|Project_Name||Performance of On-Site Wastewater Treatment Systems and their Effects on Groundwater Quality
|Project Date||1/1/1998 12:00:00 AM
|Description||Rural and suburban residents, and small communities,
depend on groundwater for their drinking
water. Many of those communities also dispose
wastewater to the shallow groundwater via on-site
systems. With increasing rural subdivision, there
is widespread concern for the possible contamination
of drinking water by partially-treated wastewater.
Nitrate-nitrogen is of particular concern.
There are many "alternative" or "innovative" or
"experimental" on-site systems in use. Each is
designed to address a particular problem - a site
constraint or wastewater constituent - that is not
handled well by conventional septic systems.
This project monitored three such systems. Its
objectives were: 1) to document their effectiveness
in treating domestic wastewater (particularly
the alteration or removal of nitrogen), and 2) to
define the minimum necessary sampling regime
to accurately characterize treated wastewater and
A new, state-of-the-art intermittent sand filter
serving a single-family home was monitored
intensely for nine months. This filter, dosed at the
rate prescribed by state regulations, cleansed the
wastewater effectively of coliform bacteria and
organic matter. Its total nitrogen removal ranged
from 15% to 30%. Nearly all of its effluentnitrogen
was in the form of nitrate. Clearly, a
lightly-loaded sand filter does not provide the
conditions for biological denitrification, and total
The second system tested was a proprietary
device, a recirculating trickling filter affixed to a
septic tank. This system suffered from a number
of mishaps. At its best, it provided 90% organic
carbon removal and 75% total nitrogen removal
ó the maximum possible with its 3:1 recycle ratio.
This was achieved during only one of ten sampling
An aerated ìpackage plantî made by Cromaglass
was studied over a 9-month period. Its initial
performance, when few houses were connected,
was poor. Thereafter, coliform removal averaged
90-99%, organic carbon removal exceeded 80%,
and total nitrogen removal exceeded 70 %.
This study involved sampling on 10 consecutive
days at a time. The results were subjected to an
analysis of variance, which showed that most
variability occurred within sampling periods, not
between them. The results reveal the inadequacy
of quarterly grab samples often used by
regulatory authority to characterize wastewater.
Instead, the investigators recommend optimizing
resources - if budget allows sampling eight times
per year, for example, these samples should be in
two or three clusters rather than spread out to
one every six or seven weeks.