United States Office of Water Planning & Standards
Environmental Protection Criteria and Standards Division
625/2-80-025 Agency Washington DC 20460
Technology Transfer
x>EPAw Capsule Report
Restoration of
Medical Lake
-------
Shore Front Park at Medical Lake
-------
Technology Transfer EPA-625/2-80-025
Capsule Report
Restoration of
Medical Lake
August 1980
This report was developed by the Center for Environmental Research Information, Office
of Research and Development, U.S. Environmental Protection Agency Cincinnati, Ohio
45268
-------
Medical Lake Before Restoration
-------
1. Summary
The Clean Lakes Program began
in 1975 to implement section 314
of the Federal Water Pollution
Control Act Amendments of 1972
(PL 92-500) which gives the States
the responsibility for cleaning up
their lakes. Specifically, the States
must classify their lakes accord-
ing to trophic conditions; identify
procedures, processes, and
methods to control the sources of
pollution affecting the lakes; and
restore water quality. The goal of
theprogram is to aid the States in
restoring freshwater lakes for
public use. To qualify for a Clean
Lakes grant, a lake must be open
and accessible for public use and
classified as freshwater. Futher-
more, restoration must result in
long-term benefits.
This report discusses the restora-
tion of Medical Lake, a fresh water
lake located in eastern
Washington State. The lake lies in
a closed basin adjacent to the
town of Medical Lake, approxi-
mately 24 km (15 miles) south-
west of Spokane. For several de-
cades, a high phosphorus con-
centration in the lake [0.3 ppm
(0.3 mg/l)] contributed to the re-
currence of algal blooms and
bouyant mats of algae. Recrea-
tional use of the lake diminished
with the presence of a thick algal
surface scum and odors as-
sociated with decaying algae and
hydrogen-sulfide-laden bottom
waters.
The restoration procedure cho-
sen for Medical Lake consisted of
successive applications of
aluminum sulfate (alum). The
purpose of the alum treatment
was to disrupt the internal phos-
phorus cycle, which was found to
be responsible for the high phos-
phorus concentration. The alum
treatment was selected as the
most practical restoration
technique after studying the his-
tory of the lake, analyzing its
water quality and biota, and re-
viewing other methods of treat-
ment.
Over a 5-week period beginning
in August 1977, 935 metric tons
(1031 tons) of liquid alum were
applied to Medical Lake. Continu-
ous water quality monitoring has
shown a marked reduction in the
phosphorus content along with a
dramatic improvement in water
clarity.
2. Theory
Laboratory analyses of Medical
Lake water samples showed a
high concentration of phos-
phorus. Futher study of the lake
and surrounding environment
indicated that most of the phos-
phorus was being produced from
within the lake. Significant exter-
nal input was ruled out because,
other than a few stormwater
drains from the town, the lake re-
ceives no sewage effluents or ag-
ricultural runoff and has no sur-
face inlets or outlets.
Within the lake, the major sources
of phosphorus were decompos-
ing algae atthe bottom sediment,
which released the nutrient dur-
ing the summer. The phosphorus
was then mixed throughout the
lake during the fall. In the spring,
algae were "fertilized" by the
phosphorus in the water and
grew very quickly. As they died,
they sank to the bottom and de-
composed. Their decomposition
released phosphorus and caused
oxygen levels to decrease which,
in turn, caused more phosphorus
to be released from the sediment.
Thus, the algal production of one
growing season served to stimu-
late algal growth during the fol-
lowing growing season (Figure 1).
-------
3. Procedure
Selection
Several methods of disrupting
the internal phosphorus cycle in
Medical Lake were considered.
These methods included dredg-
ing the lake bottom to remove
nutrient-rich sediments; drawing
down the water level to allow the
exposed sediments to dry and
consolidate, and thereby
minimize phosphorus release;
aerating either the whole lake or
only the anoxic bottom waters to
prevent phosphorus release from
the sediments; and inactivating
the phosphorus by chemicals. All
of these methods had already
been successfully applied to
other lake restoration projects.
Phosphorus inactivation by
chemical precipitation was
selected because the lake's small
drainage area and lack of surface
inputs limited the amounts of
phosphorus entering the lake.
Consequently, inactivating the
phosphorus present in the lake
system was expected to achieve
long-term quality improvement.
In addition, previous successful
attempts at in-lake chemical pre-
cipitation of phosphorus proved
encouraging. Furthermore,
chemical precipitation appeared
to be the most economical
method.
Alum is a widely known chemical
for inactivating phosphorus. It
reacts with the natural alkalinity
of water to form a cotton-like
aluminum hydroxide complex
called floe.The floe chemically
reacts with phosphorus in the
water to form an insoluble mass
which is denser than water and,
therefore, settles out. In addition,
the settling floe coagulates and
physically entraps algal cells and
organic detritus, thus resulting in
further removal of phosphorus
from the water. An effect perhaps
more important than removal of
phosphorus from the water
column is that the floe forms a
chemical barrier on the sediment,
which prevents phosphorus
release during periods of low or
absent oxygen concentrations.
