The Hicksville Water District faced a difficult task when high levels of nitrates and volatile organic compounds (VOCs) were found in two of their water supply wells. The source of the contamination was determined to be former residential septic systems that were still in place, over-fertilization of lawns and farms, and industrial operations in the area.
H2M was tasked with finding the most viable and cost effective treatment solution to correct the nitrate and VOC problem. The nitrate issue was addressed with the addition of an ion exchange system. The idea behind an ion exchange system is to run a water stream through a pressurized vessel containing ion-exchange resin. The resin consists of small beads (0.5 to 1 mm in diameter) made from an organic material. The beads appear solid, but allow for microscopic particles to pass in and out of their skins, much like living cells transfer solutions through their cell walls. In this case, the ion exchanger removes nitrates from the water stream, which is then blended back into the pumped well water.
Removal of VOCs was handled using an air stripping system. Using a tower for this process, the contaminated water is sprayed into the top of the tower and allowed to filter down through a plastic packing medium which increases the surface area of the water. At the same time, air is forced into the base of the tower and exhausted out the top. As the air and water droplets collide, VOCs attach to the air molecules and are “stripped” out of the water stream. The cleaner water then exits the tower base and is returned to the water supply.
H2M’s completed design included a new building to house the ion exchange process, a new air stripping tower, pump modifications and a new process control system. With a flow rate of 3.4 MGD, the new water treatment processes reduce nitrates and VOCs to well below maximum contaminant levels (MCL) for both compounds.