United States
Environmental Protection
Process Design Manual

Land Treatment of Municipal
Wastewater Effluents

                                               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

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.

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

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


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

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

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 	


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

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

Preceeding Page Blank
   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

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

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


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

       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.

                                                   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

                              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
                                        Slow rate (SR)
                                    Overland flow (OF)
                                 Soil aquifer treatment
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
23 - 280
Evapotranspiration and percolation

Sprinkler, surface or drip
6.5 - 44
Evapotranspiration and surface runoff,
limited percolation
Sprinkler or surface
Primary sedimentation
10 - 240
Mainly  percolation

Usually surface
"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.

Table 1-2. Site Characteristics for Land Treatment Processes
           Slow Rate
         Overland Flow
 Soil aquifer treatment
0 to 20%, Cultivated site
35%, Uncultivated
2 to 8 % for final slopes3
                                                                                          Not critical
Soil permeability
Groundwater depth
Moderate to slow
0.6 to 3 mb (2 to 10ft)
Winter storage in cold climatesd
Slow to none
Not critical11
Same as SR
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)
           Slow rate"

       Overland flow0

Soil aquifer treatment11



NH3/NH4 (as N)

Total N

Total P

Fecal coli (#/100mL)








          200 +





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


                                              (a) APPLICATION PATHWAY
                    ^JA       ^       ^fl
                    A?  w   *M   W ^A
                    ^  X   ^   X^f
                    "^y T= .   ^ -_^, L
                    Jff^    '^^o-'^1"   ^9v^
                                              (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

important in the more arid western portions of the United

  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

                                                GRASS AND
                                               'VEGETATIVE LITTER
                          SLOPE 2-8S

                                             (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.

                                                (a) HtmUUC
                                             FLODOIH6 DASIIIS
                                                                          RECOVERED 1UER
                                                              PERCOLATION   I  ' r  \
                                                            (UNSATURITEO ZONE)  IELL

                                                 (b) RECOURt PJTHim

                                                                          FLOOOINC HSIN
                                         (c)  NUTlim ORHIU6E INTO SttlFHE ITERS
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
.   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,

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

  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
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,

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.

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

                                                 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

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.
Kg of BOD
 applied per day
Area loaded

Cycle time

= 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)
BOD loading (kg BOD5/had)a
Slow Rate (SR)
Soil Aquifer Treatment (SAT)
Overland Flow (OF)	
        50 - 500
                                                           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.,

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

                                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)

Hydraulic Loading (m/yra)
                                                     Applied (mg/L)
              Soil Water Drainage (mg/L)    Sample Depth (m )
Hanover, NH
San Angelo, TX
Yarmouth, MA
Lake George, NY
Phoenix, AZ
Hollister, CA
Hanover, NH
Easley, SC
Davis, CA	
am/yr x 3.28 = ft/yr.
bm x 3.28 = ft.
cGiggey etal., 1989.








Table 2-3.  Suspended Solids Removal at Land Treatment Systems (adapted from Leach et al., 1980 and Crites et al., 2000)
                                                          Soil Water Drainage - Total suspended solids, mg/L
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)

20 - 100



"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,

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

    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

  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
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)


etal., 1995)
Virus concentration
Concentrated type 3 polio virus
Soil water drainage at
sample point

Table 2-5. Aerosol Bacteria at Various Sources (Reed et al., 1995)
                                 Downwind distance, m (ft)
              Total aerobic bacteria, #/m
                            Total coliform bacteria, #/m
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
30 (1 00)
45 (1 50)
9-30 (30-1 00)
1 1 .2 (396)
80 (2,832)
2.4 (83)
0.6 (23)
2.1 (73)
0.006 (0.2)
0.23 (8)
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
             2.6.1  Micronutrients

               Several metals are micronutrients that are considered
             essential for plant nutrition, for example:


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

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)
For waters used
on all soil, mg/L
For use up to
20 years on
fine-textured soils of
pH 6.0 to 8.5, mg/L
 "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
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)
                             Groundwater concentration
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.
                                                                                       Plant Uptake
                                                       N-     \Nitnncation
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)
Dickinson, ND
Hanover, NH
Roswell, NM
San Angelo, TX

Calumet, Ml

Ft. Devens, MA
Hollister, CA
Phoenix, AZ

Ada, OK (raw wastewater)





(primary effluent)
(secondary effluent)
Easley, SC (pond effluent)
Utica, MS (pond effluent)
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

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
                                                           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.

                                                 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)
Unstabilized primary
Aerobically digested
Anaerobically digested
"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/hayr (222 lb/acyr).

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)
(250-1 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
Second year
Third year
And so forth
(300 kg/ha)(0.50)

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)
Hanover, NH
Muskegon, Ml
Tallahassee, FL
Penn. State, PA
Helen, GA
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


Travel distance


Soil water drainage phosphorus


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,
                                                        Example 2.4
                Phosphorus Removal
Px= Po


= 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).
                                                                        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 :

                                                                        Px  = (10mg/L)(e-<48)(2>)

                                                                            = 9.1 mg/L

                                                                        Percolate phosphorus concentration at the

                                                                        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/hayr, 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.

 Solution:        1.  Lifetime crop contribution = (35 kg/hayr)(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) -

= 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]'
          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
Coastal Bermuda grass
Orchard grass
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
Sulfur removed
(kg/ha) Ibs/ac

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/hayr (0.005 lb/acyr)  and in alfalfa  of 0.91 to 1.8
kg/hayr (0.81 to  1.6 lb/acyr) 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
Sugar beets
Sweet clover
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).

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

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.


