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SC Water/Wastewater Operator practice questions

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Question 1Water Sources, Hydrology, and Raw Water Quality

In the hydrologic cycle, which reservoir holds the largest share of Earth's total water?

  1. The oceans Correct answer.
  2. The atmosphere
  3. Glaciers and polar ice
  4. Groundwater

Explanation

The oceans contain roughly 96 to 97 percent of all water on Earth, so they dominate the global water budget. Ice caps hold most of the fresh water but only about two percent of the total. Groundwater is the largest liquid freshwater store, yet it is far smaller than the oceans, and the atmosphere holds a negligible share.

Question 2Water Sources, Hydrology, and Raw Water Quality

In water supply practice, a watershed is best described as which of the following?

  1. The zone where treated water is discharged
  2. The land area drained by a treatment plant's sewers
  3. All the land area that drains to a common water body Correct answer.
  4. The pipe network that delivers water to customers

Explanation

A watershed, or drainage basin, is defined by topography: every acre of land that sheds water to a common point such as a stream gauge, reservoir, or intake. Ridges and divides separate adjacent watersheds from one another.

Question 3Water Sources, Hydrology, and Raw Water Quality

Turbidity in raw water is normally measured and reported in which units?

  1. Standard pH units
  2. Nephelometric turbidity units Correct answer.
  3. Colony-forming units per mL
  4. Milligrams per liter

Explanation

Turbidity is an optical property measured with a nephelometer and reported in nephelometric turbidity units, or NTU. Milligrams per liter describes mass concentration, pH describes acidity, and colony-forming units describe viable bacteria.

Question 4Water Sources, Hydrology, and Raw Water Quality

Coliform bacteria are monitored in raw and finished water primarily because they serve as which of the following?

  1. Bacteria that corrode distribution piping
  2. Indicators of possible fecal contamination Correct answer.
  3. Organisms that cause taste and odor complaints
  4. Pathogens that must be identified to species

Explanation

Coliforms are indicator organisms; their presence suggests fecal contamination and therefore possible pathogens, although they are not usually pathogens themselves. Testing for indicators is faster, cheaper, and more reliable than trying to culture every disease-causing organism.

Question 5Water Sources, Hydrology, and Raw Water Quality

Hardness in a raw water supply is caused mainly by which dissolved constituents?

  1. Calcium and magnesium Correct answer.
  2. Sodium and potassium salts
  3. Iron and manganese oxides
  4. Chloride and sulfate ions

Explanation

Hardness is defined as the sum of dissolved calcium and magnesium, generally picked up as water contacts limestone, dolomite, and gypsum-bearing formations. Sodium, chloride, sulfate, iron, and manganese do not count toward hardness, although they affect other water quality parameters.

Question 6Water Sources, Hydrology, and Raw Water Quality

The water table in an unconfined aquifer is best defined as which of the following?

  1. The line between two river basins
  2. The top of the saturated zone Correct answer.
  3. The level in a treatment clearwell
  4. The depth at which water must be pumped

Explanation

The water table is the upper surface of the saturated zone in an unconfined aquifer, the level at which pressure equals atmospheric pressure. It rises and falls with recharge and drought and is the level to which water stands in a shallow observation well.

Question 7Water Sources, Hydrology, and Raw Water Quality

Which statement correctly distinguishes porosity from permeability in a water-bearing formation?

  1. Porosity measures flow rate; permeability measures storage
  2. Porosity applies only to unconfined aquifers
  3. Both terms describe the same void volume
  4. Porosity is void space; permeability is flow through it Correct answer.

Explanation

Porosity is the fraction of a formation's bulk volume that consists of openings, while permeability, or hydraulic conductivity, describes how readily water moves through the connected openings. The two do not always track together: clay can be highly porous but nearly impermeable.

Question 8Water Sources, Hydrology, and Raw Water Quality

An aquifer that is bounded above and below by low-permeability layers and holds water under pressure is called which type of aquifer?

  1. An unconfined aquifer
  2. A perched aquifer
  3. A water-table aquifer
  4. A confined aquifer Correct answer.

Explanation

A confined, or artesian, aquifer is overlain by a confining layer that traps water under pressure, so the water level in a well may rise above the top of the aquifer. Unconfined aquifers have a water table and are recharged directly from above, and perched aquifers sit on a small local confining layer.

