Seeping Sickness...
...Lady Maclehose Village & other facilities guilty of toxic seepage
The majority of New Territories Exempted Houses (NTEH) use septic tank systems (STS). The STS consists of a tank, a soakaway pit and the surrounding soil into which wastewater is finally disposed. These systems collect both toilet wastes and ‘grey water’ (from baths or sinks) through pipes that drain into a buried tank that is separated into 3 layers. Sludge stays at the bottom, “scum” floats on the top and the main body of liquid in the middle which flows from the septic tank into the soakaway pit.
An Environmental Protection Dept. (EPD) publication states that: “when the STS is properly used, maintained and desludged, few solids should leave the tank together with the effluent.” The size of the tank needs to be considered in relation to the average volume of wastewater produced. According to the EPD “overflow from the tank or soakaway pit is polluting and should not be permitted”. “Polluting material is removed” they say, only “after travelling a long distance in the soil. Pollution would result if a STS is located too near to a beach, a stream, a well, etc.”
Following a resident’s complaint about effluents in the water in July 2007, EPD found an extremely high e-coli count (ranging from hundreds up to 2,000 CFU/100 ml of sample) in the stream behind Tsak Yu Wu, SK Country Park. This raised a red flag on the issue of STS when EDP officers found the source of the pollution. The government recreation facility managed by the Leisure & Cultural Services Department (LCSD), the Lady Maclehose Village, had used the same STS since they began over 30 years ago and, while the number of campers has risen drastically since the early days and they now run at capacity (280 campers) most weekends and holidays, change in the STS was not considered.
Damage to a tank had gone unnoticed for years and In addition desludging was not being done on a frequent enough basis. As a result, sewage was overflowing directly into the soil and seeping into the Lung Hang River, from there into the stream behind Tsak Yu Wu and then into Tsam Chuk Wan. A water pumping station (luckily idle at the time) also happened to be downstream from the Lady Maclehose Village.
| Septic tank system (Click image to enlarge) |
Alerted to the problem an EPD inspector insisted that the facility start pumping out
on a daily basis and recommended that they immediately install an onsite sewage treatment plant. For weeks after the discovery, sewage pumping trucks were coming three times per day. Now LCSD have installed a temporary sewage system and are working with government architects on the design of their own plant (due to be completed by the end of 2009). As of January 2008, Explore was told that recent water sampling found the water quality downstream Long Hung River to be in the order of 10s of CFU/100ml of liquid (these measurements vary with the tides, rainfall, etc.) - a magnitude of difference from the e-coli count in September 2007.
The Lady Maclehose is just one of seven recreation facilities located on Tsam Chuk Wan and all have experienced a surge of popularity (especially since SARS). EPD has stepped up monitoring of the nearby streams and coastline but this attacks the pollution after it occurs. There should be a means to inspect the source facilities and ensure that the STS are adequate and managed properly BEFORE pollutants seep out. And – are there not better ways to manage waste in rural areas?
“Current soakaway systems are cheap for the users but the cost is then shunted to the environment”, says Guang-hao Chen, Associate Professor of Civil & Environmental Engineering at HKUST. Prof. Chen is currently in the midst of a 12 month study for the EPD to develop a low-cost membrane bioreactor (MBR) which would treat sewage from village houses. It involves a special filter which cleans the sewage water so that it can be reused for the flush water. Although Prof. Chen’s research is currently focused on small-scale bioreactors, he says it can be scaled up to handle any size of sewage treatment. He believes that this type of treatment could offer a paradigm shift in thinking about sewage.
In the meantime, the government is scaling up the Sai Kung Sewage Treatment Works and building a new plant at Sha Ha. This plant is expected to enable residents all the way along Tai Mong Tsai Road to Tsam Chuk Wan to eventually be linked to the main sewage line. But this is not something that Prof. Jerry Patchell, also of HKUST, is happy about. “There must be other ways to solve the problem instead of building such a large infrastructure”, he says. “Where there is scattered population – there should be more scaled options. There is no need for the cost and environmental consequences of 5 km long trenches to serve a little village.”
Whether new solutions will be considered or adopted, we don't yet know. In the meantime, the debate goes on.
Further information:
EPD Guidance Notes on Discharges from Village Houses - a handy guide which includes information such as how to determine when to desludge, how desludging is done, and what to do if your STS overflows.