SSFL Groundwater Contamination

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SSFL Groundwater Contamination

• Tom Harmon, Ph.D. (tharmon_at_ucmerced.edu)

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Overview

• Contamination of fractured groundwater systems by
  solvents (TCE)
• TCE amounts and extent at SSFL
• How much is there?
• How fast is it moving?
• How far will it go?
• Other contaminants
• Summary

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groundwater monitoring data

• Review of monitoring reports
• trichloroethene or TCE (most data by far)
• horizontal TCE extent--how far?
• vertical TCE extent--how deep?
• other chlorinated compounds
• other contaminants (perchlorate, tritium,
  radionuclides)

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Offsite Wells or Springs
TCE 670ug/L 8/94 134XgtMCL
Vinyl Chloride 64 ug/L 3/94 32XgtMCL
Chloromethane 19ug/L 4/86 12XgtTWSL- Livestock
well
Benzene 3.8 ug/L 11/94 3.8XgtMCL
1,1-DCE 19ug/L 5/96 3XgtMCL
Trans-1,2-DCE 38ug/L 5/96 3XgtMCL
cis1,2-DCE 27ug/L 5/96 3XgtMCL
RD-56
RD-38
OS-5
RD-59
RD-32, RD-43
Carbon Tetrachloride 4.5ug/L 2/95 9XgtMCL
Outfall 002
Outfall 001
Manganese 390ug/L 3/94 7.8XgtMCL
Lead 50ug/L 12/94 4.2 Xgt MCL
Chromium 75ug/L 1/93 1.5 XgtMCL
Lead 40ug/L 1/95 3.3 XgtMCL
All above standards and backgrounds. Dates
range from 1992-94.
Not To Scale
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Summary of off-site well observations

• Clearly multiple contaminants have migrated off
  site and impacted off-site wells
• Extremities of the plume appear to be defined
  horizontally, but not as well-defined vertically
• Horizontal migration appears to have halted
• TCE is clearly the most widespread contaminant
• Motivation to know how much TCE is in the ground
  and in what physical form
• undissolved liquid
• dissolved in water
• adsorbed to SSFL sandstone

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What we usually think of when we say plumes
(contaminated bodies of groundwater)
flow
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SSFL plumes differ from those in the previous
slide because they are in a fractured sandstone
system
DNAPL
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What do we know about the amount of TCE in the
ground?

• We can very roughly calculate how of the TCE has
  dissolved using the plume maps and a measure of
  the TCE sorption to the SSFL sandstone
• Many assumptions involved
• ellipsoid plume shapes (true shape irregular)
• 100 ft thickness (true thickness irregular and
  unknown)
• average concentrations assumed in different areas
• only one sorption measurement
• Result

100,000s gallons in dissolved from the original
TCE
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Given this amount, the plumes are relatively
small, why?

• One hypothesis the TCE has been adsorbed by the
  sandstone (like a giant sponge)
• Another hypothesis only a very small portion of
  the TCE has dissolved, and
• ..the majority remains trapped in fractures
• many relatively shallow fractures (top 300 feet)
• some in relatively deep fractures (greater than
  300 feet)

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How much DNAPL or undissolved TCE remains is
difficult to estimate
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Other groundwater contamination

• Perchlorate
• observed at several locations
• unlike TCE, no clear patterns in groundwater
• other chlorinated organics
• DCE isomers, vinyl chloride are transformation
  products from TCE

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Summary SSFL groundwater

• Clearly multiple contaminants (particularly TCE)
  have migrated off site and impacted off-site
  wells
• Migration appears to have halted horizontally
• 100,000s gallons of TCE in SSFL subsurface
• may be stabilized by sandstone adsorption
• may have penetrated deeper and will appear in the
  future
• Other contaminants have been identified in SSFL
  groundwater (perchlorate for example), but no
  conclusive pathway to off-site locations has been
  confirmed