Contamination and other issues

Source Point sources Non-point sources Naturally occurring

Reactions (chemical and biological) Transport

Potential sources of contamination

Point sources

Fuel storage tanks

Landfill

Septic tank Leaking

tank in gas station

Truck fuel spill

Dry cleaner

Factory wells, spills, emissions

Households

Non-Point sources

Naturally occurring

FarmBrought by river

Brought from outside area by groundwater

• Cannot be traced to a specific spot

• Multiple sources

• Large area

• Source activities related either to land or water use

• Examples• water runoff from urban areas• construction sites• agricultural• failing septic tanks• improper animal-keeping practices• Improper forestry practices

Non-Point source pollution

How Does Groundwater Contamination Move?

Can be filtered if flows slowly, like through sands

With groundwater down water table

Not filtered if flows rapidly, like in

limestone caves

17.10.a

http://techalive.mtu.edu/meec/module04/ContaminationMovement.htm

• LNAPL - Light Non-Aqueous Phase Liquids • lighter than water• generally petroleum

NAPL - Non-Aqueous Phase Liquids

http://toxics.usgs.gov/definitions/lnapls.html

• DNAPL - Dense Non-Aqueous Phase Liquids• denser than water• chlorinated compounds • PAHs

http://water.usgs.gov/ogw/karst/kigconference/wjw_preliminaryconcept.htm

(from USGS WRIR 02-4105)

Arsenic in groundwater

Depends on rock type (sulfide minerals) Oxidation state pH Presence of Fe

Arsenic accumulation over time

Tiles on cement block

Increased coating on tiles with time

Arsenic Accumulation on Tiles

0

0.5

1

1.5

2

2.5

3

3.5

4

PC-1 PC-1a PC-2 PC-2a PC-3 PC-3a Portis Portis2

Sample Location

As:

ppb/s

q c

mFirst Quarter

Second Quarter

Third Quarter

http://portal.ncdenr.org/c/document_library/get_file?uuid=34d44ecd-33f1-41a7-9cc7-164389e7de5e&groupId=38364

Bottom:Reducing

Top:Oxidizing

Arsenic accumulation

10 cm

Reid, Haven, Eudy, Milosh, Stafford, 2007, Arsenic in Groundwater Investigations – Eastern Slate Belt (ESB): Nash and Halifax Counties, North Carolina

Source: DENR “North Carolina State of the Environment Report 2011”

2010 State-Wide Private Well Sampling Results

  Nitrate pH Arsenic Chromium Iron ManganeseState Groundwater Standard

10 mg/L

6.5-8.5

10 ug/L 10 ug/L 300 ug/L 50 ug/L

Number of samples4,110 4,901 4,870 4,892 4,896 4,900

Percent of samples exceeding standard

0.7% 18.4% below pH

of 6.5

2.4% 1.5% 57.6% 39.9%

NC population 10,000,000½ drink groundwater

2/4% of 5,000,000 people is 120,000 people

Arsenic Probability from Private Well Data (Pippin, 2005)

Probability of a groundwater sample exceeding 0.001 mg/L

0.2 1

Pippin, 2005, Arsenic Occurrence in the Unconfined Fractured Bedrock Aquifer System of the North Carolina Piedmont

Arsenic Probability from Private Well Data (Pippin, 2005)

Probability of a groundwater sample exceeding 0.001 mg/L

0.2 1

Carolina Slate BeltKings Mountain Belt

Charlotte Belt Inner Piedmont Belt

Eastern Slate Belt

Probability of a groundwater sample exceeding 0.001 mg/L

0.2 1

Data Source: USGS Estimated Use of Water in the United States County-Level Data for 2010, http://water.usgs.gov/watuse/data/2010/. Accessed February 11, 2015

0 60 12030Miles

4Legend

Population (in thousands)

1.32 - 20.3

20.3 - 41.8

41.8 - 80.3

80.3 - 147

147 - 276

Population Using Self-Supplied Groundwater

Data Source: USGS Estimated Use of Water in the United States County-Level Data for 2010, http://water.usgs.gov/watuse/data/2010/. Accessed February 11, 2015

0 60 12030Miles

4Legend

Population (in thousands)

1.32 - 20.3

20.3 - 41.8

41.8 - 80.3

80.3 - 147

147 - 276

Population Using Self-Supplied Groundwater

USGS Estimated Use of Water in the US County-Level Data for 2010

Population using private wells

Take-aways

It’s easier to keep groundwater clean than to clean up contamination

Groundwater – Surface Water all one thing Understanding the geology is critical to Public

Health Not all contamination is caused by humans Well construction is different under certain

geologic conditions

Take-aways

Test your well! Learn what to test for – • Depends on geology• Land use practices• History of land use• Contamination events

Porosity and permeability - https://www.youtube.com/watch?v=zrewtz42GmgThe space between the grains - https://www.youtube.com/watch?v=tt-mx25t7rA“best extreme caving video” - https://www.youtube.com/watch?v=TucYTJe1WsAMammoth Cave, Kentucky - https://www.youtube.com/watch?v=fTNlZl7-s4wGeology of Mammoth Cave - https://www.youtube.com/watch?v=VFLDvzc5P2kGroundwater – good, but long - https://www.youtube.com/watch?v=ci-ABWPG7LQWish we had this for eastern NC - https://www.youtube.com/watch?v=Z2HQY5A3o-s

How Do We Depict the Water Table?

Contour: water table at same elevation; blue arrows show flow

Numbers show elevations of the water table: what is the pattern?

Compare water table to other features

17.07.b

Amy Keyworth

amy.keyworth@ncdenr.gov

919-807-6460

NCDENR Division of Water Resources

Division of Water Resources