ated by the U.S. Geological Survey, in cooperation with
Wisconsin Department of Natural Resources to evaluate
the effect of Powell Marsh on the hydrology of Dead

Pike Lake and to determine the source of iron floc and

1981-86: U.S. Geological Survey Water-Resources
Investigation Report 94-4025, 42 p.

Bradbury, K.R., and Muldoon, M.A., 1990, Hydraulic con-
ductivity determinations in unlithified glacial and flu-

the potential for its transport from Powell Marsh to

vial materials, In Ground Water and vadose Zone

Dead Pike Lake.

Monitoring: American Society for Testing and materi-

model indicates ground water generally flowing from
Powell Marsh to the northwest toward Dead Pike Lake
and west toward Little Lost Creek. Simulation results

indicate that, from the south part of its watershed, Dead

als, ASTM STP 1050, Philadelphia, p. 138-151

erry,
Hall Tne., Englewood Clifts, New Jersey, 604 p.

Haitjema, H.M., 1995, Analytic element modeling of ground-
water flow: Academic Press, San Diego, CA, 394 p.

Pike Lake receives about 2.4 ft*/s of ground water and
1 ft3/s of surface water. If the Powell Marsh structures

Hem, J.D., 1989, Study and interpretation of the chemical

Water Supply-P: 2254. third edition, 263

were removed, Dead Pike Lake would receive about

3 ft"/s of ground-water flow and 0.5 ft"/s of surface
water. These results show that Powell Marsh hydrologic
structures change the distribution of the water budget

W ipply Pape: o +203 -p-
analytic element model to investigate groundwater-lake
interactions at Pretty Lake, Wisconsin: Journal of Lake
and Reservoir Management, v. 12, no. 4, p. 487-495.

___fomponents but not the overall water budget for Dead __piunt, RJ. Anderson, M.P..and Kelson, V.A., 1998, Improv __
e Lake. MP.

ing a complex finite-difference ground water flow

Water levels measured along a west to east flow

model through the use of an analytic element screening

path indicate that water moves from Vista Pond and the

model: Ground Water, v. 36, no. 6, p. 1011-1017.

marsh and discharges to ditches. Analyses of ground
and surface waters along the flow path indicate that dis-
solved iron is relatively high in ground water and low in
surface water (the ditches and Vista Pond). Naturally

Krabbenhoft, D.P. 1984, Hydrologic and geochemical con-
trols of freshwater ferromanganese deposit formation at
Trout Lake, Vilas County, Wisconsin: MS thesis, Uni-
versity of Wisconsin-Madison, 137 p.

occurring dissolved iron in ground water derived from
surficial deposits is the source of iron floc in the Powell

Krohelski, J-T., Bradbury, K-R., Hunt, R.J., and Swanson,

Dane Ci Wi ins Wi in Geological-and.

Marsh ditches and is coincident with iron floc observa-

in-Dan unty; ei

Natural History Survey Bulletin 98, 31 p.

tions. Iron and manganese precipitate and form a floc
when the ground water discharges to the ditches. The
transport and form of iron and manganese in the water
of the Dead Pike Lake area can be explained by oxida-
tion/reduction. If ditches were removed, floc forming in

ti Id-br di itis lik that th

Mitchell-Bruker, S., and Haitjema, H., 1996, Modeling
steady state conjunctive groundwater and surface water
flow with analytic elements: Water Resources Research,
y. 32, no. 9, p. 2725-2732.

Novitzki, R.P., 1982, Hydrology of Wisconsin Wetlands:

Wisconsin Geological and Natural History Survey

Information Circular Number 40, 22 p.

ved. However, it is likely that th
floc formation may be redirected to the near-shore envi-
ronment in Dead Pike Lake where ground water dis-

Patterson, G.L., 1989, Water Resources of Vilas County, Wis-
consin: Wisconsin Geological and Natural History Sur-
vey Miscellaneous Paper 89-1, 32 p.

charges. Strack, O.D.L., 1989, Groundwater Mechanics: Englewood
Cliffs, New Jersey, Prentice-Hall, 732 p.
REFERENCES
Stumm, W., and Morgan, J.J., 1970, Aquatic Chemistry, an
Attig, J.W., 1985, Pleistocene Geology of Vilas County, Wi: ‘ 7

consin: Wisconsin Geological and Natural History Sur-
vey Information Circular 50, 32 p.

Batten, W.G., and Lidwin, R.A., 1996, Water Resources of
the Lac Du Flambeau Indian Reservation, Wisconsin,

New York, 583 p.
Wisconsin Department of Natural Resources, 1995, Wiscon-

sin Lakes, Wisconsin Department of Natural Resources
PUB-FM-800 95 REV, 182 p.

14 Hydrologic Investigation of Powell Marsh and its Relation to Dead Pike Lake, Vilas County, Wisconsin


ME Measured streamflow
CJ Simulated streamflow

STREAMFLOW, IN CUBIC FEET PER SECOND

io

A B
Dead Pike Lake inlet Little Lost Creek .6 mile
at Powell Road downstream of

Dead Pike Lake

c
Little Lost Creek at
old railroad crossing -
.6 mi NW of Powell

D E
Bear Creek just below Little Lost Creek
confluence with just above Bear Creek
Sugarbush Creek

Figure 5. Measured and simulated flux (streamflow) for the ground-water-flow model of Powell Marsh and Dead Pike
Lake, Wisconsin. Location of flux calibration targets are shown in figure 3. Streamflow measurements were made on

June 14 and 15, 2000.

sured flows with some higher and some lower. Some
difficulty in measuring equilibrium streamflow condi-
tions was encountered because of beaver activity, mod-
ifications to beaver dams are common and can cause
reductions or increases in streamflow that may not be
representative of the site under equilibrium or steady-
state conditions in model simulation.

