It is no mystery why we place heavy industry next to our waterways; they provide water for processing, cooling and transport. The demise of those industries has left behind abandoned or defunct waterfront sites that are in an excellent position to fulfill new industrial needs or meet the preferential needs of those who like to live, work and play close to water. But they also have their own remediation challenges.

One of these is the need to prevent contaminants from migrating from the soil and groundwater into the adjacent river, lake or ocean. Developers accustomed to meeting regulatory requirements for inland sites may find themselves faced with a whole new set of regulations at a provincial/state or federal level which are intended to protect vulnerable shorelines and aquatic resources. In many cases, regulatory approvals require explicit consideration of the potential ecological risks from contaminated groundwater.

Evaluating groundwater risks can be a challenge. To meet regulatory expectations, groundwater must be evaluated before it becomes diluted by surface water. Simply going out in a boat and collecting water samples from along the shoreline isn’t usually acceptable. And collecting samples from the shoreline is often hampered by the presence of shore improvements like docks, rip-rap or gabion boxes. These shore improvements can make it difficult—or, more often, impossible—to install monitoring wells where they are needed the most.

One way to evaluate the ecological risks from groundwater involves drilling an array of sentinel wells parallel to the shoreline, collecting groundwater samples and performing chemical analyses and toxicity testing. Field observations about the diversity and abundance of aquatic organisms living along the shoreline are also valuable lines of evidence.

Toxicity tests selected to reflect the types of organisms that live next to the site are conducted using standardized protocols from the U.S. EPA, Environment Canada and other agencies. A wide range of organisms are covered by these protocols: micro-organisms, algae, aquatic plants, invertebrates, and fish. More than 30 different species are included and many more are covered by methods published in the scientific journals.

There are several challenges associated with groundwater toxicity testing. First, it’s important to correctly estimate the actual concentration of groundwater that reaches the receiving environment—fish don’t live in groundwater monitoring wells. Second, the geochemistry of groundwater changes as it approaches the receiving environment and, as a result, groundwater is subject to natural factors such as low oxygen content that can confound the results of toxicity tests unless properly addressed.

These challenges bring together the skills of engineers and scientists. Hydrogeologists use computer-based modelling to predict groundwater attenuation based on the type of contamination, soil composition, rates of groundwater flow, and other factors. Geochemists consider how the nature of the contamination might be altered as groundwater reaches the receiving environment.

This information is then used by environmental toxicologists in the design and interpretation of appropriate toxicity tests. Biologists go out into the field to confirm whether the aquatic community has been impaired, and the ecological risk assessor brings all the evidence together to determine whether remediation is needed.

Costs for remediation at many sites are a significant factor that the developer must consider when deciding whether the project will proceed. Everyone wants the same outcome—a site that meets both protection and redevelopment goals. However, decisions about site management and remediation should consider both biology and chemistry. The use of a multidisciplinary team of engineers and scientists leads to a risk-based approach with increased realism. Protection goals are met using a scientifically-defensible risk assessment approach that is more accurately matched to specific site conditions. Mitigation or remediation measures become more cost-effective because they focus directly on the issues of concern at the site.

Blair McDonald, an environmental scientist with Golder Associates Ltd., in North Vancouver, B.C., Canada, chairs Golder’s Canadian Risk Network.