United States
Environmental Protection
Agency
Robert S. Kerr Environmental
Research Laboratory
Ada OK 74820
Research and Development
EPA-600/S2-83-022 June 1983
Project Summary
Reducing Runoff Pollution Using
Vegetated Borderland for
Manure Application Sites
Philip W. Westerman, Michael R. Overcash, and Samuel C. Bingham
The objective of this study was to
evaluate the mechanisms and effec-
tiveness of vegetated buffer zones or
borderland areas in reducing pollution-
al impact of rainfall runoff from sites
used for land application of livestock or
poultry manure. The effect of grass
buffer-zone length on the reduction of
pollutant concentration and mass in
runoff from land application areas was
studied over a nine-month period for
several different buffer-area length/
application-area length ratios. Also,
one-dimensional mathematical models
were developed to investigate the ef-
fects of dilution and infiltration.
The field study consisted of mea-
suring rainfall runoff pollutions! char-
acteristics at various distances down-
slope from areas where caged-layer
poultry manure was applied regularly.
Evaluation of nutrients and solids in
runoff samples revealed that grass buff-
er zones effectively reduced the pollu-
tions! concentrations, and that the
amount of reduction increased with an
increase in the ratio of buffer-area
length to application-area length.
The model and experimental results
suggest that infiltration is the major
factor affecting buffer-zone length.
Soils having greater infiltration rates
will require shorter buffer lengths to
obtain the same percent reduction of
pollution potential. The results also
indicate that required buffer-area length
is a function of the application-area
length. Application areas having longer
slopes require longer buffer lengths to
obtain the same percent reduction of
the pollution potential. The pollution
potential of the application area like-
wise affects buffer length because a
greater percent reduction is required
to obtain a desired water quality stand-
ard if the application area runoff pollu-
tion potential is larger.
This Project Summary was developed
by EPA's Robert S. Kerr Environmental
Research Laboratory, Ada, OK, to an-
nounce key findings of the research
project that is fully documented in a
separate report of the same title (see
Project Report ordering information at
back).
Introduction
Land application of animal manure has
long been recognized as an efficient means
of waste disposal and as a means of
manure utilization for crop nutrients and
soil amendment. In recent years land
application of municipal and industrial
wastes has increased. Although the ex-
perimental part of this study evaluates
runoff pollution from land application sites
receiving animal manure, many of the
principles discussed apply to land applica-
tion sites receiving other wastes, especially
wastes which have high runoff pollution
potential for nutrients or oxygen demand.
Such wastes are municipal sludge, poultry
processing wastes, fermentation sludges,
and meat processing wastes.
Land application sites are a potential
source of nonpoint source water pollution.
Section 208 of the Federal Water Pollu-
tion Control Act Amendments of 1972,
Public Law No. 92-500, specifies the
development of water quality management
plans to control nonpoint source pollution.
The U.S. Environmental Protection Agency
(EPA) proposes the use of Best Manage-
ment Practices (BM Ps). These are defined
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for agriculture as management practices
which best reduce nonpoint source pollu-
tion while being consistent with sound
agricultural principles. Such BMPs are to
be used, in lieu of runoff collection and
treatment prior to stream discharge, as the
only feasible nonpoint source control
measures.
Grass buffer zones are one of the possible
BMPs. Other terms used almost inter-
changeably with grass buffer zone are
filter strip, grass filtration area, field borders,
or borderland areas. Land application sites
near streams, ditches, waterways, or water
impoundments can particularly benefit from
buffer zones which reduce runoff pollution
potential. Mechanisms acting in the buffer
area to reduce pollution potential include
dilution due to rainfall, infiltration, and
settling or filtering of materials. These
mechanisms in turn depend upon the
vegetation, soil surface condition, soil
hydrologic properties, topography and
rainfall-runoff conditions. However, very
little research has been conducted to deter-
mine the size of buffer zone needed for a
specified reduction in runoff pollution
potential.
The total amount of land required for a
complete land application system increases
as the buffer-area size increases. Buffer
zone research is essential since regulations
establishing arbitrary buffer distance can
have a tremendous impact on land-based
waste treatment system costs.
The objectives of this research were: (1)
to develop models based on hydraulic
processes to predict reductions of the
pollution potential for a land application/
buffer zone system and (2) to experimen-
tally determine effectiveness of various
buffer lengths based on reduction of runoff
pollution concentrations while maintaining
a relatively constant manure load on the
land application areas.
Conclusions
Land application of manure to a grass
area by surface spreading increased the
pollution transported by rainfall runoff
considerably when compared to a similar
area not receiving manure. Moreover, a
high pollution potential was maintained by
frequent manure applications (normally
every two to three weeks), and this allowed
evaluation of buffer areas under maximum
pollution potential conditions.
