At the surface
By Ken Hugo
When ground water wells draw on surface water
By Ken Hugo
The wells you drill obviously draw ground water into them when they are pumped.
The wells you drill obviously draw ground water into them when they are pumped. It doesn’t take too much thought to see that if you install a shallow well in gravels next to a river or lake, you are probably eventually drawing in surface water. Does it matter if it is surface water or ground water? Yes, it does, for at least a couple of reasons.
If the water is surface water it might require more treatment than ground water, as the potential for bacteria or viruses is higher in surface waters than in ground waters. Also, in Alberta, within the Bow, Oldman, Milk and soon-to-be Red Deer River basins, one cannot get water licenses for surface waters, including ground water connected to surface waters (which Alberta Environment calls reserve waters).
So when does a ground water become classified as a reserve water? There are criteria to determine if the ground water is a reserve water, but three contentious water license applications in southern Alberta have shown that it is not at all clear to many people (including myself) what is classified as reserve water.
Alberta Environment does have a guideline, entitled Assessment Guideline for Groundwater Under the Direct Influence of Surface Water (GWUDI). This guideline has an initial screen that has four components to see if the water is a GWUDI source. These are summarized as follows:
- Sensitive setting: The source should not be a spring, shallow collection system, bored well or dug well. The aquifer should not be unconfined or less than 15 m below ground surface or be in fractured or karst bedrock.
- The source shall not be within 100 m of a surface water body.
- The well should be constructed properly.
- The water should not show indications of surface water chemistry or microbiology.
These seem simple enough, but complications and uncertainties have arisen. The definition of surface water in the guidelines is relatively broad, including items such as dugouts and intermittent creeks. It can be hard in some areas of Alberta not to be within 100 m of one of these sources. I worked on a license east of Medicine Hat a few years ago where there was no surface water reported since 1925 but had extensive flooding in 2011, so these usually dry areas now had numerous surface water bodies.
Causing more confusion is whether the aquifer is confined or unconfined. Just because the well log says that clay tills or shales overlie the aquifer is not enough to say it is confined. This was the issue in three hearings in front of the Alberta Environmental Appeals Board. One hearing was for a ground water supply in the Crowsnest Pass area (SW-16-09-05, Hearing 08-106), and the other two were for ground water supply in the Okotoks area (E ½ – 24-20-1W5, Hearing 12-043 and NW-16-20-29W4 Hearing 11-179).
At all these hearings, consultants for the well owners were making the argument that the wells were of sufficient depth and overlain by shales or tills and were confined. Alberta Environment was of a different opinion and said that the overlying shales and tills were not laterally extensive, or not of sufficiently low permeability, and the aquifers were connected with surface water. As a result, they would not grant a license.
The subject has lots of grey areas to it. We were taught in Grade 8 geography that ground water is part of the hydrologic cycle, so too strict a definition of reserve waters would exclude all licenses from being granted in southern Alberta, which is not the intention of Alberta Environment. The definition of an aquitard is not defined because although shales may show very low permeability (typically 1/10,000 to 1/1,000,000 as permeable as an aquifer) they are not impermeable. But what is sufficiently low-enough permeability to prevent a connection with surface water?
How continuous these aquitards are is also a factor that was the subject of much discussion at the hearings. The consultants tried to show that the aquitards are continuous through the use of well data and cross sections. To show that the aquitards are continuous in all directions takes a lot of wells, and Alberta Environment argued there were not sufficient wells to make this determination. They also did admit that no matter how many wells one has, there is still uncertainty on what types of strata is present between the wells. However, what would be a sufficient amount of wells is not defined.
Pump tests were also much discussed at these hearings. Pump tests can be used to determine the type of aquifer, but are open to interpretation (i.e. a pump test from a fractured aquifer may look like a pump test from an unconfined aquifer). The length of the pump test was debated, as Alberta Environment guidelines for water licenses specify a minimum time for pump tests, but these times may or may not be sufficient in complicated cases. The length of time that would be needed to conduct a pump test is not easy to establish, especially because it does not become apparent until one is examining the pump test data after it is complete whether it should have gone on longer or not.
I am of the opinion that pump test data is very useful in determining how continuous the overlying shales are, but only when combined with numerous observation wells. These observations wells should be in the aquifer, but they should also measure water level response in aquitards above the aquifer or in sandstone beds above the aquitard above the aquifer. Even geotechnical standpipes that measure the water table could be measured.
Flow tests in wells in aquitards could be done to determine the permeability of the aquitard. One would have to undertake very low flow rate tests, as pumping rates of even ½ a gallon a minute or less would likely (perhaps hopefully) dry up the wells.
Recording water levels in all the wells and in surface water bodies after the pump test is finished is also useful in seeing if there is any relationship between surface water and ground water levels. A correlation between water levels and precipitation data could also be done. One would have to measure these levels not just for days, but for months or perhaps one year to see if there is a correlation or not.
So do these issues affect water well drillers? Very much so, as not being able to obtain water licenses will affect the amount of wells that people want installed. Projects that do require water licenses for large amounts of water may require more well installation, including several observation wells. Pump tests may be more complicated with longer pump tests required and water levels read in more observation wells.
Ken Hugo is a technical director and hyrdogeologist with Groundwater Information Technologies (GRIT).