.
If .grasses or other vegetation are .grown on basin surfaces,
the vegetation can be allowed to grow and die without
maintenance. Heavy mechanical equipment that would compact
the soil surface should not be operated on the infiltration
basins. For aesthetic reasons, periodic mowing of the grass
or harrowing of the soil surface may be desirable. In cold
weather climates, vegetation should be mowed during late
October or early November to prevent ice chunks from
freezing to the vegetation and thereby cooling the applied
wastewater.
5.9 Design and Construction Guidance
Some specific items that are unique to RI design and
construction should be considered:
• Underdrains will operate only in saturated
soil. If the water table does not rise, or is
not already at the elevation of the drains, they
will not recover any water.
• A filter sock can .be used in place of a gravel
envelope around plastic drain pipe in sandy
soil. The•filter sock will clog, however, with
fines if used alone in silty clay soils.
• RI basins, when constructed,, should be ripped to
alleviate traffic compaction. After ripping,
the surface should be smoothed and leveled, but
never compacted.
• If soils at the RI site contain varying
percentages of clay or silt, the heavier soils
should be segregated and used for berms. Berms
should be compacted, but infiltration surfaces
should not be compacted.
5-45
-------
5.10 References
1. Aulenbach, D.B. Long Term Recharge of Trickling Filter
Effluent into Sand. U.S. Environmental Protection
Agency. EPA-600/2-79-068. March 1979.
2. Baillod, C. R. , et al. Preliminary Evaluation of 88
Years of Rapid Infiltration of Raw Municipal Sewage at
Calumet, Michigan. In: Land as a Waste Management
Alternative. Ann Arbor Science. 1977.
3. Benham-Blair & Affiliates, Inc., and Engineering
Enterprises, Inc. Long-term Effects of Land
Application of Domestic Wastewater: Milton, Wisconsin,
Rapid Infiltration Site. U.S. Environmental Protection
Agency. EPA-600/2-79-145. August 1979.
4. Bouwer, H., et al. Rapid-Infiltration Research at
Flushing Meadows Project, Arizona. Journal Water
Pollution Control Federation. 52(10 ):2457-2470. 1980.
5. Koerner, E.T., and D.A. Haws. Long-Term Effects of
Land Application of Domestic Wastewater: Vineland, New
Jersey Rapid Infiltration Site. U.S. Environmental
Protection Agency. EPA-600/2-79-072. March 1979.
6. Pound, C.E., R.W. Crites, and J.V. Olson. Long-Term
Effects of Land Application of Domestic Wastewater -
Hollister, California, Rapid Infiltration Site. U.S.
Environmental Protection Agency. EPA-600/2-78-084.
April 1978.
7. Dornbush, J.N. Infiltration Land Treatment of
Stabilization Pond Effluent. Technical Progress
Report 3. South Dakota State University, Brookings,
South Dakota. April 1978.
8. Satterwhite, M.B., B.J. Condike, and G.L. Stewart.
Treatment of Primary Sewage Effluent by Rapid
Infiltration. U.S. Army Corps of Engineers, Cold
Regions Research-and Engineering Laboratory. December
1976.
9. Smith, D.G., K.D. Linstedt, and E.R. Bennett.
Treatment of Secondary Effluent by Infiltration-
Percolation. U.S. Environmental Protection Agency.
EPA-600/2-79-174. August 1979.
10. Broadbent, F.E., K.B. Tyler, and G.N. : Hill.
Nitrification of Ammonical Fertilizers in Some
California Soils. Hilgardia. 27:247-267. 1957.
. 5-46
-------
11. Vaccaro, R.F., et al. Wastewater Renovation and
Retrieval at Cape Cod. U.S. Environmental Protection
Agency. EPA-600/2-79-176. August 1979.
12. Merrell, J.C., Jr., et al. The Santee Recreation
Project: Santee, California (Final Report). U.S.
Department of the Interior, Federal Water Pollution
Control Administration, Water Pollution Control
Research Series Publication No. WP-20-7. 1967.
13. Lance, J.C. , C.P. Gerba, and J.L. Melnick. Virus
Movement in Soil Columns Flooded with Secondary Sewage
Effluent. Applied and Environmental Microbiology.
32:520-526. 1976.
14. Gerba, C.P. and J.C. Lance. Poliovirus Removal from
Primary and Secondary Sewage Effluent by Soil
Filtration. Applied and Environmental Microbiology.
36:247-251. 1978.
15. Gilbert, R.G., et al. Virus and Bacteria Removal from
Wastewater by Land Treatment. Applied and
Environmental Microbiology. 32(3):333. 1976.
16. Gerba, C.P. and J.C. Lance. Pathogen Removal from
Wastewater During Groundwater Recharge. In:
Proceedings of Symposium on Wastewater Reuse for
Groundwater Recharge, Pomona, California. September 6-
7, 1979.
17. U.S. Environmental protection Agency. Facilities
Planning, 1982. EPA-430/9-81-012. FRD-25. September
1981.
18. Pound, C.E., and R.W. Crites. Wastewater Treatment and
Reuse by Land Application. U.S. Environmental
Protection Agency. EPA-660/2-73-006a and b. August
1973.
19. Leach, E., C.G. Enfield, and C.C« Harlin, Jr. Summary
•of Long-Term Rapid Infiltration System Studies. U.S.
Environmental protection Agency. EPA-600/2-80-165.
July 1980.
20. Lance, J.C. , F.D. Whisler, and R.C. Rice. Maximizing
Denitrification During Soil Filtration of Sewage
Water. journal of Environmental Quality. 5:102.
1976.
5-47
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21. Clapp, R.B. and G.M. Hornberger. Empirical Equations
for Some Soil Hydraulic Properties. Water Resources
Research. 14(4):601-604. 1978.
'i '•
22. Bouwer, H. Infiltration - Percolation Systems. In:
Land Application of Wastewater. Proceedings of a
Research Symposium Sponsored by the USEPA, Region III,
Newark, Delaware. pp. 85-92. November, 1974.
23. Bouwer, H. Zoning Aquifers for Tertiary Treatment of
Wastewater. Ground Water. 14(6):386. .November-
December 1976.
24. Bianchi, W.C. and C. Muckel. Ground-Water Recharge
Hydrology. U.S. Department of Agriculture,
Agricultural Research Service. ARS 41161. December
1970.
25. Hantush, M.S. Growth and Decay of Groundwater-Mounds
in Response to Uniform Percolation. Water Resources
Research. 3(1):227-234. 1967.
26. Bouwer, H. Renovating Secondary Effluent by
Groundwater Recharge with Infiltration Basins. In:
Conference on Recycling Treated Municipal Wastewater
Through Forest and Cropland. U.S. Environmental
Protection Agency. EPA-660/2-74-003. 1974.
27. Kirkham, D., S. Toksoz, and R.R. van der Ploeg. Steady
Flow to Drains and Wells. In: Drainage for
Agriculture. J. van Schifgaarde, ed. American Society
of Agronomy Series on Agronomy, No. 17. 1974.
28. Drainage Manual. U.S. Department of the Interior,
Bureau of Reclamation. 1978.
29. Drainage for Agriculture. J. van Schifgaarde, ed.
American Society of Agronomy Series on Agronomy,
No. 17. 1974.
30. Campbell, M.D. and J.H. Lehr. Water Well Technology.
McGraw-Hill, Inc. New York. 1973.
31. Blakeslee, P.A. Monitoring Considerations for
Municipal Wastewater Effluent and Sludge Application to
Land. In: Proceedings of the Joint Conference on
Recycling Municipal Sludges and Effluents on Land,
Champaign, Illinois. July 9-13, 1973.
5-48
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32. Dunlap, W.J., et al. Sampling for Organic Chemicals
and Microorganisms in the Subsurface. U.S.
Environmental Protection Agency. EPA-600/2-77-176.
August 1977.
5-49
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-------
CHAPTER 6
OVERLAND FLOW PROCESS DESIGN
6.1 Introduction
The design procedure for overland flow (OF) is presented in
Figure 6-1. Application rate and hydraulic loading rate
determinations are the most important design steps because
these values plus the storage requirement fix the land area
requirements. Preapplication treatment can be increased if
inadequate land area is available.
6.1.1 Site Characteristics and Evaluation
Overland flow is best suited for use at sites having surface
soils that are slowly permeable or have a restrictive layer
such as a claypan at depths of 0.3 to 0.6 m (1 to 2 ft).
Overland flow can also be used on moderately permeable soils
using higher loading rates than would be possible with an SR
system. It is possible to design an OF system on very
permeable soils by constructing an artificial barrier to
prevent downward water movement through the soil, although
the capital costs of such construction may be prohibitive
for all but the smallest systems.
Overland flow may be used at sites with gently sloping ter-
rain with grades in the range of 1 to 12%. Slopes can be
constructed on nearly level terrain and terraced construc-
tion can be used when the natural slope grade exceeds about
10%. Topographic maps of proposed sites with 0.3 m (1 ft)
contour intervals should be used in detailed site
evaluation.
6.1.2
Water Quality Requirements
Most of the treated water leaving an OF site occurs as sur-
face runoff, and discharge requirements to receiving waters
must be met. Protection of ground water quality at OF sites
is generally ensured by the fact that little water (usually
less than 20%) percolates and the heavy clay soils remove
most of the pollutants. Based on limited experience with OF
on moderately permeable soils, a long-term decrease -in the
percolation rate can be expected due to clogging of soil
pores and a relatively small percentage of the applied
wastewater will percolate. If OF is considered for use on
moderately permeable soils, however, it is recommended that
consideration be given to ground water impacts as discussed
for SR systems in Chapters 4 and 9.
6-1
-------
WASTEWATER
CHARACTERISTICS
(Section 2.2. 1)
SITE CHARACTERISTICS
(SECTIONS 2.2.1, 6.t)
1
WATER QUALITY
REQUIREMENTS
(Sections 2.2. 1 , 8. 1)
p
STORA6E REQUIREMENTS
(Section 6.5)
PROCESS PERFORMANCE
(Section 6.2)
PREAPPLlCATION TREATMENT
(Section 6.3)
LOADING DESIGN
CRITERIA AND RATES
(Section 6.4.1)
LAMO REQUIREMENTS
(Section 6.4.8)
DISTRIBUTION SYSTEM
(Section 6.6)
VEGETATIVE COVER
(Section 6.7)
SLOPE CONSTRUCTION
(Section 6.8)
RUNOFF COLLECTION
(Section 6.9)
r
SYSTEM MONITORING
AND MANAGEMENT
(Section 6.10)
FIGURE 6-1
OVERLAND FLOW DESIGN PROCEDURE
6-2
-------
6.1.3
Design and Operating Parameters
The basic design and operating parameters are defined in
Table 6-1.
TABLE 6-1
OF DESIGN AND OPERATING PARAMETERS
Parameter
Definition
Range of values
in practice
Hydraulic
loading rate
Application
rate
Application
period
Application
frequency
Average flowrate divided
by the wetted slope area
Flowrate applied to the
slope per unit width of slope
Length of time per day of
wastewater application
Number of days per week
that wastewater is applied
to the slope
0.6-6.7 cm/d
6.3-40 cm/wk
0.03-0.24 m3/m-h
5-24 h/d
5-7 d/wk
Note: See Appendix G for metric conversions.
6.2 Process Performance
Knowledge of the relationship of process performance and
design criteria for OF systems is necessary before the design
can be accomplished. The removal mechanisms discussed in
this section relate to operating parameters, slope lengths,
and levels of preapplication treatment. A summary of design
and operating characteristics for existing municipal OF
systems is presented in Tables 6-2 and 6-3. Health and
environmental effects o'f trace elements and trace organics
are discussed in Chapter 9.
6.2.1
BOD Removal
Biological oxidation is the principal mechanism responsible
for the removal of soluble organic materials in the
wastewater. The diverse microbial populations in the soil
and the surface organic layer sorb and subsequently oxidize
these substances into stable end products much like the
biological slimes on trickling filter media. Suspended and
colloidal organic materials, which contribute about 50% of
the BOD load in raw domestic sewage, are removed by
sedimentation and filtration through the surface grass and
organic layers. Subsequent breakdown of the degradable
settled particulate materials is also achieved by the micro-
organisms on the slope. Typical removals of BOD are
presented in Table 6-2.
6-3
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The performance of OF systems treating primary and secondary
effluent in cold regions was evaluated in Hanover, New
Hampshire [4] . For primary effluent, it was found that
runoff BOD concentration was not substantially affected by
temperature until the soil temperature dropped to about
10 °C (50 °F). Below 10 °C, effluent BOD levels increased
with decreasing temperatures. At soil temperatures below
4 °C (39 °P) effluent BOD levels exceeded 30 mg/L. For
secondary effluent, OF effluent BOD values remained below
15 mg/L at soil temperatures of 4 °C. Storage may be
required during cold weather to meet stringent BOD discharge
requirements.
Relationships between BOD removal and the process operating
parameters are not well defined. However, results of recent
studies conducted to develop rational design methods for OF
indicate that, for primary effluent, BOD removal is largely
a function of application rate and slope length and is inde-
pendent of hydraulic loading rate within the ranges used at
existing systems [5, 8] (see Section 6.11). !
6.2.2
Suspended Solids Removal
Suspended and colloidal solids are removed by sedimentation,
filtration through the grass and litter, and adsorption on
the biological slime layer. Because of the low flow
velocities and shallow flow depths on the OF slopes, most SS
are removed within a few meters from the point of
application.
Removal of algae from stabilization pond effluent by OF
systems is somewhat variable and depends on the nature of
the algae. If OF is not being used in the locality for
treatment of pond effluent, pilot studies may be advised to
ascertain treatability.
Removal of SS requires that a thick stand of vegetation be
maintained and that gullies or other short-circuiting down
the slopes be avoided. Removal of SS is relatively
unaffected by cold weather or changes in process loading
parameters compared to BOD removal.~~~~
6.2.3
Nitrogen Removal
Important mechanisms responsible for nitrogen removal
by _ OF _include crop uptake, biological nitrification-
denitrification, and ammonia volatilization. Removal of
nitrogen by crop harvest depends on the nitrogen content of
the crop and the dry matter yield of the crop as discussed
in Section 4.3.2.1. The water tolerant forage grasses used
for OF generally have high nitrogen uptake capacities.
6-6
-------
Annual nitrogen uptake measured at the Utica, Mississippi,
system for a grass mixture of Reed canary, Kentucky 31 tall
fescue, perennial ryegrass, and common Bermuda ranged
between 222 and 179 kg/ha (198 and 160 Ib/acre). Crop
uptake at the Utica system accounted for approximately 11
and 33% percent of the applied nitrogen at the high and low
hydraulic loading rates, respectively (see Table 6-3) [7].
Ammonia volatilization is known to occur during OF.
Researchers at the Utica site estimated volatilization
losses to be about 9% of the applied pond effluent
nitrogen [7].
Nitrification-denitrification is usually the major removal
mechanism. At Utica, the losses attributable to denitrifi-
cation ranged from 34 to 42% of the applied nitrogen [7].
Nitrification takes place in the aerobic environment at the
soil surface. The nitrates then diffuse through the
organic-rich surface materials where anaerobic conditions
necessary for denitrification exist. Denitrification
requires the presence of a readily available carbon
source. Consequently, the best nitrogen removals are found
using raw wastewater or primary effluent that have high
carbon to nitrogen ratios (>3). Lesser nitrogen removals
are found using secondary or pond effluent when the carbon
to nitrogen ratios are about one.
Typical effluent values for the different nitrogen forms are
indicated in Table 6-3. The effects of operating parameters
on nitrogen removal are not well understood. Specific
design and operating criteria to optimize nitrogen removal
or ammonia conversion have not been established. However,
some general relationships can be stated:
1. Total nitrogen and ammonia removal is inversely
related to application rate and directly related to
slope length.
2. The rate of nitrification is reduced if wastewater
is applied continuously.
3. The overall nitrogen removal and ammonia conversion
efficiency is reduced as the soil temperature drops
below 13 to 14 °C (55 to 57 °F). With pond
effluent at the Utica system, nitrogen removal
efficiency decreased from 90% in the spring and
summer to less than 80% during the winter [2] .
Results obtained at the Hanover system with primary
and secondary effluents, showed that nitrogen
removal efficiency dropped to about 30% during the
6-7
-------
winter [5]. The reduced efficiency in colder
temperatures-is attributed to the decreased rate of
the biological nitrification-denitrification pro-
cess as well as reduced plant uptake.
6.2.4 Phosphorus Removal
The major mechanisms responsible for phosphorus removal by
OF include sorption on soil clay colloids and precipitation
as insoluble complexes of calcium, iron, and aluminum. When
low permeability surface soils are present, as is the case
for most OF systems, much of the applied wastewater flows
over the surface and does not contact the soil matrix and
phosphorus adsorption sites. As a result of this limited
soil contact, phosphorus removals achieved at exisftljig oF
systems generally range from 40 to 60%.Phosphorus data
from some OF systems are shown in Table 6-3.
Improved phosphorus removal efficiency can be achieved by
the addition of aluminum sulfate to the wastewater prior to
application to the land. Applications of aluminum sulfate
to raw sewage at a concentration of 20 mg/L reduced the
phosphorus concentration from 8.8 mg/L to 1.5 mg/L or 85%
removal efficiency in experiments at Ada, Oklahoma [9].
Addition of aluminum sulfate to stabilization pond effluent
in amounts equal to 1:1, aluminum to phosphorus, prior to
application resulted in significant reduction of phosphorus
in the runoff to about 1 mg/L or removal efficiency better
than 80% at the Utica system [10].
6.2.5
Trace Element Removal
The major mechanisms responsible for trace element removal
include sorption on clay colloids and organic matter at the
soil surface layer, precipitation as insoluble hydroxy
complexes, and formation of organometallic complexes with
the organic matter at the slope surface. The largest
proportion of the heavy metals accumulate in the biomass on
the soil surface and close to the point of effluent
application. Trace metal removal data reported from the
Utica system are presented in Table 6-4 to illustrate the
removal levels that can be achieved with OF.
6.2.6
Microorganism Removal
The major mechanisms responsible for removal of microorgan-
isms in OF systems include sedimentation, filtration through
surface organic layer and vegetation, sorption to soil par-
ticles, predation, irradiation, and desiccation during dry-
ing periods.
6-8
-------
TABLE 6-4
REMOVAL EFFICIENCY OF HEAVY METALS
AT DIFFERENT HYDRAULIC RATES AT
UTICA, MISSISSIPPI [7]
Hydraulic
loading
rate , cm/d
1.27
2.54
3.81
5.08
Runoff concentration, mg/L
Cadmium
0.0046
0.0036
0.0079
0.0142
Nickel
0.0131
0.0217
0.0302
0.0486
Copper
0.0129
0.0293
0.0382
0.0524
Zinc
0.0558
0.0525
0.0757
0.0853
Removal efficiency, %
Cadmium
85.4
90.9
77.7
63.2
Nickel
92.1
87.6
79.6
66.0
Copper
93.1
82.4
73.5
64.4
Zinc
88.4
87.4
78.8
75.4
Generally, the removal efficiency of OF systems for
pathogenic organisms such as viruses and indicator organisms
is comparable to that which is achieved in conventional
secondary treatment systems without chlorination. Disinfec-
tion may be required by the regulatory agency.
6.2.7
Trace Organics Removal
Removal of trace organics in OF systems is achieved by the
mechanisms of sorption on soil clay colloids or organic
matter, biodegradation, photodecomposition, and volatiliza-
tion. The importance of one or a combination of these
mechanisms will depend on the nature of the trace organic
substance.
6.2.8
Effect of Rainfall
The effect of rainfall on OF process performance was studied
at Paris, Texas; Utica, Mississippi; Ada, Oklahoma; and
Hanover, New Hampshire [11, 7, 4]. In all of these studies,
it was observed that precipitation events occurring during
application did not significantly affect the concentration
of the major constituents in the runoff. However, the mass
discharges of constituents did increase due to the increased
water volume from the storm events. In situations where
discharge permits are based on mass discharge, discussions
with regulatory officials should be held to determine if
permits can be written to reflect background loadings
occurring as a result of rainfall runoff from OF fiel-ds or
to allow higher mass discharges during periods of high flow
in receiving waters. In some cases, collection and recycle
of stormwater may be necessary.
6-9
-------
6.2.9
Effect of Slope Grade
The effect of slope grade on treatment performance has been
evaluated at several systems [2, 7, 8]. The conclusion from
all studies was that slope grade in the range of 2 to 8%
does not significantly affect treatment performance when
systems are operated within the range of application rates
reported in Table 6-2.
6.2.10
Performance During Startup
A period of slope aging or acclimation is required following
initial startup before process performance approaches satis-
factory levels. During this period, the microbial
population on the slopes is increasing and slime layers are
forming. The initial acclimation period may be as long as 3
to 4 months. If a variance to allow discharge during this
period can not be obtained, provisions should be made to
store and/or recycle the effluent until effluent quality
improves to the required level.
An acclimation period also should be provided following
winter storage periods for those systems in cold climates.
Acclimation following winter shutdown should require less
than 1 month. Acclimation is not necessary following shut-
down for harvest unless the harvest period is extended to
more than 2 or 3 weeks due to inclement weather.
6.3 Preapplication Treatment
Preapplication treatment before OF is provided to
(1) prevent operating problems with distribution systems
and, (2) prevent nuisance conditions during storage.
Preapplication treatment to protect public health is not
usually a consideration with OF systems because public
contact with the treatment site is usually controlled and no
crops are grown for human consumption.
Except in the case of harmful or toxic substances from
industrial sources (see Section 4.4.3), preapplication
treatment of municipal wastewater is not necessary for the
OF process to achieve maximum treatment. The OF process is
capable of removing higher levels of constituents than are
normally present in municipal wastewater and maximum use
should be made of this renovating capacity. Consequently,
the level of preapplication treatment provided should be the
minimum necessary to achieve the two stated objectives. Any
additional treatment, in most cases, will only increase
costs and energy use, and, in some cases, can impair or
reduce the consistency-of process performance. Algal solids
have proven difficult to remove from some stabilization pond
6-10
-------
effluents and reduced nitrogen removals have been observed
with secondary effluents. These statements do not imply
that existing treatment facilities should not be considered
for use in preapplication treatment.
The EPA has issued guidelines for assessing the level of
preapplication treatment necessary for OF systems. The
guidelines are as follows:
1. Screening or comminution—acceptable for isolated
sites with no public access.
2. Screening or comminution plus aeration to control
odors during storage or application—acceptable for
urban locations with no public access.
Municipal wastewater contains rags, paper, hair, and other
large articles that can blind and clog orifices and valves
in surface and sprinkler distribution systems. Comminution
is generally not sufficient to eliminate clogging
problems. Fine screening or primary sedimentation with
surface skimming is necessary to prevent operating difficul-
ties. For sprinkler distribution systems, screen sizes
should be less than one-third the diameter of the sprinkler
nozzle. Static inclined screens with 1.5 mm (0.06 in.)
openings have been used successfully for raw wastewater
screening.
Grit removal is advisable for wastewaters containing high
grit loads. Grit reduces pump life'and can deposit in low
velocity distribution pipelines.
6.4 Design Criteria Selection
The principal OF design and operating parameters are defined
in Section 6.1 and values used at existing systems are given
in Table 6-1. Traditionally, OF design and operation has
been an empirical procedure based on a set of general guide-
lines established through successive trials with the various
process parameters at different OF systems. The guidelines,
as presented here, reflect successful construction and oper-
ation of full-scale systems, but the degree of conservation
inherent in the guidelines has not been established. The
design criteria shown in Table 6-5 have been used at exist-
ing OF systems during spring, summer, and fall to achieve
effluent BOD and suspended solids concentrations less than
20 mg/L, total nitrogen less than 10 mg/L, ammonia nitrogen
less than 5 mg/L, and total phosphorus less than 6 mg/L.
, 6-11
-------
TABLE 6-5
OVERLAND FLOW DESIGN GUIDELINES
Hydraulic
Preapplication loading rate,
treatment cm/d
Screening
Primary sedimentation
Stabilization pond
Complete secondary
biological
0.9-3
1.4-4
1.3-3.3
2.8-6.7
Application Application
rate, period,
m3/m-h h/d
0.07-0.12 8-12
0.08-0.12 8-12
0.03-0.10 8-18
0.10-0.20 8-12
Application Slope
frequency, , length,
d/wk m
5-7
5-7
5-7
5-7
36-45
30-36
45
30-36
6.4.1
Hydraulic Loading Rate
Traditionally, hydraulic loading rate has been used as the
principal OF design parameter. Current guidelines call for
hydraulic loadings rates to be varied with the degree of
preapplication treatment as indicated in Table 6-5. For
systems operating year-round, the hydraulic loading rates
generally have been reduced during the winter to compensate
for the reduction in BOD and nitrogen removal efficiency
when soil temperatures drop below 10 to 15 °C (50 to 59 °F)
(see Sections 6.2.1 and 6.2.3). Reductions in hydraulic
loading rates during the winter have been somewhat arbitrary
and guidelines are not well established. A 30% reduction
from summer rates has been used at the Ada system while a
50% reduction has been recommended at the Utica system.
The performance of OF systems is dependent on the detention
time of the wastewater on the slope. The detention time is
in turn directly related to the application rate.
Therefore, it is possible to compensate for lower winter
temperatures by decreasing the application rate and increas-
ing the application period while maintaining the hydraulic
loading rate constant. It is also possible to increase
hydraulic loading rates for short periods, such as when a
portion of the system is shutdown for harvesting or repair,
without affecting performance, by increasing the application
period and maintaining the application rate constant.
6.4.2
Application Rate
Design guidelines for application rates based on existing
systems are presented in Table 6-5. Values at the high end
of the range may be used during spring, summer, and fall,
while values at the low end should be used when soil temper-
atures drop below about 10 °C or if maximum removal
efficiency for any constituent is desired. These rates are
based on slope lengths in the range of 30 to 40 m (98 to
6-12
-------
131 ft). Application rates less than the minimum values
shown in Table 6-5 may be difficult to distribute uniformly
with surface distribution systems.
Hydraulic loading rate is related to application rate/
period, and the slope length as shown in Equation 6-1.
Lw = (Ra)
(100 cm/m)
(6-1)
where LW =
hydraulic loading rate, cm/d
application rate, m3/h*m
application period, h/d
slope length, m
The calculation can be started in one of two ways:
1. Select application rate, period, and slope length
and calculate hydraulic loading rate, or
2. Select application period, slope length, and
hydraulic loading rate and calculate application
rate.
6.4.3 Application Period
A wide range of application periods has been used success-
fully, ranging from just a ,few hours to as high as 24 h/d.
The application periods that have been used most frequently
in existing OF projects range between 6 and 12 h/d.
Use of design application periods of 12 h/d or less allows
more operating flexibility during periods when parts of the
system must be shutdown for harvest or repair. For
instance, if the design application period is .8-h/d, waste-
water normally would be applied to one-third of the total
land area at any given time assuming a 24-hour system opera-
tion. If one-third of the system were shutdown for harvest,
the application period could be increased to 12 h/d on the
remaining two portions of the system, and the entire flow
could be applied without increasing the application rate.
Systems generally are designed to operate on a 24 hour basis
to minimize land requirements. For small systems, it may be
more convenient or cost effective to operate only during one
6-13
-------
working shift. In this case, the entire land area would
receive the full design daily wastewater flow during the
8 hour application period*, Storage facilities would be
required to hold wastewater flow during the 16 hour nonoper-
ating period.
6.4.4
Application Frequency
A design application frequency of 7 d/wk is generally used
to minimize land area requirements and eliminate or reduce
storage requirements. There does not appear to be any
advantage in terms of process performance to using less
frequent applications. For small systems with storage
facilities, it may be more convenient to use an application
frequency of 5 d/wk and shut down on weekends.
6.4.5
Constituent Loading Rates
Historically, OF design and operation has not been based on
mass loading rates of wastewater constituents such as BOD,
suspended solids, and nitrogen. The rates used at existing
systems apparently are well below those that might affect
process performance, since no correlations between process
performance and constituent loading have been found.
6.4.6
Slope Length
In general, OF process performance has been shown to be
directly related to slope length and inversely related to
application rate (see Section 6.11). Thus, longer slope
lengths should be used with higher application rates or,
conversely, shorter slope lengths should be used with lower
application rates to achieve an equivalent degree of treat-
ment. The combinations of slope lengths and application
rates that are suggested for design are indicated in
Table 6-5.
The minimum slope lengths indicated have been used with
surface distribution systems or low-pressure spray systems
that distribute the wastewater across the top of the
slope. Traditionally, longer slope lengths (45 to 60 m or
150 to 200 ft) have been used with full-circle,, high-
pressure impact sprinklers. However, nearly all of the
experience with impact sprinkler OF distribution systems has
been with high strength food processing wastewater„ There
are no data to indicate the need for longer slope lengths
when using sprinklers to apply municipal wastewater. With-
out such information, the recommended minimum slope length
for sprinkler distribution systems is 45 m (150 ft) for part
circle sprinklers. For full circle sprinklers, the
recommended minimum slope length is the sprinkler diameter
plus about 20 m (65 ft).
6-14
-------
From a process control standpoint, it is desirable to have
all slopes approximately the same length. However, this may
not always be possible due to the shape of the site bound-
aries or site topography. If slope length must differ
substantially (>10 m or 33 ft) from the design value, then
the application rate used on these slopes may need to be
adjusted. For design, a first approximation to the adjusted
rate may be made by equalizing the hydraulic loading rate on
all slopes. Equation 6-1 may be used to estimate the neces-
sary application rate. Adjustment in the field during oper-
ation may be necessary to achieve equivalent treatment.
6.4.7
Slope Grade
Although slope grades ranging from less than 1% to 10 or 12%
have been used effectively for OF, experience has shown the
optimum range to be between 2 and 8%. Slope grades less
than 2% increase the potential for ponding, while those
greater than 8% increase the risk of erosion. It has been
shown through several studies that slope grades in the range
of 2 to 8% do not affect process performance. Therefore,
there is no need to adjust slope length or application rate
for changes in slope grade within-this range. Slope grades
greater than about 8% also increase the risk of short
circuiting and channeling and may require lower application
rates or longer slope lengths to achieve adequate treatment,
although there are no performance data to confirm this.
Although there exist some circumstances where natural ground
contours can provide the slope grade necessary for effective
treatment, few sites offer conditions that are ideal for the
smooth sheet flow of water along the ground surface, which
is important to the OF concept. Therefore, it is almost
always necessary to reshape the site into a network of
slopes that conform to the length and grade guidelines
outlined previously. The grade of each slope is established
by the existing site conditions. For example, if the site
has a general slope grade of 4%, the slope should also be
shaped to 4% grades. If the site is very flat, 2% grades
should be used. If the site is quite steep, the slope
grades should be reduced to 8%. This procedure will mini-
mize the cost required to reshape the site. Since natural
grades can vary considerably within the confines of a
specific site, the individual OF slopes can vary in grade
although each should be within the 2 to 8% range.
6.4.8
Land Requirements
The area of land to which wastewater is actually applied is
termed slope area. In addition to the slope area, the total
6-15
-------
land area required for an OF system includes land for pre-
application treatment, administration and maintenance
buildings, service roads, buffer zones (see Section
4.5.4.2), and storage facilities. At existing systems,
other area requirements (not including buffer zones or
storage facilities) have ranged from 15 to 40% of the slope
area.
For systems where storage is provided, the slope area
requirement may be calculated using the following equations.
Q(365 d/yr) + AVe
(Da) (Lw)
m2/ha) (10-2 m/cm)
(6-2)
where A,, = slope area, ha
Q =
Da =
net loss or gain in storage volume due to
precipitation, evaporation, and seepage, m^/yr
average daily flow, m3/d
number of operating days/yr
design hydraulic loading rate, cm/d
The value of AV depends on the area of the storage
reservoir. Thus, €he final design slope area must be deter-
mined after the storage reservoir dimensions are determined.
Combining equations 6-1 and 6-2 allows calculation of A
based on application rate and slope length. Equations 6-2
and 6-3 can also be used for systems with no storage since
the term AVS will then be equal to zero.
Q(365 d/yr) +
(Da) (Ra) (P)
(104
(6-3)
where A_ =
0
Q =
AV,
Da =
slope area, ha
average daily flow, m3/d
net storage gain or loss, m3/yr
number of operating days per year
6-16
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Ra = design application rate, mj/h-m
P = design application period, h/d
S = .slope length, m
Equations 6-2 and 6-3 may also be used for systems in warmer
climates that operate year-round without reducing hydraulic
loading rates during the winter. As stated previously, it
is possible to compensate for lower removal efficiency at
low soil temperatures, without reducing hydraulic loading
rates, by decreasing the application rate and increasing the
application period. This winter operating procedure will
minimize slope area requirements and eliminate the need for
any winter storage.
If lower hydraulic loading rates are used during the winter,
for a system operating year-round, the designer has two
alternative approaches that may be used to determine the
slope area requirements. Under the first alternative, slope
area requirement is based only on the winter hydraulic load-
ing rate, in which case no winter storage will be
required. Under the second alternative, slope area would be
based on the higher hydraulic loading rates used during the
rest of the year, in which case a portion of the winter flow
would have to be stored. The first approach would result in
maximum land area requirements and conservative loadings
during the warmer periods of the year, but would eliminate
storage requirements. The second approach would minimize
land area requirement but may require preapplication .treat-
ment facilities for storage. An economic analysis should be
performed to determine which alternative is most cost-effec-
tive. If storage facilities are going to be provided for
other reasons (see Section 6.5), then the second alternative
will probably prove most cost effective.
Slope area requirements using the first alternative may be
computed using the following equation, assuming a 7 d/wk
application frequency:
As -
Q,.,
(Lww)(104 m2/ha)(10 2 m/cm)
(6-4)
where AS = slope area, ha
Qw = average daily flow during winter, m3/d
LWW = winter hydraulic loading rate, cm/d
6-17
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Slope area requirements using the second alternative may be
compluted using the following equation:
As -
where
Q =
AVS =
D
aw
D
(QH365 d/yr) + AVS
as
(Lww)(Daw) + (Lws)(Das)(104 m2/na)(10-2 m/cm)
slope area, ha
annual average daily flow, m /d
net gain or loss of water from storage, m^/yr
winter hydraulic loading rate, cm/d
number of operating days at winter rate
non-winter hydraulic loading rate, cm/d
number of operating days at non-winter rates
6.5 Storage Requirements
Storage facilities may be required at an OF system for any
of the following three reasons:
1. Storage of water during the winter due to reduced
hydraulic loading rates or complete shutdown.
2. Storage of stormwater runoff to meet mass discharge
limitations.
3. Equalization of incoming flows to permit constant
application rates.
Estimating storage volume requirements for the above reasons
is discussed in this section. Storage reservoir design
considerations are discussed in Section 4.6.3.
6.5.1
Storage Requirements for Cold Weather
Due to the limited operating experience with OF in different
parts of the country, cold weather storage requirements are
not well defined. In general, OF systems must be shut down
for the winter when effluent quality requirements cannot be
met due to cold temperatures even at reduced application
rates or when ice begins to form on the slope. The duration
of the shutdown period and, consequently, the required stor-
age period will, of course, vary with the local climate and
the required effluent quality.
6-18
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In studies at the Hanover system, a storage period of 112
days including acclimation was estimated to be required when
treating primary effluent to BOD and suspended solids limits
of 30 mg/L [4] . This estimate was reasonably close to the
130 storage days predicted by the EPA-1 program using 0 °C
(32 °F) mean temperature (see Section 4.6.2). For design
purposes, the EPA-1 or EPA-3 programs may be used to conser-
vatively estimate winter storage requirements for OF. A map
showing estimated storage days from the EPA-1 program is
shown in Figure 2-5 and tabulated data are presented in
Appendix F. In areas of the country below the 40 day
storage contour, OF systems generally can be operated year-
round. However, winter temperature data at the proposed OF
site should be compared with those at existing systems that
operate year-round to determine if all year operation is
feasible.
Storage is required at OF systems that are operated year-
round but at reduced hydraulic loading rates during the
winter. The required storage volume for such systems can be
estimated using the following equation:
where
Vs = (QW)(DW) - (As)(Lww)(Daw)(10-2 m/cm)
storage volume, m3
average daily flow during winter, m3/d
number of days in winter period
slope area, m2
LWW = hydraulic loading rate during winter, cm/d
(6-6)
Vs =
Qw =
Dw -
As =
D
aw
= number of operating days in winter period
The duration of the reduced loading period at existing
systems generally has been about 90 days.
Unless the winter storage reservoir is an integral part of
the preapplication treatment system, the winter storage
reservoir should be bypassed during the warm season opera-
tion to minimize algae production in the applied wastewater
and to minimize energy costs for prestorage treatment.
Stored water should be blended with fresh incoming waste-
water before application on the OF slopes.
6.5.2
Storage for Stormwater Runoff
In some cases, discharge permits may allow discharge of
Stormwater runoff from the OF system but require monthly
6-19
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mass discharges for certain constituents to be within
specified limits. In such cases, stormwater runoff may need
to be stored and discharged at a later time when mass
discharge limits would not be exceeded. A procedure for
estimating storage requirements for stormwater runoff is
outlined below.
1. Determine the maximum monthly mass discharge
allowed by the permit for each regulated
constituent.
2. Determine expected runoff concentrations of regu-
lated constituents under normal operation (no
precipitation).
3. Estimate monthly runoff volumes from the system
under normal operation by subtracting estimated
monthly ET and percolation losses from, design
hydraulic loading.
4. Estimate the monthly mass discharge under normal
operation by multiplying the values from Steps 2
and 3.
5. Calculate the allowable mass discharge of regulated
constituents resulting from storm runoff by
subtracting the estimated monthly mass discharge in
Step 5 from the permit value in Step 1.
6. Assuming that storm runoff contains the same
concentration of constituents as runoff during
normal operation, calculate the volume of storm
runoff required to produce a mass discharge equal
to the value in Step 5.
7. Estimate runoff as a fraction of rainfall for the
particular site soil conditions. Consult the local
SCS office for guidance.
8. Calculate the total rainfall required to produce SL
mass discharge equal to the value in Step 5 by
dividing the value in Step 6 by the value in
Step 7.
9. Determine for each month a probability distribution
for rainfall amounts and the probability that the
rainfall amount in Step 8 will be exceeded,
10. In consultation with regulatory officials, deter-
mine what probability is an acceptable risk before
storm runoff storage is required and use this value
(Pd) for design.
6-20
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11. Storage must be provided for those months in which
total rainfall probability exceeds the design value
(PCJ) determined in Step 10.
12. Determine the change in storage volume each month
by subtracting the allowable runoff volume in
Step 6 from the runoff volume expected from rain-
fall having an occurrence probability of Pd. In
months when the expected storm runoff exceeds the
allowable storm runoff, the difference will be
added to storage. In months when allowable runoff
exceeds expected runoff, water is discharged from
storage.
13. Determine cumulative storage at the end of each
month by adding the change in storage during one
month to the accumulated quantity from the previous
month. The computation should begin at the start
of the wettest period. Cumulative storage cannot
be less than zero.
14. The required storage volume is the largest value of
cumulative storage. The storage volume must be
adjusted for net gain or loss due to precipitation
and evaporation (see Section 4.6.3).
If stored storm runoff does not meet the discharge permit
concentration limits for regulated constituents, then the
stored water must be reapplied to the OF system. The amount
of stored storm runoff is expected to be small relative to
the total volume of wastewater applied, and therefore,
increases in slope area should not be necessary. The addi-
tional water volume can be accommodated by increasing the
application period as necessary.
6.5.3
Storage for Equalization
From a process control standpoint it is desirable to operate
an OF system at a constant application rate and application
period. For systems that do not have storage facilities for
other reasons, small equalizing basins can be used to even
out flow variations that occur in municipal wastewater
systems. A storage capacity of 1 day flow should be suffi-
cient to equalize flow in most cases. The surface area of
basins should be minimized to reduce intercepted precipita-
tion. However, an additional half day of storage can be
considered to hold intercepted precipitation in wet
climates.
For systems providing only screening or primary sedimenta-
tion as preapplication treatment, aeration should be
6-21
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provided to keep the basin contents mixed and prevent
anaerobic odors. The added cost of aeration, in most cases,
will be offset by savings resulting from reduced pump sizes
and peak power demands. The designer should analyze the
cost effectiveness of this approach for the system in
question.
6.6 Distribution
Wastewater distribution onto OF slopes can be accomplished
by surface methods, low pressure sprays, and high pressure
impact sprinklers. The choice of system should be based on
the following factors:
1. Minimization of operational difficulties, such as
• Uneven wastewater distribution onto the slopes
and the creation of short-circuiting and
channeling
• Solids accumulation at the point of
application
• Physical damage due to maintenance activities
and freezing ;
2. Capital, operating, and energy costs
6.6.1
Surface Methods
Surface distribution methods include gated aluminum pipe
commonly used for agricultural irrigation (Section 4.7.2),
and slotted or perforated plastic pipe. Commercially avail-
able gated pipe can have gate spaces ranging from 0„6 to 1.2
m (2 to 4 ft) and gates can be placed on one or both sides
of the pipe (see Figure 6-2). A 0.6 m (2 ft) spacing is
recommended to provide operating flexibility. Slide gates
rather than screw adjustable orifices are recommended for
wastewater distribution. Gates can be adjusted manually to
achieve reasonably uniform distribution along the pipe.
However, the pipe should be operated under low pressure, 1.5
to 3.5 N/cm2 (2 to 5 lb/in. ), to achieve good uniformity at
the application rates recommended in Table 6-5, especially
with long pipe lengths. Pipe lengths up to 520 m (1,700 ft)
have been used, but shorter lengths are recommended. For
pipe lengths greater than 100 m (300 ft), inline valves
should be provided along the pipe to allow additional flow
control and isolation of pipe segments for separate
operation.
6-22
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FIGURE 6-2
SURFACE DISTRIBUTION USING GATED PIPE FOR OF
Slotted or perforated plastic pipe have fixed openings at
intervals ranging from 0.3 to 1.2 m (1 to 4 ft). These
systems operate under gravity or very low pressure and the
pipe must be level to achieve uniform distribution. Conse-
quently, such methods should be considered only for small
systems having relatively short pipe lengths that can be
easily leveled.
The principal advantages of surface systems are low capital
cost and low energy consumption and power costs. The major
disadvantage with surface systems is the tendency of
discharge orifices to accumulate debris and become partially
plugged; Consequently, orifices must be inspected regularly
and cleaned as necessary to maintain proper distribution.
Another disadvantage of surface systems is the potential for
deposition of solids at the point of application when
treating wastewaters with high concentrations of' suspended
solids. Deposition problems have not been reported with
surface distribution systems applying municipal wastewater,
either screened raw or primary effluent, at conventional
6-23
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'hydraulic loading rates and application rates. However,
solids buildup has occurred when applying food processing
wastewater with solids concentrations >500 mg/L.
6.6.2
Low Pressure Sprays
o 9
Low pressure, 10 to 15 N/cm (15 to 20 Ib/in. ), fan spray
nozzles mounted on fixed risers that distribute was.tewater
across the top of the slope have been used successfully with
stabilization pond effluent (see Figure 6-3). However,
experience using this method for screened raw wastewater has
been mixed. Preapplication treatment with fine screens is
essential for this method to be used with raw wastewater or.
primary effluent.
FIGURE 6-3
DISTRIBUTION FOR OF USING LOW PRESSURE FAN SPRAY NOZZLES
6-24
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Low pressure fan nozzles mounted on rotating booms were used
previously but found to require too much maintenance to be
practical.
6.6.3
High Pressure Sprinklers'
High pressure, 35 to 55 N/cm (50 to 80 Ib/in.), impact
sprinklers have been used successfully with food processing
wastewa.ters containing suspended solids concentrations
>500 mg/L. The position of the impact sprinkler ,on the
slope depends on whether the sprinkler rotation is full-
circle or half-circle and on the configuration of the
slopes. Several possible sprinkler location configurations
are illustrated in Figure 6-4. With configuration
(a), slope lengths in the range of 45 to 60 m (150 to
200 ft) are required to prevent spraying into runoff
channels and to provide some downslope distance beyond the
spray pattern. Use of half-circle sprinklers, configura-
tions (c) and (d), or full-circle sprinkler in configura-
tion (b) allows the use of slope lengths less than 45 m
(Section 6.4.6).
