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LM25A which are recommended for abandonment) should continue to be purged and sampled <br /> with the bladder pump at low flow rates, as has over the past year given representative <br /> groundwater samples of low turbidity. [This approach could be critical for well LMI IA, if <br /> DDRW-Tracy continues to utilize it as a "background" monitoring well for inorganics. The <br /> use of turbid groundwater samples for a background monitoring well could give <br /> inappropriately high "background" levels for inorganics.] <br /> 3. We also believe that monitoring wells LM53A, LM57D, and LM59A as discussed in Sections <br /> 3.2.0.4 and 3.3.0.4 should be purged and sampled using a bladder pump to obtain more <br /> representative groundwater samples of low turbidity. We believe that this would save time <br /> and effort in trying to obtain non-turbid samples from monitoring wells that may have <br /> remaining turbidity problems. If cost is a dominant issue, the remaining wells could be <br /> sampled carefully with a bailer. <br /> 4. Section 3.3.0.2 of the report recommends that well LM25A be abandoned and replaced. EPA <br /> agrees with this recommendation with a reservation. Since two Upper Horizon monitoring <br /> wells were to be installed within a 200-foot radius upgradient of this well during Phase I of <br /> the comprehensive remedial investigation (RI) at DDRW-Tracy, the actual location of the <br /> replacement well might be postponed until the RI data collected to date can be examined. <br /> 5. EPA agrees that well LM3A should be abandoned and replacement well LM3AA should be <br /> installed immediately. This replacement well LM3AA should be located as closely as <br /> possible, in the hydraulically downgradient direction, to the industrial waste-ponds (SWMU <br /> No.3). Also, DDRW-Tracy should give consideration as a part of the ongoing RI to the <br /> installation of monitoring wells screened in the Middle and Lower Horizons of the Upper <br /> Tulare Formation in the near future to form a cluster with LM3AA. This well cluster would <br /> better define the vertical extent of contamination that may be emanating from SWMU No. 3. <br /> EPA has previously remarked on the quarterly monitoring reports for DDRW-Tracy that other <br /> contaminants such as dieldrin, chlordane, arsenic, and sometimes other metals have routinely <br /> been present in concentrations above background at well LM3A. <br /> Thank you for the opportunity to comment on this report. If you have any questions, please <br /> contact me at (415) 744-2392. <br /> Sincerely, <br /> ( <br /> �A <br /> � I1 <br /> Michael Work <br /> Federal Facilities Cleanup Office (H-9) <br /> Hazardous Waste Management Division <br /> cc: (See Distribution List) <br /> 2 <br />