SITE INFORMATION AND CORRESPONDENCE FILE 1

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CLEARWATERA11- 1 1 1995 G R o u P, t N C. ENVIRONMENTAL LTH VICES Page 3, paragraph 2 and paragraph 4 - "With regard to vapor testing and oxygen concentration ... one would assume that the concentrations of oxygen would be lowered because there was no flow through and possibly as a result of limited biological activity. PHS/EHD questions that the measurements collected would actually hinder the ability to test the feasibility of vapor extraction as a remedial alternative." and "It is unclear how the stagnant conditions of the wells will significantly affect the application of a vacuum to such an extent which would support the rational[e] to extend the vapor extraction testing for five days." As reported in Clearwater's letter dated May 16, measured concentrations of oxygen were significantly greater in wells outside of the contaminant plume than those observed in wells within the impacted area. This relationship between oxygen concentration and contaminant occurrence is not uncommon, and has been documented at other similar sites. Depleted oxygen in the contaminated zone is likely associated with biological activity in the vicinity of hydrocarbon compounds in the subsurface. As indicated in previously submitted correspondence, low oxygen concentrations prevent effective combustion in IC engines and thermal oxidizers. Based on these facts, Clearwater anticipates that the completion of a vapor extraction test as originally planned (two tests of three hours each) will not result in sufficient subsurface oxygen exchange to permit optimal IC engine performance. This will, in turn, require the introduction of atmospheric oxygen to the system through a bleed valve prior to the combustion chamber, thereby limiting the amount of vacuum the engine will be capable of providing. While a vapor extraction test is still possible under these conditions, the performance of the testing equipment during the pilot evaluation will be significantly different than the performance of equipment operating for longer term site remediation. Clearwater has recommended consideration of a longer pilot test in order to provide site information that will more accurately represent full scale remedial conditions, allowing for more effective system design and efficient site remediation. It is difficult to predict the time period required for subsurface oxygenation and consequent optimal pilot test performance. An additional four days of testing is recommended, although it should be noted that this testing time frame will be reduced in the event that field measurements indicate rapid air exchange and the achievement of effective testing conditions.