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WASHINGTON COUNTY LANDFILL LOGGING PROJECT: BOREHOLE
GEOPHYSICAL TESTS FOR PRESENCE OF FRACTURE FLOW AT A
PERFLUOROCHEMICAL CONTAMINATION SITE
Anthony C. Runkel
Robert G. Tipping
Julia R. Anderson
Minnesota Geological Survey
December 19, 2008
Informal report submitted as deliverable for contract between University of Minnesota and
Minnesota Pollution Control Agency for project entitled “Washington County Landfill Logging
Project”. This informal report has not been edited according to standard Minnesota Geological
Survey policy. Minnesota Geological Survey Open File Report 08-07
INTRODUCTION
The Washington County Landfill located near Lake Elmo, Minnesota is a source of
perfluorochemicals that have contaminated groundwater in the area. A project completed in 2007 by the
Minnesota Geological Survey (Runkel and others, 2007) determined that flow through fractures is an
important part of the bedrock hydrogeologic system in an area of Lake Elmo one to two miles southwest
of the landfill. The objective of this project, sponsored by the Minnesota Pollution Control Agency
(MPCA) was to collect borehole geophysical data from three bedrock monitor wells within a few
hundred yards of the landfill (Fig. 1) in an effort to identify bedrock fractures and characterize their
hydraulic properties in the open-hole intervals of these wells. This information will allow the MPCA to
determine if there are preferential groundwater flow paths in the bedrock at the Washington County
Landfill, an important consideration for devising remediation and monitoring strategies at the site.
STUDY AREA AND DATA COLLECTION
The three monitor wells investigated for this project are located in the northwest one-quarter of
section 15, Township 29N, Range 21W, in east-central Washington County (Figure 1). Data were
collected using borehole geophysical tools that in combination allow interpretation of a number of rock
and water properties (e.g. Fig. 2). Natural gamma logs are largely a measure of rock and sediment
potassium content, which is used to distinguish relatively coarse-grained sandstone from finer grained
sandstone, siltstone, and shale, and to recognize bedrock intervals dominated by carbonate rock
(limestone or dolostone). Caliper logs are a measure of borehole diameter. Sharp positive deflections in
such logs are used to recognize secondary pores such as fractures, although fractures with relatively
narrow aperture (fractions of an inch) yet potentially hydraulically significant, are not consistently
1
demarked on these logs. Video logs collected with a down-hole camera were obtained from the three
boreholes by a subcontractor hired by the MPCA. Video logs commonly allow direct, visual observation
of fractures in uncased parts of boreholes (Fig. 3). However, the logs collected from the three holes
investigated as part of this project were limited in value because borehole water clarity was poor, and
camera focus was inconsistent. Caliper, single point resistivity logs, and video logs also can indicate the
depth of casing bottom.
A multi-parameter E-Log tool measures a variety of water properties in addition to the standard
gamma and single point resistivity properties described above. Sharp deflections in fluid resistivity and
temperature curves collected with the multi-parameter E-Log tool (“multi-parameter tool”) are an
indication of water movement through secondary pores such as fractures (e.g. Fig. 2).
Video and caliper logs indicated that two of the three monitor wells investigated (wells Q3 and BB3)
at the landfill have open-hole intervals suitable for flowmeter analysis. These two wells were logged
with an Electro-Magnetic (EM) flowmeter tool that measures vertical flow speed (water movement up or
down a borehole), in addition to fluid resistivity and temperature. This information is used to identify
discrete fractures that accommodate active water flow in response to either ambient or induced hydraulic
gradients (e.g. Figs. 2 and 4). Boreholes with measurable ambient vertical flow also indicate the
presence of aquitard(s) between the intervals through which water enters or exits the open part of a
borehole. Flowmeter logs were also collected from these two monitor wells under stressed conditions of
water injection at rates between about 2 and 8 gallons per minute. Hydraulic conductivity of fractures
can be quantified by combining injection log data with hydraulic head measurements and estimates of
aquifer thickness and radius of hydraulic influence induced by injection. Flowmeter logging procedures
are described in greater detail in Runkel and others (2003, 2006).
