FIELD DOCUMENTS_1999-2014 - Laserfiche WebLink

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ATTACHMENT A FIELD PROCEDURES ToXICHEM will supervise the soil boring advancement and groundwater monitoring well installation at the locations presented on Figure 2. Under the supervision of TOXICHEM staff, a licensed drilling contractor will advance a 6-inch diameter soil boring. The boring will be advanced with a truck-mounted drill rig equipped with a 6-inch diameter continuous flight, hollow-stem auger. Soil samples will be collected at 5-foot intervals and logged in the field by a ToXICHEM geologist. A California registered geologist will supervise the preparation of geologic logs from the borings, noting changes in lithology utilizing the Unified Soils Classification System. Soil samples will be collected at significant changes in lithology and at 5-foot depth intervals and analyzed in the field for total volatile hydrocarbons by a photo-ionization detector. It is anticipated that the borings will be advanced to approximately 30 feet bgs due to historically fluctuating groundwater conditions. The groundwater monitoring wells will be designed and constructed in accordance with San Joaquin County Public Health Services guidelines. When the borings are completed, they will be reamed utilizing a 10-inch diameter hollow stem auger and a 4-inch diameter groundwater monitoring well will be constructed within the bore hole. Flush thread jointed, Schedule 40, polyvinyl chloride casing of 4-inch diameter will be placed down the hollow stem of the augers to the base of the boring. The wells will be constructed to approximately 30 feet bgs and the screened interval will extend from approximately 5 feet bgs. The remaining casing section will be solid and non-slotted. A well cap will be slipped on to the bottom of the well casing and a locking cap will be placed at the top of each well. The monitoring wells will be filter-packed with clean Monterey silica sand throughout the screened interval. Specification of the filter material will be determined based on lithology encountered during drilling and will likely consist of one of the following: No. 3 Monterey Sand, No. 2/12 Lonestar Sand, and/or No. 2/16 Lonestar Sand. The filter-pack material will be installed in the annular spacing between the monitoring well pipe and the auger; the filter-pack material will extend approximately 1-foot above the top of the screened interval. A 1-foot thick layer of bentonite pellets will be placed and hydrated above the filter material to provide an annular seal and the remainder of the boring will be filled with a sand-cement slurry to grade. The well casing will be enclosed inside a steel well monument. A licensed surveyor will be retained to survey the top of the casing of the well head relative to mean sea level. The initial well development will be conducted by using a 1.7 inch Brainard-Kilman mechanical lift hand pump, an air-lift or nitrogen-lift pump, or a positive displacement bladder pump dependent on the depth to ground water and the screened interval. The wells will be developed until a minimum of four well volumes have been purged (if recharge rates permit) and the discharged water appears clear of sediment. Electrical conductivity, temperature, and pH of the ground water will be recorded throughout the development process. The well development will continue until the electrical conductivity, temperature, and pH of the discharged water have stabilized. Depth to water measurements will be recorded prior to and following the well development activities. Prior to sampling, a minimum of four well volumes will be purged from the well through the use of a positive displacement bladder pump or Teflon bailer. Electrical conductivity, temperature, and pH of the ground water will be recorded throughout the purging process. The purging activities will continue until the electrical conductivity, temperature, and pH of the discharged water have stabilized. Water samples for analytical testing will be obtained through the use of the bladder pump or Teflon bailer. The water