WASHINGTON COUNTY LANDFILL LOGGING PROJECT: …

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).

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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.

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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.

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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



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 )


-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 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 t P eter S s

gamma (AP I units )

460084 Washington County Landfill Well BB3




interpreted flow

aquitard



0-1 1

0-1

4 6 8 -20 0-10 10

15 30 -20 0-10 10

0 200


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


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


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



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




interpreted flow

aquitard



4 6 80 200


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


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


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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WASHINGTON COUNTY LANDFILL LOGGING PROJECT: …