Treatment of Arsenic in Groundwater EAST HELENA D.W.A.S.W.Daladawatta Dawoud

1888 Smelter operations begin at East Helena 1899 ASARCO purchases the smelter from Helena and Livingston Lead smelting company 1969 Environmental investigations begin at the site 1984 East Helena smelter site is listed on NPL 2001 “Indefinite closed status” 2003 Batch and column studies on ground water to assess effectiveness of Arsenic remediation 2005 Installation of pilot scale PRB completed in 5days 2year evaluation on Arsenic concentration reduction

EFFECTS Smelting operations deposited – As, Pb, Cu, Zn, Cd and 15 other hazardous substances They were deposited to soil, surface water and groundwater – Contaminated soils in residential areas – Contaminated shallow groundwater near site – Elevated metal levels in air

EFFECTS people within 1.5mile radius (until 1991) 200 residential yards contaminated Diseases: – Keratosis, Melanosis, Skin lesions, Genetic mutations More than half of children high lead concentration blood Area water supply system: – Municipal – Community

ARSENIC IN GROUNDWATER High concentrations of Arsenic in; – Redox state of arsenite (As3+) – Arsenate (As5+) Arsenic concentration in groundwater was 20mg/L where MCL 0.010mg/L

TREATEMENT-ZVIPRB ZVI uses Arsenic removal mechanism; – Sorption onto corrosion product(Precipitation with iron sulfides and green rust & precipitation as Arsenic Sulfides)→Limited – Therefore 2 stage process; Initial rapid removal of Arsenic (7.5 mg arsenic/g iron) Slower removal PRB reactive media: Must serve as a long term sink for metals Maintain permeability Maintain hydraulic connectivity FeCl 3 FeCl 3 + 3H 2 O + [As] → [As]Fe(OH) 3 + 3H + + Cl -3H 2 O[As]Fe(OH) 33H +Cl -

ZVIPRB CONSTRUCTION 1.Trench excavated (30’ longx6’ wide perpendicular to plume) 2.Biopolymer slurry to hold trench open 3.Filled with 175 tons of ZVI and coarse bedding sand 4.Onsite PRB located west of slag pile and down gradient 600’ from contaminant source

ALTERNATIVE SOLUTIONS: SUB SURFACE TREATMENT Anaerobic aquifer being injected with aerated water Formation of Arsenate Precipitation/Absorption of Arsenate Abstraction of ground water with low levels of contaminants

ALTERNATIVE SOLUTIONS: ELECTRO KINETIC A current is passed through the soil (DC) The anode/cathode attracts the contaminants This leads to build up of contaminants and facilitates their removal

PERFORMANCE MONITORING Initiated in monitoring wells located within trench 29000tonnes of hazardous waste Recycled £1.3M scrap metal Arsenic concentration reduced to 0.010mg/L within barrier

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