Carbon-based denitrification bioreactors are designed to intercept tile drainage and are a promising technology for reducing NO3- export to surface water. While these systems have been tested extensively in the laboratory, the ability to study in-field bioreactors under controlled conditions with statistical replicates has been limited. Nine pilot-scale bioreactors (5.79 x 1.05 x 1.07 m) were designed and installed for systematic field testing, allowing for variation in retention time, fill material, and influent water quality parameters. Each bioreactor is constructed from a concrete trench in-line with influent flow control, dosing port, flow diffusion, and effluent water level control. Sampling ports are installed at two points in each bioreactor for access to water samples or fill materials. A potassium bromide (KBr) tracer study was conducted and Morrill Dispersion Index (MDI) values averaged 2.8 +/- 0.3, indicating plug flow characteristics. The average tracer residence time (t) was 2.3 +/- 0.3 h, in close agreement with the estimated hydraulic retention time (HRT) value of 2.1 +/- 0.3 h, which was calculated using a porosity value of 0.70. Hydraulic efficiency was good (lambda = 0.78 +/- 0.03) and there was no evidence of short circuiting (S = 0.73 +/- 0.03). This system is expected to provide useful insight regarding design for improved field performance of denitrification bioreactors.