Article 3. Pretreatment Systems
12VAC5-610-780. General.
Article 3
Pretreatment Systems
As used in this article, "pretreatment" refers to treatment works designed to prepare sewage for disposal in a soil medium.
Statutory Authority
§§ 32.1-12 and 32.1-164 of the Code of Virginia.
Historical Notes
Derived from VR355-34-02 § 4.13, eff. February 5, 1986; amended, eff. May 11, 1988.
12VAC5-610-790. Types.
Three general types of pretreatment systems are described herein. They are as follows:
A. Biological;
B. Physical; and
C. Chemical.
Statutory Authority
§§ 32.1-12 and 32.1-164 of the Code of Virginia.
Historical Notes
Derived from VR355-34-02 § 4.14, eff. February 5, 1986; amended, eff. May 11, 1988.
12VAC5-610-800. Aerobic biological systems.
Aerobic biological treatment systems will be considered on a case-by-case basis at the request of the owner. These systems shall meet the applicable criteria contained in 12VAC5-640-360 of the Alternative Discharging Sewage Treatment Regulations for Individual Single Family Dwellings or 12VAC5-580-770 of the Sewerage Regulations (12VAC5-580-10 et seq.) or criteria developed by a testing laboratory or agency approved by the division. Where an activated sludge process is used to produce a secondary effluent, provisions shall be made to protect the drainfield from bulking solids. Use of an aerobic pretreatment system shall not result in the reduction of the absorption area requirements contained in Article 5 (12VAC5-610 900 et seq.) of this chapter.
Statutory Authority
§§ 32.1-12 and 32.1-164 of the Code of Virginia.
Historical Notes
Derived from VR355-34-02 § 4.15, eff. February 5, 1986; amended, eff. May 11, 1988; Virginia Register Volume 16, Issue 16, eff. July 1, 2000.
12VAC5-610-810. Anaerobic biological systems.
Septic tanks are the most commonly used pretreatment systems and under normal circumstances are the most inexpensive units that give acceptable results with a minimum of maintenance.
The preferred material for use in constructing septic tanks is concrete. Other materials may be considered on a case-by-case basis. All materials must be resistant to corrosion, both chemical and electrolytic, and must have sufficient structural strength to contain sewage and resist lateral compressive and bearing loads.
Statutory Authority
§§ 32.1-12 and 32.1-164 of the Code of Virginia.
Historical Notes
Derived from VR355-34-02 § 4.16, eff. February 5, 1986; amended, eff. May 11, 1988; Virginia Register Volume 16, Issue 16, eff. July 1, 2000.
12VAC5-610-815. Septic tank design.
A. Tank capacity. The minimum hydraulic detention time shall be 48 hours based on daily design flow. In no case shall the septic tank capacity be less than 750 gallons. Table 5.2 contains the minimum required septic tank capacities for dwelling units.
| Table 5.2. | |
| No. of Bedrooms | Approximate Tank Volume in Gallons |
| 1 | 750 |
| 2 | 750 |
| 3 | 900 |
| 4 | 1200 |
| 5 | 1500 |
B. Tank dimensions. Septic tanks shall be rectangular in plan, cross-section and longitudinal view. The length to liquid depth to width ratio should be approximately equal or greater than 2 to 1 to 1 (2:1:1) and less than or equal to 3 to 1 to 1 (3:1:1). In no case shall the liquid depth be less than four feet or greater than eight feet. A minimum of one foot free board shall be provided. Inlet and outlet structures shall be placed on the longitudinal axis of the tank. Typical tank dimensions are found in Table 5.3.
| Table 5.3. | ||||
| Approximate Gallons | Length | Width | Liquid Depth | Freeboard |
| 750 | 7 | 3.5 | 4 | 1 |
| 900 | 8 | 4 | 4 | 1 |
| 1200 | 9 | 4.5 | 4 | 1 |
| 1500 | 9.5 | 5 | 4.7 | 1 |
C. Inlet-outlet structure.
1. General. The inlet and outlet structures shall function as a baffle. The invert of the inlet structure shall be greater than one inch but less than two inches higher than the invert of the outlet structure with the tank installed. The inlet structure shall extend six to eight inches below and eight to 10 inches above the normal liquid level. The outlet structure shall extend below the normal liquid surface to a distance of 35 to 40% of the liquid depth and eight to 10 inches above the normal liquid level. The inlet and outlet structures shall have an open space not less than four inches by four inches in cross-section or four inches in diameter.
2. Materials. All materials used for inlet and outlet structures shall have long term resistance to chemical and electrolytic corrosion. When pipe tees are used as inlet and outlet structures, the material shall be compatible with the material used in the sewer.
