Lessons Learned During In Situ Chemical Oxidation - Failure & Success?

Transcription

1 Lessons Learned During In Situ Chemical Oxidation - Failure & Success? by Gary Millard (Shell Canada Products) Nancy Hansen, Jarek Kuczynski (O Connor Associates Environmental Inc.) Presented by Gary Millard RemTech 2007, Banff, AB 1

2 Background In situ chemical oxidation products are being sold as broadly applicable for hydrocarbon remediation. We tried one of these products, RegenOx, TM at two sites. 2

3 Our Findings from Site Trials: Some key characteristics should be known about a site before using chemical oxidation in order to understand both the target effects and the side effects This will help determine if in situ chemical oxidation is the correct approach. 3

4 Presentation Outline Theory of Chemical Oxidation Case Studies & Results Discussion of Key Characteristics Conclusion 4

5 Theory of Chemical Oxidation Range of products Persulfates, percarbonates, peroxides, permanganates RegenOxTM is a chemical formulation of an oxidant complex: sodium percarbonate, 2Na 2 CO 3 3H 2 O 2, sodium carbonate (Na 2 CO 3 ), sodium silicate and silica gel; and the activator complex: ferrous sulfate (FeSO 4 ), sodium silicate and silica gel. 5

6 Theory of Chemical Oxidation Stoichiometry (how much do we need?) for oxidation of benzene: C 6 H H 2 O 2 > 6CO H 2 O RegenOx (oxidant)/benzene (wt/wt) = 20.1 Reactions occur in aqueous phase 6

7 Theory of Chemical Oxidation Slurry Mixture manufacturer recommended percent of oxidizer in solution: 9% to 4% = 5 L to 10 L water per kg RegenOx (oxidant+activator) to oxidize 1 kg benzene requires 40 kg RegenOx (oxidant+activator) in approximately 200 L to 400 L water By-products Sodium (Na), Iron (Fe), Sulfate (SO 4 ) 7

8 Theory of Chemical Oxidation Delivery methods Slurry injection, injection into existing wells, powder socks The objective is to achieve contact with affected soils. 8

9 Delivery Methods: slurry injection 9

10 Delivery Methods: injection into existing wells 10

11 Delivery Methods: powder socks or tubes 11

12 Case Studies Two sites: Both former service stations in central Alberta with coarse-grained soil Results of Field Trials of RegenOx TM Ability to deliver the slurry Observed hydrocarbon degradation Production of undesirable by-products 12

13 P Site BH23 13

14 P Site Stratigraphic Column 14 Zone of Impact Zone of Impact

15 P Site Contaminant concentrations in soil (mg/kg): B: up to 63 F1 - BTEX: up to 8900 T: up to 550 F2: up to 1000 E: up to 200 F3: <10 X: up to 1900 F4: <20 total mass of contaminants (geometric mean): 300 kg initial estimate (1000 kg post-injection estimate) volume of soil affected ~600 m 3 15

16 P Site RegenOx prescription: total mass = 12,250 kg (oxidant & activator) * diluted into at least 61,250 L of water 2 m x 2 m injection spacing maximum pumping rate was 3.8 L/min, with actual rates decreasing due to formation pressure at each injection point * estimate based on initial PHC mass estimate 16

17 P Site Approximately 50% of recommended mass was delivered over 1-year period Actual amount of RegenOx delivered to subsurface: ~ 6,000 kg (~51,000 L of water) consisting of 6 injection events each injection event lasting 1 to 3 days 17

18 P Site: Approximate Plume Area (before and after) With 50% of recommended mass of RegenOx injected there was no definitive change in the lateral extent of impacted soil or groundwater plume, although concentrations within the plume had reduced. 18

19 P Site: Dissolved Hydrocarbons in BH kg mg/l kg 865 kg 903 kg 1002 kg Dec-05 Mar-06 Jul-06 Oct-06 Jan-07 Apr-07 Aug-07 Nov-07 Benzene Toluene Ethylbenzene Xylenes PHC F1 minus BTEX PHC F2 19

20 P Site: Soil Benzene in the Vicinity of BH BH23 start of insitu remediation by chemcial oxidation BH45 program mg/kg Benzene Criterion: 0.55 mg/kg Jan-03 Jan-04 Jan-05 Jan-06 Jan-07 Jan-08 BH47 BH48 BH55 20

