Virginia Law

A. Shallow-placed systems are systems which utilize a natural, undisturbed soil horizon to treat and disperse effluent where the infiltrative surface is placed at a depth of less than 18 inches from the original soil surface. Also see Table 4.3. Shallow-placed systems may use the system designs similar to in-ground systems; however, when shallow-placed systems are installed at less than 12 inches from the ground surface, timed dosing shall be used to disperse the effluent.

B. Septic effluent prohibited. Septic tank effluent is prohibited for use in shallow-placed systems because of the increased likelihood for human and vector contact with effluent.

C. Soil criteria when utilizing secondary effluent. Secondary or better effluent may be utilized in an shallow-placed system when all of the criteria in this subsection are met. Also see Table 4.3.

1. Soil texture. In order to assure effluent dispersal under adverse conditions while maintaining adequate treatment capacity, shallow-placed systems installed shallower than 12 inches, which utilize absorption trenches, are limited to Texture Group I and II soils. Any soil texture group may be utilized for absorption trench systems installed between 12 and 18 inches.

2. Limiting features. A minimum of 12 inches of soil is required beneath the trench bottom or infiltrative surface before encountering soils with a seasonal or permanent water table. Additionally, to assure adequate hydraulic dispersal capacity, bedrock and impervious strata may not occur within 18 inches of the trench bottom.

3. Separation distances. Table 4.2 contains the minimum setback distances between an absorption field and various structures or topographic features.