This report presents chemistry results for intertidal (beach) sediment and clam tissue samples collected as part of the monitoring response to the West Point Treatment Plant (West Point) February, 2017 flooding event. The report focuses on the potential influence of untreated and reduced treatment effluent discharges on metals concentrations in intertidal sediment and clam tissue. Sediment and clam tissue samples were collected in August 2017, to align with the timing of historical sampling. Sampling and analysis methods associated with the 2017 sampling event are detailed in the Sampling and Analysis Plan (King County, 2017a). Intertidal sediment samples were collected from six stations located north and south of West Point, while butter clams (Saxidomus gigantea) were collected from five of these stations. Sampling stations were chosen based on proximity to West Point effluent discharges, proximity to combined sewer overflow (CSO) discharge locations, and availability of historical data for comparison. The objective of this study was to identify any anomalies in 2017 intertidal sediment and clam tissue data compared to historical data available.

A summary of the flooding event and associated monitoring efforts are presented in Section 2. The remainder of the report summarizes the sampling and analytical methods (Section 3) and presents sediment and clam tissue results including a comparison to historical data (Sections 4 and 5, respectively). This report is one of six documents prepared documenting results of the various monitoring activities conducted following the West Point flooding event, and will be followed by a final West Point flooding event summary report.