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Pilot Study VVorkplan May 25, 2018 Diamond Foods Inc. Page 5 diameter PVC casing extending from approximately 70 to 75 feet bgs. Along with MW-4R, the shallow and deep observation wells were developed on June 9, 2015. On June 15, 2015, Cardno ATC (now ATC) personnel conducted pre-injection baseline monitoring and sampling from wells OBSW-S, OBSW-D, MW-1, MW-3, MW-6, MW-7 and MW-8. Wells were gauged, purged, and sampled in accordance with the RWQCB Monitoring and Reporting Program No. R5-2015- 0012-003 for Diamond Foods, Inc., issued March 26, 2015. On June 16 and June 17, 2015, Cardno ATC supervised the injection of 1,500 gallons of calcium polysulfide (CPS), known commercially as Cascade® or Calmet®, into the water bearing formation below the site via existing well MW-3. To ensure that the CPS solution was fully injected into the formation, approximately 100 gallons of clean chase water was subsequently injected into MW-3. In July 2015, ATC personnel initiated three post-injection monitoring and sampling events at the subject site. Results were presented in Cardno ATC's We// Installation and Pilot Study Report, dated October 2,2015. On January 30, 2017, ATC field staff supervised the installation of one groundwater monitoring well, MW-10. The well was installed to monitor groundwater quality downgradient of the pilot study area. Well installation activities and results were presented in ATC's We// Installation and Additional Pilot Study Injection Testing Report, dated May 1, 2017. The locations of monitoring wells and soil borings are shown on Figure 2. 2.4 SENSITIVE RECEPTORS Four municipal wells (WP-1 through WP-4) located at the four corners of the facility (Figure 2) were installed in 1955 and 1956 to provide water to the plant and to the community during periods of high demand. These four municipal wells were completed to depths ranging from approximately 420 to 460 feet bgs. Well WP-4 was abandoned in 1989. Groundwater sampling performed in 1989 and 1990 indicate that the concentrations of total chromium were below the laboratory reporting limit in WP-1, WP-2, and WP-3. In 1991, total chromium was detected in WP-2 at at a concentration of 0.054 mg/L. However, neither total nor hexavalent chromium were detected in any WP-1, WP-2, or WP-3 in groundwater sampling events conducted through 1992. The municipal wells were not sampled again until 1998 at which time both total and hexavalent chromium were again below laboratory reporting limits. Total and hexavalent chromium concentrations in WP-1, WP-2, and WP-3 were also below laboratory detection limits during the next two monitoring events conducted in 1999 and 2000. The three wells were sampled again in 2001 and hexavalent chromium was detected in WP-1 at a concentration of 0.0044 mg/L. However, total and hexavalent chromium concentrations were below laboratory reporting limits in WP-2 and WP-3. WP-1 was sampled again in 2002 and total and hexavalent chromium were detected at concentrations of 0.0061 and 0.0043 mg/L, respectively. The last time any of the municipal wells were sampled was in 2004 when only WP-1 was sampled. Concentrations of both total and hexavalent chromium in groundwater were below the laboratory reporting limits at that time (ATC, 2008). In a phone conversation on March 12, 2014 between Cardno ATC and Mr. Robert Grandburg with the City of Stockton, Municipal Utilities Department, Mr. Grandburg informed Cardno ATC that the remaining municipal wells WP-1, WP-2, and WP-3 have all been destroyed.