Question 9Water Sources, Hydrology, and Raw Water Quality

Water infiltrating from the land surface moves downward through which zone before it reaches the saturated aquifer material?

  1. The confining bed under the aquifer
  2. The piezometric surface of the well
  3. The saturated zone below the water table
  4. The unsaturated zone above the water table Correct answer.

Explanation

Infiltrating water first passes through the unsaturated, or vadose, zone, where pores contain both air and water. After crossing the capillary fringe it enters the saturated zone and becomes recharge to the aquifer.

Question 10Water Sources, Hydrology, and Raw Water Quality

A surface water intake shows a sharp rise in turbidity and a drop in alkalinity a day after a heavy storm. What is the most likely explanation?

  1. Runoff carrying soil and organic matter into the stream Correct answer.
  2. Nitrifying bacteria growing in the reservoir
  3. A broken pipe in the distribution system
  4. Calcium carbonate precipitating in the stream

Explanation

Storms deliver sheet erosion, streambank scour, and organic debris to surface waters, which raises turbidity, color, and microbial load. The accompanying dilution by low-mineral rain water commonly reduces alkalinity and hardness at the same time.

Question 11Water Sources, Hydrology, and Raw Water Quality

Which source most commonly raises nitrate concentrations in shallow groundwater in rural areas?

  1. Aeration during treatment
  2. Chlorination at the treatment plant
  3. Weathering of granite bedrock
  4. Fertilizer application and septic systems Correct answer.

Explanation

Nitrate is highly soluble and mobile, so agricultural fertilizer, animal manure, and septic tank effluent are the usual sources in shallow rural wells. Because it moves with recharge rather than being filtered out, nitrate is a persistent and widespread contaminant.

Question 12Water Sources, Hydrology, and Raw Water Quality

Dissolved iron and manganese are objectionable in drinking water mainly because they do which of the following?

  1. Improve disinfection efficiency
  2. Make the water taste sweet
  3. Stain fixtures and cause color and taste complaints Correct answer.
  4. Cause cancer at any concentration

Explanation

Iron and manganese are secondary, aesthetic contaminants: they leave brown and black stains, cause metallic or bitter taste, and form deposits in mains. They are usually controlled by oxidation and filtration rather than by disinfection alone.

Question 13Water Sources, Hydrology, and Raw Water Quality

Blooms of cyanobacteria in a raw water reservoir are a concern to operators primarily because the organisms do which of the following?

  1. Produce taste and odor compounds and cyanotoxins Correct answer.
  2. Lower the pH below 4 units
  3. Remove all nitrate from the water
  4. Reduce turbidity to near zero

Explanation

Cyanobacteria release geosmin and MIB, which cause earthy and musty tastes and odors, and some species produce cyanotoxins harmful to people. Blooms also increase coagulant demand, raise oxidant demand, and shorten filter runs.

Question 14Water Sources, Hydrology, and Raw Water Quality

Base flow in a stream is best described as which of the following?

  1. The peak flow produced by a storm
  2. Spill over a dam crest
  3. Flow released from a wastewater outfall
  4. Groundwater inflow between storms Correct answer.

Explanation

Base flow is the sustained portion of streamflow fed by groundwater discharge, which keeps streams running during dry weather. Storm runoff supplies the quick peaks that ride on top of base flow.

Question 15Water Sources, Hydrology, and Raw Water Quality

Rainfall in a remote area far from industrial emissions typically has a pH of about which value?

  1. 9.5
  2. 8.2
  3. 5.6 Correct answer.
  4. 4.0

Explanation

Atmospheric carbon dioxide dissolves in precipitation to form carbonic acid, giving clean rainfall a pH near 5.6. Values around 4.0 indicate acid deposition, while values above 8 suggest alkaline dust or contact with basic minerals.

Question 16Water Sources, Hydrology, and Raw Water Quality

Which approach is the most effective long-term strategy for limiting turbidity and pathogen loads reaching a surface water intake?

  1. Adding more chlorine at the clearwell
  2. Protecting and managing the contributing watershed Correct answer.
  3. Increasing coagulant dose at the plant
  4. Flushing the distribution system more often

Explanation

Keeping sediment, nutrients, and pathogens out of the source water is the most reliable long-term barrier; watershed protection reduces raw water variability and treatment cost. Treatment adjustments and chlorine are necessary but manage the problem after contaminants have already entered the supply.

