<pubnumber>570990NPS5</pubnumber>
<title>National Pesticide Survey: Summary Results of EPA's National Survey of Pesticides in Drinking Water Wells</title>
<pages>16</pages>
<pubyear>1990</pubyear>
<provider>NEPIS</provider>
<access>online</access>
<operator>BO</operator>
<scandate>01/22/97</scandate>
<origin>hardcopy</origin>
<type>single page tiff</type>
<keyword>wells water domestic rural pesticide nitrate survey cws counties pesticides vulnerability epa drinking ground nps branch detected number estimated hals</keyword>
United States
Environmental Protection
Agency
Office of Water
Office of Pesticides and
Toxic Substances
Fall 1990
&EPA National
Survey
Summary Results of EPA's National
Survey of Pesticides in Drinking
Water Wells
NPS Finds
Low Levels of
Nitrate
Common,
Pesticides
Much Less
Common
The U.S. Environmental Protection Agency (EPA) has completed its five-year
National Survey of Pesticides in Drinking Water Wells (NPS). Between 1988 and 1990,
EPA sampled approximately 1300 community water system (CWS) wells and rural
domestic wells for the presence of 101 pesticides, 25 pesticide degradates, and nitrate
(127 analytes). The Survey results statistically represent approximately 94,600 drinking
water wells at 38,300 community water systems and over 10.5 million rural domestic
wells throughout the United States. This fact sheet provides an overview of the initial
findings of the Survey.
EPA designed the Survey with two principal objectives: (1) to determine the
frequency and concentration of the presence of pesticides and nitrate in drinking
water wells nationally; and (2) to improve EPA's understanding of how the presence of
pesticides and nitrate in drinking water wells is associated with patterns of pesticide
use and the vulnerability of ground water to contamination. The focus of the Survey
was on the quality of drinking water in wells, rather than on the quality of ground
water, surface water, or drinking water at the tap. The Survey was designed to yield
valuable information on both the frequency and levels of pesticides, pesticide
degradates, and nitrate present in rural domestic (private) wells and community
(public) drinking water wells on a nationwide basis. The Survey, however, was not
designed to provide an assessment of pesticide contamination in drinking water wells
at the local, county, or State levels.
Of the 127 analytes, nitrate was most frequently detected in NPS wells. EPA
analyzed well water samples for the combined presence of nitrate and nitrite
measured as nitrogen, which are reported as a single concentration of nitrate. Based
on the results of the NPS, EPA estimates that nitrate is present, at or above the
analytical minimum reporting limit of 0.15 mg/L used in the Survey, in about 49,300
(52.1%) CWS wells and 5,990,000 (57.0%) rural domestic wells nationwide.
Considering the precision of the Survey, EPA estimates that the number of CWS wells
containing nitrate at or above the minimum reporting limit could be as low as 45,300
or as high as 53,300, and the number of rural domestic wells could be as low as
5,2*80,000 or as high as 6,700,000 as indicated by the associated 95% confidence
intervals. The confidence intervals represent ranges, specified by an upper and lower
bound, in which EPA is reasonably confident that the national estimates fall. A major
source of nitrate in cultivated soils is from inorganic fertilizers. Nitrate fertilizers are
applied to enhance plant growth and nitrogen is necessary in the synthesis of plant
proteins. Other sources of nitrate in soil and water include animal wastes, septic
systems, plant residues, and fixation from the atmosphere.
The Survey detected pesticides and pesticide degradates in drinking water wells
much less frequently than nitrate. (Pesticide degradates are compounds that result
from the deterioration of pesticides in the environment.) Twelve of the 126 pesticides
WPS Summary Results
Printed on Recycled Paper
image:
and pesticide degradates included in the Survey were found in the sampled wells at
levels above minimum reporting limits of the Survey. Estimates of the numbers of
wells in the United States containing analytes detected in the Survey and 95%
confidence intervals are presented in Exhibits 1 and 2, along with the analytes'
associated minimum reporting (detection) limits.