MODEL RESULTS

Ground water flows from high to low elevation and
generally at right angles to contour lines on a map.
Therefore, the contour map (fig. 6A) of calibrated
model results indicates that the highest near-field water-
table elevation occurs just south of Little Trout Lake
and from this point ground-water flow is roughly radial.
In the vicinity of Powell Marsh, ground water flows to
the northwest and west. As indicated by the pathlines
(red lines on figure 6A), ground water recharging on
Powell Marsh likely will discharge to a ditch. For exam-

ple, the pathline labeled “1” on figure 6A represents a
simulated particle of water that is recharged at the water
table and is simulated discharging to the ditch. Using an
estimated porosity of 0.2, the time of travel for this par-
ticle from the water table to the ditch is approximately
12 years. It also is interesting to note that in the vicinity
of Dead Pike Lake, particles that are started at the water
table on all sides of Dead Pike Lake eventually dis-
charge to Dead Pike Lake (fig. 6A). The calibrated
model indicates that Dead Pike Lake receives about
2.4 ft/s of ground-water inflow along with 1.0 ft'/s of
surface-water inflow from the south part of the Dead
Pike Lake Basin (this part of the basin includes Powell
Marsh) and about 0.9 ft°/s of ground-water inflow from
the north part for a total inflow to the lake of 4.3 ft°/s.

In order to approximate the effect of the Powell
Marsh ditches and Vista Pond on the hydrology of Dead
Pike Lake, the calibrated model was modified by
removing the analytic elements that represent the
ditches and pond. The same particle locations and con-

8 Hydrologic Investigation of Powell Marsh and its Relation to Dead Pike Lake, Vilas County, Wisconsin


Table A2. Locations of piezometers and Vista Pond along section B-B’
[GPS, Global Positioning System; UTM, Universal Transverse Mercator]

umx umy Wisconsin State Wisconsin State Elevation
Plane X ‘Plane Y (ft above sea ‘Site description as stored by GPS unit
(meters) (meters) (feet) (feet) level)
275792.215 5107873.055 1993787.653 336535.960 1600.547 WELLA30__Piezometer A-30
27581 1600.686 WELLBS _Piezometer B-5

____275817.327__5107864.364__1993871.034__336510.583__1600.686 __WELLBI5__Piezometer B-15_—

275817.993 5107864,321 1993873.223 336510.523 160.463, WELLB30_Piezometer B-30
275831.288 5107862.842 1993916.981 336507321 1597.751 VISTAPONDDNWSEL ~ Vista Pond
275834.537 5107864.213 1993927.461 336512.219 1601.305 WELCIS” Piezometer C-15
275834.585 5107863.701 1993927.681 336510.544 1601.546 WELLCS Piezometer C-5
275840.267 5107860.934 1993946.646 336502.178 1606.114 WELLD9 Piezometer D-9
275847.110 5107863.396 1993968.771 336511.096 1602.154 VISTAPONDWSEL _ Vista Pond

Table A3. Locations of water level measurements upstream and downstream of Powell Marsh structures
[GPS, Global Positioning, System; UTM, Uni 1

“irra x (mrateray —urery (rreteray Wisconsin State Wisconsin State Eleva pt

"
Plane X (feet) Plane Y (feet) _{ft above sea level) by GPS unit

275834.007 5108254,793 1993877.372 337792.325, 1602.170 008WSELUP
275823.753 5107796.328 1993900.519 336288.382 1597.794 009WSELDN
275826.451 5107784,989 1993910.765 336251.551 1603.271 O09WSELUP
275816.945, 5107625.388 1993899.365 335727.262 1603.234 010WSELUP

——————~215802.468 5106643838 _1993973.412 __332508.324 1603206 011 WSELUP

‘273803.275 ‘35106651.756 ‘1993975077 _—*332534.376 ——SC*6US.-255——SSCSCSC~*~*«SWSELDNSS—S—SS

276577.150 5107279.865 1996433.790 334688.851 1604.861 012WSELDN
276577.602 5107273.447 1996436.066 334667.869 1605.266 012WSELUP
276488.424 5107352898 1996133.939 334917.246 1603.182 013WSELDN
276492.231 5107334.801 1996148.658 334858.402 1603.538 013WSELDNWEST
276495.515, 5107348.918 1996157.675 334905.079 1604.891 013WSELUP

__276570.225 _5107391.225 _1996397.307_335052.990__1604.818 __O14WSELDN—

276576.253 107399.411 1996416.050- 335080.568 1605: 014WSELUP.
277347.164 5106801698 1999016.789 333216.883 1605.954 01SWSELDN
277348.531 5106793.997 1999022.224 333191.811 1607.65 01SWSELUP
277281.731 5106788.424 1998803.967 333165.277 1604,812 016WSELDN
277286.445 5106783.990 1998819.966 333151.328 1607.526 016WSELUP
2772A4.408 5108333.815 1998490.332 338225.898 1603.115 017WSELDN
277252.425, 5108328.563 1998517.260 338209.678 1605.534 017WSELUP
274679.631 5106866.575 1990265.647 333099.424 1598.830 018WSELDN
274687.414 5106875.531 1990290.046 333129.740, 1602.278 018WSELUP
275820.763 5108252.980. 1993834.188 337784.741 1597.091 WSELDNDAMATSTRUCT

18 Hydrologic Investigation of Powell Marsh and its Relation to Dead Pike Lake, Vilas County, Wisconsin


CONTENTS

Abstrac

Introduction

Pe d ed:
Purpose, scope, and sources of data

Hydrologic setting
S

Study method:

Hydrogeology..
Geochemistry ..
Conceptual model
Construction of GFLOW model

Model calibration

UMRAO WH HHH

Modet results.

Relations b hi
Relations between the groun

d-surfa
water-and-surface-water system

Hydrogeology
‘Ydrogeology--

Geochemistry ..
Summary and conclusion:
References...
Appendix

1

. Coordinates and elevation of sites measured by Global Positioning System........

