INTRODUCTION

The in situ recovery of soil contaminated with volatile and semi-volatile substances by means of ventilation systems is a commonly used technique, whose efficiency is widely recognised. It basically consists of the induction of air currents through the vadose zone of the soil in order to promote the volatilisation of the lightest contaminants and their aerobic degradation. These currents are induced by means of the generation of pressure gradients between bore-holes, with the aid of vacuum pumps. AITEMIN, in collaboration with URS Dames&Moore, has perfected a prototype unit for pilot ventilation tests on soils contaminated with light hydrocarbons (gasolines) with the dual objective of facilitating the obtaining of data required for the proper configuration of decontamination projects and for remote control of the process once the work on cleaning the soil has started. For its development, a subsidy has been granted from the National R&D Plan of the Ministry of Environment. This unit is prepared for working simultaneously with three extraction bore-holes (expandable up to eight), it is mounted in a container for ease of transport, and can be handled locally or by remote control by means of telephone.

AVAILABLE EQUIPMENT

• Extraction system:
• Liquid ring high-vacuum pump
• Fluid separator
• Cooling system
• Control system for extracted vapours
• Detector of volatile organic components (VOC), from 0 to 100% LEL
• O₂, CO₂ and CH₄ sensors
• Vacuum pump for gas sampling
• Explosimeter
• Data operation and gathering system
• Software for real-time control (local and remote)
• Datalogger with expansor module
• GSM Modem

APPLICATIONS

• Permeability tests
  Determination of the permeability to air of the different levels of soil, air flows that can be extracted from each level, vacuums produced and radius of influence
• Extraction tests
  Determination of the quantity of volatiles extracted and variation in their concentration according to flow and extraction time.
• Respirometric tests
  Oxygenation of the soil and rate of biodegradation.
• Control of the decontamination
  Flow and concentration of contaminant in vapours extracted in each ventilation bore-hole, vacuums generated in the subsoil and rate of biodegradation.