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<br /> ota.ea oa.a9 or,-890989 tza9 03.90 Ob9D 09.90 ducted E at the Hill AFB, Utah,Results of in situ 1bioventing lf field ity study
<br /> ite. Air
<br /> extracted from Vent Well 13 at 212 actual Us(450 acfm),
<br /> 9 Manes erop.nc on m = 1219 cm (40 ft).
<br /> FIGURE 6. Percent recovered JP-4 attributed to bio- 3
<br /> degradation reactions at the Hill AFB, Utah, field soli '
<br /> venting site based on oxygen depletion measured in the Field In Situ Respiration Test
<br /> I SVE system vent gas.
<br /> A number of field-scale in situ respiration tests were con-
<br /> ducted during the bioventing study to assess the changes in in
<br /> from wells on the periphery of the site (Wells V12 to V15 in situ respiration as engineering management options were ap-
<br /> Figure 5) to maximize the flow path and retention time of plied at the site. Three tests were conducted from September
<br /> vapors in the contaminated zone.Figure 6 presents the results 1989 to November 1990 representing different levels of man-
<br /> of this operating mode change in terms of the percent of total agement at the site, i.e., following flow rate and operating
<br /> JP-4 recovery that could be attributed to biodegradation, ex- configuration modifications at the site, following moisture
<br /> pressed on an oxygen consumption basis,during both the con- addition, and following moisture and nutrient addition. All
<br /> ventional high-rate and modified bioventing phases of the tests were conducted by shutting down the venting system and
<br /> study. Biodegradation accounted for 15 to 2010 of the re- monitoring changes in soil gas CO2 and O, composition in all
<br /> covered JP-4 even during high-rate venting. This rate was pressure monitoring points and vent wells over a 10- to 14-d
<br /> drastically altered in September 1989,when JP-4 volatilization period.Soil gas samples were analyzed by first evacuating three
<br /> was reduced from 90 to 180 kg/d(200 to 400 Ib/d)to less than volumes of the monitoring points and vent wells using a port-
<br /> 9 kg/d (20 lb/d) by making the stated changes to the system able sampling pump prior to connecting the Gastechtor in-
<br /> flow rate and extraction configuration.'These changes allowed strument.
<br /> direct discharge of vent gas without expensive off-gas catalytic The moisture addition phase of the field treatability study
<br /> incineration treatment,and had no detrimental effect on biod- consisted of the addition of culinary water to the field site to
<br /> egradation reactions. The hydrocarbon biodegradation rates yield soil moisture levels throughout the site of approximately
<br /> of 32 kg/d(70 lb/d)observed during high rate extraction were 8 to 12016 (30 to 50% field capacity). This moisture was added
<br /> maintained at an average rate of greater than 45 kg/d (100 via surface spray irrigation at rates of approximately 110
<br /> lb/d) following system operating modifications. L/min(30 gpm),8 h/d,7 d/wk,until approximately 3,800,000
<br /> L (1,000,000 gal) were applied. Soil moisture measurements
<br /> made using a neutron density soil moisture probe indicated
<br /> In Situ Permeability Determinations that soil moisture was successfully increased from pre-irriga-
<br /> tion conditions and maintained between 8 and 1201a over the
<br /> In situ permeability measurements were once again made entire contaminated depth (16].
<br /> during the biovenring phaselof this project using the vent well Nutrients were added to the site in the form of ammonium
<br /> and vapor probe configuration utilized during bioventing op- nitrate and sodium triphosphate at a C:N:P ratio of 100:10:10,
<br /> erations. Results presented is Figure 7 were collected from the based on soil hydrocarbon analyses in September 1989, which
<br /> indicated vent well and pressure monitoring points while ex- indicated residual hydrocarbon levels throughout the site of
<br /> tracting vapor from Vent Well 13 at an operating flow rate of approximately 100 mg/kg.These nutrients were added in three
<br /> 212 actual L/s (450 acfm). ,E equal increments, three weeks apart, by surface-applying the
<br /> a Using the approach by Johnson et at.,[22]a linear regression dry mix, tilling it into the upper 15 cm (6 inch) soil horizon,
<br /> through these data yielded Slope values as input to equation and continuing surface spray irrigation at 100 L/min(30 gpm),
<br /> 3 as shown in Table 3. These data yielded a mean k value of 8 h/d, 2 d/wk, during this phase of the study.
<br /> 223173 darcys,indicative of the clean sands and gravels pres- Ali field data were analyzed assuming a first order reaction
<br /> ent at the site. '' law through linear regression of the natural log transform of
<br /> l �
<br /> Table 3 In Situ Permeability Data Collected from the Hill AFB, Utah, Bioventing Field Site, and Results from
<br /> IM Equation 4
<br /> Monitoring Depth Vacuumt Regression Slope -
<br /> Point [n! (ft}] r[m (ft)] (g/cm-s`) (3/t m-s2} k(darcys)
<br /> A 9.1 (30) 32.6 (107) 2,415 931 270
<br /> AA 9.1 (30) 6.1 (20) 12,451 1705 147
<br /> VW-6 3-15.(10-50) 13.7 (45) 5,229 1031 244
<br /> d C 1.8 (6) 25 (82) 2,191 817 307 11
<br /> S 1.8 (6) I0.4 (34) 3,038 1730 145
<br /> tVacuurn-steady-state gauge reading at end of in situ permeability tat.
<br /> l
<br /> 50 February, 1993 Environmental Progress (Vol. 12, No. 1)
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