General considerations:

Point 1: In an HT (homogenized tank) the retention time needs to be 12 hours (calculated and confirmed by the laboratory sampler as per the formula given below).

Retention time (hours) = total volume of the tank (m³) flow rate of effluent (m³/span/hour).

Indirect discharge with pretreatment:
The laboratory collects untreated wastewater (point 1: single grab in the HT) and also collects effluent (point 2: single grab if HT is present or point 3: 6 hours sample if no HT is present).

Indirect discharge without pretreatment:
The laboratory collects only untreated wastewater (that is also effluent) as a single grab from HT (point 1) to test MRSL & 5 metals.