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CES-WE practice questions

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Question 1PLACEHOLDER - official content area 1 (unverified; exam code not matched to a published blueprint)

A water sample has a hydrogen ion concentration of 1.0 × 10⁻⁵ mol/L. What is the pH of the sample?

  1. 5.0 Correct answer.
  2. 9.0
  3. 4.0
  4. 7.0

Explanation

pH is defined as the negative base-10 logarithm of the hydrogen ion activity, so pH = −log(1.0 × 10⁻⁵) = 5.0. The value 9.0 would be the pOH of the same sample, and pH plus pOH equals 14 at 25 °C.

Question 2PLACEHOLDER - official content area 1 (unverified; exam code not matched to a published blueprint)

Biochemical oxygen demand measured over five days (BOD₅) quantifies which of the following?

  1. The dissolved oxygen remaining after five days of storage
  2. Oxygen consumed by microbes over five days at 20 °C Correct answer.
  3. The mass of solids settled during five hours of quiescent settling
  4. The total oxygen demand of a sample measured at 20 °C

Explanation

BOD₅ is the difference between initial and final dissolved oxygen in a sample incubated in the dark at 20 °C for five days, and it reflects biodegradable organic matter. It is not a measure of remaining oxygen, of total (ultimate) demand, or of settleable solids.

Question 3PLACEHOLDER - official content area 1 (unverified; exam code not matched to a published blueprint)

Which statement best captures the stated objective of the Clean Water Act?

  1. Establish a national primary drinking water standard for every contaminant detected in public supplies
  2. Restore and maintain the chemical, physical, and biological integrity of the nation's waters Correct answer.
  3. Require states to classify every water body as either a drinking water source or a wildlife habitat
  4. Eliminate all point-source discharges of pollutants by 1985 and fund construction of publicly owned treatment works

Explanation

The Clean Water Act's declared objective is to restore and maintain the chemical, physical, and biological integrity of the nation's waters, pursued through tools such as water quality standards and NPDES permits. Drinking water standards come from the Safe Drinking Water Act, and the Act does not mandate a binary classification of water bodies.

Question 4PLACEHOLDER - official content area 1 (unverified; exam code not matched to a published blueprint)

In a municipal wastewater treatment plant, what does primary treatment mainly accomplish?

  1. Conversion of ammonia nitrogen to nitrate by nitrifying bacteria
  2. Removal of settleable solids and a portion of the suspended solids Correct answer.
  3. Removal of dissolved metals by ion exchange in pressure vessels
  4. Oxidation of dissolved organic matter by microorganisms in an aerated basin

Explanation

Primary treatment is physical, relying on sedimentation to remove settleable and floating material, typically about 50 to 65 percent of suspended solids. Biological oxidation, nitrification, and ion exchange are separate processes that occur in secondary or advanced treatment.

Question 5PLACEHOLDER - official content area 1 (unverified; exam code not matched to a published blueprint)

Which process returns the largest share of precipitation falling on land back to the atmosphere?

  1. Direct recharge to deep aquifers
  2. Surface runoff to streams
  3. Evapotranspiration Correct answer.
  4. Infiltration to shallow groundwater

Explanation

On a global basis, evapotranspiration accounts for the majority of precipitation that falls on land, returning water to the atmosphere through evaporation and plant transpiration. Runoff, infiltration, and deep recharge together make up a much smaller fraction of the land-phase water balance.

Question 6PLACEHOLDER - official content area 1 (unverified; exam code not matched to a published blueprint)

Turbidity in a water sample is a measurement of which property?

  1. The number of colony-forming units per 100 mL
  2. Light scattered by suspended and colloidal particles Correct answer.
  3. The mass of total suspended solids per liter of sample
  4. The concentration of dissolved colored organic matter

Explanation

Turbidity is an optical property expressing how suspended and colloidal particles scatter or absorb light, reported in nephelometric turbidity units. It correlates with suspended solids but is not a gravimetric or microbiological measurement.

Question 7PLACEHOLDER - official content area 1 (unverified; exam code not matched to a published blueprint)

In an aerobic biological treatment process, nitrification performs which conversion?

