SITE INFORMATION AND CORRESPONDENCE

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Mr Joe Aldridge - 2 - 19 August 2006 ST Services Stockton Terminal J • attempt to advance borings in the C-zone (67 to 80 feet deep) using direct push drilling technology; if the laboratory analytical results indicate that the dissolved phase constituents in groundwater originated at the NuStar facility, • use a different drilling technology. possibly hollow-stem auger or sonic. if refusal in the C- andor D zone is encountered using direct push technology, • submit soil samples for laboratory analysis. and • install groundwater monitoring wells in the C- and D-zones, if necessary. NuStar has conducted monitoring at the Site since 1992. In 2002. gasoline releases occurred from aboveground storage tanks (AGTs) G 3301 . G 3302. and D 1503. Groundwater monitoring at the Site is conducted pursuant to Monitoring and Reporting Program (MRP) No R5-2007-0818. Regional Water Board staff reviewed the 22 July 2008 Groundwater Monitoring Report. Second Quarter 2008 (Second QMR). The source area monitoring well. ST/MW-1 . has historically contained SPH. ST/MW-1 was not included in the quarterly monitoring program until 2005, when no SPH was observed. During the second quarter of 2008, this well contained the maximum concentrations of TPHg, benzene, toluene. ethylbenzene, and MTBE at 160.000 micrograms per liter (ug/L). 16.000 pg/L, 8.100 pg/L. 3.300 pg/L, and 180.000 respectively. PS/MW-14 also contained SPH until 2005 The highest concentration of TPHd was detected in PS/MW-14 at 7.700 pg/L. NuStar's efforts to use global positioning satellite (GPS) and an excavator to locate monitoring wells UP/MW-1 and UP/MW-3 proved unsuccessful Therefore. NuStar will continue to sample PS/WC-4S to allow collection of data in this area. Our comments are presented below. . The Revised VVork Plan was designed to make investigation of the C- and D-zones contingent on whether soil and groundwater pollution encountered offsite originated at the NuStar facility However. the Revised Work Plan does not specify how NuStar intends to identify the origin of SPH or dissolved product encountered during the investigation Therefore. I contacted Ms. Spencer by telephone for clarification on the criteria that will be used to make this determination In our discussion. which was documented in the attached 8 August email (Email), Ms. Spencer stated that the presence of automotive facilities east of Stork Road were potential off-site source areas. While advancing borings in the vicinity of these facilities. NuStar proposes to apply the following lines of evidence to determine whether petroleum hydrocarbons encountered during the investigation originated off-site of the NuStar facility. • The presence of separate phase hydrocarbons (SPH) based on visual observations and/or field sheen tests in A-zone soil in the borings located east (or on) Stork Road or upgradient of the facility; • elevated petroleum concentrations (indicative of the presence of SPH) in A-zone soil in the borings located east (or on Stork Road or upgradient of the facility: • a pattern and distribution of soil and groundwater concentrations in the A- and B-zones that support the presence of an off-site source. and/or • composition of the fuel compounds in soil or groundwater in off-site borings.