GEOCHEMICAL MODELING TO IMPROVE METALS REMEDIATION

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1 GEORGIA ENVIRONMENTAL CONFERENCE JEKYLL ISLAND GEOCHEMICAL MODELING TO IMPROVE METALS REMEDIATION 1

2 GEOCHEMICAL MODELING BASICS Data Required Field Parameters (ph, ORP) Water quality parameters Major cations/anions Site COPCs Minor cations/anions Questions Answered Generate or improve conceptual site model Perform fate and transport calculations Perform mixing evaluation and source determination Troubleshoot remediation problems Evaluate or support remediation alternatives Provide data to support monitored natural attenuation Tools Used Phase Diagrams Water Quality Diagrams Geochemical calculations Speciation, Precipitation, Adsorption Design and evaluate column or pilot tests Develop target Eh-pH conditions Evaluate longevity of remediation Model impact on returning to background conditions Model potential off-site impacts 2

3 CASE STUDY #1: SITE BACKGROUND Former Industrial Facility Zinc smelter, sulfuric acid plant, paint pigment plant, diammonium phosphate fertilizer plant, zinc dust plant COPCs Metals, sulfate, ammonia and phosphate Fate and Transport Site water enters the groundwater Flows into seeps Flows into downgradient lake Questions addressed Controls on current metal concentrations observed Evaluation of remediation alternatives 3

GEOCHEMICAL SETTING Slag Pile Area USEPA Low Lands/Lake/River SOLIDS NORTH SOUTH Cover Slag Pile UWBZ/Fill Precipitation Evapotranspiration Precipitation Aquitard Pile Cover UWBZ Slag Pile Runoff to

Clean Lower Concentration Elevated Concentration UWBZ Water Table Lower Aquifer?

4 GEOCHEMICAL SETTING Slag Pile Area USEPA Low Lands/Lake/River SOLIDS NORTH SOUTH Cover Slag Pile UWBZ/Fill Precipitation Evapotranspiration Precipitation Aquitard Pile Cover UWBZ Slag Pile Runoff to South Ditch or Adjacent Land Surface Pumped Aquitard Metal and Sulfate Reduction by Geochemical and Physical Processes Former Municipal Dump Seep South Ditch Seep Sediment Lake Lower Aquifer WATER Clean Lower Concentration Elevated Concentration UWBZ Water Table Lower Aquifer? Lower Aquifer Water Table Groundwater (UWBZ) Seep Lake High sulfate High metals Low ph Decrease sulfate and metals Increase in ph and ORP High carbon Moderate sulfate, metals, ph Decrease carbon, sulfate and metals Increase in ph and ORP High ph Moderate carbon, sulfate, metals Maximum Zinc = 2,640 mg/l Maximum Zinc = 1.1 mg/l Maximum Zinc = 0.87 mg/l, mostly non-detect Question: Why do Zinc concentrations decrease so rapidly over the Site?

5 OBJECTIVES Geochemical modeling performed on: Groundwater in upper aquifer Seep water along the north shore of the Lake Surface water in the Lake Goals: Evaluate adsorption and precipitation processes Calculate upper bound concentrations of dissolved metals Perform sensitivity analysis to see how concentrations may change under differing conditions Potential remedy options (low ORP) Mixing conditions (high T, high ammonia)

6 ZINC SPECIATION CALCULATIONS Common Zinc ions Zn % 90% 80% ZnSO 4 Zn(SO 4 ) 2-2 ZnCO 3 ZnHCO + 3 ZnOH + 70% 60% 50% 40% 30% 20% 10% Zn(OH)+ Zn(OH) + Zn(OH)2 2 ZnCO3 3 ZnHCO Zn(SO4)2-4 ) -2 2 ZnSO4 ZnSO 4 Zn 2+ Zn2+ Zn(OH) 2 0% UWBZ ph 6.2 SP ph 7.1 SW ph 8.4 ZnHPO 4 Groundwater (UWBZ) Shoreline Spring/Seep (SP) Dominated by zinc-sulfates and Zn 2+ ; At high sulfate concentrations (near the source), there are higher zinc-sulfate concentrations Zn 2+ dominant with some zinc-carbonates and Zn-sulfates Lake Surface Water (SW) Large amounts of Zn 2+, with some zinc-carbonates and zinc-hydroxides

