Proper Salt Storage

There are three reasons why a public works agency should construct and properly operate salt storage facilities: economy, availability and convenience.

Salt is the most economical deicing material available. Initial cost is low. Handling and storage are simple. Spreading is fast and easy.

Salt never loses its capability to deice no matter how long it is stored. Rock salt is already between 210 and 320 million years old when it is mined, and carrying over salt on storage piles to the next year or even longer does nothing to diminish its melting power. There is no loss to moisture from the air if salt is stored properly. Salt does not absorb moisture until the humidity reaches 75 percent. Any absorbed moisture will evaporate when the humidity falls below 75 percent. Any resulting thin crust on the surface of the salt is easily broken up.

Salt, however, can be lost to precipitation. Storage piles, whether large or small, should never be left exposed to rain or snow. A permanent under-roof storage facility is best for protecting salt. If this is not possible, then outside piles should be built on impermeable bituminous pads and covered with one of the many types of temporary waterproof materials, such as tarpaulins and polyethylene.

Salt storage piles also must be covered in order to prevent possible detrimental effects to the environment. Runoff should be properly controlled.

WHY STORE SALT PROPERLY?

Covered storage facilities may seem expensive, but the benefits far outweigh the costs in the long run. Salt should be stored in a roofed enclosure in order to:

• Prevent formation of lumpy salt that is difficult to handle with loaders and to move through spreaders,
• Eliminate the possibility of contaminating streams and wells with salt runoff,
• Eliminate salt loss through dissolving and runoff.

ANTI-CAKING ADDITIVES

It's important to keep salt free flowing. To do this, salt producers add anticaking agents. However, if left exposed to precipitation, anti-caking agents can be washed from the outer layer of salt.

HOW MUCH SALT IS NEEDED?

Adequate storage ensures enough salt to fight winter storms, without the problem of arranging emergency shipments throughout the winter months.

There should be storage room for an estimated average winter's salt requirements. Suppliers do their best to maintain deliveries from strategically located stockpiles. However, replenishment of agency salt storage piles becomes more difficult during heavy demand periods. Therefore, it is wise to take early delivery of winter supplies and store the salt until it is needed.

Estimating future salt requirements is tough, but the following guidelines can help.

• Don't order too little on the hope that you will have a mild winter.
• Use the average over the last 5 years to arrive at a reasonable amount to order.
• Be sure to take into account new mileage added to your road or street system.
• Take into account improvements in winter maintenance, such as going to straight salt or adding more salt routes. When anticipating needs, make realistic estimates, but be sure to consider the possibility of unseasonable or prolonged cold spells, with more snow or ice than usual. All of these conditions, often unpredictable, can affect your use of salt.

ORDER SALT EARLY

Order salt by mid summer for summer and fall delivery. Then there is reasonable assurance of getting the material well ahead of winter. Transport problems often become complicated once winter begins and the demand for salt increases. For one thing, numerous orders for salt all at one time place increased demands on the shippers and haulers that deliver salt from production points to stockpile sites and to users.

For another thing, adverse winter weather can slow shipments that arrive by truck and rail. Much of the salt is shipped at least part of the way to the user by water, and freezeups can halt water shipments.

Early ordering and stockpiling of deicing salt ensures a ready supply, with the material delivered during good weather. Plan your salt program early.

SELECT THE RIGHT SITE

The most critical step in providing good storage is selecting the storage site. S-A-L-T-E-D is the key word in picking the right spot:

• Safety
• Accessibility
• Legality
• Tidiness
• Economy
• Drainage

Safety means good visibility for operators, no direct access onto heavily-traveled roads, warning signs at entrances, security fencing, and safety for the surrounding environment.

Accessability means easy access for equipment and delivery trucks, big enough for front-end loaders to maneuver, room for a 20-foot extension of the pad in front of storage buildings, and doors large enough to accommodate equipment.

Legality means complying with local zoning ordinances and any required discharge permits.

Tidiness means making buildings as attractive as possible, keeping buildings well maintained, good housekeeping around the storage site, and screening the storage site with fencing or plantings.

