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While it could be argued that groundwater may flow along the trough to the northeast or southwest and therefore migrate TPH-G from the Human Services site to either MW-4 or MW-8, the data strongly suggests this is a low probability situation compared to other more likely scenanos This evaluation is supported by several observations A primary consideration is that the gradient into the trough is relatively strong which places MW-4 and MW-8 strongly downgradient from large portions of downtown Stockton in both northwest and southeast ' directions from the site Hence, offsite properties in these directions from the Human Services building are much more likely to create impacted groundwater at the wells than the former ' Human Services building tank site Secondly, monitor well MW-7 sits in the groundwater trough between the former tank site and MW-8 Monitoring of MW-7 dunng the past year has shown no presence of TPH-G If TPH-G was migrating from the tank site to MW-8, it would ' surely show in MW-7 As it does not, there is no evidence of a connection between the former tank site and the TPH-G found in MW-8 ' In summary, there is essentially no data to suggest the former Human Services Building tank site is related to the TPH-G findings in MW-4 and MW-8 There is, however, a very good potential that the wells are being affected from other unknown sources The implications of this situation ' is that there is very little to be gained by continued monitoring of the site by the Capital Project Division 5.0 RECOMMENDATIONS Because there appears to be no evidence of a connection between the former tank site at the ' Human Services Building property and the TPH-G concentrations currently found in MW-4 and MW-8, WESTON recommends terminating monitoring by the Capital Projects Division ' The only advantage to continued monitoring of MW-4 and MW-8 would be in support of investigations at other properties generally northwest or southeast of the Human Services Building or in support of a regional initiative for this portion of downtown Stockton In either ' case, such monitoring should not be the responsibility of the Capital Projects Division As the Environmental Health Division has wide information on investigation/remedial programs ongoing in the general vicinity of the Human Services Building, it is recommended that EHD review the ' data generated by this year's monitoring program in context with other sites or regional issues in downtown Stockton to ascertain if data from the two wells would assist other programs in the future I WX\RPTSSSJC 4TH WP 8 0X04!94