T1 refers to early time plume extent, T2 refers to intermediate time plume extent and T3 refers to longer term plume extent Figure 5 Hydrocarbon plume life cycle status and MNA applicability potential Understanding the status of the contaminant is critical in the assessment of MNA. Table 3 provides a guide to assessing plume status that should be considered when evaluating historical groundwater analytical data obtained during the NA characterisation phase (McLaughlan et al, 2006). Table 3 Guidelines for assessing overall plume status status Location of wells For monitoring For any For any receptors or wells within the sentinel wells compliance points contaminant plume, where contaminant where contaminant evaluate plume was previously was previously status (see note undetected undetected below) Contracting status is Contaminant not Contaminant not Plume, if ALL of defined as detected. detected. the following occur contracting when: decrease in plume area and mass, decrease in mass flux of contaminants to less than the assimilative capacity of aquifer Stable Plume, if Plume status is Contaminant not Contaminant not ALL of the defined as stable detected. detected. following occur when: insignificant change in plume area and plume mass; mass flux of contaminants equals assimilative capacity of aquifer. Expanding Plume, Plume status is Contaminant Contaminant detected. if ANY of the defined as detected over following occurs expanding when: consecutive increase in plume monitoring rounds area and mass; (detected in 2 mass flux of successive contaminants monitoring events). exceeds the assimilative capacity of aquifer. Concentration trend is defined by statistically-based trend analysis (e.g. Mann-Kendall, Mann-Whitney tests) Rate Constants Evaluating the rate at which contaminant concentrations decrease either spatially or temporally is essential for assessing the success of NA processes at a given site. For
T1 refers to early time plume extent, T2 refers to intermediate time plume extent and T3 refers to longer term plume extent Figure 5 Hydrocarbon plume life cycle status and MNA applicability potential Understanding the status of the contaminant is critical in the assessment of MNA. Table 3 provides a guide to assessing plume status that should be considered when evaluating historical groundwater analytical data obtained during the NA characterisation phase (McLaughlan et al, 2006). Table 3 Guidelines for assessing overall plume status status Location of wells For monitoring wells within the contaminant plume, evaluate plume status (see note below) For any sentinel wells where contaminant was previously undetected For any receptors or compliance points where contaminant was previously undetected Contracting Plume, if ALL of the following occur status is defined as contracting when: decrease in plume area and mass, decrease in mass flux of contaminants to less than the assimilative capacity of aquifer Contaminant not detected. Contaminant not detected. Stable Plume, if ALL of the following occur Plume status is defined as stable when: insignificant change in plume area and plume mass; mass flux of contaminants equals assimilative capacity of aquifer. Contaminant not detected. Contaminant not detected. Expanding Plume, if ANY of the following occurs Plume status is defined as expanding when: increase in plume area and mass; mass flux of contaminants exceeds the assimilative capacity of aquifer. Contaminant detected over consecutive monitoring rounds (detected in 2 successive monitoring events). Contaminant detected. Concentration trend is defined by statistically-based trend analysis (e.g. Mann-Kendall, Mann-Whitney tests) Rate Constants Evaluating the rate at which contaminant concentrations decrease either spatially or temporally is essential for assessing the success of NA processes at a given site. For