S E P T I C S Y S T E M E F F E C T S O N S U R FAC E A N D G R O U N D WAT E R S U P P L I E S :

C A S E S T U D I E S F R O M T H E N O R T H C A R O L I N A C O A S TA L P L A I N

Michael O’Driscoll, Associate Professor, Geological Sciences/ Director, Coastal Water Resources CenterCharles Humphrey, Associate Professor, Environmental Health Sciences

Pamlico River Estuary,

Beaufort County, NC

OUTLINE

NPS Pollution and Coastal Nutrient Challenges

Septic Systems and Water Quality Issues

Nutrient Exports from Septic Systems

Surficial Aquifer – Surface Water Connections in the NC Coastal

Plain

Case Studies (Quantifying Nutrient Exports from Septic Systems)

Site, Hillslope, and Watershed-Scale Studies

Conclusions

NON-POINT SOURCE POLLUTION (NPS)

c o m es f ro m m a ny d i f f use so u r c es .

c a u sed by r a in f a l l o r sn ow m el t m ov in g ove r a n d t h ro u g h t h e g ro u n d o r f ro m su b su r f a c e wa s tewa ter.

r u n o f f c a n p i c k u p a n d t r a n sp o r t p o l lu t a n t s .

c o nvey s t h em to su r f a c e wa te r a n d g ro u n d wa te r sy s tem s .

Point source industrial Pollution,

Calumet River

Non-point source pollution,

numerous diffuse sources

staples.com

Herding cats

eds.comepa.govepa.gov

NATIONAL INVENTORY OF IMPAIRED

STREAMS (US EPA 2014)

Streams assessed Streams assessed (status)

PRIMARY SOURCES OF STREAM WATER QUALITY

IMPAIRMENT

(GENERALLY NON-POINT SOURCE)

Source: (U.S. EPA National Water Quality Inventory- 2014)

Focus on

Nutrients

NUTRIENT INPUTS TO COASTAL WATERS-

A NATIONAL AND GLOBAL CHALLENGE

Eutrophication

of U.S. –

freshwaters

Costs U.S.

economy

approximately

$2.2 bil l ion/yr

due to property

value,

recreational use,

and biodiversity

declines and

increased cost

of water

treatment

An algae covered public beach in Qingdao, northeast China's

Shandong province on July 4, 2013. STR/AFP/Getty Images.

• Excess Nitrogen in water supplies poses human health risks, e.g. methemoglobinemia, colon cancer (Ward et al. 2005) and nuisance odor and taste issues (Dodds et al. 2009).

• Nitrogen in surface waters can contribute to algal blooms, eutrophication and fish kills (Vitousek et al. 1997).

• Nutrient management efforts in the Tar and Neuse have targeted agricultural and urban runoff, but currently do not address septic systems.

NUTRIENT CHALLENGES IN

COASTAL NORTH CAROLINA

Tar & Neuse - 350 reported fish kills between 1996-2012

2009

USGS,

2008

WASTEWATER GENERATION:

WATER QUALITY ISSUES

Potential water quality problems associated with wastewater:

Elevated nutrients (Nitrogen and Phosphorus) and associated

algal blooms

Household chemicals and pharmaceuticals

Pathogenic microorganisms, vector for waterborne diseases

Trace metals, organics, and salts

Septic tank, Washington, NC

WASTEWATER INPUTS FROM MUNICIPAL TREATMENT PLANTS:

REGULARLY MONITORED

National Pollutant

Discharge Elimination

System (NPDES) permit

program regulates

point sources that

discharge pollutants

into waters of the

United States.

GUC Wastewater Treatment Plant-

Effluent Discharges to the Tar River

(Up to 17.5 Million Gallons/ Day)

hands-on learning

Did you have to

bring us here

before lunch?

