U.S. ENVIRONMENTAL PROTECTION AGENCY
NATIONAL EUTROPHICATION SURVEY
WORKING PAPER SERIES
REPORT
ON
SILVER LAKE
MCLEOD COUNTY
MINNESOTA
EPA REGION V
WORKING PAPER No, J25
PACIFIC NORTHWEST ENVIRONMENTAL RESEARCH LABORATORY
An Associate Laboratory of the
NATIONAL ENVIRONMENTAL RESEARCH CENTER - CORVALLIS, OREGON
and
NATIONAL ENVIRONMENTAL RESEARCH CENTER - LAS VEGAS, NEVADA
697.03Z
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REPORT
ON
SILVER LAKE
MCLEOD COUNTY
MINNESOTA
EPA REGION V
WORKING PAPER No, 125
WITH THE COOPERATION OF THE
MINNESOTA POLLUTION CONTROL AGENCY
AND THE
MINNESOTA NATIONAL GUARD
NOVETCER, 1974
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•1
CONTENTS
P age
Foreword
List of Minnesota Study Lakes iv, v
Lake and Drainage Area Map vi
Sections
I. Conclusions 1
II. Lake and Drainage Basin Characteristics 3
III. Lake Water Quality Sumary 4
IV. u rient Loadings 8
V. Literature Reviewed 13
VI. Appendices 14
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11
FOREWO RD
The National Eutrophication Survey was initiated in 1972 in
response to an Administration comniiUnent to investigate the nation-
wide threat of accelerated eutrophication to fresh water lakes and
reservoirs.
OBJECTIVES
The Survey was designed to develop, in conjunction with state
environmental agencies, information on nutrient sources, concentrations,
and impact on selected freshwater lakes as a basis for formulating
comprehensive and coordinated national, regional, and state management
practices relating to point-source discharge reduction and non-point
source pollution abatement in lake watersheds.
ANALYTIC APPROACH
The mathematical and statistical procedures selected for the
Survey’s eutrophication analysis are based on related concepts that:
a. A generalized representation or model relating
sources, concentrations, and impacts can be constructed.
b. By applying measurements of relevant parameters
associated with lake degradation, the generalized model
can be transformed into an operational representation of
a lake, its drainage basin, and related nutrients.
c. With such a transformation, an assessment of the
potential for eutrophication control can be made.
LAKE ANALYSIS
In this report, the first stage of evaluation of lake and water-
shed data collected from the study lake and its drainage basin is
documented. The report is formatted to provide state environmental
agencies with specific information for basin planning [ 3O3(e)], water
quality criteria/standards review [ 3O3(c)], clean lakes [ 3l4(a,b)],
and water quality monitoring [ 1O6 and §305(b)] activities mandated
by the Federal Water Pollution Control Act Amendments of 1972.
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111
Beyond the single lake analysis, broader based correlations
between nutrient concentrations (and loading) and trophic condi-
tion are being made to advance the rationale and data base for
refinement of nutrient water quality criteria for the Nation’s
fresh water lakes. Likewise, multivariate evaluations for the
relationships between land use, nutrient export, and trophic
condition, by lake class or use, are being developed to assist
in the formulation of planning guidelines and policies by EPA
and to augment plans implementation by the states.
ACKNOWLEDGMENT
The staff of the National Eutrophication Survey (Office of
Research & Development, U. S. Environmental Protection Agency)
expresses sincere appreciation to the Minnesota Pollution Control
Agency for professional involvement and to the Minnesota National
Guard for conducting the tributary sampling phase of the Survey.
Grant J. Merritt, Director of the Minnesota Pollution Control
Agency, John F. McGuire, Chief, and Joel G. Schilling, Biologist,
of the Section of Surface and Groundwater, Division of Water Quality,
provided invaluable lake documentation and counsel during the course
of the Survey; and the staff of the Section of Municipal Works, Divi-
sion of Water Quality, were most helpful in identifying point sources
and soliciting municipal participation in the Survey.
Major General Chester J. Moeglein, the Adjutant General of
Minnesota, and Project Officer Major Adrian Beltrand, who directed
the volunteer efforts of the Minnesota National Guardsmen, are also
gratefully acknowledged for their assistance to the Survey.