  1. Nitrate to ammonia under strongly anaerobic conditions
  2. Ammonia to nitrite and then to nitrate Correct answer.
  3. Nitrate to nitrogen gas under anoxic conditions
  4. Organic nitrogen to ammonia through ammonification

Explanation

Nitrification is a two-step aerobic process in which Nitrosomonas-like organisms oxidize ammonia to nitrite and Nitrobacter-like organisms oxidize nitrite to nitrate. It consumes oxygen and alkalinity and requires a longer solids retention time than carbonaceous oxidation alone.

Question 8PLACEHOLDER - official content area 1 (unverified; exam code not matched to a published blueprint)

Which set of conditions is required for biological denitrification to proceed?

  1. Aerobic conditions maintained with low organic loading
  2. An anoxic environment and an available carbon source Correct answer.
  3. Alkaline pH and a measurable free chlorine residual
  4. High dissolved oxygen and a well-established nitrifying population

Explanation

Denitrification is carried out by facultative heterotrophs that use nitrate as an electron acceptor when oxygen is absent, so an anoxic zone plus biodegradable carbon is needed. Oxygen present above roughly 0.5 mg/L suppresses the process, and nitrate must be available as the electron acceptor.

Question 9PLACEHOLDER - official content area 1 (unverified; exam code not matched to a published blueprint)

Why are coliform bacteria used as indicator organisms in drinking water monitoring?

  1. They are the only organisms that can be counted by membrane filtration
  2. They are easy to detect and indicate fecal contamination Correct answer.
  3. They survive disinfection longer than enteric viruses and protozoa
  4. They cause the majority of waterborne disease outbreaks in treated supplies

Explanation

Coliforms are abundant in feces, survive similarly to many pathogens, and are relatively simple and inexpensive to detect, so their presence signals possible fecal contamination. They are not usually the cause of outbreaks themselves, and membrane filtration can be used for many other organisms.

Question 10PLACEHOLDER - official content area 1 (unverified; exam code not matched to a published blueprint)

Why is a free chlorine residual maintained throughout a distribution system?

  1. To prevent corrosion of cast iron and ductile iron distribution mains
  2. To protect against microbial regrowth and contamination Correct answer.
  3. To control taste and odor complaints reported by customers
  4. To oxidize dissolved iron and manganese before it reaches the customer's tap

Explanation

A persistent disinfectant residual provides a barrier against microbial regrowth in mains, storage tanks, and service lines, and guards against minor post-treatment contamination. Corrosion control and aesthetic treatment are handled by separate chemical programs, not by maintaining a disinfectant residual.

Question 11PLACEHOLDER - official content area 1 (unverified; exam code not matched to a published blueprint)

For a river at equilibrium with the atmosphere, how does the dissolved oxygen saturation concentration respond as water temperature increases?

  1. It remains constant
  2. It rises sharply at first and then stabilizes
  3. It decreases Correct answer.
  4. It increases

Explanation

Gas solubility falls as temperature rises, so warmer water holds less dissolved oxygen at saturation; this is why summer conditions intensify low-DO problems. Pressure has the opposite trend, with solubility increasing as atmospheric pressure rises.

Question 12PLACEHOLDER - official content area 1 (unverified; exam code not matched to a published blueprint)

Cultural eutrophication of lakes is most commonly driven by which input?

  1. High chloride loading from winter road de-icing
  2. Elevated calcium and magnesium hardness
  3. Excess nitrogen and phosphorus inputs Correct answer.
  4. High dissolved oxygen produced by algal blooms

Explanation

Eutrophication is driven by nutrient enrichment, chiefly phosphorus in most freshwater lakes and nitrogen where phosphorus is abundant, which fuels algal growth and subsequent oxygen depletion. Hardness, chloride, and dissolved oxygen are not the causal inputs.

Question 13PLACEHOLDER - official content area 1 (unverified; exam code not matched to a published blueprint)

Water hardness in a municipal supply is primarily attributable to which constituents?

  1. Dissolved sodium and potassium salts
  2. Dissolved calcium and magnesium Correct answer.
  3. Free carbon dioxide and carbonic acid
  4. Suspended clay and silt particles

Explanation

Hardness is conventionally expressed as the sum of divalent cations, dominated by calcium and magnesium, often reported as mg/L as calcium carbonate. Sodium and potassium are monovalent and do not contribute, and suspended solids are removed by filtration.

Question 14PLACEHOLDER - official content area 1 (unverified; exam code not matched to a published blueprint)

An activated sludge system is operated with a longer solids retention time while keeping organic loading unchanged. What is the expected effect?

