SITE INFORMATION AND CORRESPONDENCE FILE 2

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Rodger Liston Darpetro Inc. 749 E. Charter Way, Stockton, California Page 3 of 5 are at the present time , how they move through the subsurface , how they will respond to changes in the ground water flow characteristics or to potential remediation efforts , what the contaminants' ultimate environmental fate will be, and to help evaluate the risk posed by the contaminants to ground water supplies and sensitive receptors . As much key information is lacking from the current SCM , EHD does not approve or accept the 07 May 2003 SCM . Information required for an adequate SCM is given below. During the current review of your site status , EHD noted that the site still requires vertical assessment of impacted ground water. Also, the detection of 7 Itg/I 1 ,24chlorethane (1 ,2-DCA) indicates that the compound should be part of the routine analytical suite for ground water samples for this site. Detection limits of 5 . to 100 jig/[ are too high ; a detection limit of 0 . 5 µg/I should be obtained if possible . In addition , ethylene dibromide (EDB) should be added to the analytical suite . A sensitive receptor survey for potential receptors within a 2 , 000400t radius of the site must be conducted and reported . As the known plume extends across an area approximately 400 el by 2 0 feet and tot total uetrolleum hydrocarbons as gasoline (TPH-g ) nd the former UST area at concentrations in the tens of thousands and in the thousands of Itg/I , respectively, EHD believes that interim remediation of impacted ground water is appropriate for this site and the site is certainly not ready for closure consideration . In view of these needs for the site, you are directed to : Prepare a revised site conceptual model that adequately demonstrates contaminant source area (s) , geological controls on contaminant distribution , contaminant migration pathways, vertical and lateral extent of impacted media , and all receptors with a significant potential to be impacted by the contaminants . Prepare a work plan to complete the vertical and lateral extent of impacted ground water and address potential contaminant migration pathways . Initiate and continue monitoring of 1 ,2-DCA and EDB in all sampledmedia until directed otherwise by EHD . Conduct and report a sensitive receptor survey for the area within 2,000 feet of the subject site . Prepare a feasibility study and propose interim remediation of impacted ground water. The revised site conceptual model and additional site assessment work plan are due in this office by 27 October 2003 . The revised SCM , work plan and sensitive receptor survey may be combined into one report. To be sure that the SCM will adequately address the assessment, remediation and final closure requirements for this site, please include the following in the revised SCM :