The spacing of the sprinkler along the slope depends on the
design application rate and must be determined in
conjunction with the sprinkler discharge capacity and the
spray diameter. The relationship between OF application
rate and sprinkler spacing and discharge capacity is given
by the following equation: "
q =
3 m3/L)(3,600 s/h)
(6-7)
where q = OF application rate, m /h-m
Q_ = sprinkler discharge rate," L/s
5 "
Ss = sprinkler spacing, m
The sprinkler spacing should allow for some .overlap of spray
diameters. A spacing of about 80% of the spray diameter
should be adequate for OF. Using the design OF application
rate and the above criteria for spray diameter, a sprinkler
can be selected from a manufacturer's catalog. Sprinkler
selection is discussed in Appendix E. Application rate can
be adjusted by regulating the sprinkler operating pressure.
6-25
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1—0
'
C3 CD
U-QC
O c/0
CD —
tO
CD '^
LLl
0=0
6-26
-------
Sprinkler distribution systems are capable of providing a
uniform distribution across the slope and distributing a
high solids load over a large area to avoid accumulation.
Operator attention requirements are expected to be less with
sprinkler systems than with surface systems. Disadvantages
associated with sprinkler distribution include relatively
high capital costs, high energy requirements, and potential
short-circuiting due to wind drift of sprays. :>Preapplica-
tion treatment must be sufficient to prevent nozzle clogging
(Section 6.3 ).
6.6.4
Buried Versus Aboveground System
Low pressure sprays and sprinkler systems may have either
aboveground or buried piping. Surface piping generally has
a lower capital cost, but buried pipe has a longer service
life- and is not as susceptible to damage from freezing or
harvesting equipment.
6.6.5
Automation
Both gravity and pressure distribution systems can be
automated to any degree that is desired., The value of
automation increases with the 'size of the system. The
components required to effectively automate an OF system are
relatively simple and trouble-free. Care should be
exercised to avoid over-designing an automatic control
system. The primary objective is to allow the operator to
program any portion of the system to operate at any time for
any length of time. Pneumatically or hydraulically operated
diaphragm valves, tied into a centrally located control
station, are commonly used. > A clock-timer system coupled
with a liquid level controller for the pumping system is
usually adequate to provide a satisfactory control system.
6.7 Vegetative Cover
6.7.1
Vegetative Cover Function
A close growing grass cover crop is essential for efficient
performance of OF systems. The cover crop serves the
following functions in the process.
1. Erosion protection - crop provides surface
roughness which acts to spread the water flow over
the surface and reduces the velocity of surface
flow thus helping to prevent channeling.
2. Support media for microorganisms -,the biological
slime layer that develops on the slope surface is
supported by the grass shoots and vegetative
litter.
6-27
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3. Nutrient uptake - crop takes up nitrogen and
phosphorus which can be removed by harvesting.
6.7.2 Vegetative Cover Selection
An OF cover crop should have the following characteristics:
perennial grasses; high moisture tolerance; long growing
season; high nutrient uptake; and suited for the local
climate and soil conditions.
A mixture of grasses is generally preferred over a single
species. The mixture should contain grasses whose growth
characteristics compliment each other, such as sod formers
and bunch grasses and species that are dormant at different
times of the year. Another advantage of using a mixture is
that, due to natural selection, one or two grasses will
often predominate. One particular mixture which has been
found to be quite successful is Reed canarygrass, tall
fescue, redtop, dallisgrass, and ryegrass. in northern
climates, substitution of orchardgrass for the redtop and
dallisgrass is suggested. Although this mixture has proven
effective in a variety of climates, it is always best to
consult with a local agricultural advisor when selecting a
seed mix to meet the criteria given above.
Salt sensitive plants, such as most varieties of clover,
should be avoided. Pure stands of grasses whose growth
characteristics are dominated by a single seed stalk such as
Johnson grass, yellow foxtail, and most of the grains should
be avoided. In the early stages of growth, these grasses
provide a quick and effective cover. However, as the plant
matures, the bottom leaves wither and disappear, leaving
only the primary seed stalk which eventually produces the
grain crop. When this happens, the value of these crops as
OF cover vegetation is greatly reduced. Of course, crops
having low moisture .tolerance, such as alfalfa, should not
be used.
6.8 Slope Construction
6.8.1
System Layout
The general arrangement of individual slopes should be such
that gravity flow from the slopes to the runoff collection
channels and finally to the main collection channels will be
possible. A grading plan should be prepared that will mini-
mize earthwork costs. Criteria for selecting slope grades
are given in Section 6.4.7. From an operational standpoint,
it is preferable to have the grading plan result in a single
final discharge point. Occasionally, however, existing
6-28
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terrain features will make a single point discharge imprac-
tical. In such cases, it is usually more cost effective to
create multiple discharge points (and monitoring stations)
rather than attempt to overcome the terrain constraints with
extensive earthwork.
6.8.2
Grading Operations
Since the principle of smooth sheet flow down the slope is
of critical importance to consistent OF process performance,
appropriate emphasis must be placed ,on the proper
construction of the slopes. Naturally occurring slopes,
even if they are within the required length and grade range,
seldom have the uniform overall smoothness required to
prevent channeling, short-circuiting, . and ponding.
Therefore, it is necessary to completely clear the site of
all vegetation and to regrade it into a series of OF slopes
and runoff collection channels. The first phase of the
grading operation is commonly referred to as rough grading
and should be accomplished within a grade tolerance of 3 cm
(0.1 ft). If a buried distribution system is being used,
the rough grading phase is generally followed by the
installation of the distribution piping and appurtenances.
After the slopes have been formed in the rough grading
operation, a farm disk should be used to break up the clods,
and the soil should then be smoothed with a land plane (see
Figure 6-5). Usually, a grade tolerance of plus or minus
1.5 cm (0.05 ft) can be achieved with three passes of the
land plane. Surface distribution piping may be installed at
this stage.
Soil samples of the regraded site should be taken and
analyzed by an agricultural laboratory to determine the
amounts of lime and fertilizer that are needed. The
appropriate quantities should then be added prior to
seeding. A light disk should be used to eliminate any wheel
tracks on the slopes as final preparation for seeding.
6.8.3
Seeding and Crop Establishment
It has been found that a Brillion seeder is capable of doing
an excellent job of seeding the slopes. The Brillion seeder
carries a precision device to drop seeds between
cultipacker-typer rollers so that the seeds are firmed into
shallow depressions, allowing for quick germination and
protection against erosion. Hydroseeding may also be used
if the range of the distributor is sufficient to provide
coverage of the slopes so that the vehicle does no.t have to
travel on the slopes. When seeding is completed, regardless
of the means, there should be no wheel tracks on the slopes.
6-29
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FIGURE 6-5
LAND PLANE USED FOR FINAL GRADING
It is important to establish a good vegetative cover prior
to applying wastewater to the slopes. Good planning will
minimize the effort and cost required to achieve this. The
construction scheduling should be organized so that the
seeding operation is accomplished during the optimum periods
for planting grass in the particular project locality, This
is generally sometime during the fall or spring of each
year. During these periods, sufficient natural precipi-
tation is often available to develop growth. In arid and
semiarid climates or whenever seed is planted during a dry
period, it may be necessary to irrigate the site with fresh
water, if wastewater is unavailable, to establish the grass
crop. In these cases, a portable sprinkler irrigation
system should be used to provided irrigation water coverage
over the entire slope area, since use of the OF distribution
system would cause erosion of the bare slopes. It may be
necessary to sow additional seed or to repair erosion that
may occur as a result of heavy rains prior to the stabili-
zation of the slopes.
As a general rule, wastewater should not be applied at
design rates until the crop has grown enough to receive one
cutting. Cut grass from the first cutting may be left on
the slope to help build an organic mat as long as the
6-30
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clippings are short (0.3 m or 1 ft); long clippings tend to
remain on top of the cut grass thus shading the surface and
retarding regrowth.
6.9 Runoff Collection
The purpose of the runoff collection channels is to
transport the treated runoff and storm runoff to a final
discharge point and allow runoff to flow freely off the
slopes. The collection channels are usually vegetated with
the same species of grasses growing on the slopes and should
be graded to prevent erosion. There are some cases,
however, where additional construction is necessary. Sharp
bends or steep grades along runoff channels will increase
the potential for erosion, and it may be necessary to
provide additional protection in the form of riprap,
concrete, or other stabilizing agent at these points.
Runoff channels should be graded to no greater than 25% of
the slope grade to prevent cross flow on the slope.
In humid regions, particularly where the topography is quite
flat and the runoff channels have small grades, grass
covered channels may not dry out entirely. This may
increase channel maintenance problems and encourage mosquito
populations. In these cases, concrete or asphalt can be
used or a more elaborate system involving porous drainage
pipe lying in the channel beneath a gravel cover. It should
be emphasized, however, that it is usually not necessary to
go to these lengths to obtain free-flowing yet erosion-
protected runoff channels. Small channels are normally V-
shaped, while major conveyance channels have trapezoidal
cross-sections.
In addition to transporting treated effluent to the final
discharge point, the runoff channels must also be capable of
transporting all stormwater runoff from the slopes. The
channels should be designed, as a minimum, to carry runoff
from a storm with a 25 year return frequency. Both
intensity and duration of the storm must be considered. A
frequency analysis of rainfall intensity must be performed
and a rainfall-runoff relationship developed to estimate the
flowrate due to storm runoff that must be carried in the
channels. The local SCS office can provide assistance in
performing this design. References [12, 13] can also be
consulted. In some cases, it may be desirable to provide a
perimeter drainage channel around the OF site to exclude
offsite stormwater from entering the OF drainage channels.
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6.10 System Monitoring and Management
The primary objective of the OF system is to produce a
treated effluent that is within the permit requirements.
Therefore, a monitoring program and a preventive maintenance
program are necessary to ensure continued compliance with
discharge requirements.
6.10.1 Monitoring
6.10.1.1 Influent and Effluent
The influent and effluent monitoring requirements will
usually be dictated by the discharge permit established for
the system by the regulatory authorities. An open channel
flow measuring device (Parshall flume, weir, etc.) equipped
with a continuous flow recorder is generally satisfactory
for monitoring the treated effluent. Most types of portable
or permanent automatic samplers can be used for sampling.
6.10.1.2 Ground Water
The need to install ground water monitoring wells will
generally be determined by the regulatory authorities. In
certain cases, the authorities will also establish the
number and location of monitoring wells. If those decisions
are left to the designer, however, it is advisable to
consider a minimum of two ground water monitoring wells, one
located upstream of ground water movement through the
treatment site which will serve as a background well, and
the second immediately downstream from the site to show any
impacts from the treatment operation.
6.10.1.3 Soils and Vegetation
Suggested monitoring programs for soils and vegetation given
in Sections 4.10.2 and 4.10.3 for SR systems are also appli-
cable to OF systems. If the vegetation on the treatment
site is harvested and used for fodder, samples may be taken
at each harvest and analyzed for various nutritive para-
meters such as percent protein, fiber, total digestible
nutrients, phosphorus, and dry matter.
6.10.2
System Management
6.10.2.1 Operation and Maintenance
Process control involves regulating the distribution system
to provide design application rates and application periods,
and adding water to and releasing water from storage at the
6-32
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appropriate times (see Section 6.4 and 6.5). A routine
operation and maintenance schedule should be followed
including a daily inspection of system components (pumps,
valves, sprinklers, distribution orifices on surface sys-
tems, flowmeters). Application rates and periods should be
checked and maintained within design limits.
6.10.2.2 Crop Management
After the cover crop has been established, the slopes will
need little, if any, maintenance work. It will, however, be
necessary to mow the grass periodically. A few systems have
been operated without cutting, but the tall grass tends to
interfere with maintenance operations. Normal practice has
been to cut the grass two or three times a year. As
mentioned previously, the first cutting may be left on the
slopes. After that, however, it is desirable to remove the
cut grass. The advantages of doing so are that additional
nutrient removal is achieved, channeling problems may be
more readily observed, and revenue can sometimes be produced
by the sale of hay. Depending on the local market condi-
tions, the cost of harvesting can at least be offset by the
sale of hay.
Slopes must be allowed to dry sufficiently such that mowing
equipment can be operated without leaving ruts or tracks
that will later result in channeling of the flow. The
drying time required before mowing varies with the soil and
climatic conditions and can range from a few days to a few
weeks. The downtime required for harvesting can be reduced
by a week or more if green-chop harvesting is practiced
instead of mowing, raking, and baling. However, local
markets for green-chop must exist for this method to be
feasible.
It is common for certain native grasses and weeds to begin
growing on the slopes. Their presence usually has little
impact on treatment efficiency and it is generally not
necessary to eliminate them. However, there are exceptions
and the local extension services should be consulted for
advice.
Proper management of the slopes and the application schedule
will prevent conditions conducive to mosquito breeding.
Other insects are usually no cause for concern, although an
invasion of certain pests such as army worms may be harmful
to the vegetation and may require periodic insecticide
application.
6-33
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6.11 Alternative Design Methods
Recently, two rational methods have been developed for
determining OF design criteria. One, based on detention
time on the slope, was developed at the U.S. Army Cold
Regions Research and Engineering Laboratory (CRREL) [14] .
The other, based on slope distance and application rate was
developed at the University of California, Davis [15]. Both
approaches have been validated with results from other
studies and have been used for preliminary or pilot scale
design of OF systems. A design example comparing the
traditional empirical approach with these two methods can be
found in Appendix C.
6.11.1
CRREL Method
6.11.1.1 Method Description
The basis of the CRREL method is a relationship, between
detention time and mass BOD reduction using performance data
from the CRREL system, and validated with data from the
Utica and University of California, Davis, systems,, With
this relationship, the required detention time can be
calculated for a specified mass BOD reduction. This
detention time is then used in an equation which relates
detention time, slope length, and slope grade to application
rate. Thus, for an OF slope with a given length and grade,
the required application rate can be determined for a
specified detention time or, indirectly, for a specified BOD
reduction. The application rate is then used to calculate
the required land area.
6.11.1.2 Design Procedure
1. Calculate detention time.
The relationship between detention time and mass BOD reduc-
tion is expressed as:
E = (1 - Ae~Kt)100
where E = percent mass BOD removal
A = nonsettleable fraction of BOD in applied
wastewater (constant = 0.52)
K = average kinetic rate constant (0.03 min"-'-)
t = detention time, min
(6-8)
6-34
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2. Calculate average OF rate.
The average OF rate needed to obtain this required detention
time is calculated using the following equation:
q = (0.078S)/(G1/3t) (6-9)
where q = average OF flowrate (qappiied + qrunoff)/2'
m3/h-m of slope width
S = length of section, m
G = slope of section, m/m
t = detention time, min
To use Equation 6-9, section length (s) and section slope
(G) must first be determined by an investigation of the
proposed site. This investigation should yield a section
with length and width dimensions and with a specific section
slope which will be used when determining area
requirements. Actually, more than one section size can be
selected if the topography of the site is such that less
land forming would be required if the site were not composed
of uniform sections. Equation 6-9 would then be used with
the parameters from each section to determine the average OF
rate for each section.
3. Calculate application rate.
The following equation is used to determine the application
rate for each section:
Q = qw/r
where Q = application rate, m^/h per section
q = average^OF flowrate [qapplied +
(6-10)
«m
w = width of section, m
r = (1.0 + runoff fraction)/2
The runoff fraction is the fraction of the applied waste-
water which reaches the runoff collection ditches. The
runoff fraction must be assumed in order to use
Equation 6-10. The runoff fraction ranges from 0.6 to 0.9
6-35
-------
depending on the permeability of the soil and evaporation
losses.
4. Calculate annual loading rate.
The annual loading rate (m3/yr) must be determined for each
section. To do this, the number of days of application per
year must be calculated and the application period must be
selected. Given these values and the loading rates, the
annual loading rates for each section can be calculated.
5. Calculate total annual water volume.
An estimate of the volume of precipitation minus evapotrans-
piration that will collect in the storage or preapplication
treatment basin must be made and added to the annual waste-
water volume to obtain the total annual water volume.,
6. Calculate land area requirements.
The number of sections are calculated using the total annual
water volume and annual application rate to each section.
However, the number of sections of a particular size may be
determined by physical constraints at the site. The land
requirement is now calculated by multiplying the number of
sections of each particular size by its area.
6.11.2 University of California, Davis, (UCD) Method
6.11.2.1 Method Description
The basis for the UCD method is a model which describes BOD
removal as a function of slope length and application rate,
where the application rate has the units m^/h-m of slope
width. This model was developed using performance data from
the UCD system and was substantiated using data from the
CRREL system. By knowing the influent BOD requirements, the
model can predict either the required slope length or
application rate, once the other parameter has been fixed.
Once both parameters are known and a design daily flowrate
is given, the area requirements can be determined.
6.11.2.2 Design Procedure
1. Determine slope length or application rate.
Either slope length or application rate can be calculated,
once the other parameter has been fixed, using the following
equation:
CS/C0 =
(6-11)
6-36
-------
where
co =
A =
K =
S =
q =
n =
concentration BOD at point S, mg/L
initial BOD concentration, mg/L
constant = 0.72
rate coefficient (constant = 0.01975 m/h)
distance downslope, m
application rate, m /h-m slope width
exponent (constant = 0.5)
Site conditions may dictate the allowable slope length, in
which case slope length would be the independent parameter
and application rate would be the computed parameter. If
slope length is not restricted, then application rate should
be used as the independent parameter. Currently, the model
is valid in the range of 0.08 to 0.24 m3/h-m and so the
application rate selected for a design should be within this
range.
The effect of water loss due to evaporation and percolation
is incorporated into the rate coefficient (K). Significant
changes in the value of K are not expected as a result of
changes in water losses normally experienced with OF
systems. Additional field testing is necessary to confirm
this.
2. Select an application period.
See Section 6.4.4 for a discus.sion on selecting an applica-
tion period.
3. Compute the average daily flow to OF system.
To compute the average daily flowrate, the application
season (days of application per year) must be calculated.
Also, the volume of precipitation minus evapotranspiration
that will collect in the storage basin or preapplication
treatment basin must be estimated. With this information
and the average daily wastewater flowrate, the average daily
flow to the OF system can be calculated.
4. Compute the required wetted area.
The wetted area is computed using the following equation:
Area = QS/qP (6-12)
6-37
-------
where Q =
S =
q =
p =
6.11.3
average daily flow to the OF system, m3/d
slope length, m ;
application rate, m3/h-m
application period, h/d
Comparison of Alternative Methods
Although the CRREL and UCD equations appear different, the
basic approach and calculation method are quite similar.
Combining and rearranging Equations 6-8 and 6-9 from the
CRREL method produces:
where M0 =
o
M0 =
S =
/•^ —
q =
Mc/Mrt = 0.52e(~0-0°234S)/(G1/3q)
O \J
mass of BOD at point S, kg
mass of BOD at top of slope, kg
slope length, m
slope grade, m/m
average overland flow, m3/h-m
(6-13)
This is quite similar to the UCD Equation 6-11:
C /C = 0.72e(-°-01975S/q0-5)
s o
(6-14)
All terms are defined previously.
The major differences in these two rational approaches are:
1. Use of slope grade as a variable in CRREL equation
and not in UCD equation.
2. Use of mass units in CRREL equation and concen-
tration units in UCD equation.
3. Value of exponents and coefficients.
6-38
-------
6.12 References
1. Bledsoe, B.E. Developmental Research for Overland Flow
Technology. In: Proceedings of the National Seminar on
Overland Flow Technology, Dallas, Texas. U.S.
Environmental Protection Agency. EPA-600/9-81-022.
September 1980.
2. Hall, D.H., et al. Municipal Wastewater Treatment by
the Overland Flow Method of Land Application.
Environmental Protection Agency. EPA-600/2-79-178.
August 1979.
3. pollock, T.E. Design and Operation of Overland Flow
Systems - The Easley Overland Flow Facility.
Proceedings of Workshop on Overland Flow for Treatment
of Municipal Wastewater. Clemson University. Clemson,
South Carolina. June 1980.
4. Martel, C.J., et al. Wastewater Treatment in Cold
Regions by Overland Flow. CRREL Report 80-7. U.S. Army
Corps of Engineers. Hanover, New Hampshire. 1980.
5. Martel, C.J., et al. Development of a Rational Design
Procedure for Overland Flow Systems. CRREL, U.S. Army
Corp of Engineers, Hanover, New Hampshire. (In
preparation). December 1981.
6. Scott, T.M. and D.M. Fulton. Removal of Pollutants in
the Overland Flow (Grass Filtration) System. Progress
in Water Technology, Vol. 11, Nos. 4 and 5. pp 301-
313. 1979.
7. Peters, R.E., C.R. Lee, and D.J. Bates. Field
Investigations of Overland Flow Treatment of Municipal
Lagoon Effluent. U.S. Army Engineer Waterways Experi-
ment Station, Vicksburg, Massachusetts. (In
preparation).
8. Smith, R.G. Development of a Rational Basis for the
Design of Overland Flow Systems. In: Proceeding of the
National Seminar on Overland Flow Technology. Dallas,
Texas. U.S. Environmental Protection Agency. EPA-
600/9-81-022. September 1980.
9. Thomas, R.E., et al. Overland Flow Treatment of Raw
Wastewater with Enhanced phosphorus Removal. USEPA,
Office of Research and Development. EPA-660/2-76-131.
1976.
6-39
-------
10. Peters, R.E., et al. Field Investigations of Advanced
Treatment of Municipal Wastewater by Overland Flow.
Volume 2. Proceedings of the International Symposium on
Land Treatment of Wastewater. Hanover, New Hampshire.
August 1978.
11. Law, J.P., et al. Nutrient Removal from Cannery Wastes
by Spray Irrigation of Grassland. Water Pollution Con-
trol Research Series, 16080-11/69. U.S. Department of
the Interior. Washington, D.C. November 1969.
12. U.S. Dept. of Commerce. Rainfall Frequency Atlas of the
United States for Durations from 30 minutes to 24 hours
and Return Periods from 1-100 Years. Technical Paper
40. 1961.
13. Water Resources Council. A Uniform Technique for
Determing Flood Flow Frequencies. Bulletin No. 15.
1967.
14. Martel, C.J. et al. Rational Design of Overland Flow
Systems. Proceedings of the ASCE National Conference of
Environmental Engineering. July 1980.
15. Smith, R.G. Development of a Predictive Model to
Describe the Removal of Organic Material with the Over-
land Flow Treatment Process. Ph.D. Thesis. University
of California, Davis. 1980.
6-40
-------
CHAPTER 7
SMALL SYSTEMS
7.1 Introduction
The procedures in this chapter are intended primarily for
systems with wastewater flows of 950 m3/d (250,000 gal/d) or
less, but, in some situations, may be used for flows up to
3,785 m3/d (1 Mgal/d). The objectives for land treatment
systems are the same regardless of the community size.
However, the design of small systems should include special
emphasis on the ease of operation and on minimizing
construction and operating costs. Most communities in this
size range cannot hire full-time treatment plant operators,
and the treatment system must be capable of providing
consistent, reliable treatment in the absence of frequent
attention. In general, most treatment systems that meet
these objectives are nonmechanical and have no discharge to
surface waters.
The procedures described in this chapter can be used to
streamline Phase 1 of the planning process. Limited field
work should be conducted during Phase 2 to verify Phase 1
assumptions and to optimize design criteria, particularly
when designing RI systems. When more detailed planning or
design procedures are needed, the engineer should refer to
Chapters 4, 5, and 6.
7.2 Facility planning
The procedures for planning and design of small systems are
similar to, but less detailed than, the requirements for
large facilities. Maximum use is made of local expertise
and existing published information. The area Soil
Conservation Service (SCS) staff, the county agent, and
local farmers can all provide assistance and advice. The
types of information that should be obtained from these
local or published sources are summarized in Table 7-1. The
level of detail and the period over which data have been
recorded will vary with the community.
7.2.1
Process Considerations
Any of the three major land treatment processes (SR, RI, and
OF) or combinations of these processes are suitable for
small communities. Seepage ponds have been used success-
fully in many small communities and are similar to RI in
that relatively high hydraulic loading rates are used and
treatment occurs as wastewater percolates through the
7-1
-------
soil. The primary difference is that seepage ponds are
loaded continuously, whereas RI systems use a loading cycle
that includes both application and drying periods, resulting
in improved treatment and maximum long-term infiltration
rates. Other processes, including complete retention and
controlled discharge pond systems, also have potential for
small communities. information on these pond systems can be
found in the EPA Process Design Manual for Wastewater
Treatment Ponds [1].
TABLE 7-1
TYPES AND SOURCES OF DATA REQUIRED FOR DESIGN
OF SMALL LAND TREATMENT SYSTEMS
Type of data
Principal sources
Wastewater quantity and quality
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 ground water
discharge requirements
Ground water (depth and quality)
NOAA, local airports,
NOAA, local airports.
Local Wastewater authorities
SCS soil survey
SCS soil survey,
newspapers
SCS soil survey,
newspapers
SCS soil survey, NOAA, local airports,
newspapers, agricultural extension service
SCS soil survey, aerial photographs 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,
of nearby wells
USGS, drillers' logs
Design features, site characteristics, and renovated water
quality of the three major land treatment processes are
summarized in Tables 1-1, 1-2, and 1-3. General charac-
teristics of small land treatment systems are summarized in
Table 7-2. This table should be used as a guide to process
selection. Final criteria should be determined during
facilities design.
7.2.1.1 Operation and Ownership Alternatives
Small systems may be•owned and operated by a municipality or
wastewater authority, although municipal ownership and
operation are not always necessary. In all cases, overall
system management should be under the control of the muni-
cipal agency held responsible for performance. Oppor-
tunities often exist, and should be sought, for contractual
7-2
-------
agreements with local farmers to take and use partially
treated wastewater for irrigation and other purposes. By
taking advantage of such agreements, a community can avoid
investments in equipment and land, and can eliminate the
need to hire and train new employees.
TABLE 7-2
GENERAL CHARACTERISTICS OF SMALL
«950 m3/d OR <250,000 gal/d) LAND TREATMENT SYSTEMS
Process
Slow rate
Surface
application
Sprinkler
application
Minimum
preappl ication
treatment Crops
Primary
Ponds
Annuals
Perennials
or double
cropping
Application season
Growing season
(3-5 months)
Year-round with
exception of down-
time for planting,
harvesting.
maintenance, and
cold-weather
storage if necessary
Application
schedule
8 h, 1 d/wk
8 h, 1 d/wk
Storage
requirements
See Figure 2-5
See Figure 2-5
Rapid
infiltration
Overland
flow
Primary
Screening and
comminution
Not
applicable
Perennial
grasses
Year-round
Year-round with
exception of down-
time for planting,
harvesting,
maintenance, and
cold-weather
storage if necessary
2 d application, 7-30 d for
10-18 d drying emergencies
8-12 h/d,
5-7 d/wk
See Figure 2-5
Arrangements between local farmers and communities can
involve any of several alternatives. For example, the
community can provide partially treated wastewater to a
farmer, who is then responsible for all components of the
land treatment process. Alternatively, the community may
provide and maintain irrigation equipment that is used by a
farmer who is responsible for all farming operations. In
either case, the farmer agrees to take a predetermined
amount of water each year to use on his own land. A third
alternative is for the community to purchase or lease land
and equipment for land treatment and assume responsiblity
for all aspects of the system except planting, cultivating,
and harvesting. These three tasks are accomplished by the
local farmer on a contractual or crop sharing basis.
Land used for wastewater application either can be purchased
outright (fee-simple acquisition) or leased on a long-term
basis. Long-term leases should include the items summarized
in Table 2-15. Grant eligible costs of a long-term lease
are paid to the community in a lump sum at the beginning of
the leasing term.
7-3
-------
Contractual arrangements between local farmers and com-
munities should specify the following:
• The duration of the agreement.
• Projected quality of water that will be delivered
to farmers.
• Any limits on application rates, buffer zones, or
runoff control.
• Any limitations on crop types due to local or state,
requirements.
• Cost to local farmer and/or community.
• Method and timing of payments (generally annual).
• Method of transferring contract.
Arrangements between local farmers and communities are most
practical when forage grasses or grazing animals are
involved, since there is less constraint on application of
wastewater in years of high rainfall. Other agricultural
crops with shorter growing seasons or which are less water
tolerant than forage grasses may require additional storage
or other considerations. Most arrangements have involved SR
systems. Overland flow systems normally are owned by the
community to ensure control over system operation. However,
contract harvest of OF grasses is advantageous in com-
munities that lack the necessary equipment and expertise.
Rapid infiltration systems also tend to be municipally owned
and operated to ensure control over the wastewater treatment
process. No crops are involved; thus, the only potential
agreements between farmer and community are for land
leasing, property easements, or use of recovered water.
7.2.1.2 Water Rights Considerations
In the western states, water rights must be considered.
Return of renovated water, including OF runoff and SR and RI
percolate, to the original point of community discharge may
be necessary. Sometimes, RI basins can be located so that
seepage and subflow proceed directly to the stream or water
body (Figure l-2c; Section 5.7.1) that received discharge
from the previous system. The local water rights situation
should be checked with the state agency in charge.
7-4
-------
7.2.1.3 Preapplication Treatment
Most land treatment systems include a preapplication
treatment step. In small communities, wastewater storage
often is provided in the preapplication treatment process.
The use of existing treatment facilities may reduce the
capital cost of a land treatment system but may necessitate
construction of separate storage facilities.
Preapplication treatment facilities should be as close to
the application site as the topography, land availability,
and system objectives allow. Most existing treatment
facilities serving small communities are located at a
relatively low elevation to allow a gravity sewer system.
Thus, if existing facilities are used, it probably will not
be possible to locate the application site near the
preapplication treatment system. Instead, it is often
necessary to pump the partially treated wastewater to the
application site.
7.2.1.4 Staffing Requirements
Staffing requirements depend on the types of preapplication
treatment and land treatment, the size of the system, and
whether the community or a farmer operates the land
treatment portion of the system. Staffing requirements for
municipally owned and operated ' systems are presented in
Figure 2-9. Staffing requirements at a variety of smaller
systems are shown in Table 7-3.
7.2.2
Site Selection
Before a community can begin the site selection process, it
must be able to estimate the amount of • land that a land
treatment system will require. Approximate land area
requirements have been plotted as a function of average
design flow for each of the three major types of land
treatment in Figure 7-1. Although land area estimates are
.shown only for flows of 950 m3/d (250,000 gal/d) or less,
land requirements for flows of up to 3,785 m3/d (1 Mgal/d)
can be extrapolated from the curves.
In addition, for SR application periods between 6 a.nd 12
months per year, land area requirements can be interpolated
from the two SR curves. For OF application periods greater
than or less than 10.5 months per year and RI application
periods less than 12 months per year, land area requirements
can be extrapolated from the OF and RI curves,
respectively. Figure 7-1 can be used to determine what size
site to search for during the site selection process, but
should . not be used for design purposes. Final land
7-5
-------
requirements will vary with the crop grown, site char-
acteristics, and whether the site is operated by the
community or a local farmer.
TABLE 7-3
TYPICAL STAFFING REQUIREMENTS
AT SMALL SYSTEMS
Municipal staff requirements
1980 flow
Location
n3/d
gal/d Site use
Pre- Land
application treatment Annual
components, components, total,
Site control man-days/yr man-days/yr man-days
Chapman ,
Nebraska
Falkner,
Mississippi
Kennett
Square,
Pennsylvania
Ravenna,
Michigan
Santa Anna,
Texas
Way land,
Michigan
Winters,
Texas
66
106
190
275
285
950
1,130
17,400
28,000
50,000
72,000
75,000
250,000
297,000
Grass (RI)
Grasses (OF)
Forest
Open, un-
cultivated
fields
Alfalfa,
grass,
pasture
Hay , corn
Hay
City
City <89
City 130
City 68
Farmer owns, 54
city operates
equipment
City owns, 104
farmer
harvests
Farmer owned 52
<165a
<93 <182
68 198
7 75
46 100
68 172
0 52
Note: Preapplication treatment by ponds.
a. Includes labor spent maintaining three pumping stations in collection system.
The site selection process can be divided into parts: site
identification and site screening (Sections 2.2.4 and
2.2.5). In small communities, the first step in identifying
potential land treatment sites is to determine whether any
of the local farmers are willing to participate in a land
treatment project or are interested in selling or leasing
property for a land treatment site. Questionnaires and
meetings with local groups can be particularly helpful when
making this determination. If one or more farmers are
interested in participating and have enough land to take and
use the wastewater, or are interested in selling or leasing
enough property for a land treatment site, site
investigation can begin. If the local farmers are not
interested or if the interested farmers do not have enough
suitable land, it will be necessary to identify and screen
potential sites using existing soils, topographical,
hydrogeological, and land use data. The identif icaition and
7-6
-------
(ha)
(30).
acres
(25)—
(20)-
(15)—
(10)—
(5)—
gil/d
50.008
190.000
150.000 2 00.000 250.000
(»3/d) (100) (200) (300) (400) (500) (600) (700) (800) (900)(1.000)
AVERAGE DESIGN tASTEBATER FLO I! OF COMMUNITY
It
NUNIER «F MONTHS PER YEAR THAT MSTEIATER IS APPLIED TO LAND.
FIGURE 7-1
LAND AREA ESTIMATES FOR PRELIMINARY PLANNING PURPOSES
(INCLUDING LAND FOR PREAPPL I CAT I ON TREATMENT)
7-7
-------
screening processes are detailed in Chapter 2; only the
highlights are presented in this chapter.
As discussed in Section 2.2.4, existing data can be used to
classify broad areas of land near the community according to
their land treatment suitability. Factors that should be
considered include current and planned land use, parcel
size, topography, present vegetative cover, susceptibility
to flooding, soil texture, geology, distance from the area
where wastewater is generated, and need for underdrainage
(based on recommendations of local SCS representative).
Generally, the characteristics of the closest suitable site
will greatly influence the selection of the land treatment
system type to be designed. The detailed rating factor
approach in Chapter 2 is usually unnecessary because
economics will limit the number of sites that can be
considered.
7.2.3
Site Investigations
As in larger communities, field investigations are conducted
to verify any data used to select sites and- to verify
overall land treatment suitability. However, the level of
effort needed to conduct site investigations in smaller
communities is much lower. In smaller communities, it is
more practical to conduct minimal field investigations and
assume relatively conservative design criteria than to
complete the extensive and expensive investigations needed
to pinpoint optimal design criteria.
Generally, soils information available from the area SCS
office and limited field observations will yield sufficient
information for most SR and OF system designs. The first
step in the site investigation procedure should be to visit
the potential site with a local SCS representative. The
primary purpose of these site visits is to confirm the data
used to identify and select suitable sites. A few, shallow,
hand-auger borings to identify the soil profile should be
conducted to confirm the SCS data and check for impermeable
layers or shallow ground water. Infiltraton tests (see
Section 3.4.1) are usually only needed for RI sites. For RI
sites, a few backhoe pits to 3m (10 ft) or more are also
recommended, but drill holes are usually deferred until
preliminary design.
If crops will be grown, a site visit with the county agent
or local agricultural or forestry advisor is recommended.
The purpose of this site visit is to obtain advice on the
type of crops to use and on crop management practices.,
7-8
-------
7.3 Facility Design
Because only limited field investigations are conducted in
small .communities, it is important to use conservative
design criteria. The application schedules and storage
requirements presented in Table 7-2 are examples of
conservative criteria. Other design criteria that must be
identified include the level and type of preapplication
treatment and storage, the land area required, wastewater
loading rates and schedules, and pumping needs and other
mechanical details. Land area requirements are estimated
during the planning process and are refined as the hydraulic
loading rate, method of preapplication treatment, and
storage requirements are defined more precisely. ,
7.3.1
Preapplication Treatment and Storage
EPA guidance on minimum levels of preapplication treatment
is summarized in Table 7-4.
TABLE 7-4
RECOMMENDED LEVEL OF
PREAPPLICATION TREATMENT
Type of land
treatment
Situation
Recommended
preapplication treatment
Slow rate Isolated location; restricted public
access; crops not for human consumption.
Controlled agricultural irrigation;
crops not to be eaten raw by humans.
Public access areas such as parks,
golf courses.
Rapid Isolated location; restricted public
infiltration access.
Urban location; controlled public
access.
Overland flow Isolated site; no public access.
Urban location; no public access.
Primary.
Biological (ponds or in-plant
processes) with control of fecal
coliforms to <1,000 MPN/100 mL.
Biological (ponds or in-plant
processes) with disinfection to
log mean fecal coliforms of
-200 MPN/100 mL.
Prim'ary.
Biological (ponds or.in-plant
processes).
Screening or comminution.
Screening or comminution with
aeration to control odors during
storage or application.
In small communities, ponds are usually the most practical
form of preapplication treatment and storage. They are
relatively easy to operate, require minimal maintenance, are
less expensive than many types of treatment, and eliminate
the need for separate storage facilities. Although some
communities will want to use or upgrade other existing
7-9
-------
facilities for use as preapplication treatment facilities,
many small communities will1 find it advantageous to convert
to pond systems because of their consistency, reliability,
flexibility, ease of operation and maintenance, and cost.
Generally, ponds are constructed with one to three cells.
In a three-cell system, the first cell is usually small and
may be aerated to control odors. Alternatively, if
sufficient land is available, the first cell may be designed
as a facultative cell with a BOD loading of about
120 kg/ha-d (107 Ib/acre-d). The water level in this cell
is usually constant and can be controlled with an adjustable
overflow weir or a gated manhole. The final cells can be
used for storage and flow equalization. For this reason,
these two cells are made as deep as possible. Typical
design parameters for several types of ponds are presented
in Table 7-5.
TABLE 7-5
TYPICAL DESIGN PARAMETERS FOR SEVERAL
TYPES OF PONDS [2]
Aerobic Facultative Anaerobic
Pond size (individual
cells) , ha
Detention time, d
Depth , m
BOD5 loading, kg/ha-d
BOD 5 removed, %
Effluent suspended
solids , mg/L
<4
10-40
1-1.5
40-120
80-95
80-140
1-4
7-30
1-2.5
15-200
80-95
40-100
0.2-1
20-50
2.5-5
200-500
50-85
80-160
1 ha = 2.47 acres
1 m = 3.28 ft
1 kg/ha-d = 0.893 Ib/acre-d
An additional benefit of. using ponds is that the long
detention times (30 days or more) promote nitrogen removal
and pathogen inactivation. Preliminary models to estimate
nitrogen and bacterial removals in ponds are given in
Section 4.4.1.
7.3.2
Hydraulic Loading Rates
The first step in designing the land treatment portion of
the system is to select a hydraulic loading rate. As an
initial assumption, the hydraulic loading rate for SR and RI
7-10
-------
systems is based on the most limiting SCS permeability
classification of the soils at the selected site. Hydraulic
loading rates that may be used in each of the three major
types of land treatment systems have been plotted as a
function of SCS permeability classification in Figures 7-2
and 7-3. Both figures represent average hydraulic loading
rates. In Figures 7-2 and 7-3, whenever a range of loading
rates is given, the lower end of the range should be used
for primary effluents, the mid zone for pond effluents, and'
the upper portion of the range for secondary effluent.
Lower loading rates than shown in Figures 7-2 and 7-3 can be
used but will require more land. If OF is used to polish
trickling filter or activated sludge effluent, loading rates
of 30 to 40 cm/wk (12 to 16 in./wk) can be used.
Loading rates at SR and RI systems that overlie potential
drinking water aquifers may be limited by nitrogen loading
rather than soil permeability. At these systems, the ground
water concentration of nitrate is limited to 10 mg/L as'
nitrogen at the project boundary (or the background nitrate
concentration, if it is greater than 10 mg/L). Rapid
infiltration systems should not be located above drinking
water aquifers unless thorough field testing is conducted to
verify that the nitrate standard can be met or unl'ess the
renovated water will be recovered (Sections 5.4.3.1
and 5.7).
7.3.2.1
Slow Rate
For SR systems .located above drinking water aquifers, the
following equation should be used to calculate the maximum
allowable nitrogen loading rate based on nitrogen limits:
where L.
'w(n)
Pr
ET
U
Cp(Pr - ET) + 10U
Lw(n) = (1 - f)(Cn - Cp)
(7-1)
wastewater hydraulic loading rate based
on nitrogen limits, cm/yr (in./yr)
percolate nitrogen concentration,
mg/L = 10 mg/L
precipitation rate, cm/yr (in./yr)
evapotranspiration rate, cm/yr (in./yr)
crop nitrogen uptake rate, kg/ha-yr
(Ib/acre-yr)
7-11
-------
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7
CLEAR WATER PERMEABILITY OF MOST LIMITING SOIL LAYER
i n./h
cm/h
< 2.0
< 5.1
2-6
5.1-15
6-20
15-51
>20
>51
FIGURE 7-3
TYPICAL ANNUAL HYDRAULIC LOADING RITE OF SMALL Rl SYSTEMS
7-13
-------
f = fraction of applied nitrogen removed
by volatilizaton, denitrification, and
storage =0.15
:n = nitrogen concentration in applied
wastewater, mg/L
Conservative values should be assumed for nitrogen losses
and crop uptake rates to ensure adequate nitrogen removal.
For this reason, nitrogen storage and ammonia volatilization
are ignored in Equation 7-1 and the denitrification rate is
assumed to equal 15% of the nitrogen loading rate. Nitrogen
losses during preapplication treatment depend on the type of
treatment. For conventional primary or secondary treatment,
nitrogen loss is negligible. As discussed in Section 4.4.1,
the nitrogen loss in a pond can be estimated from
Equation 4-1.
Conservative nitrogen uptake values are -presented for
typical crops in Table 7-6.
TABLE 7-6
NITROGEN UPTAKE RATES FOR SELECTED CROPSa
Crop
Nitrogen uptake
rate, kg/ha-yr
Forage
Alfalfa 300
Bromegrass 130
Coastal bermudagrass 400
Kentucky bluegrass 200
Quackgrass 240
Reed canarygrass 340
Ryegrass 200
Sweet clover 180
Tall fescue 160
Field
Barley
Corn
Cotton
Milomaize (sorghum)
Potatoes
Soybeans
Wheat
70
180
80
90
230
110
60
a. Values represent lower end of ranges
presented in Table 4-12 and are
intended for use in Equation 7-1.
1 kg/ha-d = 0-. 893 lb/acre-d
7-m
-------
The calculated value from Equation 7-1 of Lw(n) ^-s tnen
divided by the number of weeks per year or expected
operation and compared with the hydraulic loading rate
obtained from Figure 7-2. At this point, the engineer should
check with the local agricultural or forestry adviser to
verify that the selected crop is tolerant of the lower of
the two calculated loading rates. If so, the lower of the
two loading rates should be used for design purposes. If
the selected crop cannot tolerate the design loading rate, a
crop with higher moisture tolerance or nitrogen uptake
should be selected.
In small communities, the application schedules presented in
Table 7-2 are recommended. Again, if a farmer agrees to
take and use the wastewater on his own land, he may continue
to use any application schedule that has resulted in a well-
managed agricultural system.
7.3.2.2 Rapid Infiltration
Hydraulic loading rates for small RI systems can be
estimated using Figure 7-3. The permeability of the most
restricting soil layer in the soil profile can be measured
using techniques described in Section 3.4. In Figure 7-3,
the lower curve should be used when primary or pond effluent
is to be applied, and the upper curve can be used when
secondary effluent is to be applied.
7.3.2.3
Overland Flow
The hydraulic loading rates for small OF systems are the
same as recommended in Chapter 6, Table 6-5. Because of
operational considerations, it is recommended that either
8 or 12 h/d application periods be used, whichever is most
convenient. Simple automation using time switches and
solenoid valves allows flexibility in selecting application
periods.
7.3.3
Land Area Requirements
Once the hydraulic loading rate has been determined, the
amount of land required for land treatment can be
calculated. For systems that operate year-round, the land
required is simply the design average wastewater flow
divided by the annual hydraulic loading rate. For systems
that are not operated year-round, the area required is
calculated as follows:
A =
Q(365)(100)
(Lw)(t)(10,000)
(Metric units)
(7-2)
7-15
-------
A =
Q(365)(100)
(Lw)(t)(7.48)(43,560)
(U.S. customary units)
where A =
Q =
Lw "
t =
area required, ha (acres)
design average wastewater flow, m^/d
(gal/d)
hydraulic loading rate, cm/wk (in./wk)
(see Section 7.3.2)
number of weeks per year during which
wastewater is applied
For example, if a system is operated 43 weeks out of the
year, the acceptable hydraulic loading rate is 5»8 cm/wk
(2.3 in./wk), and the design average wastewater flow is
900 m3/d (240,000 gal/d), the area required for land
treatment is:
A =
(Q)(365)(100)
Lw)(t)(10,000)
= (900)(365)
(5,8)(43)(10,000)
= 13.2 ha (32.5 acres)
Additional land is required for preapplication treatment,
storage, access roads, and in some cases buffer zones. A
preliminary allowance of 15 to 20% of the field area is
often made for roads, buffer zones, and small unusable land
areas. Land requirements for preapplication treatment and
storage are determined in the preliminary design of these
components.
