Assessment of accurate porewater concentrations at low detection limits can be essential in the management of aquatic contaminated sites. Porewater concentrations are used to indicate contaminant transport from adjacent upland areas and assess risk to ecological health, and they can indicate the long-term effectiveness of remedial actions.

Compared to sediment or water sampling which can be fairly straightforward, porewater sampling requires identification of an appropriate method for the duration of the study (active vs. passive), contaminant types (organic vs. inorganic), water depth in the study area (equipment design), and detection limits required (ex., solid phase micro-extraction (SPME) fiber length). Options for porewater sampling that take these considerations into account along with the pros and cons for each method will be discussed.

Porewater sampling can utilize either active methods, which include pumping with a piezometer for a point in time concentration, or passive methods where sampling devices are installed for longer periods of time (up to three months). Determination of the right method through understanding the various material options and data objectives of the program is key to success. Designing and executing cost-effective sampling programs can be challenging, particularly for larger projects requiring low detection limits. Additionally, identification of an appropriate material for a particular site’s contaminants of concern generally requires the use of more than one sampling methodology.

The evaluation of porewater for performance monitoring in Plumper Bay, Esquimalt Harbour, British Columbia, will be used as a case study in which multiple methods including piezometers, SPME, regenerated-cellulose dialysis membrane (RCDM), and nylon screen passive diffusion sampler (NSPDS) were used. In this case, sampling was conducted to identify the effectiveness of each method for use in future performance monitoring. Lessons learned from conducting the sampling program will be shared.

Amy Corp, Managing Scientist, Anchor QEA, LLC
Amy Corp is a Managing Scientist at Anchor QEA, LLC, and has more than 14 years of experience in the environmental science and chemistry fields. Amy specializes in all aspects of contaminated site remediation, including conceptual site model development, designing and performing site investigations, conducting remedial options analysis, and providing federal project management reporting. She has played a key role in several large-scale cleanups including planning and implementation for sites within working harbours.

This field study involves a comparative evaluation of typical field screening using a photoionization detector (PID) versus advanced screening using a portable field spectrometer for remedial soil excavation during challenging winter conditions. The project was carried out at a public works site at Siksika First Nation in Alberta. Historical site conditions and environmental data were limited prior to work at the site. Soil borings advanced in 2017 had identified diesel-impacted soils in the vicinity of a former above-ground fuel storage tank. Remedial excavation was recommended to remove the contaminated soil.

The excavation was conducted in January 2019. In anticipation of challenging soil field-screening conditions with temperatures ranging from -15○C to -25○C and low-volatility degraded diesel as the contaminant, a comparative field study was initiated. The objective was to evaluate how near-infrared spectroscopy (NIRS) with proprietary machine learning technology could support field decision-making and reduce remediation costs in comparison with typical soil excavation screening methodology.

The field study was carried out over one day, in which over fifty soil samples were collected. Each soil sample was analysed in the field using both the NIRS and a PID. Confirmation soil samples were also submitted for laboratory analysis.

While the PID did not register a response to any sample during field screening, the NIRS analyses showed greater than 20,000 parts per million total petroleum hydrocarbons in several samples. These analyses were later confirmed by laboratory analysis of duplicate samples. The technology also provided near real-time visualization of the contaminated areas, enabling precise excavation.

In this study, using advanced field screening technology enabled effective field-based decision-making for efficient excavation, immediate backfilling, significant costs savings, and subsequent site closure.

Alisa Le May, Partner, EnviroSearch Ltd.
Alisa Le May is a partner at EnviroSearch Ltd. With over 25 years of consulting experience in the geosciences industry, she has conducted and managed hundreds of environmental assessment and remediation projects throughout Western and Northern Canada and California. Alisa has worked on contaminated site investigations, remediation system design and construction management, remedial and maintenance dredging, underground storage tank removals, Phase I, II, and III investigations, feasibility studies, and risk‐based corrective action plans. Alisa obtained her BSc in Geology from the University of Saskatchewan and her MBA from Golden Gate University in California.