Manual 8 • Revised September 1995
$3.25
Soil Suitability and Site Selection
for Beneficial Use of
Domestic Wastewater
Biosolids
OREGON STATE UNIVERSITY EXTENSION SERVICE
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GUIDE TO
SOIL SUITABILITY
AND SITE SELECTION
FOR BENEFICIAL
USE OF
DOMESTIC
WASTE WATER
BIOSOLIDS
J. H. Huddleston
Extension Soil Scientist
Oregon State University
M. P. Ronayne
Water Quality Specialist
Oregon Department of Environmental Quality
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ACKNOWLEDGMENTS
Funding
The preparation and publication of this guide
were made possible by a grant from the United
States Environmental Protection Agency under
assistance agreenlent CP990321-Ol to Oregon
State University. The contents of this document
do not necessarily reflect the views and policies
of the Environmental Protection Agency. nor
does mention of trade names or commercial
products constitute endorsement or
recommendation for use. The EPA reference
number for this guide is EPA-910-B/95-005.
Technical Review
Reviewers whose comments were particularly
helpful in developing the guide. include Bob
Bastian. Bob Brobst. and Dick Hetherington.
EPA: Craig Cogger. Washington State University
Cooperative Extension: John Hart and Jim
Moore. Oregon State University Extension
Service: Lee Sommers and Ken Barbarick,
Colorado State University: Steve Wilson and
Stuart Childs from Cascade Earth Sciences: and
Kurt Leininger from CH M Hill.
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CONTENTS
Chapter 1. Introduction 1
Framework for Evaluating Biosolids Utilization Proposals
Unit Conversions 2
Definitions 2
Chapter 2. Biosolids Characterization 3
Biosolids Characteristics 3
Regulatory Characteristics 8
Chapter 3. Soil Characterization 11
The Roles of Soil II
Morphological Properties 12
Inferred Properties 17
Chapter 4. Site Selection 27
Keys for Rating Soil Suitability 27
How to Use Soil Surveys to Facilitate Site Selection 32
Chapter 5. Crop Management Factors 35
Choice of Crop 35
Nutrient Management 35
Soil Testing 37
Water Management 38
Soil Conservation Practices 38
Monitoring and Record-Keeping 39
Chapter 6. Design Calculations 41
Carryover Nitrogen from Previous Biosolids Applications 41
Sample Calculations 42
Chapter 7. Practical Applications 49
Guidelines for Evaluating Project Proposals 49
Worksheet for Evaluating Biosolids Data 51
Worksheet for Evaluating Soils Data 53
Worksheet for Evaluating Cropping Systems Information 55
Worksheet for Evaluating Issues and Interactions 57
Sources of Information 60
Appendixes 61
A. Technical Aspects of Soil Morphology 63
B. Estimating AWHC 67
C. Sample Clauses for Use in Permits 69
Glossary 73
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CHAPTER 1
Introduction
L and application of treated domestic
wastewater biosolids is beneficial
when it is done in a nianner that
protects public health and maintains
or improves environmental quality. Biosolids are
beneficial recyclable materials that improve soil
tilth and soil fertility and enhance the growth of
agricultural. silvicultural. and horticultural crops.
This guide differs from other publications
on the land application of biosolids because it
emphasizes the soil. Natural processes in the
soil store and release water and nutrients for
plant use, break down organic matter, immobi-
lize metals and organic contaminants, and reduce
the number of pathogenic organisms. Under-
standing these processes requires understanding
soil properties because they control both the
natural processes and the overall suitability of a
site for land application of biosolids.
Interactions among biosolids. soil, crop. and
farm management are also emphasized in this
guide. Under the right conditions, almost any
arable land can be used for the beneficial use of
biosolids. The right conditions, however, depend
on the nature of the biosolids. the properties of
the soil, the kind of crop. the cropping system.
and most importantly. the interactions that
ultimately control the decisions regarding
biosolids application and site management.
Throughout the guide both principles and
practical applications are stressed. Whether
you’re conducting a site evaluation, writing a
permit application, or reviewing a project
proposal, you need a solid base of technical
information and a healthy dose of common
sense. This guide emphasizes principles that will
supplenient your technical information and
provides practical. useful information to add to
your storehouse of common sense.
The objective of this guide is to assist
treatment plant operators. permit writers, and
others involved in biosolids management in the
development, evaluation, and implementation of
plans for the beneficial use of biosolids. The
guide provides needed information, explains
methods of evaluating the adequacy of
information in site studies and project proposals.
and identifies available resources.
The guide cannot, however, provide a
complete prescription for site management.
Because each site represents a unique combina-
tion of biosolids. soil, and farming system. a
unique set of procedures must be prepared for
each combination. In developing site-specific
plans. take advantage of local experience and
knowledge available from agricultural Extension
agents. Natural Resources Conservation Service
(NRCS) district conservationists, agricultural
consultants, and the farmers who will be using
the biosolids.
Framework for
Evaluating Biosolids
Utilization Proposals
Land application of biosolids benefits both
agriculture and society. Agriculture benefits
because biosolids supply nutrients for crop
growth and improve the physical condition of the
soil. Society benefits from the “disposal” of
“waste” in a safe and effective manner. All
biosolids utilization proposals should clearly
indicate how both sets of benefits can be
achieved, while at the same time maintaining
environmental quality and protecting the public
from health hazards associated with pathogens.
metals. organic contaminants, and vectors.
Project evaluation has three components:
I. Evaluating the completeness of the data:
2. Evaluating the accuracy of the data:
3. Evaluating the extent to which the project
accounts for issues and design considera-
tions stemming from biosolids, soil, and
cropping system interactions.
Evaluation of data completeness requires
verifying the data on fertilizer recommendations
and cropping practices as well as verifying that
the chemical and physical characterization of
both biosolids and soil are sufficient to make all
necessary design calculations. The data also
should be sufficient to ensure compliance with
all pertinent regulatory standards. If aiiv of the
required data are incomplete or missing. you
may need to request additional infonnation
before proceeding with the project review.
Evaluation of data accuracy requires
ensuring that both biosolids and soils have been
sampled and analyzed according to approved
procedures and that the data are consistent with
results from similar biosolids and soils analyzed
previously. Confidence in data calculations and
interpretations depends on this assurance. I f the
data are not valid, it is not reasonable to expect
a counts. Extension agent or anyone else to make
reco,nniendations for a bioso lids uti/ization p1mm.
Evaluation of issues and design considera-
tions requires verifying that all calculations
account for all relevant interactions, and that
management decisions reflect the principles
discussed in this guide. Some of the more
important issues include:
1. Ensuring that soil properties and soil
surveys, or on-site investigations, have
been used to help select and evaluate
potential sites:
2. Ensuring that the calculated Annual
Whole Sludge Application Rate
(AWSAR) accounts for all nutrient
interactions in biosolids and soil, and that
it delivers the right amount of nutrients at
the right time for crop utilization:
Elements of
Project
Evaluation
• Completeness of
data
• Accuracy of data
• Assessment of
interactions
Sources
of Local Help
•County Extension
agents
• Natural Resources
Conservation
Service district
conservationists
• Agricultural
consultants
• Farmers and land
managers
ii
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3. Ensuring that the timing of biosolids
applications accounts for any soil, site, or
climatic limitations, and is coordinated
with crop management plans:
4. Ensuring that appropriate management
practices have been specified to mitigate
limiting soil properties and protect the
public froni adverse effects of metals,
organic contaminants, and pathogens.
Unit Conversions
Analytical data on biosolids characteristics
and the standards established by regulatory
agencies are usually expressed in metric units.
Farmers and farm advisors, however, usually use
English units for expressing nutrient require-
ments and the amounts of biosolids to apply.
Table I is designed to help you convert from one
unit to the other.
The following tips may be useful in
siniplifving your calculations and presenting
information in terms understandable to your users:
I. Make all conversions at one time, either
at the beginning or the end. Rounding
errors in metric-English conversions can
be very large, and the number of times
units are converted should be minimized.
2. Milligrams per kilogram (mglkg) is the
same as parts per million (ppm). Thus, if
biosolids analysis data report 65.000 fig
NH 4 -NIkg. that is the same as 65.000 mg
NH 4 -N per 1,000,000 mg oven-dried
biosolids.
3. When the units are the same in the
numerator and the denominator, the same
fraction can be expressed in any unit. In
this example, the equivalent English unit
is 65.000 lb NH 4 -N per 1.000,000 lb
oven-dried biosolids. This can then be
expressed as 65 lb NH 4 -N per 1.000 lb
oven-dried biosolids. or 130 lb per ton of
oven-dried biosolids.
Definitions
Throughout the text, many soil science
terms such as adsorption. denitrification.
mineralization, soil structure, and soil texture are
used. These and several other terms are defined
in the glossary at the end of this guide.
Table 1.—Guides for converting between metric and English units
Metric unit 1 Conversion factor English unit 2
Centimeter 0.3937 Inch
Meter 3.2808 Foot
Kilometer 0.6214 Mile
Hectare 2.4711 Acre
Cubic meter 35.31 47 Cubic toot
0.00081071 Acre-foot
264.25 Gallon
Gram 0.002205 Pound
Kilogram 2.205 Pound
0.0011 Tons
Metric ton 1.10 Tons
Kilograms per hectare 0.000446 Tons per acre
0.892 Pounds per acre
Metric tons per hectare 0.892 Tons per acre
Cubic meters per hectare 0.0001 069 Million gallons per acre
Gallon of water 8.34 Pounds of water
Gallon of water 0.1336 Cubic feet of water
1 To convert metric to English, multiply the metric unit by the conversion factor in the middle column.
2 To convert English to metric, divide the English unit by the conversion factor in the middle column.
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Biosolids Characterization
CHAPTER 2
p lanning a program for beneficial use
of domestic wastewater biosolids
requires complete and accurate data.
An important part of project evalua-
tion is ensuring that the data used to make
management decisions are both complete and
accurate.
Complete characterization data for biosolids
include the amount of solids produced and the
amounts of plant nutrients, trace organic and
inorganic contaminants, and pathogens con-
tained in the solids. The data also should indicate
the percent solids in the product that will be
applied to the land and the process or processes
used to reduce pathogens and control vector
attraction.
Data accuracy depends on using standard
procedures for collecting. handling, and analyz-
ing samples. The publication Analytical Methods
for the National Sewage Sludge Survey (EPA.
1988) is a useful reference for some of these
procedures. Bacterial analyses should follow
procedures established in Standard Methods for
the Examination of Water and Wastewaier, J Sth
Edition (EPA. 1992) and Control of Paihogens
and Vector Attraction in Sewage Sludge (EPA.
1992). Analyses of inorganic pollutants need to
follow protocols described in Test Methods for
Evaluating Solid Waste. Phvsica//C/ieniical
Methods (EPA. 1982). These documents, and
any other
approved procedures. should be available from
the agency that regulates biosolids treatment and
disposal in your state.
Some rules of common sense apply to
biosolids sampling and sample handling. For
example. samples should not be put in a paper
bag and left in a truck for several days. Store
samples in glass or plastic containers to prevent
the loss of liquids, volatilization, and contamina-
tion with extraneous organic material. Samples
must be representative of the biosolids to be
applied. Further information on appropriate
sampling equipment. containers, sample preser-
vation, and quality control/quality assurance
procedures is available in the documents cited in
the paragraph above.
Biological activity does not stop once a
sample is taken. Organic matter continues to
decompose. and organic nitrogen continues to be
mineralized. To obtain good nitrogen data.
refrigerate or freeze the sample immediately and
store it in that condition until laboratory analyses
can be performed. Otherwise, the nitrogen data
may not represent the actual amounts of each
form of nitrogen that are in the biosolids.
Laboratory procedures for analyzing
biosolids are essentially standardized. Neverthe-
less. there is some variation among laboratories
in both the accuracy and the precision of
analytical data. Your state regulatory agency
should be able to provide a list of reputable
laboratories whose work is reliable.
Analytical data are expressed in terms of the
dry weight of biosolids. This is the weight of the
residue after driving off all the water in a
biosolids sample by heating in an oven at 105°C.
The dry weight includes all solids suspended in
the original biosolids mixture, plus all constitu-
ents dissolved in the liquid portion of the
biosolids. All references to dry weight. dry
pounds. or dry tons are for dry weight deter-
mined in this way.
Biosolids Characteristics
Both the nutrient value of biosolids and the
potential for environmental degradation from
land-applied hiosolids depend on the percent
solids of the hiosolids: the composition of the
biosolids: how biosolids are handled and
processed prior to land application: and the
manner, timing. and location of the application.
Types of biosolids
Treated domestic wastewater biosol ids
consist of water. dissolved solids, suspended
solids, and settleahle solids removed from
domestic wastewater during the treatment
process. The solid components contain plant
nutrients, trace inorganic and organic chemicals.
and inert solids, many of which are combined
with complex organic compounds. The percent
total solids in the biosolids determines the type
of biosolids.
Liquid biosolids consist of a mixture of
solids and water that readily flows. The solids
content usually is within a range of 2 to SC/c but
max’ be as low as 0.5% or as high as 10%.
Dewatered biosolids are more concentrated
and are produced by mechaiiically removing
some of the liquid. Many dewatering processes
produce a biosolids product. called a cake, that
contains between 16 and 22% solids . although
some dewatered biosolids may have as much as
40% solids.
Dried biosolids consist of an even more
concentrated mixture that results from evapora-
tion through air drying or heating. The solids
content of a well dried biosolids product typi-
cally is 50% or more.
Composted biosolids are produced by
combining biosolids with a bulking agent such as
sawdust and aerating the resulting mixture under
controlled teniperatures. Recycled compost also
may be used as a bulking agent. The solids
content of composted biosolids generally is
about 40%.
Rules for
Biosolids
Sampling
1. Collect samples
that are truly
representative of
the biosolids
product.
2. Store samples in
appropriate
glass or plastic
containers
3. Refrigerate or
freeze samples
to prevent
changes in
nitrogen data.
31
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The Type of
Biosohds
Influences
• Storage and
transportation
requirements
• Application
methods
• Hydraulic
loading
• Fertilizer value
The type of biosolids applied to the land has
several implications for a beneficial use program.
First, any process that reduces the volume of
biosolids reduces the storage and transportation
needs and costs.
Second. the solids content dictates the
method and timing of application to the land.
Liquid biosolids that contain less than 6% solids
can be surface applied either from tank trucks
with special deflection plates or from irrigation
guns. Liquid biosolids also may be injected
directly into the soil.
At higher solids contents, the slurry may be
too thick to pump. Dewatered biosolids. dried
biosolids. and composted biosolids must be
hauled in dump trucks and spread mechanically
with hammer throw or manure spreader devices.
Third. dewatering. drying. and composting
all affect the fertilizer value of biosolids. These
changes are discussed further in the section titled
‘Nutrients” in this chapter.
Biosolids quantity
The quantity of biosolids a wastewater
treatment plant produces each year can be
expressed either as dry tons or as gallons. If
biosolids quantity is expressed as gallons per
year. calculate the dry tons of total solids
produced as follows:
• Convert the total gallons produced to tons
(see Table 1).
• Multiply by the percent solids reported in
the laboratory data.
Dry tons is the preferred method for
expressing biosolids quantity because it is
independent of liquid content, which varies
according to the method of biosolids processing
and handling.
For liquid biosolids. the quantity produced
helps determine biosolids storage and transporta-
tion requirements. Biosolids storage is necessary
during times when soil conditions are unfavor-
able for land application. These times occur
when the ground is frozen, when soil water
tables are high. or when the soil surface is wet.
Depending on specific climatic conditions, these
times may range from a few days to a few
months.
Biosolids storage also may be required
because certain crops limit biosolids applications
to specific times of year. You probably can’t
drive over a grain or row crop after the crop has
been planted. and public health considerations
may preclude biosolids application for part of. all
of, or more than one growing season. Applica-
tions to permanent pasture. however. generafly
are limited only by the timing of livestock
grazing. provided soil and weather conditions
allow site access.
Biosolids transportation needs depend on the
quantity of biosolids produced. the percent
solids, and the times of year during which
biosolids can be applied. The larger the quantity
of biosolids produced, the greater the transporta-
tion requirements. If biosolids can be applied
only during a portion of the year. the required
hauling capacity may be even higher. The
percent solids dictates whether storage lagoons.
storage tanks, or watertight boxes are needed for
transportation.
Nutrients
Biosolids are low-analysis fertilizers. They
are a valuable source of plant nutrients, but the
nutrient concentrations are significantly lower
than in most commercial fertilizers. The nutrient
content of biosolids depends on the primary
source of the biosolids. their age. the methods of
processing prior to land spreading. and the
method of application.
The actual fertilizer value of a biosolids
product and the determination of appropriate
agronomic loading rates depend on the specific
data reported for that product. It is essential.
therefore, that these data represent the final
processed biosolids product. not an intermediate
form.
The most important nutrients in biosolids are
nitrogen. phosphorus. and potassium. Other
nutrients in biosolids include calcium. magne-
siuni. and sulfur. Biosolids also contain small
quantities of plant micronutrients such as copper.
boron, iron, zinc, and manganese. and trace
amounts of growth stimulants such as selenium.
cobalt, arsenic, and vanadium.
Nutrient contents of biosolids usually are
expressed either as percent of dry weight or as
mg/kg dry weight. Most calculations, however.
use the equivalent concentration in lb per dry
ton. To convert percent to lb/ton, multiply by 20.
To convert mg/kg to lb/ton, multiply by 0.002.
Nitrogen in biosolids occurs in both inor-
ganic and organic forms. Biosolids analytical
data usually include the amounts of inorganic
ammonium nitrogen and inorganic nitrate
nitrogen. and either the total Kjeldahl nitrogen or
the total nitrogen. To determine the amount of
organic nitrogen. either subtract the ammonium
nitrogen from the total Kjeldahl nitrogen, or
subtract the sum of ammonium plus nitrate
nitrogen from the total nitrogen.
Inorganic forms of nitrogen are dissolved in
the biosolids product and are readily available to
plants. For this reason. ammonium nitrogen and
nitrate nitrogen in the biosolids serve as short-
term, or quick-release. fertilizers.
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Organic nitrogen in biosolids is a long-term.
slow-release fertilizer. As organic matter
decomposes in the soil, microorganisms convert
the organic nitrogen to inorganic ammonium
nitrogen. This process is called mineralization.
Other organisms then convert the ammonium to
nitrate. This process is called nirr (fIcaiioiz. Only
after these conversions is the nitrogen in
biosolids organic matter readily available to
plants.
The fertilizer value of biosolids is changed
by dewatering and drying processes to reduce the
water content, and by additional processes to
reduce pathogens and vector attraction. Dewater-
ing processes reduce the fertilizer value because
they remove some of the nutrient-containing
liquid. Drying also reduces the fertilizer value
because much of the ammoniurn nitrogen
changes to gaseous ammonia and is lost by
volatilization. As a result, both dewatered and
dried biosolids deliver much less quick-release.
readily available nitrogen per dry ton to the soil
than do liquid biosolids.
Composting converts most of the inorganic
nitrogen in biosolids to organically bound
nitrogen through a process called i,n,nobilization.
Therefore. composted biosolids supply little
readily available nitrogen to plants. However, the
nitrogen released by further decomposition in the
soil continues to supply plants for a longer
period of time than do other kinds of biosolids.
Much of the fertilizer value in all biosolids
products comes from the slow release of organic
nitrogen through mineralization. The rate of this
release, usually between 8 and 30% during the
first year following land application, depends on
many factors, including the form of biosolids
applied.
In general. the highest rate of release during
the rear following application is obtained with
liquid and dewatered biosolids. Dried biosolids
and composted biosolids have slower release
rates, but because these products have much
higher solids contents, more nitrogen will be
released in the second and third year after initial
application than from other types of biosolids.
Methods of processing also affect the
mineralization rate. For aerobically processed
biosolids. the mineralization rate may be 30% or
more. Anaerobic processing often results in a
mineralization rate of about 20%. Composted
biosolids have even lower mineralization rates.
generally about 8%. during the year after
application.
The method of land application also affects
the fertilizer value of biosolids. Methods that
leave liquid biosolids on the soil surface may
result in volatilization of half or more of the
ammonia, depending on climate and temperature.
On the other hand, liquid biosolids that are
injected or worked into the soil immediately
following application retain most of their
nutrient value.
Phosphorus and potassium are important
plant nutrients, but in most cases they are needed
in smaller amounts than nitrogen. Their avail-
ability to plants is less dependent on the extent of
biosolids processing prior to land application
than is nitrogen availability. As a result, if the
agronomic loading rate is based on nitrogen. you
can use the analytical data to calculate the
amounts of P and K delivered with it and
compare them with crop requirements. If there is
still a deficiency. you can add supplemental
fertilizer.
Excessive amounts of P delivered in
biosolids applied to land usually have no short-
term impact on crop production. but monitoring
of long-term increases in soil salinity and
nutrient balance certainly are appropriate.
Particular care may be required to prevent
surface runoff and overland transport of
biosolids that could lead to an increase in the
phosphorus content of nearby rivers and lakes.
Inorganic pollutants
Trace inorganic pollutants (often referred to
as metals) in biosolids include arsenic, cadmium.
chromium, copper. lead. mercury. molybdenum.
nickel, selenium, and zinc. The data from a
biosolids analysis usually report concentrations
of trace inorganic pollutants in mg/kg dry
weight. Multiply these numbers by 0.002 to
convert the expression to pounds of pollutant per
dry ton of bio solids.
Excessive applications of trace inorganic
pollutants are of concern because:
1. Some may be toxic to animals if ingested
at high levels for long periods.
2. Some are potential carcinogens.
3. Some tend to accumulate in body tissues
and, in large quantities. may impair the
functioning of vital organs. particularly
the liver and kidneys.
4. Some may enter human food supplies.
either through animals that graze on
crops that take up trace inorganic
pollutants from soils, or through direct
consumption of accumulator crops.
5. Some may be toxic to plants.
To protect public health and help assure
beneficial use of biosolids. the Clean Water Act
required EPA to identify any potentially toxic
inorganic pollutants in biosolids and to develop
regulations governing allowable concentrations
and acceptable management practices for bio-
solids land application. Current criteria regarding
concentrations of trace inorganic pollutants in
biosolids are summarized in Table 2.
Surface
spreading of
liquid biosolids
leads to
volatilization of
up to one-half of
the ammonia
nitrogen applied.
5’
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Table 2.—Regulatory criteria for content of trace inorganic pollutants in biosolids
applied to land
(A)
(B)
(C)
Maximum level for
Ceiling concentration
Cumulative
high quality
for application of
pollutant
Trace
biosolids
biosolids to land
loading rate
inorganic
(mg/kg)
(mg/kg)
(kg/ha)
Arsenic
41
75
41
Cadmium
39
85
39
Chromium
1,200
3,000
3,000
Copper
1,500
4,300
1,500
Lead
300
840
300
Mercury
17
57
17
Molybdenum
18
75
18
Nickel
420
420
420
Selenium
36
100
100
Zinc
2,800
7,500
2,800
Specific regulations regarding trace inor-
ganic pollutant loading rates and cumulative
limits undergo periodic revision. In fact, at this
writing, the concentration limits for chromium.
molybdenum. and selenium are under review and
may be revised. Such reviews and regulatory
changes are the result of increasing understand-
ing of the reactions of these substances in soils.
their tendency to be immobilized in the soil, their
uptake by specific crops. and their effects on
plant. animal, and human health and the environ-
ment. For these reasons, you should refer to the
applicable federal and state regulations in force
when a particular land application project is
being developed.
Organic contaminants
Trace amounts of some organic chemicals
may be found in most domestic wastewater
biosolids. depending on the number and kind of
industries and homeowners that discharge wastes
into the municipal sewer system. Solvents,
paints. pesticides. and polychlorinated biphenyls
(PCB’s) are some of the classes of organic
chemicals that may occur. In general. trace
organics such as halogenated hydrocarbons.
benzo(a)pyrene. dimethyl nitrosamine. and non-
halogenated organic pesticides appear to pose the
greatest potential hazard to human health.
Federal source permits generally require
periodic analysis of biosolids for several trace
organic compounds under a priority pollutant
scan. Biosolids data, therefore, should at least
include the amounts of these compounds present.
The data usually are reported either as parts per
million, parts per billion, or as mg/kg dry weight.
Land application of biosolids provides
several possible mechanisms for mitigating toxic
effects of organic contaminants. Some organics
may be subject to volatilization or may be
decomposed by sunlight. Some undergo rapid
microbial decomposition: others decompose very
slowly. Some organics may be immobilized by
adsorption on surfaces of clay particles and
organic matter in the soil. Others may be leached
out of the soil system. Leaching losses are not
very likely because the organic matter added to
soil with biosolids applications tends to adsorb
organics and immobilize them in the soil.
Based on the limited information currently
available, organic chemicals in most domestic
wastewater biosolids applied to land should not
pose a serious threat to plants or animals. The
major concern is human toxicity caused by
ingestion of plant or animal products. the
biosolids themselves, or the biosolids-amended
soil.
Because of the extreme diversity in the
kinds of organic contaminants that may be found
in a particular biosolids product and in the
specific interactions between organic chemicals
and soil environments, prescribing universal
guidelines for managing biosolids that contain
organic chemicals is difficult. The best common
sense advice is to consult with your state
regulatory agency and to comply with all
pertinent federal and state standards. If this is
done, organic chemicals in biosolids applied to
land should not pose a public health problem.
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Pathogen reduction
Virtually all pathogenic bacteria, viruses,
protozoa, and parasitic helminth ova must be
significantly reduced or eliminated from land-
applied domestic wastewater biosolids to prevent
contamination of human and livestock food and
water supplies. Risks associated with these
pathogens in land-applied biosolids are discussed
further in the publication Technical Support
Document for Reduction of Pathogens and
Vector Attraction in Sewage Sludge (EPA,
1992).
Most of the needed pathogen reduction
takes place by processing the biosolids at the
wastewater treatment plant prior to land applica-
tion. The remainder can be accomplished by
natural processes at the application site. Patho-
gen reduction processes are discussed in detail in
the publication Con Irni of Pathogens and Vector
.4ttraction in Sewage Sludge (EPA. 1992).
All processes to treat hiosolids. whether
prior to a land application or in the soil itself, are
designed to create environments unfavorable to
pathogen survival, Pathogens prefer cool, wet.
and dark environments and do not survive in
warm, dry environments that are exposed to
sunlight. In land application systems. pathogenic
organisms become a health hazard only if:
I. The numbers of pathogenic organisms in
biosolids are not reduced to tolerable
limits: or
2. Pathogens are leached into groundwater.
carried by runoff into surface water.
ingested with plant or soil materials, or
transported by vectors.
Pathogen reduction processes used by
domestic wastewater treatment plants generally
fall into two categories: h Processes that
Significantly Reduce Pathogens (PSRP’ s). and
2) Processes that Further Reduce Pathogens
(PFRP’st. PSRP’s include aerobic digestion. air
drying. anaerobic digestion. some types of
composting. and lime stabilization. PFRP’s
include composting. heat drying, heat treatment.
thermophilic aerobic digestion. beta ray irradia-
tion. gamma ray irradiation, and pasteurization.
Biosolids that have been processed with one
of the PSRP’s or an equivalent process recog-
nized by EPA are classified as Class B biosolids.
Although some pathogens may remain, they are
safe to apply to land. Most of the domestic
wastewater biosolids produced in the United
States are Class B biosolids.
To adequately protect livestock that forage
on biosolids-amended crops. and to maintain
high standards of public health, certain site
restrictions and management practices must be
followed. Specific site management requirements
for Class B biosolids are given in Subpart B of
40 CFR part 503.32(b)(5 t.
Surface application of biosolids treated with
a PSRP or an equivalent process creates expo-
sure to both drying and sunlight, conditions that
facilitate rapid decline of most remaining
pathogens and parasites. When Class B biosolids
are applied to land used to grow food or forage
crops, lag times ranging from I to 38 months.
depending on the type of crop and the method of
application, are required to ensure elimination of
potentially harmful pathogens.
