Upload
others
View
3
Download
0
Embed Size (px)
Citation preview
What Lies Beneath? High Resolution Site Characterisation Tools
Used to Develop LNAPL Conceptual Site Models
Scott Robinson
Overview
Three Case Studies
Former Depot: end of assessment lifecycle
Active Service Station: middle of assessment lifecycle
Fuel Pipeline: start of assessment lifecycle
THE PROBLEM: LNAPL Observed in a Well
How Much Released? Mobility? Risk? Remediation?
Movement • Mobile
Stationary Migrating
• Immobile Residual (unsaturated) Entrapped (saturated)
LNAPL Condition • Unconfined • Confined * • Perched *
CRC CARE Technical Report No. 19 (2010)
ITRC LNAPL Training Part 1, Internet Training (www.itrc.web.org)
LCSM Key Points:
High Resolution Site Characterisation (HRSC) Tools
Method Target Data MIP (Membrane Interface Probe)
Volatile Organic Compounds (Dissolved phase petroleum and/or Solvents > 100 ug/L)
LIF (Laser Induced Fluorescence)
LNAPL/Residual phase petroleum hydrocarbons (gasoline, diesel, kerosene, jet fuel, etc.)
HPT (Hydraulic Profiling Tool)
Soil hydraulics (pore pressure, soil permeability). Stratigraphy and migration pathways. Screen interval.
4
Define Problem &
DQOs
Field Data & Decisions
3. Analytical Data
Processing 5. Reporting
• Shorter timeframe & less mobilisations.
• Workflow-driven, detailed, and targeted.
Data Gap
Field
Lab Data
Report Traditional
ESA
Case Study 1: Former Depot
Fuel Depot
?
?
Fuel Depot
River
= LNAPL = historical LNAPL
• 2003 decommissioned 7,200 m2 fuel depot
• Seven USTs, three ASTs, fill gantry, interceptor unit, pipe work, fuel bowsers, and fill points
• Fuel depot on adjacent cross-gradient boundary
• Tradition ESA methodology extensive 24 well network
• Semi-confined aquifer at 10 m
• Up to 2 m in-well LNAPL thickness
Case Study 1: Former Depot c
Fuel Depot
LNAPL wells & historical LNAPL wells
LIF Locations (red = peak, green = no peak)
Dissolved Phase Extent New Well
2 m
7 m
6 m & 9 m 13 LIF locations 2 targeted GW wells 4 shallow-deep SV wells
Updated LCSM:
• LIF LNAPL is not as widespread as thought Perched LNAPL =
In-well LNAPL thickness is not formation thickness Targeted wells =
Delineated stable LNAPL & dissolved phase plumes
• No Source-Pathway - Receptor Linkages
• No active remediation required
• EPA ceased regulation
Case Study 1: Former Depot
Case Study 2: Service Station
• Modern service station with a central tank farm (multiwalled tanks + HDPE lines).
• Limited 4 monitoring well network for UPSS monitoring
• 2 m LNAPL detected in MW04 during UPSS gauging
• 5 GW wells and 1 SV well installed
• Confined Aquifer > 3.5 mbgl
• Clay with sand & gravel stringers or lenses
?
?
?
?
?
Case Study 2: Service Station • 5 HPT locations = High variance Clay matrix Sand & Gravel Lenses = low peak
• 15 LIF locations = 7 peaks Largest peaks by fuel lines Both Vadose & Phreatic Zones Associated w/ Sand & Gravel Lenses
= LNAPL Well
= No LIF peaks = LIF peaks
Case Study 2: Service Station
• 5 HPT locations = High variance Clay matrix Sand & Gravel Lenses
• 15 LIF locations = 7 peaks Largest peaks by fuel lines Both Vadose & Phreatic Zones Associated w/ Sand & Gravel Lenses
• 3 Extraction wells for Active Skimming
= LNAPL Well
= No LIF peaks = LIF peaks
Initial SWL range: no mobile LNAPL, entrapped
• Biggest LIF peak does not mean greatest mobile LNAPL or greatest recovery • LNAPL mobility
• SWL = entrapped vs mobile • Geology = permeability of formation: clay vs sand
• Optimization of active skimming system based on LIF and SWLs • Turn system off at high SWL = more targeted remediation
Mobile LNAPL following low rainfall period in 2018 when SWL dropped
Air – Oil Interface
Oil – Water Interface
LIF HPT
LIF
Confined mobile LNAPL
Confined immobile LNAPL
Updated LCSM:
• LIF & HPT Delineate LNAPL in 3 directions Confined LNAPL in sand and gravel lenses = preferential pathways In-well LNAPL thickness is not the formation thickness
• LIF & HPT helped optimize remediation system Groundwater levels affect the mobility & recoverability of LNAPL Current LNAPL Tn values are low and the system is off to assess rebound
• No Source – Path - Receptor linkages
• Remediation not to reduce risk but reduce initial LNAPL migration
Case Study 3: Fuel Pipeline
• Contaminant plume generated by a pipeline release
• No monitoring well network to inform initial investigation
• Man-made fill and shale bedrock
• MIP and LIF to determine extent of contamination
• HPT to understand the stratigraphy and transport pathway(s)
• >21,000 m2 investigation area
Estimated point of release
Case Study 3: Fuel Pipeline Estimated
point of release
To Stormwater Outlet. Product
observed.
Stormwater Drains = Backfill Sands
Drainage gravels and subsoil drains in this zone, near Recreational Area
HRSC Tool Data and Soil Data. • sandy gravelly clay to 4-7 mbgs • shale Delineation achieved but with some anomalies…
2..3 m
4.7 m
4.2 m
Case Study 3: Fuel Pipeline HRSC Tool Data and Groundwater Data Targeted Wells To Stormwater
Outlet. Product observed.
Drainage gravels and subsoil drains in this zone, near Recreational Area
Stormwater line and backfilled channels
Two Water Zones: • Shallow
discontinuous perched =
9 wells
• Deep confined in shale > 7.5 m =
5 wells
2..3 m
4..7 m
Case Study 3: Fuel Pipeline
LCSM:
• HRSC allowed expediated works in 8 months Leak detected and emergency response Delineation of LNAPL & Dissolved Phases
• HRSC tools Clays and shale inhibit lateral and vertical migration Trench backfill = LNAPL preferential pathway. Delineation of impacts
• Evidence for biodegradation from GW and SV
• No complete or potentially complete SPR linkages
• No active remediation required after excavation
> 21,000 m2 investigation area GROUNDWATER SOIL
Traditional ESA
Key Take Away Messages
Define Problem &
DQOs
Field Data & Decisions
3. Analytical Data
Processing 5. Reporting
Data Gap
Field
Lab Data
Report
• Real time data assessment and adjustment of field sample locations
• Robust LCSM Vertical and lateral delineation Hydrostatic condition
• Risk based approach.
• Remediation - Is it required? Targeted?
• Sustainable approach
Reduced mobilisations Decreased exposure to health and safety risks Reduced number of well locations required and targeted
locations Less temporal data required to reach conclusions Less futile efforts to remove LNAPL based on informed LCSMs
CRC CARE Technical Report No. 19 (2010)