Publication Summary

Groundwater samples to be tested for volatile organics were collected from five monitoring wells at the Shelton site from August 2006 through May 2007. The study purpose was to continue to monitor concentrations of tetrachloroethylene (PCE) since the injection of a hydrogen release compound (HRC) for remediation treatment in June 2005. PCE was detected in well 4W with concentrations ranging from 3.2 to 10 µg/L, exceeding the MTCA cleanup standard of 5 ug/L in three of the four sample quarters. Since August 2006, contaminant concentrations have been steadily increasing, suggesting the HRC is past its effectiveness. Groundwater monitoring is scheduled to continue quarterly for another year.

PCE contamination of the 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 site wells in 1998 detected PCE in one well (4W) at a concentration of 280 µg/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 µg/L. PCE was not detected in the four deep wells.

To remediate the remaining contaminants, in June 2005 Ecology had a hydrogen release compound (HRC®) injected into the groundwater around well 4W. Groundwater monitoring continued to assess the concentrations and distribution of the contaminants. Five months following the HRC injection, PCE and TCE concentrations decreased and cis-DCE concentrations increased, indicating that enhanced degradation may have been occurring.

Between August 2006 and May 2007, groundwater samples were collected quarterly from five of the wells. PCE was detected in well 4W with concentrations ranging from 3.2 to 10 µg/L. The Model Toxic Control Act (MTCA) Method A cleanup level for PCE is 5 µg/L. TCE and cis-DCE were also detected in well 4W but at concentrations near or below the practical quantitation limit of 1 µg/L. PCE was not detected in the two deeper wells.

Since August 2006, contaminant concentrations have been steadily increasing. Parallel increases in PCE, TCE, and cis-DCE concentrations may suggest the HRC is past its effectiveness in reducing the contaminant concentrations. As of May 2007, it has been 23 months since the HRC injection. HRC typically has an effective longevity of 12 to 18 months.

Groundwater monitoring should continue in the five wells on a quarterly basis because PCE concentrations in monitoring well 4W continue to exceed the 5 µg/L cleanup level.

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

Link to EIM data for User Study ID PMART001