Big Thompson fish kill sparks mitigation questions
A massive fish kill in the Big Thompson River in early March has sparked concern about similar incidents occuring in Grand County.
The incident occurred on March 7 and was recently confirmed by Colorado Parks and Wildlife (CPW) which issued a press release stating,” there was a significant fish kill March 7 on the Lower North Fork Big Thompson and main stem Big Thompson River from Drake downstream to the canyon mouth in west Loveland.”
According to CPW the main stem of the Big Thompson suffered an estimated 52 percent loss of fish while the North Fork likely suffered a complete loss. The release states, “while details of the fish kill are still being analyzed, it appears the event was associated with concrete work being performed in building and securing rockery walls along Larimer County Road 43 and replacement of the nearby Storm Mountain Road Bridge which spans the lower North Fork.”
The release goes on to state, “site conditions, weather, soil, topography and other factors at the Storm Mountain Bridge created conditions that allowed movement of chemicals from concrete to enter the stream, causing a dramatic increase in pH (acidic balance of water) when moving downstream sickened or killed fish in its path.”
Because the Big Thompson is on the eastern side of the continental divide the fish kill did not directly impact any rivers, streams or fisheries in Grand County but the incident raises questions regarding how such accidents occur and what measures are typically undertaken to prevent chemicals or other construction materials from leeching into local watersheds.
Lurline Underbrink Curran, former Grand County Manager and current contract employee for the county on water issues, explained local citizens play a crucial role in preventing or at least mitigating such problems as they arise. “How quickly you can respond matters. Water moves fast.” Curran said. “We work hard to keep our eye on things and citizens report things to us all the time. Grand County has always been watchful and our citizens are also very watchful, but that doesn’t always prevent things either.”
Curran explained the only major highway construction project in Grand County is the Highway 9 project. “They had to put down sediment barriers all along Highway 9.”
Kevin Vecchiarelli is an erosion control specialist and serves as the Erosion Control Program Supervisor for the East Grand Water Quality Board. Vecchiarelli outlined some of the standard practices undertaken at highway construction projects near watersheds that are intended to prevent incidents like the Big Thompson fish kill from occurring. He was not familiar with the incident on the Big Thompson and his comments do not speak directly to that particular occurrence.
Among the various forms of mitigation employed at such sites are sediment basins, silt fences and sediment control logs, which are large straw bale wattles that are placed along roadsides
Vecchiarelli explained that chemicals leeching directly into watersheds are not typically the primary concern at such sites. “Generally speaking through all construction, staging materials are supposed to be placed in a stabilized construction area away from river corridors.” He said. Vecchiarelli added such staging areas typically house chemicals and various types of fuels.
“The key to what we are trying to do, when dealing with construction sites, is try to stop erosion in the first place,” Vecchiarelli said. “What really pollutes the river is the sediment. If you can keep the sediment on site there is a far better chance you won’t be polluting down stream. ”
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