Protection of Groundwater and Surface Water at a Bulk Explosives Facility Using Calculated Risk-based Soil Guidelines

Transcription

1 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

2 Agenda Background, Regulatory Framework, Mine Closure Strategy Site Investigation History, Identification of Risk, Aquatic Receptors Site-Specific Remedial Objectives Calculation, Implementation, Results Successful Outcomes

3 Site Location Near Mackenzie, BC

4 Mine Site Overview

5 Mine Site Layout

6 Risk-Based Mine Closure Strategy 2008 BC Environmental Management Act Risk-based remediation, reclamation, and closure Investigation RAP and Risk Assessment Limited remediation Site Investigation Reclamation and closure Remedial Planning and Risk Assessment Mine Site Reclamation and Closure Strategy Monitoring and Mine Reclamation Physical Remediation

7 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

8 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

9 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

10 Risk Assessment Findings and Remedial planning for AN AN concentrations cause adverse risk to aquatic receptors Additional remediation required Remedial Planning and Risk Assessment Site Investigation Mine Site Reclamation and Closure Strategy Physical Remediation Monitoring and Mine Reclamation

11 AN Impacts on-site sources

12 Implementing Mine Site Remediation Objectives at the BXL Limited in scope, areal extent Maintain limited scope avoid digging up entire site Soil source removal = 1500 m 3? Groundwater remediation? Primarily riskbased No provincial, Federal soil standards for AN Soil is the source for AN aquatic risk Protect human and ecological receptors Find threshold AN concentration for soil that will protect aquatic receptors

13 Calculating Site-Specific Remediation Objectives 1. Ammonia (EPA 1996) Where: C S = Leaching-Based Soil Value (mg/kg) C W = Groundwater Quality Standard (mg/l) K d = soil/water partitioning coefficient (L/kg) E W = water-filled soil porosity (Lwater/Lsoil) ρ b = dry soil bulk density (kg/l) DAF = Dilution Attenuation Factor (unitless)

14 Ammonia SSRO calculation Assumptions C W = Groundwater Quality Standard = 10 (mg/l) K d = soil/water partitioning coefficient = 1.5 (L/kg) E W = water-filled soil porosity = 0.02 (L water/l soil) ρ b = dry soil bulk density= 1.6 (kg/l) DAF = Dilution Attenuation Factor = 10 (unitless)

15 Nitrate SSRO 2. Nitrate (Kansas 2010) No soil partitioning coefficient (Kd ) values greater than zero can t define a leachingbased soil standard Limited options in North America KDEH and Kansas State Agronomy riskbased standards variation of EPA 1996 method

16 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

17 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

18 Remediation and Application of Site-Specific Objectives

19 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

20 Achievement of Mine Site Remediation Objectives Remedial Planning Limited in scope, areal extent Site Investigation Mine Site Reclamation and Closure Strategy Physical Remediation Primarily risk-based Monitoring and Mine Reclamation Protect human and ecological receptors

21 Successful Outcomes of Remediation Program 400 m 3 of AN impacted soil removed rather than >1200 m 3 Complete source removal using SSROs Achieved protection of aquatic receptors

22 Questions? Thank You! Liza Flemming, P.Geol. (AB, BC, NWT/NT) Project Geologist Hemmera.com Calgary Vancouver Burnaby Victoria