2. Flow and ground-water level measurements...
3.P Marsh—Dead Pike Lake water analyse

mula with analytic elem oca
flow model of Powell Marsh and Dead Pike Lake, Wisconsin... 6
4-5. Graphs showing:
4. Measured and simulated head for the ground-water-flow model of Powell Marsh and Dead Pike Lake,
Wisconsin 7
5. Measured and simulated flux for the ground-water-flow model of Powell Marsh and Dead Pike Lake,
Wisconsin ..... 8
6. Simulated water-table elevation and-selected-path lines for (A)-calibration-and-(B)-without Powell-Marsh
structures, Vilas County, Wisconsin. 9

7-10. Graphs showing:

7. West to east section, B-B’, showing the position of the water table and direction of ground-water flow

8. Comparison of iron concentrations in 0.45 and 0.1 micron-filtered water samples .......
9. Comparison of dissolved organic carbon concentrations to iron in 0.45 micron-filtered samples .
10. Relation of iron concentration in 0.45 micron-filtered samples to redox potential ....

CONTENTS Mt


APPENDIXES 1-3

15.





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17

Appendix 1



60
ll Dissolved organic carbon
fron

50 4
&
=
5
=
2 40F 4
2
=
=
ES
s
=| I
S 3t =
2 ia
6 —
z
& 2r 7
a
3
2
Ss
8

10 4

A-30 B-5 B-15 B-30 C5 C-15 D-§—-VistaPond Main Ditch

Figure 9. Comparison of dissolved organic carbon concentration to iron in 0.45 micron-filtered water samples, Vilas
County, Wisconsin. Location identifiers (for example, A—30) are those from the cross section in figure 7.

and ground water. As previously discussed, the section the DOC quality and the low correlation between DOC
B-B’ is along a flow path that intersects typical Powell and iron concentrations (fig. 9). Although a strong cor-
Marsh surface-water features (pond and ditch) and the relation may be expected between high concentrations

ground-water system. Dissolved iron concentrations of iron and DOC if organic molecules play an important
were found to be higher than what commonly is found factor, it is possible that other factors rather than DOC
in ground water in northern Wisconsin, a result of the concentrations limit iron transport. Regardless of the
high amounts of naturally occurring iron present inthe _ exact iron transport mechanism, it is important to note
aquifer. Moreover, the iron measured in the ground that water sampling demonstrated that high iron con-
water was over ten times higher than concentrations centrations transpor yy grou ipi
measured in surface water, reflecting the change in the as iron floc when the ground water is discharged into-a
solubility of the iron when exposed to the dissolved surface-water body. Thus, it appears that dissolved oxy-
oxygen present in the surface water. gen in the surface water is able to combine with the

The analyses gave near identical iron concentra- iron—whether dissolved or carried by DOC colloids—

tions for the 0.45 and 0.1 micron-filtered samples and form the oxyhydroxide floc.

(fig. 8) indicating that the iron nominally is “dissolved” Tron transport can be explained fromra tegionat

or perhaps present as iron = complexes wil i it

less than 0.1-micron sizes. The latter tra e omris related to the redox -potential-o
nism has been noted in central Vilas County where hig! ground-water system. The redox potential, in turn, is
concentrations of iron in ground water were attributable _related to the location in the ground-water-flow system.

to iron (III)-DOC complexes smaller than 0.1-micron Infiltrating water from the land surface carries oxygen

(Krabbenhoft, 1984). The relative importance of DOC- _ obtained from the atmosphere; this dissolved oxygen is

facilitated transport of iron in ground water is not well carried_with the infiltrating water as it recharges the
be eof the lack of i i e i e e e presence issolved oxy-

on ground-w m. The p nce of d

12 Hydrologic Investigation of Powell Marsh and its Relation to Dead Pike Lake, Vilas County, Wisconsin


Northwest ; 7 Southeast

‘| | | | |
b | Y Y Y Y ’
ww 1.620 y Vista Pond — r
nS —,. — Fae = oS,
24) Teas — > a =
3 & 1,500 + River ‘Dead Pike Lake __ Little Trout Lake Walton
eu Sand-and-Gravel Aquifer Lake
SS 1,500 =
ge :
= 14604 |

“= Precambrian Crystalline Rock

EXPLANATION 0
J Recharge
a-— Ground-water flow 0

VERTICAL SCALE GREATLY EXAGGERATED
2 MILES

2 KILOMETERS

Figure 2. Conceptual model of the hydrologic system in the vicinity of Dead Pike Lake. (Line of section is shown in figure 1.)

Geochemistry

Ground and surface waters were sampled and ana-
lyzed in the field for pH, temperature. specific conduc-
tance, redox potential (Eh) and dissolved oxygen (field
parameters), and in the laboratory for iron, manganese.
and DOC. Field parameters were sampled and mea-
sured by pumping the water through a flow-through
chamber enclosing the multi-parameter meter sensors.
Two sets of samples were taken, one filtered through
0.45 micron filters and one filtered through 0.1 micron
filters to assess the potential of colloidal transport.
Ground-water samples were collected using a peristaltic
pump and an in-line filter. Surface-water samples from
Vista Pond and the main ditch were “grabbed” near
shore using a 5-gallon pail. Because Vista Pond and the
main ditch are shallow and therefore well mixed. the
“grab” samples are representative of these surface-
water bodies. The surface-water samples then were fil-
tered using the in-line apparatus. Ficld and laboratory
analyses of sampled water are listed in appendix 3.

CONCEPTUAL MODEL

Prior to construction of the ground-water-flow
model, a conceptualization of the system is essential
because it forms the framework for model development.
The conceptualization reduces the actual flow system
into important component parts. This reduction is a nec-
essary simplification of the natural system because
inclusion of all of the complexities of the natural system
into a computer model is not feasible. Steps in the
development of the conceptual model include: (1) defi-

nition of aquifers and confining units, (2) identification
of sources and sinks of water and, (3) identification and
delineation of hydrologic boundaries. A conceptualiza-
tion in cross section of the shallow ground-water/sur-
face-water system in the vicinity of Dead Pike Lake and
Powell Marsh is shown in figure 2. The cross section is
based on well drillers’ construction reports and infor-
mation collected as part of other studies (see previous
cited reports).

