Implement fringe core biodegradation model from Gutierrez-Neri et al. (2009) #99
Description
Introduces biodegradation model which considers both degradation in the plume fringe by oxidisable electron acceptors, and in the plume core by anaerobic processes, separately.
Described in Gutierrez-Neri et al. (2009), but has corrections from Hunkeler et al. (2009). Further elaborated in Hohener et al. (2010).