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Subjects · Leaving Cert Construction Studies

Leaving Cert Construction Studies: Drainage & wastewater treatment

How often Drainage & wastewater treatment comes up on the Construction Studies papers, every year it was asked, and questions to try.

HL Asked on 2 of the last 9 Higher Level papers, most recently in 2023.

OL Asked on 6 of the last 9 Ordinary Level papers, most recently in 2025. most years

June 2028 is the first exam on the new Construction Studies course. These come from the 2016–2025 papers, so read them as a guide.

Drainage & wastewater treatment, Higher Level(7 marks)

Quick ones on Drainage & wastewater treatment.

(a)Effluent from a septic tank flows next to?
  1. The surface water drain on the road
  2. A percolation area or polishing filter
  3. A soakaway that takes the water from the roof
(b)What does the T-test measure on a site?
  1. The radon level in the soil gas
  2. The bearing strength of the soil for footings
  3. How fast water soaks away through the subsoil
(c)How does a packaged treatment plant differ from a septic tank?
  1. It aerates sewage for cleaner effluent
  2. It just stores sewage for tanker removal
  3. It needs no percolation or filter area
Show the answers

(a) A percolation area or polishing filter

(b) How fast water soaks away through the subsoil

(c) It aerates sewage for cleaner effluent

Your turn: Higher Level questions on Drainage & wastewater treatment.

Higher Level

Asked on 2 of the last 9 Higher Level papers, most recently in 2023.

Every paper, year by year

YearWhere it came up
2025Not asked
2024Not asked
2023Q8
2022Not asked
2021Not asked
2019Q8
2018Not asked
2017Not asked
2016Not asked

Links open the State Examinations Commission’s paper for that year.

More Drainage & wastewater treatment questions

Drainage & wastewater treatment, 3 marks

Why can a foul drain laid too steeply block?

  1. The pipe fills with air and airlocks the flow
  2. The water freezes more easily in winter
  3. Water runs ahead and leaves solids stranded
Show the answer

Water runs ahead and leaves solids stranded

On a very steep fall the liquid outruns the solids, which build up in the pipe. A moderate fall keeps them moving together at a self-cleansing speed.

Drainage & wastewater treatment, 2 marks

Why must a septic tank be desludged from time to time?

  1. To add fresh bacteria to the tank each year
  2. Sludge builds up and would pass to the percolation area
  3. To lower the water table around the tank and field
Show the answer

Sludge builds up and would pass to the percolation area

Solids settle and digest slowly. When the sludge gets too deep, solids are carried out and clog the percolation area, so a permitted contractor empties the tank.

Ordinary Level

Asked on 6 of the last 9 Ordinary Level papers, most recently in 2025. most years

Every paper, year by year

YearWhere it came up
2025Q8c
2024Q8g
2023Not asked
2022Q3, Q8e
2021Q1
2019Q8e
2018Q7
2017Not asked
2016Not asked

Links open the State Examinations Commission’s paper for that year.

More Drainage & wastewater treatment questions

Drainage & wastewater treatment, 3 marks

What happens to the solids that enter a septic tank?

  1. They are pumped straight into a stream
  2. They float out through the percolation pipes
  3. They settle as sludge and bacteria break them down
Show the answer

They settle as sludge and bacteria break them down

Heavy solids sink and a scum floats. Bacteria digest much of this, and the tank must be desludged every so often. Only liquid goes to the percolation area.

Drainage & wastewater treatment, 2 marks

Why does the trap under a sink hold water?

  1. It slows down the flow of waste water
  2. The water seal stops drain smells coming in
  3. It keeps the waste pipe cool and quiet
Show the answer

The water seal stops drain smells coming in

The U-bend always holds some water. This seal blocks foul air and gases from the drain but lets waste water flow through.

Drainage & wastewater treatment, 2 marks

What is a percolation area?

  1. Trenches of pipes where treated effluent soaks into soil
  2. A tank where the solids settle out and are digested
  3. A pit filled with loose stone that collects the roof rainwater
Show the answer

Trenches of pipes where treated effluent soaks into soil

Effluent from the septic tank flows into perforated pipes laid in gravel. It seeps into the soil, which filters and cleans it further.

Other Construction Studies topics

All of Leaving Cert Construction Studies