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July 20, 2001 <br /> 2001-0103-01 <br /> Page 6 of 7 <br /> • ® Based upon analytical results obtained from the confirmation boring (B-17), <br /> concentrations of fuel hydrocarbons in soil have been reduced substantially in the <br /> central portion of the site (TPHG concentrations are now less than 10 mg/kg; <br /> benzene, fuel oxygenates, and fuel additive concentrations are below RDL). These <br /> reductions are a result of excavation, SVE, AS, and natural biodegradation. <br /> Based upon analytical results obtained from the confirmation boring (B-17), more <br /> soluble and mobile high-risk compounds such as benzene and MTBE were not <br /> detected in soil samples collected from the saturated zone (85 and 95 feet bgs) near <br /> historic low first encountered groundwater depths (106 feet bgs in 1979). Typically <br /> considered less soluble and less mobile, TPHG was detected in soil samples collected <br /> beneath groundwater at very low concentrations ranging from 1.0 to 2.1 mg/kg. <br /> Q Residual TPHG in soil has been estimated based on data from confirmation borehole <br /> B-17. The remaining mass of TPHG in soil, using very conservative values, is less <br /> than 50 pounds. <br /> • Dissolved hydrocarbon concentrations have declined significantly over time. <br /> Samples from only two monitoring wells (MW-13 and MW-14) contained detectable <br /> concentrations of TPHG. Benzene was only detected in the sample collected from <br /> monitoring well MW-13. <br /> . o Soil generated from the removal of UST's has been removed from the site and <br /> bioremediated. <br /> • Natural attenuation processes such as adsorption, dispersion, and bioremediation are <br /> likely to continue given the documented low mass and residual concentrations at the <br /> subject site, further reducing risk in a cost effective manner. <br /> Based on the above mentioned results, Stratus is requesting site closure on behalf of A. <br /> Teichert and Son, Inc. <br /> Please call me at (530) 676-6000 if you have questions regarding the activities performed <br /> at this site or the data presented in this report. <br /> Sincerely, <br /> STRATUS ENVIRONMENTAL, INC <br /> 5 � <br /> Scott Bittinger 4a . n, R.G. <br /> Staff Geologist ger <br /> • <br /> Urontlproject file\Teichert\Stockton-1031Reports\Teichert Stockton Closure Report 0701.doc <br />