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5 • Air emissions will be regulated by a San Joaquin Valley Unified Air Pollution Control District Authority to Construct permit The system will operate 24-hours per day The system should pull a total of 100 cfm from all wells BCC estimates it will operate at 97 percent efficiency The system will be maintained on a weekly basis by BCC GROUNDWATER REMEDIATION Groundwater flows north and northeast beneath the Site under a hydraulic gradient of approximately 0 002 In general, groundwater elevations and the hydraulic, gradient have not vaned significantly at the site since monitoring began in 1987, although the elevation of the water table as measured in the monitoring wells has declined about 0 5 feet since April 1987 Groundwater is found at depths of 8 5 to 12 9 feet bgs across the Site Groundwater elevations and historical gradient data are presented in Appendix B The concentration of TPH-G and BETX in individual monitoring wells have varied over time but, in general, concentrations have decreased over time The concentration of BETX and TPH-G in groundwater samples collected from the monitoring wells on a quarterly basis since 1987 are included in Appendix C A projected zero line for benzene based on the most recent analytical data is shown on Figure 3 . Groundwater contamination will be remediated by sparging, in conjunction with vapor extraction and, if needed, groundwater extraction and treatment Sparging Sparging is the injection of air into the groundwater at a point 5 to 20 feet below the groundwater table Recent studies indicate that sparging significantly reduces the cleanup time for sites similar to ARCO Station 2093 The injection of air into the groundwater causes volatilization of hydrocarbons in the groundwater These volatilized hydrocarbons are released into the vadose zone, where they are captured by the vapor extraction system for treatment Sparging must be operated in conjunction with a vapor extraction system Groundwater will be remediated by sparging through wells installed for that purpose. Each sparge well will be located within the capture zone of one or more vapor extraction wells A blower located in the treatment area will be used to inject air under low pressure through the sparge wells Hydrogeologic Measurements and Predictions A step drawdown test was performed for b hours on well TEX-1 The flow rates were measured by reading the pump's totalizer flow meter and recording the total gallons pumped at • predetermined time increments Flow was adjusted using a gate valve A digital stop watch was used to track time Numerous flow readings were taken throughout the test to control the flow rate Water levels were recorded using either an electronic sounder or a pressure transducer controlled by a data logger (In-Situ Hermit Model SE 100013) The data from the data logger 7403gZEP0RT9\REMEDATN PLN