The Northern Basin, covering about 30 percent of Thailand, is located upstream and a major tributary to the main river of the Central Basin, the most prosperous and populated region of the Kingdom. As part of a national strategy to clean up the surface waters of the Kingdom, the Pollution
Control Department embarked on a program to improve the water quality within each region of Thailand. The project utilized a catchment or basin level planning concept rather than a local area level planning, as had been previously practiced in Thailand. The study was undertaken to develop
a 20-year action plan to improve water quality in the northern region's major rivers. Major components of the project include development of a comprehensive Geographic Information System (GIS) database covering basic environmental and pollution sources data; development of intensive water
quality modeling over key reaches of the basin's river network; and development of water quality management action and policy plans for implementation to improve water quality throughout the basin. A river pollution index (RPI) for each key reach of the river basin was also formulated
to use in identifying the areas with critical water quality, which would require attention for pollution alleviation over the planning period. The basin water quality planning process consisted of the following key activities: assessment of existing water quality status of each river reach;
establishment of water quality objectives of each river reach; prediction of river water quality over the next 20-year period under different scenarios; determination of the Critical Water Quality Planning Area (CWQPA); prioritization of municipal wastewater treatment; and establishment of
the action and policy plans. Wastewater infrastructure requirements to alleviate water quality problem within the northern river basin were developed using Mike11 models as a tool to predict water quality of each river reach under three scenarios (no treatment, 50% of total wastewater
flow treatment, and 100% of total wastewater treatment) over the 20-year planning period (1997-2016). The key planning objectives are such that at a minimum, by the end of the planning period, water quality in all river reaches be improved or maintained at Class 3 water quality standard
and the RPI in any river reach be no greater than the critical RPI for the specified intended use of that water source. The master plan recommended an establishment of the wastewater treatment infrastructures in 17, 27, and 33 communities along the river reaches by the year 2005, 2010,
and 2015 respectively. The investment costs for each implementation phase were estimated at 122, 42, and 17 million USD, a total of 181 million USD in all. In addition to wastewater treatment infrastructure establishment, the master plan recommended the implementation of a number of nonstructural
programs within each river basin during the first five years of the planning period while Thailand is undergoing economic recovery and no investment funding is available for infrastructure improvement. These programs include, for example, enforcement of the use of septic tanks for riverside
communities, implementation of pig farm pollution control programs, and raising environmental awareness of the general public.
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