All stormwater BMP’s will require maintenance at some time or time interval. Long-term maintenance costs and maintainability are very important considerations. Here are some other things you should consider when discussing maintenance of your stormwater filtration system.
1. Evaluate availability of maintenance contracting.
It is the nature of filters to occlude with captured TSS, hence maintenance is required. Acceptance of all systems should be coupled with a maintenance contract by a professional maintenance provider. Does the manufacturer stand behind the product and offer to provide maintenance?
2. Maintenance frequency varies from site to site.
Typically, if maintenance is needed more than once a year, the project will cost more over its lifetime than if the facility had been upsized to extend the maintenance cycle. Conversely, designing for maintenance intervals greater than one year may result in higher initial costs that may never be recovered by lower lifecycle maintenance costs.
3. Maintenance costs are critical. If a person states a cost, ask if they will sign a contract to do that.
Frequently, costs are understated because they do not include mobilization, heavy equipment rental, and mileage costs. Consult with a local maintenance provider when in doubt.
4. Facility access will always be needed. Even manholes are equipped for access.
Stormwater filtration systems will need to be accessed for cleaning media, washing sidewalls, repairs, media installation, and facility inspection. Review plans for height restriction, ventilation, and extraction ports. Make sure the facility is also accessible by the required equipment.
5. Working inside can be problematic.
Evaluate the complexity of the internal components and whether they pose trip hazards or make access by suction hoses difficult. Is the operator working in standing water? If you have a set of plans or photos of an existing unit, seek the opinion of people who perform the maintenance rather than rely upon the generalities of the manufacturer.
6. Check the weight of the media.
How is the media being extracted? How much would a media “vessel” that is full of sediment and has a high water content weigh? Is it practical that it be removed or lifted? As a rule of thumb, use a minimum of 70 lbs/ft3 for a lightweight media such as perlite (weighs about 5 lbs/ft3 when fresh and dry). Some media such as sand can result in cartridges weighing in excess of 300 pounds.
In addition, once media becomes clogged with sediments, it can become firmly lodged in the filter body. Typically, the spent media needs to be sucked, shaken, or dug out of the filter body, as it rarely falls from the filter body under its own weight.
7. Standing water is costly and expensive to remove.
What is the volume of water if the system is drained down and what is the volume of water if the filters are fouled? Does the system cause standing water in the upstream pipe network?