Deep Gravity Sewers Study
Read the environmental study on Sentosa's proposed Deep Gravity Sewers project, which aims to replace the island's ageing sewer network with a more efficient, long-term system.
Last updated 9 June 2026
Project Title
Environmental study for the proposed Deep Gravity Sewers project at Sentosa
Project Description
An Environmental Study was commissioned by Sentosa Development Corporation (SDC) in July 2020 for the proposed Deep Gravity Sewers project at Sentosa (hereinafter referred to as the “Project”).
This Project would involve the implementation of a pure gravitational Deep Gravity Sewers (hereinafter referred to as “DGS”) system on Sentosa to replace the island’s existing aging sewer network.
The DGS system would be more efficient, reliable, and sustainable as a long-term solution for the next 100 years, in line with PUB’s implementation of the Deep Tunnel Sewerage System (DTSS).
Project Site Information
Project Site Information
Environmental Study Summary
Following a preliminary assessment on the entire proposed DGS system, it was discussed with Technical Agencies that the key focus of the Environmental Study would be for above-ground construction worksites near identified Nature Areas (i.e., Mount Imbiah and Mount Serapong), as there would unlikely be environmental impacts during its underground operations.
The summary of impact significance (with minimum controls) and the potential residual impact significance (after considering mitigation measures for moderate and major impact significance) for the construction phase are presented in the following table.
Summary of impact significance and potential residual impact significance
Environmental Parameter | Impact Significance with Minimum Controls | Residual Significance with Mitigation Measures |
|---|---|---|
Biodiversity | Minor to Major | Negligible to Moderate |
Airborne Noise | Ecologically Sensitive Receptors: Minor | Ecologically Sensitive Receptors: Negligible |
Human Receptors: Minor to Negligible | Human Receptors: Negligible | |
Air Quality | Ecologically Sensitive Receptors: Moderate to Major | Ecologically Sensitive Receptors: Minor |
Human Receptors: Moderate to Major | Human Receptors: Minor | |
Suface Water Quality | Minor | N/A |
Note: N/A indicates no residual impact assessed as impact significance with minimum controls in place was assessed as insignificant | ||
The Technical Memo II provides an update on the following changes to the design of the proposed DGS system layout as summarised:
• Omission/ Removal of main manhole worksite (i.e. MH21);
• Minor changes/reduction of manhole worksite areas (i.e. MH22, MH24); and
• Omission/Removal of pipeline alignment and manhole worksites between MH3 and MH28 (i.e. MH29, MH30, MH31, MH32).
These key changes in design only include omission of alignment, manhole worksite or reduction of manhole worksite area. As the impact assessment in Environmental Study Final Report Rev C and Environmental Study Technical Memo Rev A is conservative, covering the worst-case scenarios, reassessment was not carried out. The summary of impact significance shown in the table above remains applicable.
The Technical Memo II also details the impact assessment of demolition of pumping stations as summarized in the table below.
Impact assessment summary
Environmental Parameter | Impact Significance with Minimum Controls |
Biodiversity | Direct impacts on biodiversity, air quality and surface water quality are not likely to be significant as long as similar mitigation measures detailed in Final Environmental Study Report are implemented to minimise impacts arising from the demolition works. |
Air Quality | |
Surface Water Quality | |
Airborne Noise | Ecological Sensitive Receptors: Negligible to Minor |
Human Receptors: Negligible |
A construction phase Environmental Monitoring and Management Plan (EMMP) was proposed to (1) ensure that any potential impacts arising from the project are within anticipated levels and (2) assess the effectiveness of the recommended minimum control measures and site mitigation measures in reducing identified environmental related impacts on key receptors. The EMMP will monitor construction activities and ensure appropriate monitoring and management procedures are in place.
Further details can be found in the associated reports from the Environmental Study listed here:
Stakeholders Consulted
Relevant business establishments in Sentosa
Publication Date
17 February 2022
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