VDH has proposed two new horizontal setback requirements necessary to protect public health and the environment – 1) a setback from the drainfield to a wetland, and 2) a setback to any constructed drainage proximate to a drainfield depending on the level of treatment.
Let’s be clear – the wetlands discussed hereafter are non-tidal wetlands. Tidal wetlands are protected by the 70’ setback to shellfish waters. Non-tidal wetlands could be any site with relatively flat topography, poor drainage and seasonal groundwater within 12" of the surface.
Wetlands will be discussed in detail in a subsequent discussion. But, it is relevant to note that the EPA encourages wetland construction for wastewater treatment and wildlife habitat (http://water.epa.gov/type/wetlands/constructed/index.cfm). VDH includes constructed wetlands in their Alternative Discharge regulations (12VAC5-640). And of course, a natural wetland is a potential receiving environment for these same permitted systems. Constructed and naturally occurring wetlands have a tremendous capacity for nutrient (nitrogen & phosphorous) uptake and polishing of treated water. One only has to review some of the 201 citations listed in the National Agriculture Library (http://www.nal.usda.gov/wqic/Bibliographies/eb9701.html) to get a glimpse of the benefits that nature provides.
Constructed drainage improvement is an important engineering strategy for managing surface and groundwater in the Coastal Plain (essentially all land area east of I-95). Constructed drainages (a surface swale or ditch, a gravel filled interceptor, or a vertical sand drain) have been effectively used to manage and mitigate saturated natural soils under and around drainfields. Typically, these systems are used in concert with high levels of wastewater treatment and disinfection. They are primarily used to maintain an unsaturated zone of underlying soil, which is beneficial to the treatment and ultimate disposal of wastewater.
One example is the construction of a gravel filled shallow drain around an elevated sand mound using gravity discharge to a drainage feature of lower elevation. Typically the wastewater undergoes secondary treatment followed by disinfection prior to being discharged to the elevated sand, which essentially acts as a single pass sand filter providing tertiary treatment and polishing. In order to even reach the trench, this highly treated, disinfected wastewater must then flow horizontally through several feet (typically 5’) of natural soils before entering the perimeter drain. Bear in mind, septic tank effluent only has to pass through a comparative thin layer of soil (18”) before entering the receiving environment.
Another example is the construction of a vertical sand drain located under or adjacent to an elevated sand mound. Again, secondary treatment is followed by disinfection and tertiary treatment before entering the sand drain. The sand drain is typically used when elevations do not allow gravity conveyance and there is a highly permeable sand stratum identified below the drainfield site. The sand drain is constructed by excavating through restrictive layers that would inhibit the vertical movement of water into an underlying permeable stratum. The excavation is then backfilled with clean sand. The drain promotes drainage from the surrounding surficial soils – helping to maintain an unsaturated zone of natural soil underlying the drainfield. Any of the highly treated, disinfected wastewater entering the sand drain must flow vertically through several feet of additional sand before entering the receiving environment.
Yet a third example involves an alternative discharging permit where the final point of discharge is a trench running parallel to the stream. This is a practice used in central and western Virginia. The theory being, it is better to get some final polishing through the soil before the treated wastewater enters the stream flow. In many cases, this trench is located within non-tidal wetlands adjacent to the stream.
In both cases, the level of wastewater treatment before entering the natural receiving environment far exceeds the regulatory minimum treatment compared to a conventional septic tank system. In statutory terms, once the wastewater achieves treatment equivalent to a septic tank system it is no longer regulated through Health Department authority. Practically speaking, statutory compliance occurs after secondary treatment and disinfection. The dispersal system and any constructed drainage improvements only add to the minimum regulatory protections of human health and the environment.
VDH has failed to illustrate, document or provide empirical or scientific evidence that these constructed drainage strategies elevate any risk to human health or the environment. The new treatment levels and separation distances are based on opinion and speculation.
A particularly egregious standard practice of VDH is to permit repairs in the Coastal Plain (read high groundwater sites) by allowing the direct discharge of partially treated, undisinfected wastewater directly into the shallow groundwater. Research of recent repair permits in Mathews County found that between November 2008 and June 2010 (20 months) VDH had issued 26 permits for discharges directly into the shallow groundwater out of 39 repair permits (67%). Apparently it is protective of human health and the environment for VDH allow the unfettered discharge of fecal and viral contaminated waste into groundwater on a systematic basis. Yet for an engineered system, extraordinary and excessive measures are necessary.
