169. The digested sludge from septic tanks, is removed after a maximum period of
A. 3 years
B. 3.5 years
C. 4 years
D. 5 years.

---

170.  The rate of accumulation of sludge per person per year, is
A. 10 litres
B. 15 litres
C.c) 20 litres
D. 25 litres

---

171. In septic tanks,
A. free board of 0.3 m may be provided
B. the baffles or tees are extended up to top level of scum
C. the clear-space between the baffle top and covering slab is about 7.5 cm
D. all the above.

---

172.  The bottom of the sewage inlet chamber of septic tanks, is provided an outward slope
A. 1 in 5
B. 1 in 10
C. 1 in 15
D. 1 in 20

---

173.  Bottom openings 15 cm x 15 cm in the standing baffle wall are provided
A. 15 cm c/c
B. 22.5 cm c/c
C. 30 cm c/c
D. 50 cm c/c.

---

174. In a septic tank of de-sludging period of 1 year, receives sewage for 100 persons @ 120 litres per person per day. If the depth is kept 1.667 m and length-width ratio is 4, the length and width of the septic tank, are :
A. 4 and 1 m
B. 4.80 m and 1.20 m
C. 5.20 m and 1.30 m
D. 6.00 m and 1.50 m.

---

175.  In case of Imhoff tanks,
A. the shape is rectangular
B. detention period is 2 hours
C. the velocity of flow is restricted to 0.30 m/minute
D. All the above.

---