Biosolids that have been treated with one or
more of the accepted processes that further
reduce pathogens (PFRP’s) are classified by
EPA as Class A biosolids. Class A biosolids
must meet very stringent limits on the density of
pathogenic bacteria. enteric viruses., and helm-
inth ova. Specific requirements for Class A
biosolids are given in Subpart B of 40 CFR Part
503.32(a)(7). Because PFRP’s eliminate virtually
all pathogenic organisms from biosolids. Class A
hiosolids can be applied to land safely regardless
of the type of crop to be grown.
Both PSRP’s and PFRP’s affect the fertilizer
value of biosolids. In particular. the amounts of
readily available nitrogen and the rates of
mineralization of organic nitrogen are affected
by the process used to reduce pathogens. When
determining the amount of biosolids to apply.
these interactions must be recognized to ensure
delivery of the right amount of nitrogen to meet a
fertilizer recommendation.
Vector attraction reduction
Vectors are organisms. mainly rodents, and
insects such as flies and mosquitoes. that are
capable of transporting infectious agents.
Because organic wastes offer a rich food source
for vectors, there is a potential for vectors to be
attracted to biosolids that have not been
adequately stabilized.
Any biosolids product that is applied to the
land must be treated to reduce vector attraction.
This can be accomplished by any one of 10
procedures for vector attraction reduction as
spelled out in EPA biosolids regulations
(40 CFR 503.33(b(l) through (10)). In general,
the first eight of these procedures involve
reducing the amount of volatile solids or
stabilizing the biosolids with temperature or
alkali treatment. Procedures 9 and 10 involve
injecting biosolids beneath the soil surface or
disking surface-applied biosolids into the topsoil
immediately after land spreading.
71
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Regulatory Characteristics
Regular biosolids
Three parameters usually dictate the amount
of regulatory oversight of bi solids applications
to land and the extent of management and site
restrictions: I) the content of inorganic pollut-
ants: 2) the degree of pathogen reduction prior to
land application: and 3) the steps taken to reduce
vector attraction.
These parameters define three classes of
biosolids quality: exempt biosolids. high quality
biosolids. and regular biosolids. All are suitable
for land application. Other combinations of trace
inorganic content and pathogen reduction exist.
but they occur so infrequently as to be treated as
special cases. If you have such biosolids. contact
your nearest state or EPA biosolids regulator.
Exempt biosolids
These are treated domestic wastewater
biosolids that contain such low levels of inor-
ganic pollutants and pathogens that they are
virtually exempt from further regulation. To
qualify, a biosolids product must have inorganic
pollutant contents below the limits given in
Column (A) of Table 2, must be a Class A
biosolid with respect to pathogen reduction, and
must meet one of the eight vector attraction
reduction requirements. Under these conditions.
biosolids are considered an unregulated fert-
ilizer grade agricultural commodity.
High quality biosolids
These biosolids contain low levels of
inorganic pollutants but have been treated only
with processes to significantly reduce pathogens
(PSRP’s). Pollutant concentrations are below the
maximums given in Column (A) of Table 2. but
the biosolids product is only a Class B with
respect to pathogen reduction.
Under these conditions, there is no regula-
tion of inorganic pollutant loadings on soils, but
some site restrictions are imposed to make sure
that additional treatment to reduce pathogens can
be accomplished at the land application site
without risk to public health.
These are biosolids that have somewhat
higher contents of inorganic pollutants than high
quality biosolids. The content of one or more
inorganic pollutants in the biosolids product
exceeds the value given in Column (A) of
Table 2. but all inorganic pollutant concentra-
tions must be within the limits given in Col-
umn (B) of Table 2. Most regular biosolids have
been treated only with a PSRP or equivalent
process and are Class B with respect to pathogen
reduction.
Use of these biosolids is regulated with
respect to both site conditions and cumulative
loading of inorganic pollutants. Cumulative
loading limits for inorganic pollutants are those
specified in Column (C) of Table 2. Accurate
records of pollutant contents and biosolids
application rates must be kept to ensure compli-
ance with regulations concerning cumulative
loading limits.
Regulatory oversight of cumulative loading
of trace inorganic pollutants also requires
knowledge of the previous history of biosolids
application at a site. If. for example. it is known
that no biosolids have been applied to a site since
July 20. 1993. then biosolids can be applied to
that site up to the cumulative loadings specified
in Table 2. If biosolids have been previously
applied since July 20. 1993. and the cumulative
inorganic pollutant loadings from those applica-
tions are known, then additional biosolids can be
added up to the limits in Table 2.
If. however, the cumulative inorganic
pollutant loadings from prior applications are not
known, then additional biosolids applications are
not allowed. Exceptions may be granted only if
baseline soil data indicate that pollutant loading
would not cause cumulative limits to exceed the
values in Table 2.
Biosolids for home
lawns and gardens
Because the use of biosolids as an amend-
ment to home lawns and gardens presents a
higher probability for human contact, hence
disease transmission, than biosolids applied to
farm fields, the standards for application to
lawns and gardens are niore rigorous. Biosolids
intended for these kinds of applications must
meet the requirements for exempt biosolids. i.e..
inorganic pollutant concentrations below those in
Column (A) of Table 2, Class A pathogen
reduction, and treated according to one of the
eight vector attraction reduction requirements
provided at a wastewater treatment plant.
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Management Practices
Lag times
Land application of both regular and high
quality biosolids at rates exceeding one dry
metric ton per hectare is subject to certain
restrictions on site selection and subsequent use
of biosolids-amended soils.
Site restrictions
Use of Class B biosolids must ensure that
soil and site conditions are selected and managed
in ways that protect environmental quality and
public health. For this reason, four management
practices must be followed in applying bulk
quantities (more than one dry metric ton) of
either high quality or regular biosolids to land:
I. Sites cannot be used if it is likely that
biosolids application could adversely
affect a threatened or endangered species:
2. Sites cannot be used if runoff from
flooded or frozen ground might carry
surface-applied biosolids into a wetland
or other body of surface water:
3. Biosolids cannot be applied on agricul-
tural land, forest land, or a reclamation
site that is 10 meters or less from surface
water bodies
4. Biosolids must be applied at a rate that is
equal to or less than the appropriate
agronomic loading rate for the soil and
crop at that site.
Restrictions on lag times between biosolids
application and subsequent uses of sites are
imposed to ensure high quality food supplies and
minimize direct public exposure. These restric-
tions include:
1. All food, feed, and fiber crops require a
lag time of at least 30 days between
biosolids application and harvest.
2. For food crops whose harvested parts are
above the soil surface and may come into
direct contact with biosolids or biosolids-
amended soil, the minimum lag time
between application and harvest is
14 months.
3. For food crops whose harvested parts are
below the soil surface, the minimum lag
time between application and harvest is:
a) 38 months if biosolids are incorpo-
rated into the soil within 4 months of
application:
b) 20 months if biosolids remain on the
land surface for more than 4 months
before incorporation.
4. Grazing is not allowed within 30 days of
biosolids application.
5. Turf to which biosolids are applied in
areas of high potential for public expo-
sure, such as lawns, golf courses. parks
and athletic fields. may not be harvested
for at least 1 year following application.
6. Public access to land application sites
must be delayed for at least:
a) 1 year where the potential for public
exposure is high
b) 30 days where the potential for
public exposure is low.
91
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110
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Soil Characterization
S ite evaluation, site selection, and site
management all begin with an assess-
ment of soil properties. These properties
control the biological, physical, and
chemical processes in soils that release plant
nutrients and immobilize toxic chemicals.
This chapter gives you a working knowledge
of the soil properties that influence the beneficial
use of biosolids. With this knowledge you should
be able to read and understand technical soil
profile and map unit descriptions in soil sune’
reports. You can then retrieve the maximum
amount of information from those descriptions.
You should also be able to evaluate site feasibil-
ity studies and permit applications for the
adequacy of soils data and the appropriateness of
proposed management plans.
Morpho/ogicti! properties define the nature
of the soil profile and are determined in the field.
Properties that are based on interpretations of
soil morphology are called h ferred properties.
Information about both morphological and
inferred properties can he obtained either from
direct field observations or from published soil
survey reports.
The Roles of Soil
Within a biosolids management program.
the three roles of soil are to provide a medium
for:
1. Plant root growth:
2. Water entry and transmission:
3. Attenuation of environmental contami-
nants.
Soil as a medium for water entry
and transmission
Rainfall, irrigation water, and the liquid
portion of biosolids can be transmitted to surface
and ground waters through soil. The rate of
transport depends on the soil properties. Soil
management for land application of biosolids
must regulate water movement over and through
the soil in order to prevent contamination of
water supplies with nitrates, phosphates, trace
inorganics. and organic pollutants.
Soils in high rainfall areas and soils that are
irrigated are subject to leaching. Water moving
through the soil transports any nutrients or toxic
chemicals that are in solution. The more perme-
able the soil, and the higher the rainfall or
irrigation, the greater the potential for leaching.
Runoff occurs when the soil cannot absorb
the rainfall or irrigation. Surface runoff increases
the potential for contamination of lakes and
streams with biosolids transported over the soil
surface by runoff water. The runoff potential of a
soil depends on the soil’s slope and wetness, and
whether the soil is frozen. Ground cover. rainfall
intensity, and the efficacy of soil conservation
measures also influence runoff. Bare soi] on
steep slopes in an area subject to high-intensity
storms represents an extreme case of runoff
potential. Thick sod cover and conservation
practices such as minimum tillage help reduce
runoff.
Soil as a medium for attenuation
of environmental contaminants
CHAPTER 3
Soil as a medium for plant roots
An aerobic environment is necessary both
for plant roots and for the soil microbes that
decompose organic residues and destroy patho-
gens. Aerobic environments provide a favorable
balance between air-filled pores and water-filled
pores. Soil management for beneficial utilization
of biosolids should strive to maintain aerobic
conditions in the soil.
Aerobic conditions are related to soil
texture, soil structure, and soil water content.
Sandy soils, and loamy soils with good structure.
provide aerobic conditions. Clayey soils, and
soils with poor structure tend to be less well
aerated. Soils that are saturated for long periods
of time are anaerobic and are not favorable for
mineralization. Saturation is more likely in soils
that are clayey. or have impermeable horizons, or
occur in low-lying landscape positions.
The contaminants of concern in a biosolids
application program are trace inorganic pollut-
ants. toxic organics, and pathogenic organisms.
Soil attenuates trace inorganics and organics by
immobilization reactions. Sonic pollutants are
immobilized by strong electrical attraction to the
negatively charged surfaces of clay and organic
matter. Most, however, are immobilized b ’
formation of complex substances with clay.
organic matter, and iron and aluminum oxides
that are very resistant to dissolution and deconi-
position. Thus, the higher the amount of clay and
organic matter in the soil, the greater its ability to
attenuate trace inorganic and organic pollutants.
Soil attenuates pathogens by holding them in
an environment that is unfavorable for their
survival. Pathogens cannot survive in warm, dry
soil. Even in moist soil, aerobic conditions lead
to rapid die-off of pathogens. The chance for
pathogens to move through the soil to
111
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groundwater increases only when biosolids are
applied to soil that remains saturated and
anaerobic for long periods of time.
Morphological Properties
The most important morphological proper-
ties are texture. structure, color, mottles, hori-
zons, and soil depth. The definitions of these
properties. their significance for land application
of biosolids. and their evaluation in the field are
described in the following sections.
Texture
Soil texture refers to the soil’s particle size
distribution. Soil particles are classified by size
into two groups: fine earth (<2 mm) and Oci, se
fragments (2 mm-l0 in). Fine earth is subdivided
into sand (.05-2.0 mm). silt (.002-.05 mm). and
clay (<.002 mm). The sand fraction is further
divided into very coarse, coarse, medium, fine,
and very fine sand. Coarse fragments include
gravel (2 mm-3 in). channers (2 mm-6 in and
flat), and cobbles (3-10 in).
Sand particles feel gritty and are so large
that each grain is visible. Silt has a smooth
feeling, like flour or corn starch. Neither sand
nor silt contribute much to the chemical behavior
of the soil.
Clay feels sticky and can be molded into
ribbons and wires. The particles are flat and can
be seen only with high-powered microscopes.
Clay has a large amount of surface area per unit
volume and is much more active chemically than
silt or sand. Many aspects of soil behavior
affecting utilization of biosolids depend heavily
on the behavior of clays in soils.
Table 3.—Names of soil texture classes
Abbreviation
Textural class
Generalized
term
S
Sand
Coarse
Ls
Loamy sand
Coarse
SI
Sandy loam
Moderately
coarse
L
Loam
Medium
Sil
Silt loam
Medium
Sicl
Silty clay loam
Moderately fine
Cl
Clay loam
Moderately fine
Sd
Sandy clay loam
Moderately fine
Sc
Sandy clay
Fine
Sic
Silty clay
Fine
C
Clay
Fine
Every soil contains a nhixture of sand, silt.
and clay. A textural triangle (figure 1) shows all
the possible combinations and is used to form
groups. or classes, of soil texture. Specific
combinations of sand, silt, and clay have names
such as loam. sandy loam, and si/ t v cla ’ loani.
All the names of soil texture classes, their
abbreviations, and their grouping into
generalized classes are shown in Table 3.
If rock fragments larger than 2 mm are
present in sufficient quantity. then names such as
gravelly loani or very cobblv clay, are used.
Precise definitions of coarse fragment modifiers
are given in Appendix A.
Figure 1 is a generalized textural triangle. A
soil that is almost all sand would be very close to
the sand corner of the triangle, and the textural
class name would be sand. Similarly, a soil
dominated by clay would be near the clay corner
of the triangle. and the class name would be clay.
Soils that contain a balanced nhixture of
sand, silt, and clay are called loams. These soils
are just below the center of the triangle. Loams
require less clay than sand or silt to balance the
mixture because clay has such a pronounced effect
on both the chemical and the physical behavior.
If the balance of a loam is changed by
adding sand, the sand begins to dominate, and
the particle size distribution moves away from
the loam toward the sand corner. The texture
changes from loam to sandy loam, then to loamy
sand, and ultimately to sand.
If clay is added to a loam, the texture moves
toward the top of the triangle. Adding just a little
more clay changes the texture from loam to clay
loam. If the sample contains more than 40%
clay, the textural class name is simply clay.
Soil Texture
Affects
• Porosity
• Water movement
• Aeration
• Water retention
• Organic matter
• Plant nutrition
• Trace inorganic
adsorption
CLAY
SAND
SILT
Figure 1.—Generalized textural triangle
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If both silt and clay are added to a loam at
the expense of sand, the texture moves away
from the sand corner towards a point in between
the silt and clay corners. The name of this
textural class is silty clay loam. Similarly, adding
both sand and clay at the expense of silt becomes
sandy clay loam.
Texture influences soil suitability for
biosolids application and utilization in many
ways. Texture is related to the size and shape of
soil pores, which affects water movement into
and within the soil. Texture influences the
balance between water-filled pores and air-filled
pores. creating different soil environments for
root growth and microorganism activity. Texture
also influences the rate of accumulation of
organic matter. Organic matter and clay content
together determine the soil’s capacity to immobi-
lize pollutants and supply nutrients.
The medium-textured soils (loam, silt loam.
and fine sandy loam) are usually best for land
application of biosolids. The range of pore sizes
in these soils allows water to flow through the
smaller pores and exchange air in the larger
pores. Medium-textured soils provide favorable
environments for root growth. store large
amounts of water for plant use, and have good
nutrient-supplying power.
Sandy soils have more large pores and fewer
small pores. Usually they are well aerated, but
they store much less water for plant use. Sandy
soils are droughty soils, and yields of dryland
crops are likely to be lower than on medium-
textured soils. Nutrient requirements are lower,
and the rate of biosolids application may need to
be adjusted accordingly.
Many sandy soils are well suited for the
production of irrigated crops. Since water enters
and moves throughout the soil readily, irrigation
can compensate for droughty conditions. In
contrast, rapid water flow through sandy soils
increases the risk of groundwater contamination.
Groundwater quality problems can stem either
from over-irrigation on a site to which
dewatered. dried, or composted biosolids have
been applied, or from applications of excessive
amounts of liquid biosolids.
Clayey soils have more very tiny pores and
fewer large pores. Air exchange and water
movement are much slower than in medium-
textured soils. Water applied as rainfall or
irrigation is more likely to cause temporary soil
saturation, reducing oxygen supplies to soil
microorganisms.
Water entry into clayey soils may be very
slow, so runoff is a greater risk. Care should be
taken when applying dried or composted
biosolids on clayey soils so that runoff doesn’t
physically wash them from the site.
Coarse fragments don’t necessarily render a
soil unsuitable for biosolids application, but they
do make management more difficult. Coarse
fragments reduce the volume of soil through
which water can flow and in which water can be
stored.
In soils containing coarse fragments. both
water flow and water retention depend on the
texture of the fine earth. If the fine earth is medium-
textured, then the soil may be suitable for
biosolids utilization, but application rates may
have to be reduced and land area requirements
increased. In other soils, coarse fragments
exacerbate problems associated with sandy or
clayey textures, and management is more
difficult.
Structure
Soil structure refers to the aggregation of
individual grains of sand, silt, and clay into
larger units called peds. Plant roots, soil organic
niatter. and clay particles provide physical and
chemical binding agents.
Soil structure is important because it
modifies some of the undesirable effects of
certain textures on soil behavior. Structure
creates relatively large pores. which favor
movement of air and water into and through the
soil. Even clayey soils can have good rates of
infiltration and permeability if they have well-
developed, stable structure.
Good soil structure also means good
aeration and a favorable balance between pores
that contain water and pores that contain air.
Structure creates a favorable environment for
root growth and microbial activity in all soils.
especially in the finer-textured soils.
Maintaining strong. stable aggregates is an
important management objective in any farming
operation. including those that utilize biosolids
as a fertilizer material. Three factors influence
the maintenance of strong. stable aggregates:
organic matter. clay, and heavy equipment.
Organic matter is vital to the formation and
maintenance of good soil structure. Living roots
help surround soil particles and bind them together.
Exudates from roots and other soil biota provide
a kind of “glue” that stabilizes peds. Decomposed
organic niatter. or humus, is particularly valuable
in the development of structure.
Biosolids are valuable soil amendments
because they can improve soil structure. Mixing
biosolids into the surface soil helps restore the
structure of overworked soils. Land on which
row crops have been grown repeatedly is
particularly prone to structural deterioration, and
the use of biosolids on this kind of land can be
very beneficial.
Good Soil
Structure
• Promotes
aeration
• Promotes
infiltration
• Improves air-
water balance
131
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Clays help aggregate soil particles due to their
chemical activity and their tendency to shrink
and swell. One niechanism of structure lormation
is the attraction between negative charges on
clay surfaces and positive charges on the edges
of clay particles and organic soil constituents.
Soil structure is very sensitive to the weight
of heavy equipment. Driving on wet soil breaks
down soil aggregates and compacts the soil.
Surface soil compaction retards germination and
emergence of plant seedlings, and reduces the
infiltration rate substantially, thus incre ising the
potential for surface runoff. To avoid these
problems, wait until the surface soil has dried out
before driving on the soil. Sod crops (hay and
pasture) protect the structure much more than
grain or row crops.
Soil structure is characterized h the shape.
size, and grade of the peds. Common shapes are
illustrated in figure 2. Granular peds are conimon
Granular
Platy
Blocky
Prismatic
Massive
Single grain
Fic ’i ,e 2.—Coinino ,, s/iape.s of. oiI . 1ruct1iie
in surface soils, and plates occur in some soils
just below the surface horizon. Blocks and prisms
are both common in subsoils. Fed size is described
with terills such as fine. medium, and coarse.
Peds are measured in millimeters. and the range
in values for each term depends on the shape.
The relationships are given in Appendix A.
Structural grade refers to the degree of
structural development and the strength of the
peds. The structural grade is described as strong.
moderate, weak, and structureless. These terms
also are defined in Appendix A.
StructLiral grade is important for hiosolids
utilization because it affects soil porosity and soil
strength. Soils with moderate or strong structures
are ideal because the have good mixtures of
large and small pores and optimum environments
for growin z plants. The peds tend to resist
breakdown under the impact of falling water
drops or from normal traffic. Soils with weak
structure tend to have fewer large pores. They are
less permeable and have slower infiltration rates.
Peds are not as stable, and the soil surface is
more likely to form a nearly impermeable crust.
Color
Soil colors provide clues about the nature of
the root zone. Dark colors usually mean favorable
amounts of organic matter. Gray colors often
indicate soils that are poorly aerated due to long
periods of wetness. Yellowish-brown and
reddish-brown colors indicate favorable air-
water relations.
Because different people might perceive and
describe the same color differently. soil scientists
describe soil color quantitatively by matching the
color of a soil clod with a standard color chip in
a special hook of soil colors. This method is
described in detail in Appendix A. Nevertheless.
generalization of soil colors into a few broad
groups helps to interpret their significance for
hiosolids utilization on land.
Dark brown, very dark brown, and black
colors are caused by accumulations of organic
matter in soils. Usually the darker the color, the
more the organic matter in the soil and the more
fertile and productive the soil is. Organic matter
is a major factor in structure development, so the
darker the soil, the better formed and more stable
the soil peds.
Some soils have black colors extending well
down into the subsoil. If the soil beneath is gray.
then the black color in these soils indicates
prolonged wetness in cool to cold climates.
Organic matter in cool, wet soils breaks down
much more slowly than in warm, moist soils.
The extra organic matter that accumulates
darkens the soil to a greater depth.
One of the
reasons biosolids
are such
valuable soil
amendments is
their potential for
improving soil
structure.
Inferences
from Soil Color
• Organic matter
content
• Degree of aeration
• Evidence of water
tables
114
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Brown and yellowish-brown colors indicate
well-aerated soil. As soil microorganisms and
plant roots use up oxygen in soil pores, oxygen
from the air above the soil readily moves in to
replace it. Well-aerated soils are ideal for crop
growth and beneficial use of biosolids. Brown
and yellowish-brown colors are caused by iron
oxide coatings on soil particles. Chemically,
these coatings are the same as rust on a piece of
iron. Iron oxide is stable, and the coatings remain
on soil particles as long as there is plenty of
oxygen in soil pores. If oxygen is not available,
as in soils that are saturated for long periods, the
iron oxide coatings are removed, and the soil
turns gray. This is why brown colors indicate
that the soil has good air-water relations and is
never wet for prolonged times.
Red and reddish brown colors also are
caused by iron oxide coatings and indicate well-
aerated soils. The soil is red, rather than brown,
only because the chemical form of the iron oxide
is a little different. These soils are very strongly
weathered and tend to be more leached, more acid,
and less fertile than brown soils.
Gray colors are the colors of wet soils.
When soil pores are full of water, oxygen can’t
get in. This creates a reducing environment, and
the iron oxide coatings begin to change to the
more soluble ferrous form. Gradually the iron
oxide coatings are stripped away and leached out
of the soil. The gray color is the natural color of
the mineral grains of the soil, darkened a little by
organic matter.
Soils that have gray colors near the surface are
poorly suited for biosolids application during times
when the water table is high. But if the soil occurs
in a climatic region having a prolonged dry period,
biosolids application may be feasible, especially
if dried or composted biosolids are being
applied.
Many wet soils are permeable enough that
artificial drainage can lower the water table. If the
soil permeability is at least moderately slow, and
tile drainage has been or can be installed to lower
the water table to a depth of 3 feet, then a wet soil
can be used for most types of biosolids application.
Before draining a wet soil, check two things.
One, outlets must be available to receive the
drained water. Two, ensure that draining a wet soil
does not violate provisions of the. Food Security
Act of 1985, or any other legislation pertaining
to natural wetlands. Check with local offices of
the Extension Service, Natural Resources
Conservation Service, Corps of Engineers, and
state and federal Fish and Wildlife Services for
possible regulations that affect wet soils.
Light gray and white colors in soils of
humid regions also are caused by stripping of
iron oxide coatings, revealing the true color of
mineral grains. These colors don’t always
indicate wetness, though. If the soil below the
white zone is brown or red and well-aerated, the
white zone is not limited by wetness. If the
underlying soil is gray, then the white layer is
probably saturated for long periods of time. In
arid regions, white subsoil may be the result of
deposition of calcium carbonate and not an
indicator of wetness. But if there is a surface
crust of white color, this indicates that water is
rising to the surface from a shallow water table,
bringing soluble salts that are left on the surface
as the water evaporates. These soils are not only
periodically wet, they are often very alkaline and
very slowly permeable, and are more limiting for
biosolids application.
Mottles
Some soils have spots of one color in a
matrix of a different color. The spots are called
mottles, and the soil is said to be mottled. Some
mottles appear as splotches of reddish brown
color in a gray matrix. Others appear as gray
mottles in a brown matrix. Both kinds are
described in terms of their abundance, size,
contrast, and color. Abundance refers to the
percentage of exposed surface area occupied by
mottles. Size is the approximatediameter of mottles.
Contrast is the relative difference between the
mottle color and the matrix color. These terms
are defined more fully in Appendix A. Mottle
colors are described using the same technical
procedure that is used to describe soil colors.
Mottling is caused by fluctuating water
tables. When the water table is high, the soil is
saturated and iron oxide is reduced. When the water
table drops, oxygen begins to reenter the soil through
root channels and large pores, which drain first. As
oxygen comes into contact with moist soil
containing reduced iron, the iron quickly
oxidizes, forming an insoluble precipitate at the
surface of a soil ped. The result is a yellowish-
brown mottle surrounded by gray soil.
By understanding these processes, we can
use observations of soil colors and soil mottles to
make inferences about the height and duration of
water tables in soils, even though the soil may be
quite dry when we look at it. Soil colors and
mottles are used to de.fine classes of internal soil
drainage. These are discussed in the section on
inferred properties.
There are three situations, however, in
which mottles do not indicate wetness. These are
the chemical weathering of rocks, relict mottling.
and coatings on soil peds.
Rocks are the parent materials of soils and
are composed of a variety of different minerals.
Each mineral reacts differently to the processes
of chemical weathering. Some turn yellow, some
Before draining a
wet soil, check
with state or local
officials for
possible
regulations that
affect the use of
wet soils.
Mottles are spots
of gray or brown
color that indicate
the height of
fluctuating water
tables.
151
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red, some gray, and some are destroyed
completely. The result of rock weathering can be
a mixture of colors that may look like drainage
mottles, even though the soil is well drained.
This situation is often encountered in the lower part
of a soil as it grades into weathered bedrock. It
also may be encountered in some glacial till soils
in which a wide variety of rocks and minerals
has been mixed together in the parent material.
The key to avoiding a false interpretation of
rock weathering is to study climate, soil. and
landscape factors carefully. In humid regions.
soils that are gray and mottled and occur in
concave depressions, low-lying areas, or on broad.
flat terraces. are probably wet soils. Soils that
occur on rounded hilltops, sloping hillsides, and
narrow ridges, as well as soils in arid regions. are
likely to be well drained soils with brown colors.
Color variations in these soils are more likely to
be associated with rock weathering than wetness.
Relict mottles are mottles that formed when
the soil environment was wetter than it is now.
Once formed, mottles are a relatively permanent
feature of the soil, even if the climate changes.
Thus, mottles in soils on convex uplands for
which there is no other evidence of periodic
water tables are probably relict mottles and do
not indicate wetness.
Some peds have coatings of substances other
than iron oxide. Organic matter, clay, and even
moisture films can create colors that differ from
the matrix color. These coatings should not be
confused with mottles caused by reduction and
oxidation of iron, and they should not be
interpreted as indicating wetness. The best way
to avoid this mistake is to break open soil peds
and evaluate the color from a freshly exposed
interior surface.
Soil horizons
A soil horizon is a layer of soil parallel to
the earth’s surface. Each horizon is defined and
described in terms of its morphological properties:
texture. structure, color. etc. Together. all of the
horizons in a soil constitute the soil profile. A
soil profile description is a complete set of
horizon descriptions for all the horizons that
occur in a soil.
Soil horizons are named using combinations
of letters and numbers. Six general kinds of
horizons can occur in soil profiles (see Figure 3):
0. A, E. B. C. and R. These are called master
horizons. Gradual changes from one master
horizon to another give rise to transition horizons.
These are named with two letters. for example.
AB. BA. and BC. Special kinds of master
horizons are recognized by adding lower case
Figure 3—Generoli:.ed soil profile
letters, as in Ap. Bt. Bk, and Cr. Master horizons.
transition horizons, and special kinds of master
horizons all are described more completely in
Appendix A.
