Publication Summary

Groundwater samples to be tested for volatile organics were collected from five monitoring wells at the Shelton site from September 2007 through May 2008. The purpose was to continue monitoring tetrachloroethylene (PCE) in the vicinity of well 4W where a spill of dry cleaning chemicals is reported to have occurred in 1993. PCE was detected in well 4W with concentrations ranging from 14 to 43 ug/L, exceeding the MTCA cleanup standard of 5 ug/L. Since August 2006, contaminant concentrations have been steadily increasing, suggesting the HRC injected in June 2005 to remediate the contamination is past its effectiveness. Groundwater monitoring is scheduled to continue semi-annually for another year.

Tetrachloroethylene (PCE) contamination of shallow groundwater underlying Shelton Laundry and Cleaners was discovered in 1997. The source of contamination was assumed to be a 1993 spill outside the dry cleaners. Monitoring of four shallow wells in 1998 detected PCE at a concentration of 280 ug/L (well 4W). The Model Toxic Control Act (MTCA) Method A cleanup level for PCE is 5 ug/L.

In 2002 Ecology installed four deep wells and began monitoring the groundwater quality of all eight wells. From 2002 to 2005, PCE concentrations in well 4W ranged from 10 to 25 ug/L. PCE was not detected in the four deep wells.

To remediate the remaining contaminants, in June 2005 Ecology contractors injected a hydrogen release compound (HRC) into the groundwater around well 4W. Five months following the HRC injection, groundwater monitoring results indicated that the HRC may have been effective in reducing the contaminant concentrations.

However, since August 2006, 15 months following the HRC injection, contaminant concentrations have steadily increased, suggesting the HRC is no longer effective. HRC typically has an effective longevity of 12 to 18 months.

Between September 2007 and May 2008, groundwater samples were collected quarterly from three shallow wells and two deep wells. PCE was detected in well 4W with concentrations ranging from 14 to 43 ug/L, exceeding the MTCA cleanup level. TCE and cis-DCE were also detected in well 4W, mostly at concentrations near or below the practical quantitation limit of 2 ug/L. TCE exceeded the cleanup level of 5 ug/L in September 2007 with a concentration of 9.5 ug/L. PCE, TCE, and cis-DCE were not detected in the two deep wells.

Groundwater monitoring should continue in the five wells on a semi-annual basis since PCE concentrations in monitoring well 4W continue to exceed the cleanup level.

This site may benefit from a second injection of a hydrogen release compound.