METHODS COMPARISON OF FIELD PARAMETER QUANTIFICATION OF UNSATURATED FLOW AT AN EXISTING WASTEWATER INFILTRATION SYSTEM; MINES PARK, GOLDEN, COLORADO

Mountain watersheds commonly experience water quality and sustainability issues associated with septic-tank wastewater treatment systems (SWTS). The current understanding of SWTS is poorly understood and the design of these systems is generally accomplished through the use of judgment and experience rather than rigorous quantitative methods. An established wastewater infiltration experimental site at Mines Park, Golden, CO, is the location of a detailed vadose-zone characterization of unsaturated hydraulic conductivity (K(u)). In addition, a comparison was conducted of various methods utilized for estimating or measuring K(u). The method comparison addresses both the consistency between the various methods and the understanding of K(u) variability over the area typical of a domestic SWTS. Experimental field data was collected from a two-tier 30-foot long trench excavated at the Mines Park wastewater infiltration experimental site. The utilized methods of field data collection include Guelph permeameter measurements (8 locations) and tension-disk infiltrometer measurements (6 locations). Soil samples, representative of the two-tier trench, were also collected for in-lab experimentation at the Bureau of Economic Geology. The in-lab experiments include van Genuchten-Mualem transformations of capillary-pressure curves determined from both hanging-column and pressure-plate measurements (14 locations) and estimated from soil grain-size classifications and bulk density (14 locations). Differences in K(u) from the various methods are illustrated by comparing K(u) versus water content curves. Statistical analyses are used to demonstrate the significance of the spatial variability in the two-tier trench. This research will advance the use of rigorous quantitative measurements and methods to better understand the impact of wastewater pollutants on water quality and water sustainability in mountain watersheds.