A single soil profile never has all possible
horizons. Most soils have an A horizon, one or
two specific types of B horizons, a C horizon.
and one or two transition horizons. Some soils
have only an A horizon and one or more C
horizons. Others have bedrock (R horizon) at
shallow depths. Some soils have an A-E-B-C
horizon sequence. or even an O-E-B-C profile.
Soil horizons are important for biosolids utili-
zation because of their effect on transmission of air
and water through soil. Any horizon that differs
markedly in texture, structure, or density from
the one above or below affects water movement.
Horizons that are very clayey and have a
weak or massive structure, and horizons that
have very high densities. are called restrictii’e
layers. Examples of restrictive horizons include
clavpans (Bt. or argillic. horizons that are clavey
and massive ). fragipans (Bx horizons that are
silty and very dense), and Cd horizons (very dense
glacial till). Water cannot move into and through
these layers as fast as it moves down through the
soil above them. During periods of excess
rainfall or irrigation, water perches on top of the
restrictive layer. saturating the soil and creating
shallow, but temporary. water tables.
Restrictive layers thus limit the times during
which a soil can be used for land application of
biosolids, Liquid biosolids can be applied only
during dry seasons, when there is no perched
water table. Dried biosolids can be applied to the
surface at other times, as long as the water table
0 Litter layer
A Mineral surface horizon, dark
colored, granular structure
E Strongly leached horizon,
light colored, platy structure
B Subsoil horizon ci maximum
development, “brown,”
blocky structure
C Weathered “parent material,”
“brown,” massive structure
R Hard bedrock
Any horizon that
differs markedly
in texture,
structure, or
density from the
one above or
below affects
water movement.
Kinds of
Restrictive Layers:
• Claypans—
some Bt horizons
• Fragipans—
Bx horizons
• Duripans—
Bkqm horizons
• Petrocalcic
layers—
Bkm horizons
• Dense till—
Cd horizons
• Weathered
bedrock—
Cr horizons
• Hard bedrock—R
horizons
16
-------
is not at the surface and the soil is capable of
supporting the weight of application equipment.
Another hazard associated with restrictive
layers is increased potential for surface runoff.
As soon as the soil above the restrictive layer
fills with water, any additional increments of
water must run off. The shallower the depth to a
restrictive layer. the sooner this occurs, and the
more likely biosolids lying on the surface will be
carried into surface waters. This hazard is
particularly serious on soils that are sloping, in
addition to having a restrictive layer.
Gray horizons that are saturated for long
periods of time are said to be gleved. They are
called Bg horizons. The limitations they present
are siniilar to those caused by restrictive horizons.
Gleyed soils can be used for land application of
biosolids as long as the soil is dry enough to
support the weight of application vehicles and as
long as liquid wastes are prevented from entering
horizons of saturated soil.
Rapid/v drainini horjonc have sandy’
textures and are often gravelly or cobbly. They
have the potential to transmit biosolids liquids
into groundwater aquifers before soil treatment is
complete. The risk is not very great with surface
applications, however. Most biosolids. even
liquid ones, do not carry enough water to wet the
soil above a rapidly draining layer enough to
cause rapid transmission of incompletely treated
waste. There is some potential. though. that
heavy rain or irrigation right after a biosolids
application could move some liquid directly into
the rapidly draining layer.
Soil profile descriptions are an excellent
source of information about the kinds of horizons
that are present in a soil. By reading a profile
description, you can find out if abrupt textural
changes occur, if restrictive horizons. gleyed
horizons, or rapidly draining horizons are
present. and if they are, at what depth they occur.
Soil depth
The terms shallow, moderately deep. and
deep have very specific meanings in soil science.
They apply when the soil profile contains
bedrock (R horizon), weathered bedrock (Cr
horizon). or a cemented horizon (Bkqm or Bkm).
Shallow always means that one of these
horizons occurs at a depth between 0 and 20 inches.
Moderately deep means that one occurs at a depth
between 20 and 40 inches. Deep means that none
of them occur within a depth of 40 inches.
These terms do not app/v to restrictive
layers. gleyed horizons, or rapidly draining
materials. Descriptions of soils that contain these
horizons usually indicate that the soil is deep.
even though the restrictive layer may occur at a
depth less than 20 inches.
Study the profile descriptions and map unit
descriptions in a soil survey report carefully to
deterniine if a particular soil has a restrictive
layer. and if so. the depth at which it occurs.
Inferred Properties
Several aspects of soil behavior are difficult
to measure directly in the field, but inferences can
be made about these properties on the basis of
primary morphological properties. Inferred
properties that are particularly important for land
application of domestic wastewater biosolids
include permeability, infiltration, internal
drainage class, available water holding capacity.
leaching potential. shrink-swell potential.
trafficability. pH. and nutrient availability.
Permeability
Soil permeability is the rate that water
moves through the soil. Permeability depends on
the amount, size, shape. and arrangement of soil
pores. and on the degree of homogeneity of the
pore structure from horizon to horizon.
Water moves through soil pores in response
to two general kinds of forces. One is gravity.
which pulls on water all the time. The other is an
attraction between water molecules and the
surfaces of soil particles. Very thin films of
water are bound very tightly’ to soil particles. The
thicker the water film, the lower the attractive
force at the outer edge of the film. As a result.
water moves along an energy gradient from
moist soil, where the attractive forces are
relatively weak, toward dry soil, where the
attractive forces are relatively strong.
In saturated soils, water moves through large
pores because the gravitational attraction is much
greater than the water-soil attraction. Water
moving in this way is called gravitational ‘it’atcr.
As long as the soil remains saturated, we refer to
this water movement as saturated flow.
If a saturated soil is allowed to drain under the
influence of gravity with no further additions of
water, then gravitational water is gone after a few
days. All the water remaining in the soil is held
against the force of gravity by the attractive force
between water and soil particles. We refer to the
water content at this point as field capacity.
Any further water movement occurs as
unsaturated flow. Water moves around the soil
particles from thick films toward thin films. i.e
from lower attractive forces toward higher forces.
or from moister soil toward drier soil. The rate of
Soil profile
descriptions in
soil survey reports
are an excellent
source of
information about
soil horizons
• Abrupt textural
changes
• Gleyed horizons
• Mottled horizons
• Rapidly draining
horizons
• Restrictive layers
171
-------
Soil Properties
that Influence
Permeability
• Texture
• Coarse
fragments
• Structure
• Organic matter
• Restrictive layers
unsaturated flow is variable, depending on the
pore structure and the moisture content of the
soil. The maximum rate occurs when the soil is at
field capacity. As plants remove water and the soil
dries, all of the moisture films become thinner.
and the rate of flow decreases substantially.
Because of the complexity of the soil pore
system. permeability in the field is difficult to
measure. A soil’s hydraulic conductivity is easier
to determine by measuring the rate of saturated
flow in a vertical direction through a sample of
soil in the laboratory. By relating the lab data to a
soil’s texture, structure, and horizons, then the soil
permeability can be estimated by observing soil
properties. The specific relationships between
soil morphology and the classes of hydraulic
conductivity are summarized in Table 4.
Several properties influence permeability.
Coarse-textured soils, for example, have larger
pores and more rapid permeability than fine-
textured soils. Coarse fragments can’t conduct
any water: their effect is to reduce the volume of
soil available for movement and retention of
water. Good soil structure enhances permeability
by providing stable aggregates that have small
pores within peds and large pores between them.
Organic matter enhances permeability through its
effect on forming and stabilizing soil structure.
Whenever the pore structure changes drastically
and abruptly from one horizon to another, there
is a major impact on permeability. But if the
texture and structure change gradually from one
horizon to the next, the rate of water movement
is relatively unaffected, and water continues to
move down through the profile.
Soil scientists use the permeability of the
least permeable horizon in a soil to characterize
the permeability of the whole soil. Because of
the effect of soil layering, however, each
horizon’s permeability should be evaluated
separately. This is the only way to determine if
restrictive layers or layers of coarse grained
materials are present. the depth at which they
occur, and whether there is enough soil above
these layers to provide adequate protection for
groundwater.
Soils that have
moderate or
moderately slow
permeability are
well suited for
land application
of sewage
biosolids.
118
Table 4.—Relationships between hydraulic conductivity, permeability class, and
soil morphology
Hydraulic
conductivity
Permeability
class
Morphological
characteristics
(in/hr.)
<0.06
Very slow
Massive, clayey (>35% clay) horizons with
few or no roots
Continuous strongly cemented horizons with
few or no roots
0.06-0.20
Slow
Clayey (>35%) horizons with either weak
structure, platy structure, or slickensides
Continuous moderate or weak cementation
0.20-0.60
Moderately slow
Clayey (>35%) horizons with moderate
structure but no slickensides
Medium-textured soils (18-35% clay) with
weak structure
Sandy soils that are cemented
Soils with very few medium or larger
continuous vertical pores
0.60-2.0
Moderate
Medium-textured soils (18-35% clay) with
moderate structure
Fine sandy barns
Soils with a few medium or larger continuous
vertical pores
2.0-6.0
Moderately rapid
Medium-textured soils (18-35% clay) with
strong structure
Sandy loams and loamy fine sands
Soils with common medium or larger
continuous vertical pores
6.0-20.0
Rapid
Coarse sandy barns and fine sands
Soils with many medium or larger continuous
vertical pores
>20.0
Very rapid
Sands and coarse sands that contain more
than 15% coarse fragments
-------
Table 5.—Sample data included in soil survey reports
Tabular data in soil survey reports (see
Table 5) give numbers for the permeability of
each different layer in the soil. For this purpose.
horizons that have similar properties are grouped
together. and only the major differences are
shown. The numbers given in these tables
represent the value of the laboratory test of
hydraulic conductivity. Since the sample is very
small and measures only vertical flow, this test
does not reflect actual field behavior because it
does not consider unsaturated flow. Neverthe-
less, the test provides a form of soil characteriza-
tion that allows comparison of different soils.
In general. soils that have moderate or
moderately slow permeability (see Table 4) are
well suited for application of all types of
biosolids. Soils that have slow permeability
throughout and do not have a water table
problem are suitable for application of dewa-
tered. dried, and composted biosolids. Liquid
biosolids also can be applied as long as care is
taken not to saturate the soil. Slowly permeable
soils that do have a water table problem are
usually somewhat poorly drained or poorly
drained (see page 21). As long as the permeabil-
ity is uniform throughout. lowering the water
table with tile drains may be possible. Where this
is done. biosolids can be applied safely.
Soils that have a slowly or very slowly
permeable restrictive layer at relatively shallow
depth (for example. 12 to 20 inches) have serious
limitations for applications of liquid biosolids.
Other biosolids. however, can be applied as long
as the soil above the restrictive layer is not
saturated.
Soils that are very slowly permeable
throughout are poorly suited for land application
of liquid biosolids. The rate of water movement
is too slow to provide both adequate treatment
and sufficient oxygen supplies. Correction of this
limitation is very difficult and costly without any
guarantee of complete success. Even very slowly
permeable soils, however. may be used for dried
or composted biosolids during seasons when the
soil is dry enough to support heavy equipment.
Soils with moderately rapid or rapid
permeability are useable for land application of
biosolids. but leaching of nitrates and other
chemicals in solution could be a problem in areas
where a lot of water is added to the soil. The risk
can be reduced by applying only dried or
composted biosolids and avoiding times of high
rainfall or excessive irrigation.
Infiltration
Infiltration is the rate that water enters the
soil. Infiltration depends primarily on the pore
geometry at the soil surface, and pore geometry
depends on the texture and structure of the
surface soil. The relationship between texture
and infiltration is illustrated by the data shown in
Table 6. Clearly. coarse-textured soils have
much faster infiltration rates than fine-textured
soils. Note that even small increases in clay
content, as in the change from sand to loamy
sand. can have marked effects on infiltration.
Table 6.—Typical infiltration rates of soil
texture classes
Soil texture
Infiltration rate
inches per hour
Sand
2.0 - 5.0
Loamy sand
1.0- 1.5
Loam
0.5 - 0.75
Silt loam
0.2 - 0.3
Clay loam
0.15-0.3
Silty clay loam
0.1 - 0.2
Clay
0.05 - 0.15
Moist
Available
Soil name
bulk
Water
Soil
Shrink-
Erosion
Organic
and Depth
Clay
density
Permeability
Capacity
reaction
swell
factors
matter
map symbol (in.)
(%)
(gm/cc)
(in/hr)
(in/in)
(pH)
potential
K T
(%)
52B,52D 0-11
27-40
1.20-1.40
0.6-2.0
0.16-0.18
5.6-6.5
Mod
0.32 2
2-4
Hazelair 11-15
35-50
1.05-1.20
0.2-0.6
0.13-0.19
5.1-6.5
High
0.28
15-36
60-70
1.00-1.20
<0.06
0.09-0.12
5.1-6.5
High
0.24
>36
—
—
—
—
—
—
—
53 0-5
3-10
1.20-1.40
6.0-20
0.05-0.07
5.6-6.5
Low
0.10 5
2-4
Heceta 5-60
3-15
1.30-1.60
6.0-20
0.05-0.07
5.6-6.5
Low
0.10
54D, 54G 0-12
18-27
0.90-1.00
0,6-2.0
0.19-0.21
4.5-5.5
Low
0.32 3
4-8
Hembre 12-44
25-32
1.00-1.15
0.6-2.0
0.16-0.20
4.5-5.5
Low
0.28
Soils that have a
slowly or very
slowly permeable
restrictive layer at
shallow depth
have serious
limitations for
application of
liquid biosolids.
Soil Properties that
Affect Infiltration
• Texture
• Aggregate
stability
• Organic matter
• Antecedent
moisture
• Subsoil
permeability
• Plant cover
191
-------
Techniques for
Maintaining
Optimum
Infiltration Rates
• Don’t drive on
wet soil
• Keep organic
matter levels high
• Grow sod crops
wherever possible
Classes of Internal
Drainage
• Excessively
drained
• Somewhat
excessively
drained
• Well drained
• Moderately well
drained
• Somewhat poorly
drained
• Poorly drained
• Very poorly
drained
120
Aggregate stability is the most important
effect of soil structure on infiltration. Strong. stable
peds at the soil surface create and maintain
relatively large pores. Organic matter is particu-
larly important in this regard. Soils that are well
supplied with organic matter are more likely to
have moderate infiltration rates than soils that are
deficient in organic matter. If the organic matter
content is low, and soil peds are not very stable.
then the impact of falling water drops breaks the
pods apart. Soil grains wash into the larger pores.
clogging them and sealing the soil with a crust of
very low porosity. This process of ped break-
down is called slaking. and the formation of a
crust that seals the soil is called puddling.
Infiltration also depends on the moisture
content and the permeability of the soil beneath
the surface. The higher the moisture content, the
slower the infiltration rate. This means that soils
that are nearly saturated arc not going to accept
wastewater liquids readily. These soils are too
wet to drive on, so the only situation in which a
problem might occur is with application of liquid
biosolids through irrigation cannons.
Permeability affects infiltration because water
has to move away from the surface before
additional water can enter the soil. Obviously if
water is applied continuously at rates greater than
soil permeability, then saturated conditions form
and additional water can’t enter the soil. A likely
consequence is surface runoff accompanied by
surface water contamination.
Infiltration is important for land application
of biosolids because of its relationships to
water quality. By itself, rapid infiltration is a
desirable trait, but if coupled with rapid
permeability and high rates of hydraulic loading.
then there is a greater risk of groundwater
contamination with either nitrates or pathogens.
Slow infiltration is a more common problem.
This increases the potential for surface runoff
and subsequent contamination of surface waters.
The problem is exacerbated by the tendency for
soil structure to deteriorate in the surface soil.
further lowering the infiltration rate.
Since infiltration is tied to water quality.
maintaining optimum infiltration rates is an
important objective of soil management for
biosolids application. These rates can be main-
tained by:
I. Not driving on wet soil to avoid compac-
tion and structural breakdown:
2. Keeping organic matter levels high by
incorporating biosolids and other organic
residues into the soil;
3. Using sod crops in the rotation as much
as possible.
Internal drainage class
Internal drainage refers to the ability of free
water to escape from a soil. Internal drainage is
not the same thing as permeability because
permeability indicates only the rate that water
moves if it has some place to go. Classes of
internal drainage are based on the height that a
water table rises in the soil and the length of time
that the soil remains saturated.
Rapidly permeable soils that are never
saturated are called excessii’eiv drained. Soils
that are rarely saturated above 3 or 4 feet are
called well drained. Soils that are periodically
saturated in the lower part of the soil profile are
called either moderate/v well drained or
somewliatpoor!v drained, depending on the
depth to the water table and the duration of
saturated conditions. Soils that are thoroughly
saturated for long periods of time are called
poor/v drained, or even ‘C!T po(niv drained.
Internal drainage is important because it
affects both the oxygen supply and the tempera-
ture of the environment in which plant roots and
soil microorganisms live. Ideally, about half the
pores in the soil should contain water. The other
half should be filled with air. Well drained soils
can provide this condition, but poorly drained
soils cannot.
Drainage affects temperature because wet
soils are cold soils. Biological processes.
especially those that decompose organic residues
and release nitrogen for plant use, do not operate
as fast in cold soils. As a consequence. if
biosolids are applied to a cool season grass or
pasture crop. nitrogen may not be released until
later in the year. after the soil has warmed up and
after the crop’s peak demand for nitrogen has
passed. The excess nitrogen that is released later
in the year may be lost either into the groundwa-
ter by leaching or into the atmosphere by
denitrificarion.
When oxygen is limiting. denitrification
occurs in wet soils because some of the inorganic
nitrogen is converted to nitrogen gas and escapes
to the atmosphere. Denitrification losses usually
are not large. but if you do not account for theni in
planning your application rate to meet crop needs.
the crop may suffer from nitrogen deficiency.
Internal drainage is also important because it
indicates the volume of soil available for plant
root development and uptake of soil nitrogen.
Because these processes occur mainly in aerobic
environments, only the soil above a water table is
available for biosolids utilization. The more
poorly drained the soil, the more restrictive it is
for both crop growth and beneficial utilization of
biosolids. Soils of any drainage class, however.
can be used for land application of biosolids.
provided that shallow water tables are neither
-------
present at the time of application nor for a period
of time thereafter.
The extent to which drainage is limiting
depends on the type of biosolids. the permeabil-
ity of the soil, and the climate. Poorly and
somewhat poorly drained soils are most restric-
tive for application of liquid biosolids. If they
have uniformly slow or moderately slow
permeability, however, they may be artificially
drained, provided suitable outlets are available.
These soils are less limiting than soils that have
very slow permeability or shallow restrictive
layers that preclude effective drainage.
Climate dictates the amount and frequency
of rainfall, hence the frequency with which water
tables are high. In huniid continental climates.
where summer storms occur periodically, there
may be only a few weeks when water tables in
somewhat poorly and poorly drained soils are
low enough to apply biosolids safely. In arid
regions and in marine climates, water tables may
be low enough during dry periods to allow land
application of biosolids for several months.
Water table tiuctuations in soils are rarely
observed directly. Most of the time soils are
studied in the field during dry seasons, and the
internal drainage class is determined by inference
from the evidence in the soil’s morphology.
Color, mottling. permeability, restrictive
horizons, pH. and landscape position are the
most important indicators of soil drainage class.
Soil variability across the U.S. precludes the
use of a single. standard definition of soil
drainage classes. Interactions between rainfall,
temperature. organic matter. biological activity.
and parent materials are so complex that inter-
pretations of internal drainage must be tailored to
regional conditions.
In general. a soil that is sandy or gravelly
and has rapid or very rapid permeability is
excessive/v drained. A soil that is brownish or
reddish, has moderate to slow permeability, and is
not mottled in the upper meter or so. is well drained.
The lower part of the soil occasionally may be
saturated for a day or so. but neither the
frequency nor the duration of water tables is enough
to adversely impact a biosolids utilization pro-
gram.
A moderate/v well drained soil is brown or
red in the upper part and has a few gray or
yellowish brown mottles in the lower part. Water
tables periodically rise into the lower part of the
soil, saturating it for short periods of time. When
the water table retreats, the large pores drain
easily. but small pores within soil peds stay wet
long enough for some iron to be reduced. The effect
is not large but it is enough to create either some
small gray mottles within peds or some small
yellowish brown mottles on the surfaces of peds.
A somewhat poor/v drained soil is mottled
higher in the profile, although the surface
horizon is usually not mottled, and there may be
a second horizon of well-oxidized. unmottled
soil beneath the surface soil. Water tables rise
higher and persist longer than in moderately well
drained soils.
Somewhat poorly drained soils often have
slow or very slow permeability. If the duration of
saturated conditions is relatively short, mottles
may appear as spots of bright color in a matrix that
still has a brown color. As the duration increases.
however, the soil gradually becomes grayer and
grayer. until the horizon is characterized by a
dark gray matrix containing many prominent
yellowish brown or reddish brown mottles.
Another manifestation of somewhat poor
drainage is high pH and high sodium content.
This occurs in arid regions. where locally high
water tables cause water to move upward through
the soil, carrying salts and sodium with it. and
depositing those salts at the surface as the water
evaporates. These soils have limited agricultural
value and are difficult to reclaim. Biosolids
application, however. may be particularly
beneficial in improving the physical condition of
the soil.
A poor/v drained soil usually is either
mottled in the surface horizon or is gray and
unmottled throughout the profile. The soil is wet
for such long periods of time that most of the
iron has been reduced and leached away. leaving
only the gray color of uncoated mineral grains.
Some poorly drained soils can be improved
with artificial drainage if the permeability is at
least slow. Often. the permeability is very slow.
there is a shallow restrictive layer. or the land-
scape position is so low that outlets are not
available. These soils are suited for land applica-
tion only if the water table retreats naturally for a
period of several weeks during the growing season.
Available water holding capacity
(AWHC)
Available water holding capacity refers to
the amount of water that soils can store for plants
to use. Like permeability and infiltration, the
water holding capacity depends on the amount
and size distribution of soil pores. Not all of the
pores can retain water for plant use. Conse-
quently. only a portion of the total amount of
water in a soil is available.
Gravitational water is not available because
it drains out of the soil as soon as the water table
drops. When the soil is at field capacity. plants
can remove water easily, but each increment of
water removed makes it increasingly difficult for
Internal drainage
does not prevent
land application
of biosolids
provided that
shallow water
tables are not
present at the
time of
application.
Indicators of
Restricted
Drainage
• Gray colors
• Mottles
• Very slow
permeability
• Shaflow
restrictive layers
• Very high pH
• Low-lying
landscape
positions
211
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The higher the
water holding
capacity, the
more productive
the soil, and the
better it is for
beneficial use of
Wa ste water
biosolids.
Factors
Conducive to
High Leaching
Potential
• Rapid infiltration
• Rapid
permeability
• High rainfall
• Heavy irrigation
• Heavy
applications of
liquid biosolids
122
plants to withdraw the next increment. When a
soil is so dry that a plant cannot remove any
more water, the soil is said to be at the wilting
point. This marks the low moisture end of the
available water supply. Water in the soil between
field capacity and the wilting point is called
available water. Water that remains in the soil at
the wilting point is called unavailable water. It is
held so tightly in very small pores. or in very thin
moisture films, that most plants cannot extract it.
Some soils, especially the clays, contain large
amounts of unavailable water.
AWHC is important for land application of
biosolids for two reasons. First, it is a measure of
the ability of the soil to sustain vigorous growth
and high yields of common agronomic crops. In
general. the more productive the soil, the better it
is for beneficial utilization of wastewater
biosolids. Second. it is a measure of the soil’s
capacity to store water applied to the soil as
rainfall. irrigation, or liquid biosolids. The higher
the AWHC. the more suitable the soil, particu-
larly for application of liquid biosolids.
AWHC. like permeability, is difficult to
measure in the field. AWHC can be measured in
the laboratory, but this test has the same kinds of
limitations as the hydraulic conductivity test. The
usual practice is to estimate AWHC using the
key morphological properties of texture, coarse
fragments. and depth of rooting. Structure and
organic matter increase the volume of water-
storing pores. especially in the A horizon.
AWHC is expressed as the number of inches
of water stored in the entire depth of soil. If the
available water from a column of soil wet to field
capacity could be drained into a pan with an area
identical to that of the soil column. then the
depth of water in the pan would be a measure of
the AWHC of the soil.
A deep (>40 inches). medium-textured soil
with no coarse fragments and no restrictive
horizons can store 12 inches or more of available
water. This is an excellent soil for crop growth
and for land application of biosolids.
Soils that are shallow to bedrock or to
restrictive layers. and soils that have a large
volume of coarse fragments. may have AWHC’s
as low as I or 2 inches. These are very poor soils
for growing most common crops. and for most
biosolids utilization programs.
Soil AWHC also can be expressed as the depth
of available water per unit depth of soil. This is
particularly useful in non-uniform soils, because
you can calculate the amount of available water
in each horizon separately. then sum over all
horizons within the depth of rooting.
Each class of soil texture has a characteristic
AWHC. expressed commonly as inches of
available water per inch of soil depth
(Appendix B). If you’re working in the metric
system. the same numerical value can be used as
cm of water per cm of soil.
To determine the total AWHC for a given
horizon, multiply the inches per inch of available
water by the thickness of the horizon. If coarse
fragments are present. niultiply again by the
proportion of the soil that is fine earth. See
Appendix B for an example of this procedure.
Information on water holding capacity is
given in two places in soil survey reports. The first
is the map unit description, which reports the
total soil AWHC as a range (for example. 10 to
12 inches or 1 to 3 inches). The second is the
tabular data (see Table 5) in which the AWHC is
given for each major layer in the soil. As with
permeability data, horizons with similar proper-
ties are grouped together. The AWHC data.
however, represent water storage capacities that
already take into account the presence of coarse
fragments. Simply multiply a representative
value times the thickness of the layer and sum
over all horizons within the effective depth of
rooting.
Leaching potential
Leaching refers to the removal of materials
in solution by water passing through the soil.
Leaching potential is a composite interpretation
developed from information on a soil’s infiltra-
tion. permeability, water holding capacity. and
hydraulic loading. It is one component in the soil
water budget. which balances all water inputs
against all water losses.
Whether from rainfall. irrigation, or waste-
water liquids, water added to the soil follows
several possible pathways. Some may be taken
up by plants and transpired into the atmosphere.
A small amount may be lost directly from the
soil by evaporation. These two are often com-
bined into a single factor called evapotranspira-
tion. Some water may be lost by runoff from the
soil surface, and some may be stored in the soil.
if the available water holding capacity is not full.
Water not accounted for by any of the above
processes passes through the soil. This water
creates the leaching potential. Whether this water
moves slowly by unsaturated flow or rapidly by
saturated flow, any soluble nutrients. trace
inorganics. or organics move through the soil
with it.
A high leaching potential would occur if
liquid biosolids were added to a rapidly perme-
able soil already wet to field capacity. A very
low leaching potential would occur if dried
biosolids were added to a soil that has moder-
ately slow permeability and is dry to the wilting
point. Combinations of permeability. water
holding capacity. climate, and type of biosolids
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intermediate between these two extremes would
represent intermediate leaching potentials.
Biosolids applications alone rarely create
enough hydraulic loading to increase the
leaching potential significantly. For example. a
biosolids product containing 2% solids and
25 lb of available nitrogen per dry ton, applied in
sufficient amount to deliver 150 lb N per acre.
adds about 2.5 inches of water to the soil. Even
this level of hydraulic loading should not cause a
problem on deep well drained soils that are not
already wet to field capacity.
Recognizing the leaching potential that
exists under natural soil and rainfall conditions.
or under irrigation, is important. If the leaching
potential is naturally high. then even dried
biosolids applied to the soil are subject to
leaching. In such cases, site management should
time the application of biosolids to coincide with
periods of low hydraulic loading. The objective
is to provide sufficient tinle for immobilization
of pollutants before the next pulse of added
water passes through the soil.
Trafficabi I ity
Trafficability refers to the soil’s ability to
support the weight of farm equipment. heavy
trucks, or irrigation equipment with a minimum
of compaction or structural deterioration.
