ENHANCED IN SITU BIOREMEDIATION OF CADMIUM AND LEAD IMPACTED GROUNDWATER

Transcription

1 ENHANCED IN SITU BIOREMEDIATION OF CADMIUM AND LEAD IMPACTED GROUNDWATER Andrew Madison 1, Michael Borda 1, Marie Lewis 1, Christopher Hemingway 2 & Stuart Mitchell 1 1 Golder Associates Inc., Mt. Laurel, New Jersey 2 Golder Associates Inc., Newark, New Jersey 2015 RE3 Conference

2 Objective Develop and implement an efficient and cost-effective treatment strategy to reduce concentrations of cadmium and lead in groundwater prior to discharge to a local creek. September 25,

3 Site Background Former Sales Office (FSO) Creek (local discharge) Septic System 3 Former lead-acid battery manufacturing facility Septic system of the Former Sales Office (FSO) introduced cadmium (Cd), lead (Pb) and increased acidity to groundwater Septic system and piping was removed in 1991 Cd impacts have been observed in a local creek that borders the Site and is downgradient of the FSO

4 Site Background Cd Impacts Cd Isoconcentration Contours (μg/l) September 25,

5 Site Background Pb and ph Pb Isoconcentration Contour (μg/l) ph September 25,

6 Site Background Creek Impacts Cd & Pb Impacted Groundwater Seeps September 25,

7 Pilot Study - Geochemical Setting Mobility of Cd is controlled by chemical speciation which is dependent on ph and redox state (measured by oxidation reduction potential [ORP]) Geochemical modeling of current Site conditions indicated that Cd was highly soluble: 80% of total Cd was present as Cd 2+ 20% of total Cd was present as CdSO 4 (original form) Indigenous microorganisms were limited by the lack of available organic carbon System was anaerobic and electron acceptors (oxygen, iron-oxides, manganese-oxides) were limited; however groundwater had elevated levels of sulfate September 25,

8 Pilot Study Design Goal: Stimulate indigenous sulfate reducing microorganisms to generate sulfide to precipitate Cd and Pb as insoluble metal sulfide species (CdS, PbS and mixed Cd- and Pb-iron sulfides) Process: Intrinsic microbes obtain energy from the oxidation of the injected organic carbon substrate (i.e., lactate) By providing organic carbon, microbial reduction of sulfate to sulfide will be enhanced (CH 2 O) n + SO 4 2- S 2- + CO 2 + H 2 O Cd 2+ CdS (s) September 25,

9 Pilot Study Implementation Installed one injection well (IW-1) Installed several monitoring points along primary groundwater flowpaths September 25,

10 Pilot Study Implementation Bromide Tracer Prior to initiation of bioremediation approach, a tracer test was conducted A known concentration of bromide was injected into IW-1 and monitored for 1-month using ion-specific electrodes Confirm primary groundwater flow paths within the Pilot Study Area Evaluate effects of dilution and dispersion of the amendment solution September 25,

11 Pilot Study Implementation Lactate Injection 4 Quarterly Lactate (NaC 3 H 5 O 3 ) Injections in IW-1: June kg of lactate in 1,000 gallons of water Mass of lactate was designed based on a stoichiometric electron donor demand calculation (i.e., enough lactate to exhaust electron donors [oxygen, nitrate and iron-oxides] and drive sulfate reduction) and expected dilution across Pilot Study Area September kg of lactate in 1,000 gallons of water December kg of lactate in 1,000 gallons of water March kg of lactate in 1,000 gallons of water September 25,

12 IW-1 Results - TOC September 25,

13 IW-1 Results Geochemical Conditions Shift to Iron Reducing Conditions Shift to Sulfate Reducing Conditions and Formation of FeS x September 25,

14 IW-1 Results Cd and Pb Cd and Pb below groundwater MCLs since November 2012 September 25,

15 MW-29 Results TOC September 25,

16 MW-29 Results Geochemical Conditions Shift to Iron Reducing Conditions Shift to Sulfate Reducing Conditions and Formation of FeS x September 25,

17 MW-29 Results Cd and Pb Cd and Pb below groundwater MCLs downgradient of IW-1 since February 2012 September 25,

18 MW-26 Results TOC 400 ft Downgradient of IW-1 September 25,

19 MW-26 Results Geochemical Conditions Shift to Iron Reducing Conditions Shift to Sulfate Reducing Conditions and Formation of FeS x September 25,

20 MW-26 Results Cd and Pb Geochemical changes 400 feet downgradient of IW-1 were observed in MW-26 September 25,

21 Pilot Study Conclusions Natural geochemical conditions can be favorably modified by addition of organic carbon (i.e., lactate) Addition of lactate promoted microbially-mediated sulfate reduction sufficient to sequester Cd and Pb in the immediate area of injection Geochemical changes were stable for greater than an 18-month period and were observed approximately 400 feet downgradient of IW-1 Concentrations of Cd and Pb remained below groundwater MCLs for greater than an 18-month period following cessation of pilot injections September 25,

22 Full-Scale Implementation Full-scale implementation is currently ongoing September 25,