Case Study: Enhanced Bioremediation Pilot

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ENHANCED BIOREMEDIATION PILOT USING iSOC
TECHNOLOGY AT A FORMER MANUFACTURED GAS PLANT
CASE STUDY PREPARED BY MR. DAVID WORK, PE RETEC
GROUP
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The Site

• Large former Manufactured Gas Plant Operated
  from the 1850s to the 1930s.
• Primary remedial solution Excavation and
  In-Situ Solidification (ISS).
• In 2002, 66,000 cubic yards of impacted soil
  were excavated and 35,000 cubic yards of impacted
  material below the water table were solidified.
• Site remediation carried out by the Retec Group.

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The Site
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Lithology
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The Problem

• The downgradient off-site alluvial wells meet
  the risk reduction standards for groundwater.
• ISS and excavation was successful.
• Small area of onsite residually impacted
  material.
• The COI trend in one onsite alluvial well was
  upward.
• MNA parameter trend was downward in well.
• Regulators wanted action.

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Feasibility Study

• Excavation Ruled out due to cost.
• ISS Ruled out due to cost.
• Chemical Oxidation Ruled out due to cost and
  uncertainty.
• Enhanced Bioremediation was determined to be the
  best alternative for this area.

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Implementation

• Historically two choices air sparging or
  Oxygen Release Compound (ORC).
• Interbedded clays and sands prevent air
  sparging.
• ORC socks have a small radius of influence.
• ORC slurry injected into treatment zone was
  going to be labor intensive and expensive (i.e.
  generally requires multiple applications).
• iSOC Technology selected for evaluation in a
  pilot study.

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Pilot Design

• iSOC Technology selected as economical and
  effective.
• Pilot cell located at historically impacted
  well.
• Pilot duration - 6-months.
• Monitor O2 levels in wells and piezometers.
• Measure COI change in monitoring well.
• Periodically monitor for nutrient depletion.

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Microbial Activity
Benzene Degraders
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iSOC Technology Description

• Microporous hollow fiber provides a large
  surface area for mass transfer greater than 7000
  m2/m3.
• Surface oxygen source is applied to unit and
  diffuses O2 into groundwater, dissolved oxygen
  (DO) levels are typically 40 -200 PPM depending
  on depth in groundwater.
• Natural convection current fills well with
  uniform DO, resulting in supersaturated levels,
  diffuses to groundwater around the well.
• Observed radius of influence is /- 15 feet.

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Surface Components
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Pilot Test Layout
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Pilot Layout
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Pilot Layout
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Pilot Cell Results
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DO Trend
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OM

• Long term OM is favorable versus ORC and air
  sparging.
• Total 6-month pilot costs Capital 7,500,
  Analysis and Reporting 7,000.
• On a separate site RETEC designed a 24 iSOC
  system, OM with iSOC is estimate at 30K/year.
• Same site, ORC OM estimated at 60-80K/year and
  air sparging at 30-50K per year each with
  significant upfront capital costs.

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Conclusions

• iSOC Technology has been successful in
  stimulating enhanced bioremediation to control
  COI levels in GW.
• One of the first MGP site in the nation to use
  diffusion iSOC Technology.
• Combination of low OM cost and effectiveness
  provides many benefits over other forms of O2
  delivery.