Laboratory Tests and Field Investigations of DNAPL Source Zone Remediation Using Granular Iron

Transcription

1 Laboratory Tests and Field Investigations of DNAPL Source Zone Remediation Using Granular Iron Sharon L.S. Wadley and Robert W. Gillham Department of Earth Sciences University of Waterloo Waterloo, Ontario, Canada RTDF Meeting October 15-16, 16, 2003

2 DNAPL Remediation Using Isolation Technology and Granular Iron Soil-mixing augers used to mix iron-bentonite slurries in situ Bentonite Initially, a lubricant and viscosifer to facilitate injection Subsequently, reduces hydraulic conductivity of mixed zone Mixing homogenizes contaminated region Contaminant diffuses to iron surface within mixed zone where dechlorination takes place

3 Research Objectives To determine, through laboratory testing, whether mixing granular iron, bentonite and saturated materials contaminated with free-phase chlorinated ethenes would prove an effective remediation method To demonstrate the concept in a field setting, to evaluate the remediation potential and installation method

4 Experiments 1. Preliminary Batch Experiment 2. Field Demonstration 3. Laboratory Experiment

5 Experimental Preparation Hypovials contained: (Wt%) Master Builders Iron (med-fine): 1.3 g (5%) Baroid Benseal Bentonite: 3.5 g (12%) Borden Sand: 23.5 g (83%) Distilled water: 49.3 ml (average) Free-phase TCE: 0.11 g (2x solubility) Periodically, hypovials were sacrificed to measure aqueous concentrations of TCE and potential degradation products

6 TCE and Chloride Concentrations TCE Concentration (mg/l) t ½ = 11.1 hrs (normalized to 1 m 2 Fe / ml solution) Solubility Max Cl Chloride Concentration (mg/l) Elapsed Time (days)

7 Organic Degradation Products Concentration (mg/l) VC 11DCE tdce cdce Total organic degradation products < 1% original TCE Elapsed Time (days)

8 Field Demonstration: Objectives To determine whether mixing slurries of granular iron and bentonite into contaminated geological material promotes in situ removal of DNAPL To test the feasibility of producing uniform iron/bentonite/soil/dnapl mixtures

9 (m bgs) 0 CFB Borden: Geology Surface Aquifer (Beach sand) 3 4 Upper Aquitard (Silty clay) 7.5 Stiff Blocky Texture Soft Plastic Texture Lower Aquitard (Diamict( Diamict) Forested Site 9x9 m Cell 11.5 Lower Aquifer (Silty sand)

10 Site History x9m sheet-piling cell constructed in Borden aquifer and keyed into aquitard L PCE released to monitor migration - 39 days later PCE was found in aquitard L DNAPL removed 9x9 m Cell 1998 KMnO 4 experiment Estimated PCE remaining 1998: 350 L (200 L in aquifer and 150 in aquitard)

11 9x9 m Cell Borden, ON

12 61 cm 81 cm

13 Iron-Bentonite (IB) Slurry

14 Iron-Bentonite Mixing Process IB slurry delivered to subsurface through drill rods Mixing blades were raised and lowered several times to homogenize region Tapered blades prevented materials from surfacing

15 Location of Mixed Zones 9x9 m Cell (m bgs) 0 MZ1 (5% IB) MZ2 (10% IB) MZ3 (5% Ben.) MZ4 (5% IB) Surficial Aquifer Aquitard Fractures Lower Aquifer Sand Microbeds 11.5

16 Location of Mixed Zones: Plan View Door 9x9m Cell N MZ1 (5% IB) MZ2 (10% IB) 1991 PCE Release MZ3 (5% Ben.) Background and MZ4 in Aquitard (5% IB) B2 B1 B3 Background Aquifer (B1, B2, B3) DNAPL in Aquitard Background Aquitard KMnO 4 Injections

17 Field Sampling & Analyses Coring at Site Soil samples were stored in methanol and acetonitrile Laboratory Analyses GC/ECD analyses for PCE and TCE GC/PID analyses for VC and DCE isomers Combination electrode for Cl - analyses

18 Iron Distribution in Aquifer Mixing Zone 2 (10% Iron-bentonite) well-mixed but not homogenized 6.5 ft 7.0 ft

19 Aquifer PCE Concentrations (Background) Concentration (µg( g PCE / g soil) B2 B ,000 10,000 B1 0.5 DNAPL Depth (m bgs) B3 near sheet- piling wall B2 near centre of 9x9m Cell B1 B2 B3 3.5

20 Mixing Zone #1 PCE Concentrations (5% Iron-bentonite) Concentration (µg( g PCE / g soil) ,000 10,000 Depth (m bgs) t ½ = 368 hrs (normalized to 1 m 2 Fe / ml solution DNAPL Mixing Limits Day 0 Day 39 Day 101 Day

