Researchers at Purdue University have...
Water Storage Tanks House Antennas for the Communications Industry
Following the adoption of the Telecommunications Act of 1996, water storage facilities have become fair game for the installation of antennas and associated ground equipment. A storage tank pulling double duty raises maintenance and safety issues for consideration by municipalities and their system operators.
To a number of people, the erection of an antenna tower is
seen as a blight over the landscape. This perception has pressured community
planners into limiting their existence through strict zoning provisions.
However, with nearly 120 million cellular subscribers nationwide, limiting the
number of antenna tower sites based on the not-in-my-back-yard (NIMBY) factor
is quite difficult. The importance of communications in our daily lives makes
their existence a necessary nuisance. In addition, antennas provide a valuable
revenue source for a number of communities.
In an effort to limit the construction of stand-alone sites
and their battles, placement of equipment on existing water storage facilities
makes sense. The problem is water tanks were not designed for the routing of
cables and attachment of antennas. Provider technicians also require
unobstructed site access to maintain service. Does this type of access conflict
with the need by municipalities to protect stored water?
Obviously, there are a number of pros and cons to the issue
of antenna placement on water storage tanks. These issues require careful
consideration and attention to details. If handled properly, the process can
result in a win-win for all concerned parties.
Following completion by the provider of the Antenna Site
Application Form, or a formal letter to the community expressing interest to
develop a specific site, it is most important for municipal staff to meet with
the provider’s engineer. The purpose of this meeting is to conduct a site
walkthrough in order to develop a conceptual plan. Asking the right questions
at this stage will save headaches later. This plan should include
• Location of the Base Transmission (BTU/BTS) cabinets (inside or outside),
• Underground utility routing,
• Routing of coaxial cables,
• Approximate location of tank penetrations, and
Identifying the location of BTS cabinets is important
because it can potentially affect the routing of coaxial cabling to the
antennas and underground service and telco. (Typical installation is from the
demarcation point to the telephone riser.)
If the cabinet is located in the interior of the tank, is
there enough space for the proposed equipment and maneuvering space for
operational maintenance? Additionally, is there space for the future
co-location of others?
If equipment is located outside the tank, how will the
placement impact the mobilization of maintenance equipment? For example, tank
repainting may necessitate the erection of a full containment (enclosure)
system to limit dust emissions and paint drift. Enclosures may require the
temporary installation of special outriggers that extend over the tank bowl or
drip-line. Location of provider equipment inside this line could cause damage
from excessive dust or overheating from placement of protective covers.
Location of ground equipment at the point of the outrigger extension would
interfere with the placement of the anchoring and daily operation of the
The routing of underground utilities could include both
service lines (electrical and telephone) and coaxial cables. The concept plan
should indicate whether proposed lines would cross existing municipal
utilities. With the design or location of the tank, would it be better for the
lines to be routed direct from provider’s ground equipment to the tank
base, or to have individual lines routed underground to each proposed antenna
sector? Does the location of the utility trench allow for future use by others?
The importance in the routing of coaxial cables cannot be
overstressed. Poor overall planning can produce major problems with respect to
aesthetics and future facility maintenance, affecting access and safety.
Over time every tank requires minor paint repairs or
complete recoating. The incorporation of 15/8* cables from numerous
provider’s can make the process even more difficult. From the
provider’s viewpoint, expensive equipment needs to be protected. Cables
may need to be wrapped to prevent possible damage from the coating removal
operation. The owner needs full access in order to provide complete maintenance
for the long-term integrity of the facility. Depending on the design, finding a
solution that satisfies both can be difficult. In most cases, a solution can be
realized with good up front planning at the earliest stages of the proposed
With standpipes and ground storage reservoirs, cables can be
grouped at a single location on the shell wall closest to the providers ground
equipment. Once the cables reach the roof center, the cables can be routed to
the required antenna locations. Cables can be sufficiently spaced from the wall
and roof of the tank (approximately 4* or more) with pre-designed,
off-the-shelf and prepainted brackets. These brackets can be used with
additional components to allow for multiple cables and provide suitable
alignment. These brackets can be permanently welded (though damage could occur
to the interior paint system), or installed using capacitor stud welding.
This same type of bracket also can be used for cable
installations on legged-style elevated tanks. However, consideration should be
given for placement of brackets on the inside portion of the leg. This will
prevent damage to tarps used as part of the previously mentioned containment
enclosure and provide a less obtrusive look. If antennas are to be mounted to
the catwalk or horizontal struts, cables to respective antenna sectors can be
attached directly underneath or to the backside.
