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Files - 2 - 10 August Water sampled from Trench 1 near the leaking gasoline lines on 8 July 1998 had analytical detections up to 16,000 gg/1 of tph-g, 4900 gg/L MtBE, and 690 gg/L benzene, as well as toluene, ethylbenzene, and toluene. Soil from this trench also had significant detections. This indicates a relatively fresh leak. Groundwater samples from other areas and ditch water samples had traces or no detections of the gasoline compounds. Ditch water samples taken on 8 July 1998 had detections up to 6800 gg/L tph-d and 62,OOOgg/L tph-mo, and ditch water samples taken on 3 July 1998 also contained tph-d and tph-mo, but at much lower concentrations. This suggests a fresh discharge occurred on 8 July and would be consistent with a source from the truck washing area. Soil from Trench 1 sampled on 8 July 1998 had detections of 10,000 mg/kg tph-d, 7800 mg/kg tph-mo and all of the gasoline components (tph-g, BTEX, and MtBE) but at generally slightly lower concentrations than the water. Soil from other trenches, including Trench 4 from near the leaking diesel dispenser, had traces to non-detection. The distribution of soil "hits" suggests that soil contamination may be limited in extent, but the "hits" on the west side of the gasoline tank raise a concern for an additional potential source aside from the truck wash area and the existing diesel tank. Apparently no groundwater samples were analyzed for tph-d or tph-mo. Probably because of the low detections in soil, no groundwater samples were taken from Trench 4 (near the diesel dispenser). It is not clear why groundwater from Trench 1 was not analyzed for diesel and motor oil range products when these constituents were reported in the soil. But on this basis, it is not established that tph-d and tph-mo are absent in the groundwater. I am concerned about the relatively small number of groundwater samples, the lack of groundwater analyses for tph-d and tph-mo, the incomplete understanding of the groundwater hydrology, and the detections of all the COCs in both the groundwater and the soil near the gasoline tank. GROUNDWATER CONDITIONS AND SITE CONCEPTUAL MODEL: The work plan contains apparently inconsistent statements regarding groundwater depth and behavior. Groundwater is first described(pgs 2 and 4) as approximately 5 feet below ground surface (bgs), implying unconfined conditions, but later(page 6) it is described as encountered at 8 feet bgs and rising under pressure to approximately 5 feet bgs, implying semi-confined to confined conditions. Both statements are based on observations during the summer of 1998. During a telephone conversation in mid-July 1999, AGE staff confirmed that groundwater was encountered at 8 feet, below the base of a peaty layer, and flowed into excavations that were left open, rising to a static level of about 5 feet. During the same telephone conversation, AGE staff agreed that one goal of the proposed monitoring wells should be to obtain basic hydrogeologic data. Existing information is based upon site assessment performed during the summer of 1998. Based on the above, my understanding of the site is that peaty soil overlies a granular, low transmissivity clay or silty clay that acts as a semi-confining layer, and that the peat is not normally saturated on a year-round basis (if at all). The peaty layer comprises most of the first 5 feet depth of the on-site soil.