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F 27 June 1996 =.r= AGE-NC Project No. 95-0118 Page 9 of 23 decrease towards the end of the test. Albeit minor, the increase indicates that air flow through saturated soil at the site is adequate for performance of IAS. The decrease of pressure overtime time maybe due to ch aned flow rate air flow CFMmabe he soil. This could indicate that a lower in'ection ressure <12 s� through J p ( psi) ( ) y ,necessary to maintain IAS efficacyat the site. Surging of the sparging system (performed during the IAS'Icst) may also.,help prevent channeling and allow the soil porosity to be restored to a static state.The rebound of the porosity should improve hydrocarbon vapor migration through soil, inducing:more favorable subsurface air flow characteristics. r__, 6.2.2. DISSOLVED OXYGEN Initially, dissolved oxygen concentrations showed no increase in any of the observations wells, but an increase was noted after two days (48 hours) of testing at most monitoring points. The overall increase of dissolved oxygen in wells nearest the sparging points(M)V-2,MW-3,VW-1) indicates circulation of the injected air and augmentation of dissolved oxygen content in the ground water surrounding the sparging point.Dissolved oxygen data collected during the pilot test indicates that intimate contact and interaction between the injected air and ground water was occurring, and l therefore IAS should effectively reduce hydrocarbon concentrations in ground water and the saturated portion of the vadose zone through stripping out the hydrocarbons. 6.2.3. ORGANIC VAPORS The highest concentration of organic vapors (OVs) was detected in VW4, ranging froin 200 ppm at initiation of the IAS test to 2,140 ppm after 24 hours of testing. The increase in OVs nay indicate that volatilization of hydrocarbons was occurring within the saturated vadose zone in response to the air sparging. j 6.2.4. GROUND WATER DEPTH During the IAS pilot test, ground water elevation increases between 0.2 to 0.4 feet in wells MW-2, MW-3 and VW-2 were noted, indicating ground water mounding. The tendency for ground water mounding during performance of IAS can cause the dissolved hydrocarbon plume to migrate beyond ,J its original horizontal extent.