(a)
Design. The maximum slope of the undisturbed soil of a proposed
absorption area where a trench system may be permitted is 25%. For slopes
between 15% and 25%, detailed design in relationship to elevation shall be
provided. The designer shall inspect the installation and verify that, to the
best of his knowledge and belief, the system was installed in accordance with
the plans and specifications. Copies of the plans and specifications and the
designer's report are to be attached to the applicant's copy, sewage
enforcement officer's copy and the Department's copy of the application for
sewage permit.
(b)
Construction. Trenches in an absorption area shall be
constructed in accordance with the following:
(1) There shall be a minimum of two trenches
per field.
(2) Trenches shall
follow approximately the ground surface contours so that variations in trench
depth shall be minimized.
(3) There
shall be at least 6 feet of soil between the treatment tank or dosing tank and
the nearest trench.
(4) The width
of the bottom of the individual trench shall be 12 to 72 inches.
(5) The depth to the bottom of the absorption
area shall be 12 to 36 inches.
(6)
The bottom of the absorption area shall be level to a tolerance of 2 inches per
100 feet.
(7) The minimum width of
undisturbed earth between trenches shall be 5 feet. When elevated sand mound
trenches are used, the distance between trenches shall be measured from the toe
of the sand of each trench.
(8) The
minimum depth of aggregate material under laterals shall be 6 inches.
(9) Laterals shall be placed in the center of
the trench. The first or last discharge hole of a lateral may be no more than 5
feet nor less than 2 feet from the ends of the trench.
(10) Laterals shall be level to a maximum
tolerance of 4 inches of fall per 100 feet toward the terminal end of the
lateral.
(11) The minimum depth of
aggregate material over the laterals shall be 2 inches.
(12) The depth of aggregate shall be uniform
throughout the absorption area.
(13) The top of the aggregate material shall
be covered with geotextile fabric, untreated building paper or a 2-inch layer
of hay, straw or similar material to prevent backfill material from settling
into the aggregate.
(14) The
minimum depth of earth cover over the aggregate in all installations shall be
12 inches. Where the top of the aggregate is less than 12 inches from the
undisturbed soil surface, the soil cover shall extend beyond the absorption
area by at least 3 feet on all sides.
(15) The backfill material shall consist of
soil suitable for the growth of vegetation, and be seeded to control erosion.
(16) Trench laterals shall be
fitted with end caps.
Notes
The
provisions of this § 73.52 adopted August 2, 1971, effective
8/14/1971, 1 Pa.B. 1649; amended
April 26, 1974, effective 5/13/1974, 4 Pa.B. 817; amended August 30,
1974, effective 9/16/1974, 4
Pa.B. 1805; amended January 21, 1983, effective 1/22/1983, 13 Pa.B. 508; amended November 7,
1997, effective 11/8/1997, 27
Pa.B. 5877.
The provisions of this § 73.52 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).
This section cited in 25 Pa. Code §
71.63 (relating to retaining
tanks); 25 Pa. Code §
73.44 (relating to pressurized
distribution design); 25 Pa. Code §
73.53 (relating to seepage beds);
25 Pa. Code §
73.54 (relating to subsurface sand
filter beds and trenches); and 25 Pa. Code §
73.55 (relating to elevated sand
mounds).