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iv
NATIONAL EUTROPHICATION SURVEY
STUDY LAKES
STATE OF MINNESOTA
LAKE NAME COUNTY
Albert Lea Freeborn
Andrusia Beltrami
Badger Polk
Bartlett Koochiching
Bear Freeborn
Bemidji Beltrami
Big Stearns
Big Stone Big Stone, MN; Roberts,
Grant, SD
Birch Cass
Bl ackduck Bel trami
Blackhoof Crow Wing
Budd Martin
Buffalo Wright
Calhoun Hennepin
Carlos Douglas
Carrigan Wright
Cass Beltrami, Cass
Clearwater Wright, Stearns
Cokato Wright
Cranberry Crow Wing
Darling Douglas
Elbow St. Louis
Enibarass St. Louis
Fall Lake
Forest Washington
Green Kandiyohi
Gull Cass
Heron Jackson
Leech Cass
Le Homme Dieu Douglas
Lily Blue Earth
Little Grant
Lost St. Louis
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V
LAKE NAME
COUNTY
Madison
Mal medal
Mas hkenode
McQuade
Mi nnetonka
Mi nnewaska
Mud
Nest
Pelican
Pepin
Rabbit
Sakatah
Shagawa
Silver
Six Mile
Spring
St. Croix
St. Louis Bay
Superior Bay
Swan
Trace
Trout
Wagonga
Wall ma rk
White Bear
Wi nona
Wol f
Woodcock
Zumbro
Blue Earth
Pope
St. Louis
St. Louis
Hennepin
Pope
Itasca
Kandiyoh I
St. Louis
Goodhue, Wabasha, MN;
Pierce, Pepin, WI
Crow Wing
Le Sueur
St. Louis
McLeod
St. Louis
Washington,
Washington,
Pierce, WI
St. Louis,
St. Louis,
Itasca
Todd
I tas ca
Kandiyoh i
Chi sago
Was hi ngton
Douglas
Beltrami, Hubbard
Kandiyoh i
Olmstead, Wabasha
Dakota
MN; St.
C ro ix,
MN; Douglas, WI
MN; Douglas, WI
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SILVER LAKE
®
Tributary Sampling Site
X
Lake Sampling Site
j
Direct Drainage Area Limits
O ‘?Mi.
Map Location
(
C)
4A1
)
.- ..-..-...
Scale
(
ii
/
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SILVER LAKE
STORET NO. 2782
I. CONCLUSIONS
A. Trophic Condition:
Survey data and the reports of others show that Silver Lake
is eutrophic. Survey limnologists noted that the lake was ex-
tremely turbid on all sampling dates (due in large part to the
number of phytoplankton present; see page 6). In a 1952 report
on a waterfowl and muskrat habitat survey, Minnesota Department
of Conservation biologists noted that heavy algal growths were
present (Johnson, 1952).
Of the 60 Minnesota lakes sampled in the fall when essen-
tially all were well-mixed, 48 had less mean total phosphorus,
43 had less mean dissolved phosphorus, and 38 had less mean
inorganic nitrogen. For all 80 lakes sampled, 91% had less
mean chlorophyll a, and 95% had greater mean Secchi disc trans-
pa ren cy.
Because of the inorphornetry of this water body, it is unlikely
that it would be considered anything but eutrophic regardless of
cultural influences. The primary beneficial use of the lake has
been as waterfowl and game habitat.
B. Rate-Limiting Nutrient:
The results of the algal assay indicate Silver Lake was
nitrogen limited at the time the sample was collected. Lake
data indicate nitrogen limitation at all sampling times.
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2
C. Nutrient Controllability:
During the sampling year, Silver Lake received a total
phosphorus load at a rate about four times the rate proposed
by Vollenweider (in press) as “dangerous”; i.e., a eutrophic
rate (see page 12). Of this load, it is estimated that the
Village of Silver Lake contributed 87%. It is calculated that
80% removal of phosphorus at Silver Lake would result in a
loading rate of 1.4 lbs/acre/yr or 0.16 g/m 2 /yr (the eutrophic
rate is 0.14 g/m 2 /yr).
While the reduced loading rate resulting from 80% phosphorus
removal would just exceed the eutrophic rate, it is concluded
that such a level of removal would improve the trophic condition
of the lake and would significantly enhance the waterfowl and
game habitat potential of Silver Lake.
