Laboratory Analysis and Process Monitoring
What to know
Operators rely on lab data to run treatment and demonstrate compliance. Know the difference between process monitoring (frequent, operational, e.g., turbidity, residual, pH) and compliance monitoring (prescribed methods, frequencies, and reporting). Understand grab vs. composite samples, chain of custody, and holding times. Learn core methods: turbidimetry/nephelometry for turbidity, DPD for chlorine residual, membrane filtration and enzyme substrate for coliform, pH electrodes, and spectrophotometry for nitrate, fluoride, and metals. Understand quality assurance/quality control: blanks, duplicates, spikes, calibration, and control charts. Know that certified labs and approved methods are required for compliance, and that field meters must be calibrated per manufacturer and regulatory schedules.
Traps
Questions often confuse process and compliance monitoring requirements, or assume any lab result is compliance-valid - method, lab certification, and holding time matter. Watch for DPD vs. other chlorine methods, and for turbidity reported in NTU versus other units.
Worked example / rule of thumb
A field chlorine reading of 0.8 mg/L taken with an uncalibrated meter is not compliance-grade - calibrate, verify with a standard, and re-sample if needed. Rule of thumb: sample handling errors (holding time, preservation, contamination) are the most common cause of invalid data.
Study tip
For each parameter, know the method, unit, typical frequency, and whether it is process or compliance.