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Pilkington Libbey Owens Ford <br /> Standby Generator Diesel Supply Line <br /> May 31,2000 <br /> Page 2 <br /> Monitoring data also indicate that RW-6 is essentially cross-gradient rather than down-gradient of <br /> the source area. Quarterly groundwater monitoring of RW-6,therefore, will not assist in <br /> investigating down-gradient water quality. RW-1 is located in the immediate vicinity of the release. <br /> Groundwater monitoring at RW-1,therefore,would not provide additional down-gradient <br /> groundwater data. <br /> 2. "The report states that the cost of$1,300 to remove a gallon of diesel is not cost effective. <br /> The report should compare this cost with other removal methods,such as groundwater <br /> extraction and treatment." Because diesel product thickness measurements have indicated a <br /> scarcity of diesel present at the recovery wells, PLOF believes that other diesel removal methods will <br /> be no more cost-effective than skimming has been. The historical data indicate that there is only a <br /> very small volume of product available to be recovered. Although active diesel recovery methods <br /> such as groundwater extraction may increase the available volume of diesel product,the probable <br /> increased volume will be minimal(based on a scarcity of product at RW-1 and RW-3 through RW- <br /> 6). In addition, pumping at the site may also aggravate the problem by smearing diesel down below <br /> the water table. Because these methods will add substantial expense(including the capital costs <br /> associated with air-stripping, carbon filtration,etc. and the cost of operations and maintenance), the <br /> cost per unit volume of product removed will probably increase substantially. <br /> Based on the above discussion, the most cost-effective method is presently operating at the site. As <br /> discussed in the Report—Quarterly Groundwater Monitoring and Diesel Recovery,dated October <br /> 13, 1999, the facility substructure is acts as a cut-off wall and the basement sumps acts as a <br /> groundwater extraction system. Monitoring indicates that the groundwater gradient at the site is <br /> controlled by the sump pumping. If so, both hydraulic control and containment are already in effect <br /> at the site. A schematic drawing of the sump pumping and cut-off wall is attached to this letter. <br /> Recent measurements indicate that as much as approximately two feet of diesel product has <br /> gradually accumulated in RW-2 since the skimming was discontinued on September 29, 1999. RW- <br /> 2 is located near the containment wall. Because of this,PLOF proposes that skimming be reinitiated <br /> at RW-2 on a reduced basis from the original skimming effort. Once a month the skimmer will be <br /> allowed to remove the recoverable product in RW-2 for three days. Based on past data,this <br /> skimming will remove the product thickness down to less than 0.1 foot. This procedure should <br /> greatly increase the cost-effectiveness of the recovery and should not markedly reduce the volume of <br /> diesel removed per unit time. PLOF believes that the proposed skimming,the potential containment <br /> and pumping(as discussed), and passive bioremediation potentially occurring at the site(to be <br /> discussed below)are the most cost-effective mitigation. <br /> 3. "I concur with the proposal to sample the basement sumps. A map with convenient scale <br /> should show the locations of the sumps in relation to the spill area,MWs,and RWs." The <br /> basement sumps were sampled as part of the quarterly groundwater monitoring conducted on May <br /> 24, 2000. A map with a convenient scale showing the sump locations will be provided in a quarterly <br /> monitoring report to be submitted at the end of June,2000. <br /> �M CONDOR <br />