Alabama Administrative Code
Title 420 - ALABAMA STATE BOARD OF HEALTH
Chapter 420-3-1 - ONSITE SEWAGE TREATMENT AND DISPOSAL
Site Evaluation
Section 420-3-1-.47 - Unified System For Site Evaluation

Universal Citation: AL Admin Code R 420-3-1-.47

Current through Register Vol. 42, No. 11, August 30, 2024

(1) An engineer or geologist may evaluate a site using the unified system method.

(2) The percolation test method may be used in combination with this method to aid in evaluating a site.

(3) Lab analysis may be substituted for estimates at any time but is required for Texture Group 4B and 4C soils (estimated permeability more than 90 MPI). However, in the case where the results from this method conflict with an evaluation by a representative of the LHD or ADPH, ADPH evaluation results shall be final.

(a) If the design is utilizing drip irrigation at a 05 gpd/sq. ft. loading rate, lab analysis is not required.

(b) For any other design using a soil loading rate of greater than 240 MPI, lab analysis is not required.

(4) For Small-Flow single-family dwellings, a minimum of two observation pits or two soil borings shall be required for each EDF, and one observation pit or boring shall be performed in the REDF for lots of less than 15,000 sq. ft. See Table 17 for exceptions. The pits or borings shall be located no closer than 30 feet apart. The pits or borings shall be evenly spaced to represent the EDF area.

(5) For Large-Flow systems and establishments, a minimum of two observation pits or two soil borings shall be required for the initial 600 gpd. One observation pit or boring shall be required for each additional 600 gpd of flow or portion thereof thereafter. The pits or borings shall be evenly spaced to represent the EDF area. The method by which each test is located shall be specified.

(6) Soil borings shall be dug to a minimum depth of 48 inches to determine the limiting zone depth, unless prevented by bedrock or an additional 6 inches once ASHES is encountered. The minimum diameter of the soil boring shall be 2.5 inches.

(7) When observation pits are used, they shall be a minimum of 60 inches deep unless prevented by hard bedrock and constructed in such a fashion as to be easily accessible and safe for the evaluator.

(a) The vertical section of the observation pit wall shall be picked to a width of at least 12 inches, from the ground surface to the floor of the observation pit, for observations and note-taking.

(b) The soil in the picked zone shall be moist so that the proper colors can be observed and noted. If additional moisture is needed, apply water with a spray bottle. All colors recorded shall be from moist and unmixed samples.

(8) The upper and lower depths of each layer of soil shall be recorded in inches from the surface of the ground. Each layer shall be given a numerical identification, beginning with the surface as No. 1 and numbering consecutively with depth.

(9) The color(s) and texture of each layer shall be recorded, using unified designations, starting with the surface, and continuing to the minimum required depth. Any other pertinent information about the site, including percent slope and landform position, shall be reported. From this information, the location, depth, and amount of EDF can be proposed to the LHD.

(10) Soil colors shall be determined using a Munsell chart or equivalent and reported for each layer. Soil colors may occur as:

(a) Only one color.

(b) One dominant color with secondary colors (mottles or redoximorphic features).

(c) Several colors with approximate equal coverage (mottled). To the extent possible, all colors should be recorded, with the dominant color first.

(11) The depth to the ASHES shall be determined from 420-3-1-.42 Soil Restriction Depth and Vertical Separation. EDF bottoms shall have a minimum separation distance above the ASHES or other restrictive layer, or horizon as established in Table 7. If there is uncertainty about whether a feature qualifies as a restrictive layer or horizon, the LHD shall be consulted.

(12) Once the upper and lower depths of each layer are determined and colors are noted, the permeability can be assigned for each layer. Use Table 20 to assign soil permeability classes based on the Unified System (Reference: FHA No 373, Engineering Soil Classification for Residential Development).

Previous Rule .71 was renumbered .47 per certification published December 30, 2022; effective February 13, 2023.

Author: David Gray, Boyd Rogers, Richard Smith

Statutory Authority: Code of Ala. 1975, §§ 22-2-2(4); 22-2-2(6); 22-10-1, et seq.; 22-26-1et seq.

Disclaimer: These regulations may not be the most recent version. Alabama may have more current or accurate information. We make no warranties or guarantees about the accuracy, completeness, or adequacy of the information contained on this site or the information linked to on the state site. Please check official sources.
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