The shallow ground-water system consists of later-
ally extensive deposits of sand and gravel about 100 ft
thick. The underlying bedrock unit (Precambrian crys-
talline rock) forms the base of the aquifer system and is
assumed to be nearly impermeable. Therefore, the
model included only the most transmissive upper
deposits. The water table in the vicinity of the Powell
Marsh and Dead Pike Lake is near the land surface
except in areas of high relief or elevation. In these areas,
the depth to the water table may be more than 50 ft (Bat-
ten and Lidwin, 1996).

Ground water moves from higher to lower poten-
tials (or heads) as indicated by the flow arrows in
figure 2. As a result, ground water gencrally moves
toward and discharges to lower-lying surface-water fea-
tures and recharges (as indicated by the vertical arrows
above the section in figure 2) elsewhere. Recharge is
that portion of precipitation that does not evaporate,
transpire, or run off, and is the primary water source to
the ground-water system.

Dead Pike Lake receives surface water from Pow-
ell Marsh by way of an inlet channel and because of its
position in the ground-water basin, it is likely that Dead
Pike Lake receives ground-water flow on all sides as

4 — Hydrologic Investigation of Powell Marsh and its Relation to Dead Pike Lake, Vilas County, Wisconsin


Hydrologic Investigation of Powell Marsh and its Relation
to Dead Pike Lake, Vilas County, Wisconsin

By James T. Krohelski, William J. Rose, and Randall J. Hunt

Abstract

An analytic element ground-water-flow
model was constructed to help understand the
ground- and surface-water hydrology in the vicin-
ity of Dead Pike Lake and Powell Marsh, Vilas
County, Wisconsin. The model was used to simu-
late the effect of removing Powell Marsh control
structures (ditches and Vista Pond) on the hydrol-
ogy of Dead Pike Lake. Measurements and model
simulation results show that ground water in the
vicinity of Powell Marsh moves to the northwest
and west. If Powell Marsh structures are removed
from the simulation, it does not affect the general
direction of ground-water flow nor the total flow to
Dead Pike Lake. Without the simulated structures,
slightly more ground-water flow enters Dead Pike
Lake and slightly less surface-water flows at the
Dead Pike Lake inlet than with the simulated struc-
tures.

Ground-water levels measured in piezome-
ters installed along a flow path indicated that
ground-water flow primarily is horizontal in the
marsh and moves upward in the vicinity of a ditch
where it discharges. Flow from Vista Pond is
downward to the ground-water system but eventu-
ally also discharges upward to the ditches. Based
on analyses of water samples from piezometers, the
ditch, and Vista Pond, it was shown that dissolved
iron is transported in the ground water. When
ground water is discharged, iron and manganese
react with dissolved oxygen, then precipitates, and
forms the oxyhydroxide floc present in the Powell
Marsh ditches. The processes involved in the trans-
port and floc formation are not unique to the
ditches, but are an expected outcome where dis-
charging ground water and oxygenated surface
water meet. Therefore, although floc formed in the
ditches would no longer be available for transport

if ditches were removed, it is likely that the floc
formation would be redirected to the near-shore
areas of Dead Pike Lake where increased ground-
water discharge is expected.

INTRODUCTION

Dead Pike Lake and Powell Marsh are located in
western Vilas County, Wis. (fig. 1). Local residents are
concerned that iron floc from Powell Marsh ditches is
damaging the aesthetic quality of their lake. The U.S.
Geological Survey (USGS) in cooperation with the
Wisconsin Department of Natural Resources (WDNR)
began a study in June 2000 to evaluate the effects of
Powell Marsh on the hydrology of Dead Pike Lake and
to determine the source of iron floc and the potential for
transport from Powell Marsh to Dead Pike Lake.

Purpose, Scope, and Sources of Data

This report describes the hydrologic relation
between Powell Marsh and Dead Pike Lake, and char-
acterizes the distribution of iron (Fe) and manganese
(Mn) in the hydrologic system. Also, the processes
responsible for iron transport at various points in the
hydrologic system including Vista Pond, marsh, aquifer,
ditch, and lake are described. Finally, the effects of
altering the ditch system conveying the iron floc to
Dead Pike Lake are summarized.

Available geologic and hydrologic data used during
this study consisted of interpretive geologic maps pre-
sented by Attig (1985), and measured hydraulic conduc-
tivity, ground-water levels and contour maps of the
water table and depth to rock by Patterson (1989) and
Batten and Lidwin (1996). These data form the basis for
development of a ground-water-flow model by provid-
ing estimates of saturated thickness, the hydraulic prop-
erties of the shallow aquifer, and estimates of water-
table elevation. These previous studies (Patterson,
1989; Batten and Lidwin, 1996) reported that extremely

Abstract 1


CONVERSION FACTORS, VERTICAL DATUM, AND ABBREVIATIONS

Multiply By To Obtain
Length
inch (in) 25.4 millimeter
foot (ft) 0.3048 meter
mile (mi) 1.609 kilometer
Area
acre (A) 0.4047 hectare
quare foot (ft*) 0.09290 quare-meter
square mile (mi*) 2.590 square kilometer
Volume
cubic foot (ft) 0.02832 cubic meter
Hydraulic Conductivity*
foot per day (ft/d) 0. 3048 meter per day

Sea level: In this report, “sea level” refers to the National Geodetic Vertical Datum of 1929 (NGVD of 1929)}—a geodetic datum derived
from a general adjustment of the first-order level nets of both the United States and Canada, formerly called Sea Level Datum of 1929.

*Hydraulic conductivity: The standard unit for hydraulic conductivity is cubic foot per day per square foot of aquifer cross-sectional area

Other abbreviations:

f/s cubic feet per second
gpm gallons per minute
mg/L ___ milligrams per liter

in/yr inches per year

The stratigraphic nomenclature used in this report is that of the Wisconsin Geological and Natural History Survey and does

not necessarily follow usage of the U. S. Geological Survey.

IV CONVERSION FACTORS, VERTICAL DATUM, AND ABBREVIATIONS



60 T T T T T
A R?=0.71
30

50 ry
&
=
&
g oP 4
=
:
=
= B °

30 15
id 8 >< fg
3 30 o 5
E bd D
GS ob 4
2 ?
Ss
&
2
S
=

10

Main Ditch,
Vista Pond
0 1 L 1 1 1 1 *
-300 -250 -200 -150 =100 -50 0 50
REDOX POTENTIAL

Figure 10. Relation of iron concentration in 0.45 micron-filtered samples to redox potential, Vilas County, Wisconsin.

