Important Facts for Drinking Water: PCE (Tetrachloroethene)

Definition

__Mean Tetrachloroethene Levels for Utah__ [[br]] 1) Yearly distribution of number of community water systems (CWS) by mean PCE concentration [[br]] 2) Yearly distribution of number of people served by CWS by mean PCE concentration __Maximum Tetrachloroethene Levels for Utah__ [[br]] 3) Yearly distribution of number of CWS by maximum PCE concentration [[br]] 4) Yearly distribution of number of people served by CWS by maximum PCE concentration

Numerator

1) Count of community water systems categorized by mean PCE concentration for each year reported (cut-points: <=5, >5 ug/L PCE, Not Detected) 2) Number of people served by community water systems categorized by mean PCE concentration for each year reported (cut-points: <=5, >5 ug/L PCE, Not Detected) 3) Count of community water systems categorized by maximum PCE concentration for each year reported (cut-points: <=5, >5 ug/L PCE, Not Detected) 4) Number of people served by community water systems categorized by maximum PCE concentration for each year reported (cut-points: <=5, >5 ug/L PCE, Not Detected)

Denominator

Not applicable. There are no rates in this PCE indicator.

Data Interpretation Issues

Data reported to other sources, such as the U.S. Environmental Protection Agency, may differ slightly. A community water system (CWS) is a public water system which serves at least 15 service connections used by year-round residents or regularly serves at least 25 year-round residents. Population data for each community water system are estimates based on number of connections. Inconsistent outliers and other data errors were not included in calculations in order to provide a more accurate representation of water quality. These calculations include all available data which varies by year and water system. This data does not include information about private water sources such as well water or tribal water systems. The current measures are derived for community water systems (CWS) only. Private wells may be another source of population exposure to PCE. Transient non-community water systems, which are regulated by EPA, also may be an important source of PCE exposure. Measures do not account for the variability in sampling, numbers of sampling repeats, and variability within systems. Concentrations in drinking water cannot be directly converted to exposure because water consumption varies by climate, level of physical activity, and between people (EPA 2004). Due to errors in estimating populations, the measures may overestimate or underestimate the number of affected people. (From the National Environmental Public Health Tracking Network [NEPHTN] Nationally Consistent Data and Measures [NCDM] PCE indicator document, version 5) Ground water systems may have multiple wells with different PCE concentrations that serve different parts of the population. Compliance samples are taken at each entry point to the distribution system. In systems with separate wells serving some branches or sections of the distribution system, the system mean would tend to underestimate the PCE concentration of people served by wells with higher PCE concentrations. Exposure may be higher or lower than estimated if data from multiple entry points for water with different PCE levels are averaged to estimate levels for the CWS. (From the NEPHTN NCDM PCE indicator document, version 5)

Why Is This Important?

People drink and use water every day. The majority of Americans are provided with high quality drinking water. About 90% of people in the U.S. get their water from a community water system versus a smaller water supply such as a household well. The U.S. Environmental Protection Agency (EPA) sets regulations for treating and monitoring drinking water delivered by community water systems. Currently, there are water quality standards and monitoring requirements for over 90 contaminants. Drinking water protection programs play a critical role in ensuring high quality drinking water and in protecting the public's health. Because people drink and use water every day, contaminants in drinking water have the potential to affect many people. The number of people served by a community water system varies from as low as 25 to hundreds of thousands. Community water systems in the U.S. provide among the highest quality drinking water in the world. However, some contaminants are present at low levels, and it is still possible that drinking water can become contaminated at higher levels. If a person is exposed to a high enough level of a contaminant, they may become ill. Tetrachloroethene (PCE) is a volatile halogenated short-chain hydrocarbon. Tetrachloroethene is used in dry cleaning, metal cleaning, the synthesis of other chemicals, and household products such as water repellents, silicone lubricants, and spot removers. PCE is produced and used in high volumes in the U.S. and has been detected in urban and ambient air and occasionally in soils and drinking water most likely contaminated by industrial discharge (Moran et al., 2007; Rowe et al., 2007). Because of its volatility, this solvent does not persist in the soil or water following the discontinuation of contamination. (From the National Environmental Public Health Tracking Network (NEPHTN) Nationally Consistent Data and Measures (NCDM) PCE indicator document, version 5) In an analysis of occurrence data from the Environmental Protection Agency (EPA) 6 Year Review of National Primary Drinking Water Regulations, PCE was detected in 1,262 systems serving close to 32 million people in the United States (EPA, 2009). Concentrations of PCE were greater than the maximum contaminant level (MCL) in 241 systems serving close to 15 million people. PCE was the fifth highest occurring regulated volatile organic chemical found based on the percent of detections from the 6 Year Review data (EPA, 2009). (Modified from the NEPHTN NCDM PCE indicator document, version 5)