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Stantec
<br /> Further Assessment Work Plan
<br /> Stockton Charter Way Commingled Plume
<br /> February 15, 2011
<br /> work. A copy of the HASP will be available on-site at all times during field work. The field staff
<br /> and subcontractors performing field activities will review the HASP prior to beginning field
<br /> operations, as described in this work plan, at the Site.
<br /> 3.2 Permitting
<br /> Prior to performing the well decommissioning activities, necessary permits will be obtained from
<br /> the SJCEHD.
<br /> 3.3 Preliminary Field Activities
<br /> Well locations will be marked or cleared of underground facilities prior to decommissioning. As
<br /> required by the California Government Code 4216, Underground Service Alert (USA) North and
<br /> 811 will be notified at least two working days before excavation/drilling activities. Well locations
<br /> will be marked with white paint to indicate the area of excavation/drilling. This will allow USA
<br /> North members, including local utility companies, to identify and mark the horizontal path of their
<br /> underground facilities located within the area of excavation/drilling. The area will be cleared if
<br /> no underground facilities are found. In conjunction with USA North and 811, a private utility
<br /> locating company will be utilized for clearing proposed well boring locations for underground
<br /> utilities.
<br /> 3.4 Well Decommissioning
<br /> Prior to decommissioning, the well borings will be air-knifed to approximately 5-8.1 ft below
<br /> ground surface (bgs), depending on client health and safety requirements, to investigate that no
<br /> underground facilities exist within the area of excavation/drilling. A total of 20 groundwater
<br /> monitoring wells (AMW-10, AMW-12, CMW-1 through CMW-3, SLMW-1, SLMW-7S, SLMW-7D,
<br /> SMW-1, SMW-4, SMW-5, SMW-6, SMW-7, SMW-9, SMW-10, SMW-11, SMW-13, SMW-17,
<br /> SMW-18-80, and SMW-18-120) will be decommissioned in accordance with the SJCEHD Well
<br /> Standards (SJCEHD, 2005).
<br /> Prior to performing decommissioning activities, each well casing will be inspected for
<br /> obstructions; if obstructions are found, they will be removed. For wells to be decommissioned
<br /> due to reasons other than being cross-screened (AMW-10, AMW-12, SMW-18-80, and
<br /> SMW-18-120), a hole at least one foot larger in diameter than the original borehole will be
<br /> excavated around the well casing to a depth of three feet below ground surface. The well
<br /> casing will be cut off and removed six inches above the bottom of this excavation. Each well will
<br /> be pressure-grouted with neat cement using a tremie pipe system forming a mushroom grout
<br /> cap/surface seal at a minimum one foot over the shortened top of casing. If groundwater is
<br /> expelled during the grouting process, it will be properly contained, characterized, and disposed.
<br /> The former well locations will be backfilled and resurfaced with appropriate materials to match
<br /> the existing grade.
<br /> Cross-screened wells to be decommissioned (CMW-1 through CMW-3, SLMW-1, SLMW-7S,
<br /> SLMW-7D, SMW-1, SMW-4, SMW-5, SMW-6, SMW-7, SMW-9, SMW-10, SMW-11, SMW-13,
<br /> and SMW-17) will be over-drilled removing material within the original borehole including the
<br /> well casing, filter pack, and annular seal. The borehole will then be grouted with neat cement
<br /> using a tremie pipe system forming a grout cap/surface seal from the bottom of the borehole to
<br /> Stockton Charter Way Commingled Plume Further Assessment Work Plan.doc 7
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