First, the main problems of urban water supply safety
1. The water supply source is single and the resources are insufficient.
Limited by water resources and water supply funds, most cities have a single water supply source, such as Changchun, which is mainly surface water, while most other cities are groundwater. The excessive proportion of groundwater supply leads to long-term overexploitation of groundwater, continuous decline of water level and depletion of groundwater resources, which seriously threatens the safety of urban water supply. Cities are the places where water resources are used most intensively. Generally speaking, the urban area is relatively small, and the groundwater and surface water resources are limited. Especially in the urban areas under construction, most of them are impermeable layers. Rainwater quickly collects and goes side by side, and groundwater recharge decreases, which intensifies the speed of groundwater depletion. In eastern high plains, most cities are short of water, and the groundwater has been in a continuous downward trend.
2. The water pollution has intensified.
Cities are the biggest source of water pollution. The discharge of urban garbage, industrial wastewater and domestic sewage is increasing, the rate of sewage treatment and discharge up to standard is low, and the pollution of surface water and groundwater is serious, which further reduces the available amount of water resources. For example, Changchun, Harbin, Songyuan, dehui city and other cities cannot be used because of groundwater pollution.
3. Water purification and water supply facilities are aging and do not meet the requirements of new water supply quality in the city.
The water supply facilities in many cities have exceeded their service life, and they have been in disrepair for a long time, resulting in serious water leakage. Water cut-off caused by aging of pipe network often happens. Most urban water purification plants are poorly equipped and backward in technology, especially the new water quality standard for urban water supply will be formally implemented, which puts forward stricter requirements for urban water supply facilities.
4. Lack of emergency water supply capacity
In recent years, major water pollution incidents occurred in Songhua River and Mangniu River, which seriously threatened the water supply safety of coastal towns. In the risk of water pollution accidents, almost all cities show insufficient anti-risk ability, which does not meet the requirements of ensuring the safety of urban water supply. There is no emergency plan for urban water supply in most cities, and the water supply capacity can only be maintained. There is no backup water source and water supply facilities, and there is a lack of emergency dispatching ability in an emergency.
Second, the main city standby water supply source
(1) Changchun City
Changchun is a city that is seriously short of water. Urban water supply mainly includes Shitoukoumen Reservoir, Xinlicheng Reservoir and four underground water sources in the city. The project of "Diversing Songhua River into the Great Wall" was put into use on 1998, and the Songhua River water was transferred to Shitoukoumen Reservoir for urban water supply. More than 85% of urban water supply is surface water, and the daily water supply is 60.27× 104m3, and its groundwater is only10.4/kloc-0 /×104m3. Surface water is easy to be polluted, and there is the possibility of sudden pollution. Therefore, the pollution of surface water supply is an important problem for the safety of urban water supply in Changchun. In addition, the "water diversion project" may also be damaged by natural disasters such as earthquakes. In order to deal with the emergency of urban water supply, it is suggested to take the following two emergency measures: first, the stopped water source can be activated; The second is to develop two major water sources, Yitong Valley and Qijiazi, which are located 30 kilometers south of Changchun.
Yitong River water source is located in Leshan-Ma 'an Township, a suburb of Changchun City, with a distribution area of 205.85km2 The exploitation horizon is Quaternary loose rock pore water, with an aquifer thickness of 15 ~ 20m and abundant water. The maximum water inflow of a single well can reach 3000 ~ 5000m3/d. The groundwater reserve is 7.74× 108m3, the mining recharge is19.15×104m3/d, and the recoverable amount is 8.0×/kloc-. However, the pore water of shallow loose rocks has high iron content and needs to be removed.
Qijia Water Source is located in Shuangyang District, 32km away from Changchun City, with a distribution area of186.84km2, including two concentrated mining areas, Yinma River and Yitong River. The mining layer consists of pore phreatic water of loose rocks and fissure pore water of clastic rocks. The thickness of the aquifer is 8 ~ 25m, and the maximum water inflow of a single well is 3000m3/d ... The fissure pore water of tertiary clastic rocks is hidden under the pore water of quaternary loose rocks, and the lithology of the aquifer is sandstone and fine sandstone, and the maximum water inflow of a single well is 1000m3/d ... The groundwater reserve of Yinmahe Basin is 2.53x108m3. The mining recharge amount is 18.74× 104m3/d, and the exploitable amount is10.75×104m3/d. The groundwater reserve in Shuangyang River Basin is 3.10×1d. However, it should be noted that the iron content in shallow groundwater is high, so iron removal treatment is needed.
(2) Baicheng City
Baicheng city is located on the alluvial fan of Taoer River. Groundwater is mainly used for urban water supply. Fan-shaped ground groundwater resources are abundant, and the planned project of "diverting water from tender to white" can meet the long-term water demand of Baicheng city. The possibility of water shortage is not great, and the main hidden danger of water supply safety is groundwater pollution. The fan-shaped aquifer is covered with a thin protective layer, which is sandy soil and the groundwater environment is fragile. As the standby (emergency) water source in Baicheng City, the Neogene Taikang Formation confined water buried under fan-shaped land can be selected. The top of the aquifer is 40-80 m deep, the thickness of the aquifer is10-30 m, the lithology of the aquifer is sandstone and gravel sandstone, and the water inflow of a single well is mostly 2000-3000 m3/d, and the water-rich section can be used as a city backup (optional), but the development of the confined water of Taikang Formation should be well protected, and the groundwater in this layer should not be developed as much as possible except for emergency to avoid pollution.
