Going with the Flow

Ionce asked the owner of a large plumbing outfit in London what he would do if he were an insurer wishing to avoid flood and sewage back up claims. His answer was instructive: “Insure properties on streets with large trunk mains.” In fact, there are several ways to prevent water damage losses due to sewer and storm water back up, including the use of sump pumps. But certainly an upgraded system of trunk mains should be at the top or near the top of any list of methods for mitigating flood damage due to sewer back-up.

TRUNK MAINS

Our municipalities’ streets are serviced by trunk mains located below grade. Trunk mains are pathways used to transport waste generated by buildings (sewage) and the environment (rainwater). Trunk mains are directly fed by underground connections extending from residential and commercial properties, as well as by storm water grates at street level. Trunk mains are configured to transport two types of effluent: sewage and storm water. Sewage is destined for municipal water treatment facilities through the sanitary system; storm water is released directly into the environment, untreated, through the storm sewer system.

In older subdivisions, it is very likely a single trunk main is used to carry effluent from both the storm and sanitary sewage systems. Where this is the case, chronic sewage back-up often arises after a heavy rainfall because the trunk main simply isn’t large enough to handle the volume of flow. Municipalities remedy this situation by excavating roadways and installing new trunk mains beneath them. When new trunk mains are installed, it is a now a common practice to use dual trunk mains: one trunk main is exclusive to sanitary sewage and one is exclusive to storm water. This dual configuration has proven to be effective in minimizing the potential for sewer back-up occurrences. It should be noted that the first line of defence against floods and sewer back-ups is an upgraded system of trunk mains.

Trunk mains for storm water are larger than those associated with sanitary sewage. Trunk mains associated with sanitary sewage are installed deeper in the ground. Municipalities will install trunk mains according to a rating system based on years — i. e. 20-, 50-or 100-year sys tems. A calculation involving the slope and diameter of the trunk main, in addition to the projected weather patterns for a given area, are used to determine the year rating of the system. For example, a trunk main deemed as being a 20-year system would likely be subjected to only one water-related event — i. e. a rainstorm — over a 20-year period that will exceed its threshold capacity. A 100-year system would be superior in that it is expected to have only one water-related event that would exceed its threshold capacity over a period of a century. Generally, municipalities will opt for the 20-year system, since it is the least expensive way to go. Municipalities do maintain documentation pertaining to trunk main upgrades and record the year ratings. Theoretically, this statistical information might be used to project the frequency and severity of water-related events in a given area over a given time period.

SUMP PUMPS

Sump pumps are mechanical devices that collect water on the exterior of a building. They can cost between $90 and $100 for submersible types, and between $50 and $70 for the column types. They are electrically operated; as such, they are subject to malfunction and power outages. Sump pumps are typically installed inside premises; they are used when soil or topography makes the removal of storm water on the property or adjacent to the building difficult. Sump pumps can also be used in relation to sanitary sewage systems.

Sump pumps operate by collecting water on the exterior of a building (i. e. after the water has passed through weeping tiles installed in the ground adjacent to the building). Collected water is channelled into a pit located at the basement level. A sump pump is equipped with a float that tells it when to start up; typically, this happens when five to 10 gallons of water have been collected. Collected water passes through a vertical pipe, which then directs the water to the exterior of the building and out into the storm sewer connection that feeds the trunk main in the street.

One key component of the sump pump is a check valve — a valve allowing flow in only one direction — designed to prevent storm water effluent from back-flowing or backing up in the opposite direction. Theoretically, sump pumps are designed to move water away from a building against standing water or water that has back-flowed upstream of the check valve. Some plumbing installations are configured to allow back-flowing water to escape through an intentional gap established outside the building, where the connection to the sump pump meets the storm water connection. Escaping water will simply settle back into the ground and be collected by the weeping tiles for a second time.

A properly installed sump pump should not operate more than twice daily under ideal conditions. If a sump pump operates more than two times per day, it is very likely a water back-up situation is imminent. It is a very bad sign indeed if a sump pump operates at all during the winter months.

Since sump pumps rely on electricity to operate, they are prone to failure in the absence of hydro-electric power. Such blackouts can occur, of course, during thunderstorms (when water back-up becomes an issue). There is no prescribed maintenance for sump pumps, and it is entirely possible they might not work at all if they have been dormant for long periods of time. It is recommended that sump pumps be equipped with a back-up power supply — such as a marine battery, for example — that is designed to be exhausted of power and recharged with little or no consequence to performance.