  1. Filamentous bulking caused by starving the floc-forming organisms
  2. A higher food-to-microorganism ratio with more waste sludge production
  3. A lower mixed liquor suspended solids concentration in the aeration basin
  4. A lower food-to-microorganism ratio with less waste sludge produced Correct answer.

Explanation

A longer solids retention time retains more biomass in the system, which lowers the food-to-microorganism ratio and reduces the mass of excess sludge that must be wasted. It also tends to favor nitrification and a more stable, older sludge.

Question 15PLACEHOLDER - official content area 1 (unverified; exam code not matched to a published blueprint)

Total alkalinity in a natural water sample is primarily caused by which species?

  1. Dissolved silica and phosphate
  2. Bicarbonate, carbonate, and hydroxide Correct answer.
  3. Calcium, magnesium, and iron
  4. Chloride, sulfate, and nitrate

Explanation

Alkalinity is the acid-neutralizing capacity of water, and in most natural waters it is dominated by bicarbonate, with carbonate and hydroxide contributing at higher pH. Calcium and magnesium contribute to hardness and are associated with alkalinity but are not the acid-consuming species.

Question 16PLACEHOLDER - official content area 1 (unverified; exam code not matched to a published blueprint)

A construction project will disturb about three acres of soil. Which authorization is typically required for stormwater discharges from the site?

  1. A Clean Air Act operating permit covering fugitive dust from the site
  2. NPDES stormwater permit coverage and a pollution prevention plan Correct answer.
  3. A RCRA hazardous waste manifest for every truckload of soil leaving the site
  4. Coverage under an underground injection control permit issued by EPA

Explanation

Construction activities disturbing one acre or more require coverage under an NPDES general construction stormwater permit, including a stormwater pollution prevention plan and best management practices. The other permits address different media and are triggered by different conditions.

Question 17PLACEHOLDER - official content area 1 (unverified; exam code not matched to a published blueprint)

Under the Safe Drinking Water Act, a maximum contaminant level (MCL) is best described as which of the following?

  1. A non-enforceable goal for contaminants that have known health effects
  2. An enforceable limit on a contaminant concentration in delivered drinking water Correct answer.
  3. A treatment technique that a public water system must install at the entry point
  4. The concentration at which a contaminant becomes detectable by an approved laboratory method

Explanation

An MCL is the highest concentration of a contaminant allowed in water delivered to users of a public water system, and it is enforceable. Maximum contaminant level goals are the separate non-enforceable health goals, and treatment technique requirements apply where MCLs are not feasible.

Question 18PLACEHOLDER - official content area 1 (unverified; exam code not matched to a published blueprint)

Under 40 CFR Part 503, biosolids classified as Class A must meet which requirement?

  1. Only the ceiling concentration limits for the ten regulated metals
  2. A minimum of 50 percent solids with no pathogen testing required
  3. Site-specific land application rates approved by the receiving state
  4. Fecal coliform and Salmonella limits plus vector attraction reduction Correct answer.

Explanation

Class A designation requires pathogen reduction to specified fecal coliform and Salmonella densities, achieved through processes such as time-temperature treatment, along with vector attraction reduction. Metals limits and site management apply as separate requirements to all biosolids, not as the basis for Class A status.

Question 19PLACEHOLDER - official content area 1 (unverified; exam code not matched to a published blueprint)

What is the purpose of a sharp-crested V-notch weir in an open channel?

  1. To aerate the flow as it passes over the crest
  2. To maintain a constant downstream water surface elevation
  3. To remove grit and other dense solids from the flow
  4. To determine flow rate from the measured upstream head Correct answer.

Explanation

For a V-notch weir, discharge is related to the head above the notch by a published rating equation, so measuring head yields flow rate. The weir does not regulate downstream stage, add oxygen, or perform solids removal.

Question 20PLACEHOLDER - official content area 1 (unverified; exam code not matched to a published blueprint)

Under what condition is a flow-weighted composite sample clearly preferable to a single grab sample?

  1. When constituent concentration and flow both vary through the day Correct answer.
  2. When the parameter is a dissolved gas that must be analyzed immediately
  3. When only one aliquot can be collected because of access limits
  4. When the discharge is known to be constant in both flow and quality

Explanation

Flow-weighted compositing proportionally weights each aliquot by discharge, producing a sample representative of the total mass load when flow and concentration fluctuate. For truly constant conditions, a grab sample may suffice, and for unstable parameters such as dissolved gases grab samples are required.

