Remediation of Chlorinated Solvents in Groundwater using Carbon Amendments: Analytical Challenges and Solutions

Transcription

1 Remediation of Chlorinated Solvents in Groundwater using Carbon Amendments: Analytical Challenges and Solutions Heather Lord, Samantha Clay, Atena Georgescu, Mariana Cojocar: Maxxam, Mississauga. Eric Veska: Stantec, Markham. Copyright Maxxam 2014

2 Overview Activated Carbon-based Remedial Approaches In-situ application of carbon-based amendments for chlorinated solvent remediation has emerged in the last decade. Two stage approach: Adsorption: used since the 1950 s for ex situ remediation Degradation: ~ two decades of in situ use Considered as more effective than subsurface degradation alone due to the added retardation of contaminant migration 2

3 Overview: Activated Carbon Amendments Activated carbon particles ranging from colloidal to powdered to granular o plus chemical or biological additives to promote degradation BOS-100 and BOS-200 introduced in early-2000s, COGAC and PlumeStop are more recent All are still considered emerging technologies for subsurface remediation Comparison of activated carbon based products that have been used for in-situ remediation* Product Size Manufacturer Additive Target CoCs Degradation BOS-100 granular Calgon zero valent iron cvoc Abiotic reductive dechlorination BOS-200 powdered Calgon electron acceptors, P, N, CaSO 4, bacteria PHC Aerobic (short-term) and anaerobic (long-term) bioaugmentation COGAC granular or powdered Remington calcium peroxide, sodium persulfate cvoc and PHC Chemical Oxidation, aerobic and anaerobic biostimulation PlumeStop colloidal Regenesis polymer, H 2 and O 2 releasing compounds, bacteria cvoc or PHC cvoc: anaerobic biodegradation; PHC aerobic biodegradation carbon-iron colloidal non-commercial colloid stabilizer, zero valent iron cvoc Abiotic reductive dechlorination * Adapted from: Fan, D. et al Journal of Environmental Management 3

4 Typical Application Process Investigation: Pre-injection subsurface characterization. Loading Rate: Provide sufficient contact between amendment and contaminant. Injection: Powdered and Granular: low permeability formations, direct push injection and formation fracturing Colloidal: high permeability formations: direct push or injection wells contaminant adsorption on activated carbon Characterize distribution post-injection by soil coring 4

5 Chemical Assessment of Remedial Performance Measure contaminant concentrations from separate monitoring wells Need to consider if adsorption or degradation is responsible for reduction in dissolved contaminant concentration Adsorption: migration retarded Degradation: contaminant removal Amendment may appear in monitoring wells, in which case it can interfere with lab analysis 5

6 Settling Laboratory analysis is conducted by decanting groundwater from settled material Complete settling is not always possible within required hold times In samples where material is not settled, analytical complications are likely 6

7 Lab Processes - Internal Standard (calibration) Recovery Surrogate sample VOC MMS Residual activated carbon in samples adsorbs both contaminants and lab QC spikes (surrogates/internal standards). At high carbon loadings (in top layer), laboratory QC fails o IS and RS recoveries low or high Samples must be diluted to pass QC cvoc measured from vial headspace Dilution may cause DL increase above guideline limit 7

8 Site 1: Low concentration cvoc Vinyl Chloride (VC) was the remnant contaminant of concern following a 15 year effort including air sparging, pump & treat, vapour extraction VC has a low Site Condition Standard of 1.7 µg/l, Concentration polished at last stage using colloidal carbon 230 kg injected Monitoring started 1 month after injection Low flow sampling 8

9 Site 2: High concentration cvoc High concentration cvoc MOECC Site Condition Standard for 1.7 µg/l is again the target Plumestop used as first line of treatment: 2500 kg injected At 3 months post injection Plumestop concentration too high in many cases to permit direct analysis of cvoc Passive Diffusion Bag monitoring pre- and post-injection 9

10 Vinyl Chloride in monitoring well post-injection prior to injection VC 5 µg/l Site 1 All sampling by low-flow Before 6-months, RDLs raised above guideline Could not verify remedial progress at this stage After 6-months repeated samplings showed total VC < guideline and good RDL Guideline (1.7 µg/l) Std. RDL (0.2 µg/l) 10