The video log of one of the three monitor wells (well R3) indicates it has an open-hole interval with
a substantially variable diameter, including cavernous intervals with loose fragments of sandstone that
2
are as large as several centimeters in length (e.g. Fig 3A). The open-hole of the well did not include
intervals with consistent, relatively narrow, borehole apertures of adequate extent to collect a
meaningful flowmeter log. Additionally, the loose fragments of bedrock greatly increase the potential
for tool damage or loss in the well. As a result, an EM flowmeter log was not collected for this well.
Instead, the hydrogeologic conditions were characterized by measuring fluid conductivity and
temperature under ambient and stressed conditions using only the multi-parameter tool (Fig. 5).
GEOLOGIC SETTING AND BOREHOLE CONSTRUCTION
Unconsolidated glacial deposits dominated by sandy till and sand bodies range in thickness from
about 40 to 150 ft in the vicinity of the Washington County landfill (Meyer and others, 1990;
unpublished MGS mapping in progress). They are generally thinner where overlying the St. Peter
Sandstone and thicken over buried bedrock valleys of the Prairie du Chien Group. Bedrock beneath the
glacial deposits is gently tilted less than one-half a degree to the west, with uppermost bedrock in the
general vicinity of the landfill consisting of either the St. Peter Sandstone or Shakopee Formation
(Upper Prairie du Chien Group) (Fig. 1). The landfill area is located on the western edge of a wide (~ 1
mile), buried bedrock valley. Therefore the bedrock is progressively more deeply eroded eastward
across the study area, with St. Peter Sandstone as uppermost bedrock beneath the glacial deposits in the
west, and Shakopee Formation to the east (Fig. 1) (Mossler and Bloomgren, 1990; unpublished MGS
mapping in progress).
The three wells we investigated range in depth from about 115 to 125 ft, and are located where the
lower part of the St. Peter Sandstone is uppermost bedrock (Figs. 1, 2, 4, and 5). The wells have open-
hole intervals exposing the Shakopee Formation or St. Peter Sandstone. Unconsolidated glacial sediment
and approximately 10 to 30 ft of uppermost bedrock at each site is cased (4 inch diameter steel) and
grouted. Wells Q3 and BB3 have open-hole intervals that expose only the Shakopee Formation (Figs. 2
3
and 4). The open-hole interval in well R3 apparently exposes only St. Peter Sandstone (Fig. 5), although
the drilling record indicates that when the well was initially constructed the Shakopee Formation may
have been penetrated from a depth of about 125 to the reported original total borehole depth of 133 ft.
The video and geophysical logs indicate that this lowermost part of the borehole is now filled with sand.
RESULTS
Video and caliper logs, in combination with flowmeter and multi-parameter tool logging
demonstrates the presence of preferential groundwater flow paths through fractures in the bedrock at the
three landfill monitor wells. The presence of hydraulic fractures is best documented in the Shakopee
Formation, in wells Q3 and BB3, which have open-hole intervals amenable to flowmeter logging. In
each of these wells, a very weak ambient downflow entered the borehole through bedding plane
fracture(s) in the upper part of the open-hole interval, and exited through fracture(s) in the lower part of
the open-hole (Figs 2 and 4). Fracture flow was clearly documented under stressed conditions whereby
water was injected into the boreholes at rates of about 2 to 8 gallons per minute. Greater than 95 percent
of injected water in each hole exited at a single, discrete fracture with an aperture of less than 0.5 ft.
Hydraulic conductivity of these fractures ranged from 1100 to 7000 ft per day, assuming a fracture
aperture of 0.5 ft and a 10 ft radius of influence induced by injection (Table 1).
The video and caliper logs for monitor well R3 showed clear evidence of both vertical joints and
relatively large bedding plane fractures in the lower part of the St. Peter Sandstone (Figs. 3A and 3B).