21 Mixing Zone #2 PCE Concentrations (10% Iron-bentonite) Concentration (µg( g PCE / g soil) , Depth (m bgs) DNAPL Mixing Limits Day 0 Day 35 Day 97 Day

22 Mixing Zone #3 0.0 PCE Concentrations (Control - 0% Iron, 5% Bentonite) Concentration (µg( g PCE / g soil) ,000 10,000 Depth (m bgs) DNAPL Mixing Limits Day 0 Day 35 Day 97 Day

23 Degradation Products in the Aquifer TCE and DCE isomers Total DCE in iron-mixed zones < 0.5 µg VOC / g soil TCE was detected in background and mixed-zones Chloride Uncontaminated aquifer measures mg/l Background cores in 9x9m Cell mg/l Amounts detected in iron-mixed zones did not correspond to PCE degradation Possibly due to nearby KMnO 4 experiment Therefore, could not confirm PCE degradation

24 Cell Experiment: Objectives Examine DNAPL disappearance using a substantial amount of free- phase PCE, and under conditions in which the degradation process could be examined more reliably than the field demonstration

25 Construction Gas-venting valve 28 cm 30 cm ID 10 side ports (1.5 cm diameter) Composition: PVC pipe and plate welded

26 Assembly Borden sand, Baroid Benseal bentonite, and Master Builder medium- fine granular iron Distilled water mixed until saturated Free-phase PCE (dyed red with Sudan IV) Cell was packed and sealed as quickly as possible

27 Cell Contents (by volume) Cell 1 (control) 2 3 Borden Sand (Volume %) Bentonite (Volume % when wet) Iron (%) PCE (% pore space) 6% (0.5 L) 8% (0.5 L) 7% (0.5 L) Porosity of Cell a a) Estimated using amount of water used to saturate cell

28 Sampling Procedure Cored from side: Shallow, Central and Deep ports cm cm

29 Sampling Procedure Cored from side: Shallow, Central and Deep ports 5 30 cm 4 samples taken from each port: 1 st 2 nd st & 3 rd stored in methanol nd & 4 th stored in acetonitrile cm Analyses: PCE, TCE DCE isomers Vinyl Chloride Chloride

30 Concentration ( (µg g PCE / g soil) 25,000 20,000 15,000 10,000 5,000 0 Cell 1 (Control) PCE Concentrations Shallow Port (18 cm*) Central Port (11 cm*) Deep Port (3 cm*) Average Elapsed Time (days) DNAPL * Port height above base

31 Concentration ( (µg g PCE / g soil) 25,000 20,000 15,000 10,000 5,000 0 Cell 2 (5% Fe) PCE Concentrations DNAPL Shallow Port (17 cm*) Central Port (11 cm*) Deep Port (4 cm*) Average Elapsed Time (days) 70% removed * Port height above base

32 Concentration ( (µg g PCE / g soil) 25,000 20,000 15,000 10,000 5,000 0 Cell 3 (10% Fe) PCE Concentrations DNAPL Shallow Port (18 cm*) Central Port (11 cm*) Deep Port (4 cm*) Average Elapsed Time (days) 96% removed * Port height above base

33 Chloride Concentrations 50,000 10% iron Concentration ( (mg/l mg/l) 40,000 30,000 20,000 10,000 5% iron Cell 1 Cell 2 Cell Elapsed Time (days) 0% iron

34 Organic Degradation Products Total degradation products measured less than 1% of original PCE added to cells TCE was main product detected (<100 µg/g soil) DCE isomers generally less than 2 µg/g soil, but showed regular trends VC only detected briefly in cells with iron None detected at end of experiment

35 Conclusions: Laboratory Experiments Batch experiment: Batch experiment showed that concept is viable Half-life life was relatively low, possibly due to continuous mixing of hypovials Cell experiment: Experiment using larger cells showed removal of more significant amounts of free- phase PCE

36 Conclusions: Field Demonstration Degradation of PCE was apparent, despite limited DNAPL and irregularity of degradation products Longer half-life life due to static conditions of test Field testing at a larger scale with commercial soil-mixing equipment appears to be warranted

37 Acknowledgements NSERC / Motorola / EnviroMetal Technologies Industrial Research Chair in Groundwater Remediation Geomatrix Graduate Scholarship The Gillham Group Greg Friday, Wayne Noble Paul Johnson, Others in the field and laboratory Bob Ingleton,, Mike Pollice,, Sam Vales Iain McIlwraith, Alpa Jadeja,, Geoffrey Okwi