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%.e ..i <br /> 10 February 1998 <br /> �- AGE-NC Project No. 95-0144 <br /> Page 4 of 5 <br /> • Petroleum hydrocarbons were detected in soil samples collected beneath the former UST No. <br /> r 8 location at depths of 20 and 25 feet bsg. Only traces of ethylbenzene and xylenes were <br /> detected in the soil sample collected at a depth of 40 feet bsg, directly beneath the former <br /> UST location. <br /> • Only low concentrations of hydrocarbons were detected in the sample collected at a depth <br /> of 30 feet bsg in probing GP36, located northeast of the former UST location. Petroleum <br /> hydrocarbons were not detected in the remaining samples collected from probing GP36. <br /> • Petroleum hydrocarbons were encountered in soil samples collected at depths as great as 60 <br /> feet bsg in probing GP37, located down-gradient of the former UST location. <br /> • Sandy silt to sand was encountered from a depth of 15 feet to 35 feet bsg. Clay was <br /> encountered from approximately 35 to 40 feet bsg. This clay layer was encountered in <br /> numerous borings advanced at and near the site, and appears to be laterally continuous. This <br /> layer may act as a retarding boundary slowing the vertical migration of contaminants at the <br /> site. <br /> • Petroleum hydrocarbons have previously been detected in MW-13. This monitoring well <br /> may define the down gradient extent of impacted ground water from UST No.8. <br /> v <br /> _ 5.0. RECOMMENDATIONS <br /> Based upon data collected from the site, AGE recommends the following: <br /> • The lateral extent of the more highly impacted soil is limited to the former UST location. <br /> Lower concentrations of impacted soil extend toward the north, under the building. <br /> Excavation of impacted soil would greatly reduce the future migration of contaminants. <br /> Excavation should be performed concurrent with activities at the former location of UST No. <br /> 1. <br /> • Monitoring wells should be installed near the former location of UST No. 8 to define and <br /> monitor the extent and concentrations of contaminants in ground water. Wells should be <br /> installed at the former location of UST No.8 and down gradient. These wells should be duel <br /> completed to monitor ground water below the confining layer at 40 feet bsg as well as first <br /> ground water. One well should also be installed upgradient of the former UST location. <br /> Monitoring well installation should be performed following excavation activities. Proposed <br /> well locations are illustrated on Figure 2. <br /> Advanced Gec Enci ran mental,Inc. <br /> r <br />