S E P T I C S Y S T E M D I S C H A RG E S A R E N O T R E G U L A R LY

M O N I T O R E D I N N C : C H A L L E N G I N G T O Q U A N T I F Y T H E N U T R I E N T I N P U T S T O

G R O U N D W AT E R A N D S U R FA C E W AT E R S

• Current ly, approx imate ly 2 mi l l ion ons i te wastewater t reatment systems (OW TS) or sept ic systems in NC

• ~ 60% of Coastal NC res idences use sept ic systems (NCNERR 2001)

• Some coastal watersheds 30 -40 systems/sq . mi le and local dens i t ies > 100 (Pradhan et a l . 2007)

• Sept ic sys tems are potent ia l sources o f N not accounted fo r in NC nut r ient sens i t i ve wate r management

(Modified from Pradhan et al. 2007)

NC Nutrient Sensitive

Coastal Watersheds

CASE STUDIES FROM THE NORTH CAROLINA COASTAL PLAINT H E S U R F I C I A L AQ U I F E R A N D I T S C O N N E C T I O N W I T H S T R E A M S A N D E S T U A R I E S

P O T E N T I A L FO R S U B S U R FAC E WA S T E WAT E R M I G R AT I O N T O S T R E A M S A N D E S T UA R I E S

USGS, 1996

Sandy surficial aquifer

well-connected with

surface waters and

wetlands

Tar-Pamlico

Neuse

N O N - P O I N T S O U R C E

P O L L U T I O N A N D

S T R E A M -

G R O U N D WAT E R

I N T E R AC T I O N S

Nor th Carol ina Coasta l P la in :

Sandy sur f ic ia l aqui fer i s usual ly wel l -connected wi th sur face water bodies.

To understand non -point source po l lut ion problems must cons ider s t ream -groundwater

interact ions and the ef fects of land -use change on the sur f ic ia l aqui fer.

Land-use change

can alter stream-

groundwater

interactions.

Heath (1987)

Crighton, 2011

•Total N concentration in wastewater : 26-98 mg/L (US EPA, 2002; Ptacek 1998).

•Some treatment of N occurs in tank and in soils, in sandy soils N is generally in the nitrate form.

•Nitrate is generally mobile in the sandy surficial aquifer and can migrate > 100 ft from drainfield.

•US EPA MCL for drinking water (Nitrate-N) is 10 mg/l.

Septic System Wastewater Discharge and Nitrogen (N) Export

Dissolved

N

Nitrate

NITROGEN ATTENUATION (RETENTION OR LOSS) BET WEEN

DRAINFIELD AND SURFACE WATER IS HIGHLY VARIABLE

Variable treatment of Nitrogen ( Val iela et al . 1997, Oakley et al . 2011) due to:

Biological uptake

Dilut ion/dispersion

Denitr i f icat ion

Cation exchange

Modified from Kroeger et al. (2006). Massachusetts Military Reservation Treatment Plant, Cape Cod, MA

DRAINFIELD

HILLSLOPE

WATERSHED

DISTANCE RESIDENCE TIME

1-10 Meters Hours-Days

10-100 Meters Months-Years

Kilometers Years-Decades-Centuries

As distance increases, greater opportunities

for subsurface attenuation.

COMMON MONITORING METHODS: STREAM AND ESTUARY S ITES

Low-tech

High-tech

Hand-auger

Geoprobe

Ground

Penetrating Radar

Electrical Resistivity Mapping

OhmMapper (Geometrics, Inc.)

Scale=100km

N

Greenville

1. Site 1 - Residential/Estuary (Beaufort Co.)

2. Elementary School - Large system/River (Craven Co.)

3. High School - Large system (Craven Co.)

STUDY AREA: CENTRAL NORTH CAROLINA COASTAL PLAIN

NEUSE AND TAR-PAMLICO WATERSHEDS

Study Sites 4. Science Center/Pond, River (Pitt Co.)

