United States
Environmental Protection
Agency
Process Design Manual
Land Treatment of Municipal
Wastewater Effluents
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EPA/625/R-06/016
September 2006
Process Design Manual
Land Treatment of Municipal Wastewater Effluents
Land Remediation and Pollution Control Division
National Risk Management Research Laboratory
Office of Research and Development
U.S. Environmental Protection Agency
Cincinnati, Ohio
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Notice
This document has been reviewed in accordance with U.S. Environmental Protection Agency policy and
approved for publication. Mention of trade names or commercial products does not constitute
endorsement or recommendation for use.
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Foreword
The U.S. Environmental Protection Agency (EPA) is charged by Congress with protecting the Nation's land,
air, and water resources. Under a mandate of national environmental laws, the Agency strives to formulate
and implement actions leading to a compatible balance between human activities and the ability of natural
systems to support and nurture life. To meet this mandate, EPA's research program is providing data and
technical support for solving environmental problems today and building a science knowledge base
necessary to manage our ecological resources wisely, understand how pollutants affect our health, and
prevent or reduce environmental risks in the future.
The National Risk Management Research Laboratory (NRMRL) is the Agency's center for investigation of
technological and management approaches for preventing and reducing risks from pollution that threaten
human health and the environment. The focus of the Laboratory's research program is on methods and
their cost-effectiveness for prevention and control of pollution to air, land, water, and subsurface resources;
protection of water quality in public water systems; remediation of contaminated sites, sediments and
ground water; prevention and control of indoor air pollution; and restoration of ecosystems. NRMRL
collaborates with both public and private sector partners to foster technologies that reduce the cost of
compliance and to anticipate emerging problems. NRMRL's research provides solutions to environmental
problems by: developing and promoting technologies that protect and improve the environment; advancing
scientific and engineering information to support regulatory and policy decisions; and providing the technical
support and information transfer to ensure implementation of environmental regulations and strategies at
the national, state, and community levels.
This publication has been produced as part of the Laboratory's strategic long-term research plan. It is
published and made available by EPA's Office of Research and Development to assist the user community
and to link researchers with their clients.
Sally Gutierrez, Director
National Risk Management Research Laboratory
in
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Abstract
The U.S. Environmental Protection Agency guidance on land treatment of municipal and industrial
wastewater was updated for the first time since 1984. Significant new technological changes include
phytoremediation, vadose zone monitoring, new design approaches to surface irrigation, center-pivot
irrigation, drip and micro-sprinkler irrigation, and capital and operating costs. Also included in the new
manual are new performance data on soil-aquifer treatment, a rational model for balancing oxygen uptake
with BOD loadings, and industrial wastewater land application guidance, emphasizing treatment of food
processing wastewater. Costs and energy use of land treatment technologies are updated.
Slow-rate land treatment remains the most popular type of land treatment system. Many slow-rate
systems are now designed as water reuse systems. Trends in distribution have been toward sprinkler and
drip irrigation systems.
A CD which accompanies the document contains copies of earlier editions of the land treatment manual
and the latest manual for water reuse.
KEYWORDS: land treatment, soil aquifer treatment, spray irrigation, groundwater monitoring,
vadose zone sampling, costs
IV
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Contents
Notice ii
Foreword iii
Abstract iv
Contents v
Figures viii
Tables x
Acknowledgments xiii
Chapter 1 Introduction and Process Capabilities 1-1
1.1 Purpose 1-1
1.2 Scope 1-1
1.3 Treatment Processes 1-1
1.4 Slow Rate Land Treatment 1-2
1.5 Overland Flow Treatment 1-4
1.6 Soil Aquifer Treatment 1-4
1.7 Limiting Design Parameter Concept 1-7
1.8 Guide to Intended Use of Manual 1-7
1.9 References 1-7
Chapter 2 Wastewater Constituents and Removal Mechanisms 2-1
2.1 Biochemical Oxygen Demand 2-1
2.2 Total Suspended Solids 2-2
2.3 Oil and Grease 2-2
2.4 pH 2-3
2.5 Pathogenic Organisms 2-3
2.6 Metals 2-6
2.7 Nitrogen 2-8
2.8 Phosphorus 2-11
2.9 Potassium 2-14
2.10 Sodium 2-14
2.11 Macronutrients and Micronutrients 2-14
2.12 Trace Organics 2-16
2.13 Phytoremediation 2-18
2.14 References 2-19
Chapter 3 Water Movement in Soil and Groundwater 3-1
3.1 Soil Properties 3-2
3.2 Water Movement through Soil 3-4
3.3 Saturated Hydraulic Conductivity 3-7
3.4 Unsaturated Hydraulic Conductivity 3-8
3.5 Percolation Capacity 3-8
3.6 Mounding of Groundwater 3-9
3.7 Drainage Requirements 3-11
3.8 Field Testing Procedures 3-12
3.9 References 3-18
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Chapter4 Role of Plants in Land Treatment 4-1
4.1 Vegetation in Land Treatment 4-1
4.2 Evapotranspiration 4-1
4.3 Plant Selection 4-4
4.4 Crop Management, Water Quality, and Nutrient Cycle 4-14
4.5 References 4-16
Chapters Site Planning and Selection 5-1
5.1 Preliminary Land Requirements 5-1
5.2 Site Identification 5-4
5.3 Site Selection 5-8
5.4 Phase 2 Planning 5-8
5.5 Cost and Energy Considerations 5-17
5.6 References 5-23
Chapter6 Preapplication Treatment and Storage 6-1
6.1 EPA Guidance 6-1
6.2 Types of Preapplication Treatment 6-2
6.3 Design of Storage Ponds 6-7
6.4 Operation of Storage Ponds 6-12
6.5 References 6-12
Chapter 7 Distribution Systems 7-1
7.1 Types of Distribution Systems 7-1
7.2 General Design Considerations for All Types of Distribution Systems 7-3
7.3 Surface Distribution 7-4
7.4 Sprinkler Distribution 7-11
7.5 Micro Irrigation Distribution System Planning and Design 7-22
7.6 Pumping Stations and Mainlines 7-26
7.7 Distribution Pumping 7-26
7.8 Tailwater Pumping 7-26
7.9 Mainlines 7-27
7.10 References 7-27
Chapter 8 Process Design - Slow Rate Systems 8-1
8.1 System Types 8-1
8.2 Land Area Determination 8-1
8.3 Total Acidity Loading 8-4
8.4 Salinity 8-4
8.5 Design Considerations 8-7
8.6 Crop, Soil, and Site Management Requirements 8-9
8.7 References 8-15
Chapter 9 Process Design - Overland Flow Systems 9-1
9.1 System Concept 9-1
9.2 Design Procedures 9-2
9.3 Land Area Requirements 9-5
9.4 Design Considerations 9-6
9.5 System Monitoring and Management 9-8
9.6 References 9-9
Chapter 10 Process Design - Soil Aquifer Treatment 10-1
10.1 Treatment Requirements 10-1
10.2 Aquifer Characteristics 10-4
10.3 Hydraulic Loading Rates 10-5
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10.4 Land Area Requirements 10-7
10.5 Hydraulic Loading Cycle 10-7
10.6 Design Considerations 10-8
10.7 Cold Weather Operation 10-9
10.8 Drainage 10-10
10.9 References 10-12
Chapter 11 Industrial Wastewater Land Application
11.1 Types of Industrial Wastewaters Applied
1 1 .2 Water Quality and Pretreatment Requirements
11.3 Design Considerations
114 Slow-Rate Land Treatment
115 Overland Flow Treatment
116 Soil Aquifer Treatment
11.7 References
11-1
11-1
11-1
11-4
11-6
11-7
11-8
11-9
Vll
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Figures
Number Page
1-1 Slow Rate Hydraulic Pathways 1-3
1-2 Overland Flow 1-5
1-3 SAT Hydraulic Pathways 1-6
2-1 Nitrogen Cycle in Soil 2-9
3-1 Natural Resources Conservation Service (NRCS) Soil Textural Classes 3-2
3-2 Porosity, Specific Yield, Specific Retention vs. Soil Grain Size for In situ Consolidated Soils,
Coastal Basin, CA 3-6
3-3 Specific Yield vs. Hydraulic Conductivity 3-6
3-4 Soil Moisture Characteristics 3-6
3-5 Approximate Preliminary Percolation Rate vs. NRCS Soil Permeability for SR and SAT 3-9
3-6 Schematic of Groundwater Mound 3-9
3-7 Mounding Curve for Center of a Square Recharge Area 3-10
3-8 Mounding Curve for Center of a Rectangular recharge Area, with Different Ratios of
Length L to Width W 3-10
3-9 Rise and Horizontal Spread of a Mound Below a Square Recharge Area 3-11
3-10 Rise and Horizontal Spread of Mounds Below a Rectangular Recharge Area when
L = 2W 3-11
3-11 Parameters Used in Drain Design 3-12
3-12 Small-scale Pilot Test Basin 3-13
3-13 U.S. Army Corps of Engineers (USAGE) Basin Test 3-13
3-14 Grove Preparation for USAGE Test 3-14
3-15 Grove Preparation for USAGE Test 3-14
3-16 Typical Test Results, USAGE Infiltration Test 3-14
3-17 Test Installation for Cylinder Infiltrometer 3-15
3-18 Definition Sketch for Air Entry Permeameter 3-15
3-19 Air Entry Permeameter in Use 3-15
3-20 Definition Sketch for Auger Hole Technique 3-17
3-21 Equipment Setup for Auger Hole Test 3-17
4-1 Evaporation from Bare Soil which was Initially Wet 4-1
4-2 Nitrogen Uptake for Annual and Perennial Crops 4-9
4-3 Effect of Salinity on Growth of Field Crops 4-11
4-4 Suitable pH of Mineral Soils for Various Crops 4-12
5-1 Two-Phase Planning Process 5-1
5-2 Estimated Storage Days Based on Climatic Factors Alone 5-2
5-3 Landscape Positions 5-6
5-4 Sample Log for Test Pit Data 5-15
5-5 Well and Piezometer Installations 5-16
5-6 Vertical Flow Direction Indicated by Piezometers 5-16
5-7 Typical Shallow Monitoring Well 5-17
5-8 Solid Set Sprinkling (buried) Costs, ENR CCI = 6076. (a) Capital Cost; (b) Operation and
Maintenance Cost 5-19
5-9 Center Pivot Sprinkling Costs, ENR CCI = 6076. (a) Capital Cost; (b) Operation and
Maintenance Cost 5-20
5-10 Gated Pipe — Overland Flow or Ridge-and-Furrow Slow Rate Costs, ENR CCI = 6076.
(a) Capital Cost; (b) Operation and Maintenance Cost 5-20
5-11 Rapid Infilitration Basin Costs, ENR CCI + 6076. (a) Capital Cost; (b) Operation and
Maintenance Cost 5-21
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Number Page
6-1 Virus Removal in Ponds 6-6
6-2 Fecal Coliform Removal in Ponds - Detention Time vs. Liquid Temperature 6-6
7-1 Typical Surface Distribution Methods - Ridge and Furrow 7-4
7-2 Typical Gated Pipe Distribution Unit 7-6
7-3 Equal Opportunity Time Along Entire Strip 7-8
7-4 Greater Opportunity Time at Head of Strip: Flow Rate Too Small 7-9
7-5 Greater Opportunity Time at Tail End of Strip: Flow Rate Too Large 7-10
7-6. Typical Discharge Valve for Border Strip Application 7-10
7-7 Forest Solid Set Sprinkler Irrigation at Clayton County 7-14
7-8 Move-Stop Sprinkler Systems 7-15
7-9 Side-Wheel Roll Sprinkler System 7-16
7-10 Continuous Move Sprinkler Systems 7-17
7-11 Reel-Type Traveling Gun Sprinkler 7-18
7-12 Center Pivot Sprinkler Unit 7-19
7-13 Center Pivot Irrigation System 7-19
7-14 Intersection Between an Elliptical Moving Application Rate Profile Under a Center-pivot
Lateral and a Typical Infiltration Curve 7-20
7-15 Schematic of the Revolving -Sprinkler Infiltrometer 7-20
7-16 Comparison of Relative Application Rates Under Various Center Pivot Sprinkler Packages 7-20
7-17 Anticipated Center Pivot Performance versus Soil Texture 7-21
7-18 Comparison of Wetting Profiles in Sandy Soil 7-23
7-19 Typical Micro Irrigation System Layout 7-23
7-20 Distribution Pumps in the Side of a Storage Pond Dike 7-26
7-21 Typical Tailwater Pumping Station 7-27
8-1 Leaching Requirement as a Function of Applied Salinity and ECe of Crop Salinity
Threshold 8-5
8-2 Example Spreadsheet Used to Calculate the Irrigation Requirements Including Irrigation
Efficiency and Leaching Requirements 8-7
8-3 Slow Rate Design Procedure 8-8
9-1 Distribution Alternatives for Overland Flow 9-1
9-2 Overland-Flow Application Rates and Slope Length 9-3
9-3 Bale Wrappers Tightly Seal Each Bale of Hay in Plastic for Storage 9-9
9-4 Plastic Silage Bags for Storing Cut Hay 9-9
10-1 Definition Sketch for Lateral Drainage from SAT Systems Underdrains 10-10
10-2 Centrally Located Underdrain 10-11
10-3 Underdrain System Using Alternating Infiltration and Drying Strips 10-11
11-1 Side Roll Sprinklers Apply Potato-Processing Wastewater Throughout the Winter at
Aberdeen, Idaho 11-6
11-2 Solid Set Sprinklers Apply Tomato-Processing Wastewater to Overland Flow Slopes 11-8
IX
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Preceeding Page Blank
Tables
Number Page
1-1 Comparison of Land Treatment Process Design Features 1-1
1-2 Site Characteristics for Land Treatment Processes 1-2
1-3 Expected Effluent Water Quality from Land Treatment Processes 1-2
2-1 Typical Organic Loading Rates for Land Treatment Systems 2-1
2-2 BODS Removal at Typical Land Treatment Systems 2-2
2-3 Suspended Solids Removal at Land Treatment Systems 2-3
2-4 Virus Transmission through Soil at SAT Land Application Sites 2-5
2-5 Aerosol Bacteria at Various Sources 2-6
2-6 Recommended Limits for Constituents in Reclaimed Water for Irrigation 2-7
2-7 WHO Recommended Annual and Cumulative Limits for Metals Applied to Agricultural Crop Land ..2-7
2-8 Trace Metals in Groundwater Under Hollister, CA Soil Aquifer Treatment Site, mg/L 2-8
2-9 Total Nitrogen Removal in Typical Land Treatment Systems 2-10
2-10 Annual Mineralization Rates for Organic Matter in Biosolids 2-11
2-11 Typical Percolate Phosphorus Concentrations 2-12
2-12 Sulfur Uptake by Selected Crops 2-15
2-13 Boron Tolerance of Crops 2-16
2-14 Values of ECD for Crops with No Yield Reduction 2-16
2-15 Volatile Organic Removal by Wastewater Sprinkling 2-17
2-16 Physical Characteristics for Selected Organic Chemicals 2-18
2-17 Percent Removal of Organic Chemicals in Land Treatment Systems 2-19
3-1 Soil Textural Classes and General Terminology Used in Soil Descriptions 3-2
3-2 Range of Available Soil Moisture for Different Soil Types 3-6
3-3 Field Estimating of Soil Moisture Content 3-7
3-4 Measured Ratios of Horizontal to Vertical Conductivity 3-8
3-5 Comparison of Infiltration Measurement Techniques 3-13
4-1 Range of Seasonal Crop Evapotranspiration 4-2
4-2 Selected Examples of Monthly Normal ETo 4-2
4-3 Example Evapotranspiration Values for Southern San Joaquin Valley of California 4-3
4-4 Pan Coefficient for Class A Evaporation Pans Placed in a Reference Crop Area 4-3
4-5 Length of Four Crop Growth Stages for Typical Annual Crops 4-4
4-6 Crop Coefficient, Kc, for Midseason and Late Season Conditions 4-4
4-7 Crop Coefficient, Kc, for Perennial Forage Crops 4-5
4-8 Yield Based N, P, and KUptake of Various Crops 4-5
4-9 Typical Effective Rooting Depth of Plants 4-8
4-10 Grasses Used at Overland Flow Sites 4-9
4-11 General Effects of Trace Element Toxicity on Common Crops 4-10
4-12 Forested Land Treatment Systems in the United States 4-11
4-13 Nitrogen Uptake for Selected Forest Ecosystems with Whole Tree Harvesting 4-13
4.14 Biomass and Nitrogen Distributions by Tree Component for Stands in Temperate
Regions 4-14
4-15 Golf Course Grass Salt Tolerances 4-14
4-16 Pasture Rotation Cycles for Different Numbers of Pasture Areas 4-17
5-1 Typical Composition of Raw Municipal Wastewater 5-1
5-2 Characteristics of Food Processing Wastewaters Applied to the Land 5-2
5-3 Preliminary Loading Rates for Initial Estimate of Land Requirements 5-2
5-4 Summary of Climatic Analyses 5-3
XI
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5-5 Site Identification Land Requirements, ha/m3-d (acres/mgd) 5-4
5-6 Types and Sources of Data Required for Land Treatment Site Evaluation 5-4
5-7 Land Use Suitability Factors for Identifying Land Treatment Sites 5-5
5-8 Grade Suitability Factors for Identifying Land Treatment Sites 5-5
5-9 Soil Textural Classes and General Terminology Used in Soil Descriptions 5-6
5-10 Typical Soil Permeabilities and Textural Classes for Land Treatment 5-7
5-11 Rating Factors for Site Selection 5-9
5-12 Economic Rating Factors for Site Selection 5-9
5-13 Subsurface Factors for Forested SR 5-10
5-14 Soil Factors for Forested SR 5-10
5-15 Surface Factors for Forested SR 5-10
5-16 Composite Evaluation of SR Forested Sites 5-11
5-17 Sequence of Field Testing - Typical Order of Testing 5-11
5-18 Summary of Field Tests for Land Treatment Processes 5-11
5-19 Interpretation of Soil Physical and Hydraulic Properties 5-12
5-20. Interpretation of Soil Chemical Tests 5-13
5-21 Textural Properties of Mineral Soils 5-14
5-22 Soil Structure Grades 5-14
5-23 Description of Soil Mottles 5-15
5-24 Costs of Field Preparation 5-18
5-25 Comparison of Sprinkler Distribution Capital Costs 5-19
5-26 Costs of Underdrains 5-21
5-27 Costs of Tailwater Return Systems 5-21
5-28 Costs of Runoff Collection for Overland Flow 5-21
5-29 Costs of Recovery Wells 5-21
5-30 Options for Land Acquisition and Management at Selected SR Systems 5-22
5-31 Benefits of Land Treatment Systems 5-22
5-32 Energy Requirements for Land and Aquatic Treatment Systems 5-23
5-33 Energy Value of Nutrients in Wastewater 5-23
6-1 Guidelines for Assessing the Level of Preapplication Treatment 6-2
6-2 Reaction Rates for Aerated Ponds, BOD 6-3
6-3 Variation of Plug Flow Apparent Rate Constant with Organic Loading Rate for Facultative Ponds.... 6-3
6-4 Typical pH and Alkalinity Values in Facultative Ponds 6-5
6-5 Changes of Microorganisms Concentration During Storage 6-6
6-6 Application of Membranes for the Removal of Constituents Found in Wastewater 6-7
6-7 Estimation of Storage Volume Requirements Using Water Balance Calculations 6-9
6.8 Final Storage Volume Requirement Calculations 6-10
7-1 Description, Advantages, and Disadvantages, of Distribution Systems 7-1
7-2 Sprinkler System Characteristics 7-3
7-3 Optimum Furrow Spacing 7-5
7-4 Suggested Maximum Lengths of Furrows, ft 7-5
7-5 Design Guidelines for Graded Borders for Deep-Rooted Crops 7-6
7-6 Design Guidelines for Graded Borders for Shallow-Rooted Crops 7-7
7-7 Recommended Reductions in Application Rates Due to Grade 7-12
7-8 Recommended Spacing of Sprinklers 7-13
7-9 Pipe Friction Loss Factors to Obtain Actual Loss in Line with Multiple Outlets 7-13
7-10 Recommended Maximum Lane Spacing for Traveling Gun Sprinklers 7-18
7-11 Typical Values for Surface Storage 7-21
7-12 Recommended Soil Contact Pressure for Center Pivots 7-22
7-13 Relative Resistance to Plugging for Various Emission Devices 7-24
7-14 Recommended Design Factors for Tailwater Return Systems 7-27
8-1 Nitrogen Loss Factor for Varying C:N Ratios 8-4
8-2 Suggested Minimum Process Control Monitoring 8-10
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8-3 Suggested Minimum Effluent Monitoring 8-11
8-4 Flow Measurement Alternatives 8-11
8-5 Soil Monitoring Parameters 8-13
8-6 Vadose Zone Sampling/Monitoring Alternatives 8-14
8-7 Example Crop Monitoring Parameters 8-15
8-8 Routine Maintenance Inspection Checklist for Land Application Sites 8-15
9-1 Comparison of Actual and Predicted OF Effluent BOD Concentrations Using Primary and Raw
Municipal Wastewater 9-4
9-2 BOD Removal for Overland Flow Systems 9-4
9-3 Application Rates Suggested for BOD Removal in Overland Flow Design, m3/h m (gal/min ft)....9-4
9-4 Ammonia Concentrations (in g/m3) in OF Systems in Garland, TX 9-5
10-1 BOD Removal for Soil Aquifer Treatment Systems 10-1
10-2 Nitrogen Removal for Soil Aquifer Treatment Systems 10-3
10-3 Phosphorus Removal for Soil Aquifer Treatment Systems 10-3
10-4 Fractional Attenuation of Estrogenic Activity (Relative to Primary Effluent) During Secondary
Treatment and Soil Aquifer Treatment 10-4
10-5 Typical Wet/Dry Ratios for SAT Systems 10-6
10-6 Typical Hydraulic Loading Rates for SAT Systems 10-6
10-7 Suggested Hydraulic Loading Rates Based on Different Field Measurements 10-7
10-8 Suggested SAT Loading Cycles 10-8
10-9 Minimum Number of Basins Required for Continuous Wastewater Application 10-8
11-1 Characteristics of Various Industrial Wastewaters Applied to Land 11-2
11-2. Comparison of Inorganic and Total Dissolved Solids Measurements in Milk Processing
Wastewater and Shallow Groundwater 11-2
11 -3 Water Quality Parameters in the Settling Basin and First Cell of a Wetland Receiving Dairy
Wastewater, Mercer Co., KY 11-4
11-4 BOD Loading Rates at Existing Industrial Slow Rate Systems 11-5
11-5 Nitrogen Mineralization of Industrial Wastewaters 11-5
11-6 Performance of Paris, TX., Overland Flow System 11-7
11-7 Performance of Overland Flow System at Davis, CA 11-8
11-8 Treatment Performance for Hilmar Cheese Soil Aquifer Treatment System 11-9
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Acknowledgments
This document was developed with the assistance of many individuals. It is an update of the land treatment
manuals that were written in the 1970s and 1980s, and all the contributors have attempted to present up-to-
date and useful information. They include the authors and technical expert reviewers listed here:
Project Officer and Author:
Dr. James E. Smith, Jr.
US EPA National Risk Management Research Laboratory, (G-75), Cincinnati, OH 45268
Coordinating Author:
Robert B. Brobst, P.E
Biosolids Program Manager, US EPA Region 8, 999 18th St., Suite 500, Denver, CO 80202-2466
Contractor:
Brown and Caldwell, 2701 Prospect Park Dr., Rancho Cordova, CA 95670
Ronald W. Crites - Lead
Robert A. Beggs
Lance Hershman
Diane Nascimento
Jordan W. Smith
Special Contributions, Technical Assistance and Review:
Robert K. Bastian
US EPA Office of Wastewater Management, Washington, DC
Robert B. Brobst, P.E.
US EPA Region 8, Denver, CO
Dr. Micheal Overcash
North Carolina State University, Raleigh, NC
Antonio Palazzo
US Army Cold Regions Research and Engineering Laboratory, Hanover, NH
Dr. Robert Rubin
North Carolina State University, Raleigh, NC
Preparation of Manual for Publication:
US EPA National Risk Management Research Laboratory, Cincinnati, OH
Jean Dye
Ann White
Steve Wilson
The authors wish to dedicate this manual to the memory of Sherwood C. "Woody" Reed whose advocacy of the
use of natural systems for wastewater treatment, including land treatment, ponds, and constructed wetlands
generated much of the scientific data that went into the development of the 1977 and 1981 editions of this
manual. He conducted or managed numerous field investigations and developed guidance materials, project
case studies, cost curves, and other materials that have been used extensively in EPA, Water Environment
Federation, and Corps of Engineers publications. He has also written numerous journal articles, conference
papers, and textbooks and taught courses on natural systems and wastewater treatment throughout the U.S.
and around the world.
XIV
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Chapter 1
Introduction and Process Capabilities
1.1. Purpose
The purpose of this manual is to provide design criteria
and supporting information for the planning, design,
construction, and operation of land treatment systems.
Recommended procedures for the planning, design, and
evaluation of land treatment systems for wastewater
management are presented along with information on
the expected performance and removal mechanisms.
This document is a revision and supplement to the
Process Design Manual for Land Treatment of Municipal
Wastewater published in 1981 (US EPA, 1981) and the
Supplement on Rapid Infiltration and Overland Flow that
was published in 1984 (US EPA, 1984). EPA has
chosen to provide copies of these manuals, as well as a
copy of the original manual (US EPA, 1977) on a CD,
which is included with this manual.
1.2. Scope
Land treatment is defined as the application of
appropriately pre-treated municipal and industrial
wastewater to the land at a controlled rate in a designed
and engineered setting. The purpose of the activity is to
obtain beneficial use of these materials, to improve
environmental quality, and to achieve treatment goals in
a cost-effective and environmentally sound manner. In
many cases the production and sale of crops can
partially offset the cost of treatment. In arid climates the
practice allows the use of wastewaters for irrigation and
preserves higher quality water sources for other
purposes.
The scope of this manual is limited to the three
principal land treatment processes, which are:
Slow Rate (SR)
Overland Flow (OF)
. Soil Aquifer Treatment (SAT), also known as Rapid
Infiltration (Rl)
Subjects that are new to this revision of the design
manual include phytoremediation or phytoextraction and
land application of food processing wastewater.
1.3. Treatment Processes
Typical design features for the three land treatment
processes are compared in Table 1-1. The typical site
characteristics are compared in Table 1-2. The expected
quality of the treated water from each process is
presented in Table 1-3. In most cases the compliance
standards are imposed at the treatment boundary. The
average and expected upper range values are valid for
the travel distances and applied wastewater as
indicated. The lower values of expected concentrations
may reflect background shallow groundwater, especially
for slow rate. The fate of these materials (plus metals,
pathogens, salts, and trace organics) is discussed in
Chapter 2.
Table 1-1. Comparison of Land Treatment Process Design Features
Feature
Slow rate (SR)
Overland flow (OF)
Soil aquifer treatment
(SAT)
Minimum pretreatment
Annual loading rate, m/yr
Typical annual loading rate, m/yr
Field area required, haa
Typical weekly loading rate, cm/wk
Disposition of applied wastewater
Application techniques
Need for vegetation
Primary sedimentation
0.5-6
1.5
23 - 280
1.9-6.5
Evapotranspiration and percolation
Sprinkler, surface or drip
Required
Screening
3-20
10
6.5 - 44
6-40b
Evapotranspiration and surface runoff,
limited percolation
Sprinkler or surface
Required
Primary sedimentation
6-125
30
3-23
10 - 240
Mainly percolation
Usually surface
Optional
"Field area in hectares not including buffer area, roads, or ditches for 3,785 m3/d (1 mgd) flow.
bRange includes screened wastewater to secondary effluent, higher rates for higher levels of pre-application treatment.
1-1
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Table 1-2. Site Characteristics for Land Treatment Processes
Parameter
Slow Rate
(SR)
Overland Flow
(OF)
Soil aquifer treatment
(SAT)
Slope
0 to 20%, Cultivated site
35%, Uncultivated
2 to 8 % for final slopes3
Not critical
Soil permeability
Groundwater depth
Climate
Moderate to slow
0.6 to 3 mb (2 to 10ft)
Winter storage in cold climatesd
Slow to none
Not critical11
Same as SR
Rapid
1 m (3 ft) during application0
1 .5 to 3 m (5-1 0 ft) during drying
Not critical
aSteeper slopes may be feasible at reduced application rates.
blmpact on groundwater should be considered for more permeable soils.
°Underdrains can be used to maintain this level at locations with shallow groundwater.
dMay not be required for forested systems.
Table 1-3. Expected Effluent Water Quality from Land Treatment Processes3 (mg/L unless otherwise noted)
Parameter
Slow rate"
(SR)
Overland flow0
(OF)
Soil aquifer treatment11
(SAT)
BOD5
TSS
NH3/NH4 (as N)
Total N
Total P
Fecal coli (#/100mL)
<2
<1
<0.5
3e
10
10
<4
5f
4
200 +
5
2
0.5
10
1
10
aQuality expected with loading rates at the mid to lower end of the range shown in Table 1 -1.
bPercolation of primary or secondary effluent through 1.5 m (5 ft) of unsaturated soil.
Treating comminuted, screened wastewater using a slope length of 30-36 m (100-120 ft).
dPercolation of primary or secondary effluent through 4.5 m (15 ft) of unsaturated soils; phosphorus and fecal coliform removals increase with flow
path distance.
Concentration depends on loading rate, C:N ratio, and crop uptake and removal.
'Higher values expected when operating through a moderately cold winter or when using secondary effluent at high rates.
All three processes require intermittent loading. The
application period may range from a few hours for
overland flow systems to a few days for soil aquifer
treatment systems. The resting or drying period is critical
to renew aerobic conditions in the soil, renew infiltration
rates in SR and SAT systems, and allow oxidation of
BOD and ammonia.
1.4. Slow Rate Land Treatment
Slow rate land treatment is the application of
wastewater to a vegetated soil surface. The applied
wastewater receives significant treatment as it flows
through the plant root/soil matrix. The potential hydraulic
pathways for the treated water are shown in Figure 1-1.
The design flow path depends on infiltration, percolation,
lateral flow, and evapotranspiration within the
boundaries of the treatment site. Solids removal
generally occurs at the soil surface and biological,
chemical and additional physical treatment occurs as the
wastewater percolates through the plant root/soil matrix.
Off-site runoff of any of the applied wastewater is
specifically avoided by the system design. The hydraulic
pathways of the applied water can include:
. Vegetation irrigation with incremental percolation
(e.g., precipitation or non-contaminated water for
salt management).
. Vegetative uptake with evapotranspiration.
. Percolation to underdrains or wells for water
recovery and reuse.
. Percolation to groundwater and/or lateral subsurface
flow to adjacent surface waters.
Slow rate land treatment can be operated to achieve a
number of objectives including:
. Further treatment of the applied wastewater.
. Economic return from the use of water and nutrients
to produce marketable crops.
. Exchange of wastewater for potable water for
irrigation purposes in arid climates to achieve overall
water conservation.
. Development and preservation of open space and
greenbelts.
1-2
-------
EVAPOTRANSPIR»TION
PERCOLATION
(a) APPLICATION PATHWAY
^JA ^ ^fl
A? w *M W ^A
^ X ^ X^f
"^—y T=» . ^ -_^, L
•Jff^— •'^^o-'^1" ^9v^
UHOERDRAINS
IELLS
(1) RECOVERY PATHWAYS
(c) SUBSURFACE PATHWAY
Figure 1-1. Slow Rate Hydraulic Pathways.
These goals are not mutually exclusive but it is unlikely
that all can be brought to an optimum level within the
same system. In general, maximum cost effectiveness
for both municipal and industrial systems will be
achieved by applying the maximum possible amount of
wastewater to the smallest possible land area. That will
in turn restrict the choice of suitable vegetation and
possibly the market value of the harvested crop. In the
more humid parts of the United States, optimization of
treatment is usually the major objective for land
treatment systems. Optimization of agricultural potential
or water conservation goals are generally more
1-3
-------
important in the more arid western portions of the United
States.
Optimization of a system for wastewater treatment
usually results in the selection of perennial grasses
because a longer application season, higher hydraulic
loadings, and greater nitrogen loadings compared to
other annual agricultural crops. Site selection is
important with municipal wastewater which requires
greater hydraulic capacity. Annual planting and
cultivation can also be avoided with perennial grasses.
However, corn and other crops with higher market
values are also grown on systems where treatment is a
major objective. Muskegon, Ml (US EPA, 1980) was a
noted example with over 2020 ha (5,000 acres) of corn,
alfalfa and soybeans under cultivation.
Forested systems also offer the advantage of a longer
application season and higher hydraulic loadings than
typical agricultural crops, but may be less efficient than
perennial grasses for nitrogen removal depending on the
type of tree, stage of growth and general site conditions.
Early research at the Pennsylvania State University (US
EPA, 1974) established the basic criteria for full-scale
forested systems. Subsequent work in Georgia,
Michigan, and Washington State further refined the
criteria for regional and species differences (McKim,
1982). A large-scale slow rate forested system in
Clayton County, GA, designed for 75,700 m3/d (20 mgd)
uses 1460 ha (3650 acres) and has been in continuous
operation since 1981 (Reed and Bastian, 1991; Nutter et
al., 1996). The largest operational land treatment system
in the United States is the 3232-ha (8,000-acre) forested
system in Dalton, GA.
1.5. Overland Flow Treatment
Overland flow (OF) is the controlled application of
wastewater to relatively impermeable soils on gentle
grass covered slopes. The hydraulic loading is typically
several inches of liquid per week and is usually higher
than for most SR systems. Vegetation (e.g., perennial
grasses) in the OF system contributes to slope stability,
erosion protection, and treatment.
The design flow path is essentially sheet flow down the
carefully prepared vegetated surface with runoff
collected in ditches or drains at the toe of each slope
(Figure 1-2). Treatment occurs as the applied
wastewater interacts with the soil, the vegetation, and
the biological surface growths. Many of the treatment
responses are similar to those occurring in trickling filters
and other attached growth processes. Wastewater is
typically applied from gated pipe or nozzles at the top of
the slope or from sprinklers located on the slope surface.
Industrial wastewaters and those with higher solids
content typically use the latter approach. A small portion
of the applied water may be lost to deep percolation and
evapotranspiration, but the major portion is collected in
the toe ditches and discharged, typically to an adjacent
surface water. Because these systems discharge to
surface waters, a National Pollutant Discharge
Elimination System (NPDES) permit is required.
The SR and SAT concepts may include percolate
recovery and discharge, but the OF process almost
always includes a surface discharge and the necessary
permits are required. The purpose of overland flow is
cost-effective wastewater treatment. The harvest and
sale of the cover crop may provide some secondary
benefit and help offset operational costs, but the primary
objective is treatment of the wastewater. Crop removal
should be encouraged since removing the crop also
removes N and P. Design procedures are presented in
Chapter 9. One of the largest municipal overland flow
systems in the U.S. is in Davis, CA (Crites et al., 2001)
designed for 18,925 m3/d (5 mgd) flow and covering 80
ha (200 acres).
1.6. Soil Aquifer Treatment
SAT land treatment is the controlled application of
wastewater to earthen basins in permeable soils at a
rate typically measured in terms of meters of liquid per
week. As shown in Table 1-2, the hydraulic loading rates
for SAT are usually higher than SR systems. Any
surface vegetation that is present has a marginal role for
treatment due to the high hydraulic loadings. In these
cases, water-tolerant grasses are typically used.
Treatment in the SAT process is accomplished by
biological, chemical and physical interactions in the soil
matrix with the near surface layers being the most active
zone.
1-4
-------
HASTEMTER
GRASS AND
'VEGETATIVE LITTER
EVAFBTRAHSP1RATION
RUNOFF
COLLECTION
SLOPE 2-8S
PERCOLATION
(a) HYDRAULIC PATHWAY
SPRINKLER CIRCLES
(b) PICTORIAL VIEW OF SPRINKLER APPLICATION
Figure 1-2. Overland Flow.
The design flow path involves surface infiltration,
subsurface percolation and lateral flow away from the
application site (Figure 1-3). A cyclic application, as
described in Chapter 10, is typical when the operational
mode includes a flooding period followed by days or
weeks of drying. Continuous application of well treated
wastewater can be accomplished with low application
rates. This allows aerobic restoration of the infiltration
surface and drainage of the applied percolate. The
geohydrological aspects of the SAT site are more critical
than for the other processes and a proper definition of
subsurface conditions and the local groundwater system
is essential for design.
1-5
-------
EViPOttTION
(a) HtmUUC
FLODOIH6 DASIIIS
RECOVERED 1UER
PERCOLATION I ' r \
(UNSATURITEO ZONE) IELL
lUClBMtli
(b) RECOURt PJTHim
FLOOOINC HSIN
(c) NUTlim ORHIU6E INTO SttlFHE I»TERS
Figure 1-3. SAT Hydraulic Pathways.
The purpose of a soil aquifer treatment system is to
provide a receiver aquifer capable of accepting liquid
intended to recharge shallow groundwater. System
design and operating criteria are developed to achieve
that goal. However, there are several alternatives with
respect to the utilization or final fate of the treated water:
. Groundwater recharge.
. Recovery of treated water for subsequent reuse or
discharge.
. Recharge of adjacent surface streams.
. Seasonal storage of treated water beneath the site
with seasonal recovery for agriculture.
The recovery and reuse of the treated SAT effluent is
particularly attractive in dry areas in arid regions and
studies in Arizona, California, and Israel (Idelovich,
1981) have demonstrated that the recovery of the
treated water may be suitable for unrestricted irrigation
on any type of crop. Groundwater recharge may also be
attractive, but special attention is required for nitrogen if
drinking water aquifers are involved. Unless special
measures (described in Chapter 10) are employed, it is
unlikely that drinking water levels for nitrate nitrogen (10
mg/L as N) can be routinely attained immediately
beneath the application zone with typical municipal
wastewaters. If special measures are not employed,
there must then be sufficient mixing and dispersion with
the native groundwater prior to the downgradient
extraction points. In the more humid regions neither
recovery nor reuse are typically considered. Examples
of SAT include the Lake George, NY, system operating
since 1939, the Calumet, Ml, site operating since 1888,
1-6
-------
and the Hollister, CA, system operating since 1946 (US
EPA., 1978).
1.7. Limiting Design Parameter Concept
The design of all land treatment systems, wetlands,
and similar processes is based on the Limiting Design
Parameter (LDP) concept (Crites et al., 2000). The LDP
is the factor or the parameter, which controls the design
and establishes the required size and loadings for a
particular system. If a system is designed for the LDP it
will then function successfully for all other less-limiting
parameters of concern. Detailed discussions on the
interactions in land treatment systems with the major
wastewater constituents can be found in Chapter 2.
Experience has shown that the LDP for systems that
depend on significant infiltration, such as SR and SAT, is
either the hydraulic capacity of the soil or the ability to
remove nitrogen to the specified level, when typical
municipal wastewaters are applied. Whichever of these
two parameters requires the largest treatment area
controls design as the LDP, and the system should then
satisfy all other performance requirements. Overland
flow, as a discharging system, will have an LDP which
depends on the site-specific discharge limits, and the
parameter which requires the largest treatment area
controls the design.
1.8. Guide to Intended Use of Manual
The first chapter introduces the processes and the
concept of limiting design parameter. In Chapter 2 all of
the wastewater constituents of concern are discussed
along with their fate in land treatment systems and the
removal mechanisms. In Chapter 3 the movement of
water through soil and groundwater is discussed
including equations and physical test methods and
procedures. In Chapter 4 the vegetation used in land
treatment, the nutrient uptake and sensitivity to
wastewater constituents, and management are
described.
Planning guidance is provided in Chapter 5 including
site selection procedures. Preapplication treatment and
storage guidance is presented in Chapter 6 and
wastewater distribution systems are introduced in
Chapter 7. The process design chapters are 8, 9, and 10
covering slow rate, overland flow, and soil aquifer
treatment, respectively. Equations and procedures are
presented along with a briefcase study of each process.
Much design and research activity in recent years has
focused on industrial wastewater. In Chapter 11, the
unique aspects of treating high-strength wastewater from
food processors and other sources are discussed.
Guidance on land application of biosolids can be found
in Crites and Tchobanoglous (1998) and US EPA
(1995).
1.9. References
Crites, R.W. and G. Tchobanoglous (1998) Small and
Decentralized Wastewater Management Systems.
McGraw-Hill Book Co. New York.
Crites, R.W., S.C. Reed, and R.K. Bastian (2000) Land
Treatment Systems for Municipal and Industrial
Wastes. McGraw-Hill Book Co. New York.
Crites, R.W., S.C. Reed, and R.K. Bastian (2001)
Applying Treated Wastewater to Land. BioCycle,
42(2) 32-36.
Idelovitch, E. (1981) Unrestricted Irrigation with
Municipal Wastewater, in: Proceedings, National
Conference on Environmental Engineering, ASCE,
Atlanta GA, July 8-10.
McKim, H.L. (1982) Wastewater Application in Forest
Ecosystems, Report 82-19, USA CRREL, Hanover,
NH.
Nutter, W.L., L. Philpott, and L.A. Morris (1996) Long-
Term Environmental Impacts of Municipal
Wastewater Irrigation to Forests at Clayton County,
Georgia, Proceedings, Land Application of Wastes
in Australia and New Zealand: Research and
Practice, Australian Conference.
Olson, J.V., R.W. Crites, and P.E. Levine (1980)
Groundwater Quality at a Rapid Infiltration Site,
Journal Envir. Engr. Div, Vol 106(5):885-889,
American Society of Civil Engineers.
Reed, S.C. and R.K. Bastian (1991) Potable Water Via
Land Treatment and AWT, Water Envir. Technology,
3(8)40-47, WEF, Alexandria, VA.
US EPA (1974) Renovation of Secondary Effluent for
Reuse as a Water Resource, EPA 660/2-74-016, US
EPA CERI, Cincinnati, OH.
US EPA (1977) Process Design Manual for Land
Treatment of Municipal Wastewater, EPA 625/1-77-
008, US EPA CERI, Cincinnati, OH.
US EPA (1978) Long-Term Effects of Land Application
of Domestic Wastewater. US EPA. EPA-600/2-78-
084. Ada, OK.
US EPA (1980) Muskegon County Wastewater
Management System, EPA 905/2-80-004, US EPA
Great Lakes Programs Office, Chicago, IL.
US EPA (1981) Process Design Manual for Land
Application of Municipal Wastewater, EPA 625/1-81-
013, US EPA CERI, Cincinnati, OH.
1-7
-------
US EPA (1984) Process Design Manual, Land US EPA (1995) Process Design Manual, Land
Treatment of Municipal Wastewater: Supplement on Application of Sewage Sludge and Domestic
Rapid Infiltration and Overland Flow, EPA 625/1-81- Septage, EPA/625/R-95/001, US EPA NRMRL,
013A, US EPA CERI, Cincinnati, OH. Cincinnati, OH
1-8
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Chapter 2
Wastewater Constituents and Removal Mechanisms
An understanding of the basic interactions between
the wastewater constituents of concern and the soil
treatment system is essential for the determination of the
limiting design parameter (LDP) for a particular system.
These interactions are generally the same for all of the
land treatment processes and are therefore discussed
together in this chapter.
2.1 Biochemical Oxygen Demand
All land treatment processes are very efficient at
removal of biodegradable organics, typically
characterized as biochemical oxygen demand (BOD5).
Removal mechanisms include filtration, absorption,
adsorption, and biological reduction and oxidation. Most
of the responses in slow rate (SR) and soil aquifer
treatment (SAT) occur at the soil surface or in the near-
surface soils where microbial activity is most intense.
Treatment oxidation-reduction reactions generally occur
in the upper 1/3 of the slope on the OF sites. Intermittent
or cyclic wastewater application on these systems is
necessary to allow the restoration of aerobic conditions
in the soil profile and maintenance of the infiltration
capacity at the soil surface.
2.1.1 BOD Loading Rates
To establish a basis for the amount of degradable
organic matter that can be land applied, the BOD loading
rate is calculated. The BOD loading rate is defined as
follows:
LBOD = (kg of BOD applied/day) / (area loaded per day) (cycle time)
Example 2.1
BOD Loading Rates
Conditions: Wastewater with a BOD of 250 mg/L. Slow rate
land treatment field area of application of 2 ha/day.
Flow of 1000 m3/d. Cycle time of 7 days between
wastewater applications.
Find: Cycle-average BOD loading rate
Solution: 1. Calculate the kg of BOD applied per day
Kg of BOD applied = 250 mg/L x 1,000 m3/d x
0.001 kg/g = 250" kg/d
2. Calculate the BOD loading rate using Eq. 2-1
L = 250 kg/d / (2 ha/d)(7 d) = 17.9 kg/ha-d
The BOD is a 5-day test of the oxygen demand
required by microorganisms to biodegradable organics.
Other quicker tests, often more reliable, include the
chemical oxygen demand (COD) which is always larger
than the BOD and the total organic carbon (TOC) test,
which ranges from greater than the BOD for untreated
wastewater to less than the BOD for treated effluent
(Tchobanoglous et al., 2002). The treatment of BOD
occurs throughout the loading (application period),
drainage, and the reaeration (drying or resting) period or
cycle. To maintain aerobic conditions in the soil, the rate
of reaeration in a given cycle should match or exceed
the rate of BOD exertion. A "rational" model that predicts
the rate of reaeration depending on soil conditions, the
depth of application and the reaeration period has been
developed (Smith and Crites, 2001) and is presented in
Chapter 8. Typical BOD loading rates for the three
processes are presented in Table 2-1.
Where
LBOD
Kg of BOD
applied per day
Area loaded
Cycle time
(2-1)
= kg/ha-d
= concentration, mg/L x flow, m3/d x 1000 L/1
m3x 0.001 kg/g x 1 g/1000 mg
= total wetted area receiving wastewater per
day, ha
= time between subsequent applications to a
given subplot (days of application plus days of
drying), days
Table 2-1. Typical Organic Loading Rates for Land Treatment
Systems (adapted from Reed et al., 1995)
Process
BOD loading (kg BOD5/ha»d)a
Slow Rate (SR)
Soil Aquifer Treatment (SAT)
Overland Flow (OF)
50 - 500
145-1000
40-110
akg/ha.d x 0.89 = Ib BOD5/ac.d
bLower end of range is typical of municipal systems and upper end is
typical of industrial strength wastewater.
-------
Essentially all of the treatment in overland flow
systems (OF) occurs at or near the soil surface or in the
mat of plant litter and microbial material. Settling of most
particulate matter occurs rapidly in OF systems as the
applied wastewater flows in a thin film down the slope.
Algae removal is an exception since the detention time
on the slope may not be sufficient to permit complete
removal by physical settling (Witherow and Bledsoe,
1983). The biological material and slimes which develop
on the OF slope are primarily responsible for ultimate
pollutant removal. These materials are similar to those
found in other fixed film processes, such as trickling
filters, and the presence of aerobic zones and anaerobic
microsites within the slime layer is to be expected. In a
properly managed system, with acceptable loadings, the
aerobic zones dominate. However, there are still
numerous anaerobic sites that contribute to the
breakdown of the more refractory organics (Crites et al.,
2000).
2.12 BOD Removal
A few examples of removal of BOD by land treatment
processes receiving municipal wastewater are
summarized in Table 2-2. Long-term effects studies (US
EPA, 1979; Hossner et al., 1978; Koerner and Haws,
1979; Leach et al., 1980; and US EPA, 1978) generated
much of the available data. Because the basic treatment
mechanism is biological, all three processes have a
continually renewable capacity for BODS removal as
long as the loading rate and cycle allows for preservation
and/or restoration of aerobic conditions in the system.
Laboratory studies in 1998 with soil columns indicated
that BODS removal to low "background" levels was
independent of the level of pretreatment, independent of
soil type, and essentially independent of infiltration rate
(ASU et al., 1998). These responses confirm the results
presented in Table 2-2 and also confirm the fact that
high levels of preapplication treatment are not necessary
for effective BODS removal in municipal land treatment
systems.
2.2 Total Suspended Solids
Total suspended solids (TSS) are generally not an
LDP in the design of municipal land treatment systems.
SR and SAT systems are very effective for removal of
suspended solids. Filtration through the soil profile is the
principal removal mechanism. OF systems depend on
sedimentation and entrapment in the vegetative litter or
on the biological slimes and are typically less efficient
than SR or SAT. However, OF systems can produce
better than secondary effluent quality for total suspended
solids when either screened wastewater or primary
effluent is applied.
TSS removal at a number of land treatment systems
receiving municipal wastewaters is summarized in
Table 2-3. Suspended solids removal in OF systems
receiving facultative lagoon effluents is not always
effective due to the variability of algal species present
and the short detention time on the slope. The seasonal
variation in performance of the Davis, CA system, shown
in Table 2-3, clearly illustrates this problem. See Chapter
9 for additional information on this issue.
2.3 Oil and Grease
Oil and grease, also known as fats, oil, and grease
(FOG), should not be a factor for land treatment of
typical municipal wastewaters unless there is a spill
somewhere in the municipal collection system. There is
Table 2-2. BOD5 Removal at Typical Land Treatment Systems (adapted from Crites et al., 2000)
BOD5
Process/Location
Hydraulic Loading (m/yra)
Applied (mg/L)
Soil Water Drainage (mg/L) Sample Depth (m )
SR
Hanover, NH
San Angelo, TX
Yarmouth, MA°
SAT
Lake George, NY
Phoenix, AZ
Hollister, CA
OF
Hanover, NH
Easley, SC
Davis, CA
am/yr x 3.28 = ft/yr.
bm x 3.28 = ft.
cGiggey etal., 1989.
1.2-7.6
3
1
43
110
15
7.6
8.2
12.5
40-92
89
85
38
15
220
72
200
112
0.9-1.7
1.0
<2.0
1.2
1.0
8.0
9
23
10
1.5
7.6
1.0
3.2
9
7.6
-------
Table 2-3. Suspended Solids Removal at Land Treatment Systems (adapted from Leach et al., 1980 and Crites et al., 2000)
Process/location
Soil Water Drainage - Total suspended solids, mg/L
Applied
Effluent"
Slow Rate (SR)
Hanover, NH
Typical value
Soil Aquifer Treatment (SAT)
Phoenix, AZ
Hollister, CA
Typical Value
Overland Flow (OF)
Ada, OK (raw wastewater)
Hanover, NH (primary)
Easley, SC (screened wastewater)
Utica, MS (fac. lagoon)
Davis, CA (fac. lagoon)
Summer
Fall
Winter
60
120
20 - 100
274
120
160
59
186
30
121
86
65
10
2
8
7
80
24
13
"Example depths and loading rates for SR and SAT systems are shown in Table 2-2.
still no need to design the land treatment component for
such an emergency because standard containment and
clean-up procedures can be used when needed. Oil and
grease are more likely to be a routine component in
industrial wastewaters. The most likely sources are
petroleum, and animal and vegetable oils. Loading rates
and removals are discussed in Chapter 11 (US EPA,
1972).
2.4 pH
The pH range suitable for biological treatment is
typically between 5 and 9 (Crites and Tchobanoglous,
1998). Soil generally has a large buffer capacity such
that wastewater pH can be attenuated and biological
treatment efficiency is not impaired. Organic acids in
food processing wastewater are easily degradable, as
described in Chapter 11, and do not impose a limitation
on wastewater treatment.
Crops can also tolerate a relatively large range in pH.
Optimum pH for crop growth has been reported to be
between 6.4 and 8.4. Low soil pH can result in metals
becoming more soluble and potentially leaching to
groundwater. A pH of 6 or above is currently considered
adequate to protect against crop uptake of most metals
(Page et al., 1987). Metal concentrations in municipal
effluent are typically well below the values of concern in
Section 2.6. If the practitioner is concerned about excess
metal uptake into the crop, monitoring of the crop would
be prudent.
2.5 Pathogenic Organisms
The known pathogens of concern in land treatment
systems are parasites, bacteria, and viruses. The
potential pathways of concern are to groundwater,
contamination of crops, translocation or ingestion by
grazing animals, and human contact through off site
transmission via aerosols or runoff. The removal of
pathogens in land treatment systems is accomplished by
adsorption, desiccation, radiation, filtration, predation,
and decay due to exposure to sunlight (UV) and other
adverse conditions. Fecal conforms are used as an
indicator of fecal contamination. Fecal contamination
occurs from livestock as well as other warm blood
animals. It is not uncommon to find "background" fecal
coliform concentrations of 102 or greater concentration.
The SR process is the most effective, removing about
five logs (105) of fecal conforms within a depth of a 0.6 m
(2 ft). The SAT process typically can remove two to
three logs of fecal conforms within several meters of
travel, and the OF process can remove about 90 percent
of the applied fecal conforms (Reed et al., 1995).
2.5.1 Parasites
Parasites may be present in all municipal wastewaters.
Parasites, such as Ascaris, E.histolytica and
Cryptosporidium have been recovered from
wastewaters. Under optimum conditions the eggs of
these parasites, particularly Ascaris can survive for
many years in the soil (US EPA. 1985). Because of their
weight and size, parasite cysts and eggs will settle out in
preliminary treatment or in storage ponds, so, if present
most will be found in the raw sludge and possibly in the
biosolids.
There is no evidence available indicating transmission
of parasitic disease from application of wastewater in
properly operated land treatment systems.
Transmission of parasites via sprinkler aerosols should
not be a problem due to the weight of the cysts and
eggs. The World Health Organization (WHO) considers
parasite exposure by field workers to be the most
significant risk for irrigation with wastewater. They
recommend ponds for the short-term retention of
untreated wastewater as a simple solution for the
problem (Chang et al, 1995).
-------
2.5.2 Crop Contamination
The major concerns for crop contamination are
directed toward retention and persistence of the
pathogens on the surfaces of the plant until consumed
by humans or animals, or the internal infection of the
plant via the roots. The persistence of polio virus on the
surfaces of lettuce and radishes, for up to 36 days, has
been demonstrated. About 99 percent of the detectable
viruses were gone in the first five to six days. The
general policy in the U.S. is not to grow vegetables to be
consumed raw on land treatment systems without high
levels of treatment, including filtration and disinfection.
Internal contamination of plants with viruses has been
demonstrated with transport from the roots to the leaves.
However, these results were obtained with soils
inoculated with high concentrations of viruses and then
the roots were damaged or cut. No contamination was
found when roots were undamaged or when soils were
not inoculated with the high virus concentrations (Crites
etal., 2000; US EPA 1985).
Criteria for irrigation of pasture with primary effluent in
Germany require a period of 14 days before animals are
allowed to graze. Bell and Bole demonstrated that fecal
conforms from sprinkling of wastewater on the surfaces
of alfalfa hay were killed by ten hours of bright sunlight
(Bell and Bole 1978). Similar experiments with Reed
canarygrass found 50 hours of sunlight were required.
It was recommended that a one-week rest period prior to
grazing be provided to ensure sufficient sunlight, for
Reed canary, orchard, and brome grasses used for
forage or hay (Bell and Bole, 1978). Because fecal
conforms have survival characteristics similar to
salmonella, these results should be applicable to both
organisms. However, the current management practice
for restricting grazing at biosolids application sites is a
minimum of 30 days in the U.S.A.
2.5.3 Runoff Contamination
Wastewater constituents that are applied to the land
enter the plant root/soil matrix. Suspended solids
become part of the soil after these are filtered out of the
wastewater. The rainfall runoff from fields irrigated with
wastewater may contain dissolved wastewater
constituents.
Runoff from a land treatment site might be a potential
pathway for pathogen transport. Proper system design
and operation should eliminate runoff from adjacent
lands entering the site and runoff of applied wastewater
from the site. Overland flow is an exception in the latter
case because treated effluent and stormwater runoff are
discharged from the site. The quality of rainfall runoff
from an overland flow system is equal or better in quality
than the normal (non-rainfall induced) renovated
wastewater runoff.
The NPDES permitting authority should be consulted
with respect to the current storm water regulations (40
CFR 122.26). Storage of runoff for up to one "time-of-
concentration" or 24 hours may be necessary to capture
the first flush of stormwater.
2.5.4 Groundwater Contamination
The risk of groundwater contamination by pathogens
involves the movement of bacteria or virus to aquifers
that are then used for drinking purposes without further
treatment. The risk is minimal for OF systems but
highest for SAT systems due to the high hydraulic
loading and the coarse texture and relatively high
permeability of the receiving soils.
The removal rate of bacteria can be quite high in the
finer-textured agricultural soils commonly used for SR
systems. Results from a five-year study in Hanover, NH
(Jenkins and Palazzo, 1981) applying both primary and
secondary effluent to two different soils indicated
essentially complete removal of fecal conforms within a
1.5 m (5 ft) soil profile. The soils involved were a fine
textured silt loam and a coarser textured loamy sand and
the concentrations of fecal coliform in the applied
wastewaters ranged from 105 for primary effluent to 103
for secondary effluent. In similar research in Canada
(Bell and Bole, 1978), undisinfected effluent was applied
to grass-covered loamy sand. Most of the coliform were
retained in the top 75 mm (3 in) of soil and none
penetrated below 0.68 m (27 in). Die-off occurred in two
phases: an initial rapid phase within 48 hours of
application when 90 percent of the bacteria died,
followed by a slower decline during a two-week period
when the remaining 10 percent were eliminated (Jenkins
and Palazzo, 1981).
Removal of virus, which is at least partially dependent
on cation exchange and adsorption reactions, is also
quite effective in these finer textured agricultural soils.
Most of the concern and the research work on virus
transmission in soils have focused on SAT systems. A
summary of results from several studies is presented in
Table 2-4. The SAT basins in the Phoenix system
consisted of about 0.77 m (30 in) of loamy sand
underlain by coarse sand and gravel layers. During the
study period indigenous virus were always found in the
applied wastewater, but none were recovered in the
sampling wells.
At Santee, CA, secondary effluent was applied to
percolation beds in a shallow stratum of sand and
gravel. The percolate moved laterally to an interceptor
trench approximately 458 m (1,500 ft) from the beds.
Enteric virus was isolated from the applied effluent but
-------
none were ever found at the 61 m (200 ft) and 122 m
(400 ft) percolate sampling points.
Lance and others have examined the problem of virus
desorption in the laboratory (Lance and Gerba, 1980).
Using soil columns it was shown that applications of
distilled water or rainwater could cause adsorbed viruses
to move deeper into the soil profile under certain
conditions. However, viruses were not desorbed if the
free water in the column drained prior to application of
the distilled water. This suggests that the critical period
would be the first day or two after wastewater
application. Rainfall after that period should not cause
additional movement of viruses in the soil profile. A
desorbed virus should have further opportunities for
readsorption in the natural case, assuming there are no
macropores Lance's work with polio virus in soil
columns, containing calcareous sand, indicated that
most viral particles are retained near the soil surface.
Increasing the hydraulic loading from 0.6 m/d per day to
1.2 m/d (2 to 4 ft/d) caused a virus breakthrough (about
one percent of the applied load) at the bottom of the 2.4
m (8 ft) column (Lance and Gerba, 1980). However, 99
percent of the viral particles were still removed at
hydraulic loadings as high as 12 m/d (39 ft/d). Lance
suggested that the velocity of water movement through
the soil may be the single most important factor affecting
the depth of virus penetration in soils. Column studies
(Arizona State University et al, 1998) have confirmed the
earlier work by Lance. In this recent study, high virus
removal efficiencies (>99%) were observed in one meter
of soil at low infiltration rates. Assuming a first order
decay relationship, if 99 percent removal of virus
occurred in one meter of soil then 99.999 percent would
be removed in three meters of soil. This same study
routinely observed a four log (99.99%) removal of
Cryptosporidium after passing through one meter of soil
even at the highest infiltration rates.
2.5.5 Aerosols
Pathogen concentrations in aerosols caused by
sprinkling wastewater is a function of their concentration
in the applied wastewater and the aerosolization
efficiency. Aerosolization efficiency, which is the
percentage of the wastewater that is converted to
aerosols during sprinkling, can vary from 0.1 percent to
nearly 2 percent, with 0.3 to 1 percent being typical
(Crook, 1998).
The potential for aerosol transport of pathogens from
land treatment sites is a controversial health issue. The
lay public, and many professionals, tend to
misunderstand what aerosols are and confuse them with
the water droplets, which emerge from sprinkler nozzles.
Aerosols are almost colloidal in size ranging from 20
microns in diameter and smaller. UV light, heat and
desiccation significantly reduce small aerosol particles. It
is prudent to design any land treatment systems so that
the larger water droplets emerging from the sprinklers
are contained within the site. The public acceptance of a
project will certainly be enhanced if it is understood that
neither their persons nor their property will become "wet"
from the sprinkler droplets (Reed et al., 1995).
Bacterial aerosols are present in all public situations
and will tend to increase with the number of people and
their proximity. Sporting events, theaters, public
transportation, public toilets, etc., are all potential
locations for airborne infection. Bacterial concentrations
in aerosols at various locations, all of which involve the
use or treatment of wastewaters, are summarized in
Table 2-5. The cooling water for the power plant that is
cited uses some disinfected effluent as make-up water.
The aerosol concentration at this cooling tower is
roughly the same as measured just outside the sprinkler
impact zone at the California (Pleasanton) operation
where undisinfected effluent is used. It does not appear
that bacterial aerosols at or near land treatment sites are
any worse than other sources. In fact, the opposite
seems true, the aerated pond in Israel and the activated
sludge systems have higher aerosol concentrations than
the land treatment systems listed in the table. Aerosol
studies in metropolitan areas for example have indicated
a bacterial concentration of 0.11 particles/m3 (4
particles/ft3) per cubic foot or air in downtown Louisville,
Table 2-4. Virus Transmission through
Location
Phoenix, AZ (Jan to Dec 1974)
Gainesville, FL (Apr to Sept 1974)
Santee, CA(1966)
Soil at SAT Land Application Sites (Reed
Sampling depth or distance (m)
3-9
7
61
etal., 1995)
Virus concentration
Applied
8
27
24
2
75
11
0.14
0.14
0.14
0.14
0.14
0.14
0.14
0.14
Concentrated type 3 polio virus
(pfu/L)
Soil water drainage at
sample point
0
0
0
0
0
0
0.005
0
0
0
0
0
0
0
0
-------
Table 2-5. Aerosol Bacteria at Various Sources (Reed et al., 1995)
Location
Downwind distance, m (ft)
Total aerobic bacteria, #/m
(#/ft3)3
Total coliform bacteria, #/m
(#/ft3)3
Activated sludge tank, Chicago, IL
Activated sludge tank, Sweden
Power plant cooling tower, California
Aerated pond, Israel
Sprinklers", Ohio
Sprinklers0, Israel
Sprinklers0, Arizona
Sprinklers0, Pleasanton, CA
9-30(30-100)
0(0)
0(0)
30 (1 00)
30(100)
30(100)
45 (1 50)
9-30 (30-1 00)
1 1 .2 (396)
80 (2,832)
2.4 (83)
-
0.4(14)
-
0.6 (23)
2.1 (73)
0.006 (0.2)
-
-
0.23 (8)
0.003(0.1)
0.094 (3.3)
0.006 (0.2)
0.006 (0.2)
aAerosol counts are per cubic meter of air sampled (#/ft). b. Disinfected effluent applied, c. Undisinfected effluent applied.
KY, during daylight hours, and an annual average of 1.6
bacterial particles/m3 in Odessa, Russia. The aerosols
from the land treatment systems listed in Table 2-5 fall
within this range.
An epidemiological study at an activated sludge plant
in the Chicago area (Camann, 1978) documented
bacteria and virus in aerosols on the plant site.
However, the bacterial and viral content of the air, the
soil, and the surface waters in the surrounding area were
not different than background levels and no significant
illness rates were revealed within a 4.8 km (3 mile)
radius of the activated sludge plant. A similar effort was
undertaken at an activated sludge plant in Oregon with a
school playground approximately 10 m (30 ft) from the
aeration tanks. It can be inferred from these studies,
since the concentrations of bacteria and viruses in land
treatment aerosols are similar to those from activated
sludge treatment systems. The risks of adverse health
effects should be similar to those presented by properly
operated land treatment systems.
The aerosol measurements at the Pleasanton, CA
land treatment system demonstrated that salmonella and
viruses survived longer than the traditional coliform
indicators (Camann, 1978). However, the downwind
concentration of viruses was very low at 1.1
plaque-forming units (pfu/m3) (0.0004 pfu/ft3).
x 10"
The source for these measurements was undisinfected
effluent from high-pressure impact sprinklers, and the
sampling point was 49 m (160 ft) from the sprinkler
nozzle. The concentration cited is equal to one virus
particle in every 7 m3 (250 ft3) of air. Assuming a normal
breathing intake of about 0.002 m3/min (0.07 ft3/min) it
would take 59 hours of continuous exposure by a system
operator to inhale that much air. In normal practice an
operator at Pleasanton might spend up to one hour per
day within 49 m (160 ft) of the sprinklers. This is
equivalent to the time an activated sludge operator
spends servicing the aeration tanks. At this rate the
operator at Pleasanton would be exposed to less than
four virus particles per year and the risk to the adjacent
population would appear to be non-existent.
US EPA guidelines have recommended a fecal
coliform count of 1,000/100 ml for recreational
applications, based on standards for general irrigation
water and for bathing waters and body contact sports.
With respect to the aerosol risk of spraying such waters,
Shuval has reported that when the coliform
concentration at the nozzle was below 1,000/100 ml, no
viruses were detected at downwind sampling stations,
the nearest of which was 10 m (33 ft) away. (Shuval and
Teltch, 1979). Procedures have been developed for
estimating the downwind concentrations of aerosol
microorganisms from sprinkler application of wastewater
(US EPA, 1982).
2.6 Metals
The removal of metals in the soil is a complex process
involving the mechanisms of adsorption, precipitation,
ion exchange, biogeochemical reactions, uptake (by
plants and microorganisms) and complexation.
Adsorption of most trace elements occurs on the
surfaces of clay minerals, metal oxides, and organic
matter; as a result, fine textured and organic soils have a
greater length of time that water is in contact with the
soil. The SR land treatment process is the most effective
for metals removal because of the finer textured soils
and the greater opportunity for contact and adsorption.
SAT can also be quite effective but a longer travel
distance in the soil will be necessary due to the higher
hydraulic loadings and coarser textured soils. Overland
flow (OF) systems allow minimal contact with the soil
and typically remove between 60 and 90 percent
depending on the hydraulic loading and the particular
metal.
2.6.1 Micronutrients
Several metals are micronutrients that are considered
essential for plant nutrition, for example:
-------
• Copper
• Iron
• Manganese
• Molybdenum
• Nickel
• Zinc
2.6.2 Metals
The major concern with respect to metals is the
potential for accumulation in the soil profile and then
subsequent translocation, via crops or animals, through
the food chain to man. The metals of greatest concern
are cadmium (Cd), lead (Pb), mercury (Hg), and arsenic
(As). The concentrations of metals that can be safely
applied to crops are presented in Table 2-6. Most crops
do not accumulate lead but there is some concern with
respect to ingestion by animals grazing on forages or
soil to which biosolids have been applied. In general,
zinc, copper, and nickel will be toxic to the crop before
their concentration in plant tissues reaches a level that
poses a significant risk to human or animal health.
Cadmium is the greatest concern because the
concentration of concern for human health is far below
the level that could produce toxic effects in the plants.
WHO has published guidelines for annual and
cumulative metal additions (based on US EPA's Part
503 rule) to agricultural crop land (Chang et al., 1995).
Adverse effects should not be expected at these loading
rates. These loading rates are presented in Table 2-7.
Although they were developed for biosolids applications,
it is prudent to apply the same criteria for wastewater
applications.
2.6.3 Metals Removal in Crops and Soils
It is not possible to predict the total renovative capacity
of a land treatment site with simple ion exchange or soil
adsorption theories. Although the metals are
accumulated in the soil profile, the accumulation
resulting from repeated applications of wastewater does
not seem to be continuously available for crop uptake.
Work by several investigators with biosolids
demonstrates that the metals uptake in a given year is
more dependent on the concentration of metals in the
biosolids most recently applied and not on the total
accumulation of metals in the soil.
The capability of metal uptake varies with the type of
crop grown. Swiss chard, and other leafy vegetables
take up more metals than other types of vegetation.
Metals tend to accumulate in the liver and kidney tissue
of animals grazing on a land treatment site or if fed
harvested products. Tests done on a mixed group of 60
Hereford and Angus steers that graze directly on the
pasture grasses at the Melbourne, Australia land treat-
Table 2-6. Recommended Limits for Constituents in Reclaimed
Water for Irrigation (Rowe, D.R. and I. M. Abel-Magid, 1995)
Element
Aluminum
Arsenic
Beryllium
Boron
Cadmium
Chromium
Cobalt
Copper
Fluoride
Iron
Lead
Lithium
Manganese
Molybdenum
Nickel
Selenium
Zinc
For waters used
continuously
on all soil, mg/L
5.0
0.10
0.10
0.75
0.010
0.10
0.050
0.20
1.0
5.0
5.0
2.5a
0.20
0.010
0.20
0.020
2.0
For use up to
20 years on
fine-textured soils of
pH 6.0 to 8.5, mg/L
20.0
2.0
0.50
2.0-10.0
0.050
1.0
5.0
5.0
15.0
20.0
10.0
2.5a
10.0
0.050b
2.0
0.020
10.0
"Recommended maximum concentration for irrigating citrus is
0.075 mg/L.
bFor only acid fine-textured soils or acid soils with relatively high
iron oxide contents.
Table 2-7. WHO Recommended Annual and Cumulative Limits for
Metals Applied to Agricultural Crop Land (Chang et al., 1995)
Annual loading rate3
Metal (kg/ha°)
Arsenic 2.0
Cadmium 1.9
Chromium 150
Copper 75
Lead 15
Mercury 0.85
Molybdenum 0.90
Nickel 21.0
Selenium 5.0
Zinc 1 40
Cumulative loading rate3
(kg/ha°)
41
39
3,000
1,500
300
17
18
420
100
2,800
aLoading kg/ha per 365 day period.
bCumulative loading over lifetime of site.
°kg/ha x 0.89 = Ib/ac.
ment site (untreated raw sewage applied) showed that
"the concentrations of cadmium, zinc and nickel found in
the liver and kidney tissues of this group are within the
expected normal range of mammalian tissue."
(Anderson, 1976). Anthony (1978) has reported on
metals in bone, kidney and liver tissue in mice and
rabbits which were indigenous to the Pennsylvania State
University land treatment site and no adverse impacts
were noted.
The average metal concentrations in the shallow
groundwater beneath the Hollister, CA, rapid infiltration
site are shown in Table 2-8. After 33 years of operation
-------
Table 2-8. Trace Metals in Groundwater Under Hollister, CA Soil
Aquifer Treatment Site, mg/L (Pound, Critesand Olson, 1978)
Metal
Groundwater concentration
Cadmium
Cobalt
Chromium
Copper
Iron
Lead
Manganese
Nickel
Zinc
0.028
0.010
O.014
0.038
0.36
0.09
0.96
0.13
0.081
the concentration of cadmium, chromium, and cobalt
were not significantly different from normal off-site
groundwater quality. The concentration of the other
metals listed was somewhat higher than the off-site
background levels.
The metal concentrations in the upper foot of soils in
the SAT basins at the Hollister, CA system are still below
or near the low end of the range for typical agricultural
soils, after 33 years of operation.
In OF systems, the major mechanisms responsible for
trace element removal include sorption on clay colloids
and organic matter at the soil surface and in the litter
layer, precipitation as insoluble hydroxy compounds, and
formation of organometallic complexes. The largest
proportion of metals accumulates in the biomass on the
soil surface and close to the initial point of application.
2.7 Nitrogen
The removal of nitrogen in land treatment systems is
complex and dynamic due to the many forms of nitrogen
(N2, organic N, NH3, NH4, NO2, NO3) and the relative
ease of changing from one oxidation state to the next.
