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J Pilot Study Workplan November 7, 2014 Project#54.62583.0001 Page 1 1.0 PURPOSE OF PILOT STUDY On behalf of Diamond Foods, Inc., Cardnc ATC has prepared this pilot study workplan to evaluate the effectiveness of in-situ chemical reduction for site remediation at the Diamond Foods Inc. facility located at 1050 South Diamond Street in Stockton, California. In April 2014, Cardno ATC prepared a Feasibility Study/Remedial Action Plan (FS/RAP) that analyzed remediation alternatives for reducing hexavalent chromium in soil and groundwater. Calcium polysulfide (Cascade®) was been identified as a potential remedial technology for mitigation of hexavalent chromium impacts at the site, and a 2005 treatability study found that the technology could successfully be applied at the site (Prima, 2005). The FS/RAP recommended performing a pilot test in order to determine the effectiveness of in-situ injection of ferrous iron solution and calcium polysulfide (Cascade®). A pilot study workplan was requested by the Central Valley Regional Water Quality Control Board in correspondence dated September 18, 2014. 2.0 BACKGROUND 2.1 DESCRIPTION OF FACILITY The Diamond Foods operates a food production facility located northeast of the intersection of Charter Way and South Diamond Street in Stockton, California (Figure 1). The facility is approximately 755,000 square feet in size. Walnuts and other types of nuts are processed and packaged at the facility. The site boundaries along with pertinent features are shown on Figure 2. 2.2 SITE HISTORY The Diamond Foods facility has been operating as mainly a walnut processing plant since the 1950s. Five underground concrete vaults were located north and east of the main processing building and formerly contained refrigerants used in the plant cooling systems. Several of these vaults are believed to be the source of the hexavalent chromium impacts at the site. Vaults 1, 5, and 6, installed between 1974 and 1976, were constructed of unlined concrete and historically contained propylene glycol. Vaults 1 and 5 had 1,200-gallon capacities and Vault 6 had a 500-gallon capacity. These vaults were located along the eastern side of the property adjacent to large walnut storage bins. Vaults 7 and 8 were installed in the 1950s and were located against the north wall of the processing building, and both were constructed of poured concrete with fiberglass and asphalt lining. Vault 7 had a capacity of 3,000 gallons and was used to store a sodium dichromate chill water solution. Vault 8 had a 5,000-gallon capacity and was used to store a chill water solution containing both sodium dichromate and calcium chloride. In addition, copper sulfate solution may have been stored in these two tanks at some point in their history (Weiss, 1988). All five vaults were removed from service and cleaned in June 1990 (Weiss, 1991). In May 1993, all five vaults were abandoned in place by filling them with a controlled density fill material. The locations of the former vaults are shown on Figure 2. 2.3 PREVIOUS INVESTIGATIONS Several phases of subsurface soil and groundwater investigation have been conducted at the site since December 1988. Initially, several investigations were conducted to evaluate the integrity of the vaults (Weiss, 1989). In January 1991, three groundwater monitoring wells were installed to monitor the first encountered groundwater saturated zone in the vicinity of the former vaults. At the time, groundwater was encountered at a depth of approximately 71 feet below ground surface (bgs) in each boring. The three wells were screened at a minimum of 56 feet and at a maximum of 89 feet bgs and were identified as MW-1, MW-2 and MW-3. In January 1991, Weiss personnel collected groundwater samples from each well. Samples collected from monitoring wells MW-1 and MW-2 (adjacent to Vaults 1 and 6, respectively) were analyzed for ethylene and