Horizontal Wells in Water Supply Applications
By Louis B. Fournier, Ph.D.
ore than 2000 horizontal wells have been consist of a vertical central shaft, called a caisson.
M completed for environmental remediation
purposes since 1988. Directionally drilled
horizontal wells have been used for many remedia-
The caisson is manufactured from reinforced con-
crete and serves as a collection point for water that
enters the system through a network of radically ori-
Using directionally drilled horizontal
wells to extract water from aquifers
tion applications including ground water extraction ented well screens. In general, the caisson is con-
for pump-and-treat systems, total fluids extraction, structed in place using the open caisson method with
causes less drawdown over a wider
air sparge, biosparge, soil vapor extraction, nutrient multiple lifts. area, so that upwelling does not or
injection, and ground water containment/migration Laterals can be either drilled or hydraulically
control. projected. A packer and pumping system is used to may not occur.
Only a few directionally drilled horizontal wells control water during lateral installation. This wet
have been installed in the United States for potable well or pumping station allows entry for periodic
water supply. It is anticipated that the use of these inspection of the system and permits any required
1. Any length screen can be installed with direc-
wells in this application will grow dramatically as maintenance to be performed. The caisson can be
tional drilling. In remediation applications,
human population increases and the demand for completed with a pump house or flush grade top slab
screen lengths have commonly reached approxi-
potable water increases proportionately. Because to minimize visual impact on the surroundings.
mately 1500 feet long, but this is not considered
much of the population growth is expected in The system can pump from subsurface aquifers
to be the maximum possible length. Increased
today’s relatively undeveloped nations, it is likely or from nearby rivers by inducing flow to the cais-
screen lengths serve to increase the volume of
that much of the increase in water demand will son. In riverbank infiltration systems, river water is
water pumped from the well.
be in these areas as well. But it is also likely that filtered by the formation to remove solids and parti-
2. Longer screens also can result in a lower
continuing population growth in certain areas of cles. Such systems have been installed around the
entrance velocity for pumped water. Lower
the United States will fuel the demand for water. world to enhance water production from available
entrance velocities generally reduce well plug-
Horizontal water supply wells will play a part in sources, whether it is ground water, river water, lake
ging and, therefore, create a decrease in the need
meeting this demand. water, or water from canals. One manufacturer and
for or the frequency of maintenance.
For example, continuing development brought consultant on these types of wells, Collector Wells
about in part by the baby boomers reaching retire- International Inc., on its Web site, describes such 3. In the extreme, a long enough well may reduce
ment age will increase water demand in Florida. wells being used in Sioux Falls, South Dakota; the need for multiple screens oriented radially
The increase is not only related simply to population St. Helens, Oregon; Jacksonville, Florida; and from the central caisson and therefore could
growth; it is also related to the need for more busi- Crystal City, Missouri. Similar projects are being result in construction of a smaller caisson or no
nesses, recreational areas, restaurants, etc. to serve evaluated for Delaware, Ohio; El Paso, Texas; and caisson. A pump could even be placed within
the incoming flux of retirees — all of which require other cities within the United States and around the the header of the horizontal well in some
water supply for their activities. world. applications.
Installing more vertical water supply wells to The water supply system for Noida, India, illus- 4. In general, radial collection wells must be placed
accommodate the increased water demand is one trates the future of water supply systems around the in unconsolidated formations consisting of sand
option, as is increasing water production from exist- world. The rate of water supply in Noida per day is or gravel deposits. Directionally drilled wells, in
ing vertical wells. However, both face a common 59.4 gallons (225 liters) per capita. There are 184 contrast, can be placed in consolidated rock or
limitation. Excessive pumping down of a water sup- tube wells, 6 Ranney wells, 33 overhead tanks, and sand and gravel deposits. Directionally drilled
ply aquifer in coastal areas can result in upwelling of 23 underground reservoirs. The total supply capacity horizontal wells can also be placed in fractured
underlying salt water layers into these vertical water is 78.52 million gallons (302 million liters) a day rock formations where rain water has been cap-
supply wells. Such upwelling can result in a salt- and the water treatment is by online filtration and tured in the fractures. When placed in vertically
contaminated drinking water supply and system that chlorination. oriented fractures, horizontal wells offer the
can no longer be used for its intended purpose. The water supply is adequate and is shortly to be opportunity to traverse many fractures so that
Using directionally drilled horizontal wells to extract supplemented with Ganga (Ganges) water, which is they meet water production requirements.
water from aquifers causes less drawdown over a being brought to the area through a project launched On islands and in coastal areas around the world,
wider area, so that upwelling does not or may not a few years ago. An ambitious plan is also under placement of horizontal wells beneath the ocean
occur. Hence the use of horizontal wells for with- way to set up rain water harvesting facilities in floor or beaches might offer a non-visible way of
drawing ground water under conditions that exist in Noida as an alternate source through advanced and extracting salt water for desalination units. One such
Florida appears to offer substantial long-term bene- indigenous technology. project is in the planning stages in Mexico, where
fits and less risk of eventual salt contamination of As a result of the investment in its water supply industry and human uses have outpaced the ability
drinking water supply aquifers. (followed by improvements in the sewage treatment of typical ground water supplies to meet demand.
system), Noida has established a congenial atmos- Another has been installed in the Caribbean.
