SITE INFORMATION AND CORRESPONDENCE 1993-1995

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Mr. Fernando Amador -2- 6 April 1995 Section 4.4.1, Conceptual Model of the Ground Water Flow, of the RDFS stated that on 2S August 1992, the Zone A ground water flow direction was southeast to southwest. A southwest flow direction would explain contamination southwest of the site. The source of the regional gradient should be cited. Based on a southeast gradient, monitoring well (MW) 16 is cross-gradient of the site (Area I) and not upgradient. 4. Section 3.2.4, Aquifer Test Design Appendix C stated that the purpose of the pumping test (in MW 19)was to evaluate hydraulic conditions of the underlying aquifers and to determine if ground water pumping and treating is a viable remedial alternative for the site. The memo did not explain why MW 19 was selected as the pumping well and whether or not pump-and-treat is a viable remedial alternative. 5. Section 3.3, Analytical Results The memo stated that a QA/QC review showed that most QA/QC parameters were within control limits. The memo should explain which parameters were outside the control limits and whether the results for these parameters are invalid since they are outside the control limits. The memo should also include measures taken or planned to meet data quality objectives in the future. 6. Section 3.3.1, Soil Analytical Results Table 3-9 does not include sample results for total petroleum hydrocarbons as diesel or gasoline (TPHd/g) for MWs 17 and 18 as stated in the memo. Isocentration maps of soil contamination in Zones A, B, and C should be included in the memo to clearly identify data gaps, if any. 7. Section 3.3.2, Hydropunch Sampling Results The memo stated that Hydropunch samples were taken from MWs 14-17 in Zones A and B, and that Zone C MWs 14-16 are upgradient and cross-gradient of the site, suggesting that there may be upgradient sources. The memo should explain why samples were not taken in M-1R and MWs 18 and 19 which are Zone A wells. Since the gradients at the site have not been fully established, it is premature to say which direction is upgradient or downgradient. Potential offsite sources should be identified to determine if they are contributing to the contamination onsite. 8. Section 3.3.3, Ground Water Analytical Results The memo stated that in Zone A, the PNA plume has not been defined in the downgradient direction. Figure 3-8, 3-9, and 3-10 show that the extent of PNA contamination has not been defined in all directions in Zones A, B, and C. Figures 3-16 and 3-17 show that the benzene contamination in Zones B and C have not been defined. Table 3-13 shows that MW 17 in Zone B and MWs 13 and 16 in Zone C were not tested for TPHd/g and BTEX. The memo should explain this inconsistency in the sampling program. In Figure 3-15, Benzene Isoconcentration Plot, Zone A, the notation next