United States
Environmental Protection
Agency
Robert S. Kerr Environmental
Research Laboratory
Ada OK 74820
Research and Development
EPA-600/S2-84-161 Dec. 1984
Project Summary
Overland Flow Treatment of
Domestic Wastewater in
Northern Climates
J. Borrelli, V. R. Hasfurther, L. O. Pochop, and R. D. Delaney
A pilot overland flow wastewater
treatment system at La ramie, Wyoming,
was tested to determine the ability of
overland flow to treat municipal
wastewater in a location having long,
cold, and dry winters. The wastewater
distribution system functioned well
even during the coldest weather. The
pilot system treated raw wastewater
adequately during the six warmer
months of the year; however, during the
six colder months, treatment was in-
adequate for both raw wastewater and
primary effluent when applied on an
intermittent schedule.
This Project Summary was developed
by EPA's Robert 5. Kerr Environmental
Research Laboratory, Ada, OK, to an-
nounce key findings of the research
project that is fully documented in a
separate report of the same title (see
Project Report ordering information at
back).
Introduction
Overland flow, although a relatively
new process for municipal wastewater
treatment in the United States, has been
shown to be a viable wastewater treat-
ment system in warm climates; however,
its effectiveness during the winter in the
colder regions of the United States is still
open to question. This study was devel-
oped to evaluate the.ability of overland
flow treatment systems to treat municipal
wastewater in a cold, dry northern climate
using cyclic dosing for eight hours a day,
five days a week.
Overland flow plots were constructed
adjacent to the City of Laramie, Wyoming,
wastewater lagoons. The construction
phase of the project began in September
1980 and operation of the system began
in August 1981. The system operated on
a regular schedule from August 1981
through July 1983.
Seven plots were constructed with the
dimensions, slopes, and application rates
shown in Table 1. Raw municipal waste-
water was applied directly to two plots
while the other five plots were treated
with primary effluent fed from a settling
pond having three days' detention time.
Application was by gated pipe with flow
rates controlled by the gate settings.
During the fall of 1980, the plots were
laid out and graded. Final grading and
planting occurred the following spring.
Two of the primary plots were seeded on
June 12, 1981 with forages of various
species ('Garrison' creeping meadow
foxtail, reed canary grass, western
wheatgrass, timothy, tall fescue, smooth
broomgrass, redtop grass, and alsike
clover) to determine survival ability. The
remaining plots were covered with a
transplanted sod consisting mainly of
sedges, rushes, and 'Garrison creeping
meadow foxtail. The sod was used to
represent fully established forage prior to
the startup of the overland flow treatment
system.
During operation the system applied
wastewater eight hours per day, five days
per week. Water quality data were col-
lected every two weeks beginning August
1, 1981. The water quality data included
samples of the applied raw and primary
wastewater and the effluent from each
plot, as well as samples from adjacent
monitor wells.
System Operation
The wastewater distribution system
was designed to operate during Laramie s
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Table 1.
Parameters for Plots
Plot
No.
1
2
3
4
5
6A
6B
Type of
Influent
Raw
Raw
Primary
Primary
Primary
Primary*
Primary*
Type of
Vegetation
Sodded
Sodded
Sodded
Sodded
Sodded
Seeded
Seeded
Length
(m)
59.8
60.1
61.6
62.2
61.9
61.9
60.7
Width
(m)
9.2
8.2
6.4
6.7
6.7
6.7
6.7
Slope
1%)
1.3
1.3
1.6
1.6
1.6
1.5
1.5
Hydraulic
Loading
(cm/ week/
15
10
30
20
15
20
20
Application
Rate
(m3/m hr)
0.22
0.15
0.46
0.31
0.23
0.31
0.30
*Plots 6A and 6B were taken as a single plot.
coldest weather. The system operated
and applied wastewater without problems
in cold weather. The only difficulty was
that the low flow rates required for the
project dictated that the oversized sliding
gates controlling the application rates
were manually opened only slightly
(01.0cm). This problem was caused by
solid particles in the raw wastewater
plugging the gated pipe openings control-
ling wastewater delivery to plots 1 and 2.
