QUESTION 4
(a)  Give FOUR examples of situations where a drain needs extra protection.
 1 when a drain passes under a buiding
 2 where min cover isnt achieved of 500mm and drains over 2.5m (subject to engineer design)
 3 subject to vehical trafic
 4 Roots which can penetrate the drain 
(4 marks)

(b)  (i)  State the term used to describe the lowering of the water table in an area.
(1 mark) Dewatering

 (ii)  When lowering the water table, a perforated pipe may be driven into the ground. 
State the term given to this pipe. spear head
(1 mark)

 (iii)  State the name given to the distance between the inlet level and the outlet level of a
septic tank. cascade
(1 mark)

 (iv)  The use of a mechanical type valve (reflux valve) is unacceptable to the owner of 
a property who is having problems with drain surcharge. State what could be used 
in its place.
(1 mark)

 (v)  State the most probable cause of accumulation of explosive gases in a drain.
(1 mark) Poor ventilation
Total 9 marks