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I ` Addendum to Interim Corrective Action Plan Frontier Transportation, Inc. April 14, 2006 Page 4 BEII encountered predominantly heterogeneous clays from 0' to 30' bg and fine-grained sands from 30 ' to 40 ' bg during well advancement of MW- 15 through F : J MW 18 . �1 4"i� ,f ' is I 6" 4V/ I � 1n f�f �� Is �f . First subsurface water was encountered at depths from 11 ' to 12' bg during tank ? 3 removal and monitoring well installation at this site in 1995 and 1996. Since then, /2 sha ow subsurface water has been encountered the e between Thep past groundwater gradients included in quarterly groundwater ori to ring g 5 5 aa9 ! < reports have identified the flow of groundwater in a generally western direction L - beneath the site. it f l 4.0) AMENDMENTS d v I 0 7 - A. Soil Vapor Extraction 5 I � ,I I BEA agrees that soil analysis, as indicated by recent boring logs from monitoring wells MW- 15, through MW-21 , identifies almost exclusively heterogeneous clay to silty, fine-grained sand. The permeability for these soils is typically 10-5 to 10-7 cm/sec, lsupporting that the soil column in the unsaturated zone is tightly packed, and contains j high moisture content, significantly reducing subsurface airflow. Therefore, soil vapor extraction fails as a cost and technologically effective method according to the USEPA guidelines for Soil Vapor Extraction, which identifies limited effectiveness for a system .� in heterogeneous clayey soils. BEA agrees that soil vapor extraction will have minimal effect on the vadose zone. Be Neutron Logging Thermalization (NTL) I� BEA concurs that NTL will not be useful for corrective action with the current !I site conditions. The main benefit of NTL was to monitor the aqueous migration of the ozone injection. However, the presence of free phase in MW-2 and MW-21 removes the possibility of using ozone injection/sprging. The free phase LNAPL must be removed completely, via extraction, before other groundwater treatments would be effective in contaminant removal. i � C. Excavation of the Source Area Contaminant Mass !I . The apparent source area in the soil horizon extending from 15 ' to > 18 ' bgs in the removed UST excavation area. Soil samples collected in coarser-grained sands in water bearing zone extending from approximately 13 ' bgs to less than 20' bgs according w site boring logs. At least in the source area the predominant liquid phase material is non-aqueous gasoline. Using an average porosity of 20% to 35 % for coarse grained 4 J