= [(EC),/(EC)D]x100
= leaching requirement as a percent
= average conductivity of irrigation water (including natural
precipitation), mmho/cm
= required conductivity in drainage water to protect the crop,
                                                     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,
                                         Electrical Conductivity ECD,
                                                     Bermuda grass
                                                     Sugar beets
                                                     Tall fescue
                                                     Orchard grass
                                                       Once  the  leaching  requirement  (LR)  has  been
                                                     determined the  total water  application  can then  be
                                                     calculated with Equation 2-6.

                                                             = (CU)/(1 -LR/100)
                   = required total water application, inches
                   = consumptive water use by the crop between water
                   applications, inches
                   = leaching requirement (as a percent)
                                                      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

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

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 =




          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
  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)

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)
PCB 1242
Calculated K'M for Eq. 2-12,
            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
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
           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.

= overall rate constant for combined volatilization and
= 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)
PCB 1242
2.4 x 103
7.1 x 103
3.8 x 105
2.3 x103
2.2 x 104
Vapor pressure0
7 x 1 0'4
4x 10"4
8.28 x 1 0'2
2.03 x 1 0'4
a. Octanol-water partition coefficient.
d. Molecular weight, g/mol.
                        b. Henry's law constant, 105 atm(m/mol) at 20C and 1 atm.
                     c. Vapor pressure at 25C.

Table 2-17. Percent Removal of Organic Chemicals in Land Treatment Systems (Reed et al., 1995)
PCB 1242
Sandy soil
Silty soil
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,

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,

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,

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-

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,
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,

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.

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-

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
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.


  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,

  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.

                                                    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
Moderately fine
3.2.1 Basic soil textural
class names
Loamy Sand
Sandy loam
Fine sandy loam
Very fine sandy loam
Silt loam
Clay loam
Sandy clay loam
Silty clay loam
Sandy clay
Silty clay

  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.

  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

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
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

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

  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

  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

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

  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.

          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














- .-




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
Easily ribbons out
between fingers,
has slick feeling

Forms a ball,
ribbons out
between thumb and

Somewhat pliable,
will form a ball
when squeezed

Hard, baked,

1 .9-2.5
Medium texture

Same as fine

'I. P-0 IIII1
Forms a very
pliable ball,
sticks readily if
high in clay

Forms a ball,
sticks slightly
with pressure

crumbly but hold
together from
. 1:0-1.5 II
Powdery, dry,
slightly crusted
but easily
broken down
into powdery
Same as
fine texture

weak ball,
easily, will
not stick

Tends to
ball under
but will not
dry, will not
form a ball

I 0.8:1.2
Dry, loose,


Same as fine

slightly, may
form a very
weak ball
Appears dry,
will not form
a ball when

Appears dry,
will not form
a ball

Dry, loose,
grained flows

* 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
                                                             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
Ky. ft/d
3x 10'8-0.03
66 - 300
330 - 3300
  The conductivity of soils at saturation is an  important
parameter because it  is used in Darcy's equation  to

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,
Table 3-4.  Measured Ratios of Horizontal to Vertical Conductivity
              Horizontal conductivity Kh, m/d (ft/day)
75 (246)
1 00 (328)
72 (236)
72 (236)
86 (282)
Near terminal moraine
Irregular succession of sand and gravel layers (from
measurements in field)
(From analysis of recharge flow system)
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:
        Where Kam = arithmetic mean vertical conductivity

  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 = 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  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
                                                             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
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:

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



Figure 3-7.  Mounding Curve for Center of a Square Recharge Area
(Bianchi and Muckel, 1970).
a = aquifer constant = ^,ft2/d                        (3-7)

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.

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

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).

                   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,

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

6.   The rate of replenishment (wastewater application
    plus natural precipitation) is Lw + P.

To determine drain placement, the following equation is
useful (Luthin, 1978):
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
        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,

  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.

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

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.
3.8.3 Flooding
Cylinder infiltrometer
Sprinkler infiltrometer
Air entry permeameter
3.8.2 Water
per test, L
1 ,000-1 ,200
Time per
test, h
Equipment needed
Backhoe or blade
Cylinder or earthen berm
Pump, pressure tank
sprinkler, cans
AEP apparatus,
standpipe with reservoir
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.

                Groove cutting too!
                                    Handle ,
    Center rod
Figure 3-14. Grove Preparation for USAGE Test.

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

  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.

                  / 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
   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.
                       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).

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

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
    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

15. Calculate the saturated hydraulic conductivity Ks as

         2(dHldt)LR?                             (3-10)
     s  Ht+L-0.5PaRc

    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

"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
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


-* r  -

Soil Surface
Water Table ^
W 1




 //////////// Impermeable'Layer'

Figure 3-20. Definition Sketch for Auger Hole Technique.

                                   - Measuring point

                                      - Standard
                       /          Y

 Exhaust hose
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):
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

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:
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-
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.

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
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.
Withers, B. and S. Vipond  (1987)  Irrigation Design and
    Practice, Second Edition. Cornell University Press,
    Ithaca, NY.

                                             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

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
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
 I 0.2
       Stage 1
                     75    100    125
                        Time, hours
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

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
  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
Table 4-1.  Range of Seasonal Crop Evapotranspiration
ETc, in
ETc, in
Deciduous trees
Grains (small)
Sugar beets
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
                                                               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)

Paris, TX
Central, MO
Jonesboro, GA
Seabrook, NJ
Hanover, NH
Brevard, NC

Table 4-3.  Example Evapotranspiration Values for Southern San Joaquin Valley of California (Burt, 1995)
                                         Evapotranspiration Rate, Millimeters/Month (Inches/Month)


orchard w/o
cover drop


orchard w/
cover drop


Small Grains

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
Medium, 40-70
High, >70
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.,

  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-
  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,

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

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






Pasture grass


Sugar beets


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)
Grain, small
Sugar beets

Table 4-5. Crop Coefficient, Kc, for Perennial Forage Crops
(Doorenbos and Pruitt, 1977)

