The invention disclosed relates to a method and apparatus for the
denitrification of
groundwater in situ in an
aquifer under substantially anaerobic conditions, the method comprising(a) providing a network, including an extraction well for removal of
groundwater from the
aquifer and a plurality of injection wells for returning
groundwater to the
aquifer, the injection wells being arranged in a line substantially perpendicular to the direction of
groundwater flow, the extraction well being located downstream or upstream of the line of injection wells, and the spacing of the wells and the number of injection wells being determined by the mathematical relationshipwhere J is the
cost of treatment, CP and CI are the costs of extraction and injection wells, respectively; n is the number of injection wells, and W is the distance across the
protected area, and wherein the water
stream is evenly distributed between injection wells, according to the relationship:where F is the
water flow rate (e-extraction well, i-
injection well) and n is the number of injection wells,(b) removing groundwater from the aquifer by the extraction well,(c) adding a
carbon source to the groundwater in a controlled manner,(d) returning the
carbon source amended groundwater to the aquifer by the injection wells in even distribution, the
water flow rate being controlled, and(e) monitoring the
nitrate concentration of the groundwater removed from the extraction well, a decrease in
nitrate concentration being indicative of
denitrification.