Question 21PLACEHOLDER - official content area 1 (unverified; exam code not matched to a published blueprint)

The method detection limit (MDL) for an analytical procedure is best described as which of the following?

  1. The upper concentration the method can measure without dilution
  2. The concentration giving a signal distinguishable from a blank at 99 percent confidence Correct answer.
  3. The average concentration measured in seven replicate blank samples
  4. The lowest concentration that can be reported without any statistical qualification

Explanation

The MDL is derived from replicate low-level or blank analyses and represents the concentration at which the analyte can be distinguished from the blank at a stated confidence level, commonly 99 percent. The reporting limit is typically set higher, and the upper range is defined by the calibration curve rather than the MDL.

Question 22PLACEHOLDER - official content area 1 (unverified; exam code not matched to a published blueprint)

Lime is added to metal-bearing industrial wastewater, raising the pH to about 10. Heavy metals are removed mainly by which mechanism?

  1. Precipitation of insoluble metal hydroxides Correct answer.
  2. Ion exchange onto the lime particles themselves
  3. Volatilization of metal complexes at high pH
  4. Reduction of dissolved metals to their elemental forms

Explanation

Raising pH drives the formation of sparingly soluble metal hydroxide solids, which are then separated by sedimentation or filtration. Lime also provides alkalinity and can aid coagulation, but the removal mechanism is hydroxide precipitation.

Question 23PLACEHOLDER - official content area 1 (unverified; exam code not matched to a published blueprint)

Alum is dosed into secondary effluent to remove phosphorus. What is the principal removal mechanism?

  1. Oxidation of phosphate to sulfate by dissolved oxygen
  2. Precipitation of aluminum phosphate and adsorption onto aluminum floc Correct answer.
  3. Biological uptake by phosphorus-accumulating organisms
  4. Stripping of phosphorus as phosphine gas under mixing

Explanation

Aluminum salts hydrolyze to form floc that both precipitates aluminum phosphate and adsorbs phosphate from solution, which is then removed with the sludge. Biological uptake belongs to enhanced biological phosphorus removal processes, and phosphate cannot be oxidized to sulfate.

Question 24PLACEHOLDER - official content area 1 (unverified; exam code not matched to a published blueprint)

A 48-hour LC50 value reported for an effluent toxicity test represents which of the following?

  1. The concentration at which all test organisms died within 48 hours
  2. The lowest concentration that caused any mortality among the test organisms
  3. The average concentration measured in the effluent over 48 hours
  4. The concentration lethal to half of the test organisms within 48 hours Correct answer.

Explanation

LC50 is the statistically estimated concentration causing mortality in 50 percent of the exposed organisms over the stated exposure period. It is a median lethal concentration, not a threshold for any mortality or a total-kill value.

Question 25PLACEHOLDER - official content area 1 (unverified; exam code not matched to a published blueprint)

According to Darcy's law, the specific discharge through a saturated sand column is directly proportional to which quantities?

  1. The hydraulic gradient and the hydraulic conductivity Correct answer.
  2. The capillary rise and the surface tension of the water
  3. The grain size and the length of the flow path
  4. The porosity and the total volume of the column

Explanation

Darcy's law states that specific discharge equals the product of hydraulic conductivity and hydraulic gradient, with a negative sign indicating flow in the direction of decreasing head. Porosity and path length influence velocity and travel time but are not the direct proportionality in the flux equation.

Question 26PLACEHOLDER - official content area 1 (unverified; exam code not matched to a published blueprint)

The 5-day biochemical oxygen demand (BOD5) test measures which of the following?

  1. The total organic carbon content of the sample
  2. The chlorine demand exerted by reducing agents
  3. Oxygen consumed by microbes degrading organic matter Correct answer.
  4. The maximum oxygen the water can hold at saturation

Explanation

BOD5 measures the dissolved oxygen consumed by microorganisms as they oxidize biodegradable organic matter during a 5-day incubation at 20°C in the dark. It reflects biodegradable organic load, not total carbon, saturation capacity, or chlorine demand.

Question 27PLACEHOLDER - official content area 1 (unverified; exam code not matched to a published blueprint)

Ultraviolet disinfection of treated wastewater inactivates microorganisms primarily by which mechanism?

  1. Raising the water temperature above the lethal limit
  2. Stripping dissolved oxygen from the water
  3. Oxidizing cell membranes with hydroxyl radicals
  4. Damaging nucleic acids so cells cannot replicate Correct answer.

