LNAPL Recovery and Remedy Transitions A Case Study at a Railyard Fueling Facility

Transcription

1 LNAPL Recovery and Remedy Transitions A Case Study at a Railyard Fueling Facility Jeremy Coughlin and LeeAnn Thomas, CP Andy Pennington and Dawn Gabardi, Arcadis

2 SITE BACKGROUND AND LCSM CP acquired the railroad property in Site investigation/characterization Diesel LNAPL near fueling and wastewater facilities

3 REMEDIAL OBJECTIVES No immediate LNAPL-related risks o Limited, stable dissolvedphase impacts o No groundwater or vapor-phase receptors; no off-site impacts Mobile NAPL occurrence concerns drive objectives State regulations require that all free product present in the mobile phase be recovered or treated to the extent technically feasible Risk and Safety Concerns Fire/Explosion hazards Human or ecological exposures Mobile LNAPL Occurrence Concerns Measurable LNAPL in monitoring wells Requirement to recover LNAPL to maximum extent practicable LNAPL Migration Concerns Ongoing/continuing release Migration of LNAPL to new areas or offsite Other LNAPL Concerns Staining or odors Stakeholder perceptions Geotechnical concerns Adapted from ITRC LNAPL Update

4 LNAPL REMEDIAL EFFORTS Excavation Bioventing system Vacuum-enhanced Skimming LNAPL skimming system Manual removal/recovery High-vacuum extraction Bailing and Socks (interim steps) Methods and approach adapted based on results and recovery

5 LNAPL SKIMMING & BIOVENTING Skimmer system installed 2011, with recovery rates tracked by well Vacuum enhancement in blower connected to subsurface piping/wellheads No significant increase in LNAPL recovery, but significant benefit via bioventing (tracking CO 2 effluent) Performance Indicators LNAPL Recovery Rates and Volume LNAPL Transmissivity Biodegradation Rates

6 FUELING AREA EXCAVATION Upgrades in 2015 removed buried piping and ~ 6,600 tons of impacted soil Excavation to 10 feet in main fueling area, 5 feet along buried piping runs Removed ~ 58,000 lbs (8,000 gals) diesel petroleum hydrocarbons

7 FUELING AREA Current layout (2016)

8 LNAPL RECOVERY Recovery/Removal Method Total Volume (gallons) Years Active Manual/periodic removal present High-vacuum extraction 1, LNAPL Recovered (Gallons) LNAPL Recovery via HVE (per event) Aug-10 Feb-11 Sep-11 Apr-12 Oct-12 May-13 Skimming Bioventing/vacuumenhanced biodegradation Excavation/Soil Removal in Fueling Area 1, present 8, LNAPL Recovered (Gallons) LNAPL Recovery via Skimming (per year)

9 LNAPL RECOVERABILITY METRICS T n as a Threshold Metric: Is action warranted to address concerns? 2012 T n between 2 and 10 ft 2 /d in center of area 2013 and 2014 low T n around perimeter of LNAPL T n as a Performance Metric: Is action beneficial and still needed? T n calculations from skimming data 2017 two rounds of baildown tests Results within or below ft 2 /d range LNAPL recovery data corroborate transmissivity results - readily recoverable LNAPL has been removed.

10 LNAPL & DISSOLVED-PHASE FOOTPRINT OVER TIME LNAPL footprint consistent year-overyear; LNAPL is not expanding or migrating Consistent footprint around LNAPL areas; Downgradient wells are consistently below standards

11 NATURAL SOURCE ZONE DEPLETION ASSESSMENT 2016 Estimated Total LNAPL Removed since 2010 How does natural degradation compare to feasible recovery rates? Measured CO 2 flux at 30 locations with a flux chamber and 8 locations with time-averaged sorbent traps Conducted after Fueling Area excavation 8,200 gal Excavation 3,600 gal Other Remedial Efforts NSZD rate ~ 1,500 gal/ac/yr 3,000-4,000 gal/year sitewide (vs. ~640 gal/yr from other remedies) Natural LNAPL losses since 2010 on the order of 20,000 gallons ~20,000 gal NSZD 20,000 gal

12 TREATMENT TRAIN CONCEPT As remediation progresses, different technologies become more suited to reaching project goals Threshold/performance metrics and LCSM guide remedy selection and transition LNAPL Removed (Gallons) Cumulative LNAPL Removal Totals (2010-) NSZD HVE Skimming Excavation Bioventing Manual Removal Characterize Concerns/Objectives; Short-term Response Address Mobile LNAPL Occurrence Concerns and Regulatory Requirements with LNAPL Mass Removal Transition to lowerenergy, phase-change technologies NSZD underlies all efforts and is the final technology in the treatment train Layered technologies help match resource use to risk and goals

13 CURRENT STATUS; LOOKING BACK Transition to NSZD Working with agency to establish that policy requirements are met What would we have done differently in retrospect? o Early definition of endpoints o More use of T n as a performance metric o Define strategy and goals to agency and anticipate questions Technologies and Metrics Used Concern Technology Data/Metrics Informing Selection and Transition LNAPL Migration Recoverable LNAPL in Wells Non-recoverable but mobile LNAPL Short-term containment or recovery Skimming, Manual Removal, NSZD Site Characterization Fluid Level Monitoring Short-term recovery data LNAPL Transmissivity Recovery Decline Curves NSZD rates Bioventing, NSZD CO 2 production NSZD rate measurements Ratio of active recovery to NSZD Residual LNAPL presence NSZD NSZD rate measurements

14 QUESTIONS & DISCUSSION