Some examples of the main land-based polluting activities sources have been identified by Dato Ahmad Fuad Embi, former Deputy Director-General Drainage and Irrigation Department (pers comm. Dato Ahmad Fuad Embi, former Deputy Director-General Drainage and Irrigation Department, 31 May 2010), based on his knowledge of numerous studies and observations, as:
· Earth Works - Inadequate and incompetent land management practices during land clearance, earthworks, during construction or development activities, result in substantial surface erosion and suspended sediment pollution during high-intensity rain events;
· Wet Markets - In almost all cases, the biggest single contributor of solid waste and biochemical oxygen demand (BOD) to urban drains and rivers (e.g., 70% in Sg Pinang in Penang state). Almost all have waste water without treatment facilities;
· Abattoirs/Slaughterhouses - Also a big contributor of BOD, from blood and animal entrails;
· Chicken Processing Stalls - Usually conveniently situated next to main drains or rivers, to enable flushing of feathers and chicken remains directly to the waterways. This is a big source of BOD;
· Landfills near Rivers - Usually the biggest source of solid wastes when situated on the banks of the river concerned. High flows constantly erode the wastes from the site and the toxic leachate seeps out continuously;
· Squatters on River Reserves - Big sources of solid waste, untreated sewage, together with pest infestation, to the rivers concerned;
· Shared (‘Kongsi’) accommodation for workers at construction sites - These are big sources of solid waste, sewage, etc., as they are not served by any public services or facilities;
· Plastic Bags - Almost all urban rivers have beds heavily lined with plastic bags. Plastic bags are a big source of pollution everywhere, especially at night markets locations;
· Individual Septic Tanks in old housing areas - Old housing areas use septic tank sewage systems which, in most cases, are never or rarely desludged. These are sources of very high BOD concentrations discharged to the drains in such areas;
· Old Sewage Treatment Plants (STPs) not under the national sewerage system management - About 50% of existing STPs are not under the national sewerage services. These are mostly run by private contractors commissioned by the Local Authorities. Most are old ‘end-of-life’ facilities, and release a lot of effluent to drains and rivers;
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· Restaurants and food stalls - Almost all restaurants, food shops, in urban areas release substantial amounts of waste food and fats which end up rotting in the drains in urban areas, making them stink and creating health hazards by breeding disease vectors (mosquitoes, cockroaches, rats);
· Sand Mines in and upsteam of rivers - Sand mining in upper catchment hills cause severe degradation of pristine headwaters, resulting in heavy sedimentation in the river channels;
· Pig Farming Areas - Present Pig Farming areas are all badly regulated, passing out concentrated effluents to rivers, leaving them stinking and dead from the sludge lining up the river banks;
· Aquaculture in tidal flats - Large scale clearing of mangrove areas is a typical result of aquaculture activities, especially in the upper Perak state area. The sludge from prawn farms are toxic and have contaminated many estuaries; and
· Logging of Permanent Forest Reserves - The threatened logging of the Ulu Muda permanent forest reserves by the Kedah State Government can have severe consequences to the catchment, resulting in heavy sedimentation, degradation of water quality, depletion of aquatic and fish life, and would have a permanent effect on the water supply to Sg Muda, especially in the dry season.