(3) Songyuan City
Songyuan groundwater accounts for 88% of the total urban water supply. Due to the high cost of water diversion, surface water supply projects have stopped in recent years. Groundwater exploitation horizons include Da 'an Formation confined water, Quaternary confined water, gully diving and Yinlongkeng spring water. In Xincun and Erlong water sources, the Da 'an Formation confined water is exploited, which is mainly used for domestic water; Quaternary diving is mainly used for industrial water. In recent years, the groundwater level of the confined water in Da 'an Formation has decreased greatly, and there is still the potential to expand the spring diversion. The hidden dangers of water supply safety in this city mainly include: first, the second Songhua River is polluted by water, which leads to groundwater pollution; Second, the confined water of Da 'an Formation is exhausted and the resources are insufficient.
As a backup (emergency) water source, on the one hand, the Quaternary confined water can be developed as a backup water source within the protection scope of the existing Xincun and Erlong water sources; On the other hand, it is also necessary to change the existing water supply structure, that is, increase the water diversion and reduce the exploitation of Upper Tertiary confined water as a backup water source. The average discharge of Longkeng Spring Group for many years is 0.5 m3/s, and the diversion flow is 0.4 m3/s, while the current diversion spring is only 0.07 ~ 0.09 m3/s, which has great expansion potential.
The Quaternary confined water within the protection scope of Xincun and Erlong water sources has a buried depth of 35 ~ 68 m, a thickness of 13.9 ~ 55.0m, and the lithology is gravelly medium-coarse sand and gravel, with good water permeability, and the water inflow of a single well is generally greater than 3000 m3/d, with abundant water. The hydrochemical types are low mineralized sodium bicarbonate and sodium magnesium fresh water, which meet the drinking water standard and are suitable for drinking. Within the control range of two water sources, the natural recharge resources of Quaternary confined water are 690× 104m3/a, the exploitation resources are 830× 104m3/a, and the daily water supply is 2.27 × 104m3.
(4) Harbin
There are 7 water sources in Harbin, including 3 surface water sources and 4 underground water sources. The annual groundwater exploitation is 2.383 1× 108m3, accounting for 38.38% of the total water supply, including 0.9023x108m3 for urban domestic water, 0.7123x108m3 for industrial water and 0.7/23x/08m3 for agriculture. Municipal and enterprise-owned groundwater recharge wells are mainly distributed in the built-up area of 156 km2, * * * has 1430 production wells, and the well pattern density is 9. 17 eyes /km2. Farmland irrigation wells 188 1 mouth are distributed in the suburbs of 1480 km2, and the density of wells is 1.27 eyes /km2. The Sifangtai, Zhushuntun and Sanshu surface water sources in Harbin are all located in Harbin section of Songhua River, with Songhua River water as the water supply source. Because there are many towns and factories along the upstream coast, the river water is polluted, especially in the case of sudden pollution, the water supply safety in Harbin will be seriously affected. If necessary, underground water sources such as Jiangbei Songpu and Hasi Sunjiawazi can be used.
(5) Daqing City
The urban water supply in Daqing City is relatively scattered. Except Daqing City, all oil production plants generally have their own water source wells, with as many as 50 water sources. Quaternary confined water and Taikang formation confined water are mainly mined in the west of placanticline, while Cretaceous Mingshui formation confined water is mainly mined in the east of placanticline. In addition, there are three major water transfer projects in Daqing, namely, the North Transfer Project, the Middle Transfer Project and the South Transfer Project. The water diversion project will introduce Nenjiang water into the reservoirs around Daqing and then supply all kinds of water. Among them, the North-to-Middle Transfer is an important surface water source for production and life, and the South Transfer is mainly used for agricultural water. The hidden dangers of water supply safety mainly include: surface water pollution, groundwater pollution and groundwater resource depletion.
(6) Qiqihar City
At present, there are 4 underground water sources 14 wells, 68 water supply wells, 3 enterprise-owned water source wells16 wells and 4,273 agricultural irrigation wells in Qiqihar City, and the density of mechanical wells is 1. 16 eyes /km2. There are two systems in the urban area: municipal water supply mainly for industrial and domestic use and well water supply by enterprises, and decentralized water supply mainly for farmland irrigation in the suburbs. Quaternary pore confined water is mainly exploited for industrial and domestic water supply, Quaternary pore phreatic water is mainly exploited for suburban agricultural water supply, and surface water is used for some industries and agriculture (including domestic water) in Linnanjiang.
In 2003, the groundwater volume in Qiqihar City was 2.8 15× 108m3, and the exploitation modulus was 6.97×104m3/(a km2), in which the domestic water consumption was 0.7397× 108m3 and the industrial water consumption was 0.36438. Part of domestic water comes from surface water (Nenjiang water), and the annual water supply is 0. 1095× 108m3. Permanganate index, dissolved oxygen and ammonia nitrogen in Liuyuan section of Nenjiang River seriously exceeded the standard, accounting for 50%, 25% and 8.3% respectively. In the east of Nenjiang River, groundwater pollution by "three nitrogen" is also increasing year by year. The main hidden danger of urban water supply is river water or groundwater pollution. In case of emergency in urban water supply, standby underground water sources such as workers' huts in the north of the city can be activated (see table 12-2).
Table 12-2 List of groundwater reserve sources in major cities of Songnen Plain
sequential