oEPA
The Second Unregulated Contaminant Monitoring Rule (UCMR 2)
Data Summary: 2008-2010
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 2 required monitoring between 2008 and 2010 for the 25 contaminants listed in Table 1. UCMR 2
contaminants were monitored under the UCMR Assessment Monitoring (AM) or Screening Survey (SS) design.
For more information, refer to the EPA's UCMR 2 website. Summary details for contaminant occurrence are
shown in Table 2 and represent the final release of UCMR 2 analytical results. Before conducting your own
assessment of the data, please review the Data Considerations section.
1 UCMR 2 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-24-005
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Table 1. Contaminants and Methods
Contaminant
CASRN1
EPA
Method
Contaminant Classification
Monitoring
Requirement2
2,2',4,4'-tetrabromodiphenyl
5436-43-1
527
Flame retardant
AM
ether (BDE-47)
2,2',4,4',5-pentabromodiphenyl
60348-60-9
527
Flame retardant
AM
ether (BDE-99)
2,2',4,4',5,5l-hexabromobiphenyl
59080-40-9
527
Flame retardant
AM
(HBB)
2,2',4,4l,5,5l-hexabromodiphenyl
68631-49-2
527
Flame retardant
AM
ether (BDE-153)
2,2',4,4',6-pentabromodiphenyl
189084-64-8
527
Flame retardant
AM
ether (BDE-100)
dimethoate
60-51-5
527
Pesticide
AM
terbufos sulfone
56070-16-7
527
Pesticide
AM
1,3-dinitrobenzene
99-65-0
529
Explosives and related compounds
AM
2,4,6-trinitrotoluene (TNT)
118-96-7
529
Explosives and related compounds
AM
hexahydro-l,3,5-trinitro-l,3,5-
121-82-4
529
Explosives and related compounds
AM
triazine (RDX)
N-nitroso-diethylamine (NDEA)
55-18-5
521
Nitrosamines; disinfection byproducts
SS
N-nitroso-dimethylamine (NDMA)
62-75-9
521
Nitrosamines; disinfection byproducts
SS
N-nitroso-di-n-butylamine (NDBA)
924-16-3
521
Nitrosamines; disinfection byproducts
SS
N-nitroso-di-n-propylamine
621-64-7
521
Nitrosamines; disinfection byproducts
SS
(NDPA)
N-nitroso-methylethylamine
10595-95-6
521
Nitrosamines; disinfection byproducts
SS
(NMEA)
N-nitroso-pyrrolidine (NPYR)
930-55-2
521
Nitrosamines; disinfection byproducts
SS
acetochlor
34256-82-1
525.2
Pesticide
SS
alachlor
15972-60-8
525.2
Pesticide
SS
metolachlor
51218-45-2
525.2
Pesticide
SS
acetochlor ethane sulfonic acid
187022-11-3
535
Pesticide
SS
(ESA)
acetochlor oxanilic acid (OA)
194992-44-4
535
Pesticide
SS
alachlor ethane sulfonic acid (ESA)
142363-53-9
535
Pesticide
SS
alachlor oxanilic acid (OA)
171262-17-2
535
Pesticide
SS
metolachlor ethane sulfonic acid
171118-09-5
535
Pesticide
SS
(ESA)
metolachlor oxanilic acid (OA)
152019-73-3
535
Pesticide
SS
1 CASRN - Chemical Abstracts Service Registry Number
2 AM - Assessment Monitoring, SS - Screening Survey. For more information on UCMR 2 monitoring design, refer to the EPA's UCMR 2
website.
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Information About UCMR 2 Results
The purpose of this document is to summarize and provide additional information about UCMR 2 results.
The UCMR 2 minimum reporting levels (MRLs) are the lowest concentrations that laboratories were permitted
to report to the EPA during UCMR 2 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 2 Data Summary1
Contaminant
UCMR MRL2 (ng/L)
Total number of
results3
Number of
results >MRL
Total number of
PWSs with results3
Number of PWSs with
results >MRL
BDE-47
0.3
32,149
0
4,140
0
BDE-99
0.9
32,149
0
4,140
0
HBB
0.7
32,143
0
4,140
0
BDE-153
0.8
32,139
0
4,140
0
BDE-100
0.5
32,149
0
4,140
0
dimethoate
0.7
32,150
0
4,140
0
terbufos sulfone
0.4
32,149
1
4,140
1
1,3-dinitrobenzene
0.8
32,152
0
4,139
0
TNT
0.8
32,151
0
4,139
0
RDX
1
32,150
4
4,139
3
NDEA
0.005
18,096
46
1,198
26
NDMA
0.002
18,098
1,861
1,198
324
NDBA
0.004
18,101
9
1,198
5
NDPA
0.007
18,107
0
1,198
0
NMEA
0.003
18,101
3
1,198
3
NPYR
0.002
18,101
41
1,198
21
acetochlor
2
11,193
0
1,198
0
alachlor
2
11,193
0
1,198
0
metolachlor
1
11,192
3
1,198
3
acetochlor ESA
1
11,157
2
1,198
2
acetochlor OA
2
11,157
0
1,198
0
alachlor ESA
1
11,156
5
1,198
3
alachlor OA
2
11,157
0
1,198
0
metolachlor ESA
1
11,157
52
1,198
19
metolachlor OA
2
11,157
3
1,198
1
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 |ag/L to
nanograms/liter (ng/L, or parts per trillion), multiply the value by 1,000. UCMR results are presented as single measurements and do not represent a locational running annual
average.
2 UCMR MRL - EPA-established UCMR Minimum Reporting Level. Based on laboratory capability; not related to contaminant health effects information.
