Proposed Text:

12VAC5-610-950. Absorption area design.

A. The absorption area is the undisturbed soil medium beginning at the soil gravel or sand interface which is utilized for absorption of the effluent. The absorption area includes the infiltrative surface in the absorption trench and the soil between and around the trenches when trenches are used.

B. Suitability of soil horizon. The absorption trench bottom shall be placed in the soil horizon or horizons with an average estimated or measured percolation rate less than 120 minutes per inch. Soil horizons are to be identified in accordance with 12VAC5-610-480. The soil horizon must meet the following minimum conditions:

1. It shall have an estimated or measured percolation rate equal to or less than 120 minutes per inch.

2. The soil horizon or horizons shall be of sufficient thickness so that at least 12 inches of absorption trench sidewall is exposed to act as an infiltrative surface; and

3. If no single horizon meets the conditions in subdivision 2 of this subsection, a combination of adjacent horizons may be utilized to provide the required 12-inch sidewall infiltrative surface. However, no horizon utilized shall have an estimated or measured percolation rate greater than 120 minutes/inch.

4. Any substitution that decreases the "Area Required per Bedroom" or "Area Required per 100 gallons" listed in Table 5.4 shall be supported by saturated hydraulic conductivity or percolation testing.

Justification:

  The 25 percent reduction in area is removing a factor of safety established by the Virginia Department of Health.  "http://www.vdh.virginia.gov/EnvironmentalHealth/ONSITE/gmp/documents/2010/GMP-035-dde.pdf".     

  If the proposed regulations are to start removing Agency factors of safety in the DESIGN of onsite sewage systems, then   actual field test data should be an industry minimum to provide support for the removal of safety factors.