United States
Environmental Protection
Agency
Robert S Kerr Environmental
Research Laboratory
Ada OK 74820
EPA 600/8-90/054
June 1990
oEPA
Research and Development
Agricultural Drainage
Wells: Impact on Ground
Water
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EPA/600/8-90/054
Agricultural Drainage Wells:
Impact on Ground Water
by
Ralph D. Ludwig, Ronald L Drake
and Donald A. Sternitzke
Dynamac Corporation
Robert S. Kerr Environmental Research Laboratory
Ada, OK 74820
EPA Contract No. 68-C8-0058
Project Officer
John E. Matthews
Applications & Assistance Branch
Robert S. Kerr Environmental Research Laboratory
Ada, OK 74820
Robert S. Kerr Environmental Research Laboratory
Office of Research and Development
U.S. Environmental Protection Agency
Ada, OK 74820
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Disclaimer
The information in this document has been funded wholly or in part by the United States Environmental Protection
Agency under Contract No. 68-C8-0058 to Dynamac Corporation. It has been subjected to the Agency's peer and
administrative review, and it has been approved for publication as an EPA document.
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Contents
1. List of Figures iv
2. List of Tables v
3. Introduction 1
4. What are agricultural drainage wells? 1
5. Location of agricultural drainage wells 1
6. Agricultural drainage well designs 3
7. Potential contaminants entering agricultural drainage wells 4
8. Impact of agricultural drainage wells 4
9. Transport and fate of agricultural drainage well contaminants 6
A. Suspended solids 6
B. Pesticides 6
C. Nutrients 8
D. Microbes 9
E. Salts 9
F. "Incidental" contaminants 10
10. Discussion 10
11. Recommendations 14
12. References 15
13. Appendix A 17
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Figures
1. Surface and subsurface runoff entering agricultural drainage well completed into bedrock 2
2. Schematics of agricultural drainage wells 3
3. Contaminants and their transport pathways into agricultural drainage wells 4
IV
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Tables
1. States in which presence of agricultural drainage wells has been confirmed 2
2. Ranges for several water quality parameters monitored in runoff entering four
agricultural drainage wells in northcentral Iowa 5
3. Predominant transport modes and persistence in soils of selected agricultural herbicides 7
4. Confirmed presence of pesticides in ground water of 17 different States 8
5. Levels of bacteria detected in surface return flow 9
6. Practices for controlling direct runoff and their effectiveness 11
7. Principal types of cropland erosion control practices and their effectiveness 12
8. Practices for the control of pesticide loss from agricultural applications and their effectiveness 13
9. Practices for the control of nutrient loss from agricultural applications and their effectiveness 14
A-1. Agricultural herbicides: Types, transport modes, toxicities, and persistence in soil 18
A-2. Agricultural insecticides and miticides: Types, transport modes, and toxicities 20
A-3. Agricultural fungicides: Transport modes and toxicities 22
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Introduction
As part of the Safe Drinking Water Act (SDWA) enacted in
1974, Congress mandated the development of a Federally
approved Underground Injection Control (DIG) program for
each State, Possession, and Territory. The aim of the
program was to prevent contamination of Underground
Sources of Drinking Water (USDW) by injection wells. A well
is defined in Title 40 of the Code of Federal Regulations as
either a dug hole or a bored, drilled or driven shaft whose
depth is greater than its largest surface dimension. Injection
is defined as the subsurface emplacement of fluids in a well
where a fluid is any material that flows or moves whether it
is semisolid, liquid, sludge or gas.
Under the UIC program, five classes of injection wells are
recognized. These are:
Class I: Wells used to inject hazardous wastes or
dispose of industrial and municipal fluids
beneath the lowermost USDW.
Class II: Wells used to inject fluids associated with the
production of oil and natural gas or fluids/
compounds used for enhanced hydrocarbon
recovery.
Class III: Wells which inject fluids for the extraction of
minerals.
Class IV: Wells which dispose of hazardous or radio-
active wastes into or above a USDW. (These
wells are now banned.)
Class V: Wells not included in the other classes,
generally inject nonhazardous fluid into or
above a USDW.
Seven main categories of Class V injection wells consisting
of over 30 individual well types are recognized under the
UIC program. The well types range in complexity from
simple shallow cesspools to sophisticated geothermal
reinjection wells which may be thousands of feet deep.
USEPA and State records show that at least 170,000 Class
V wells are in existence in the United States and its
Territories and Possessions of which about 57 percent are
drainage wells and 26 percent are sewage related wells.
Conceivably, more than one million Class V wells may be in
existence. According to the EPA (1989), of the five classes
of wells recognized under the UIC program, Class V wells
may pose the greatest environmental threat to the Nation's
ground-water resources.
What are agricultural drainage wells?
Agricultural drainage wells are one of many Class V well
types which may pose a high potential for ground water
contamination. Agricultural drainage wells are currently
among 15 Class V well types which have been designated
"high priority" by the USEPA under a preliminary screening
program conducted by the Office of Drinking Water.
Agricultural drainage wells can be defined as constructed
subsurface disposal systems used to accelerate the
drainage of agricultural surface runoff and/or subsurface
flow. Accelerated drainage is required in many regions of
the United States in order to provide a well-aerated root
zone for optimum crop growth. In Iowa, for example,
accelerated drainage is necessary in many areas for
optimizing row-crop production. Glanville (1985) cites an
example in northcentral Iowa where about five million
gallons of excess water must be drained annually from a flat
40-acre field.
Generally, an agricultural drainage well system consists of a
buried collection basin or cistern, one or more tile lines
entering the cistern, and a drilled, or dug, cased well
(Report to Congress, 1987). Agricultural drainage wells may
receive field drainage from precipitation, snowmelt, and
floodwaters; irrigation return flow; and animal yard, feedlot,
or dairy runoff. In drier regions such as the western United
States, irrigation return flow is a principal component of flow
entering agricultural drainage wells. In wetter regions
characterized by poor soil drainage, field drainage is likely
to be a principal component. Both irrigation return flow and
field drainage can take the form of surface and subsurface
runoff. Figure 1 shows a typical agricultural drainage well
system for collection of both surface and subsurface flow.
Location of agricultural drainage wells
Generally, agricultural drainage wells may be found in areas
having low soil permeabilities, shallow water tables, and
insufficient natural surface drainage (Report to Congress,
1987). According to an inventory of agricultural drainage
wells reported in the 1987 Report to Congress, 1,338 such
wells have been identified throughout the United States. Of
those wells identified, the majority were confined to just a
few states with the greatest number of wells being identified
in Idaho (572), Iowa (230), New York (150), Texas (108),
and Indiana (72). A list of States in which the presence of
agricultural drainage wells has been confirmed is provided
in Table 1. The difficulties and uncertainties inherent in
compiling the inventory, however, suggest that the total
number of wells identified in the report (1,338) may be a
gross underestimate. This is partially attributable to the
reluctance on the part of many well owners to admit to the
existence of wells on their property, the ease with which
agricultural drainage wells can be constructed, the lack of
permit requirements, and the large number of farming
operations in the United States (Report to Congress, 1987).
The difficulties and uncertainties inherent in compiling an
inventory of agricultural drainage wells lead to several
discrepancies in the reported number of wells. For
example, in contrast to the 572 agricultural drainage wells
reported for the State of Idaho in the 1987 Report to
Congress, Graham et al. (1977) claim that over 2000
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*
Figure 1. Surface and subsurface runoff entering agricultural drainage well completed into bedrock (modified from Glanville, 1985).
Table 1. States in which presence of agricultural drainage wells has been confirmed (Source:
Report to Congress, 1987).
State
New York
Puerto Rico
West Virginia
Florida
Georgia
Kentucky
Illinois
Indiana
Michigan
Minnesota
Oklahoma
Texas
Iowa
Missouri
Nebraska
Colorado
North Dakota
Idaho
Oregon
Washington
EPA Region
II
II
III
IV
IV
IV
V
V
V
V
VI
VI
VII
VII
VII
VIII
VIII
X
X
X
No. of Wells
Confirmed
150
unknown
unknown
unknown
43
unknown
6
72
15
54
unknown
108
230
unknown
5
unknown
1
572
16
66
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agricultural drainage wells are present within the eastern
Snake River plain of Idaho alone. These wells reportedly
drain approximately 320,000 acres of land.
In Texas, 300 agricultural drainage well systems are
reported to be in operation within a 250 square mile area in
southwestern Hidalgo county alone (Texas Water
Commission, 1989). This is in contrast to the 108
agricultural drainage wells reported for the State of Texas
(1987 Report to Congress). Fluids entering these wells,
consisting of irrigation return flow and rainfall runoff, have
been observed to contain high concentrations of dissolved
solids, nitrate, and the herbicides, bromacil and simazine
(Knape, B.K., 1984). Bromacil and simazine, however,
have reportedly not impacted local ground water resources
(Molofsky, S.J., 1985). An undetermined number of
agricultural drainage wells are also known to exist in
Runnels County and Oldham County, Texas (Texas Water
Commission, 1989).
