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Past Questions
An elevated steel tank sways excessively during wind. What is the likely reason?
A)
Inadequate bracing in the staging
B)
Heavy water inside
C)
Faulty valve
D)
Wrong roof slope
Step-by-step reasoning: 1. Analysis of the problem: 'Swaying' refers to lateral displacement of a structure. In the context of an elevated steel tank, this is a stability issue related to lateral loads (wind). 2. Structural Role of Bracing: In steel staging (the supporting framework), bracing is specifically designed to resist lateral forces (wind and seismic loads) by creating triangulated frames that prevent the structure from racking or swaying. 3. Evaluating Option (a): If the bracing is inadequate or missing, the structure lacks the necessary lateral stiffness, leading to excessive sway under wind pressure. This is the most likely structural cause. 4. Evaluating Option (b): Heavy water inside increases the vertical dead load. While this increases the gravitational stability (making it harder to overturn), it does not cause lateral swaying; in fact, increased mass can sometimes reduce the frequency of vibration, but the primary cause of 'excessive sway' is a lack of stiffness. 5. Evaluating Option (c): A faulty valve is a mechanical/plumbing issue and has no impact on the structural stiffness or lateral stability of the tank staging. 6. Evaluating Option (d): The roof slope affects drainage and wind pressure coefficients slightly, but it cannot cause the entire elevated staging to sway excessively; that is a function of the supporting framework's rigidity.
A septic tank is estimated using which parameter?
A)
Flow velocity
B)
No. of users and detention time
C)
Sump height
D)
Reinforcement ratio
A septic tank is a primary sewage treatment unit that works on the principle of anaerobic digestion and sedimentation. To design (estimate) the capacity of a septic tank, the most critical parameters are: 1. The number of users (which determines the total volume of sewage generated per day) and 2. The detention time (the average time the sewage remains in the tank to allow solids to settle and organic matter to decompose, typically ranging from 24 to 48 hours). The total volume is calculated as: Volume = (Sewage flow per person per day × Number of users) × Detention time.
Why other options are incorrect:
- a. Flow velocity: While important for pipes, the septic tank is designed for stagnation/low velocity to allow sedimentation; it is not the primary estimation parameter.
- c. Sump height: This is a dimensional result of the design process, not the primary parameter used to estimate the required capacity.
- d. Reinforcement ratio: This is a structural engineering parameter used for the construction of the tank walls, not for estimating the functional capacity of the treatment unit.
The ideal maximum super-elevation for plain terrain in highways is:
A)
1 in 20
B)
1 in 100
C)
1 in 40
D)
1 in 15
Super-elevation (banking) is provided on horizontal curves to counteract the centrifugal force acting on a vehicle, preventing it from skidding or overturning. According to the Indian Roads Congress (IRC) guidelines, the maximum limit for super-elevation (e) is specified based on the terrain to ensure safety and comfort for slow-moving vehicles (preventing them from sliding inward).
1. For Plain and Rolling Terrain: The maximum super-elevation is limited to 7% or 0.07. In fractional terms, 0.07 is approximately 7/100. However, in many standard textbooks and older IRC specifications often referenced in competitive exams, the limit for plain terrain is cited as 7% (which is close to 1 in 14.3). Among the given options, '1 in 15' (which is approximately 6.67%) is the closest standard value used to represent the maximum limit for plain terrain.
2. For Hilly Terrain: The maximum super-elevation is limited to 10% (1 in 10).
Evaluating the options:
- Option (a) 1 in 20 (5%): This is a common value but not the 'maximum' limit for plain terrain.
- Option (b) 1 in 100 (1%): This is too low for a maximum limit.
- Option (c) 1 in 40 (2.5%): This is too low for a maximum limit.
- Option (d) 1 in 15 (~6.67%): This aligns with the IRC maximum limit of 7% for plain terrain.
Contractor’s ledger is maintained to:
A)
Record wage slips with each contractor
B)
Track financial transactions with each contractor
C)
Store tenders with each contractor
D)
Record test results with each contractor
In the context of Estimation and Costing and Project Management in Civil Engineering, a 'Ledger' is a primary accounting record used to track financial transactions. A Contractor's Ledger specifically serves as a subsidiary ledger where all financial dealings with a particular contractor are recorded. This includes: 1. Payments made to the contractor (Running Account bills), 2. Deductions made (such as security deposits, income tax, or recovery for materials supplied by the department), and 3. The final balance due to or from the contractor.
