U.S. ENVIRONMENTAL PROTECTION AGENCY
NATIONAL EUTROPHICATION SURVEY
WORKING PAPER SERIES
REPORT
ON
BL/CKHOOF LAKE
CROW WING COUNTY
MINNESOTA
EPA REGION V
WORKING PAPER No, 87
PACIFIC NORTHWEST ENVIRONMENTAL RESEARCH LABORATORY
An Associate Laboratory of the
NATIONAL ENVIRONMENTAL RESEARCH CENTER - CORVALLIS, OREGON
and
NATIONAL ENVIRONMENTAL RESEARCH CENTER - LAS VEGAS, NEVADA
& GPO—697.032
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REPORT
ON
BLACKHOOF LAKE
CROW WING COUNTY
MINNESOTA
EPA REGION V
WORKING PAPER No, 87
WlTH THE COOPERATION OF THE
MINNESOTA POLLUTION CONTROL AGENCY
AND THE
MINNESOTA NATIONAL GUARD
DECEMBER, 1974
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1
CONTENTS
Page
Foreword ii
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 Summary 4
IV. Nutrient Loadings 8
V. Literature Reviewed 13
VI. Appendices 14
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•I1
FOREWORD
The National Eutrophication Survey was initiated in 1972 in
response to an Administration commitment 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 [ 314(a,b)],
and water quality monitoring [ lO6 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
Embarass 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 Blue Earth
Malmedal Pope
Mashkenode St. Louis
McQuade St. Louis
Minnetonka Hennepin
Minnewaska Pope
Mud Itasca
Nest Kandlyohi
Pelican St. Louis
Pepin Goodhue, Wabasha, MN;
Pierce, Pepin, WI
Rabbit Crow Wing
Sakatah Le Sueur
Shagawa St. Louis
Silver McLeod
Six Mile St. Louis
Spring Washington, Dakota
St. Croix Washington, MN; St. Croix,
Pierce, WI
St. Louis Bay St. Louis, MN; Douglas, WI
Superior Bay St. Louis, MN; Douglas, WI
Swan Itasca
Trace Todd
Trout Itasca
Wagonga Kandiyohi
Wallmark Chisago
White Bear Washington
Winona Douglas
Wolf Beltrami, Hubbard
Woodcock Kandiyohi
Zumbro Olmstead, Wabasha
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BLACKHOOF LAKE
0 Tributary Sampling Site
X Lake Sampling Site
Sewage Treatment Facility
Map Location
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BLACKHOOF LAKE
STORET NO. 2712
I. CONCLUSIONS
A. Trophic Condition:
Survey data show that Blackhoof Lake is eutrophic. Of the
60 Minnesota lakes sampled in the fall of 1972, when all essen-
tially were well-mixed, 25 had less mean total phosphorus, 30
had less mean dissolved phosphorus, and 19 had less mean inor-
ganic nitrogen. For all Minnesota data, 29 lakes had less mean
chlorophyll a, and 25 had greater Secchi disc transparency.
Depletion of dissolved oxygen with depth occurred in July
and September.
B. Rate-Limiting Nutrient:
The results of the algal assay indicate nitrogen limitation
at the time the sample was collected. The lake data indicate
nitrogen limitation during the July and October sampling periods
and a borderline phosphorus limitation during September.
C. Nutrient Controllability:
1. Point sources--During the sampling year, the Ironton
wastewater treatment plant is estimated to have contributed over
71% of the total phosphorus load to the lake.
The present loading rate of about 10 lbs/acre/yr or 1.13
g/m 2 /yr is more than twice that proposed by Vollenweider (in
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2
press) as “dangerous”; i.e., a eutrophic rate (see page 12).
Removal of 85% of the phosphorus at Ironton would reduce the
loading rate to 4.3 lbs/acre/yr or 0.48 g/m 2 /yr (a eutrophic
rate); 100% removal would reduce the loading rate to 3.2 lbs/
acre/yr or 0.36 g/m 2 /yr (a mesotrophic rate). If the latter
level of control can be achieved, the trophic condition of
Blackhoof Lake should improve.
2. Non-point sources--Non-point sources accounted for
27.9% of the total phosphorus load reaching Blackhoof Lake
during the sampling year.
