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Mr, lnf ima 04/03/2006 Page 2 of 4 zone. BBL proposes the reduction of groundwater monitoring well clusters from six as defined in the CAP(summarized as bullet item 3 above)to four; 2. The reinstallation of an A-zone groundwater monitoring well in the vicinity of groundwater monitoring well MW-1, which was previously destroyed in 2004; 3. Soil lithology and stratigraphy underlying the site has been sufficiently defined as illustrated in the CAP cross-sections (Figures 4 and 5), and will be supplemented with the addition of the four deep wells proposed above. Therefore, the completion of six additional CPT borings, as defined in the CAP(summarized as bullet item 2 above),is not considered necessary at this time; 4. Evaluate the vapor inhalation pathway to determine if residual benzene, toluene, ethyl benzene, and total xylenes (BTEX) concentrations defined in the A-zone represents a significant risk to human health;and 5. Complete a focused excavation, as defined in the CAP (summarized as bullet item 1 above), as a contingency,to eliminate a vapor inhalation pathway or if it is determined that natural attenuation alone can not meet acceptable groundwater clean-up levels in a reasonable time frame. The following sections define the proposed work tasks that will be implemented as part of the CAP revision. Task 1 —Groundwater Monitoring Well Installation Three distinct water bearing zones (i.e.; sand layers within the low permeability clay/silt/sand deposits) have been identified as A-zone (approximately 25 to 30 bgs), B-zone (approximately 42 to 50 feet bgs), and C-zone (approximately 74 to 80 feet bgs). These three zones are the zones of higher transmissivity where groundwater is flowing beneath the site. The predominant groundwater flow direction is to the north/northwest,as presented on the rose diagram(Figure 1). All existing groundwater monitoring wells previously installed and used for quarterly monitoring were screened within the A-zone. Vertical profile groundwater sampling conducted in 2004 (grab sampling) identified petroleum hydrocarbons beneath the site in the B-zone and C-zone. The horizontal extent of petroleum hydrocarbon impacts within the B-zone and C-zone is unknown since the existing monitoring well network does not provide data for these depth intervals. BBL proposes to install nine additional monitoring wells as part of this task. Monitoring well clusters screening the B-zone and C-zone will be located near existing A-zone monitoring wells MW-2, MW4, and MW-9. An additional cluster of three monitoring wells screening the A-zone, B-zone and C-zone will be installed in close proximity to destroyed monitoring well MW-1. Locations of proposed monitoring wells are shown on Figure 2. The A-zone well will be screened at an approximate depth interval of 25 to 30 feet bgs. The B-zone wells will be screened at an approximate depth interval of 40 to 50 feet bgs. In order to prevent the potential for cross contamination between the A-and B-zones the wells will be double-cased. The outer casing will be set and sealed at a depth of approximately 35-feet bgs. Once the casing is set, the borehole will be advanced to the 50-foot depth to allow for the installation of the B-zone monitoring wells. The C-zone wells will be screened at an approximate depth interval of 70 to 80 feet bgs. Similar to the B-zone wells, 08262822.dm BLASLAND, BOUCK&LEE, INC. engineers,scientists,economists