Over the years, the definition of a “mega” superfund site has evolved. Initially, large landfills and/or significant groundwater contamination plumes were often identified as “mega” sites and remedial costs were estimated at $50 million to $100 million-plus. These complex sites, unfortunately, now appear to be “modest” in comparison to the newest manifestation of “mega” sites – contaminated sediment sites.
Contaminated sediment sites are often associated with urban waterways, and the sediments in those waterways have been impacted by heavy metals, PCBs, mercury and dioxin from decades of direct and indirect discharges from municipal sewers, industry and others. From the late 18th century through the late 19th century, many urban waterways were looked upon as open sewers and used accordingly. In fact, a number of these waterways, such as the Cuyahoga River in Cleveland, OH, and the Buffalo River in Buffalo, NY, were pronounced “dead.”
Starting in the late 1960s, efforts started to improve water quality by imposing restrictions on what could be discharged to waterways, and billions were spent by municipalities and industry to greatly reduce the pollutants they discharged. These efforts led to very significant and noticeable improvements in rivers and lakes across the U.S., including many urban waterways.
While these efforts led to improved water quality, they did not significantly address the contamination long-present in sediments. As water quality improved, attention shifted to contaminated sediments and their ongoing impacts to water quality. Things like fish consumption and swimming restrictions were, in many instances, linked to impacted sediments.
Addressing contaminated sediments presents a number of unique challenges. Depending upon the waterway, gross removal of impacted sediments can involve: 1) dredging; 2) dewatering and disposal of millions of cubic yards of sediment; and 3) significant environmental risk from the re-suspension of sediments that can occur from dredging activity. Capping of sediments can also be an option. Capping, however, can be incompatible with navigable waterways, which require routine navigation dredging. Natural recovery, which allows natural degradation of organic contaminants and the covering of impacted sediments with new, cleaner sediments over time, is also an option. The remedial timeframe, however, may not be acceptable to all.
Finally, remedial cost is another reason contaminated sediment sites are the new “mega” sites. Bank-to-bank dredging of enormous quantities of sediments is very costly. Even if a confined disposal area is available for sediment disposal, costs can exceed $1 billion for large sites. If dewatering and upland disposal is required for dredged sediments, the costs can increase by three to five times. Even “hot spot” dredging with capping, while less expensive, can still be very costly. Only with a contaminated sediment site would a $900 million remedial option be considered the most reasonable by those, including municipalities, who are, or will be, asked to fund the remedy.
Published September 25, 2014.
