Lac Lavon Water Quality Assessment
Prepared for
Black Dog Watershed Management Organization
January 2009
Lac Lavon Water Quality Assessment
Prepared for
Black Dog Watershed Management Organization
January 2009
4700 West 77th Street
Minneapolis, MN 55435-4803
Phone: (952) 832-2600
Fax:
(952) 832-2601
Lac Lavon Water Quality Assessment
January 2009
Table of Contents
1.0 Introduction.............................................................................................................................................1
1.1
Characteristics of Lac Lavon ...................................................................................................... 1
1.2
Water Quality Goals ................................................................................................................... 1
2.0 Lac Lavon Water Quality Monitoring ....................................................................................................2
2.1 Water Quality Monitoring............................................................................................................... 2
2.1.1
Secchi Disc Transparency.............................................................................................. 2
2.1.2
Chlorophyll a ................................................................................................................. 5
2.1.3
Total Phosphorus ........................................................................................................... 5
2.2 Aquatic Macrophyte Surveys.......................................................................................................... 6
2.3 Fish Surveys.................................................................................................................................... 6
3.0 Lac Lavon Water Quality Assessment..................................................................................................11
3.1 Lac Lavon Current Water Quality Assessment............................................................................. 11
3.2 Proposed Monitoring for Lac Lavon............................................................................................. 12
3.2.1
Continued Water Quality Monitoring .......................................................................... 12
3.2.2
Sediment Sampling and Analysis for Mobile Phosphorus........................................... 12
3.2.3
Macrophyte Surveys .................................................................................................... 13
3.2.3
Lake Level ................................................................................................................... 13
3.3 Summary of Proposed Monitoring................................................................................................ 13
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List of Figures
Figure 1. Lac Lavon Lake (Apple Valley & Burnsville) Summer Average Water Clarity & Trend ..... 3
Figure 2. Lac Lavon 2008 Secchi Disc Transparency.......................................................................... 4
Figure 3. Lac Lavon Lake (Apple Valley & Burnsville) Summer Average Chlorophyll a
Concentrations & Trend Analysis ..................................................................................... 7
Figure 4. Lac Lavon 2008 Chlorophyll a Concentrations .................................................................... 8
Figure 5. Lac Lavon Lake (Apple Valley & Burnsville) Summer Average Total Phosphorus
Concentrations & Trend Analysis ..................................................................................... 9
Figure 6. Lac Lavon 2008 Total Phosphorus Concentrations ............................................................ 10
List of Appendices
Appendix A
2008 Lac Lavon Water Quality Monitoring Data (Barr Engineering)
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1.0 Introduction
1.1
Characteristics of Lac Lavon
Lac Lavon lies on the Burnsville/Apple Valley border. The 184-acre watershed of Lac Lavon
encompasses portions of Burnsville and Apple Valley. According to the Apple Valley stormwater
management plan, the only surface water outlet from Lac Lavon is a 12-inch diameter emergency
overflow outlet to Keller Lake. A valve controls the flows in the overflow pipe; normally the valve is
closed. Lac Lavon is unique in that it is an abandoned gravel pit, so its primary water source is
groundwater. Lac Lavon’s water surface area is approximately 60 acres, with 65 percent of the lake
less than 15 feet (4.6 meters) deep. The lake has a maximum depth of 32 feet (9.8 meters). Lac
Lavon is not a DNR-protected water.
Existing watershed land use is low density residential and park. Two city parks—a City of Burnsville
park with a public beach on the west shore, and a City of Apple Valley park with a path to a fishing
pier on the northeast shore—are located on Lac Lavon. Very little, if any, change in density is
expected in the Lac Lavon watershed.
Lac Lavon is used for a variety of recreational purposes, including fishing, swimming, aesthetics and
wildlife viewing. The City of Burnsville public beach and the City of Apple Valley park with fishing
pier provide for most of the recreational use of the lake. There is no public boat access on Lac Lavon.