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3
II. LAKE AND DRAINAGE BASIN CHARACTERISTICS
A. Lake Morphometryt:
1. Surface area: 183 acres.
2. Mean depth: 14.5 feet.
3. Maximum depth: 30 feet.
4. Volume: 2,654 acre/feet.
5. Mean hydraulic retention time: 257 days.
B. Tributary and Outlet:
(See Appendix A for flow data)
1. Tributaries -
Name Drainage area* Mean flow*
Unnamed Stream (A-i) 5.8 mi 2 3.8 cfs
Minor tributaries & 2
immediate drainage - 1.9 mi 1.4 cfs
Totals 7.7 mi 5.2 cfs
2. Outlet -
Unnamed Stream (B-i) 8.0 mi 2 ** 5.2 cfs
C. Preci pi tati Øfl***:
1. Year of sampling: 28.8 inches.
2. Mean annual: 24.8 inches.
t DNR lake survey map (1969); mean depth by random-dot method.
* 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 .
** Includes area of lake.
See Working Paper No. 1, “Survey Methods”.LlBR Ry,EpA
National try onmoritat Research Cent
200 S W 35t ’
Corvallis, Oregon 97330
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4
III. LAKE WATER QUALITY SUMMARY
Blackhoof Lake was sampled three times during the open-water season
of 1972 by means of a pontoon-equipped Huey helicopter. Each time, sam-
ples for physical and chemical parameters were collected from two or more
depths at a single station on the lake (see map, page vi). During each
visit, a single depth-integrated (15 feet to surface) sample was collected
for phytoplankton identification and enumeration, and a similar sample was
collected for chlorophyll a analysis. During the last visit, a single five-
gallon depth-integrated sample was taken for algal assays. The maximum
depth sampled was 21 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 summary 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
(10/24/72)
Parameter Minimum Mean Median Maximum
Temperature (Cent.) 5.1 5.3 5.3 5.4
Dissolved oxygen (mg/i) 11.0 11.1 11.2 11.2
Conductivity (pmhos) 225 229 230 230
pH (units) 8.1 8.2 8.2 8.3
Alkalinity (mg/i) 101 103 103 103
Total P (mg/i) 0.033 0.047 0.049 0.058
Dissolved P (mg/i) 0.015 0.030 0.032 0.040
NO + NO (mg/i) 0.080 O.0C7 0.090 0.090
Am1 onia mg/1) 0.040 0.050 0.050 0.060
ALL VALUES
Secchi disc (inches) 54 62 60 72
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6
B. Biological characteristics:
1. Phytoplankton -
Sampling Dominant Number
Date Genera per ml
06/02/72 1. Anabaena 29,273
2. Microcystis 2,091
3. Dinobryon 1,000
Other genera 270
Total 32,634
09/04/72 1 . Microcystis 627
2. Merismopedia 602
3. Anabaena 313
4. Melosira 313
5. Coelosphaerium 289
Other genera 856
Total 3,000
10/24/72 1. Melosira 3,735
2. Anabaena 2,620
3. Asterionella 1,898
4. Fragilaria 813
5. Flagellates 663
Other genera 1,175
Total 10,904
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 Chlorophyll a
Date Number ( pg/l )
06/02/72 01 19.8
09/04/72 01 5.7
10/24/72 01 *
* Sample lost.
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7
C. Limiting Nutrient Study:
1. Autoclaved, filtered, and nutrient spiked -
Ortho Inorganic Maximum yield N/P
Spike (mg/i) Conc. (mg/i) Conc. (mg/i) ( mg/i-dry wt) Ratio
Control 0.028 0.266 5.6 10/1
0.005 P 0.033 0.266 4.9 8/1
0.010 P 0.038 0.266 5.5 7/1
0.020 P 0.048 0.266 6.1 6/1
0.050 P 0.078 0.266 7.1 3/1
0.050 P +
10.0 N 0.078 10.266 26.2 132/1
2. Discussion -
The control yield of the assay alga, Selenastrum capri-
cornutum , indicates that the potential primary productivity
of Blackhoof Lake was moderately high at the time the sample
was taken. The lack of significant increase in yield with
increasing levels of orthophosphate, until nitrogen was also
added, shows that the sample was nitrogen limited. Note
also, the N/P ratio of the control sample.
