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30 June 1999 <br /> AGE-NC Project No. 98-0468 <br /> Page,l l of 12 <br /> at concentrations of 660 µg/l and 32 /.zg/l, respectively. The reported detection of MTBE <br /> ' exceeded the secondary MCL of 5.0µg/l and action level of 13 µg/l for MTBE in ground <br /> water. Additionally, the vertical and lateral extent of MTBE and TBA impacts in ground <br /> water have not been delineated north of the site. The lateral extent of MTBE.impact in <br /> ground water is shown on Figure 6. <br /> ' 7.0. RECOMMENDATIONS <br /> Based upon data reviewed and collected at the site, AGE recommends: <br /> • Implementation of additional.site assessment activities to further evaluate the vertical and <br /> lateral extent of petroleum hydrocarbon impact to soil and ground water related to the former <br /> ' USTs. It is recommended that the additional site assessment activities consist of the ' <br /> advancement of up to five soil. probe borings for the collection and analysis of soil and <br /> ground water samples. The proposed soil probe boring locations are shown on Figure 2. It <br /> ' is proposed that one soil boring each.be located northeast of boring B-2 and southwest of <br /> boring B-3 to evaluate the extent-of TPH-d impacts in ground water. Two soil probe borings. <br /> 4 are proposed at locations north of well MW-4 to assess the vertical and iateral'extent of <br /> MTBE and TBA impacts in ground water. Also, one soil boring is proposed in the vicinity <br /> of previous soil probe boring SB-5 to delineate the vertical extent of petroleum hydrocarbon <br /> ' impacts in soil.. . <br /> • Implementation of a quarterly ground water monitoring program for the period of one <br /> calender year to monitor and evaluate impacts to ground water, as well as trends in ground <br /> water elevation, flow direction, and gradient. Ground water monitoring activities conducted <br /> in May, 1999 would constitute the first quarter of the ground water monitoring program: It <br /> is recommended that the next quarterly ground water.monitoring event be conducted in <br /> August 1999. <br /> ' 8.0. LIMITATIONS <br /> AGE's professional services'were performed using that degree of care and skill ordinarily,exercised <br /> by environmental consultants practicing in this or similar.localities. The findings were based upon <br /> analytical results provided by an independent laboratory.,Evaluations of the geologic/hydrogeologic <br /> a' conditions at the site for the purpose of this-investigation were made from a limited number of- <br /> available data points,,(i.e., soil borings and soil and ground water samples)and subsurface conditions <br /> may vary beyond these data points. No other warranty, expressed or implied, is made as to the <br /> professional recommendations contained in this report. <br /> Advanced CeoEnvironmental,Inc.' <br />