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I r <br /> ri K t� ;! �._, .,a.rr. .. f..s m -- �,i-- a-c._„-.� �-•.^�-'�I w <br /> � r <br /> t w <br /> I <br /> Site Backgroundr Information ,Former Stockton Plating Facility <br /> } u <br /> Page 3 of 7 <br /> I, r sio <br /> 2' 1 µg/1 compared to the initial value of 7,000 µg/1 detected on 11 December 1998 r n q x <br /> d� <br />' - The lateral extent of hydrocarbon-impacted ground water has been assessed down-gradient <br /> and cross-gradient of the former UST area(Figure 2) <br /> 41 4 <br /> ` ' Ir <br /> FEASIBILITY TESTING OF ON-SITE GROUND WATER EXTRACTION <br /> In a document titled Corrective Action Plan - November 1995, dated 15 November 1995, AGE I ' <br /> recommended implementation of soil vapor extraction in conjunction with in-situ air sparging for <br />' remediation of the petroleum hydrocarbon-impacted soil and ground water at the site At the time i <br /> the CAP was prepared, ground water extraction was generally not viewed as an effective and cost <br /> efficient method of ground water remediatiori,but this method has gained more favor recently as a <br /> method to address impacted ground water when other technologies (e g , air--spargmg) may not be <br /> controllable or effective, due in part to reduced extracted water treatment and disposal costs <br /> Since the approval of the CAP in December 1995,the local and regional ground water elevation has <br /> risen significantly(20 feet)and has maintained a depth-to-water of approximately 25 feet bsg AGE <br /> . believes that the sustained increase of ground water elevation has significantly decreased the <br /> potential effectiveness of the proposed SVEJAS method as a stand alone treatment for impacted soil , <br /> and ground water, due to a reduction in thickness of the impacted vadose zone and an increase in L <br /> thickness,and volume,lof impacted soil(and ground water)in the saturated zone The impacted soil , <br />' is primarily fine,grained, which may make the upward and lateral path of sparged air through the " <br /> saturated zone unpredictable and stripped hydrocarbons unrecoverable <br /> rThe vertical extent of hydrocarbon-impacted soil had not been fully assessed`when the CAP was <br /> developed The mass of adsorbed hydrocarbons now known to be within the saturated zone is I <br /> significant Recent evaluation of soil and ground water below 50 feet bsg has documented significant ; ' <br /> concentrations of dissolved and adsorbed hydrocarbons that must be satisfactory mitigated to achieve , <br /> site closure FI <br /> 1 I r <br /> n t At the present time,dissolved hydrocarbon concentrations are known to extend to 80 feet bsg,where <br /> low concentrations suggest that 80 feet bsg is close to the dissolved plume's vertical extent The ' <br /> anticipated limited overall effectiveness and reliability of IAS technology to remediate the impacted <br /> soil and ground water require a r'e-evaluation of this proposed method <br /> AGE conducted aground water extraction pumping test on 18 October 2001 Analysis of the ground <br /> ` water,extraction data indicted that ex-situ ground water treatment was feasible The radius of <br /> influence generated by a pumping rate of five gallons per minute was interpreted to be adequate to , <br /> control further off-site migration of contaminants toward the east, in the predominantly down- <br /> gradient direction I The results of the pumping tests were reported in the AGE-prepared Ground <br /> I _ Advanced GeolEnviranmental,Inc <br /> 1 5 = I <br /> J <br /> 5 ' <br /> 1� <br /> r I Y <br /> I <br />