Refining NAPL distribution using FLUTeTM liners Tamie R Weaver, ERM, Melbourne Mike Mercuri, Matrix Drilling, Melbourne Steve McKeown, ERM, Cape Town Joe Fiacco, ERM, Boston Lance Robert, ERM, Barcelona Abstract E111 The world’s leading sustainability consultancy Dr Weaver is a technical director in hydrogeology at ERM in Melbourne. She has many years’ experience as a university lecturer and consultant hydrogeologist assessing the fate and transport of contaminants in groundwater from contaminated sites, waste facilities and in the natural environment. Presenting on behalf of colleagues within and outside of ERM in Australia and overseas. Mike Mercuri – Matrix Drilling Steve McKeown – ERM Cape Town Joe Fiacco – ERM Boston Lance Robert – ERM Barcelona The world’s leading sustainability consultancy Assess Risks and Inform Remediation ■ Extent and distribution of contamination ■ Non aqueous phase liquids (Light vs Dense, mobile vs residual) ■ Type and extent of dissolved phase contamination ■ Contaminant storage vs contaminant transport ■ Preferential pathways for contaminant migration vs storage in the rock matrix ■ Maturity of the plume ■ Is the plume expanding, stable, or declining ■ Is NAPL still present ■ Transfer of contaminants to vapour / surface water (exposure pathways and risks) ■ Address regulatory requirements (e.g. remaining NAPL in aquifers) The world’s leading sustainability consultancy CSM and Remediation Where is contaminant stored / transported? Areas and methods for remediation? The world’s leading sustainability consultancy Investigations in Fractured Rock ■ Increased uncertainty / complexity regarding contaminant distribution ■ Exacerbated if LNAPL or DNAPL are present ■ Difficult to predict behaviour away from investigated area ■ Small features can be important Uncertainties drive ■ “More targetted” assessment – technologies such as FLUTe, downhole logging, passive flux meters, short screened / multilevel wells, targetted aquifer testing, bail-down testing ■ Distribution and occurrence of NAPL, dissolved phase The world’s leading sustainability consultancy FLUTeTM liners – NAPL Distribution Apply to an open borehole before well construction ■ NAPL FLUTeTM (identify where non-aqueous phase liquid is present in the borehole) ■ Identify zones, layers, filled fractures or globules of NAPL ■ Assess NAPL as ongoing secondary source zone away from primary source ■ Identify NAPL in unsaturated zone ■ Does not address whether remaining Hydrocarbon NAPL is mobile or residual stainingg ■ Potential to “smear” NAPL during drilling The world’s leading sustainability consultancy Considerations “Standard” wells ■ Sample extended part of aquifer ■ Where did NAPL (usually LNAPL) enter well from? ■ Does same feature / unit host NAPL at different locations? LNAPL on water table in well NAPL FLUTe Liners ■ FLUTe identifies specific areas where NAPL is present in borehole ■ May / may not relate to recoverable / mobile NAPL ■ Compare occurrence across different locations. ■ Unsaturated zone assessment LNAPL in formation (unsaturated zone) The world’s leading sustainability consultancy Petroleum Release Site Objectives: ■ Contaminant Migration ■ Risk to Aquifers ■ LNAPL Recoverability Multiple techniques ■ ■ ■ ■ ■ ■ ■ Geological mapping Surface geophysics Coring Downhole geophysics Packer tests NAPL FLUTeTM Monitoring wells The world’s leading sustainability consultancy NAPL FLUTeTM Liner Installation and Staining The world’s leading sustainability consultancy ■ NAPL distribution – discrete zones related to fracturing and bedding planes ■ Not a “pool”, but contained within vertically discrete and laterally defined transmissive fractured zones ■ Combine with other assessments to refine CSM The world’s leading sustainability consultancy Outcomes Refined Conceptual Site Model ■ Identified transmissive fracture zones: 3.5 – 5 mbgl; 14 – 19 mbgl; and 46 mbgl ■ Very limited hydraulic connection between the two shallow sets (5 and 15 mbgl) and deep (46 mbgl) transmissive fracture sets ■ Lateral migration of LNAPL in 2 shallowest bedding-plane fracture zones, not in deepest fracture set (NAPL FLUTe) ■ Delineate lateral and vertical extent of LNAPL (NAPL FLUTe) Risks and Risk Mitigation ■ Replaced drinking water supply well – now drilled to deeper part of aquifer ■ Identified areas of potential vapour risk based on LNAPL extent. The world’s leading sustainability consultancy Example: Chlorinated hydrocarbons in groundwater Site Conditions ■ Fractured siltstone and sandstone ■ TCA concentrations in groundwater to 30-50% solubility of TCA ■ No evidence of DNAPL in wells Issues ■ ■ ■ ■ Is DNAPL actually present? How extensive, how thick, where in the aquifer? Where to focus remediation? Type of remediation to implement? The world’s leading sustainability consultancy Example: DNAPL site 12 m Residual DNAPL Zone (approximately 10 m deep) DNAPL staining on NAPL FLUTe liner Monitoring well NAPL FLUTe, no staining NAPL FLUTe, staining The world’s leading sustainability consultancy Verifying FLUTe liner results ■ Comparison with downhole logging ■ Care re spread of DNAPL in the borehole during drilling ■ Comparison with dissolved phase TCA concentrations ■ >10% concentrations, DNAPL identifiable in the borehole (FLUTe and borehole imaging) ■ ~1-2% concentrations, DNAPL was not identified in the actual borehole ■ Targetted remediation depth. DNAPL absent in shallow aquifer The world’s leading sustainability consultancy Conclusions Groundwater contamination in fractured rock systems is complex ■ exacerbated with presence of LNAPL and/or DNAPL Combined tools, including FLUTe, coring +/- downhole logging with dissolved phase clarify extent and form of NAPL occurrence ■ Move away from the concept of a “pool” of NAPL. ■ NAPL focussed along transmissive zones ■ trapped in pores / dead end fractures ■ Clearer indication of form / extent of NAPL in aquifer ■ More informed decisions regarding risk management ■ More informed decisions about effective remedial approaches The world’s leading sustainability consultancy Thank you 16 The world’s leading sustainability consultancy
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