Testing of an in situ chemical oxidation treatment on a plume of chlorinated aliphatic hydrocarbons: Results, conclusions and future possibilities

Transcription

1 Testing of an in situ chemical oxidation treatment on a plume of chlorinated aliphatic hydrocarbons: Results, conclusions and future possibilities

2 Project Objective The pumping and treatment of a plume of dissolved chlorinated aliphatic hydrocarbons (CAH) is generally a hydraulic confinement method rather than a rehabilitation solution. The estimated pumping time for rehabilitating a plume of dissolved CAH can be very long, often on a scale of tens or hundreds of years. In order to reduce the pumping times and complete a possible rehabilitation, in situ processes have been evaluated and applied. The study reported presents the challenges encountered in the application of one in situ treatment method, chemical oxidation. Testing of chemical oxidation Introduction Montréal, April 26,

3 Presentation Contents 1. Background 1. a. Challenges and context of the sector to be treated 2. Chemical oxidation testing 1. a. Preparatory testing and hydrogeological characterization b. Completion of the injection test 3. Evaluation of chemical oxidation treatment effectiveness 1. a. Results and geochemical monitoring of the groundwater b. Costs associated with the various work 4. Conclusion Testing of Chemical Oxidation Introduction Montréal, April 26,

4 Background Chemical oxidation treatment of an unconfined aquifer

5 Hydrogeological Context A Maximum 50 µg/l A' Chemical Oxidation Background Montréal, April 26,

6 Methods available for preventing CAH from migrating off the property Methods evaluated as of June 2013 Soil- bentonite containment wall Reac5ve barrier with filtra5ng gates Chemical oxida5on Hydraulic confinement Chemical oxidation with potassium permanganate was selected for the performance of this oxidant in treating the CAH present at the site and for its persistence in the soil. Chemical Oxidation Choice of Treatment Method Montréal, April 26,

7 Objective of Chemical Oxidation Treatment The main CAH to be treated are trichloroethylene (TCE), dichloroethylene (DCE) and vinyl chloride (VC). Trichloroethylene (TCE) is a chlorinated aliphatic hydrocarbon that was mostly used as a metal degreaser. Oxydant TCE 2KMnO 4 +C 2 HCl 3 2CO 2 + 2MnO 2 + 2K + + H + + 3Cl - Chemical Oxidation Testing Treatment Objective Montréal, April 26,

8 In situ chemical oxidation testing Chemical oxidation treatment of an unconfined aquifer

9 In Situ Chemical Oxidation Testing (INCO) Work completed: Planning of the INCO and installa5on of 13 injec5on wells and 24 observa5on wells. Soil sampling and piezocone survey. Preparatory tes5ng (2 pumping tests, 2 salt tracing tests, 30 permeability tests) Injec5on of potassium permanganate in 13 wells Monitoring of injec5on opera5ons (volume injected, flow, pressure, water level measurements and conduc5vity in the observa5on wells) Monitoring of geochemical condi5ons in the observa5on wells Chemical Oxidation Work Completed Montréal, April 26,

10 Results from the Pre-injection Tests Impact radius under injection estimated at 10 m Natural demand for oxidant 6 g/kg MnO 4 No presence of organic matter in the soil The permeability of the aquifer varies between 10-4 and 10-7 m/s Following the tests, a single phase of injection was conducted from September 27 to October 31, 2014 (~ 400 m 3 of permanganate solution pumped into 13 injection wells). Chemical Oxidation Results of the Pre-injection Work Montréal, April 26,

11 Chemical Oxidation Effectiveness (north sector) Concentration TCE (ug/l) TCE au nord du fossé (site 13PI03) 13PI03 14TRC07 14TRC08 14TRC09 14TRC10 14TRC11 14TRC12 1 Avant l'injection Après l'injection Date d'échantillonnage 6 m of hydraulic load 6 litres/minute 23 m 3 of solution Chemical Oxidation Chemical Oxidation Effectiveness Montréal, April 26,

