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Advisory Council on the Environment

Deep Bay Water Quality Regional Control Strategy Study

 

(ACE Paper 55/98)
for information

PURPOSE

The purpose of this paper and the attached Executive Summary of the Deep Bay Water Quality Regional Control Strategy Study is to inform Members of the key findings of the Study and to notify Members of the recommendations on management options, and the actions proposed, to control water quality in Deep Bay.

BACKGROUND

The Hong Kong - Guangdong Environmental Protection Liaison Group (HKGEPLG) has designated Deep Bay as the highest priority study area requiring protective conservation action from both Governments. In December 1993, the HKGEPLG endorsed a study to assess the dispersive and assimilative capacity of Deep Bay and to develop strategic management options to protect the water quality of the Bay from further deterioration. In July 1995, Hong Kong Environmental Protection Department commissioned the Deep Bay Water Quality Regional Control Strategy Study.

As a part of the study, the development trends and land use control systems of the catchment were reviewed and a Pollution Load Inventory was compiled. A suite of mathematical models was developed for determining the assimilative capacity of Deep Bay, which is the maximum pollution load that can be accepted without causing failure of the HKGEPLG jointly-agreed Water Quality Objectives (WQOs). Based on the assimilative capacity, a number of management strategy options were considered and recommendations made.

A new population forecast for Shenzhen became available in mid 1998 and this new information was incorporated into the Study Final Report and Executive Summary issued in August 1998 which were then endorsed at the 10th HKGEPLG Meeting on 19 November 1998.

POLLUTION LOAD AND ASSIMILATIVE CAPACITY OF DEEP BAY

The computed assimilative capacity of Deep Bay and the measured pollution load in 1996 for the bay are given in the following table.
 

  Oxygen demand (tonne BOD /day) Nutrient - Nitrogen (tonne TN /day) Nutrient - Phosphorus (tonne TP /day) Bacteria (E. coli count /day)
Assimilative Capacity 5.2 0.67 0.17 9.8 x 1013
1996 measured Pollution Load 52 22 3.9 9.8 x 1013

Major sources of pollution for Deep Bay include livestock wastes and wastewater from residential, commercial and industrial uses within the catchment. It is clear from the above table that the assimilative capacity was greatly exceeded, and hence non-compliance of the Water Quality Objectives was evident in 1996.

The study also concludes that compliance with the WQO for inorganic nitrogen for the mariculture zone in the outer Bay is hindered by the high concentration of inorganic nitrogen in the Pearl River Estuary, the waters of which exchange with those in Deep Bay. The pollution load to the Pearl River has to be addressed to achieve full compliance for inorganic nitrogen.

ACTIONS ON POLLUTION ABATEMENT TO DATE

A livestock waste control scheme (LWCS) was first introduced in Hong Kong in late 1987. After extensive consultation with the livestock industry, the revised LWCS commenced in mid 1994. The whole of Hong Kong was delineated into Prohibition Areas, Restriction Areas, and Control Areas and effluent discharge standards on BOD5 and SS were imposed according to a staged control programme, and the scheme is scheduled for full implementation by 1999. As a result of the LWCS, organic pollution in terms of BOD5 arising from livestock rearing activities in the Hong Kong side of the catchment has significantly reduced from about 104 tonnes/day in 1988 to about 5 tonnes/day in 1997.

Besides the LWCS, enforcement of the Water Pollution Control Ordinance (WPCO) has resulted in a reduction of pollution load since the declaration of the Deep Bay Water Control Zone in Hong Kong in 1990. As at 1997, organic pollution in terms of BOD5 has been reduced by roughly 80% due to WPCO enforcement

On the Hong Kong side, sewerage networks in the Deep Bay catchment are being constructed mainly under the North District Sewerage Master Plan (SMP) and the Yuen Long & Kam Tin SMP. The North District SMP will provide for the proper collection, treatment, and disposal of wastewater in the Sheung Shui and Fanling area. This comprises an extension of the sewerage network to the east, south and west of Fanling, and provision of village sewerage to 55 villages within the Deep Bay catchment. There is also a component to upgrade the Shek Wu Hui Sewage Treatment Works to handle a flow of 80,000 m3/d. Works under this SMP commenced in late 1997, and is scheduled for completion by 2005.

The Yuen Long & Kam Tin SMP will provide collection, treatment, and disposal of wastewater from Yuen Long, Tin Shui Wai, Kam Tin, San Tin and Ngau Tam Mei. Under the scheme, wastewater will be exported and disposed of at Urmston Road via the North West New Territories Effluent Tunnel. The SMP works commenced in 1993. A study is currently ongoing to review the sewerage and sewage treatment requirements, taking into account the recent and projected population increases for the area. The consultancy study is due to be completed by end of this year.

