An Introduction To Permeable Reactive Barriers PRB Volker

An Introduction To Permeable Reactive Barriers (PRB) Volker Birke Ernst Karl Roehl University of Applied Sciences University of Karlsruhe Applied Geosciences Karlsruhe Fachhochschule Nordostniedersachsen University Fachhochschule of Applied Sciences Nordostniedersachsen Lüneburg Buxtehude Suderburg AGK Applied Geosciences University of Karlsruhe

Definition: Permeable Reactive Barriers are "passive in situ treatment zones of reactive material that degrades or immobilizes contaminants as ground water flows through it. PRBs are installed as permanent, semipermanent, or replaceable units across the flow path of a contaminant plume. Natural gradients transport contaminants through strategically placed treatment media. The media degrade, sorb, precipitate, or remove chlorinated solvents, metals, radionuclides, and other pollutants. " EPA (1999), Remedial Technology Fact Sheet, 542 -R-99 -002 University Fachhochschule of Applied Sciences Nordostniedersachsen Lüneburg Buxtehude Suderburg AGK Applied Geosciences University of Karlsruhe

Source: http: //www. eti. ca/eti. html University Fachhochschule of Applied Sciences Nordostniedersachsen Lüneburg Buxtehude Suderburg AGK Applied Geosciences University of Karlsruhe

contamination source LNAPL heavy metals GW clean groundwater plume Aquifer DNAPL Aquitard reactive barrier LNAPL = light non-aqueous phase liquids DNAPL = dense non-aqueous phase liquids University Fachhochschule of Applied Sciences Nordostniedersachsen Lüneburg Buxtehude Suderburg AGK Applied Geosciences University of Karlsruhe

PRB Concept: "Emission oriented remediation approach" Decontamination of the plume (vs. removal of the contaminant source) Passive system No active pumping of groundwater Low maintenance following installation University Fachhochschule of Applied Sciences Nordostniedersachsen Lüneburg Buxtehude Suderburg AGK Applied Geosciences University of Karlsruhe

Basic Concept: "Emission oriented remediation approach" Clean-up of the plume, not the source Passive system: No pumping required Application: Unclear location of source(s) Slow contaminant release from source Low solubility of contaminants Large volumes of contaminated soil Built-up areas University Fachhochschule of Applied Sciences Nordostniedersachsen Lüneburg Buxtehude Suderburg AGK Applied Geosciences University of Karlsruhe

Site Characteristics: Flow field (hydraulics) Contaminant concentrations Total contaminant mass expected Groundwater characteristics Treatability Study: Choice of attenuation mechanism and reactive material Column tests Determination of required residence time Calculation of barrier thickness University Fachhochschule of Applied Sciences Nordostniedersachsen Lüneburg Buxtehude Suderburg AGK Applied Geosciences University of Karlsruhe

Types of reactive walls: Degradation: Chemical and/or biological reactions converting the contaminants to harmless by-products. Sorption: Contaminant removal from groundwater through adsorption or complexation. Precipitation: Fixation of contaminants in insoluble compounds and minerals. University Fachhochschule of Applied Sciences Nordostniedersachsen Lüneburg Buxtehude Suderburg AGK Applied Geosciences University of Karlsruhe

Types of reactive walls: a) Continuous Barrier (CRB) University Fachhochschule of Applied Sciences Nordostniedersachsen Lüneburg Buxtehude Suderburg b) Funnel-and-gate (F&G) system AGK Applied Geosciences University of Karlsruhe

Source: Gavaskar et al. 1998 University Fachhochschule of Applied Sciences Nordostniedersachsen Lüneburg Buxtehude Suderburg AGK Applied Geosciences University of Karlsruhe

Reactive Material Requirements · High contaminant attenuation · Good selectivity for target contaminants · Fast reaction rates · High hydraulic permeability · Long-term stability · Environmental compatibility · Sufficient availability in homogenous quality · Cost-effectiveness University Fachhochschule of Applied Sciences Nordostniedersachsen Lüneburg Buxtehude Suderburg AGK Applied Geosciences University of Karlsruhe

