ARCHIVED REPORTS XR0006100 - Laserfiche WebLink

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EXCAVATION The excavation will commence at the former UST area and then proceed to the north, towards the former northern pump island area where borings THI, E and F sample results indicated high level soil contamination exists and remove contaminated soils to the 10 foot depth, see Figures 3 and 4 Continuous cores obtained from well RIB indicated that the first water bearing sand is at approximately 12 feet below the surface in this area, see Figure 4 Once this depth has been achieved, relatively undisturbed soil samples from the base and sidewall of the excavation will be obtained for field testing using a portable gas chromatograph (Photvac 1OS50) for the presence of TPHg, Benzene and MTBE Based on the field screening results a determination will be made to expand the over-excavation area The excavation will then proceed into the saturated zone, by first digging a dewatering trench along the western edge of the excavation to the 20 foot depth, top of clay that separates the first water sand from the second water sand Dewatering point(s) will be placed into this deeper excavation as discribed above in Pumping Plan C1 The excavation will then be expanded to the north and east to the 20 foot depth as shown on Figure 3 Once this depth has been achieved, relatively undisturbed soil samples from the base and sidewall of the excavation will be obtained for field testing using a portable gas chromatograph (Photvac 1OS50) for the presence of TPHg, Benzene and MTBE If field screening indicates that further excavation is warranted, potholes will be excavated to approximately the 25 foot depth Samples will be obtained from the sidewalls and base of the excavation to document the results as directed by San Joaquin County Health ® After completion of the excavation, geofabric liner will be placed to line the excavation floor and sidewalls This fabric will allow the migration of groundwater but will limit the amount of fine materials from advancing into the excavation One-half inch clean rounded pea gravel will then be placed at the base of the excavation(approximately one foot thick) to hold the liner in place Once the pea gravel base has been placed, horizontal air sparging piping will be placed with vertical risers to connect the horizontal pipe will be positioned One-half inch pea gravel will then be place to the six foot depth below surface (approximately one foot above the highest groundwater level) At the six foot depth a horizontal vapor extraction pipe will be placed with a vertical riser to surface One-half inch pea gravel will be placed on and above the vapor extraction pipe to the five foot depth Then the entire excavation will be covered with geofabric and compacted backfilled with clean road base to subgrade surface prior to be covered with asphalt to provide a vapor barrier Air Sparging Pipe The air sparging horizontal pipe will consist of 5 foot lengths of inch schedule 40, hand slotted to 0 030 to 0 040 inch connected individually to blank 1/2 inch diameter schedule 40 pipe with treaded unions positioned in an array that will allow the slots to cover the entire bottom of the excavation, see Figure 6 !/2 inch schedule 40 PVC pipe risers will connect to the honzontal pipe with 900 elbows The '/2 inch risers will be brought to surface in such a position to be placed into a traffic vault that will allow each riser to be fitted with an individual flowmeter valve and a common manifold that will feed the compressed clean air to each flowmeter valve i 6 Sanchez Rev WP 2-02