Unit 6, 7, 8 Test

Question 1

Backwashing

Answer 1

Air and clean water forced up, carries away accumulated impurities. Key part of rapid filters.

Question 2

Chlorination

Answer 2

Most important in preventing waterborne disease spread, low concentration of Cl2 dissolved in water. Side effect: THMs

Question 3

Clarification

Answer 3

Combination of coagulation-flocculation, sedimentation, and filtration.

Question 4

Coagulation-Flocculation

Answer 4

Coagulants rapidly mixed in water, neutralizes charges of clay particles, forms flocs. Flocculation is gentle mixing of water to increase flocs.

Question 5

Collector Sewers (submains)

Answer 5

Tie lateral sewers to interceptors/trunklines.

Question 6

Combined Sewers

Answer 6

Carries both clean and dirty water, risk of CSO (combined sewage overflow). In 19th century, no treatment, still in older towns.

Question 7

Detention Time

Answer 7

Theoretical amount of time water stays in a settling tank. TD=V/Q (in hours)

Question 8

Disinfection

Answer 8

Making water completely free of disease causing organisms, final stage. Destroys (oxidizes) or inactivates (scrambles DNA of) pathogens.

Question 9

Drop-manhole & Manhole

Answer 9

Manhole: underground, access to sewer pipe for cleaning, repair, sampling, flow measuring. Drop-manhole: when lateral sewer joins deeper submain sewer.

Question 10

Effluent

Answer 10

Water flowing out of tank. In settling tank, skimmed from surface over weirs on tank.

Question 11

Filtration

Answer 11

Removes suspended particles by passing water through layer of porous granular material (sand). After coag.-floc., slow-sand or rapid.

Question 12

Freeboard

Answer 12

Height of tank above actual side water depth (SWD), about .45m or 1.5ft above SWD. Prevents water splashing over sides.

Question 13

Industrial Sewage

Answer 13

Water used for manufacturing. Carries chemical compounds.

Question 14

Infiltration

Answer 14

Excess rain/snowmelt infiltrates into leaky/broken sewers. Causes SSO (sanitary sewer overflow).

Question 15

Inflow

Answer 15

Water flowing through roof drains connected to sewers. Also causes SSO.

Question 16

Influent

Answer 16

Water flowing into the tank, directed against a baffle. Baffle distributes water uniformly across tank width.

Question 17

Interceptor (trunk line)

Answer 17

Carries sewage from submain to treatment plant. Usually in lowest point of service area.

Question 18

Inverted siphon

Answer 18

Sewer built under stream/road. Under pressure to carry flow.

Question 19

Lateral Sewers

Answer 19

Collects wastewater directly from homes/buildings (from service connections). Smallest diameter in system, carries by gravity to submains.

Question 20

Maximum Contaminant Levels

Answer 20

Enforceable limits of standards for a substance.

Question 21

Minimum self cleaning velocity

Answer 21

Velocity that will keep sewage solids suspended in flow. Select size and shape of sewer so full-flow velocity is not less than 0.6m/s (2ft/s).

Question 22

Overdesign

Answer 22

Overestimating amount of sewage, is more expensive. Can lead to land development too soon, causing strain on other resources.

Question 23

Pipe bedding

Answer 23

How pipe is placed in a trench and how it’s supported.
Class A: Best, pipe cradled in concrete and backfill added.
Class B: Compacted granular backfill and backfill on top.
Class C: Compacted backfill halfway up
Class D: Loose backfill.

Question 24

Plan & Profile

Answer 24

Plan: top view of sewer line. Profile: side view of sewer line, magnified 10:1 to see elevation change. Plan drawn above profile and carefully aligned.

Question 25

Potable

Answer 25

Safe for human consumption and skin contact.

Question 26

Primary Standards

Answer 26

To protect public health. Maximum permissible limits of potentially harmful substances, enforceable by law.

Question 27

Safe Drinking Water Act

Answer 27

Est. 1974, Estimated minimum drinking water standards. For actually consumed water, public water supply.

Question 28

Sanitary Sewage

Answer 28

(Domestic sewage) Human wastes and wash water from homes, public buildings, or commercial/industrial establishments.

Question 29

Secondary Standards

Answer 29

Designed for aesthetics, not enforceable by law.

Question 30

Sedimentation

Answer 30

Dissolved or suspended water impurities, easiest to remove through gravity. Under quiescent (low flow) conditions, particles denser than water will settle to bottom.

Question 31

Separate Sewers

Answer 31

Storm water is carried in separate storm sewers to storage or disposal. Sanitary sewage/industrial wastewater is carried in sanitary sewers to treatment plant.

