Minn. R. Part 7080.2230 - AT-GRADE SYSTEMS
Subpart 1.
At-grade system.
To qualify as an at-grade system, the system must meet or exceed the following requirements:
A.
employ flow values in parts
7080.1850 to
7080.1885;
B. meet or exceed applicable technical
requirements of parts
7080.1900 to
7080.2030,
7080.2050, and
7080.2100;
C. meet or exceed the requirements of part
7080.2150, subparts
2 and
3;
D. employ flow measurement; and
E. meet the requirements of subparts
2 and
3.
Subp. 2.
Location of at-grade
systems.
A. The upper 12 inches of the
absorption area must be original soil with a loading rate of 0.45 gallons per
day per square foot or greater as shown in Table IX or IXa in part
7080.2150, subpart
3, item E.
B. At-grade systems must not be installed in
areas with slopes greater than 25 percent.
C. Setbacks must be according to part
7080.2150, subpart
2, item F. Setbacks must be
measured from the absorption area.
Subp. 3.
Design and construction of
at-grade systems.
A. The at-grade bed
absorption width must be determined according to part
7080.2150, subpart
3, item M, and must not
exceed a width of 15 feet. The at-grade bed absorption width for slopes of one
percent or greater does not include any width of the media necessary to support
the upslope side of the pipe.
B.
The at-grade absorption length must be calculated by dividing the design flow
by the soil loading rate found in Table IX or IXa in part
7080.2150, subpart
3, item E, for the upper 12
inches of soil and dividing by the absorption bed width.
C. At-grade systems must employ pressurized
distribution by meeting or exceeding the applicable requirements of parts
7080.2050 and
7080.2100. At-grade systems
located on slopes of one percent or greater require only one distribution pipe
located on the upslope edge of the distribution media, with the absorption bed
width being measured from the distribution pipe to the downslope edge of the
media. Multiple distribution pipes are allowed to be used to provide even
distribution, if necessary, based on site conditions.
D. The upslope edge of an at-grade absorption
bed must be installed along the natural contour.
E. At-grade materials must be placed by using
construction techniques that minimize compaction.
F. Six inches of loamy or sandy cover
material must be installed over the distribution media. Cover must extend at
least five feet from the ends of the media bed and be sloped to divert surface
water. Side slopes must not be steeper than four horizontal units to one
vertical unit. Six inches of topsoil borrow must be placed on the cover
material.
G. One vertical
inspection pipe of at least four inches in diameter must be installed along the
downslope portion of the absorption bed. The inspection pipes must have
three-eighths inch or larger perforations spaced vertically no more than six
inches apart. Perforations must not exist above the distribution medium. The
inspection pipes must extend to the absorption bed/soil interface and must be
secured and capped flush with or above finished grade.
Notes
Statutory Authority: MS s 115.03; 115.55
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