Pedestal and fluted column style elevated tanks provide
still another challenge. They also can provide the easiest solution. The
greatest difficulty for locating on these types of tanks arises when the need
for height necessitates antenna placement on the roof of the tank. This
requires the routing of cables through the dry portion of the access tube (the
section that runs through the water storage area). In most cases, the diameter
of this tube is anywhere from 36* to 48*. The space is made even
smaller with the addition of the access ladder, lighting and overflow pipe. In
addition, the bottom bowl manway providing access into the bottom of the tank
may be located in the lower section of the access tube. This opening needs to
remain clear to allow for safe access during cleaning and maintenance. Space
limitations extend to the roof where clearance must be maintained around the
roof vent and other roof openings. If the routing is not planned for in a
clean, uniform manner tripping hazards can result.
Cable routing is made easier, safer and cleaner when
antennas can be mounted on the tank’s exterior riser or column. In this
situation, cables can be grouped utilizing standard support components to
create a cable tray. The tray can be attached using stud welds or clamped to
the lip of the interior riser/flute stiffener ring.
As part of the conceptual plan, identification of the
number, size and location of tank penetrations should be made. Placement of
penetrations for service and coax cables in certain areas of the tank can
require special design considerations to maintain structural integrity. In
addition, it may be necessary for the owner to provide partial draining of the
tank until installation is complete. Placement for other penetrations that
affect the tank’s condensate ceiling or access tube also should be
evaluated to identify any possible conflicts that could prevent proper seal or
adequate room for bending of cables.
The location of antennas (elevation and azimuth) is fixed by
the provider in order to provide coverage to a given area. New equipment must
not interfere with existing or emergency equipment. The provider’s radio
frequency (RF) engineer normally determines this first by setting up portable
equipment to conduct a drive by test. An intermodulation study can obtain even
more information. Frequencies used by the providers are regulated by the FCC to
protect users of each allowed spectrum.
A well-done installation is one that imparts the least
amount of disruption to the owner, with few surface repairs, and is completed
on schedule. The conceptual plan can play a huge role in achieving this
success. The following questions should be addressed at a site walkthrough.
Can cable size be reduced?
Smaller cable diameters have a better bending radius for
getting around tight areas and will take up less space within the tanks access
tube. Finally, thinner diameters allow more cables though the same penetration,
in turn requiring fewer penetrations.
Is coax available in a color other than black, or do coax
cables even need to be painted?
The answer is yes and no. There are manufacturers that can
provide coax in colors other than black. However, there may be a long lead-time
and it is more expensive. This extra expense may be more than offset by the
cost for initial and future maintenance painting. However, painting cables is
not necessary and becomes more of an aesthetics issue. More times than not
peeling occurs even when adequate attention is given to surface preparation and
repainting is needed. Additionally, painting is a weather-related item that can
prolong the project, especially during off-season construction.
Can the need for welding be reduced?
Normally this answer is yes. Welding is used to install
service and coax penetrations, coax or antenna mounting brackets and structural
supports in certain situations. Whether shielded metal arc welding (SMAW) or
stud welding, the process will have a negative impact on the tanks existing
paint system. Welding burns the paint around the heated area on both sides.
Finishing the weld by grinding causes hot metal shavings to imbed themselves in
the paint making rust visible in a short period of time. Stud welding is less
detrimental as a means of attachment. Bolting is even better where applicable.
Alternatives also are available for smaller penetrations. Holes for these
penetrations, for single or smaller diameter cables, can be drilled and a
galvanized or non-ferrous threaded coupling installed. Threaded caps then are
screwed to both sides providing a snug seal.
Many of these alternative considerations are related to
painting. As stated earlier, painting can affect the overall scheduling of the
project. Therefore, planning should be made not only to reduce the necessity
for welding but also to limit the need for painting. A good start is to
consider the installation of non-corrosive materials. In addition, when
painting exterior components is necessary, a shop application should be
Even with the addition of telecommunications equipment,
water tanks are still, first and foremost, water storage tanks. The system
operator still will need to maintain them. Therefore, it is most imperative
that safe access is maintained in compliance with applicable OSHA guidelines.
This would include RF exposure training for all employees involved. Exposure
limits are available by contacting the FCC. Providers are required to provide
related information on their equipment. One final concern is making sure all
accesses to the water reservoir are securely locked. If additional security is
required in the facility, provisions can be made for the provider technician to
sign in to obtain a key at each visit. Another alternative is to have a
personal lock installed in a daisy-chain sequence.
We are a society constantly in need of up to the moment
information. We want to feel safe and secure. Wireless communications
technology provides our society this service. This service does come at a
perceived cost for some as the landscape becomes covered in transmission
towers. With the progression of all forms of technology, advances will come
that will provide us with better service and less visual impact. In the
meantime, as water storage tanks continue to pull double duty as makeshift
telecommunications towers, proper planning is essential to maintaining the
integrity of the facility while serving its intended purpose of water storage.