11 How much carbon causes QC to fail? Measurement of carbon amendment concentration Carbon amendment concentration in water samples are measured using a UV-Vis Spectrophotometer at λ=565nm Provides guidance for loadings likely to cause QC failures and elevated DL Observation: where water above settled layer in VOC vial is translucent, QC will likely not fail due to carbon adsorption of lab QC spikes µg/l 11

12 Surrogate Recovery (%) Surrogate Recovery (%) Surrogate QC failures seen at suspended carbon concentrations >100 mg/l Surrogate recovery in samples with carbon amendment Site 1 50 Site Settled Carbon Amendment Concentration (ug/ml) Settled Carbon Amendment Concentration (ug/ml) D4-1,2-DCA D8-Toluene 4-BFB SS acceptance criteria % recovery Surrogates: d 4-1,2-Dichloroethane; d 8 - Toluene; 4-Bromofluorobenzene 12

13 Internal Standards (quant ion area % of CCV) Internal Standard (ion area % of CCV) IS QC failures also seen at suspended carbon concentrations >100 mg/l Internal standard recovery in samples with carbon amendment Site Site Carbon Amendment Concentration (ug/ml) Carbon Amendment Concentration (ug/ml) FB ClBen 1,2-DCB IS acceptance criteria % of CCV peak area above dotted line Internal standards: Fluorobenzene; d 5 -Chlorobenzene; d 4 -Dichlorobenzene 13

14 Solutions/sampling alternatives 1. External Standard Calibration: Contaminant response compared directly to calibration curve disregard failing internal standard responses and surrogate recoveries Not a validated method Expected to report free COC concentration 2. Passive Diffusion Bag Sampling Standard analyses, no carbon in samples, no problems with QC, 0.2 µg/l RDL achievable Known to report free COC concentration 14

15 Passive Diffusion Bags (PDB) Example: BTEX, naphthalenes, chlorinated hydrocarbons Equilibration sampling in Groundwater Low Density Polyethylene tube filled with distilled water Deploy in monitoring well Protective Mesh Sock Diffusion Bag (inside mesh sock) Equilibrates within 7-14 days Once equilibrated: water concentration in PDB = well Transfer water from PDB to VOC vials and submit to lab for standard VOC analysis. Weight Hanger Weight Filling and Sampling Port 15

16 Vinyl Chloride in monitoring well post-injection prior to injection VC 5 µg/l Site 1 Reguar VC analysis reports total concentration Ext. Std. and PDB estimates free concentration (RDL 0.2 µg/l) Ext. Std. PDB Guideline Std. RDL Free concentration assessment provides early evidence of remedial progress Three repeated standard analyses at 8-14 months verify remedial success (total conc). 16

17 Site 1: Low flow vs PDB at 4 months post injection Low Flow RDL PDB RDL <RDL 17

18 Low flow vs. Passive diffusion bags Surrogates 140 Low flow Site PDB Site DCA d4 toluene d8 BFB Carbon Amendment Concentration settled (ug/ml) Carbon Amendment Concentration (ug/ml) No measurable carbon amendment concentration in PDBs Surrogate recoveries in PDBs cluster close to 100% recovery 18

19 Low flow VS Passive diffusion bags Internal Standards Low flow Site Carbon Amendment Concentration settled (ug/ml) PDB Site FB 40 Cl Ben DCB Carbon Amendment Concentration (ug/ml) Negligible carbon amendment concentration in PDBs Again good clustering of IS recoveries in PDB samples 19

20 Site 2: High VOC, High Carbon Load 10,000 1,000 PDB before and 3 months after injection, three wells 1wk pre 3mo post Low Flow vs. PDB in same well 3 months post injection IP 302 IP 305 IP 109 free concentration reduction Free and total concentrations equivalent insufficient adsorption 20

21 Conclusions Colloidal activated carbon shown to be an effective remedial approach at low concentration cvoc sites Early stage remedial progress seems promising at high cvoc site High suspended carbon in monitoring wells interferes with lab analysis Dilutions required to enable lab QC to pass, but may result in RDL elevated above guideline Where it is not possible to obtain results with sufficiently low RDL due to residual suspended carbon, approaches to assess freely dissolved contaminant concentrations can verify remedial progress through adsorption. 21

22 Contact Us Name of Contact Job Title of Contact