A SIMPLE, INEXPENSIVE METHOD FOR MEASURING AQUIFER SEDIMENT CHARACTERISTICS IN THE LAB OR CLASSROOM

A simple apparatus consisting of a plastic bottle with pull top, sediment (medium to coarse) and some sort of support allows students of any age to learn about aquifer characteristics such as porosity, permeability, specific yield and specific retention. More sophisticated apparatus is available commercially or can be constructed in the lab; the apparatus described here has the advantage of being easy to construct with materials that are inexpensive or free. This apparatus has been used successfully with students from kindergarten through college, as well as with teachers; the level of detail and sophistication is easily varied to accommodate different abilities. The apparatus can also be re-used many times.

To assemble the apparatus, take a pull-top plastic bottle (e.g. water or sports drink) and cut off the bottom evenly. Using clear packing tape, firmly tape the bottle upside down to a support (a ring stand works well, and can be placed on a table for ease of use, but lacking that a table leg or chair leg is quite serviceable). The general idea is that the bottle will be filled to the very brim (the cut edge) with dry sediment (coarse sand or fine gravel work particularly well). With the pull top closed, measured volumes of water will be added until the sediment is completely saturated. The pull top will then be opened, and water will drain out into a measuring vessel. Students can determine the volume of the sediment, the volume of water added to saturate, and the volume of water that drains out. From these data, they can calculate the porosity, the specific yield and the specific retention of the sediment. (Young students can make simple qualitative observations that nevertheless teach a lot about aquifers and water resources.) Fine sediment takes a very long time to saturate and to drain, but this is also instructive. Permeability can be studied by observing how the water percolates through the sediment to the saturation point. Students can also incorporate sediment size analysis to broaden the study.