Why Cover Salt?
The Audit Commission Report (1988) on Improving Highway Maintenance considered the savings that can be made by covering road salt by eliminating leaching and reducing overspreading. It quoted TRL (Transport Research Laboratory) work that estimates leaching losses at 0.25% per inch of rainfall per annum. For the UK this can equate to up to 6% salt loss each year.
From the Roads Liaison Group publication of 2005, “Well Maintained Highways”:
“The environmental effects of highway maintenance depots can be particularly significant in the case of Winter Service where operations will inevitably involve unusual hours or working. Every effort should be made to minimise the environmental intrusion of depots and, so far as is practicable, the effect of Winter Service operations.
A significant contribution to this can be made by providing covered storage for all vehicle, equipment and materials, which can also reduce waste and maintenance problems. Salt barns can help in maintaining low moisture content, preventing leaching and easing handling and are strongly recommended where additives are used.”
The following minimum spread rates of salt are suggested for different operational scenarios.
Precautionary Salting
Salt stored under cover 10g/m2
Salt stored in the open 15g to 20g/m2
Proper covered storage of salt treated with ABPs (Agricultural By-Products) such as Safecote will eliminate any concerns over increased BOD (Biological Oxygen Demand) in the depot effluent and allow perhaps even lower rates of spread to be achieved consistently.
From the National Salting Research Groups Best Practice Guidance for Spreading Salt (March 2005):
“If salt is stored unprotected in the open then target spread rates will not be achieved.
The cost of salting operations and damage to the environment will increase because distribution to the road surface will not be controlled effectively.”
From the Environment Agency publication PPG10, Pollution Prevention Guidelines, Highway Depots:
“The environmental impact of rock salt is well documented and providing the application rates specified within the highway authority guidelines are followed, the use of salt on highways is unlikely to lead to levels in the water environment that could affect aquatic life or drinking water supplies. However because of the large quantities stored, there is a risk of pollution of rivers and groundwaters, due to run-off from rock salt stockpiles. This can come from the salt and the sodium ferrocyanide anti-caking agent that is often added to it.”
PPG10 also recommends that salt stores are roofed and that measures are taken to ensure that salt from the store is not allowed to encroach onto the open yard.
These statements neatly capture why a purpose built salt storage facility is so important in delivering effective winter service whilst minimising the environmental impact of the operation. Precautionary application rates can be halved to the nationally recommended level of 10g/m2 bringing a financial saving which can pay back the investment in a few years.