Water Quality Issues

Pollutant Loadings and Mitigation

Water quality in the Shing Mun River catchment has shown long term improvements due to implementation of WPCO and WDO and remedial pollution control works in tributary nullahs. The overall rate of compliance with WQOs in 1998 was 83%. However, Shing Mun River Channel is contaminated with oxygen-demanding sediment and has elevated levels of E. coli. Livestock and chemical waste has been eliminated from catchment of the Shing Mun River though some unsewered villages are exerting an organic pollution load. Localised inputs of aluminium (3,000 ? l^-1 in 1997) from Sha Tin WTW are now declining.

The other rivers and streams in the WCZ generally have good water quality, having improved since designation of the WCZ in 1987 and associated pollution control measures.

Livestock and chemical waste has been eliminated from catchment of the Shing Mun River through some unsewered villages are exerting an organic pollution load. Localised inputs of alumimium (3,000 ? l^-1 in 1997) from Sha Tin WTW are now declining.

All watercourses are subject to occasional localised organic pollution from unsewered villages. Two stages of sewerage works are in progress or planned as part of the SMP to widen the sewer network to 165 villages (around 90,000 population to be served).

Total BOD loadings in the Shing Mun River have been reduced by 89% (7,400 kg day^-1) since 1987, and by 73% (4,680 kg day^-1) in the Lam Tsuen and Tai Po River catchment.

Reduced organic pollutant loadings in all watercourses has been achieved through regulatory and pollution control infrastructure measures under the SMP resulting in the following reductions in BOD loads between 1989 and 1998:

- 73% (280 kg day^-1) for Ho Chung River
- 46% (190 kg day^-1) for Sha Kok Mei Stream
- 42% (161 kg day^-1) for Tai Chung Hau Stream

The WCZ is characterised by a number of river catchment systems. Despite modest long term water quality improvements in some parameters for the River Indus (and its tributary, the River Beas) and River Ganges, compliance with organic WQOs (in particular BOD₅ and COD) is still poor. In 1998 all sections of the River Indus were ranked 'Fair' and the lower reaches of the Ganges were ' Very Bad '. E. coli levels remain high in both river catchments.

Yuen Long Creek and Kam Tin River also have poor WQO compliance levels and a WQI class of 'Very Bad' or 'Bad' despite long term decreases in organics and nutrients parameters. Compliance with BOD₅ WQO was 0% for both rivers in 1998 however.

Fairview Park Nullah also experiences high organic pollution levels, and Tin Shui Wai Nullah showed a decline in WQO compliance from 1997 to 1998, but the other watercourses in the WCZ are generally of better, and improving, water quality.

Pollutant loadings in the Indus and Ganges catchments are characterised by a heavy organic input from livestock waste and some contribution from unsewered housing and industry. However, overall BOD load reductions of between 86% and 90% have been achieved in these rivers between 1990 and 1998 (96% reduction in River Beas).

Livestock wastes affect both watercourses. BOD loadings are still high (1,370 kg day^-1 in Yuen Long Creek and 2,409kg day^-1 in Kam Tin River). Although loadings have been reduced by 93% in Yuen Long Creek and 88% in Kam Tin River since 1990 due to the LWCS, loadings actually increased in 1998 in the Kam Tin River.

BOD loadings in all watercourses have been reduced principally through reduced livestock waste pollution under the LWCS.

Poor base flow in polluted tidal reach of Shing Mun Main Channel which has high E. coli levels.

Current BOD loads to Tolo Harbour from catchment rivers approx 2,850 kg day^-1, principally from domestic sewage sources.

There are 1236 licensed effluent discharges to the WCZ including 18 Sewage Treatment Plant (STP) discharges and 1058 discharges from industrial and commercial sources.

New sewerage facilities at 14 villages in Sha Tin and 10 in Tai Po to date. SMP will provide sewerage for 165 villages by 2004.

Under Tolo Harbour Action Plan (Effluent Export Scheme), treated sewage from Tai Po and Shatin STWs will be exported to Victoria Harbour for discharge.

Assuming new sewerage infrastructure is linked to Sha Tin STW, organic loadings in catchment rivers and coastal waters should continue to decline.

Capacity enhancement will be affected by the naturally limited dispersive capacity of the WCZ. Capacity will therefore only be maintained and enhanced through continuous improvements to sewerage services and treatment standards/capacity.

Draining rivers are generally of good quality but elevated E. coli levels are of concern where Mui Wo River meets Silvermine Bay beach.

