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National Contaminant Occurrence Database (NCOD)

EPA has developed NCOD to satisfy the statutory requirements set by Congress in the 1996 amendments to the Safe Drinking Water Act (SDWA) to maintain a national drinking water contaminant occurrence database using occurrence data for both regulated and unregulated contaminants in public water systems.

This site provides a library of water sample analytical data (or “samples data”) that EPA is currently using and has used in the past for analysis, rulemaking, and rule evaluation. The drinking water sample data, collected at Public Water Systems, are for both regulated and unregulated contaminants. The data have been extensively checked for data quality and analyzed for national representative-ness.

From this site you can download Microsoft Excel PivotTables® to help you access, organize, and analyze the sample data by contaminant, geography, sample date, and various water system attributes. You can also download the underlying databases.

Importantly, you can view or download the EPA reports, which provide information to understand the data and their quality, and analyses that have been performed using them.

This site has recently been rebuilt. Previously, you could obtain only “raw,” unchecked data. But now you can access both the latest UCMR data, which are being collected and added to the NCOD, as well as static datasets that have been used in published regulatory analyses. These latter (static) datasets have been extensively quality-checked, and their corresponding reports provide full descriptions (meta data) of the data. Now you can also analyze the data across several attributes using PivotTables. Brief descriptions of the NCOD data sets, their corresponding reports, and descriptions of the data contained in the PivotTables® are included below.

Unregulated Occurrence Data

Unregulated occurrence data are sample data from monitoring in public water systems for contaminants not having health-based standards set under the SDWA at the time of the monitoring.

Rounds 1&2

The Round 1 dataset contains public water system monitoring sample results for 62 (then) unregulated contaminants, generally collected between 1988 and 1992, from 40 states and primacy entities. These data are from the first round of required monitoring of unregulated contaminants. Round 1 data were stored in a database called the Unregulated Contaminant Monitoring Information System (URCIS).

The Round 2 dataset (the second round of unregulated contaminant monitoring) contains public water system monitoring sample data for 48 (then) unregulated contaminants, generally collected between 1993 and 1997, from 35 states and primacy entities. Round 2 data were obtained from the EPA Safe Drinking Water Information System (SDWIS/FED).

The summary report (June 2001) below includes summary descriptions of the contaminants from each dataset, data quality assessments, and contaminant occurrence analyses. Also included is a description of how individual state data sets were assembled into a single “national cross-section” data set that is indicative of contaminant occurrence nationally. The complete National Occurrence report (May 2001) provides full descriptions and details.

1999 Unregulated Contaminant Monitoring Rule (UCMR 1999)

EPA uses data generated by the UCMR (1999) to evaluate and prioritize contaminants on the EPA Contaminant Candidate List (CCL). The CCL is a list of contaminants EPA is considering for possible new drinking water standards. Additional information on the rule is available on the UCMR main page.

The occurrence data associated with the revised UCMR (1999) is meant to assist the Agency in determining whether or not to regulate a certain contaminant. The UCMR (1999) was designed to assess contaminant occurrence nationally. Therefore, extreme caution should be used in any interpretation of data, which reflects only a subset of the entire database. The monitoring is scheduled during the period from 2001 until 2003. So, any interpretation of data before all the data are collected (probably mid-2004) may lead to false conclusions.

Regulated occurrence data

Regulated occurrence data are sample data from monitoring in public water systems for contaminants with health-based standards set under the SDWA.

Six-Year Review of NPDWRs

The SDWA requires EPA to review each national primary drinking water regulation (NPDWR) at least once every six years and revise them, if appropriate. SDWA specifies that any revision must maintain or increase public health protection.

EPA conducted detailed contaminant occurrence analyses for 61 regulated contaminants, using data provided by a national cross-section of 16 states. Most of the sample data were collected between 1993 and 1997.

  • About Six-Year Review - This site includes reports that describe the contaminants, data quality assessments, the development of a nationally-representative cross-section of states, and contaminant occurrence analyses performed.
  • Download Six-Year Review Data

Ambient/source water data

Ambient occurrence data are results from monitoring in surface and ground water sources.

EPA

EPA maintains two data management systems containing water quality information for the nation's ambient waters: the Legacy Data Center, and STORET

The Legacy Data Center, or LDC, contains historical water quality data dating back to the early part of the 20th century and collected up to the end of 1998. The STORET database contains data collected beginning in 1999, along with older data that has been properly documented and moved from the LDC.

Both systems contain raw biological, chemical, and physical data on surface and ground water collected by federal, state and local agencies, Indian Tribes, volunteer groups, academics, and others. All 50 States, territories, and jurisdictions of the U.S., along with portions of Canada and Mexico, are represented in these data systems.

U.S. Geological Survey (USGS)

The USGS disseminates water data it has collected to the public through a system called the National Water Information System (NWIS).Exit EPA Disclaimer Many types of data are stored in the NWIS network, including: site information, time-series (flow, stage, precipitation, chemical), peak flow, and groundwater and surface water quality measures.

 

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