6. Organic Compounds: Hydrocarbons. General Comments Borden, Canada, tracer test Laurens, SC, gasoline spill Bemidji, MN, crude oil spill

Transcription

1 6. Organic Compounds: Hydrocarbons General Comments Borden, Canada, tracer test Laurens, SC, gasoline spill Bemidji, MN, crude oil spill

2

3 In the subsurface, biogeochemical processes that control contaminant fate vary in space and time, and alter the aquifer aqueous and solid phase chemistry Sequential Depletion of TEAs

4 (e.g. Acetic Acid)

5

6 Examples of Experimental and Case Studies of Organic Contaminant Fate and Transport: Hydrocarbons

7 Benzene,Toluene, and Xylene: Aerobic Degradation Relative to Chloride in a Field-Scale Test at Base Borden 1800 L injected with 2.36 mg/l benzene, 1.75 mg/l toluene, 1.08 mg/l p-xylene, 1.09 mg/l m-xylene, 1.29 mg/l o-xylene, and 1280 mg/l chloride; samples taken up to 434 days Barker, 1987

8 DO profile before Injection, note low DO zone at ~219 m DO profile 32 days after injection, Some DO loss due to biodegradation of B+X Barker, 1987

9 Benzene and Xylene profile 32 days after injection, note movement of B+X greatest in the low DO zone Barker, 1987

10 Mass of Benzene, Toluene, and Xylene Degradation Relative to Chloride in a Field- Scale Test Significant mass loss of all hydrocarbons Only benzene detected after day 200, gone at day 434 Chapelle

11 Barker, 1987 Approximate first-order rates in d -1 for BTX compounds: Benzene Toulene Xylene 0.03 estimated using mass vs time data in fig. 7; Barker, 1987

12 Natural Attenuation Of Petroleum Hydrocarbons: Laurens, SC, Gasoline spill source location - Piedmont Region - Saprolite soil (micaeous clay-sand) - Fractured bedrock 80 feet Chapelle, 2000

13 Groundwater levels, contours, and general direction of flow at the Laurens, SC site June, Ground water ~6-17 ft BLS - Hydraulic Conductivity ~ 3 ft/d - Hydraulic Gradient ~ Porosity ~ GW velocity ~0.15 ft/d to SE Chapelle, 2000

14 Water table >100K K 10-50K 0.5-1K 5-10K 1-5K Sediment concentration values in mg/kg No measured free product in any of the monitoring wells Cross-section showing the total gasoline organic concentrations in sediments beneath the Laurens, SC site Chapelle, 2000

15 Total BTEX concentrations (in mg/l) at the Laurens, SC site Max C = 106,000 mg/l at well MW-6 Benzene = 28,300 mg/l Toluene = 66,700 mg/l Ethylbenzene = 3260 mg/l Xylene = <7500 mg/l 80 feet Chapelle, 2000

16 DO concentrations at the Laurens, SC site (in mg/l) Note reduced DO at the location of the highest petroleum hydrocarbon concentrations, indicative of aerobic biodegradation of hydrocarbons Chapelle, 2000

17 Using the biodegradation rates in the table above (from Chapelle, 2000), calculate the time and distance needed to reduce contaminants to below the appropriate MCL

18 ~ 200 feet from MW-6 Benzene Concentrations (in mg/l) First-order equation: C/C o = exp(-kt) From table 4, k for Benzene is d -1 MCL for Benzene is 5 mg/l C/C o = 5/28,300 = 1.77E-4 time is 865-1,730 d 80 feet at v = 0.15 ft/d, distance would be ft Chapelle, 2000

19 MTBE Concentrations (in mg/l) First-order equation: C/C o = exp(-kt) From table 4, k for MTBE is d -1 at 200 feet and v = 0.15 ft/d travel time =1330 d and C/C o = or 4.4 to 3,350 mg/l a 10 3 difference! Chapelle, 2000

20 Ground Water Contamination by Crude Oil near Bemidji, Minnesota USGS Research Site for over 25 years Isabelle Cozzarelli, Barbara Bekins, and others

