Filtering drainage water

Tile drains and French drains are typically used to control subsurface drainage, especially on greens and fairways with shallow water tables or fine soil texture. Tile drains are defined as "drains constructed by laying drain tile with unsealed joints in the bottom of a trench which is then refilled," whereas French drains are a "type of drain consisting of an excavated trench, refilled with pervious materials such as coarse sand, gravel or crushed stones, through whose voids water percolates and flows toward an outlet" (ASAE Standard S526.2, 2001). Tile drainage and other subsurface drainage features are considered essential by turfgrass managers to maintain water tables at depths necessary for healthy plant growth; maintain sufficient water and air in soil void space to stimulate essential microbial activity; avoid rutting and soil compaction by maintenance equipment; and to allow site use soon after heavy rains. Subsurface drainage increases the subsurface movement of excess water and facilitates infiltration. However, discharge from subsurface tile drains is known to carry elevated levels of dissolved pollutants such as phosphorus, nitrogen and pesticides. Agronomic practices alone such as application timing, placement and rate have not appreciably reduced the pollutant transport in tile drains. Nutrient and pesticide transport through subsurface drainage systems may become a component of surface runoff if the drainage water discharges directly into surface water or onto the surface offsite or downslope. Subsurface drains conveying water directly into a stream or pond will bypass natural and managed filtering processes, including upland and riparian buffer zones. To protect these surface waters and comply with regulatory and/or permitting laws, treatment of the waters prior to their entry into a surface water body may be required. In-situ physical and structural approaches are being considered to address this concern. In laboratory bench scale studies, natural minerals and industrial byproducts (e.g. zeolite, fly ash) have exhibited a range of success removing nitrogen, phosphorus and pesticides. For example, industrial byproducts high in aluminum, iron and calcium, such as fly ash, blast furnace slag and water treatment residual are ideal phosphorussorbing materials, while clinoptilolite, a naturally-occurring, inexpensive zeolite, has been shown to effectively remove ammonium-nitrogen from aqueous solutions. With respect to pesticides and other organic contaminants, adsorption to activated carbon is the preferred method for their removal from source waters. Inexpensive, activated carbons developed from coal, lignin (paper industry) and coconut byproducts have exhibited high contaminant-removal efficiencies. Current research is designed to address the potential for utilizing a blend of these types of byproducts in an end-of-tile filter to significantly reduce the transport of nutrients and pesticides from golf course tile drainage outlets. The research will be conducted in two phases. The first phase is a controlled large-scale laboratory experiment designed to evaluate the filter's effectiveness while operating at flow rates comparable to those measured in the field. The second phase is a before-and-after field assessment of the filters under prevailing management practices on an existing golf course.