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1 i Ms. Margaret Lagorio Page 5 of 8 The location of boring TB5 was within the radius of influence of all vapor extraction wells at the site and, in particular, was only about 10 feet from vapor well VW6. Vapor well VW6 was online continuously during operation of the system. The contamination in the area of T135 has presumably been cleaned up. Figure 7 depicts the radius of influence of the vapor wells at the site and the location of boring T135. Soil vapor extraction succeeded in removing approximately 12,700 pounds of hydrocarbons from the subsurface at significant expense. The mass removal rate when the system was shut down was only 2 pounds of hydrocarbons per day. At that rate it would require more than 60 days of system operation to increase the total soil cleanup by 1%. Confirmation borings indicate that very little vadose soil contamination remains and that which does remain is not amenable to cleanup. At the time the vapor extraction system was shut down the unit cost of cleanup had reached over $300/gallon TPHg. Additional expenditure is not warranted for the incremental cleanup that might be attainable by renewed vapor extraction. Summary information concerning the operation of the vapor extraction system is included in Attachment B. We trust it is not the position of PHS/EHD that an active remedial effort, once begun, must proceed to 100% cleanup. However, we cannot see how the Responsible Party's efforts or the expenditure of significant quantities of State funds for vapor extraction have resulted in moving this case any nearer to closure. We can only assume that additional effort and expenditure would have the same lack of effect. The presence of the vapor extraction system and enclosure are interfering with the property owner's use of the property. We again recommend removing the system. FEASIBILITY OF GROUNDWATER EXTRACTION OR AIR SPARGING The July 20 letter from PHS/EHD also directed the Responsible Party to investigate the feasibility of air sparging or groundwater extraction to remediate soil and groundwater. Feasibility of Groundwater Extraction Groundwater pump and treat has been shown at countless sites to be somewhat effective for- migration control but grossly inefficient at contaminant mass removal. There is no evidence to - suggest that this plume is migrating and the plume does not contain the highly mobile oxygenate additives. Migration control does not appear to be needed. Soil sampling beneath the current water table has identified significant quantities of sorbed contaminants indicating a situation in which groundwater extraction would not be effective in removing contaminant mass. Moreover, the nearby plumes of offsite contamination, containing not only TPHg/BTEX but also oxygenate additives, could be drawn beneath the property by the operation of a groundwater extraction system. Finally, the duration of any pump and treat effort could be expected to be open-ended. We do not recommend groundwater extraction for this site. roek\closu a\workplm\respo e.doc