Publication Summary

The Palermo Wellfield subdrain system was monitored in September 2005 and June 2006. The subdrain lowered groundwater levels three to five feet below ground surface for the northern and central homes, but not the two southern homes.

Sediment appears to be accumulating in subdrain cleanouts CO-3 through CO-8. Sediment deposition or scouring does not appear to be occurring in the catch basins and lagoon.

PCE (26 ppb) and TCE (25 ppb) concentrations continue to be highest in water samples from the southern and central portions of the subdrain. 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 as surface water in the yards and crawlspaces of area homes. In 2000, a subdrain system was constructed to reduce the human health risk from the contaminated water by lowering the groundwater table.

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

The most recent monitoring was conducted in September 2005 and June 2006. Groundwater levels were three to five feet below the ground surface near the northern and central homes; this meets the remediation goals. As in the past, groundwater levels were less than three feet near the two southern homes.

Total depths measured in subdrain cleanouts CO-3 through CO-8 appear to have decreased, indicating that sediment may be accumulating in the central and southern parts of the trunk drain. If sediment has accumulated in the perforated pipe, the sediment should be removed so the subdrain system continues to operate within the parameters established during the validation monitoring. It does not appear that sediment deposition or scouring is occurring in the catch basins and lagoon.

PCE and TCE concentrations continue to be highest in water samples from the southern and central portion of the trunk drain, with average concentrations of 26 ppb for PCE and 25 ppb for TCE. PCE and TCE concentrations from stations 361 (lagoon effluent) and 364 (treated water discharge to the Deschutes River) were below the remediation goals of 0.8 ug/L for PCE and 2.7 ug/L for TCE.

Link to EIM data for User Study ID PALERMO