7.3.4
Distribution Systems
Detailed information on SR distribution systems is presented
in Section 4.7 and Appendix E. Additional considerations
for small communities are presented in this section.
Distribution methods are selected on the basis of terrain,
type of land treatment system, and local practice. In small
communities, it is prudent to choose a distribution method
that is used locally or that will result in a system that
requires only part-time operational attention. If a locally
7-16
-------
used distribution method is selected, any specialized
equipment and necessary expertise will be more readily
available.
Traveling guns require relatively high amounts of labor and
are more adaptable to systems where several, odd-shaped
fields are irrigated each season, so they are usually owned
and operated by a local farmer. Both solid set and center
pivot irrigation systems can be adapted to either muni-
cipally owned or farmer owned small irrigation systems.
Center pivots will generally not be applicable for very
small SR systems (below 16 ha or 40 acres).
Distribution systems for Rl and OF facilities are described
in Sections 5.6.1 and 6.6, respectively.
7.4 Typical Small Community Systems
To illustrate some of the features of small scale land
treatment systems, four cases are described in this sec-
tion. These include two SR options, one RI, and one OF
system. It is not intended that the site specific criteria
for these four systems be applied for process design else-
where. The concepts will be valid, but specific criteria
will depend on individual site characteristics.
7.4.1 Slow Rate Forage System
7.4.1.1 Introduction
A pond system using SR application of wastewater onto
several grassed plots is often a workable design for a small
community that does not generate sufficient wastewater flow
to be economically beneficial for irrigating a cash crop.
7.4.1.2 Population
The community, located in eastern Nebraska, has a present
population of approximately 300. The design population for
the treatment facility is 310.
7.4.1.3
Flow
The flow to the treatment facility is strictly domestic
wastewater, because there are no industries in the
community. The system is designed to treat an average per
capita flow of 0.25 m3/d (65 gal/d), or a total flow of
76 m3/d (20,000 gal/d). Low per capita flows are very
common for small communities having no industries and very
minimal commercial development. Actual flows to the system
have gradually increased as residents switched from their
7-17
-------
old septic tank systems to the municipal collection
system. Flows are commonly in the 57 to 95 m3/d (15,000 to
25,000 gal/d) range.
7.4.1.4
Climate
The normal annual precipitation is 84 cm/yr (33 in./yr) and
the average annual gross lake evaporation is 109 cm/yr
(43 in./yr). The mean number of days in which the maximum
daily temperature exceeds 32 °C (90 °F) is 40, and the mean
number of days in which the minimum daily temperature falls
below 0 °C (32 °F) is 130. In an average year, there are
232 days between the last killing frost in the spring and
the first frost in the fall.
7.4.1.5
Site Characteristics
The silt loam soils at the proposed treatment site are deep,
nearly level, and well drained. Surface soils are silt loam
and the subsoils are silty clay loam. Permeability is
moderately slow in the 1.0 to 1.5 cm/h (0.4 to 0.6 in./h)
range. • The site is relatively level and does not overlie a
potable aquifer.
7.4.1.6 Treatment Facility Design
The treatment facility consists of a single cell unaerated
pond followed by a series of four grassed plots which
receive wastewater from the pond. Effluent is not
disinfected. The pond provides both wastewater treatment
and storage. The degree of treatment in the pond is not a
significant factor in design, other than providing at least
the necessary primary treatment for removal of heavy solids
and rags that could plug distribution piping. The storage
volume facilitates operation of the system, since it is not
necessary to have an overflow during periods of heavy
precipitation or other unfavorable conditions, and the
grassed plots can be allowed to dry between applications to
allow mowing and maintenance. The design information is
summarized in- Table 7-7. ;
The single cell pond is sized similarly to the first cell of
a conventional facultative pond system. The design BOD
loading is 34 kg/ha:d (31 lb/acre:d), a generally accepted
loading rate in Nebraska, and results in minimal septicity
or blue-green algae problems. Higher loadings may be
allowed by other states where ponds do not become ice
covered in the winter. By having a 1.8 m (6 ft) water
depth, 1.2 m (4 ft) of storage volume is provided above the
0.6 m (2 ft) water level. The storage volume in the 0.7 ha
(1.7 acre) pond is 7,378 m3 (1.95 Mgal) above the 0.6 m
7-18
-------
(2 ft) depth. This capacity provides adequate storage
during the approximately 133 days (19 weeks) each winter
that the plots are not irrigated, based on the design flow
and seepage losses of 0.3 cm (0.125 in.) per day.
TABLE 7-7
. DESIGN INFORMATION
FOR SR SYSTEM
Design flow, rfr/d
BOD loading, kg/d
Design population
Treatment pond
Size, ha
Depth, m
Capacity above 0.6m level,
Bermed grassed plots
Number
Size (each), ha
m-
76
24
310
0.7
1.8
7,378
4
0.35
The total size of the grassed plots was determined as
follows. Calculated design losses from the pond, including
seepage and net evapotranspiration, totaled 142 cm/yr
(56 in./yr). Using this value, the design overflow from the
pond (Q0) was calculated: • , •.
Q0 = (76 m3/d x 365 d/yr)
- (142 cm/yr x 1 m/100 cm x 7,000 m2
=-17,800 m3/yr (4.7,Mgal/yr)
(7-3)
Using the limiting soil permeability of l.Q cm/h
(0.4 in./h) , a hydraulic loading rate of 3.8 cm/wk
(1.5 in-./wk) was obtained from Figure 7-2. Next, the area
required for SR was calculated (Equation 7-4):
A = [(17,800 m3)/(3.8 cm/wk x 33 wk)] (7-4)
x (100 cm/m) x (ha/10,000 m2)
= 1.4 ha (3.5 acres)
Four grassed plots, each 0.35 ha (0.88 acre) were designed.
t
Multiple small plots were selected for several reasons.
Each plot is small enough to facilitate uniform flooding.
7-19
-------
Also, the use of multiple plots makes it possible for the
operator to mow or make repairs on a dry plot while the
other plots are being used for wastewater application.
Any one plot does not receive more water than can percolate
within 12 hours. This helps prevent damage to the grass
cover and also provides some leeway in case precipitation is
received after a cell has been flooded. Ignoring evapo-
transpiration, the limiting soil permeability rate of 1.0
cm/h (0.4 in./h) dictates that not more than 12 cm (4»7 in.)
can be applied per each 1 day application period. To obtain
an average hydraulic loading rate ,of 3.8 cm/wk (1.5 in./wk),
each application period must be followed by 21 days of
drying. in practice, one plot is flooded on each of 4 con-
secutive days. After an additional 18 days of drying,
flooding is resumed. This sequence continues for approxi-
mately 232 days. During the winter (approximately 133
days), all wastewater is stored•in the pond.
The overflow control structure designed for this system
requires minimal operator attention. The structure uses an
overflow pipe that can be raised or lowered in increments to
release the necessary volume of effluent. A cross-sectional
detail of the structure is included in Figure 7-4.
The grassed plots are quite shallow, having only 0.6 m
(2 ft) high dikes. The slopes are 4:1, making the basins
readily accessible to mowing equipment. This design helped
minimize the amount of earthwork necessary during con-
struction and also maximized the amount of usable area since
less dike area was required. Local SCS offices and publi-
cations were consulted to obtain the necessary information
for selecting a seeding mixture, which needed to be suitable
for periodic flooding. A mixture of Reed canarygrass,
switchgrass, redtop, and intermediate wheatgrass was
planted. •
Effluent distribution to the grassed plots is by gated pipe
along the toe of the inner slope of one side. This allows
more uniform flooding of the basin as compared to a single
inlet structure ^ The area under the pipe and in the
direction of flow from the pipe has a layer of rock to
minimize erosion and channelization of the flow.
7-2Q
-------
TWIST LINK
MACHINE CHAIN
REINFORCED
CONCRETE PIPE
CONCRETE FILLET
SHEAR GATES
CAST IRON
PIPE RISER
FIGURE 7-4
OVERFLOW CONTROL STRUCTURE FOR
POND DISCHARGE TO SR SYSTEM
7.4.1.7
Performance
When the facility was first started up, flows were quite low
until all of the residences were connected. The pond
provided complete retention of all flows during the first
2 years of operation, with no overflow to the grassed
plots. In the third year, only two application periods were
used: one in the spring and one in the fall. The number
of applications per year has been gradually increasing as
flows have approached the anticipated design loadings. A
good stand of grass has been maintained in the application
plots. This grass cover enhances infiltration and provides
maximum evapotranspiration of the wastewater applied.
7.4.1.8 Staffing
The system requires only one part-time operator. Duties at
the pond include mowing, valve operation, weed control, and
maintenance of fences, access road, valves, and distribution
piping.
7-21
-------
7.4.2 Slow Rate Forest System
7.4.2.1 Introduction
This forested SR system is located at Kennett Square in
southeastern Pennsylvania. The system, consisting of a
series of treatment ponds followed by sprinkler application,
has been operated since 1973. The system serves two
retirement communities and is operated by the wastewater
authority.
7.4.2.2 Population and Flow
The population of the two communities totals 725. The flow,
which is entirely domestic wastewater, is currently 189 mP/d
(50,000 gal/d). The design flow is 265 m3/d (70,000 gal/d).
7.4.2.3
Climate
Precipitation and evaporation are nearly equal with average
annual precipitation at 110 cm (43 in.) and average annual
pan evaporation estimated to be 120 cm (47 in.). Average
annual temperature is 11.9 °C (53.4 °F).
7.4.2.4 Site Characteristics
The application area is covered with a native stand of
beech, maple, poplar, and oak trees. The soils are basi-
cally silt loams with predominant slopes between 3 and 8%.
Soils are moderately deep and permeable with slightly acidic
pH values. The soil permeability of 1.5 to 5 cm/h (0.6 to 2
in./h) would support a loading rate of 5 cm/wk (2 in./wk) or
more on a hydraulic loading basis (Figure 7-2).
7.4.2.5 Treatment Facility Design
The layout of treatment facilities is presented in
Figure 7-5; photographs of the treatment pond and sprinkler
application are shown in Figure 7-6. Wastewater is treated
in three treatment ponds, disinfected, and applied via
sprinklers onto 3.24 ha (8 acres). The first pond is
aerated, covers a surface area of 0.128 ha (0..3 acre), and
is 4 m (13 ft) deep. Aeration is provided by a 7.5 kW
(10 hp) floating surface aerator. Wastewater then flows by
gravity through two nonaerated ponds that are 2.1 m (7 ft)
and 2.4 m (8 ft) deep and cover 0.68 ha (1.69 acres) and
0.30 ha (0.75 acre), respectively. Total detention in the
three ponds is 80 d at current flows.
7-22
-------
-ICrt 0,3
LU
I—
CO
ce
oo
7-23
-------
TREATMENT POND
SPRINKLER APPLICATION IN EXISTING HARDWOOD FOREST
FIGURE 7-6
SR FACILITIES AT KENNETT SQUARE, PENNSYLVANIA
7-24
-------
The design hydraulic loading rate is 5.1 cm/wk (2 in./wk),
which is the State of Pennsylvania guideline. The nitrogen
loading is 279 kg/ha-yr (248 lb/acre-yr) for the design flow
which is somewhat high for application to an existing
hardwood forest. Because of the relatively mild climate,
year-round application was planned.
The application area is divided into 14 separate areas or
plots. Wastewater is applied for 24 hours on 4 to 6 plots
each day, 5 days per week. On this schedule, an individual
plot receives effluent every fourth day. Storage for
weekends and cold weather is possible in the treatment
ponds. The main lines and laterals are buried with drain
valves to drain the lines after applications are complete.
A buffer zone of approximately 46 to 61 m (150 to 200 ft) is
maintained between the application site and the nearest
residence. This area is covered with grass and trees. All
stormwater runoff from the community is diverted around the
site. Stormwater generated onsite is allowed to run off
onto adjacent land. Site access is controlled by signs and
fencing; however, there are some nature trails in the area
to which access is permitted.
7.4.2.6 Operation and Performance
The system has operated satisfactorily for 8 years. During
winter operation, sprinkling is practiced until the
temperature drops to -6.7 °C (20 °F). Frost heave problems
have affected valve boxes placed in the forest. Screening
of the applied water is needed to avoid nozzle clogging from
debris that falls into the ponds.
Treatment performance of the system can be measured using
the ground water monitoring wells. The depth to ground
water varies from 3.6 to 9.1 m (12 to 30 ft) in the 11
monitoring wells. The range of nitrate nitrogen concen-
trations is from 0 to 4.8 mg/L and indicates satisfactory
performance, in spite of the relatively high nitrogen
loading (Section 7.4.2.5).
7.4.2.7 Staffing and Budget
One operator spends approximately 6 h/d, 5 d/wk operating
and maintaining the wastewater treatment system. Of this
total, 2 h/d is associated with the SR land treatment
system.
A total of $15,000/yr is budgeted for operation and main-
tenance of the system. Of this total, 37% or $4,070/yr is
associated with land treatment.
7-25
-------
7.4.3 Rapid Infiltration
7.4.3.1 Introduction
An RI system for a small community need not be designed for
intensive wastewater applications at maximum RI rates, which
could involve the need for recovery of renovated water and a
relatively high level of operation and management. Instead,
the design can be simplified to meet the objectives of
wastewater treatment and still maintain ease of operation.
The following example illustrates an adaptation of an RI
system that normally operates at very low application rates,
but has the capability of treating the exceptionally high
flows that occur occasionally.
7.4.3.2 Population
The facility serves the small, rural community of Chapman in
east central Nebraska.. The community is primarily resi-
dential, with a small commercial district, but with no in-
dustries. The present population is estimated to be 400.
7.4.3.3
Flow
The treatment pond was designed to serve a population of
500. When the treatment facility was designed, there was no
past history of wastewater flows and an average per capita
contribution of 0.26 m3/d (70 gal/d), or total flow of
132.5 mj/d (35,000 gal/d), was assumed. Actual dry-weather
flows have averaged approximately 66 m3/d (17,400 gal/d).
This flow amounts to less than 0.19 m-3 /capita* d (50
gal/capita-d), but is typical for this type of small, rural
community where average water use is low. The fact that the
town does not have a municipal water system is another
reason that water use and wastewater flows are very low.
In contrast to the low average dry-weather flows, however,
are very high peak flows during periods when parts of the
collection system are subject to infiltration from high
ground wate.r elevations. Peak flows have ranged to as high
The
as 1,341 m-Vd (354,400 gal/d) on a monthly average.
peak flows are sustained, and have in the past stayed high
for as long as 6 months at a time. This is a significant
factor affecting a treatment facility since the pond system
must handle, at times, flows ranging from 2 to 10 times the
design average flow.
7.4.3.4 Climate
The normal annual precipitation is 63.5 cm/yr (25 in./yr)
and the average annual gross lake evaporation is 114.3 cm/yr
7-26
-------
(45 in./yr). There are 45 days per year when maximum daily
temperatures exceed 32 °C (90 °F) and 150 days when the
minimum temperature is below 0 °C (32 °F). The mean length
of the frost-free period in the area is 160 days.
7.4.3.5 Site Characteristics
Soils in the area formed in alluvium on river bottom lands,
and the topography is relatively flat. At the pond site,
the predominant soil type is a moderately deep, nearly
level, somewhat poorly drained loam formed in calcareous
loamy alluvium. The depth to the water table ranges from
0.6 to 1.2 m (2 to 4 ft). The loam surface layer and
subsoil have moderate permeability of 1.5 to 5.1 cm/h (0.6
to 2.0 in./h). The underlying gravelly sand, which is found
51 to 102 cm (20 to 40 in.) below the ground surface, has
very rapid permeability of over 51 cm/h (20 in./h).
7.4.3.6 Treatment Facility Design and
Performance
The treatment facility includes a pond and a single RI
basin; design criteria for these facilities are summarized
in Table 7-8. The pond consists of two cells, one having a
suface area of 0.7 ha (1.8 acres) and the other having
0.4 ha (1.0 acre). The maximum water depth of the cells is
1.5 m (5.0 ft). Dikes around the pond have an overall
height of 2.4 m (8 ft). The soils at the bottom of the pond
were medium and fine sands. Bentonite was added at the rate
of 4.5 kg/m2 (20 tons/acre) to the bottom of the pond to
limit seepage to less than 0.64 cm/d (0.25 in./d).
TABLE 7-8
DESIGN INFORMATION FOR CHAPMAN RI SYSTEM
Design flow, m /d
BOD loading, kg/d
Year built
Design population
Pond cell No. 1
Surface area, ha
Depth, m 3
Capacity above drawoff level, m
Pond cell No. 2
Surface area, ha
Depth, m 3
Capacity above drawoff level, m
Total detention time above drawoff
level at design flow, d
Infiltration basin size, ha
Hydraulic loading rate at design flow, m/yr
132.5
45
1965
500
0.7
1.5
6,190
0.4
1.5
3,160
70
0.6
5
7-27
-------
The design of the pond is such that the two cells can be
operated either in series or parallel. The overflow control
box can be adjusted so that the water level in either of the
cells can be drawn down or set for constant overflow from
one or both cells. Water is drawn from the pond cells at
the 0.6 m (2 ft) depth.
The normal operating sequence for the system has been series
flow through the two cells when the pond is not ice covered,
with a constant overflow from the second cell in series to
the infiltration basin. During the winter when the pond
cells are ice covered, operation is switched to parallel to
spread the incoming load over the maximum surface area.
This results in a shorter recovery period in the spring when
the ice cover melts and the cells go from the anaerobic to
the aerobic state. There is normally some overflow to the
infiltration basin during the winter. At the design flow,
the net ..yearly overflow to the infiltration basin v/ould be
29,300 m^ (7,444,000 gal).
The two pond cells are followed by a single RI basin. To
take advantage of the higher permeability of the-underlying
soil materials, the top 0.9 m (3 ft) of RI basin soil was
stripped during basin construction. However, the design
hydraulic loading rate was limited to 5.0 m/yr (16.4 ft/yr)
to simplify basin operation. A basin area of 0.6 ha
(1.4 acres) was necessary to allow the design loading rate
at the design pond overflow rate. Following construction,
the basin was seeded with a mixture of Reed canarygrciss and
bromegrass. A grass cover has been maintained to help
preserve the soil's permeability.
Currently, the average influent flow is approximately half
the design flow (Table 7-9) and the net overflow to the
infiltration basin averages 5,150 m3/yr (1,360,000
gal/yr). The resulting hydraulic loading rate is 0.9 m/yr
(2.9 ft/yr). However, during periods of heavy infiltration
into the collection system, the average daily flow to the RI
basin is 1,375 m3/d (350,000 gal/d). This results in a
periodic hydraulic loading rate of 22.6 cm/d (8.9 in./d), or
82.5 m/yr (271 ft/yr) expressed as an annual rate. Although
this temporary rate is well below the measured soil permea-
bility of at least 51 cm/h (20 in./h), it exceeds the recom-
mended loading shown in Figure 7-2 somewhat.
7-28
-------
TABLE 7-9
WASTEWATER FLOWS TO CHAPMAN RI SYSTEM
m3/d
Monthly flows
Year
1974
Jan-Jun
Jul-Dec
1976
1977
1979a
Avg daily flow
870.6
63.0
65.5
65.9
8.6.3
Minimum
292
55.1
58.7
60.2
71.9
Maximum
1,341
79.0
82.1
78.3
132.1
a. During the months of May, June, and July,
flows were above normal and were in the
122-132 m-Vd range. This corresponded to
a period of high ground water elevations.
Although the design and actual average hydraulic loading
rates are considerably lower than the range of 50 to 60 m/yr
(165 to 200 ft/yr) recommended in Figure 7-2, the use of a
lower rate was advantageous for several reasons, including:
• A grass cover can be maintained in the bottom of
the basin to help preserve soil permeabiity.
• The treatment facility is able to treat peak
wastewater flows that greatly exceed design average
flows.
7.4.3.7 Ground Water Quality
Since high ground water levels are typical of the area in
which the treatment facility is located, the performance of
the facility in terms of possible ground water contamination
is an important consideration. The pond has been in
operation for 15 years, so there has been adequate time for
possible water quality changes caused by pond operation to
have been detected. The data indicate that the facility has
not caused increased ground water levels of nitrates or
chlorides that could be associated with wast.ewater
discharges.
7.4.3.8 Costs and Staffing
The total cost for constructing the collection system and
treatment ponds in 1965 was $110,958. The treatment
facility portion of the total amounted to $40,520.
7-29
-------
The entire system has been operated by one part-time
operator whose duties include maintenance of three pumping
stations in the collection system and operation and
maintenance at the pond site. Work at the treatment
facilities consists of operating valves, mowing, weed
control around the edge of the water in the pond cells and
in the RI basin, and maintenance of access road and
fences. Since there is no surface discharge of effluent
from the facility, laboratory testing of water quality has
not been required.
7.4.4
Overland Flow
7.4.4.1
Introduction
A smal^L, full-scale OF system is operating at Carbondale,
Illinois, treating pond effluent. The wastewater is
domestic in nature and generated at the 54 unit Cedar Lane
Trailer Court. The population of 135 has been relatively
stable since construction in the 1950s. Wastewater flow is
38 mj/d (10,000 gal/d).
Prior to 1976, wastewater was treated using a septic tank
followed by a 0.28 ha (0.7 acre) stabilization pond and
surface water discharge. Effluent from the pond did not
meet Illinois intermittent stream requirements, which
include a 1.5 mg/L ammonia nitrogen limit on the dis-
charge. An upgrading of the treatment, therefore, was
required.
7.4.4.2 Site Characteristics
The terrain is rolling and the grass covered site, which is
near the pond, has slopes ranging from 7 to 12%. The soil
is fine granular glaciated material with low permeability.
A section of the slope" 10 m (30 ft) wide and 60 m (200 ft)
long (downslope) was used.
7.4.4.3 Treatment Facility Design
The hydraulic loading rate is 44 cm/wk (17.3 in./wk), which
is higher than recommended in Figure 7-2. The first. 30 m
(100 ft) of slope is at 7% grade and the last 30 m is at
12%. The pond effluent is pumped to the top of the slope
and applied uniformly across the top of the slope via a 10
cm (4 in.) perforated pipe. The predominant grass on the
slope is tall fescue. The system was constructed by
Southern Illinois University and used for several years as a
research facility. No storage is provided other than the
existing stabilization pond [3].
7-30
-------
7.4.4.4 Operation
During 1976 and 1977, application rates varied from 0.29 to
0.57 m3/m-h (24 to 42 gal/ft-.h). The application period
varied from 4 to 24 h/d. A typical. application period was
9 h/d. Runoff from the slopes accounted for over 80% of the
applied wastewater. Erosion was not a problem.
7.4.4.5
Performance
The treatment performance of the OF system was monitored
relatively intensely in the fall of 1976. The results are
presented in Table 7-10.
TABLE 7-10
TREATMENT PERFORMANCE OF CARBONDALE OF SYSTEM [4]
mg/L except as noted
Constituent Applied wastewater
BOD
SS
Phosphorus , total
Ammonia nitrogen
Fecal coliforms,
30-110
20-60
3-4
20-40
Treated runoff
4-7
4-7
0.2-0.
0.1-1.
5
5
colonies/100 mL
35,000
600-2,500
In 1977 when application rates and daily application periods
were increased, the treatment performance declined. For
example, when application times of 24 h/d were used, removal
of ammonia dropped off significantly. The runoff after 60 m
(200 ft), however, contained less than 1 mg/L ammonia when
application periods were 12 h/d or less.
7.5 References
1. Environmental Protection Agency. Process Design Manual
for Wastewater Treatment Ponds. (In Preparation).
2. Metcalf & Eddy, Inc.
Treatment, Disposal, Reuse,
New York, N.Y. 1979.
Wastewater Engineering:
McGraw Hill Book Company.
Hinrichs, D.J. et al. Assessment of Current information
on Overland Flow Treatment of Municipal Wastewater.
Environmental protection Agency, Office of Water
Programs. EPA 430/9-80-002. MCD-66. May 1980.
7-31
-------
4. Muchmore, C.B. Overland Flow as a Tertiary Treatment
Procedure Applied to a Secondary Effluent. Presented at
Illinois Workshop on Land Application of Sewage Sludge
and Wastewater. Champaign, Illinois. October 18-20,
1976.
7-3:
-------
CHAPTER 8
ENERGY REQUIREMENTS AND CONSERVATION
8.1 Introduction
Land treatment systems energy needs consist of preappli-
cation treatment, transmission to the application site,
distribution pumping (if necessary), and tailwater recovery
or pumped drainage (if required). The energy required for
preapplication treatment varies considerably depending on
the degree of treatment planned. The degree of treatment
depends on type of system, local conditions, and regulatory
requirements. Determining energy requirements for all pre-
application treatment systems is beyond the scope of this
manual; however, equations for estimating energy consumption
of minimum preapplication unit processes are presented in
Section 8.6. Energy required for construction is too site-
specific to be included in this manual.
Energy for transmission from the preapplication treatment
site to the land treatment site depends on topography and
distance. This is especially important when considering
alternative sites. The energy required for transmission
pumping can range anywhere from zero to nearly 100% of the
energy requirements for a land treatment system. This may
often justify a higher priced parcel of land closer to the
application site. Transmission pumping is sometimes de-
signed to also provide pressure for sprinkler application.
For sites located below preapplication treatment facilities
with surface application systems, pumping usually will not
be required.
Slow rate systems vary in terms of distribution energy and
possible tailwater control. Distribution systems may be
surface or sprinkler. Tailwater control requirements depend
on the type of distribution system and discharge stan-
dards. Sprinkler systems can be controlled so that no
tailwater is produced. Surface systems will usually have
tailwater that must be contained and reapplied.
Rapid infiltration systems are usually designed for surface
distribution and application and so require minimal en-
ergy. There is no tailwater pumping, but pumped drainage
may be necessary to control ground water levels or recover
treated percolate.
Overland flow systems can use surface distribution with low
head requirements (Section 6.6.1). Sprinkler systems can
also be used so energy will be required for
8-1
-------
pressurization. There is no significant subsurface drainage
with OF so this potential energy requirement is avoided.
8.2 Transmission Pumping
Under conditions with favorable topography, a gravity
transmission system may be possible and pumping not
required. If pumping is required, the energy needs vary
substantially depending on the required head and how the
transmission system is designed. The effect of topography
on pumping costs and energy use should be thoroughly evalu-
ated during the planning process.
Energy efficient design involves coordination of all ele-
ments of the system including sizing of pumps, pipelines,
and storage facilities, as well as system operating strat-
egy. The system operating strategy involves placement and
sizing of storage facilities. Wet wells are typically not
designed for significant ;flow equalization. Transmission
pumping systems are sized to handle the peak community
flows. This can be accomplished by multiple pumps, one pump
with a variable speed drive, or some combination. Each sys-
tem has differing constraints that alter decisions on its
design. Ideally, all flow is equalized to provide nearly
constant flow pumping. This allows selection of a pump at a
maximum efficiency.
Variable speed drives, which are not as efficient as con-
stant speed drives, would not be required. Unfortunately,
flow equalization is not always feasible. in some in-
stances, equalization costs may not be recovered by energy
savings. The choice of pumping and equalization system
design is site-specific. Regardless of the pumping system
used, pipeline size can be optimized. Optimization of pipe-
line size will provide the optimum transmission system.
The following pipe size optimization procedure was taken
from reference [1]. Obviously, larger pipe sizes result in
lower pumping energy; however, excessively large pipes are
not economical.
where
Jopt
A
Q
C
Dopt = AQ°-486C-°-316(KT/PE)°-17
optimum pipeline diameter, m (ft)
constant, 3.53 (2.92)
average flow, m3/s (ft3/s)
Hazen-Williams coefficient
(8-1)
3-2
-------
K = average price of electricity, $/kWh
T = design life, yr
p = unit cost of pipe, $/linear m-iran dia.
($/linear ft-in. dia.)
E = overall pumping system efficiency,
decimal
For example, at a flow of 0.219 m3/s (7.7 ft3/s), a Hazen-
Williams coefficient of 100, a pipeline cost of $0.26/linear
ra-mm diameter, an overall pumping system efficiency of 75%,
electricity at $0.045/kWh, and a design life of 20 years,
the optimum pipe diameter is 0.50 m (20 in.) [2].
With the line size determined and a pumping system selected,
the actual energy requirement can be determined .by the fol-
lowing equation.
Energy, kwh/yr =
where Q = flow, L/min (gal/min)
TDK = total dynamic head, m (ft)
t = pumping time, h/yr
F = constant, 6,123 (3,960)
E = overall pumping system efficiency, decimal
The overall efficiency varies not only with design specifics
but also with the quality of liquid being pumped. Raw
wastewater pumping requires pumps that pass larger solids
than treated effluent. These pumps are less efficient.
When a specific design is being contemplated, the overall
efficiency should be determined using pump, motor, and
driver efficiencies determined for the equipment to be
used. For initial planning or preliminary work such as site
selection, overall system efficiencies can be assumed as
follows.
Raw wastewater 40%
Primary effluent 65%
Secondary or better effluent, tailwater,
recovered ground water, or stormwater 75%
8-3
-------
8.3 General Process Energy Requirements
8.3.1 Slow Rate
Energy consumption for SR consists, of transmission,
distribution, possible tailwater reapplication, and crop
management. A wide range of surface and sprinkler
distribution techniques is possible. Surface systems
require energy for distribution and tailwater reapplication
to the site. Sprinkler systems are highly variable w.ith
possible pressure requirements ranging from 10 to 70 m (30
to 230 ft). Generally, pressures will be in the 15 to 30 m
(50 to 100 ft) range.
Crop production energy varies substantially between the type
of crops grown. Table 8-1 shows energy requirements for
corn and forage crops.
TABLE 8-1
ENERGY REQUIREMENTS FOR
CROP PRODUCTION [3]
Requirement, MJ/ha
Operation
Tillage and seeding
Cultivation
Herbicide/ insecticide
Harvest
Drying
Transportation
Total
Corn
1.41
0.37
0.37
0.37
4.69b
1.04
8.25
Alfalfa
0.22
NA
0.37
1.51a
NAC
1.53
3.63
a. Hay.
b. Mechanically dried; may in some cases
be field dried.
c. Not applicable, field dried.
8.3.2 Rapid Infiltration
Rapid infiltration system energy requirements are primarily
thpse needed for transmission. Surface distribution is
normally used. There are no crops grown so no fuel is
consumed for that purpose. Occasionally, there are
situations where recovery wells and pumps are used. Fuel
will be needed for basin scarification, but the quantity is
not significant because the operation is infrequent.
8-4
-------
8.3.3 Overland Flow
Overland flow treatment can use either surface distribution
or sprinkler distribution. Surface distribution requires
minimal energy (see Section 8.6), while sprinkler
distribution requires pressurization e'nergy.
To prevent nozzle clogging, raw wastewater or primary
effluent should be screened prior to distribution.
Mechanically cleaned screens are preferred over comminution
since shredded material returned to the stream can still
cause clogging. The amount of energy required for screening
is insignificant compared to the pumping energy required.
Equation 8-2 applies for the pumping energy computation.
Overland flow systems require a cover crop that is often
harvested and removed from the site. Energy is required in
the form of diesel fuel for operating harvesting
equipment. Fuel required is the same as presented in
Table 8-1 for alfalfa harvest.
A summary of energy requirements for land treatment
processes is shown on Table 8-2. The values presented are
typical of actual practice.
TABLE 8-2
MOST COMMON UNIT ENERGY REQUIREMENTS FOR LAND
TREATMENT OF MUNICIPAL WASTEWATER
Treatment
system
Slow rate
Total
Component
Pumping for distribution
Crop planting, cultivation,
harvest, drying, transport
Energy credit for fertilizer
value of wastewater
Electricity,
kWh/1,000 m3
0.14
—
0.14
Fuel,
MJ/1,000 mj
--
0.68
(0.50)
0.18
Total equivalent,
kWh/1,000 m3
0.14
0.20
(0.14)
0.20
Total
Rapid
infiltration
Total
Overland flow
Total
value of wastewater
Distribution (gravity)
Recovery wells
Tr ansraiss ion
Forage harvest
—
0.14
—
0.05
0.05
0.10
—
0.10
(0.50)
0.18
--
—
--
0.22
0.22
(0.14)
0.20
—
0.05
0.05
0.10
0.06
0.06
Note: See Appendix G for metric conversions; kWh are used for electricity and total
equivalent energy, MJ used for fuel.
J-5
-------
8.4 Energy Conservation
8.4.1 Areas of Potential Energy Savings
With respect to energy conservation, there are two main
areas to review. First is transmission to the site.
Location of the facility should, if possible, provide for
adequate drop in elevation between the preapplication
treatment and the land treatment sites. This layout is
sometimes possible with RI systems and certain SR systems.
It is more difficult to design OF systems in this manner
since sloping land is necessary as part of the process. For
OF systems, site grading is usually required to obtain
desired slope so distribution pumping is typically
necessary.
The second area of potential energy savings is with the
distribution method. For domestic wastewater with minimal
preapplication treatment, surface systems are preferred,
since surface systems are not as subject to clogging and
usually require less energy.
Distribution for SR systems is a function of topography and
the crop. Surface systems can be used on level or graded
sites (see Section 4.7.1). In the past, surface systems
were preferred by the agricultural industry; however, due to
increased labor costs and poor irrigation efficiencies, some
existing surface systems have been converted to sprinkler
irrigation. For municipal authorities where labor wages are
higher than farm worker wages, the increased labor costs are
important.
Sprinkler distribution systems are relatively high-pressure
devices. Recent advances have been made in sprinkler nozzle
design to lower headloss without sacrificing uniformity of
application. Figure 8-1 illustrates a center pivot system
with two types of sprinklers. The impact sprinklers have a
typical pressure loss of approximately 60 to 65 m (200 to
215 ft); whereas, drop nozzles have a headloss of 15 to 20 m
(50 to 65 ft). This difference represents an energy savings
of about 95 kWh/1000 m-*, without sacrificing distribution
efficiency.
Surface systems may not require pumping energy except for
tailwater recycling. In this case, automated surface
systems (Figure 8-2) can be introduced to minimize tailwater
recycling requirements.
8-6
-------
DROP NOZZLE SYSTEM
IMPACT SPRINKLER SYSTEM
FIGURE 8-1
CENTER PIVOT SYSTEM
8-7
-------
Reuse pump
Tailwater Collection
FIGURE 8-2
AUTOMATIC SURFACE IRRIGATION SYSTEM [4]
8.4.2 Example: Energy Savings in Slow Rate Design
The following example illustrates how effective planning and
design can result in energy conservation. A summary of
assumed system characteristics used for this example is
presented in Table 8-3.
TABLE 8-3
EXAMPLE SYSTEM CHARACTERISTICS
Average flow,
System
Preapplication treatment
Application season
Hydraulic loading, m/yr
Net land area, ha
Crop
Topography
Tailwater control
38,000
Slow rate
Pond
May to October (5 months)
1.2
1,130
Corn
Nearly level, suitable for
all types of irrigation
No surface discharge of
applied wastewater allowed
8-8
-------
Three systems will be considered: surface distribution by
ridge and furrow, and two examples of center-pivot appli-
cation. Since transmission of wastewater is essentially the
same with all alternatives, it will not be included in this
discussion.
Ridge and furrow distribution does not require pumping for
distribution; but due to a no discharge of tailwater
requirement, energy is required to return tailwater back to
the application point (assumed head: 3 meters). Depending
on the system design,the maximum tailwater recycle will
range from 30 to 70% of that applied. Conventional ridge
and furrow designs result in lower efficiency, with the
higher recycle pumping requirement. Alternatively, ridge
and furrow systems with automated recycle cutback or
automated valves can improve efficiency by lowering pumping
requirements. The potential savings from system automation
is summarized in Table 8-4.
TABLE 8-4.
COMPARISON OF CONVENTIONAL AND AUTOMATED RIDGE
AND FURROW SYSTEMS FOR 38,000 m3/da
System
Tail-
water Electric- Labor
pumping, ity, Labor, cost,
kWh/yr $/yr h/yr $/yr
Total
Amortized annual
Capital capital, cost,
cost, $ $/yr $/yr
Conventional
Automated
Difference
89,300
33,500
55,800
2,950
1,100
1,850
2,800
1,400
1,400
30,800
15,400
15,400
16,000
45,000
-29,000
1,520
4,300.
-2,780
35,270
20,800
. 14,470
a. Electricity at $0.036/kWh. Labor at 1.2 h/ha-d for automated systems;
2.5 h/ha/d for conventional systems. Labor cost at $11.00/h. Capital costs
for pipeline, distribution system, reuse system meters (January 1980) .
Capital amortized at 7-1/8% for 20 years.
The potential savings using automated irrigation systems are
significant; both energy consumption and cost can be reduced
substantially. In this example, energy requirements were
reduced by about two-thirds, at an overall cost savings of
over 50%.
If a center pivot irrigation system is used, tailwater
recovery is not needed. However, pumping energy is required
to provide nozzle pressure. In this case the main factor in
energy conservation is nozzle design. The general goal is
to achieve uniform distribution at the lowest possible
pressure loss. A conventional center pivot rig employs
impact sprinklers on top of the pivot pipeline. These
devices require a pumping pressure of approximately 65 m
(21 ft). Alternatively, drop nozzles are used in modern
8-9
-------
rigs which develop a headloss of about 15 m (150 ft). Drop
nozzles have an additional advantage of producing less aero-
sol than impact systems. Capital costs, and operation and
maintenance requirements (except for electricity) are
comparable between these two systems. The impact on energy
savings is shown on Table 8-5. In this instance, costs were
reduced and aerosols were decreased by designing to conserve
energy.
TABLE 8-5
COMPARISON OF IMPACT AND DROP-TYPE
CENTER PIVOT SYSTEM NOZZLE DESIGNS
ON ENERGY REQUIREMENTS,
38,000 m3/day
Nozzle type
Impact
Drop
Difference
Electricity,
kWh/yr
2,230,000
1,030,000
1,200,000
Energy
cost, $/yr
73,600
34,000
39,600
8.4.3 Summary
For purposes of comparison the total energy (electricity
plus fuel) for typical 3,785 m3/d (1 Mgal/d) systems is
listed in Table 8-6 in order of increasing energy require-
ments. It is quite apparent from Table 8-6 that increasing
energy expenditures do not necessarily produce increasing
water quality benefits. The four systems at the top of the
list, requiring the least energy, produce effluents com-
parable to the bottom four that require the most.
8.5 Procedures for Energy Evaluations
The following section provides step-by-step procedures for
computing energy use for each of the three land treatment
systems. Examples are also provided. The energy compu-
tation requires site selection and a decision concerning
location of preapplication and storage facilities because
elevation differences for pumping are critical. The distri-
bution method must also be determined.
8-10
-------
TABLE 8-6
TOTAL ANNUAL ENERGY FOR TYPICAL 3,785 m3/d
(1 Mgal/d) SYSTEM (ELECTRICAL PLUS FUEL,
EXPRESSED AS 1,000 kWh/yr) [5]
Treatment system
Rapid infiltration (facultative pond)
Slow rate, ridge + furrow (facultative pond)
Overland flow (facultative pond)
Facultative pond + intermittent filter
Facultative pond + microscreens
Aerated pond + intermittent filter
Extended aeration + sludge drying
Extended aeration + intermittent filter
Trickling filter + anaerobic digestion
RBC + anaerobic digestion
Trickling filter + gravity filtration
Trickling filter + N removal + filter
Activated sludge + anaerobic digestion
Activated sludge + anaerobic digestion + filter
Activated sludge + nitrification + filter
Activated sludge + sludge incineration
Activated sludge + AWT
Physical chemical advanced secondary
NOTE: RBC = rotating biological contactor.
8.5.1 Slow Rate
Step 1: Transmission Pumping
1. Elevation at site m
2. Elevation at source m
3. Elevation difference m
4 . Average annual f lowrate
5. Pumping system efficiency
6. Pipeline diameter cm
7. Pipeline length m
8. Pipeline headless m
9. Total dynamic head m
Effluent quality, mg/L Energy,
i nnn
BOD
5
1
5
15
30
15
20
15
30
30
20
20
20
15
15
20
<10
10
SS P
1 2
1 0.1
5 5
15
30
15
20
15
30
30
10
10
20
10
10
20
5 <1
10 1
N kWh/yr
10 150
3 181
3 226
10 241
15 281
20 506
683
708
783
794
805
5 838
889
911
1,051
1,440
<1 3,809
4,464
L/min
%
10. Energy requirement kWh/yr
(Eq. 8-2)
8-11
-------
Step 2: Distribution Energy
1
2
3
4
5
6
7
1.
2.
3.
4.
5.
6 .
1,
2,
3,
4,
5,
6,
7.
8,
Step 5:
Flowrate
L/min
Pressure head required
System efficiency %
Operating time h/yr
Pipeline headloss m
Total dynamic head
Energy requirement
m
m
kWh/yr
(Eq. 8-2)
Step 3: Tailwater Pumping (if required)
Flowrate
Lift required
Headloss
L/min
m
m
^
Assumed pumping system efficiency
Operating time _ h/yr
Energy requirement _ kWh/yr
(Eq. 8-2)
Step 4: Crop Production (Table 8-1)
Tillage and seeding _ MJ/ha-yr
Cultivation _ MJ/ha-yr
Insecticides and herbicides
Harvest _ MJ/ha-yr
Drying _ MJ/ha-yr
Transportation __ MJ/ha-yr
MJ/ha-yr
Crop area
ha
Total fuel requirement Mj/yr
Combine Steps 1 through 4, expressed as kWh/yr
8.5.2 Rapid Infiltration
Step 1: Transmission Pumping
m
m
m
1. Elevation at site _
2. Elevation at source
3. Elevation difference ^_^___
4. Average flow _ L/min
5. Assumed pumping system efficiency
6. Pipeline diameter _ cm
7. Pipeline length _
8. Pipeline headloss _
9. Total dynamic head _ m
10. Energy requirement _ kWh/yr
m
m
(Eq. 8-2)
3-12
-------
Step 2: Drainage Water Control (if necessary)
1,
2,
3,
4,
5,
6,
7.
Elevation of water source
Elevation of discharge
Difference in elevations
Pumping system efficiency
Operating hours h/yr~
Pumped flow L/min
m
m
m
Energy requirement
kWh/yr
Step 3: Combine Steps 1 and 2
8.5.3 Overland Flow
Step 1: Transmission Pumping
1
2
3
4
5
6
7
8
9
10
Elevation at site
Elevation at source
Elevation difference
Average annual flow
m
m
m
L/min
m
Assumed pumping system efficiency
Pipeline diameter cm
Pipeline length ~
Pipeline headloss _
Total dynamic head
Energy requirement
m
m
kWh/yr
Step 2: Distribution System
1,
2.
3
4,
5
6,
7
Type of system
Flowrate L/min
Pressure head required m
Assumed pumping efficiency
Operating time h/yr
Total dynamic head
Energy requirement
m
kWh/yr
Step 3: Grass Removal (Table 8-1)
1,
2,
3,
4,
(Eq. 8-2)
(Eq. 8-2)
Maintenance requirements, fuel use
Grass removal frequency harvest/yr
Fuel for harvest
(Eq. 8-2)
MJ/harvest
Total fuel required
MJ/ha
Mj/year
Step 4: Combine Steps 1 through 3/ express as kWh/yr
8.5.4 Examples
Using the previously presented step-by-step procedures, the
following example problems were developed.