Radial Collector Wells phere for industrial growth by attracting industrial In areas where water-bearing zones are thin and
In the past, horizontal wells have been used for giants and information technology companies from water production is hampered by the inability of a
water supply purposes when installed as part of a India and abroad to establish a permanent base for single vertical well to achieve production require-
Ranney or similar system wherein screened horizon- their operations. ments, the choice is to install either many vertical
tal spurs are installed radially into a central caisson Similarly, radial collection wells at the Okhla wells, each with small production, or a single hori-
from which water is pumped. Generically, these are Water Works provide about 5 million gallons of zontal well centered in the thin water-bearing zone.
referred to as radial collector wells. These systems water per day to south and southwest Delhi, India. Several thousand feet of horizontal screen could be
installed over a larger area for water collection.
Directionally Drilled Water could be removed with a single water pump
Louis Fournier, Ph.D., is the president of STAR Horizontal Water Wells for each well. As a very rough approximation, the
Environmental LLC, an environmental consulting firm that total length of well screen in the ground in an area is
specializes in horizontal well design and applications. The
It is anticipated that directionally drilled horizon- proportional to the quantity of water that can be pro-
company is located at 175 North 15th Street, Ponchatoula, tal wells, when used for water intake, could increase duced. Thus, in order to meet the production capabil-
LA 70454. He can also be reached at (985) 370-0708 and water production over radial collector well systems. ities of a horizontal well with, say, 1000 feet of
email@example.com. Directionally drilled horizontal wells offer several
major benefits over normal radial collector wells. horizontal directions/continues on page 36
34/ June 2005 Water Well Journal NGWA.org
horizontal directions/from page 34 Institute described the installation of a 10-inch- choice of using a series of vertical pump wells or a
diameter HDPE well using a chain trencher. The horizontal well for water production. Let’s say that
screen, the total number of vertical wells required, purpose was to have a low-cost installation in a rural the horizontal well could place 1000 feet of screen
say, with 20 feet of screen each, would be 50. community. It was estimated that the project reduced in the ground, and you know the cost of that effort.
With today’s concerns about terrorism, there may total project costs by 66% of that of a traditional ver- Now, let’s say you could use vertical wells and each
be advantages of having a single wellhead rather tical well water supply system. vertical well would have 50 feet of screen in the
than a vertical wellfield to protect. A directionally Longbore Inc., a horizontal well drilling compa- ground in contact with the water-bearing formation.
drilled horizontal well can provide such a wellhead ny which specializes in the installation of long direc- Dividing 1000 by 50 gives the number of vertical
with minimal impact on overlying structures and tionally drilled horizontal wells, installed 10 wells wells that will provide the same total length of
facilities. Moreover, the need to interconnect vertical with screens ranging from 702 to 840 feet long at screen as the single horizontal well (20 vertical
wells is eliminated. depths varying from 37 to 42 feet below grade. Total wells). The total cost of installing these 20 vertical
well lengths were 1274 to 1547 feet. Longbore com- wells can be compared with the cost of installing the
Cost Comparisons pleted the wells at a former Department of Defense single horizontal well. To this must be added mani-
Articles have been published that detail the cost facility. The subsurface is composed of sand and folding costs for the vertical wells, pump costs, site
comparisons of horizontal versus vertical wells for a gravel with cobbles up to 12 inches in diameter. access costs, and all other related costs. Keep in
variety of applications. These articles compare costs The well screen and casing consisted of SDR-11, mind that the horizontal well will likely have a sin-
of different soil and ground water remediation tech- 65⁄8 inches in diameter HDPE. The screen was gle pump, a single point of exit for the well, and no
nologies for various cleanup projects. Such cost designed with 0.020-inch slots. The drilling fluid manifolding costs.
comparisons are not directly applicable to water pro- consisted of bentonite and a mixed metal hydroxide Compared with typical collector wells, the key
duction projects, but they do contain some very viscosifier. Well development was performed using benefit of the use of directionally drilled wells will
important and directly applicable concepts. chemical treatment along with overpumping. Each likely be the elimination of the costs (and difficul-
In general, the use of directionally drilled hori- well produced up to 80 gallons per minute, but was ties) related to the installation of the caisson.
