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amec�9 <br /> were from the intermediate, and 4 were from the lower aquifer zone. These results are shown <br /> in Table B.4-3. Certain monitoring wells were included for sampling during both events. The <br /> Q2 and Q3 results from the same well were similar indicating that major ion chemistry did not <br /> change substantially between monitoring events. <br /> A Piper diagram was constructed to show the proportions of the major cations (sodium plus <br /> potassium, calcium and magnesium) and the major anions (carbonate plus bicarbonate, <br /> sulfate and chloride) on a charge equivalent basis (Figure B.4-2). The cation data from Table <br /> B.4-3 are plotted in the triangle on the left side of Figure B.4-2, anions on the right triangle, <br /> and the central diamond integrates the cation and anion data as a single data point that <br /> summarizes the major dissolved mineral composition or"hydrochemical facies." Also shown in <br /> Figure B.4-2 are three distinct groundwater chemical compositions identified in a recent study <br /> conducted by the U. S. Geological Survey (USGS) of groundwater in the Eastern San Joaquin <br /> Groundwater Subbasin which includes Ripon (Izbicki et al., 2006). The three groups of <br /> groundwater types, identified using the USGS based on their different chemical compositions, <br /> were compared to the major ion composition of groundwater samples from this study as <br /> follows: <br /> 1. Group 1: Calcium-magnesium-bicarbonate type water representative of shallow <br /> background conditions. Shallow groundwater that has not been substantially affected <br /> by anthropogenic salt contamination should fall under this category. Most of the <br /> groundwater samples from the Upper and Intermediate aquifer zones analyzed during <br /> this study plot within Group 1, consistent with background major ion chemistry, <br /> although the samples cluster near the right side of Group 1, suggesting some <br /> anthropogenic impact of chloride may exist as many samples plot close to Group 3 <br /> (see below). <br /> 2. Group 2: Sodium-bicarbonate type water representative of deeper background <br /> conditions. Deeper groundwater tapped for public and agricultural supply falls under <br /> this category (the distinction between shallow and deep wells is set at 300 feet in <br /> Izbicki et al. (2006), however, near Ripon, this distinction is most appropriate as above <br /> or below the Corcoran Clay). Lower aquifer wells M-6D and M-20D, and groundwater <br /> samples from intermediate aquifer wells TH-10, M-31 C1 and M-25C2 plot within or <br /> close to this zone. This is generally consistent with the trend of increasing sodium- <br /> bicarbonate type water with depth reported in the USGS study. <br /> 3. Group 3: Mixed-cation-chloride type water impacted by salinity. Groundwater with <br /> a major ion composition that plots in Group 3 has been characterized as impacted by <br /> sources of salinity. Onsite groundwater samples from the upper aquifer zone (EW-1 <br /> and EU-4) and intermediate aquifer zone (M-25C1) plot in Group 3, along with <br /> intermediate aquifer zone samples from monitoring wells south of the site (M-8C1 and <br /> AMEC Geomatrix, Inc. <br /> \\oad-fs1\doc_safe\9000s\9837.006\4000 REGULATORYTS Assessment_Apx B_012711\Attachment B.4\Attach B-4.docx 134-5 <br />