Why other options are incorrect:
- Option (a): Wage slips are typically maintained in a 'Wage Register' or 'Muster Roll', not a ledger.
- Option (c): Tenders are legal documents stored in a 'Tender File' or 'Contract Agreement' folder, not a ledger.
- Option (d): Test results are recorded in a 'Quality Control Register' or 'Material Test Register'.
Steel structures are preferred over RCC when:
A)
High strength-to-weight ratio is required
B)
Low-rise construction is needed
C)
Bricks are not available
D)
Paint costs are low
Step-by-step reasoning:
1. **Strength-to-Weight Ratio**: Structural steel has a significantly higher strength-to-weight ratio compared to Reinforced Cement Concrete (RCC). This means that for the same load-bearing capacity, a steel member is much lighter than an RCC member. This is critical for long-span structures, high-rise buildings (to reduce the dead load on foundations), and prefabricated structures.
2. **Evaluating Option (b)**: Low-rise construction is typically more economical using RCC or masonry due to lower material costs and lack of need for specialized fabrication. Steel is preferred for high-rise or large-span structures.
3. **Evaluating Option (c)**: The availability of bricks affects masonry construction, not the choice between the two primary structural frames (Steel vs. RCC).
4. **Evaluating Option (d)**: Paint costs are a maintenance expense. While steel requires painting for corrosion protection, the decision to use steel over RCC is based on structural and functional requirements, not the cost of paint.
Conclusion: The primary engineering advantage of steel over RCC is its high strength-to-weight ratio, making option (a) the correct choice.
For public tenders, which publication is mandatory?
A)
e-Tender portal or national newspapers
B)
Private media and social media
C)
SMS notification
D)
Worksite banner
In public procurement and government contracting (Estimation and Costing), transparency and wide publicity are mandatory to ensure fair competition and prevent corruption. According to standard government procurement guidelines (such as the General Financial Rules - GFR), public tenders must be advertised in a manner that reaches a broad audience of qualified contractors.
1. **e-Tender Portals**: Modern governance mandates the use of Central Public Procurement Portals (CPPP) or state-specific e-procurement portals to ensure a digital audit trail and accessibility.
2. **National Newspapers**: For high-value works, publication in widely circulated newspapers is mandatory to ensure that the tender is 'public' and not restricted to a few known parties.
Why other options are incorrect:
- **Option b**: Private media and social media are supplementary tools but lack the legal standing and officiality required for mandatory public notifications.
- **Option c**: SMS notifications are used for alerts but cannot serve as the primary legal publication of a detailed tender document.
- **Option d**: Worksite banners are used for project information after the contract is awarded, not for the initial invitation of bids.
The unit of measurement for RCC in footings is:
A)
RMT
B)
Sq.m
C)
Cum
D)
Kg
In civil engineering estimation and costing, the unit of measurement is determined by the nature of the item.
1. **RCC (Reinforced Cement Concrete)**: Concrete is a three-dimensional material. For structural elements like footings, slabs, beams, and columns, the quantity is calculated by multiplying length × width × thickness (or depth). Therefore, the unit of measurement is volume, which is expressed in Cubic Meters (Cum) in the metric system.
2. **Analysis of other options**:
- **RMT (Running Meter)**: Used for linear items such as pipes, railings, or cornices.
- **Sq.m (Square Meter)**: Used for area-based items such as plastering, painting, or flooring.
- **Kg (Kilogram)**: Used for weighing materials, specifically the steel reinforcement bars used within the RCC, but not for the concrete itself.
Since the question asks for the unit of RCC in footings, the correct unit is Cubic Meters (Cum).
The radius of curvature is least in:
A)
Highways
B)
Railways
C)
City roads
D)
Rural roads
Railways have the least radius of curvature because trains can negotiate only relatively gentle curves due to their guided wheel-rail system and safety/comfort limits, so the minimum permissible curve radius is much smaller than for roads. Highways and city roads generally require larger radii for vehicle stability and speed, while rural roads usually have the least traffic constraints but still do not require as small a radius as railways in standard design context.
A contract is said to be completed when:
A)
All work is executed and recorded with final measurements
B)
Running bill is submitted
C)
Contractor leaves site
D)
Defect liability ends
In civil engineering contracting and estimation, a contract is considered 'completed' from a technical and administrative standpoint when the physical execution of the work is finished and the final measurements are recorded in the Measurement Book (MB). This process allows for the preparation of the Final Bill, which settles the accounts between the client and the contractor.
