SITE INFORMATION AND CORRESPONDENCE

Home Browse Search

Mr. Shelby Lathrop - 2 - 5 June 2008 Former Tosco Bulk Terminal No. 10013 and piezometers P-1 through P-6. The results showed no significant increases in DO content in post-injection monitoring, and DO levels were substantially below the target concentration of 10 mg/L. Post-injection DO concentrations ranged from 0.5 mg/L in MW-2 to 6.8 mg/L in P-5. Total petroleum hydrocarbons as diesel (TPHd) was detected in all eight wells in concentrations ranging from 320 micrograms per liter (Ng/L) in MW-8 to 66 pg/L in MW-17B. TPH as gasoline (TPHg) detections were limited to three downgradient wells (MW-16, MW- 17B, and MW-20) and exceeded the water quality objective (WQO) of 5 pg/L. However, TPHg was non-detect in MW-16 and MW-20 in February and March. Di-isopropyl ether (DIPE) and methyl tertiary butyl ether (MTBE) concentrations also were highest in these three wells. The concentration of tertiary butyl alcohol (TBA) in source area well MW-2 increased from a baseline concentration of 480 pg/L to 1,100 pg/L. TBA was also detected at 160 pg/L in MW- 17B. With the exception of arsenic and alkalinity, the geochemical parameters show no distinct trends. There appears to be a decreasing arsenic trend in all eight monitoring wells while alkalinity concentrations show an increasing trend in the shallow wells. Near the end of June 2008 (the end of the six-month period), ConocoPhillips proposes to perform an additional round of groundwater sampling and to prepare a final pilot study report with an assessment of pilot test results. Based on these results, ConocoPhillips is considering installing replacement DO injection points in the vicinity of source area wells MW-2 and MW-8 and additional injection wells upgradient of the well clusters MW-16/MW-17B/MW-18C and MW-20/MW-21 B/MW-22C. ConocoPhillips conducts groundwater monitoring at the Site pursuant to Monitoring and Reporting Program (MRP) No. R5-2004-0824. The 30 April 2008 First Quarter 2008 Groundwater Monitoring Report (First QMR) describes the results groundwater monitoring conducted on 19 March 2008. The groundwater flow directions in the previously described A, B, and C zones were calculated to flow to the southeast. The gradients ranged from 0.001 feet per foot (ft/ft) in the A zone to 0.007 ft/ft in the C zone. During the first quarter, the highest concentrations of TPHd and TBA were detected in MW-2 at 130 pg/L and 540 pg/L, respectively. TBA was also detected in the B and C zones in MW- 21 B and MW-18C at 45 pg/L and 54 pg/L, respectively. Toluene and xylene were not detected, and MTBE levels were below its WQO. Our comments are provided below. 1 . We concur that the Report shows the oxygen injections presently are ineffective at achieving the target DO concentration of 10 mg/L. The COCs show no consistently discernible concentration trends, with some decreases and some increases. The most noteworthy increase is the TBA concentration in source area well MW-2 from a baseline concentration of 480 pg/L to 1 ,100 pg/L on 24 March. Based on these results, we concur that optimization of the delivery system is warranted. By 25 July 2008, ConocoPhillips must submit the six-month report showing the results of the pilot study and if necessary, recommendations for remediation system upgrades. The recommendations must also include methodologies for cleaning up TBA in the C zone.