Question 17Water Sources, Hydrology, and Raw Water Quality

Over fifteen years, a coastal well field has shown steadily rising chloride while pumping rates increased. What is the most probable cause?

  1. Corrosion of well casing releasing iron chloride
  2. Landward migration of saltwater as freshwater head drops Correct answer.
  3. Chloride released by natural rainfall recharge
  4. Chlorine feed at a nearby treatment plant

Explanation

Heavy pumping lowers the freshwater head in the aquifer, allowing denser saltwater to migrate landward or upward toward the well screens, which shows up as a gradual chloride rise. Reducing pumping, relocating wells, or installing a barrier are the usual corrective measures.

Question 18Water Sources, Hydrology, and Raw Water Quality

A facility is designed for the 100-year flood. This design criterion means the design flow has which probability?

  1. About a 1% chance each year Correct answer.
  2. One flood exactly every 100 years
  3. Certain flooding once per century
  4. A guarantee of safety for 100 years

Explanation

The 100-year flood has a one percent probability of being equaled or exceeded in any given year; it is a statistical statement, not a schedule. Over a 30-year period, the chance of at least one such event is roughly 26 percent, which is why the term is often misunderstood.

Question 19Water Sources, Hydrology, and Raw Water Quality

In a dimictic lake, fall turnover mixes the entire water column mainly because of which process?

  1. Warmer inflow raising the surface temperature
  2. Algal photosynthesis oxygenating the hypolimnion
  3. Ice cover trapping gases beneath the surface
  4. Surface cooling removing the density difference between layers Correct answer.

Explanation

During summer, warm less-dense water floats on cold dense water and stratification resists mixing. As the surface cools in autumn, its density approaches that of the deep water, the density gradient weakens, and wind can then mix the full depth, carrying oxygen down and nutrients up.

Question 20Water Sources, Hydrology, and Raw Water Quality

Two production wells screened in the same confined aquifer sit close together. When both pump heavily, the specific capacity of each drops. What is the best explanation?

  1. Screens plug equally whenever pumping starts
  2. Overlapping cones of depression increase drawdown Correct answer.
  3. The aquifer's transmissivity falls when two wells run
  4. Water becomes more viscous at higher pumping rates

Explanation

Where the drawdown fields of the two wells overlap, the effects add, so each well experiences greater total drawdown for the same pumping rate and its specific capacity declines. The aquifer properties do not change; the loss is a hydraulic interference effect, which is avoided by spacing wells adequately.

Question 21Water Treatment Processes

What is the primary purpose of adding alum during the coagulation step of a surface water treatment plant?

  1. To remove dissolved gases such as hydrogen sulfide
  2. To raise the pH of the water to 8.5 or higher
  3. To destabilize suspended particles so they can stick together Correct answer.
  4. To kill bacteria and viruses in the raw water

Explanation

Alum and other coagulants add positive charge that neutralizes the negative surface charge on colloids, reducing repulsion so particles can collide and agglomerate. This step makes the later flocculation, settling, and filtration processes effective.

Question 22Water Treatment Processes

Gentle, slow mixing after coagulant addition is used mainly to:

  1. Disinfect the water before sedimentation
  2. Strip dissolved carbon dioxide from the water
  3. Encourage small particles to collide and form larger floc Correct answer.
  4. Increase the flow velocity through the basin

Explanation

Flocculation is slow, gentle mixing that promotes collisions between destabilized particles so they grow into larger, settleable floc. Excessive mixing shear would break the floc apart instead of building it.

Question 23Water Treatment Processes

Which process removes the largest share of settled floc before water reaches the filters?

  1. Sedimentation Correct answer.
  2. Aeration
  3. Fluoridation
  4. Recarbonation

Explanation

Sedimentation allows gravity to settle the floc formed in coagulation and flocculation before the water is filtered. Removing these solids first lowers the load on the filters and lengthens filter runs.

Question 24Water Treatment Processes

A free chlorine residual is maintained in the distribution system mainly to:

  1. Protect against microbial contamination throughout the system Correct answer.
  2. Reduce the concentration of fluoride
  3. Raise the pH of the finished water
  4. Prevent corrosion of cast iron and steel pipe

Explanation

A disinfectant residual continues to inactivate microorganisms and guards against contamination that may enter after treatment, such as during main breaks or repairs. It is the main reason a measurable residual is required in the distribution system.

