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GAMA Special Studies on Nitrate in California Groundwater

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GAMA Special Studies on Nitrate in California Groundwater. Bradley K. Esser Jean E. Moran & Michael Singleton Lawrence Livermore National Laboratory. Presented to: National Water Quality Monitoring Conference 2006 San Jose, California May 9, 2006. - PowerPoint PPT Presentation
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GAMA Special Studies on Nitrate in California Groundwater Presented to: National Water Quality Monitoring Conference 2006 San Jose, California May 9, 2006 Bradley K. Esser Jean E. Moran & Michael Singleton Lawrence Livermore National Laboratory This work was performed under the auspices of the U.S. Department of Energy by the University of California Lawrence Livermore National Laboratory under Contract No. W-7405-Eng-48. The Groundwater Ambient Monitoring and Assessment program is sponsored by the California EPA State Water Resources Control Board and carried out in a collaboration between the U.S. Geological Survey and Lawrence Livermore National Laboratory
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Page 1: GAMA Special Studies on Nitrate in  California Groundwater

GAMA Special Studies on Nitrate in California Groundwater

Presented to:National Water Quality Monitoring Conference 2006

San Jose, California

May 9, 2006

Bradley K. Esser

Jean E. Moran & Michael SingletonLawrence Livermore National Laboratory

This work was performed under the auspices of the U.S. Department of Energy by the University of CaliforniaLawrence Livermore National Laboratory under Contract No. W-7405-Eng-48.

The Groundwater Ambient Monitoring and Assessment program is sponsored by the California EPA State Water Resources Control Board and carried out in a collaboration between the U.S. Geological Survey and Lawrence Livermore National Laboratory

Page 2: GAMA Special Studies on Nitrate in  California Groundwater

Nitrate is contaminating California’s groundwater (which supplies half the drinking water supply)

ppm ppm

0%

10%

20%

30%

40%

50%

60%

70%

20 to 45 > 45

Nitrate in CaliforniaPublic Drinking-Water Supply Wells

California state-wideSanta Clara CountyStanislaus County

Fra

ctio

n o

f w

ells

Nitrate (mg/L)

Impacted

Polluted

California DHS data obtained through Geotracker (geotracker.swrcb.ca.gov), August 2003.

Page 3: GAMA Special Studies on Nitrate in  California Groundwater

NO3-

NO3-

NO3- → N2

Effective management of subsurface nitrate contamination requires better tools for

characterizing & simulating nitrate sources, sinks and transport

Case Studies Dairy farm: subsurface denitrification Coastal basins: urbanization Central valley basin: septic discharge

MICROBIAL control of denitrification

MICROBIAL control of denitrification

Heterotrophic denitrification

4NO3- + 5CH2O + 4H+

2N2 + 5CO2 + 7H2O

Page 4: GAMA Special Studies on Nitrate in  California Groundwater

Dairy Farm in Kings County, CADairy farm

Why is there no nitrate at depth? Denitrification? Mixing with old water?

Is dairy nitrate loading being mitigated by natural or induced subsurface processes? Does operation of the dairy

create subsurface conditions conducive to denitrification?

No nitrate

Unsaturated Zone

Low or no nitrate

OX

ICA

NO

XIC

Depth (ft)

High nitrate

AN

OX

IC

Dairy

Page 5: GAMA Special Studies on Nitrate in  California Groundwater

We use “excess nitrogen” to distinguish denitrification from dilution

10

15

20

25

0.25 0.30 0.35 0.40 0.45

Upper aquifer (48-50')Upper aquifer (65-70')Lower aquifer (175-180')Excess air (15 deg C)N

itro

gen

(um

ol/m

ol H

2O

)

Argon (mol/mol H2O)

Atm. equib.at 15 C

Excess N2(equivalent to ~29 ppm NO

3)

+ excess air MIMS: Membrane inlet mass spectrometry Measures nitrogen, argon, oxygen Fast and inexpensive Field deployable

The end product of denitrification is molecular nitrogen (N2, gas)