The gates applying influent to the primary
wastewater plots did not encounter a
plugging problem. On these latter plots,
the gates could be left for several days
before a scum formed requiring cleaning.
The plugging problem on the raw plots
caused the system to be labor intensive.
To relieve the plugging problem, the
size of the sliding gate openings was
increased to allow passage of solids to the
raw plots. To maintain the desired appli-
cation rates, fewer gates were operated,
causing a decrease in the uniformity of
application.
Surge flow was also tested as a method
for increasing flow rates while water was
applied at the same volume. In the surge
flow method, water is applied in an
intermittent or pulsating fashion accord-
ing to a specified cycle of on and off times.
The sewage flow test indicates that this
application method is a feasible solution
to plugging problems in an overland flow
waste treatment system using a gated
pipe. On other full-scale projects, fine
screens have successfully controlled
plugging problems.
Although the distribution system per-
formed satisfactorily in cold weather, the
plots did not function well as treatment
systems. Winter operation led to a number
of problems with the ice pack accumu-
lation and therefore reduced waste water
treatment efficiency. Ice pack formation
began near the lower ends of the plots.
Once the ice packs began forming, they
continued to develop as flowing water
froze on the top of the plots. When applied
wastewater flowed beneath the ice packs,
some treatment did occur in the soil
media; however, a uniform flow of
wastewater could not be consistently
maintained. The water which did flow
under the ice packs generally channeled
its way through the packs instead of
spreading out uniformly over the soil.
Also, the ice pack seldom completely
covered the entire surface of the plots but
rather only the lower portions of the plots.
In general, the lack of uniform sheet flow
and the tendency for channeling to occur
seriously affected treatment.
Development and change of the vege-
tative cover on the seeded plots occurred
throughout the duration of this project. Of
the eight seeded species, only the
'Garrison' creeping meadow foxtail and
western wheatgrass survived the first
winter. During the first year of operation,
however, the degree of vegetative cover-
age on the seeded plots was much less
than that on the sodded plots. A dramatic
change in vegetation composition occur-
red during the second year of operation.
The 'Garrison' creeping meadow foxtail
was the dominate species at the end of
the second winter (the beginning of the
third growing season) on both the seeded
and sodded plots. The sedges and rushes
originally in the sodded plots did not
compete well with the 'Garrison' creeping
meadow foxtail which increasingly dom-
inated the seeded plots in the second and
third years. Yield samples taken during
the third growing season (the summer of
1983) indicate that the vegetative cover
on the seeded plots had increased to a
point similar to the cover on the sodded
plots (Table 2).
System Performance
During the summer months (May
through October) the system provided
acceptable treatment; however, treat-
ment effectiveness decreased during the
winter months (November through April).
Average summer and winter influent and
effluent concentrations are shown in
Table 3 for N03-N, NH3, TKN, BOD, TSS,
and Total Phosphates. The low winter
treatment levels may be partially attrib-
uted to the low air temperatures during
this period and partially to the channeling
of water within the ice pack. Further, the
total precipitation from November 1981
through April 1982 was only 5.61 cm
while from November 1982 through April
1983 it was 20.12 cm. These values
indicate very little opportunity for a snow
cover to develop on the plots and to
provide an insulating layer for the soil
prior to the freezing of the soil. Generally,
because the flow tended to occur on top of
the ice pack, there was seldom any snow
accumulation on the plots.
Comparison of treatment on the seeded
and the sodded plots showed treatment
on the seeded plots to be inferior until the
middle of the summer of 1982. During the
last year of the study, there were no
consistent treatment differences between
seeded and sodded plots. Not until the
middle of the summer of 1982 did the
vegetation on the seeded plots develop a
crop canopy thick enough to nearly cover
the soil. Generally then, in a northern
climate, up to a year will be required to
establish adequate vegetation on seeded
plots to achieve treatment similar to that
obtained from established plots.
