Quality Monitoring Flashcards

Which analytical method is used to determine the presence and concentration of Giardia and Cryptosporidium in water samples under EPA Method 1623?

Answer: Immunofluorescence assay (IFA) with filtration and concentration

EPA Method 1623 uses filtration to concentrate the sample, immunomagnetic separation (IMS), and immunofluorescence assay (IFA) to identify and enumerate Giardia cysts and Cryptosporidium oocysts.

A treatment plant operator measures raw water TOC of 4.5 mg/L and alkalinity of 90 mg/L as CaCO3. According to the Disinfectants/DBP Rule enhanced coagulation requirements, what must the operator do?

Answer: Achieve specified TOC removal percentages based on the source water TOC and alkalinity combination

Enhanced coagulation requires systems to remove a specified percentage of TOC based on a source water TOC and alkalinity matrix defined in the Stage 1 DBPR to reduce DBP precursors.

What does a CT value represent in disinfection calculations?

Answer: Disinfectant concentration (mg/L) multiplied by contact time (minutes)

CT is the product of the disinfectant residual concentration (C in mg/L) and the contact time (T in minutes), used to calculate log inactivation credit for pathogens.

During distribution system monitoring, a sample location consistently shows lower chlorine residuals than surrounding sites. What condition does this most likely indicate?

Answer: A dead-end or low-flow zone with high water age

Persistently low chlorine residuals at an isolated location often indicate a dead-end or low-flow area where water stagnates, increasing water age and allowing greater chlorine decay.

An operator receives a lab report showing a nitrate concentration of 12 mg/L as N in the finished water. What regulatory concern does this raise?

Answer: The MCL of 10 mg/L as N is exceeded, posing a risk of methemoglobinemia in infants

The federal MCL for nitrate is 10 mg/L as N; at 12 mg/L, the system is in violation and must provide immediate public notification due to the risk of methemoglobinemia ('blue baby syndrome') in infants.

Which quality monitoring tool uses grab samples collected at multiple points in the distribution system to create a spatial map of water quality parameters?

Answer: Distribution system sampling plan / water quality profile

A distribution system sampling plan collects grab samples at strategically chosen sites to create a spatial picture of chlorine residuals, pH, turbidity, and other parameters throughout the system.

What is the purpose of the chlorine-to-ammonia ratio in a system that uses chloramines as a secondary disinfectant?

Answer: To maintain a ratio that forms monochloramine while preventing dichloramine and trichloramine formation

A Cl2:NH3-N weight ratio of approximately 5:1 or less favors monochloramine formation, which is the most effective and least odorous form; higher ratios produce dichloramine and trichloramine with poor taste and less stability.