Section 58.01.08.544 - GENERAL DESIGN OF FINISHED WATER STORAGEThe materials and designs used for finished water storage structures must provide stability and durability as well as protect the quality of the stored water. Finished water storage structures must be designed to maintain water circulation and prevent water stagnation. Steel structures and facilities such as steel tanks, standpipes, reservoirs, and elevated tanks must be designed and constructed in accordance with applicable AWWA Standards, incorporated by reference into these rules at Subsection 002.01. Other materials of construction are acceptable when properly designed to meet the requirements of Section 544.
01.Sizing and Isolation Requirements. a. Storage facilities must have sufficient capacity, as determined from engineering studies that consider peak flows, fire flow capacity, and analysis of the need for various components of finished storage as defined under the term "Components of Finished Water Storage" in Section 003. The requirement for storage may be reduced when the source and treatment facilities have sufficient capacity with standby power to supply peak demands of the PWS.b. All storage structures which provide pressure directly to the distribution system, such as elevated storage structures or ground level storage structures with associated pumping systems, must be designed so they can be isolated and drained for cleaning or maintenance without causing a loss of pressure in the distribution system.02.Location. Storage facilities must be located in a manner that protects against contamination, ensures structural stability, protects against flooding, and provides year-round access by vehicles and equipment needed for repair and maintenance.a. If the bottom elevation of a storage reservoir must be below normal ground surface, it must be placed above the seasonal high groundwater table. The top of a partially buried storage structure may not be less than two (2) feet above normal ground surface.b. Minimum separation distances from storage facilities must meet the following requirements: Minimum Separation Distances From Storage Facilities (feet) |
Feature of Concern | Storage Facility Type |
| Below Ground | Partially Buried | Ground Level | Above Ground |
Non-Potable Pipelines | 50 | 50 | | |
Non-Potable Pipelines Constructed of Water Class Pipe | 20 | 20 | | |
Standing Water | 50 | 50 | 50 | |
Possible Sources of Contamination | 50 | 50 | 20 | 20 |
Nearest Property Line | 50 | 50 | 20 | 20 |
Municipal or Industrial Wastewater Treatment Plant | 500 | 500 | 500 | 500 |
Land Which is Spray Irrigated With Wastewater or Used for Sludge Disposal | 500 | 500 | 500 | 500 |
03.Protection from Contamination. All finished water storage structures must have suitable watertight roofs which exclude birds, animals, insects, and excessive dust. The installation of appurtenances, such as antennas, must be done in a manner that ensures no damage to the tank, coatings or water quality, or corrects any damage that occurred.04.Protection from Trespassers. Fencing, locks on access manholes, and other necessary precautions must be provided to prevent trespassing, vandalism, and sabotage.05.Drains. No drain on a water storage structure may have a direct connection to a sewer or storm drain. The design must allow draining the storage facility for cleaning or maintenance without causing loss of pressure in the distribution system.06.Overflow. Overflow pipes of any storage structure or facility must discharge to daylight in a way that will preclude the possibility of backflow to the reservoir and, where practical, be provided with an expanded metal screen installed within the pipe that will exclude rodents and deter vandalism. The overflow pipe must be of sufficient diameter to permit waste of water in excess of the filling rate and be designed to mitigate blockage or freezing (see Subsection 544.11). The overflow must discharge over a drainage inlet structure or a splash plate and, when practical, discharge at an elevation between twelve (12) and twenty-four (24) inches above the receiving surface. a. When an internal overflow pipe is used on above-ground tanks, it must be located in the access tube.b. The overflow for ground-level, partially buried, or below-ground storage structures or facilities must have a vertical section of pipe at least two (2) pipe diameters in length and be screened with a twenty-four (24) mesh non-corrodible screen installed within the pipe when practical or an expanded metal screen installed within the pipe plus a weighted flapper valve or check unless otherwise approved by the Department.07.Access. Finished water storage structures must be designed with reasonably convenient access to the interior for cleaning and maintenance. At least two (2) manholes will be provided above the waterline at each water compartment where space permits, as determined by the Department. One (1) manhole may be allowed on smaller tanks on a case-by-case basis.a. The following access requirements apply to above-ground and ground-level