Septic tanks and soakaway pits (STS) systems will not work in country park enclaves

The Town Planning Board has recently sought comments on three Draft Outline Zoning Plans for areas in “country park enclaves”, namely:

1. Hoi Ha - Draft Hoi Ha Outline Zoning Plan No. S/NE-HH/1;

2. Pak Lap - Draft Pak Lap Outline Zoning Plan No. S/SK-PL/1;

3. So Lo Pun - Draft So Lo Pun Outline Zoning Plan No. S/NE-SLP/1.

In terms of dealing with sewage issues, there is no existing public sewer or planned sewerage project in any of these enclaves 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 each property having their own individual STS system and these would need to comply with relevant standards and regulations, such as EPD’s Practice Note for Professional Person (ProPECC) 5/93. According to the relevant EPD standards and regulations (Guidance Notes on Discharges from Village Houses¹), this means:

1. Dispersing untreated wastewater into the surrounding soil and relying on the soil to remove polluting material from the wastewater;

2. Polluting material being removed from the wastewater only after it has travelled a long distance in the soil; and

3. An STS system is not feasible in areas with a high ground water table.

This is accepted policy. According to the Minutes of 1032^nd  Meeting of the Town Planning Board held on 26.4.2013³, at Para 82, the Chairman of the Town Planning Board stated:

“ … on sewerage concern, the use of septic tanks for sewage treatment purpose in Small House developments was common and acceptable”²

Unfortunately, this statement and the Government’s whole approach to STS systems in these enclaves is wrong, for the following reasons:  

Issue 1 – The underlying geology in these enclaves will not support the use of STS systems

The use of STS systems for sewage treatment purpose in Small House developments, as proposed in the Draft Outline Zoning Plans is not acceptable, 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 these enclaves.

The surface sediment is porous and highly permeable

The first problem is the superficial surface sediment in each of these enclaves comprises porous and permeable sedimentary deposits, as follows:

1. The surface sediment in Hoi Ha is a mixture of alluvium, beach deposits and debris flow deposits.

2. The surface sediment in Pak Lap is a mixture of alluvium and beach deposits.

3. The surface sediment in So Lo Pun is a mixture of terraced alluvium, debris flow deposits and estuarine and intertidal deposits.

All of these deposits are porous and permeable and allow for rapid drainage, so no matter how far the distance, adequate purification cannot be achieved and because each of these enclaves is at the mouth of a watercourse, this means all of the pollutants in the wastewater will ultimately be deposited untreated into the sea.

See the Geological Survey maps below: 

Hong Kong Geological Survey map (Sheet 8 – Sai Kung) - Geology at Hoi Ha³

Key:  Alluvium (Qa), Beach Deposits (Qb) and Debris Flow Deposits (Qd)

Hong Kong Geological Survey map (Sheet 12- Clearwater Bay) - Geology at Pak Lap⁴

Key:  Alluvium (Qa) and Beach Deposits (Qb)

Hong Kong Geological Survey map (Sheet 3 – Sheung Shui) - Geology at So Lo Pun⁵

Key:  Alluvium (Qpa), Debris Flow Deposits (Qpd) and Estuarine and Intertidal Deposits (Qi)

Issue 2 – The underlying geology means these enclaves are susceptible to alluvial flooding

The second problem is that because of these deposits are permeable and lie on top of impermeable deposits and because each of these enclaves is on a watercourse, it is susceptible to alluvial flooding. Alluvial (or permeable superficial deposits) flooding occurs where rivers or streams are hydraulically connected to alluvial material because the river valley comprises permeable deposits overlying impermeable rocks. See an illustration of how this occurs in the diagram below:

Diagram illustrating how alluvial flooding occurs⁶

Evidence of Alluvial Flooding in the three enclaves

One of the most obvious signs of this in such areas is the presence of surface flooding and illustrations provided in each of the Draft Outline Zoning Plans shows evidence to suggest that alluvial flooding is taking place in each of these enclaves. See the pictures below:

