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17.36.918    HORIZONTAL SETBACKS, FLOODPLAINS

(1) Minimum horizontal setback distances (in feet) are as follows:

 

TABLE 1

SETBACK DISTANCES

(in feet)

 

From

To Sealed

components (1)

and other components (2)

To Absorption

systems (3)

Public or multiple-user

drinking water wells/springs

100

100

Individual and shared

drinking water supply wells

50

100

Other wells (4)

50

100

Suction lines

50

100

Cisterns

25

50

Roadcuts, escarpments

10 (5)

25

Slopes > 35 percent (6)

10 (5)

25

Property boundaries (7)

10

10

Subsurface drains

10

10

Water mains (8)

10

10

Drainfields/sand mounds (3)

10

-

Foundation walls

10

10

Surface water, springs

50

100

Floodplains

--Sealed components

- no setbacks (1)

Other components - 100 (2)

100

(1) Sealed components include holding tanks, sealed pit privies, and the components addressed in Department Circular DEQ-4, Chapters 4 and 5. Holding tanks and sealed pit privies must be located at least ten feet outside the floodplain or any openings must be at least two feet above the floodplain elevation.

(2) Other components include the components addressed in Department Circular DEQ-4, Chapter 7.

(3) Absorption systems include the systems addressed in Department Circular DEQ-4, Chapters 6 and 8 subject to the limitations in ARM 17.36.916.

(4) Other wells include, but are not limited to, irrigation and stock watering, but do not include observation wells as addressed in Department Circular DEQ-4.

(5) Sewer lines and sewer mains may be located in roadways and on steep slopes if the lines and mains are safeguarded against damage.

(6) Down-gradient of the sealed component, other component, or drainfield/sand mound.

(7) Easements may be used to satisfy the setback to property boundaries.

(8) Sewer mains that cross water mains must be laid with a minimum vertical separation distance of 18 inches between the mains.

 

(2) The reviewing authority may require greater horizontal separation distances than those specified in Table 1, if it determines that site conditions or water quality requirements indicate a need for the greater distance.

(3) If the floodplain has not been designated and its level relative to a wastewater system is in question, the applicant shall submit evidence adequate to allow the reviewing authority to establish the location of the floodplain.

(4) Sealed components of wastewater treatment systems, if located within a 100-year floodplain, must be designed and constructed to prevent surface water and ground water inundation, and pump lines must be pressure tested prior to use. Pipes must have a pressure rating of at least two times the operating pressure or pump shutoff pressure, whichever is greater. Pipes must be tested at 1 1/2 times the operating pressure or pump shutoff pressure, whichever is greater, or must be tested as specified by the manufacturer.

(5) The setbacks in this rule are not applicable to gray water irrigation systems that meet the requirements of ARM 17.36.919.

History: 75-5-201, MCA; IMP, 75-5-305, MCA; NEW, 2003 MAR p. 222, Eff. 2/14/03; AMD, 2009 MAR p. 1786, Eff. 10/16/09; AMD, 2014 MAR p. 1824, Eff. 8/8/14.

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