Introduction: The surficial deposits in our area – the Appalachian Upland Plateau – are comprised of sediments formed during the advance and retreat of the Wisconsin Ice sheet. The sequence of glacial and post-glacial sediments form a record of the processes which were active in a given area. The types of sediment and their lateral and vertical relationships are critical for a variety of reasons, including the quality and extent of aquifers for groundwater. In this week’s lab we will explore the surficial and shallow subsurface geology in the Madison, NY area. The stratigraphy and history of the late glacial sediments in this area is well-constrained by well-log data, and this will form a source of information for our study The goal of the lab is to produce maps and cross-sections that illustrate the subsurface geometry of the various deposits. The use of stratigraphic data of this sort is a first-order concern for studies of aquifers, land-use zoning such as landfill location, construction and resource extraction.

Maps and other data: You will need to have the following files on your Zip disc before you begin:

1. Munnsville 7.5 minute DRG (from CUERD)

2. Finger Lakes Surficial Geology coverage (as ArcView shapefile – used in lab #3)

3. Key to the Surficial Geology shapefile (as .txt file in Lab #5 folder on the network server)

4. Madison Wells Data (as Excel file in Lab #5 folder on network server)

5. Madison Basemap (.bmp file in Lab #5 folder on network server)

Examine the Regional Surficial Geology in ArcView: Open ArcView and add the Munnsville 7.5 Minute Quad as an image. Add the Finger Lakes Surficial Geology coverage as a feature. Examine the relationship between the topography and the types of surficial deposits. Locate the Madison-Bouckville outwash plain, and note its relationship to the Valley Heads Moraine ice margin to the northeast in the Oriskany Creek Valley.

1. Briefly describe the relationship between the surficial geology, topography and glacial depositional history of the area.

2. Given your understanding of the relationship between topography and surficial geology, assess the accuracy of the map unit boundaries as represented by the surficial geology shapefile.

Open and examine the Excel File containing well data: Stratigraphic information for the wells located on the base map is contained in the Excel file labeled Madison Well Data in the lab #5 folder on the network server. Copy this file to your Zip disk and open it. Note that the elevation of the ground surface is given, the depth to water table (top of the saturated zone), followed by the thickness of the glacial depositional units in the well, and the total depth to bedrock. We will discuss the significance of these units at the beginning of lab. It is useful to compare this data to the surficial geology illustrated in the Finger Lakes Surficial Geology coverage that you examined in ArcView (above).

You will need to convert the thickness and depth data to elevations in Excel. You will find it useful to make a separate spreadsheet files that contain thickness and elevation. The elevation data will allow you to define the top and bottom surfaces of the various layers, whereas the thickness data defines the thickness of each layer.

Digitize the map co-ordinates of the wells: Use Surfer to open the Madison Basemap file. Note that we will work with the arbitrary coordinate system of the map file, and that the well sites are located on the map. Remember to load the map as a basemap so that the co-ordinate system will be shown. The well locations are at the upper right corner of the label box. As you digitize each point, you will find it useful to copy the coordinates from the inset window to your Excel spreadsheet file that contain the thickness and elevation data. Alternatively, you can digitize all the points, label each one in the data entry window as you digitize, and then copy the coordinate locations to the Excel file. We will go over this procedure in class.

Prepare contour and vector map depicting the shape a flow pattern on the water table: You will need to prepare a file which contains coordinate (x,y) data and elevation of the water table surface for each of the well locations. You may wish to add the locations and elevations of the lakes as data points for the water table analysis, since the elevation of a lake is controlled by the local water table elevation. The data file will then be gridded, and the contour and vector maps prepared from the gridded data file. You should overlay these maps on the base map

Prepare a structure contour map of the bedrock surface using Surfer: A structure contour map depicts, using contour lines of elevation, the shape of a subsurface surface. To prepare a data file for Surfer, you will need to extract the coordinate (x,y) data and the elevation of the bedrock surface (z) from the Excel files above, and make an Excel file that contains only that data. The data is then gridded, and the grid file is contoured in Surfer. You map wish to use the Wireframe option to make a more interesting map display of the bedrock surface, although the contour map can be overlain on the basemap for a more effective display of the topography and subsurface geometry.

Prepare isopach maps of the till (layer 4) and lake clay (layer 2): To construct isopach maps using Surfer, you will need to make data files which contain the x,y coordinate data and the thicknesses of the layers. These files then will be gridded and contoured. The isopach maps, as contour maps can be overlain on the basemap.

Locate three or more wells which lie on an approximately SW-NE line parallel to the trend of the valley, and three or more which lie on a NW-SE line. Use the well data, and your understanding of the trends examined in the structure contour map and isopach maps (above) to construct schematic cross-sections that illustrate the vertical and lateral variation in thickness of the units. You can use Surfer as a graphics editor to construct the cross-sections, or hand-draw on graph paper.

Questions:

1. Generally describe the glacial erosional and depositional history of the area based on the analyses above.

2. The Village of Madison municipal water supply depends on withdrawal of water from the small lake located to the east of well #W7564 (note the ‘pumping station’). There is concerned that the pollution of Madison Lake by agricultural run-off and infiltration of septic tank might affect the water quality at the village source. What do you think? How is your opinion supported by the analyses above? (since the glacial till and lacustrine silty clay are important barriers to groundwater flow, you may wish to examine the geometry of these units, and their subsurface elevations relative to the directions of groundwater flow)