Remediation is Enhanced Oil Recovery: Know Your Source G.D. Beckett, R.G., C.HG. A QUI- V ER, INC. & SDSU

Which Scenario Works Best? Oil

It’s Sort Of Obvious.. E&P expends effort knowing oil distribution –Aim for the oil –Missing the oil misses revenues Environmental restoration has a more spotty record –Sampling difficulty below water tables –Some misnomers & misconceptions about NAPL Thickness exaggeration Sorption vs. residual –Dissolved-phase thinking –Hydrologic time bias in most environmental data sets

Talk Outline A few source principles & observations –Chemistry will not be discussed –Focus is source location relative to cleanup mechanisms Site examples where the source zone was missed Site example where source zone was pegged Conclusions

NAPL is the Source of Risk Gasoline LNAPL Mass Water, Vapor & Sorbed Mass Equivalent Volumes

Schematic of LNAPL Source Distribution IIIIII IVV I II III IV V

Equilibrium LNAPL Saturation (uniform dune sand) Hydrocarbon Saturation Z above oil/water interface (ft) Predicted Saturations Measured Saturations LNAPL

Hydrocarbon Saturation Z Above Oil/Water Interface (cm) Measured Predicted H 2 O LNAPL LNAPL Saturation in Heterogeneous Soil (interbedded silty sands and sand) after Huntley et al., 1997

PHOTOGRAPH OF NAPL GANGLIA Courtesy of Daugherty & Peuron; Orange County Health Care Agency

Courtesy of Terra Tek, Salt Lake City, UT A Peak Into the Pore Domain (brine to oil mobility spectrum)

The Sites Two Misses & One Hit Site 1: Service station adjacent to tidal stream –Tidal influence affects product distribution & cleanup –Several years of cleanup have not changed gw impacts Site 2: Service station with deep vadose zone –Rise in gw table strands product –5 years of cleanup with no meaningful gw benefit Site 3: Former fuel terminal with effective targeting –Dewatering with enhanced airflow delivery –Source zone characterization was key to success

SITE 1 Gasoline LNAPL Adjacent to Tidal Stream

Site Plan & Plume Map gw flow

LNAPL Source & Geologic Distribution (after the fact) SectionDistance(ft) LIFIntensityContour CPTGeologicValue Clays Silty SiltySand Sand Sand CB-1CB-3CB-4CB-7CB-6CB-10

Remediation Actions Horizontal IAS, 18 fbg, uncontrolled flow responses –Airflow in creek –No direct capture by SVE SVE from available wells, pulling upper zone Groundwater pumping & skimming Combined SVE & groundwater recovery

Remediation Results after 7 years Free product thickness decrease in wells –Product still present at low water stands No statistical reduction in gw concentrations Product discharges to adjacent creek –Despite hydraulic containment in water phase System upsizing to pump more water –Increase drawdown into deeper impact zone –Force airflow into dewatered zone

SITE 2 Stranded LNAPL from Groundwater Rise No gw benefit from SVE & Pumping

Site Plan & Initial Plume Distribution

Schematic Cross-Section Dispensers SVE & Pumping Well Sandstone Shale F.P. Zone UST

Site Groundwater Elevation Hydrograph

SVE/P&T System Summary; Low flow gw pumping planned (< 2 gpm) –Never really ran much, head loss issues –No effective dewatering –Water level rise over period of cleanup SVE from multilevel screens –Packers not maintained by new contractor –SVE from full interval –> 10,000 ppmv TPH initial to 500 ppmv final –However, discrete well sampling = 9,600 ppmv final

Chemical Hydrograph, Sentry Well MW-8

Site Plan & Post SVE/Pumping Plume

Site Plan & Initial Plume Distribution

Site 2 Wrap Up Water table rose –No effective dewatering of smear zone SVE did not access full smear zone –Ran to asymptotic –Lower zone pneumatically inefficient Dissolved concentrations unchanged at key points Despite this, no risk & site obtained NFA status

Fuel Terminal & Operations Site LNAPL Smear Found & Targeted Highly Effective Remediation Response

General Site Conditions AST & terminal operation sources Heterogeneous, interbedded fine materials Water table approx. 15 feet below grade (fbg) Observed free product gasoline in 12 wells Widespread dissolved phase impacts –Initial TPHg max = 500,000 ug/L –Initial Benzene max = 58,000 ug/L –Initial MTBE max = 24,000 ug/L

Site Plan; Plume Width  600 ft

Original Lithology & Source Understanding

Section Distance (ft) Elevation (ft msl) Clays/silts Updated Source & Lithologic Setting LNAPL zones Sands Silty Sands

Changes in Thinking LNAPL stranded below, not at the water table Original design unable to access impacted zones Went to dewatering, enhanced airflow strategy –Specific target = smear zone Large improvement in subsurface cleanup efficiency Large improvement in mass per unit time per cost

Estimated Cleanup Improvement Factor (multiphase calculations) Mass Recovery Improvement Factor Stratigraphic Elevation (m) Area #1 Area #2

MTBE Through Remediation

Benzene Through Remediation

Recovery to Date Full hydraulic capture 400,000 lbs TPH recovered over 6 months –18,000 as free phase; 2,000 in water phase; 15,000 in biodecay; 365,000 in vapor phase Free product no longer observed in cleanup area –80-day removal, multiphase estimate was 2-3 months Orders of magnitude reduction in MTBE & benzene –On average and against pre-cleanup maximums –Mole fraction changes consistent with principles

Conclusions Targeting depends first on knowing smear zone –Common limitations to characterization efforts –Like E&P, no oil, no production Efficient designs directly access smear zone –Geologic efficiency is order of magnitude Tracking of success is fairly straightforward –Chemical milestones, molar & otherwise –Physical relationships between fluid zones No matter what, you cannot have it all –Some soil zones won’t produce in any phase –Always uncertainty in geologic distributions