CCWD has no problems meeting this standard in its treated water, as arsenic has been undetected. In CCWD's raw water, data from the past 10 years shows the vast majority of samples tested were below the detection level. In a few isolated raw water samples, arsenic was found between 4 and 7 ppb, well below the maximum allowable level. Arsenic occurs naturally in the environment, being the twentieth most common element in the Earth's crust. It is added to the environment by the weathering of rocks, burning of fossil fuels, smelting of ores and manufacturing.
Arsenic concentrations are usually highest in groundwater.
CCWD uses surface water, which usually has very low concentrations. Gasoline producers began using it extensively in 1992 to meet federal clean air requirements. But MTBE's use is now being phased out in California by 2003, and nationally in the next few years, because it has contaminated some groundwater supplies as the result of leaking fuel tanks or fuel spills. So far, MTBE has been undetectable at CCWD's Delta intakes, based on State of California testing standards that set the minimum level for detection at 5 parts per billion. To protect the water after it is pumped from our intakes, CCWD does not allow gasoline-fueled recreational boats in its reservoirs.