Figure 5c in TPB Paper 9368 - Draft Hoi Ha Outline Zoning Plan

The water logging in Photo 4, suggesting the presence of a high water table as a result of Alluvial Flooding

Plan 12 in TPB Paper 9420 – Draft Pak Lap Outline Zoning Plan

The presence of “water ferns”, suggesting the presence of a high water table as a result of Alluvial Flooding

Figure 5c in TPB Paper 9331 - Draft So Lo Pun Outline Zoning Plan

 Freshwater Marshes at the Central Part of So Lo Pun. The water logging in Photo 10, suggesting the presence of a high water table as a result of Alluvial Flooding

In such systems, the groundwater in the alluvial deposits and the stream are hydraulically connected, which means they are not separate, but are part of the same interconnected system. The implications of this on allowing the use of STS systems in each of these enclaves are considerable:

1. Polluting material will not be removed from the wastewater, but will flow untreated directly through the underlying sedimentary deposits into the stream;

2. On-site septic tanks and soakaway (STS) systems will not function because of the high ground water table in each of these enclaves; and

3. Buffer zones will not work because of the hydraulic connectivity between the groundwater in the alluvial deposits and the streams.

The implications for human health and the likely impact on the environment are of even more concern

Issue 3 - Threat to human health

Outbreaks of groundwater borne pathogens linked to STS systems in the USA⁷

According to investigations conducted in the Northwest United States, outbreaks of groundwater borne viral pathogens linked to Septic Tank Systems have been documented in several locations, with the following significant findings:

1. More than 400 people were infected with gastroenteritis related to contaminated groundwater in 1995;

2. A number of major outbreaks of gastroenteritis have been attributed Norwalk-like virus in numerous states; and

3. Improperly constructed drainfields, high water tables or inappropriate geological settings can allow pathogenic bacteria and viruses to reach groundwater, where they can survive for days and travel up to 30 metres.

These findings are significant, because they relate to “viral outbreaks”. SARS and Bird Flu are both viral infections and Hong Kong has had outbreaks of both of these diseases in recent years - H5N1 in 1997 and SARS in 2003. Moreover, the threat of a virus with future global pandemic potential reaching, then spreading from Hong Kong has not subsided.

Specific health concerns in Hong Kong

In an article in the South China Morning Post on 15 August 2013¹⁸ on an H7N9 bird flu outbreak in China, the results of a study show: “The H7N9 bird flu that emerged on the mainland in March may be spreading through human faeces”. In respect of these findings, Hong Kong microbiologist Yuen Kwok-yung is quoted as saying: "This has important implications on the infection control strategies for H7N9 virus infection, as the influenza virus in stools may contaminate the surrounding environment".⁸

It should be noted, Hong Kong’s contingency plan for pandemics is mainly geared towards standard control measures like personal and environmental hygiene, social distancing and hospital infection control.

Issue 4 - Threats to species and habitats of conservation and ecological significance

Releasing untreated wastewater into the environment will have devastating consequences⁹

It is widely recognized that conventional septic systems are not adequate for removing nitrate, and only partly remove phosphorus, certain pathogens, and certain other compounds, especially where soils or ground water conditions are marginally suitable. Anything that is not removed by the soil will end up in groundwater. It is important to note the two main nutrient products of STS systems are nitrogen and phosphorous.

Nutrient enrichment of surface waters by nitrogen and phosphorus is one of the leading causes of pollution of lakes, rivers, and coastal bays in the United States. Nutrient enrichment can cause a host of negative ecological effects on streams and lakes, including loss of water clarity, proliferation of aquatic weeds, algae blooms, and drop-offs in dissolved oxygen, a critical factor for fish and other aquatic life.

In terms of the three enclaves, Hoi Ha Wan is home to coral communities and So Lo Pun is home to an Ecologically Important Stream (EIS) and marshland habitats, both of which will be highly susceptible to any increases in nitrogen and phosphorous levels in the groundwater, which because of the local geology will not be filtered by STS systems as planned.

