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5 July 20, 2001 2001-0103-01 Page 5 of 7 • estimated at less than 50 pounds (Stratus Confirmation Soil Boring and Site Closure Report dated November 1, 1999). Following remediation, the extent of hydrocarbons remaining in groundwater has declined significantly at the subject site. Concentrations of TPHG and benzene in groundwater samples collected from monitoring well MW-13 have been reduced from 32,000 and 920 pg/L to 5,100 and 55 µLg/L, respectively following remediation. Concentrations of TPHG and benzene in samples collected from monitoring well MW-14 have been reduced from 17,000 and 3,100 µg/l, to 1,100 µg/L and below RDL, respectively following remediation. Concentrations of TPHG and benzene in monitoring well MW-11 have been reduced to below laboratory RDL's. (Stratus Confirmation Soil Boring and Site Closure Report dated November 1, 1999). Historical tabular summaries of soil and groundwater data are presented in Tables 2 and 3, respectively. Fate and Transport ModelinjZ No automated computerized risk assessment modeling was performed. Actual site data from pre- and post-treatment soil and groundwater sampling and analyses was employed to define plume limits, attenuation and control. Recommendations Based on the data presented in this report, as well as supporting data in previous reports submitted by others, it is Stratus's opinion that further environmental investigation and remedial action is not warranted and site closure should be granted. In order to obtain a no further action status and final closure, Stratus also recommends that the remaining on- site wells be properly destroyed under permit by PHS/EHD. Closure Rationale Rationale to demonstrate that the conditions currently at the site will not adversely impact water quality, health, or other beneficial uses are as follows: ® The absence of water supply wells in close proximity to the subject site substantially reduces risks to drinking water supplies from this source (water related ingestion pathway is significantly reduced). ® Approximately 13,400 pounds of TPHG have been removed from the site by excavation and engineered remedial actions (dermal and inhalation pathway is substantially reduced). © All underground storage tanks (UST's) have been removed from the site, impacted soil immediately beneath the UST's has been removed and there is no known new source or potential for fuel hydrocarbon contamination. 11F'rontlproject file\Teichertl.Stockton-1031ReportslTeichert Stockton Closure Report 0701.doc