Bear Mountain Vista HOA

JEFFCO MOUNTAIN WELL WATER

This paper was published in 3 of Joan Spalding's articles...

This paper was published in 3 of Joan Spalding's "Environmentally Speaking: columns in the Canyon Courier. September 29, 1999 Canyon Courier, pp. 5B-6B:

by Jim Peterson Professional Geologist © 1999

Nearly everyone who has a well in the Evergreen-Conifer area is at risk of running out of water. The few exceptions are those with wells in large alluvium or soil deposits next to permanent streams such as Bear Creek. Some of us never will run out of water, some will at an unpredictable time in the future, and some already have. You may have lived here ten years and never had a problem, but that does not necessarily mean that you won't run your well dry in five years, or next year, or even next month. Quite a few residents have learned this the hard way already, and more are sure to in the future. Hauling in water, drilling a new well, deepening an old one, or hydrofracturing are all very expensive. You should always use mountain well water cautiously and never waste it. Habits acquired from being on city water, where the supply seems limitless, can cause you a small disaster up here. Showering daily out of habit even when you aren't dirty, taking long showers just because they feel good, even little things like letting the faucet run while you are brushing your teeth, all waste water that you may someday desperately need. Washing your cars at home, hosing down the driveway to wash away the pine needles, or trying to grow a patch of lawn is downright foolish, and a violation of most well permits. Only a small number of well permits in the Evergreen-Conifer area allow any outdoor use of water, and even people who have those permits would be wise to not use more water than truly necessary, because a well permit is merely a piece of paper. Though it gives you a right to use a certain amount of water, it does NOT guarantee that the water is available in the ground. The first victim of anyone who wastes a little too much water is likely to be the one who wastes it, because their well will probably be the first to dry up.

I will now describe the general geology and ground water situation of the Evergreen-Conifer area in fairly simple terms, avoiding technical terminology as much as possible. Later, I will make an analogy that may help you understand the situation better if you have difficulty with this description.

The term "ground water" means water under the ground, not on the surface. It is the water supply that is tapped by wells. An aquifer is a geologic formation that contains enough ground water, and allows it to flow enough, to be a good source for wells. A major aquifer can be a vast (but still finite) source of water. Many of the major aquifers in the United States are sandstones, such as the Ogallalla Aquifer that underlies the Great Plains including eastern Colorado. Sandstones are commonly excellent aquifers, because they typically have high porosity and permeability. In other terms, there is typically a lot of empty space (porosity) between the grains of a sandstone, and the spaces are connected (permeability).

A clean sandstone with well-rounded grains of nearly uniform size may have a porosity of 35%. This means that, for example, if you have a 10,000-gallon pool, and you put in a block of this type of sandstone that would fill the pool, you could still gradually pour in 3,500 gallons of water, because the pore space in the sandstone would absorb it. You could then drill a hole to the bottom anywhere in the block of sandstone and pump out most of the water, because water would flow toward the pump from all directions. If you drilled two or more holes and pumped from all of them, they would interfere with each other because they all tap the same interconnected water supply. Likewise, putting water in at any point on top of the block would eventually recharge the entire block because of the interconnectedness of the pores.

Many Evergreen-Conifer area residents on wells believe, incorrectly, that their wells tap such an aquifer, with its large capacity, three-dimensional permeability, broad recharge area, and clear potential for interference from nearby wells. However, there are no sandstones in the mountainous areas of Jefferson County, nor are there any other significant aquifers (with the limited exception of scattered alluvial deposits along permanent streams). The point in describing them is merely to compare and contrast them to what we do have here.

October 6, 1999 Canyon Courier, pp. 8B-9B:

Bedrock in the Evergreen-Conifer area is mostly granite and gneiss (pronounced "nice") which are dense igneous and metamorphic crystalline rocks having only a negligible amount of pore space. These rock types make poor aquifers, because they lack porosity and permeability (the interconnectedness of pore space). The water that our wells draw from these rocks is stored in fractures, simply cracks in the rock. Most of these fractures are narrow, rarely more than a few inches wide. A note on your well log indicating a fracture two feet thick is deceptive, because the well cuts through it at a steep angle, not directly across it, so the measured thickness is not the true thickness. Fractures here may be hundreds, even thousands of feet long, and may go hundreds of feet underground, but their total volume is not large. Indeed, most of their volume is filled with fragments of rock, sand and clay.

Take the same 10,000-gallon pool and put in a solid block of granite or gneiss that would fill the pool, and it would absorb practically no water. If you pour 3,500 gallons of water on this block, no matter how slowly, it will simply flow away on the surface. If there is a narrow, near-vertical crack through the block, it will take in a little water, but not much. To tap it and pump it out, you will have to drill a hole that intersects the crack, and not too near the top. Sprinkle a little soil on the surface so you can't see the crack, and drilling becomes a hit-or-miss affair.

Regional geologic stresses caused fractures to form in roughly parallel sets in the mountains of Jefferson County, with three main sets having different directional orientations. Most of these fractures dip steeply into the ground (are nearly vertical), and the spacing between fractures varies greatly. There is some interconnection of fractures, but the spacing of intersections also varies greatly. Some of the fractures are water-bearing, but others may be plugged, or may open down the side of the mountain so they are mostly drained by gravity. Thus, some fractures contain water that may be tapped by a well, and others do not.

