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otr5ite System Configuration and High Rate Venting Opera-
<br /> ', AnalyUcal Trailer
<br /> tions
<br /> } I 8lovver Cataatytic
<br /> I_I ` lncfnrator
<br />+ f _ sail pile A one-well pilot scale vent test was conducted by Oak Ridge i
<br /> = New JP Nacional Laboratory (ORNL) to evaluate in situ air perinea-
<br /> Tanks :.
<br /> bility ac the site. This study resulted in the design by ORNL
<br /> of a venting system consisting of 15 vertical wells and 10 lateral
<br /> wells in the excavated soil pile and under the tanks(Figure 4).
<br /> ;,v? ,,< %r,; �L ,,LL a The vertical wells were placed at 12 m (40 ft) intervals to a
<br />�. depth of 15 m (50 ft) bgs and were slotted over an interval
<br /> 8ackfi'l from 3 to 15 in (10 to 50 ft) bgs. Twenty-one pressure man-
<br /> Uteral vents itoring points(PMP)were installed at various depths through-
<br /> out the site to provide point measurements of subsurface
<br /> l pressure and soil gas conditions(Figure 5), and a background
<br /> Vertical vents '' well was placed approximately 210 m(700 ft)north of the site
<br />€ FIGURE 4. Conceptual diagram of the Hill AFB, Utah, in the same geological unit and at the same depth as the vent
<br />€ field venting site. From Dupont at al. [1 61 wells to provide a control for basal soil respiration levels during
<br /> �s the study.
<br /> by estimating pump operating conditions at these required air Prior to initiation of bioventing studies at the Hili site, the
<br /> flow rates based on field determined in situ air permeability SVE system was operated under a conventional mode to max-
<br /> measurements. The feasibility of pulse pumping and vacuum mize the recovery of volatile components of the JP-4 through
<br /> pump/blower scheduling can be assessed based on required volatilization. Venting was initiated at a rate of 36 m/h (26
<br /> versus maximum oxygen transfer rates possible under a given acfm, approximately 0.04 pore volumes/d), and gradually in-
<br /> set of field and pump/blower operational constraints. An ex- creased to approximately h/ (1,500 acfm, approxi-_
<br /> ample of such calculations are presented below in the case mately 2.5 pore volumes/d)) aas s thea hydrocarbon levels in the
<br /> study for the bioventing system operated at Hill AFB, Utah. vent gas decreased over time. Vent gas was collected through
<br /> t I, Wells V5 to V11 (Figure 5), where the bulk of the soil con-,
<br /> i
<br /> � tamination was located. The venting rats during the start-up
<br /> Case Study—SP-4 Contaminated Site, Hill AFB, Utah period was limited by the operating conditions of the catalytic
<br /> incinerator used to treat the collected vent gas. This high-rate
<br /> Site Description operating mode continued from December 18, 1988, through
<br /> September 15, 1989, during which time approximately
<br /> The site at Hill AFB, Utah, was the location of a JP-4 jet 7,000,000 m3 (300,400,000 acf, approximately 340 pore vol-
<br /> fuel spill that occurred in January 1985, after the failure of umes)of soil gas and 62,600 kg(138,000 Ib)TPH were extracted
<br /> an automatic shut-off valve. Failure of the valve resulted in from the site due to volatilization and in situ biodegradation
<br /> .�r
<br /> the release of approximately 102,000 L (27,000 gal) of JP-4, of the JP-4.
<br /> pp Y
<br /> some 7,600 L (2,000 gal) of which were recovered as free Three in situ respiration tests were conducted during the
<br /> product.The balance of the released fuel migrated away from high-rate operating period [181 to assess microbial activity at
<br /> the tank and contaminated an area around it of approximately the site during conventional soil venting.These tests were can-
<br /> " depth
<br /> Q.4 hectares (1 ac) to a depth of approximately 15 m (50 ft). ducted at cumulative extracted air volumes of 970 m (42,000
<br /> The soil at the site consists of mixed coarse sand and gravel.' acf), 13,000 m3 (540,000 act), and 1,000,000 m3 (45,000,000
<br /> deposits with interspersed, discontinuous clay stringers to a acf),and showed first order oxygen uptake rates ranging from
<br /> confuted ground water,table at approximately 180 m(600 feet) 0.85/d to nondetectable in the pressure monitoring points
<br /> below ground surface I(bgs). JP-4 contamination resulted in throughout the site.Comparison of results from specific mon-
<br /> soil total pertroleum hydrocarbon(TPH)concentrations at the itoring points over time also indicated the incremental removal
<br /> fsite as high as 15,000 mg/kg, with average TPH levels of of residual hydrocarbons as respiration rates declined through-
<br /> , >1,000 mg/kg. PrioF to initiation of the full scale venting out the treatment period_ It was concluded that significant
<br /> I system, the fuel tanks were excavated, refurbished, and in- respiration was occurring during conventional SVE without
<br /> stalled in a concrete cradle above ground. nutrient or moisture addition, and that enhancement of biod-
<br /> egradation could be possible under modified site management
<br /> conditions. This became of increasing interest as the residual
<br /> aoa n.Lnate coin t of sats soil TPH levels had not reached the regulatory action level of
<br /> >10,000 mJikg-7-s, it 30 mg/kg dry wt. soil, and the conventional SVsystem hy-
<br /> immediatoy(040.inq the=0 'i
<br /> E
<br /> a__4,east drocarbon recovery rate decreased significantly over time due
<br /> ! vi v2 vs va to non-volatile residual contaminants accumulating in the soil
<br /> ' over time.
<br /> 8
<br /> � Y• E"F
<br /> •
<br /> P v's v6 v7 'Kva M';s vt Modified Btoventxng System Operating Conditions
<br /> • TSS ..vsa vic
<br /> 5 u' A Based on results of vapor probe and vent gas measurements
<br /> I ; X 4* W taken during the high-rate venting period, it was found that
<br /> . v.s
<br /> v:2 Z via vi_a at high extraction rates, i.e., 2,100 m'/h (1,500 acfm), the
<br /> entire contaminated zone was aerated to near atmospheric O:
<br /> levels. In addition, due to the extraction of vapors from the
<br /> AA Ea areas of maximum contamination at the interior of the site,
<br /> r�•,�n hydrocarbon levels above the allowable discharge limit of 50
<br /> 20 ppmv were found in the vent gas-To maximize biodegradation
<br /> i and minimize volatilization,operating flow rates were reduced
<br /> FIGURE 5. Site map showing vent well and pressure
<br /> 1 monitoringpoint locations at the Hill AFB, Utah, site. to the lowest races possible utilizing the existing venting system.
<br /> From Flinches et al. [18] i.e.,490 to 970 m3/h(350 to 700 acfm),and vent gas was drawn
<br /> nr„l 19 un. it February. 1993 49
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