Type

11e. T 11f.

12VAC5-613-30. Applicability and Scope K specifically says spray is not covered by these regs.  Spray systems for single family homes <1000 GPD are provided for by GMP 74 under a general permit from DEQ to VDH.  To me they are alternative systems.

There are two issues with this table and its application.  There has been no proof or consensus that the soil infiltrative surface knows the difference between TL2 and TL3 water quality to justify different loading rates.  Standoff’s to limitations may be different.  Secondly, the application of microorganisms and nitrified effluent by gravity to meet environmental goals has no demonstrated basis and is a polluting practice (see above).  Nitrates move with water and Gravity flow creates saturated flow at the point of discharge that promotes migration directly to the water table within a detectable plume. It is recommended that gravity distribution be prohibited for nitrified effluent.

If gravity dispersal with treated effluent is allowed, better guidance is necessary.  Just saying the size should be increased (loading rate reduced) is not enough.

12. Septic tank effluent may only be discharged to a soil treatment area when the vertical separation to a limiting feature consists of at least 18 inches of naturally-occurring, in-situ soil. Trench type AOSSs designed to disperse septic tank effluent require at least 12 inches of soil cover over the soil treatment area;

This requirement comes from 12VAC5-610 (Sewage Handling and Disposal Regulations) regarding to standard trench type systems and should be revised to address those configurations.

12 VAC 5-610-950  Adsorption area design, E. Minimum cross section dimensions for adsorption trenches. 1. Depth, addresses the installation depth of trenches, requiring a minimum of 12” sidewall in mineral soil (indicating 12” minimum installation depth for trenches), 12” cover, increased depth and increased area (with shallow soils) for slopes. 

Will this section, specifically the sidewall, still apply?

Table 2  Minimum Effluent Requirements for Vertical Separation to Limiting Features

Septic Effluent should be defined as >60 Mg/L BOD.

15. The organic loading rate …

Remove this section as it is in conflict with other portions of the regulation.

12VAC5-613-90. Performance requirements; ground water protection.

A. The AOSS shall not pose a greater risk of ground water pollution than systems otherwise permitted pursuant to 12VAC5-610. After wastewater has passed through a treatment unit or septic tank and through the soil in the soil treatment area, the concentration of fecal coliform organisms shall not exceed 2.2 cfu/100 ml at the lower vertical limit of the project area boundary.

This section is cited in 12VAC5-613-30. Applicability and scope.D

D. Small AOSSs designed, constructed…

Deem to comply status for the prescriptive designs is excellent however citing a fecal standard begs compliance.  Septic tank effluent dispersed by classical Low Pressure Pipe would likely not meet the 2.2 cfu/100 ml requirement with an 18” seperation to limitation.  Duncan / Reneau’s Wastewater Renovation with Soil Depth as Influenced by Additional Treatment of Septic Tank Effluent exhibited excellent results, but remember the soil column’s were dosed six times a day.  On a performance basis, LPD systems dose may 1X day based on average flow.

Gravity dispersal from TL-1 and TL-2 certainly cannot be expected to meet the 2.2 cfu/100 ml requirement with the respective 12 and 6” seperation to limitation.

I recommend the sentence be removed or changed to a higher limit such as 200 cfu/100 ml to be an achievable standard and to somewhat coincide with other standards.

D.  (2) A mass loading of 4.5 lbs N or less per person per year….The root zone whereby nutrients are recycled is typically less than 12”.   Further, shallow trench, bed, and mound type systems at shallow depths may allow for access to more carbon, however these constructed interfaces do not allow for replentishment of carbon or access by plant roots.  Drip dispersal and spray irragation provided for slow rate land application and recycling.

Chapter 6 of the EPA Non-Point Manual states:  “Effluent standards can be met by either system design or performance, as verified by third party design review or field verification. Except in sandy or loamy sand soils, a 5 mg/L N reduction credit is given when using time dosed, pressurized effluent dispersal within 1 foot of the ground surface and more than 1.5 feet above a limiting soil/bedrock condition.”

2. All large AOSSs shall demonstrate less than 3 mg/l TN at the project boundary…..

Table 3 Maximum TN Effluent Quality Requirements for Large AOSSs

Table 3 in under section D addresses Chesapeake Bay Requirements however “2” above says “all” AOSSs.  I understand that the minimum nutrient limits maybe met in the entire treatment works, including the soil, by meeting these standards of treatment plus application of other approved BMP’s such as from EPA Chapter Six above.

I assume that outside the Chesapeake Bay area dilution can be utilized in the calculation to meet the 3 mg / l as provided by GMP 72.

A major concern is that designers will elect to utilize multiple deem to comply small AOSS treatment units in lieu of cluster systems as encourage by the EPA.  With the current requirement many facilities such as schools, churches, existing hamlets / communities, businesses, and small subdivisions may not be able to afford to be built.

I agree that deem to comply, that is 50% reduction, with approved BMP’s, should be expanded to large AOSS’s <10,000 GPD.  The 3 mg/l will then have to start at that point also.

I also concur that 10,000 to 40,000 gpd would have to meet an minimum effluent limit of 20 mg/l TN PLUS field management to comply with the 3 mg/l TN at the project boundary.  Above 40,000 gpd, all systems would have to treat to 10 mg/l TN prior to disposal on land with field management to reduce the total to 3 mg/l at project boundary.

I know that the 3 mg/l is a currently technically achievable by treatment.  Perhaps addressing through percentage reduction is a more realistic.

Tom W. Ashton, R.E.H.S., C.P.S.S., A.O.S.E

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