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
• Location of antennas.
Location of Base Transmission Cabinets
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 containment system.
Underground Utility Routing
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?
Routing of Coaxial Cables
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 installation.
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.
Approximate Location of Penetrations
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.
Location of Antennas
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.
Planning for Success
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 considered.
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.