Groundwater contains “excess air” above equilibrium solubility “Excess nitrogen” is the non-air component due to denitrification

Excess N2 allows quantification of degree of denitrification

Degree of denitrification = Excess nitrogen/(excess nitrogen + residual nitrate)

Dairy farm

Page 6: GAMA Special Studies on Nitrate in  California Groundwater

Excess nitrogen indicates that denitrification has occurred in deeper waters

f = CNO3- / (CNO3- + Cexcess N2)

4

6

8

10

12

14

16

18

20

0%20%40%60%80%100%

KCD groundwaters

Dep

th (

m)

Initial Nitrate Remaining

Denitrification

Oxi

c

Anoxi

c

Dairy farm

Page 7: GAMA Special Studies on Nitrate in  California Groundwater

We are using molecular biology to characterize where denitrification occurs

Bacterial population actively denitrifying(PCR for nitrite reductase RNA)

Bacterial population capable of denitrification(PCR for nitrite reductase DNA)

Quantitative real-time polymerase chain reaction (PCR) is a rapid, sensitive, and highly specific method that can be used to quantify denitrifying bacterial populations based on a diagnostic, functional gene.

DNA mRNA protein

NO2- NO

Nitrite reductase (NirS, NirK)

Dairy farm

Page 8: GAMA Special Studies on Nitrate in  California Groundwater

Real-time qPCR of denitrifier bacterial populations show that denitrification occurs at the oxic-anoxic interface

Dairy farm

Page 9: GAMA Special Studies on Nitrate in  California Groundwater

Stable isotopic composition of nitrate indicates denitrification of a manure nitrogen source

-5

0

5

10

15

20

25

0 10 20 30 40 50 60 70

Stanislaus County

Kings County

18 O

NO

3 (‰

vs. V

SM

OW

)

15N

NO3 (‰ vs. Air)

18O = 0.5 15

N

Starting composition for manure-derived nitrate

Den

itrifi

catio

n

Merced

Dairy farm

Ranges based on compilation of data in Kendall, 1998.

Page 10: GAMA Special Studies on Nitrate in  California Groundwater

Production of methane and carbon dioxide in manure lagoons appears to “strip” atmospheric gases from lagoon waters

Dairy farm

We can use dissolved gases to distinguish between lagoon seepage and field-applied wastewater

Page 11: GAMA Special Studies on Nitrate in  California Groundwater

1.0x10-2

1.5x10-2

2.0x10-2

2.5x10-2

3.0x10-2

3.5x10-2

4.0x10-2

4.5x10-2

5.0x10-2

1x10-4 2x10-4 3x10-4 4x10-4 5x10-4 6x10-4 7x10-4 8x10-4

Dissolved gases in Groundwater and Lagoons

16-33 ft. BGS

35-53 ft. BGS

65-168 ft. BGS

Manure Lagoons

15 C Eq. + xs Air

21 C Eq. + xs Air

Dis

solv

ed

N2 (

cm3 a

t S

TP

/ g

wa

ter)

Dissolved Ar (cm3 at STP / g water)

Den

itrifi

catio

n

Gas Stripping

Excess Air

Equilibrium at 21 C and 15 C

Manure lagoon seepage appears to beassociated with denitrification

Dairy farm

Page 12: GAMA Special Studies on Nitrate in  California Groundwater

No nitrateVery old water(pre-dairy)

Unsaturated Zone

Low or no nitrate Older water(dairy operating)

OX

ICA

NO

XIC

Depth (ft)

High nitrateYoung water

AN

OX

IC

Dairy

Two aquifers with low nitrate – two different mechanisms mitigating impact

UPPER LOCAL AQUIFER Chemical mitigation: degradation Active denitrification mitigates

impact of high-nitrate recharge Denitrification may be driven by

dairy operations

LOWER REGIONAL AQUIFER Physical mitigation: transport Confining layer prevents recharge

of high-nitrate irrigation water

Dairy farm

Page 13: GAMA Special Studies on Nitrate in  California Groundwater

1.0x10-2

1.5x10-2

2.0x10-2

2.5x10-2

3.0x10-2

3.5x10-2

4.0x10-2

4.5x10-2

3x10-4 4x10-4 4x10-4 5x10-4 5x10-4 6x10-4 6x10-4 7x10-4

Gilroy, CA

Livermore, CA

Chico, CA

Den

itrifi

catio

n

Excess Air

Dis

solv

ed N

2 (

cm3 a

t ST

P /

g w

ater

)

