Problem $4\mathrm{.}1$

Given a flow rate of $8500\frac{m^3}{d}$ and an overflow rate of $50\frac{m^3}{d{m}^2},$ calculate the following

design parameters of a proposed circular primary sedimentation tank:

$($i$)$ Height of the sedimentation tank $($assuming a criterion of diameter$/$height ratio of $3\mathrm{.}5)$

$(2$ marks$)$

$($ii$)$ Hydraulic retention time $($HRT$)$ of the sedimentation tank. $(1$ mark$)$

Problem $4\mathrm{.}2$

There is an outdoor renovation project ongoing next to the lobby $(\frac{G}{F})$ of one of the hall in

HKUST. You are a civil engineering student living in the hall and would like to estimate the

noise level at your room. Give your answers to the nearest dB for this question.

$($i$)$ Someone claimed that under the same noise source, if receiving distance is doubled,

the sound pressure level would be attenuated by approximately $6dB.$ Do you agree? $($Hint:

Assuming two receivers with distances and sound levels $r_1,L_1$ and $r_2,L_2$ respectively and prove

the relationship above.$)(2$ marks$)$

$($ii$)$ Hence, if you are living on the $8^{th}$ floor, and the measured noise level under unmitigated

scenario is $98dB$ on the $2^{nd}$ floor, what is the estimated noise level at your room without any

mitigation measures? $(2$ marks$)$

$($iii$)$ Suggest one engineering solution that the can be taken to minimize the noise impact to

the residents in the hall. $(2$ marks$)$