7 ZINC ADSORPTION Neutrally charged zinc ions are more mobile ZnSO 4 ZnCO 3 Zn(OH) 2 ZnHPO 4 100% 90% 80% 70% 60% 50% 40% 30% 20% 10% Zn(OH)+ Zn(OH) + Zn(OH)2 2 ZnCO3 3 ZnHCO Zn(SO4)2-4 ) -2 2 ZnSO4 ZnSO 4 Zn 2+ Zn2+ 0% UWBZ ph 6.2 SP ph 7.1 SW ph 8.4 Groundwater (UWBZ) At low to typical ph, Zn 2+ is not expected to sorb significantly and Zn(SO 4 ) 2 2- may adsorb at high sulfate concentrations; Higher adsorption is expected at ph > 6.5 and lower sulfate concentrations Shoreline Spring/Seep (SP) Under typical conditions, >80% of zinc is expected to adsorb Lake Surface Water (SW) Typically lower adsorption is expected (~50%), particularly at higher ph and carbon concentration

8 ZINC MINERALOGY 1.E+12 Zn(OH) 2 Solubility is a strong function of ph 1.E+10 Smithsonite (ZnCO 3 ) Solubility depends on carbon concentration and speciation Sphalerite (ZnS) Relevant at low ORP May co-precipitate with other sulfides Zinc Concentration (mg/l) 1.E+08 1.E+06 1.E+04 1.E+02 1.E+00 1.E-02 GW Screening Level ph Maximum Dissolved Zinc Concentration Based on Zn(OH) 2 Solubility

9 ZINC PRECIPITATION Zn(OH) 2 Maximum zinc concentration (mg/l) Carbon concentration (mg/l) Zn(OH) 2 Limits zinc solubility in high-ph groundwater and the lake ZnCO 3 10 GW Screening level = 5 mg/l Smithsonite (ZnCO 3 ) Limits zinc solubility in the seeps Observed precipitate at Site UWBZ ph 6.2 SP ph 7.1 Zn(OH) 2 SW ph 8.4 SW Screening level = mg/l ph range Measured Zinc (mg/l) Maximum Dissolved Zinc (mg/l) Relevant Mineral Saturation Conditions Groundwater (UWBZ) ,640 5,000 Zn(OH) 2 Very undersaturated to near equilibrium Shoreline Sprint/Seep (SP) Smithsonite (ZnCO 3 ) Very undersaturated to slightly undersaturated Lake Surface Water (SW) Zn(OH) 2 Slightly undersaturated to near equilibrium

Zn(OH) 2 Eh (volts) Zn(OH) 2 Sphalerite Smithsonite Sphalerite ph UW BZ Samples UW BZ Samples

10 EH-PH DIAGRAMS FOR ZINC Typical Lake Conditions Maximum observed Zinc Concentrations Typical Groundwater Conditions High Sulfate Zn(OH) 3 - ZnSO 4 Zn(OH) 3 - ZnHCO 3 + ZnHCO 3 + Eh (volts) Zn(OH) 2 Eh (volts) Zn(OH) 2 Sphalerite Smithsonite Sphalerite ph UW BZ Samples UW BZ Samples (near lake) SP Samples SW Samples Zn(OH) 4 2- ph UW BZ Samples UW BZ Samples (near lake) SP Samples SW Samples

11 GEOCHEMICAL TRANSFORMATIONS Slag Pile Area USEPA Low Lands/Lake/River SOLIDS NORTH SOUTH Cover Slag Pile UWBZ/Fill Precipitation Evapotranspiration Precipitation Aquitard Pile Cover UWBZ Slag Pile Runoff to South Ditch or Adjacent Land Surface Pumped Aquitard Metal and Sulfate Reduction by Geochemical and Physical Processes Former Municipal Dump Seep South Ditch Seep Sediment Lake Lower Aquifer WATER Clean Lower Concentration Elevated Concentration UWBZ Water Table Lower Aquifer? Lower Aquifer Water Table Groundwater (UWBZ) Seep Lake High sulfate High metals Low ph Decrease sulfate and metals Increase in ph and ORP High carbon Moderate sulfate, metals, ph Decrease carbon, sulfate and metals Increase in ph and ORP High ph Moderate carbon, sulfate, metals Zn 2+, ZnSO 4, or Zn (SO 4 ) 2 2- species ZnSO 4, or Zn (SO 4 ) 2 2- species decrease Zn 2+ or ZnCO 3 species ZnCO 3 species decrease Zn 2+, Zn(OH) 2, or ZnCO 3 species Zn(OH) 2 may precipitate at high ph ZnCO 3 precipitate at high carbon Zn(OH) 2 species increase Zn(OH) 2 precipitate at high ph Answer: Zn(OH) 2 precipitates at high ph limiting zinc concentrations in the lake.

