SITE INFORMATION AND CORRESPONDENCE

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Mr. Thomas Kosel - 2 - 25 July 2007 Constituents of concern (COCs) at this Site include total petroleum hydrocarbons as gasoline (TPHg), TPH as diesel (TPHd), benzene, toluene, ethyl benzene, and xylenes (BTEX), methyl tertiary butyl ether (MTBE), tertiary butyl alcohol (TBA), di-isopropryl ether (DIPE), ethyl tertiary butyl ether (ETBE), and tertiary amyl methyl ether (TAME). Most recently, TBA, MTBE, and TPHd have had the highest concentrations. During 2006, A zone well MW-14 contained the maximum TBA concentration of 2,800 micrograms per liter (pg/L) in May 2006. The B and C zones also had TBA at a maximum concentration of 23 pg/L in MW-22C. Downgradient well MW-20 had the maximum MTBE concentration at 15 pg/L, and downgradient well MW-21 B had the maximum TPHd concentration at 210 pg/L in November 2006. The First QMR describes groundwater gradient and flow direction in the three zones as ranging from 0.001 to 0.003 ft/ft in a southwesterly direction during the month of February. DTW during the first quarter ranged from about three to about 14 feet bgs. The maximum concentrations of TPHg and TPHd were 250 pg/L and 90 pg/L respectively. The maximum concentrations of TBA and MTBE were 890 pg/L and 15 pg/L, respectively. Generally, ConocoPhillips presently monitors three wells quarterly, six wells semi-annually and seven wells annually with sampling for select parameters varying from quarterly to semi- annually. Presently only groundwater level measurement is conducted in three (MW-10, MW-5 and MW-6) wells. Groundwater monitoring is not conducted in six existing piezometers. ConocoPhillips proposes reducing the groundwater monitoring frequency to semi-annually for 11 of the 19 wells and six piezometers, and annually for six wells including MW-10. ConocoPhilips is proposing elimination of MW-5 and MW-6 from the monitoring program, and semi-annual reporting during the first and third quarters. In the 4 April 2006 Work Plan for Oxygen Injection Pilot Test, Former Tosco Bulk Terminal No. 10013 (Work Plan), ConocoPhillips proposed conducting the oxygen injection pilot test utilizing an injection well network in the source area of groundwater pollution at the Site. The implementation schedule provided in the Annual Report shows that construction of the pilot system was to occur between 28 May 2007 and 20 July 2007. In our 21 July 2006 letter, Regional Water Board staff requested additional information including baseline groundwater data prior to performing the pilot study. Earthtech submitted the Specs that provide system installation plans and specifications for an engineering contractor. On 6 July 2007, Earthtech notified Regional Water Board staff by email that they had completed installation of the pilot study system consisting of 12 injection wells. The Second QMR describes groundwater gradient and flow direction in the three zones as 0.001 ft/ft in a southwesterly direction during the month of May 2007. DTW during the second quarter ranged from about four to about 14 feet bgs. TPHg and TPHd were ND. The maximum concentrations of TBA and MTBE were 39 pg/L and 13 pg/L, respectively. Second quarter monitoring however, is not conducted in wells MW-1, MW-2, and MW-3 where the highest COC concentrations are typically observed. Oxygen injection is scheduled to commence during the third quarter. Our comments are provided below. 1. The MW-19C and MW-22C monitoring data show that the plume was not defined vertically and laterally. The first quarter monitoring data show that continued natural attenuation of