1.2
Water Quality Goals
The Black Dog Watershed Management Organization (BDWMO) has classified Lac Lavon as a
Category I water body. A water quality action level of 3.6 meters (11.8 feet) for summer average
Secchi disc transparency (SDT) was established by the BDWMO for Lac Lavon in 2002. When a
statistical trend analysis indicates that water transparency has degraded beyond this level (i.e., SDT
< 3.6 meters), then a diagnostic study of potential causes is mandated. Summer-average SDTs were
calculated from data collected prior to 2002 and were used to develop a water quality action level of
3.6 meters for Lac Lavon. The summer average SDT has dropped below the action level of
3.6 meters four out of the past 7 years. The BDWMO has not established water quality action levels
for summer average chlorophyll a or total phosphorus concentrations. At the time water quality
actions levels were being established, there were limited chlorophyll a and total phosphorus data
available for Lac Lavon.
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2.0 Lac Lavon Water Quality Monitoring
2.1
Water Quality Monitoring
Lac Lavon has been monitored regularly from 2002 through 2008 with the measurement of Secchi
disc transparency (SDT), chlorophyll a, and total phosphorus at the surface. Monitoring was
conducted through the Metropolitan Council’s Citizen-Assisted Monitoring Program (CAMP).
Sporadic monitoring was also conducted from 1989 through 2001. In addition to monitoring of water
quality parameters, aquatic macrophyte surveys and fish surveys have been conducted by the
Minnesota Department of Natural Resources (DNR). Barr Engineering Co. (Barr) collected
additional water quality data in 2008, including total phosphorus at 1-meter depth intervals from
3 meters to near bottom.
2.1.1
Secchi Disc Transparency
The summer average (May 15 to September 15) SDT was calculated for years where data was
available (Figure 1). The summer average SDT has fluctuated between 3.1 and 5.2 meters since
monitoring began in 1989. However, it should be noted that the highest summer average SDT of
5.2 meters in 2001 is based on only two measurements taken in late May and mid-July. Late May to
mid-July is often the period of the year when Lac Lavon has the highest water clarity of the season,
so SDT in 2001 is biased towards a period of the season with higher water clarity compared with
other years.
Four of the past 7 years have experienced a summer average SDT less than the action level of
3.6 meters. The lowest summer average SDT of 3.2 meters occurred in 2008, while one of the years
of highest SDT occurred just 3 years prior in 2005. There is no statistically significant trend in the
summer average SDT.
In addition to the CAMP monitoring, Barr collected SDT measurements in 2008. CAMP SDT
measurements and Barr SDT measurements are plotted together in Figure 2. Barr measurements of
SDT were lower on average than CAMP measurements, but the same overall trend was observed for
both sets of measurements. SDT is lowest in April, increases greatly in early-June, peaks in July,
then decreases in August and September.
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Figure 1. Lac Lavon Lake (Apple Valley & Burnsville)
Lac
Lavon& Trend
Summer Average Water
Clarity
BDWMO Classification: Category I
0
0.0
Category IV and V
Category III
1
3.3
Category II
2
6.6
3
9.9
Action Level = 3.6 m (11.8 ft)
4
13.2
5
16.5
Secchi Disc Transparency (ft)
Secchi Disc Transparency (m)
Category I
No Statistically Significant
Trend Over Time
Black Dog WMO Lake
Classification System
Maximum Lake Depth
Not Shown (9.8 m, 32 ft)
6
1985
19.8
1990
1995
2000
2005
2010
1/27/2009
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Print
2:21
PM
Figure 2. Lac Lavon 2008 Secchi Disc Transparency
0.0
0.5
CAMP Observations
Barr Observations
Secchi Disc Transparency (m)
1.0
1.5
2.0
2.5
3.0
3.5
4.0
4.5
5.0
4/2/08
4/22/08
5/12/08
6/1/08
6/21/08
7/11/08
7/31/08
8/20/08
9/9/08
9/29/08
10/19/08
11/8/08
Time
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2:20 PM
Figure 2
Lac Lavon 2008 Secchi Disc Transparency
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2.1.2
Chlorophyll a
Samples have been collected from the surface of Lac Lavon and analyzed for chlorophyll a in various
years beginning in 1989. The summer average (May 15 to September 15) chlorophyll a
concentrations were calculated and are plotted in Figure 3. There is a statistically significant
increasing trend in chlorophyll a concentrations over the period of 1998-2008. The highest summer
average chlorophyll a occurred in 2008. One of the lowest summer average chlorophyll a
concentrations occurred just 3 years prior in 2005. It should be noted that the year 2001 summer
average chlorophyll a concentration is based on only two measurements collected during a period of
the summer that typically has the lowest algae productivity, and is therefore biased towards low
chlorophyll a concentrations.