Grass for hay
Clover, grass legumes
Humid, light
to moderate


Dry, light to
moderate wind


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
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
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

  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

Plant Part
50 bu
1 Ton straw
30 bu
0.5 Tons straw

                                              Typical Yield/acre-yr
Percent of Dry Harvested Material
urop ui






Oil Crops

Oil palm





Fiber Crops


Forage Crops
Big bluestem
Birdsfoot trefoil
Little bluestem
Red clover
Tall fescue
Northern hardwoods
Douglas fir
Fruit Crops
ry vveignt ID/DU











Plant Part
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
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


















Silage Crops

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
Sugar beets
All types
Turf Grass
Vegetable Crops
Bell peppers
Beans, dry
Lettuce (heads)
Snap beans
Sweet corn
Sweet potatoes
Table beets
Wetland Plants
Water hyacinth
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







Percent of Dry Harvested Material















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

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)
                        Effective rooting depth, m (ft)
Deciduous Orchard
Grains, small
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.


  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

  Table 4-8. Grasses Used at Overland Flow Sites (US EPA, 1973)
                                                                      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
            I  200

                                                                     Orch ardgrass
        Reed Canarygrass
        and Corn
                                                                                      Rye and Corn
                                        L>1 _
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  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

Table 4-9. General Effects of Trace Element Toxicity on Common Crops (Kabata-Pendias and Pendias 2000)
                                                                                Sensitive Crop
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
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
Chlorotic and necrotic leaf tips, interveinai chlorosis in new leaves, retarded growth
of entire plant, injured roots resemble barbed wire. _

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.

No specific crop
No specific crop
No specific crop
                                                                                Cereals and spinach.

  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).


  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.


                                                       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.

  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
 fi. Barley hay
 u Pe/ennial rye
 ft l.i: J';:;:.''..

   Birdsfoot trefoil
   Beardess wildrye

 [ Cabbage
 . ".. v L'-['i:"..!':j
  Rf-\ pepper

  Grn 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)
Dalton, GA
Clayton, Co., GA
Helen, GA
St. Marys, GA
Mackinaw City, Ml
State College, PA
West Dover, VT

Design Flow, mgd

Tree Types
Loblolly pines,
Mixed pine and
Slash pine
Aspen, birch,
white pine
Mixed hardwood,
balsam, hemlock,

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
Sweet clover
Buffalo grass
Wheatgrass (tall)
Garder beets
Sugar beets
Spinach White clovers
Red clovers Carrots
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
Bent grass (except creeping)
Fescue (red & sheep's)
Western wheat grass
Poverty grass
eastern gamagrass
Love grass, weeping
Redtop grass
Napier grass
Trees & shrubs
Currant Tulip tree
Ash Lilac
Beech Yew
Sugar maple Lucaena
Poplar Ponderosa pine
Red oak
Birch Andromeda
Dogwood Willow oak
Douglas fir Pine oak
Magnolia Red spruce
Oaks Honey Locust
Red cedar Bitter hickery
Hemlock (Canadian)
Flowering cheery
American holy
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
Range of
acid soils

' ) Ji


Slightly acid
and slightly
alkaline soils
* 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.

  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
Lake states forests:
Mixed hardwoods
Hybrid poplar3
Western forests:
Hybrid poplar3
Douglas fir plantation
Tree Age,
Average Annual
Nitrogen Uptake
  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,

  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

  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.

  Table 4-12. Biomass and Nitrogen Distributions by Tree Component for Stands in Temperate Regions (US EPA, 1 981 )
  Conifers, %
                                                                                       Hardwoods, %
Tree component
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
                      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)
        Very Sensitive (<1.5)
      Annual bluegrass
      Colonial bentgrass
   Rough bluegrass
    Moderately Sensitive (1.6 - 3.0)
     Kentucky bluegrass
   Most zoysia spp.
    Moderately Tolerant (3.1 - 6.0)
     Creeping bentgrass
      Fine-leaf fescues
     Blue grama
   Annual ryegrass
        Tolerant (6.1 -10.0)
      Seaside bentgrass
   Common bermudagrass
        Tall Fescue
      Perennial ryegrass
Zoysia japonica (some)
Zoysia matrella (some)
     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.

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

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.

Table 4-14. Pasture Rotation Cycles for Different Numbers of Pasture Areas
      Number of Pastures
                                   Rotation Cycle
     Regrowth Period
Grazing Period
  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

  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

    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.

US EPA  (1981)   Process  Design  Manual:  Land
    Treatment of Municipal Wastewater.  EPA 625/1 -81 -

USGA    (1994)  Wastewater Reuse  for Golf  Course
    Irrigation.  Lewis Publishers.

                                                  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

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
  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


[ 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)
Concentration, g/m (mg/L)
Suspended Solids
Nitrogen, total
  Organic nitrogen
  Ammonia nitrogen
Phosphorus, total

  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
Concentration, g/m3 (mg/L)*
Suspended Solids
Total fixed dissolved solids
Total nitrogen
pH, units
Temperature, C	
      200 - 33,000
      200 - 3,000
'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
     Loading Rate,
   mm/week (in/week)
Slow rate
Soil Aquifer Treatment
  Primary effluent
  Secondary effluent
Overland flow
  Screened wastewater and
   primary effluent
  Secondary effluent	

       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

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
.   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 0C or greater
    than  or equal to 32.5C

  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

                                 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)
                                F = 13443   (U.S. customary)

         =   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
                                 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
                                    Data Required
Annual average, maximum,
                                                                                    Water balance
Rainfall storm
Intensity, duration
Days with average below freezing
Velocity, direction
Annual, monthly average
Frost-free period
Annual distribution
Runoff estimate
Storage, treatment efficiency, crop
growing season
Cessation of sprinkling
Water balance

 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)

                            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)

Applying screened wastewater
0.0096 (90)
0.021 (200)
0.024 (225)
0.027 (250)
0.029 (275)
0.037 (350)
0.036 (335)
0.0032 (30)

Applying secondary effluent

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
 Soil type and permeability
 (mean monthly and growing season)	
 (mean monthly, maximum monthly)	
 Evapotranspiration and evaporation
 (mean monthly)	
 Land Use

 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	

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
.   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.


