State Water Resources Research Institute Program


Project ID: 2011AR289B
Title: Evaluation of septic system absorption field products with differing architectures in a profile-limited soil
Project Type: Research
Start Date: 3/01/2011
End Date: 2/29/2012
Congressional District: 3
Focus Categories: Non Point Pollution, Wastewater, Water Quality
Keywords: household wastewater, wastewater treatment, septic systems, absorption field
Principal Investigator: Brye, Kristofor R. (University of Arkansas)
Federal Funds: $ 15,389
Non-Federal Matching Funds: $ 31,074
Abstract: The State of Arkansas currently has approved on-site wastewater treatment system absorption field products of various architectures, including chambers, gravel-less pipe, and pipe and polystyrene aggregate, which can be used as alternatives to the standard pipe-and-gravel system to renovate household wastewater. However, all absorption field products are loaded based on loading rate charts developed for the standard pipe-and-gravel system installed in a 24-inch wide trench. Consequently, there is virtually no scientific data to support what the maximum loading rate could be for any particular product based on soil morphology and the design criteria used in Arkansas. The loading of a gravel less product with the same amount of effluent as a standard pipe-and-gravel trench could be exceeding the long term acceptance rate of the soil. Furthermore, with the recent rapid population growth and urbanization taking place in northwest Arkansas, maintaining and improving the quantity of high quality drinking water supplies will be imperative. Northwest Arkansas has already experienced phosphorous (P) enrichment of surface waters from non point source pollution activities generally assumed to be mostly related to the concentrated poultry production in the region. However, the potential contribution of on site septic systems to non point source pollution in the region is largely unknown and needs to be studied. A field study that incorporates multiple trench media products of varying architectures installed at a single location and loaded with the same strength effluent, such as the one being proposed, will provide a sound scientific basis for sizing individual on site wastewater systems with differing product architectures. Because Arkansas uses soil morphology as a key indicator of perched seasonal water tables and the current loading rates were developed based on the storage approach (originally calculated using a standard pipe-and-gravel product in a 24-inch wide trench), a call for a study conducted on a profile limited soil with actual product lengths comparable to that used at individual home sites in an effort to determine the role that product architecture has on in-trench storage is overdue and greatly needed. Therefore, the objectives of this study will be to evaluate the effect of absorption field product architecture (i.e., chamber, gravel less pipe, pipe and aggregate, and polystyrene aggregate) and soil conditions (i.e., previously dry and previously wet) on in-trench effluent storage and bio-mat occurrence and persistence in a profile limited soil that is loaded at the maximum rate allowed by current State of Arkansas regulations based on soil surrounding morphology. This study will be conducted on the grounds of the Bethel Heights Wastewater Treatment Facility in Bethel Heights, AR where 13 septic tank absorption field products that have already been installed in a Captina silt loam soil will be simultaneously evaluated in a side-by-side comparison study. In-product storage of free solution (i.e., climatic water and effluent) and the presence/absence and thickness of a biomat will be the primary variables measured in this study. Preliminary data obtained thus far indicates that all products being tested behave similarly when the soil is previously dry as measured by the depth of free-solution stored within the products, but that there are differences among products and compared to the standard pipe-and-gravel product when the soil is previously wet (i.e., hydrologically stressed). Protection of the environment, particularly surface and groundwater resources, and human health are the ultimate benefits in the short- and long-term of the proposed study.

Progress/Completion Report, 2011, PDF

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