oEPA
The First Unregulated Contaminant Monitoring Rule (UCMR 1)
Data Summary: 2001-2005
Background
The EPA uses the Unregulated Contaminant Monitoring Rule (UCMR) program to collect nationally
representative data for contaminants that may be present in drinking water but do not have regulatory
standards set under the Safe Drinking Water Act (SDWA). This monitoring is used by the agency to understand
the frequency and level of occurrence of unregulated contaminants in the nation's drinking water systems.
Every five years, taking into consideration the EPA's Contaminant Candidate List (CCL), the agency develops a
new list of UCMR contaminants for monitoring. SDWA calls for the EPA to:
• Issue a list of unregulated contaminants to be monitored by certain public water system (PWS) types1
every five years
• Require large PWSs (i.e., those that serve more than 10,000 people) to monitor their water for the
contaminants
• Require a nationally representative sample of small PWSs serving 10,000 or fewer people to monitor2
• Make analytical results available in a National Contaminant Occurrence Database (NCOD) for drinking
water
UCMR 1 required monitoring between 2001 and 2005 for the 26 contaminants listed in Table 1. UCMR 1
contaminants were monitored under the UCMR Assessment Monitoring (AM) or Screening Survey (SS) design.
The UCMR 1 SS was designed to determine if additional monitoring would be needed. After UCMR 1, the SS
design was adapted to be representative of national occurrence. For more information, refer to the EPA's
UCMR 1 website. Summary details for contaminant occurrence are shown in Table 2 and represent the final
release of UCMR 1 analytical results. Before conducting your own assessment of the data, please review the
Data Considerations section.
1 UCMR 1 requirements applied to community water systems (CWSs) and non-transient non-community water systems (NTNCWSs). They
did not apply to transient non-community water systems (TNCWSs). The use of "PWS" throughout this document refers to participating
CWSs and NTNCWSs. For more information on PWS types, visit the agency's website.
2 SDWA, as amended by Section 2021 of America's Water Infrastructure Act of 2018, calls for the EPA to require small PWSs serving
between 3,300 and 10,000 people to monitor for UCMR contaminants, subject to the availability of EPA appropriations and sufficient
laboratory capacity, and to require a nationally representative sample of small PWSs serving fewer than 3,300 people to monitor. This
expansion in small PWS monitoring applies to the fifth UCMR (UCMR 5) and subsequent monitoring cycles.
March 2024
Office of Water (MS-140)
EPA 815-S-24-006
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Table 1. Contaminants and Methods
Contaminant
CASRN1
EPA Method
Contaminant Classification
Monitoring
Requirement2
perchlorate
14797-73-0
314.0
Solid rocket propellants, munitions,
fireworks, airbag initiators for
vehicles, matches, and signal flares
AM
methyl-tertiary-butyl-ether
(MTBE)
1634-04-4
502.2, 524.2
Fuel additive; solvent
AM
molinate
2212-67-1
507, 525.2
Pesticide
AM
s-ethyl-dipropylthiocarbamate
(EPTC)
759-94-4
507, 525.2
Pesticide
AM
terbacil
5902-51-2
507, 525.2
Pesticide
AM
4,4'-dichloro dichlorophenyl
ethylene (DDE)
72-55-9
508, 508.1,
525.2, AOAC3
990.06
Pesticide
AM
dimethyl tetrachloroterephthalate
(DCPA) mono/di-acid degradate
887-54-7;
2136-79-0
515.1, 515.2,
515.3, 515.4
Pesticide
AM
nitrobenzene4
98-95-3
524.2
Industrial chemical
AM
2,4-dinitrotoluene
121-14-2
525.2
Explosives and related compounds
AM
2,6-dinitrotoluene
606-20-2
525.2
Explosives and related compounds
AM
acetochlor
34256-82-1
525.2
Pesticide
AM
1,2-diphenylhydrazine
122-66-7
526
Industrial chemical
SS
diazinon
333-41-5
526
Pesticide
SS
disulfoton
298-04-4
526
Pesticide
SS
fonofos
944-22-9
526
Pesticide
SS
prometon
1610-18-0
526
Pesticide
SS
terbufos
13071-79-9
526
Pesticide
SS
2-methyl-phenol
95-48-7
528
Chemical intermediate
SS
2,4-dichlorophenol
120-83-2
528
Pesticide
SS
2,4-dinitrophenol
51-28-5
528
Pesticide; explosives and related
compounds
SS
2,4,6-trichlorophenol
88-06-2
528
Pesticide
SS
diuron
330-54-1
532
Pesticide
SS
linuron
330-55-2
532
Pesticide
SS
Aeromonas
NA
1605
Bacteria
SS
1 CASRN - Chemical Abstracts Service Registry Number, NA - Not Available
2 AM - Assessment Monitoring, SS - Screening Survey. The SS design included 300 PWSs that were randomly selected from those PWSs
required to conduct AM. A different set of 300 PWSs were selected for the chemical contaminant SS and the Aeromonas SS. For more
information, refer to the EPA's UCMR 1 website.
