Publication Summary

Groundwater samples for BTEX, TPH-G, and VOCs were collected in October 2007 and April 2008 from 25 monitoring wells in downtown Montesano to determine the lateral extent of contamination in the surficial aquifer.

High concentrations of gasoline-range petroleum hydrocarbons were detected in wells from three source areas: Tony′s Short Stop/Grays Harbor Grange, Key Bank (Sterling)/Whitney′s Inc., and Brumfield-Twidwell.

Benzene exceeded the MTCA Method A cleanup level of 5 ug/L in ten wells, with concentrations ranging from 7 to 14,000 ug/L. TPH-G exceeded the cleanup level of 800 ug/L in eight wells (1100 to 236,000 ug/L). Tetrachloroethene exceeded the cleanup level of 5 ug/L in one Key Bank well.

The surficial aquifer beneath downtown Montesano, Washington is contaminated with petroleum products.

The contamination is largely the result of releases from three identified source areas: 1. Tony′s Short Stop/Grays Harbor Grange 2. Whitney′s Inc./Key Bank (Sterling Savings) 3. Brumfield-Twidwellll.

To characterize the lateral extent of contamination, the Washington State Department of Ecology (Ecology) collected groundwater samples from 25 monitoring wells during October 2007 and April 2008. Samples were analyzed for benzene, toluene, ethylbenzene, and xylene (BTEX), total petroleum hydrocarbons as gasoline (TPH-G), and volatile organic compounds (VOCs).

The highest concentrations of gasoline-range petroleum hydrocarbons were detected in monitoring wells at or near the source areas. BTEX and TPH-G concentrations were higher than allowable Model Toxic Control Act (MTCA) cleanup levels for groundwater. Benzene and TPH-G reached concentrations of 14,000 ug/L and 236,000 ug/L, respectively. Free-phase petroleum product observed in wells at the source areas continue to serve as a source of dissolved-phase contamination.

Chlorinated solvents were also detected in wells within the study area. VOC concentrations were below MTCA cleanup levels for groundwater, except for tetrachloroethene in well KBMW-1. The presence of chlorinated compounds in wells at Key Bank, at Ecology well ESMW-7, and at the Grange suggests the possible presence of a VOC-contaminated plume in these parts of the study area.

Ecology also collected water samples from the city′s storm drain and abandoned sanitary sewer to determine if these underground utilities were providing another contaminant migration pathway. Petroleum-related contaminants were detected. This is of concern since the storm drain empties into the Chehalis River system.

Because of the high concentrations of groundwater contamination and the potential for contaminants to continue to migrate from the source areas, additional investigations are being conducted to better define the nature and extent of the contamination. Some remediation has already been completed at Tony′s Short Stop and Brumfield-Twidwell. Work on these projects is continuing.

Link to EIM data for User Study ID PMARTI004