The geological environmental problems caused by groundwater are mainly manifested in a series of geological disasters such as seawater intrusion, over-exploitation funnel, land subsidence and ground fissures caused by groundwater over-exploitation.
1. Sea (salty) water intrusion
Sea (salty) water intrusion refers to the phenomenon that sea (salty) water directly infects the fresh water layer due to the decline of land groundwater level.
The sea (salty) water intrusion in this area started at 1976, mainly along the coast of Laizhou Bay. According to the investigation of 1999, the cumulative invasion area is 573.20km2, and the invasion scope has been expanding in recent years, spreading to other areas of the peninsula. In 2002, the invasion area reached 1653.3km2, including Yantai 750.8km2, Qingdao 136km2, Weihai 284.9km2, Weifang 4 13km2 and Dongying 68.6km2.
The general trend of sea (salty) water intrusion is to expand the invasion area and accelerate the speed. For example, the invasion area of 1992 is 982.4km2, which reached 1653.3km2 in 2002, an increase of 670.9km2 compared with 1992, and it is developing at an annual rate of 67. 1km2.
2. Groundwater Overexploitation Funnel
(1) Overview
The exploitation of groundwater resources makes the groundwater level drop in the mining area, changes the natural flow field of groundwater, and forms the groundwater level drop funnel. If the exploitation amount exceeds the recharge amount for a long time (that is, over-exploitation), the groundwater funnel will gradually develop and expand. Since 2000, the dynamic change of groundwater level in the whole region has shown a downward trend. By the end of 2000, there were five shallow groundwater overexploitation areas in the plain area, with a total area of 6280km2, of which Yantai was 1349 km2, and Weifang, Zibo and Dongying had the largest areas, with a total area of 4289km2 (Table 6-6).
Table 6-6 Overview of Shallow Groundwater Overexploitation Area in Shandong Peninsula
(2) Types and hazards of shallow groundwater over-exploitation funnel
More than 20 over-exploitation funnels have been formed in the over-exploitation area of shallow groundwater. See Table 6-7 for some representative funnels, which are mainly divided into fissure karst water and pore water.
Table 6-7 Statistics on the Present Situation of Main Groundwater Overexploitation Funnels in Shandong Peninsula City
The over-exploitation funnel of karst water is represented by the over-exploitation funnel of Dawu water source in Zibo. The water source is located in Dawu Township, Linzi District, Zibo City. The allowable exploitation amount is 39.00× 104m3/d, the average exploitation amount for many years is 5 1.56× 104m3/d, and the actual exploitation amount is 49.00× 1998. At that time, the closed funnel area of 37m water level was 2. 1km2. After the central water level was 36.4m, the water level dropped rapidly and the funnel expanded year by year. 10 central water level drops to-13.8m, and 10 central water level drops by 50.2m. The formation of Dawu Funnel led to the abandonment of many motor wells in this area, and caused a large number of sewage backflow, resulting in groundwater pollution. When 199 1.96 mg/L, the salinity was 3265438, and when 1995, it rose to 479. 14mg/L, which increased by 65438 in five years.
The pore water over-exploitation funnel is represented by Huantai-Guangrao-Shouguang-Hanting-Changyi over-exploitation funnel. Huantai-Guangrao-Shouguang-Hanting-Changyi Overmining Funnels are five independent funnels before 1995. With the continuous increase of groundwater exploitation, the funnel expands correspondingly, and the 0m water level line of groundwater at 1995 connects the funnels to form an east-west belt funnel (Figure 6-5). 1997 The funnel has an area of 22 10km2 and a buried depth of 45.37m ... The formation of the funnel caused a large area of seawater (salty water) intrusion in this area, which made the water shortage more serious. In Huantai section, the pumping and water output of some wells are greatly reduced, resulting in groundwater pollution.
3. Ground subsidence and ground collapse
Land subsidence is a geological phenomenon that groundwater is artificially extracted from loose Quaternary strata, which leads to the compaction of aquifer and its upper soil layer and the vertical and slow loss of ground elevation. For example, near Dongying city in northern Shandong and the Yellow River Delta, the land subsidence caused by over-exploitation of groundwater and oil and gas in 2000 reached 284 ~ 397 mm. In 2002 ~ 2003, the land subsidence was 22 ~ 23mm.
