Ground-water quality in the Lompoc Plain, Santa Barbara County, California, 1983

Groundwater is the main source of water in the Lompoc plain, California. The lower member of the younger alluvium is the main water-bearing zone. Long-term groundwater levels in most of the plain have not changed significantly since the 1940's. Groundwater quality in the plain in 1983 tended to deteriorate from east to west. Dissolved-solids concentrations throughout the plain exceeded the U.S. Environmental Protection Agency secondary maximum contaminant level of 500 mg/L for drinking water. In samples from some wells, concentrations of one or more of the following constituents--sodium, chloride, nitrate, and iron-exceeded primary and secondary maximum contaminant levels for drinking water. Concentration of constituents in some samples also exceeded recommended levels for irrigation water. The predominant ions generally were calcium, magnesium, sulfate, and bicarbonate--except in the western part, where sodium and chloride were the predominant dissolved ions. From 1972 to 1983, dissolved-solids concentrations in the main water-bearing zone generally decreased in the central part of the plain but increased throughout most of the study area. The largest increases, greater than 1,000 mg/L, were in the extreme western part of the plain. (USGS)