Grass buffer areas effectively reduced
pollutional concentrations of nutrients
(such as total phosphorus (P) and total
Kjeldahl nitrogen (TKN)), organic material
(total organic carbon (TOC)), and solids in
runoff from manured areas. However, to
reduce concentrations to within 10% of
the concentrations in runoff from a similar
area not receiving manure may require a
buffer area as large as the manure-applica-
tion area for soils with low infiltration ca-
pacity. The pollution concentration reduc-
tion per unit length of buffer zone was
greatest for shortest buffer lengths. Thus,
a cost-benefit analysis of buffer zones
should consider that as the buffer zone
increases, there is less improvement in
water quality per unit length increase in
buffer zone.
One-dimensional overland flow models
that were developed were useful in pre-
dicting reductions of concentration and
mass in a buffer zone. The models are
simple in nature, and the results can be
generalized in a family of curves. The
theoretical model for predicting reduction
in pollution concentration is simple be-
cause it considers only dilution and infiltra-
tion as the pollution-reduction mechanisma
The mass model considers loss of chemical
constituents due only to infiltration. Com-
plete mixing of pollutants in overland flow
of surface water and infiltrating water is
assumed, and the results indicate that
these assumptions are reasonable.
The models can be generalized by plot-
ting percent reduction of pollution poten-
tial (above background conditions) versus
the ratio of buffer-area length to applica-
tion-area length. This can be done for
concentration and for mass, resulting in a
family of curves for various values of the
ratio of rainfall rate to infiltration rate.
Thus, the graphs are easy to use if the
rainfall and infiltration rates can be quanti-
fied for the period of concern. The infiltra-
tion rate is dependent on soil types; thus,
there is some justification for basing buffer
length on soil hydrologic groups such as
the four groups defined by the Soil Con-
servation Service (SCS). Soils with high
infiltration rates would require less buffer
length.
Experimental results indicated that all
pollution parameters which were measured
were reduced at similar rates through the
buffer zones. Thus, the theoretical model
can be applied to all nutrients even though
the assumptions used in developing the
model seem more appropriate for soluble
pollutants than for insoluble pollutants.
The theoretical model predicted reductions
similar to the experimental results.
The experimental results should not be
applied to sites with much longer applica-
tion area lengths without further research.
However, the theoretical model would
indicate similar results for larger application
areas. Both the experimental results and
theoretical model results apply only to
when the application area and buffer area
are similar in vegetative cover, soil surface
condition, topography, and hydrologic
properties.
The results of this research provide
some guidelines which can be used in
determining the amourrt of buffer area
needed to reach a predetermined accept-
able level of pollution potential of runoff
from land application areas. The results of
the dilution-infiltration model can be used
in evaluating the cost-effectiveness of
changing the buffer-zone length.
Recommendations
More research should be conducted on
the effectiveness of buffer zones in re-
ducing pollution potential of runoff from
land application sites of various larger
sizes and sites loaded at various rates of
manure application. The results of this
study indicate that to reduce the concentra-
tion of pollutants in runoff from land
application sites to near that of similar
surrounding areas receiving no manure
requires a buffer-zone length about equal
to the application-area length. This is
more buffer zone than is normally being ^
recommended. If settling, vegetative ad- •
sorption or other additional factors be-
sides dilution and infiltration are acting to
reduce the pollution in the runoff, then
less buffer zone may be needed. Addition-
al research is needed on the mechanisms
acting in the buffer zone.
In order to use the dilution-infiltration
models on an event-by-event basis, more
research is needed on characterizing the
effective infiltration rate/rainfall rate ratio,
especially for events of highly varying
rainfall rates. Also, the capability to predict
pollution potential of manure-application
sites for different manure types, application
rates and soil-vegetation systems needs
further development. Effect of lelative
amounts of manure adhering to leaves and
vegetation compared to that which is in
contact with soil needs to be evaluated in
terms of affecting the runoff pollution
potential of the land application site.
Effectiveness of using alternating strips
of application areas and buffer areas needs
further research. This method may prove
to be a more efficient use of land than
having one wide buffer area downslope of
the manure area because the initial part of
the buffer zone seems most effective in
reducing pollutants. Also, the effect of
type of vegetation in the buffer area
further research.
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Experimental Study
A nine-month field study using caged-
layer poultry manure and tall fescue buffer
areas was conducted to evaluate several
buffer-area length/application-area length
ratios over the range from 0.2 to 2.6. An
application area with no buffer area and a
control plot were also included. The
general representation of a buffer area is
shown in Figure 1.