Location identifiers (tor example as 30) are those form the cross s section shown in in figure 7. na ‘coefficient of Getermination,

data, A trendline i is most reliable when its Re is at or near 1 1

gen in the recently recharged water causes the water to
have a high oxidation potential; thus, iron is in the oxi-
dized form and is not soluble. Along its subsurface flow
path, the °-ground water encounters conditions that-c can.

has had greater exposure to these conditions will con-
tain less dissolved oxygen. Given enough distance the
dissolved oxygen will be completely consumed and the
ground water becomes reducing. When the ground
water becomes sufficiently reducing, iron containing

strated by the field data collected in this study; water
samples from deeper piezometers represent longer
ground-water-flow paths with more reducing condi-
tions, and more dissolved iron on (Fig. 10). Water samples

. Vi issolved iron (fig. 10). Surface waters in the ditch and

Vista Pool has a constant source of oxygen from the
atmosphere, and thus, are always oxidizing. These sites
have low dissolved iron, but higher amounts of particu-
late iron floc representing the change of iron from the
dissolved to solid phase. Results from these surface-

minerals in the aquifer can dissolve and the iron can be

water samples can be considered to represent the end of

transported by the ground-water system.

the ground-water-flow path.

As the ground water flows from the recharge area
to the discharge area, additional water is added to the
top of the saturated zone as the aquifer receives
recharge from infiltrating water. Thus, deeper water
(deeper than the infiltrating water) will have traveled

SUMMARY AND CONCLUSIONS

There is concern that iron floc from Powell Marsh
ditches is damaging the aesthetic quality of Dead Pike

further than shallower water. This result is demon-

Lake in western Vilas County, Wis. A study was initi-

SUMMARY AND CONCLUSIONS 13


high iron concentrations (greater than 20 mg/L) could
be present in the sand-and-gravel sediment in the vicin-
ity of Powell Marsh.

In addition to the available data, field data were
collected for the study. A Global Positioning System
(GPS) was used to locate and determine elevations of
surface-water features, such as streams and lakes
throughout the study area and above and below control
structures at Powell Marsh. Elevations and site loca-
tions of lakes, streams, control structures, and piezome-
ters were measured (Michael T. Anderson, Wisconsin
Department of Natural Resources, written commun.,
2000). The coordinates and elevations of the sites mea-
sured by GPS are listed in appendix 1.

Piezometers, some nested, were installed along a
west to east section in Powell Marsh and used to deter-
mine the direction of ground-water flow, the relation
between the ground-water system, Powell Marsh
ditches, and Vista Pond, and to obtain water samples for
analyses of dissolved organic carbon (DOC), iron and
manganese. Surface-water samples were collected from
the main ditch and Vista Pond for DOC, iron, and man-
ganese. Streamflow measurements were made at five
sites during the study. Some of the ground-water-level
measurements and the streamflow measurements were
used in model calibration. The ground-water-level and
streamflow measurements are listed in appendix 2.

Hydrologic Setting

Dead Pike Lake is a 297-acre drainage lake (fig. 1).
An inlet flowing to the south side of Dead Pike Lake
drains a portion of Powell Marsh. The marsh consists of
an extensive system of drainage ditches constructed in
the 1950s, some of which drain into the Dead Pike Lake
inlet. Sand-and-gravel deposits of the Copper Falls For-
mation (Pleistocene age) are present throughout the
area. These deposits range in thickness from 100 to
200 ft (Attig, 1985). In low-lying areas, | to 5 feet of
peat overlie the sand and gravel. Reported values of
horizontal hydraulic conductivity range from about 1 to
50 ft/d based on slug tests and 950 ft/d based on a multi-
well aquifer test (Patterson, 1989; Batten and Lidwin,
1996). An aquifer test generally integrates a much
larger volume of aquifer compared to a slug test and
often yields higher and more representative values of
hydraulic conductivity (Bradbury and Muldoon, 1990).

STUDY METHODS

Methods used to understand the hydrogeology and
geochemistry of the study area include development of
a ground-water-flow model and analysis of ground
water and surface water along a flow path. These
methods are described in the following section.

Hydrogeology

An analytic element ground-water-flow model,
using the computer program GFLOW (Haitjema, 1995),
was constructed to simulate the shallow ground-water
system and its interaction with surface-water features.
A complete description of analytic elements is beyond
the scope of this report; a brief description is given
below. The reader is referred to Strack (1989) and
Haitjema (1995) for detailed discussions of this method.

Unlike most modeling methods, the analytic ele-
ment method assumes an infinite aquifer and does not
use a grid or involve interpolation between grid cells. To
construct an analytic element model, features important
to ground-water flow and surface-water features are
entered as mathematical elements or strings of ele-
ments. Each element is represented by a mathematical
equation. The effects of these individual solutions are
superposed or added together to arrive at a solution for
the larger ground-water-flow system. Unlike finite-dif-
ference modeling where the solution is calculated only
at grid nodes, with analytic-element modeling, heads
and flows can be computed anywhere in the model
domain without nodal averaging. The GFLOW model
used here is an areal model and the analytic elements are
two-dimensional and only can simulate steady-state
conditions (that is, heads do not vary with time). The
analytic element method (Strack, 1989; Haitjema,
1995) and the comparison of analytic element to finite-
difference numerical model techniques (Hunt and
Krohelski, 1996: Hunt and others 1998) have been dis-
cussed by others.

The GFLOW model was calibrated by trial-and-
error; that is, by varying hydraulic conductivity and
stream resistance until there was a reasonable match
between measured and simulated ground-water levels
(heads) and streamflows.

