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I <br /> EIIC�t® <br /> Mr James L Barton <br /> July 28, 2005 <br /> Page 2 <br /> Ithe groundwater monitoring well network Groundwater is not considered to be an <br /> exposure pathway because there no drinking water wells exist within the well network <br /> I • The nearest surface water body is the Calaveras River and is located over 4,000 feet to <br /> the south-southeast Based on the distance from the site, surface water Is not <br /> considered to be a potential exposure pathway <br /> • The majority of dissolved and residual concentrations of petroleum hydrocarbons is <br /> located approximately 50 to 70 feet below ground surface (bgs) and the site and <br /> surrounding areas are predominately paved Therefore, soil and biota are not <br /> considered to be exposure pathways <br /> • In ENSR's opinion, inhalation of vapors through indoor air vapor intrusion is considered <br /> I the only potential exposure pathway to receptors at this site ENSR prepared a vapor <br /> intrusion pathway evaluation as a separate document and has included it as <br /> Attachment A The model calculation spreadsheets are presented as Attachment B <br /> A site conceptual model depicting the exposure pathway described herein is included as <br /> Figure 3 <br /> From recommendations made in the Vapor Intrusion Pathway Evaluation, prepared as a <br /> separate document and included as Attachment A to this letter, ENSR requests removing the <br /> following wells from the sampling program because they have no constituent concentrations <br /> above screening levels <br /> I 6 MW-5 • MW-15 • MW-22S • MW-28 <br /> • MW-7 • MW-17 • MW-22D a MW-29 <br /> MW-9 • MW-18 • MW-23S m MW-30 <br /> • MW-10 • MW-19S • MW-23D • MW-31 <br /> • MW-10A • MW-19D • MW-25S • MW-32 <br /> • MW-13 • MW-21 S • MW-27 a AS-26 <br /> • MW-14A • MW-21D <br /> Additionally, based on the Vapor Pathway Evaluation, it is recommended that monitoring cease <br /> for the following constituents that have no concentrations above screening levels for the <br /> groundwater-to-indoor air pathway <br /> I6 n-Butylbenzene <br /> 0 sec-Butylbenzene <br /> o 1,2-Dichloroethane <br /> G Ethylbenzene <br /> J IPm)ects10694015098-2931WorlunglReportsietter Requesting Reducbon in 5amphng15098 Letter Requesting Reducbon in Sampling doe <br /> Celebrating 35 Years of Excellence rn Environmental Services <br />