Ind. Admin. Code tit. 410, r. 6-8.3-58 – Dispersal area

Sec. 58. (a) A dispersal area is required for a soil absorption system when:

(1) the soil loading rate used to determine the size of the soil absorption system is five-tenths (0.5) gallons per day per square foot (gpd/ft2) or less; or
(2) there is a horizon in the upper sixty (60) inches of the profile description with:
1. (A) bedrock;
2. (B) densic material;
3. (C) dense till;
4. (D) soil with fragic properties; or
5. (E) layers transitional to dense till (horizons in a soil developed from Wisconsin glacial till that shows effervescence when treated with a ten percent (10%) hydrochloric acid solution), unless:
  1. (i) the on-site soils evaluation report shows that the presence of the horizon is not detrimental to the proper functioning of an on-site sewage system; and
  2. (ii) the determination in item (i) is made using the guidelines as set forth in the soil manuals, technical bulletins, and handbooks of the NRCS guidelines and as approved by the department.

(b) When the conditions in subsection (a) apply, the following requirements shall be met:

(1) For soil absorption system sites with a slope of one-half percent (1/2%) or less, a minimum dispersal area as described in Table II in subsection (c) shall be maintained on each side of the outside edge of the:
1. (A) outer trench parallel to the length of the trench; or
2. (B) INDOT Specification 23 sand and parallel to the long axis of the elevated sand mound.
(2) For soil absorption system sites with a slope of greater than one-half percent (1/2%), a minimum dispersal area as described in Table II in subsection (c) shall be maintained on the downslope side of the soil absorption system from the outside edge of the:
1. (A) downslope trench parallel to the length of the trench; or
2. (B) INDOT Specification 23 sand downslope and parallel to the long axis of the elevated sand mound.

(c) For sites that do not meet the conditions of subsection (a), the minimum dispersal area shall be ten (10) feet. For sites that meet the conditions of subsection (a), the dispersal area shall be as indicated in Table II, as follows:

Table II - Minimum Dispersal Areas¹ for Soil Absorption Systems
Slope < 1/2 %²: On-site sewage system without perimeter drain	One-fourth (1/4) width of soil absorption system⁵
Slope 1/2 %³: On-site sewage system without perimeter drain	One-half (1/2) width of soil absorption system⁵
Any slope: On-site sewage system with perimeter drain⁴	Ten (10) feet or the distance to the perimeter drain
¹No buildings, foundations, slabs, garages, patios, barns, aboveground and belowground swimming pools, retaining walls, roads, driveways, parking areas, or paved sidewalks are allowed in the dispersal area.
²Dispersal area is located on each side of the outside edge of the outer trench parallel to the length of the trench, or on each side of the outside edge of the sand area and parallel to the long axis of an elevated sand mound.
³Dispersal area is located on the downslope side of the soil absorption system.
⁴For on-site sewage systems with a subsurface perimeter drain without a seasonal high water table, the design and construction of the drain shall meet the requirements of section 59 of this rule.
⁵Dispersal area width shall not be less than ten (10) feet. A dispersal area width of more than twenty-five (25) feet is not required.

(d) Any disturbance within a dispersal area shall not create compacted soil material.

(e) The location of the dispersal area shall meet the following requirements:

(1) A dispersal area shall be located on the property, or adjoining property with easement, except that the easement is not required for lots platted prior to January 1, 2011.
(2) Nothing that would impede the flow of water shall be allowed in a dispersal area. This includes, but is not limited to, the following:
1. (A) buildings;
2. (B) foundations;
3. (C) slabs;
4. (D) garages;
5. (E) patios;
6. (F) barns;
7. (G) aboveground and belowground swimming pools;
8. (H) retaining walls;
9. (I) roads;
10. (J) driveways;
11. (K) parking areas;
12. (L) paved sidewalks;
13. (M) closed loop geothermal systems; or
14. (N) other structures.
(3) A dispersal area shall not be located in a closed depression where surface runoff or subsurface water movement will have an adverse effect on on-site soil absorption system performance or in areas subject to ponding.
(4) For soil absorption system sites with a slope of greater than one-half percent (1/2%), no part of the dispersal area may slope toward the soil absorption system.

(Indiana Department of Health; 410 IAC 6-8.3-58; filed Oct 19, 2012, 2:06 p.m.: 20121114-IR-410120156FRA; readopted filed Sep 26, 2018, 2:48 p.m.: 20181024-IR-410180328RFA; readopted filed Nov 14, 2024, 1:24 p.m.: 20241211-IR-410230798RFA)