Predicting Saturated Hydraulic Conductivity from Percolation Test Results in Layered Silt Loam Soils

Article excerpt

Introduction

The disposal of effluent from conventional septic tanks, wastewater treatment systems, and sewage treatment works has potential to cause serious problems in our environment and particularly in the soil ecosystem (Patterson, 1996).

Rural and suburban areas frequently do not have a public sewer system, therefore, the residents of these areas often depend on septic tank systems to dispose of their sewage. The size of these onsite waste disposal systems is usually determined by one or more percolation tests made on the proposed site (Schmidt et al., 1980).

A number of alternative techniques for making a percolation test have been proposed (Mulqueen & Rodgers, 2001; Rodgers & Mulqueen, 2004; Schmidt et al., 1980). The simplest and most commonly used test is performed by digging a borehole in the soil, filling it with water to presoak the soil, and then determining the rate of fall of the water surface in the hole (Fritton, Long, Aron, & Petersen, 1983; Schmidt et al., 1980). Numerous variations of this simple percolation test are available. Standard percolation test procedures have been published by the U.S. Environmental Protection Agency (Schmidt et al., 1980). These procedures are used by individual states throughout the U.S. with some modifications to yield their own percolation test procedure (Schmidt et al., 1980).

Since the percolation test is the tool most widely used to measure water flow capabilities of a field soil, several attempts have been made to find empirical relationships between the saturated hydraulic conductivity (Ks) and the percolation time (PT) with a hope of replacing the percolation test with a hydraulic conductivity test (Fritton, Ratvasky, & Petersen, 1986; Mulqueen & Rodgers, 2001; Winneberger, 1974).

Most of these studies have dealt with homogeneous soils. In reality, however, field soils are inherently heterogeneous and usually consist of distinct layers or horizons of relatively homogeneous materials. Therefore, the objectives of the study described here were to first, develop an empirical relationship between the saturated hydraulic conductivity (Ks) of layered silt loam soils and their percolation times (PT) in order to understand the influence of individual layers; and second, to statistically compare this relationship with the equations developed by Winneberger (1974) and Fritton and co-authors (1986).

Materials and Methods

Soils and Sites Description

Field research was conducted on three soils in Centre County, Pennsylvania. The soils were classified as a fine, mixed, mesic, Typic Hapludalf (Hagerstown silt loam); a fine-loamy, mixed, mesic, Typic Fragiudult (Monongahela silt loam); and a fine-silty, mixed, mesic, Dystric Fluventic Eutrochrept (Nolin silt loam). All of these sites were located in the Ridge and Valley Physiographic Province of Pennsylvania (Braker, 1981). These soils were layered in different ways as follows: (Hagerstown) a silt loam Ap horizon underlain by a high clay content B horizon in the top meter, (Monongahela) a silt loam Ap horizon underlain by a fragipan in the top meter, and (Nolin) a silt loam alluvial soil underlain by a gravel layer in the top meter (Braker, 1981). The Hagerstown silt loam site was located in Ferguson Township on the Pennsylvania State University Agronomy Research Farm at Rock Springs, 30 m E-NE of the Agronomy field laboratory building (40[degrees]42'55" N, 77[degrees]56'15" W). It is about 16 km west of downtown State College, Pennsylvania. The soil is well drained and developed in limestone residuum parent material. The site was in a sod area. The Nolin silt loam site was located 50 m west of the sheep barn and 100 m south of the wooden pedestrian bridge over Spring Creek on Puddintown Road west of Houserville in College Township (40[degrees]50'01" N, 77[degrees]49'40" W). The soil was formed in recent alluvium from limestone and exists on flood plains. …