gama special studies on nitrate in california groundwater presented to: national water quality...
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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 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
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.
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
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
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
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
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
Real-time qPCR of denitrifier bacterial populations show that denitrification occurs at the oxic-anoxic interface
Dairy farm
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.
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
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
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
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)
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.
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.
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
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
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
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)
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
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)
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.
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