Suspended and bedded sediments (SABS)

In addition to nutrients, Septic Tanks also produce Suspended and Bedded Sediments (SABS). SABS are defined by the US Environmental Protection Agency (EPA) as particulate organic and inorganic matter that suspend in or are carried by the water, and/or accumulate in a loose, unconsolidated form on the bottom of natural water bodies¹⁰.

According to the Civil Engineering and Development Department (CEDD) in Hong Kong:

“… human activities such as sewage discharge generate suspended sediments”¹¹.

The effect SABS have on fish populations include:

1. Behavioral effects, such as inability to see prey or feed normally;

2. Physiological effects, such as gill clogging; and

3. Effects due to sediment deposition, such as burial and suffocation of eggs and larvae.

In terms of the three enclaves, Pak Lap Wan is home to a healthy amphioxus community whilst in So Lo Pun the Ecologically Important Stream (EIS) and its adjoining freshwater marsh support a healthy and natural population of Oryzias curvinotus, all of which will be highly susceptible to the effects of SABS.

How does this relate to the enclaves

The full extent of the problem can be seen when the Proposed Land Use map for each of the enclaves in the Draft Outline Zoning Plan is overlain onto the Hong Kong Geological Survey Map of each of the enclaves, as is done below:

Proposed Land Uses – Figure 11 - Draft Hoi Ha OZP

Overlay of Proposed Land Uses map on

Hong Kong Geological Survey map of Geology at Hoi Ha

Land Use Proposal – Plan 1 - Draft Pak Lap OZP

Overlay of Land Use Proposal map on

Hong Kong Geological Survey map of Geology at Pak Lap

Proposed Land Uses – Figure 12 - Draft So Lo Pun OZP

Overlay of Proposed Land Uses map on

Hong Kong Geological Survey map of Geology at So Lo Pun

Summary

To summarise this information:

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 consequences for the environment.

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.

Conclusion

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.

References

¹See EPD Document “Guidance Notes on Discharges from Village Houses”:

http://www.epd.gov.hk/epd/english/environmentinhk/water/guide_ref/files/guide_wpc_dv.pdf

²See para 82 of the Minutes of 1032^nd  Meeting of the Town Planning Board held on 26.4.2013:

http://www.info.gov.hk/tpb/en/meetings/TPB/Minutes/m1032tpb_e.pdf

³Hong Kong Geological Survey map. Sheet 8 – Sai Kung.

⁴Hong Kong Geological Survey map. Sheet 12 – Clear water Bay.

⁵Hong Kong Geological Survey map. Sheet 3 – Sheung Shui.

⁶Mckenzie,A.A, Bloomfield, J.P, Hulbert, A and Rutter H.K, 2010. Confidence and Groundwater Flood Susceptibility Mapping. [online]  British Geological Survey. Available at:
ncg.nuim.ie/gisruk/materials/proceedings/PDF/6B2.pdf

⁷Septic System Impact of Surface Waters. 2005. Tri-State Water Quality Council.

⁸H7N9 bird flu may be spread through human faeces, research suggests. [online]. SCMP. 15 August 2013 Available at:

www.scmp.com/news/hong-kong/article/1296797/h7n9-bird-flu-may-be-spread-through-human-faeces-research-suggests

⁹Septic System Impact on Surface Waters – A review for the Inland Northwest. 2005. [online] Tri-State Water Quality Council. Available at:

watercenter.montana.edu/training/decisions/landuse/docs/septic_system_impacts.pdf

¹⁰What are Suspended and Bedded Sediments (SABS)? [online] 2003. US Environmental Protection Agency. Available at:  http://water.epa.gov/scitech/datait/tools/warsss/sabs.cfm

¹¹Suspended Sediment in Hong Kong Waters.GEO Report No. 106.[online] By S. Parry.CEDD HKSAR Government. November 2000. Available at:  http://www.cedd.gov.hk/eng/publications/geo_reports/doc/er106.pdf

Note

Hong Kong Geological Survey maps are available from the Maps Publication Centre, Survey and Mapping Office, 23/F, North Point Government Offices, 333 Java Road, North Point, Hong Kong. 