In contrast to the 230 agricultural drainage wells reported
for the State of Iowa in the 1987 Report to Congress,
Musterman and Fisher (1981) estimated the existence of
between 460 and 920 agricultural drainage wells in
northcentral Iowa alone. Glanville (1985) reported that 700
agricultural drainage wells, some more than 100 years old,
are estimated to be in use in Iowa. In northcentral Iowa, as
many as eight agricultural drainage wells per square mile
are reported to exist (Glanville, 1985). Since 1957, permits
have been required for the construction of new agricultural
drainage wells in Iowa. Only two such permits have
reportedly been issued since that date.
The discrepancies and uncertainties noted with regard to
the number of agricultural drainage wells in existence
appears to reflect the limited information currently available
regarding the presence and distribution of agricultural
drainage wells. This apparent lack of information stresses
the need to carry out more thorough and detailed
inventories at the State and Federal levels.
Agricultural drainage well designs
Design of agricultural drainage wells varies from State to
State (Report to Congress, 1987). The design depends on
whether the wells are to be used for the collection of
surface flow, subsurface flow, or both. Figure 2 depicts two
typical agricultural drainage well designs. In Iowa, cisterns
are generally constructed from poured concrete, grouted
bricks, large diameter clay tiles or metal culverts. According
to Baker and Austin (1984), most agricultural drainage wells
in Iowa either have surface inlets connected to the sub-
surface drainage systems, or the cisterns are low enough to
allow surface drainage to enter the wells directly when
pondage occurs.
Concrete Cover
Land Surface
4' I.D.
Minimum
Free Fall
1'mamimum
Filter V —'
20" Concrete Pipe
"*— Reinforced
Concrete
Top
••— Concrete
or Brick
4" Corrugated
Plastic Drain
Tile
Minimum 4" Casing
Drain Well - Usually 75-100' Deep
Cap
®
Filter
Concrete
Except as Indicated, Materials and
Dimensions are as Shown in Figure to Loft.
Figure 2. Schematics of agricultural drainage wells (A) with well inside cistern and (B) with well adjacent to cistern (from Texas
Department of Water Resources, 1984).
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To limit costs, agricultural drainage wells are usually
completed in the shallowest permeable zone which can
meet the discharge volume requirements. Small-capacity
wells may be completed in the vadose zone although most
wells are more likely to be completed in shallow bedrock
aquifers exhibiting high permeability properties. According
to the 1987 Report to Congress, wells in Iowa tend to be
completed in fractured, vuggy carbonate formations while
wells in Idaho tend to be completed in fractured basalt
formations. In efforts to minimize costs, most wells are
completed to depths of less than 100 feet. Wells in Idaho
are reported to range in depth from 20 to 300 feet with
casing depths ranging from 5 to 200 feet below land surface
(Report to Congress, 1987). Casing diameters are reported
to range from 3 to 24 inches depending on the design
capacity of the wells. Large-capacity wells may have
screened or inverted inlets, settling ponds, and surface
seals. According to Graham et al. (1977), agricultural
drainage wells in the eastern Snake River Plain of Idaho are
typically 10-30 centimeters (4-12 inches) in diameter, 30-50
meters (100-164 feet) in depth and are capable of
accepting flows up to eight cubic meters (282 cubic feet)
per minute.
suspended solids, pesticides, fertilizers (e.g. nitrogen and
phosphorous compounds), salts, organics, metals, and
microbes including pathogens. Surface runoff is generally
low in salinity but may contain large quantities of suspended
solids, microbes, and pesticides. Contaminants such as
pesticides, bacteria, and metals may be attached to
suspended solids in surface runoff thereby facilitating the
entry of these contaminants into agricultural drainage wells.
Subsurface flow is not likely to contain significant levels of
suspended solids or bacteria (due to the effects of natural
soil filtration processes), but may contain high
concentrations of dissolved solids including dissolved
pesticides and nutrients (e.g. nitrates). Baker et al. (1985)
conducted a study in northcentral Iowa which indicated that
nitrate concentrations entering agricultural drainage wells
via subsurface flow were as high as 30 mg/l. (The EPA
Drinking Water Standard for nitrate as N is 10 mg/l.)
Figure 3 indicates the transport pathways by which
contaminants enter agricultural drainage well systems.
Table 2 shows ranges for several water quality parameters
monitored in runoff entering agricultural drainage wells in
northcentral Iowa.
Potential contaminants entering
agricultural drainage wells
Potential contaminants entering agricultural drainage wells
depend on the particular farming practices in effect and the
particular soil type(s) present. Contaminants may include
Nitrates
Impact of agricultural drainage wells.
The impact of agricultural drainage wells on the subsurface
environment will depend on the volume of fluid entering the
wells, the type and concentration of contaminants present
in the injected fluid, and the nature of the subsurface
Sediment,
Bacteria,
Pesticides
Figure 3. Contaminants and their transport pathways into agricultural drainage wells (modified from Glanville, 1985).
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Table 2. Ranges for several water quality parameters monitored
in runoff (surface and subsurface) entering four agricultural
drainage wells in northcentral Iowa (from Baker et al., 1985).
Constituent (mg/liter)
Range of Concentration
NH.-N
N03-N
PO. -P
Cl
Ca
Fe
Dissolved solids
Suspended solids
Atrazine
Cyanazine
Alachlor
Dieldrin
Metribuzin
Dicamba
0.01-3.78
1.50-34.0
0.01-1.99
1.0-120.0
13-150
0.01 - 2.60
75 - 745
0-5,360
0 - 0.50
0 - 80.0
0 - 55.0
0 - 0.028
0-0.41
0-12.0
environment into which the fluid is injected. Since
agricultural drainage wells are generally completed in highly
permeable formations, such as fractured bedrock, the
potential for widespread environmental impact is high. In
general, surface runoff can be expected to have the
greatest potential negative impact on the subsurface
environment both because it may contain high levels of
suspended solids, pesticides and bacteria, and because it
may be produced in copious volumes. Surface runoff has
direct access to the drainage wells and therefore the high
permeability formations into which the agricultural drainage
wells are completed. Subsurface flow into agricultural
drainage wells may exhibit significant impacts in cases
where the flow contains high levels of dissolved
contaminants (e.g. pesticides, nitrates).
In cases where agricultural drainage wells are completed in
the vadose zone, the ability of the injected fluid to
potentially impact an underlying aquifer is dependent on the
elevation of the injection point relative to the elevation of the
water table, the permeability and contaminant attenuation
properties of the vadose zone material, the presence of
aquicludes and/or aquitards below the area of injection, and
the existing quality of the ground water.
For agricultural drainage wells completed in the saturated
zone, the likelihood of serious ground-water contamination
is considerably more imminent than for drainage wells
completed in the vadose zone. Formations deemed
attractive for the completion of agricultural drainage wells
are often also those formations serving as local supplies of
drinking water. The high permeability properties
characteristic of these formations can often result in rapid
and extensive contamination of downgradient drinking water
wells. The extent to which nearby water supply wells may
be affected by an agricultural drainage well will depend
upon the distance of the injection point from the supply
wells, the area of influence of the supply wells, the physical,
chemical, and biological contaminant attenuation properties
of the formation into which the agricultural drainage wells
are completed, the volume of the agricultural drainage fluids
being injected, and the types and concentrations of
contaminants present in the injected fluid.
Contamination of drinking water supplies arising from the
presence of agricultural drainage wells has been reported in
Idaho and Iowa. In Iowa, the presence of contaminated
supply wells has been reported to coincide with areas highly
concentrated with agricultural drainage wells. Baker et al.
(1985) conducted a study of the impact of agricultural
drainage wells on farm water supply wells in Humboldt and
Pocahontas Counties in Iowa. The farm wells were located
in three different regions, each about 20 square miles in
area. Agricultural drainage wells were prevalent in two of
the regions but not in the third. The study showed that one-
third of farm wells, in the two regions where large numbers
of agricultural drainage wells were present, contained
nitrate levels exceeding the recommended drinking water
standard. This compared to only 9 percent of farm wells
exceeding the nitrate standard in the region not exhibiting a
high concentration of agricultural drainage wells. The study
also indicated that in most cases, little nitrate contamination
was found in water supply wells more than 1.25 miles from
an agricultural drainage well. It is assumed that the three
different regions studied were similar in geologic character.
