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3 <br /> I <br /> � which is triggered when process air flow falls below approximately 40 cfm; (3) emergency shut- <br /> off switches located on the unit and inside the ARCO AM/PM building, and; (4) an emergency <br /> shutoff switch located in the condensation drum which is triggered when 40 gallons have , <br /> collected. The treatment unit will be surrounded by an 8-foot-high fence. t <br /> Air emissions will be regulated by a San Joaquin Valley Unified Air Pollution Control <br /> District Authority to Construct permit. The system will operate 24-hours per day. The system <br /> should pull a total of 100 cfm from all wells. BC estimates the system will operate at 95 percent <br /> efficiency when influent concentrations are at design levels. The system will be maintained on <br /> a weekly basis by BC. <br /> GROUNDWATER REMEDIATION <br /> Groundwater flows north and northeast beneath the Site under a hydraulic gradient of <br /> approximately 0.002. In general, groundwater elevations and the hydraulic gradient have not <br /> varied significantly at the site since monitoring began in 1987, although the elevation of the water <br /> table as measured in the monitoring wells has declined about 0.5 feet since April 1987. <br /> Groundwater is found at depths of 8.5 to 12.9 feet bgs across the Site. Groundwater elevations <br /> and historical gradient data are presented in Appendix B. <br /> The concentration of TPH-G and BETX in individual monitoring wells have varied over <br /> time but, in general, concentrations have decreased over time. The concentration of BETX and l <br /> TPH-G in groundwater samples collected from the monitoring wells on a quarterly basis since <br /> 1987 are included in Appendix C. A projected zero line for benzene based on the most recent <br /> analytical data is shown on Figure 3. Free phase hydrocarbon product has been identified in off <br /> site well ATR-8. The origin of this product has not been defined. However, ARCO is in the <br /> process of having the product analyzed and compared to groundwater samples containing j <br /> dissolved hydrocarbons collected from on site wells SMW-1 and ATR-3. The County has <br /> approved on site remediation while the off site investigation proceeds. <br /> Groundwater contamination will be remediated by sparging, in conjunction with vapor <br /> extraction and, if needed, groundwater extraction and treatment. <br /> Sparging <br /> Sparging is the injection of air into the groundwater at a point 5 to 20 feet below the <br /> groundwater table. Recent studies indicate that sparging significantly reduces the cleanup time <br /> for sites similar to ARCO Facility 2093. The injection of air into the groundwater causes <br /> volatilization of hydrocarbons in the groundwater. These volatilized hydrocarbons are released <br /> into the vadose zone, where they are captured by the vapor extraction system for treatment. <br /> Sparging must be operated in conjunction with a vapor extraction system. <br /> Groundwater will be remediated by sparging through wells installed for that purpose. Each <br /> sparge well will be located within the capture zone of one or more vapor extraction wells. A <br /> blower located in the treatment area will be used to inject air under low pressure through the <br /> sparge wells. <br /> r <br /> 0410Y95\E:\74Q3\RFP0RM740M 1.H-k <br /> QMS-PS20W <br />