Could Small House development in Country Park enclaves pose a global health threat?

Health threat

In an article in the South China Morning Post on 15 August 2013 on the H7N9 bird flu, the results of a study show:

“The H7N9 bird flu that emerged on the mainland in March may be spreading through human faeces”

In respect of these findings, Hong Kong microbiologist Yuen Kwok-yung is quoted as saying:

"This has important implications on the infection control strategies for H7N9 virus infection, as the influenza virus in stools may contaminate the surrounding environment"

A copy of the article is at the bottom of the page.

Small house development plans in Country Park enclaves

In Hong Kong, Draft Outline Zoning Plans have been drawn up in respect of three Country Park enclaves, Hoi Ha, Pak Lap and So Lo Pun.

In each of the Draft Outline Zoning Plans, it is stated 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.

According to the relevant EPD standards and regulations (Guidance Notes on Discharges from Village Houses), 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. Under Para 24 (b) of the Guidance Notes: “A STS system is not feasible in areas with high ground water table”. Furthermore, pollution would result if a STS is located too near to a beach or a stream. See link to Guidance Notes on Discharges from Village Houses:

http://www.epd.gov.hk/epd/english/environmentinhk/water/guide_ref/files/guide_wpc_dv.pdf

The Chairman of the Town Planning Board does not see an issue with this. According to the Minutes of 1032^nd  Meeting of the Town Planning Board held on 26.4.2013, at Para 82, it is recorded:

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

See link to Minutes of 1032^nd  Meeting of the Town Planning Board held on 26.4.2013:

http://www.info.gov.hk/tpb/en/meetings/TPB/Minutes/m1032tpb_e.pdf

Unfortunately, this statement is factually wrong. The use of septic tanks for sewage treatment purpose in Small House developments, as proposed in the Draft Outline Zoning Plans is not acceptable, 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 Hoi Ha, Pak Lap or So Lo Pun and therefore do not understand, nor have they considered the health risks associated with using STS systems in these areas.

Underlying Geology will not support the use of on-site septic tanks and soakaway (STS) systems in Hoi Ha, Pak Lap or So Lo Pun

The problem is the underlying surface sediment in all of these enclaves are a combination of either alluvium, beach deposits, debris flow deposits or estuarine and intertidal deposits. Such superficial sedimentary deposits are porous and highly permeable and allow for rapid drainage, so no matter how far the distance, interstices in these deposits means adequate purification cannot be achieved through the use of on-site septic tanks and soakaway (STS) systems.

Furthermore, because there are no restrictions on the flow of water through such deposits, they will reflect the level of the water table at any given time. Figure 5c (Photo 4) in TPB Paper 9368 on the Draft Hoi Ha Outline Zoning Plan shows surface water logging, suggesting the presence of a high water table, which means that not only should STS systems not be located in such an area, but if they are human faecal matter will seep into the environment. This is already happening in Hoi Ha from existing systems, as evidenced by E. coli counts from surveys in the bay.

Figure 5c in TPB Paper 9368 – Note the water logging in Photo 4, suggesting the presence of a high water table

The governments own guidelines state: “A STS system is not feasible in areas with high ground water table”.

Comment

Hong Kong’s contingency plan for pandemics is mainly geared towards standard control measures like personal and environmental hygiene, social distancing and hospital infection control.

If 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 these enclaves, how can they have considered the environmental hygiene issues. In fact, are they even aware of them?

Because of this, the Draft Outline Zoning Plans for Hoi Ha, Pak Lap and So Lo Pun are not fit to be use as development planning documents. The government needs to withdraw these documents, go back to the drawing board, do their homework properly and re-submit comprehensive documents to the Town Planning Board, so that the public of Hong Kong and the Town Planning Board are properly briefed. Only then can appropriate decisions be made.