Measurements were taken to deter-
mine the water balances for the plots. The
water balances were determined by meas-
uring the application rate and effluent
flow rate from the plots and by calculating
the evapotranspiration losses using the
SCS Blaney-Criddle formula as calibrated
for the Laramie area for mountain
meadow vegetation. Infiltration was then
calculated as the difference between
water applied and the sum of the effluent
volume plus evapotranspiration. The
water recovery for the plots with the
higher application rates (20 and 30
cm/wk) ranged from 27 to 52 percent
Table 2. Forage Yields from Test Plots for
1983
Plot No.*
1
2
3
4
5
6A
6B
Seasonal Yield
(t/haj
8.69
10.97
8.27
8.58
9.74
7.56
10.20
'Plots 1 through 5 sodded; plots 6A and 6B
seeded.
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Table 3.
Comparison of Treatment During Summer and Winter (mg/l)
Influent
Parameter
NH3
TKN
N03
BOD5
TSS
T-P
Period
Summer*
Winter
Summer
Winter
Summer
Winter
Summer
Winter
Summer
Winter
Summer
Winter
Raw
21.5
23.1
28.9
32.7
2.4
3.4
125.7
145.2
46.6
61.3
17.5
18.0
Primary
15.3
21.2
22.3
26.3
2.2
2.0
101.3
109.3
22.8
18.4
16.8
17.7
Plotl
9.4
18.2
12.3
23.4
4.5
5.8
25.6
67.2
50.1
30.9
12.3
16.2
Plot 2
7.6
17.9
12.8
23.1
3.1
4.7
26.7
69.9
57.4
28.6
13.2
16.8
Effluent
Plot3
7.7
19.5
12.2
23.7
3.7
4.9
38.4
81.6
14.8
17.9
13.6
17.2
Plot 4
7.1
19.4
11.1
23.3
3.3
4.9
37.0
81.4
12.5
25.6
12.2
16.5
Plots
4.5
17.6
9.3
21.9
2.7
8.5
33.4
78.6
49.0
38.2
11.0
16.7
Plot 6
10.3
20.4
15.8
24.9
2.7
2.5
48.2
85.0
19.3
31.7
13.3
17.2
*Summer = May through October.
Winter = November through April.
with an average recovery of 39 percent.
Infiltration accounted for approximately
50 percent of the applied water. Infiltra-
tion rates after establishment of vegeta-
tion were nearly twice that measured
before establishment of vegetation. Water
quality data from adjacent monitor wells
showed a significant increase in nitrogen
content over the life of the study. On
future projects with soils of this type, it
will be necessary to reduce infiltration by
compaction or other means to protect the
groundwater.
Conclusions
The results of this project show that a
wastewater distribution system for over-
land flow treatment can be made to
operate in a severe northern climate such
as exists at Laramie. The distribution
system applied wastewater virtually
without any problems for two years except
for plugging of the gated pipe used for
delivery of wastewater on the raw plots.
Vegetation, mainly 'Garrison' creeping
meadow foxtail, survived when planted
from seed and was nearly fully estab-
lished during the second growing season.
It did require about a year for the seeded
plots to provide treatment equivalent to
plots with fully established vegetation.
The overland flow treatment system
provided good treatment during the six
summer months but was less effective
during the winter months. Much of the
reason for the lack of treatment during
the winter months at Laramie appears to
be due to the low amounts of snowfall
received prior to the soil freezing. The
plots were generally bare except for the
ice packs which developed on the lower
portions of the plots due to the freezing of
the wastewater. The design and operating
condition of the study resulted in a
comparative low level of treatment in the
winter months.
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John Borrelli. Victor R. Hasfurther, Larry 0. Pochop, and Ronald D. Delaney are
with University of Wyoming. Laramie, WY 82071.
Lowell E. Leach is the EPA Project Officer (see below).
The complete report, entitled "Overland Flow Treatment of Domestic Wastewater
in Northern Climates," (Order No. PB 85-115 806; Cost: $14.50, 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
Ada, OK 74820
•ft US GOVERNMENT PRINTING OFFICE. 559-016/7872
United States
Environmental Protection
Agency
Center for Environmental Research
Information
Cincinnati OH 45268
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