Ground Water Protection Council
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Key Message
Onsite wastewater treatment systems (septic systems) have the
potential to contaminate ground water and surface water
resources, including drinking water supplies, with nitrates and
other nutrients, chemicals, pathogens, and pharmaceuticals.
However, when properly located, designed, constructed, and
maintained, septic systems provide an effective and efficient
means of treating domestic sewage and protecting water quality.
Furthermore, there are economic and ecological advantages to
managing wastewater within the watershed where it is produced.
Thousands of unsewered communities and rural residences will
continue to depend on onsite systems for wastewater treatment
and disposal. Today, as the population migrates farther from
metropolitan areas, about one-third of all new development is
served by decentralized treatment systems (USEPA, 2004). Onsite
systems allow communities to develop while providing them with
the means for adequately handling wastewater. To minimize the
impacts of these systems on
ground water, we need to:
- Ensure that onsite systems
are properly designed
installed, and maintained.
- Take full advantage of
innovative designs and
sound science.
- Adopt effective management
solutions.
- Actively educate the public
on what wastes should not
be put into their systems,
and how these systems
should be maintained.
Curlew Lake in northern Washington State
showing eutrophication along the shore near
densely spaced septic systems. (Photo from
Curlew Lake Eutrophication Study, 1986,
Washington State University.)
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why onsite wastewater
treatment matters to
ground water...
Nationwide, decentralized wastewater
treatment systems (septic systems,
private sewage systems, on-site sewage
disposal systems) collect, treat, and
release about 4 billion gallons of
effluent per day from an estimated
26 million homes and businesses
(USEPA, 2002). More than half of these
systems were installed over 30 years ago
when rules were nonexistent,
substandard, or poorly enforced. The
percentage of homes and businesses
served by these systems varies from
state to state, from a high of about
55% in Vermont to a low of about
10% in California (USEPA, 2002).
View inside a septic system with clogged drainage.
Photo: DCvision2006
Responsibility for potential
impacts on ground water
from onsite systems also
rests to some extent with
local planning and zoning
entities, whose zoning and
subdivision requirements
may or may not take into
account the ability of the
land to support a desired
development density in a
given area. Most health districts
now restrict septic systems
in vulnerable areas and
have rules about spacing
and density per acre.
However, too few of these
entities take into account
the incremental effect of
additional decentralized
wastewater systems within a
given water supply region or
watershed. While the nutrient
load from one septic
tank system may be insignificant,
the cumulative effect
of adding more systems may
trigger problems.
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Recommended Actions
To USEPA and the Research Community:
- Fund and conduct demonstration projects to test the applicability of the
various management models described in USEPA’s National Guidelines for
Management of Onsite and Cluster (Decentralized) Wastewater
Treatment Systems (EPA 832-B-03-001) within a wide range of hydrogeologic
and institutional settings (e.g., economic, legal, administrative,
regulatory), including utilities that would install, manage, operate, and
monitor performance-based septic systems located in areas of highpriority
aquifers.
- Commission additional research regarding onsite system residuals, including
emerging/unregulated contaminants such as pharmaceuticals, and the
extent to which they are migrating to ground water, and compile and
evaluate the latest advances in onsite wastewater treatment science and
technology.
To USGS and State Geological Surveys:
- Conduct additional hydrogeologic and aquifer-vulnerability mapping at a
scale that allows use by local and state governments for the purpose of
siting onsite wastewater treatment systems and determining the need for
advanced treatment for specific contaminants, including unregulated contaminants
and pharmaceuticals and personal-care products.
To State and Local Agencies:
- Develop coordination protocols among all potentially involved agencies to
promote more consistent regulatory oversight of both domestic and commercial
onsite wastewater treatment systems.
- Encourage effective septic system siting, installation, inspection, and maintenance
as described in USEPA’s National Guidelines for Management of
Onsite and Cluster (Decentralized) Wastewater Treatment Systems, and
recommend that communities use one or more of the management models
described in the guidelines.
To Homeowners:
- Operate your waste-disposal system according to recommended practices.
- Maintain your system on a regular schedule.
- If you sell your home, inform the new owner about your septic system
and share maintenance records.
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“Community” leaching fields serving multiple
single-family homes, with their open space, environmental
and aesthetic benefits, are now fully approvable
in most states. This plat shows a proposed community
leaching field in Connecticut that will be assessed by the
Department of Environmental Protection for approval
of the hydraulics of the proposed system, the treatment
of nitrogen and pathogens, and the mixing of treated
wastewater into the area’s ground water system. The
location of the proposed system’s leaching fields, affected
soils, the supporting ground water system, and adjacent
uses are factors that will influence the design and
feasibility of the system.
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