"Solid waste Fill Site Analysis: Proximities & Parameters"
Impacts of On-site Wastewater Treatment Systems on Water Quality and Quantity in Urbanizing Watersheds
1. BACKGROUND
Approximately 42% of housing units use onsite
waste water treatment systems (OWTS, also
known as septic systems) to treat and dispose
wastewater in the southeastern USA, the
national average being 25% (USEPA, 2002).
There is suggestive evidence that septic
systems contribute to widespread fecal
pollution of surface waters and are assumed to
be 100% water consumptive in suburban
watersheds of metro-Atlanta area, GA.
However, the extent of their impact on fecal
pollution at the watershed level is still
uncertain, with the complexity of non-point
sources that make it difficult to isolate their
influence.
Our overall goal was to determine the impact
of septic systems on water quality and quantify
and evaluate the economics and the social
acceptance of technology to reduce pollution
stemming from septic systems. It also includes
education and extension activities on the
impact of septic systems on water resources.
Impacts of On-site Wastewater Treatment Systems on Water Quality and
Quantity in Urbanizing Watersheds
M. Habteselassie1, D. Radcliffe1, E. Bauske2, M. Risse3, J. Mullen4, C. Clarke5, R. Sowah1, N. Hoghooghi1
1Crop and Soil Sciences, 2GA Center for Urban Agriculture, 3GA Sea Grant and Marine Extension, 4Agricultural and Applied Economics, The
University of Georgia, 5USGS Southern Atlantic Water Science Center, Atlanta, Georgia
…RESULTS
The study suggests that septic system density above 100 units km-2 presents potential water quality
problems at watershed level and that the effect is seasonal.
Multiple regression model indicated that septic density together with four other watershed characteristics
accounted for 60% of the variability in fecal pollution in spring (data not shown).
The effect of septic density in spring can be attributed to the shallow seasonal groundwater table (Peck et
al., 2011), which may have promoted the transport of effluent from septic drainfields through groundwater
into receiving streams.
Mean septic systems water use was approximately 5.7% consumptive, contrary to common assumptions
of septic systems by water planning agencies in Georgia.
Online survey of Gwinnet country residents (study area) indicated that residents are willing to pay for
septic systems upgrade to improve water quality and that they prefer to pay equal shares (whether they
use septic systems or not) to fix the problem if it benefits everyone.
Project findings were widely distributed to the public via outreach publications and face-to-face contacts.
Graduate and undergraduate students were also trained under the project.
REFERENCES
1. Landers, M.N. and Ankcorn, P.D. 2008. Methods to evaluate influence of septic
systems on baseflow in selected watersheds in Gwinnett County, GA. USGS.
2. Peck, J.A. et al. 2011. Groundwater Conditions and Studies in Georgia, 2008–
2009. USGS.
3. USEPA. 2002. Onsite Wastewater Treatment Systems Manual. EPA/625/R-
00/008.
ACKNOWLEDGMENT
SUMMARY & CONCLUSION
Figure 3. Stream yield of markers that represent total (A), human (septic; B) and ruminant (C) derived fecal
contaminations in the high or low density watershed groups; B shows only for seasons that tested positive.
A B C
RESULTS
Objective 1:– Septic systems impact on water quality and quantity
Objective 2:– Economics and social acceptance of technology to
reduce impact of septic system on water quality
Objective 3:– Education and extension programs on septic systems
Date
N
ov-11
M
ar-12
July-12
N
ov-12
A
pr-13
July-13
N
ov-13
M
ar-14
july-14
Baseflowyield(cm.s
-1
.Km-2
)
0.000
0.002
0.004
0.006
0.008
0.010
0.012
0.014
0.016
0.018
0.020
LDS
HDS
Sampling date
Baseflowyield(cm/s/km2)
b)
Evapotranspiration
Percolation
Surfacerunoff
Groundwater
Lateralsoil
Totalwateryield
Figure 4.
Correlation
between nitrate
and septic density
(A) and N and O
isotopic signatures
of the water
samples for
source
identification (B)
Figure 1. Study sites and monitoring
stations in metro-Atlanta area, GA
(Landers and Ankcorn, 2008).
The study area (Fig 1) is in the Southern Piedmont region of USA and includes 12 watersheds with high
density (HD: >77 units km-2) and 12 watersheds with low density (LD: <38 units km-2) of septic systems.
