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Mr. Robert Garcia • - 2 - . 23 August 2000 <br /> 1. In our 25 May 2000 letter, staff recommended monitoring recovery wells RW-1 and RW-2 to <br /> supplement the current program. The wells are downgradient of the two groundwater contaminant <br /> plumes. Leprino agreed with this recommendation, except Leprino recommended monitoring these <br /> wells for only a period of two quarters. RW-1 and RW-2 are included in the final MRP and must <br /> be sampled on a quarterly basis. Due to the on-site construction activities, which impaired <br /> monitoring of several wells, and detection of elevated TEH concentrations, quarterly monitoring of <br /> these wells is necessary to evaluate the potentiometric surface and to determine whether the new <br /> recovery wells (RW-4a and RW-5a) are effective. <br /> 2. Leprino stated in the Letter that monitoring of recovery well RW-3 should occur until MW-11 can <br /> be located and/or repaired. I agreed with this recommendation; however, the report shows that <br /> MW-11 was accessible and monitored during the second quarter. Therefore, this temporary <br /> modification is no longer needed and is not included in the MRP. <br /> 3. During the site visit, I noted that the location of the wells depicted in the previous monitoring <br /> report were not consistent with the actual locations. In the Report, HSI recommends completing a <br /> survey of the site wells. The well survey needs to be completed and included in the third quarter <br /> monitoring report due by 30 October 2000 to provide the accurate elevations and locations of the <br /> wells. <br /> 4. Our 25 May 2000 letter requested Leprino to evaluate remedial alternatives to expedite removal of <br /> free-phase product and dissolved contaminants in groundwater at the site. The Letter proposes to <br /> continue collecting data to evaluate the recovery system's effectiveness. If results do not show the <br /> system provides an effective remedy, Leprino proposed modifying the existing recovery program. <br /> Data from the report shows significant TEH contamination in groundwater along the northern <br /> property boundary, which shows offsite migration of contaminants is likely and the plume is not <br /> being captured completely. The two operating recovery wells are in the northwest and northeast <br /> portions of the site and are designed to capture the free-phase product plume in those specific <br /> areas. The design capacity of the wells does not allow capture of dissolved phase contaminants <br /> along the northem property boundary. Therefore, an evaluation of remedial alternatives is <br /> necessary to choose an alternative to remediate the whole plume. In addition, new monitoring <br /> wells need to be installed to define the downgradient extent of the plume. <br /> Leprino must submit a capture zone analysis in the third quarter 2000 groundwater monitoring report <br /> due by 30 October 2000. The third quarter report needs to include an evaluation of the recovery <br /> system's effectiveness and any recommendations needed to improve the system. Also by that date, <br /> please submit a work plan to define the full extent of groundwater contamination and provide a schedule <br /> to submit an evaluation of remedial alternatives. The remedial alternative evaluation may be prepared <br /> following delineation of the downgradient plume. <br /> If you have any questions, you may contact me at(916) 255-3119. <br /> II <br /> A HYring Geologist <br /> cc: Mr. Michael Infurna, San Joaquin County Environmental Health Services, Stockton <br /> Mr. Brendan Shine, HSI GeoTrans, Westminster, CO <br />