Submarine sewage outfalls at Shek O (primary screening only), Stanley (Bluff Head) and Silvermine Bay.

There are 876 licensed effluent discharges to the WCZ of which more than 50% are from domestic STPs and village houses/septic tanks.

Full connection of houses at Chung Hau village (Lantau) to STW during 2000. Small scale sewerage connections in Mui Wo village in progress.

Sewerage extension being constructed for South Lantau to direct sewage to Siu Ho Wan STW by 2004. Cheung Chau village sewerage system is proposed by 2004.

Pollution from catchment streams is generally low though some have high E. coli levels arising from remaining unsewered areas. Current BOD loads to Port Shelter from catchment rivers are approximately 550 kg/day, almost entirely from domestic sources.

There are 362 licensed effluent discharges to the WCZ including 143 from domestic sources (STPs and village septic tanks) and 123 from industrial and commercial sources. There is a submarine sewage outfall at Sai Kung (secondary treatment).

Both river and marine water quality is good though rising levels of E. coli suggest that the assimilative capacity for sewage inputs is reducing. SMP measures should help to address this problem.

Capacity enhancement will be affected by the naturally limited dispersive capacity of the WCZ.

Organic pollution with a daily BOD load of around 278 kg discharges from Tseng Lan Shue Stream, arising from domestic and institutional wastewater discharges.

There are 138 licensed effluent discharges to the WCZ including 10 discharges from STPs and 79 from industrial and commercial sources.

Assimilative capacity for a number of pollutants is currently very limited due to sewage and industrial wastewater loadings.

Capacity enhancement will also be affected by the naturally limited dispersive capacity of the WCZ.

Significant amounts of organic and faecal pollution from livestock and domestic waste sources discharges from watercourses.

Current BOD loadings are estimated to be approximately 9,600 kg day^-1 of which 57% derives from livestock waste and 26% from domestic sources, mainly unsewered villages.

There are 2803 licensed effluent discharges to the WCZ including 31 STP discharges, 1029 from village houses and septic tanks and 1210 from industrial and commercial sources.

Focused pollution control efforts have increased assimilative capacity though both freshwater and marine water quality and sediments remain significantly polluted in many places. Capacity remains exceeded in terms of organic inputs and significant improvements in the level of treatment and sewerage are required.

Capacity enhancement is affected by the naturally limited dispersive capacity of the WCZ.

Inputs from the two monitored watercourses in the WCZ have relatively low pollution with a BOD loading of approximately 740 kg day^-1.

There is a submarine sewage outfall at Pillar Point. Tuen Mun River carries loadings of untreated sewage (particularly after heavy rain). There are 1149 licensed effluent discharges to the WCZ of which 80% are from industrial and commercial sources.

EIA studies show that sediments in areas near shipyards and floating dock sites are TBT contaminated.

Raw sewage discharges from Sham Tseng Nullah and squatter areas. Pai Min Kok Stream has good water quality but elevated E. coli which may be affecting Anglers' Beach.

There are 1023 licensed effluent discharges to the WCZ of which 832 are from industrial and commercial sources, and 32 are from STPs.

Effluent from Sha Tin and Tai Po STWs discharges to Kai Tak Nullah. This polluted stream enters Kwun Tong Typhoon Shelter which has highly contaminated sediment and poor water quality.

1997 heavy metal discharges to local waters estimated at 3,000kg day^-1.

There are 10,318 licensed effluent discharges of which 10,003 are from industrial and commercial sources and 264 are from institutional and government facilities.

East Kowloon Sewerage Improvement Stage II will extend sewerage infrastructure and reduce wastewater inputs to Kai Tak Nullah.

Tsing Yi Chemical Waste Treatment Plant has reduced heavy metal discharges by 1,700kg day-1. SSDS Stage I and new sewerage infrastructure will further reduce daily metals loads to 500-700 kg day^-1.

Stonecutter's Island STW was opened in 1997 providing chemically enhanced sewage treatment. Further sewers are being constructed (part of the SSDS) in Kowloon and will link to the STW.

When fully implemented, the SSDS is predicted to allow proper treatment of 70% of the sewage entering Victoria Harbour and the Western Anchorage Area, though Phase I discharge at Stonecutters Island will increase pollution locally around the outfall.

In the long term, the SSDS will enhance assimilative capacity although other discharges (eg industrial) must also be addressed and sediment contamination is a long term threat.

Capacity enhancement is affected by the limited dispersive capacity of some parts of the WCZ.