When dam removals occur, sediment impoundments have the potential to hold significant contamination from upstream activities. This contamination can influence the decision to remove the whole dam. The most notorious example is the Fort Edwards Dam removal from the Hudson River in 1973, which released a significant amount of polychlorinated biphenyls (PCBs) from the GE plant located 1 mile upstream from the dam (Hetling et al. 1978). The survey of the downstream effect found 40 different hotspots where PCBs exceeded 50 ppm (mg/L) and led to its eventual removal by extensive dredging from 2009 to 2015 (EPA 2020). The Housatonic River flows through Connecticut and receives water and sediment contaminated with PCBs from another GE plant located in Pittsfield, MA (EPA 2021). Sediment contamination should be heavily considered before a dam is removed from the system because this site, in particular, required extensive monitoring and cleanup.

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Small dams can also release historical sediments downstream. After removing the Manatawny Creek dam in Pennsylvania contaminated sediments were found downstream due to the redistribution of sediment released from behind the dam (Ashley et al. 2006). From Ashley et al., 2006, three questions were determined necessary when considering dam removal: 

1. Is there a potential source of chemical contamination that has been or currently is being introduced into the system?

2. Are there significant inventories of fine-grain sediment in the impoundment area that will be released?

3. Are the contamination levels with the impoundment significantly higher than those found upstream or downstream?

Answering these questions could affect the dam removal process by adding the need to cap or dredge the surrounding sediment. This remediation technique would lead to additional costs and would affect the feasibility of removing a number of dams.