ARCHIVED REPORTS_FEASIBILITY STUDY AND CORRECTIVE ACTION PLAN

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TABLE A SFBRWQCB Non-Drinking Water Time to Reach Constituent Concentration ESL Non-Drinking Water ESL Well ID of Concern (99/L) ( ) (Years) TPHd 1,280 210 14 MW-20 TPHg 2,500 210 18 (1216A1) Benzene 87.0 46 0 MW 34 TPHd <48.5 210 Achieved TPHg <50 210 Achieved (12/6/11) Benzene <0.500 46 Achieved MW-36 TPHd <47.2 210 Achieved TPHg <50 210 Achieved (12/6/11) Benzene <0.500 46 Achieved 4.3 GROUNDWATER ANALYSIS AND PLUME MODELING The Groundwater Spatio-Temporal Data Analysis Tool (GWSDAT) was used to model the site-specific chemical plumes using historical groundwater monitoring data. GWSDAT is a program developed by Shell Global Solutions to analyze the historical trends of chemicals in groundwater. The program provides visual models with constituent-specific concentration contours to aid in reporting trends for groundwater data. The GWSDAT program uses Microsoft Excel as the primary user interface and for data entry. The GWSDAT program uses the open source statistical program R for statistical calculations and graphical outputs. CRA used historical groundwater monitoring data as the input to the GWSDAT program for generating plume models for SPH thickness, dissolved-phase TPHg, TPHd, benzene,MTBE,and tertiary-butyl alcohol (TBA). For SPH thickness, CRA generated annual (third quarter) contour maps from 1991 to 1999, which is the time period when SPH was consistently detected. The contour maps illustrate the depletion of SPH over time. For each dissolved-phase constituent, CRA generated concentration contour maps for every five years using first quarter groundwater monitoring data from 1990 through 2011. The historical plume models show that the magnitude of concentrations and the horizontal extent of the plume have decreased for TPHg,TPHd,benzene,MTBE, and TBA. The concentration contour maps generated using GWSDAT program are presented in Appendix D. 247729(33) 9 CONESTOGA-ROVERS&ASSOCIATES