Best Practice on Oil Contaminated Sites: A Reliable and Cost-Effective Site Characterization Using a Dual LIF Simultaneous UVOST®-TarGOST®; A Cone Penetration Testing Approach

Abstract

Turning a brownfield from industrial to residential or commercial use has been a trend in recent years. Even more so when land has become valuable, like many of the former manufactured gas plants (MGP) which lie in today’s hearts of the cities. Prior to landuse alternation, land contamination assessment is required in order to ensure that health and environmental risks to receptors are in compliance with legal regulations. Conventional site characterizations based on soil and groundwater sampling may involve significant uncertainties due to insufficient sampling density under limited budgets. Estimations of free phase product (NAPL) spatial extensions might be highly affected by traditional sampling schemes, which often may happen to miss the contaminant bodies. Applying a denser sampling grid may be not feasible due to time and cost constraints (large sites, accessibility issues, depth specific problems). High resolution methods like Membrane Interphase Probe (MIP), Laser Induced Flurescence (LIF), Hydraulic profiling Tool (HPT), Electrical Conductivity (EC) respectively Cone Penetration Testing (CPT) are recognized as rapid, low-invasive and cost-efficient site characterization methods in terms of contamination, hydraulics and lithology. This paper displays best practice scenarios to cope with oil contaminated sites when reaching amazing economical efficiencies (up to more than 100m per day) and preserving at the same time the vertical high-resolution capabilities. A Dual LIF site characterization system was developed by combining a UVOST, and a TarGOST system under a single Dual LIF probe coupled afterwards to a CPT cone. The combined system was deployed at a Swedish site. The site main contaminants are oil-related with reports over coal-tar specific type of NAPL. A no. of 45 UVOST-TarGOST-CPT profiles down to around 10m bgl were carried out indoor, and outdoor of site facilities. They revealed the type, spread, and intensity of site contamination. For calibration, and validation aims, several soil samples were recovered by depth oriented MacroCore sampling. As high-resolution site characterization method, LIF displays significant advantages over traditional characterization techniques. Especially for NAPL detection and delineation, a LIF deployment followed by complementary target-oriented soil sampling delivers the key to reliable site models. A combined use of UVOST and TarGOST under a CPT environment proved to potentiate the high-resolution methodology by enforcing validation resp. resolution capabilities in terms of contaminants (heavy vs light contaminant classes, different saturation degrees, vertical differentiation of NAPLs), and geotechnical parameters (lithology, soil density and consistency). This combined UVOST-TarGOST-CPT methodology applied for the first time in Europe, illustrates the need for site specific screening methods able to provide reliable images of the site under cost efficiency requirements. Moreover, reliable site models open the perspective of successful remediation strategies, and land redevelopment scenarios. Comparisons of site characterization campaigns display significant cost, and time savings using environmental high resolution techniques against conventional methods of drilling/sampling/testing, with direct reflection into the bottom-line profitability of projects. Analyzed scenarios point out, that cost reductions above 30% and time reductions above 20% are fully reachable added-value objectives.