4. Laboratory
Analysis
Study of the literature indicated
that at least an 87 percent reduc-
tion of the phosphorus concentra-
tion in Medical Lake was neces-
sary to eliminate algal blooms.
Laboratory tests confirmed that
the 87 percent reduction was the
most cost effective.
The amount of alum required for
the treatment was initially esti-
mated after studying the results
of other whole-lake alum treat-
ments and the literature on phos-
phorus removal by aluminum sul-
fate.The literature on the chemis-
try of phosphorus inactivation
with alum showed that alkalinity
and pH affect the efficiency of the
phosphorus inactivation process
such that the amount of alum
needed to remove a given
amount of phosphorus increases
as the alkalinity and pH of the
water increase. Thus, laboratory
experiments were clearly re-
quired to determine the exact
alum requirements for Medical
Lake.
Tests performed on Medical Lake
water samples indicated that an
-------
Summer
Algae die, sink to the bottom,
and decompose. Phosphorous is
released. Algae also bloom on
the surface.
Fall
Bottom waters mix with upper
waters (turnover), spreading the
phosphorous throughout the lake.
Winter
The high phosphorus concentration
remains below the ice cover.
Spring
The high phosphorous concentration
present in lake water fertilizes the
algae. The algae bloom throughout
the lake.
Figure 1
Internal Phosphorus Cycle
-------
87 percent reduction in ortho-
phosphorus(a) occurred only
when the alum concentration
equaled 150 mg/l, resulting in
an alum to orthophosphorus
ratio of almost 1000:1 (Table 1).
Additional tests indicated that
vigorous mixing of the alum as a
liquid slurry rather than as dry
crystals was necessary to achieve
the 87 percent orthophosphorus
reduction at an alum concentra-
tion of 150 mg/l (Table 2). Tests
also indicated that multiple alum
doses could be more effective in
reducing orthophosphorus levels
than a single dose, and that com-
bined surface and subsurface ap-
plications could provide a greater
reduction than surface applica-
tions alone.
The amount of alum necessary to
achieve a final whole-lake con-
centration of 150 mg/l was 935
metric tons (1031 tons), much
higher than the original estimate.
This difference again proved that
laboratory tests were critical in
determining the appropriate
amount of alum.
(a)Orthophosphorus is dissolved reactive
phosphorus. For the laboratory analyses,
orthophosphorus was measured as an indi-
cation of overall phosphorus reduction.
Table 1.
Medical Lake Jar Test to Determine the Concentration of
Alum for Effective Phosphorus Reduction
Alum (mg/l)
Ortho-P(mg/l)
% Reduction
0
40
125
150
200
0.156
0.149
0054
0020
0005
0
4
65
87
97
Table 2.
Medical Lake Tank Test to Determine the Kind of Mixing
Affecting Phosphorus Reduction
Alum (mg/l)
Mixing
Ortho-P (mg/l)
% Reduction
0
150
150
150
None
Light
Strong
Vigorous
0.26
0.14
0.09
0035
0
46
65
87
-------
5. Dispensing
System
Alum Dispensing System and Barge
The alum dispensing system was
designed to provide a fast, effi-
cient, and safe means of placing
alum into the water at prescribed
depths in a well-mixed uniform
concentration. Two pontoon
barges were used to disperse the
alum, a 12-m (40-ft) barge for
deeper areas and a 8.5-m (30-ft)
barge for shallow areas. Each
barge was outfitted with tanks,
pump, and injection man-
ifold.The tanks were filled by an
onshore distribution system.
The barge tanks were constructed
from the bottom halves of
fiberglas septic tanks which were
reinforced and coated internally
with an epoxy resin. The tanks
were vented at the top and fitted
with outlets at the bottom for
transferring alum to the pump.
Four tanks were mounted under
the large barge and two under the
small barge. The tanks were in-
terconnected to inhibit massive
"sloshing". The tanks were
mounted underneath the barges
to permit the lake water to sup-
port some of the alum weight,
thus allowing each barge to carry
more alum than could be sup-
ported directly on the barge deck.
The distribution pumps were
5-cm centrifugal pumps made of
fiberglas-reinforced thermoplas-
tic polyester. Each pump was dri-
ven by a 3-hp gasoline engine.
The distribution manifolds were
designed for even distribution of
the alum and consisted of lengths
of PVC pipe drilled with an in-line
series of holes of varying sizes.
The large barge had a 5.0-cm (2-
in.)diameter manifold, 4.0 m (13
ft.) long with 156 holes spaced 2.5
cm (1 in.) apart. The holes in the
pipe diminished in diameter near
the center of the manifold to give
uniform distribution. The small
barge had a 3.8-cm (1 1/2-in.)
diameter manifold, 2.7 m (9 ft)
long with 108 holes. Again, the
holes diminished in size toward
the center. The piping was strap-
ped to a manifold angle-iron
frame leading to the deck. The
manifold frame and piping
formed a rectangle. The angle-
iron frame was rotated for surface
or subsurface application.