Why other options are incorrect:
- Option (b): A 'Running Bill' (or interim payment certificate) is submitted periodically during the progress of the work to maintain cash flow; it does not signify completion.
- Option (c): A contractor leaving the site does not legally or technically imply completion; the work must be verified and measured first.
- Option (d): The 'Defect Liability Period' (DLP) begins AFTER the work is completed and handed over. The contract for execution is finished, but the contractor remains liable for defects for a specific duration (usually 6-12 months). Completion of the DLP is the release of the security deposit, not the completion of the work contract itself.
The widening of pavement on curves is done to:
A)
Counteract centrifugal force and accommodate vehicle turning
B)
Avoid accidents and reduce psychological fear
C)
Increase Road length
D)
Reduce sight distance
Extra widening of pavements on horizontal curves is necessary due to two primary reasons: 1. Mechanical Widening: When a vehicle negotiates a curve, the rear wheels do not follow the same path as the front wheels (this is known as 'off-tracking'). To accommodate this wider path of the vehicle, additional width is required. 2. Psychological Widening: Drivers tend to maintain a greater lateral distance from the edge of the pavement and from other vehicles when navigating a curve due to the centrifugal force acting on the vehicle, which creates a sense of instability. Therefore, widening is provided to ensure the vehicle stays within the pavement boundaries and to counteract the effects of centrifugal force by providing more maneuvering space.
Analysis of other options:
- Option b: While widening may indirectly reduce fear, the primary engineering purpose is the physical accommodation of the vehicle's path.
- Option c: Widening increases the area of the pavement, not the longitudinal length of the road.
- Option d: Widening does not reduce sight distance; in fact, sight distance is managed through 'set-back' distances or clearing obstructions on the inside of the curve.
In government accounts, what does ‘head of account’ mean?
A)
Executive officer/ Drawing and Disbursing Officer
B)
Head of Administrative Department
C)
Accounting code for expenditure classification
D)
Head of Accounting Section
In government accounting and financial management, a 'Head of Account' is a unique alphanumeric code used to classify and track government receipts and expenditures. It ensures that funds are spent for the specific purpose for which they were allocated in the budget.
1. **Classification**: It allows the government to categorize spending by department (Major Head), sub-department (Sub-Major Head), specific program (Minor Head), and the nature of the expense (Detailed/Object Head).
2. **Audit and Control**: By using these codes, auditors can easily verify if the expenditure aligns with the sanctioned budget for a particular project or administrative unit.
Why other options are incorrect:
- Option (a) refers to a person (the DDO) who is authorized to draw funds, not the accounting classification itself.
- Option (b) refers to a person/position of authority within a department.
- Option (d) refers to a personnel role within the accounting office.
Which is a disadvantage of steel tanks over RCC tanks?
A)
Easy fabrication
B)
Prone to corrosion
C)
High ductility
D)
Light weight
To determine the disadvantage of steel tanks compared to Reinforced Cement Concrete (RCC) tanks, we evaluate the properties of both materials:
1. **Corrosion (Option b):** Steel is highly susceptible to oxidation and corrosion, especially when in contact with water or exposed to atmospheric moisture. This requires expensive protective coatings, linings, or cathodic protection to ensure durability. In contrast, RCC is naturally more resistant to corrosion (provided the concrete cover is adequate), making 'prone to corrosion' a significant disadvantage of steel tanks.
2. **Fabrication (Option a):** Steel tanks are generally easier and faster to fabricate and assemble (often using welding or bolting) compared to the time-consuming process of formwork, reinforcement tying, and curing required for RCC tanks. This is an advantage, not a disadvantage.
3. **Ductility (Option c):** Steel has high ductility, which allows it to undergo significant deformation before failure and better withstand seismic loads. This is generally considered a structural advantage.
4. **Weight (Option d):** Steel tanks have a much higher strength-to-weight ratio than RCC tanks, making them lighter for the same capacity. This reduces the load on the foundation and simplifies transportation. This is an advantage.
Therefore, the only negative attribute listed is the susceptibility to corrosion.
The sinking fund is created for:
A)
Construction cost
B)
Labor charges
C)
Running cost
D)
Future replacement of a structure
A sinking fund is a fund formed by periodically setting aside a specific amount of money over the useful life of a structure or asset. The primary objective is to ensure that at the end of the asset's service life, there is sufficient accumulated capital (including interest earned) to either replace the structure entirely or perform major renewals/overhauls.
