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Hydrologic data collected in 1975~77 as part of a comprehensive waterresources investigation of Boulder County by the U.S. Geological Survey, in cooperation with the Boulder County Health Department and the Colorado Geological Survey, are presented in this report. The data, in tabular and graphic form, consist of water-quality analyses of selected constituents and geohydrologicsite, water-treatment, and sewage-treatment data for 609 wells and 48 springs; water-quality analyses for 102 of the wells and 9 of the springs; water quality analyses of streamflow from 34 sites; and specific conductance and watertemperature measurements of streamflow from 3 sites. State and local officials in Boulder County may find these data useful in planning for residential, commercial, and industrial development.

Sediment oxygen demand (SOD) was determined at three sites in a gravel‐bottomed central Missouri stream by: (1) two variations of an instream method, and (2) a laboratory method. SOD generally was greatest by the instream methods, which are considered more accurate, and least by the laboratory method. Disturbing stream sediment did not significantly decrease SOD by the instream method. Temperature ranges of up to 12° Celsius had no significant effect on the SOD. In the gravel‐bottomed stream, the placement of chambers was critical to obtain reliable measurements. SOD rates were dependent on the method; therefore, care should be taken in comparing SOD data obtained by different methods. There is a need for a carefully researched standardized method for SOD determinations.

The use of residential wastewater-treatment systems in Evergreen Meadows, Marshdale, and Herzman Mesa has degraded groundwater quality to some extent in each community. Age of community; average lot size; slope of land surface; composition, permeability, and thickness of surficial material; density, size, and orientation of bedrock fractures; maintenance of wastewater-treatment systems; and presence of animals are factors possibly contributing to the degradation of groundwater quality. Ground water in Evergreen Meadows, the youngest community and the community with the largest average lot size, is the least degraded and most suitable for use as a drinking-water supply. Ground water in Marshdale, the oldest community and the community with the smallest average lot size, is degraded to the degree that disinfection of the water to avoid bacterial contamination may be warranted in parts of the community. Ground water in Herzman Mesa is the most degraded and least suitable for use as a drinking-water supply. Bacterial contamination and excessive concentrations of dissolved nitrite plus nitrate are the major waterquality problems. Disinfection of the water to eliminate bacteria may be warranted in the community. When compared with effluent from aeration-treatment tanks, effluent from septic-treatment tanks is characterized by greater biochemical oxygen demand and greater concentrations of detergents. When compared with effluent from septictreatment tanks, effluent from aeration-treatment tanks is characterized by greater concentrations of dissolved oxygen, nitrite, nitrate, sulfate, and dissolved sol ids. Changes in the effluent in the aerobic soi1-absorption fields associated with the two systems were: Biochemical oxygen demand and concentrations of detergents and sulfate decreased in both systems; concentrations of dissolved oxygen and nitrite increased in septic systems and decreased in aeration systems; concentrations of nitrate increased in both systems; and concentrations of dissolved solids remained about the same in septic systems and increased in aeration systems.

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