Danny Reible y The University of Texas at Austin Biogeochemistry - PowerPoint PPT Presentation

Danny Reible y The University of Texas at Austin

� Biogeochemistry beneath the cap � Active Capping ‐ Permeable adsorptive barrier A ti C i P bl d ti b i � Material Options � Management of upwelling water /gas/NAPL M t f lli t / /NAPL � Effectiveness of materials � Placement of materials � Placement of materials � Capping design ‐ modeling � Monitoring Cap Performance Monitoring Cap Performance � Definition of Cap Objectives

� Metals often effectively contained by a conventional cap M t l ft ff ti l t i d b ti l � AVS vs. SEM ‐ Capping will enhance reducing conditions Salt Zn 2+ (ppb) > 0 10 20 30 40 AVS SEM ‐ 1 0 Metals will not be toxic 1 Depth (cm) M 2+ + FeS (s) → MS (s) + Fe 2+ 2 3 3 Sediment D < AVS SEM 4 5 6 Divalent metals may be Divalent metals may be 7 toxic 3 8

Conceptual Model Pre-Cap Post-Cap O 2 F OOH FeOOH O 2 O 2 FeOOH FeOOH Methyl mercury Methyl mercury 2- SO 4 2- SO 4

� Mobility and toxicity generally not redox sensitive � Degradation is redox sensitive D d ti i d iti � Hydrocarbon degradation facilitated aerobically � Chlorinated organics reductively dechlorinate but many Chl i t d i d ti l d hl i t b t sediment contaminants refractory � Dynamics controlled by sorption in cap and � Dynamics controlled by sorption in cap and groundwater upwelling

� Potentially greater effectiveness than with sand can be achieved with “active” or amended caps � Encourage fate processes such as sequestration or degradation of contaminants beneath cap � Discourage recontamination of cap g p � Feasible if high value components are placed in thin layer in a controllable manner � Effective if time/capacity of active cap sufficient to � Effective if time/capacity of active cap sufficient to manage finite mass of contaminants � Significant stakeholder acceptance advantage g p g

� Permeability Control � Discourage upwelling through contaminated sediment b di by diverting groundwater flow i d fl � Contaminant Migration Control � Slow contaminant migration, typically through Sl t i t i ti t i ll th h sorption related retardation � Contaminant Degradation Aid � Contaminant Degradation Aid � Less well developed, contaminant specific but designed to encourage contaminant fate processes

Demonstrated � Clays for permeability control � Clays for permeability control � Activated Carbon or other carbon sequestration agent � Organoclays for NAPL control & some dissolved control � Significant swelling and permeability reduction with NAPL � Significant swelling and permeability reduction with NAPL � Clay and sequestration agent mixtures � Phosphate additives for metals � Rock phosphate (i.e. apatite) demonstrated k h h d d � Iron Sulfide for Hg and MeHg control � Siderite (FeCO3) for pH control � Zero valent iron � Oxygen or hydrogen release compounds/technologies � Biopolymers � Biopolymers � Electrochemical controls on redox conditions Speculative

� Commercially available C i ll il bl � AquaBlok � Bentomat B t t � HDPE � Can successfully divert groundwater upwelling C f ll di t d t lli � Where will the groundwater go? � Plan for gas accumulation and release Pl f l i d l � Long term effectiveness in the face of gas/tidal dynamics? dynamics?

13 Vlassopoulos and � pH 12 Serrano, 2008 11 � Siderite Siderite 10 � Ferrous Sulfate 9 pH � Alum 8 � Metals 7 6 � Apatite Available FeCO 3 ~ 2 g/cm of layer thickness/cm 2 2 cm/yr upwelling = 1000 years of pH protection y p g y p p 5 5 � Iron Sulfide 4 0 .5 1 1.5 2 � Organics FeCO 3 reacted (g/L) � Organoclay � Activated carbon

� NAPL present ‐ Organoclays � Capacity of O(1 g NAPL/g organoclay) � Placement within a laminated mat for residual NAPL or to allow replacement if capacity exceeded � Placement in bulk for significant NAPL volumes Placement in bulk for significant NAPL volumes � Multiple organoclay layers or organoclay/activated carbon layer for both NAPL and dissolved contaminant control � Dissolved contaminants only ‐ Activated carbon l d l d b � Placement in mat may be necessary to allow easy placement � Placement as amendment also possible � Placement as amendment also possible � Activated carbon typically more subject to fouling than organoclay

Hg (PM199) on µg/kg 1.E+06 1.E+06 Hg Concentratio y = 6920.9x 0.7212 1.E+04 R² = 0.9516 Hg (PM199) Sorbed H 1.E+02 Power (Hg (PM199)) 1.E+00 Spec a Special Hg formulations exist g o u a o s e s 0.001 0.1 10 1000 Hg Water Phase Concentration, µg/L Conventional formulations may be similarly effective if Hg (MRM) Hg complexed with suspended Hg complexed with suspended organic matter ation µg/kg y = 9417.7x 0.6709 1.E+06 R² = 0.935 ed Hg concentra 1.E+04 1 E+04 Hg (meas) 1.E+02 Power (Hg (meas)) Sorb 1.E+00 0.001 0.1 10 1000 Hg concentration µg/L

mg/g 100 ncentration 10 AC Site ediment con AC Lab 1 OC Site 1/10 OC Lab Se 1/100 0 2 4 6 8 10 12 Water Concentration mg/L

