By Michael E. Perrault, P.E.

When does a septic system design need to include a pressure distribution leaching system? Prior to the 1995 changes to the Massachusetts Sanitary Code (310CMR 15.00), a pressure distribution system design was not required. The 1995 Code revision did not have any actual design criteria except for a requirement to utilize a pressure distribution system when certain thresholds were reached. The actual design methods were contained in a Department of Environmental Protection (DEP) policy document . This “policy” called Title 5 Pressure Distribution Design Guidance, has been further revised to address the technical questions that were raised by the original policy (Policy#BRP/DWM/WpeP/G02-2, effective May 24, 2002). The more recent revision to the Sanitary Code appears to have added more confusion.

My office recently prepared a septic system repair design for a small manufacturing facility located in an industrial park. The total facility design flow was less than 2,000 gallons per day (GPD). The proposed design included a gravity style distribution to the leaching system, but needed a pump system to bring the flow from the septic tank to the gravity distribution system.

The local health agent reviewing the design plan was of the opinion that the design needed to use a pressure distribution system. Unlike a conventional gravity style system, a pressure distribution system uses a force main pipe from the pump chamber to a larger diameter manifold pipe (can be a central manifold or an end manifold). A series of smaller lateral pipes are fed from the manifold pipe. These lateral pipes have a series of small diameter holes spaced along the length of the lateral pipe. These holes in the lateral pipes thereby spray the pumped effluent under pressure into the leaching system. Pressure distribution systems are more expensive to install as compared to the conventional gravity systems.

When the health agent first questioned the design, I explained that the Sanitary Code, under 310CMR15.254(1) allowed for dosing pumps for systems with a total design flow less than 2,000 GPD provided that there is a gravity distribution system. The health agent did not agree with my reading of the Code and contacted the regional office of the DEP to get an “official” opinion. The DEP engineer actually sent a fax that stated that all pumped systems had to be pressure dosed and attached the section of the Code related to pressuring distribution (310CMR15.254(2)). Once I was given a copy of this DEP fax document, I contacted the same engineer at the DEP and suggested that he not skip to the second paragraph in the Code section 15.254 that he cited, but start at the first item that clearly allows for pump dosing to a gravity distribution system for design flows under 2,000 GPD.

I explained that pressure distribution systems, while an option, are not typically used on small systems. For example, if an existing small single family house, under a repair design, needed to have a slightly elevated leaching system due to high groundwater, and the plumbing location prohibited a total gravity system, then, under the “all systems using a pump” opinion, this property would be forced to have a pressure distribution leaching system.

I then went through the appropriate Code section wording with the DEP engineer and discussed the differences between the two paragraphs. The DEP engineer then issued a new fax to the health agent correcting the earlier fax and noting that the pumped system design was allowed and that “pumped” systems without pressure distribution is acceptable provided that they meet the Code criteria.

At that point, the health agent, under the authority of the Board of Health, approved the design plan and issued the construction permit.

If I had not insisted that the DEP engineer had been incorrect, my client would have had to pay for an expensive pressure distribution system.

An engineer who does not have a good working knowledge of the Massachusetts Sanitary Code as well as the experience in both pump dosing and pressure distribution system design would not have questioned the health agent’s opinion and definitely would not question a DEP engineer.

There is no substitution for experience.

I recently heard about an example of how experience impacted a pressure distribution system project. A local contractor, was installing a pressure distribution system (not one of my designs, thank you) when the local health agent had him tear out the manifold and lateral connections. The design plan, according to my source, did not detail how these connections were to have been made and the contractor built what he thought was correct. A more experienced design engineer would have had that detail presented on his plan, since that piping connection is one of the more critical components of the pressure distribution system. This lack of detail not only resulted in more work and expense for the contractor but delayed the completion of the system construction.

This is one of my typical pressure distribution system design details.

Clients do not appreciate an engineer gaining on-the-job training on their projects.

While there are some people that base their decision to hire an engineer on the lowest price, the smart consumer looks at experience, reputation and integrity in combination with the cost to establish the “value” of a project.

For those non-city folks that rely on a septic system instead of a city sewer, having a failed septic system is a major headache. It is amazing to hear the horror stories, as well as, the vast amount of mis-information being circulated about septic tanks, leaching systems, septic system repair costs, etc.

With over 30 years of experience in the design engineering of subsurface sewage disposal systems, commonly called “Septic Systems”, I’ve prepared this easy to follow 12 step outline as a guide in replacing a Septic System. There is one very important pre-qualification before you start, you need to retain a qualified professional civil engineer or registered sanitarian. I have to stress the word “qualified”, unless you want to enjoy being the leading role in the next release of “Horror Stories from the Leaching Field”. Take the time to do a little homework, such as going to your local Health Board office and asking what civil engineers are designing septic systems in your Town and whose design plans are typically approved without having to be sent back for corrections and revisions. Once you get a few names, do a little research on the web, Better Business Bureau, etc. Then you should contact these civil engineers and talk with them about your problem septic system and ask for a written proposal that will outline the tasks and costs. Just like you wouldn’t eat a rotten piece of fruit, if you don’t have a good feeling about a particular civil engineer, then do not hire him!

Now you are ready to go forward with the 12 steps.

1. A test application is submitted to the local Health office (some States, like Rhode Island, control the testing, etc. so the application would have to go to a State agency.)
2. You hire an excavation contractor to dig the test holes. If you do not know a local excavating contractor, then your engineer should provide you with a few contact names. (FYI - by hiring a contractor for the test holes, you are not making a commitment or obligation to hire him to install the replacement septic system.) This excavation contractor will need to follow local / state safety regulations (such as obtaining a “dig-safe” number and having the underground electric, telephone, CATV, gas, etc. located before the test holes are dug.
3. The engineer coordinates with the Health Agent, excavating contractor and you (the client) to set the testing date.
4. The engineer performs the official deep hole soil evaluation and associated “perc” percolation testing. Soil samples may have to be obtained and taken to a lab for further testing. The engineer prepares the official forms (soil logs) and submits a copy to the local health office and to you.
5. The engineer performs a limited existing conditions topographic “topo” survey of your property where the replacement septic system is proposed. (FYI - Unless you have a small lot or do not know where your lot lines and/or lot corners are located, you typically would not need to have your property line surveyed.)
6. The engineer uses the results of the soil evaluation, perc. testing, topo survey in combination with the current and anticipated building use (number of bedrooms, garbage grinder, etc.) and State / Local Sanitary Codes to design a replacement septic system for your property.
7. The formal design plans (with the original seal and signature of the professional civil engineer) and construction permit application are submitted to the local Health Agency for review and approval.
8. The engineer provides you with additional copies of the design plans for you to submit to licensed contractors to obtain a price quote / bid.
9. Once you have selected a contractor, he coordinates with the local Health Agency (to obtain the permit) and the engineer, prior to starting the work.
10. The Health Agent visits the construction site as the work progresses to observe and confirm Code compliance.
11. The engineer, in most States, must visit the construction site to observe the critical construction stages, make measurements and prepare a formal plan showing the completed “as-built” septic system. The engineer submits a copy of this plan to you and the local Health Agency along with a signed compliance statement. Some States also require the contractor to sign and submit a compliance statement.
12. The local Health Agency reviews the “as-built” plan, etc. and issues a “Certificate of Compliance” which signifies that the replacement septic system as installed is in compliance with the State and Local Sanitary Code.

One other item, if you have wetlands on or near your property and the anticipated work will be within 100 ft. of these wetlands, then additional permitting will be necessary before you can have the replacement septic system installed.