Trafficabilitv is important because:
I. Compaction and rutting of the soil reduce
infiltration and permeability:
2. Loss of traction can delay and increase
the cost of the biosolids application:
3. Crops don’t grow as well in compacted
and rutted soil, and the potential for
surface runoff is greater.
Trafficability depends mainly on three
things: texture, moisture content, and plant
cover. Soil moisture is the most important factor.
All soils support weight when they’re dry and
lose strength when they’re wet. The most
important rule is: Avoid driving on an Soil ‘ vlie,i
there ‘s free water (gravitational water) in the top
18 inches. Wait until the soil has dried out at
least to field capacity before driving over it. This
is as true for normal agricultural operations as it
is for land application of biosolids.
Sandy and gravelly soils provide the best
support for vehicular traffic. Unless they are
completely saturated you should be able to drive
on them soon after a rain. A sandy soil can be
compacted. however, so wait until the soil is
dry enough.
Loams and sandy barns should be able to
support most traffic if they are at least as dry as
field capacity. The higher the content of silt and
clay, however, the less stable the soil. Again, if
you’re not sure if the soil is dry enough, be safe
and wait.
Silt barns, silty clay loams, clay barns, and
clays have the lowest strength and are the most
susceptible to compaction. Even at field capacity
these soils contain a lot of water. The weight and
vibrations from heavy vehicles are likely to
break down soil aggregates. compact the soil.
and seal the surface. For these soils, wait until
the soil is considerably drier than field capacity.
even to the point where the surface few inches is
practically at the wilting point.
There is a simple field test to determine if the
soil is above or below field capacity. Take a
sample with a shovel or an auger, grab a handful.
and work it in your hand, squeezing it between
your thumb and fingers. if it sticks to your fingers.
the moisture content is above field capacity. If
you can work it easily but it doesn’t stick to your
hand, it’s approximately at field capacity. If it
won’t stick together in a single. cohesive mass,
it’s considerably drier than field capacity.
Soils with a thick, continuous sod crop provide
better vehicle support than bare soils. Plants
remove some of the water, speeding up the drying
of the soil, and the sod acts as a cushion that
prevents breaking through to the mineral soil.
If a soil is wetter than field capacity.
especially if it’s a silt loam or silty clay loam, even
a sod cover may not be sufficient to support
traffic. Attempting to drive on such soils may
result in the same loss of traction as in a bare soil.
Shrink-swell potential
To a greater or lesser degree. clays tend to
expand when they wet up and shrink when they
dry. Modest shrink-swell activity is beneficial in
forming a well-developed, blocky structure
common to medium-textured soils.
Certain clays undergo large volume changes
upon wetting and drying. These clays are
commonly called montmorillonites. or smectites.
When they dry. they shrink so much that deep.
wide cracks form in the soil. The masses of soil
themselves are so hard and have such tiny pores
that neither roots nor water can penetrate readily.
Upon wetting. these clays expand so much that
all of the cracks are tightly closed, and the soil is
one large. structureless mass of clay. In this
condition, both infiltration and permeability are
very slow, and the soil provides a hostile
environment for aerobic biological activity.
Most soil survey reports contain information
on the shrink-swell potential of the soils in that
area (see Table 5). Any soil, all or part of which
is rated “high” for shrink-swell behavior.
requires careful management for biosolids
utilization. One of the best ways to overcome the
Soil that is too
sticky to work with
your fingers is too
wet to drive on.
Any soil, all or
part of which is
rated “high” for
shrink-swell
behavior,
requires careful
management for
biosolids
utilization.
231
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Factors that Affect
Cation Exchange
Capacity
• Amount of
organic matter
• Soil pH
• Amount of clay
• Kinds of clay
minerals
124
limitations of these soils is to continually add
and incorporate organic matter into the surface
soil.
Soil pH
Soil pH is a measure of the degree of acidity
or alkalinity of the soil. Technically pH is a
measure of the concentration of hydrogen ions in
the soil solution. Numbers on the pH scale run
from 0 to 14. A neutral soil has a pH of 7.0.
Lower numbers indicate more acid soils and
higher numbers indicate more alkaline soils.
Each whole number unit on the scale represents
a 10-fold increase or decrease in hydrogen ion
concentration.
Most agricultural crops to which biosolids
may he applied do best when the soil pH is
between 6.0 and 7.0. Phosphorus availability in
particular is at a maximum when the soil pH is
nearly neutral. In strongly acid soils, where the
pH is less than 5.0. some elements such as iron
and aluminum may become toxic to plants. and
phosphorus is often deficient. At very high pH
values, those greater than 9.0. phosphorus also is
very slowly available, and high sodium contents
severely restrict plant growth.
Acid agricultural soils can be limed to
correct excess acidity. Usual rates of liming are
on the order of 2 to 4 tons per acre. It is not
feasible to lime acid forest soils, but in such
situations, trees generally are well adapted to
growing under acid conditions.
Excessively high soil pH can be corrected
by a combination of treatment with gypsum or
elemental sulfur, leaching. and drainage to
remove salts. Such treatments are expensive and
relatively impermanent. however, and may create
Table 7.—Reaction classes for pH values
pH
Reaction class
<4.5
Extremely acid
4.5 - 5.0
Very strongly acid
5.1 - 5.5
Strongly acid
5.6 - 6.0
Moderately acid
6.1 - 6.5
Slightly acid
6.6 - 7.3
Neutral
7.4 - 7.8
Mildly alkaline
7.9 - 8.4
Moderately alkaline
8.5 - 9.0
Strongly alkaline
>9.0
Very strongly alkaline
additional environmental problems where salts
leached from the soil are discharged. Thus, it is
unlikely that a site would be treated to lower pH
simply to make it more suitable for the land
application of biosolids.
Information on soil pH can be obtained from
soil survey reports. In some soil surveys. pH data
are tabulated under the heading of soil reaction
(see Table 5). The data are given as expected ranges
of pH for a given layer and are particularly
useful for making comparisons among soils that
may be used for land application of biosolids.
Some soil surveys and soil profile descriptions
report the pH as a reaction class, using terms
such as slightly alkaline, or strongly acid. Each
of these terms refers to a standard range in pH
values. These are defined in Table 7.
Nutrient availability
The best way to determine nutrient avail-
ability is to take a representative sample and have
it tested. This is discussed in more detail in
ChapterS. You can, however, make some pre-
liminary inferences about nutrient availability
from some key soil properties. The most
significant of these are texture, color, and soil pH.
Plants extract nutrients from the soil only if
the nutrients are dissolved in the soil solution.
Dissolved nutrients are in an electrically charged.
or ionic form. Many nutrients, such as calcium.
potassium. magnesium. and iron carry a positive
charge. These are called cations. Others, such as
phosphorus and nitrate nitrogen, carry a negative
charge and are called anions.
Cations—calcium, magnesium, potassium.
The availability of nutrient cations depends on
the soil’s Cation Exchange Capacity (CEC). The
atomic structure of tiny, fiat clay particles
generates a small amount of negative electrical
charge within each particle. To balance this
charge. cations in the soil solution are attracted
to and held near the surfaces of the clay particles.
This process. called adsorption, retains cations in
the soil so they are not readily lost by leaching.
Organic matter in soils also provides sites of
negative charge for cation adsorption. In soils
that are nearly neutral. i.e. that have a pH around
7.0. some of the hydrogen ions in organic soil
compounds dissociate, creating additional sites
of negative charge. Cations in the soil solution
can be adsorbed at these sites as well.
If the soil becomes more acid, the concentra-
tion of hydrogen ions in the soil solution increases.
and the hydrogen reclaims its place on the
negatively charged site. This blocks the site from
exchange with other cations in the soil solution.
and the soil CEC decreases. For this reason, the
-------
exchange capacity associated with organic matter
is referred to as pH-dependent CEC.
The numerical value for soil CEC is a
measure of the total amount of negative charge
available to adsorb cations. The CEC value is
expressed in terms of milliequivalents per
100 grams of soil. A typical CEC value is
17 meq/l00 grams soil. The actual value for a
specific soil’s CEC depends on four things:
amount of clay, amount of organic matter. pH of
the soil, and kind of clay minerals. The CEC
increases as the amounts of clay and organic
matter increase, and it is higher in neutral soils
than in acid soils.
The kind of clay minerals affects CEC
because different clays have different atomic
structures, and therefore different CEC values.
Clays that are very sticky and have high shrink-
swell potentials have relatively high CEC’s.
Soils that contain these clays may have CEC
values of -tO or 50 meq/l00 gin.
Clays in brown soils of cool climates
typically have CEC’s in the upper teens to
mid 20’s. Clays in the red soils that are common
in the southeastern U.S. have relatively low CEC
values, typically in the low teens.
In review, the availability of the nutrient
cations is directly related to the soil’s cation
exchange capacity. The higher the CEC. the
more these cations are retained in the soil, where
they are available for plant uptake. The lower the
CEC. the greater the need for supplemental
sources of nutrients for optimum plant growth.
and the greater the potential for loss of nutrients
by leaching into the groundwater.
CEC is not subject to large changes through
soil management. The most important practice is
to maintain high levels of soil organic matter.
Additions of domestic wastewater biosolids can
be beneficial for this purpose. Encouraging
optimum plant growth and returning crop
residues also help maintain high organic matter
levels. Liming the soil to raise soil p 1 -1 helps
release some of the pH-dependent CEC. Prevent-
ing soil erosion not only protects environmental
quality but also keeps the organic matter-rich
topsoil in place.
Anions—nitrate, phosphate. The availabil-
ity of nutrient anions depends mainly on their
solubility in water and the rate of water move-
ment in soil. Anion exchange capacity does exist.
but it is very small relative to the cation exchange
capacity and has little effect on the retention of
nitrate and phosphorus in the soil.
Nitrate is very soluble in water and moves
with the flow of soil water. When plants are
actively growing. their uptake of soil water
creates a hydraulic gradient toward plant roots.
and the nitrate goes with the soil water into the
plant. Conversely, when there is a hydraulic
gradient downward, as there is following a rain
or an irrigation, water in the soil moves toward
the groundwater. and nitrate in solution goes in
that direction.
Because of nitrate solubility. nitrate manage-
ment depends heavily on the rate and timing of
nitrate applications. Nitrate should not be added
to the soil, either as biosolids or as ordinary
fertilizer, when plants don’t need or can’t use it.
or at times of high leaching potential.
Nitrate management also depends on good
management of the organic nitrogen reservoir.
The objective is to encourage mineralization to
coincide with times when plants are growing
vigorously and can use the nitrogen released.
Land application of biosolids should therefore be
timed to match conditions that favor either slow
mineralization or uptake of mineralized nitrogen.
Should mineralization occur when plants are not
present. or at times when plants can’t use all the
nitrate produced. leaching into groundwater may
occur.
Phosphorus avail ability follows another set
of rules. As with all other plant nutrients.
phosphorus is available only when it is in ionic
form in the soil solution. There are several forms
of available phosphorus. all of which are some
variety of phosphate and are negatively charged
anions.
Much of the phosphorus in soil occurs as
organic phosphorus. Decomposition of organic
matter slowly releases this phosphorus so that it
can enter the soil solution as phosphate ions.
Inorganic phosphate compounds are not
very soluble in most soils, and leaching losses
are rare. A greater problem exists in encouraging
phosphorus to go into solution and supplement-
ing with more readily available forms of phos-
phorus fertilizer when natural soil processes
provide insufficient amounts.
The key soil properties for judging phospho-
rus availability are soil color and soil pH. Many
soils that have strong red or reddish brown colors
are very old, highly weathered soils that contain
relatively high amounts of iron and aluminum
oxides in the clay fraction. These clays readily
react with phosphate ions to form complex
precipitates that are insoluble.
Soil pH controls phosphate solubility. In
acid soils, especially the highly weathered
reddish soils, phosphate forms complex.
insoluble precipitates with aluminum ions. In
alkaline soils, insoluble calcium phosphates
form. The best remedy for both situations is to
maintan the soil p1-I as nearly neutral as possible.
Values of soil pH between 6.0 and 7.0 generally
are acceptable for maintaining phosphate
availability.
Nitrate should not
be added to soil
when plants don’t
need or can’t use
it, or at times of
high leaching
potential.
Plan biosolids
applications
so that
mineralization of
organic nitrogen
coincides with
times of vigorous
plant growth.
Phosphate is
sparingly soluble
in most soils.
Leaching losses
are rarely a
problem.
25
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126
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CHAPTER 4
Site Selection
A ny site on which a commercial crop
can be produced using normal farming
practices holds some potential for
beneficial use of domestic wastewater
biosolids. Distinguishing the better sites from the
poorer sites is the focus of this chapter. The best
sites can accept biosolids in any form and
without restrictions on the timing of the applica-
tion, other than those imposed by the crop itself.
Poor sites may restrict the type of biosolids
applied, the method of application. and the timing
of the application. Poor sites also are likely to be
more expensive to manage because additional
biosolids processing may be necessary. storage
may be needed during times that are unfavorable
for application, or special practices are needed to
mitigate problems caused by high water tables.
restrictive layers. or steep slopes.
Several keys are used to facilitate the
determination of soil-site suitability ratings for
land application of biosolids. These suitability
ratings. when used in conjunction with the
maps in soil survey reports, provide powerful tools
for making preliminary evaluations of proposed
sites for beneficial use of biosolids.
Keys for Rating Soil Suitability
For all soil-site evaluations, the frame of
reference is the set of properties of an “ideal”
soil. Departures from the ideal point to specific
limitations that lower the suitability rating for
land application of biosolids. Rating keys.
therefore. are based on departures from the ideal
soil. Once the limitations have been identified.
management practices for dealing with them can
be specified.
The ideal soil
The ideal soil is deep. well drained, and
medium-textured (silt loam, loam, or very fine
sandy loam). It has a black to very dark brown
surface and a brown or yellowish-brown subsoil.
It is neither red nor gray nor mottled.
The subsoil has no restrictive layers (claypan.
fragipan. or dense glacial till) within 40 inches. No
tillage pan or traffic pan has formed beneath the
Ap horizon.
The ideal soil should have more than 3%
organic matter and a pH between 6.5 and 8.2.
The available water holding capacity should be
12 inches or more.
The texture and organic matter together give
the ideal soil moderate or strong grades of
structure in all horizons. But the structure must
be stable, and the soils must have a low shrink
swell potential.
The ideal soil must allow water to enter and
pass through easily, but not too fast. The
infiltration rate should be moderate to rapid. and
the permeability should be moderately slow to
moderately rapid throughout.
The ideal setting for the ideal soil is a nearly
level to very gently rolling surface having slopes
between 0 and 3%. The site must not be on an
active floodplain.
Departures from the ideal soil
Very few soils qualify as ideal. Most depart
in at least a small way, for at least one of the
critical properties. Those soils that have only a
few small departures are still suitable for land
application of biosolids: their limitations can be
overcome easily with a minimum of special
management practices.
The greater the number of properties that
depart from ideal and the greater the degree of
departure, the more severely limited is the soil.
Many of these soils can still be used for biosolids
application, but very careful management is
required, for these sites are much less forgiving
than sites with more suitable soils.
The number and degree of departures from
ideal form the basis for rating soil suitability for
biosolids application. The keys in Tables 8 to 12
show how soil properties are used to rate a soil.
In these keys. the ideal soil is rated excellent.
Soils with a few, easily managed departures are
rated good. Fair suitability and poor suitability
represent increasing degrees of the severity of
limitations that must be overcome with careful
management.
These suitability ratings are nor absolute.
quantitative predictors of soil behavior for
beneficial use of biosolids. They are guides to
the relative suitability of a soil and facilitate
comparison among soils of alternative sites.
Fair or poor ratings do not mean that the site
cannot be used in a biosolids application system.
They indicate that there are more problems to
manage and that it will probably cost more to
overcome the limitations, Many such sites.
however, can and do play an important role in an
overall biosolids management operation.
The suitability of a soil depends as much on
interactions among several properties as it does
on each property individually. These interactions
are expressed by combining information from
two. three or four major properties in each key.
For example. in the depth-texture key (see
Table 8). texture. coarse fragments, and depth to
bedrock all interact to express the nature of the
physical environment for root growth and
biological activity.
271
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In the infiltration key (see Table 9). texture.
structure, organic matter, and shrink-swell
potential interact to control the rate of entry of
rainfall, irrigation water, and biosolids liquids.
The drainage-permeability key (see
Table 10) shows how the effect of soil drainage
class depends on the permeability of the soil.
whether a restrictive layer is present. and if so, at
what depth.
Nutrient availability (see Table 11) depends
on interactions among texture. pH. and organic
matter.
The utility of sloping sites (see Table 12) for
land application depends not only on the
steepness of the slope but also on the infiltration
rate. the depth to bedrock or a restrictive layer.
and the type and density of plant cover.
The procedure for using these five keys
begins by assembling all the data required for
each key. Morphological data (texture. structure.
coarse fragments. depths to bedrock or restrictive
layers) niay be taken either from soil profile
descriptions in soil survey reports or from soil
profile descriptions made by professional soil
scientists in pits dug at a proposed site.
Data on inferred properties (drainage.
permeability, and shrink-swell behavior) may be
obtained from map unit descriptions and tables in
soil survey reports. These inferences also can be
drawn from the morphological properties of the
soils described at the site.
Chemical data (pH and organic matter) may
be available in some soil surveys or from
laboratory analysis of properly collected
samples. For preliminary evaluation, field tests
of pH and field estimates of organic matter may
suffice.
Site data (% slope and type of plant cover)
may be taken either from map unit descriptions
or from on-site observations.
The next step in the procedure is to use the
data assembled to enter each key and determine
the suitability rating for that particular interac-
tion. Some of the keys give dual ratings, one for
liquid biosolids and one for dewatered or dried
biosolids. This recognizes that soils and sites are
more sensitive to liquid biosolids applications.
and that the impacts of unfavorable permeability
or water table conditions may be less severe
where dewatered or dried biosolids are applied.
The final step in the evaluation process is to
determine the overall suitability of the site. This
is simply the lowest of the five separate ratings
obtained from the keys.
Several examples for using the keys are
shown in Table 13. The soils included are
representative soils from widely separated
geographic areas of the United States. Two
examples are discussed here.
128
Table 8.—Depth/texture key for rating soil suitability for land application of biosolids
Subsoil Coarse
texture 1 fragments 2
Depth
>40
to bedrock
20-40
(in.)
<20
Sand None
Loamy sand Gravelly, Cobbly
Very gray., very cob.
Extremely gray., cob.
G 3
F
P
P
G
F
P
P
F
P
P
P
Sandy loam None
Loam Gravelly, Cobbly
Silt loam Very gray., very cob.
Extremely gray., cob.
E
G
F
P
G
G
F
P
F
F
P
P
Sandy clay loam None
Clay loam Gravelly, Cobbly
Silty clay loam Very gray., very cob.
Extremely gray., cob.
G
G
F
P
G
G
F
P
F
F
P
P
Sandy clay None
Silty clay Gravelly, Cobbly
Clay Very gray., very cob.
Extremely gray., cob.
G
F
P
P
F
F
P
P
P
P
P
P
1 Use the texture of the subsoil horizon within 40 inches
See page 12 for definitions of soil textures.
2 Refer to Appendix A for definitions of coarse fragment
3 E = Excellent; G = Good; F = Fair; P = Poor.
that has the
classes.
highest
clay content.
-------
Table 9.—Infiltration key for rating soil suitability for land application of biosolids
Use data from the surface horizon only
Sandy loam Sandy clay loam Sandy clay
Sand Loam Clay loam Silty clay
- Loamy sand Silt loam Silty clay loam Clay
Grade of Organic Shrink-swell Potential 2
structure 1 matter (%) Low-Med High
Weak 0-1 GtE 3 FIG FIG P/F P/F
1-3 GIE G 1E F/G P/F P/F
> 3 GIE GIE G/E FIG P/F
Moderate 0-1 GtE G/E G/E P/F P/F
1-3 G/E G/E G/E F/G P/F
> 3 G/E E/E E/E F/G P/F
Strong 0-1 G/E G/E G/E F/G P/F
1-3 G/E EIE E/E F/G P/F
> 3 GtE EIE E/E GtE P/F
Massive 0-1 G/E P/F P/F P/F P/F
1-3 OlE F/G P/F P/F P/F
> 3 G/E F/G F/G P/F P/F
Single grain — OlE — — —
I Refer to page 14 and Appendix A for definitions of structural grades.
2 to page 23 for definition of shrink-swell potential.
Entries to the left of the slash are for liquid biosolids. Entries to the right are for dewatered,
dried, and composted biosolids. E = Excellent; G = Good; F = Fair; P = Poor.
Table 10.—Drainage/permeability key for rating soil suitability for land application of biosolids
ED&
SWED WD
Drainage
MWD
class 1
SWPD
PD&
VPD
A. Soils with uniform permeability 2
(same class or adjacent classes)
Very rapid P/F P/F
P/F
P/F
P/F
Rapid & Moderately rapid FfG G/E
G/E
F/G
P/F
Moderate & Moderately slow GtE E/E
E/E
GtE
F/G
Slow — G/E
G/E
F/G
F/G
Very slow — F/G
F/G
P/F
P/F
B. Soils with slowly or very slowly permeable restrictive layers 4
Depth to restrictive layer
<20 inches P/F F/G
P/F
P/F
P/F
20-40 inches FIG GtE
F/G
F/G
P/F
> 40 inches GtE E/E
GtE
F/G
P/F
C. Soils with rapidly draining horizons 5
Depth to rapidly draining horizon
<20 inches P/F F/G
FIG
P/F
P/F
20-40 inches F/G GtE
GtE
F/G
P/F
> 40 inches GtE E IE
E/E
GtE
F/G
ED = Excessively drained; SWED = Somewhat excessively drained; WD = Well drained;
MWD = Moderately well drained; SWPD = Somewhat poorly drained; PD = Poorly drained;
VPD = Very poorly drained.
2 Refer to page 18 for definitions.
Entries to the left of the slash are for liquid biosolids. Entries to the right are for dewatered, dried, and
composted biosokds. E = Excellent; G = Good; F = Fair; P = Poor.
Refer to page 16 for definitions.
Refer to page 17 for definitions. 29
-------
Table 11.—Nutrient availability key for rating soil suitability for land application of
biosolids
Use data from the surf
Soil texture
ace horizon only
Organic
matter (%) <4.5
Soil pH 1
4.5-5.5 5.5-6.5 6.5-8.2 8.2-9.0 >9.0
Sand, Loamy sand 0-1 P 2 P P F F P
1-3 P P F F F P
>3 P P F G G P
Sandy loam, Loam, 0-1 P P F F F P
Sandyclayloam, 1-3 P F F G G P
some Clays > 3 F F G E G F
Loam, Silt loam, 0-1 P P F G F P
Siltyclayloam, 1-3 P F G E G F
Clay loam, most Clays > 3 F F G E G F
‘See page 24 for definition.
2 Ratings apply equally to all biosolids. E = Excellent; G = Good; F = Fair; P = Poor.
Table 12.—Slope effect key for rating soil suitability for land application of biosolids
Slope (%)
Depth to bedrock or to
restrictive layer (in.)
lnfiltrat
E
ion rating
G
(from Ta
F
ble 9)
P
0-3
<20
20-40
>40
G 12
E
E
G
E
E
F
G
G
P
G
G
3-7 or 3-8
<20
20-40
>40
F
G
E
F
G
G
P
F
G
P
P
F
7-12or8-15
<20
20-40
>40
F
F
G
F
F
F
P
F
F
P
P
P
2-20 or 15-30
<20
20-40
>40
P
F
F
P
F
F
P
P
P
P
P
P
> 20 or> 30
<20
20-40
>40
P
P
F
P
P
P
P
P
P
P
P
P
‘Ratings apply equally to all biosolids. E = Excellent; G = Good; F = Fair; P Poor.
2 Increase the rating one class for applications on forested soils that have organic surface horizons.
130
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The Woodburn soil is a deep. moderately well
drained soil on nearly level lacustrine terraces in
the Willamette Valley of western Oregon. Textures
are silt loam in the surface horizon and silty clay
loam in the subsoil. There are no restrictive layers
and no tillage pans. The surface horizon has weak
structure, but it contains over 3% organic matter.
The permeability is moderate above 32 inches and
slow below 32 inches. The pH is 5.6-6.5 through-
out.
The first key, depth and texture, gives this
soil a good rating because the subsoil texture is a
little heavier than ideal. The second key.
infiltration, gives the soil a good rating for liquid
biosolids and an excellent rating for dried
biosolids. Weak structure is the limiting factor.
The third key. drainage and permeability.
also gives the soil a good rating for liquid
biosolids and an excellent rating for dried
biosolids. The only limitation is a temporary
water table between 24 and 40 inches.
The fourth key. nutrient availability, gives
the soil a good rating for all types of biosolids.
The soil pH is a little lower than ideal, but high
levels of organic matter and medium texture
partially compensate. The fifth key. slope, gives
the soil an excellent rating for both liquid and
dried biosolids applications.
Overall, the Woodburn soil has one excellent
and four good ratings for liquid biosolids. and
three excellent and two good ratings for dewa-
tered or dried biosolids. The suitability is
considered “good” for either type of biosolids
application.
The Volusia soil is a deep. somewhat poorly
drained soil formed in dense glacial till on low.
rolling uplands in the southern tier of New York
State. The textures are channery silt loam
throughout the profile. The surface horizon has
weak structure and contains more than 3%
organic matter. The pH is between 5.1 and 5.5.
Volusia has a dense, slowly permeable
fragipan at 17 inches that restricts movement of
both water and plant roots. Both the colors and
the presence of mottles indicate that perched
water tables stand above the fragipan for
significant periods of time.
Table 13.—Suitability ratings for five representative soils in the United States
Cecil (SC)
Clarion (IA)
Soil series (state)
Plainfield (WI)
Volusia (NY)
Woodburn (OR)
Soil Properties
Texture of subsoil Clay
Loam
Sand
Silt loam
Silty clay loam
Coarse fragments None
None
None
Channery
None
Depth (in) > 40
> 40
> 40
> 40
> 40
Texture of surface Sandy loam
Loam
Loamy fine sand
Silt loam
Silt loam
Structure grade Weak
Weak
Weak
Weak
Weak
Organic matter, % 1-3
> 3
1-3
> 3
> 3
Shrink-swell potential Low
Low
Low
Low
Low
Drainage class WD
WD
ED
SWPD
MWD
Permeability Moderate
Moderate
Rapid
Very slow
Slow
Depth to restrictive
layer (in) > 40
> 40
> 40
17
> 40
Depth to rapidly
draining layer (in) > 40
> 40
> 40
> 40
> 40
pHofsurfacesoil 5.1-5.5
6.1-6.5
6.6-7.3
5.1-5.5
5.5-6.5
Slope (%) 6-10
2-5
2-6
8-15
0-3
Suitability ratings (Tables 8-12)
Depth/Texture key GIG
E/E
GIG
GIG
GIG
Infiltration key GtE
GtE
GtE
GtE
GtE
Drainage/Permeability key E/E
E/E
FIG
P/F
G/E
Nutrient Availability key F/F
G/G
F/F
F/F
GIG
Slope key F/G
GIE
G/E
F/F
EIE
Overall rating
Liquid biosolids Fair
Good
Fair
Poor
Good
Dewatered/Dried biosolids Fair
Good
Fair
Fair
Good
311
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Despite the fragipan. this is considered to be
a deep soil, and the textures by themselves are
favorable for beneficial use of biosolids. Only
the coarse fragments cause the depth/texture
rating to drop from excellent to good. The
infiltration key rates Volusia as good for liquid
biosolids and excellent for dried biosolids. the
only limitation being weak structure.
Interactions between drainage, permeability.
and the restrictive layer. however, cause the soil
to have a poor drainage/permeability rating for
liquid biosolids and a fair rating for dried
biosolids.
The nutrient availability key gives the soil
only a fair rating because both the clay content
and the pH are considerably lower than ideal.
The slope rating is fair for all kinds of biosolids
applications because of the relatively high runoff
potential on 8-15% slopes of soils that have a
shallow restrictive layer.