  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
Forest Slow Rate
Moderately high
Very low
Overland Flow
Very low
Soil Aquifer Treatment
Very low
Table 5-8.  Grade Suitability Factors for Identifying Land Treatment Sites (Moser, 1978)

                                  Slow Rate Systems
Grade Factor, %
Very low
Overland Flow
Soil Aquifer Treatment

  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

  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).
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


  Common soil-texture terms and the relationship to the
NRCS textural  class  names are  listed  in  Table 5-9

  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
Moderately coarse
Moderately 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

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.

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.

  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

  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
Permeability class range
Textural class
Unified soil classification
Slow Rate
(0.06 - 2.0)
Moderately slow to moderately
Clay loams to sandy Loams
GM-d, SM-d, ML, OL, MH, PT
Soil Aquifer Treatment
(> 2.0)
Sandy and sandy loams
Overland Flow
(< 0.2)
Clays and clay loams
GM-u, GC, SM-u, SC, CL, OL, CH,

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

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
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

  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

  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.,

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

  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

5.4   Phase 2 Planning

  Phase 2, the site investigation phase, occurs only if
sites with potential  have  been identified  in Phase 1.

During Phase 2, field investigations are conducted at the
selected  sites to  determine  whether land treatment is
Table 5-11. Rating Factors for Site Selection (Taylor, 1981)
                                              Slow Rate Systems
Soil depth, ft*(a)
1 -2
> 10
Minimum depth to groundwater, ft
Permeability, in/h*(b)
Grade, %
Existing or planned land use
High-density residential/urban
Low-density residential/urban
Agricultural or open space
Overall suitability rating5
Overland Flow
Rapid Infiltration
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)
                                       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

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)
                               Rating Value*
Depth to groundwater on barrier, fta
Depth to bedrock, fta
Type of bedrock
Exposed bedrock, % of total area
1 -10
*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)
Infiltration rate, in/ha
Hydraulic conductivity, in/ha
CEC, meq/100g
> 15
Shrink-swell potential (NRCS)
Erosion classification (NRCS)
Severely eroded
Not eroded
*5-11, poor; 12-16, good;
ain/h x 2.54 = cm/h.
Rating Value*

and 17 -21,
Dominant vegetation
Hardwood or mixed
Vegetation age, years
Mixed pine/hardwood
Slope, %
Distance to flowing stream, fta
Adjacent land use
High-density residential/urban
Low-density residential/urban
*3 -4, not feasible; 5-9, poor;
15-19, excellent.
aft x 0.3048 = m.
Rating Value*
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

                                                              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.

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
Hydraulic Loading, in/week3
Not feasible
< 1.0
< 1.0
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
Information to
Estimates now

Additional field
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

Vertical conductivity
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
                            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

Specific data relating to crop
and soil management,
phosphorus and heavy metal
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
                      Slow Rate
                                                                    Soil Aquifer Treatment (SAT)
                                                               Overland Flow
Wastewater constituents
Soil physical properties

Soil hydraulic properties

Soil chemical properties
           Nitrogen, phosphorus, SAR*, EC*,
           Depth of profile, texture and
           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
                           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

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

  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)
Depth of soil profile, fta
    <1 -2
Texture and structure
    Fine texture, poor structure
    Fine texture, well-structured
    Coarse texture, well-structured
Infiltration rate, in/hb
Subsurface permeability
    Exceeds or equals infiltration rate
    Less than infiltration
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
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

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
pH of saturated soil paste
CEC, meq/100 g
    1 -10
Exchangeable cations, % of CEC (desirable range)
ESP, % of CEC
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)

Reduced permeability in fine-textured soils
Reduced permeability in coarse-textured soils
ECe, mmhos/cm at 25% of saturation extract
    > 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

Table 5-21. Textural Properties of Mineral Soils
     Soil Class
                                                             Feeling and Appearance
                                      Dry Soil
                                                                                        Moist Soil
Sandy Loam
Silt loam
Clay loam
 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
 Aggregates are firm but may be crushed under
 moderate pressure. Clods are firm to hard.
 Smooth, flourlike feel dominates when soil is
 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
 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

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
                                               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).

Table 5-23. Description of Soil Mottles (US EPA, 1980)

2% of exposed face
2 - 20% of exposed face
20% of exposed face

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 8
Texture Structure Color Soil Saturation
Silt Loam
Silly Clay
	 J^fiB.01  _
Clay Loam


Granuiar I




Gray and
Red Patches,

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

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
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
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.

                     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
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,

Mixing of Wastewater Percolate with
  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:

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

  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

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

  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

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

  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
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.

  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
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)

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.

                      100        1000
                       Field area, acres
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.


  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.
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,

 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
         100-ft spacing                      52
         400-ft spacing                      22
         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
 0.1 mgda of Recovered Water
  Capital, $
   Power, $/year
   Labor, $/year
   Materials, $/year
 1.0 mgd of Recovered Water
  Capital, $
   Power, $/year
   Labor, $/year
   Materials, $/year	



                                                                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.,
ENR CCI = 6076
Type of Cost
Capital costs:
Gravity pipe system
Open ditch system
O&M costs:
Gravity pipe
Open ditch
Gravity pipe
Open ditch



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
1.0 mgd of recovered water:
Capital, $:
  50 ftb depth
  100 ft depth
O&M, $/yr:
  Power, 50-ft depth
  Power, 100-ft depth

 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

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 =

Energy Use
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
900,000 - 1 ,000,000
58,000 - 71 ,000
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
Bakersfield, CA
Camarillo, CA
Dickinson, ND
Lubbock, TX
Mesa, AZ
Muskegon, Ml
Petaluma, CA
Roswell, NM
San Antonio, TX
Tooele, UT
Area, acres3
1 0,400
Acquisition Option
Fee simple
Fee simple and contract
Fee simple
Fee simple
Fee simple
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.

