jar546
CBO
Many of you probably do not know this about me, but years ago, when I lived in Pennsylvania, I performed thousands of private onlot sewage inspections. I was not a Sewage Enforcement Officer, also known as an SEO, but I was a PSMA Certified Inspector who knew Title 25, Chapter 73, inside and out. I was heavily involved with the Pennsylvania Septage Management Association, PSMA, and even served as the President of Region 5 at one point. I spent a lot of time refining procedures, helping with legislative efforts, and pushing for better educational standards. Let’s just say, when it comes to septic systems, I know my ****. Literally. 
Now working in Florida as a Building Official, I find it surprising how little attention septic systems sometimes get during plan review and inspections when changes are made to a building. This article is meant to educate inspectors and plans examiners on the critical importance of understanding how a building project can impact an existing septic system, using Pennsylvania's extremely detailed Chapter 73 as a backdrop.
Pennsylvania requires that onlot systems be sited in undisturbed soil, at appropriate slopes, and with precise isolation distances to protect water supplies and surface waters. Systems cannot discharge untreated sewage anywhere but into properly constructed subsurface absorption areas or permitted holding tanks.
Critical minimum horizontal isolation distances include:
When acceptable soil conditions exist:
Understanding Title 25 Chapter 73 is about more than just passing a test or checking a box. It is about doing the job the right way to protect public health, protect the environment, and protect property owners from huge expenses later.
If you made it this far through the article, congratulations, you now know a little more about why I always say I know my ****. I earned that the hard way, one excavation and one inspection at a time.
Now working in Florida as a Building Official, I find it surprising how little attention septic systems sometimes get during plan review and inspections when changes are made to a building. This article is meant to educate inspectors and plans examiners on the critical importance of understanding how a building project can impact an existing septic system, using Pennsylvania's extremely detailed Chapter 73 as a backdrop.
Understanding the Scope of Chapter 73
Chapter 73 sets the technical standards for individual and community onlot sewage treatment systems. It covers everything from site testing to tank specifications to how absorption areas must be built. It applies to anyone designing, permitting, installing, or inspecting a private sewage system.Pennsylvania requires that onlot systems be sited in undisturbed soil, at appropriate slopes, and with precise isolation distances to protect water supplies and surface waters. Systems cannot discharge untreated sewage anywhere but into properly constructed subsurface absorption areas or permitted holding tanks.
Site Investigation and Isolation Distances
Before designing a system, soil testing is mandatory. The site must be investigated by excavating test pits to identify limiting zones like high water tables or bedrock. This is not optional.Critical minimum horizontal isolation distances include:
- Septic tank to private well: 50 feet minimum
- Drainfield to private well: 100 feet minimum
- System components to property lines, buildings, and driveways: 10 feet minimum
- Drainfield to streams, lakes, or surface water: 50 feet minimum
Soil Testing and Percolation Tests
If the seasonal high water table is within 20 inches of the surface, a conventional system is not allowed unless an approved alternate or experimental system is used.When acceptable soil conditions exist:
- Six or more percolation tests must be conducted evenly across the proposed absorption area.
- The tests must follow strict procedures, including presoaking and timed measurements.
- Percolation rates are averaged to size the drainfield.
Treatment Tanks and Building Sewers
Septic tanks in Pennsylvania must meet the following:- Minimum size treatment tank: 900 gallons (3 bedroom), 1250 gallons (4 bedroom), 1500 gallons (5 bedroom).
- Standard residential flow assumption: 400 gallons per day for up to three bedrooms, plus 100 gallons for each additional bedroom.
- The final ten feet of the building sewer before the septic tank must not exceed a slope of 1/8 inch per foot.
- If you have more than 1/8 inch per foot slope in the last ten feet, solids can pile up at the tank inlet instead of settling properly inside the tank.
Additions and Renovations
Anytime a home adds a bedroom, the septic system must be re-evaluated.- A three-bedroom system designed for 400 gallons per day becomes undersized if a fourth bedroom is added, which pushes the design flow to 500 gallons per day.
- This triggers a possible need to install a larger tank and expand the absorption area.
- Even if the tank is large enough, the drainfield must be evaluated against the new loading rate.
Advanced Systems
Chapter 73 also addresses:- Elevated sand mounds for sites with shallow limiting zones.
- Buried sand filters and pressurized dosing systems.
- Experimental and alternate system approvals.
Why It Matters
Private septic systems are the last line of defense between human waste and drinking water supplies. Mistakes in design, construction, or inspection can cause groundwater contamination, surface water pollution, property damage, and costly system failures.Understanding Title 25 Chapter 73 is about more than just passing a test or checking a box. It is about doing the job the right way to protect public health, protect the environment, and protect property owners from huge expenses later.
If you made it this far through the article, congratulations, you now know a little more about why I always say I know my ****. I earned that the hard way, one excavation and one inspection at a time.