"k Pacific Southwest
Region IX
California
RICHARDSON BAY
EFFLUENT DILUTION STUDY
A Working Paper
-------
RICHARDSON BAY EFFLUENT DILUTION STUDY
A WORKING PAPER*
January 1971
*A Working Paper presents results of investigations which are
to some extent limited or incomplete. Therefore, conclusions
or recommendations, expressed or implied, are tentative.
ENVIRONMENTAL PROTECTION AGENCY
'REGION ix
San Francisco, California 94111
-------
TABLE OF CONTENTS
Page
Background and Purpose 1
Summary and Conclusions 3
Dye Trac er Study 4
Data Analysis 4
Algal Growth Potential and Nutrients 9
Discussion 14
FIGURES
1. Richardson Bay 2
2. Dilution contours of Richardson Bay
S.D. treatment plant effluent on
November 7, 1970 6
3. Aerial view of visible dye field
on November 7 , 1970 7
4. Color gradations in visible dye field 8
5. Dilution contours in Richardson Bay
at lower low slack water on
November 8, 1970 10
6. Algal growth responses in laboratory
experiments with increasing percentage
additions of sewage treatment plant
effluent 11
TABLES
1. Algal growth responses in laboratory
conditions 12
2. Nutrient concentrations in bay water
and effluent (mg/1) 13
-------
RICHARDSON BAY EFFLUENT DILUTION STUDY
Background and Purpose
The discharge of sewage effluent into Richardson Bay has
affected its ecology, economics and aesthetic appeal. One
notable effect has been the contamination of shellfish beds,
resulting in the termination of commercial shellfishing more
than forty years ago and the eventual quarantining of all
shellfish beds in Richardson Bay. Another is severe
eutrophication in certain portions of the bay, a problem made
obvious by the stench of decaying algae during the summer
months.
Two waste water treatment plants discharge secondary treated
municipal effluent into the head of Richardson Bay (Figure 1).
The Richardson Bay Sanitation District plant, which discharges
approximately 0.2 mgd, is located on the north shore of
Richardson Bay to the east of Strawberry Point, and the Mill
Valley Sanitation District plant, which discharges approximately
1.5 mgd, is located at the upper end of the bay arm to the
west of Strawberry Point. The treatment processes in both
plants are similar, except that the sludge in the Richardson
Bay plant is incinerated, while the sludge in the Mill Valley
plant is centrifuged and dried.
The outfall from the Richardson Bay plant terminates under
18 inches of gravel a few feet out from the high tide line.
At high tide the flow produces a boil, and at low tide it
creates a rivulet which meanders down the mud flats for a
few hundred feet to the water's edge. The Mill Valley
effluent flows into an open canal. From there it is channeled
through mud flats to the waters of Richardson Bay.
As a first step toward alleviating the bacteriological and
eutrophication problems in Richardson Bay, the San Francisco
Bay Regional Water Quality Control Board requested that the
Federal Water Quality Administration (now the Water Quality
Office of the Environmental Protection Agency) measure the
dilution of effluent from the Richardson Bay S.D. plant by
the receiving waters. The dilution factors would then be used
by the Board in drafting a resolution prescribing waste dis-
charge requirements.
The Board also requested that the Water Quality Office measure
nutrient concentrations and algal growth potentials (AGP) in
(1) bay water from representative locations and in (2) sewage
discharged from both treatment plants. AGP experiments were
-1-
-------
Figure 1. Richardson Bay
-2-
-------
also to be performed on various dilutions of effluent in San
Francisco Bay water in order to correlate growth stimulation
effects with dilution contours.
Summary and Conclusions
Dilution of the Richardson Bay S.D. treatment plant effluent
in Richardson Bay was measured with fluorescent dye. The dye
was added to the effluent at continuous rate during a two week
period, and its buildup in the bay was monitored daily. Although
the dye field shifted with wind direction, a comparison of each
day's concentration contours showed that a consistent gradient
had developed after the first week and indicated a steady state
condition. Effluent dilution figures were developed from
steady state contours. Nutrient concentrations and algal growth
potentials were measured in both the effluent and receiving
water to relate dilution to eutrophication.
