ENHANCED IN SITU BIOREMEDIATION OF CADMIUM AND LEAD IMPACTED - - PowerPoint PPT Presentation

Andrew Madison1, Michael Borda1, Marie Lewis1, Christopher Hemingway2 & Stuart Mitchell1

ENHANCED IN SITU BIOREMEDIATION OF CADMIUM AND LEAD IMPACTED GROUNDWATER

1Golder Associates Inc., Mt. Laurel, New Jersey 2Golder Associates Inc., Newark, New Jersey

2015 RE3 Conference

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, 2015 2

Site Background



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

• bserved in a local creek that

borders the Site and is downgradient of the FSO

3

Former Sales Office (FSO) Septic System Creek (local discharge)

Site Background – Cd Impacts

September 25, 2015 4

Cd Isoconcentration Contours (μg/L)

Site Background – Pb and pH

September 25, 2015 5

Pb Isoconcentration Contour (μg/L) pH

Site Background – Creek Impacts

September 25, 2015 6

Cd & Pb Impacted Groundwater Seeps

Pilot Study - Geochemical Setting

 Mobility of Cd is controlled by chemical speciation which is dependent

• n 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 Cd2+  20% of total Cd was present as CdSO4 (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, 2015 7

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

• rganic carbon substrate (i.e., lactate)

 By providing organic carbon, microbial reduction of sulfate to sulfide

will be enhanced

September 25, 2015 8

(CH2O)n + SO4

2- S2- + CO2 + H2O

Cd2+  CdS(s)

Pilot Study Implementation

 Installed one

injection well (IW-1)

 Installed several

monitoring points along primary groundwater flowpaths

September 25, 2015 9

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, 2015 10

Pilot Study Implementation – Lactate Injection

 4 Quarterly Lactate (NaC3H5O3) Injections in IW-1:  June 2012 – 25 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 2012 – 75 kg of lactate in 1,000 gallons of water  December 2012 – 75 kg of lactate in 1,000 gallons of water  March 2013 – 75 kg of lactate in 1,000 gallons of water

September 25, 2015 11

IW-1 Results - TOC

September 25, 2015 12

IW-1 Results – Geochemical Conditions

September 25, 2015 13

Shift to Iron Reducing Conditions Shift to Sulfate Reducing Conditions and Formation

• f FeSx

IW-1 Results – Cd and Pb

September 25, 2015 14

Cd and Pb below groundwater MCLs since November 2012

MW-29 Results – TOC

September 25, 2015 15

MW-29 Results – Geochemical Conditions

September 25, 2015 16

Shift to Iron Reducing Conditions Shift to Sulfate Reducing Conditions and Formation of FeSx

MW-29 Results – Cd and Pb

September 25, 2015 17

Cd and Pb below groundwater MCLs downgradient of IW-1 since February 2012

MW-26 Results – TOC

September 25, 2015 18

400 ft Downgradient of IW-1

MW-26 Results – Geochemical Conditions

September 25, 2015 19

Shift to Iron Reducing Conditions Shift to Sulfate Reducing Conditions and Formation of FeSx

MW-26 Results – Cd and Pb

September 25, 2015 20

Geochemical changes 400 feet downgradient of IW-1 were

• bserved in MW-26

Pilot Study Conclusions

 Natural geochemical conditions can be favorably modified by addition of

• rganic 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, 2015 21

Full-Scale Implementation

September 25, 2015 22

Full-scale implementation is currently ongoing