8-13
-------
8.5.4.1 Slow Rate
The slow rate system is designed to treat pond effluent as
follows:
Average flow
Season
Applied flow
Crop grown
Distance to site
Tailwater pumping
Area
Step 1: Transmission Pumping
15,000 L/min
5 months
36,000 L/min
Corn
100 m
Not required
650 ha
1. Elevation at site 50 m
2. Elevation at source 48 m
3. Elevation difference 2 m
4. Average annual flowrate 15,000 L/min
5. Pumping system efficiency 40%
6. Pipeline diameter 76 cm
7. Pipeline length 100 m
8. Pipeline headloss 3.4 m
9. Total dynamic head 5.4 m
10. Energy requirement 289,711 kWh/yr
Step 2: Distribution Energy
1. Flowrate 36,000 L/min
2. Pressure required 10 m
3. System efficiency 75%
4. Operating time 3,600 h/yr
5. Pipeline headloss 2 m
6. Total dynamic head 12 m
7. Energy requirement 338,658 kWh/yr
Step 3: Tailwater Pumping (if required) (not required with
sprinklers)
1 . Flowrate L/min
2. Lift required m
3. Assumed pumping efficiency _ _ %
4. Operating time _____ h/yr
___
5. Energy requirement
kWh/yr
8-14
-------
Step 4: Crop Production (full)
1. Tillage and seeding 1.41 MJ/ha-yr
2. Cultivation 0.37 MJ/ha-yr
3. Insecticides and herbicides 0.37 Mj/ha*yr
4. Harvest 0.37 MJ/ha«yr
5. Drying 4.69 MJ/ha-yr
6. Transportation 1.04 MJ/ha-yr
7. Crop area 650 ha
8. Total fuel requirement 5,120 MJ/yr = 1,422 kWh/yr
Step 5: Total energy use = 629,791 kWh/yr
8.5.4.2 Rapid Infiltration
The rapid infiltration system is designed to treat primary
effluent as follows:
Flowrate
Distance to site
Drainage
Step 1: Transmission Pumping
15,000 L/min
5,000 m
pumped wells
1. Elevation at site 1,115 m
2. Elevation at source 1,105 m
3. Elevation difference 10 m
4. Average flow 15,000 L/min
5. Assumed pumping system efficiency 65%
6. Pipeline diameter 50 cm
7. Pipeline length 5,000 m
8. Pipeline headloss 20 m
9. Total dynamic head 30 m, operating 8,760 h/yr
10. Energy requirement 990,465 kWh/yr
Step 2: Drainage Water Control (if necessary)
1. Elevation of water source 1,105 m
2. Elevation of discharge 1,115 m
3. Difference in elevations 10 m
4. Pumping system efficiency 75%
5. Operating hours 2,920 h/yr
6. Pumped flow 10,000 L/min
7. Energy requirement 63,585 kWh/yr
Step 3: Total energy use = 1,054,050 kWh/yr
8-15
-------
8.5.4.3 Overland Flow
An overland flow system is planned for a small community,
The system will be used to treat screened raw wastewater,
Design parameters are as follows:
Design flow
Distribution method
Distance from source to site
Hydraulic loading
Land area
Step 1: Transmission Pumping
137 m/d
Gated pipe
100 m
4.5 m/yr
1 ha
1. Elevation at site 125 m
2. Elevation at source of 120 m
3. Elevation difference 5m
4. Average annual flow 95 L/min
5. Assumed pumping system efficiency 40%
6. Pipeline diameter 10 cm
7. Pipeline length 100 m
8. Pipeline headloss 1.22 m
9. Total dynamic head 6.22 m
10. Energy requirement 2f113 kWh/yr
Step 2: Distribution System
1. Type of system - gated pipe
2. Flowrate 95 L/min
3. Pressure head required 3 m
4. Assumed pumping efficiency 40%
5. Operating time 8,760 h/yr
6. Total dynamic head 3.3 m
7. Energy required 1,121 kWh/yr
Step 3: Grass Removal
1. Maintenance requirements, fuel use 0.59 MJ/harvest
2. Grass removal frequency 3 harvest/yr
3. Fuel for harvest (including transportation)
3.04 MJ/ha ,
4. Total fuel required 3.63 Mj/yr = 1.0 kWh
Step 4: Total energy use = 3,235 kWh/yr
8.6 Equations for Energy Requirements
In addition to Equation 8-1, a large number of equations
have been developed from the curves in reference [6] and are
presented in reference [5] . Selected equations are pre-
sented in this section to allow the engineer to estimate
8-16
-------
energy requirements for minimum preapplication treatment and
for the three land treatment processes. In all equations,
Y is the energy requirement in kWh/yr.
8.6.1 Preapplication Treatment
Mechanically Cleaned Screens
log Y = 3.0803 + 0.1838(log X)
- 0.0467 (log X)2
+ 0.0428 (log X)J
where Y = electrical energy required, kWh/yr
X = flow, m3/d (Mgal/d)
Assumptions = normal run times are 10 min/h,
bar spacing 1.9 cm (0.75 in.),
worm gear drive is 50% efficient
(8-3)
Comminutors
log Y = 3.6704 + 0.3493(log X)
+ 0.04.37(log X)2
+ 0.0267 (log X)J
(8-4)
Grit Removal
,0.24
Y = AX
A = 73.3 (530)
X = flow, m3/d (Mgal/d)
Assumptions = nonaerated, square tank, 2 h/d operation
Aerated Ponds
Y = AX1'00
A = 68.7 (260,000)
X = flow, m3/d (Mgal/d)
(8-5)
(8-6)
Assumptions = low speed mechanical aerators, 30 d detention,
1.1 kg 02/kWh
Other preapplication treatment processes will involve many
potential sludge treatment and disposal options and are
included in reference [5].
8-17
-------
8.6.2 Land Treatment Processes
For sprinkler application in each land treatment process and
OF and RI distribution, use the previous checklist and
Equation 8-2. Equations are presented for ridge and furrow,
and graded border SR application along with the assumptions.
Ridge and Furrow
Application = 250 d/yr, tailwater return at
25% annual leveling and ridge
and furrow replacement
Y = AX1'00 - electrical
A = 3.17 (12,000)
X = flow, m3/d (Mgal/d)
Y = AX**00 - fuel
Y = MJ/yr (106 Btu/yr)
A = 1.55 (20)
(8-7)
(8-8)
X = flow,
(Mgal/d)
Graded border
Application = 250 d/yr, tailwater return at 25%
(8-9)
Y = AX1.00
A = 4.2 (16,000)
X = flow, m3/d (Mgal/d)
8.7
1.
References
Culp/Wesner/Culp. Energy Considerations in Wastewater
Treatment. CWC, Cameron Park, California. September,
1980.
Patton, J.L., and
Distribution Energy
No. 6. June 1980.
M.B. Horsley.
Appe t i te. AWWA
Curbing
Journal,
the
72,
4.
5.
Stout, B.A. Energy Use in Agriculture. Council for
Agricultural Science and Technology. Ames, Iowa.
Report Number 68. August 1977.
Eisenhauer, D.E. and P. E. Fischbach. Automation of
Surface Irrigation. Proceedings of the Irrigation
Association Annual Conference. February 1978.
Middlebrooks, E.J. and C.J. Middlebrooks. Energy
Requirements for Small Flow Wastewater Treatment
Systems. Reprint of CRREL SR 79-7. MCD-60, OWPO,
USEPA. April 1979.
8-18
-------
6. Wesner, G.M., et al. Energy Considerations in
Municipal Wastewater Treatment, MCD-32. USEPA, Office
of Water Program Operations. March 1977.
8-19
-------
-------
Chapter 9
HEALTH AND ENVIRONMENTAL EFFECTS
9.1 Introduction
Wastewater constituents that are of major concern for. health
or environmental reasons are:
• Nitrogen
• Phosphorus
• Dissolved solids
• Trace elements
• Microorganisms
• Trace organics
Potential effects of these constituents vary among the three
major types of land treatment, as shown in Table 9-1. The
relationship of wastewater constituents to health effects is
presented in Table 9-2.
In general, constituent removals are greatest for SR
systems. Health and environmental effects of RI systems
depend on site selection and design factors such as
hydraulic loading rate and length of application and resting
cycles. Overland flow has the fewest potential impacts on
ground water because very little water penetrates below the
soil surface. However, renovated water from OF systems is
normally discharged to local surface waters as a point
source, and, therefore, can affect surface water quality.
Recently, the EPA has funded extensive studies at several
operating land treatment systems to evaluate potential long-
term health and environmental effects. The ten study sites
are presented in Table 9-3. Results from these and other
studies are included in this chapter.
9-1
-------
TABLE 9-1
LAND TREATMENT METHODS AND CONCERNS [1]
Potential Concerns
Nitrogen
Health: drinking water aquifers
Environment: eutrophioation
crops
Phosphorus
Environment: eutrophication
Dissolved solids
Health: drinking water aquifers
Environment: soils
crops
ground water
Trace elements
Health: drinking water aquifers
crops
Environment: crops
animals
Microorganisms
Health: drinking water aquifers
crops
aerosols
Environment: animals
Trace organics
Health: drinking water aquifers
crops
SR
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
RI
X
X
—
X
X
X
__
X
X
—
__
—
X
—
--
X
"
OF
. __
X
—
X
—
X
X
__
X
__
X
__
X
X
X
__
""~
Note: An X in the matrix indicates the possibility for
concern. The magnitude of the impact is not considered.
TABLE 9-2
RELATIONSHIP OF POLLUTANTS TO HEALTH EFFECTS3
Pollutant (agent)
Principal health effect
Nitrate nitrogen
Sodium
Trace elements
Microorganisms
Bacteria
Virus
Protozoa
Helminths
Trace organics
Methemoglobinemia
Cardiovascular
Toxicity
Infection, disease
Toxicity, carcinogenesis
a. Adapted from reference [2J,
9-2
-------
TABLE 9-3
EPA LONG-TERM EFFECTS STUDIES
Date
operation
Location started
Slow rate
systems
Camarillo, 1966
California [3]
Dickinson, 1959
North Dakota [4]
Mesa, 1950
Arizona [5]
Roswell, 1944
New Mexico [6]
San Angelo, 1959
Texas [ 7 ]
Tooele, 1967
Utah [8]
Flow
during
study ,
raVs
0.130
0.044
0.208
0.175
0.241
0.061
Level of
preapplioation
treatment
Secondary
(activated
sludge) with
disinfection
Secondary
(aerated
ponds ) with
disinfection
Secondary
(trickling
filters)
Secondary
(trickling
filters followed
by oxidation
ditch) with
disinfection
Primary
Secondary
(trickling
filters) with
disinfection
Crops
Tomatoes ,
broccoli
Forage
grasses
Grain, .corn,
barley
Corn, alfalfa,
sorghum
Forage grasses.
pasture
Forage grasses.
alfalfa. Test
plots of beans.
carrots, lettuce.
Hydraulic
loading
rate , m/yr
1.6
1.4
4-8.6
0.8
2.9
0.6
peas, radishes,
sweet corn, wheat
Rapid
infiltration
systems
Hollister, 1945 0.044
California [9]
Lake George, 1939 0.058
New York 110]
Milton, 1957 0.013
Wisconsin til]
Vineland, 1926 0.215
New Jersey [12]
Primary
Secondary
(trickling
filters)
Secondary
(activated
sludge)
Primary
15
43
224
19
Note: See Appendix G for metric conversions.
9.2 Nitrogen
Both nitrates and ammonia are of concern in land treatment
systems. Other nitrogen compounds either are harmless or
are degraded during land treatment.
Storage ponds can be used in conjunction with land treatment
to achieve high nitrogen removals. Although such ponds work
well for SR and OF systems, the resulting algal growth may
cause soil clogging at RI systems. The use of storage ponds
for nitrogen removal is described in greater detail in
Section 4.4.1.
9-3
-------
9.2.1 Crops
In the general case, nitrogen is beneficial for crops,
increasing yields and quality. However, uptake of excess
nitrogen in some crops can increase succulence beyond
desirable levels causing lodging in grain crops and reduced
sugar content in beets and cane, for example. High levels
of nitrogen or application beyond seasonal needs may induce
more vegetative than fruit growth, and also delay
ripening. High-nitrate content in forages can be a concern
if these are the principal ration for livestock. Cattle can
also suffer from grass tetany, which is related to an
imbalance of nitrogen, potassium, and magnesium in pasture
grasses. These potential nitrogen related crop effects are
not expected with typical municipal wastewaters applied to
properly designed and well managed land treatment systems.
9.2.2 Ground Water
As indicated in previous chapters, EPA guidance requires a
maximum contaminant level (MCL) of 10 mg/L nitrate as
nitrogen at the land treatment boundary. This is to avoid
the potential of methemoglobinemia in very young infants
using the water supply. AS a result, nitrogen is often the
limiting parameter for land treatment design. Methods to
satisfy this requirement are described in the design
chapters (Sections 4.5.2 and 5.4.3.1).
9.2.3 Surface Water
Un-ionized ammonia is toxic to several species of young
freshwater fish. The oxygen carrying capacity of certain
fish can be impaired at concentrations as low as 0.3 mg/L
un-ionized ammonia (approximately 2.5 mg/L total ammonia
nitrogen at normal pH values) [13]. For this reason, many
land treatment systems that discharge to surface waters are
designed to provide nitrification. using normal application
rates, OF and SR systems produce a well nitrified
effluent. Renovated water from Ri systems contains very
little ammonia nitrogen if relatively short application
periods are alternated with somewhat longer drying periods
(Table 5-13).
Land treatment systems that discharge to surface waters in
which nitrogen is the limiting nutrient are designed to
achieve nitrogen removal to avoid algal blooms and increased
rates of eutrophication. Methods for achieving nitrogen
removal are described in Sections 4.5.2, 5.4.3.1, and 6.5.2.
9-4
-------
9.3 Phosphorus
Phosphorus is not known to cause adverse health effects.
Like nitrogen, it is an important nutrient for crops.
Because there are no drinking or irrigation water standards,
the principal concern is that phosphorus can be the limiting
nutrient that controls eutrophication of surface waters.
9.3.1 Soils
The principal phosphorus removal mechanisms at SR and RI
systems are soil adsorption and precipitation. Removals
achieved at operating SR and RI systems are shown in Tables
4-3 and 5-3.
9.3.2 Crops
Normal crop uptake of phosphorus occurs in both SR and OF
systems with loadings far in excess of crop needs. No
adverse effects on crops from phosphorus have been reported.
9.3.3 Ground Water
Phosphorus concentrations found in percolates from SR and RI
systems are presented in Tables 4-3 and 5-3. As shown in
these two tables, percolate phosphorus concentrations are
reduced substantially within relatively short travel
distances.
9.3.4 Surface Water
Because phosphorus concentrations in SR and RI percolates
generally are quite low (less than 1 mg/L), adequate
phosphorus removal usually occurs before any percolate
intercepts surface water. At OF systems, where phosphorus
removal averages 50 to 60%, additional treatment may be
necessary if phosphorus is limited by the discharge permit.
9.4 Dissolved Solids
Salt concentrations in domestic wastewater vary widely,
according to the salinity of the local water source and the
chemicals added during preapplication treatment (if any).
Depending on the salinity of the applied wastewater, soil
properties, crops, and water for livestock and human
consumption may be affected.
9.4.1 Soils
High concentrations of sodium in applied wastewater can
cause substitution of sodium ions for other cations in the
9-5
-------
soil. This substitution tends to disperse clay particles
within the soil, leading to decreased permeability, lowered
shear strength, and increased compressibility [14]
Wastewater with an SAR of less than 4 has caused no changes
xn these properties [8]. No adverse soil impacts are
expected unless the SAR exceeds 9.
9.4.2 Crops
Salinity, as measured by the electrical conductivity of the
water, can cause yield reductions in crops. Crops vary
widely in tolerance to salinity. The salinity tolerances
and leaching requirements of several field and forage crops
are given in Table 9-4. Salinity effects are generally only
of concern in arid regions where accumulated salts are not
flushed from the soil profile by natural precipitation. No
salinity problems have been reported at the systems listed
in Table 9-3.
Boron toxicity can occur because this element tends to be
unaffected by most preapplication treatment processes.
Fruit and citrus trees are affected at 0.5 to 1.0 mg/L-
field crops can be affected at 1.0 to 2.0 mg/L; and most
grasses are relatively tolerant at 2.0 to 10.0 mg/L.
Sodium and chloride ions are usually present together in
wastewaters. Most tree crops are sensitive to sodium and
chloride taken up by the roots. Leaves of many crops may
show leaf-burn due to excessive sodium or chloride
adsorption or bicarbonate deposition under low-humidity,
high-evaporation conditions. Irrigating at night or
increasing the rotation speed of sprinkler heads can help
avoid these problems.
9.4.3 Ground Water
The salinity of percolate from some systems may limit the
potential for reuse of renovated water. National drinking
water standards recommend that finished potable water
contains less than 500 mg/L total dissolved solids (TDS),
but more saline waters have been used without ill effects.
Excessive TDS can cause poor taste in drinking water, may
have laxative effects on consumers, and may corrode
equipment in water distribution systems. Salinity
restrictions on water for livestock uses are not as
stringent as for drinking water. in general, a TDS of
10,000 mg/L is the upper limit for healthy larger animals
such as cows and sheep; a limit of 5,000 mg/L TDS should be
used for smaller animals (including poultry), lactating
animals, and young animals [13].
9-6
-------
TABLE 9-4
TOLERANCE OF SELECTED CROPS TO
SALINITY IN IRRIGATION WATER [15]
Field crops
Barley
Sugarbeets
Cotton
Saf flower
Wheat
Sorghum
Soybean
Rice (paddy)
Corn
Sesbania
Broadbean
Flax
Beans (field)
Forage crops
Bermudagrass
Tall wheatgrass
Crested wheatgrass
Tall fescue
Barley (hay)
Perennial rye
Harding grass
Birdsfoot trefoil
Beardless wild rye
Alfalfa
Orchardgrass
Meadow foxtail
Clover
Notes :
ECe = electrical
ECW = electrical
Yield decrement
salinity of
0%
EC-, ECy,
mmho/cm mmho/cm
8 5.3
6.7a 4.5
6.7 4.5
5.3 3.5
4.7a 3.1
4 2.7
3.7 2.5
3.3 2.2
3.3 2.2
2.7 1.8
2.3 1.5
2 1.3
1 0.7
8.7 5.8
7.3 4.9
4 2.7
4.7 3.1
5.3 3.5
5.3 3.5
5.3 3.5
4 2.7
2.7 1.8
2 1,3
1.7 1.1
1.3 0.9
1.3 0.9
conductivity of saturation
conductivity of irrigation
to be expected due to
irrigation water
LR,
%
12
11
11
12.5
8
7.4
10
9
12
7
8
7
6
13
11
6
8
10
10
10
10
6
5
4
4
6
ECe,
mmho/cm
18
16
16
14
14
12
9
8
7
9
6.5
6.5
3.5
18
18
18
14.5
13.5
13
13
10
11
8
8
6.5
4
50%
ECW,
mmho/cm
12
10.7
10.7
8
9.3
8
6
5.3
4.7
6
4.3
4.3
2.3
12
12
12
9.7
9
8.7
8.7
6.7
7.3
5.3
5.3
4.3
2.7
]
LR,
% mi
27
26
26
28.5
23
22
23
22
26
23
24
24
19
27
27
27
24
25
24
24
24
26
19
20
18
19
Maximum
ECdwr
mho/cm
24
42
42
28
40
36
26
24
18
26
18
18
12
44
44
44
40
36
36
36
28
28
28
26
24
14
extract.
water
.
LR = leaching requirement: that fraction of the irrigation water that must
be leached through the active root zone to control soil salinity at the
tolerance level. This is in addition to the irrigation water taken up by
the plants. LR = EC, x 100/EC
-------
If the salinity of a community's wastewater is significantly
•higher than the salinity of the ground water, land treatment
may be limited to processes that discharge to surface waters
or renovated water recovery may be required to protect
ground water quality. This condition occurs most frequently
in the arid western states where water resources are limited
and protection of ground water from increasing salinity is a
major concern.
9.5 Trace Elements
Trace elements (heavy metals) in municipal wastewaters are
contributed by both domestic and industrial dischargers;
contributions vary widely with industry. Frequently,, trace
element concentrations in municipal wastewaters are lower
than the limits established for drinking water. Therefore,
in most communities, land treatment is unlikely to cause
direct adverse health or environmental effects [16].
The fate of trace elements during land treatment is a
concern primarily for two reasons:
Trace elements, particularly
accumulate in the food chain.
cadmium, can
• Trace elements can move through soil and enter
ground water.
9.5.1 Soils
Movement of trace elements into and through the soil may
occur during wastewater application or after land treatment
operations have ceased. For this reason, it is important to
understand removal mechanisms and the conditions that
influence retention in and transport through the soil -(see
Sections 4.2.4 and 5.2.4).
Concentrations of trace elements retained in the soil
profile at SR and RI sites are highest near the soil surface
and decrease with depth [17]. Removal efficiencies at
selected systems are presented in Tables 4-4 and 5-4. Soils
can retain a finite amount of trace elements; the capacity
or design life for metals removal is at least the same order
of magnitude as for phosphorus. For example, in typical New
England soils, the design life for copper and cadmium based
only on ion exchange capacity could be several hundred years
using an SR system and seasonal wastewater application [1].
At OF systems, trace elements are adsorbed at the soil
surface in the organic-layer of decomposing organic material
and plant roots. Because adsorption occurs as the applied
9-8
-------
wastewater flows across the soil surface, metals tend to
accumulate near the point of wastewater application. In
pilot studies near Utica, Mississippi, approximately 50% of
the monitored trace elements (cadmium, copper, nickel, and
zinc) was removed on the upper third of the treatment slope
[18]. Data from the same pilot studies, presented in Table
9-5, indicate that most of the trace elements entering this
system are retained near the soil surface. The system has
not approached its full capacity for trace element removal.
TABLE 9-5
MASS BALANCE OF TRACE ELEMENTS IN OF
SYSTEM AT UTICA, MISSISSIPPI [18]
Metal
Cadmium
Copper
Nickel
Zinc
Component
Applied
Grass
Runoff
Soil
Applied
Grass
Runoff
Soil
Applied
Grass
Runoff
Soil
Applied
Grass
Runoff
Soil
Grams
46.21
0.54
3.50
42 . 14
90.39
3.59
13.13
73.67
110.11
1.50
5.20
103.39
264.05
20.03
32.06
212.03
Percent
of applied
1.2
7.6
91.2
4.0
14.5
81.5
1.4
4.7
93.9
7.6
12.1
80.3
The results of one study on an abandoned RI basin are
reported in Table 5-5. These data, collected approximately
1 year after the last wastewater application, indicate that
relatively little leaching occurred both during the 33 years
of operation and in the year following operation. Leaching
should not be a problem provided a soil pH of at least 6.5
is maintained. At this pH, most trace elements are
precipitated as insoluble compounds. Methods for adjusting
soil pH are discussed in Section 4.9.1.3.
9.5.2 Crops
Bioconcentration of trace elements in the food chain is most
likely to occur during the operational years of a land
treatment system. Plant uptake of trace elements occurs
when the elements are present in soluble or exchangeable
9-9
-------
form in the root zone. Generally, this occurs in increasing
amounts as more adsorption sites are occupied and as the
soil pH decreases. To minimize the plant uptake of trace
elements, the soil pH should be maintained at 6.5. or
above,. The trace elements that are of greatest concern are
cadmium, copper, molybdenum, nickel, and zinc.
With regard to health effects, nickel and zinc are of least
concern because they cause visible adverse effects in plants
before plant concentrations are high enough to be of concern
to animals or man. Cadmium, copper, and molybdenum all may
be harmful to animals at concentrations that are too low to
visibly affect plants. Copper is not a health hazard to man
or monogastric animals, but can be toxic to ruminants (cows
and sheep). These animals' tolerance for copper increases
as available molybdenum increases. Molybdenum itself may
cause adverse effects in animals at 10 to 20 ppm in forage
that is low in copper [13] . Cadmium is toxic to both man
and animals in doses as low as 15 ppm, but ruminants absorb
very small proportions of the cadmium they ingest. Once
absorbed, however, this metal is stored in the kidneys and
liver [19] , so that most meat and milk products remain
unaffected by high cadmium concentrations ingested by
livestock [13] .
With regard to effects on crops, trace elements have not
caused any adverse effects on any of the crops grown at the
SR systems listed in Table 9-3. Similarly, analyses of
forage crops grown at the Melbourne., Australia, system,
which has operated since 1896, show relatively little
increase in trace element uptake over forage crops irrigated
with potable water [20]. Typical trace element
concentrations in forage grasses are presented in Table 9-6
with concentrations in forage crops grown at selected SR
sites.
At the OF site near utica, trace elements have had no
adverse effects on the grasses grown. As with the soil in
this system, grass uptake of trace elements is greatest near
the point of wastewater application and decreases with
distance down the treatment slope. Grass uptake accounted
for only 1.2, 1.4, 4.0, and 7.6% of the applied cadmium,
nickel, copper, and zinc, respectively [18]. If. trace
element uptake is a concern, the use of Festuca rubi'a (red
fescue) at OF systems is recommended because trace element
uptake by this plant is approximately a third the trace
element uptake of most grasses [18].
9-10
-------
TABLE 9-6
TRACE ELEMENT CONTENT OF FORAGE. GRASSES AT
SELECTED SR SYSTEMS [4, 7, 21]
ppm
Melbourne,
Australia
Trace
element
Boron
Cadmium
Chromium
Cobalt
Copper
Iron
Lead
Manganese
Molybdenum
Nickel
Zinc
Typical
range
1.0-80
0.2-0.8
0.1-0.5
0.05-0.5
2.0-15
250-600
0.1-10
15-200
0.1-4.0
0.1-3.5
8.0-60
Control
site
NTa
0.77
6.9
<0.64
6.5
970
<2.5
149
NT
2.7
50
Wastewater
irrigated
forage
NT
0.64-1.28
6.9-28
<0. 64-1. 28
11-19
361-987
<2.5
44-54
NT
2.7-9.1
58-150
Dickinson,
North Dakota
Control
site
14.1
<5
2
<1
7.4
NT
<5
53
<0.05
<0.5
22
Wastewater
irrigated
forage
19.6
<5
<5
<1
6.8
NT
<5
78
<0.05
<0.5
37
San Angelo,
Texas
Wastewater
irrigated
forage
NT
0.2-0.5
<0.5-1.5
NT
3.8-9.1
NT
NT
NT
NT
1.2-4.0
10-61
a. Not tested.
9.5.3 Ground Water
Trace elements in ground water can limit its use for
drinking or irrigation purposes. For this reason, the
potential for trace element contamination of ground water is
a concern at SR and RI systems overlying potable aquifers or
aquifers that can be used as irrigation water supplies.
Drinking and irrigation water standards are presented in
Table 9-7.
The most toxic metals to man--cadmium, lead, and mercury—
were demonstratably absent in the percolate at five of the
six SR sites listed in Table 9-3; the sixth site gave
inconclusive data because fallout from nearby smelters
contaminated the soils. Concentrations of the metals have
not approached toxic levels in any of the sites studied
after up to 50 years of operation.
Cadmium, lead, and mercury concentrations in shallow ground
water were comparable to concentrations in control wells at
two of the three RI sites where trace metals were monitored
[17] . At Hollister, shallow ground water concentrations of
cadmium and lead were only slightly higher than control well
concentrations and were well within drinking water
standards. At the sites studied, trace element con-
tamination of ground water has not been a problem. As long
as the soil pH is maintained at 6.5 or higher, ground water
contamination is likely to remain nonexistent.
9-11
-------
TABLE 9-7
TRACE ELEMENT DRINKING AND IRRIGATION
WATER STANDARDS [8, 13, 22-27]
mg/L
Irrigation water
Drinking
Aluminum (Al)
Antimony (Sb)
Arsenic (As)
Barium (Ba)
Beryllium (Be)
Boron (B)
Cadmium (Cd)
Chromium (Cr+6)
Cobalt (Co)
Copper (Cu)
Iron (Fe)
Lead (Pb)
Manganese (Mn)
Mercury (Hg)
Molybdenum (Mo)
Nickel (Ni)
Selenium (Se)
Silver (Ag)
Thallium (Tl)
Vanadium (V)
Zinc (Zn)
a. Normal irrigation
b. Normal irrigation
c. Recommended Water
on Water Quality
water
—
0.145d
0.05^
1.0e
—
—
0.01e
0.05e
—
1.0*
0.3f
0.05e
0.05f
0.002e
—
—
0.016
0.05e
0.004d
—
5f
practice
practice
Quality
Criteria.
For fine
textured
soils3
20C
—
2°
—
0.5C
0.75°
0.05C
1.0C
5C
5C
20°
10C
10. Oc
—
0.05°
2.0°
0.02C
4-89
—
1.0C
10C
for 20 years.
, no time limit
Standards, 1972
d. EPA Toxic Pollutants Standards for Human
For
any soil
—
—
0.1°
__
O.lc
2c
0.01C
O.lc
0.5°
0.2C
5C
5.0C
0.02C
—
0.01C
0.2°
0.02°
—
0.1°
2c
.
Report to
Health.
For
livestock
5°
— «
0.2C
__
--
5.0p
0.05C
1.0C
1.0C
0.5C
— «.
O.lc
— «_
0.016
_._
_..
0.05C
_„
— .-
0.1<"
25C
EPA
e. EPA Primary Drinking Water Standards.
f. EPA Secondary Drinking Water Standards.
g. EPA Recommended Irrigation
Water Standards.
9.6 Microorganisms
Three classes of microorganisms can be pathogenic to man and
animals:
a Bacteria
© Viruses
© Parasitic protozoa and helminths
9-12
-------
Several approaches have been used at land treatment systems
to minimize the public health impacts of pathogens. Many SR
and RI systems use primary sedimentation prior to land
treatment, thereby removing most helminths. Holding ponds
also can be . used before land treatment to inactivate most
pathogens. Generally, a long detention time (about 30 days)
and moderate temperatures are required for effective
pathogen removal (Section 4.4.1). Many SR and RI systems
rely on the filtering capacity of the soil to remove
bacteria, helminths, and protozoa, and on soil adsorption
for virus removal.
There are five potential pathways for pathogen transport
from land treatment systems:
• Soils
• Crops
• Ground water
• Surface waters
• Aerosols
9.6.1 Soils
Straining and microbiological activity are the primary
mechanisms for bacterial removal as wastewater passes
through soil. Finer soils, of course, tend to have higher
capacity for pathogen removal. Depending on the particular
system design, there will be either a mat on top of or a
zone within the soil where intense microbiological activity
occurs. Here, bacteria, protozoa, and helminths and their
eggs are removed by straining and the predations of other
organisms, which consume the dead organisms along with the
BOD in the applied wastewater and convert them primarily to
carbon dioxide and ammonia. No lasting adverse effects to
soil have been noted that result from these organisms.
Bacteria removal in the finer textured soils commonly
encountered at SR systems is usually quite high (as shown in
Table 4-6). Research has shown that complete bacteria
removal generally occurs within the top 1.5 m (5 ft) of the
soil profile [28]. Similar research has indicated that die-
off occurs in two phases: during the first 48 hours
following wastewater application, 90% of the bacteria died;
the remainder of the bacteria died during the following
2 weeks [29].
9-13
-------
Removal efficiencies at selected Rl systems are presented in
Table 5-6. As indicated by this table, effective bacteria
removals are achieved at RI sites when adequate soil travel
distance is provided.
At OP sites, bacteria are removed near the soil surface by
filtration, biological predation, and ultraviolet radia-
tion. Fecal coliform removals in excess of 95% can be
obtained by maximizing the OF residence time (increasing the
removal of suspended solids) and applying wastewater at a
slow and relatively continuous rate [30]. For example,
daily application of wastewater for extended periods (12 to
18 hours) results in better removal efficiency than shorter
application periods (6 hours) alternated With weekend
drying.
Adsorption is the primary mechanism for virus removal at
land treatment systems. Virus removal at SR systems is
quite effective. Virus removal at Rl sites depends on
initial concentration, hydraulic loading rate, soil type,
and distance traveled through the soil. Virus transmission
through soil at RI systems is presented in Table 9-8.
Removal at OF sites is generally the same order of magnitude
as virus removal during conventional secondary treatment.
It is possible for parasite eggs, such as Ascaris and
helminths, to survive for months to years in soil. Although
no conclusive evidence has been found to link transmission
of parasitic infections to operating land treatment systems,
vegetables that will be consumed raw should not be grown at
land treatment sites for at least 1 to 2 years after land
treatment operations are terminated.
9.6.2 Crops
In the United States, the use of wastewater for irrigation
of crops that are eaten raw is not common. At present,
crops usually grown include fiber, feed, fodder, and
processed grains. No incidents of infection resulting from
crops receiving wastewater have been identified in the
United States. Sewage farms in Paris apply raw wastewater
to fruit and vegetable crops (not eaten raw) which are
approved for public consumption by the Ministry of Health,
with no reported health problems.
Systemic uptake of pathogens by crops and subsequent
transmission through the food chain is not a problem. When
extremely high concentrations of viruses were applied to
damaged roots and leaves, plants did take up organisms along
with water and nutrients [31]. Several studies performed
using typical wastewaters on undamaged crops show no
pathogen uptake [4, 6],
9-14
-------
TABLE 9-8
VIRUS TRANSMISSION THROUGH SOIL AT
RI SYSTEMS [1]
Sampling Virus concentration, PFU/L
Location
Phoenix,
Arizona
(Jan- Dec
1974)
Gainesville,
Florida
(Apr-Sep
1974)
Santee,
California
(1966)
Ft. Devens,
Massachusetts
(1974)
Medford,
New York
(Nov 1976-
Oct 1977)
Vineland,
New Jersey
(Aug 1976-
May 1977)
aj-snance,
m At source
3-9 8
27
24
2
75
11
7 0.14 (avg over study period)
0.14 (avg over study period)
0.14 (avg over study period)
0.14 (avg over study period)
0.14 (avg over study period)
0.14 (avg over study period)
0.14 (avg over study period)
0.14 (avg over study period)
61 Concentrated type 3 polio
17 Indigenous virus, 276 (avg)
f2 bacteriophage seed,
2.2 x 105
0.75-8.34 Indigenous virus, 1.1-81.0
0.75 Polio virus seed, 7 x 104
(6 cm/h infiltration rate)
0.75 1-84 x 105 {100 cm/h
infiltration rate)
0.6-16.8 13 (avg over study period)
13 (avg over study period)
13 (avg over study period)
13 (avg over study period)
At sample point
0
0
0
0
0
0
0.005
0
0
0
0
0
0
0
0
8.3 (avg)
1.3 x 105
17 samples negative;
6 positive, at 0.47
(avg); range 0.14-0.66
Range 0-25.5
Range 0.03 x 104 to
97.5 x 104
9 of 10 positive, 1.62 avg
7 of 10 positive
2 of 10 positive, 1.95 avg
0 of 10 positive, 0.48 avg
When wastewater is applied by sprinklers, the potential
exists for pathogens to survive on the surface of a plant.
Sunlight is an effective disinfectant, killing pathogens in
a few hours to a few days; but any place that stays warm,
dark, and moist could harbor bacteria. For this reason,
wastewater is not used to irrigate crops that are eaten raw
unless a very high degree of preapplication treatment is
provided. To protect livestock, grazing should not be
allowed on pasture irrigated with disinfected pond or
secondary effluent for 3 to 4 days following wastewater
application. At least 1 week should be allowed between
applications of primary effluent and grazing. Longer
resting periods are recommended for cold, northern climates,
particularly when forage crops such as Reed canarygrass,
orchardgrass, and bromegrass are irrigated [29, 32].
The National Technical Advisory Committee on Water Quality
advises a standard of-1,000 fecal coliforms/100 mL for water
used in agriculture [20]. 'Even lower fecal coliform
9-15
-------
concentrations can be achieved, without disinfection, by
settling and storing the effluent before application
(Section 4.4.1).
9.6.3 Ground Water
Because viruses can survive outside an animal host for
longer periods of time than bacteria and other pathogens,
and because ingestion of only a few viruses may cause
disease, virus transmission is the , primary concern when
evaluating the ground water pathway. Other pathogens are
removed largely by filtration or natural die-off before they
have an opportunity to migrate into ground water. Although
no viral standards have been established, SR and RI systems
that discharge to potable aquifers are designed to meet the
bacterial standard listed in Table 2-4. The intent, of this
standard is to ensure that renovated water is essentially
bacteria- and virus-free.
As indicated in Section 9.6.1, virus removal at SR systems
is quite effective, mainly due to the adsorptive capacity of
soils used for SR systems. Thus, most research on virus
transmission has been focused on RI systems and coarser
textured soils, such as the studies summarized in
Table 9-8. As indicated in this table, viruses can enter
ground water, particularly when large virus concentrations
are applied at high loading, rates to very permeable soils.
However, the number of viruses that are transmitted is low,
and the risk to potential consumers is minimal provided
adequate distance between the treatment site and any ground
water wells is maintained.
Coliform levels found in ground water underlying SR and RI
systems are shown in Tables 4-6 and 5-6. These tables
indicate that over 99% of the applied coliforms is removed
within short travel distances. Provided adequate distance
is allowed, it is possible for any well-operated SR or RI
system to meet the coliform standard for drinking waters.
9.6.4 Surface Water
Land treatment systems that discharge to surface waters used
for drinking, irrigation, or recreation must meet local
discharge standards for microorganisms. As mentioned
previously, SR and RI systems should have no problems
meeting discharge standards. The microbiological quality of
renovated water from OF systems generally is comparable to
effluent from conventional secondary treatment systems
without chlorination. Bacteria removals of 90 to 95% or
higher and virus removals of 70 to 90% are typical at OF
systems (Section 6.2.6).
9-16
-------
9.6.5 Aerosols
Aerosols are very small airborne droplets, less than 20
microns in diameter, that may be carried beyond the range of
discernible droplets from sprinklers. Sprinkler generated
aerosols are slightly smaller than ambient aerosols; two-
thirds to three-fourths of the 'sprinkler generated aerosols
are in the potentially respirable size range of 1 to 5
microns [33]. Aerosols may carry bacteria and viruses, but
do not normally contain pathogenic protozoa or helminths and
their eggs. Aerosols may come from sources other than
wastewater treatment sites, such as cooling towers and
public facilities. As a result of these other sources,
ambient bacterial concentrations in the air of some cities
are comparable to the concentrations found near land
treatment sprinkler zones.
As aerosols are generated, they are immediately subjected to
an "impact factor" that may reduce bacteria concentrations
by 90% and virus concentrations by 70% within seconds [2] .
Further reduction may be caused by desiccation, temperature,
deposition, and solar radiation. Aerosol dispersion,
influenced by wind speed, air turbulence, and local
topography, occurs concurrently.
The concentration of bacteria and viruses in aerosols is a
function of their concentration in the applied wastewater
and the aerosolization efficiency of the spray process. The
latter of these factors depends on nozzle size, pressure,
angle of spray trajectory, angle of spray entry into the
wind, and impact devices [34]. Studies have shown that
approximately 0.32% of the liquid leaving the nozzle is
aerosolized [35].
Bacteria cannot be detected in aerosols at distances of even
10 m (33 ft) from sprinklers unless the bacteria con-
centrations in the applied wastewater are at least 10^ to
104/mL, [36]. When undisinfected wastewater is sprinkler
applied, aerosol bacteria have been found to travel a
maximum distance of 400 m (1,312 ft) from a sprinkler line
[37]. Under some conditions, viruses have been-detected at
distances of up to 100 m (328 ft) [2]. Concentrations of
bacteria and enteroviruses that have been detected near
various SR land treatment sites are shown in Tables 9-9 and
9-10.
9-17
-------
TABLE 9-9
AEROSOL BACTERIA AT LAND
TREATMENT SITES [2]
Kastewater type
Raw or primary
Ponded,
chlorinated
Secondary/
nondisinfected
Distance
downwind
Location from site, m
Germany 90-160'-'
Germany 63-400b»°
California 32&
Kibbutz Tzora, 10
Israel 10
20
60
70
100
150
200
250
300
350
400
Deer Creek, Control value
Ohio 21-30
41-50
200
Ft. Huachuca, Control value
Arizona Control value
45-49°
120-152°
Pleasanton, Control value
California 30-50
100-200
Bacteria
Coliforms
Col i forms
Coliforms
Coliforms
Fecal coliforms
Coliforms
Coliforms
Salmonella
Coliforms
Coliforms
Coliforms
Coliforms
Coliforms
Colifonrs
Coliforms
Standard plate count
Standard plate count
Standard plate count
Standard plate count
Standard plate count
Coliforms
Standard plate count
Klebsiella
Standard plate count
Standard plate count
Standard plate count
Total coliforms
Fecal coliforms
Fecal streptococci
Pseudomonas
Klebsiella
Clostridium perfringens
Mycobacterium
Standard plate count
Total coliforms
Fecal coliforms
Fecal streptococci
Pseudomonas
Klebsiella
Clostridium perfringens
Mycobacterium
Density
range3. No.
— „
—
—
11-496
35-86
0-480
0-501
30-102
0-88
4-32
0-17
0-21
0-7
0-4
23-403
46-1, 582^
0-1,429<3
<0-223
-------
TABLE 9-10
AEROSOL ENTEROVIRUSES AT LAND
TREATMENT SITES [2]
Wastewater
type
Nondisinf acted
Location
Pleasanton,
Distance
downwind
from
sprinkler, m
50
Wastewater entero-
viruses, PFU/L
Range
45-330
Mean
188
Aerosol entero-
viruses, PFU/m
Range
0.011-0.017
Mean
0.014
secondary California
effluent
Raw
wastewater
Kibbutz
Tzora,
Israel
36-42
50
70
100
0-650
—
170-13,000
0-82,000
125
650
6,585
16,466
0-0.82
—
0-0.026
0-0.10
0.015
Q.14
0.013
0.038
The data in Tables 9-9 and 9-10 can be used to estimate
human exposure to aerosol bacteria and enteroviruses. For
example, a reasonable estimate may be obtained by using data
from Pleasanton, California. At a distance of 50 m (164 ft)
downwind from a sprinkler, an adult male engaged in light
work and breathing at a rate of 1.2 m-^/h (42 ft^/h) would
inhale an average of 1 plaque-forming unit (PFU) of
enterovirus after 59 hours of exposure. Although this
represents an extremely low rate of potential viral
exposure, methods for recovering enteric viruses currently
are not entirely efficient and actual viral exposure may be
somewhat higher [38] .
As shown by the data in Table 9-11, aerosol fecal coliform
concentrations are lower at SR systems than at activated
sludge facilities. Thus, the risk of disease transfer from
SR sites should be no greater than from activated sludge
facilities. For this reason, epidemiological studies of the
health effects of aerosols from activated sludge plants may
be used to conservatively estimate the health effects of SR
facility aerosols.
Epidemiological studies of activated sludge plants indicate
that there is no significant disease rate increase for
nearby populations [39-44]. Based on these studies, it does
not appear that land treatment system employees or people
living near sprinkler irrigation sites should anticipate a
risk of disease due to aerosols.
9-19
-------
TABLE 9-11
COMPARISON OF COLIFORM LEVELS
IN AEROSOLS AT ACTIVATED SLUDGE AND
SLOW RATE LAND TREATMENT FACILITIES [37, 45]
Maximum
Median
Minimum
Activated sludge
Aerosols, No./m
Upwind 28 0 0
Over basins 146 14 0
Downwinda 141 7 0
Wastewater, No./lOO mL 8 x 107 1.6 x 106 1.1 x 104
Aerated pond
Aerosols, No./m
Downwind
30 m 452 ~ 4
100 m 5 -- 1
150 m 4 — —
200 m 5 — 0
250 m 4 —- 0
Wastewater, No./lOO mL 105 -- 104
Slow rate land treatmenta
Aerosols, No./m3
Upwind 1.0 BDC BD
Downwindd 12.2 1.0 BD
Wastewater, No./lOQ mL 1.86 x 105 8.1 x 104 2.4 x 104
a. Fecal coliform levels reported.
b. Total coliform levels reported.
c. Below detection.
d. Up to 30 m (98 ft) downwind.
If necessary, several measures can be used to further reduce
bacterial and viral exposure through aerosols. First,
operating sprinklers during daylight hours increases the
number of microorganisms killed by ultraviolet radia-
tion [2] . Sprinkling during early morning hours is prefer-
able in arid or semiarid areas for water conservation
purposes. Second, the use of downward-directed„ low
pressure sprinklers results in fewer aerosols than upward-
directed high pressure sprinklers. Ridge-and-furrow irri-
gation or surface flooding are recommended when these
application techniques are feasible [2]. Third, when public
residences are near the sprinkler system, buffer zones may
be used to separate the spray source and the general
public. In general, public access to the irrigation site
should be limited. Finally, planting vegetation around the
site can reduce the aerosol concentrations leaving the site
[46] . Coniferous or deciduous vegetation have achieved up
9-20
-------
to 50% aerosol removal by filtration. Planted as a barrier,
these types of vegetation should be able to reduce aerosol
concentrations several orders of magnitude through vertical
dispersion and dilution.
