Contributions to Aquifer. Geology & Geological Engineering

Transcription

1 Modeling the Electron Donor Contributions to Aquifer Denitrification: Karlsruhe, Karlsruhe ND Scott F. F Korom Geology & Geological Engineering

2 Denitrification NO3- NO2- NO N2O N2 Four Requirements (Firestone, 1982) Nitrous oxides Suitable bacteria Restricted O2 availability Suitable tab e e do donors o s [o [organic ga c C, Su inorganic sulfide, and Fe(II)]

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4 ISMs: Finished Product Ground dsurface Water Table

5 Network of In-Situ Mesocosms 2 sites sites Site Estimated 0 Order Rate (mg/l/day) 1. Larimore, ND (6 tests) 2. Hamar, ND < 0.01 (2 tests) 3. Karlsruhe, ND, G Site 3. Karlsruhe, ND, S Site (2 tests) 4. Robinson, ND Akeley, MN Perham, MN, M Site 6. Perham, MN, W Site Luverne, MN New Providence, IA, Deep New Prov., IA, Shallow Oakes C1 9. Oakes G (2 tests) (2 tests) sites sites

6 Network of In-Situ Mesocosms 2 sites sites Site Estimated 0 Order Rate (mg/l/day) 1. Larimore, ND (6 tests) 2. Hamar, ND < 0.01 (2 tests) 3. Karlsruhe, ND, G Site 3. Karlsruhe, ND, S Site (2 tests) 4. Robinson, ND Akeley, MN Perham, MN, M Site 6. Perham, MN, W Site Luverne, MN New Providence, IA, Deep New Prov., IA, Shallow Oakes C1 9. Oakes G (2 tests) (2 tests) sites sites

7 Adapted from Schuh et al. (2003) Estimated total nitrate-n nitrate N load of 4.2E6 4 2E6 pounds, at $0.20/lb = $840,000.

8 Korom et al. (2012) Korom et al. (2012)

9 Nitrate to 20% of initial value; Bromide to 44% of initial value.

10 Nitrate to 20% of initial value; Bromide to 44% of initial value.

11 Nitrate to 20% of initial value; Bromide to 44% of initial value.

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14 Barite (BaSO 4 ) Gypsum (CaSO 4 2H 2 O) Epsomite (MgSO 4 7H 2 O) Jarosite-K [KFe 3 (SO 4 ) 2 (OH) 6 ] Calcite (CaCO 3 ) Magnesite (MgCO 3 ) Quartz (SiO 2 )

15 Organic C 0.017% Sulfide (as FeS 2 ) 0.19% Non-pyritic Fe(II) 0.49% Total Fe(II) 0.66% Tesfay (2006)

16 Organic C 0.017% Sulfide (as FeS 2 ) 0.19% Non-pyritic Fe(II) 0.49% Total Fe(II) 0.66% Tesfay (2006)

17 Organic C 0.017% Sulfide (as FeS 2 ) 0.19% Non-pyritic Fe(II) 0.49% Total Fe(II) 0.66% Tesfay (2006)

18 Geochemical Modeling of Denitrification at Karlsruhe S Site Denitrification half-reaction: 2NO H e - N 2 + 6H 2 O e - Donor half-reactions: Organic Carbon CH 2 O + H 2 O CO 2 + 4H + + 4e - Pyrite FeS 2 + 8H 2 O 2SO Fe H e -

19 Mössbauer analysis showed Fe(II)/Total Fe = 50 65%. XRD analysis showed Fe(II) minerals present were: Clinochlore [(Mg,Fe 2+ )5Al(Si 3 Al)O 10 (OH) 8 ] Biotite [K(Mg,Fe 2+ ) 3 (Al,Fe 3+ )Si 3 O 10 (OH) 2 ] Amphibole [(Ca 2 Mg 2 1.5Fe 2+ Fe 3+ )Si 8 O 22 (OH) 2 ] Minimizing Fe(II) [(4Fe 2+ 2Fe 3+ )Si 8 O 22 (OH) 2 ] Maximizing Fe(II)

20 Geochemical Modeling of Denitrification at Karlsruhe S Site Denitrification half-reaction: 2NO H e - N 2 + 6H 2 O e - Donor half-reactions (continued): Ferrous Iron Ca 2 Mg 2 Fe 2.5 Si 8 O 22 (OH) H + + 8H 2 O 2Ca Mg Fe 2+ + Fe H 4SiO 4 OR Fe 6 Si 8 O 22 (OH) H + + 8H 2 O 4Fe Fe ( ) 2 2 8H 4 SiO 4

21 Geochemical Modeling of Denitrification at Karlsruhe S Site 1. Model: PHREEQC (Parkhurst and Appelo, 1999). 2. For each sampling date use Br dilution to estimate diluted NO 3 conc. 3. Import water quality data for each date and reduce Na with Br dilution factor. 4. Force denitrification by pyrite to match actual sulfate increase. 5. React remaining nitrate lost with the following e - donors: a. By organic C only b. Equal amounts of mixed-fe amphibole and organic C. c. 90% organic C and 10% hornblende. 6. Force water into equilibrium with calcite, magnesite, and quartz. 7. Repeat steps 2-6 for each successive sampling date. This methodology forced exact matches between simulated and actual dissolved concentrations for sulfate, nitrate, and Br and resulted in an exact match for silica and approximate matches for Na, K, Mn, Fe, ammonium, Al, Ba, F, and Cl. The remaining four analytes, ph, inorganic C, Ca, and Mg were compared to see which mix of e - donors best explained the evolution of these analytes with denitrification in the ISMs.

22 Korom et al. (2012)

23 ISM-S1S1 Pyrite 4-18% Organic C 77-91% Fe(II) hornblende 3-6% Organic C 49-73% Fe(II) mixed-fe amphib % ISM-S2 Pyrite 4-18% Organic C 75-92% Fe(II) hornblende 2-8% Organic C 43-68% Fe(II) mixed-fe amphib % Korom et al. (2012)

24 Postma (1990) Lab study on the kinetics of denitrification by detrital Fe(II)-silicates Af d it [Na [N 3(Fe (F 2+,Mg) M )4Fe F 3+Si8O22(OH)2] for f amphiboles. hib l Arfvedsonite Augite [(Ca,Na)(Mg,Fe,Al)(Si,Al)2O6] for pyroxenes. Estimated zero-order nitrate reduction rates of roughly 4 x 10-5 M/yr (0.6 mg NO3-N/L/yr). Using our zero-order zero order rates and multiplying each by the fraction attributed to Fe(II)-silicates in the simulations gives a range of 2.2 x 10-5 to 1.3 x 10-4 M/yr for hornblende ( mg NO3-N/L/yr) 1.4 x 10-4 to 7.3 x 10-4 M/yr for mixed-fe amphib. ( mg N/L/yr). BUT, he used nitrate-n concentrations ~ 10-5 M (~0.1 to 0.2 mg/l). We used nitrate concentrations 102 to 103 greater.

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26 Conclusions Using CH2O for organic C and ( ) pyrite py silicates for Fe(II), explained 4-18% of the ( ) ( silicates)) denitrification, Fe(II) explained 2-43%, and OC 43-92%, depending explained p p g on the sample date. y Fe(II) ( ) ((silicates)) were Rates by greater than lab rates, but concentrations were 102 to 103 times greater.

27 Acknowledgments g William Schuh, ND State Water Commission ND Department of Health ND WRRI (USGS & ND SWC) Eben Spencer, Tedros Tesfay, and Jason Warne Thank you!