Rethinking LNAPL Recovery Metrics. Delivering sustainable solutions in a more competitive world

Transcription

1 Rethinking LNAPL Recovery Metrics

2 Overview LNAPL Concepts LNAPL Mobility/Recoverability Implications for LNAPL Remediation LNAPL Resources

3 LNAPL Concepts

4 Simplified Subsurface LNAPL Processes Release Source Vapor Phase LNAPL Dissolved Phase Source: Modified from Huntley and Beckett, 2002

5 Well Thickness vs Formation Thickness Visible Light UV Light LNAPL Groundwater Source of Photos: Kirkman

6 LNAPL Saturation Source: Modified API, 2004

7 Saturation Profile Shark s Fin Air-Oil Interface Free Oil Saturation Profile in Aquifer Mobile LNAPL Theoretical Air-Water Interface Observed Monitoring Well Product Thickness Residual LNAPL 0 Oil Saturation (% Pore Space) Oil-Water Interface Source: Modified API, 2004

8 LNAPL Saturation in Homogenous Soils AIR Silts Fine Sand Coarse Sand LNAPL Source: Modified API, 2004

9 LNAPL Saturation in Homogenous Soils Homogenous soils Shark s Fin Heterogeneous soils (Inter-bedded silt and sand) City Skyline Sand Silt Sand Source: Modified API, 2004

10 Gauged LNAPL Thickness in Heterogeneous Soil Types Source: AFCEE, 2010

11 Gauging Data There are several inaccurate conceptual views regarding gauged LNAPL thickness that include: LNAPL thickness measured in a well is always representative of what is in the formation LNAPL thickness in a well directly relates to the rate of potential recovery LNAPL thickness in a well directly relates to the total recoverable volume Changes in LNAPL thickness always indicate redistribution of LNAPL laterally

12 The Main Point.. Unless conditions are ideal, the gauged LNAPL thickness in monitoring well is generally a poor metric to evaluate site conditions and make remedial decisions.

13 LNAPL Mobility/Recoverability

14 LNAPL Saturation/Transmissivity The zone of highest LNAPL saturation has the highest LNAPL conductivity Low LNAPL saturation results in low LNAPL conductivity Vertical equilibrium (VEQ) conditions in a sand tank LNAPL Transmissivity = Sum Hydraulic recovery rate is proportional to transmissivity for a given technology LNAPL Tn is a direct measure of the recoverability and reflects the degree of impact (saturation)

15 Estimating Transmissivity ASTM E Raw results from baildown tests Recovery system performance Skimming well Dual pump system Source: ASTM Standard Guide for Estimation of LNAPL Transmissivity E

16 LNAPL Baildown Test DTP DTW POTENT SURF C90-98 Initial DTW Initial DTP LNAPL THICKNESS LNAPL thickness in well

17 API Baildown Test Analysis Excel Based Tool User Friendly Available on API website

18 LNAPL Mobility/Recoverability Pilot Tests Skimming Tests Essentially continuous baildown test Calculate transmissivity Observe reductions in recovery Pumping Tests Determine oil/water recovery ratios Calculate transmissivity

19 LNAPL Mobility/Recoverability LDRM LNAPL Distribution and Recovery Model (LDRM) Benefits Paradigm Change - Old Measurable product = recovery - New Measurable product = possible recovery Estimates of recovery volume - Total recoverable volume - Analysis of skimming vs. dual pump vs. vacuum enhanced Caveats Screening level models Applicable only to unconfined aquifers & LNAPL Not a magic bullet Limited regulatory approval

20 Implications for LNAPL Remediation

21 Mobile Oil Volume (gallons) Negative Consequences Pancake layer approach can lead to significant overestimation of total LNAPL volume Well thickness may not dictate relative recoverability Recovery wells focus remedial efforts on wrong area of the site and perform poorly Remedial objectives are based on a thickness objective that is likely not achievable 10,000 9,000 8,000 7,000 6,000 5,000 4,000 3,000 2,000 1,000 0 Coarse Sand Fine Sand Silt Pancake

