Publication Summary

Ground water samples were collected from October 1995 to November 1997 from seven monitoring wells at the Monterey Apartments project site, located in the Queen Anne District of northwest Seattle. These samples were collected to define the current distribution and concentrations of a petroleum plume resulting from a past contaminant release.

Ground water samples were collected from October 1995 to November 1997 from seven monitoring wells at the Monterey Apartments project site, located in the Queen Anne District of northwest Seattle. These samples were collected to define the current distribution and concentrations of a petroleum plume resulting from a past contaminant release.

Samples from monitoring wells MW-10, MW-9, VP-8, VP-7, MW-4, RW-2 and MW-6 were collected and analyzed for benzene, toluene, ethylbenzene and xylene (BTEX), total petroleum hydrocarbons as gasoline (TPH-G), volatile organics (VOAs), as well as total recoverable lead. High BTEX concentrations were detected in six of the seven wells sampled. Well MW-6 was not sampled past January 1997 because it consistently contained a layer of free product floating on the ground water surface.

A summary of all results from October 1995 to November 1997 are shown in the attached table. Overall, concentrations are similar for most of the wells over the monitoring period. High BTEX concentrations were detected in six of the seven wells ranging in average concentration from 3,620 ppb (MW-9) to 45,000 ppb (MW-4). BTEX was also detected in well MW-10, which is the upgradient well for this project, but at concentrations near the method detection limit. The highest BTEX concentrations occurred in wells VP-7 and MW-4, with average concentrations of 24,000 ppb and 45,000 ppb, respectively. These wells are located about 180 feet from the former tank area and are the farthest downgradient wells for this project. TPH-G concentrations correlate with BTEX concentrations, ranging from an average concentration of 0.7 ppm (MW-10) to 98 ppm (MW-4). Lead was also detected in all of the wells. Lead concentrations over the monitoring period ranged from being near the detection limit in MW-10 to a high of 48 ug/L in RW-2.

Samples were also collected for volatile organics from select wells to assess possible migration of non-petroleum contaminants onto the project site. 1,3,5-Trimethylbenzene and 1,2,4-trimethylbenzene are the only volatile organics, other than BTEX, that were regularly detected in four of the sampled wells. High concentrations of both contaminants were detected in wells MW-9, MW-6, RW-2 and VP-8. Wells VP-7 and MW-4 were not sampled for volatile organics. Tetrachloroethene, tricloroethene and cis-1,2-dichloroethene were detected primarily in well VP-8. Concentrations in VP-8 ranged from not detected to maximum concentrations of 167 ug/L (PCE), 106 ug/L (TCE) and 483 ug/L (cis-1,2-DCE).

Link to EIM data for User Study ID PMART005