Publication Summary

Groundwater samples for dissolved metals and WAD cyanide were collected in May and September 2008 from the former American Plating site in Tacoma to provide post-interim action groundwater data.

Dissolved cadmium, chromium, copper, and nickel, as well as WAD cyanide continue to be detected at low concentrations in groundwater at the site. With the exception of nickel and WAD cyanide, most concentrations are below the regulatory site cleanup levels. However, it is assumed that a further reduction in measured concentrations may occur due to natural attenuation processes as groundwater flows toward the regulatory point of compliance along the banks of the Thea Foss Waterway.

This report is one in a series that describes groundwater monitoring results at the former American Plating site located on the Thea Foss Waterway in Tacoma, Washington.

During May and September 2008, groundwater samples were collected from four site monitoring wells. The samples provided groundwater data on dissolved metals (cadmium, chromium, hexavalent chromium, copper, and nickel) and weak acid dissociable (WAD) cyanide. A volatile organic compounds (VOC) sample was also collected from one well in May.

Dissolved cadmium, chromium, copper, and nickel, as well as WAD cyanide, continue to be detected in groundwater samples collected at the site. No VOC were detected.

Due to the proximity of the site to the waterway, the groundwater cleanup levels were developed based on protection of human contact with surface water (MTCA Method B surface water levels) and on protection of marine organisms (WAC 173-201A). The surface water cleanup level for cyanide (1 ug/L for acute exposure) is based on the weak acid dissociable (WAD) cyanide. The point of compliance for the groundwater cleanup levels is along the banks of the waterway where groundwater discharges to the surface water.

In 2008 most concentrations detected in the groundwater samples were below the cleanup levels, with the exception of nickel (8.9 and 13.3 ug/L) and WAD cyanide (3 J and 6 ug/L). However, it is assumed that a further reduction in these measured concentrations may occur due to natural processes such as sorption and tidal dispersion as groundwater flows toward the point of compliance.

The Foss Waterway Development Authority plans to eventually develop this area as a public park.

("J" in 5th paragraph above = analytical result is an estimate.)