Information Gathering for Well Design

The process involving a lot of details and a lot of parties is critical to the success of the well installation.

By Marvin F. Glotfelty, RG

A lot of information is produced during the drilling, installation, aquifer testing, and water quality sampling of a well.

Much of that information is obtained during the drilling process itself, such as the penetration rate log, the lithologic log, the geophysical logs, depth-specific groundwater quality sample results, and hydrologic testing (falling head test) results. In many cases, the information obtained during drilling the borehole will provide a basis for adjusting the well design to make it more compatible with site-specific conditions and project objectives.

The field observations and various other measurements we make during drilling operations are critical to the success of the well installation. However, other information that is also critical to the success of the well installation must be obtained through person-to-person communication rather than by use of a measuring device such as a Marsh funnel, mud scale, or Imhoff cone.

Probably the most universal way to gain information is experience. A good description of experience is provided by a quote from the author Rita Mae Brown: “Good judgment comes from experience, and experience comes from bad judgment.”

The “school of hard knocks” provides many important lessons, but those lessons are sometimes obtained at a high price or with enduring consequences. Most of us would prefer to learn from the experience of others rather than by making nearly every mistake ourselves—and paying the price for our poor judgment with each lesson learned.

A challenge with the well drilling trade is there is no single well design, drilling method, or construction technique that will optimize the performance of each and every well. Hydrogeologic conditions may vary from place to place (even within short distances), and a landowner’s intended use of a well may also be significantly different than a neighboring well owner.

The variability of local conditions and client expectations make each well installation unique. Each well installation project introduces a distinct set of construction material requirements, appropriate well installation techniques, and optimal well development procedures. Thus, the lessons learned during one well drilling project cannot necessarily be applied to the next well down the road. Groundwater professionals need to resolve the mysteries posed by these project-specific variables, which must often be achieved through conversations between stakeholders.

Information Conveyance from Well Owner to Designer

At the start of a well drilling project, the landowner will typically contact the well designer (who could be a hydrogeologist or a water well contractor) to coordinate the well installation program. The initial conversations regarding “when, where, and at what cost” for drilling the well may seem obvious, but if the project details are not fully addressed and clarified between all the parties, the result could be inaccurate assumptions or a misunderstanding of the project objective.

Such communication failures may lead to an inaccurate understanding of the well’s intended purpose, which may result in a poorly designed well. The specific purpose of the well should be shared with all stakeholders. Is the well to be installed intended for household supply, summertime use only, municipal supply, industrial supply, agricultural supply, dewatering, hydrological testing, monitoring, etc.?

The purpose of the well essentially defines the project expectations of the well owner. Those project expectations include such things as the anticipated water production rate, water quality expectations, the work schedule and mobilization date, and the project budget.

The specific location of the well should be determined by the well owner with consultation provided by the well designer to assure proper offset from septic systems, property boundaries, etc.

If the stake that marks the drilling location is inevitably bumped over prior to rig mobilization, it’s best to have the landowner replace it. Wells have been drilled at inconvenient locations, and even on the wrong parcel of land, which creates a headache for everyone involved.

Proper siting of a well prior to rig mobilization is one of those things that should definitely be addressed with planning and good communication, rather than by learning from the experience of bad judgment.

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Information Conveyance from Well Driller to Designer

In cases where the well designer is a hydrogeologist or engineer, there is a need for good lines of communication and exchange of information between that well designer and the driller.

When a well designer prepares a technical specification, each and every requirement in that specification should be there for a reason, and not just a copy-and-paste of verbiage from bid documents for other wells. That means the well designer should have a fundamental understanding of the well drilling and construction process.

Figure 1. Nested well design.

All too often, sections of the technical specifications such as plumbness and alignment requirements, lost circulation conditions, or low penetration conditions are inappropriate or unnecessary. The unsuitable verbiage in the specifications usually results from the well designer having a poor understanding of the drilling trade, so the requirements that have been called for are superfluous or ineffective.

It is the responsibility of the well designer to draft a specification that will not only meet the intended purpose of the well but will also provide for a constructible well. A constructible well will allow the driller to reasonably and safely implement the means and methods that have been specified by the well designer.

An example of a well that does not meet the needs for constructability is presented in Figure 1. Nested wells are commonly used to monitor water levels and collect water quality samples from multiple isolated depth intervals within a single wellbore. The individual screened intervals of nested wells are isolated from one another with a cement or bentonite annular seal.

Figure 2. Wide annulus problem.

