The Groundwater Project

An Introduction to Hydraulic Testing in Hydrogeology

By bringing together over 60 years of academic teaching and research experience and an additional 90 years of applied hydrogeology consulting, the book An Introduction to Hydraulic Testing in Hydrogeology is a soon-to-be classic.

In an interview with Everton de Oliveira, the authors William W. Woessner, PhD; A. Campbell Stringer, MS, PG; and Eileen Poeter, PhD, PE explain that they wanted to provide their readers with the basic theory and tools needed to understand the responsible application of hydraulic testing methods to generate field-scale hydrogeologic properties of groundwater systems. Their book emphasizes basic concepts, principles, and methods so their readers can correctly apply hydraulic testing and analytical methods.

Dr. Woessner got the idea for this book after he and Dr. Poeter finished writing Hydrogeologic Properties of Earth Materials and Principles of Groundwater Flow. This first book focused on laboratory methods and referenced field hydraulic testing methods but did not provide details on application. Dr. Woessner felt another piece of work was needed that would address the hydraulic testing specifically—and on an introductory level.

Knowing that he couldn’t do it alone, Dr. Woessner got Mr. Stringer involved for his practical fieldwork background and Dr. Poeter for her expertise in mathematics. The authors stressed that even though the three of them were the core group, a number of reviewers and other collaborators worked on this book as well.

Not just mathematics

The aim of the book is to help hydrogeologists understand hydraulic testing and what these tests can mean for them in their work. Feeling that hydrogeologists might sometimes shy away from hydraulic testing because they are wary of the math involved, the authors wanted to break down that barrier and take the fear out of advanced math by helping their readers understand the whole process.

In Dr. Poeter’s words: “We start by talking about the purpose of testing so that people understand why they even want to do it. Then we give lots of illustrations that present the conceptual setting where the tests are done and help people realize that they need to understand the hydrogeologic setting before they design their tests. From there, we move on to how the tests are conducted and how the field data is corrected and analyzed before we dive into the mathematics that underpins the interpretation. And to help make the mathematics more accessible to people, we explain the math step-by-step with lots of diagrams and worked examples. We also added links to exercises throughout the book so that readers can work out the concepts as they’re reading.”

Mr. Stringer added that although people sometimes get scared off by the mathematics, in practical applications, it’s the conceptual part that is most important to understand. “We see it all the time. People are trying to plug in inappropriate data to mathematically analyze it, and then they come up with answers that are not meaningful. So the conceptualization is the most important thing for people to understand. These days, there are online tools to help people with the mathematics. So I’m not sure that a deep understanding of the mathematics is necessary to successfully apply these tools. It’s more important for people to understand how this is all developed and how it’s all applied.”

Understanding the tests

In the book, the authors guide their readers through the different types of hydraulic tests. They explain how they work and how they were developed, but also their limitations. Because only by understanding the different tests can hydrogeologists apply them correctly in their fieldwork, adjust them when necessary, and get accurate data.

“The book is trying to say that people have done this before and here’s what they came up with,” Dr. Woessner explains. “And now you can use their findings—with the understanding what the limitations are of a particular method. We’re trying to get across that when things don’t quite work out or don’t fit well, there’s a reason for it. So how do you adjust? What do you do to try to make an estimate even though you know that it’s not the perfect situation? Our book might explain why things are not working out during a test.”

Mr. Stringer emphasizes that the key to doing your own testing is to ask the right questions. “The most important thing in preparing tests is to ask, ‘What questions are we trying to answer with this test?’ And then we need to collect the information that we have available to us in advance to understand as much as we can about the system that’s being tested. Only then can we design the test to fit the setting as well as the question that we’re trying to ask.”

From simple to more complex

The book’s organization also helps make hydraulic tests more accessible: the authors start with simpler tests before moving on to the more complex ones. Much in the same chronological order that these tests were developed historically.

“We weren’t thinking ‘Oh, let’s follow historical development,’” Dr. Poeter says, “so much as that historical development started by analyzing some of the simple conditions and then moved on to more complex conditions. And so we progress in the same logical way: from simpler to more complex. The book also starts with designs that are easier to interpret and then moves to tests that are more challenging to interpret. So we go from simpler, easier to evaluate, and more commonly used to more complex, more difficult to evaluate, and less commonly used tests.”

Dr.  Woessner adds: “We equip our readers with a lot of different tools in our book. For example, what if you don’t have a pumping well? Or what if you have data from performance tests of well drillers drilling a well and pumping it for an hour or two and recording what’s happening? Because sometimes that’s all that’s available and you don’t have the budget to run a fancier or more involved test. There is a lot of data out there that you could interpret if you knew how to interpret it. So we’re trying to give our readers some tools to open up that area and get some estimates of hydraulic properties even when they don’t have perfect data.”

By hand and with software

The authors also include discussions about software and tools that are widely available for people to use when interpreting hydraulic tests. But they emphasize the importance of doing the calculations by hand.

Dr. Poeter stresses that all the work in the book can be done with paper and pencil. “Because that’s how hydrogeologists did it for a long time before we had computers at our fingertips. But we also provided a lot of links to various commercial and free software options.”


“The whole reason that the book is designed the way it is,” Dr. Woessner explains, “is that when I was teaching, I would always have the students do a curve matching exercise by hand. Because that’s what they’re going to do in the field. That’s the methodology that actually is used to solve those equations. And so we even provided graph paper in the book.”


“And as far as which software tools our readers should have,” he continues, “if they have any kind of program that they like, even PowerPoint or Excel, they can do the same thing. The curve matching technology in dedicated software is a sophisticated way to do what you would do by hand. But then it’s still up to the hydrogeologist to look at that curve match that was produced by the software and ask, ‘Does that make any sense?’”


Concluding remarks

When asked if they had any last remarks, the authors shared their hopes for the book.

Dr.  Woessner stressed that “it was a real team effort, so I hope the readers appreciate that. And we hope the book is used because I see it as providing the tools that you need to analyze and apply hydraulic testing appropriately.”

“I would just like to add,” Mr. Stringer notes, “that these tests can also add a lot of conceptual knowledge to the system because many systems don’t behave in an ideal way. And so when you go in thinking you know something about a system and then you see a different response . . . Our book can be very helpful in understanding a complex system.”

“I just hope that hydrogeologists will pick up the book and have a look,” Dr. Poeter says. “I think it’s very well suited to introductory groundwater courses, but I hope that experienced hydrogeologists might also glean a few new ideas from it. And it’s free of charge which is very nice now that textbooks are so expensive.”


Dr. Woessner concludes: “I want to make a point of that. Maybe people don’t realize that this is all voluntary work. None of the authors are compensated for any of The Groundwater Project books. And so I hope people realize that the time and effort we’ve put in this book has been time and effort that we think is needed.”