Nitrate in Private Water Supplies

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