1. Soil Contamination- Overview and Case Study

2. How soil becomes Contaminated
Urban runoff
Agricultural runoff
Mining
Industrial Operations
Atmospheric Deposition
Contaminated Groundwater

3. Sources of Contamination

4. Gas Works Park

5. Gas Works Park
Previous site of coal and oil gasification (1900 to 1956)
Waste accmulations include: coal, tar, and oil
Polynuclear aromatic hydrocarbons (PAH’s )and volatile organic compounds (VOC’s) are present in groundwater
PCB’s, heavy metals, and cyanides also present
“Gas Works deposit” is as thick as 9 feet across the park and overlies the Vashon Till- consists of waste products from prior operations (
Developed by Seattle Parks and Recreation and subsequently studies by USGS and UW

6. Borehole and Well Sites- Contour Map

7. Water Table Contour Map and Flow Paths

8. Geologic Cross Sections
Important to understand the “Gas Works Deposit” as It’s interaction with the Ground Water is the main concern

9. Contamination processes
Weathering of Hydrocarbons in soil and NAPL’s
Weathering- dissoultion, volatilization, biodegradation
These processes release water-soluble, low molecular weight orgainc compunds into water, leaving behind stained soils containing insoluble, high molecular weight compounds

10. Not Quite Polluted Enough…
…to become a superfund site (in 1980)
But polluted enough to cost tens of millions of dollars to clean up…
Puget Sound Energy and City of Seattle still continuing to monitor and clean the site

11. Main Concerns/ Remediation Techniques
Benzene (toxic/ Carcinogenic)
Naphthalene (Toxic/ non-carcinogenic)
PAHs (vary depending on type but can be both Toxic and Carcinogenic)
Air sparging/ Soil Vapor Extraction (AS/SVE)
Monitored Natural Attenuation (possible phyto-remediation to be used in future)
Direct Soil contact Remedy

12. Air Sparging

13. Air Sparging/ Soil Vapor Extraction (AS/SVE)

14. Phytoremediation