LNAPLTransmissivity (Tn)

R e m e d i a ti o n D e s i g n , P r o g r e s s a n d E n d p o i n t s

H2A Environmental, Ltd.

J. Michael Hawthorne, P.G.mhawthorne@h2altd.com

www.h2altd.comSeptember 2010

Outline

• LNAPL multi-phase fluid mechanics review

• LNAPL metrics review

• LNAPL transmissivity (Tn) principles

• Applicability

• Summary

Intr

oduc

tion

LNAPL at the Pore Scale

• LNAPL co-exists with water in aquifer pores

• LNAPL only partially fills the aquifer pore space

• The degree of LNAPL saturation depends upon lithology and fluid properties

Sediment GrainsWetting Fluid (Water)

Non-Wetting Fluid (Air or LNAPL) Filling Large Pore Spaces

Mul

ti-Ph

ase

Flui

d M

echa

nics

RTDF 2006

Ideal vs. Observed LNAPL Saturations

RTDF 2006

Mul

ti-Ph

ase

Flui

d M

echa

nics

Saturation curve height = thickness of mobile LNAPL interval

T vs. Tn / Tn vs. Sn

• Transmissivity (T) for water– Unit cross-section, gradient, time– Aquifer thickness

– Single fluid (krw drops out)

• LNAPL Transmissivity (Tn)– Unit cross-section, gradient, time– Mobile LNAPL interval thickness

– Multi-fluid (krn matters)

w

rwww

gkkK

n

rnnn

gkkK

bKT ww

nnn bKT

Mul

ti-Ph

ase

Flui

d M

echa

nics

“How Much, How Fast”

Ideal LNAPL Metric

• Collective property incorporates: – Aquifer properties (e.g., permeability)

– Aquifer type (sand vs. clay)

– LNAPL properties (e.g., viscosity)

– LNAPL type (condensate vs. crude oil)

• Fundamental or characteristic property – Repeatable

• Saturation / mass driven

• Easy and cheap to measure

LNAP

L M

etric

s

Non-Ideal Metrics - ThicknessLN

APL

Met

rics

• Same mass exhibits different thicknesses in different soil types

• Inconsistent under varying hydrostatic conditions

Modified after RTDF (2006)

Modified after Kirkman (2009)

Non-Ideal Metrics – Recovery DataLN

APL

Met

rics

Benefits• Direct measure of remediation

performance

• Provides predictive data for decline curve analysis

Problems

• Strongly affected by system operational settings

• Varies by technology – not directly comparable

• Can’t be used to predict performance prior to startup

Tn – An Improved Metric

Tn Advantages

• Direct numeric measure of hydraulic recoverability

• Varies directly with LNAPL saturation / mass

• Normalizes all sites to a single measurement standard

• Multiple Methods

• Measurable prior to, during and after remediation

LNAP

L M

etric

s

LNAPL Transmissivity (Tn)

• Analog to aquifer transmissivity• Provides basis for mobility /

recoverability analyses• Four measurement methods

– Baildown / skimming tests– Recovery data analysis

• skimming• Vacuum enhanced skimming• Total fluids pumping• Multi-phase extraction

– Physical properties / modeling– Tracer tests

• Hydraulic recovery only• Dissolved and vapor phase risk

issues are separateTran

smis

sivi

ty (T

n) Prin

cipl

es

Applicability – Uses for Tn

1. Alternative to laboratory Sn

2. Model calibration parameter3. Technical impracticability threshold4. Remediation design parameter5. Operational progress metric6. Recovery end point

Appl

icab

ility

Applicability - TI DemonstrationAp

plic

abili

ty

3. Technical Impracticability (TI) requires either:– Recovery system data

• “Can I please turn it off now?”• Direct recoverability threshold metric

– Data from a pilot test and modeling study• “Can I please not turn it on?”

• Robust calibration parameter for TI modeling

Applicability – Remediation Design

4. Remediation design parameter– Compare different technologies (calibrated model)

• Technology-specific production curves• Predicted rate and total volume decline curve analyses• Sustainability

– Design parameters• Equipment sizing• Waste management / recycling volumes

– Design cost-benefit analysis• Projected operational lifetime• Capital vs. mobile infrastructure

Appl

icab

ility

Applicability – Operational Progress5. Operational Progress Metric

– Recovery data decline curve analysis (progress towards endpoint)

– Non-recovery wells to monitor plume progress to endpoint

Appl

icab

ility

Tn Endpoint Analysis

6. Hydraulic recovery end point (0.3 to 0.8 ft2/day)

Appl

icab

ility

(Kirk

man

201

0)

Tn Endpoint AnalysisAp

plic

abili

ty

Summary

• Tn is an improved metric for hydraulic recoverability

• Four calculation methods:– Baildown / manual skimming testing– Recovery data analysis– Physical properties analysis– Tracer testing

• Tn use as a metric– Indirectly as a robust model calibration parameter– Directly as a recoverability threshold (0.3-0.8 ft^2/day)

• Remediation and Tn

– TI threshold– Design parameter – End point for hydraulic recovery

Sum

mar

y