SITE INFORMATION AND CORRESPONDENCE

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Mr. Jim Lancaster - 2 - 11 September 2000 SOIL AND GROUNDWATER ANALYSES EPA Method Analytes 8015M Total petroleum hydrocarbons as diesel and gasoline (TPHd and TPHg, respectively) 8020 Benzene, toluene, ethylbenzene, and xylenes (collectively BTEX) 8260 Methyl tertiary butyl ether (MTBE), di -isopropyl ether (DIPE), tertiary butyl alcohol (TBA), tertiary amyl butyl ether (TAME), ethyl tertiary butyl ether (ETBE), methanol, ethanol, 1,2 dichloroethane (1,2 DCA), and 1,2 dibromoethane (1,2 EDB). The Work Plan also summarizes the well abandonment procedures. GZA will abandon MW -1 by pumping neat cement grout under pressure into the casing via a tremie pipe. GZA will also remove the surface completion box and backfill.it with cement. I have the following comments on the Work Plan: GZA needs to review the regional and local hydrogeologic information including local domestic and municipal well logs to determine: (1) Where the lower water -bearing zones are likely to be encountered; (2) The likely groundwater flow direction; and (3) The presence (or lack thereof) of a confining layer between the upper and lower water -bearing zones. 2. The location of the boring is proposed between MW -8, where free product is present, and MW -3 and MW -6, where elevated contaminant concentrations are found. Although the Work Plan states that GZA does not anticipate intersecting free product, I am concerned that free product will be encountered. Therefore, the boring should be relocated to minimize the risk of encountering free product. I am also concerned that contamination from the shallow water -bearing zone may be carried down to the deep aquifer. Dual casing should be used to isolate the shallow aquifer, minimizing the potential of cross contamination. 4. The Work Plan states that the boring will be "closely downgradient of the source area," but does not provide any information on the groundwater flow direction in the lower aquifer. Unless background information is available, the actual flow direction in the lower aquifer is unknown and one boring will be insufficient to determine the vertical extent of contamination. If contamination is found, Woolsey will need to install two additional monitoring wells to determine the flow direction of the lower aquifer, identify which deep well is downgradient of the source area, and determine the vertical extent of contamination. 5. Woolsey should collect and analyze soil samples using EPA Method 5035 for volatile compounds, including total petroleum hydrocarbons as gasoline, benzene, toluene, ethylbenzene, xylenes, and fuel oxygenates. Also, a minimum of three soil samples [one sample from each groundwater interface and one sample from the confming layer (if one exists)] needs to be collected from the boring.