In Idaho, water supply wells near agricultural drainage wells
have also shown signs of contamination. In a study
conducted by Graham (1979), the presence of excessive
levels of coliform bacteria in domestic water supplies during
the irrigation season was linked to the presence of
agricultural drainage wells. Levels of coliform bacteria in
excess of Idaho's drinking water standards were observed
in 31 percent of the domestic wells in areas exhibiting a
high concentration of agricultural drainage wells. The quality
of the water was significantly inferior to that of other areas
upgradient of the agricultural drainage well areas. In a study
conducted by Graham et al. (1977) in the eastern Snake
River Plain area of southern Idaho, bacterial levels and
turbidity within the recharge zone created by the agricultural
drainage wells were far in excess of drinking water
standards. Deep percolation of the injected wastewater
resulted in bacterial contamination of a deep perched zone
and an artesian ground-water system. Suspended solids,
as measured by turbidity, were apparently filtered out by
the deep percolation process.
Agricultural drainage wells may also be responsible for
contamination of supply wells in California. Although
agricultural drainage wells have not been inventoried in
California, agricultural drainage wells are reported to exist
(Report to Congress, 1987; Spencer et al., 1985).
In addition to potentially impacting ground-water resources,
agricultural drainage wells may also have an adverse
impact on wetlands. Although the impact of agricultural
drainage wells on wetlands is beyond the scope of this
report, an investigation in this area may be warranted.
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Transport and Fate of Agricultural
Drainage Well Contaminants
The transport and fate of a particular contaminant entering
an agricultural drainage well will depend on the combined
properties of the contaminant and the formation into which
the contaminant has been introduced. Depending on these
properties, the contaminant may be partitioned to various
degrees between the different constituents comprising the
formation. The partitioning of the contaminant will govern its
mobility and therefore its ability to impact the subsurface.
Important formation-related properties governing the
partitioning process will include permeability, "qualitative"
porosity (i.e. presence or absence of extensive void/fracture
network), organic content, clay content, microbial activity,
redox potential, temperature and pH. These formation
properties combined with the specific characteristics of the
contaminants will impact on important transport and fate
phenomena such as adsorption, filtration and
biodegradation.
The contaminants of primary concern in fluids entering
agricultural drainage wells include suspended solids,
pesticides, microbes, nutrients, salts, and metals. Sus-
pended solids, bacteria, and pesticides are of particular
concern in surface runoff while soluble components such as
nitrates, salts and some pesticides are of concern in
subsurface flow. Insoluble components such as microbes,
many pesticides, and suspended solids may, in some
cases, conceivably also enter agricultural drainage wells by
way of subsurface flow through soil macropores (e.g.
channels created by earthworms, root systems, etc.). The
size and often extensive network of macropores may
occasionally afford such contaminants a relatively
unobstructed transport pathway to the subsurface.
Macropores provide preferential flow paths and, while
normally accounting for only a small percentage of the total
soil porosity, may be responsible for a large percentage of
the total flow through soils. The significance of macropores
in the subsurface transport of contaminants is still under
investigation.
The subsurface transport and fate of contaminants known to
enter agricultural drainage wells are discussed in the
ensuing sections.
A. Suspended Solids
Suspended solids entering agricultural drainage wells are of
concern not only because of their objectionable presence in
drinking water but because they may also act as a vehicle
for the transport of other potential contaminants such as
pesticides, bacteria, and metals (i.e. facilitated transport).
Pesticides, bacteria, and metals are all capable of strongly
sorbing onto the surfaces of suspended solids such as clay
minerals and organics. Once in the subsurface, these
contaminants may slowly desorb from the suspended solids
and contribute to degradation of ground-water quality. The
extent to which suspended solids will be transported in the
subsurface will depend on the nature of the suspended
solids (e.g. particle size, density), the size and pattern of
fractures and/or voids in the formation in which the
agricultural drainage well is completed, and the local
ground-water flow conditions. Suspended solids entering a
formation lacking an extensive network of fractures or voids
will likely not be transported far and will tend to be filtered
out within the immediate vicinity of the well. Lighter, smaller
suspended solids entering a formation with an extensive
network of fractures and/or voids and a high ground-water
flow velocity may conceivably be transported over very
large distances. The practice of completing agricultural
drainage wells in karst and/or highly fractured bedrock
formations which may lack good filtering capabilities,
suggests that, in some cases, suspended solids entering
agricultural drainage wells may contribute to contamination
of underground drinking water sources.
B. Pesticides
Pesticides such as bactericides, fungicides, insecticides,
nematocides, rodenticides, and herbicides pose a threat to
ground-water supplies because of their toxic properties.
Because most pesticides are relatively insoluble and tend to
be strongly sorbed to soil particles, pesticides entering
agricultural drainage wells are more likely to be associated
with surface runoff than subsurface flow. More soluble
pesticides such as the anionic herbicides chloramben, 2,4-D
and dicamba may, however, be present in subsurface flow.
Table 3 provides a list of selected herbicides and their
predominant transport modes. Also included in Table 3 is
the approximate persistence of each herbicide in soil.
Persistence in Table 3 refers to the time required for 90
percent or more of the applied pesticide to disappear from
the site of application. The values for persistence provided
are, at best, approximations since persistence may be
highly variable depending on factors such as climate, soil
texture, moisture content, acidity, temperature, and
microbiological activity in the soil ( EPA-USDA, 1975).
Tables A-1, A-2 and A-3 in Appendix A provide a detailed
list of pesticides and their predominant transport modes.
According to the 1987 Report to Congress, pesticides
commonly detected in significant concentrations in flows
entering agricultural drainage wells include atrazine,
cyanazine, and metribuzin.
Pesticides exhibiting lower water solubility properties are
those more likely to be adsorbed to suspended solid
particles. Since suspended solids do enter agricultural
drainage wells, they may act as an important vehicle by
which pesticides are able to enter the subsurface. The more
persistent pesticides such as the chlorinated hydrocarbons,
appear to be transported largely attached to sediments
(Task Committee on Agricultural Runoff and Drainage of the
Water Quality Committee of the Irrigation and Drainage
Division, 1977).
Once in the subsurface environment, the transport and fate
of a pesticide will depend on the subsurface formation
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Table 3. Predominant transport modes and persistence in soils
of selected agricultural herbicides (from EPA-USDA Report No.
EPA-600/2-75-0268,1975).
Common Name of
Herbicide
Alachlor
Atrazine
Barban
Bromacil
Chloramben
Cyanazine
2,4-D Acid
DCPA
Dinoseb
Diuron
Glyphosate
Metribuzin
Simazine
Trifluralin
Predominant
Transport
Mode
sediment/water
sediment/water
sediment
water
water
sediment/water
water
sediment
sediment/Water
sediment
sediment
water
sediment
sediment
Approximate
Persistence in
Soils (days) *
40-70
300-500
20
700
40-60
_
10-30
400
15-30
200-500
150
150-200
200-400
120-180
* From reported literature values corresponding to the time required for
90 percent or more of applied pesticide to disappear from sites of
application.
properties and the pesticide characteristics. More soluble
pesticides not readily susceptible to biodegradation are
likely to travel the greatest distances. Pesticide charac-
teristics which will influence the mobility of pesticides in the
subsurface include solubility, sorptive characteristics and
susceptibility to bbdegradation. In general, pesticide
biodegradation and adsorption can be expected to decrease
with depth due to decreasing microbial activity and
decreasing organic content, respectively. Although most
pesticides reportedly degrade quite rapidly after application
to fields (Ochs, 1980), many pesticides do reach ground
water and appear to persist for significant lengths of time.
Table 4, which lists pesticides detected in ground water,
their ranges, and the number of states in which they have
been detected, provides evidence of the wide-scale
contamination of ground water by pesticides in the United
States. Agricultural drainage wells, in some or many cases,
may play a major role.
The transport of pesticides to agricultural drainage wells can
be expected to be dependent on a number of factors
including the physical and chemical properties of the
pesticide, its formulation, the rate and type of application,
the crop to which it was applied, tillage practices,
topography of the field, weather conditions, and amount and
intensity of rainfall following application. Most pesticide
residues are found in the top layer of tilled cropland soils,
the layer that erodes in the process of sheet erosion (Task
Committee on Agricultural Runoff and Drainage of the
Water Quality Committee of the Irrigation and Drainage
Division, 1977). This suggests that pesticides entering agri-
cultural drainage wells may be correlated with the sediment
load.
Spencer et al. (1985) reported on the concentration of
pesticides in surface irrigation runoff water following the
application of pesticides to large fields of cotton,
sugarbeets, alfalfa, lettuce, onions, and canteloupes in the
Imperial Valley, California. The concentrations in runoff
water were dependent upon the characteristics of the
pesticides, their methods and rates of applications, the time
elapsed between application and the first irrigation, the
number of irrigations since the pesticide application,
irrigation efficiency, and other soil management practices.
