State of Oregon              

Department of Environmental Quality  Memorandum

I have reviewed the information provided by Alpine Environmental Consultants on May 2, 2024 regarding contamination detections at this site in 2023. The purpose of this review was to try and determine if contamination found in 2023 was from releases prior to 1989, and not from releases that could have occurred from the operating service station during the 35 year time span since the site was given a No Further Action on January 23, 1989, and determine if further action is needed at this site. In the 1989 DEQ NFA letter, it states that “…if new information comes to light the DEQ may require further investigation.” This language has always been included in our NFA determinations.

Some of the test methods for petroleum hydrocarbons during the 1988 and 1989 sampling are different than what have been standard practice for the past couple of decades. Particularly, TPH fraction testing (TPH-G, TPH-D, and TPH-O) was not available during the old investigations. Rather, in 1988 an oil and grease test was done to give a total TPH. Because of this, it is difficult to compare newer data with the old.

Some of the recent chemical analytical results exceed current DEQ risk based concentrations (RBCs), particularly for the vapor intrusion pathway. For example, the pit water sample collected in February 2023 contained TPH-G at a concentration of 2,110 micrograms per liter (ug/L). This concentration is about four times the current vapor intrusion RBC for groundwater for commercial use sites, which is 520 ug/L. TPH-D was detected in this sample at 11,800 ug/L, exceeding DEQ’s RBC (1,700 ug/L) by a factor of about seven. Ethylbenzene, a gasoline constituent, was also detected in the 2023 groundwater sample at a concentration that exceeds the commercial vapor intrusion RBC. BTEX compounds were tested for in 1988 in groundwater, and concentrations of BTEX constituents were much higher then. For example, ethylbenzene was detected at 4,800 ug/L in one test pit sample in 1988. In the 1980s vapor intrusion had not been identified as a pathway of potential concern at cleanup sites. The VI pathway did not become part of investigations and site screening until the mid-2000s.

Some of the site data could point to an older release, particularly the lack of elevated benzene and toluene concentrations. With the TPH-G and TPH-D range data, comparing with historic oil and grease sample results is not possible.

Given the uncertainty with the comparison of the old and newer data, DEQ cannot conclude that the contamination detected in 2023 was from the 35 year old initial release. Some of the concentrations of contaminants currently at the site exceed DEQ RBCs for vapor intrusion.

The site reportedly uses well water for its water supply. The well is located very near the former UST facilities. Well testing has been done, but some of the sampling has been done incorrectly, and samples have been out of temperature and/or out of hold time. While there are no known impacts to the site water supply well at this time, DEQ is concerned that residual contamination associated with the former UST system could threaten this well. City water ___________

This site is located in downtown Shady Cove. The current zoning is ___________. This zoning allows XYZ uses. The service station has closed and the USTs decommissioned.