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W. Soon Kim Page 14 August 11, 1995 102429.AS.T8 Figures 4 and 5 present best fit lines found by linear regression of the respiration rate test data. Respiration test data is presented in Table 4. The slope of these linear equations is the calculated oxygen up-take rate in mg/Uday for groundwater and percent concentration change per day for vadose zone soil gas. Figure 5 also presents the regression analysis of carbon dioxide concentration to describe the carbon dioxide production rate in percent/day. For piezometer NP-1-80 the dissolved oxygen up-take rate increased from -0.71 to -1.67 mg/L/day. For NP-1-90 the rate increased from-0.53 to -2.68. The initial dissolved oxygen concentration in the groundwater after blower shutdown increased from 4.5 and 3.5 mg/L last quarter to 6.5 each for NP-1-80 and NP-1-90 respectively. Greater dissolved oxygen up-take rates and increased dissolved oxygen in the groundwater are indicators of increased aerobic biodegradation activity andbetter oxygen distribution in the contaminated groundwater zone. Groundwater dissolved oxygen concentration and measurement times are attached. The slopes of best fit lines presented in Figure 5 indicate that the steady-state, soil-vapor oxygen concentration was higher in the shallow piezometer NP-2-45 than in the deeper NP-2- 65. The oxygen up-take rate was also greater at the shallow depth. Best fit lines are based on data excluding the first 60 minutes after blower shutdown to ensure that steady state conditions are evaluated. Carbon dioxide concentration was conversely greater in the deeper piezometer, and carbon.dioxide accumulates faster in the deeper piezometer NP-2-65. This is the first quarterly measurement of vadose zone biological respiration so no baseline data is available for comparison. In general terms,the decline in soil vapor oxygen,concentration and the rise in carbon dioxide are indicators of biological activity in the vadose zone. We could quantitatively correlate the oxygen consumption and carbon dioxide production with the resultant gasoline mass biodegradation. Soil vapor oxygen concentrations less than 18.5 percent are considered rate limiting in an aerobic biological system. When most of the soil vapor oxygen is consumed, carbon dioxide conversion to methane begins with the onset of anaerobic biological activity. The initial oxygen concentration measure in.NP-2-65 on 8/4195 at 8:00 AM was 20.6 percent(i.e., nearly atmospheric oxygen). In the first 30 minutes after blower shutdown, oxygen concentration dropped to 8.8 percent. Carbon dioxide jumped in the same period from 0.5 to 5.8 percent. Without operation of the AS/SVE system, deep vadose zone conditions would quickly revert back to anaerobic conditions. BTEX Concentration in NP-1 Table 5 presents the BTEX results for the three piezometer depths 70',.80',and 90'. Since AS/SVE start up, BTEX concentrations have not decreased appreciably. Gasoline constituents that are being consumed by biodegradation and stripped by air sparging are