Watch Desert Wars September 25, 2006 at 8 pm on KUED Channel 7
Alan H. Welch: To understand the role of the USGS within this process, it's perhaps important to understand the role of the USGS in general. We're an independent fact-finding and reporting agency. We don't have policy or management responsibilities and as such we will evaluate impacts of human or natural phenomenon, but we don't then make recommendations as to what a particular action should or is recommended to be. So within this process we're conducting a study that was mandated by congress to look at a particular part of the country with the intent of coming up with an integrated look at the hydrology of this particular part of the country. USGS role in this process is as an independent fact-finding agency. We have no responsibility for management or policy recommendations. We provide information that other agencies can use to make decisions. Within this particular issue the survey is conducting a study of a part of Eastern Nevada and an adjacent part of Utah to understand the hydrology of that part of the country.
Interviewer: What is known about that hydrology at this point. Tell me a little bit about the aquifer itself. How was it discovered and what is the history of it?
Alan H. Welch: That part of the country has undergone hydrological studies for over a hundred years. We've understood for a long time that groundwater within this basin system travels considerable distances and we see large warm springs that are issue from recharge that occurred in mountain blocks tens to hundreds of miles removed from where the water is really discharging. This part of the world has had relatively little stress on it, by which I mean, very little pumping and so we know quite a bit about this system but that understanding is limited because the stresses on the system so far have been quite limited. The recharge occurs both in the mountain blocks as well as where the geology results in flow off of the mountain blocks into the valleys where it recharges into the sediments that lie within the basins themselves. We're conducting as part of the BARCASS Study a modeling effort to describe the distribution both in time and space of recharge, to the overall aquifer system.
Interviewer: Tell me what BARCUSS is and the potential for BARCASS?
Alan H. Welch: BARCUS, which stands for Basin and Range Carbonate Aquifer Study System, is a study that was mandated by congress to describe in a consistent fashion the hydrology of White Pine and adjacent areas in Eastern Nevada. The study is a finite three-year study. There are currently discussions to look at additional areas using the same methodology as we're using in this study as well as to take what we've learned from this study and move on to producing a calibrated groundwater model, which is something that can be used to evaluate potential impacts due to development of the resource.
Interviewer: Explain what an aquifer is and the size of this one.
Alan H. Welch: An aquifer is composed of earth materials that transmit water. Within this part of the world, we have what we think of as two different aquifer systems. They interact, but consist of sediments, which partially fill basins, which can have depths up to and exceeding five to ten thousand feet thick. Beneath those, as well as within the mountain blocks, are bedrock aquifers, which primarily consist of carbonate rocks, which were formed several hundred million years ago and are now transmitting water over large distances. The carbonate aquifer has a thickness in excess of 10,000 feet, so we see a very large aquifer system which has a bedrock underlying a variety of basin fill aquifers which are exploited both for municipal as well as agricultural use.
Interview: So what happens if an aquifer, or groundwater in this case is pumped too much and what would alleviate the fears of the ranchers here that that would not happen (from a scientific standpoint)?
Alan H. Welch: From a scientific standpoint, if you pump an aquifer, the water table will drop and that lowering of the water table will diminish the amount of evapotranspiration, which is the amount of water that is lost from plant growth as well as evaporation from open water surfaces as well as the soil. So as that pumping occurs, evapotranspiration declines in equilibrium, then we come to a system where the amount of groundwater that is pumped is equal to that which is then less from evapotranpiration over time.
Interviewer: What can be done to alleviate the rancher's fears on over-pumping?
Alan H. Welch: What we can do with groundwater flow models is predict what the response in water level as well as spring flow would be both in space and time given a particular pumping scenario, so by understanding that then people with water rights or other interests can then decide whether that is an acceptable or unacceptable impact on the environment.
Interviewer: How would the pumping of this aquifer effect the National Parks and Fish Springs National Wildlife refuge?
Alan H. Welch: The real question in terms of understanding impacts on places like the Great Basin National Park and Wildlife Refuge is the amount as where the water is pumped. There may very well be places where the impacts of pumping may be minimal or something that would occur only over a very large time scale so the place that one diverts water as well as the volume is key to understanding what the impacts are going to be.
Interviewer: How was this large carbonic aquifer discovered?
Alan H. Welch: A carbonate aquifer was really recognized as something that is transmitting water over large distances well in the past, over 50 years ago. It has been largely understood from looking at flows from springs that there have been a limited number of wells drilled for water supply and there are a fair number of wells that have been drilled for oil and gas exploration that we do use to help us understand the properties of the aquifer.
Interviewer: Tell me again what the acronym stands for.
Alan H. Welch: The BARCASS Project, which stands for Basin and Range Carbonate Aquifer System Study, is a study of the hydrology of White Pine and adjacent areas. It's a description of the hydrology of the area, but does not include an attempt to look at impacts from future development.
Interviewer: Talk about the concerns of the ranchers.
Alan H. Welch: It is well-known that if we develop and aquifer, by which I mean if we increase the pumping from the aquifer, will draw lower water levels as well as potentially dry up springs. We have many examples, both within this study area, as well as many other places in the world that this has occurred. The question is not whether there will be impacts--it's whether or not those impacts will adversely affect aquifers that are used by current water users. So we know there will be impacts. We just don't know whether those will be acceptable impacts. From a science standpoint what we can do is provide information as to what the response would be given different pumping locations and pumping volumes and provide answers as to what the timing and extent of those impacts would be, but we cannot prevent those impacts from happening. All we can do is provide a basis to make decisions from predicted impacts.
Interviewer: What happens to that groundwater table if it's pumped and is lowered even ten feet?
Alan H. Welch: When you develop and aquifer, like pumping from wells that can have several different impacts--one is on spring flow. By lowering the water table you are preventing that water from issuing from the surface so springs can and do dry up in response to development of aquifers. The second thing that can happen is that by lowering the water table, vegetation that relies on shallow groundwater no longer will have that water and there will be a change in the vegetation type as a result.
Interviewer: The ranchers are obviously worried about the groundwater pumping. Are these legitimate concerns from a scientific standpoint?
Alan H. Welch: From a science standpoint the impact on pumping on current water users, including people who are using water for agriculture, is a legitimate concern from a standpoint that it is quite possible that water tables will decline and limit their spring flow as well as requiring greater pumping depths. Whether that will occur is dependent on where pumping is taking place, the volume and length of that pumping. So it's very much dependent on the details of where and what is going to happen and what will and will not be impacted. There may very well be places where there will be minimal impact on any water users, but until we're able to scientifically study it using things like groundwater flow models, we can't make those predictions. When you pump an aquifer two things will happen—one is that you will initially have a water level at a particular depth, perhaps very near the surface. As you pump that water table will decline and vegetation that depends on that water, where it's very shallow, will no longer be able to use that water. Also if you have a water table that comes out at the surface and is expressed as a spring, that spring flow can then diminish because we're dropping the water table and then that water can no longer reach the earth's surface and discharge.