new api guide on petroleum natural source zone depletion
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© 2017 CH2M
Fourth International Symposium on Bioremediation and Sustainable Environmental Technologies
New API Guide on Petroleum Natural Source Zone Depletion (NSZD)
Tom Palaia
Chief Technologist
Julio Zimbron
Founder
Eric Nichols
Principal
2Delivering Sustainable Solutions to Complex Local Challenges, Worldwide© 2017 CH2M
New API NSZD Guide
• Applicability: Measurement of mass depletion rates in LNAPL source zones
• Goal: Practice consistency
• What’s new:
– Emphasis on vadose zone mass losses as biogas (CH4 and CO2)
– Strategies for planning NSZD evaluations
– Field procedures and QA/QC
– Data evaluation guidance
From T.Palaia, 2016. Applied NAPL Science Review, Vol.
6, Issue 1. May.
3Delivering Sustainable Solutions to Complex Local Challenges, Worldwide© 2017 CH2M
NSZD Concepts and Usage
• NSZD quantification based on
stoichiometric conversion of
chemical fluxes in:
a) Groundwater
b) Vadose zone
• Aqueous-based losses <<
vapor-based losses
(at most sites)
• API NSZD guide focuses on
vapor phase-related
processes
4Delivering Sustainable Solutions to Complex Local Challenges, Worldwide© 2017 CH2M
NSZD Evaluation ConsiderationsSite conditions of concern
• No evidence of LNAPL
• Permanently saturated/frozen soils
• Thin vadose zone
• Large [CH4] near ground surface
• Lack of LNAPL delineation
• Intermittent flooding
• High natural organic matter in soils
• Impermeable ground cover
• Active on-going remediation
• Regional sources of CH4 and/or CO2
from deep reservoirs
• Large depth to LNAPL
• Cold climate
• Saturated silt/clay geology overlying hydrocarbon impacted soils
• Natural CO2 from calcareous sands/rock
NOT RECOMMENDED
RECOMMENDED WITH CARE
5Delivering Sustainable Solutions to Complex Local Challenges, Worldwide© 2017 CH2M
NSZD Evaluation ConsiderationsKey LCSM elements
• Lateral and vertical extent of LNAPL
• LNAPL type and fluid density
• Depth to groundwater and fluctuation
• Ambient temperature clime
• Depth to top of hydrocarbon impacts
• Soil type and moisture content
• Methane in shallow soil gas
• LNAPL distribution and hydrostratigraphy
6Delivering Sustainable Solutions to Complex Local Challenges, Worldwide© 2017 CH2M
NSZD Evaluation ConsiderationsNomograms to screen rates
7Delivering Sustainable Solutions to Complex Local Challenges, Worldwide© 2017 CH2M
NSZD Evaluation ConsiderationsBackground correction
• Background gaseous influence varies
widely
– Affects all methods
• Requires planning and special data
handling
– Background gas flux monitoring outside
the LNAPL footprint
– Supplementing field analysis with a
second method
• Measuring 14C in soil vapor to estimate
fossil fuel fraction of CO2
Higher
Background
Low
Background
Too high
Background?
8Delivering Sustainable Solutions to Complex Local Challenges, Worldwide© 2017 CH2M
NSZD Estimation – Field Methods
• Gradient
• Passive Flux Trap
• Dynamic Closed Chamber
Soil Flux Chamber
Gradient Method
CO2 Trap
9Delivering Sustainable Solutions to Complex Local Challenges, Worldwide© 2017 CH2M
Gradient MethodOverview
• Based on Fick’s first law of
diffusion:
– Assumes diffusion is dominant
and homogeneous, isotropic
geology
• Requires depth-discrete vapor
monitoring data for O2 and CO2
– Fixed gas concentration profiles
– Effective vapor diffusion
coefficients (tracer test)
10Delivering Sustainable Solutions to Complex Local Challenges, Worldwide© 2017 CH2M
Gradient MethodApplication
Accuracy is
affected by choice
of lower boundary
control point
Above the methane oxidation zone, flux of
reactants should be relatively constant with
depth
11Delivering Sustainable Solutions to Complex Local Challenges, Worldwide© 2017 CH2M
Gradient MethodConsiderations and caveats
• Simple in concept, but difficult to obtain robust results
• Challenges:
– Variations in soil moisture affect gas profiles
– Heterogeneous soils will affect soil gas profiles
– Single “snap-shot” in time
– Selection of lower boundary control point
– Diffusion only, advection of gases will confound the results
Site without vadose zone impacts
12Delivering Sustainable Solutions to Complex Local Challenges, Worldwide© 2017 CH2M
Dynamic Closed Chamber (DCC) MethodOverview
• Developed as a short-term
measurement of total CO2 efflux
