ARCHIVED REPORTS_XR0007998 - Laserfiche WebLink

Home Browse Search

Updated Site Conceptual Model and First Quarter 2002 Monitoring and Remediation Report Cleanup and Abatement Order No 5-00-707 EAI Project No 1232 2.0 SITE CONCEPTUAL MODEL UPDATE In a letter dated February 8, 2002, the RWQCB requested completion of an Updated SCM for this matter The initial SCM was submitted to the RWQCB in an EAI report titled "Supplemental Investigation Report, Problem Assessment Report, and Work Plan, Cleanup and Abatement Order No 5-00-707, Montgomery Ward Auto Service Center and Former Unocal Site, 5400 and 5606 Pacific Avenue, Stockton, California," dated October 13, 2000 This report incorporates additional soil and ground water information obtained after completion of the initial SCM ' Since completion of the initial SCM, 11 new wells (MW-81), MW-9, MW-18D, MW-23S, MW-23D, MW-24S, MW-24D, MW-25S, MW-25D, AS-26 and MW-27) have been installed at the site Appendix A contains the boring logs and well construction details for these new wells Tables 2 and 3 present the soil analytical testing results for the Wards and Unocal sites, respectively These soil samples were analyzed for TPH-G, benzene, toluene, ethylbenzene, and xylenes (BTEX), MTBE and lead Soil samples that were obtained and analyzed after January 2001 were analyzed for additional compounds not contained in Tables 2 or 3 ' Therefore, soil samples that were analyzed after January 2001 are presented in Table 4 Figure 3 presents the TPH-G and benzene concentrations detected in soil during installation of wells at the Wards and Unocal site Figure 4 graphically presents the well screen intervals for all wells associated with this matter and Table 5 presents a tabular summary of well construction data Site stratigraphy is segregated into four hydro-stratigraphic units that generally correspond to screened intervals on ground water monitoring wells The shallowest wells are screened in the hydro-stratigraphic unit designated as Unit A and the deepest wells are screened across hydro-stratigraphic Unit D (see Figure 4 and Table 5) The approximate ' depth intervals corresponding to the hydro-stratigraphic units are as follows H dro-Strati ra hic Unit Depth Interval feet 17 s A 30-50 B 50-70 C 85-90 D 98-103 Figures 5 and 6 present cross-sections A-A' and B-B' The cross-sections are drawri through the former Unocal and Wards sites, through the contaminant source areas, and parallel to the current ground water flow direction These cross-sections include r • The lithology encountered during the drilling of each boring, • The TPH-G and benzene concentrations detected in soil during installation of the ' ground water monitoring wells, BHM 1233RO2i1 -4- ENVIRONMENTAL AVDIT, INC