Subpart
1.
General.
Treatment and dispersal of all sewage for new construction or
replacement ISTS must be in compliance with this part and parts
7080.2200 to
7080.2400 as adopted into local
ordinances.
Subp. 2.
General technical requirements for all systems.
All new construction or replacement ISTS must be designed to
meet or exceed the provisions in items A to F.
A. All treatment and dispersal methods must
be designed to conform to all applicable federal, state, and local
regulations.
B. Treatment and
dispersal processes must prevent sewage or sewage effluent contact with humans,
insects, or vermin.
C. Treatment
and dispersal of sewage or sewage effluent must be in a safe manner that
adequately protects from physical injury or harm.
D. An unsaturated zone in the soil must be
maintained between the bottom of the soil treatment and dispersal system and
the periodically saturated soil or bedrock during loading of
effluent.
E. Soil treatment and
dispersal systems must not be designed in floodways. Soil treatment and
dispersal systems installed in flood fringes must meet the requirements in part
7080.2270. All soil treatment
systems located in areas subject to excessive run-on must have a diversion
constructed upslope from the system.
F. ISTS components must be set back in
accordance with Table VII.
TABLE VII |
MINIMUM SETBACK DISTANCES (FEET) |
Feature |
Sewage tank, holding tank, or sealed privy |
Absorption area or unsealed privy |
Building sewer or supply pipes |
|
|
|
|
Water supply wells |
* |
* |
* |
Buried water lines |
* |
* |
* |
Structures |
10 |
20 |
Property lines ** |
10 |
10 |
Ordinary high water level of public waters |
*** |
*** |
* Setbacks from buried water lines and water supply wells are
governed by chapters 4714 and 4725, respectively.
** Infringement on property line setbacks must be made through
accepted local procedures.
*** Setbacks from lakes, rivers, and streams are governed by
chapters 6105 and 6120.
Subp.
3.
Other technical requirements for systems.
Items A to M are required for specific designs as determined in
parts
7080.2200 to
7080.2400.
A. Employ components registered under parts
7083.4070 and
7083.4080 that are installed,
used, and operated according to the conditions placed on
registration.
B. Employ structural
components and joint sealants that meet or exceed the system's expected design
life.
C. For acceptable treatment
of septic tank effluent by soil, the soil treatment and dispersal systems must
meet the requirements of subitems (1) and (2).
(1) A minimum three-foot vertical soil
treatment and dispersal zone must be designed below the distribution media that
meets the criteria in units (a) to (c):
(a)
the zone must be above the periodically saturated soil and bedrock. The zone
must be continuous and not be interrupted by seasonal zones of
saturation;
(b) any soil layers
that are any of the United States Department of Agriculture (USDA) soil
textures classified as sand with 35 to 50 percent rock fragments or loamy sand
with 35 to 50 percent rock fragments must be credited at only one-half their
thickness as part of the necessary treatment zone. Soil layers, regardless of
soil texture, with greater than 50 percent rock fragments must not be credited
as part of the necessary treatment zone. Layers that are given full, partial,
or no credit must, in any layering arrangement in the soil profile, be
cumulatively added to determine the amount of soil treatment zone in accordance
with other soil treatment zone provisions; and
(c) the entire treatment zone depth must be
within seven feet from final grade.
(2) The distribution system or media must not
place a hydraulic head greater than 30 inches above the bottom of the bottom
absorption area.
D. The
system's absorption area must be original soil.
E. The system's absorption area and mound
absorption ratio must be sized according to Table IX or IXa.
TABLE IX
LOADING RATES FOR DETERMINING BOTTOM ABSORPTION AREA AND
ABSORPTION RATIOS USING DETAILED SOIL DESCRIPTIONS *
|
|
Treatment Level C |
Treatment Level C |
Treatment Level A, A-2, B, B-2 |
Treatment Level A, A-2, B, B-2 |
|
|
Absorption area loading rate
(gpd/ft2) |
Mound absorption ratio |
Absorption area loading rate
(gpd/ft2) |
Mound absorption ratio*** |
USDA soil texture |
Soil structure and grade |
|
|
|
|
Sand, coarse sand, loamy sand, loamy coarse sand, fine
sand, very fine sand, loamy fine sand, loamy very fine sand, 35 to 50% rock
fragments |
Single grain, granular, blocky, or prismatic structure;
weak grade |
** |
1.0 |
** |
1.0 |
Sand, coarse sand, loamy sand, loamy coarse sand, <35%
rock fragments |
Single grain, granular, blocky, or prismatic structure;
weak grade |
1.2 |
1.0 |
1.6 |
1.0 |
Fine sand, very fine sand, loamy fine sand, loamy very fine
sand, <35% rock fragments |
Single grain, granular, blocky, or prismatic structure;
weak grade |
0.6 |
2.0 |
1.0 |
1.6 |
Sandy loam, coarse sandy loam, fine sandy loam, very fine
sandy loam |
Granular, blocky, or prismatic structure; weak to strong
grade |
0.78 |
1.5 |
1.0 |
1.6 |
Sandy loam, coarse sandy loam, fine sandy loam, very fine
sandy loam |
Platy with weak grade or massive |
0.68 |
1.8 |
0.87 |
1.8 |
Loam |
Granular, blocky, or prismatic structure; weak to strong
grade |
0.6 |
2.0 |
0.78 |
2.1 |
Loam |
Platy with weak grade or massive |
0.52 |
2.3 |
0.68 |
2.4 |
Silt loam, silt |
Granular, blocky, or prismatic structure; weak to strong
grade |
0.5 |
2.4 |
0.78 |
2.1 |
Silt loam, silt |
Platy with weak grade or massive |
0.42 |
2.9 |
0.65 |
2.5 |
Clay loam, sandy clay loam, silty clay loam |
Granular, blocky, or prismatic structure; moderate to
strong grade |
0.45 |
2.6 |
0.6 |
2.7 |
Clay, sandy clay, silty clay |
- |
** |
** |
** |
** |
* Proposed absorption areas must meet item L and must have very
friable and friable consistence or loose noncemented sands.
