Environmental Engineering

Solid Waste & Noise

Municipal solid-waste management and the logarithmic addition/attenuation of noise — two high-yield environmental scorers.

PART 1

Topic Breakdown & Traps

The Engineering Principle

MSW management follows the hierarchy reduce → reuse → recycle → recover (energy) → sanitary landfill as the final disposal route. Noise is measured on the logarithmic decibel scale, so levels do not add arithmetically: doubling equal sources adds

3 dB

, and a point source attenuates by

6 dB

per doubling of distance.

The Core Formula Matrix

Decibel addition:

L_{t o t a l} = 10 lo g_{10} (\sum 1 0^{L_{i} /10})

Two equal sources:

L + 10 lo g_{10} 2 \approx L + 3 dB

Point-source distance attenuation:

Δ L = 20 lo g_{10} \frac{r _{2}}{r _{1}}

Sanitary landfill = engineered final disposal with liner, cover & leachate control.

The ‘IIT Traps’

⚠
Decibels add logarithmically. $60 + 60 dB = 63 dB$ , not $120 dB$ .
⚠
**Distance attenuation uses $20 lo g$ for a point source** (pressure), giving $6 dB$ per doubling.
⚠
Open dumping is not sanitary landfilling — the latter is engineered with liners and daily cover.

📚 Standard references

Environmental Engineering Vol. II — S.K. Garg

PART 2

Progressive 3-Tier Question Suite

Q1BASIC1 Mark · NAT

Two independent sources each produce

60 dB

at a point. The combined level is _____ dB.

Q2MEDIUM1 Mark · MCQ

The most appropriate final disposal method for municipal solid waste is:

Q3HARD2 Marks · NAT

A point source gives

80 dB

10 m

. At

40 m

the level is _____ dB.