Section 410IAC6-8.3-74. Subsurface trench on-site sewage systems: general design and construction requirements

   (a) The minimum absorption area (in square feet) required for each subsurface trench soil absorption system shall be based on the following:

(1) The number of bedrooms and bedroom equivalents in the dwelling.

(2) The appropriate soil loading rate (in gallons per day per square foot) determined from Table IV in section 70(b)(8) of this rule. The soil loading rate used for this computation shall be the soil loading rate of the most restrictive horizon in the first twenty-four (24) inches below the trench bottom.

(3) The absorption area shall be computed using the following formula:

Area	=	150 g × number of bedrooms and bedroom equivalents
		Soil loading rate in gpd/sq. ft.

  (b) Subsurface trench soil absorption systems shall be as long and narrow as the site permits while not exceeding maximum trench length.

  (c) All subsurface trench on-site sewage systems shall be located in accordance with the separation distances shown in Table I in section 57(a) of this rule.

  (d) Special caution shall be taken to prevent wheeled and tracked vehicles from compacting the area selected for placement of the soil absorption system before, during, and after construction of the trenches, especially during wet weather. Alteration of soil structure by movement of vehicles may be grounds for rejection of the site or the soil absorption system, or both.

  (e) Subsurface soil absorption systems shall not be constructed during periods of wet weather when the soil is sufficiently wet at the depth of installation to exceed its plastic limit, as follows:

(1) This applies to soils classified as the following:

(A) Sandy loam.

(B) Silt loam.

(C) Loam.

(D) Clay loam.

(E) Silty clay loam.

(F) Sandy clay.

(G) Silty clay.

(H) Clay.

(2) Sufficient samples shall be evaluated throughout the soil absorption system site, from the soil surface to the proposed depth of the soil absorption system trench bottoms, to assure that the plastic limit of the soil is not exceeded.

(3) The plastic limit of a soil shall be considered to have been exceeded when the soil can be rolled between the palms of the hands to produce threads one-eighth (1/8) inch in diameter without breaking apart and crumbling.

  (f) Vegetation at the soil absorption system site that would interfere with the soils evaluation, system layout, or system construction shall be cut and removed prior to installation without causing compacted soil material.

  (g) If trees are present within the proposed soil absorption system:

(1) soil absorption trenches may be routed around trees provided the trenches follow the contour of the site; or

(2) tree stumps and root balls may be removed provided the resulting excavation will not exceed the permit requirements for width and depth of the soil absorption trench.

  (h) Excessive smearing of the usable absorption trench sidewalls or bottom during construction may:

(1) result in irreversible damage to the soil infiltrative surface; and

(2) be grounds for rejection of the site or the on-site sewage system, or both.

  (i) The residential sewer shall be a minimum of four (4) inches in diameter. Four (4) inch sewers shall be installed with a positive slope of:

(1) not less than four (4) inches in twenty-five (25) feet; and

(2) not more than thirty-six (36) inches in twenty-five (25) feet.

  (j) A six (6) inch residential sewer, if utilized, shall be installed with a positive slope of:

(1) not less than two (2) inches in twenty-five (25) feet; and

(2) not more than thirty-six (36) inches in twenty-five (25) feet.

  (k) A vertical drop may be installed in a residential sewer. Each vertical drop shall have a cleanout located immediately upslope.

  (l) Effluent sewers shall meet the following requirements:

(1) Effluent sewers shall be a minimum of four (4) inches in diameter.

(2) Effluent sewer pipe shall have a positive grade of at least two and four-tenths (2.4) inches per one hundred (100) feet or a grade of two-tenths percent (0.2%).

  (m) All sewer and effluent sewer joints shall be sealed according to the manufacturer's recommendations in order to be watertight and to withstand the pressures exerted on them.

  (n) The absorption trenches of a subsurface trench soil absorption system shall be constructed along the contour.

  (o) The minimum depth from original grade to the bottom of a trench of a subsurface trench soil absorption system shall not be less than ten (10) inches, and the maximum depth from final grade to the bottom of a trench of a subsurface trench soil absorption system shall not be more than thirty-six (36) inches.

  (p) All subsurface trench soil absorption systems shall be designed to utilize trenches with a minimum width of eighteen (18) inches and a maximum trench width of thirty-six (36) inches.

  (q) There shall be a minimum separation of seven and one-half (7 1/2) feet, on center, between soil absorption system trenches, measured perpendicular to the trenches.

  (r) No single absorption trench in a subsurface trench soil absorption system shall exceed one hundred (100) feet in length, except for subsurface trench pressure distribution on-site sewage systems.

  (s) Each trench and distribution lateral in a subsurface trench soil absorption system shall be uniformly level throughout its length and width.

  (t) The distal ends of distribution laterals and trenches shall not be tied together.

  (u) The distal end of each distribution lateral shall be capped, with the cap joint sealed according to the manufacturer's recommendations in order to be watertight and to withstand the pressures exerted on it.

  (v) Perforated pipe distribution laterals in the absorption trench of a subsurface trench soil absorption system shall be completely surrounded by aggregate that meets the specifications in section 68 of this rule. There shall be at least six (6) inches of aggregate below the pipe.

  (w) The minimum depth of aggregate above the distribution laterals shall be:

(1) two (2) inches throughout the entire length and width of trenches having a depth of twelve (12) inches or greater; or

(2) two (2) inches above the distribution lateral for the entire length of trenches having a depth of ten (10) inches to twelve (12) inches.

  (x) The aggregate used in a subsurface trench soil absorption system shall be covered with a geotextile fabric barrier in such a manner as to prevent the aggregate from becoming clogged with the earth fill. The barrier material shall:

(1) meet the minimum requirements in section 69 of this rule;

(2) be placed on the aggregate to prevent soil particle movement into the aggregate; and

(3) cover the aggregate from side to side and from end to end.

  (y) A minimum of twelve (12) inches of cover shall be provided over the aggregate in the trenches, and any fill required to provide cover shall be crowned over the entire soil absorption system to promote surface runoff.

  (z) Tire chips, if used for aggregate, will have protruding wires and shall be removed from the ground surface during site cleanup. (Indiana State Department of Health; 410 IAC 6-8.3-74; filed Oct 19, 2012, 2:06 p.m.: 20121114-IR-410120156FRA)