The following conclusions were drawn from this study:
1. Low dilutions are limited to a narrow band in the
vicinity of the Richardson Bay S.D. outfall. Dilutions
of less than 100:1 persist in a band extending 50 to 100
feet from the water's edge at high slack water and from
1000 to 2000 feet along the shore in either direction
from the outfall. Dilutions of less than 10:1 occur
within 25 feet of the discharge point. Beyond 100 feet
from the water's edge the effluent disperses rapidly,
with dilutions of 500:1 occurring within 300 feet of the
outfall and 1000:1 within 1500 feet. The width, length
and orientation of the low dilution field are strongly
affected by the general wind direction.
2. Flushing takes place rapidly within the portion of
Richardson Bay studied. All dye was removed from the
bay within a week after the injection has been dis-
continued.
3. Effluent concentrations of 0.5 to 1.0% in San
Francisco Bay water did not noticeably stimulate algal
growth in laboratory experiments. However, a 5% effluent
solution in bay water produced an 8-fold increase in
growth over unspiked bay water, and in pure effluent
the increase in growth over bay water was more than
100-fold.
-3-
-------
4. Nutrient analyses showed the total nitrogen con-
centration in the Mill Valley S.D. effluent was 4 times
the concentration in the Richardson Bay S.D. plant
effluent, although neither nitrogen nor phosphorous
levels in the waters of Richardson Bay showed any
significant areal variation.
Dye Tracer Study
Dilution factors were determined by introducing a dye tracer
to the Richardson Bay S. D. waste water treatment plant effluent
and measuring its concentration in Richardson Bay. Measurements
made daily at the same stage of tide documented the buildup
until it approached a steady state level. Tracer concentrations
were plotted, joined into isopleths (lines of equal concentration),
and then converted to dilution contours on the basis of the
average effluent flow rate.
Fluorescent dye (Rhodamine WT) was introduced into the plant
discharge line downstream from the chlorination chamber at a
rate of 10 milliliters per minute for a period of 14 days.
The plant discharge rate during this period averaged 0.216 mgd,
making the dye concentration in effluent approximately 2 X 104 ppb.
Dye concentrations in Richardson Bay were monitored from a
research vessel during higher high slack water each day from
October 27 through November 9, and during lower low slack water
on November 3, 5 and 8. Background runs were made at both high
and low slack waters prior to the dye release, and on Novem-
ber 16, a week after terminating the release, to check for
persisting concentrations. Continuous measurements made by
standard fluorometeric methods were recorded on a strip chart.
Vessel locations were pinpointed frequently by cross bearings
or fixes on convenient landmarks. Monitoring cruises, which
followed roughly the same routes each day, were timed to begin
45 minutes before slack water and end 45 minutes after.
On the 12th day of the release, November 7, aerial photographs
were taken of the visible dye that persisted in a band along
the shoreline near the outfall, while discrete samples were
taken from a small skiff to relate dye concentration to color
intensity in the photographs.
Data Analysis
Fluorometer measurements were tabulated from the recorder
strip charts at points identified by location fixe^ and at
-4-
-------
intermediate points where abrupt concentration changes occurred.
A computer program was written to convert fluorometer units to
parts of dye per billion parts of water, to subtract background
and to correct the dye concentration for temperature effects.
The cruise track for each day and all location fixes were
plotted on individual work charts of Richardson Bay and the
dye concentrations then plotted at the appropriate points.
Isopleths were plotted for as many concentrations as possible,
and the completed charts then compared in chronological order
to study trends. The 200, 40, 20 and 1 ppb isopleths that best
reflected steady state concentrations were selected from the
work chart and transferred to another chart for final presentation.
