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Evaluanorn of Inlenm Remedial Action-Tosco(Former BP)No 11 192 Apni 13,2001 MTBE Mass Removal The estimated mass of MTBE removed was calculated using the average nd Ba er°concentration each the pre-purging (mW-3-PRE) and post-purging (MW-3-POST) g g pounds of MTBE purging event Based on these average concentrations, an estimated total of 26 62ember 100 and January 2, was removed from the site Bunn eight iMTBE removedevents between ,�and he calculation method are 2001 The estimated MTBE removed, presented in Table 1 Discussion and Conclusions Based on the analytical results groundwater samples, l heaeightlldecrease in purging andtlsampling events concentration MTBE well MW-3 was observed a couples o rior to purging (MW-3 PRE series) and following Concentrations it, groundwater samples collected p purging (MW-3 POST ser ies) showed vofsamples (Fig ure 1) showsand eno decrease, yet s for the eight pthe final MW-3 The trendline for the MW-3 POST series of samples (Figure b MTBE, down from 120,000 ppb POST sample (January 2, 2001) was reported to contarn 9ppro ppb 26 63 pounds of MTBE were in the first MW-3 POST sample (November 16, 2000) Approximately removed through the purging and disposal of 27,200 gallons of groundwater from the site The cumulative volume of groundwater purged and the MTBE concentrations for the three sample sets are plotted on Figure 1 steady Based on Tosco's and GR's experience with this type ealiZ d inrthegfirst eight weeks rogram at er This s�purg ng reductions in MTBE concentrations are not always to medial action for asix-month period more likely program was originally proposed as an interim reincreases,BE removed produce reductions in MTBE concentrations d crease s the cumulative mul other sites f WITpe f Purging and disposal MTBE concentrations have been observed permitting or capital outlay program is cost effective as is does not require the engineering design, the rogram can be implemented, associated with more traditional remedial methods In addition, modified or terminated quickly with minimal disrupt 3 service station ly opthe cost effeatiolls �t eness of er relatively limited water production rates observed in negati e the purging program at the subject site ses of work, GR will further During the forthcoming delineation assessment an assess site conditions and look for feasible methods dto enhance well l the potenlation t l al purging capabilities at the site This could include proposing a purpose-designed extraction well if conditions suggest me a are TBE production rates could be enhancedextent er Last t currenthe y happears,�h sn ltm ted extent trations in the pcombined with proven to have limited lateral a ro ram more technically feasible and potentially enhanced purging rates would make this purging p g cost effective if resumed, the purging program would be proposed again as an intenm remedial action as long as plume delineation work continues lredelineated aivaUon of all possible remedial methods should be conducted only after the plume s fu y 2 140245 04