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I Frontier Transportation, Inc. B23502.01 ' October 16, 1996 Page 12 TABLE T 5umma.y of Groundvrater Analyti Rmdts August 30;1996 Well No. Benzene Toluene Ethyl-benzene Xylenes TPH-G MTBE TPH-D µg/L Pg/L ug/L pg/L µg/L AA 98 18.8 55.8 130 1,800 11300 <50 ✓ MW-2 12.7 7.9 4.5 120 850 12.3 95 96.6 ✓ ftg/L = micrograms per liter ' TPH-G = total petroleum hydrocarbons-gasoline range iiME = methyl tertiary butyl ether TPH-D = total petroleum hydrocarbons-diesel range < = less than method detection limit ' 6.0 EVALUATION Laboratory analysis of soil samples collected during drilling activities indicate that PPC impacted soil extends to groundwater. Based upon the groundwater elevation data collected from monitoring wells MW-1 through MW-3 on August 30, 1996, the groundwater flow direction is toward the northwest. Analysis of groundwater samples collected from monitoring wells MW-1 through MW-3 detected concentrations of BTEX, TPH-G, and MTBE. In addition, groundwater samples collected from monitoring wells MW-2 and MW-3 had detectable concentrations of TPH-D. It should be noted that the TPH-D concentrations detected in the groundwater samples were an order of magnitude lower than the corresponding TPH-G concentrations from the same well. 1 Since dissolved phase PPC concentrations in the upgradient (MW-3) and downgradient (MW-1) wells do not appear to demonstrate significant attenuation, delineation of PPC impacted groundwater does not appear to be complete. 7.0 RECOMMENDATIONS 1 Additional delineation of PPC impacted groundwater appears to be warranted northwest, west, and east of the former gasoline USTs. It should be noted that additional delineation of impacted groundwater toward the east will require public and/or private property access which can be both time consuming and costly to obtain. Twining recommends the following: i • Install three additional groundwater monitoring wells (MW-4 through MW-6), two downgradient and one upgradient of the existing wells to provide additional data for evaluation of flow direction and gradient and further delineate PPC impacted groundwater; and 0 Assess the need for active soil and/or groundwater remediation.