The first three of these concentrations correspond to dilution
factors of lOOil, 500:1 and 1000:1, respectively, and 1 ppb
contour represents the limit of detectable dye over background.
Background levels varied between 0.3 and 0.8 ppb, depending upon
tidal stage and the location of measurement.
The orientation of the dye field was strongly affected by wind
velocity. Even at high tide, the water in upper Ricardson Bay
is only a few feet deep (Figure 1) and therefore' highly
responsive to wind effects. As the dye-tagged effluent entered
the receiving water it was quickly mixed by wave action and the
mixture pushed against the shoreline by the wind. This created
a hydraulic gradient which carried the dilute effluent along
the shoreline and eventually back into the bay. As the direction
of the wind changed, the location of the effluent field and its
bayward route changed accordingly.
A steady state condition which might, therefore, be described
as "shifting" was evidently reached near the end of the first
week of the dye release. On November 1 and 2, when the wind was
from the southeast, the dye concentrated to the west of the
outfall. The wind then shifted to the southwest, and from
November 3, to the end of the release period the dye concentrated
to the east of the outfall. The contours drawn for November 3
through 8 show a similar distribution for each day, with no
further buildup.
Figure 2 shows the dilution contours measured during higher high
slack on November 7. This date was selected for display because
of the coincident aerial photographs and discrete samples.
Figures 3 and 4 show the visible band of dye extending along the
shoreline from the release point. The red colot provides a
rough quantitative measure of concentration since a dilution of
400:1 or less is visible, and the distinct edge of color implies
a steep concentration gradient. In Figure 4 varying concentrations
indicated by the different shades of red are distinguishable,
representing dilutions ranging from 7:1 to 400:1.
-5-
-------
PAGE NOT
AVAILABLE
DIGITALLY
-------
-
dye band
Figure 3. Aerial View of Visible Dye Field on November 7, 1970
-------
00
Figure 4. Color Gradations in Visible Dye Field
-------
Figure 5 shows the dilution contours measured during low slack
on the evening of November 8. The monitoring area was limited
because of depth, and darkness prevented observation of visibly
red areas.
Algal Growth Potential and Nutrients
On November 2, samples for nutrient and AGP analyses were
collected from four locations in Richardson Bay and from the two
waste water treatment plants. The bay samples were taken near
the predicted time of higher high slack water from the following
points shown in Figure 1:
1. Entrance to Richardson Bay, 43 minutes before higher
high Slack. Since the tide was still flooding, the
sample was probably not affected by either of the
treatment plants.
2. Center of Richardson Bay abeam the north end of
Belvedere Island, 31 minutes before slack. Water at
this location would be subject to the effects of both
treatment plants.
3. East side of Strawberry Point about 3000 feet from
the Richardson Bay S.D. plant, 21 minutes before
slack. This sample should be affected primarily
by the Richardson Bay S.D. plant.
4. West side of Strawberry Point about 2000 feet up-
stream from Kappas Yacht Harbor, 39 minutes after
slack. This sample should be affected primarily
by the Mill Valley plant, although wastes from
nearby houseboat communities could have an additional
effect.
The amounts of algal growth under laboratory conditions in the
above samples and in San Francisco Bay water spiked with
different amounts of effluent from each of the plants are listed
in Table 1.
Growth measurement was calculated from the intensity of fluore-
scent light emitted by extracted chlorophyll a in an acetone
solution. Increases as a function of percent effluent added are
shown in Figure 6. The responses appear to be curvilinear
and therefore no regression equations have been calculated from
the results. Nutrient values from the water samples are listed
in Table 2.
-9-
-------
Taras
Tide Rips I g |: /
RACC
Figure 5. Dilution Contours in Richardson Bay at Lower
Low Slack Water on November 8, 1970
-10-
-------
1050
Algol growth responses in laboratory experiments
with increasing percentage additions of sewage
treatment plant effluent. Each point is the
average of four replicates.
