25 Pa. Code § 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 flow(gallons per day) | Tank capacity (gallons) |
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.
Notes
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).
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