General. Waste stabilization ponds may be used if designed and
constructed in accordance with the following criteria and provided that the
effluent is discharged in accordance with the requirements of Section
905.110 (see Appendix A,
Illustration R as an illustration of these requirements). A septic tank sized
according to Appendix A, Illustration F or an aerobic treatment plant shall
precede a waste stabilization pond.
a)
Location: A waste stabilization pond shall be located as distant as practical
from residences, but in no case closer than the distances shown in Appendix A,
Illustration D, and in an area where trees will not interfere with sunlight on
the surface.
b) Dimensions. Ponds
shall have a length not exceeding 3 times the width.
c) Capacity. When domestic sewage from a
septic tank is to be discharged to the waste stabilization pond, the capacity
of the pond shall be equivalent to 60 times the average daily flow. When
preceded by a Class II aerobic treatment plant, the capacity of the pond shall
be equivalent to 18 times the average daily flow.
d) Depth. The wastewater depth for a waste
stabilization pond shall be uniform and 3 feet to 5 feet.
e) Freeboard. A minimum freeboard of 2 feet
shall be provided.
f) Embankments.
Embankments shall be constructed of impermeable materials and shall be
compacted. Embankment slopes shall be in one to 2 (vertical to horizontal)
below the water line and one to 3 or flatter above the water line. The top
width of the embankment shall be a minimum of 2 feet. Embankments shall be
seeded or rip-rapped from the outside toe to the high water line. Perennial,
low growing, spreading grasses that withstand erosion and can be kept mowed are
most satisfactory for seeding of embankments.
g) Inlet. The inlet line shall be placed 12
to 24 inches above the bottom of the pond at a point opposite the overflow
structure and shall be supported at no greater than 10-foot intervals along its
length. It shall discharge at least 10 feet from the water's edge. The inlet
line shall be sloped in accordance with Section
905.20(g).
h) Outlet. The outlet structure shall be
designed to prevent the discharge of floating solids. This shall be
accomplished through baffling. The baffle shall consist of a sanitary T or
90° elbow. If the 90° elbow is used, a 1/4 inch hole shall be drilled
into the top of the elbow to provide an air break. The outlet baffle shall
extend 12 inches below the invert of the overflow. The outlet baffle shall be 3
to 5 feet from the embankment.
i)
Bottom. The bottom of the waste stabilization pond shall be cleared and leveled
to the required elevation and shall be lined with an impermeable natural or
man-made material. The pond shall be kept free of vegetation that would grow to
or above the water surface.
j)
Drainage. All surface water shall be diverted away from the waste stabilization
pond.
