Publication Summary

The Palermo Wellfield subdrain system was monitored in November 2006 and June 2007. 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 that accumulated in subdrain cleanouts CO-3 through CO-8 was removed in 2006. 2007 data indicate that some sediment is still present in cleanouts CO-4, CO-5 and CO-8. Sediment deposition or scouring does not appear to be occurring in the catch basins and lagoon.

PCE (22 µg/L) and TCE (22 µg/L) 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 µg/L (PCE) and 2.7 µg/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.

The most recent monitoring was conducted in November 2006 and June 2007. Groundwater levels were three to five feet below 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 the subdrain cleanouts were close to the 2001 original depths. Total depths measured in CO-4, CO-5, and CO-8 indicate some sediment is present in these 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.

PCE and TCE concentrations continue to be highest in water samples from the southern and central portion of the perforated pipe, with average concentrations of 22 µg/L for PCE and 22 µg/L for TCE. PCE and TCE concentrations from station 364 (treated water discharge to the Deschutes River) were below the remediation goals of 0.8 µg/L for PCE and 2.7 µg/L for TCE.

Link to EIM data for User Study ID PALERMO