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Upflow Reactors for Riparian Zone Denitrification

Department of Earth Sciences, University of Waterloo, 200 University Ave. W., Waterloo, ON, Canada
Upper Thames River Conservation Authority, 1424 Clarke Road, London, ON, Canada

View larger version (71K): [in a new window]   Fig. 1. Caddy-Bott Creek site, showing water table elevation (31 Oct. 2003) and location of the five upflow reactor test cells installed through the riparian sediments at the edge of the creek. Water level datum is the creek elevation at CD6.

View larger version (51K): [in a new window]   Fig. 2. Hydraulic head values and ground water flow directions associated with the upflow reactors at: (a) the Woodstock site and (b) the Caddy-Bott Creek site. Head values (m) were measured 4 May 2003 at the Woodstock site and 31 Oct. 2003 at the Caddy-Bott Creek site.

View larger version (28K): [in a new window]   Fig. 3. Flow rates and NO3–N attenuation in the Woodstock reactor during 20 mo of operation, beginning 25 Apr. 2002.

View larger version (10K): [in a new window]   Fig. 4. Nitrate-N attenuation vs. hydraulic retention time in the Woodstock reactor. Data from the first 2 mo of operation, semi-quantitative analyses from Month 7, and monitoring events when effluent NO3–N was < 1 mg L–1 or flow rate was < 50 mL min–1 are excluded.

View larger version (22K): [in a new window]   Fig. 5. Depth profiles of (a) NO3 and Eh, and (b) alkalinity and pH in the Woodstock reactor during Month 13 of operation (4 May 2003, flow rate 0.3 L min–1, temperature 8°C).

View larger version (20K): [in a new window]   Fig. 6. Comparison of grain size curves for the aquifer and shallow riparian sediments (soil zone and stream alluvium) at the Caddy-Bott Creek site. The alluvium is from core CD6 and the aquifer samples are from core CD6 and the reactor pit excavations (see Table 1).

View larger version (28K): [in a new window]   Fig. 7. Simulation of ground water flow lines associated with (a) the riparian zone of a small creek with an unconfined aquifer present and (b) modified flow lines with a high-hydraulic-conductivity (K) wood medium reactor present connecting the creek and the underlying aquifer sediments. Left and right boundary conditions are constant head (1.0- and 0.975-m head, respectively); top and bottom boundaries are zero flux, except for the creek, which has a constant head of 0.98 m. Each stream tube (area between adjacent flow lines) carries an equal amount of ground water flux. The model reflects field conditions observed at the Caddy-Bott Creek site.