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3
II. LAKE AND DRAINAGE BASIN CHARACTERISTICS
A. Lake Morphometry*:
1. Surface area: 422 acres.
2. Mean depth: 4 feet.
3. Maximum depth: 7 feet.
4. Volume: 1,688 acre/feet.
5. Mean hydraulic retention time: 2.3 years.
B. Tributary and Outlet:
(See Appendix A for flow data)
1. Tributaries —
Name Drainage areat Mean flowt
None
Minor tributaries & 2
immediate drainage - 1.5 mi 1.0 cfs
Totals 1.5 mi 2 1.0 cfs
2. Outlet —
.2tf 1.0 cfs
Silver Lake Creek 2.2 nu
C. Preci pitationttt:
1. Year of sampling: 32.9 inches.
2. Mean annual : 27.0 inches.
* Anonymous, 1972.
t Drainage areas are accurate within ±5%; mean daily flows are accurate
within ±10%; and ungaged flows are accurate within ±10 to 25% for
drainage areas greater than 10 mi 2 .
tt Includes area of lake.
ttt See Working Paper No. 1 , uSurvey Methods”.
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4
III LAKE WATER QUALITY SUI44ARY
Silver Lake was sampled three times during the open—water season
of 1972 by means of a pontoon-equipped Huey helicopter. Each time,
samples for physical and chemical parameters were collected from one
station on the lake and from one or n re depths (see map, page vi).
During each visit, a single depth-integrated (near bottom to surface)
sample was collected for phytoplankton identification and enumeration;
and during the last visit, a single five-gallon depth-integrated sample
was taken for algal assays. Also each time, a depth-integrated sample
was collected for chlorophyll a analysis. The maximum depth sampled
was 4 feet.
The results obtained are presented in full in Appendix B, and the
data for the fall sampling period, when the lake was essentially well-
mixed, are summarized below. Note, however, the Secchi disc suiiniary
is based on all values.
For differences in the various parameters at the other sampling
times, refer to Appendix B.
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5
A. Physical and chemical characteristics:
FALL VALUES
Parameter Minimum Mean Median Maximum
Temperature (Cent.) 4.9 4.9 4.9 4.9
Dissolved oxygen (mg/i) 10.3 10.3 10.3 10.3
Conductivity ( ..imhos) 500 500 500 500
pH (units) 8.9 8.9 8.9 8.9
Alkalinity (mg/i) 186 188 188 189
Total P (mg/i) 0.284 0.310 0.310 0.336
Dissolved P (mg/i) 0.123 0.126 0.126 0.130
NO + NO (mg/i) 0.110 0.120 0.120 0.130
Arr onia mg/1) 0.250 0.255 0.255 0.260
ALL VALUES
Secchi disc (inches) 6 10 12
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6
B. Biological characteristics:
1 . Phytoplankton -
Sampling Dominant Number
Date Genera per nfl
07/03/72 1. Microcystis 29,189
2. Anabaena 21 ,982
3. Lyngbya 11,622
4. Merlsiropedia 7,387
5. Chroococcus 3,514
Other genera 9,099
Total 82,793
08/29/72 1. Oscillatoria 26,727
2. Lyngbya 22,727
3. Merisnopedia 9,091
4. Microcystis 5,636
5. Flagellates 4,909
Other genera 9 ,637
Total 78,727
10/26/72 1. Oscillatoria 25,714
2. Flagellates 8,797
3. Microcystis 2,256
4. Anabaena 526
5. Dinobryon 526
Other genera j 73O
Total 39,549
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7
Maximum yield
( mg/i-dry wt. )
25.9
28.2
25.0
25.8
22.2
46.4
39.4
Chlorophyll a
gJ1) -
C. Limi
1.
2. Chlorophyll a-
(Because of instrumentation problems during the 1972 sampling,
the following values may be in error by plus or minus 20
percent.)
Sampling Station
Date Number ______________
07/03/72 01 277.8
08/29/72 01 48.9
10/26/72 01 51.6
ting Nutrient Study:
Autoclaved, filtered, and nutrient spiked -
Ortho P Inorganic N
pjke (mg/i) Conc. (mg/i) Conc. (mq/1 ) _____________
Control 0.066 0.864
0.005 P 0.071 0.864
0.010 P 0.076 0.864
0.020 P 0.086 0.864
0.050 P 0.116 0.864
0.050 P + 10.0 N 0.116 10.864
10.0 N 0.066 10.864
2. Discussion —
The control yield of the assay alga, Selenastrum capri-
cornutum , indicates that the potential primary productivity
of Silver Lake was very high when the sample was taken.