EPA estimates that 9,850 (10.4%) CWS wells and 446,000 (4.2%) rural domestic
wells in the United States contain at least one pesticide or pesticide degradate (Exhibit
3) at or above the minimum reporting limits used in the Survey. Considering the
precision of the Survey, the number of CWS wells containing pesticides or pesticide
degradates could be as low as 6,330 or as high as 13,400 and the number of rural
domestic wells could be as low as 246,000 or as high as 647,000. The two pesticide
analytes most frequently detected were DCPA acid metabolites and atrazine.
DCPA acid metabolites, a degradate of DCPA (dimethyl tetrachloroterephthal-
ate), is the most commonly detected pesticide or pesticide degradate in the Survey.
The estimated numbers of CWS wells and rural domestic wells containing DCPA acid
metabolites, at or above the Survey minimum reporting limit of 0.10 /vg/L, are 6,010
(6.4%) and 264,000 (2.5%), respectively (Exhibit 3). Considering the precision of the
Survey, the number of CWS wells containing DCPA acid metabolites could be as low
as 3,170, or as high as 8,840, and the number of rural domestic wells could be as low
as 129,000 or as high as 477,000. The parent compound, DCPA, is extensively used
on home lawns, golf courses, and farms for control of many annual grasses and
broadleaf weeds.
Atrazine is the second most commonly detected pesticide. EPA estimates that
atrazine is present, at or above the Survey minimum reporting limit of 0.12 ji/g/L, in
about 1,570 (1.7%) CWS wells and 70,800 (0.7%) rural domestic wells nationwide
(Exhibit 3). Considering the precision of the Survey, the number of CWS wells
containing atrazine could be as low as 420 or as high as 2,710, and the number of
rural domestic wells could be as low as 13,300, or as high as 214,000. Atrazine is
known by the common names AAtrex, Atratol, Gesaprim, and Zeaphos, and is used to
control many annual broadleaf weeds and certain grasses on cropped land. It is also
used for general weed control on non-cropped industrial land, selective weed control
in conifer restoration and Christmas tree plantations, and non-selective control of
vegetation on fallow land.
In addition to DCPA acid metabolites and atrazine, ten other pesticides were
detected above Survey reporting limits. With some exceptions, these analytes were
detected at both CWS wells and rural domestic wells. The following list identifies all
pesticides or pesticide degradates that were detected above minimum reporting limits
and whether they were detected in a CWS well or rural domestic well:
CWS wells: atrazine, DCPA acid metabolites,
dibromochloropropane, dinoseb, hexachlorobenzene, prometon,
and simazine; and
• rural domestic wells: alachlor, atrazine, bentazon, DCPA acid
metabolites, dibromochloropropane, ethylene dibromide, ethylene
thiourea, gamma-HCH (lindane), prometon, and simazine.
Exhibits 1 and 2 provide national estimates for the number of CWS wells and rural
domestic wells containing individually detected pesticides and pesticide degradates,
along with the associated 95% confidence intervals. In addition, three analytes (alpha-
chlordane, gamma-chlordane, and beta-HCH) were detected by EPA laboratories at
concentrations much lower than the respective minimum reporting levels used by the
contract laboratories. The EPA laboratories did not analyze water samples from every
WPS Summary Results
image:
A Scien-
tifically
Selected,
Representa-
tive Sample
of Wells
well, thus national estimates cannot be produced for these pesticides. A fourth
analyte, 4-nitrophenol, was detected, but national estimates could not be produced
due to limitations of the laboratory analytic method for this particular chemical.
! .
A large number of Survey analytes were not detected in any of the sampled
wells at levels above NPS reporting limits. Because only a relatively small group of
wells in the population were sampled, wells containing specific pesticides might not
have been selected for participation in the Survey. EPA estimates that the maximum
number of wells nationally that are potentially contaminated by pesticides that were
not detected in the Survey is 750 CWS wells (0.8%) and 83,100 rural domestic wells
(0.8%), respectively. These estimates are the upper bounds corresponding to a 95%
confidence interval.