Overall. Volusia earns two good. two fair, and
one poor for liquid biosolids. and one excellent.
one good. and three fair for dried biosolids. The
suitability for liquid biosolids is rated as poor. hut
for dewatered or dried biosolids. the suitability is
fair.
Overcoming limitations is largely a matter
of applying common sense in conjunction with
knowledge of soil. biosolids. crop. and climate.
Most of the possibilities have already been
discussed in Chapter 3.
Since the intrinsic texture or depth of the
soil is difficult to modify. manage such limitations
by applying only dried or dewatered biosolids
and timing applications to coincide with dry
seasons.
The best way to manage rapid infiltration in
coarse-grained soils is to use dried biosolids
products having relatively high percent solids.
Do not apply biosolids during rainy seasons
when the leaching potential is high.
The best cure for low infiltration rates is to
add organic matter. Biosolids are excellent
amendments because they provide a source of
organic matter. Mixing biosolids into the surface
soil by disking is preferable to leaving them on
top of the soil surface. If infiltration has been
reduced by formation of a tillage or compaction
pan just below the surface horizon, shattering the
pan by ripping the soil when it is dry may be
very helpful.
Drainage problems in some soils of uniform
permeability may be corrected with artificial
drainage. This may not be a cost-effective solution.
however, and there are federal and state regulations
that preclude drainage of some wetlands.
If you can’t drain the soil, then minimize the
problem by using dewatered or dried biosolids
and plan on applying them only during dry
seasons after water tables have receded. This
may be the only remedy for soils that have
temporary. perched water tables above slowly
permeable restrictive layers.
If pH is limiting, you may be able to solve
the problem by liming. The feasibility of liming
depends on the economics of the farming
operation. If the pH is not much below 6.5. for
example. only 2 to 4 tons of lime may be
required. and if a high value crop is being grown.
then liming to mitigate acid soils is feasible.
Steep slopes need to be managed to encour-
age infiltration and minimize surface runoff.
Appropriate ways to deal with steep slopes in a
biosolids utilization program are to use high-
solids products. to apply only on pasture or hay
fields, and to practice soil conservation with
cross-slope farming. reduced tillage. and
diversion terraces.
Soil surveys are inventories of the soil
resources of an area. The information in a soil
survey is useful in finding possible biosolids
utilization sites and assessing the relative
suitabilities of the alternative sites under
consideration.
Components of soil surveys
Published soil survey reports contain three
interrelated parts: maps. text, and tables. Soil maps
show the spatial distribution of the different kinds
of soils that occur in an area. The text describes
the properties of each of the kinds of soils shown
on the maps. The tables provide additional data
about soil properties and interpretations of those
properties for a variety of land uses.
Maps. Lines drawn on soil maps surround
areas called delineations. Each delineation
represents the size. shape. and location of a
specific body of soil. Each delineation contains a
symbol that identifies the map unit of that
delineation. Each map unit has two components:
the dominant kind or kinds of soil, and other
soils that are known to occur but are too small to
be shown separately at this scale of the map.
These other soils are called inclusions.
Overcoming soil
limitations is
largely a matter
of applying good
common sense in
conjunction with
a good
understanding of
soil, biosolids,
crop, and
climate.
How to Use Soil Surveys to
How to deal with limiting properties Facilitate Site Selection
Kinds of Soil
Survey Information
Maps
• Delineations
• Symbols and legends
Text
• Map unit descriptions
• Soil profile
descriptions
Tables
• Soil and water
features
• Physical and
chemical properties
• Engineering
properties
• Estimated yields
132
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On most soil maps the smallest area that can
reasonably be shown is 3 to 4 acres. Any body of
soil smaller than that is an inclusion in a larger
delineation of a different kind of soil. Inclusions
also occur because the boundaries between
different soils are not sharp lines but gradual
zones of transition. The lines on a soil map are
placed as nearly as possible at the center of that
transition zone. It is unrealistic to expect natural
soil boundaries to change abruptly within a few
feet. as the map might suggest.
Inclusions are important because they may
affect the suitability of a site. That’s why soil
maps, though very helpful in preliminary site
analyses. must be supplemented with on-site
evaluations before final decisions are made.
Text. Soil survey text contains both map
unit descriptions and soil profile descriptions.
Map unit descriptions give the name of the
dominant soil, the texture of the surface horizon.
and the range of slopes on which the soil occurs.
Information on depth. drainage, permeability.
AWHC. and landscape of the dominant soil is
also presented. Map unit descriptions identify the
other kinds of soils that are most likely to be
found as inclusions and indicate how much of
the area the inclusions are likely to occupy.
Soil profile descriptions give detailed.
technical information on the properties of each
major kind of soil, or soil series, found in the soil
survey area. Each series is described in terms of the
horizons that are present and the texture, color.
structure. pH. and other properties of each horizon.
Tables. Tabular information summarizes
key properties and interpretations for each map
unit. Of all the tables, four are particularly
relevant to land application of wastewater
biosolids.
The table on Physical and Chemical
Properties provides information on clay content.
permeability. AWHC. pH. shrink-swell potential.
and in some cases, organic matter content.
The table on Soil and Water Features gives
information on runoff potential (hydrologic group).
flooding, water tables, and depth to bedrock.
The table on Engineering Properties contains
additional data on texture and coarse fragments.
The table on Yields Per Acre of Crops and
Pasture shows the kinds of crops that are
commonly grown and the relative yields that can
be obtained under good management.
Using soil survey information to
rate soil suitability
The objective here is to extract from soil
surveys all the information needed to make a
preliminary evaluation of site suitability by
rating each of the soils present according to the
criteria in tables 8-12. Soil surveys can be used
either to evaluate sites that have already been
identified or to help locate potential sites for
future consideration.
Evaluation of known sites. The first step is
to locate the area in question on the Index to
Map Sheets. This index identifies the specific
map sheet or sheets that include the area. Turn to
those specific map sheets and locate the area.
Make a list of all map unit symbols for the
delineations that cover the potential land
application area. Use the legend to determine the
specific soil name that corresponds to each
symbol.
The next step is to read about the soils in
both the map unit descriptions and in the soil
profile descriptions. Much of the information
needed is in these nan-atives. Finally, consult the
relevant tables to complete your data collection
process.
You should now have enough information to
rate the dominant soil of a map unit using the
five keys in tables 8-12. Then write the suitabil-
itv for each delineation on the map or color each
delineation according to its suitability class.
Two things should now be apparent: the
amount of land in each suitability class, and the
pattern of adFnLvture of soils in different classes.
The pattern is much more significant. Areas of
uniform suitability. even if they are uniformly
fair or even poor. are easier to manage than areas
of non-uniform suitability. Such an area is
illustrated in Figure 4.
Using Soil
Surveys for
Preliminary Site
Evaluation
• Locate the site
on the Index to
Map Sheets
• Locate the site
on the
corresponding
detailed map
sheet
• List all map unit
symbols shown
• Identify symbols
in the legend
• Read map unit
descriptions
• List inclusions
likely to be
present
• Read
descriptions of
dominant soils
and inclusions
• Consult tables
for relevant data
Figure 4.—Soil ;iiap showing a pattern that is not
limiting for land application of sludge.
331
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When small areas of fair or poor soils are
distributed entirely throughout larger areas of
good or excellent soils, the pattern may limit the
management of the entire site to that of the least
suitable soil. Figure 5 shows a pattern of an area
of dominantly well drained and moderately well
drained soils dissected by thin strips of poorly
drained soil.
One problem with limiting patterns is that
suitable soil areas may be too small to manage
independently, yet managing the whole area as if
it were suitable increases the potential for
contamination of surface or groundwater in the
poorly suited areas.
Another problem is that access to the more
suitable areas may be limited to times when the
trafficability of the poorly suited soils is
acceptable. The only viable solution to
management of these kinds of soil patterns is to
manage the entire area as though it all consisted
of the more limiting soils in the pattern.
The last step in using soil survey information
is to consider possible effects of the inclusions
within each map unit delineation. The
descriptions of each map unit state explicitly
what kind of included soils are most likely to
occur. Read the map Unit and soil profile
descriptions of the inclusions to determine their
properties. If necessary. determine the suitability
rating for each of the inclusions.
Locating potential sites. The other use of
soil surveys is to help find some possible sites
for biosolids application. Start with the General
Soil Map. a small scale map of the entire soil
survey area. Map units for the General Soil Map
are Soil Associations. Each soil association
consists of two or three major soils that occur in
a regular. predictable pattern on the landscapes
represented by the corresponding areas shown on
the General Map. The legend for the General
Map is printed on the same page as the map.
Each association is described in more detail in
the text, usually near the beginning of the report.
Use these two sources to identify associations
dominated by deep. well and moderately well
drained soils on nearly level landscapes.
Associations dominated by poorly drained soils.
soils on flood plains, or soils on steep slopes are
not as likely to have large areas of suitable soils.
Return to the General Soil Map and locate
the areas where the more suitable associations
occur. Locate the corresponding areas on the
Index to Map Sheets and select two or three map
sheets. Turn to these sheets and find the areas
dominated by map units of suitable soils. There
may not be any good areas for land application
on a particular map sheet, but you can use this
process for some initial screening to identify
areas that warrant further investigation.
Limitations to the use of soil maps
Published soil surveys are excellent tools for
generalized site evaluation and preliminary site
screening, Soil surveys cannot be used for
detailed site evaluations because of the scale of
the map. This is not the fault of the soil survey.
nor does it reflect on the accuracy with which the
map was made. It means only that standard soil
survey maps cannot resolve soil differences that
are smaller than four or five acres in size. To
assume otherwise is to use the information
provided incorrectly.
The only solution to this problem is to make
an on-site investigation, and, if necessary, have a
more detailed soil map made by a professional
soil scientist. This investigation will reveal
exactly what kinds of inclusions are present.
their location, and the extent to which they, or
the pattern of admixture of other soils, may limit
the use of the site.
Detailed on-site studies are particularly
necessary for major projects and projects in
which liquid biosolids are going to be applied.
Where only dried biosolids will be applied, or
where biosolids will be applied only once or at
infrequent intervals, the information obtained
from the soil survey may be adequate to assess
site suitability.
Fiure 5.—Soil nap showing a limiting pattern for
1(111(1 application of slud ’e
Using Soil Surveys
for Locating
Potential Sites
• Consult the
General Soil Map
• Select a soil
association
dominated by
suitable soils
• Locate a large
area of that
association on the
General Soil Map
• Locate the same
area on the
Index to Map
Sheets
• Turn to the
corresponding
detailed maps
and study the
soil patterns
• Consult text and
tables as
necessary
134
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Crop Management Factors
CHAPTER 5
D esigning. implementing. or evaluating
a plan for beneficial use of domestic
wastewater biosolids requires working
within the farmer’s or site operator’s
existing management system. Biosolids utiliza-
tion is not likely to alter decisions on the crops to
grow. the crop rotations to use, and whether to
drain. irrigate, or lime the soil. The crop manage-
ment system dictates when a field is accessible.
the frequency of biosolids applications, the
expected amount of nutrients the biosolids must
deliver, and the application methods.
Crop management factors that bear directly on
the design of a biosolids utilization program
include crop choice, nutrient management. water
management. and conservation practices.
Application of biosolids to farmland also
requires the management practice of long term
momtoring.
Choice of Crop
Biosolids can be applied to row, grain.
pasture. horticultural, and tree crops. Some
crops. such as leafy green vegetables and root
crops. may accumulate trace inorganics. and
should not be grown on soils to which biosolids
have been applied. The crops most likely to be
used in a biosolids management program are
pasture and forage. grain and grass seed, and row
crops. Row crops include food crops (crops
grown for direct human consumption or animal
feeds) and non-food crops such as cotton.
Christmas trees, and ornamentals.
Pasture and forage crops offer the greatest
flexibility for application of biosolids because
access is not limited by the crop’s growth stage.
Biosolids may be applied whenever climatic and
soil moisture conditions are favorable. The sod
created by pasture and forage crops also pro-
motes infiltration, controls erosion, and enhances
site trafflcabilitv.
One disadvantage of pasture sites is that
biosolids cannot be easily worked into the soil.
With surface applications, up to 50% of the
NH 4 -N in the biosolids may be lost by volatiliza-
tion. This must be considered when calculating
the amount of biosolids needed to meet nutrient
requirements. Furthermore. some of the benefits
of biosolids as a physical soil conditioner cannot
be realized with surface applications .Another
disadvantage is that a waiting period after
application, usually 30 days. is necessary before
animal grazing can resume.
Grain and grass seed crops are well suited for
biosolids utilization, although application may be
limited to a single annual application approxi-
mately a month prior to planting. At that time.
you can drive over the soil and apply biosolids
in any form and work them into the soil. This
preserves both the ammonia and the physical ben-
efits.
For fall-seeded crops. biosolids can be
applied in August or September. Usually there
are enough times when the soil is dry enough to
apply biosolids without undue risk of runoff.
leaching, or soil compaction.
In some climatic regiom. fall applications to
warm, moist soil may create nearly optimum
conditions for mineralization of organic nitrogen.
As a result, the production of nitrate is out of
phase with crop needs. The excess nitrate is
subject to leaching as soil moisture increases
through the following winter and spring.
For spring-seeded grains, the window of
opportunity for applying biosolids is much
narrower. In many areas the soil does not dry out
enough to support traffic until planting time. In
this situation, it may be necessary to apply the
biosolids. plow and/or disk them into the soil.
and plant the grain immediately.
Low amounts of readily available N in most
biosolids indicate that supplemental fertilizers
may be needed to start spring seeded crops.
Subsequent mineralization, however, is more
likely to match plant needs throughout the
remainder of the growing season. These relation-
ships must be considered when determining the
total amount of biosolids to apply to the field.
Row crops, especially annual ones, are
generally planted in the spring, and the same
principles apply as for spring grains. A single
application prior to planting is the most common
procedure. Access is good. but trafficability may
be limiting, and starter fertilizers may be
necessary.
Farmers need to be aware that unprocessed
fruit and vegetable crops cannot be planted on
biosolids-amended soils for several months (see
“lag times” in Chapter 2). Processed fruits and
vegetables can be grown on biosolids-aniended
soils, but some processors may not accept such
crops simply to avoid possible repercussions
from consumers.
Row crops grown for animal feed, such as
corn and soybeans. and row crops that are not
eaten. such as cotton, are good choices for a
biosolids utilization program.
Nutrient Management
Biosolids are fertilizer materials and are
therefore an integral part of the nutrient manage-
ment program. The crop type. yield. rotation, and
soil test data are all used to design an overall soil
fertility management program.
Work closely with
farmers and their
Extension agents
or crop
consultants to
make sure that
biosolids can be
properly fitted into
the overall crop
management
plan.
351
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The amount of
fertilizer nutrients
that biosolids must
deliver depends on:
• Kind of crop
• Expected yield
• Amounts of
residual nutrients
• Amounts of other
commercial
fertdizers used
136
Fertilizer recommendations are based on a
combination of farmer experience and long-term
research to correlate soil test data with crop
response to added fertilizer. These research
results are available in many states as fertilizer
guides published by the Extension Service.
County Extension agents and agronomic
consultants use fertilizer guides to assist farm
managers develop nutrient management programs.
Fertilizer nutrients are expressed in terms of
pounds N. pounds and pounds K O. For
example. a bag of fertilizer labeled 16-8-8 delivers
16% N. 8% P 2 O . and 8% K . O by weight.
Biosolids data, by contrast, are expressed in
terms of the elemental concentrations of N. P.
and K. not their oxide equivalents. Although
biosolids data and fertilizer conventions are the
same for nitrogen. biosolids P must be converted
to P,O. and biosolids K to K,O. in order to
accurately assess the nutrient value of a hiosolids
product.
To convert P to multiply by 2.27. or to
convert P,O to P. multiply by 0.44. Thus, adding
100 pounds of biosolids P to soil is the same as
adding 227 pounds of P.O . Conversely, if a fertil-
izer recommendation calls for 100 pounds of P,O .
that would require only 44 pounds of biosolids P.
To convert K to K,O. multiply by 1.20. or to
convert K 2 0 to K. multiply by 0.83. Adding
50 pounds of biosolids K to a soil adds the
equivalent of 60 pounds of K . O. whereas a
fertilizer recommendation calling for 50 pounds
of K 2 0 would require only 42 pounds of
biosolids K.
The amount of fertilizer nutrients that
biosolids must deliver depends on the kind of
crop. expected yield of the crop. amount of
residual nutrients in the soil, and use of commer-
cial fertilizers or lime.
The kind of crop and the expected yield of
the crop determine the total nutrient requirement
for the crop. Grass pastures and hay crops. for
example. may require up to 250 pounds per acre
of fertilizer nitrogen during the growing season.
If the grass contains a legume. only 70-80
pounds of nitrogen should be applied. Spring
grains and grass seed crops need about
150 pounds N per acre, whereas row crops
require approximately 250 pounds N per acre.
Higher yields mean greater nutrient uptake.
and this implies a greater need for nutrients to be
supplied from fertilizers or biosolids. Crop yields
depend on the weather and the farmer’s
management program. Historical records of crop
yields, and the knowledge of local county
Extension agents and crop consultants may be
your best guides to estimating crop yields.
Fertilizer recommendations must account for
residual nutrients from all sources. Prior crops.
residue management. and prior biosolids applica-
tions affect the amount of residual nutrients in the
soil,
If biosolids are applied to a field where
spring grain will be grown and the previous crop
was grass hay or pasture. then there is essentially
no residual nitrogen. All of the crop’s needs must
come from supplemental sources. If the previous
hay crop contained a legume. then as much as
75 lb N/a may remain in the soil. If the previous
crop was a row crop. as much as 50 lb/a of
residual N may remain. If the previous crop was
a grain crop. there may be only 25 lb/a
residual N.
Crop residues are valuable soil amendments
and should be returned to the soil. Both hiosolids
and crop residues add plant nutrients, help
maintain soil organic matter levels, and improve
the physical condition of the soil.
Harvestingpasture. hay. and silage crops leaves
little residue to return to the soil. Residual nutrients
from these crops are correspondingly low. Field
corn, grain, and grass seed crops leave relatively
large amounts of residue. Working these residues
into the soil returns larger aniounts of nutrients.
Removing these residues, either by burning or by
baling, lowers the residual nutrient supply.
Prior applications of biosolids may result in
significant increases in nutrient pools. The rule
of thumb for nitrogen is: the mineralization rate
of organic nitrogen in subsequent years is about
half of the previous year’s rate. Calculations of
residual nitrogen from prior biosolids applica-
tions are illustrated in Chapter 6.
Some biosolids deliver more potassium and
phosphorus than a crop needs in a single year.
These excesses add to the residual nutrient
supply. especially when biosolids are applied to
the same field several years in a row.
The amount of biosolids to apply depends
on whether the fertility plan intends to meet all.
or only a portion. of a crop’s needs with land-
applied biosolids. Many row crops. for example.
require more nitrogen at the beginning of the
growing season than can be supplied by slow
mineralization of organic nitrogen. Farmers can
meet this need by placing fertilizer in a band near
the seed when planting. This reduces the amount
of biosolids required to provide the remaining
nitrogen needed.
For fall-planted grains, nutrient management
may include a broadcast application of fertilizer
in the spring. This would substantially reduce the
amount of biosolids applied and worked into the
soil prior to planting. This spring fertilizer need
might be met with biosolids. if a liquid biosolids
product, which could be applied with an irriga-
tion gun, were used.
-------
Soil Testing
Regular soil testing is essential in evaluating
residual nutrient supplies and formulating
fertilizer recommendations. Soil testing is also
essential in planning and designing good crop
and biosolids management programs.
Getting a good sample is vital in getting
good soil test information. Neither the biosolids
generator nor the biosolids regulator should be
expected to sample or test the soil. For biosolids
utilization programs. the farmer, site operator.
county Extension agent. or crop consultant
should sample the soil. Soil samples should truly
represent the field on which biosolids will be
applied. Most state agricultural Extension
Services can provide a list of acceptable soil
testing laboratories and have publications on
obtaining a good sample (see Figure 6).
If a field contains two or more distinctly
different kinds of soils, separate samples of each
soil should be taken. For each kind of soil.
several subsamples should be taken from all over
the field, mixed together in a bucket, and a small
portion withdrawn for analysis. The soil should
not be contaminated with manure. biosolids,
lime, fertilizer, or other substance.
Soil test data on available potassium and
phosphorus are the basis for recommendations
on supplemental potassium and phosphorus
amounts.
Nitrogen values may fluctuate widely as
environmental conditions and biological activity
in the soil change. Therefore, soil tests for nitrate
are not often used to measure residual N or as the
basis for crop nitrogen requirements.
Instead, research results on crop responses
under controlled conditions are used to forecast
nitrogen needs. If soil test nitrate values are
reported. check that the samples were properly
handled prior to analysis. Proper handling means
minimizing the opportunity for mineralization
between sampling and analysis. This can be done
by refrigerating or freezing the sample. If the
sample is dry to the wilting point, little minerali-
zation will occur, as long as the sample is
maintained in the dry state.
Soil testing is
essential in
order to plan
good crop
and biosolids
management
programs. The
most important
part of a good
soil testing
program is getting
a good sample
of soil to test
knportance of Taldng
Good Sod Samples
A ned we in the only pleats asp
cile&g whether lane end leibuzer
we needed. I’ cer.ifasodsam-
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515 wiSeacre c i the field, the
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dwfl,Sdc ci the field. The
lodneseg dead. 0 ..s a hely ou
Wee good sod —
Whus to 1s1 Sod Samples
be sod sençlee w any come-
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reconhteendsiatus eeely enough i n
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Nd ssmpdng thee lecturer the-
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etsi f leeS frozen. is permsssi-
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a a im bating at come ci sod in
— defit Natmdy. d i r —
ateig e — p bating ino i
Using a p 1 St at ae te contact a
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Where to lofts Sod Samples
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Was S sufbcserd. A ccn ls
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a) Deed torto ises fleck frames
b) Line Sedge at nssruse —
AclenS thopainge
d) Fences at coeds
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been bonded
I) Eroded Anode
q) Las spat
In geneS, do nut sample any wee
cia Se that asses widely triter
the rare ci the field in colic. tactility.
Sops enhas (sandy. deurey. sac).
drainage at pmdurflnity. i i the an.
twinS sea in begs eteoughin te
a flat lerdear overse a s
dIrect from the rest ci the field.
samples aepsrsely. F inwises Or
app residues sit on the sod 5w.
lept then atgenc m acedt
shotS be pushed aside end i r s
induded in the sod sample
On oontiured Acids, sample eact ’
strip separately it fi in lire acres or
bags. taking S lead one cornpos-
it. ssnpla per fist acres Cores
from ran at three sina i tint’s may
becombined to gsa a single car-
posits sample if the combined area
doewff easd five acres and ii as
drips trace idereicat cropping and
manageniws a ires
SpecS coewldeestlons lot no-sill
flade. Fields that have nat beer
sled r live 5 wats or once may
decelop an acid lewd the w i
lace horn the tine ci nitrogen far-
tiara Such an acid layer could
reduce the etlecfiseness ci I llative
herbicides. Sod phosphorus (F)
and porasslum (K) are also lately to
build up in the suctace sod if 4 is
sat deed. tan acid tais is tics.
perlad. take a separase sample to
depth ci only tee inches When
sending the sod in the lala indicate
the sampling depth ass only rem
sties This sample ins be rested
!“pling Soils for Testing
U. SenSes, LO. Beesdy end .Lt Pers
— ci ansp . ....,. t s tlee tree, Sea; eceae,s esreocee ci . 2oaae
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a; — sheen in S f.
Figure 6—Example brochure
Ott soil test sampling
371
-------
Water Management
Wet soils that are
artificially drained
require more
careful
management
than naturally
well drained soils.
Runoff and
erosion control
are absolutely
essential to sound
management of a
biosolids
application
program. The
best way to
promote
infiltration and
reduce erosion
is to keep the
soil under a
permanent sod
crop.
38
Water management deals with deficiencies
and excesses of water in the soil. Deficiencies
are managed with irrigation, and excesses are
managed with drainage.
Irrigation affects biosolids management in
two ways. First, crop yields are higher on
irrigated land than on dryland, which increases
the amount of nutrients that the biosolids must
deliver. Second. irrigation increases the hydrau-
lic loading of the soil, which increases the
potential for both leaching and runoff. The risk
is not large. however, as long as the irrigation
system is well designed and the irrigation
program is well managed.
Good biosolids management. with respect to
irrigation, includes not irrigating immediately
after the biosolids application, avoiding over-
irrigation, and refraining from applying biosolids
on flood or furrow irrigated fields. County
Extension agents and crop consultants can provide
advice on irrigation practices and scheduling.
Drainage of wet soils affects crop manage-
ment and land application of biosolids. Farmers
and site operators are unlikely to drain soils only
to accommodate a biosolids application pro-
gram. Soils that are already drained present a
wider choice of suitable crops. Higher yields.
higher nutrient requirements. and higher
biosolids application rates are more likely on
drained soils.
Artificially drained soils require more
careful management than naturally well drained
soils. Drainage with surface ditches may lower
the water table, but because the ditches drain
into natural streams, care is required to avoid
direct input of biosolids into surface drainage
ditches. Limiting biosolids applications to the dry
times of year when water tables are naturally low
and ditches are empty is a good management
practice.
Drainage through subsoil tile lines
effectively lowers the water table. but tile drains
ultimately empty into surface waters. Leaching
of excess nitrogen applied either as biosolids or
as commercial fertilizer can and does occur.
Planning biosolids applications so that the
release of nitrogen coincides as nearly as
possible with plant uptake of nitrogen is a good
management practice for this situation.
Soil Conservation Practices
Runoff and erosion control are essential to
sound management of land application of
biosolids. Overland flow increases the potential
for contamination of surface waters with
biosolids. Erosion decreases soil productivity.
increases sediment loads in streams, and carries
biosolids into surface waters.
Soil conservation practices are designed to
promote infiltration and slow down the velocity
of water that flows over the surface. The best
way to promote infiltration and reduce erosion is
to keep the soil under permanent sod crop plant
cover, such as pasture and hay crops. Some
perennial grass seed crops are also very effective
in reducing runoff and erosion.
For cultivated crops. particularly grain
crops. reduced tillage can be an effective erosion
control measure. Reduced tillage. as opposed to
conventional tillage. does not turn the soil over
with a moldboard plow. Instead the soil is disked
or mixed slightly with sweep plows in such a
way as to partially incorporate crop residues.
loosen the soil, break up compacted layers. and
leave a rough soil surface.
Some studies have shown that additions of
hiosolids enhance the erosion control
effectiveness of reduced tillage. The organic
matter in hiosolids augments the organic matter
in crop residues and enhances the formation of
stable soil aggregates that increase the porosity
and infiltration rate of the surface soil.
Widely spaced row crops provide little
protection for the soil surface, particularly in
early stages of growth. For these crops. reduced
tillage is better than conventional tillage. and
injecting or working biosolids into the soil is
better than surface applications.
As soil slope increases, the potential for
runoff and erosion increases dramatically.
Permanent cover sod crops are particularly
valuable for controlling erosion on steep soils.
Residue incorporation and reduced tillage methods
are particularly important for grain and row crops.
Effective erosion control on steep slopes may
require additional conservation practices. Cross-
slope farming. i.e.. planting crop rows on
the contour instead of up and down hills, is one
practice.
Diversion terraces are low ridges con-
structed at intervals across a slope. These
terraces interrupt the flow of water down slope
so that high velocities of flow cannot occur.
Water caught behind a terrace has more time to
soak into the soil, and excess water can be
diverted across the slope to a grassed waterway.
where it can be conducted safely downslope
without causing erosion.
Sometimes runoff is inevitable, even from
pastures and well-protected crop fields. This is
especially true during high-intensity storms and
when the soil is frozen. Regardless of other
conservation practices that may be in place. biosolids
should not be put on the soil at these times.
-------
Monitoring
and Record-keeping
If biosolids are going to be applied to a fann
field over a number of years. the soil should be
sampled and tested regularly to monitor residual
nutrient supplies, accumulations of trace
inorganics and organic contaminants, and
increases in soil salinity from year to year. For
row crops. grains, and other cultivated crops.
annual sampling is a good idea. For pastures that
are managed at a low level of intensity, sampling
does not need to be done as frequently.
