Using pre-screening methods for an effective and reliable site characterization at megasites

Using pre-screening methods for an effective and reliable site characterization at megasites Mette Algreen 0 1 2 3 4 5 Mariusz Kalisz 0 1 2 3 4 5 Marcel Stalder 0 1 2 3 4 5 Eugeniu Martac 0 1 2 3 4 5 Janusz Krupanek 0 1 2 3 4 5 Stefan Trapp 0 1 2 3 4 5 Stephan Bartke 0 1 2 3 4 5 0 Institute for Ecology of Industrial Areas , 6 Kossutha Street, Katowice , Poland 1 Department of Environmental Engineering, Technical University of Denmark , 2800 Kgs., Lyngby , Denmark 2 Responsible editor: Philippe Garrigues 3 Helmholtz Centre for Environmental Research-UFZ , Permoserstr. 15, 04318 Leipzig , Germany 4 Fugro Consult GmbH , Volkmaroder Str. 8c, 38104 Braunschweig , Germany 5 SolGeo AG , Dornacherplatz 3, 4501 Solothurn , Switzerland This paper illustrates the usefulness of prescreening methods for an effective characterization of polluted sites. We applied a sequence of site characterization methods to a former Soviet military airbase with likely fuel and benzene, toluene, ethylbenzene, and xylene (BTEX) contamination in shallow groundwater and subsoil. The methods were (i) phytoscreening with tree cores; (ii) soil gas measurements for CH4, O2, and photoionization detector (PID); (iii) direct-push with membrane interface probe (MIP) and laser-induced fluorescence (LIF) sensors; (iv) direct-push sampling; and (v) sampling from soil and from groundwater monitoring wells. Phytoscreening and soil gas measurements are rapid and inexpensive pre-screening methods. Both indicated subsurface Mette Algreen and Mariusz Kalisz contributed equally to this work. Contamination; Tree core; Probe technologies; Brownfields; Phytoscreening; Direct-push; Soil gas; Site characterization - Megasites are per definition especially large and prominent brownfields, typically with several pollution sources with various contaminants (Schdler et al. 2012; Schirmer et al. 2012). Their sustainable regeneration demands to carefully consider the local complexities and uncertainties (Bartke and Schwarze 2015). Investors shy away from regeneration which involves the removal of actual or potential pollutions originating from previous use, because these can seriously impair the marketability of contaminated land. The reduced merchantability does not depend so much on the (level of) expected remediation costs but rather on their uncertainty and the remaining effect of stigmatizationan effect that can be reduced by improved site characterization (Bartke 2011). Conventional site characterization approaches are based on sampling soil and groundwater from bore holes and monitoring wells. This tends to be time consuming and costly. At the same time, these approaches may involve uncertainties due to insufficient historical data or sampling density owed to limited budgets. The subsequent risk assessment may then be inaccurate and the results doubtful. Uncertainties can be reduced by applying a denser sampling grid, which, however, may be very expensive when applying traditional methods for large plots such as megasites. If contaminated properties are to be merchantable and reactivated, economically efficient site characterization strategies are a prerequisite. Every site is unique with respect to the contaminants and their behavior under the conditions specific to each site. Therefore, the methods to characterize and monitor a site need to be tailored to the site-specific conditions (French et al. 2014). Several rapid, low- or non-invasive and cost-efficient techniques have been developed recently and can now be applied as part of the screening and monitoring strategy for megasites (Rein et al. 2011; Rein et al. 2015, submitted; Kstner et al. 2012). Each screening method is related to a different level of precision and delivers different information about the contamination status and also on the ongoing processes at the site. We therefore assessed the opportunities of an optimized site characterization using the information gathered from fast and non-expensive pre-screening methods. In this study, the pre-screening methods of tree coring, soil gas measuring, and direct-push (DP) with high-resolution technologies, membrane interface probe (MIP), and laser-induced fluorescence (LIF) sensors have been applied on a former Soviet military airbase near the city of Szprotawa in southwestern Poland. Phytoscreening by tree coring is a qualitative and semiquantitative method using trees as bioindicators for subsurface pollution. The technique takes advantage of the uptake and translocation of water from soil and groundwater by trees, and of herein dissolved pollutants. By sampling and analyzing a core from the stem, subsurface pollution can be detected. So far, this pre-screening method has mainly been applied at sites contaminated with chlorinated solvents (Wittlingerova et al. 2013; Sorek et al. 2008; Larsen et al. 2008; Gopalakrishnan et al. 2007; Ma and Burken 2002; Vroblesky et al. 1999). For a couple of years, the feasibility of this method to detect other compounds such as heavy metals and benzene, toluene, ethylbenzene, and xylenes (BTEX) has been of scientific interest (Algreen et al. 2012, 2014; Wilson et al. 2013; Sorek et al. 2008). Results have not always been convincing, and more research on the feasibility of the method is needed. Tree coring requires a minimum of sampling equipment. It is particularly well suited for forested areas and can also be applied in inaccessible, swampy, or remote areas as long as there are trees. It is a non-invasive technique, which is of advantage if there are cables, pipes, or explosives in the underground (Algreen and Trapp 2014). Also, the lack of trees, their deformation, or miserable growth can show high levels of toxic substances in the underground (Trapp et al. 2001). Soil gas measurement is a rapid semi-quantitative method restricted to volatile contaminants in the vadose zone. During sampling, the gas contained in the interstitial spaces of the soil is extracted from a temporary or permanent probe and analyzed on site or in the laboratory. Soil gas measurements are offered commercially for a variety of volatile organic compounds (VOCs) including chlorinated hydrocarbons (e.g., Bishop et al. 1990; Rivett 1995) and petroleum derivatives like BTEX (Caldwell et al. 2012; Ramalho et al. 2014). The method allows real-time on-site measurements, which facilitate a higher degree of flexibility in the field. Besides BTEX and VOC, also methane, CO2, and oxygen levels can be monitored. High methane and low oxygen levels originate from aerobic biodegradation processes. Direct-push-based technologies were developed for a variety of drilling methods with pushing or hammering options to enable both screening and in-detail subsurface investigations in comparatively short time periods and at relatively low costs. This technique is performed by pushing and hammering small-diameter hollow steel rods into the ground to acquire high-resolution depth profiles of different parameters. Di (...truncated)