The onshore system consisted of
a supply tank and pump with a
supply line down a dock to a valve
and short flexible hose for con-
nection to the fill lines on the
barges. Loading took about 20 to
30 minutes for the large barge
and 15 minutes for the small
barge. The time for dispensing
the alum varied depending on the
type of application. Subsurface
injection took about 45 minutes
with the large barge and 25 mi-
nutes with the small barge. Sur-
face discharges took less time be-
cause the barges experienced
less manifold drag and the pump-
ing rate was increased.
-------
6. Application
The lake was divided into six
equal zones with marker buoys to
facilitate the systematic applica-
tion of alum. The perimeter of the
lake was also marked with buoys
at the 5-m (16-ft) depth to indicate
shallow water.
The sequence of applications
(passes) was as follows: two sub-
surface applications; two surface
applications; two more subsur-
face applications followed by one
surface and one subsurface ap-
plication. Two successive appli-
cations were not made in the
same zone until all other zones
had been treated. An entire zone
could not be completed with a
single barge load, so an indica-
tion buoy was placed to mark the
point where the alum in the barge
was depleted. The barge pilots
treated each zone in a series of
back and forth passes utilizing the
zone marker buoys and land-
marks onshore to maintain orien-
tation.
Initially, attempts were made to
control alum flow rate and barge
speed to insure even application.
However, the flow meters failed
because of the high acidity of the
alum solution. Consequently,
barge speed was maintained by
pilot judgment, generally not ex-
ceeding the speed achievable
when the barge was fully loaded
with alum.
Aerial View of Alum Application
-------
Medical Lake After Alum Treatment
7. Water Quality
Monitoring
Water quality monitoring was
conducted prior to, during, and
after the alum application. The
most critical parameters were
continuously monitored. These
parameters included total phos-
phorus and orthophosphorus and
chlorophyll a. Secchi disk read-
ings were also taken. Orthophos-
phorus is the most readily availa-
ble form of phosphorus for
biological uptake, although de-
pending on water conditions,
phosphorus may be found in dif-
ferent phases. Total phosphorus
therefore, also was monitored to
determine if the phosphorus was
actually being removed from the
-------
ALUM TREATMENT
DJMAMJJASONDJ FMAMJJASONDJ FMAMJJASOND
Figure 2.
Mean monthly total and orthophosphorous concentrations (mg 1~1 P) before, during and
following alum treatment.
ALUM TREATMENT
DJMAMJJASONDJ FMAMJJASONDJFMAMJJASOND
Figure 3.
Mean monthly chlorophyll a concentrations (mg nv3) before, during and following alum
treatment.
-------
cycle or just changing its form
(Figure 2). Levels of chlorophyll a
were important to follow because
they indicate the amount of algae
present in the water column (Fig-
ure 3). Secchi disk readings were
taken to monitor the clarity of the
water.
The results of the monitoring to
date show that the alum applica-
tion to the lake was highly suc-
cessful in decreasing phosphorus
levels, eliminating nuisance algal
blooms, and greatly increasing
water clarity. Total phosphorus
levels have remained below 0.1
ppm (mg/l) since the treatment.
Chlorophylls data showthatalgal
concentrations in the water col-
umn dropped significantly after
the alum treatment and have re-
mained consistently low ever
since. No enhanced algal growth
has occurred after spring thaw,
indicating that phosphorus is no
longer being supplied to the lake
in significant amounts by the sed-
iments during the previous sum-
mer.
The treatment improved water
clarity as evidenced by increased
Secchi disk visibilities (Figure 4).
Improved water clarity is another
indication of reduced algal
growth.
DJMAMJJ ASONDJ FMAMJ JASONDJ FMAMJ JASOND
Figure 4.
Mean monthly Secchi disk visibilities (meters) before, during and following alum treatment.
-------
8. Project Costs
Total project costs (Table 3) in-
clude the cost of alum; labor costs
for monitoring alum application,
data analysis, and project man-
agement; and equipment rental
and outfitting. Water quality
monitoring and data analysis for
the 3-year project accounted for a
large part of the expenditures.
The price of the alum was also
significant.
Table 3.
Project Costs for Medical Lake Restoration (1977 $)
Alum S 90,000
Labor
Monitoring (1 /77-6/80)
(Biological, Physical, Chemical) 55,000
Chemical Application (8/77-9/77) 5,000
Project Management Planning, Coordination,
and Data Analysis (1 /77-6/80) 72,000
Equipment
Barge Rental 8,000
Vehicle Rental 1,150
Pumps, Supplies 7,250
Bond 1,500
Total $239,900
9. Benefits
The absence of algal scums and
noxious odors as well as the
increase in water clarity and fish
habitat, resulted in changes in
the use of the lake. Some of these
changes include swimming, boat-
ing, and fishing.
Recreational users of the shore
front park increased on summer
weekends from fewer than 100 to
an estimated 1,000. Property val-
ues rose accordingly. Futher-
more, the Washington State De-
partment of Game experimen-
tally stocked the lake with rain-
bow trout 6.4 cm (21/2-in.fingerl-
ings) in 1978 and 1979. By July
1979, some of the fish had grown
to47 cm (181/2-in.). Publicfishing
is expected to be permitted dur-
ing 1981.
GPO1980-M-660-948
------- |