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a✓ Name Mr.James Barton,RWQCB May 14,2008 Work Plan for Additional Site Assessment Former Dolly Madison Bakery,Stockton,California Page 3 An additional subsurface investigation was completed at the site in May 2000. Two cone penetrometer test (CPT) borings were advanced to depths of 120 feet bgs, with associated soil and groundwater sampling. Quarterly monitoring of groundwater was generally completed at wells MW-1 and MW-2 between March 1997 and May 2004. Depth to groundwater beneath the site ranged from approximately 18.5 to 25 feet bgs during this time. An additional well sampling event was completed in November 2005. Quarterly monitoring and sampling of groundwater was resumed in June 2007. A CAO was issued for the property on October 8, 2007. This document requested that the extent of impact to the subsurface be more fully assessed. Between December 2007 and March 2008, Stratus directed the completion of five shallow screened groundwater monitoring wells (MW-3 through MW-7), three "mid-depth" screened monitoring wells (MW-8, MW-9, and MW-14), four "deeply" screenedmoritoring wells (MW-10 through MW-13), and five soil gas monitoring wells (SGW-1 through SGW-5). Stratus also oversaw completion of two vapor extraction wells (VW-2 and VW-3) and an air sparge well (AS-1) at this time. Table 1 summarizes historical drilling and well construction information for the site assessment work completed at the property. Site Geology The geology beneath the site generally consists of interbedded intervals of fine grained soils (silt and clay mixtures) and sand, silty sand, and clayey sand soils to 120 feet bgs, the maximum depth explored beneath the site. The sand intervals identified appear to generally exhibit lateral continuity; however thicknesses of these sand intervals are variable and the sands were not observed at all boring locations. Interpreted geologic relationships are illustrated on cross sections A to A' (Figure 4) and B to B' (Figure 5). The surface trace of each cross section is depicted on Figure 2. Fine grained soils were predominately observed between surface grade and approximately 20 feet bgs. Sandy soils, approximately 4 to 12 feet in thickness, have been reported between approximately 19 and 37 feet bgs; the shallow groundwater monitoring well network are situated within these sandy strata. A separate sandy interval (predominately clayey sand), approximately 2 to 7 feet in thickness, was observed between approximately 40 and 48 feet bgs. A predominately clayey sand interval, generally 4 to 8 feet in thickness, was also noted between approximately 58 and 70 feet bgs; the mid-depth monitoring well network were screened at this depth interval. The deep monitoring well network were screened within sandy soils (approximately 4 to 12 feet in thickness) identified between approximately 75 and 90 feet bgs;this water bearing interval appears to extend continuously across the area surrounding the subject property, based on information obtained during K ATitnothy Kong Progertylwork Ptans\uono ma3,08workplan.doc