Virginia Law

A. Sand-on-sand is a process of modifying a soil absorption system site using fill material which is similar in texture to the original, naturally occurring material. Filling is accomplished in a manner which allows for adequate treatment and disposal of effluent, protection from frost and traffic damage, and does not promote the creation of restrictive horizons. Sand-on-sand systems are considered Type II systems and are used to overcome limitations encountered with certain high water table soils. A detailed description of the siting criteria used for sand-on-sand systems is found in 12VAC5-610-597.

B. Site preparation. All surface vegetation and organic matter, including but not limited to grass, shrubs, trees, leaf litter, branches, limbs, and tree stumps shall be removed. Special consideration shall be given to site preparation to avoid soil compaction and other damage which may create discontinuities and restrictive horizons when the fill material is placed on the site.

C. Fill material. Fill material may be added to such a site and used for residential onsite wastewater disposal for flows up to 1,000 G.P.D. on sites meeting the criteria established in 12VAC5-610-597 provided that:

1. The fill material used is the same texture as the underlying material;

2. The coarse fragment content of the fill material is neither greater than 10% by volume nor noncarbonaceous and inorganic material greater than two mm in size;

3. The fill material is placed in such a manner as to prevent the formation of any restrictive horizons;

4. The fill material covers an area 10 feet greater in all horizontal dimensions than the soil absorption system;

5. The sides of the filled area are sloped at not greater than 1:10 (rise:run);

6. The fill material provides at least six inches of cover over all portions of the system; and

7. The fill material is stabilized to prevent surface erosion.

D. Application rate. All sand-on-sand systems shall be designed on a 30 mpi loading rate and shall use a method of pressure distribution which achieves unsaturated flow conditions.

E. Fill depth. All sand-on-sand systems utilizing gravel trench designs shall have a minimum of 25 inches of fill over the original site.

F. System placement. The drainfield trenches shall be placed so that there is six inches of fill, or more, beneath the trench bottom and six inches of fill over the trenches.

G. The remaining design and construction criteria for sand-on-sand systems are the same as for the design and construction of a similar system in original undisturbed soils.