Bruce:
I think these 2 are your best choices, unless there's something else out there that I'm missing. I don't know how much effluent volume you will be dealing with, and that might make a difference in what system you choose. The RSF seems to give more treatment at the expense of more area consumed. If a mound in your yard isn't objectionable, then that's what I'd take a long, hard look at. The downside is the pump - one more thing to go wrong,
Recirculating Sand Filter - A modified intermittent sand filter in which effluent from the filter is recirculated through the septic tank and/or the sand filter before it is discharged to the soil absorption field. The addition of the recirculation loop in the system may enhance removal effectiveness and allow media size to be increased to as much as 1.5 mm in diameter.
Buried or recirculating sand filters can achieve a very high level of treatment of septic tank effluent before discharge to surface water or soil. Dosed recycling between sand filter and septic tank or similar devices can result in significant levels of nitrification/dentrification, equivalent to between 50 and 75 percent of overall nitrogen removal, depending on the recycling ratio. Regular buried or recirculating sand filters may require as much as 1 square foot of filter per gallon of septic tank effluent.
Mound Systems - An alternative to conventional OSDS and are used on sites where insufficient separation distance or permeation conditions exist. Mound systems are typically designed so the effluent from the septic tank is routed to a dosing tank and then pumped to a soil absorption field that is located in elevated sand fill above the natural soil surface. There is evidence suggesting that pressure dosing provides more uniform distribution of effluent throughout the absorption field and may result in better performance. A major limitation to the use of mounds is slope.
Where adequate area is available for subsurface effluent discharge, and permanent or seasonal high ground water is at least 2 feet below the surface, the elevated sand mound may be used in coastal areas. This system can treat septic tank effluent to a level that usually approaches primary drinking water standards for BOD5, suspended solids, and pathogens by the time the effluent plume passes the property line for single-family dwellings. A mound system will not normally produce significant reductions in levels of total nitrogen discharged, but should achieve high levels of nitrification.
