A one-sentence question can require a one-page answer. I'm not sure how the editor will handle her word limit, but she did invite this, so let's see what we can do.
First, we need to clarify Mike Ploughe's role in the tritium letter. Mike supervised the certified water technicians who took the water samples, he maintained the chain of custody and delivered the samples to a certified testing laboratory. When they became available, Mike shared the results.
In my opinion, this work was both timely and technically sound. I further thought that it was information the public ought to have as they ponder the current debate. But Mike seldom blows his own horn, so I wrote the letter. Mike had nothing to do with it. If there are errors, they are mine and mine alone.
In response to Tom Garrett's recent letter to the editor, let's discuss some of the topics he introduced and then try to tie them together.
What is a Water Table?
The words "water table" typically conjure visions of a gravel-filled basin with water forming an underground lake. Wells are envisioned to be straws sucking from different depths within this lake. If my straw sucks water, the lake level goes down and if I suck enough water, somebody else's straw ends up sucking air.
Except, perhaps, for sundry small pockets, there is no such water table in our area. Groundwater originates as rain in the high country and that portion which soaks into the ground flows to "the Valley" via cracks. Some of these cracks are horizontal (in which case they might seem to be a "water table"). Others are vertical or sloping in one direction or other. If the cracks are steep, it is entirely possible to drill a high-producing well in one spot, but move a few feet and get a dry hole. For example, RH-1 and RH-2 are, in effect, the first and second Tower Wells. One is good, the other is not worth developing.
How might tritium move?
The Tower Well is tapping cracks, cracks full of flowing water. Because of the resulting good mixing, one would expect homogeneity. But even if you opt for a classic, static water table mode, there is still diffusion. Chlorine goes from one corner of a swimming pool to "all-over" in half an hour or so. Tritiated water can diffuse a long way in 100 years. So, if the Tower Well is significantly connected to the shallow Star Valley wells in the way Garrett suggests, how come the tritium concentrations differ by an order of magnitude? Which, of course, is the question raised by my previous letter.
Safe Yield and the Big Picture
I contend that the terms "safe yield," "recharge" and "sustainable yield" all have the same definition. That definition is: An amount of water that comes into a defined volume of earth over a given period of time. Liquid water can only arrive via the percolation of precipitation and the inflow of groundwater from elsewhere, and, it can only leave via wells and the outflow of groundwater - in this case, to Phoenix.
All three terms refer to the sum of the percolated precipitation and the inflowing groundwater. This is the resource that ideally is available for use, without tapping whatever underground storage there may or may not be.
A good first step in preventing/resolving controversy is to agree on the meaning of the words. If there is a different definition and/or a different way of calculating it, let's open the discussion.
Is there enough water?
The Mayor's Water Task Force put pencil to paper and came up with the following: Payson recharge = ~1,800 Acre-ft.;Star Valley recharge = ~4,000 A-ft./yr.; Available Blue Ridge surface water = ~3,000 A-ft./yr. The local area's total annual water availability is therefore about 8,800 A-ft./yr.
At buildout, Payson will require about 3,600 A-ft./yr. and if/when Star Valley builds out to the same population density, it will require about 1,000 A-ft./yr. This the area's total water need at buildout will be about 4,600 A-ft.yr.
On this basis, I believe that there is plenty of water to meet all of the area's future needs. I further believe this conclusion to be robust. By robust, I mean that while you may argue with some of the above numbers, there is no reasonable way they can be wrong enough to alter the conclusion.
What does the Tower Well look like?
The drilling log indicates dry, hard granite for the first 170 feet. At 170 feet, the driller encountered wet rock. The driller continued through wet rock to 294 feet, at which point the well was yielding less than 10 gpm.
To provide some perspective, in Star Valley proper, the wells were essentially all less than 200 feet deep - some have water levels less than 10 feet below grade. Thus, even at first brush, the Tower Well appears to be a different kind of animal, but let's go on.
There was no additional water until 335 feet, where a second fracture zone contributed an additional 20 gpm. The granite continued down to 435 feet, with no additional water flow. Between 435 feet and 439 feet is a layer of basalt. Basalt is often full of holes and is sometimes a good water conduit, but not this time. Below the basalt, the driller continued in granite to 492 feet, where significant water was finally found: 150 gpm. At 537 feet, the well yielded more than 300 gpm. Drilling continued to 560 feet, at which point the large amount of water prevented further drilling. Subsequent testing by a registered hydrologist, not associated with the Town of Payson, demonstrated a pumping rate of 525 gpm, 24 hours a day for seven days. During the test, three other wells in the area were monitored and no problems were identified.