Dissolved Ar (cm3 at STP / g water)

Denitrification may not be common in drinking water basins in California

Denitrification may not be common in drinking water basins in California

Equilibrium (19 C)

Page 14: GAMA Special Studies on Nitrate in  California Groundwater

Groundwater nitrate issues City & private wells contaminated Significant land use changes To manage or not to manage!

Convert septic to sewage? Regulate animal waste? Educate growers?

Potential nitrogen sources NW: Wastewater treatment W: Historic? SE: Septic, animals, vineyards

LLNL multi-tracer approach Stable nitrate isotopes - source Excess nitrogen – denitrification Stable water isotopes – recharge, flow GW age – recharge, flow. natural nitrate

Livermore-Amador Basin: Multiple nitrate sourcesLivermore-Amador Basin

1H 3

1P 22N 2 2R 1

10A 2 12A 212D 2

12G 1

13E 1

1F 22B 23A 1

3K 35J 15N 1

7C 2

7N 1

8K 2

10F 3

10Q 1

11C 1

14A 3

16E 418E 1

22B 1

11J 2

15J 2

9Q 4

8H 2

1H 3

1P 22R 1

11P 4

12A 2

12H 2

5N 16P 1

7C 2

7H 27N 1

8K 2

10F 3

15J 216B 316E 4

18E 1

22B 1

3A 1

14H 1

10Q 1

2N 2

10A 2

12G 1

3K 35J 1

1F 2

9Q 4

13E1

2B2

1H 3

1P 22N 2 2R 1

10A 211G 1

12A 2

12D 2

12G 1

1F 22B 23A 1

3K 35J 15N 16P 1

7C 2 7H 2

7N 1

8K 2

10C 4

10F 3

10Q 1

11C 1

14H 116E 4

22B 1

11P 4

15J 2

9Q414A3

18E 1

15R 6

8H 2

1980

1990

2000

NW

W

SE

Moore et al (2006) Appl. Geochem.

Page 15: GAMA Special Studies on Nitrate in  California Groundwater

Groundwater nitrate issues City & private wells contaminated Significant land use changes To manage or not to manage!

Convert septic to sewage? Regulate animal waste? Educate growers?

Potential nitrogen sources NW: Wastewater treatment W: Historic? SE: Septic, animals, vineyards

LLNL multi-tracer approach Stable nitrate isotopes - source Excess nitrogen – denitrification Stable water isotopes – recharge, flow GW age – recharge, flow. natural nitrate

Livermore-Amador Basin: Multiple nitrate sourcesLivermore-Amador Basin

SE Livermore source area

Moore et al (2006) Appl. Geochem.

Page 16: GAMA Special Studies on Nitrate in  California Groundwater

A multi-tracer approach for a complex source term

Livermore-Amador Basin

Groundwater H3/He ages delineate flow and ambient conditions.

Old groundwater has 10-20 mg/L NO3 with soil N

isotopics. Artificial recharge on Arroyo Mocho

Mobilizes nitrate in source areas. Dilutes nitrate near supply wells.

Multiple sources of nitrate exist.

NW: wastewater, decreasing.W: livestock, decreasing.SE: fertilizer and soil N.

Septic sources are minor

Ranges based on compilation of data in Kendall, 1998.

NoSeptic

Page 17: GAMA Special Studies on Nitrate in  California Groundwater

Llagas Basin, Santa Clara County: Vulnerability

Modified from SCVWD (2002)

Llagas basin

Nitrate contamination Pervasive shallow (“domestic”) None deep (“municipal”)

Important groundwater basin Not managed; sole source Rural to suburban transition

Questions about groundwater nitrate Source: animal vs septic vs fertilizer? Timing: historic or current? Distribution: why no nitrate at depth?

