Drinking Water Treatment and Distribution
The Drinking Water Treatment and Distribution domain tests whether you can trace a gallon of water from source to tap and prove each barrier worked. New Hampshire exams lean on conventional surface-water treatment, disinfection contact time (CT), turbidity control, and distribution-system integrity, including cross-connection control and pressure maintenance.
Treatment barriers
Surface water systems must filter and disinfect unless they qualify for avoidance; groundwater under the direct influence of surface water is treated like surface water. The Surface Water Treatment Rule requires at least 3-log (99.9%) Giardia and 4-log (99.99%) virus removal or inactivation, usually split between filtration and disinfection. CT is free-chlorine residual (mg/L) multiplied by effective contact time (minutes) and a baffling factor (0.1–1.0) that corrects gross detention time for short-circuiting.
Conventional filtration must produce combined filter effluent ≤0.3 NTU in at least 95% of monthly samples and never >1 NTU; individual filters have their own trigger levels. Distribution operators protect pressure (typically ≥20 psi), keep a disinfectant residual, exercise valves and hydrants, and control cross connections with air gaps or testable backflow assemblies.
Worked example
A clearwell holds 40,000 gal; flow is 0.8 MGD; baffling factor 0.6; free chlorine 0.8 mg/L; required CT is 20 mg·min/L. Flow = 0.8 × 1,000,000 ÷ 1,440 = 556 gpm. Gross detention = 40,000 ÷ 556 = 72 min. Effective time = 72 × 0.6 = 43.2 min. CT = 0.8 × 43.2 = 34.6 mg·min/L, so the requirement is met-but only while the residual and flow are sustained at those values.
Traps
Using gross instead of baffled detention time, applying a free-chlorine CT table to chloramines, reading turbidity from a grab sample instead of the continuous analyzer, and assuming positive pressure at the plant means positive pressure at the dead end.