While the dimensions of the nested well shown in the figure all fit reasonably well on paper, this well design is indicative of a well designer with a poor understanding of drilling operations. The designer of this well ambitiously included a 59/16-inch outside diameter (OD) PVC casing and also six 2⅜-inch OD PVC casings within a 10¾-inch borehole. The well designer also envisioned using a 2⅜-inch OD tremie pipe for installation of the sand filter pack and bentonite seals, which would fill the remaining space within the boring. This well designer’s best-laid plan is to obtain hydrologic data from multiple depth intervals, but while the well design is conceptually feasible, it is not practically achievable for several reasons:

  1. The borehole may be several hundred feet deep and will almost certainly have some irregularities, such as
    washed-out zones or ledges, as well as possible intervals of swelling clay that would effectively reduce the borehole diameter. Even if flush threaded PVC casing strings are used, there will be the risk of abrasion and binding of the multiple casing strings during well installation.
  2. Casing centralizers would likely become entangled during the construction of this well due to the tight casing spacing within the relatively small boring. Thus, the well’s screened intervals would have to be installed without centralizers, so they would not be well-centered in the borehole.

    This means there will be a large annulus on one side of each screened interval and almost no annulus on the opposite side of the well screen (Figure 2). Therefore, the driller will probably be unable to completely develop the thick annulus side of each screened interval because he will be unable to convey adequate energy through the thick envelope of sand to break down and remove the wall cake on the borehole face. On the opposite side of the screen where there is almost no annulus and minimal filter pack sand, the likelihood of sand invasion during pumping is increased due to inadequate filter media.
  3. Even well-drilled boreholes that are reasonably straight and plumb will have some degree of horizontal drift. The borehole may be tilted by only 1 or 2 degrees, but all the uncentralized casing strings will still migrate to the low side of the borehole. Thus, even though the casings can be positioned in an evenly spaced pattern at the wellhead (Figure 3, left diagram), they will all still be lying against the same side of the borehole at depth in response to the forces of gravity (Figure 3, right diagram). The off-center screened intervals will further magnify the issues described in item 2.
  4. Isolation of the screened intervals in a nested well requires a good bentonite or cement seal between each section of well screen. The numerous casing strings would all need to be hung in tension during installation of the filter pack sand and bentonite seals (cement would probably not be used with PVC casing, due to the heat emitted during curing). The seals between screened intervals would need to be placed in such a manner as to provide a complete seal to isolate each screened interval (Figure 3). While this is not impossible, it makes the well construction process extremely challenging for the driller.
Figure 3. Well plumbness impact.

These four items are indicative of a complex well design that may result in an ineffective monitoring well or an unsuccessful well installation. In some cases, complicated well designs or challenging well installation conditions are unavoidable. However, when possible, the best rule of thumb for well design is to keep it simple and keep it constructible to the greatest extent possible.

Information Conveyance from Well Designer to Driller

When the well designer is a hydrogeologist or engineer, information needs to flow both to the driller as well as being received from the driller.

As stated previously, every section of a well’s technical specification should be there for a reason. Most drillers are accustomed to conducting well construction programs in compliance with the technical requirements of the well designer. However, it has been my experience that variability in logistical requirements is a challenge to some drill crews. The rules of the game are changed from well to well due to differing well site layouts, different client/designer requirements, different reporting requirements, and even different regulatory mandates that apply to various areas.

The primary job of the drilling crew is to be laser-focused on drilling, installing, and developing the well in an efficient and safe manner in accordance with the specifications. Well designers do their best to provide clarity and avoid ambiguity in the technical specifications. Nonetheless, unclear wording and ambiguous statements still sometimes occur in the well installation bid documents.

Those uncertainties can be cleared up with simple explanations from the well designer. The well designer should communicate the rationale for each specified item and how it supports the project expectations.

Many of the logistical requirements in technical specifications are intended for the drilling site to be a good neighbor.

Well installation projects are commonly located in close proximity to residential neighborhoods but require a 24-hour per day work schedule. For these situations, the requirements for sound abatement should be clear and detailed. The height, linear extent, and general characteristics of sound attenuation walls should be concisely described with  reference to specific decibel limits and ASTM Standards such as Standard E 90 or E 413.

Some other good-neighbor requirements are traffic control, dust control, and night lighting (directed toward work areas while avoiding adjacent residences). The specific routes for vehicles or pipelines are not always known at the outset of the drilling program, so it is important for the well designer to communicate with the driller daily as the work progresses and conditions change.

Have a Drilling Question for Glotfelty?
Is there a drilling issue that you have wondered about for a long time? A question you have wanted a second opinion on for a while? Send them to The Art of Water Wells column author Marvin F. Glotfelty, RG, and he will utilize his more than 35 years of experience to tackle the question for you. Email Glotfelty at mglotfelty@geo-logic.com, and the answer will appear in an upcoming NGWA: Industry Connected Video.

Marvin F. Glotfelty, RG, is the principal hydrogeologist for Clear Creek Associates, a Geo-Logic Associates Co. He is a licensed well driller and registered professional geologist in Arizona, where he has practiced water resources consulting for more than 35 years. He is author of The Art of Water Wells (NGWA Press, 2019) and was The Groundwater Foundation’s 2012 McEllhiney Lecturer. Glotfelty can be reached at mglotfelty@geo-logic.com.