Why other options are incorrect:
- a. Construction cost: This is the initial capital expenditure (CAPEX) required to build the structure, not a fund set aside for the future.
- b. Labor charges: These are operational or construction expenses paid as the work progresses.
- c. Running cost: Also known as Operation and Maintenance (O&M) costs, these are recurring expenses for the daily functioning of the structure, whereas a sinking fund is a long-term capital reserve.
Flexible pavements consist of the following components except:
A)
Subgrade
B)
Base course
C)
Wearing course
D)
RCC slab
Flexible pavements are designed to distribute loads through a layered system of materials that deform under load. The typical components of a flexible pavement from bottom to top are: 1. Subgrade (the natural soil), 2. Sub-base course, 3. Base course, and 4. Surface course (also known as the Wearing course).
- Option (a) Subgrade: This is the foundation layer of any pavement.
- Option (b) Base course: This layer provides structural support and distributes the load to the sub-base/subgrade.
- Option (c) Wearing course: This is the top layer that resists wear and tear and provides a smooth riding surface.
- Option (d) RCC slab: Reinforced Cement Concrete (RCC) slabs are the primary structural components of 'Rigid Pavements,' not flexible pavements. Rigid pavements rely on the slab's flexural strength to support loads, whereas flexible pavements rely on the layered distribution of stress.
Which element is included in geometric design of highways?
A)
Soil strength
B)
Drainage pipes
C)
Horizontal alignment
D)
Material grade
Geometric design of highways refers to the design of the visible dimensions of the roadway to ensure safety, efficiency, and comfort for road users. It focuses on the physical layout of the road. The primary elements of geometric design include: 1. Cross-section elements (lane width, camber, shoulders, kerbs), 2. Sight distance (Stopping Sight Distance, Overtaking Sight Distance), and 3. Alignment (Horizontal alignment consisting of straight paths and curves, and Vertical alignment consisting of gradients and vertical curves).
Analysis of options:
- Option (a) Soil strength: This is a part of Pavement Design (Geotechnical/Structural design), not geometric design.
- Option (b) Drainage pipes: This falls under Drainage Design/Hydraulic design.
- Option (c) Horizontal alignment: This is a core component of geometric design as it determines the path of the road in a plan view.
- Option (d) Material grade: This is a part of Material Engineering/Pavement Design (specifying the quality of bitumen or concrete).
The deflection in flexible pavement is measured using:
A)
Straightedge
B)
Benkelman beam
C)
Penetrometer
D)
Total station
Step-by-step reasoning:
1. **Understanding Deflection**: In flexible pavements, deflection refers to the temporary vertical deformation of the pavement surface under a wheel load. Measuring this deflection is critical for assessing the structural adequacy of the pavement and determining the need for overlays.
2. **Benkelman Beam (BB)**: The Benkelman Beam is a standard instrument used globally for measuring the rebound deflection of flexible pavements. It consists of a beam with a dial gauge that measures the difference in elevation between a reference point and the loaded point when a standard axle load is applied.
3. **Evaluating other options**:
- **Straightedge**: Used primarily to measure surface irregularities, rutting, or flatness (roughness) of the pavement, not structural deflection.
- **Penetrometer**: Used to measure the consistency or hardness of materials (like bitumen or soil), not the deflection of a completed pavement structure.
- **Total Station**: An electronic/optical instrument used in surveying for measuring angles and distances; it is not used for measuring the minute vertical deflections caused by wheel loads.
Therefore, the Benkelman beam is the correct instrument for measuring deflection in flexible pavements.
Which type of brickwork estimate differs for modular and traditional bricks?
A)
Item rate estimate
B)
Revised estimate
C)
Supplementary estimate
D)
Annual maintenance
In civil engineering estimation, the quantity of bricks required per cubic meter of brickwork depends entirely on the size of the brick used.
1. **Modular Bricks**: Standard size is 190 mm x 90 mm x 90 mm. With mortar, the nominal size becomes 200 mm x 100 mm x 100 mm. This results in exactly 500 bricks per cubic meter.
2. **Traditional (Non-Modular) Bricks**: These vary by region (e.g., 9" x 4.5" x 3"). Because the dimensions differ from modular bricks, the number of bricks required per cubic meter changes.
An **Item Rate Estimate** (also known as a Detailed Estimate) involves calculating the exact quantities of materials (like the number of bricks) and multiplying them by the unit rate. Therefore, the quantity takeoff for brickwork in an item rate estimate will differ significantly depending on whether modular or traditional bricks are specified.
