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Mr. James L. Barton <br /> November 27, 2006 <br /> Page 7. <br /> Table 3 <br /> Highest Detection Concentration of Hydrocarbon Constituents and Associated Water Quality Criteria <br /> Constituent Highest Detected Concentration Water Quality Criteria (Ng/L) and <br /> over Last Four Years with Source (see Note 1) <br /> Corresponding Well, Date, and <br /> TPHg Concentration <br /> 1,3,5-Trimethylbenzene 410 pg/L (MW-2—Dec. 18, 2003) 330 (California State Action Level for <br /> TPHg—2,800 pg/L Drinking Water established by DHS) <br /> 1,2,4-Trimethylbenzene 2,900 (MW-2 —July 14, 2006) 330 (California State Action Level for <br /> TPHg — 19,000 pg/L Drinking Water established by DHS) <br /> Isopropylbenzene (cumene) 110 (MW-2—July 14, 2006) 770 (California State Action Level for <br /> TPHg — 19,000 pg/L Drinking Water established by DHS) <br /> n-Butylbenzene 59 (MW-2— February 26, 2004) 260 (California State Action Level for <br /> TPHg — 31,000 pg/L Drinking Water established by DHS) <br /> n-Propylbenzene 320(MW-2 —July 14, 2006) 260 (California State Action Level for <br /> TPHg — 19,000 pg/L Drinking Water established by DHS) <br /> Napththalene 590 (MW-2— December 18, 2003) 170 (California State Action Level for <br /> TPHg -2,800 pg/L Drinking Water established by DHS) <br /> sec-Butylbenzene 37 (MW-250 — February 26, 2004) 260 (California State Action Level for <br /> TPHg-- 31,000 NgiL Drinking Water established by DNS) <br /> L Note 1: Source: Marshack, D., 2003. A Compilation of Water Quality Goals. August and updates. <br /> Comparing relative criteria in Tables 1 and 3, the primary hydrocarbon constituents controlling Site <br /> remediation and eventual Site closure are TPHg and benzene. Analysis for full VOC scan by EPA Method <br /> 8260B and reporting all peaks are unnecessary when TPHg and BTEX concentrations are also being <br /> quantified. In addition, the full VOC scan and reporting results in excessive costs for analysis and <br /> reporting that are not necessary to monitor progress in groundwater restoration and satisfy the regulatory <br /> drivers cited in the CAO. <br /> ENSR requests that the monitoring program be revised to only require groundwater samples be analyzed <br /> for TPHg, BTEX, and 1,2-DCA, as appropriate on a well-by-well basis (discussed later in Section 2.4). <br /> MTBE and EDB are not included as monitoring constituents for reasons discussed in Sections 2.2 and 2.3, <br /> respectively. In addition, ENSR's groundwater monitoring program recommendations on a well—by-well <br /> basis and justified by past occurrences of analytes in each well are presented in Section 2.4. <br /> ENSR I AECOIA <br />