A program to monitor the ground- and surface water quality in the Livermore-Amador Valley has been operated since 1976. As of 1982, this monitoring network consisted of approximately 130 wells, about 100 of which were constructed specifically for this program, and 9 surface water stations. Increased demand on the groundwater for municipal and industrial water supply in the past has caused a decline in water levels and a gradual buildup of salts from natural surface-water recharge and land disposal of treated wastewater from waste treatment plants. Results of this study identify the salt buildup to be the major problem with the groundwater quality. Established water quality objectives for dissolved solids are exceeded in 52 of 130 wells. Concentrations of dissolved nitrate are also in excess of basin objectives and health standards. Water quality in both surface and groundwater is highly variable areally. Magnesium to calcium magnesium bicarbonate groundwater are found in the areas where most of the high volume municipal wells are located. Large areas of sodium bicarbonate water occur in the northern part of the valley. Except for two stations on Arroyo Las Positas which has sodium chloride water, surface water is mixed-cation bicarbonate water. (USGS)
