Preliminary Evaluation of Septic‐System Absorption‐Field Architecture Types in a Profile‐Limited Soil

Abstract

Managing household wastewater is an issue that affects hundreds of thousands of people in rural communities nationwide, many of whom rely on septic systems as their primary means of household wastewater disposal. Septic system absorption field products with architectures quite different from traditional pipe-and-gravel systems are being installed in many states with variances from initial design specifications. The objective of this study was to evaluate the performance, as measured by the in-product height of stored solution, of four differing absorption-field product architecture types in a profile-limited soil that was loaded at the maximum allowable rate based on soil morphology. Five chamber, two gravel-less pipe, two polystyrene aggregate, and four pipe-and-gravel systems were installed in a profile-limited, Captina silt loam soil (fine-silty, siliceous, active, mesic Typic Fragiudult) and dosed with raw effluent at rates determined by current State of Arkansas regulations via individual peristaltic pumps. Free-solution monitoring ports were installed within each product, where the depth to free solution was measured periodically and used to evaluate product performance. Data collected from January through August 2009 indicated that preliminary system performance was unaffected by product architecture type. All products performed similarly under dry soil conditions. However, differences among individual products were observed during periods of hydrologic stress (i.e., wet soil conditions). Surfacing of effluent was not observed atop any product, indicating that the current loading rate design method is functioning properly. Preliminary results indicate that some alternative absorption-field products perform similarly to the traditional pipe-and-gravel system, thus providing flexibility and options for homeowners.

Increased Effluent Dosage Effects on On-Site Wastewater Treatment Systems of Differing Architecture Type

“…Prater et al [15] extended the study initiated by Mathis et al [14] and summarized results of in-product storage after three continuous years. Biomat presence and thickness were also monitored after about 1.5 years of effluent dosing, where loading rates were based on soil morphology and the soil storage concept [16] and set at the maximum allowable loading rate by Arkansas regulations.…”

“…More recently than the studies in Colorado [6]- [8], Mathis et al [14] studied architecture type (i.e., chamber, gravel-less-pipe, polystyrene-aggregate, and pipe-and-aggregate) effects on in-product solution storage under wet-and dry-soil conditions for the first eight months after dosing began at the Bethel Heights Wastewater Treatment Facility (BHWTF) in Bethel Heights, AR. The study was conducted on a Typic Fragiudult.…”

“…The study was conducted on a Typic Fragiudult. Thirteen OWTS products were installed [14] (Table 1). Raw effluent that entered the BHTWF directly from its various OWTS tank connections without any other treatment was delivered from a basin to a corresponding absorption-field product.…”

“…Effluent loading rates for the 13 products were determined by a conservative estimate as stated in the Arkansas rules and regulations in order to mimic real-world applications. Loading rates were between 11.6 to 81.1 L•d −1 and were determined based on the estimated effluent the soil around each trench could handle, which was based on soil morphological observations [14]. During the study, none of the products failed, where a product failure was characterized as effluent surfacing, which showed that, under the perched seasonal water table and precipitation conditions at the study site, the products were stable and functioned as expected within the first eight months after maximum allowable dosing began [14].…”

“…Loading rates were between 11.6 to 81.1 L•d −1 and were determined based on the estimated effluent the soil around each trench could handle, which was based on soil morphological observations [14]. During the study, none of the products failed, where a product failure was characterized as effluent surfacing, which showed that, under the perched seasonal water table and precipitation conditions at the study site, the products were stable and functioned as expected within the first eight months after maximum allowable dosing began [14]. However, the Mathis et al [14] study did not address potential groundwater contamination.…”