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GeosynteC <br /> consultants <br /> Concentration trend graphs for TCE, PCE, cis-1,2-DCE, and VC for select wells are <br /> included in Appendix E. <br /> 4.2 Results <br /> The results of the MAROS analysis are summarized in Table 5 and the results for each <br /> individual well are included in Table 6. More than 50% of the wells at RRI had non- <br /> detects for all the historical samples collected and analyzed for benzene, PCE, TCE, 1,2- <br /> DCE, and VC. Benzene was historically sampled in 345 wells and 41 wells (12%) had <br /> detections.PCE,TCE, 1,2-DCE,and VC were historically sampled in 340 wells and were <br /> detected in 22 wells (6%), 51 wells (15%), 161 wells (47%), and 134 wells (39%), <br /> respectively. Twenty-one wells, or 6% of the wells, had insufficient samples (i.e., less <br /> than four samples per well)to determine concentration trends. Most wells with detections <br /> had decreasing or probably decreasing trends with concentrations decreasing by more <br /> than an order of magnitude over the last 30 years (Appendix E). Twenty-one (6%)of the <br /> wells historically sampled had an increasing or probably increasing trend of at least one <br /> COC. <br /> The concentrations of the COCs were generally higher in the dry season (summer)when <br /> there is less recharge to groundwater than during the wet season (winter) when there is <br /> more recharge to groundwater(Appendix E). <br /> RRI Groundwater Monitoring Work Plan 21 1 June 2018 <br />