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t N tl t l t t I Fust Weekly Lvent of November 16,2000,Groundwater Purging and Dgxmal Casco(Fonner 13P)Station No iii 1192 • Deoemlx-r 7 2000 1! MTBE Mass Removal The estimated mass of MTBE removed.was calculated using the average the MTBE concentration from the pre-purging (MW-3-PRE) and post-purging' (MW-3-POST) grab groundwater samples t F Based on this average concentration, an estimated total of 2 87 pounds of MTBE was removed from r the site during the November 16, 2000 purging event ' The estimated MTBE removed and the calculation method are presented in Table 1 Well Search GR personnel conducted a visual search of a 19 block area centered on the site to look for evidence of water wells in this vicinity Specific features which might indicate the presence of wells, such as pressure tanks, old water tower structures, or extra power lues to well houses were not observed in this area A search of the GeoTracker N%ebsite GM//veotracker2 arsenaultlegg con) Avill be conducted to locate municipal wells in the vicinity of the site In addition, GR is currently initiating a DWR well search for wells within 2000 " feet ofthe site The results of the well search efforts will be presented in a future report Performance Test In conjunction with the November 16, 2000 groundwater purging and sampling, GR conducted a performance test to qualitatively analyze the purging rates and the radii of Influence generated during the removal of groundwater from MW-3 and MW-7 Purging groundwater from MW-3 resulted in very minimal to no changes in the static groundwater levels in the other monitoring wells e-xcept in MW-7, located less than 4 feet from MW-3, as shown on Figure 1 Similarly purging groundwater from MW-7 resulted in no change in the static groundwater levels in the other monitoring wells except in MW-3 In this pair of wells, purging groundwater from one resulted in a 3 to 6 foot drop in groundwater levels in the adjacent well After purging was completed, the recovery of MW-3 was monitored The water level recovered from 25' 15 feet to 15 50 feet in 21 minutes Based on the results of the water levels collected during the performance test, the radii of influence formed by purging of MW-3 and MW-7 could not be ' observed due to the large distances (95 to 130 feet) bet\vicen the purged N\ells and the other c costing wells at the site Performance test data arc summarized in Table 2 s The On\A vacuum`trick purged groundwater from MW-3 for 329 minutes Approximately 2,400 gallons were removed at a purge rate of 7 3 gallons per minute (gpm) The vacuum trick removed groundwater r , from MW-7 for 103 minutes, recovering approximately 600 gallons of groundwater fora purge rate of 5 8 gpm! Based on these results, MW-3 can be purged ata greater rate and should be used for future purging events Purging rates are summanzed in Table 1 r , 14020502