The Tehama-Colusa Canal Service Area consists of about 450 square miles of irrigable land located on the west side of the Sacramento Valley, Calif. Upon the completion of the Tehama-Colusa Canal, it is expected that most of the service area will switch from passive forms of agriculture (dry farming and grazing) to intensive irrigated farming. Importation and application of surface water may affect the chemical quality of native ground water. This study documents the chemical quality of native ground water before large-scale importation and application of surface water provide the potential of altering the ground-water chemistry. Analyses of samples from 222 wells show that most of the area is underlain by ground water of a quality suitable for most agricultural and domestic uses. In the vicinities of College City-Arbuckle and the city of Williams, boron, chloride, sodium, and dissolved solids may be a threat to future agricultural activities where boron- or chloride-sensitive crops would be grown. The source of degraded ground water in the two areas is local intermittent streams that drain areas having numerous saline springs and seeps. (Woodard-USGS)
