CIVL 395 Environmental Impact Assessment [3]

Housing Development in Tuen Mun Area 1 Proposed Bridge at Tuen Mun Area 18

HS Kan

March 2007

Water Quality Impact Assessment

Sewerage Impact Assessment

Water Pollution Control Ordinance Cap 358 (WPCO)

All kinds of wastewater, whether discharged into communal sewers, storm drains, river courses or waterbodies are subject to control, except

Domestic sewage discharge into sewers Discharge of unpolluted water

All discharges subject to control shall be covered by an effluent discharge licence

Physical, chemical and microbial quality Flow Dependent upon

• Location of discharge• Beneficial use of the receiving water

Pre-treatment as necessary

Technical Memorandum on EIA Process, EIAO Cap499 Annex 6

4 aquatic components to be considered Water quality Hydrology Bottom sediments ecology

To achieve Water Quality Objectives under the WPCO Aesthetic enjoyment

• Sight, smell, taste, touch Human health

• Potable use, irrigation, bathing & recreational, contamination of seafood Pathogenic indicators E. coli Bioaccumulation, paralytic shellfish poisoning, etc

Aquatic life• Integrity and balance of the aquatic ecosystem

Natural properties of the waterbody – temp, salinity, DO, pH, turbidity, etc. Nutrient input, accumulation of harmful substances Physical environment of the waterbody – sedimentation, etc.

Industrial use• Prevention of deleterious chemicals, flotables, biological growths, etc.

Cooling water systems, shipping

Water Quality Impact Assessment Description of the environment

Marine water, coastal water, river, etc Identification of pollutant sources

Existing or planned From the project itself and elsewhere, e.g. concurrent projects

Identification of water sensitive receivers Beaches, water recreation areas, flushing water intakes, cooling water

intakes, fish culture zones, marine parks, corals, mangroves, SSSI, etc. Existing or planned

Baselining the environment Existing water quality monitoring measurements, etc Dedicated baseline surveys Common parameters measured:

DO, turbidity, SS, BOD, Inorganic N, Ammonia N, chlorophyll-a, E. coli

Impact evaluation Prediction of the transport of pollutants from the sources to the

receivers Oceanographic data Flow tracking Numerical modelling

Mitigation measures and monitoring

Baselining the Environment

Water Quality Modelling Physical, chemical and biological processes Hydrodynamic modelling

Coastline and bathymetry Oceanographic and meteorological information Non-steady flow and transport phenomena

Water quality modelling Pollutant inventory Advection-diffusion-reaction mechanisms Physical process, e.g.

oxygen exchange with the atmosphere sedimentation of suspended substances

Biochemical process, e.g. nitrification algal growth decay

Boundary conditions, extent of model Calibration and validation important

Water Quality Numerical Modelling – the Waterbody

Water Quality Numerical Modelling – the Waterbody

Water Quality Numerical Modelling – Output

Other Water Quality Assessment Criteria

Water quality for flushing water intake at sea Colour < 20 Hazen units Turbidity < 10 NTU Suspended solids < 10 mg/l Dissolved oxygen > 2 mg/l Ammonium-N < 1 mg/l BOD5 < 10 mg/l Synthetic detergents < 5 mg/l E. coli < 20,000/100 ml

Water Quality Impacts – Construction phase

Construction site runoff Exposed soil surfaces Oil from machineries, etc

Bentonite slurry, grout, etc from piling works Sewage from workforce

Presence of sewers, chemical toilets Accidental spillage of chemicals Mitigation measures

Good housekeeping with regular tidying Shielding of stockpiled materials Intercepting channels Silt traps Oil separators Reuse and proper disposal of bentonite Protection of drainage facilities

Sewerage Impact Assessment To safeguard public health Additional flows & loads arising Impacts on existing sewerage facilities

Sewers Pumping stations Sewage treatment works Disposal facilities Others e.g. dry weather flow interceptors

Proper pre-treatment, treatment and/or disposal of flows arising, at all stages of the project

DSD Sewerage Manual

Existing Sewers & Drains

Unit Flow Factors

Note: Peaking factor is applied globally.

Note: Peaking factor is applied globally.

Additional information in relation to SIA

Public housing estate at Site B Housing type: Low-cost rental No. of employees: 20

Private housing Housing type: R1 No. of employees: 20

Private housing club house Restaurant with an average daily flow of 1000 m³/day No. of employees: 35

Primary school No. of students: 700 No. of employees: 80

MH-B2

CL 16.40

A1 12.45

X1 12.40

MH-B1

CL 16.50

X1 14.70

MH-A1

CL 21.80

X1 20.70

MH-A2

CL 18.70

A1 17.15

X1 17.10

MH-A3

CL 15.20

A1 13.10

X1 13.00

MH-B3

CL 7.50

A1 5.20

X1 5.15

Existing Sewers

LEGEND

CL Cover level (ground level)

A Incoming sewer invert level

X Outgoing sewer invert level

300

300

375

300

300

Some particular points to consider Depth and alignment of new sewers Connection to existing sewerage system

Need new pumping stations? Any constraints due to the Light Rail Transit?

Trenchless methods Minimum clearance requirements?

Impacts on the existing residents and other people during construction stage Impacts on all residents and other people during the operation stage

ASSUME: Capacity of existing sewerage is adequate.

Solid Waste

Solid Waste Numerous ordinances and regulations

Waste Disposal Ordinance Waste Disposal (Chemical Waste) (General) Regulations Public Cleansing and Prevention of Nuisance Regulation under

the Public Health and Municipal Services Ordinance Provides control on illegal tipping of wastes on unauthorized sites

Website for ordinances and regulations: http://www.justice.gov.hk/Home.htm

Construction & Demolition (C&D) Materials Accounts for some 40% of waste disposed of to landfills in 2003

Insufficient landfill space Over 80% of C&D materials is inert

Distinguishes between Public fill – the inert portion C&D waste – the non-inert portion

Material with more than 30% inert content need sorting before disposal to landfill

For projects generating 50,000 m³ or more C&D materials, the preparation of a C&D Material Management Plan

Solid Waste Other wastes in construction stage

Used bentonite General refuse Contaminated soil/sediments

Assessment EIAO-TM Annexes 7 and 15

Estimate the types and quantities of wastes Identify opportunities for waste reduction and beneficial use

of the waste Alternative design and alternative materials Assess impacts associated with the handling and disposal of

wastes

Solid Waste Control and mitigation

Contaminated soil/sediments EPD’s Guidance Notes for Investigation and Remediation of Contaminated

Sites of Petrol Filling Stations, Boatyards, and Car Repair/Dismantling Workshops

Works Bureau Technical Circular No. 3/2000 on dredged sediment C&D Materials

Waste Management Plan Designated disposal sites

• 3 strategic landfills: WENT, NENT, SENT Trip-ticket system Sorting of C&D materials Use of recycled aggregates Use of non-timber formwork and recyclable materials for temporary works Charging scheme

Good housekeeping Proper chemical waste handling procedures Reduction, Recycle, Reuse