Document Type

Technical Report

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Septic tank system, Filter fields, Soil absorption systems, Effluent renovation, Septic tank effluent treatment, Fragiudults, Loamy-skeletal soils, Soils-stony, Climatic stress periods


Four experimental filter fields were constructed with built-in monitoring equipment in Nixa soils. These soils contain many chert fragments and a fragipan about 60 cm below the soil surface. The fragipan restricts downward movement of water and is the designlimitingfeature. The four filter fields were: 1. A "standard" filter field, 76 cm deep. The bottom of the trench was in the fragipan. 2. A "modified standard" filter field, 30 cm deep. The bottom of the trench was above the fragipan. 3. A "modified pressure" filter field, 40 cm deep. The bottom of the trench was above the fragipan. In addition, a pressure-distribution system was used to insure uniform distribution of effluent in the trench. Inadvertently, this field was installed in a different soil, and the results cannot be compared directly with the other three. 4. Another "modified pressure" filter field with the bottom of the trench only 6 cm below the soil surface. Observation of these systems confirms that placing filter fields higher in the soil above the hydraulically limiting horizon results in improved hydraulic performance. The presence of the fragipan amplified the adverse effects attributable to climatic stress. The seepage beds which are higher in the soil profile are able to handle the effluent load and climate load with less danger of surfacing.

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