5. Site 100– Residential/River (Pitt Co.)

PAMLICO RIVER (ESTUARY) STUDY SITE

M o n i to r in g I n s t a l la t io ns

2 9 P iez o m ete r s ( d ep t h : 1 . 4 to 3 . 7 m ; 4 - 1 2 f t )

6 l y s im ete r s ( d ep t h : 0 . 9 -1 . 8 m ; 3 - 6 f t )

Ta n k sa m p l in g ( in le t a n d o u t le t )

E s t u a r y sa m p l in g

S o i l / H y d ro geo log ica l C h a r a c te r i za t io n

G eo p hy s i c a l su r vey in g ( e lec t r i ca l r es i s t i v i t y )

S o i l / sed im en t c o r in g

S lu g tes t in g

To p o g r a p h ic su r vey in g

Wa ter Qu a l i t y S a m p l in g

B i - m o n t h ly sa m p l in g o f g w a n d w w fo r 2 p e r io d s

( wet yea r a n d d r y yea r ) , Oc to b er 2 0 0 9 -2011 .

N u t r ien t a n a l y ses ( N O3 - N , N H 4 - N , T KN a t E C U - C E L )

F ie ld / wa te r q u a l i t y sa m p l in g ( D . O . , S p ec . C o n d . ,

Tem p . , GW L eve l , P, C l , p H , E . c o l i , E n te ro c o cc us ) .

Pamlico River Estuary R. Howard

Methods:

drainfield

COLLABORATORS

Max Zarate (CDC)

Dave Lindbo (NCSU)

Nancy Deal (DHHS)

NITROGEN RETENTION/LOSS IN A COASTAL

SEPTIC SYSTEM DRAINFIELD

N concentration declines in drainfield

– dilution and retention/loss similar

influence

N load declines from 11.3 kg N/yr from tank to 0.85 kg N/yr in GW leaving drainfield

(88% attenuation over 5 m distance)

10 mg/l Drinking water

Nitrate Standard

TRAC ING WAS TEWATER -

AF F EC TED GRO UNDWATER

F RO M THE D RAINF IELD

NC setback (15-30 m) depending on size of system

and class of neighboring surface water

15 m setback(wet)

(dry)

Drinking water standard

NIT

RO

GE

N

Resistivity - defined by the resistance to flow of electric current in a material .

Measured by injecting electric current into the subsur face with current

electrodes and measuring voltage dif ference between potential electrodes.

OhmMapper (Geometrics, Inc., 2001)

METHODS: CAPACITIVELY COUPLED RESISTIVITY

G EOPHYSICAL M ETHODS TO T RACE WASTEWATER P LUMES :

C APACIT IVELY C OUPLED R ESIST IV IT Y

INTERPRETATION : SUBSURFACE WASTEWATER INPUTS CAN

DECREASE RESISTIVITY

waste

water

Wastewater inputs typically increase dissolved ions in groundwater

• increase pore water conductivity

• decrease subsurface resistivity

Modified from Samouelian et al. (2005)

Site Install Date

Septic Tank

Capacity (L)

Max Design

Flow (L/d)

Distribution

Device

Dispersal Area

(m2)

Vertical

Separation (m) Soil Series

Pitt Co.

Residence 1998/2004 3780 1360 D-box 155 < 0.1 m Goldsboro and Lynchburg

Craven Co.

Elementary 1987 37,800 37,800 D-box (2) 892 > 3 m Autryville

Craven Co.

High School 1999 73,827 73,827 LPP (2) 1115 > 1 m Tarboro

ATFS 2012 3780 1512 D-box 59 > 3 m Wagram

METHODS :

ONSITE WASTEWATER SYSTEM CHARACTERISTICS AND SAMPLING

Tank and GW sampling

pH, specific conductivity,

temperature, dissolved

nitrogen, and d.o.

Soil and sediment coring

July, Sept., Nov. 12,

March 13

Concurrent with

geophysical surveys

Tank samplingSandy surficial

aquifer core at JWS

Doesn’t get

any better…..

RESULTS: CRAVEN CO. ELEMENTARY SCHOOL

GW CONDUCTIVIT Y VS. RESISTIVIT Y

1

10

100

1000

10000

0 200 400 600 800 1000 1200

Re

sis

tivi

ty (

oh

m-m

)

Groundwater Specific Conductivity (uS/cm)

Background

Drainfield

Resistivity below

300 ohm-m ~

wastewater-

affected

groundwater

Wastewater-affected groundwater

RESULTS: ELEMENTARY SCHOOL

GW CONDUCTIVIT Y VS. DISSOLVED NITROGEN

0

10

20

30

40

50

60

70

0 200 400 600 800 1000 1200

Gro

un

dw

ate

r To

tal D

isso

lve

d N

itro

ge

n

(mg

/l)

Groundwater Specific Conductivity (uS/cm)

10 mg/l

EPA MCL (Nitrate)

Elevated groundwater conductivity (> 361 uS/cm)

can indicate areas with elevated TDN

Denitrification ?