zontal wells for pumping ground water does not in pumped at approximately 25 gpm for the treatment Directionally drilled horizontal wells offer many
and of itself save substantial amounts of money over activities. advantages over alternative water production sys-
vertical wells in the same application — only per- The costs of radial collection well systems ver- tems, which are just now being fully realized and
haps 20% of the total project cost. However, there sus directionally drilled horizontal well systems have appreciated. For emerging nations, they offer the
can be very substantial savings in total project costs not been compared in the literature. Intuitively, possibility of lower-cost water supply. They also
if other factors are considered, such as access issues directionally drilled horizontal wells should be sig- offer the advantage of being able to be installed in
and well manifolding costs. That is, it is difficult and nificantly less expensive. For example, a riverbank virtually any water-bearing formation.
costly to install a vertical wellfield with a large num- filtration system was installed along the Missouri The techniques and tools for directional drilling
ber of wells over a wide area all of which must be River by the Board of Public Utilities, Kansas City, are rapidly being developed in support of ground
manifolded together, particularly in a residential or Kansas, in 1997. This collector well was designed to water and soil remediation applications. The use of
urban area. By contrast, if one or two horizontal produce up to 28,000 gpm (40 mgd) to meet expand- these techniques and tools in water supply applica-
wells can be installed with minimal impact on over- ing demand. The reinforced concrete collector well tions is relatively straightforward and potentially
lying structures and no manifolding requirements, caisson (20-foot-diameter) was constructed to a enormously beneficial. WWJ
then these costs and difficulties are eliminated. depth of 124 feet below grade (and 17 feet above)
Horizontal water wells are often more effective for a total height of 141 feet. A total of 14 lateral Bibliography
at producing water than vertical wells in lower per- screens were installed adjacent to and beneath the A&L Horizontal Potable Water Well. www.alunderground.
meability formations. For a pump-and-treat remedia- riverbed for a total screen length of 2800 feet. com/waterwel.htm (accessed April 14, 2005).
tion project at Williams Air Force Base in Mesa, Conceptually, this same screen length could be Bardsley, David. 2001. Horizontal wells work. Water Well
Arizona, models estimated that one horizontal well placed in the ground using directional drilling with Journal, vol. 55, no. 11: p. 68 (available online at
could replace 80 vertical wells due to the low perme- two to three horizontal wells. Using in-well pumps, www.org/ngwapdf/NovHDD.pdf).
ability of the formation. the total system cost should be significantly reduced. Collector Wells International Inc. www.collectorwellsint.com
Over the years, horizontal wells with 1000 feet (accessed April 12, 2005).
or more of screen have been rather routinely Conclusions Fournier, Louis B. 2002. Directionally drilled horizontal
installed for ground water and soil remediation. Directionally drilled horizontal wells offer an wells offer cost savings and technical advantages over
On Long Island, New York, four remediation wells opportunity to significantly reduce the costs and dif- alternative soil and groundwater remediation systems.
Remediation Journal, vol. 13, issue 1: pp. 87–98.
were installed under a lined petroleum terminal ficulties of conventional water product wells and
about 45 feet below grade. Each had approximately systems in a number of ways. In principle, horizon- Horizontal Environmental Remediation Wells: Case
1220 feet of screen. At the Savannah River DOE site tal wells can be viewed as a logical alternative to
Pg06.HW.Case.Hist.html (accessed April 12, 2005).
in Aiken, South Carolina, two directionally drilled both vertical water wells and Ranney collector type
Kaback, Dawn. Horizontal Environmental Wells—Part 1
horizontal wells with over 1440 feet of screen were systems. Their key feature is their ability to get more
(available online at www.drilleronline.com).
installed. In Ann Arbor, Michigan, a well with 1400 screen into the ground and, therefore, increase water
Krug, John D., P.E. 1993. Minimizing water supply costs
feet of screen was installed from a residential area to production due to an increased use of the water-
in rural communities. Plastics Pipe Institute Insider
a remote treatment facility. bearing formation. Secondary benefits include Newsletter, vol. 3, no. 3: pp. 1–3 (available online at
A major advantage of directional drilling for reduced volumetric flow of water per unit of screen, www.plasticpipe.org/pdf/newsltr/Fall1997.pdf).
such installations is that the wells can be put in place which may result in decreased operation and mainte- Longbore Inc. Case History. www.longbore.com/us/
without disruption of overlying facilities and struc- nance costs. CaseHistories1.htm (accessed April 12, 2005).
tures. However, this is not the only method of instal- One back-of-the-envelope way of comparing the Water Resources—Ranney Collector Wells. www.ranney
lation that has shown the benefits and savings of cost of different water production systems and alter- method.com/default.html (accessed April 12, 2005).
horizontal wells in water production applications. natives is by computing the cost per foot of “screen
An article published in 1997 by the Plastics Pipe in the ground.” For example, suppose you have the
36/ June 2005 Water Well Journal NGWA.org