Geology topics

Timothy A. Brown

Publications and source records attributed to Timothy A. Brown.

3 recordsLinked to original sources

USGS2000

Altitude, depth, and thickness of the Galena-Platteville Bedrock Unit in the subcrop area of Illinois and Wisconsin

The Galena-Platteville bedrock unit is a carbonate deposit of Ordovician age, composed of the Galena and Platteville Groups in Illinois and the Sinnippee Group in Wisconsin. It is the uppermost bedrock unit (subcrop) in most of northern Illinois and southern and eastern Wisconsin. The subcrop area is shaded in figure 1 of sheet 1 (Batten and others, 1997). The unit is predominately dolomite, with limestone in some areas, and has a weathered surface. Across the subcrop area, the hydrologic characteristics of the bedrock unit vary substantially. The bedrock unit may be either a confining unit or an aquifer. In areas where the Galena-Platteville bedrock unit is an aquifer, the unit is a dependable source of water for many private wells and some municipal-water-supply systems. Ground water in the Galena-Platteville bedrock aquifer is susceptible to contamination because the bedrock unit is near land surface in much of the study area, and the fractures in the unit allow rapid movement of water providing limited capacity to attenuate contaminants. The subcrop (study) area covers approximately 7,850 square miles in northern Illinois and Wisconsin. In the study area, volatile organic compounds and other contaminants have been detected in the aquifer at various sites (Mills, 1993; Kay and others, 1994). Many sources of contaminants, including landfills and industrial facilities, are known or suspected. In order to determine the possible effects of contamination on the ground-water supply, an understanding of the regional hydrogeologic framework of the Galena-Platteville bedrock unit is needed. Published and unpublished map and point data describing the geologic properties of the Galena-Platteville bedrock unit are available from many sources. The U.S. Geological Survey (USGS), in cooperation with the U.S. Environmental Protection Agency (USEPA), has selected and compiled a large portion of the available data to create computer data bases and maps. The objective of this effort is to compile and publish these data in a series of reports (U.S. Geological Survey Water-Resources Investigations Reports (WRIR) 974054-A, WRIR 97-4054-B, WRIR 97-4054-C). This is the third in that series of reports. The report describes the altitude, thickness, and depth from land surface of the subcrop area of the Galena-Platteville bedrock unit. The report series will enable investigators involved in site-specific studies within the subcrop area to understand the regional geologic framework of the unit and to find additional reference sources. This report consists of four sheets that show the altitude (sheet 1), depth from land surface (sheet 2), total thickness (sheet 3), and location of altitude data (sheet 4) of the lithologic units that constitute the Galena-Platteville bedrock unit within the subcrop area. The sheets also show major known geologic features within the Galena-Platteville study area in Illinois and Wisconsin. A geographic information system (GIS) was used to generate data layers (coverages) from point data and from published and unpublished contour maps at various scales and detail. Standard GIS procedures were used to change the coverages into the maps shown on the sheets presented in this report. A list of references for the data used to prepare the maps is provided.

Illinois, Wisconsin↗

USGS1999

Areal studies aid protection of ground-water quality in Illinois, Indiana, and Wisconsin

In 1991, the U.S. Geological Survey, in cooperation with the U.S. Environmental Protection Agency, initiated studies designed to characterize the ground-water quality and hydrogeology in northern Illinois, and southern and eastern Wisconsin (with a focus on the north-central Illinois cities of Belvidere and Rockford, and the Calumet region of northeastern Illinois and northwestern Indiana). These areas are considered especially susceptible to ground-water contamination because of the high density of industrial and waste-disposal sites and the shallow depth to the unconsolidated sand and gravel aquifers and the fractured, carbonate bedrock aquifers that underlie the areas. The data and conceptual models of ground-water flow and contaminant distribution and movement developed as part of the studies have allowed Federal, State, and local agencies to better manage, protect, and restore the water supplies of the areas. Water-quality, hydrologic, geologic, and geophysical data collected as part of these areal studies indicate that industrial contaminants are present locally in the aquifers underlying the areas. Most of the contaminants, particularly those at concentrations that exceeded regulatory water-quality levels, were detected in the sand and gravel aquifers near industrial or waste-disposal sites. In water from water-supply wells, the contaminants that were present generally were at concentrations below regulatory levels. The organic compounds detected most frequently at concentrations near or above regulatory levels varied by area. Trichloroethene, tetrachloroethene, and 1,1,1-trichloroethane (volatile chlorinated compounds) were most prevalent in north-central Illinois; benzene (a petroleum-related compound) was most prevalent in the Calumet region. Differences in the type of organic compounds that were detected in each area likely reflect differences in the types of industrial sites that predominate in the areas. Nickel and aluminum were the trace metals detected most frequently at concentrations above regulatory levels in both areas. Contaminants in the shallow sand and gravel aquifers and carbonate aquifers appear to have moved with ground water discharging to local lakes, streams, and wetlands. Ground-water flow and possibly contaminant movement is concentrated in the weathered surface zones and in deeper fractures of the carbonate aquifers underlying both areas.

Illinois, Indiana, Wisconsin↗

USGS1996

Geohydrology, water levels and directions of flow, and occurrence of light-nonaqueous-phase liquids on ground water in northwestern Indiana and the Lake Calumet area of northeastern Illinois

A study was performed by the U.S. Geological Survey, in cooperation with the U.S. Environmental Protection Agency, to describe the geohydrology and distribution of light-nonaqueousphase liquids in an industrialized area of northwestern Indiana and northeastern Illinois. The geologic units of concern underlying this area are the carbonates of the Niagaran Series, the Detroit River and Traverse Formations; the Antrim Shale; and sands, silts, and clays of Quaternary age. The hydrologic units of concern are surface water, the Calumet aquifer, the confining unit, and the Silurian-Devonian aquifer. Water levels collected in June 1992 indicate that the water-table configuration generally is a subdued reflection of topography. Recharge from landfill leachate and ponded water, discharge to sewers, and pumping also affect the water-table configuration. A depression in the potentiometric surface of the Silurian-Devonian aquifer results from pumping. Light-nonaqueous-phase liquids were detected near petroleum handling, industrial and waste-disposal facilities. Horizontal ground-water velocity at the water table in the confining unit ranged from 4.4x10 -4 to 1.0x10 -3 feet per day. Horizontal ground-water velocity in the Calumet and Silurian-Devonian aquifers ranged from 1.0x10 -2 to 3.4x10 -1 and from 1.4x10 -2 to 2.9x10 -2 feet per day, respectively. Vertical hydraulic gradients indicate generally downward flow from the Calumet aquifer into the confining unit, then into the Silurian-Devonian aquifer. Calculated vertical groundwater velocity through the weathered and unweathered parts of the confining unit are 3.8x10 -2 and 1.5x10 -3 feet per day, respectively.

Illinois, Indiana↗