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
Ponds and wetlands
PT + SR(surface)
Ponds and hyacinths
PT + SR(spray)
Primary Energy
Secondary Energy
Total Energy
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
Nitrogen as N
Phosphorus as P
Potassium as K
Content of effluent,
Content of effluent,
Energy to produce, transport and
apply fertilizer, kWh/lb
Energy value of nutrients in wastewater,
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.

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,

Middlebrooks,  E.J.  and  C.H.  Middlebrooks   (1979)
    Energy Requirements for Small  Flow  Wastewater
    Treatment  Systems,  USA CRREL,  Special Report

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-

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.

                                               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

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,

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

  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).

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
    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

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:
     effluent BOD5 from cell n, mg/L
     influent BOD5to system, mg/L
     reaction rate constant (see Table 6-2) at 20C
     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/
kcT      = reaction rate const, at temperature T
k20      = reaction rate const, at 20C (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:
 Af + 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 20C
                                                        Complete mix
                                                        Partial mix
                                                          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
           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.
                                                                = e - Kft


= 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)
kp, per day
*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).

  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

  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 =
= 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 20C
= 1.104 d'1 for SF wetlands at 20C
= 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 1C or less, assume  that
                                                    denitrification effectively ceases.
                                                    f = -
       = 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 20C
  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


         effluent total N, g/m3 (mg/L)
         influent total N, g/m3 (mg/L)
         temperature-dependent reaction rate const., d"1

= 0.0064 at 20C
= 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):
     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

  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) ]
= median pH in the bulk liquid
= alkalinity of the influent (as CaCO3), g/m3 (mg/L)
Peterborough, NH
Eudora, KS
Kilmichael, MS
Corinne, UT
Annual Median pH
Annual Average
g/m3 (mg/L)
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).

  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)
                                            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
Haifa, Israel
(summer, 35 days):
Total coliform
Fecal coliform
Fecal streptococcus
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
1 x 103
2.4 x103
5.0 x102
2.3 x104
2.4 x104
3.7 x103
                     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 =
= actual detention time, d
= influent fecal conforms, #/100 ml
= final fecal coliforms, #/100 ml
= rate constant, use 0.5 for temperature of 20C
                                                                                        Final concentrations
                                                                                       . ZOO/100 mL
                                                                        Initial concentration = 107/100mL
                                                                              Time, days
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.

6.2.7   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

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)
                                                 Type of Membrane
                                                UF          NF
Biodegradable organics
Heavy metals
Priority organic pollutants
Synthetic organic compounds
                    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
                                                                               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

  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

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)
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.	


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.


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:
                                                                W, =
                                                                     40,000 m3
                                                                      30.4 ha   10,000 m
                             100 cm
                                                                                                = 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.
                                                                Required Storage Volume =  (23.9 cm)(30.4 ha
                                                                                                     100 cm
                                               = 72,656 nf

Table 6-7.  Estimation of Storage Volume Requirements Using Water Balance Calculations

* Maximum storage month.
6.3.2 Final Design

l_w, crn

of Storage

Wm, m3


Wa, cm

72,656 m3
Change in Storage,
cm (3)-(2)

= 1R1R4 m2
Cumulative Storage,


  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 6-2.  Calculations to Determine Final Storage Volume
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.
1.   Using the initial estimated storage volume and  an assumed
    storage pond depth  compatible with local conditions, calculate a
    required  surface area for the storage pond:
As      = area of storage pond, m2
Vs(est)   = estimated storage volume, m3
ds      = assumed pond depth, m
For example, assume ds = 4 m
        4 m
    Calculate the monthly net volume of water gained or lost from
    storage due to precipitation, evaporation, and seepage:
     =  (P, -E-S\AS
                    100 cm
AVS = net gain or loss of storage volume, m3
Pr  = monthly precipitation, cm
E   = monthly evaporation, cm
    = monthly seepage, cm
= 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.

      (Lw\ 10,000^ I
           ha ,
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|0.01I
  v      \     ha k   cm
                              = 28.4 ha
                                                                  Note:  The final design calculation reduced the field area from 30.4 ha
                                                                  to 28.4 ha.

    Calculate the monthly volume of applied wastewater using the
    design monthly hydraulic loading rate and adjusted field area:
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)
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


ET, cm


Pr, cm

gain/loss, m3
-1 ,835
-1 ,253


Vw, m3

AVS, m3 (3)+(4)-(5)

Storage, m3
31 ,840

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

  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)
   = storage volume, m3 (million gallons)
   = average daily flow during winter, m /d (mgd)

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

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

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

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

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

  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

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

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,

Reed,  S.C., R.W.  Crites,  E.J.  Middlebrooks  (1995J
    Natural  Systems   for Waste  Management  and
    Treatment, Second Edition,  McGraw-Hill, New York,

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,

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.

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,

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,

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,

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,

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.

