CWEA Grade 1 Lab Analyst: Core focused
exam Study Guide
Section 1: Laboratory Safety and Procedures
Section 2: Sample Collection and Preservation
What is a composite sample? - ANSWER ✓ A sample formed by combining multiple
discrete samples collected at regular intervals over a specific time period.
What is a grab sample? - ANSWER ✓ A single sample collected at a specific time and
place, representing conditions only at that moment.
Why is it crucial to measure and record pH and temperature immediately upon
sample collection? - ANSWER ✓ Because they are unstable parameters that can
change quickly due to exposure to air or temperature shifts.
For a BOD sample, what preservation method is used? - ANSWER
✓ Refrigeration at 4°C, and it should be analyzed within 48 hours of collection.
Why is nitric acid added to a sample intended for metal analysis? - ANSWER ✓ To
acidify the sample, which keeps metals dissolved in solution and prevents them from
adsorbing to the container walls.
What does "Headspace" in a sample bottle refer to, and why is it important? -
ANSWER ✓ It is the air space between the sample and the cap. Minimizing headspace is
critical for volatile analytes to prevent loss or pressure buildup.
What is the typical maximum holding time for a preserved Total Suspended Solids
(TSS) sample? - ANSWER ✓ 7 days.
Why must sample bottles for bacteriological testing be sterile? - ANSWER ✓ To
prevent contamination from external microorganisms that would skew the results.
What information must be recorded on a sample chain-of-custody form? -
ANSWER ✓ Sample ID, date/time of collection, sampler name, preservation methods,
requested analyses, and recipient's signature upon transfer.
What is a field blank, and what is its purpose? - ANSWER ✓ A sample of analytefree
water carried to the sampling site, exposed to the ambient conditions, and bottled. It
checks for contamination during the sampling process.
, Section 3: Analytical Methods and Calculations
What is the formula for calculating Percent Removal? - ANSWER ✓ % Removal =
[(Influent Concentration - Effluent Concentration) / Influent Concentration] x 100
What does BOD5 measure? - ANSWER ✓ The amount of dissolved oxygen consumed
by microorganisms while decomposing organic matter in a water sample at 20°C over a
5-day period in the dark.
What is the primary standard used to standardize an EDTA titrant in hardness
testing? - ANSWER ✓ Calcium Carbonate (CaCO₃).
In a titration for alkalinity, what color change indicates the phenolphthalein
endpoint? - ANSWER ✓ Pink to colorless.
What is the purpose of the Winkler method? - ANSWER ✓ To determine the
concentration of dissolved oxygen (DO) in a water sample.
How do you calculate the Actual MLSS concentration from a Total Suspended
Solids test? - ANSWER ✓ MLSS (mg/L) = [(Weight of dried residue & filter) - (Tare
weight of filter)] / Sample Volume (L)
What is the difference between Total Solids and Total Suspended Solids? -
ANSWER ✓ Total Solids include all material left after evaporation, while TSS is the
portion of total solids retained on a filter.
What is a nephelometer used to measure? - ANSWER ✓ Turbidity, by detecting light
scattered by particles in the water.
What is the purpose of a calibration curve? - ANSWER ✓ To establish the relationship
between the analytical response (e.g., instrument signal) and the concentration of the
analyte.
What is the formula for calculating a geometric mean? - ANSWER ✓ The nth root of
the product of n numbers (e.g., for 3 numbers A, B, C: Geometric Mean = ³√(A x B x C)).
If a sample is diluted, how is the final result calculated? - ANSWER ✓ Final Result =
(Measured Result) x (Dilution Factor).
exam Study Guide
Section 1: Laboratory Safety and Procedures
Section 2: Sample Collection and Preservation
What is a composite sample? - ANSWER ✓ A sample formed by combining multiple
discrete samples collected at regular intervals over a specific time period.
What is a grab sample? - ANSWER ✓ A single sample collected at a specific time and
place, representing conditions only at that moment.
Why is it crucial to measure and record pH and temperature immediately upon
sample collection? - ANSWER ✓ Because they are unstable parameters that can
change quickly due to exposure to air or temperature shifts.
For a BOD sample, what preservation method is used? - ANSWER
✓ Refrigeration at 4°C, and it should be analyzed within 48 hours of collection.
Why is nitric acid added to a sample intended for metal analysis? - ANSWER ✓ To
acidify the sample, which keeps metals dissolved in solution and prevents them from
adsorbing to the container walls.
What does "Headspace" in a sample bottle refer to, and why is it important? -
ANSWER ✓ It is the air space between the sample and the cap. Minimizing headspace is
critical for volatile analytes to prevent loss or pressure buildup.
What is the typical maximum holding time for a preserved Total Suspended Solids
(TSS) sample? - ANSWER ✓ 7 days.
Why must sample bottles for bacteriological testing be sterile? - ANSWER ✓ To
prevent contamination from external microorganisms that would skew the results.
What information must be recorded on a sample chain-of-custody form? -
ANSWER ✓ Sample ID, date/time of collection, sampler name, preservation methods,
requested analyses, and recipient's signature upon transfer.
What is a field blank, and what is its purpose? - ANSWER ✓ A sample of analytefree
water carried to the sampling site, exposed to the ambient conditions, and bottled. It
checks for contamination during the sampling process.
, Section 3: Analytical Methods and Calculations
What is the formula for calculating Percent Removal? - ANSWER ✓ % Removal =
[(Influent Concentration - Effluent Concentration) / Influent Concentration] x 100
What does BOD5 measure? - ANSWER ✓ The amount of dissolved oxygen consumed
by microorganisms while decomposing organic matter in a water sample at 20°C over a
5-day period in the dark.
What is the primary standard used to standardize an EDTA titrant in hardness
testing? - ANSWER ✓ Calcium Carbonate (CaCO₃).
In a titration for alkalinity, what color change indicates the phenolphthalein
endpoint? - ANSWER ✓ Pink to colorless.
What is the purpose of the Winkler method? - ANSWER ✓ To determine the
concentration of dissolved oxygen (DO) in a water sample.
How do you calculate the Actual MLSS concentration from a Total Suspended
Solids test? - ANSWER ✓ MLSS (mg/L) = [(Weight of dried residue & filter) - (Tare
weight of filter)] / Sample Volume (L)
What is the difference between Total Solids and Total Suspended Solids? -
ANSWER ✓ Total Solids include all material left after evaporation, while TSS is the
portion of total solids retained on a filter.
What is a nephelometer used to measure? - ANSWER ✓ Turbidity, by detecting light
scattered by particles in the water.
What is the purpose of a calibration curve? - ANSWER ✓ To establish the relationship
between the analytical response (e.g., instrument signal) and the concentration of the
analyte.
What is the formula for calculating a geometric mean? - ANSWER ✓ The nth root of
the product of n numbers (e.g., for 3 numbers A, B, C: Geometric Mean = ³√(A x B x C)).
If a sample is diluted, how is the final result calculated? - ANSWER ✓ Final Result =
(Measured Result) x (Dilution Factor).
