SITE INFORMATION AND CORRESPONDENCE

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Mr. Mike Lecision - 2 - 1_� 12 April 2002 the next quarterly monitoring report, DWG must include a discussion of these pollutants, including their origin and the effect they have on the subsurface transport of hexavalent chromium. 4. The QMR includes a provision for future work that includes sampling the onsite facility well designated FW. Please also provide the construction details for FW that we requested in our 18 October 2001 letter. The well detail information is necessary to determine if it is appropriate to continue to include FW in the monitoring well network that is used to establish groundwater gradient. Groundwater from FW shall also be analyzed for sodium, calcium, and chloride. 5. The SI says, "Due to the high density of the soil encountered at the site the number of samples collected was less than originally estimated. Soil samples were collected at five-foot intervals to depths of 21 to 25 feet bgs and then at 40 feet bgs." The SI goes on to report soil samples for about 20 feet below ground surface and about 40 feet bgs,but contains no results for the samples"collected at five-foot intervals to a depth of 21 to 25 feet bgs." The intent of the investigation was to delineate the soil and groundwater pollution. DWG must explain why high density soil prevented the collection of a sample, why this occurred everywhere on-site, and why this was not anticipated from historical records. Neither DWG nor its consultant ATC states that the soil pollution is fully defined. The Soil Analytical Results section of the SI says, "The highest concentrations of chromium VI were detected in the samples from off-site boring SB9 at 1.5 and 2.6 milligrams per kilogram (mg/kg) . . . Chromium VI was not detected in the soil sample from SB8 at 40 feet bgs above method detection limits." DWG reported various levels of hexavalent chromium concentrations in all other soil samples. The SI contains no evaluation of the soil pollution. We interpret the data contained in the SI to mean that hexavalent chromium pollution extends from the surface down to about 40 feet bgs in most of the areas investigated. 6. The SI reports that grab groundwater samples were collected from depths of 56 to 60 feet bgs at each of the boring locations. Unfortunately, the SI contains no evaluation of the groundwater analytical results. Generally it makes no sense that groundwater would contain 6,600µg/1 in MW-3 and less than 100 feet away in the downgradient direction contain 5.1 µg/1. Sampling and analysis errors may have occurred or there may be localized chemical reactions, but there also maybe a significant vertical gradient drawing the pollution into the deeper groundwater DWG must submit field notes and a report from the analytical laboratory that describes how the groundwater samples were handled. DWG must also discuss the SI results and any correlation between the pollutant concentrations in the grab groundwater samples and the concentrations found in the wells. DWG must also determine the vertical extent of the pollution. 7. The SI cites the Total Threshold Limit Concentration(TTLC) for hexavalent chromium at 500 mg/kg,but does not say why it is relevant. Generally, the TTLC is used to classify a