Work out stream assimilative capacity instantly with clear inputs, formula shown and shareable results.
Assimilative capacity is the load a river can accept while still meeting its environmental quality standard: headroom between standard and background, multiplied by the low flow. Rearranging the mixing equation gives the maximum effluent concentration a discharge may have, which is how consent limits are derived.
Assimilative load
Capacity (kg/day) = (EQS - background) x low flow (m3/s) x 86.4
Permissible concentration
C_effluent = (EQS x (Q_river + Q_effluent) - background x Q_river) / Q_effluent
Assimilative capacity assessments are regulatory determinations requiring statutory low-flow data and approved environmental quality standards. This is an indicative calculation only.
There is no assimilative capacity and no new discharge of that substance can be permitted. Catchment-wide measures are needed before any additional load can be accepted.
Not to bioaccumulative or persistent substances, where a no-deterioration or zero-discharge approach applies regardless of calculated dilution.