This will depend on the project, and the contaminant flux. The need for re-application of electron donors / acceptors such as HRC and ORC differs sharply from bio applications where PlumeStop is not employed. In the majority of settings, it is good practice to co-apply the PlumeStop with compatible electron donors / acceptors to ensure conditions are optimal for early microflora colonization of the PlumeStop biomatrix and to support the degradation of the initial contaminant loading. Whether or not the donors / acceptors need to be re-applied thereafter will be influenced by any on-going contaminant flux (where PlumeStop may be used as a barrier for example) and the background status of the aquifer in relation to natural attenuation parameters – i.e. naturally available electron donors / acceptors etc. Naturally available donors / acceptors will not support degradation as fast as would be secured using added donors / acceptors such as ORC or HRC, but with PlumeStop, this is no longer all that important, as the contaminants are partitioned into the PlumeStop and are not impacting the water. Whether they degrade quickly or slowly on the PlumeStop doesn’t really matter, so long as the degradation can keep pace with any on-going influx and thereby secure the necessary bio-regeneration of sorption sites.
That’s the long answer. The short answer is, “Sometimes yes, sometimes no depending on the setting”, and when, “Yes”, the ORC/HRC dose requirements may be more forgiving than when ORC/HRC are be used alone owing to the powerful product synergy and reduced reliance on rate of bio to address back-diffusing / desorbing / incoming contamination. Note too that the local concentration effect of PlumeStop bringing the contaminants and bacteria together in the PlumeStop matrix will itself increase instantaneous rate of degradation.
