For any livestock waste control facility (or any waste control facility for that matter), the siting, design, and construction are governed by good engineering design and applicable regulations. A good geological investigation is warranted and should be conducted unless it is known with good certainty that the particular facility has little risk to groundwater resources.
We have approached the geology of our small facilities as follows. In most cases, we can establish depth to groundwater and soil texture readily from well logs and soil surveys. From this initial investigation, we decide if there is a risk to groundwater; if there is, we do a subsurface investigation to establish soil types and the local depth to groundwater (and perched water) so that we can provide a reasonable separation. Every site is different, and the local geology must be well understood. We interview or consult the local experts or state geologist if we have any questions about the geology of a site.
Our definition of reasonable separation means there is adequate rooting depth and a reasonable separation between the bottom of the root zone and groundwater. Additionally, your state regulatory authority may dictate this. Potential VTA sites where groundwater is within 10 feet of the finish graded surface should be considered problematic and approached with caution. One of the challenges of designing a VTA in a sensitive area such as a site with a perched water table or clay pan is weighing the risk of groundwater impact from a VTA versus a pond. We don’t think we have a definitive answer for you on this yet.
Author: Chris Henry, University of Nebraska