21 P Site: Soil TEX, F1 and F2 in the Vicinity of BH BH23 start of insitu remediation by chemical oxidation program 3000 mg/kg BH45 BH47 BH Jan-03 Jan-04 Jan-05 Jan-06 Jan-07 Jan-08 BH55 Toluene Ethylbenzene Xylenes F1 - BTEX F2 21

22 S Site BH18 BH13 BH22 22

23 S Site Stratigraphic Column 23 Zone of Impact

24 S Site Contaminant concentrations in soil (mg/kg): B: up to 0.2 F1 - BTEX: up to 400 T: up to 0.55 F2: up to 3670 E: up to 11.0 F3: up to 2430 X: up to 37.2 F4: up to 2790 total mass of contaminants (geometric mean): 300 kg (initial estimate) volume of soil affected ~500 m 3 24

25 S Site RegenOx prescription: total mass = 12,200 kg (incl. oxidant & activator) diluted into 122,000 L of water 2 m x 2 m injection spacing injection rate was 1.9 to 3.8 L/min per pump at each injection point 25

26 S Site Actual amount of RegenOx (oxidant) delivered to subsurface: ~ 4,980 kg (~60,000 L of water) Approximately 50% of recommended mass was delivered over 1-year period consisting of 2 injection events each injection event lasting 2 to 3 days 26

27 S Site Plume Before Injection 27

28 S Site Plume After Injection 28

29 S Site: Dissolved Hydrocarbons in BH kg Jul-06 Oct-06 Jan-07 Apr-07 Jul-07 Oct-07 BTEX & F1 (mg/l) 3290 kg F2 (mg/l) Benzene Toluene Ethylbenzene Xylenes F1 minus BTEX F2 29

30 S Site: Soil Hydrocarbons in Vicinity of BH13 & BH22 7 BH BTEX (mg/kg) BH kg 3290 kg F1, F2, F3 (mg/kg) 1 BH35 & BH Jan-03 Jan-04 Jan-05 Jan-06 Jan-07 Jan-08 0 Benzene Toluene Ethylbenzene Xylenes F1 minus BTEX F2 F3 30

31 S Site: Soil Hydrocarbons in Vicinity of BH BH18 BH kg 3290 kg BTEX (mg/kg) F1, F2, F3 (mg/kg) 4 BH Aug-06 Nov-06 Feb-07 May-07 Aug-07 Nov-07 Benzene Toluene Ethylbenzene Xylenes F1 minus BTEX F2 F3 31

32 Success of Delivery Slurry was delivered easily at S site there seemed almost no limit to what we could inject We had trouble injecting at P site short circuiting to ground low injection rates achieved Why? 32

33 Success of Delivery P Site versus S Site D 50 =103µm n=0.27 k=3.1 x 10-6 m/s D 50 =10 920µm n= k=3.1 x 10-4 m/s D 50 =5µm n=0.44 k=2.2 x 10-7 m/s D 50 =44µm 33

34 Failure of Delivery Differences in hydraulic conductivity High initial injection pressure at P Site may have fractured the formation, creating preferential pathways Existing infrastructure at P Site created further alternative pathways 34

35 Hydrocarbon Degradation Ability to deliver was different Natural TOC was similar Both ranged from 0.5% to 0.6% Total hydrocarbon masses and maximum concentrations were different Different oxidant exposure to impacts, specifically, short circuiting due to injection pressures greater than formation would accommodate This all affects the amount of oxidant required. 35

36 Undesirable By-Products Both sites had FAL and drinking water receptors Sodium is a major component of RegenOx Drinking water criterion for sodium is 200 mg/l 36

37 P Site : Sodium (Na) concentration in groundwater 37 Sodium (mg/l) Mar-06 May-06 Jul-06 Sep-06 Nov-06 Jan-07 Mar-07 May-07 Jul-07

38 S Site : Sodium (Na) concentration in groundwater versus time 38 Sodium (mg/l) Mar-06 Jun-06 Sep-06 Dec-06 Mar-07 Jun-07 Sep-07

39 Conclusions Practical considerations to in situ chemical oxidation: How much oxidant will you need? How long will it take? Can you live with the side effects? Know these answers before you embark on a full-scale injection program. 39

40 Acknowledgements G & R Remediation Regenesis Canada Colors and Chemicals Limited Alberta Environment 40