The lake data indicate nitrogen limitation in July (N/P
ratio = 7/1) and October (N/P = 5/1) and phosphorus limitation
in September (N/P 14/1).
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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 each of the tribu-
tary sites indicated on the map (page vi), except for the high runoff
months of April and May when two samples were collected. 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 tribu-
tary sites nearest the lake.
In this report, nutrient loads for sampled tributaries were deter-
mined by using a modification of a U.S. Geological Survey computer
program for calculating stream loadings*. Nutrient loadings for unsam—
pled “minor tributaries and immediate drainage” (“ZZ” of U.S.G.S.) were
estimated by using the mean annual concentrations in the unnamed stream
at station A-2 and mean annual ZZ flow.
The Village of Ironton did not participate in the Survey, and the
nutrient loads were estimated at 2.5 lbs P and 7.5 lbs N/capita/year.
The nutrient loads attributed to the inlet are those measured at station
A-l minus the estimated Ironton loads.
* See Working Paper No. 1.
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9
A. Waste Sources:
1. Known municipalt -
Pop. Mean Receiving
Name Served Treatment Flow (rngd) Water
Ironton 562 act. sludge 0.056* Unnamed stream
2. Known industrial - None
Anonymous, 1974
* Estimated at 100 gal/capita/day.
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10
B. Annual Total Phosphorus Loading - Average Year:
1. Inputs -
lbs P/ % of
Source yr total
a. Tributaries (non-point load) -
Unnamed Stream (A-i) 360 18.1
b. Minor tributaries & immediate
drainage (non-point load) - 170 8.5
c. Known municipal SIP’s -
Ironton 1,410 70.9
d. Septic tanks* - 20 1 .0
e. Known industrial — None - —
f. Direct precipitation** - 30 1.5
Total 1,990 100.0
2. Outputs -
Lake outlet - Unnamed Stream (B-i) 310
3. Net annual P accumulation - 1,680 pounds
* Estimate based on 25 lakeshore dwellings; see Working Paper No. 1.
** 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) —
Unnamed Stream (A-i) 9,750 50.8
b. Minor tributaries & immediate
drainage (non-point load) - 2,870 14.9
c. Known municipal STP’s -
Ironton 4,220 22.0
d. Septic tanks* - 590 3.1
e. Known industrial - None - -
f. Direct precipitation** - 1,760 9.2
Total 19,190 100.0
2. Outputs -
Lake outlet - Unnamed Stream
(B—i) 11,190
3. Net annual N accumulation - 8,000 pounds
* Estimate based on 25 lakeshore dwellings; see Working Paper No. 1.
** See Working Paper No. 1.
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12
D. Mean Annual Non-point Nutrient Export by Subdrainage Area:
Tributary lbs P/mi 2 /yr lbs N/mi 2 /yr
Unnamed Stream (A-i) 62 1 ,681
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 olgiotrophic or becoming oligotrophic if mor-
phometry permitted. A mesotrophic rate would be considered one
between “dangerous” and “permi ssi bi e”.
Total Phosphorus Total Nitrogen
Units Total Accumulated Total Accumulated
lbs/acre/yr 10.9 9.2 104.9 41.7
grams/m’/yr 1.22 1.03 11.8 49
Vollenweider loading rates for phosphorus
(g/m 2 /yr) based on mean depth and mean
hydraulic retention time of Blackhoof Lake:
“Dangerous” (eutrophic rate) 0.48
“Permissible” (oligotrophic rate) 0.24
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13
V. LITERATURE REVIEWED
Anonymous, 1974. Wastewater disposal facilities inventory. MPCA,
Minneapolis.
