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CHAPTER 3

Quality Design Fundamentals

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3.1 INTRODUCTION

1) Non-point source (NPS) pollutants from typical

urban areas

2) Estimation of annual pollutant load based on theevent mean concentration (EMC)

3) Simplified procedures required for preliminary

sizing and designing stormwater quality control

facilities or Best Management Practices (BMPs)

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3.2 POLLUTANTESTIMATION

a) Typical Runoff Pollutants

Many different contituents can be found in Malaysia

The contituents that recommended as typical pollutantscharacterising urban runoff in Malaysia :

Gross pollutants

Total suspended solids (TSS)

Biochemical oxygen demand (BOD)

Chemical oxygen demand (COD)

Total nitrogen (TN) Lead (Pb)

Zinc (Zn)

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BMPs design based on 3 types of selected pollutants :

i. Gross pollutants

ii. Total suspended solids (TSS)iii. Nutrients (TN and TP)

These stormwater pollutants are potentially generatedfrom various landuses as given in table 3.1 below :

Table 3.1

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b) Water Quality Volume (WQV)

Before any assessment can be made of pollutant

loads, runoff volumes are necessary to estimate

Runoff estimation is necessary to :

To size certain BMPs

To design the outlet structures of the BMPs

WQV = CV.(Pd).A

Equation 3.1

WQV = Water quality volume (m)

CV = Area-weighted volumetric runoff coefficient for the landuse (Table 2.5)

Pd = Rainfall depth for water quality design storm (m)

A = Contributing drainage area (m)

Note :

CV < C , for large ARICV= C , for small ARI Chapter 2

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c) Load Estimate

Event mean concentrations (EMC) widely used method to

estimate runoff pollutants from urban areas for different land

activities

The reliability of this method depends on the accuracy of the

EMC values for the intended parameters and landuses

Table 3.2 below shows the recommended mean EMC values for

various pollutants

Table 3.2

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L = Annual pollutant load (kg/year)

R = Mean annual rainfall-MAR (mm/year)

EMC = Event mean concentration (mg/L)

A = Catchment area (ha)

CV = Area-weighted volumetric runoff coefficient for the landuse (Table 2.5)

Equation 3.2

L = R. EMC. A. CV/ 100

Load estimated by EMC method :

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3.3 POLLUTANTCONTROL

Stormwater pollutants :i. Particulates

ii. Dissolved substances

iii. Floatables (litters and hydrocarbon)

Physicochemical nature of each group of

pollutants is different.

Therefore, mechanism to remove them from

the water is also different.

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a) Particulate pollutants

Primary pollutants found in stormwater and are

removed through sedimentation and filtration.

Sedimentation occurs when particles have a greater

density than the surrounding liquid.

The smallest particle settling size in the field is

around 0.01 mm.

Sometimes, the smallest particles become

electrically charged, which can further interfere withtheir ability to settle out.

The Newton's and Stoke's laws are often used to

quantify the sedimentation process.

Particulates can also be removed by filtration

through use of infiltration facilities. The mechanismis different from sedimentation process, where

media is used for example sand, to increase the

efficiency of the pollutant filtration process.

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b) Dissolved pollutants

Removed through adsorption, microbial fixation,

biochemical degradation and plant uptake

(phytoremediation).

The dominancy of the process mechanism depends

on the type of BMPs. Soil or plant-based media is

required to remove the dissolved pollutants (Metals,

TN, TP, BOD, COD, etc).

Two most common BMPs used to remove dissolvedpollutant from stormwater are wetlands and

bioretention facilities.

Wetlands support various types of microphytes and

macrophytes that either absorb or adsorb dissolved

pollutants from the storm runoff.

For dissolved pollutants by bioretention facility is

mainly done by media and plant uptakes.

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c) Floatable pollutants

Floatable pollutant in the form of runoff can be in

the form of litters (refuse or trash) or oil and grease

(floating hydrocarbon).

The litters are floating or submerged particles large

enough to be removed by screen, trash rack, nets

and other mechanical devices.

Opening of the litter trapping devices depend on the

size of the particles to be trapped. However, finescreens pose high potential to choke or clog the

drainage system.

Captured floatable pollutants should be removed

from the gross pollutant trap at the soonest

possible time, preferably before the next storm

occurs.

The removal of floating oil and grease is based upon

the rise rate velocity of oil droplet and rate of runoff.

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EXAMPLE3.A

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SOLUTION :

(Table 3.2) (R xCv)

Eq 3.2 x 0.001

(Table 2.5)

Mean annual rainfall (MAR)

L=(R.EMC.A.Cv)/100

(0.7+0.8+0.8)/3

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