MT Water/Wastewater Operator cheat sheet

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

Log inactivation credit is assigned from tables of required CT by target pathogen (Giardia, viruses) and by disinfectant; 3-log Giardia and 4-log virus are typical groundwater/surface water targets under the Surface Water Treatment Rules.

Turbidity limits: combined filter effluent must be ≤0.3 NTU in 95% of monthly measurements and never exceed 1 NTU (conventional/filtration systems); individual filter effluent ≤1 NTU.

Coagulation optimum pH and dose are found by jar testing: rapid mix (flash mix) ~1–30 s at high velocity gradient, flocculation 15–45 min at low velocity gradient, then sedimentation.

Alkalinity and pH govern coagulant demand: alum consumes about 0.45 mg/L alkalinity (as CaCO3) per mg/L of alum dosed and lowers pH; add lime or caustic to restore pH.

Chlorine dose vs. residual: applied dose = demand + residual; free chlorine exists as HOCl (stronger biocide) below pH ~7.5 and shifts to OCl− as pH rises.

Disinfection byproduct precursors (TOC) are removed by enhanced coagulation; TOC removal requirements step up with source water alkalinity (e.g., >2.0 mg/L TOC and low alkalinity require higher percent removal).

Backwash: filter run terminated by headloss, turbidity breakthrough, or run time; backwash rate must fluidize media (typically 15–20 gpm/ft², ~50–60% bed expansion) with air scour where available.

Fluoride is dosed to an optimal concentration (commonly 0.7 mg/L) and must not exceed the MCL of 4.0 mg/L; secondary maximum contaminant level is 2.0 mg/L.

Minimum residual disinfection in distribution: a detectable residual must be maintained throughout; common state targets are ≥0.2 mg/L free chlorine (or ≥0.5 mg/L total chlorine) at the extremities.

Water age drives quality loss: storage tank turnover, dead-end flushing, and looped mains reduce age; target storage turnover of roughly 3–5 days or less.

Pressure standards: typical minimum 20 psi at all points under normal demand and never below 20 psi during main breaks or fire flow; normal operating range often 40–80 psi.

Head loss in pipes: Hazen-Williams hf = 10.44 × L × Q^1.852 / (C^1.852 × d^4.87) in US units (L and d in feet, Q in cfs); higher C = smoother pipe = less loss.

A main break or repair requires a boil-water notice when pressure drops below 20 psi; the notice is lifted only after repair, flushing, and two consecutive negative bacteriological samples 24 hours apart.

Cross-connection control hierarchy: air gap (best) > reduced-pressure-zone backflow preventer > double check valve; test annually and after repair.

Coliform rules: total coliform presence triggers repeat sampling at the site and upstream/downstream; E. coli presence or repeat total coliform positives require public notice within 24 hours.

Flushing velocity should exceed 2.5 ft/s to scour sediment; compute flow needed as Q (gpm) ≈ 2.45 × d² (inches) for 2.5 ft/s.

Lead and copper: 90th percentile action level 0.015 mg/L lead and 1.3 mg/L copper; corrosion control (pH/alkalinity adjustment or inhibitor) is required when exceeded.

BOD5 is measured over 5 days at 20 °C with nitrification suppressed; typical untreated domestic wastewater is 200–250 mg/L BOD5 and 200–250 mg/L TSS.

F/M ratio = (food, lb BOD/day) / (MLVSS, lb); conventional activated sludge runs ~0.2–0.4 day⁻¹; low F/M favors nitrification and lower sludge production but risks filamentous bulking if too low.

Solids retention time SRT = MLSS mass / solids leaving per day; nitrifiers need SRT of roughly 8–15+ days depending on temperature; short SRT washes out nitrifiers.

Sludge volume index SVI = (settled sludge volume, mL/L after 30 min × 1000) / MLSS mg/L; SVI 80–150 indicates good settling; >200 signals bulking.

Return activated sludge RAS ratio = Qr/Q; typical 0.5–1.5; wasting rate sets SRT, and wasting is calculated from desired SRT and system solids inventory.

Nitrification consumes about 7.14 mg alkalinity (as CaCO3) per mg NH3-N oxidized and 4.57 mg O2 per mg N; denitrification recovers roughly 2.86 mg O2 per mg NO3-N.

Secondary clarifier surface overflow rate for activated sludge typically 400–800 gpd/ft² at average flow; solids loading rate 20–30 lb/day/ft² for conventional systems.

Chlorine disinfection of effluent: dose = demand + residual; CT = residual × contact time; fecal coliform limits are commonly 200 cfu/100 mL (monthly geometric mean) with 400 cfu/100 mL max.

Anaerobic digestion: mesophilic 35–38 °C, thermophilic 52–57 °C; volatile solids reduction of 38% or more qualifies as Class B biosolids under 40 CFR Part 503; pH kept near 6.8–7.4.

Gravity sewer design: minimum velocity 2 ft/s (self-cleansing) and maximum about 10 ft/s (scour/erosion); slopes set to achieve these for the design flow.