The highest concentrations occurred when herbicides were
applied in irrigation water. As would be expected,
concentrations of pesticides were also higher in the first
irrigation following application. The time elapsed between
pesticide application and a given irrigation event was shown
to be inversely related to the logarithm of the concentration
of the pesticide, suggesting an approximate first-order rate
of decrease in runoff concentration with time. Spencer et al.
reported that the percentages of the applied pesticides lost
in runoff were generally very low, with all seasonal totals for
insecticide runoff below 1 percent of the amounts applied,
and seasonal losses of soil-applied herbicides usually 1 to 2
percent of the amounts applied. The amount of pesticides in
runoff waters did not correlate well with the amounts of
sediment in the runoff water, the runoff water volume, or the
accumulative water applied.
Spencer et al. also reported that none of the pesticides in
the aforementioned study were identified in tile drain
effluents at concentrations above minimum detectable
levels of 1 to 2 parts per trillion. This suggested that the
pesticides used were not sufficiently mobile or persistent to
reach the ground water. According to a 1975 U.S.
Department of Agriculture (USDA) report, the total amount
of pesticide that will generally run off the land during the
crop year is less, often much less, than 5 percent of the
application. Nevertheless, this small amount of pesticide
runoff could still exhibit a significant impact on receiving
surface waters and ground water.
Baker et al. (1985) monitored pesticide levels in water
entering agricultural drainage wells from row-cropped areas
in northcentral towa during periods of flow in 1981 and 1982
and observed that pesticide levels were always less than
100 mg/l and usually less than 1 mg/l. The pesticides
detected included alachlor, atrazine, carbofuran, chlordane,
cyanazine, 2,4-D, dicamba, dieldrin, and metribuzin. These
pesticides were detected at maximum concentrations of 55,
0.5, 0.6. 1.8, 80, 0.4, 12, 0.028, and 0.41 u.g/liter,
respectively. More than half of the samples taken of water
draining into the agricultural drainage wells did not show
detectable levels of pesticides. It is not known in the study
cited whether pesticides associated with suspended solids
were included in the analyses.
Pesticides may indirectly add other pollutants to soil and
water (U.S. Department of the Interior, 1969). Organic
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Table 4. Confirmed presence of pesticides In ground water of 17 different States (from Hallberg, 1987; after Cohen et al., 1986).
Pesticide Name
Typical Concentration
(mg/l)
MCL (m) or
Proposed MCL (p)
(mg/l)
Number of States
Herbicides
alachlor
atrazine
bcomacil
cyanazine
DCPA (and acid
products)
dinoseb
metolachbr
metribuzin
simazine
0.10-10.0
0.3-3.0
300
0.1-1.0
50.0 - 700.0
1.0 - 5.0
0.1-0.4
1.0 - 4.0
0.2-3.0
2(P)
3(P)
7(m)
4
5
1
2
Insecticides and Nematicides
aldicarbfsulfoxide
and sulfone)
carbofuran
DBCP
1,2-DCP
dyfonate
EDB
oxamyl
1 ,2,3-trichloropropane
(impurity)
1.0-50.0
1 .0 - 50.0
0.2-20.0
1 .0 - 50.0
0.1
0.05 - 20.0
5.0-65.0
0.1-5.0
10(p)
40 (p)
0.2 (p)
5(P)
0.05 (p)
200 (m)
15
3
5
4
1
8
2
2
pesticides can contain metals such as mercury, zinc,
manganese, copper, chromium, cadmium and tin which can
be released during decomposition.
C. Nutrients
Nutrients, in the form of nitrogen and phosphorous
compounds, are essential to plant growth and are
commonly applied in agricultural regions as fertilizer.
Nitrogen, in the form of nitrate-nitrites, is of greatest
concern in drinking water because of its often high
concentrations and its link to methemoglobinemia in infants.
High concentrations of nitrate may also have adverse
effects on livestock and may stimulate eutrophic processes
in surface waters. Nitrates-nitrites are highly soluble and are
not readily adsorbed by soils. They can therefore be
expected to be present in both surface and subsurface
flows entering agricultural drainage wells. Often nitrates-
nitrites are added directly to irrigation water.
A previously cited study conducted by Baker et al. (1985) in
northcentral Iowa indicated that farm wells within 2 km of
drainage wells showed elevated levels of nitrates. Some
elevated levels were observed in areas with an unsaturated
zone thickness of 15 meters or more. Other areas, where
the unsaturated zone thickness was 15 meters or more and
where there were no drainage wells nearby, reportedly did
not show elevated levels of nitrates. These observations
were cited as evidence that the presence of nitrates, in this
study, were likely attributable to agricultural drainage wells
rather than the infiltration of nitrates from the land surface.
As part of their study, Baker et al. also observed that during
periods between runoff events, when all the drainage to the
agricultural drainage wells was subsurface drain flow,
nitrate concentrations were highest in the range 10-30 mg/l.
When the agricultural drainage wells received both surface
and subsurface runoff during periods of snowmelt and
rainfall, concentrations of nitrate often dropped below 10
mg/l. Concentrations of nitrates entering the agricultural
drainage wells were observed to exceed the Federal
Primary Drinking Water Standard of 10 mg/l for 85 percent
of the samples with an overall average of 16 mg/l.
A compilation of data from the Big Spring basin aquifer in
northeastern Iowa indicated that in the 1930s, nitrate
concentrations in the aquifer were less than 1 mg/l. In the
1950s and 1960s, the nitrate concentrations in the aquifer
averaged about 3 mg/l and by 1983, the average
concentration was 10.1 mg/l. The increases in nitrate
concentrations were reported to directly parallel increases in
the amount of nitrogen fertilizer applied (Hallberg, 1987).
Although the extent to which agricultural drainage wells (if
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present in northeastern Iowa) may have contributed to the
observed increases in nitrate concentrations is not known, it
can be assumed that the presence of agricultural drainage
wells may have facilitated the increased contamination
trend.
Phosphorus in fertilizers does not appear to present a
significant concern with regard to contamination of ground
water by agricultural drainage wells. Phosphorous is not
toxic to man or animals in the forms commonly found in
water. Phosphorous (in the form of phosphate) is readily
adsorbed by inorganic and organic soil matter. Surface
runoff containing high levels of suspended solids may,
however, exhibit high concentrations of adsorbed
phosphorous. If drained into highly fractured or karst
formations, the phosporous could conceivably reach
surface waters and stimulate eutrophic processes.
D. Microbes
The introduction of microbes (e.g. bacteria, viruses) into
ground waters is of concern where surface runoff enters
agricultural drainage wells. Microbial populations entering
agricultural drainage wells may include pathogenic
organisms which cause diseases such as bacillary and
amoebic dysentry, cholera, typhoid and paratyphoid fever,
bacterial gastroenteritis, infectious hepatitis, and
poliomyelitis. Graham et al. (1977), identified sediment
loads and bacteria from return flows as the most serious
threat to ground water quality in a study conducted in Idaho.
Table 5 indicates the levels of bacteria detected in surface
return flow in the study. The levels of bacteria detected
were very high relative to the EPA Drinking Water
Standards.
The migration of bacteria in the subsurface to potential
supply wells will be governed by the subsurface formation
characteristics. In the presence of extensive formation voids
and/or fractures, bacteria may travel significant distances. In
a previously cited study conducted in southeast Minidoka
County, Idaho, Graham et al. (1979) reported that excessive
levels of indicator bacteria were observed in domestic
ground-water supplies and were apparently attributable to
the discharge of irrigation wastewater to nearby agricultural
drainage wells. Total coliform and fecal coliform counts with
highs of 284 and 27, respectively, were detected in domestic
water supply wells. In at least one study area, the detection
of indicator bacteria coincided closely with discharges to
agricultural drainage wells located one half mile or more
away. The apparent significant migration of bacteria
observed is likely attributable to the fractured nature of the
basalt formations into which agricultural drainage wells in
southeast Minidoka County are completed.
E. Salts
The addition of fertilizers and soil conditioners to crops may
contribute substantial amounts of the major ions to runoff
(Seitz et al., 1977). Major ions may include calcium,
magnesium, sodium, potassium, chloride, sulfate, and
carbonate. Some soils, in addition, may already exhibit
relatively high natural salt contents. Evaporation, trans-
piration, and recycling of irrigation waters tend to
concentrate the major ions such that the levels entering
agricultural drainage wells may be of concern. Sulfate
concentrations in excess of 250 mg/l, for example, may be
cathartic (i.e. exhibit a laxative effect). Salts are more likely
to enter agricultural drainage wells via subsurface flow.
Table 5. Level* of bacteria detected in surface return flow (from Report to Congress, 1987; after Graham et al., 1977). The EPA Drinking
Water Standard for total conforms is one organism/100 ml.
