Wardle Challenges Weds.pdf - NEIWPCC

Predicting petroleum
movement in fractured bedrock
Alex Wardle
Petroleum Program, Northern Regional Office,
Department of Environmental Quality, Commonwealth of
Virginia
National Tank Conference,
Sacramento, California, April 2009

The problem
• “Groundwater flow
conditions in the fractured
bedrock media in the area
of the site are generally
undefinable.”
• “… the existing
groundwater
contamination onsite
could, with little or no
reduction in concentration,
impact nearby water wells
and environmental
receptors”
A. Consultant, 2000(-2007)

Summary
• Bedrock contaminant movement – too far, too
fast, erratic and in the wrong direction?
• Is contaminant movement in bedrock
predictable?
• “Sand box” investigation techniques confuse,
prolong and may even “create” cases when
used in bedrock
• If not the long screen well, how to investigate?
• Case studies showing how understanding the
fracture system helps resolve cases

Outline
• Review of contaminated drinking water
well cases
• Basic principles
• Case studies showing
– Speed and directionality of bedrock
contaminant flow
– Investigation techniques

Petroleum releases and polluted
wells

Well review
• Geologic province and structural dip
direction
• Type of petroleum (non regulated
heating oil or regulated gasoline)
• Age of well
• Distance from release
• Direction from release to well
• Concentration of MTBE or benzene
in well
• Wells included in the survey were
those assessed, treated or replaced
under DEQ’s alternative water
supply program
N
Bearing
Distance

30%
25%
20%
15%
10%
Wells and Distance
5%
0%
Piedmont and Blue Ridge: distance between
release and impacted well
0 to 50
51 to 100
101 to 150
151 to 200
201 to 250
251 to 300
301 to 350
351 to 400
401 to 450
451 to 500
Distance, ft
501 to 600
601 to 700
701 to 800
801 to 900
901 to 1000
1000+

Concentration and Distance of
ug/l
5000
4000
3000
2000
Benzene
1000
0
Release
Blue Ridge/Piedmont
MTBE
0 100 200 300 400 500 600 700 800 900 1000 1100 1200
ft

Wells and Direction
Piedmont/Blue Ridge: direction to
impacted well
10
5
(10) (5) 0 5 10
(5)
(5)
(10)
15
10
5
(10)
(15)
N
0
W 0
E
(15) (10) (5) 0 5 10 15
S
Direction to affected
well
Geologic structures

What’s going on? Geology,
• Geologic Structure:
– Direction;
– Length;
– Frequency
geometry, stress
• In-situ geologic stresses determine which
fracture sets are more consistently open

Release
Simple Fracture
Strike
Dip
“affected” zone
Piedmont/Blue Ridge: direction to
impacted well
10
5
0
(10) (5) 0 5 10
(5)
(10)
N
W E
S

How to analyze?
• From Hobbs, Means &
Williams 1976

Plane A
Vertical fracture

dipping fractures

Plane A
Pair of fractures
Plane B

Plane A
Steeply dipping pair of fractures
Plane B

Length and frequency..

Compressive stress

Shear Stress

In-situ stress
• The earth is stressed
• Those earth stresses
are directional
• Depending on the
direction, some
fractures will be open,
some closed
• Fractures parallel to
maximum shear stress
are more likely to be
open fractures
• Figures from Rogers 2003

Reinecker, J., Heidbach, O., Tingay, M., Sperner, B., & Müller, B. (2005):
The 2005 release of the World Stress Map (available online at www.worldstress-map.org).
Northern Virginia
principal stress
25’ to 50’
Piedmont/Blue Ridge: direction to
impacted well
10
5
0
(10) (5) 0 5 10
(5)
(10)
N
W E
S

Summary for northern Virginia
1. Frequent, long, north south trending geologic features
2. In situ stresses tend to open fractures trending from
345 to 45
3. The most at risk receptors will therefore be located
north or south of a release
4. If you find an affected receptor, look for the sources of
contamination to the north or south
5. Investigate bed rock geologic structures to confirm
likely pathways and design your investigation and
remediation based on the directionality and
discreteness of those structures

• Geologic maps
• Field mapping
• Surface geophysics
Tools
• Direct push soil and groundwater
investigation
• Down hole geophysics in existing potable
wells
• Last, groundwater monitoring wells

Example bed rock problems
• Gas station: SCR shows groundwater flow to
east. There are wells all around: which ones are
at risk?
• There is a tanker release. Drinking water wells
150 feet away: SCR says groundwater velocity
could be as low as 0.004 ft/day.. Or as high as 7
ft/day… What to do?
• Gas taste in a small community well. 191 ug/l
benzene found: six months later concentrations
are BDL. Next month back to 270 ug/l. No
source….

