Täckning av förorenade sediment internationella erfarenheter och svenska exempel

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1 Renare mark , Oskarshamn Täckning av förorenade sediment internationella erfarenheter och svenska exempel Henrik Eriksson, Golder Associates AB Joe Jersak, SAO Environmental Consulting AB

2 Varför täckning av förorenade sediment? Det är dyrt att efterbehandla mark, men det är gratis jämfört med sediment täckning vs. muddring? Sediment har en fördel. De kan självrena sig Begränsade erfarenheter i Sverige annorlunda bild internationellt 2

3 Sweden s contaminated sediment problem Bigger, more widespread than you may think Both inland and coastal aquatic environments impacted Different types of contaminated sediment Minerogenic (mineral-based) Organic, i.e. fiberbank deposits and fiber-rich sediments Multiple organic, organometallic, and metallic contaminants Numerous impacted sites or areas across the country Minerogenic sites/areas in at least 17 countries Fiberbank sites/areas in at least 10 countries Risk assessments still being sorted out but, when completed, likely numerous sites will need some form of remediation Reference: SGI / SAO, 2016 (Appendix A) 3

4 The solutions Do nothing (often considered as a baseline) Ex-situ and in-situ remediation technologies available Ex-situ: based on removal, often dredging In-situ: MNR, EMNR, capping, and capping-based treatment Combinations Each has advantages and limitations All are internationally recognized and accepted Each is proven-effective.. IF and WHEN correctly chosen, designed, and implemented on a project- and site-specific basis No one-size-fits-all technology for all sites Avoid a pre-conceived notion on what should be best for a site Reference: SGI / SAO, 2016 (Appendix B) 4

5 The solutions: costs Dredging-based removal > in-situ capping >> MNR Reference: SGI / SAO, 2016 (Appendix B) 5

6 In-situ capping: a very brief overview Capping contaminated sediments Isolation capping Thin-layer capping Conventional materials Active materials Conventional materials Active materials Reference: SGI / SAO, 2016 (main text) 6

7 A few main points Isolation & thin-layer capping (two main strategies) Each strategy has different cap performance objectives, regardless of materials used Conventional vs active materials (and capping) Applies to both capping strategies Should consider conventional as default When needed, active materials are more effective or efficient in different ways 7

8 Isolation capping: conventional or active Cap performance objectives Physical isolation of benthic organisms from sediment Chemical isolation of organisms in BAZ from migrating contaminants Protection of sediment from erosion, dispersal conventional active new sediment biologically active zone (BAZ) caps activated carbon contaminated sediment not to scale 8

9 Thin-layer capping: conventional or active Cap performance objective To significantly reduce, but not necessarily eliminate, organism exposure to and bioaccumulation of sediment contaminants conventional active caps contaminated sediment not to scale Conventional thin-layer capping (e.g. with sand) enhanced MNR Active thin-layer capping (e.g. with AC) in-situ treatment 9

10 To meet cap performance objectives Designed capping remedies must be consistent with site-specific conditions and sediment properties Possible groundwater upwelling Geotechnical stability of the capped sediment Sediment bearing capacity Slope stability Sediment-borne gases Technique for cap construction critical, especially when capping soft sediments 10

11 Conventional vs. Active materials SAO SAO Conventional Anchor QEA Anchor QEA Active AquaBlok, Ltd. BioBlok Solutions AS Prof. D. Reible NGI

12 Cap construction: equipment & techniques BioBlok Solutions AS Prof. D. Reible BioBlok Solutions AS AquaBlok, Ltd. AquaBlok, Ltd. AquaBlok, Ltd. BioBlok Solutions AS AquaBlok, Ltd. US ACE US ACE US ACE

13 Cap monitoring: tools & techniques benthic flux chamber ROV camera GPS positioning NGI BioBlok Solutions AS BioBlok Solutions AS cores biological studies SPI camera Dr. J. Germano AquaBlok, Ltd. BioBlok Solutions AS Prof. U. Ghosh

