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Remedial Status Report-Tosco (Former BP Oil)Station No. 11195 August 28, 2000 average concentration of 115,000 parts per billion (ppb) was calculated from the December 30, 1998 data and used to estimate the mass of MtBE removed in the 39,000 gallons of groundwater purged fromthe pit during UST removal in January 1999. A second MtBE concentration average of 3828.2 ppb was calculated from the conductor casing grab samples (February 1, 1999 E and later) and used to estimate MTBE removal between February 1999 and April 2000. The average MtBE concentration (27535 ppb) derived from the two most recent groundwater samples was used to estimate the MtBE mass removed in 8,000 gallons purged from MW-5. An estimated total of 43.84 pounds of MtBE have been removed from groundwater beneath the site during the purging of 192,260 gallons of groundwater through April 25, 2000. The estimated MtBE removed and the calculation method are presented in Table 1. Conclusions and Recommendations As illustrated in Table 1, petroleum hydrocarbon concentrations in groundwater within the former UST pit have been dramatically reduced by purging groundwater from the pit on a regular basis. MtBE concentrations have decreased from 130,000 ppb on December 30, 1998 to as low as 31 ppb on October 9, 1999. The most recent sample from the conductor casing was reported to contain 5,400 ppb of MtBE. TPHg and benzene concentrations have decreased from 60,000 and 1,500 ppb on December 30, 1998 to not detected (<500 ppb and <5 ppb, respectively) for both analytes on April 6, 2000. MtBE concentrations in groundwater samples from the existing monitoring wells have been stable or greatly decreased during the last two sampling events. This trend is documented in. GR's Second Quarter 2000 Groundwater Monitoring and Sampling Report, dated July 19, 2000, which accompanies this status report. These two sampling events fall within or immediately following regularly scheduled groundwater removal from January 31 through April, 25, 2000, during which 60,500 gallons of groundwater were removed from the site. However, an elevated MtBE concentration (49,000 ppb) persisted in MW-5 during the first quarter sampling event (February 22, 1999). Therefore, GR recommended that groundwater be purged from MW-5 on a weekly basis, in addition to purging the conductor casing. During April, 2000 groundwater purging, approximately 7,500 gallons of groundwater was removed from MW-5. Consistent with other wells at the site, MtBE concentrations detected in MW-5 (6,070 ppb) were significantly reduced during the second quarter 2000. In conclusion, groundwater analytical results from the former UST pit document significant decreases in dissolved hydrocarbon concentrations as a result of the groundwater purging program. In addition, the most recent quarterly sampling results show significant reductions in MtBE concentrations in the existing monitoring wells. As a result of the purging, Tosco has succeeded in removing an estimated 43.88 pounds of MtBE from the site as of April 25, 2000. Therefore, GR is proposing continued weekly groundwater removal from the former UST pit conductor casing. Though greatly reduced, the highest MtBE concentration currently exists in MW-5. As a result, GR recommends continued groundwater removal from MW-5 in addition to 140193.48 2