A good start would be for the government to pay a visit to the Maps Publication Centre, Survey and Mapping Office, 23/F, North Point Government Offices, 333 Java Road, North Point and buy Sheets 3, 8 and 12 of the Hong Kong Geological Survey, then asked a trained geologist to look at the maps of the enclave areas, then tell the government what they see.

Message to the Hong Kong Government – these are your maps and millions of dollars were spent compiling them, so you could make informed decisions in cases such as this. Everyone else is using them! Why aren’t you?

SCMP ARTICLE

The following is an article in the South China Morning Post on 15 August 2013:

TEXT OF ARTICLE

H7N9 bird flu may be spread through human faeces, research suggests.

The H7N9 bird flu that emerged on the mainland in March may be spreading through human faeces, as university researchers found the virus in the stools of four out of six people killed by the bug in Zhejiang .

Theoretically, the virus could spread in the same way as severe acute respiratory syndrome (Sars) did during the 2003 outbreak in Amoy Gardens, Kowloon Bay - through sewage pipes - University of Hong Kong microbiologist Yuen Kwok-yung, a top researcher behind the cross-border study, told the South China Morning Post.

"This has important implications on the infection control strategies for H7N9 virus infection, as the influenza virus in stools may contaminate the surrounding environment," Yuen and his team reported.

But the team also suggested that the fact the virus may be transmitted via faeces was the reason why, so far, few cases of human-to-human infection had been recorded, Yuen said.

HKU conducted the joint study with Zhejiang University's First Affiliated Hospital in Hangzhou and published the results in the Clinical Infectious Diseases journal on Tuesday. They tested 12 patients who were admitted to the intensive care unit between April 10 and 23. Half of them have died.

During post-mortem tests, stool samples collected from four of the six fatalities returned positive results for the H7N9 strain.

The rate - 67 per cent - was much higher compared with those found for human flu or H5N1 bird flu, which ranged from 5 per cent to 33 per cent, the report said.

None of the blood or urine samples from the six dead patients carried H7N9. Other tissue samples, from the lung, heart, liver, kidney and bone marrow, also tested negative.

Earlier this month, Chinese researchers said their findings indicated that the H7N9 bird flu "has not gained the ability for efficient sustained transmission from person to person", although a father infected with the deadly virus was believed to have passed it to his daughter in Wuxi , Jiangsu .

In 2003, Hong Kong dealt with the deadly Sars outbreak, after it had first appeared on the mainland in late 2002.

At the Amoy Gardens housing estate 329 people were infected with Sars, of whom 42 died. The cause was traced to the sewage system which, because of its design, released the virus into the air when toilets were flushed.

It is not known whether H7N9 bird flu can be transmitted in the same way, but Yuen believed it was "theoretically possible".

"The efficiency of human-to-human transmission is very poor up until now," he said.

He stressed that the faeces of sick birds were still suspected to be the most common means by which the bird flu virus spreads.

Human waste should be handled more carefully under infection control measures, Yuen said.

The H7N9 virus was first identified in eastern China, with the first known human case reported in March. Thus far there have been 135 confirmed cases and 45 deaths. 

Source

http://www.scmp.com/news/hong-kong/article/1296797/h7n9-bird-flu-may-be-spread-through-human-faeces-research-suggests

Geology will not support the use of On-site septic tanks and (STS) soakaway system at Pak Lap

According to the Minutes of 1032^nd  Meeting of the Town Planning Board held on 26.4.2013, 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 Pak Lap 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 Pak Lap can be found in the Draft Pak Lap Outline Zoning Plan at the following link:

http://www.info.gov.hk/tpb/en/papers/TPB/1044-tpb_9420.pdf

Underlying geology of Pak Lap

The problem with this is the underlying surface sediment in Pak Lap comprises porous and highly permeable sedimentary deposits, which are a mixture of alluvium (Qa) and beach deposits (Qb). 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 discharges into the amphioxus communities in Pak Lap Wan.