                                                        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.
Surface Irrigation

Wild Flooding



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
                                         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

 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
 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

  The principal limitations or disadvantages  of surface
systems include the following:

1.   Land leveling costs may be excessive on uneven
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.

  Table 7-2.  Sprinkler System Characteristics
Typical application
rate, in/h
Labor required per
application, h/acre
Nozzle pressure range,
Size of single system,
Maximum grade, %
Solid Set
30-1 00
No limit
No limit
End tow
Side roll
Stationary gun
Continuous move
Traveling gun
Center pivot
Linear move
0.25-1 .0
0.25-1 .0
0.25-1 .0
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:

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

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:


         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
Q = CAaD/ta

                                                                     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.
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.

  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
                                          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
  Medium sandy-silt loam-uniform                    36
  Medium sandy-silt loam-over more compact           40
  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,
                                          Average depth of wastewater applied, in1
% 3
0.05 1000
0.2 1200
0.5 1300
1 .0 920
2.0 720
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
qe =  C/G
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

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).

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

  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,
Grade, %
Unit flow per foot
of strip width,

Average dept of
water applied, in

Border strip, ft
0.4-1 .6
40-1 00
Loamy sand
40-1 00
Sandy loam
40-1 00
Clay loam
600-1 000

 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
Clay, 24 in
deep over
Loam, 6 to
18 in deep
over hardpan
Grade, %
1 .5-4.0

1 .5-4.0

1 .0-4.0

Unit flow per foot of strip
width, gal/min



Average depth of
water applied, in






Border strip, ft



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

  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
ta = LD/Cq


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

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
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

  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
                               Distance Along Strip
Figure 7-3. Equal Opportunity Time Along Entire Strip (Burt, 1995).

                           Distance Along Strip
                                                                     No Runoff- Water ponded

                                                                     at lower end
Figure 7-4. Greater Opportunity Time at Head of Strip: Flow Rate Too Small (Burt, 1995).

                                   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
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
      2.   Select border width and length from Table 7-6
          for design conditions for shallow-rooted
          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
                 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

               5.   Determine number of applications per day
                   assuming a 12 h/d operating period.
                   Number of applications =12 h/d/0.83
                   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^
                   = (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

  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

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 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
                      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
                      R = qsC/SsSL
         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
                                  rate reduction
Over 20
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

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.,

        Wind Speed
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
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

1.   Determine design application rate, R.
    Assume an 8 h application period.
    R = D
    t=  2 in
    = 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
Value of F
                    = 2 in/8 h
                3.   Calculate required sprinkler discharge
                    rearranging Equation 7-7.
                    qs = R S;SL
                    qs = (0.25)(60)(60)
                    = 9.3 gpm

                4.   Select sprinkler nozzle size, pressure, and
                    wetted diameter to provide necessary
                    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
                                                                                                     = 48%>40%

                   Lateral spacing, SL = 60
                                 = 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
               7.   Determine system flow capacity, Q.
                   Q = AaR = (10acres)(0.25in/h)(27,154
                   gal/acrein)( 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

  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)
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

design OF application rate  and the above criteria for
overlap, a sprinkler can be selected from a manufacturer's

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.
             (I) -PORTABLE HAND IOVED
                                      (b)  END  TOW
                      HEEL-SUPPORTED LATERAL
                      ITH  MULTIPLE SPRINKLER
                                   LATERAL IITN  SPRINKLER
                (c)  SUE  WHEEL IOLL
                                 (d)  STATIONAIT  GUN
Figure 7-8. Move-Stop Sprinkler Systems.

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

  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

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

                                                                FLEXIBLE SUPPLY
          DRIVE  UNI
             HOSE  J
       GUN CART
                                              (b)  TRAVELING GUN (REEL-HPE)
                                                                         FLEXIBLE HOSE
             (c)  CEMTER  PIVOT
      (d)  LINEAR MOVE
Figure 7-10. Continuous Move Sprinkler Systems.

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

                        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)
                        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.
                        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
      Wind speed, mi/h
                                     Lane spacing,
                                   . of wetted diameter

    Calculate the travel speed using Equation 7-9 as rearranged:
            Sp = 1.6d;

    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

 11.  Determine the system capacity, Q
    Q = (qs)(number of units)
Example 7-3: Establish Preliminary Design Criteria for Reel Type
Traveling Gun System
                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)
                = 0.24 in./h ( < 0.4 in./h, OK)
                    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
                = 0.5 ft/min
                8.   Calculate the area covered by a single unit
                A =  (240)(0.5)(15h)(-h)(10d)
                = 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

 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

  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

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

          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
                                 ELLIPTICAL APPLICATION
                                 RATE PROFILE
Figure 7-14. Intersection Between an Elliptical Moving Application
Rate Profile Under a Center-pivot Lateral and a Typical Infiltration
  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,
                                                               Figure 7-16. Comparison of Relative Application Rates Under Various
                                                               Center Pivot Sprinkler Packages.

  The flow capacity of a center pivot system is given by
Equation 7-10.
Q =  1,890 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

          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
                                     Storage (in.)
1 % - 3%
3% - 5%
  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    =   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.
Tcr=  2nL
   60 (WJ

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
  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
                                                                Figure 7-17. Anticipated Center Pivot Performance versus Soil
                                                                  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

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	
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

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.

                                          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
.   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

     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
  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	
                            Moderately High
                            Moderately Low
                            Very Low	
*Not recommended for use in any wastewater irrigation system.

 7.5.6  Submain, Manifold and Lateral

  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

  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

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

 7.5.11 Chemical Treatment  to Prevent

  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

  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

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

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

3960  =
e    =
         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.

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
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
Texture range
Clay to clay loam
Clay loam to silt loam
Silt loams to sandy
Maximum duration of
tailwater flow, % of
application time
Estimated tailwater
volume, % of
application volume
Suggested maximum
design tailwater
volume, % of
application volume
 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

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.