Now let's take an even closer look at the Tower Well. Where does its 525 gpm come from?
First, we need to ask some questions about how the well was constructed. Once the hole was drilled, it was cased, that is, sleeved with a pipe to keep it from caving in. A pump was lowered inside this casing, but the casing is perforated along its entire length. In other words, when the pump is turned on, it draws water from each of the "water horizons" discussed above. Using simple ratios, a good first order guess might be that about 16 gpm comes from the 294 foot fracture zone, 47 gpm comes from the 335 foot zone and 462 gpm comes from below 500 feet.
If we adjust for differences in well head elevations, it seems possible that 16 + 47, or 63 gpm, of the Tower Well's output could be coming from strata also being used by Star Valley shallow wells. So, might one expect to see an effect when the Tower Well is turned on? Possibly. This might be what the Star Valley newspaper refers to in their published level water graphs. Is 63 gpm enough to dry anyone up? Not likely.
So, what would happen if we simply blocked the upper two horizons, so that the Tower Well took only water from below 500 feet? Good question.
Interestingly, some insight should be gained from a piece of property in the middle of Star Valley, which has two wells. Well "A" is a typical local well, 90 feet deep, drilled in the 1980s. Well "B," drilled in 2004, is located 58 feet away on the same lot and it is 565 feet deep, deeper than the Tower Well. Well "B" was tested by an independent registered hydrologist at 200 gpm, 24 hours a day, for seven days. If your proposal of "fractured rock down to and below the depth of the Tower Well" is accurate, one would have expected the cone of depression to dry up the shallow well, when the deep well was pumped for that long, but that didn't happen. At the end of a week's steady pumping, the static water level in Well "B" had dropped 136 feet; Well "A" dropped only 12 feet! Similarly, with all the alleged free communication through the fractured rock (remember it's only 58 feet away on the very same lot) one would expect the water chemistry in the shallow well to be the same as in the deep well, but it isn't!
To be useful, a theory has to fit all the data and the fractured rock theory doesn't. These well logs are a matter of public record, available to anyone interested enough to dig them out.
But, there is more. There is another deep well in Star Valley drilled in early 2005 to a depth of 610 feet, again deeper than the Tower Well. Again, it was tested by an independent registered hydrologist, using the standard 24/7 pumping procedure at 250 gpm with monitoring in several nearby wells. There was essentially no impact on the shallow wells being monitored, but there was an interaction with the 565 foot deep well discussed above.
Having said all that, let's have a go at the "clarification" Garrett requested in his letter.
- Yes, I am saying that, based on the drilling logs, the Tower Well is drawing most of its water from a different source than other wells in Star Valley (Chris Benjamin's deep well and two other deep wells being possible exceptions).
- Yes, I am saying that the well log shows more than 150 feet of "dry rock" between the relatively minor upper water flows and the Tower Well's major production zone.
- With respect to mixing, I cannot accept Garrett's vision of the local groundwater being a quiescent, stagnant, underground lake, with no temperature, density or flow gradients to promote mixing. The Star Valley safe yield study identified a groundwater flow of at least 4,000 acre-feet per year going through the study area, through a bunch of little cracks. The resulting Reynolds numbers and the associated mixing coefficients must be very large. In other words, I am saying that the local groundwater is a dynamically flowing system, not at all like an underground lake. If sources are appreciably connected, they are mixing and one would expect their chemistry to be the same within a relatively narrow range. But they are not.
- From all this, I conclude that this area has no water availability problem and probably no water extraction problems. Similarly, the Water Task Force has identified no engineering or legal problems. The problems that exist are not water problems. It is my opinion that the boogeyman is an emperor with no clothes.
- There are, however, a number of ways to get the needed water. Associated with these options are some very significant strategy considerations and very large cost and financing issues. This is where all the concern should be. These are the things that will kick us and our kids and grandkids in that area of the anatomy most closely associated with their pocketbooks. To this end, the Water Task Force developed a spreadsheet, which can be used by both the public and the decision makers to understand all the variables and their relationships. Copies are available in the Payson Public Library and online for anyone interested in taking the time necessary to understand the issues.
Tom, there is no need to apologize for taking pot shots and nitpicking. You said it well: "a clear understanding of this issue is vital to its resolutions."