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Pressure Mani Wnng rDint Q
<br /> 0 Table 5 Potential 02 Transfer Rate Data and Predicted
<br /> i IA Well Operating Vacuum at the Hill AFB,Utah,Bioventing
<br /> -.05 Field Site
<br /> i
<br /> -.t I Vent Well
<br /> l
<br /> � .,15 Potential Oz Operating �
<br /> -.z
<br /> y -0.002x•0.065,r2 0.945 Transfer Rate Vacuum
<br /> -.25 �� Q(L/s.(acfm)j (kg/d) [g/ -s' {in H2O}]
<br /> ` =
<br /> 4.7 (10) 120 503 (0.20)
<br /> U --3 " 300 1,710 (0.69)
<br /> 35 IE 1I.8 (25}
<br /> 23.6 (50) 600 4,110 (j.6) I
<br /> a 47.2 (100) 1,200 9,560 0.8)
<br /> 45 70.8 (150) 1,800 15,500(6.2)
<br /> 94.4 (200) 2,400 21,700 (8.7)
<br /> -.53000 28,200 {11.3}
<br /> N 118 (250) ,
<br /> .55 142 (300) 3,600 34,800 (14.0)
<br /> sa a so 100 iso zoo z50 300 165 (350) 4,200 41,500 (16.6)
<br /> Timu(h) 189 .(400) 4,800 48,200 (19.4)
<br /> FIGURE 8. A sample first order regression analysis of 212 (450) 5,400 55,100 (7.2"1)
<br /> oxygen uptake rate jdata obtained during in situ respi- 236{500} 6,000 62,000(24.9)
<br /> ration measurements. 354(750) 91000 97,000 (38.9)
<br /> i� 472 (1,000) 12,000 132,000 (53.0) j
<br /> I
<br /> CO,and 02 concentrations normalised to the background well
<br /> at each sampling interval, i.e., ln(C,t w,a/Ct,.=xUo�a d=i,
<br /> versus time.Each regression line was tested for the significance ume=61,670 m' (2,178,000 ft') air filled pore space=0.4,
<br /> of its slope,i.e.,the probability of the slope not equalling zero atmospheric OZ content=21%,Ox density=1.43 g/L.An anal-
<br /> being 20.05. In addition, an evaluation of overlapping 95 ysis of the potential O,transfer rate into the Hill site at various
<br /> percent confidence intervals of each regression slope was used flow rates is summarized in Table 5 using the assumptions
<br /> to test for significant differences among treatments. listed above for soil conditions; the mean in situ air permea-
<br />+ figure 8 shows results of a typical oxygen uptake rate de-
<br /> bility value of 223 darcys determined for the site;and equation
<br /> termination obtained'during these in situ respiration studies. 5 with R,=4,298 cm (141 ft) at 212 L/s (450 acfm) as deter-
<br /> OZ uptake was found Ito be more consistent and more sensitive mined from the extrapolation of vacuum versus radial distance
<br />{ than CO, production rates in detecting effects of treatments data from Table 3 to a 0 vacuum value (it was assumed that
<br /> on microbial activity�at the site.This was particularly true for R varies linearly with flow rate in this coarse grained material).
<br /> the moisture addition cases,where the interaction of CO2 with Rf„=7.6 cm (3 in), H=305 cm (10 ft), and P.=1.013 x 106
<br /> the added water greatly affected observed CO, production g/cm-s, (1 arm).
<br /> rates. Upon comparison of Table 4 O,uptake estimates with Table
<br /> Mean and maximum 02 uptake data are presented in Table 5 potential OZ transfer rates, it becomes apparent that only
<br /> 4 as a function of engineering management treatment along very low flows, on the order of 12 L/s (25 acfm), are needed
<br /> with equivalent oxygen demand values expressed in kg/d. As to transfer the maximum uptake rate expected under optimized
<br /> indicated in Table 4;the addition of moisture to the field site engineering management conditions. At these low flow rates,
<br /> yielded a significant increase in oxygen uptake rate not ob- however, the radius of influence of the extraction wells is very
<br /> served with nutrient addition.Statistical results presented else- small, =244 cm (8 ft) at 12 L/s (25 acfm), limiting the effec-
<br /> where [161 based on an analysis of overlapping 95 percent tiveness of single wells to remediate large contaminated areas.
<br /> confidence intervals`of the slopes of significant regression re- At the Hill AFB site,the extent of contamination was roughly
<br /> 1 lationships for the three treatment cases during the bioventing 6,400 cm (209 ft) square, precluding the use of this low flow
<br /> t study indicated that in no case did nutrients significantly in- rate. What could have been implemented, however, was the
<br /> c Crease respiration rates above statistically significant levels fol- use of the multiple wells operated at higher flow rates in a
<br /> lowing moisture addition alone. CO, production rates were sequential fashion for short periods of time to supply the
<br /> not found to be significant at any monitoring point or vent
<br /> well following moisture addition indicating the sensitivity of while limiting the vol-
<br /> oxygen need for microbial metabolism,
<br /> the CO,production' to changes in environmentsl
<br /> ume of contaminated air extracted from the soil. This was
<br /> done to some extent by reducing the vacuum flow rate to 212
<br /> conditions that affect CO, distribution in the subsurface-
<br /> actual were calculated actual L/s (450 acfm). However, rather than operating on a
<br /> The O: demand data presented in Table sail vol- continuous basis, all of the daily oxygen demand could have
<br /> assuming the following: total contaminated
<br /> �y been supplied to the site in little over an hour at this flow rate
<br /> (261 kg maximum demand from Table 4/5,500 kg/d supplied
<br /> ecause
<br /> Table 4 In Situ 0,Uptake Rate Data and Equivalent 02
<br /> Demand Requirements Collected from the Hill AFB, of a radbus of influence of h 4,300 suppcm {144 ft}theanatd212 actual
<br /> L/s(450 acfm),the Hill system could have been operated with
<br /> Utah, Bioventing Field Site two wells centered on opposite boundaries of the contaminated
<br /> �` Mean Or Mean O, Max. O, Max. Oz area, running sequentially for approximately 0.75 h/d, for a
<br /> ManagementUptake Demand Uptake Demand total operating time of 1.5 h/d. This scenario would have
<br /> I` Treatment Rate (1/d) (kg/d) Rate (1/d) {kg/d) supplied the entire contaminated zone with oxygen,and would
<br /> s)
<br /> Low Rate 0.016 24.4 0.026 40.1 thave prouced the reatmentand/or disposal.
<br /> m volume of extracted soil gas or
<br /> Venting i 26I
<br /> Moisture 4.030 45.3 0.168
<br /> Addition87 1 TPH Removal Performance
<br /> Nutrient O.OIb 24.4 0.060
<br /> &1%40isture As indicated above, 65014 contaminant recovery was accom-
<br /> Addition ptished by conventional high rate SVE during the first nine
<br /> 7February, 1993 51
<br /> C.. irnnrtlonf?� progress (V 12. No. 1)
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