1. Contamination and other issues
Source
Point sources
Non-point sources
Naturally occurring
Reactions (chemical and biological)
Transport
Contamination and other issues
Source
Point sources
Non-point sources
Naturally occurring
Reactions (chemical and biological)
Transport

2. Potential sources of contamination
Lots of potential sources

3. Point sources Factory wells, spills, emissions Fuel storage tanks
Landfill
Septic tank
Leaking tank in gas station
Truck fuel spill
Dry cleaner
Factory wells, spills, emissions
Households
Point sources

4. Non-Point sources Naturally occurring Brought by river Farm
Brought from outside area by groundwater

5. Non-Point source pollution
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
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

6. How Does Groundwater Contamination Move?
With groundwater down water table
Can be filtered if flows slowly, like through sands
Not filtered if flows rapidly, like in limestone caves
EXPLANATION
Contamination largely moves with groundwater down the slope of the water table
Can be naturally filtered out with enough time: flows slowly and in contact with material like sand
Not filtered if flows rapidly through a rock, such as a limestone with open cavities
Importance for considering the direction of groundwater flow when sighting the relative positions of a water well and contamination sources, such as a septic tank
In general, put the well uphill of a septic tank, but be aware of what is farther up the hill
17.10.a

7.
Contaminant movement video

8. NAPL - Non-Aqueous Phase Liquids
LNAPL - Light Non-Aqueous Phase Liquids
lighter than water
generally petroleum
NAPL - Non-Aqueous Phase Liquids – not in solution (not dissolved)
Floaters and sinkers
LNAPL - Light Non-Aqueous Phase Liquids
lighter than water
generally petroleum

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

10. Orientation of the rocks will affect groundwater and contaminant movement
This is why we have well construction rules specific to location
Goal is to seal off upper part of well so it does not become a conduit for surface pollution
(from USGS WRIR )

11. Arsenic in groundwater
Depends on rock type (sulfide minerals)
Oxidation state pH
Presence of Fe
Arsenic in groundwater
Depends on rock type (sulfide minerals)
Oxidation state pH
Presence of Fe
Eh vs Ph for Arsenic

12. Arsenic accumulation over time
Tiles on cement block
Increased coating on tiles with time
Arsenic accumulation over time
Two tiles were collected quarterly over one year to determine the precipitation rate of the coating
558 days = 1.6 years
Arsenic in coating increases with time

13. Arsenic accumulation
10 cm
Bottom:
Reducing
Top:
Oxidizing
Arsenic accumulation
Same study
Cobbles in the stream are coated in black on oxidized side – iron, manganese, arsenic precipitate out
Turn the rock over, nice quartz pegmatite (good for gold mining) – reducing, no coating, heavy metals in solution
One message is that the more you oxidize the water in your well, the more arsenic will dissolve into the water
Oxidize by agitation via pumping cycles
Reid, Haven, Eudy, Milosh, Stafford, 2007, Arsenic in Groundwater Investigations – Eastern Slate Belt (ESB): Nash and Halifax Counties, North Carolina

14. 2010 State-Wide Private Well Sampling Results
Nitrate pH
Arsenic
Chromium
Iron
Manganese
State Groundwater Standard
10 mg/L
10 ug/L
300 ug/L
50 ug/L
Number of samples
4,110
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%
2010 State-Wide Private Well Sampling Results
This is a great data set
Goes back to 2008
All new wells in the state are sampled for 20 parameters
Nutrients, metals, fecal
Don’t always have good locations
Iron and manganese statewide
Secondary standard – aesthetic – color, odor, taste, not human health
2.4% of 5,000,000 people is about 120,000 people affected by arsenic in their well
NC population 10,000,000
½ drink groundwater
2/4% of 5,000,000 people is 120,000 people
Source: DENR “North Carolina State of the Environment Report 2011”

15. Arsenic Probability from Private Well Data (Pippin, 2005)
Probability of a groundwater sample exceeding mg/L
Arsenic Probability from Private Well Data (Pippin, 2005)
Pippin, 2005, Arsenic Occurrence in the Unconfined Fractured Bedrock Aquifer System of the North Carolina Piedmont

16. Arsenic Probability from Private Well Data (Pippin, 2005)
Probability of a groundwater sample exceeding mg/L
Arsenic Probability from Private Well Data (Pippin, 2005)
With geologic map overlay
Carolina Slate Belt
Kings Mountain Belt
Charlotte Belt
Inner Piedmont Belt
Eastern Slate Belt

17. Probability of a groundwater sample exceeding 0.001 mg/L
Population using private wells
Arsenic probability areas – top map
Population using private wells – bottom map
There are a lot of people in the high arsenic probability areas who drink from private wells
Moral of the story – test your well, find out what to test for – ask your local public health dept or us
USGS Estimated Use of Water in the US County-Level Data for 2010

18. 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
It’s easier to keep groundwater clean than to clean up contamination
It’s not always obvious where it will go once it hits the water table
Understanding the geology is critical to Public Health
What’s in the rocks
Where contamination may migrate
Not all contamination is caused by humans
Arsenic and radon are both naturally occurring in NC
Not all occurrences are natural
Iron and Manganese are high throughout the state
Well construction is different under certain geologic conditions
Test your well! Learn what to test for –
depends on geology,
land use practices,
history of land use

19. Take-aways Test your well! Learn what to test for – Depends on geology
Land use practices
History of land use
Contamination events

20. Mammoth Cave, Kentucky - https://www.youtube.com/watch?v=fTNlZl7-s4w
Porosity and permeability -
The space between the grains -
“best extreme caving video” -
Mammoth Cave, Kentucky -
Geology of Mammoth Cave -
Groundwater – good, but long -
Wish we had this for eastern NC -
Websites
Porosity and permeability -
The space between the grains -
“best extreme caving video” -
Mammoth Cave, Kentucky -
Geology of Mammoth Cave -
Groundwater – good, but long -
Wish we had this for eastern NC -

21. How Do We Depict the Water Table?
Numbers show elevations of the water table: what is the pattern?
Compare water table to other features
Contour: water table at same elevation; blue arrows show flow
Exercise to do while playing with the groundwater models
What is the pattern of elevations, and which way do you think groundwater would flow?
EXPLANATION
Contours mark where water table is at same elevation; blue arrows show flow
We visualize system to compare water table to other features, such as farms with wells that pump high volumes (this is a different area)
EXERCISE
Have students contour a simple map showing only the elevation of points, and then draw arrows perpendicular to contours and in a downslope direction
17.07.b

22. Amy Keyworth amy.keyworth@ncdenr.gov 919-807-6460
NCDENR Division of Water Resources
My contact information
Division of Water Resources