United States
Environmental Protection
Agency
Robert S. Kerr Environmental
Research Laboratory
Ada OK 74820
^P
"'
Research and Development
EPA-600/S2-81 -226 Dec. 1981
Project Summary
Infiltration Land Treatment of
r ~ Stabilization Pond Effluent
N. Dornbush
A rapid infiltration pilot wastewater
treatment system consisting of three
0.07 hectare basins was operated for
four seasons at Brookings, South
Dakota. The objectives of the study
were to demonstrate that rapid infil-
tration land treatment could upgrade
stabilization pond effluent to meet
stringent effluent requirements and to
identify winter operating constraints
for the system.
After passing through 1.3 m of the
soil profile, the following quality was
observed: BODs was less than 4 mg/l
all of the time and generally less than 2
mg/l; the suspended solids rarely
exceeded 4 mg/l; total phosphorus
rarely exceeded 1 mg/l; ammoniacal
nitrogen was less than 2 mg/l and
usually less than 1.1 mg/l; and nitrate
nitrogen rarely exceeded 10 mg/l.
Winter operation of the pilot units
with intermittent applications was not
practical. Ice accumulated with each
successive flooding and operation had
to be discontinued in early January.
This Project Summary was develop-
ed by EPA's Robert S. Kerr Environ-
mental Research Laboratory. Ada.
OK, to announce key findings of the
research report that is fully docu-
mented in a separate report of the
same title (see Project Report ordering
information at back).
Introduction
Stabilization ponds are the predomi-
nant type of treatment employed by
municipalities of 5,000 persons or less
in the Upper Great Plains Region. How-
ever, the ability of these ponds to meet
present and future effluent standards is
limited. A rapid infiltration system,
designed and operated to make the
maximum use of an available in-place
soil, is considered as a potentially
economical solution to meet future
effluent requirements of stabilization
ponds.
Of the 180 stabilization ponds opera-
ting in South Dakota, about 40 have not
discharged for at least one year accord-
ing to recent reports. These "no-
discharge" facilities would actually be
infiltration ponds in South Dakota since
usual evaporation, precipitation and
wastewater flow rates suggest an
annual seepage rate in excess of 1.8 m
(6 ft). Other ponds are also believed to
exceed the 1.6 mm/day (1/16 in./day)
allowable seepage rate. These losses to
groundwater do not, however, imply
contamination of groundwater since
earlier studies revealed the seepage to
be of excellent quality. The original
objectives of this study were as follows:
1. Demonstrate the use of rapid infil-
tration land treatment as a means
of up-grading existing secondary
treatment to meet new effluent
standards for BOD, suspended
solids, and fecal conforms while
removing phosphorus and oxidiz-
ing ammonia nitrogen to nitrate to
meet new ammonia standards;
2. determine acceptable loading
rates for both a scarified and
undisturbed silty loam soil, under-
drained with perforated pipe at a
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depth of 0.8 m (30 in.), for climatic
conditions similar to those at
Brookings, South Dakota; and
3. identify winter operating con-
straints imposed by the climatic
conditions at this site.
Conclusions and
Recommendations
System Description
The construction of the three pilot
basins consisted of grading the soil
surface to form dikes about 0.9 m (3 ft)
high. Initially, dikes were constructed to
enclose the middle basin without dis-
turbing the existing soil and vegetal
cover of alfalfa and brome grass. Addi-
tional dikes were formed to enclose two
adjacent pilot units using the upper 0.2
m (8 in.) of soil. To prevent leakage and
to define a measurable infiltration area,
a plastic membrane was installed in the
dikes and covered with a soil layer. The
resulting three basins shown in Figure
1, about 15 m by 45 m (50 ft by 150ft) in
size, were designated as north, middle,
and south for reference.
Perforated plastic underdrains were
installed under each basin at a depth of
about 0.8m (30 in.) which was about 0.3
m (1 ft) above the natural ground water
level at the time of construction. Unper-
forated plastic pipe was used to connect
the underdrains to the sampling point.