Findings Synthetic fertilizer source Oxic shallow; anoxic at depth No denitrification shallow or deep Distribution controlled by transport

Nitrate isotopic composition indicates source

Page 18: GAMA Special Studies on Nitrate in  California Groundwater

The effect of heterogeneity on nitrate transport

If sources stabilized, shallow gw concentrations will level off this century. If sources eliminated, shallow gw impacts may linger for 40-100+ years.

Including heterogeneity into transport modeling results in: More wells impacted. More dispersion than a homogenous model with high (10m) dispersivity. Rising nitrate concentrations in deep wells this century

Llagas basin

Carle et al (2006) Geosphere

Page 19: GAMA Special Studies on Nitrate in  California Groundwater

Chico & Butte County: Conversion from septic to sewer

Groundwater quality issues Reliant on groundwater High nitrate since 1980’s Management plan in effect

LLNL Study Goal: Improve understanding of

nitrate fate and transport Multi-tracer approach:

Stable isotopes, excess N2

3H-3He age, recharge T Trace organics

Early findings No denitrification Trace organics associated with septic

(caffeine & nonylphenol) detected Recent recharge in Chico low in NO3

Chico

Isotopically light water

Warmer recharge temperatures(from noble gas concentrations)

Page 20: GAMA Special Studies on Nitrate in  California Groundwater

Looking to the future: GAMA Special Studies

Septic systems Field-based Studies of Water

Quality Impacts of Septic Systems to Groundwater Basins

Emerging contaminants Development of standard methods

for wastewater indicator compounds and emerging contaminants for technology transfer

Septic system

Caffeine

Page 21: GAMA Special Studies on Nitrate in  California Groundwater

Acknowledgements

LLNL Funding LLNL Water Initiative Laboratory Directed Research &

Development Glenn T. Seaborg Institute

The LLNL “Nitrate” team G. Bryant Hudson Steve Carle Harry Beller Walt McNab Staci Kane Michael Singleton Tracy LeTain Cheryl Moody-Bartel Roald Leif Will McConihe

SWRCB Funding Groundwater Ambient

Monitoring & Assessment (GAMA) Program in collaboration with the USGS

Agencies University of California

Cooperative Extension Central Valley Regional

Water Quality Control Board Universities

University of California-Davis (Thomas Harter)

University of Texas at Austin (Brad Cey)

Page 22: GAMA Special Studies on Nitrate in  California Groundwater

Contact Information and Publications

Contact information Bradley K. Esser, L-231

Lawrence Livermore National LaboratoryLivermore, CA 94551-0808email: [email protected]

Publications Llagas Basin Study: Carle S. F., Esser B. K., and Moran J. E. (2006) High-

resolution simulation of basin scale nitrate transport considering aquifer system heterogeneity. Geosphere (Special Issue: Modeling Flow and Transport in Physically and Chemically Heterogeneous Media), In Press.

Livermore-Amador Basin Study: Moore K., Ekwurzel B. E., Esser B. K., Hudson G. B., and Moran J. E. (2006) Sources of groundwater nitrate revealed using residence time and isotope methods. Applied Geochemistry, In Press.

Page 23: GAMA Special Studies on Nitrate in  California Groundwater

A multi-tracer approach for a complex source term

Livermore-Amador Basin

Groundwater H3/He ages delineate flow and ambient conditions.

Old groundwater has 10-20 mg/L NO3 with soil N

isotopics. Artificial recharge on Arroyo Mocho

Mobilizes nitrate in source areas. Dilutes nitrate near supply wells.

Multiple sources of nitrate exist. N source is of historical livestock origin and is

decreasing. SE source is a combination of fertilizer and soil N. NE source is treated wastewater. Septic sources, if present, are a minor contribution.

Nitrate-N isotopic composition

Nitrate-N & -O isotopic composition


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