Explanation

UV light near 254 nm is absorbed by microbial nucleic acids, producing lesions that block replication. It does not rely on chemical oxidation, heat, or oxygen stripping.

Question 28PLACEHOLDER - official content area 1 (unverified; exam code not matched to a published blueprint)

A jar test performed during drinking water treatment is used mainly to determine which of the following?

  1. The pump curve for the finished water
  2. The optimum coagulant dose and pH Correct answer.
  3. The required chlorine residual
  4. The filter media size gradation

Explanation

Jar tests simulate coagulation and flocculation on a bench scale so the operator can compare coagulant doses and pH values. The combination giving the best settled clarity at acceptable chemical cost is selected.

Question 29PLACEHOLDER - official content area 1 (unverified; exam code not matched to a published blueprint)

Reverse osmosis removes dissolved salts from water by which mechanism?

  1. Pressure driving water across an ion-rejecting membrane Correct answer.
  2. Volatilization of dissolved gases in a packed tower
  3. Adsorption of dissolved salts onto granular activated carbon
  4. Ion exchange onto a bed of regenerated resin beads

Explanation

Reverse osmosis applies pressure greater than the osmotic pressure to force water through a semipermeable membrane. Dissolved ions are rejected and leave in the concentrated brine stream.

Question 30PLACEHOLDER - official content area 1 (unverified; exam code not matched to a published blueprint)

Specific conductance of a water sample is most useful as an indicator of which property?

  1. The concentration of dissolved ions Correct answer.
  2. The concentration of dissolved organic matter
  3. The free chlorine residual
  4. The turbidity caused by suspended clay

Explanation

Specific conductance measures the ability of water to carry an electrical current, which depends mainly on the concentration and mobility of dissolved ions. It is not a direct measure of organics, turbidity, or chlorine.

Question 31PLACEHOLDER - official content area 1 (unverified; exam code not matched to a published blueprint)

Biogas produced by anaerobic digestion of wastewater sludge consists mainly of which two gases?

  1. Hydrogen sulfide and ammonia
  2. Carbon monoxide and hydrogen
  3. Methane and carbon dioxide Correct answer.
  4. Nitrogen and oxygen

Explanation

Anaerobic digestion produces biogas that is typically about 60 to 65 percent methane and 35 to 40 percent carbon dioxide, with trace gases. Methane is the energy-rich component.

Question 32PLACEHOLDER - official content area 1 (unverified; exam code not matched to a published blueprint)

A Parshall flume in an open channel measures flow by relating discharge to which quantity?

  1. The pressure difference across an orifice
  2. The channel slope over the flume length
  3. The downstream water velocity
  4. The upstream depth of water Correct answer.

Explanation

A Parshall flume creates a critical-flow condition in a converging throat, and discharge is computed from the upstream depth using a standard rating equation. Downstream conditions are not used for the flow calculation.

Question 33PLACEHOLDER - official content area 1 (unverified; exam code not matched to a published blueprint)

A chain-of-custody form accompanying a water sample documents which of the following?

  1. The reagent lot numbers used in the analysis
  2. The record of sample possession and handling Correct answer.
  3. The final analytical result reported by the laboratory
  4. The laboratory's accreditation certificate number

Explanation

A chain-of-custody form records who collected the sample, when it was collected, and every transfer of possession before analysis. This documentation supports the legal defensibility of the data.

Question 34PLACEHOLDER - official content area 1 (unverified; exam code not matched to a published blueprint)

Chemical oxygen demand (COD) of a wastewater sample is usually greater than its BOD5 because COD does which of the following?

  1. Measures only the biodegradable organic fraction of the sample
  2. Includes only the nitrogenous oxygen demand of the sample
  3. Includes both biodegradable and refractory oxidizable matter Correct answer.
  4. Is measured over a much longer incubation period than BOD5

Explanation

COD uses a strong chemical oxidant under acidic, heated conditions, so it oxidizes most organic matter plus some inorganic reducing agents. BOD5 measures only what microorganisms can degrade in five days, so COD is normally higher.

Question 35PLACEHOLDER - official content area 1 (unverified; exam code not matched to a published blueprint)

An aeration tank with a volume of 2,000 m3 receives a flow of 8,000 m3/d. What is the hydraulic retention time?