3 Method 990.06 is from the Association of Official Analytical Chemists (AOAC).
4 Nitrobenzene was also included as an SS contaminant using EPA Method 526. Results are reported as LL-nitrobenzene (see Table 2).
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Information About UCMR 1 Results
The purpose of this document is to summarize and provide additional information about UCMR 1 results.
The UCMR 1 minimum reporting levels (MRLs) are the lowest concentrations that laboratories were permitted
to report to the EPA during UCMR 1 monitoring1. UCMR MRLs are determined using data from multiple
laboratories that participate in the EPA's MRL-setting studies and are not associated with contaminant health
effects information. The EPA establishes UCMR MRLs to ensure consistency in the quality of the information
reported to the agency.
Community water systems (CWSs) required to monitor under UCMR must inform their customers of UCMR
results (including the average and range of results) in their annual Consumer Confidence Report (CCR). See 40
CFR 141.153(d)(7) for the CCR regulatory requirements and Section IV of the EPA's guidance Preparing Your
Drinking Water Consumer Confidence Report for details on the content of the report. Additional resources are
available on the EPA's CCR Compliance Help webpage.
Non-transient non-community water systems (NTNCWSs) (e.g., a school that operates its own drinking water
system) and CWSs required to monitor under UCMR must inform their customers of the availability of UCMR
results through Tier 3 Public Notification (PN). See 40 CFR 141.207 for the PN regulatory requirements and the
EPA's PN Compliance Help webpage for guidance.
UCMR occurrence data are used to inform the agency's Regulatory Determination process (i.e., the process that
addresses potential regulatory actions for unregulated contaminants). State and local officials may also use the
UCMR data to assess the need for actions to protect public health. States may establish requirements or levels
(regulatory or non-regulatory) for drinking water contaminants not yet regulated by the EPA. PWSs are
responsible for being aware of and complying with their state's requirements, if any.
1 More specifically, an MRL is the quantitation limit for a contaminant that is considered achievable, with 95% confidence, by at least 75%
of laboratories nationwide using a specified analytical method (recognizing that individual laboratories may be able to measure at lower
levels). Note: The Agency for Toxic Substances and Disease Registry (ATSDR) uses the term "MRL" for a different purpose (i.e., to describe
"Minimal Risk Level"). The UCMR term and the ATSDR term have no relationship to each other.
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Table 2. UCMR 1 Data Summary1,2
Contaminant
UCMR MRL3
(Hg/L)
Total number
of results4
Number of
results >MRL
Total number of
PWSs with
results4
Number of
PWSs with
results >MRL
perchlorate
4
34,728
647
3,870
160
MTBE
5
34,131
26
3,877
19
molinate
0.9
34,298
1
3,879
1
EPTC
1
34,297
0
3,879
0
terbacil
2
34,299
0
3,879
0
4,4'-DDE
0.8
34,370
1
3,880
1
DCPA mono/di-acid
1
34,278
787
3,882
177
degradate
nitrobenzene
10
33,937
2
3,867
2
LL-nitrobenzene5
0.5
2,556
0
349
0
2,4-dinitrotoluene
2
34,126
1
3,879
1
2,6-dinitrotoluene
2
34,126
0
3,879
0
acetochlor
2
34,274
0
3,875
0
1,2-diphenylhydrazine
0.5
2,354
0
310
0
diazinon
0.5
2,354
0
310
0
disulfoton
0.5
2,348
0
310
0
fonofos
0.5
2,354
0
310
0
prometon
0.5
2,354
0
310
0
terbufos
0.5
2,349
0
310
0
2-methyl-phenol
1
2,308
0
304
0
2,4-dichlorophenol
1
2,308
0
304
0
2,4-dinitrophenol
5
2,305
0
304
0
2,4,6-trichlorophenol
1
2,308
0
304
0
diuron
1
2,360
1
308
1
linuron
1
2,357
0
308
0
Aeromonas
CFU/lOOmL6
5,042
130
293
42
1 Analytical results from the UCMR program are reported by laboratories and provided by the agency in micrograms/liter (|ag/L, or parts
per billion). To convert results in pg/L to nanograms/liter (ng/L, or parts per trillion), multiply the value by 1,000. Note that Aeromonas
was reported in different units than the chemical contaminants. UCMR results are presented as single measurements and do not
represent a locational running annual average.
