LNAPL Transmissivity Endpoints

LNAPL Transmissivity End Points
Why, How and When
Andrew Kirkman P.E.
1
LNAPL Transmissivity (Tn)
• LNAPL Transmissivity summarizes the following
key considerations in LNAPL recovery into one metric:
Well
− LNAPL Density
− LNAPL Viscosity
Tn = ∑Kn ∆bn
LNAPL
− Soil permeability
− Magnitude of LNAPL saturation in soil
(i.e., LNAPL concentration)
− Thickness that LNAPL flows over
ρ n ⋅ g ⋅ k ⋅ k rn
Kn =
µn
Water
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How Transmissivity Relates to Reduction of
Mobile LNAPL
Permeability
K2<K1K1>0
A Pipe
Zero
=
Permeability
Max
Permeability
As LNAPL is recovered the number of pores occupied by
LNAPL decreases, which in turn decreases its relative
permeability. This is reflected in a decrease in LNAPL
Transmissivity
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Gauged Thickness –
Poor Metric for Recoverability
•
MW-4 Confined recovers to 5 feet thickness fast than wells
33 feet of starting thickness
•
MW-18 expected to take 3 years to recover to ~35 ft of thickness
MW-1 2008
MW-4 2004 UNCONFINED
MW-18 2007
with
MW-4 2008 CONFINED
MW-6 2008
RECOVERED LNAPL THICKNESS (FT)
35.0
30.0
25.0
20.0
15.0
10.0
5.0
0.0
1
10
100
1000
ELAPSED TIME (MIN)
10000
100000
~ 2 weeks
LNAPL Transmissivity Endpoints
1000000
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Gauged LNAPL Thickness Versus
Recovery - Poor Correlation
WATER ENHANCED RECOVERY AT 1 FOOT OF DRAWDOWN (GPD)
LNAPL SKIMMING RATE (GPD)
LNAPL RECOVERY METRIC VALUE
GAUGED LNAPL THICKNESS (FT)
100
33.00
33.15
10
19.03
5.40
2.60
1
0.1
0.01
MW-18
MW-6
MW-4 CONFINED
MW-4
UNCONFINED
MW-1
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LNAPL Transmissivity Versus Recovery
Good Correlation
• LNAPL Transmissivity exhibits improved correlation
• LNAPL Recovery Rate is a Function of both drawdown induced and LNAPL
transmissivity
LNAPL RECOVERY METRIC VALUE
• Skimming drawdown is controlled by equilibrium fluid levels and soil profile
WATER ENHANCED RECOVERY AT 1 FOOT OF DRAWDOWN (GPD)
LNAPL SKIMMING RATE (GPD)
LNAPL TRANSMISIVITY (FT2/DAY)
100
35
10
31
5.2
1
0.1
0.22
0.01
0.007
0.001
MW-18
MW-6
MW-4 CONFINED
MW-4 UNCONFINED
MW-1
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Why use LNAPL transmissivity?
•LNAPL Thickness
− Inconsistent between hydraulic scenarios (perched, confined, unconfined)
− Inconsistent between soil types
− Poor indicator of LNAPL recovery
•LNAPL Recovery Rate More Robust Metric than LNAPL Thickness
− Need recovery system or pilot test data
− Operational variability and technology differences make it difficult to use
across technologies and/or sites
•Transmissivity
− Estimated with recovery data or field testing on monitoring wells
− Consistent across soil types
− Consistent across confined, unconfined or perched conditions
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In well LNAPL thickness is a poor metric
• ITRC (2010) - recover LNAPL from areas with the largest equilibrium in well
thicknesses BUT
− Poor metric: correlates unfavorably with LNAPL recoverability
− Does not account for soil and LNAPL properties, soil heterogeneity, and LNAPL aquifer
conditions (unconfined/perched/confined)
• ASTM (2005) –
− LNAPL regulatory policies that define remediation metrics by small LNAPL thickness in
wells are…often inconsistent with risk-based screening levels and with current technical
knowledge regarding LNAPL mobility and recoverability ¶ 5.14.