STUDY METHODS 3


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Appendix 2



U.S. Department of the Interior
U.S. Geological Survey

Hydrologic Investigation of Powell Marsh
and its Relation to Dead Pike Lake,
Vilas County, Wisconsin

Water-Resources Investigations Report 02-4034

Prepared in cooperation with the
Wisconsin Department of Natural Resources

science for a changing world



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Hydrologic Investigation of Powell Marsh and its Relation to Dead Pike Lake, Vilas County, Wisconsin

6


well. Other inlet channels may intermittently provide
water to Dead Pike Lake during periods of high flow
(spring snowmelt and intense precipitation). Outflow
from Dead Pike Lake is through Little Lost Creek,
which begins at the west end of the lake. When Little
Lost Creek is flowing, the stage of Dead Pike Lake
largely is controlled by the elevation of this outlet. In
addition to ground-water flow, other hydrologic budget
components for Dead Pike Lake include precipitation
falling on the lake and water evaporating from the lake
surface. In northern Wisconsin, annual precipitation
exceeds evaporation by about 6 in/yr (Novitzki, 1982).
Overland flow is assumed to be insignificant because
infiltration rates of the sandy surface deposits are rarely
exceeded by precipitation rates. Thus, overland flow is
not included in the hydrologic conceptual model for the
lake.

CONSTRUCTION OF THE GFLOW MODEL

Initial model development included estimating the
elevation of the base of the shallow aquifer system, an
areally uniform recharge rate, and a horizontal hydrau-
lic conductivity. The base of the model approximates
the bottom of the high-conductivity unconsolidated sed-
iments (approximately 1,500 ft above sea level). The
recharge rate and horizontal hydraulic conductivity,
along with streambed resistance were considered cali-
bration parameters, and thus were varied during model
calibration. Recharge was set to 10.0 in/yr and horizon-
tal hydraulic conductivity set to 100 ft/d. These param-
eters are similar to those used by Hunt and others (1998)
in the construction of a ground-water-flow model of the
nearby Trout Lake area.

Based on the conceptual model, the location and
elevation of far-field surface-water features were added
(fig. 3). These features are distant rivers and lakes that
are simulated with coarse linesinks and no resistance
between the surface-water features and the ground-
water system (that is, simulated as having a good
hydraulic connection). The purpose of simulating the
far field is to have the model explicitly define the
regional ground-water-flow field near Dead Pike Lake
and Powell Marsh (called the near field). The near field
encompasses the features in the area of interest, as well
as other nearby features that affect the hydrology of the
lakes (fig. 3). Streambed sediment resistance in the near
field initially was set equal to 0.3 day. Resistance in ana-
lytic element modeling is calculated by dividing the
streambed sediment thickness by the vertical hydraulic

conductivity. In this model, the value of 0.3 day corre-
sponds to a I-ft sediment thickness with a vertical
hydraulic conductivity of 3.3 ft/d, which is representa-
tive of a good connection between the ground-water and
surface-water systems. The width of the stream was
assigned according to stream order, and ranged from 10
to 50 ft.

Streams and lakes in the far field are not used for
flux calibration, thus are simply modeled as individual
linesinks. In near-field streams, a special more sophisti-
cated type of linesink was used, called a “‘stream ele-
ment” (Mitchell-Bruker and Haitjema, 1996). This
element consists of linked linesinks that route water
from high-elevation linesinks to low-elevation line-
sinks. During the routing through the stream network,
the amount of water captured and lost by the stream is
tabulated. This accounting allows the modeler to easily
obtain a flux from any linesink in the stream network
that includes flows from all the upstream linesinks.
More importantly, the accounting also ensures that the
amount of stream water lost to the ground-water system
is restricted to the amount of water available (that is,
captured from upgradient linesinks in the network). For
streams where the headwaters are not included in the
model domain, a headwater inflow term can be speci-
fied. This option was utilized for Sugarbush Creek, a
steam with an appreciable headwater reach that is in the
far field (fig. 3). Based on field measurements at the
outlet of Sugarbush Lake, the amount of headwater
inflow was set equal to 2.3 ft*/s, and was added to the
stream element immediately downgradient of the lake
(fig. 3). Lakes were simulated using linesinks with
resistance. Dead Pike Lake was linked to the stream net-
work with stream elements based on the methodology
of Hunt and others (1998).

MODEL CALIBRATION

Calibration targets are measured field data, which
are used to evaluate how well the model represents the
actual ground-water system. The targets used here
include both ground-water levels and streamflows
(fig. 3). Ground-water levels for two wells (VI-761 and
VI-653) were obtained from previously published
reports (Patterson, 1989; Lidwin and Batten, 1996) and
one well drilled for this study (A30). In addition to the
ground-water levels, targets representing the lake levels
for Sherman, Homestead, Pier, Sandy Beach and Little
Trout Lakes also were used. The stage of these lakes is
assumed to represent water-table elevation. Streamflow

CONSTRUCTION OF THE GFLOW MODEL 5


89°52'30"

46°07'30" —

Approximate boundary
of Powell Marsh

46°02'30° —

“engino»

Sugarbush Lakes Crooked Lake
re
ay
0 2 4 MILES
0 2 4 KILOMETERS
ay at | | al y EXPLANATION
Hess sco N S 1 N

Figure 1. Location of Powell Marsh and Dead Pike Lake, Vilas County, Wisconsin. (A-A’ section shown in figure 2; B-B' section
shown in figure 7.)