2 UCMR 1 contaminants (except Aeromonas) may have untreated (i.e., raw) water results included in the summary.
3 UCMR MRL - EPA-established UCMR Minimum Reporting Level. Based on laboratory capability; not related to contaminant health
effects information. Note that the MRL for Aeromonas is in different units than the chemical contaminants.
4 UCMR 1 contaminants were monitored under either the UCMR Assessment Monitoring (AM) or Screening Survey (SS) design, affecting
the number of results and PWSs with results for each contaminant. PWSs were required to collect Aeromonas samples six times during a
12-month period, compared to two or four times for other UCMR 1 contaminants, increasing the total SS results for Aeromonas. For more
information on UCMR 1 monitoring design, refer to the EPA's UCMR 1 website.
5 LL - Lower Limit. LL-nitrobenzene is nitrobenzene as analyzed using EPA Method 526 for UCMR 1 SS design, which had a lower UCMR
MRL compared to nitrobenzene as analyzed using EPA Method 524.2 for UCMR 1 AM design.
6 CFU/lOOmL - Colony forming units per one hundred milliliters. Within the 5,042 Aeromonas samples reported for UCMR 1, 99.6% of
samples (5,022) had a detection limit of 0.2 CFU/lOOmL, representing the actual minimum observation possible of 1 CFU detected per
500mL of filtered sample. The remaining 0.4% of Aeromonas samples (20 of 5,042) had elevated and varying detection limits of 0.3, 0.8,
0.9,1,1.6, 9, and 9.1 CFU/lOOmL, when sample matrix suspended solids prevented filtration of the full 500mL of sample.
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Data Considerations
The UCMR 1 analytical results are publicly available through the UCMR Archival Data Finder and as text files. Caution should
be used in any interpretation of the UCMR 1 data since some untreated (i.e., raw) source water data from several states are
also included in the results. Any positive result from untreated source waters, which are subsequently treated, is generally
not used to conduct drinking water exposure assessments. Rather, such cases generally triggered finished water sampling
at the entry point to the distribution system.
UCMR 1 contaminants were monitored under either the UCMR Assessment Monitoring (AM) or Screening Survey (SS)
design. The UCMR 1 SS design included approximately 300 PWSs randomly selected from those PWSs required to conduct
AM and was designed to determine if additional monitoring would be needed. After UCMR 1, the SS design was adapted to
include more PWSs, to exclude those PWSs required to participate in AM, and to be representative of national occurrence.
For more information, refer to the EPA's UCMR 1 website.
The UCMR Archival Data Finder allows people to easily search for, summarize, and download the UCMR 1 analytical results.
Results can be filtered using multiple data fields, including public water system (PWS), PWS size, state, EPA Region,
contaminant, sample type, and results at or above UCMR minimum reporting levels (MRLs) (data definitions provided in
Table 3). Selected results can be viewed online or downloaded as a Microsoft Excel file (.xlsx). Additional resources for the
UCMR Archival Data Finder are available here.
For those interested in large-scale data processing using statistical or data analysis software, the EPA recommends using the
occurrence data text files containing the UCMR 1 analytical results as well as additional information reported during
monitoring. Data are provided in tab delimited text files (.txt) (see below for descriptions), with field names included in the
first row of each file and no text qualifier. The EPA recommends importing all ID fields into your choice of software (e.g.,
Microsoft Excel, Microsoft Access) as text since some of the IDs can otherwise be misinterpreted as long integer field types
when they contain alpha characters.
