How and how often are you getting estimates of hydraulic conductivity (K) at your sites? I have used labs before, but the estimated values differ significantly as compared to back-of-the-envelope estimates from Freeze and Cherry (1979). If you are using slug tests to determine K, are you noticing an effect of poorly developed sandpacks, and are you doing slug tests at contaminated sites? Are folks using pumping tests anymore? Is anyone using low flow data to estimate K? For those that are not aware, there is a science to calculating K from low flow sampling data that is very intriguing, one which I would love to apply when I finally collect data. See https://lnkd.in/gND4AbCd. I'm trying to determine the framework that consultants are working within, and how and with what frequency consultants are ascertaining K values at their sites. As an aside, hydraulic conductivity (K) describes the ability of a porous media to transmit water and can vary many orders of magnitude for the same type of material. For instance, the value of K for a clean sand can vary five orders of magnitude, ranging from about 10E-4 to 1 cm/sec (Freeze and Cherry, 1979). Values of K are necessary to inform contaminant transport.
For those still following this thread, check-out this article in Groundwater on the "Evaluation of Hydraulic Conductivity Estimates from Various Approaches with Groundwater Flow Models." https://ngwa.onlinelibrary.wiley.com/doi/abs/10.1111/gwat.13348
It is important to take into account the scale effect. You can test a small core of a few centimeters long in the lab. The radius of influence of a week of pumping test could be a few hundred meters. A numerical flow model of a detrital aquifer could be several square kilometers. This is especially relevant in anisotropic and heterogeneous media, such as fissured aquifers. A good example is to get very different values of K with 2 similar wells being very close to each other
All of the above. The end use of the data is the driver for using one method over another. Something not mentioned here is methodical well development and data collection (during development).
Hey Matthew…are you interested in looking at low flow data already collected or from active sites where currently collecting data and can modify the extraction rates?
In my company, I teach the principal that there's three tiers of K estimation: Gold = a pump test with nearby observation wells; Silver = a slug test with nearby observation wells; and Bronze, which is basically everything else (literature based on USCS classification, ex-situ disturbed sample lab analysis, and senior geo's best guess).
We do a lot of slug tests and I have yet to use low flow data for estimating K but I will use it for a site where I don't have a slug test done. I'll let you know if I am able to use this estimate for a site/well that has had a slug test and low flow sampling done.
Steve Rosell
1y
I love the discussion these technical posts generate. Thanks Matthew.
Is your question concerning shallow wells (-100m), or deeper-seated oil & gas wells (km's depth)?
Quite a bit. For water/shallow wells we use empirical calculations from grain size distribution, specific capacity tests when available for nearby wells and for some sites run pumping tests sometimes we use charts like the one above. For small monitoring wells we sometimes use slug tests. You can make up for the limitations by doing lots of them. Occasionally we do lab testing of undisturbes aquitard cores - I think that’s the best application for lab tests. For deep wells we use Repeat Formation Test tool pressure transients, core lab tests, sidewall core tests, fall off tests and occasionally interference tests.
PhD Student, University of Waterloo
1yGrain size analyses can also be used to estimate hydraulic conductivity. O'Hannesin [1981] used grain size analyses to infer K values. They found that K varied over a range of about one order of magnitude. The resultswere in general agreement with slug tests and permeater analyses for the sandy aquifer at Borden. I've collected grain size data for my sites, but never extrapolated K. Is anyone familiar with extrapolating K from grain size distribution?