Authority: IC 16-19-3-4

Affected: IC 16-19-3-4

Sec. 78. (a) On-site sewage system feasibility, location, and selection shall be based on the:

1. (1) site evaluation;
2. (2) information obtained from the on-site soils evaluation; and
3. (3) DDF.

If site conditions are acceptable, subsurface trench soil absorption systems are the systems of choice.

(b) All of the following site conditions in this section must be met if subsurface trench on-site sewage systems are to be constructed:

1. (1) Sufficient area exists on the lot for an appropriately sized subsurface trench on-site sewage system, while meeting the:

   1. (A) separation distances of section 61 of this rule; and
   2. (B) dispersal area requirements of section 62 of this rule.
2. (2) The topographic position of the site on which the on-site sewage system is to be built is convex, hill slope, or flat. If surface and subsurface drainage can be diverted around the site, a toe slope position can be used.
3. (3) The site has a slope of fifteen percent (15%) or less.
4. (4) Site conditions permit distribution of effluent to each trench of the subsurface soil absorption system so that each trench can be loaded with a proportionate volume of effluent.
5. (5) Site conditions permit any seasonal high water table at the site of the proposed subsurface trench soil absorption system to be lowered to at least thirty-four (34) inches below original grade, in accordance with section 63 of this rule.

6. (6) When there are no horizons from original grade to thirty-four (34) inches below original grade in a soil developed from Wisconsin glacial till that shows effervescence when treated with a ten percent (10%) hydrochloric acid solution, unless:

   1. (A) 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. (B) the determination in clause (A) 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.

7. (7) When there are no soil horizons at the site from the original grade to thirty-four (34) inches below the original grade with:

   1. (A) less than twenty percent (20%) clay by volume and greater than thirty-five percent (35%) coarse fragments by volume; or
   2. (B) greater than or equal to twenty percent (20%) clay by volume and greater than sixty percent (60%) coarse fragments by volume.

8. (8) All soil horizons at the site from the original grade to thirty-four (34) inches below the original grade have a soil loading rate of not less than twenty-five hundredths (0.25) and not more than one and twenty-hundredths (1.20) gallons per day per square foot as determined from Table V, as follows:

   Table V – Soil Loading Rates for Subsurface Trench On-Site Sewage Systems (in gpd/ft2)
   	SOIL STRUCTURE CLASSES
   SOIL TEXTURE CLASSES	Single Grain	Granular	Strong: Angular, Sub-Angular Blocky, Prismatic	Moderate: Angular, Sub-Angular Blocky, Prismatic	Weak: Angular, Sub-Angular Blocky, Prismatic; Platy1	Fragic Characteristics: Very Coarse Prismatic	Structureless, Massive, Friable, V. Friable	Structureless, Massive, Compact, Firm, V. Firm; Platy2
   Gravel, Coarse Sand	1.20	N/A	N/A	N/A	N/A	N/A	N/A	N/A
   Loamy Coarse Sand, Medium Sand	1.20	1.20	N/A	N/A	1.20	N/A	N/A	N/A
   Fine Sand, Loamy Sand, Loamy Fine Sand	0.75	0.60	N/A	0.75	0.75	N/A	0.75	N/A
   Very Fine Sand, Loamy V. Fine Sand	0.50	0.50	N/A	0.75	0.60	N/A	0.60	N/A
   Sandy Loam, Coarse Sandy Loam	N/A	0.75	N/A	0.60	0.60	0.00	0.60	0.00
   Fine Sandy Loam, V. Fine Sandy Loam	N/A	0.75	N/A	0.60	0.60	0.00	0.60	0.00
   Loam	N/A	0.75	0.75	0.50	0.50	0.00	0.50	0.00
   Silt Loam, Silt	N/A	0.75	0.75	0.50	0.30	0.00	0.30	0.00
   Sandy Clay Loam	N/A	0.60	0.60	0.50	0.30	0.00	0.30	0.00
   Silty Clay Loam, Clay Loam, Sandy Clay	N/A	0.60	0.60	0.30	0.25	0.00	0.25	0.00
   Silty Clay, Clay	N/A	0.60	0.50	0.30	0.25	N/A	0.25	0.00
   Organic Soil Materials	N/A	N/A	N/A	N/A	N/A	N/A	0.00	N/A
   Limnic Soil Materials	N/A	N/A	N/A	N/A	N/A	N/A	N/A	0.00
   Bedrock	N/A	N/A	N/A	N/A	N/A	N/A	N/A	N/A
   N/A NOT APPLICABLE
   1Naturally occurring platy structure.
   2Platy structure caused by mechanical compaction has a soil loading rate of 0.00 gpd/ft2 unless broken up by methods approved by the department.

(c) Subsurface trench soil absorption systems shall not be constructed as follows:

1. (1) In areas where surface runoff or subsurface drainage will have an adverse effect on the on-site sewage system, unless the surface runoff or subsurface drainage can be effectively diverted around the system.
2. (2) With the bottom of any of the trenches below the RFE.
3. (3) In areas subject to ponding.
4. (4) Wholly or partly located in a drainage way.
5. (5) Where compacted soil material is identified in the soil at a depth greater than twelve (12) inches, unless the compaction is broken up by a method approved by the department.

(Indiana Department of Health; 410 IAC 6-10.1-78; filed Oct 19, 2012, 2:07 p.m.: 20121114-IR-410120157FRA; readopted filed Sep 26, 2018, 2:48 p.m.: 20181024-IR-410180328RFA; readopted filed Nov 14, 2024, 1:24 p.m.: 20241211-IR-410230798RFA)