ARCHIVED REPORTS XR0007821 - Laserfiche WebLink

Home Browse Search

Appendix A - Site Background Information Former Stockton Plating Facility Page 3 of 7 former UST TK1-90 area, the benzene concentration detected on 28 January 2002 was 2 1 µg/1 compared to the initial value of 7,000 µg/1 detected on 11 December 1998 • The lateral extent of hydrocarbon-impacted ground water has been assessed down-gradient and cross-gradient of the former UST area (Figure 2) FEASIBILITY TESTING OF ON-SITE GROUND WATER EXTRACTION In a document titled Corrective Action Plan - November 1995, dated 15 November 1995, AGE recommended Implementation of soil vapor extraction in conjunction with in-situ air sparging for remediation of the petroleum hydrocarbon-impacted soil and ground water at the site At the time the CAP was prepared, ground water extraction was generally not viewed as an effective and cost efficient method of ground water remediation,but this method has gained more favor recently as a method to address impacted ground water when other technologies (e g , air-sparging) may not be controllable or effective, due in part to reduced extracted water treatment and disposal costs • Since the approval of the CAP in December 1995,the local and regional ground water elevation has risen significantly(20 feet)and has maintained a depth-to-water of approximately 25 feet bsg AGE believes that the sustained increase of ground water elevation has significantly decreased the potential effectiveness of the proposed SVE/IAS method as a stand alone treatment for impacted soil and ground water, due to a reduction in thickness of the impacted vadose zone and an increase in thickness,and volume,of impacted soil(and ground water)in the saturated zone The impacted soil is primarily fine grained, which may make the upward and lateral path of sparged air through the saturated zone unpredictable and stripped hydrocarbons unrecoverable The vertical extent of hydrocarbon-impacted soil had not been fully assessed when the CAP was developed The mass of adsorbed hydrocarbons now known to be within the saturated zone is significant Recent evaluation of soil and ground water below 50 feet bsg has documented significant concentrations of dissolved and adsorbed hydrocarbons that must be satisfactory mitigated to achieve site closure At the present time,dissolved hydrocarbon concentrations are known to extend to 80 feet bsg,where low concentrations suggest that 80 feet bsg is close to the dissolved plume's vertical extent The anticipated limited overall effectiveness and reliability of IAS technology to remediate the impacted soil and ground water require a re-evaluation of this proposed method AGE conducted a ground water extraction pumping test on 18 October 2001 Analysis of the ground water extraction data indicted that ex-situ ground water treatment was feasible The radius of influence generated by a pumping rate of five gallons per minute was interpreted to be adequate to Advanced GeoEnvironmental,Inc