Reactive Materials targeting Organic Contaminants Main source: Dahmke et al. (1996) + own additions University Fachhochschule of Applied Sciences Nordostniedersachsen Lüneburg Buxtehude Suderburg AGK Applied Geosciences University of Karlsruhe

Reactive Materials targeting Inorganic Contaminants Main source: Dahmke et al. (1996) + own additions University Fachhochschule of Applied Sciences Nordostniedersachsen Lüneburg Buxtehude Suderburg AGK Applied Geosciences University of Karlsruhe

PRB Operating Requirements Hydraulic conductivity: A minimum permeability must be guaranteed during barrier operation to avoid that contaminated groundwater by-passes the system. Homogeneity: In areas of favoured flow-paths there is the danger of a fast consumption of the reactive material's contaminant attenuation capability. University Fachhochschule of Applied Sciences Nordostniedersachsen Lüneburg Buxtehude Suderburg AGK Applied Geosciences University of Karlsruhe

PRB Operating Requirements Barrier life-time: Period during which the reactive material keeps its ability to remove the target contaminants from the groundwater. Period during which the PRB keeps its hydraulic performance. University Fachhochschule of Applied Sciences Nordostniedersachsen Lüneburg Buxtehude Suderburg AGK Applied Geosciences University of Karlsruhe

Long-term Performance Aspects The barrier life-time is governed by: · Type and concentration of contaminants · Type and kinetics of sorption and/or degradation processes. · Type and mass of reactive material · Hydraulic characteristics of the site (flow velocity) · Geochemical characteristics of the groundwater (Eh, p. H, composition) University Fachhochschule of Applied Sciences Nordostniedersachsen Lüneburg Buxtehude Suderburg AGK Applied Geosciences University of Karlsruhe

Long-term Performance Aspects Considerations on mass flux Hydraulic model of the former gas works site in Portadown, Northern Ireland. Source: Kalin, R. , presentation at PRB-net Workshop, April 2001, Belfast, Northern Ireland University Fachhochschule of Applied Sciences Nordostniedersachsen Lüneburg Buxtehude Suderburg AGK Applied Geosciences University of Karlsruhe

Long-term Performance Aspects Processes that might impair the long-term performance of PRBs: · Coatings on the particle surface of the reactive material by precipitation of secondary minerals corrosion ("rust") · Clogging of the pore space between the particles by precipitation of secondary minerals gas formation (H 2) Biomass production · Consumption of the reactivity by arriving at the material's sorption capacity dissolution of the reactive material University Fachhochschule of Applied Sciences Nordostniedersachsen Lüneburg Buxtehude Suderburg AGK Applied Geosciences University of Karlsruhe

Zero-valent Iron (Fe 0) Walls granular Fe 0 foamed Fe 0 aggregates Organic contaminants: abiotic reductive degradation of chlorinated hydrocarbons (e. g. , PCE, TCE, VC) Inorganic contaminants: abiotic reductive immobilisation of heavy metals and others (e. g. , Cr, U, Mo, Tc, As, NO 3). Costs: 200 - 400 €/t University Fachhochschule of Applied Sciences Nordostniedersachsen Lüneburg Buxtehude Suderburg AGK Applied Geosciences University of Karlsruhe

Zero-valent Iron (Fe 0) Walls Results of column tests conducted using commercial iron and groundwater from a contaminant plume at an industrial site. PCE dechlorination, formation of c. DCE, and subsequent c. DCE degradation. Source: Gillham & O'Hannesin, 1994 University Fachhochschule of Applied Sciences Nordostniedersachsen Lüneburg Buxtehude Suderburg AGK Applied Geosciences University of Karlsruhe

Zero-valent Iron (Fe 0) Walls Degradation of chlorinated hydrocarbons Electron transfer from Fe 0 surface (oxidation) to the chlorinated hydrocarbon (reduction, dehalogenation): 2 Fe 0 3 H 2 O 2 H+ + 2 e. X-Cl + H+ + 2 e- 2 Fe 2+ + 4 e 3 H+ + 3 OHH 2 X-H + Cl- 2 Fe 0 + 3 H 2 O + X-Cl 2 Fe 2+ + 3 OH- + H 2 + X-H + Cl- University Fachhochschule of Applied Sciences Nordostniedersachsen Lüneburg Buxtehude Suderburg AGK Applied Geosciences University of Karlsruhe

