SITE INFORMATION AND CORRESPONDENCE

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Mr. Robert Donovan • - 2 - 46 18 2 - 18 Apri12001 6. The Work Plan states `logging" (lithology) will not be conducted for boring locations within 50 feet of previous cone penetrometer profile locations. The Lettererably across the site." All borings states, "The depth to the per up and lower boundaries of the water-bearing zones varies considerably must be logged to provide additional information on the depths of the four water-bearing zones, to determine whether the B/C aquitard is continuous across the site, and to provide additional data points for cross-section diagrams. 7. The Work Plan does not include soil sampling frequency, methodology to choose soil samples for analyses, the soil sample analyses to be performed, or the number of soil samples to be submitted per boring. A minimum of one soil sample must be collected per monitoring well installation in the "smear zone" or capillary fringe and where observation or photoionization detector readings indicate potentini contamination. The soil samples must be submitted for the following analyses: EPA Analytical Maximum Detection Limit Constituent Method Total etroleum h drocarbons as diesel 8015 modified 50 Total etroleum h drocazbons as gasoline 8015 or 8260B 50 Benzene 8260B 0.5 Toluene 8260B 0.5 Eth Ibenzene 8260B 0.5 Total xylenes 8260B 0.5 Methyl tertiary but I ether 8260B 5.0 8. The Letter states in comment 5 that all contour lines on isoconcentration figures are not shown based on irregularities in concentration gradients, a decrease in concentration toward the interior of the site, the difficulty of fitting all lines on the map, and the fact that additional contour lines would obscure important site features. Many of the isoconcentration figures submitted show each order of magnitude contour line without obscuring site features and illustrating irregularities within the site. All isoconcentration maps must contour down to the lowest order of magnitude or non-detect. 9. The plumes are not defined north and northwest of CPT/HOO-05, TO/WC-1M, TOWC-lS, and PS/P-29, southwest of SP-4 and TS/M-1, and near CPT/HOO-16. The Letter suggests a deferment of additional groundwater monitoring wells citing data from a 1993 and a 1994 report, lack of analytical data from the deeper zones, and fieldwork proposed in the Work Plan. A deferment is granted until completion of the Work Plan and one additional groundwater monitoring event that includes samples from the deeper zones. Board staff will re-evaluate the four water-bearing zone plumes at that time. The Work Plan is hereby approved, provided these comments are incorporated into the fieldwork. By 29 June 2001, please provide an investigation report with results of fieldwork. The next quarterly