                                                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)

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-
  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
       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 0C (32  F). A
       less conservative, but acceptable, approach is to
       use  a  lower  minimum   temperature.  The
       recommended  lowest  mean  temperature for
       operation  is -4C  (25F).  For forested sites,
       operation can often continue during subfreezing

        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

  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     =     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

A =  Q/C Lh                                           (8-3)

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

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.
  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]
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
          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
             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
                  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.

 Table 8-1. Nitrogen Loss Factor for Varying C:N Ratios
C:N ratio
Food processing wastewater
Primary treated effluent
Secondary treated effluent
Advanced treatment effluent
0.25 - 0.5
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  =

 Table 8-1)

 U  =
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).
                                                  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

  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
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):
    L  Z-LR
C   =
ca  =
LR  =
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
                                                                                  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


  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.
                                                                                     Total pore space = 42%
                                                                                     Field capacity = 0.18 mm/mm
                                                                                     Steady state infiltration = 18.3
Waste Stream
Flow = 3,785 m3/d (1.0 mgd)
Nitrifiable ammonia  = 4 mg/L

Total nitrogen = 15 mg/L
EC = 1.2 dS/m

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

40 mg/L + 4 mg/L x 4.56 = 58.2 mg/L TOD

  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 =    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.

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

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

  Table 8-1 is 0.25. Table 4-9 lists the average N
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.


  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.

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
Winter Wheat 30 Acres



Sudan J 90 Acres


1 5.8
1 4.2
31 .0

Figure 8-2. Example Spreadsheet Used to Calculate the Irrigation Requirements Including Irrigation Efficiency and Teaching Requirements.

                  Are Associated with Columns
      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
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.

                                             (Chapter 2)
     (Chapter 5)
                                                                        PROCESS PERFORMANCE
                                                                              (Chapter 2)
                                    PREAPPLICATION TREATMENT
                                            (Chapter 6)
     (Chapter 4)
                                                                            LOADING RATES
                                                                              (Chapter 8.2)
                                            (Chapter 6)
     (Chapter 8.2)
                                                                              (Chapter 7)
                                      DRAINAGE AND RUNOFF
                                            (Chapter 7)
                                         SURFACE WATER
Figure 8-3.  Slow Rate  Design Procedure.
  (Chapter 2)


(Chapter 8.6)

(Chapter 8.6.8)

  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

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:
         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

  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

  The  personnel responsible  for  operating  the  land
application system often conduct monitoring. During site

 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

 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
                            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
       Field-by-Field Loadings
            Soil Testing
           Crop Sampling
      Routine Inspection Needs
Total daily flow (gallons)
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)

operations  monitoring,  sampling  in   more  than  one
location  within  a  distribution  system  is  performed  to
evaluate  changes   or  problems  such   as   uneven
  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
                                            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
Table 8-3.  Suggested Minimum Effluent Monitoring
                                                                                              Water Quality
Lagoon or storage
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
          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

          Constituent loading can be calculated from flows and
          constituent concentrations
Pumps and pipelines
   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
Intrusive flow
Non-intrusive flow

Open channel flow

Incoming water
supply correlation

Pump run time and
output calculation
In-field methods
Impeller, paddle wheel
Hot wire anemometer

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
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
Primarily applicable to sprinkler irrigation systems or surface
irrigation using siphon tubes or gated pipe	
                                              Measures net irrigation (amounts actually applied) rather than gross
                                              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	

  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

  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
.   Assessment of the land application site condition
  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

Table 8-5.  Soil Monitoring Parameters
                             Sampling considerations
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
   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

Table 8-6. Vadose Zone Sampling/Monitoring Alternatives
Soil Sampling
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
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
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

  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.

Table 8-7. Example Crop Monitoring Parameters
Crop management chronology
Biomass removed
Constituents removed
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
                                                                                             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,

                                     US EPA. (1995). Groundwater Well  Sampling, Standard
                                         Operating Procedure 2007.

                                                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)

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

  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
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

  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

  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

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(-)
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

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).
         Family of lines represent
         different application
         rates. m3/h  m
                        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.

  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
Hanover, NH
Ada, OK
Easley, SC
Applied Wastewater
Application Rate
BOD5 Concentration (g/m3)0
Slope Length (m)b
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
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
BOD Concentration (g/m3)0
Slope Length (m)b
 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)
Screening/ primary
Aerated cell
(1-day detention)
Stringent Requirements
and Cold Climates*
Moderate Requirements
and Climates*
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)
'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.
= 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)

 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 4C (39F) will limit the nitrification
  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  70F).  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)
Mar. - Oct.

Nov. - Feb.

Application Rate (mj/h m)a
  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 =

A   =
Q   =
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 = -
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

 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
8C (50F), 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):
BOD =0.22672-6.53r + 53
  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 3.9C (39F) 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
0C  (32F) but daytime air temperatures  exceed 2C
(36F), 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).

 9.4.4  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-

  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

  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

  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

over 2.5 cm (1 inch)  in depth,  then  field traffic should

  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.

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:

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,

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

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

Smith, R.G. and E.D. Schroeder (1983)  Physical Design
   of Overland Flow Systems,  Journal WPCF, 55(3):

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.