2

Hydrologic Investigation of Powell Marsh and its Relation to Dead Pike Lake, Vilas County, Wisconsin


Appendix 1. Coordinates and elevations of sites measured by Global Positioning System

TABLES
AI. Location of lake and stream-elevation measurements, Vilas County, Wisconsin... we 17
A2. Locations of piezometers and Vista Pond along section B-B’, Vilas County, Wisconsin... woe 18
A3. Locations of water-level measurements upstream and downstream of Powell Marsh structures, Vilas County,
Wisconsin... . 18

16 Hydrologic Investigation of Powell Marsh and its Relation to Dead Pike Lake, Vilas County, Wisconsin



drologic Investigation of Powell Marsh and its Relation ta Dead Pike Lake, |Vilas County, Wisconsin WRIR

®) Printed on recycled paper



U.S. DEPARTMENT OF THE INTERIOR
Gale A. Norton, Secretary

LS GEOLOGICAL SURVEY
Charles G. Groat, Director

For additional information write to: Copies of this report can be purchased from:

District Chief U.S. Geological Survey
8505 Researeh Way $$$ Bx 2528



EXPLANATION

_10~ Simulated water-table contour,
in feet above sea level—contour
interval is 2 feet

\_ Pathline showing direction
of flow from water table to
surface-water discharge point

Figure 6. Simulated water-table elevation and selected path lines for (A) calibration and (B) without Powell Marsh structures

(ditches and Vista Pond), Vilas County, Wisconsin.

tour interval used to present the calibrated model are
presented for the case without the Powell Marsh fea-
tures in figure 6B. Model results with the Powell Marsh
features removed indicate a water-table elevation in the
vicinity of Little Trout Lake would be about 2 ft higher
than the simulated conditions in the calibrated model.
Although the shape of the contours is approximately the
same as the simulation with the features. indicating that
the general direction of ground-water flow is the about
the same, the gradient as indicated by the spacing of the
contours (compare figure 6A to 6B) in the vicinity of
Powell Marsh is slightly steeper. The travel time from

recharge to discharge of the pathline labeled “1” is
much longer (36 years compared to 12 years) because
the simulated pathline does not discharge to the ditch
but to the inlet stream of Dead Pike Lake, a longer dis-
tance from the site where the pathline was started
(recharged). The model simulation without the Powell
Marsh features also indicates that the amount of water
entering Dead Pike Lake is approximately the same as
the simulation when the Powell Marsh features were
included. Ground-water inflow from the south is

3.0 ft°/s and 0.5 ft’/s from the inlet stream as compared
to 2.4 ft’/s of ground-water flow from the south and

MODEL RESULTS 9


60

Wl 0.45 micron-filtered sample
C 0.1 micron-filtered sample |

DISSOLVED IRON CONCENTRATION, IN MILLIGRAMS PER LITER

== fib

A-30 B-5 B-15 B-30 C5

VistaPond Main Ditch Dead Pike

Lake

C-15 0-9

Figure 8. Comparison of iron concentrations in 0.45 micron-filtered water samples, Vilas County, Wisconsin. Location
identifiers (for example, A-30) are those from the cross section shown in figure 7.

-water levels measured in nest

ment and discharge
into the eastern ditch. At nest “A”, ground-water levels
were identical in the “A-7” and “A-30” piezometers
indicating only horizontal flow. Ground-water levels in
piezometer nest “B” indicate horizontal movement
from site “A” to “B” (west to east) and upward at “B”
discharging to the western ditch.

Geochemistry

The form (dissolved and/or precipitated) and trans-
port of iron and manganese in ground water is affected
by environmental conditions, particularly in changes of

tion/oxidation state (or “‘redox”) refers to the relative
availability of electron donors or acceptors in aqueous
systems (Stumm and Morgan, 1970). Systems with an
appreciable concentration of “electron donors” are
described as having reducing conditions with a negative
Eh value; systems with an appreciable concentration of

electron acceptors” result in oxidizing conditions with
a positive value. Dissolve oxygen Is an eé1 icient
electron acceptor; thus, the presence of dissolved oxy-
gen is considered to be a strong indicator of oxidizing
conditions. Generally, iron in a reduced state, Fe (II), is
soluble and will travel along with ground water, but iron
in-an oxidized state, Fe (II), in the presence of oxygen
may forma precipitate or oxyhydroxide floc; when ina

chemistry-can-be-affected-by additional complicating
factors. For example, iron complexes can form with
DOC (Hem, 1989). Fe (II) in complexes may be consid-
erably more resistant to oxidation or the DOC can stabi-
lize Fe (III), preventing or delaying the formation of.
iron floc. Iron solubility also is a function of pH, the.

oxidation or reduction. For brevity this discussion will amount of hydrogen ion in solution, but because al
focus on iron but it also applies to manganese. Reduc- waters on Powell Marsh sampled during the study were

similar (pH between 5.8 and 6.9, appendix 3), the dis-
cussion presented here will focus on the effects of redox
and the presence or absence of oxygen.

To gain insight into the processes that lead to the
formation of iron floc in the Powell Marsh ditch net-
work, water samples were collected from both surface

RELATIONS BETWEEN THE GROUND-WATER AND SURFACE-WATER SYSTEMS an



Hydrologic Investigation of Powell Marsh
and its Relation to Dead Pike Lake,

Vilas County, Wisconsin

By James T. Krohelski, William J. Rose, and
Randall J. Hunt

U.S. GEOLOGICAL SURVEY

Water-Resources Investigations Report 02-4034

Prepared in cooperation with the
Wisconsin Department of Natural Resources

Middleton, Wisconsin

2002

2002

a USGS

~___ S¢ience fora changing world



Appendix 3. Powell Marsh—Dead Pike Lake water analyses along section B-B’

(mg/L, milligrams per liter; °C, degrees Celsius; organic C, organic carbon; Mn, manganese; Fe, iron; --, no data]

; “th Dissolved
Site Date wreatent mg/L. ° mg/L mg/L °¢ conauctance oxygen PH Redox
: w water 2

0.45 micron 8.88 85 49
Omicron 8629557

Piezometer B- 6/15/00. R: iter. 23.39. A3. 33 10.45. 24. 2 6.2 114
0.45 micron AZ A 3
O.micton 2494 43.31

PiezometerB-15___6/15/00___—Rawwater_ 16375929 9.15 26 9 65-149
0.45 micron 16.49.6128,
O.1 micron 15.91 6B

Piezometer B-30 6/14/00 -—-sRawwater «8561.2 9.83 40 2 69-226
0.45 micron 7.89 9423,
ot 7495 24

Piezometer C-5 6/15/00 Raw water 3.25 Zz 26 12.36 13 29 6. “77
O45micron 3.12228
O.micon 3.441923,

Piezometer C-1 ol Raw water 8.9831 13 re] 2 2.90.
O4Smicron —572—~SSCSCSCS*«SS
O1micron 5.2635

