GeoLab 11

GEO 109L – Earth, Environment, & Society Lab Lab Exercise 11 – Groundwater Introduction Next to the oceans and ice caps, groundwater is the largest water reservoir on Earth. We rely on our groundwater resources for individual water access as well as municipal, industrial, and agricultural water supply on a large scale. Because of the constant and increasing demands, it is essential for individuals and local, state, and federal agencies to work to maintain the quantity and quality of this resource. In this week’s lab we will investigate both the nature of the materials that groundwater moves through as well as how exactly we study this part of the hydrologic cycle that we cannot readily observe (it is underground)! Materials:  Flow Test Materials  Stopwatch  Ruler  Calculator  Pencil Lab Exercise Part 1 – Flow Test In order for scientists and water engineers to understand the speed at which groundwater moves through an aquifer, which ultimately affects the rate at which water can be pumped out and how fast potential contaminates move from a source to other areas of the aquifer, they first must perform tests on well bore samples from the aquifer. These tests, referred to as flow tests, send a certain amount of water through a sample under a set pressure in order to observe how much water can be stored in the material and how fast it moves entirely through the sample. We will recreate a portion of this type of test today in lab. We are going to simplify the test and use open funnels under the force of gravity to drive our flow test. Follow the procedure (green box) and then answer the questions following. Your flow test set up is already set up in the center of your table. You have three sediment (unconsolidated or loose) types. Each funnel holds approximately 100 cm 3 of sediment. You also have a 250 ml beaker with 100 ml of water in it and an empty 100 ml beaker or 250ml beaker with graduated cylinder.  Place the empty 100 ml beaker (or 250 ml beaker) under one of your funnels.  You will complete three flow tests, one at a time. DO NOT START THE FLOW TEST UNTIL YOUR TIMER IS READY .  You will be recording multiple time points during the test. The time it takes for the first water to leave the funnel AND how long it takes until water stops leaving the funnel (all/most of the water has moved through the sample).  Once the timer is ready, start timing and pour the 100 ml of water into the funnel (if the water nears the lip of your funnel, wait until the water level drops to finish adding all the water).  Record your times in the table following . IF YOUR WATER TAKES LONGER THAN 2 MINUTES to move through your sample. Stop your test at 2 minutes and record how much water moved through during that time. Lab 11 | 1 NAME: ____________________ Table # ___

1) RECORD YOUR FLOW TEST RESULTS BELOW 2) Rank your three sediments below in order of highest (a) to lowest (c) permeability. a) b) c) 3) In the table below, write next to each K value (hydraulic conductivity) which sediment type you think best fits. 4) Below is a cross-section (side view) of the Great Miami Buried Valley Aquifer (GMBVA). Dayton and most of Southwest Ohio relies on the GMBVA for the majority of our water needs. This aquifer is composed of a pre- existing (pre-Ice Age) bedrock valley that was filled with loose sediment as the Ice Age glaciers advanced and retreated over 500,000 years. The sediments include Sand, Gravel, and Clay. Determine which of the sediments of the GMBVA are an AQUIFER layer or a CONFINING layer. Sand and Gravel: ______________ Clay: ______________ 2 Sediment Type Time Water First Leaves Funnel (secs) Time Last Water Leaves Funnel (secs) Amount of Water After 2 minutes (ml) Fine Sand Gravel Clay Sediment Type K value gravel 1,000 ft/day Fine sand 100 ft/day clay 1 ft/day

14) How long would it take for contamination to reach the wetlands from site D? Show your work. 6 ¼ days 15) If contamination was moving from either site C or D towards the well field or the wetlands, what would be some possible options to prevent the contamination from reaching these valuable sites? (Assuming that the contamination risk was known in advance!) To prevent the contamination from reaching that I would close off the ground water systems until the issue has been handled and stop all water usage as soon as it made known. For the remaining questions you will need to use the large laminated groundwater table contour map of the area around Wright-Patterson Air Force Base, which is located over a portion of the Great Miami Buried Valley Aquifer (GMBVA). The large red box on your groundwater map is the border of the Fairborn, OH USGS Topographic Quadrangle Map. This map has also been provided for reference. 16) Your map has been marked with red stars at specific locations (with red labels). As a group, use the dry erase markers and draw groundwater flow lines from each of the red star locations – draw the direction of flow all of the way to the edge of the red box. Once you have finished drawing your groundwater flow lines for this portion of the GMBVA, call you instructor over to your table. Your instructor will INITIAL your lab exercise to confirm completion of this part of the lab. 17) Describe the overall flow of groundwater on the Wright-Patt map. Make sure to describe the general areas the groundwater is flowing from (recharge areas) and where it is general flowing to (discharge areas). If possible, use the Fairborn, OH map to assist you in providing specific names for areas and features on the map. 4

Two specific locations have been marked on the Wright-Patt map for you. Location A corresponds to the current active portion (near the runways) of the Air Force base. Location B corresponds to the lorcation of the City of Dayton’s Rohrer’s Island Well Field. This well field is one of the sources for our municipal water supply. 18) What is the hydraulic gradient between locations A and B? Show your work. 19) Given a K value (hydraulic conductivity) of 500 ft/day and porosity of 25%, what is the groundwater velocity between A and B? Show your work. 20) If a contaminant entered the groundwater system at location A, how long would it take to reach the Rohrer’s Island Well Field (Location B)? (Note: We have chosen this example because there are significant contamination sites at the Wright-Patt Air Force Base, which are actively studied and monitored. Lab 11 | 5