Schilling, Joel, 1974. Personal communication (lake map). 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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TRIBUTARY FLOW INFORMATION FOP MINNESOTA 10/30/74
LA E CODE ?71? F3LACP(HOOF LAPcE
TOTAL OPAINAGE APEA (IF LAKE 7.06
SIJI3—ORA IWAC,E NORMALIZED FLOWS
TRIBUTARY AREA JAN FE I MAR AP MAY JUN JUL AUG SEP OCT NOV DEC MEAN
?71?AI 5.83 1.57 1.46 2.11 6.06 7.52 6.26 4.97 3.91 2.86 3.24 2.96 2.37 3.78
271241 7.96 ‘.32 2 .IQ 2.99 p.40 10.30 8.53 6.81 5.45 3.85 4.50 4.16 3.35 5.25
?71?17 2.13 0.79 0.67 0.96 2.07 2.63 2.33 1.76 1.29 1.06 1.10 0.94 1.01 1.39
SUMMARY
TOTAL DRAINAr,E AREA OF LAicE 7.96 TOTAL FLOW IN = 61.90
SUM OF SJR—DRAINAGE AREAS = 7.96 TOTAL FLOW OUT = 62.85
MEAN MONTHLY FLOWS AND DAILY FLOWS
TPIRUTAPY AONTH YEAR MEAN FLOW DAY FLOW OAY FLOW DAY FLOW
271241 10 7? 3.02 1 3.20
I I 72 3.10 19 3.00
1’ 72 2.69 21 2.7’)
1 73 2.09 6 2.10
73 1.93 4 1.90
3 73 3.) 16 3.20
4 73 3.76 9 3.60 24 4.40
5 73 4. l 3 4.20 20 4.30
6 71 4.01 11 4.4 1)
7 73 7.42
7 73 2.63 13 2.60
8 73 3.40 17 3.60
9 73 1.83 17 3.60
?71?H1 10 72 4.19 15 4.10
11 7? 4.64 19 4.?0
7? 3.M0 21 3.80
73 3.C9 6 3.10
2 71 2.74 4 2.90
1 73 4.60 16 4.60
4 71 5.?9 9 5.00 24 6.10
c 73 5.05 3 S.20 20 4.50
6 73 3 .7S 11 4.10
7 73 3.61 13 3•58
8 71 4.74 17 5.00
73 5.16 17 4.80
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Ti- I lJTARY FLflw INFOPMATTUN FOP MINNESOTA 10/30/74
LAKI CO )E ?7)? P-3LACt
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APPENDIX B
PHYSICAL and CHEMICAL DATA
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STORET PETRIEVAL DATE 74/10/30
271201
46 28 18.0 094 00 38.0
BLACKHOOF LAKE
27 MINNESOTA
11EPALES 2111202
0023 FEET
OATE
F POM
TO
T1M OFPTI-f
OF
DAY FEET
3
72/07/02 10 05 0000
10 05 00?0
72/09/04 16 10 0000
16 30 0004
16 30 0015
16 30 0018
16 30 0021
72/10/24 11 45 0000
11 45 0004
11 45 0015
11 45 0019
DEPTH
00010
WATFP
TEMP
CFJ’JT
00100
nO
‘iC,/L
00077
T AMSP
SECCHI
INCHES
00094
CNDUCTVY
FIELD
MICROMHO
00400
PH
SO
00410
1 ALK
CACO3
MG/L
00630
NO2 N03
N—TOTAL
MG/L
00610
NH3-N
TOTAL
MG/L
00665
PHOS—TOT
MG/L P
00666
P 4OS—DIS
MG/L P
0.040
0.060
0.090
0.100
0.050
0.100
0.040
0.540
0.130
0.120
0.620
1.770
0.040
0.188
0.020
0.022
0.034
0.199
0.013
0.088
0.013
0.015
0.022
0.164
0.090
0.090
0.090
0.060
0.050
0.050
0.033
0.053
0.058
0.015
0.037
0.040
p4.0
10.2
72
200
8.60
96
R.5
0.0
230
7.20
105
18.9
54
275
8.00
94
18.8
7.8
199
8.00
96
15.?
u.3
220
7.32
112
12.9
0.0
240
7.20
122
11.1
5.4
11.2
60
230
225
8.10
8.20
103
103
5.1
11.0
230
8.30
101
5.1
11.2
230
8.20
103
32217
CHL PI-iYL
.