Barr collected surface samples for laboratory analysis of chlorophyll a in 2008 in addition to the
CAMP monitoring of chlorophyll a. The results of the Barr and CAMP 2008 chlorophyll a
monitoring are plotted in Figure 4. There is some variability in the chlorophyll a results.
Chlorophyll a data collected by Barr showed a high degree of fluctuation from April through June.
CAMP chlorophyll a data had a clearer trend of elevated concentrations in April and early May,
decreasing in June and July, then increasing again in late August and September. As one would
expect, this correlates inversely with SDT.
2.1.3
Total Phosphorus
Samples were collected from the surface of Lac Lavon and analyzed for total phosphorus. The
summer average (May 15 to September 15) total phosphorus concentrations were calculated and are
plotted in Figure 5. There is no statistically significant trend in the summer average total phosphorus
concentrations during the period of 1999-2008. The highest recorded summer average total
phosphorus concentration was in 2008. However, two of the samples collected early in the season
had unusually high total phosphorus concentrations. The samples collected by the Citizen-Assisted
Lake Monitoring Program (CAMP) on 6/1/08 and 6/14/08 had total phosphorus concentrations of
151 µg/L and 63 µg/L, respectively. It seems likely that these two data points are erroneous, as
samples collected in May and late-June did not exceed 27 µg/L total phosphorus. Additionally,
samples collected at the surface by Barr on 6/3/08 and 6/23/08 had total phosphorus concentrations
of 25 and 16 µg/L, respectively. The CAMP and Barr surface total phosphorus data are plotted in
Figure 6. The Metropolitan Council is currently investigating the two unusually high total
phosphorus concentration collected as part of the CAMP monitoring.
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In addition to surface samples, Barr collected samples at 1-meter depth intervals from 3 meters to the
bottom of Lac Lavon (approximately 9 meters). Samples were analyzed for concentrations of total
phosphorus and total dissolved phosphorus. Water quality data collected by Barr in 2008 are
presented in Appendix A. Increased concentrations of total phosphorus were observed in samples
collected near the bottom on several occasions. In particular, samples collected in mid- and lateSeptember near the bottom had concentrations of 470 and 700 µg/L total phosphorus, respectively.
2.2
Aquatic Macrophyte Surveys
The Minnesota DNR has conducted aquatic macrophyte surveys on Lac Lavon on a regular basis,
typically twice a year, since 1996. Three non-native species have been identified in Lac Lavon:
Curlyleaf pondweed, Eurasian watermilfoil, and brittle naiad. Curlyleaf pondweed and Eurasian
watermilfoil are known to commonly reach nuisance levels in Minnesota lakes. The Lac Lavon
Association has conducted herbicide treatments to control Eurasian watermilfoil in various years,
starting in 1996. Curlyleaf pondweed is typically not observed at nuisance levels in Lac Lavon.
2.3
Fish Surveys
The Minnesota DNR has conducted fish surveys of Lac Lavon, most recently in 2004. The most
abundant fish netted in the survey in 2004 were bluegill, followed by northern pike. Black crappie,
sunfish, largemouth bass, black bullhead, and white sucker were also observed. Rainbow trout,
tullibee (cisco), and smallmouth bass have been stocked in Lac Lavon in the past 5 years, but were
not caught in the 2004 fish survey. The numbers and type of fish caught in 2004 were very similar to
the numbers and type of fish caught in the 1999 survey. There does not appear to be any major
changes to the Lac Lavon fish community from 1999 to 2004. Common carp, which can have a
negative impact on water quality, were not observed in either the 1999 or 2004 survey.
