The idea of using permeable reactive barriers to capture nutrients in groundwater is not new. But until recently the method has been mostly cumbersome. It involves digging a deep trench and burying wood chips or some other source of carbon. As nutrient-rich groundwater passes through, bacteria, in the presence of carbon, consume the nutrient. The nutrient of most interest to us on the Cape is, of course, nitrogen, which is impacting our estuaries.
This method is not only cumbersome; it is also very disruptive. Homeowners on the waterfront would not want their backyards excavated.
A new, much less disruptive method will be tested in Falmouth next year. Matthew Charette, a senior scientist at WHOI, will lead a pilot program in which emulsified vegetable oil will be injected into the ground. Once underground, the oil spreads laterally to create the barrier.
It is not as simple as that, of course. The oil, which is being developed by Terra Systems, must be formulated so that it is safe and so that it will spread effectively through the soil.
The method is being tried in Orleans and has been used to clean up other pollutants of groundwater.
But the implications for Cape Cod could be dramatic. Falmouth, Mashpee and Sandwich are planning sewer systems that are not only expensive to build but expensive and energy-intensive to operate. Oil-injected barriers, if they work, could be a game changer; these systems would be far less expensive than laying miles of pipes and building or enlarging treatment centers.
It will be some time before the results of the pilot program are known. And if the results are promising, there will be the question of how to employ the method on a broad scale.
But we can be assured that the science of the system is sound, with WHOI and the Waquoit Bay National Estuarine Research Reserve behind it.
The Cape has been a national leader in nitrogen remediation, first with the use of shellfish. Injected reactive barriers may well be the next case.