SITE INFORMATION AND CORRESPONDENCE

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CPA0057 Sites _2 .RECE! Y .. 27 April 2016 West Charter Way and Lincoln Street Stockton, San Joaquin County "�\Y 0 W 2016 ENVIRONMENTAL HEALTH DEPARTMENT pollution currently exist in the deeper water-bearing zones. The horizontal and vertical extent of petroleum impacts have not yet been defined. In the Work Plan, Stantec proposes to; • Install one soil vapor probe ASG-1 to evaluate potential for vapor intrusion to indoor air. • Install groundwater monitoring wells SMW-31 B, SMW-32B, SMW-33B, SMW-35D, SMW-36D, and SMW-34E, to complete horizontal and vertical delineation of petroleum pollution in groundwater from the Site. • Install remediation wells ART-1 through ART-6, SLAS-1 through SLAS-3, SLVE-2, SAS-1, SAS-2 and SVEW-5 to implement cleanup of soil and groundwater at the Site. In the Site Management Plan, Stantec provided a draft Gantt chart, stating dates predicted for task completions and deliverables. Estimated delivery dates are dependent on: approval by all responsible parties; Atlantic Richfield Company (ARC), Chevron, Bimbo Bakeries USA (BBU) and Shell Oil Products USA (Shell); approval by the State Cleanup Fund; timely responses from local agencies and utility companies; and subcontractor availability. Review of the draft Gantt chart, in part, shows well installations to complete lateral and vertical delineation of petroleum pollution will be completed by early August 2016 along with submission of a Site Assessment Report. Expansion of the remedial system using Accelerated Remediation Technologies (ART) in addition to, additional soil vapor extraction and air-sparging wells (SVE/AS) as proposed in the Feasibility Study/ Corrective Action Plan, will be completed by the end of August 2016 with a Start-up Report estimated to be submitted 26 August 2016. Stantec intends to operate the expanded cleanup systems until August 2018. In the 4Q2015 Semi-Annual Groundwater Monitoring Report (4Q15), submitted 29 February 2016, Stantec reported that Blaine Tech Services gauged 63 monitoring wells and sampled 47 monitoring wells using low-flow sampling methods in October 2015. The groundwater samples were submitted to Pace Analytical in Davis for analysis of total petroleum hydrocarbons as gasoline (TPHg), benzene, toluene, ethybenzene, totals xylenes (collectively BTEX), methyl t-butyl ether (MtBE) and tert-butyl alcohol (TBA) by US EPA method 8260B. Investigation derived waste (IDW) from well sampling is understood to be currently stored at the former Texaco (Shell) property pending results of laboratory analyses. Documentation of IDW disposal will be provided in the next Groundwater Monitoring Report due 30 June 2016. In the 4Q15, Stantec noted the following historical maximum concentrations of benzene and MTBE detected at the Site: • Benzene—SLMW-10D at a concentration of 2,500 Ng/L • Benzene—SMW-248 at a concentration of 17,000 Ng/L • Benzene—SMW-268 at a concentration of 1,000 Ng/L • Benzene—SMW-29D at a concentration of 5,000 Ng/L • MTBE—SMW-19-81 at a concentration on 1,400 pg/L Based on these results, Stantec indicates additional delineation is needed in the deeper groundwater zones to adequately determine plume stability and establish trends to achieve regulatory closure of this Site.