ARCHIVED REPORTS_FIELD NOTES AND PERMITS THROUGH 4_4_1997

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tevineoFficke-Recon ENGINEERS,HVDROGEOLOGISTS 8 APPLIED SCIENTISTS depth of 76.5 feet bgs); however, note that well MW-100 was continuously sampled whereas soil samples from MW-11 were collected at 5-foot intervals. Additionally, well MW-100 was terminated at approximately 62 feet below ground surface (bgs), because of refusal of the sampler at a dense, hard clay unit and our concerns about the potential of screening a well across the underlying A/B aquitard. However, subsequent evaluation of the boring logs and the site geologic setting suggested that the hard clay unit was not the anticipated A/B aquitard. Consequently, wells MW-11 and MW-100 do not appear to completely screen the A -zone aquifer. As you know, a fully penetrating pumping well is generally preferred for performing and analyzing aquifer test data. In addition, the recent data collected from the MW-I I and MW-100 area indicated that the subsurface stratigraphy along the proposed alignment of the IRA extraction system could be variable, and as a result it was thought that the aquifer test as originally proposed may not have been representative of conditions throughout the system alignment. (Final recommendations for the aquifer testing program will be included as part of an interim data deliverable forthcoming in January 1997.) Therefore, before constructing any additional wells or conducting the aquifer test, we determined that it would be prudent to further explore the nature of the A-zone aquifer using CPT and PIPP sampling. A CPT boring (CPT-100) and PIPP sampler were driven on November 8, 1996 at a location adjacent to well MW-100. The data collected from CPT-100 indicate that, in this area of LC, the top of the A/B aquitard is present at approximately 75 feet bgs, and that a sand with a high estimated permeability is present at approximately 70 to 75 feet bgs. Based on these data, a fully penetrating A-zone well (MW-101) was installed on November 14, 1996, at a location equidistant from wells MW-11 and MW-100 (see Figure 1), to a final depth of approximately 75 feet bgs. Additional CPT/PIPP Sampling Because of the variable A-zone stratigraphy recorded at MW-100, MW-101, and CPT-100, additional CPT and PIPP sampling has been initiated along the proposed alignment of IRA extraction wells along the downgradient property boundary of LC, adjacent to Pacific Avenue. The purpose of the sampling is to further characterize subsurface stratigraphy and volatile organic compound (VOC) distribution across the downgradient property boundary in order to properly design the proposed aquifer test and the Phase I IRA extraction system. Of the 18 CPT/PIPP locations proposed along the downgradient boundary, 10 have been completed. The remaining eight CPT/PIPP locations will be completed after the conclusion of access negotiations with the various property owners and tenants. The remaining locations include three points at the Chevron station at the corner of Pacific Avenue and Benjamin Holt Drive, three points on the Payless RWQBSCH.LTR:SRL 2