The nitrogen present in typical municipal wastewater is
usually present as organic nitrogen (about 40 percent)
and ammonia/ammonium ions (about 60 percent).
Activated sludge and other high-rate biological
processes can be designed to convert all of the
ammonia ion to nitrate (nitrification). Typically only a
portion of the ammonia nitrogen is nitrified and the major
fraction in most system effluents is still in the ammonium
form (ammonia and ammonium are used
interchangeably in this text).
Because excessive nitrogen is a health risk, it is
important in the design of all three land treatment
concepts to identify the total concentration of nitrogen in
the wastewater to be treated as well as the specific
forms (i.e., organic, ammonia, nitrate, etc.) expected.
Experience with all three land treatment processes
demonstrates that the less oxidized the nitrogen is when
entering the land treatment system the more effective
will be the retention and overall nitrogen removal.
2.7.1 Soil Responses
The soil plant system provides a number of
interrelated responses to wastewater nitrogen. The
organic N fraction, usually associated with particulate
matter is entrapped or filtered out of the applied liquid
stream. The ammonia fraction can be lost by
volatilization, taken up by the crop or adsorbed by the
clay minerals in the soil. Nitrate can be taken up by the
vegetation, or converted to nitrogen gas via
denitrification in macro or micro anaerobic zones and
lost to the atmosphere or leached through the soil
profile. The decomposition (mineralization) of organic
nitrogen contained in the particulate matter proceeds
slowly. This aspect is more critical for sludge and
biosolids application systems where the solids fraction is
a very significant part of the total application. As the
organic solids decompose, the contained organic
nitrogen is mineralized and released as ammonia. This
is not a major concern for most municipal wastewater
land treatment systems, with the exception of those
systems receiving facultative lagoon effluent containing
significant concentrations of algae. The organic content
of the algae must be considered in project design
because it can represent a significant ammonia load on
the system.
Nitrification is effective in all three of the basic land
treatment concepts as long as the necessary aerobic
status of the site is maintained or periodically restored.
However, having the system produce nitrate from
ammonium reduces the efficiency to remove nitrogen
since it increases leaching to groundwater. Under
favorable conditions (i.e., sufficient alkalinity, suitable
temperatures, etc.) nitrification ranging from 5 to 50 mg/L
per day is possible. Assuming that these reactions are
occurring with the adsorbed ammonia ions in the top four
inches of a fine-textured soil means that up to 67 kg/ha
(60 Ib/acre) can be converted to nitrate per year.
The maintenance and/or restoration of aerobic
conditions in the soil are the reason for the short
application periods and cyclic operations that are
required in land treatment systems. In SAT systems, for
example, the ammonia adsorption sites are saturated
with ammonium during the early part of the application
cycle. The aerobic conditions are restored as the system
drains during the rest period and the soil microbes
convert the adsorbed ammonium to nitrate. At the next
application cycle ammonium adsorption sites are again
available and much of the nitrate is denitrified as
anaerobic conditions develop. Denitrifying bacteria are
common soil organisms and the occurrence of anaerobic
conditions, at least at microsites, can be expected at
both SR and OF systems as well as SAT.
-------
2.7.2 Nitrogen Cycle
The nitrogen cycle in soil is presented in Figure 2-1.
Nitrification is a conversion process, not a removal
process for nitrogen. Denitrification, volatilization, soil
storage and crop uptake are the only true removal
pathways available. Crop uptake is the major pathway
considered in the design of most slow-rate systems, but
the contribution from denitrification and volatilization can
be significant depending on site conditions and
wastewatertype. Immobilization and soil storage can be
significant with wastewaters having a carbon-to-nitrogen
(C:N) ratio of 12:1 or more. In SAT, ammonia adsorption
on the soil particles followed by nitrification typically
occurs, but denitrification is the only important actual
removal mechanism. For OF, crop uptake, volatilization,
and denitrification can all contribute to nitrogen removal.
Crop uptake of nitrogen is discussed in detail in Chapter
4 and in the process design chapters. Nitrogen removal
data for typical SR, SAT, and OF systems are shown in
Table 2-9.
Denitrification
Plant Uptake
N- \Nitnncation
ammonium
Leaching
Figure 2-1. Nitrogen Cycle in Soil.
-------
Table 2-9. Total Nitrogen Removal in Typical Land Treatment Systems (US EPA, 1981 and Crites et al., 2000)
Process/Location Process
Applied Wastewater (mg/L)
Soil Water Drainage (mg/L)
SR
SAT
OF
Dickinson, ND
Hanover, NH
Roswell, NM
San Angelo, TX
Calumet, Ml
Ft. Devens, MA
Hollister, CA
Phoenix, AZ
Ada, OK (raw wastewater)
12
28
66
35
24
50
40
27
34
3.9
7.3
10.7
6.1
7
20
3
10
(primary effluent)
(secondary effluent)
Easley, SC (pond effluent)
Utica, MS (pond effluent)
19
16
7
20
5
8
2
7
2.7.3 Nitrates
The U.S. primary drinking water standard for nitrate
(as N) is set at 10 mg/L. The pathway of concern in SR
and SAT systems is conversion of wastewater nitrogen
to nitrate and then percolation to drinking water aquifers.
When potable aquifers, sole source aquifers, or wellhead
protection areas are involved, the current guidance
requires that all drinking water standards be met at the
land treatment project boundary. As a result, nitrogen
often becomes the LDP for SR systems because of its
relatively high concentration as compared to other
drinking water parameters. Chapter 8 presents complete
design details for nitrogen removal in these systems.
There are a number of safety factors inherent in the
approach that insures a conservative design. The
procedure assumes that all of the applied nitrogen will
appear as nitrate (i.e., complete nitrification) and within
the same time period assumed for the application (no
time lag or mineralization of ammonia) and there is no
credit for mixing or dispersion with the in-situ
groundwater.
2.7.4 Design Factors
The nitrogen mass balance for SAT systems would not
usually include a component for crop uptake. The
percolate nitrogen concentration is not a concern for OF
systems since the percolate volume is generally
considered to be negligible. As indicated previously,
application of biosolids does include a mineralization
factor to account for the previous organic nitrogen
deposits. There are four potential situations where a
mineralization factor might be included in the nitrogen
balance for SR and OF systems:
• Industrial wastewaters with high solids
concentrations having significant organic nitrogen
content.
• Grass covered systems where the grass is cut but
not removed.
• Pasture systems with intense animal grazing and
animal manure left on the site.
• Biosolids or manure added to the site as
supplemental fertilizers.
2.7.4.1 Organic Nitrogen
Mineralization rates, developed for wastewater
biosolids are given in Table 2-10. The values are the
percent of the organic nitrogen present that is
mineralized (i.e., converted to inorganic forms such as
ammonia, nitrate, etc.) in a given year. The fraction of
the biosolids organic N initially applied, or remaining in
the soil, that will be mineralized during the time intervals
shown are provided as examples only and may be quite
different for different biosolids, soils and climates.
Therefore, site-specific data, or the best judgment of
individuals familiar with N dynamics in the soil-plant
system involved, should always be used in preference to
these suggested values. For example, 40 percent of the
organic nitrogen in raw sludge would be mineralized
during the first year, 20 percent the second year, and so
forth. With consistent annual applications to a site, the
cumulative mineralization approaches 60 percent.
The mineralization rate is related to the initial organic
nitrogen content, which in turn is related to treatment
level for the biosolids in question. Easily degraded
-------
Table 2-10. Annual Mineralization Rates for Organic Matter in Biosolids (US EPA 1995)
Mineralization rate (%)
Time after biosolids
application (years)
0-1
1-2
2-3
3-4+
Unstabilized primary
40
20
10
5
Aerobically digested
30
15
8
4
Anaerobically digested
30
10
5
a
Composted
10
5
a
"Annual rate drops to 3%. Once the mineralization rate becomes less than 3%, no net gain of plant available nitrogen above that normally obtained
from the mineralization of soil organic matter is expected. Therefore, additional credits for residual biosolids N do not need to be calculated.
industrial biosolids would be comparable to raw
municipal biosolids. Industrial solids with a high
percentage of refractory or stable humic substances
might be similar to composted biosolids. A specific test
procedure is available to determine under incubation
what the actual mineralization rate is for a particular
waste that is high in organic nitrogen (Gilmour and Clark,
1988; Gilmour et al., 1996).
Animal manures would be similar to digested sludges
and it would be conservative to assume that grass
cuttings and other vegetative litter would decay at the
same rates as digested sludges. The examples below
illustrate the use of the factors in Table 2-10 for two
possible situations.
Example 2.2
Nitrogen Cycling in Greenbelts
Conditions: Slow-rate land treatment site used as a greenbelt
parkway. The grasses are cut but not removed
from the site. At the annual wastewater loading
rates used, the grasses will take up about 250
kg/ha»yr (222 lb/ac»yr).
Find: The nitrogen contribution from the on-site decay
of the cut grass.
Solution: The most conservative assumption is to use
aerobically digested sludge rates from Table 2-
10 and to assume that all of the nitrogen is in the
organic form.
1 . In first year:
2. In second year:
The 2nd year cutting
Residue from 1 st year
Total, 2nd year
3. In third year:
The 3rd year cutting
Residue from 2nd year
Residue from 1 st year
Total, 3rd year
4. In fourth year:
The 4th year cutting
Residue from 3rd year
Residue from 2nd year
Residue from 1 st year
Total, 4th year
5. In fifth year:
250 kg/ha (0.30)
250 (0.3)
(250-75) (0.1 5)
(250)(0.30)
(250-75)(0.15)
(250-1 01 )(0.08)
(250-1 13)(0.04)
= 75 kg/ha
= 75kg/ha
= 26
= 101 kg/ha
= 75 kg/ha
= 26
= 12
= 1 1 3kg/ha
= 75kg/ha
= 26
= 12
= 5
= 118 kg/ha
= 75 kg/ha
The 5th year cutting
Residue from 4th year
Residue from 3rd year
Residue from 2nd year
Residue from 1 st year
Total, 5th year
(250-1 18)(0.04)
= 26
= 12
= 5
= 5
= 1 23 kg/ha
6. As shown by the sequence above, the amount of nitrogen
contributed becomes relatively stable after the third or fourth year and
increases only slightly thereafter. In this example, it can be assumed
that about 120 kg/ha of nitrogen is returned to the soil each year from
the cut grass. For this case, that would be about 48 percent of the
nitrogen originally taken up by the grass, so the net removal is still
very significant (52 percent). The 48 percent returned is also
significant, and would be included in the nitrogen mass balance in a
conservative design.
1 . Annual available
organic nitrogen
2. Using digested
mineralization rates
from Table 2-1 1 :
First year
contribution
Second year
contribution
Third year
contribution
And so forth
(300 kg/ha)(0.50)
(150)(0.30)
45 + (150-45)(0.15)
45+16+ ((1 50-61 )(0.08))
= 150 kg/ha
= 45 kg/ha
= 61 kg/ha
= 68 kg/ha
These two examples illustrate the critical importance of
knowing the form of nitrogen is in when it is applied to
the land treatment site. This is particularly important if
elaborate pretreatment is provided because the nitrogen
may not then be in the simple, and easily managed,
combination of organic nitrogen and ammonia that is
present in untreated municipal wastewater and primary
effluents. Any nitrogen losses which occur during this
preapplication treatment or storage should be
considered. Facultative lagoons or storage ponds can
remove up to 85 percent of the contained nitrogen under
ideal conditions (Reed et al., 1995). Such losses are
especially significant when nitrogen is the LDP for
design because any reduction in nitrogen prior to land
application will proportionally reduce the size and
therefore the cost of the land treatment site.
2.8 Phosphorus
The presence of phosphorus in drinking water supplies
does not have any known health significance but
-------
phosphorus is considered to be the limiting factor for
eutrophication of fresh, non-saline surface waters so its
removal from wastewaters is often necessary.
Phosphorus is present in municipal wastewater as
orthophosphate, polyphosphate, and organic
phosphates. The orthophosphates are immediately
available for biological reactions in soil ecosystems. The
necessary hydrolysis of the polyphosphates proceeds
very slowly in typical soils so these forms are not as
readily available. Industrial wastewaters may contain a
significant fraction of organic phosphorus.
2.8.1 Removal Mechanisms
Phosphorus removal in land treatment systems can
occur through plant uptake, biological, chemical, and/or
physical processes. The nitrogen removal described in
the previous section is almost entirely dependent on
biological processes so the removal capacity can be
maintained continuously or restored by proper system
design and management. In contrast, phosphorus
removal in the soil depends to a significant degree on
chemical reactions which are slowly renewable. As a
result, the retention capacity for phosphorus will be
gradually reduced over time, but not exhausted. At a
typical SR system for example it has been estimated
thata 0.3 m (1 ft) depth of soil may become saturated
with phosphorus every ten years (US EPA, 1981). The
removal of phosphorus will be almost complete during
the removal period and percolate phosphorus should not
be a problem until the entire design soil profile is utilized
some SR sites phosphorus may limit the design life of
the site; an example might be a site with coarse textured
sandy soils with underdrains at a shallow depth which
discharge to a sensitive surface water. In this case
theuseful life of the site might range from 20 to 60 years
depending on the soil type, underdrain depth,
wastewater characteristics, and loading rates.
Crop uptake contributes to phosphorus removal at SR
systems, but the major removal pathway in both SR and
Rl systems is in the soil. Typical plant concentrations for
nitrogen are 1 percent to 2 percent and for phosphorus
the concentrations are 0.2 percent to 0.4 percent. The
phosphorus is removed by adsorption/precipitation
reactions when clay, oxides of iron and aluminum, and
calcareous substances are present. The phosphorus
removal increases with increasing clay content and with
increasing contact time in the soil. The percolate
phosphorus values listed in Table 2-11 for SR systems
are close to the background levels for natural
groundwater at these locations.
Soil Aquifer Treatment
There is no crop uptake in SAT systems and the soil
characteristics and high hydraulic loading rates typically
used require greater travel distances in the soil for
effective phosphorus removal. Data from several of the
SAT systems in Table 2-11 indicate a percolate
phosphorus concentration approaching background
levels after travel through the sub soils. Most of these
systems (Vineland, Lake George, Calumet, Ft Devens)
had been in operation for several decades prior to
collection of the percolate samples.
Table 2-11. Typical Percolate Phosphorus Concentrations3 (Crites et al., 2000)
Location
SR
Hanover, NH
Muskegon, Ml
Tallahassee, FL
Penn. State, PA°
Helen, GA°
SAT
Hollister, CA
Phoenix, AZ
Ft. Devens, MA
Calumet, Ml
Boulder, CO
Lake George, NY
Vineland, NJ
Soil type
Sandy loam
Loamy sand
Fine sand
Silt loam
Sandy loam
Gravely sand
Gravely sand
Gravely sand
Gravely sand
Gravely sand
Sand
Sand
Travel distance
(m)
1.5
1.5
1.2
1.2
1.2
6.7
9.1
1.5
9.1
3.0
0.9
183
9.1
122
Soil water drainage phosphorus
(mg/L)
0.05
0.04
0.1
0.8
0.17
7.4
4.5
9.0
0.1
2.3
1.0
0.014
1.5
0.27
1 Applied wastewater, typical municipal effluent, TP « 8 to 14 mg/L.
1 Total percolate travel distance from soil surface to sampling point SR systems.
: Forested SR system.
-------
An equation to predict phosphorus removal at SR and
SAT land treatment sites has been developed from data
collected at a number of operating systems (US EPA
1980). The equation was developed from performance
data with the coarse textured soils at SAT sites.
Equation 2-2 is solved in two steps, first for the vertical
flow component, from the soil surface to the subsurface
flow barrier (if one exists) and then for the lateral flow to
the outlet point x. The calculations are assuming
saturated flow conditions, so the shortest possible
detention time will result. The actual vertical flow in most
cases will be unsaturated, so the actual detention time
will be much longer than is calculated with this
procedure, and therefore the actual phosphorus removal
will be greater. If the equation predicts acceptable
phosphorus removal then there is some assurance that
the site will perform reliably and detailed tests should not
be necessary for preliminary work. Detailed phosphorus
removal tests should be conducted for final design of
projects where phosphorus removal is critical.
2.8.3 Overland Flow
The opportunities for contact between the applied
wastewater and the soil are limited to surface reactions
in OF systems and as a result phosphorus removals
typically range from 40 to 60 percent. Phosphorus
removal in overland flow can be improved by chemical
addition and then precipitation on the treatment slope.
At Ada, OK, the US EPA demonstrated the use of alum
additions (Al to TP mole ratio 2:1) to produce a total
phosphorus concentration in the treated runoff of 1 mg/L
(US EPA, 1981). At Utica, MS, mass removals ranged
between 65 and 90 percent with alum as compared to
less than 50 percent removal without alum (Crites,
1983).
Example 2.4
Phosphorus Removal
Conditions:
Px= Po
Where:
Px
Po
k
W
Kx
Thus:
Kv
G
Ah
(2-2)
= total phosphorus in percolate at distance x on the flow
path (mg/L)
= total phosphorus in applied wastewater, mg/L
= rate constant, at pH 7, d"1
= 0.048 d"1 (pH 7 gives most conservative value)
= detention time to point x, d
= (x)(W)/(Kx)(G)
= distance along flow path, m (ft)
= saturated soil moisture content, assume 0.4
= hydraulic conductivity of soil in direction x, m/d (ft/d)
= vertical conductivity, KH = horizontal conductivity
= hydraulic gradient for flow system, dimensionless
= 1.0 for vertical flow
= Ah/L for horizontal flow
= elevation difference of water surface between origin of
horizontal flow and end point x, m (ft)
= length of horizontal flow path, m (ft).
Find:
Solution:
Assume a site where wastewater percolate moves
5 m vertically through the soil to the groundwater
table and then 45 m horizontally to emergence in
a small stream. The initial phosphorus
concentration is 10 mg/L, the vertical hydraulic
conductivity Kv= 1 m/d, the horizontal hydraulic
conductivity KH = 10 m/d, and the difference in
groundwater surface elevations between the site
and the stream is 1 m.
The phosphorus concentration in the percolate
when emerging in the stream and the total
detention time in the soil.
Use Equation 2-2. Phosphorus concentration at
end of vertical flow :
1m/d
Px = (10mg/L)(e-<°°48)(2°>)
= 9.1 mg/L
Percolate phosphorus concentration at the
stream:
t = (45 m)(0.4)/(10 m/d)(1 m/45 m) = 81 d
Px = (9.1 mg/L)(e-(0048)(81))
= 0.1 8 mg/L
Total detention time in soil =2d + 81d =83d
Typical municipal wastewaters will have between 5
and 20 mg/L of total phosphorus. Industrial wastewaters
can have much higher concentrations, particularly from
fertilizer and detergent manufacturing. Food processing
operations can also have high phosphate effluents.
Some typical values are: Dairy products 9 to 210 mg/L
PO4, Grain Milling 5 to 100 mg/L PO4, Cattle feed lots 60
to 1,500 mg/L PO4.
Example 2.5
Determine Phosphorus Loading to Match
Useful Life of Site
Conditions: Assume a silty loam soil, adsorption tests
indicate a useful capacity for phosphorus equal
to 9,000 kg/ha per meter of depth. Site to be
grass covered, grass uptake of phosphorus is
35 kg/ha»yr, grass to be harvested and taken
off site. The projected operational life of the
factory and the treatment site is equal to 30
years. The phosphorus concentration in the
wastewater is 20 mg/L. The treatment site is
underdrained with drainage water discharged to
adjacent surface waters with an allowable
discharge limit of 1.0 mg/L TP. Because of the
underdrains, the practical soil treatment depth
is 2 m.
Find: The acceptable annual wastewater loading
during the 30 yr useful life.
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Solution: 1. Lifetime crop contribution = (35 kg/ha»yr)(30
yr) = 1050 kg/ha
2. Lifetime soil contribution = (9000 kg/ha) (2
m) = 18000 kg/ha
3. Total 30 yr phosphorus removal capacity =
19,050 kg/ha (Step 1 + Step 2).
4. Average annual phosphorus loading =
(19,050 kg/ha)/(30 yr) = 635 kg/ha.yr
5. Wastewater loading (Q) = (635
kg/ha.yr)/(20 g/m3) = 3.175m/yr
Note: Design credit is not taken in this example for the 1.0 mg/L TP
allowed in the underdrain effluent. This is because the treatment
system will essentially remove all of the phosphorus during the
useful life of the system until breakthrough occurs; until that point is
reached the effluent concentration should be well below the
allowable 1 mg/L level.
2.9 Potassium
As a wastewater constituent, potassium usually has no
health or environmental significance. It is, however, an
essential nutrient at sufficient levels for vegetative
growth, and is not typically present at sufficient levels in
wastewaters in the optimum combination with nitrogen
and phosphorus. If a land treatment system depends on
crop uptake for nitrogen removal, it may be necessary to
add supplemental potassium to maintain nitrogen
removals at the optimum level. Equation 2-3, developed
by A. Palazzo, can be used to estimate the supplemental
potassium that may be required where the in-situ soils
have a low level of natural potassium. This most
commonly occurs in the northeastern part of the U.S.
= (0.9)(U) -
(2-3)
Where:
Ks
U
KWW
= annual supplemental potassium needed, (kg/ha)
= estimated annual nitrogen uptake of crop, (kg/ha)
= potassium applied in wastewater, (kg/ha)
(kg/ha) x (0.8922) = Ib/ac
2.10 Sodium
Sodium is typically present in all wastewaters. High
levels of sodium can be directly toxic to plants but most
often its influence on soil salinity or soil alkalinity is the
more important problem. Growth of sensitive plants
becomes impaired where the salt content of the soil
exceeds 0.1 percent. Salinity also has a direct bearing
on the osmotic potential of the soil solution, which
controls the ability of the plant to absorb water. Adverse
crop effects can also occur from sprinkler operations in
arid climates using water with significant concentrations
of sodium or chloride (see Chapter 4). The leaves can
absorb both elements rapidly and their accumulation on
the leaf surfaces in arid climates can result in toxicity
problems (Reed et al., 1995).
Sodium is not permanently removed in the soil but is
rather involved in the soil cation exchange process.
These reactions are similar to those occurring in water
softening processes and involve sodium, magnesium,
and calcium. In some cases, where there is an excess
of sodium with respect to calcium and magnesium in the
water applied to high clay content soils, there can be an
adverse effect on soil structure. The resulting
deflocculation and swelling of clay particles can
significantly reduce the hydraulic capacity of the soil.
The relationship between sodium, calcium, and
manganese is expressed as the Sodium Adsorption
Ratio (SAR) as defined by Equation 2-4.
SAR = (Na)/[(Ca + Mg)/2]'
(2-4)
Where:
SAR
Na
Ca
Mg
Sodium adsorption ratio
Sodium concentration, milliequivalents/L
Calcium concentration, milliequivalents/L
Magnesium concentration, milliequivalents/L
A SAR of 10 or less should be acceptable on soils with
significant clay content (15 percent clay or greater).
Soils with little clay, or non-swelling clays can tolerate an
SAR up to 20. It is unlikely that problems of this type will
occur with application of municipal effluents in any
climate since the SAR of typical effluents seldom
exceeds 5 to 8. Industrial wastewaters can be of more
concern. The washwater from ion exchange water
softening could have an SAR of 50, and some food
processing effluents range from about 30 to over 90. As
discussed in Chapter 4, SAR problems are affected by
the TDS of the wastewater, with more adverse effects
occurring with low TDS water. Many western states have
recommended irrigation water quality for SAR and EC.
Local state agricultural universities should be consulted.
The common remedial measure for SAR induced soil
swelling or permeability loss is the surface application of
gypsum or another inexpensive source of calcium. The
addition of water allows the calcium to leach into the soil
to exchange with the sodium. An additional volume of
water is then required to leach out the salt solution.
2.11 Macronutrients and Micronutrients
Most plants also require magnesium, calcium, and
sulfur, and depending on soil characteristics, there may
be deficiencies in some locations. Other micronutrients
important for plant growth include iron, manganese, zinc,
boron, copper, molybdenum and nickel. Generally, there
is a sufficient amount of these elements in municipal
-------
wastewaters, and in some cases an excess can lead to
phytotoxicity problems.
2.11.1 Sulfur
Sulfur is usually present in most wastewaters either in
the sulfate or sulfite form. The source can be either
waste constituents or background levels in the
community water supply.Sulfate is not strongly retained
in the soil but is usually found in the soil solution.
Sulfates are not typically present in high enough
concentrations in municipal wastewaters to be a concern
for design of land treatment systems. Secondary
drinking water standards limit sulfate to 250 mg/L,
irrigation standards recommend 200 to 600 mg/L
depending on the type of vegetation. Industrial
wastewaters from sugar refining, petroleum refining, and
Kraft process paper mills might all have sulfate or sulfite
concentrations requiring special consideration. Crop
uptake accounts for most sulfur removal with the low
levels in municipal wastewater.
If sulfur is the LDP, then the design procedure is similar
to that described previously for nitrogen. It is prudent to
assume that all of the sulfur compounds applied to the
land will be mineralized to sulfate. The 250 mg/L
standard for drinking water sulfate would then apply at
the project boundary when drinking water aquifers are
involved. It should be assumed in sizing the system that
the major permanent removal pathway is to the
harvested crop and the values in Table 2-12 can be
used for estimating purposes. If industrial wastes have
particularly high organic contents there may be
additional immobilization of sulfur. It is recommended
that specific pilot tests be run for industrial wastewaters
of concern to determine the potential for removal under
site specific conditions.
2.11.2 Boron
Boron is an essential micronutrient for plants but
becomes toxic at relatively low concentrations
(<1 mg/L) for sensitive plants. The soil has some
Example 2.6 Sodium Adsorption Ratio
Conditions: A municipal effluent with: Na 50 mg/L, Ca15
mg/L, Mg 5 mg/L
Find: The SAR of this effluent.
Solution: Atomic weights: Na = 22.99, Ca = 40.08,
Mg = 24.32
Meq Na = (1)(50 mg/L)/(22.99) = 2.17
Meq Ca = (2)(15 mg/L)/(40.08) = 0.75
Meq Mg = (2)(5 mg/L)/(24.32) = 0.41
SAR = (2.17)/[(0.75 + 0.41)/2]°5 = 2.85
Table 2-12. Sulfur Uptake by Selected Crops
Crop
Corn
Wheat
Barley
Alfalfa
Clover
Coastal Bermuda grass
Orchard grass
Cotton
Harvested mass
Metric As
tons/ha noted
12.5 200bu/ac
5.6 83 bu/ac
5.4 100 bu/ac
13.4 6ton/ac
9.0 4 ton/ac
22.4 10 ton/ac
15.7 7 ton/ac
1.3(USA) 2.5
bale/ac
Sulfur removed
(kg/ha) Ibs/ac
49
25
28
34
20
50
56
26
43.8
22.3
25
30.4
17.9
44.6
50
23.2
adsorptive capacity for boron if aluminum and iron
oxides are present. The soil reactions are similar to
those described previously for phosphorus but the
capacity for boron is low. A conservative design
approach assumes that any boron not taken up by the
plant is available for percolation to the groundwater.
Plant uptake of boron in corn silage of about 0.006
kg/ha»yr (0.005 lb/ac»yr) and in alfalfa of 0.91 to 1.8
kg/ha»yr (0.81 to 1.6 lb/ac»yr) have been reported
(Overcash and Pal, 1979). At the SR land treatment site
in Mesa, AZ the applied municipal effluent had 0.44
mg/L boron, and the groundwater beneath the site
contained 0.6 mg/L. At another SR operation at
Camarillo, CA the wastewater boron was 0.85 mg/L and
the groundwater beneath the site was 1.14 mg/L. The
increase in boron, in both cases, is probably due to
water losses from evapotranspiration. Table 2-13 lists
the boron tolerance of common vegetation types.
Table 2-13. Boron Tolerance of Crops (Reed et al., 1995)
I. Tolerant
Semi-tolerant
Sensitive
Alfalfa
Cotton
Sugar beets
Sweet clover
Turnip
Barley
Corn
Milo
Oats
Tobacco
Wheat
Fruit crops
Nut trees
Industrial wastewaters with 2 to 4 mg/L boron could be
successfully applied to crops in Category I in Table 2-13,
1 to 2 mg/L boron for Category II and less than 1 mg/L
for Category III (Overcash and Pal, 1979). Boron may
not be the LDP for process design and may be the
determinant on which crop to select. Both OF and SAT
systems will be less effective for boron removal than SR
systems because of the same factors discussed
previously for phosphorus. Injection experiments at the
Orange County, CA, groundwater recharge project
injected treated municipal effluent with 0.95 mg/L
boron.After 166 m (545 ft) travel in the soil the boron
concentration was still 0.84 mg/L (Reed, 1972).
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2.11.3 Selenium
Selenium is a micronutrient for animals but is non
essential for plants. However, in high concentrations it is
toxic to animals and birds and many plants can
accumulate selenium to these toxic levels without any
apparent effect on the crop. Plants containing 4 to 5
mg/L selenium are considered toxic to animals (Reed et
al., 1995). Selenium can be adsorbed weakly by the
hydrous iron oxides in soils and this is of more concern
in the southeastern US where soils tend to have very
high iron oxide contents. In arid climates with significant
evaporation, surficial soils can eventually accumulate
toxic levels of selenium as occurred at the famous
Kesterson Marsh in California. Selenium is not likely to
be the LDP for land treatment design with municipal
wastewaters.
2.11.4 Fixed Dissolved Solids
There are a number of potential measurements of
salinity including total dissolved solids (IDS), electrical
conductivity (EC), and fixed dissolved solids (FDS). The
FDS is the more appropriate test for salinity in any
wastewater with a significant portion of volatile dissolved
solids (VDS). For industrial wastewaters (see Chapter
11), FDS is the most appropriate test. Alternatively, the
sum of the inorganic cations and anions can be used as
a measure of salinity.
Salinity problems are of most concern in arid regions
because applied water will be increased in salinity due to
evapotranspiration, and because system design in arid
regions is typically based on applying the minimal
amount of water needed for the crop to grow. The
combination of these factors will result in a rapid build-up
of salts in the soil unless mitigation efforts are applied. A
standard approach is to determine crop water needs and
then add to that a leaching requirement (LR) to ensure
that an adequate volume of water passes through the
root zone to remove excess salts. The LR can be
determined if the salinity or electrical conductivity (EC) of
the irrigation water, and the maximum allowable EC in
the percolate to protect a specific crop are known (Reed
et al., 1995). The salt content of irrigation waters is often
expressed as mg/L of TDS, and can be converted to
conductivity terms (mmho/cm) by dividing mg/L by
0.640. [Note: this relationship is only valid for water with
essentially no volatile dissolved solids.] Equation 2-5 can
be used to estimate the LR.
LR
Where:
LR
EC,
ECD
= [(EC),/(EC)D]x100
(2-5)
= leaching requirement as a percent
= average conductivity of irrigation water (including natural
precipitation), mmho/cm
= required conductivity in drainage water to protect the crop,
mmho/cm
Typical values of ECD for crops without yield reduction
are given in Table 2-14.
Table 2-14. Values of ECD for Crops with No Yield Reduction (Ayers,
1977)
Crop
Electrical Conductivity ECD,
mmho/cm
Bermuda grass
Barley
Sugar beets
Cotton
Wheat
Tall fescue
Soybeans
Corn
Alfalfa
Orchard grass
13
12
10
10
7
7
5
5
4
3
Once the leaching requirement (LR) has been
determined the total water application can then be
calculated with Equation 2-6.
Where:
LW
CU
LR
= (CU)/(1 -LR/100)
= required total water application, inches
= consumptive water use by the crop between water
applications, inches
= leaching requirement (as a percent)
(2-6)
Example 2.7
Leaching Requirement
Conditions: Given a wastewater effluent with 800 mg/L
salinity, corn is the growing crop with ECD = 5
mmho/cm, consumptive use between irrigations
= 3 inches.
Find: The total water requirement.
Solution: Conductivity of the effluent = (800/0.640) =
1.25 mmho/cm
LR = (1.25)/(5)x100 = 25%
Lw = (3)/(1 - 0.25) = 4 inches
A "rule of thumb" for total water needs to prevent salt
buildup in arid climates is to apply the crop needs plus
about 10 to 15 percent. Salinity problems and leaching
requirements are not to be expected for land treatment
systems in the more humid portions of the US because
natural precipitation is higher and higher hydraulic
loadings are typically used to minimize the land area
required.
2.12 Trace Organics
Volatilization, adsorption, and then biodegradation are
the principal methods for removing trace organic
compounds in land treatment systems. Volatilization can
-------
occur at the water surface of treatment and storage
ponds, and SAT basins, in the water droplets used in
sprinklers, in the water films on OF slopes, and on the
exposed surfaces of biosolids. Adsorption occurs
primarily on the organic matter, such as plant litter and
similar residues, present in the system. Microbial activity
then degrades the biologically degradable adsorbed
materials.
2.12.1 Volatilization
The loss of volatile organics from a water surface can
be described with first order kinetics, since it is assumed
that the concentration in the atmosphere above the
water surface is essentially zero. Equation 2-7 is the
basic kinetic equation and Equation 2-8 can be used to
estimate the "half life" of the contaminant of concern.
C,/C0 =
Where:
C,
Co
KVOL
KM
y
*1/2
Where:
*1/2
(2-7)
concentration at time t, mg/L
concentration at t = 0, mg/L
volatilization mass transfer coefficient, cm/h
= overall volatilization rate coefficient, h"
= depth of liquid, cm
= (0.6930(y)/(KVOL)
= time when concentration Ct = 1/2(C0), h
(2-8)
The volatilization mass transfer coefficient (KM) is a
function of the molecular weight of the contaminant and
the air/water partition coefficient as defined by the
Henry's law constant as shown by Equation 2-9.
KVM = [(Bi)/(y)][(H)/(B2 + H)(M )] (2-9)
Where:
KVM = volatilization mass transfer coefficient, h"
H = Henry's law constant, 105(atm)(m3)(mor1)
M = molecular weight of contaminant of concern, g/mol
B-i, B2 = coefficients specific to system of concern, dimensionless
flow (Reynolds number 100 to 400). The average depth
of flowing water on this slope was about 1.2 cm.
Using a variation of Equation 2-9, Parker and Jenkins
determined the volatilization losses from the droplets at
a low-pressure, large droplet wastewater sprinkler
(Parker and Jenkins, 1986). In this case the y term in the
equation is equal to the average droplet radius; as a
result, their coefficients are only valid for the particular
sprinkler used. Equation 2-10 was developed by Parker
and Jenkins for the organic compounds listed in
Table 2-15.
ln(C,/C0) = 4.535[K'M +11.02x10"4] (2-10)
Table 2-15. Volatile Organic Removal by Wastewater Sprinkling
(Parker and Jenkins, 1986)
Substance
Chloroform
Benzene
Toluene
Chlorobenzene
Bromoform
n-Dichlorobenzene
Pentane
Hexane
Nitrobenzene
m-nitrotoluene
PCB 1242
Napthalene
Phenanthrene
Calculated K'M for Eq. 2-12,
(cm/min)
0.188
0.236
0.220
0.190
0.0987
0.175
0.260
0.239
0.0136
0.0322
0.0734
0.144
0.0218
2.12.2 Adsorption
Sorption of trace organics to the organic matter
present in the land treatment system is thought to be the
primary physicochemical mechanism of removal. The
concentration of the trace organic which is sorbed
relative to that in solution is defined by the partition
coefficient KP which is related to the solubility of the
chemical. This value can be estimated if the octanol-
water partition coefficient K0w and the percentage of
organic carbon in the system are defined. Jenkins, et al.,
1985 determined that sorption of trace organics on an
overland flow slope could be described with first order
kinetics with the rate constant defined by Equation 2-11.
KSORB = (B3/y)[ KOW/(B4
(2-11)
Billing (Dilling, 1977) determined values for a variety of volatile
chlorinated hydrocarbons at a well mixed water surface:
B! =2.211 B2 =0.01042
Jenkins et al (Jenkins et al., 1985) determined values for a number of
volatile organics on an overland flow slope:
B! =0.2563 B2 =5.86x10'4
The coefficients for the overland flow case are much
lower because the movement of water down the slope is
non turbulent and may be considered almost laminar
Where:
KSORB = sorption coefficient, h"1
B3 = coefficient specific to the treatment system
= 0.7309 for the OF system studied
y = depth of water on OF slope, 1.2 cm
KOW = octanol-water partition coefficient
B4 = coefficient specific to the system
= 170.8 for the overland flow system studied
M = molecular weight of the organic chemical, g/mol
In many cases the removal of these organics is due to
a combination of sorption and volatilization. The overall
-------
process rate constant KSv is then the sum of the
coefficients defined with Equations 2-9 and 2-11, with
the combined removal described by Equation 2-12.
C,/C0
Where:
Ksv
C,
Co
(2-12)
= overall rate constant for combined volatilization and
sorption
= KVM + KSORB
= concentration at time t, mg/L (or
= initial concentration, mg/L (or
Table 2-16 presents the physical characteristics of a
number of volatile organics for use in the equations
presented above for volatilization and sorption.
2.12.3 Removal Performance
A number of land treatment systems have been studied
extensively to document the removal of priority pollutant
organic chemicals. This is probably due to the concern
for groundwater contamination. Results from these
studies have generally been positive. The removal
performance for the three major land treatment concepts
is presented in Table 2-17. The removals observed in
the SR systems were after 1.5 m (5 ft) of travel in the
soils specified, and a low pressure, large droplet
sprinkler was used for the applications. The removals
noted for the OF system were measured after a flow on
a terrace about 30 m (100 ft) long, with application via
gated pipe at the top of the slope. The SAT data were
obtained from sampling wells about 200 m (600 ft) down-
gradient of the application basins.
The removals reported in Table 2-17 for SR systems
represent concentrations in the applied wastewater
ranging from 2 to 111 u.g/L, and percolate concentrations
ranging from 0 to 0.4 u.g/L The applied concentrations in
the OF system ranged from 25 to 315 u.g/L and from 0.3
to 16 u.g/L in the OF runoff. At the SAT system influent
concentrations ranged from 3 to 89 u.g/L and the
percolate ranged from 0.1 to 0.9 u.g/L
2.13 Phytoremediation
Phytoremediation involves the use of plants to treat or
stabilize contaminated soils and groundwater (US EPA,
2000). The technology is complex and is only introduced
here. The technology has emerged as a response to the
clean-up efforts for sites contaminated with toxic and
hazardous wastes. Contaminants which have been
successfully remediated with plants include petroleum
hydrocarbons, chlorinated solvents, metals,
radionuclides, and nutrients such as nitrogen and
phosphorus. In 1998 it was estimated by Glass that at
least 200 field remediations or demonstrations have
been completed or are in progress around the world
(Glass, 1999). However, the "remediation" technology as
currently used is not "new" but rather draws on the basic
ecosystem responses and reactions documented in this
and other chapters in this book. The most common
applications depend on the plants to draw contaminated
soil water to the root zone where either microbial activity
or plant uptake of the contaminants provides the desired
removal. Evapotranspiration, during the growing season
provides for movement and elimination of the
contaminated groundwater. Once taken up by the plant
the contaminants are either sequestered in plant
biomass or possibly degraded and metabolized to a
volatile form and transpired. In some cases the plant
roots can also secrete enzymes which contribute to
degradation of the contaminants in the soil.
Obviously, food crops and similar vegetation, which
might become part of the human food chain, are not
used on these remediation sites. Grasses and a number
of tree species are the most common choices. Hybrid
Table 2-16. Physical Characteristics for Selected Organic Chemicals (Reed et al., 1995)
Substance
Chloroform
Benzene
Toluene
Chlorobenzene
Bromoform
m-Dichlorobenzene
Pentane
Hexane
Nitrobenzene
m-nitrotoluene
Diethylphthalate
PCB 1242
Napthalene
Phenanthrene
2,4-Dinitrophenol
KOW
93.3
135
490
692
189
2.4 x 103
1.7x103
7.1 x 103
70.8
282
162
3.8 x 105
2.3 x103
2.2 x 104
34.7
Hb
314
435
515
267
63
360
125,000
170,000
1.9
5.3
0.056
30
36
3.9
0.001
Vapor pressure0
194
95.2
28.4
12.0
5368
2.33
520
154
0.23
0.23
7 x 1 0'4
4x 10"4
8.28 x 1 0'2
2.03 x 1 0'4
-
Md
119
78
92
113
253
147
72
86
122
137
222
26
128
178
184
a. Octanol-water partition coefficient.
d. Molecular weight, g/mol.
b. Henry's law constant, 105 atm(m°/mol) at 20°C and 1 atm.
c. Vapor pressure at 25°C.
-------
Table 2-17. Percent Removal of Organic Chemicals in Land Treatment Systems (Reed et al., 1995)
SR
Substance
Chloroform
Benzene
Toluene
Chlorobenzene
Bromoform
Dibromochloromethane
m-nitrotoluene
PCB 1242
Napthalene
Phenanthrene
Pentachlorophenol
2,4-Dinitrophenol
Nitrobenzene
m-Dichlorobenzene
Pentane
Hexane
Diethylphthalate
Sandy soil
98.57
>99.99
>99.99
99.97
99.93
99.72
>99.99
>99.99
99.98
>99.99
>99.99
a
>99.99
>99.99
>99.99
99.96
a
Silty soil
99.23
>99.99
>99.99
99.98
99.96
99.72
>99.99
>99.99
99.98
>99.99
>99.99
a
>99.99
>99.99
>99.99
99.96
a
OF
96.50
99.00
98.09
98.99
97.43
98.78
94.03
96.46
98.49
99.19
98.06
93.44
88.73
a
a
a
a
SAT
>99.99
99.99
>99.99
>99.99
>99.99
>99.99
a
>99.99
96.15
a
a
a
a
82.27
a
a
90.75
a. Not reported.
Poplar trees have emerged as the most widely used
species. These trees grow faster than other northern
temperate zone trees, they have high rates of water and
nutrient uptake, they are easy to propagate and
establish from stem cuttings, and the large number of
species varieties permit successful use at a variety of
different site conditions. Cottonwood, willow, tulip,
eucalyptus, and fir trees have also been used. Wang, et
al., for example, have demonstrated the successful
removal by hybrid poplar trees (H11-11) of carbon
tetrachloride (15 mg/L in solution) (Wang et al., 1999).
The plant degrades and dechlorinates the carbon
tetrachloride and releases the chloride ions to the soil
and carbon dioxide to the atmosphere.
Indian mustard and maize have been studied for the
removal of metals from contaminated soils (Lombi et al.,
2001). Alfalfa has been used to remediate a fertilizer spill
(Russelleetal., 2001).
2.14 References
Anderson, N. (1976) Notice Paper Number 15,
Legislative Assembly, Victoria, Australia.
Anthony, R.G. (1978) Effects of Municipal Wastewater
Irrigation on Selected Species of A Animals, in:
Proceedings, Land Treatment Symposium, U.S.A.
CRREL, Hanover, NH.
Arnold, R.G., D.D. Quanrad, G. Wilson, P. Fox, B.
Alsmadi, G. Amy, and J. Debroux (1996) The Fate
of Residual Wastewater Organics During Soil-
Aquifer Treatment, presented at: Joint AWWA/WEF
Water Reuse Conference, San Diego, CA.
Arizona State University, University of Arizona,
University of Colorado (1998) Soil Treatability Pilot
Studies to Design and Model Soil Aquifer Treatment
Systems, AWWA Research Foundation, Denver,
CO.
Asano T., Editor (1998) Wastewater Reclamation and
Reuse Vol. 10 Water Quality Management Library,
Technomic Publishing Co., Lancaster, PA.
Ayers, R.S. (1977) Quality of Water for Irrigation, Jour.
Irrigation Division, ASCE, Vol 103(IRZ):135-154,
ASCE, New York, NY.
Bastian, R.K. (1993) Summary of 40CFR Part 503,
Standards for the Use or Disposal of Sewage
Sludge, US EPA, OWM, Washington, DC.
Bausmith, D.S. and R.D. Neufeld (1999) So;7
Biodegradation ofPropylene Glycol Based Aircraft
Deicing Fluids, Jour. WEF, 71(4):459-464.
Bell, R.G. and J.B. Bole (1978) Elimination of Fecal
Coliform Bacteria from Soil Irrigated with Municipal
Sewage Lagoon Effluent, Jour. Envir. Qual. Vol. 7,
193-196.
Burken, J.G., J.L. Schnoor (1996) Phytoremediation:
Plant Uptake ofAtrazine and Role of Root Exudates,
Jour. ASCE EED 122/11 958-963, ASCE, New York,
NY.
Camann, D (1978) Evaluating the Microbiological
Hazard of Wastewater Aerosols, Contract Report
DAMD 17-75-C-5072, US AMBRDL, Ft. Detrick, MD.
Chang, A.C., A.L. Page, and T. Asano (1995)
Developing Human Health-related Chemical
Guidelines for Reclaimed Wastewater and Sewage
Sludge Applications in Agriculture, WHO/EOS/95.20,
World Health Organization, Geneva, 114 pp.
-------
Crites , R.W. (1983) Chapter 9 - Land Treatment,
WPCF MOP FD-7 Nutrient Control, WPCF,
Alexandria, VA.
Crites, R. and G. Tchobanoglous (1998) Small and
Decentralized Wastewater Management Systems,
McGraw Hill Co., New York, NY.
Crites, R.W., S.C. Reed, and R.K. Bastian (2000) Land
Treatment Systems for Municipal and Industrial
Wastes. McGraw-Hill Book Co. New York.
US EPA (1980) Muskegon County Wastewater
Management System, EPA 905/2-80-004, US EPA
RS Kerr Laboratory, Ada, OK.
Dilling, W.L. (1977) Interphase Transfer Processes II,
Evaporation of Chloromethanes, Ethanes,
Ethylenes, Propanes, and Propylenes from Dilute
Aqueous Solutions, Comparisons with Theoretical
Predictions, Environ. Sci. Technol. 11:405-409.
Giggey, M.D., R.W. Crites, and K.A. Brantner (1989)
Spray Irrigation of Treated Septage on Reed
Canarygrass, JWPCF, 61:333-342.
Gilmour, J.T. and M.D. Clark (1988) Nitrogen Release
from Wastewater Sludge: A Site-Specific Approach,
JWPCF, 60:494-498.
Gilmour, J.T., M.D. Clark and S.M. Daniel (1996)
Predicting Long-Term Decomposition of Biosolids
with the Seven Day Test. Jour. Env. Qual., 25:766-
770.
Glass, D.G. (1999) International Activities in
Phytoremediation: Industry and Market Overview,
Phytoremediation and Innovative Strategies for
Specialized Remedial Applications, p 95-100,
Battelle Press, Columbus, OH.
Harrison, R.B., C. Henry, D. Xue, J. Canary, P. Leonard,
and R. King (1997) The Fate of Metals in Land
Application Systems, in: Proceedings "The Forest
Alternative - Principals and Practice of Residuals
Use, University of Washington, Seattle, WA.
Hutchins, S.R., M.B. Thomsom, P.B. Bedient, and C.H.
Ward (1985) Fate of Trace Organics During Land
Application of Municipal Wastewater, Critical Review
Environmental Control, 15(4)355-416.
Jenkins, T.F. and A.J. Palazzo (1981) Wastewater
Treatment by a Slow Rate Land Treatment System,
CRREL Report 81-14, USA CRREL, Hanover, NH.
Jenkins, T.F., D.C. Leggett, L.V. Parker, and J.L.
Oliphant (1985) Trace Organics Removal Kinetics
in Overland Flow Land Treatment, Water Research,
19(6)707-718.
Lance, J.C. and C.P. Gerba (1980) Poliovirus
Movement During High Rate Land Filtration of
Sewage Water, Jour. Env. Qual., 9(1):31-34.
Lombi, E., F.J. Zhao, S.J. Dunham, and S.P. McGrath
(2001) Phytoremediation of Heavy Metal -
Contaminated Soils: Natural Hyperaccumulation
versus Chemically Enhanced Phytoextraction. JEQ,
Vol. 30, pp. 1919-1926.
Overcash, M.R. and D. Pal (1979) Design of Land
Treatment Systems for Industrial Wastes, Ann Arbor
Science, Ann Arbor, Ml.
Page, A.L., T.J. Logan, and J.A. Ryan (1987) Land
Application of Sludge: Food Chain Implications.
Lewis Publishers, Chelsea, Ml.
Parker, L.V. and T.F. Jenkins (1986) Removal of Trace-
Level Organics by Slow-Rate Land Treatment,
Water Research, 20(11)1417-1426.
Reed, S.C. (ed) (1972) Wastewater Management by
Disposal on the Land, Special Report 171, USA
CRREL, Hanover, NH.
Reed, S.C., R.W. Crites and E.J. Middlebrooks (1995)
Natural Systems for Waste Management and
Treatment - Second Edition, McGraw Hill, New York,
NY.
Rowe, D. R. and I. M. Abdel-Magid (1995), Handbook of
Wastewater Reclamation and Reuse, CRC Press,
Inc., 550 pp.
Russelle, M.P., J.F.S Lamb, B.R. Montgomery, D.W.
Elsenheimer, B.S. Miller, and C.P. Vance (2001)
Alfalfa Rapidly Remediates Excess Inorganic
Nitrogen at a Fertilizer Spill Site. JEQ, Vol. 30, pp.
30-36.
Sheikh, B., P. Cort, W. Kirkpatrick, R. Jaques and T.
Asano (1990) Monterey Wastewater Reclamation
Study for Agriculture. Research JWPCF, 62:216-
226, WEF, Alexandria, VA.
Shuval, H.I. and B. Teltch (1979) Hygienic Aspects of
the Dispersion of the Enteric Bacteria and Virus by
Sprinkled Irrigation of Wastewater, in Proceedings of
AWWA Water Reuse Symposium.
Smith, J.W. and R.W. Crites (2001) Rational Method for
the Design of Organic Loading Rates in a Land
Application System. Proceedings of WEFTEC 2001,
Atlanta, GA.
Tchobanoglous, G., F.L. Burton and H.D. Stensel (2002)
Wastewater Engineering, Treatment and Reuse,
Fourth Edition, McGraw-Hill, New York.
US EPA (1972) Oily Waste Disposal by Soil Cultivation,
EPA-R2-72-110, US EPA, Washington, DC.
-------
US EPA (1973) National Academy of Science - National
Academy of Engineering Water Quality Criteria
1972: A Report of the Committee on Water Quality
Criteria. EPA-R3-73-033. Washington, DC.
US EPA (1978) Long Term Effects of Land Application
of Domestic Wastewater - Hoi lister, CA Rapid
Infiltration Site, EPA/600/2-78-084, US EPA,
Cincinnati, OH.
US EPA (1978) Sewage Disposal on Agricultural Soils:
Chemical and Microbiological Implications. EPA-
600/2-78-131a.
US EPA, (1979) Long Term Effects of Land Application
of Domestic Wastewater, Dickinson, ND Slow Rate,
EPA-600/2-79-144, US EPA ORD, Washington, DC.
US EPA (1979) Long Term Effects of Land Application
of Domestic Wastewater - Roswell, NM, EPA 600/2-
79-047, ORD, US EPA Washington, DC.
US EPA (1979) Long Term Effects of Land Application
of Domestic Wastewater - Roswell, NM, EPA 600/2-
79-047, ORD, US EPA Washington, DC.
US EPA (1980) Summary of Long Term Rapid
Infiltration Studies, EPA-600/2-80-165, US EPA R.S.
Kerr Laboratory, Ada, OK.
US EPA (1981) Process Design Manual for Land
Treatment of Municipal Wastewater, EPA-625/1 -81 -
013, US EPA CERI, Cincinnati, OH.
US EPA (1982) Estimating Microorganism Densities in
Aerosols from Spray Irrigation of Wastewater, US
EPA/-600/9-82-003, US EPA, Cincinnati, OH.
US EPA (1984) Process Design Manual Land
Treatment of Municipal Wastewater - Supplement on
Rapid Infiltration and Overland Flow, EPA-625/1 -81-
013a, US EPA CERI, Cincinnati, OH.
US EPA (1985) Health Effects of Land Application of
Municipal Sludge, EPA/600/1-85/015, NTIS #PB86-
19745678, NTIS, Springfield, VA.
US EPA. (1995) Process Design Manual for Land
Application of Sewage Sludge and Domestic
Septage. EPA/625/R-95/001.
US EPA (2000) Introduction to Phytoremediation,
EPA/600/R-99/107. Washington, DC.
Wang, X., L.E. Newman and M.P. Gordon (1999)
Biodegradation of Carbon Tetrachloride by Popular
Trees: Results from Cell culture and field
Experiments, in: Phytoremediation and Innovative
Strategies for Specialized Remedial Applications,
Battelle Press, Columbus, OH.
Witherow, J.L.and B.E. Bledsoe (1983) Algae Removal
by the Overland Flow Process, JWPCF, Vol. 55, No.
10, 1256-1262.
-------
Chapter 3
Water Movement in Soil and Groundwater
The hydraulic capacity of the soil to accept and
transmit water is crucial to the design of soil aquifer
treatment (SAT) systems and important in the design of
most slow rate (SR) systems. The physical and chemical
and microbial properties of soil influence the ability of
water to move through soil. The important hydraulic
factors for SAT and SR treatment systems that are
discussed in this section are infiltration, vertical
permeability (percolation), horizontal permeability,
groundwater mounding, and the relationship between
predicted capacity and actual operating rates.
3.1 Soil Properties
The hydraulics of soil systems are controlled by the
physical, biological, and chemical properties of soil.
Important physical properties include texture, structure,
and soil depth. Chemical characteristics that can be
important include soil pH and buffer capacity, the redox
potential of soil, organic matter, cation exchange
capacity, exchangeable sodium percentage, and
background nutrient levels. Preliminary information on
these soil properties and on soil permeability can be
obtained from the Natural Resources Conservation
Service (NRCS) and its soil surveys and maps.
Soil surveys will normally provide broad scale soil
maps delineating the apparent boundaries of soil series
with the surface texture and slope. A written description
of each soil series provides limited information on
chemical properties, engineering applications,
interpretive and management information, slopes,
drainage, erosion potentials, and general suitability for
most kinds of crops grown in the particular area.
Additional information on soil characteristics and
information regarding the availability of soil surveys can
be obtained directly from the NRCS. The NRCS serves
as the coordinating agency for the National Cooperative
Soil Survey, and as such, cooperates with other
government agencies, universities, the Agricultural
Extension Services, and private consultants in obtaining
and distributing soil survey information. Such information
is valuable in preliminary evaluations for land treatment
systems, but verification at any specific site is critical
and essential in design and permitting. Much of the
NRCS information is available on the Internet at
www,nrcs,usda,gov/technical/efotg including soil survey
information.
3.1.1 Physical Properties
Physical properties of soils relate to the solid particles
of the soil and the manner in which they are aggregated.
Soil texture describes the size and distribution of the soil
particles. The manner in which soil particles are
aggregated is described as the soil structure. Together,
soil texture and structure help determine the ability of the
soil to hold and transport water and air. Soil structure
and texture are important characteristics that relate to
permeability and suitability for land treatment.
Texture
Soil textural classes are defined on the basis of the
relative percentage of the three classes of particle size-
sand, silt, and clay. Sand particles range in size from 2.0
mm to 0.05 mm; silt particles range from 0.05 mm to
0.002 mm; and particles smaller than 0.002 mm are
clay. From the particle size distribution, the Natural
Resources Conservation Service's (NRCS's) textural
class can be determined using the textural triangle
shown in Figure 3-1. Common soil-texture terms and the
relationship to textural class names are listed in Table 3-
1. The particle size classification used by NRCS is the
USDA classification system; others include AASHO,
ASTM, and ISSS.
Fine-textured soils do not drain rapidly and retain large
percentages of water for long periods of time. As a
result, infiltration and percolation are slower and crop
management is more difficult than with more freely
drained soils such as loams. Fine-textured soils are
generally best suited to overland flow systems. Medium-
textured soils exhibit the best balance for wastewater
renovation and drainage. Loam (medium texture) soils
are generally best suited for slow rate systems. Coarse-
textured soils (sandy soils) can accept large quantities of
water and do not retain moisture in the root zone very
long. This feature is important for crops that cannot
withstand prolonged submergence or saturated root
zones. A moderately coarse-textured soil is best for SAT
systems. Coarse-textured soils with a significant silt or
clay content (>10%) are not desirable for SAT systems
because these soils have relatively low permeabilities.
3-1
-------
100,
Percent sand
Figure 3-1. Natural Resources Conservation Service (NRCS) Soil Textural Classes (Nielson et al., 1973).
Table 3-1. Soil Textural Classes and General Terminology Used in
Soil Descriptions
3.2 General terms
3.2.2 Com
mon name
Sandy soils
Loamy soils
Clayey soils
Texture
Coarse
Moderately
coarse
Medium
Moderately fine
Fine
3.2.1 Basic soil textural
class names
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
Structure
Structure refers to the shape and degree of soil
particle aggregation. The pattern of pores and
aggregates defined by soil structure influences water
movement, heat transfer, air movement, and porosity in
soils. If soil aggregates resist disintegration when the
soil is wetted or tilled, it is well structured. The large
pores in well-structured soils conduct water and air,
making well-structured soils desirable for infiltration. A
well-structured soil is generally more permeable than
unstructured material of the same type. SAT systems
are suited for sand or loamy sand.
Soil Depth to Annual High Water Level
Adequate soil depth is needed for retention of
wastewater constituents on soil particles, for plant root
development, and for microbial action. Adequate depth
is also required in SR and SAT systems to separate the
zone of wastewater treatment from the saturated soil
layers. Retention of wastewater constituents, is a
function of residence time of wastewater in the soil.
Residence time depends on the application rate and the
soil permeability.
The type of land treatment process being considered
will determine the minimum acceptable soil depth. For
SR, the soil depth can be 0.6 to 1.5 m (2 to 5 ft),
depending on the soil texture and crop type. For
example, soil depths of 0.3 to 0.6 m (1 to 2 ft) can
support grass or turf, whereas deep rooted crops do
better on soil depths of 1.2 to 1.5 m (4 to 5 ft). Because
soils form in layers, the horizontal layering is important in
assessing soil depth. Forested SR systems can be
established with soil depths of 0.3 m (1 ft) or more.
3-2
-------
The soil depth for SAT should be at least 1.5 m (5 ft)
and preferably 1.5 to 3 m (5 to 10 ft). Overland flow
systems require sufficient soil depth to form slopes that
are uniform and to maintain a vegetative cover. A
finished slope should have a minimum of 0.15 to 0.3 m
(6 to 12 in) of soil depth.
3.1.2 Chemical Properties
Soil chemical properties affect plant growth,
wastewater renovation, and can affect hydraulic
conductivity. Soil pH affects plant growth, bacterial
growth, and retention of elements such as phosphorus in
the soil. Soil pE (redox potential) affects the existence of
oxidized or reduced species of chemical elements in the
soil. Organic matter can improve soil structure and
thereby improve the hydraulic conductivity. Sodium can
reduce the hydraulic conductivity of soil by dispersing
clay particles and destroying the structure that allows
water movement. The chemical properties of soil should
be determined prior to design to evaluate the capacity of
the soil to support plant growth and to renovate
wastewater.
Soil pH and Buffer Capacity
Soil pH has been called the master variable because it
affects chemical, biological, and physical soil properties.
Likewise, soil pH is influenced by many factors such as
precipitation, irrigation water, carbonic acid dissociation,
organic matter, mineral weathering, bio-uptake and
release, aluminum hydroxy polymers, and nitrogen
fertilizers (Sposito, 1989). Soil pH has a significant
influence on the solubility of various compounds, the
activities of microorganisms, and the bonding of ions to
exchange sites. Soil pH can limit crop growth by
influencing the availability of root uptake of elements,
including nutrients and metals. The activity of soil
microorganisms is also affected by pH. Soil pH affects
chemical solubility, biochemical breakdown by
microorganisms, and adsorption to soil particles, thereby
influencing the mobility of chemical constituents in the
soil. Soil physical properties can also be influenced by
soil pH by influencing the dispersion of clays and the
formation of soil aggregates. The soil buffering capacity
is important to prevent drastic fluctuations in soil pH that
can have a detrimental affect on plants and soil
microorganisms. Most buffering is provided by cation
exchange or the gain or loss of H+ ions of pH-dependent
exchange sites on clay and humus particles. The well-
buffered soil would have a higher amount of organic
matter and/or highly charged clay than the moderately
buffered soil (Brady and Weil, 2002). Soil organic matter
has many reactive sites in which hydrogen ions can
associate and dissociate. Exchangeable ions on the
surface of clay minerals and humus can also associate
or dissociate with hydrogen ions. Therefore, the cation
exchange capacity (CEC), the quantity of exchangeable
cations that a particular soil can adsorb, influences the
soil's buffering capacity.
Soil Redox
The redox potential (Eh) of soil is a measure of the
reduction and oxidation states of chemical elements in
soil and affects soil aeration. The redox potential of a
soil is dependent on the presence of oxidizing agents
such as oxygen and pH. Redox potential is measured in
volts with an electrode. The electron activities of
chemical species in soil can also be expressed as pE, a
nondimensional parameter related to Eh by the following
equation:
(3-1)
2.3RT
Where Eh = redox potential in volts
R (universal gas constant) = 8.314 Jmol'V1
T = temperature in Kelvin
F (Faraday constant) = 96,500 coulombs mol"1
2.3 RT/F = 0.059 volts at 25 deg C
pE = hypothetical electron activity
The influence of soil redox on both chemical and
microbial species can greatly affect the mobility of
chemical constituents in the soil as well as wastewater
renovation. In addition, soil pE indirectly affects soil
structure because of the influence on microbial activity.
If a soil is well aerated, oxidized states such as Fe(lll)
and nitrate (NO3~) are dominant. Reduced forms of
elements, such as Fe(ll) and ammonium (NH4+), are
found in poorly aerated soils. Low pE's correspond to
highly reducing species and high pE's to oxidizing
species. The largest pE value observed in the soil
environment is just below +13.0 and the smallest is near
-6.0 (Sposito, 1989). The most important chemical
elements affected by soil redox reactions are carbon,
nitrogen, oxygen, sulfur, manganese, and iron. As the
pE of a soil drops below +11.0, oxygen can be reduced
to water. Below pE +5.0, oxygen is consumed in the
respiration processes of aerobic microorganisms. With
no oxygen present in the soil, nitrate can be reduced at
pE values below +8.0 and nitrate is utilized by
microorganisms as an electron acceptor. Generally,
denitrifying bacteria function in the pE range between
+10 and 0. As the soil pE drops between +7 and +5,
iron and manganese are reduced. Iron reduction does
not occur until oxygen and nitrate are depleted.
Manganese reduction however can proceed in the
presence of nitrate. As the pE decreases below +2.0, a
soil becomes anoxic. Sulfate reduction can occur when
pE is less than 0 and is catalyzed by anaerobic
3-3
-------
microorganisms. Sulfate reducing bacteria do not grow
at pE values above +2.0.
Organic Matter
Soil organic matter (SOM generally only referred to as
OM) contents range from 0.5 to 5 percent on a weight
basis in the surface of mineral soils to 100 percent
organic matter, if fertilizers are added (Sparks, 1995).
The organic content of soil influences the structure and
formation of soil aggregates. Water retention of the soil
is increased by organic matter because the infiltration
rate and water holding capacity of the soil is increased
through improved soil structure. Organic matter provides
the energy substrate for soil microorganisms, which in
turn aid in the formation of aggregates. Decaying
organic matter (humic substances) reacts with silicate
clay particles and iron and aluminum oxides and form
bridges between soil particles. In addition, the pH and
buffer capacity of a soil is influenced by organic matter
content.
Soil organic matter has a high specific surface area
and the majority of the surface soil cation exchange
capacity (CEC) is attributed to SOM. Because of the
large amount of surface sites, organic matter is an
important sorbent of plant nutrients, metal cations, and
organic chemicals. The uptake and availability of plant
nutrients, particularly micronutrients, is greatly affected
by soil organic matter. Organic matter also forms stable
complexes with polyvalent cations such as Fe3+, Cu2+,
Ca2+, Mn2+, and Zn2+, and decreases the uptake of
metals by plants and the mobility of metals in the soil.
Salinity and Exchangeable Sodium Percentage
Soil salinity and sodicity (high sodium content) can
have a major effect on the structure of soils. Salinity, the
concentration of soluble ionic substances, affects plant
growth primarily in the soil root zone. Electrical
conductivity (EC) is a measure of soil salinity. Guidelines
exist for controlling root zone salinity and calculating
leaching requirements of applied irrigation water for
varying types of crops according to salt tolerance. High
levels of salinity in the root zone of crops can reduce the
ability of plants to move water from the soil through the
plant.
Soils containing excessive exchangeable sodium are
termed "sodic" or "alkali." A soil is considered sodic if the
percentage of the CEC occupied by sodium, the
exchangeable sodium percentage (ESP), exceeds 15
percent. If a soil has high quantities of sodium and the
EC is low, soil permeability, hydraulic conductivity, and
the infiltration rate is decreased due to the swelling and
dispersion of clays and slaking of aggregates (Sparks,
1995). Fine-textured soils may be affected at an ESP
above 10 percent, but coarse-textured soil may not be
damaged until the ESP reaches about 20 percent.
3.2 Water Movement through Soil
Estimates of the hydraulic properties of the site are
crucial to designing land treatment systems. The
capacity of the soils to accept and transmit water is
important for the design of SAT systems and may be
limiting in the design of SR systems. Water movement in
soil can be characterized as either saturated flow or
unsaturated flow.
3.2.1 Infiltration Rate
The rate at which water enters the soil surface,
measured in millimeters per hour (mm/hr) or inches per
hour (in/hr), is the infiltration rate. The infiltration rate is
usually higher at the beginning of water application than
it is several hours later. Infiltration rates are related to
the extent of large, interconnected pore spaces in the
soil. Coarse textured soils with many large pores have
higher infiltration rates than fine textured-soils or soils in
which the pore space is reduced in size by compaction
or a breakdown of soil aggregates.
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
drier the deeper layer of soil, the larger the potential
gradient between the wetting front and the soil beneath,
and hence the more rapid the intake rate (Withers and
Vipond, 1987). 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 rate.
Infiltration rates are affected by the ionic composition
of the soil-water, the type of vegetation, the rate and
duration of water application, 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 wetting event (Jarrett and Fritton, 1978) (Parr
and Bertran, 1960). 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, requiring reliance on field-developed
correlations between clean water infiltration rates and
satisfactory operating rates for full-scale systems.
Generally, whenever water is ponded over the soil
surface, the rate of water application exceeds the soil
3-4
-------
infiltration or permeability. It should be recognized that
good soil management practices can maintain or even
increase operating rates, whereas poor practices can
lead to substantial decreases.
Techniques for measuring soil infiltration rate in the
field are discussed in Section 3.8.1. Infiltration rates can
also be estimated with the use of simple mathematical
models. The US EPA funded research for the
determination of methods based on soil physics to
quantify the rate of soil water movement due to
infiltration. The three types of methods are divided into
empirical models (examples are Kostiakov and Morton),
and Mechanistic Approaches such as Green-Ampt
models, and Richards equation models, and the Philips
model (an analytical solution to the Richards equation).
Evaluations of selected models under different site
conditions were also conducted (US EPA 1998; US
EPA, 1998).
3.2.2 Intake
The rate at which water in a furrow enters the soil is
referred to as the intake rate (Hansen et al., 1980).
Irrigation texts have used the term "basic intake rate" as
synonymous with infiltration rate (Pair et al., 1975). In
furrow irrigation the intake rate is influenced by the
furrow size and shape. Therefore, when the
configuration of the soil surface influences the rate of
water entry, the term intake rate should be used rather
than the term infiltration rate (which refers to a relatively
level surface covered with water).
3.2.3 Permeability
The permeability or hydraulic conductivity (used
interchangeably in this manual) is the velocity of flow
caused by a unit hydraulic gradient. Permeability is an
intrinsic soil property, not influenced by the gradient, and
this is an important difference between infiltration and
permeability.
Vertical permeability is also known as percolation.
Lateral flow is a function of the gradient and the
horizontal permeability (which is generally different from
the percolation rate). Permeability is affected mostly by
the soil physical properties. Changes in water
temperature can affect permeability slightly (Hansen et
al., 1980).
3.2.4 Transmissivity
Transmissivity of an aquifer is the product of the
permeability (K) and the aquifer thickness. It is the rate
at which water is transmitted through a unit width of
aquifer under a unit hydraulic gradient.
3.2.5 Specific Yield
The term specific yield is the volume of water released
from a known volume of saturated soil under the force of
gravity and inherent soil tension (U.S. Department of the
Interior, 1978). The specific yield is also referred to as
the storage coefficient and the drainable voids. The
primary use of specific yield is in aquifer calculations
such as drainage and mound height analyses.
For 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 satisfactory to estimate it from
knowledge of other soil properties, either physical as in
Figure 3-2 (Todd, 1964), or hydraulic as in Figure 3-3
(U.S. Department of the Interior, 1978). To clarify
Figure 3-2, specific retention is equal to the porosity
minus the specific yield.
For fine-textured soils, especially as the water table
moves higher in the profile, the specific yield may not
have a constant value because of capillarity (Childs,
1969) (Duke, 1972). The effect of decreasing specific
yield with increasing water table height can lead to
serious difficulties with mound height analysis.
3.2.6 Water-Holding Capacity
Soil water can be classified as hygroscopic, capillary,
and gravitational. Hygroscopic water is a very thin film
on the surface of soil particles and is not removed by
gravity or by capillary forces. Capillary water is the water
held by surface tension in soil pores against gravity.
Gravitational water is the water that occupies the
larger pores of the soil and will drain by gravity if
favorable drainage is provided (Hansen et al., 1980).
The water-holding capacity of a soil refers to the
condition where the volumetric water content at
saturation is essentially the same as total porosity.
3-5
-------
© LSATURATED"
1/18 1/8 1/4 1/2 1 2 4 8 16 32 64 128 256
Maximum 10% grain size, mm
Figure 3-2. Porosity, Specific Yield, Specific Retention vs. Soil Grain
Size for In situ Consolidated Soils, Coastal Basin, CA (Todd, 1964).
cm / h
30
20
10
8
6
3
0
0
|
/
/
,
/
^
^
JF
_
r^--*
*-*^
^
.
_,, — •
I
4—
i
I
-
"•
- .-
-i— •
— i —
i
1 0.2 0.30.4 0.60.81 2 34 6 8 10 20 30 40 60 80 1
25 0.5 0.8 1 1.6 22.5 58 10 15 2025 50 80 100 1502002
Hydraulic conductivity
Figure 3-3. Specific Yield Vs. Hydraulic Conductivity (Department of
the Interior, 1978).
Soil water can also be classified according to its
availability to plant root systems. As illustrated in Figure
3-4, the maximum available water occurs at saturation
(point 1), when all the pore space is filled with water.
When the soil water drops to point 3, only hygroscopic
water is left, which is mostly unavailable to plants.
^\. Gra\
Gravitational Water
FIELD CAPACITY
Capillary Water
(available water capacity)
(D j PERMANENT WILTING POINT |
^^ Hygrc
\
-------
Table 3-3. Field Estimating of Soil Moisture Content*
Fine texture
No free water after
squeezing, wet,
outline on hand
IIIIIM
Easily ribbons out
between fingers,
has slick feeling
^^0.0-0.6
Forms a ball,
ribbons out
between thumb and
forefinger
0.6-l"2
Somewhat pliable,
will form a ball
when squeezed
1.2-1.9
Hard, baked,
cracked
1 .9-2.5
Medium texture
Same as fine
texture
'I. P-0 IIII1
Forms a very
pliable ball,
sticks readily if
high in clay
0.0-0.5"
Forms a ball,
sometimes
sticks slightly
with pressure
as-i.o
Somewhat
crumbly but hold
together from
pressure
. 1:0-1.5 II
Powdery, dry,
sometimes
slightly crusted
but easily
broken down
into powdery
condition
1.5-2.0
Moderately
coarse
texture
Same as
fine texture
do
Forms
weak ball,
breaks
easily, will
not stick
II°.o:q.4
Tends to
ball under
pressure
but will not
hold
together
6.4-0.8
Appears
dry, will not
form a ball
I 0.8:1.2
Dry, loose,
flows
through
fingers
1.2-1.5
Coarse
texture
Same as fine
texture
0.0
Sticks
together
slightly, may
form a very
weak ball
under
pressure
IlIIO;M-2lZ!