Livestock waste control, wastewater treatment facilities and sewage export schemes that are already in place in Hong Kong have successfully reduced a significant portion of the pollution load discharged to Deep Bay (Figure 1). However, due to the anticipated substantial development in the catchment in future years, the assimilative capacity will likely continue to be greatly exceeded if no further control actions are taken.

MANAGEMENT STRATEGIES

Substantial further control of the pollution load to Deep Bay should be planned if the assimilative capacity is to be met. In view of the low assimilative capacity of Deep Bay, particularly with respect to nutrients, even advanced treatment of the wastewater streams is insufficient to reduce the pollution load to meet the assimilative capacity. The practical and recommended means is to export waste from the Deep Bay catchment.

For the Hong Kong catchment, wastewater arising from residential, commercial and industrial activities where there is no current or planned treatment should be collected and exported from the Deep Bay catchment. Effluent from the Shek Wu Hui Sewage Treatment Works should also be exported from the catchment, as a long term goal.

Regarding livestock waste, mandatory adoption of dry muck out with other zero discharge methods, such as soakaway pits, is recommended for chicken farms and small pig farms. The pollution load from large pig farms adopting wet muck out method should be further controlled and reduced.

By the year 2000, all livestock farms in the Shenzhen side of the catchment would be removed to districts outside Deep Bay. The remaining waste streams in Shenzhen would therefore be wastewaters arising from residential, commercial and industrial activities. As for the Hong Kong side, the study recommends that effluent from treatment works should be exported from the catchment as a long term goal. The portion of flow where there is no current or planned treatment should also be collected and exported from the Deep Bay catchment.

ACTION REQUIRED

Members are requested to note the findings and recommendations for the management strategy options to control water quality in Deep Bay.

NEXT STEP

We will initiate discussions with the relevant Mainland authorities on the sharing of the assimilative capacity and the measures to be taken to reduce the pollution load from the Guangdong side, and their timing.

Notwithstanding the need to further consider the sharing of the assimilative capacity between the two sides, we will, in support of the policy commitment recently given by the Chief Executive with regard to Deep Bay1 , press ahead with a series of programmes/actions to reduce pollution load from the Hong Kong side and to move towards the goal of meeting the assimilative capacity of Deep Bay. These programmes/actions include :
 

(a) Implement the works programme of the Yuen Long/Kam Tin Sewerage Master Plan (SMP) as mentioned in paragraph 11. Target completion date of the works is around 2003.
(b) Implement the works programme of the Review of the Yuen Long/Kam Tin Sewerage and Sewage Treatment Requirements as mentioned in paragraph 11. The Consultancy Study is still on-going and is expected to be completed later this year. Tentatively, construction works under this review would be complete by 2008.
(c) Construct a second outfall at Urmston Road if required. At present, the NWNT Effluent Export System comprises of a single outfall at Urmston Road whilst a drainage reserve is allowed for a second outfall. A review will be conducted to confirm the need to construct this second outfall. It is expected that majority of the domestic, commercial and industrial wastewater generated in the North West New Territories would be exported from Deep Bay upon completion of items (a) to (c).
(d) Implement the works programme of the North District SMP as mentioned in paragraph 10.
(e) Conduct a study to review the North District SMP. The SMP will be reviewed to handle increase in flow due to the rapid development projected for North District, and to determine a route to export effluent away from Deep Bay as mentioned in paragraph 14.
(f) Implement the works programme of the proposed North District SMP Review. This is subject to the results of item (e) and no programme is available at this stage. It is expected that the majority of the domestic, commercial and industrial wastewater generated in the North East New Territories would be exported from Deep Bay upon completion of items (d) to (f).
(g) Several options were put forward in the Deep Bay Study to reduce livestock waste from large pig farms that are currently adopting wet muck out systems. These options would be considered for further reducing livestock waste loads as mentioned in paragraph 15.

Some of these programmes are ongoing while some are still at an early conceptual stage. It is anticipated that the target completion date for all the actions above is around 2013.

Environmental Protection Department
December 1998


1  In the Policy Objectives booklet on "Improve Our Urban, Rural & Marine Environment" pertaining to the 1998 Policy Address exercise, the HKSAR government has taken forward an initiative "to develop a comprehensive programme of capital works to upgrade the sewerage infrastructure to remove sewage out of Deep Bay".



 

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