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Nitrate in Private Water Supplies
Bryan Swistock, Penn State Extension
Penn State College of Agricultural Sciences research and extension programs are funded in part by
Pennsylvania counties, the Commonwealth of Pennsylvania, and the U.S. Department of Agriculture.
Nitrate Sources in Groundwater
Naturally occurring
nitrate in groundwater is
typically below
detectable levels
Surface water
Groundwater Moves!
Barnyard, yards, dumps, mines, septic systems, etc.
Aquifer Contamination
Well Head
Contamination
Groundwater Contamination
Soil
Bedrock
Aquifer
From U.S. Geological Survey
Nitrate Drinking Water Standards
• Primary MCL = 10 mg/L as NO3-N
• 45 mg/L as NO3
• 3.0 mg/L often cited as human influenced
Nitrate
• One of the most controversial standards!
• Argument to relax standard o Lack of methemoglobinemia cases
o Costs of treatment for public water supplies
• Arguments to tighten standard o Possible links to bladder cancer
o Prevalence of the problem
Data Sources • Statewide Survey – 1989-1991
o Penn State (Swistock, Sharpe and Robillard)
o 1,600 wells, springs and cisterns across PA
• Spruce Creek Watershed Study – 2005 o Penn State University (Swistock and Sherwin)
o 50 water wells intensively studied in a central PA watershed
• Center for Rural PA Statewide Project o Penn State (Swistock et al. 2007)
o 701 samples across PA
• Penn State Ag Analytical Laboratory o 2,040 samples across PA from 2007 through 2016
o Samples submitted by homeowners and farmers
NO3-N in Private Water Systems (1989-1991)
32
7 12 9
42
6
80
9
1 1 2 5 1
40
0
20
40
60
80
100
State NW SW NC SC NE SE
% A
bo
ve C
on
cen
trat
ion
> 3 mg/L
> 10 mg/L
Sample of 1,600 systems
NO3-N by Water Supply Type
0
1
2
3
4
5
Me
an N
O3
-N
Hand-Dug
Springs
Drilled Well
Cistern
NO3-N and Distance to Active Field
0
2
4
6
8
10
0-100 100-500 500-1000 >1000
Ave
rage
NO
3-N
(m
g/L
)
Distance to Active Field (ft)
NO3-N by Well Depth
0
50
100
150
200
Ave
rage
We
ll D
ep
th (
ft)
> 10 mg/L
< 10 mg/L
Spruce Creek Well Sampling Project Penn State Center for Watershed Stewardship
Spruce Creek Well Sampling
• 50 private water supplies o Sampled February 22 - April 7, 2005
o 48 drilled wells, 2 springs
o Drilled between 1950 and 2002
• Well depths o Average depth = 220 feet
o Range 35 to 725 feet
• Well construction o 44 of 48 had casing above ground, 4 were in buried pits
o 13 of 48 had a sanitary well cap
o 5 of 48 had been grouted
o Only three wells had both a sanitary cap and grout seal
Summary of Testing Results
68 60
6 10
6 6 0
0
20
40
60
80
Overall Coliform E. coli Nitrate pH TDS Arsenic
% a
bo
ve t
he
dri
nki
ng
wat
er s
tan
dar
d
Nitrate Results
• 10% exceeded drinking water standard
• Maximum concentration 13.3 mg/L
• None of the 5 homes with high nitrate had treatment equipment
• Weak correlation with distance to cornfield and barnyard o Farm well average NO3-N = 3.98 mg/L
o Rural home well average NO3-N = 2.80 mg/L
• No correlation with distance to septic
Nitrate Correlations
0
2
4
6
<100 ft 100-500 ft 500-1000 ft >1000 ft
Cornfield
Barnyard
Septic
Ave
rage
Nit
rate
-N c
on
cen
trat
ion
(m
g/L
)
Distance to Activity
2006-2007 Study
• Funded by The Center for Rural Pennsylvania and the Pennsylvania Water Resources Research Center
• MWON volunteers and Penn State Staff collected samples
Methods
• 701 private wells throughout PA
• Wells had to be at least one mile apart
• Raw water samples collected by trained Master Well Owner volunteers and Extension personnel
• Analyzed for coliform bacteria, E. coli pH, lead, arsenic, nitrate, triazine pesticides and hardness
• Homeowner survey and volunteer survey were used to collect information about the well and management
172 volunteers collected samples, Of the 701 well samples, 79 were from MWON volunteer
Wells and 622 were homeowner Wells
Location of 701 Private Wells
Wastewater Characteristics
o 89% have on-lot wastewater systems
• 72% traditional septic system
• 14% sand mound
• 2% alternative system
• 1% don’t know what happens to their wastewater
o Septic tank pumping
• 28% never pumped
• 33% pumped > every four years
• 39% at least every three years
33
14
2
12
2 0.5
39
9
19
6
0.1 0
10
20
30
40
50
60
Current Study
Past Studies
% F
ailin
g D
rin
kin
g W
ate
r S
tan
da
rds
Prevalence of Health-Related Pollutants in Rural Drinking Water Supplies
Overall = 2% exceed MCL
Important Variables
Explaining Nitrate
Occurrence
• Geology
• Distance to cornfield
• Distance to other crop fields
• Well depth
0
1
2
3
4
5
<50' 50-100' 100-500' 500-1000' >1000'
NO
3-
Co
nce
ntr
atio
n (
mg
/L)
Distance to Cornfield
Nitrate Correlation to Cornfields
11
18
31
0
8
0 0
10
20
30
40
50
60
% A
ware
of
Pro
ble
m in
Th
eir
Wa
ter
Awareness of Nitrate Issues in Drinking Water
Does Awareness Translate to Action?
• 76% of homeowners with wells that failed standards took some action within six months to solve the problem
• Actions included removing source of pollution, improving well construction, buying bottled water, installing treatment
Education to Avoid Nitrate in Water
Contaminant
% avoiding contaminant before
this study
% avoiding contaminant 6-12 months after testing
Coliform bacteria 33 % 50 %
E. coli bacteria 42 % 71 %
Nitrate 12 % 62 %
Lead 0 % 75 %
Arsenic 20 % 80 %
Nitrate in Private Water Supplies
% Above 10 mg/L
3.8% of 2,040 samples > 10 mg/L
0%
0%
0%
0%
2% 6%
9%
3% 0%
9%
3%
4%
4% 23%
0%
0%
20%
4%
9%
0%
30%
3%
<1%
8%
9%
0% 11%
3%
6%
0%
8%
0%
0% 0%
0%
9%
0%
(for counties with at least 20 samples)
0% 3%
Nitrate Water Treatment
• Can be Point-of-Entry or Point-of-Use since it is only a drinking water issue
• Avoidance – give young children and pregnant women alternate water
• Reverse Osmosis
• Bottled water
• Anion Exchange
Anion Exchange
Point of Use Treatment
Process Treats
Carbon filter Chlorine, organics
Reverse Osmosis
(RO)
Most solutes – Not bacteria
Distillation Many except light organics
e.g., treat only kitchen tap
How common is Water Treatment?
0
10
20
30
40
53% have some water treatment
Systems capable of nitrate removal are not common
Perc
ent
of S
urv
ey R
espondents
Summary and Conclusions
• Nitrate occurs in about 5% of private water supplies
• Much more common in southeastern and southcentral counties
• More common in shallow wells or springs
• Correlated to nearby agricultural use
• Relatively easy to treat or avoid