For analytes with established or proposed EPA Lifetime Health Advisory Levels
(HALs) or Maximum Contaminant Levels (MCLs), most observed detections of nitrate,
pesticides, and pesticide degradates were at levels well below these standards. An
MCL is an enforceable standard defining the maximum permissible level of a
contaminant in water that is delivered to any user of a public water system. MCLs set
achievable levels of drinking water quality to protect human health. Although the MCL
is not legally applicable to rural domestic wells, it was used as a standard of quality for
a source of drinking water. A Lifetime HAL represents the concentration of a
contaminant in water that may be consumed over an average human lifetime without
causing adverse health effects. Lifetime HALs are based on health effects that were
found in animals given high doses of analytes in laboratory studies. These levels
include a margin of safety. Well water containing an analyte at levels exceeding EPA's
MCLs or HALs may not be safe to consume.
Based on the results of the Survey, EPA estimates that 1,130 (1.2%) CWS wells
and 254,000 (2.4%) rural domestic wells nationwide contain nitrate exceeding EPA's
HAL and MCL of 10 milligrams per liter (mg/L) (Exhibit 4). Considering the precision of
the Survey, the number of CWS wells with detectable levels of nitrate above the
standard could be as low as 370 or as high as 2,600, and the number of rural
domestic wells could be as low as 122,000 or as high as 464,000.
Based on those pesticides and pesticide degradates with, HALs or MCLs, EPA
estimates that at most 750 (0.8%) CWS wells nationally have at least one pesticide
detection above the respective HALs/MCLs (Exhibit 5). EPA estimates that 60,900
(0.6%) rural domestic wells nationally contain at least one pesticide detection above
the MCL/HAL This number could be as low as 9,430 or as high as 199,000.
The NPS was designed to provide statistically reliable estimates of the presence
of pesticides and nitrate in the nation's well water supply. EPA used survey research
methods to select a sample of wells that was representative of the total population of
CWS wells and rural domestic wells in the U.S. The Survey design ensured that water
samples would be taken from wells located in areas with a wide range of levels of
pesticide use and ground-water vulnerability. The Survey design also ensured that a
known proportion of the wells selected were from areas where pesticides were more
heavily used and also from areas that were the most vulnerable to ground-water
contamination. This scientific sampling process was designed to achieve a high level
of precision. The Survey had two distinct statistical design components: one for
sampling CWS wells and another for sampling rural domestic wells.
NPS Summary Results
image:
Community Water System (CWS) Wells
CWS wells were defined for the NPS as wells in systems of piped drinking water
that either have at least 15 connections or serve at least 25 permanent residents. To
be eligible, a system must have had at least one operating well (at the time of
sampling) that was being used to supply drinking water. EPA targeted two categories
of CWS wells in the Survey:
1. Community water system wells nationally, which included all CWS
wells in the continental United States plus Alaska and Hawaii; and
2. Community water system wells in counties with high ground-water
vulnerability, which made up about 22% of all CWS wells.
EPA adapted and modified a classification system called the DRASTIC index to
define vulnerability of ground water to contamination. The letters in DRASTIC stand
for features of the area around the well that may cause sensitivity to contamination
(depth to water, recharge (net), aquifer media, soil media, topography, impact of
vadose (unsaturated) zone, conductivity (hydraulic) of the aquifer). A DRASTIC score
was computed for all of the counties in the nation. Counties were assigned high,
moderate or low vulnerability according to their DRASTIC scores. Selected findings for
CWS wells located in counties with high ground-water vulnerability are presented in
Exhibit 6. As shown in Exhibit 6, EPA estimates that 7,630 (36.7%) CWS wells in
counties with high ground-water vulnerability contain nitrate, and 1,930 (9.3%) contain
at least one pesticide above the Survey minimum reporting limit. Considering the
precision of the Survey, the number of nitrate detections could be as low as 6,590 or
as high as 8,760, and the number of pesticide detections could be as low as 1,200 or
as high as 2,700. As presented earlier, the estimated percent of CWS wells nationally
that contain nitrate is 52.1%, and the estimated percent containing at least one
pesticide is 10.4%. Comparisons between national estimates and estimates for CWS
wells in counties with high ground-water vulnerability should be made with caution.
The confidence intervals presented do not account for the relationship between these
two groups.