– Industry standard method in
ecosystem studies
• Field measurement of CO2
concentration over time in closed
chamber with pressure equalization
• Can collect short- or long-term
measurements
• Diffusion + advection
13Delivering Sustainable Solutions to Complex Local Challenges, Worldwide© 2017 CH2M
DCC MethodApplication
• Site survey based on total CO2
fluxes
• Requires background correction
– Measure total CO2 flux at
unimpacted locations
– Take into account differing
ground cover and vegetation
14Delivering Sustainable Solutions to Complex Local Challenges, Worldwide© 2017 CH2M
DCC MethodConsiderations and caveats
• Real-time results, can measure
20-30 locations per day
– High data density achievable
• Relatively inexpensive
– Moderately labor intensive
• Total CO2 fluxes vary diurnally
• Background correction can be
difficult in diverse conditions
– Not carbon-isotope friendly With permission from Ma et al, 2013
15Delivering Sustainable Solutions to Complex Local Challenges, Worldwide© 2017 CH2M
Passive Flux Trap MethodOverview
• Two sorbent layers separate soil
gas efflux from ambient CO2
• Deployment for multiple
consecutive days
– 2 weeks typical to avoid short-
term effects
• Diffusion + advection
– Sorbent is porous and allows
free air flow
• Field method with lab analysis
16Delivering Sustainable Solutions to Complex Local Challenges, Worldwide© 2017 CH2M
Passive Flux Trap MethodApplication
• Field efforts are minimal
• No power or moving parts
• 14C analysis (also known as carbon dating) allows splitting between
modern and fossil fuel CO2 contributions (Method DASTM 6866-12)
17Delivering Sustainable Solutions to Complex Local Challenges, Worldwide© 2017 CH2M
Passive Flux Trap MethodConsiderations and caveats
• Long-term, time-integrated flux
• Fossil fuel analysis (14C) is standard
• Higher quality data, but also higher
cost
• Relatively long turn-around time
(4 weeks)
• As other methods, continuous gas
transport is needed
– Carefully consider soil water
saturation
18Delivering Sustainable Solutions to Complex Local Challenges, Worldwide© 2017 CH2M
Method Comparison Caveats
• Each method has specific limitations
• Sand-tank studies have validated
each method
• Order-of-magnitude accuracy is
expected
19Delivering Sustainable Solutions to Complex Local Challenges, Worldwide© 2017 CH2M
Methods Summary
Gradient Passive Flux TrapDynamic Closed
Chamber
Best for sites with:
Vadose zones >5 feet
with existing vapor
probes
Variable effects of soil
respiration on O2
and CO2 flux
Uniform background
gas flux
Intrusiveness High, for new probesLow, shallow
installation
Low, shallow
installation
Transport processes Diffusion Diffusion, advection Diffusion, advection
Instantaneous or time-
averaged
measurement?
Instantaneous Time-averaged Both
Method of background
correction
Background O2 and/or
CO2 flux monitoring14C
Background CO2 efflux
monitoring
20Delivering Sustainable Solutions to Complex Local Challenges, Worldwide© 2017 CH2M
Methods Summary (continued)
Gradient Passive Flux TrapDynamic Closed
Chamber
Spatial coverage/data
densityLow Moderate High
Real-time dataYes, using field gas
analyzerNo Yes
Laboratory analysis Optional Yes No
Field labor intensity High Low Moderate
Relative one-time
implementation cost
$$$
($-$$ existing probes &
field analyzer)
$$ $
21Delivering Sustainable Solutions to Complex Local Challenges, Worldwide© 2017 CH2M
Emerging Method
• Biogenic heat
22Delivering Sustainable Solutions to Complex Local Challenges, Worldwide© 2017 CH2M
Closing
• New API NSZD guide will be available
online soon
• Written to be useful for regulators, owners,
and practitioners alike
• Many options to consider and results to
anticipate
• Practical guidance for:
– NSZD screening
– Method and procedure decision support
– Field work design and implementation
– Data analysis
Thank you!
© 2017 CH2M
Fourth International Symposium on Bioremediation and Sustainable Environmental Technologies
Tom Palaia
Chief Technologist
Julio Zimbron
Founder
Eric Nichols
Principal
24Delivering Sustainable Solutions to Complex Local Challenges, Worldwide© 2017 CH2M
• Tom Palaia, CH2M
tom.palaia@ch2m.com
(303) 679-2510
• Julio Zimbron, E-Flux
jzimbron@soilgasflux.com
(970) 492-4343
• Eric Nichols, Substrata
eric@substrata.com
(603) 770-6577
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