DBCP pesticide in drinking water wells in Fresno and other communities in the central valley of California.

Spatial and temporal patterns of DBCP contamination of well water in eastern Fresno County were studied for the period 1979-1983. Associations were found between DBCP levels and land use, hydrological and geological variables and type of well. Large seasonal, monthly and daily fluctuations in DBCP concentrations appear to be due to well use patterns and time of sampling. These findings indicate that use of a formal sampling plan is essential for reliable monitoring of this and other pesticides in well water. Suggestions are made for improvements in the DBCP monitoring program in California.