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LandWatch
State of Monterey County Report 1999
3.7
Water Quality
Groundwater use in the Salinas Valley is adversely affected by nitrate contamination. A 1995 report from the Monterey County Water Resources Agency, making use of 1993 data, indicated that of the 240 wells listed, 59 wells (25%) had nitrate concentrations exceeding the drinking water standard of 45 mg/l as NO3.(14) Of 262 water wells sampled in a 1998 report from the Monterey County Water Resources Agency, data indicated that 100 wells (38%) had nitrate concentrations exceeding the drinking water standard of 45 mg/l as NO3 (Table 14).(15) A report prepared by the University of California, Davis found that in the Salinas Valley (excluding the Forebay and Upper Valley) there is a 40- to 60-year time lag between changes in nitrate loading at the surface and corresponding changes in groundwater quality at depths of 180 feet and shallower. The report concluded that nitrate concentrations may continue to rise for many years to come.(16)
Also affecting water quality is MTBE (Methyl Tertiary Butyl Ether), a gasoline additive that is highly soluble in water and that moves rapidly into groundwater aquifers from leaking underground storage tanks, pipelines, and other components of the gasoline distribution system. A 1998 report from the Central Coast Regional Water Quality Control Board documented 37 MTBE discharges between January 1, 1995 and July 1, 1998. Of the 37 discharges, MTBE was detected in 36 sites in shallow (less than 50 foot deep) groundwater that is not currently being used for drinking water.(17) MTBE is an unregulated, volatile organic substance, and testing by small water systems for the presence of MTBE is not currently required by Monterey County Environmental Health. In March 1999, the Governor ordered that MTBE be removed as a gasoline additive by 2002.
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