Economics means permanent covered storage and locating the storage site to avoid long distance hauling.

Drainage means good drainage away from the stockpile, sloping bituminous pads (1/4 inch per foot downward from the center), containing runoff, installing retention curbs if necessary, and dispossing of salt brine in conformance with applicable federal and state regulations and local ordinances.

HOW MUCH SPACE WILL IT OCCUPY

There is a limit to how much salt can be stored in a given area. From certain facts about salt's physical characteristics, we can determine in advance how much space a known amount will occupy.

When deicing salt falls freely into a pile, it forms a cone with sides that slope at an angle of 32 degrees, salt's natural angle of repose. The density of deicing salt ranges from 72 pounds per cubic foot loose to 84 pounds compacted. When calculating storage space requirements, use the figure 80 pounds per cubic foot or 2160 pounds per cubic yard. Thus, a ton of salt would require 25 cubic feet of storage space.

PUT IT ON A PAD

Permanent, covered storage is recommended, but some agencies still store salt in outdoor stockpiles on bituminous or concrete pads. This low-cost method provides maximum storage space and easy access. Whether stored inside or outside, salt must be on an impermeable pad, or base.

The pad site should be located away from wells, reservoirs and groundwater sources and situated so that if any drainage inadvertently leaves the storage area it will not affect them.

Concrete pads should be constructed of air-entrained concrete. The pad should be treated with a good quality concrete sealant to prevent spalling.

Slope pads to allow surface water to drain away. Let local conditions control the direction of slope to avoid excessive grading. Minimum slope is two percent. Slopes steeper than five percent may make front-end loaders unstable.

For good drainage, install ditches, pipes and tile where necessary. In some cases, it may be necessary to channel water to a collection point, preferably a specially designed sump area.

COVER THE SALT

If outdoor storage is used, the salt must be properly covered. North American Salt Company has an easy-to-use "stockpile calculator."  Salt stored in bins or on pads may be covered with a suitable waterproof material. Old tires lashed together with rope or cable and placed uniformly over the flexible cover and tied down make a suitable weighting system. Poly-cord nets are also available for tying down covers. Be sure to weight down the base of covers to keep wind from peeling them off salt piles. Timbers, including railroad ties, may be used for that purpose.

For smaller deicing salt stockpiles, the best storage is the ground level storage building. There are as many types of storage building as there are ideas. Many agencies have developed their own particular design.  Buildings may be constructed of railroad ties, pressure-treated timbers, assorted lumber, old bridge timbers and decking, concrete blocks, corrugated sheet metal or various other materials on hand. Prefabricated buildings are also available. Use pressure-treated posts and timbers in pole-type buildings. Make sure all hardware is galvanized. Concrete block buildings should be waterproofed inside. In case of open ends, cover should be supplied for exposed salt.  Areas around the building must be well lighted for safe nighttime operations. On the inside of buildings, place lights to the side and high enough to keep from covering wiring or light fixtures with salt when the building is full.

CONSTRUCTION TIPS

Wind and snow are enemies of storage buildings. Design storage buildings to withstand snow loading of 25 pounds or more per square foot of roof and winds of 80 miles per hour.

The following design considerations should be taken into account to allow for effects of wind and snow:

• Location and Arrangement Use trees to help shield buildings against strong winds and snow, but avoid constructing too close to a tree line, which could cause snow to accumulate around the building.
• Foundation and Anchorage Anchor buildings securely to resist the pushing and lifting forces of wind. Generally, embed strong, pressure-treated poles four feet or more into undisturbed soil or encase in concrete. Use closer pole spacings, heavier poles and deeper embedment for very high pole buildings.
• Joints and Construction Practices Use large enough coated nails and plenty of them. Secure building corners properly, use joint connector devices and fasten rafters properly at plate lines. Whole roof and wall sections may blow off as a unit because a building literally comes apart at the seams when not properly secured. Avoid skimpy knee bracing, poor location of crossties, poorly fastened joints or framing members that are too small. Poor construction causes many building failures.
• Building Materials Don't use lumber with defects such as knots or splits. These may cause supports to fail, especially under the weight of heavy snow. Failure of a weak member puts more load stress on adjacent members, leading to their failure. Use enough nails of the proper type and length in corrugated sheeting to avoid wind damage. Use 90 to 100 screw shank nails per 100 square feet of corrugated steel roofing. One-half to two-thirds of the nail should be embedded in the support member. Use only exterior type plywood for sheathing, gusset plates, braces, doors and other building parts exposed to moisture and weathering.