  1. 6 hours Correct answer.
  2. 12 hours
  3. 24 hours
  4. 4 hours

Explanation

Hydraulic retention time equals tank volume divided by flow: 2,000 m3 divided by 8,000 m3/d equals 0.25 day. Multiplying by 24 hours per day gives 6 hours.

Question 36PLACEHOLDER - official content area 1 (unverified; exam code not matched to a published blueprint)

A sludge volume index (SVI) of 250 mL/g in an activated sludge system most likely indicates which condition?

  1. Excellent settling and compaction
  2. Excessive accumulation of inorganic grit
  3. Poor settling from filamentous bulking Correct answer.
  4. A very low mixed liquor suspended solids concentration

Explanation

SVI is the settled sludge volume in mL/L divided by the mixed liquor suspended solids in g/L after 30 minutes. Values near 100 mL/g indicate good settling, while values above about 150 mL/g suggest filamentous bulking and poor compaction.

Question 37PLACEHOLDER - official content area 1 (unverified; exam code not matched to a published blueprint)

As chlorine is added to water containing ammonia, the free chlorine residual remains near zero until which point?

  1. The chlorine demand of the water falls to zero
  2. The breakpoint, where ammonia has been oxidized Correct answer.
  3. The water reaches a pH of exactly 7.0
  4. The combined chlorine residual reaches its maximum

Explanation

Chlorine reacts rapidly with ammonia to form chloramines, which register as combined chlorine and keep free chlorine low. Once the ammonia is destroyed at the breakpoint, further chlorine additions produce a free chlorine residual.

Question 38PLACEHOLDER - official content area 1 (unverified; exam code not matched to a published blueprint)

A total maximum daily load (TMDL) established under the Clean Water Act specifies which of the following?

  1. The maximum volume of dredged material that may be dumped
  2. The maximum discharge allowed from one industrial outfall
  3. The pollutant load a waterbody can receive and still meet standards Correct answer.
  4. The maximum contaminant concentration allowed at a drinking water tap

Explanation

A TMDL is the maximum pollutant load that a waterbody can assimilate and still meet its applicable water quality standards. It is allocated among point sources, nonpoint sources, and a margin of safety.

Question 39PLACEHOLDER - official content area 1 (unverified; exam code not matched to a published blueprint)

Discharge of dredged or fill material into waters of the United States requires a permit under which Clean Water Act section?

  1. Section 402
  2. Section 401
  3. Section 303
  4. Section 404 Correct answer.

Explanation

Section 404 of the Clean Water Act regulates the discharge of dredged or fill material into waters of the United States, including many wetlands. Section 402 establishes the NPDES permit program for pollutant discharges.

Question 40PLACEHOLDER - official content area 1 (unverified; exam code not matched to a published blueprint)

The federal Lead and Copper Rule requires water systems to implement corrosion control primarily because of which concern?

  1. These metals are the principal causes of water hardness
  2. These metals promote bacterial regrowth in pipes
  3. These metals interfere with chlorine disinfection
  4. These metals can leach from plumbing into the water Correct answer.

Explanation

Lead and copper can dissolve from service lines, solder, and brass fixtures when water is corrosive. Corrosion control treatment, such as pH adjustment and inhibitor addition, keeps these metals from leaching into drinking water.

Question 41PLACEHOLDER - official content area 1 (unverified; exam code not matched to a published blueprint)

Fluoride is added to public drinking water at a controlled concentration mainly to do which of the following?

  1. Reduce the incidence of dental caries Correct answer.
  2. Prevent corrosion of distribution pipes
  3. Improve the taste of the finished water
  4. Control growth of coliform bacteria

Explanation

Fluoride at about 0.7 mg/L strengthens tooth enamel and reduces the incidence of dental caries. It is not added for corrosion control, taste improvement, or disinfection.

Question 42PLACEHOLDER - official content area 1 (unverified; exam code not matched to a published blueprint)

A combined sewer overflow (CSO) occurs when which situation develops?

  1. A sanitary sewer receives infiltration from shallow groundwater
  2. A treatment plant receives more sludge than it can digest
  3. Stormwater and sewage together exceed sewer capacity Correct answer.
  4. An industrial discharger exceeds its permitted flow

Explanation

Combined sewers carry both sanitary sewage and stormwater. During heavy rain, the combined flow can exceed the capacity of the interceptor or treatment plant, causing a mixture to discharge to surface water.