Runoff amount and concentrations of
total solids (TS), volatile solids (VS), TOC,
chemical oxygen demand (COD), P, TKN,
nitrate nitrogen (N03-N), ammonia nitro-
gen (NH3-N), and chloride (C1~) were
measured for all rainfall events but only
the large rainfall events were reported.
A high pollution potential was maintained
by frequent applications of manure. The
concentrations of pollutants which were
measured in runoff from nine of the largest
rainfall-runoff events were greater than
concentrations in background runoff (from
similar plots not receiving manure) by 58%
for TOC, 98% for TKN, and 613% for P.
The portion of the solids transport attri-
buted to manure solids was estimated
using VS/TS ratios and was between 30%
and 50% for two selected runoff events.
However, filtering of some runoff samples
with Whatman 41 filter paper also indicated
that the total nutrient transport could be
reduced only 34% for P, 26% for TKN, and
less for other nutrients by filtering. Thus,
considerable portions of the nutrients in
runoff were in soluble forms.
Concentration reductions increased with
increasing buffer-area length to manure-
area length ratio. However, to reduce
concentrations to within 1 0% of the con-
centrations in background runoff required
a buffer area about equal in length to the
application area, where the range of manure
application areas was 8.7 m to 1 3 m long.
Dilution-Infiltration Equations
One-dimensional overland flow models
were developed to predict reductions of
concentration and mass in a buffer zone.
The model for predicting reduction in
pollutant concentration considers only
dilution and infiltration as the pollution-
reduction mechanisms, and the mass
model considers loss of chemical con-
stituents due only to infiltration of runoff
liquid. In both cases, complete mixing of
pollutants in overland flow of surface
water and infiltrating water is assumed.
The equation for concentration reduction
above a background level is:
Pc=(100)
100
Rainfall
Manure
Application
Area
Soil Surface
Slope
where
Pc= percent reduction in concentration
above background level
C0= pollutant concentration in runoff
entering the buffer area
Cx= pollutant concentration in runoff at
distance x into the buffer zone
CB = pollutant concentration in runoff
for similar area not receiving manure
K = buffer-area length/application-area
length ratio, and
D = infiltration rate/rainfall rate ratio.
The equation for percentage mass re-
duction (above a background level), definedl
as Pm, is:
Pm= 100
1 -
/ 1 \ li~rD
VTTK)V
(2)
As seen m Equations (1) and (2) the per-
cent reduction (above background levels)
in concentration and mass is not de-
pendent upon the pollution concentration
or mass transport into the buffer area.
However, if a certain concentration or
mass transport value is chosen as the
water quality limitation, then the pollutant
concentration and mass transport coming
off the application area and the back-
ground levels must be known.
The dilution-infiltration models are gen-
eralized by plotting percent reduction of
pollution potential (above background con-
ditions) versus the ratio of buffer-area
length to application-area length. This is
done for concentration and mass, resulting
in a family of curves for various values of
the ratio of rainfall rate to infiltration rate.
The theoretical model would seem to
apply better to soluble pollutants than to
insoluble pollutants, but the experimental
data indicate all pollution parameters which
were measured were reduced at similar
rates through the buffer zones. The the-
oretical model for concentration reduction
predicted results similar to the experimen-
tal results for an average infiltration rate/
rainfall rate ratio of 0.7, which was reason-
able for the clay loam soil used in the
experiment. Experimental results from
this research were also in general agree-
ment with other comparable studies.
Infiltration
Figure 1. Schematic of manure-application area and buffer area.
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Philip W. Westerman and Michael R. Overcash are with North Carolina State
University. Raleigh. NC 27650; Samuel C. Bingham is presently with the U.S.
Department of Agriculture. Rutherfordton, NC 17650.
R. Douglas Kreis is the EPA Project Officer (see below).
The complete report, entitled "Reducing Runoff Pollution Using Vegetated
Borderland for Manure Application Sites," (Order No. PB 83-189 274; Cost:
$ 11.50, subject to change) will be available only from:
National Technical Information Service
5285 Port Royal Road
Springfield, VA 22161
Telephone: 703-487-4650
The EPA Project Officer can be contacted at:
Robert S. Kerr Environmental Research Laboratory
U.S. Environmental Protection Agency
P.O. Box1198
Ada. OK 74820
United States
Environmental Protection
Agency
Center for Environmental Research
Information
Cincinnati OH 45268
Postage and
Fees Paid
Environmental
Protection
Agency
EPA 335
Official Business
Penalty for Private Use $300
PS 0000329
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