Zero-valent Iron (Fe 0) Walls Uranium Molybdenum Removal of uranium and molybdenum from contaminated groundwater in porous Fe 0 aggregates of a PRB system (Durango uranium mill tailings, Colorado, USA). Source: http: //www. doegjpo. com/perm-barr/index. htm University Fachhochschule of Applied Sciences Nordostniedersachsen Lüneburg Buxtehude Suderburg AGK Applied Geosciences University of Karlsruhe

Zero-valent Iron (Fe 0) Walls Reductive immobilisation of heavy metals Reduction of mobile and oxidised metal compounds followed by mineral precipitation Chromium: Fe 0 2 H 2 O 2 H+ + 2 e. Fe 0 Cr(VI)O 42 - + 4 H 2 O + 3 e- Fe 2+ + 2 e 2 H+ + 2 OHH 2 Fe 3+ + 3 e. Cr(III)(OH)3 + 5 OH- Fe 0 + Cr(VI)O 42 - + 4 H 2 O Fe(III)Cr(III)(OH)6 + 2 OHUniversity Fachhochschule of Applied Sciences Nordostniedersachsen Lüneburg Buxtehude Suderburg AGK Applied Geosciences University of Karlsruhe

Zero-valent Iron (Fe 0) Walls Coatings might block access to the reactive surfaces. Further precipitation blocks the pore spaces between some iron particles increasing flow velocity and decreasing the residence time. Source: Powell & Associates Science Services http: //www. powellassociates. com/ University Fachhochschule of Applied Sciences Nordostniedersachsen Lüneburg Buxtehude Suderburg AGK Applied Geosciences University of Karlsruhe

Zero-valent Iron (Fe 0) Walls Iron corrosion Fe 0 2 H 2 O 2 H+ + 2 e. Fe 0 + 2 H 2 O Fe 2+ + 2 e 2 H+ + 2 OHH 2 Fe 2+ + H 2 + 2 OH- Fe 0 H 2 O ½O 2 + 2 e. Fe 0 + H 2 O + ½O 2 Fe 2+ + 2 e. H+ + OHO 2 Fe 2+ + 2 OH- Anoxic: Oxic: University Fachhochschule of Applied Sciences Nordostniedersachsen Lüneburg Buxtehude Suderburg AGK Applied Geosciences University of Karlsruhe

Zero-valent Iron (Fe 0) Walls Precipitation of secondary minerals Carbonates HCO 3 - + OHFe 2+ + CO 32 Ca 2+ + CO 32 Iron minerals Fe 2+ + 2 OH 3 Fe(OH)2 (s) CO 32 - + H 2 O Fe. CO 3 (s) Ca. CO 3 (s) Siderite Calcite Fe(OH)2 (s) Fe 3 O 4 (s) + 2 H 2 O + H 2 Magnetite University Fachhochschule of Applied Sciences Nordostniedersachsen Lüneburg Buxtehude Suderburg AGK Applied Geosciences University of Karlsruhe

Zero-valent Iron (Fe 0) Walls Iron geochemistry Stability fields for the system Fe-CO 2 -H 2 O with the following solid phases: • Am. iron hydroxide Fe(OH)3 • Siderite Fe. CO 3 • Iron hydroxide Fe(OH)2 • Zero-valent iron Fe (25°C, Fetotal = 10 -5 M, Ctotal = 10 -3 M, from: Stumm & Morgan 1996). University Fachhochschule of Applied Sciences Nordostniedersachsen Lüneburg Buxtehude Suderburg AGK Applied Geosciences University of Karlsruhe

Zero-valent Iron (Fe 0) Walls Clogging Carbonate, Ca and Fe concentration in groundwater passing through a Fe 0 wall. Obvious precipitation of calcite and siderite, especially in the upstream pea gravel (Denver Federal Center, Denver, USA). Source: Mc. Mahon, P. B. , Dennehy, K. F. & Sandstrom, M. W. (1999), Ground Water, 37, 396 -404. University Fachhochschule of Applied Sciences Nordostniedersachsen Lüneburg Buxtehude Suderburg AGK Applied Geosciences University of Karlsruhe