Many public works agencies have erected dome type structures for salt storage. Most are of wood with concrete base, but some are concrete or thermospheric structures. Other popular designs offer similar advantages and some unique features such as doors at each end for easier access. Choose a design that efficiently uses interior space, with no supporting posts or beams to get in the way. Sloping walls that accommodate the natural angle of repose (32) of deicing salt helps minimize pressure on walls. The shape of the building and proper positioning can lessen wind resistance. Building and bin walls must withstand pushing from front-end loaders and pressure from stored salt.

Exhaust fumes from front-end loaders, and spreader trucks in the case of large under-roof storage, can become obnoxious or hazardous if the storage facility is not properly ventilated. Forced ventilation may be necessary if natural air flow proves insufficient.

FILLING THE BUILDING

The most common method of filling inside storage facilities is to dump salt directly into the building or directly in front of it and push it inside with a front-end loader. Conveyors are sometimes used, particularly the new fast ones. Slingers--short conveyor belts capable of throwing the salt some distance--are used by a few trucking firms, but this is a slow method.

DELIVERY TIPS

Salt is delivered to most storage sites by truck. There are several ways that can speed completion of deliveries.

• Allow enough room for maneuvering. The average length of large trailer trucks that deliver deicing salt is 48 feet and some are 55 feet long.
• Room for turning and backing should be at least twice the length of the longest delivery truck entering storage yards.
• When dumping, trailers may rise 30 feet above the ground level. Allow for this when planning the size of overhang in front of storage buildings and when locating power lines and lights.
• Help truckers find the spot. A hard-to-find storage site may slow salt delivery. Place signs indicating locations of salt storage points and furnish maps for these storage points to truckers.
• Don't keep truckers waiting. If a storage facility is properly designed, a truckload of bulk salt can be unloaded in three or four minutes. But truckers are often kept waiting.
• Shipments generally cannot be unloaded unless a delivery ticket is signed. Make sure someone is available to sign delivery tickets or otherwise accept and authorize deliveries. Delays can be costly.
• Inspect the salt you receive. Salt is tested by suppliers for shipping weight, gradation and correct level of anticaking additive when loaded. If additional tests are necessary, try to make them quickly, using standardized equipment and procedures.
• The same trucks that deliver salt haul other materials. Occasionally foreign objects left in trucks get into salt and can damage spreaders or loaders. If you find foreign objects in your salt, tell both the trucker and the salt supplier. Only if they know of the problem can they take corrective action.

SUMMARY

Good storage of salt is extremely important. Protection of the surrounding environment and the salt itself, and ease of handling salt, are necessary and can be ensured through proper storage.

• Salt should be stored under roof or, if in the open, properly covered.
• All salt, inside or outside, should be stored on an impermeable pad.
• Producers and users of salt should take steps to assure proper salt storage, including proper maintenance of facilities and good housekeeping practices.
• Adequate storage capacity can minimize the need for delivery during critical storm periods and can ensure that salt is available when needed.

Good planning is essential to good storage, and proper storage is a vital part of Sensible Salting.

For further information, you may wish to order highway salt publications from the Salt Institute. Proper storage, of course, means complying with all applicable regulatory standards.  Wisconsin's, for example, are online.  You may want to consider federal stormwater runoff regulations.  Note our disclaimer.

Think you're doing a good job? The Salt Institute annually recognizes agencies for their "Excellence in Storage" through an awards program.

For further information, check with storage building design-builders.

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