PROPOSED CHLORIDE TMDL LINKING SURFACE AND GROUNDWATER IN THE CALLEGUAS CREEK WATERSHED, CALIFORNIA

A Total Maximum Daily Load (TMDL) and new water quality objective (WQO) are being proposed simultaneously for chloride by the Los Angeles Regional Water Quality Control Board (RWQCB) to protect the agricultural and groundwater recharge beneficial uses in the Calleguas Creek Watershed, Ventura County, California. If the proposed requirements are ultimately imposed, point source dischargers will find it necessary to implement advanced wastewater treatment, including microfiltration and reverse osmosis.In order to characterize the chloride balance in the watershed for development of the TMDL, surface and groundwater linkages were modeled. Additionally, an investigation of the chloride limitations and requirements for agricultural beneficial uses was conducted for development of the water quality objective to protect the most sensitive agricultural crops in the region.This paper presents the findings, conclusions, and recommendations of an independent scientific assessment of the proposed chloride water quality objective and associated TMDL for reasonableness and economic impacts, including comprehensive surface and groundwater modeling and a chloride mass balance to assure beneficial use attainability.