Question 43PLACEHOLDER - official content area 1 (unverified; exam code not matched to a published blueprint)

A pump lifts 0.05 m3/s of water against a total head of 20 m. Using a water density of 1000 kg/m3 and g equal to 9.81 m/s2, what power is required at 70 percent efficiency?

  1. 20 kW
  2. 10 kW
  3. 14 kW Correct answer.
  4. 28 kW

Explanation

Hydraulic power equals density times gravity times flow times head. For these values the hydraulic power is about 9.81 kW, and dividing by 0.70 efficiency gives about 14 kW.

Question 44PLACEHOLDER - official content area 1 (unverified; exam code not matched to a published blueprint)

The toxic fraction of total ammonia in water increases as which parameter increases?

  1. Dissolved oxygen
  2. Chloride concentration
  3. Alkalinity
  4. pH Correct answer.

Explanation

The ammonia equilibrium shifts from ammonium toward un-ionized ammonia as pH rises. Un-ionized ammonia crosses fish gill membranes more readily and is the more toxic form.

Question 45PLACEHOLDER - official content area 1 (unverified; exam code not matched to a published blueprint)

Two monitoring wells are 100 m apart, and the water level in one is 0.5 m higher than in the other. What is the hydraulic gradient between them?

  1. 0.5
  2. 0.05
  3. 5.0
  4. 0.005 Correct answer.

Explanation

The hydraulic gradient is the head difference divided by the distance between measurement points: 0.5 m divided by 100 m equals 0.005. It is dimensionless when both terms are expressed in the same units.

Question 46PLACEHOLDER - official content area 1 (unverified; exam code not matched to a published blueprint)

In water at pH 8.5 and 25°C, free chlorine is present predominantly as which species?

  1. Chloride ion (Cl−)
  2. Hypochlorite ion (OCl−) Correct answer.
  3. Hypochlorous acid (HOCl)
  4. Dissolved chlorine gas (Cl2)

Explanation

Hypochlorous acid has a pKa near 7.5 at 25°C. At pH 8.5 the equilibrium lies well toward the hypochlorite ion, so OCl− is the predominant free chlorine species.

Question 47PLACEHOLDER - official content area 1 (unverified; exam code not matched to a published blueprint)

A clearwell provides 30 minutes of contact time at a free chlorine residual of 2.0 mg/L. What is the CT value?

  1. 60 mg·min/L Correct answer.
  2. 0.067 mg·min/L
  3. 32 mg·min/L
  4. 15 mg·min/L

Explanation

CT is the product of disinfectant residual concentration and contact time: 2.0 mg/L multiplied by 30 minutes equals 60 mg·min/L. It is compared with required CT values to verify disinfection.

Question 48PLACEHOLDER - official content area 1 (unverified; exam code not matched to a published blueprint)

In the Hazen-Williams equation for full pipe flow, head loss varies with flow rate approximately in proportion to which exponent?

  1. Q raised to 0.5
  2. Q raised to 2.0
  3. Q raised to 1.0
  4. Q raised to 1.85 Correct answer.

Explanation

The Hazen-Williams equation expresses head loss as proportional to Q raised to about 1.852, along with a roughness coefficient and pipe diameter. The exponent is approximately 1.85, not 1 or 2.

Question 49PLACEHOLDER - official content area 1 (unverified; exam code not matched to a published blueprint)

A pollutant decays by first-order kinetics with a rate constant of 0.20 per day. How long is needed for 90 percent removal?

  1. 4.5 days
  2. 11.5 days Correct answer.
  3. 2.3 days
  4. 5.0 days

Explanation

For first-order decay, the ratio of remaining concentration to initial concentration equals e raised to the negative kt. Setting the ratio to 0.10 gives t equal to ln(10) divided by 0.20, which is about 11.5 days.

Question 50PLACEHOLDER - official content area 1 (unverified; exam code not matched to a published blueprint)

A positive Langelier Saturation Index (LSI) for a water sample indicates that the water tends to do which of the following?

  1. Dissolve calcium carbonate and become corrosive
  2. Hold more dissolved oxygen at saturation
  3. Become more acidic as it warms
  4. Precipitate calcium carbonate scale Correct answer.

Explanation

A positive LSI means the water is supersaturated with respect to calcium carbonate and tends to deposit scale. A negative index indicates undersaturation and a tendency to dissolve calcium carbonate, which can be corrosive.