UC•IL
DATE
F ‘ OM
To
TU.IE DEPT-I
OF
DAY FEET
72/07/07 10 05 0000
72/OQ/04 16 30 0000
19 •
5.7J
J VALUE (NOWN TO RE IN EPRo
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APPENDIX C
TRIBUTARY DATA
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STOPET ET, 1EVAL F)AFE 74/10/30
K VALUE KNOWN TO RE LESS
THAN D DICATED
?712A1 LS2712A1
‘ .6 28 30.0 093 59 30.0
UNNAME [ ) E4ST TRIB TO BLACKHOOF
21 CO fIR SHEET #2
1/HLACI
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ST WET ET?1EVAL DATE 74/lo/: o
?712A2 LS?712A2
47 29 00.0 093 SR 30.0
UNN4MED STREAM
27 CO #1 SHEET#2
T/hLACKHOOF LAKE
SECONL)APY RD BRDG S IP ONTON
11EPALES 2111204
4 0000 FEET DEPTH
‘ 1 . 1610 00671 00665
DATE TIME DFPTH NU? NO3 TOT KJFL r13N Pr1OSDIS PHOS—TOT
FRO’i OF N—TOTAL N TOTAL O Tr-4O
TO 1)AY FEET MG/L 1( /L MG/L MG/L P MG/L °
72/10/15 1 30 0.077 0.750 ‘ 1.120 0.007 0.054
72/H/I ’) 1410 ( ‘.0,6 0.S 0 0.078 0.019 0.039
72/12/2 1 14 50 ).01’. 1.0 (’ 0.370 0.015 0.034
71/01/OF 15 00 0.04 ’ . 1. ”0 ) 0.260 0.015 0.070
73/02/04 10 15 0.034 0 •5Q 0 0.179 0.011 0.025
73/03/16 0 40 0.0 5 1.050 O.?52 0.028 0.065
73/04/OQ 09 25 0.037 1.9r 10 0.087 0.029 0.050
73/04/24 10 45 0.O ’2 0.A30 0.039 0.015 0.035
71/0 /03 14 00 0.0l0’( 0. 90 0.040 0.025
71/05/20 12 0 0.Oe,1 0 . 90 0.0?6 0.090 0.125
71/06/11 11 ‘0 0.077 1. fl0 0.072 0.026 0.070
73/07/13 10 50 0.010K 1.400 0.094 0.018 0.090
73/08/17 15 20 0.010K 0.970 0.040 0.012 0.075
71/09/17 10 45 C.010c 0. ’ ) 0.0 0 0.035
K VALUE KNOWN TO BE LESS
THAN INDICATED
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STOPET PETP1EVAL flAir: 74/10/30
?712B1 LS2712F31
46 28 00.0 094 01 00.0
UNNAMLI) STREAM
27 Co #18 SHEET #2
T/BLACKHOOF LAKE
CO HWY 28 RRDG SSW IRONTON
1IEPALES 2111204
4 0000 FEET DEPTH
( 0630 0062 5 00610 00 71 00665
DATE TIMF DF°TrI NO?&N03 101 KJFL ‘1H3—N PrIOSDIS PHOS—TOT
FPOM OF i’J— IOTAL N rUTAL ORTHO
TO DAY FEET M(,/L MG/L MGIL G/L P MG/L P
7?/10/15 1245 D.0 ’i l 0. ’ 67 0.110 0.00 5K 0.037
7?/11/1 1500 (.01(’ )K 0. 50 0.014 0.006 0.033
72/12/2 ) 14 15 0.096 1.200 0.019 0.006 0.042
7V0 1/06 14 10 0. 7 ciO 0. € ’O 0.?70 0.013 0.030
73/02/04 10 35 0.2?O 0. ”3G 0.050 0.005K 0.02?
71/03/16 16 00 0.350 1.370 0.132 0.010 0.035
71/04/09 09 00 0.180 0. 70 0.110 0.007 0.040
71/04/24 10 35 0.1 0.6 0 0.010 0. O O Si ( 0.015
73/05/03 13 45 0.033 ).- 60 0.012 0.011 0.030
73/ S/20 17 00 u.013K 0.780 0.009 0.008 0.020
71/06/li 14 20 0.01D 1.?0(’ 0.013 3.007 0.020
71/07/13 10 30 0.010K 0.955 0.019 0.005K 0.025
73/08/Il 1510 ( ‘.010K 0. 10 0.011 0.011 0.030
73/09/17 10 0 0.013K l.7A0 3.070 0.011 0.030
K VALUF KNOWN TO BE LESS
THAN INDICATED
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