Case Study 1: Manassas
Which way? Groundwater direction and
contaminant flow
• Historically polluted well water
• New well installed in early 1990s, initially
clean
• Case opened in 1995, new well
contaminated with MTBE
• Wells at all surrounding properties
• Reluctant RP no longer owner,
characterization delayed to 2001

Manassas Site setting

Groundwater flow 2002

MTBE October 2001

MTBE October 2002

MTBE August 2004

MTBE March 2005

MTBE September 2005

MTBE August 2006

Down hole geophysics
• North-south trending fracture system;

Manassas

MTBE June 2007

MTBE September 2007

Surface geophysics

Enhanced oxygen degradation
• Select or add wells in fracture system;

MTBE March 2008

MTBE June 2008

Groundwater flow 2008

MTBE September 2008

MTBE December 2008

Best laid plans….

Madison

Tanker Spill

Tanker Spill

Tanker Spill

MTBE vs benzene transport times
Conc ug/l
2500
2000
1500
1000
500
MTBE -
Antique
Benzene -
Antique
0
11/18/02 11/18/03 11/18/04 11/18/05 11/18/06 11/18/07 11/18/08
70 days, MTBE
in well
660 days,
Date
benzene in well

Tanker Spill – initial
investigation

Distance, ft
MTBE transport time
700.00
600.00
500.00
400.00
300.00
200.00
100.00
Antique well
MW2
MW7
Pond
0.00
0 500 1000 1500 2000
time, days

Tanker Spill

Surface geophysics

Madison Spill

Site layout and characterization

Corrective action
• Wells replaced in geologically low risk
locations
• Dual phase extraction implemented
recovering from wells in fracture system

Where from – Fauquier case?
• Petroleum taste in well
serving seven
properties reported
September 2006
• Carbon filter installed
by DEQ
• Investigations continue

350
300
250
200
150
100
50
0
Benzene and groundwater
10/2/2006 10/2/2007 10/2/2008
540
530
520
510
500
benzene
toluene
ethylbenzne
xylene
MTBE
Elevation water BR2
benzene MW6

Investigation steps
• Survey sources
• Investigate geology
• Sample surrounding potable
wells
• Complete surface
geophysics
• Install initial direct push and
monitoring wells
• Expand surface geophysics
and complete downhole
geophysics in monitoring
and potable wells

Investigation steps
• Survey sources
• Investigate geology
• Sample surrounding potable
wells
• Complete surface
geophysics
• Install initial direct push and
monitoring wells
• Expand surface geophysics
and complete downhole
geophysics in monitoring
and potable wells

Geophysics and geology

Geophysics and well
construction
• Well drilled to 100 feet
• Drilling records indicate
water strike at 70 feet
• Drilling and geophysics
indicates bedrock at 13
feet
• Down hole geophysics
confirm significant inflow
and fracture at 70 feet
• How to construct well?

Fauquier

Fauquier

Continuing characterization

• Probable source
and pathway
identified;
• New well location
to be proposed and
investigated;
• Design effective
containment and
remediation.
Conclusions

Conclusions
• Geologic structures are an important determinant in
petroleum contaminant movement.
• The geologic structures most important in determining
contaminant flow direction are predictable.
• Established tools exist to reveal the important structures.
• Understanding geologic structures allows a meaningful
site characterization and effective remediation to be
designed
• Receptors can be prioritized and protected.
• Finally: assume anisotropy and beware the long screen
well.

With thanks
• My DEQ regional office colleagues:
– Randy Chapman, Dell Cheatham, Joe Glassman, Jay Green,
Kurt Kochan, Mark Miller and Cynthia Sale
• The ladies and gentlemen who gathered the field data
and did the field work:
– Matt Voorhees and Kris McCandless of Total Environmental
Concepts;
– Eric Rager and David Berry of Apex Environmental Consultants;
– Amber Fidler and John Tabella of SCS Engineers of Reston;
– Scott McQuown of ARM Group Geophysics Division;
– Andy Forrest of Forrest Environmental Services