Australian geology expert Kevin Laurie evaluates the sewage systems of Hoi Ha, Pak Lap and So Lo Pun–do these systems constitute sufficient protection for the natural habitats?
I have seen your articles on Hoi Ha – what about doing one on all the enclaves under threat of development, including Tai Long Sai Wan.
I’ve conducted a review of the use of on-septic tanks and soakaway pits (STS) systems to dispose of sewage and wastewater in Hoi Ha, Pak Lap and So Lo Pun. Because of the local geology they won’t work, which means any Small House development in these areas will have to consider different means to dispose of sewage. This is a major problem, which has not been considered by the government or the Town Planning Board in their deliberations. Full details of the problem can be found in the attached blog post:
The keys points on this issue are listed below:
1. On-septic tanks and soakaway pits (STS) systems will not work in Hoi Ha, Pak Lap or So Lo Pun because the underlying geology will not support their use;
2. Each of the proposed development areas in these three enclaves is susceptible to alluvial flooding because of the underlying geology, which even according to the governments own guidelines means STS systems cannot be used in such areas;
3. Buffer zones will not separate the discharges from STS systems from the streams, no matter how great the distance, because the groundwater in the alluvial deposits are hydraulically connected to the water in the stream, which means they are not separate, but are part of the same interconnected system;
4. The use of STS systems in these enclaves also poses an unacceptable health risk. One of the strategies for preventing the spread of a global pandemic from Hong Kong is environmental hygiene, something which using STS systems in these enclaves threatens. On this matter, understanding the implications of the following information is critically important – H7N9 bird flu may be spreading through human faeces and this has important implications on the infection control strategies for the virus, as the influenza virus in stools may contaminate the surrounding environment;
5. The use of STS systems in these enclaves also poses an unacceptable risk to the environment, as wastewater will neither be filtered nor buffered as proposed in the government guidelines, with potentially devastating environmental consequences.
It should be noted, these issues are not confined to these three enclaves. Similar issues are evident in Tai Long Sai Wan and are likely to be present in most of the enclaves under threat of development. This is not selective criticism, it is a straight forward question of geography and the siting of human habitation.
In short, the government needs to find an alternative solution to the use of on-septic tanks and soakaway pits (STS) systems in Hoi Ha, Pak Lap and So Lo Pun and any other enclaves which are situated in similar circumstances.
International Scientific Consultant,
National Dinosaur Museum,