The spacing between fractures and the fact that most are nearly vertical in the mountainous parts of Jefferson County means that drilling a well here can be a bit of a crap-shoot. As some of you know from experience, you can drill 600 feet or more and get nothing but dust, then you can drill again 50 feet away and hit water at a few hundred feet down. Those few of us lucky enough to have a well that taps a fracture intersection may be drawing water from multiple fractures, and therefore have a relatively large supply and relatively more recharge. Most of us have tapped only one or two water-bearing fractures, and our wells may be far from intersections, limiting both supply (the volume available) and recharge.

Recharge is the water from rain or melting snow that enters the fracture and replaces what we draw from our wells. Soil thickness on top of the bedrock on the hills and mountains ranges from zero to perhaps 15 or 20 feet at the deepest points in some meadows (there is more in some wide valleys). Soil will retain some water, but not all of it is available to the fractures that supply our wells. Most of the water simply flows gradually down slope through the soil along the surface of the bedrock and does not enter the fractures. If the fracture your well taps is on a rock ridge, most of the runoff is going to be rapid and away from your well's fracture, so most of the water will not enter the fracture and recharge will be poor. If your well's fracture is in a little valley filled with soil, water will tend to run toward it and the soil may delay the flow so more can enter the fracture, and recharge may be good. However, clayey soil may clog the top of the fracture and resist penetration by the water. In any event, although a lot of snow and rain may fall, very little of it enters the fracture systems. Recharge is seasonal, of course, being essentially nonexistent in bare rock or thin soil areas in the dry months. What all this means is that recharge here is a very uncertain thing. The fractures in the mountains vary greatly in the amount of water they can hold, and recharge is also varied. These are the factors that determine whether a well is a good one or not, but there is no practical way to determine either fracture volumes or recharge rates. The flow rate given by a pump test does NOT tell you this, as explained below.

October 13, 1999 Canyon Courier, pp. 5B-6B:

If you have difficulty visualizing the situation underground, here¡¦s an analogy:
Imagine that your well-water supply is an interest-bearing bank account with special features and restrictions. Drilling a well opens the account. The good news is Mother Nature has already made an initial deposit, and will add to it annually. You pay a fee to open the account (drilling costs, pump, etc.), but needn't deposit funds before making withdrawals.

This seems great, but there are problems: you can¡¦t determine how big your account is, or the interest rate, so it¡¦s impossible to know the balance.

One restriction is a limit on how much you can withdraw in a given time period (so many dollars per day). You can determine that limit, but it won¡¦t tell you your balance or interest rate. Another restriction is a cap on the account. Even with interest, there¡¦s a maximum balance. The best possible situation is that interest exceeds withdrawals, and the account stays at the maximum amount.

Because of the cap, if your account starts with ,000 and earns 30% annual interest, it won't grow to ,000 next year if unused??{it remains at ,000. However, you could withdraw over six dollars a day and the high interest will keep the account full. Interest is paid only in certain seasons, so the balance might drop below ,000 at times, but as long as interest exceeds withdrawals every year, it will always return to ,000.

But what if your account starts at ,000, with 10% interest? If you withdraw only one dollar per day, interest will not keep up with withdrawals. You withdraw per year, but interest would be under . Your withdrawals gradually deplete the account. After many years, by withdrawing just a little more than is replenished every year, the balance eventually reaches zero, and you¡¦re broke.

Let's equate this bank account to your well: The account is the fracture your well taps. The interest is the recharge. The account balance is the total volume of available water in the fracture. The account has a cap because when the fracture is full, it can¡¦t hold any more water. The amount you can withdraw in a given time period is indicated by your pump test, in gallons per minute (GPM).

Recharge is water from natural sources that enters the ground and replaces water drawn from a well. Many people, including some so-called experts, think a pump test shows a well's recharge rate. Wrong! A pump test gives only the recovery rate at which water moves through fractures to your well. It tells you neither the recharge rate nor the total volume of water available.

A huge misconception is that a pump test tells whether a well is good or bad. Pump tests are used because they are the only practical tests to perform, and some information is better than none. A pump test tells if you can withdraw water from your well at a useful rate, but does not tell how much water you actually have or how long the supply will last. It may give you a false sense of security if you don't understand what it really means. Most people, even some engineers and geologists, misunderstand this. The idea that a 1 GPM well is poor and a 15 GPM well is good may or may not be true.

If the total volume and recharge rate are adequate for a 1 GPM well, you could use it forever and never run dry if you don't use too much in a short time (and if you do, the well will recover fairly soon). On the other hand, if the total volume is small and the recharge rate inadequate, a 15 GPM well may be pumped dry quickly, even if pumped at less than 15 GPM, and may run dry often unless allowed to recover for a long time (perhaps months or years). It will always be susceptible to being pumped dry quickly. So a 1 GPM well could be a good one, and a 15 GPM well could be lousy. A storage tank can help if the 1 GPM pump rate is an occasional problem, but will do little or no good for the 15 GPM well if the volume of water available and recharge rate are inadequate.

The critical point is that there¡¦s no practical way to know whether you have a good well or a bad one until it runs dry. Then you know you have a bad well. The best you can know is that it¡¦s been good so far, but that could end next week. Everyone using a well in the Evergreen-Conifer area should use water conservatively. The supply is NOT infinite, and yours may already be low. You won't know (and can't find out) until it's too late.

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