ARCHIVED REPORTS XR0011192 - Laserfiche WebLink

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6.0 CONCLUSIONS AND RECOMMENDATIONS Approximately 4,978,620 cu ft of vapors were withdrawn and combusted between October 1 and December 31, 1996 VOC concentrations (as measured by PID) in the shallow well vapor stream were essentially unchanged from the previous quarter, whereas concentrations in the deep zone ,lumped sharply after the installation of the new extraction Well We conclude from tliis that the effective(clean-up) radius of influence of VE-I "deep" has been relatively small,perhaps less than 15 feet, although the radial distance at which some air flow has occurred may be sigmficantly larger The data indicate that gasoline remains in the soil, but its volume is unknown. It is worth noting, however, that the volume that has already been extracted exceeds the volume originally estimated by the two previous consultants (WGR and RSI) The mean VOC concentration measured in the combined well influent stream during the 12 monitoring events was 1,500 ppm Using this value, we calculate that 1,970 pounds of hydrocarbons were destroyed Added to estimates from previous quarters, this brings the estimated total to over 15,000 pounds,or approximately 2,000 gallons of gasoline Contaminant concentrations in the groundwater sample from MW-5 were unchanged from those . registered in the third quarter The 2-foot rise in the elevation of the static water table does not appear to have had an appreciable effect on the concentration of dissolved hydrocarbons in the groundwater ` Monitoring of the vapor extraction unit since its installation in July, 1994 has demonstrated that a significant decline has occurred in the vapor concentrations being received at the inlet port The combustion of a large quantity of gasoline has also been documented In addition, a stable groundwater gradient and flow direction and stable groundwater contaminant concentrations have been recorded Therefore, in view of recent changes in regulatory policy regarding petroleum cleanup levels and risks to the environment, Upgradient recommends that Apache Plastics defer further remedial efforts and monitoring activities until PHS/EHD has reviewed the status of the investigation, including Emcon's report, presented it its internal Technical-Review Committee, and provided further directive regarding the site 6