Effluent quality monitoring: the record that proves a treatment plant is meeting its consent.

Those listed in the plant's Consent to Operate. For most effluent plants that includes pH, BOD, COD, total suspended solids, total dissolved solids and oil and grease, with sector-specific additions (heavy metals, phenols, colour, cyanide, ammoniacal nitrogen) depending on the industry and the disposal route. The consent, not a general list, is the authority.

At the frequency the consent specifies, which varies with category and scale from daily in-house checks to periodic external analysis. Beyond the statutory minimum, plants with variable production benefit from more frequent inter-stage checking, because it is what makes a drift correctable rather than a violation already recorded.

For results to carry weight with the board, analysis should come from a laboratory with appropriate recognition, NABL accreditation and, where required, recognition under the Environment (Protection) Act. In-house testing is valuable for operational control, but the compliance record is stronger when periodic analysis is externally done and certified.

Online continuous effluent and emission monitoring systems transmit real-time data from the outlet to the Pollution Control Board's server. CPCB and State Board directions mandate it for specified industrial categories and scales, and where it applies the requirement appears in the unit's consent. It supplements rather than replaces laboratory analysis, and calibration and uptime become compliance obligations in themselves.

The exceedance stands on record, so the response matters. The cause is traced, usually through inter-stage data: corrective action is taken and documented, and the plant is re-sampled to demonstrate return to compliance. Repeated or unaddressed exceedance is what leads to show-cause notices, directions and, in serious cases, closure or revocation of consent.

Because the outlet alone tells you that something is wrong, not what. Inlet characterisation shows whether the plant is receiving what it was designed for, a change in production or an accidental discharge to drain is a common cause of a sudden outlet failure. And inter-stage results locate the unit that is under-performing.

It is the substance of the environmental statement and of periodic returns to the board, of half-yearly compliance reports where an Environment Clearance applies, and of whatever the consent requires to be submitted. Data collected consistently through the year makes those submissions a compilation exercise; data assembled retrospectively rarely holds together.