Publication Summary

This is the quality assurance project plan for the Pataha Creek Effectiveness Monitoring Total Maximum Daily Load Study.

The Washington State Department of Ecology is required to develop and implement Total Maximum Daily Loads (TMDLs) for impaired waters, and evaluate the effectiveness of the cleanup plan in achieving the needed improvement in water quality.

Ecology developed ammonia nitrogen (NH3-N), chlorine (Cl2), and biochemical oxygen demand (BOD) TMDLs for Pataha Creek. These TMDLs and associated wasteload and load allocations were approved by the United States Environmental Protection Agency in September 1994.

The allocations were based on the Washington State water quality criteria for acute (daily maximum) and chronic (monthly average) conditions at the edge of the mixing or dilution zone to provide protection for human and aquatic organisms. Evaluation of available data from the facility indicates compliance with the National Pollutant Discharge Elimination System (NPDES) permit limits set for NH3-N and BOD. Facility improvements and conversion to UV disinfection eliminated the use of chlorine as a disinfectant in October 2002.

This Quality Assurance Project Plan describes the procedure that will be used to monitor the effectiveness of the TMDL in returning the waterbody to its designated use classification. The study will be conducted by the Freshwater Monitoring Unit of Ecology′s Environmental Assessment Program.