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ExxonMobil Oil Corporation * - 2 - 10 July 2008 <br /> 75 E. Alpine Ave., Stockton <br /> The Report sensitive receptor survey states that the nearest private water well is located approximately <br /> 720 feet northwest of the site at the First Baptist Church of Stockton, while the nearest public supply <br /> wells is located 1,800 feet south of the site. Note that groundwater monitoring in February 2008 of <br /> shallow wells MW6 (100 feet north of the site) and MW7 (165 feet southeast of the site across the <br /> intersection of EI Dorado Street and Alpine Avenue) reported only toluene (4.7 micrograms per Liter or <br /> ug/L, and 7.9 ug/L, respectively) in those offsite wells. <br /> The Workplan proposes three onsite and three offsite (enclosed Figure 4) CPT/MIP borings, to be <br /> completed to a maximum depth of 120 feet bgs. Actual total depth of the borings will be determined in <br /> the field when MIP concentrations fall below the 50 ug/L detection limit for total petroleum <br /> hydrocarbons (MIP does not give individual constituents or concentrations). In an email received from <br /> ETIC on 9 July 2008, a tentative schedule was proposed to initiate the CPT/MIP fieldwork by <br /> 15 September 2008 and to provide a report by 31 October 2008. <br /> Prior soil data from 2007, included in the Workplan, did not show vertical delineation of petroleum <br /> hydrocarbons when borings MW2, MW3, MW4, and MW5 were terminated at 45 feet bgs. Quarterly <br /> monitoring reports submitted since the first quarter of 2007 have shown that groundwater flow direction <br /> is consistently towards the northeast, while the depth to groundwater varied from 33 to 37 feet below <br /> ground surface (bgs). Maximum groundwater concentrations reported in February 2008 were total <br /> petroleum hydrocarbons as gasoline (TPHg), 189,000 ug/L; TPH as diesel, 13,200 ug/L; benzene, <br /> 18,900 ug/L; toluene, 68,100 ug/L; ethylbenzene, 4,720 ug/L; xylenes, 27,000 ug/L; methyl tert-butyl <br /> ether (MTBE), 885 ug/L, tert butyl alcohol (TBA), 497 ug/L, ethylene dibromide (EDB), 177 ug/L; and <br /> 1, 2-dichlorethane (1,2-DCA), 113 ug/L. <br /> Comments: <br /> 1. My Letter provided deadlines for the installation of deep groundwater monitoring wells and the <br /> reporting necessary to complete the vertical delineation of petroleum hydrocarbons at your site. <br /> Although there have been delays caused by offsite access issues with the shallow wells, by <br /> failure to provide a work plan to install deep wells onsite, ExxonMobil is functionally out of <br /> compliance with Regional Board staff directives. To avoid future enforcement action by this <br /> agency, it is imperative that the following directives be met within the established deadlines. <br /> 2. In order to expedite the investigation and remediation of the site, new figures showing the <br /> locations of the proposed monitoring wells, and typical well installation cross sectional details, <br /> shall be faxed to (916) 464-4704 or emailed electronically to me at ibartonowaterboards.ca.gov <br /> by 18 July 2008. <br /> A) The onsite soil borings and deep monitoring wells shall be placed to provide vertical <br /> delineation of impacts to soil and groundwater at the locations noted above. <br /> /A 4 B) Soil samples shall be collected below 45 feet bgs near MW4 and analyzed to determine <br /> � vertical extent. A deep groundwater monitoring well shall also be indicated on the new <br /> off5i�(t w� figure near MW4 and installed in this phase of the investigation. <br /> /V R anax o- .50 usa <br /> �— 6u,7tS'(-R <br />