Other options are incorrect because:
- **Revised Estimate**: This is a modification of an existing estimate due to changes in design or rates; it is a process, not a specific type of quantity calculation based on brick size.
- **Supplementary Estimate**: This is prepared for additional works not included in the original estimate.
- **Annual Maintenance**: This refers to recurring costs for upkeep and does not specifically dictate the fundamental calculation method for initial brickwork volume/quantity.
The unit of moment of inertia in steel design is:
A)
N/m
B)
kN
C)
kg/m²
D)
mm⁴ or cm⁴
The Moment of Inertia (I), also known as the second moment of area, is a geometric property of an area which reflects how its points are distributed with regard to an axis. Mathematically, it is defined as the integral of the square of the distance (r) from the axis to an infinitesimal element of area (dA): I = ∫ r² dA. Since the unit of area (dA) is length squared (L²) and the unit of distance squared (r²) is also length squared (L²), the resulting unit is length to the power of four (L⁴). In steel design and structural engineering, the most common units used for length are millimeters (mm) and centimeters (cm), making the units of moment of inertia mm⁴ or cm⁴.
Analysis of other options:
- Option (a) N/m is a unit of linear load or stiffness.
- Option (b) kN is a unit of force.
- Option (c) kg/m² is a unit of area density (mass per unit area).
The term ‘tender’ in government contracts refers to:
A)
Completion report submitted by a contractor
B)
Drawing set submitted by a contractor to perform the specified work
C)
Bid submitted by a contractor to perform the specified work
D)
Inspection record submitted by a contractor to perform the specified work
In the context of civil engineering estimation and costing, a 'Tender' is an invitation for bids for the execution of a project. When a contractor submits their proposal—which includes the quoted price (bid amount) and the terms under which they agree to perform the work—this submission is referred to as the tender.
Step-by-step analysis of options:
- Option (a) is incorrect because a completion report is submitted after the work is finished, not at the bidding stage.
- Option (b) is incorrect because drawings are typically provided by the client/department (as part of the tender documents) or submitted as 'shop drawings' during execution, not as the tender itself.
- Option (c) is correct as it accurately defines the tender as the formal bid/offer submitted by the contractor to undertake the work for a specific sum of money.
- Option (d) is incorrect because inspection records are quality control documents generated during the construction phase.
The value of CBR is mainly used to design:
A)
Rigid pavement
B)
Flexible pavement
C)
Bridges
D)
Shoulders
The California Bearing Ratio (CBR) is a penetration test used to evaluate the mechanical strength of road subgrades and base course materials.
1. **Why Flexible Pavement:** Flexible pavements (like asphalt roads) distribute loads through a layered system where the strength of the underlying soil (subgrade) is critical. The CBR value is the primary parameter used in the design of flexible pavements (e.g., using the IRC or US Army Corps of Engineers methods) to determine the required thickness of the pavement layers to prevent shear failure of the subgrade.
2. **Why not Rigid Pavement:** Rigid pavements (concrete roads) rely on the flexural strength of the concrete slab to distribute loads over a wide area. While the modulus of subgrade reaction (k-value) is used for rigid pavements, the CBR is not the primary design parameter.
3. **Why not Bridges or Shoulders:** Bridges are designed based on structural engineering principles (beams, piers, foundations) and geotechnical bearing capacity, not CBR. Shoulders are secondary components and their design is typically derived from the main pavement design rather than being the primary application of the CBR test.
Which structure needs cost estimation of both excavation and lining?
A)
Overhead tank
B)
Boundary wall
C)
Tube well
D)
Steel truss
In civil engineering estimation, different structures require different types of quantity take-offs.
1. **Tube Well**: A tube well involves drilling or digging a deep vertical hole into the ground (Excavation/Boring). To prevent the walls of the borehole from collapsing and to filter water, a casing pipe or a lining of concrete/steel is installed inside the hole. Therefore, both the volume of excavation (boring) and the cost of lining (casing) must be estimated.
2. **Overhead Tank**: While it requires excavation for the foundation, the main structure is an elevated tank. The term 'lining' is not a primary characteristic of the entire structure's estimation in the same way it is for a well.
3. **Boundary Wall**: This requires excavation for the foundation trenches and masonry work, but it does not involve 'lining' (which refers to a continuous internal layer/casing of a void).
4. **Steel Truss**: This is a superstructure element. While its supports (columns/pedestals) require excavation, the truss itself does not involve excavation or lining.