Appears dry,
will not form
a ball when
squeezed
0.2-0.5
Appears dry,
will not form
a ball
0.5-0.8
Dry, loose,
single
grained flows
through
fingers
0.8-1.0
* The numerical values are the amount of water (in) that would be
needed to bring the top foot of soil to field capacity.
3.2.8 Permanent Wilting Point
The soil moisture content at which plants will wilt from
lack of water is known as the permanent wilting point. By
convention, the permanent wilting point for most
cultivated plants is taken to be that amount of water
retained by the soil when the water potential is -15 bars.
The soil will appear to be dusty, but some water remains
in the micopores and in thin films around soil particles.
The available moisture content or plant available water
is generally defined as the difference between the field
capacity and the permanent wilting point (between -0.1
to -0.3 and -15 bars). This represents the moisture that
can be stored in the soil for subsequent use by plants.
The amount of capillary water remaining in the soil that
is unavailable to plants can be substantial, especially in
fine-textured soils and soils high in organic matter. For
SR systems with poorly drained soils, this stored
moisture is important to design loadings.
As an approximation the permanent wilting
percentage can be obtained by dividing the field capacity
by 2. For soils with high silt content, divide the field
capacity by 2.4 to obtain permanent wilting percentage.
3.3 Saturated Hydraulic Conductivity
Saturated flow through soils takes place when soil
pores are completely filled with water. At least part of the
soil profile may be completely saturated under certain
conditions. Hydraulic conductivity is a measure of the
ease with which liquids and gases pass through soil. In
general, water moves through saturated soils or porous
media in accordance with Darcy's equation:
Q ..dH
(3-2)
Where
q = flux of water, the flow, Q per unit cross-sectional area, A, m/d (ft/d)
Q = flow rate, m3/d (ff/d)
A = area of cross-section perpendicular to the flow, m2 (ft2)
K = hydraulic conductivity (permeability), m/d (ft/d)
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 saturation, K may vary overtime 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 uniform soil. The K value for flow in
the vertical direction will not necessarily be equal to K in
the horizontal direction. This condition is known as
anisotropy. It is especially apparent in layered soils and
those with large structural units. An illustration of
anisotropic conditions is shown in Table 3-4.
The value of K depends on the size and number of
pores in the soil or aquifer material. Orders of
magnitudes for vertical conductivity (Kv) values in ft/day
for typical soils are (Bouwer, 1978):
Soil or Aquifer Material
Clay soils (surface)
Deep clay beds
Clay, sand, gravel mixes (till)
Loam soils (surface)
Fine sand
Medium sand
Coarse sand
Sand and gravel mixes
Gravel
Ky. ft/d
0.03-0.06
3x 10'8-0.03
0.003-0.3
0.3-3.0
3-16
16-66
66 - 300
16-330
330 - 3300
The conductivity of soils at saturation is an important
parameter because it is used in Darcy's equation to
3-7
-------
estimate groundwater flow patterns 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
accurate for design purposes (Bouwer, 1978) (Freeze
and Cherry, 1979) (Taylor and Ashcroft, 1972) (Richard,
1965) (O'Neal, 1952). 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 (Bouwer,
1978).
Table 3-4. Measured Ratios of Horizontal to Vertical Conductivity
Site
Horizontal conductivity Kh, m/d (ft/day)
Kh/Kv
Remarks
1
2
3
4
5
6
6
42(138)
75 (246)
56(184)
1 00 (328)
72 (236)
72 (236)
86 (282)
2.0
2.0
4.4
7.0
20.0
10.0
16.0
Silty
Gravelly
Near terminal moraine
Irregular succession of sand and gravel layers (from
measurements in field)
(From analysis of recharge flow system)
K
3.4 Unsaturated Hydraulic Conductivity
Darcy's law for velocity of flow in saturated soils also
applies to unsaturated soils. As the moisture content
decreases, however, the cross-sectional area through
which the flow occurs also decreases and the
conductivity is reduced.
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 flow becomes confined to the 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 loam 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 in medium or fine textured soils after irrigation has
stopped, and why there is little horizontal spreading of
moisture in sandy soils after irrigation.
3.5 Percolation Capacity
The percolation capacity of SR and SAT systems is a
critical parameter in planning, design, and operation.
The capacity will vary within a given site and may
change with time, season and different management.
For planning purposes the infiltration capacity can be
estimated from the vertical permeability rates assigned
by the NRCS (Figure 3-5).
3.5.1 Design Percolation Rate
To account for required intermittent applications
(reaeration), the variability of the actual soil permeability
within a site, and the potential reduction with time, a
small percentage of the vertical permeability is used as
the design percolation rate. This small percentage
ranges from 4 to 10 percent of the saturated vertical
permeability as shown in Figure 3-5. The value used for
clear water permeability should be for the most
restrictive layer in the soil profile. Design rates based on
field measurement (Section 3.8) may be calculated
using different percentages. If the planned application
season is less than 365 days, the percolation rate
should be reduced to coincide with the planned
application period.
3.5.2 Calculation of Vertical Permeability
The rate at which water percolates through soil
depends on the average saturated permeability (K) of
the profile. If the soil is uniform, K is assumed to be
constant with depth. Any differences in measured values
of K are then due to normal variations in the
measurement technique. Thus, average K may be
computed as the arithmetic mean of n samples:
K1+K2+K3+-
Where Kam = arithmetic mean vertical conductivity
(3-3)
3-8
-------
Many soil profiles approximate a layered series of
uniform soils with distinctly different K values, generally
decreasing with depth. For such cases, it can be shown
that average K is represented by the harmonic mean of
the K values from each layer (Bouwer, 1969):
D
(ZA)
K,
Kn
Where
D = overall soil profile depth
dn = depth of nth layer
Kt,m = harmonic mean conductivity
Permeability of most restrictive layer In soil profile
Figure 3-5. Approximate Preliminary Percolation Rate vs. NRCS Soil
Permeability for SR and SAT.
The Zones A through G Refer to Clearwater Permeability for the Most
Restrictive Layer in the Soil Profile (Kv = in/h): A = very slow), <0.06; B
= slow, 0.06 to 0.20; C = moderately slow, 0.20 to 0.60; D = moderate,
0.60 to 2.0; E = moderately rapid, 2.0 to 6.0; F = rapid, 6.0 to 20; G =
very rapid, >20
If a bias or preference for a certain K value is not
indicated by statistical analysis of field test results, a
random distribution of K for a certain layer or soil region
must be assumed. In such cases, it has been shown
that the geometric mean provides the best and most
conservative estimate of the true K (Bouwer, 1969)
(Rogowski, 1972) (Nielson et al., 1973):
rV, = (Ki . K2 . Ks . ...Kn)1/n
Where Kgm = geometric mean conductivity
(3-5)
3.5.3 Profile Drainage
For SR and SAT systems the soil profile must drain
between applications to allow the soil to reaerate. The
time required for profile drainage is important to system
design and varies with the soil texture and the presence
of restrictions (such as fragipans, clay pans, and
hardpans). In sandy soils without vertical restrictions,
the profile can drain in one to two days. In clayey soils
drainage may take five days or more. The drying period
between applications also depends on the evaporation
rate.
3.6 Mounding of Groundwater
If water that infiltrates the soil and percolates vertically
through the zone of aeration (also known as vadose
zone or unsaturated zone) encounters a water table or
an impermeable (or less permeable) layer, a
groundwater "mound" will begin to grow (Figure 3-6).
Soil Surfoce
Wastewoter Application
i
Figure 3-6. Schematic of Groundwater Mound.
If the mound height continues to grow, it may
eventually encroach on the zone of aeration to the point
where renovation capacity is affected. Further growth
may result in intersection of the mound with the soil
surface, which will reduce infiltration rates. This problem
can usually be identified and analyzed before the system
is designed and built if the prior geologic and hydrologic
information is available for analysis.
3.6.1 Prediction of Mounding
Groundwater mounding can be estimated by applying
heat-flow theory and the Dupuit-Forchheimer
assumptions (Rogowski, 1972). These assumptions are
as follows:
3-9
-------
1. Flow within groundwater 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 groundwater depths at
several existing SAT sites. To compute the height at the
center of the groundwater mound, one must calculate
the values of:
W/[4 a t ]1'2 and Rt
Where W = width of the recharge basin, ft
(3-6)
i.o
0.8
„ 0.6
.«|S
— 0.4
W
Jtat
Figure 3-7. Mounding Curve for Center of a Square Recharge Area
(Bianchi and Muckel, 1970).
a = aquifer constant = ^,ft2/d (3-7)
V
Where:
K = aquifer (horizontal) hydraulic conductivity, ft/d
D = saturated thickness of the aquifer, ft
V = specific yield or fillable pore space of the soil, ft3/ft3
t = length of wastewater application, d
R = I/V, ft/d, rate of rise if no lateral flow occurred
where I = application rate, ft/d
Once the value of W/[4at]1/2 is obtained, one can use
dimensionless plots of W/[4at]1/2 versus h0/Rt, provided
as Figure 3-7 (for square recharge areas) and Figure
3-8 (for rectangular recharge areas), to obtain the value
of h0/Rt, where h0 is the rise at the center of the mound.
Using the calculated value of Rt, one can solve for h0.
0.8 -
Figure 3-8. Mounding Curve for Center of a Rectangular recharge
Area, with Different Ratios of Length L to Width W (Bianchi and
Muckel, 1970).
Figure 3-9 (for square recharge areas) and
Figure 3-10 (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/[4 a t]1/2 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 h0/Rt
from the correct plot. Multiplying this number by the
calculated value of Rt results in the rise of the mound,
H0, at a distance x from the center of the recharge site.
The depth to the mound from the soil surface is then the
difference between the distance to the groundwater
before recharge and the rise due to the mound.
To evaluate mounding beneath adjacent basins,
Figure 3-9 and Figure 3-10 should be used to plot
groundwater table mounds as functions of distance from
the center of the plot 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. Additional discussions on groundwater
mounding and predicting mounds is included in
reference (Bouwer, 1999) (Bouwer et al., 1999). At sites
where drainage is critical because of severe land
limitations or extremely high groundwater tables, the
engineer should use the approach described in
reference (Nielson et al., 1973) to evaluate mounding.
3-10
-------
(•*->
Figure 3-9. Rise and Horizontal Spread of a Mound Below a Square
Recharge Area (Bianchi and Muckel, 1970).
EdgB of 03oi
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 3.7).
2. If the calculated underdrain spacing is '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.
3.7 Drainage Requirements
Generally, underdrains are spaced 15 m (50 ft) or
more apart. Depths of drains vary from 0.9 to 2.4 m (3
to 8 ft) for SR systems and 2.4 to 4.6 m (8 to 15 ft) for
SAT systems. In soils with high lateral permeability, the
underdrains may be as much as 150 m (500 ft) apart.
The closer the drain spacing is, the more control there
will be over depth of the groundwater table. The cost of
drains increases with decreasing drain spacing, so the
economics of using more drains must be weighed
against finding a site with deeper groundwater, or less
vertical restriction to percolation, or using a lower
application rate.
One method of determining drain spacing is the
Hooghhoudt method. The parameters used in the
method are shown in Figure 3-11. The assumptions
used in this method are (Luthin, 1978):
Figure 3-10. Rise and Horizontal Spread of Mounds Below a
Rectangular Recharge Area when L = 2W (Bianchi and Muckel, 1970).
3-11
-------
Hydraulic loading rate Lw •*> P
I M i M I I
Soil surface
Impermeable layer
Figure 3-11. Parameters Used in Drain Design (Luthin, 1978).
1. The soil is homogeneous with a lateral permeability,
K.
2. The drains are evenly spaced a distance S apart.
3. The hydraulic gradient at any point is equal to the
slope of the water table above that point.
4. Darcy's Law is valid.
5. An impermeable layer underlies the drain at a depth
d.
6. The rate of replenishment (wastewater application
plus natural precipitation) is Lw + P.
To determine drain placement, the following equation is
useful (Luthin, 1978):
(3-8)
where S = drain space, 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)
Lw = 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.)
Once the drain spacing has been calculated, drain
sizing should be determined. Usually, 150 or 200 mm (6
or 8 in) drainage laterals are used. The laterals connect
to a collector main that must be sized to convey the
expected drainage flow. Drainage laterals should be
placed so that they will be free flowing; the engineer
should check drainage hydraulics to determine
necessary drain slopes. The outlet conditions associated
with drainage are critical and, once established, must
not be modified.
3.8 Field Testing Procedures
Field testing procedures for measuring and estimating
the infiltration rate and permeability of a soil are
summarized in this section.
3.8.1 Infiltration Rate
The infiltration rate of a soil is defined as the rate at
which water enters the soil from the surface. When the
soil profile is saturated with negligible ponding above the
surface, the infiltration rate is equal to the effective
saturated conductivity of the soil profile.
Although the measured infiltration rate on a particular
site may decrease in time due to surface clogging
phenomena, the subsurface vertical permeability at
saturation will generally remain constant. 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.
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
infiltration including flooding basin, cylinder
infiltrometers, sprinkler infiltrometers and air-entry
permeameters. A comparison of these four techniques
is presented in Table 3-5. 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 flooding (ponding over
the soil surface) and rainfall simulators (sprinkling
infiltrometer). The flooding type of infiltrometer supplies
water to the soil without impact, whereas the sprinkler
infiltrometer provides 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. The sprinkler test is
especially useful for agricultural SR operations. As
discussed previously, soil sorting and surface sealing
can occur with some soils and a sprinkler test will
evaluate the possibility. Sprinkler tests are not really
needed for grassed or forested sites or where surface
application of wastewater is anticipated.
3-12
-------
Because the basic intent of all these tests is to define
the saturated vertical hydraulic conductivity of the soil
(Kv), and since wastewater will typically be "clean" after
a few inches of travel, it is usually acceptable to use
clean water for these tests. There are exceptions, and
the actual wastewater should be used when:
1. High suspended solids or algae are expected in
effluents used for SAT.
2. Industrial effluents with significantly different pH or
ionic composition than the soil and soil water.
3. Effluents that will contain toxic or hazardous
materials with potential for reaction with the soil
components.
Basin Tests
All infiltration tests should always be run at the actual
locations and depths that will be used for the operational
system. This is especially important for SAT systems.
Pilot-scale basin tests are strongly recommended.
These should be at least 9.3 m2 (100 ft2) in area, located
in the same soil zone that will be used in the full-scale
system. Construction of the test basin should be done
with the same techniques that will be employed full
scale. The test basin should then be operated for
Table 3-5. Comparison of Infiltration Measurement Techniques
several weeks using the same wet and dry cycles that
are planned for full scale. A typical small-scale pilot test
basin is illustrated in Figure 3-12.
The number of test basins required will depend on the
system size and the uniformity of the soils and
topography. One will serve for relatively small systems
with uniform soils. In larger systems a separate basin
should be used for every major soil type, which may
require one basin for every 2-4 ha (5-10 acres) of total
system area. When extremely variable conditions are
encountered, the test basin should be full sized (0.4 to
1.2 ha or 1 to 3 acres) to insure reliability. If successful,
it can then be incorporated into the operational system.
A smaller-scale basin type test has been developed by
the U.S. Army Corps of Engineers (Abele et al., 1980).
The purpose was to have a reproducible procedure with
a larger surface area and zone of influence than existing
infiltrometers and permeameters. The test facility prior
to flooding (note the cylinder infiltrometer in the right
foreground) is illustrated in Figure 3-13. The metal ring is
aluminum flashing and is 3 m (10 ft) in diameter.
Installation details are provided in Figure 3-14 and
Figure 3-15.
Measurement
technique
3.8.3 Flooding
basin
Cylinder infiltrometer
Sprinkler infiltrometer
Air entry permeameter
(AEP)
3.8.2 Water
use
per test, L
2,000-10,000
400-700
1 ,000-1 ,200
10
Time per
test, h
4-12
1-6
1.5-3
0.5-1
Equipment needed
Backhoe or blade
Cylinder or earthen berm
Pump, pressure tank
sprinkler, cans
AEP apparatus,
standpipe with reservoir
Comments
Tensiometers may be used
Should use large-diameter cylinders (3 ft diameter)
(1 meter)
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 conductivities from all soil layers
Figure 3-12. Small-scale Pilot Test Basin (Crites, et. al., 2000).
Figure 3-13. U.S. Army Corps of Engineers (USAGE) Basin Test.
3-13
-------
Groove cutting too!
Handle ,
Center rod
Figure 3-14. Grove Preparation for USAGE Test.
Tsnsiometer
Figure 3-15. Grove Preparation for USAGE Test.
Tensiometers are used in the central part of the test
area to insure that saturated conditions prevail during
the test period. One should be placed in each soil
horizon. In soils lacking well-developed horizons, a
uniform spacing down to about 0.6 m (2 ft) will be
suitable. 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.
Typical test results are illustrated in Figure 3-16. The
"limiting" value of 6.35 mm/h (0.25 in./h) was selected for
design in this case.
0 100 200 300
Elapsed Time (min.)
Figure 3-16. Typical Test Results, USAGE Infiltration Test.
Cylinder Infiltrometers
The equipment setup for a test is shown in
Figure 3-17. To run a test, a metal cylinder is carefully
driven or pushed into the soil to a depth of about 100 to
150 mm (4 to 6 in). Cylinders from 150 to 350 mm (6 to
14 in) diameter have generally been used in practice,
with lengths of about 250 to 300 mm (10 to 12 in).
Lateral flow is minimized by means of "buffer zone"
surrounding the central ring. The buffer zone is
commonly provided by another cylinder 400 to 750 mm
(16 to 30 in) diameter, driven to a depth of 50 to 100 mm
(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 (75 to
100 mm or 3 to 4 in) earthen dikes.
3-14
-------
/• Gauge index
- Engineer's scale
/• Welding rod
Water surface
Ground level
Figure 3-17. Test Installation for Cylinder Infiltrometer.
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.
Test results can be plotted as shown on Figure 3-16
and design values derived. The procedure is relatively
simple and quick and uses a small amount of water. The
test has been commonly used for some time in
agricultural projects and is familiar to most field
investigation firms. However, the small size of the test
limits the zone of influence. A large number of tests
would be required for most situations. An ASTM
standard exists for the test.
Air Entry Permeameters (AEP)
This device, developed by Dr. Herman Bouwer
(Bouwer, 1978) has been successfully used for the
investigation and design of land treatment systems. A
sketch of the device is shown on Figure 3-18 and
Figure 3-19 illustrates the device in use. The cylinder is
steel, about 10 in (250 mm) in diameter and about 5 in
(125 mm) deep. Operating instructions for the unit are:
1. The cylinder is driven into the ground to a depth of 3
to 4 in (75 to 100 mm) (a cylinder driver with sliding
weight is used for this purpose).
2. Using a section of 1-in x 2-in (25 to 50 mm) lumber
and a hammer, the soil along the inner perimeter of
the cylinder is packed down and against the cylinder
3.
4.
wall to insure a good bond between the cylinder and
the soil. In loose or cracked soil, compacting around
the outside of the cylinder may also be necessary.
In case of a bare soil surface, the soil is covered
with a 12.5 to 25 mm (1/2- to 1-in) layer of coarse,
clean sand. A disk or similar object is placed on the
sand in the center of the cylinder to break the water
stream from the supply pipe.
The surface of the foam rubber gasket is cleaned
and a thin coat of grease is applied.
Reservoir
Wet front
Figure 3-18. Definition Sketch for Air Entry Permeameter.
•-,
i \i-rn
Figure 3-19. Air Entry Permeameter in Use (from H. Bouwer).
3-15
-------
5. The lid-assembly with the air valve open and the
gauge and supply valves closed is placed on the
cylinder. The gauge should be properly primed and
air bubbles should not be present in the tubing
connecting the gauge to the cylinder. A round
bubble-level is placed on the lid to determine the
highest point. The lid assembly is then rotated so
that the air escape valve is at the highest point.
6. The lid is fastened with four small C-clamps or
welder's vice-grip pliers until it rests firmly on the rim
of the metal cylinder. Lead weights are placed on
the lid to offset the upward hydrostatic force when
the supply valve is open.
7. The plastic reservoir at the top of the galvanized
pipe is filled with water and the air in the pipe is
allowed to escape. The supply valve at the bottom of
the galvanized pipe is opened while maintaining the
water supply to the plastic reservoir. When the
water has driven out the air from inside the cylinder,
the air valve is closed.
8. The vacuum gauge is removed from the holder and
lifted to about the water level in the plastic reservoir.
The gauge valve at the plastic lid is opened, which
causes the needle on the gauge to go to zero.
Tilting the gauge will then reset the memory pointer
to zero. The gauge valve is closed and the gauge is
replaced on the gauge holder.
9. Time and water level readings are taken so that the
rate of fall of the water level in the reservoir, dH/dt,
(just before closing the supply valve) can be
calculated.
10. When the depth of the wet front is expected to be at
about 100 mm (4 in) the supply valve is closed.
Experience will tell how much or how long water
needs to be applied to achieve this depth.
11. The gauge valve is opened. When the gauge
indicates approximately atmospheric pressure inside
the cylinder, the weights are removed from the
plastic lid.
12. When the memory pointer has lost contact with the
gauge needle, minimum pressure has occurred. As
soon as loss of contact is observed, the memory
pointer is read, the gauge valve is closed, and the
air escape valve is opened. The lid assembly is
removed and the depth of the wet front is measured.
This can be done by pushing a quarter-inch rod into
the soil and observing the depth where the
penetration resistance is considerably increased.
Another way is to quickly remove any remaining
water in the cylinder, taking the cylinder out of the
soil, and digging with a spade to visually determine
the position of the wet front. Dyes and electric-
conductivity probes may also offer possibilities for
wet-front detection. To facilitate accurate
assessment of the depth of the wet front, the soil
should not be too wet at the time of the test.
13. Calculate Pa as:
Pa = Pmin + G + L
(3-9)
Where
Pa = air entry value of soil in inches of water
Pmin = minimum pressure head in inches water as determined by
maximum reading on the vacuum gage
G = height of gage above soil surface, in.
L = depth of wet front, in.
If, for example, the maximum gage reading corresponds to -33 in.
water and L + G = 18 in., Pa is calculated as -14 in. water.
14. Calculate the water entry (air exit) value Pw as 0.5
Pa
15. Calculate the saturated hydraulic conductivity Ks as
2(dHldt)LR? (3-10)
s Ht+L-0.5PaRc
Where
dH/dt = rate of fall of water level in reservoir just before closing
supply valve.
H, = height above soil surface of water level in reservoir when
supply valve is closed.
Rr = radius of plastic reservoir.
Rc = radius of permeameter cylinder
16. Calculate K at zero soil water pressure head for
sorption as 0.5 Ks.
Note: For most agricultural and coarse-textured soils,
Pa numerically will be small compared to Ht. Under those
conditions, Pa is not important and can be taken as zero
(or as some arbitrary small value, for example - 4 in.) in
the above equation. This greatly simplifies the
equipment and the field procedure, since the vacuum
gage and the measurement of minimum pressure inside
the cylinder are then not needed.
The AEP test takes less time and less water than
cylinder infiltrometers, and the simplicity of the test
permits a very large number of repetitions with very
small quantities of water. However, the small size of the
apparatus limits the zone of influence so the results are
only valid for the few inches below the test surface.
Several repetitions with depth will be necessary to
characterize the soil profile at a particular location. A
successful approach is to dig a test pit with a backhoe
with one end of the pit inclined to the surface. Benches
can then be excavated by hand in the different horizons
or at depths of choice and an AEP test run on each
3-16
-------
"step." The bench should be about 3 ft wide. The other
walls of the test pit can then be used for the routine soils
investigations. A combination of test basins on the site,
supplemented by AEP tests in the remaining areas is
recommended as the investigation techniques for most
projects.
3.8.2 Horizontal Hydraulic Conductivity
The groundwater flow path will be parallel to the
hydraulic gradient. In the general situation this is
essentially horizontal, except immediately beneath an
application zone when mounding occurs. The flow of
water will be vertical at the center of the mound and at
an angle parallel to the gradient at the edge of the
mound. The capability of the soil at the edge of the
mound to transmit the applied flow in a lateral direction
in time. The determination of this horizontal conductivity
is therefore essential, particularly for SAT systems.
Most soils are not homogeneous, but rather are at
least somewhat stratified, reflecting deposition or
consolidation patterns. There are often thin layers or
lenses of fine textured material that will impede vertical
flow between highly permeable layers of soil. As a result
the potential for flow in the horizontal direction is often
many times greater than in the vertical direction. In
situations with shallow groundwater or where mounding
or lateral flow are a significant factor for design, it is
necessary to measure the horizontal conductivity (Kh) in
the field.
Auger Hole Test
The auger hole test is the most common and most
useful of the field tests available for determining
horizontal hydraulic conductivity. A hole is bored to a
certain distance below the water table. The water in the
hole is then pumped out. The rate at which the hole
refills is a function of the hydraulic conductivity of the
soil, and the geometry of the hole. It is possible to
calculate the Kh with the measured rate of rise and the
other factors defined on Figure 3-20. The general set up
for the test is shown in Figure 3-21. The equipment
required includes a suitable pump, an auger, a
stopwatch, and a device for measuring the depth of
water in the hole as it rises. In unstable soils a
perforated casing or well screens will be necessary to
maintain an open hole. The Bureau of Reclamation uses
100 mm (4 in) thin wall pipe with 60, 1/8 in by 1-in slots
per ft of length.
Reference Point
3
H
-*— Łr — »-
—
Soil Surface
Water Table ^
-=-
F
W 1
t
)
1
c
\
Q
//////////// Impermeable'Layer'
Figure 3-20. Definition Sketch for Auger Hole Technique.
- Measuring point
- Standard
/ Y
Exhaust hose
Double-acting
diaphragm pump
Static water level
Finish test
Start test
Figure 3-21. Equipment Setup for Auger Hole Test.
The determination of hydraulic conductivity is affected
by the location of the barrier or lower impermeable layer.
In the case where the barrier is at the bottom of the hole,
Kh can be defined as (terms as shown on):
K_=-
15,000r2
(A/
(3-11)
Where
Kt, = horizontal hydraulic conductivity, m/d
r = radius of hole, m
H = initial depth of water in hole, m
H = (D-B)
A = depth (from reference point) to water after pumpout, m
R = depth (from reference point) to water after refill, m
3-17
-------
y = average depth to water in hole during the refill period, m
y = (R-B)- 1/2Ay
Ay = raise of water level in the timed interval At, m
Ay = (A-R)
At = time required to give Ay, s
The more usual case is when the impermeable layer is
some distance below the bottom of the hole; in this case
Kh is given by:
Kh=-
16,667r2
H
(3-12)
All terms as defined previously.
This equation is only valid when:
2 % in < 2r < 5 % in
10 in < H < 80 in
y >0.2H
G> H
y < % H - (D - A)
Measurement of horizontal hydraulic conductivity may
still be necessary in the absence of a groundwater table.
An example might be the presence of fragipan or other
hard pan layers at shallow depth. These would restrict
vertical flow and might result in unacceptable mounding
unless the horizontal conductivity of the overlying
material is suitable. The shallow well pump-in test
described in U.S. Department of the Interior (1978) can
be used in such cases. In effect, it is the reverse of the
auger hole test described above.
3.9 References
Abele, G., H. McKim, B. Brockett, and J. Ingersol (1980)
Infiltration Characteristics of Soils at Apple Valley,
MN. Clarence Cannon Dam, MO., and Deer Creek,
OH., Land Treatment Sites.
Bianchi, W.C. and C. Muckel (1970) Ground-Water
Recharge Hydrology. U.S. Department of
Agriculture, Agricultural Research Service. ARS
41161. December.
Bouwer, H. (1999) Artificial Recharge of Groundwater:
Systems, Design, and Management.
In: Hydraulic Design Handbook. Mays, L.W. (ed.).
Me Graw-Hill, New York, NY.
Bouwer, H., J.T. Back, and J.M. Oliver (1999)
Predicting Infiltration and Ground-Water Mounds for
Artificial Recharge. Journal of Hydrologic
Engineering. October.
Bouwer, H. (1978) Groundwater Hydrology, New York:
McGraw-Hill Book Co.
Bouwer, H. (1969) Planning and Interpreting Soil
Permeability Measurement. Journal Irrigation and
Drainage Div. ASCE 28:391-402.
Brady, N. C. and R.R. Weil (2002) The Nature and
Properties of Soils, Thirteenth Edition. Prentice Hall.
Upper Saddle River, NJ.
Childs, E.G. (1969) An Introduction to the Physical
Basis of Soil Water Phemomena. John Wiley &
Sons, Ltd. London.
Crites, R. W., R. K. Bastian, and S. C. Reed. 2000. Land
Treatment System for Municipal and Industrial
Wastes. McGraw-Hill, New York, NY.
Duke, H.R. (1972) Capillary Properties of Soils -
Influence upon Specific Yield. Transcripts of the
American Society of Agricultural Engineers. 15:688-
691.
Freeze, R.A., and J.A. Cherry (1979) Groundwater.
Prentice-Hall. Englewood Cliffs, NJ.
Hansen, V.E., O.W. Israelson and G.E. Stringham
(1980) Irrigation Principles and Practices, Fourth
Edition. John Wiley & Sons, New York.
Jarrett, A.R. and D.D.Fritton (1978) Effect of Entrapped
Soil Air on Infiltration. Transactions American
Society of Agricultural Engineers. 21:901-906.
Luthin, J. N. (1978) Drainage Engineering, Third
Edition, Water Science and Civil Engineering
Department, University of California - Davis, Robert
E. Krieger Publishing Company, Huntington, NY.
Nielson, D.R., J.W. Biggarand K.T. Erb (1973) Spatial
Variability of Field-Measured Soil-Water Properties.
Hilgardia. 42:215-259.
O'Neal, A.M. (1952) A Key for Evaluating Soil
Permeability by Means of Certain Field Clues.
Proceedings Soil Science Society of America.
16:312-315.
In:
3-18
-------
Pair, C.H. etal. (1975) Sprinkler Irrigation, Fourth
Edition. Sprinkler Irrigation Association, Silver
Spring, MD.
Todd, O.K. (1964) Groundwater. In: Handbook of
Applied Hydrology. Chow, V.T. (Ed.) McGraw-Hill
Book Co., New York.
Parr, J.F. and A.R. Bertran (1960) Water Infiltration into
Soils. In: Advances in Agronomy, Norman, A.G.
(Ed.) Academic Press, New York; pp. 311-363.
Richards, L.A (1965) Physical Condition of Water in
Soil. In: Methods of Soil Analysis. Parti,
Agronomy 9. Black, C.A. (ed.). American Society of
Agronomy, Inc., Madison, Wl. pp. 131-136.
Rogowski, A.S. (1972) Watershed Physics: Soil
Variability Criteria. Water Resources Research
8:1015-1023.
Sparks, D. L (1995) Environmental Soil Chemistry.
Academic Press. San Diego.
Sposito, G. (1989) The Chemistry of Soils. Oxford
University Press, Inc., New York.
Taylor, S.A. and Q.L. Ashcroft (1972) Physical
Edaphology. W.H. Freeman & Co., San Francisco.
U.S. Department of the Interior, Bureau of Reclamation
(1978) Drainage Manual, 1st edition.
US EPA (1998) Estimation of Infiltration Rate in the
Vadose Zone: Compilation of Simple Mathematical
Models. Volume I. U.S. Environmental Protection
Agency, Subsurface Protection and Remediation
Division, National Risk Management Research
Laboratory, Ada, OK 74820. EPA/600/R-97/128a.
US EPA. (1998) Estimation of Infiltration Rate in the
Vadose Zone: Application of Selected Mathematical
Models, Volume II. National Risk Management
Research Laboratory, US EPA, Ada. OK.
EPA/600/R-97/128b.
Withers, B. and S. Vipond (1987) Irrigation Design and
Practice, Second Edition. Cornell University Press,
Ithaca, NY.
3-19
-------
Chapter 4
Role of Plants in Land Treatment
In this chapter the characteristics of crops that affect
their use in land treatment - water use and tolerance,
nutrient uptake, and toxicity concerns - are described.
Guidance on crop selection for each land treatment
process is provided. Crop management aspects of
agricultural, silivicultural, and horticultural crops are also
discussed.
4.1 Vegetation in Land Treatment
The primary role of vegetation in a land treatment
system is to recycle nutrients in the waste into a
harvestable crop, but vegetation plays a distinct role in
each land treatment process. SR also offers an
opportunity for economic return by sale of harvested
crops. In OF vegetation is the support media for
biological activity and is needed for erosion protection.
The grass in OF systems also removes significant
nutrients and slows the flow of wastewater so that
suspended solids can be filtered and settled out of the
flow stream. Vegetation is not typically part of SAT
systems. It can play a role in stabilization of the soil
matrix and can maintain long-term infiltration rates, but
does not appear to have a major impact on treatment
performance for SAT systems.
Plant uptake is not the only form of nutrient
transformation or removal from the soil-plant systems
utilized in land treatment, but plant growth does impact
all mechanisms either directly or indirectly. Municipal
effluent often has an insufficient carbon to nitrogen ratio
to support high rates of denitrification. Plant roots can
supply a source of degradable carbon that can assist
denitrification (Meyer, 2002).
4.2 Evapotranspiration
Evapotranspiration (ET) is the sum of plant
transpiration and evaporation from plant and soil
surfaces. As commonly defined, ET does not include
other components of evaporation or losses such as:
. Deep percolation
. Wind drift
. Droplet evaporation in the air
. Run-off
Sophisticated computer models separate transpiration
and evaporation components of ET. However, more site-
specific data for reference ET are available. Crop ET
based on reference ET adjusted for a specific crop is
sufficiently accurate for water balances and irrigation
scheduling.
4.2.1 Transpiration
Transpiration is the water that passes from the soil into
the plant roots. Less than 1 percent of the water taken
up by plants is actually consumed in the metabolic
activity of the plant (Rosenberg, 1974) the remainder
passes through the plant and leaves by evaporation
through the stomata.
The drier and hotter the air, the higher the transpiration
rate. The drier the soil, the slower the transpiration,
because the water is held tighter to the soil and plants
adjust the stomata to conserve liquid, reducing growth.
A specific plant variety will have a genetic potential to
transpire a certain quantity during the growing season.
The transpiration on a given day depends on the plant
growth stage, weather conditions, the availability of
water, and general plant health. Non-plant based models
used to calculate ET assume transpiration is not
impacted by plant health or water stress.
4.2.2 Evaporation
Evaporation s water converted from liquid to vapor that
does not pass through the plant. Evaporation may occur
from wet soil or plant surfaces. When plants are young,
a large portion of ET is evaporation from the soil surface.
When plants achieve 70 to 80 percent canopy cover, soil
evaporation will increase ET by only 10 to 25 percent.
The increase of ET due to soil evaporation only occurs
immediately after irrigation when the soil surface is wet
(stage 1) as illustrated in Figure 4-1. Actual evaporation
(E) drops off with time, relative to potential evaporation
(Ep) stage 2 in Figure 4-1.
Jj" 0.8
CO
g-0.4
,2
I 0.2
Stage 1
25
50
75 100 125
Time, hours
150
175
200
Figure 4-1. Evaporation from Bare Soil which was Initially Wet
(Hanks, 1992).
Soil evaporation is increased by maintaining moist
surface conditions. Surface or sprinkler irrigation losses
are similar to drip irrigation on a wetted surface area
4-1
-------
basis. However, with drip irrigation a small percentage
of the surface is wet all the time compared to surface
and sprinkler irrigation that has a large percentage of the
area wet for only a small amount of time. The exceptions
are sub-surface drip, which has very little evaporation,
and surface sprinklers with small frequent sprinkler
applications, which can evaporate up to 100 percent of
the applied water. When applications are so small that
only the plant canopy and soil surface is wetted nearly
all the water is lost to evaporation without any infiltration
into the soil. Research is inconclusive whether water
evaporated from the plant surface reduces plant
transpiration requirements.
4.2.3 Calculating ET
Crop evapotranspiration (ETc) is commonly estimated
based on a rigorously defined reference crop
evapotranspiration (ETo) and a crop coefficient (Kc)
representing the specific crop and growth stage.
ETc = ETo-Kc
(4-1)
Crop ETc allows for the calculation of required
irrigation water. The difference between applied water
and ETc is equal to the amount of deep percolation.
Table 4-1 contains a range of expected ETc of a variety
of crops throughout the United States. Further
discussion of ETo and Kc is included in the subsequent
subsections.
Table 4-1. Range of Seasonal Crop Evapotranspiration
Crop
ETc, in
Crop
ETc, in
Alfalfa
Avocado
Barley
Beans
Clover
Corn
Cotton
Deciduous trees
Grains (small)
Grapes
24-74
26-40
15-25
10-20
34-44
15-25
22-37
21-41
12-18
16-35
Grass
Oats
Potatoes
Rice
Sorghum
Soybeans
Sugar beets
Sugarcane
Vegetables
Wheat
18-45
16-25
18-24
20-45
12-26
16-32
18-33
39-59
10-20
16-28
Table 4-2. Selected Examples of Monthly Normal ETo (US EPA, 1981)
In humid regions, ETo is sufficiently accurate to predict
ET for perennial full cover crops. Table 4-2 contains
monthly estimated reference ET values for various
humid and subhumid climates. In areas such as the San
Joaquin Valley of California monthly ET rarely varies
more than 10 percent.
Table 4-3 shows an example of alfalfa and grass ETo
with the corresponding evapotranspiration rates of
various crops.
4.2.4 Reference ET
Reference ET (ETo) is a term used to describe the
evapotranspiration rate from a known surface, such as
grass or alfalfa (alfalfa ETo normal exceeds grass ETo
by 0 to 30 percent). ETo is expressed in either
centimeters or inches. The ETo for an average year is
referred to as normal year ETo.
Rather than measuring the water consumption in the
reference crop, ETo is often calculated from weather
data or pan evaporation. Pan evaporation, as defined by
the U.S. Weather Bureau's Class A pan, is commonly
used for sizing pond systems and therefore, is often
available to engineers designing land application
systems. Pans store more heat than crops and
consequently result in more evaporation. The pan
evaporation is normally higher than ET (10 percent for
humid conditions and 15 percent for dry conditions).
The coefficients in Table 4-4 can be used to convert pan
evaporation to ETo using Equation 4-2.
ETo =
Where, ETo
(4-2)
reference evapotranspiration
pan coefficient (Table 4-4)
pan evaporation
Evaporation pans are difficult to maintain and
numerous weather networks now gather ET data with
models that have been developed over the last 50 years.
The evapotranspiration models are based on different
Centimeters/Month (Inches/Month)
Jan
Feb
Mar
Apr
May
June
July
Aug
Sept
Oct
Nov
Dec
Annual
Paris, TX
0.6
0.6
1.4
2.7
4.0
5.9
6.4
6.5
3.9
2.6
1.1
0.6
36.3
Central, MO
0.3
0.5
1.2
2.6
4.3
5.8
6.8
6.1
4.1
2.5
1.0
0.4
35.6
Jonesboro, GA
0.5
0.5
1.2
2.3
4.4
5.9
6.3
6.0
4.4
2.3
1.0
0.5
35.3
Seabrook, NJ
0.1
0.1
0.8
1.6
3.0
4.6
5.6
5.4
4.0
2.0
0.8
0.1
28.1
Hanover, NH
0.0
0.0
0.0
1.2
3.3
5.2
5.5
4.8
3.0
1.6
0.1
0.0
24.7
Brevard, NC
0.1
0.1
0.8
1.8
3.0
4.1
4.6
4.2
3.0
1.8
0.6
0.1
24.2
4-2
-------
Table 4-3. Example Evapotranspiration Values for Southern San Joaquin Valley of California (Burt, 1995)
Evapotranspiration Rate, Millimeters/Month (Inches/Month)
Month
January
February
March
April
May
June
July
August
September
October
November
December
TOTAL
ETo,
alfalfa
0.88
2.41
3.75
6.19
7.98
9.03
9.32
8.44
6.03
4.55
1.92
0.71
61.2
ETo,
grass
0.69
1.97
3.13
5.24
6.78
7.65
7.92
7.14
5.08
3.75
1.52
0.55
51.4
Alfalfa
Hay
0.73
1.99
3.11
5.11
6.71
7.32
7.80
6.92
5.16
3.63
1.61
0.60
50.7
Cotton
0.48
2.06
6.68
10.03
8.76
4.47
0.77
33.3
Citrus
0.85
1.52
2.32
3.75
4.85
5.06
5.27
4.73
3.57
2.69
1.18
0.38
35.9
Deciduous
orchard w/o
cover drop
1.49
3.63
5.58
6.83
7.59
6.85
4.87
3.02
0.07
40.8
Deciduous
orchard w/
cover drop
0.68
1.98
3.33
5.89
8.10
9.08
9.58
8.41
5.89
3.90
1.58
0.50
58.9
Grape
Vines
0.05
1.16
4.13
6.00
6.72
5.96
3.30
1.22
0.14
28.7
Small Grains
0.41
1.99
3.92
6.37
6.24
0.63
0.09
19.8
Table 4-4. Pan Coefficient for Class A Evaporation Pans Placed in a
Reference Crop Area (Doorenbosand Pruitt, 1977)
Wind, km/h (mi/h)
Relative Humidity, %
Light, <4.5
Moderate, 4.5
Strong, 11-18
Very Strong, >18
Low, <40
0.75
0.70
0.65
0.55
Medium, 40-70
0.85
0.80
0.70
0.60
High, >70
0.85
0.80
0.75
0.65
climatic variables. Relationships were often subject to
rigorous local calibrations, but proved to have limited
global validity. Testing the accuracy of the methods
under a new set of conditions is laborious, time-
consuming and costly, and yet evapotranspiration data
are frequently needed at short notice for project planning
or irrigation scheduling design.
In an effort to meet the need for reliable
evapotranspiration data, the Food and Agriculture
Organization of the United Nations (FAO) published
Irrigation and Drainage Paper No. 24 (Doorenbos and
Pruitt, 1977). The paper presented four methods with
different data needs to calculate the reference crop
evapotranspiration (ETo): the Blaney-Criddle, radiation,
modified Penman, Penman-Monteith and pan
evaporation methods. The modified Penman method
was considered to offer the best results with minimum
possible error in relation to a living grass reference crop.
The Blaney-Criddle method was recommended when
only mean air temperature was available (Jensen et al.,
1973).
The methods reviewed by FAO were calibrated for ten-
day or monthly calculations. The Blaney-Criddle method
was recommended for periods of one month or longer.
Proliferation of remote sensing of climatic data and the
more accurate assessment of crop water use has
revealed weaknesses in the methodologies (Allen et al.,
1998). Deviations from computed to observed values
were often found to exceed ranges indicated by FAO
Paper 24. The modified Penman was frequently found to
overestimate ETo, even by up to 20 percent for low
evaporative conditions. The FAO published Irrigation
and Drainage Paper No. 56 (Allen et al., 1998) and
recommend the FAO Penman-Monteith method as the
sole ETo method for determining reference
evapotranspiration. The FAO Penman-Monteith equation
with 24-hour data produces accurate results (Allen et al.,
1998). The method, the derivation, the required
meteorological data and the corresponding definition of
the reference surface are described in FAO paper 56.
While the Blaney-Criddle is not recommended for
irrigation scheduling it has sufficient accuracy for initial
planning. The Arizona Department of Environmental
Quality uses a water reuse model based on Blaney-
Criddle.
Unless the site is remote, seasonal ETo data are
normally available from the local agricultural extension
offices, Land Grant Universities, or agricultural research
stations. The California Irrigation Management
Information System (CIMIS) operates over 100 weather
stations. CIMIS uses the Modified Penman to define
normal monthly ETo and daily ETo. Daily ETo is
available for download via the internet the following
morning. The state climatalogist often will be aware of
such networks. A list of state climatology offices is
included in Appendix A.
4.2.5 Crop Coefficients
Crop coefficients (Kc) are determined by the ratio of
the measured ETc and ETo. The derived Kc is a
dimensionless number (usually between 0.1 and 1.2)
that is multiplied by the ETo value to arrive at a crop ET
(ETc) estimate. Because of the method of calculation,
4-3
-------
Kc is dependent on the reference ETo used in the
calculation. Crop coefficients vary by crop, stage of
growth, and by climate. Care should be used to match
the Kc to the proper ETo. Local agricultural extension
offices have Kc values for crops commonly grown in
their area.
Crop coefficients change based on the growth stage of
the plant and are commonly divided into four growth
stages. Table 4-5 shows the estimated length of growth
stages for various crops.
1 Initial growth stage (10 percent ground cover)
2 Crop-development (up to 80 percent groundcover)
3 Midseason stage (effective full groundcover)
4 Late-season stage (full maturity until harvest)
If local crop coefficients are not available, estimates
from Table 4-6 and Table 4-7 can be used. The
reference ETo in Tables 4-6 and 4-7 is calculated from
FAO modified Penman-Montieth. Coefficients for annual
crops (row crops) will vary widely through the season,
with a small coefficient in the early stages of the crop
(when the crop is just a seedling) to a large coefficient
when the crop is at full cover (the soil completely
shaded). Orchards with cover crops between tree rows
will have larger coefficients than orchards without cover
crops.
4.3 Plant Selection
Varieties (cultivars) of major grain, food, and fiber
crops are bred specifically for different regions of the
United States because of differences in growing
seasons, moisture availability, soil type, winter
temperatures, and incidence of plant diseases.
Otherregional issues include infrastructure for post-
harvest processing and demand for harvested products.
A regional approach, therefore, is recommended for
selection and management of vegetation at land
treatment sites (Jensen et al., 1973). One of the easiest
methods for determining regional compatibility is to
investigate the surrounding plant systems. Once regional
issues are considered, the final criteria should be based
Table 4-6. Crop Coefficient, Kc, for Midseason and Late
Conditions (Doorenbos and Pruitt, 1977)
Crop Crop stage Kc Humid3
Alfalfa0
Barley
Clover
Corn
Cotton
Grain
Grapes
Oats
Pasture grass
Rice
Sorghum
Soybeans
Sugar beets
Wheat
1-4
3
4
1-4
3
4
3
4
3
4
3
4
3
4
1-4
3
3
4
3
4
3
4
3
4
0.85
1.05
0.25
1.00
1.05
0.55
1.05
0.65
1.05
0.30
0.80
0.65
1.05
0.25
0.95
1.1
1.00
0.50
1.00
0.45
1.05
0.90
1.05
0.25
Season
KcDry"
0.95
1.15
0.20
1.05
1.15
0.60
1.20
0.65
1.15
0.25
0.90
0.70
1.15
0.20
1.00
1.25
1.10
0.55
1.10
0.45
1.15
1.00
1.15
0.20
a Humidity 70 percent, light wind 0-16 mi/h.
"Humidity 20 percent, light wind 0-16 mi/h.
c Peak factors are 1.05 for humid conditions and 1.15 for dry conditions.
on nutrient uptake, compatibility with hydraulic loading
(quantity and timing), and salt tolerance.
4.3.1 Nutrients
Historically, EPA Design Manuals have presented
nutrient management as a simple load per acre
determination. The recommended loading did not
consider the site specific nutrient requirements of a crop.
The description that follows is intended to add a
component of comprehensive nutrient management to
the EPA guidelines on wastewater irrigation and reuse.
Crop nutrient additions should be based on the
development of a nutrient management plan (NMP). A
NMP is a pollution prevention plan applied to agricultural
Table 4-5. Length of Four Crop Growth Stages for Typical Annual Crops (Doorenbos and Pruitt, 1977)
Growth Stage (Days)
Crop
Barley
Corn
Cotton
Grain, small
Sorghum
Soybeans
Sugar beets
1
15
20-30
30
20-25
20
20
25-45
2
20-30
35-50
50
30-35
30-35
30-35
35-60
3
50-65
40-60
55-60
60-65
40-45
60
50-80
4
30-40
30-40
45-55
40
30
25
30-50
4-4
-------
Table 4-5. Crop Coefficient, Kc, for Perennial Forage Crops
(Doorenbos and Pruitt, 1977)
Condition
Crop
Alfalfa
Minimum
Mean
Peak
Grass for hay
Minimum
Mean
Peak
Clover, grass legumes
Minimum
Mean
Peak
Pasture
Minimum
Mean
Peak
Kc
Humid, light
to moderate
wind
0.50
0.85
1.05
0.60
0.80
1.05
0.55
1.00
1.05
0.55
0.95
1.05
Kc
Dry, light to
moderate wind
0.40
0.95
1.15
0.55
0.90
1.10
0.55
1.05
1.15
0.50
1.00
1.10
Kc (minimum) represents conditions just after cutting.
Kc (mean) represents value between cuttings.
Kc (peak) represents conditions before harvesting under
dry soil conditions. Under wet conditions increase values
by 30 percent.
and silvicultural operations. The elements of a NMP
include:
1. Site maps, including a soil map
2. Location and description of sensitive resource areas
3. Soil, plant, water, and organic material sample
analysis results
4. Current and planned crop production sequence or
crop rotation
5. Expected yield
6. Quantification of all nutrient sources available
7. A nutrient budget for the crop rotation being planned
8. Recommended rates, timing, and method of nutrient
application
9. Operation and maintenance of the nutrient
management plan
Crop yields are measured in units of production.
Typically yields for crops such as soybeans, corn and
other grain crops are expressed in bushels per acre
while forage crop yields are expressed as pounds per
acre. Bushel is a volumetric unit (30.3 L/bu) and the
mass per bushel varies with the crop. Yield-based
uptake of N, P, and K for various crops is presented in
Table 4-8.
The specific yield expected for a site can be estimated
from soil information available from the NRCS or from
local offices of the Cooperative Extension Service.
Responsible farm operators, as a part of normal
production records, will develop accurate measures of
crop yield. Crop nutrient requirements are based on an
assessment of realistic yield estimates of the receiver
site.
A key component of a comprehensive nutrient
management plan is to balance the required level of
those nutrients necessary for plant growth with the
nutrient loading from the wastewater and subsequent
nutrient losses. Insufficient levels of plant nutrient will
result in deficiencies in crop quality and reduced crop
yield while the over-application of nutrients may result in
adverse environmental impact. The relationship of
nutrient availability to yield is non-linear. If the nitrogen
loading is reduced to half of the expected uptake, it can
not be assumed that half the uptake will result. The
actual yield and nutrient uptake will be a function of the
initial soil reserve and resulting nutrient stress. Soil and
tissue analysis are used determine proper nutrient
deficiency and proper nutrient loading.
Plants require 16 essential nutrients to produce
biomass. Wastewater from municipal, industrial and
agricultural sources generally contain many of these
essential nutrients. These nutrients should be applied to
sites at rates to optimize plant production while creating
no adverse environmental conditions. Nutrient
management efforts must consider all nutrients
managed on a site including: soil reserves, nutrient
applications from commercial sources and waste
addition, crop residues, and legume credits.
Nitrogen, phosphorus, and potassium are considered
the essential macronutrients and are required at
moderately high levels to support a healthy crop.
Nitrogen is particularly sensitive because of the potential
for this nutrient to migrate through the root zone of plants
and to groundwater. Recently regulatory agencies are
beginning to consider phosphorus as a limiting nutrient
because of the potential to exit a site with runoff. Any
wastewater treatment operation should include a nutrient
management plan that incorporates plans for
management of nitrogen, phosphorus, and potassium.
Table 4-6. Yield Based N, P, and K Uptake of Various Crops
Typical Yield/acre-yr
Percent of Dry Harvested Material
Grain Crops
Barley
Buckwheat
48
48
Plant Part
50 bu
1 Ton straw
30 bu
0.5 Tons straw
N
1.82
0.75
1.65
0.78
P
0.34
0.11
0.31
0.05
K
0.43
1.25
0.45
2.26
4-5
-------
Typical Yield/acre-yr
Percent of Dry Harvested Material
urop ui
Corn
Oats
Rice
Rye
Sorghum
Wheat
Oil Crops
Flax
Oil palm
Peanuts
Rapeseed
Soybeans
Sunflower
Fiber Crops
Cotton
Pulpwood
Forage Crops
Alfalfa
Bahiagrass
Big bluestem
Birdsfoot trefoil
Bluegrass-pasted
Bromegrass
Clover-grass
Dallisgrass
Guineagrass
Bermudagrass
Indiangrass
Lespedeza
Little bluestem
Orchardgrass
Pangolagrass
Paragrass
Red clover
Reed
canarygrass
Ryegrass
Switchgrass
Tall fescue
Timothy
Wheatgrass
Forest
Leaves
Northern hardwoods
Douglas fir
Fruit Crops
Apples
Bananas
Cantaloupe
Grapes
Oranges
Peaches
Pineapple
Tomatoes
ry vveignt ID/DU
56
32
45
56
56
60
56
—
22-30
50
60
25
Plant Part
120bu
4.5 Tons straw
80 bu
2 Tons straw
5,500 Ib
2.5 Tons straw
30 bu
1 .5 Tons straw
60 bu
3 Tons straw
40 bu
1 .5 Tons straw
15 bu
1 .75 Tons straw
22,000 Ib
5 Tons fronds & stems
2,800 Ib
2. 2 Tons vines
35 bu
3 Tons straw
35 bu
2 Tons stover
1,100lb
4 Tons stover
600 Ib. Lint and
1, 000 Ib seeds
burs & stalks
98 cords
bark, branches
4 tons
3 tons
3 tons
3 tons
2 tons
5 tons
6 tons
3 tons
10 tons
8 tons
3 tons
3 tons
3 tons
6 tons
10 tons
10.5 tons
2.5 tons
6.5 tons
5 tons
3 tons
3. 5 tons
2.5 tons
1 ton
50 tons/harvest
76 tons/harvest
12 tons
9,900 Ib.
1 7,500 Ib.
12 tons
54,000 Ib.
15 tons
17 tons
22 tons
N
1.61
1.11
1.95
0.63
1.39
0.60
2.08
0.50
1.67
1.08
2.08
0.67
4.09
1.24
1.13
1.07
3.60
2.33
3.60
4.48
6.25
2.25
3.57
1.50
2.67
1.75
0.12
0.12
2.25
1.27
0.99
2.49
2.91
1.87
1.52
1.92
1.25
1.88
1.00
2.33
1.10
1.47
1.30
0.82
2.00
1.35
1.67
1.15
1.97
1.20
1.42
0.75
0.20
0.16
0.13
0.19
0.22
0.28
0.20
0.12
0.43
0.30
P
0.28
0.20
0.34
0.16
0.24
0.09
0.26
0.12
0.36
0.15
0.62
0.07
0.55
0.11
0.26
0.49
0.17
0.24
0.79
0.43
0.64
0.22
1.71
0.18
0.85
0.22
0.02
0.02
0.22
0.13
0.85
0.22
0.43
0.21
0.27
0.20
0.44
0.19
0.85
0.21
0.85
0.20
0.47
0.39
0.22
0.18
0.27
0.10
0.20
0.22
0.27
0.06
0.02
0.02
0.02
0.09
0.10
0.02
0.03
0.35
0.04
K
0.40
1.34
20.49
1.66
0.23
1.16
0.49
0.69
0.42
1.31
0.52
0.97
0.84
1.75
0.16
1.69
0.50
1.75
0.76
3.37
1.90
1.04
1.11
2.92
0.83
1.45
0.06
0.06
1.87
1.73
1.75
1.82
1.95
2.55
1.69
1.72
1.89
1.40
1.20
1.06
1.45
2.16
1.87
1.59
1.66
1.42
1.90
2.00
1.58
2.68
0.46
0.10
0.16
0.54
0.46
0.50
0.21
0.19
1.68
0.33
Silage Crops
4-6
-------
Crop Dry Weight Ib/bu
Alfalfa haylage (50%dm)
Corn silage (35% dm)
Forage sorghum (30% dm)
Oat haylage (40% dm)
Sorghum-sudan (50% dm)
Sugar Crops
Sugarcane
Sugar beets
Tops
Tobacco
All types
Turf Grass
Bluegrass
Bentgrass
Bermudagrass
Vegetable Crops
Bell peppers
Beans, dry
Cabbage
Carrots
Cassava
Celery
Cucumbers
Lettuce (heads)
Onions
Peas
Potatoes
Snap beans
Sweet corn
Sweet potatoes
Table beets
Wetland Plants
Cattails
Rushes
Saltgrass
Sedges
Water hyacinth
Duckweed
Arrowweed
Phragmites
Typical Yield/acre-yr
Plant Part
10 wet/5 dry
20 wet/7 dry
20 wet/6 dry
10 wet/4 dry
1 0 wet/5 dry
37 tons
20 tons
2,100 Ib.
2 tons
2. 5 tons
4 tons
9 tons
0.5 ton
20 tons
13 tons
7 tons
27 tons
10 tons
14 tons
18 tons
1.5 tons
14.5 tons
3 tons
5.5 tons
7 tons
15 tons
8 tons
1 ton
1 ton
0.8 ton
N
2.79
1.10
1.44
1.60
1.36
0.16
0.20
0.43
3.75
2.91
3.10
1.88
0.40
3.13
0.33
0.19
0.40
0.17
0.20
0.23
0.30
3.68
0.33
0.88
0.89
0.30
0.26
1.02
1.67
1.44
1.79
3.36
2.74
1.83
Percent of Dry Harvested Material
P
0.33
0.25
0.19
0.28
0.16
0.04
0.03
0.04
0.33
0.43
0.41
0.19
0.12
0.45
0.04
0.04
0.13
0.09
0.07
0.08
0.06
0.40
0.06
0.26
0.24
0.04
0.04
0.18
0.27
0.26
3.65
1.00
0.10
K
2.32
1.09
1.02
0.94
1.45
0.37
0.14
1.03
4.98
1.95
2.21
1.40
0.49
0.86
0.27
0.25
0.63
0.45
0.33
0.46
0.22
0.90
0.52
0.96
0.58
0.42
0.28
0.62
0.87
2.13
0.52
Treated wastewater contains many essential nutrients,
but in ratios often inadequate for many plants. The
nutrients often present in treated wastewater include
nitrate nitrogen, ammonium nitrogen, and organic
nitrogen, organic and inorganic phosphorus, potassium,
and others. Prior to developing a nutrient management
plan, the form of nutrient present in a wastestream must
be determined and specific plans must be developed to
assure proper utilization. All crops require a balanced
nutrient input: optimum N:P:K ratios are generally 4:1:2.
If these ratios are not available in wastewater,
adjustments should be made to correct the imbalances.
4.3.2 Agricultural Crops
Common agricultural forage and field crops are
integral to SR process for nitrogen removal. OF systems
require a perennial close-growing grass crop to support
microbial populations. Both systems require crops with
low sensitivity to wastewater constituents and minimum
management requirements.
The highest uptake of nitrogen, phosphorus, and
potassium can generally be achieved by perennial
grasses and legumes. It should be recognized that
whereas legumes normally fix nitrogen from the air, they
will preferentially take up nitrogen from the soil-water
solution 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.
Alfalfa removes nitrogen and potassium in larger
quantities and at a deeper rooting depth than most
agricultural crops as shown in Table 4-7. Corn is an
attractive crop because of the potentially high rate of
economic return as grain or silage. Intercropping is a
method of expanding the nutrient and hydraulic capacity
of a field corn crop system. A dual system of rye
intercropped with corn to maximize the period of nutrient
uptake was studied in Michigan and Minnesota
(Brockway et al., 1982). For such dual corn-ryegrass
cropping systems, rye can be seeded in the standing
corn in August, or after the harvest in September. The
4-7
-------
growth of rye in the spring, before the corn is planted,
allows the early application of high nitrogen wastewater.
While planting the corn, a herbicide can be applied in
strips to kill some rye so that the corn can be seeded in
the killed rows. With the remaining rye absorbing
nitrogen, less is leached during the early growth of the
corn. Alternatively, forage grasses can be intercropped
with 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.
Table 4-7. Typical Effective Rooting Depth of Plants (Burt, 1995)
Plant
Effective rooting depth, m (ft)
Alfalfa
Avocado
Banana
Barley
Beans
Citrus
Corn
Cotton
Deciduous Orchard
Grains, small
Grapes
Grass
Lettuce
Melons
Potatoes
Safflower
Sorghum
Strawberries
Sugarbeet
Sugarcane
Tomatoes
1.2-2.0 (4-6)
0.6-1.0 (2-3)
0.6-1.0 (2-3)
1.0-1.5 (3.5)
0.3-1.0 (1-3)
0.6-1.5 (2-5)
1.0-1.5 (3-5)
1.2-2.0 (4-6)
1.2-2.0 (4-6)
1.0-1.2 (3-4)
1.0-2.0 (3-6)
1.0-1.2 (3-4)
0.3-0.6 (1-2)
0.6-1.0 (2-3)
0.6-1.0 (2-3)
1.5-2.0 (5-6)
1.0-1.5 (3-5)
0.3-0.6 (1-2)
1.0-1.5 (3-5)
1.2-2.0 (4-6)
1.0-1.5 (3-5)
Turf grass
0.2-0.5 (0.5-1.5)
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 summer crops of short season
varieties of soybeans, silage corn, or sorghum and
winter crops of barley, oats, wheat, vetch, or annual
forage grass as a winter crop.
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. However,
any crop, including food crops, may be grown with
reclaimed wastewater after suitable preapplication
treatment. In Monterey, CA, disinfected tertiary effluent
is used to grow lettuce, broccoli, celery, cauliflower, and
artichokes. At the level of treatment achieved at
Monterey, the use of the reclaimed water is more of a
recycled water project than a land treatment. Fewer
metals were found in the reclaimed wastewater than
conventional fertilizers. Because recycled water quality
is similar to that of other water sources, Monterey is not
labeling the produce to indicate that it is grown with
recycled water (Jaques et al.,1999).
The grass crop for OF must have high moisture
tolerance, long growing season, and be suited to the
local climate. A mixture of grasses is generally preferred
over a single species as shown in Table 4-8. The
mixture should contain grasses whose growth
characteristics complement 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 of grasses is
that, due to natural selection, one or two grasses will
often predominate. A successful combination of grasses
has been Reed canarygrass, tall fescue, and ryegrass
(see Table 4-8). In the south and southwest, dallisgrass,
bermudagrass and redtop have also been successful. In
northern climates, substitution of orchardgrass for the
dallisgrass and redtop is recommended.
At Hanover, NH, barnyardgrass invaded the OF slopes
and began to dominate the perennial grasses. Being an
annual grass, when the barnyardgrass died, it left bare
areas that were subject to erosion (Palazzo et al., 1982).
Grasses to be avoided include those sensitive to salt
(like clover) and those that have long slender seed stalks
(Johnson grass and yellow foxtail). In the early stages of
development Johnson grass will provide an effective
cover; however, with maturity the bottom leaves die off
and the habitat for microorganisms becomes reduced.
Nitrogen
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. For planning and nutrient balances, the rate of
nitrogen uptake can be correlated to the rate of plant
transpiration. 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 plant uptake curves
assume that the applied nitrogen exceeds the rate of
uptake (is not limiting growth) and that the applied
nitrogen is plant-available (in the inorganic form).
Some forage crops can have even higher nitrogen
uptakes than those in. Californiagrass, a wetland
4-8
-------
Table 4-8. Grasses Used at Overland Flow Sites (US EPA, 1973)
Site
Type of Grass
Ada, OK.
Carbondale, IL
Davis, CA
Easley, SC.
Hanover, NH
Hunt-Wesson (Davis, CA.)
Campbell Soup Co. (Paris, TX.)
Utica, MS
Annual ryegrass, bermudagrass, and Kentucky 31 fescue
Tall fescue
Fescue and perennial ryegrass
Kentucky 31 fass fescue
Orchardgrass, quackgrass, Reed canarygrass,
perennial ryegrass
Fescue, trefoil, Reed canarygrass
Reed canarygrass, redtop, tall fescue
Reed canarygrass, Kentucky 31 fescue, perennial ryegrass, common bermudagrass
300
I 200
S
"S.
=>
1
Q.
100
Orch ardgrass
Reed Canarygrass
and Corn
Rye and Corn
Corn
L>1 _
Apr
May
Jun
Jul
Months
Aug
Sep
Oct
Figure 4-2. Nitrogen Uptake for Annual and Perennial Crops.
species, widely distributed in the subtropics, was grown
with effluent in Hawaii (Handley, 1981). Mean crop yield
was 96 mt/ha-yr (43 tons/acre-yr and nitrogen uptake
was 2.1 mt/ha-yr (1,870 Ib/acre-yr. The nitrogen crop
uptake for turfgrasses in Tucson (common
bermudagrass overseeded with winter ryegrass) is 0.59
mt/ha-yr (525 Ib/acre-yr) (Pepper, 1981).
Essentially all nitrogen absorbed from the soil by plant
roots is in the inorganic form of either nitrate (NO3) or
ammonium (NH4) Generally young plants absorb
ammonium more readily than nitrate; however, as the
plant ages the reverse is true. Soil conditions that
promote plant growth (warm and well aerated) also
promote the microbial conversion of ammonium to
nitrate. As a result, nitrates are generally more abundant
when growing conditions are most favorable. Once
inside the plant, the majority of the nitrogen is
incorporated into amino acids, the building blocks of
protein. Protein is approximately 16 percent nitrogen by
weight. Nitrogen makes up from 1 to 4 percent of the
plants harvested dry weight.
Phosphorus
Phosphorus is part of the plant genetic material
ribonucleic (RNA) and energy transfer with adenosine
triphosphate (ATP). Phosphorus is available for
absorption by plants from the soil as the orthophosphate
ions (H2PO4~2 and HPO4"3). Aluminum, iron, calcium,
and organic matter quickly bind phosphorus into highly
insoluble compounds. The concentration of
orthophosphate ion in soil solution is commonly less
than 0.05 mg/L, so an equilibrium is established between
the soluble ion and the adsorbed form in soil.
The amount of phosphorus in municipal effluent is
usually higher than plant requirements. Fortunately, the
relative immobility of phosphorus in soil profile allows for
application of phosphorus in excess of crop
requirements.
4-9
-------
Table 4-9. General Effects of Trace Element Toxicity on Common Crops (Kabata-Pendias and Pendias 2000)
Element
Symptoms
Sensitive Crop
Al
As
Cd
Co
Cr
Cu
Fe
Hg
Mn
Mo
Ni
Pb
Rb
Se
Zn
Overall stunting, dark green leaves, purpling of stems, death of leaf tips, and
cora.Np.jd and damaged root system.
Red-brown necrotic spots on old leaves, yellowing and browning of roots,
dIepressed (jjje rjng.
Margin or leaf tip chlorosis, browning of leaf points, decaying growing points, and
wilting and dying-pff of older leaves.
Brown margin of leaves, chlorosis, reddish veins and petioles, curled leaves, and
brown stunted roots.
Interveinal chloriosis in new leaves followed by induced Fe chlorosis and white leaf
m.aI9!,n.s. an™ I'ES..' E
Chlorosis of new leaves, injured root growth.
Dark green leaves followed by induced Fe Chlorosis, thick, short, or barbed-wire
roots, depressed tillering.
Margin and leaf tip necrosis; chlprpticand red-brown points .of leaves.
Dark green foliage, stunted growth of tops and roots, dark brown to purple leaves
of some plants ("bronzing" disease of rice).
Severe stunting of seedlings and roots, leaf chlorosis and browning of leaf points.
Chlorosis and necrotic lesions on old leaves, blackish-brown or red necrotic spots,
accumulation of MnO2 particles in epidermal cells, drying tips of leaves, and
stunted roots.
Xi?!!.9.y!f!i.n.9. PI pi°.yy.n]n.,9 °I !ea.y..e.s..' Depressed ro,?i .9i°.yyt!]>
.
nterveina chlorosis in new eaves, gray-green leaves, and brown and stunted
roots.
bark green leaves, wilting of older leaves, stunted foliage, and brown short roots.
Dark Leaves, stunted I foliage, and increasing amount of shoots.
Interveinal chlorosis or black spots at Se content at about 4 mg/L and complete
bleaching or yellowing of younger leaves at higher Se content; pinkish spots on
roots.
Chlorotic and necrotic leaf tips, interveinai chlorosis in new leaves, retarded growth
of entire plant, injured roots resemble barbed wire. _
Cereals
No specific crop
Cereals, potatoes, tomatoes, cucumbers,
sunflowers, mustard
Legumes (bean, soybean), spinach radish,
carrots, and oats.
No specific crop
No specific crop
Cereals and legumes, spinach, citrus, seedlings,
and gladiolus.
Gladiolus, grapes, fruit trees, and pine trees
Rice and tobacco
Sugarbeets, corn and roses.
Cereals, legumes, potatoes, and cabbage.
Cereals
Cereals
No specific crop
No specific crop
No specific crop
Cereals and spinach.
Potassium
Potassium is used in large amounts by many crops,
but typical wastewater is relatively deficient in this
element. For example, at 15 mg/L, a typical wastewater
contains 40 Ib/acre-ft. In many cases, fertilizer potassium
(or biosolids potassium) may be needed for optimal plant
growth depending on the soil and crop. For soils having
low levels of natural potassium, a relationship has been
developed to estimate potassium loading requirements,
see Equation 2-3 in Chapter 2 (US EPA, 1981).
Micronutrients
In addition to the three major macronutrients, calcium
and sulfur are also macronutrients, and there are many
micronutrients. The micronutrients important to plant
growth (in descending order) are: iron, manganese, zinc,
boron, copper, molybdenum, nickel and occasionally,
sodium, silicon, chloride, and cobalt. Most wastewaters
contain an ample supply of these elements. Symptoms
of trace element toxicity are presented in Table 4-9. The
descriptions should be used to indicate sensitive crops
and diagnoses of toxicity should be confirmed with
tissue analysis. The concentration of these elements in
most municipal wastewaters is well below the toxic level
of all crops; however, phytotoxicity may occur as a result
of long-term accumulation of these elements in the soil.
Salinity
Salts can accumulate in the soil causing osmotic
stress on plants. Osmotic stress caused by salt is similar
to the impact of moisture stress and is amplified as soil
dries. All water has salts. Municipal effluent has an
approximate increase of 150 to 380 mg/L total dissolved
solids (not all inorganic salts) over the source water
depending on what industries also discharge (Metcalf
and Eddy, 1991). Under dry conditions, salts are not
adequately leached out of the root zone and can build up
to cause osmotic stress. Plants that are salt sensitive or
only moderately tolerant show progressive decline in
growth and yields as levels of salinity increase. Figure
4-3 contains salt tolerance of common crops. Some
species are tolerant to salinity, yet sensitive during
germination. It is general practice to use supplemental
water for germination when available.
4-10
-------
PH
Natural biochemical reactions drive the soil pH to a
stable condition. A range of pH between 3 and 11 has
been applied successfully to land treatment systems.
Extended duration of low pH can change the soil fertility
and lead to leaching of metals. When the acidity is
comprised of mostly organic acids, then the water will be
neutralized as the organics are oxidized.
Most field crops grow well in soils with a pH range of
5.5 to 8.0. Some crops, like asparagus or cantaloupes
with a high calcium requirement, prefer a soil pH greater
than 7.0. If the pH of the soil begins to drop, liming is
recommended to return the pH to the desirable range for
crop production. Figure 4-4 shows a range optimal pH
of various crops on a mineral soil. The pH range shown
in Figure 4-4 is that of the soil extract, not the effluent,
which will neutralized in the soil.
Because soil can treat large amounts of organics
acids, it is recommended the pH of wastewater be pH
5.0 and 9.0). Chemical acids and bases used during pH
adjustment will add to the dissolved solids and should be
avoided if salinity is a problem. Organic acids, such as
acetic acid, can be used to reduce pH with out adding to
the fixed dissolved solids, but the organic component will
increase BOD.
