In Situ Treatment of Contaminated Soil and Groundwater: Lessons Learned from the Field

Transcription

1 In Situ Treatment of Contaminated Soil and Groundwater: Lessons Learned from the Field Presented by Alan Weston, Ph.D. Conestoga-Rovers & Associates Niagara Falls, NY, USA

2 Agenda 1. Introduction to In Situ Treatment 2. In Situ Technologies 3. Case Studies 4. Conclusion 2

3 In Situ Remediation Treatment of soil or groundwater in place Achieved by adding reagents or manipulating subsurface conditions Can be an effective alternative to traditional dig and haul or pump and treat technologies 3

4 In Situ Remediation Less intrusive, public acceptance Transition to MNA and closure achieved more easily Less disruption to property, use can continue 4

5 In Situ Remediation Technologies include: - Monitored natural attenuation (MNA) - In situ chemical oxidation (ISCO) - In situ enhanced biodegradation (ISEB) - Permeable reactive barrier (PRB) - Air Sparge / Soil vapor extraction (AS/SVE) - In situ stabilization (ISS) - Phytoremediation Wetlands - Soil Flushing 5

6 Agenda 1. Introduction to In Situ Treatment 2. In Situ Technologies 3. Case Studies 4. Conclusion 6

7 In Situ Technologies In Situ Chemical Oxidation (ISCO) Destruction of of contaminants using oxidizing reagents Catalyzed Sodium Persulfate, Fenton s Reagent, Permanganates or ozone may be used to reduce high concentrations Treatability study is recommended determine optimum dosage of reagents ISCO is site specific and successful treatment is a function of an effective delivery system 7

8 In Situ Technologies In Situ Enhanced Biodegradation (ISEB) Contaminants are metabolized into less toxic or non-toxic compounds by microbes Biodegradation is enhanced through the addition of carbon/energy sources, electrons acceptors, nutrients and microbial cultures, Enhanced aerobic conditions favor the biodegradation of BTEX, petroleum hydrocarbons, PAH, oxygenates Enhanced anaerobic conditions favor the biodegradation of chlorinated solvents 8

9 In Situ Technologies Air Sparge/Soil Vapor Extraction (AS/SVE) Vertical sparge wells inject air, into the water table to strip VOC out of groundwater Air is drawn through the soil by a vacuum Vertical or horizontal SVE wells installed in the unsaturated zone above sparge zone for vapor collection Decrease in pressure is created allowing release of vapor. Extracted gas flow is vented to the atmosphere or treated 9

10 Agenda 1. Introduction to In Situ Treatment 2. In Situ Technologies 3. Case Studies 4. Conclusion 10

11 Case Study #1. Large Scale In Situ Remedial Action: CRA Self Implementation Large Site in Illinois was impacted with chlorinated solvents CRA reviewed site data and performed a remedial technology assessment ISCO and SVE were the technologies recommended for further consideration for on-site impacts 11

12 On-Site Treatment Area AS/Injection Well SVE Well Treatment Area 80 ft x 700 ft Road

13 Case Study 1 A laboratory treatability study was performed to test ISCO Results of ISCO testing showed that KMnO 4 and catalyzed Na 2 S 2 O 8 would be suitable oxidants Na 2 S 2 O 8 was chosen for on-site treatments based on lower costs, no regulatory issues and sustainability (lower carbon footprint) SVE implementation was also recommended 13

14 ISCO performed first Case Study 1 4,000 gallons of catalyzed Na 2 S 2 O 8 solution was pumped into each A/S well 167,000 gallons was pumped into horizontal trenches Personnel from local offices installed trenches and performed injections with ITG help 1 month after ISCO injection was complete the A/S and SVE systems were connected 14

