PUB00052 - Laserfiche WebLink

Home Browse Search

In many of these cases, the pollutants overwhelmed the natural ability of the soils to filter out the pollufion, or the pollutants passed through fhe soil in a shorter time than required for decomposition or consump- tion by organisms in the soil. A better understanding of those natural dynamics is important as additional contaminated sites are discovered and money for cleanup diminishes. In some cases, abandoned or improperly constructed water wells have become conduits for pollutants - contaminating the aquifers that the wells once tapped. Counties, cities and water agencies are encouraged to take measures to prevent wellhead pollufion by enforcing well design, rehabilitafion and destruction standards, but fhose efforts in some locations do not always live up to their intent. Groundwater Pollution The quality of California's groundwater is in some ways remarkable. Thousands of people drink water pumped from fhe ground with litfle or no treatment But the qualify of California's groundwater is beginning to reflect decades of casual stewardship. Many communities now face expensive remedies to remove contaminants - some resulting from practices that were legal and thoughf fo be benign, while others resulted from years of neglect. Military bases and industrial facilities for years dumped fuels, used solvents and other liquid wastes into pits, where the pollutants leached into the groundwafer. Tens of thousands of gasoline tanks were buried in the ground with few precautions to limit the contamination from inevitable leaks. Garbage dumps were built with inadequate safe- guards or none at all. Where crop dusters and other farm equipment was washed, agricultural chemicals were sprayed on the ground and washed into pits wifh Iiltle concern for the quality of groundwafer. Residential septic tanks and agricultural feedlots also were sources for nitrates, bacteria and viruses. Lack of knowledge in the past led to such practices and if was commonly assumed that if leaks occurred, they would cause no problem underground. Contamination might be less of a concern if communities could easily replace tainted wells with new wells or new suriace water supplies. The number of wells that are known to be seriously affecfed by pollution is relatively small when compared to the hundreds of thousands of wells that have been drilled in the state. But because most wells are not tested, the full extent of the contaminalion is not known. NATURALLY OCCURRING POLLUTANTS The natural quality of groundwater in California - that is before manmade pollutants are considered - depends on the source of water that recharges the aquifer and the surrounding geology. For instance, snow melt streaming down (or through) the granite and volcanic rocks of the Sierra Nevada or Cascade Mountains remains fairly pure as it seeps into aqui. fers on the east side of the Central Valley. However, water flowing through the marine sedimentary rocks that comprise the Coast Ranges picks up naturat minerals and elements. The concentrations of those elements increase with use. When water high in dissolved solids is used as irrigation water, the minerals accumulate in the soils and must be ftushed out to preserve soil produc- tivity. The runoff can contain those trace elements in concentrations high enough to compromise crops, the health of humans, fish and wildlife. Boron is an element that is an essential micro-nutri- ent in trace amounts, but toxic to plants in slightly greater concentrations. Boron is found in groundwa- ter in concentrations harmful to plants in the north- ern and southwestern Sacramento Valley and in the Tulare Basin. Mercury and chromium have been 14 found in wells in the western San Joaquin Valley at concentrations that exceed federal wildlife standards. Arsenic, hydrogen sulfide and radon are all leached out of the soils by percolating groundwater and can be found in California's aquifers. The U.S. Environmental Protection Agency (EPA) is expected to promulgate a health standard for radon, which comes from decaying uranium. Radon as a gas dissolves in groundwater, and then volatilizes as water pours through faucets. It can then be inhaled or ingested and is believed to be a major cause of lung cancer. Radon is a larger problem on the East Coast and in other western states than in California, but radon has been found in some wells in the Sierra Nevada foothills and in San Bernardino County. After some controversy over the appropriate safety level, Congress called for an independent analysis to help determine what level of safety should be set for radon. The more stringent the federal standard, the more wells that will be affected by the reguta- tion. Thirty million people nationwide could be affected by the standard. Of 449 wells surveyed in southern California, 67 percent would not meet the strictest standard for radon now under consideration.