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City of Stockton A68101.02F <br /> July 24, 1947 Page 13 <br /> ' Based on data collected during this and previous investigations, the lateral extent of PPC <br /> migration in soil appears to extend in an asymmetrical pattern along a roughly north=south <br /> axis from the vicinity of SB-4 to SB-7. This pattern would suggest that the direction of PPC <br /> migration has been influenced by groundwater flow. Drawing 5 shows the approximate <br /> lateral extent of soil impacted by PPCs. <br /> 6.2 Groundwater Characterization: The analytical results of groundwater samples <br /> collected from the soil probe holes suggest that groundwater has been extensively impacted <br /> by PPCs. The concentrations detected in the samples collected from soil probe locations <br /> SB-4, SB-5, and SB-7 suggest that free gasoline and/or diesel product exist on the <br /> groundwater surface in these locations. Previous work had detected PPCs in groundwater <br /> samples collected from MW-3 but had not detected PPCs in groundwater samples collected <br /> from MW-1 or MW-2. <br /> ' Groundwater monitoring well MW-3 has been compromised by the removal of the wellhead <br /> protective cover. The repair or abandonment of this well should be performed to prevent <br /> it from becoming a conduit for the movement of surface contamination to groundwater. <br /> The direction of groundwater flow has consistently been calculated to the north. The <br /> present configuration of the groundwater monitoring wells is not adequate to detect the <br /> presence of a plume of contamination to the north. Therefore, the lateral extent of PPC <br /> migration in groundwater is unknown. <br /> 7.0 CONCLUSIONS <br /> • The lateral extent of PPC migration in soil appears to extend in an asymmetrical <br /> pattern along a roughly north-south axis extending between soil probe locations SB-4 <br /> and SB-7; <br /> • PPC impacted soil was identified in soil below the groundwater table, as encountered <br /> ' during our field investigation, and this soil provides a continuous source of PPCs to <br /> groundwater; <br /> • Groundwater beneath the site appears to be significantly contaminated with PPCs. <br /> High PPC concentrations in groundwater samples suggest that free product is present <br /> on the groundwater surface at soil probe locations SB-4, SB-5, and SB-7; and <br /> ' • The current configuration of the groundwater monitoring wells is not adequate to <br /> delimit the lateral extent of PPC contamination in groundwater. <br /> i <br />