Stabilization pond effluent was
applied to the pilot system through 15
cm (6 in.) irrigation pipes (Figure 1).
Meters recorded the flow to the units
and float recorders monitored water-
surface elevation in each basin.
Operation of the pilot basins during
the summers of 1975 and 1976
involved once-per-week inundation.
The south and middle basins were
flooded with a volume equivalent to 0.6
m (24 in.) each week while the north
basins received 0.45 m (18 in.) per
week.
In 1977 a second, deeper underdrain-
age system was installed in the basins
at a depth of about 1.3 m (4.5 ft) in an
effort to improve the nitrogen removal
capability of the unit. Both underdrain
systems were connected to a new,
deeper sampling box.
In 1977, all three basins received a
weekly total of 0.6 m (2 ft) of waste-
water. However, instead of one flooding
per week, 0.2 m (8 in.) of water was
applied to the basins each Monday,
Wednesday, and Friday. In 1978, the
basins were operated much the same as
in 1977.
Loading Rates
Loading rates of 0.6 m/week (24 in./
week) were easily maintained from
spring through fall when single weekly
wastewater applications were used.
When the soil was sustained in a near-
saturated condition, infiltration rates
diminished from about 15 mm/hour
(0.55 in./hour), the rate representative
of an eight-day test, to about 3 mm/
hour (0.1 in./hour). Equilibrium loading
rates for a nearly continuously wetted
area would be about 45 cm/week (18
in./week) for the scarified basins
compared to 60 cm/week (24 in./week)
for unscarified soils containing the
highly organic surface layer.
Groundwater Response
To illustrate the response of the
groundwater under the basins during a
flooding cycle, cross sections were
prepared of the water level at various
times before and after the weekly
wastewater applications (Figure 2).
Four-week averages of piezometer
readings during the summer period of
July 20 - August 10, 1976, were selec-
ted as representative. The water level
represented by the 10:00 p.m. reading
of the piezometers on the day of f loodmc
is probably near the maximum ground-
water height following a flooding. The
usual procedure of applying wastewatei
to the basins in a south-middle-north
sequence required about 11 hours in
1976 starting about 7:00 a.m. At thai
time a water depth of about 40 cm (1.3
ft) was being attained on the north and
south basins when flooding was com-
pleted. Those two basins were empty
about 20 to 30 hours later while the
middle basin emptied in about 8 hours.
About 2 days after flooding started, the
ground water had reached near normal
levels. In the remaining 5 days before
flooding resumed, groundwater under
the basins was lowered an additional
0.3 m (1 ft) to exhibit the "dished-out"
profile just before the flooding cycle was
repeated.
Effluent Quality
The analytical data obtained for
periods of operation from 1975 to 1978
are summarized as mean concentra-
tions in Table 1. During each season,
the effluent from the stabilization pond
experienced wide variations in quality.
The infiltration basins, however, have
produced effluents of far more uniform
quality, and each successive year has
generally demonstrated an improved
quality of effluent.
Six-Mile
Creek
Earth Dikes Sealed with Sheet Plastic
Underdrain
System
amp/ing Box
n
{
I
?
-------
100.40 -
100.00 ~
99.60-
99.20 -
98.80 -
^98.40-
-s
7 98.00 -
.o —
| 97.60 -
5 97.20 -
96.80-
96.40 -
96.00 -
95.60-
95.20[-
Middle
Surface Elevation
North
10 p.m.
the Day of Flooding
Horizontal
Scale
0' "50"
^
\9 a.m. 2nd Day After
I Flooding \
\ ' !
\Day Before Flooding
-| ^ p—-
1 I i
30.6
30.5
30.4
30.3
30.2
30.1
fr\
30.0 8"
29.9 |
o'
29.8 51
29.7 |
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14-
12-
10-
!