Temperature and fluid resistivity logs collected during injection indicate that most or all injected water
exited the borehole at a discrete fractured interval at about 120 ft (Fig. 5). The hydraulic conductivity of
this interval is calculated at 6200 ft/day, assuming a fracture aperture of 0.5 ft and a 10 ft radius of
influence induced by injection (Table 1).
4
DISCUSSION
The results of our borehole geophysical logging indicate that the bedrock exposed in the open-hole
intervals of the three tested wells near the Washington County Landfill has attributes typical of the
Shakopee Aquifer and lower St. Peter aquitard documented elsewhere in southeastern Minnesota
(Runkel and others 2003; Tipping and others, 2006; Runkel and others, 2007). Previous studies have
demonstrated that the Shakopee is a karstic aquifer in which the largest volume of groundwater is
transported along secondary pores, with bedding plane fracture networks accommodating the bulk of
horizontal flow. Hydraulic conductivity of bedding plane fractures in the Shakopee Formation in
southeastern Minnesota varies greatly, is known to commonly exceed several thousand ft/day,
comparable to values measured in this project, and flow speeds along such fracture networks have been
measured at hundreds of ft/day or faster. Intervals with bedding plane fractures are commonly separated
vertically from one another by carbonate rock with relatively few interconnected fractures. Ambient
flow within boreholes open only to the Shakopee Formation at other sites in the Lake Elmo area (Runkel
and others, 2007) and elsewhere across southeastern Minnesota (Tipping and others, 2003) indicates
that these latter intervals serve as local aquitards that hydraulically separate bedding plane fracture
networks.
The lower St. Peter Sandstone in monitor well R3 has hydrogeologic properties comparable to other
Paleozoic sandstone aquitards in southeastern Minnesota. Coarse clastic beds should be expected to have
moderate to high intergranular hydraulic conductivity, and fine clastic beds have a low to very low
intergranular conductivity. The presence of fracture(s) with high hydraulic conductivity in monitor well
R3 is consistent with properties of the lower St. Peter Sandstone aquitard documented in the nearby
Lake Elmo area (Runkel and others, 2007). Bedding plane fractures were shown to dominate hydraulics
5
in the boreholes tested in that area. Additionally, vertical fractures in the lower St. Peter (e.g. Fig. 3A)
that hydraulically breach this aquitard should be expected in the Washington County landfill, because
such fracture systems are relatively well developed where aquitards are uppermost bedrock (Runkel and
others, 2003).
6
REFERENCES
Meyer, J.H., Baker, R.W., and Patterson, C.J., 1990, Surficial Geology, pl. 3, of Meyer, G.N., and
Swanson, L.S., (editors) Geological atlas of Washington County, Minnesota. Minnesota
Geological Survey County Atlas Series C-5. Part A scale 1:100,000.
Mossler, J.H., and Bloomgren, B.A., 1990, Bedrock Geology, pl. 2, of Meyer, G.N., and Swanson,
L.S., (editors) Geological atlas of Washington County, Minnesota. Minnesota Geological Survey
County Atlas Series C-5. Part A scale 1:100,000.
Runkel, A.C., Tipping, R.G., Alexander, E.C., Jr., Green, J.A., Mossler, J.H., Alexander, S.C., 2003.
Hydrogeology of the Paleozoic bedrock in southeastern Minnesota. Minnesota Geological Survey
Report of Investigations, vol. 61, 105 pp., 2pls.
Runkel, A.C., Tipping, R.G., Alexander, E.C., and Alexander, S.C., 2006, Hydrostratigraphic
characterization of intergranular and secondary porosity in part of the Cambrian sandstone
aquifer system of the cratonic interior of North America: Improving predictability of
hydrogeologic properties: Sedimentary Geology, v. 184, p. 281-304.