15 Results Percent Reduction PCE TCE DCE MW-2 74% 99% 100% MW-3-98% 91% MW-5 100% 78% - MW-6 88% 97.5% 100% MW % 99.7%

16 Results Greater than 74% removal of all chlorinated solvents was observed Horizontal and vertical injections achieved good dispersal of oxidant in the subsurface One injection event was required Lessons Learned Cost saving obtained by: - Use of sodium persulfate - Field implementation performed by CRA personnel no need specialists 16

17 Case Study #2. Treatment of Metals in Groundwater Groundwater at a site was contained lead and silver Source area concentrations exceeded local regulatory criteria and posed a water quality risk to a downgradient creek A treatability study was performed to test reducing agents for their ability to precipitate these compounds from groundwater 17

18 Treatability Study Results Al Ba Be Cu Control Na Dithionite Na Metabisulfite Na Sulfide Ca Polysulfide Pb g Ni Ag Zn 18

19 Full Scale Application Sodium sulfide injections were performed at 30 injection wells in the primary source zone at the Site Increased sulfide was observed in all monitoring wells indicating that the injected materials reached these wells In all the treatment areas, dissolved lead and silver were reduced to non-detect levels by the 1-month sampling event Levels of total lead and silver had increased by the 1- month sampling event due to suspended particulates Dissolved iron increased in the wells treated by the sodium sulfide injection. Soluble ferrous iron is produced under reducing conditions 19

20 Lessons Learned Sodium sulfide is effective for the precipitation of lead and silver in groundwater Presence of light metal sulfides can interfere with dissolved metals analysis Any perturbation to the groundwater (e.g. sampling) has the potential to resuspend metals sulfides in the groundwater 20

21 Case Study 3 - Anaerobic Biodegradation of Chlorinated Solvents Former chemical manufacturing facility in Michigan Various chlorinated solvents in groundwater Emulsified soy lactate was injected to stimulate biodegradation of chlorinated compounds 21

22 Injection Layout Soy Lactate Barrier Injections by direct push 22

23 [VOC] (ug/l) [c-1,2-dce] 200 Injection Performed Monitoring Results Mar-10 May-10 Jun-10 Aug-10 Sep-10 Nov time 1,1-DCE 1,2-DDP TCE VC Ethene c-1,2-dce 23

24 Results Strongly reducing conditions were created throughout the treatment area Reductions in chlorinated CVOC concentrations occurred after 90 days and after 180 days Reductions in concentrations of breakdown products such as cis-1,2-dce were observed The presence of dissolved ethane and ethene indicated that complete biodegradation of the chlorinated compounds was occurring 24

25 Lessons Learned Results Emulsified soy lactate is effective in stimulating reductive dechlorination The performance of a laboratory treatability study and careful design of the field implementation can lead to a smooth, problem free treatment 25

26 Case Study 4: isoc PRB for BTEX Site in Texas had BTEX In groundwater In situ submerged oxygen curtain (isoc) units were installed at the Site in order prevent further migration of the BTEX plume by treating the BTEX at the perimeter of the plume. The isoc units were placed as a barrier, downgradient of the BTEX source area. Nutrients were injected into the isoc wells 26

27 isoc Barrier Location of isoc Barrier 27

28 Results Concentrations of oxygen in groundwater in isoc wells >30 mg/l Benzene and petroleum hydrocarbon concentrations showed an immediate decrease after the isoc system was started A cycle of decreasing concentrations followed by rebound has been observed and is expected to continue until LNAPL has been removed from the capillary fringe Concentrations downgradient of the barrier are low 28

29 Lessons learned Results LNAPL can be treated by in situ enhanced biodegradation, however it takes time Requires operation of the isoc treatment system until LNAPL has been removed 29

30 Agenda 1. Introduction to In Situ Treatment 2. In Situ Technologies 3. Case Studies 4. Conclusion 30

31 Conclusion In situ treatment has the potential to complete treatment efficiently and cost effectively An understanding of site conditions is required in order to determine whether in situ technologies are appropriate for the site Necessary to determine which in situ technology is right for the site Safe and effective application of the technology can be performed by CRA 31