Amphioxus communities in Pak Lap Wan

In 2003 - 2004 surveys were conducted by City University of Hong Kong in Pak Lap Wan, to determine the extent of distribution of amphioxus as well as their abundance, habitat preference and community structure. Results showed the presence of amphioxus in shallow water depth between 5 and 23 m with high population abundance being found at some specific locations in Pak Lap Wan.

Sediment analysis indicated that amphioxus was only confined to sediments containing a high percentage of sand and granule, with a median diameter, low organic content and low moisture content. Further research on the habitat requirements of amphioxus was conducted by monitoring the sediment and water quality at one site in Pak Lap Wan from November 2003 to October 2004 and the results indicate that seawater at the amphioxus habitats had two essential characteristics:

1. Oceanic;

2. Low content of suspended solids.

Such findings were consistent with results obtained from laboratory observations, namely that amphioxus could not survive at low salinity and high suspended solids in the water could induce physical damage on the animal’s oral cirri. From this, it was concluded that clear oceanic water combined with sand sediment with low organic content are the most important habitat requirements for amphioxus.

See results of study at the following link:

http://dspace.cityu.edu.hk/handle/2031/4884

Zonings proposed in Draft Pak Lap Outline Zoning Plan (S/SK-PL/1)

Geological Survey Map of Pak Lap village area

Legend of Geological Survey map

Overlay of Draft Pak Lap Outline Zoning Plan on Geological Survey Map of Pak Lap village area

Comment

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

Because of this, the Draft Pak Lap Outline Zoning Plan (S/SK-PL/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 Pak Lap. 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 sensitive amphioxus communities in Pak Lap Wan.

Development at Pak Lap threatens Hong Kong living fossil Amphioxus

Hong Kong is blessed with the presence of three classic living fossils:

1.Amphioxus (Branchiostoma belcheri, B. belcheri tsingtauense, B. malayanum, Epigonichthys culltellus and E. lucayanus);

2. Lingula (Lingula lingua); and

3. Two species of horseshoe crab (Tachypleus tridentatus and Carcinoscorpius rotundicauda)

Amphioxus

Amphioxus belongs to the Cephalochordata, a very small branch of the animal kingdom.

Also known as lancelets, cephalochordates are small, eel-like animals that spend much of their time buried in sand. However, because of their remarkable morphology, they have proved crucial in understanding the morphology and evolution of chordates in general -- including vertebrates.

Water is taken in through the mouth, drawn in by the beating of cilia located on the wheel organ, a set of ridges lying inside the mouth. The water is first filtered by the oral cirri, slender projections that surround the opening of the mouth.

Since cephalochordates have no hard parts, their fossil record is extremely sparse. However, fossil cephalochordates have been found in very old rocks, predating the origin of the vertebrates. Yunnanozoon, from the Cambrian of south China is over 500 million years old and the oldest known cephalochordate fossil^1.

Study on “The ecology and biology of amphioxus in Hong Kong” 

In 2003 - 2004 surveys were conducted by City University of Hong Kong along the coast of Sai Kung at 34 sites in four bays, Nam She Wan, Tai Long Wan, Long Ke Wan, and Pak Lap Wan, to determine the extent of distribution of amphioxus as well as their abundance, habitat preference and community structure.

Results showed that amphioxus are present in shallow water depth between 5 and 23 m in all of the four bays, with high population abundance being found at some specific locations in Tai Long Wan and Pak Lap Wan, with a maximum of 460 and 290 individuals/m², respectively.

Sediment analysis indicated that amphioxus was only confined to sediments containing a high percentage of sand and granule, wth a median diameter, low organic content and low moisture content.

Further research on the habitat requirements of amphioxus was conducted by monitoring the sediment and water quality at one site in Tai Long Wan and another in Pak Lap Wan from November 2003 to October 2004. The results indicate that seawater at the amphioxus habitats had two essential characteristics:

1. Oceanic;

2. Low content of suspended solids.

Such findings were consistent with results obtained from laboratory observations: Amphioxus (B. belcheri) could not survive at low salinity and high suspended solids in the water could induce physical damage on the animal’s oral cirri. 