Parameter
Number of
Determinations
Low
Mean
High
Total coliforms
(organisms/100 ml)
Fecal conforms
(organisms/100 ml)
Fecal streptococci
(organisms/100 ml)
45
45
38
580 29,000 96,000
65 850 13,000
900 7,400 16,000
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F. "Incidental" contaminants
A potential concern, where applicable, is the presence of
agricultural drainage wells near roadsides, equipment
preparation or maintenance areas, or other trafficked areas
susceptible to accidental or intentional spillage/discharge of
environmentally objectionable materials. The presence of
agricultural drainage wells in these areas would provide
virtually unobstructed conduits for the movement of
potentially hazardous materials to the subsurface. The
extent to which such subsurface contamination scenarios
may occur is not known.
Discussion
The evidence that agricultural practices can lead to the
contamination of ground water is undeniable. The use of
pesticides and fertilizers has increased dramatically over
the past 20 to 30 years. Agricultural pesticide use in the
United States, for example, has more than doubled since
1964. Nitrogen fertilizer use on corn has increased from 72
kg/ha in 1965 to over 150 kg/ha in 1982 (Hallberg, 1987).
Contamination of the subsurface from agricultural practices
is being increasingly documented. Examples include
California where 3,000 supply wells have been observed to
be contaminated with 57 pesticides of which 22 have been
traced to agricultural use (Ground Water Monitor, 1985). In
Iowa, where agricultural drainage wells are commonly used,
pesticides are more commonly found in ground water than
are industrial chemicals (Ground Water Monitor, 1985). The
increasing number of agriculture-related ground-water
contamination scenarios being documented warrants
increasing concern.
The specific contribution of agricultural drainage wells to the
increasing number of ground-water contamination scenarios
being documented nation-wide is presently not known.
However, it must be assumed that the presence of
agricultural drainage wells can only serve to facilitate
subsurface contamination. Confirmed cases of ground-
water contamination by agricultural drainage wells have
been identified in Iowa and Idaho based on studies cited
herein. This confirmed evidence suggests that either
alternatives to the use of agricultural drainage wells should
be sought or the quality of fluids entering agricultural
drainage wells should be better controlled.
Possible solutions to the problems associated with the use
of agricultural drainage wells are as follows:
1. The complete elimination of agricultural drainage
wells and a return to natural drainage conditions.
2. The complete elimination of agricultural drainage
wells with drainage of excess water being directed
to surface waters.
3. The elimination of surface water inlets associated
with agricultural drainage well systems.
4. Control of surface runoff and surface erosion.
5. Improved fertilizer and pesticide management.
6. Pretreatment of surface runoff followed by
recycling and/or controlled disposal to agricultural
drainage wells.
The complete elimination of agricultural drainage wells
and a return to natural drainage conditions would likely
reduce the impact of agricultural drainage on ground water
in most hydrogeologic regimes. However, elimination of
wells would potentially result in serious socio-economic
repercussions. Kanwar et al. (1986) predict that the
elimination of agricultural drainage wells in northcentral
Iowa would cost the farmers of the area $270 per hectare
per year in crop production. Glanville (1985) predicts that
the elimination of agricultural drainage wells in northcentral
Iowa would result in a drop in corn yields by an average 50
bushels per acre and a drop in soybeans by an average 18
bushels per acre. Additional economic burdens according to
Glanville would include mired farm equipment, delayed
planting and harvesting, and fertilizer losses.
The construction of alternative drainage systems allowing
for the drainage of excess water to surface waters has been
suggested as a possible solution (Kanwar et al., 1986).
Glanville (1985) claims this could be expensive in some
cases with capital costs in northcentral Iowa ranging from
$100 per acre on land lying near existing drainage facilities
to over $300 per acre on remote fields requiring pumped
drainage or deep ditches and tile mains. According to
Kanwar et al. (1986), the costs in northcentral Iowa would
range from $200 to $964 per hectare. However, even if the
implementation of such alternative drainage systems were
economically feasible, the potential impact of the drainage
water on receiving surface waters must be considered.
Nutrients entering surface waters, for example, may give
rise to serious eutrophication problems while pesticides may
exhibit toxic effects to aquatic plant and animal life.
Options for the control of surface runoff and surface erosion
could include discouraging the practice of applying excess
quantities of irrigation water. Measures which may reduce
the volumes of surface runoff generated in drier regions
include irrigation scheduling, the use of high-efficiency
irrigation methods, alternate furrow irrigation, and the use of
drought tolerant crops (if possible). In those regions of the
nation where "water appropriation rights" are in effect and
excess irrigation water is applied in order to avoid loss or
reduction of future water allocations, efforts should be made
to change the governing rules or regulations to discourage
such practices. Table 6 provides a list of additional options
which could be considered in controlling surface runoff and
erosion. Table 7 provides some comments regarding the
practical application of the various options. For detailed
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Table 6. Practices for controlling direct runoff and their effectiveness (from EPA-USDA Report No. EPA-600/2-75-026a, 1975)
Runoff Control Practice
Effectiveness of Practice
No-till plant in prior crop residues
Conservation tillage
Sod-based rotations
Meadowless rotations
Winter cover crop
Improved soil fertility
Timing of field operations
Plow plant systems
Contouring
Graded rows
Contour strip cropping
Terraces
Grassed outlets
Ridge planting
Contour listing
Change in land use
Other practices
Contour furrows
Diversions
Drainage
Landforming
Construction of ponds
Variable effect on direct runoff from substantial
reductions to increases on soils subject to compaction.
Slight to substantial runoff reduction.
Substantial runoff reduction in sod year; slight moderate
reduction in rowcrop year.
None to slight runoff reduction.
Slight runoff increase to moderate reduction.
Slight to substantial runoff reduction depending on
existing fertility level.
Slight runoff reduction.
Moderate runoff reduction.
Slight to moderate runoff reduction.
Slight to moderate runoff reduction.
Moderate to substantial runoff reduction.
Slight increase to substantial runoff reduction.
Slight runoff reduction.
Slight to substantial runoff reduction.
Moderate to substantial runoff reduction.
Moderate to substantial runoff reduction.
Moderate to substantial reduction.
No runoff reduction.
Increase to substantial decrease in surface reduction.
Increase to slight runoff reduction.
None to substantial runoff reduction. Relatively
expensive. Good pond sites must be available.
May be considered as a treatment device.
discussions of the options listed, the reader is referred to
the joint EPA-USDA publication "Control of Water Pollution
from Cropland; Volume 1" (1975).
The elimination of surface water inlets on agricultural
drainage wells to prevent direct entry of surface water
runoff would be expected to significantly reduce the impact
of agricultural drainage wells on ground-water quality.
Surface runoff generally carries the bulk of contamination
(in the form of suspended solids, bacteria and pesticides)
and is therefore of greatest concern. The elimination of
surface water inlets may, however, give rise to surface
ponding problems and thereby significantly retard land
drainage. Crop yields would likely be impacted, although
this impact would probably be less than the impact which
would result from total elimination of agricultural drainage
wells.
Improved fertilizer and pesticide management would serve
to reduce the amount of nutrients and pesticides entering
agricultural drainage wells. In Iowa, it has been suggested
that fall application of nitrogen be discouraged since
significant amounts are leached out of the root zone by
spring rains before crops can use it. Spring and early
11
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Table 7. Principal type* of cropland erosion control practices and their effectiveness (from EPA-USDA Report No.
EPA-600/2-75-026a, 1975).
Erosion Control Practice
Effectiveness of Practice
No-till plant in prior-
crop residues
Conservation tillage
Sod-based rotations
Meadowless rotations
Winter cover crops
Improved soil fertility
Timing of field
operations
Plow-plant systems
Contouring
Graded rows
Contour strip cropping
Terraces
Grassed outlets
Ridge planting
Contour listing
Change in land use
Other practices
Most effective in dormant grass or small grain; highly effective in crop residues; minimizes spring
sediment surges and provides year-round control; reduces man, machine and fuel requirements;
delays soil warming and drying; requires more pesticides and nitrogen; limits fertilizer- and
pesticide-placement options; some climatic and soil restrictions.
Includes a variety of no-plow systems that retain some of the residues on the surface.
Good meadows lose virtually no soil and reduce erosion from succeeding crops; total soil loss
greatly reduced but losses unequally distributed over rotation cycle; aid in control of some
diseases and pests; more fertilizer-placement options; less realized income from hay years;
greater potential transport of water soluble P; some climatic restrictions.
Aid in disease and pest control; may provide more continuous soil protection than one-crop
systems.
Reduce winter erosion where corn stover has been removed and after low-residue crops; provide
good base for slot-planting next crop; usually no advantage over heavy cover of chopped stalks or
straw; may reduce leaching of nitrate; water use by winter cover may reduce yield of cash crop.
Can substantially reduce erosion hazards as well as increase crop yields.