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Figure 3. Lac Lavon Lake (Apple Valley & Burnsville)
Summer Average Surface Chlorophyll a Concentrations &
Trend Analysis
BDWMO Classification: Category I
50
Black Dog WMO Lake
Classification System
Category III
Chlorophyll a Concentration (μg/L)
40
30
Category II
20
Statistically Significant
Trend Over Time
(94th Percentile)
10
Category I
0
1985
1990
1995
2000
2005
2010
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Chl a Print
2:21 PM
Figure 4. Lac Lavon 2008 Chlorophyll a Concentrations
20
18
CAMP Observations
Barr Observations
Chlorophyll a Concentration (m g/L)
16
14
12
10
8
6
4
2
0
4/2/08
4/22/08
5/12/08
6/1/08
6/21/08
7/11/08
7/31/08
8/20/08
9/9/08
9/29/08
10/19/08
11/8/08
Time
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2:20 PM
Figure 5. Lac Lavon Lake (Apple Valley & Burnsville)
Summer Average Surface Total Phosphorus Concentrations
& Trend Analysis
BDWMO Classification: Category I
80
Category III
60
Total Phosphorus Concentration (μg/L)
Category II
40
Category I
No Statistically Significant
Trend Over Time
Black Dog WMO Lake
Classification System
20
0
1985
1990
1995
2000
2005
2010
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TP Print
2:21 PM
Figure 6. Lac Lavon 2008 Total Phosphorus Concentrations
160
140
Total Phosphorus Concentration (m g/L)
CAMP Observations
Barr Observations
120
100
80
60
40
20
0
4/2/08
4/22/08
5/12/08
6/1/08
6/21/08
7/11/08
7/31/08
8/20/08
9/9/08
9/29/08
10/19/08
11/8/08
Time
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2:20 PM
3.0 Lac Lavon Water Quality Assessment
3.1
Lac Lavon Current Water Quality Assessment
The water quality of Lac Lavon remains very good overall. There is variability in water quality from
year-to-year in Lac Lavon, and 2008 had the lowest summer average SDT on record, 3.18 meters,
which was below the action level of 3.6 meters established by the BDWMO. However, 2005 and
2007 had summer average SDTs of 4.6 and 3.94 meters, respectively, that were far better than the
lake’s established “action level”. There does not appear to be a significant trend in the summer
average SDT, and SDT has fluctuated above and below the action level of 3.6 meters for the past
7 years. The variations in water quality from season to season could be attributed to a variety of
factors, including variations in climate. The amount of precipitation in a season will affect the
amount of runoff and external phosphorus that enters Lac Lavon. The length of time ice covers the
lake in winter, the time of ice out, the occurrence of early summer storms that mix the lake, and
several other climate variations can all have significant impacts on a lake’s water quality for a given
season, especially if internal phosphorus loading from lake sediments is occurring.
There is evidence some internal phosphorus loading is occurring in Lac Lavon. Sediment samples
were collected by Blue Water Science from multiple littoral zone locations (5 to 10 feet deep) around
Lac Lavon in 2003. An additional sample was collected from the deepest area of Lac Lavon.
Analyses showed concentrations of “mobile” phosphorus in the deep sediment sample were high.
Mobile phosphorus is the fraction of the total phosphorus that can potentially be released from the
sediment if the sediment becomes anoxic (i.e., oxygen depleted). Prolonged periods of oxygen
depletion over a large area of sediment can result in the release of a significant amount of phosphorus
to the deep water of a lake. If this phosphorus-rich deep water reaches the shallower water of the
lake, it can cause increased algal growth. In some instances, large amounts of phosphorus from
internal loading can cause rapid late-summer algae blooms when the deep, phosphorus-enriched
water mixes with the surface as the thermal stratification of the lake breaks down. This did not occur
in Lac Lavon in 2008, as evidenced by the water quality data that was collected. The water near the
bottom of Lac Lavon, which had elevated concentrations of total phosphorus by mid-summer,
remained thermally stratified through September. However, internal loading of phosphorus may still
be contributing significant amounts of phosphorus to Lac Lavon and affecting summer water quality.
An examination of chlorophyll a data collected with a field probe in 2008 indicates the highest
concentrations of algae are often at 6 to 7 meters depth, just above the zone where oxygen levels drop
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and internal phosphorus release can occur. Furthermore, internal loading can also occur over the
winter months when ice cover prevents atmospheric oxygen from entering the lake.
The ecosystem of Lac Lavon appears relatively stable. There was little change in the fish population
from 1999 to 2004. The Lac Lavon Association takes actions to control the growth of Eurasian
watermilfoil, and Curlyleaf pondweed typically does not reach nuisance levels of growth.
3.2 Proposed Monitoring for Lac Lavon
The following section presents the proposed monitoring activities for Lac Lavon that will provide
further understanding of the lake’s biogeochemical interactions.