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Short Term Recovery Evaluation
LNAPL Recovery Rate
Water Recovery Rate
0.5
50
0.4
40
0.3
30
0.2
20
0.1
10
0
0
Dec-06
To = Tw ρ r
Qo
Jan-07
Feb-07
Mar-07
LNAPL Recovery Rate (gpd)
Water Recovery Rate (1000 gpd)
2
LNAPL Transmissivity (ft /day)
LNAPL Transmissivity
Apr-07
Qw
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Pa
ge
So What Transmissivity Value Means
there’s a Bunch of LNAPL There
• New Catastrophic release scenario’s have resulted in observed values of 80 ft2/day
− ~1% of other sites exhibit Tn values this high several /decades after the release period
• Consider the Theim Equation
− 80 ft2/day with 1 ft of drawdown results in 816
− Or 80% recovery of a 700k release in 2 years with 6 skimming wells
• LNAPL Tn of 0.1 ft2/day with 0.1 ft of drawdown results in <0.2 gpd
− How does this rate compare with the remaining LNAPL mass?, mobile mass?, residual mass?
− Does it matter if migration is documented
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LNAPL Transmissivity in Practice
1
10
20
0.01
3.7E+05
Skimming LNAPL at 5 ft2/day
results in 7300 GPY skimming
100
3.7E+04
10
3.7E+03
1
3.7E+02
0.1
3.7E+01
SKIMMING
RANGE
VACUUM ENHANCED
SKIMMING RANGE
MULTI-PHASE & WATER
ENHANCED RECOVERY
Example Technology Drawdown Ranges
0.01
0.1
LNAPL RECOVERY RATE (GPY)
•
5
LNAPL TRANSMISSIVITY CURVES
Skimming LNAPL at 0.1 ft2/day
results in less than 400 GPY
skimming
LNAPL RECOVERY RATE (GPD)
•
0.1
1
LNAPL DRAWDOWN (FT)
LNAPL Transmissivity Endpoints
3.7E+00
10
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Ongoing support for LNAPL Transmissivity
• 2006 ASTM Guide of LNAPL Conceptual Site Models (E2531-06)
• 2009 ITRC Guide for LNAPL technology selection – includes
LNAPL transmissivity range 0.1 to 0.8 ft2/day that corresponds to
closed sites in various states
• 2011 ASTM Guide for Estimation of LNAPL Transmissivity
(E2856-13)
• API LNAPL Transmissivity work book
− search for LNAPL Baildown Test on API.org
− API multiple tools and documents – most pertinent here LNAPL
baildown test spreadsheet and guide document
• Applied NAPL Science Review (www.napl-ansr.com)
− Online publication related to advancing LNAPL understanding
within the remediation industry
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ASTM LNAPL Transmissivity Standard
(E2856-13)
• Increase Accuracy of calculations for LNAPL Transmissivity
• Identify critical assumptions and best practices
• Resolved various approaches into a more unified practice
• Include multiple methods in a single standard to provide
comparison of methods
• Provide standardization to generate a consistent and larger
database of information
• Methods include:
1.
2.
Baildown/Slug Tests (Lundy & Zimmerman
1999, Huntley, 2000 & Kirkman 2012)
3.
Manual Skimming Tests
4.
Tracer Tests (Sale, 2007)
Recovery System Data
(Charbeneau, 2007)
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LNAPL Concern – ITRC introduced composition vs saturation concern
Benzene Concentration
in Groundwater (mg/L)
Reduced
LNAPL
saturation
B
C
15%
30%
LNAPL Saturation
Changed
LNAPL
composition
(less benzene)
Source: Dr. Sanjay Garg
and ITRC LNAPL training
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LNAPL Transmissivity and Endpoints for Hydraulic
Recovery
ITRC Endpoint Range 0.1 to 0.8 ft2/day
• Represents the LNAPL transmissivity that occurred at multiple sites that were closed with the following
support data/evidence
− LNAPL Recovery was asymptotic and small compared to residual LNAPL in place
− No risk to receptors via vapor or dissolved phase existed
− Remaining LNAPL was stable and not migrating
− Institutional controls were in place to prevent exposure
− Land/ groundwater use restrictions or;
− Active facilities ensured land use would remain industrial
− On going remediation would not significantly improve site conditions
− Plume already stable
− No complete pathways / risk to receptors
• Following Closure of LNAPL Transmissivity data was compiled and reviewed to generate the empirical
ITRC range
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Stop Metric Example