RESULTS: ELEMENTARY SCHOOL

GW TDN VS. RESISTIVIT Y

0

10

20

30

40

50

60

70

1 10 100 1000 10000

Gro

un

dw

ate

r To

tal D

isso

lve

d

Nit

rog

en

(m

g/l)

Resistivity (ohm-m)

< 400 ohm-m

resistivity

suggests wastewater

effects

May identify areas

where N is above 10

mg/l (USEPA MCL)

10 mg/l

Denitrification?

May help understand the relationship between distance and TDN attenuation

0

10

20

30

40

50

60

70

80

90

1 10 100 1000 10000

Gro

un

dw

ate

r To

tal D

isso

lve

d N

itro

ge

n

(mg

/l)

Resistivity (ohm-m)

10 mg/l TDN

RESULTS: RELATIONSHIP BETWEEN RESISTIVIT Y AND

GROUNDWATER NITROGEN CONCENTRATIONS

TDN is below 10 mg/l

when resistivity is > 400 ohm-m

Summary data for all 4 sites

Resistivity surveys

may screen areas with

elevated gw nitrogen

Craven Co., HighSchool

3-D Resistivity Map

1.3 m depth

R E S IS T IV IT Y S U RV E YS C A N

H E L P M O NITO R WA S T EWATE R

P LU M E S I N T H E S U B S U RFAC E

Low- resistivity under the drainfield

(dark green; resistivity is < ~500 ohm-m)

11/14/2012

T1

T1’Transect

Resistivity declined with depth, helped characterize a plume that

was diving.

RESULTS: DETECTION OF A DIVING PLUME,

HIGH SCHOOL- 2-D TRANSECT

De

pth

(m

)

Active drainfield

7/13/2011

Dark green and blue-resistivity < ~ 320 ohm-m

In plume area-groundwater conductivity is > 300 mS/cm

Groundwater conductivity at spring also indicates approximate N-S orientation of ww plume

RESULTS: DETECTION OF

GROUNDWATER AND

SURFACE WATER IMPAIRMENT

Humphrey et al. 2013

3D resistivity;

4 m depth

(9/10/2012)

Drainfield

SPRING

0

10

20

30

40

50

Gro

un

dw

ate

r a

nd

wa

ste

wa

ter

TD

N

(mg

/l)

This spring is 30 m downgradient

from the drainfield. ~ NC setback

distance

Spring= groundwater that

discharges at land sur face.

Useful for testing if 30 m OWTS-

sur face water setbacks for large

systems are adequate.

SPRING: A WINDOW TO THE SURFICIAL AQUIFER

SPRING

N

Piezometers 16-20 in riparian

zone adjacent to spring

50 m

SHALLOW AQUIFER CONNECTION TO SURFACE WATER

SPRING - ~30 M FROM DRAINFIELD

05

101520253035404550

9/1

0/2

01

21

1/1

4/2

01

23

/25

/20

13

6/1

3/2

01

19

/10

/20

12

11

/14

/20

12

3/2

5/2

01

3

9/1

0/2

01

21

1/1

4/2

01

23

/25

/20

13

6/1

3/2

01

11

0/2

8/2

01

11

2/2

1/2

01

19

/10

/20

12

11

/14

/20

12

3/2

5/2

01

3

9/1

0/2

01

21

1/1

4/2

01

23

/25

/20

13

9/1

0/2

01

21

1/1

4/2

01

23

/25

/20

13

16 17 18 spring 20 19

Co

nce

ntr

atio

n (

mg

/l)

cl tdn

High Cl/low TDN- suggests denitrification at piezometer 17

Elevated

nitrogen and

chloride

suggest

wastewater-

affected

groundwater

migration to

surface

waters.

