Formatted Title
Sustainable High Resolution/Remediation Design Characterization Allows Optimization of Future In Situ Remediation Footprint
Background/Objectives
A large industrial property in Sweden was planned for redevelopment to residential, commercial and school buildings. The site is roughly 70,000 square meters and former industrial activities included use of both chlorinated solvents and possibly other organic compounds (e.g., mineral oils).
Historical investigations had initially established the presence of a trichlorethylene (TCE) source under one of the former production areas, but complete delineation could not be achieved as long as industrial activities were present/active on site.
Local geology consists of silty clay in the upper 6 to 12 m of the site, followed by different intervals of highly saturated lenses (sandy silt). Silty clay lenses are found present very heterogeneously between each saturated layer. Bedrock is found at different depths ranging from approximately 10 meters below ground level (m bgl) to more than 30 m bgl.
The redeveloper objective was to ensure that a proper high resolution / remedial design effort would guarantee a full delineation of both soil and groundwater contamination to allow for detailed planning of the construction project (10+ residential buildings, schools and commercial buildings), without encountering unexpected sources during the construction phase.
Approach/Activities
In November 2022, as industrial activities were gradually stopped, the redeveloper decided to perform a full site environmental screening starting from the initially observed source area and then covering the entire site. The investigation efforts led to the completion of approximately 130 membrane interface probe (MIP) locations (2,500 linear meters covered), collection of 700 high density soil samples and installation of 60 monitoring wells. All works were completed within the same main mobilization, reducing transportation costs drastically. The use of MIP probing allowed soil coring only where necessary, reducing the amount of soil waste generated. Similarly, groundwater wells installation was tailored according to the MIP results ensuring screens were installed in the correct depths.
The overall approach allowed the redeveloper to establish with high level of accuracy the amount of soil contaminant mass present on site (including the expected contaminated areas located under future residential or school buildings), evaluate the exact pattern of the spreading of groundwater contamination. A phased in situ remediation approach was planned to allow the redeveloper to account for disposal of soil only to the depths required for construction of the new buildings foundations. All remaining contaminated soil would be treated in situ, while Ejlskov in situ remediation technologies (Trap&Treat) were planned for use within the groundwater bearing unit avoiding any pumping of contaminated water or leaving fixed installations in the ground.
Results/Lessons Learned
The outcome of the investigation showed that planning of construction activities (both small and large scale) should start at an early stage with a high-resolution site characterization. This type of activity can provide highly valuable information that redevelopers can use more efficiently when planning new buildings’ locations, their use, depths of basements, etc. The benefits (economic, social) can be easily judged as all stakeholders involved in the project (end client, consultant, authorities, contractors, city planners) can obtain a much accurate overview of the soil and groundwater contamination avoiding assumptions on long term planning. Having large amount of environmental data prior to start any construction activity, allows reducing risks of unexpected findings (e.g., new contamination sources) during the construction process, which would ultimately lead to higher costs and delays, hence increasing the overall project footprint.