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The Pennsylvania Code website reflects the Pennsylvania Code changes effective through 50 Pa.B. 4000 (August 1, 2020).

25 Pa. Code § 73.31. Standards for septic tanks.


§ 73.31. Standards for septic tanks.

 (a) Capacity.

   (1)  The minimum liquid septic tank capacity for any installation is 900 gallons.

   (2)  For single-family dwelling units, not served by a community onlot system, a minimum daily flow of 400 gpd shall be used to determine required septic tank capacity. This figure shall be increased by 100 gallons for each additional bedroom over three. The daily flow indicated provides for use of garbage grinders, automatic washing machines, dishwashers and water softeners.

   (3)  The minimum septic tank capacity shall be calculated from the following table using estimated sewage flows from paragraph (2), or §  73.17(a)—(c) (relating to sewage flows):

Design flowTank capacity
(gallons per
0—500(3.5 x flow exceeding 400 gpd) + (900)
500—5,000(1.50 x flow exceeding 500 gpd) + (1,250)
5,000—7,500(1.45 x flow exceeding 5,000 gpd) + (8,000)
7,500—10,000(1.35 x flow exceeding 7,500 gpd) + (11,625)
over 10,000(1.50 x the daily flow)

   Note: Septic tanks may be connected in series to attain required capacity.

 (b)   Construction.

   (1)  Tanks shall be watertight and constructed of sound and durable material not subject to excessive corrosion or decay.

     (i)   Precast concrete tanks shall have a minimum wall thickness of 2 1/2 inches and be adequately reinforced.

     (ii)   Precast slabs used as covers shall have a thickness of at least 3 inches and be adequately reinforced.

     (iii)   Tanks having a liquid capacity of 5,000 gallons or less may not be constructed of blocks, bricks or similar masonry construction.

     (iv)   Tanks having a capacity in excess of 5,000 gallons may be constructed onsite to meet the standards of the National Concrete Masonry Association for reinforcement and waterproofing as listed in the most recent edition of its publication ‘‘Concrete Masonry Foundation Walls,’’ copyright 1957 NCMA.

     (v)   Steel tanks shall meet United States Department of Commerce Standards 177-62.

   (2)  The depth of liquid in any tank or its compartments shall be:

     (i)   Not less than 2 1/2 nor more than 5 feet for tanks having a liquid capacity of 600 gallons or less.

     (ii)   Not less than 3 feet nor more than 7 feet for tanks having a liquid capacity of more than 600 gallons.

   (3)  No tank or compartment may have an inside horizontal dimension less than 36 inches.

   (4)  Septic tank installations shall consist of tanks with multiple compartments or multiple tanks. The first compartment or tank shall have at least the same capacity as the second but may not exceed twice the capacity of the second. Tanks or compartments shall be connected in series and may not exceed four in number in any one installation.

 (c)  Inlet and outlet connections.

   (1)  The bottom of the inlet shall be a minimum of 3 inches above the bottom of the outlet.

   (2)  Inlet baffles or vented tees shall extend below the liquid level at least 6 inches. Penetration of the inlet device may not exceed that of the outlet device.

   (3)  The outlet baffles or vented tees of each tank or compartment shall extend below the liquid surface to a distance equal to 40% of the liquid depth. Penetration of outlet baffles or tees in horizontal cylindrical tanks shall be equal to 35% of the liquid depth.

   (4)  The inlet and outlet baffles or vented tees shall extend above liquid depth to approximately 1 inch from the top of the tank. Venting shall be provided between compartments and each tank.

   (5)  The outlet baffles or vented tees of the last compartment or tank shall be equipped with a solids retainer.

 (d)  Treatment tank access.

   (1)  Access to each tank or compartment of the tank shall be provided by a manhole with an inside dimension of at least 20 inches square (20 x 20) or in diameter, with a removable cover. The top of the tank containing the manhole or the top of a manhole extension may not be more than 12 inches below grade level. If access is extended to grade, the access cover shall be airtight. Grade level access covers shall be secured by bolts or locking mechanisms, or have sufficient weight to prevent unauthorized access.

   (2)  The ground shall slope away from any access extended to grade level.

 (e)  Inspection port. A maximum 4-inch diameter inspection port with sealed cover shall be installed to grade level above the inlet tee.


   The provisions of this §  73.31 amended under section 9 of the Pennsylvania Sewage Facilities Act (35 P. S. §  750.9); The Clean Streams Law (35 P. S. § §  691.1—691.1001); and section 1920-A of The Administrative Code of 1929 (71 P. S. §  510-20).


   The provisions of this §  73.31 adopted August 2, 1971, effective August 14, 1971, 1 Pa.B. 1649; amended April 26, 1974, effective May 13, 1974, 4 Pa.B. 817; amended August 30, 1974, effective September 16, 1974, 4 Pa.B. 1805; amended January 21, 1983, effective January 22, 1983, 13 Pa.B. 508; amended November 7, 1997, effective November 8, 1997, except subsection (b)(4) effective January 7, 1998, 27 Pa.B. 5877; corrected November 21, 1997, 27 Pa.B. 6079. Immediately preceding text appears at serial pages (217321) to (217323).

Cross References

   This section cited in 25 Pa. Code §  73.45 (relating to dosing tanks); 25 Pa. Code §  73.62 (relating to standards for holding tanks); 25 Pa. Code §  73.63 (relating to standards for privies); and 25 Pa. Code §  73.161 (relating to general).

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