3.2.1
Continued Water Quality Monitoring
Continued monitoring of SDT, chlorophyll a, and total phosphorus are necessary to evaluate whether
Lac Lavon water quality is meeting the BDWMO’s criteria. The continued collection of samples at 1
meter depth intervals and analyzing for total phosphorus and total dissolved phosphorus will provide
further data for evaluating the dynamics of phosphorus in Lac Lavon, including whether internal
phosphorus is a significant factor in overall lake water quality. Although only data collected from
mid-May through early September is used to determine the summer average water quality, data
collected earlier in the year are useful in evaluating the biogeochemical processes in the lake.
Collecting lake water quality data within several days of ice out is helpful in evaluating the internal
phosphorus loading potential of a lake, as internal phosphorus loading often occurs as oxygen
becomes depleted during the period of ice cover. Similarly, dissolved oxygen and phosphorus
measurements collected underneath the ice in late winter can be used to assess internal loading
during the winter months.
There are several relatively deep holes in Lac Lavon other than the deepest one that is currently
sampled on a regular basis, but there is little or no available data for these other deep areas of the
lake. Collecting oxygen and temperature depth profiles of two of the deeper regions, in addition to
continued monitoring of the deep hole that was monitored in 2008, would be a relatively inexpensive
way to provide further understanding of the internal phosphorus loading of the lake.
3.2.2
Sediment Sampling and Analysis for Mobile Phosphorus
Of the sediment samples collected in 2003, only one of the sediment samples was collected from a
deep area of the lake where internal phosphorus loading is most likely to occur. All of the sediment
samples were collected with sampling devices (soil auger and Eckman dredge) that did not maintain
the physical structure of the sediment; therefore, it was not possible to focus analyses on the
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sediment-water interface. Collecting sediment samples with a sediment coring device that maintains
the delicate structure of the sediment-water interface until it is brought to the surface allows a more
accurate analysis of the internal phosphorus loading potential. Mobile phosphorus analysis on three
sediment cores from the three deepest areas of the lake would provide valuable data on the sediment
mobile phosphorus potential for the areas most likely to experience depleted oxygen. When
combined with dissolved oxygen measurements, the sediment data could be used to determine which
portions of the lake are most likely to contribute to internal phosphorus loading.
3.2.3
Macrophyte Surveys
It is anticipated that the DNR will continue to conduct macrophyte surveys of Lac Lavon. The results
of the macrophyte surveys should be monitored for any major changes to the aquatic plant
community. In particular, Curlyleaf pondweed should be watched closely, as high densities of
Curlyleaf pondweed can have a negative impact on water quality. Curlyleaf pondweed has an earlier
life cycle than native plant communities. Dense growth can occur early in the season, resulting in an
early summer die off. The early introduction of a large amount of decaying vegetation can cause an
increase in the internal phosphorus loading of a lake.
3.2.3
Lake Level
There is limited information on the water level of Lac Lavon over the years. Lac Lavon has no
regularly flowing outlet, and the lake level changes in response to precipitation, evaporation, and
groundwater flux. Monthly monitoring of the lake level would be an inexpensive but useful
measurement for estimating the groundwater flux into Lac Lavon. Also, dramatic changes in lake
level from one year to the next can have an impact on water quality.
3.3
Summary of Proposed Monitoring
The additional monitoring of phosphorus, chlorophyll a, and other parameters at 1-meter depth
intervals in 2008 provided useful data for understanding the dynamics of Lac Lavon. It is
recommended that the monitoring conducted in 2008 be repeated in 2009. In addition to a repeat of
the monitoring of 2008, the following monitoring should be considered for addition:
x
Measure lake water quality within days of ice-out (or alternatively measure water quality beneath
the ice in late-winter);
x
Collect water quality parameters (oxygen, temperature, chlorophyll a, etc.) with a field probe at
1-meter intervals in two additional deep areas of the lake; and
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x
Collect three sediment cores in the three deepest areas of Lac Lavon and analyze for mobile
phosphorus.
x
Collect monthly or bi-monthly lake level data.
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Appendix A
2008 Lac Lavon Water Quality Monitoring Data (Barr Engineering)
Lac Lavon: 2008 Water Quality Data Collected by Barr Engineering Company
Date
Sampled
Max.
