nitrate contamination: potential solutions · background: nitrate zone septic tank contaminates ~...
TRANSCRIPT
Nitrate Contamination: Nitrate Contamination: Tools, Insights, and Tools, Insights, and Potential SolutionsPotential Solutions
Christian A. Kropf Christian A. Kropf Sr. Hydrogeologist Sr. Hydrogeologist
Washoe County Dept. of Water ResourcesWashoe County Dept. of Water Resources
May 5, 2009May 5, 2009
Recipe for SuccessRecipe for Success
1. Apply for a large EPA Grant
2. Receive large EPA Grant
3. Hire the best scientists you can!
Presentation OutlinePresentation Outline
Nitrate: What’s the big deal?
Nitrate contamination case study
Characterization tools and insights
Applying this information regionally
Potential solutions
Background: NitrateBackground: Nitrate
Nitrate-N MCL is 10 ppm
Do not bind with soils & highly soluble
Travels with groundwater
Little or no retardation or degradation
Conservative solute that tends to accumulate in ground water
Background: NitrateBackground: Nitrate
One septic tank contaminates ~ 900 gallons of water per day to the MCL of 10 ppm NO3
18,000+ septic systems in Washoe County– 1.3 Billion gallons of septic effluent to groundwater annually– ~ 5.7 Billion gallons of groundwater to the MCL of 10 ppm annually– ~ 17,500 AFY or enough to serve ~ 50,000 homes!
Greatest potential for nitrate contamination of groundwater arises in areas of low rainfall recharge and high development density (Hantzsche and Finnemore, 1992)
Septic tanks are the most frequently reported cause of groundwater contamination associated with disease outbreaks (Yates, 2006)
Background: NitrateBackground: Nitrate
Methemoglobinemia (blue-baby syndrome):blood lacks the ability to carry oxygen throughout the body - especially in infants
Others: non-Hodgkin's lymphoma, gastric cancer, hypertension, thyroid disorder and birth defects.
Indicator contaminant: bacterial, viral, and pharmaceutical contamination
Loca
tion
Map
Loca
tion
Map
Site DescriptionSite Description
Reno-Sparks
Presentation OutlinePresentation OutlineSpanish Springs ValleySpanish Springs Valley
Recipe for ContaminationRecipe for Contamination
2,000+ homes on septic
½ within 2,000 ft of municipal wells
Increasing nitrate concentrations
Letter from the NDEP
Pre
viou
s C
ondi
tion
Pre
viou
s C
ondi
tion
July 2002
0.0
1.0
2.0
3.0
4.0
5.0
6.0
7.0
8.0
9.0
10.0
11.0
12.0
13.0
1979 1980 1981 1982 1983 1984 1985 1986 1987 1988 1989 1990 1991 1992 1993 1994 1995 1996 1997 1998 1999 2000 2001 2002 2003 2004 2005 2006 2007 2008 2009
Date
Nitr
ate
- N (m
g/L)
Municipal Well ContaminationMunicipal Well Contamination
20081979
12
Characterization Tool KitCharacterization Tool Kit
TeamSoftwarePlanConceptual model Rough mass balance from septicsInitial characterizationFollow-up characterizationMunicipal well Quality and Flow profilesSource identification Source magnitudeVadose zone assessmentGroundwater flow & contaminant transport model
Team MembersTeam Members
GIS analyst - CountyModeler - DRIWQ specialist - CountyGeochemist – USGS/CountySoil scientist – UNRHydrogeologist – CountyDatabase specialist - CountyGrant writer!! – CountyInterns and graduate students!! – County and UNR
SoftwareSoftware
AccessMS Office – Excel and PowerPoint!SurferGrapherArcGISAerial photosGMS – or any MODFLOW pre- & post-processorStatistical software – Excel, Origins, SAS
Conceptual ModelConceptual Model
8.4 in./year Precipitation
5%In
filtr
atio
nNH4
+Biomass NO3-
Almost Complete Nitrification
0.4 in./year0.4 in./year0.4 in./year
Slow Shallow Gradient
Dilution
Little Denitrification
Municipal Pumping: 8 ppm10
-30
year
sIn
crea
sing
tim
e an
d ag
e of
gro
undw
ater
Dilution
Little Denitrification Mon
itor W
ell
Pum
ping
Wel
l
CLAY
Mon
itor W
ell
62 ppm ?
40 ppm ?
15 ppm ?
Mixing
17 ppm
3 ppm ?
Age?
Initi
alIn
itial
Cha
ract
eriz
atio
nC
hara
cter
izat
ion
MW
04
MW
06
MW
13Li
ndbe
rgh MW
10
Cor
doba
MW
14M
W15
10 31
4
23
1811
1.1
5
Scale ~ 170 ft per Horizontal Unit
?
?
?
?
?
