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WENDY L. COHEN -2- 10 April 1995 gradient. One well will be selected for further gradient testing to determine whether the water table is influenced by tidal impacts on the nearby Middle River. Water levels in the test well will be monitored every 15 minutes for a 24-hour period. Both the soil and ground water samples will be analyzed for total purgeable petroleum hydrocarbons (TPPM, total extractable hydrocarbons(TEPH), and benzene, toluene, ethylbenzene, and xylene (BTEX)by standard methods. My comments on the work plan are outlined below. COMMENTS ON WORK PLAN Soil The soil boring and sampling program on page 4-3 of the work plan does not clearly state whether all borings will be cored or only those which are selected for well installation, nor does the plan state whether coring will be continuous or at intervals (i.e., every five feet). Coring should be continuous unless otherwise justified. The program also does not explain the criteria for sample selection, other than that the samples will be collected at intervals"no greater than five feet." Above the water table, samples with the highest PID readings in each sampling interval should be selected for laboratory analysis. Below the water table, a screening method should be selected which is effective on wet cores. Coring and sampling should continue to at least 15 feet below the water table to determine lithology, regardless of screening results, and beyond 15 feet below the water table if the results of screening show hydrocarbons. The work plan does not adequately demonstrate that diethylene glycol, triethylene glycol, and tetraethylene glycol, which have been previously detected in the reboiler unit condensate, do not break down into compounds for which there are water quality objectives (i.e., ethylene glycol). Therefore, the soil samples proximate to the reboiler unit should be tested for glycol compounds using high performance liquid chromatography (HPLC). Additional borings are needed northwest and northeast of the reboiler area toward the site boundaries for lateral representation of the extent of hydrocarbons in the soil. Ground Water Since the lateral extent of hydrocarbons in the soil is not likely to be the same as in the ground water, well locations should be selected based on gradient information, as well as soil analysis results. Water levels should therefore be measured, and gradient information updated, as each well is installed, so that the information may be used in selecting the location for the next well. Additional wells are needed in the central part of the site, within approximately 50 feet of the reboiler unit, to gather ground water contamination level data for interim remedial design purposes. As requested in our 5 December 1994 letter and accompanying memorandum, ground water samples should be analyzed for glycol compounds using HPLC, and for semi-volatile organic compounds by standard methods. 7DM:jdmAsb