9.7 Trace Organics
Concern over trace organics arose when chlorinated
hydrocarbons and other trace organics were found in potable
water supplies. At land treatment sites, the concern is
that trace organics may travel through the soil profile and
enter drinking water aquifers or accumulate in the soil
profile and be taken up by plants.
9.7.1 Soils
Many trace organics are adsorbed as they move through the
soil profile at SR and RI systems. Chloroform is one such
compound, as indicated in Table 4-7; other chlorinated
hydrocarbons behave similarly. Although the adsorptive
capacity of a soil is limited, once trace organics have been
adsorbed they may be biodegraded or volatilized and released
to the atmosphere. In either case, the. adsorption site
becomes available for adsorption of additional organic
molecules.
The amount of trace organics that can be removed during
movement through the soil is not well understood. Some
research has been conducted in West Germany using natural
sand beds to filter contaminated river water. The river
water contains high concentrations of trace organics,
particularly chlorinated hydrocarbons. The observed removal
efficiencies are presented in Table 9-12. As shown in this
table, trace organics removal can be highly effective, even
in coarser soils. ,
TABLE 9-12 .
TRACE ORGANICS REMOVALS DURING
SAND FILTRATION [47]
Constituent
% removal
Chlorobenzene 96
Dichlorobenzene 45
Trichlorobenzene 12
Chlorotoluene 94
Dichlorbtoluene 62
Dissolved organic chlorides 38
Dissolved nonpolar organic chlorides 73
Dissolved organic.carbon 68
Benzene 80
Toluene 95
9-21
-------
9.7.2 Crops
Plants can absorb many organic pesticides and some
organophosphate insecticides through their roots, with
subsequent translocation to plant foliage. Uptake of these
organics is affected by the solubility, size, concentration,
and polarity of the organic molecules; the organic content,
pH, and microbial activity of the soil; and the climate
[48] . However, a recent study on health risks associated
with land application of sludge has found that the level of
pesticide and herbicide absorption is quite low; not more
than 3% of the molecules that were in the soil passed into
plant foliage [48]. Most trace organics are too large to
pass through the semipermeable membrane of plant roots.
Thus, it is unlikely that crop uptake of trace organics
during land treatment is significant enough to be 'harmful to
man or animals.
9.7.3 Ground Water
As mentioned in Section 9.7.1, soil adsorption of trace
organics at SR and RI sites can be an effective removal
mechanism. For this reason, only low levels of trace
organics would be expected to migrate to underlying ground
water. The results of studies at two SR systems
(Table 9-13) and two RI systems (Table 5-8) indicate that
significant removals do occur at these systems with the
exception of the Milton RI site which was operated at
continuous (no drying) extremely high wastewater loadings.
At the Milton site, high removals are achieved by the time
ground water travels a distance of 45 m (160 ft)
downgradient. Endrin, methoxychlor, and toxaphene were not
detectable in the wastewaters of any of the four
communities, and the concentrations of lindane, 2,4-D, and
2,4,5-TP silvex were all well below drinking water limits in
the ground waters underlying the land treatment sites
(Table 2-4).
Recent research at the phoenix RI site has examined the
removal of refractory volatile organics during RI using
secondary effluent [54]. The results are presented in
Table 9-14. As shown by this table, fairly high removal
efficiencies were obtained (70 to 100%).
Similar research conducted at the Fort Devens RI site
indicated that 80 to 100% of the applied refractory organics
is removed during RI; average removal of trace organics was
96% [50]. Based on the results of these studies, it does
not appear that normal concentrations of trace organics in
applied wastewaters would cause problem levels in ground
waters underlying SR and RI sites. Detailed studies on the
9-22
-------
fate of trace organics during land treatment are underway at
the Muskegon SR site; these studies should provide
additional insight into the potential risk of ground water
contamination.
TABLE 9-13
TRACE ORGANICS REMOVALS AT SELECTED SR SITES [4, 6]
ng/L
Endrin
Lindane
Methoxychlor
Toxaphene
2,4-D
2,4, 5-TP
silvex
Roswell ,
Wastewater
<0.03
560
<0.01
<0.1
29.0
28.0
New Mexico
Ground water
<0.03
74.3
<0.01
<0.1
10.4
25.8
Dickinson,
Wastewater
<0.03
397
<0.01
<0.1
17.0
93
North Dakota
Ground water
<0.03
53.6
<0.01
<0.1
6.2
47.1
TABLE 9-14
REMOVAL OF REFRACTORY VOLATILE ORGANICS
BY CLASS AT PHOENIX RI SITE [49]
Class (typical example)
Removal, %
Chloroalkanes (tetrachloroethylene) 70
Chloroaromatics (p-dichlorobenzene) 94
Alkyabenzenes (o-xylene) 98
Alkyaphenols (p-isopropylphenol) 85
Alkylnaphthalenes (2-methylnapthalene) 100
Alkanes (hexatriacontane) 71
Alcohols (2,4-diraethl-3-hexanol) 95
Ketones (2,6-d-t-butyl-p-benzoquinone) 98
Indoles, Indenes (IH-indole) 96
Amides (N-[3-methylphenyl] acetamide) 74
Alkoxyaromatics (butoxymethylbenzene) 91
Weighted average 92
9.7.4 Surface Water
Discharge from the OF process will directly impact surface
water in most cases. The effectiveness of trace organics
removal during OF has been studied at a pilot system in
Hanover, New Hampshire. Chlorinated primary effluent was
used in these studies; this effluent contained 6.7 to 17.8
9-23
-------
ug/L chloroform, 10.2 to 33.1 ug/L toluene, and lesser
amounts of bromodichloromethane, 1,1,1-trichloroethane,
tetrachloroethylene, and carbon tetrachloride [51]. Using a
30.5 m (100 ft) long slope with a 5% grade, chloroform and
toluene removals were as presented in Table 9-15. These
efficient removal rates are thought to result from
volatilization as the wastewater flows over the slope or
sorption near the soil surface followed by either microbial
degradation or volatilization. Based on these results, it
appears that volatile trace organics contamination of
surface waters by renovated water from OF systems should not
be a problem unless initial concentrations are excessive.
Studies are underway on the removal of nonvolatile organic
compounds.
TABLE 9-15
CHLOROFORM AND TOLUENE REMOVAL
DURING OF [51]
Application
rate,
cm/h
Chloroform
0.40
0.60
0.80
1.05
1.32
Toluene
0.40
0.60
0.80
1.05
1.32
Concentration at various travel distances.
Waste-
water
17.8
6.7
13.2
6.7
9.0
33.1
10.2
28.7
21.5
18.8
3.8 m
12.4
5.7
6.4
—
7.8
20.7
6.2
10.0
—
9.9
7.6 m
6.9
3.8
5.9
5.9
6.8
4.9
2.4
7.8
9.8
7.7
15.7 m
3.1
2.1
3.7
4.1
6.1
BDa
0.5
3.9
7.4
6.3
22.9 m
0.9
1.5
—
1.4
— •
BD
BD
--
1.4
ug/L
Runoff
0.3
0.5
0.8
1.1
1.9
BD
BD
BD
0.7
0.8
Total
removal ,
%
98.3
92.5
93.9
83.6
78.9
100.0
100.0
100.0
96.7
95.7
9.8
a. BD - concentration was below a detection limit estimated at
0.01 pg/L.
References
Reed, S. , R. Thomas, and N. Kowal. Long Term Land
Treatment, Are There Health or Environmental Risks?
Proceedings of the ASCE National Convention, Portland,
Oregon. April 1980.
Kowal, N.E. Health Effects of Land Treatment.
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Health Effects Research Laboratory. Cincinnati,
Ohio. EPA-600/1-81-055. July 1981.
9-24
-------
3. Stone, R. and J. Rowlands. Long-Term Effects of Land
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5. Stone, R. and J. Rowlands. Long-Term Effects of Land
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7. Hossner, L.R., et al. Sewage Disposal on Agricultural
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8. Reynolds, J.H., et al. Long-Term Effects of Land
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10. Aulenbach, D.B. Long-Term Recharge of Trickling Filter
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John
Ayers, R.S. Quality of Water for Irrigation. journal
of the Irrigation and Drainage Division, ASCE 103
(IR2): 135-154. 1977.
Uiga, A., R.C. Fehrmann, and R.W. Crites. Relative
Health Factors Comparing Activated Sludge Systems to
Land Application Systems. Proceedings of the Symposium
on Land Treatment of Wastewater, Hanover, New
Hampshire. August 20-25, 1978.
Leach, L.E., C.G. Enfield, and C.C. Harlin. Summary of
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July 1980.
Peters, R.E., C.R. Lee, and D.J. Bates. Field
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Anthony, R.G., et al . Effects of Municipal Wastewater
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Reed, S.C. Health Aspects of Land Treatment.
Technology Transfer Seminars, Land Treatment of
Municipal Wastewater Effluents. U.S. Environmental
Protection Agency and U.S. Army Corps of Engineers.
June 1979.
Seabrook, B.L. Land Application of Wastewater in
Australia. U.S. Environmental Protection, Agency. EPA-
430/9-75-017. May 1975.
Federal Register. Water Quality Criteria.
1979. pp. 15926-15970.
March 15,
Federal Register. Water Quality Criteria. July 25,
1979. pp. 43660-43697.
Federal Register. Water Quality Criteria.
1979. pp. 56628-56657.
October 1,
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25. Metcalf & Eddy, Inc. Wastewater Engineering:
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26. Manual of Treatment Techniques for Meeting the Interim
primary Drinking Water Regulations. U.S. Environmental
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27. McKee, J.E. and H.W. Wolf. Water Quality Criteria.
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28. Jenkins, T.F. and A.J. Palazzo. Wastewater Treatment
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Hampshire. August 1981.
Bell, R.G. and J.B. Bole. Elimination of Fecal
Coliform Bacteria from Soil Irrigated with Municipal
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Enumeration Problems of Fecal Coliform Bacteria in
Runoff Waters from Terrestrial Ecosystems. Technical
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Experiment Station. Vicksburg, Mississippi. September
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31. Shuval, H.I. Land Treatment of Wastewater in Israel.
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Point-of-View. International Commission on Irrigation
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33. Bausum, H.T., et'al. Microbiological Aerosols from a
Field Source During Sprinkler Irrigation with
Wastewater. proceedings of the Symposium on Land
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August 20-25,' 1978.
34. Schaub, S.A., et al. Monitoring of Microbiological
Aerosols at Wastewater Sprinkler Irrigation Sites.
Proceedings of the Symposium on Land Treatment of
Wastewater, HanoVer, New Hampshire. August 20-25,
1978.
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35. Sorber, C.A., et al. A Study of Bacterial Aerosols at
a Wastewater Irrigation Site. journal WPCF. 48(10):
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36. Johnson, p.E. , et al. The Evaluation of
Microbiological Aerosols Associated with the
Application of Wastewater to Land: Pleasanton,
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EPA-600/1-80-015. 1980.
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Workers Engaged in Wastewater Collection and
Treatment. Proceedings of the Symposium ' on Land
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August 20-25, 1978.
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Presented at the 53rd Annual Conference of the Water
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from an Activated Sludge Plant. U.S. Environmental
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43. Crites, R.W. and A. Uiga. An Approach for Comparing
Health Risks of Wastewater Treatment Alternatives - A
Limited Comparison of Health Risks Between Slow Rate
Land Treatment and Activated Sludge Treatment and
Discharge. U.S. Environmental Protection Agency.
EPA-430/9-79-009, MCD-41. 1979.
44. Pahren, H.R. and W. Jakubouski, eds. Wastewater
Aerosols and Disease. U.S. Environmental Protection
Agency. EPA-600/9-80-028. December 1980.
9-28
-------
45. Sorber, C. et. al. Bacterial Aerosols Created by Spray
Irrigation of Wastewater. In: Proceedings of the
Sprinkler Irrigation .Technical Conference, Sprinkler
Irrigation Association. Rockville, Maryland. 1975.
46. Spendlove, J.C., et al. Supression of Microbial
Aerosols by Vegetation. Presented at the Water
pollution Control Federation Conference, Houston,
Texas. October 7-12, 1979.
47. Sontheimer, H. Experience with River Bank Filtration
Along the Rhine River. Proceedings of the Symposium on
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Application of Municipal Sludge. journal WPCF.
51(11): 2588-2601. 1979.
49. Tomson, M.B., et al. Ground Water Contamination by
Trace Level Organics .from a Rapid Infiltration Site.
Water Research. In Press. 1981. ;
50. Tomson, M.B., et al. Trace Organic Contamination of
Ground Water: Methods for Study and Preliminary
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of volatile Trace Organics from Wastewater by Overland
Flow Land Treatment. journal of Environmental Science
and Health. A15(3):211-224. 1980.
9-29
-------
-------
APPENDIX A
SLOW RATE DESIGN EXAMPLE
A.I Introduction
This design example is presented to .illustrate the pro-
cedures described in Chapter 4 for the preliminary design of
slow rate (SR) systems. The example is detailed enough to
allow cost comparison with other alternatives. The focus of
this example is on determining the major design variables in
land treatment systems including crop selection, hydraulic
loading rate, land area requirements, storage requirements,
and application method. Supplemental components such as
pumping and headworks requirements are discussed briefly and
listed for cost comparison purposes.
A. 2 Statement of Problem
A.2.1
Background
City A is located in central Missouri in an area charac-
terized by fertile soils -and intensive farming. Rainfall is
more plentiful than is needed for most crops, but is distri-
buted unevenly during the year, Supplemental irrigation is
beneficial to most crops in summer.
The existing wastewater treatment facility consists of a
single stage trickling filter with anaerobic digestion and
sludge drying, beds. The facility is in poor structural
condition and unable to meet present NPDES permit
requirements.
A.2.2
Population and Wastewater Characteristics
Population and wastewater characteristics are presented in
Table A-l. Industrial flows are expected to be nontoxic and
biodegradable.
A.2.3
Discharge Requirements
Surface discharge of wastewater is prohibited for streams in
the area, and the ground water aquifer is used as a drinking
water source so drinking water quality will be expected at
the project boundary.
A-l
-------
TABLE A-l
POPULATION AND WASTEWATER CHARACTERISTICS
Design year
Population
Average annual flow, m /d
Industrial
Municipal
Total
Maximum monthly avg flow, m3/d
Infiltration into sewers
Wastewater strength, mg/L
BOD 5
SS
Total nitrogen, mg/L (as N)
Total phosphorus, mg/L (as P)
2005
18,900
416
7,154
7,570
9,085
None
(nonexcessive)
200
200
38
8
A.2.4
Site Characteristics
The proposed site for the treatment facility is shown in
Figure A-l. The site was chosen because of its isolation
from population centers, its location downwind from the
city, and the availability of flat, well-drained soils in
the area. According to an old SCS map, shown in Figure A-l,
Bosket fine sandy loam dominates the treatment site and
Cooter silty clay dominates the treatment pond site. Both
areas have 0 to 1% slope.
A.2.5
Climate
The area is subject to frequent changes in weather with no
prolonged periods of very cold or very hot weather. The
last freeze is usually5 in late March and the first freeze in
early November. •
Climatic data, obtained from the National Oceanic and
Atmospheric Administration's Climatography of the United
States, are shown in Table A-2 for the nearest United States
No. 20 recording station to City A. The data represent the
worst year in 5 for monthly average precipitation and
temperature.
A-2
-------
PROPOSED
POND
TREATMENT
SITE
PROPOSED SR SITE
Predominant
soil series
Bosket '
Broseley
Canalou
Cooter
Crevasse
Gideon
Lilbourn
Sikeston
Map
symbol
BtA,
BtB
ByA,
ByC
Cd
Co
CsB
Gd,
Ge
Lb
St
Depth to
seasonal high Depth from
water table, m surface, cm
>1.5 0-64
64-147
147-198
>1.5 0-94
94-160
160-190
0.6-0.9 0-51
51-122
122-160
0.6-0.9 0-38
38-152
>1.0 0-25
25-152
0-0.3 0-114
114-173
0-0.5 0-94
0-0.3 0-30
Permeability,
Dominant USDA texture
Fine sandy loam
Clay loam and sandy clay loam
Fine sandy loam and sand
Loamy fine -and
Fine sandy loam
Loamy fine sand
Loamy sand
Sandy loam
Sand
Silty clay
Loamy sand and sand
Loamy sand
Sand
Loam
Clay loam
Fine sandy loam
Sandy clay loam ,
cm/n
• 5-15
1.5-5
5-15
15-51
5-15
15-51
15-51
15-51
15-51
0.15-0.5
15-51
15-51
15-51
1.5-5
1.5-5
5-15
1.5-5
FIGURE A-1
SOILS MAP
A-3
-------
TABLE A-2
CLIMATIC DATA FOR THE WORST YEAR IN 5
Temperature °C
Month
Jan
Feb
Mar
Apr
May
Jun
Jul
Aug
Sep
Oct
Nov
Dec
Annual
Mean daily,
Mean minimum
-0.7
-0.9
1.3
12.7
16.7
21.1
24.1
24.4
19.8
11.9
4.6
-0.1
-6.6
-8.1
-5.6
4.6
8.3
13.9
16.7
15.9
9.6
0.2
-3.1
-6.6
Days with
mean
temperature,
<.-4 °C
20
15
12
0
0
0
0
0
0
4
12
17
80
Total
precipitation ,
cm
10.1
10.4
15.1
15.8
17.4
14.2
14.0
12.2
14.7
9.9
14.8
13.0
162
A.3 Slow Rate System Selection
The selection of the type of land treatment process is dic-
tated by site conditions, climate, and regulatory require-
ments. In the case of City A, the prohibition of surface
discharge eliminated overland flow from consideration. The
limit of 10 mg/L nitrate in the ground water, coupled with
the high ground water table, eliminated rapid infiltration
as an alternative. The SR process appeared feasible based
on land availability, soil permeability, and climate.
A.3.1
Preapplication Treatment
The existing treatment facilities cannot be used for pre-
application treatment without extensive rehabilitation.
Consequently, treatment prior to land application is to be
provided by a series of treatment/storage ponds. The pri-
mary cell is designed according to state standards:; BOD
loading equals 38.1 kg/ha-d (34 lb/acre-d) with an operating
depth of 1.0 m. The secondary cell is designed for storage.
A-4
-------
A.3.2
Crop Selection
As discussed in Section 4.3, the crop selected for the SR
process depends on whether the objective is crop production
for revenue or minimization of land area by maximizing
hydraulic loading rates. For City A, the objective is to
minimize land area. Based on the selection criteria in
Chapter 4 and conversations with the local farm advisor,
City A chose to evaluate water tolerant forage grasses and
deciduous forest as two possible crops in an SR system. The
proposed site shown in Figure A-l would be used for either
crop.
A.4 System Design
A.4.1 Forage Crop Alternative
Minimizing land area requires the use of the maximum allow-
able hydraulic loading rate which is governed either by soil
permeability or nitrogen loading. Once the hydraulic
loading rate is determined, field area and storage require-
ment are obtained.
A.4.1.1 Hydraulic Loading Based on Soil
Permeability
The general water balance equation is used to determine the
allowable hydraulic loading based on soil permeability
(Section 4.5.1) and is shown as:
where LW =
ET =
Pr
pw
Lw = ET - Pr + Pw (4-3)
wastewater hydraulic loading rate, cm/unit time
evapotranspiration rate, cm/unit time
precipitation rate, cm/unit time
percolation rate, cm/unit time
The computation is performed on a monthly basis in the' form
of a water balance table shown in Table A-3. The procedure
follows that presented in Section 4.5.1 and is outlined
below:
1. Design precipitation for each month is based on a
5_vear return period and is obtained from climatic
data (Table A-2). The frequency analysis is per-
formed according to standard procedures available
A-5
-------
in most hydrology texts or reference books. The
precipitation values are entered in Column (1).
2. Estimated monthly evapotranspiration (ET) values
for the forage grass are obtained from the local
Cooperative Extension Service and are entered in
Column (2).
3. The net ET for each month is determined by sub-
traction of Column (1) from Column (2).
4. The maximum design percolation rate is based on 4%
of the minimum permeability in the soil profile—
1.5 cm/h (0.6 in./h). A value of 4% is used
because it is necessary to be conservative for
preliminary design. Further optimization will be
possible during final design. The limiting perme-
ability is 1.5 cm/h in the clay loam layer at 64 cm
(25 in.) in the Bosket soils (Figure A-l)» The
maximum daily percolation rate is computed as
follows:
Pw (daily) = 0.04 (1.5 cm/h)(24 h/d)
= 1.44 cm/d
The monthly rate is then determined by multiplying
the daily rate by the number of operating days
during the month. Some months may have non-
operating days due to farming operations or cold
weather.
Green chop harvesting is planned for this system
such that downtime for harvesting will not be
necessary. Operation will stop on days when the
mean temperature is less than -4 °C (25 °F). Based
on the climatic data in Table A-2, nonoperating
days due to cold weather are expected during the
months of October through March.
For example, in January, the design percolation
rate is:
Operating days = 31 - 20 = 11 d
Pw (Jan) = (1.44 cm/d)(11 d/mo)
= 15.8 cm/mo
The design percolation rate for each month is
entered in Column (4).
A-6
-------
5. The allowable hydraulic loading rate for each month
is computed by adding Column (3) and Column (4).
The annual hydraulic loading rate is computed by
summing the monthly rates and equals 326 cm
(128 in.).
TABLE A-3
HYDRAULIC LOADING RATES BASED ON SOIL
PERMEABILITY: FORAGE CROP ALTERNATIVE
cm
Month
Jan
Feb
Mar
Apr
May
Jun
Jul
Aug
Sep
Oct
Nov
Dec
Annual
(1)
Precipitation
Pr
10.1
10.4
15.1
15.8
17.4
14.3
14.1
12.3
14.7
9.9
14.8
13.0
162
(2)
Evapo-
transpiration
ET
0.3
0.7
2.1
5.6
9.7
13.4
15.7
13.9
8.9
5.0
1.8
0.6
78
(3)
ET - Pr
(2)-(l)
-9.8
-9.7
-13.0
-10.2
-7.7
-0.9
1.6
1.6
-5.8
-4.9
-13.0
-12.4
-84
(4)
Percolation
PW
15.8
18.7
27.4
43.2
44.6
43.2
44.6
44.6
43.2
38.9
25.9
20.2
410
(5)
Hydraulic Loading
Lw(P)
(3) + (4)
6.0
9.0
14.4
33.0
36.9
42.3
46.2
46.2
37.4
34.0
12.9
7.8
326
A. 4.1.2 Hydraulic Loading Based on Nitrogen
Loading
The annual hydraulic loading rate based on nitrogen is
determined by using equation 4-4, shown below:
Jw(n)
= (Cp)(Pr - ET) + (U)(10)
(1 - f)(Cn) - Cp
(4-4)
where LW(n) = allowable annual hydraulic loading rate
based on nitrogen limits, cm
A-7
-------
cp
Pr
ET
U
f
cn
= percolate nitrogen concentration, mg/L
= design precipitation, cm/yr
= evapotranspiration rate, cm/yr
= crop nitrogen uptake, kg/ha' yr
= fraction of applied nitrogen removed by
volatilization, denitrification, and storage
= applied wastewater nitrogen concentration,
mg/L
The computation was performed using annual rates according
to the procedure presented in Section 4.5.2 and is outlined
,as follows:
1. Determine parameter values for Equation 4-4.
a. Crop uptake (U)
U = 224 kg/ha'yr (from Table 4-11)
b. Volatilization + denitrification +
(V + D + S)
2.
storage
f = 0.2 (estimated, Section 4.2.2)
c. Applied nitrogen concentration (C )
Compute reduction in nitrogen concentration
during storage based on a 53 day storage
period which is the minimum detention time in
the treatment/storage ponds (Table A-7 ) .
Cn = (38 mg/L)e-°-0075(53>
= 26 mg/L
d. Percolate nitrogen concentration (C,-.)
P
C = 10 mg/L (required)
Solve Equation 4-4.
= 10(84) + 224(10)
= 285 cm/yr (112 in./yr)
A-8
-------
A.4.1.3 Design Hydraulic Loading Rate
As shown in Sections A.4.1.1 and A.4.1.2, the allowable
annual hydraulic loading rate based on soil permeability is
326 cm (128 in.) and the rate based on nitrogen limits is
285 cm (112 in.). Since nitrogen loading limits the hydrau-
lic loading rate in this example, the allowable hydraulic
loading rate is determined by comparing monthly Lw^p^ and
Lw(n)'
Monthly hydraulic loading rates based on nitrogen limits are
determined using Equation 4-4 with monthly values for Pr and
ET obtained from Table A-3. Sufficient data on nitrogen
uptake versus time for forage crops were not available, re-
quiring monthly values for U to be estimated from the ratio
of monthly ET to the total growing season ET multiplied by
the annual crop uptake value (Table A-4, Column 2).
TABLE A-4
DESIGN HYDRAULIC LOADING RATE
Month
Jan
Feb
Mar
Apr
May
Jun
Jul
Aug
Sep
Oct
Nov
Dec
Annual
(1)
Pr-ET,
cm
9.8
9.7
13.0
10.2
7.7
0.9
-1.6
-1.6
5.8
4.9
13.0
12.4
(2)
u,
kg/ha
0.9
2.0
6.1
16.1
28.0
38.5
45.3
40.1
25.7
14.4
5.2
1.7
(3)
Lw(n) »
cm
9.9
10.8
17.7
24.4
33.0
36.5
40.5
35.6
29.2
17.9
16.9
13.1
(4)
LW(P) '
cm
6.0
9.0
14.4
33.0
36.9
42.3
46.2
46.2
37.4
34.0
12.9
7.8
(5)
Design Lw,
cm
6.0
9.0
14.4
24.4
33.0
36.5
40.5
35.6
29.2
17.9
12.9
7.8
267
A-9
-------
The monthly values of Lw,n) and Lv(r)) are compared with the
lower value used for the monthly design hydraulic rate
(Table A-4, Column 5). Summing the design monthly hydraulic
loading rate gives the design annual hydraulic loading rate,
267 cm (105 in.).
A.4.1.4 Field Area Requirements
The design annual hydraulic loading rate is used to deter-
mine the field area requirement:
(4-6)
where
Aw =
Q =
AV,, =
A = Q(365) + AVg
104 (Lw)
field area, ha
average daily flow, m3/d
net gain or loss in stored wastewater volume
due to precipitation, evaporation, and
seepage at storage pond, m3/yr
Lw = design annual hydraulic loading rate,-m/yr
For the first calculation of field area, AVS is assumed zero
(see Section A. 4. 1.6) and the field area is calculated ass
(365 d/yr) =
Aw = 7,570 m
(104mVha)(2,67 m/yr)
A.4.1.5 Storage Requirements
Storage of wastewater is required for periods when available
wastewater exceeds design hydraulic loading rate. A water
balance computation is used to estimate the storage
requirement. The procedure is outlined as follows:
1. Enter the design monthly :loading rates from
Table A-4 (Column 5) into Table A-5, Column 1.
2. Determine available wastewater for each month.
w = Q(D)(O.OD
"a
where
W.
Aw
= monthly available wastewater, cm/mo
A-10
-------
Q = average daily flow, m3/d
D = days per month
w
= field area, ha
The average daily flow is assumed constant. For
example the monthly wastewater available for
June is:
,
a June
= (7,570 m yd) (30 d/mo) (0.01)
103.4 ha
= 22.0 cm/mo
The monthly values of available wastewater are
entered in Column (2) of Table A-5.
TABLE A-5
STORAGE VOLUME DETERMINATION:
FORAGE CROP ALTERNATIVE
cm
Month
Sep
Oct
Nov
Dec
Jan
Feb
Mar
Apr
May
Jun
Jul
Aug
(1)
Hydraulic
load ing j
Lw
29.2
17.9
12.9
7.8
6.0
9.0
14.4
24.4
33.0
36.5
40.5
35.6
(2)
Wastewater
available,
"a
22.0
22.7
22.0
22.7
22.7
20.5
22.7
22.0
22.7
22.0
22.7
22.7
(3)
Change in
storage,
(2)-(l)
-7.2
4.8
9.1
14.9
16.7
11.5
8.3
-2.4
-10.3
-14.5
-17.8
-12.9
(4)
Cumulative
storage,
Sc
0.2a
4.8
13.9
28.8
45.5
57.0
65.3
62.9
52.6
38.1
20.3
7.4
a. Rounding error, assume zero.
A-ll
-------
3.
4.
5.
Compute the change in storage each month by sub-
tracting hydraulic loading [Column (1)] from avail-
able wastewater [Column (2)]. Enter the results
Column (3).
in
Compute the cumulative change in storage in the end
of each month by adding the change in storage in
Column (3) to the accumulated quantity from the
previous month in Column (4).
Compute the required total storage volume using the
maximum cumulative storage in Column (4) and the
estimated field area:
= (65.3 cm)(103.4 ha)(102 m3/cm-ha)
= 675,200 m3
A.4.1.6 Final Storage and Pond Design
The facultative pond for preapplication treatment, serves as
the storage reservoir. A two-cell pond system is selected
with the design criteria of the primary cell based on the
state's BOD loading criteria of 38.1 kg BOD/ha'd
(34 lb/acre*d) and an operating depth of 1.0 m.
Ap = area (primary)
_ (7570 m3/d)(200 mg/L)(10"6 kg/mg)(103 L/m3)
38.1 kg/ha-d
= 39.7 use 40 ha
Vp = volume (primary)
- (40 ha)(lO* m2/ha)(1.0 m)
= 400,000 m3
The storage volume in the second cell is the difference
between the required total storage and the volume of the
primary cell.
vsec = Vs - Vp
= 675,200 - 400,000
= 275,200 m3
The actual volume of the secondary pond will change due to
evaporation, precipitation and seepage in the two cell pond
A-12
-------
area. To obtain the final storage volume the following
steps are used.
1. Calculate the storage area of the second cell using
a volume of 275,200 m3 and an operating depth of
1.5 m.
Asec ~ fec
(4-8)
_ 275,200
~T75
= 183,500 m'
use 18 ha
Determine the monthly net gain or loss in storage
volume due to precipitation, evaporation, and seep-
age (Table A-6, Column 3). Annual lake evaporation
equals 89 cm (33 in.) and is distributed monthly in
the same ratios of monthly ET to annual ET. A
maximum seepage rate of 0.15 cm/d is allowed by
state standard. As an example, the net gain or
loss for July is:
july
= (Precipitation - evaporation - seepage)
x (surface area)
= (14.1 - 18.0 - 4.6H58 ha)
x [(102 m/cm) (104 m2/ha)]
= -49,300 m3
3. Tabulate the volume of wastewater available each
month, Qm. In this example, the daily flow is
assumed constant and monthly flows vary according
to the number of days per month (Table A-6,
Column 4).
Qm = (7,570 m3/d)(31 d)
mjuly
= 234.7 x 103 m3/mo
4. Determine the adjusted field area accounting for
the net gain from storage.
£AV
(4-10)
(Lw)(10 m/ha)
A-13
-------
= (108.0 + 2,763.3)(103 m3)
2.67 m (104)
= 107.5 ha (266 acres)
TABLE
FINAL DETERMINATION
A-6
OF STORAGE VOLUME
Month
Sep
Got
Nov
Dec
Jan
Feb
Mar
Apr
May
(Tun
Jul
Aug
Annual
(1)
Evaporation ,
cm
10.2
5.7
2.1
0.7
0.3
0.8
2.4
6.4
11.1
15.3
18.0
15.9
(2)
Seepage,
cm
4.5
4.6
4.5
4.6
4.6
4.2
4.6
4.5
4.6
4.5
,4.6
4.6
(3)
Net gain/loss
AVB
m3 x 103
0
-2.3
47.6
44.7
30.2
31.3
47.0
28.4
9.9
-31.9
-49.3
-47.6
108.0
(4)
Available
wastewater
,Qnu ,
m3 x 10J
227.1
234.7
227.1
234.7
234.7
212.0
234.7
227.1
234.7
227.1
234.7
234.7
2,763.3
(5)
Applied
wastewater
m^x'lO3
313.9
192.4
138.7
83.8
64.5
96.8
154.8
262.3
354.7
392.4
435.4
382.7
2,872.4
(6)
Change in
storage*3
m3 x 103
-86.8
40.0
136.0
195.6
200.4
146.5
126.9
-6.8
-110.0
-197.2
-250.0
-195.6
(7)
Cumulative
storage
Sc,
m3 x 103
85.7
-l.la
40.0
176.0
371.6
572.0
718.5
845. 4b
838.6
728.5
531.3
281.3
a. Rounding error, assume zero.
b. Design storage volume
5. Calculate the monthly volume of applied wastewater
(Table A-6, Column 5) using the design monthly
hydraulic loading rate and adjusted field
For example:
area.
V
w
July "July w
= (40.5 cm)(107.5 ha)(102)
= 435.4 x 103 m3
(10~2 m/cm)
(4-11)
A-14
-------
6. Determine the net change "in storage each month
(Table A-6, Column 6) based on monthly applied
wastewater, Vw, available wastewater, Q , and net
.w
storage gain/loss, AVS.
Change in storage = Q + AV_ - V,
'w
7. Calculate the cumulative storage volume for the end
of each month (Column 7) to determine the maximum
design storage volume.
Vs = 845,400 nr
8. Adjust the depth of the second cell to accommodate
the increased storage volume.
s
= 845,400 - 400,000 = 445,400
= vsec _ 445,400 m3
2
(4-12)
180,000 m
= 2.47m, use 2.5m.
The depth of ground water prevents lowering the depth of the
pond more than 1.5 m (5 ft) below the ground surface. Con-
sequently, most of the storage pond volume will be above
ground surface and require embankments. The design criteria
for the storage lagoons are shown in Table A-7.
TABLE A-7
DESIGN CRITERIA FOR STORAGE LAGOONS:
FORAGE CROP ALTERNATIVE
Primary cell
Surface area, ha 40.0
Total depth, m 1.5
Operating depth, m 1.0
Total storage, d 79
Storage above 0.5 m, d 53
Secondary cell
Surface area, ha 18.0
Total depth, m 3.0
Operating depth, m 2.5
Total storage at 2.5 m, d 59
Total storage at operating depth
Days 112
m3 850,000
A-15
-------
A.4.1.7 Distribution and Application
When selecting the type of distribution system, the designer
must consider the terrain, crop, soils, and capital and
operation/maintenance costs. Based on a cost comparison not
included in the example, the designer recommended a center
pivot irrigation system as the most cost-effective system
for the forage crop alternative.
The design of the distribution system is based on the maxi-
mum hydraulic loading rate per application. In this case,
the maximum monthly loading equals 40.5 cm (15.9 in.) in
July. An application frequency of four times per month is
selected to allow adequate drying between applications (see
Appendix E for guidelines on making this determination).
The hydraulic loading rate per application then equals
10.1 cm (4.0 in.) .
In consultation with manufacturers of center pivot equip-
ment, it was determined that two center pivot systems could
be used for distribution each irrigating an area of 53.8 ha
and using a revolution period of 170 hours. The unit capa-
city is then determined as follows (Section E.2.6):
Q = CAD/t
='28.1 (53.8)(10.1)
170
=89.8 L/s
where Q = discharge capacity, L/s (gal/min)
C = constant, 28.1 (453)
A = field area for one center pivot, ha (acre)
D = hydraulic loading/application depth, cm (in.)
t = number of operating hours per application
Using the unit capacity, the design of the center pivot
system is completed. , In order to determine the nozzle and
pipeline size, the design must consider headlosses in the
line and the pressure required to ensure proper operation of
the nozzles.
Unit capacity also is used to develop design criteria for
the pumps. Pumps are required to deliver wastewater to the
site and at a pressure sufficient to allow proper
A-16
-------
distribution of the wastewater. Assuming the two pivots
operate simultaneously, the pumps are sized for a total flow
of 179.6 L/s. The designer chose four pumps and one standby
rated at 45 L/s. The force main is sized using a maximum
velocity of 1.7 m/s and the following formula;
A =
where A = area of pipe
Qt = total flow
V = maximum velocity
For circular pipes:
D =
where D = pipe diameter
Applying the equation gives:
D =
(180.L/s) (10~3 m3/L) (_4_)
= 0.37 m, use 0.38 m
1.7 m/s
ir
A final consideration in the design of ' the center pivot
system is the disruption of the tracking system due to wet
soil conditions. Because of the pivot rotational speed, the
application rate at the unit capacity equals 1.0 cm/h during
the 9 to 10 h period it takes to pass a given point.
Although this rate is less than the permeability or basic
infiltration rate of the surface soil, precautions need to
be taken. These precautions include preparing the tracking
route by either soil compaction or gravel installation.
A summary of design data for the treatment site is given in
Table A-8. Figure A-2 shows the pond and distribution
system layout.
A.4.1.8 Cost Estimates
Cost estimates of the forage crop irrigation system are
determined from EPA publication "Cost of Land Treatment
Systems" EPA-430/9-75-003, using the criteria shown in
Table A-9. Cost estimate calculations and total costs are
presented in Tables A-10 and A-ll, respectively.
A-17
-------
LJJ
Ul
in
A-18
-------
TABLE A-8
SLOW RATE SYSTEM DESIGN DATA:
FORAGE CROP ALTERNATIVE
Irrigation system
Annual hydraulic loading rate, cm
Fiel<3 area, ha
Buffer, m
Application frequency, No./mo
Maximum hydraulic loading per application, cm
Application equipment, No. of center pivots
Lateral length, m
Operating pressure, N/cm*
Field dimensions with buffer zone, m x m
Total area, ha
Pumping station
Duty pumps, No. at m3/min
Standby pumps. No. at m3/min
Pumping time (peak flow)
h/d
d/wk
h/wk
Force main
Velocity, m/s
Average
Maximum
Pipe diameter, m
Maximum headloss, m/1,000 m
267
107.5
15
4
10.1
2
408
34.5
1,662 x
140.6
846
4 at 2.7
1 at 2.7
24
7
168
1.1
1.7
0.38
6 '
TABLE A-9
COST ESTIMATE CRITERIA:
FORAGE CROP ALTERNATIVE3
Circulation date
Sewage treatment plant index update, 370.1/177.5
Sewer index update, 397.2/194.2
Operation and maintenance update, 2.13/1.00
Construction cost locality factor
Operation and maintenance/labor cost factor
Power cost locality factor
Interest rate, i
Interest period, n
Present worth factor, PWF
Capital recovery factor, CKF
October 1980
085
045
2.13
.0
.0
.0
.125%
20
0.2525
0.0953
a. Based on "Cost of Land Treatment Systems,1
EPA-430/9-75-003.
A-19
-------
TABLE A-10
COST ESTIMATE CALCULATIONS:
FORAGE CROP ALTERNATIVE
1. Preliminary treatment
Capital ($48,000 x 2.085) $100,100
Operation and maintenance ($9,400 x 2.13) 20,000
2. Treatment
Capital
Primary cell ($150,000 x 1.7 x 2.085) $531,700
Asphalt liner ($352,000 x 2.085) 733,900
Operation and maintenance ($10,000 x 2.13) 21,300
3. Pumping to application site
Peak flow =180 L/s
Avg flow = 135 L/s
Capital ($210,000 x 2.085 x 0.80) 5350,300
Operation and maintenance ($26,100 x 2.13) 55,600
4. Force main (2.6 km: 0.38 m)
Capital ($162,100 x 2.045) $331,500
Operation and maintenance ($400 x 2.13) 900
5. Storage (D = 59d, depth = 3.0 m)
Capital ($447,000 x 2.045) $914,100
Operation and maintenance ($2,400 x 2.13) 5,100
6. Field preparation
Pond area (58 ha x 1.25 = 72.5 ha, brushes and trees)
Capital ($80,000 x 2.045) $163,600
Application site (53.8 ha x 2 = 107.6 ha, pasture)
Capital ($1,700 x 2.045) 3,500
7. Distribution, center pivots (107.6 ha)
Capital {$135,000 x 2.045) $276,100
Operation and maintenance ($18,400 x 2.13) 39,200
8. Administrative and laboratory
Capital ($64,000 x 2.045) $130,900
Operation and maintenance ($10,200 x 2.13) 21,700
9. Monitoring wells (six wells at 12 m depth)
Capital ($4,800 x 2.045)
Operation and maintenance ($600 x 2.13)
10. Roads and fences (application site, 140.6 ha)
Capital ($102,000 x 2.045)
Operation and maintenance ($2,700 x 2.13)
11. Planting and harvesting
Operation and maintenance
Variable costs ($319/ha x 107.5 ha)
Fixed costs ($247/ha x 107.5 ha)
12. Annual crop revenue
107.5 ha x 15.6 tons/ha x $42/ton
13. Land costs
Pond area (72.5 ha x $2,000/ha)
Application area (140.6 ha x $3,700/ha)
$ 9,800
1,300
$208,600
5,800
$ 34,300
26,600
$ 70,400
$145,000
520,200
A-20
-------
TABLE A-11
SUMMARY OF COSTS: FORAGE CROP ALTERNATIVE
Component
Capital
Salvage0
Operation and
maintenance
Preliminary treatment
Treatment/storage ponds
Pumping
Force main
Site clearing
Distribution
Administration building
Monitoring
Roads and fences
Planting and harvesting
Crop revenue
Total construction
$ 100,100
2,179,700
350,300
331,500
167,100
276,100
130,900
9,800
208,600
—
—
$3,754,100
$ 20,000
1,089,800
42,000
165, ,800
0
0
26,200
0
68,200
—
—
$1,412,000
$ 20,000
26,400
55,600
900
0
39,200
21,700
1,300
5,800
60,900
-70,400
$ 161,400
Engineering, contingencies,
overhead, etc.
Land
Total project
Present worth
Total present worth
Equivalent annual cost
938,500 0 0
665,200 1,201,400 0
$5,357,800 $2,613,400 $ 161,400
. -659,000 1,693,600
$6,392,400
$ 609,200
a. Salvage values are determined by straight line depreciation
over the useful life of the components, e.g., useful life of
ponds N = 40 yr; planning period P = 20 yr; salvage value
F = (1 - P/N) (initial cost) = 0.5(2,179,700) = 1,089,800.
b. Equivalent annual cost = present worth x 0.0953.
A-21
-------
A. 4. 2
Deciduous Forest Crop Alternative
As in the forage crop design, the selection of the maximum
allowable hydraulic loading for the forest crop alternative
minimizes the required land area. In the City A region,
deciduous trees, in particular poplar, grow well. The
poplar is a fast-growing tree and a pulp wood market exists.
A.4.2.1 Hydraulic Loading Based on Soil
Permeability
The monthly water balance calculations are determined as in
the forage crop water balance. The growing season for the
deciduous tree selected lasts 214 days based on an average
mean temperature of 10 °C (50 °F). Evaporation from the
forest during the growing season is assumed to equal that
from a full cover pastureland. No evaporation is assumed
for the nongrowing season; wastewater applied during this
time is limited by precipitation and percolation. Because
the site is the same for both forage and forest alternative,
the design percolation rate is the same. Applying these
assumptions to the water balance Equation 4-3 results in a
maximum hydraulic loading of 321 cm (126 in.) and a maximum
monthly loading of 46.2 cm (18.2 in.).
A. 4.2.2 Hydraulic Loading Based on Nitrogen
Loading
Equation 4-4 is used to determine the hydraulic loadings
based on nitrogen loading as in the forage crop alternative
(Section A.4.1.2). No crop growth or nitrogen uptake was
assumed for the months of December through March. using a
whole-tree harvest approach, the total annual nitrogen up-
take is assumed to equal 200 kg/ha (178 Ib/acre) (see
Section 4.3.2.1). Based on these assumptions, the annual
hydraulic loading equals 268 cm (105.5 in.).
A. 4.2.3 Design Hydraulic Loading Rate
As in the forage crop alternative, nitrogen loading limits
the hydraulic loading rate. Design monthly hydraulic
loading rates are determined by comparing the monthly
hydraulic loading rates based on soil permeability and
nitrogen loading and using the lower value. Based on this
comparison the design annual hydraulic loading rate is
254 cm (100 in.).