Fall plowing facilitates more timely planting in wet springs, but it greatly increases winter and
early spring erosion hazards; optimum timing of spring operations can reduce erosion and
increase yields.
Rough, cloddy surface increases infiltration and reduces erosion; seedling stands may be poor
when moisture conditions are less than optimum. Mulch effect is lost by plowing.
Can reduce average soil loss by 50% on moderate slopes, but less on steep slopes; loses
effectiveness if rows break over; must be supported by terraces on long slopes; soil, climatic, and
topographic limitations; not compatible with use of large farming equipment on many topographies.
Does not affect fertilizer and pesticide rates.
Similar to contouring but less susceptible to row breakovers.
Rowcrop and hay in alternate 50- to 100-foot strips reduce soil loss to about 50% of that with the
same rotation contoured only; fall seeded grain in lieu of meadow about half as effective; alternat
ing com and spring grain not effective; area must be suitable for across-slope farming and
establishment of rotation meadows.
Support contouring and agronomic practices by reducing effective slope length and runoff
concentration; reduce erosion and conserve soil moisture; facilitate more intensive cropping: con-
ventional gradient terraces often incompatible with use of large equipment, but new designs have
alleviated this problem; substantial initial cost and some maintenance costs.
Facilitate drainage of graded rows and terrace channels with minimal erosion; involve establish-
ment and maintenance costs and may interfere with use of large implements.
Earlier warming and drying of row zone; reduces erosion by concentrating runoff flow in mulch-
covered furrows; most effective when rows are across slope.
Minimizes row breakover; can reduce annual soil loss by 50%; loses effectiveness with post-
emergence com cultivation.
Sometimes the only solution. Well managed permanent grass or woodland effective where other
control practices are inadequate: lost acreage can be compensated for by more intensive use of
loss erodible land.
Contour furrows, diversions, subsurface drainage, land forming, closer row spacing, etc.
12
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summer nitrogen applications would improve nitrogen
utilization. It has also been suggested that three well-timed
nitrogen applications rather than a single pre-plant
application be considered. This would result in a 35 percent
reduction in nitrate levels (Glanville, 1985). Reductions in
the quantities of fertilizers and pesticides applied would also
significantly reduce impacts on ground water. According to
Hallberg (1986), a reduction in N-fertilizer application rates
of 90 kg-N/ha in Hall County, Nebraska, resulted in no
reduction in corn yields over four years. Hallberg also
reports that recent studies in Pennsylvania show that some
current methods recommend fertilizer-N applications more
than 100 kg-N/ha greater than rates that would produce
economic optimum production. In contrast, however,
according to figures provided by Baker and Austin in 1984,
decreasing the nitrogen application rate in Iowa from 150 to
75 kg/ha was predicted to decrease net return for corn by
about $26/acre. Other measures which may reduce the
quantity of fertilizer and pesticide contaminants entering
agricultural drainage wells might include the use of slow-
release fertilizers and the development and use of more
biodegradable pesticides. Tables 8 and 9 provide options
which may be considered for controlling pesticide and
fertilizer loss. For detailed discussions on the various
Table 8. Practices for the control of pesticide loss from agricultural applications and their effectiveness (from EPA-USDA Report No.
EPA-600/2-75-026a, 1975)
Pesticide Control Practice
Effectiveness of Practice
Broadly Applicable Practices
Using alternative pesticides
Optimizing pesticide placement
with respect to loss
Using crop rotation
is planted.
Using resistant crop varieties
Applicable to all field crops; can lower aquatic residue levels; can hinder development of target
species resistance.
Applicable where effectiveness is maintained; may involve moderate cost.
Universally applicable; can reduce pesticide loss significantly; some indirect cost if less profitable crop
Applicable to a number of crops; can sometimes eliminate need for insecticide and fungicide use; only
slight usefulness for weed control.
Optimizing crop planting time
Optimizing pesticide formulation
Using mechanical control methods
Reducing excessive treatment
Optimizing time of day for
pesticide application
Applicable to many crops; can reduce need for pesticides; moderate cost possibly involved.
Some commercially available alternatives; can reduce necessary rates of pesticide application.
Applicable to weed control; will reduce need for chemicals substantially; not economically favorable.
Applicable to insect control; refined predictive techniques
required.
Universally applicable can reduce necessary rates of pesticide application.
Practices Having Limited Applicability
Optimizing date of pesticide
application
Using integrated control programs
Using biological control methods
Using lower pesticide application
rates
Managing aerial applications
Planting between rows in minimum
tillage
Applicable only when pest control is not adversely affected; little or no cost involved.
Effective pest control with reduction in amount of pesticide used; program development difficult.
Very successful in a few cases; can reduce insecticide and herbicide use appreciably.
Can be used only where authorized; some monetary savings.
Can reduce contamination of non-target areas.
Applicable only to row crops in non-plow based tillage; may reduce amounts of pesticides ncecssary.
13
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Table 9. Practices for the control of nutrient loss from agricultural applications and their effectiveness (from EPA-USDA Report No.
EPA-600/2-75-0268,1975)
Nutrient Control Practice
Effectiveness of Practice
Eliminating excessive fertilization
Leaching Control
Timing nitrogen application
Using crop rotations
Using animal wastes for fertilizer
Plowing-undergreen legume crops
Using winter cover crops
Controlling fertilizer release of transformation
Control of Nutrients in Runoff
Incorporating surface applications
Controlling surface applications
Using legumes in haylands and pastures
Control of Nutrient Loss bv Erosion
Timing fertilizer plow-down
May cut nitrate leaching appreciably, reduces fertilizer costs;
has no effect on yield.
Reduces nitrate leaching; increases nitrogen use efficiency;
ideal timing may be less convenient.
Substantially reduces nutrient inputs; not compatible with
many farm enterprises; reduces erosion and pesticide use.
Economic gain for some farm enterprises; slow release of
nutrients; spreading problems.
Reduces use of nitrogen fertilizer; not always feasible.
Uses nitrate and reduces percolation; not applicable in some
regions; reduces winter erosion.
May decrease nitrate leaching; usually not economically
feasible; needs additional research and development.
Decreases nutrients in runoff; no yield effects; not always
possible; adds costs in some cases.
Useful when incorporation is not feasible.
Replaces nitrogen fertilizer; limited applicability; difficult to
manage.
Reduces erosion and nutrient loss; may be less convenient.
options listed, the reader is again referred to the joint EPA-
USDA publication "Control of Water Pollution from
Cropland; Volume 1" (1975).
Pretreatment of surface runoff and subsequent recycling
and/or controlled discharge of treatment effluents may also
significantly reduce the level of contaminants entering
agricultural drainage wells. Surface runoff, because of its
often high suspended solids, pesticide and bacteria content,
is likely to exhibit a greater impact on ground water than
subsurface flow. A pretreatment process might simply
involve the use of a constructed settling pond which would
subject the surface runoff entering the pond to a certain
residence time. Settling of suspended solids could be
induced and the supernatant could then be allowed to enter
the agricultural drainage well. Alternatively, where feasible,
the supernatant could be recycled. Issues of concern
pertaining to the implementation of pretreatment settling
ponds include potential difficulties in siting ponds and
potentially high construction costs.
Recommendations
In addressing the problem of contamination of ground water
by agricultural drainage wells, some States have proceeded
to recommend guidelines for protecting USDW in areas
near agricultural drainage wells (Report to Congress, 1987).
These guidelines include:
1. Locating and proper plugging of all abandoned wells
within the immediate area of agricultural drainage wells
(Iowa);
2. Requiring that fluids meet drinking water standards at
the point of injection (Nebraska, Oregon);
3. Requiring irrigation tailwater recovery and pumpback
(Oregon);
14
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4. Reducing the volume of irrigation return flow (where
applicable) by applying only the quantity of water
necessary (California);
5. Closing surface inlets in order to allow infiltration
through soil to decrease the transport of bacteria, some
pesticides, and sediment to the aquifer (Missouri);
6. Raising the inlets above the maximum ponding levels
(Iowa);
7. Discouraging use and encouraging elimination of
agricultural drainage wells by developing alternative
drainage methods (Iowa).
Further efforts should be made at the State and Federal
levels to generate a more accurate inventory of agricultural
drainage wells currently in existence. Once a more accurate
inventory can be obtained, rational decisions regarding
potential modifications or alternatives to agricultural
drainage wells can be made. A more accurate inventory will
also provide an opportunity to better correlate the presence
of agricultural drainage wells with specific ground-water
contamination scenarios.
The practice of applying excess fertilizer and pesticide
should be curtailed as a first step in addressing not only the
problem of agricultural contaminants entering agricultural
drainage wells, but in addressing the problem of ground-
water contamination due to agricultural practices, in
general. Current federal programs tolerate and sometimes
encourage inefficient fertilizer and pesticide use. Govern-
ment grading standards require fruits and vegetables to
meet stringent cosmetic standards with little bearing on
nutritional quality yet at the expense of adding excess
pesticides (Ground Water Monitor, Sept. 12, 1989).