D. Top access and watertightness. All septic tanks shall be watertight and shall be provided with a watertight top. As a minimum, access manholes shall be provided over the inlet and outlet structures and shall have a minimum open space of 18 inches by 18 inches. When the septic tank has in excess of 30 inches of soil cover, an access manhole shall be brought to within 18 inches of the ground surface and shall be provided with a tight fitting cover. In wet areas the manhole covers shall be watertight.
E. Construction of septic tanks. The contractor and/or manufacturer shall design and construct the septic tank to withstand the lateral and bearing loads to which the septic tank is expected to be subjected.
F. Placement of septic tanks. The precast septic tank shall be bedded with at least six inches of sand or fine gravel where rock or other undesirable conditions are encountered. The tank shall be placed level. Where excavation is required, the hole shall be sufficiently large to permit placement of the tank. Backfilling the excavation for all septic tanks shall be done in layers with sufficient tamping to avoid settling. Backfill material shall be free of large stones and debris.
Statutory Authority
§§ 32.1-12 and 32.1-164 of the Code of Virginia.
Historical Notes
Derived from Virginia Register Volume 16, Issue 16, eff. July 1, 2000.
12VAC5-610-817. Maintenance.
A. In order to encourage proper maintenance and reduce the likelihood of solids being discharged to an absorption field, all septic tanks constructed after July 1, 2000, shall be designed to allow for routine inspection without being uncovered (i.e., have an inspection port as provided for in subsection B of this section) or have an effluent filter as provided for in subsection C of this section, or be designed for reduced maintenance as provided for in subsection D of this section.
B. Inspection port. An inspection port is a three-inch or larger port pipe or structure which allows access to the septic tank for the purpose of measuring sludge and scum accumulation. The inspection port shall terminate at or above grade and be designed to allow an inspection of sludge buildup in the septic tank. The inspection port shall be constructed of schedule 40 PVC pipe, or its equivalent, and shall be fitted with a watertight threaded cap. The recommended location of the inspection port shall be in or near the manhole cover on the inlet side of the septic tank away from the inlet tee. Other locations may be approved by the district health department on a case-by-case basis.
C. Effluent filters. An effluent filter is a device which has one or more of the following purposes: (i) to manage solids to provide greater service life to a pump or other components of an onsite system; (ii) to manage the total suspended solids (TSS) passed to the absorption field, potentially enhancing absorption field life; or (iii) some other purpose recognized as beneficial by the department.
1. All effluent filters shall be designed to improve the quality of effluent leaving the tank in a manner which is consistent with their purpose.
2. Septic tank outlet filters shall be constructed from a material which resists the corrosive nature of the environment within a septic tank.
3. A tamper proof child resistant at-grade access port shall be provided to assure the filter can be readily maintained as necessary.
D. Reduced maintenance septic tanks. Septic tanks which are sized 30% larger than shown in Table 5.3 and which are baffled such that the first compartment is nominally the volume required in Table 5.3 shall be considered to be a reduced maintenance septic tank.
Statutory Authority
§§ 32.1-12 and 32.1-164 of the Code of Virginia.
Historical Notes
Derived from Virginia Register Volume 16, Issue 16, eff. July 1, 2000.
12VAC5-610-820. Miscellaneous.
A. Multiple septic tanks in series. The required volume for a septic tank may be satisfied by the utilization of two septic tanks in series; however, the first septic tank in series shall equal to 1/2 to 2/3 the required total volume.
B. Physical and/or chemical systems. Physical or chemical systems, or both, utilized as pretreatment for subsurface disposal of sewage shall meet the applicable criteria contained in 12VAC5-580-930 through 12VAC5-580-960 of the Sewerage Regulations.
C. Water stop. A water stop is a method for sealing the annular space around a conduit or pipe, or both, for the purpose of preventing infiltration or exfiltration, or both. Conduits or pipes passing through the walls of a pretreatment unit shall be provided with a water stop.
Statutory Authority
§§ 32.1-12 and 32.1-164 of the Code of Virginia.
Historical Notes
Derived from VR355-34-02 § 4.17, eff. February 5, 1986; amended, eff. May 11, 1988; Virginia Register Volume 16, Issue 16, eff. July 1, 2000.
12VAC5-610-830. (Repealed.)
Historical Notes
Derived from VR355-34-02 §§ 4.18 and 4.19, eff. February 5, 1986; amended, eff. May 11, 1988; repealed, Virginia Register Volume 16, Issue 16, eff. July 1, 2000.