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J�`�E�rFsy <br /> � u <br /> w UNITEDSTATES ENVIRONMENTAL PROTECTION AGENCY <br /> t '1F017 <br /> REGION IX <br /> 1 F017cno17 75 Hawthorne Street RECEIVE <br /> San Francisco, CA 94105-3901 Ij <br /> APR 15 1993 <br /> ENVIRONMENTAL HEALTH <br /> April 9, 1993 PERMIT/SERVICES <br /> Marshall Cloud <br /> Environmental Protection Office <br /> DDDDR�W-Tracy Location <br /> P.O. Box 960001 <br /> Stockton, CA 95296-0250 <br /> RE: Final Engineering Report for the Well Monitoring Program, <br /> Montgomery/Watson (MW) letter of March 31, 1993, <br /> Future Well Monitoring for the Comprehensive RI <br /> Dear Marshall: <br /> Pursuant to my discussion with Steve Light on April 6, 1993, EPA is providing <br /> comments on the Final Engineering Report for Well Monitoring. Generally, EPA is in <br /> concurrence with the content and the recommendations in the Final Engineering Report. <br /> EPA has noted, however, that the proposed analyses for the April groundwater monitoring <br /> round is more extensive than the January round (some metals and pesticides are presently <br /> being monitored semiannually for many wells in this upcoming April 1993 round). Should <br /> DDRW-Tracy desire to conserve resources, EPA would not opposed a reduction in the <br /> analyses. For example, the analytical burden could be reduced by temporarily eliminating <br /> analyses for constituents which have consistently have not been detected in the first four <br /> quarters. <br /> EPA is also taking this opportunity to provide comments on the MW letter of March <br /> 31, 1993, regarding the proposed analyses for the April groundwater monitoring round. <br /> Chemicals of concern (COCs) previously decided upon for Operable Unit (OU) No. 1 at <br /> DDRW-Tracy include the organochlorine pesticide, dieldrin, and the metals arsenic, <br /> chromium, and manganese; these COCl have been rolled over into the Comprehensive <br /> Remedial Investigation,/Feasibility Studies (RI/FS). Ore deficiency EPA has discovered in <br /> the MW proposal is not analyzing more monitoring wells for organochlorine pesticides (via <br /> EPA Method 8080). Concentrations of dieldrin have been detected above California's <br /> (Proposition 65) Action Level of 0.020 µg/L at the following monitoring well locations in <br /> September 1992: LM3, LM15, LM28, LM29, LM49, LM50, LM55, LM66, LM101, LM103, and <br /> LM104. (Wells LM49, LM50, LM55, and LM66 are presently off-base DDRW-Tracy.) Well <br /> LM3 has had the highest concentration levels of dieldrin and of arsenic since September <br /> 1991. EPA feels that this dieldrin should be monitored on at least a semiannual basis in <br /> well LM3, LM55, and in LM66, due to some variability in dieldrin's concentration levels. <br /> Monitoring well LM16 has historically had elevated levels of DDT concentrations and <br /> should, therefore, be monitored semiannually for organochlorine pesticides. Of these <br /> I <br /> Printed on Recycled Paper <br />