Geology will not support the use of On-site septic tanks and (STS) soakaway system at So Lo Pun.

According to the Minutes of 1032^nd  Meeting of the Town Planning Board held on 26.4.2013, under Agenda Item 9 - Draft So Lo Pun Outline Zoning Plan No. S/NE-SLP/D Preliminary Consideration of a New Plan (TPB Paper No. 9331), at Para 82, it is stated:

“The Chairman said that on sewerage concern, the use of septic tanks for sewage treatment purpose in Small House developments was common and acceptable”

THIS IS WRONG, because the Town Planning Board have NOT BEEN BRIEFED about the GEOLOGICAL CONSTRAINTS of allowing the use of on-site septic tanks and soakaway (STS) systems in So Lo Pun or any of the other Country Park enclaves.

Proposals in Draft OZP for treatment of sewage and wastewater.

According to the Draft OZP, there is no existing sewer or planned public sewer for the area, and at present, each house is typically served with its own on-site septic tanks and soakaway (STS) system. Any increase in residential developments would require additional facilities, including their own individual STS system, which 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 the polluting material from the wastewater and adequate purification can only be achieved after the wastewater has travelled a fairly long distance through the ground. The relevant standards and regulations also note, pollution would result if a STS is located too near to a beach or a stream. 

Details of planned zonings for So Lo Pun can be found in the Draft So Lo Pun Outline Zoning Plan (S/NE-SLP/1) at the following link:

http://www.districtcouncils.gov.hk/north/doc/tc/committee_meetings_doc/dmweic/n_dmweic_2013_032_ch.pdf

Underlying geology of So Lo Pun

The problem with this is the underlying surface sediment in So Lo Pun comprises porous and highly permeable sedimentary deposits, which are a mixture of terraced alluvium (Qpa), debris flow deposits (Qpd) and estuarine and intertidal deposits (Qi). Such deposits allow for rapid drainage, so no matter how far the distance, interstices in these deposits means adequate purification cannot be achieved before the wastewater reaches the sea.

Worse still, the lower reaches of the watershed at So Lo Pun are categorized as an Ecologically Important Stream, which means all of the pollutants in the wastewater will ultimately flow through this Ecologically Important Stream, before being deposited in the sea.

Zonings proposed in Draft So Lo Pun Outline Zoning Plan (S/NE-SLP/1)

Geological Survey Map of So Lo Pun Village

Legend on Geological Survey Map

Overlay of Draft So Lo Pun Outline Zoning Plan on Geological Survey map of So Lo Pun

Comment

The Town Planning Board has NOT BEEN PROPERLY BRIEFED on the Geological Contraints of allowing Small House type development in So Lo Pun.

Because of this, the Draft So Lo Pun Outline Zoning Plan (S/NE-SLP/1) is an INVALID PLANNING DOCUMENT.

The underlying geology will not support the use of on-site septic tanks and soakaway (STS) systems to disperse untreated wastewater into the surrounding soil in So Lo Pun. Pollution will not be filtered as proposed, and the discharge of untreated wastewater into the environment will lead to irreparable damage being caused to the Ecologically Important Stream, Freshwater Marsh and marine environment at So Lo Pun.