SITE INFORMATION AND CORRESPONDENCE

Home Browse Search

Pilkington Libbey Owens Ford Standby Generator Diesel Supply Line May 31,2000 Page 3 4. "The report proposes to monitor MW 3 and RW 1 for natural attenuation (NA) parameters. In addition to these wells,the NA monitoring program also should include MW 2,RW 2,and RW 6 because they are boundary wells." To establish the efficacy of natural attenuation at a site it is beneficial to monitor three monitor wells in the direction of groundwater flow. Preferably one well will be up-gradient of the contaminant plume (uncontaminated), one will be in the middle of the dissolved contaminant plume(contaminated), and one well will be down-gradient of the dissolved contaminant plume (uncontaminated). MW-3 and RW-I satisfy the first two of these three criteria (up-gradient and mid-plume). There are, however, no down-gradient uncontaminated wells at the site. According to Protocol for Monitoring Intrinsic Bioremediation in Groundwater, Chevron Research and Technology Company,Health,Environment, and Safety Group, March 1995, "monitoring wells containing free product are not routinely sampled for dissolved contaminants and should not be included in the evaluation of intrinsic bioremediation." Sampling of RW-2 for natural attenuation parameters,therefore, is not useful. MW-2 and RW-6 are best described as cross- gradient with respect to the contaminant plume. Sampling of both wells for intrinsic bioremediation parameters will not provide meaningful data on the levels of the background parameters nor the progress of intrinsic bioremediation across the site. PLOF does agree that sampling one of these wells as a boundary well may assist in the statistical analysis of the potential site intrinsic bioremediation. Based on the above discussion and because MW-2 is currently sampled quarterly for diesel constituents, MW-2 will be monitored quarterly for intrinsic bioremediation parameters (in addition to MW-3 and RW-1). Monitoring of MW-2 may assist in verification of intrinsic bioremediation at the site. 5. "LOF should explain the fate of both the separate phase and dissolved diesel." The actions proposed in the Report—Quarterly Groundwater Monitoring and Diesel Recovery, dated October 13, 1999, as modified and expanded by the actions proposed in this letter, will likely assist in clarifying the current general distribution of dissolved and separate phase diesel at the site. Two general observations,however, can be expressed at this time: 1) The volume of diesel remaining in the subsurface following the initial product recovery(pumping of the valve pit)was likely less than estimated from the results of the initial site investigation. It is possible that the direct push technique employed during the initial investigation distorted the apparent diesel product thickness in some or all of the boring locations. This possibility is substantiated by the field observations during the attempted trenching activities (relative scarcity of observed floating diesel) and by the scarcity of diesel product in the recovery wells; 2)The migration of dissolved and separate phase diesel has likely occurred towards the facility sumps, as shown in the attached figure. The relative abundance of diesel at the location of RW-2,the relative scarcity of diesel at the other recovery wells, and the groundwater gradient direction all support the view that the sump pumping has drawn the diesel towards the facility basement wall. As previously described,the facility basement wall should act as a cut-off to further migration of floating diesel. LaCONDOR