22 Recovery Focused Remedial Actions Baildown tests provided data to estimate LNAPL recoverability Three different wells at same site Each well had considerable measured LNAPL thicknesses, but. Wells had very different LNAPL transmissivity values Recommendation was to focus recovery on well with lower LNAPL thickness Approximate Gauged Thickness Recovery Rate Based on Baildown Test Data 1 GPM - Water Enhanced Recovery (GPD) LNAPL Transmissivity Location (ft) LNAPL Skimming (GPD) (ft 2 /day) MW MW MW Source: AFCEE, 2010

23 Recovery Focused Remedial Decisions Source: AFCEE, 2010

24 Recovery vs. Thickness WATER ENHANCED RECOVERY AT 1 FOOT OF DRAWDOWN (GPD) LNAPL SKIMMING RATE (GPD) GAUGED LNAPL THICKNESS (FT) Source: AFCEE, 2010

25 Recovery vs. Transmissivity WATER ENHANCED RECOVERY AT 1 FOOT OF DRAWDOWN (GPD) LNAPL SKIMMING RATE (GPD) LNAPL TRANSMISIVITY (FT2/DAY) Source: AFCEE, 2010

26 Remedial Endpoints Defines endpoints of recovery Identifies when hydraulic/pneumatic recovery is complete Possible closure for sites where residual LNAPL does not pose a risk to receptors Refocuses remedial efforts for sites where residual LNAPL risk to receptors exists Directly related to remaining mobile LNAPL volume Referenced in ITRC LNAPL guidance (2009) Transmissivities between and 0.07 m 2 /day Further reductions can be inefficient, costly, and may be of limited use in reducing LNAPL mass, migration potential, or longevity

27 Remedial Endpoints Source: AFCEE, 2010

28 Tier 3 Tier 2 Tier 1 Tiered Approach Field Data Laboratory Analyses Data Analysis Gauging data Slug Test Baildown testing (one test per well) Continuous soil boring logs LNAPL and water density Vertical distribution of LNAPL LNAPL transmissivity estimates Estimate initial technology LNAPL recovery rates Evaluate historical recovery data If system exists Baildown testing (multiple tests per well) Direct push borings (LIF, MIP) Pilot test single technology Baildown/ manual skimming Testing Grain size analyses (multiple tests over time) Intrinsic permeability Soil core borings Soil core photography Pilot testing multiple technologies Soil core analyses Aquifer pump tests Fluid interfacial/ & surface tensions Gas chromatogram of LNAPL Source: AFCEE, 2010 LNAPL and water viscosity Recovery modeling based on site specific and published values Identification of LNAPL type(s) based on LIF data Recovery modeling to site specific soil core data Estimation of recoverable volumes Identification of LNAPL type(s) based on GC data

29 LNAPL Resources

30 CRC CARE Technical Report 18 (2010) Provides overview of LCSM development process Site Characterization Strategies Investigation Methods Data Presentation and reporting Provides clarity to the site investigation process and development of a robust LCSM. Does not provide remedial alternatives guidance nor define remedial strategies.

31 ITRC Guidance Document (Dec 2009) Promotes principles that facilitate timely and successful LNAPL remediation Characterize the LNAPL site by preparing an LNAPL Conceptual Site Model Establish achievable remedial objectives Establish metrics for each remedial objective Develop a remedial strategy to achieve the objectives Hopefully, achieve an acceptable outcome Provides a framework to set LNAPL remedial objectives and match to goals/metrics for potentially applicable technologies Promotes technology understanding and applicability and aids in the selection of an appropriate remedial technology

32 ASTM LNAPL Tn Standard (updated 2013) Standard for estimation of transmissivity to add weight to the metric Describes how to calculate transmissivity and conduct Baildown tests Skimming tests Slug tests Tracer tests Evaluate recovery system data

33 ASTM LNAPL CSM Standard (likely 2014) Existing LCSM Standard published in 2006 is currently being revised Will define LCSM data requirements and data collection methods possible components include: Site Setting Geology/Hydrogeology LNAPL Chemical/Physical Properties LNAPL Delineation (including mobile and residual LNAPL) LNAPL Body Stability LNAPL Recoverability Dissolved-phase/Vapor-phase Natural Source Zone Depletion

34 Discussion Contact info: David de Courcy-Bower, P.E Milwaukee, WI