Runkel, A.C., Mossler, J.H., and Tipping, R.G., 2007, The Lake Elmo downhole logging project:
Hydrostratigraphic characterization of fractured bedrock at a perfluorochemical contamination
site: Minnesota Geological Survey Open File Report 07-5, 11p. plus figures and appendices.
Tipping, R.G., Runkel, A.C., Alexander, E.C., and Alexander, S.C., 2006, Evidence for hydraulic
heterogeneity and anisotropy in the mostly carbonate Prairie du Chien Group, southeastern
Minnesota, USA: Sedimentary Geology, v. 184, p. 305-330.
7
FIGURE CAPTIONS
Figure 1. Washington County Landfill study area showing monitor wells BB3, R3, and Q3 that were logged with
a variety of borehole geophysical tools for this project. Six digit numbers adjacent to monitor well
names refer to Minnesota County Well Index Unique Numbers. Bedrock geology showing uppermost
bedrock beneath unconsolidated glacial sediment is also shown. Geology is based on Minnesota
Geological Survey mapping in progress by Julia Anderson, and may differ from published map that is
ultimately produced.
Figure 2. Borehole geophysical logs collected from monitor well Q3. Gamma and caliper logs provide
information on rock matrix and secondary pores such as fractures. Flowmeter logging provides
information on water flow within the open borehole. Flowmeter and multi-parameter tool logs in this
well indicate that under ambient conditions there is very weak (<0.2 liters/min measured) downflow
that enters the borehole from a fracture at approximately 112.5 feet and exits the hole at approximately
118 ft. Under conditions of injection at a rate of about 2 gallons per/minute all measurable injected
water exits borehole at a fracture at 112.5 ft. Calculated hydraulic conductivity of this fracture is 7000
ft/day (Table 1).
Individual, averaged station flow values collected during injection were inadvertently unrecorded, but
the range of values for each individual station were recorded. The dashed red line showing "injection
interpretation" is drawn at the approximate median of the range for each station. Trolling flowmeter
logs are collected while raising the tool uphole at a rate of 10 ft/min, and the flow values are therefore a
cumulative measure of both ambient flow and flow through the tool that occurs because it is moving
continuously uphole. For additional explanation of flowmeter and other borehole logging procedures
see text of this report; and Runkel and others, (2003, 2006, 2007). Location of well Q3 shown in Figure
1.
8
Figure 3. Bedrock fractures exposed in open-hole intervals of monitor wells near Washington County Landfill.
A) Downhole view at approximately 120 ft depth in monitor well R3. Arrows point to vertical fractures
marked by V-shaped notches in borehole wall. Dashed line follows top of prominent bedding plane
fracture. B) Sidehole view at approximately 118.3 ft depth in monitor well R3 showing bedding plane
fracture, marked by arrow. C) Sidehole view at approximately 112.5 ft depth in monitor well Q3
showing bedding plane and subvertical fractures (arrows) D) Downhole view at approximately 114 ft
depth in monitor well BB3. Dashed line follows top of bedding plane fracture. Photographs culled from
borehole video logs. Quality of photographs is commonly poor because of limited water clarity and
inconsistent camera focus in the original borehole video. Video log provided by MPCA.
Figure 4. Borehole geophysical logs collected from monitor well BB3. Under ambient conditions there is weak
downflow that enters borehole via fractures at approximately 104 and 111 ft. Downflow exits borehole
via two fractures at approximately 114 and 116.5 ft. Under conditions of injection at a rate of about 8
gallons/minute, 95% or more of injected water exits borehole via fracture at approximately 104 ft.
Calculated hydraulic conductivity of this fracture is 1100 ft/day (Table 1). Any remaining injected
water exits via fractures at 111 and 114 ft. See Figure 2 caption and text of report for additional
explanation of logging procedures. Location of well BB3 shown in Figure 1.
