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Minnesota Administrative Rules

7080.1930 SEPTIC TANK CAPACITY.

Subpart 1.

Dwellings.

The liquid capacity of septic tanks must be at least as large as the liquid capacities given in Table V.

TABLE V
Number of bedrooms Septic tank liquid minimum capacities (gallons)
3 or less 1,000
4 or 5 1,500
6 or 7 2,000
8 or 9 2,500

Where more than nine bedrooms are present, the septic tank capacity must be calculated by the following formula: 2,500 + ([# of bedrooms - 9] x 250).

Subp. 2.

Garbage disposals.

If a garbage disposal unit is anticipated or installed in a dwelling, the septic tank capacity must be at least 50 percent greater than that required in subpart 1 and must include either multiple compartments or multiple tanks. In addition, an effluent screening device is recommended.

Subp. 3.

Sewage pumping.

If sewage is pumped from a sewage ejector or grinder pump from a dwelling to a septic tank, the septic tank capacity must be at least 50 percent greater than that required in subpart 1 and must include either multiple compartments or multiple tanks. In addition, an effluent screening device is recommended.

Subp. 4.

Sewage pumping and garbage disposals.

If conditions in both subparts 2 and 3 apply to a dwelling, the mitigative requirements of either subpart 2 or 3 apply; the requirements of both subparts 2 and 3 need not be additive.

Subp. 5.

Septic tank capacity for multiple dwellings.

A.

For systems serving ten or fewer dwellings with a common septic tank, the liquid capacity must be determined by adding the capacities for each dwelling as determined in this part or according to subpart 6.

B.

For systems serving more than ten dwellings with a common septic tank, the requirements of subitem (1) or (2) apply:

(1)

total septic tank liquid capacity for common tanks serving multiple dwellings under gravity flow to common tanks is determined by multiplying the design flow by 3.0 or according to subpart 6; or

(2)

total septic tank liquid capacity for common tanks serving multiple dwellings under pressure flow to common tanks is determined by multiplying the design flow by 4.0 or according to subpart 6.

C.

Total septic tank liquid capacity for systems employing individual tanks at each dwelling discharging into a collection system must be determined:

(1)

by a Minnesota licensed professional engineer; or

(2)

according to the Prescriptive Designs and Design Guidance for Advanced Designers, incorporated by reference under part 7080.1550, subpart 2.

Subp. 6.

Prior to other treatment devices.

Septic tank liquid capacity prior to other treatment devices must accord with manufacturer's requirements, accepted engineering principles, or as identified in the product registration recommended standards and criteria.

Subp. 7.

Septic tank capacity for other establishments.

Total septic tank liquid capacity for other establishments with domestic strength waste as described in part 7080.1550, subpart 2, item B, subitem (1), is determined by multiplying the design flow by 3.0 if receiving sewage under gravity flow, by multiplying the design flow by 4.0 if receiving sewage under pressure flow, or in accordance with subpart 6. Additional design considerations, such as equalization tanks, additional capacity, grease interceptors, or secondary treatment, are required for influent concentrations that exceed the levels identified in part 7080.1550, subpart 2, item B, subitem (1).

Statutory Authority:

MS s 115.03; 115.55

Published Electronically:

October 10, 2013

700 State Office Building, 100 Rev. Dr. Martin Luther King Jr. Blvd., St. Paul, MN 55155 ♦ Phone: (651) 296-2868 ♦ TTY: 1-800-627-3529 ♦ Fax: (651) 296-0569