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A t ^R August 25, 1988 Harding Lawson Associates r 17060,008.03 Mr. Hal Miller The Southland Company Page 5 were also detected in the water sample taken from MW-14 (0.1 parts per billion [pph]) . These concentrations appear to be anomalous and not relac:ed to the release of petroleum hydro- carbons at the 7-ElevF,' site. Using these results, HLA has determined a 'aero lir',," within which both soil and ground- water contamination appear to be confined (Plate 1) . These chemical results confirm the soil gas data. INSTALLATION OF DEEP WELL Y On the basis of data gathered during Tasks 3 and 4, HLA recommends installing the planned deep well near MW-ICS, at the southeastern corner of the building (Plate 1 Pur— Pose of this well is to check that the gasoline constituents identified in the shallow zone have not been transported downward. Accordingly, the well will be screened in the second water-bearing zone. The well .will be installed in.two phases, using a gaud-rotary i, drilla rig. First, a 12-inch hole will be drilled thra the first water bearing zone and will penetrate the underly ing stiff, low permeability clay formation. An 8-inch steel, conductor casing .will then be pushed several feet into the clay formation and the annular space between the borehole T and the casing will be grouted to its full depth using the , tremie method. After the grout has set, the drilling.fluids generated will removed from inch borehinside the casing. We will then extend a 5- inch through the conductor casing to the second water-bearing zone or to a depth of -approximately 60 feet. We will geophysically log the borehole, obtaining a continu- ous record of gamma, resistivity, and/or_ spontaneous poten- --tial. - Using -this technique,;wewill identify the permeable E zone for screening.. , After the logging,..the borehole will be rebored to an 8-inch diameter. Upon reaching total depth, .we will then construct a 4-inch, Schedule40,, PVC well in the water bearing zone with 5 to ]0 a feet. of .020-inch screen and 50 to 60 feet of casin g. Will be placed in the annular space around the screen to and approximately one foot above the top of the screen. A 2 to 3-foot bentonite plug will be placed immediately above the sand. The. remainder of the annular space will be ' ted using the tremie method with a cement-bentonite slurry. well will be completed with a' p water-tight ca andslightly The _t MINER