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Protection of Groundwater and Surface
Water at a Bulk Explosives Facility Using
Calculated Risk-based Soil Guidelines
Presented to: Water Technologies Symposium 2012
Presented by: Liza Flemming, P.Geol. (AB , BC), HEMMERA
April 12, 2012
Agenda
Background, Regulatory Framework, Mine Closure Strategy
Site Investigation History, Identification of Risk, Aquatic Receptors
Site-Specific Remedial Objectives – Calculation, Implementation, Results
Successful Outcomes
Site Location – Near Mackenzie, BC
Mine Site Overview
Mine Site Layout
Risk-Based Mine Closure Strategy
2008 BC Environmental Management Act
Risk-based remediation,
reclamation, and closure
Investigation
RAP and Risk
Assessment
Limited remediation
Reclamation and closure
Mine Site Reclamation and Closure Strategy
Remedial Planning and
Risk Assessment
Physical Remediation
Monitoring and Mine
Reclamation
Site Investigation
BXL Facility Site Background and Setting
Bulk explosives fabrication to support
mining activities,1990s to 2010
ammonium nitrate and diesel
Part of 2010 mine site investigation
Soil, groundwater, remedial planning, and
Risk Assessment
BXL Investigation and Risk Assessment –
2010/2011
Soil Investigation Characterized AN
concentrations above
background
Groundwater Several locations exceed BC
CSR for ammonia and/or nitrate
Screening Level Risk
Assessment Defined receptors and
pathways for AN contamination
Screening Level RA: Site Hydrogeology and
Potential Receptors
Complex local hydrogeology Unconfined sand and gravel aquifer – low yield
Seep flow and discharge to Kemess Creek
Multiple aquatic receptors Ecological in and around Kemess Creek
Drinking water users
No soil receptors Risk eliminated via
reclamation
Risk Assessment Findings and Remedial
planning for AN
AN concentrations
cause adverse risk to
aquatic receptors Additional remediation
required
Mine Site Reclamation and Closure Strategy
Remedial Planning and
Risk Assessment
Physical Remediation
Monitoring and Mine
Reclamation
Site Investigation
AN Impacts – on-site sources
Implementing Mine Site Remediation
Objectives at the BXL
Maintain limited scope – avoid
digging up entire site
Soil source removal = 1500 m3?
Groundwater remediation?
No provincial, Federal soil
standards for AN
Soil is the source for AN aquatic risk
Find threshold AN concentration for
soil that will protect aquatic
receptors
Limited in scope, areal
extent
Primarily risk-based
Protect human and ecological
receptors
Calculating Site-Specific Remediation
Objectives
1. Ammonia (EPA 1996)
Where:
CS = Leaching-Based Soil Value (mg/kg)
CW = Groundwater Quality Standard (mg/L)
Kd = soil/water partitioning coefficient (L/kg)
EW = water-filled soil porosity (Lwater/Lsoil)
ρb = dry soil bulk density (kg/L)
DAF = Dilution Attenuation Factor (unitless)
Ammonia SSRO calculation
Assumptions
CW = Groundwater Quality Standard = 10 (mg/L)
Kd = soil/water partitioning coefficient = 1.5 (L/kg)
EW = water-filled soil porosity = 0.02 (L water/L soil)
ρb = dry soil bulk density= 1.6 (kg/L)
DAF = Dilution Attenuation Factor = 10 (unitless)
Nitrate SSRO
2. Nitrate (Kansas 2010)
No soil partitioning coefficient (Kd ) values
greater than zero – can’t define a leaching-
based soil standard
Limited options in North America…
KDEH and Kansas State Agronomy risk-
based standards – variation of EPA 1996
method
Site Specific Remedial Objectives
Vegetated Areas
Upper 0.6 m total
nitrate+ammonia (as N)
> 0.6 m total
nitrate+ammonia (as N)
Total ammonia
200 mg/kg 40 mg/kg 143 mg/kg
Non-Vegetated Areas
Upper 0.2 m > 0.2 m Total ammonia
85 mg/kg total
nitrate+ammonia (as N)
40 mg/kg total
nitrate+ammonia (as N)
143 mg/kg
Implementation of Physical Remediation
Plan
Source removal using SSROs as
guidelines
Targeted excavations, limited extent
field screening
Characterize impacts with test pits
Surface to depth, field screening for AN
concentrations
Remediation and Application of Site-Specific
Objectives
Remediation and Application of Site-Specific
Objectives
Five excavation areas and 13 delineation
test pits
Confirmatory samples collected from
excavation walls and/or bases
Receptor-pathway analysis
Groundwater sampling and toxicological
surface water markers
Achievement of Mine Site Remediation
Objectives
Mine Site Reclamation and Closure
Strategy
Remedial Planning
Physical Remediation
Monitoring and Mine
Reclamation
Site Investigation
Limited in
scope, areal extent
Primarily
risk-based
Protect
human and ecological receptors
Successful Outcomes of Remediation
Program
400 m3 of AN impacted soil removed
rather than >1200 m3
Complete source removal using SSROs
Achieved protection of aquatic receptors
Questions? Thank You!
Liza Flemming, P.Geol. (AB, BC, NWT/NT)
Project Geologist
403.410.3828
Hemmera.com
Calgary | Vancouver | Burnaby | Victoria
