SITE INFORMATION AND CORRESPONDENCE_2006-2007

Home Browse Search

OARR ASSOCIATES Mr. Mark Adams March 30, 2006 Page 2 of 3 Sample Location Approx. Depth' Date(s) PCE Concen. in Total Haz (ft-bgs) g.w. (ug/L) Subst.' (approx. ug/L) CPT-014 79 5/14/97 29,000 31,000 CPT-040 75 9/3/97 27,000 30,700 CPT-100-65 65 11/8/96 25,000 26,200 CPT-100-75 75 11/8/96 9,100 10,460 CPT-241A-54 54 11/26/97 28,000 30,000 CPT-241A-66 66 11/26/97 13,000 14,000 CHMW-003A 48-68 1999-2005 6,000-15,000 6,400-15,400 MW-108A 40-60 1997-2005 4,000-5,800 4,100-5,900 As can be seen on this table, PCE concentrations observed in groundwater in the Eastern Hot Spot are of similar magnitude to those observed in the "Historical Source Area." Over time, the high VOC concentrations in the Eastern Hot Spot have diffused into the large volume of silts and clays present in the A-Zone sediments. These fine-grained sediments provide for long-term sequestered storage of VOCs, making remediation more difficult. Simply relying on the existing groundwater pump-and-treat system to remediate these highly-contaminated fine-grained sediments is likely to be insufficient. For these reasons, remedial action alternatives must be evaluated for groundwater in the Eastern Hot Spot, as well as the "Historical Source Area." Much time has passed since LFR's original Draft Feasibility Study was produced May 5, 2000. Significant advancements have occurred in remediation technology over the past six years, and more emphasis has been placed on remediation to mitigate vapor migration and the potential for inhalation exposure. It is important to address these issues when updating and revising the Draft Feasibility Study. In addition, the time frames required to complete site remediation under various remedial alternatives need to be estimated and given due consideration when comparing the effectiveness of remedial alternatives. This was one of the important comments Farr 'CPT sample depth or screened-depth interval for monitoring wells, in feet below ground surface (ft-bgs) 'One-half the reporting limit used to estimate the concentration of"non-detect" hazardous substances.