12 Chemical Oxidation Effectiveness (south sector) Concentration TCE (ug/l) TCE au sud du fossé 14PI07 14PI11 14PI12 14PI14 14TRC22 14TRC23 14TRC24 14TRC25 13PZ602 1 Avant l'injection Après l'injection Date d'échantillonnage 4-9 m of hydraulic load 5-8 litres/minute m 3 of solution Chemical Oxidation Chemical Oxidation Effectiveness Montréal, April 26,

13 Pe-pH Conditions Chemical Oxidation Chemical Oxidation Effectiveness Montréal, April 26,

14 Results Chemical oxidation treatment of an unconfined aquifer

15 Follow-ups on Groundwater Quality Several groundwater quality follow-ups were conducted in the 8 months following the injection of permanganate. Iron and manganese are present naturally in high concentrations in groundwater (iron mg/l and manganese mg/l) Potassium (K) was detected in the observation wells following the INCO up to a radius of 6 m, but the oxidant MnO 4 - did not penetrate any further than 2 m. The identical redox conditions before and after the injection demonstrate that the elevated DCO in this aquifer consumes the oxidant very quickly before it can react with the CAH. Chemical Oxidation Results of the Chemical Analyses Montréal, April 26,

16 Extent of the Plume Zone to be Treated µg/l 100 µg/l 50 µg/l 300 µg/l Chemical Oxidation Extent of the Plume Montréal, April 26,

17 Results of the Chemical Oxidation Evaluation In situ demand for oxygen greater than what was estimated in the laboratory A more limited action radius than expected Precipitation of the oxidizing solution in the soil A more extended contaminated zone is probable Need to inject a larger volume of solution and to densify the network of injection wells. Involves much higher costs to treat the targeted zone. Chemical Oxidation Evaluation of the Treatment Method Montréal, April 26,

18 Cost Associated with the Work Work Main Costs Ratio Injection test including the preparatory work Application of the in situ oxidation at full scale with 3 injection phases Hydraulic confinement Detailed characterization of the aquifer, injection trailer, development of injection wells, oxidant Development of 50 injection wells to cover the entire zone to be treated and the oxidant Development of wells and the pumping station Chemical Oxidation Costs Associated with the Work Montréal, April 26,

19 Lessons drawn from the tests and future possibilities Chemical oxidation treatment of the unconfined aquifer

20 Knowledge Acquired from the Aquifer Aquifer range where all the CAH concentrations are located Concentrations in TCE, DCE, VC Extent of the zone to be treated/confined Hydraulic properties of the aquifer (permeability, anisotropy, drainage speed) Geochemistry of the aquifer and groundwater matrix This knowledge has made it possible to better understand the site and to plan a hydraulic confinement system that is appropriate to the hydraulic context. Chemical Oxidation Knowledge of the Aquifer Montréal, April 26,

21 Future possibilities for reducing pumping times Activated colloidal coal coated in biodegradation-stimulating compounds (BOS 100 TM, PlumeStop TM ) could be used to stop the CAH plume and treat it. It would be preferable to stimulate CAH biodegradation in a reductive environment (anaerobic). To achieve this, we would need to understand the geochemical conditions and use the best electron donor for these conditions (e.g. nitrates, sulfates or Fe). However, the costs could be significant if using these products. Chemical Oxidation Future Possibilities Montréal, April 26,

22 Conclusions Chemical oxidation treatment of the unconfined aquifer

23 Conclusion Chemical Oxidation Detailed hydrogeological knowledge of the area to be treated is required to ensure the effectiveness of the chemical oxidation. The quantity and quality of the hydrogeological data could involve a considerable but necessary investment. Other in situ treatment methods could be considered, but the costs are higher. Connecting the unconfined aquifer to the hydraulic confinement system is the least costly and preferred option for this site. Chemical Oxidation Conclusion Montréal, April 26,