70 n mg/g 60 oncentration 50 50 40 AC Site 30 Sediment co OC Site 20 OC Lab 10 S 0 0 2 4 6 8 10 12 Water Concentration mg/L Water Concentration mg/L

– Expect bioavailability reduction proportional to – Expect bioavailability reduction proportional to porewater concentration (inversely proportional to partition coefficient, K d ) – Equivalent sand cap thickness – diffusion/dispersion q p p dominated (u<<1 cm/day) K R = d L L L active active ~ R R K K eff ff active active sand d sand ~ 10 -4 K oc Log K d 0.01K oc f oc K oc ~ 1-10K oc ~ 100K oc f f oc ~ 0.01 ‐ 0.05 16

To Appear Journal of Soil and Sediment Contamination – Summer 2009 ACTIVE CAP DESIGN MODEL including steady state design model from Lampert and Reible (2009)* Version 3.13 2/9/2008 Instructions: This spreadsheet determines concentrations and fluxes in a sediment cap at steady-state worksheet 1), unsteady state (worksheet 2), assuming advection, diffusion, dispersion, bioturbation, deposition/erosion, sorption onto colloidal organic matter, and boundary layer mass transfer. An active cap layer with enhanced sorption is considered by ll id l i tt d b d l t f A ti l ith h d ti i id d b converting to an equivalent conventional cap thickness. Depth is defined from the cap-water interface. A constant deposition rate can be entered but is not allowed to result in a net contaminant velocity <0 (relative to the changing cap-water interface) . The cells in blue are input cells; these can be changed for the design of interest. DO NOT CHANGE THE CELLS IN RED (or the spreadsheet will not function properly). A second worksheet calculates the transient profiles for a semi-infinite case. The third worksheet title "array" allows the user to create an array of outputs for a given input (e.g. to study different compounds for a given site) a given site). Contaminant Properties Contaminant Chlorobenzene Transient Concentration Profiles 0.00 Organic carbon partition coefficient, log K oc 2.52 log L/kg Bioturbation Layer Cap-Water Interface Colloidal organic carbon partition coefficient, log K DOC 2.15 log L/kg 10.00 Bioturbation Layer y 6 0E 06 cm 2 /s 6.0E-06 cm /s W t Water diffusivity, D w diff i it D Series13 20.00 0.00 yr -1 Cap decay rate (porewater basis), λ 1 2 Depth, cm 1.21E-11 0.00 yr -1 30.00 Bioturbation layer decay rate (porewater basis), λ 2 Containment Layer 1.0E+00 Effective Cap Layer 2.0E+00 40.00 3.0E+00 Sediment/Bioturbation Layer Properties 4.0E+00 50.00 5.0E+00 Contaminant pore water concentration, C 0 1 ug/L g 6 0E+00 6.0E+00 Underlying Sediment Biological active zone fraction organic carbon, ( f oc ) bio 0.05 7.0E+00 60.00 Underlying Sediment 8.0E+00 Colloidal organic carbon concentration, ρ DOC 10 mg/L 9.0E+00 70.00 1.0E+01 Darcy velocity, V 2 cm/yr 0.00 0.20 0.40 0.60 0.80 1.00 Infinity Dimensionless Concentration Depositional velocity, V dep 0 cm/yr Bioturbation layer thickness, h bio 10 cm

� Spreadsheet model � Transient model until penetration of chemical isolation layer Transient model until penetration of chemical isolation layer � Steady state model (bioturbation &isolation layer) � Variant for additional active cap layer ‐ transient and ss p y � Numerical model � Matlab version Matlab version � Multiple layers, nonlinear sorption, finite source � Available at http://www caee utexas edu/reiblegroup/ � Available at http://www.caee.utexas.edu/reiblegroup/

| Performance Measures Manag ing Co ntaminatio n Manag ing Co ntaminatio n • I so latio n o f c o ntaminate d se dime nt- Cap stability? • E E li liminatio n o f se dime nt re suspe nsio n – Cap stability? i ti f di t i C t bilit ? • Re duc tio n in c o ntaminant flux to wate r – F lux? • Re duc tio n in c o ntaminant ac c umulatio n in be nthic • Re duc tio n in c o ntaminant ac c umulatio n in be nthic o rg anisms- F lux? Co ntaminant iso latio n? Bio ac c umulatio n? Thi Thin Layer Capping L C i Thick Layer Capping Thi k L C i vs. T hin L aye r Cap T hic k L aye r Cap

Percent Sediment and Phen C/C 0 versus Depth 15 17 Clean Sand Cap Phenanthrene 19 (cm) % Sediment 21 Cap sediment Intermixing Zone Cap-sediment Intermixing Zone Depth 23 Sediment 25 27 29 29 0% 50% 100% 150% C/C 0 and Percent Passing