Some biosolids may be quite high in soluble
salts. Long-term. heavy applications may cause
an increase in soil salinity, even to the point
where salt-sensitive crops are affected.
Nitrogen in soil generally does not accumu-
late to levels dangerous for plant survival. The
only problems with excess nitrogen are excessive
vegetative growth that leads to a plant condition
called lodging, and in some cases, a delay in
flowering and fruit development.
The major risk from long term applications
of nitrogenous materials is the possible increase
of nitrate nitrogen in groundwater sources used
for drinking water. This occurs onl when nitrate
nitrogen leaches through the soil. The relevant
parameters are the amount of biosolids applied.
soil permeability, timing of mineralization in
relation to crop uptake. and interactions with
rainfall or imgarion water.
Phosphorus does not accumulate to toxic
levels in the soil. However excessive amounts of
available phosphorus may lead to decreased crop
vigor through nutrient imbalances. For this
reason. long-terni phosphorus accumulations
should be monitored.
Phosphorus is not very mobile in the soil
and is not subject to large leaching losses. Heavy
applications over a long period of time, however.
will move some phosphorus through the soil. The
rate and distance of movement may be of concern
near lakes whose eutrophication rate could
increase rapidly with small additions of phospho-
rus.
The greatest concern about excessive
phosphorus loading is overland flow. Either the
physical transport of biosolids or the erosion of
soil enriched with phosphorus could cause
significant deterioration of surface water quality.
Monitoring programs should watch for signs that
excessive additions of phosphorus to lakes and
streams could occur.
Excess potassium is not a serious problem if
biosolids are applied only once or at intervals
separated by several years. It is possible. though.
that regular additions of excess potassium could
elevate soil salinity to harmful levels or could
cause potassium to accumulate to the point that
potassium interferes with magnesium nutrition of
plants. One result of this is a condition known as
grass tetany. which afflicts animals that graze on
Mg-deficient forages. For this reason. regular
soil—test monitoring of potassium levels in
biosolids-amended soils is a good idea.
Similarly, regular monitoring of trace
inorganic and organic chemicals in biosolids-
amended soils is important to ensure that
accumulated amounts do not exceed cumulative
limits set by regulatory agencies.
A good monitoring program also means a
good record-keeping program. Careful, complete
records should be kept of the amounts of dry
solids, trace inorganics. organics. and nutrients
applied to each field each year. These records
are necessary to evaluate the significance of data
collected in the monitoring program and to
document compliance with all pertinent regula-
tory standards.
Avoid application
of biosolids during
times of high-
intensity storms
and times when
the soil is frozen.
391
-------
140
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Design Calculations
he general procedure for designing a
biosolids application system is as fol-
lows:
1. Assemble data on biosolids. soil.
cropping system, and fertilizer
recommendations.
2. Calculate amounts of nutrients the
biosolids must deliver. Subtract from
fertilizer recommendations the amounts
supplied by residual nutrients and the
amounts supplied by other commercial
fertilizers.
3. Calculate the amount of available N per
dry ton of biosolids. Add the fractions of
NH 4 -N and NO-N recovered to the
amount of organic N mineralized.
4. Calculate the Agronomic Loading Rate.
Divide lb biosolids N required by lb/ton
available N in the biosolids product.
5. Calculate the amounts of P and K
delivered in the agronomic loading rate.
Compare with fertilizer recommendations
for P Oç and K,O.
6. Calculate the application area required.
Divide the total amount of biosolids
produced each year by the amount
applied per acre.
7. Calculate the Allowable Accumulation
Period. Multiply lb per dry ton of each
trace inorganic by the Agronomic
Loading Rate, then divide each trace
inorganic’s annual loading rate into the
cumulative limit set by regulatory
standards.
Every location, every site is unique. Domes-
tic wastewater biosolids are extremely variable
in the amounts of total N. organic N. phosphorus.
potassium. trace inorganics. and organics they
contain. The numbers used in this guide repre-
sent a single. specific example and are intended
only to illustrate the principles involved in
calculating nutrient requirements and loading
rates.
Before completing calculations for a
particular biosolids product. soil, and crop. you
should consult with agriculture professionals.
soil scientists, and wastewater treatment agencies
in your area to make sure you have the right
numbers for that situation.
Here’s a list of some of the specific numbers
needed:
I. Crop requirements and fertilizer recom-
mendations for N. P. and K.
2. Amounts of residual N supplied by
previous crops. crop residues, and prior
applications of biosolids.
3. Amounts of available P and K in the soils
at your application sites.
4. Amounts of N. P. and K that may be
supplied with other commercial fertilizers.
5. Amounts of nitrate nitrogen and ammonia
nitrogen actually delivered to and
recovered from the soil.
6. Annual mineralization rates for the type
of biosolids, climate, and time of year
applied.
Carryover Nitrogen from
Previous Biosolids
Applications
Organic nitrogen applied in biosolids
continues to decompose and release mineral
nitrogen over a period of several years. Nitrogen
carryover from prior biosolids applications is an
important issue that may need careful checking
in your calculations.
The critical point is whether or not the amount
of fertilizer nitrogen recommended for a crop has
already accounted for nitrogen mineralized from
prior biosolids applications.
Extension agents are accustomed to
developing fertilizer recommendations based on
residual nitrogen from both the previous crop and
crop residues. They may not be as accustomed to
calculating the amount of carryover nitrogen
from previous biosolids applications before
making recommendations for additional fertil-
izer.
The sample calculations that follow in this
guide assume that the recommended fertilizer
nitrogen has accounted for all residual nitrogen
sources, including prior biosolids applications. If
this were not true, then you may need to calcu-
late the carryover and reduce the biosolids
loading rate accordingly.
Here’s how the procedure works.
First, check with professional agronomists in
your area to determine specific rates of minerali-
zation of organic nitrogen in years subsequent to
the initial application. A common approximation
is to use a rate that is one half of the previous
year’s rate.
Second. calculate the amount of nitrogen
mineralized in each year for 2 or 3 years after the
initial application. Suppose. for example. an
anaerobically processed biosolids delivers 100 lb
per ton of organic nitrogen when it is first
applied. If the first year’s mineralization rate is
20%. then each dry ton of biosolids will have
20 lb of nitrogen mineralized and 80 lb of
organic nitrogen remaining in the soil to start
year 2.
If the mineralization rate for year 2 is 10%,
then 8 lb (0.1 x 80 lb) of organic N per ton of
biosolids will be mineralized, and 72 lb will
CHAPTER 6
T
Make sure that
fertilizer
recommendations
account for a!!
sources of
residual nutrients
in the soil:
• the previous crop
• returned crop
residues
• prior biosolids
applications
41!
-------
142
remain. In year 3. the mineralization rate might
be 5%. and 5% of 72 lb yields 3.6 lb per ton of
mineralize.d nitrogen for year 3.
Third. calculate the cumulative amount of
carryover N. If the same kind of biosolids were
to be applied at the same rate for three years
consecutively, then at the beginning of the third
ear the amount of carryover nitrogen from
previous biosolids applications would be 3.6 lb
from the first year’s application plus 8 lb from the
second year’ s application, for a total of 11.6 lb.
This is the amount that should be subtracted
from the fertilizer recommendation. If the
fertilizer recommendation did not allow for this
residual nitrogen, then the amount of nitrogen
required from the current year’s biosolids
application should be reduced by that amount.
Sample Calculations
The steps necessary to calculate agronomic
loading rates. sizes of application areas, arid
allowable accumulation periods are detailed
below. They are intended to be logical, orderly.
consistent, and simple. English units of measure-
ment (gallons. pounds. tons, and acres) are
preferred because the are more familiar to most
operators. Extension agents. and farmers.
Current regulatory standards for cumulative
loadings of trace inorganics (Table 21 are
assumed to be valid. Should they change. you
may need to adjust your calculations of allowable
accumulation period accordingly.
Each step in the calculations is illustrated
using the actual data for a liquid biosolids
product generated by a city of about 10.000
people. This biosolids product was anaerobically
processed. and the example assumes that it will
he applied to a row cl-op.
-------
Step 1.—Assemble relevant data
Kinds of Data Example
Biosolids
Type Liquid Anaerobically Processed
Volume
Gallons produced yearly 2.673.550 gal
Percent solids 1.93%
Dry tons produced yearly 215.17 tons
Dry tons = Gallons x 8.34 x c/ Solids
2.000 100
Nutrients (% x 20 = lb/ton) Percent lb/ton
Total Kjeldahl N 10.7 214.0
NH 4 -N 5.45 109.0
NO -N 0.015 0.3
Organic N (TKN - NH;N) 5.25 105.0
Phosphorus 0.78 15.6
Potassium 0.015 0.3
Trace inorganics (mg/kg x .002 = lb/ton) mg/kg lb/ton
Arsenic 11 0.02
Cadmium 6 0.01
Chromium 61 0.12
Copper 453 0.91
Lead 442 0.88
Mercury 3 0.01
Molybdenum 11 0.02
Nickel 34 0.07
Selenium 10 0.02
Zinc 897 1.79
Application method Once per year. spring
Disked into soil
Soil
Data from soil testing laboratory
pH 6.0
Soil test P (Bray P1) 10 ppm
Soil test K (NH 4 OAc extractable) 120 ppm
Estimated residual N 35 lb/acre
(includes prior biosolids applications)
Crop
Information from farmer, farm advisor.
fertilizer guides
Type Field corn
Expected yield 170 bushels
Rotation Follows grain
Total fertilizer N recommendation
(accounts for all residual N) 265 lb/acre
Supplemental fertilizer N 30 lb/acre, banded
Fertilizer P requirement 75 lb P,O /acre
Fertilizer K requirement 50 lb K,O/acre
43
-------
Step 2.—Determine the amount of available N the biosolids must provide
Procedure
Example
Biosolids N needed
= Total Fertilizer N recommended -
Biosolids N needed = 265 lb/acre - 30 th!acre
Supplemental Fertilizer N
Biosolids N needed = 235 lb/acre available N
Step 3.—Calculate the amount of available nitrogen per dry ton of biosolids
Procedure
Example
Use the lb/ton data for NH 4 -N. NO,-N. and
organic N in Step 1.
A. Available NH 4 -N
= lb/ton NH 4 -N x Fraction Recovered
Assuming the biosolids analysis data are for
the processed biosolids that will be applied
to the land, the fraction recovered can be
taken as 0.85 for biosolids that are worked
into the soil and 0.5 for biosolids that are left
on the soil surface.
B. Available N0 3 -N
= lb/ton N0 3 -N x Fraction Recovered
Assuming the analytical data are for
the processed biosolids that will be applied
to the land, the fraction recovered can be
taken as 1.0.
C. Mineralized Organic N
= lb/ton Organic N x Mineralization Rate
The mineralization rate for the year immedi—
ately following land application usually
varies from about 8 to 30%. depending on
the type of biosolids. the type of processing.
the method of application, the time of
application, the cropping system. and the
local climate. Consult local agronomists and
soil scientists to determine the best number
for your land application program.
Total Available N in biosolids
= A + B + C above.
NH 4 -N = 109 lb/ton
NO,-N = 0.3 lb/ton
Organic N 105 lb/ton
Available N1-1 4 -N =109 lb/ton xO.85 = 92.6 lb/ton
Available NO,-N =0.3 lb/ton xl.0 = 0.3 lb/ton
A reasonable mineralization rate for anaerobically
processed liquid biosolids is 20%.
AvailaNe Org-N =105.0 lb/ton xO.2 = 2L0 lb/ton
Total Available N in biosolids = 92.6 +0.3 + 21.0
= 113.9 lb/ton
144
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Step 4.—Calculate the Agronomic Loading Rate (ALR)
Procedure
Example
ALR (tons/acre)
From Step 2:
the amount of biosolids N needed is 235 lb/ acre.
biosolids N needed for crop (lb/acre)
F! 1?1 Step 3:
the available N in the biosolids is 113.9 lb/ton.
available N in biosolids (lb/ton)
ALR = 235 lb/acre = 2.1 tons per acre
113.9 lb/ton
Step 5.—Determine the fertilizer P and K value of the biosolids
Procedure
Example
A. Calculate the amounts of P and K delivered Using the data from Step 1 and the ALR from Step 4.
annually
P (lb/acre)
= biosolids P (lb/ton) x ALR
(tons/acre/year)
K (lb/acre)
= biosohds K (lb/ton 11 x ALR
(tons/acre/ year)
B. Convert P to P,0 and K to K,O
(see page 36).
P x 2.27 =
K x 1.20 = K.,O
C. Compare nutrients delivered in biosolids
with fertilizer recommendations for
P and K.
P = 15.6 lb/ton x 2.1 tons/acre = 32.8 lb P per acre
K = 0.3 lb/ton x 2.1 tons/acre = 0.6 lb Kper acre
32.8 lb P/acre x 2.27 = 74.5 lb P O per acre.
0.6 lb K/acre x 1.20 = 0.72 lb K O per acre.
Phosphorus added to the soil very nearly
equals the recommended fertilizer rate of 75 lb
P 2 O per acre. For cool season. spring crops.
however, the farmer may wish to band-place 20
lb or so P,O per acre just to make sure there is
enough Pa ailable to meet initial crop demands.
In this case the small excess P delivered by the
biosolids should not create a problem. but
careful monitoring of available Pin the soil is a
good idea.
This biosolids product has virtually no
fertilizer potassium value. Supplemental fertilizer
will be needed to provide the 50 lb K O per acre
recommended (see Step 1).
451
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Step 6.—Calculate the area of land required
Procedure Example
Acres land = From Step]:
The amount of dry’ biosolids produced is 215.17
tons dry biosolids produced annually tons per year.
Agronomic Loading Rate Fi-omim Step 4:
The Agronomic Loading Rate is 2. tons per acre.
Acres land =
215.17 tons biosolids /year = 103 acres/year
2.1 tons/acre
Table 14.—Cumulative loading rates for trace inorganics
Load
ing Rate
Trace Inorganic
mg/kg
lb/acre
Arsenic
41
37
Cadmium
39
35
Chromium
3,000
2,676
Copper
1,500
1,338
Lead
300
268
Mercury
17
15
Molybdenum
18
16
Nickel
420
375
Selenium
100
89
Zinc
2,800
2,498
146
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Step 7.—Calculate the allowable accumulation period
Procedure
A. Calculate the amount of each trace inor-
ganic applied per acre per year.
Trace inorganic (lb/ton) x ALR =
Amount trace inorganic (lb/acre/
year)
Example
Use trace inorganic data from Step 1 and the
ALR from Step 4.
Arsenic: 0.02 lb/ton x 2.1 ton/acre/year =
0.04 lb/acre/year
Cadmium: 0.01 lb/ton x 2.1 ton/acre/year =
0.02 lb/acre/year
Chromium: 0.12 lb/ton x 2.1 ton/acre/year =
0.25 lb/acre/year
Copper: 0.91 lb/ton x 2.1 ton/acre/year =
1 .91 lb/acre/year
Lead: 0.88 lb/ton x 2.1 ton/acre/year =
1.85 lb/acre/year
Mercury: 0.01 lb/ton x 2.1 ton/acre/year =
0.02 lb/acre/year
Molybdenum 0.02 lb/ton x 2. 1 ton/acre/year =
0.04 lb/acre/year
Nickel 0.07 lb/ton x 2.1 ton/acre/year =
0.15 lb/acre/year
Selenium 0.02 lb/ton x 2.1 ton/acre/year =
0.04 lb/acre/year
Zinc 1.79 lb/ton x 2.1 ton/acre/year=
3.76 lb/acre/year
B. Calculate the number of years for each
trace inorganic to reach its cumulative
limit, as defined by regulatory standards
(see Table 14).
Years to reach cumulative limit =
cumulative limit (lb/acre)
annual amount of trace
inorganic applied (lb/acre/year)
Use data from Table 14 and Step 7A above.
Arsenic: 37 lb/acre / 0.04 lb/acre/year =
925 years
Cadmium: 35 lb/acre / 0.02 lb/acre/year =
1.750 years
Chromium 2.676 lb/acre / 0.25 lb/acre/year
10.704 years
Copper: 1.338 lb/acre / 1.91 lb/acre/year
701 years
Lead: 268 lb/acre / 1 .85 lb/acre/year =
145 years
Mercury 15 lb/acre / 0.02 lb/acre/year =
750 years
16 lb/acre / 0.04 lb/acre/year =
400 years
Nickel: 375 lb/acre/0.15 lb/acre/year=
2.500 years
Selenium 89 lb/acre / 0.04 lb/acre/year =
2.225 years:
Zinc 2.498 lb/acre / 3.76 lb/acre/year =
664 years
Molybdenum
C. The Allowable Accumulation Period is the
minimum number of years to reach any
one trace inorganic’s cumulative limit.
In this example. the allowable accumulation
period is 145 years. the minimum for Lead.
471
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148
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Practical Applications
CHAPTER 7
O ne of the objectives of this guide was
to assist those responsible for
evaluating project proposals. This
chapter presents detailed checklists for
that purpose. Project developers and permit
writers can use the same checklists as a guide to
the kinds of information that should be included.
Another objective was to identify sources of
information pertaining to soils, crops. and land
application of wastewater biosolids . Several of
those sources are listed in this chapter.
Guidelines for Evaluating
Project Proposals
The framework for project evaluation
discussed in Chapter 1 identified data
completeness. data accuracy. and issues and
interactions as the three components of the
evaluation process. The worksheets that follow
are designed to guide your review with respect to
each of these three components.
The first step in evaluating project proposals
is to assess the completeness of the data. The
more complete the data, the better the proposal is
likely to be. If data are missing or incomplete, it
may be necessary to request additional informa-
tion before proceeding with the review.
The next step in project evaluation is to check
the accuracy of the data. This is crucial, for no
matter how well planned the project might be. if
the raw data are bad, the calculations and designs
based on the data are likely to be bad as well.
One way to judge data accuracy is to see if
samples of both biosolids and soils have been
collected, handled, stored, and analyzed accord-
ing to standard, approved procedures. For
biosolids. standard procedures should be
available from the agency that manages the
biosolids utilization program in your state. That
agency may also be able to provide a list of
analytical laboratories whose work is known to
be reliable. For soils, standard sampling and
analytical procedures are available from your
county Extension agent. That person can also
provide a list of reliable soil testing laboratories.
Another way to judge data accuracy is to
compare the data with results for similar
biosolids and soils analyzed previously. If the
data are consistent, then you can be reasonably
comfortable with their accuracy. If there are
significant deviations, then you should at least
expect a good explanation of the reasons for the
differences, and you may wish to request a
re-analysis for the anomalous data.
Should there be any doubt about the
accuracy of the data, get a second opinion.
Agricultural consultants, agricultural Extension
agents. and waste management specialists in
state environmental regulatory agencies all may
be able to provide assistance.
The final step in project evaluation is to
assess the adequacy with which interactions
among biosolids. soil, and cropping system have
been addressed. This is the most difficult step.
but it’s critical because the amount of biosolids
to apply. the timing of the application, the
prevention of disease and other public health
problems. and the protection of environmental
quality all depend on these interactions.
The most important criterion for evaluating
interactions is to judge them against the principles
and the common sense discussed in this Guide. If
the proposal demonstrates a clear understanding
of the principles that control these interactions,
and if the calculations and management plans
account for the effects of the interactions, then
the project is probably a good one.
Conversely, if the proposed project violates
one or more of the principles of biosolids
behavior in soil, or if the interactions are
disregarded in developing the proposal, then the
proposal should either be rejected outright or
returned for further planning and development.
One other criterion for evaluating interactions
is to check their consistency with other success-
ful land application projects. If the management
plan is patterned after one or more previous
projects that are known to function properly, and
if all limiting factors have been accounted for.
then the proposal is probably adequate.
To help you conduct your evaluation of
interactions, the worksheet for interactions is
designed with questions that require a yes or no
answer. Any question answered “no” should be
taken as a warning that the report may be
inadequate or incomplete. At the very least,
further information may be required. and it may
be necessary to disapprove of the entire project.
Project proposals
that are based on
complete and
accurate data,
that are well
thought out, and
that address all
the pertinent
interactions
among biosolids,
soil, and cropping
system are
suitable for
approval.
491
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150
In summary, proposals that are based on
complete and accurate data, are well planned. and
address all the pertinent interactions, are suitable
for approval. Proposals that are incomplete, fail
to substantiate data accuracy. and fail to account
for important principles and interactions, should
be disapproved.
Proposals between these two extremes need
careful evaluation. Some proposals may need to
be returned for more data. better data, or
clarification of explanations regarding data
anomalies, mitigation of soil limitations, or effects
of interactions on system design. Other proposals
may be approved subject to specific conditions.
Some examples of restrictive clauses that may be
included in permits are given in Appendix C.
Proposals based on questionable or incorrect
data should be disapproved. If the proposals
don’t make sense or fail to account for soil
conditions and farm management plans. they
should not be approved.
Finally, remember to seek help from local
experts for difficult situations that require
professional judgment. With their help, and with
your own understanding of the principles and
interactions involved in the biosolids-soil-crop
system. you should soon become sufficiently
experienced to make many of these judgment calls.
-------
Worksheet for Evaluating Biosolids Data
I. Completeness (see pages 4-7)
A. Quantity
Gallons produced annually _______________
Dry weight produced annually (Kg or Tons) ______________
Percent solids ________________
B. Type
Liquid ______________
Dewatered ________________
Dried _______________
Composted ______________
C. Nutrients (% or mg/kg)
Total Kjeldahl N _______________
NH 4 -N
NO,-N ___________
Organic N _______________
Total P ______________
Total K ______________
D. Trace inorganics (mg/kg)
Arsenic _________________
Cadmium ______________
Chromium ______________
Copper
Lead ______________
Mercury
Molybdenum
Nickel _________________
Selenium _______________
Zinc ________________
E. Organic contaminants (mg/kg)
Aldnnldieldrin ______________
Benzo(a )pyrene
Chlordane ______________
DDT. DDE. DDD __________
Dimethyl nitrosamine ________________
Heptachlor
Hexachlorobenzene
Hexachiorobutadiene
Lindane
PCB s
Toxaphene
Trichloroethylene 51
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152
F. Pathogen reduction processes (PSRP’s, PFRP s)
Aerobic digestion
Anaerobic digestion —
Lime stabilization
Air-dried
Composted —
Heat-dried —
High temperature digestion —
Gamma irradiation
G. Method of land application
Spread on surface
Spreader plate
Portable sludge cannon —
Dry manure spreader
Incorporated into the soil
Liquid injection —
Surface applied and disked —
II. Accuracy (see page 1)
A. When were biosolids sampled?
Just prior to land application? —
Before processing and treatment? —
B. Were sampling and analytical procedures identified?
Yes No ________
C. Were samples taken according to approved procedures?
Yes________ No _______
D. How were samples handled prior to analysis?
Stored in proper container to avoid contamination? ______________
Length of time between sampling and analysis?
Refrigerated or frozen if necessary?
E. How were samples analyzed?
By an approved laboratory? Yes ______ No ______
Using standard procedures? Yes ______ No ______
F. Are the results consistent with data from other biosolids of this type?
Yes No
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Worksheet for Evaluating Soils Data
I. Completeness
A. Soil types present, list (see page 32)
(e.g. Windthorst fine sandy loam. 3-5% slopes)
B. Data needed to rate suitability for land application (see pages 12-24,
tables 8-12)
Texture of surface soil _______________________
Texture of subsoil _______________________
Depth to bedrock or cemented pan
Coarse fragments in surface soil _______________________
Coarse fragments in subsoil _____________________
Structure grade of surface soil ______________________
Organic matter content ______________________
Shrink-swell potential
Drainage class ______________________
Permeability of surface soil ______________________
Permeability of subsoil ______________________
Kind of restrictive layer
Claypan
Fragipan
Duripan
Petrocalcic _________________________
Weathered bedrock (Cr)
Solid bedrock (R)
None _____________________
Depth to restrictive layer
Depth to coarse-grained layer
pH of surface soil
Slope of soil surface _____________________
C. Water table information (see pages 20-21)
Are somewhat poorly drained or
poorly drained soils present? Yes ______No _______
Position of water table (in. below surface)
Duration of water table (days or months)
Times when water table is high (months)
53
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154
D. Analytical data (see pages 24-25)
pH
Available P (Bray #1)
Available K (NH 4 OAc extract)
E. Site data
Size (acres)
Slope (%)
Amount of rainfall (inches)
Distribution of rainfall (months)
Times when soil is frozen (months)
II. Accuracy (see pages 32-34)
A. Sources
Modern soil survey report
Other NRCS information
On-site investigations
By a certified soil scientist
By someone other than a soil scientist
B. Sampling (see page 37)
According to approved procedures? Yes _______ No _______
Steps taken to avoid contamination? Yes No
C. Analysis (see page 37)
Done by an approved laboratory? Yes ______ No ______
Done according to standard procedures? Yes ______ No ______
D. Consistency
Are data consistent with results from other soils similar to these?