A-22
-------
A.4.2.4 Field Area Requirements
Applying Equation 4-6 and assuming the net gain/loss from
storage, AVS, is zero, the initial field area is:
A = (7,570 m3/d)(365 d/yr) =108.8ha
(104 ra2/ha)(2.54 m)
A. 4.2.5 Storage Requirements
As in the case with forage, storage of wastewater during
nonoperating time depends on monthly hydraulic loadings and
available wastewater. Applying the water balance
Equation 4-3 and following steps 1-4 of Section A.4.1.5
results in Table A-12. The net storage volume required for
year-round application is shown below:
Vst = (64.6 cm)(108.8 ha)(102) = 702,800 m3
TABLE A-12
INITIAL DETERMINATION OF STORAGE VOLUME:
FOREST CROP ALTERNATIVE
cm
Month
Oct
Nov
Dec
Jan
Feb
Mar
Apr
May
Jun
Jul
Aug
Sep
Annual
P
, 9.9 .
14.8
13.0
10.1
10.4
15.1
15.8
17.4
14 . 2
14.0
12.2
14.7
162
ET
5.0
0
0
0
0
0
5.6
9.7
13.4
15.7
13.9
8.9
72 "
ET-P
-4.9
-14.8
-13.0
-10.1
-10.4
-15.1
-10.2
-7»7
-0.9
1.6
1.6
-5.8
-90
PW
38.9
25.9
20.2
15.8
18.7
27.4
43.2
44.6
43.2
44.6
44.6
43.2
410
Lw(P)
34.0
11.1
7.2
5.7
8.3
12.3
33.0
36.9
42.3
46.2
46.2
37.4
321
Lw(n)
17.3
13.7
12.0
9.4
9.6
14.0
23.8
32.0
35.1
38.7
34.1
28.2
268
Available
wastewater
Lw Wa
17.3
11.1
7.2
5.7
8.3
12.3
23.8
32.0
35.1
38.7
34.1
28.2
254
21.5
20.9
21.5
21.5
19.5
21.6
20.9
21.6
20.9
21.6
21.6
20.9
Change in
storage
4.
9.
14.
15.
11.
9.
-2.
-10.
-14.
-17.
-12.
-7.
2
8
3
8
2
3
9
4
2
1
5
3
Cumulative
storage
sc
, 0.2a
• 4.2
14.0
28.3
44.1 .
55.3
64.6
61.7
51.3
37.1
20.0
.7.5
a. Rounding error, assume zero.
A-23
-------
A. 4.2.6 Final Storage and Pond Design
The steps outlined in Section A.4.1.6 are followed to deter-
mine the final storage and pond design. The design of the
primary cell remains the same with the secondary cell being
used to incorporate the net gain/loss from the pond area due
to precipitation, evaporation, and seepage. As before, the
initial depth of the secondary cell is assumed at 1.5 m
(5 ft) resulting in a storage pond area of 20 ha
(50 acres). The adjusted field area is calculated to be
113.2 ha (280 acres). The results of secondary cell design
are shown in Table A-13.
TABLE A-13
DESIGN DATA FOR STORAGE POND:
FOREST CROP ALTERNATIVE
Secondary cell
Surface area, ha
Total depth, m
Operating depth, m
Storage at operating depth, d
Total storage at operating depth
Days
20
2.9
2.4
63
116
880,000
A.4.2.7 Distribution and Application
Solid set sprinkler systems, both surface and buried, are
the most common methods used in forest crops for distri-
buting wastewater. in the case of City A, the proposed
treatment site is under pasture and the subsoils are uniform
without much debris, consequently either system would
work. The installation cost for the surface system is less
than the buried system, but the cost for operation and main-
tenance is less for the buried system. After comparing
total cost and discussing with City A their desire for low
operation and maintenance cost, the designer selected the
buried solid set sprinkler system.
The design of the sprinkler system is based on the maximum
hydraulic load per application. An application frequency of
4 times per month is chosen to allow adequate aeration of
the tree root system. Based on a maximum monthly hydraulic
loading of 38.7 cm (15.2 in.), the maximum hydraulic loading
per application of 9.7 cm (3.8 in.) is obtained. Referring
to manufacturers literature for solid set irrigation
A-24
-------
systems, design data are obtained and presented in
Table A-14. The pond and irrigation system layout is shown
in Figure A-3.
TABLE A-14
DESIGN DATA:
FOREST CROP ALTERNATIVE
Irrigation system
Annual hydraulic loading rate, cm
Field area, ha
Buffer, m
Application frequency, No./mo
Total area, ha
Maximum hydraulic loading per application, cm
Distribution system
Spacing, m x m
Sprinkler flow, L/s at N/cm
Lateral length, m
Sprinklers per line, No.
Application period, h
Settings per day. No.
Operating time, h/d
Laterals per setting, No.
Pumping rate, 9 x 24 x 0.85, L/s
Pumping station
Duty pumps. No. at m /min
Standby pumps, N.o. at m /min
Pumping time
h/d
d/wk
h/wk
Force main
Velocity, m/s
Average
Maximum
Pipe diameter, m
Maximum headless, m/1,000 m
254
113
15
4
123.5
9.7
Buried solid
set sprinklers
18 x 21
0.85 @ 36, 0.63 cm diam
432
24
12
2
24
9
184
4 at 2.76
1 at 2.76
24
6
144
1.1
1.7
0.38
6.4
A-25
-------
I— >-
a. i—
zee
C9
CO
>-
CO
A-26
-------
A. 4.2.8 Cost Estimates
Cost estimates are determined by the same method used for
the forage crop alternative (Table A-9) and are summarized
in Table A-15. Crop revenue is based on a harvest of one-
fourth of the area every year beginning the fourth year, an
annual growth rate of 25 tons/ha, a dry weight of 0.4 ton/
cord, and a stumpage price of $4/cord used for pulpwood.
TABLE A-15
SUMMARY OF COSTs DECIDUOUS FORESTS
Component
Preliminary treatment
Treatment/storage ponds
Pumping
Force main
Site clearing
Distribution
Administration building
Monitoring
Roads
Planting and harvesting
Crop revenue
Total construction
Capital
$ 100,100
2,206,300
325,300
314,000
167,500
1,295,700
130,900
9,800
112,500
14,000
—
$4,676,100
Salvage
$ 20,000
1,103,100
39,000
157,000
0
0
26,200
0
75,000
—
—
$1,420,300
Operation and
maintenance
$ 20,000
26,800
55,600 .
900
0
54,200
21,700
1,300
4,900
2,800
-28,000
$ 160,200
Engineering, contingencies,
overhead, etc.
Land
Total project
Present worth
Total present worth
Annual equivalent cost
1,169,000
606,900 1,096,100
$6,452,000 $2,516,400 $ 160,200
— -635,400 1,681,000
$7,497,600
$ 714,500
A-27
-------
A. 4. 3
Selected SR Design
Comparing annual equivalent costs, the forage crop alter-
native is the most cost-effective alternative, with an
annual equivalent cost of $609,200/yr, and is selected.
Management of the selected alternative consists of an
initial seedbed preparation, seeding, cultivating,
irrigating, and harvesting four times per year. Prior to
harvesting, the field requires a drying period of 2 to 3
weeks. The harvested forage grass is then chopped and
hauled away for use. The harvesting may be handled either
by City A personnel or contracted outside. Assuming
contract harvesting, the estimated staff requirement for all
of the remaining operation is 1.5 man-years per year.
A.4.4
Energy Requirements
The two areas of operation that contribute most to the
system energy requirements are pumping and crop
production. Assuming 3,900 hours of operating time, 75%
overall system efficiency, and 20% headloss through the
distribution system, the energy required for pumping is
shown below:
TDK = pipe losses + operating pressure + losses through
at sprinkler distribution
system
= 2,600 m (5.5 m) +35+7
1,000 m
= 56.3 m
Energy = (Q)(TDH)(t)
yy (6,123)(E)
= 515,200 kWh/yr
Energy required for forage crop production is computed using
the energy requirement factor given in Table 8-1.
Energy = 107.5 ha x (3.63 Mj/ha)
3.6 MJ/kWh
= 110 kWh/yr
Therefore, the total annual energy budget for this SR
example is:
110 + 515,200 = 515,310 kWh/yr
A-28
-------
The total energy budget for an activated sludge and anaer-
obic digestion treatment system of equal size would be
680,000 kWh/yr electrical energy and 3,100 x 106 BTU/yr fuel
energy or a total of 967,000 kWh/yr.
A-29
-------
-------
APPENDIX B
RAPID INFILTRATION DESIGN EXAMPLE
B.I Introduction
The design example described in this appendix is intended to
demonstrate only the RI design procedures described in
Chapter 5; therefore, components that are common to most
wastewater treatment systems, such as transmission systems
and pumping stations, are described but not designed in
detail. However, a cost estimate and an energy budget are
developed for the entire system.
B.2 Design Considerations
B.2.1
Design Community
Community B is located in the southeastern United States on
the Coastal Plain. The area in which the community is loc-
ated is characterized by relatively flat areas lying between
numerous creeks and swamps that drain into North Creek. One
of these creeks, South Creek, borders the northeast edge of
the community. The elevation of Community B is 45.7 m (150
ft); near the community, elevations range from 42.7 to
54.9 m (140 to 180 ft).
B.2.2
Wastewater Quality and Quantity
The design average daily flow is 6,060 m3/d (1.6 Mgal/d) and
the design peak flow is 9,090 m3/d (2.4 Mgal/d).
Expected wastewater characteristics under design flow con-
ditions are presented in Table B-l. Wastewater is essenti-
ally domestic in character and expected concentrations of
trace elements and organics are low.
TABLE B-l
PROJECTED WASTEWATER CHARACTERISTICS
Parameter
Value
c, mg/L
Total suspended solids, mg/L
Total nitrogen, mg/L
Ammonia nitrogen (as N), mg/L
Total phosphorus (as- P), mg/L
pH, units
175
150
50
20
10
6.9
B-l
-------
B.2.3
Existing Wastewater Treatment Facilities
The existing treatment facilities provide primary treatment,
and treated wastewater fails to meet present discharge
requirements. The facilities are old and would require
significant repairs and additions to produce treated water
that would meet all discharge requirements.
B.2.4
Discharge Requirements
Discharge requirements for surface waters are presented in
Table B-2. The ammonia nitrogen limit during summer months
is intended to prevent ammonia toxicity to fish. The inhi-
bited test for carbonaceous BOD does not measure nitrogenous
BOD. The test is often specified for systems that nitrify
wastewater, because such systems tend to have higher BODc
concentrations although the water quality is equivalent.
TABLE B-2
SURFACE WATER DISCHARGE REQUIREMENTS
Parameter
North South
Creek Creek
BOD5/ mg/L
(inhibited test for carbonaceous BOD)
30
20
Dissolved oxygen, mg/L
PH
Total suspended solids, mg/L
Fecal coliforms, MPN/100 mL
Ammonia nitrogen (as N) , mg/L
(May-October only)
5
6-9
30
200
2
5
6-9
20
200
2
B.2.5
Climate
Average temperature and precipitation in Community B were
obtained from local climatological data and are shown by
month in Table B~3. A rainfall frequency distribution
curve, developed from 26 years of recorded data, indicates
that the wettest year in 10 yields 137 cm (54 in-) of preci-
pitation in Community B. The average total annual precipi-
tation (rain plus snow) is 111 cm (43.7 in.).
B-2
-------
TABLE B-3
AVERAGE METEOROLOGICAL CONDITIONS
Temper a tui
Month °C
Jan
Feb
Mar
Apr
May
Jun
Jul
, Aug
Sep
Oct
Nov
Dec
Year
8.6
9.3
12.6
17.5
22.2
26.0
27.0
26.6
23.8
18.3
12.6
8.4
17.8
Precipitation, cm
Rain
6.71
8.05
9.24
9.17
7.34
10.87
15.85
11.61
10.41
5,54
5.87
7.77
108.43
Snpwa
0.25
0.51
1.02
0.00
0.00
0.00
0.00
0.00
0.00
0.00
Trace
0.76
2.54
a. Water equivalent.
B.3 Site and Process Selection
Community B contacted landowners within a 4 km (2.5 mile)
radius of the existing treatment facilities to determine
their interest in leasing or selling their property for land
treatment. Five potential sites were identified during
Phase 1 of the planning process and screened in accordance
with the procedure in Chapter 2. Two of the sites were
available for purchase and had soils suitable for RI
(Sites 1 and 2 on Figure B-l). One of these two sites
(Site 2) and the three remaining sites had enough land to be
suitable for SR. None of the soils in the area were suit-
able for OF (Table B-4). Therefore, OF was eliminated from
consideration as a viable alternative.
During phase 2 of the planning process, field investigations
were conducted at each of the five sites. Based on the
field investigations, preliminary design criteria and cost
estimates were developed. This analysis indicated that the
two RI alternatives were more cost effective than any of the
SR alternatives and lower in total present worth than the
best conventional secondary treatment and discharge
alternative. The preliminary analysis also indicated that
an RI facility at Site 1 would be slightly less expensive
than an RI system at Site 2. For these reasons, the alter-
native selected by Community B was RI at Site 1.
B-3
-------
LEGEND
Cx COXVIUE SERIES
HcB HUCKABEE SERIES
LaB.LaD.LkA LAKELAND SERIES
NoA.NoB.NsB NORFOLK SERIES
OK OKENEE SERIES
Pm PLUMMER SERIES
Sw SWAMP
e 2(0
'
SCALE
410 600
811 HOC
^mmmmi
METERS
FIGURE B-1
SOILS MAP, SITES 1 AND 2
B-4
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B-5
-------
B.4 Site Investigations
The selected site for Ri is 2.4 km (1.5 miles) from the
existing wastewater treatment facilities. The site contains
48 ha (120 acres) of land and was covered with brush and
trees. Near North Creek, the ground surface drops verti-
cally about 6 m (20 ft), forming a relatively steep bluff as
indicated in Figure B-2. West of the bluff, elevation
varies less than'0.6 m (2 ft).
B.4.1 Soil Characteristics
As indicated by Figure B-l and Table B-4, the soils at
Site 1 that are best suited for RI are the Lakeland sands
(LaB and LaD in Figure B-l). These permeable soils are
found at Site 1 only near the center of the site. Thus, RI
is potentially feasible only in a limited portion of
Site 1. Because it would have cost Community B as much to
buy only the land needed for the treatment system as to buy
the entire site (the unused portion of the site being mostly
swamp and therefore undevelopable), acquisition of the
entire site was necessary.
To verify that Site 1 has adequate soil depth and depth to
ground water for RI, and to ascertain the absence of
shallow, impermeable soil layers, nine test holes were
drilled as shown in Figure B-2. A typical boring log from
the investigation is presented in Table B-5. At this parti-
cular test hole, the presence of ground water at a depth of
3.2 to 3.5 m (10 to 11 ft) and an impermeable clay layer at
6.5 m (21 ft) means that percolation could occur only to a
depth of about 3.2 to 3.5 m (10 to 11 ft) and that the flow
of water below this depth is primarily horizontal rather
than vertical.
TABLE B-5
TYPICAL LOG OF TEST HOLE
Depth, m USDA texture
Remarks
0-1
1-2
2-2.2
2.2-3.2
3.2-3.5
3.5-6.5
>6.5
Loamy sand
Sandy loam
Loamy sand
Sand
Sand
Sand
Clay
With thin silt lenses
Ground water table
Saturated
Impermeable
B-6
-------
GO
ce
CM Z
i O
CD O
LU CC
OS UJ
=3 I—
CO
-------
B.4.2
Ground Water Characteristics
At the selected site, the depth to ground water ranges from
1.5 to 4.6 m (5 to 15 ft) and is typically 3 m (10 ft). The
ground water aquifer is 1.5 to 4.6 m (5 to 15 ft) thick and
is underlain by impermeable clay. The clay layer prevents
deep vertical percolation and causes the ground water to
flow laterally toward North Creek, as indicated by the
approximated ground water contours shown in Figure B-2.
Because of the shallow ground water table, there is a poten-
tial for mounding of the percolate and underdrains must be
considered. Horizontal hydraulic conductivity in the
aquifer was measured using the auger hole technique
(Section 3.6.2.1) and averaged 3.4 m/d (11 ft/d).
Furthermore, although ground water quality is adequate for
water supply purposes, the aquifer is too thin to allow
production wells to extract ground water economically. The
closest domestic water supply well to the Ri site is 1.6 km
(1 mile) southwest and upgradient of the site. This well
and others in the area pump water from depths of 90 to over
150 m (300 to over 500 ft). Thus, the shallow aquifer
underlying the area to be used for RI and between the Ri
area and North Creek will not be used as a potable water
source. Current ground water quality data are presented in
Table B-6.
TABLE B-6
GROUND WATER QUALITY
Parameter
Concentration
pH, units
Specific conductance, ymhos
Nitrate nitrogen, mg/L
Fecal coliforms, MPN/100 mL
6.8
120
8.4
0
B.4.3 Hydraulic Capacity
Basin infiltration tests at the selected site were performed
with clear water using 3.6 by 3.6 by 0.5m (12 by 12 by
1.5 ft) basins filled to a depth of 22 to 30 cm (9 to
12 in.). Because the soil and ground water characteristics
were generally uniform throughout the site, only two basin
infiltration tests were performed. If the results of these
two tests had conflicted, additional tests would have been
conducted. Results from one of the two infiltration tests
are plotted in Figure B-3. As shown in this figure, the
resulting limiting infiltration rate at this basin was
B-8
-------
3XV1NI 110 >3 '3XV1NI 031VinMn99V
B-9
-------
2.5 cra/h (1 in./h). This was the minimum infiltration rate
from the two tests and was used as the basis for design.
B.5 Determination of Wastewater Loading Rate
B.5.1 Preapplication Treatment Level
The existing treatment facilities are old and necessary
repair work would nof be cost effective. Therefore, new
preapplication treatment facilities are needed. To consoli-
date the treatment facilities, Community B decided to locate
the preapplication treatment facilities adjacent to the RI
facilities at Site 1. Because Site 1 is close to the
community, biological treatment prior to land treatment was
appropriate (Section 5.3.1). The area experiences mild
winter weather, making ponds the most cost-effective form of
preapplication treatment.
The land available for preapplication treatment was somewhat
limited; to minimize the pond area, an average depth of
3.6 m (12 ft) was selected. The pond design included sur-
face aerators to be used periodically for odor control and
to keep the pond from becoming entirely anaerobic. The pond
was divided into three aeration cells for flexibility and
reliability. A design detention time of 3 days was selected
and adjustable weirs were included in each cell to allow
wastewater withdrawal after 1 to 2 days if treatment effi-
ciency is high or if the BOD:N ratio must be increased to
promote denitrification during RI. The expected effluent
quality from the aerated lagoons is 75 mg/L BOD,- and
99 mg/L SS. Because of the short detention time^ the
nitrogen content will remain at 50 mg/L and the ammonia
nitrogen content will be approximately 20 mg/L.
B.5.2 Hydraulic Loading Rate
The annual hydraulic loading rate was designed to be within
10 to 15% of the limiting basin infiltration rate
(Table 5-11 and Section 5.4). A median value of 12.5% was
selected and the wastewater loading rate was calculated as
follows:
12.5% x 2.5 cm/h x 0.01 m/cm
x 365 d/yr
=27.4 m/yr (90 ft/yr)
B-1Q
-------
B.5.3 Hydraulic Loading Cycle
Because the renovated water will flow laterally or be
drained into North Creek, nitrification or ammonium nitrogen
removal is necessary during the months of May through
October. To maximize nitrification, a loading cycle of
2 days of flooding alternated with 12 days of drying was
selected (Section 5.4.2). Using this loading cycle and the
assumed loading rate, the volume of water applied during
each loading cycle is:
(2d + 12d)/cycle
365 d/yr
m/
100 cm
m
= 105 cm/cycle (41.4 in. /cycle)
B.5.4 Effect of Precipitation on Wastewater Loading
Rate
As shown in Table B-3, precipitation in Community B averages
111 cm/yr (3.6 ft/yr) and varies throughout the year from
5.5 to 15.9 cm/mo (2.2 to 6.2 in./mo). As mentioned in
Section B.2.5, the wettest year in 10 would yield 137 cm
(54 in.) of precipitation. This amount roughly corresponds
to a maximum monthly precipitation of 20 cm/mo
(8.0 in./mo). Adding maximum monthly precipitation to the
average wastewater loading rate of 2.3 m/mo (7.5 ft/mo)
resulted in a maximum monthly hydraulic loading rate of
2.5 m/mo (8.2 ft/mo). This combined loading rate is 13% of
the test basin infiltration rate and, therefore, was accep-
table (Section 5.4.1).
For land requirement calculations, the previously calculated
wastewater loading rate (27.4 m/yr or 90 ft/yr) was used
because precipitation is relatively insignificant most of
the time.
B..5.5 Underdrainage
As discussed in Section 5.7.2, at RI sites where both the
ground water table and 'the impermeable layer underneath the
aquifer are relatively close to the soil surface, it may be
possible to avoid lengthy mounding equations by using the
following procedure:
1. Assume underdrairis are needed.
2. Use Equation 5-4 to calculate drain spacing.
3. If the calculated drain spacing is reasonable
(between 10 m and 50 m or 33 ft and 160 ft), drains
should be used.
B-ll
-------
4. If the calculated spacing is less than 10 m, no
mounding calculations are needed but the cost of
the underdrains may cause the system not to be cost
effective and may necessitate reconsideration of
other sites identified during phase 1.
5. If the calculated spacing is greater than 50 m, an
evaluation of ground water mounding is necessary.
Because Site 1 is underlain by a relatively shallow imper-
meable layer, underdrains would be the appropriate drainage
method. A drain depth of 3m (10 ft) and an allowable
ground water mound height above the drains of 0.6 m (2 ft)
were assumed. Using Equation 5-4, drain spacing was
calculated:
4KH
Lw
where S = drain spacing, m
•(2d + H)
1/2
K = horizontal hydraulic conductivity, m/d
= 3.4 m/d (Section B.4.2)
H = allowable height of the ground water mound
above the drains, m
= 0.6 m
d = distance from drains to underlying impermeable
layer, m
= 3 m
LW = annual wastewater loading rate, m/d
= 2365 d/yr = 0'°75 m/d
P = average precipitation rate, m/d
= i'll m/vr = 0.003 m/d
365 d/yr
S = / 4 x 3.4 m/d x 0.6 m [(, x 3 m) + 0<6 m]Vl/2
\0.075 m/d + 0.003 m/d ' u ° J/
= 26 m (85 ft)
Because this spacing is reasonable and will keep the mound
from becoming a problem, additional mounding calculations
were not necessary. Because the percolate collected in the
underdrains will be discharged into North Creek, it was
necessary to design the remainder of the system to meet the
discharge requirements summarized in Table B-2.
B-12
-------
B.5.6 Nitrification
To determine whether the proposed system could meet the
summer ammonia nitrogen discharge requirements, the nitrifi-
cation potential of the system was evaluated. First, the
nitrogen loading rate was calculated as follows:
10CnLw
Ln ~ 365
where Ln = nitrogen loading rate, kg/ha«d
Cn = applied total nitrogen concentration, mg/L
L,7 = annual loading rate, m/yr
W
Ln = 10 x 50 mg/L x 27.4 m/yr
365
= 37.5 kg/ha-d (33.5 lb/acre-d)
This loading rate is well within the range of nitrification
rates reported under favorable temperature and moisture
conditions (Section 5.2.2). Because nitrification is
required only during summer months when temperatures are
fairly high, temperatures at the RI system will be favorable
for the required nitrification. Furthermore, the relatively
short application periods and longer drying periods of the
selected loading cycle will ensure favorable moisture condi-
tions and should allow virtually complete nitrification
within a relatively short soil travel distance
(Section 5.4.2).
B.6 Land Requirements
B.6.1 preapplication Treatment Facilities
The average liquid depth of the aerated pond was designed to
be 3.6 m (12 ft), based on an average detention period of
3 days. An additional 1m (3.3 ft) of freeboard was pro-
vided to allow the liquid depth to vary during peak flows
and emergency conditions. Each pond cell berm was designed
to have a 1:3 slope (verticalhorizontal) on both interior
and exterior sides and to be 1.2 m (4 ft) wide on top.
Thus, the total area required for the pond is approximately
1.7 ha (4.2 acres).
B-13
-------
B.6.2 Infiltration Basins
The area needed for infiltration was calculated as follows:
A = (365 Q)/(104 Lw)
where A = area required, ha
Q = average wastewater flow, m3/d
Lw = annual loading rate, m
A = (365 x 6,060 m3/d)/(104 x 27.4 m/yr)
= 8.1 ha (19.9 acres)
B.6.3 Other Land Requirements
Additional land was required for berms around the infiltra-
tion basins and for access roads. Preliminary system lay-
outs indicated that a total of about 14 ha (35 acres) would
be required. This number was used for preliminary cost
estimates; actual land requirements were developed during
final system design.
B.7 System Design
B.7.1 General Requirements
A schematic of Community B's Ri system is shown in
Figure B-4. The existing screening and grit removal facili-
ties will be retained and used because they are necessary to
protect the new pumping station.
A pumping station will be constructed at the site of the
abandoned treatment facilities to pump the screened waste-
water through a 30 cm (12 in.) force main to the treatment
ponds. Three 3.14 mj/min (830 gal/min) pumps will be in-
cluded. Two pumps operated together will be able to handle
a peak flow of 9,090 m*/d (2.4 Mgal/d). The third pump will
be a standby. Standby power at the pumping station will be
provided by a diesel generator. Distribution to the infil-
tration basins will be by gravity flow from the ponds.
Infiltration basins were located on the area having the most
suitable soils. Because this area is relatively flat, very
little grading was required and nearly equal-sized basins
could be located adjacent to one another. The selected
14 day loading cycle required that at least 7 basins be
constructed to enable dosing of at least one basin every
2 days. For this reason, the area having suitable soils was
divided as shown in Figure B-5, with 7 basins ranging in
size from 0.98 to 1.3 ha (2.4 to 3.2 acres).
B-14
-------
Ul UJ
co ce
ee o
LU
LU
:r
CO
CO
>-
CO
CD I—
•t
LU ce
o: »—
o —i
ca —
a.
«c
a:
ca
o
o
B-15
-------
B-16
-------
To control the basin loading rate, adjustable overflow weirs
were designed for each pond cell. During normal operation,
the overflow weirs are to be set at the 3.65 m (12 ft) .level
of the pond (the average water depth). This means that the
instantaneous wastewater flow to a basin at any time 'during
a 2 day loading period will equal the wastewater flow just
pumped into the pond. In other words, although the design
average wastewater flowrate is 6,060 m^/d (1.6 Mgal/d), up
to 9,090 m3/d (2.4 Mgal/d) may be delivered to each basin
during peak flows (Section B.2.2). The peak wastewater
application rate was calculated as follows:
Qmax x 100 cm/m
A
mn
10,000 m2/ha x 24 h/d
where
Q
max
= peak application rate, cm/h
= peak wastewater flow, m3/d
A . = basin area of smallest basin, ha
9,090 m3/d x 100 cm/in
= 3.86 cm/h
0.98 ha x 10,000 m2/ha x 24 h/d
In contrast, the average wastewater loading rate is:
R _ Q x 100 cm/m x N
AT x 10,000 m2/ha x 24 h/d
where R = average application rate, cm/h
Q = average wastewater flow, m3/d
N = number of infiltration basins
Am = total area covered by basins, ha
R =
6,060 m3/d x 100 cm/m 7
8.1 ha x 10,000 m2/ha x 24 h/d
= 2.18 cm/h
Comparing the peak and average application rates to the
lowest measured basin infiltration rate of 2.54 cm/h or
1.0 in./h (Section B.4.3], it can be seen that during appli-
cation, infiltration would exceed application at least half
the time. Also, all of the water applied during a 1 day
period would infiltrate during the same period.
B-17
-------
Therefore, the basin depth necessary to allow up to 12 hours
of flooding at the peak application rate:
D "
12 h
where
D = maximum depth for wastewater, cm
= basin area of largest basin, ha
I = limiting infiltration rate, cm/h
D = (3.86 cm/h - 2.54 cm/h) x 12 h
= 16 cm (6.2 in.)
The required total depth was found by rounding off D to
15 cm (6.0 in.) and by adding 30 cm (12 in.) of freeboard
(Section 5.6.1). The resulting design basin depth was 45 cm
(18 in.). This depth should provide more than adequate
freeboard during normal operations and will provide a margin
of safety for unexpected conditions and emergencies.
A typical slope, of 1:2 was selected for the sides of the
berms, on both interior and exterior sides, and the width of
each berm was set at 122 cm (48 in.). A single road around
the outer edge of the basins was included with ramps into
each basin for access. With these additions, the area
covered by the infiltration basins was approximately 8.3 ha
(20.5 acres), including 8.1 ha (19.9 acres) available for
infiltration.
B.7.2
Underdrainage
Drain laterals and a collector drain were located as shown
in Figure B-6. Drain lateral sizing will vary between 15
and 20 cm (6 and 8 in.), as recommended in Section 5.7.3.
The collector drain will be 20 cm (8 in.) in diameter to
ensure free flowing conditions. To meet the dissolved oxy-
gen requirements for discharge to North Creek, the renovated
water will be routed through a cascade aerator placed at the
bluff west of North Creek.
B.8 Maintenance and Monitoring
B.8.1 Maintenance
Occasional cleaning and ripping of the basins will be re-
quired to maintain design infiltration rates
(Section 5.8.2). Also, periodic maintenance of the ponds,
pumping station, screens, and grit chamber will be
necessary. A staff of two full-time employees should be
able to handle all the operation and maintenance needs of
Community B's system (Section 2.3.3.1).
B-18
-------
o
Q 30 60 90
SCALE m
OUTFALL
LATERALS
COLLECTOR DRAIN
FIGURE B-6
UNDERDRAIN LOCATIONS
B-19
-------
B.8.2 Monitoring
The renovated water will be monitored at the outfall for the
parameters listed, in Table B-2. Three monitoring wells to
monitor ground water concentrations of ammonia nitrogen and
total dissolved solids will be installed as shown in
Figure B-5. An observation well will be installed between
the bluff and Basin 4 to monitor ground water levels and
evaluate underdrain performance.
B.9 System Costs
Total costs of Community B's RI system are presented in
Table B-7. Capital costs were estimated using the EPA
report on Cost of Land Treatment Systems [1] . Costs were
updated to October 1980 using the EPA Sewage Treatment Plant
Construction Cost index value of 397.2. Contractor's over-
head and profit are included in the cost estimates. The
land was assumed to cost $4,900/ha ($2,000/acre). Operation
and maintenance costs were estimated using the cost curves
and current local prices for power and labor. Present worth
was determined using an interest rate of 7-1/8% for
20 years.
B.10 Energy Budget
In Community B, energy required for land treatment will be
used primarily to convey screened wastewater to the land
treatment site. The amount of energy needed for this pur-
pose can be estimated using the format presented in
Section 8.6.2, as follows:
Elevation at treatment site
Elevation at pump station
Elevation difference
Average flow
Assumed pumping system
efficiency
Pipeline diameter
Pipeline length
Pipeline headless
Total dynamic head
44 m (145 ft)
32 m (105 ft)
12 m (40 ft)
4,208 L/min
(1,111 gal/min)
40%
30 cm (12 in.)
2,680 m (8,000 ft)
12 m (40 ft)
24 m (80 ft)
B-20
-------
TABLE B-7
COST OF COMMUNITY B RI SYSTEM
Thousands of Dollars, October 1980
Capital costs
Transmission pumping
Transmission main
Aerated lagoons
Field preparation
Infiltration basins
Underdrains
Cascade aerator
Outfall pipe
Monitoring wells
Service roads and fencing
Standby power
Laboratory equipment
Sewer rehabilitation
Land acquisition
Legal, administrative, engineering,
interest, contingencies
Total capital costs
Operation and maintenance costs
Annual labor
Annual materials
Annual power
Total operation and maintenance costs
Total project costs
Total capital costs
Present worth of operation and
maintenance
Total present worth of costs
Salvage value of land
Net present worth
290
289
153
94
153
65
17
18
10
52
48
24
113
273
332
1,931
15
7
IT.
39
1,931
409
B-21
-------
Energy requirement (using
Equation 8-2)
361,000 kWh/yr
The energy required for scarification is within the range of
error of the estimated energy required to convey wastewater
to the treatment site. For this reason, energy requirements
for scarification are neglected. The energy required by the
three cell pond would be approximately 395,000 kWh/yr. The
total energy requirement of the system is 756,000 kWh/yr.
B.ll References
1. Reed, S.C., et al. Cost of Land Treatment Systems.
U.S. Environmental Protection Agency. EPA-430/9-75-
003. September 1979.
B-22
-------
Appendix C
OVERLAND FLOW DESIGN EXAMPLE
C.I Introduction
The purpose of this design example is to demonstrate the
design procedures described in Section 6.4. This example
represents a preliminary design suitable for Step 1 facility
planning. It does not go into the details of system com-
ponents such as specific equipment and hardware.
C.2 Statement of the Problem
Community C, a small rural community in the mid-Atlantic
United States, has a 30 year old wastewater treatment system
that is not meeting its discharge permit. The community is
totally residential with no industry discharging into'the
sewer system and has ~a 20 year design wastewater flow
projection of 1,890 m /d (0.5 Mgal/d). The objective of
this project is to provide the community with a wastewater
treatment system capable of meeting the discharge
requirements.
C.3 Design Considerations
C.3.1 Wastewater Characteristics and Discharge
Requirements
The raw wastewater characteristics are presented in Table
C-l. Although not listed in Table C-l, the concentrations
of trace elements are within the typical range for municipal
wastewater, and are therefore amenable to land treatment.
The state regulatory agency has imposed the following limi-
tations for any point source discharge; BOD,-/ 20 mg/L;
suspended solids, 20 mg/L; fecal coliforms, 200 HPN/100 mL.
TABLE C-l
RAW WASTEWATER CHARACTERISTICS
Parameter
Value
BOD,-, mg/L
Suspended solids, mg/L
Total nitrogen, as N, mg/L
Ammonia as N
Organic as N
Total phosphorus, as P, mg/L
200
200
40
25
15
10
C-l
-------
C.3.2 Climate
Average monthly temperature and precipitation data for
Community C were obtained from the U.S. Department of
Commerce, National Oceanic and Atmospheric Administration
(NOAA), Asheville, North Carolina, and are shown in Table C-
2. A 25 year, 1 hour storm for the community was determined
using the Rainfall Frequency Atlas of the United States,
U.S. Department of Commerce, Technical Paper 40, and was
found to yield 8.1 cm (3.2 in.).
TABLE C-2
AVERAGE METEOROLOGICAL CONDITIONS
Month
Jan
Feb
Mar
Apr
May
Jun
Jul
Aug
Sep
Oct
Nov
Dec
Year
Temperature,
°C
5.2
6.2
10.0
14.7
19.6
24.3
25.8
25.1
22.1
16.2
10.2
5.8
14.2
Precipitation
(Pr) , cm
8.7
9.3
10.2
8.8
.9.2
9.1
11.2
11.3
8.2
8.5
7.0
9.3
110.8
Potential evapo-
transpiration,
(ET) , cm
0.3
0.2
1.9
4.3
9.3
13.1
15.6
13.8
9.7
5.2
2.0
0.2
75.6
Net
precipitation
(Pr-ET) , cm
8.4
9.1
8.3
4.5
-0.1
-4.0
-4.4
-2.5
-1.5
3.3
5.0
9.1
35.2
C.4 Site Evaluation and Process Selection
C.4.1 General Site Characteristics
A preliminary site investigation determined that approxi-
mately 35 ha (86 acres) of land near the, existing wastewater
treatment system is available (Figure C-l). A USGS- map
showed the site to have a moderate to gentle slope that
drains naturally into Crooked Creek, the small stream that
receives the treated effluent from the existing treatment
system. A large portion of the site is wooded with pines,
hardwoods, and thick undergrowth.
C-2
-------
o
LU
CO
CD
Q_
CD
ce
Q_
-------
C.4.2 Soil Characteristics
As shown in Figure C-l, the proposed site is dominated by
soil of the Enon series. These soils have a fine sandy loam
top soil underlain with clays having a slow permeability.
Also present is Colfax sandy loam, which is underlain with
clay loam and mixed alluvial land along the stream. Both of
these soils have permeabilities ranging from slow to very
slow.
C.4.3 Process Selection
The slow permeability of the Enon soils will prohibit the
use of RI and will severely limit the use of this site for
SR treatment. Preliminary estimates indicated that OF
treatment was more cost effective than an SR system on this
site and was lower in total present worth than the best
conventional secondary treament and discharge alternative.
Therefore, OF treatment was the alternative selected by
Community C.
C.5 Distribution Method
High pressure sprinklers are used in this example to illus-
trate the procedure. Gravity distribution is usually more
cost effective and energy efficient. For high solids con-
tent wastewaters, such as food processing effluent,
sprinklers can offer the advantage of greater solids dis-
persion over the application area.
C.6 Preapplication Treatment
Continued operation of the existing treatment facilities
would not be cost effective because of the need for sludge
treatment and disposal. A new system consisting of the
minimum recommended treatment, that is, two-stage screening,
was selected. An economic analysis indicated the cost
savings from using less land (higher hydraulic loading
rates) did not offset the cost of preapplication treatment
(Section 6.3) beyond screening.
The two-stage screening system includes a coarse screen (bar
rack) and a fine screen. Since sprinkler application was
selected as the distribution method, the fine screen must be
capable of removing particles that could clog the sprinkler
nozzles. The screen mesh will be 1.5 mm (0.06 in.), as
recommended in Section 6.3. The new two-stage screening
system will be located at the headworks of the abandoned
existing plant.
C-4 •
-------
C.7 Wastewater Storage
C.7.1 Storage Requirement
The required storage for this project was calculated using
historical air temperature data obtained from the NOAA in
Asheville, North Carolina, and the design method described
in Section 6.4 for moderate climate zones. Twenty years of
data were reviewed for the air temperature limitations
specified by the design method to determine the critical
year, or the year that would have required the most storage.
The required storage days for the critical year are given on
a monthly basis in Table C-3. The total storage requirement
is 44 days, or 83,160- m (22.0 Mgal) of wastewater at the
design flow of 1,890 m /d (0.5 Mgal/d).
TABLE C-3
STORAGE REQUIREMENTS
Month
Nov
Dec
Jan
Feb
Mar
Total
Storage,
days
0
15.5
14.5
14.0
0
44.0
Potential
application,
days
30
15.5
16.5
14.0
31
The storage pond will be filled only during cold weather
when temperatures fall below -4 °C (25 °F). The procedure
for applying the stored wastewater on the OF site is
described in Section 6.5.
C.7.2 Storage Facility Description
Storage consists of a facultative pond. The design depth is
2 m (6.6 ft) and the surface area is 4.2 ha (10.4 acres).
Wastewater will be diverted to storage in December, January,
and February and will be drawn out of storage over the
period from March through May. The daily BOD loading on the
storage pond during the days of storage will be 89 kg/ha (80
Ib/acre) and odors should not be a problem. The net
precipitation falling on the storage pond will add 18,600
m (5 Mgal) so that a total of 101,760 m (26.9 Mgal) will
have to be removed from the storage pond each spring.
Seepage from the pond is neglected for the storage period.
C-5
-------
The pond berm has interior and exterior side slopes of 3:1
(horizontal:vertical), a height above grade of 2.6 m (8.5
ft), and a crest width of 3.7 m (12 ft) which will serve as
a service road. The interior berm has a 30 cm (12 in.)
layer of riprap for embankment protection. The pond is
lined with compacted local clay to meet applicable state
requirements. The exterior berm slopes -are planted to
grass. The total area required for the storage pond is 5.4
ha (13.3 acres).
C.8 Selection of Design Parameters
C.8.1 Hydraulic Loading Rate
From Table 6-5, the range of hydraulic loading rates for
screened wastewater application is 0.9 to 3 cm/d (0.35 to
1.2 in./d). The selected hydraulic loading rate is 1.4 cm/d
(0.57 in./d). This rate has been used successfully with
screened raw wastewater in a similar climate (Sections 6.4
and 6.2). A more conservative loading rate is unnecessary
because prolonged subfreezing temperatures are not common.
A higher loading rate during periods of near freezing
temperatures would be inappropriate.
C.8.2 Application Period and Frequency
The application period selected is 8 h/d. This period can
be increased to 12 h/d during drawdown from storage and
during harvest periods (Table 6-5). The application fre-
quency is 7 d/wk.
C.8.3 Slope Length and Grade
As recommended in Section 6.4.6, the minimum slope length
for OF using full circle sprinklers is 30 m (100 ft) plus
one sprinkler radius. The sprinklers chosen for this
project (Section C.9) have a spray radius of 21.4 m (70 ft).
Thus, the minimum slope length is 51.4 m (168 ft). To be
more conservative, the design slope length is 61 m (200 ft).
The grade will range from 2 to 4% depending on existing
grades that are within this range.
C-6
-------
C.8.4 Application Rate
Using the selected hydraulic loading rate, application
period and frequency, and slope length, the application rate
is calculated:
where
w
S =
P =
^a p(ioo cm/m)
application rate, m^/m-h
hydraulic loading rate, 1.4 cm/d
slope length, 61 m
application period, 8 h
0 _ 1.4(61)
a 8(100)
= 0.071 m3/m°h
This is within the acceptable range from Table 6-5.
C.8.5 Land Requirements
The slope area can be calculated from Equation 6-2.
AVg]/(DaLw(100)]
As = [Q(365)
where A = slope area, ha
s 3
Q = average daily flow, m /d
AVS = net change in storage = 18,600 m /yr (C.7.2)
Da = number of operating days per year
iv^ = hydraulic loading rate, cm/d
Ac = [1,890(365) + 18,600]/[(365 - 44 ) ( 1 .4 ) ( 100 )
o
= 15.8 ha (39 acres)
C.9 Distribution System
Impact sprinklers with 2^*1 mm (9/32 in.) diameter nozzles
'operating at 41.4 N/cm (60 Ib/in. ) are selected to
apply the wastewater. The OF slope and the sprinkler
positions are shown in Figure C-2. the sprinkler spacing of
24 m (80 ft) provides adequate overlap of the spray diameter
which is 42.7 m (140 ft).
C-7
-------
HIPACT SPRINKLER
\
PVC LATERAL LINE
RUNOFF COLLECTION CHANNEL
•
FT
\
\
\
\ „---
i \ s^
\
SPRINKLER
SPACIN6
24 IB
/x
/ ^
/ ' ' —
/
- I I/ '
1
I
I
I
~**^ f/ '
/^
^' \
— " \
\
/ \ FL01
IMPACT CIRCLE FOR 7.1 sm \ DIRECTION
1
r
T
1 NOZZLE 42.7 ra ' 0.5* ~"
\ / CHANNEL
\
^ ^,^^~
V'
/ X.
/ *^ — .
/
/
/
/
/ SLOPE
'""""•>. /
X /
^,s \
- — -" \
\
\
\
1
1 I • •
\
\
\
\
1 ^^^^
/ ~" ~ .
/
1
1
1
f
/
/
— -— t
"^^ ^ .'
s \
•— " \
\
\
\
1
1 s} J* . 1 * A
(S V
* 21 •_
40 -
-------
C.10 Preliminary System Layout
The field area and slope lengths have now been determined.
Given these, a preliminary layout of the treatment system
was made on a USGS map using the guidelines from Section
6.6. The dimensions for storage have also been determined
and were added to the overall layout. Using this and
remembering that area is required for collection waterways,
service roads, buffer zones, etc., the size of the survey
area was determined. It can not be overemphasized that a
sufficient amount of land greater than the apparent needs
must be surveyed so that changes in the system layout that
may occur do not require that additional land be surveyed.
This not only adds a greater cost to the project, but also
takes additional time that delays the design.
For this project, the entire site was surveyed so that any
future expansions to the system could be performed without
another survey. From this survey, a contour map with
contour intervals of 0.3 m (1.0 ft) was developed (Figure C-
3); however, due to the scale of Figure C-3, only the 3.05 m
(10.0 ft) contours are used.
C.ll System Design
C.ll.l Treatment Slopes
Given the slope area requirements and the slope length, the
contour map developed from the survey, and the site
development guidelines in Section 6.6, the treatment slopes
were laid out (see Figure C-4). This layout has the slopes
all graded in -the same direction (southeast) while the
runoff collection channels convey the effluent northeast to
a collection waterway. With this layout, all effluent is
discharged from the site at a single point as indicated on
the figure.
