The EIA(DE) Study has assessed the potential environmental impacts associated with the construction and operation of the Designated and Potentially Designated Elements of the proposed Yuen Long and Kam Tin Sewerage and Sewage Disposal Stage 1 Sewers, Rising Mains and Ancillary Pumping Stations. The findings of the assessments are summarised in the following sections.
The potential air quality impacts arising from the construction and operation of the sewers/rising mains and sewage pumping stations has been addressed. With the implementation of the recommended mitigation measures in the EIA (DE) Study Report and an effective monitoring and auditing programme, the potential construction dust and odour impacts will be minimised and kept within the relevant criterion. Cumulative construction phase dust impacts are expected to be within the relevant standards.
A construction noise assessment has been undertaken taking the cumulative impacts arising from projects proposed in the vicinity of the Study Area of this Project into consideration. Unmitigated sources of construction noise associated with the proposed development would cause exceedances of the daytime construction noise criteria. Mitigation measures such as quiet plant, moveable noise barriers and limiting the use of PME have been recommended.
As the works area for the sewer laying works will be small, the use of mitigation measures such as movable noise barriers and/or enclosures are only considered practicable for the small sized PME. As road opening is the noisiest construction activity associated with the sewer laying works, the use of handheld breakers instead of excavator mounted breakers together with the use movable noise barriers and/or enclosures is recommended to further reduce the potential noise impacts at the nearby NSRs. However, in view of the close proximity of some NSRs to the works site, noise exceedances are predicted even with the adoption of all practical mitigation measures. It is anticipated that the sewers will be constructed in segments of up to 50m in length and noise exceedances of up to 6dB(A) may arise on isolated occasions during the three month maximum period required to construct each segment. Exceedances of up to 12 dB(A) are predicted during reinstatement works; however, the period of such an exceedance is expected to last no more than 2 days. It is recommended that regular monitoring of noise levels is undertaken as part of the EM&A programme.
Noise impacts due to the operation of the proposed sewage pumping stations would not be insurmountable, provided that the planning recommendations described in the EIA (DE) Study are followed.
Potential impacts to surface water quality due to land based construction activities would primarily occur due to surface run-off and wastewater generation from within the construction sites. The potential impacts will be readily controlled by on-site mitigation measures as specified in the EIA (DE) Report.
Detailed water quality modelling was undertaken to determine the effects on marine water quality of decreasing the discharges of untreated sewage effluent to inland waterways. This reduction will be achieved by the diversion of effluent to the Yuen Long STW and hence will result in an increase in the treated effluent flows from the STW. The results of the water quality modelling indicated that there would be improvements in marine water quality in the vicinity of the mouth of the Shan Pui River, via which the Yuen Long STW discharges to Deep Bay. An assessment of the impacts of the works on inland water quality determined that there would be a 10% reduction in polluting discharges and that there would thus be an improvement in water quality.
Good waste management practices have been recommended in the EIA(DE) Report to ensure that adverse environmental impacts from the handling and disposal of construction and operational wastes are prevented or minimised. No unacceptable environmental impacts were predicted from the storage, handling, collection, transport, and disposal of wastes arising from the construction and operation of this Project.
Based on the available information and the findings of the site inspections, there is no evidence to suggest that the potentially contaminated sites identified in this study will be the source of significant off-site migration of contaminants to the proposed alignment of the sewers and locations of the pumping stations. Should any of the excavated soils be found to be contaminated, they could be treated by standard methods prior to disposal at the strategic landfills. It is therefore not considered that the presence of potentially contaminated sites adjacent to the proposed works areas will cause any insurmountable environmental impacts.
The ecological resources recorded within the Study Area included secondary woodland, grassland/shrubland, cultivated land, fishpond, marsh, stream/ channel & nullah and mangrove habitats, as well as the associated wildlife. Of these habitats, grassland/shrubland, streams/channel & nullahs and urbanised areas have low ecological value. Cultivated land, fishponds located outside the Wetland Conservation Area (WCA) and Wetland Buffer Area (WBA) and secondary woodland areas surveyed within the Study Area, are of moderate ecological value. Mangrove, marsh and fishponds within the WCA and WBA are of high ecological value.
The proposed sewer alignment and pumping station sites are mainly located on existing roads/ footpaths, which are classified as urbanised/disturbed habitats of minimal ecological value. The impact on the relatively low quality habitats is considered to be low, and no adverse residual impact is expected after the implementation of the recommended mitigation measures. The most sensitive issue is the potential for an indirect impact within the WCA and WBA, in which the scheduling of works and noisy activities outside of the winter period is expected to counteract any predicted impacts. Mitigation measures in the form of good construction practice and the use of quietened construction plant/ equipment and movable barriers have been recommended to minimise potential disturbance to the surrounding environment.
Active fish ponds were identified within the Study Area, with the majority concentrated to the north west. Although fish ponds were observed in other areas, these appeared to be inactive and/or abandoned. No active fish ponds are expected to be impacted by the construction and operation of the proposed sewerage system and pumping stations.
No direct impact to the identified historical buildings or features is predicted. Appropriate mitigation measures have been recommended to minimise indirect impacts, where necessary.
Set back of construction works to avoid encroachment of safe margins, attention of site works to remove underlying obstructions, careful selection of construction plant and construction method, structure survey of Ng Ka Tsuen historic compound and vibration monitoring have been recommended to ensure that the structural integrity of the Ng Ka Tsuen historic compound would not be affected by the construction of the Ng Ka Tsuen Sewage Pumping Station. Precaution on start up and stopping of pumps and noise radiation is also recommended to ensure any operational vibration impact is kept to a minimum.
No significant archaeological deposits would be impacted by the proposed sewerage facilities expect the Shui Tsan Tin, Ng Ka Tsuen and Pang Ka Tsuen Sewage Pumping Stations. A six month period has been recommended to allow for an archaeological field investigation to be undertaken at each of the sites. The investigations would be undertaken once the land is resumed and access is gained, but before any construction takes place. Mitigation measures agreed with the AMO, should be implemented to mitigate any potential impacts. Before undertaking any fieldwork, a qualified archaeologist should obtain a Licence from the Authority under the Antiquities and Monuments Ordinance (Cap. 53).
The Study Area is low-lying flat land forming of a series of broad alluvial valley floors draining into Deep Bay. The main land uses are villages, industry and some agricultural activities. The density of development is generally highest next to the main roads and major intersections in the east of the Study Area, giving way to agricultural land and fish ponds in the west.
The project elements likely to affect the landscape and visual baseline conditions during the construction phase will be the activity associated with the construction of the sewage pumping stations and underground sewers and rising mains. The project elements likely to affect the landscape and visual baseline conditions during the operation phase will be the sewage pumping stations only.
In order to mitigate these impacts, a number of on-site landscape mitigation measures have been recommended and outlined in the EM&A Manual for incorporation into the Project. With the implementation of the mitigation measures, the residual landscape and visual impacts are considered acceptable for the following reasons:
· there will be some slight/moderate adverse effects on the baseline condition, but these can be eliminated, reduced or offset to a large extent by landscape mitigation measures;
· The Project would result in the loss of 30 trees. Compensatory planting for each Pumping Station site has been recommended;
· The introduction of the Project into the study area will result in mainly negligible landscape impacts assuming mitigation measures are incorporated into the scheme;
· The introduction of the Project into the study area will result in mainly negligible visual impacts assuming mitigation measures are incorporated into the scheme;
· there would be no significant adverse effect on the appearance of the Study Area; and
· there would be no interference with key views.