SITE INFORMATION AND CORRESPONDENCE_1998-2000

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Wendy Cohen • - 3 - 6 October 1999 log relative to the surface features. Additionally,LFR did not post the friction logs consistently in the same direction on each cross section(i.e., some are posted facing left,the others to the right). This introduces an additional error of up to 40 feet between CPT locations. Cross sections need to be redrawn in the Final RI Report using each boring location as the point of reference for the boring geology. 6. I reviewed the boring log for Boring MW-210B for consistency with Cross Section C-C' (I did not compare other boring logs to the respective cross sections). There are four units of sand shown in the upper 70 feet of Boring MW-210B on the cross section that are not on the boring log. Although LFR logged the upper 70 feet of the boring by drill cuttings, it is unlikely the five-foot section of sand shown on the cross section from 20 to 25 feet below the ground surface would have been missed during drilling operations. Additionally, the lower 68 feet of the boring log does not match the cross section. LFR collected continuous core soil samples for 64 of the lower 68 feet of Boring MW-210B. The geologic cross sections need to be consistent with data presented on the soil boring logs. Friction and other downhole geophysical logs are relative measurements that may or may not be indicative of subsurface grain-size distribution. Friction data collected from CPT borings should be used to correlate geology in areas where soil samples are not available,not for subsurface interpretation in areas where actual soil data are available. Soil data shall be used where available along the cross sections (e.g., the borings for monitoring wells MW-200B, PZ-001A,PZ-002A, PZ-003A,PZ-004A, and PZ-010A-2 should have been used for Cross Section A-A'). Cross sections need to be revised using soil boring logs as the standard reference. 7. LFR did not consider ground surface elevation in the preparation of the cross sections. Elevation differences across the site should not vary greatly,but it is not noted on the cross sections. Elevation data should be checked for the boring locations or benchmarks (may include monitoring well elevation data) in the immediate vicinity of the boring locations, if available. If there is not a significant elevation difference on the cross sections,there should be a note on each stating such. If there is a significant elevation difference on any of the cross sections (i.e., greater than five feet of elevation change over 1,000 feet), then the cross sections in the Final RI Report need to be prepared to a mean sea level reference,not the depth below ground surface standard used in the Draft RI Report. 8. Sandy silt and silt are described as coarse-grained sediments on the geologic cross section figures. Sandy silt and silt are fine-grained sediments. 9. LFR obtained groundwater samples at some locations (e.g., CPT-111 as shown on Figure 23 and CPT-028 as shown on Figure 30) in a clay unit within five feet of a sand unit. It is not clear if LFR obtained these samples within the sand unit and they are mislabeled on the figures, or if LFR actually obtained them within the clay unit. If the samples are mislabeled, the figures need to be corrected in the Final RI Report. Otherwise, the Final RI Report needs to provide an explanation discussing the reasons for obtaining the samples within the clay unit instead of the sand unit. 10. There are several references in the Draft RI Report to the A-zone aquifer being partially or fully confined. There are no data to support this conclusion.