DISSOLVED URANIUM IN THE GROUNDWATERS OF THE WESTERN PENINSULAR RANGES BATHOLITH, SAN DIEGO COUNTY, CALIFORNIA

Detectable levels of dissolved uranium can be found in most municipal and private potable water systems; however, ingestion of levels above the Maximum Contaminant Level (30 ug/L) have been shown to cause kidney issues as well as other health effects. Although public water wells are tested at least annually for water quality, private water wells in rural areas are not tested as frequently, if at all. Recently, dissolved uranium in excess of state and federal standards has been discovered in the groundwater in and around the Descanso region of San Diego County. This area is located within the Western Peninsular Ranges Batholith and is characterized by moderately fractured Cretaceous igneous intrusions with multiple late Cretaceous pegmatitic dikes. Based on reviews of mine claim data and field observations, the uranium deposits (uranophane) occur as a rind or film on weathered surfaces of the fractured pegmatite intrusions. Available data suggests the groundwater is fracture controlled and stratified as wells proximal to each other have highly variable uranium concentrations. In this study, chemical data from multiple municipal and private wells are compared to the state and federal limits on uranium and the effectiveness of insitu mitigation techniques utilized in the region are also assessed. The results of this study show that more stringent testing of private wells in the region may be necessary.