• To download the occurrence data text files (data definitions provided in Table 4). select one of the following zip
files from UCMR 1 (2001-2005) Occurrence Data:
o UCMR 1 Occurrence Data Text Files to view all the analytical results (i.e., results for all contaminants
reported by all PWSs).
o UCMR 1 Occurrence Data Text Files by State to view all the analytical results, organized by Tribes and
states. Within that zip file, one text file (UCMRl_AII_Tribes_AK_LA.txt) will have all results for Tribal
PWSs and for the states starting alphabetically with A through L; another file (UCMRl_AII_MA_WY.txt)
will have all results for the states starting alphabetically with M through W. The results are organized this
way to address file size limitations and streamline data management.
o UCMR 1 Occurrence Data Text Files by Method Classification to view all the analytical results, organized
by analytical method. Within that zip file, you will find individual text files with results organized by
method (e.g., a Method 314.0 file with results for perchlorate).
• The following text file for additional data elements (i.e., information beyond analytical results for the 26 UCMR 1
contaminants) is also contained in each of the above zip files:
o UCMRl_Aeromonas_AddtlDataElem.txt - Supplemental data from SS monitoring for Aeromonas (data
definitions provided in Table 5)
For step-by-step details on using the UCMR Archival Data Finder and occurrence data text files, please refer to the
document Instructions for Accessing UCMR Results. Additional reference material is available on the EPA's UCMR 1 website.
In addition to reporting occurrence data for UCMR 1 contaminants, the EPA tasked the laboratories contracted to analyze
small PWS samples with reporting results for 1,3-dichloropropene (CASRN 542-75-6, DTXSID1022057). This additional
unregulated contaminant was within the scope of the methods already performed for the UCMR 1 contaminants. The
results for 1,3-dichloropropene from small PWS monitoring are included in the UCMR Archival Data Finder and the
occurrence data text files.
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Table 3. UCMR 1 Data Definitions for the UCMR Archival Data Finder
The data definitions below are specific to the UCMR 1 data. The UCMR Archival Data Finder also contains data from
additional UCMR cycles, which may have different definitions for the provided fields. Please refer to the document
Instructions for Accessing UCMR Results for data definitions specific to each cycle.
Field Name
Definition
UCMR Cycle
UCMR cycle and monitoring years. Results may have sample collection dates outside the designated
UCMR sample collection timeframe (e.g., resample collection): UCMR 1 (2001-2005)
PWS ID
Public Water System (PWS) Identification Code. The code used to identify each PWS. The code begins
with the standard 2-character postal state abbreviation or Region code for Tribes; the remaining 7
numbers are unique to each PWS in the state
PWS Name
Name of the PWS
Contaminant
The UCMR 1 contaminant analyzed
Result
Numeric value of the analytical result in |ag/L for the chemical contaminants and CFU/lOOmL for the
microbial contaminants. Results less than the UCMR MRL are indicated by 10,000)
Facility Water Type
Source of water at the facility: SW (surface water), GW (ground water), GU (ground water under the
direct influence of surface water), [blank] (unknown)
Sample Point Type
Sampling Point Type Code: EP (entry point to the distribution system), SR (source water - untreated
water), LD (location in the distribution system where the disinfectant residual is the lowest which is
approved by the state for THM [DBP] and/or total coliform sampling), MD (midpoint in the
distribution system where the chlorine residual would be expected to be typical for the system such
as the location for sampling coliform indicator bacteria as described in 40 CFR 141.21), MR (point of
maximum retention is the point located the furthest from the entry point to the distribution system
that is approved by the state for trihalomethane [THM] (disinfectant byproducts [DBP]) and/or total
coliform sampling), UK (not definitively known)
EPA Region
EPA Region (states): Region 1 (CT, ME, MA, NH, Rl, VT), Region 2 (NJ, NY, PR [Puerto Rico], VI [Virgin
Islands]), Region 3 (DE, DC, MD, PA, VA, WV), Region 4 (AL, FL, GA, KY, MS, NC, SC, TN), Region 5 (IL,
IN, Ml, MN, OH, Wl), Region 6 (AR, LA, NM, OK, TX), Region 7 (IA, KS, MO, NE), Region 8 (CO, MT, ND,
SD, UT, WY), Region 9 (AZ, CA, HI, NV, GU [Guam], MP [Northern Marianas Islands]), Region 10 (AK,
ID, OR, WA)
State
State abbreviation. Tribal PWSs without primacy are attributed to an EPA Region (05, 06, 07, 08, 09)
Associated Facility ID
Null for UCMR 1
Associated Sample Point ID
Null for UCMR 1
Monitoring Requirement
AM (Assessment Monitoring), SS (Screening Survey)
1 A fixed PWS applicability date was not codified for UCMR 1, unlike the subsequent UCMR cycles, resulting in some revisions to
population served that occurred during the UCMR 1 monitoring period.