Manning's equation: V = (1.486/n) × R^(2/3) × S^(1/2) in US units; typical n = 0.013 for concrete pipe, R = hydraulic radius = area/wetted perimeter.

Infiltration/inflow (I/I): infiltration enters through defects (groundwater), inflow enters through direct connections (downspouts, sumps, manholes); each is quantified separately.

Lift station wet well sizing uses pump cycle time: usable volume = inflow × cycle time; minimum cycle time limits pump starts (often 10–15 starts/hour max).

Force mains require air/vacuum relief valves at high points and check valves at pumps; velocity should exceed 2 ft/s to prevent solids deposition.

Confined space entry requires pre-entry testing for oxygen (19.5–23.5%), LEL (<10%), H2S, and CO; forced ventilation and a standby attendant are mandatory.

Sewer cleaning: high-velocity jetting removes grease and roots; bucket machines and rodding handle heavy debris; CCTV inspection grades structural defects (cracks, offset joints, infiltration).

Grease trap and FOG program: interceptors sized by fixture units or flow; FOG is removed at the source to prevent sanitary sewer overflows (SSOs).

Manhole rehabilitation: lining, grouting, and frame/seal replacement reduce I/I; a smoke test locates illegal storm connections.

Safe Drinking Water Act (SDWA) primary standards are enforceable MCLs; secondary standards (SMCLs) address aesthetics (e.g., iron 0.3 mg/L, chloride 250 mg/L).

Surface Water Treatment Rule: 99.9% (3-log) Giardia and 99.99% (4-log) virus removal/inactivation; combined filter effluent ≤0.3 NTU in 95% of monthly samples.

Total Coliform Rule: routine samples per population; any total coliform positive triggers repeat samples; E. coli positive requires public notice within 24 hours.

Consumer Confidence Report (CCR, annual water quality report) must be delivered to customers by July 1 covering the prior calendar year.

Clean Water Act: NPDES permits set effluent limits; 40 CFR Part 503 governs biosolids; 40 CFR Part 403 covers pretreatment and prohibited discharges.

Sanitary sewer overflow reporting: SSOs must be reported to the state and, where applicable, the public; bypasses and overflows require notification and corrective action.

Operator certification: each state sets grades (e.g., Class I–IV) based on system complexity; continuing education (CEU/contact hours) is required for renewal.

Public notice categories under the SDWA: Tier 1 (immediate, 24 hours), Tier 2 (30 days), Tier 3 (annual CCR) based on the violation's health risk.

Recordkeeping: SDWA monitoring records generally kept 3 years (5 years for some), and NPDES monitoring reports (DMRs) submitted monthly.

Hazardous atmosphere limits for confined spaces: oxygen 19.5–23.5%, combustible gas <10% LEL, H2S <10 ppm (or <5 ppm per some standards), CO <35 ppm (8-hour TWA 25 ppm).

Hydrogen sulfide is heavier than air, deadens the sense of smell at higher concentrations, and can be immediately dangerous to life or health (IDLH 100 ppm).

Methane (CH4) is lighter than air, explosive range 5–15% in air, and is generated by anaerobic decomposition in sewers and digesters.

Chlorine gas is heavier than air; use a self-contained breathing apparatus for leaks; the IDLH is 10 ppm; never use water on a chlorine leak-use caustic or soda ash.

Lockout/tagout (LOTO): isolate all energy sources, verify zero energy, apply locks and tags, and only the person who applied a lock may remove it.

Electrical safety: use GFCI protection, verify de-energized circuits with a tester, and maintain approach distances; arc flash PPE per NFPA 70E.

Fall protection is required at 4 ft in general industry; guardrails, lifelines, and harnesses apply to tank and ladder work.

Chemical handling: consult the SDS for PPE, incompatibilities, and first aid; never mix chlorine and ammonia (forms toxic chloramines) or acid and hypochlorite (releases chlorine gas).

Emergency response: know the location of eyewash/showers, spill kits, and the emergency action plan; report all injuries and near misses.

Budget categories: O&M (labor, chemicals, power, repairs) vs. capital improvement (CIP) funded by reserves, bonds, or SRF loans; depreciation tracks asset replacement.

Rate-setting: a cost-of-service approach allocates fixed costs across customer classes; fixed charges stabilize revenue, volumetric charges encourage conservation.

Asset management: condition assessment, criticality ranking, and a capital replacement schedule extend asset life; a computerized maintenance management system (CMMS) tracks work orders.

Key performance indicators: non-revenue water (produced minus billed), energy per million gallons treated, SSO count per 100 miles of sewer, and days of inventory.

Staffing and certification: verify operator grade matches plant classification; maintain a training plan for CEUs and cross-training to cover absences.

Regulatory reporting: submit DMRs, CCRs, and monitoring reports on schedule; maintain records for the required retention period and be ready for inspections.

Emergency preparedness: a written emergency response plan, mutual aid agreements, backup power, and a public notification plan are core requirements.

Procurement: competitive bidding thresholds, sole-source justification, and contract documents; maintain an up-to-date operations and maintenance manual.

Customer service and public relations: respond to complaints (taste/odor, low pressure) with documentation; transparency builds trust and supports rate increases.