SpringN-attenuation in riparian buffer

Background TDN

EPA

NO3

MCL

Riparian Zone Piezometers and Spring

Elevated groundwater nitrogen

IMPORTANCE OF RIPARIAN BUFFERS

Median TDN

decline from

drainfield to spring

(n=6) 84%

but chloride data

suggests that

dilution plays a

large role

At Piezometer 17-

median Nitrogen

decline from

drainfield to

piezometer (N=4)

98.6%

~ 6.9 mg/l N difference

Up to 15 mg/l

N is lost when

that

groundwater

flows through

the

Forested

riparian buffer

Good treatment

Not so good

treatment

WAT E RSHE D - S CALE E S T IM ATES O F S E P T IC SYS T EM

N I T ROG EN I N P U T S TO S U RFAC E WAT ERS

Compared watersheds served by community sewer system (Greenville Utilities) and OWTS (septic systems)

Seasonally sampled groundwater, monthly surface water, discharge sampling for 1 year (2011-2012)

Iverson et al. (2015)

Septic

watersheds

Sewered (CSS )

Watersheds

(send their waste to

GUC treatment plant)

GUC treatment plant

TDN ATTENUATION BETWEEN DRAINFIELD AND STREAM

For comparison, wastewater treatment plant achieves about 82% Nitrogen reduction

12.6 kg-N/yr

to drainfield

0.6

kg-N/yr

to stream STREAM~96% Nitrogen attenuation

between drainfield and stream

AT THE WATERSHED-SCALE:

MORE STREAMFLOW AND MORE NITROGEN EXPORTED FROM

SEPTIC SYSTEM WATERSHEDS

Iverson et al. 2015 - In Press

Streamflow (Discharge) Nitrogen Leaving the Watershed

• Elevated Nitrogen load from septic watersheds

(but for sewered watersheds the N inputs are farther downstream to the Tar River)

• ~2 kg N/ha/yr difference (low density 1-2 OWTS/ha- would increase w/ density)

• Measureable- but…. Wet atmospheric N input~11 kg N/ha/yr (Whitall et al. 2003)

Row crop agriculture~ 15-35 kg N/ha/yr (O’Driscoll 2012)

N-15 ISOTOPES FOUND IN NITRATE:

CAN HELP DIST INGUISH IF SURFACE WATER NITRATE SOURCE IS

FROM FERTIL IZER OR WASTE

Iverson et al. 2015 - In Press

SURFACE WATER IN

SEPTIC WATERSHEDS

SURFACE WATER IN

SEWERED WATERSHEDS

ALTHOUGH WATER QUALIT Y IMPACTS MAY BE SUBTLE

OTHER STUDIES HAVE SHOWN THE EFFECTS OF SEPTIC

SYSTEMS ON NUTRIENT CONCENTRATIONS IN STREAMS

Decommissioned septic systems and

shifted to municipal wastewater treatment

Withers et al. 2014

Trinity River, Texas ~ 5 0 0 m i l l i o n g a l l o n s / d a y w a s t e w a t e r d i s c h a r g e d f r o m

D a l l a s

F l o w s d o w n T r i n i t y R i v e r

W a s t e w a t e r c o m p r i s e s 5 0 % o f f l o w t o d r i n k i n g w a t e r t r e a t m e n t p l a n t f o r H o u s to n

U S E P A s t u d i e d w a t e r s u p p l i e s o f 7 6 m i l l i o n ( N R C 2 0 1 2 )

2 0 m i l l i o n p e o p l e d r i n k w a t e r t h a t i s c o m p r i s e d o f a t l e a s t 1 % w a s t e w a t e r

D u r i n g l o w f l o w i n c r e a s e s t o ~ 1 0 % w a s t e w a t e r O f 7 6 m i l l i o n s t u d i e d

2 0 m i l l i o n p e o p l e d r i n k w a t e r t h a t i s c o m p r i s e d o f a t l e a s t 1 % w a s t e w a t e r