Figure 5. Borehole geophysical logs collected from monitor well R3. Video log showed that this open-hole was
too rubbly and irregular in diameter for flow-logging. Measurements were therefore collected with
multi-parameter tool under ambient and stressed conditions of injection at a rate of about 2.5
gallons/minute. Fluid resistivity logs indicate that most injected water exits the hole at a fracture(s) at
approx 120'. Calculated hydraulic conductivity of this fracture is 6200 ft/day. See Figure 2 caption and
text of report for additional explanation of logging procedures. Location of well R3 shown in Figure 1.
Note that Shakopee Formation may have been exposed in lower part of open-hole when originally
drilled to depth of 133 ft. Hole now likely backfilled with sand to 124 ft.
9
188767
188774
460084
Q3
R3
BB3
Stillwater
34th34 th
31st
Isle
35th
36th
37th
Jam
ica
Ave
Jamica Ave
0 100 200 400 600 800 MetersN
N
Op
Os
LegendSection boundary
Landfill boundary
Wells logged for this project
StreetOp
Os St. Peter Sandstone
Shakopee Formation(Prairie du Chien Group)
Proposed well
15
FIGURE 1
XXXXXXX 676433
DE P T HIN F T .
S hakopee F ormation
S t P eter S s
S t P eter
gamma (AP I units )
188767Washington County Landfill Well Q3
hole diameter (in.) s tation flow (liters/min)trolling flow (gal/min) temperature (F ) fluid res is tivity (ohm-meters )
Interpretaion overview: S
flow measurement with tool s tationary
interpreted flow
aquitard
flow abruptly enters/exits
flow gradually (intergranularly?) enters or exits
0-1 1
0-1 1
4 5 6 -10 -5 00 200
0 200
downhole flow uphole flow
downhole flow uphole flow
downhole flow uphole flow
120
110
100
90
80
70
110
120
100
90
80
70
110
120
100
90
80
70
DE P T HIN F T .
gamma (AP I units )
hole diameter (in.) s tation flow (liters/min)trolling flow (gal/min) temperature (F ) fluid res is tivity (ohm-meters )
-8 -4 0-12 24 5 6
120
110
100
90
80
70
90
100
110
120
80
70
90
100
110
120
80
70
casing bottom
casing bottom
Glacial sediment
S hakopee F ormation
S t P eter S s
S t P eter S s
Glacial sediment
52.2556
52.3558
28.831
2934
540-20 -10 59 24 28 32 36 40 44 48 52
Ambient logsEM flowmeter tool
multiparameter tool
FIGURE 2
INJTRL1
INJTRL3
INJTRL4
15 30
100
110
100
11054 58
15 30
100
110
100
11055 58.6
0 22
100
110
100
110
0 20
100
110
17 25
54 55
100
110
injection interpretationAmbient Injection
Ambient Injection
INJECTION INTERPRETATION
AMBIENT INTERPRETATION
we
ak
do
wn
flow
enters hole
exits hole
stro
ng d
ownf
low
~100% exits hole
Ambient station
naturalcaliper flowmeter flowmeter
natural caliper flowmeter flowmeter
FIGURE 3
A B
C D
XXXXXXX 676433
DE P T HIN F T .
S hakopee F m
S t P eter S s
S t P eter S s
G lacial sediment
S t P eter S s
G lacial sediment
S hakopee F ormation
S t P eter S s
gamma (AP I units )
460084 Washington County Landfill Well BB3
hole diameter (in.) s tation flow (liters/min)trolling flow (gal/min) temperature (F ) fluid res is tivity (ohm-meters )
Interpretaion overview: S
flow measurement with tool s tationary
interpreted flow
aquitard
flow abruptly enters/exits
flow gradually (intergranularly?) enters or exits
0-1 1
0-1
4 6 8 -20 0-10 10
15 30 -20 0-10 10
0 200
downhole flow uphole flow
120
110
100
90
80
70
110
120
100
90
80
70
110
120
100
90
80
70
DE P T HIN F T .
