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BROAOB�IV T 4820 Business Center Drive,$u0e 110 IT]707-455r119do[Fj�O 863-9046 broedl�entm CM Ceeatiny Solutions. Quil[fi�rg Teust- June 13, 2014 Project No. 13-90-103 Re: Addendum to Site Assessment Work Plan, Former ARCO Station No. 443, 2478 E. Oak Street, Stockton, California; SJCEHD Site Code: RO-1781 Dear Mr. Morescalchi: Broadbent&Associates, Inc. (Broadbent) is pleased to submit this Addendum to Site Assessment Work Plan for Former ARCO Station No. 443 located at 2478 East Oak Street, California (Site). The original work plan (Work Plan) that was submitted in November 2013 proposed the installation of two soil gas wells and two soil borings for the collection of soil and soil gas samples at the Site. This addendum recommends installation of an additional soil boring SB-2, between the two previously drilled soil boring locations, identified as SB-26 and SB-27 in the -- — attached drawing. This boring will provide additional characterization and a data point between SB-26 and SB-27. The boring will be installed and sampled using the procedures identified in the Work Plan. After collecting samples between 0 and 5 feet bgs and another one between 5 and 10 feet bgs, the boring will be backfilled with cement grout and resurfaced to the existing grade. This addendum also recommends collection of shallow soil samples from the borings advanced for soil gas well installation, whenever possible. The Work Plan had proposed installation of two soil gas wells for collection of soil gas samples. San Joaquin County Environmental Health Department(SJCEHD) response letter dated January 6, 2014 required that purge volume tests, leak tests, and soil gas sampling should not be collected within 48 hours after the soil gas well installation. SJCEHD also recommended that if the helium shroud used in leak test is infused with tracer helium compound, at least five minutes equilibrium time should be allowed to be elapsed prior to the sample collection. In conducting this investigation, Broadbent will follow the recommendations from the SJCEHD letter. The Work Plan had indicated that the soil samples will be collected by driving a split-spoon sampler. However, to avoid potential damage to unidentified utilities, the shallow sample will be collected in 2 ounce glass jars directly from the hand auger. The deeper sample may be collected in a similar fashion directly from a hand auger or by using a slide hammer drive tube assembly. Broadbent intends to conduct the investigation in accordance with the Work Plan, this addendum, and SJCEHD letter. Should you have questions or require additional information, please do not hesitate to contact us at(707)455-7290.