Question 25Water Treatment Processes

Turbidity in finished water is normally reported in which unit?

  1. Nephelometric turbidity units (NTU) Correct answer.
  2. Microsiemens per centimeter
  3. Milligrams per liter as calcium carbonate
  4. Standard pH units

Explanation

Turbidity is an optical measurement of the light scattered by suspended particles, reported in nephelometric turbidity units. The reading rises as more suspended material scatters light.

Question 26Water Treatment Processes

Filter backwashing is performed to:

  1. Increase the filter loading rate
  2. Add coagulant to the filter media
  3. Remove accumulated solids and restore headloss Correct answer.
  4. Disinfect the filter underdrain

Explanation

Backwashing reverses flow through the filter bed, expanding the media and washing out trapped particles. This restores the headloss and turbidity performance the filter needs to operate properly.

Question 27Water Treatment Processes

Aeration of an iron-bearing groundwater is used primarily to:

  1. Convert dissolved iron to a filterable solid Correct answer.
  2. Soften the water by removing calcium
  3. Disinfect the water by adding dissolved oxygen gas
  4. Increase the chloride concentration

Explanation

Dissolved ferrous iron must be oxidized to ferric iron, which forms an insoluble solid that filters can capture. Manganese behaves similarly during oxidation.

Question 28Water Treatment Processes

Which chemical is commonly fed to raise pH and increase alkalinity during treatment?

  1. Chlorine gas
  2. Sodium fluoride
  3. Hydrated lime Correct answer.
  4. Alum

Explanation

Hydrated lime is an alkaline chemical that raises pH and adds alkalinity. It is used for corrosion control and is also a key chemical in lime softening.

Question 29Water Treatment Processes

A jar test is run at a treatment plant to determine:

  1. The chlorine demand of the distribution system
  2. The particle size distribution of the filter media
  3. The maximum flow rate the filters can accept
  4. Best coagulant dose for settled water clarity Correct answer.

Explanation

A jar test simulates coagulation, flocculation, and settling on a bench scale while the coagulant dose is varied. The operator selects the dose that gives the clearest settled water under the plant's mixing and settling conditions.

Question 30Water Treatment Processes

In disinfection practice, CT refers to:

  1. The total chlorine applied to the basin
  2. The chlorine threshold for turbidity
  3. Disinfectant concentration multiplied by contact time Correct answer.
  4. Chlorine test

Explanation

CT is the product of disinfectant concentration (mg/L) and credited contact time (minutes). It is compared against tables that account for pH, temperature, and disinfectant type to determine log inactivation credit.

Question 31Water Treatment Processes

At the breakpoint on a chlorine dose-residual curve:

  1. Chlorine demand is zero
  2. Ammonia concentration increases with dose
  3. Combined chlorine residual reaches its maximum
  4. Free chlorine residual rises rapidly with further dose Correct answer.

Explanation

The breakpoint is the dose at which ammonia has been essentially destroyed, so additional chlorine begins to appear as free residual and the curve climbs steeply. Before that point, most applied chlorine is consumed by demand and chloramine formation.

Question 32Water Treatment Processes

Why is anthracite placed above sand in a dual-media filter?

  1. Coarser, lighter media lets solids penetrate deeper Correct answer.
  2. Anthracite chemically removes dissolved organics
  3. Anthracite is denser and settles below sand during backwash
  4. Anthracite provides alkalinity to the finished water

Explanation

Anthracite is lighter than sand, so it stays on top after backwash, and it is coarser, allowing solids to penetrate deeper into the bed. Deeper penetration distributes headloss through more of the media and lengthens filter runs.

Question 33Water Treatment Processes

A sedimentation basin receives 2.0 MGD and has a surface area of 1,000 square feet. What is the surface overflow rate?

  1. 2,000 gpd/ft² Correct answer.
  2. 2.0 gpd/ft²
  3. 500 gpd/ft²
  4. 20,000 gpd/ft²

Explanation

Surface overflow rate equals flow divided by surface area: 2,000,000 gpd divided by 1,000 ft² equals 2,000 gpd/ft². It represents the settling velocity a particle must exceed to be removed.

Question 34Water Treatment Processes

A clearwell holds 500,000 gallons and receives a flow of 2.5 MGD. What is the detention time in hours?