gamma (AP I units ) hole diameter (in.) s tation flow (liters/min)trolling flow (gal/min) temperature (F ) fluid res is tivity (ohm-meters )-8 -4 0-12 24 6 8
120
110
100
90
80
70
90
100
110
120
80
70
90
100
110
120
80
70
casing bottom
casing bottom
Ambient logs
naturalcaliper flowmeter flowmeter
natural caliper flowmeter flowmeter
51.553.75
5254
17.919.0
18.519.7
INJTRL1
INJTRL3
INJTRL4
15 30
100
110
100
11054 58
15 30
100
110
100
11055 58.6
0 22
100
110
100
110
0 20
100
110
17 25
54 55
100
110
53 55 57 59
EM flowmeter tool
multiparameter tool
AmbientEarly InjectionLate Injection
AmbientEarly InjectionLate Injection
enters hole
AMBIENT INTERPRETATION
INJECTION INTERPRETATION
wea
k do
wnf
low
enters hole
exits hole
exits hole
wea
k do
wnf
low
exits hole
exits hole
stro
ng d
ownf
low
>95% exits hole
< 5% exits hole
< 5% exits hole
1
downhole flow uphole flow
downhole flow uphole flow
Ambient station
Injection station
Injection interpretation FIGURE 4
XXXXXXX 676433
DE P T HIN F T .
S t P eter S s
? S hakopee F m?(now backfilled? )
gamma (AP I units )
188774Washington County Landfill Well R3
hole diameter (in.) s tation flow (liters/min)trolling flow (gal/min) temperature (F ) fluid res is tivity (ohm-meters )
Interpretaion overview: S
flow measurement with tool s tationary
interpreted flow
aquitard
flow abruptly enters/exits
flow gradually (intergranularly?) enters or exits
4 6 80 200
downhole flow uphole flow
130
120
110
100
90
70
130
120
110
100
90
70
casing bottom
Glacial sediment
INJTRL1
INJTRL3
INJTRL4
15 30
100
110
100
11054 58
15 30
100
110
100
11055 58.6
0 22
100
110
100
110
0 20
100
110
17 25
54 55
100
110
AMBIENT CONDITIONSINJECTION, EARLY INJECTION, LATER
NON
E
NON
E
INJECTION INTERPRETATION
stro
ng d
ownf
low
Most injectedwater exits hole
FIGURE 5
1951.050.9 51.1 51.2 51.3 51.4 22 25 28 31 34 37 40
naturalcaliper flowmeter flowmeter
TABLE 1
CONDUCTIVITY OF INDIVIDUAL FRACTURES
Well name unique_no fracture depth
injection rate (gpm)
change in swl (ft)
estimated radius of influence (ft)
aquifer thickness (ft) T (ft2/day) K (ft/day)
Q3 188767 112.5 ft 1.95 0.07 10 0.5 3500 7000 R3 188774 120 ft 2.52 0.1 10 0.5 3100 6200 BB3 460084 104 ft 7.95 1.82 10 0.5 550 1100
BULK CONDUCTIVITY OF OPEN HOLE
Well name unique_no fracture depth
injection rate (gpm)
change in swl (ft)
estimated radius of influence (ft)
aquifer thickness (ft) T (ft2/day) K (ft/day)
Q3 188767 XXX 1.95 0.07 5 10 2900 290 R3 188774 XXX 2.52 0.1 5 10 2600 260 BB3 460084 XXX 7.95 1.82 5 10 455 45.5
Table 1. Horizontal hydraulic conductivity measurements for the three tested monitor wells at the
Washington County Landfill. Values calculated by flowmeter logging during well injection at rates between 2 and 8 gallons per minute, according to the procedure described in Runkel and others (2006). Graphic depictions of the flowmeter logging conducted on these wells is in Figures 2, 4, and 5. Aquifer thickness values of 0.5 ft correspond to estimated maximum aperture of fractures based on caliper and video logs.
APPENDIX
COPIES OF GAMMA, CALIPER, AND MULTI-PARAMETER GEOPHYSICAL LOGS COLLECTED FROM MONITOR WELLS R3, BB3, AND Q3 (Available as paper copies only)
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