It All Flows Downhill

Spring/Summer 2004

By Daphne Buckles

On the East End of Long Island, there are increasing concerns about water quality, not only for the drinking water supply, but for the potential pollution of freshwater and estuarine surface waters. As the push for development on Long Island increases, many of the remaining vacant parcels lie over the high areas of the aquifer, or adjacent to wetlands and surface waters, making the importance of an effective onsite septic system all the more crucial.

A conventional septic system is generally comprised of a septic tank; an initial treatment to remove the solids in the waste stream; and a leaching field or soil absorption system, where the remainder of the effluent is discharged through an outlet on the septic tank into the soil where it percolates through and is further decomposed by bacteria and other microorganisms. A number of the wastewater contaminants can generally be removed through filtration while others, which are water soluable, can reach bays or ponds.

Sewage generally contains enteric bacteria, pathogens, viruses, and eggs of intestinal parasites to which benthic organisms are susceptible. These pathogens can accumulate in fish gills and filtering mechanisms of shellfish, posing a human health risk when eaten.

Most wastewaters also contain nitrates and phosphates, usually derived from organic wastes, detergents or fertilizers. An overabundance of these nutrients can cause excessive plant or algal growth, known as eutrophication. This can lead to a depletion in oxygen levels, resulting in the further die-off of fish and invertebrates. Studies have shown that only 20% of nitrogen that passes through a conventional septic system is effectively removed.

In response to these inefficiencies, alternative technologies have been introduced that have proven to be effective in removing a significant percentage of excess nutrients. These designs require less reliance on site conditions and provide removal of additional pollutants that conventional systems cannot address. Some of these technologies include: recirculating and intermittent sand filters, gravelless and chamber technologies, peat biofilters, and trickle filters.

Many municipalities are realizing the need for such systems in critical areas where surface and ground water qualit