Also, the lack of significant change in yields with increased
levels of orthophosphate, and the response to the addition
of nitrogen alone, show that the lake was nitrogen limited.
The lake data indicate nitrogen limitation at all sampling
times (all N/P ratios were less than 3/1, and nitrogen limi-
tation would be expected).
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8
IV. NUTRIENT LOADINGS
(See Appendix C for data)
For the determination of nutrient loadings, the Minnesota National
Guard collected monthly near-surface grab samples from the tributary
site indicated on the map (page vi), except for the colder months when
ice cover and low flows prevented sampling. Sampling was begun in
October, 1972, and was completed in September, 1973.
Through an interagency agreement, stream flow estimates for the
year of sampling and a “normalized” or average year were provided by
the Minnesota District Office of the U.S. Geological Survey for the
lake outlet.
In this report, outlet nutrient loads were determined by using a
modification of a U.S. Geological Survey computer program for calcu-
lating stream loadings. Nutrient loadings for unsampled “minor tribu-
taries and immediate drainage” (“ZZ” of U.S.G.S.) were estimated by using
the nutrient loads, in lbs/mi 2 /year, in an unimpacted tributary of nearby
Cokato Lake at station 2719C1 (126 lbs P and 2,924 lbs N/mi 2 /yr) and
multiplying by the ZZ area in mi 2 .
The Village of Silver Lake declined participation in the Survey, and
nutrient loads were estimated at 2.5 lbs P and 7.5 lbs N/capita/year.
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9
A. Waste Sources:
1 . Known municipal -
Pop. Mean Receiving
Name Served Treatment Flow (mgd) Water
Silver Lake 694* trickling O.070** Silver Lake
filter
2. Known industrial — None
* Anoymous, 1973.
** Estimated at 100 gal/capita/day.
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10
B. Annual Total Phosphorus Loading - Average Year:
1 . Inputs —
lbs P1 % of
Source yr total
a. Tributaries (non—point load) —
None
b. Minor tributaries & immediate
drainage (non-point load) — 190 9.5
c. Known municipal -
Silver Lake 1,740 87.0
d. Septic tanks - Unknown
e. Known industrial — None - -
f. Direct preclpitation* - 70 3.5
Total 2,000 100.0
2. Outputs —
Lake outlet — Silver Lake 1,460
3. Net annual P accumulation — 540 pounds
* See Working Paper No. 1.
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11
C. Annual Total Nitrogen Loading - Average Year:
1. Inputs —
lbsN/ %Of
Source yr total
a. Tributaries (non—point load) -
None
b. Minor tributaries & iniiiediate
drainage (non—point load) - 4,390 32.1
c. Known municipal —
Silver Lake 5,200 38.1
d. Septic tanks - Unknown
e. Known industrial - None
f. Direct precipitation* - 4,070 29.8
Total 13,660 100.0
2. Outputs -
Lake outlet - Silver Lake Creek 9,350
3. Net annual N accumulation - 4,310 pounds
* See Working Paper No. 1.
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12
E. Yearly Loading Rates:
In the following table, the existing phosphorus loading
rates are compared to those proposed by Vollenweider (in press).
Essentially, his “dangerous” rate is the rate at which the
receiving waters would become eutrophic or remain eutrophic;
his “permissible” rate is that which would result in the
receiving water remaining oligotrophic or becoming oligotrophic
if morphometry permitted. A rnesotrophic rate would be considered
one between “dangerous” and “permissible”.
Total Phosphorus Total Nitrogen
Units Total Accumulated Total Accumulated
1bs/acr /yr 4.7 1.3 32.4 10.2
grams/rn /yr 0.53 0.14 3.6 1.1
Vollenweider loading rates for phosphorus
(g/m 2 /yr) based on mean depth and mean
hydraulic retention time of Silver Lake:
“Dangerous” (eutrophic rate) 0.14
“Permissible” (oligotrophic rate) 0.07
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13
V. LITERATURE REVIEWED
AnonynDus, 1972. Survey questionnaire. MPCA, Minneapolis.
