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In-situ chemical oxidation in dense subsoil in the inner city area, Stuttgart

ISCO remediation of an LCHC leak by depth-differentiated injection of activated persulphate
  • ISCO system technology with batching tank and activation tank © ZUT
    ISCO system technology with batching tank and activation tank © ZUT
  • Hydraulic pre-removal and soil vapor extraction in the run-up to ISCO remediation. © ZUT
    Hydraulic pre-removal and soil vapor extraction in the run-up to ISCO remediation. © ZUT
Place
Stuttgart
Client
City of Stuttgart, Office for Environmental Protection
Parameters
- LCHC, especially PCE, max. 110,000 µg/L
- source of damage: area 375 m², depth approx. 10 m below underground car park
- 15 injection levels, GW measuring points and three soil vapor extraction levels, horizontal/sloping
Performance period
- Pilot test: Jan-Jul 2021 (duration: approx. 6 months)
- Remediation: from March 2023 (duration approx. 30 months)

Challenging site conditions

A former dry-cleaning site in the city center emits the highest CHC load of all contaminated sites in Stuttgart. Following successful laboratory and field tests, the damaged area is now being remediated using depth-differentiated, pressure-controlled injection of activated persulphate. The low permeability of the aquifer and its heterogeneous structure as well as the cramped spatial conditions in an underground car park and laundry room pose particular challenges.

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Principle of ISCO injection using the cuff tube method © ZUT
Principle of ISCO injection using the cuff tube method

Special features

  • Public invitation to tender
  • Laboratory/pilot test
  • Join Venture with consulting company BOSSCON
  • Depth-differentiated, pressure-controlled injection
  • Method for activating persulfate patented

Scope of services

  • Drilling work in underground garage and laundry room on 2nd floor
  • Preparation/dosing station for activated persulphate
  • Implementation of ISCO injection campaigns
  • Creation of a hydraulic numerical flow model
  • Temporary soil vapor extraction and hydraulic pollutant removal
  • Monitoring
  • View into the UV reactor (opened for photography)
    View into the UV reactor (opened for photography)
  • Oxidizing agents are not only added in the laundry room but also outside.
    Oxidizing agents are not only added in the laundry room but also outside.

UV activation of the oxidizing agent

The oxidizing agent used is activated before being injected into the ground. A UV lamp is used for this, which significantly reduces electricity costs compared to thermal activation and still shows effective activation.

The activated oxidizing agent is fed into the aquifer via input levels in the underground car park and in the outdoor area.