WORK PLANS - Laserfiche WebLink

Home Browse Search

Broadbent&Associates,Inc. • Vacaville,CA Well Abandonment Work Plan ARCO Station No,4932 March 30,2014 Page 2 The Site-specific HASP will be prepared for use by personnel implementing the work plan. A copy of the HASP will be available on-site during work. A safety tailgate meeting will also be conducted daily to review potential hazards and scope of work. Borehole Clearing A precautionary drilling technique(i.e., a hand auger, air knife, pressurized water knife and/or high vacuum extraction,etc.)will be utilized through the initial six and one-half(6.5)feet of the subsurface in the borings that require overdrilling to minimize impacts to unknown or abandoned buried utilities. Well Abandonment Well abandonment will be conducted in accordance with the SJCEHD's December 24, 2013 letter and Well Standards prepared by SJCEHD for compliance with the San Joaquin County Ordinance Code Section 9-1115.6. Based on the current and historical site data,the following abandonment methods are proposed: • The following wells have laboratory data from the last groundwater sampling event that reported non-detectable concentrations of contaminants of concern for acceptable laboratory detection limits,and are not located in the areas of known or suspected soil contamination: MW-8 through MW-11, DMW-2, EW-5, and 5-6. '7 These wells will be destroyed by pressure grouting from the bottom upwards while leaving the well casing in place. The top three feet or more of the well will be cleared out using air vacuum/ air knife to create a borehole that is at least one foot larger in diameter than the auger originally utilized to install the well. The exposed well casing will be cut-off and the soil around the cut-off casing will be removed to the depth of an additional six inches below the new"top" of the cut- off casing. The grout sealant will be spilled out of the top of the well casing to form a mushroom cap seal with at least twelve inches of neat cement grout that will be poured six inches above and six inches below the top of the cut-off casing. After the cement grout has set,the excavation will be backfilled with clean soil or road base fill and resurfaced to match the existing grade(i.e. -concrete,asphalt). • The laboratory data for the last sampling events from the following wells demonstrate the presence of contaminants of concern remaining in the groundwater: DMW-5, DMW-9, DMW-10, EW-1 through EW-4, EW-6, EW-7, MW-1 through MW-7,and SVE-1. In addition, the following wells are located in an area of known or suspected soil contamination based on the soil iso- concentration maps provided in Broadbent's November 2013 Case Closure Request: DMW-1, DMW-3, DMW-4, DMW-6, DMW-7,SVE-2,and 5-1 through 5-5. These wells will be destroyed by over-drilling to remove the contents of the well (well casing, screen,filter pack,grout,sealant, etc.). The top six and a half feet of the well will be cleared out using air vacuum/air knife to create a borehole that is at least one foot larger in diameter