An estimate for a public building was underquoted by 15%. During execution, rates increased sharply. What action is most appropriate?
A)
Revise the estimate with current cost index and seek approval
B)
Issue a new tender
C)
Cancel the project
D)
Request contractor to continue at old rates
In public works and government contracting, when an estimate is found to be inadequate due to underquoting or sharp increases in material and labor rates during execution, the standard administrative procedure is to revise the estimate. This is typically done using a 'Cost Index' (a percentage increase applied to the basic schedule of rates to reflect current market conditions). Once the revised estimate reflects the actual current costs, it must be submitted to the competent authority for technical sanction and financial approval to ensure the project has sufficient funding to reach completion.
Why other options are incorrect:
- Option b (Issue a new tender): This is impractical if the project is already under execution, as it would lead to legal disputes with the current contractor and significant delays.
- Option c (Cancel the project): This is an extreme measure and not a standard engineering management response to a cost overrun in a public building.
- Option d (Request contractor to continue at old rates): This is unrealistic and often leads to the contractor abandoning the site or compromising the quality of work, as they cannot sustain losses due to sharp market rate increases.
Which document forms the basis for inviting tenders?
A)
Rate analysis sheet
B)
Bill of Quantities (BOQ)
C)
Measurement Book
D)
Valuation report
In civil engineering estimation and costing, the process of inviting tenders requires a standardized document that lists all the items of work and their respective quantities. This document is known as the Bill of Quantities (BOQ). Contractors use the BOQ to quote their rates for each item, ensuring that all bidders are pricing the same scope of work, which allows for a fair and transparent comparison of bids.
Why other options are incorrect:
- a. Rate analysis sheet: This is a detailed calculation used by the engineer to determine the unit rate of an item based on labor, materials, and overheads. It is used for internal estimation, not as the primary document for inviting tenders.
- c. Measurement Book (MB): The MB is the primary record where actual measurements of work executed on-site are recorded for the purpose of payment. It is used during and after construction, not before inviting tenders.
- d. Valuation report: A valuation report is used to determine the current market value or fair price of a property or asset, typically for insurance, sale, or mortgage purposes, and is unrelated to the tendering process for new construction.
A contractor is delaying work repeatedly but blames frequent rainfall. What is the correct course of action?
A)
Terminate the contract immediately and seek justification
B)
Verify rainfall records and consider time extension only if justified
C)
Ignore the delay and let the contractor complete the work at the earliest
D)
Change the contractor and re-tender the project
In contract management and civil engineering estimation/costing, delays are handled based on the 'Conditions of Contract'. Rainfall is generally considered a 'Force Majeure' or an 'Act of God' if it exceeds the normal average for that region and period.
1. **Verification**: The engineer-in-charge must first verify the claim by checking official meteorological records (rainfall data) to see if the rainfall was indeed abnormal or excessive enough to hinder work.
2. **Justification**: If the records prove the rainfall was excessive, the contractor is entitled to an 'Extension of Time' (EOT) without penalty (liquidated damages).
3. **Why other options are incorrect**:
- Option (a) is too harsh and legally risky; termination requires a breach of contract, and a valid weather claim would make termination wrongful.
- Option (c) is negligent; ignoring delays without documentation leads to project mismanagement and lack of accountability.
- Option (d) is an extreme measure that causes significant project delays and legal disputes, to be used only after all other remedies fail.
Septic tanks are designed primarily for:
A)
Drinking water storage
B)
Primary treatment of sewage
C)
Stormwater collection
D)
Rainwater harvesting
A septic tank is a underground wastewater collection tank where sewage is stored. It functions as a primary treatment unit through two main processes: sedimentation and anaerobic digestion. 1. Sedimentation: Heavier organic and inorganic solids settle to the bottom to form a layer of sludge. 2. Anaerobic Digestion: Bacteria break down the organic matter in the absence of oxygen. The resulting liquid (effluent) is then typically discharged into a soak pit or drainage field for further secondary treatment.
Why other options are incorrect:
- Option (a) Drinking water storage: Septic tanks handle waste (sewage), which is contaminated and hazardous; they are never used for potable water.
- Option (c) Stormwater collection: Stormwater is typically handled by separate storm drains or detention ponds to prevent the septic system from overflowing or flooding.
- Option (d) Rainwater harvesting: This involves collecting clean rain for reuse, whereas a septic tank is designed for the disposal and treatment of waste.