Publication Summary

During October 2004 and March 2005, groundwater samples from monitoring wells in downtown Montesano were collected for benzene, toluene, ethylbenzene, and xylene (BTEX) and total petroleum hydrocarbons as gasoline (TPH-G).

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

Benzene concentrations did not meet (exceeded) the Model Toxics Control Act Method A cleanup standard of 5 ug/L in 10 of the 32 wells, with concentrations ranging from 5.1 to 8500 ug/L. TPH-G concentrations exceeded the standard of 800 ug/L in nine wells, with concentrations ranging from 1100 to 81,000 ug/L.

Groundwater beneath downtown Montesano is contaminated with petroleum products. The contamination is likely the result of historic releases from leaking underground storage tanks. To determine the lateral extent of groundwater contamination in the downtown area, samples were collected from existing monitoring wells during October 2004 and March 2005. Samples were submitted for analysis of benzene, toluene, ethylbenzene, and xylene (BTEX), as well as total petroleum hydrocarbons as gasoline (TPH-G).

The highest concentrations of gasoline-range petroleum hydrocarbons were detected in monitoring wells from three sites which have been identified as potential source areas. These sites include Tony′s Short Stop/Grays Harbor Grange, Key Bank (Sterling)/Whitney′s Inc., and Brumfield-Twidwell. BTEX and TPH-G concentrations in samples collected from these wells did not meet (exceeded) the Model Toxic Control Act (MTCA) cleanup standards. Benzene concentrations exceeded the MTCA Method A cleanup standard of 5 ug/L in ten of the sampled wells, with concentrations ranging from 5.1 to 8500 ug/L. TPH-G concentrations exceeded the MTCA Method A cleanup standard of 800 ug/L in nine of the sampled wells, with concentrations ranging from 1100 to 81,000 ug/L.

Results of this project confirm that the surficial aquifer throughout the project area is contaminated with gasoline-range petroleum hydrocarbons, including the presence of free-phase petroleum product at the Key Bank (Sterling) site. Because of the potential for contaminants to migrate downgradient from source areas, additional investigations are being conducted to better define the nature and extent of the contamination at the three potential source areas.

Link to EIM data for User Study ID PMART004