Archive for January, 2008
A good rule of thumb is that a vegetative treatment area (VTA) needs to be at least as large as the feedlot, open lot, or barnyard area. If local sizing procedures are available from your land-grant university or USDA Natural Resources Conservation Service, those recommendations should be followed. Consult design professionals, such as an engineer or technical consultant experienced with VTS design, before constructing any type of livestock waste control facility.
For additional information on sizing , refer to Chapter 6 of the NRCS collaborative report on Vegetative Treatment Systems for Open Lot Runoff.
Author: Chris Henry, University of Nebraska
We think that vegetative treatment systems (VTS) have potential for the runoff from feed storage areas. However, from our experience, one of the challenges for forage storage areas is that loose, finely ground fibrous materials (such as ground hay) are a challenge for some solid separating structures. Such fibrous materials cause bridging when carried with runoff, often plugging some settling structure types. This is especially troublesome with inlets for pumping stations, such as the sprinkler VTS. An inline pressure filter (which would include the use of a large opening inlet strainer) has some potential to overcome this obstacle. The design constraint for a VTS for this application will be the management of the water, as the nutrient concentration is expected to be very low relative to an open lot. There are very little data available on this, and to our knowledge, few if any have been built for this application.
Author: Chris Henry, University of Nebraska
Two systems are being monitored in Nebraska, a sloped VTA and a level VTA system. The level VTA, surrounded by a 1-foot high berm, impounds any runoff from the sloped VTA. We have a water level logger in the level VTAs and know the berm elevation with respect to the logger elevation. We also log the rain events at each site, so we compare the precipitation event to the depth logger and know when, and if, the level VTA is inundated (water goes over the berm). While we don’t know the volume, it is a simple way to evaluate our design for potential discharges.
Iowa State University is monitoring CAFO sites, and those systems are being monitored for inflow and outflow, using flumes and pipe flow sensors to measure flow. They are also measuring nutrient content of the flow with ISCO samplers and with these data can estimate nutrient mass going into and out of the VTA. For the Iowa sites, we can differentiate from a discharge related to direct rainfall runoff from the VTA and runoff coming from the feedlot because our settling basin valves are normally closed during rainfall events. And the monitoring equipment puts a time stamp on all collected flow data.
Because the permitted CAFOs are required to record and sample all discharges, the ISU project includes development of a low-cost method for meeting this need.
Author: Chris Henry, Biological Systems Engineering, University of Nebraska
At all of the research sites in the Iowa vegetative treatment system demonstration project, we are collecting monthly groundwater samples from locations up-gradient of the vegetative treatment area (VTA), within the VTA, and down-gradient of the VTA. With the additional funds we are in the process of procuring, we will be able to collect a total of three years' monitoring data. Obviously, the longer we monitor, the better our understanding of long-term performance will be. And, for that reason, we are continuing to try to identify funding that will enable us to do so.
Author: Lara Moody, Iowa State University
Vegetation management is critical to the success of a vegetative treatment area (VTA). Soil fertility may vary with the length of the VTA. A soil and fertility sampling program should be designed to capture that variability and, where appropriate, provide supplemental nutrient applications. Additional vegetation management considerations include periodic harvesting, weed control, and soil moisture management.
Environmental management considerations are essential for maintaining environmental performance. Soil sampling for regions of excess nutrient accumulation, forage harvesting for nutrient removal, VTA inspection and repair of conditions impacting sheet flow, and active management (or possibly passive management) of the release of runoff into the VTA are all key to environmental performance.
Records for monitoring performance are essential for both permitted and non-permitted facilities. Records should include 1) a precipitation log, 2) indicators of good management (e.g., records of vegetative treatment system inspections and resulting repairs, timing of solids harvest for settling basin, soil samples, crop and nutrient harvesting), and 3) records of any discharges associated with runoff additions to VTA.
Chapter 8 of the NRCS collaborative report on Vegetative Treatment Systems for Open Lot Runoff discusses these operation and maintenance considerations in detail,
Author: Rick Koelsch, University of Nebraska
