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)