20 Source Water & Watershed Protection Practice Questions & Answers

1. 1. A reservoir stratifies in summer. Which layer becomes anoxic and releases soluble iron, manganese and hydrogen sulfide into the raw water?

   • A.The hypolimnion, the cold dense bottom layer isolated from mixing✓ Answer
   • B.The thermocline, the middle zone of rapid temperature change
   • C.The epilimnion, the warm upper layer stirred by wind action
   • D.The littoral zone, the shallow shoreline band of rooted plants

   The thermocline blocks mixing, so the hypolimnion receives no reaeration while bacteria decomposing settled organic matter consume the remaining dissolved oxygen. Under the resulting reducing conditions, insoluble ferric iron and manganese oxides in the sediment are reduced to soluble ferrous and manganous forms, and sulfate reduction generates hydrogen sulfide.

   Source: CSUS Water Treatment Plant Operation, Vol. 1, Chapter 2, Source Water, Reservoir Management, and Intake StructuresReport a problem with this question

2. 2. In late October, raw water from a reservoir intake shows a sudden rise in turbidity, manganese and chlorine demand at the same time. What is the most likely cause?

   • A.Spring runoff is carrying eroded soil in from the tributary streams
   • B.Algal photosynthesis is raising the pH in the surface layer
   • C.Saltwater intrusion is pushing brackish water toward the intake
   • D.Fall turnover is mixing the bottom layer up through the reservoir✓ Answer

   As surface water cools in autumn its density approaches that of the bottom water, the thermocline breaks down, and wind mixes the whole reservoir. The anoxic bottom water carrying reduced iron and manganese, sulfides, ammonia and resuspended sediment is distributed through the water column, which raises turbidity, metals and chlorine demand together.

   Source: CSUS Water Treatment Plant Operation, Vol. 1, Chapter 2, reservoir turnoverReport a problem with this question

3. 3. A plant draws from a stratified reservoir through a multiple-port intake. What is the operating advantage of that design?

   • A.The operator can settle suspended solids before they reach the screens
   • B.The operator can draw from the depth with the best raw water quality✓ Answer
   • C.The operator can prevent stratification from forming in the reservoir
   • D.The operator can raise the intake flow without changing the pump speed

   Water quality in a stratified reservoir varies sharply with depth: the epilimnion carries algae and taste-and-odor compounds while the hypolimnion carries dissolved iron, manganese and sulfides. Ports at several elevations let the operator select an intermediate depth that avoids both problems and shift ports as conditions change through the season.

   Source: Recommended Standards for Water Works (Ten States Standards), surface water intake structuresReport a problem with this question

4. 4. Which observation most strongly suggests that a well is groundwater under the direct influence of surface water?

   • A.Raw water carries dissolved hydrogen sulfide with a rotten-egg odor
   • B.Raw water nitrate rises each spring after fertilizer is applied nearby
   • C.Raw water hardness is high and stays nearly constant through the year
   • D.Raw water temperature swings seasonally and turbidity climbs after rainfall✓ Answer

   True groundwater is thermally buffered by the formation and varies only a degree or two annually, and it does not respond to individual storms. Seasonal temperature swings and turbidity or particle-count spikes correlated with rainfall show that surface water is reaching the well quickly, which is the pattern a microscopic particulate analysis is then used to confirm.

   Source: US EPA Surface Water Treatment Rule, definition and determination of groundwater under the direct influence of surface waterReport a problem with this question

5. 5. A state determines that a spring-fed source is groundwater under the direct influence of surface water. What does that determination change for the system?

   • A.The source must now be treated under the surface water treatment requirements✓ Answer
   • B.The source must now be sampled for hardness rather than for microorganisms
   • C.The source must now be reclassified as a confined artesian aquifer supply
   • D.The source must now be blended with a second well before it is distributed

   The determination is regulatory, not geological: it says the aquifer cannot be relied on as a filter for pathogens. The source is therefore regulated as surface water, meaning filtration plus disinfection to the required log removal and inactivation credits for Giardia, viruses and Cryptosporidium rather than disinfection alone.

   Source: US EPA Surface Water Treatment Rule, applicability to groundwater under direct influence of surface waterReport a problem with this question

6. 6. A well is pumped at a steady rate for several hours. What does the resulting cone of depression describe?

