Protection of a drinking water well from nitrate contamination by recirculating nitrate treatment well system

The investigation of a technique for protecting a downstream drinking water well from nitrate contamination of groundwater is presented. A recirculating nitrate treatment well system is proposed in which groundwater is drawn into the well, denitrified in the treatment chamber, and returned to the top of the aquifer. Well hydraulics were experimentally examined in a two-dimensional aquifer model, and ambient groundwater velocities of 1 to 3 m/day were simulated in combination with well recirculation rates of 25 to 200 ml/min. An on-line feed control system was developed for testing the treatment barrier associated with well recirculation and biological denitrification. The impacts of carbon feed, groundwater flow, nitrate loading, and well recirculation on the performance of system operation were also investigated.;Hydraulic problems identified with experimental apparatus included blow-through of contaminant at the well intake by high ambient groundwater velocities and submergence by the well hydraulics of depth-distributed contaminant plumes without interception. The problems associated with biological denitrification were found to be possible permeability loss by screen fouling and blinding of soil pores by overfeed of carbon. These identified problems were corrected by maintaining a greater well recirculation rate and adjusting carbon feed at stoichiometric ratio of nitrate load to the well.;This study has demonstrated that the recirculating nitrate treatment well system may be a feasible process for protecting drinking water wells from groundwater contamination in a sandy unconfined aquifer. Experimental results provide guidance in identifying affecting parameters that could possibly affect the performance of the treatment system. On the basis of experimental results, the procedures of system design were also developed for evaluating the feasibility of the proposed methodology.