Alternative agricultural practices designed to reduce
fertilizer and pesticide use may include diversification rather
than continuous planting of fields to a single crop or few
crops, biological pest control, and genetic improvements in
crops to resist pests and disease.
Studies should probably be conducted to determine the
feasibility of using pretreatment settling ponds in treating
surface runoff. Studies should include determination of the
ease of pond siting and construction, average costs of pond
construction, sediment removal effectiveness, and quality of
supernatant generated for recycling and/or disposal. A pilot
study at a selected location in Iowa or Idaho may be
warranted.
Studies should probably also be conducted to establish the
feasibility of achieving more optimal designs for agricultural
drainage well systems. These studies should focus on
systems designed to improve injectate quality. More optimal
designs might include systems which will maximize the
subsurface flow component and minimize surface runoff
while still providing adequate drainage.
References
1. Baker, J.L. and T.A. Austin, (1984). Impact of
Agricultural Drainage Wells on Groundwater Quality.
Completion Report, EPA Grant No. G007228010
2. Baker, J.L.. R.S. Kanwar and T.A. Austin, (1985).
Impact of Agricultural Drainage Wells on
Groundwater. Journal of Soil and Water Conservation.
November-December 1985, pp. 516-520
3. Glanville, T.D., (1985). Agricultural Drainage Wells in
Iowa. Iowa State University Publication Pm-1201
4. Graham, W.G., (1979). The Impact of Intensive
Disposal Well Use on the Quality of Domestic
Groundwater Supplies in Southeast Minidoka County.
Idaho. Idaho Department of Water Resources
5. Graham, W.G., D.W. Clapp and T.A. Putkey, (1977).
Irrigation Wastewater Disposal Well Studies-Snake
Plain Aquifer. EPA-600/3-77-071
6. Ground Water Monitor, (1985). Recent Laws Fail to
Protect Country from Pesticide Contamination.
Environmentalists Say. May 28, 1985: p.67
7. Ground Water Monitor, (1989). NRG Study Urges
Fundamental Reforms in Federal Agricultural Policies.
September 12, 1989: p. 182
8. Hallberg, G.R., (1986). Overview of Agricultural
Chemicals in Ground Water. Proceedings of
Conference on Agricultural Impacts on Ground Water,
August 11-13, 1986, Omaha, Nebraska
9. Hallberg, G.R., (1987). The Impacts of Agricultural
Chemicals on Ground Water Quality. GeoJournal
15.3:283-295
10. Kanwar, R.S., J.L. Baker and S.W. Melvin, (1985).
Economics of Alternative Drainage to the Use of
Agricultural Drainage Wells. Paper No. 85-5528,
American Society of Agricultural Engineers Meeting,
Chicago, December 17-20, 1985
11. Mysterman, J.L. and R.A. Fisher, (1981). Underground
Injection Control in Iowa. Completion Report, Grant No.
G00716501. Department of Environmental
Engineering, University of Iowa, Iowa
12. Ochs, W.J. et al., (1980). Drainage Requirements: In
Design and Operation of Farm Irrigation Systems.
Edited by Jenson, M.E., American Society of
Agricultural Engineers, pp. 271-275
13. Sertz, H.R., A.M. La Sala, Jr.. and J.A. Moreland.
(1977). Effects of Drain Wells on the Ground-Water
Quality of the Western Snake Plain Aquifer. Idaho. U.S.
Geological Survey, Open-File Report 76-673
15
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14. Spencer, W.F., M.M. Cliath, J.W. Blair and R.A.
LeMert, (1985). Transport of Pesticides from Irrigated
Fields in Surface Runoff and Tile Drain Waters. U.S.
Department of Agricultural Conservation Research,
Report No. 31
15. Task Committee on Agricultural Runoff and Drainage of
the Water Quality Committee of the Irrigation and
Drainage Division, (1977). Quality Aspects of
Agricultural Runoff and Drainage. Journal of the
Irrigation and Drainage Division, December 1977, pp.
475-495
16. Knape, B.K., ed., M984V Underground injection
operations in Texas - A classification and assessment
of underground injection activities: Texas Department
of Water Resources Report 291, 197 p.
17. Texas Water Commission, (1989). Ground-water
Quality of Texas-An Overview of Natural and Man-
Affected Conditions. Report 89-01
18. Mobfsky, S.J., (1985), Ground-water evaluation from
test hole drilling near Mission. Texas: Texas
Department of Water Resources Report 292, 60 p.
19. U.S. Department of Agriculture, (1975). Control of
Water Pollution from Cropland: Volume I. A Manual for
Guideline Development. ARS-H-5-1
20. U.S. Department of the Interior, (1969). Characteristics
and Pollution Problems of Irrigation Return Flow. Utah
State University Foundation, Contract No. 14-12-408
21. U.S. Environmental Protection Agency Report to
Congress, (1987). Class V Injection Wells
22. U.S. Environmental Protection Agency (Office of
Drinking Water) Draft Report (1989). Class V
Regulatory Strategy
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APPENDIX A
17
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Table A-1. Agricultural herbicides: Types, transport modes, toxicities, and persistence in soil (from EPA-USDA Report No.
EPA-600/2-75-026a, 1975)
Common Names
of Herbicides
Alachlor
Ametryne5
Amitrole
Asulam
Atrazine
Barban
Benefin
Bensulide
Bentazon
Bifenox
Bromacil
Bromoxynil
Butylate
CacodylicAcid
COM
CDEC
Chloramben
Chlocbromuron
Chloroxuron
Chlorpropham
Cyanazine
Cycloate5
2, 4-D Acid
2, 4-D Amine
2, 4-D Ester
Dalapon
2,4-DB
DCPA
Diallate
Dicamba
Dichlobenil
Dinitramine
Dinoseb
Diphenamid
Diquat
Diuron
DSMA
Endothall
EPIC
Fenac5
Fenuron
Fluometuron
Fluoroditen
Glyphosate
Isopropalin
Linuron
MBR8251
MCPA
Metribuzin
Molinate
Monuron
MSMA
Naptalam
Chemical Class '
AM
TZ
TZ
CB
TZ
CB
NA
AM
DZ
AR
DZ
NT
CB
AS
AM
CB
AR
UR
UR
CB
TZ
CB
PO
PO
PO
AL
PO
AR
CB
AR
NT
NA
PH
AM
CT
UR
AS
PH
CB
AR
UR
UR
AR
AL
NA
UR
AM
PO
TZ
CB
UR
AS
AR
Predominant
Transport
Mode
SW
SW
W
W
SW
S
S
S
W
S
W
SW
S
S
W
SW
W
SW
S
SW
SW
SW
W
W
S
W
S
S
S
W
S
S
SW
W
S
S
S
W
SW
SW
W
SW
S
S
S
S
SW
SW
W
W
SW
S
W
Rat, Acute
Oral LD,,,
mg/kg
1200
1110
2500
>8000
3080
1350
800
770
1100
4600
5200
250
4500
700
850
3500
2150
3700
1500
334
2000
370
370
500-875
6590
300
3000
395
1028
3160
3000
5
970
400
3400
600
38
1360
1780
6400
7900
15000
4320
5000
1500
633
650
1930
501
3500
700
1770
Toxicity 3
Fish'LC^,
mg/liter
2.3
Low toxicity
>50
65000
12.6
71.3
60.03
0.72
190
1.8
70
0.05
4.2
8>40
2.0
4.9
67.0
0.56
VI 5
610
4.9
4.5
9>50
8>15
"4.5
>100
4
>500
5.9
35
10-20
6.7
7.1004
25
12.3
>60
>15
1.15
19
7.5
53
10>60
0.18
Low toxicity
Toxic
16
312
10
>100
0.29
1.8
>15
>180
Approximate
Persistence
in Soil,
days
40-70
30-90
15-30
25-40
300-500
20
120-150
500-700
40-60
700
40-80
20-40
20-40
40-60
300-400
120-260
120-220
10-30
10-30
10-30
15-30
400
120
60-180
90-120
15-30
90-180
>500
200-500
30
350-700
30-270
150
150
120
30-180
150-200
80
150-350
20-60
18
-------
Table A-1. Agricultural herbicides: Types, transport modes, toxicities, and persistence in soil (continued)
Common Names of
Herbicides
Chemical Class'
Predominant
Transport
Mode2
Toxicity3
Rat, Acute
Oral LD,,,,
mg/kg
Fish4 LCK
mg/liter
Approximate
Persistence
in Soil, days
Nitralin
Nitrofen
Oryzalin
Paraquat
Pebulate5
Phenmedipham
Pidoram
Profuralin
Prometone5
Prometryne5
Pronamide8
Propachlor5
PropaniP
Propazine5
Propham
Pyrazon
Silvex
Simazine
2,4, 5 -T
TCA
Terbacil
Terbutryne5
Triallate5
Trifluralin
Vemolate6
NA
PO
AM
CT
CB
CB
AR
NA
TZ
TZ
AM
AM
AM
TZ
CB
DZ
PO
TZ
PO
AL
DZ
TZ
CB
NA
CB
S
S
S
S
S
S
W
S
S
S
S
W
S
S
W
W
SW
S
W
W
W
SW
S
S
SW
2000
2630
>10000
150
921
2000
8200
2200
1750
3750
5620
710
1384
5000
5000
2500
375
5000
300
3370
5000
2400
1675
3700
1625
Low toxicity
Toxic
Low toxicity
6400
116.3
,o20
2.5
Toxic
1.3
>10
>100
632
1240
"0.36
5
0.5-16.7
13>2000
"86
Low toxicity
4.9
«0.1
9.6
>500
50-60
100
550
320-640
>400
30-90
60-270
30-50
1-3
200-400
20-60
30-60
2000-400
20-70
700
20-70
30-40
120-180
50
Chemical type designations: AL aliphatic acids; AM, amides and anilides; AR. aromatic acids and esters; AS, arsenicals; CB.