4.3.3 Silviculture
Existing forested land or newly planted stands provide
an excellent area for land treatment systems. The most
common forest crops 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 4-10. The growth
response of trees 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 recommendations on
the likely response of selected species.
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 taken up
by the trees. During the initial stages of growth (1 to 2
yr), tree seedlings are establishing a root system;
EC. (dSfm) at 25':C
Barley
fi. Barley hay
u Pe/ennial rye
ft l.i: J'••;:;:.'•'.•.
Birdsfoot trefoil
Beardess wildrye
AlWFa
•Spinach
Tomato
Broccoli
[ Cabbage
Potato
3 S-.WP: COTI
. ".•••. v L'-['i:"..!':j
Lettuce
Rf-\ pepper
Onto)
CiTTOt
Gr»n beans
The indicated sal tolerances apply to the period of rapid plant growth and maturation,
from (he late seeding stage forward. Crops in each category are ranked in order of
decreasing salt tolerance. Width of the bar next to each crop indicates the effect of
increasing salinity on yield. Shading indicates 10, 25, 50. and 100% yield reductions.
Figure 4-3. Effect of Salinity on Growth of Field Crops (USDA, 1992).
Y eld Red:jc:iCTi
Table 4-10. Forested Land Treatment Systems in the United
States (Critesetal., 2000)
Location
Dalton, GA
Clayton, Co., GA
Helen, GA
St. Marys, GA
Mackinaw City, Ml
State College, PA
West Dover, VT
Design Flow, mgd
30.0
19.5
0.02
0.3
0.2
3.0
0.55
Tree Types
Pines
Loblolly pines,
hardwood
Mixed pine and
hardwood
Slash pine
Aspen, birch,
white pine
Mixed hardwood,
pine
Hardwood
balsam, hemlock,
spruce
4-11
-------
biomass production and nutrient uptake are relatively
slow. To prevent leaching of nitrogen to groundwater
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.
Nitrogen Uptake
The estimated annual nitrogen uptake of forest
ecosystems in selected regions of the United States is
presented in Table 4-11. These rates are considered
Herbaceous plants
Alfalfa
Sweet clover
Asparagus
Buffalo grass
Wheatgrass (tall)
Garder beets
Sugar beets
Cauliflower
Letuce
Cantaloupe
Spinach White clovers
Red clovers Carrots
Peas
Cabbage
Kentucky blue grass
Cotton Rice
Timothy Bermuda grass
Barley Tomatoes
Wheat Vetches
Fescue (tall & meadow) Millet
Corn Cow peas
Soybeans Lespedeza
Oats Rye
Alsike clover Buckwheat
Crimson clover
Red top
Potatoes
Bent grass (except creeping)
Fescue (red & sheep's)
Western wheat grass
Tobacco
Poverty grass
eastern gamagrass
Love grass, weeping
Redtop grass
Cassava
Napier grass
4
Trees & shrubs
Walnut
Alder
Eucalyptus
Arborvitae
Currant Tulip tree
Ash Lilac
Beech Yew
Sugar maple Lucaena
Poplar Ponderosa pine
Juniper
Myrtle
elm
Apricot
Red oak
Birch Andromeda
Dogwood Willow oak
Douglas fir Pine oak
Magnolia Red spruce
Oaks Honey Locust
Red cedar Bitter hickery
Hemlock (Canadian)
Cypress
Flowering cheery
Laurel
American holy
Aspen
White spruce
White Scotch pine
Loblolly pine
Black locust
Autumn olive Teaberry
Blueberries Tea
Cranberries Blackjack oak
Azalea Sumac
Rhododendron Birch
white pine Coffee
Red pine
(
Strongly acid
and very strongly
acid' soils
..„
*
Soil pH
5 €
Range of
moderately
acid soils
' ) Ji
r
7+
Slightly acid
and slightly
alkaline soils
•SJ
* I
L ,i
Ranges of pH in mineral soils that present appropiate conditions for optimal growth of various plants. Note that the pH ranges are quite broad,
but that plant requirement for calcium and sensitivity to aluminum toxicity generally decreases from the top group to the bottom group
Figure 4-4. Suitable pH of Mineral Soils for Various Crops.
4-12
-------
Table 4-11. Nitrogen Uptake for Selected Forest Ecosystems
With Whole Tree Harvesting
Eastern forests:
Mixed hardwoods
Red pine
Old field with white
spruce plantation
Pioneer succession
Aspen sprouts
Southern forests:
Mixed hardwoods
Loblolly pine with
no understory
Loblolly pine with
understory
Lake states forests:
Mixed hardwoods
Hybrid poplar3
Western forests:
Hybrid poplar3
Douglas fir plantation
Tree Age,
Years
40-60
25
15
5-15
40-60
20
20
50
5
4-5
15-25
Average Annual
Nitrogen Uptake
lb/(acre-year)
200
100
200
200
100
250
200
250
100
140
270
200
3Short-term rotation with harvesting at 4 to 5 years; represents
first-growth cycle from planted seedlings.
*lb/acre-yr = 1.12 Ig/ha-yr1.
maximum estimates of net nitrogen uptake including
both the understory and overstory vegetation during the
period of active tree growth.
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 4-11 unless 100
percent of the aboveground biomass is harvested
(whole-tree harvesting). If only the merchantable stems
are removed from the system, the net amount of
nitrogen removed by the system will be less than 30
percent of the amount stored in the biomass (Keeney,
1980).
The distributions of biomass and nitrogen for naturally
growing hardwood and conifer (pines, Douglas fir, fir,
larch, etc.) stands in temperate regions are shown in
Table 4-12. 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.
Leaves make only 2 percent of the biomass on a dry
weight for northern hardwoods. Harvesting hardwoods
with leaves will increase nutrient removal by the
following percentages:
12% Calcium
15% Potassium
4% Phosphorus
19% Nitrogen (Hornbeck and Kropelin, 1982).
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 yr for southern pines, 50 to 60 yr for hardwoods,
and 60 to 68 yr 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.
Eastern Forests. During the past 35 years
wastewater has been applied to several forest
ecosystems at the Pennsylvania State University
(Sopper and Kerr, 1979). Satisfactory renovation was
obtained in all systems (eastern mixed hardwoods and
red pine) when wastewater was applied during the
growing season at 2.54 cm/wk (1 in/wk) with annual
nitrogen loadings of 150 kg/ha (134 Ib/acre). The white
spruce/old field forest ecosystem produced a percolate
nitrogen concentration of 7.4 mg/L (nitrate-N) when the
hydraulic loading was 5 cm/wk (2 in/wk) and the annual
nitrogen loading was 308 kg/ha (275 Ib/acre).
Southern Forests. In a study of a southern mixed
hardwood (80% hardwood, 20% pine) forest near Helen,
Georgia on a 30% slope with a loading rate of 7.5 cm/wk
(3 in/wk), about 60% of the applied nitrogen was
accounted for in uptake and denitrification. The nitrogen
loading was 680 kg/ha (608 Ib/acre) and the percolate
nitrate-N concentration was 3.7 mg/L (Nutter and
Schultz, 1978).
Lake States Forests. Studies at Michigan State
University have shown rather poor nitrogen removal by
mature northern hardwoods. Younger forest systems
and poplar plantations have shown greater nitrogen
uptake, especially during the years when herbaceous
cover is present (McKim et al., 1982).
Western Forests. The wastewater renovation
capacity of a newly established plantation of Douglas fir
and a mature 50-yr old Douglas fir forest was studied
with wastewater nitrogen loadings of 350 to 400 kg/ha-yr
(310 to 360 Ib/acre-yr) (Cole and Schiess, 1978). The
uptake rates, presented in Table 4-11, reflect a
substantial uptake by the understory grasses.
4-13
-------
Table 4-12. Biomass and Nitrogen Distributions by Tree Component for Stands in Temperate Regions (US EPA, 1 981 )
Conifers, %
Hardwoods, %
Tree component
Roots
Stems
Branches
Leaves
Biomass
10
80
8
2
Nitrogen
17
50
12
20
Biomass
12
65
22
1
Nitrogen
18
32
42
8
Phosphorus and Trace Metals
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 in the
biomass is quite small.
4.3.4 Horticultural
Horticultural plants offer a benefit over agricultural
production crops because the harvest is not ingested.
Although it has been clearly demonstrated that reuse
irrigation with highly treated effluent meets the water
quality criteria for turf grass use (USGA, 1994), many
golf course managers are reluctant to use effluent at the
risk of loss from visual appearance in both irrigation
ponds and turf quality. Devitt and Morris (2000)
monitored golf course quality at both courses with
effluent and with municipal water. Because of the
nutrient content of the effluent irrigation ponds with
effluent had increased algal growth and loss of clarity.
However, effluent ponds with aquatic vegetation
phosphate levels were lower and clarity higher,
suggesting that the plant played a significant role in
maintaining healthier ponds. Turf quality without
sufficient leaching showed impaired quality independent
of water type. Various golf course grasses can be
chosen as a salt management strategy. Table 4-13
shows salt tolerances of various grasses. Salt issues for
turf quality can be managed with sufficient leaching, but
a greater concern is associated with mixed landscape
plant receiving overhead spray irrigation (Devitt and
Morris, 2000).
4.4 Crop Management, Water Quality,
and Nutrient Cycle
Crop planting, harvesting and pest control are
management areas requiring proper techniques to
ensure a healthy crop.
4.4.1 Crop Planting, Harvesting
Cultivating
Local extension services or other 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,
Table 4-13. Golf Course Grass Salt Tolerances
ECe (dS/m)
Grass
Very Sensitive (<1.5)
Annual bluegrass
Colonial bentgrass
Rough bluegrass
Centipedegrass
Moderately Sensitive (1.6 - 3.0)
Kentucky bluegrass
Most zoysia spp.
Moderately Tolerant (3.1 - 6.0)
Creeping bentgrass
Fine-leaf fescues
Bahiagrass
Buffalograss
Blue grama
Annual ryegrass
Tolerant (6.1 -10.0)
Seaside bentgrass
Common bermudagrass
Tall Fescue
Perennial ryegrass
Zoysia japonica (some)
Zoysia matrella (some)
Kikuyu
Wheatgrasses
Very Tolerant (10.1 to 20.0)
Hybrid bermudagrasses (some)
St. Augustinesgrass
Salt grass
Alkaligrass (Fults, Salty)
Superior Tolerance (>20.0) Seashore paspalum (some)
aThe plant classification values and rankings are based on those traditionally used for all plants (Carrow and Duncan, 1998). The exception is the
"Superior Tolerance" class, which is added to classify grasses that are true halophytes with salinity tolerances well above most plants.
4-14
-------
application should be discontinued 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
experts and sufficient land area should be available to
account for the time required for drying.
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. When supplemental
fertilizer is required, records should be kept documenting
the type of fertilizer used, area of application, amount
applied.
4.4.2 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
groundwater. 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. See
Chapter 2 for nitrogen cycling from livestock.
In terms of pasture management, cattle or sheep must
not be allowed on wet fields to avoid severe soil
compaction and 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 removed. In general, a pasture area should
not be grazed longer than 7 days. Typical regrowth
periods between grazings range from 14 to 36 days.
Depending on the period of regrowth provided, one to
three water applications can be made during the
regrowth period. Rotation grazing cycles for 2 to 8
pasture areas are given in Table 4-16. At least 3 to 4
days of drying time following an application should be
allowed before livestock are returned to the pasture.
4.4.3 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.
4.4.4 Overland Flow Crop Management
After the cover crop has been established, the OF
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. 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 conditions, the cost of harvesting can at least be
offset by the sale of hay (US EPA, 1981).
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. Care must be taken to minimize pathogen
effects. 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, but usually they have 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.
4.4.5 Forest Crop Management
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.
4-16
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Table 4-14. Pasture Rotation Cycles for Different Numbers of Pasture Areas
Number of Pastures
Rotation Cycle
Days
Regrowth Period
Days
Grazing Period
Days
28
30
28
35
36
42
40
14
20
21
28
30
36
35
14
10
7
7
6
6
5
Established Forests. 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 by the forest.
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, 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. 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 objectives of these operations would be to maintain
an age class distribution in accordance with the concept
of optimum nutrient storage. 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.
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 percent of nitrogen
accumulated in the aboveground biomass would be
removed.
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
groundwater is increased when application of
wastewater is resumed.
Reforestation. Wastewater nutrients often stimulate
the growth of the herbaceous vegetation to such an
extent that it competes with and shades 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 yr. 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 8 to 12 ft (2.4 to
3.6 m), 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 (US EPA, 1981). Planted stock will produce
only 50 percent to 70 percent of the biomass produced
following cutting and resprouting (US EPA, 1981). 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.
4.5 References
Allen, R. G., L. S. Pereira, D. Raes, and M. Smith
(1998) Crop evapotranspiration - Guidelines for
computing crop water requirements - FAO Irrigation
4-17
-------
and drainage paper 56. FAO - Food and Agriculture
Organization of the United Nations. Rome.
Brockway, D.G. et al. (1982) The Current Status on the
Selection and Management of Vegetation for Slow
Rate and Overland Flow Application Systems to
Treat Municipal Wastewater in the North Central
Region of the United States. In: Land Treatment of
Municipal Wastewater, D'ltri, F.M. (Ed.) Ann Arbor,
Ml: Ann Arbor Science, pp.5-18.
Burt, C. M. (1995) The Surface Irrigation Manual.
Waterman Industries, Inc.
Carrow, R. N. and R. R. Duncan (1998) Salt-Affected
Turfgrass Sites: Assessment and Treatment. Ann
Arbor Press, Chelsea, Ml.
Crites, R.W., S.C. Reed, and R.K. Bastian (2000) Land
Treatment Systems for Municipal and Industrial
Wastes. McGraw-Hill Book Co. New York.
Cole, D.W. and P. Schiess (1978) Renovation of
Wastewater and Response of Forest Ecosystems:
the Pack Forest Study. Proceedings of the
International Symposium on Land Treatment of
Wastewater. Vol. 1, Hanover, NH. pp. 323-331.
Devitt, D. A. and R. L. Morris (2002) Monitoring Golf
Course Transition to Reuse Water in Southern
Nevada. American Water Works: Water Sources
Conference-Reuse, Resources, Conservation.
January 27-30, 2002, Las Vegas, NV.
D'ltri, F.M. (1982) Land Treatment of Municipal
Wastewater: Vegetation Selection and Management,
Ann Arbor, Ml: Ann Arbor Science.
Doorenbos, J. and W. O. Pruitt (1977) Crop
Requirements, FAO Irrigation and Drainage Paper
24. Food and Agricultural Organization of the United
Nations, Rome.
Handley, L.L. (1981) Effluent Irrigation of
Californiagrass. Proceedings Water Reuse
Symposium II, Vol. 2, AWWA Research Foundation,
Washington, DC.
Hanks, R.J. (1992) Applied Soil Physics. Second
edition. Springer-Verlang. New York.
Hornbeck, J. W. and W. Kropeline (1982) Nutrient
removal and leaching from a whole-tree harvest of
northern hardwoods. Journal of Environmental
Quality. 11:309-316.
Jaques, R., G. Antosz, R. Cooper, and B. Sheikh (1999)
Pathogen Removal Effectiveness of a Full-Scale
Recycling Plant. WEFTEC '99, New Orleans, LA.
Jensen, M.E. et al. (1973) Consumptive Use of Water
and Irrigation Water Requirements. ASCE
Committee on Irrigation Water Requirements.
Kabata-Pendias, A and H. Pendias. (2000). Trace
Elements in Soil and Plants, 3rd ed. CRC, Boca
Raton, FL.
Keeney, D.R. (1980) Prediction of soil nitrogen
availability in forest ecosystems: a literature review.
Forest Science. 26:159-171.
Metcalf and Eddy (1991) Wastewater Engineering:
Treatment, Disposal, Reuse. 3rd Edition. Rev. G.
Tchobanoglous and F. Burton. McGraw-Hill, Inc.
Nutter, W.L., R.C. Schultz, and G.H. Brister (1978)
Land Treatment of Municipal Wastewater on Steep
Forest Slopes in the Humid Southeastern United
States. Proceedings of the International Symposium
on Land Treatment of Wastewater, Vol. 1. Hanover,
NH. pp. 265-274.
Palazzo, A.J., T.F. Jenkins, and C.J Martel (1982)
Vegetation Selection and Management for Overland
Flow Systems. In: Land Treatment of Municipal
Wastewater, D'ltri, F.M. (Ed.) Ann Arbor, Ml: Ann
Arbor Science, pp. 135-154.
Pepper, I.L. (1981) Land Application of Municipal
Effluent on Turf. In: Proceedings of the 1981
Technical Conference Silver Spring, MD: The
Irrigation Association.
Rosenberg, N. J. (1974) Microclimate: The Biological
Environment. John Wiley & Sons. New York.
Sopper, W.E. and S.N. Kerr (1979) Renovation of
Municipal Wastewater in Eastern Forest
Ecosystems, In: Utilization of Municipal Sewage
Effluent and Sludge on Forest and Disturbed Land.
University Park, PA: The Pennsylvania State
University Press, pp. 61-76.
USDA. (1992) Part 651 -
Management Field Handbook.
Agricultural Waste
US EPA (1973) Wastewater Treatment and Reuse by
Land Application. Vol. II. EPA-660/02-73-006B, Aug.
1973.
US EPA (1981) Process Design Manual: Land
Treatment of Municipal Wastewater. EPA 625/1 -81 -
013.
USGA (1994) Wastewater Reuse for Golf Course
Irrigation. Lewis Publishers.
4-18
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Chapter 5
Site Planning and Selection
Site selection and process considerations in land
treatment are interrelated. The ability of the land
treatment processes to remove wastewater constituents
described in Chapter 2, the discharge quality criteria,
and the soil and other site characteristics affect the
choice of the appropriate land treatment process. The
presence of a suitable site within an economical
transmission distance from the wastewater source will
determine if a land treatment system can be
implemented. Because the selection of a process and
site for land treatment are related, a 2-phased planning
procedure is often used. The two phases are presented
in Figure 5-1 (US EPA, 1981b). Phase 1 involves
identification of potential sites via screening of available
information and experience. If potential sites for any land
treatment processes are identified, the study moves into
Phase 2. Phase 2 includes an in-depth consideration of
the processes including field investigations, preliminary
design and cost estimates, evaluation of the alternatives,
and selection of the most economical and appropriate
alternative.
5.1 Preliminary Land Requirements
The first phase involves estimating preliminary land
area requirements based on wastewater and climate
characteristics, identifying potential sites and, evaluating
the sites based on technical and economic factors, and
selecting potential sites.
Preliminary land requirements can be estimated for
each land treatment process, based on wastewater
characteristics, required loading rates, storage needs
and climatic conditions.
5.1.1 Wastewater Characteristics
Wastewater characteristics include average annual
flows and concentrations of constituents such as BOD5,
suspended solids, nitrogen, phosphorus and trace
elements.
Municipal wastewater flows range typically from 246 -
379 liters per capita per day [65 to 100 gallons per capita
per day (gpcd) (Crites and Tchobanoglous, 1998).
Industrial wastewater flows are too variable to generalize
and must be estimated from information specific to the
product and wastewater generating operations. Existing
wastewater flow records or water use records should be
used whenever available.
Wastewaler Characterization
Land Treatment System Suitability
Estimation o( Land Requirements
Phasel
*
|
[ Site Screening/Evaluation |
}
Land Treatment not Feasible
Because of Limiting Factors
or Project Requirements
Land Treatment not Feasible
if no Sites are Found
FieW Investigations
Phase 2
Development of Preliminary
Design Criteria and Costs
Evaluation of Alternatives
Han Selection
Land Treatment not Feasible
if Other Alternatives
are More Cost-Effective
Initiation of Land
Treatment System Design
Figure 5-1. Two-Phase Planning Process.
Constituent concentrations that are seen typically in
municipal wastewater are presented in Table 5-1. These
characteristics represent typical medium strength
wastewater. For municipal land treatment systems,
BOD5 and suspended solids loadings seldom limit
system capacity. If nitrogen removal is required, nitrogen
loading may limit the system capacity. Nitrogen removal
capacity depends on the crop grown, if any, and on
system management practices. In some cases, other
wastewater constituents such as phosphorus or trace
elements may control design. This is rare, however, and
most municipal systems will be limited either by
hydraulic capacity or nitrogen loading.
Table 5-1. Typical Composition of Raw Municipal Wastewater
(Crites and Tchobanoglous, 1998)
Constituent
Concentration, g/m (mg/L)
BOD5
Suspended Solids
Nitrogen, total
Organic nitrogen
Ammonia nitrogen
Phosphorus, total
Potassium
210
210
35
13
22
7
15
5-1
-------
Industrial wastewaters vary widely in their
characteristics, especially for organics, metals, and
nitrogen. Characteristics of food processing wastewaters
that have been applied directly to the land are presented
in Table 5-2 (Crites, 1982a). Wastewater
characterization is necessary in planning for industrial
land application systems (see Chapter 11). It is
important to consider whether there are sufficient
nutrients in industrial wastewaters to support plant
growth in SR systems. Applications may need to
supplement nutrients with other sources for proper plant
fertility (e.g., commercial fertilizers.
Table 5-2. Characteristics of Food Processing Wastewaters
Applied to the Land
Constituent
Concentration, g/m3 (mg/L)*
BOD5
Suspended Solids
Total fixed dissolved solids
Total nitrogen
pH, units
Temperature, °C
200 - 33,000
200 - 3,000
<1,800
10-1,900
3.5-12.0
<65
'Except as noted.
5.1.2 Preliminary Loading Rates
In the absence of site information, typical loading rates
can be assumed to initiate the planning process. For SR
systems the degree of preapplication treatment (either
primary or secondary) has little affect on the loading
rate. For OF and SAT systems, higher loading rates can
usually be used with higher quality effluent. Typical
loading rates for preliminary estimates of land
requirements are presented in Table 5-3 (Crites, et al.,
2000). The rates in Table 5-3 are necessarily
conservative. Once a potential site has been analyzed
and the ability to meet discharge requirements is
assessed, the loading rates can be modified. In
calculating the annual loading rates in SR systems it
should be noted that annual crops (e.g., corn) differ from
perennial (e.g., grass). Loading rates will vary annually
with annual crops and may be more consistent with
perennial crops.
Table 5-3. Preliminary Loading Rates for Initial Estimate of
Land Requirements
Process
Loading Rate,
mm/week (in/week)
Slow rate
Agricultural
Forest
Soil Aquifer Treatment
Primary effluent
Secondary effluent
Overland flow
Screened wastewater and
primary effluent
Secondary effluent
38(1.5)
25(1.0)
305 (12)
508 (20)
102 (4)
203 (8)
5.1.3 Storage Needs
Storage for wastewater may be necessary due to cold
weather, excessive precipitation, or crop management.
Land treatment systems also may need storage for flow
equalization, system backup and reliability, and system
management, including crop harvesting (SR and OF)
and spreading basin maintenance (SAT). Reserve
application areas can be used instead of storage for
these system management requirements.
For preliminary estimates it is usually sufficient to base
storage needs on climatic factors. A map showing
storage days based on cold weather and excessive
precipitation is presented in Figure Figure 5-2 (Whiting,
1976. This figure should be used for a preliminary
estimate of storage needed for OF systems. For SR
systems using agricultural crops, the crop management
time for harvesting and planting should be added to the
storage days taken from Figure 5-2. The values in
Figure 5-2 may not be valid for SAT and forested SR
systems, since both are sometimes operated during
subfreezing weather. For SAT and forested SR system,
a minimum storage of 7 to 14 days can be assumed for
preliminary estimates of land area. If application rates
are reduced during cold weather, additional storage will
be required.
Figure 5-2. Estimated Storage Days Based on Climatic Factors Alone.
5.1.4 Climatic Factors and Data Sources
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 SAT systems, (6) crop selection, and (7)
the amount of stormwater runoff. For this reason, local
precipitation, evapotranspiration, temperature, and wind
values must be determined before design criteria can be
5-2
-------
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 communities. The "Monthly Summary of
Climatic Data" provides basic information, including total
precipitation, temperature 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 Climatological Data", is
published for a small number of major weather stations.
Included in this publication are the means, and extremes
of all the data on record to date for each station. The
"Climate Summary of the United States" provides 10-
year summaries of the monthly climatic 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 1.27 cm (0.10 and 0.50 inch) during each
month (see www for further information).
. 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
. Mean number of days per month that the
temperature was less than or equal to 0°C or greater
than or equal to 32.5°C
A fourth reference that can be helpful is EPA's "Annual
and Seasonal Precipitation Probabilities" (Thomas and
Whiting, 1977a). This publication includes precipitation
probabilities for 93 stations throughout the United States.
Data requirements for planning purposes are
summarized in Table 5-4 (Crites et al., 2000).
5.1.5 Site Area Estimate
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, environmental sensitivity, 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
emergencies.
Preliminary site area requirements can be estimated
from wastewater flows, storage needs, and preliminary
loading rates. The relationship between field area,
loading rates, and operating period is shown in Equation
5-1, presented in both metric and English standard units.
F=365_Q_ (metric)
LP
or
F = 13443— (U.S. customary)
LP
(5-1)
Where:
F
Q
P
3.65
0.0001
= field area, ha (acres)
= average flow, m3/d (mgd)
= loading rate, cm/wk (in/wk)
(Preliminary values from Table 5-3)
= period of application, wk/yr
= metric conversion factor =
ha-m 100 cmx365 days xl/m
m Id year
13,443= conversion factor =
acre-ft 12 inch x 365 days x -\ /ft
3.069-
mgd
year
The period of application (P) from Equation 5-1 can be
approximated by dividing the estimated storage period
from Figure 5-2 by 52 wks./yr. Typical site areas
requirements for a 3,785 m3/day (some editors like
0.044m3sec"1) (1 mgd) flow for all three systems are
presented in Table 5-5 (Crites et al., 2000). For SR and
SAT systems the numbers in Table 5-5 include 20
percent extra area over the calculated field area to
account for unusable land. For OF systems, in Table 5-
5, the extra land area is 40 percent to account for the
additional inefficiency in constructing OF slopes.
Table 5-4. Summary of Climatic Analyses
Factor
Data Required
Analysis
Use
Precipitation
Annual average, maximum,
minimum
Frequency
Water balance
Rainfall storm
Temperature
Wind
Evapotranspiration
Intensity, duration
Days with average below freezing
Velocity, direction
Annual, monthly average
Frequency
Frost-free period
Annual distribution
Runoff estimate
Storage, treatment efficiency, crop
growing season
Cessation of sprinkling
Water balance
5-3
-------
5.2 Site Identification
To identify potential land treatment sites it is necessary
to obtain data on land use, soil types, topography,
geology, groundwater, surface water hydrology, and
applicable water rights issues. The types and sources of
data needed to identify and evaluate potential sites are
presented in Table 5-6 (Crites et al., 2000).
5.2.1 Use of Overlay Maps
The complexity of site identification depends on the
size of the study area and the nature of the land use.
One approach is to start with land use plans and identify
undeveloped land. Map overlays can then help the
planner or engineer to organize and study the combined
effects of land use, slope, relief, and soil permeability.
Use of Geographic Information Systems (CIS) will ease
this process. Criteria can be set on these four factors,
and areas that satisfy the criteria can then be located. If
this procedure is used as a preliminary step in site
identification, the criteria should be reassessed during
each iteration. Otherwise, strict adherence to such
criteria may result in overlooking either sites or land
treatment opportunities.
5.2.2 Site Suitability Factors
Potential land treatment sites are identified using a
deductive approach (Sills et al., 1978). 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, soils,
geology, groundwater and surface water hydrology.
Table 5-5. Site Identification Land Requirements, ha/m3-d (acres/mgd)
System
Land Requirements, ha/m3-d (acres/mgd)
Slow rate, agricultural:
No storage
1 month's storage
2 month's storage
3 month's storage
4 month's storage
5 month's storage
6 month's storage
Slow rate, forest:
No storage
1 month's storage
Soil aquifer treatment:
Primary effluent
Secondary effluent
Overland flow:
Storage (months)
0
1
2
3
4
Applying screened wastewater
0.0096 (90)
0.0107(100)
0.0117(110)
0.0128(120)
0.0149(140)
0.021 (200)
0.024 (225)
0.027 (250)
0.029 (275)
0.034(315)
0.037 (350)
0.044(415)
0.033(310)
0.036 (335)
0.0032 (30)
0.0016(15)
Applying secondary effluent
0.019(180)
0.021 (200)
0.023 (220)
0.026 (240)
0.030 (280)
Table 5-6. Types and Sources of Data Required for Land Treatment Site Evaluation
Type of Data
Principal Source
Topography
Soil type and permeability
Temperature
(mean monthly and growing season)
Precipitation
(mean monthly, maximum monthly)
Evapotranspiration and evaporation
(mean monthly)
Land Use
Zoning
Agricultural practices
Surface and groundwater discharge requirements
Groundwater (depth and quality)
ySGS topographic quads
NRCS soil survey
NRCS soil survey, NOAA, local airports, newspapers
NRCS soil survey, NOAA, local airports, newspapers
NRCS soil survey, NOAA, local airports, newspapers, agricultural extension service
NRCS soil survey, aerial photographs from the Agricultural Stabilization and Conservation
Service, and county; assessor's plats
Community planning agency, city or county, zoning maps
NRCS soil survey, agricultural extension service, country agents, crop consultants
State or EPA
State water agency, USGS, driller's logs of nearby wells
5-4
-------
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 may
conform with the following land use objectives:
. Protection of open space that is used for land
treatment
. Production of agricultural or forest products using
wastewater on the land treatment site
. Reclamation of land by using wastewater to
establish vegetation on scarred land
. Augmentation of parklands by irrigating such lands
with wastewater
. 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 current land
use, site visits are recommended to determine existing
land use. Aerial photographic maps may be obtained
from the Natural Resources Conservation Service
(NRCS) or the local assessor's office. USGS is an
additional source for aerial photo or satellite images.
Many of the information sources are available on
Internet. Other useful information may be available from
the USGS, 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, these should be plotted on a study area
map. Then, land use suitability may be plotted using the
factors shown in Table 5-7 (Moser, 1978).
Both land acquisition procedures and treatment
system operation are simplified when few land parcels
(few land owners) are involved and contiguous parcels
are used. Therefore, parcel size is an important
parameter. Usually, information on parcel size can be
obtained from county assessor or county recorder maps.
Again, the information should be plotted on a map of the
study area.
Topography
Steep grades limit a site's potential because the
amount of runoff and erosion that may occur is
increased, crop cultivation is made more difficult, and
saturation 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 5-8 (Moser, 1978).
Relief is another important topographical consideration
and is the difference in elevation between one part of a
land treatment system and another. The primary impact
of relief is the effect on the cost of conveying wastewater
to the land application site. Often, the economics of
pumping wastewater to a nearby site must be compared
with the cost of constructing gravity conveyance to more
distant sites.
Table 5-7. Land Use Suitability Factors for Identifying Land Treatment Sites (Moser, 1978)
Type of System
Land Use Factor
Open or cropland
Partially forested
Heavily forested
Built upon (residential,
commercial, or industrial)
Agricultural Slow Rate
High
Moderate
Low
Low
Forest Slow Rate
Moderately high
High
High
Very low
Overland Flow
High
Moderate
Low
Very low
Soil Aquifer Treatment
High
Moderate
Low
Very low
Table 5-8. Grade Suitability Factors for Identifying Land Treatment Sites (Moser, 1978)
Slow Rate Systems
Grade Factor, %
0-12
12-20
20+
Agricultural
High
Low
Very low
Forest
High
High
Moderate
Overland Flow
High
Moderate
Eliminate
Soil Aquifer Treatment
High
Low
Eliminate
5-5
-------
A site's susceptibility to flooding also can affect its
desirability. The flooding hazard of each potential site
should be evaluated in terms of both the possible
severity and frequency of flooding as well as the extent
of flooding. In some areas, it may be preferable to allow
flooding of the application site provided offsite storage is
available. Further, crops can be grown in flood plains if
flooding is infrequent enough to make farming
economical.
The landscape position and landform for each suitable
area should be noted. Figure 5-3 can be used as a guide
for identifying landscape positions. This information is
useful in estimating surface and subsurface drainage
patterns. For example, hilltops and sideslopes can be
expected to have good surface and subsurface
drainage, while depressions and footslopes are more
likely to be poorly drained (US EPA, 1980).
Convex
Slope
Figure 5-3. Landscape Positions.
Overland flow sites can be located in flood plains
provided they are protected from direct flooding which
could erode the slopes. Flood plain sites for SAT 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 country as part of the Uniform National Program
for Managing Flood Losses. These maps are based on
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 Engineers and
local flood control districts. Many county/city zoning
offices have flood plain information
Soils
Common soil-texture terms and the relationship to the
NRCS textural class names are listed in Table 5-9
(Critesetal.,2000).
In general, 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
sloping 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 characteristics
that relate to permeability and acceptability for land
treatment. Structure refers to the degree of soil particle
aggregation. A well structured soil is generally more
permeable than unstructured material of the same type.
The SAT process is suited for sandy or loamy soils.
Soils surveys are usually available from the NRCS.
Soil surveys normally contain maps showing soil series
boundaries and textures to a depth of about 1.5 m (5 ft).
In a survey, limited information on chemical properties,
grades, drainage, erosion potential, general suitability for
locally grown crops, and interpretive and management
information is provided. Where published surveys are
not available, information on soil characteristics can be
obtained from the NRCS, through the local county agent.
Much of this information is now available on the web at
NRCS's Electronic Field Office Guide
(http://www.nrcs.usda.qov/technical/efotq/, (verified
August 22, 2005).
Although soil depth, permeability, and chemical
characteristics significantly affect site suitability, data on
these parameters are often not available before the site
investigation phase. If these data are available, they
should be plotted on a study area map along with soil
Table 5-9. Soil Textural Classes and General Terminology Used in Soil Descriptions
General Terms
Common Name
Sandy soils
Loamy soils
Clayey soils
Texture
Coarse
Moderately coarse
Medium
Moderately fine
Fine
Basic Soil Textural Class Names
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
5-6
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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 5-10 together with desired
soil texture (Crites et al., 2000). The NRCS permeability
class definitions are also shown in Figure 3-5.
Geology
Certain geological formations are of interest during
phase 1 investigations. Discontinuities and fractures in
bedrock may cause short-circuiting or other unexpected
groundwater flow patterns. Impermeable or semi-
permeable layers of rock, clay, or hardpan can result in
perched groundwater 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.
Groundwater
A knowledge of the regional groundwater conditions is
particularly important for SAT and SR sites. Overland
flow will not usually require an extensive hydrogeologic
investigation. There is sufficient removal of pollutants in
the applied wastewater before reaching a permanent
groundwater resource is the primary concern. The depth
to groundwater and seasonal fluctuation are measures
of the aeration zone. When several layers of stratified
groundwater underlie a particular site, the occurrence of
the vertical leakage between layers should be evaluated.
Direction and rate of groundwater flow and aquifer
permeability together with groundwater depth are useful
in predicting the effect of applied wastewater on the
groundwater regime. The extent of recharge mounding,
interconnection of aquifers, perched water tables, the
potential for surfacing groundwater, and design of
monitoring and withdrawal wells are dependent on
groundwater flow data.
Much of the data required for groundwater evaluation
may be determined through use of existing wells. Wells
that could be used for monitoring should be listed and
the relative location described. Historical data on quality,
water levels, and quantities pumped from the operation
Table 5-10. Typical Soil Permeabilities and Textural Classes for Land Treatment
of existing wells may be of value. Such data include
seasonal groundwater-level variations, as well as
variations over a period of years. The USGS maintains a
network of about 15,800 observation wells to monitor
water levels nationwide. Records of about 3,500 of these
wells are published in Water-Supply Paper Series,
"Groundwater-Levels in the United States." Many local,
regional, and state agencies compile drillers' boring logs
that are also valuable for defining groundwater
hydrology. Even though USGS has the monitoring well
network the local, state people have better data.
Land treatment of wastewater can provide an
alternative to surface discharge of conventionally treated
wastewater. However, the adverse impact of percolated
wastewater on the quality of the groundwater must be
considered. Existing groundwater quality should be
determined and compared to quality standards for its
current or intended use. The expected quality of the
renovated wastewater can then be compared to
determine which constituents in the renovated water
might be limiting. The USGS "Groundwater Data
Network" monitors water quality in observation wells
across the country. In addition, the USGS undertakes
project investigations or groundwater studies in
cooperation with local, state, or other federal agencies to
appraise groundwater quality. Such reports may provide
a large part of the needed groundwater data.
Surface Water Hydrology
Surface water hydrology is of interest in land treatment
processes because of stormwater run-on and runoff.
Considerations relating to surface runoff control apply to
both SR and OF. SAT processes are designed for no
runoff.
The control of stormwater runoff both onto and off a
land treatment site must be considered. First, the
facilities constructed as part of the treatment system
must be protected against erosion and washout from
extreme storm events. For example, where earthen
ditches and/or terraces are used, erosion control from
stormwater runoff must be provided. The degree of
control of runoff to prevent the destruction of the physical
system should be based on the economics of replacing
equipment and structures. There is no standard extreme
storm event in the design of drainage and runoff
Land Treatment Processes
Soil permeability range, mm/h
(in/h)
Permeability class range
Textural class
Unified soil classification
Slow Rate
1.5-50
(0.06 - 2.0)
Moderately slow to moderately
rapid
Clay loams to sandy Loams
GM-d, SM-d, ML, OL, MH, PT
Soil Aquifer Treatment
>50
(> 2.0)
Rapid
Sandy and sandy loams
GW, GP, SW, SP
Overland Flow
<5
(< 0.2)
Slow
Clays and clay loams
GM-u, GC, SM-u, SC, CL, OL, CH,
OH
5-7
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collection systems, although a 10-year return, 24-hr
storm is suggested as a minimum. See Chapter 9 for
further discussion of storm water runoff of overland flow
sites.
5.2.3 Water Rights
Land application of wastewaters may cause several
changes in drainage and flow patterns (Dewsnup and
Jensen, 1973):
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. 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 (Dewsnup and Jensen, 1973).
Most riparian or land ownership rights are in effect east
of the Mississippi, whereas most appropriative rights are
in effect west of the Mississippi River.
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 orgroundwater).
The state or local water master or water rights
engineer should be consulted to avoid potential
problems. Other references to consider are the
publications, "A Summary-Digest of State Water Laws,"
available from the National Water Commission (US EPA,
1977b), and "Land Application of Wastewater and State
Water Law," Volumes I and II (US EPA, 1977b and
1978). If problems develop or are likely with any of the
feasible alternatives, a water rights attorney should also
be consulted.
5.3 Site Selection
Once the data on site characteristics are collected and
mapped, the site evaluation and selection process can
proceed. If the number of sites are few and their relative
suitability clearly apparent, a simple economic
comparison will lead to selection of the best site. If a
number of sites are to be compared, a site screening
procedure can be used.
5.3.1 Site Screening Procedure
The general procedure for site suitability rating can be
used to compare different sites or it can be used to
screen a large site that may have portions suitable to
different land treatment processes. A procedure
incorporating economic factors is presented for SAT and
OF systems. A procedure specific to SR forest systems
is also included.
The general procedure is to assign numerical values to
various site characteristics, with larger numbers
indicating highest suitability. The individual numbers for
each site or sub-area are then added together to obtain
the overall suitability rating. The rating factors in Table
5-11 are applicable to all processes. Site rating factors
and weightings should vary to suit the needs of the local
area and type of sites available.
5.3.2 Screening Procedure with Economic
Factors
In addition to the rating factors listed in Table 5-11
(Taylor, 1981) the economics of site development are
often critical. These include distance from the
wastewater source, elevation differences and the costs
for land acquisition and management. Table 5-12
presents rating factors for these concerns (Crites et al.,
2000).
5.3.3 Procedure for Forested SR Systems
A procedure has been developed for forested SR
systems that incorporates climatic, soil, geologic,
hydrologic and vegetation factors (Taylor, 1981). The
procedure involves the use of rating values for
subsurface factors (Table 5-13), soils (Table 5-14), and
surface factors (
Table 5-15) together with the composite rating in Table
5-16.
Based on the ratings in these tables, an estimate of
the preliminary hydraulic loading can be made using
Table 5-16. This procedure was developed for sprinkler
irrigation of forested sites in the southeastern United
States.
5.4 Phase 2 Planning
Phase 2, the site investigation phase, occurs only if
sites with potential have been identified in Phase 1.
5-8
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During Phase 2, field investigations are conducted at the
selected sites to determine whether land treatment is
Table 5-11. Rating Factors for Site Selection (Taylor, 1981)
Slow Rate Systems
Characteristic
Soil depth, ft*(a)
1 -2
2-5
5-10
> 10
Minimum depth to groundwater, ft
<4
4-10
>10
Permeability, in/h*(b)
<0.06
0.06-0.2
0.2-0.6
0.6-2.0
>2.0
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 rating5
Low
Moderate
High
Agricultural
Ef
3
8
9
0
4
6
1
3
5
8
8
8
6
4
0
0
E
E
0
0
1
1
4
<15
15-25
25-35
Forest
E
3
8
9
0
4
6
1
3
5
8
8
8
8
6
5
4
2
0
0
0
1
4
3
<15
15-25
25-35
Overland Flow
0
4
7
7
2
4
6
10
8
6
1
E
8
5
2
E
E
E
E
0
0
1
1
4
<16
16-25
25-35
Rapid Infiltration
E
E
4
8
E
2
6
E
E
1
6
9
8
4
1
E
E
E
E
0
0
1
1
4
<16
16-25
25-35
Note: The higher the maximum number in each characteristic, the more important the characteristic; the higher the ranking, the greater the suitability.
* Depth of the profile to bedrock.
f Excluded; rated as poor.
* Permeability of most restrictive layer in soil profile.
§Sum of values.
aft x 0.3048 = m
bin/h x 2.54 = cm/h
Table 5-12. Economic Rating Factors for Site Selection
(Taylor, 1981)
Characteristic
Rating Value
Distance from wastewater source, miles3
0-2 8
2-5 6
5-10 3
>10 1
Elevation difference, ftb
<0 6
0-50 5
50 - 200 3
>200 1
Land cost and management
No land purchase, farmer-operated 5
Land purchased, farmer-operated 3
Land purchased, city- or industry-operated 1_
amile x 1.609 = km
bft x 0.3048 = m
technically feasible. When sufficient data have been
collected, preliminary design criteria are calculated for
each potential site. Using these criteria, capital and
operation and maintenance 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.
5.4.1 Field Investigations
The factors regarding groundwater conditions, soil
properties, and other site attributes not only influence the
initial site selection and concept feasibility decisions but
are critical for the final system design. As with all other
engineering projects, the type of test required and the
specific procedure are relatively easy to describe. The
more difficult decision is how many tests, and in what
5-9
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locations, for a particular project. 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.
Table 5-13. Subsurface Factors for Forested SR
(Taylor, 1981)
Table 5-15. Surface Factors for Forested SR (Taylor, 1981)
Characteristics
Rating Value*
Depth to groundwater on barrier, fta
<4
4-10
Depth to bedrock, fta
<5
5-10
Type of bedrock
Shale
Sandstone
Granite-gneiss
Exposed bedrock, % of total area
<33
10-33
1 -10
None
0
4
6
0
4
6
2
4
6
0
2
4
6
*0 - 9, site not feasible; 10-13, poor; 14-19, good;
and 20-24, excellent.
aft x 0.3048 = m .
Table 5-14. Soil Factors for Forested SR (Taylor, 1981)
Characteristics
Infiltration rate, in/ha
<2
2-6
>6
Hydraulic conductivity, in/ha
>6
<2
2-6
CEC, meq/100g
<10
10-15
> 15
Shrink-swell potential (NRCS)
High
Low
Moderate
Erosion classification (NRCS)
Severely eroded
Eroded
Not eroded
*5-11, poor; 12-16, good;
ain/h x 2.54 = cm/h.
Rating Value*
3
1
2
3
1
2
3
and 17 -21,
2
4
6
2
4
6
1
2
excellent.
Characteristics
Dominant vegetation
Pine
Hardwood or mixed
Vegetation age, years
Pine
>30
20-30
<20
Hardwood
>50
30-50
<50
Mixed pine/hardwood
>40
25-40
<25
Slope, %
>35
0-1
2-6
7-35
Distance to flowing stream, fta
50-100
100-200
>200
Adjacent land use
High-density residential/urban
Low-density residential/urban
Industrial
Undeveloped
*3 -4, not feasible; 5-9, poor;
15-19, excellent.
aft x 0.3048 = m.
Rating Value*
2
3
3
3
4
1
2
3
1
2
3
0
2
4
6
1
2
3
1
2
2
3
9-14 good; and
Table 5-17 presents field tests for a land treatment
project. When possible, available data are first used for
calculations or decisions that may then necessitate
additional field tests. Guidance for wastewater
constituents and soil properties is provided for each land
treatment process in Table 5-18 (Crites et al., 2000).
Generally relatively modest programs of field testing and
data analysis will be satisfactory, especially for small
systems.
5.4.2 Soil Properties
A critical element in site selection and process design
is the capability of the site soils to move the design
quantities of water in the expected direction at the
expected rates. These are important requirements for
slow rate (SR) systems and are absolutely critical for soil
aquifer treatment (SAT) because of the much higher
hydraulic loadings.
5-10
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Table 5-16. Composite Evaluation of SR Forested Sites (Taylor, 1981)
Evaluation ratings from Tables 5-13 to 5-15
Poor Good
3 0
2 1
2 0
1 2
1 1
1 0
0 3
0 2
0 1
0 0
Excellent
0
0
1
0
1
2
0
1
2
3
Hydraulic Loading, in/week3
Not feasible
< 1.0
< 1.0
1.0-1.5
1.0-1.5
1.5-2.0
2.0-2.5
2.0-2.5
2.5-3.0
2.5-3.0
a in/week x 2.54 = cm/week
Table 5-17. Sequence of Field Testing - Typical Order of Testing (US EPA, 1981 b)
Field Tests
Test Pits
Bore Holes
Infiltration Rate
Soil Chemistry
Remarks
Information to
obtain
Estimates now
possible
Additional field
tests
Additional
estimates
Number of tests
Usually with a backhoe,
includes inspection of existing
NRCS reports, road cuts, etc.
Depth of profile, texture,
structure, soil layers
restricting percolation
Need for vertical conductivity
testing
Vertical conductivity
(optional)
Refinement of loading rates
Depends on size, soil
uniformity, needed soil tests,
type of system. Typical
minimum of 3-5 per site
Drilled or augered includes
inspection of driller's logs for
local wells, water table levels
Depth to groundwater, depth
to impermeable layer(s)
Groundwater flow direction
Horizontal conductivity
Mounding analysis,
dispersion, need for drainage
Depends on system type
(more for Rl than SR), soil
uniformity, site size. Typical
minimum of 3 per site
Match the expected method of
application, if possible
Expected minimum infiltration
rate
Hydraulic capacity based on
soil permeability (subject to
drainage restrictions)
Depends on size of site,
uniformity of soil. Typical
minimum of 2 per site.
Includes review of NRCS
survey
Specific data relating to crop
and soil management,
phosphorus and heavy metal
retention
Crop limitations. Soil
amendments. Possible
preapplication requirements
Quality of percolate
Depends on uniformity of soil
types, type of test, size of site
Table 5-18. Summary of Field Tests for Land Treatment Processes
Properties
Processes
Slow Rate
(SR)
Soil Aquifer Treatment (SAT)
Overland Flow
(OF)
Wastewater constituents
Soil physical properties
Soil hydraulic properties
Soil chemical properties
Nitrogen, phosphorus, SAR*, EC*,
boron
Depth of profile, texture and
structure
Infiltration rate
Subsurface permeability
pH, CEC, exchangeable cations (°/
of CEC), EC*, metals*, phosphorus (optional)
adsorption (optional)
BOD, SS, nitrogen, phosphorus
Depth of profile, texture and structure
Infiltration rate
S ui bsu rfa ce pe rme a b i I ity
pH, CEC, phosphorus adsorption
BOD, SS, nitrogen, phosphorus
Depth of profile, texture and
structure
Infiltration rate (optional)
pH, CEC, exchangeable cations
(% of CEC)
*May be more significant for arid and semiarid areas.
Background levels of metals in the soil should be determined if food chain crops are planned.
Physical Characteristics
Site identification and selection will ordinarily be based
on existing field data available from a NRCS 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. The field exploration is important
and has two purposes: (1) verification of existing data
and (2) identification of probable, or possible, site
limitations. 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
5-11
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of rock outcroppings would signify the need for more
detailed subsurface investigations than might normally
be required. If a stream were located near the site, there
would need to be additional study of the surface and
near-surface hydrology; nearby wells require details of
the groundwater flow, and so on. These points may
seem obvious. There are many systems that have failed
because of just such obvious conditions: limitations that
were not recognized until after design and construction
were complete.
The methods of construction and system operation
that will be used can also be critically important
depending on the soil properties encountered and must
be considered in the site and concept selection process.
The characteristics of the soil profile in the undisturbed
state may be completely altered when the design
surface is exposed or by inadvertent compaction during
construction. Fine textured soils are particularly
susceptible to compaction. For example, if the design
surface layer contains a significant clay fraction and if
that surface is exposed for growth of row crops in a SR
system the impact of rainfall and sprinkler droplets may
result in sorting of the clay fines and a partial sealing of
the surface. Such problems can be managed, but the
field investigation must provide sufficient data so that
such conditions can be anticipated in the design.
SAT Systems
Soil properties, topography, and construction methods
are particularly critical for SAT systems. A site with a
heterogeneous mixture of soil types containing scattered
lenses of fine textured soil may be impossible to
adequately define with a typical investigation program. If
such a site cannot be avoided for SAT, a large-scale
pilot test basin is suggested for definition of site
hydraulic characteristics. If the pilot test is successful,
the test basin, if properly located, can then be included
in the full scale system.
An SAT site with undulating topography may require a
scattered array of basins to remain in desirable soils or
may necessitate major cut and fill operations for a
compact site. SAT basins should always be constructed
in cut section if at all possible. Experience has shown
that construction with soils that have a fine fraction
(passing No. 200 sieve [< 0.075mm]) of more than 5
percent can result in problems (Reed, 1982). Clayey
sands with fines exceeding 10 percent by weight should
be avoided altogether as fill material for basin infiltration
surfaces. Pilot scale test basins are recommended
whenever SAT systems are to be designed on backfilled
soils.
Construction
Construction activity, either cut or fill, for SAT or SR
systems can have a drastic effect on soil permeability if
clayey sands are present. Such activity should only be
permitted when the soil moisture is on the dry side of
"optimum." Optimum Moisture refers to a moisture soil
density relationship: used in the construction industry to
obtain optimum soil compaction. Inadvertent compaction
with the soil on the wet side of optimum moisture content
could result in the same bulk density for the soil but an
order of magnitude reduction in permeability. If such
compaction is limited to the top foot of the surface layer,
a final ripping and disking may correct the problem.
Compaction of this type on sequential layers of fill may
not be correctable.
The importance of soil texture for concept and site
selection was described in Chapter 3 of this manual,
and is based on the USDA soil classes (Figure 3-1).
Table 5-19 summarizes the interpretation of these
physical and hydraulic properties.
Table 5-19. Interpretation of Soil Physical and Hydraulic Properties
(Crites, etal.,2000)
Property
Depth of soil profile, fta
<1 -2
>2-5
5-10
Texture and structure
Fine texture, poor structure
Fine texture, well-structured
Coarse texture, well-structured
Infiltration rate, in/hb
0.2-6
>2.0
<0.2
Subsurface permeability
Exceeds or equals infiltration rate
Less than infiltration
Interpretation
Suitable for OF*
Suitable for SR and OF
Suitable for all processes
Suitable for OF
Suitable for SR and possibly OF
Suitable for SR and SAT
Suitable for SR
Suitable for SAT
Suitable for OF
Infiltration rate limiting
May limit application rate
'Suitable soil depth must be available for shaping of overland flow
slopes.
Slow rate process using a grass crop may also be suitable.
aft x 0.3048 = m
bin/h x 2.54 = cm/h.
Chemical Properties
The influence of soil chemical properties on
permeability and infiltration was discussed in detail in
Chapter 3. Adverse chemical reactions between the
wastewater and the soil are not expected for municipal
and most industrial effluents. The main concern is
usually retention or removal of a particular chemical by
the soil system and Chapter 2 provides more details.
Differences in the chemical characteristics between
the applied wastewater and the soil may induce
chemical changes in the soil. At Muskegon, Ml, for
5-12
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example, the initial wastewater applications flushed
dissolved iron out of the soil profile, showing up as a
reddish turbidity in the drain water. Fresno, CA, also had
turbidity problems when high-quality river water
(snowmelt) was applied to relatively saline soils
(Nightingale, 1983). This low salinity water dispersed the
submicron soil colloids in the upper 3.66 m (12 ft) of the
soil profile. The colloids are then flocculated as mixing
occurs with the more saline groundwater. This turbidity
problem has persisted for 10 years but does not affect
water quality in down gradient wells.
Soil chemistry data is usually obtained via routine
laboratory tests on representative samples obtained
from test pits or borings. Table 5-20 summarizes the
interpretation of typical soil chemical tests.
Test Pits and Borings
Following an 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 gravel and other anomalies
should be carefully noted. For OF site evaluations, the
depth of soil profile evaluation can be the top 0.9 m (3 ft)
or so. The evaluation should extend to 1.5 m (5 ft) for SR
and 3 m (10 ft) or more for SAT systems.
Representative samples are obtained from the test pits
and analyzed to determine the physical and chemical
properties discussed above. It is possible with
experience to estimate soil texture in the field with small
samples taken directly from the walls of the test pit. To
determine the soil texture, moisten a sample of soil
about 12.7 to 25.4 mm (0.5 to 1 in) in diameter. There
should be just enough moisture so that the consistency
is like putty. Too much moisture results in a sticky
material, which is hard to work. Press and squeeze the
sample between the thumb and forefinger. Gradually
press the thumb forward to try to form a ribbon from the
soil. By using this procedure, the texture of the soil can
be easily described with the criteria given in Table 5-21
(US EPA, 1980).
If the soil sample ribbons (loam, clay loam, or clay), it
may be desirable to determine if sand or silt
predominate. If there is a gritty feel and a lack of smooth
talc-like feel, then sand very likely predominates. If there
is a lack of a gritty feel but a smooth talc-like feel, then
silt predominates. If there is not a predominance of
either the smooth or gritty feel, then the sample should
not be called anything other than a clay, clay loam, or
loam. If a sample feels quite smooth with little or no grit
in it, and will not form a ribbon, the sample would be
called silt loam.
Table 5-20. Interpretation of Soil Chemical Tests (US EPA, 1981)
Test Results
Interpretation
pH of saturated soil paste
<4.2
4.2-5.5
5.5-8.4
>8.4
CEC, meq/100 g
1 -10
12-20
>20
Exchangeable cations, % of CEC (desirable range)
Sodium
Calcium
Potassium
Magnesium
ESP, % of CEC
<5
>10
>20
Too acid for most crops to do well
Suitable for acid-tolerant crops and forest systems
Suitable for most crops
Top alkaline for most crops; indicates a possible sodium problem
Sandy soils (limited adsorption)
Silty loam (moderate adsorption)
Clay and organic soils (high adsorption)
5
60-70
5-10
10-20
Satisfactory
Reduced permeability in fine-textured soils
Reduced permeability in coarse-textured soils
ECe, mmhos/cm at 25% of saturation extract
<2
2-4
4-8
8-16
> 16
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
5-13
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Table 5-21. Textural Properties of Mineral Soils
Soil Class
Feeling and Appearance
Dry Soil
Moist Soil
Sand
Sandy Loam
Loam
Silt loam
Clay loam
Clay
Loose, single grains which feel gritty. Squeezed in
the hand, the soil mass falls apart when the
pressure is released
Aggregates easily crushed; very faint velvety
feeling initially, but with continued rubbing the
gritty feeling of sand soon dominates
Aggregates are crushed under moderate
pressure; clods can be quite firm. When
pulverized, loam has velvety feel that becomes
gritty with continued rubbing. Cast bear careful
J]iajTdJmg__
Aggregates are firm but may be crushed under
moderate pressure. Clods are firm to hard.
Smooth, flourlike feel dominates when soil is
pulverized.
Very firm aggregates and hard clods that strongly
resist crushing by hand. When pulverized, the soil
takes on a somewhat gritty feeling due to the
harshness of the very small aggregates which
persist
Aggregates are hard; clods are extremely hard
and strongly resist crushing by hand. When
pulverized, it has a gritlike texture due to the
harshness of numerous very small aggregates
which persist
Squeezed in the hand, it forms a cast which crumbles when touched.
Does not form a ribbon between thumb and forefinger
Forms a cast which bears careful handling without breaking. Does not
form a ribbon between thumb and forefinger
Cast can be handled quite freely without breaking. Very slight tendency
to ribbon between thumb and forefinger. Rubbed surface is rough
Cast can be freely handled without breaking. Slight tendency to ribbon
between thumb and forefinger. Rubbed surface has a broken or rippled
appearance
Cast can bear much handling without breaking. Pinched between the
thumb and forefinger, it forms a ribbon whose surface tends to feel
slightly gritty when dampened and rubbed. Soil is plastic, sticky, and
puddles easily.
Cast can bear considerable handling without breaking. Forms a flexible
ribbon between thumb and forefinger and retains its plasticity when
elongated. Rubbed surface has a very smooth, satin feeling. Sticky
when wet and easily puddled
Beginning at the top or bottom of the pit sidewall,
obvious changes in texture with depth are noted.
Boundaries that can be seen are marked. When the
textures have been determined for each horizon (layer),
its depth, thickness, and texture layer are recorded.
Soil structure (Table 5-22) has a significant influence
on soil acceptance and transmission of water. Soil
structure refers to the aggregation of soil particles into
clusters of particles, called peds, that are separated by
surfaces of weakness. These surface of weakness are
often seen as cracks in the soil. These planar pores can
greatly modify the influence of soil texture on water
movement. Well-structured soils with large voids
between peds will transmit water more rapidly than
structureless soils of the same texture, particularly if the
soil has become dry before the water is added. Fine-
textured, massive soils (soils with little structure) have
very slow percolation rates.
Table 5-22. Soil Structure Grades (US EPA, 1980)
Grade Characteristics
Structureless No observable aggregation
Weak Poorly formed and difficult to see. Will not
retain shape on handling
Moderate Evident but not distinct in undisturbed soil.
Moderately durable on handling
Strong Visually distinct in undisturbed soil. Durable on
handling
Soil structure can be examined in the pit with a pick or
similar device to expose the natural cleavages and
planes of weakness. The color and color patterns in soil
are also good indicators of the drainage characteristics
of the soil. It is often advantageous to prepare the soil pit
so the sun will be shining on the face during the
observation period. Natural light will give true color
interpretations. Artificial lighting should not be used.
Color may be described by estimating the true color
for each horizon or by comparing the soil with the colors
in a soil color book. In either case, it is particularly
important to note the colors or color patterns. Soil color
is generally measured by a Munsell Soil Color Chart
(see www. munsell.com) verified August 25, 2005.
Seasonally high groundwater tables are preferably
detected by borings made during the wet season of the
year for the site. An indication of seasonally high
groundwater can be observed by the presence of redox
features (mottles or discolored soils) in the wall of the
test pit. Mottling in soils is described by the color of the
soil matrix and the color or colors, size, and number of
the mottles. Each color may be given a Munsell
designation and name. However, it is often sufficient to
say the soil is mottled. A classification of mottles used by
the USDA is shown in Table 5-23. Color photographs of
typical soil mottles can be used to assist in identification
(US EPA, 1980).
5-14
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Table 5-23. Description of Soil Mottles (US EPA, 1980)
Character
Abundance
Size
Contrast
Class
Few
Common
Many
Fine
Medium
Coarse
Faint
Distinct
Prominent
2% of exposed face
2 - 20% of exposed face
20% of exposed face
Limit
0.25 ina longest dimension
0.25 - 0.75 ina longest dimension
7-75 ina longest dimension
Recognized only by close observation
Readily seen but not striking
Obvious and striking
All of the data collected in the test pit on texture,
thickness of each horizon, structure, color, and presence
of water should be recorded in the field. A sample log is
shown in Figure 5-4 (Crites et al., 2000).
0
2
4
Ł• 6
JC
cl
0 8
10
12
14
Texture Structure Color Soil Saturation
Silt Loam
Silly Clay
J^fiB.01 — _
Clay Loam
Sandy
I
1
"
Granuiar I
Platy
Blacky
Piaty
— _____ —
Massive
Brown
Gray and
Red Patches,
Brown
Background
Mottling up to
4 ft Indicates
Seasonal Water
in x 2.54 = cm
Figure 5-4. Sample Log for Test Pit Data.
In some site evaluations, the backhoe pits will not yield
sufficient information on the profile. 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 3.51 m (11.5 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-
spoon sampler.
Boring methods, which can be used to probe deeper
than auguring, include churn drillings, 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.
5.4.3 Groundwater Conditions
The position, the rate of flow, and the direction of flow
of the natural groundwater beneath the site are critical
elements in the field investigation. Some key questions
to be answered by the investigation 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 groundwater table respond to the
proposed wastewater loadings?
4. In what direction and how fast will the mixture of
percolate and groundwater 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. Do any restrictions exist along the site boundary that
may limit the groundwater flow?
7. If any of the conditions measured or predicted above
are found to be unacceptable, what steps can be
taken to correct the situation?
Groundwater Depth and Hydrostatic Head
A groundwater table is defined as the contact zone
between the free groundwater and the capillary zone. It
is the level assumed by the water in a hole extended a
short distance below the capillary zone. Groundwater
conditions are regular when there is only one
groundwater surface and when the hydrostatic pressure
increases linearly with depth. Under this condition, the
piezometric pressure level is the same as the free
groundwater level regardless of the depth below the
groundwater table at which it is measured. Referring to
Figure 5-5 (US EPA, 1981b), the water level in the
"piezometer" would stand at the same level as the "well"
in this condition.
5-15
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Piezometer
Grouncfwater table
Figure 5-5. Well and Piezometer Installations.
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 located. The basic difference between water
level measurement with a well and hydrostatic head
measurement with a piezometer is shown in Figure 5-5.
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
groundwater below.
Reliable determination of either groundwater 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. Called hydrostatic time
lag, this may be from hours to days in materials of
practical interest.
Two or more piezometers located together, but
terminating at different depth, 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 living aquifers. Figure
5-6 shows several observable patterns with
explanations. Details on the proper installation of wells
and piezometers are described in the US DOI "Drainage
Manual" (1978).
Groundwater Flow
Exact mathematical description of flow 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 (see Equation 3-1, and related discussion in
Chapter 3) to determine the volume of flow and the
mean travel time, as well as estimating the mounding
that will be created by the wastewater applications. The
calculation procedures are presented in detail. The
necessary field data include:
1. Depth to groundwater.
2. Depth to any impermeable barrier.
3. Hydraulic gradient determined from water levels in
several observation wells at known distances apart.
Establishing the gradient also determines the
direction of flow.
4. Specific yield (see Chapter 3).
5. Hydraulic conductivity in the horizontal direction (see
Chapters).
Figure 5-6. Vertical Flow Direction Indicated by Piezometers (US
EPA, 1981).
Data for items 1 and 3 can be obtained from periodic
water-level observations, over a period of months, from
simple wells installed on the site. Figure 5-7 illustrates a
typical shallow well.
The number and locations required will depend on the
size of the project and the complexity of the groundwater
system. Typical locations are up gradient of the site,
several on the site, and on the down-gradient boundary.
In general, groundwater levels will tend to reflect the
surface contours and flow toward adjacent surface
waters. In a complex situation it may be necessary to
install a few exploratory wells and then complete the
array based on the preliminary data. If properly located,
many of these wells can also serve for performance
monitoring during system operation. It is necessary to
determine the elevation at the top of each well. The
depth to water can then be determined with a weighted,
chalked tape or other sensing devices. Contours
showing equal groundwater elevation can then be
interpolated from the well data and plotted on a site map.
This in turn allows determination of the hydraulic
gradient and the flow direction.
Subsurface Permeability and Infiltration Rate
Methods for investigating subsurface permeability and
infiltration rate are discussed in Sections 3.8.1 and 3.8.2,
respectively.
5-16
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Mixing of Wastewater Percolate with
Groundwater
An analysis of the mixing of percolate with native
groundwater is needed for SR and SAT systems that
discharge to groundwater if the quality of this mixture as
it flows away from the site boundaries is a concern. The
concentration of any constituent in this mixture can be
calculated as follows:
(5-2)
Where
Cmix = concentration of constituent in mixture
Cp = concentration of constituent in percolate
Qp = flow of percolate
Cgw = concentration of constituent in groundwater
Qgw = flow of groundwater
Figure 5-7. Typical Shallow Monitoring Well (Crites etal.,2000).
The flow of groundwater can be calculated from
Darcy's Law (Equation 3-1) if the gradient and horizontal
hydraulic conductivity are known. This is not the entire
groundwater flow, but only the flow within the mixing
depth. Equation 5-2 is only valid if there is complete
mixing between the percolate and the native
groundwater. This is usually not the case. Mixing in the
vertical direction may be substantially less than mixing in
the horizontal direction, and density, salinity, and
temperature differences between the percolate and
groundwater may inhibit mixing and the percolate may in
some cases "float" as a plume on top of the groundwater
for some distance. The percolation of natural rainfall
down gradient of the application site can also serve to
dilute the plume.
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. This ratio
indicates the relative spread of the percolate and can be
used to relate the mixing of percolate with groundwater.
Thus, an upper limit of 3 for the dilution ratio can be
used when groundwater flow is substantially (5 to 10
times) more than the percolate flow. If the groundwater
flow is less than 3 times the percolate flow, the actual
groundwater flow should be used in Equation 5-2.
5.4.4 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 loading rates described previously (Section
5.6.2), the engineer should then select the appropriate
hydraulic loading rate for each land treatment process
that is suitable for each site under consideration. Based
on the hydraulic loading rates, estimates for land area,
preapplication treatment, storage, and other system
requirements can be determined. Reuse and recovery
options should also be outlined.
5.5 Cost and Energy Considerations
Once the preliminary design criteria have been
identified, the land treatment alternatives should be
evaluated on the basis of capital costs, revenue-
producing benefits, and energy requirements. Based on
these final evaluations, an appropriate plan can then be
selected and the land treatment system design initiated.
There are eight major categories of capital costs for
land treatment systems:
1. Transmission
2. Pumping
3. Preapplication treatment
4. Storage
5. Field preparation/Crop establishment
6. Distribution
7. Recovery
8. Land acquisition
In addition, there are costs associated with monitoring,
administration buildings, roads, and service and interest
factors. There also may be costs for fencing, relocation
5-17
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of residents and purchase of water rights. Depending on
the site management, SR and OF systems may have
costs associated with crop planting, cultivating and
harvesting.
Operation and maintenance (O&M) costs associated
with all of the eight categories of capital costs except for
land purchase and field preparation. These O&M costs
can be divided into categories of labor, power and
materials. Labor and materials for distribution and
recovery are presented in this chapter. Power costs for
pumping can be estimated from the energy
requirements. All costs in this chapter are for July 1999
using an Engineering News-Record Construction Cost
Index (ENRCCI) of 6076. These costs are only planning
level values and should not be used for designed system
cost estimating.
5.5.1 Transmission
Transmission of wastewater to application sites can
involve gravity pipe, open channels or pressure force
mains. Pumping can also be involved with gravity flow
transmission, but is required for force main transmission.
Costs of transmission depend on the pipe or the channel
size and can be estimated using US EPA (1981c).
5.5.2 Pumping
Pumping facilities for land treatment, as described in
Chapter 7, range from full pumping stations to tailwater
pumping facilities (see Section 5.5.7). Capital costs for
transmission pumping depend on the type of structure
that is designed. For example, a fully enclosed wet
well/dry well structure, pumps, piping and valves,
controls and electrical can cost $500,000 for a 3,785
m3/d (1 mgd) peak flow and a 45-m (150-ft) of total
pumping head. For structures that are built into the dike
of a pond, the capital cost of the pumping station for the
same flow and head can be $300,000.
5.5.3 Preapplication Treatment
Preapplication treatment for land treatment (Chapter 6)
ranges from preliminary screening to advanced
secondary treatment where reuse systems are
developed. Where a completely new land treatment
system is to be constructed, it is usually cost-effective to
minimize preapplication treatment and use screening or
short detention-time ponds for OF and treatment ponds
for SR and SAT. Costs of preapplication can be
estimated from data in Reed, et al. (1979), US EPA
(1981c), Tchobanoglous, et al. (1979), and Asano and
Tchobanoglous (1992). Many processes can be used
for preapplication treatment, including wetlands or
overland flow for treatment prior to SAT or SR systems.
Overland flow slope construction costs include the
same items as for land leveling. A cut of 265 m3/ha (500
yd /acre) would correspond to nominal construction on
pre-existing slopes. A cut of 529 m3/ha (1,000 yd3/acre)
corresponds to constructing 45-m (150-ft) wide slopes at
2 percent slope from initially level ground. A cut of 741
m/ha (1,400 yd3/acre) corresponds to 75-m (250-ft)
slope widths on 2.5 percent slopes from initially level
ground.
5.5.4 Storage
Storage ponds vary in cost depending on initial site
conditions, need for liners, and the depth and volume of
wastewater to be stored. Cost data are available from
Reed et al. (1979), US EPA (1981c), Tchobanoglous et
al. (1979), and Crites (1998).
5.5.5 Field Preparation
Costs for field preparation can include site clearing
and rough grading, land leveling and overland flow slope
construction. Costs of each of these types of field
preparation are presented in Table 5-24 for various
conditions. Site clearing costs include bulldozing of
existing vegetation, rough grading, and disposal of
debris onsite. Offsite disposal of debris will cost 1.8 to
2.2 times the values in Table 5-24 (US EPA., 1979b).
Land leveling costs include surveying, earthmoving,
finish grading ripping in two directions, disking,
equipment mobilization, and landplaning. In many cases,
106 m3/ha (200 yd3/acre) will be sufficient, while 397
m3/ha (750 yd3/acre) represents considerable
earthmoving.
Table 5-24. Costs of Field Preparation
ENR CCI = 6076
Type of Cost
Site Clearing
Grass only
Open field, some brush
Brush and trees
Heavily wooded
Land Leveling
200 yd3/acrea
500 yd3/acre
750 yd3/acre
Overland flow slope construction
500 yd3/acre
1 ,000 yd3/acre
1 ,500 yd3/acre
Capital Cost, $/acreb
30
220
1,450
2,890
360
720
1,010
1,300
2,170
2,890
ayda/acre x 1.9 = m^/ha
"acre x 0.4047 = ha
5.5.6 Distribution
Slow rate systems are capable of using a wide variety
of sprinkler and surface distribution systems. In
contrast, OF systems usually employ fixed sprinkler of
gated pipe surface distribution and Rl systems generally
employ surface spreading basins.
5-18
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Solid set sprinkling, described in Chapter 7, is the
most expensive type of sprinkler system. As shown in
Table 5-25 (Crites, 1998), portable and continuous-move
systems are considerably less expensive on an initial
capital cost basis. Capital and O&M costs are presented
in detail for solid set and center pivot sprinkling.
Table 5-25. Comparison of Sprinkler Distribution Capital Costs
Sprinkler Type
Comparative Cost
Portable hand move
Traveling gun
Side roll
Center pivot
Linear move
Solid set
0.13
0.22
0.22
0.50
0.65
1.00
Solid Set Sprinkling
The capital and O&M costs for buried solid set
systems are presented in Figure 5-8. For the SR system
in Figure 5-8, the laterals are spaced 30 m (100 ft) apart
and the sprinklers are 24 m (80 ft) apart on the lateral.
