Abigail A. Tomasek | Geology Reports

USGS2015

Assessment of aquifer properties, evapotranspiration, and the effects of ditching in the Stoney Brook watershed, Fond du Lac Reservation, Minnesota, 2006-9

The U.S. Geological Survey, in cooperation with the Fond du Lac Band of Lake Superior Chippewa, assessed hydraulic properties of geologic material, recharge, and evapotranspiration, and the effects of ditching on the groundwater resources in the Stoney Brook watershed in the Fond du Lac Reservation. Geologic, groundwater, and surface-water data were collected during 2006–9 to estimate hydrologic properties in the watershed. Streamflow and groundwater levels in the shallow glacial deposits in the Stoney Brook watershed were analyzed to estimate groundwater-flow directions, groundwater recharge, and evapotranspiration within the watershed and to assess the effect of ditches on surrounding groundwater resources. Groundwater, streamflow, and precipitation data collected during the study (2006–9) can be used to update the U.S. Department of Agriculture’s Natural Resource Conservation Service and Fond du Lac Resource Management Division surface-water models, which are used to evaluate the effect of proposed adjustments to the ditching system on streamflow on wild rice production and aquatic habitats. Specific yields calculated from the well water levels ranged from 0.11 to 0.40, and hydraulic conductivities determined from water levels measured during well slug tests ranged from 1 to 7 feet per day. The values for specific yields were similar to values obtained in other studies done in glacial materials of similar composition in Minnesota. The higher hydraulic conductivity estimate (7 feet per day) was similar to lower hydraulic conductivities estimated in another hydrologic study conducted in Carlton County, Minnesota. The installation of drainage ditches in the Stoney Brook watershed has reduced water levels in lakes connected to the ditch system, and has locally reduced groundwater levels in shallow groundwater adjacent to the ditches and lakes. Differences in near-ditch groundwater hydrographs relative to far-ditch groundwater hydrographs indicate that the effect of the ditches on groundwater is only localized to near-ditch areas. These hydrograph differences resulted in large differences between recharge estimated at wells near and far from ditches. In this study, recharge estimated at wells within 50 feet of a ditch was influenced by ditch-water levels. Annual groundwater recharge estimates from water levels and streamflows during 2006–9 ranged from 0.36 to 34.8 inches, and varied with climate, geology, and well location relative to ditches. The higher recharge estimates were determined from analysis of groundwater levels in wells near the ditches because the shallow groundwater in these wells received both infiltration from ditches and areal groundwater recharge from precipitation. The water-table fluctuation method using a manual groundwater recession approach for wells far from ditches provided the best estimates of areal groundwater recharge to the shallow glacial aquifer because water levels in these wells were not affected by water infiltrating from ditches (bank storage). For wells more than 400 feet from ditches, mean annual areal groundwater recharge estimates using the manual groundwater recession approach for wells screened mostly in outwash sands during 2007, 2008, and 2009 ranged from 4.47 to 18.6 inches (wells 5, 7, 13, 14 and 15), and ranged from 0.43 to 2.85 inches for wells screened mostly in clayey sand or sandy clay (wells 9 and 16). Recharge estimates at wells far from ditches were similar to basinwide recharge estimates from streamflow. Daily fluctuations in water levels in two wells indicated that the evapotranspiration extinction depth in the Stoney Brook watershed is approximately 4.6 to 6 feet below the land surface. A polynomial regression fit of the daily evapotranspiration rates during 2006–9 for well 1 produced a total evapotranspiration estimate of 16.1 inches from June 26 to October 6 for every year. Evapotranspiration estimated from daily water-level fluctuations in wells near ditches is relatively high. The ditch-water surface allowed for relatively high evaporation compared to the land surface, which, with a good hydraulic connection to surrounding groundwater, resulted in relatively high fluctuations in daily groundwater levels near ditches, resulting in high evapotranspiration estimates.

Minnesota↗

USGS2012

Wastewater indicator compounds in wastewater effluent, surface water, and bed sediment in the St. Croix National Scenic Riverway and implications for water resources and aquatic biota, Minnesota and Wisconsin, 2007-08

The U.S. Geological Survey and the National Park Service cooperated on a study to determine the occurrence of wastewater indicator compounds including nutrients; organic wastewater compounds (OWCs), such as compounds used in plastic components, surfactant metabolites, antimicrobials, fragrances, and fire retardants; and pharmaceuticals in the St. Croix National Scenic Riverway in Minnesota and Wisconsin. Samples of treated wastewater effluent from two wastewater-treatment plants (WWTPs), located in St. Croix Falls, Wisc. (SCF-WWTP) and Taylors Falls, Minn. (TF-WWTP), were collected from 2007 to 2008. During this time, surface-water and bed-sediment samples from the St. Croix River below Sunrise River near Sunrise, Minn., upstream from the two WWTPs (Sunrise site), and from the St. Croix River above Rock Island near Franconia, Minn., downstream from the WWTPs (Franconia site), also were collected. The Franconia site was selected because of the two large WWTP discharge points and the presence of mussel beds in this area of the St. Croix River. A variety of OWCs and pharmaceuticals were detected in wastewater effluent from both WWTPs. Compounds detected varied between the two WWTPs and varied over time from samples collected at each site. The concentration and numbers of OWCs detected were greater in the wastewater effluent samples from SCF-WWTP (38 OWCs and 7 pharmaceuticals detected) than from TF-WWTP (20 OWCs and 3 pharmaceuticals detected). Four endocrine active compounds, compounds known to affect the endocrine systems of fish-4-nonylphenol, 4-nonylphenol diethoxylate, acetyl hexamethyl tetrahydronaphthalene, and hexahydrohexamethyl cyclopentabenzopyran-also were detected in effluent samples from both WWTPs. Concentrations of phosphate flame retardants were greater in effluent from SCF-WWTP than from TF-WWTP with the concentration of tris(2-butoxyethyl) phosphate greater than 200 micrograms per liter. Seven OWCs, including one endocrine active compound, and two pharmaceuticals were detected in surface-water samples from the Sunrise site. Twelve OWCs and three pharmaceuticals were detected in surface-water samples from the Franconia site. Eighteen OWCs were detected in bed-sediment samples from the Sunrise site, whereas 21 OWCs were detected in bed-sediment samples from the Franconia site. Eight pharmaceuticals were detected in bed-sediment samples from both sites. The results of this study indicate that aquatic biota in the St. Croix River are exposed to a wide variety of organic contaminants that originate from diverse sources including WWTP effluent. The data on wastewater indicator compounds indicate that exposures are temporally and spatially variable and that OWCs may accumulate in bed sediment. These results also indicate that OWCs in water and bed sediment increase downstream from discharges of wastewater effluent to the St. Croix River; however, the presence of OWCs in surface water and bed sediment at the Sunrise site indicates that potential sources of compounds, such as WWTPs or other sources, are upstream from the Taylors Falls-St. Croix Falls area.

Scientific Investigations Report↗