A performance enhancement technique that can be applied to sump pumps is called piggybacking. Piggybacking is a concept that employs two sump pumps that operate on an alternative basis, thereby minimizing the overall level of wear and tear on either unit. A diesel generator is recommended as a back up power supply for piggybacking arrangements.

Water back-flow protection for the sanitary system can be achieved in two ways. The first is the use of gated devices. These devices are capable of reacting to a reversal of flow by isolating the entire plumbing system inside of the building. The gate is configured to remain open as effluent moves away from the building but will close if effluent from the sanitary system moves towards the building. Gated devices are installed in a horizontal configuration at a point where the sanitary main leaves the building. Some non-mechanical devices use a float to maintain a gate in an open position. When rising water (effluent) is noted inside of the pipe, the float reacts by closing the gate and creating a wall between the incoming and outgoing effluent. Also, mechanical devices are available that will electronically close the gate when a reversal of flow is detected. These electronic devices are seldom used because they are expensive and rely on hydro-electric power.

The fact that the gate is normally in the open position allows effluent to pass unrestricted from the premises to the exterior of the building. In contrast, some backwater preventers are designed to remain closed at all times, opening only to allow effluent to move from inside of a building to the exterior. It is against the National Plumbing Code to install devices that are designed to be in a closed configuration on a mainline inside of a building, because in such situations sewer gases cannot be properly vented to the exterior. Sewage back-up situations involving the sanitary system can be caused by tree roots, collapsed sewers and blockage from debris.

A second way to minimize the potential for sewer back-up is to install a sewage ejector. A sewage ejector is located in the basement of building and i
s comprised of a tank, piping and an electrically operated motor. The tank is used to collect the effluent generated by building occupants. When the effluent reaches a specified level inside of the tank, the motor operates to pump the effluent away from the building through a piping arrangement. To reduce the chances of sewage back-up, the piping can be looped above the tank. If the piping arrangement proves to be an insufficient barrier to sewage moving in reverse, the incoming sewage will simply back flow into the tank. The effectiveness of the tank is of course limited if the tank’s volume capacity is less than the volume of sewage back flowing into the building.

There is no definitive way to eliminate the back-flow of sewage and storm water into a building. The strategies available will minimize the potential and consequentially the frequency and severity of these occurrences.

A properly installed sump pump can prove to be beneficial in the management of storm water. But as we know this is a mechanical device dependent on electrical power; as such, it can be subject to mechanical failure, especially after periods of inactivity.

The frequency and severity of sewage back-up inside of a building can be minimized through the use of a back water preventer. The only drawback here is that once the gate of this device is closed, effluent can no longer move away from the building. And so, for example, if a person flushes a toilet inside of the building after the gate is closed, there would be an overflow of effluent generated by the occupants inside of the building. Although this might sound like a bad situation, certainly it is better to have three or four gallons of your own effluent on the floor than to have 50 or 100 gallons of your neighbours’ effluent on your floor!

The real nemesis here is heavy and sudden rain impinging on trunk mains that cannot handle the onslaught. A control point here would be to determine areas where trunk mains have been upgraded versus areas where they have not been upgraded. Having said this, problems still arise in areas where upgraded dual trunk mains have been installed. For example, a sudden and heavy rain overcoming the storm sewers may settle above ground, creating a potential flooding situation from storm water. A sewage back-up situation could arise if this storm water enters a sanitary manhole, thereby entering the sanitary sewage system and overtaxing it.

FLOOD AND SEWAGE BACK-UP

Flood and sewage back-up are often intertwined or married to one another. It should be noted that municipalities require building and property owners to serve as their own ‘flood plains’ and storm water managers. Many commercial buildings can be quite large and situated on properties with sprawling parking lots, thereby creating a lot of water run-off. After a heavy rainfall, it is not uncommon to see standing water on the roof of such buildings (assuming the roof is flat of course) and in the parking lot. Water on top of the roof and in the parking lot will share a common pathway when they leave the property to enter the storm sewer system. Municipalities require storm water to leave properties at a controlled rate so as not to overwhelm the municipal system. This means there could be accumulations of water on rooftops and above ground for extended periods of time, as this water awaits introduction into the storm sewage system. Roof structures are now designed to withstand the added weight of the water loading.