21 After the oil flowed to lower lying areas and infiltrated, it formed 3 pools in the subsurface ~80% Oil recovered ~300,000 L remained

22 The North Pool of oil has been the primary focus of research Note GW flow is to Northeast GW velocity ~ m/d

23 Schematic Cross Section of North Pool 1

24 Unsaturated Zone Cross section - Variable saturation, and over time, physical oil loss has occurred due to dissolution and volatilization

25

26 Effect of oil saturation vs location on degradation (a) contours of oil saturation in north pool cross section (b) degree of oil degradation compared with wt percent oil Upgradient>Downgradient Indicates the degree of oil degradation seems to vary primarily with location

27

28

29

30 Upgradient Downgradient

31

32 (Spatial and Temporal Variations)

33 Initial crude oil composition dominated by saturated hydrocarbons (~60%) and aromatic compounds (~35%); dominant hydrocarbons were alkanes (C 6 -C 32 ) Crude oil composition has changed over time ( ) due to physical, chemical, and biological processes

34 1 3 Lower-number Alkanes next 2 Higher-number Alkanes first 4 Only recalcitrant Compounds remain

35

36 DO in

37 Degradation of T,o-X>B,E GW concentrations of BTEX down gradient from the north oil pool, demonstrating selective biodegradation of these compounds

38 Iron-reduction dominates where Fe 3+ is at or near background concentration Fe3+ Fe 3+ Fe 2+ Note depletion of Fe 3+ and increased Fe 2+ under the oil body in the same location and down gradient

39

40 Although the biogeochemical zones are relatively stable, there is some change over time

41 Dissolved Fe 2+ in

42 Fe 2+, BTEX, and CH 4 in the anoxic zone, 50 m down gradient from oil pool center in 1993 (9322) and 1998 (9829/33)

43 Fe 3+ Fe 2+ Dissolved NVDOC, BTEX, CH 4, Iron (II, III) at the edge of the anoxic plume (70 m f/oil pool center) in 1993 (9320), 1997 (9701/2)

44 (~ 50 m) (~ 90 m) Benzene, Ethylbenzene, o-xylene, and 1,3,5-TMB at 50m (532b) and 90m (530b), between 1986 and 1996

45

46 Anoxic

47 Distribution of microbial types in the anaerobic plume beneath the north oil pool; iron reducers dominate in the anoxic zone, note reduced aerobes numbers, particularly in the methanogenic zone 2

48 Benzene

49 First-order degradation rates for Bemidji BTEX microcosms (black diamonds), well data (black squares), modeling (black triangles); other studies are noted by black circles, and grey squares, diamonds, and triangles.

50 Anoxic Conditions (Fe 2+ ) GW monitoring and simulation of the plume chemistry indicated significant aerobic and anaerobic degradation of the oil Model- (Mn 2+ ) V = Volatile; BTEX, methane NV = NonVolatile; e.g. organic acids DOC = Dissolved Organic Carbon

51 Generalized Saturated Zones 1 - Uncontaminated (native) GW 2 - Low DO; high DOC, DIC 3 Anoxic; high HC, Mn 2+, Fe 2+, CH Low HC, aerobic degradation 5 - Oxygenated w/ trace BTEX Unsaturated Zones 6 - Atmospheric O2 7 - Lower O 2 ; trace HC, CO 2, CH Anoxic, large HC, CO 2, CH 4 (note: HC = Hydrocarbons) 1

52 Summary - Hydrocarbons are common contaminants in US aquifers - Of these compounds, specific alkanes degrade more quickly than others, and among aromatic compounds some degrade much more quickly than others. - Degradation rates vary depending on the redox conditions. - In general, aerobic degradation rates are larger than anaerobic rates. - There were distinct differences in the degradation pattern and rates of natural attenuation of hydrocarbons at the three sites; Borden tracer test (selected hydrocarbons), Bemidji, MN (crude oil spill), and Laurens, SC (gasoline spill).

53 Next Organics: Solvents