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' Geolog uaI Techxxs/he Page 2 Additional Investigation Work Plan Cardoza(Main St) Project No 662 2 October 8,2001 ' 2.0 PROPOSED INVESTIGATION To further investigate the extent of soil and groundwater impacted with gasoline range ' petroleum hydrocarbons, Geological Technics Inc proposes to install one water table well and five deep discrete screened wells The locations of the proposed wells are indicated in Figure 2 In addition, GTI will collect soil and groundwater samples, and analyze these ' samples for petroleum hydrocarbon compounds A water table/deep well pair MW-4/MW-104 will be placed adjacent to the east side of the former UST excavation Well MW-4 will be constructed with 5 feet of-screen-above the water table and ten feet below Deep well MW-104 will be screened from 50-55 feet below a/ e, grade surface (bgs)to determine if a"di+vine"plume is present VF5 3 Well MW-105 will be located in the predominant down gradient direction as shown in Figure 3 — Groundwater Gradient Rose Diagram Well MW-106 will be placed to the north of the site in the direction of the highest recorded groundwater gradient (a magnitude of 0 018 ft/ft - April 27, 2001 event) These deep wells will be screened similar to the above deep well A summary of well construction is given in the table in Section 2 5 Deep wells MW-101 and MW-103 will be placed adjacent to wells MW-1 and MW-3, ' respectively These wells will be screened as above for vertical plume definition A site conceptual model, based on the limited data obtained in the investigation, is present in Figure 4,and 4A The model assumes a limited amount of MTBE soil contamination in the vicinity of the former UST excavation leaching to groundwater with an associated groundwater plume extending north, east and south beneath the current water table at approximately 23 feet bgs The orientation of the proposed wells will aid in the refinement ' of the site conceptual model 2.1 Soil Borings Soil boring permits will be secured as necessary and the local regulatory agency will be notified 48 hours prior to commencing work The subsurface will be cleared of ' underground utilities by notifying Underground Service Alert These boreholes will be drilled using an 8-inch outside diameter, continuous flight, hollow stem auger owned and operated by V&W Drilling (C57# 720904) The boreholes will be ' advanced to depths ranging 30 — 40 feet bgs The expected depth to groundwater is approximately 20 to 25 feet below ground surface 2.2 Soil Sampling Procedure I Soil samples will be collected for geological and analytical evaluation at five-foot intervals ' A boring log providing sediment description using the U S C S and field observations will be maintained by a professional geologist working under the supervision of a registered geologist Soil samples will be collected in 6 0-inch brass liners using a 2 0-inch modified California split spoon sampler All soil samples will be sealed with aluminum foil or Teflon ' sheets, capped, labeled and placed in a cooler at 4° Celsius for transport to the laboratory following Chain of Custody protocol 1 .