carbamates and thiocarbamates; CJ, cationics; DZ, diazines; NA. nitroanilines; ML nitrites; PH. phenols and dicarboxylic acids; PO.
phenoxy compounds; TZ. triazines and triazoles; JJH, ureas.
Where movement of herbicides in runoff from treated fields occurs, S denotes those chemicals that will most likely move primarily
with the sediment, W. denotes those that will most likely move primarily with the water, and SW denotes those that will most likely
move in appreciable proportion with both sediment and water.
Expressed as the lethal dose, or lethal concentration, to 50% of the test animals (LD..,, or LC^, respectively).
48- or 96-hour LC^ for bluegills or rainbow trout, unless otherwise specified.
Trade name; no corresponding common name exists.
24-hour LC^
For goldfish.
Forkillifish.
For spot.
11 Formullet
12 For harlequin fish.
13 For catfish.
14 Forsunfish.
19
-------
Table A-2. Agricultural insecticides and mitiddes: Types, transport modes, and toxicities (from EPA-USDA Report No.
EPA-600/2-75-0268,1975)
Common Names of
Insectiddes-Miticides
Aldicarb9
Aldrin
Allethrin
Azinphos ethyl6
Azinphos methyl
Benzene hexachloride
Binapacryl
Bux6
Carbaryl
Carbofuran5
Carbophenothion
Chlorbenside
Chlordane
Chlordimeform
Chlorobenzilate6
Chlorpyrifos
DDT
Demeton5
Diazinon5-6
Dicofol6
Dicrotophos
Dieldrin
Dknethoate
Dioxathion
Disulfoton
Endosulfan
EndnVi
EPN
Ethion
Ethoprop
Fensulfothion5
Fonofos6
Heptachlor
Landrin6
LJndane
Malathion
Metaldehyde
Methidathion
Methomyl
Methoxychlor
Methyl demeton6
Methyl parathion6
Mevinphos
Mexacarbale
Monocrotophos
Mated
Ovex
Oxythioquinox
Parathion
Perthane6
Phorate5
Phosalone
Phosmet6
Chemical Class
CB
OCL
PY
OP
OP
OCL
N
CB
CB
CB
OP
S
OCL
N
OCL
OP
OCL
OP
OP
OCL
OP
OCL
OP
OP
OP
OCL
OCL
OP
OP
OP
OP
OP
OCL
CB
OCL
OP
O
OP
CB
OCL
OP
OP
OP
CB
OP
OP
S
S
OP
OCL
OP
OP
OP
Predominant
Transport
Mode
W
S
S
S
S
S
U
S
sw
W
S
S
S
W
S
U
S
W
sw
S
W
S
W
S
S
S
S
S
S
U
sw
S
S
sw
S
W
W
U
U
S
W
sw
W
sw
W
S
S
S
S
S
sw
S
S
Rat, Acute
Oral LDM
mg/kg
0.93
35
680
7
11
1000
120
87
500
8
10
3000
335
162
700
97
113
2
76
684
22
46
185
23
2
18
7.3
8
27
61.5
2
8
90
178
88
480
1000
25
17
5000
65
9
4
22.5
21
250
2000
1100
4
>4000
1
96
147
Toxicity3
Fish4 LC,,,
mg/liter
0.003
0.019
0.019
0.01
0.79
0.04
0.29
1
0.21
0.23
0.01
1
0.71
0.02
0.002
0.081
0.03
0.1
8
0003
9.6
0.014
004
0 001
0.0002
0.1
0.23
1
70.15
0.03
0009
0.95
0018
0.019
> 100.0
-09
0.007
4
1.9
0017
1 73
7
0078
07
0.096
0.047
0007
00055
34
0.03
20
-------
Table A-2. Agricultural insecticides and miticides: Types, transport modes, and toxicities (continued).
Toxicity3
Comon Names of
Insecticides-Miticides
Phosphamidon
Propargite6
Propoxur
TDE
TEPP
Tetrachlorvinphos
Tetradifon
Thionazin
Toxaphene
Trichlorfon
Chemical Class1
OP
S
CB
OCL
OP
OP
OCL
OP
OCL
OP
ireoominam
Transport
Mode2
W
U
W
S
W
s
sw
W
s
W
Rat Acute
Oral LD,,,,
mg/kg
11
2200
95
3360
I
4000
14000
12
69
275
Fish4 LC,,,,
mg/liter
8
0.03
'0.025
0.009
90.39
0.53
1.1
'0.10
0.003
.0.16
Chemical type designations: C_B. carbamates; M, miscellaneous nitrogenous compounds; 0., cyclic oxygen compounds;
QCLorganochlorines; Q£, organophosphorus compounds; £¥, synthetic pyrethrin; S, aromatic and cyclic sulfur com-
pounds.
Where movement of insecticides in runoff from treated fields occurs, S denotes those chemicals that will most likely
move primarily with the sediment, W. denotes those that will most likely move primarily with the water, SW denotes
those that will most likely move in appreciable proportion with both sediment and water, and ii denotes those whose
predominant mode of transport cannot be predicted because properties are unknown.
Expressed as the lethal dose, or lethal concentration, to 50% of the test animals (LD,,, or LCM, respectively).
48- or 96-hour LC for bluegills or rainbow trout, unless otherwise specified.
Registered as both insecticide and nematicide. Nematodes are controlled only on limited acreage and predominantly in
the Southern states, but application rates when used as nematicides are 2- or 3-fold higher than when used as insect!
cides.
Trade name; no corresponding common name exists.
24-hour LC^
Forkillifish
For minnows
21
-------
Table A-3. Agricultural fungicides: Transport modes and toxicities (from EPA-USDA Report No. EPA-600/2-75-026a, 1975)
Toxicity'
Common Names
of Fungicides
Predominant Transport Mode
Rat, Acute Oral LD,,,,
mg/kg
mg/liter
Anilazine
Benomyl
Captafol
Captan
Carboxin
Chloranil
Chloroneb
Cycloheximide
DCNA
Dichlone
Dichlozoline
Dinocap
Dodine
ETMT
Fenaminosulf
Ferbam
Folpet
Maneb
Metiram
Naoam
Ocycarboxin
Parinol
PCNB
SMDC
Thiram
TPTH
Zineb
Ziram
S
S
S
S
SW
W
U
W
S
S
U
S
W
U
W
SW
S
S
U
W
W
U
S
W
S
U
S
W
2710
>9590
5000
9000
3200
4000
11000
2.5
4040
1300
3000
980
1000
2000
60
>17000
>10000
6750
6400
395
2000
>5000
1650
820
375
108
>5200
1400
0.015
0.5
*0.031
0.13
2.2
5
>4200.0
1.3
0.047
=0.14
0.9
23
"12.6
61.56
71.0
>4.2
421.1
8-5.0
0.7
71.0
40.79
0.5
41.0
Where movement of fungicides in runoff from treated fields occurs, S, denotes those chemicals that will most likely move primarily
with the sediment, W denotes those that will most likely move primarily with the water, SW denotes those that will most likely move
in appreciable proportion with both sediment and water, and U denotes those whose predominant mode of transport cannot be
predicted because properties are unknown.
Expressed as the lethal dose, or lethal concentration, to 50% of the test animals (LDM or LC,,,, respectively).
348- or 96-hour LC,,, for bluegills or rainbow trout, unless otherwise specified.
For catfish
For harlequin fish
For mullet
LC
Forfathead minnow
22
*U S GOVERNMENT PRINTING OFFICE 1 990-748-1 59/0048B
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