Laterals are buried 0.45 m (18 in) and mainlines are
buried 0.9 m (36 in). The pipe material is PVC while the
risers are galvanized steel. Flow to the laterals is
controlled by hydraulically operated automatic valves.
There are 5.4 sprinklers per acre at the specified
spacing. If more sprinklers are included (smaller
spacing), increase the capital and labor costs by using
Equation 5-3:
Cosf Factor = 0.68 + 0.06(S) (5-3)
Where:
Cost factor = multiplier times from Figure 5-8
S = sprinklers/acre
Conversion factor: acre = 0.4047 ha
For overland flow, the slopes are 75 m (250 ft) wide at
a 2.5 percent grade. The laterals are 21 m (70 ft) from
the top of the slope and sprinklers are 30 m (100 ft)
apart. Other factors are the same as for the SR system.
For O&M, the labor rate is $15.00/h including fringes.
Materials cost includes replacement of sprinklers and
valve controllers every 10 year.
Center Pivot Sprinkling
Capital and O&M costs for center pivot sprinkling in
Figure 5-9. The center pivot machines are electrically-
driven and heavy-duty units. Multiple units are included
for areas over 16 ha (40 acres) with a maximum area
per unit of 53 ha (132 acres). Distribution piping is buried
0.9 m (3 ft). Labor costs are based on $15.00/h and
power costs are based on 3.5 days/week operation for
each unit and $0.02/MJ ($0.08/kWh). Materials cost
includes minor repair parts and overhaul of units every
10 years.
Surface Distribution for OF or SR
Costs for gated pipe distribution for OF and SR systems
are presented in Figure 5-10. The OF slope is 60 m (200
ft) wide with the gated aluminum pipe distribution at the
top of the slope. For SR systems, the furrows or borders
are 360 m (1,200 ft) long on rectangular-shaped fields.
Graded border systems, under similar conditions of
border length, can use buried pipelines with alfalfa
valves at similar capital costs. Labor costs are based on
a $15.00/h wage including fringes. Materials cost
includes replacement of gated pipe after 10 years.
Soil Aquifer Treatment Basins
Costs for SAT basins are presented in Figure 5-11.
There are a minimum of 2 basins and a maximum basin
size of 8 ha (20 acres). Costs include inlet and outlet
control structures and control valves. Dikes are 1.2 m (4
ft) high with an inside slope of 3:1, an outside slope of2:1
and a 1.8-m (6-ft) wide dike crest. Dikes or berms are
formed from excavated native material. Labor costs
Figure 5-8. Solid Set Sprinkling (buried) Costs, ENR CCI = 6076.
(a) Capital Cost; (b) Operation and Maintenance Cost.
5-19
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100 1000
Field area, acres
(b!
Figure 5-9. Center Pivot Sprinkling Costs, ENR CCI = 6076.
(a) Capital Cost; (b) Operation and Maintenance Cost.
are based on a $15.00/h wage including fringe benefits.
Materials cost includes rototilling or disking the basin
surface every 6 months and major repair of the dikes
every 10 years.
5.5.7 Recovery
Recovery systems can include underdrains (for SR or
SAT), tailwater return for SR surface application, runoff
collection for OF, and recovery wells for SAT.
Underdrains
Costs for underdrain systems are presented in Table
5-26 for spacings between drains of 30 and 120 m (100
and 400 ft). Drains are buried 1.8 to 2.4 m (6 to 8 ft)
deep and discharge into an interception ditch along the
length of the field.
Labor costs are based on a $15.00/h wage rate
including fringes, and labor involves inspection and
unclogging of drains at the outlets. Materials cost
includes high-pressure jet cleaning of drains every 5
years, annual cleaning of interception ditches, and major
repair of the interception ditch after 10 years.
100
Figure 5-10. Gated Pipe — Overland Flow or Ridge-and-
Furrow Slow Rate Costs, ENR CCI = 6076.
(a) Capital Cost; (b) Operation and Maintenance Cost.
Tailwater Return
Tailwater from ridge-and-furrow or graded border
systems must be recycled either to the storage ponds or
to the distribution system. Typically 25 to 30 percent of
the applied flow should be expected as tailwater. Capital
costs, presented in Table 5-27, include drainage-
collection ditches, storage sump or pond, pumping
facilities, and a 60-m (200-ft) return force main. Labor, at
$15.00/h including fringe benefits, includes operation of
the pumping system and maintenance of the ditches,
sump, pump, and return system. Materials cost includes
major repair of the pumping station after 10 years.
Power cost is based on $0.02/MJ ($0.08/kWh).
Runoff Collection for OF
Runoff collection can consist of an open ditch or a
buried pipeline with inlets. Costs for open ditches,
presented in Table 5-28, include a network of ditches
sized for a 5.1-cm/h (2-in/h) storm, culverts under
service roads, and concrete drop structures every 300 m
(1,000 ft) (for larger systems). For gravity pipe systems,
5-20
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Figure 5-11. Rapid Infiltration Basin Costs, ENR CCI = 6076.
(a) Capital Cost; (b) Operation and Maintenance Cost.
Table 5-26. Costs of Underdrains (US EPA., 1979b)
ENR CCI = 6076
Type of Cost $/acreb
Capital costs
100-fta spacing 2,890
400-ft spacing 1090
O&M costs
Labor
100-ft spacing 52
400-ft spacing 22
Materials
100-ft spacing 140
400-ft spacing 90
aftx 0.3048 = m.
"acre x 0.4047 = ha.
Table 5-27. Costs of Tailwater Return Systems (Reed et al., 1979)
ENR CCI = 6076
Type of Cost
Cost
0.1 mgda of Recovered Water
Capital, $
O&M:
Power, $/year
Labor, $/year
Materials, $/year
1.0 mgd of Recovered Water
Capital, $
O&M:
Power, $/year
Labor, $/year
Materials, $/year
60,000
375
375
180
145,000
4,000
900
700
the costs include a network of interceptor pipes with
inlets every 75 m (250 ft) and accessholes every 150 m
(500 ft).
Labor costs are based on $15.00/h including fringe
benefits. Materials cost includes biannual cleaning of
ditches and major repair every 10 years.
Table 5-28. Costs of Runoff Collection for Overland Flow (Reed et al.,
1979)
ENR CCI = 6076
Type of Cost
Capital costs:
Gravity pipe system
Open ditch system
O&M costs:
Labor
Gravity pipe
Open ditch
Materials
Gravity pipe
Open ditch
$/acrea
2,300
360
$/acre-year
8
30
7
40
a acre x 0.4047 = ha.
Recovery Wells
Costs for recovery wells for SAT systems are
presented in Table 5-29 for well depths of 15 and 30 m
(50 and 100 ft). Capital costs include gravel-packed
wells, vertical turbine pumps, simple shelters over each
well, controls, and electrical work. Labor, at $15.00/h,
includes operation and preventative maintenance.
Materials cost includes repair work performed by
contract, and replacement of parts. Power cost is based
on $0.02/MJ ($0.08/kWh). Monitoring wells are generally
a minimum of 100 mm (4 in) in diameter and typically
cost $130 to $200/m ($40 to $60/ft) (US EPA, 1979).
Table 5-29. Costs of Recovery Wells (Reed etal., 1979)
ENR CCI = 6076
Type of Cost
Cost
1.0 mgd of recovered water:
Capital, $:
50 ftb depth
100 ft depth
O&M, $/yr:
Power, 50-ft depth
Power, 100-ft depth
Labor
Materials
29,000
50,000
9,500
18,900
6,000
800
a mgd x 3.7854x10 = m /day.
qmgd x 3.7854x103 = m3/day.
bftx 0.3048 = m.
5.5.8 Land
Land can be controlled by direct purchase, lease, or
contract. The land for preapplication treatment and
storage is usually purchased, however, field area for SR
5-21
-------
systems is sometimes leased or a contract is formed
with the landowner. Options used by selected
communities for land acquisition and management for
selected SR systems are presented in Table 5-31
(Crites, 1981 and Christensen, 1982). As shown in Table
5-31, contracts for effluent use are utilized in several SR
systems. Fee simple purchase is generally used for OF
and SATsites.
5.5.9 Benefits
Revenue producing benefits from land treatment
systems can include sale of crops, lease of land, sale of
wastewater or recycled water, and contracts that may
involve all of these benefits. Examples of revenue-
producing benefits are presented in Table 5-30 (Crites,
1981, 1982, and 1998, Christensen, 1982, US EPA,
1995, and US EPA, 1979a). The examples are for SR
systems, which generally have the greatest potential for
revenue production. Crop sale from OF systems can
offset a small portion of O&M costs, but generally cannot
be expected to more than offset the cost of harvesting
and removal of the grass or hay. For SAT systems in
water-short areas, the potential for recovery and reuse of
the percolate should be investigated.
Sale of crops can be a significant source of revenue if
the community is willing to invest in the necessary
equipment for crop harvest and storage. For ezample,
Muskegon County realized gross revenues of
$1,000,000 from the sale of corn (US EPA 1979a).
Cash rent for SR cropland is very popular in the west
with 5-year agreements being common. Rents range
from $2 to $32/ha ($5 to $80/acre). Contracts for
wastewater irrigation, rental of irrigation equipment, or
for the use pastureland for cattle grazing have also been
utilized. Examples include El Reno, OK; Dickinson, ND;
Mitchell, SD; Tuolumne County, CA; Santa Rosa, CA;
and Petaluma, CA.(Crites, 1982 and NACD, 1981).
5.5.10 Energy Requirements
The energy requirements for land treatment systems
include power for pumping, preapplication treatment,
wastewater distribution, and fuel for crop planting and
harvesting and for biosolids transport and spreading. In
addition, energy is needed for heating and cooling of
buildings, lighting and vehicle operation.
Pumping. Pumping for transmission, distribution,
tailwater return, and recovery is a major energy use in
most land treatment systems. The energy required can
be calculated using Equation 5-4:
Energy Use =
Where
Energy Use
Q
TH
t
F
E
annual usage, kWh/year
flowrate, gal/min
total head, ft
pumping time, h/year
constant, 3960 x 0.746 = 2954
overall pumping efficiency, decimal
The overall efficiency depends on the type of
wastewater and the specifics of pump and motor
selection. In the absence of specific information on pump
and motor efficiency, the following overall pumping
system efficiencies can be used:
Table 5-30. Benefits of Land Treatment Systems
Sale of crops
Muskegon, Ml
San Angelo, TX
Lease of land
Bakersfield, CA
Coleman, TX
Manteca, CA
Mesa, CA
Winters, CA
Sale of effluent
Cerritos, CA
Irvine Ranch, CA
Las Virgines, CA
Marin MWD, CA
$/yr
900,000 - 1 ,000,000
58,000 - 71 ,000
$/acre-yra
80
5
40
50
20
$/acre-ftb
40
118
160
300
acre x 0.4047 = ha.
acre-ft x 0.123 = ha-m.
Table 5-31. Options for Land Acquisition and Management at Selected SR Systems
Location
Bakersfield, CA
Camarillo, CA
Dickinson, ND
Lubbock, TX
Mesa, AZ
Muskegon, Ml
Petaluma, CA
Roswell, NM
San Antonio, TX
Tooele, UT
Area, acres3
2,400
475
250
4,000
160
1 0,400
550
285
740
1,200
Acquisition Option
Fee simple
Contract
Contract
Fee simple and contract
Fee simple
Fee simple
Contract
Contract
Fee simple
Contract
Management Option
Leaseback to farmer
Landowner accepts water
Cash lease for water sale to farmer
Leaseback, farmer owns effluent
Leaseback for cash rent
Managed by county
Cash rent for irrigation equipment
Cash lease for water sale to farmer
Managed by city
Cash lease for water sale to farmer
a acre x 0.4047 = ha.
5-22
-------
and Middlebrooks et al., (1979). Energy for crop
production is minor compared to energy for distribution.
For example, energy requirements for corn production
are 51.3 MJ/ha (5.7 kWh/acre) and for alfalfa are 22.5
MJ/ha (2.5 kWh/acre). Fuel usage can be converted to
energy using 34,596 KJ/L (124,000 Btu/gal) for gasoline
and 3,906 KJ/L (14,000 Btu/gal) for diesel (US EPAij,
1978 and WPCF, 1981).
5.5.11 Energy Conservation
Sprinkler distribution systems are candidates for
energy conservation. Impact sprinklers may require 45 to
60 m (150 to 200 ft) of head to operate. Recent
advances have been made in sprinkler nozzle design to
allow operation at lower pressures without sacrificing
uniformity of application. Use of drop nozzles with
pressure requirements of 15 m (50 ft) of head can result
in significant energy conservation.
Energy conservation is also possible in land treatment
systems through the use of surface distribution. A
comparison of primary and secondary energy usage of
various land and aquatic treatment systems is presented
in Table 5-32 (Tchobanoglous et al., 1979). Primary
energy is that fuel or power used directly in operations.
Secondary energy is that used in the construction of
facilities or manufacturing of chemicals.
Energy conservation through the use of land
application of wastes can also be realized through
savings in energy use for manufacturing of commercial
fertilizer. A presentation of energy needs to produce
fertilizer and the energy value of nutrients in wastewater
is given in Table 5-33 (Middlebrooks et al., 1979 and
WPCF, 1981).
Table 5-32. Energy Requirements for Land and Aquatic Treatment Systems
Equivalent energy, 1 ,000 kWh/yeara
System
PT + SAT
Ponds and wetlands
PT + SR(surface)
PT + OF
Ponds and hyacinths
PT + SR(spray)
Primary Energy
187
121
187
192
167
327
Secondary Energy
102
198
135
159
195
173
Total Energy
289
319
322
351
362
500
Note: PT = primary treatment; SAT = soil aquifer treatment; SR = slow rate and OF = overland flow.
akWhx3.6 = MJ.
Table 5-33. Energy Value of Nutrients in Wastewater
Nutrient
Nitrogen as N
Phosphorus as P
Potassium as K
Content of effluent,
mg/La
20
10
15
Content of effluent,
lb/acre-ftb
54
27
38
Energy to produce, transport and
apply fertilizer, kWh/lb°
2.79
0.10
0.10
Energy value of nutrients in wastewater,
kWh/acre-ftd
190
13
10
amg/L = g/rn^.
blb/acre-ft x 3.69 = kg/ha-m.
°kWh/lb x 7.9 = MJ/kg.
dkWh/acre-ft x 29.3 = MJ/ha-m.
5.6 References
Christensen, L.A. (1982) Irrigating with Municipal
Effluent, USDA, ERS-672, Washington, DC.
Crites, R.W. (1981) Economics of Reuse, Proceedings
of the Water Reuse Symposium II, Volume 3,
AWWA, p. 1745-1751.
Crites, R.W. (1982) Land Treatment and Reuse of
Food Processing Waste, Proceedings of the
Industrial Wastes Symposia, Water Pollution Control
Federation, 55th Annual Conference, St. Louis, MO.
Crites, R.W. (1982) Innovative and Alternative
Treatment at Petaluma, CA, .Presented at the
Hawaii Water Pollution Control Association Annual
Conference, Honolulu, HI.
Crites, R.W. and G. Tchobanoglous (1998) Small and
Decentralized Wastewater Management Systems,
McGraw-Hill, New York, NY.
Crites, R.W. (1998) Cosfs of Constructed Wetlands,
Proceedings WEFTEC '98, Orlando, FL. Water
Environment Federation, Alexandria, VA.
Crites, R.W., S.C. Reed, and R.K. Bastian (2000) Land
Treatment of Municipal and Industrial Wastewater,
McGraw-Hill Book Co., New York, NY.
5-23
-------
Dewsnup, R.L. and Jensen, D.W. (Eds.) (1973) A
Summary Digest of State Water Laws, National
Water Commission, Washington, DC.
Loehr, R.C. (1974) Agricultural Waste Management-
Problems, Processes, and Approaches, New York:
Academic Press.
Metcalf & Eddy, Inc. (1976) Land Application of
Wastewater in the Salinas-Monterey Peninsula
Area, U.S. Army Engineer District San Francisco,
CA.
Middlebrooks, E.J. and C.H. Middlebrooks (1979)
Energy Requirements for Small Flow Wastewater
Treatment Systems, USA CRREL, Special Report
79-7.
Moser, M.A. (1978) 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, NH.
Nightingale, H.I. et al. (1983) Leaky Acres Recharge
Facility: A Ten-Year Evaluation, AWRA Water
Resources Bulletin, Vol. 19, 3, p. 429.
Reed, S.C. (1982) The Use of Clayey Sands for Rapid
Infiltration Wastewater Treatment, USA CRREL IR
805, p.55.
Richard, D., T. Asano, and G. Tchobanoglous (1992)
The Cost of Wastewater Reclamation in California,
Department of Civil and Environmental Engineering,
University of California, Davis.
Sills, M.A., et al. (1978) 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, NH.
Taylor, G.L. (1981) Land Treatment Site Evaluation in
Southeastern Mountainous Areas, Bulletin of the
Association of Engineering Geologists, 18: 261-266.
Tchobanoglous, G., J.E. Colt, and R.W. Crites (1979)
Energy and Resource Consumption in Land and
Aquatic Treatment Systems, Proceedings: Energy
Optimization of Water and Wastewater Management
for Municipal and Industrial Applications Conference,
USDOE, Volume 2, New Orleans.
US DOI (1978) Drainage Manual, U.S. Department of
the Interior, Bureau of Reclamation.
US EPA (1976) Use of Climatic Data in Estimating
Storage Days for Soil Treatment Systems, EPA -
600/2-76-250, U.S. Environmental Protection
Agency, Cincinnati, OH.
US EPA (1977a) Annual and Seasonal Precipitation
Probabilities, EPA-600/2-77-182, U.S.
Environmental Protection Agency, Cincinnati, OH.
US EPA (1977b) Land Application of Wastewater and
State Water Law: An Overview
(Volume I), EPA-600/2-77-232, U.S. Environmental
Protection Agency, Cincinnati, OH.
US EPA (1978a) Land Application of Wastewater and
State Water Law: State Analyses
(Volume II), EPA-600/2-78-175, U.S. Environmental
Protection Agency, Cincinnati, OH.
US EPA (1978b) Energy Conservation in Municipal
Wastewater Treatment, EPA-430/9-77-011.
US EPA (1978) Energy Conservation in Municipal
Wastewater Treatment, EPA-430/9-77-011.
US EPA (1979a) Waste water: Is Muskegon County's
Solution Your Solution? EPA-905/2-76-004, U.S.
Environmental Protection Agency, Washington, DC.
US EPA (1979b) Cosf of Land Treatment Systems, EPA
430/9-75-003, U.S. Environmental Protection
Agency, Washington, DC.
US EPA (1980) Design Manual - Onsite Wastewater
Treatment and Disposal Systems, EPA 625/1-80-
012 U.S. Environmental Protection Agency,
Cincinnati, OH.
US EPA (1981 a) The Role of Conservation Districts
and the Agricultural Community in Wastewater Land
Treatment, EPA-430/9-77-011.
US EPA (1981b) Process Design Manual for Land
Treatment of Municipal Wastewater, EPA 625/1-81-
013, U.S. Environmental Protection Agency,
Cincinnati, OH.
US EPA (1981c) Construction Costs for Municipal
Wastewater Conveyance Systems: 1973-1979, EPA
430/9-81-003, U.S. Environmental Protection
Agency, Washington, DC.
US EPA (1982) Operation and Maintenance
Considerations for Land Treatment Systems, EPA-
600/2-82-039.
US EPA (1995) Process Design Manual - Land
Application of Sewage Sludge and Domestic
Septage, EPA/625/R-95/001, U.S. Environmental
Protection Agency, Washington, DC.
Water Pollution Control Federation (1981) Energy
Conservation in the Design and Operation of
Wastewater Treatment Facilities, Manual of Practice
No. FD-2.
5-24
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Chapter 6
Preapplication Treatment and Storage
The level of preapplication treatment required prior to
any of the land treatment processes should involve both
engineering and economic decisions that recognize the
potential performance of the land treatment process and
the sensitivity of the receiver environment. An approach
would be to start with the final effluent or percolate
quality requirements for the site and climatic conditions
and, then determine the contribution the land treatment
processes can provide. A level of preapplication
treatment can then be adopted for those constituents
that will not be removed or reduced to an acceptable
concentration by the land treatment process. The
method of preapplication treatment should then be
selected as the simplest and most cost-effective system
possible.
6.1 EPA Guidance
The level of preapplication treatment required should
also be based on the degree of public access to the site
and/or on the type and end use of the crop grown. The
guidelines for preapplication treatment developed by the
US EPA are summarized in Table 6-1. The level of
treatment increases as the degree of public access
increases when the crop is for direct human
consumption and when environmental sensitivity
increases. The chemical and microbiological standards
in general are based on water quality requirements for
irrigation with surface water and on bathing water quality
limits for the recreational case (Thomas and Reed,
1980).
6.1.1 Slow Rate Systems
SR systems may require preapplication treatment for
several reasons, including public health protection
relating to human consumption of crops and crop
byproducts that are eaten uncooked or direct exposure
to applied effluent, prevention of nuisance conditions
during storage, distribution system protection, or soil and
crop considerations and watershed considerations (e.g.,
TMDLs). Preliminary treatment, except for solids
removal, is often de-emphasized because SR systems
are capable of achieving final water quality objectives
with minimal pretreatment. In many cases, SR systems
are designed for regulatory compliance following
preliminary treatment so the potential for reuse can be
realized. Systems designed to emphasize reuse
potential require greater flexibility in the handling of
effluent, which can be achieved with higher pretreatment
levels.
The treatment objective should be to maximize
nitrification if surface discharge is required and ammonia
discharge requirements are stringent. Nitrification may
be achieved using either primary or secondary treatment
prior to application.
6.1.2 Soil Aquifer Treatment Systems
Primary sedimentation or the equivalent is the
minimum recommended preapplication treatment for all
SAT systems. This level of treatment reduces wear on
the distribution system, prevents unmanageable soil
clogging, reduces the potential for nuisance conditions,
and allows the potential for maximum nitrogen removal.
For small systems, a short-detention-time pond is
recommended. Long-detention-time facultative or
aerobic ponds are not recommended because of their
propensity to produce high concentrations of algae. The
algae produced in stabilization ponds will reduce
infiltration rates significantly. If facultative or stabilization
ponds are to be used with SAT, it is recommended that
an aquatic treatment or constructed wetland system be
used between the pond and the SAT basins to reduce
TSS levels (Crites and Tchobanoglous, 1998).
6-1
-------
Table 6-1. Guidelines for Assessing the Level of Preapplication Treatment (Thomas and Reed, 1980)
Slow Rate Systems
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 lagoon or in-plant 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 lagoons or in-plant processes with additional BOD or TSS removal as needed for aesthetics plus disinfection to a
geometric mean of 125 E.coli per 100 ml and 33 enterococci per 100 ml (EPA water quality criteria for bathing waters) - acceptable for
application in public access areas such as parks and golf courses
Rapid Infiltration Systems (Soil Aquifer Treatment)
A. Primary treatment - acceptable for isolated locations with restricted public access
B. Biological treatment by lagoons or in-plant processes - acceptable for urban locations with controlled public access
Overland Flow Systems
A. Screening or comminution - acceptable for isolated sites with no public access
B. Screening or comminution plus aeration to control odors during storage or application - acceptable for urban locations with no public access
biological nutrient removal and membrane processes are
also discussed.
6.1.3 Overland Flow Systems
Preapplication treatment before OF is provided to
prevent operating problems with distribution systems, to
prevent nuisance conditions during storage and possibly
to meet stream discharge requirements. 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.
Municipal wastewater contains rags, paper, hair and
other coarse solids that can impair 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 difficulties. For small systems, Imhoff
tanks or 1- to 2-day aerated detention ponds are
recommended. Static or rotating fine screens have also
been used successfully at Davis, CA. and Hall's Summit,
LA. (WPCF, 1989). 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 openings have been used successfully for raw
wastewater screening (US EPA, 1981).
Grit removal is advisable for wastewaters containing
high grit loads. Grit reduces pump life and can deposit in
low-velocity distribution pipelines.
6.2 Types of Preapplication Treatment
Preapplication treatment operations and processes
can include fine screening, primary treatment, lagoons or
ponds, constructed wetlands, biological treatment,
membranes, and disinfection. Removal efficiencies and
design criteria for these treatment operations and
processes are documented in Crites and Tchobanoglous
(1998). Because ponds and constructed wetlands are
often compatible with land treatment systems, the
efficiencies of these preapplication treatment methods
are described in the following sections. In addition,
6.2.1 Constituent Removals in Ponds
Effluent from any conventional wastewater treatment
process can be applied successfully to the land as long
as the site and soils are compatible. In many cases, a
pond or lagoon will be the most cost-effective choice for
treatment. Ponds can be used with land treatment for
basic treatment, flow equalization, for emergency
storage, and where there are seasonal constraints on
the operation of land treatment systems. In cases where
storage is needed, it will usually be most cost-effective to
combine the treatment and storage functions in a
multiple cell pond system. Where odor control or high
strength wastes are a factor, the initial cell may be
aerated and followed by one or more deep storage cells.
In remote locations an anaerobic primary cell can be
designed for the treatment of high-strength wastes and
solids removal and be followed by storage cells. The
treatment occurring in the storage cells will be similar to
that in a facultative pond. Basic design criteria for
conventional pond systems are available from a number
of sources (Crites and Tchobanoglous, 1998; Reed et
al., 1995; US EPA, 1983; and Middlebrooks et al., 1982).
The pond unit can be specifically designed for the
removal of a particular wastewater constituent. More
typically, the detention time in the pond component is
established by the storage requirements for the system.
The removal of various constituents that will occur within
that detention time can then be calculated. If additional
removal is required, the cost-effectiveness of providing
more detention time in the pond can be compared to
alternative removal processes. The removal of nitrogen
in the pond unit is particularly important because
nitrogen is often the Limiting Design Parameter (LDP) for
slow rate systems. Any reduction of nitrogen in the pond
unit directly impacts on the design of the land treatment
component.
6-2
-------
6.2.2 BOD and TSS Removal in Ponds
BOD5 is usually not the LDP for design of the
municipal land treatment component in any of the
processes. However, many regulatory agencies specify
a BOD5 requirement for the wastewaterto be applied, so
it may be necessary to estimate the removal that will
occur in the pond components. There may be a
combination of an aerated or anaerobic cell followed by
the storage pond.
Aerated Ponds
The BOD5 removal that will occur in aerated cells can
be estimated with:
1
(6-1)
Where:
Cn
Co
kc
t
n
effluent BOD5 from cell n, mg/L
influent BOD5to system, mg/L
reaction rate constant (see Table 6-2) at 20°C
total hydraulic resident time, d
number of cells
The reaction rate constant, kc, is dependent on the
water temperature, as shown in Equation 6-2:
Ix _ Ix f)(T-20)
KcT ~K20t/
(6-2)
Where:
kcT = reaction rate const, at temperature T
k20 = reaction rate const, at 20°C (see Table 6-2)
6 = 1.036
T = temperature of pond water, °C
The temperature of the pond can be estimated with the
following equation:
AfT.+QT,
Af + Q
(6-3)
Where:
Tw
Ta
T
A
f
Q
= pond temperature, °C
= ambient air temperature, °C
= pond influent temperature
= surface area of pond, m2
= proportionality factor = 0.5
= wastewater flow rate, m3/d
The selection of an apparent reaction rate value from
Table 6-2 depends on the aeration intensity to be used.
The "complete mix" value assumes high intensity
aeration [about 20 W/m3 (100 HP/MG)], sufficient to
maintain the solids in suspension. The "partial mix" value
assumes that there is sufficient air supplied to satisfy the
oxygen demand [about 2 W/m3 (10 HP/MG)], but that
solids deposition will occur.
Table 6-2. Reaction Rates for Aerated Ponds, BOD5
Type of Aeration k at 20°C
Complete mix
Partial mix
2.5
0.276
The suspended solids in the effluent from a complete
mix aerated cell will be nearly the average concentration
in the cell. The suspended solids in the partial mix pond
effluent will be lower, depending on the detention time.
For a detention time of 1 day, assume the suspended
solids are
(mg/L)].
similar to primary effluent [60 to 80 g/m
Facultative Ponds
The BOD5 removal that will occur in a facultative cell
can be estimated using Equation 6-4.
Ł,
c,
= e - Kft
(6-4)
Where:
Cn
C0
= effluent BOD5, g/m3 (mg/L)
= influent BOD5, g/m3 (mg/L)
= plug flow apparent reaction rate constant (see Table 6-3)
= detention time, days
The apparent rate constant for plug flow also varies
with temperature with a e value of 1.09.
Table 6-3. Variation of Plug Flow Apparent Rate Constant with
Organic Loading Rate for Facultative Ponds (Neel et al., 1961)
kg/ha-day*
22
45
67
90
112
kp, per day
0.045
0.071
0.083
0.096
0.129
*kg/ha-day x 0.8928 = Ib/acre-day.
The TSS concentrations from facultative cells depend
on the temperature and detention time. Algae
concentrations can reach 120 to 150 g/m3 (mg/L) or
more in warm temperatures and may be as low as 40 to
60 g/m3 (mg/L) in cooler temperatures (Stowell, 1976).
Anaerobic Ponds
Anaerobic ponds are rarely used with municipal
wastewaters unless there is a large industrial waste
component. The ponds are typically 3 to 4.5 m (10 to 15
ft) deep. BOD5 loading rates may be as high as 500
kg/ha day (450 Ib/ac-day), detention times range from 20
to 50 days, depending on the climate, and a BOD5
conversion of about 70 percent is typical. Effluent TSS
values range from 80 to 160 g/m3 (mg/L).
6-3
-------
A primary anaerobic cell is used at a number of
municipal pond systems in rural areas of the western
provinces of Canada (Higo, 1966). The anaerobic cells
are also designed for solids removal and retention and
are typically followed by one or more long-detention-time
facultative cells. Effluent from these cells is comparable
to primary effluent. Detectable odors have been noted to
at least 305 m (1,000 ft) around these systems, so a
remote location or other odor control is needed.
6.2.3 Constituent Removals in Constructed
Wetlands
Constructed wetlands have been used to remove
BOD5, TSS, nitrate-nitrogen, and metals, among other
constituents, from wastewater (Crites and
Tchobanoglous, 1998; Reed et al., 1995; Reed 1999;
USEPA 1999). Constructed wetlands can be free water
surface (FWS) or subsurface flow (SF). Free water
surface constructed wetlands are best suited to
preapplication treatment, especially for flows above 0.1
mgd (387 m3/d).
Area for BOD Removal
The field area needed for a constructed wetland can
be calculated using Equation 6-5.
A =
Q(lnC0-lnC.)
(6-5)
Where:
A
Q
Co
Ce
K
= field area, m2 (acres)
= average flow, (in + out)/2 m3/d (acre-ft/d)
= influent BOD, mg/L
= effluent BOD, mg/L
= apparent removal rate constant
= 0.678 d'1 for FWS wetlands at 20°C
= 1.104 d'1 for SF wetlands at 20°C
= water depth, m (ft)
= porosity
= 0.75 to 0.9 for FWS wetlands
= 0.28 to 0.45 for SF wetlands
The average flow should be the annual average flow
into the wetlands plus the effluent flow divided by two.
The apparent K factor is temperature dependent and
Equation 6-2 can be used for different water
temperatures, with the e factor being 1.06. The porosity
of FWS wetlands depends on the density of the
vegetation, with 0.75 being appropriate for high plant
densities and 0.85 being appropriate for moderate plant
densities. Where open water areas are interspersed
with vegetated zones the porosity will be 0.8 to 0.9. For
SF constructed wetlands the porosity depends on the
particle size of the gravel used. Coarse sand and
gravelly sand has a porosity of 0.28 to 0.35. Fine gravel,
widely used in SF systems, has a porosity of 0.35 to
0.38. Medium to coarse gravel has a porosity of 0.36 to
0.45 (Reed et al., 1995). These porosity values are
measured by a field test and are much higher then those
given in Figure 3-2, which are measured in a laboratory
using a standard ASTM method. The values from Figure
3-2 are for in-situ soil and gravel deposits which have
been naturally consolidated, and they are not
appropriate for design of SF constructed wetlands.
Area for Nitrate Removal
Constructed wetlands can be effectively designed for
nitrate removal for effluents containing high nitrate.
Equation 6-6 can be used to predict nitrate reduction.
For water temperatures of 1°C or less, assume that
denitrification effectively ceases.
f = -
(6-6)
Where:
t
Ci
cf
K,
= actual detention time, days
= influent nitrate concentration, g/m3 (mg/L)
= effluent nitrate concentration, g/m3 (mg/L)
= rate constant, use 1.0 for temperature of 20°C
The temperature adjustment can be made using
Equation 6-2, using a e value of 1.15.
6.2.4 Nitrogen Losses in Storage Ponds
The loss of nitrogen from ponds and water bodies has
been recognized and predictive models are available
(Reed, 1984). The removal of nitrogen in a pond is
dependent on pH, temperature, and detention time.
Under ideal conditions up to 95 percent has been
observed. Volatilization of the ammonia fraction is
believed to be the major pathway responsible for long-
term permanent losses.
Because nitrogen is often the limiting design
parameter (LDP) for land treatment design, it is essential
to determine (i.e., operationally monitor) the losses that
will occur in any preliminary pond units for treatment or
storage. This may influence the basic feasibility of a
particular process, or control the amount of land needed.
The equations presented below can be used for
facultative ponds and for storage ponds. The nitrogen
losses in short detention time aerated ponds can usually
be neglected. The procedure is based on total nitrogen
in the system because numerous transformations from
one form of nitrogen to another are likely during the long
detention time.
The first design equation is (Reed et al., 1995):
= exp -kt + 60.6 (pH
-6.6)]}
(6-7)
Where:
Ne
No
knt
effluent total N, g/m3 (mg/L)
influent total N, g/m3 (mg/L)
temperature-dependent reaction rate const., d"1
6-4
-------
PH
= 0.0064 at 20°C
= detention time, days
= median pH in pond during time t
Table 6-4. Typical pH and Alkalinity Values in Facultative Ponds
The temperature adjustment can be made using
Equation 6-2, using a theta value of 1.039.
The second design equation is presented below (Reed
etal., 1995):
1
(6-8)
u 1 + f (0.000576F - 0.00028) exp [(1.08 - 0.042F)(pH - 6.6)]
Terms are the same as for Equation 6-7.
Application of Equation 6-7 requires information on the
wastewater nitrogen concentration, the detention time,
pH and temperature conditions to be expected. In a
typical case the nitrogen concentration will vary from
month to month so actual long-term data are desirable
for design.
For the first iteration, the detention time should be
determined based on (a) any BOD removal required, or
(b) by the storage time needed. If additional nitrogen
removal is necessary then the cost-effectiveness of
providing more detention time can be compared to other
alternatives.
Equation 6-7 is based on plug flow kinetics and is valid
when a pond is discharging and the detention time is
then the total detention time in the system. A value of
one-half the detention time should be used for the filling
and storage (non-discharge) periods for storage ponds.
The pH is controlled by the algae interactions with the
carbonate buffering system in the pond. If possible, pH
values should be obtained from an operating pond in the
vicinity. The median pH values for four facultative ponds
in the U.S. are given in Table 6-4 (US EPA, 1977; US
EPA, 1977; and US EPA, 1977). A rough estimate of the
pH to be expected can be obtained with:
pH = 7.3 exp [ 0.005 (Alk) ]
(6-9)
Where:
PH
Alk
= median pH in the bulk liquid
= alkalinity of the influent (as CaCO3), g/m3 (mg/L)
Location
Peterborough, NH
Eudora, KS
Kilmichael, MS
Corinne, UT
Annual Median pH
7.1
8.4
8.2
9.4
Annual Average
Alkalinity,
g/m3 (mg/L)
85
284
116
557
6.2.5 Phosphorus Removal in Ponds
Phosphorus removal in ponds is limited. Chemical
addition using alum or ferric chloride has been used to
reduce phosphorus to below 1 g/m3 (mg/L) (Reed et al.,
1995). Application of chemicals can be on a batch or
continuous-feed basis. For controlled release ponds the
batch process is appropriate. The State of Minnesota
has 11 facultative pond systems that use the addition of
liquid alum directly into secondary cells via motorboat to
meet a spring and fall discharge limitation of 1 g/m3
(mg/L) (Surampalli et al., 1993).
For continuous-flow applications, a mixing chamber is
often used between the last two ponds or between the
last pond and a clarifier. In Michigan, both aerated ponds
and facultative ponds have been used with continuous-
flow applications. Influent phosphorus concentrations for
21 treatment facilities ranged from 0.5 to 15 g/m3 (mg/L)
with an average of 4.1 g/m3 (mg/L) and the effluent
target is 1 g/m3 (mg/L) (Surampalli et al., 1993).
6.2.6 Pathogen Removal in Ponds
The design of systems that include a pond component
should evaluate the bacteria and virus reductions that
will occur in the pond. In some cases the reductions that
will occur in a pond will produce acceptable levels so an
extra disinfection step will not be required. At Muskegon,
Ml, for example, the fecal conforms in the storage pond
effluents were consistently below required levels so that
chlorination was terminated (Reed, 1979). The effluent in
this case is applied to corn, with poultry feed a major use
of the harvested corn. Water-quality changes through
the storage pond at Muskegon, Ml, and in a pilot-scale
pond in Israel are summarized in Table 6-5 (US EPA,
1976; Kott, 1978).
6-5
-------
Removal of bacteria and virus in ponds is strongly
dependent on temperature and detention time. Virus
removal in model ponds is illustrated in Figure 6-1
(Sagik, 1978). Similar results were observed at
operational facultative ponds in the southwest, southeast
and north central United States. In summer months,
virus removal exceeded 2 log (i.e., 99 percent) in the first
two cells of these systems. The overall removal on a
year-round basis exceeded 1.5 log (i.e., 95 percent).
Removal of fecal conforms was even higher.
Table 6-5. Changes of Microorganisms Concentration During Storage (US EPA, 1979)
Location
Input Concentration, count/100 ml
Output Concentration, count/100 ml
Muskegon County, Ml (winter):
Fecal coliform
Haifa, Israel
(winter, 73 days):
Total coliform
Fecal coliform
Fecal streptococcus
Enterovirus
Haifa, Israel
(summer, 35 days):
Total coliform
Fecal coliform
Fecal streptococcus
Enterovirus
1 x 106
2.3 x107
1.1 x 106
1.1 x 106
1.1 x 103
1.4x 107
3.5 x 106
6.0 x 105
200
1 x 103
1.84x104
2.4 x103
5.0 x102
0
2.3 x104
2.4 x104
3.7 x103
0
40 6O SO 1OO 12O
Time, days
Figure 6-1. Virus Removal in Ponds (Sagik, 1978).
Results very similar to those in Figure 6-1 have been
demonstrated for fecal conforms in facultative ponds in
Utah (Bowles et al., 1979). An equation was developed,
based on Chick's Law which describes the die-off of
fecal conforms in a pond system as a function of time
and temperature:
t =
ln(C,/Cf)
(6-10)
Where:
t
Ci
c,
k,c
= actual detention time, d
= influent fecal conforms, #/100 ml
= final fecal coliforms, #/100 ml
= rate constant, use 0.5 for temperature of 20°C
70
so
40
Final concentrations
. ZOO/100 mL
Initial concentration = 107/100mL
30
Time, days
4O
SO
60
Figure 6-2. Fecal Coliform Removal in Ponds - Detention Time vs.
Liquid Temperature.
Removal of fecal coliform with time is shown in
Figure 6-2. Temperature and detention times to achieve
final concentrations of 200 CFU/100 ml for irrigation
standards and 1,000 CFU/100 ml for recreation water
standards are shown in Figure 6-2. The detention time
used in the equation is the actual detention time as
measured by dye studies. In the ponds used for model
development the actual detention time ranged from 25 to
89 percent of the theoretical design detention time due
to short-circuiting. The geometric mean was 46 percent.
If the actual detention time in the pond system is not
known, it is suggested that this factor be applied when
using the equation to estimate fecal coliform die-off to
ensure a conservative prediction.
6-6
-------
6.2.7 Biological Nutrient Removal
Because both nitrogen and phosphorus can impact
receiving water quality, the discharge of one or both of
these constituents must often be controlled. Nitrogen
may be present in wastewaters in various forms (e.g.,
organic, ammonia, nitrites, or nitrates). Most of the
available nitrogen in both septic tank effluent and in
municipal wastewater is in the form of organic or
ammonia nitrogen. In wastewater treatment, about 20
percent of the total nitrogen settles out in sedimentation
processes. During biological nitrogen removal treatment,
ammonia nitrogen is converted to nitrate nitrogen, and
then to nitrogen gas (Crites and Tchobanoglous, 1998).
Phosphorus is present in municipal wastewaters in
organic form, as inorganic orthophosphate, or as
complex phosphates. The complex phosphates
represent about one-half of the phosphates in municipal
wastewater and result from the use of these materials in
synthetic detergents. Complex phosphates are
hydrolyzed during biological treatment to the
orthophosphate form (PO4~3). Of the total average
phosphorous concentration, about 10 percent is
removed as particulate material during primary
sedimentation and another 10 to 20 percent is
incorporated into bacterial cells during biological
treatment. The remaining 70 percent is normally
discharged with secondary treatment plant effluents.
Although ponds can act as a pretreatment method,
more aggressive biological processes, allowing
increased hydraulic loading rates and enhanced nitrogen
removal, may be required to comply with discharge
standards. Details on biological nutrient removal can be
found in Crites and Tchobanoglous (1998) and WEF
(1998).
6.2.8 Membrane Processes
With the development of various membranes for a
wide range of applications, membrane treatment is
rapidly becoming widespread and effectively competing
with conventional water treatment processes. Membrane
processes include microfiltration (MF), ultrafiltration (UF),
nanofiltration (NF), reverse osmosis (RO), and
electrodialysis (ED). Membrane treatment is generally
used for total dissolved solids (TDS) reduction and
removal of viruses, pathogens, and bacteria prior to the
reuse of the treated effluent. The principal applications of
the various membrane technologies for the removal of
the constituents found in wastewater are summarized in
Table 6-6.
Table 6-6. Application of Membranes for the Removal of Constituents Found in Wastewater (Crites and Tchobanoglous, 1998)
Constituents
MF
Type of Membrane
UF NF
RO
Comments
Biodegradable organics
Hardness
Heavy metals
Nitrate
Priority organic pollutants
Synthetic organic compounds
__
TSS
Bacteria
Removed as pretreatment for NF and RO.
Used for membrane disinfection.
Removed as pretreatment for NF and RO
with MF and UF.
Protozoan oocysts and cysts
Viruses
Used for membrane disinfection.
6.3 Design of Storage Ponds
For SR and OF systems, adequate storage must be
provided when climatic conditions require operations to
be curtailed or hydraulic loading rates to be reduced.
Most SAT systems are operated year-round, even in
areas that experience cold winter weather. SAT 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. Land treatment systems also may need
storage for flow equalization, system backup and
reliability, and system management, including crop
harvesting (SR and OF) and spreading basin
maintenance (SAT). Reserve application areas can be
used instead of storage for these system management
requirements.
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 is then 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. As
discussed in Section 6.2.1, ponds can offer additional
treatment benefits. These benefits should be determined
6-7
-------
and considered when calculating the final size of the
storage pond.
6.3.1 Estimation of Storage Volume Using
Water Balance Calculations
An initial estimate of the storage volume requirements
may be determined using a water balance calculation
procedure, as described below:
1. Determine the design monthly hydraulic loading rate.
2. Convert the actual volume of wastewater available
each month to units of depth (cm) using the
following relationship:
w =
= (Q,Xio2)
(6-11)
Where:
Wa = depth of available wastewater, cm
Qm = volume of available wastewater for the month, m3
Aw = field area, ha
3. Formulate a water balance table listing the results
for each month. In some instances, influent
wastewater flow varies significantly with the time of
year. The values used for Qm should reflect monthly
flow variation based on historical records.
4. Compute the net change in storage each month by
subtracting the monthly hydraulic loading from the
available wastewater in the same month.
5. Compute the cumulative storage at the end of each
month by adding the change in storage during one
month to the accumulated quantity form the previous
month. The computation should begin with the
reservoir empty at the beginning of the largest
storage period.
6. Compute the required storage volume using the
maximum cumulative storage and the field area.
The water balance calculation method is illustrated by
Example 6-1.
Example 6-1. Storage Volume Requirements Using Storage Water
Balance Calculations.
Conditions
1. Annual wastewater hydraulic loading rate, LW = 1.2 m/yr
2. Total yearly flow is 365,000 m3/yr, with monthly flow rates given in
Column (2) of Table 6-7.
3. Assume total land application area of 30.4 ha.
Calculations
1. Tabulate the design monthly hydraulic loading rate as indicated in
Column (1) of Table 6-7.
2. Convert actual volume of wastewater available each month to
units of depth (cm) with Equation 6-11. Results are tabulated in
Column (3) of Table 6-6.
For example, April:
5.
W, =
40,000 m3
30.4 ha 10,000 m
ha
100 cm
m
= 13.2 cm
Compute the net change in storage each month by subtracting
the monthly hydraulic loading rate from the available wastewater,
as indicated in Column (4) of Table 6-7.
Compute the cumulative storage at the end of the each month by
adding the change in storage during one month to the
accumulated quantity from the previous month, as indicated in
Column (5) of Table 6-7.
Calculate the required storage volume using the maximum
cumulative storage.
(10,000
Required Storage Volume = (23.9 cm)(30.4 ha
ha
100 cm
= 72,656 nf
6-8
-------
Table 6-7. Estimation of Storage Volume Requirements Using Water Balance Calculations
Month
April
May
June
July
August
September
October
November
December
January
February
March
* Maximum storage month.
6.3.2 Final Design
0)
l_w, crn
10
10
10
10
10
10
10
10
10
10
10
10
of Storage
(2)
Wm, m3
40,000
42,500
50,000
42,500
45,000
35,000
25,000
15,000
15,000
15,000
15,000
25,000
Volume
(3)
Wa, cm
13.2
14.0
16.4
14.0
14.8
11.5
8.2
4.9
4.9
4.9
4.9
8.2
72,656 m3
A —
(4)
Change in Storage,
cm (3)-(2)
3.2
4.0
6.4
4.0
4.8
1.5
-1.8
-5.1
-5.1
-5.1
-5.1
-1.8
= 1R1R4 m2
(5)
Cumulative Storage,
cm
0
3.2
7.1
13.6
17.6
22.4
23.9*
22.1
17.0
12.0
6.9
1.8
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 required storage
volume should be determined by conducting a monthly
water balance, which must include the net precipitation,
evaporation, and seepage from the pond. This method
requires an iterative solution with some assumed initial
conditions because the pond area is not known. The
overall storage volume must be increased to include
enough freeboard to retain an appropriate storm event
(i.e., at a minimum a 25y24h precipitation event. It is
usually convenient to assume a depth for the initial
calculation. This procedure is illustrated in the following
example:
Example 6-2. Calculations to Determine Final Storage Volume
Requirements
Conditions
1. Monthly evapotranspiration (ET) and precipitation (Pr) data
indicated in Table 6-8, Columns (1) and (2).
2. Assume seepage from pond is negligible.
3. Initial conditions and estimated storage volume from Example 6-1.
Calculations
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:
(6-12)
d.
Where:
As = area of storage pond, m2
Vs(est) = estimated storage volume, m3
ds = assumed pond depth, m
For example, assume ds = 4 m
2.
4 m
Calculate the monthly net volume of water gained or lost from
storage due to precipitation, evaporation, and seepage:
= (P, -E-S\AS
m
100 cm
(6-13)
Where:
AVS = net gain or loss of storage volume, m3
Pr = monthly precipitation, cm
E = monthly evaporation, cm
= monthly seepage, cm
3.
4.
5.
= storage pond area, m
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. Results are tabulated in Column (3) of Table 6-8.
Tabulate the volume of wastewater available each month (Qm),
given in Example 6-1.
Calculate an adjusted field area to account for annual net
gain/loss in storage volume.
(6-14)
(Lw\ 10,000^ I
ml
ha ,
0.01-
Where:
Aw' = adjusted field area, ha
IAVS = annual net storage gain/loss, m3
IQm = annual available wastewater, m3
Lw = design annual hydraulic loading rate, cm
For example:
-24,104 m3 +365,000 m3
(120 cm] 10,000—|0.01—I
v \ ha k cm
= 28.4 ha
Note: The final design calculation reduced the field area from 30.4 ha
to 28.4 ha.
6-9
-------
6.
Calculate the monthly volume of applied wastewater using the
design monthly hydraulic loading rate and adjusted field area:
(6-15)
Where:
Vw = monthly volume of applied wastewater, m3
Lw = design annual hydraulic loading rate, cm
Aw' = adjusted field area, ha
Results are tabulated in Column (5) of Table 6-8.
7. Calculate the net change in storage each month by subtracting
the monthly applied wastewater (VW) from the sum of available
wastewater (Qm) and net storage gain/loss (AVs) in the same
month. Results are tabulated in Column (6) of Table 6-8.
8. Calculate the cumulative storage volume at the end of each
month by adding the change in storage during one month to the
monthly cumulative volume is the storage volume requirement
used for design. Results are tabulated in column (7) of Table 6-8.
For this example, design Vs = 64,565 m3.
9. Adjust the assumed value of storage pond depth (ds) to yield the
required design storage volume using Equation 6-16.
„ _ Y._ (6-16)
d,=
64,565 m3
18,164 m2
ds = 3.55 m
If the pond 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 (AVS) will be different for a new pond area.
Table 6-8. Final Storage Volume Requirement Calculations
Month
April
May
June
July
August
September
October
November
December
January
February
March
Annual
(1)
ET, cm
13.2
17.7
21.8
23.9
22.1
14.7
10.9
5.1
2.5
2.3
5.1
9.7
(2)
Pr, cm
2
0.5
0.3
0
0
0.3
0.8
1.3
2.5
3
2.8
2.8
(3)
AVS Net
gain/loss, m3
-2,034
-3,124
-3,905
-4,341
-4,014
-2,616
-1 ,835
-690
0
127
-418
-1 ,253
-24,104
(4)
Qm,m3
40,000
42,500
50,000
42,500
45,000
35,000
25,000
15,000
15,000
15,000
15,000
25,000
365,000
(5)
Vw, m3
28,400
28,400
28,400
28,400
28,400
28,400
28,400
28,400
28,400
28,400
28,400
28,400
340,800
(6)
AVS, m3 (3)+(4)-(5)
9,566
10,976
17,695
9,759
12,586
3,984
-5,235
-14,090
-13,400
-13,273
-13,818
-4,653
(7)
Cumulative
Storage, m3
0
9,566
20,541
38,236
47,995
60,581
64,565*
59,331
45,240
31 ,840
18,567
4,750
Maximum monthly cumulative volume.
6.3.3 Storage for Overland Flow
Storage facilities may be required at an OF system for
any of the following reasons:
1. Storage of water during the winter due to reduced
hydraulic loading rates or system shutdown
2. Storage of stormwater runoff to meet mass
discharge limitations
3. Equalization of incoming flows to permit constant
application rates
6.3.4 Storage Requirements for Cold
Weather
In general, OF systems must be shut down for the
winter when effluent quality requirements cannot be met
due to cold temperature even at reduced application
rates or when ice begins to form on the slope. The
duration of the shutdown period and, consequently, the
required storage period will, of course, vary with the local
climate and the required effluent quality.
In studies at Hanover, NH, a storage period of 112
days, including acclimation, was estimated to be
required when treating primary effluent to BOD and TSS
limits of 30g/m3 (mg/L).
In areas of the country below the 40-day storage
contour on Figure 5.2, 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 those OF sites where winter
loading rates are reduced below the average design
rate. The required storage volume can be calculated
using Equation 6-17.
V = (QW)(DW) - (AsXUwXDaw) (Metric)
V = (QW)(DW) - (As)(Lww)(Daw)(7.48/106) (U.S. Customary) (6-17)
Where:
V
Qw
= storage volume, m3 (million gallons)
= average daily flow during winter, m /d (mgd)
6-10
-------
Dw = number of days in the winter period
As = slope area, m2 (ft2)
L,™ = hydraulic loading rate during winter, m/d (ft/d)
Daw = number of operating days in winter period
The duration of the reduced loading period at existing
systems generally has been about 90 days.
6.3.5 Storage for Stormwater Runoff
Stormwater runoff from the overland slopes must be
considered because OF is a surface discharging system.
Facilities that have a discharge must be covered by a
multisector Stormwater permit or obtain coverage under
an individual NPDES permit. 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
regulated 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 of Step 5.
7. Estimate runoff as a fraction of rainfall for the
particular site soil conditions. Consult the local
NRCS office for guidance.
8. Calculate the total rainfall required to produce a
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, determine
what probability is an acceptable risk before storm
runoff storage is required and use this value (Pd) for
design.
11. Storage must be provided for those months in which
total rainfall probability exceeds the design value
(Pd) 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 rainfall
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.
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 additional water volume can be
accommodated by increasing the application period as
necessary.
6.3.6 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 sufficient to equalize flow in most
cases. The surface area of basins should be minimized
to reduce intercepted precipitation. However, an
additional half-day of storage can be considered to hold
intercepted precipitation in wet climates.
For systems providing only screening or primary
sedimentation as preapplication treatment, aeration
should be provided to keep the storage basin contents
mixed and the surface zone aerobic. The added cost of
aeration, in most cases, will be offset by savings
resulting from reduced pump sizes and peak power
6-11
-------
demands. The designer should analyze the cost-
effectiveness of this approach for the system in question.
6.4 Operation of Storage Ponds
The scheduling of inputs or withdrawals from storage
ponds will depend on the overall process, including
agricultural operations and the treatment functions
expected for the pond unit. Storage units in an SAT
system are typically only for emergency conditions and
should be used accordingly. These ponds should remain
dry during routine operations and then be drained as
rapidly as possible after the emergency is resolved. In
some cases a separate pond is not provided in SAT
systems but extra freeboard is constructed into one or
more of the infiltration basins.
Storage ponds for OF systems may be bypassed in
many cases during the late spring and summer months
to avoid performance problems caused by algae. The
storage pond contents are then gradually blended with
the main wastewater stream so that the pond is drawn
down to the specified level at the start of the next
storage period. In areas with non-continuous algal
blooms, the pond discharges should be coordinated with
periods of low algae concentration.
Operation of storage ponds for SR systems will
depend on whether or not any treatment function has
been assigned to the pond. If a specified level of
nitrogen or fecal coliform removal is expected, then the
incoming wastewater should continue to flow into the
pond and the withdrawals should be sufficient to reach
the required pond level at the end of the application
season. When these factors are not a concern, or when
it is desired to maximize the nitrogen application to the
land, the main wastewater stream should bypass the
storage and be applied directly. Regular withdrawals
over the season can then draw down the pond.
For SR systems emphasizing water reuse and urban
irrigation, steps may be needed to minimize algae in the
storage ponds. These steps can include pre-storage
treatment in constructed wetlands, post-storage
treatment by constructed wetlands, dissolved air flotation
(DAF), filtration, or reservoir management that may
include mixing, aeration, or selective depth removal of
the highest quality water.
6.5 References
Brown and Caldwell (2000) Screening of Feasible
Technologies, Prepared for the San Francisco
Public Utilities Commission.
Bowles, D.S., E.J. Middlebrooks, and J.H. Reynolds
(1979) Coliform Decay Rates in Waste Stabilization
Ponds, Journal WPCF, 51:87-99.
Chudoba, P. and Pujol, R. (1998) A Three-Stage
Biofiltration Process: Performances of a Pilot Plant,
Water Science Technology, 38(8-9)257-265.
Crites, R.W. and G. Tchobanoglous (1998) Small and
Decentralized Wastewater Management Systems,
McGraw-Hill, New York, NY.
Crites, R.W., S.C. Reed, and R.K. Bastian (2000) Land
Treatment Systems for Municipal and Industrial
Wastes, McGraw-Hill, New York, NY.
Higo, T.T. (1966) A Study of the Operation of Sewage
Ponds in the Province of Alberta, Department of
Public Health, Government of Alberta.
Kott, Y. (1978) Lagooned Secondary Effluents as
Water Source for Extended Agricultural Purposes,
Water Research, 12(12):1101-1106.
Middlebrooks, E.J. et al. (1982) Wastewater
Stabilization Lagoon Design, Performance and
Upgrading, Macmillan Publishing Co., New York.
Neel, J.K., J.H. McDermott, and C.A. Monday (1961)
Experimental Lagooning of Raw Sewage, Journal
WPCF, 33(6):603-641.
Reed, S.C. (1984) Nitrogen Removal in Wastewater
Ponds, CRREL Report 84-13, Cold Regions
Research and Engineering Laboratory, Hanover,
NH.
Reed, S.C., R.W. Crites, E.J. Middlebrooks (1995J
Natural Systems for Waste Management and
Treatment, Second Edition, McGraw-Hill, New York,
NY.
Reed, S.C. (2001) Wetland Systems. Chapter 9 in:
Natural Systems for Wastewater Treatment, WEF
Manual of Practice, Second Edition, Water
Environment Federation, Alexandria, VA.
Pano, A. and E.J. Middlebrooks (1982) Ammonia
Nitrogen Removal in Facultative Wastewater
Stabilization Ponds, Journal WPCF, 54(4):344-351.
Sagik, B.P. (1978) The Survival of Human Enteric
Viruses in Holding Ponds, Contract Report DAMD
17-75-C-5062, United States Army Medical
Research and Development Command, Ft. Detrick,
MD.
Stowell, R. (1976) A Study of Screening of Algae from
Stabilization Ponds, Masters Thesis, Department of
Civil Engineering, University of California, Davis.
Surampalli, R.Y., et al. (1993) Phosphorus Removal in
Ponds, Proceedings of the 2nd International
Association of Water Quality International Specialist
Conference, Oakland, CA.
6-12
-------
Thomas, R.E. and S.C. Reed (1980) EPA Policy on
Land Treatment and the Clean Water Act of 1977,
Journal WPCF, 52:452.
US EPA (1976a) Use of Climatic Data in Estimating
Storage Days for Soil Treatment Systems, EPA-
600/2-76-250, U.S. Environmental Protection
Agency, Office of Research and Development,
Cincinnati, OH.
US EPA (1976b) Is Muskegon County's Solution, Your
Solution?, U.S. Environmental Protection Agency,
Region V, Chicago, IL.
US EPA (1977a) Performance Evaluation of Existing
Lagoons, Peterborough, N.H., EPA-600/2-77-085,
U.S. Environmental Protection Agency, Cincinnati,
OH.
US EPA (1977b) Performance Evaluation of an Existing
Seven Cell Lagoon System, EPA 600/2-77-086, U.S.
Environmental Protection Agency, Cincinnati, OH.
US EPA (1977c) Performance Evaluation of an Existing
Lagoon System at Eudora, Kan., EPA-600/2-77-167,
U.S. Environmental Protection Agency, Cincinnati,
OH.
US EPA (1977d) Preliminary Survey of Toxic Pollutants
at the Muskegon Wastewater Management System,
U.S. Environmental Protection Agency, ORD,
Washington, DC.
US EPA (1979) Health Aspects of Land Treatment, US
GPO 1979-657-093/7086, U.S. Environmental
Protection Agency, Cincinnati, OH.
US EPA (1980) Enteric Virus Removal in Wastewater
Lagoon Systems, Report IAG 79-0-X0728, U.S.
Environmental Protection Agency HER, Cincinnati,
OH.
US EPA (1981) Process Design Manual for Land
Treatment of Municipal Wastewater, EPA 625/1-81-
013, U.S. Environmental Protection Agency,
Cincinnati, OH.
US EPA (1983J Design Manual - Municipal
Wastewater Stabilization Ponds, EPA-625/1-83-015,
U.S. Environmental Protection Agency, Cincinnati,
OH.
US EPA (1999) Manual: Constructed Wetlands
Treatment of Municipal Wastewaters, EPA/625/R-
99/010, September 1999, National Risk
Management Research Laboratory, Office of
Research and Development, U.S. Environmental
Protection Agency, Cincinnati, OH.
WPCF (2001) Natural Systems, Manual of Practice,
No. FD-16, Water Pollution Control Federation,
Alexandria, VA.
6-13
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Chapter 7
Distribution Systems
Design of the distribution system involves two steps: (1)
selection of the type of distribution system, and (2) detailed
design of system components. The three major types of
distribution systems are surface, sprinkler, and drip
systems. Only basic design principles for each type of
distribution system are presented in this manual, and the
designer has referred to several standard agricultural
engineering references for further design details (e.g., Burt,
1995; Pair, 1983). Factors that distinguish land treatment
from conventional irrigation include:
. Supplemental irrigation water source may be needed
to meet crop water use requirements
. Application generally occurs over a longer season than
conventional irrigation. There is often abundant treated
effluent available in the late summer and fall when
irrigation requirements are decreasing.
. Water use efficiency is not always the optimum
approach for managing treated effluent.
Table 7-1. Description, Advantages, and Disadvantages of Distribution Systems
. A higher level of environmental monitoring is required
including accurate flow measurements, controls on
runoff, and documentation of water and constituent
loading rates.
. Additional factors control irrigation rate and frequency
when compared to conventional irrigated agriculture.
7.1 Types of Distribution Systems
SR systems utilize all types of distribution systems. OF
systems are generally sprinkler, spray or surface irrigation
with gated pipe. The goal of a distribution for a SR systems
is to obtain even distribution through the entire application
area, while the goal of the OF distribution system is to
spread the water evenly at the top of the slope, creating
uniform flow across the slope. SAT (rapid infiltration)
systems employ infiltration basins, which are often
operated similar to level border irrigation systems.
Table 7-1 contains the description, advantages and
disadvantages of various system types.
Type
Description
Advantages/Disadvantages
Surface Irrigation
Wild Flooding
Furrow
Border
Sprinkler Irrigation
Solid Set
Hand Move
End Tow
Wheel Line
Big Gun
Broad Class of irrigation where water is
Uncontroled appication to a vegetated surface
via gravity or low head pumping
Application to a graded field via small ditches
between crop rows
Application to a leveled field in 20-100 foot
wide strips, bordered by dikes.
Application of water to the soil through sprinkling
or spraying
Permanently or semi-permanently installed
sprinklers are used in blocks.
Moveable sprinkler lateral segments cover field
in sets.
Entire sprinkler laterals are towed to new set
locations after each irrigation.
Engine moveable sprinklers cover field in sets.
Large diameter orifices operating at high
pressure spread water. Travelling hose reels
allow big guns to irrigate strips over uneven
ground.
Poor uniformity of application
Not generally suitable for effluent application
Primarily for row crops
Careful leveling is required.
Uniform application is difficult on coarse textured soils.
Primarily for grass or perennial crops
Careful leveling is required.
Uniform application is difficult on coarse textured soils.
Remaining solids not distributed evenly.
Components can be sensitive to process water chemistry.
Almost eliminates runoff.
Susceptible to wind drift.
Highest pumping cost
Good method for coarse textured soils or uneven ground
Good for winter irrigation if subsurface piping is used.
Harvest and tillage are difficult around the sprinkler risers.
Rapid rotation among blocks is feasible to provide smaller applications.
High labor
Labor requirement to move sprinklers makes long sets common.
Least expensive system
Less labor than hand move sprinkler lines
Labor requirement to move sprinklers makes long sets common.
Requires sturdy laterals and care during moves
Limited to grass or hay crops
Less labor than hand move sprinkler lines
Labor requirement to move sprinklers makes long sets common.
Only suitable for low height crops and rectangular fields
Inexpensive equipment
Requires high pressure for maximum area coverage
Water impact can damage crops and soil at low pressure.
Relatively high irrigation rate
7-1
-------
Type
Description
Advantages/Disadvantages
Center Pivot Mechanical sprinkler system with fixed central
water supply moves in a circle to irrigate 20 to
more than 400 acres.
Linear Move Mechanical sprinkler system with end or center
feed water supply moves in a straight line to
irrigate fields up to 5000 feet long.
Micro Irrigation Water is applied to the soil surface as drops or
smaller streams through emitters. Preferred
term is drip irrigation.
Surface Drip Low flow emitters placed on the ground surface
apply water to crop root zone but not between
rows
Subsurface Drip Emitters are buried 6-12 inches deep as a
semi-permanent installation.
Micro-Spray Small spray heads or jets on stakes next to
permanent crops
Moderate initial capital expense but less labor
Flexible, efficient irrigation with proper design.
Frequent light irrigation of fields is used in winter to minimize soil storage
May not be suitable for boggy or sticky soils
High instantaneous application rates
High initial capital expense but less labor
Efficient irrigation with proper design
May not be suitable for boggy or sticky soils
High instantaneous application rates
Covers large rectangular fields
Emitter clogging limits utility of micro irrigation
Some difficulties with animal damage
High capital cost
Precise control of irrigation water
Popular for permanent crops
Easier to observe emitter performance and system plugging than with
subsurface emitters
More difficult to observe system performance
Buried lines sometimes damaged by tillage operations
Eliminates exposure to wastewater
Only suitable for permanent crops
Easier to observe performance than with drip emitters
Generally more resistant to plugging than drip emitters
7.1.1 Surface Distribution
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. Surface topography of land requires little additional
preparation to make uniform grades for surface
distribution.
The principal limitations or disadvantages of surface
systems include the following:
1. Land leveling costs may be excessive on uneven
terrain.
2. Uniform distribution cannot be achieved with highly
permeable soils.
3. Runoff control and a return system must be provided
when applying wastewater.
4. Periodic maintenance of leveled surfaced is required
to maintain uniform grades.
The two general types of surface distribution are the
ridge and furrow and the diked border systems. Variations
of these two types of methods can be found in standard
references (e.g., Burt, 1995; Hart, 1975; Booher, 1974).
7.1.2 Sprinkler Distribution
Sprinkler distribution uses a rotating nozzle as opposed
to spray distribution which refers to a fixed nozzle orifice.
Most nozzles used in land treatment systems are of the
sprinkler type.
Sprinkler distribution systems simulate rainfall by creating
a rotating jet of waterthat breaks up into small droplets that
fall to the soil surface. The advantages and disadvantages
of sprinkler distribution systems relative to surface and
micro distribution systems were summarized in Table 7-1.
In this chapter, 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 7-2 along with respective operating characteristics.
7.1.3 Micro Irrigation Distribution
Micro irrigation (also referred to as drip or trickle
irrigation) includes surface and subsurface low-flow
emission devices that supply water to the root zone of each
individual plant. The three major categories of micro
irrigation devices are:
. surface drip emitters
. subsurface drip emitters
. micro-sprays
Drip emitters can be discreet devices manually inserted
into drip lateral hose or can be manufactured integrally into
the lateral hose. Drip emitters can also be installed on short
"pigtail" tubes coupled to the drip lateral hose. Thin wall
hose with integrated emitters is sometimes referred to as
"drip tape." Micro-sprays are small, low flow spray or jet
devices. The advantages and disadvantages of micro
irrigation for distribution of effluent compared with surface
and sprinkler irrigation methods were listed in Table 7-1.
7-2
-------
Table 7-2. Sprinkler System Characteristics
Type
Typical application
rate, in/h
Labor required per
application, h/acre
Nozzle pressure range,
Ib/in2
Size of single system,
acres
Maximum grade, %
Solid Set
Permanent
Portable
0.05-2.0
0.05-2.0
0.008-0.016
0.03-0.04
30-1 00
30-60
No limit
No limit
40
40
Move-stop
Hand-move
End tow
Side roll
Stationary gun
0.01-2.0
0.01-2.0
0.1-2.0
0.25-2.0
0.08-0.24
0.03-0.06
0.016-0.048
0.03-0.06
30-60
30-60
30-60
50-100
2-40
20-40
20-80
20-40
20
5-10
5-10
20
Continuous move
Traveling gun
Center pivot
Linear move
0.25-1 .0
0.25-1 .0
0.25-1 .0
0.016-0.048
0.008-0.024
0.008-0.024
50-100
15-60
15-60
40-100
40-160
40-360
20-30
15-20
15-20
7.2 General Design Considerations for All
Types of Distribution Systems
The hydraulic loading rate will be determined based on
the limiting design factor as shown in Chapters 8, 9, and 10
depending on the treatment system.
Design parameters that are common to all distribution
systems are defined as follows:
Depth of Wastewater Applied. The depth of wastewater
applied is determined using the relationship:
Where:
D
Lw
F
(7-1)
depth of wastewater applied per application, mm (in.)
monthly hydraulic loading, per application mm/mo (in./mo)
frequency of applications, applications/mo
7.2.1 Application Frequency
The application frequency is defined as the number of
applications per month or per week. The application
frequency used for design is a judgment decision made by
the designer considering: (1) the objectives of the system,
(2) the water and nutrient needs or tolerance of the crop,
(3) the moisture retention properties of the soil, (4) the
labor requirement of the distribution system, (5) the
application characteristics of the type of distribution system,
and (6) the capital cost of the distribution system. Some
general guidelines for determining an appropriate
application frequency are presented here, but consultation
with a local farm adviser is recommended.
Except forthe watertolerant forage grasses, most crops,
including forest crops, generally require a drying period
after reaching saturation 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
for most distribution methods, with continuous move
sprinkler and micro irrigation methods being the exception.
Continuous move sprinkler and micro irrigation methods
have a higher irrigation frequency, but still maintain
adequate root zone aeration. Continuous move sprinkler
irrigation systems usually apply water at a rate higher than
the long-term infiltration rate of the soil. In order to take
advantage of surface micro-storage and the high initial
infiltration rate of most soils, continuous move sprinkler
systems typically apply water for a brief period of time
every 1 to 4 days. The smaller application amounts and
brief application periods allow adequate root zone aeration
to take place between irrigations. Micro irrigation systems
usually apply water for several hours every day. Because
of low average application rate and that the soil surface
area is not saturated, micro irrigation practices allow for
root zone aeration.
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 the capacity
needed in each part of the distribution system.
7.2.2 Application Rate
Treated wastewater application rate is the rate at which
water is applied to the field by the distribution system. In
general, the application rate should be restricted by the
infiltration rate of the soil and/or vegetated surface to
prevent unpermitted runoff and tailwater return
requirements. Specific guidelines relating application rates
7-3
-------
to infiltration properties are discussed under the different
types of distribution systems.
7.2.3 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 h.
7.2.4 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.
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:
(7-2)
Where:
Aa
Aw
Na
application zone area
field area
No. of application zones
The number of application 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 h, effectively
two applications can be made each operating day. If the
application frequency is once per week and the system is
operated 7 d per week, then there are 7 operating days
between successive applications on the same zone and the
number of application zones is:
Na = (2 applications/day)(7 operating days) = 14
If the field area is 35 acres, then the application zone is:
A = — = 2.5acres
14
Q = CAaD/ta
Where:
Q
C
Aa
D
ta
(7-3)
discharge capacity, L/s (gal/min)
constant, 28.1 (453)
total application area, ha (acres)
gross depth of water applied during peak periods, cm (in.)
application period, h
Values for water applied and application period on a per-
day basis are usually incorporated into the above formula.
The effective amount of time available per day for
application must take into account time lost in moving
distribution equipment and system maintenance.
7.3 Surface Distribution
Ridge and furrow and graded border distribution are most
often associated with slow rate systems. For overland flow,
surface application can be used with either gated aluminum
pipe or bubbling orifices. For soil aquifer treatment, the
common method of application is basin flooding.
7.3.1 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. The design variables for furrow systems (see
Figure 7-1) include furrow grade, spacing, length, and
stream size (flowrate). The furrow grade will depend on the
site topography. A grade of 2 percent 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 percent.
(a)
7.2.5 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:
Figure 7-1. Typical Surface Distribution Methods- Ridge and Furrow.
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 7-3.
7-4
-------
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 7-4.
Table 7-3. Optimum Furrow Spacing
Soil condition
Optimum
spacing, in1
Coarse sands-uniform profile 12
Coarse sands-over compact subsoils 18
Fine sands to sandy loams-uniform 24
Fine sands to sandy loams-over more compact 30
subsoils
Medium sandy-silt loam-uniform 36
Medium sandy-silt loam-over more compact 40
subsoils
Silty clay loam-uniform 48
Very heavy clay soils-uniform 36
12.54 centimeters per inch.
