LA Water Operator cheat sheet

CT = disinfectant residual (mg/L) x contact time (min); the required CT increases as water temperature falls and as pH rises.

Chlorine demand (mg/L) = chlorine dose applied minus the free chlorine residual remaining after the specified contact time.

Breakpoint chlorination consumes roughly 7.6 mg of chlorine per mg of ammonia-nitrogen; beyond the breakpoint, additional chlorine persists as free residual.

1 mg/L of alum (Al2(SO4)3-14H2O) destroys about 0.45 mg/L of alkalinity as CaCO3, so lime or caustic may be needed to restore pH and alkalinity.

Rapid mix typically targets a velocity gradient of 300-1000 per second for 30 seconds or less; flocculation tapers from about 60-70 per second down to 10-25 per second.

California combined filter effluent limit: 0.30 NTU or less in at least 95% of monthly measurements, and never above 1.0 NTU.

A sand filter bed is backwashed to roughly 20-25% expansion; backwash water use is normally 2-5% of daily plant production.

Chlorine and chloramines do not inactivate Cryptosporidium at practical doses; credit requires UV, ozone, or chlorine dioxide.

Jar testing is the standard decision rule for selecting coagulant dose and pH before changing full-scale chemical feed rates.

1 psi = 2.31 ft of water column; 1 ft of water = 0.433 psi, so 100 ft of elevation equals about 43.3 psi.

Gallons in one foot of pipe = 0.0408 x (inside diameter in inches) squared.

Continuity: Q = A x V; 1 cfs = 448.8 gpm and 1 MGD = 694.4 gpm = 1.547 cfs.

Hazen-Williams head loss rises as the C factor falls: about 130 for new cement-lined main, 80-100 for old tuberculated steel.

A detectable disinfectant residual must be maintained throughout the distribution system; operators commonly target at least 0.2 mg/L free chlorine at the extremities.

Minimum operating pressure is 20 psi at all points in the system under normal conditions and during fire flow.

Thrust blocks or restrained joints are required at bends, tees, valves, and hydrant branches because internal pressure creates unbalanced forces at changes in direction.

Water hammer is a pressure surge from rapid velocity change; mitigation is slow valve closure, air valves, surge tanks, and adequate pump inertia.

Water age control: flush dead ends and undersized mains routinely, since stagnant water consumes residual and drives disinfection byproduct formation.

A routine total coliform-positive sample triggers repeat sampling within 24 hours: one at the original site, one upstream, and one downstream.

Bacteriological samples must be chilled in transit, arrive within the holding time, and be analyzed within 30 hours of collection.

Free chlorine residual is measured by DPD colorimetric or amperometric titration and should be tested on site because residual decays in the container.

Turbidity is measured by nephelometry (90-degree light scatter) and reported in NTU; it is the primary real-time indicator of filtration performance.

Total hardness (as CaCO3) = 2.497 x Ca (mg/L) + 4.118 x Mg (mg/L).

Alkalinity is titrated to the pH 4.5 endpoint and reported as mg/L CaCO3; it buffers pH and reacts with alum and other coagulants.

Nitrate samples preserved with H2SO4 to pH below 2 have a 48-hour holding time; nitrite and nitrate are reported as nitrogen unless stated otherwise.

A pH meter is calibrated before each use with fresh pH 4, 7, and 10 buffers, checking slope and temperature compensation to within about 0.1 unit.

Conductivity in microsiemens per centimeter correlates with dissolved solids; TDS is roughly 0.55-0.7 times the conductivity reading.

Permit-required confined space entry requires a signed permit, pre-entry and continuous atmospheric testing, an attendant outside, a retrieval system, and continuous communication.

Acceptable entry atmosphere: oxygen 19.5-23.5%, flammable gas below 10% of the lower explosive limit, and hydrogen sulfide below 10 ppm.

A four-gas meter monitors oxygen, combustible gas (LEL), hydrogen sulfide, and carbon monoxide simultaneously.

Chlorine gas is about 2.5 times denser than air; leaks settle in low areas, so evacuate upwind and uphill and approach from above.

Chlorine emergency kits match container size: A kit for cylinders up to 150 lb, B kit for ton containers, C kit for rail tank cars.

Cal/OSHA requires a protective system (sloping, shoring, or shield) in excavations 5 ft deep or more, with a ladder within 25 ft of lateral travel.

Spoil and equipment must be kept at least 2 ft back from the edge of an excavation to prevent cave-in loading.

Lockout/tagout procedure: notify affected workers, isolate the energy source, apply the lock and tag, and verify de-energization with a meter before work.

Any atmosphere at or above an IDLH value (chlorine 10 ppm, hydrogen sulfide 100 ppm, ammonia 300 ppm) requires supplied-air respiratory protection.

The federal Safe Drinking Water Act (1974, amended 1986 and 1996) is administered in California by the SWRCB Division of Drinking Water under primacy.

Stage 2 DBPR limits: total trihalomethanes 80 micrograms/L and HAA5 60 micrograms/L, each as a locational running annual average.

Lead and Copper Rule action levels: lead 0.015 mg/L and copper 1.3 mg/L, evaluated at the 90th percentile of tap samples.

Primary MCLs: nitrate 10 mg/L as N, nitrite 1 mg/L as N, arsenic 0.010 mg/L, fluoride 2.0 mg/L in California.

The Consumer Confidence Report must reach customers by July 1 each year and cover monitoring results for the previous calendar year.

Acute violations such as E. coli detection or nitrate exceedance require notification to the state within 24 hours and public notice within 24 hours.

Cross-connection control programs require annual testing of reduced-pressure and double-check assemblies by a certified tester, with records retained for review.

Operator certification for treatment (T1-T5) and distribution (D1-D5) requires passing an exam plus continuing education contact hours for renewal.