Land subsidence is a geological disaster caused by the change of mechanical relationship between soil and groundwater, which leads to the increase of groundwater velocity and the migration of soil particles in the process of man-made over-exploitation of groundwater. This kind of disaster mostly occurred in Zibo, Jinan, Weifang and other places in the Paleozoic hidden karst development area in central and southern Shandong. For example, Xiye Village, Yiyuan County, Zibo 1978, the coking plant pumped a lot of water, which caused the ground to collapse. To 1989, the ground collapsed at 1 1, with a distribution area of 0.003km2, causing dozens of houses to crack.
In addition to the above-mentioned types of seawater intrusion, over-exploitation funnel, land subsidence and land collapse, there are many types and disasters caused by groundwater in Shandong Peninsula urban agglomeration, such as ground fissures, soil erosion, collapse, landslides, mudslides, land salinization, coastal erosion, vegetation degradation and endemic diseases, which not only worsen the geological and ecological environment, but also cause huge losses to people's lives and property (Table 6-8).
Figure 6-5 Isogram of Groundwater Decline in Ziwei Overexploited Area (slightly modified according to Wang, et al., 2002)
Second, the comprehensive evaluation zoning of groundwater geological environment quality
Principles and methods of comprehensive evaluation
The basic idea of comprehensive evaluation is to decompose the geological environment system into n subsystems, then select evaluation factors from each subsystem, and then superimpose the index values corresponding to each evaluation factor according to the weight value to get the evaluation index of each evaluation unit, that is, the geological environment quality index. The fuzzy quality index proposed in this section is a comprehensive quality index (FQI) obtained by fuzzy mathematical operation. The fuzzy quality index actually reflects the geological environment quality of the evaluation unit. The greater the FQI value, the worse the geological environment quality. The smaller the FQI value, the better the geological environment quality. According to the FQI value, the quality area is divided, with FQI= 1, which is the area with excellent geological environment quality; 1 < fqi ≤ 2, which is a good geological environment area; 2 < fqi ≤ 3, which is a medium geological environment area; 3 < fqi ≤ 4, which is an area with poor geological environment quality; 4 < fqi ≤ 5, which is an area with poor geological environment quality (Figure 6-6).
Table 6-8 List of Geological Environment Problems Caused by Underground Mountain in Shuidong Peninsula Urban Agglomeration Area
Figure 6-6 Comprehensive Evaluation of Geological Environment Quality Caused by Groundwater in Shandong Peninsula Urban Agglomeration
2. Comprehensive evaluation results
In the evaluation, the evaluation units in the region are statistically calculated, the evaluation index values and weights are determined, the fuzzy operation is carried out by microcomputer, the FQI isoline map is automatically generated by MapGIS software, and then the isoline is corrected according to the actual situation of the environmental geological evaluation units, so that the evaluation results are more in line with the actual situation of the study area. Finally, according to the FQI contour map, the geological environment quality of the evaluation area is divided (Figure 6-7).
Figure 6-7 Division of Geological Environment Quality Caused by Groundwater in Shandong Peninsula Urban Agglomeration Area
From the evaluation results, it can be seen that the areas with poor geological environment quality are distributed in the Yellow River Delta, Laizhou Bay coast, boundary river valley, landslide distribution area in the south of Laizhou City and land subsidence and landslide distribution area in the northeast of Qixia City, among which the areas with poor quality are located in the middle and lower reaches of the Yellow River Delta and Dongying and Weibei areas. The areas with medium and good geological environment quality are distributed in the periphery of the areas with poor quality, the Yellow River Plain and some river valleys and coastal plains at the estuary of rivers. The areas with excellent geological environment quality are distributed in the low mountain area of Jiaodong Peninsula, the south of alluvial-diluvial plain in central and southern Shandong and the Yellow River plain.
