The Need and Development of TMDLs for the San Joaquin Valley of California

Abstract

Water quality impairments in the San Joaquin River (SJR) have occurred as a result of large-scale water development projects coupled with discharges from agricultural and municipal sources. Consequently, the SJR is listed as impaired on the Clean Water Act (CWA) 303(d) list of impaired waters for a number of pollutants including salt and boron, the organophosphorous pesticides diazinon and chlorpyrifos, and oxygen demanding substances. The CWA requires that a Total Maximum Daily Load (TMDL) must be developed for waters on this impaired waters list. TMDLs are required to be established at the level necessary to implement applicable water quality standards. The TMDLs establish the pollutant assimilative capacity of a waterbody, and then allocate maximum allowable loading of that pollutant to its various sources. The Central Valley Regional Water Quality Control Board (Central Valley Water Board) has the responsibility and authority to develop TMDLs for these and other listings in the SJR and other water bodies in California’s Central Valley. It is anticipated that the SJR TMDLs adopted by the Central Valley Water Board will be implemented using a mix of regulatory tools including prohibitions of discharge, establishment of fixed load limits in waste discharge requirements, and waivers of waste discharge requirements if certain other conditions are met. It is the flexibility provided through waivers of waste discharge requirements and load limits tied to real time water quality conditions that has encouraged watershed and stakeholder groups to develop plans for achieving water quality objectives. These plans include the use of tools beyond the purview of the Central Valley Water Board to regulate. Establishment of the regulatory backstop provided by the TMDLs provides the regulatory incentive for watershed and stakeholder groups to follow through with the adaptive implementation needed to address the diverse water quality impairments. In the absence of such adaptive implementation, attainment of standards will be achieved through enforcement of: 1) prohibitions of discharge; and 2) fixed load limits in waste discharge requirements that are developed for agricultural and municipal discharges. This paper will describe the technical and regulatory elements of the Central Valley Water Board’s TMDLs for salt and boron, diazinon and chlorpyrifos, and oxygen demanding substances.