Abstract
Surface inlets are installed in subsurface drainage systems to reduce ponding duration and surface runoff, but can contribute to water quality concerns by allowing water to directly enter buried drains. Blind inlets consist of perforated pipes covered with gravel and are separated from an overlying sand layer by a geotextile membrane and have been shown to be more effective in reducing losses of sediment, nutrients, and pesticides than typical tile line risers. In this study, we investigated whether the effectiveness of blind inlets to sorb pollutants, with emphasis on the herbicide atrazine, could be further improved by amended them with materials other than limestone. The media, shredded tires (tire chips), electric arc steel furnace slag (steel slag), and oak-derived biochar were chosen because they are readily available, inexpensive, and do not present environmental concerns. Kinetic sorption and isotherms were determined to ascertain atrazine sorption by these materials, in addition to testing for potential metal leaching using the Synthetic Precipitation Leaching Procedure (SPLP) and the Toxicity Characteristic Leaching Procedure (TCLP). The kinetic data were fitted using pseudo first- and second-order reaction equations and indicated that atrazine sorption rate was 38 times faster and equilibrium was reached 5 times earlier for biochar than tire chips. The 24-h sorption isotherm data were fitted to the Freundlich sorption equation. The sorption coefficient for biochar was higher than for tire chips, steel slag, and limestone. Per the SPLC and TLCP tests, there was no leaching of heavy metals at levels of environmental concern. Our results suggested that the effectiveness of blind inlets as well as other conservation practices that include filter media such as rain gardens and filter socks could be improved by incorporating more reactive materials than sand and gravel with biochar being a particularly effective alternative.
Highlights
The Conservation Effects Assessment Project (CEAP) is a U.S Department of Agriculture multi-agency effort to evaluate the environmental benefits of conservation practices and to develop new and/or modify the existing ones to manage the agricultural landscape for environmental stewardship
We investigated atrazine sorption by tire chips, steel slag, and biochar that could be used in the blind inlet as bed materials
The rate of sorption was ~38 times faster for biochar than the tire chips and equilibrium was reached in ~6 hours compared to ~30 hours for tire chips
Summary
The Conservation Effects Assessment Project (CEAP) is a U.S Department of Agriculture multi-agency effort to evaluate the environmental benefits of conservation practices and to develop new and/or modify the existing ones to manage the agricultural landscape for environmental stewardship These conservation practices include reduced tillage, nutrient management, buffer strips, and drainage water management, among others. Fields with subsurface drainage systems and prolonged standing water in depressional areas can drastically reduce crop yields This concern can be partially alleviated by installing surface inlets that reduce the duration of ponding [1]. Blind inlets are a relatively new conservation practice designed to replace surface inlets and reduce these concerns while maintaining high infiltration rates They are infiltration galleries constructed by covering perforated drainage pipes with gravel followed by a geotextile membrane and topped with a layer of sand. Blind inlets, compared to tile risers, have been shown to reduce annual losses of phosphate-P (up to 72%), ammonium-N (up to 59%), nitrate-N (up to 24%) [2] [3]; and herbicides including atrazine (up to 82%), metolachlor (up to 80%), 2,4-D (up to 81%), and glyphosate (up to 72%) [4]
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