Zero-valent Iron (Fe 0) Walls Carbonate precipitation Carbonate concentrations in the zero-valent iron filling of a Fe 0 wall (industrial site contaminated by chlorinated hydrocarbons, New York, USA). Source: Vogan, J. L. et al. (2000), J. Haz. Mat. , 68, 97 -108. University Fachhochschule of Applied Sciences Nordostniedersachsen Lüneburg Buxtehude Suderburg AGK Applied Geosciences University of Karlsruhe

Zero-valent Iron (Fe 0) Walls Silicon dioxide Distribution of dissolved silicon dioxide in a Fe 0 wall (Moffett Naval Station, Mountain View, CA). Source: Gavaskar et al. (2000) University Fachhochschule of Applied Sciences Nordostniedersachsen Lüneburg Buxtehude Suderburg AGK Applied Geosciences University of Karlsruhe

Zero-valent Iron (Fe 0) Walls Consumption Dissolved iron with p. H in Fe 0 column experiments (ZVI): Clear dissolution of iron, but only relevant at p. H values < 7. Source: U. S. Department of Energy Grand Junction Office (GJO) http: //www. doegjpo. com/perm-barr/ University Fachhochschule of Applied Sciences Nordostniedersachsen Lüneburg Buxtehude Suderburg AGK Applied Geosciences University of Karlsruhe

Zero-valent Iron (Fe 0) Walls Groundwater constituents · Decrease of concentration in the wall: Ca, Mg, Si, bicarbonate, sulphate, H+ · Showing some influence on the reaction kinetics (corrosion, dehalogenation): Bicarbonate, sulphate, nitrate, phosphate, chloride, dissolved oxygen University Fachhochschule of Applied Sciences Nordostniedersachsen Lüneburg Buxtehude Suderburg AGK Applied Geosciences University of Karlsruhe

Zero-valent Iron (Fe 0) Walls Mass balancing Precipitation in a Fe 0 wall, Copenhagen, Denmark (Kiilerich et al. , 2000): 13, 3 kg iron hydroxides, 2, 7 kg Ca. CO 3, 2, 7 kg Fe. CO 3 and 0, 8 kg Fe. S per 1000 kg iron filling per year Loss of porosity in a Fe 0 wall, Denver Federal Center, Denver, USA (Mc. Mahon et al. , 1999): 0, 35 % of total porosity per year (calculated only for the assumed precipitation of calcite and siderite) University Fachhochschule of Applied Sciences Nordostniedersachsen Lüneburg Buxtehude Suderburg AGK Applied Geosciences University of Karlsruhe

Activated Carbon Activated carbon: • Adsorption of organic contaminants • Specific surface: approx. 1000 m 2/g • Granular Reaction kinetics: Diffusion controlled Critical parameter: contact time! University Fachhochschule of Applied Sciences Nordostniedersachsen Lüneburg Buxtehude Suderburg AGK Applied Geosciences University of Karlsruhe

Activated Carbon Retardation: Retardation factor: f(c) = adsorption isotherm (linear, Freundlich, Langmuir) va = groundwater flow velocity v. S = contaminant transport velocity PAH: Trichloroethene: Chlorobenzene: University Fachhochschule of Applied Sciences Nordostniedersachsen R > 3000 (Schad & Grathwohl, 1998) R 5000 - 20000 R 10000 - 20000 (Köber et al. , 2001) Lüneburg Buxtehude Suderburg AGK Applied Geosciences University of Karlsruhe

Activated Carbon Maximum barrier life-time estimation: d = reactive wall thickness va = groundwater flow velocity R = retardation factor Horizontal flow through an activated carbon reactor of 1, 8 m diameter with a flow velocity of 0, 5 m/d and a retardation factor of R = 3000: maximum life-time = 30 years University Fachhochschule of Applied Sciences Nordostniedersachsen Lüneburg Buxtehude Suderburg AGK Applied Geosciences University of Karlsruhe

