Appendix S — Design Guideline of a Septic Tank

The volume of a septic tank may be computed using the following equation: V  PQ  PSY (8.S.1)

Where,

V = Volume of the septic tank (litre) P = Number of persons served Q = Flow, litre/capita/day ( )

The flow may be computed considering waste water flow 60% to 70% of the water consumption or on the basis of the plumbing fixtures discharging simultaneously into the septic tank, Sec 6.9.12.7. In absence of these data the waste water flow for the Occupancy groups A, C and D may be considered 120 lpcd for cities, 50 lpcd for district town and 20 lpcd for thanas and rural areas. For other Occupancy groups a waste water flow of 10 may be considered.

t = Liquid retention time, day (minimum 1 day Sec 6.9.12.11) s = Volume required for sludge and scum (0.04 m3/capita/year, Sec 6.9.12.10) v = Desludging frequency, year (Minimum 1 year, Sec 6.9.12.12). If computed volume is less than 2000 litres then minimum volume of the septic tank shall be 2000 litre (Sec 6.9.12.8).

Table 8.S.1: Reduction factors for various occupancies.

      Type of Development                                                           Factor
(i)   Church:               Hall-Seating capacity                                   0.01
                            Residential Staff                                       1.00
(ii) School:                Primary & Secondary School-student and staff            0.25
                            population per session
(iii) School:               Institution of Higher Learning-Total enrolment and      0.25
                            staff
(iv) Community Centre:      Staff/worker                                            0.25
                            Resident                                                1.00
                            Kindergarten-student and staff population per session   0.08
                            Maximum gathering                                       0.01

       Type of Development                                       Factor

(v) Factory:              One shift per 24 hours                 0.50
                          Two/three sifts per 24 hours           1.00

(vi) Market:              Hawker /employee                       0.25

(vii) Hawker/Cooked       No. of stall                           1.75
      Food center:

(viii)Cinema:             Hall-seating capacity                  0.03

                          Staff                                  0.50

(ix) Bar & Snack Bar,
     Coffee- House,       Seating capacity                       0.20
     Restaurant:

(x) Hotel:                No. of beds                            0.70

                          Staff/worker                           0.50

(xi) Office:              No. of staff                           0.50