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What Fraction Can Be Removed for a
Given Starting LNAPL Transmissivity
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Reversed Decline
0.5
1.0
1.5
ELAPSED TIME (YEARS)
2.0
2.5
3.0
3.5
4.5
RESIDUAL
VOLUME
0%
4.0
10%
15
13
Remaining Volume Above
Residual
40%
50%
60%
70%
80%
90%
LNAPL Recovered Above LNAPL Transmissivity of 0.6 ft2/day
30%
LNAPL
Recovered
After
Reaching
0.6 ft2/day
REMAINING VOLUME (GAL)
20%
17
11
9
7
5
LNAPL TRANSMISSIVITY (FT2/DAY)
0.0
3
1
-1
-3
100%
Remaining Volume In Place
LNAPL Transmissivity
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Fraction of LNAPL Within Proposed Endpoint Range
>10 years - Elapsed Time
Fraction of LNAPL Beyond Proposed Recovery Endpoint/Continued to be Recovered with Significant Effort
Fraction of LNAPL Beyond Proposed Endpoint Range/was not Recovered
Residual LNAPL Fraction (unrecoverable)
100%
Residual Fraction
FRACTION OF TOTAL LNAPL WITHIN MOBILE
INTERVAL PRIOR TO RECOVERY EFFORTS (%)
90%
2 years
80%
0.6 years
0.6 years
70%
60%
8 years
12 years
8 years
50%
Mobile Fraction
Not Recovered
2 years
40%
30%
13.5 years
11 years
2 years
20%
6 years
3.75 years
11 years
10%
Recovery Time and Fraction
Beyond Endpoint
8 years
14 years
7.5 years
Time Until11Transmissivity
of
years
2
2
0.6 ft /day (0.55 m /day)
0%
14
14
6
2
3.6
Well 7
Wells 8 - 21
Well 22
Well 1
Well 2
Site 1
Page 20
>50 years
10 years
2/day)
10Starting 1.4
4.6
1.4
0.0015
- 0.0023
LNAPL Transmissivity
(ft
Well 3
Well 4
Site 2
Page 20
Well 5
Well 6
4 years
0.35
Wells 23 - 24
Well 25
Site 3
Site 4
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LNAPL Transmissivity vs Residual Fraction
Residual LNAPL Fraction (unrecoverable)
Fraction of LNAPL Beyond Proposed Endpoint Range/was not Recovered
>10 years - Elapsed Time
Fraction of LNAPL Beyond Proposed Recovery Endpoint/Continued to be Recovered with Significant Effort
>10 years - Estimated Time
Fraction of LNAPL Within Proposed Endpoint Range
FRACTION OF TOTAL LNAPL WITHIN MOBILE
INTERVAL PRIOR TO RECOVERY EFFORTS (%)
100%
90%
2 years
80%
0.6 years
0.6 years
70%
10 years
60%
8 years
12 years
8 years
50%
13.5 years
40%
30%
2 years
11 years
>10 years
2 years
20%
6 years
3.75 years
11 years
8 years
14 years
7.5 years
11 years
10%
>50 years
10 years
0%
14
14
6
2
3.6
10
4 years
1.4
4.6
1.4
0.0015 - 0.0023
0.35
Well 4
Well 5
Well 6
Wells 23 - 24
Well 25
Site 3
Site 4
INITIAL LNAPL TRANSMISSIVITY (FT2/DAY)
Well 7
Wells 8 - 21
Well 22
Well 1
Site 1
Well 2
Well 3
Site 2
NOTES:
1. RECOVERABLE LNAPL VOLUMES ARE BASED ON DECLINE CURVE ANALYSIS, MASS BALANCE AND MODEL CALIBRATION
2. RESIDUAL SATURATIONS ARE BASED ON SOIL CORE ANALYSES AND/OR MODEL CALIBRATION TO FIELD DATA
3. MODEL CALIBRATION INCLUDED, SOIL AND FLUID
TYPE, AND LNAPL TRANSMISSIVITY DATA
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Summary
• LNAPL transmissivity can be used as a start or stop metric for Maximum Extent Practicable (Source
Reduction via Hydraulic Recovery)
• Guidance has been improved over the past twelve years and provides a good foundation to
− Improve accuracy of LNAPL transmissivity estimates
− Provide multiple methods to estimate LNAPL transmissivity throughout the life of a site
• ITRC range combined with site LNAPL transmissivity data provides an absolute reference point for
hydraulic recovery/transmissivity values
• Sites exhibiting LNAPL transmissivity value below 0.8 ft2/day with existing recovery systems should
consider the effectiveness of continued hydraulic recovery in reducing remaining LNAPL source mass
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Thank you
Andrew Kirkman, P.E.
Remedial Performance Application - Scenario 2
• Weak decline supports using individual well measurements
(e.g., baildown tests) to measure LNAPL transmissivity across the
plume
Graphics provided by
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Remedial Performance Application - Scenario 1
• Strong decline indicates recovery system is well
representative of capture zone
Graphics provided by
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