Receiving Water Quality Monitoring for Assessment of Storm Water Runoff Impacts, A Case Study

A receiving water quality monitoring program was developed to measure beneficial use impacts resulting from toxicity in storm water runoff. Significant toxicity has been identified through field sampling in San Diego Creek, the primary tributary to Upper Newport Bay in Orange County California and in Upper Newport Bay. The goals of the water quality monitoring program are to determine the persistence, fate and significance of the aquatic toxicity in the receiving water. The program is being completed in two phases reflecting the funding from two EPA grants. A 205(j) planning grant is providing resources for characterizing the toxicity in the receiving waters using standard EPA tests. A 319(h) implementation grant is providing resources for determining the source of the toxicity in the watershed, and ultimately, to develop source control BMPs for the constituents identified as a part of the planning portion of the program. The initial receiving water testing began in the fall of 1997. To date, there is toxicity to Ceriodaphnia (freshwater zooplankton), Mysidopsis bahia (marine zooplankton), and, in an isolated case, Pimphales promelas (fathead minnow larvae). About one-half of the toxicity has been identified through directed Toxicity Investigation Evaluations (TIEs) as resulting from organophosphorous pesticides. The remaining toxicity was not identified through a conventional TIE. Additional investigation is currently underway to identify the compounds responsible for the unidentified portion of the toxicity and the significance of the toxicity in the Bay to aquatic life. Background In most cases, conventional water quality monitoring is carried out by measuring a suite of chemical constituents at various locations at a fixed, sampling frequency. The data may be compared to U.S. EPA water quality criteria and/or state standards based on the EPA criteria. Exceedance of the criterion values represents an “impaired” water body that requires action to eliminate the exceedance.