Source(s): TUD (Sonora/Jamestown System) and GCSD annual drinking water reports. Detailed evaluation of the TUD and GCSD drinking water is available on their respective websites: www.tudwater.com/quality.pdf and www.gcsd.org/documents/2006CCR.pdf

MCL = maximum contamination levels. Ideally, the level of the chemical should be less than this number.

AL = Action Level. Level at which drinking water must be cut off.

Note: For Trihalomethane (TTHM) prior to 2004, the Environmental Protection Agency (EPA) Maximum Contamination Level (MCL) was 100 ppb (parts per billion). In 2004, it changed to 80 ppb as did the reporting methods.

Total Trihalomethanes (TTHM) are a byproduct of chlorinating water that contains natural organics. The EPA discovered that TTHM are present in virtually all chlorinated water supplies. Many years ago the EPA required large towns and cities to reduce TTHM levels in potable water. However, recent changes in national drinking water quality standards now require that water treatment systems of smaller towns begin to reduce TTHM. TTHM do not pose a high health risk compared to waterborne diseases, but they are among the most important water quality issues to be addressed in the U.S. water supply. Lead Action Level (AL) is 15 ppb.

Lead is measured using lead/copper samples taken at individual homes, and testing is required every 3 years

Why is this important?

High quality drinking water is essential to human health. Contaminated drinking water can cause disease, birth defects, infant mortality, and increased cancer rates.

Ninety-five percent of our drinking water originates from local surface water sources including rivers, lakes, streams, reservoirs and springs. Most of this water is transported to publicly operated water treatment plants through a man-made earthen ditch system. Five percent of the drinking water is pumped from groundwater wells.

What is the measure?

Drinking water quality is measured by levels of biological and chemical contaminants as reported by the two major water purveyors in Tuolumne County. Maximum Contaminate Levels (MCL), which are limits of biological and chemical contaminants allowed in drinking water, are established and monitored by California and the federal government. Local water purveyors regularly monitor and report water-sampling results for compliance with the MCLs.

How are we doing?

Water sampling test results reveal that our drinking water is essentially contaminant free and meets the MCL for all current primary drinking water standards.

In 2007, water delivered by the Tuolumne Utilities District (TUD) met drinking water standards for all tested contaminates except for iron and manganese, which are considered secondary (non-health related) standards by the state. Groveland Community Services District (GCSD) met all standards in 2007 except for total trihalomethanes (TTHM) and haloacetic acids, which are byproducts of the use of chlorine in drinking water treatment. GCSD upgraded its water treatment plants in 2007, to help meet the state MCL for these contaminants.