EVALUATING THE PROPOSED CHLORIDE TMDL IN THE CALLEGUAS CREEK WATERSHED, CALIFORNIA

A new water quality objective (WQO) and Total Maximum Daily Load (TMDL) for chloride are being proposed by the Los Angeles Regional Water Quality Control Board (RWQCB) for the protection of agricultural crops and groundwater recharge beneficial uses in the Calleguas Creek Watershed, Ventura County, California. It is significant that the TMDL and water quality objectives are being proposed simultaneously to protect the groundwater quality of the underlying aquifer. Surface and groundwater linkages were modeled in order to characterize the chloride balance in the watershed for development of the TMDL. 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.If the proposed requirements are ultimately imposed, point source dischargers will find it necessary to implement advanced wastewater treatment, including microfiltration and reverse osmosis. The Calleguas Creek Watershed Joint Powers Association (JPA) represents the five municipal wastewater treatment facilities that discharge treated wastewater into the waters of the Calleguas Creek Watershed. The JPA includes the Camarillo Sanitary District, the City of Thousand Oaks, Ventura County Waterworks District No.1, City of Simi Valley, and the Camrosa Water District.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.