The U.S. Geological Survey, in cooperation with the Metro Wastewater Reclamation District, studied the groundwater quality effects of the application of anaerobic digested municipal sewage sludge at agronomic rates to farmland near Platteville. Beginning in the fall of 1985, the sludge was injected annually into the sandy farmland in a 1-square-mile area. Generally, water-quality samples were collected from observation wells two or three times during each irrigation season from 1985 through 1990 and once each winter or late spring from 1987 through early 1991. Water levels were measured, and water-quality, soil and soil-moisture samples, and precipitation data were collected at selected sites throughout the study area. This report presents the data collected during 1985-91 from observation wells, irrigation wells, domestic wells, and other selected sites in the study area.

Physical, chemical, and biological water-quality data were collected and compiled for sites in Standley Lake, its primary inflows, and its outflow from June 21, 1989, to October 30, 1990. Data were collected to determine the limnological characteristics of Standley Lake and the processes that could affect nutrient availability, algal growth, and the occurrence and potential sources of compounds that cause taste and odor problems. These data include measurements of water temperature, pH, dissolved oxygen, and specific conductance in the lake and in the inflows and outflow. Light transparency also was measured in the lake. Lake water, inflow and outflow water, bottom sediment, and interstitial pore water periodically were analyzed for concentrations of nutrients and trace elements. Lake water also was analyzed for concentrations of chlorophyll a, densities and biovolumes of phytoplankton, and densities of zooplankton. Artificial and natural substrates from the lake were analyzed for periphyton density and biomass. The inflows were analyzed for densities and biovolumes of phytoplankton. R.71 W. 105' 3°15'R.70W. R69W. 3. Determine whether the availability of phosphorus limits algal growth during periods when algae suspected of causing taste and odor problems may be present in Standley Lake. 4. Determine the compounds responsible for taste and odor problems in the water delivered from Standley Lake and the potential sources of these compounds to water in the lake. Objectives 1-3 were accomplished by the U.S. Geological Survey. Objective 4 was accomplished by Drexel University, Philadelphia, Pa., using water and biota samples provided by the U.S. Geological Survey; results of this part of the study are presented in two reports from Drexel University (I.H. Suffet and Djanette Khiari, Drexel University, written commun., 1991; Patricia Cascallar and Wesley 0. Pipes, Drexel University, written commun., 1991). Purpose and Scope This report describes the methods of data collection and presents the physical, chemical, and biological data collected from Standley Lake, its primary inflows, and its outflow. Physical data include measurements of temperature, pH, dissolved oxygen, and specific conductance in the lake and in the inflows and the outflow. Transparency, or light penetration, also was measured in the lake. Chemical data include concentrations of nutrients and trace elements in the lake water, the inflows and outflow, the bottom sediment, and the interstitial pore water. Biological data include concentrations of chlorophyll a, densities and biovolumes of phytoplankton, densities of zooplankton, and densities and biomass of periphyton in the lake and densities and biovolumes of phytoplankton in the inflows. Samples were collected from several locations in Standley Lake, from three surface inflows to the lake, and from the outflow to the city of Westminster's Semper Water Treatment Plant. Sampling began on June 21, 1989, and concluded on October 30, 1990. Description of the Study Area f Standley Lake is located in the cit...

Periphyton samples were collected concurrently with macroinvertebrate samples at the 11 sites according to a modified method described in Porter and others (1993). A device called an SG-92, which is constructed from part of a syringe body, a toothbrush, and a rubber O-ring, was used to scrub the attached periphyton from a rock surface and allow that solution of water and algae to be collected in a hand pipette for transfer to a wide-mouth plastic jar. The device has an area of 3.66 cm2, which is used in density calculations. Five rocks were collected at each of the five cross sections, and the SG-92 was used on five separate spots on each rock at streamside. The cumulative sample area then was 458 cm2 for the composited periphyton sample. Formalin was added to each composite sample to equal 3 to 5 percent of the total sample volume for preservation.

Median 239>240pu concentrations in lakesediment grab samples from Standley Lake, Great Western Reservoir, and Mower Reservoir were 0.037, 0.105, and 0.351 picocuries per gram (pCi/g), and the differences between the reservoirs were statistically significant at p<0.05. The highest 239'240pu concentrations were measured in lake-sediment grab samples collected from reservoirs closest to Rocky Flats Environmental Technology Site, which is consistent with the spatial pattern of 239>240pu concentrations identified in soil surrounding the site in previous studies. The maximum concentration of 239>240pu dissolved in lake water was 0.009 picocuries per liter, well below limits suggested by the Colorado Department of Public Health and Environment. Dissolved gross alpha and uranium isotope concentrations were below National Drinking Water Standards in all water samples. There was no statistically significant difference between 239>240pu concentrations in lakesediment grab samples collected from Standley Lake in 1983-84 and in 1992; however, there was a small, but statistically significant difference at Great Western Reservoir (p<0.05). Mean 239'240Pu concentrations at Great Western Reservoir were 0.140 pCi/g lower in 1992, and median concentrations were 0.040 pCi/g lower. One possible explanation for the difference in concentrations in lake-bottom-sediment grab samples is that new sediments with relatively low 239'240pu concentrations may have buried older sediments containing higher concentrations of 239'240Pu; the grab-sampling technique collects only the top 2 to 4 inches of sediment from the lake bottom. In lake-bottom-sediment cores, trends in 239'240Pu concentrations with depth in 1992 were Abstract similar to trends identified in the 1983-84 study. Maximum 239'240pu concentrations occurred at depths ranging from 13 to 31 inches below the sediment-water interface at most sites. There was a small, but statistically significant (p<0.05) difference in 239'240pu concentrations in co-located lake-bottom-sediment cores collected in 1983-84 and in 1992. Measured concentrations tended to be higher in 1983-84 than in 1992. The median difference between data sets was 0.050 pCi/g, and differences tended to increase with concentration; in samples with concentrations above 1.5 pCi/L, concentrations were 10 to 30 percent higher in 1983 84 than in 1992. The differences in concentrations could be attributable to spatial variations in sediment and 239'240pu deposition. INTRODUCTION Standiey Lake, Great Western Reservoir, and Mower Reservoir are man-made water bodies used for domestic water supply and irrigation in northeastern Jefferson County, Colorado (fig. 1). These reservoirs (hereinafter referred to as lakes) are located 1.5 to 3.3 mi east of the Rocky Flats Environmental Technology Site (RFETS, formerly known as the Rocky Flats Plant), which is about 16 mi northwest of Denver, Colorado. The RFETS, which is owned by the U.S. Department of Energy (DOE) and operated by contractors, was built in 1951 and has been used for plutonium ...

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