You are enjoying some “inside” time in the office of the consulting firm that yo

Question

You are enjoying some “inside” time in the office of the consulting firm that you work for, when your boss comes to you frantically looking for answers. A client is in her office and wants to know why the water from his well (that you installed) has so much dissolved sodium (Na) and very little calcium (Ca) in it. It is known that his property (where the well is located) has a large deposit of gypsum just beneath the soil layer. Consequently, he developed his system to work with calcium saturated water and the sodium is causing problems with his manufacturing process. Your boss asks you to carefully review the well log. She then wants you to call her office immediately and explain what it indicates about the subsurface conditions that might be relevant to the problem. The client is anxiously waiting for answer. You find the log, but remember that it took two days to install the well and while you took good notes on the first day, you blew off the second day to attend a Britney Spears concert. You immediately contact the well driller, with whom you have worked many times, and who you asked to cover for you that second day. He tells you that he did in fact record a log, but was positive that he gave it to you some time ago. You are pretty sure that you didn’t receive it, but not so sure as to disagree with him. The only information he has is that the well was screened at the very bottom of the aquifer in a thin gravel layer that he found, about 95m to 100m below ground surface (bgs). You know that the ground water flow is only downward as the aquifer is only recharged from precipitation, and there is no flow out of the aquifer. Your recorded log from the first day, down to 80m bgs, indicates gypsum and sandstone deposits, but nothing else. Your boss and the client are waiting for your answer on the subsurface composition of the aquifer. You decide that you could not live with the fact that people would find out that you are a closet Britney Spears fan, and are sure that if your boss found out that you blew off work you would most likely be fired. So, you have to give her an educated guess as to what kind of material you expected to see in the “unrecorded” boring log of 80m bgs to 95m bgs. What was you educated guess, and why did you decide on this?

Explanation / Answer

My Guess would be:

        Presence of a sandy shale layer below 80 mts bgs which grades coarsens down gradually to coarser sands at 95 mts bgs.

        This is because presence of shaly material indicates the richness of the fromation in Na. Although Gypsum is rich in Ca, it helps in exchanging displaceble sodium from cation exchange site in soils or rocks high in Na. As we know that the recharge of the aquifer is from the top to the bottom, gypsum particles coming in contact with the shale particles replaces Na and the ground water gets richer with Na. This is the only reason the client was getting water rich in Na although she was expecting water to be rich in Ca.

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