United States
Environmental Protection
Agency
Water Engineering
Research Laboratory
Cincinnati OH 45268
Research and Development
EPA/600/S2-86/052 June 1986
&EPA Project Summary
An Evaluation of Septic
Leachate Detection
Patricia L. Deese
This study assesses the value of septic
leachate detection (SLD) for improving the
accuracy and reducing the cost of facility
planning in lakeside communities. If SLD
could meet either or both of these goals,
it would have wide application in thou-
sands of U.S. municipalities considering
the need to upgrade water pollution con-
trol facilities.
The study focused on the hypothesis of
leachate detection technology, the status
of SLD equipment, and its cost effect-
iveness. The study showed that present
leachate detection technology is not
capable of producing quantifiable results
that can assist facility planners without
additional developmental work. Methods
are suggested to assist in this effort, but
cost effectiveness remains open to
question.
This Project Summary was developed
by EPA's Water Engineering Research Lab-
oratory, Cincinnati, OH, to announce key
findings of the research project that is futty
documented in a separate report of the
same title (see Project Report ordering in-
formation at back}.
Introduction
Faced with the deterioration of local sur-
face water and groundwater quality, auth-
orities in lakeside communities often as-
sume that effluent from onsite domestic
wastewater systems is a primary source
of contamination. This assumption should
be carefully verified before a community
commits itself to an expensive sewage col-
lection system designed to eliminate com-
pletely effluent discharges to the lake.
Documenting ~a cause-and-effect rela-
tionship between deteriorating surface
and grounwater quality and the use of on-
site wastewater systems has long been a
challenge. Techniques available for the
task include reviews of local health depart-
ment records, mail or door-to-door sanitary
surveys, shoreline and windshield surveys,
identification of other potential contami-
nant sources, hydrologic and geohydrologic
studies, and ambient water quality moni-
toring. Though conventional shoreline sur-
veys often reveal direct discharge drains,
storm drains, wetlands, unusual concen-
trations of algae or rooted aquatic plants,
and tributaries, there is no convenient or
generally accepted way to verify the exis-
tence, location, or impact of subsurface ef-
fluent plumes using conventional planning
techniques.
Wastewater facility planners traditionally
use some combination of the above tech-
niques along with mass balance analysis
to estimate the potential impact of domes-
tic wastewater on the lake. The object of
this study was to determine whether sep-
tic leachate detection (SLD) surveys could
contribute significantly to such evalua-
tions by improving or expediting the cur-
rent approach.
SLD is based on the theory that effluent
from onsite wastewater systems forms
detectable subsurface effluent plumes
that travel through the groundwater sys-
tem and emerge intact in a lake. Develop-
ing a method for proving the existence of
such subsurface effluent plumes entails
three preliminary steps: (1) establishing
standard procedures for data collection
and analysis, (2) selecting the water quali-
ty variables to be used as indicators of ef-
fluent plumes, and (3) setting certain levels
of these variables as criteria for the pre-
sence of plumes. These criteria should take
the form of recognizable and reproducible
deviations from background concentra-
tions of the indicator variables.
In theory, data for such surveys could be
collected using any number of ambient
-------
water quality monitoring techniques. How-
ever, verifying the location of plumes
emerging along the shoreline with tradi-
tional grab sampling procedures presents
unique problems. A monitoring device that
continuously measures levels of the desir-
ed water quality indicators and instantly
records changes in their concentrations
could be used to pinpoint emerging sub-
surface effluent plumes. Traditional grab
samples could then be analyzed to verify
the presence or absence of such plumes.
When this study began, there were two
commercially available water quality moni-
toring devices designed specifically for use
in SLD surveys.
Research Methods
The findings of this study are based on
analysis of information from the following
sources:
• General literature on the disciplines
of groundwater movement, onsite
wastewater systems, ambient water
quality, and limnology.
• Published and unpublished SLD sur-
vey reports.
