ISCO Treatment of Gasoline in Soil and Groundwater - Case Study

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Courtesy of EN Rx

Gasoline contaminants in soil and ground water

Currently, it is a common practice to complete some type of biological or chemical oxidant treatment to an open excavation in the hopes that it has some positive effect on the future need for additional treatment. For almost all of these treatments, it is impossible to determine what the actual impact of the treatment is separate from the excavation. However, this site posed one such case where the treatment zone clearly lied directly below the excavation and volatilization, mixing or other excavation qualities would not have impacted the zone .

HISTORY

  • Leaking Underground Storage Tank (UST) had contaminated an area at this active gas station ?? Stiff sandy clays and sand stringers created a difficult cleanup scenario.
  • Excavation appeared to be the most cost-effective solution to remove the source mass.

PRE-CLEAN DATA

  • Groundwater contamination from 5-25ft bls, however a seasonal high water table has not been noted since 2005 during a season of significant rainfall due to hurricanes.

  • The most resistant clays are from 30 to 40 feet. Clayey silty sands exist from 40 to 60 feet which are moist to dry due to the clays confining condition for water. Karst limestone starts at approximately 60 ft

  • BTEX contaminant mass was estimated at greater than 100,000 pounds.

  • The overwhelming majority of the mass was less than 40 feet which became the primary concern of the excavation.

  • Limited contamination existed below this depth although it was not adequately investigated as only two points document it.

    REMEDIATION ACTIVITIES

  • Excavation commenced to a depth of 38 to 40 feet. Further depth was not possible due to physical constraints.

  • An application of 10,000 gallon of reagent was applied to the 10,000 sf floor.

  • The two points that document deep contamination from approximately 40 to 50 feet bls were used to calculate a

    approximate 8 foot treatments. This treatment zone was to be contacted by percolation. Enough fluid volume was

    added to saturate approximately 8 feet.

The OVA clearly shows the effect of the treatment from three post treatment soil boring locations. It appears DW-8 may

also indicate our treatment was specific to the approximate 8 ft designed.

Case Study 0106: Treatment Results – Sub Floor

Depth

DW-2

SS-47

DW-8

DW-9

DW-10

40'-42'

90

100

8

0

1

42'-44'

442

700

0

4

0

44'-46'

118

200

0

5

0

46'-48'

65

1100

8

0

1

48'-50'

3

440

71

0

0

50'-52'

175

terminus

96

1

0

52'-54'

6

12

1

0

54'-56'

8

8

1

0

56'-58'

7

3

2

0

All results in parts per million Organic Vapor Response by Flame Ionization Detector.

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