Commercial System Design: Designing for Management

O&M needs to include all aspects of the system and should be outlined in a detailed plan for the owner

Commercial System Design: Designing for Management

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Due to the complexity of many commercial systems, an operating permit at a local or state level is advisable to be certain that system management is occurring. Even if an operating permit is not required, system management should be included in the O&M manual along with the design.

Installers need to educate the owner about the value added in performance and longevity. Both the user/owner of the system and the service provider need to receive information about how to use and maintain the system. Often the user is not properly educated although they directly influence what goes down the drain and can have a dramatic influence on the performance of the system. For example, if a restaurant has a deep fat fryer, are they properly recycling their grease?

To ensure proper functioning of the entire septic system, commercial systems included, it is important to educate the users of the system. The proper disposal of hazardous materials and knowledge of what should and should not be disposed of in the treatment system are essential to its successful operation. The operation and management plan typically includes a discussion of the proper use of the system and this portion of the manual must be provided to builders and homeowners. An annual visit with the system owner is valuable to discuss issues about usage, waste strength, non-biodegradables, landscaping, etc. If there are any seasonal operational changes they should be addressed in the manual, as temperature changes affect the performance of many systems and seasonal operation changes may be necessary to maintain temperature and allow for access to equipment. Change in flow over the season can affect system operation. Considering developing a management plan at for the owner.

Flow verification
All management of commercial systems should include determining the actual flow to the system and then comparing this to the design flow. Automated systems with telemetry are preferred, as they provide daily up-to-date flow information for the system’s service provider and user.

If this is not available, flows can be calculated from water meters, running time clocks and event counters at the time of system evaluation. If biannual readings are taken, it is advisable to note if the average flow over this time is greater than 70 percent of the design flow. If flows are greater than 70 percent of design, flow measurement frequencies shall be increased to determine if the system is being overused.

Collection system
The management should cover all aspects of the collection system. Long-term management requires access to the pipe. If there’s a problem, this access is used to clean the piping. These clean-outs can be located either near the building or near the tank. The key for operating the building sewer is to ensure that effluent drains through the pipe by preventing buildup, plugging and freezing. If septic tank effluent grinder/pressure septic tanks, grinder pump stations, or individual septic tanks at each user’s location are utilized in the design, operation and maintenance for those tanks needs to occur. If the collection system is proprietary in nature, the manufacturer must be consulted to determine the required management of the system, including pump replacement, screen cleaning and tank/sump cleaning frequencies. The O&M manual should include provisions in the case of line blockage, such as location of clean-outs and cleaning with a jetter. At a frequency of no less than annually, any sewer manholes or lift stations should be evaluated to ensure proper operation and check for infiltration into the system. At this time all alarm systems and electrical components should be tested. Maintenance schedules developed for the above sewer main and lift station activities should clearly note when and/or how often each activity will take place.

Grease interceptors
Removal of solids through use of a grease trap and periodic pumping protects downstream components that will malfunction if bypass occurs. Access for maintenance is critical for optimum performance because of the need for regularly scheduled pumping of the component. As part of the collection system and overall system operation, grease interceptors should be evaluated quarterly at a minimum to determine if cleaning or pumping is needed.

Septic tank
If a septic tank is operating properly, solids are retained and take up increasingly more volume. At some time, they must be removed. (If there is little accumulation of solids, either the property is extremely conservative with water use and waste generation or there is a problem causing solids to pass through the tank.)

When there is little clear zone left, proper solids separation will no longer occur, detention time for settling is further reduced, and solids will wash out of the tank, eventually clogging the soil treatment area and causing system failure. On commercial properties with domestic waste, sludge and scum levels in septic tanks should be tested once or twice per year. If the waste is nondomestic waste, due to the potential for high-strength waste, these septic tanks shall be evaluated biannually or quarterly for buildup of sludge and scum. If an effluent screen is present in the septic or pump tank, the screen should be evaluated and cleaned based on the manufacturer’s recommendations and adjusted based on the flow and usage from the facility. In some situations, with commercial properties, the septic tank effluent may also be sampled to ensure that the septic tank is meeting domestic strength levels.

Advanced pretreatment units
When servicing advanced treatment units, the management plan from the product manufacturer should be followed. The operating permit may require effluent sampling, and if so, the plan should indicate where the sample should be collected. Monitoring is necessary to determine relative performance of the system. Both field tests and lab tests may be used. Field tests should be routinely employed to monitor performance at the time of system maintenance. Simple field tests should be used to the greatest extent practical to monitor system performance. The most basic parameters that provide information related to performance and can be monitored in the field are dissolved oxygen, pH and temperature. Grab or composite wastewater samples may be used to collect representative samples. Specific laboratory tests are performed to measure parameters of interest to determine if compliance limits contained in the operating permit are met. Laboratory tests for BOD, TSS, O&G, fecal coliform bacteria and nitrogen may be needed.

Soil treatment systems
During the routine evaluation of the tanks and advanced treatment units, the soil treatment area should also be evaluated. The management plan should include the location of all inspection ports and clean-outs, and list frequency of assessment and cleaning as appropriate. At a minimum, the soil treatment area should be evaluated at the time of evaluation of grease traps and/or septic tanks. The amount of ponding in the soil dispersal system should be measured yearly. The distal heights on pressure distribution systems can be verified and laterals cleaned or jetted as needed.

The management plan should include a schedule for mowing, planting, weeding, and other landscape care and maintenance. Evaluation to verify that surface water is not collecting on the soil treatment system site, and verification that the site is not being driven on or compacted in any other manner should be done on a regular basis. Also, with commercial sites consider fencing off or barricading the tanks, pretreatment units and soil treatment area to prevent traffic, provide extra safety and prevent vandalism. 

About the author
Sara Heger, Ph.D., is an engineer, researcher and instructor in the Onsite Sewage Treatment Program in the Water Resources Center at the University of Minnesota. She presents at many local and national training events regarding the design, installation and management of septic systems and related research. Heger is education chair of the Minnesota Onsite Wastewater Association (MOWA) and the National Onsite Wastewater Recycling Association (NOWRA), and serves on the NSF International Committee on Wastewater Treatment Systems. Send her questions about septic system maintenance and operation by email to

This article is part of a series on the design and maintenance of commercial septic systems:


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