The furrow stream size or application rate is expressed
as a flow rate per furrow. The optimum stream size is
usually determined by trial and adjustment in the field after
the system has been installed (Merriam and Keller, 1978).
The most uniform distribution (highest application
efficiency) generally can 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 a
theoretical application efficiency of greaterthan 90 percent
for most soils if tailwater is returned.
Table 7-4. Suggested Maximum Lengths of Furrows, ft
Furrow grade,
Clays
Average depth of wastewater applied, in1
Loams
Sands
% 3
0.05 1000
0.2 1200
0.5 1300
1 .0 920
2.0 720
6
1300
1540
1640
1300
890
9
1300
1740
1840
1640
1100
12
1300
2030
2460
1970
1300
2
400
720
920
820
590
4
900
1200
1200
980
820
6
1300
1540
1540
1200
980
8
1300
1740
1740
1540
1100
2
200
400
400
300
200
3
300
600
600
500
300
4
500
800
800
700
500
5
600
1000
1000
800
600
12.54 centimeters per inch.
2 30.48 centimeters per foot.
The application period is the time needed to infiltrate the
desired depth of water plus the time required forthe 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 Merriam and Keller, (1978).
Design of supply pumps and transmission systems
should be based on the maximum allowable stream size,
which is generally limited by erosion considerations when
grades are greater than 0.3 percent. The maximum
nonerosive stream size can be estimated from the
equation:
qe = C/G
Where:
qe
c
G
(7-4)
maximum unit stream size, gpm.
constant, 10
grade, %
For grades less than 0.3 percent, the maximum allowable
stream size is governed by the flow capacity of the furrow,
estimated as follows:
qc = CFa
Where:
qc
c
Fa
(7-5)
furrow flow capacity, gpm
constant, 74
cross-sectional area of furrow, ft2
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 gated surface pipe
(Figure 7-2).
7-5
-------
Figure 7-2. Typical Gated Pipe Distribution Unit.
The spacing of the risers is governed either by the head
loss 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 are alfalfa valves
(mounted on top of the riser) or orchard valves (mounted
inside the riser). Valves must be sized to deliverthe design
flow rate.
Gated surface pipe may be aluminum or plastic. 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 adjusted in the field to
achieve the desired stream size.
7.3.2 Graded Border Distribution
Table 7-5. Design Guidelines for Graded Borders for Deep-Rooted Crops1
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 percent. Terracing of graded borders can be used
for grades up to 20 percent. Graded border irrigation may
not be suitable for the application of wastewater with
substantial amounts of settleable solids to grass or hay
crops because of poor resulting solids distribution.
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 Table 7-5 and Table
7-6.
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 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 Table 7-5 and Table 7-6.
Soil type and
infiltration rate,
in/h
Grade, %
Unit flow per foot
of strip width,
gal/min
Average dept of
water applied, in
Width
Border strip, ft
Length
Sand
>1.0
0.2-0.4
0.4-1 .6
0.6-1.0
50-70
40-50
25-40
4
4
4
40-1 00
30-40
20-30
200-300
200-300
250
Loamy sand
0.75-1.0
0.2-0.4
0.4-0.6
0.6-1.0
30-50
25-40
13-25
5
5
5
40-1 00
25-40
25
250-500
250-500
250
Sandy loam
0.5-0.75
0.2-0.4
0.4-0.6
0.6-1.0
25-35
18-30
9-18
6
6
6
40-1 00
20-40
20
300-800
300-600
300
Clay loam
0.25-0.5
0.2-0.4
0.4-0.6
13-18
9-13
7
7
40-100
20-40
600-1 000
300-600
7-6
-------
0.6-1.0
5-9
20
300
Clay
0.10-0.25
0.2-0.3
9-18
40-100
1200
2.54 centimeters per inch.
230.48 centimeters per foot.
33.785 liters per 1 US gallon.
Table 7-6. Design Guidelines for Graded Borders for Shallow-Rooted Crops1'
Soil profile
Clay loam,
24 in deep
over permeable
subsoil
Clay, 24 in
deep over
Permeable
subsoil
Loam, 6 to
18 in 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 foot of strip
width, gal/min
25-35
18-30
9-18
13-18
9-13
5-9
5-20
Average depth of
water applied, in
2-4
2-4
2-4
4-6
4-6
4-6
1-3
Width
15-60
15-20
15-20
15-60
15-20
15-20
15-20
Border strip, ft
Length
300-600
300-600
300-600
600-1000
600-1000
600
300-1000
12.54 centimeters per inch.
230.48 centimeters per foot.
33.785 liters per 1 US gallon.
The application rate or unit stream size for graded border
irrigation is expressed as a flow rate per unit width of
border strip. 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 percent 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 limiting runoff or ponding at the bottom
end.
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 ponding or 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 range of stream sizes given
in Table 7-5 and Table 7-6 for various soil and crop
conditions may be used for preliminary design. Wastewater
with significant amounts of settleable solids should be
applied at relatively higher flow rates to improve the
distribution of solids on the field. Procedures given in the
Border Irrigation chapter of the USDA NRCS National
Engineering Handbook (USDA, 1980) 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:
ta = LD/Cq
Where:
ta
L
D
C
q
(7-6)
application period, h
border strip length, ft
depth of applied water, in
constant, 96.3
unit stream size, gpm/ft of width
Opportunity Time (Shut-off Time)
The majority of graded border systems used for
wastewater land treatment are operated with diked ends,
allowing no runoff. Forthis case, the duration of application
is not a simple function of calculating the run time based on
the flow rate and the area of the border strip. Uniform
infiltration of water is achieved when the entire length of the
system has equal opportunity to infiltrate. Equal opportunity
time occurs when the advance rate of the wetting front is
equal to the recession of the water. The recession of water
is a function of the slope and percolation rate. A guideline
to assist the applicator in achieving uniform distribution is to
set the flow rate so the total volume is applied when the
wetting front advances 60 percent of the strip length for
clay soil and 90 percent of the length for sandy soils.
The percolation rate changes throughout the season and
depends on the surface preparation. Unfortunately, the
same flow rate will not supply equal distribution throughout
the season.
The results of equal opportunity time at the head and tail
of the strip are shown in Figure 7-3. Equal opportunity time
is achieved when the advance time matches the recession
time. With diked ends, the water which would normally
runoff, ponds and adds to the opportunity time at the end of
the strip. If the shut-off advance distance is left constant
7-7
-------
and the flow rate is reduced, the head of the strip receives
a greater opportunity time. In Figure 7-4, the opportunity at
the head of the strip, T1, is greater than the opportunity
time as the tail of the strip, T2. If the flow rate is reduced
even furtherthe wetting front will not even reach the end of
the strip. If the flow rate is increased above the optimal,
the tail end of the strip receives a greater opportunity time
from the ponded water and T2 is greaterthan T1, as shown
in Figure 7-5 (Burt, 1995).
The conveyance and application devices used for border
distribution are basically the same as described for ridge
and furrow distribution. 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 7-6, 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
A
Ł
•lH
H
o
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.
7.3.3 Surface Distribution for Overland
Flow
Municipal wastewatercan be surface applied to overland
flow slopes, but industrial wastewater should usually be
sprinkler applied if there are higher concentrations of BOD
and solids. Surface distribution methods include gated
aluminum pipe commonly used for agricultural irrigation,
and slotted or perforated plastic pipe. Commercially
available 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. 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,
2 to 5 Ib/in.2, to achieve good uniformity at the application
rates recommended in Chapter 9, 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 90 m (300 ft), inline valves should be
provided along the pipe to allow additional flow control and
isolation of pipe segments for separate operation.
No Runoff- Water ponded
at lower end
0
end
Distance Along Strip
Figure 7-3. Equal Opportunity Time Along Entire Strip (Burt, 1995).
7-8
-------
A
OJ
a
•1H
H
0
0
Distance Along Strip
No Runoff- Water ponded
at lower end
end
Figure 7-4. Greater Opportunity Time at Head of Strip: Flow Rate Too Small (Burt, 1995).
7-9
-------
Ł
•lH
H
0
0
Distance Along Strip
Figure 7-5. Greater Opportunity Time at Tail End of Strip: Flow Rate Too Large
(Burt, 1995).
No Runoff- Water ponded
at lower end
end
Solution
Figure 7-6. Typical Discharge Valve for Border Strip Application.
application frequency, F : 3 times per month, field
area, Aw: 120 acres, crop: pasture.
Calculate the depth of wastewaterto be
applied using Equation 7-1.
D = LW/F
D = 12 in = 4 in
3
2. Select border width and length from Table 7-6
for design conditions for shallow-rooted
crops.
Width = 40ft
Length = 600ft
3. Select unit flow per width of strip, gpm from
Table 7-6.
q = 30 gpm/ft of width
Example 7-1: Establish Preliminary Design Criteria for a Graded
Border System
Conditions
Deep clay loam soil, finished grade, G: 0.3%,
maximum monthly hydraulic loading, Lw: 12 in,
4. Calculate the period of application, ta, using
Equation 7-6.
ta = LD /96.3q
ta = (600 ft)(4)/ (96.3)(30)
= 0.83 h
7-10
-------
5. Determine number of applications per day
assuming a 12 h/d operating period.
Number of applications =12 h/d/0.83
application
Determine the number of application zones.
Application cycle is 10 day (30 d/mo)
3 cycles/mo
Application zones = (10d)(15
applications/d) = 150
Calculate the area per zone, Aa.
Aa = Aw/number of zones
= 120 acres
150 zones
A, = 0.8 acres
8. Determine the number of border strips per
application zone.
Number of borders = A^
(L)(W)
= (0.8 acres)(43.560 ft%acre)
(600 ft)(40 ft)
= 1.45, use 2
9. Determine system flow capacity, Q.
Q = (2 borders)(W)(q) = (2)(40 ft)(30 gpm/ft)
= 2,400 gpm
The system must be capable of supplying
2,400 gpm during the maximum month.
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.
Consequently, such methods should be considered only for
small systems having relatively short pipe lengths that can
be easily leveled. The advantages and disadvantages of
surface, spray, and sprinkler systems are compared in
Chapter 9.
7.3.4 Surface Distribution for Soil Aquifer
Treatment (SAT)
Although sprinklers may be used, wastewaterdistribution
for SAT 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.
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 so that at least one basin can be loaded at
all times, unless storage is provided.
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 ac) for small to medium sized systems
to 2 to 8 ha (5 to 20 ac) for large systems. For a 24-ha (62-
ac) system, if the selected loading cycle is 1 day of
wastewater application alternated with 10 days of drying, a
typical design would include 22 basins of 1.3 ha (2.8 ac)
each. Using 22 basins, two 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. 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 orrectangularto maximize land use. In areas where
groundwater mounding is a potential problem, less
mounding occurs when long, narrow basins with their
length normal to the prevailing groundwater flow are used
than when square or round basins are constructed. Basins
should be at least 300 mm (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 1:2 (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 at grades of 10 to 20 percent and
are from 3 to 3.6 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.
7.4 Sprinkler Distribution
Sprinkler distribution is common to SR systems, is
generally used with industrial OF systems, and can be
used with SAT systems. Forest SR, OF and many
agricultural SR systems use solid set (stationary) sprinkler
7-11
-------
distribution, whereas move-stop and continuous move
sprinklers are restricted to SR systems.
7.4.1 Design Application Rates
For all SR sprinkler systems the design application rate
cm/h (in./h) should be less than the infiltration rate of the
surface soil to avoid surface runoff. For final design, the
application rate should be based on field infiltration rates
determined from previous experience with similar soils and
crops or from direct field measurements.
For solid set or move-stop sprinkler irrigation systems,
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 percent of the bare soil application rate.
Application rates for continuous move irrigation systems
should not exceed the instantaneous infiltration rate and
any available surface micro-storage during the period of
water application. Recommended reductions in application
rate for sloping terrain are given in Table 7-7. 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.
permanently located and the lateral lines are portable
surface pipe, the system is called semipermanent or
semiportable.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.
Application Rate
For solid set systems, the application rate is expressed
as a function of the sprinkler discharge capacity, the
spacing of the sprinklers along the lateral, and the spacing
of the laterals along the main according to the following
equation:
R = qsC/SsSL
(7-7)
Where:
R
qs
c
ss
SL
application rate, in./h
sprinkler discharge rate, gpm
constant = 96.3
sprinkler spacing along lateral, ft
lateral spacing along main, ft
Table 7-7. Recommended Reductions in Application Rates Due to
Grade [McCulloch et al, 1973]
Percent Grade
Application
rate reduction
0-5
6-8
9-12
13-20
Over 20
0
20
40
60
75
Solid Set 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 from 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 30 m (40 to 100 ft). A system is called fully permanent
or stationary when all 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
Detailed procedures for sprinkler selection and spacing
determination to achieve the desired application rate are
given in the references (e.g., Fryetal., 1971; NRCS1983;
and Pairetal., 1983).
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 7-7.
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 7-8.
The sprinkler and nozzle size should be selected to
operate within the pressure range recommended by the
7-12
-------
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.
Table 7-8. Recommended Spacing of Sprinklers [McCulloch et al.,
1973]
Wind Speed
Km/h
0-11
11-16
>16
(mi/h)
(0-7)
(7-10)
(>10)
Spacing, % of wetted diameter
40 (between sprinklers)
65 (between laterals)
40 (between sprinklers)
60 (between laterals)
30 (between sprinklers)
50 (between laterals)
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 percent of the operating pressure of the sprinklers. This
will result in sprinkler discharge variations of about 10
percent 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 7-9. For long lateral lines,
capital costs may be reduced by using two or more lateral
sizes that will satisfy the head loss requirements. Elevation
losses or gains should be incorporated into the hydraulic
loss calculations. Flexible flow-regulating sprinkler nozzles
can be used in difficult terrain or design conditions.
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 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.
Example 7-2: Establish Preliminary Design Criteria for Solid Set
Sprinkler System
Conditions
Solution
Infiltration rate: 0.6 in/h, depth of wastewater
applied, D : 2 in., crop: forage grass, applications
zone area, Aa: 10 acres, average wind speed : 5
mph.
1. Determine design application rate, R.
Assume an 8 h application period.
R = D
t= 2 in
8h
= 0.25 in/h ( < 0.6 in/h)
2. Select sprinkler and lateral spacings.
use Ss = 60 ft
SL = 60ft
Table 7-9. Pipe Friction Loss Factors to Obtain Actual Loss in Line
with Multiple Outlets
Numbers 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
0.369
0.379
0.370
0.365
0.362
0.357
0.355
0.350
RD/ta
= 2 in/8 h
3. Calculate required sprinkler discharge
rearranging Equation 7-7.
qs = R S;SL
96.3
qs = (0.25)(60)(60)
96.3
= 9.3 gpm
4. Select sprinkler nozzle size, pressure, and
wetted diameter to provide necessary
discharge.
Use a 7/32 in. nozzle at 50 Ib/in.2 pressure.
Wetted diameter = 125ft
Check selected spacing against criteria in
Table 7-8 for the average wind speed.
Sprinkler spacing, Ss = 60
125
= 48%>40%
7-13
-------
Lateral spacing, SL = 60
125
= 48%<65%
6. Change sprinkler spacing to 50 ft (OK at
40%), and lateral spacing to 80 ft (OK at
64%). Recalculate qs = 10.4gpm The same
nozzle is satisfactory if the pressure is
increased to 55 Ib/in2. Wetted diameter is 127
ft.
7. Determine system flow capacity, Q.
Q = AaR = (10acres)(0.25in/h)(27,154
gal/acre»in)( 1 hr )/60 min = 1,131 gpm
7.4.2 Solid Set Forest Systems
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). 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. This
spacing, with sprinkler overlap, provides good wastewater
distribution at a reasonable cost. Operating pressures at
the nozzle should not exceed 379 kPa (55 Ib/ in2 ),
although pressures up to 586 kPa (85 Ib/in2) may be used
with mature or thickbarked 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.
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 7-7). 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 (10-ft) wide 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-m (5-ft) radius should be kept
clear around each sprinkler. This practice allows better
distribution and more convenient observation of sprinkler
operation. Water distribution patterns will still not meet
agricultural standards, but this is not as important in forests
because the roots are quite extensive.
Figure 7-7. Forest Solid Set Sprinkler Irrigation at Clayton County.
7.4.3 Solid Set Overland Flow Systems
Sprinkler distribution systems recommended for OF
systems are discussed in Chapter 9. High pressure, 50 to
80 Ib/in2, impact sprinklers have been used successfully
with food processing wastewaters containing suspended
solids concentration >500 mg/L. The position of the impact
sprinkler on the slope is also discussed in Chapter 9.
Spacing for low-pressure fixed spray heads at the top of
the overland flow slopes should meet the same criteria as
spacing for rotating sprinklers.
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
diameter of coverage. The relationship between OF
application rate and sprinkler spacing and discharge
capacity is given by the following equation:
R = a (7-8)
ss
Where:
R = OF application rate, gpm/ft of slope width
q = sprinkler discharge rate, gpm
Ss = sprinkler spacing, ft
The sprinkler spacing should allow for some overlap of
sprinkler diameters. A spacing of about 80 percent of the
wetted diameter should be adequate for OF. Using the
7-14
-------
design OF application rate and the above criteria for
overlap, a sprinkler can be selected from a manufacturer's
catalog.
7.4.4 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 wheel line (also known as side-roll) systems. Single
sprinkler move-stop systems include stationary gun
systems. Diagrams of operation for the different types of
move-stop sprinkler systems are shown in Figure 7-8.
PREVIOUSLY
APPLIED
AREA
LATERAL WITH
SPRINKLERS
MULTIPLE
LATERAL IITH MULTIPLE
SPRINKLERS
MAIN
PREVIOUSLY
APPLIED
AREA
DISASSEMBLED
MAIN LEN8THS
(I) -PORTABLE HAND IOVED
(b) END TOW
•AIM
•HEEL-SUPPORTED LATERAL
•ITH MULTIPLE SPRINKLER
PREVIOUSLY
APPLIED
AREA
LATERAL IITN SPRINKLER
CONNECTIONS
MAIN
BUN-TYPE
SPRINKLER
(c) SUE WHEEL IOLL
(d) STATIONAIT GUN
Figure 7-8. Move-Stop Sprinkler Systems.
7-15
-------
Portable Hand Move Systems
Portable hand move systems consist of a network of
surface aluminum lateral pipes connected to a main line
which may be portable or permanent. The major
advantages of these 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.
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.
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.
Wheel Line
Wheel line or side-roll systems are basically lateral lines
with sprinklers that act as the axle for a series of large
diameter wheels. The lateral line is aluminum pipe, typically
100 to 125 mm (4 to 5 in) in diameter and up to 406 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 7-9). The end of the
lateral is connected by a 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 or end of the
lateral.
The principal advantages of wheel line systems are lower
labor requirements and overall cost than hand-move
systems, 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.
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. 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.
*"
Figure 7-9. Side-Wheel Roll Sprinkler System.
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 should be based on the relative costs and
availability of equipment and labor.
7.4.5 Continuous Move Systems
Continuous move sprinkler systems are self-propelled
and essentially move continuously during the application
period. The three types of continuous move systems are
(1) traveling gun, (2) center pivot, and (3) linear move.
Diagrams showing the operation of continuous move
sprinkler systems are shown in Figure 7-10.
Traveling Gun Systems
Traveling gun systems are self-propelled, single large
gun sprinkler units that are connected to the supply source
by a hose 63 to 127 mm (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. In both cases, a cable
anchored at the end of the run guides the unit in a straight
7-16
-------
FLEXIBLE SUPPLY
HOSE
TARE-UP
REEL
SELF-PROPELLED
DRIVE UNI
BUN-TYPE SPRINKLER;
PREVIOUSLY
APPLIED
AREA
FLEXIBLE
HOSE J
SPRINKLER
GUN CART
LANE
SPACING
(a) TRAVELING GUM (HOSE DRAG)
(b) TRAVELING GUN (REEL-HPE)
SUPPLY
FLEXIBLE HOSE
^OPTION)
LATERAL
• ITH
MULTIPLE
SPRINKLER
PREVIOUSLY
APPLIED
AREA
SUPPORTS
POWER
DRIVE
SUPPORTS
LATERAL 1ITH
MULTIPLE SPRINKLERS
CENTER ,
DITCH ^
(OPTION)
PREVIOUSLY
APPLIED
AREA
(c) CEMTER PIVOT
(d) LINEAR MOVE
Figure 7-10. Continuous Move Sprinkler Systems.
7-17
-------
path during the application. The flexible rubber hose is
dragged behind the unit. The reel-type traveler (see
Figure 7-11) consists of a sprinkler gun cart attached to a
take-up reel by a semi-rigid 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 to 403 m (660 and 1,320 ft), and
spacings between travel lanes range between 50 to 100 m
(165 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 7-11. Reel-Type Traveling Gun Sprinkler.
The more important advantages of a traveling gun
system are low labor requirements and relatively clog-free
nozzles. They may also be adapted to fields of somewhat
irregular shape and topography. Disadvantages are high
power requirements, hose travel lanes required for hose
drag units for most crops, and drifting of sprays in windy
conditions. Traveling gun systems are generally more
suited to systems with low operating hours per year.
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 (see Table 7-10), and the travel speed.
The minimum application rate of most traveling gun
sprinklers is about 5.8 mm/h (0.23 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 = as—
(s.)(Sp)
Where:
D
si
SP
c
(7-9)
depth of water applied, in
sprinkler capacity, gpm
space between travel lanes, ft
travel speed, ft/min
conversion constant, 1.60
The typical design procedure is as follows:
1. Select a convenient application period, h/d, allowing at least 1 h
between applications to move the gun.
2. Estimate the area to be irrigated by a single unit. This value
should not exceed 80 acres (32 ha).
3. Calculate the sprinkler discharge capacity using Equation 7-7.
qs = (435)(D)(A)
Ct
(7-10)
Where:
qs
D
A
c
t
4.
sprinkler discharge capacity, gpm
depth of wastewater applied per application, in
area irrigated per unit, acres
cycle time between applications, d
operating period, h/d
Select a sprinkler size and operating pressure from
manufacturer's performance tables that will provide the estimated
discharge capacity.
5. Calculate the application rate using Equation 7-8.
(7-11)
application rate, in/h
sprinkler capacity, gpm
sprinkler wetted radius, ft
6. Compute the lane spacing as a percentage of the wetted diameter
against spacing criteria in Table 7-10.
7. Adjust sprinkler selection and lane spacing as necessary to be
compatible with soil intake rate.
Table 7-10. Recommended Maximum Lane Spacing for Traveling Gun
Sprinklers
Wind speed, mi/h
Lane spacing,
. of wetted diameter
0-5
5-10
80
70-75
60-65
50-55
9.
Calculate the travel speed using Equation 7-9 as rearranged:
Sp = 1.6d;
DS,
Calculate the area covered by a single unit.
A = StCtravel distance. ft/d)(cvcle. d)
43,560 ft2/acre
10. Determine the total number of units required.
Units required = field area
unit area
7-18
-------
11. Determine the system capacity, Q
Q = (qs)(number of units)
Example 7-3: Establish Preliminary Design Criteria for Reel Type
Traveling Gun System
Conditions
Solution
Loam soil, infiltration rate : 0.4 in/h, depth of
wastewater applied, D : 3 in, field area : 100 acres,
application cycle : every 10 d, average wind speed
: 5 mph.
1. Select a 15 h/d application period
2. Estimate 25 acres/unit
3. Calculate the sprinkler discharge capacity
qs = (435)(3)(25)
= 217.5 gpm
4. Select a sprinkler with a 230 gpm capacity
and a wetted diameter of 340 ft.
5. Calculate the application rate
R = 96.3(230)
(170)2
= 0.24 in./h ( < 0.4 in./h, OK)
6.
Lane spacing should be less than 70% to
75% of wetted diameter
S, = 0.7 (340) = 238 ft
use 240 ft
7. Calculate the travel speed
(3)(240)
= 0.5 ft/min
8. Calculate the area covered by a single unit
A = (240)(0.5)(15h)(-h)(10d)
43,560
= 24.8 acres
9. Calculate the number of units required
Units required = 100 acres
24.8 acres/unit
= 4.03
use 4 units
10. Calculate the system capacity, Q
Q = (qs)(number of units) = (230 gpm)(4) = 920
gpm
Center Pivot Systems
Center pivot systems consist of a truss supported lateral
with multiple sprinklers or spray nozzles that are mounted
on self-propelled, continuously moving tower units (see
Figure 7-12 and Figure 7-13) 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 or other low-
pressure sprinkling devices to reduce energy requirements.
Water is supplied by a buried main to the pivot, where
power is also furnished. The lateral is usually constructed
of 150 to 200 mm (6 to 8 in.) steel pipe 60 to 780 m (200 to
2,600 ft) in length. A typical system with a 393 m (1,288 ft)
lateral is centered on a 64 ha (160-ac) parcel. The circular
pattern reduces coverage to about 52 ha (130 ac), although
systems with swing out corner laterals or high-pressure
corner guns are available to irrigate a portion of the
corners.
The tower units are driven electrically or hydraulically and
may be spaced from 24 to 76 m (80 to 250 ft) apart. Control
of the travel speed is achieved by varying the average
speed of the end tower motor. Most systems run the end
tower motor for an adjustable percentage of a short interval
(1 to 2 minutes), while a few systems control the speed
directly. Cable or other guidance mechanisms are
employed to sense the alignment of the towers and actuate
the inner tower motors to keep up with the outer tower.
Figure 7-12 Center Pivot Sprinkler Unit.
Figure 7-13. Center Pivot Irrigation System.
An important limitation of the center pivot system is the
required variation in sprinkler discharge 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 discharge per unit of lateral length provided by the
7-19
-------
sprinklers must increase with distance from the center to
provide a uniform depth of application. Increasing the
discharge rate can be accomplished by decreasing the
spacing of the sprinklers along the lateral and increasing
the discharge capacity of the individual sprinklers. The
resulting application rates at the outer end of the pivot
lateral can be so high as to be unacceptable for many soils.
Since center pivot sprinkler systems typically apply water
on a more frequent basis and for shorter durations than
move-stop sprinkler systems, short term soil infiltration and
surface storage characteristics are more important than the
long-term infiltration rate. On a short term basis, the
infiltration rate normally decreases exponentially with the
amount of water infiltrated. In addition, infiltration rates
normally decrease over the season due to surface soil
sealing from sprinkler droplet impact. Figure 7-14 shows a
graphical representation of water application, infiltration
rate, and potential runoff with center pivot irrigation.
Potential runoff will become actual runoff if there is not
sufficient surface storage to retain the excess water.
Figure 7-15. Schematic of the Revolving - Sprinkler Infiltrometer.
Di = kp(Tp)p
Where:
(7-12)
depth infiltrated for average sprinkle application rate at
time of ponding
time-to-ponding coefficient dependent on soil and water
characteristics at the time of the test and the
measurement units used
time-to-ponding exponent dependent on soil and water
characteristics at the time of the test
INFILTRATION
ELLIPTICAL APPLICATION
RATE PROFILE
TIME
Figure 7-14. Intersection Between an Elliptical Moving Application
Rate Profile Under a Center-pivot Lateral and a Typical Infiltration
Curve.
Equation 7-12 can be used to describe short-term
infiltration characteristics of soils (Keller and Bleisner,
1990). The coefficients for Equation 7-12 can be
determined by fitting a curve (or regression of the
logarithms) of sprinkling infiltration test data which
measures depth to ponding at various application rates as
shown in Figure 7-15 (Reinders and Louw, 1985). Soil
surface and moisture conditions should be as close to
anticipated field conditions as possible.
A variety of sprinkler spacing packages are available
from the manufacturers along with various types of impact
sprinklers, rotating plate sprinklers, and fixed sprays. The
rotating plate sprinklers and fixed sprays can also be
placed on offset booms to increase the wetted width and
thereby decrease application rates. The selection of the
sprinkler package should take into account the soil
infiltration rate curve, slope, wind conditions, potential for
soil compaction, and pressure requirements. Typical
relative application rates for various types of application
packages are shown in Figure 7-16. The center pivot flow
rate and application rate near the end of the center pivot
can be calculated using Equations 7-12 and 7-13,
respectively.
Figure 7-16. Comparison of Relative Application Rates Under Various
Center Pivot Sprinkler Packages.
7-20
-------
The flow capacity of a center pivot system is given by
Equation 7-10.
Q = 1,890 D A
(7-13)
Where:
Q
D
A
flow capacity, gpm
average daily depth of wastewater application, in/d
area of application, acres
The average application rate at the end of the center
pivot lateral is given by Equation 7-14.
I =2nL. D
W T
Where:
I
L
D
W
(7-14)
average application rate of the last sprinklers, in/h (mm/h)
center pivot length, ft (m)
average daily depth of wastewater application, in/d (mm/d)
wetted width of the last few sprinklers or sprays (including
offset boom length, if offset booms are used), ft (m)
average operating hours per day
Surface storage is dependent upon slope, crop, and
cultural practices. Some preliminary values for surface
storage as a function of slope are shown in Table 7-11
(Rogers et al, 1994).
Table 7-11. Typical Values for Surface Storage
Slope
Storage (in.)
0-1%
1 % - 3%
3% - 5%
0.5
0.3
0.1
0.0
Operating center pivots at a higher rotation rate will
decrease the depth of application per irrigation. This takes
greater advantage of surface storage and higher early
instantaneous infiltration rates to reduce runoff. If the
coefficients for Equation 7-9 can be estimated from
infiltrometer or other data and surface storage is estimated
from Table 7-11, the application time that will not cause
runoff can be calculated with Equation 7-12. The maximum
rotational time that will not cause runoff can then be
calculated using Equation 7-13. (Keller and Bleisner, 1990).
SS=iID_Kp(Ta)p
60
Where:
SS = Surface Storage
I = Average application rate near end of center pivot
Ta = Time of application to pond and fill surface storage
Kp = Time to ponding coefficient from Eq. 7-9.
P = Time to ponding exponent from Eq. 7-9.
Solve for Ta by convergent trial and error.
(7-15)
Tcr= 2nL
60 (WJ
Ta
Where:
Tcr
L
W
(7-16)
Critical maximum rotation time which will not cause runoff
Length of center pivot lateral
Wetted width of sprinklers at end of center pivot lateral
(including offset booms)
Time of application to pond and fill surface storage from
Eq.7-15
A sprinkler package with a sufficient wetted width should
be selected such that the calculated time of rotation for no
runoff is greaterthan 24 hours at a minimum. Short rotation
times can cause crops to be shallow rooted, and the more
frequent wetting can increase mold disease in some crops.
Ideally, design rotation times should be 48 hours or greater.
Sprinkler packages should be selected to minimize or
eliminate estimated runoff. If good soil infiltration test data
are not available, it is usually best to rely upon local
experience in the selection of sprinkler packages.
Figure 7-17 can also be used to obtain a rough idea of the
feasibility of center pivot irrigation if only soil texture is
known.
Figure 7-17. Anticipated Center Pivot Performance versus Soil
Texture.
Water droplet kinetic energy can adversely affect
infiltration rates as an irrigation season progresses. For
soils that have low structural cohesion or are otherwise
susceptible to sealing, water droplet energy should be
considered when selecting a sprinkler package. Water
sprinkler or spray devices have relatively smaller nozzles
droplet energy is typically lower for fixed sprays than for
7-21
-------
sprinklers. Water droplet energy is also lower when and/or
are operated in the higher end of their pressure ranges.
A 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. Runoff exacerbates these conditions. As a
result, high flotation tires are used and low tire pressures
are recommended according to the data in Table 7-12.
Table 7-12. Recommended Soil Contact Pressure for Center Pivots
Percent fines Pounds per square inch
20
40
50
25
16
12
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 percent
restrict the use of center ditches. Manufacturers should be
consulted for design details.
Application rate under a linear move system is a function
of the system flow, wetted width of the sprinkler package,
and the system length as shown in Equation 7-17.
Equation 7-15 can then be used to calculate the maximum
time of application for a linear move system for no runoff,
where time of application is equal to wetted width divided
by travel speed. Flow, wetted width, total travel distance,
and travel speed are all factors which can be adjusted
during the planning process to arrive at a linear move
system design which minimizes potential runoff.
I = CQ
LW
Where:
I
C
Q
L
W
(7-17)
average application rate, mm/h (in/h)
unit conversion factor = 1 (96.3)
system flow rate, L/h (gpm)
linear move length, m (ft)
wetted width of the sprinklers or sprays (including offset
boom length, if offset booms are used), m (ft)
7.5 Micro Irrigation Distribution System
Planning and Design
Micro irrigation encompasses drip ortrickle irrigation and
micro-spray irrigation systems. Micro irrigation systems
usually deliver water to emission devices immediately
adjacent to individual plants. Flow rates of micro irrigation
emission devices range from 2 L/h (0.5 gal/h) for low flow
emitters to 120 L/h (30 gal/h) for the largest micro-sprays.
Micro irrigation is not typically used for large-scale
wastewater land treatment systems. It is most commonly
used for landscape irrigation with effluent that has been
treated to tertiary levels (oxidation, filtration, and
disinfection). Micro irrigation can be used to distribute
wastewater with lower degrees of treatment than tertiary,
but much more care is then needed in equipment selection
and operation. Micro irrigation is gaining increased
attention as a distribution method for wastewater from
small and onsite treatment systems. Micro irrigation is also
used for such specialized applications such as landscape
irrigation around treatment plants and to provide water for
odor biofilters. Micro irrigation has little to offer for OF and
conventional SAT systems.
There are a number of very good references for micro
irrigation design (e.g., Keller and Bliesner, 1990). Rather
than cover that material extensively, the information
provided in this chapter will give an overview of micro
irrigation design issues with special attention to the
prevention of plugging.
7.5.1 Soil Wetting
Micro irrigation devices typically only wet a portion of the
horizontal cross sectional area of the soil (see Figure 7-18).
The target percentage of area wetted is generally 33
percent to 67 percent for wide spaced crops such as trees
and vines (Keller and Bliesner, 1990). Yields can suffer at
wetted areas lower than 33 percent while some of the
benefits such as reduced water use and fewer weeds
diminish at values above 67 percent. The minimum target
percentage for closely spaced crops is also 33 percent, but
the higher density of emission devices often translates into
a wetted area of over 67 percent. Field tests with emission
devices are usually the best way to determine wetted width
for a given type of device at the planned irrigation site.
7-22
-------
SALT
ACCUMULATION
BOTTOM OF
'nooj iom ~
DEEP PERCOLATION
Aw-25 If
Figure 7-18. Comparison of Wetting Profiles in Sandy Soil.
7.5.2 Micro Irrigation Design Criteria
In addition to wetted width, the most important micro
irrigation system design criteria are as follows:
. Efficiency of filtration
. Permissible variations of pressure head
. Base operating pressure to be used
. Degree of control of flow or pressure
. Relation between discharge and pressure a the pump
or hydrant supplying the system
. Allowance for temperature correction for long path
emitters
. Chemical treatment to dissolve or prevent deposits
. Use of secondary safety screening
. Incorporation of flow monitoring
. Allowance for reserve system capacity or pressure to
compensate for reduced flow due to clogging
Of the above criteria, the filtration and chemical treatment
criteria are critical when wastewater is to be used in the
micro irrigation system.
7.5.3 General System Layout
Agricultural scale micro irrigation distribution systems
normally include mainlines, submains, laterals, and
emitters. Sometimes manifolds are also utilized to control
flow and pressure to a number of laterals off a submain.
Landscape or small scale micro irrigation may only have
submain and lateral piping. A typical layout for an
agricultural micro irrigation system is shown in Figure 7-19.
FLOW CONTROL
"-*. rl f'Clf .' SFnOSnJBT m -
-------
them. The relative resistance to plugging of various types
of emitters is shown in Table 7-13.
Susceptibility to gradual plugging can usually be
overcome with an aggressive chemical treatment and
flushing program, except in the case of porous pipe.
It should be noted that the flow rate for an emission
device is determined by the size of the flow path within the
emission device. An 8 L/h emitter will have a larger flow
path than a 2 L/h emitter, and therefore be much more
resistant to plugging. Distribution systems for effluent
should always use emission devices with the highest
possible flow rates that still meet the basic system design
criteria.
Inline drip emitters or drip tape can be especially
sensitive to plugging because of the low flow rates of each
emitter. Emission devices incorporating inlet filtering,
automatic flushing, and larger flow paths are strongly
recommended when considering inline or tape products.
Manufacturer's specific recommendations should also be
considered in the selection of emission devices and the
corresponding filtration and water treatment for any specific
application.
Table 7-13. Relative Resistance to Plugging for Various Emission Devices
Emitter Type
Resistance to Catastrophic
Particulate Plugging
Resistance to Gradual Plugging
Multiple Flexible Orifice (continuous flushing) High
Compensating Diaphragm - turbulent path (continuous flushing) Moderately High
Micro-Sprays Moderate
Compensating Diaphragm - straight path or groove Moderate
Long Path Turbulent Moderate
Long Path Straight or Spiral Moderately Low
Porous Pipe* High
Moderate
Moderately High
High
Moderately Low
Moderate
Low
Very Low
*Not recommended for use in any wastewater irrigation system.
7.5.6 Submain, Manifold and Lateral
Design
The distribution piping should be designed to minimize
overall costs (capital and energy) and maintain a high
uniformity. Pressure regulator valves or devices are
normally installed either at the beginning of the submain or
at the inlet to the manifold. Piping downstream of the last
pressure regulation point should be designed to keep the
minimum emitter flow rate greater than 90 percent of the
average emitter flow rate. Lateral length and diameter are
usually key factors for emission uniformity. When barbed
emitters or couplings are used, it is important to include
minor losses caused by the barbs in the laterals. There are
graphical and numerical solutions available in micro
irrigation design guides that combine emitter flow
characteristics with losses in laterals, manifolds, and
submains to enable calculation of average and minimum
flow rates.
Laterals should also be designed with automatic flush
valves or a flushing manifold at the ends of the laterals to
enable regular flushing and prevent the buildup of
sediments in the lateral. This is critical for the long term
prevention of plugging in effluent distribution systems.
7.5.7 Subsurface Drip Irrigation System
Considerations
Subsurface drip irrigation is appealing because the
laterals are out of the way for cultural practices and less
susceptible to physical damage. With subsurface drip
irrigation, wetting of the ground surface is minimal. This can
be a desirable aesthetic consideration for disposal/reuse of
treated effluent.
The main disadvantage of subsurface drip irrigation is
that emitter performance is not readily observable, so
plugging can become serious before the irrigator
recognizes the problem. Subsurface emitters can also be
susceptible to root intrusion, and laterals can be subject to
root pinching. Emitters impregnated with herbicide to
prevent root intrusion are commercially available. Root
intrusion can also be prevented by regular shock
chlorination as discussed later in this section.
7.5.8 Subsurface Drip Irrigation for Small
and Onsite Systems
There is an increasing level of interest in using drip
irrigation components for the subsurface distribution of
effluent from small and on-site wastewater treatment
systems. These systems typically have septic tank or other
sedimentation treatment followed by intermittent sand
filtration or other small scale secondary treatment. The
effluent is then applied below grass or landscape areas to
provide supplemental irrigation and disposal. The emission
device selection and system design considerations are the
same as discussed in this section. One of the differences
for small and on-site systems is that relatively higher flow
rate emitters can be used. A second difference is that
emission devices should be designed to prevent root
intrusion through chemical impregnation or physical
7-24
-------
features. The designer may also want to consider sleeving
the laterals in larger PVC or polyethylene perforated drain
pipes for easy replacement if the laterals become
irreversibly plugged.
7.5.9 Micro-Spray System Considerations
In comparison to drip emitters, micro-sprays have a direct
area of coverage. The area of spray coverage plus
subsurface lateral movement of water should provide
adequate coverage of the root zone of the crop at maturity.
Micro-sprays are commonly used for trees and landscape
beds in place of multiple drip emitters. The proper
functioning of micro-sprays is easier to observe than for
drip emitters, and micro-sprays are generally less
susceptible to gradual plugging than drip emittershe main
disadvantage of micro-sprays is that the mounting stakes
are generally more susceptible to damage than individual
drip emitters.
7.5.10 Filtration
Primary wastewater treatment must be provided as an
absolute minimum prior to any micro irrigation system
filters. Partial or full secondary treatment is also highly
recommended. High-rate automatic sand media filtration is
the filtration of choice for effluent micro irrigation systems.
For systems smaller than 10 L/s (150 gpm), more
advanced biological treatment followed by automated disk
filters may be satisfactory. Screen filters are only
recommended for highly treated effluent, and should be
very significantly oversized.
In general, filtration should be provided to 74 micron (200
mesh) equivalent screen size. Small systems with emitters
which are highly resistant to plugging can use somewhat
coarser filtration depending upon the manufacturer's
recommendations. Filter units should be oversized and
should have plenty of backflush flow capacity. For
automated filter banks, three or more filter units per bank
will provide better backflushing performance than two unit
banks.
7.5.11 Chemical Treatment to Prevent
Plugging
Chemical water treatment should be provided for all
effluent micro irrigation systems except possibly tertiary
effluent with adequate residual chlorine. Chemical
treatment is used to prevent and dissolve organic (algae
and bacterial slime) and minerals deposits which can form
in lateral lines and emission devices. Chlorine and acids
are most commonly used for chemical treatment.
Hydrogen peroxide can be substituted for chlorine when
high concentrations of oxidant are needed to restore
system capacity.
For tertiary treated wastewater, maintaining 1.0 mg/L of
free residual chlorine at the ends of laterals is generally
adequate to prevent plugging. For primary or secondary
effluent, the most effective strategy is to inject sufficient
chlorine to bring the concentration of free chlorine at the
ends of the laterals to 10 mg/L during the last 20 minutes of
the irrigation cycle or to at least 2 mg/L during the last hour
of an irrigation cycle (Tajrishy, 1993). If a micro irrigation
system has to be restored from a gradual buildup of
organic material in the emission devices, concentrations of
up to 100 mg/L chlorine can be temporarily used to treat
the system. Liquid sodium hypochlorite is generally the
preferred form of chlorine because of safety and handling
considerations.
Depending upon water chemistry, acid injection may also
be needed. Acid injection may be needed to keep effluent
pH below 7.5 during chlorination to maintain chlorine
effectiveness. Acid is also sometimes used on an
intermittent basis to dissolve mineral precipitates. During
intermittent acid treatment, the pH may be reduced to a
range of 3 to 4. Care must be taken during intermittent acid
treatment to keep the pH above the level specified by the
manufacturer where emitter damage could occur.
Positive displacement chemical injection pumps or
differential pressure venturi tube injectors are the most
common devices used for chemical injection.
7.5.12 Water Use and Scheduling
Irrigation water needs are based on ET and leaching
fraction in a similar manner as for sprinkler or surface
irrigation. With micro irrigation, there is less evaporative
loss from the soil surface and a lower leaching requirement
than for other types of irrigation. When scheduling micro
irrigation, the evapotranspiration can be estimated by
multiplying the ET for a crop with full coverage by the
percentage of the area that is actually wet or shaded by the
crop, whichever is greater. Micro irrigation systems typically
irrigate the entire area daily, rotating through each flow
zone for several hours to apply the appropriate depth of
water.
7.5.13 Other Operational Considerations
Regular flushing of micro irrigation laterals is very
important for preventing the buildup of solids and
sediments in the laterals. For larger systems, flush
manifolds with automatic valves connected to the ends of a
group of laterals are preferred. These can be operated
briefly at the beginning and/or end of every irrigation. For
smaller systems, automatic flush caps can be installed on
the end of every lateral. Monthly manual flushing should
also be performed for laterals with automatic end flush
caps because the automatic flush caps do not flush at full
operating flow and pressure.
One other operational issue for the irrigation of crops
using effluent with elevated salinity is that light rains during
the growing season can move salts into the root zone. For
7-25
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this reason, the irrigation system should be turned on
during light rains to help flush salts away from the roots.
7.6 Pumping Stations and Mainlines
Different types of pumping stations are used for
transmission, distribution, and tailwater pumping.
Transmission pumping of either raw or treated wastewater
usually involves a conventional wastewater pumping
station. Distribution pumping of treated wastewater can
involve either a conventional wastewater pumping station
or structure built into a treatment/storage pond. Tailwater
pumping is used with surface distribution systems and may
also be used with some sprinkler distribution systems.
The number of pumps to be installed depends on the
magnitude of the flow and the range of flows expected.
Unless there is storage available for many days of
operation, the pumps should have capacity equal to the
maximum expected inflow with at least one pump out of
service. Pumps should be selected with head-capacity
characteristics that correspond as nearly as possible to the
flow and head requirements of the overall system (Sanks
etal., 1989).
The horsepower required for pumping can be estimated
using Equation 7-19.
Hp = _QH_
3960 e
Where:
HP
Q
H
3960 =
e =
(7-19)
horsepower required, hp
flow, gpm
total head, ft
conversion factor
pumping system efficiency
Efficiencies range from about 40 to 50 percent when
pumping raw wastewater up to a range of 65 percent to 80
percent when pumping primary or secondary effluent.
7.7 Distribution Pumping
Distribution pumping stations can be located next to
preapplication treatment facilities or can be built into the
dikes of treatment/storage ponds (see Figure 7-20).
Depending on the method of distribution the pumps may
discharge under pressure. Peak flows depend on the
operation plan and the variation in application rates
throughout the operating season. For example, if the land
application site is to receive wastewater for only 8 h/d, the
pumps must be able to discharge at least three times the
average daily flow rate (24/8 = 3).
The basis of the pump design is the total head (static
plus friction) and the peak flow requirements. Flow
Figure 7-20. Distribution Pumps in the Side of a Storage Pond Dike.
requirements are determined based on the hours of
operation per day or per week and the system capacity
(see next section). Details of pumping station design are
available in standard references (Sanks et al., 1989;
Hydraulic Institute, 1983).
7.8 Tailwater Pumping
Most surface distribution systems will produce some
runoff that is referred to as tailwater. When partially treated
wastewater is applied, tailwater must be contained within
the treatment site and reapplied. Thus, a tailwater return
system is an integral part of an SR system using surface
distribution methods. A typical tailwater return system
consists of a sump or reservoir, a pump(s), and return
pipeline (see Figure 7-21).
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 application 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 percent of the
distribution system capacity is recommended. 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.
7-26
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Figure 7-21. Typical Tailwater Pumping Station.
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 7-14.
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 percent)
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.
7.9 Mainlines
Mainlines are pressurized pipelines that transmit the
wastewater from the pumping station to the application site.
The considerations in mainline design are velocity and
friction loss. Velocities should be in the range of 1 to 1.5
m/s (3 to 5 ft/s) to keep any solids in suspension without
developing excessive friction losses. Optimum velocities
and pipe sizes depend on the cost of energy and the cost
of pipe.
Mainlines are usually buried. Pipe materials for
conveyance of pressurized effluent are usually PVC
(polyvinyl plastic) orductile iron. Undersome low pressure
conditions reinforced concrete pipe (RCP) may also be
used.
Table 7-14. Recommended Design Factors for Tailwater Return Systems
Permeability Class
Very slow to slow
Slow to moderate
Moderate to
moderately rapid
PermeabilityRate, in/h
0.06-0.2
0.02-0.06
0.6-6
Texture range
Clay to clay loam
Clay loam to silt loam
Silt loams to sandy
loams
Maximum duration of
tailwater flow, % of
application time
33
33
75
Estimated tailwater
volume, % of
application volume
15
25
35
Suggested maximum
design tailwater
volume, % of
application volume
30
50
70
7.10 References
Booher, L.J.,( 1974) Surface Irrigation,. FAO Agricultural
Development Paper NO. 94, Food and Agricultural
Organization of the United Nations, Rome.
Burt, C.M., (1995) The Surface Irrigation Manual.
Waterman Industries, Inc., Exeter, CA.
Dillon, R.C., Hiler, E.A., and Vittetoe, G., (1972). Center-
pivot Sprinkler Design Based on Intake Characteristics,
ASAE Trans. 15:996-1001.
Fry, A.W. and A. S. Gray, (1971). Sprinkler Irrigation
Handbook, 1Cfh Ed., Rain Bird Sprinkler Manufacturing
Corporation, Glendora, CA.
Hart, W.E., (1975). Irrigation System Design, Colorado
State University, Department of Agricultural
Engineering, Ft. Collins, CO.
Hydraulic Institute, (1983) Hydraulic Institute Standards,
Cleveland, OH.
Keller, J. and Bliesner, R. D., (1990) Sprinkle and Trickle
Irrigation, Chapter 14, Van Nostrand Reinhold, New
York, NY.
King, B.A., and Kincaid, D.C., (1997) Optimal Performance
from Center Pivot Sprinkler Systems, University of
Idaho Cooperative Extension System Bulletin 797.
McCulloch, A.W. et al, (1973) Lockwood-Ames Irrigation
Handbook, Lockwood Corporation, Gering, NB.
Merriam, J.L. and Keller, J., (1978) Irrigation System
Evaluation: A Guide for Management, Utah State
University, Logan, UT
Pair, C.H. et al, (1983) Irrigation, Fifth Ed., Irrigation
Association, Silver Spring, MD
7-27
-------
Reinders, F. B. and Louw, A..A.. (1985) The Measurement
of Infiltration as a Design Input for Mechanized
Irrigation Systems. S.A. Irrigation 7(1):9-21.
Rogers, D.H., et al. (1994) Sprinkler Package Effects on
Runoff, Cooperative Extension Service, Kansas State
University, Publication L-903.
Sanks, R.L., G. Tchobanoglous, B.E. Bosserman, D.
Newton, and G.M. Jones (1989) Pumping Station
Design, Butterworth Publishers, Stoneham, MA.
Tajrishy, Massoud A.M., Pretreatment Requirements of
Secondary Effluent for Drip Irrigation. Dissertation, DC
Davis, 1993.
U.S. Department of Agriculture, Soil Conservation Service,
(1980) Border Irrigation, Irrigation, Chapter 4, Natural
Resources Conservation Service National Engineering
Handbook, Section 15.
U.S. Department of Agriculture, Soil Conservation Service,
(1983) Sprinkler Irrigation, Irrigation, Chapter 11 in
NRCS National Engineering Handbook, Section 15.
7-28
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Chapter 8
Process Design - Slow Rate Systems
The process design approach to slow rate (SR)
systems for land treatment of municipal wastewater,
must address water, nutrient and oxygen balances.
These balances are discussed in this chapter. The
expected treatment performance and removal
mechanisms were described in Chapter 2.
8.1 System Types
Slow rate (SR) land treatment involves the controlled
application of wastewater or to a vegetated land surface.
There are two basic types of SR systems:
Type 1 - maximum hydraulic loading, i.e.: apply the
maximum amount of water to the least possible land
area; a "treatment" system.
Type 2 - optimum irrigation potential, i.e.: apply the
least amount of water that will sustain the crop or
vegetation; an irrigation or "water reuse" system with
treatment capacity being of secondary importance.
Many of the system components (vegetation,
preapplication treatment, transmission, distribution, etc.)
may be identical for both types. A Type-1 SR "treatment
system" may be limited by soil permeability or by
nitrogen loading. The Type-1 system utilizes deep
percolation of treated wastewater for additional capacity
beyond evapotranspiration. To optimize reuse, the
capacity of a Type-2 SR is limited by crop water or
nutrient requirements.
In general, industrial operations with easily degraded
wastes and municipalities in the humid parts of the
country will seek to minimize land and distribution
system costs, and will implement Type-1 systems. In the
arid parts of the world, where the water has a significant
economic value, it is often cost-effective to design a
Type-2 system.
8.2 Land Area Determination
The Limiting Design Parameter (LDP) for a slow rate
system can be determined after completing a series of
constituent balances including a water balance, organic
loading, and nutrient balance.
For Type-1 systems, the maximum deep percolation
rate or drainage determines the hydraulic loading. The
percolation rate and the hydraulic loading are
determined as:
Lh=Etc-P + Pw (8-1)
Where:
Lh = hydraulic loading rate, cm/mo
ETc = crop evapotranspiration, cm/mo
P = precipitation, cm/mo
Pw = deep percolation rate, cm/month
If a Type-1 system is being designed, the design
percolation rate, Pw, is a function of the limiting
permeability or hydraulic conductivity in the soil profile.
The hydraulic conductivity can be measured in the field,
as described in Chapter 3. If published data on soil
permeability are used, a safety factor of 4 to 10 percent
of the published value should be used. (See Example 8-
1.)
If a Type-2 system is being designed, then the Pw is
the amount of water required to leach salts out of the
root zone so plant growth will not be inhibited. Limiting
permeability is discussed in Chapter 3 and leaching is
described in Section 8.4.
In a Type-1 system, the limiting permeability may
determine a hydraulic loading rate in excess of the crop
water tolerance, so care must be taken to ensure proper
growing conditions.
The monthly value of the design percolation rate
depends on crop management, precipitation, and
freezing conditions:
• 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 further adjustments are
necessary. Where rainfall runoff occurs during
periods of non-operation, the runoff may be
subtracted from the total precipitation.
• Freezing temperature. Subfreezing tempera-
tures may cause soil frost that reduces
infiltration rates. Operation is usually stopped
when this occurs. The most conservative
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, but acceptable, approach is to
use a lower minimum temperature. The
recommended lowest mean temperature for
operation is -4°C (25°F). For forested sites,
operation can often continue during subfreezing
8-1
-------
conditions, with special attention to prevent
freezing in the distribution system.
• Seasonal crops. When a single annual crop is
grown, wastewater is not normally applied
during the winter season, although applications
may occur after harvest and before the next
planting.
Procedures for determining the storage days needed
based on climatic factors are presented in Chapter 6.
The additional agronomic factors listed above can be
determined from local experience in the area once the
type of crop is tentatively identified. It is necessary to
select the general type of vegetation at an early stage of
design so that the crop uptake of nitrogen or other
constituents can be estimated.
Example 8-1: Water Balance for Type-1 SR System
Given: Type-1 system in a humid climate with soils having
a limiting permeability of 2 cm/hr. Flow is 1,000
m3/d. Storage needs are 3 mo/yr, precipitation is
50 cm/yr and ET is 40 cm/yr. Conduct a
preliminary water balance and initial land area
requirements evaluation.
Solution: Hydraulic loading rate is based on the 2 cm/hr soil
permeability. Use a safety factor of 7 percent
(midpoint between 4 and 10 percent).
1. Determine annual percolation:
Percolation is 2 cm/hr x 24 hr/d x 0.07 = 3.36 cm/d
Assume 1 application per week for 9 months (9 mo x 4.33 wk/mo
= 39 weeks)
39 weeks x 3.36 cm/wk = 131 cm/yr
2. Determine water balance for application area:
Lh = ETc -P + Pw
Lh = 40 cm/yr - 50 cm/yr + 131 cm/yr =121 cm/yr
3. Determine land required for application:
Annual flow = 1,000 m3/d x 365 = 365,000 m3/yr
Although the storage reservoir will accumulate 10 cm/yr from excess
rainfall, the percolation from the storage reservoir is assumed equal to
the gain from rainfall.
Area = 365,000 m3/yr 4-1.21 m/yr = 301,600 m2
Area = 301,600 m2/10,000 m2/ha = 30.16 ha
An estimate of the design precipitation on an annual
basis is suitable for preliminary calculations during site
planning. Monthly values are needed for final design.
The monthly precipitation should be based on a 5-year
return period analysis. When monthly precipitation data
are not available a 10-year return period may be
distributed monthly based on the ratio of average
monthly-to-average-annual precipitation.
The design ET rate is a critical component in the water
balance for both crop production and water quality
concerns. In the latter case, a high water loss due to ET
will tend to increase the concentration of constituents in
the remaining percolate. See Chapter 4 for discussion
and procedures for estimating ET for a particular crop.
A further modification is necessary to account for
water losses to percolation and evaporation in the
conveyance and distribution systems. This overall
efficiency of a distribution system ranges from about 75
percent to over 95 percent. The final water balance
equation for the irrigation case (Type-2 system) is:
Lh=(ETc-P)
(1-LR)
ES
(8-2)
Lh = hydraulic loading, cm/month
P = design precipitation, cm/month
ETc = crop evapotranspiration, cm/month
ES = distribution system efficiency, fraction
(0.65 to 0.75 for surface systems)
(0.70 to 0.85 for sprinklers)
LR = leaching requirement, fraction, defined in Equation 8-10
The land area required can be calculated using Equation
8-3.
A = Q/C Lh (8-3)
Where:
A = field area, ha
Q = Annual flow, m3/yr
C = conversion factor, 10,000 m2/ha
Lh = hydraulic loading rate, m/yr
8.2.1 Oxygen Balance
The plant/soil system removes biodegradable organics
through filtration, adsorption, and biological reduction
and oxidation. Most of the biological activity occurs near
the surface where organics are filtered by the soil and
oxygen is present to support biological oxidation.
However, biological activity continues with depth.
The BOD loading rate is defined in Equation 2-1 as
the average BOD applied over the field area in one
application cycle. The oxygen demand created by the
BOD is balanced by the atmospheric reaeration of the
soil profile during the drying period.
Excess organic loading can result in (1) odorous
anaerobic conditions (2) untreated organics passing
through the soil profile, (3) reduced environments
mobilizing oxidized forms of iron and manganese and/or
(4) increases in alkalinity via carbon dioxide dissolution.
Prevention from excess loading of organics is a function
of maintaining an aerobic soil profile, which is managed
by organic loading, hydraulic loading, drying time,
oxygen flux, and cycle time.
Aerobic conditions and carbon dioxide venting can be
maintained by balancing the total oxygen demand with
oxygen diffusion into the soil. McMichael and McKee
(1966) reviewed methods for determining oxygen
diffusion in the soil after an application of wastewater.
They discussed three principal mechanisms for
reaeration: (1) dissolved air carried in the soil by
percolating water, (2) the hydrodynamic flow of air
resulting from a "piston-like" movement of a slug of
8-2
-------
water, and (3) diffusion of air through the soil pores.
Dissolved oxygen in wastewater has an insignificant
impact on high BOD waste streams. The "piston-like"
effect may have a substantial impact on the oxygen
available immediately after drainage, but quantifying the
exact amount is dependent on the difficult to model
dynamics of draining soils. McMichael and McKee
(1966) solved the non-steady state equation of oxygen
diffusion based on Pick's law. They used the equation as
a tool for determining the flux of oxygen (mass of O2 per
area) that diffuses in the soil matrix over a given time.
The flux of oxygen across the soil surface does not
address the destination of the oxygen, but as long as a
gradient exists the oxygen will continue to diffuse into
the soil pores. The gradient is based on the oxygen
concentration at the soil surface and the initial
concentration in the soil. McMichael and McKee (1966)
assumed total depletion of oxygen in the soil matrix.
Overcash and Pal (1979) assumed a more conservative
140 g/m3 based on a plant growth limiting concentration
(Hagen et al. eds., 1967).
The total oxygen demand (TOD) is the sum of the
BOD and the nitrogenous oxygen demand (NOD) and
plant requirement. The NOD is defined as:
NOD = 4.56 x Nitrifiable Nitrogen (8-4)
Nitrifiable nitrogen is the ammonium concentration,
which is often insignificant when compared to high BOD
waste streams.
TOD = BOD + NOD
(8-5)
From the TOD the time required to diffuse an
equivalent amount of oxygen can be determined. The
diffusion equation follows:
No2 = 2(Co2-Cp) • [Dp-t/Tt]
(8-6)
No2 = flux of oxygen crossing the soil surface (g/m2)
Co2 = vapor phase O2 concentration above the soil surface
(310 g/m3)
Cp = vapor phase O2 concentration required in soil to prevent
adverse yields or root growth (140 g/m3)
t = aeration time; t = Cycle time-infiltration time
Dp = effective diffusion coefficient
Dp = 0.6 (s)(Do2)
where s = fraction of air filled soil pore volume at field
capacity
Do2 = oxygen diffusivity in air (1.62 m2/d)
Equation 8-6 can be rearranged to solve for time:
t = 7T-[No2/2(Co2-Cp)]2
Dp
(8-7)
Cycle time is a function of required aeration time plus
the time for the soil to reach field capacity. The time to
reach field capacity is estimated with the infiltration time
calculated by dividing the depth applied by the steady
state infiltration rate.
i = 3600 • d/l
(8-8)
time to infiltrate, hours
depth, cm
steady state infiltration rate, cm/s
There are numerous variables involved in determining
the oxygen balance, all which must be evaluated on a
site-specific basis. An important point to note is that
supplemental irrigation water without a significant
oxygen demand can increase the required cycle time
due to increasing drain and reaeration time. The time
required for the upper zone of the soil to drain is a
function of climatic conditions and the depth of the
wastewater applied. To achieve the desired loading in
surface applications mixing, of supplemental water is
often required because of larger applications. Most
surface applications can not apply less than 7.6 cm (3
inches) in a uniform manner.
8.2.2 Nitrogen Balance
Nitrogen loading is commonly the LDP. However,
when the wastewater contains a high carbon to nitrogen
(C:N) ratio, significant denitrification and immobilization
occur. The main concern associated with the land
application of wastewater with high nitrogen
concentrations is the potential for nitrate to be
transported into the groundwater.
Nitrogen in wastewater goes through transformations
when applied to the soil matrix. The transformations are
both chemical and biological and are a function of
temperature, moisture, pH, C:N ratio, plant interactions,
and equilibrium with other forms of nitrogen.
Because of large influence of organic carbon on
available nitrogen, a factor has been developed to
account for nitrogen lost to denitrification, volatilization,
and soil storage.
Table 8-1 contains the nitrogen loss factor as a
function of the C:N. Actual losses are dependent on
other factors including climate, forms of the nitrogen
applied, and application method.
8-3
-------
Table 8-1. Nitrogen Loss Factor for Varying C:N Ratios
C:N ratio
>8
1.2-8
0.9-1.2
<0.9
Example
Food processing wastewater
Primary treated effluent
Secondary treated effluent
Advanced treatment effluent
f
0.5-0.8
0.25 - 0.5
0.15-0.25
0.1
Adapted from Reed et al., 1995.
While existing inorganic and organic nitrogen in the
soil may supply short-term crop needs, nitrogen
deficiencies and resulting reduced yield and nitrogen
uptake will result if the gross applied nitrogen does not
exceed crop demand. Also, depletion of the soil organic
reserves will reduce soil health. Combining the crop
uptake and the nitrogen loss factor will estimate the
desired nitrogen loading. For additional information see
Chapter 4.
Ln=U/(1-f)
Where:
Ln =
f
Table 8-1)
U =
(8-9)
Nitrogen loading, kg/ha (Ib/acre)
nitrogen loss factor (
Estimated crop uptake as a function of yield, kg/ha
(Ib/acre) (Chapter 4)
8.3 Total Acidity Loading
Natural biochemical reactions maintain the soil pH
near neutral. A range of wastewater pH between 3 and
11 has been applied successfully to land treatment
systems. Extended duration of low pH can change the
soil fertility and lead to leaching of metals. When the
acidity is comprised of mostly organic acids, the water
will be neutralized as the organics are oxidized.
The acidity of wastewater can be characterized by the
total acidity with units of mg CaCO3/L. The total acidity
represents the equivalent mass as CaCO3 required to
adjust the pH to a specific pH, commonly defined as 7.0.
The soil buffer capacity is reported as mg CaCO3/kg or
tons CaCO3/acre. The buffer capacity represents the soil
response to neutralize an equivalent amount of acidity. A
balance between the total acidity applied in the
wastewater and the buffer capacity of the soil can
indicate the capacity of the soil to effectively neutralize
the acid in the wastewater. The buffer capacity of the soil
is restored after organic acids are cleaved.
Most field crops grow well in soils with a pH range of
5.5 to 7.0. Some crops like asparagus or cantaloupes
with a high calcium requirement prefer a soil pH greater
than 7.0. If the pH of the soil begins to drop, liming is
recommended to return the pH to the desirable range for
crop production. Likewise, if the pH increases, sulfuric
acid addition may be recommended. Chapter 4 contains
the range optimal soil pH of various crops.
Because of the soil capability to treat large amounts of
organics acids, it is recommended that the pH of
wastewater only be adjusted for extreme pH conditions
(pH < 5.0 and > 9). If the mineral (non-organic) cause of
the high or low pH is a threat to crops or groundwater,
adjustment may be necessary.
8.4 Salinity
Municipal WWTP treated effluent has a TDS of 150-
380 mg/l of TDS over the source water. In non-oxidized
wastestreams, approximately 40 percent of the dissolved
solids will consist of volatile dissolved solids that will be
removed in the treatment process or will degrade in the
soil. Plant macronutrients, such as nitrogen,
phosphorous and potassium; and minerals, such as
calcium and magnesium, are part of the fixed dissolved
solids (FDS) and are partially removed in land
application systems that incorporate growing and
harvesting of crops. The remaining inorganic dissolved
solids are either leached from the soil profile or
precipitate out into non-soluble forms. When inorganic
dissolved solids accumulate in the soil, an increase in
the osmotic stress in plants may result in reduced yields
or failed germination.
Salt removal by plants is estimated using the ash
content of the harvested crop and can be calculated
similarly to nutrient uptake. Ash content is approximately
10 percent of the dry weight. Often salts in excess of
crop uptake are applied and leaching of salts is required
to limit salt build-up in the root zone.
The leaching requirement is the ratio of the depth of
deep percolation to the depth of the applied water (see
Equation 8-10). The same ratio exists between the
concentration of the conservative salts applied and the
concentration of conservative salts in the percolate. The
EC of water can reliably indicate the salt concentration
when little or no dissolved organics are present. The
equation is only valid when weathering and precipitation
of salts are insignificant (Hoffman, 1996).
(8-10)
Where:
LR = leaching fraction, unitless
Dd = drainage depth, m
Da = depth applied, m
Ca = concentration of salt applied, dS/m
Cd = concentration of salt in drainage, dS/m
8-4
-------
If Equation 8-10 is solved for Cd, the salt concentration
of the drainage is equal to the concentration of the salt
applied divided by the leaching fraction as presented in
Equation 8-11.
c =i
* LR
(8-11)
All terms are described above.
The leaching requirement is determined based on the
crop sensitivity presented in Chapter 4. The average root
zone salts calculated based on solving the continuity
equation for salt throughout the root zone (Hoffman and
van Genchten, 1983):
(8-12)
L Z-LR
Where:
C =
ca =
LR =
Z
S =
mean rootzone salt concentration, dS/m
salt concentration of applied water, dS/m
leaching fraction as defined in EQ 8-10
root zone depth,m
empirical constant = 0.2Z
To determine the desired EC value of drainage, both
the crop sensitivity to salinity and the groundwater
quality should be reviewed. The groundwater uses,
quality, and flux beneath the site should be reviewed to
determine the impact of the leachate of groundwater.
High EC values can be offset by small leaching depths
resulting in insignificant loading to the groundwater.
Also precipitation of minerals continues to occur below
the root zone reducing the loading to groundwater.
The salinity thresholds presented in Chapter 4 are
based on EC extracts of the soil (ECe) normally
measured under trial conditions of 50 percent leaching.
The average root zone salinity is adjusted to the ECe by
dividing by a factor of two. The osmotic stress of 50
percent leaching fraction is accounted by subtracting c
at a given leaching fraction by the c at 50 percent
leaching. Hoffman (1985) found the best agreement
when comparing this model to published ECe threshold
values. The results of this model are presented in Figure
8-1.
2345
ilinity of Applied Water, (C ), dS/m
Figure 8-1. Leaching Requirement as a Function of Applied Salinity
and ECe of Crop Salinity Threshold.
Example 8-2. Type-2 SR Design Loading Rate and Required Area
Given:
Secondary treated wastewater is used to irrigate sudan grass and
winter wheat in Merced, CA. The historical yield of the area is 8
tons/acre and for sudan and 75 bushels/acre for winter wheat and an
additional 1.5 tons/acre of straw. The field configuration and soil type
allow for uniform distribution with a minimum of application of 10 cm
(3.9 inches) with 12 hour sets.
Soil
Total pore space = 42%
Field capacity = 0.18 mm/mm
Steady state infiltration = 18.3
cm/d
Waste Stream
Flow = 3,785 m3/d (1.0 mgd)
BOD5=40mg/L
Nitrifiable ammonia = 4 mg/L
Total nitrogen = 15 mg/L
EC = 1.2 dS/m
Solution:
Oxygen Balance
The total oxygen demand (TOD) is the sum of the
BOD and the nitrogenous oxygen demand (NOD) and
plant requirement.
Using Equation 8-5, the total oxygen demand can be
determined.
40 mg/L + 4 mg/L x 4.56 = 58.2 mg/L TOD
8-5
-------
At a hydraulic loading rate of 10 cm the organic
loading is 58 kg/ha (52 Ib/acre) or 5.8 g/m2. The time
required to diffuse an equivalent amount of oxygen can
be determined with Equation 8-7.
t = 7t 7T • [No2/2(Co2-Cp)]2
Dp
Where:
Dp = effective diffusion coefficient
Dp = 0.6 (s)(Do2)
percentage of sudan as 1.36 percent N. A 8 ton/acre
harvest will require 245 kg-N/ha (218 Ib-N/acre). Winter
wheat at 75 bushel/acre at 60 Ib/bushel is equivalent to
4,000 kg/ha (4,500 Ib/acre). At 2.08 percent nitrogen,
wheat removes an additional 105 kg/ha (94 Ib/acre). If
the 1.5 tons of straw per acre is also removed an
additional 22 kg/ha (20 Ib/acre) of nitrogen is removed.
Equation 8-8 provides the nitrogen limited loading.
l_n=U/(1-f)
Where:
s = fraction of air filled soil pore volume at field capacity
Do2 = oxygen diffusivity in air (1.62 m2/d)
Dp = 0.6 • (0.42-0.18) • 1.62 m2/d = 0.388 m2/d
t = 7i (0.388 m2/d) • [5.8 g/m2/2(310 g/m3-140/g/m3)]2 = 0.002 days
The small time required for diffusion of secondary
treated wastewater shows that drain time is more critical
than the diffusion time for small application depths of
treated municipal effluent. Equation 8-8 can be used to
estimate the time to reach field capacity.
ti= 10cm =0.54d
18.3 cm/d
The minimum cycle time is the sum of the application
time, the diffusion time, and the drain time. The resulting
minimum cycle time is just over 1 day. The oxygen
balance then limits application to 10 cm every third set or
1.5 days.
Total Area for oxygen balance =
1.5 days x 3,785 m3/d * 0.1 m = 56,780 m2 = 5.7 ha
The frequent irrigation suggested by the small oxygen
demand does not consider the water logging from a
crop.
Nitrogen Balance Based on Crop Removal
The nitrogen loading is determined by the nitrogen
uptake and estimates of nitrogen losses. The C:N ratio
can be estimated from the BOD:N ratio. The result is a
C:N ratio of 2.6. The corresponding nitrogen loss factor
from
Table 8-1 is 0.25. Table 4-9 lists the average N
Where:
Ln for sudan = 245/(1 -0.25) = 327 kg-N/ha
Ln for winter wheat = 127/(1 -0.25) = 169 kg-N/ha
At a total nitrogen content of 15 mg/L, the sudan grass
nitrogen requirement is met with a application of 2.18 m
(86 inches). The winter wheat requires an application of
1.13 m (44 inches). The minimum area for a nitrogen
balance could be achieved when the area was double
cropped and a total of 3.31 meters was applied.
Total Area for nitrogen balance =
3,785 m3/d x 365 d/yr * 3.31 m/yr = 417,000 m2 = 41.7 ha
A hydraulic load of 3.31 m per year exceeds the crop
irrigation requirements and a Type-2 SR system could
be designed around 42 ha, if considerations for
percolation and crop water-logging are made.
