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l - " V �� 1117 Lone Palm Avenue, Suite B _ Modesto, CA 95351 www.atcassociates.com 209-579-2^ " ' ASS OCIATES I N C . Fax 209-579-t Environmental, Geotechnical and Materials Engineers indicates A-MW2 is generally screened in similar sediments. Cross-section A-A' (Figure 5) depicts subsurface lithology and screened intervals of MW11R and A-MW2 based on logs of these wells. Copies of well logs and CPT logs used to generate cross-sections (Figures 5 through 9) are included in Attachment 1 . According to Stratus' s Quarterly Groundwater Monitoring Report, Fourth Quarter 2005, for Former Apache Plastics Facility Located at 2050 East Fremont Street, Stockton, California, toluene was detected in the groundwater sample collected from A-MW2 on November 22, 2005 , at a concentration of 3 .2 micrograms per liter (µg/L). Historical data generated by Stratus indicate petroleum hydrocarbon constituents are typically not detected above laboratory reported detection limits in groundwater samples collected from this well . Incorporating A-MW2 into the quarterly monitoring program for the subject site should provide better groundwater plume definition off-site towards the south. In order to further evaluate the lateral extent of the shallow groundwater plume, ATC proposes to pursue access to selected existing off-site wells associated with the former Apache Plastic—sRacility. – 'I Cooperative efforts from ATC, the former Apache Plastics facility owner, and the environmental consultant for the former Apache Plastics facility (Stratus Environmental, Inc.) should result in improved understanding of subsurface conditions for both sites and reduce redundant expenses and investigation efforts. Existing groundwater monitoring wells associated with the former Apache Plastics facility are screened in similar depth intervals as the wells associated with the subject site, and j are well positioned to help define the extent of groundwater contamination. According to Stratus ' quarterly groundwater monitoring report for the second quarter of 2005 , the shallow groundwater flow direction has consistently been toward the east and southeast except for the first quarter of 2005, when the reported flow direction was toward the east, northeast. Apache Plastics facility well MW2 (designated as A-MW2 on Figure 3) can provide groundwater quality data southeast of the subject site. INTERMEDIATE GROUNDWATER ZONE The lateral extent of petroleum impacted groundwater in the intermediate zone is not well defined. Monitoring wells MW4 and MW12 are slightly impacted, and MW5 and MW6 are the most impacted. MW6 is located in the southern portion of the site . Historical water level measurements collected from these wells indicate a southerly groundwater flow direction. However, an anomaly is suggested by the most recent water level measurements collected from these wells on December 7 2006 which_ indicates a northerly groundwater flow direction. The proximity of MW6 to the southern property boundary of the subject site dictates the need for off-site data to assist in plume definition to the south. The nearest off-site groundwater monitoring wells that are potentially screened in the intermediate groundwater zone are A-MW8, A-MW9, and A-MW11 . A-MW8 and A-MW9 are located across East Fremont Street approximately 85 feet southeast and approximately 70 feet south of the subject site, respectively. A-MW 11 is located in the right-of-way at the southwestem corner of the subject site. The intermediate zone wells associated with the subject site (MW4, MW5, MW6, and MW12) are screened l s:\Environmental\28349\comparative study.doc 4 ATC Associates Inc,