  1. 24 hours
  2. 12 hours
  3. 2.0 hours
  4. 4.8 hours Correct answer.

Explanation

Detention time equals volume divided by flow: 500,000 gallons divided by 2,500,000 gallons per day equals 0.2 day, which converts to 4.8 hours.

Question 35Water Treatment Processes

If a dose of 3.0 mg/L of chlorine produces a free residual of 0.8 mg/L, what is the chlorine demand?

  1. 3.0 mg/L
  2. 0.8 mg/L
  3. 3.8 mg/L
  4. 2.2 mg/L Correct answer.

Explanation

Chlorine demand is the difference between the applied dose and the residual remaining: 3.0 minus 0.8 equals 2.2 mg/L. Demand reflects the chlorine consumed by reducing agents, organics, and other substances in the water.

Question 36Water Treatment Processes

Which benefit is most closely associated with using chloramines rather than free chlorine for secondary disinfection?

  1. Lower trihalomethane formation and a more persistent residual Correct answer.
  2. Stronger oxidizing power against viruses
  3. Complete removal of taste and odor compounds
  4. No need to monitor residual in the distribution system

Explanation

Chloramines are weaker oxidants than free chlorine, so they form far fewer trihalomethanes and last longer in the distribution system. The tradeoff is weaker inactivation of some pathogens and the need to monitor total chlorine carefully.

Question 37Water Treatment Processes

Granular activated carbon is used in treatment primarily to:

  1. Raise the Langelier saturation index
  2. Supply oxygen for iron oxidation
  3. Adsorb taste, odor, and organic compounds Correct answer.
  4. Neutralize the negative charge on colloids

Explanation

Activated carbon has a large internal pore surface that adsorbs dissolved organic molecules, including many taste- and odor-causing compounds. It also helps remove some disinfection byproduct precursors.

Question 38Water Treatment Processes

After excess-lime softening, carbon dioxide is often added in a process called recarbonation to:

  1. Increase the calcium hardness of the water
  2. Oxidize dissolved manganese
  3. Disinfect the softened water
  4. Lower the pH and stabilize the water Correct answer.

Explanation

Excess-lime softening leaves the water at high pH and supersaturated with calcium carbonate. Recarbonation with carbon dioxide lowers the pH and converts excess lime to bicarbonate, stabilizing the water so it will not deposit scale in the distribution system.

Question 39Water Treatment Processes

Under the surface water treatment rule, filtered water turbidity for conventional filtration must:

  1. Never exceed 5 NTU
  2. Be maintained above 1 NTU
  3. 0.3 NTU or less in 95 percent of samples Correct answer.
  4. Be measured only once per week

Explanation

The rule requires combined filter effluent turbidity of 0.3 NTU or less in at least 95 percent of monthly measurements and never above 1 NTU. These limits ensure that filtration is consistently removing pathogens such as Giardia and Cryptosporidium.

Question 40Water Treatment Processes

Which statement about UV disinfection is accurate?

  1. It inactivates Cryptosporidium but leaves no residual Correct answer.
  2. It is ineffective against Cryptosporidium
  3. It leaves a measurable residual that protects the distribution system
  4. It works best in water with high turbidity

Explanation

UV light damages microbial nucleic acids and is highly effective against Cryptosporidium, which is resistant to chlorine. Because it provides no residual protection, a chemical disinfectant is still needed in the distribution system.

Question 41Water Treatment Processes

A chlorine contact basin has a theoretical detention time of 60 minutes and a baffling factor of 0.5. If the free chlorine concentration at the outlet is 2.0 mg/L, what is the credited CT value in mg·min/L?

  1. 120
  2. 30
  3. 15
  4. 60 Correct answer.

Explanation

Credited contact time is the theoretical detention time multiplied by the baffling factor: 60 minutes times 0.5 equals 30 minutes. CT is then 2.0 mg/L times 30 minutes, or 60 mg·min/L.

Question 42Water Treatment Processes

Which condition is needed for excess-lime softening to remove magnesium hardness?

  1. pH near 7.0
  2. A free chlorine residual of 2.0 mg/L
  3. Dissolved oxygen below 2 mg/L
  4. pH of about 10.5 to 11.0 Correct answer.

