SITE INFORMATION AND CORRESPONDENCE

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Mr. Gregory Torlai, Jr. . - 3 - . 29 April 2009 H&H Marina dewatering of the sump, direct extraction from the sump has not been possible since October 2007. According to the Annual Report, between 29 September and 12 December 2008, it is estimated that the treatment system operated at about 0.5 gallons per minute and removed about 0.0034 lbs of MTBE from groundwater. Between the April and December 2008, maximum concentrations of TPHg, MTBE, and TBA in influent gfoundwater samples were 600 micrograms per liter (tag/L), 900 pg/L, and 6,500 pg/L, respectively. The effluent was non-detect (ND) for all constituents detectable by EPA Methods 8015M and 8260. Based on the consistent historical lack of detections of some CDCs and the recent detections of others in Site monitoring wells, Appendix H in the Assessment Report contains recommendations for altering the monitoring requirements of MRP No. R5- 2004-0828, ceasing sampling in MW-13, which has been dry since it was installed, removing the requirement to sample for TPHd, and including lead scavengers 1 ,2-DCA and ethylene dibromide (EDB) in the constituents required for analysis. To address the low mass removal rates currently being achieved by the IRM system, H & H recommends (1) retrofitting MW-2 as an additional extraction point, (2) upgrading the IRM system power supply, and (3) installing three additional groundwater extraction wells. To complete the site assessment, H & H proposes to drill boring B-22 once conditions allow and advance an additional boring in the vicinity of B-21 to verify the detection of MTBE in the groundwater sample obtained from that boring. Our comments are presented below. 1. We concur with H & H's recommendations for optimizing the extraction and treatment system and advancing the missing boring at location B-22 to complete lateral delineation of the plume to the southeast. This boring should be advanced deep enough to obtain a grab groundwater sample that is non-detect (ND) for all CDCs. However, if the proposed confirmation sampling verifies the MTBE detection at B-21, the location of proposed extraction well EW-4 (misidentified as EW-2 on Figure 15) should be adjusted to a location that is more central to MW-14, B-21 and MW-5 to address the MTBE detected in these three samples. 2. We concur that EW-2 is needed to delineate the plume and provide hydraulic capture at the southeast extent of the September 2007 plume. However, the detection of TPHg at 140 pg/L at 55 feet bgs shows that the plume is not vertically delineated to ND in this area. Therefore, the appropriate depth for this well is not currently known. 3. H & H has concluded that the detection of 1 ,2-DCA in MW-2 constitutes evidence of a pre-1991 release from the former USTs, which were removed in 1991. Leaded gasoline was not banned until 1996 and even then, its use was still allowed for marine engines. Thus, leaded gasoline could have been discharged to the ground