Central Coast ground water quality poorest in state
September 27, 2013
By KAREN VELIE
In southern San Luis Obispo County and northern Santa Barbara County researchers found more wells with high concentrations of nitrates, arsenic and molybdenum than anywhere else in the state, according to a recent report by the U.S. Geological Survey (USGS).
The USGS report lists water basins tested in 38 study areas. In the South Coast Range, which runs from Lompoc to Los Osos, researchers said 10 percent of the wells they tested had high concentrations of nitrate. Trace elements such as naturally occurring arsenic and molybdenum were found at high concentrations in 27 percent of aquifers in the South Coast Range.
In comparison, elsewhere in California researchers found high concentrations of nitrate in less than 1 to 8 percent of the groundwater used for public supply, and trace elements in 6 to 28 percent. High concentrations are defined as being above the U.S. Environmental Protection Agency or California Department of Public Health’s established maximum contaminant levels.
“Interesting, I’ve never seen molybdenum in 27 percent of the wells,” Justin Kulongoski, a USGS research hydrologist said.
One well in Arroyo Grande tested high in molybdenum. Most of the wells with high concentrations of molybdenum were located in the Santa Ynes and Lompoc areas. High levels of molybdenum can cause cancer and stunt growth in humans and animals.
In San Luis Obispo, one well located in the Tank Farm Road and U.S. Highway 101 area tested high for PCBs.
In Santa Maria, researchers found about 25 percent of the ground water basin had high nitrate levels. High levels of nitrate can stunt cognitive development in fetuses, infants and children.
Researchers found 8 percent of wells in the Paso Robles and Templeton areas, which are in the Monterey/Salinas study unit, had high concentrations of nitrate.
In Los Osos, researchers found one well high in nitrate. Because of reports of high nitrate levels in the Los Osos basin, a $173 million sewer is currently under construction.
Nevertheless, the USGS study focused on public supply aquifers which are generally several hundred feet deeper than residential wells. The study which led to the construction of the Los Osos sewer focused on the upper portion of the aquifer. Statewide, researchers have found about 40 percent of upper level aquifers have high nitrate levels.
As part of the statewide study assessing groundwater quality, scientists analyzed untreated groundwater from wells — not treated tap water. Groundwater is typically treated by water distributors prior to delivering it to customers to ensure compliance with water quality standards.
Elevated concentrations of nitrate generally occur as the result of human activities such as applying fertilizer, septic systems and livestock in concentrated numbers.