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Stallworth Auto Detail . 3 - April 2012 <br /> Site History/Assessments <br /> In May 1991 , soil contamination was identified during the removal of USTs. To date , 14 <br /> monitoring wells have been installed and monitored regularly. A Site map showing the location <br /> of the former USTs , monitoring wells and groundwater level contours is provided at the end of <br /> this five year summary . <br /> Remediation Summary <br /> • Free Product: No free product was documented throughout the life of this case . <br /> • Soil Excavation : Unknown . <br /> • In-Situ Soil Remediation : Soil vapor extraction , conducted from September 2010 <br /> through present removed approximately 10 , 201 pounds of TPHg . In October 2011 , the <br /> rate of removal was 1 . 3 pounds of TPHg/day. <br /> Groundwater Remediation : In-situ chemical oxidation proposed . <br /> General Site Conditions <br /> • Geology and Hydrogeology: The Site is underlain by interbedded and intermixed sand , <br /> silt and clay. The depth to groundwater varies between 26 and 28 feet bgs and the <br /> groundwater gradient is northeast to east at approximately 0 . 005 ft/ft. <br /> • Groundwater Trends: There are more than 11 years of groundwater monitoring data for <br /> this Site. Benzene trends are shown below, source area (MW-8) , near down gradient <br /> (MW-7 and MW-11 ) and far down gradient (MW- 10) <br /> Benzene Trend for MW-B <br /> 2so00 <br /> 20000 - -- -- <br /> • <br /> 15000 --- <br /> w 10000 - -- — <br /> • <br /> m <br /> 5000 --- <br /> o -- - - - -- <br /> 0 0 o S o 0 0 0 <br /> Benzene Trend for MW- 7 <br /> 4000 - —.— . - - - ---- <br /> 3500 -._ . -- <br /> 3000 — - - <br /> 2500 <br /> 2000 _ _ ..— <br /> 1500 <br /> m" loon - <br /> 500 <br />