Rural Domestic Wells
Rural domestic wells were defined for the NPS as drinking water wells
supplying occupied housing units located in rural areas of the United States,
excluding government reservations. Rural households were defined as households
outside of incorporated or unincorporated places with a population of 2,500 or more
and outside of urban fringe areas as defined by the U.S. Bureau of the Census. EPA
targeted five categories of domestic wells in the Survey:
1. Rural domestic wells nationally, which includes all rural domestic
wells in the continental United States plus Alaska and Hawaii;
2. Rural domestic wells in counties with high pesticide use;
3. Rural domestic wells in counties with high ground-water
vulnerability;
4. Rural domestic wells in the "cropped and vulnerable" areas of
counties; and
5. Rural domestic wells in counties with high pesticide use and high
ground-water vulnerability.
WPS Summary Results
image:
Detailed
Local
Information
Proven
Analytical
Methods
Pesticide use for the second and fifth categories was defined using county
agricultural pesticide sales data and information about cropping activities for 28 crops.
For the third and fifth categories, EPA used the DRASTIC index to define what it
means for ground water to be highly vulnerable to contamination. For the fourth
category, a DRASTIC score was computed for each county subregion in which the
domestic wells were sampled. Areas within counties were assigned high, moderate or
low vulnerability according to DRASTIC scores. Areas were defined as "cropped and
vulnerable" if they had both a DRASTIC score for the county subregion and a cropping
level exceeding certain specified limits. Exhibit 7 shows the estimated percent of rural
domestic wells belonging to the four subgroups of interest. As shown in Exhibit 7,
EPA estimates that approximately 11.0% of rural domestic wells are in counties with
high pesticide use and 27.3% are in counties with high ground-water vulnerability.
Approximately 3.3% of rural domestic wells fall into both of these categories. Also,
approximately 35.1% of rural domestic wells are in "cropped and vulnerable" county
subregions.
Selected findings for rural domestic wells belonging to the second, third, fourth,
and fifth categories are provided in Exhibits 8 and 9, which show the estimated
number and percent of rural domestic wells containing nitrate and at least one
pesticide, respectively. As shown in Exhibit 8, EPA estimates that 1,950,000 (52.8%)
rural domestic wells in "cropped and vulnerable" county subregions contain nitrate
whereas 313,000 (27.0%) contain nitrate above the Survey minimum reporting limit in
counties with high pesticide use. Considering the precision of the Survey, the number
in "cropped and vulnerable" county subregions could be as low as 1,420,000 or as
high as 2,480,000, and the number in counties with high pesticide use could be as
low as 158,000 or as high as 467,000. As indicated earlier, the estimated percent of
rural domestic wells nationally that contain nitrate is 57.0%.
Approximately 2.4% of rural domestic wells nationally contain detectable levels
of nitrate above the HAL and MCL of 10 mg/L. For most of the subgroups EPA
estimates that a greater percent of rural domestic wells contain levels of nitrate above
10 mg/L For instance, 5.2% of rural domestic wells in counties with high pesticide
use contain nitrate at concentration levels above 10 mg/L.
Exhibit 9 presents estimates for pesticide detections in each of the rural
domestic well subgroups. This exhibit indicates that 202,000 (5.5%) rural domestic
wells in "cropped and vulnerable" county subregions contain at least one pesticide
above the Survey detection levels. In contrast, 4.2% of rural domestic wells nationally
contain at least one pesticide.
EPA developed a set of questionnaires to collect additional detailed information
regarding the sampled wells. Trained State officials and survey research contractors
administered NPS questionnaires to well owners and operators, residents and farmers,
and county agricultural extension agents to gather information about the well
construction, farming practices, and pesticide use near the wells.
EPA combined proven aspects of existing analytical methods with new
techniques developed expressly for the Survey to produce the analytical chemistry for
the Survey. EPA used eight analytical methods to analyze the 127 analytes
(pesticides, pesticide degradates, and nitrate) included for study in the NPS.
Contract laboratories were used by EPA to analyze well water samples. In
addition, EPA laboratories analyzed duplicate samples (for about 10 percent of the
field samples collected) to provide quality assurance oversight. In this way, EPA
ensured the accuracy of results reported by the contract laboratories.
