25 Pa. Code § 73.55 - Elevated sand mounds
(a)
Design.
(1) The maximum
slope of the undisturbed soil, to the extremities of the berm, of a proposed
absorption area where elevated sand mound trenches may be permitted is
12%.
(2) The maximum slope of the
undisturbed soil, to the extremities of the berm, of a proposed absorption area
where an elevated sand mound bed may be permitted is 12%.
(3) The limiting zone is the base elevation
for measuring the required depth of sand to achieve a minimum of 4 feet of
satisfactory material between the bottom of the aggregate and the top of the
limiting zone.
(4) A minimum of 1
foot of sand shall be placed under the aggregate in all elevated sand mound
systems.
(5) Existing mineral soil
shall be utilized. No mineral soil in the area of the elevated sand mound may
be removed or disturbed for the purpose of adding or mixing fill
material.
(6) Elevated sand mound
trenches shall meet the requirements of §
73.52(b)
(relating to standard trenches) and this section.
(7) Elevated sand mound beds on slopes up to
8% shall meet the requirements of §
73.53 (relating to seepage beds)
and subsection (b). Other sand mound beds shall comply with subsection
(d).
(b)
Construction.
(1) Vegetation shall
be cut close to the ground throughout the area to be utilized for the
absorption area and berm. Bushes and trees shall be cut flush with the ground
surface; roots shall be left in place. Cut vegetation or organic litter shall
be raked and removed from the absorption and berm areas.
(2) The proposed absorption area not
obstructed by stumps or other obstacles shall be roughed or plowed parallel
with the contour to a maximum depth of 6 inches, using a multiple share chisel
plow or similar implement attached to light-weight equipment. Rotary tilling is
prohibited.
(3) Under no
circumstances may equipment travel on the plowed soil surface until the sand is
in place.
(4) Immediately after
plowing, sand shall be placed over the exposed plowed surface. Sand shall be
placed from the upslope side of the bed using only lightweight
equipment.
(5) The slope of the
sand not directly beneath the aggregate area shall be approximately
50%.
(6) The top of the sand
directly beneath the aggregate shall be level to a tolerance of ±2
inches per 100 feet.
(7) The mound
shall be surrounded by a berm consisting of mineral soil containing less than
20% coarse fragments with no coarse fragments greater than 4 inches in
diameter, more stable and less permeable than the sand, and lightly compacted
during construction to contain and protect the mound interior. The width of
this berm shall be a minimum of 3 feet at the top of the aggregate.
(8) Upon completion, the outside slope of the
berm may be no greater than 50% and shall be seeded to assure the stability of
the berm. The cover over the aggregate shall be a minimum of 1 foot of soil
suitable for the growth of vegetation.
(9) No equipment may be permitted on the
downslope side of the mound with the exception of lightweight equipment that is
used to form the downslope berm. To the greatest extent possible, aggregate and
the cover material shall be placed from the upslope side of the
mound.
(10) When a mound system
with trenches is used, the area between the individual trenches shall be filled
with mineral soil. A minimum distance of 5 feet shall separate sand of
individual trenches. This measurement shall be from the toe of the
sand.
(11) The area surrounding the
mound shall be grated to provide for diversion of surface runoff
waters.
(c)
Sand. Sand suppliers shall provide certification in writing to
the sewage enforcement officer and permittee, with the first delivery to the
job site from every sand source listing the amount of sand delivered, and that
all sand supplied meets the requirements posted in the Department of
Transportation specifications Publication #408, section 703. The size and
grading shall meet bituminous concrete sand Type B #1 or #3 requirements from a
Department of Transportation certified stockpile. The sieve analysis shall be
conducted in accordance with PTM #616 and #100.
(d)
Elevated sand mound
beds. Elevated sand mound beds on slopes greater than 8% shall meet
the requirements of §
73.53 and subsection (b). In
addition, the following apply:
(1) The
absorption area shall have a minimum length to width radio of 4 to 1.
(2) The long axis of the absorption area
shall be perpendicular to the slope. The bed construction shall follow the
ground surface contours.
(3) Upon
completion, the outside slope of the berm may be no greater than
33.3%.
(4) Designing the location
of multiple absorption areas so that one absorption area is placed
hydraulically upgradient or downgradient from the other may cause the lower
absorption area to fail because of excessive hydraulic loading from the upper
absorption area. Unless the potential for such an impact is shown to be
nonexistent by the applicant through the alternative/experimental system
process, this type of absorption area placement is prohibited.
Notes
The provisions of this § 73.55 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 § 73.51 (relating to general); 25 Pa. Code § 73.54 (relating to subsurface sand filter beds and trenches); and 25 Pa. Code § 73.162 (relating to intermittent sand filters).
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