   • A.The compacted soil layer settling above the pumped aquifer
   • B.The pressure rise built up along the pump column and discharge
   • C.The seasonal decline in recharge across the whole aquifer
   • D.The lowered water surface sloping down toward the pumping well✓ Answer

   Pumping removes water faster than the formation can transmit it to the borehole, so the water level drops most at the well and less with distance, forming an inverted cone. Its outer edge is the radius or zone of influence, and anything contaminating within that zone will be drawn toward the well, which is why cone geometry drives wellhead protection area delineation.

   Source: AWWA Water System Operations, Water Treatment, groundwater hydraulics and well drawdownReport a problem with this question

7. 7. A well has a static water level of 62 ft (18.9 m) and a pumping water level of 118 ft (36.0 m) while producing 280 gpm (1,060 L/min). What is the specific capacity of this well?

   • A.2.4 gpm per foot of drawdown
   • B.5.0 gpm per foot of drawdown✓ Answer
   • C.280 gpm per foot of drawdown
   • D.4.5 gpm per foot of drawdown

   Drawdown is the pumping level minus the static level, so 118 ft minus 62 ft equals 56 ft. Specific capacity is the yield divided by the drawdown, so 280 gpm divided by 56 ft equals 5.0 gpm per foot, and the units of gallons per minute per foot are what distinguish specific capacity from the well yield itself.

   Source: AWWA Water System Operations, Water Treatment, well yield and specific capacity calculationsReport a problem with this question

8. 8. A well's specific capacity has fallen steadily over three years while nearby wells and regional water levels are unchanged. What is the most likely explanation?

   • A.The pump motor is drawing low voltage and turning below its rated speed
   • B.The screen and gravel pack are plugging with incrustation and biofouling✓ Answer
   • C.The aquifer is being depleted faster than natural recharge can replace it
   • D.The discharge check valve is leaking back into the well between cycles

   If the aquifer were declining, the static level and neighboring wells would fall too, but here only this well is losing capacity. Carbonate incrustation, iron and manganese deposits and iron-bacteria slimes build up on the screen openings and in the gravel pack, increasing entrance losses so drawdown grows for the same yield, and the remedy is rehabilitation by surging, jetting, acid or chlorine shock treatment.

   Source: CSUS Water Treatment Plant Operation, Vol. 1, well maintenance and rehabilitationReport a problem with this question

9. 9. How does an unconfined aquifer differ from a confined artesian aquifer?

   • A.Its water is always harder because it sits deeper within the rock formation
   • B.Its water is always free of pathogens because rainfall cannot reach it
   • C.Its upper surface is the water table, open to pressure from the atmosphere✓ Answer
   • D.Its upper surface is a clay layer that holds the water under added pressure

   An unconfined aquifer is bounded below by an impermeable layer but open above, so its upper surface is the water table and it is at atmospheric pressure, rising and falling directly with recharge. A confined aquifer lies beneath a confining layer and is under pressure, so water in a well rises to the potentiometric surface, which can stand above the top of the aquifer.

   Source: AWWA Water System Operations, Water Treatment, aquifer types and groundwater occurrenceReport a problem with this question

10. 10. Compared with groundwater from a deep confined aquifer, raw surface water from a river is generally:

    • A.Softer but higher in turbidity, organics and pathogens, and far more variable✓ Answer
    • B.Softer and lower in turbidity, organics and pathogens, and far more stable
    • C.Harder and higher in turbidity, organics and pathogens, and far more stable
    • D.Harder but lower in turbidity, organics and pathogens, and far more variable

    Groundwater has long contact time with mineral formations, so it dissolves calcium and magnesium and arrives hard, mineralized and thermally stable. Surface water is fed by runoff that has had little contact with rock, so it is softer but picks up suspended solids, natural organic matter and pathogens, and its quality can change within hours of a storm.

    Source: AWWA Water System Operations, Water Treatment, comparison of surface water and groundwater characteristicsReport a problem with this question

11. 11. Why is Cryptosporidium of particular concern in a surface water supply?

