DE Water Operator cheat sheet

CT (contact time) = disinfectant residual concentration (mg/L) × effective contact time (minutes); units are mg·min/L.

Log inactivation credit is read from CT tables using: disinfectant type, residual, temperature, pH (chlorine), and target pathogen.

Free chlorine: hypochlorous acid (HOCl) is the dominant disinfectant; its fraction rises as pH falls (pKa ≈ 7.5).

Chlorine demand = applied dose − residual after contact time; the residual that remains is what earns CT credit.

Coagulation jar test: rapid mix, then slow mix with alum or ferric salt; optimum pH is lower for alum (~5.5–6.5) than for ferric (~4–5).

Flocculation uses tapered, slow mixing (G ≈ 10–75 s⁻¹) to build floc particles that settle in the clarifier.

Filtration: conventional rapid sand media is sized 0.45–0.55 mm effective size with a uniformity coefficient ≤1.5; filter loading rates are typically 2–6 gpm/ft².

Turbidity limits: combined-filter-effluent ≤0.3 NTU in 95% of monthly samples and never >1 NTU for conventional filtration systems.

Disinfection byproducts: TTHM and HAA5 are formed from natural organic matter plus chlorine; removing precursor organics before chlorination lowers them.

Pressure rule (USEPA): minimum 20 psi at all points in the distribution system under all flow conditions, including fire flow and main breaks.

Static pressure from elevation: 1 psi ≈ 2.31 ft of water head; psi = head (ft) / 2.31.

Flow: Q = A × V; for a full pipe, A = πD²/4. Keep units consistent (cfs with ft, gpm with in and ft/s via 0.4085).

Hazen-Williams: head loss varies with Q^1.85 and inversely with C^1.85 and D^4.87; lower C means rougher, older pipe.

Dead-end mains and low-flow zones are the highest risk for nitrification (chloraminated systems) and biofilm; flushing and looping address both.

Cross-connection control: an air gap is the only truly non-mechanical backflow protection; RPZ is used where backpressure or back-siphonage hazards are high.

Storage tank turnover: long detention times consume residual; target turnover and monitor residual at the tank outlet and extremes of the system.

Main disinfection after repair: chlorinate to 25–100 mg/L for at least 24 hours (or per state rule), then flush and sample for coliform and chlorine residual before returning to service.

Surface water (rivers, lakes, reservoirs) requires filtration and disinfection under the Surface Water Treatment Rules; groundwater under direct influence (GWUDI) is treated as surface water.

Groundwater is generally lower in turbidity and microbial load but may carry iron, manganese, hardness, arsenic, radionuclides, and nitrate.

Turbidity is measured in NTU; it is a surrogate for particle and pathogen removal, not a direct pathogen measurement.

Total hardness is reported as mg/L CaCO₃; soft (<60), moderately hard (60–120), hard (120–180), very hard (>180).

Iron and manganese: iron >0.3 mg/L or manganese >0.05 mg/L causes staining and taste complaints; treatment is oxidation (aeration, chlorine, permanganate) followed by filtration.

Nitrate >10 mg/L as N triggers a public notice because of methemoglobinemia risk in infants.

Alkalinity and pH govern corrosion control; Langelier Saturation Index near 0 is balanced, negative is corrosive, positive is scale-forming.

Source water assessment: identify potential contaminant sources in the delineated area, rate their susceptibility, and use results to target monitoring and treatment.

Safe Drinking Water Act (1974, amended 1986 and 1996) authorizes national drinking water standards; states hold primacy to enforce them.

National Primary Drinking Water Regulations (NPDWRs) are enforceable health-based MCLs; National Secondary Drinking Water Regulations (NSDWRs) are non-enforceable aesthetic limits.

Total coliform rule logic: routine samples test for total coliform; any positive triggers repeat samples and testing for E. coli and fecal indicators.

Surface Water Treatment Rule: 99.9% (3-log) Giardia and 99.99% (4-log) virus removal/inactivation; combined filter effluent turbidity limits apply.

Stage 2 Disinfectant/Disinfection Byproducts Rule: LRAA (locational running annual average) limits for TTHM (80 µg/L) and HAA5 (60 µg/L).

Lead and Copper Rule: action levels of 0.015 mg/L lead and 1.3 mg/L copper at the 90th percentile of tap samples; corrosion control is the primary strategy.

Public notification tiers: Tier 1 (immediate, within 24 hours) for acute violations such as MCL exceedance for E. coli or nitrate; Tier 2 within 30 days; Tier 3 within one year.

Consumer Confidence Report (annual drinking water report) must be delivered to customers by July 1 each year and include source, detected contaminants, and health effects language.

Operator certification: state-issued, graded by system classification (treatment and distribution), with continuing education required for renewal.

Confined space entry requires a permit, atmospheric testing (oxygen 19.5–23.5%, LEL <10%, H₂S <10 ppm), ventilation, attendant, and retrieval system.

Chlorine gas is heavier than air and accumulates in low areas; SCBA is required for escape from chlorine atmospheres, not air-purifying cartridges.

Chlorine leak response: evacuate upwind and to higher ground; do not attempt to stop a leak without proper respiratory protection and training.

Sodium hypochlorite and acid must never be mixed - mixing produces chlorine gas; store oxidizers separately from acids and organics.

H₂S: rotten-egg odor, olfactory fatigue occurs quickly, and it is flammable and toxic; use a calibrated meter, not smell, for detection.

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

Trench and excavation: protective system required at 5 ft depth or deeper; spoil piles and equipment kept at least 2 ft from the edge.

Electrical: GFCI protection on portable tools and wet locations; treat all circuits as energized until verified de-energized and tested.

Recordkeeping: maintain monitoring results, CT calculations, chemical usage, and maintenance logs; state rules set retention periods, commonly at least 3–5 years and longer for some records.

MOR (monthly operating report) summarizes flows, chemical doses, residuals, turbidity, and compliance data submitted to the state each month.

Budget categories: personnel, chemicals, power, maintenance, debt service, and capital reserve; rate design must cover full cost of service.

Water loss: compare production meter totals with billed consumption; unaccounted-for water above roughly 10% warrants leak survey and meter testing.

Asset management: rank assets by criticality (likelihood × consequence of failure) and fund repair/replacement before failure, not after.

Staffing and certification: match the highest-grade operator to the system classification; ensure backup coverage and documented standard operating procedures.

Emergency response plan: identify hazards, chain of command, notification lists, alternate water sources, and mutual aid agreements; exercise the plan annually.

Security and vulnerability: control access to treatment chemicals and facilities, and report suspicious activity; vulnerability assessments are required for larger systems.