Section 593. Physical features

Article 2

12VAC5-610-593. Physical features.

Physical features, landscape position and soil characteristics affect the ability of soil-based systems to treat and disperse effluent. In order to correctly select and place a sewage system in the environment such that public health and the environment are protected, it is necessary to understand and consider the local hydrologic conditions, the regional geology, and the nature of the soils occurring on the site being evaluated. At a minimum, the following features shall be considered:

1. Marshes and swamps. Placement of subsurface soil absorption systems on or in swamps and marshes is prohibited.

2. Seasonal water table. A vertical separation distance between the point of effluent application and a seasonal water table shall be maintained which reflects the quality of the effluent and the receiving environment. Minimum vertical separation distances may be found in Articles 2 (12VAC5-610-594 et seq.) and 3 (12VAC5-610-597 et seq.) of this part and Tables 4.3 and 4.4.

3. Slope. Subsurface soil absorption trench systems shall not be placed on slopes greater than 50% unless terraced. Criteria for other types of onsite systems are contained in Tables 4.3 and 4.4.

4. Drainage ways. Subsurface soil absorption systems shall not be placed at a position in a drainage way subject to intermittent flooding.

5. Fill material. Placement of subsurface soil absorption systems in fill materials is generally prohibited except in three specific situations. The Wisconsin Mound system is considered a fill system as is the sand-on-sand system. These systems are governed by criteria found in 12VAC5-610-960, 12VAC5-610-965, and Table 4.4. Fill material consisting of colluvial soil derived from sandstone (noncarbonaceous) in the mountainous area may be considered on a case-by-case basis for placement of subsurface soil absorption systems.

6. Sink holes. Placement of a subsurface soil absorption system at the low point of a sink hole is prohibited. For set back distance see Table 4.2.

7. Flood plains. Subsurface soil absorption systems shall not be placed in flood plains subject to annual or more frequent sustained (24 hours) flooding.

8. Alluvial and colluvial deposits. Placement of subsurface soil absorption areas in alluvial and colluvial deposits with shallow depths, extended periods of saturation, or possible flooding is prohibited.

9. Shrink-swell soils. When soils containing horizons with shrink-swell characteristics (see definitions in 12VAC5-610-120) have been identified, they shall be rejected for use for subsurface soil absorption systems.

10. Soil restrictions. Soil restrictions in themselves may form the basis for outright rejection of the site.

11. Free standing water. The presence of free standing water in a profile hole may be grounds for rejection of the site.

Systems Using Naturally Occurring Undisturbed Soil

Historical Notes

Derived from Volume 16, Issue 16, eff. July 1, 2000.

Statutory Authority

§§ 32.1-12 and 32.1-164 of the Code of Virginia.