Test 30 - Septic Tanks and Design

Question 1 ప్రశ్న 1

Which description most accurately states the treatment function of a conventional septic tank?

A It provides complete aerobic oxidation of dissolved pollutants before direct surface-water discharge. B It provides primary settling and flotation with anaerobic decomposition of retained solids, while its effluent requires suitable further treatment or disposal. C It is principally a soil infiltration unit whose watertightness is unnecessary. D It achieves the same solids removal as a membrane bioreactor without further effluent treatment.

Question 2 ప్రశ్న 2

For a two-compartment septic tank with equal water depth and cross-sectional width, what partition arrangement accords with the capacity proportion described in IS 2470 (Part 1)?

A The first compartment occupies about two-thirds of the effective liquid length and the second about one-third. B The compartments have equal effective lengths to maximize flow reversal. C The first compartment occupies one-third of the effective length and the second two-thirds. D The compartment lengths are fixed by the outlet pipe diameter rather than the relative liquid capacities.

Question 3 ప్రశ్న 3

Why are properly placed submerged inlet and outlet tees or baffles provided in a septic tank?

A To promote a high-velocity surface jet that entrains floating scum into the outlet. B To transfer bottom sludge directly into the soil absorption arrangement. C To reduce inlet disturbance and draw the outgoing liquid from below the scum layer but above accumulated bottom sludge. D To eliminate the need for a watertight tank shell by equalizing groundwater pressure.

Question 4 ప్రశ్న 4

Which nominal detention-time range is described for septic tanks designed on the stated average-flow basis in IS 2470 (Part 1)?

A 6–12 hours. B 12–18 hours. C 48–72 hours as a compulsory minimum for all installations. D 24–48 hours.

Question 5 ప్రశ్న 5

In calculating a septic tank's usable hydraulic detention volume, how should roof freeboard and reserved sludge-storage capacity be treated?

A Freeboard above the normal liquid level is excluded, and adequate detention volume must remain available despite sludge and scum accumulation. B Freeboard is counted as permanently water-filled detention volume, whereas sludge storage is ignored. C Both freeboard and future sludge deposits increase the volume available for liquid residence. D Sludge storage and detention volume are interchangeable without affecting effluent solids carryover.

Question 6 ప్రశ్న 6

A plot proposed for septic-tank effluent disposal has a seasonally high groundwater table and soil that infiltrates poorly. Which decision is most defensible?

A Install an ordinary soak pit regardless of groundwater conditions because septic effluent is pathogen-free. B Discharge directly to the nearest stormwater drain because low soil permeability improves effluent quality. C Assess a suitably engineered secondary treatment or alternative disposal arrangement rather than assuming a conventional soak pit is viable. D Increase septic-tank inlet velocity until the effluent can be forced into impermeable soil.

Question 7 ప్రశ్న 7

Which operating practice best protects a septic tank's treatment performance over its service life?

A Stop all desludging permanently because anaerobic digestion consumes every incoming solid. B Inspect sludge and scum accumulation and arrange safe desludging before excessive deposits interfere with settling and outlet performance. C Add large amounts of disinfectant periodically to ensure complete destruction of all anaerobic microorganisms. D Keep the outlet submerged in bottom sludge so that denser effluent leaves the tank.

Question 8 ప్రశ్న 8

What is the main design concern if stormwater runoff and groundwater infiltration are allowed to enter a septic tank?

A They necessarily improve anaerobic digestion by increasing the food-to-microorganism ratio. B They increase available sludge storage because the tank becomes more dilute. C They reduce actual flow without affecting the hydraulic residence time. D They can hydraulically overload the tank, shorten effective detention and impair the downstream absorption system.

Question 9 ప్రశ్న 9

Which set of geometrical recommendations is consistent with IS 2470 (Part 1) for a rectangular septic tank?

A Minimum liquid depth of 0.5 m and maximum length-to-width ratio of 1:1. B Minimum width of 0.5 m and a requirement for a circular plan in every case. C Minimum width of 0.75 m, at least 1.0 m depth below water level, and a length-to-width ratio generally between 2 and 4. D Minimum plan length of 10 m for all households, irrespective of user population.

Question 10 ప్రశ్న 10

Before a worker enters a septic tank for an unusual repair, what is the most appropriate safety requirement?

A Treat it as a hazardous confined space and use trained personnel, atmospheric testing, isolation, ventilation and approved entry/rescue procedures. B Permit immediate entry if the liquid level has been lowered because methane and hydrogen sulfide then disappear. C Rely on a lit flame to test whether the tank atmosphere contains sufficient oxygen. D Allow lone entry without respiratory evaluation because anaerobic bacteria remove all hazardous gases.

Question 11 ప్రశ్న 11

A small institution has 45 users, each contributing an explicitly assumed average of 100 L/day of wastewater to its septic tank. What is the average daily inflow?

