Underlying geology at Tai Long Sai Wan will not support village house development.

This is a comment on proposals by Mr. LAU Wong-fat in LegCo to open up Tai Long Sai Wan to village house development.

Treatment of sewage and wastewater

As with most country park enclaves, there is no existing sewer or planned public sewer at Tai Long Sai Wan, and at present, any sewage treatment will typically be done using on-site septic tanks and soakaway (STS) system.  According to current practice, any new village house would require additional facilities, including their own individual STS system, which would need to comply with relevant standards and regulations, such as EPD’s Practice Note for Professional Person (ProPECC) 5/93.

EPD standards and regulations

According to the relevant EPD standards and regulations, this involves dispersing untreated wastewater into the surrounding soil and relying on the soil to remove polluting material from the wastewater and adequate purification can only be achieved after the wastewater has travelled a fairly long distance through the ground.

Underlying geology of Tai Long Sai Wan

The problem with this is the surface sediment in Tai Long Sai Wan comprises porous and highly permeable sedimentary deposits, which are a mixture of alluvium (Qa), beach deposits (Qb) and debris flow deposits (Qd). Such deposits allow for rapid drainage, so no matter how far the distance, adequate purification cannot be achieved before the wastewater reaches the sea, and because Tai Long Sai Wan is at the mouth of a watershed, this means all of the pollutants in wastewater from any proposed new developments will ultimately be deposited untreated into the sea. See map below.

Summary

The underlying geology in Tai Long Sai Wan will not support the use of on-site septic tanks and soakaway (STS) systems to disperse untreated wastewater into the surrounding soil, pollution will not be filtered, and the discharge of untreated wastewater into the sea will lead to irreparable environmental damage being caused.

On-site septic tanks and soakaway (STS) systems are not a viable option in Tai Long Sai Wan and alternative systems must be used.

In addition to the environmental damage, when such developments are approved, no one factors in the social costs to inshore fishermen, who still blame local pollution as one of the major factors in falling inshore fish stocks in Hong Kong. If Mr. LAU Wong-fat succeeds, who is going to compensate them? 

Following the “polluter pays” principle, if the indigenous villagers want to build village houses in remote and pristine areas, where they know there is no infrastructure to support such developments, surely they should pay for protecting the environment and disposing of their waste in a non-harnful and responsible manner. 

Geological Survey Map (Sheet 8) of Tai Long Sai Wan

Legend for Geological Survey Map