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1 Langston Is Market, 1561 S Seventh Street,Lathrop, California ' Mork Plan-Phase II Lateral& Vertical Extent of January 10, 1996 Second Groundwater Aquifer,Revised Page: 3 ' compacted backfilling began Replacement of the groundwater morutoring wells was conducted between September 21 and 23, 1995 ' The interim remedial excavation removed the secondary source of soil contamination in the area of the former underground storage tank The de-watering of the excavation significantly reduced the groundwater contamination plume Contamination was detected below the "Stockton Blue" clay in bonng EW-1 No contamination was detected at this interval in any of the other borings 3.0 Work Plan This work plan has been developed for the purpose of conducting diree (3) sort borings throuih the second aquifer and completing each as a monitoring well These wells will be du r-retely screened for the purpose of defining the gradient and direction of the second aye ifer groundwater, and to deterrnuie both vertical and lateral extent of the contamination identified in the well replacement phase of the interim remediation The locations of the three (?)wells are proposed as shown on Figure 2 ko 3'.1 Drilling Nernuts will be obtained as necessary for all wells (including bonngs) before dr ll.rig lit_gins The sod borings will be accomplished using a mobile mounted drilling rig 2mpioving the use of a hollow stem flight auger no less than 3 t/4" i d and 8" o d All drilking equipment will be thoroughly steam-cleaned bo-fore urlling to prevent the introduction of contamination from off site, and betwE. n bon'..-,s to prevent ...o6s contamination - The borings will be logged under the direct supervision of a registered pf-ofessional using the Unified Soil Classification System (Figure 5) The color, texture, moisture, plasticity (if applicable), consistency of the earth materials, pertinent soil or bedrock characteristics and any evidence of contarnination will be noted All water bearing zones and the depths at which they were encountered will be noted on these logs All borings will be drilled in such a manner as to prevent cross contamination between strata g Exploratory soil borings within the unsaturated zone will be backfilled with a cement and three percent(3%)Bentonite nuxture I Borings into the saturated zone will be drilled to a maximum of 20 feet beneath the top of the aquifer being explored If a deeper aquifer is to be investigated, conductor casing will first be grouted into place to seal off the upper aquifer and drilling will proceed through the conductor casing after the grout has been allowed to set for 48 hours The two south wells should not need conductor casing, as the adjacent borings SB-10 and MW-2 tested "ND"