NH Water/Wastewater Operator cheat sheet

CT (contact time) = disinfectant residual concentration (mg/L) × contact time (min); CT required rises as temperature falls and pH rises for free chlorine.

Free chlorine: raise dose or contact time to hit required CT; chloramine forms when ammonia is added, giving a weaker but more persistent residual.

Conventional surface water train: coagulation → flocculation → sedimentation → filtration → disinfection; filtration must reduce turbidity to ≤0.3 NTU in 95% of monthly samples (and never exceed 1 NTU).

Detention time (h) = tank volume (gal) ÷ flow (gal/h); overflow rate (gpm/ft²) = flow ÷ clarifier surface area.

Distribution minimum pressure is 20 psi under normal conditions; a boil-water notice is triggered by pressure loss or confirmed contamination.

Head loss in pipe rises with flow squared (Hazen-Williams); flushing velocity should exceed 2.5 ft/s to scour sediment.

Pump horsepower = (flow in gpm × head in ft) ÷ (3,960 × pump efficiency); brake horsepower adds motor efficiency.

Backflow prevention: air gap is the highest protection; reduced-pressure-zone assemblies protect against both backsiphonage and backpressure.

BOD5 measures oxygen consumed over 5 days at 20°C; typical domestic wastewater BOD5 is 200–250 mg/L and TSS 200–250 mg/L.

F/M ratio = (food, lb BOD/day) ÷ (microorganism mass, lb MLVSS); low F/M favors nitrification, high F/M favors bulking risk.

Sludge age (MCRT) = mass of solids in aeration tank ÷ mass wasted plus effluent solids per day.

Return activated sludge (RAS) rate is set to keep mixed liquor suspended solids (MLSS) in the 2,000–4,000 mg/L range for conventional plants.

Collection system: minimum self-cleansing velocity is about 2 ft/s; infiltration and inflow raise treatment costs and can cause sanitary sewer overflows.

Gravity sewer slope is set so flow achieves scour velocity; manholes are placed at grade changes, direction changes, and maximum spacing.

Chlorine disinfection of effluent uses CT; fecal coliform limits are typically 200 cfu/100 mL (monthly geometric mean) with chlorine residual maintained.

Anaerobic digestion reduces volatile solids; typical volatile solids destruction is 40–60% and biogas (methane ~60–65%) is recoverable.

Turbidity is measured in NTU with a nephelometer calibrated against formazin standards; report to two significant figures below 1 NTU.

Total coliform presence triggers repeat sampling; E. coli confirmation requires public notification within 24 hours under the Total Coliform Rule.

Chlorine residual is measured by DPD colorimetric or amperometric titration; record free and total chlorine to 0.01 mg/L.

pH is measured with a calibrated electrode using pH 4, 7, and 10 buffers; calibrate before each sampling day.

Sample holding times: chlorine and pH are analyzed immediately (15 min); nitrate 48 hours; metals 6 months after preservation with HNO3 to pH <2.

Chain of custody must record sampler, date/time, location, preservation, and transfer signatures for legal defensibility.

Nitrate is analyzed by ion chromatography or cadmium reduction; MCL is 10 mg/L as N; nitrite MCL is 1 mg/L as N.

Lead and copper sampling uses first-draw 1-L samples after 6 hours of no use; 90th percentile action level is 0.015 mg/L lead, 1.3 mg/L copper.

Safe Drinking Water Act sets MCLs, Treatment Techniques, and monitoring; states with primacy enforce and report to EPA.

Stage 2 Disinfectants/Disinfection Byproducts Rule: TTHM MCL 80 µg/L and HAA5 MCL 60 µg/L, based on locational running annual averages.

Consumer Confidence Report must be delivered to customers annually by July 1 and include source water, detected contaminants, and health effects language.

Clean Water Act NPDES permits limit effluent parameters and require monthly discharge monitoring reports (DMRs).

Confined space entry requires atmospheric testing (O2 19.5–23.5%, LEL <10%, H2S <10 ppm), a permit, attendant, and rescue plan.

Chlorine gas is heavier than air; use SCBA and evacuate upwind; never use ammonia to neutralize a chlorine release.

Operator certification requires state exam plus continuing education (often 2.0 CEUs per 2-year cycle); Grade level tied to system classification.

Hazard communication requires SDS access, labeling, and training; lockout/tagout applies before servicing pumps and blowers.