    • A.Its oocyst wall dissolves in chlorine, so filtration adds little further benefit
    • B.Its oocysts grow in the distribution mains, so flushing is the main barrier
    • C.Its oocyst wall resists chlorine, so removal by filtration is the main barrier✓ Answer
    • D.Its oocysts settle out quickly, so raw water storage alone removes them

    The thick-walled oocyst is highly resistant to free chlorine at the concentrations and contact times used in drinking water treatment, unlike bacteria and most viruses. Regulations therefore credit physical removal by coagulation, sedimentation and filtration, backed by ultraviolet or ozone where inactivation credit is needed, and treat watershed protection as the first barrier.

    Source: US EPA Interim Enhanced Surface Water Treatment Rule and Long Term 2 Enhanced Surface Water Treatment Rule, Cryptosporidium controlReport a problem with this question

12. 12. A reservoir develops an earthy, musty taste and odor in late summer from geosmin and 2-methylisoborneol. What should the operator expect about conventional treatment?

    • A.These compounds are filtered out, so a slower filter rate resolves the odor
    • B.These compounds pass through, so activated carbon or oxidation is required✓ Answer
    • C.These compounds break down, so a higher chlorine residual resolves the odor
    • D.These compounds settle out, so a longer sedimentation basin detention works

    Geosmin and 2-methylisoborneol are dissolved metabolites released by cyanobacteria and actinomycetes and are detectable at nanogram-per-liter levels, so they are not particles that coagulation, sedimentation and filtration can capture. Removal requires adsorption on powdered or granular activated carbon, or oxidation by ozone or an advanced oxidation process; free chlorine does not destroy them and can worsen other odors.

    Source: AWWA Water System Operations, Water Treatment, taste and odor control and algal metabolitesReport a problem with this question

13. 13. Natural organic matter in a surface water source matters to the treatment operator chiefly because it:

    • A.Reacts with hardness minerals to form scale inside the raw water mains
    • B.Adds hardness that must be removed before the water is disinfected
    • C.Reacts with disinfectants to form regulated disinfection byproducts✓ Answer
    • D.Settles rapidly in the basin and overloads the sludge removal equipment

    Humic and fulvic acids, tannins and lignins leached from soil and vegetation are precursors that combine with chlorine to form trihalomethanes and haloacetic acids. Because precursor concentration in the source drives byproduct formation downstream, operators track it as total organic carbon or ultraviolet absorbance at 254 nanometers and manage the watershed and coagulation to reduce it.

    Source: AWWA Water System Operations, Water Treatment, natural organic matter as disinfection byproduct precursorReport a problem with this question

14. 14. Fertilizer applied to cropland across a watershed washes into a stream during rainfall. This is best classified as:

    • A.A nonpoint source, spread widely and delivered by runoff✓ Answer
    • B.A point source, discharged from one identifiable outlet pipe
    • C.A cross connection, entering through a direct piped pathway
    • D.A background source, occurring naturally in the soil profile

    A point source enters from a discrete conveyance such as a pipe or outfall that can be located and permitted, while a nonpoint source originates diffusely across the land surface and reaches water through runoff. Because there is no single outlet to control, nonpoint nutrient loading is managed with best management practices, buffer strips and land-use measures in the watershed protection plan.

    Source: US EPA Source Water Assessment Program guidance, point and nonpoint contaminant source inventoryReport a problem with this question

15. 15. A coastal utility notices chloride steadily rising in a well near the shore during a drought. What is the most likely cause?

    • A.Road salt applied to the highway leaching down through the well annulus
    • B.Seawater intrusion drawn inland as pumping outpaces freshwater recharge✓ Answer
    • C.Fertilizer applied on nearby fields infiltrating through the unsaturated zone
    • D.Corrosion of the well casing releasing chloride from the steel into the water

    In a coastal aquifer, fresh groundwater floating on denser saltwater holds the interface offshore. Drought reduces recharge while pumping lowers the freshwater head, so the interface migrates inland and upward toward the pumping well, and the fix is reduced or rotated pumping rather than treatment at the wellhead.

    Source: CSUS Water Treatment Plant Operation, Vol. 1, groundwater sources and saltwater intrusionReport a problem with this question

16. 16. During a well site inspection, which finding is the clearest sanitary defect requiring correction?

    • A.The discharge line carries a meter and a check valve downstream of the pump
    • B.The casing vent turns downward with a screen and the ground slopes away from the well
    • C.The sounding tube is capped and the water level is logged at each site visit
    • D.The casing vent opens upward without a screen and ponded water surrounds the well✓ Answer

    An upward-facing unscreened vent lets insects, dust and rainwater enter the casing, and ponded water at the wellhead provides a reservoir of potentially contaminated surface water directly against the annulus. Sanitary construction requires a screened, downturned vent, a watertight seal and cap, and grade sloped to drain away from the casing.