Anonymous, 1973. Wastewater disposal facilities inventory. MPCA,
Minneapolis.
Johnson, Clare L., 1952. Waterfowl arid muskrat habitat survey--
Silver Lake, McLeod County. MN Dept. of Conservation, St.
Paul.
Schilling, Joel, 1974. Personal comunication (map and report).
MPCA, Minneapolis.
Vollenweider, Richard A., (in press). Input-output models. Schweiz.
A. Hydrol.
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VII. APPENDICES
APPENDIX A
TRIBUTARY FLOW DATA
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IRIH(’TA9Y FLOW INFORMATION FOR MINNESOTA 10/30/74
LAKE CODE 278? SILVER IA’(E
TOTAL F ’ AINAGE AP ft OF LAKE
5(JR—D RAINAI,E NORMALIZED FLOWS
TPIRIJTA9Y APFA JAN FEN MAW ARM MAY JUN JUL AUG SEP OCT NOV DEC MEAN
?78?AI 7.1R 0.14 •‘() 0.41 1.15 2.27 2.73 1.81 0.73 1.41 0.46 0.30 0.33 1.02
?78?Z7 2. 1W 0.43 0.24 0.5? 1.12 2.15 2.75 1.73 0.66 1.34 0.41 0.27 0.38 1.00
SUMMARY
TOTAL DRAINAr,E AREA OF LAKE = 2.18 TOTAL FLOW IN = 12.00
SUM OF SUN—OPAINAGE AREAS = 2.18 TOTAL FLOW OUT = 12.16
MEAN MONTHLY FLOWS AND u)AILY FlOWS
TRIROTAPY MONIr4 YEAR UEAN FLOW •)AY FLOW DAY FLOW DAY FLOW
278261 0 7? 1.24 15 1.20
II 77 I.?Q 1 1.50
1’ 7 ?
I 71 I. ?’ 9 1.00
2 71 0.55 Il 1.30
1 73 1.70 28 2.50
4 73 ?.04 15 2.20
5 73 2.50 ?5 2.90
73 1.77 2 2.90 12 2.00
7 71 0. ’ 13 0.58
N 71 0. 6 11 0.50
9 73 0.73
778277 10 77 1.1 15 1.00
II 7? 1.14 19 1.10
I ? 7’
1 71 l. 5 9 1.30
2 71 0.66 II 1.5’)
1 71 ?. 5 28 3.00
4 71 I.°8 15 2.10
5 71 ?.16 25 2.70
5 71 1.7 2 3.00 I? 2.00
7 73 0.50 13 0.56
H 71 0.51 11 0.45
9 7 0.13
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APPENDIX B
PHYSICAL and CHEMICAL DATA
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ST RET TPTEVAL DATE 74/ Ifl/30
278201
44 53 54.0 094 12 00.0
SILVER LAKE
27 MINNESOTA
1 IEPALES 2111202
3 0007 FEET DEPTH
00013 00300 00077 00094 00400 00410 00630 00610 00665 00666
DATE TIME 1W’ TI-4 WATER DO TRANSP CNOUCTVY PH 1 ALK N02&N03 NH3—N PHOS—TOT PHOS—DIS
FROM OF TEUP SECCHI FIELD CACO3 N—TOTAL TOTAL
TO DAY FEET CENT MG/L INCHES MICROMHO SU MG/L MG/L MG/L MG/I P MG/L P
7?f07/O3 17 40 000’) 23.) 9.5 12 410 9.00 173 0.140 0.130 0.600 0.310
7?/08#’29 18 09 0000 460 9.05 181 0.010K 0.070 0.690 0.700
18 09 0004 21.0 5.? 480 8.65 186 0.130 0.240 0.790 0.463
72/10/2 ’ 10 00 0000 1? 500 8.90 186 0.110 0.250 0.284 0.123
10 00 0004 4.9 10.3 500 8.90 189 0.130 0.260 0.336 0.130
3 717
DATE TIMF DE°TH C,-4L’ PI1YL
FROM OF A
TO DAY FEET IIG/L