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Field Name
Definition
Minimum Reporting Level
(MRL)
Minimum Reporting Level defined by UCMR 1 in |ag/L for the chemical contaminants and CFU/lOOmL
for the microbial contaminants. Based on laboratory capability; not related to contaminant health
effects information
UCMR1 Sample Type
RFS (raw field sample), RDS (raw duplicate field sample), TFS (treated field sample), TDS (treated
duplicate field sample), [blank] (unknown)
CASRN
Chemical Abstracts Service Registry Number (CASRN) is a unique identifier assigned by the Chemical
Abstracts Service (a division of the American Chemical Society) to every chemical substance (organic
and inorganic compounds, polymers elements, nuclear particles, etc.) in the open scientific
literature. It contains up to 10 digits, separated by hyphens into three parts
DTXSID
1
Distributed Structure-Searchable Toxicity Substance Identifier (DTXSID) is a unique substance
identifier used in the EPA's CompTox Chemicals database, where a substance can be any single
chemical, mixture, or polymer
Table 4. Data Definitions for Text Files: UCMR1_AII, UCMRl_AII_Tribes_AK_LA,
UCMR1_AIl_MA_WY, and \JCMRl_MethodNumber
Field Name
Definition
PWSID
Public Water System (PWS) Identification Code. The code used to identify each PWS. The code begins
with the standard 2-character postal state abbreviation or Region code for Tribes; the remaining 7
numbers are unique to each PWS in the state
PWSName
Name of the PWS. This field is blank for some records
Size
Size category of the PWS for UCMR 1, based on retail population as indicated by the Safe Drinking
Water Information System (Federal) (SDWIS/FED) in 20001: S (< 10,000), L (> 10,000)
FacilitylD
Identification code for each applicable facility associated with water treatment or delivery at the PWS
FacilityName
Name of the facility at the PWS. This field is blank for some records
FacilityWaterType
Source of water at the facility: SW (surface water), GW (ground water), GU (ground water under the
direct influence of surface water), [blank] (unknown)
SamplePointID
Identification code for each sample point location at the PWS
SamplePointName
Name of the sample point at the PWS. This field is blank for some records
SamplePointType
Sampling Point Type Code: EP (entry point to the distribution system), SR (source water - untreated
water), LD (location in the distribution system where the disinfectant residual is the lowest which is
approved by the state for THM [DBP] and/or total coliform sampling), MD (midpoint in the distribution
system where the chlorine residual would be expected to be typical for the system such as the location
for sampling coliform indicator bacteria as described in 40 CFR 141.21), MR (point of maximum
retention is the point located the furthest from the entry point to the distribution system that is
approved by the state for trihalomethane [THM] (disinfectant byproducts [DBP]) and/or total coliform
sampling), UK (not definitively known)
AssociatedFacilitylD
Null for UCMR 1
AssociatedSamplePointID
Null for UCMR 1
CollectionDate
Date of sample collection (month, day, year)
SamplelD
Identification code for each sample. Created using a concatenation of PWSID, FacilitylD, SamplePointID,
CollectionDate, MethodID, and UCMRlSampleType
Contaminant
The UCMR 1 contaminant analyzed
MRL
Minimum Reporting Level (MRL) defined by UCMR 1 in |ag/L for the chemical contaminants and
CFU/lOOmL for the microbial contaminants. Based on laboratory capability; not related to contaminant
health effects information
Units
Units of the UCMR MRL and analytical results: ng/L (micrograms per liter), CFU/lOOmL (colony forming
units per one hundred milliliters)
MethodID
Identification code of the analytical method
AnalyticalResultsSign