    Source: Recommended Standards for Water Works (Ten States Standards), well construction and wellhead protectionReport a problem with this question

17. 17. Why must an abandoned well within a wellhead protection area be properly sealed?

    • A.It is an open conduit letting surface water and contaminants reach the aquifer✓ Answer
    • B.It is a stagnant column letting dissolved oxygen corrode the surrounding rock
    • C.It is an unmetered source letting the aquifer lose water to evaporation losses
    • D.It is a settled borehole letting the ground subside above the pumped formation

    An unsealed borehole bypasses the natural confining layers and soil filtration that normally protect the aquifer, so spills, runoff and shallow contaminated water can travel straight down and also move between aquifers. Sealing with neat cement grout from the bottom up restores that barrier, and abandoned wells are a standard item in a contaminant source inventory.

    Source: US EPA Wellhead Protection Program guidance, abandoned well sealingReport a problem with this question

18. 18. Which set of activities matches the four required elements of a source water assessment under the Safe Drinking Water Act?

    • A.Delineate the area, purchase the land, fence the boundary, restrict all recreation
    • B.Delineate the area, inventory sources, determine susceptibility, inform the public✓ Answer
    • C.Rate the operators, staff the plant, schedule the sampling, file the annual report
    • D.Sample the raw water, treat the raw water, blend the sources, report the results

    The 1996 amendments require each state to delineate the source water protection area, inventory potential contaminant sources within it, determine the system's susceptibility to those sources, and make the results available to the public. Assessment is the mandatory diagnostic step, while the protection measures that follow, such as land acquisition and use restrictions, are voluntary and locally chosen.

    Source: Safe Drinking Water Act Amendments of 1996, Source Water Assessment Program required elementsReport a problem with this question

19. 19. An operator inspecting a raw water intake finds head loss across the traveling screen climbing week over week. What does that indicate?

    • A.The screen is fouling with debris or mussels and needs cleaning✓ Answer
    • B.The intake channel is scouring and is deepening below the ports
    • C.The reservoir level is rising and is flooding the intake ports
    • D.The raw water pump is worn and is losing discharge pressure

    Head loss across a screen is the pressure difference driving flow through its openings, so it rises as the open area is progressively blocked by leaves, silt, aquatic growth or attached zebra and quagga mussels. A rising differential is the standard trigger for cleaning, and ignoring it starves the pumps and can collapse the screen under the load.

    Source: AWWA Water System Operations, Water Treatment, intake screening and inspectionReport a problem with this question

20. 20. Records show the static water level in a supply well declining a little further each year over a decade. What does that trend most likely indicate?

    • A.Withdrawals from the aquifer are exceeding its long term recharge✓ Answer
    • B.Leakage past the check valve is draining the discharge column
    • C.Deposits on the well screen are restricting flow into the borehole
    • D.Readings from the airline gauge are drifting out of calibration

    Static level is measured with the pump off and the well recovered, so it reflects the aquifer rather than conditions inside the well. A screen problem would raise drawdown and cut specific capacity while leaving the static level alone, whereas a static level falling year after year means the water budget is negative and long term overdraft, with its risk of subsidence and intrusion, must be addressed.

    Source: AWWA Water System Operations, Water Treatment, groundwater level monitoring and aquifer overdraftReport a problem with this question

Practice questions written against the standardized Water Treatment Operator Need-to-Know Criteria published by Water Professionals International (formerly the Association of Boards of Certification) and standard references from the CSUS Office of Water Programs and AWWA. This site is not affiliated with or endorsed by WPI/ABC, AWWA, or the US EPA. Operator certification is issued by your state's certifying authority, which sets plant classification tiers, operator grades, eligibility, and the passing standard — confirm those with your state before testing. Contaminant limits and monitoring requirements are set federally and are revised over time, so no answer here should be relied on as a current regulatory value; consult the regulations in force for your system. This bank covers the drinking-water treatment exam only — wastewater treatment, wastewater collection, and water distribution are separate certifications. About the Need-to-Know Criteria →