Salinity
The leaching fraction is a function of the crop and the
water quality. Figure 4-3 shows that 10 percent yield
reduction occurs at 5.9 dS/m for sorghum and 7.0 dS/m
for wheat. The most restrictive crop is sorghum. Using
an ECe of 5.9 dS/m and an applied EC of 1.1 dS/m,
Figure 8-1 suggests a leaching requirement less than
0.05. To ensure productivity a leaching fraction of 0.05
should be used.
Water Balance
Crop coefficients gathered from local extension service
are utilized in the water balance below. The area used to
calculate the irrigation requirement including irrigation
efficiency and leaching requirement is adjusted until the
irrigation requirement meets the flow.
8-6
-------
10
11
12
Month days
January 31
February 28
March 31
April 30
May 31
June 30
July 31
August 31
September 30
October 31
November 30
December 31
TOTAL 365
Wastewater
Volume
MG
31.0
28.0
31.0
30.0
31.0
30.0
31.0
31.0
30.0
31.0
30.0
31.0
365.0
Precipitation
5-yr
in.
3.56
3.14
2.97
1.77
0.91
0.19
0.02
0.03
0.33
0.99
2.10
2.83
18.8
Normal
ETo
in.
1.0
1.5
3.2
4.7
6.6
7.9
8.5
7.2
5.3
3.4
1.4
0.7
51.4
Winter Wheat 30 Acres
k
1
1
1
0.2
1
ETc
In
1.0
1.5
3.3
0.0
0.0
0.0
0.0
0.0
0.0
0.0
0.3
0.7
Irrigation
in
0.0
0.0
0.4
0.0
0.0
0.0
0.0
0.0
0.0
0.0
0.0
0.0
0.4
MG
0.0
0.0
0.3
0.0
0.0
6.0
0.0
0.0
0.0
0.0
6.0
0.0
0.3
Sudan J 90 Acres
(
k
0.8
1.1
1.1
1.1
1.1
1.1
1.1
0.8
ETc
In
0.0
0.0
0.0
3.8
6.9
8.3
8.9
7.6
5.6
3.6
1.1
0
Irrigation
in
0.0
0.0
0.0
2.5
7.4
10.0
11.0
9.3
6.5
3.2
0.0
0.0
49.9
MG
0.0
0.0
0.0
6.0
18.2
24.5
26.9
22.7
1 5.8
7.8
0.0
0.0
121.8
Water
Balance
MG
31.0
28.0
30.7
24.0
12.8
5.5
4.T
8.3
1 4.2
23.2
30.0
31 .0
Figure 8-2. Example Spreadsheet Used to Calculate the Irrigation Requirements Including Irrigation Efficiency and Teaching Requirements.
Are Associated with Columns
Notes:
7 Wastewater flow based on design flow x number of days per month (in this case 1 MGD)
2 Monthly precipitation with a 5-yr return period
3 Normal monthly ETo
4 Crop coefficient from local extension office
5 ETc = k x ETo
6 Irrigation Requirement = Precipitation -[kx ETo x (1 + Leaching Fraction) •*• Irrigation Efficiency]
7 Irrigation Requirement converted to volume = inches x .027152 x acres = MG
8-11 Same as 5-6
12 Total wastewater volume - crop requirement
A Type-2 system can be managed with a crop rotation
plan allowing for a portion of the available area to be
fallow at all time. The fallow area can receive water
during harvesting and planting when applications are not
possible. During the summer, application could be
applied to the fallow portion that will be planted in wheat
the subsequent fall. During the winter months, one or
two applications per month can be applied to wheat with
the remainder going on the fallow ground where the
sudan will be planted. The crop rotation will allow for
application all winter.
8.5 Design Considerations
The design procedure is outlined in Figure 8-2 (US
EPA., 1981). Additional design consideration of buffer
zone,
storage requirements, distribution system, and crop
selection must also be addressed for both Type-1 and
Type-2 systems.
8.5.1 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 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.
8-7
-------
WASTEWATER
CHARACTERISTICS
(Chapter 2)
SITE CHARACTERISTICS
(Chapter 5)
PROCESS PERFORMANCE
(Chapter 2)
PREAPPLICATION TREATMENT
(Chapter 6)
CROP SELECTION
(Chapter 4)
LOADING RATES
(Chapter 8.2)
STORAGE
(Chapter 6)
FIELD AREA
(Chapter 8.2)
DISTRIBUTION
(Chapter 7)
DRAINAGE AND RUNOFF
CONTROL
(Chapter 7)
SURFACE WATER
Figure 8-3. Slow Rate Design Procedure.
SUBSURFACE
WATER QUALITY
REQUIREMENTS
(Chapter 2)
1
SYSTEM MONITORING
(Chapter 8.6)
CROP MANAGEMENT
(Chapter 8.6.8)
8-8
-------
The requirements for buffer zones in forest SR
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 public. A
minimum buffer zone width of 50 ft should be sufficient
to meet all objectives, if the zone contains trees with a
dense leaf canopy.
8.5.2 Storage Requirements
A detailed discussion and calculation procedures for
storage are presented in Chapter 6. When storage is a
component in a SR system, it may be advantageous not
to bypass the pond in the application season to allow
reductions in conforms and nitrogen to occur as
described in Chapter 6. Algal production in storage
ponds should not affect SR operations. In fact, algae will
incorporate the inorganic nitrogen into cells as inorganic
nitrogen, which will reduce the leaching potential of the
nitrogen
8.5.3 Crop Selection
The type of crop selected will directly influence the
land area required, if crop uptake is a critical factor in
determining the design hydraulic loading. In most cases,
crop selection will be one of the first design decisions in
SR design. See Chapter 4 for discussion of crop
selection procedures.
8.5.4 Distribution System
It is necessary for Type-2 irrigation systems to decide
on the method of distribution that will be used, at an
early stage of design. The system efficiency (see
Equation 8-2) is a significant factor in determining the Lh
and the amount of land that can be irrigated. An early
decision on distribution method is less critical for Type-1
treatment system. Distribution systems are discussed
further in Chapter 7.
8.5.5 Application/Irrigation Scheduling
A regular, routine application schedule is usually
adopted for Type-1 SR treatment systems for
operational convenience. Sprinklers with an application
rate of 0.2 to 0.3 in/hr are often employed in SR
systems. This will not usually exceed the intake rate of
most soils, so surface runoff is avoided. It is then typical
to operate the sprinkler unit continuously for a sufficient
number of hours to achieve the design loading. The
application is then repeated at regular cycle intervals.
Operation can either be manual, automated with time
switches or some combination.
The scheduling of a Type-2 SR irrigation system is
dependent on the climate and the crop to be grown. The
purpose is to maintain sufficient moisture in the root
zone to sustain plant growth. The water available for
plant use is defined as the difference between the field
capacity and the wilting point (see Chapter 3).
The usual range of the deficit that is allowed ranges
from 30 to 50 percent of the available water in the root
zone, depending on the crop type and the stage of
growth, and soil type (Figure 3-2). An irrigation event is
scheduled when the soil moisture reaches the
predetermined deficit. Ideally irrigation maintains soil
moisture level for optimum plant growth. This can be
measured using soil moisture sensors or estimated
based on ETc. Soil moisture sensors can be used in a
completely automated system to start-up, shutdown and
shift applications from field to field.
The amount of water to be applied in each irrigation
event can be determined with:
(1-LR)
ES
(8-13)
Where
IT
ID
LR
ES
total depth of water to be applied during an irrigation, cm
soil moisture deficit to be replaced, cm
leaching requirement as defined in EQ 8-10
irrigation efficiency, fraction
8.6 Crop, Soil and Site Management
Requirements
Site management is a critical part of operating and
monitoring a land application system. Detailed
monitoring and observations provide information for
documenting and evaluating performance of a facility's
land application program.
This section addresses routine land application site
monitoring including:
. Documentation of flow and water quality;
. Use of supplemental irrigation water;
. Soil conditions;
. Soil sampling and analysis;
. Groundwater sampling and analysis;
. Crop yield and biomass data collection; and
. Maintenance and routine inspection observations.
In all of these areas, interrelated data gathering, short-
term and long-term observations, and some analysis of
basic data is required to maximize the usefulness of the
information. Data organization, calculations, analysis,
and record keeping are critical to the success of a
monitoring program.
8.6.1 Basic Structure of a Monitoring
Program
The personnel responsible for operating the land
application system often conduct monitoring. During site
8-9
-------
monitoring, the system operator will collect data required
to document operations and will make both quantitative
and qualitative observations. These observations may
include details regarding functioning of the physical
infrastructure, as well as crop management issues,
including both field management, such as disking or
leveling, and irrigation. During the course of monitoring,
the observer will learn more about the behavior of the
land application system. This often leads to developing
improved operating procedures based on experience
and can be invaluable for solving temporary problems
that occur within the land application site.
The monitoring and operations activities described
above fall in the general category of "process control."
These observations are made in order to develop and
implement protocols for managing the land application
system. This can include changing irrigation practices;
scheduling harvesting, replanting, and other crop
management activities; scheduling preventative
maintenance and repair; and expanding or improving the
system.
A second, equally important monitoring objective is to
provide system operations documentation for regulatory
oversight and compliance. Often, process control
monitoring and regulatory reporting requirements are
similar in scope. Table 8-2 provides examples of typical
conditions that address site monitoring for process
control. Regulatory requirements vary from state to
state, and often within states, so the individual state
agency should beto state, and often within states, so the
individual state agency should be contacted. Process
control observations are often gathered more frequently
than regulatory monitoring requirements for short-term
decision-making. Those short-term decisions may
require more complex evaluation and decision-making
Table 8-2. Suggested Minimum Process Control Monitoring
Sampling Category
than the more straight-forward task of documenting
compliance.
For a land application site with more than one field,
field-by-field flows must also be recorded to determine
loading rates. Process control monitoring also requires
that irrigation amounts (including both effluent and
supplemental irrigation water) be measured on a daily
basis so that a decision about where to apply facility
flows for the following day can be made. This decision
must also incorporate additional information as well as a
more complex analysis that takes into account time of
last irrigation, soil moisture status in the field, current
and projected weather conditions, cropping patterns, and
scheduling needs for other fields within the land
application program.
8.6.2 Water Monitoring
Permits issued to a facility for land application routinely
require measurement of flow and detailed observations
to document timing and distribution of flows. Monitoring
of supplemental water flow, if used, is also required for
land application systems. A supplemental irrigation water
supply is required when effluent cannot be used to meet
all irrigation water requirements. Table 8-3 summarizes
monitoring for flow and water quality that may be
required as part of a monitoring plan.
Sampling locations must be selected to allow
collection of samples from a location that is
representative of the flow to be monitored. Effluent
quality can change from point to point within the
distribution system, particularly when storage is a
component. Facility personnel should consider these
changes when selecting a sampling point for regulatory
compliance or to calculate field loading rates. For
Operational Management
Effluent
Field-by-Field Loadings
Soil Testing
Crop Sampling
Groundwater
Routine Inspection Needs
Total daily flow (gallons)
BOD, TSS, FDS, Total N, SAR
Monthly effluent application, inches
Daily climate data (precipitation, evapotranspiration)
Calculation of loading rate for LDP
Annual pH, EC, TKN, K, NH3-N, ESP (Sample each field, 3 depths per application zone, composite
samples from a minimum of 3 locations)
Annual available P, available K for crop nutrient supply analysis
Date, biomass, and crop harvested
Annual tissue ash weight, total N
Quarterly NO3-N, pH, EC, water level for each well
Annual Ca, Mg, Na, K, CI, SCu, HCO^COs for each well
Pumping system operating pressures, field operating pressures, proper operation of irrigation system,
leaks along pipeline, ponding, crop health, runoff, etc.
Definitions: Biochemical Oxygen Demand (BOD), Total suspended solids (TSS), Electroconductivity (EC), Total Kjeldahl Nitrogen (TKN), Nitrate-
Nitrogen (NO3-N), NH3-N, Ammonia Nitrogen (NH4-N)
8-10
-------
operations monitoring, sampling in more than one
location within a distribution system is performed to
evaluate changes or problems such as uneven
distribution.
Samples can be either grab or composite and sample
collection can be performed either manually or using
automated sampling equipment. Samples meant to
represent a single point in time and give a "snapshot" of
conditions at that instant are usually collected via grab
sampling. Grab sampling involves filling containers
manually.
8.6.3 Flow Measurement
Detailed measurements of effluent flow are required to
determine irrigation volumes and field constituent
loading rates. Flow monitoring and sampling for water
quality analysis are typically conducted at a central,
accessible location. Ideally, there should be one exit
location identified for sampling. Table 8-4 outlines
methods used to measure effluent flows and
summarizes the advantages and disadvantages of these
methods.
Table 8-3. Suggested Minimum Effluent Monitoring
Parameter
Flow
Water Quality
Effluent
Lagoon or storage
pond
Field by field
application amounts
Daily or monthly facility flow
Water level in relation to maximum and minimum
operating levels
Effluent application
Visible inspection for runoff, equipment malfunctioning,
erosion, crop condition
Monthly nitrogen (TKN, NO3-N, NH3-N), FDS, salt ions,
BOD, other parameters known to be of concern and
present
Monthly nitrogen species, salt ions, BOD, other
parameters known to be of concern and present (If all
water passes through the pond, the pond water quality
should be used rather than effluent quality into the
pond.)
Constituent loading can be calculated from flows and
constituent concentrations
Pumps and pipelines
Climate
Visible inspection for leaks
Pressure checks to identify leaks, other equipment
failures, need for maintenance
Vibration in pumps and excess heat
Daily or weekly precipitation and temperature
Daily or weekly evapotranspiration
Table 8-4. Flow Measurement Alternatives
Method
Alternatives
Advantages/Disadvantages
Intrusive flow
meters
Non-intrusive flow
meters
Open channel flow
measurements
Incoming water
supply correlation
Pump run time and
output calculation
In-field methods
Impeller, paddle wheel
Hot wire anemometer
Magnetic
Ultrasonic/Doppler
Weir-type
Discharge volume is estimated as a
percentage of incoming water consumption
Flow for individual fields can be estimated
proportionally from total flow
Rain gauge/catch cans in individual fields
Use of soil water measurements to calculate
net irrigation
Intrusive devices can clog with solids or from biological growth;
higher friction loss/pressure drop
Low pH or high EC can cause failure of sensing components
resulting in higher maintenance
These sensors have no parts in the flow
Higher capital cost: often, these are used at main pump station and
alternate methods are used for individual fields
Requires controlled channel to establish proper conditions for
measurement
Simple, reliable operation; measurements can be recorded
Supply water is clean, relatively simple to measure using meters
A correlation between incoming flow, in-plant loss, and effluent
discharge is required
Requires a master pump station flow meter or some calibration
Irrigation fields must be maintained so they operate according to
specifications
Primarily applicable to sprinkler irrigation systems or surface
irrigation using siphon tubes or gated pipe
Measures net irrigation (amounts actually applied) rather than gross
irrigation
Assumptions in water budget method make method approximate;
calibration required. Measurement of soil moisture at bottom of root
zone provides useful information related to leaching
Rain gauges are applicable to sprinkler irrigation only
8-11
-------
Direct flow measurement devices provide reliable data
when properly installed and maintained (including
periodic inspection, preventative maintenance, and
calibration). The type of measurement device or
flowmeter selected depends upon the flow conveyance
used in the facility.
The type of meter installed should allow measurement
of both the instantaneous and record the total volume -
this type of meter is known as a totalizing flowmeter.
Flow measurement requires sufficient straight length of
pipe or channel to develop uninterrupted, smooth non-
turbulent flow to provide consistent and reliable data.
Typically, a straight length of approximately ten (10)
diameters should be available upstream of the flowmeter
and the piping should remain straight for approximately
four (4) pipe diameters downstream.
8.6.4 In-Field Distribution of Irrigation
Water
For land application systems, total flow and the
distribution of effluent among irrigation fields (for facilities
with multiple fields) should be measured. This is required
to calculate hydraulic and other constituent loadings for
the land application area. The type of application method
(pumped conveyance, surface irrigation, sprinklers, etc.)
influences the choice of in-field distribution monitoring
method. The most commonly used flow measurement
methods are listed in Table 8-4 and described in this
section. These typically involve either direct
measurement of flow at the field inlet; estimating the flow
based on readings taken at the field inlet, estimating
application amounts based on readings taken of soil
moisture, or direct measurement of the amounts applied
in the field.
For systems where effluent is pumped to the field(s),
the direct measurement flowmeters described in the
previous section are appropriate for in-field flow
measurement. Use of hour-meters and estimation of flow
from pump discharge and system pressure data are also
feasible for estimating in-field distribution of water. Use
of on-going pressure measurements in conjunction with
this method is recommended because suspended solids
may affect system pressures and water delivery by
restricting flow in the pipelines or plugging sprinkler
nozzles or gated pipe openings. Monitoring pressures in
the field can be combined with performing on-going
maintenance/inspection of the irrigation system.
For a facility using surface irrigation methods, with
either gated pipe openings or siphon tubes for
transferring water from the irrigation ditches to the field
sections, these can be calibrated to allow measurement
of flow to the different portions of the field. Gated
openings are holes in horizontal pipe sections to allow
water to spill out into the field and siphon tubes are
smaller diameter tubing laying in the irrigation ditch to
convey the water by siphoning. Estimates of field flows
must take into account the loss and return or "tailwater"
flow, if return of the tailwater from the end of the irrigated
area is practiced.
For facilities applying with sprinkler type systems, net
irrigation, can be measured using rain gauges placed
within the fields. This method is a simple and effective
way to measure the actual water applied to different
areas. Rain gauges are installed in land application
fields and are typically read weekly, although some
facilities use daily measurements. Since the
measurement technology is simple and inexpensive,
several rain gauges should be installed at each site for
comparison. For fields that receive both effluent and
supplemental irrigation water, field notes regarding dates
and hours of water flow from these two sources must be
used to separate these water sources. Background
rainfall amounts are recorded separately, usually at a
nearby location not receiving irrigation, and subtracted
from the total recorded in the field locations.
8.6.5 Soil Monitoring and Testing
Soil testing and analysis is an important part of land
application site monitoring. Soils data are used for three
primary purposes in land application systems, as follows:
. Assessment of nutrient supply for crops;
. Evaluation of treatment efficiency of the soil plant
system;
. Assessment of the land application site condition
overtime.
A well-designed soil sampling program addresses both
environmental and agricultural production objectives.
Your state land grant university should be consulted for
extraction solutions and analytical methods for your local
area. Basic monitoring parameters and the use of the
measurements are summarized in Table 8-5.
The most common soil sampling methods for land
application systems rely on removal of a soil core or soil
sample within land application fields. Sampling depths
vary and your local land grant university has
recommendations. Generally pastures are samples 0-4"
and row crop fields 0.6". Increasingly, in-situ
measurements of soil aeration status and moisture
content have been used. These latter methods are
8-12
-------
Table 8-5. Soil Monitoring Parameters
Parameters
Sampling considerations
General
pH, EC, Organic matter,
TKN, NO3-N, NH3-N, PO4,
Na, Ca, Mg, HCO3,
Available K, Available P, SO4,
C03, Cl
Measure following harvest of each
crop:
• Make a composite sample
from a minimum of 3 locations
per application zone,
depending on field size
• Basic soil test to assess
general condition
• Nutrient analysis to asses
loading impacts
• Salt analysis to calculate the
Sodium Adsorption Ratio and
Exchangeable Percentage
• Nutrient analysis to assess soil
fertility (SR and OF systems
look for K deficiency)
• Additional ions to complete a
salt balance. This need not be
done at every sampling event.
customarily used for more research-oriented purposes
and are included here for completeness. Soil sampling
is commonly done once or twice during cropping years
at multiple depths and at multiple locations in the field.
Often samples from different locations in the field are
composited so that average conditions can be assessed.
It is recommended that soil samples be collected before
planting and following harvest for evaluation of the
nutrient requirements and uptake of crops.
Since soil moisture monitoring is primarily performed
for operational purposes, rather than regulatory
compliance, the frequency and depths of sampling can
be selected based on site-specific needs. Soil moisture
depth monitored below the root can be used to
document the presence of leaching.
8.6.6 Vadose Zone Sampling
The unsaturated soil from the soil surface to
groundwater is the vadose zone. Monitoring or sampling
of the vadose zone can be accomplished by sampling
soil or soil-water. Vadose zone samples are too variable
and therefore of little value to measure performance of
land treatment.
Vadose zone monitoring has been used to assess land
application programs primarily for research purposes.
Vadose zone monitoring is more complex than
monitoring of other media in a land application system
because both water movement and solution
concentrations must be measured. In fact, vadose zone
monitoring is often considered to be primarily a research
tool because considerable analysis is required to
properly interpret results and measurement methods are
intricate and susceptible to error due to installation
method and operation. Use of these techniques for
operational management or regulatory compliance does
not appear to be as useful as other methods for
addressing soil and groundwater conditions.
Common techniques used to measure vadose zone
properties are summarized in Table 8-6. Additional
technical information is available in ASTM standards
(ASTM 1992). All but one of the methods in Table 8-6 is
designed to measure concentrations of constituents in
the water in the vadose zone soil pores. Key differences
among methods include ability to measure water flow as
well as water quality, disturbance required to install the
device, and the need to install replicate sensors to
address measurement variability. The different types of
lysimeters used to measure soil water constituent
concentrations are summarized in Table 8-6.
Soil sampling can be included in a list of vadose zone
sampling methods because this can yield basic
monitoring information. Soil concentrations of
constituents of interest are measured and a water
budget developed using techniques discussed
previously can provide an estimate of water flow.
Changes in soil concentrations at a given depth over
time can be used to assess whether a land application
site is managed properly.
Suction lysimeters are relatively simple to operate.
Samples are collected from the device by applying a
vacuum (generally for 24 hours prior to sampling), which
draws soil solution into the lysimeter, and samples can
then be collected. The sample is analyzed to determine
concentrations but interpretation of this "simple" result is
complex. Suction lysimeters often appear to be a low-
cost monitoring choice because the basic sampling
equipment is relatively inexpensive. This is often not the
case when replicate installations to provide
representative results and the requirement to provide an
accompanying water flow measurement are included in
the cost of monitoring.
The more capital-intensive pan and basin lysimeters
are improvements over the suction lysimeter method
because these provide a solution sample that has been
collected as a result of downward flow of water. These
provide both a sample for chemical analysis and an
estimate of water flow based on the volume of water
collected. These sensors are often considered to be a
permanent installation because of the relatively complex
installation procedure. The disadvantage of pan
lysimeters is that the sample can exceed holding time for
some constituents because it is not necessarily
withdrawn as soon as it appears in the sampler. In
addition, if the soil profile is disturbed by the installation,
the movement and water quality changes represented by
the sample may not reflect that of the undisturbed soil
profile.
8-13
-------
Table 8-6. Vadose Zone Sampling/Monitoring Alternatives
Method
Description
Advantages/Disadvantages
Soil Sampling
Suction
Lysimeter
Pan Lysimeter
Basin Lysimeter
Wick Lysimeter
Soil samples are collected and analyzed for pH,
EC, Cl, NO3-N
A porous ceramic tube is placed in the soil so
soil solution samples can be collected and
analyzed
A small collection pan (1 -5 ft2) is buried at a
selected depth so that soil solution samples
can be collected via gravity drainage for
analysis
A large collection pan (50-400 ft2) is
constructed and covered with soil so that soil
solution samples can be collected via gravity
drainage for analysis
A porous wick designed to match the soil water
retention characteristics of the soil is buried at a
selected depth so that solution samples can be
collected using a low negative pressure.
Simple and reliable
Samples totals, not just solution fraction
Destructive sample
Requires a soil water balance calculation to determine whether flow occurs
Inexpensive, simple technique to implement
Extracts soil solution that is not mobile
Known to have large measurement variability
Requires a soil water balance calculation to determine whether flow occurs
Extracts soil solution during flow events
Provides a measure of both flow and water quality
Installation can approximate undisturbed conditions
Moderate variability among replicate samples
Extracts soil solution during flow events
Provides a measure of both flow and water quality
Installation creates disturbed soil conditions
Large sample decreases variability
Extracts soil solution at near zero water potential
Installation can approximate undisturbed conditions
Requires a soil water balance calculation to determine whether flow occurs
8.6.7 Groundwater
Groundwater monitoring is required at most land
application sites. Details regarding the establishment of
a program, monitoring well construction, hydrogeologic
evaluation, and monitoring methods follow agency
guidelines and industry standards.
8.6.8 Crop Management and Biomass
Removal
Crop management is an important part of operating
and maintaining a land application system. A healthy
and productive crop is required to remove nutrients and
salts. Plant material quality is an indicator of the
biological integrity of the site. Although it is of secondary
importance, the value of crops harvested from the site
may provide an additional incentive to assure that proper
attention is paid to the land application fields. Attention
to crop needs, including irrigation water and nutrients,
will result in better management for agricultural
production, water treatment, and environmental
protection objectives.
Much of crop management is accomplished in the
same way for a land application site and conventional
agricultural operations. Because effluent supplies
organic fertilizer, crop responses to effluent irrigation
differ from those in a conventional irrigation
water/inorganic commercial fertilizer scenario. Daily
monitoring (addressed in the next section) is required to
assess whether each crop is healthy enough or whether
some management action must be taken.
Recommendations for routine monitoring of crops are
provided in Table 8-7. Local county representatives and
land grant universities should be contacted to help in
developing crop management plans. Careful daily
observations are important for ongoing management
activities and should be maintained in a field log for
reference. The actual measurements required for crop
monitoring include biomass removal and tissue sampling
to determine constituent levels removed. Because
nutrient uptake is the primary function of the crop,
analysis for nitrogen is recommended. Salt management
at land application sites includes a number of soil
processes, salt loading and crop uptake need not match
as closely as nitrogen levels.
8.6.9 Routine Maintenance and Inspection
Thorough daily inspections to identify operational
problems and gather data to make irrigation and
cropping decisions are recommended as part of routine
monitoring. Each facility should develop a customized
inspection form. Table 8-8 provides an example
Inspection form useful for guiding daily inspections.
It is common that a routine inspection form also
incorporates collection of meter readings, pressure
checks, times that various activities take place, etc. This
is an appropriate combination of tasks and should be
encouraged. Because land application treatment is a
biological process, it is somewhat unpredictable and
observations used to adjust management according to
actual field conditions are important. In addition, results
and observations made during inspection are an
appropriate topic at periodic facility staff meetings or
informal meeting of field or maintenance personnel.
8-14
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Table 8-7. Example Crop Monitoring Parameters
Parameter
Crop management chronology
Biomass removed
Constituents removed
Description
Dates of cropping activities should be logged including date of planting, date of harvest, dates of primary
tillage operations, application of fertilizer, observations of crop health
This can be accomplished by counting bales, bushels, trucks or other field-scale measurements. Water
content should be determined so that data can be converted to dry weight.
Sample crops for TKN, NO3-N
Salts can be evaluated if appropriate for a specific site.
Table 8-8. Routine Maintenance Inspection Checklist for Land Application Sites
Feature
Condition
Recommended Action
Facility Discharge
Lagoon or Pond
Main Pump Station
Transmission Piping
Booster Pumps
Fields irrigated
Fields condition
Crop condition
Samples Collected
Check amount of flow, evidence of unusual conditions
Pond level, odor, scum on surface, presence of excessive solids
Current operations, flow, pressure, odor, leaks, mechanical concerns
Leaks, odor, pressure at intermediate locations
Current operations, flow pressure, odor, leaks, mechanical concerns
For each field: list irrigation run times, effluent or supplemental water supply, odor
For each field: assess irrigation uniformity, runoff, erosion, irrigation system condition,
odor, solids on surface
For each field: general crop health, need for farming activities
List samples taken
8.7 References
American Society of Agronomy. 1986. Methods of Soil
Analysis, Part 1, Physical and Mineralogical
Methods 2nd edition, A. Klute, Editor, Madison, Wl.
Crites, R. W., S. C. Reed, and R. K. Bastian. 2000.
Land Treatment Systems for Municipal and Industrial
Wastes. McGraw-Hill. New York, NY.
Hagen, R. M., H. R. Haise, T. W. Edminster, eds. 1967.
Irrigation of Agriculture Lands, Agronomy Series No.
11. Madison, Wl.
Hoffman, G. J. and M. van Genuchten. 1983. "Water
Management of Salinity Control." Limitation to
Efficient Water Use in Crop Production, Chapter 2C.
H. Taylor, W. Jordan, and T. Sinclair, eds. ASA.
Monograph, pp 73-85.
Hoffman, G. J. 1985. Drainage Required to Manage
Salinity. Journal of Irrigation and Drainage Division.
ASCE111.pp 199-206.
Hoffman, G. J. 1996. "Leaching Fraction and Root Zone
Salinity Control", Agricultural Salinity Assessment
and Management. ASCE No. 71. K. K. Tanji, ed.
Corrected Edition. ASCE. New York, NY.
McMichael, F. C. and J. E. McKee. 1956. Wastewater
Reclamation at Whittier Narrows. State Water
Quality Control Board. Publication No. 33.
US EPA 1981. Process Design Manual for Land
Treatment of Municipal Wastewater, EPA-625/1-81-
013, U.S. Environmental Protection Agency, CERI,
Cincinnati, OH.
US EPA. (1982). Handbook for Chemical and Sample
Preservation of Water and Wastewater, EPA-600/4-
82-029, Washington, DC.
US EPA. (1983). Methods for Chemical Analysis of
Water and Waste, EPA-600/4-79-020, Washington,
DC.
US EPA. (1995). Groundwater Well Sampling, Standard
Operating Procedure 2007.
8-15
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Chapter 9
Process Design - Overland Flow Systems
The process design approach to overland flow (OF)
systems for land treatment of municipal wastewater is
discussed in this chapter. The expected performance
and removal mechanisms are described in Chapter 2.
Because OF systems discharge, permit conditions and
rainfall runoff must be considered in the design.
9.1 System Concept
Overland flow (OF) is defined as the controlled
application of wastewater onto grass-covered, uniformly-
graded, gentle slopes, with relatively impermeable
surface soils. The process was first applied in the United
States for industrial wastewaters in Napoleon, OH and
Paris, TX (Bendixen et al., 1969; Glide et al., 1971).
Early application of the process for municipal
wastewaters occurred in England, where it was termed
"grass filtration," and in Melbourne, Australia (Scott and
Fulton, 1979; US EPA, 1975). Many of these OF
systems have been in continuous and successful
operation since the late 19th century. Research efforts by
EPA (US EPA, 1976) and the U.S. Army Corps of
Engineers (Peters et al., 1978; Carlson et al., 1974) and
the performance of operational systems (Peters et al.,
1981; US EPA, 1979; US EPA., 1981) led to modeling
efforts and the development of rational design criteria
(Jenkins et al., 1978; US EPA, 1981; Smith and
Schroeder, 1982).
9.1.1 Site Characteristics
Overland flow is best suited for use at sites having
surface soils that are slowly permeable (clays), or that
have a restrictive layer, such as a hardpan or claypan at
depths of 0.3 to 0.6 m (1 to 2 ft). Moderately permeable
soils can be used if the subsurface layer is compacted to
restrict deep percolation and ensure a sheet flow down
the graded slope.
Overland flow may be used at sites with grades
between 1 and 12 percent. Slopes can be constructed
on level terrain by creating a 2 percent slope. Grades
steeper than 10 percent should be terraced (slopes of 2
to 8 percent built up, followed by a steep drop and
another terrace) so that erosion (from heavy rainfall and
heavy wastewater application) is minimized. For the
desired slope range of 2 to 8 percent, the actual slope
does not affect the treatment performance (Jenkins et
al., 1978). The slope must be graded so that it is smooth
and of nearly constant grade. This is especially true
near the upper reaches of the slope to prevent
channeling of wastewater and poor treatment. Site
grades less than 2 percent may require special
measures to avoid ponding of water on the slope. The
potential for short-circuiting and erosion is higher for
slopes greater than 8 percent.
9.1.2 System Configuration
The general system layout should match as closely as
possible the natural topography at the site to minimize
expensive earthwork. The total field area for treatment is
determined by methods described later in this chapter.
Individual treatment slopes are laid out on a topographic
map of the site until the field area requirements are
satisfied. The individual slopes must be connected with a
network of ditches for collection of treated runoff and
stormwater runoff for conveyance to the final system
discharge point.
The choice of the system layout is also influenced by
the type of wastewater distribution. High-solids-content
wastewaters typically are applied using high-pressure
sprinklers to ensure uniform distribution of the solids on
the treatment slope. Low-pressure systems involving
gated pipe or sprinklers have been used successfully for
screened, primary, secondary or pond effluents. The
various possibilities for both high- and low-pressure
types are illustrated in Figure 9-1 (Jenkins et al., 1978).
Chapter 7 contains design details on both types of
distribution systems.
Figure 9-1. Distribution Alternatives for Overland Flow.
Most industrial systems are of the type shown in
Figure 9-1 (a) or (b), with the sprinklers for type (b)
9-1
-------
located at the one-third point down the slope so that all
the wastewater applied is contained on the treatment
surface. Empirical criteria were developed through trial-
and-error experience, so that slope lengths from 30 to 45
m (100 to 150 ft) would provide adequate treatment for
most wastewaters. If, for example, a sprinkler with a 30
m (100 ft) diameter wetted circle is located at the one-
third point on a 45 m (150 ft) long slope, the "average"
travel distance for all the applied wastewater would then
be 30 m (100 ft). Solids content of less than 100 g/m3
typically allows the use of low-pressure systems. A
slotted or gated pipe at the top of a 30 m (100 ft) slope
should provide the same degree of treatment as the 45
m (150 ft) slope with the pressure sprinklers at the one-
third point. Low-pressure systems are not suitable for
high-solids content wastewater because deposition of
the solids will occur in the immediate vicinity of the
application point, results in excess accumulation and
either maintenance requirements or incomplete
treatment and the production of odors.
9.1.3 Performance Standards and System
Capabilities
OF systems can be designed to achieve high levels of
treatment. OF can be used as a pretreatment step to a
water reuse system or can be used to achieve
secondary treatment, advanced secondary treatment, or
nitrogen removal, depending on discharge requirements.
Most OF systems have an outlet to surface water for the
treated runoff and therefore require NPDES discharge
permits. For municipalities depending on WQS the
permit will limit BOD and TSS, and that is the basis for
the design approach presented in this chapter. If the
permit contains other requirements (i.e.: nitrification of
ammonium, phosphorus removal, etc.), then the
following multi-step procedure can be used to determine
the limiting design parameter (LDP) for the system:
1. Determine the slope length, loading rates, etc. for
BOD removal.
2. Estimate the slope length and loading rate for other
parameters.
3. Select the parameter that results in the lowest
application rate as the LDP.
The effluent quality from properly designed and
operated OF systems can consistently produce effluents
with 10 g/m3 (mg/L) BOD and 15 g/m3 (mg/L) TSS
(WEF, 2001). OF systems can be designed to nitrify to 1
g/m3 (mg/L) of ammonium-nitrogen and can produce
effluent total nitrogen concentrations of 5 g/m (mg/L)
(WEF, 2001). In concept, the system can be thought of
as a plug-flow, attached-growth biological reactor with a
vegetated surface (Martel, 1982). The near-surface soil
and surface deposits and the grass stems and roots
provide a matrix for the microbial components that result
in the bulk of the treatment. The grass also serves as a
sink for nutrients as well as water removal by
evapotranspiration.
Vegetation on the treatment slopes is essential to
regulate and retard the flow, minimize velocity, and
minimize erosion, short-circuiting and channeling. The
choice of vegetation is more limited for OF systems as
compared to SR systems because perennial, water-
tolerant grasses are the only feasible possibilities for OF
systems, as described in Chapter 4. Reed canarygrass,
tall fescue and other similar grasses can withstand daily
saturation and flourish under frequently anaerobic
conditions.
In some respects the OF process offers more flexibility
and control of effluent quality than SAT and SR systems
do. For most SAT or SR systems there is no access to
the wastewater once it is applied to the soil. All of the
responses and constraints have to be anticipated and
programmed into the design because there will be
limited opportunities to control the responses once the
system is operational. In contrast, most of the
wastewater is continuously accessible in an OF system
and this allows greater flexibility in operational
adjustments.
9.2 Design Procedures
The procedure for design of OF systems is to establish
the limiting design parameter; select the application rate,
application period, and slope length; calculate the
hydraulic loading rate; and calculate the field area
required. The storage volume, if any, must also be
determined, and the field area increased to account for
stored volume. Because BOD is often the LDP for
municipal systems, the design approach discussed in
this section is tailored for BOD removal. Design
considerations for systems limited by nitrogen and total
suspended solids are also described below.
9.2.1 BOD5
Laboratory and field research at the University of
California at Davis has resulted in the development and
validation of a rational design procedure for OF when
BOD is the limiting design parameter (Smith, 1981;
Smith and Schroeder, 1982 and 1983). The design
model assumes first-order, plug-flow kinetics which can
be described with the following equation:
C-R „ ,-kz.
-?-—=A exp(—-)
(9-1)
Where:
Cz = BOD5 concentration of runoff at a distance (z) downslope,
g/m3 (mg/L)
R = background BOD5 concentration, typically 5 g/m3 (mg/L)
C0 = BOD5 concentration of applied wastewater, g/m3 (mg/L)
A = empirically-determined coefficient dependent on the value of q
9-2
-------
k = empirically-determined exponent (less than one)
z = distance downslope, m or ft
q = application rate, m3/h m (downslope) (gal/min ft (downslope))
n = empirically-derived exponent
The equation is presented graphically in Figure 9-2 for
primary effluent (Smith and Schroeder, 1985). It has
been validated for screened raw wastewater and primary
effluent, as shown in Table 9-1 (Smith and Schroeder,
1982). The equation has not been validated for industrial
wastewater with BOD values of 400 g/m3 (mg/L) or
more. The OF process does not produce an effluent free
of suspended and organic material. This is because the
effluent from an OF slope will approach a nonzero,
steady-state concentration value regardless of slope
length. The 5 g/m3 (mg/L) BOD residual or background
concentration is due to the release of natural decaying
organic material and solids from the soil-plant system
rather than a component of the influent BOD (Reed et
al., 1995; Tedaldi and Loehr, 1991). For facultative pond
effluent, the application rate should not exceed 0.10
m3/h m (0.12 gal/min ft).
Q
O
m
Family of lines represent
different application
rates. m3/h • m
0.02
20 30
Distance down slope, m
Application Rate
The application rate is defined as the flowrate applied
to the slope per unit width of slope. The application rate
used for design of municipal OF systems depends on
the limiting design factor (usually BOD), the
preapplication treatment, and the climate. The removal
of BOD for various application rates and different types
of wastewater is presented in Table 9-2 (Crites and
Tchobanoglous, 1998). A range of suggested application
rates is presented in Table 9-3 for different climates and
levels of required removal (Crites and Tchobanoglous,
1998; Reedetal., 1995).
Application Period
Application periods usually range from 6 to 12 h/d for 5
to 7 d/wk. For municipal wastewater an 8 h/d application
period is typical. For industrial wastewaters the
application period can be as short as 4 h/d.
Occasionally, municipal OF systems can operate 24 h/d
for relatively short periods. The ability to nitrify is
impaired with an application schedule beyond 12 h on
and 12 h off (Kruzic and Schroeder, 1990). The typical 8
h on and 16 h off schedule allows the total field area to
be divided into three subareas and for the system to
operate 24 h/d when required.
Slope Length
Slope lengths in OF practice have ranged typically
from 30 to 60 m (100 to 200 ft). The longer the slope the
greater the removal of BOD, TSS, and nitrogen. The
recommended slope length depends on the method of
application. For gated pipe or spray heads where the
wastewater is applied at the top of the slope, a slope
length of 36 to 45 m (120 to 150 ft) is recommended. For
high-pressure sprinkler application, the slope should be
between 45 to 61 m (150 and 200 ft). The minimum
slope length for sprinkler application should be the
wetted diameter of the sprinkler plus about 20 to 21 m
(65 to 70 ft) (Crites and Tchobanoglous, 1998).
Hydraulic Loading Rate
A rational approach to design is to first select the
application rate and then determine the hydraulic loading
rate. Using the application rate approach allows for the
designer to consider varying the application rate and
application period to accomplish a reduction or increase
in hydraulic loading. The relationship between the
application rate and the hydraulic loading rate is
presented in Equation 9-2.
Figure 9-2. Overland-Flow Application Rates and Slope Length.
_qPF
(9-2)
9-3
-------
Where:
LW
wastewater hydraulic loading rate, m/d (in/d)
application rate per unit width of slope, m3/min m
(gal/min ft)
application period, h/d
conversion factor, 60 min h (96.3 min ft2 in/h gal)
Z = slope length, m (ft)
Hydraulic loading rates have generally ranged from 20
to100mm/d (0.8 to 4 in/d).
Table 9-1. Comparison of Actual and Predicted OF Effluent BOD Concentrations Using Primary and Raw Municipal Wastewater
Location
Hanover, NH
Ada, OK
Easley, SC
Applied Wastewater
Primary
Primary
Primary
Primary
Raw
Raw
Application Rate
(m3/hm)a
0.25
0.37
0.12
0.10
0.13
0.21
BOD5 Concentration (g/m3)0
Slope Length (m)b
30.5
30.5
30.5
36
36
53.4
Actual
17
19
8.5
8
10
23
Predicted
16.3
17.5
9.7
8.2
9.9
9.6
am3/h mx 1.34 = gal/min ft.
bm x 3.28 = ft.
°g/m3 = 1 mg/L.
Table 9-2. BOD Removal for Overland Flow Systems
Location
Ada, OK
Easley, SC
Hanover, NH
Melbourne, Australia
Municipal Wastewater Type
Raw wastewater
Primary effluent
Secondary effluent
Raw wastewater
Pond effluent
Primary effluent
Secondary effluent
Primary effluent
Application Rate*
(m3/h m)a
0.09
0.12
0.24
0.26
0.28
b"."i5
0.09
0.29
BOD Concentration (g/m3)0
Slope Length (m)b
36.6
36.6
36.6
54.9
45.7
30.5
30.5
250
Influent
150
70
18
200
28
72
45
507
Effluent
8
8
5
23
15
9
5
12
Application rate is average flow, rn^/h, divided by the width of the slope, m.
am3/h mx 1.34 = gal/min ft.
bm x 3.28 = ft.
°g/m3 = 1 mg/L.
Table 9-3. Application Rates Suggested for BOD Removal in Overland Flow Design, m /h m (gal/min ft)
Preapplication
Treatment
Screening/ primary
Aerated cell
(1-day detention)
Secondary
Stringent Requirements
and Cold Climates*
0.08-0.12(0.11-0.16)
0.09-0.12(0.12-0.16)
0.19-0.24(0.25-0.32)
Moderate Requirements
and Climates*
0.19-0.29(0.25-0.39)
6.1 9-0^39 1(0.25^0.52)
0.24-0.39 (0.32-0.52)
Least Stringent
Requirements and
Warm Climates*
0.30-0.45 (0.40-0.60)
0^39-0^48(0^52-0^64)
0.39-0.48 (0.52-0.64)
'Stringent requirements: BOD = 10 g/m*, TSS = 15
Moderate requirements: BOD and TSS < 20 g/m3.
*Least stringent requirements: BOD and TSS & 30 g/m3.
Organic Loading Rate. Organic loading rates for OF
are typically less than 100 kg/ha d (90 Ib/acre d). The
oxygen transfer efficiency through the thin water film
(usually 5 mm or 0.2 in) limits the aerobic treatment
capacity of the OF process to the above rates. The
organic loading rate can be calculated using
Equation 9-3.
LBOD=0.\LW)(C0
(9-3)
Where:
LBOD
0.1
= BOD loading rate, kg/ha d (Ib/acre d)
= conversion factor (0.225 in U.S. customary units)
Lw = hydraulic loading rate, mm/d (in/d)
C0 = influent BOD5 concentration, g/m3 (mg/L)
When the BOD of the applied wastewater exceeds
about 800 g/m3 (mg/L), the treatment efficiency becomes
impaired by the oxygen transfer efficiency. Effluent
recycle has been used to reduce the concentration to
around 500 g/m3 (mg/L) and achieve 97 percent BOD
removal at a BOD loading rate of 56 kg/ha d (50
Ib/acre d) (Perry et al., 1981). It should be noted that
Figure 9-2 has only been validated to 400 g/m3 (mg/L)
BOD.
9-4
-------
9.2.2 Total Suspended Solids
With the exception of algae, wastewater solids will not
be the LDP for overland flow design. Suspended and
colloidal solids are effectively removed because of the
low velocity and the shallow depth of flow on the
treatment slope. Maintenance of a thick grass cover and
elimination of channel flow are essential for solids
removal. The removal of suspended matter is relatively
unaffected by cold weather or other process loading
parameters (US EPA, 1981).
When lagoons or storage ponds are used in overland
flow systems the presence of algae in the wastewater
may result in high suspended solids in the final effluent
because of the inability to remove some types of algae
(Witherow and Bledsoe, 1983). Many small-diameter,
free floating species of algae and diatoms have little or
no tendency to aggregate and are particularly difficult to
remove. Examples are the green algae Chamdomonas
and Chlorella and the diatoms Anomoeoneis. In contrast,
the green algae Protococcus has a "sticky" surface and
is effectively removed on the OF slope. Because control
of algal species in ponds may be a problem, it may be
necessary to isolate or bypass the ponds with the algal
blooms. Therefore, during periods of algal blooms,
storage ponds for OF systems should be off-line and
only used when absolutely necessary. Once the algal
bloom periods have passed, the affected pond cell can
be returned to service.
If overland flow is otherwise best suited to a site with
an existing pond system, design and operational
procedures are available to improve algae removal. The
application rate should not exceed 0.10 m3/h m (0.13
gal/min ft) for such systems, and a nondischarge mode
of operation can be used during algae blooms. In the
Table 9-4. Ammonia Concentrations (in g/m3) in OF Systems in Garland, TX
nondischarge mode, short application periods (15 to 30
min) are followed by 1- to 2-h rest. The OF systems at
Heavener, OK and Sumrall, Ml operate in this manner
during algae blooms (Crites and Tchobanoglous, 1998).
9.2.3 Nitrogen
There are many mechanisms that remove nitrogen in
OF systems, but the major pathways are
nitrification/denitrification, crop uptake, and adsorption of
ammonium on materials with cation exchange capacity
(CEC). Nitrification/denitrification, which accounts for
most of the nitrogen removal, depends on adequate
detention time, temperature, and BOD/nitrogen ratios
(Reed et al., 1995). Denitrification appears to be most
effective when screened raw or primary effluent is
applied, because of the high BOD/nitrogen ratio. Soil
temperatures below 4°C (39°F) will limit the nitrification
reaction.
Up to 90 percent removal of ammonium was reported
at application rates of 0.10 m3/h m (0.13 gal/min ft) at
the OF system at Davis, CA (Kruzic and Schroeder,
1990). Slope lengths of 45 to 60 m (150 to 200 ft) may
be required to achieve this level of ammonia removal.
At Garland, TX, nitrification studies were conducted
with secondary effluent to determine if a 2-g/m3 (mg/L)
summer limit for ammonia and a 5-g/m3 (mg/L) winter
limit could be attained. Removal data for the two periods
are presented in Table 9-4 for different application rates
(Zirschky et al., 1989). Winter air temperatures ranged
from 3° to 21 °C (26° to 70°F). The recommended
application rate for Garland was 0.43 m3/h m (0.56
gal/min ft) for a slope length of 60 m (200 ft) with
sprinkler application (Zirschky et al., 1989).
Length Downslope (m)
Month
Summer
Mar. - Oct.
Winter
Nov. - Feb.
Application Rate (mj/h m)a
0.57
0.43
0.33
0.57
0.43
0.33
46
1.51
0.65
0.14
2.70
1.29
0.73
61
0.40
0.27
0.03
1.83
0.39
0.28
91
0.12
0.11
0.03
0.90
0.03
0.14
am3/h-mx 1.34 = gal/min-ft.
bm x 3.28 = ft.
Note: Summer-applied ammonia nitrogen = 16.0 g/m3; winter-applied ammonia nitrogen = 14.1 g/m3
9.3 Land Area Requirements
The field area, the area of land to which wastewater is
actually applied, for OF depends on the flow, the
application rate, the slope length, and the period of
application. The total land area required for an OF
system should include land for preapplication treatment,
administration and maintenance buildings, service roads,
buffer zones, and storage facilities. If there is no
seasonal storage, the field area can be calculated using
Equation 9-4.
A =
QZ_
qPF
(9-4)
9-5
-------
Where:
A =
Q =
Z
q =
p =
F =
field area, ha (acres)
wastewater flowrate, m3/d (gal/min)
slope length, m (ft)
application rate, m3/h m (gal/min ft)]
period of application h/d
conversion factor, 10,000 in SI units (726 in U.S. units)
If wastewater storage is a project requirement, the
application field area is determined using Equation 9-5.
Equation 9-5 was developed using an application rate of
0.048 m3/h m (0.06 gal/min ft).
A = -
365Q
(9-5)
DLWF
Where:
A =
Q =
Vs =
D =
Lw =
F =
field area, ha (acres)
wastewater flow, m3/d (ft3/d)
net loss or gain in storage volume due to precipitation,
evaporation, and seepage, m3/yr (ft3/yr)
number of operating days per year
hydraulic loading rate, cm/d (in/d)
conversion factor, 100 in SI units (3630 in U.S. units)
9.4 Design Considerations
Considerations for design of overland flow systems
include winter operation, storage of wastewater required
for rainfall runoff or crop harvesting, distribution systems,
runoff collection and permit requirements for rainfall
runoff, slope design and construction, and vegetation
selection.
9.4.1 Winter Operation
In general, OF systems shut down for cold winter
weather when effluent quality requirements cannot be
met because of cold temperatures or when ice begins to
form on the slope. Sometimes the reduction of the
application rate can allow the operation to continue
during cold weather. If a shutdown is required,
wastewater must be stored. The most conservative
approach would be to assume a storage period that is
equal in length to that required for SR systems (Chapter
6 and 8). At wastewater and soil temperatures above
8°C (50°F), the BOD removal efficiency is independent
of temperature (Smith and Schroeder, 1982). In low
temperature studies in New Hampshire, the following
relationship between effluent BOD and temperature was
developed (Jenkins et al., 1978):
ŁBOD =0.22672-6.53r + 53
(9-6)
Where:
EBOD =
T
effluent BOD, g/m3 (mg/L)
soil temperature, °C
Equation 9-5 was developed for an application rate of
0.048 m3/h m (0.06 gal/min ft). At a soil temperature of
less than 3.9°C (39°F) the effluent BOD will exceed 30
g/m3 (mg/L), based on Equation 9-6.
Wastewater applications should cease when an ice
cover forms on the slope. Operation of sprinkler systems
can be very difficult at air temperatures below freezing.
In locations where night-time air temperatures fall below
0°C (32°F) but daytime air temperatures exceed 2°C
(36°F), a day-only operation may be chosen in which all
the field area is used within 10 to 12 hours.
9.4.2 Storage of Rainfall Runoff
A detailed discussion and calculation procedures for
storage are presented in Chapter 6. Research and field
studies at a number of systems have found that rainfall
runoff either during or after wastewater applications did
not significantly affect the concentration of the major
constituents in the runoff (Smith and Schroeder, 1982;
US EPA, 1981). This must be considered as part of total
maximum daily load (TMDL) requirements.
Based on work at the Davis, CA, overland flow system
stormwater discharges are the result of natural organics
and litter on the slope and not wastewater constituents
and in fact were less than the losses from control slopes
where no wastewater had been applied.
9.4.3 Distribution Systems
Municipal wastewater can be surface-applied to OF
slopes; however, industrial wastewater should be
sprinkler-applied. Surface application using gated pipe
offers lower energy demand and avoids aerosol
generation. Slide gates at 0.6-m (2-ft) spacings are
recommended over screw-adjusted orifices. Pipe lengths
of 100 m (300 ft) or more require in-line valves to allow
adequate flow control and isolation of pipe segments for
separate operation.
With the orifice-pipe or fan-spray types of low-pressure
distribution, the wastewater application is concentrated
along a narrow strip at the top of each slope. As a
consequence, a grass-free application strip 1.2 to 2 m (4
to 6 ft) wide should be provided with these types of
distribution systems to allow operators to inspect the
area easily and to access the outlets without damaging
wet slopes. Gravel is a suitable material for this
unvegetated strip, but it tends to work into the soil and
requires replacement overtime.
Sprinkler distribution is recommended for wastewater
with BOD or TSS levels of 300 g/m3 (mg/L) or more.
Impact sprinklers located about one-third of the way
down the slope are generally used. Wind speed and
direction must be considered in spacing between
sprinklers (Reed et al., 1995).
9-6
-------
9.4.4 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. Runoff
channels should be graded to no greater than 25 percent
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 to construct the
channels. Small channels are normally V-shaped, while
major conveyance channels have a 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. In
most cases, it is desirable to provide a perimeter
drainage channel around the OF site to exclude offsite
stormwater from entering the OF drainage channels.
9.4.5 Slope Design and Construction
The OF site is divided into individual treatment slopes
each having the selected design length. Site geometry
may require that the slope lengths vary somewhat.
Slopes should be grouped into a minimum of four or five
hydraulically-separated, approximately-equal application
zones to allow operating and harvesting or mowing
flexibility. This arrangement allows one zone to be taken
out of service for mowing or maintenance while
continuing to operate the system at design application
and loading rates (WEF, 2001).
Smooth, uniform sheet flow down the slope is critical
to consistent process performance, so emphasis must
be placed on the proper construction of the slopes.
Naturally occurring slopes, even if these are the required
length and grade, seldom have the uniform grade and
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
should be accomplished within a grade tolerance of 0.03
m (0.1 ft). If buried piping is used, this grading phase is
generally followed by the installation of the distribution
piping and appurtenances.
After the slopes have been formed in the first grading
operation, a farm disk should be used to break up the
clods, and the soil should then be smoothed with a land
plane. Usually a grade tolerance of plus or minus 0.015
m (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
amount of lime (or gypsum) and fertilizer that are needed
to optimize crop establishment. The appropriate
amounts 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.
9.4.6 Vegetation Selection and
Establishment
The various grass mixtures used for overland flow
systems are described in Chapter 4. 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, and possibly market potential. In the
northern humid zones, various combinations of orchard
grass, Reed canarygrass, tall fescue and Kentucky
bluegrass have been most successful since this mixture
contains species that produce high biomass and are
rhizomatous. Including rhizomatous species in the
mixture is important to prevent channeling of water
running down the slope. The use of a nurse grass such
as annual ryegrass is recommended because it will grow
quickly and protect the soil surface while the other
grasses establish.
A Brillion seeder is capable of doing an excellent job of
seeding the slopes on newly prepared sites that contain
bare soils. The Brillion seeder carries a precision device
to drop seeds between cultipacker-type rollers so that
the seeds are firmed into shallow depressions. This
allows for quick germination and protection against
erosion. When reseeding existing sites, a no till seeder
can be used. This seeder slices the soil surface and
drops seed into the slices. Hydroseeding may also be
used if the range of the distributor is sufficient to provide
coverage of the slopes so that the vehicle does not have
to travel on the slopes. Traffic on the slopes in the
direction of the water flow should be avoided whenever
possible to keep channelization to a minimum. Vehicle
access should be in the cross-slope direction and
allowed only when the soil is dry. If a vehicle creates ruts
9-7
-------
over 2.5 cm (1 inch) in depth, then field traffic should
stop.
A good vegetative cover is essential prior to
application of wastewater. Grass planting should be
undertaken only during the optimum periods for planting
in particular, and the overall construction schedule must
be adjusted accordingly. In arid and semiarid climates,
portable sprinklers may be necessary to provide
moisture for germination and growth of the grass. The
wastewater distribution system should not be used until
the grass is established to avoid erosion of the bare soil.
The construction contract should have a contingency to
cover reseeding or erosion repair in the case of intense
rainfall during the period between final site grading and
grass establishment.
As a general rule, wastewater should not be applied at
design rates until the grass 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
clippings are relatively short (0.3 m, < 1 ft). Long
clippings tend to remain on top of the cut grass, thus
shading the surface and retarding regrowth.
A period of slope aging or maturing and acclimation is
required following initial startup before process
performance will approach satisfactory levels. During
this period, the microbial population on the slopes is
increasing and the 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 cannot 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 a month. Acclimation is not
necessary following shutdown for harvest unless the
harvest period is extended to more than 2 or 3 weeks
due to inclement weather.
9.5 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. A
detailed description of crop, soil, and site management
requirements for land treatment systems is given in
Chapter 8.
9.5.1 Crop Management
After the cover crop has been established, the slopes
will need little maintenance work. Grass should be cut
two or three times a year. Removal of cut grass from the
slopes is optional, especially if the system is designed
for BOD/TSS removal. Removal from the slope is mainly
to allow the new grass to grow and to avoid
decomposition byproducts from being discharged off the
slope. Other advantages are that additional nutrient
removal is achieved, channeling problems may be more
readily observed, and revenue can be generated from
the sale of hay. Before harvesting, each slope must be
allowed to dry out so that equipment can travel over the
soil surface without leaving ruts. If a vehicle creates ruts
over 2.5 cm (1 inch) in depth, access to the site should
cease. Ruts could develop into channeling, especially if
oriented downslope, and ruts across the slope may
create a mosquito problem. The drying time necessary
before mowing is usually about 1 to 2 weeks; however,
this can vary depending on the soil and climatic
conditions. After mowing and conditioning, the hay
should be dried before raking and baling. This may take
another week or so depending on the weather.
However, during unusually wet years, site conditions
limit vehicle access and mobility. Under these
circumstances, weather permitting, hay can be shredded
on the treatment slopes and left in place with no baling
or removal (Tedaldi and Loehr, 1991).
If the necessary drying times can not be met, the cut
grass can be collected and stored. Two methods include
bale wrapping and storing cut grass in plastic silage
bags. The bale wrappers tightly seal each bale in a
sturdy, UV resistant plastic to resist sun damage and
adverse weather conditions. Wrapped bales undergo a
fermentation process that prevents spoilage from yeasts,
aerobic bacteria, molds, and insects, while maintaining a
high protein and nutrient content. A bale wrapper is
shown in Figure 9-3. Alternatively, unbaled hay can be
compacted tightly into silage bags (Figure 9-4). The
airtight environment encourages anaerobic conditions to
produce feed quality silage low in nitrates and free from
pest contamination. These methods allow storage of
grasses with high moisture content, minimizing the time
needed for drying cut grass. Both, wrapped bales and
silage bags may be stored away from the treatment
slopes, allowing the application of wastewater to
continue without too much off-time for drying and
conditioning of cut vegetation.
9-8
-------
Figure 9-3. Bale wrappers tightly seal each bale of hay in plastic for
storage. (Courtesy of New Holland.)
Figure 9-4. Plastic silage bags for storing cut hay. (Courtesy of Ag-
Bag, International, Ltd.)
Monitoring programs for soils and vegetation are the
same for OF as for SR systems (Chapter 8). If the grass
is used as fodder, samples may be required during each
harvest and may be analyzed for various nutritional
parameters such as protein, fiber, total digestible
nutrients, phosphorus, nitrate, and dry matter.
9.6 References
Bendixen, T.W., R.D. Hill, FT. DuByne, and G.G.
Robeck (1969) Cannery Waste Treatment by Spray
Irrigation-Runoff, Journal WPCF, 41: 385.
Carlson, C.A., et al. (1974J Overland Flow Treatment of
Wastewater, USA, WES Misc., Paper Y-74-3,
Vicksburg, MS.
Crites, R.W. and G. Tchobanoglous (1998J Small and
Decentralized Wastewater Management Systems,
McGraw-Hill, New York, NY.
Glide, L.C., A.S. Kester, J.P. Law, C.H. Neeley, and
D.M. Parmelee (1971) A Spray Irrigation System for
Treatment of Cannery Wastes, Journal WPCF, 43:
2011.
Jenkins, T.F., et al. (1978) Pilot Scale Study of Overland
Flow Land Treatment in Cold Climates, In:
Proceedings: Developments in Land Methods of
Wastewater Treatment and Utilization - Melbourne,
Australia, Pergamon Press, New York, Progress in
Water Technology, 11 (4-5): 207.
Jenkins, T.F., et al. (1978) Performance of Overland
Flow Land Treatment in Cold Climates, In:
Proceedings State of Knowledge in Land Treatment
of Wastewater, Vol.2, USA, CRREL, Hanover, NH.
Kruzic, A.J. and E.D. Schroeder (1990J Nitrogen
Removal in the Overland Flow Wastewater
Treatment Process - Removal Mechanisms, Res. J.
Water Pollution Control Federation, 62(7): 867-876.
Martel, C.J. (1982) Development of a Rational Design
Procedure for Overland Flow Systems, CRREL
Report 82-2, CRREL, Hanover, NH.
Peters, R.E., et al. (1978) Field Investigations of
Advanced Treatment of Municipal Wastewater by
Overland Flow, Vol.2, Proceedings of the
International Symposium on Land Treatment of
Wastewater, USACOE, CRREL, Hanover, NH.
Peters, R.E., C.R. Lee and D.J. Bates (1981J Field
Investigations of Overland Flow Treatment of
Municipal Lagoon Effluent, USA, WES, Tech. Report
EL-81-9, Vicksburg, MS.
Perry, L.E., E.J. Reap, and M. Gilliand (1981) Pilot
Scale Overland Flow Treatment of High Strength
Snack Food Processing Wastewaters, Proceedings
National Conference on Environmental Engineering,
ASCE, EED, Atlanta, GA.
Reed, S.C., R.W. Crites and E.J. Middlebrooks (1995J
Natural Systems for Waste Management and
Treatment, Second Edition, McGraw-Hill, New York,
NY.
Scott, T.M. and D.M. Fulton (1979) Removal of
Pollutants in the Overland Flow (Grass Filtration)
System, Progress in Water Technology, II (4 and
5):301-313.
Smith, R.G. and E.D. Schroeder (1982) Demonstration
of the Overland Flow Process for the Treatment of
Municipal Wastewater- Phase II Field Studies, Dept
of Civil Engineering, University of California, Davis,
Report to California State Water Resources Control
Board.
9-9
-------
Smith, R.G. and E.D. Schroeder (1983) Physical Design
of Overland Flow Systems, Journal WPCF, 55(3):
255-260.
Smith, R.G. and E.D. Schroeder (1985) Field Studies of
the Overland Flow Process for the Treatment of Raw
and Primary Treated Municipal Wastewater, Journal
WPCF, 57(7): 785-794.
Tedaldi, D.J. and R.C. Loehr (1991) Performance of an
Overland Flow System Treating Food-Processing
Wastewater, Research Journal WPCF, 63: 266.
US EPA (1975). Land Application of Wastewater in
Australia, EPA 430/9-75-017, U.S. Environmental
Protection Agency, OWPO, Washington, DC.
US EPA (1976). Overland Flow Treatment of Raw
Wastewater with Enhanced Phosphorus Removal,
EPA-660/2-76-131, U.S. Environmental Protection
Agency, ORD.
US EPA (1979). Municipal Wastewater Treatment by
the Overland Flow Method of Land Application, EPA
600/2-79-178, U.S. Environmental Protection
Agency, RSKERL, Ada, OK.
US EPA (1981). Process Design Manual for Land
Treatment of Municipal Wastewater, EPA 625/1-81-
013, U.S. Environmental Protection Agency, CERI,
Cincinnati, OH.
US EPA (1981). Development of a Rational Basis for
Design and Operation of the Overland Flow
Process, Proceedings: National Seminar on
Overland Flow Technology for Municipal
Wastewater, EPA 600/9-81-022, U.S. Environmental
Protection Agency, Washington, DC.
US EPA (1981). Overland Flow Treatment of Poultry
Processing Wastewater in Cold Climates, EPA
600/S1-81-234, U.S. Environmental Protection
Agency, RSKERL, Ada, OK.
WEF (2001) Natural Systems for Wastewater Treatment,
Draft, Manual of Practice, Alexandria, VA.
Zirschky, J. et al. (1989) Meeting Ammonia Limits Using
Overland Flow, Journal WPCF, 61: 1225-1232.
9-10
-------
Chapter 10
Process Design - Soil Aquifer Treatment
The process design of soil aquifer treatment (SAT)
systems is generally governed by the infiltration rate into
and permeability through the soil to a defined outlet
(e.g., groundwater for recharge).. SAT systems utilize
the highest hydraulic loading rate of any land treatment
system. The site selection criteria for SAT are also more
stringent. The typical design procedure for soil aquifer
treatment is outlined as follows:
1. Characterize the soil and groundwater conditions
with field measurements.
2. Predict the hydraulic pathway of percolate, based on
the site hydrogeology and discharge requirements to
adjacent surface water or groundwater.
3. Select the infiltration rate from field test data (see
Chapters).
4. Determine the overall treatment requirements by
comparing wastewater characteristics to the water
quality requirements, including potential restrictions
on the system imposed by downstream users.
5. Select the appropriate preapplication treatment level
appropriate for the site and the treatment needs (see
Chapters).
6. Calculate the annual hydraulic loading rate based on
the treatment needs, the infiltration rate, and the
preliminary wet/dry ratio.
7. Calculate the land requirements.
8. Check the potential for groundwater mounding and
determine the need for underdrains (see Chapter 3).
9. Select the hydraulic loading cycle and the number of
basin sets.
10. Calculate the application rate and check the final
wet/dry ratio.
11. Lay out the basins and design berms, structures,
etc.
12. Determine monitoring requirements and locate
monitoring wells.
10.1 Treatment Requirements
Soil aquifer treatment is an especially effective
process for BOD, TSS, and pathogen removal and can
provide significant removals of nitrogen, phosphorus,
metals, and trace organics. Removal mechanisms of
wastewater constituents such as BOD, suspended
solids, nitrogen, phosphorus, heavy metals,
microorganisms, and trace organics are discussed in
Chapter 2. Typical results from various operating
systems are discussed for BOD, TSS, nitrogen,
phosphorus, and trace organics.
10.1.1 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 biota. 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.
BOD loadings on industrial SAT systems range from
112 to 667 kg/ha d (100 to 600 Ib/ac d). BOD loadings
beyond 336 kg/ha d (300 Ib/ac d) require careful
management to avoid production of adverse odors.
Suspended solids loadings of 112 to 224 kg/ha d (100
to 200 Ib/ac d) or more require frequent disking or
scarifying of the basin surface to avoid sealing of the
surface soil. Typical values of BOD loadings and BOD
removals for SAT systems are presented in Table 10-1
(Crites and Tchobanoglous, 1998).
Table 10-1. BOD Removal for Soil Aquifer Treatment Systems (Crites and Tchobanoglous, 1998)
Location
Applied Wastewater BOD,
Ib/ac-d*
Applied Wastewater BOD,
mg/L
Percolate Concentration,
mg/L
Total Ib/ac-yr applied divided by number of days in the operating season.
fCOD basis.
Conversion units: 1 Ib/ac-d = 1.12 kg/ha-d; 1 mg/L = 1 g/m .
Removal,
Boulder, CO
Brookings, SD
Calumet, Ml
Ft. Devens, MA
Hollister, CA
Lake George, NY
Milton, Wl
Phoenix, AZ
Vineland, NJ
48'
11
95f
77
156
47
138
40
43
131'
23
228f
112
220
38
28
15
154
10'
1.3
58f
12
8
1.2
5.2
0-1
6.5
92
94
75
89
96
97
81
93 - 1 00
96
10-1
-------
10.1.2 Nitrogen
Nitrogen removal has been observed during SAT at
many sites recharging effluent containing ammonia-
nitrogen. A common hypothesis for this nitrogen removal
in SAT is the two-step process of autotrophic nitrification
and heterotrophic denitrification. Recharge basins are
typically operated to consist of a wetting cycle when
water is applied followed by a drying cycle. Due to the
net positive charge of the ammonium ion, it is adsorbed
onto the soil in the upper region of the vadose zone
during the wetting cycle. As the soil dries and air/oxygen
enters the soil, the oxidation of ammonia to nitrate by
autotrophic nitrifiers may occur. This process results in a
high nitrate concentration at the beginning of the
following wetting cycle. This nitrate, which tends to be
more mobile, is transported with the percolating water
deeper into the vadose zone. Once the nitrate reaches
an anoxiczone, heterotrophic denitrification may convert
the nitrate to nitrogen gas in the absence of oxygen
(Gable and Fox, 2000). The nitrogen gas then migrates
through unsaturated soil back to the surface where it is
lost to the atmosphere. Some volatilization of the
ammonia can also occur at the soil surface.
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 0°C (32°F). Nitrification rates decline
sharply in acidic soil conditions and reach a limiting
value at approximately pH 4.5. The denitrification
reaction rate is reduced substantially by pH values below
5.5. Thus, both soil temperature and pH must be
considered if nitrogen removal is important.
Furthermore, alternating aerobic and anaerobic
conditions must be provided for significant nitrogen
removal. Because aerobic bacteria deplete soil oxygen
during flooding periods, resting and flooding periods
must be alternated to result in sequencing aerobic and
anaerobic soil conditions.
Nitrogen removal is also a function of detention time,
BOD:N ratio (adequate organic carbon source), and
anoxic conditions. Experiments with secondary effluent
at Phoenix, AZ, showed for effective nitrogen removal
(80 percent or more), the liquid loading rate should not
exceed 150 mm/day (6 in/d) (Lance et al., 1976). When
primary effluent is used, the maximum hydraulic
application rate is recommended not to exceed 200
mm/day (8 in/day). Nitrogen removal by denitrification
requires both adequate organic carbon, which acts as a
"food" source for microorganisms, and adequate
detention time. The potential limitation on the amount of
nitrogen removal can be approximated using the
following equation:
A/ =
roc-5
(10-1)
Where:
N = change in total nitrogen, g/m3 (mg/L)
TOC = total organic carbon in the applied wastewater, g/m3
(mg/L)
The 5 g/m3 (5 mg/L) of residual TOC, in Equation 10-1,
is typical for municipal wastewater after passage through
about 1.5 m (5 ft) of soil. The coefficient 2 in the
denominator of Equation 10-1 is based on experimental
data where 2 g of wastewater carbon were required to
denitrify 1 g of wastewater nitrogen (US EPA, 1980J. In
terms of BOD:N ratio, a ratio of 3:1 or more is
recommended to ensure adequate carbon to drive the
denitrification reaction.
The two-step nitrification-denitrification process is
consistent with field observations. However, few SAT
systems have the BOD:N ratios that can sustain
heterotrophic denitrification. Most secondary effluents
applied to SAT systems have BOD:N ratios of
approaching 1, where a BOD:N ratio of greater than 3
(occurring in most primary effluents) is necessary to
sustain high nitrogen removal efficiencies. Additionally,
most SAT systems have carbon (C) to nitrogen ratios of
1, where typically a C:N ratio greater than 2 is needed to
carry out optimal heterotrophic denitrification
(Kopchynski et al., 1999). These conditions would result
in nitrogen removal efficiencies of about 30 percent,
whereas, much higher nitrogen removal efficiencies
have been observed in SAT systems. This would
suggest that some other mechanisms are responsible for
the additional nitrogen removal. The anaerobic
ammonium oxidation (Anammox) process is proposed
as a sustainable mechanism for denitrification in SAT
systems (Gable and Fox, 2000).
Anammox is an anaerobic, autotrophic bacterial
process that occurs when both nitrate and ammonium
are present (Van de Graaf et al., 1995, 1996, 1997).
The nitrate is reduced to nitrogen gas while the nitrate
oxygen is used for the oxidation of ammonium. Since the
process is autotrophic, no organic carbon is required.
The infiltration process provides an ideal environment for
the growth of Anammox microorganisms. While the true
mechanisms of Anammox are still being researched and
defined, recent tests provide evidence that some type of
anaerobic ammonium oxidation could be occurring in
SAT systems (Gable and Fox, 2000; Woods et al., 1999;
Van de Graaf et al., 1997).
