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On June 2, 2015, monitoring well MW-4 was replaced. The casing of MW4 had previously been found to
<br /> be obstructed and could not be sampled. Well replacement activities consisted of over-drilling and re-
<br /> installing one existing site-related monitoring well within the same boring. The replacement well (MW-4R)
<br /> was constructed with a 20-foot screen interval of 0.010-inch slotted Schedule-40, 2-inch diameter PVC
<br /> extending from 45 to 65 feet bgs. On June 9, 2015, replacement monitoring well MW-4R was developed.
<br /> On June 3 and 4, 2015, two nested groundwater observation wells, OBSW-S and OBSW-D were installed
<br /> at the site near existing monitoring well MW-3 and in the vicinity of Vaults 7 and 8. The wells were
<br /> constructed to the depths of approximately 55 feet below ground surface (bgs) and 75 bgs, respectively.
<br /> Shallow observation well OBSW-S was constructed with 10 feet of 0.010-inch slotted Schedule 40 2-inch
<br /> diameter PVC casing extending from approximately 45 to 55 feet bgs. Deep observation well OBSW-D was
<br /> constructed with 5 feet of 0.010-inch slotted Schedule 40 2-inch diameter PVC casing extending from
<br /> approximately 70 to 75 feet bgs. Along with MW-4R, the shallow and deep observation wells were
<br /> developed on June 9, 2015.
<br /> On June 15, 2015, Cardno ATC (now Atlas) personnel conducted pre-injection baseline monitoring and
<br /> sampling from wells OBSW-S, OBSW-D, MW-1, MW-3, MW-6, MW-7, and MW-8. These wells were
<br /> gauged, purged, and sampled in accordance with the RWQCB Monitoring and Reporting Program No. R5-
<br /> 2015-0012-003 for Diamond Foods, Inc., issued March 26, 2015.
<br /> On June 16 and June 17, 2015, Cardno ATC supervised the injection of 1,500 gallons of calcium polysulfide
<br /> (CPS), known commercially as Cascade®or Calmet®, into the water bearing formation below the site via
<br /> existing well MW-3. To ensure that the CPS solution was fully injected into the formation, approximately
<br /> 100 gallons of clean chase water was subsequently injected into MW-3.
<br /> In July 2015, ATC personnel initiated three post-injection monitoring and sampling events at the subject
<br /> site. Results were presented in Cardno ATC's Well Installation and Pilot Study Report, dated October 2,
<br /> 2015.
<br /> On January 30, 2017, ATC field staff supervised the installation of one groundwater monitoring well, MW-
<br /> 10. The well was installed to monitor groundwater quality downgradient of the pilot study area. In February
<br /> 2017, ATC supervised the injection of 4,700 gallons of calcium polysulfide into the water bearing formation
<br /> below the site. A total of eight injection points were selected to reduce the highest concentrations of
<br /> hexavalent chromium in groundwater reported in monitoring wells MW-5 and MW-6 and in observation
<br /> wells OBSW-S and OBSW-D near the source area. Well installation activities, injection activities, and
<br /> results were presented in ATC's Well Installation and Additional Pilot Study Injection Testing Report, dated
<br /> May 1, 2017.
<br /> In February 2019,ATC supervised the injection of 4,700 gallons of calcium polysulfide, known commercially
<br /> as Cascade®or Calmet®, into the water bearing formation below the site. A total of eight injection points
<br /> were selected to reduce the highest concentrations of hexavalent chromium in groundwater reported in
<br /> monitoring wells MW-5, MW-7, MW-10, and in observation wells OBSW-S and OBSW-D near the source
<br /> area. Field activities and results of baseline and the one-month post injection monitoring events were
<br /> presented in ATC's Baseline Monitoring, First Quarter 2019 Groundwater Monitoring and Additional Pilot
<br /> Study Injection Testing Report dated May 1, 2019.
<br /> The locations of monitoring wells and soil borings are shown on Figure 2.
<br /> SCOPE OF SERVICES
<br /> Health and Safety Plan
<br /> As required by the Occupational Safety and Health Administration (OSHA) Standard "Hazardous Waste
<br /> Operations and Emergency Response"guidelines (29 CFR 1910.120), and by the California Occupational
<br /> Safety and Health Administration (Cal-OSHA) "Hazardous Waste Operations and Emergency Response"
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