Current through Register Vol. 56, No. 24, December 18, 2024
(a)
Proposed sewerage systems shall connect into downstream sewer lines and pump
stations that have adequate conveyance capacity.
(b) Gravity sanitary sewers, including
outfalls, shall be designed to carry at least twice the estimated average
projected flow when flowing half full. In the case of large interceptor sewer
systems, consideration may be given to modified designs. In addition, sanitary
sewer conveyance systems shall meet the following requirements:
1. Materials used in sewer construction shall
be acceptable to the Department for the purposes and conditions they are
intended to serve;
2. Sewers shall
be designed with the following minimum hydraulic slopes (grades producing
velocities of greater than 10 feet per second are not recommended unless
supported by adequate justification acceptable to the Department):
PVC Pipe (Polyvinylchloride) |
Pipe diameter (based on Kutter's or Manning's formula
with n = | Fall in feet |
0.01) | per 100 feet |
of sewer |
8 inches | 0.30 |
10 inches | 0.20 |
12 inches | 0.15 |
14 inches | 0.12 |
15 inches | 0.10 |
16 inches | 0.09 |
18 inches | 0.075 |
20 inches | 0.065 |
21 inches | 0.06 |
24 inches | 0.05 |
27 inches | 0.042 |
30 inches | 0.035 |
36 inches | 0.028 |
All Other Pipe Material (based on Kutter's
or Manning's formula with n = |
0.013) |
Pipe Diameter | Fall in feet |
per 100 feet |
of sewer |
8 inches | 0.40 |
10 inches | 0.29 |
12 inches | 0.22 |
14 inches | 0.17 |
15 inches | 0.16 |
16 inches | 0.14 |
18 inches | 0.12 |
20 inches | 0.10 |
21 inches | 0.095 |
24 inches | 0.080 |
27 inches | 0.067 |
30 inches | 0.058 |
36 inches | 0.046 |
i. When grades
or sizes less than those specified in this paragraph are proposed,
justification for the use of such grades shall be provided with the treatment
works approval application.
ii. The
minimum diameter of sewer extensions shall be eight inches, however,
consideration will be given to the use of smaller diameter sewers for lateral
connections;
3. Sewers
crossing streams and/or located within 10 feet of the stream embankment, or
where site conditions so indicate, shall be constructed of steel, reinforced
concrete, ductile iron or other suitable material;
4. Sewers conveying sanitary flow, combined
sanitary and stormwater flow, or industrial flow shall be separated from water
mains by a distance of at least 10 feet horizontally. If such lateral
separation is not possible, the pipes shall be in separate trenches with the
sewer at least 18 inches below the bottom of the water main, or such other
separation as approved by the Department;
i.
Where appropriate separation from a water main is not possible, the sewer shall
be encased in concrete, or constructed of ductile iron pipe using mechanical or
slip-on joints for a distance of at least 10 feet on either side of the
crossing. In addition, one full length of sewer pipe should be located so both
joints will be as far from the water line as possible. Where a water main
crosses under a sewer, adequate structural support for the sewer shall be
provided. The Department may also require additional structural support for
storm sewers crossing over sewer lines;
5. Any sewer within 100 feet of a water
supply well or a below-grade reservoir shall be constructed of steel,
reinforced concrete, ductile iron or other suitable material, shall be
completely watertight and shall be tested for watertightness after
installation;
6. The construction
of sewer lines through storm sewer pipes or manholes will not be
approved;
7. Sewer lines, including
force mains and laterals, shall be constructed at least three feet below the
proposed grade (as measured from the top of the pipe to the grade
elevation);
8. Sewer pipes,
including force mains and laterals, shall be sized to adequately convey the
projected contributory flow in accordance with this subchapter. In general,
sewer lines that are larger than hydraulically necessary to carry the projected
flow and for which the larger size is proposed only for the purpose of
achieving the minimum slope requirements specified in this section are not
permitted;
9. Sewer lines shall not
be approved for the use of storage or detention of sewage unless they are
designed as an integral part of an existing combined sewerage system
(sanitary/storm) where in-line storage is being proposed as a corrective
measure to prevent the discharge of untreated wastewater from the treatment
works;
10. New sewerage systems or
extensions shall be designed as separate systems, in which all water from
roofs, cellars, streets and other areas is excluded; except that separate
connections to an existing combined system may be approved when it is
demonstrated to the satisfaction of the Department that no other alternative is
feasible. In addition, the Department may permit, on a case-by-case basis, the
introduction of contaminated stormwater from containment areas into sanitary
sewers;
11. To minimize the
development of septic conditions, the Department may require special
operational and/or maintenance procedures for treatment works if the initial
contributory flows to the treatment works will be substantially below the
design capacity; and
12. When a
smaller sewer joins a larger one, the invert of the larger sewer should be
lowered sufficiently, or the smaller pipe raised sufficiently, to maintain the
same energy gradient. An approximate method for securing these results is to
place the 0.8 depth point of both sewers at the same elevation.
(c) For sewers other than circular
in cross section, the submitted data shall include the geometrical shape,
dimensions and hydraulic characteristics of the proposed sewer.
(d) Approval for curved sewers will be
considered by the Department only under the following circumstances:
1. Areas where curved streets comprise the
general layout, or the use of curved sewers would permit substantial savings in
cost to avoid deep cuts due to rocks or obstructions;
2. The minimum diameter of the sewer is eight
inches and the minimum radius of curvature is 100 feet; and
3. Manhole spacing does not exceed 300
feet.
(e) All sanitary
sewers, manholes, and cleanouts shall be tested by an infiltration,
exfiltration or pressure test after being flushed and before being placed into
use. The maximum rate of infiltration/exfiltration shall not exceed 100 gallons
per inch diameter per mile per day.