72/07/03 17 40 0000 ‘77. J
72/08/29 18 09 0000 4 •QJ
7?/10/ )0 00 0000
j V LLIV .( tO. t T - I
K VALUE KNOWN TO BE LESS
TrIAN INDICATED
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APPENDIX C
TRIBUTARY DATA
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STOPET RETRIEVAL D4T 74/10/30
2782A1 LS2782A1
44 53 00.0 094 13 00.0
UNNAMED OUTLET OF SILVER LAKE
27083 Co #43
O/SILVEi LAKE
CO HWY 24 1 MI S .25 M I E SILVER LAKE
1 1EPALES 2111204
4 0000 FEET DEPTH
00630 00675 00610 00671 00665
DATE TIME OE TH t’1O2&NO1 TOT KJEL NH3—N PHOS—DIS PHOS—TOT
FROM OF N-TOTAL N TOTAL ORTHO
TO DAY FEET MG/L MG/L MG/L MG/L P MG/L P
72/10/15 15 00 0.890 2.500 0.210 0.210 0.315
72/i1/IQ 14 00 1.110 4.000 0.350 0.220 0.690
73/03/11 14 10 4.000 3.570 0.830 0.294 0.490
73/03/28 06 40 0.078 1.890 0.048 0.147 0.240
73/04/15 14 45 0.140 3.700 0.054 0.138 0.340
73/05/25 14 20 0.252 4.500 0.105 0.660 0.800
73/06/0? 14 30 0.270 2.800 0.068 0.650 0.820
73/07/13 16 50 0.430 4.400 0.710 1.100 1.300
73/08/11 14 40 O.8’ O 6.800 1.800 1.000 1.570
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sTOPET P r Fv ‘)AI ’ 74/10/30
278 51
TF278251
P000694
‘i’. 57 00.0 094 13 00.0
SILVER LAKE
270Mg Co W43
0/SILVER LAKE
SILVEP LAKE
1 IEPALES
2141204
4
0000
FEET
DEPTH
‘ ‘)A1 1
O06 5
0)f’ IO
00671
00665
50051
50053
DATE
T!Mr
‘)EPT-I
‘ O’ IO1
11)1 KJ L
Nrtl—N
P1-lOS-OhS
l-’HOS--TOT
FLOW
CONDUIT
FROM
OF
1 -1—Tt)TAL
N
TOTAL
OPTr-$O
RATE
FL0W4460
TO
ThY
FFET
M(,/L
1(/L
MG/L
MG/L P
N&/L P
INST MGD
MONTHLY
73/01/15
11 00
C {T)—
‘- -‘
19.100
16.001)
71/0I/1 ’-
13 00
71/1)?/1S
11 00
CP(T}
3.1-),
6 5.uOO
7.000
7.100
13.500
71,fl?/I
I I 00
71/03/1
It 01)
CP(T )
3.0)u
‘.‘1’)O
1.900
.4OO
4 . (0Q
71/03/1 5
13 10
73/04/16
11 10
1. )
? • 0
?.HOO
2. OO
5.000
71/O5/1
it no
CP(T)—
‘ 1.1 5
43• 100
10.400
‘..600
- 1.500
73/05/IS
13 1)0
71/06/IS
Ii 0’)
CP(T)—
(‘.170
45.000
15.700
5.300
‘i. 00
71/06/IS
ii ‘ 0
7l/07/I’
11 00
CPU)—
3.143
4P.)0O
?3.500
4.900
R.500
71/07/16
‘3 1{j
71/OR/IS
11 ‘10
CP(T)—
.01)
71.)OU
‘, .S 01)
4.100
11.500
71/OP/iS
1’ Of)
73/09/1w
II
CPU)—
... 0
29.400
11.500
5.900
7.000
71/09/17
11 00
71/10/1
11 00
CPU)—
‘.‘,Cii
1’.’-J’
3.? 0
1.700
3.150
71/10/iS
I l 111)
73/11/iS
Ii
CPU)—
( .?‘iI
3ô.C0U
14.000
2.900
.9on
7l/lI/1
Ii 00
71/17/17
11 co
CPU)—
0.4’ .o
?4.’MO
S. fl0
3. 151)
b.000
73/17/17
1?
31
76/01/17
II ‘10
fP(T)—
i.I’
?i.”’v
1S. o0
6.600
‘ 4.100
74/0 1/17
I I 00
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