Name______
Groundwater Transport
Simulation Apparatus for the Laboratory
The groundwater simulation apparatus is a terrarium with input ports at the up-slope end to simulate recharge, and outflow ports on the down-slope end to simulate discharge (Fig. 1). The terrarium is filled with a layer of fine-gravel (aquifer) confined by two clay layers (aquitards) to simulate stratigraphy. There is an injection well at the top of the simulator and a field of twelve monitoring wells in the down-flow direction. Wells are plastic tubes with screened ports and placed at regular spacings and depths in the aquifer layer. Water based dye is poured into the injection well so that it can permeate the strata and move down the gradient towards the monitoring wells.
The apparatus is meant to simulate a real life hazardous waste spill through an injection well. The area of the terrarium would equate to several tens of acres. The affected area would be the shallow aquifer and the process of tracking the spill would take several weeks to several years. It is important to keep the real-life representation in mind during the experiment.
Fig. 1) Top view of the simulation apparatus showing the location of the injection well, sampling wells, and stream.
Laboratory Procedure
1.)Your instructor will dump a slug of dye into the injection well after water flow in the tank has reached equilibrium. The stop watch will be started at the same time. When the time is called (~ minutes), students will withdraw water samples for each of the monitoring wells using a transfer pipette. The sample will than be transferred to a vial. The concentration of the dye is then estimated using a color tone calibration chart by visually matching the color. Be sure to record the time, well, and concentration of dye for each sample taken. This process is repeated at regular intervals until all of the dye has passed through the well field. The data will be recorded on the board, and each student needs to record the data in the attached table.
2.)The recorded color data can be plotted as a series of contour diagrams for each time step. To make the contour plots, you need three variables: “X” and “Y” for the position and a third value for the quantity to be contoured. In topographic maps, the third variable is elevation. In this lab, the third variable is the color “concentration” at each well. Plot a contour map for each of the sampling times (Conc. 1, Conc. 2,etc.) by hand in the boxes on the attached page. Your instructor will tell you which time intervals to plot. See Fig. 2.
3.)Answer the questions below.
a.) Calculate the velocity of he groundwater flow. To do this, measure how far the slug has moved from one sampling time to the next sampling time as it passes through the well field. Pick features of the field that are identifiable (same concentration) from one contour plot to the next. Some estimating is involved because a feature of the contour map may only be visible on one or two plots and then other features will have to be used. Velocity (V) = distance/time.
Concentration _____, at well (a) _____, at time (a) _____ sec
Same concentration, at well (b) _____, at time (a) _____ sec
Distance between wells (a) and (b)______cm / time between (a) and (b)______sec =
V (velocity) ______cm/sec
b.) Calculate the slope of the aquifer. First measure the top of the aquifer unit at both the up and down slope ends, as well as the length of the aquifer, and calculate the slope of the tank (slope = Δh/l).
Δh(change in height) _____cm = (height of aquifer up slope)_____cm – (height down slope)_____cm
l = length of the aquifer ______cm
Slope ______= Δh(change in height)______cm/ l(length) ______cm
c.) Calculate the hydraulic conductivity (K), using Darcy’s law;
K = Velocity /Slope
K(hydraulic conductivity) ______cm/sec = V (velocity) ______cm/sec / Slope ______
d.) What happens to the water in the stream, shortly after the slug is poured into the injection well? Why do you think this happens?
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