ARCHIVED REPORTS_2011 REVISED FEASABILITY STUDY

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amec— Compound Specific Isotope Analysis: stable isotope ratios of carbon (in TCE, cDCE and vinyl chloride) and hydrogen (in TCE and cDCE) were analyzed using a gas chromatograph connected to an isotope-ratio mass spectrometer (GC-IRMS) by ZymaX (hydrogen isotope ratios were analyzed in the Q3 event but not Q2 samples). Stable isotope ratios of chlorine in TCE were also analyzed by Zymax using a conventional quadrapole-type (mass filter) GC-MS. Additional background information on CSIA can be found in EPA (2008). The number of wells sampled and analyses performed varied between the Q2 and Q3 events; the two sampling programs are summarized in Table B.4-1. Results of intrinsic remediation sampling are included in Table 6 and Appendix A of the Q2 and Q3 monitoring reports (ECM, 2010b and 2010c). ECM conducted a preliminary round of sampling for certain intrinsic remediation parameters in Q4 of 2008 (ECM, 2009). The analytical results of the initial sampling conducted by ECM are summarized in Table B.4-2. 3.0 RESULTS AND DISCUSSION The major and minor ion composition of groundwater was used to interpret anthropogenic impacts to groundwater quality (Section 3.1). Geochemical conditions are summarized in Section 3.2 with respect to redox conditions and associated COC degradation processes. Stable isotope ratios of carbon, hydrogen and chlorine were used to interpret potential sources for CDCs and assess intrinsic remediation processes and estimate degradation rates in Section 3.3. 3.1 MAJOR AND MINOR ION COMPOSITION OF GROUNDWATER As described in Section 3.1.1, the major ion composition of groundwater indicates that groundwater beneath Ripon is generally higher in salinity compared to regional (background) levels for the basin, and that the substantial salinity impacts have been detected in two lower aquifer monitoring wells, suggesting a conduit mechanism for salinity impacts. Groundwater samples collected from wells near the WWTP (i.e., wells TH-10, M-1 7C1 and M-31 Cl) were not substantially impacted by salinity, but did have higher COC concentrations. Nitrate and boron contamination are present at highest concentrations in shallow groundwater and these constituents are present at lower concentrations but exceed regional or background levels in deeper aquifer zones. 3.1.1 Major Ions Major ions (sodium, potassium, calcium, magnesium, chloride, sulfate, carbonate and bicarbonate)were analyzed in groundwater samples from 26 monitoring wells during the second and third quarterly groundwater monitoring events (Q2 and Q3, respectively; ECM, 2010b and ECM, 2010c). Of the 26 monitoring wells, 12 were from the upper aquifer zone, 10 AMEC Geomatrix, Inc. \\oad-fs1\doc_safe\9000s\9837.006\4000 REGULATORYTS Assessment_Apx B_012711\Attachment B.4\Attach B-4.docx 1344