14 Capping strategy, design, and materials Most appropriate for each depends on many factors Remedial (cap) performance objectives Sediment contaminant(s) Site conditions Sediment characteristics Construction equipment / placement technique Site s depositional vs erosional character Concentration(s) and spatial extent of contamination Rate and degree of risk reduction required Costs Etc. All are project- and site-specific decisions 14

15 Capping projects, worldwide Completed, initiated, planned (last few decades) Pilot- or full-remedial scale Isolation capping projects Thin-layer capping projects Location Conventional Active Conventional (EMNR) Active (in-situ treatment) Internationally (includes all projects) Norway Sweden Capping is NOT new, novel, or un-tested Reference: SGI / SAO, 2016 (Appendix C) 15

16 Projektexempel: Lillesjön, Nässjö kommun Historiska utsläpp från närbelägen impregneringsplats (Grimstorp) Ytliga sediment arsenikförorenade över en stor del av sjön Huvudstudie utförd med kommunen som huvudman Riskreduktion motiverad bland annat pga interncirkulation + framtida risk för ökad spridning Åtgärdsutredningen belyste flera olika alternativ: 1. Adm. restriktioner 2. Biomanipulering 3. Täckning 4. Muddring 16

17 Lillesjön Preliminary goals for sediment remediation Near-shore (most accessible) sediment: 100 mg As/kg Surface sediments elsewhere: either 17 or 100 mg As/kg Some key site conditions and sediment characteristics Total As conc. in sediment: 101 mg/kg (mean), 481 mg/kg (max.) Land-side contaminant source(s): being controlled Water depths: ~ 3 m (mean), ~ 6 m (max). Bathymetry: gently sloping Sediment characteristics: gyttja, very fine-grained, high TOC, very low shear strength Boat activity: few pleasure boats, no commercial traffic High levels of sediment re-suspension: mainly from bioturbation by fish? Groundwater upwelling: possible, but likely at a low rate Can a capping-based remedy meet goals at this site? Yes Conceptual capping approach and design considerations Conventional isolation cap likely most appropriate Should consider possible gas effects May want to encourage faunal re-colonization of cap (can occur within 1-2 yrs) 17

18 Projektexempel: Karlshäll, Luleå kommun Tillverkning av slipmassa , användning av fenylmercuriacetat som slembekämpningsmedel Förstudie, huvudstudie: Luleå kommun huvudman Finansierat med statsbidrag från Naturvårdsverket Åtgärder map kvicksilver motiverade bland annat pga spridning idag, framtida risk för ökad spridning kopplat till landhöjningen mm Förberedelser inför åtgärder pågår muddring med lokalt omhändertagande är huvudspåret Täckning har utretts som alternativ eller komplement, bland annat med anledning av förekomst av sjunktimmer 18

19 Karlshäll Two sediment types: some key characteristics Characteristic Fiberbank deposit material Fiber-rich sediment General Organic Minerogenic Total Hg concentration mg/kg (range) 6 mg/kg TS (average) mg/kg (range) 0.5 mg/kg TS (average) Me-Hg concentration ng/g TS Approx. 0.2 ng/g TS Shear strength (presume undrained) Very soft, approx. 1-2 kpa Very soft, approx. 1-2 kpa Total organic content (by LOI) % 3 20% Water content (presume dry-wt. basis) 533% % Dry matter (TS) content 5-15% 30-50% Bulk density (presume wet) 1.02 mt/m mt/m 3 Relative presence of gas More abundant Less abundant Depth of contamination Mostly down to 1 m Maximum down to 1.8 m Generally down to 30 cm 19

20 Karlshäll Some key site conditions Land-side contaminant source(s): being controlled Fiberbank deposits in shallower areas, fiber-rich sediments deeper Water depths: 3-5 m (typical range), ~ 10 m (max.). Bathymetry: gently sloping Flow velocities: baseline flow, relatively low < ~ 2 cm/s. Peak flow unknown Boat activity: relatively few pleasure boats, no commercial traffic Primary erosive forces: waves and ice scour likely dominate in near-shore areas Groundwater upwelling: appears to occur, may be significant in some areas Abundant sunken timber (highest density in shallower areas) Land and sea-bottom uplift (~ 10 mm/yr) Can one or more capping-based remedies meet goals at this site? Yes Conceptual capping approach and design considerations Possible options: cap all sediments with no pre-removal, remove most fiberbank deposit material and cap residuals, cap fiber-rich sediments with no pre-removal In general, conventional isolation capping (armored) likely most appropriate If capping fiberbank deposits (with no pre-removal), need to: (a) use more robust cap, (b) evaluate if a geotextile necessary, (c) consider gas effects, and (d) re-consider including active material in design Some (but not all) sunken timber should be removed before any capping 20