Activated Carbon Factors influencing barrier life-time: Groundwater composition · Competition effects: Natural groundwater constituents and contaminants compete for the adsorption sites · Precipitation of secondary minerals: Coatings block the access to the particle surfaces and alter the reaction kinetics Formation of biomass · Negative effect: clogging of the free pore space · Positive effect: biological degradation of sorbed contaminants possible University Fachhochschule of Applied Sciences Nordostniedersachsen Lüneburg Buxtehude Suderburg AGK Applied Geosciences University of Karlsruhe

PRB Construction University Fachhochschule of Applied Sciences Nordostniedersachsen Lüneburg Buxtehude Suderburg AGK Applied Geosciences University of Karlsruhe

Karlsruhe, Germany University Fachhochschule of Applied Sciences Nordostniedersachsen Lüneburg Buxtehude Suderburg AGK Applied Geosciences University of Karlsruhe

Monitoring Targets: Validation of Performance Longevity University Fachhochschule of Applied Sciences Nordostniedersachsen Lüneburg Buxtehude Suderburg AGK Applied Geosciences University of Karlsruhe

Monitoring Longevity: · Checking of hydraulics · Checking groundwater chemistry Hydrochemical parameters: p. H, electr. conductivity cations: Ca 2+, Mg 2+, Fet, anions: HCO 3 -, SO 42 -, Cl-, PO 42 -, NO 3 - · Investigation of the reactive material Coring: carbonate, XRD, REM University Fachhochschule of Applied Sciences Nordostniedersachsen Lüneburg Buxtehude Suderburg AGK Applied Geosciences University of Karlsruhe

Current Research Focus of current R&D: · Selection of appropriate materials and processes for selective and efficient removal of groundwater pollutants. · Evaluation of longevity and long-term performance; development of models. · Upscaling – applicability and transfer of lab-scale results into the field · Hydraulics of PRBs. University Fachhochschule of Applied Sciences Nordostniedersachsen Lüneburg Buxtehude Suderburg AGK Applied Geosciences University of Karlsruhe

Current Research: Tri-Agency-Initiative Tri-Agency Initiative, USA: University Fachhochschule of Applied Sciences Nordostniedersachsen Lüneburg Buxtehude Suderburg AGK Applied Geosciences University of Karlsruhe

Current R&D „Reaktionswände und -barrieren im Netzwerkverbund“ („RUBIN“), BMBF, Germany · · · · PRB projects co-operating in a network (RUBIN) Launched May 2000, 3 years Financial means: ca. 4 Mill. Euro. Coordination: University of Applied Sciences (Prof. H. Burmeier, Dr. V. Birke, Dipl. -Ing. D. Rosenau) 11 projects 8 projects dealing with design, erection and operation of pilot- or full-scale PRBs in Germany and/or important general preparatory R&D work 3 projects addressing general issues and missions. University Fachhochschule of Applied Sciences Nordostniedersachsen Lüneburg Buxtehude Suderburg AGK Applied Geosciences University of Karlsruhe

Conclusions PRB long-term behaviour is a function of the deployed reactive material. PRB longevity is influenced by the pollutants to be treated and the groundwater ingredients, i. e. , groundwater chemistry. The main groundwater components reveal a specific, important influence predominantly due to their higher concentrations compared to the pollutant´s concentrations. Surface reactions at the reactive material cause significant changes in geochemical conditions (p. H, Eh) regarding pore space that is passed by groundwater and therefore hydrochemical changes in the composition of the groundwater. University Fachhochschule of Applied Sciences Nordostniedersachsen Lüneburg Buxtehude Suderburg AGK Applied Geosciences University of Karlsruhe

Conclusions Mineral formation (coatings), alteration of surfaces, gas evolution and biomass can influence reactivity and permeability of a PRB. Alteration of surfaces and mineral formation can be mostly observed directly upgradient of a PRB. However, only pertaining to a few cases, detrimental effects regarding efficiency of the PRB have been observed so far. Geochemical processes are predominantly well-known and well understood. However, quantitative approaches for longterm behaviour/performance are still lacking. Current R&D projects address these issues. University Fachhochschule of Applied Sciences Nordostniedersachsen Lüneburg Buxtehude Suderburg AGK Applied Geosciences University of Karlsruhe