Sign indicating whether the analytical result is less than (<) the UCMR MRL or equal to (=) a numeric
value at or above the UCMR MRL
AnalyticalResultValue
Numeric value of the analytical result in pg/L for the chemical contaminants and CFU/lOOmL for the
microbial contaminants. Null (or blank) values represent results less than the UCMR 1 MRL
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Field Name
Definition
SampleEventCode
Null for UCMR1
MonitoringRequirement
AM (Assessment Monitoring), SS (Screening Survey)
Region
EPA Region (states): 1 (CT, ME, MA, NH, Rl, VT), 2 (NJ, NY, PR [Puerto Rico], VI [Virgin Islands]), 3 (DE,
DC, MD, PA, VA, WV), 4 (AL, FL, GA, KY, MS, NC, SC, TN), 5 (IL, IN, Ml, MN, OH, Wl), 6 (AR, LA, NM, OK,
TX), 7 (IA, KS, MO, NE), 8 (CO, MT, ND, SD, UT, WY), 9 (AZ, CA, HI, NV, GU [Guam], MP [Northern
Marianas Islands]), 10 (AK, ID, OR, WA)
State
State abbreviation. Tribal PWSs without primacy are attributed to an EPA Region (05, 06, 07, 08, 09)
UCMRlSampleType
RFS (raw field sample), RDS (raw duplicate field sample), TFS (treated field sample), TDS (treated
duplicate field sample), [blank] (unknown)
Table 5. Data Definitions for Text File: UCMR1 Aeromonas AddtlDataElem
Field Name
Definition
PWSID
Public Water System (PWS) Identification Code. The code used to identify each PWS. The code
begins with the standard 2-character postal state abbreviation or Region code for Tribes; the
remaining 7 numbers are unique to each PWS in the state
FacilitylD
Identification code for each applicable facility associated with water treatment or delivery at
the PWS
SamplePointID
Identification code for each sample point location at the PWS
CollectionDate
Date of sample collection (month, day, year)
UCMRlSampleType
RFS (raw field sample), RDS (raw duplicate field sample), TFS (treated field sample), TDS
(treated duplicate field sample)
SamplelD
Identification code for each sample. Created using a concatenation of PWSID, FacilitylD,
SamplePointID, CollectionDate, MethodID, and UCMRlSampleType
PH
pH measurement of the sample
pHMethod
Identification code of the analytical method used to measure pH: EPA 150.1, SM4500-H+B,
[blank] (not reported)
Temperature
Temperature measurement of the sample
Temperaturellnits
Deg C (degrees Celsius), [blank] (not reported)
TemperatureMethod
Identification code of the analytical method used to measure temperature: SM 2550, [blank]
(not reported)
Turbidity
Turbidity measurement of the sample
Turbidityllnits
NTU (Nephelometric Turbidity unit), [blank] (not reported)
TurbidityMethod
Identification code of the analytical method used to measure turbidity: EPA 180.1, SM 2130 B,
[blank] (not reported)
FreeDisinfectantResidual
Free disinfectant residual measurement of the sample
FreeDisinfectantResidualUnits
mg/L (milligrams per liter), [blank] (not reported)
FreeDisinfectantResidualMethod
Identification code of the analytical method used to measure free disinfectant residual: SM
4500-CI D, SM 4500-CI F, SM 4500-CI G, [blank] (not reported)
TotalDisinfectantResidual
Total disinfectant residual measurement of the sample
TotalDisinfectantResidualUnits
mg/L (milligrams per liter), [blank] (not reported)
TotalDisinfectantResidual Method
Identification code of the analytical method used to measure total disinfectant residual: SM
4500-CI D, SM 4500-CI F, SM 4500-CI G, [blank] (not reported)
Region
EPA Region (states): 1 (CT, ME, MA, NH, Rl, VT), 2 (NJ, NY, PR [Puerto Rico], VI [Virgin Islands]),
3 (DE, DC, MD, PA, VA, WV), 4 (AL, FL, GA, KY, MS, NC, SC, TN), 5 (IL, IN, Ml, MN, OH, Wl), 6 (AR,
LA, NM, OK, TX), 7 (IA, KS, MO, NE), 8 (CO, MT, ND, SD, UT, WY), 9 (AZ, CA, HI, NV, GU [Guam],
MP [Northern Marianas Islands]), 10 (AK, ID, OR, WA)
State
State abbreviation. Tribal PWSs without primacy are attributed to an EPA Region (05, 06, 07,
08, 09)
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