** Conduct percolation test and size under Table IXa. May need
to be designed under part
7080.2300.
*** Assume a hydraulic loading rate to the sand at 1.6
gpd/ft2.
TABLE IXa |
LOADING RATES FOR DETERMINING BOTTOM ABSORPTION AREA AND
ABSORPTION RATIOS USING PERCOLATION TESTS |
Percolation rate (MPI) |
Treatment level C absorption area loading rate
(gpd/ft2) |
Treatment level C mound absorption ratio |
Treatment levels A, A-2, B, and B-2 absorption area loading
rate (gpd/ft2) |
Treatment levels A, A-2, B, and B-2 mound absorption
ratio |
<0.1 |
- |
1.0 |
- |
1.0 |
0.1 to 5 |
1.2 |
1.0 |
1.6 |
1.0 |
0.1 to 5 (fine sand and loamy fine sand) |
0.6 |
2.0 |
1.0 |
1.6 |
6 to 15 |
0.78 |
1.5 |
1.0 |
1.6 |
16 to 30 |
0.6 |
2.0 |
0.78 |
2.0 |
31 to 45 |
0.5 |
2.4 |
0.78 |
2.0 |
46 to 60 |
0.45 |
2.6 |
0.6 |
2.6 |
61 to 120 |
- |
5.0 |
0.3 |
5.3 |
>120 |
- |
- |
- |
- |
F. If
drainfield rock medium is employed, a durable, nonwoven geotextile fabric must
be used to cover the distribution rock medium. The fabric must be of sufficient
strength to undergo installation without rupture. The fabric must permit
passage of water without passage of overlying soil material into the rock
medium.
G. All excavation into the
absorption area, or surface preparation of the upper 12 inches of absorption
area, must be in a manner to expose the original soil structure in an unsmeared
and uncompacted condition. Excavation is only allowed when the soil moisture
content is at or less than the plastic limit and is not frozen or
freezing.
H. Excavation equipment
or other vehicles must not be driven on the excavated or prepared absorption
area. Foot traffic on these areas must be minimized and not cause compaction.
The exposed areas must be immediately covered with media or the designed
coverage materials. If the areas are exposed to direct rainfall, they must be
allowed to dry and must be re-prepared according to item G.
I. A minimum of six inches of topsoil borrow
must be placed over the system.
J.
A close-growing, vigorous vegetative cover must be established over the soil
treatment and dispersal system and other vegetatively disturbed areas. The
sodding, seeding, or other vegetation establishment must begin immediately
after the placement of the topsoil borrow. If the climatic season does not
allow immediate establishment of vegetation, the soil treatment and dispersal
system must be protected from erosion and excessive frost and a vegetative
cover must be established as soon as favorable climatic conditions exist. The
vegetative cover established must not interfere with the hydraulic performance
of the system and must provide adequate frost and erosion protection. Trees,
shrubs, deep-rooted plants, or hydrophytic plants must not be planted on the
system.
K. Sewage tank effluent
concentrations to the soil dispersal system must not exceed a BOD concentration
of 170 mg/l, a CBOD5 concentration of 125 mg/l, a TSS
concentration of 60 mg/l, or an oil and grease concentration of 25
mg/l.
L. The distribution media
must not be in contact with soils with any of the USDA soil textures classified
as sand with 35 percent or more rock fragments or loamy sand with 35 percent or
more rock fragments or any soils that have a percolation rate of less than 0.1
minute per inch.
M. The contour
loading rate for soil dispersal systems must be between 1 and 12 gallons per
lineal foot per day.
Subp.
4.
Systems with a design flow greater than 2,500 gallons per
day.
At a minimum, systems designed under this chapter with a design
flow of greater than 2,500 gallons per day, which impact water quality of an
aquifer, as defined in part
4725.0100, subpart 21, must employ
best management practices for nitrogen reduction developed by the commissioner
to mitigate water quality impacts to groundwater.