A 0.45 m3/day. B 45.0 m3/day. C 5.4 m3/day. D 4.5 m3/day.

Question 12 ప్రశ్న 12

A septic tank retains 3.6 m3 of effective flow-through liquid volume after allowing for occupied sludge-storage space. If average wastewater inflow is 2.4 m3/day, what is the nominal hydraulic detention time?

A 24 hours. B 36 hours. C 48 hours. D 60 hours.

Question 13 ప్రశ్న 13

A septic tank is to provide a project-selected nominal hydraulic detention of 36 hours at an average flow of 3.2 m3/day. What effective flow-through volume is required, excluding future sludge storage?

A 3.2 m3. B 4.0 m3. C 4.8 m3. D 7.2 m3.

Question 14 ప్రశ్న 14

For an illustrative design, allow 0.06 m3 of accumulated sludge-and-scum storage per person per year. How much storage is needed for 40 users between scheduled desludging events separated by two years?

A 4.8 m3. B 2.4 m3. C 6.0 m3. D 8.0 m3.

Question 15 ప్రశ్న 15

Under an explicitly simplified additive design model, a septic tank needs 5.4 m3 of effective flow-through liquid volume plus 2.1 m3 reserved for accumulated sludge and scum. What minimum combined capacity below the normal water level must be provided?

A 5.4 m3. B 6.3 m3. C 9.6 m3. D 7.5 m3.

Question 16 ప్రశ్న 16

A proposed two-compartment septic tank has total liquid capacity of 9.0 m3. The first chamber is designed for twice the volume of the second. What are the respective chamber capacities?

A 4.5 m3 and 4.5 m3. B 6.0 m3 and 3.0 m3. C 3.0 m3 and 6.0 m3. D 7.0 m3 and 2.0 m3.

Question 17 ప్రశ్న 17

A rectangular septic tank requires 12 m3 of total liquid capacity at a uniform 1.5 m liquid depth. Its internal length is twice its width. Which internal length and width satisfy these requirements?

A 6.0 m and 1.33 m. B 3.0 m and 2.67 m. C 4.0 m and 2.0 m. D 5.0 m and 1.6 m.

Question 18 ప్రశ్న 18

What total liquid capacity is provided by a rectangular septic tank of internal length 3.0 m, width 1.5 m and normal liquid depth 1.4 m, ignoring any displacement by partitions?

A 6.30 m3. B 4.50 m3. C 7.20 m3. D 8.10 m3.

Question 19 ప్రశ్న 19

A septic tank has a designed normal liquid depth of 1.50 m and an explicitly specified freeboard of 0.30 m above water level. What minimum internal vertical depth from floor to underside of cover does this simplified geometry require?

A 1.20 m. B 1.50 m. C 2.10 m. D 1.80 m.

Question 20 ప్రశ్న 20

Two identical septic tanks operating in parallel are to share a calculated total required liquid capacity of 14 m3 equally. What capacity must each tank provide under this equal-duty arrangement?

A 14 m3. B 7 m3. C 3.5 m3. D 28 m3.

Question 21 ప్రశ్న 21

A septic tank has a total below-water liquid capacity of 6.0 m3, of which accumulated sludge and scum presently occupy 1.5 m3. At an average wastewater inflow of 4.0 m3/day, what is the nominal detention time based on the remaining flow-through volume?

A 27 hours. B 24 hours. C 36 hours. D 30 hours.

Question 22 ప్రశ్న 22

For a septic-tank sedimentation-area check at 25°C, IS 2470 (Part 1) states 0.92 m2 of plan area per 10 L/min of peak flow. At a design peak flow of 30 L/min, what plan area follows from this criterion alone?

A 0.92 m2. B 1.84 m2. C 2.76 m2. D 3.68 m2.

Question 23 ప్రశ్న 23

A proposed subsurface effluent-disposal area is designed with an explicitly site-approved hydraulic application rate of 50 L/(m2 day). What effective absorption area is required to handle 1,500 L/day of septic-tank effluent?

A 20 m2. B 25 m2. C 50 m2. D 30 m2.

Question 24 ప్రశ్న 24

A site-approved effluent dispersion system has two trenches, each 15 m long and 0.60 m wide. If the allowable hydraulic loading on trench-bottom area is explicitly specified as 70 L/(m2 day), what combined daily effluent flow can the trenches accept?

A 630 L/day. B 1,260 L/day. C 1,800 L/day. D 2,100 L/day.

Question 25 ప్రశ్న 25

A septic system serves 50 persons, each contributing an assumed 120 L/day. A simplified design specifies 36 hours of available hydraulic detention plus an additional sludge-and-scum storage allowance of 0.04 m3 per person per year for a two-year interval. Ignoring freeboard, what minimum combined capacity below normal water level is required?

A 13.0 m3. B 9.0 m3. C 11.0 m3. D 18.0 m3.

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