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L. 27 December 2004 AGE-NC Project No. 98-0433 Page 4 of 4 • The highest concentration of TPH-g was in the area of monitoring well MW-9, located adjacent to the former UST area.Compared to the previous quarter,the TPH-g concentration in ground water decreased in well MW-1,and increased in wells MW-6,MW-8,and MW-9; • TPH-g was detected for the first time in well MW-5 at a concentration of 8,30 [Ig/l. 0 TPH-d concentrations decreased in well MW-1 and increased in wells W-6 and MW-9; ►`} '�y • Benzene detected in sample MW-6 (27 µg11)was above the DHS' Maximum Contaminant Level (MCL). MTBE detected in samples MW-1, MW-6, MW-8, and MW-9 at concentrations as great as 3,900 µg/1 was significantly above the DHS' primary MCL. Nb I Nvl"+° i4L,,, • The lateral extents of dissolved MTBE and TAME are generally definedl�y the current well network, including the wells sampled at the Ripon Farm Service site directly south of the subject site. The vertical extent of MTBE at the former UST area is not defined below a depth of 40 feet bsg. vJ A, • The lateral extent of TPH-g is undefined northwesyf the site.BTEX is defined in the former UST area, however, it is undefined in the area of MW-6. w 5.0. RECOMMENDATIONS ' Based on the results of this investigation, AGE recommends: • Continued quarterly monitoring at the site; the next monitoring event should be scheduled for first quarter 2005. • Coordinate the ground water monitoring activities of Jimco Truck Plaza and the adjacent Ripon Farm Service (22871 South Highway 99)to occur concurrently. �. • Preparation of a Corrective Action Plan (CAP) to mitigate the dissolved MTBE near the former UST location and near the on-site domestic well. Y 6.0. LIMITATIONS w Our professional services were performed using that degree of care and skill ordinarily exercised by environmental consultants practicing in this or similar localities. The findings were based mainly upon analytical results provided by an independent laboratory. Evaluations of the hydrogeologic conditions at the site for the purpose of this investigation were made from a limited number of available data points (i.e. ground water samples), and subsurface conditions may vary away from these data points. No other warranty, expressed or implied, is made as to the professional interpretations, opinions, and recommendations contained in this report. 6. Advanced GeoEnvironmental,Inc- l..