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1,2-DCA. The petroleum hydrocarbon and 1,2-DCA constituents in off-site groundwater are from other sources. The occurrence of these constituents at the site and potential off-site sources are described in greater detail in the April 19, 2010, Groundwater Corrective Action Plan (AMEC Geomatrix, 2010a). 5 Groundwater Interim Remedial Action Plan UniFirst proposes interim remedial action that will promote in-situ bioremediation of the CVOCs in groundwater at the site and extend the characterization of CVOCs in groundwater. Soil vapor boring installation and soil vapor sampling were part of previous work plan editions but since the work has been completed they and are not discussed in this revision. The remedial action is proposed to consist of six phases: monitoring well installation, injection well placement evaluation, pre-injection monitoring, injection well installation, injection, and post-injection monitoring. These phases are described in the following subsections. 5.1 Monitoring Well Installation Installation of a new monitoring well (MW-11)will be conducted in the sidewalk area across the street, north of the MW-10 well cluster, along the eastern portion of the northern boundary of the site (Figure 5). The area where well MW-11 is proposed likely contains underground utilities. The well location will be adjusted as needed to prevent damage to utilities. Well MW-11 will be installed with screened intervals at approximately the same depth as wells MW-5C and MW-10C as shown on Figure 6. WSP will contract with a California-licensed driller to install the well. Fieldwork will be conducted under the direct supervision of a professional engineer or geologist. The monitoring well will be installed in conformance with WSP's field protocols (Appendix B). Prior to commencing subsurface work, WSP will obtain drilling permits from the San Joaquin County Environmental Health Department (SJCEHD). WSP will obtain encroachment and traffic permits from the City of Stockton to work in the city right a way. At least 2 business days before the borings are advanced, WSP will mark the boring locations and notify Underground Services Alert. The boring locations will also be cleared by a private underground utility locating service. The concrete sidewalk will be cored using a diamond bit drill. Each location will be cleared of utilities to a minimum depth of 5 feet bgs using a hand auger. Based on recent depth-to-groundwater measurements, groundwater at this portion of the site is at about 17 feet bgs. Drilling equipment will be decontaminated before drilling and equipment stored on racks to prevent contact with the ground surface. The boring will be advanced using a hollow-stem auger drilling rig to a depth of approximately 115 feet bgs. Samples will be collected for logging at 5-foot intervals using a 1.5-foot-long split spoon sampler and logged for lithology using ASTM International Test Method D2488. Well construction will be adjusted in the field depending on the actual depth to first-encountered groundwater and lithology at the drilling locations. Hydrated bentonite chips will be used to backfill the bottom of the borings should the boring be advanced deeper than the final screened interval. The well will be constructed of 2-inch polyvinyl chloride well casing with a 10-foot in length, 0.01-inch factory slotted screen interval. The well filter pack will consist of 2/12 sand below a hydrated bentonite chip transition seal. The well will then be sealed from the top of the transition seal to near the ground surface with neat grout cement. The surface completion will consist of a flush-mounted well box. Upon completion, the monitoring wells will be surveyed for location and elevation consistent with the GeoTracker survey standard. A minimum of 48 hours after drilling and installation, the well will be developed to remove sediments and stagnant water. Well development water will be placed in bins or drums pending waste characterization. Well development will consist of surging and bailing until groundwater field parameters (turbidity, pH, electrical conductance, and temperature) stabilize. Initial monitoring of the newly installed well MW-11 will be performed during the next regularly scheduled semiannual monitoring event following well development. Subsequent monitoring of well MW-11 will be performed during both semiannual and annual monitoring events for the next 3 years and then change to annual monitoring. 2019 Groundwater Interim Remedial Action Work Plan—Revision 3 Page 4 UniFirst Facility,Stockton,California Project No.0132902023 I:\13000s\13290\Arch ive\13290-177.docx