With respect to effluent and groundwater quality standards for systems otherwise permitted pursuant to the regulations (see 32.1-163.6), the systems consist of three basic types:

 

1.      Pit Privies underlain by 24” of unsaturated soil

2.      Conventional Septic Tanks underlain by 18” of unsaturated soil, and

3.      Alternative Onsite Systems underlain by 12” of unsaturated soil.

 

From the statutory language, it follows that the effluent and groundwater quality standards for engineered systems must be at least equivalent to one of the three above – presuming that the three above are all equivalent with respect to protecting human health and the environment. 

 

The statutory definition of Treatment Works reads -

 

"Treatment works" means any device or system used in the storage, treatment, disposal or reclamation of sewage or combinations of sewage and industrial wastes, including but not limited to pumping, power and other equipment and appurtenances, septic tanks, and any works, including land, that are or will be (i) an integral part of the treatment process or (ii) used for ultimate disposal of residues or effluents resulting from such treatment.

 

From the above definition it is evident that a treatment works may include a soil component such as the mandated depth of unsaturated soil underlying a drainfield. This soil component adds to the remedial treatment of the wastewater. But, immediately after passing through the required soil depth the wastewater effluent effectively becomes groundwater. For Septic Tank systems, the effluent becomes unregulated groundwater 18” below the bottom of the drainfield trenches. The Health Department has no jurisdiction or regulatory authority thereafter.

 

Therefore, an engineered system under 32.1-163.5 must produce equivalent effluent that is as protective of human health and the environment as septic tank effluent after passing through 18” of soil. So the question is – What is the effluent quality standard at that point? There is no quantifiable standard available in the current regulations (12VAC5-610). Therefore one has to look at available research. Data from Reneau’s published study in 2001 shows that after passing through 18” of soil, septic tank effluent had a 45% probability of exceeding a fecal coliform count of 200 cfu/100ml. Further the data shows that partially treated effluent (Secondary Effluent) passing through 12” of soil had about a 23% probability of exceeding a fecal coliform count of 200 cfu/100ml. 

 

While one study is clearly not definitive we can also look at other standards for guidance. For instance, the DEQ VPDES General Permit (9VAC25-110) for small flow discharges to surface water is 200 cfu/100 ml; the VDH Alternative Discharge (12VAC5-640) limit is 200 cfu/100ml to surface water and 100 cfu/100ml to a dry ditch; the DEQ surface water quality standard (9VAC25-260) for swimming is 200 cfu/100ml; and, the DEQ reuse standard (9VAC25-740) for no potential public contact is 200 cfu/100 ml.

 

It is reasonable then, to surmise, that the groundwater quality standard for bacterial contaminants is a Fecal Coliform count of 200 cfu/100 ml. This is the statutory standard for systems otherwise permitted pursuant to the regulations and becomes the standard for engineered systems at the end of the Treatment Works.

 

A similar review related to effluent quality (BOD₅ and TSS) finds that the DEQ VPDES General Permit (9VAC25-110) for small flow discharges to surface water is 30 mg/l; the DEQ reuse standard (9VAC25-740) for no potential public contact is 30 mg/l; and, the VDH Alternative Discharge (12VAC5-640) limit is 30 mg/l to surface water. 

 

Again, based on this elementary review of current standards, it is reasonable to surmise that the effluent standard quality standard quality standard for BOD₅ and TSS is 30 mg/l.

 

In summary, the standard for engineered systems designed pursuant to 32.1-163.6 can be reasonably quantified by looking at published research and current standards of similar nature. The point of compliance is the end of the Treatment Works; which may include a soil component underlying the point of effluent application to the soil. VDH has no statutory authority to exceed these standards. 

 

it is incumbent upon VDH to develop a defensible rationale for the standards that relates back to systems otherwise permitted pursuant to the regulations. In simplistic terms, there is no statutory authority to require engineered systems to be more protective, or meet higher effluent standards, than conventional septic tank effluent passing through 18” of soil.