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Yuanqing Tong, Centre for Hydrogeology and Environmental Geology, CGS (China)
Jinying Li, Centre for Hydrogeology and Environmental Geology, CGS (China)
Xiuming Wang, Centre for Hydrogeology and Environmental Geology, CGS (China)
Jijiao Fan, Centre for Hydrogeology and Environmental Geology, CGS (China)
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Yimuquan well field is in Nanqi, northwest of Baoding, Hebei Province, People's Republic of China, which is the most important water source for the city's industry and people's daily use. It was developed in 1958, when 21 wells were exploited, with water-yield of 20,000,000m3/a. Hereafter, the water-yield was increasing annually, and reached 60,000,000 m3/a in 1980s. In late of 1980s, the protection zone of the well field was divided, and the local government issued regulations of well field protection zone, which resulted in good effects.
Yimuquan well field is located in the mid-lower part of alluvial fan, with an average height of 30m above sea level and average annual rainfall of 544mm. With the increase of water-yield, the water table decreases. Phreatic water aquifer has been drained of and is confronted with the problem of surface contamination. At present, groundwater depth is 30-50m, mainly shallow layer confined water.
When first exploited in the region, groundwater flowed from northwest to southeast. But with the formation of the funnel, the flow direction has changed and the groundwater flows towards the centre of the funnel. There are three aquifers in the water source region: phreatic water-confined water with its depth of 0-50m and coarse particle material; phreatic water with its depth of 50-140m and medium-sized particle material; phreatic water with its depth of 140-250m and medium and fine particle material. Based on investigation and calculation, in the well field funnel, aquiclude of aeration zone is divided into several areas of different depths. According to the permeability coefficient in the zone of aeration, the groundwater source funnel region is divided into four areas: k≥0.5m/d, 0.5-0.25 m/d, 0.25-0.05 m/d, Q0.05 m/d. In this region, the lithological character, which plays the main role in protecting aeration zone, is clay, and clayey. Thus, according to the protection function of aeration zone, the well field is divided into four grades: excellent (I), medium (II), poor (III), and worse (IV). Protection area of well field is divided into three zones: zone of activity prohibition, with its lag time of bacteria existing 60 days in groundwater; zone of activity limitation (I) and zone of activity limitation (II), which are based on the weakening mechanism of chemical contamination, with its lag time of 10 and 20 years respectively. Different protective measures and demands of the three protection zones are put forward.
At present, in order to meet the demands of dividing protective zones of potable well fields issued recently by EPA of China, new assessment of Yimuquan water field protection zones is being supplemented and revised. Thus, well fields division will be more scientific, its protection improved, and its implementation more feasible.
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