Experience with nitrification has been that rates of up
to 67 kg/ha d (60 Ib/ac d) can be achieved under
favorable moisture and temperature conditions. Total
nitrogen loadings should be checked to verify that these
are not in excess of the 56 to 67 kg/ha d (50 to 60
10-2
-------
Ib/ac d) range. Ammonia will be retained in the upper
soil profile when temperatures are too low [below 2.2°C
(36°F)] for nitrification. Recent field studies at an SAT
site in Truckee, CA, demonstrated that predictable and
consistent biological nitrogen removal occurred both in
multiple years of treating normally fluctuating flows and
loadings and during a short term study in which effluent
total nitrogen concentrations were increased up to 80
percent (Woods et al., 1999). Typical removals of total
nitrogen and percolate concentration of nitrate nitrogen
Table 10-2. Nitrogen Removal for Soil Aquifer Treatment Systems*
Applied Total Nitrogen
Location
Calumet, Ml
Dan Region, Israel
Ft. Devens, MA
Hollister, CA
Lake George, NY
Phoenix, AZ
W. Yellowstone, MT
Ib/acd
20.7
28.9
37.0
14.9
12.5
40.0
115.6
mg/L
24.4
13.0
50.0
40.2
12.0
18.0
28.4
and total nitrogen are presented in Table 10-2. To
determine the nitrogen loading rate from the hydraulic
loading rate, use:
, L«CF (10-2)
" D
Where:
Ln = nitrogen loading rate, kg/ha d (Ib/ac d)
Lw = wastewater hydraulic loading rate, m/yr (in/yr)
C = wastewater nitrogen concentration, g/m3 (mg/L)
F = conversion factor, 10 kg m2/g ha (0.226 Ib L/mg ac in)
D = number of operating days per year
Percolate, mg/L
Nitrate-N Total N
3.4 7.1
6.5 7.2
13.6 19.6
0.9 2.8
7.0 7.5
5.3 5.5
4.4 14.1
Total N Removal, %
71
45
61
93
38
69
50
'Adapted from Crites (1985a).
Conversion units: 1 Ib/ac-d = 1.12 kg/ha-d; 1 mg/L = 1 g/m3.
10.1.3 Phosphorus
Phosphorus removal in SAT is accomplished by
adsorption and chemical precipitation. The adsorption
occurs quickly and the slower occurring chemical
precipitation replenishes the adsorption capacity of the
soil. Typical phosphorus removals for SAT are presented
in Table 10-3, including travel distances through the soil.
If phosphorus removal is critical, a phosphorus
adsorption test using the specific site soil can be
conducted (Reed and Crites, 1984). To conduct an
adsorption test, about 10 g of soil is placed in containers
solution. After periodic shaking for up to 5 days the
solution is decanted and analyzed for phosphorus. The
difference in concentrations is attributed to adsorption
onto the soil particles. The detailed procedure is
presented (US EPA 1975). Actual phosphorus retention
at an SAT site (long term) will be 2 to 5 times greater
than the values obtained in the 5-day phosphorus
adsorption test (US EPA, 1981). An equation to predict
phosphorus removal is presented in Section 2.8.2.
Phosphorus removal can also be tested using
mathematical models detailed in Ryden et al. (1982) and
Enfield (1978).
Table 10-3. Phosphorus Removal for Soil Aquifer Treatment Systems*
Average Concentration in
Distance of Travel, ft
Average Concentration in
Location Applied Wastewater, mg/L
Boulder, COT
Brookings, SD*
Calumet, Ml*
Ft. Devens, MA*
Hollister, CA*
Lake George, NY*
Phoenix, AZ*
Vineland, NJ*
•Adapted from US EPA (1981).
*Total phosphate measured.
*Soluble phosphate measured.
§Seepage.
Conversion units: 1 mg/L = 1 g/m3;
6.2T
3.0*
3.5*
3.5*
9.0*
Tils'*
zT*
2.1*
T-l'T'*'
7.9*
48*
4.8*
1 ft = 0.305 m.
Vertical
8-10
2.6
10- 30
§
50
22
10
§
30
20
6.5 - 60
13-52
Horizontal Renovated Water, mg/L
0
0
0-400
5580§
100
6
o
1970§
0
100
6
850 - 1 700
0.2-4.5
0.45
0.1 -0.4
0.03
0.1
7.4
< 1
0.014
2T-5
0.51
1.54
0.27
Removal, %
40-97
85
89-97
99
99
29
>52
99
40-80
94
68
94
10-3
-------
10.1.4 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 activity. Removal
rates depend on the constituent, the applied
concentration, the loading rate, and the presence of
easily degradable organics to serve as a primary
substrate (Crites, 1985b).
If local industries contribute large concentrations of
synthetic organic chemicals and the SAT 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.
SAT systems have been utilized for the removal of
endocrine disrupting chemicals found in municipal
wastewaters (Conroy et al., 2001; Quanrqud et al.,
2002). Endocrine disrupters originate from industrial,
agricultural, and domestic sources. These include a
combination of natural hormones, pharmaceutical
products, and industrial chemicals such as
polychlorinated biphenyls, organochlorine pesticides,
phenoxyacid herbicides, phthalates and tirazines.
Following conventional secondary treatment, percolation
through approximately 36 m (120 ft) of unconsolidated
sediments to the local aquifer reduced residual
estrogenic activity by >95 percent (Table 10-4) (Quanrud
et al., 2002). The fate of micropollutants originating from
Pharmaceuticals and active ingredients in personal care
products have been studied at two groundwater
recharge facilities in Arizona (Drewes et al., 2001 a).
Preliminary studies indicate that groundwater recharge
offers a high potential to remove acidic drugs such as
lipid regulators and analgesics. Other compounds such
as antiepileptic drugs and X-ray contrast agents showed
no clear indication of removal during travel times of more
than six years.
Additional studies of long-term SAT at field sites in
Mesa, AZ, indicate that substantial removal of effluent
organic matter can occur. Identified trace organics were
efficiently removed as a function of travel time to very
low concentrations or below detection limits. Drewes et
al (2001 b) found that the character of bulk organics
present in final SAT water resembled the character of
natural organic matter present in drinking water.
Table 10-4. Fractional Attenuation of Estrogenic Activity
(Relative to Primary Effluent) During Secondary Treatment
and Soil Aquifer Treatment
Sample Location
Primary
Secondary Unchlorinated
Secondary Chlorinated
Secondary Dechlorinated
Storage Pond
0.8m (2.5 ft)
3.1 m (10ft)
5.2m (17ft)
18.3m (60ft)
36.6m (120ft)
Fractional Removal
0.00
0.62
0.65
0.65
0.68
0.77
0.83
0.83
0.93
0.99
10.2 Aquifer Characteristics
The geohydrological aspects of the SAT site are more
critical than for the other processes, and a proper
definition of subsurface conditions and the local
groundwater system is essential for design. Therefore,
site selection is critical to the success of an SAT project.
Important factors in subsurface evaluation and selection
are the soil depth, soil permeability and aquifer
transmissivity, depth to groundwater, groundwater flow
direction, and distance to outlet. In addition, due to high
loading rates of applied wastewater in SAT, the effects
of groundwater mounding and the transport of percolate
within an aquifer should be considered.
10.2.1 Soils Investigation
Potential sites are located using the methods detailed
in Chapter 5. SAT sites require deep, permeable soil
without a shallow groundwater. Once a potential site is
located, it is necessary to investigate the soil profile.
Soil investigations can include backhoe pits, soil borings,
and groundwater wells.
Backhoe pits are excavated normally to a depth of 2.4
to 3 m (8 to 10 ft). Pits should be located on each major
soil type and landscape aspect. The number of pits will
vary with the site size. For example, an 8-ha (20-ac) site
may need 6 to 10 backhoe pits to define the variability of
the soil profile within the treatment zone. Backhoe pits
are excavated so that a soil scientist can walk into the pit
and can observe the soil profile. The various soil
horizons can be identified visually, and the presence of
fractured near-surface rock, hardpan, redoximorphic
features, layers or lenses of gravel or clay, or other
anomalies can be identified and recorded. If the pit
extends into groundwater, it can also be used for in-
place testing of lateral soil permeability. Soil samples
can be taken from each soil layer and analyzed for
particle size, pH, and
10-4
-------
EC. Once observations are complete, level benches can
be excavated at different depths in the soil profile
(coinciding with different soil layers) to allow infiltration
testing (US EPA, 1984).
Soil borings are used to characterize the deeper soils
[greater than 3 m (10 ft)] and to determine depth to
bedrock and groundwater. All borings should penetrate
below the water table if it is within 9 to 15 m (30 to 50 ft)
of the surface. Fewer borings are needed typically than
backhoe pits, with 1 soil boring per 2 ha (5 ac) being
typical. Backhoe pits should be used to characterize
soils typical on a site. Generally this requires pits in each
landscape position represented on the site.
10.2.2 Groundwater Investigations
The depth to groundwater, thickness and permeability
of the aquifers, and groundwater quality are important to
determine. Because of the expense of drilling wells, the
site and the SAT process should be well established as
the preferred wastewater management alternative prior
to drilling. Existing onsite and nearby wells should be
surveyed and sampled, and well logs should be
analyzed prior to drilling onsite wells. Once the SAT site
appears to be acceptable, groundwater wells should be
drilled. The EPA recommends three wells for a complete
SAT site investigation (US EPA, 1984). If the general
groundwater flow direction has been identified, the wells
should be located so that one is in the middle of the
basin area, one is upgradient, and the third well is
downgradient near the project boundary. A triangulation
(pump-out) test can be used to characterize groundwater
flow and direction.
10.2.3 Infiltration Test
A critical element of SAT site evaluation is to conduct
field measurements of infiltration rates, permeability, and
transmissivity. The limiting rate of hydraulic flow in an
SAT system may be the basin surface, a subsurface
layer, or the lateral flow away from the site. All three
elements must be considered and measured. The
surface and subsurface permeability can be measured
using infiltration tests located at the elevation that will
correspond to the basin surface and at critical depths in
the subsurface.
The backhoe pits and soil borings can be used to
estimate the presence of restriction to vertical flow and
to locate layers that need to be tested for infiltration rate
(permeability or hydraulic conductivity). There are a
number of infiltration tests, but the preferred tests for
SAT systems are the flooded basin technique and the
cylinder infiltrometer (see Section 3.8.1).
10.2.4 Groundwater Mounding
During SAT, the applied wastewater travels initially
downward to the ground water, resulting in a temporary
groundwater mound beneath the infiltration site.
Mounds continue to rise during the flooding period and
only recede during the resting discharge period.
Excessive mounding will inhibit infiltration and reduce
the effectiveness of treatment. For this reason, the
capillary fringe above the groundwater mound should
never be closer than 0.6 m (2 ft) to the bottom of the
infiltration basin. 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 groundwater should be
1.5 to 3 m (5 to 10 ft) below the soil surface within 2 to 3
days following a wastewater application. An analysis that
can be used to estimate the mound height that will occur
at various loading conditions is discussed in Chapter 3.
The Hantusch method can be used to estimate whether
a site has adequate natural drainage or whether
mounding will exceed the recommended values without
constructed drainage.
10.3 Hydraulic Loading Rates
Selecting the appropriate design hydraulic loading rate
is the most critical step in the process design procedure.
As indicated in Chapter 5, an adequate number of
measurements must be made of the infiltration rate and
of the subsurface permeability. The hydraulic loading
rate is a function of the site-specific hydraulic
characteristics, including infiltration, percolation, lateral
flow, and depth to groundwater, as well as quality of the
applied wastewater and the treatment requirements.
10.3.1 Design Infiltration Rate
The tests for infiltration rate described in Chapter 5
should be reviewed and an appropriate test selected.
Using Equation 3-2 or 3-3 in Chapter 3, the mean
infiltration rate is then calculated from the field data.
During preliminary design the infiltration rate can be
estimated from the NRCS permeability data which is
based on soil texture. For final design, however, actual
field data should be used.
10.3.2 Wet/Dry Ratio
Intermittent application is critical to the successful
operation of all land treatment systems. The ratio of
wetting to drying in successful SAT systems varies, but
is always less than 1.0. Typical wet/dry ratios are
presented in Table 10-5 (Crites et al., 2000). For primary
effluent the ratios are generally less than 0.2 to allow for
adequate drying and scarification/removal of
10-5
-------
the applied solids. For secondary effluent, the ratio
varies with the treatment objective, from 0.1 or less
where nitrification or maximum hydraulic loading is the
objective, to 0.5-1.0 where nitrogen removal is the
treatment objective. These drying periods are necessary
to restore the infiltration capacity and to renew the
biological and chemical treatment capability of soil
system.
Table 10-5. Typical Wet/Dry Ratios for SAT Systems (Crites et al., 2000)
Location
Preapplication Treatment Application Period, days
Drying Period, days
Wet/Dry Ratio
Barnstable, MA
Boulder, CO
Calumet, Ml
Ft. Devens, MA
Hollister, CA
Lake George, NY
Phoenix, AZ
Vineland, NJ
Primary
Secondary
Untreated
Primary
Primary
Secondary
Secondary
Primary
1
0.1
2
2
1
0.4
9
2
7
3
14
14
14
5
12
10
0.14
0.03
0.14
0.14
0.07
0.08
0.75
0.20
10.3.3 Design Hydraulic Loading Rate
The design hydraulic loading rate for SAT systems
depends on the design infiltration rate and the treatment
requirements. The procedure is to calculate the hydraulic
loading rate based on a percentage of the test infiltration
rate. This value is then compared to the loading rate
based on treatment requirements and the lower rate is
selected for design. The most commonly used
measurements for infiltration rates are the basin
infiltration test and the cylinder infiltrometer (see
Chapters).
The 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 a fraction of
the measured clear water permeability of the most
restrictive soil layer.
Basin infiltration tests are the preferred method.
However, the small area compared to the full-scale
basin, allows a larger fraction of the wastewater to flow
horizontally through the soil from the test site than from
the operating basin. Therefore, test infiltration rates are
higher than the rates operating systems would achieve.
Thus, design annual hydraulic loading rates should be
no greater than 7 to 10 percent of measured basin test
infiltration rates (US EPA, 1981.
Cylinder infiltrometers greatly overestimate operating
infiltration rates. When cylinder infiltrometer
measurements are used, annual hydraulic loading rates
should be no greater than 2 to 4 percent of the minimum
measured infiltration rates. Annual hydraulic loading
rates based on air entry permeameter test results should
be in the same range.
Typical hydraulic loading rates for SAT systems and
the relationship between the actual loading rates and the
loading rates determined by operating basin infiltration
rates and cylinder infiltrometer rates are shown in
Table 10-6 (US EPA, 1981). Design guidance for
hydraulic loading rates is summarized in Table 10-7
(Crites et al., 2000). Where high wet/dry ratios and mild
climates are expected, the upper end of the range of
values in Table 10-7 can be used. Conversely, where
long drying periods are needed, the lower end of the
range should be used.
Table 10-6. Typical Hydraulic Loading Rates for SAT Systems (Crites et al., 2000)
Location
Actual Annual Loading Rate,
ft/year
Annual Loading Rate
% of operating basin infiltration rate
% of cylinder infiltrometer rate
Boulder, CO
Brookings, SD
Ft. Devens, MA
Hollister, CA
Phoenix, AZ
Vineland, NJ
100-160
78 - 118
95
50
200
70
10-38
16-24
13
24
27
4-10
2
3
1.6
Conversion unit: ft = 0.3048 m.
10-6
-------
Table 10-7. Suggested Hydraulic Loading Rates Based on Different Field Measurements
Field Measurement
Annual Loading Rate
Basin infiltration test
Cylinder infiltrometer and air entry permeameter measurements
Vertical hydraulic conductivity measurements
7 to 10% of minimum measured infiltration rate
2 to 4% of minimum measured infiltration rate
4 to 10% of conductivity of most restricting soil layer
10.4 Land Area Requirements
The application area for SAT systems
determined using Equation 10-3.
can be
A =
Q(0.0001)(365) (metric)
= Q(3.06)(365) (U.S. customary)
(10-3)
Where:
A
Q
Lw
365
0.0001 =
3.06 =
application area, ha (acres)
average design flow, m3/day (mgd)
annual hydraulic loading, m/yr (ft/yr)
days/yr
metric conversion, ha m to m3/day
U.S. customary conversion, acre ft to mgd
Other land requirements include area for buffer zones,
preapplication treatment, access roads, berms, and
storage (if necessary). Buffer zones can be used to
screen SAT sites from public view. Access roads and
ramps, typically 3 to 3.6 m (10 to 12 ft) wide, are needed
so that maintenance equipment for surface scarification
can enter each basin. Climatic storage is generally
unnecessary for SAT systems. The equivalent of short
storage for emergencies can be attained by making the
basins deep enough so that some storage can be
realized. Area for future expansion should also be
considered.
Table 10-8. Suggested SAT Loading Cycles
10.5 Hydraulic Loading Cycle
Loading cycles are selected to maximize either the
infiltration rate, nitrogen removal, or nitrification. To
maximize infiltration rates include drying periods that are
long enough for soil reaeration and for drying and
oxidation of filtered soils.
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.
Recommended hydraulic loading cycles are
summarized in Table 10-8 (Crites et al., 2000).
Generally the shorter drying periods in Table 10-8
should only be used in mild climates. In cold climates the
longer drying periods should be used.
10.5.1 Number of Basin Sets
The number of basins or sets of basins depends on
the topography and the hydraulic loading cycle. The
decision on the number of basins and the number to be
flooded at one time affects both the distribution system
hydraulics and the final wet/dry ratio. As a minimum, the
system should have enough basins so that at least one
basin can be flooded at all times. The minimum number
of basins required for continuous wastewater application
is presented in Table 10-9 as a function of the loading
cycle (Crites et al., 1998).
Loading Cycle Objective
Applied Wastewater
Season
Application period*, days
Drying Period, days
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
•Regardless of season or cycle objective, application periods for primary effluent should be limited to 1 to 2 days to prevent excessive soil clogging.
10-7
-------
10.5.2 Application Rate
The application rate is set by the annual loading rate
and the loading cycle. The application rate is used to
determine the required hydraulic capacity of the piping to
the basins. The application rate is calculated as follows:
1. Add the application period to the drying period to
obtain the total cycle time, days.
2. Divide the number of application days per year,
usually 365 except where storage is planned, by the
total cycle time to obtain the number of cycles per
year.
3. Divide the annual hydraulic loading by the number of
cycles per year to obtain the loading per cycle.
4. Divide the loading per cycle by the application period
to obtain the application rate, cm/d (ft/d).
The discharge rate to the basins can then be
determined using Equation 10-4.
Q = 6.94AR (metric)
= 18.9/4R (U.S. customary)
Where:
Q
A
R
6.94 =
18.9 =
discharge capacity, m /min (gpm)
basin area, ha (acres)
application rate, m/day (in/d)
metric conversion constant
U.S. customary conversion constant
Table 10-9. Minimum Number of Basins Required for Continuous
Wastewater Application
Loading Application
Period, days
1
2
1
2
1
2
3
1
2
3
1
2
1
2
7
8
9
7
8
9
Cycle Drying
Period, days
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
Minimum Number of
Infiltration Basins
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
10.6 Design Considerations
Issues to be addressed during SAT system design
include wastewater distribution, basin layout, surfaces,
and drainage, and flow equalization or storage.
10.6.1 Distribution
Although sprinklers may be used, wastewater
distribution is usually accomplished 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. At the SAT
system in Truckee, CA, with a 12.1 ha (30 ac) leach
field, wastewater effluent is distributed throughout eight
leach fields with 29,000 m (75,000 ft) of perforated
plastic piping buried at a depth of 1.5 to 1.8 m (5 to 6 ft)
(Woods etal., 1999).
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. Outlets used at currently
operated systems include valved raisers for underground
piping systems and turnout gates from distribution
ditches.
10.6.2 Basin Layout
Basin layout and dimensions are controlled by
topography, distribution system hydraulics, and loading
rate. 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.
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,
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 flooding
depth, in case initial infiltration is slower than expected
and for emergencies. Basin dikes and berms are
normally compacted soil with slopes ranging from 1:1 to
1:2 (vertical distance to horizontal distance). Basin dikes
and berms should be planted with grass or covered with
rip rap to prevent erosion.
Entry ramps should be provided for all basins. These
ramps are formed of compacted soil at grades of 10 to
20 percent and are from 3 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.
10-8
-------
The basin surface may be bare or covered with
vegetation. Vegetation covers tend to remove
suspended solids by filtration 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. 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 sludge-like solids collect in the
voids between gravel particles and because gravel
prevents the underlying soil from drying (Bouwer et al.,
1980).
The type of drainage used must be incorporated into
the basin design. See Section 10.9 for a discussion on
drainage. If underdrains are required, basin design must
consider placement of drains and drain outlet
characteristics.
10.6.3 Storage and Flow Equalization
Although SAT 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 SAT site
occurs at the Milton, Wl, 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
(US EPA., 1979).
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 (US
EPA, 1978).
10.6.4 Construction Considerations
Construction of rapid infiltration basins must be
conducted carefully to avoid compacting the infiltrative
surface. Basin surfaces should be located in cut
compacted in the berms. The berms need not be higher
sections, with excavated material being placed and than
1 to 1.3 m (3 to 4 ft) in most cases. Erosion of the berm
slopes should be avoided because erodible material is
often fine-textured and can blind or seal the infiltrative
surface.
10.7 Cold Weather Operation
In regions that experience cold weather, longer loading
cycles may be necessary during winter months.
Nitrification, denitrification, oxidation (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 is
reduced as the rate of nitrogen removal decreases.
Similarly, longer resting periods are needed to
compensate for reduced nitrification and drying rates.
Ponds in cold climates can be used as preliminary
treatment during the winter months. Ice may form in the
SAT basin, but will float under normal conditions, so
applications of warmer wastewater can continue. In
addition, proper thermal protection is needed for pumps,
piping, and valves (Crites et al., 2000).
SAT systems that operate successfully during cold
winter weather without any cold weather modifications
can be found in Victor, MT, Calumet, Ml, and Lake
George, NY. However, some modifications have been
used to improve cold weather treatment in other
communities. 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, SD,
where basins were not mowed. Applied wastewater
froze on top of the existing ice, preventing infiltration
completely (Dornbush, 1978).
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 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, CO, and Westby, Wl.
The third type of 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.
At Truckee, CA the SAT distribution system consists
of subsurface perforated piping, similar to an onsite
leachfield (Woods et al., 1999).
10-9
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10.8 Drainage
SAT 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 and
reaeration will be inadequate for oxidation of ammonia
nitrogen to occur.
Renovated water may be isolated to protect either or
both the groundwater and the renovated water. In both
cases, there must be some method of engineered
drainage to keep renovated water from mixing with
native groundwater.
Natural drainage often involves flow through the
subsurface 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 SAT basins.
Outlet devices must be stabilized to assure no loss of
soil material around drainage outlets.
10.8.1 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
(Bouwer, 1974):
w =
KDH
dL
(10-5)
Where:
W =
K =
D =
total width of infiltration area in direction of groundwater flow,
m(ft)
permeability of aquifer in direction of groundwater flow, m/d
(ft/d)
average thickness of aquifer below the water table and
perpendicular to the direction of flow, m (ft)
elevation difference between the water level of the water
course and the maximum allowable water table below the
spreading area, m (ft)
lateral flow distance from infiltration area to surface water, m
(ft)
annual hydraulic loading rate (including rainfall input), m/d
(ft/d)
Examples of these parameters are shown in
Figure 10-1.
Figure 10-1. Definition Sketch for Lateral Drainage from SAT Systems
Underdrains.
For SAT 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 underdrains. 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.
SAT 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 10-2 and
10-3 (US EPA, 1974a). 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.
Procedures for estimating underdrain spacings are
provided in Chapter 3. 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 US Bureau
of Reclamation "Drainage Manual" and in the American
Society of Agronomy manual, "Drainage for Agriculture."
Simulation methods for design and evaluation of
drainage systems for wastewater land treatment sites
are also available. One such water management model,
DRAINMOD, can be used for describing the
performance of an artificially drained land treatment
system over a long period of climatological record
(Skaggs et al., 1982; Skaggs, 1991). The model is a
computer simulation program which predicts, on an
hour-by-hour, day-by-day basis, the response of the
water table and the soil water regime above it to rainfall,
10-10
-------
evapotranspiration, given intensities of surface and
subsurface drainage, controlled drainage, subirrigation
and sprinkler, or surface irrigation. The model keeps
track of the amount of water irrigated, water table
depths, drainage volumes and evapotranspiration, on a
daily basis, with monthly and yearly summaries. Thus, a
given drainage design and irrigation strategy can be
analyzed for a long period of climatological record to
determine their suitability. More specifically, the effects
of drain spacing, surface drainage, application
frequency, and loading rates on water table depth,
drainage outflow volumes, and required wastewater
storage volumes can be analyzed. An economic analysis
can be conducted to demonstrate how the model can be
used to optimize the design of wastewater irrigation-
drainage systems.
Figure 10-2. Centrally Located Underdrain.
i-JLL
I I I
JUU-
Figure 10-3. Underdrain System Using Alternating Infiltration and
Drying Strips.
10.8.2 Recovery Wells
Soil aquifer treatment systems that utilize unconfined
and relatively deep aquifers should use wells if
necessary to improve drainage or to remove renovated
water for reuse. Wells are used to collect renovated
water directly beneath the SAT sites at both Phoenix,
AZ. and Fresno, CA. Wells are also involved in the reuse
of recharged wastewater at Whittier Narrows, CA;
however, the wells pump groundwater 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. Well
design is described in detail in Campbell and Lehr
(1973).
10.8.3 Aquifer Storage
Use of highly treated wastewater for aquifer storage is
an increasingly important practice in many regions of the
world where conventional freshwater resources are
limited and local aquifers are overused. There are
several advantages to storing treated wastewater
underground: (1) the cost of artificial recharge may be
less than the cost of equivalent surface reservoirs; (2)
the aquifer serves as an eventual distribution system
and may eliminate the need for surface pipelines or
canals; (3) water stored in surface reservoirs is subject
to evaporation, to potential taste and odor problems
caused by algae and other aquatic growth, and to
pollution; (4) suitable sites for surface reservoirs may not
be available or environmentally acceptable; and (5) the
storage of treated wastewater within an aquifer may also
provide psychological and aesthetic secondary benefits
as a result of the transition between reclaimed
wastewater and groundwater (Metcalf and Eddy, 1991).
Locating the extraction wells as great a distance as
possible from the spreading basins increases the flow
path length and residence time of the applied
wastewater. These separations in space and time
contribute to the assimilation of the treated wastewater
with the other aquifer contents.
To minimize potential health risks, careful attention
must be paid to groundwater recharge operations when
a possibility exists to augment substantial portions of
potable groundwater supplies (Metcalf and Eddy, 1991).
Long-term loading of aquifers can pose a serious threat
to groundwater quality, especially in dry climates with
static or very slow moving aquifers. Chemicals of
concern include salts, pesticide residues and nitrates,
disinfection byproducts (DBPs), pharmaceutically active
chemicals, pathogens, and DBP precursors such as
humic substances and other dissolved organic matter
which produce a new suite of DBPs when groundwater
is abstracted again and chlorinated or otherwise
disinfected for potable use. Fujita et al. (1996) identified
dissolved organic carbon characteristics and evaluated
specific trace organic monitoring techniques, which allow
operators of groundwater recharge programs to acquire
information about the movement and mixing of
wastewater introduced into aquifer systems. All
significant aquifer recharge projects should have a
groundwater impact analysis to allow the best possible
predictions of how the project will affect groundwater
quality and water table levels, how the situations can
best be handled, and what damage and liability aspects
can be expected (Bouweret al, 1999).
10-11
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10.9 References
Bouwer, H. (1974) Infiltration-Percolation Systems, In:
Proceedings of the Symposium on Land Application
of Wastewater, Newark, DE, p.85.
Bouwer, H., et al. (1980) Rapid-Infiltration Research at
Flushing Meadows Project, Arizona, Journal WPCF
52(10): 2457-2470.
Bouwer, H., P. Fox, and P. Westerhoff (1999)
Integrating Water Management and Re-use: Causes
for Concern?, Water Quality International,
January/February, pp. 19-22.
Campbell, M.D. and Lehr, J.H. (1973) Water Well
Technology, McGraw-Hill, New York, NY.
Conroy, O., K.D. Turney, K.E. Lansey, and R.G. Arnold
(2001) Endocrine Disruption in Wastewater and
Reclaimed Water, In: Proceedings of the Tenth
Biennial Symposium on Artificial Recharge of
Groundwater, Tucson, AZ, pp. 171-179.
Crites, R.W. (1985a) Micropollutant Removal in Rapid
Infiltration, in T. Asano (ed.), Artificial Recharge of
Groundwater, Butterworth Publishers, Stoneham,
MA, pp. 579-608. Crites, R.W. (1985b) Nitrogen
Removal in Rapid Infiltration Systems, Journal of
Environmental Engineering Division ASCE, 111 (6):
865-873.
Crites, R.W. and G. Tchobanoglous (1998) Small and
Decentralized Wastewater Management Systems,
McGraw-Hill, New York, NY.
Crites, R.W., S.C. Reed, and R.K. Bastian (2000) Land
Treatment Systems for Municipal and Industrial
Wastes, McGraw-Hill, New York, NY.
Davis, S.N. (1969) Flow Through Porous Media, R.J.M.
DeWeist, Editor, Academic Press, New York, NY.
Dornbush, J.N. (1978) Infiltration Land Treatment of
Stabilization Pond Effluent, Technical Progress
Report 3, South Dakota State University, Brookings,
SD.
Drewes, J., A. Sollner, A. Sarikaya, M. Reinhard, P. Fox,
and W. Montgomery-Brown (2001 a) Membrane
Treatment versus Soil-Aquifer Treatment for Indirect
Potable Reuse - Performance, Limitations, and
Concerns, American Water Works Association,
Membrane Conference Proceedings.
Drewes, J., T. Heberer, and K. Reddersen (2001 b) Fate
of Pharmaceuticals During Groundwater Recharge,
In: Proceedings of the Tenth Biennial Symposium on
Artificial Recharge of Groundwater, Tucson, AZ, pp.
181-190.
Enfield, C.G. (1978) Evaluation of Phosphorus Models
for Prediction of Percolate Water Quality in Land
Treatment, Proceedings of the International
Symposium on Land Treatment of Wastewater,
Volume 1, CRREL, Hanover, NH, p.153.
Fujita, Y., W. Ding, and M. Reinhard (1996)
Identification of Wastewater Dissolved Organic
Carbon Characteristics in Reclaimed Wastewater
and Recharged Groundwater, Water Environment
Research, 68 (5): 867-876.
Gable, J.E. and P. Fox (2000) Nitrogen Removal
During Soil Aquifer Treatment By Anaerobic
Ammonium Oxidation (ANAMMOX), Proceedings of
the Joint Conference Held by WEF and AWWA, San
Antonio, TX.
Kopchynski, T., P. Fox, and M. Berner (1999) Pilot
Scale Studies to Determine Mechanisms of DOC
and Nitrogen Removal in Soil Aquifer Treatment
(SAT) Systems, Submitted to Water Research.
Lance, J.C., F.D. Whisler, and R.C. Rice (1976J
Maximizing Denitrification During Soil Filtration of
Sewage Water, Journal of Environmental Quality, 5:
102.
Metcalf and Eddy, Inc. (1991) Wastewater Engineering
Treatment, Disposal, and Reuse, Third Edition,
McGraw-Hill, Inc.
Quanrad, D., Q. Conroy, K. Turney, K. Lansey, and R.
Arnold (2002) Fate of Estrogenic Activity in
Reclaimed Water During Soil Aquifer Treatment,
Water Sources Conference Proceedings, American
Water Works Association, Las Vegas, NV.
Reed, S.C. and R.W. Crites (1984J Handbook of Land
Treatment Systems for Industrial and Municipal
Wastes, Noyes Publications, Park Ridge, NJ.
Ryden, J.C., J.K. Syers, and I.K. Iskandar (1982J
Evaluation of a Simple Model for Predicting
Phosphorus Removal by Soils During Land
Treatment of Wastewater, U.S. Army Corps of
Engineers, CRREL, Special Report 82-14.
Skaggs, R.W. and A. Nassehzadeh-Tabrizi (1982)
Drainage Systems for Land Treatment of
Wastewater, Journal of the Irrigation and Drainage
Division, Proceedings of the American Society of
Civil Engineers, Vol. 108, No. IRS, pp. 196-211.
Skaggs, R.W. (1991) Modeling Plant and Soil Systems,
Agronomy Monograph No. 31, pp. 205-243.
US EPA (1974a). Renovating Secondary Effluent by
Groundwater Recharge with Infiltration Basins, In:
Conference on Recycling Treated Municipal
Wastewater Through Forest and Cropland, EPA-
10-12
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660/2-74-003, U.S.
Agency.
Environmental Protection
US EPA (1975) Kinetic Model from Orthophosphate
Reactions in Mineral Soils, EPA-660/2-75-022, U.S.
Environmental Protection Agency, Office of
Research and Development, Ada, OK.
US EPA (1978J Long-Term Effects of Land Application
of Domestic Wastewater: Hollister, California, Rapid
Infiltration Site, EPA-600/2-78-084, U.S.
Environmental Protection Agency.
US EPA (1979). Long-Term Effects of Land Application
of Domestic Wastewater: Milton, Wisconsin, Rapid
Infiltration Site, EPA-600/2-79-145, U.S.
Environmental Protection Agency.
US EPA (1980) Summary of Long-Term Rapid
Infiltration System Studies, EPA-600/2-80-165
Metcalf and Eddy, Inc. (1991) Wastewater
Engineering: Treatment, Disposal, and Reuse, Third
Edition, McGraw-Hill, Inc.
US EPA (1981). Process Design Manual for Land
Treatment of Municipal Wastewater, EPA-625/1-81-
013, U.S. Environmental Protection Agency, CERI,
Cincinnati, OH. US EPA (1984) Process Design
Manual for Land Treatment of Municipal
Wastewater, Supplement on Rapid Infiltration and
Overland Flow, EPA 625/1-81-0139, Center for
Environmental Research Information (CERI), U.S.
Environmental Protection Agency, Cincinnati, OH.
Van de Graaf, A., A. Mulder, P. De Brujin, M. Jetten, L.
Robertson, and G. Kuenen (1995) Anaerobic
Oxidation of Ammonium Is a Biologically Mediated
Process, Applied and Environmental Microbiology,
61(4): 1246-1251.
Van de Graaf, A., P. De Brujin, L. Robertson, M. Jetten,
and G. Kuenen (1996) Autotrophic Growth in
Anaerobic Ammonium-oxidizing Mircro-organisms in
a Fluidized Bed Reactor, Microbiology, 142: 2187-
2196.
Van de Graaf, A., P. De Brujin, L. Robertson, M. Jetten,
and G. Kuenen (1997) Metabolic Pathway of
Anaerobic Ammonium Oxidation on the Basis of 15N
Studies in a Fluidized Bed Reactor, Microbiology,
143:2415-2421.
Woods, C., H. Bouwer, R. Svetich, S. Smith, and R.
Prettyman (1999) Study Finds Biological Nitrogen
Removal in Soil Aquifer Treatment System Offers
Substantial Advantages, Water Environment
Federation, WEFTEC '99, New Orleans, CA.
10-13
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Chapter 11
Industrial Wastewater Land Application
Land treatment, in many ways, was rediscovered for
treatment of industrial wastewater. In 1934, corn and
pea canning wastewater was reported to be applied
successfully using the ridge and furrow method in
Hampton, Iowa (Bolton, 1947). In addition to food
processing wastewaters, pulp and paper, chemical,
fertilizer, meat processing, dairy, brewery, and winery
wastewaters have been land applied successfully for
many years (Crites, 1982; Ludwig et al., 1951; US EPA,
1973). This chapter is adapted from Chapter 13 of Land
Treatment Systems for Municipal and Industrial Wastes
(Crites etal., 2000).
11.1 Types of Industrial Wastewaters
Applied
11.1.1 Food Processing
Because of the rural location of many food processing
facilities, and because waste from food processing
facilities is suitable for application to land, this
technology has been used widely. Vegetable processing
in New York (Adamczyk, 1977), citrus processing in
Florida (Wright, 1993) and potato processing in Idaho
(Smith, 1977) are industrial wastewaters and areas
where land application is the treatment process of
choice. Soup and tomato processing wastewater were
two of the first food processing wastewaters that were
treated by spray-runoff or overland flow (Bendixen,
1969; Glide, 1971; US EPA, 1973). Winery wastewaters
were treated successfully using rapid infiltration (Coast
Laboratories, 1947; Crites et al., 1981). Additional
sources of information can be found for brewery wastes
(Crites et al., 1978; Keith et al., 1986), vegetables
(Beggs et al., 1990; Canham, 1958; Lane, 1955; Luley,
1963; Madison et al., 1993), soup (Law et al., 1970), fruit
(Crites et al., 1974; Luley, 1963; Ludwig, 1951; Crites et
al., 1994) coffee and tea (Loehr et al., 1988; Molloy,
1964), dairy products (Breska et al., 1957; Lawton et al.,
1959; McKee, 1955; Scott, 1962), meat processing
(Henry et al., 1954; Schraufnagel, 1962), and winery
stillage and wastewater (Crites, 1996).
11.1.2 Pulp and Paper
There have been many types of pulp and paper mill
wastewaters that have been land applied successfully
(Wallace, 1976). Much of the literature on land
application of pulp and paper wastewater dates from the
1950s and 1960s (Billings, 1958; Blosser et al., 1964;
Flower, 1969; Koch et al., 1959; Meighan, 1958;
Parsons, 1967; Voights, 1955). Experiments with
insulation board mill wastewater resulted in the
demonstration that BOD loading rates over 2,240
kg/ha d (2,000 Ib/ac d) caused vegetation to be killed
(Phillip, 1971).
11.1.3 Other Industrial Wastes
Other industrial wastewaters that have been land
applied include chemical (Overcash et al., 1979;
Woodley, 1968), fertilizer, tannery (Parker, 1967),
pharmaceutical (Coloves, 1962), explosives (Lever,
1966), wood distillation (Hickerson et al., 1960) and oily
wastewaters.
11.2 Water Quality and Pretreatment
Requirements
All wastewaters to be land applied must be
characterized before the limiting design parameter (see
Chapter 2) can be determined. The limiting design
parameter is based upon the fact that soil has a finite
assimilative capacity for inorganic and organic
constituents. That capacity must not be exceeded if an
environmentally sound and economically feasible land
treatment system is to result. A variety of parameters
can limit waste application rates. Examples include
nitrate leached from the site to groundwater; synthetic
organic compounds in surface water, groundwater, and
crops; salts that inhibit seed germination or alter soil
structure; or metals that may be toxic to plants (Loehr et
al., 1985). In-plant source control or pretreatment to
reduce the concentrations of specific constituents may
be required or the size of the land treatment system
must be expanded to assimilate the most restrictive
constituent.
11.2.1 Wastewater Constituents
Industrial wastewaters may contain significant
concentrations and wide variations of constituents such
as BOD, COD, TSS, TDS, nitrogen, pH, organic
compounds, and metals. Ranges of concentrations in
land-applied wastewaters are summarized in Table 11-1
(US EPA, 1973). The impact and importance of these
constituents are described in the following.
BOD
The degradable organic matter, as measured by the
BOD test, can be present in very high concentrations in
industrial wastewater. Because the soil mantle is very
efficient in the removal of BOD, it is often more cost-
effective to apply the wastewater to the land than to
remove it by pretreatment.
11-1
-------
Table 11-1. Characteristics of Various Industrial Wastewaters Applied to Land
Constituent
Food Processing
Pulp and Paper
Dairy
BOD, g/mj
COD, g/m3
TSS, g/m3
Fixed Dissolved Solids (FDS),
g/m3
Total Nitrogen, g/m
pH, units
Temperature, °C
200-10,000
300-15,000
200 - 3,000
1,800
10-100
3.2-12
63
60 - 30,000
200-100,000
2,000
6-11
91
4,000
1,500
90 - 400
5-7
Conversion units: g/rn^ = rng/L.
Organics in the form of sugars are more readily
degradable than starchy or fibrous material.
Consequently, those industrial wastewaters that contain
predominantly sugars, such as food processing
wastewaters, may be applied at a higher organic loading
rate than wastewaters from the pulp and paper industry,
which often contain starchy or fibrous organic material
that are resistant to degradation.
Total Suspended Solids
Suspended solids may include coarse solids, such as
peelings and chips, or fine solids such as pulp or silt.
The presence of high concentrations of suspended
solids in a wastewater does not restrict its application to
a land treatment system because suspended solids can
normally be separated quite simply by physical
pretreatment. Failure to provide adequate suspended
solids removal, however, can lead to operational
problems with clogging of sprinkler nozzles or nuisance
problems with solids settlement in surface irrigation
systems. Surface buildup as a result of uneven
distribution or high concentrations of TSS can lead to
reduced infiltration rates and inhibition of plant growth in
ponded areas of irrigated fields.
Total Inorganic Dissolved Solids
Salts, correctly measured only by the total inorganic
(fixed, not volatile) solids test, are important to land
treatment systems because there are no effective
removal mechanisms for salt. The plants will take up a
minor amount of TDS (usually the macronutrients and
micronutrients) and some compounds will precipitate in
the soil (metal complexes and phosphate compounds).
As a result of the minimal removal, mineral salts either
build up in soil concentration or are leached to the
groundwater. Industrial wastewaters with very high
inorganic solids concentrations are generally not suitable
for land application unless special provisions are made
to collect soil drainage.
It is very important to measure the inorganic dissolved
solids in the industrial process water because the
standard total dissolved solids (TDS) test will include the
organic acids, alcohols and other dissolved organic
compounds that may be present in the wastewater. As
an example, a milk processing wastewater was tested
for fixed dissolved solids (FDS), TDS, electrical
conductivity (EC) for both the wastewater and the
shallow groundwater (after slow-rate land treatment).
The results are summarized in Table 11-2 (Crites et al.,
2000). The ratios of FDS/TDS and FDS/EC are
presented for both waters and for upgradient shallow
groundwater. A typical ratio of FDS/EC in clean water is
0.64 (Westcot et al., 1984). As the wastewater infiltrates
through the soil, a significant portion of the TDS, in the
form of organic material, is removed. Initially, the organic
portion consists of 48 percent of the TDS and exceeds
1,000 g/m3 (mg/L). The slow-rate land treatment process
reduces the organic TDS to 200 g/m3 (mg/L),
approximately 17 percent of the TDS. The FDS portion
of the wastewater increases from 53 percent of the TDS
to 83 percent after treatment, resulting in a buildup of
inorganic salts in the groundwater.
Table 11-2. Comparison of Inorganic and Total Dissolved Solids Measurements in Milk Processing Wastewater and Shallow Groundwater
Fixed Dissolved TDS, g/m3 EC, g/m3 FDS/TDS ratio FDS/EC ratio
Water Source Solids (FDS), g/m3
Process Wastewater
Shallow Groundwater
Upgradient
Groundwater
1,203
1,000
200
2,250
1,200
300
1,680
1,700
310
0.53
0.83
0.67
0.71
0.58
0.64
Conversion units: g/m = mg/L.
11-2
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Nitrogen
Industrial wastewaters from livestock, potato, dairy,
meat-packing, and explosives production may be high in
nitrogen. For these wastewaters, nitrogen is often the
limiting design factor. The C:N ratio does not have to be
in as close a balance for land treatment as it does for
suspended growth systems, however, C:N ratios beyond
30:1 will affect crop growth or biological nutrient removal
because of the competition for available nitrogen.
PH
The pH of industrial wastewater can vary
tremendously, even hourly, depending on the type of
wastewater and the cleaning agents used. A range of pH
between 3 and 11 has been applied successfully to the
land (Crites, 1982). If the low pH is from the presence of
organic acids, land treatment will have a neutralizing
effect as the organic acids are oxidized or degraded.
Temperature
High-temperature industrial wastewater, such as spent
cooking liquors from pulping operations, can sterilize
soil, thereby precluding the growth of vegetation and
reducing the treatment capability of the soil mantle
(Guerri, 1971). High-temperature wastewaters should,
therefore, be cooled prior to land application.
Color
The color in most industrial wastewaters is associated
with degradable organic material and is effectively
removed as the wastewater percolates through the soil
mantle. In some wastewaters, such as spent sulfite
liquor, the color is due to inert compounds such as
lignins. It has been observed that the color from inert
compounds can move through the soil (Blosser et al.,
1964). Groundwater contamination is of concern from
land application of industrial wastewaters with color
resulting from inert components.
Metals
Heavy metals are effectively removed by most soil
systems. Metals can be the limiting design factor in slow-
rate and rapid infiltration systems and the rate of
retention in the soil may affect the longevity of a soil
system due to buildup in the soil.
Sodium
The sodium adsorption ratio (SAR), and the problems
caused by high values, are defined in Chapter 2. Some
industrial wastewaters that use caustic for cleaning may
have a high sodium adsorption ratio and may require
pretreatment for correction. Municipal systems should
consider industrial discharges to the system (e.g., in cold
climates de-icing salts may cause a problem).
11.2.2 Pretreatment Options
Options for pretreatment of industrial wastewaters may
need to be evaluated because of more stringent
discharge and land application limits. Pretreatment for
industrial wastewaters may range from fine screening to
biological treatment. The more typical of the
pretreatment operations and processes are described in
the following.
Fine Screening
Fine screening is usually a minimum level of
pretreatment prior to land application of industrial
process/rinse water. Fine screens can range from fixed
parabolic inclined screens to rotary drum screens (Crites
et al., 1998). Coarse solids that can clog sprinkler heads
or settle out at the head end of flood irrigation checks
can be removed economically using fine screens.
Screens also protect downstream pumps or other
pretreatment units from large objects that may get
washed into the wastewater stream.
Ponds
Ponds can range from anaerobic to deep facultative to
aerated. Aerated lagoons or ponds are quite common to
the pulp and paper industry and to many food
processing wastewaters. Ponds can be used to equalize
the flows, reduce peak organic loadings, and store the
wastewater for short periods of time. A sedimentation
pond or lagoon can be a lined basin or concrete basin.
The ponds can be designed by overflow rate or
detention time. Sludge may be allowed to accumulate for
season operations and cleared out after the season
concludes. If significant winter storage is required and
the wastewater has a relatively high BOD, pretreatment
will usually be needed to reduce the BOD to 100 g/m3
(mg/L) or less (US EPA, 1973) to avoid odor production.
Alternatively, the storage pond can be aerated to avoid
odor production.
Adjustment of pH
If the pH of the wastewater is outside the range of 4 to
9 due to inorganic acids or bases, pH adjustment may
be needed. Sometimes an equalization pond will serve
to let the wastewater self-neutralize, particularly if large
swings in the wastewater pH occur diurnally. Generally
the pH will attenuate quickly as a result of land treatment
and adjustment is not normally needed.
Cooling
High-temperature wastewaters [above 66°C (150°F)]
should be cooled so that adverse effects on vegetation
and soil do not occur. High-temperature wastewaters
can also have detrimental effects on plastic pipelines. If
11-3
-------
the wastewater temperature needs to be reduced, either
ponding or cooling towers can be used.
Dissolved Air Flotation
Dissolved air flotation (DAF) is a unit process in which
pressurized flow containing tiny air bubbles is introduced
at the bottom of a special tank or clarifier (Crites et al.,
1998). The dissolved air will float suspended solids and
the DAF unit will remove the solids through a float
skimming device. Sedimentation also occurs in DAF
units so that the settled solids must be removed. DAF
units are most effective for treating settleable solids and
fats, oil and grease (FOG).
Constructed Wetlands
Constructed wetlands are being used for pretreatment
of industrial wastewaters (Crites, 1996; Crites et al.,
1998; Reed et al., 1995). Treatment of livestock
wastewater with constructed wetlands after treatment
through ponds is becoming more prevalent (Hunt et al.,
1995). Removals of various constituents through the
settling basin and first cell of a wetland receiving dairy
wastewater in Mercer Co., KY are summarized in
Table 11-3 (Hunt et al., 1995).
Table 11-3. Water Quality Parameters in the Settling Basin and First Cell of a Wetland Receiving Dairy Wastewater, Mercer Co., KY
Constituent
DO
BOD
TSS
VSS
TP
SP
TKN
NH3-N
Settling Basin, g/m3
0.5
465
3,516
2,085
113.8
60.5
197.0
78.8
Influent, g/m3
0.6
452
1,132
898
71.6
26.5
107.5
32.8
Effluent, g/m3
0.8
158
408
357
47.1
15.0
123.8
10.3
Percent
Reduction
—
66
88
83
59
75
37
87
Conversion units: g/m = mg/L.
Dairy wastewater has been treated using constructed
wetlands using a detention time of 7.7 days, a hydraulic
loading rate of 39.4 mm/d (1.55 in/d), and a mass COD
loading rate of 554 kg/ha d (494 Ib/ac d) (Moore et al.,
1995).
Anaerobic Digestion
Anaerobic digestion can be used to reduce the organic
content of wastewater and produce methane gas (also
known as biogas). Anaerobic digestion can be
conducted in a variety of reactors and using a variety of
processes (Crites et al., 1998). Typically a BOD of about
2,500 g/m3 (mg/L) or higher is needed in an industrial
wastewater to make anaerobic digestion attractive.
Anaerobic digestion using some of the low-rate methods
is generally favored in the food processing industry.
11.3 Design Considerations
Design considerations specific to industrial
wastewaters include higher solids and organic loadings,
nitrogen transformations, and the control and attenuation
ofpH.
11.3.1 BOD Loading Rates and Soil
Reaeration
An important design consideration specific to industrial
wastewater is an accurate assessment of solids and
organic loadings. Oxygen exchange into soils greatly
depends on air-filled pore spaces because the diffusion
coefficient of oxygen is over 10,000 times more rapid in
air than in water. As a result, if organic loadings are
intermittent and atmospheric oxygen is allowed to diffuse
directly into the soil, high organic loading rates can be
sustained without the generation of odors (Reed et al.,
1995).
Research at Cornell on acclimated soils of SR systems
receiving food processing wastewater documented that
organic loading rates on a COD basis can exceed 4,480
and 19,094 kg/ha d (4,000 and 17,000 Ib/acre d) for
soil temperatures of 16°C and 28°C (61 °F and 82°F),
respectively (Jewell et al., 1975). Field sampling of the
groundwater at application rates exceeding 8,960
kg/ha d (8,000 Ib/acre d) of COD was less than 0.8
percent of the applied COD (Jewell et al. 1978). Based
on the experience in New York State, guidelines have
been established that organic loading rates should not
exceed 560 kg/ha • d (500 Ib/acre d) based on BOD
(Adamczyk, 1977). BOD loading rates for various food
processing slow rate systems are summarized in
Table 11-4 (Crites et al., 1998; Reed etal., 1984).
11-4
-------
Table 11-4. BOD Loading Rates at Existing Industrial Slow-Rate Systems
Location
Winery stillage
Brewery
Winery stillage
Winery
Citrus
Tomato processing
Potato processing
Tomato processing
Cheese processing
Potato processing
Tomato processing
Industry
BOD Loading Rate, kg/ha day (Ib/acre day)
Almaden, McFarland, CA.
Anheuser-Busch, Houston, TX.
Bisceglia Brothers, Madera, CA.
Bronco Wine, Ceres, CA.
Citrus Hill, Frostproof, FL.
Contadina, Hanford, CA.
Frito-Lay, Bakersfield, CA.
Harter Packing, Yuba City, CA.
Hilmar Cheese, Hilmar, CA.
Ore-Ida Foods, Plover, Wl.
Tri Valley Growers, Modesto, CA.
470 (420)
403 (360)
312(279)
143(128)
447 (399)
103 (92)
94 (84)
393 (351)
249 (222)
213(190)
224 (200)
In OF treatment, organic loading rates and BOD
concentrations must be limited to avoid overloading the
oxygen transfer to the attached microorganisms. The
initial work by Campbell Soup Company (Glide et al.,
1971) indicated that excellent BOD removals could be
expected at applied BOD concentrations of about 800
g/m3 (mg/L) (Crites, 1982). When higher strength
wastewaters were applied at similar loading rates [16 to
36 mm/d (0.6 to 1.4 in/d)], however, an oxygen transfer
problem began to develop. To overcome this problem,
pretreat or recycling of the treated effluent can be used
(Crites, 1982). If a recycle operation is used, the
collection system should include a sump from which the
treated runoff can be returned to the distribution system.
Nitrogen Transformations
Permit limits in the past have focused on ammonia,
nitrate, and total Kjeldahl nitrogen (TKN), with the
assumption that organic nitrogen measured in the TKN
test is biodegradable. It is recognized that
nonbiodegradable organic nitrogen exists and that the
TKN test, a chemical digestion procedure, is not always
a good indicator of the biodegradability of an organic
nitrogen compound. Although nonbiodegradable organic
nitrogen may remain after exposure to rigorous
anaerobic and aerobic treatment, studies support the
premise that this form of TKN does not pose the same
hazards to the environment as biodegradable organic
nitrogen (Kobylinski et al., 1995). The presence of
nonbiodegradable organic nitrogen may, however,
Table 11-5. Nitrogen Mineralization of Industrial Wastewaters
impact the ability of an industrial land treatment system
to comply TKN limits written into NPDES permits.
Industrial wastewaters have a common tendency to
have very high C:N ratios, which may effect the
biological nutrient removal processes of the treatment
system. Incubation studies conducted on various
industrial wastewaters demonstrated the effect of C:N
ratios on the mineralization of organic nitrogen. The data
presented in Table 11-5 indicate that wastewaters with
relatively low C:N ratios maintain a higher mineralization
potential than wastewaters with high C:N ratios (King,
1984). In this review wastewaters with C:N ratios greater
than 23:1 displayed negative mineralization values,
indicating inefficient conversion of organic nitrogen into
inorganic forms of nitrogen.
11.3.2 pH Control and Attenuation
Many food-processing wastewaters have a low pH that
can range from 3.7 to 6, as the result of the presence of
organic acids. The action of the soil microbes in
oxidizing the organic acids and the soil buffering
capacity usually result in a relatively rapid attenuation of
the pH. A review of sites receiving winery stillage waste
with a typical pH of 3.7 found that the soil pH was
reduced from 6.7 to 5.8 in the topsoil [0 to 15 cm (0 to 6
in)], but only from 7.1 to 6.6 at the 0.6 m (2 ft) depth, and
only from 7.45 to 7.16 at the 1.8 m (6 ft) depth (Crites et
al., 1981).
Waste water
C:N
Organic-N Mineralized (%)
Textile Sludge
Vacuum Filtered Solids
Solids from Lagoon
Wood Processing Wastes
Paper Mill Sludge
Fiberboard Mill Sludge
Poultry Processing Waste
Waste-Activated Sludge
Fermentation Waste
Sludge from Brewery Wastewater Treatment Plant
Sludge from Enzyme Production
2.5
4.4
82.2
23.0
3.0
2.4
8.0
43
9
-45
-12
52
46
24
11-5
-------
11.4 Slow-Rate Land Treatment
The procedure for design of slow-rate land treatment
systems is presented in Chapter 8. The preferred
method of wastewater distribution is sprinkler application
(irrigation). Although surface application methods (flood
or furrow irrigation) have been used successfully, a
number of disadvantages have been observed. The
applied solids tend to settle out near the point of
application, producing a nonuniform distribution of solids
and organics through the field. Flood or furrow irrigation
also results in saturated flow through the soil and may
reduce the effectiveness of treatment for some
constituents and result in anaerobic conditions that can
cause leaching of iron and manganese. Relatively low-
cost methods of sprinkler application, such as center
pivots, are usually preferred. See Chapter 7 for details
on sprinkler application. Two brief case studies are
included here.
11.4.1 Typical Examples
Slow-rate land treatment is the most popular method
of industrial wastewater land treatment. Two examples
of food processing wastewater land application are
presented in the following illustrating a year-round
application in Idaho and a seasonal application of tomato
processing wastewater in California.
Potato Process Water— Idaho
Bruneret al., 1999 reported the J.R. Simplot Company
Food Group has operated a potato processing plant in
Aberdeen, Idaho since 1973. This facility produces a
variety of fried potato products. The 330-day processing
season begins on about September 1 and ends on about
July 31 each year. The current average daily flow from
the facility is about 2,650 m3/d (0.7 Mgal/d, for an annual
flow of about 874,427 m3 (231 million gallons). All water
used for potato processing is recycled through sprinkler
irrigation on to a 190 ha (469 acre) agricultural receiver
site containing silt loam soil and grass as the receiver
crop. Groundwater is about 10 to 20 m (30 to 60 ft)
below the ground surface at this site.
Process water is generated during the washing,
cutting, blanching, and cooling of the potatoes. Water
used to wash soil from the potatoes in the raw product
receiving area is screened to remove potato vines,
rocks, and small potatoes, and then is diverted to a set
of settling basins. The settled effluent is land applied on
a designated area of the facility's agricultural land, and
the overflow from the basins is pumped to the land
application site with the process water stream. Water
used within the processing plant is screened and then
directed to a primary clarifier. The underflow potato
solids from the clarifier are mechanically separated using
centrifuges and are fed to cattle. Excess oil from the
fryers is removed by a separate clarifier and recycled off
site.
Southern Idaho has a semi-arid climate, with an
annual average precipitation of about 23 centimeters (9
inches). The growing season for grass occurs during the
months of April through October. Under intensely
managed conditions, grass on land application sites in
southern Idaho typically consumes about 107
centimeters (42 inches) of water annually.
The objective of Simplot's potato process water
irrigation system is to provide a cost-effective, reliable,
and environmentally sound beneficial reuse of the water,
nitrogen, and other crop nutrients. The challenging
aspects of this system have been the management of
applied salts and organics to protect groundwater
quality, and to minimize odors.
A view of the side roll sprinkler system is shown in
Figure 11-1.
Figure 11-1. Side roll sprinklers apply potato processing wastewater
throughout the winter at Aberdeen, Idaho. (Courtesy of Cascade Earth
Science.)
Tomato Processing System in California
Tomato processing wastewater has been land applied
at a number of sites in California's Central Valley for
many years. Operations include direct land application to
open land; furrow, flood and sprinkler irrigation of
agricultural crops; and provision of irrigation water to
private farmers for pasture application. One site has 36
ha (90 acres) for the direct land application of 3,875
m^/d (1.0 Mgal/d). Wastewater is passed through a fine
screen and applied to border strips for flood irrigation.
BOD and TSS concentrations have averaged 1,700 g/m3
(mg/L) and 300 g/m3 (mg/L), respectively, resulting in a
BOD loading of 190 kg/ha d (170 Ib/acre d) and a TSS
loading rate 33 kg/ha d of (30 Ib/acre d). The regulatory
agency has placed a limit of 224 kg/ha d (200
11-6
-------
Ib/acre d) of BOD to avoid the generation of odors.
Upgradient and downgradient groundwater monitoring
wells have been sampled regularly and have
demonstrated improvement of water quality after land
application and no adverse impacts on quality of the
groundwater (Beggs et al., 1990).
11.5 Overland Flow Treatment
The procedure for design of overland flow land
treatment systems is presented in Chapter 9. Overland
flow systems receiving high-strength wastewater are
recommended to use sprinkler application to distribute
the solids and organics evenly. Two brief case studies
are included here.
11.5.1 Typical Examples
Overland flow has been used to treat a variety of food
processing wastewaters including apple, tomato, potato,
soup, meat packing, poultry, peanuts, and pimientos
(Crites, 1982). Two examples are presented briefly to
illustrate a year-round system and a seasonal system.
In the year-round example the treated runoff is discharge
to surface water. In the more seasonal operation, the
treated runoff is reused for crop irrigation.
Soup Producer in Texas
One of the oldest and best-known overland flow
systems is the Campbell Soup Company's Paris, TX
operation. Developed in the 1960s, the Paris site has
had its origins documented (Glide et al., 1971),
performance evaluated (Law et al., 1970), microbiology
investigated (Vela, 1974), and long-term effects studied
(Tedaldi, 1991 and 1992).
The original 120 ha (300 acre) site was expanded to
360 ha (900 acres) by 1976. The original slopes ranged
from 1 to 12 percent, but those from 2 to 6 percent
Table 11-6. Performance of Paris, TX, Overland Flow System
demonstrated the best performance, least erosion and
least ponding. Before application, the wastewater is
screened to remove large solids, and grease is
skimmed. No storage of the screened wastewater occurs
and the screened wastewater is pumped continuously
from a 375-m3 (99,075-gal) sump to spray the
application slopes. The overland flow terraces are 60 to
90 m (200 to 300 ft) long. The hydraulic loading rate was
15 mm/d (0.6 in/d). The slopes are seeded to a mixture
of Reed canarygrass, tall fescue, red top and perennial
ryegrass. Wastewater is applied using standard
agricultural impact-type solid set sprinklers [8.0-mm
(0.315-in) nozzle diameter]. Application periods are 6 to
8 hr/d for 5 d/wk. Long-term operation and performance
data collected at the site indicate that the OF system
consistently achieved very high removal efficiencies from
a surface discharge standpoint. The performance of the
system is summarized in Table 11-6 (Crites, 1982; Glide
etal., 1971; Lawetal., 1970).
Tomato Processor in California
A 129 ha (320 acre) overland flow treatment system
was constructed near Davis, California in 1969 to treat
15,100 m3/d (4 Mgal/d) of tomato processing
wastewater. Screened wastewater is pumped to the
overland flow field and sprinkled onto constructed 2.5
percent slopes. The slopes are 53 m (175 ft) long based
on the experience at Paris, TX. Reed canarygrass
predominates as the vegetation. The cannery operates 3
to 4 months during the summer (July through mid-
October) fresh processing season and, for the past few
years, operates a remanufacturing processing season
from October through March. The solid-set sprinklers are
shown in Figure 11-2.
Constituent
Influent
Effluent
Percent Removal
BOD, g/mj
COD, g/m3
TSS, g/m3
Total N, g/m3
Total P, g/m3
Chloride, g/m3
pH, units
572
806
245
17.2
7.4
44
4.4-9.3
3.1
45
38
2.8
4.3
43
6.6
99.5
94.4
84.5
83.7
41.9
2.3
—
Conversion units: g/m = mg/L.
11-7
-------
Figure 11-2. Solid set sprinklers apply tomato processing wastewater
to overland flow slopes.
ranch. The performance of the overland flow system is
summarized in Table 11-7.
11.6 Soil Aquifer Treatment
The design of soil aquifer treatment systems is
described in Chapter 10. Few SAT systems exist for
industrial wastewater. The reasons include the difficulty
in siting SAT systems and the typical high strength of
industrial wastewater, which requires a high level of
treatment.
The few SAT systems that exist are at the low end of
the hydraulic loading rate range for municipal
wastewater. The loading rates for BOD, TSS, and
nitrogen, however, are generally quite high.
Treated runoff averages 7,550 m^/d (2 Mgal/d). The
treated runoff is reused for crop irrigation on a nearby
Table 11-7. Performance of Overland Flow System at Davis, CA.
Constituent Influent
Effluent
Percent Removal
BOD, g/mj (mg/L)
TSS, g/m3 (mg/L)
pH, units
1,490
1,180
4.5
17
25
8.16
98.9
97.9
—
Source: Brown and Caldwell files, Sacramento, CA.
11.6.1 Cheese Processing Wastewater in
California
Hilmar Cheese Company has been producing cheese
products and land-applying the process water at their
plant near the Town of Hilmar, five miles south of
Turlock, CA, since 1985. The land use surrounding the
plant site is primarily agricultural, with a mixture of
fodder, orchard, and pasture crops being grown. The
soils in the area are characteristically sandy, and there is
a relatively shallow groundwater table (3 m or 10 ft).
The land has been leveled for surface irrigation.
The area used for soil aquifer treatment has been
expanded with each increase in process water flow,
reaching 56 ha (140 acres) by 1998. The process water
flowrate is 2,840 m^/d (0.75 Mgal/d). The average
loading rate is 65 mm/wk (2.6 in/wk) because the
application area is rotated between wastewater
applications for about 6 months and cropping with either
corn or barley for 6 months. The BOD loading rate can
range from 89 to 734 kg/ha d (80 to 655 Ib/acre d), with
248 kg/ha d (222 Ib/acre d) being typical.
A comparison of the process water characteristics and
the monitoring well groundwater quality is presented in
Table 11-8 (Nolte and Associates, 1996). As shown in
Table 11-8 the upgradient groundwater has much higher
nitrate-nitrogen values as a result of areawide
fertilization practices. The downgradient wells have
much lower nitrate-nitrogen as a result of denitrification.
Hilmar Cheese is reclaiming byproducts from the cheese
production including the whey protein and lactose.
However, it should be noted that TKN, EC, TDS and
FDS increased significantly. An ultrafiltration system
concentrates the remaining fats and proteins into a slurry
that is used for cattle feed (Struckmeyer, 1999).
11.6.2 Winery Wastewater in California
Winery wastewater is characterized by low pH,
relatively high BOD, and a low nutrient content. Land
application using soil aquifer treatment has been
practiced successfully at a number of California wineries
for many years (Coast Laboratories, 1947; Crites, 1987;
Critesetal., 1974).
A Central Valley winery was constructed in 1974 with a
soil aquifer treatment system for treatment and disposal
of process water. Products include wine and wine
coolers. Washwater is collected into a central sump and
pumped to a series of seven individual infiltration basins.
Washwater flows vary by the season, being highest
during the August to October crush period. Annual
average washwater flows are 760 m^/d (0.2 Mgal/d).
Operation of the infiltration system is cyclical.
Washwater is loaded onto one basin at a time for a
period of several days and then the washwater is moved
11-8
-------
to the next basin. The basins cover 4 ha (10 acres) and
are rectangular. In the late winter, when the flows are
reduced, about half the basins are taken out of service
and planted to an annual cereal crop, such as oats,
wheat or barley. During July, after the crop is harvested,
the basins are ripped to a depth of 2-m (6-ft). The basins
are then disked and leveled for the next washwater
application (Crites, 1987).
The washwater quality varies with the season. BOD
values are highest during the crush [up to 4,700 g/m3
(mg/L)] and lowest during the spring [about 300 g/m3
(mg/L)], with an average of 950 g/m (mg/L). The total
nitrogen concentration averages 33 g/m3 (mg/L) and the
BOD to nitrogen ratio averages 28:1. The pH ranges
from 4.1 to 7.9. The low values of pH occur during the
crush, but do not have an adverse effect on either the
soil or the groundwater (Crites, 1987).
Table 11-8. Treatment Performance for Hilmar Cheese Soil Aquifer Treatment System
Constituent
Process Water
Upgradient Groundwater
Downgradient Groundwater
BOD, g/mj
TKN, g/m3
Nitrate-N, g/m3
EC, dS/m
TDS, g/m3
FDS, g/m3
2,852
93
18
1,688
2,727
1,155
2
1.1
35
650
480
340
2
9.3
0.4
1,100
600
540
Conversion units: g/m = mg/L.
11.7 References
Adamczyk, A.F. (1977J Land Disposal of Food
Processing Wastewaters in New York State, In:
Land as a Waste Management Alternative, Loehr,
R.C. (ed.), Ann Arbor Science Publishers, Ann
Arbor, Ml.
Beggs, R.A. and R.W. Crites (1990J Odor Management
for Land Application of Food Processing
Wastewater, Proceedings of the 6tn International
Symposium on Agricultural and Food Processing
Wastes, Chicago, IL.
Bendixen, T.W., et al. (1969) Cannery Waste Treatment
by Spray Irrigation-Runoff, Journal WPCF, 41: 385.
Billings, R.M. (1958) Stream Improvement through
Spray Disposal of Sulphite Liquor at the Kimberly-
Clark Corporation, Niagara, Wisconsin, Mill,
Proceedings of the 13tn Industrial Waste
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Blosser, R.O. and E.L. Owens (1964) Irrigation and
Land Disposal of Pulp Mill Effluents, Water and
Sewage Works, 111: 424.
Bolton, P. (1947) Disposal of Canning Plant Wastes by
Irrigation, Proceedings of the Third Industrial Waste
Conference, Purdue University, Lafayette, IN.
Breska, G.J., et al. (1957) Objectives and Procedures
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Proceedings of the 12tn Industrial Waste
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Bruner, D J., S.B. Maloney and H. Hamanishi (1999)
Expansion of a Spray Irrigated Land Application
System for a Year-Round Potato Processing Facility
in Idaho, Cascade Earth Science, Pocatello, ID.
Canham, R.A. (1958) Comminuted Solids Inclusion with
Spray Irrigated Canning Waste, Sewage & Industrial
Wastes, 30: 1028.
Coast Laboratories (1947) Grape Stillage Disposal by
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Colovos, G.C. and N. Tinklenberg (1962) Land Disposal
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Crites, R.W. (1982) Land Treatment and Reuse of Food
Processing Waste, Presented at the 55^ Annual
Conference of the Water Pollution Control
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Crites, R.W. (1987) Winery Wastewater Land
Application, Proceedings of a Conference on
Irrigation Systems for the 21st Century, Irrigation
and Drainage Division, American Society of Civil
Engineering, Portland, OR.
Crites, R.W. (1996) Constructed Wetlands for
Wastewater Treatment and Reuse, Presented at the
Engineering Foundation Conference, Environmental
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Santa Fe, NM.
Crites, R.W., et al. (1978) Treatment of Brewery Spent
Grain Liquor by Land Application, Proceedings of
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Houston, TX.
11-9
-------
Crites, R.W. and R.C. Fehrmann (1981) Land
Application of Winery Stillage Wastes, Industrial
Wastes, 27: 14.
Crites, R.W., C.E. Pound, and R.G. Smith (1974)
Experience with Land Treatment of Food Processing
Wastewater, Proceedings of the Fifth National
Symposium on Food Processing Wastes, Monterey,
CA.
Crites, R.W. and R.G. Stratton (1994J Land Application
of Pineapple Process Water for Reuse, Presented at
the Hawaii WPCA, Honolulu, HI.
Crites, R.W. and G. Tchobanoglous (1998) Small and
Decentralized Wastewater Management Systems,
McGraw-Hill, New York, NY.
Crites, R.W., S.C. Reed, and R.K. Bastian (2000) Land
Treatment Systems for Municipal and Industrial
Wastes, McGraw-Hill, New York, NY.
Flower, W.A. (1969) Spray Irrigation for the Disposal of
Effluents Containing Deinking Wastes, TAPPI, 52:
1267.
Glide, L.C., et al. (1971) A Spray Irrigation System for
Treatment of Cannery Wastes, Journal WPCF, 43:
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Guerri, E.A. (1971) Sprayfield Application Handles
Spent Pulping Liquors Efficiently, Pulp & Paper, 45:
93-95.
Henry, C.D., et al. (1954) Sewage Effluent Disposal
Through Crop Irrigation, Sewage & Industrial
Wastes, 26: 123.
Henry, C.L. and S.A. Wilson (1988) Denithfication
Following Land Application of Potato Processing
Wastewater, Agronomy Abstracts, American Society
of Agronomy, Madison, Wl.
Hickerson, R.D. and E.K. McMahon (1960) Spray
Irrigation of Wood Distillation Wastes, Journal
WPCF, 32: 55.
Hunt, P.G., et al. (1995) Sfafe of the Art for Animal
Wastewater Treatment in Constructed Wetlands,
Proceedings of the Seventh International
Symposium on Agricultural and Food Processing
Wastes, ASAE, Chicago, IL.
Jewell, W.J. and R.C. Loehr (1975) Land Treatment of
Food Processing Wastes, Presented at the
American Society of Agricultural Engineering, Winter
Meeting, Paper No. 75-2513, Chicago, IL.
Jewell, W.J., et al. (1978) Limitations of Land Treatment
of Wastes in the Vegetable Processing Industries,
Cornell University, Ithaca, NY.
Keith, L.W. and W.D. Lehman (1986) Land Treatment of
Food Processing Wastewater—Case History,
Utilization, Treatment, and Disposal of Waste on
Land, Soil Science Society of America, Madison, Wl.
King, L.D. (1984) Availability of Nitrogen in Municipal,
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