storage structures. Each access manhole must be framed a minimum of four (4) inches above the surface of the roof at the opening. The actual height above the surface of the roof must be sufficient to prevent incidental contamination from snow accumulation, storm water runoff or accumulation, irrigation water, or other potential sources of contamination.b. The following access requirements apply to, partially buried or below-ground storage structures. Each access manhole must be elevated a minimum of twenty-four (24) inches above the surface of the roof or the ground level, whichever is higher. The actual height above the surface of the roof or the ground level must be sufficient to prevent incidental contamination from snow accumulation, storm water runoff or accumulation, irrigation water, or other potential sources of contamination.c. Each manhole must be fitted with a solid water tight cover designed to prevent the entrance of contaminants. Each cover may be hinged only on one (1) side and have a locking device. Unless otherwise approved by the Department based, each cover will have a framed opening with the lid extending down around the frame at least two (2) inches, and the frame will be at least four (4) inches high.08.Vents. Finished water storage structures must be vented. The overflow pipe may not be considered a vent. Open construction between the sidewall and roof is not permissible. Vents must:a. Prevent the entrance of surface water and rainwater and extend twelve (12) inches above the roof.b. Exclude birds and animals.c. Exclude insects and dust, as much as this function can be made compatible with effective venting and be designed to mitigate blockage or freezing (see Subsection 544.11).d. On ground-level, partially buried, or below-ground structures, open downward with the opening at least twenty-four (24) inches above the roof or the ground level and covered with twenty-four (24) mesh non-corrodible screen or similar non-corrodible screen. The screen is to be installed within the pipe at a location least susceptible to vandalism.e. On above-ground tanks and standpipes, open downward, and be fitted with twenty-four (24) mesh or similar non-corrodible screen.09.Roof and Sidewall. The roof and sidewalls of all water storage structures must be watertight with no openings except properly constructed vents, manholes, overflows, risers, drains, pump mountings, control ports, or piping for inflow and outflow. Particular attention is to be given to the sealing of roof structures which are not integral to the tank body.a. Any pipes running through the roof or sidewall of a metal storage structure must be welded, or properly gasketed. In concrete tanks, these pipes must be connected to standard wall castings which were poured in place during the forming of the concrete.b. Openings in the roof of a storage structure designed to accommodate control apparatus or pump columns must be curbed and sleeved with proper additional shielding to prevent contamination from surface or floor drainage.c. The roof of the storage structure must be sloped to facilitate drainage. Downspout pipes may not enter or pass through the reservoir. Parapets, or similar construction which tends to hold water and snow on the roof, will not be approved unless adequate waterproofing and drainage are provided.d. Reservoirs with pre-cast concrete roof structures must be made watertight with the use of a waterproof membrane or similar product.10.Construction Materials. Materials used in storage facility construction must meet the requirements for water contact surfaces set forth in Subsection 501.01. Porous materials such as wood or concrete block are not acceptable for use in storage construction.11.Protection from Freezing. Finished water storage structures and their appurtenances, especially the riser pipes, overflows, and vents, must be designed to prevent freezing.12.Internal Catwalk. Every catwalk over finished water in a storage structure must have a solid floor with sealed raised edges, designed to prevent contamination.13.Silt Stops. Removable silt stops must be provided to prevent sediment from entering the reservoir discharge pipe.14.Grading. The area surrounding a ground-level, partially buried, or below-ground structures must be graded in a manner that will prevent surface water from standing.15.Coatings and Cathodic Protection. Proper protection must be given to metal surfaces by paints or other protective coatings, by cathodic protective devices, or by both.16.Disinfection. Storage facilities must be disinfected in accordance with AWWA Standard C652, incorporated by reference into these rules at Subsection 002.01. Two (2) or more successive sets of samples, taken at twenty-four (24) hour intervals, must indicate microbiologically satisfactory water before the facility is placed into operation.17.Abandonment. All unused subsurface storage tanks must be removed and backfilled, or abandoned by extracting residual fluids and filling the structure with sand or fine gravel.Idaho Admin. Code r. 58.01.08.544