                                               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
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
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,
              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)
                      Applied Wastewater BOD,
Applied Wastewater BOD,
Percolate Concentration,
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 .
Boulder, CO
Brookings, SD
Calumet, Ml
Ft. Devens, MA
Hollister, CA
Lake George, NY
Milton, Wl
Phoenix, AZ
Vineland, NJ
93 - 1 00

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 30C to 35C (86F to 95F). Both processes
proceed slowly between 2C and 5C (36F and 41 F)
and  stop near 0C  (32F).  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/ =
N    =   change in total nitrogen, g/m3 (mg/L)
TOC  =   total organic carbon in the applied wastewater, g/m3

  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

Ib/ac d) range. Ammonia will be retained in the upper
soil profile when temperatures are too low [below 2.2C
(36F)] 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
Calumet, Ml
Dan Region, Israel
Ft. Devens, MA
Hollister, CA
Lake George, NY
Phoenix, AZ
W. Yellowstone, MT
and total nitrogen are presented in Table 10-2. To
determine the nitrogen loading rate from the hydraulic
loading rate, use:
, LCF (10-2)
" D
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, %
'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.
Conversion units: 1 mg/L = 1 g/m3;
1 ft = 0.305 m.
10- 30


6.5 - 60

Horizontal Renovated Water, mg/L
850 - 1 700

0.1 -0.4
< 1

Removal, %


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
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
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

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

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
Table 10-5. Typical Wet/Dry Ratios for SAT Systems (Crites et al., 2000)
                        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
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

  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)
 Actual Annual Loading Rate,
                                                                         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
        78 - 118


Conversion unit: ft = 0.3048 m.

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)
0.0001 =
3.06   =
application area, ha (acres)
average design flow, m3/day (mgd)
annual hydraulic loading, m/yr (ft/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
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
         Application period*, days
Drying Period, days
Maximize infiltration rates
Maximize nitrogen removal
Maximize nitrification
1 -2
1 -2
1 -3
1 -3
1 -2
1 -2
1 -2
1 -2
1 -3
1 -3
Regardless of season or cycle objective, application periods for primary effluent should be limited to 1 to 2 days to prevent excessive soil clogging.

10.5.2 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
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)
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
Cycle Drying
Period, days
Minimum Number of
Infiltration Basins
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

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.

  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.,

  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

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
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).

10.8 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

  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 =
W  =

K   =

D   =
   total width of infiltration area in direction of groundwater flow,
   permeability of aquifer in direction of groundwater flow, m/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
   annual hydraulic loading rate (including rainfall input), m/d
  Examples  of  these   parameters  are  shown   in
Figure 10-1.
                                                        Figure 10-1. Definition Sketch for Lateral Drainage from SAT Systems
  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,

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 I I
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

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).

10.9  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):

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,

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.
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:

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-

   660/2-74-003,    U.S.
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-
                               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,

                               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.

                                            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

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

11.2 Water Quality and  Pretreatment

  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

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.


  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.

Table 11-1.  Characteristics of Various Industrial Wastewaters Applied to Land
                              Food Processing
Pulp and Paper
BOD, g/mj
COD, g/m3
TSS, g/m3
Fixed Dissolved Solids (FDS),
Total Nitrogen, g/m
pH, units
Temperature, C
200 - 3,000
60 - 30,000



90 - 400

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
Conversion units: g/m = mg/L.


  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.

  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.


  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.


  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.


  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.


  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 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.


  High-temperature wastewaters [above 66C (150F)]
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

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
Settling Basin, g/m3
Influent, g/m3
Effluent, g/m3

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.,

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

11.3.1  BOD Loading Rates and Soil

  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.,

  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 16C and  28C (61 F and  82F),
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).

Table 11-4. BOD Loading Rates at Existing Industrial Slow-Rate Systems
                                         Winery stillage
                                         Winery stillage
                                         Tomato processing
                                         Potato processing
                                         Tomato processing
                                         Cheese processing
                                         Potato processing
                                         Tomato processing
                                                                               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)
447 (399)
 103 (92)
 94 (84)
393 (351)
249 (222)
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
                                                                                         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	







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

  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
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

 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.
                                                                                         Percent Removal
BOD, g/mj
COD, g/m3
TSS, g/m3
Total N, g/m3
Total P, g/m3
Chloride, g/m3
pH, units

Conversion units: g/m = mg/L.

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

  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
                                                                                         Percent Removal
BOD, g/mj (mg/L)
TSS, g/m3 (mg/L)
pH, units

Source:  Brown and Caldwell files, Sacramento, CA.
11.6.1 Cheese Processing Wastewater in

  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

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
                                   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
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
    Conference, Purdue University, 96: 71.

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
    for a  Study of Spray Irrigation  of Dairy Wastes,
    Proceedings  of   the   12tn   Industrial  Waste
    Conference, Purdue University, 94: 636.

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
    Intermittent Irrigation,  Prepared for Wine Institute,
    San Francisco, CA.

Colovos, G.C. and N. Tinklenberg (1962)  Land Disposal
    of Pharmaceutical Manufacturing Wastes,  Biotech.
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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
    Federation, St. Louis, MO.

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
    Engineering in the Food Processing Industry, XXVI,
    Santa Fe, NM.

Crites, R.W.,  et al. (1978)  Treatment of Brewery Spent
    Grain Liquor by  Land Application,  Proceedings of
    the  Third Annual Conference on  Treatment and
    Disposal  of  Industrial Wastewater and  Residues,
    Houston,  TX.

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,

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
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Glide, L.C., et al.  (1971) A Spray Irrigation System for
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Guerri,  E.A.  (1971)    Sprayfield Application  Handles
    Spent Pulping Liquors Efficiently, Pulp & Paper,  45:

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   WastewaterCase   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,
    Industrial,   and   Animal   Wastes,   Journal  of
    Environmental Quality, 13 (4): 609-612.

Kobylinski, E.A., Davey, J.W., and Shamskhorzani, R.
    (1995)  Nonbiodegradable Organic Nitrogen is an
    Enigma for Regulations, In: Proceedings of the WEF
    68th Annual Conference and Exposition,  Miami
    Beach, FL, No. 3, pp. 501-511.

Koch, H.C. and D.E. Bloodgood (1959)  Experimental
    Spray Irrigation of Paperboard Mill Wastes, Sewage
    & Industrial Wastes, 31: 827.

Lane, L.C. (1955J Disposal of Liquid and Solid Wastes
    by Means  of Spray Irrigation  in the Canning and
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