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Six-Year Review Contaminant Occurrence Data

Six-Year Review & Other Related Links

The Safe Drinking Water Act (SDWA) requires EPA to review each National Primary Drinking Water Regulation (NPDWR) at least once every six years and revise them, if appropriate.  The purpose of the review, called the Six-Year Review, is to identify those NPDWRs for which current health effects assessments, changes in technology, and/or other factors provide a health or technical basis to support a regulatory revision that will maintain or strengthen public health protection. To support the national contaminant occurrence and exposure assessments performed under the Six-Year Review process, EPA analyzes SDWA compliance monitoring data from public water supplies for regulated drinking water contaminants.  This analysis allows EPA to characterize the national occurrence of contaminants to help the Agency determine if there may be a meaningful opportunity to improve public health protection.

Six-Year Review 2 Occurrence Data (1998-2005)

In March 2010, the Agency announced the review results for the Agency’s second Six-Year Review (called Six-Year Review 2).  EPA analyzed occurrence data for the Six-Year Review 2 for 69 regulated contaminants, using data provided by 47 states/primacy agencies.  This data represents compliance monitoring sample results collected between January 1998 and December 2005. (Note: While the Six-Year Review 2 effort included a detailed review of 71 NPDWRS, acrylamide and epichlorohydrin are treatment technique regulations and occurrence monitoring data are not required).

Six-Year Review 2 Contaminant Occurrence Data 

The zip files below contains 69 individual Microsoft Access files (one file per contaminant).  The number of records and the size of the files range considerably from contaminant to contaminant, generally reflecting the frequency of required sampling. 

Data Elements Contained in the Six-Year Review 2 MS Access files

The following is a data dictionary for the chemical data sets; it contains the list of data elements, column names, and a brief description of the data for each data element. 


Six-Year Review-ICR Dataset Data Element List

Data Element

Column Name


Inventory Data

State Code


2- digit state code

Public Water System Identification Number (PWSID)


The code used to identify each PWS.  The code begins with the standard 2-character postal state abbreviation or region code; the remaining 7 numbers are unique to each PWS in the state.

System Name


Name of the PWS. 

Federal Public Water System Type Code


A code to identify whether a system is:
• Community Water System (C);
• Non-transient Non-community Water System (NTNC); or
• Transient Non-community Water System (NC; nitrate/nitrite only).



Highest average daily number of people served by a PWS, when in operation.

Source Water Type


Type of water at the source.  Source water type can be:
• Ground water (GW); or
• Surface water (SW); or
• Ground water under the direct influence of surface water (GU)

Chemical-Specific Information

State ID


State-specific unique identification code

Sampling Point Identification Code


A sampling point identifier established by the state, unique within each applicable facility, for each applicable sampling location (e.g., entry point to the distribution system).  This information enables occurrence assessments that address intra-system variability.

Sample Identification Number


Identifier assigned by state or the laboratory that uniquely identifies a sample. 

Sample Collection Date


Date the sample was collected, including month, day, and year.



4-digit SDWIS contaminant identification number for which the sample is being analyzed. 

Sample Analytical Result - Sign


The sign indicates whether the sample analytical result was:
• (0) "less than" means the contaminant was not detected or was detected at a level "less than" the MRL. 
• (1) "equal to" means the contaminant was detected at a level "equal to" the value reported in "Sample Analytical Result - Value."

Sample Analytical Result - Value


Actual numeric (decimal) value of the analysis for the chemical result, or the MRL if the analytical result is less than the contaminant's MRL.

Sample Analytical Result - Unit of Measure


Unit of measurement for the analytical results reported (usually expressed in either µg/L or mg/L for chemicals; or pCi/L for radionuclides). 

For more information on how these data were reviewed and analyzed please see the Federal Register Notice for the Six-Year Review 2.

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Six-Year Review 1 Occurrence Data (1993-1997)

In July, 2003 the Agency announced the review results for the Agency’s first Six-Year Review (called the Six-Year Review 1).  EPA completed its first detailed contaminant occurrence analyses in 2003 for 69 regulated contaminants, using data provided by a national cross-section of 16 states. Most of the sample data were collected between 1993 and 1997.

Six-Year Review 1 Contaminant Occurrence Data

Six-Year Review 1 Detailed Data in Text Files

Data included in the Six-Year Review 1 PivotTable

This PivotTable contains information on Six-Year Review 1 sample data including:  

Any or all of the above facts for a contaminant:
-can be categorized by any combination of the following water system attributes:

-or any combination of the following sample attributes:

* To avoid double-counting, the Pivot Tables will not sum the number of PWSs with and without detects across this dimension/attribute. Details on these attributes are provided in the Pivot Tables.

Fields included in the Six-Year Review 1 database table

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