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

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

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-

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
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
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
                                                              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
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

Tests performed on Medical Lake
water samples indicated that an

                                                                               Algae die, sink to the bottom,
                                                                               and decompose. Phosphorous is
                                                                               released. Algae also bloom on
                                                                               the surface.
                                                                               Bottom waters mix with upper
                                                                               waters (turnover), spreading the
                                                                               phosphorous throughout the lake.
                                                                              The high phosphorus concentration
                                                                              remains below the ice cover.
                                                                              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)
                                               % Reduction
Table 2.
Medical Lake Tank Test to Determine the Kind of Mixing
Affecting Phosphorus Reduction
         Alum (mg/l)
Ortho-P (mg/l)
                                               % Reduction

5.   Dispensing
                               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-

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
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
Figure 2.
Mean monthly total and orthophosphorous concentrations (mg 1~1 P) before, during and
following alum treatment.
                        ALUM TREATMENT
Figure 3.
Mean monthly chlorophyll a concentrations (mg nv3) before, during and following alum

                         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
                         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-

The treatment improved water
clarity as evidenced by increased
Secchi disk visibilities (Figure 4).
Improved water clarity is another
indication of reduced algal
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
                                 Table 3.

                                 Project Costs for Medical Lake Restoration  (1977 $)

                                         Alum                                      S 90,000


                                          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


                                          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.