Publication Summary

The Palermo Wellfield subdrain was monitored from October 2007 through November 2008. The subdrain met or was near the remediation goal of lowering groundwater three feet below ground surface for the central and northern homes, but did not for the two southern homes.

Some sediment is present in the central and southern subdrain cleanouts. Vegetation growth at the south end of the lagoon does not appear to be affecting the lagoon′s performance.

Average PCE and TCE concentrations in samples from the subdrain are 15 ug/L and 24 ug/L. Concentrations in the treated water that discharges to the Deschutes River were below the remediation goals of 0.8 ug/L (PCE) and 2.7 ug/L (TCE).

In the late 1980s, groundwater contaminated with trichloroethene (TCE) and tetrachloroethene (PCE) migrated from an upland commercial area to the City of Tumwater′s Palermo Wellfield in the Deschutes River valley. The contaminated groundwater also surfaced at the base of Palermo bluff and ponded in the yards and crawlspaces of area homes. In 2000, the U.S. Environmental Protection Agency (EPA) constructed a subdrain system to lower the groundwater table and reduce the human health risk from the contaminated water.

In December 2002, the Department of Ecology assumed the lead for monitoring the subdrain system. The monitoring goal was to collect water-level and PCE/TCE data to determine if the subdrain system is operating within the remediation goals set for the project.

Ecology conducted its most recent monitoring in October 2007 and June and November 2008. Groundwater levels met the remediation goal of three feet below ground surface for the central homes and were near the remediation goal for the northern homes. As in the past, depths to groundwater were less than three feet near the two southern homes.

Overall, total depths measured in the eight subdrain cleanouts were close to the 2001 original depths. Sediment is present in some cleanouts located in the central and southern end of the perforated pipe. It does not appear that sediment deposition or scouring is occurring in the catch basins and lagoon. However, vegetation growth is occurring at the south end of the lagoon but does not appear to be adversely affecting the lagoon′s performance.