Yes ____No ____
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Worksheet for Evaluating
Cropping Systems Information
I. Completeness
A. Crop (see page 35)
Kind of crop
Trace inorganic accumulator? Yes No _________
Expected crop yield _________________________
Anticipated planting date ____________________________
Anticipated harvest date ____________________________
Can/will biosolids be applied while
the crop is growing? Yes _______ No _______
B. Fertility management (see pages 35-36)
Previous crop
Crop residue management
Estimated residual nitrogen
Fertilizer N requirement
Coniniercial N fertilizer used
Pre-plant
Mid-season ______________________________
N required from biosolids ____________________________
Fertilizer P requirenient
(lb P 2 O per acre I _____ _________________
Fertilizer K requirement
(lb K,O per acre)
C. Water management (see page 38)
Are wet soils artificially drained? Yes No _________
Surface ditches? Yes _____ No ________
Subsurface tiles? Yes ________ No _________
Will the crop be irrigated? Yes ________ No _________
Flood? Yes _______ No ________
Furrow? Yes _______ No ________
Sprinkler? Yes _____ No ________
Big gun? Yes _____ No _____
D. Runoff and erosion control (see page 38)
Perennial sod crop Yes ______ No _____
Reduced tillage Yes _______ No _____
Contour farming Yes _______ No ________
Terraces and diversions Yes _______ No _________
Grassed waterways Yes ________ No _____
Cross-slope drains Yes _______ No ________
Other ___________________ Yes _______ No ________
-________________ 55
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156
II. Accuracy (see pages 35, 39)
A. Sources of data
Land Grant University fertilizer guides Yes _______ No ________
Consultation with farmers Yes _______ No ________
County Extension agent recommendations Yes _______ No ________
Crop consultant recommendations Yes _______ No ________
Other _________________________ Yes _______ No ________
B. Consistency of data
Are crop yields, fertilizer recommendations, and management practices
typical for this area? Yes ________ No
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Worksheet for Evaluating Issues and Interactions
I. Soil Surveys and Site Investigations (see pages 32-34)
A. Soil identification
Were soil surveys used in the planning stage to make
preliminary determinations of the soils present? Yes ________ No _________
Were the data in the tables and map unit descriptions
of soil surveys used as the basis for evaluating
soil suitability for land application of biosolids? Yes ________ No _________
Were soil identifications made from soil maps
verified by field investigations at the site? Yes No
Were additional soils data obtained from soil pits dug
at the site? Yes No _________
B. Soil patterns
Were the inclusions in soil map units (pages 32-33) identified.
their properties listed, and their limitations for land
application accounted for? Yes No
Were patterns of admixture of soils of different
suitability classes recognized? Yes ________ No _________
Were plans made for managing sites in which
more limiting soils are disbursed among more
suitable soils? Yes __________ No ______
II. Nitrogen issues and interactions
A. Mineralization rate (see pages 5,11, 35-36, 44)
Was the determination of the mineralization rate made
by a qualified professional? Yes ________ No _________
Did the determination of the mineralization rate account for effects of:
method(s) of biosolids processing prior
to application? Yes _______ No _______
method of application? Yes ______ No ________
timing of application? Yes _______ No ________
climatic conditions? Yes _______ No _________
B. Agronomic Loading Rate (see pages 5-6, 20, 35-36, 41-45)
Did the calculation of the amount of biosolids to apply account for these losses:
volatilization during processing? Yes ______ Mo _______
volatilization during application? Yes — No _________
denitrification in the soil? Yes ________ No _________
Did the calculation of the amount of biosolids to apply account for these fertilization factors?
the type of crop? Yes _______ No _________
the expected yield of the crop? Yes ______ No ________
the farmer’s usual management practices? Yes — No ________
the timing of biosolids application in relation to
mineralization rates and crop demands for N? Yes _____ No 57
-------
the amount of fertilizer recommended? Yes ________ No _________
the estimated residual N in the soil?
from the previous crop? Yes _______ No ________
from crop residues? Yes ________ No _________
from prior biosolids applications? Yes No
the amount of pre-plant commercial
fertilizer used? Yes ________ No _________
the amount of mid-season commercial
fertilizer used? Yes ________ No _________
lii Protection of Environmental Quality
A. Leaching to groundwater (see pages 11, 13, 17-23, 38)
Have plans been made to minimize the potential for transport of mobile constituents
through the soil due to any of the following?
application on wet soils with high water tables Yes ________ No _________
application during periods of high rainfall Yes ________ No _________
heavy irrigation after biosolids application Yes ________ No _________
application on sandy or gravelly soils that
have rapid or very rapid permeability.
especially if irrigated Yes ________ No _________
B. Runoff and erosion (see pages 11, 13, 19-20, 38)
Have plans been made to minimize the potential for surface runoff that could transport
biosolids to streams and lakes with respect to:
weather conditions in the area? Yes _______ No ________
applications on sloping soils during rainy seasons
or after irrigation? Yes ________ No _________
applications on frozen soils? Yes ________ No _________
conservation practices on sloping soils? Yes ________ No _________
non-application buffer areas around
upland waterways? Yes ________ No _________
IV. Mitigation of Limiting Soil Conditions (see pages 15, 27-32)
A. Have limiting properties of soils rated fair or poor been identified?
Yes No
B. Have methods for dealing with soil limitations been specified?
Proper timing on soils with high water tables? Yes _______ No ________
Proper timing and application rates on soils with
slowly permeable restrictive layers? Yes ________ No _________
Proper timing and application rates on soils with
‘ rapid or very rapid permeability? Yes _______ No ________
Proper timing and conservation practices
on sloping soils? Yes _______ No ________
58
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V. Protecting Public Health
A. Trace inorganics and organic contaminants
(see pages 5-6, 47)
Have all loading rates for trace inorganics
been calculated correctly? Yes ________ No
Has the allowable accumulation period been based
on the most limiting loading rate? Yes _______ No ________
B. Pathogens and vector reduction (see pages 7-9)
Have all PSRP ’s and PFRP ’s and their effects on the
pathogen content of the biosolids been identified? Yes _______ No ________
Have appropriate vector reduction treatments been
completed? Yes _______ No
Have lag times between biosolids application and crop
grazing or harvest taken into account the type of
crop and its position in the food chain? Yes ________ No _________
Have steps been taken to restrict public access to
the application site? Yes ________ No
C. Drinking water
Is it absolutely clear that the project will not
contaminate drinking water supplies with nitrates.
trace inorganics. organics. or pathogens? Yes No
VI. Monitoring and Compliance
A. Monitoring (see page 39)
Are there plans for monitoring:
Nitrates, trace inorganics. organics
in ground water? Yes No ________
Nitrogen. phosphorus. and pathogens in
surface water? Yes ________ No _________
Accumulations of soil P and K? Yes _______ No ________
Have plans been made for careful, thorough
record-keeping? Yes ________ No _________
B. Compliance (see pages 5-9, 15)
Does the plan conflict in any way with regulations
affecting natural or nian-made wetlands? Yes ________ No _________
Does the plan comply with all pertinent local. state.
and federal regulations? Yes ________ No _________
591
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Sources of Information
160
The following is a short list of available
sources of helpful information on land applica-
tion of domestic wastewater biosolids. These
sources can direct you to more detailed sources if
necessary.
Contacts
• Soil scientists, crop scientists and agronomists
in Agricultural Experiment Stations and Exten-
sion Services at state Land Grant universities
• County Extension agents
• Natural Resources Conservation Service
district conservationists
• Private crop. soil or agronomic consultants
• Field representatives of farm service
companies
• Representatives of state environmental
management agencies
Publications
Soils
County soil survey reports
Donahue. R L., R.W. Miller. and J.C. Shickluna.
Soils: An Introduction to Soils and Plant
Growth. Prentice-Hall. Inc.. Englewood
Cliffs. NJ. 1983.
Harpstead. M.I. and F.D. Hole. Soil Science
Simplified, Iowa State University Press.
1980.
Singer. M.J. and D.N. Munns. Soils: An
Introduction. MacMillan Publishing Co..
NY. 1987.
Stevenson, F.J.. Cycles of Soil: Carbon.
Nitrogen. Phosphorus. Su1fi r, Micronuiri-
ents. John Wiley and Sons. New York. 1986.
Crop Management
State fertilizer guides
State soil sampling and testing brochures
Tisdale. S.L.. W.L. Nelson. and J.D. Beaton.
Soil Fertility and Fertilizers. MacMillan
Publishing Co.. NY. 1985.
Land Application of Wastewater Biosolids
“Analytical Methods for the National Sewage
Sludge Survey.” EPA Office of Water
Regulations and Standards WH-522, Indus-
trial Technology Division. August 1988.
“Control of Pathogens and Vector Attraction in
Sewage Sludge’ EPA-625/R-92-013.
December 1992.
“Controlling Pathogens in Municipal Waste-
water Sludge for Land Application. Third
Draft.” Prepared by Eastern Research Group.
Inc., Arlington. MA. for EPA Pathogen
Equivalency Committee. November 1988.
Elliott. L.F. and F.J. Stevenson. eds.. “Soils for
Management of Organic Wastes and Waste-
waters.” American Society of Agronomy.
Madison. WI. 1977.
“Guidance for Writing Case-by-Case Permit
Requirements for Municipal Sludge.” EPA
Office of Water Enforcement and Permits,
September 1988.
Journal of Environmental Quality. American
Society of Agronomy. Madison. Wi.
Logan. T.L and R.L.Cheney, “Utilization of
Municipal Wastewater and Sludge on
Land—Metals.” in Page. A.L. ed.. Utilizatioii
of Municipal Was!t’water and Sludge p,
Land. Univ. California, Riverside. 1983.
“Process Design Manual for Land Application
of Municipal Sludge.” EPA-625/1-83-016,
October 1983.
Runge. E.C A.. K.W. Brown. B.L. Carlile. R.H.
Miller. and E.M. Rutledge. eds.. “Utilization,
Treatment, and Disposal of Waste on Land,”
Soil Science Society of America. Madison.
WI, 1985.
Sommers. L.E. and K.A. Barbarick. “Con-
straints to Land Application of Sewage
Sludge.” in Runge. E.C.A. et al. eds..
Utilization, Treaunent. and Disposal of
Waste on Land, Soil Science Society of
America. Madison. WI. 1985.
Standard Methods for the Examination of Water
and Wastewater. 18th edition. American
Public Health Association. Washington. DC.
1992.
State Extension and Agricultural Experiment
Station publications on land application of
sewage sludge.
Technical Support Document for Reduction of
Pathogens and Vector Attraction in Sewage
Sludge. EPA. I 992a.
Test Methods for Evaluating Solid Waste.
Physical/Chemical Methods. EPA SW-846.
second edition, with Updates I and II. and
third edition, with Revision I. 1982.
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APPENDIXES
611
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162
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Technical Aspects of Soil Morphology
Field Determination of
Soil Texture
Moisten the soil and knead it between your
thumb and fingers. If the sample sticks to your
fingers. it’s too wet. Continue kneading it. or add
a little dry soil, just until it is no longer sticky.
Estimate the amount of sand the soil contains
by the grittiness of the sample. If there is more
than 50% sand, the soil is coarse-textured (sandy
loam, loamy sand, or sand). If there is between
20 and 50% sand, you’ll notice the sand, but
there’s enough silt and clay present to give the
sample good body. Loam and clay loam are the
most likely textures. If there is less than 20%
sand, you’ll have difficulty feeling it, and the
texture will be silt loam, silty clay loam, or clay.
Push the sample upward between your
thumb and finger to form a ribbon. The longer
the ribbon is. the more the clay. If the sample
contains less than 27% clay, you can form only a
short, broken ribbon. The textural name contains
the word loam, hut not clay. If the sample has 27
to 40% clay, you should get a ribbon I to 2V:
inches long. Textural names contain both the
words clay and loam. If the sample has more
than 40% clay, you should get a long ribbon. The
texture is either clay or silty clay.
If the soil contains coarse fragments. you
may need to add the appropriate modifier to the
textural class name. Estimate the volume of
coarse fragments present by looking at the
vertical face of exposed soil. The proportion of
the area occupied by coarse fragments equates to
the percent of coarse fragments in the soil. Select
the correct modifier from Key I on page 60.
Field Evaluation of
Soil Structure
Soil structure is described in terms of the
grade. size, and shape of soil peds. Criteria for
evaluating size and grade are given in Keys 2
and 3 on page 60. Shapes of soil peds are
illustrated in figure 3. page 10.
Soil structure is determined in the field by
observing both an undisturbed vertical cut and
the way the soil breaks out into your hand. The
easier it breaks out. the stronger the grade. Weak
and moderate structures will not break out of the
cut face into individual peds. You’ll have a large
mass of soil in your hand. and you need to gently
break this mass apart by applying gentle pres-
sure. If the soil breaks easily along a natural
plane of weakness, that plane separates structural
units. If the soil merely fractures. you don’t have
structure.
Continue breaking the soil apart until you
can’t subdivide it any further without fracturing
it. Then observe the size and shape of the peds in
your hand. The grade is determined according to
the way the soil breaks out of the face, the ease
with which it separates under gentle pressure.
and the amount of unaggregated material left in
your hand. Record your observations, such as
moderate fine granular or weak medium suban-
gular blocky.
Technical Method for
Determining Soil Color
Technical descriptions of soil profiles use
Munsell color notations to describe soil colors.
Each color is characterized by its hue, value, and
chroma. A symbol. such as IOYR 4/3. is used to
record these color characteristics.
Hue represents the spectral wavelength of
the color. A hue of 1 OR represents a pure red
color. A hue of lOY has a pure yellow color. In
soils, a very common hue is 1OYR. which
represents a color exactly half way between pure
red and pure yellow. Other common soil hues are
5YR (3 parts red and 1 part yellow) and 7.5YR
(5 parts red and 3 parts yellow).
Value represents the amount of light
reflected back to the eye. Value is measured on a
scale of 0 to 10. from no reflection to complete
reflection. Low numbers represent dark soil
colors, as most of the incident light is absorbed.
High numbers represent light colors, as most of
the light is reflected. Common values for soil
colors are 3 and 4. representing 30% and 40% of
the light reflected. Value is shown in the color
symbol as the numerator of the fraction that
follows the hue.
Chroma represents the amount of dilution
with white light. On a scale of 0 to 20. 20
represents the pure color, and 0 i’epresents
infinite dilution with white light. Chromas of soil
colors range between 0 and 8 and are commonly
between 1 and 4. The lower chromas are black or
gray colors, whereas the higher chromas are the
bright yellowish or reddish colors. Chroma is
shown as the denominator of the fraction in the
color symbol.
The Munsell Color Company makes small
color chips for each combination of hue, value,
and chroma. Chips of those colors that are most
frequently found in soils are arranged in special
books of soil color charts. To determine soil
color in the field. match the color of a soil
aggregate with a chip of the same color. Then
record the corresponding symbol for that chip’s
hue. value, and chroma.
APPENDIX A
631
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Key 1.—Coarse fragment modifiers of
textural class names
% by
vol.
Gravel Cobbles Channers
2mm-3 in. 3-10 in. 2mm-6 in.
<15
no modifier
15-35
Gravelly Cobbly Channery
35-60
Very gray. Very cob. Very chan.
>60
Extremely Extremely Extremely
gray, cob. chan.
Key 2.—Size ranges for soil peds (all sizes
are in millimeters)
Granular,
Platy
Blocky
Prismatic,
Columnar
Veryfine
0- 1
0- 5
0- 10
Fine
1 - 2
5 - 10
10 - 20
Medium
2- 5
10-20
20- 50
Coarse
5-10
20-50
50-100
Very coarse
>10
>50
>100
164
Key 3.—Grades of soil structure
Strong
The soil mass is well divided into distinct, easily recognizable peds that are obvious
on the face of a soil pit. When dug out of the pit face, the soil falls into your hands as
distinct, stable peds that resist further breakdown. Little or no soil remains as
unaggregated loose grains.
Moderate Peds can be seen in a pit face, and they are easily detected when you gently break
apart a mass of soil held in your hands. Grains of soil that are not part of any
aggregate are apparent. Peds are stable against weak forces, but may break down
under stronger pressure.
Weak
Peds are difficult to detect, even when you break soil apart in your hands. Many
grains are not part of any aggregate. Peds easily break down when small forces
are applied.
Structureless The grade applied to massive and single grain soils.
-------
Criteria for
Describing Soil Mottles
Soil mottles are described in terms of their
abundance, size. contrast, and color. These terms
are defined below.
Abundance—the percentage of exposed surface
area occupied by mottles:
Few—less than 2%
Common—2-20%
Many—more than 20%
Size—the approximate diameter of individual
mottles:
Fine—< 5 mm
Medium—5-15 mm
Coarse—> 15 mm
Contrast—the relative difference between the
mottle color and the matrix color:
Faint—Mottles are evident only upon close
scrutiny. Mottle color and matrix color are
nearly the same.
Distinct —Mottles are readily seen though
not striking. Mottle color and matrix color
are different, though not widely so.
Prominent—Mottles are so conspicuous that
they are the outstanding visible feature of the
horizon. Mottle color and matrix color are
widely different.
Color—The hue, value, and chroma of the
mottles, as described using a Munsell book
of soil colors.
Horizon Definitions
Master Horizons. The six master horizons
(0. A, E. B. C. R ) are defined below.
0 Horizon—The 0 stands for organic.
o horizons don’t have to be iooqc organic
material, but most are nearly so. Wet soils in
bogs and swamps often ha e 0 horizons of
peat and muck. Forest soils usually have thin.
surficial 0 horizons that consist of leaves and
twigs in various stages of decay.
A Horizon—This is the surface horizon of a
mineral soil. Its unique characteristic is a
dark color formed by the accumulation of
organic matter. Granular or fine blocky
structures are typical.
E horizon—E horizons have light gray or white
colors. Where present. they usually occur
immediately beneath an 0 or an A horizon.
They are common in sandy soils that formed
under coniferous forests and in medium to fine
textured soils that formed under deciduous
forests. They also occur immediately above
very slowly permeable claypans or fragipans
in situations that indicate wetness.
B horizon —B horizons are subsoil horizons of
maximum alteration due to soil-forming
processes. In some soils, the B has the brightest
yellowish-brown or reddish brown color. In
others, it has the best developed blocky or
prismatic structure. Many B horizons are
distinguished by accumulations of clay, iron
and aluminum oxides, or carbonates.
C Horizon—The C horizon is weathered
geologic material below the A or B horizon.
Anything you can dig with a spade but that
has not been changed very much by soil
forming processes is considered a C horizon.
R Horizon—R stands for rock. It refers to hard
bedrock that you cannot dig with a spade.
Depending on the depth to bedrock, it may
occur directly beneath any of the other
master horizons.
Transition Horizons. Master horizons rarely
change abruptly from one to another. In some
cases. we can describe the nature of the
transition as a characteristic of the boundary
between two horizons. But if the transition
zone is more than 5 inches thick, we usually
describe it as a transition horizon.
AB Horizon —This horizon occurs between the
A and the B. It’s dominated by properties of
the A. but some properties of the B are
evident. Dark colors associated with organic
matter are fading as organic matter decreases,
and the structure often changes from granular
to blocky.
BA Horizon—This horizon also occurs between
the A and the B. but it’s more like the B than
the A. Structure is the same shape as in the
B. but the grade is a little weaker. The color
may be a little darker than the B. or the clay
content may be a little less than the maxi-
mum in lower horizons.
BC Horizon—This is a transition from B to C.
Properties of the B are dominant, but some
influence of the C is evident. Often the clay
content will be less than the maximum in the
B. or the color will be fading. If the C is
massive the BC has structure, but the peds
are larger and the grade is weaker than in the B.
651
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166
Special Kinds of A. B. and C Horizons. Many
horizons are the result of unique processes
that leave a distinct mark on the horizon.
These horizons are identified with a lower
case letter immediately following the master
horizon symbol. There are over 25 such
horizons, Oniy the more common ones are
defined below.
Ap Horizon—This is the plow layer of the soil.
Cultivation thoroughly mixes the upper 8 to 12
inches of soil and destroys any natural horizons
that may have been present. Even if all of the
original A horizon has been lost by erosion.
plowing the exposed B or C horizon automati-
cally makes the surface horizon an Ap.
Bt Horizon—This is a textural B horizon, or
argillic horizon, formed by accumulation of
silicate clays. Some of the clay comes from
weathering of minerals within the Bt. Most
of it comes from translocation of clay from
horizons higher in the profile. Deposition of
clay platelets on the surfaces of peds in the
Bt creates waxy coatings called clay skins. Bt
horizons are quite common, and they usually
have moderate or strong blocky and pris-
matic structures.
Bg Horizon —This horizon is gleved. The soil
is so wet for so long that most of the iron is
reduced and leached away. Gleyed horizons
are gray. and they may or may not be
mottled. Gleying is not restricted to the Bg.
Other gleyed horizons include Ag. BAg.
BCg. Cg.
Bk Horizon—This horizon is enriched with
calcium carbonate leached from horizons
above. It is common in soils of dry’ regions
that receive limited rainfall. Usually you can
see white streaks or nodules of lime, and the
soil effervesces strongly when a drop of HCI
is placed on it. Bk horizons contain more
calcium carbonate than the C horizons
beneath them.
Bkm Horizon—This horizon is called a
pet rocalcic horizon. It is enriched with
calcium carbonate (k) and is strongly
cemented (m). Petrocalcic horizons occur
only in the southwestern United States in
environments that have had enough moisture
to leach carbonates part way down, but not
entirely Out of. the soil. Subsequently these
carbonate deposits have crystallized to
completely cement the horizon.
Bkqin Horizon—This horizon is called a
duripan. It is enriched with calcium carbon-
ate (k) and silica (qi. and it is strongly
cemented (m). Duripans are most common in
soils that contain some volcanic ash in
regions of limited rainfall that have distinct
rainy and dry seasons. Lime and silica
leached from the upper 10 to 20 inches are
deposited in the Bkqni. cementing the soil
grains so firmly that it’s just like rock. The
duripan is usually only 6 to 10 inches thick,
but it is cemented so strongly that neither
roots nor water can go through it.
Bs Horizon—This horizon is called a spodic
horizon. It’s common in sandy soils devel-
oped under coniferous vegetation in cool,
moist climates,. The leachate from the litter at
the soil surface is very acid. causing iron.
aluminum, and organic matter to be removed
from upper horizons and deposited in the Bs
horizon. The color is usually bright yel-
lowish-brown or reddish-brown, and it fades
with depth. Sometimes there is a thin black
horizon at the top of the Bs. and often a white
E horizon is above it.
Bw Horizon —This is a t’eathered horizon, also
called a cambic horizon. It is altered enough
to have structure, more intense color, or to
have been leached, but it does not have
enough accumulation of secondary minerals
to be a Bt. Bs. or Bk horizon. Bw horizons
are common in cool region mountain soils
under high rainfall, in arid soils, and in
relatively young soils.
Bx Horizon—This refers to a special feature
called afragipan. It is a massive, dense, but
not cemented soil horizon. It is often mottled
and has gray streaks of silt scattered through-
out. The density is so high that neither roots
nor water can penetrate effectively, except in
some of the silt streaks.
Cr Horizon—Weathered bedrock, or rock that
is soft enough to slice with a knife or a spade.
is called Cr. It’s rock material, and you can
often see original rock structure. but it’s not
hard enough to be designated R.
-------
Estimating AWHC
Calculation of AWHC from
Soil Properties and
Estimated Values
APPENDIX B
Steps in the procedure for calculating
estimated AWHC are as follows:
1. Identify the horizons present in the
soil profile.
2. Measure the thickness of each horizon.
3. Determine the depth to a root-limiting layer.
4. Determine the texture and the coarse
fragment content for each horizon.
5. Find the AWHC rate that corresponds to
the texture of each horizon (see Key 4).
6. Multiply AWHC x Depth x Percent fine
earth for each horizon.
7. Total the products from Step 6 for all
horizons within the depth of rooting
(see Key 5).
Key 4.—AWHC rates
Sand,
Loamy sand
.06 in/in.
Sandy loam
.12 in/in.
Clay, Silty clay,
Sandy clay,
Sandy clay loam
.15 in/in.
Loam, Silt loam,
Clay loam, Silty clay loam
.20 in/in.
Key 5.—Sample calculations of AWHC
Horizon
Depth
Texture
% coarse
fragments
AWHC
Fraction
Thickness fine earth
AWHC
A
0 - 12
Silt loam
0
.2 x 12
x 1.0
=
2.4
BA
12-20
Siltloam
0
.2 x 8
x 1.0
=
1.6
Bt
20 - 36
Silty clay
loam
0
.2 x 16
x 1.0
=
3.2
BC
36 - 48
Silty clay
loam
0
.2 x 12
x 1.0
=
2.4
C
48-60
Siltloam
0
.2 x 12
x 1.0
=
2.4
Total soil AWHC
=
12.0
A
0 - 4
Loam
0
.2 x 4
x 1.0
=
0.8
BA
4 - 10
Clay loam
0
.2 x 6
x 1.0
=
1.2
Bw
10 - 18
Gray, clay
loam
30
.2
x 8
x .7
=
1.1
Bkqm
18 -28
(Duripan)
100
---
---
---
0
Ck
28 - 40
Loam
10
---
---
---
0
Total soil AWHC
=
3.1
671
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168
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The following clauses are examples qf the
kind of information that can be included in
permits. Underlined words or phrases indicate
places where the permit writer needs to substi-
nile information specific to a given application.
This pennit is issued in accordance with an
application submitted by the City of Central
Point for Gary Jones (site owner ) at Tax Lots
403 and 405. Sections 12 and 13, Township 24
S., Range 53 E.. Missouri Meridian . dated
March 17. 1990 . and is subject to the following
conditions:
I. This permit applies only to those areas
( Fields I through 9)mapped by the USDA
Natural Resources Conservation Service
as belonging to the Hillsboro soil series
(approximately 5 acres) highlighted
on the site map submitted under that
application.
2. Biosolids volatile solids shall be
reduced by 38% or more by the
anaerobic digestion process prior to
3. Prior to land spreading. biosolids
quality shall be assessed to determine
percent total and volatile solids.
nitrate nitrogen, ammonia nitrogen. TKN,
phosphorus. potassium, and metals
( arsenic, cadmium, copper, chromium,
lead, mercury, nickel, and zinc) .
4. Land spreading of biosolids shall be via
pressurized distribution plate application .
5. Biosolids shall be transported by tank
trailers equipped with valves adequate
to prevent leakage. Each tank trailer
shall have a current Department
wastewater biosolids permit number
posted at all times on the doors of the
“motorized vehicle” as defined by
United States Department of Transpor-
tation Regulations. Title 49. U.S.C .
6. Immediately following land spreading.
biosolids tankers shall be cleaned
on-site to prevent drag-out of biosolids
onto public roadways.
7. Central Point’s annual biosolids land
spreading rates specifically delineated
for each crop are indicated below.
Application rates shall not exceed
those indicated in Key 6.
Key 6.—Biosolids from lagoon
Gallons
Dry tons
per acre
per acre Limited by
Crop: Dry wheat
21,760
3.4
Nitrogen, 40 lb/acre
Dry barley
16,000
2.5
Nitrogen, 30 lb/acre
Dry pasture
26,880
4.2
Nitrogen, 50 lb/acre
Field corn*
107,820
16.8
Nitrogen, 200 lb/acre
Irrigated pasture*
75,265
11.8
Nitrogen, 140 lb/acre
512,000 80 Organic matter, 3-4%
added to the acre
furrow slice
*To prevent runoff, biosolids land application would have to occur in four or more separate
installments followed by a sufficient period of time to enable solids to dry between applications. In
many instances, it may be more practical to grow field corn followed by a cover crop such as alfalfa
or clover to decrease the need for biosolids nitrogen, or to supplement biosolids nitrogen with
commercial fertilizer.
Due to the high quantity of water associated with liquid biosolids, land application of lagoon solids
at rates sufficient to supply 4% organic matter would be impractical unless solids were dewatered
first.
Sample Clauses for Use in Permits
APPENDIX C
land spreading.
Reclamation **
691
-------
170
8. Based on Central Point’s biosolids
analysis data, the Jones Site has ar
ultimate loading of 435 dry tons per
acre. Copper is the pollutant which
limits loading. Should future analyses
show substantial changes in the
characteristics of Central Point’s
biosolids pollutant content, the ultimate
loading rate and allowable accumula-
tion period may have to be adjusted.
9. No land spreading of biosolids shall
occur within the 100 year flood plain of
Eagle Creek .
10. A 100 foot (minimum ) setback shall be
maintained between Buckhorn Creek
and the nearest point of biosolids land
application.
11. A 50 foot (minimum ) setback shall be
maintained from all seasonal streams
and points of hiosolids land application.
12. A 3(X) foot (minimum ) setback shall be
maintained between the Crestline
Recreation Trail and the nearest point of
hiosolids land application.
13. A 600 foot (mininlum ) setback shall be
maintained between areas of biosolids
land application and the Oak Grove
Elementary School .
14. No land spreading of bio ;olids shall
occur within 100 feet of the shoreline of
the Beaver Flat Marsh .
15. No land spreading of biosolids shall
occur in areas where slopes exceed
20%.
16. Land spreading of biosolids shall cease
when precipitation exceeds 1/4 inch per
hour.
17. Depth to groundwater shall be measured
from Piezometers 1, 2. 3. and 4 in
Fields 4. 8 and 9 prior to land spreading
of biosolids. No biosolids shall be
applied when pe anent groundwater is
within 4 feet of ground surface.
18. Application of biosolids is not permitted
from November 15 to April 15 due to
frozen soil conditions.
19. No land spreading of biosolids shall
occur on the site annually between
November 1 and April 15 without
separate case-by-case written authoriza-
tion from the Department.
20. Areas where biosolids have been
applied shall be clearly marked by flag
pins or stakes noting the date of
application immediately following
application.
21. No food crops (for direct human
consuniption) whose harvested parts are
grown below ground shall be planted on
any biosolids-amended field for at least
38 months following land spreading of
biosolids.
22. No food chain crops for direct human
consumption whose harvested parts are
grown above ground (e.g.. tomatoes)
shall be grown on fields authorized to
receive biosolids for at least 14 months
following land spreading of biosolids.
23. The western perimeter of the biosolids
land application site shall be posted by
sions at 150 foot (maximum ) intervals
and enclosed by a fence. Access to the
biosolids land spreading area shall be
via locked gate.
24. Public access to the site shall be
restricted for at least 12 months after
land spreading of biosolids has ceased.
25. There shall be no storage or stockpiling
of wastewater biosolids at the Jones Site
without separate written authorization
from the Department.
26. In the event an odor problem is reported
to the Department after biosolids have
been spread on land at the Jones Site .
inimediate steps. such as. but not
limited to. the addition of liming
materials, must be taken to counteract
that condition.
27. Central Point WWTP shall keep site
records adequate to quantify the date.
location and amount of biosolids
applied, segments of each field that
received biosolids. pounds of arsenic.
cadmium, copper, chromium, lead,
mercury, nickel, and zinc applied to
each segment receiving biosolids. and
the type of crop grown. These data shall
be submitted to the Department on a
monthly basis through the life of the
permit.
