The Story of Moab's Water
Moab is known as a Colorado River town, but the key to its existence is the LaSal Mountains. With peaks over 12,000’, the LaSal Mountains contain the snowpack that recharges several aquifers that produce potable water for Moab. Hydrogeologist Tom Lachmar talks about the path water takes from the high peaks of the LaSals to the Colorado River. We also talk with Tom about the several water studies that have been conducted on Moab’s aquifers and what the results mean for the future.
Meet the Scientist: Thomas Lachmar
Dr. Tom Lachmar has over 40 years of experience in hydrogeology, both in academia and in industry for private consulting firms. His current research project evaluates the geothermal potential of the Camas Prairie in south-central Idaho. Other recent research projects include: examining water samples, geophysical logs and core from two deep geothermal exploration boreholes in the Snake River Plain, Idaho; evaluating the possible connection between the Logan River in lower Logan Canyon and groundwater in Cache Valley, Utah; and investigating metals contamination at an abandoned mine near Challis, Idaho. Previous research projects included: determining the feasibility of constructing an artificial salmon spawning channel near Hyder, Alaska; investigating the fate of salt water injected into the Navajo Sandstone in central Utah; and characterizing, modeling and monitoring the groundwater flow system in Cache Valley. Other research interests have included: investigating the hydraulic properties of faults in central Utah as they relate to CO2 sequestration; assessing the impact of groundwater flowing through mine tailings on heavy metals contamination of the North Fork of the American Fork River; conducting laboratory treatability experiments for bioremediation of TCE from Hill AFB; the identification and geochemical characterization of perched water bodies at the INL; the relationship between stream losses and water table depths at Great Sand Dunes NP; and wellhead protection in a confined to semiconfined aquifer setting in the Salt Lake Valley. He has had 19 grants and contracts funded for a total of $1,032,697, 12 as PI ($355,171) and 7 as Co-PI ($677,526). He has 27 publications, 15 as first author, 9 as second author with students as first author, and 3 with colleagues as first author. He has published 41 abstracts, 13 as first author, 20 as second author with students as first author, and 8 with colleagues or their students as first author.
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Interview Transcript - Mountain Snow to Desert Flow
Science Moab: Can you give us a brief rundown of how water fits into a landscape?
Lachmar: The vast majority of water on the earth is in the oceans. It sits out under the sun, and the water evaporates up into the atmosphere, and then winds blow it on land. Then we get precipitation and precipitation can do a number of things. What people see on the surface is the surface runoff. When it rains, the water travels on the surface, but it also soaks into the subsurface as well. The streams are flowing when it’s not raining, and that’s a result of water that was able to infiltrate into the ground and is reappearing in low places on the earth. So the vast majority of the time that streams are flowing, it’s because of water coming from the ground into the streams.
Science Moab: How does the water seep through the subsurface? Is there a specific way it moves?
Lachmar: Whatever way it can find its way down. Some of it does flow off during events, the rest seeps down into the subsurface very slowly. These materials are porous, so they will absorb water, but their permeability is actually very low, so the water will percolate down through the portion that’s not saturated until you get to the water table. And all the pore spaces, the empty parts between the soil particles or in the cracks in the rock, are full of water. Above that is mostly air and the water is trying to move down. It’s denser than air, so it displaces [the air] as it moves downward until it reaches the water table. Then it’s in the saturated zone, where the pore spaces are filled entirely with water and it moves very slowly. We’re talking centimeters per year. What we’re seeing at the surface usually was precipitated decades or centuries or maybe even millennia ago.
Science Moab: Where’s the water in Moab coming from? Is it snowmelt?
Lachmar: There’s a lot of snow in the La Sals, and that’s where it looks like the majority of the recharge is coming from. It’s snowmelt that percolates down. The majority ends up in the groundwater and then it moves to the Colorado River because that’s the lowest water level. But it would take more than 100 years, I would imagine, for groundwater to move from the La Sals to the river. The La Sals are tertiary, shallow, intrusive igneous rocks, so they themselves are not very permeable. But the older sedimentary rocks around the flanks of the La Sals, they’ve been pushed up, and then they’re exposed so that’s where the water gets in: sedimentary rocks. At a relatively high elevation, those rocks are not horizontal, and actually are dipping towards the Colorado River. So the water gets into those rocks, the sandstones, the Navajo Wingate and Kayenta sandstones are the main aquifers. Being sandstones, they’ve got good permeability and they store water and it also moves relatively quickly. And every spring when the snow melts in the La Sals, that adds some to compensate for what’s being withdrawn.
Science Moab: Can you talk a bit about the studies on Moab water you were hired to evaluate?
Lachmar: Two studies came to different conclusions. The folks that paid for them wanted to know what we should take as fact. From my perspective, one had a rosy scenario in terms of how much recharge, how much is available, etc. It was quite reasonable, but very little data was actually collected to support it. Everything obeys the fundamental laws and principles and rules in groundwater, but they didn’t actually go out and measure things to get at estimating recharge rates. The other study used a lot of water chemistry, measuring what’s in the water to estimate where the recharge is and roughly how much there is. And that study was less rosy. Moab is growing and water use is increasing. So the second report was saying we’re probably pumping as much or nearly as much water as we should right now. We probably shouldn’t be planning on a large increase in the amount of water removed from the aquifer. From my perspective, the most important message that I gave to the parties that hired me is that they need to be monitoring the water levels and the pumping rates in the wells that they have, so that they can document if those water levels start going down or the pumping rates start decreasing. They know that in advance and can do something so that it doesn’t get worse.
Science Moab: What is best practice for managing an aquifer?
Lachmar: The water is contained in the pore spaces in the rock or the consolidated loose material. So it’s completely undisturbed. Once all the water in the river has been appropriated, people start putting wells in to get groundwater which would end up in the river. You put in the first well, and you start pumping water out, the water table goes down. It’s inevitable impact. The second person puts in a well, it goes down a little bit more. There’s no best or worst practice, it’s more a matter of what you can live with, and the state engineer decides what we’re going to live with.
