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TECHNICAL APPROACH SUMMARY .�k The objectives of the proposed scope{of,work are to further define the impact to groundwater below the water table, and to establish a:groundwater monitoring capability downgradient of the ' plume of impacted groundwater. T61;a'chieve these objectives, cone penetration test (CPT) borings will be advanced for discrete groundwater sampling at six on-site locations, a two-well monitoring well cluster will be installed downgradient of the existing monitoring well network, and 4 quarterly groundwater monitoring, samp;ling and analysis will continue. { To further determine the soil stratigraphy; and to evaluate the vertical and lateral extent of impacted groundwater beneath the groundwater table, six CPT borings will be drilled for the collection of discrete deeper groundwater samples. One CPT boring will be located at CPT-1 and advanced deeper than the 125-foot total depth of CPT-1 to identify and discretely sample 1 any groundwater-bearing intervals' below 125 feet. The five other proposed CPT locations will be approximately 100 feet east, 60'fbet south, 210 feet west, 140 feet northwest, and 150 feet i north (downgradient) of CPT-1. Tle.proposed CPT borings will be extended to a maximum depth of 200 feet, but the actual di;ti oflthe borings,will be based on field observations and the Ellperformance of the CPT rig. r From the proposed CPT boring at.CPT4i groundwater samples will be collected from the sand jj and gravel interval at approximately;,)25'feet, and from any deeper groundwater-bearing L intervals identified. From the other,five CPT locations, all significant groundwater-bearing intervals will be sampled. All of the'groundwater samples will be collected with a Hydropuncho t and analyzed for TPH-as-gasoline;)BTEX, MTBE, DIPE, ETBE, TAME, TBA, 1,2-DCA and EDB j by EPA Method 82606. No additional,soil samples will be collected for laboratory analysis. To establish a groundwater monitoring.capability downgradient of the known plume of impacted groundwater, a cluster of two groundwater monitoring wells will be installed north of the existing Th hallo"`` Monitoring well will be constructed as a groundwater table monitoring well network. e s g well, and the deep monitoring well ►will be1constructed in the next deeper groundwater-bearing zone. Both wells will be installed ui'8-inch diameter hollow-stem auger soil borings, and will be constructed with 20 feet of two-inch'i ianieter well screen and blank casing. Given that the groundwater table is approximately,40{feet bgs, the shallow well screen interval will span from approximately 30 to 50 feet bgs. Since the deep well will presumably be located outside of the plume of impacted groundwater, a:con'd66or casing will not be used to seal off the overlying groundwater during drilling. Unless'feid robservations dictate otherwise, the proposed deep well will consist of well screen spanning'fromapproximately 55 to 75 feet bgs. Both of the wells will be developed by they driller, following the placement of the sand packs and 1 prior to the installation of the well seals. :The tops of both wells will be secured with a water-tight locking caps and above-grade stove,pipe monuments. A licensed land surveyor will survey each ' E of the newly-installed wellhead "I Th,e wells will be incorporated into the on-going quarterly 4 groundwater monitoring and sampling program at the site. Groundwater samples will be analyzed for TPH-as-gasoline, BTEX, MTBE, DIPE, ETBE, TAME, TBA, 1,2-DCA and EDB by EPA Method 82606. '''= �;' A project report documenting all:of the''proposed work will be prepared by a state of California Registered Geologist and submitted to PHS/EHD and RWQCB, as early as January 2002. 3 i