C.ll.2 Runoff Channel Design
The runoff collection channels are formed by the
intersection of the foot of one treatment slope with the
backslope of the next treatment slope (Figure C-2). These
channels will be graded to no greater than 25% of the slope
grade of the treatment slope to prevent cross-flow on the
treatment slope. This slight grade will be sufficient to
cause flow to the collection waterways and will preclude the
need for any type of erosion protection other than planting
the channels with the same grasses as are used on the
treatment slopes.
C-9
-------
CO
CO
en
o
£
Q_
U_
O
C-10
-------
o
>-
LLJ
T I—
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CJ >-
CO
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CD—I
— LL.
oc
UJ
x _« B:
C-ll
-------
C.11.3 Collection Waterways
The collection waterways transport the effluent from the
runoff collection channels to the receiving stream (Figure
C-4). These waterways were designed to handle both the
design runoff from the system plus precipitation that falls
on the site during a 25 year storm.
The Rational Method, which can be found in any soil and
water engineering text, was used to determine the storm
runoff from the treatment slopes. The 25 year storm runoff
for each slope was determined and the flows accumulated as
each runoff" collection channel contributed flow to the
collection waterway. The flow increases in quantity as it
comes downgrade until all runoff collection channels have
fed it. Therefore, the collectipn waterway must also
increase in size as it comes downgrade to prevent high flow
velocities that cause erosion.
Working from the treatment slope with the highest elevation
down (northeast corner of spray field to southeast corner),
the waterway was designed for the expected effluent runoff
and the 25 year stormwater flow for each section between
runoff collection channels. The procedure for designing
grassed waterways, which can be obtained from the SCS, was
used to size each section. Since the topography of the site
is such that the collection waterway will have a slope of 4%
or less/ there was no need for embankment protection at
bends; the grass is sufficient to prevent erosion.
C.11.4 Pumping System
The pumping system includes three pumps, each with a
capacity of 1,325 L/min (350 gal/min) at a total head of
72.5 m (238 ft). The headless was determined by summing all
the headlosses, from the farthermost sprinkler back to the
pump, of the critical piping path or that path that produces
the greatest headless.
The pumps work in parallel and feed a 20.3 cm (8 in.) force
main that runs to the spray field. The combined capacity of
the three pumps is three times the average design .flowrate
so there is an adequate safety factor for peak flows and
diurnal fluctuations.
The pumping station is located immediately after the two
stage screening unit on the existing treatment plant site.
As shown in Figure C-4, the storage basin is at a higher
elevation, which means wastewater must be pumped to storage
and then flow back to the pumping station through a separate
pipeline by gravity. Sufficient land was not available to
C-12
-------
locate the storage basin between the screening unit and the
pumping station to allow gravity flow intq storage and out
pumping station. During favorable days in the
a valve is opened on the return pipeline from the
the pumping station and wastewater is
to the
spring/
storage
applied
flowrate.
pond to
to the slopes at 1.5 times the average daily
C.11.5 Monitoring and Collection Systems
A monitoring station is located on the site, as shown in
Figure C-4. This station consists of a Parshall flume with
a continuous flow metering device and a composite sampler.
The Parshall flume was designed to handle the 25 year storm
flow without sustaining significant damage. A standby
chlorination system was installed at this location and three
ground water monitoring wells were installed as shown in
Figure C-4 to satisfy state regulatory requirements.
C.I2 Land Requirements
The final land area requirement was determined after all the
components of the OF system had been sized and located on
the site plan. A 15 m (50 ft) buffer zone around the
application site was recommended by the state agency since
residential developments are close to the site. The buffer
zone will remain wooded and will require 2.3 ha (5.7 acres)
of land. All of the land requirements of the system are
listed in Table C-4. Although the total land requirement is
29.3 ha (72.3 acres), the entire 35 ha (85 acre) site was
purchased since the owner refused to sell only a portion of
the property.
TABLE C-4
LAND REQUIREMENTS
Area
Item
ha
acres
Field area with collection channels 15.8 39.0
Storage pond
Buffer zone
Miscellaneous
Roads, collection waterways,
monitoring station
Surplus landa
Total
5.4 13.3
2.3 5.7
29.3 72.3
a. Surplus land is that land which does not fit
economically into the grading plan.
C-13
-------
C.13 Cover Crop Selection
Based on experiences with varieties of grasses at other OF
systems, it was decided to use the mixture given in Section
6.7 which includes Reed canarygrass, tall fescue> redtop,
dallisgrass, and ryegrass. The local agricultural agent
concurred and also suggested orchardgrass be added to the
mix since this grass flourished in the area.
C.14 System Costs
Total costs for the OF system for Community C are presented
in Table C-5. Capital costs were estimated using the EPA
technical report on Cost of Land Treatment Systems [1].
Costs " were updated to September 1980 using the EPA Sewage
Treatment Plant Construction Cost Index value of 362 and the
EPA Sewer Construction Cost Index of 387. . Contractor's
overhead and profit are included in the cost estimates,. The
land was assumed to cost $4,.900/ha ($2,000/acre) . Operation
and maintenance costs were estimated using the cost curves
and current local prices for power and labor. Present worth
was determined using an interest rate of 7-1/8% for 20
years.
TABLE C-5
COST OF COMMUNITY C OF SYSTEM
Thousands of Dollars, September 1980
Capital costs
Preapplication treatment 42
Pumping 271
Force main 29
Piping to and from storage 20
Storage pond 316
Site'clearing 70
Slope construction 60
Runoff collection , , 14
Distribution (sprinklers, laterals, controls) 72
Agriculture (preparation and seeding) 20
Service roads 24
Chlorination and flow monitoring 56
Monitoring wells 5
Contingencies (30%) 300
Land 172
Total capital costs • 1,471
Operation and maintenance costs
Annual labor 27
Annual materials 7
Annual power 8
Total operation and maintenance costs 42
Total-project costs
Total capital costs 1,471
Present worth of operation and maintenance 441
Total present worth of costs 1,912
Present worth of salvage value of land (78)
Net present worth 1,834
-------
C.15 Energy Budget
Pumping, crop production, and chlorination require quanti-
fiable primary energy. For pumping raw wastewater, stored
wastewater, and accumulated precipitation at a head of 72.5
m (238 ft), 222,000 kWh/yr is required. Crop harvest will
require 20,000 kWh/yr and disinfection, if used, will
required 5,000 kWh/yr. The total primary energy budget is
247,000 kWh/yr. If a gravity distribution system had been
possible, the pumping requirements would have been reduced
to about 58,000 kWh/yr due to the lower pumping head
requirement of approximately 20 m (66 ft).
C.16 Alternative Design Methods - Design Example
The data used to design the OF system in the previous
example will be used with the alternative CRREL and UCD
design methods. These two methods determine the land area
and loading requirements for a system and thus would not
alter the other parts of the design procedure just used.
These methods represent a rational OF design procedure, but
have been' used to a limited extent for design as of
September 1981.
C.16.1 CRREL Method
Given:
Daily flowrate = 1,890 m3/d
Influent BOD = 200 mg/L
Effluent BOD = 20 mg/L
Storage requirement = 44 days 3
Volume of precipitation in storage = 18,600 m /yr
Runoff fraction, r = 60%
Constants for the design equation are (see Section 6.11.1):
A = 0.52 ,
K = 0.03 min"
The necessary calculations are:
1. Calculate detention time on the slope:
(1.0)(200) - 0.6(20)
% BOD removal = •* (i.Q)(200)
x 100 = 94%
C-15
-------
Using Equation 6-8 (Section 6.11.1.2)
E = (1 - Ae~Kt)100
94 = (1 - 0.52e~°*03t)100
t = 72 min
Calculate average overland flowrate. The site
investigation revealed the site had a gentle slope
of 4 to 6%. For design purposes, the natural
slope of 5% will be used and a section size of 40
m long and 30 m wide (131 by 98 ft) will be used,
based on site characteristics. The average
overland flowrate is calculated using Equation 6-9
from Section 6.11.1.2.
q = (0.078S)/(G1/3t)
= [0.078(40 m)]/[(0.05)1/3(72)]
=0.12 m3/m-h
Calculate application rate. Using Equation 6-10
from Section 6.11.1.2, the application is
calculated.
Q = qw/r
= [(0.12 m3/m-h)(30 m)]
= 4.5 m /h per section
0.6)/2]
Calculate annual loading rate. An application
period of 8 h/d and an application frequency of 7
d/wk will be used in this example. Since the
storage requirement is 44 days and the application
frequency is 7 d/wk, the number of days of
application is 321 d/yr. The annual loading rate
per section is therefore:
Annual loading
= (321 d/yr)(8 h/d)
3
x (4.5 m /h per section)
Rate per section = 11,556 m /yr
Calculate total annual water volume. Given a
daily flowrate of 1,890 m and a volume of
precipitation that ends up in the storage as
18,600 m /yr, the total annual water volume is
708,450
C-16
-------
6. Calculate land area requirements. The number of
sections required is:
No. sections = (708,450 m /yr)
4 (11,556 m /yr per section)
= 62 sections
The total area requirement is
Area = [(62 sections)(30 m x 40 m/section)
4 10,000 m2/ha
= 7.4 ha (18.3 acres)
For comparison to the previous example, the weekly
hydraulic loading rate can be calculated as:
4.5 m3/h x 8 h/d x 7 d/wk = 252 m3/wk
252 m3/wk x (1/1,200)(section/m2)
x 100 cm/m
=21 cm/wk
C.16.2 University of California, Davis, Method
Given:
Daily flowrate = 1,890 m3/d
Influent BOD = 200 mg/L
Effluent BOD = 20 mg/L
Storage requirement = 44 days 3
Volume of precipitation in storage = 18,600 m /yr
Constants for the design equation are (see Section 6.11.2):
A = 0.72
n = 0.5
K = 0.01975 m/h
The necessary design calculations are:
1. Compute the required removal ratio CS/CQ.
C /C = 20/200 = 0.10
s o
C-17
-------
The length of slope is not restricted by
topography, so select a value for the application
rate (q) in the valid range of the model (see
Section 6.11.2)
Select q = 0.16 m3/m-h
Compute the required value of slope length (S)
using Equation 6-11 from Section 6.11.2.
Cs/Co = Ae'
0.1 = 0.72e
S = 40 m
-0.04938S
4. Select an application period (P)
P = 8 h/d
5. Compute the average daily flow to the OF system
using 44 days of storage, a 7 d/wk application
frequency, and 18,600 nT/yr additional water in
storage from precipitation.
Q = [(365 d)(l,890 m3/d)
+ 18,600 m3)]/(365 - 44)
= 2,207 m3/d
6. Compute the required wetted area using Equation
6-5 from Section 6.11.2.
Area = QS/qP
= ['(2,207 m3/d)(40)]/[(0.16 m3/m-h)
x (8 h)(10,000 m2/ha)]
= 6.9 ha (17.0 acres)
For comparison to the other examples, the weekly
hydraulic loading rate can be calculated as:
(2,207 m3/d)(7 d/wk) = 15,449 m3/wk
(15,449 m3/wk)(1/68,500 m2)(100 cm/m) = 22.6 cm/wk
C-18
-------
C.16.3 Comparison of Methods
Although the CRREL and UCD equations appear different', the
basic approach and calculation method are quite similar.
Combining and rearranging Equations 6-8 and 6-9 from the
CRREL method produce:
Ms/Mo
= 0.52e(~°-00234S)/(Gl/3q)
(6-13)
where
M = mass of BOD at point S, kg
M = mass of BOD at top of slope, kg
§ = slope length, m _
q = average overland flowrate, m /m-h
G = slope grade, m/m
This is quite similar to the UCD Equation 6-11:
Cs/C0 = o.72e(-0-01975S)/^°'5)
All terms as defined previously.
The major difference in these two rational approaches are
the use of slope as a variable in the CRREL equation and the
value of the coefficients and exponents. Comparison of the
results from all three methods are tabulated below:
Method
Traditional
CRREL
UCD
Land
area, ha
15.8
7.4
6.9
Slope
length, m
60
40
40
Hydraulic
loading, cm/wk
10
21
22.6
The major difference between the three methods is the slope
length required. The hydraulic loadings are similar since
the traditional method would permit at least 15 cm/wk during
the warm months. The CRREL and UCD methods are based on
assumed gravity distribution, so a shorter slope can be used
since there is no need to provide space above the
application point for full circle sprinkler impact. If
gravity application had been used in the traditional design,
the gated pipe could have been placed at the sprinkler
nozzle location shown in Figure C-2. This would result in a
40 m (130 ft) slope length which is identical to that
determined by the rational methods.
C.17 References
1. Reed, S.C. et al. Cost of Land Treatment Systems.
U.S. Environmental Protection Agency. EPA-430/9-75-
003. September 1979.
C-19
-------
-------
APPENDIX D
LOCATION OF LAND TREATMENT SYSTEMS
This appendix contains lists of publicly owned treatment
facilities and selected industrial facilities that employ
land treatment. The lists were derived from a variety of
sources including the EPA Needs Surveys, the literature, and
individual states' lists and the Corps of Engineers.
The number of land treatment systems increased steadily from
about 300 in 1940 to about 700 in 1976. It is probable that
there are more industrial and more private land treatment
systems than there are publicly owned land treatment
systems. The present count of publicly owned land treatment
systems is 839 SR, 323 RI, and 18 OF systems that are oper-
ating or are under construction in 1981.
D.I
Slow
Rate
Systems
REGION I
Maine
Greenville
Massachusetts
Franklin
New Hampshire
Mt. Sunappee
Wolfeboro
Vermont
West Dover
REGION II
New Jersey
East Windsor
Neptune
REGION III
Maryland
Caroline Acres
Deep Creek Lake
Highlands
Rossmoor
St. Charles
Snowden's Mill
Swanton
Tuckahoe
Village Center
Village Inn at Wisp
White
Virginia
John Kerr Lake
Pennsylvania
Benner Twp (Bureau of Corr.)
Gettysburg
Hamilton Twps
Kennett Square
State College
REGION IV
Florida
Apopka
Bay County
Brevard County
Coco Beach
East Point
Elgin AFB
Fort Walton Beach
Billiard
Jennings
Largo
L. Buena Vista (Disneyworld)
Lynn Haven
MacDill AFB
Marco Island
Newsberry
Okaloosa County
Pensacola (Scenic Hills)
St. Petersburg
Tallahassee
Tyndall AFB
Venice
Winter Haven
Zephyr Hills
Georgia
Braselton
Camp Oliver (Ft. Stewart)
Clayton Co. (R.L. Jackson)
Holiday Trav-L-Park (Lowndes Co.)
Jonesboro (Clayton Co.)
Kings Bay (Navy)
Skidaway Island
Stonewall Courthouse (Fulton Co.)
Mississippi
Arkabutla Lake
North Carolina
Pine Hurst
Seaboard
Woodland
South Carolina
Hilton Head Isl. (Bread Crk)
Hilton Head Isl. (Forest Beach)
Hilton Head Isl. (Plantation)
Sea Pines
REGION V
Illinois
Camp Point
Rend Lake, Big Muddy River
Michigan
Allegan
Belding
Bellaire
Beulah
Bloomingdale
Bowne Township
Caledonia
Cassopolis
Chatham
Clarence Township
Clark Township
Colon
Columbiaville
Crystal Township
Denton Township
East Jordan
Farwell
Fremont
Grayling
Harbor Springs
Harrison
Hart
Honor
Houghton Co. BPW
Kalkaska
Kingsley
Lake Odessa
D-l
-------
Lawton
Leoni Township
Livingston Co.
Mackinaw
Hanton
Marion
Harkey-Houghton
McBain
Hiddleville
Huskegon
Paw Paw
Pinckney
Quincy
Ravenna
Roscomraon
Springport
Sunfield
Union City
Verroontville
Wayland
Wixon
Whitehall
Webberville
Minnesota
Annandale
Battle Lake
Beardsley
Belgrade
Belle Plalne
Blackduck
Breezy Point
Caas Lake
Detroit Lakes
Eden Valley
Elysian
Frazee
Hayward
Henning
Kensington
Kiraball
Lake Henry
New Auburn
New York Mills
Ortonville
Paynesville
Pequot Lakes
Walker
Watkins
Wyoming
Ohio
ear Creek
Wisconsin
Arena
Avoca
Sauk City
Stone Lake
REGION VI
Arkansas
Amity Landing,
Caddo River
New Mexico
Alaroogordo
Cimarron
Clayton
Clovis
Doming
Dexter
Eunice
Gallup
Jal
Lordaburg
Los Alamos
DeGray Lake
Loving
Lovington
New Mexico Dept of Corr.
(Santa Fe Co.)
Portales
Raton
Roswell
San Jon
Silver City
Tularosa
Oklahoma
Amber
Apache
Bixby
Boise City
Byng
Calumet
Carter
Clinton
Cordell
Crescent
Davidson
Devol
Dill City
Duncan
Edmond
El Reno
Erick
Fairview
Frederick
Gage
Garber
Geary
Granite
Helena
Hobart
Hydro
Kingfisher
Lahoma
Laverne
Lone Wolf
Moore
Noble
Ochelata
Oklahoma City (Willow Ck)
Pauls Valley
Pond Creek
Sentinel
Shattack
Spencer
Sportsmans Acres
Stillwater
Terral
Tupelo
Velma
Texas
Abernathy
Abilene
Albany
Amarillo
Amherst
Andrews
Anson
Anton
Aspermont
Austin (Williamson)
Benjamin
Bexar County
Big Lake
Blanco
Bonham
Booker
Bovina
Brady
Brownfield
Burnett
Castroville
Chillicothe
Claude
Clyde
Coahoma
Coleman
Colorado City
Comfort
Crane
Crockett County
Crosbyton
Cross Plains
Crystal City
Dalhart
Darrouzett
Del Rio
Denver City
Devine,
Dimmitt
Dublin
Dumas
Earth
Eldorado
El Paso (Ascarte)
El Paso (Fabens)
El Paso (Socorro)
Estelline
Fabens
Falfurias
Falls City
Farwell
Florence
Floydada
Ft. Stockton
Fredericksburg
Freer
Friona
Fritch
Georgetown
Goldsmith
Goldthwaite
Gorman -
Graford
Grandfalls
Granger Lake
Greenfield
Groom
Gustine
Hale Center
Happy
Hart
Hedley
Hereford
Holliday
Hondo (East)
Hondo
Houston (CIWA)
Idalou
Ingleside
Johnson City
Karnes City
Kermit
Kerrville
Kilgore
Kingsville
Kress
Lames a
Levelland
Littlefield
Llano
Lockney
Loraine
Lorenzo
Lubbock
Lubbock (NW)
D-2
-------
Lubbock (Yellowhouse)
McCaraey
McLean
Mason
Matador
Mathis
Meadow
Memphis
Midland
Miles
Monahans
Morton
Muleshoe
Munday
New Home
Nordheim
North Fork Lake
Odonnell
Olton
Orange Grove
Ozona
Paducah
Pearsall
Pecos
Perryton
Petersburg
Plains
Poteet
Poth
Fremont
Quitaque
Rails
Rankin
Richland Springs
Rio Grande City
Roaring Springs
Robinson (North)
Robinson (South)
Roby
Ropesville
Roscoe
Rot an
Runge
Sabinal
San Angelo
San Angelo (Airport)
San Antonio (partial)
San Suba
Santa Anna
Seagraves
Seminole
Shallowater
Shamrock
Silverton
Slaton
Snyder
Somerville Lake
Sonora
Stanton
Stinnett
Stockdale
Stratford
Sudan
Sundown
Sunray
Sweetwater
Tahoka
Texline
Tolar
Troy
Tulia
Turkey
Uvalde
Van Horn
Vega
Weinert
Wellington
Wheeler
White Deer
Wilson
Winters
Wolfford
Youth Center
REGION VII
Iowa
New Hampton
Storm Lake
Kansas
Belleville
Bucklin
Chanute
Cheney
Colby
Elkhart
Elsmore
Enterprise
Formosa
Glen Elder
Goodland
Great Bend
Hays
Hugoton
luka
Kinsley
Leoti
Madison
Minneola
Montez.uma
Park Meadows
Parker
Plains
Plainville
Quinter
Ransom
Rolla
Russell
St. Francis
St. John
Scott City
Stockton
Sublette
Sylvia
Syracuse
Treece
Odall
Ulysses
West Plains
Missouri
Bennet Spring
Brunswick
Clarence Cannon Dam, Salt River
Clearmont
Crowder St. Park
Lockwood
Mark Twain National Forest
Montauk
Vandalia
Wright City
Nebraska
Clay Center
Davenport
David City
Gordon
Humphrey
Morrill
Oak
Phillips
Schuyler
SpaIding
Upland
REGION VIII
Colorado
Air Force Academy
Aurora
Burlington
Colo. Springs
Donala Development
Fitzsimmons AMC
Ft. Carson
Greeley
Holyoke
Inverness Development
Lake of the Pines
Northglenn
Snowmass
Steamboat Springs
Tammeron Development
Taylor Park
Wray
Montana
Aerial Fire Depot
Big Sky Development
Eureka
Rexford
Richey
Roberts
Rocky Boy
Roy
North Dakota
Alexander
Bowman
Dickinson
Sheyenne
Valley City
Watford
South Dakota
Eagle Butte
Gettysburg
Huron
Lake Andes
Mitchell
Utah
Bear River Central Disposal
Heber
Provo River Cental Disposal
Roosevelt
Spanish Fork
Tooele
Vernal
Wyoming
Cowley
Snowy Range Central Disposal
Thayne
REGION IX
Arizona
Alpine
Arizona City
Benson
C'asa Grande
Catalina
Coolidge
Ft. Huachuca
Gilbert
Joseph City
D-3
-------
Lake Havasu (South WWTF)
Lake Havasu (Island WWTF)
Hesa
Page
Prescott
Safford
St. Johns
Taylor
Tucson
Tucson (Airport)
Williams AFB
Winslow
California
Apple Valley
Angels
Antelope Valley
Armona CSD
Arvin
Atascadero
Avenal
Bakersfield (No. 1 and 2)
Bakersfield (No. 3)
Bass Lake
Beale AFB
Bear Creek Estates
Bear Valley
Bodega Bay
Bolinas
Brentwood
Buena Vista
Butte Community College
Buttonwillow
Boulder Creek
Calif. Inst. for Hen (Chino)
Calif. Hed. Facility
(Vacaville)
Calif. Hens Colony (SLO)
Calipatria
Calistoga
Cnraarillo
Cnraarillo St. Hospital
Cambria
Camp Pendleton
Caittpo
Castle AFB
Chico
China Carap (Harin)
China Lake
Chowchilla
Clearlake Oaks
Coachella
Coachella Valley
Coalinga
Colt Ranches (Hendota)
Colfax
Corning
County Estates (Ramona)
Cutler-Orosi
Delano
Dinuba
Douglas Flat
Earlimart
Edgemont
El Dorado Hills
El Toro
Exeter
Fairfield
Fnllbrook
Fed. Corr. Inst.
(Santa Barbara)
Fernbridge
Ferndale
Fontana
Forestville
Ft. Hunter-Liggett
Furnace Creek
George AFB
Golden Gate Park (SF)
Goldside Estates
Gonzales
Graton
Groveland
Guadalupe
Gustine
Half Moon Bay
Hanford
Healdsburg
Hemet
Houston Creek (Crestline)
Indian Mills
Indio
lone
Ivanhoe
Kerman
Kern Co. Ind. Farm
King City
La Canada
La Crescenta
Lag una
Laguna Hills
La Honda
Lake Arrowhead
Lake Berryessa
Lake Berryessa (Napa Co.)
Lake Cachuma
Lake Co. (Clearlake Highlands)
Lake Elsinore
Lake Elsinore (Canyon Lake)
Lake Hughes
Lakeport
La Hont
Las Virgines
Le Grande
Lemon Cove
Lemoore
Limoneira Ranch
Lincoln
Lindsay
Livermore
Lodi
Los Alisos
Los Angeles Co.
(Acton Rehab. Center)
Los Angeles Co.
(Lancaster)
Los Angeles Co.
(Palmdale)
Los Angeles Co.
(Warm Springs)
Los Banos
Loyalton
McFarland
Hadera Co. (North Fork)
Halibu (Probation Camp)
Hanteca
March AFB
Headowood
Hendocino City
Merced
Michelson (Irvine Ranch)
Moccasin
Hodesto
Mokelumne Hill
Moulton-Niguel No. 1A
Houlton-Niguel No. 3
Mt. Vernon
tfurphys
Newcastle
North Fork
North Lakeport
North River No. 1
North Shore
Novato
Oakshores
Occidental
Ocotillo
Orange Cove
Pacific Union College (Angwin)
Palmdale
Palm Springs
Parlier
Ferris
Petaluma
Pixley
Plymouth
Pomona
Prado Regional Park
Quincy
Ramona
Rancho California
Richardson Bay
Richardson Springs
Ridgecrest
Riverdale
Rohnert Park
Rosamond
Sacramento (Metro Airport)
San Bernardino
San Bernardino Co. No. 70
San Buenaventura
San Clemente
San Joaquin Co. Gen. Hospital
San Juan Bautista
San Luis Obispo
San Luis Rey (Oceanside)
San Pasqual Acad.
(Escondido)
Santa Maria ,
Santa Nella
Santa Paula
Santa Rosa (Laguna)
Santa Rosa (Oakmont)
Santa Rosa (West College)
Scotts Valley
Seeley Creek (Crestline)
Sea Ranch
Shady Glen
Shafter
Shasta Dam
Shastina
Sheridan
Smith River
Snelling
Sonoma Valley
South Tahoe
Spanish Flat
Strathmore
Sun City
Sunnymead
Sunol Valley
Susanville
(Dept of' Corrections)
Sutter Creek
Taft
Tehachapi
Terra Bella
Thousand Oaks
Toraales
Tulare
Tulare Correction Center
Twentynine Palims
U.S. Vet. Admin,, Hosp.
(Livermore)
Veteran Home (Yountville)
Wasco
Weed
Western Hi HE (Chino)
D-4
-------
Westport
Willits
Wilseyville
Windsor
Windsor (Sonoma Co. Airport)
Winton
Woodlake
Woodland
Woodville
Woodward Bluff
Yountville
Hawaii
Hanalei
Kailua Kona
Kaunakakai
Keauhou
Lahaina
Schofield Barracks
Wai me a
Nevada
Carson City
Dayton
Douglas Co.
Elko
Gerlach
Glen Meadows
Incline Village
Las Vegas (partial)
Las Vegas (Clark Co.)
(partial)
Lemmon Valley
Owyhee
Winnemucca
REGION X
Idaho
Albion
Ashton
Boise (Gowen Field)
Bottle Bay
Bruneau
Donnelly
Enunett
Garfield Bay
Hazelton
Melba
Menan
Mt. Home
New Plymouth
Plummer
Rupert
Santa
St. Anthony
Wendell
Oregon
Adrian
Arch Cape
Ely
Boardman
Brownsville (North)
Brownsville (South)
Burns
Butte Falls
Corvallis (Airport)
Cottage Grove Lake
Cove
Creswell
Culver
Dexter Lake
Eagle Point
Echo
Eugene (Airport)
Forest Grove
Freeman Creek, Dworshak Dam
Gaston
Grouse Creek, Applegate Lake
Haines
Hillsboro, West Side
Hines
Jordan Valley
Junction City
Lakeside
Lakeview
Long Creek
Lowell
Madras
Metolius
Milton Freewater
Moro
Paisley
Prairie City
Richardson Point Park
Fernridge Reservoir
Richland
St. Paul
Seneca
Sherwood
Siletz
Somerset West
Stewart Lake, Lost Creek
Sutherlin
Ukiah
Unity
Wasco
Yamhill
Washington
Camp Booneville
Cusick
Ephrata
Grandview
Naches
Prosser
Quincy
Soap Lake
Walla Walla (Industrial)
Warden
Waterville
iTakiraa (industrial)
D.2 Rapid
Infiltration
Systems
REGION I
Massachusetts
Barnstabie
Chatham
Concord
Edgartown
Fort Devens
Nantucket (2 )
Wareham
REGION II
New Jersey
Cranbury
Seabrook Farms (industrial)
Vineland
New York
Birchwood-North Shore
(Holbrook)
Cedar Creek (Wantagh)
College Park (Farmingdale)
County Sewer District
(Central Islip)
County Sewer District
(Holbrook)
County Sewer District
(Holtsville)
County Sewer District #5
(Huntington)
County Sewer District #11
(Ronkonkoma)
County Sewer District 112
(Holtsville)
Heatherwood (Calverton)
Huntington Sewer District
Lake George
Riverhead
Strathmore Ridge (Brookhaven)
REGION III
Maryland
Calhoun Marine
Engineering School
Fort Smallwood
Jensen's Inc. - Hyde Park
Quality Inn of Pecomore, Inc.
South Dorchester K-8 Center
REGION IV
Florida
Avon Park
Lehigh Acres
Sandlake (Orlando)
Tavares
Williston
Kentucky
Horse Cave
REGION V
Illinois
Meredosia
Sangaman Valley
Michigan
Alpha
Bangor
Baraga
Bates Township
Calumet
Chatham
Crystal Falls
Decatur
Dimondale
Edmore
Forsythe Township
Gaastra
Cedar Springs (Grand Rapids)
Grayling
Hopkins
Howard
Marcellus
Olivet
Onekama
Ottawa County Road Commission
Pentwater
Shelby
Stockbridge
Tekonsha
Minnesota
Medina
D-5
-------
Wisconsin
Almond
Baldwin
Balsam Lake
Bacron
Birchwood
Boyceville
Coloma
Deer Park
Penwood
Fifield
Fontana
North Moraine (Glenbeulah)
Glenwood City
Grantsburg
Hammond
Haugen
Iron River
Kellnersville
King Veterans Home
Knapp
Lone Rock
Lyndon Station
Haribel
Hattoon
Merrimac
Hilton
Hinong
Mount Calvary
Neshkoro
Plainfield
Roberts
Rosholt
Sand Creek
Scandinavia
Sextonville
Spooner
Spring Green
Stetsonville
Stone Lake
Rozellville (Stratford)
Kelly Lake (Suring)
Unity
Warrens
Wautoma
Wheeler
White Lake
Wild Rose
Williams Bay
Winter
Wittenberg
Wyocena
REGION VI
Plains
Stevensville
Victor
North Dakota
Parshall
Reeder
Louisiana
Ft. Polk
New Mexico
Hobbs
Springer
Vaughn
REGION VII
Nebraska
Chapman
Elwood
REGION VIII
Colorado
Sterling
Montana
Bazin
Bozeman
Corvallis
South Dakota
Madison
REGION IX
Arizona
Arcosanti (Cordes Junction)
Lo Lo Mai Springs
Mammoth
Phoenix (23rd Avenue)
Papago Tribal Wastewater
Treatment System (Sells)
St. David
Thatcher
Marana (Tucson)
Green Valley (Tucson)
Arizona Correctional Training
Facility (Tucson)
Corona de Tucson (Tucson)
Sunrise Resort (White River)
Wickenburg
Willcox
California
Applegate
Arbuckle
Baker
Banning
Barstow
Bieber
Pfeiffer Big Sur State Park
Biola College (Los Angeles)
Bishop
Placer County (Blue Canyon)
Blue Lake
Blythe
Bombay Beach
Desert Lake (Boron)
Bridgeport
Buellton
Burney
Byron
California City
Calpella
Camino Heights
Caruthers
Cascade Shores
Warm Springs Rehabilitation
Facility (Castaic)
Ceres
Chester
Chualar
Coalinga
Corcoran
Corona
Courtland
Glen Helen Rehabilitation
Center (Crestline)
Del Rey
Delhi
Desert Crest
Desert Hot Springs
Desert Shores
Discovery Bay
Whittier Narrows (Los
Angeles County, El Monte)
Escalon
Etna
Farmersville
Fillmore
Firebaugh
Floriston
Fontana
Franklin
Fresno i
Gait
Garberville
Gilroy
Gorman
Grass Valley
Grayson
Greenfield
Gridley
Hamilton City
Silver Lake (Helendale)
Pleasant Ridge School
(Higgins Corner)
Hilmar
Hollister
Hopland
Huron
Idyllwild
Inyokern
Isleton
Julian
June Lake
Selma Community (Kingsburg)
Knights Landing
La Selva Beach
Laguna Niguel
Lake of the Pines
Copper Cove (Lake Tulloch)
Laton
Lechuza
Linda
Linden
L'innell
Livingston
Lompoc
Lone Pine
Lopez Lake
Madera
Madison
Malaga
Mammoth Lakes
Maricopa '
Mariposa
McCloud
McKittrick
Mineral
Mojave
Montague
Montalvo
Moorpark
Mt. Shasta
Newell
Oakdale
Orland
Victor Valley (Oro Grande)
Palm Desert
California Youth Authority
(Paso Robles)
Pauma Valley
Pine Valley
Pinecrest
D-6
-------
Poplar (Woodville Farm)
Porterville
Portola
Rancho Ponderosa
Rancho Santa Fe
Redlands
Reedley
Rialto
Richvale
Ripon
Riverbank
Running Springs
Salida
Salton City
San Ardo
Hemet San Jacinto
San Miguel
San Onofre State Beach
Sanger
Santee
Seeley
Shelter Cove
Smith Flat
Donner Summit (Soda Springs)
Soledad
Springville
St. Helena
Stirling City
Stratford
Tipton
Tranquillity
Tres Pinos
Tahoe-Truckee
Valley Center
Weaverville
Westley
Westwood
Wheatland
Whispering Palms
Whitter (Los Angeles County/
San Jose Creek)
Willow Creek
Woodbridge
Yreka
Yuba City
Yucaipa
Nevada
Alamo
Beatty
Blue Diamond
Boulder City
Empire
Eureka
Gabbs
Goldfield
Hawthorne
Henderson
Jackpot
McDermitt
McGill
Montello
Overton
Panaca
Paradise Spa
Paradise Valley
Pioche
Stead
Tonopah
Wendover
Yerington
REGION X
Washington
Ritzville
D.3 Overland
Flow Systems
REGION I
REGION II
New York
Harriraan (pilot scale)
REGION III
Maryland
Beltsville
Chestertown (industrial)
Virginia
Gretna
REGION IV
Georgia
Woodburry
Mississippi
Cleveland
Falkner
South Carolina
Easley (R&o)
REGION V
Illinois
Carbondale
Fillmore
Indiana
Middleburry (industrial)
Michigan
Glenn (industrial)
Ohio
Alum Creek Lake
Napoleon (industrial)
REGION VI
Louisiana
Vinton
Idaho
Dent Acres
Oklahoma
Ada (R&D)
Heavener
Texas
El Paso (industrial)
Paris (industrial)
Rocky Point, Sulphur River
Sherman
REGION VII
REGION VIII
REGION IX
California
Davis
Davis (industrial)
Newman
Sebastopol (industrial)
Nevada
Minden-Gardnerville
D-7
-------
-------
APPENDIX E
DISTRIBUTION SYSTEM DESIGN FOR SLOW RATE
E.I introduction
Details of distribution system design for the SR process are
presented in this appendix for both surface and sprinkler
distribution methods. Some aspects covered here are also
applicable to RI or OF distribution techniques. The level
of detail presented in this appendix is sufficient to
develop preliminary layouts and sizing of distribution
system components. References are cited that provide more
complete design information.
E.2 General Design Considerations
Several design parameters are common to all distribution
systems and are defined in the following.
E.2.1
Depth of Water Applied
The depth of water applied is the hydraulic loading per
application expressed in cm (in.) and can be determined
using the relationship:
where D =
Lw -
F =
D = LW/F (E-D
depth of water applied, cm (in.)
monthly hydraulic loading, cm (in.)
application frequency, number of applications
per month
The monthly hydraulic loadings will have been established as
a result of the water balance calculations developed in
Section 4.5.
E.2 .2
Application Frequency
The application frequency is defined as the number of
applications per month or per week. The application
frequency to use for design is a judgment decision to be
made by the designer considering: (1) the objectives of the
system, (2 ) the water needs or tolerance of the crop,
(3) the moisture retention properties of the soil, (4) the
labor requirements of the distribution system, and (5) the
capital cost of the distribution system. Some general
E-l
-------
guidelines for determining an appropriate application
frequency are presented here, but consultation with a local
farm adviser is recommended.
Except for the water tolerant forage grasses,' most crops,
including forest crops, require a drying period between
applications to allow aeration of the root zone to achieve
optimum growth and nutrient uptake. Thus, more frequent
applications are appropriate as the ET rate and the soil
permeability increase. In practice, application frequencies
range from once every 3 or 4 days for sandy soils to about
once every 2 weeks for heavy clay soils. An application
frequency of once per week is commonly used.
The operating and capital costs of distribution systems can
affect the selection of application frequency,, With
distribution systems that must be moved between applications
(move-stop systems), it is usually desirable to minimize
labor and operating costs by minimizing the number of moves
and therefore the frequency of application. On the other
hand, capital costs of the distribution system are directly
related to the flow capacity of the system. Thus, the
capital cost may be reduced by increasing the application
frequency to reduce system capacity.
E.2.3
Application Rate
Application, rate is the rate at which water is applied to
the field by the distribution system. In general, the
application rate should be matched to the infiltration rate
of the soil or vegetated surface to prevent excessive runoff
and tailwater return requirements. Specific guidelines
relating application rates to infiltration properties are
discussed under the different types of distribution systems.
E.2.4
Application Period
The application period is the time necessary to apply the
desired depth of water (D). Application periods vary
according to the type of distribution system, but, in
general are selected to be convenient to the operator and
compatible with regular working hours. For most
distribution systems, application periods are less than
24 hours.
E.2 .5
Application Zone
In most systems, wastewater is not applied to the entire
field area during the application period. Rather, the field
area is divided into application plots or zones and
wastewater is applied to only one zone at a time.
E-2
-------
Application is rotated among the zones such that the entire
field area receives wastewater within the time interval
specified by the application frequency. Application zone
area can be computed with the following:
where Aa =
Aw -
Aa = Aw/Na (E-2)
application zone area, ha (acres)
field area, ha (acres) (see Section 4.5.4.1)
No. of application zones
The number of applicati9n zones is equal to the number of
applications that can be made during the time interval
between successive applications . on the same zone as
specified by the application frequency. ,. .
For example, if the application period is 11 hours,
effectively 2 applications can be made each operating day.
If the application frequency is once per week and the system
is operated 7 days per week, then there are 7 operating days
between successive applications on the same zone and the
number of application zones is:
N = (2 applications/day)(7 operating days)
a = 14
If the field area is 100 ha (40 acres), then the application
zone is:
A_ = 100 ha/14
d
= 7.14 ha
E.2.6
System Capacity
Whatever type of distribution system is selected, the
maximum flow capacity of the system must be determined so
that components, such as pipelines and pumping stations, can
be properly sized. For systems with a constant application
rate throughout the application period, the flow capacity of
the system can be computed using the following formula:
Q = CAaD/ta
(E-3)
E-3
-------
where Q =
C =
Aa =
D =
discharge capacity, L/s (gal/min)
constant, 28.1 (453)
application area, ha (acres)
depth of water applied, cm (in.)
application period, h
Other methods of computing system flow capacity are
illustrated for each of the distribution systems.
E.3 Surface Distribution Systems
E.3.1
Ridge and Furrow Distribution
The design procedure for ridge and furrow systems is
empirical and is based on past experience with good
irrigation systems and field evaluation of operating
systems. For more detailed design procedures, the designer
is referred to references [1] and [2].
The design variables for furrow systems include furrow
grade, spacing, length, and stream size (flowrate)
(Figure E-la). The furrow grade will depend on the site
topography. A grade of 2% is the recommended maximum for
straight furrows. Furrows can be oriented diagonally across
fields to reduce grades. Contour furrows or corrugations
can be used with grades in the range of 2 to 10%.
The furrow spacing depends on the water intake
characteristics of the soil. The principal objective in
selecting furrow spacing is to make sure that the lateral
movement of the water between adjacent furrows will wet the
entire root zone before it percolates beyond the root
zone. Suggested furrow spacings based on different soil and
subsoil conditions are given in Table E-l.
The length of the furrow should be as long as will permit
reasonable uniformity of application, because labor
requirements and capital costs increase as furrows become
shorter. Suggested maximum furrow lengths for different
grades, soils, and depths of water applied are given in
Table E-2.
E-4-
-------
FURROW SPACIN6
- FURROW STREAM SIZE q
(a) RIDGE AND FURROW
BORDER
(b) GRADED BORDER
FIGURE E-1
SURFACE DISTRIBUTION METHODS
E-5
-------
TABLE E-l
OPTIMUM FURROW SPACING [3]
Soil condition
Optimum
spacing, cm
Coarse sands - uniform profile 30
Coarse sands - over compact subsoils 46
Fine sands to sandy loams - uniform 61
Fine sands to sandy loams - over
more compact subsoils 76
Medium sandy-silt loam - uniform 91
Medium sandy-silt loam - over
more compact subsoils 102
Silty clay loam - uniform 122
Very heavy clay soils - uniform 91
TABLE E-2
SUGGESTED MAXIMUM LENGTHS OF CULTIVATED
FURROWS FOR DIFFERENT SOILS, GRADES, AND
DEPTHS OF WATER TO BE APPLIED [1]
m
Avg depth
Furrow
grade, %
0.05
0.1
0.2
0.3
0.5
1.0
1.5
2.0
Clays
7.5
300
340
370
400
400
280
250
220
15
400
440
470
500
500
400
340
270
22.5
400
470
530
620
560
500
430
340
30
400
500
620
800
750
600
500
400
5
120
180
220
280
280
250
220
180
of water applied2, cm
Loams
10
270
340
370
400
370
300
280
250
15
400
440
470
500
470
370
340
300
20
400
470
530
600
530
470
400
340
5
60
90
120
150
120
90
80
60
Sands
7.5
90
120
190
220
190
150
120
90
10
150
190
250
280
250
220
190
150
12.5
190
220
300
400
300
250
220
190
From Equation E-l.
The furrow stream size or application rate is expressed as a
flowrate per furrow. The optimum stream size is usually
determined by trial and adjustment in the field after the
system has been installed [2]. The most uniform
distribution (highest application efficiency) generally can
E-6
-------
be achieved by starting the application with the largest
stream size that can be safely carried in the furrow. Once
the stream has reached the end of the furrow, the
application rate can be reduced or cut back to reduce the
quantity of runoff that must be handled. As a general rule,
it is desirable to have the stream size large enough to
reach the end of the furrow within one-fifth of the total
application period. This practice will result in an
application efficiency of greater than 90% for most soils if
tailwater is returned (see Section 4.8.2.1).
The application period is the time needed to infiltrate the
desired depth of water plus the time required for the stream
to advance to the end of the furrow. The time required for
infiltration depends on the water intake characteristics of
the furrow. There is no standard method for estimating the
furrow intake rate. The recommended approach is to
determine furrow intake rates and infiltration times by
field trials as described in reference [2].
Design of supply pumps and transmission systems^ should be
based on providing the maximum allowable stream size, which
is generally limited by erosion considerations when grades
are greater than 0.3%. The maximum nonerosive stream size
can be estimated from the equation:
qe = C/G
where qe = maximum unit stream size, L/s (gal/min)
C = constant, 0.6 (10)
G = grade, %
(E-4)
For grades less than 0.3%, the maximum allowable stream size
is governed by the flow capacity of the furrow, estimated as
follows:
where qc
C
qc = CFa
furrow flow capacity, L/s (gal/min)
constant, 50 (74)
2 2
cross-sectional area of furrow, m'' (ft )
(E-5)
E-7
-------
Various conveyance systems and devices are used to apply
water to the head of the furrows. The most common
conveyance systems are open ditches or canals (lined and
unlined), surface pipelines, and buried low-pressure
pipelines. For wastewater distribution, pipelines are
generally used. If buried pipelines are used to convey
water, vertical riser pipes with valves are usually spaced
at frequent intervals to release water into temporary
ditches equipped with siphon tubes or into hydrants
connected to portable gated surface pipe (Figure E-2 ).
FIGURE E-2
ALUMINUM HYDRANT AND GATED PIPE
AT SWEETWATER, TEXAS
The spacing of the risers is governed either by the headless
in the gated pipe or by widths of border strips when graded
border and furrow methods are alternated on the same field.
