A. Prior to approval by the board of a subdivision for which on-site disposal systems are proposed to be used, the subdivider shall obtain the approval of the environmental officer for this method of sewage disposal. The subdivider shall demonstrate that an on-site disposal system can be installed pursuant to minimum design criteria on each proposed lot. Any lot that cannot meet minimum design criteria for an on-site disposal system shall be excluded from the subdivision and shall not be approved as part of the subdivision as a separate lot. Prior to the construction of an on-site disposal system on any lot of the subdivision, additional testing, specific design approval and a certificate of approval to construct shall be required as provided in this article.
B. The following information shall be submitted to the environmental officer pursuant to subsection A:
1. A tentative plat showing the net usable acreage for each lot;
2. A geological report prepared by an engineer, geologist or other qualified person.
C. Size of Lots: The minimum size for single-family residential lots shall be one acre, including easements and designated rights-of-way. In addition, each lot shall be of sufficient size to accommodate an on-site disposal system for a four-bedroom house and provide for at least one hundred percent expansion of the system within the bounds of the property, allowing a minimum of five feet distance to the property lines. For all other uses, the lot shall be sufficient size to meet Bulletin 12 disposal density requirements, to accommodate the on-site disposal system and provide for at least one hundred percent expansion of the system within the bounds of the property allowing a minimum of five feet distance to the property lines.
D. The geological report submitted pursuant to subsection A shall include at least the following:
1. General description of the area;
2. A vicinity map having sufficient detail to enable a person unfamiliar with the area to find the site;
3. Description of methods used in making the soil profile and percolation tests;
4. Map giving location of soil profiles and percolation tests;
5. Boring log results;
6. Percolation test results;
7. Depth to groundwater;
8. Description of topography;
9. Detailed description of present and planned land uses adjacent to the proposed subdivision.
E. Number of Percolation Tests and Boring Logs:
1. Percolation tests and boring logs shall be conducted sufficient to accurately depict soil conditions. The location of percolation test sites and the depth of boring logs shall be determined by the environmental officer.
2. There shall be a minimum of one percolation test and one ten-foot boring log per acre, or one percolation test and boring log per lot for lots larger than one acre.
3. In areas proposed for on-site disposal systems where the slope of the terrain is five percent or less, the depth to groundwater is greater than fifty feet and an impermeable strata is greater than fifteen feet below the existing ground surface, fewer percolation and boring log tests than one per acre may be approved by the environmental officer if the boring log test results indicate a uniform soil structure and percolation test results indicate that the percolation rate is uniform in the area and is between one and fifteen minutes per inch.
4. The environmental officer may require additional tests when, based upon the geology and physical conditions of a particular site, the environmental officer deems it necessary.
5. The results of all tests conducted pursuant to this subsection shall be submitted to the department for review pursuant to subsection A.
F. Boring Logs: Data on the types of soil strata, rock or impervious strata shall be obtained from boring logs to a depth to be determined by the environmental officer, but not less than four feet below the bottom of the proposed subsurface on-site disposal system using disposal trenches. Data on groundwater shall be obtained to fifty feet below the bottom of the subsurface on-site disposal system by borings or existing hydrogeological data.
G. Soil Depths: Impervious soil strata or bedrock shall be four feet or more below the bottoms of proposed subsurface disposal systems. If installation in more shallow soils is proposed, it shall be demonstrated that:
1. The bedrock is permeable; and
2. The bedrock does not limit construction practices necessary to meet minimum design criteria; and
3. Contamination of water supplies is improbable.
H. Topography: Topographic map of proposed site. The contour intervals shall be such as to clearly identify all washes, watercourses, rocks, outcroppings and similar features. The maximum contour interval shall be:
GRADE | CONTOUR INTERVAL (FEET) |
0—5% | 2 |
5—10% | 5 |
Greater than 10% | 10 |
I. Septic System Locations: In areas of rough terrain or poor absorption, the location of the on-site disposal system and reserve area shall be shown for each lot on the final plat plan.
(Ord. 1991-137 § 13 (part), 1991)