Section 410IAC6-10.1-83. Subsurface trench gravity on-site sewage systems: design and construction requirements

   (a) Subsurface trench gravity on-site sewage systems shall meet all of the requirements of:

(1) section 82 of this rule; and

(2) this section.

  (b) A distribution box or series of distribution boxes shall be installed between the septic tank and the subsurface soil absorption system, and each absorption system trench shall be connected directly to a distribution box using an effluent sewer.

  (c) Distribution boxes shall be installed level on either undisturbed soil, sand, sand mix, aggregate not larger than one-half (1/2) inch in diameter, or engineered base, and the outlets shall be checked to assure that they are at a uniform elevation.

  (d) Effluent sewer pipe in a subsurface trench gravity on-site sewage system shall meet the following requirements:

(1) For installation prior to a distribution box, effluent sewer pipe shall be bedded according to manufacturer requirements and backfilled with debris-free soil material or aggregate without damaging the pipe.

(2) For installation after a distribution box, effluent sewer pipe shall be stabilized, bedded, and backfilled without damaging the pipe with debris-free soil material to prevent the movement of effluent along the outside of the pipe.

  (e) The invert elevation of the end of each effluent sewer pipe connected to a distribution box shall be at the same elevation so that each gravity distribution lateral receives an equal volume of effluent.

  (f) Each effluent sewer from an outlet of a distribution box that directly serves a trench shall extend into the aggregate in the trench.

  (g) All soil absorption system gravity distribution laterals shall have an internal diameter of four (4) inches.

  (h) Gravity distribution laterals in the aggregate trenches shall be installed level along their length:

(1) for two (2) hole gravity distribution laterals, the laterals shall be placed in the aggregate with the rows of holes located at one hundred twenty (120) and two hundred forty (240) degrees from vertical (rows of holes at four (4) o'clock and eight (8) o'clock); and

(2) for three (3) hole gravity distribution laterals, the laterals shall be placed in the aggregate with the rows of holes located at one hundred twenty (120), two hundred forty (240), and three hundred sixty (360) degrees from vertical (rows of holes at four (4) o'clock, eight (8) o'clock, and twelve (12) o'clock).

  (i) In order to provide equal flow distribution in gravity feed subsurface soil absorption systems, each absorption field trench must be individually connected to a distribution box. The distribution box shall be at least five (5) feet from the proximal end of each soil absorption field trench and shall be connected to the absorption field trench by unperforated pipe that is laid with a gravel free backfill to the point where the unperforated pipe enters the aggregate in the trench. All absorption trenches served by a common distribution box must be constructed so that each trench served by the distribution box is loaded with an equal volume of effluent. (Indiana State Department of Health; 410 IAC 6-10.1-83; filed Oct 19, 2012, 2:07 p.m.: 20121114-IR-410120157FRA)