The valves used in risers usually are alfalfa valves
(mounted on top of the riser) or orchard valves (mounted
inside the riser). Valves must be sized to deliver the
design flowrate.
E-£
-------
Gated surface pipe may be aluminum, plastic, or rubber.
Outlets along the pipe are spaced to match furrow
spacings. The pipe and hydrants are portable so that they
may be moved for each irrigation. The hydrants are mounted
on valved risers, which are spaced along the buried pipeline
that supplies the wastewater. Operating handles extend
through the hydrants to control the alfalfa or orchard
valves located in the risers. Control of flow into each
furrow is accomplished with slide gates or screw adjustable
orifices at each outlet. Slide gates are recommended for
use with wastewater. Gated outlet capacities vary with the
available head at the gate, the velocity of flow passing the
gate, and the gate opening. Gate openings are usually
adjusted in the field to achieve the desired stream size.
EXAMPLE E-l:
DETERMINATION OF PRELIMINARY DESIGN CRITERIA
FOR A RIDGE AND FURROW DISTRIBUTION SYSTEM
sandy loam over clay
Design Conditions
1. Soil conditions:
2. Final grade: 0.5%
3. Maximum monthly hydraulic loading (1^) : 40 cm
4. Application frequency (FJ : 4 times per month (1/wk)
5. Total field area (Aw) : 100 ha
6. Crop: corn
Design Calculations
1. Determine depth of water to be applied during application.
D = LW/F
^ = 40/4
= 10 cm
2. Determine the application zone area with Equation E-2.
Assume four applications per day will be performed,
7 d/wk.
(E-l)
Application zone area (A_) =
a
-^-5 - =-= - •r-.
28 application zones
100 ha
(E-2)
28
= 3.6 ha
Select furrow spacing from Table E-l.
Sf = 76 cm
Select furrow length from Table E-2.
L = 370 m
E-9
-------
5. Estimate maximum furrow stream size (application rate) from Equation E-4.
ge
(E-4)
-1.2 L/S
This flow is used until the stream reaches the end of the furrow, at which
time the flow is reduced.
Calculate the number of furrows used per application zone.
(Aa) (104 m2/ha)
No. of furrows =
(Lf)(Sf)(0.01 m/cm)
(3.6 ha)(104 m2/ha)
(370 m)(76 cm/furrow)(0.01 m/cm)
=127 furrows
Calculate the maximum flow that must be delivered to each application area
(distribution system capacity).
Q = (No. of furrows)(qe)
= (127)(1.2 L/s)
= 152 L/s (2,417 gal/min)
E.3.2
Graded Border Distribution
Preliminary design considerations for straight", graded
border distribution systems are discussed here. Quasi-
rational design procedures have been developed by the SCS
for all variations of border distribution systems and are
given in Chapter 4, Section 15, of the SCS Engineering
Handbook [5] .
The design variables for graded border distribution are:
1. Grade of the border strip
2. Width of the border strip
3. Length of the border strip
4. Unit stream size
Graded border distribution can be used on grades up to about
7%. Terracing of graded borders can be used for grades up
to 20%.
The widths of border strips are often selected for
compatibility with farm implements, but they also depend to
a certain extent upon grade and soil type, which affect the
uniformity of distribution across the strip. A guide for
estimating strip widths is presented in Tables E-3 and E-4.
E-10
-------
TABLE E-3
DESIGN GUIDELINES FOR GRADED BORDER
DISTRIBUTION, DEEP ROOTED CROPS [1]
.Soil type
and
infiltration
rate
Sandy ,
^2.5 cm/h
Loamy sand ,
1.8-2.5 cm/h
Sandy loam
1.2-1.8 cm/h
Clay loam,
0.6-0.8 cm/h
Clay,
0.3-0.6 cm/h
Grade, %
0.2-0.4
0.4-0.6
0.6-1.0
0.2-0.4
0.4-0.6
0.6-1.0
0.2-0.4
0.4-0.6
0.6-1.0
0.2-0.4
0.4-0.6
0.6-1.0
0.2-0.3
Unit flow
per 1 m of
strip width,
L/s
10-15
8-10
5-8
7-10
5-8
3-6
5-7
4-6
2-4
3-4
2-3
1-2
2-4
Avg depth3
of water
applied, cm
7-10
7-10
7-10
10-13
10-13
10-13
10-15
10-15
10-15
15-18
. 15-18
15-18
15-20
Border
Width
12-30
9-12
6-9
12-30
8-12
8
12-30
6-12
6
12-30
6-12
6
12-30
strip, m
Length
60-90
60-90
75
75-150
75-150
75
90-250
90-180
90
180-300
90-180
90
350+
a. From Equation E-l.
TABLE E-4
DESIGN GUIDELINES FOR GRADED BORDER
DISTRIBUTION, SHALLOW ROOTED CROPS [1
Soil profile
Clay loam, 60 cm
deep over per-
meable subsoil
Clay, 60 cm deep
over permeable
subsoil
Loam, 15-45 cm
deep over hardpan
Grade , %
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 1 m of
strip width.
L/s
6-8
4-6
2-4
3-4
2-3
1-2
1-4
Avg depth
of water
applied, cm
5-10
5-10
5-10
10-15
10-15
10-15
3-8
Border
Width
5-18
5-6
5-6
5-18
5-6
5-6
5-6
strip, m
Length
90-180
90-180
90
180-300
180-300
180
90-300
a. From Equation E-l.
The length of border strips should be as long as practical
to minimize capital and operating costs. However, extremely
long runs are not practical due to time requirements for
patrolling and difficulties in determining stream size
adjustments. Lengths in excess of 400 m (1,300 ft) are not
recommended. In general, border strips should not be laid
E-ll
-------
out across two or more soil types with different intake
characteristics or water holding capacities, :and border
strips should not extend across slope grades that differ
substantially. The appropriate length for a given site
depends on the grade, the allowable stream size, the depth
of water applied, the intake characteristics of the soil,
and the configuration of the site boundaries. For
preliminary design, the length of the border may be
estimated using Tables E-3 and E-4.
The application rate or unit stream size for graded border
irrigation is expressed as a flowrate per unit width of
border strip, L/s-m (ft^/s-ft). The stream size must be
such that the desired volume of water is applied to the
strip in a time equal to, or slightly less than, the time
necessary for the water to infiltrate the soil surface.
When the desired volume of water has been delivered onto the
strip, the stream is turned off. Shutoff normally occurs
when the stream has advanced about 75% of the length of the
strip. The objective is to have sufficient water remaining
on the border after shutoff to apply the desired water depth
to the remaining length of border with very little runoff.
Use of a proper stream size is necessary to achieve uniform
and efficient application. Too rapid a stream results in
inadequate application at the upper end of the strip or in
excessive surface runoff at the lower end. If the stream is
too small, the lower end of the strip receives inadequate
water or the upper end has excessive deep percolation.
Actually achieving uniform distribution with minimal runoff
requires a good deal of skill and experience on the part of
the operator. The optimum stream size is best determined by
field trials as described in reference [2] . The range of
stream sizes given in Tables E-3 and E-4 for various soil
and crop conditions may be used for preliminary design.
Procedures given in reference [5] may be used to obtain a
more accurate estimate of stream size.
The application period necessary to apply the desired depth
of water may be determined from the following equation:
where ta =
L =
D =
C =
ta = LD/Cq
application period, h
border strip length, m (ft)
depth of applied water, cm (in.)
constant, 360 (96.3)
(•E-6)
E-12
-------
q = unit stream size, L/s-m of width (gal/min-
ft of width
The conveyance and application devices used for border
distribution are basically the same as described for ridge
and furrow distribution (Section E.3.1). Open ditches with
several evenly spaced siphon tubes are often used to supply
the required stream size to a border strip. When buried
pipe is used for conveyance, vertical risers with valves are
usually spaced at intervals equal to the width of the border
strip and are located midway in the border strip. With this
arrangement, one valve supplies each strip. Water is
discharged from the valve directly to the ground surface, as
indicated in Figure E-3, and is distributed across the width
of the strip by gravity flow. For border strip widths
greater than 9 m (30 ft), at least two outlets per strip are
necessary to achieve good distribution across the strip.
Hydrants and gated pipe can be used with border systems.
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 distribution if crop
changes are desired.
FIGURE E-3
OUTLET VALVE FOR BORDER STRIP APPLICATION
E-13
-------
EXAMPLE E-2:
DETERMINATION OF PRELIMINARY DESIGN CRITERIA
FOR GRADED BORDER DISTRIBUTION SYSTEM
Design Conditions
1. Soil conditions: deep clay
2. Final grade: 0.5%
3. Maximum monthly hydraulic loading (1^): 40 cm
4. Application frequency (F): 4 times/month
5. Total field area (Aw): 100 ha
6. Crop: pasture
Design Calculations
1. Determine depth of water to be applied (D).
D = 10 cm (see Example E-l)
2. Select strip width and length from Table E-4 based on design conditions.
W - 12 m
L = 180 m
3. Select unit stream size (q) from Table E-4.
q = 4 L/s-m
4. Estimate period of application (ta) using Equation E-6.
ta - § <*-
(180 m)(10 cm)
(360)(4 L/s)
= 1.25 h
5. Determine number of applications per day. Assume a 12 h/d operating period.
No. of applications = (12 h/d)(1.25 h/application) .
= 15
6. Determine application zone area (Aa). Assume application 7 d/wk.
_ Aw
Aa (7 d)(15 applications/d)
_ 100 ha
~ 105
= 0.95 ha
7. Determine number of border strips per application zone.
No. of strips = ^s
(0.95 ha)(104 m2/ha)
(180 m)(12 m/strip)
8.
= 4.4
= 5
Determine system flow capacity (Q)
Q = (5 strips) (W) (q)
= (5) (12 m) (4 L/s-m)
* 240 L/s (3,803 gal/min)
E-14
-------
E.4 Sprinkler Distribution Systems
E.4.1
Application Rates
The principal design variable for all sprinkler systems is
the application rate, cm/h (in./h). The design application
rate should be less than the saturated permeability or
infiltration rate of the surface soil (see Chapter 3) to
prevent runoff and uneven distribution. Application rates
can be increased when a full cover crop is present (see
Section 4.3.2.4). The increase should not exceed 100% of
the bare soil application rate. Recommended reductions in
application rate for sloping terrain are given in
Table E-5. A practical minimum design application rate is
0.5 cm/h (0.2 in./h). For final design, the application
rate should be based on field infiltration rates determined
on the basis of previous experience with similar soils and
crops or from direct field measurements.
TABLE E-5
RECOMMENDED REDUCTIONS IN APPLICATION
RATES DUE TO GRADE [6]
Percent
Grade
0-5
6-8
9-12
13-20
over 20
Application
rate reduction
0
20
40
60
75
E.4.2
a. Percent of level ground
application rate.
Solid Set Sprinkler Systems
Solid set sprinkler systems remain in one position during
the application season. The system consists of a grid of
mainline and lateral pipes covering the field to be
irrigated. Impact sprinklers are mounted on riser pipes
extending vertically frorii the laterals. Riser heights are
determined by crop heights and spray angle. Sprinklers are
spaced at prescribed equal intervals along each lateral
pipe, usually 12 to 27 m (40 to 90 f t). A schematic layout
of a solid set sprinkler system is shown in Figure E-4. A
system is called fully permanent or stationary when all
E-15
-------
lines and sprinklers are permanently located. Permanent
systems usually have buried main and lateral lines to
minimize interference with farming operations. Solid set
systems are called fully portable when portable surface pipe
is used for main and lateral lines. Portable solid set
systems can be used in situations where the surface pipe
will not interfere with farming operations and when it is
desirable to remove the pipe from the field during periods
of winter storage. When the mainline is permanently -located
and the lateral lines are portable surface pipe, the system
is called semipermanent or alternatively semiportable.
SURFACE OR
BURIED LATERALS
WITH MULTIPLE
SPRINKLER
LATERAL
SPACIN6
WETTED DIAMETER
OF SPRINKLER
SURFACE OR
BURIED MAIN
PREVIOUSLY IRRIGATED
AREA
SPRINKLER
SPACING
FIGURE E-4
SOLID SET SPRINKLER SYSTEM
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 farming equipment by fixed risers.
E.4.2.1 Application Rate
For solid set systems, the application rate is expressed as
a function of the sprinkler discharge capacity, the spacing
E-16
-------
of the sprinklers along the lateral, and the spacing of the
laterals along the main according to the following equation:
I = qsC/SsSL
where I = application rate, cm/h (in./h)
qs = sprinkler discharge rate, L/s, (gal/min)
C = constant = 360 (96.3)
S_ = sprinkler spacing along lateral, m (ft)
s
ST = lateral spacing along main, m (ft)
(E-7)
Detailed procedures for sprinkler selection and spacing
determination to achieve the desired application rate are
given in references [6, 7, 8].
E.4.2.2 Sprinkler Selection and Spacing
Determination
Sprinkler selection and spacing determination involves an
iterative process. The usual procedure is to select a
sprinkler and lateral spacing; then determine the sprinkler
discharge capacity required to provide the design
application rate at the selected spacing. The required
sprinkler discharge capacity may be calculated using
Equation E-7.
Manufacturers' sprinkler performance data are then reviewed
to determine the nozzle sizes, operating pressures, and
wetted diameters of sprinklers operating at the desired
discharge rate. The wetted diameters are then checked with
the assumed spacings for conformance with spacing
criteria. Recommended spacings are based on a percentage of
the wetted diameter and vary with the .wind conditions.
Recommended spacing criteria are given in Table E-6.
The sprinkler and nozzle size should be selected to operate
within the pressure range recommended by the manufacturer.
Operating pressures that are too low 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. Sprinklers with low design
operating pressures are desirable from an energy
conservation standpoint.
E-17
-------
TABLE E-6
RECOMMENDED SPACING OF SPRINKLERS [6]
Average wind speed
km/h
0-11
11-16
>16
(mi/h) Spacing, % of wetted diameter
(0-7) 40
65
(7-10) 40
60
(>10) 30
50
(between
(between
(between
(between
(between
(between
sprinklers)
laterals)
sprinklers)
laterals)
sprinklers)
laterals)
E.4.2.3 Lateral Design
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 20% of the operating pressure
of the sprinklers. This will result in sprinkler discharge
variations of about 10% along the lateral. 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 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 E-7. For long lateral lines, capital
costs may be reduced by using two or more lateral sizes that
will satisfy the headloss requirements.
The following guidelines should be used when laying out
lateral lines:
1. Where possible, run the lateral lines across the
predominant land slope and provide equal lateral
lengths on both sides of the mainline.
2. Avoid running laterals uphill where possible. If
this cannot be avoided, the lateral length must be
shortened to allow for the loss in static head.
3. Lateral lines may be run down slopes from a
mainline on a ridge, provided the slope is
relatively uniform and not too steep. With this
arrangement, static head is gained with distance
E-18
-------
downhill, allowing longer or smaller lateral lines
to be used compared to level ground systems.
4. Lateral lines should run as nearly as possible at
right angles to the prevailing wind direction.
This arrangement allows the sprinklers rather than
laterals to be spaced more closely together to
account for wind distortion and reduces the amount
of pipe required.
TABLE E-7
FACTOR (F) BY WHICH PIPE FRICTION LOSS
IS MULTIPLIED TO OBTAIN ACTUAL LOSS IN
A LINE WITH MULTIPLE OUTLETS [3]
No. of outlets
1
2
3
4
5
6
7
8
9
10
15
20
25
30
40
50
100
Value of F
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
EXAMPLE E-3 :
DETERMINATION OF PRELIMINARY DESIGN CRITERIA
FOR SOLID SET SPRINKLER SYSTEM
Design Conditions
1. Soil conditions: loam, permeability - 0.75 cm/h
2. Crop: forage grass
3. Depth of water applied (D): 7.5 cm
4. Application zone area (Aa): 10 ha
5. Average wind speed: 8 km/h
E-19
-------
Assume 50% greater than bare soil
Design Calculations
1. Determine design application rate (I) .
permeability rate due to cover crop.
Use I - 1.13 cm/h (0.45 in./h)
2. Select sprinkler and lateral spacings.
Use Ss = 12.2 m (40 ft)
SL = 18.3 m (60 ft)
3. Calculate required sprinkler discharge using Equation E-7.
= (I) (Ss) (SL)
(1.13 cm/h) (12.2 m) (18.3 m)
360
=0.7 L/s (11.1 gal/rain)
Select sprinkler pressure and nozzle size from manufacturer's
performance data to provide qs.
Use 0.56 cm (7/32 in.) nozzle at 48 N/cm2 (70 lb/in.2).
Wetted diameter = 38.1 m (125 ft)
Check selected spacing against spacing criteria in Table E-6.
(100%)
Sprinkler spacing = ^t''
= 32%
Lateral spacing = , ''
<40%
(100%)
= 48% <65%
Determine system flow capacity (Q)
Q = (Aa) (I)
= (10 ha)(1.13 cm/h)(10* m2/ha)(10~2 m/cm)(0.28
= 314 L/s (4,975 gal/min)
Determine application period.
ta - D/I
_ 7.5 cm
1.13 cm/h
= 6.6 h
m3/h'
E.4.3
Move-Stop Sprinkler Systems
With move-stop systems, sprinklers (or a single sprinkler)
are operated at a fixed position in the field during
application. After the desired amount of water has" been
applied, the system is turned off and the sprinklers (or
sprinkler) are moved to another position in the field for
the next application. Multiple sprinkler move-stop systems
include portable hand-move systems, end tow systems, and
side-wheel roll systems. Single sprinkler move-stop systems
include stationary gun systems. The operational
characteristics of these systems and a discussion of design
procedures are described in the following paragraphs.
E-20
-------
E.4.3.1 Portable Hand-Moved Systems
portable hand-moved systems consist of a network of surface
aluminum lateral pipes connected to a main line which may be
portable or permanent. Lateral lines are constructed of
aluminum pipe in 9 or 12 m (30 or 40 ft) lengths with
sprinklers mounted on vertical risers extending from the
lateral at equal intervals. There are not enough lateral
lines to cover the entire field; thus, lateral lines must be
hand-moved between applications to different positions along
the main to apply water to the entire field. A schematic of
a portable hand moved system is shown in Figure E-5a. 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
interference with farm machinery. The principal
disadvantage is the high labor requirement to operate the
system.
E.4.3.2 End Tow Systems
End tow systems are multiple-sprinkler laterals mounted on
skids or wheel assemblies to allow a tractor to pull the
lateral intact from one position along the main to the
next. As indicated in Figure E-5b, 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 than hand moved systems to accommodate the pulling
requirements.
The primary advantages of an end tow system are lower labor
requirements than hand moved systems, relatively low 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.
E.4.3.3 Side Wheel Roll
Side wheel roll or wheel move systems are basically lateral
lines of sprinklers suspended on a series of wheels. The
lateral line is aluminum pipe, typically 10.2 to 12.7 cm (4
to 5 in.) in diameter and up to 403 m (1,320 ft) long. The
wheels are aluminum and are 1.5 to 2.1 m (5 to 7 ft) in
diameter (see Figure E-6). The end of the lateral is
connected by flexible hose to hydrants located along the
main line. The unit is stationary during application and is
moved between applications by an integral engine powered
drive unit located at the center of the lateral (see
Figure E-5c). The drive unit is controlled by an operator.
E-21
-------
PREVIOUSLY
APPLIED
AREA
LATERAL WITH MULTIPLE
SPRINKLERS
MAIN
LATERAL WITH MULTIPLE
SPRINKLERS
(a) -PORTABLE HAND MOVED
PREVIOUSLY
APPLIED
AREA
DISASSEMBLED
MAIN LENGTHS
(b) END TOW
•HEEL-SUPPORTED LATERAL
MAIN, VITH MULTIPLE SPRINKLER
PREVIOUSLY
APPLIED
AREA
LATERAL BI1IH SPRINKLER
CONNECTIONS
MAIN
(c) SIDE IHEEL IOLL
6UN-TYPE
SPRINKLER
(d) STATIONARY GUN
FieURE E-5
MOVE-STOP SPRINKLER SYSTEMS
E-22
-------
FIGURE E-6
SIDE WHEEL ROLL SPRINKLER SYSTEM
The sprinklers are mounted on swivel connections to ensure
upright positions at , all times. Sprinkler spacings are
typically 9.2 to 12.5 m (30 or 40 ft) and wheel spacings may
range from 9.2 to 30.5 m (30 to 10O ft). Side wheel
laterals may be equipped with trail lines up to 27 m (90 ft)
in length located at each sprinkler connection on the axle
lateral. Each trail line has sprinklers mounted on risers
spaced typically at 9 to 12 m (30 to 40 ft). Use of trail
lines allows a larger area to be covered by a single unit,
which reduces either the number of moves or the number of
•units required to cover a given field.
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.
E-23
-------
E.4.3.4 Stationary Gun Systems
Stationary gun systems are wheel-mounted or skid-mounted
single sprinkler units, which are moved manually between
hydrants located along the laterals (see Figure E-5d).
Since the sprinkler operates at greater pressures and
flowrates than multiple sprinkler systems, the irrigation
time is usually shorter. After an application 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 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.
E.4.3.5 Design Procedures
The design procedures regarding application rate, sprinkler
selection, sprinkler and lateral spacing, and lateral design
for move-stop systems are basically the same as those
described for solid set sprinkler systems. An additional
design variable for move-stop systems is the number of units
required to cover a given area. The minimum required number
of units is a function of the area covered by each unit, the
application frequency, and the period of application. More
than the minimum number of units can be provided to reduce
the number of moves required to cover a given area., The
decision to provide additional units must be based on the
relative costs of equipment and labor.
E.4.4
Continuous Move Systems
Continuous move sprinkler systems are self-propelled and
move continuously during the application period. The three
types of continuous move systems are (1) traveling gun,
(2) center pivot, and (3) linear move. Schematics of the
systems are shown in Figure E-7.
E-24-
-------
ANCHOR
FLEXIBLE SUPPLY
HOSE
TAKE-UP
REEL
SELF-PROPELLED
DRIVE UNIT WITH
BUN-TYPE SPRINKLER
PREVIOUSLY
APPLIED
AREA
(a) TRAVELING GUN (HOSE DRAG)
(b) TRAVELING GUN (REEL-TYPE)
POWE
DRIVE
SUPPORTS
SUPPLY MAIN~V
FLEXIBLE HOSE
{OPTION)
LATERAL
WITH
.MULTIPLE
SPRINKLER
PREVIOUSLY
APPLIED
AREA
LATERAL WITK
MULTIPLE SPRINKLERS
PREVIOUSLY
APPLIED
AREA
(c) CENTER PIVOT
(d) LINEAR MOVE
FIGURE E-7
CONTINUOUS MOVE SPRINKLER SYSTEMS
E-25
-------
E.4.4.1 Traveling Gun Systems
Traveling gun systems are self-propelled, single large gun
sprinkler units that are connected to the supply source by a
hose 6.4 to 12.7 cm (2.5 to 5 in.) in diameter. Two types
of travelers are available, the hose drag-type and the reel-
type. The hose drag 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 (see Figure E-8). In
both cases, a cable anchored at the end of the run guides
the unit in a straight path during the application. The
flexible rubber hose is dragged behind the unit. The reel-
type traveler consists of a sprinkler gun cart attached to a
take-up reel by a semirigid polyethylene hose. The gun is
pulled toward the take-up reel as the hose is slowly wound
around the hydraulic powered reel. Variable speed drives
are used to control travel speeds. Typical lengths of run
range between 201 and 403 m (660 and 1,320 ft), and spacings
between travel lanes range between 50 and 100 m (i.65 and
330 ft). After application on a lane is complete, the unit
shuts off automatically. Some units also shut off the water
supply automatically. The unit must be moved by tractor to
the beginning of the next lane.
FIGURE E-8
HOSE-DRAG TRAVELING GUN SPRINKLER
E-26
-------
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 power
requirements, hose travel lanes required for hose drag units
for most crops, and drifting of sprays in windy conditions.
In addition to the application rate and depth of
application, the principal design parameters for traveling
guns are the sprinkler capacity, spacing between travel
lanes, and the travel speed.
The minimum application rate of most traveling gun
sprinklers is about 0.6 cm/h (O.23 in./h), which is higher
than the infiltration rate of the less permeable soils.
Therefore, the use of traveling guns on soils of low
permeability without a mature cover crop is not
recommended. The relationship between sprinkler capacity,
lane spacing, travel speed, and depth of application is
given by the following equation:
D =
(E-8)
(St)(Sp)
where D = depth of water applied, cm (in.)
qs = sprinkler capacity, L/s (gal/min)
St = space between travel lanes, m (ft)
S = travel speed, m/min (ft/min)
C = conversion constant, 6.01 (1.60)
The usual design procedure is as follows:
1. Select a convenient application period (usually
about 11 or 23 hours) to allow time (about 1 hour)
for moves between applications.
2. Measure the longest travel lane length (403 m or
1,320 ft maximum for hose drag; 360 m or 1,180 ft
maximum for reel-type) based on site boundaries.
3. Calculate the travel speed necessary to travel the
longest travel lane in the desired application
period.
E--27
-------
7.
8.
Select a sprinkler and sprinkler operating pressure
from manufacturers' performance tables with wetted
diameters compatible with site boundaries and with
application rates suitable for soil conditions.
Sprinkler operating pressures should be above
55 N/cm2 (80 lb/in.z).
Compute the required lane spacing to provide the
desired depth of water application using
Equation E-8.
Check lane spacing against spacing criteria in
Table E-8.
TABLE E-8
RECOMMENDED MAXIMUM LANE SPACING
FOR TRAVELING GUN SPRINKLERS
Wind speed
km/h (mi/h) Lane spacing, % of wetted diameter
0 (0)
0-8 (0-5)
0-16 (0-10)
80
70-75
60-65
50-55
Adjust sprinkler selection and lane
necessary to meet spacing criteria.
spacing as
Select a hose size for the unit such that friction
loss of the design sprinkler flow capacity does not
exceed 28 N/cm2 (40 lb/in.2).
9. Determine the total area covered by a single unit
Unit area, m2 = (St)(avg travel distance per day)
x (days between application)
10. Determine total number of units required
Units required = (field area, m2)
x (unit area, m2)
11. Determine the system supply capacity (Q)
Q = (qt,)(No. of units)
o
E~28
-------
E.4.4.2 Center Pivot Systems
Center pivot systems consist of a lateral with multiple
sprinklers or spray nozzles that is mounted on self-
propelled, continuously moving tower units (see Figure E-9)
rotating about a fixed pivot in the center of the field.
Sprinklers on the lateral may be high pressure impact
sprinklers; however, the trend is toward use of low pressure
spray nozzles to reduce energy requirements. Water is
supplied by a well or a buried main to the pivot, where
power is also furnished. The lateral is usually constructed
of 15 to 20 cm (6 to 8 in.) steel pipe 61 to 793 m (200 to
2,600 ft) in length. A typical system with a 393 m (1,288
ft) lateral covers a 64 ha (160 acre) parcel (see
Figure E-10). The circular pattern reduces coverage to
about 52 ha (13O acres), although systems with traveling end
sprinklers are available to irrigate the corners.
The tower units are driven electrically or hydraulically and
may be spaced from 24 to 76 m (80 to 250 ft) apart. The
lateral is supported between the towers by cables or
trusses. Control of the travel speed is achieved by varying
the running time of the tower motors.
An important limitation of the center pivot system is the
required variation in sprinkler application rates along the
length of the pivot lateral. Because the area circumscribed
by a given length of pivot lateral increases with distance
from the pivot point (as does the ground speed of the unit),
the application rate provided by the sprinklers along the
lateral must increase with distance from the center to
provide a uniform depth of application. Increasing the
application rates can be accomplished by decreasing the
spacing of the sprinklers along the lateral and increasing
the sprinkler discharge capacity. The resulting application
rates at the outer end of the pivot lateral can be
unacceptable for many soils.
Application rates approaching 2.5 cm/h (1.0 in./h) may be
necessary at a distance of 400 m (1,300 ft). The designer
should be particularly aware of this limitation at sites
where soil permeabilities vary within, the pivot circle.
Areas of slower permeability can be flooded, causing crop
damage and traction problems for the drive wheels. This
particular problem has been encountered at the Muskegon
project. Determination of the proper sprinkler spacings and
capacities for a center pivot rig is beyond the scope of
this manual. The designer should consult the manufacturer
for design details.
E-29
-------
1 **•
FIGURE E-9
CENTER PIVOT RIG
FIGURE E-10
CENTER PIVOT IRRIGATION SYSTEM
E-30
-------
Another limitation of center pivots is mobility under
certain soil conditions. Some clay soils can build up on
wheels and eventually cause-the unit to stop. Drive wheels
can lose traction on slick (silty) soils and can sink into
soft soils and become stuck.
E.4.4.3 Linear Move Systems
Linear move systems are constructed and driven in a_similar
manner to center pivot systems, except that the unit moves
continuously in a linear path rather than, a circular path.
Complete coverage of rectangular fields can thus be achieved
while retaining all the advantages of a continuous move
system. Water can be supplied to the unit through a
flexible hose that is pulled along with the unit or it can
be pumped from an open center ditch constructed down the
length of the linear path. Slopes greater, than 5% restrict
the use of center ditches. Manufacturers should be
consulted for design details.
E.5 References
1. Booher, L.J. Surface Irrigation. FAO Agricultural
Development Paper No. 94. Food and Agricultural
Organization of the United Nations. Rome. 1974.
2. Merriam, J.L. and J. Keller. Irrigation System
Evaluation: A Guide for Management. Utah State
University, Logan, Utah. 1978.
3. McCulloch, A.W. et al. Lockwood-Ames Irrigation
Handbook. W.R. Ames Company, Gering, Nebraska., 1973.
4. Hart, W.E. Irrigation System Design. Colorado State
University, Department of Agricultural Engineering.
Fort Collins, Colorado. November 10, 1975.
5. Border Irrigation. Irrigation, Chapter 4. SCS National
Engineering Handbook, Section 15. U.S. Department of
Agriculture, Soil Conservation Service. August 1974.
6. Fry, A.W. and A.S. Gray. Sprinkler Irrigation
Handbook. Rain Bird Sprinkler Manufacturing
Corporation, Glendora, California. 10th edition. 1971.
7. Sprinkler Irrigation. Irrigation, Chapter 11. SCS
National Engineering Handbook, Section 15. U.S.
Department of Agriculture, Soil Conservation Service.
July 1968.
E-31
-------
8. Pair, C.H. et al.f eds. Sprinkler Irrigation, Fourth
Edition. Sprinkler Irrigation Association. Silver
Spring, Maryland. 1975.
E-32
-------
APPENDIX F
ESTIMATED STORAGE DAYS FOR LAND TREATMENT
USING EPA COMPUTER PROGRAMS
Computer programs have been developed to estimate storage
days for land treatment systems based on climatic conditions
(Section 4.6.2). Selected locations for which the EPA-1
program have been used are presented in Table F-l for
recurrence intervals of 10 and 20 years. The EPA-2 program
(for SR systems) uses soil information as well as rainfall
(see reference 35 in Chapter 4 for details). The EPA-3
program (for SR or OF systems ) uses temperature, rainfall,
and snow depth. Storage days for communities for which EPA-
2 has been run are listed in Table F-2 for recurrence
intervals of 10 and 20 years. Storage days for communities
for which EPA-3 has been run are listed in Table F-3 for
recurrence intervals of 10 and 20 years.
TABLE F-l
STORAGE DAYS USING EPA-1 FOR 20 YEAR (5%)
AND 10 YEAR (10%) RETURN INTERVALS
Percentiles
Station Name
Bridgeport
Boise
Pocatello
Des Moines
Hampton
Logan
Shenandoah
Greenville
Muskegon
International Falls
Minneapolis
Park Rapids
Billings
Bozeman
Great Palls
Missoula
Buffalo
Rochester
Water town
State
CT
ID
ID
IA
IA
IA
IA
ME
MI
MN
MN
MN
MT
MT
MT
MT
NY'
NY
NY
0.05
68
87
125
111
136
107
95
172
119
172
143
159
102
152
102
128
108
121
128
0.10
64
77
109
106
126
105
77
169
116
168
143
155
100
144
91
121
103
115
126
Station Name
Bismarck
Devils Lake
Burns
Aberdeen
Brookings
Pierre
Rapid City
Burlington
Spokane
Ashland
Eau Claire
Green Bay
Lacrosse
Madison
Rhinelander
Weyerhauser
Afton
Casper
Gillette
Ruck Springs
Wheatland
State
ND
ND
OR
SD
SD
SD
SD
VT
WA
WI
WI
WI
WI
WI
WI
WI
WY
WY
WY
WY
WY
Percentiles
0.05
144
168
119
142
136
136
100
136
106
149
147
139
134
125
156
148
156
101
113
142
66
0.10
140
156
102
138
131
126
99
.134
100
148
141
135
127
119
149
145
144
95
108
136
58
F-l
-------
TABLE F-2
STORAGE DAYS USING EPA-2 FOR 20 YEAR jf5%)
AND 10 YEAR (10%) RETURN INTERVALS*
Percentiles
Station name
Bay Minette
Brewton
Clanton
Mobile
Selma
Thomasville
Dumas
Little Rock
Avon Park
Belle Glade
Bradenton
Clermont
Daytona Beach
Orlando
Punta Gorda
Tampa
Augusta
Ma con
Newnan
Savannah
Alexandria
Franklinton
Houma
Lafayette
Lake Providence
Leesville
Monroe
New Orleans
Schriever
Shreveport
St Joseph
Winnfield
Aberdeen
Biloxi
Canton
Clarksdale
Columbia
Greenwood
Jackson
Meridian
Pontotoc
Poplarville
Stoneville
Vicksburg
Charlotte
Pinehurst
Raleigh
Weldon
State
AL
AL
AL
AL
AL
AL
AR
AR
FL
FL
FL
FL
FL
FL
FL
FL
GA
GA
GA
GA
LA
LA
LA
LA
LA
LA
LA
LA
LA
LA
LA
LA
MS
MS
MS
MS
MS
MS
MS
MS
MS
MS
MS
MS
NC
NC
NC
NC
0.05
13
16
20
14
18
23
19
12
12
10
13
11
8
11
16
30
10
11
15
16
19
16
16
12
18
31
12
16
15
10
11
15
23
13
15
16
27
15
12
13
19
22
17
27
12
12
13
11
0.10
13
11
11
11
11
13
14
12
9
8
12
7
8
9
11
17
9
9
10
11
14
15
11
10
14
16
12
9
13
8
11
14
13
10
11
11
16
12
10
11
14
13
15
23
11
9
12
10
Station name
Wilmington
Wilson
Eugene
Forest Grove
Headworks
Hillsboro
Medford
Portland
Salem
Arecibo
Coloso
Guayama
Humacao
San Juan
Columbia
Conway
Darlington
Hampton
Summerville
Bristol
Crossville
Brownsville
Corpus Christi
Dallas
Houston
Luling
Mexia
Paris
Port Isabel
Sealy
Sugar Land
Blackstone
Buchanan
Chatham
Columbia
Diamond Springs
Leesville
Lynchburg
Norfolk
Richmond
Washington DC
Aberdeen
Longview
Olympia
Seattle
Vancouver
State
NC
NC
OR
OR
OR
OR
OR
OR
OR
PR
PR
PR
PR
PR
SC
SC
SC
SC
SC
TN
TN
TX
TX
TX
TX
TX
TX
TX
TX
TX
TX
VA
VA
VA
VA
VA
VA
VA
VA
VA
VA
WA
WA
WA
WA
WA
Percentiles
0.05
10
12
34
134
150
119
19
126
34
11
17
24
25
7
13
9
11
10
16
23
24
11
11
15
36
40
42
16
10
32
77
21
31
21
23
15
31
23
17
15
22
213
53
58
40
28
0.10
9
11
31
129
144
111
11
110
25
10
13
16
19
6
8
9
9
8
8
19
22
6
5
12
26
36
35
11
9
26
51
16
19
19
21
11
3L6
18
14
14
19
181
35
38
24
19
Available water capacity range from 15 to 30 cm (6 to 12 in.) in top 1.5 m
(5 ft) of soil profile. ' Depletion rate usually set at 1.9 cm/d (0.75 in./d)
F-2
-------
TABLE F-3
STORAGE DAYS USING EPA-3 FOR 20 YEAR (5%)
AND 10 YEAR (10%) RETURN INTERVALS
Percen tiles
Station Name
Sterling
Belle Plaine
Des Moines
Grinnell
Indianola
Keosauqua
Logan
Newton
Osceola
Oskaloosa
Shenandoah
Winterset
Ashton
Ottawa
Plymouth
Baltimore
Beltsvilleb
Blackwater Refuge
State
CO
IA
IA
IA
IA
IA
IA
IA
IA
IA
IA
IA
ID
IL
MA
MD
MD
MD
a. Temperature thresholds
0.05
118
133
135
139
122
111
126
134
122
130
114
134
151
115
95
77
76
35
: mean
0.01
110
128
128
133
113
91
114
126
118
121
101
127
148
89
91
57
58
29
0 °C
Station Name
Chestertown
Westminster
Freehold
Pemberton
Santa Fe
Minden0
Reno
Rochester
Coatesville
George School
Lancaster
Philadelphia
York
Corsicana"
Alta
Diversion Dam
Lander
Pavillion
Riverton
(32 °F) ; minimum
State
MD
MD
NJ '
NJ
NM
NV
NV ,
NY
PA
PA
PA .
PA
PA
TX
WY
WY
WY
WY
WY
-4 °C
Percen tiles
0.05
73
86
88
80
98
69
61
123
89
87
86
80
85
8
172
140
146
140
150
(25 °F) ;
0.10
46
82
77
72
88
63
57
122
85 '
83
84
66
80
6
160
137
139
137
144
maximum
snow 2.54 cm (1 in.); Precipitation 1.27 cm
(40 °F)
Precipitation thresholds:
(0.5 in.).
Drawdown rate: ratio of flow output from storage on favorable days to
average daily wastewater flow =0.5.
b. Temperature thresholds; minimum -5.5 °C (22 °F); maximum"!.7 °C (35 °F).
c. Temperature thresholds: minimum -6.7 °C (20 °F); maximum 1.7 °C (35 °F).
d. Temperature thresholds; minimum -2.2 °C (28 °F); maximum 2.2 °C (36 °F).
F-3
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APPENDIX G
GLOSSARY OF TERMS
CONVERSION FACTORS
GLOSSARY OF TERMS
acre-foot—A liquid measure of a volume equal to covering a
1 acre area to 1 foot of depth.
aerosol—A suspension of colloidal solid or liquid particles
TnaTr or gas, having small diameters ranging from 0.01 to
50 microns.
aquiclude—A geologic formation which, although porous and
capableof absorbing water slowly, will not transmit it
rapidly enough to furnish an appreciable supply for a well
or spring.
available
can be taken up
growth; the moisture
ultimate wilting point
moisture—The part of the water in the soil that
by plants at rates significant to their
content of the soil in excess of the
coppice—sprouting from tree stumps.
cultivar—A cultural variety of a plant species.
evapotranspiration—The combined loss of water from a given
areaandduring a specified period of time, by evaporation
from the soil surface, snow, or intercepted precipitation,
and by the transpiration and building of tissue by plants.
field area—The "wetted area" where treatment occurs in a
land application system.
field capacity—(field moisture capacity)—The moisture
contentofsoil in the field 2 or 3 days after having been
saturated and after free drainage has practically ceased;
the quantity of water held in a soil by capillary action
after the gravitational or free water has been allowed to
drain; expressed as moisture percentage, -dry weight basics.
fragipan—A loamy, dense, brittle subsurface horizon that is
very low in organic matter and clay but is rich in silt or
very fine sand. The layer is seemingly cemented and slowly
or very slowly permeable.
horizon (soil)—A layer of soil, approximately parallel to
thesoil surface, with distinct characteristics produced by
soil-formltvq processes.
G-l
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infiltrometer—A device by which the rate and amount of
water infiltration into the soil is determined (cylinder,
sprinkler, or basin flooding).
matric potential—Attractive forces of soil particles for
water and water molecules for each other.
micronutrient—A chemical element necessary in only small
trace amounts (less than 1 mg/L) for microorganisms and
plant growth. Essential micronutrients are boron, chloride,
copper, iron, manganese, molybdenum, and zinc.
mineralization—The conversion of a compound from an organic
form to an inorganic form as a result of microbial
decomposition.
sodic soil—A soil that contains sufficient sodium to
interfere with the growth of most crop plants, and in which
the exchangeable sodium'percentage is 15 or more.
soil water—That water present in the soil pores in an
unsaturated (aeration) zone above the ground water table.
Such water may either be lost by evapotranspiration or
percolation to the ground water table.
tensiometer—A device used to measure the negative pressure
(or tension) with which water is held in the soilj a porous,
permeable ceramic cup connected through a tube to a
manometer or vacuum gage.
till—Deposits of glacial drift laid down in place as the
glacier melts, consisting of a heterogeneous mass of rock
flour, clay, sand, pebbles, cobbles, and boulders
intermingled in any proportion; the agricultural cultivation
of fields.
tilth—The physical condition of a soil as related to its
ease of cultivation. Good tilth is associated with high
noncapillary porosity and stable, granular structure, and
low impedance to seedling emergence and root penetration.
transpiration—The net quantity of water absorbed through
plant roots that is used directly in building plant tissue,
or given off to the atmosphere as a vapor from the leaves
and stems of living plants.
volatilization—The evaporation or changing of a substance
from liquid to vapor.
wilting point—The minimum quantity of water in a given soil.
necessary to maintain plant growth. When the quantity of
moisture falls below this, the leaves begin to drop and
shrivel up.
G-2
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CONVERSION FACTORS .
Metric .to" U.S. Customary
* ; . '..'.• Metric . .
Name
qentimeter (s) '
centimeter (.s) per hour
f . • ' .
cubic meter
cubic meters per day
cubic meters per hectare
cubic meters per second
degrees Celsius
gram ( s )
hectare
Joule
"kilogramCs)
kilograms per hectare
kilograms per hectare
• per day
kilograms 'per square
centimeter. •
kilometer
kilowatt
liter
liters per hectare per day
liters per second
megagram (metric tonne)
megagrams per hectare
.mega joule
megaiiters (liters x 106)
meters (s)
meters per second
micrograms per liter
milligrams per liter
nanograms per liter
Newtons per square
centimeter
square centimeter
square kilometer
square meter
Symbol
cm
cm/h
m3
m3/d
m3/ha
m3/s
°C
g
ha
J
kg
kg/ha
kg/ha -d
kg/cm2
km
kW
L
L/ha-d
L/s
Mgfor t)
mg/ha
MJ
ML
m
m/s
pg/L
mg/L
ng/L
N/cm2
cm
km2
m2
Multiplier
0.3937
0.3937
8.1071 x 10~4
35.3147
264.25
2.6417 x 10~4
1,069 x 10~4
22.82
1.8(°C) + 32
0.0022
2.4711
0.004
9.48 x 10"4
2.205
0,0004
0.893
14.49
0.6214
1.34
0.0353
0.264
o.ii
0.035
22.826
15.85
0.023
1.10
0.446
0.278
0.264
3.2808
2.237
1.0
1.0
1.0
1.45
0.155-
0.386
10.76
U.S.
customary
Abbreviation
in.
in./h
acre-f t
ft3
' Mgal
Mgal/d
Mgal/acre
Mgal/d
•F
Ib
acre
mi2
Btu
Ib
tons/acre
Ib/acre-d
Ib/in . 2
mi
hp
ft3 ;
gal .
gal/acre -d
ft3/S
gal/d
gal/rain
Mgal/d
ton (short)
tons/acre
kWh
Mgal
ft
mi/h
ppb
ppm
ppt
Ib/in.2
in.2
mi2
ft2
unit .. '
Name - ,
inches
inches per hour
acre-foot
cubic foot
million gallons
million gallons
per day
million gallons
per acre
million gallons
per day
degrees Fahrenheit
pound (.s)
acre
square miles
British thermal unit
pound (s)
tons per acre
pounds per acre per day
pounds per square inch
mile •
horsepower
cubic foot
gallon (s)
gallons per acre per day
cubic feet per second
gallons per day
gallons per minute
million gallons per day
ton (short)
tons per acre
kilowatt hour
million gallons
foot (feet)
miles per hour
parts per billion
parts per million
parts per trillion
pounds per square inch
square inch
square .mile
square foot
•U.S.COVBWMENIPRINTINCOmCE:l993 -750.002, 60170
G-3
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