3 UCMR 2 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. For more information, refer to the EPA's UCMR 2 website. For the nitrosamines, samples were collected at the entry point to the distribution
system (EP) and the distribution system at maximum residence time (MR), increasing their total SS results.
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Data Considerations
The UCMR 2 analytical results are publicly available through the UCMR Archival Data Finder and as text files.
The UCMR Archival Data Finder allows people to easily search for, summarize, and download the UCMR 2 analytical results.
Results can be filtered using multiple data fields, including public water system (PWS), PWS size, state, EPA Region,
contaminant, source water 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 2 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
(.zip) files from UCMR 2 (2008-2010) Occurrence Data:
o UCMR 2 Occurrence Data Text Files to view all the analytical results (i.e., results for all contaminants
reported by all PWSs). The UCMR2_All.txt file may be too large to be imported into Excel, in which case
you can try other applications (e.g., Microsoft Access) or import a subset of the data as described below.
o UCMR 2 Occurrence Data Text Files by State to view all the analytical results, organized by Tribes and
states. Within that zip file, one text file (UCMR2_AII_Tribes_AK_LA.txt) will have all results for Tribal
PWSs and for the states starting alphabetically with A through L; another file (UCMR2_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 2 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 527 file with results for seven contaminants).
• The following text file for additional data elements (i.e., information beyond analytical results for the 25 UCMR 2
contaminants) is also contained in each of the above zip files:
o UCMR2_Disinfectant_AddtlDataElem.txt - Disinfectant Type (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 2 website.
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Table 3. UCMR 2 Data Definitions for the UCMR Archival Data Finder
The data definitions below are specific to the UCMR 2 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 2 (2008-2010)
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. Utah PWS IDs begin with 4 letters (UTAH) followed by
5 numbers
PWS Name
Name of the PWS
Contaminant
The UCMR 2 contaminant analyzed
Result
Numeric value of the analytical result in |ag/L for the contaminant. 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), MX (any combination of SW, GW, and GU)
Sample Point Type
Sampling Point Type Code: EP (entry point to the distribution system), MR (distribution system at
maximum residence time)
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, AS [American Samoa], GU [Guam], MP [Northern Marianas
Islands], NN [Navajo Nation]), Region 10 (AK, ID, OR, WA)
State
State abbreviation. Tribal PWSs without primacy are attributed to an EPA Region (01, 05, 06, 08, 09)
Associated Facility ID
Maximum residence time facility ID associated with the entry point facility (SS facilities only)
Associated Sample Point ID
Maximum residence time sample point ID associated with the entry point ID sample point (SS
facilities only)
Monitoring Requirement
AM (Assessment Monitoring), SS (Screening Survey)
Minimum Reporting Level
(MRL)
Minimum Reporting Level defined by UCMR 2 in |ag/L for the contaminant. Based on laboratory
capability; not related to contaminant health effects information
UCMR1 Sample Type
Null for UCMR 2
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
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
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Table 4. Data Definitions for Text Files: UCMR2AII, UCMR2_AII_Tribes_AK_LA,
UCMR2_AIl_MA_WY, and UCMR2_MethodNumber
Field Name
Definition
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. Utah PWS IDs begin with 4 letters (UTAH) followed by 5
numbers
PWSName
Name of the PWS
Size
Size category of the PWS for UCMR 2, based on total population (retail plus population served by
purchasing systems that purchase all of their water) as indicated by the Safe Drinking Water
Information System (Federal) (SDWIS/FED) as of June 30, 2005: S (< 10,000), L (> 10,000)
FacilitylD
Identification code (5-digit number) for each applicable facility associated with water treatment or
delivery at the PWS
FacilityName
Name of the facility at the PWS
FacilityWaterType
Source of water at the facility: SW (surface water), GW (ground water), GU (ground water under the
direct influence of surface water), MX (any combination of SW, GW, and GU)
SamplePointID
Identification code for each sample point location at the PWS
SamplePointName
Name of the sample point at the PWS
SamplePointType
Sampling Point Type Code: EP (entry point to the distribution system), MR (distribution system at
maximum residence time)
AssociatedFacilitylD
Maximum residence time facility ID associated with the entry point facility (SS facilities only)
AssociatedSamplePointID
Maximum residence time sample point ID associated with the entry point ID sample point (SS facilities
only)
CollectionDate
Date of sample collection (month, day, year)
SamplelD
Identification code for each sample
Contaminant
The UCMR 2 contaminant analyzed
MRL
Minimum Reporting Level (MRL) defined by UCMR 2 in |ag/L for the contaminant. 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)
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 contaminant. Null (or blank) values represent
results less than the UCMR MRL
SampleEventCode
Identification code for each sample event: SE1, SE2, SE3, SE4
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, AS [American Samoa], GU [Guam],
MP [Northern Marianas Islands], NN [Navajo Nation]), 10 (AK, ID, OR, WA)
State
State abbreviation. Tribal PWSs without primacy are attributed to an EPA Region (01, 05, 06, 08, 09)
UCMRlSampleType
Null for UCMR 2
Table 5. Data Definitions for Text File: UCMR2 Disinfectant AddtlDataElem
Data Element Definition and Response Options
DisinfectantType
The type of disinfectant in use at the time of UCMR sampling to maintain a residual in the distribution system for
each Screening Survey sampling point. To be reported by PWSs required to conduct Screening Survey monitoring.
The PWS must report using the following codes for each Screening Survey sampling location (i.e., EP, MR): CL =
chlorine, CA = chloramine, OT = all other types of disinfectant (e.g., chlorine dioxide), ND = no disinfectant used
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