WPS Summary Results
image:
Limitations of
WPS Findings
Where to Go
for More
Information
Well Water
Quality
Questions
The National Pesticide Survey was designed to estimate the extent of pesticide
contamination of drinking water wells, nationally. The Survey provides statistically
reliable estimates for the 94,600 community water systems wells and 10.5 million
domestic wells in the U.S. The NPS results represent the condition of drinking water
in wells at the time of sampling, on a nationwide basis. The Survey was not designed
to provide this information at the State or local levels. It does not provide accurate
information about ground water in general, or about domestic well water in non-rural
areas.
This fact sheet is part of a series of NPS outreach materials, fact sheets and
reports. The following additional fact sheets are available through EPA's Public
Information Center (401 M Street SW, Washington DC 20460, 202-382-2080):
Survey Design
Survey Analytes
Quality Assurance/
Quality Control
Analytical Methods
Project Summary
Fact Sheet for each
detected analyte
Glossary
How EPA Will Use
The NPS Results
Additional information on the Survey and on pesticides in general can be
obtained from the following sources:
U.S. EPA Safe Drinking Water Hotline
1-800-426-4791 (In Washington, DC (202) 382-5533)
Monday-Friday, 8:30 am to 4:30 pm Eastern Time
National Pesticide Telecommunications Network
1-800-858-7378
24 hours a day
U.S. EPA Office of Pesticide Programs (OPP) Docket
401 M Street, SW Room NEG004
Washington, DC 20460
(202) 382-3587
National Technical Information Service (NTIS)
5285 Port Royal Road
Springfield, VA 22161
(703) 487-4650
Information on regulation of
pesticides in drinking
water
Information on health
effects and safe
handling of pesticides
' V
Background documents
for Survey (available
for review)
Copies of the
NPS Phase I Report
(available 1991)
and
NPS Phase II Report
(when available)
If you are concerned about the presence of pesticides and nitrate in your
private water well, contact your local or State health department. Other experts in
your State environmental agency or agriculture and health department may also be
helpful to you. If you receive your drinking water from a community water system and
have questions about your water quality, contact your local community water system
owner/operator or the State water supply agency.
WPS Summary Results
image:
U.S. EPA Regional Office Contacts
Region
1
(CT, ME, MA,
NH, Rl, VT)
II
(NJ, NY, PR, VI)
111
(DE, DC, MD,
PA, WV, VA)
IV
(AL, FL, GA, KY,
MS, NC, SC,
TN)
V
(IL, IN, Ml, MN,
OH, Wl)
VI
(AR, LA, NM,
OK, TX)
VII
(IA, KS, MO,
NE)
VIII
(CO, MT, ND,
SD, UT, WY)
IX
(AZ, CA, HI, NV)
X
(AK, ID, WA,
OR)
Prinking Water
Water Quality Branch
(617) 565-3531
Drinking/Ground-Water
Protection Branch
(212) 264-1800
Drinking Water/Ground-Water
Protection Branch
(215) 597-8227.
Water Quality Management
Branch
(404) 347-2126
Safe Drinking Water Branch
(312) 353-2151
Drinking Water Branch
(214) 655-7150
Drinking Water Branch
(913) 551-7032
Drinking Water Branch
(303) 293-1430
Drinking Water Branch •
(415) 744-2250
Drinking Water Branch
(206) 442-4092
Pesticides
Office of Pesticides and Toxic
Substances
(617) 565-3273
Pesticides and Toxic Substances
