Resources of Colorado

Quality of Ground Water and Surface Water in an Area of Individual Sewage Disposal System Use Near Barker Reservoir, Nederland, Colorado, August–September 1998

by Jennifer L. Flynn and L.B. Barber

Available from the U.S. Geological Survey, Branch of Information Services, Box 25286, Denver Federal Center, Denver, CO 80225, USGS Open-File Report 00–214, 8 p., 8 figs.

This document also is available in pdf format: pdf symbol OFR 00–214.pdf
(Requires Adobe Acrobat Reader)


Barker Reservoir is a mountain reservoir adjacent to Nederland, Colorado (fig. 1), that supplies 40 percent of the drinking water for the city of Boulder, Colorado. The local geology is quite complex in this region of the Colorado Mineral Belt (Lovering and Goddard, 1950). The study area is primarily Precambrian igneous and metamorphic rock, except for Quaternary alluvium and colluvium in streambeds and drainages that lead to the reservoir (Gable, 1972). The reservoir is fed by North Beaver Creek and Middle Boulder Creek. Ground water that discharges into Barker Reservoir flows beneath residential developments on the north and south sides of the reservoir. Homes on both sides of the reservoir use individual sewage disposal systems (ISDS’s) for disposal of domestic wastewater.

ISDS’s, also called septic systems, are a common source for reported contamination of ground water (Canter and Knox, 1986). A system that is not properly designed or maintained may leak sewage into surrounding soil, which then can contaminate surface water or ground water. Even properly functioning systems can contribute considerable loads of chemical constituents that are not removed during infiltration (Wilhelm and others, 1994).

ISDS design can vary, but a basic system includes a septic tank and a leach field. Solid and liquid household waste is transported from the residence through a sewage pipe to the tank, where biological processes begin breakdown of the waste. Solid waste that does not liquefy settles in the tank and must be pumped out periodically. Liquid is decanted from the top of the tank and transported to the leach field where it is distributed through perforated pipe or another means to the soil. Liquid waste flows through the soil, undergoing biological and chemical processes as it travels to the water table.

ISDS effluent is composed of the domestic water supply (ground water or municipal water) that has been modified by chemicals introduced by household activities (detergents, cleaning agents, human wastes, and so forth). ISDS treatment reduces the concentrations of water-quality properties such as biological oxygen demand and total suspended solids by physical and biological processes but has little effect on many chemical constituents such as dissolved ions like sodium and chloride.

The U.S. Geological Survey (USGS), in cooperation with the City of Boulder, Colorado, conducted this study to evaluate whether ISDS’s affect the quality of ground water entering Barker Reservoir or its tributaries. This report describes the results of water-quality samples collected in August and September of 1998. Water-quality samples were collected from 12 wells and 10 springs or surface-water drainages near Barker Reservoir.

Table of Contents

Data Collection
     Individual Sewage Disposal System
     Quality Assurance/Quality Control
Water Quality
     Major Ions
     Total Organic Carbon
     UV Absorbance

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Water Resources of Colorado

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