The evaluation results are basically consistent with the present situation of geological environment in the working area. The poor quality areas have poor geological environment background conditions, developed geological disasters and strong geological environment destruction. For example, the coastal areas of the Yellow River Delta have no fresh water, poor water environment and the highest coastal erosion rate in the whole region. The evaluation results are consistent with the present situation. Excellent area has good geological environment background, excellent water environment, no major pollution sources and less geological disasters, and the evaluation results are consistent with the current situation.
Three, groundwater environmental quality development trend analysis and control measures
1. Analysis on the development trend of groundwater environmental quality
Generally speaking, the development trend of groundwater environmental quality in Shandong Peninsula cities is mainly decline and gradual deterioration. Although some areas have been improved due to the strengthening of governance, such as the seawater intrusion rate in Laizhou Bay has been controlled to some extent, and the problems of groundwater overexploitation and the disconnection of famous springs in karst areas in central and southern Shandong Province have been alleviated to some extent, the overall trend is still mainly downward. From the piedmont to the coastal plain, the pollution will further expand, from point pollution and strip pollution to the surface, from shallow to deep penetration, from the city to the surrounding area. In addition to the direct or indirect infiltration of sewage into the ground, the pollution of fresh water aquifers by salt water or deep high salinity hot water and oilfield water will further occur.
In 2002, the seawater intrusion area exceeded 1653 km2, an increase of 670km2 compared with 1992, with an average annual growth rate of 67. 1km2. The area of over-exploitation funnel has exceeded 628km2. With the extension of mining time and the increase of mining volume, especially the decrease of surface precipitation year by year, all these will inevitably lead to the increase of over-exploitation, and the groundwater level will continue to decline, with the predicted decline rate of 1 ~ 2m per year, and other corresponding geological and environmental problems will continue to occur. Even if the South-to-North Water Transfer Project is fully implemented, it is expected that the situation will not change fundamentally, mainly because the agricultural development in the plain area is a big water user, and water transfer can not solve the problem of agricultural water supply, and it is more likely to aggravate the soil salinization problem that has been slowed down in the plain area. It is suggested that while strengthening water control projects, we should pay attention to the study of groundwater conservation, speed up the study of flood resources utilization, salt water conversion and seawater desalination, and speed up the formulation of emergency water source plans for water crises in large and medium-sized cities. It is not only possible, but also feasible and sustainable to solve the water resources problem in North China. Take measures such as source pollution control, comprehensive water saving, and high-quality optimized water use to improve the utilization rate of water resources. Speeding up the adjustment of regional industrial structure, reforming urban water supply system and opening up sources in an all-round way are the fundamental ways to improve the quality of regional groundwater environment.
2. Groundwater environmental quality control measures
In view of the deterioration of water resources and environment, serious water pollution, uneven distribution of water resources in time and space, serious water shortage in cities and towns and low effective utilization rate of water, the author puts forward the idea of developing circular economy and promoting the sustainable development of water resources and environment from the perspective of economic sustainable development strategy. Circular economy has three main principles, namely, reduction, reuse and recycling. To implement Scientific Outlook on Development's strategic thinking, the main measures are to strengthen scientific planning, scientific monitoring and scientific management, save water, rationally develop and utilize water, improve technology, prevent pollution and expand water sources.
The core of groundwater control countermeasures is to coordinate the development and utilization of groundwater resources with the ecological environment, maintain a benign cycle of water environment system and realize the optimal joint development and utilization of water resources system. It is a complex systematic project to meet the demand of social development for water resources and promote the sustained and stable development of social economy, which requires the joint efforts and mutual support of many parties. Through comprehensive and in-depth analysis and research on the distribution conditions, present situation and existing problems of water resources development and utilization in the Peninsula and Shandong Province, the following management countermeasures are put forward:
1) Unified planning, comprehensive development, joint dispatching and rational utilization of water resources.
2) Strengthen the monitoring of groundwater dynamic geological environment and guide the rational development and utilization of groundwater.
3) Strengthen water-saving management, raise awareness of saving and popularize water-saving technology.
4) Strengthen the investigation and evaluation of groundwater resources to provide a basis for rational development of water sources.
5) Protect the underground aquifer system to prevent groundwater from being polluted, especially in areas where the protection function of the underground aquifer system is fragile.