SITE INFORMATION AND CORRESPONDENCE

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Mr. Vaughn • 4 • 12 May 1995 be sampled from the SVE well at approximately 1,4, 8, 16, and 24 hours of operation, and will be analyzed for TPH-g and BTEX (8015/8020). In addition, one air sample will be analyzed for VOCs (USEPA modified TO-14). As a secondary indicator of subsurface air flow, induced vacuum readings will be collected from the observation wells. At the trench, an additional test will evaluate air flow vs. vacuum characteristics for SVE piping installed within the trench. This will be accomplished by extracting vapor from the horizontal and vertical vapor piping for 1 hour. Each test will be followed by a 2-hour extended test to evaluate induced vacuum in observation wells installed in native soils. Air samples will be collected after 60 and 180 minutes of cumulative operation from the horizontal and vertical extraction piping. The samples will be analyzed for TPH-g and BTEX by USEPA methods 8015 (modified)/8020. The results of this testing will be used to compare the operation of vertical and horizontal wells within the trench, and to compare induced vacuum in native soils using SVE installed in both native soils and trench backfill. Air Sparge Tests: STTC proposes to perform short-term air sparge tests on a single well each in the STA and in the NTA if applicable, and in the interceptor trench near the STA. The testing will include a 1/2 hour step test to evaluate the air flow and pressure characteristics of the sparge well at various flow rates. After this test, a four-hour test will be performed using compressed air and a helium tracer. Additionally, the consultant will attempt to evaluate changes in dissolved oxygen and HC vapor concentrations in selected ground water monitoring wells as a result of air sparging. During the 4- hour test, monitoring will be performed at observation wells every 30 minutes for the following: induced pressure response within the vadose zone; helium concentrations within the observation well casing (vadose zone) and within the submerged tubing head space within the observation well (saturated zone); and depth to water using dedicated slope indicators encased in sealed well-head assemblies. Dissolved oxygen will also be measured in some of the wells at the beginning and end of each test. Changes in vadose-zone HC concentrations will be monitored at four wells using FID or PID, taking a set of measureements before sparging is initiated and again 2 to 4 hours after sparging is completed. An additional air-sparge test will be performed at the trench location to compare the effectiveness of compressed-air injection within the trench using vertical and horizontal air-sparge points. This information will be used to evaluate cost-effectiveness of compressed-air injection for future use in air-stripping or enhanced in-situ biodegradation methods. The air-injection testing will be done using individual 2-hour tests with compressed air and helium gas. The same parameters listed above will be monitored every 30 minutes in the vadose zone, the trench, and/or piezometers within the trench. Combination SVE and Air Sparging Tests: STTC proposes to perform short-term combination SVE and air sparge testing at the STA and the trench. Compressed-air injection, with helium tracer, will be performed at a single air sparge well with simultaneous SVE from one or two vapor wells, for 4 hours. Samples will be analyzed as above. Induced vacuum and pressure measurements will be collected from adjacent observation well (vadose-zone pressures) to evaluate the effect of the simultaneous operations.