4—
One Flooding
Per Week
1975
1976
1977
Upper
Drains
Three Floodings
Per Week
Lower
Drains
1978
Upper
Drains
Lower
Drains
-16
-14
-12
-10
- 8
-6
- 4
-2
INMS
INMS
INMS
INMS
INMS
INMS
Figure 3. Annual mean nitrogen concentrations for influent (I), north (N),
middle (MJ, and south (Sj drain effluents for infiltration basins,
1975-1978.
accounted for the reductions of
ammonia. By contrast, in 1977 and
1978 when more frequent wastewater
applications prevented effective aera-
tion of the soil, nitrate and total nitrogen
in the drain effluents was reduced
significantly. The exceptions were the
effluents from the middle basin where a
much higher infiltration rate resulted in
intermittent drying and aeration of that
basin.
A rather wide range of concentrations
of the various nitrogen forms was noted
throughout each of the four years of
operation. For the stabilization pond
effluent (influent), NH3-N usually was
the major component with substantial
concentrations of organic nitrogen and
comparatively small quantities of
nitrate. Nitrate -N was predominant in
the drain effluents followed by
ammonia -N and organic -N.
Winter Operating Constraints
Continuous operation of infiltration-
percolation systems, even in northern
climates, has been considered as one of
the major advantages of this type of land
application system. Where winter
operation has been practiced effectively,
the wastewater has been applied
periodically in some cases to infiltration
basins. In other instances, the water
levels have been maintained in the
basins so that seepage has been on a
more-or-less continuous basis. The
wastewater has generally been applied
to the basins shortly after biological
treatment, usually with trickling filters.
Consequently, the wastewater probably
was warm enough to prevent the soil
from freezing under an ice cover.
Application of wastewater from the
stabilization pond did not prove to be
effective for melting the snow and ice
accumulations. During winter, the
wastewater as it came from the stabili-
zation pond was already near a freezing
temperature. At other facilities where
winter operation has been reported,
warmer effluents from secondary treat-
ment plants have been applied directly
to the land. At Brookings, the tempera-
ture of the effluent of the trickling filter
plant is near 19°C (50°F), even through
the most severe winter month of
January. With a full-scale system, the
effluent of this plant might be applied
with more success directly to infiltration
basins during the winter.
The entire winter period when waste-
water was not applied during the 1975-
76 winter was from early January to
early April, a period of less than three
months. The April inundation of the pilot
units was undertaken to verify that
wastewater could be applied and
treated by that date although visual
observations indicated that wastewater
could have been applied at an earlier
date. The quality of the effluent for that
particular flooding, however, was poor
and apparent short-circuiting was
evident.
From observations and experience
during the winter operations, it
appeared that the ice problems that
occurred with the stabilization pond
4
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effluent would not be overcome with
operational changes at the existing pilot
basins. Wastewater applications were
continued into December although
reduced volumes were applied because
of accumulated ice. Historically, the
annual average air temperature in the
Brookings area drops to freezing about
November 12, so it would appear that
wastewater applications from stabiliza-
tion ponds could safely continue on a
regular basis for at least a month
beyond that date. Consequently,
existing stabilization ponds in South
Dakota which are frequently designed
with six months of detention could
probably be operated to provide both the
preapplication treatment and the neces-
sary emergency storage capacity to
carry through the most severe winters.
James N. Dornbush is with the Civil Engineering Department, South Dakota
State University, Brookings, SD 57007.
Carl G. En field is the EPA Project Officer (see below).
The complete report, entitled Infiltration Land Treatment of Stabilization Pond
Effluent," (Order No. PB 82-109 919: Cost: $8.00, 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:
Robert S. Kerr Environmental Research Laboratory
U.S. Environmental Protection Agency
P.O. Box 1198
Ada. OK 74820
. S. GOVERNMENT PRINTING OFFICE: 1902/539-092/3431
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