The Governing Framework

Pennsylvania regulates "onlot" (on-site) sewage treatment under a multi-layer framework:

• Pennsylvania Sewage Facilities Act (Act 537) — the state statute authorizing municipal sewage facility planning and regulating onlot treatment.
• 25 Pa. Code Chapter 73 — Standards For Onlot Sewage Treatment Facilities (the DEP regulation implementing Act 537).
• Pennsylvania Department of Environmental Protection (DEP) — promulgates rules, provides oversight and training.
• Municipal Sewage Enforcement Officers (SEOs) — certified by DEP, employed by individual municipalities, they administer permits and inspections at the local level.

Design Sewage Flow — Section 73.17

25 Pa. Code § 73.17 establishes the design daily flow for residential use:

The 400 gpd baseline is already inclusive of water use from garbage grinders, automatic washing machines, dishwashers, and water softeners — so PA does not require the 50% garbage-disposal upsize that Georgia and some other states impose.

Multi-Compartment or Tanks-in-Series — Required

Section 73.31 requires all permitted septic tank installations to be multi-compartment or multi-tank:

• At least 2 compartments OR 2 tanks in series.
• First compartment/tank has same or greater capacity than second (but not more than 2x).
• Maximum 4 compartments or 4 tanks in series.

For a 3-bedroom home at 400 gpd design flow, required tank capacity is typically 1,000 gallons minimum. A 1,000-gallon two-compartment tank satisfies PA Section 73.31, as do two 500-gallon tanks in series.

Act 537 Official Plans

Pennsylvania's Sewage Facilities Act (Act 537) requires every municipality to prepare and maintain an "Official Plan" documenting how sewage is handled — whether by sewer connection, community onlot systems, or individual onlot systems. When you propose a new onlot installation, your project must either:

• Fit within the municipality's existing Official Plan, or
• Trigger an Official Plan revision (for larger-volume or non-conventional installations).

Most single-family residential installations fit within the existing plan. Commercial, multi-unit, or non-conventional systems often require plan revision, adding weeks or months to the permit timeline.

Tank Types — Chapter 73 Distinctions

• Septic Tank (§ 73.31) — standard anaerobic primary treatment for conventional onlot systems.
• Aerobic Treatment Tank (§ 73.32) — advanced treatment unit for sites with poor soils; requires maintenance contract.
• Holding Tank (§ 73.62) — used for temporary storage without treatment; requires service-contracted pumping. Most commonly used for cabins and very low-occupancy or seasonal installations where a conventional system isn't feasible.

Permit Process — Municipal SEO

1. Identify your municipality's SEO. Every Pennsylvania municipality contracts with (or employs) a DEP-certified SEO. Your local borough, township, or city has contact info for the current SEO.
2. Perc test and site evaluation. The SEO conducts or oversees a percolation test and soil profile assessment. PA uses percolation rate as the primary design criterion.
3. Design submittal. Licensed installer or designer prepares plans. Advanced systems may require PE review.
4. Permit issuance. Typical SEO fees $400–$1,200 (municipality sets fee). Timelines 2–6 weeks plus any Act 537 plan revision.
5. Installation. By a PA-registered installer.
6. Pre-backfill inspection. SEO verifies tank placement, multi-compartment configuration, and dispersal field.
7. Permit to occupy / certificate of completion.

Pennsylvania-Specific Considerations

• Rural vs. suburban zoning. Some urbanized Pennsylvania townships restrict new onlot installations in favor of sewer connection. Confirm with SEO before parcel purchase.
• Frost depth. 36–48 inches in most of the state, deeper in northern tier and higher elevations. Tank burial must account for frost plus maintenance access.
• Limestone (karst) geology. Central Pennsylvania has limestone bedrock with rapid groundwater transmission. Karst areas may require advanced treatment or engineered alternatives.
• Marcellus Shale region. Northeastern PA rural parcels often have shallow bedrock limiting dispersal-field depth. Mound systems and shallow-pressurized dispersal common.
• Chesapeake Bay watershed. Counties in the Susquehanna and Potomac drainage face Chesapeake Bay TMDL nitrogen-loading considerations. No additional OWTS rules yet but advanced treatment is sometimes specified in sensitive areas.

Material Approvals

PA accepts polyethylene tanks meeting 25 Pa. Code § 73.31 construction standards. Norwesco, Snyder, Enduraplas, and Chem-Tainer all produce PA-compliant tanks. Order-time verification:

• IAPMO or NSF 46 listing
• ASTM D1998 compliance for polyethylene
• Two-compartment configuration (or plan for two tanks in series)
• Anti-buoyancy anchoring for high-water-table parcels (common in northern tier, Chesapeake drainage)

Frequently Asked Questions

Who is the SEO for my property?

Your municipality (borough, township, or city) appoints or contracts with the SEO. Call your local municipal office; they have current SEO contact info. PA's SEO model is distinctive — SEOs work for municipalities, not DEP or county health.

Can I install a 1,000-gallon single-compartment tank in Pennsylvania?

No. Section 73.31 requires multi-compartment or tanks-in-series. A 1,000-gal single-compartment tank doesn't meet the current code. Order a 1,000-gal two-compartment tank (most manufacturers make this standard) or two 500-gal tanks in series.

Why is the baseline flow 400 gpd instead of a per-bedroom rate like other states?

PA's 400 gpd baseline applies to 1-3 bedroom dwellings, with a +100 gpd step per additional bedroom. The 400 gpd base includes use from garbage grinders, washers, dishwashers, and water softeners — so no separate upsize for those appliances.

What's an Act 537 Official Plan?

Every Pennsylvania municipality maintains a plan under the Sewage Facilities Act documenting how sewage is handled in its territory. Your new onlot installation must fit the existing plan or trigger a revision. Single-family residential usually fits; commercial or multi-unit often requires revision.

Can I have an aerobic treatment system instead of conventional?

Yes, under Section 73.32. Common for sites with poor soils. Requires a maintenance contract with a DEP-certified maintenance provider and periodic inspection.

Source Citations

• 25 Pa. Code Chapter 73 (full table of contents)
• 25 Pa. Code § 73.11 — General Provisions
• 25 Pa. Code § 73.17 — Sewage flows
• 25 Pa. Code § 73.31 — Septic tank standards
• 25 Pa. Code § 73.32 — Aerobic treatment tank standards
• 25 Pa. Code § 73.62 — Holding tank standards