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27 December 1996 AGE-NC Project No 95-0143 Page 13 of 19 ' 6 1 3 MONITORING ACTIVITIES One of the potential problems associated with air sparging is lateral spreading of the contaminant ' plume Tlus can be caused by either mounding of ground water above injection points or lateral air flow away from sparging wells To detect this problem, ground water elevations in monitoring wells and extraction wells (if appropriate) should be monitored on a monthly basis, at the minimum, to ' detect mounding and the presence of organic vapor 614 FEASIBILITY Remediation of sizeable dissolved ground water plumes requires the installation of a considerable number of injection and extraction wells An intensive piping network for injection and extraction must also be installed Aar injection and extraction rates must be balanced to prevent the forced migration of contaminants However, air sparging has proven itself as a very effective method for remediation of soil in the smear zone An in-situ air sparging pilot test was performed for the same client at 423 North Madison Street from 02 to 07 February 1996 This site is located approximately 600 feet east of the subject property Installation of monitoring wells has revealed very similar lithology between the two sites Two sparging wells were supplied with approximately 15 psi of air during the test Induced pressure, organic vapor concentrations, ground water depth and dissolved oxygen concentrations were measured at surrounding monitoring wells Ground water samples were collected from monitoring wells before and after the sparging test Detailed procedures and results of the test were included in a February11-9 96 Corrective Action Plan re aced for the Madison site i rt Z3 Ma IIncreased concentrations of organic vapor were observed at surrounding monitoring wells Induced pressure showed an initial increase during the pilot test, but diminished over the time of the test Initially, dissolved oxygen increased at the site,but also decreased over the duration of the sparging test These two anomalies may have been caused by channeling of the air flow from the sparging points A lower injection pressure, approximately 10 psi, combined with surging the injected air should be used to minimize the effects of air channeling and promote maximum interaction of the injected air with ground water A closer injection well spacing would be required with a lower injection rate Only slight ground water mounding was observed during the sparging test Data from the air sparging pilot test from the Madison site are included on Table 4 Due to the close proximity of the test site to the subject property and similar lithology, it is assumed that the two sites would yield similar "sparging" conditions Another concern with airsparging is precipitation of iron, which can cause clogging of sparging points Laboratory analysis of water samples indicated low concentrations of iron in water at the i i '