Explanation

Magnesium hardness is removed only when the pH is raised high enough, about 10.5 to 11.0, to precipitate magnesium hydroxide. Lime is added in excess to reach that pH, and the water is usually recarbonated afterward.

Question 43Water Treatment Processes

A filter run should be terminated when:

  1. The coagulant feed is interrupted
  2. Effluent turbidity breaks through or terminal headloss is reached Correct answer.
  3. The filter has run for exactly 24 hours
  4. The backwash water is clear

Explanation

A filter is taken out of service when it can no longer produce acceptable water, either because particles break through and raise effluent turbidity or because headloss reaches the terminal value. The media are then backwashed before the filter returns to service.

Question 44Water Treatment Processes

Enhanced coagulation is practiced mainly to:

  1. Raise the finished water pH
  2. Reduce chlorine demand in the clearwell
  3. Increase filter run length
  4. Remove natural organic matter that forms disinfection byproducts Correct answer.

Explanation

Enhanced coagulation increases coagulant dose or adjusts coagulation pH to improve removal of natural organic matter, the main precursor to trihalomethanes and other disinfection byproducts. It is a required byproduct control strategy for many surface water systems.

Question 45Water Treatment Processes

At the same dose and temperature, raising the pH from 6.5 to 8.0 will most likely cause the free chlorine CT credit to:

  1. Stay the same, because pH does not affect chlorine speciation
  2. Increase, because ammonia is converted to nitrogen gas
  3. Increase, because hypochlorous acid dominates at higher pH
  4. Decrease, because hypochlorous acid converts to hypochlorite ion Correct answer.

Explanation

Hypochlorous acid is the dominant and far more effective free chlorine species near pH 6.5, while at pH 8.0 much of it converts to the far weaker hypochlorite ion. For the same residual, the higher pH therefore earns less inactivation credit, which is why CT tables include a pH correction.

Question 46Water Treatment Processes

Which treatment process is primarily responsible for destabilizing colloidal particles so they can agglomerate?

  1. Flocculation
  2. Sedimentation
  3. Filtration
  4. Coagulation Correct answer.

Explanation

Coagulation is the rapid-mix chemical step that neutralizes the surface charge on colloidal particles, allowing them to come together. Flocculation follows coagulation and provides gentle mixing so particles can collide and grow into larger floc. Sedimentation and filtration remove particles after destabilization and floc formation have occurred.

Question 47Water Treatment Processes

Which chemical is most widely used as a primary coagulant in surface water treatment?

  1. Sodium chloride
  2. Aluminum sulfate Correct answer.
  3. Calcium hydroxide
  4. Sodium hypochlorite

Explanation

Aluminum sulfate, commonly called alum, reacts with natural alkalinity to form aluminum hydroxide floc that enmeshes and settles particles. It is the most common primary coagulant used in conventional surface water plants. The other chemicals serve different purposes, such as disinfection, pH adjustment, or regeneration.

Question 48Water Treatment Processes

What is the main purpose of flocculation following coagulant addition?

  1. To sterilize filter media
  2. To promote collisions and grow larger floc particles Correct answer.
  3. To remove dissolved gases
  4. To disinfect the water

Explanation

Flocculation provides gentle, sustained mixing that creates velocity gradients, causing destabilized particles to collide and aggregate into larger, settleable floc. It is a physical process and does not disinfect the water or strip dissolved gases. Aeration and disinfection are separate treatment steps.

Question 49Water Treatment Processes

Which unit process removes settleable solids from water primarily by gravity?

  1. Disinfection
  2. Aeration
  3. Sedimentation Correct answer.
  4. Adsorption

Explanation

Sedimentation allows particles denser than water to settle to the basin bottom under relatively quiescent conditions. Clarifiers and settling basins are designed around this principle. Aeration, adsorption, and disinfection address dissolved gases, dissolved contaminants, and pathogens rather than settleable solids.

Question 50Water Treatment Processes

Why do inclined tube settlers improve particle removal in a clarifier?

  1. They increase the effective settling area within the basin Correct answer.
  2. They increase the flow velocity through the basin
  3. They add coagulant chemicals to the water
  4. They cool the water to increase particle density

Explanation

Inclined tubes create many shallow settling paths, so a particle only has to fall a short distance before contacting a surface and being removed. The modules also provide a large effective settling area within the basin footprint. They do not feed chemicals, increase flow velocity, or cool the water.