Q: We are a riverfront landowner with a significant 25-foot (7.6 m) riprap slope protecting our property from erosion and scour. There is a woven monofilament geotextile filter under the riprap to stop the embankment soil from piping into the river. This system has worked well for the past 10 years, even with two 100-year storm events. However, last month, we had a crude-oil spill upstream from our property. Residual oil is now coating the riprap and geotextile of the protected embankment, and we are concerned about slope instability. Do you know of any way to clean up oil without damaging the geotextile or rebuilding the protected embankment?
A: There are two methods of cleanup that have worked in the past. The first is a shoreline flushing/washing with pressurized steam cleaners and surfactants that can rinse oil from the shoreline into the water, where it can be more easily collected with skimmers and trapped by booms. This is a rather violent process that tends to sterilize the spill area. It is tough on the flora and fauna, and may be rough on the geotextile filter. Please note that any remediation procedure needs to be preapproved by regulators prior to implementation.
The second method is oil spill remediation via microbes. When we talk about microbes that are able to clean up oil, we’re talking primarily about bacteria and fungi. Bacteria can break down oil to carbon dioxide and water. However, no single organism can break down all the components of crude oil or refined fuels spilled into the environment. There are some bacteria that can degrade several hydrocarbons or a class of hydrocarbons. The combined action can degrade almost all of the component crude oil. Such microbes are readily available through several commercial outlets. They typically are broadcast at the spill site with sawdust or clay carriers. Over time, the microbes colonize to break down the oil to carbon dioxide and water. It is an environmentally friendly approach, although it takes time.