Branch
(212) 340-6769
Toxics and Pesticides Branch
(215) 597-8598
Pesticides and Toxics
Substances Branch
(404) 347-5201
Pesticides and Toxic Substances
Branch
(312) 886-6006
Pesticides and Toxics Branch
(214) 655-7235
Toxics and Pesticides Branch
(913)551-7400
Toxic Substances Branch
(303) 293-1730
Pesticides and Toxics Branch
(415) 556-5268
Pesticides and Toxic Substances
Branch
(206) 442-1198
Ground Water
Ground-Water Management and
Water Supply Branch
(617) 565-3610
Drinking/Ground-Water Protection
Branch
(212) 264-5635
Drinking Water/Ground-Water
Protection Branch
(215) 597-8227
Ground-Water Protection Branch
(404) 347-3866
Office of Ground Water
(312) 886-1490
Ground-Water Branch
(214) 655-6446
Office of Ground-Water Protection
(913) 551-7446
Ground-Water Branch
(303) 293-1796
Water Quality Planning and
Standards Branch
(415) 465-2181
Drinking Water Branch
(206) 442-4092
A/PS Summary Results
image:
Exhibit 1
Estimated Number and Percent of Community Water System Wells
Containing NPS Analytes
Analyte
Nitrate3
DCPA acid metabolites
Atraztne
Slmazlno
Prometon
Hexachlorobenzene
Dibromochloropropane
(DBCP)
Dinosob
95%
Confidence
Estimated Interval
Number (lower - upper)
49,300 (45,300 - 53,300)
6,010 (3,170-8,840)
1,570 (420-2,710)
1,080 (350-2,540)
520 (78-1,710)
470 (61 - 1 ,630)
370 (33 - 1 ,480)
25 (1 - 870)
95%
Confidence
Estimated Interval
Percent (lower - upper)1
52.1 (50.0 - 56.3)
6.4 (3.4 - 9.3)
1.7 (0.5-2.9)
1.1 (0.4-2.7)
0.5 (0.1 - 1 .8)
0.5 (0.1-1.7)
0.4 (<0.1-1.6)
<0.1 (<0.1 - 0.9)
Minimum
Reporting
Limit2
0.15 mg/L
0.10/ig/L
0.12/ig/L
0.38 iLQlL
0.15/tg/L
0.060 jig/L
0.010/ig/L
1 .3 iigli.
1 Numbers between zero and 0.05 are reported as less than 0.1 (<0.1).
2 EPA established specific reporting limits for each analyte.
3 EPA analyzed samples for the combined presence of nitrate and nitrite measured as nitrogen, which is reported as a
single concentration of nitrate in milligrams per liter (mg/L).
A/PS Summary Results
image:
Exhibit 2
Estimated Number and Percent of Rural Domestic Wells
Containing NPS Analytes
Analyte
Nitrate3
DCPA acid metabolites
Atrazine
Dibromochloropro-
pane (DBCP)
Prometon
Simazine
Ethylene dibromide
Gamma-HCH (Lindane)
Ethylene thiourea
Bentazon
Alachlor
95%
Estimated Confidence Interval
Number (lower - upper)
5,990,000 (5,280,000 - 6,700,000)
264,000 (1 29,000 - 477,000)
70,800 (1 3,300 - 21 4,000)
38,400 (2,740-164,000)
25,600 (640 - 142,000)
25,100 (590-141,000)
19,200 (160-131,000)
13,100 (14-120,000)
8,470 (1-111,000)
7,160 (1 - 109,000)
3,140 (1 - 101,000)
95%
Confidence
Estimated Interval
Percent (lower - upper)1
57.0 (50.3 - 63.8)
2.5 (1.2-4.5)
0.7 (0.1 - 2.0)
0.4 (<0.1-1.6)
0.2 (<0.1-1.4)
0.2 (<0.1-1.3)
0.2 (<0.1-1.2)
0.1 (<0.1-1.1)
0.1 (<0.1 - 1.1)
0.1 '(<0.1 - 1.0)
<0.1 (<0.1 - 1.0)
Minimum
Reporting
Limit2
0.15 mg/L
0.10/tg/L
0.12/tg/L
0.010fig/L
0.15/tg/L
0.38 /tg/L
0.010/tg/L
0.043 fig/L
4.5 ngJL
0.25 /ig/L
0.50 /ig/L
1 Numbers between zero and 0.05 are reported as less than 0.1 (<0.1).
2 EPA established specific reporting limits for each analyte.
3 EPA analyzed samples for the combined presence of nitrate and nitrite measured as nitrogen, which is reported as a
single concentration of nitrate in milligrams per liter (mg/L).
