Groundwater contamination (Contamination of concern,Determination of contamination,Groundwater remediation and showing the case problem)

• Groundwater Contamination
  • When soluble or insoluble substances are introduced into the hydrogeologic environment as a result of man’s activities
• Groundwater Pollution
  • When the level of contamination concentration restricts potential use of groundwater
• Groundwater Remediation
  • The process of extracting, filtering, and remediating groundwater to a level of and usable water.

Soluble is the contamination ease to dissolved in groundwater while the contamination has already leaked to subsurface.

insoluble is the contamination difficult to dissolve in groundwater while the contamination has already leaked to subsurface

Contaminants of Concern

• Contaminants are referred to as COC or Contaminants of Concern
• The location where the contamination is coming from is known as point source pollution
• COC ‘s are organized into two categories
  • Metals
  • Volatile Organic Compounds or VOC’s
    • Light Non-Aqueous-Phase Liquid (LNAPL)
      • Floats on top of the aquifer
    • Dense Non-Aqueous-Phase Liquid (DNAPL)
      • Sinks to the bottom of the aquifer

Table of contaminants

Determination of Contamination

• Methods of sampling contamination
  • Sample existing water wells
  • Drill holes and take depth samples at different depths
  • Soil sampling
• Look for few indicators or properties present to determine COC’s

Key Indicators

Common Groundwater Remediation:

1. Physical/Permeable Reactive Barrier
2. Pump and Treat
3. Vapor Extraction
4. Bioremediation
5. In-situ Oxidation
6. Natural Attenuation/Phytoremediation

Physical/Permeable reactive barrier

• Physical Barrier
  • Impermeable barrier to separate contaminated section of groundwater from the plume
• Permeable Reactive Barrier:
  • Permeable barrier that treats contaminated groundwater that passes through with reactive material
  • Reactive materials: iron filings, activated carbon, peat
  • Works only good for shallow aquifers

Pump and treat

• strategically placed wells to extract and treat water
• Discharge water to sub-surface, surface, or municipal sewer system
• Effectiveness depends on geology of aquifer and contaminant
• Slow and costly
• NAPLs cannot be removed

Vapor extraction

• air is pumped into the soil below the contaminated groundwater which then mixes with the contaminated aquifer
• Another pump extracts the mixture of air and voc and treats the mixture to be released into the air
• Difficult to be used in low permeable zones and 9 meters below surface

Bioremediation

• The use of microbial organisms to breakdown carbon-based contaminants
• They are injected into the groundwater
• The final product is usually carbon dioxide or methane

In-situ oxidation

• In-situ means on site
• A remediation method where oxidation agent is injected into the contaminated groundwater
• End product is carbon dioxide and water

Natural Remediation

• Natural Attenuation
  • Natural processes with no human intervention
• Phytoremediation
  • The growing of trees or plants that are able to suck up the contaminated groundwater through their roots
  • Limited to mostly metals and few VOCs
  • Limited also by how far the roots of the plants can grow to

Case problem: Perchlorate

• What is Perchlorate
  • A naturally occurring and manmade contaminant
  • Most manmade perchlorate are ingredients in solid fuel for rockets and missiles
  • It can be also be found in safety flares, fireworks, pyrotechnics, explosives, common batteries and automobile restraint systems
• Problem with Perchlorate
  • It has been increasingly being found in groundwater due to military activities
  • EPA has not put a maximum concentration level for perchlorate in groundwater

Risk Assessment/Hazards

• Perchlorate interferes with iodide uptake to the thyroid gland
  • In adults, that deals with metabolism
  • In children, that deals with development
  • In pregnant women, may affects fetus/newborn development
  • Chronic exposure and lowering of thyroid may cause a tumor

Should there be a limit?

• The Facts
  • It has shown up in 20 states in groundwater and increasing due to military activities e.g. Aero Jet activities
  • Levels above 0.007 milligrams per kilogram per day (mg/kg-d) has known to temporarily inhibit the thyroid gland’s ability to absorb iodine from bloodstream. This was based on a 70 kg healthy person.
  • Thyroid gland returns to normal when intake of perchlorate ceases
  • From that and EPA’s criteria for contaminant evaluation, they have not found any significant or potential harm from perchlorate intake hence why they have not established a MCL for it