• Observation of a shoreline survey
conducted using an SLD device.
• Participation in an SLD training course.
• Interviews with SLD device developer,
manufacturer, users, and client
communities.
• Consultations with experts in ground-
water hydrology, limnology, ambient
water quality monitoring, onsite
wastewater systems, and statistical
analysis.
Information about the SLD concept was
gathered during the initial phase of the
research. A detailed literature review was
conducted and consultations were held
with experts in the various scientific dis-
ciplines to determine whether the SLD
hypothesis was supported by wastewater
treatment, groundwater movement, water
quality monitoring, and limnologic theory.
The water quality data generated by SLD
surveys were also analyzed to determine
whether the survey results met the basic
criteria for scientific proof—repeatability
and statistical significance. The draft report
was then submitted to experts for peer
review and comments.
Results and Conclusions
The SLD concept makes two assump-
tions about the behavior and characteris-
tics of septic effluent in lakeshore regions.
The first assumption is that septic leach-
ate plumes usually exist in the ground-
water and often migrate toward lakes. This
contention is supported by both ground-
water theory and empirical evidence. The
second assumption is that septic leachate
plumes emerge into lakes in a discrete, in-
tact, and identifiable form. According to
groundwater theory, the plume may be
identifiable, but in many instances is not.
Practical experience does not support
the concept of the SLD surveys either. In
the 15 SLD surveys reviewed for this study,
little empirical evidence supported the
assumption that septic leachate plumes
are distinct and identifiable. No controlled
research has been conducted to document
the false positive and false negative rate
of SLD surveys. The limited field evidence
suggests that the false positive rate is
above 30%. Such a high rate strongly indi-
cates that the device is often actuated by
natural phenomena other than the pres-
ence of a septic leachate plume.
No field documentation exists for false
negative rates. Since each false negative
represents a pollution source that has been
missed by the survey, it is imperative that
the frequency of false negatives be relativ-
ely small. Otherwise, the screening tool
can grossly underestimate the septic
leachate problem and cause planners to
make poor decisions about wastewater
treatment needs. The rate of false nega-
tives is independent of the rate of false
positives, and it must be documented
through both laboratory and field ex-
periments before the data from SLD
surveys can be considered valid.
SLD surveys are designed to screen for
septic leachate plumes. Grab samples of
the lakewater must be used to confirm or
deny the presence of a plume. SLD surveys
are relatively expensive when compared
with sanitary surveys, but they may be
less expensive than detailed groundwater
monitoring at individual lots.
As presently espoused, SLD surveys can
locate only those septic leachate plumes
that are from systems within 25 m of the
lake and that remain discrete and iden-
tifiable after reaching the lake. Though we
assume that is important to identify these
plumes, the major source of nutrient load-
ing for many lakes may be systems that
are not included in the SLD survey because
they are set back more than 25 m from the
shoreline or because they have dispersed
plumes.
The full report was submitted in partial
fulfillment of Contract No. 68-03-3057 by
Urban Systems Research and Engineering,
Inc., under the sponsorship of the U.S. En-
vironmental Protection Agency.
-------
Patricia L Deese was with Urban Systems Research and Engineering, Inc.,
Cambridge, MA 02138.
James F. Kreissl is the EPA Project Officer (see below).
The complete report, entitled "An Evaluation of Septic Leachate Detection,"
(Order No. PB 86-191 616/AS; Cost: $16.95, subject to change) will be
available only from:
National Technical Information Service
5285 Port Royal Road
Springfield, VA 22161
Telephone: 703-487-4650
The EPA Project Officer can be contacted at:
Water Engineering Research Laboratory
U.S. Environmental Protection Agency
Cincinnati, OH 45268
United States
Environmental Protection
Agency
Center for Environmental Research
Information
Cincinnati OH 45268
Ml
Official Business
Penalty for Private Use $300
EPA/600/S2-86/052
00
00329 PS
PROTECTION AGENCY
CHICAGO
------- |