Mi Valley ST
f> D Richardson Bay STP
too
Percent Effluent in Bay Water
-------
TABLE 1. ALGAL GROWTH RESPONSES IN LABORATORY CONDITIONS
S. F. Bay water with additions of Mill Valley STP effluent
Percent effluent 0 0.5 1.0 5.0 10 20 40 75 100
Increase in chl. a (ug/1) 8.0 10.7 9.7 58.2 199 300 550 683 703
Maximum chl. a (ug/1) 9.0 12.2 11.2 59.7 200 302 553 686 707
Growth rate/day 0.79 0.76 0.87 1.30 1.12 0.45 0.45 0.72 0.81
S. F. Bay water with additions of Richardson Bay STP effluent
Increase in chl. a (ug/1) 8.0 10.2 12.9 60.8 173 416 364 796 972
Maximum chl. a (ug/1) 9.0 11.7 14.4 62.3 174 418 366 799 975
Growth rate/day 0.79 0.85 0.80 1.13 1.44 1.37 0.59 1.05 0.98
Richardson Bay samples without effluent addition
San Francisco North end East of West of
Bay Belvedere Saddle Saddle
Increase in chl. a (ug/1) 8.0 5.2 3.8 4.9
Maximum chl. a (ug/1) 9.0 6.2 6.4 6.4
Growth rate/day 0.79 0.67 0.48 0.74
-12-
-------
TABLE 2. NUTRIENT CONCENTRATIONS IN RICHARDSON BAY WATER AND EFFLUENT (mg/1)
Location
Abeam No. end of
Belvedere Island
East of saddle on
Strawberry Pt.
West of saddle on
Strawberry Pt.
Buoy 2 at entrance
to Richardson Bay
Richardson Bay S.D.
Mill Valley S.D.
NH -N
0.25
—
0.25
0.22
0.45
21.1
Org-N
0.62
0.89
0.71
0.76
9.7
24.5
N03~N
0.01
0.01
0.04
0.04
1.5
1.20
Total N
0.88
1.15
1.00
1.02
11.7
46.8
P04-P
0.08
0.11
0.11
0.08
9.0
0.92
Total P
0.10
0.16
0.15
0.14
10.5
4.80
-13-
-------
Discussion
The movement of the dye both during and after the release
period indicated that most of the volume of water in the portion
of the bay studied was replaced every tidal cycle. During the
release period, a steady state condition was reached when a
narrow band of high concentration developed along the shoreline
in the vicinity of the outfall. Beyond the outer boundary of
the band a steep concentration gradient indicated a limited
area of mixing, and beyond this point the water at high tide
could only consist of replacement from the outer bay. After
termination of the release, the visible band of red disappeared
within one day, and within a week only background levels could
be detected with the fluorometer.
For both treatment plants, the 0.5% and 1.0% additions of
effluent did not cause growth statistically higher than the 0%
controls (San Francisco Bay water). However, the 5.0% addition
of the Richardson Bay STP effluent increased chorophyll a
concentration almost 8-fold over that found in the control,
or from approximately 8 to 60 ug/1. In general, increasing or
higher percentage addition of effluent to the bay water gave
higher algal growth, with 100% effluent response more than 100
times that of the controls.
Analyses of effluent samples showed the ammonia concentration
from the Mill Valley plant to be more than 40 times that of the
Richardson Bay plant, and the total nitrogen concentration to
be more than four times higher. This disparity may be caused
by the method in which the centrate from the sludge dewatering
process is disposed. Phosphate concentrations were reversed;
Mill Valley effluent showed on 0.92 mg/1 of P04-P/1 compared
to 9.0 mg/1 from the Richardson Bay plant.
Nutrient levels in the four bay samples were almost identical
(0.88 - 1.15 mg/1 total nitrogen and 0.10 - 0.15 mg/1 total
phosphorous). This similarity could be at least partly
attributed to the high dilution occurring at flood tide. It
should be noted that there was no statistical difference in
the algal bioassay responses among the four samples.
GPO 982 621
-14-
------- |