The relationship between the system type (wastewater application point) and the depth to a limiting layer shall be as follows:
Depth to Limiting Layer in inches | Septic Tank Effluent (greater than 10,000 FC organisms/100 ml) Minimum Twenty-four inches (24") Separation Required | Secondary Treated Effluent(less than 10,000 FC organisms/100 ml) Minimum Sixteen inches (16") Separation Required | NSF Standard 350 Effluent (less than 240 E. coli MPN/100 ml) Minimum Twelve inches (12") Separation Required |
Less than 6 | NA | NA | NA |
6 to <10 | Mound with increased sand (a) | Drip in fill (b), Mound (a)(c) | Drip in fill (b), Mound (c), Modified Mound |
10 to <16 | Mound (minimum 12" depth to limiting layer), Mound with increased sand (a) | Mound, Drip on grade/in fill (b), Modified Mound (a), Illinois Raised Filter Bed | All the above, Drip on grade, Illinois Raised Filter Bed, At-grade |
16 to <24 | Mound, Modified Mound (d) | All the above, Drip in ground/on grade, In-ground trenches (h), At-grade | All the above, in-ground trenches (h), (g) |
24 to <28 | All the above, At-grade | All the above, In-ground trenches (g) | All the above |
28 to 36 | All the above, In-ground trenches (f)(g)(h) | All the above, In-ground trenches (e)(g) | All the above |
36 and above | All the above | All the above | All the above |
Footnotes: a. Maximum 4 gallon per day per linear foot loading rate, single bed or separated un-stacked multiple beds, time dosing. b. Acceptable fill is coarse sand (USDA texture 0.5mm to 1.0 mm). Proper depth of fill needed for separation distance and cover over the drip piping must be placed before installation of distribution system. A minimum of ten inches (10") of soil cover, four (4) of which must be coarse sand fill, must be placed over the drip piping for protective cover. c. Drip distribution acceptable with sand footprint sized according to sand loading rate and mound basal area sized according to least permeable (lowest SLR) soil horizon in existing soil above the limiting layer. d. Limiting layer must be at least eighteen inches (18"). e. Limiting layer must be at least twenty-eight inches (28") using a twelve inch (12") standard gravel trench, less if using a state approved, less than twelve inches (12") thick, low profile proprietary infiltration product. f. Limiting layer must be at least thirty-six inches (36") using a twelve inch (12") gravel trench, less if using a state approved, less than twelve inches (12") thick, low profile proprietary infiltration product. g. Protective topsoil cover needed when the top of the infiltration trench gravel or infiltration product is zero inches (0") to less than six inches (6") below original grade or top of sand fill. Depth of soil cover over a proprietary infiltration product shall be in accordance with the manufacturer’s specifications. h. When the sidewall of the infiltration trench will extend above existing grade, the soil treatment area shall be plowed and filled in accordance with § 171.142 and § 171.143 and the minimum depth of sand fill shall be ten inches (10"). The ten inch (10") depth sand fill material shall extend a minimum of ten feet (10') beyond all seepage trenches before sloping. A minimum of one-half of the depth of the infiltration trench shall be installed into existing grade. | |||