ARCHIVED REPORTS XR0007812 - Laserfiche WebLink

Home Browse Search

. 31 January 2002 AGE-NC Project No 95-0128 Page 7of8 screened interval located within a silt (Appendix K) The geotechnical analysis of the soil at the site indicated a best permeability of 1X10-6 cm/s (Appendix J) • Laboratory analysis of exti acted water during the pumping test detected elevated concentrations of TPH-g, BTEK and MTBE (Appendix H) I 50. RECOMMENDATIONS In 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 tune the CAP was ' prepared, gi ound water extraction was genes ally not viewed as an effective and cost efficient method of ground water t ernediation, but has gained mor e favor i ecently as a-method to adds ess impacted gi ound water, due to i educed treatment and disposal costs, where air-sparging may not be controllable of effective ' Since the approval of the CAP in December 1995, the local and regional ground water elevation has risen significantly and has maintained an elevation at approximately 25 feet bsg AGE believes that 1 the sustained increase ofground water elevation has significantly decreased the potential effectiveness ' of the proposed SVE/IAS as a stand alone treatment for impacted soil and ground water due to a = reduction of the thickness of the impacted vadose zone and an increased thickness, and volume, of impacted soil (and gi ound water) in the saturated zone The impacted soil is primarily fine grained, ' which may make the upwai d and later al path of sparged an through the saturated zone unpredictable r and stripped hydrocarbons unrecoverable ' The vertical extent of hydi ocarbon-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 ' concenti ations of dissolved and adsorbed hydi ocaibons that must be satisfactory mitigated to achieve site closure At this time, dissolved hydrocarbon concentrations are known to extend to 80 feet bsg, where low concentrations suggest that 80 feet bsg is close to the adsorbed plume margin The ' anticipated limited over all effectiveness and reliability of 1AS technology to remediate impacted soil, and ground water require a i e-evaluation of the proposed method to remediate ground water and ' reduce the hydrocarbon mass AGE recommends the use of ground water extraction as an alternative ground water remediation ' technique at the site Giound water extraction should provide adequate capture of the dissolved hydrocarbons based on site-specific hydrogeologic conditions and hydrocarbon distribution The limited areal distribution of high concentrations of dissolved hydrocarbons near the source of the release favors a high potential for capturing the major portion of the dissolved hydrocarbons on the site A ground water exti action system in the soul ce area and along the down-gradient portion of significantly impacted ground water should effectively address the plume of impacted ground water ' 4dvaneed GeoEnvironmental Inc