SITE INFORMATION AND CORRESPONDENCE_1985-1997

Home Browse Search

ORC-concrete briquets. ane exact magnitude of this vu+ vc•z PL-3 vu number would be affected by(1)the groundwater veloc- 14 ity, (2) the concentration of benzene and toluene, (3) 12 - the mass of benzene and toluene degraded, and (4) the i ro degree of saturation and mixing within the screen. - e D.O. concentrations within the ORC-concrete well ° e 0 screen (OCL-2) were as high as 19 mg/L initially 2 (Day 4). Figure 7a shows that D.O. later stabilized to o t 8 to 9 mg/L (Day 18 to Day 38). These concentrations are approximately 24 to 58 percent of the maximum 0.0 0.5 1.0 1.5 2.0 expected D.O. (33 mg/L). Given the low sampling DISTANCE FROM SOURCE(m) frequency during the initial phases of the experiment, it is possible that D.O. may have been greater before 3600 vu•r vL•: PL-3 PL-4�.... Day i the B/T arrived at the well screen or during the acclima- 3000 - Day 2 tion of the native microorganisms to the B/T(i.e.,before '"4600 - significant biotransformation occurred). D.O. concen- W z000 �- Dayz trations in this line were also high at the points downgra- = 1600 �- Day 3 dient of the well screen containing ORC-concrete W f0e0 -a— Day: briquets: 9 to 15 mg/L at OCL-3, and 6 to 9 mg/L at m 600 Days OCL-4.Thus, even when there were significant oxygen o *- Day 2 sinks present in the ground water (i.e., BIT), the ORC 0.0 0.6 1.0 1.6 2.0 concrete released enough oxygen to generate an oxygen DISTANCE FROM SOURCE(m) plume that migrated at least 1 in from the well screen. This latter possibility is supported by the monitoring 3600 vc-' ve-z PL-3 vc� results from Day 68,37 days after B/T/NO3/Br injection 3000 ceased. On this day, D.O. was found to be 45.6 mg/L �2600 within the screen(OCL-2),consistent with oxygen solu- w 2aoo bility at 7 C(58 mg/L),and 4.9 mg/L 0.5 in downgradient W 1600 (OCL-4). The D.O. for Day 68 within the screen is also o 1000 fairly close to the expected D.O. (during the zeroth 600 order release phase) in the absence of an oxygen sink 0 (55 mg/L).These data illustrate that the ORC-concrete 0.0 0.6 1.0 t.s- 2.0 briquets were capable of producing and sustaining very DISTANCE FROM SOURCE(m) elevated concentrations of D.O. for at least 10 weeks Figure 8. Concentration of la)D.O., (b)benzene, and(c)tolu- after the ORC briquets were placed in the ground. ene along the Pencil Line. Figures 7b and 7c present the benzene and toluene data,respectively, along the ORC-Concrete Line. Both water flow paths were changing somewhat over th figures show relatively uniform and high concentrations course of the experiment,perhaps due to time and are: of B/T on Day 18,indicating that extensive biodegrada- variations in percolation of snowmelt. tion had not occurred. After this date, Figures 7b and Pencil Line 7c indicate that B/T concentrations decreased signifi- The D.O.concentration in ground water flowing pa cantly, in many cases to below the detection limit at the pencils can be estimated making the same assum OCL-2 and at other points further downgradient of the tions that were made for the ORC-Concrete Line. F( oxygen source. the pure powder, however, the oxygen release rates a. Figures 7b and 7c also indicate that B/T concentra- approximately 1.6 mg of 02 per day per gram of OR tions at OCL4 increased over time after about Day 34, for the first four days and 0.4 mg of 02 per day p rising to fairly high values by Day 39. However, the gram of ORC for the next 150 days.Thus,the expecte D.O. values at OCL-4 remained steady through Day 36 D.O. concentrations in ground water were appro) at about 8 mg/L, then apparently dropped by Day 38 mately 27 mg/L for the first four days and 6.8 mg/L f to 1.5 mg/L. Unfortunately, due to equipment failure, the remainder of the experiment.These lower values we it was not possible to measure D.O. on Day 39. On due to the smaller mass of ORC present in the pent Day 68, the D.O. in OCL4 remained low (0.2 mg/L). when compared to the mass of ORC present in tl Note, however, that the high B/T concentrations briquets. Given the estimated D.O. demand discuss( observed at OCL-4 were not detected in prior sampling above for the B/T concentrations used in the experimer of upgradient monitoring points. This suggests that the the D.O. in the vicinity and downgradient of the penc B/T detected at OCL-4 on the later dates did not flow should have been approximately 11 mg/L initially, b through the ORC-concrete well screen or by sampling would be expected to drop below the detection limit aft point OCL-3. The low observed D.O. would also be four days or so. consistent with this hypothesis. It is probable that, Figure 8a shows that initial D.O. levels immediate despite our efforts to minimize such effects, the ground downgradient of the pencils (PL-2), were greater the 126 a WINTER 1994 GWMR