Depth
(m)
Secchi
Disc
(m)
05/02/08
9.0
1.2
0-2
FD (Field Duplicate) 0-2
0.0
1.0
2.0
3.0
4.0
5.0
6.0
7.0
8.0
8.5
8
9.4
05/16/08
8.7
1.3
0-2
FD (Field Duplicate) 0-2
0.0
1.0
2.0
3.0
4.0
5.0
6.0
7.0
8.0
06/03/08
9.1
1.7
0-2
FD (Field Duplicate) 0-2
0.0
1.0
2.0
3.0
4.0
5.0
6.0
7.0
8.0
8.6
Sample
Depth (m)
Chl. A
(ug/L)
Hach Chl.
a
(ug/L)
Specific
Total Diss.
Cond.
Total Phos- Phos(umho/cm
phorus
phorus
@ 25 C)
(mg/L)
(mg/L)
pH
(Std.
Units)
eh
(mV)
0.0099
----0.013
0.012
0.011
0.008
0.009
0.0086
0.015
--8.2
8.1
8.1
8.1
8.0
8.0
7.9
7.8
7.7
7.5
--148
150
151
151
151
151
154
155
159
160
0.020
0.018
---0.024
0.028
0.020
0.022
0.019
0.034
0.011
----0.013
0.013
0.012
<0.010
<0.010
0.011
--8.8
8.7
8.8
8.7
8.3
8.1
7.9
7.8
7.7
--132
133
131
131
140
143
146
147
149
0.025
0.025
---0.027
0.031
0.033
0.075
0.054
0.056
0.064
0.011
----0.012
0.013
0.012
0.017
0.014
0.012
0.013
--8.9
8.9
8.8
8.7
8.6
8.1
8.0
7.9
7.8
7.7
--164
166
167
169
173
182
185
184
115
2
Turbidity
(NTU)
D.O.
(mg/L)
Temp.
(Celsius)
--7.6
7.9
8.8
8.1
8.3
9.1
7.9
6.3
4.3
2.7
3.4
--
--11.0
11.0
11.0
11.0
10.9
10.9
10.4
9.4
5.1
1.2
--9.3
9.3
9.3
9.3
9.3
9.3
8.6
7.8
6.7
6.4
--528
528
528
528
528
528
529
530
548
561
0.026
0.031
---0.039
0.034
0.031
0.026
0.025
0.025
0.041
1.8
5.3
--1.1
1.6
8.5
18.1
5.0
2.4
1.1
0.8
1.5
3.7
--
--13.3
13.4
15.8
14.3
8.8
6.9
4.7
3.5
0.5
--17.3
17.2
14.6
13.6
11.5
9.7
9.0
8.5
8.4
--545
544
537
539
550
551
554
557
561
19.0
17.0
--3.8
3.7
4.0
8.5
13.1
5.2
2.7
3.1
0.6
0.6
3.3
--11.8
11.9
12.0
11.7
10.3
3.8
0.9
0.4
0.3
0.3
--19.0
19.0
19.0
17.8
16.4
11.4
9.7
9.0
8.4
8.1
--537
537
537
537
539
549
549
550
570
576
P:\Mpls\23 MN\19\2319375\WorkFiles\2008 Lac Lavon WQ Data\Lac Lavon-08 wq DATA_KDM.xls
A-1
Lac Lavon: 2008 Water Quality Data Collected by Barr Engineering Company
Date
Sampled
Max.
Depth
(m)
Secchi
Disc
(m)
06/23/08
9.4
3.5
0-2
FD (Field Duplicate) 0-2
0.0
1.0
2.0
3.0
4.0
5.0
6.0
7.0
8.0
9.0
3.2
3.2
07/07/08
9.1
3.7
0-2
FD (Field Duplicate) 0-2
0.0
1.0
2.0
3.0
4.0
5.0
6.0
7.0
8.0
8.5
07/21/08
9.1
3.8
0-2
FD (Field Duplicate) 0-2
0.0
1.0
2.0
3.0
4.0
5.0
6.0
7.0
8.0
8.5
Sample
Depth (m)
Chl. A
(ug/L)
Hach Chl.
a
(ug/L)
Total Diss.
Specific
Cond.
