Cheap-&-Easy vs. Quality-&-Longevity

It’s critical to know the proper approach for well construction and rehabilitation.

By Marvin F. Glotfelty, RG

I select some items based on low cost when I’m shopping, but for things upon which I will rely (such as work boots or camping gear), my purchases are based on the quality of the item rather than the lowest cost.

Selection of professionals to perform a skill-based job are made by some folks based on the cheapest option, while other folks make that selection on the basis of the quality that will be provided. I like this quote regarding the quality of workmanship:

“If you think it’s expensive to hire a professional to do the job, wait until you hire an amateur.”
– Red Adair, American oilwell firefighter

The value of a water well can be defined by weighing its construction and operational costs against the benefits from the groundwater produced by the well. The characteristics of water wells are extremely variable, as are the costs of installation and maintenance of those various wells.

For a small single-family residential well, the well installation and maintenance costs will be relatively low, and the quantity of groundwater produced by such a well will be quite modest. However, the reliability and quality of that water supply will be critical to the family who lives at the residence.

For larger wells that serve municipalities, industrial facilities, or agricultural areas, the well installation and maintenance costs can be very high. Nonetheless, in consideration of the technical, regulatory, and logistical challenges associated with these larger water-supply systems, the cost for an efficient and reliable water supply is well spent.

Of course, it’s possible for a water well to be overdesigned or excessively maintained, which would constitute a waste of money. If a well were designed to last 50 years, when it was to be used for a three-month dewatering project, then that well would have been overdesigned.

In individual situations, almost any well design and maintenance program may be appropriate, but the correct approach for each scenario must be judged based on local conditions and economics that relate to the unique circumstances of the water well.

The design and construction of water wells can generally be categorized into two groups: “cheap-&-easy” wells and “quality-&-longevity” wells. For water wells that will be in service for the foreseeable future (drinking water wells, power plant wells, etc.), we want to follow the quality-&-longevity approach for the design of the well, and also for its operation and maintenance.

However, even as we follow that approach, there are multiple alternative decision points that must be navigated by groundwater professionals, such as selection of the construction materials, drilling method, and well development method/duration. Such options are not trivial, as they can impact the cost of the well by tens of thousands of dollars, or even hundreds of thousands of dollars.

Thus, it is sometimes appropriate for groundwater professionals to support their well design/maintenance decisions by considering the financial impact of those actions throughout the long-term operation (life-cycle) of the well.

Life-Cycle Economic Analysis of Well Design

The design and construction methods of a water supply well should reflect a consideration of its cost during the entire life of the well, which typically ranges from 25 years to more than 100 years.

Figure 1. Well comparisons for life-cycle economic analysis (The Art of Water Wells, p. 130, NGWA Press 2019).

Too often, well designs and installation methods are focused only on the initial capital cost of the well installation without regard to the operational expenses that will occur during the future years of the well’s use. A well with the lowest construction cost will not necessarily provide the best overall value during future years of use, so if the well’s design reflects only a single-minded focus on the construction cost,
then the life-cycle cost of the well may be unnecessarily high.

As the 2012 NGWA McEllhiney Lecturer, I gave a series of presentations on the topic “Life-Cycle Economic Analysis of Water Wells.” I discussed in the lecture a 75-year lifecycle comparison between hypothetical water wells that were identical except for having well screens composed of different steel types.

Video recordings of the McEllhiney Lecture are available via YouTube and details of the life-cycle economic analysis of wells are included in chapter 5 of my book, The Art of Water Wells (NGWA Press 2019).

The life-cycle economic analysis involved a cost-comparison throughout the operational life of the three well designs shown in Figure 1, which have screens composed of low-carbon steel (LCS), high strength low alloy steel (HSLA), and stainless steel (SS). Based on actual costs for a dozen similarly designed wells in 2011 (when the analysis was conducted), the respective average installation costs for these three well designs were:

Cost of LCS screened well: $512,314
Cost of HSLA steel screened well: $566,974
Cost of SS screened well: $776,362

All three wells have an LCS upper blank casing (only the screened intervals are different), and the wells all have an 18-inch diameter and 1210-foot depth. Based on typical production well data provided by the city of Phoenix for 2011, the pumping rate of each well was considered to be 1200 gallons per minute with the well operating 65% of the time, on annual average.

Longevity of the well types and clogging of their respective screen types were assumed based on empirical data from the Phoenix metropolitan area.

That empirical data indicated the operational life of LCS wells, HSLA wells, and SS wells in the Phoenix, Arizona, area is 25 years, 40 years, and over 75 years, respectively.

The empirical data also indicated that the expected specific capacity decline (due to screen clogging) of those well types would be 25% after five years for LCS wells, 25% after six years for HSLA wells, and 25% after 30 years for SS wells.

In addition to the well performance characteristics, the economic analysis considered replacement well installation costs, additional site construction costs, hydrogeologic and engineering consulting costs, operations and maintenance labor costs, well cleaning costs, pump and motor replacement costs, and electrical costs.