WPS Summary Results
image:
Exhibit 3
Estimated Percent of Community Water System Wells and
Rural Domestic Wells Containing at Least One Pesticide, and
Containing DCPA Acid Metabolites and Atrazine
Community Water System Wells
Containing at Least One Pesticide
Detections
(10.4%)
Rural Domestic Wells
Containing at Least One Pesticide
Detections
(4.2%)
No Detections
(89.6%)
Community Water System Wells
Containing DCPA Acid Metabolites
Detections
(6.4%)
No Detections
(95.8%)
Rural Domestic Wells
Containing DCPA Acid Metabolites
Detections
(2.5%)
No Detections
(93.6%)
Community Water System Wells
Containing Atrazine
Detections
(1.7%)
No Detections
(97.5%)
Rural Domestic Wells
Containing Atrazine
No Detections
(98.3%)
No Detections
(99.3%)
10
A/PS Summary Results
image:
Exhibit 4
Estimated Percent of Community Water System Wells and
Rural Domestic Wells Containing Nitrate
Community Water System Wells
Nitrate not
Detected
(47.9%)
Nitrate Detected
Below 10 mg/L (MCL)
(50.9%)
Nitrate Detected
At or Above 10 mg/L (MCL)
(1.2%)
Rural Domestic Wells
Nitrate not
Detected
(43.0%)
Nitrate Detected
Below 10 mg/L (MCL)
(54.6%)
Nitrate Detected
At or Above 10 mg/L (MCL)
(2.4%)
WPS Summary Results
11
image:
Exhibit 5
Estimated Number and Percent of Community Water System Wells
and Rural Domestic Wells with at Least One Pesticide Detection above
Health Based Standard
Description
CWS wells above MCL1/HAL2
Rural domestic wells above MCL/HAL
Estimated
Number
0
60,900
95% Confidence
Interval
(lower - upper)
(0 - 750)
(9,430 - 199,000)
Estimated
Percent
0.0
0.6
95% Confidence
Interval
(lower - upper)
(0.0 - 0.8)
(0.1 -1.9)
Maximum Contaminant Level (MCL) is the maximum permissable level of a contaminant in water that is delivered to
any user of a public water system. MCLs are enforceable standards.
EPA sets Lifetime Health Advisory Levels (HALs) for chemicals in drinking water. An HAL is the concentration of a
contaminant in water that may be consumed over a person's lifetime without harmful effects. Lifetime HALs are based
on health effects that were found in humans or animals given high doses of chemicals in laboratory studies. This level
includes a margin of safety.
12
NPS Summary Results
image:
Exhibits
Estimated Number and Percent of Community Water System Wells
in Counties with High Ground-Water Vulnerability Containing NPS Analytes
Analyte
Nitrate1 above NPS
detection limit
Nitrate concentrations
above MCL2/HAL3 of 10
mg/L
At least one pesticide
above NPS detection
limits
At least one pesticide
above MCL/HAL
Estimated 95% Confidence Interval
Number (lower - upper)
7,630 (6,590 - 8,670)
0 (0 - 430)
1,930 (1,200-2,700)
0 (0 - 430)
95% Confidence
Estimated Interval
Percent (lower - upper)
36.7 (32.1 - 41 .3)
0.0 (0.0 - 2.0)
9.3 ,(5.8-12.9)
0.0 (0.0-2.1)
EPA analyzed samples for the combined presence of nitrate and nitrite measured as nitrogen, which is reported as a
single concentration of nitrate in milligrams per liter (mg/L).
Maximum Contaminant Level (MCL) is the maximum permissable level of a contaminant in water that is delivered to
any user of a public water system. MCLs are enforceable standards.
EPA sets Lifetime Health Advisory Levels (HALs) for chemicals in drinking water. An HAL is the concentration of a
contaminant in water that may be consumed over a person's lifetime without harmful effects. Lifetime HALs are based
on health effects that were found in humans or animals given high doses of chemicals in laboratory studies. This level
includes a margin of safety.