21 Karlshäll: Column-scale capping studies General objectives Demonstrate proof-of-concept for in-situ isolation capping of Site sediments minus a geotextile component for basal support Provide information for use in a follow-up pilot capping project Evaluate how fiberbank-deposit versus fiber-rich sediments respond over time to placement and presence of a robust conventional isolation cap erosionprotection layer (25 cm) chemicalisolation layer (50 cm) gradual vs rapid cap placement sediment (75 cm) 21

22 Karlshäll: Column-scale capping studies Specific objectives Monitor and evaluate sediment responses during and after capping Over the short term (during days) Sediment suspension Cap and sediment mixing Signs of bearing-capacity failure Over the longer term (weeks months) Signs of bearing-capacity failure Sediment consolidation (rate, extent) Sediment gases (formation, release) 22

23 Karlshäll: Column-scale capping studies - results sediment suspension cap/sediment mixing gases sediment consolidation 23

24 Några avslutande ord om naturlig övertäckning 24

25 Naturlig övertäckning, introduktion Sedimenten, en sjös historiska arkiv Gamla synder kan begravas Industriella materialutsläpp som överlagras med naturliga sediment. Exempel: Anrikningssand Fibersediment Utsläpp av lösta ämnen som fastläggs i sediment. Överlagring med samma typ av sediment 25

26 Processer som motverkar övertäckning Det kan finnas källor kvar Diffusion och metallvandring i sediment (mobilisering av metaller genom frisättning) Fysiska störningar: Bioturbation Vind Vågor Landhöjning Båttrafik sedimentdjup (cm) TJM Cu i sediment vår 2004 sommar

27 Projektexempel: Kisasjön Lagring av stormfällt timmer (efter Gudrun) i sjön Sjön drabbas av syrebrist Historiska utsläpp i sjön av uppströms beläget pappersbruk Misstanke om att fibersediment förekom i sjön Misstanke att Hg förekom i fibersedimenten Har timmerlagringen påverkat tillgänglighet och spridning av kvicksilver? 27

28 Resultat fiberbanken - övertäckning Karaktärisering sediment 0 Fiberbank Ljusbrun Fibersediment Ljusbrun 28

29 Resultat kvicksilver i fiberbank och djuphåla Sediment fiberbank Djup [cm] Hg [mg/kg TS] mar-06 aug-06 Dessutom: låg frisättning av Hg + Me-Hg till bottenvatten och porvatten 50 Sediment djuphåla Hg [mg/kg TS] 0 0,2 0,4 0,6 0,8 1 1,2 1, Djup [cm] mar-06 aug

30 Slutsatser Kisasjön Övertäckning av historiska utsläpp av fibersediment (innehållande Hg) har skett/sker Uppåtriktad metallvandring och anrikning av Hg i ytliga sediment förefaller inte ske En naturlig återhämtning av sjön sker Timmerlagringens effekt? Metylering sker (främst i djuphålan) Viss tillfällig inverkan kan lagringen ha haft (syrebrist och tillförsel av näringsämnen) Har ej gett upphov till spår av Hg eller Me-Hg i vattenfas eller fisk 30

31 Avslutning Principiell inriktning på åtgärder för förorenade sediment: Naturlig återhämtning Täckning Muddring Muddring vanligast förekommande i Sverige internationella erfarenheter mer omfattande vad gäller täckningslösningar Erfarenheter från genomförda projekt visar att täckning kan vara kostnadseffektivare Täckningslösningar har utretts som alternativ till muddring i ett antal svenska ärenden under senaste åren 31

32 Tack för uppmärksamheten! Henrik Eriksson, Joe Jersak,