-------
28. The Department shall have the right to.
at reasonable times, and upon presenta-
tion of credentials: enter Central Point
WWTP’s place of recordkeeping to
review biosolids management opera-
tions and records: have access to and
obtain copies of any records required to
be kept under the terms of this permit:
inspect any monitoring equipment
required under this permit: inspect any
collection, transport, or land spreading
vehicles acknowledged under Central
Point’s biosolids management plan:
sample any ground or surface water.
soils, or vegetation from the Jones Site
arid obtain any photographic documen-
tation or evidence deemed appropriate.
29. The Department shall be notified within
one hour of any spills or other threats to
the environment that may occur as a
result of hiosolids handling. Failure to
provide notification within one hour
may be considered cause for taking
enforcement action against Central
nt. Spills that occur after normal
working hours shall be reported to the
Emergency Management Division
( EMD ) within one hour . The telephone
number for EMD is 1-800-452-I 103 .
30. The Department may impose any
additional restrictions or conditions
deemed necessary to assure adequate
biosolids management. Any variations
from the approved biosolids application
plan for the Jones Site must be
approved in writing in advance by
the Department.
31. This permit is subject to revocation
should health hazards, environmental
degradation. or nuisance conditions
develop as a result of inadequate
biosolids treatment or site management.
If operations are not conducted in
accordance with terms specified under
this permit. the Department shall initiate
necessary remedial action.
711
-------
172
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GLOSSARY
731
-------
174
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Absorption
Filling up of soil pores with water, much as
a sponge soaks up water.
Adsorption
Retention of water in soil by attraction
between water molecules and the surfaces of
soil particles. Also, retention of cations in
soil by attraction between their positive
charges and the negatively charged surfaces
of clay and organic matter particles.
Aeration
The movement of air back and forth
between the atmosphere and the pores of a
soil. See Well-aerated soil.
Aerobic
Having oxygen gas as part of the
environment, or occurring only in the
presence of oxygen gas.
Aerobic digestion
The biochemical decomposition of organic
matter in domestic wastewater biosolids into
carbon dioxide and water by
microorganisms in the presence of air.
Agricultural land
Land on which a food crop. a feed crop. or a
fiber crop is grown. This includes range land
and land used as pasture.
Agronomic loading rate
The amount of biosolids that would need to
be applied to a site in order to supply the
recommended amount of nitrogen or
phosphorus for a growing crop.
Agronomic rate
The whole sludge application rate, on a dry
weight basis, that is designed to I) provide
the amount of nitrogen needed by the food
crop. feed crop. fiber crop. cover crop. or
vegetation grown on the land: and 2) mini-
mize the amount of nitrogen in the waste-
water biosolids that passes below the root
zone of the crop or the vegetation grown on
the land to the groundwater.
Allowable accumulation period
The number of years that biosolids can be
applied on a particular site. The allowable
accumulation period depends on the amount
of inorganic pollutants contained in the
biosolids and the amount of biosolids
applied each year.
Anaerobic digestion
The biochemical decomposition of organic
matter in domestic wastewater biosolids into
niethane gas and carbon dioxide by
microorganisms in the absence of air.
Annual pollutant loading rate
The maximum amount of a pollutant that
can be applied to a unit area of land during a
365-day period.
Annual whole sludge application rate
The maximum amount of wastewater
biosolids. on a dry weight basis, that can be
applied to a unit area of land during a
365-day period.
AWHC
Available Water Holding Capacity. The
maximum amount of water a soil can store
for plant use. A good soil can provide 9 to
12 inches of available water. A poor soil
might provide only 2 or 3 inches of available
water.
Beneficial use
Taking advantage of the nutrient content and
soil conditioning properties of a biosolids
product to supply some or all of the fertilizer
needs of an agronomic crop or stabilizing
vegetative cover.
Biosolids
Solids derived from primary. secondary. or
advanced treatment of domestic wastewater
which have been treated through one or
more controlled processes that significantly
reduce pathogens and reduce volatile solids
or chemically stabilize solids to the extent
that they do not attract vectors. This term
refers to domestic wastewater treatment
facility solids that have undergone adequate
treatment to permit their land application.
Biosolids derived products
Materials derived from composting domestic
wastewater treatment facility solids or other
processes. such as thermal drying. which
result in a material that meets pollutant
concentrations in 503.l3(b)(3). the Class A
pathogen requirements in 503.32(a). and one
of the vector attraction reduction require-
ments in 503.33(b)( I) to 503.33(b)(8).
Biosolids derived products also include any
soil amendments which, in part. contain
biosolids meeting these criteria. Biosolids
derived products are acceptable for
distribution to the general public for
immediate use.
Bulk wastewater biosolids
Domestic wastewater biosolids that are not
sold or given away in a bag or other
container for application to the land.
Cation
A positively charged ion in the soil solution.
751
-------
CEC
Cation Exchange Capacity. The amount of
positively charged cations such as calcium.
potassium. copper. and nickel that can be
retained in the soil by attraction to the
negatively charged surfaces of soil clays and
organic matter. CEC is expressed in terms of
milliequivalents per 100 grams of soil.
Channers
Small, flat, oblong coarse fragments in soils.
ranging in length of the longest dimension
from 2 mm to 6 inches.
Claypan
A restrictive layer that consists of a horizon
of clayey soil that is dense and massive, but
not cemented. Claypans usually lie directly
beneath a horizon of medium-textured soil.
and the change froni that horizon to the
claypan is abrupt.
Coarse fragments
Rock fragments larger than 2 mm in
diameter. Gravel, cobbles, and channers are
the most common kinds of coarse fragments
in soils.
Coarse-grained materials
Soils that consist of loamy sand or sand
textures and often contain large amounts of
gravel or cobbles. These soils have high
rates of saturated hydraulic conductivity and
rapid or very rapid permeability.
Coarse-textured soil
A soil whose texture is sand or loamy sand.
Cobbles
Large. rounded coarse fragments in soils.
ranging in diameter from 3 to 10 inches.
Contour cropping
Planting crops in rows that run across slopes
and around hills, rather than up and down
slopes. Contour crop rows slow down runoff
and help conserve soil.
Cover crop
A small grain crop. such as oats. wheat, or
barley, not grown for harvest.
Crop rotation
The sequence of crops grown on a field over
a number of years. Crop rotation cycles flay
run from as few as 3 years to as many as 9
or 10 years.
Cross-slope farming
See Contour cropping.
Cumulative pollutant loading rate
The maximum amount of an inorganic
pollutant that can be applied to an area of
land.
Deep soil
Soil that is more than 40 inches deep to hard
bedrock (R horizon), soft or weathered
bedrock (Cr horizon). or a cemented horizon
such as a duripan (Bkqm horizon) or
petrocalcic (Bkm) horizon.
Denitrification
Loss of nitrogen from soil by conversion of
nitrate (NO:) to nitrogen gas (N 2 ).
Denitrification occurs when parts of the soil
become reduced by exclusion of oxygen.
either under saturated or near-saturated
conditions, or as oxygen demand is created
during decomposition.
Diversion terrace
A raised berm of earth constructed
horizontally across a slope in order to
intercept runoff and divert it laterally to a
grassed waterway that can conduct the water
safely downslope without eroding the soil.
Domestic wastewater biosolids
Solid, semisolid, or liquid residue generated
during the treatment of domestic sewage in a
treatment works. Wastewater biosolids
include, but are not limited to. domestic
septage: scum or solids removed in primary.
secondary. or advanced wastewater
treatment processes: and a material derived
from wastewater biosolids. Wastewater
biosolids do not include ash generated
during the firing of biosolids in an
incinerator, or grit and screening generated
during preliminary treatment of domestic
wastewater biosolids in a treatment works.
Domestic wastewater treatment facility
solids
The accumulated suspended and settleable
solids of domestic wastewater. deposited in
tanks or basins mixed with water to form a
semiliquid niass.
Drainage class
The degree of wetness of a soil, as
determined by the depth to a water table and
the length of time the soil remains saturated.
Common drainage classes include excess-
ivelv drained, well drained, moderately well
drained, somewhat poorly drained, and
poorly drained.
Droughty
Incapable of storing much water in the soil
for plant use. Sandy soils, shallow soils, and
sloping soils on southerly aspects are likely
to be droughty unless they are resupplied
with rainfall or irrigation water at short
intervals.
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Dry weight basis
Calculated on the basis of having been dried
at 105°C until reaching a constant mass (i.e..
essentially 100% solids content)
Duripan
A restrictive layer. also denoted as a Bkqrn
horizon, that is so thoroughly cemented with
silica, with or without calcium carbonate.
that it resembles a layer of rock in the soil.
Exempt biosolids
Domestic wastewater treatment facility
solids containing trace pollutant
concentrations that are below federal
alternative pollutant limits recognized under
503.l3(b)(3) that have been treated by a
Class A pathogen reduction process
recognized under 503.32(a) and one of the
vector attraction reduction procedures
established under 503.33(b)( I) to (8). These
solids are recognized as soil amendments
that are acceptable for distribution and
marketing to the public.
Equivalent
The number of grams of any particular
chemical (calcium. copper. potassium) that
is equal in reacting power to 1 gram of
hydrogen.
Feed crops
Crops produced primarily for consumption
by animals.
Fiber crops
Crops such as flax and cotton.
Field capacity
The moisture content of a soil when free
drainage immediately after a rain or an
irrigation has virtually ceased. It represents
the maximum amount of water a soil can
retain against the force of gravity.
Fine earth
All soil material that is smaller than 2 mm in
diameter. Fine earth includes sand
(.05-2.0 mm). silt (.002-05 mm). and clay
(<.002 mm).
Fine-textured soil
A soil whose texture is silty clay, sandy
clay, or clay.
Floodplain
The nearly level surface next to a river that
is covered with water when the river floods.
Food crops
Crops consumed by humans. These include.
but are not limited to. fruits, vegetables, and
tobacco.
Fragipan
A restrictive layer, also denoted as a Bx
horizon, that is extremely dense and
compact but is not cemented and is not very
high in clay content.
Glacial till
An unstratified, heterogeneous mixture of
sand, silt, clay, coarse fragments. rocks and
boulders that was deposited at the margins
and beneath the ice of continental or alpine
glaciers.
Gleyed
Soil that is very wet for long periods of time
and is characterized by gray colors, with or
without mottles.
Gravel
Small, rounded coarse fragments in soils.
ranging in diameter from 2 mm to 3 inches.
Gravitational water
Water that fills large pores when soil is
saturated and drains away freely under the
influence of gravity. Gravitational water is
not available for plant use.
Groundwater
Water below the land surface in the
saturated zone.
Hardpan
A generic term for a very dense or cemented
layer in soils. Very dense “hardpans”
include fragipans. claypans. tillage pans. and
compacted layers. Cemented “hardpans”
include duripans and petrocalcic horizons.
Heavy texture
A general term that refers to soils that have a
high clay content. The higher the clay
content, the “heavier” the soil. Clays. silty
clays, and some silty clay barns would all
be considered heavy soils.
Humus
The relatively resistant fraction of soil
organic matter that forms during biological
decomposition of organic residues. Humus
usually constitutes the major fraction of soil
organic matter.
Hydraulic conductivity
A quantitative measure of the rate of water
movement through soil. The most common
laboratory measurement determines the rate
of saturated flow in a vertical direction.
Classes of vertical, saturated hydraulic
conductivity are empirically related to
classes of soil permeability.
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Immobilization
Conversion of an element from the inorganic
form to the organic form by microbes.
Immobilized elements are not readily
available for uptake by plants. Nitrogen and
phosphorus are common elements
immobilized in this way.
Inclusion
An area of soil that is too small to show
separately on a soil map at the scale at
which the map is being made. Inclusions are
present only because of limitations of the
scale of mapping. and they are normal parts
of the definition of map units. Inclusions can
be mapped separately only by making very
detailed maps at very large scales.
Infiltration
The rate that water enteiw the soil.
Infiltration depends on the size of pores and
the stability of soil aggregates right at the
soil surface. If water cannot infiltrate, then it
either ponds on the surface or runs off over
the surface.
Inorganic nitrogen
Nitrogen that is in the animonium (NH 4 )
or nitrate (NO ) form, either in hiosolids or
in the soil.
Internal drainage
The ability of free water to escape from a
soil. Internal drainage is characterized by the
depth to and duration of water tables in soils
aiid classified in terms of drainage classes.
Internal drainage class
See Drainage class.
Lacustrine
A term that refers to sediments that were
originally deposited at the bottom of a lake
and are now exposed due to uplift of the
land or lowering of the water level.
Land application
The spraying or spreading of domestic
wastewater biosolids onto the land surface:
the injection of domestic wastewater
biosolids below the land surface: or the
incorporation of domestic wastewater
biosolids into the soil so that the biosolids
can either condition the soil or fertilize crops
or vegetation grown in the soil, or both.
Leaching
Removal of soluble minerals, nutrients.
organic chemicals and pesticides from the
soil by water passing through the soil.
Legume
A crop that forms a specific association with
soil bacteria that are capable of fixing
nitrogen. that is. transforming nitrogen gas
to organically combined nitrogen. Common
legumes include alfalfa. clovers. peas. and
soybeans. Nitrogen fixation can provide
most of the nitrogen nutrition of the legume
crop. and it can provide large amounts of
residual nitrogen for succeeding crops.
Light texture
A general term that refers to soils that have a
very low clay content. The lower the clay
content. the “lighter” the soil. Loamy sands.
sandy loams. and some loams all would be
considered light soils.
Loam
A specific class of soil texture that contains
a balanced mixture of sand, silt, and clay.
Generally the sand content is between 30
and 50 7c. the silt content is between 30 and
50%. and the clay content is between 10 and
27%.
Lodging
A process whereby cereal grains, upon
taking up excess amounts of nitrogen. put on
excess vegetative growth. lose strength in
the stems, and tip over. Lodging reduces
grain yields because grain lying flat is
difficult to combine.
Map unit
A collection of all soil-landscape areas
shown on a soil map that have the same
name and the same kind or kinds of soils.
Map units contain one or two dominant
soils, plus small areas of other kinds of soils
of minor extent. Map unit names identify the
dominant soil or soils. The minor com-
ponents collectively are called inclusions.
and they are identified in the map unit
description.
Map unit description
The part of the text of a soil survey report
that describes the characteristics of the soil
and landscape of the dominant soils in a map
unit. The map unit description also tells the
kind and amount of the inclusions in the
map unit, and it gives general information
on use and management of the map unit for
agriculture. forestry. and urban
development.
Matrix color
The dominant color in a variegated or
mottled soil. The color that occupies a
greater percentage of the exposed surface
area than any other color.
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Medium-textured soil
A soil whose texture is loam or silt loam.
Milliequivalent
One one-thousandth of an equivalent. In soil
science milliequivalents are used to quantify
the capacity of a soil to adsorb positively
charged ions independently of the particular
kind of substance.
Mineralization
Biochemical conversion of nitrogen in the
organic matter of soils and biosolids to
inorganic nitrogen. Mineralization produces
nitrogen in the ammonium (NH 4 ) form.
which is then converted to the nitrate (NO;)
form by the nitrification process.
Minimum tillage
Preparation of a seedbed for planting a crop
without conventional moldboard plowing.
Tillage operations range from disking or
chisel plowing the soil before planting to
planting directly into soil that has not been
tilled since the harvest of the previous crop.
Minimum tillage usually leaves enough
plant residues on the soil surface to provide
a measure of erosion protection.
Moderately coarse-textured soil
A soil whose texture is sandy loam.
Moderately deep soil
Soil that is 20 to 40 inches deep to hard
bedrock (R horizon), soft or weathered
bedrock (Cr horizon), or a cemented horizon
such as a duripan (Bkqm horizon) or
petrocalcic (Bkm) horizon.
Moderately fine-textured soil
A soil whose texture is silty clay loam, clay
loam, or sandy clay loam.
Moderately well drained
A soil that has a temporary water table for
short periods of time in the lower part of the
subsoil. The soil is usually mottled
somewhere between 24 and 40 inches.
Montmorillon ite
A type of soil cla that has a very high
shrink-swell potential.
NH 4 -N
The amount of nitrogen in the ammonium
form. Each 100 pounds of ammonium-
nitrogen contains 78 pouiids of actual
nitrogen.
Nitrification
The biological conversion of ammonium
(NH 4 ) to nitrate (NO;) in soil. As the
nitrogen cycle operates in most soils, the
nitrification step follows the mineralization
step. in which organic nitrogen is converted
to ammonium (NH 4 ).
N0 3 -N
The amount of nitrogen in the nitrate fonr.
Each 100 pounds of nitrate nitrogen contains
22 1/2 pounds of actual nitrogen.
Nutrient-supplying power
The ability of a soil to provide nutrients in
amounts needed for plant growth. Medium-
textured soils that are high in organic matter
generally have a high nutrient-supplying
power. Sandy soils that are low in organic
matter generally have a low nutrient-
supplying power.
Organic nitrogen
Nitrogen that is combined in the molecular
structure of organic compounds. Most of the
organic nitrogen in soils occurs as proteins
and amino acids or amine groups.
Pasture
Land on which animals feed directly on feed
crops such as legumes. grasses. grain
stubble, or stover.
Pathogenic organisms
Disease-causing organisms. These include.
but are not limited to. certain bacteria.
protozoa. viruses, and viable helminth ova.
Ped
An aggregate of individual grains of sand.
silt, and clay into a single unit of soil
structure. Ped shapes include granular. platy.
blocky, and prismatic. Ped sizes may vary
from 1-mm granules to 40-cm prisms.
Permeability
The rate that water moves through the soil.
Permeability depends on the amount, size.
and interconnectedness of soil pores. These
in turn are related to soil texture, soil
structure. and soil density.
Petrocalcic horizon
A restrictive layer. also denoted as a Bkm
horizon, that is enriched with calcium
carbonate. and in which the calcium
carbonate has cemented the horizon into a
rocklike layer.
pH
A number that indicates the relative acidity
or alkalinity of a soil. A pH of 7.0 indicates
a neutral soil. Lower numbers indicate acid
soils: higher numbers indicate alkaline soils.
Pollutant
An organic substance, an inorganic
substance, a combination of organic and
inorganic substances, or a pathogenic
organism that, after discharge and upon
exposure, ingestion, inhalation, or
assimilation into an organism either directly
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from the environment or indirectly by
ingestion through the food chain, could, on
the basis of information available to the
Administrator of EPA. cause death. disease.
behavioral abnormalities, cancer, genetic
mutations, physiological malfunctions
(including malfunction in reproduction). or
physical deformations in either organisms or
offspring of the organisms.
Pollutant limit
A numerical value that describes the amount
of a pollutant allowed per unit amount of
biosolids (e.g.. milligrams per kilogram of
total solids): the amount of a pollutant that
can be applied to a unit area of land
(e.g.. kilograms per hectare): or the volume
of a material that can be applied to a unit
area of land (e.g.. gallons per acre).
Poorly aerated
Soils in which air is not readily exchanged
between the soil and the atmosphere. Wet
soils are poorly aerated because air nioves
more slowly through water than through air-
filled pores.
Poorly drained
A soil that is saturated at or near the surface
for long periods of time. Poorly drained soils
are usually gleyed. and they often have
mottles in the A or Ap horizon.
Pores
Spaces. or voids, between mineral grains
and aggregates in the soil. The amount, size.
shape. and continuity of soil pores control
the rates of air and water movement into and
throughout the soil.
Public contact site
Land with a high potential for contact by the
public. This includes, but is not limited to.
public parks. ball fields, cemeteries, plant
nurseries. turf farms, and golf courses.
Puddling
Formation of a dense, massive surface soil
when medium- to fine-textured soils are
tilled when they are too wet.
Range land
Open land with indigenous vegetation
Readily available nitrogen
Nitrogen that is in the soil in the ammonium
(NH 4 ) or nitrate (NO;) form. Ammoniuni
and nitrate are dissolved in the soil solution
and can be taken up and utilized by plants
immediately.
Reclamation site
Drastically disturbed land that is reclaimed
using domestic wastewater biosolids. This
includes. but is not limited to. strip mines
and construction sites.
Reduced tillage
See Minimum tillage.
Residual nitrogen
Nitrogen that remains in the soil after the
harvest of a crop. Residual nitrogen is either
immediately available or will become
available to the succeeding crop. Sources of
residual nitrogen include inorganic nitrate
that is not leached from the soil. organic
nitrogen in crop residues, and organic
nitrogen in previous biosolids applications.
Restrictive layer
A general term for any soil horizon that is
slowly or very slowly permeable and
underlies more permeable soil horizons.
Restrictive layers slow down or stop the
downward movement of water in soils. and
they impede plant root penetration.
Runoff
Water that flows over the surface of soil
toward a stream or lake without sinking into
the soil.
Saturated flow
Movement of water in soil when all the
pores are completely full of water, that is.
when the soil is saturated. Rates of saturated
flow through large pores are relatively rapid.
and the potential for contamination of
groundwater with water-borne pollutants is
high.
Shallow soil
Soil that is less than 20 inches deep to hard
bedrock (R horizon), soft or weathered
bedrock (Cr horizon), or a cemented horizon
such as a duripan (Bkqm horizon) or
petrocalcic (Bkm) horizon.
Shrink-swell potential
The tendency of a soil to change volume due
to gain or loss of moisture. Soils with high
shrink-swell potentials expand appreciably
when they wet up and contract appreciably
when they dry out.
Slaking
The breakdown of structural aggregates
under the impact of falling droplets of water.
Grains of silt and clay washed off peds clog
soil pores. creating a thin surface crust that
seals the soil, reduces infiltration, and
increases runoff and erosion. Silty soils that
are low in organic matter and have weak
structure are particularly susceptible to
slaking.
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Slickensides
Polished, shiny surfaces on clayey soil
aggregates, caused by the movement of two
masses of soil past each other as soil
expands upon wetting. Slickensides are
evidence of high shrink-swell potential in
soils that contain large amounts of
niontrnorillonite clays.
Soil
A natural body that develops in profile form
in response to forces of climate and
organisms acting on a parent material in a
specific landscape position over a long
period of time. Soil covers the earth in a thin
layer and supplies plants with air, water.
nutrients, and mechanical support.
Soil amendment
Anything that is added to the soil to improve
its physical or chemical condition for plant
growth. Lime. gypsum. inorganic fertilizers.
and organic materials, including wastewater
biosolids. are all soil amendments.
Soil conditioner
Any material applied to improve
aggregation and stability of structural soil
aggregates. Domestic wastewater biosolids
provide these benefits. and are therefore soil
conditioners.
Soil drainage class
The degree of wetness ofa soil, as
determined by the depth to a water table in
the soil and the length of time the soil
remains saturated. Common drainage classes
include excessively drained, well drained.
moderately well drained, somewhat poorly
drained, and poorly drained.
Soil horizon
A layer of soil that is approximately parallel
to the earth’s surface. Each horizon results
from specific soil-forming processes . and
each is distinguished from horizons above
and below by a unique set of physical.
chemical, and biological properties.
Soil profile
A vertical exposure that allows you to see all
of the soil horizons that are present.
Soil profile description
A technical record of the soil properties that
can be observed and measured in the field
for each and every horizon in the entire soil
profile.
Soil series
The set of all soils whose profiles are
essentially alike, within narrowly defined
ranges of variability. The soil series is the
lowest unit of soil classification. Names of
soil series are usually taken from geographic
entities in areas where the soil was first
described, for example. the Appling Series.
the Tama Series, the Willamette Series.
Soil slope
The inclination of the land surface.
expressed as percent. A 10% slope means
that the elevation changes by 10 feet for
every 100 feet of horizontal distance.
Soil structure
The arrangement of individual grains of
sand, silt, and cIa into larger units called
aggregates. or peds. Plant roots. humus. and
soil clays all help to hold soil peds together.
Soil structure is characterized by the size.
shape. and strength of the peds.
Soil survey
The process by which a soil map is made.
Soil scientists walk over the land, observe
soil and landscape properties. classify the
soils, and locate soil boundaries in the field.
They use air photo base maps to record the
location of soil boundaries and label each
delineation with a map unit symbol.
Soil survey report
A book in which the results of the soil
survey of an area, often a county, are
published. The soil survey report contains
three related components: the soil maps. text
that describes the properties and behavior of
the soils and map units, and tables that give
quantitative data and interpretations for soil
use tmd management.
Soil texture
The amounts of sand, silt, and clay that
make up a soil. Specific combinations of
sand, silt, and clay form textural classes.
each of which is named with a term such as
silt loam, clay loam, or sandy loam.
Somewhat poorly drained
A soil that is saturated in the upper part of
the subsoil for significant periods of time
during rainy seasons. The soil is usually
gray and mottled somewhere between 10
and 24 inches.
Starter fertilizer
Fertilizer applied to the soil at the time a
crop is planted to provide a source of
nutrients that will be readily available at the
time the plains are beginning to grow
vigorously. Starter fertilizers bridge the gap
between planting and subsequent availability
of nutrients from mineralization of organic
matter.
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Terrace
A landform consisting of a long, narrow,
nearly level surface at or near the margin
and above the level of a body of water.
Stream terraces are above the level of the
stream’s floodplain, and they are usually
marked by an escarpment that descends
from the terrace to the floodplain.
Terracing
Construction of one or more diversion
terraces across a slope.
Tillage pan
A compact. dense layer of soil at the base of
the surface layer of a cultivated soil.
Compaction occurs when the soil is plowed
or disked when it is too wet.
Total solids
The materials in domestic wastewater
hiosolids that remain as residue when the
hiosolids are dried at 103 to 105°C.
Traffic pan
A compacted layer beneath the surface layer
of a cultivated soil that occurs as the result
of the cumulative effects over time of
driving over the soil with heavy equipment.
Treatment of wastewater biosolids
The preparation of wastewater biosolids for
final use or disposal. This includes, but is
not limited to. thickening. stabilization, and
dewatering. II does not include storage of
biosolids.
Unsaturated flow
Movement of water through soil when some
soil pores. particularly the larger ones, are
filled with air. Unsaturated flow occurs as
water moves through films of water around
soil particles in response to an energy
radient from moist soil to dr ’ soil. Rates of
unsaturated flow are very slow.
Unstabilized solids
Organic materials in domestic wastewater
hiosolids that have not been treated in either
an aerobic or an anaerobic treatment
process.
Vector attraction
The characteristic of domestic wastewater
biosolids that attracts rodents, flies.
mosquitoes. or other organisms capable of
transporting infectious agents.
Volatile solids
The amount of the total solids in domestic
wastewater biosolids lost when the biosolids
are combusted at 550°C in the presence of
excess air.
Volatilization
Conversion of ammonium (NH 4 ) in the soil
to ammonia gas (NHJ and escape of
ammonia into the atmosphere.
Water table
The top of a zone of saturated soil. Water
tables in soils are classed as perched.
apparent, or artesian. A perched water table
refers to a zone of saturation that is
underlain by unsaturated soil. Perched water
tables are associated with restrictive layers.
An apparent water table refers to a thick
zone of saturated soil in which there is no
evidence of restrictive layers. An artesian
water table refers to water under pressure
that is trapped beneath an impermeable
layer. The water table rises when the
impermeable layer is breached.
Weathering
The physical disintegration and chemical
decomposition of rocks in place upon
exposure to the atmosphere. Weathering
produces earth material that, upon further
modification by chemical and biological
processes. is transformed into soil.
Well-aerated
Soil that allows easy exchange of air
between the soil and the atmosphere. Well-
aerated soils have plenty of pores that are
big enough and sufficiently interconnected
to provide pathways for air movement. They
usually have good structure and are well or
moderately well drained.
Well drained
A soil that is rarely saturated above a depth
of 40 inches. Well drained soils are well-
aerated and have brown, yellowish brown.
or reddish brown colors. They are not
mottled above 40 inches or so.
Wetlands
Those areas that are inundated or saturated
by surface water or ground water at a
frequency and duration to support. and that
under normal circumstances do support. a
prevalence of vegetation typically adapted
for life in saturated soil conditions.
Wetlands generally include swamps.
marshes, bogs. and similar areas.
Wilting point
The nioisture content of a soil at which a
plant can no longer extract water. Without
addition of water, plants will wilt and
ultimately die. Some soils, particularly
clavey soils, contain relatively large
amounts of water at the wilting point, but it
is held so tightly in the very small pores of
the clays that plants can’t use it.
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The Orceon State [ nis Crsits Extension Sers ice educates ( )regonians h delis cring research-based, objective information to
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