Question 32

Short-circuiting

Answer 32

When most water flows through settling tank in less time than estimated (detention time). Effectiveness of sedimentation is reduced.

Question 33

Side Water Depth

Answer 33

Actual depth of water in settling tank.

Question 34

Storm Sewage

Answer 34

Surface runoff from rain showers or other precipitation.

Question 35

Surcharging

Answer 35

When pipes are under-designed, waste water backs up into manholes. Can back up into basements, hydraulic grade line is above pipe crown.

Question 36

Turbidity

Answer 36

Presence of suspended particles in water. Measure amount of light scattered and reflected (NTUs). Cloudiness interferes with disinfection by shielding contaminants.

Question 37

Identify the five categories of primary contaminants. Give three examples of each.

Answer 37

Organic - Benzene, carbontetrachloride, THMs Inorganic chemicals - Lead, arsenic, fluoride Microorganisms - Bacteria, viruses, protozoa Turbidity - Clay, silt, plankton Radionuclides - Radium, alpha emitters, uranium

Question 38

Describe the process of sedimentation.

Answer 38

Gravity allows denser particles to settle at bottom of settling tank under quiescent conditions. Discrete vs hindered settling.

Question 39

Describe the process of coagulation/flocculation.

Answer 39

Coagulant is rapidly mixed with water to neutralize colloid charges, allowing them to floc together. Flocculation is gently stirring to increase colloid collisions, growing flocs.

Question 40

Describe the process of filtration.

Answer 40

Remove suspended particles by passing water through a layer of porous granular material. Slow sand filters pass water through sand. Rapid filters are much faster, cleaned by backwashing.

Question 41

Explain the importance of chlorination.

Answer 41

Extremely effective in disinfecting water. Destroys/inactivates pathogens, preventing spread of communicable diseases. Organic compounds can interact with to form THMs - but it's better to have disinfected water than reduce THMs.

Question 42

Identify 4 categories of water demand

Answer 42

Domestic - drinking, cooking hygiene Municipal/public - fire protection, street cleaning Industrial/commercial - restaurants, laundries, manufacturing Loss from leaks

Question 43

Define per capita demand

Answer 43

Total annual water demand divided by 365 days, then divided by total population served.

Question 44

Identify why water demand may change seasonally daily and hourly

Answer 44

Seasonally: Hot and dry season will have more water demand, up to 200% Daily: Weekdays will typically have less water demand as people are at work/school, weekends will have more as people are home. Hourly: Water demand is higher in the mornings when people usually wake up and in the evening when dinner is being made and showers are taken.

Question 45

Identify minimum and maximum pressures and why they’re important

Answer 45

Minimum pressures (50 psi) allow home appliances to function properly. Maximum pressures (110 psi) are kept to prevent leaks or water main breaks.

Question 46

Explain why a gridiron arrangement is preferable as a pipe layout design

Answer 46

A gridiron layout allows the water to circulate in a loop so that water doesn't stay stagnant. It also allows water to get around to an area if a section is shut off.

Question 47

Explain important issues with pipe installation

Answer 47

Should be about1-2m (3-6ft) below ground. Under pressure not gravity, so it can flow with topographical ground. Should not be installed in same trench as a sewer, at lease 10ft (3m) horizontally and 18in. (.5m) above.

Question 48

Differentiate between equalizing storage and conservation reservoirs

Answer 48

Equalizing storage is the volume of water in a tank available to satisfy peak hourly demands in a community. Conservation reservoirs are larger and store water to be used in long dry weather periods.

Question 49

List the circumstances which require a sewer manhole.

Answer 49

Change in pipe diameter, change in slope, change in direction, uppermost end of laterals, at least every 400ft, pipe intersections.

Question 50

Explain the importance of properly estimating the amount of sewage expected from a sewer system.

Answer 50

If you underestimate, you may under-design the sewer which can result in surcharging. Surcharging is when pipes can't hold peak flows and sewage can back up into manholes/basements. Overestimating is more expensive and can result in overdesigning which can cause land development too soon, and put strain on other resources.

Question 51

Explain sanitary sewer overflows

Answer 51

(SSO) is when raw/untreated sewage is accidentally discharged, it can back up into manholes or basements. May happen with excess wet weather, old combined sewers, or from infiltration/inflow.

Question 52

Explain when sewage lift stations are required.

Answer 52

It's used for when sewage needs to be pumped from a lower to higher elevation to a treatment plant or another gravity sewer. Also used when flat topography would make the sewer line too deep.