D u r i n g l o w f l o w i n c r e a s e s t o ~ 1 0 % w a s t e w a t e r

DEFACTO REUSED WATER

NRC, 2012

Major Wastewater Treatment D ischarges in the Tar -Pamlico Watershed (upstream Greenv i l le )

Warrenton WW TP (2 Mi l l ion Gal lons/Day)

Enf ie ld WW TP (1 Mi l l ion Gal lons/Day)

Tarboro WW TP (5 Mi l l ion Gal lons/Day)

Louisburg WW TP (1 .4 Mi l l ion Gal lons/Day)

Oxford WW TP (3 .5 Mi l l ion Gal lons/Day )

Tar River Regional WW TP (Rocky Mount) (21 Mi l l ion Gal lons/Day)

Total Wastewater Inputs ~ 33 Mil l ion Gallons/Day (~ 2% of Tar Flow)

Greenville uses ~ 10.9 Mil l ion Gallons/Day - Tar River for water supply

DEFACTO WASTEWATER REUSE:

OCCURS IN GREENVILLE!

Our Water Is Previously Used!

Or ……

Gently used

Pre-loved

Not quite new

Pre-owned

Like new

S c r e e n i n g o f s i t e s u s i n g r e s i s t i v i t y s u r v e y s m a y h e l p d e t e c t a r e a s o f g w i m p a i r m e n t .

S p r i n g s d o w n g r a d i e n t o f s e p t i c s y s t e m s m a y p r o v i d e a w i n d o w t o t h e s u r f i c i a l a q u i f e r .

N - 1 5 i s o t o p e s i n N i t r a t e m a y h e l p t o i d e n t i f y N i t r a t e i n p u ts a s s o c i a t e d w i t h w a s t e w a t e r

A t t h e w a t e r s h e d - s c a l e , m e a s u r a b l e i n c r e a s e s i n N f r o m C o a s t a l P l a i n w a t e r s h e d s u s i n g s e p t i c s y s t e m s .

F o r C o a s t a l P l a i n s i t e s w i t h i n 3 0 m o f s t r e a m s a n d e s t u a r i e s , e s t i m a t e s s u g g e s t ~ 1 k g o r 2 l b s - N /

r e s i d e n c e / y r c a n m a k e i t t o s u r f a c e w a t e r . B u t m u c h v a r i a b i l i t y d e p e n d i n g o n s o i l s , w a t e r u s e , e t c .

D e f a c t o w a s t e w a t e r r e u s e i s n o t w e l l - q u a n t i f i e d . R e s e a r c h n e e d e d t o u n d e r s t a n d r i s k s t o w a t e r s u p p l i e s .

CONCLUSIONS

With population

growth-

wastewater inputs

to our groundwater

and surface water

systems are likely.

S T U D E N T S

D u s t i n D e L o a t c h

G u y I v e r s o n

E l i o t A n d e r s o n - E v a n s

R o b H o w a r d

J o n a t h a n H a r r i s

S a r a h H a r d i s o n

A d a m T r e v i s a n

M a t t S m i t h

C O L L A B O R A T O R S

C h a r l i e H u m p h r e y ( E C U )

E b a n B e a n ( E C U )

M a x Z a r a t e ( C D C )

D a v e L i n d b o ( N C S U )

N a n c y D e a l ( D H H S )

A l e x M a n d a ( E C U )

S i d M i t r a ( E C U )

D a v e M a l l i n s o n ( E C U )

T E C H N I C A L S U P P O R T

J i m W a t s o n

J o h n W o o d s

A n d - H o m e o w n e r s

a n d F a c i l i t i e s M a n a g e r s !C r a v e n C o u n t y P u b l i c S c h o o l S y s t e m

C r a v e n C o u n t y S c h o o l M a i n t e n a n c e

P i t t C o u n t y P l a n n i n g

G r e e n v i l l e U t i l i t i e s C o m m i s s i o n

D r . J o h n B r a y

ACKNOWLEDGMENTS

F U N D I N G

C e n t e r s f o r D i s e a s e C o n t r o l a n d P r e v e n t i o n

N C W R R I

N C D E N R 3 1 9

Thanks for your attention!