From this, it was concluded that clear oceanic water combined with sand sediment with low organic content are the most important habitat requirements for amphioxus².

Amphioxus body plan and feeding position (in sediment)³

Amphioxus in real life⁴

Amphioxus feeding tentacles (cilia)⁵

References

¹Description courtesy of University of California – Museum of Palaeontology at:

http://www.ucmp.berkeley.edu/chordata/cephalo.html

²Chen, Yan, The ecology and biology of amphioxus in Hong Kong, 2007, City University, Hong Kong at:

http://dspace.cityu.edu.hk/handle/2031/4884

³Diagram courtesy of (Pearson Education Inc) at:

http://snowbio.wikispaces.com/Lancelet+(fish-like+chordate)

⁴Photos courtesy of Marine Biological Association of the UK at:

http://www.mba.ac.uk/pmf/amphioxus.htm

⁵Cilia image courtesy of Science Daily at:

http://www.sciencedaily.com/releases/2013/02/130206190630.htm

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

Underlying geology will not support the use of on-site septic tanks and soakaway (STS) systems in Hoi Ha, posing a threat to the coral communities in Hoi Ha Wan Marine Park

Introduction

This is a comment on Draft Hoi Ha Outline Zoning (OZP) Plan No. S/NE-HH/1.

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.

Underlying geology of Hoi Ha Village

The problem with this is the underlying surface sediment in Hoi Ha village 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, interstices in these deposits means adequate purification cannot be achieved before the wastewater reaches the sea, and because Hoi Ha village is at the mouth of a watershed, this means all of the pollutants in the wastewater will ultimately be deposited in Hoi Ha Wan.

See the maps at the bottom of the page..

Threat to coral communities in Hoi Ha Wan

Coral communities are sensitive receivers and the coral communities in Hoi Ha Wan lie downstream from Hoi Ha village. The watershed feeds into these communities. Coral communities thrive in nutrient-poor habitats by containing many species whose complex food chains recycle essential nutrients with great efficiency, making them especially sensitive to any process that disrupts recycling. For example, if wastewater is not properly treated nutrients such as nitrogen and phosphorous in the waste can stimulate prolific growth of algae, which overgrows corals, or form algal mats which prevents new polyps from settling and establishing themselves. Worst still, some chemicals in the wastewater could simply kill the more sensitive species of coral in the bay.

Threats to coral communities in Hoi Ha Wan from pollution and sediment specifically highlighted

Hoi Ha Wan is an enclosed bay. When it was designated as an SSSI, one of the stated reasons was because critically the bay was not affected by pollution and the only identified hazard to the reef was that future changes to land use may cause water pollution or sedimentation.  When the Marine Park was designated, pollution was specifically identified as a threat to the coral communities, but water quality in the park was good because there was no large water disposal nearby. It was also noted, the government’s approach to water treatment was not treatment, but disposal, yet this is what is now being planned.

Comment

Given the short distance between Hoi Ha village and the sea and because of the porous and permeable nature of the underlying surface sediment in the area, what is certain is the STS system will not remove pollutants from the wastewater as envisaged. This untreated, nutrient rich mix will then feed into Hoi Ha Wan and over time this will result in the degradation or destruction of the coral communities.

It is important to note, two of the worst nutrient threats to coral communities are excess nitrogen and phosphorous, whilst two of the main nutrient products of STS systems are nitrogen and phosphorous.

Summary

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 Hoi Ha. 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 coral communities in Hoi Ha Wan.

Geological Survey Map of Hoi Ha Village

                                         

Proposed development in Hoi Ha (Draft Hoi Ha Outline Zoning (OZP) Plan No. S/NE-HH/1)

Overlay of proposed development in Hoi Ha village on local geology

Petition

If you want to object to the proposed development in Hoi Ha, please sign the petition here:

http://www.change.org/en-GB/petitions/town-planning-board-hong-kong-residents-only-please