Other watershed characteristics for HD septic group include mean septic density (216 units km-2), median
distance from stream (96 m), mean drainage area (2 km2), developed area (69%), agricultural use (4%),
forest cover (25%) and imperviousness (18%). For LD septic group: mean septic density (22 units km-2),
median distance from stream (128 m), mean drainage area (3 km2), developed area (23%), agricultural use
(33%), forest cover (37%) and imperviousness (7%).
On average, stream flow was higher in HD than LD watershed groups, the difference being the highest
during dry season (Fig 5). Model analysis of water balance output variables indicated a 3.1% increase in
total water yield at watershed-scale (Fig 6) and a 5.9% increase at sub-basin scale due to septic systems.
Mean septic systems water use was approximately 5.7% consumptive, contrary to common assumptions by
water planning agencies in Georgia.
Figure 5. Baseflow yield in streams of
watersheds with LD or HD septic systems as
estimated by the velocity meter method.
Figure 6. Watershed scale water balance (a) and %
increase (b) in total flow contributed to stream with or
without septic systems as modeled by SWAT.
Results are based on baseflow samples that were collected seasonally 9 times between 2011 and 2014.
E. coli, enterococci and Bacteroides marker for human-derived contamination (a proxy for septic influence)
showed positive and significant correlation with septic density above 100 units km-2 in spring (Fig 2),
indicating the seasonal nature of the impact of septic systems on water quality.
While both groups of watershed were affected by fecal contamination (Fig 3A), the input from septic
systems was higher in the watersheds with HD of septic systems than those with LD of septic systems. The
fecal contamination in LD watershed group mainly came from ruminants (Fig 3C).
Similar to fecal indicator bacteria data, nitrate-N was strongly and significantly correlated with septic density
above 100 units km-2 (Fig 4A). N and O isotope signatures of the water samples suggested humans and
animals to be the main sources of pollution in HD and LD watershed groups, respectively (Fig 4B),
consistent with results from Bacteroidales markers (Fig 3).
Gwinnett County residents in GA (with in the study site) were recruited to complete an online survey to
examine their perceptions of local water quality and the sources of water quality impairments.
The survey also included a choice experiment in which respondents selected one of three policy options
for addressing water pollution issues due to septic systems.
The respondents’ perception was that septic systems were not among the biggest contributors of water
contamination in the county.
Given a choice between the status quo and two septic systems upgrade programs, respondents tend to
prefer one of the upgrade programs, but enthusiasm wanes as the status quo probability of failure to meet
water quality standards decreases.
There was no clear preference for one funding mechanism over another, implying that both septic systems
and sewer users generally prefer to pay equal shares to fix the problem if it benefits everyone.
Findings of the project were summarized in
extension bulletins and short video that were
distributed to the public in prints and made
available online. Video was shown on public
access TVs in multiple counties in GA.
Seventy one Master Gardener Extension
volunteers from 13 counties of GA received 6
hours of training on septic systems and were
provided with outdoor displays and literature for
use in their programming efforts.
Study findings were also disseminated via
scientific publications (3 journal articles and 4
proceedings) and meetings (>15 abstracts).
Graduate and undergraduate students were also
trained. Two MS students graduated from the
project. Currently, two PhD students are being
trained. Several undergraduate students were
involved in the project as student workers.
Project (2011-51130-
31165) is funded by
USDA/NIFA, National
Integrated Water
Quality Program.
B
Figure 2. Correlation between water quality indicators [E. coli stream yield - A), enterococci stream yield - B,
marker yield for human derived fecal pollution - C] and septic system density
R = 0.67
Septic density (units km-2)
0 100 200 300 400
Copiessec-1km-2
0
10000
20000
30000
40000
50000
60000
R = 0.36
Septic density (units km-2)
0 100 200 300 400
Copiessec-1km-2
0
1000
2000
3000
4000
5000
6000
R = 0.42
Septic Density (units km-2)
0 100 200 300 400
Copiessec-1km-2
0
5e+4
1e+5
2e+5
2e+5
3e+5
3e+5
HD
LD
R = 0.32
Septic Density (units km-2)
0 100 200 300 400
Copiessec-1km-2
0
1e+5
2e+5
3e+5
4e+5
5e+5
HD
LD
R = 0.42
Septic Density (units km-2)
0 100 200 300 400
Copiesseckm
0
5e+4
1e+5
2e+5
2e+5
3e+5
3e+5
HD
LD
R = 0.32
Septic Density (units km-2)
0 100 200 300 400
Copiessec-1km-2
0
1e+5
2e+5
3e+5
4e+5
5e+5
HD
LD
B CA Enterococci (spring)E. coli (spring)
Human marker (spring)
A