The electrical cost to lift water to the point of use was variable during the 75-year analysis period in response to clogging of the various well screen types. Clogging of the well screen will increase the water-level drawdown, which causes a detrimental economic impact. This detrimental effect can be
quantified by considering changes to the total lift requirement of the water, called total dynamic head (TDH), while pumping at a given flow rate of gallons per minute (gpm) using the following formula (source: www.engineeringtoolbox.com):

Energy cost per hour =
(gpm) × (TDH) × (0.746) × (electric cost is $/kW-Hr)
_____________________________________
(3,960) × (pump efficiency) × (motor efficiency)

The typical pump efficiency for new equipment ranges from 70% to 82%, and the typical motor efficiency for new equipment ranges from 85% to 95%. For this analysis, the pump and motor efficiencies were assumed to be 78% and 87%, respectively, and the electric cost for pumping was 8¢ per kilowatt-hour ($/kW-Hr), based on 2011 data from the city of Phoenix. Also, in accordance with city of Phoenix average well utilization for 2011, each well was assumed to be pumped 65% of the time, on annual average.

As shown in Table 1, all those costs were tracked for each well type throughout the 75-year life-cycle. The initial construction cost of the SS well was more than the LCS well by about $264,000 and more than the HSLA well by about $209,400. However, the cumulative cost of the SS well was actually found to be the most cost-efficient option in the long term. At the end of the 75-year period, the SS well was less expensive than the LCS well by about $3.3 million, and less expensive than the HSLA well by about $2.1 million.

Water well installations occur at a broad range of locations, and they serve many different purposes, so there is no single well design or drilling method that is optimal for every situation. It is important, however, to match the well installation attributes with the local hydrogeology and intended use of the well throughout its operational life.

Life-Cycle Economic Analysis of Well Rehabilitation

Installation of a water well is not the only activity that can be costly, as the economic impact of maintaining wells can also be significant. Biochemical scale or biofilm will accumulate in almost all wells, and clogging of the well screen can result in an increased water-level drawdown (increased TDH) during pumping. The need for rehabilitation of a well to improve its performance will vary from place to place depending on the local hydrogeologic conditions, well construction details, and pumping schedule.

The frequency and method of well screen cleaning (rehabilitation) should be consistent with the local conditions, so various well rehabilitation approaches may be more or less effective depending on the site-specific situation. Numerous mechanical and chemical methods are available to undertake well rehabilitation, and those well cleaning approaches will have variable levels of effectiveness at a given well.

The different well cleaning approaches also have a broad range of costs. For larger production wells, the typical well cleaning cost ranges from less than $40,000 to more than $200,000. Of course, the cost of cleaning smaller residential wells is much lower, but the general economic considerations presented in this column can be scaled to address rehabilitation of smaller wells too.

There are a wide range of chemical, biological, and mechanical problems that can cause clogging of well screens, and the alternative methods for well rehabilitation are similarly diverse. For clarity, let’s consider a simplified hypothetical scenario to illustrate the economics of well rehabilitation.

Assume a water well serves a facility that requires 1200 gpm that must be delivered 65% of the time on annual average. The well has a static water level at 200 feet below land surface, and when the well was originally installed, it had a specific capacity of 10 gpm per foot of drawdown (gpm/ft).

After years of operation, the specific capacity of the well has now dropped to 5 gpm/ft. The electric cost for pumping this well is 8¢ per kilowatt-hour, and the pump and motor efficiencies are 78% and 87%, respectively. The well pumps into a tank at the land surface, so the TDH equals the lift required to bring water from pumping water level up to the land surface.

The well owner is considering a high-quality rehabilitation technique, and let’s say that rehabilitation would cost $100,000 and would result in an improvement of the well’s specific capacity by bringing it up to 88% of the original performance. The owner is also considering a lower-cost rehabilitation technique that would cost only $50,000 but would improve the specific capacity up to only 65% of the original value. A third option for the well owner is doing nothing where they continue to pump the clogged well in an inefficient manner.

The economic comparison of these options is shown in Table 2. We can use the energy cost formula shown earlier to calculate the economic impacts of each well rehabilitation option. A reasonable assessment of the rehabilitation alternatives can be made by comparing the cumulative cost of each alternative after a 10-year post-cleaning period. We’ll assume the respective well rehabilitation results for each alternative
will remain consistent throughout the 10-year duration, which is unrealistic but simplifies the analysis.

The original energy cost to pump groundwater from the hypothetical well was $48,559 per year, and that energy cost increased to $66,768 per year after the well became clogged. So, if the well was operated in its current (unrehabilitated) condition for the subsequent 10 years, the additional electrical cost would add up to $182,090.

The high-quality ($100K) rehabilitation technique would improve the well’s performance such that the electrical cost increase after 10 years would be only $24,280. That means that the $100K cost for this treatment would be paid back in about 6.3 years. If the well owner opted for the lower-cost ($50K) rehabilitation technique, that $50K investment would be paid back in the similar timeframe of 6.0 years, but the well’s performance during the 10-year post-cleaning period would result in an additional electrical cost of $98,630.

This is just a hypothetical example, and under different site-specific conditions, the most cost-effective option may change. An economic analysis such as this can be useful to support the selection of the most cost-effective well rehabilitation alternative, and choosing the optimal approach for well rehabilitation (even if it’s not the lowest cost option) may provide significant cost savings to the well owner in the long run.

Learn The Art of Water Wells

Get The Art of Water Wells by Marvin F. Glotfelty, RG, a 2019 book from NGWA Press that is a comprehensive overview of well systems and delivers practical information applicable to real-world situations. The book is ideal for everyone working in the groundwater field. It provides practical information of water wells—covering everything from site selection to design, drilling methods, economics, and more. Click here to order it, call (800) 551-7379, fax (614) 898-7786, or email customerservice@ngwa.org.

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.