12 CASE STUDY #1 CONCLUSIONS Model current site conditions Demonstrate how the geochemistry at the Site impacts observed chemical concentrations Explain observed changes in metals concentrations Predict maximum dissolved concentrations throughout the Site Discuss the impact on adsorption processes Provide advice for remediation decisions Compare predicted maximum dissolved concentrations to remedial objectives Caution against remediation decisions that may decrease the ph at the Lake

13 CASE STUDY #2: BACKGROUND Site background: Site operated from 1941 through 1992 manufacturing hydraulic and pneumatic valves Main COPC is Cr(VI) Pump and treat not performing as well as desired Pilot test injection of reductant at IW-1 Objectives: Evaluate pilot test of injection of reductant to reduce Cr(VI) concentrations Review data Generate plots of chemical concentrations over time Evaluate spatial trends in concentration data with respect to injection locations Generate geochemical figures (Eh-pH diagrams)

14 PILOT TEST First quarter 2013, 1.2 million gallons of calcium polysulfide (reductant) was injected into IW ORP (mv) Wells most affected by reductant injection GW-29 GW-03 GW-25A GW-14A GW-14B Calcium Concentration (µg/l) 0 50, , , , , , , , ,000 14

15 QUARTER SAMPLING RESULTS Parameter GW-08 (background) GW-03 GW-14A GW-14B GW-25A Hexavalent Chromium (µg/l) 1.3 <0.067 < J <0.067 ORP (mv) Dissolved Oxygen (mg/l) Nitrate-N (µg/l) 17,000 6,600 <25 <1,300 <25 Manganese (µg/l) J 2, ,190 Iron (µg/l) 31.1 J Arsenic (µg/l) J Calcium (µg/l) 142, , , , ,000 Sulfide (µg/l) <30 2,600 24,000 51,000 14,000 Sulfate (µg/l) 79, , , , ,000 Question: Why is arsenic present at these wells and is it a problem? 15

16 ARSENIC TRENDS (Q DATA) Arsenic Concentration (µg/l) GW-14B GW-14A GW-25A 0 100, , , , ,000 Calcium Concentration (µg/l) Arsenic Concentration (µg/l) GW-14B 30 GW-14A GW-25A ORP (mv) High arsenic concentrations at wells most affected by the pilot test. 16

17 ARSENIC CONCENTRATIONS OVER TIME Arsenic Concentration (µg/l) Small scale injection at GW-14A Larger-scale injection at IW-1 GW-14B GW-14A GW-08 MCL = /08 2/09 2/10 2/11 2/12 2/13 2/14 Date 17

IRON EH-PH DIAGRAMS Fe(OH) 3 is a dominant mineral in adsorption processes Fe(OH) 3 dissociates when reductant is injected Solubility calculations confirm results

18 IRON EH-PH DIAGRAMS Fe(OH) 3 is a dominant mineral in adsorption processes Fe(OH) 3 dissociates when reductant is injected Solubility calculations confirm results Arsenic (V) is typically adsorbed onto Fe(OH) 3 Confirmed with adsorption calculations Process is reversible Answer: Dissolution of Fe(OH) 3 releases adsorbed arsenic 18

19 ARSENIC EH-PH DIAGRAMS As (V) reduces to form As (III) As (III) generally more mobile and toxic This should return to normal as conditions return to background Pump and treat is still active so arsenic should not migrate off-site 19

20 CASE STUDY #2 CONCLUSIONS Model site conditions before and after pilot test injection Demonstrate how the geochemistry at the Site impacts observed chemical concentrations Explain observed changes in metals concentrations Evaluate potential impacts due to longer term injection scenarios Provide advice for remediation decisions Predict impact of injection on metals concentrations Recommend monitoring of arsenic concentrations both on- and off-site if low-orp conditions are present

21 THANK YOU! Kimberly Souder P

Opportunities for Zinc Compound Recovery from Mining Influenced Water

Opportunities for Zinc Compound Recovery from Mining Influenced Water Linda Figueroa 1, Kathleen Whysner 2 1 Colorado School of Mines, 1500 Illinois Street, Golden, Colorado 80401, USA, lfiguero@mines.edu