Sanitary catch basins were historically used in older communities to help manage wastewater from properties before it entered the municipal sewer system. Unlike typical catch basins designed for stormwater management, dewatering parking areas, or controlling rainwater in landscaped regions, sanitary catch basins play a critical role in separating contaminants before the wastewater reaches a treatment plant. While these systems are now largely obsolete due to modern sewer designs, they can still be found in older buildings. Inspectors should document their presence. Further inspection is optional and lies outside the scope of the ComSOP.
Sewer System Differences
Separate Sanitary Sewer
Modern municipal sewer systems utilize two separate pipes: one for stormwater and another for sanitary waste. Hence, this type of sewer system is referred to as a separate sanitary sewer. Sanitary waste is located inside what is commonly referred to as the “public sewer.” Only the pipe that contains the sanitary waste is sent to the treatment plant. Separate sanitary sewer systems do not require catch basins since the treatment facilities can effectively treat the contaminants from the sanitary waste.
Separate sanitary sewer in dry weather (Source: EPA.gov)
Separate sanitary sewer in wet weather (Source: EPA.gov)
Combined Sewer System
Most modern communities use separate sanitary sewer systems, but some older communities use combined sewer systems. In a combined sewer system, both stormwater and wastewater flow through the same pipes to the treatment plant. During heavy rainfall, overflow points may be triggered and release untreated or partially treated wastewater and stormwater into nearby water bodies.
Older communities had wastewater treatment plants that lacked the capacity to effectively treat certain contaminants (i.e., phosphates, lye, and fats, oils, and grease [FOG]) from properties. To address this, treatment plants implemented sanitary catch basins at individual properties. These catch basins act as a buffer to help manage sanitary waste before it enters the public sewer system. Combined sewer systems and their sanitary catch basin counterparts are typically found at residential and multi-family properties in communities built before 1960.
Combined sewer system in dry weather (Source: EPA.gov)
Combined sewer system in wet weather (Source: EPA.gov)
Purpose and Design of Sanitary Catch Basins
The primary purpose of a sanitary catch basin is to separate some of the sanitary waste into a controlled vessel before the wastewater enters the municipal sanitary sewer system and eventually reaches the treatment plant. Waste that is not toilet- or urinal-based will flow into this catch basin. The solids and liquids will separate. The liquids will flow into the lateral, while the solids remain. The reason for this is to allow periodic cleaning and maintenance of the solids that might accumulate in this catch basin.
A catch basin can be connected to stormwater drainage systems, like roof drains, as well as certain topographical drainage features, such as patio drains. But the most common design is to control and contain only the building sewer as it exits the building.
These basins are typically located near buildings in landscaped areas, parking lots, and other places that are not affected by vehicle traffic. Constructed from masonry, they are about 4 feet in diameter and covered with a cast-iron lid. Occasionally, they can also be found in basements and other interior locations. Although the catch basin is part of the building’s sanitary waste system, it is not connected to any solid waste devices, such as toilets, showers, or other brown/black water systems.
A brown/black water system refers to solid waste, while a gray water system involves only liquid waste. The most common types of liquid waste draining into the catch basin are gray water from laundry and kitchen activities. This is why catch basins are often situated on the side of the building that is closest to laundry and kitchen discharge points.
Inside the catch basin, there are at least two pipes. One pipe is positioned higher than the other: the higher pipe receives discharge from the building, while the lower pipe leads to the municipal sewer. There may be a sump depth of 2 to 3 feet beneath the lower pipe where waste can accumulate. This depth is usually determined by the volume of discharge coming from the building.
What a Catch Basin Lid Might Look Like
Catch basin lids are typically stamped with the word “Sewerage.” However, you may still find lids with this marking as part of other sewer systems. Be aware of the prominence of combined sewer systems in your service area, and consider the age of the community that the subject property is in to adequately determine the type of sewer system present. In the U.S., these systems are primarily found in the Northeast and around the Great Lakes, while in Canada, they exist in cities like Vancouver, Hamilton, Toronto, Winnipeg, and Edmonton, among others.
View of a catch basin lid
Catch basin located at the rear of a multi-family property in the open space
Catch basin located on the floor of a partially finished basement
Inspecting Sanitary Catch Basins
Visual Inspection
Commercial property inspectors should examine the exterior of the catch basin. This includes assessing the condition of the cast-iron lid, and looking for any irregularities in the ground surrounding the basin. Depressions around the basin could indicate a potential structural failure. This would raise concerns, and inspectors should recommend further investigation. Note any visual inspection limitation in your report as well.
Inspectors are not required to open the lids to these catch basins, nor ever enter them. Some inspectors may choose to open the lids. This should be done with an abundance of caution. If choosing to do so, the inspector could visually inspect the integrity of the interior walls of the catch basin. These are typically made of brick or some form of masonry, and erosion to the walls or damage to the masonry may cause a collapse. At no point should the inspector ever walk away from an open catch basin lid, leave it unattended, or enter a catch basin.
After reviewing the structure, the inspector should observe the water levels. There will be at least two different pipes in these catch basins. One pipe discharges from the building, and the other pipe exits toward the lateral. The building discharge should be higher in the interior elevation than the lateral discharge pipe. If the building pipe is submerged or under water, then there is a good chance the discharge from the building is backing up into that pipe and the building.
Note: These catch basins are designed to be regularly cleaned. If the water levels are incorrect, maintenance will be necessary.
Catch basin’s interior structure
Blocked catch basin lid
Optional Verification Testing
Most public sewers have undergone design updates, making catch basins unnecessary, in most cases. Some inspectors may check whether these basins are still in use. To do this, they can run water from a lower fixture, such as from a laundry room, kitchen, or utility sink, and observe the interior of the catch basin. If water flows into it, this indicates that it is still in use. If no water is observed, then the catch basin is no longer operational and can be removed from the building’s sewer system. This operational test is not required by the ComSOP and should only be performed if it can be done safely.
The main reasoning behind verifying whether the catch basin is operational is to determine whether the unit is decommissioned. Since many older treatment systems have been updated to separate sanitary sewer systems, these sanitary catch basins may be abandoned and can be removed from the plumbing system.
Conclusion
Sanitary catch basins were once crucial components of the waste discharge systems in buildings. Although their prevalence has decreased over time, they can still be found at some properties today. Inspectors can infer that if a catch basin lid reads “Sewerage” at any residential or multi-family property in an older community, it is likely a combined sewer system. However, you may still find lids with this marking as part of other sewer systems. Be aware of the prominence of combined sewer systems in your service area to accurately determine the type of sewer system present.
Inspectors should be knowledgeable about these basins and how to evaluate this aspect of the plumbing system. In most cases, inspectors should recommend that clients consider upgrading their building’s waste discharge system to a more modern option that requires less maintenance. Such upgrades can help mitigate certain hazards associated with such an existing system, especially for people who may come into contact with it during routine maintenance.
Additional Resources for Commercial Property Inspectors: