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2 �� Cardno� Workplan for Soil Gas Study—Subslab Sampling 807 N.Hunter Street Stockton,California ATCNovember 25,2014 Shaping the Future UniFirst Corporation (UniFirst), a company that supplies uniforms to industry was named the responsible party for the release as the result of its purchase of the property that included the 819 N. Hunter address which had been formerly used by a dry cleaning operation. The investigation/remediation effort is being overseen by the California Regional Water Quality Control Board Central Valley Region's (RB's) Site Cleanup Section. Ms. Amy Terrell is the agent of the RB who oversees the actions associated with this investigation and cleanup. UniFirst has contracted with AMEC Geomatrix, Inc. of Fresno, California (Geomatrix), an environmental consulting firm, to investigate and remediate the release. In November 2003, heating oil began to surface during Unifirst Corporation's, site renovation activities at 819 N. Hunter Street. This led to a haz mat emergency response action. During the follow up remediation efforts and on- going construction activities, an underground storage tank (UST) reported to contain heating oil was discovered and removed. The emergency response action and follow-up remediation activities resulted in the removal of approximately 22,000 gallons of oil and water as well as the removal and disposal of excavated soil containing petroleum hydrocarbon constituents and CVOCs. In a January 2007, the RB issued a letter, directing Unifirst to evaluate the nature and extent of the CVOCs that had been detected in the groundwater samples, install monitoring wells and conduct quarterly groundwater monitoring. UniFirst responded and created a groundwater monitoring network consisting of four on-site groundwater monitoring wells (MW-1 through MW-4), and seven off-site groundwater monitoring wells (MW-5A, MW-58, MW-5C, MW-6, MW-7, MW-8, and MW-9). The on-site wells, MW-1 through MW-4, and off-site well MW-5A are shallow screened wells. Wells MW-5B, MW-6, MW-7, and MW-8 are screened in the intermediate part of the aquifer; and MW-5C and MW-9 are screened in the deep zone. CVOCs, primarily tetrachloroethene (PCE), were detected in the groundwater samples collected from the monitoring wells. The distribution of CVOCs appears to be widespread, with the groundwater samples collected from all but one monitoring well demonstrating contamination by CVOCs. The only exception was MW-9, which is the farthest distance from the release site and screened in the deepest part of the aquifer of all the monitoring wells. The 804 N. Hunter portion of the subject site is nearby to the CVOCs release source area and within the CVOCs impacted groundwater plume. Following the removal of a what appears to be a significant petroleum hydrocarbon mass (i.e. excavation of contaminated soil, extraction of contaminated water), detected groundwater concentrations of non-chlorinated petroleum hydrocarbons rapidly declined. Eventually the RB determined that the remaining non-chlorinated petroleum hydrocarbons no longer adversely affected water quality or human health and safety at the subject and adjacent properties. As a result, the RB issued a "No Further Action" letter in regards to the petroleum release. Meanwhile the investigation/remediation of the CVOCs continued. In August 2010, the RB sent a letter, requesting Unifirst to devise a remediation plan to reduce the mass of CVOCs in groundwater. According to Ms. Terrell, Geomatrix proposed and implemented a pilot study where hydrogen release compound (HRC), a commercially available material was injected into three water bearing zones at the center of the plume mass through several individual injection points parallel to N. Hunter on the east side of the property where the evidence suggests the release is to have occurred. According to Geomatrix, the HRC serves as an electron donor to stimulate naturally occurring microbial degradation of the CVOCs in groundwater via reductive dechlorination. The injection took place during the week of June 27, 2011. www.cardnoatc.com