Total Phos- Phosphorus
phorus
(umho/cm
(mg/L)
(mg/L)
@ 25 C)
pH
(Std.
Units)
eh
(mV)
0.0097
----0.011
0.0087
0.013
0.014
0.021
0.011
0.011
--8.8
8.8
8.7
8.7
8.7
8.5
8.1
7.9
7.7
7.5
--161
162
162
162
165
170
176
153
35
-22
0.014
0.014
---0.016
0.014
0.021
0.026
0.17
0.1
0.078
0.0079
----0.01
0.012
0.012
0.012
0.021
0.012
0.012
--8.6
8.6
8.6
8.6
8.4
8.3
7.8
7.6
7.5
7.4
--129
129
130
131
136
143
163
158
-86
-105
0.017
0.015
---0.017
0.019
0.019
0.033
0.1
0.066
0.068
0.01
----0.013
0.011
0.011
0.012
0.019
D
0.011
--8.6
8.6
8.6
8.6
8.5
8.3
8.4
7.7
7.6
7.4
--148
144
140
138
143
148
144
8
-95
-111
Turbidity
(NTU)
D.O.
(mg/L)
Temp.
(Celsius)
--0.4
0.4
0.7
1.4
2.7
2.7
26.4
2.3
1.4
1.3
1.4
--10.0
10.0
9.9
9.8
10.8
10.6
1.0
0.3
0.2
0.2
--23.6
23.3
23.2
23.1
20.4
14.6
10.8
9.5
8.5
8.2
--530
530
530
530
535
560
567
573
592
617
0.016
0.013
---0.015
0.017
0.023
0.068
0.13
0.061
0.051
1.3
2.7
--0.4
0.4
0.5
0.5
0.8
1.9
6.4
24.8
1.2
1.3
1.3
--
--9.7
9.7
9.6
9.3
8.8
9.7
2.0
0.4
0.3
0.3
--25.2
25.2
25.2
24.6
23.8
18.2
12.1
10.7
9.0
8.6
--507
507
508
510
514
535
552
553
590
606
20.0
4.0
--0.3
0.4
0.4
0.5
0.8
1.2
107.1
1.7
0.8
0.7
0.8
--
--0.7
9.8
9.8
9.8
8.8
9.3
11.5
0.9
0.6
0.3
--26.3
26.3
26.1
25.9
24.4
20.9
14.5
11.6
9.6
9.2
--497
496
496
496
502
526
542
559
591
606
P:\Mpls\23 MN\19\2319375\WorkFiles\2008 Lac Lavon WQ Data\Lac Lavon-08 wq DATA_KDM.xls
A-2
Lac Lavon: 2008 Water Quality Data Collected by Barr Engineering Company
Date
Sampled
Max.
Depth
(m)
Secchi
Disc
(m)
08/04/08
9.1
2.3
0-2
FD (Field Duplicate) 0-2
0.0
1.0
2.0
3.0
4.0
5.0
6.0
7.0
8.0
8.5
4.0
2.7
08/18/08
9.1
3
0-2
FD (Field Duplicate) 0-2
0.0
1.0
2.0
3.0
4.0
5.0
6.0
7.0
8.0
8.5
09/03/08
8.5
2.7
0-2
FD (Field Duplicate) 0-2
0.0
1.0
2.0
3.0
4.0
5.0
6.0
7.0
8.0
Sample
Depth (m)
Chl. A
(ug/L)
Hach Chl.
a
(ug/L)
Specific
Total Diss.
Cond.
Total Phos- Phos(umho/cm
phorus
phorus
@ 25 C)
(mg/L)
(mg/L)
pH
(Std.
Units)
eh
(mV)
0.012
----0.012
0.014
0.016
0.014
0.018
0.016
0.016
--8.8
8.9
8.9
8.9
8.9
8.5
8.3
7.6
7.4
--
--102
102
102
102
102
115
123
-49
-114
--
0.02
0.020
---0.023
0.019
0.021
0.037
0.066
0.092
0.22
0.016
----0.015
0.014
0.02
0.02
0.014
0.024
0.02
--8.8
8.8
8.9
8.9
8.9
8.5
8.0
7.7
7.5
7.4
--96
99
96
95
94
110
127
36
-83
-99
0.027
0.015
---0.016
0.014
0.03
0.025
0.083
0.091
0.023
----0.0091
0.0091
0.016
0.01
0.011
0.016
--8.8
8.8
8.8
8.8
8.9
8.9
8.3
7.9
7.6
--108
106
104
103
103
103
127
84
-76
Turbidity
(NTU)
D.O.
