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v <br /> A S S O C I A T E S I N C <br /> BENCH SCALE TREATABILITY STUDY FOR <br /> REDUCING HEXAVALENT CHROMIUM <br /> Diamond Walnut Growers <br /> 1050 South Diamond Street <br /> Stockton, California <br /> LO INTRODUCTION <br /> ATC Associates Inc (ATC) has prepared this report on behalf of Diamond Walnut Growers <br /> (DWG) to summarize the results of a bench scale treatability study for reducing hexavalent <br /> 1 chromium (CrVI) in the subsurface at the facility located at 1050 South Diamond Street in <br /> Stockton, California (Figure 1) This work was conducted pursuant to a directive from the <br /> California Regional Water Quality Control Board (CRWQCB) and in general accordance with <br /> ATC's Revised Workplan for a Bench Scale Treatability Study for Reducing Hexavalent <br /> Chromium at Diamond Walnut Growers, dated July S, 2004 The work was authorized by Mr <br /> Mike Lescisin of DWG <br /> 1.1 Objective <br />�i The purpose of the bench scale treatability study was to evaluate the effectiveness of two <br /> potential remedial option methods of reducing CrVI in situ in groundwater and soil under <br /> laboratory conditions prior to implementation in the field The potential remedial options <br /> evaluated were use of ferrous iron solution and calcium polysulfide (Cascade") The scope of <br /> work included collecting soil and groundwater samples from the site, and conducting laboratory <br /> testing of the soil and groundwater media to evaluate the potential of ferrous iron solution and <br /> calcium polysulfide to reduce and stabilize CrVI via injection into the subsurface <br /> 12 Site Location <br /> The DWG plant is located northeast of the intersection of Charter Way and South Diamond Stieet in <br /> Stockton, California (Figure 1) The site boundaries along with pertinent features are shown on <br /> Figure 2 <br /> 1.3 Site Back round <br /> According to DWG, the facility has been operating as a walnut processing plant since the 19505 <br /> Five underground concrete vaults were located north and east of the main processing building <br />' and formerly contained refrigei ants used in the plant cooling systems (Figure 2) Vaults 1, 5, and <br /> h, installed between 1974 and 1976, weie concrete and historically contained propylene glycol <br /> Vaults 1 and 5 had 1,200-gallon capacities and Vault 6 had a 500-gallon capacity These vaults <br /> rwere located along the eastern side of the property adjacent to large walnut storage bins (Figure <br /> �. 2) Vaults 7 and S were constructed with poured concrete and lined with fiberglass and asphalt, <br /> and were used to store calcium chloride and sodium dichromate chill water solution Vaults 7 <br /> 51Lnvironmenlal1625831reports\bench test rpt dOL l <br />