Relocation of Sha Tin Sewage Treatment Works to Caverns

Project Background

To promote sustainable development, after undertaking researches and consultations, in 2014, the Drainage Services Department (DSD) moved forward with relocating the aging Sha Tin Sewage Treatment Works into caverns. The project is expected to be completed by 2031. Upon completion, not only will 28 hectares of land be released for other beneficial uses, the current issues relating to landscape, odour and aging facilities arising from the existing sewage treatment works will also be resolved.

Scope of Project

The future cavern complex for the relocated STSTW will be the largest of its type ever built in Hong Kong. It needs to be implemented in stages. Tentatively, the Project will be implemented in the following phases, namely –

Site preparation and access tunnel construction (Contract No.: DC/2018/05 commenced on 28 February 2019 and completed on 10 April 2022. Contractor: China State Joint Venture);

Main caverns construction, modification and construction of upstream sewerage and pumping stations (Contract No.: DC/2020/05 commenced on 5 July 2021 and anticipated completion date on 6 February 2027. Contractor: China State – Alchmex Joint Venture);

Sewage treatment facilities installation; and

Decommission and demolition of existing STSTW.

Benefits of Relocating STSTW to Caverns

Like! Better control odour and improve the environment

Like! Releasing of 28 hectare of land for other beneficial use

Like! Long term planning for the aging sewage treatment facilities and adopt advanced sewage treatment technology to improve our services

Existing Sha Tin Sewage Treatment Works

Sha Tin Sewage Treatment Works (STSTW) is the largest secondary sewage treatment works in Hong Kong. It occupies 28 hectares of land and serves a population of about 630,000 in Sha Tin and Ma On Shan Districts, which produce 250,000m³ of sewage per day.

STSTW was commissioned in 1982. To meet the continuous population growth in Sha Tin and Ma On Shan, the STSTW Extension Works were progressively. The treatment capacity of the STSTW was increased to 340,000m³ per day after the Extension Works.

Commissioning Year:	1982
Footprint:	About 28 hectares
Sewage Treatment Level:	Secondary
Design Daily Sewage Treatment Capacity:	340,000m³
Current Sha Tin Population:	About 630,000

Sewage Catchment Areas in Sha Tin

There are six sewage pumping stations for transferring the sewage collected via the existing underground sewerage network within the six sewage catchment areas in Sha Tin district to the STSTW for centralised treatment.

Effluent Export Route

At present, the treated effluent from the STSTW is pumped to the effluent export tunnel starting at Nui Po Shan of A Kung Kok, and then transported to Kai Tak River in Wong Tai Sin for discharge. This arrangement can make use of the flushing effect by the treated, clean effluent from the STSTW, and hence improve the water quality and environment of the Kai Tak River.

Traffic Impact Assessment (Investigation and Design Stage)

Construction Stage

A Kung Kok Street is a main route for many buses and mini-buses to/from Ma On Shan area. In response to the comments from members of the Health and Environment Committee of Sha Tin District Council on the proposal made in the feasibility study stage during the meeting in March 2016 and findings from the further Traffic Impact Assessment conducted, the investigation and design consultant recommended the following mitigation measures to further minimize the traffic impact on this road during construction:

Temporary access roads and temporary bridge connecting to Ma On Shan Road are proposed (refer to figure below) for use by dump trucks to deliver excavated materials away from the site; and
Restricting construction vehicles passing through A Kung Kok Street during morning and afternoon peak hours through site management.

Being part of the temporary traffic arrangement, a section of existing footpath and cycle track would be utilized as a haul road for construction vehicles, and temporary diversion of footpath and cycle track are therefore proposed. The existing footpath and cycle track would be re-opened to the public upon completion of the construction work.

The traffic model analysis shows that the expected traffic impacts to the nearby road network would be minimized with the implementation of the proposed mitigation measures.

Operational Stage

Proposed Improvement Works to Mui Tsz Lam Road

In order to reduce the traffic impact of the relocation project to the nearby road network at A Kung Kok Street, the proposed main entrance and emergency exit of the relocated STSTW would be located at Mui Tsz Lam Road.

To facilitate the operation of the relocated STSTW and enhance the overall traffic safety, improvement to a section of Mui Tsz Lam Road including construction of a roundabout for the entrance of the relocated STSTW is proposed. (refer to figure below).

Mui Tsz Lam Road will not be completely closed during the construction works. Temporary traffic arrangement would be implemented to minimize the potential traffic impact induced by the construction works.

According to the Traffic Impact Assessment, the traffic impact of the relocated STSTW during operation stage is considered minimal.

The above schemes were presented to Traffic and Transport Committee (T&TC) of Sha Tin District Council on 9 May 2017. T&TC members expressed general support on the proposed schemes.

Environmental Impact Assessment (EIA)

In accordance with the Environmental Impact Assessment (EIA) Study Brief (No. ESB-273/2014) and the Technical Memorandum on EIA Process, we had delivered an EIA report for the Sha Tin Cavern Sewage Treatment Works (Application No. EIA-240/2016) to the Director of Environmental Protection. The Director of Environmental Protection approved the EIA report on 28 November 2016 and issued the Environmental Permit on 31 March 2017 under the EIA Ordinance. For details, please visit the EIA Ordinance website at: http://www.epd.gov.hk/eia/english/alpha/aspd_681.html

The EIA report provides a detailed assessment of the likely environmental impacts and environmental benefits arising from the construction and operation stages of the proposal. The eleven key environmental aspects of the EIA study include:

Technology

Sewage and Sludge Treatment Technologies

We are actively exploring advanced sewage and sludge treatment technologies to reduce the required cavern space and shorten the construction period.

Odour Control Measures

General odour control measures include:

Dosing of chemicals at upstream sewage pumping stations to suppress odour generation from sewage
Covering up of the source of odour, e.g. inlet works, primary sedimentation tanks and sludge treatment facilities to suppress odour emission
Installation of deodourising units to clean up the collected foul air
Dosing of chemicals at sludge treatment facilities to suppress odour generation from sludge

Nearby Estate / Village	Horizontal Distance from Ventilation Shaft (about)
Chevalier Garden	1250m
Kam Tai Court	1550m
A Kung Kok Fishermen Village	1000m
Tai Shui Hang Village	1450m
Mui Tsz Lam Village	1400m

Caverns as natural barriers are highly conducive to effective odour control. We will furthermore enclose all odour sources and provide de-odourisation facilities inside the caverns. The location of the cavern ventilation shaft has also been further optimized and shifted to a more remote spot.

Through the multi-barrier control measures, detailed EIA analysis indicates that the arrangement will not cause any perceivable odour. The maximum predicted odour level at any of the nearby residential areas / development (Chevalier Garden, Kam Tai Court, Mui Tsz Lam Village, A Kung Kok Fishermen Village, Tai Shui Hang Village, Shing Mun Springs, the Castello, Sha Tin Hospital, etc) will be less than one Odour Unit. This is far lower than the five Odour Unit limit stipulated in the Environmental Impact Assessment Ordinance.

The outlet of the ventilation shaft will be inconspicuous and landscaped to blend in with the surroundings of Nui Po Shan.