(mg/L)
Temp.
(Celsius)
--0.4
0.5
0.6
0.6
0.7
3.1
7.2
1.2
0.5
--
1.7
--
--9.0
9.0
9.0
8.9
8.9
8.4
8.7
0.3
0.2
--
--25.7
25.6
25.6
25.6
25.6
22.9
16.6
12.4
9.7
--
--488
489
488
488
488
531
544
566
608
--
0.019
0.019
---0.019
0.019
0.017
0.035
0.09
0.065
0.092
5.3
2.7
--0.2
0.2
0.4
0.4
0.5
0.6
7.0
1.7
0.6
0.6
1.3
--
--9.2
9.2
9.3
9.3
9.2
7.6
2.6
0.5
0.2
0.2
--25.9
25.3
25.0
24.9
24.8
23.2
18.1
13.1
10.4
9.4
--504
505
503
504
504
541
568
584
644
674
5.3
5.3
--0.3
0.3
0.5
0.5
0.6
0.6
2.9
0.6
0.4
1.8
--
--8.7
8.6
8.6
8.6
8.5
8.5
2.7
0.4
0.2
--22.7
22.7
22.7
22.7
22.6
22.6
19.7
13.9
10.1
--509
509
509
510
510
510
568
596
682
P:\Mpls\23 MN\19\2319375\WorkFiles\2008 Lac Lavon WQ Data\Lac Lavon-08 wq DATA_KDM.xls
A-3
Lac Lavon: 2008 Water Quality Data Collected by Barr Engineering Company
Date
Sampled
Max.
Depth
(m)
Secchi
Disc
(m)
09/17/08
9.3
2.8
0-2
FD (Field Duplicate) 0-2
0.0
1.0
2.0
3.0
4.0
5.0
6.0
7.0
8.0
8.5
5.3
5.3
09/30/08
9.4
2.2
0-2
FD (Field Duplicate) 0-2
0.0
1.0
2.0
3.0
4.0
5.0
6.0
7.0
8.0
9.0
5.3
6.7
Sample
Depth (m)
Chl. A
(ug/L)
Hach Chl.
a
(ug/L)
Specific
Total Diss.
Cond.
Total Phos- Phos(umho/cm
phorus
phorus
@ 25 C)
(mg/L)
(mg/L)
Turbidity
(NTU)
D.O.
(mg/L)
Temp.
(Celsius)
--0.3
0.4
0.4
0.6
0.5
0.4
0.5
0.5
0.5
0.5
1.9
--
--9.2
9.1
9.0
9.0
8.1
7.7
6.7
0.4
0.3
0.3
--19.8
19.8
19.6
19.3
18.6
18.5
18.4
14.4
10.4
9.8
--519
519
519
518
520
521
523
612
701
742
0.018
0.015
---0.016
0.018
0.018
0.019
0.068
0.11
0.47
--0.5
0.5
0.7
0.8
0.8
0.7
1.8
0.7
0.5
0.6
3.8
--
--8.3
8.3
8.2
8.2
8.2
7.8
6.6
0.4
0.3
0.2
--18.5
18.5
18.4
18.4
18.4
18.3
18.1
15.3
11.0
9.9
--522
522
522
522
522
523
527
597
712
751
0.017
0.019
---0.018
0.017
0.02
0.019
0.051
0.22
0.7
P:\Mpls\23 MN\19\2319375\WorkFiles\2008 Lac Lavon WQ Data\Lac Lavon-08 wq DATA_KDM.xls
pH
(Std.
Units)
eh
(mV)
0.013
----0.011
0.011
0.013
0.0097
0.013
0.014
0.015
--8.5
8.6
8.6
8.7
8.7
8.6
8.5
7.7
7.4
7.3
--167
169
169
166
167
168
171
38
-41
-59
0.0094
----0.011
0.013
0.013
0.011
0.015
0.012
0.015
--8.2
8.3
8.4
8.5
8.5
8.5
8.3
7.8
7.4
7.2
--111
110
109
108
107
108
113
60
-70
-100
A-4