WPS Summary Results
13
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Exhibit 7
Estimated Percent of Rural Domestic Wells Belonging
to Four Subgroups of Interest
Counties with High Pesticide Use
High Pesticide
Use (11.0%)
Counties with High
Ground-Water Vulnerability
High Ground-water
Vulnerability (27.3%)
Not High Pesticide
Use (89.0%)
"Cropped and Vulnerable'
County Subregions
Not High Ground-water
Vulnerability (72.7%)
Counties with High Pesticide Use
and Ground-Water Vulnerability
High Pesticide Use
and Vulnerability
(3.3%)
Not "Cropped
and Vulnerable'
(64.9%)
"Cropped and
Vulnerable"
(35.1%)
Not High Pesticide
Use and Vulnerability
(96.7%)
14
A/PS Summary Results
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Exhibit 8
Estimated Number and Percent of Subgroups of
Rural Domestic Wells Containing Nitrate1
Description
Nitrate above NPS
detection limit
In counties with high
pesticide use
In counties with high
ground-water
vulnerability
In "cropped and
vulnerable" county
subregions
In counties with high
pesticide use and high
ground-water
vulnerability
Nitrate concentrations
above MCL2/HAL3 of 10
mg/L
In counties with high
pesticide use
In counties with high
ground-water
vulnerability
In "cropped and
vulnerable" county
subregions
In counties with high
pesticide use and high
ground-water
vulnerability
Estimated 95% Confidence Interval
Number (lower - upper)
31 3,000 (1 58,000 - 467,000)
1 ,350,000 (738,000 - 1 ,950,000)
1 ,950,000 (1 ,420,000 - 2,480,000)
1 36,000 (1 9,000 - 253,000)
60,100 (23,200-124,000)
60,400 (12,100-176,000)
1 47,000 (58,000 - 302,000)
26,400 (8,000-61,100) .
95% Confidence
Estimated Interval
Percent (lower - upper)
27.0 (14.9 - 39.2)
46.8 (30.0 - 63.6)
52.8 (45.0 - 60.6)
39.7 (12.8-66.7)
5.2 (2.0-10.7)
2.1 (0.4 - 6.1)
4.0 (1.6-8.2)
7.7 (2.3 - 7.9)
1 EPA analyzed samples for combined presence of nitrate and nitrite measured as nitrogen, which is reported as a single
concentration of nitrate in milligrams per liter (mg/L).
2 Maximum Contaminant Level (MCL) is the maximum permissable level of a contaminant in water that is delivered to any user
of a public water system. MCLs are enforceable standards.
3 EPA sets Lifetime Health Advisory Levels (HALs) for chemicals in drinking water. An HAL is the concentration of a
contaminant in water that may be consumed over a person's lifetime without harmful effects. Lifetime HALs are based on
health effects that were found in humans or animals given high doses of chemicals in laboratory studies. This level includes a
margin of safety.
NPS Summary Results
15
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Exhibits
Estimated Number and Percent of Subgroups of Rural Domestic Wells
Containing at Least One Pesticide
1
Categories of Interest
At least one pesticide detected:
In counties with high pesticide use
In counties with high ground-water vulnerability
In 'cropped and vu!nerable"'county subregions
In counties with high pesticide use and high
ground-water vulnerability
At least one pestcide detected above MCL1/HAL2:
In counties with high pesticide use
In counties with high ground-water vulnerability
In "cropped and vulnerable" county subregions
In counties with high pesticide use and high
ground-water vulnerability
95% Confidence
Estimated Interval
Number (Lower - Upper)
41,100 (2,980-79,200)
79,700 (9,260-150,000)
202,000 (37,600 -
367,000)
4,820 (59 - 29,900)
3,140 (1 - 40,400)
6,280 (1 -88,100)
3,140 (1 - 87,300)
0 (0-21,600)
95%
Confidence
Estimated Interval
Percent (Lower - Upper)
3.6 (0.2 - 6.9)
2.8 (0.4 - 5.1)
5.5 (0.9-10.1)
1.4 (<0.1 -8.8)
0.3 (<0.1 - 3.5)
0.2 (<0.1 -3.1)
0.1 (<0.1 - 2.4)
0.0 (0.0 - 6.3)
1 EPA sets enforceable standards for public water systems, called Maximum Contaminant Levels (MCLs). These regulatory
standards set achievable levels of drinking water quality to protect human health.
2 EPA sets Lifetime Health Advisory Levels (HALs) for chemicals in drinking water. EPA believes that water containing a
chemical at or below its Lifetime HAL is acceptable for drinking every day over the course of one's lifetime, and does not pose
health concerns. Lifetime HALs are based on health effects that were found in humans or animals given high doses of
chemicals in laboratory studies. This level includes a margin of safety.
WPS Summary Results
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