Unilin Wood Products Facility is located in Mount Gilead, North Carolina and has been operation for many years producing high quality wood products. The facility has received several required permits to operate in compliance with NCDENR regulations successfully. The facility receives wood chips and stores these chips in open piles until processed. The wood chips produce organic exudates that may contain high levels of sugars and other organic matter found in the xylem and phloem portion of woody vegetation. The rainwater contacting the wood chip migrates through the pile and transports the organic matter to the existing stormwater pond system.
Historically, the Stormwater Section in the NCDENR Fayetteville Regional Office expressed concerns about the pollutant levels (e.g. Biological Oxygen Demand (BOD), Chemical Oxygen Demand (COD), and Total Organic Carbon (TOC)) in the stormwater exiting the site. Samples of the stormwater exiting the facility were collected and analyzed and found to contain high concentrations of these above-mentioned pollutants that had impacted the surface water at the Facility.
Conventional treatment methods are expensive. Engineered wetlands offered an alternative natural system approach to handle and treat the industrial stormwater generated at Unilin. Pilot testing was conducted which allowed examination of several treatment configurations. We determined the wetland that was most successful at removing the elevated COD and TSS was a hybrid wetland system with both free water surface areas and subsurface flow areas providing treatment. Engineered wetlands offer an approach which may be much better suited for the sporadic nature of stormwater runoff from the Unilin facility. Wetland systems have been successful for other water sources although application treating moderately high strength industrial stormwater would be a new and novel application for this technology and has never been implemented at a similar facility in North Carolina.
We are currently in the construction phase of a four (4) acre wetland that is necessary to accommodate the equalized stormwater flow from the design event. The minimum treatment items necessary consists of the equalization area, two (2) independent treatment wetlands each with a minimum of 1.5 acres and a single one (1) acre polishing wetland. Liquid would flow from equalization through the treatment wetland to the polishing wetland and ultimately enter an intermittent stream on the Unilin property.