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Ms. Emily Cushman September 12, 2016 Blast perforation was approved for VW-4 by the San Joaquin County Environmental Health Department (SJCEHD) previously but negotiations with the SJCEHD for blast perforation of well MW-15 and 11 sparge points(SP-1, SP-3, SP-4, SP-5, SP-6, SP-7, SP-8, SP-9, SP-10, SP-12, SP-13) is ongoing. In order to move the Site forward and towards closure, Arcadis recommends that these remaining wells and sparge points be abandoned using the pressure grout method.Well construction details for these wells are included in Table 1, and well logs are included in Attachment A.The sections below describes the proposed activities to pressure grout the remaining wells. PRE-FIELD ACTIVITIES Site Health and Safety Plan As required by the Occupational Safety and Health Administration (OSHA)"Hazardous Waste Operations and Emergency Response"guidelines (29 CFR 1910.120),Arcadis will prepare a site-specific Health and Safety Plan(HASP). The field staff and contractors will review the HASP prior to beginning field operations at the site. Permitting and Notifications Arcadis will obtain all necessary well destruction permits from SJCEHD and any necessary encroachment permits from the City of Stockton. Arcadis will ensure that access agreements are in place prior to performing work. Utility Locating Underground Service Alert(USA)will be notified a minimum of 48 hours prior to commencing field activities to identify public utility lines that may be in conflict with the well locations. In conjunction with USA, a private utility locating company will be utilized to further evaluate the potential presence of underground utilities in the vicinity of the wells. Pressure Grouting Activities Before pressure grouting, depth to groundwater will be measured to within 0.01 feet below top of casing (BTOC) in each monitoring well using a water level indicator to calculate the volume of groundwater present in the well columns. The calculated volume of each well (solid casing volume plus borehole volume in the screened interval)will be used to verify that the volume of backfill material placed in the well is, at a minimum, equal to the volume of the well casing. Backfill materials will be prepared according to an approximate water-to-grout ratio of 6 gallons of water to two 47-pound bags(94 pounds)of Type ll- V Portland Cement. The surface seal and well box at each well location will be removed using a jack hammer. Once the well casing is filled with grout, pressure will be applied to the well casing at approximately 20 pounds per square inch (psi)for 5 minutes. The wells will be pressure capped and allowed to settle for approximately 15 to 30 minutes.After pressure grouting,the top three feet will be removed using either a hand auger or an air knife and vacuum truck. Due to the presence of previously identified utilities adjacent to VW-4,Arcadis proposes to only remove the top one foot. Arcadis will place arcadis.com Page: EAProjects\76PP Project Folders\351515-Stockton\5 Deliverables\Work Plans\351515 Work Plan Addendum_FINAL_091216.docx 2/4