? CLAY
CLAY
NO3- Concentrations presented in ppm NO3
--N
Reality Mimics ConceptReality Mimics ConceptE-W Cross Section Through Spanish Springs Valley
Follo
wFo
llow
-- upup
Cha
ract
eriz
atio
nC
hara
cter
izat
ion
Reality Mimics Concept: Q3 2008Reality Mimics Concept: Q3 2008E-W Cross Section Through Spanish Springs Valley
4340
4360
4380
4400
4420
4440
4460
4480
4500
4520
4540
4560
-10 -5 0 5 10 15 20 25 30 35 40 45 50 55 60 65 70 75 80
Horizontal Distance Units
Elev
atio
n (ft
asl
)
MW
04
MW
06
MW
13
Lind
berg
h
MW
10
Cor
dob
MW
14M
W15
6.0
5.3
9.4
16.2
5.7
Scale ~ 200 ft per Horizontal Unit
CLAY
NO3- Concentrations presented in ppm NO3
--N
MW
26M
W05
MW
28 MW
29
MW
17M
W30
9.8
12.016.1
2.8
8.439
4.9
8.495.3
CLAY
0
5
10
15
20
25
Nitr
ate-
N (m
g/L)
Source IdentificationSource Identification
Inside
23.2
5.0
Outside
SourceSourceIDID
WellLysimeter
Neutron
3 Homes1 Park1 School
49 Lysimeters10 Neutron Holes6 Monitor Wells4 Flux Meters
Nitrate Source StudyNitrate Source Study
Septic nitrate discharge from 1 to >500 mg/L as N
Median value of 44 mg/L Nitrate-N similar to the range of published values for septic tanks
Denitrification literature value of around 25% appears about right for Spanish Springs Valley septic tanks
Approximately 30 tons of N per year is being conveyed to the aquifer from septic tanks
Groundwater Age Dates, Nitrate, and Development in SSV
0
5
10
15
20
25
30
35
40
45
50
1945 1950 1955 1960 1965 1970 1975 1980 1985 1990 1995 2000 2005Date
Nitr
ate
- N (m
g/L)
Source ID: NOSource ID: NO33 & GW Age Date& GW Age Date
Start of Development
67% of Samples Above MCL
14% of Samples Above MCL
Shallow Sample Age Date & NitrateDeep Sample Age Date & Nitrate
N vs O Isotopes
-10.00
0.00
10.00
20.00
30.00
40.00
50.00
60.00
70.00
80.00
90.00
100.00
-15.00 -10.00 -5.00 0.00 5.00 10.00 15.00 20.00 25.00 30.00 35.00 40.00Nitrate - 15N
Nitr
ate
- 18O
NO3 in Precipitation
NO3 fertilizer
NH4 in fertilizer & rain
Soil N Manure & Septic waste
(adapted from Kendall 2007)
Source Identification:Source Identification:N and O Isotopes in NitrateN and O Isotopes in Nitrate
Shallow WellsDeep Wells
NO
NO
33S
ourc
e R
eS
ourc
e R
e --th
ink
thin
kSeptic Source?
Buried Swamp?
Soil cores refuted swamp
Recharge from a mining operation leaching naturally-occurring nitrate from vadosezone?
Plausible!
Source MagnitudeSource Magnitude
233 g/d/h from engineering estimate based on usage records
228 g/d/h from modeled estimate
INSIGHT! Don’t be afraid to recheck your data!– New data– New software– New processing ability
Source Magnitude: RecheckSource Magnitude: Recheck
SSV Septic Users Gallons per Day per House
0
200
400
600
800
1000
1200
1400
1600
1800
2000
2200
Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec
Month
Gal
lons
per
Day
Average Gallons per Day
Nitrate - N (mg/L)
Vad
ose
Vad
ose
Zone
Nitr
ate
Zone
Nitr
ate
Tran
spor
t Mod
els
Tran
spor
t Mod
els SIMULATION
Modeled from soil cores230 gal/day/house44 mg/L Nitrate-N applied Accounts for precipitation and soil moistureAccounts for naturally occurring Nitrate in subsurface
Bottom of Trench
GroundwaterU
nsat
urat
ed S
oil Z
one
RESULTS2-3 yrs for leading edge6-10 yrs for max concentration
Gro
undw
ater
Nitr
ate
Gro
undw
ater
Nitr
ate
Tran
spor
t Mod
els
Tran
spor
t Mod
els
Expanding the Scope of Expanding the Scope of Investigation CountyInvestigation County--WideWide
SepticsWells– Municipal,
monitoring,domestic
Depth to WaterGeologyConcentration(Nitrate and others)Precipitation
GIS-BasedRegional
RiskAssessment
Regional Risk AssessmentRegional Risk Assessment
Literature review & compile data & data gapsID potential areas of concern (Project Areas)Prioritize Project Areas for further study
79% - 95% of all septic systems in a basin were found in these individual Project AreasDensities ranged from 50 – 350 septics/mile2
High Risk = High septic density, Shallow depth to water, Shortest distance to sensitive receptors
Sep
tic N
itrat
eS
eptic
Nitr
ate
Pro
ject
Are
asP
roje
ct A
reas
Met
hods
: Sep
tic D
ensi
tyM
etho
ds: S
eptic
Den
sity Basin Stats
Septics: 1,397Area: 29.5 mi2
Density: 47/mi2
NV Limit: 92 /mi2
Project AreaSeptics: 1,325Area: 7.5 mi2
Density: 177/mi2Max D: 350 /mi2
NV Limit: 92 /mi2
Potential SolutionsPotential Solutions
Continue monitoring of past projectsBaseline Dataset Creation – Fill data gaps, DTW, water quality (PPCP’s)
ASR or at least Recharge to dilute nitrateNo more RIBsWatering restrictions / efficiency Phased sewers through remediation districtNO MORE HIGH DENSITY SEPTICS!
Potential (THE!) SolutionPotential (THE!) Solution
Questions?Questions?