SITE INFORMATION AND CORRESPONDENCE_1985-1997

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tao 18 16AL-1 AL-2 AL-2 AL-4 na 4 un 14 eo __9-- —12 0 10 • • 4m E 8 4 2 o j4 �• 0 A a m mo xoo • �� 0.0 0.6 1.0 1.5 2.0 / DISTANCE FROM SOURCE(m) AL4 AL-2 AW ALS u a 1500 �— Dry 16 n3000 - ,n TIME e.y.la 2500 Dry 22 Dry 2E Figure 4. Typical bromide breakthrough curve. m 2000 1500 - Dry 0. = 1000 --1.-- Dry Y Spatial Distribution of Dissolved Oxygen, Benzene, M Soo _ Dry x and Toluene o 0.0 0.5 1.0 1.5 2.0 Aquifer Line (no ORC) DISTANCE FROM SOURCE(m) The monitoring points in this line sampled ground water that did not flow past any portion of the site AL-1 AL-2 AL-3 ALS asoo containing ORC powder or ORC-concrete briquets 3000 (Figure 1).Figure 5a shows that the D.O.concentrations t 2600 in the Aquifer Line were similar to the background w 2000 D.O.concentrations measured upgradient of the source W 1600 wells. Figures 5b and 5c show the benzene and toluene 3 1000 concentrations, respectively, along the Aquifer Line. ° Sao The benzene concentrations decreased by approxi- 0 mately 20 to 25 percent along this line for a given sam- 0.0 0.5 1.0 1.5 2.0 pling date. DISTANCE FROM SOURCE(m) Toluene concentrations were relatively high at the first monitoring point (AL-1) before Day 33, demon- Figure ne ng Concentration Aqurter Linef(a) D.O., (b)benzene, and (c)tolu- strating behavior similar to benzene. However, Fig- ure 5c shows that toluene concentrations decreased sig- nificantly with time at AL-1.The toluene concentration the two ions since KNO3 was used in the injection SOIL decreased from approximately 750 to 2700 µg/L on or tions as the nitrate source (background values for bot before Day 33 to less than 500 µg/L after Day 33 at all are very low in the Borden ground water). Howeve monitoring points. These data suggest that the concen- there was an apparent excess of potassium with respe( trations were decreasing before the solutes reached to nitrate,with a molar ratio of 2:1 (OCL-1)on Day 3- AL-1, and that these lower values were subsequently Concrete Line (no ORC) observed at downgradient points. Since the solute injection technique remained con- Figure 6a shows that the D.O. concentrations in th stant throughout the experiment,the decline in concen- Concrete Line were also similar to the background D.( tration after Dav 25 is indicative of mass removal. D.O. concentrations measured upgradient of the source well was not detected after Day 25 in any of the Aquifer Figures 6b and 6c present the benzene and toluene col Line samples; thus, the toluene removal is most likely centrations, respectively, along the Concrete Line, occurring under anaerobic conditions and is probably which the well screen contained concrete briquets wit! due to denitrification (degradation in which NO3 rather out ORC. As was the case for the Aquifer Line, It than 02 is the electron acceptor). The fact that toluene benzene values decreased approximately 20 percent I is showing the effect, while benzene apparently does 25 percent across the transport path. Except for tl not, is consistent with previous research that indicates Day 22 samples, which showed concentrations at tl that toluene is degraded under denitrifying conditions first monitoring point apparently much higher than tl and that benzene is recalcitrant. other sampling dates, toluene concentrations were ah Potassium to nitrate ratios in samples collected on relatively high at the first monitoring point,demonstra Day 35 appear to confirm that nitrate was preferentially ing behavior similar to benzene. After Day 26 toluer removed between the source wells and the first row of was depleted to less than 1500µg1L in all of the samplit monitoring points. If nitrate was not removed, there points for the remainder of the experiment.The redu should have been a 1:1 molar correspondence between tion in concentration after Day 26 may be due to natur 124 ■ WINTER 1994 GWMR