Piezometer D-9 6/15/00 Rawwater 9.791919 12.28 i 24 58-22
0.45 micron 12331918,
O.micon 1145 92 19

Vista Pool 6/15/00 Rawwater ‘13.38 O24 175 21 7.94 6 27
0.45 micron__14.55 o1 14
0.1 micron 18.5: 01 7

Main Ditch 6/15/00 Rawwater «1785 ~=—O7S«10 17.23 80 635 6 21
0.45 micron 1797 06-4.
0.1. micron 14.56 052.2
0.45 micron -00 7
0.1 micron .00 2

20 Hydrologic Investigation of Powell Marsh and its Relation to Dead Pike Lake, Vilas County, Wisconsin





1,615 T T T T T
VI-653
*
Troutlakeg

wm 1610 F |
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a
= Line of perfect agreement
a
nn
w 1,605 4
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im Well A30 y, Homestead Lake
W 1,600 + 5 |
2 @,Sherman Lake
= Vi6ly ‘
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3 7
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1,585 \ 1 ! 1 !

1,585 1,590 1,595 1,600 1,605 1,610 1,615

MEASURED HEAD, IN FEET ABOVE SEA LEVEL

Figure 4. Measured and simulated head for the ground-water-flow model of Powell Marsh and Dead Pike Lake, Wisconsin.
Location of head calibration targets are shown in figure 3. Head measurements were made on June 14 and 15, 2000
except for wells VI-761 and VI-653, which are from Batten and Lidwin, 1996.

or flux targets consisted of five sites in the near field
where streamflow was measured during this study
(fig. 3). These targets were used to constrain the simu-
lated fluxes and associated regional recharge. The rela-
tion of the target to the model calibration is such that
lower values of the streamflow target result in lower
rates of recharge and lower corresponding horizontal
hydraulic conductivity.

Using a recharge rate of 10 in/yr, an aquifer hydrau-
lic conductivity of 100 ft/d, and a higher stream resis-
tance for Bear and Sugarbush Creeks than other near-
field streams, a reasonable match between measured
and simulated head and flux was obtained. A stream
resistance of 10, which results in a vertical hydraulic
conductivity of 0.1 ft/d if the sediment thickness is | ft,
was assigned to Bear and Sugarbush Creeks. All other
near-field streams were assigned a resistance of 1. The
effect of increasing stream resistance was to reduce the
amount of ground water discharging to Bear and Sugar-
bush Creeks and to increase water-table elevation in the
vicinity of Powell Marsh. No data were collected to ver-
ify a high streambed resistance in Bear and Sugarbush

Creeks. However, field reconnaissance indicated that
these streams are low gradient and contain large wet-
lands in their basins, which are typified by fine-grained
streambeds and, therefore, yield high streambed resis-
tance. Comparison between measured and simulated
head is shown in figure 4. Calibration statistics based on
eight head targets include the following differences
between measured and simulated heads: a maximum of
3.8 ft, a minimum of -2.2 ft, an average of 0.8 ft, a
median of 1.0 ft, a mean absolute of 1.6 ft and a root
mean squared of 2.0 ft. These statistics are similar to
those of other calibrated models (Hunt and others,
1996) and is considered a good steady-state model
match.

The calibration to flux indicates that measured
streamflow generally brackets simulated streamflow
(fig. 5). Streamflow flux targets are based on only one
measurement rather than the preferred method of hav-
ing enough measurements over the range of high and
low flows to determine flow duration (Krohelski and
others, 2000). The calibration to flux is reasonable
because most of the simulated flows are close to mea-

MODEL CALIBRATION 7


West East
B B
1,610
AT BS bg ;
1,605 F A30 B15 ce Vista Pond |

Pe

7

ELEVATION, IN FEET ABOVE SEA LEVEL
B
8
T

1,585 + 4
1,580 F 4
1,575 + — 4
1,570 F 7
1,565 1 | 1 L L

40 80 120 160 200 240

DISTANCE FROM WEST TO EAST, IN FEET

Figure 7. West to east section, B-B’, showing the position of water table (dashed line) and direction of ground-water flow
indicated by arrows, Vilas County, Wisconsin. Section trace is shown on figure 1. Piezometers locations are identified by

letter ID and depth designation in feet.

1.0 ft°/s from the inlet stream in the calibrated model.
As in the calibrated model case, there is 0.9 ft?/s from
the north part of the basin. Total inflow to Dead Pike
Lake is 4.4 ft’/s in the simulation without the Powell
Marsh features, compared to 4.3 ft*/s for the model that
includes the Powell Marsh features. This result indi-
cates that the Powell Marsh features do not change the
overall lake water budget, but rather redistributes the
water budget components slightly.

RELATIONS BETWEEN THE GROUND-
WATER AND SURFACE-WATER SYSTEMS

Field data were collected during the study to deter-
mine the hydrologic relation between the ground- and
surface-water systems and to determine the geochemi-
cal process of iron and manganese transport. Piezome-
ters made of 1-inch diameter PVC with 1-ft-long
number 10 screens were installed along section B-B’
(fig. 1). The section is about 200 ft long and was chosen

to intersect Vista Pond and the Main Ditch, which is
split into two channels along the section (fig. 7).

Hydrogeology

Piezometer nests are located at 4 sites along the
section B-B' to determine vertical and horizontal gradi-
ents. The location of the piezometers in section and the
direction of ground-water flow based on ground-water
and surface-water level measurements are shown on
figure 7. The deepest piezometers are finished 30 ft
below land surface. A 12-ft sediment core was obtained
close to piezometer site “A”. The core consisted of a
2-ft peat layer underlain by medium to coarse sand. The
surface elevation of Vista Pond and ground-water levels
measured in the piezometer “D-9” indicate flow from
Vista Pond to the west toward the ditches. The ground-
water level in “D-9” was well below the level of Vista
Pond but above levels in nest “C” indicating downward

10 Hydrologic Investigation of Powell Marsh and its Relation to Dead Pike Lake, Vilas County, Wisconsin