Hanying¹，Yan Shi-long¹ , CAO Jin-liang^2,3 Wang gui-xi¹，Ren jian-hui¹, Zhang zhen-kui¹

1 Shanxi Geology investigation institute,Taiyuan,030024；

2 China University of Geosciences,Wuhan 430074;

3 Shanxi province center of Geo-Environment Mornitoring,Taiyuan 030024)

Abstract: Taiyuan basin is the center of polity, economy and culture of Shanxi province. Groundwater is main exploitation layer for industry, agriculture and living in Taiyuan basin. With the development of social economy and improvement of living condition, groundwater resource requirements are on the increase. That brings about a series of change of groundwater system under the influence of human activities. Based on the systemic theory, this paper studies the system structure, formation and distributing of the groundwater in Taiyuan basin, discusses the basic character of Yanshan deformation structure and Himalayan deformation structure, discusses the geological epoch of Taiyuan basin and makes a map of the conformation compendium of Taiyuan broken basin. Based on this, it analyses the rule of change of groundwater table, flow field, formation and development of ground water descent funnel and water quality in Taiyuan basin and Taiyuan city because of the effect of human and nature. It discusses space-time evolvement characters of hydrodynamic field and hydrochemistry field that suffers human activities.

Key words: Taiyuan basin, system structure, descent funnel, hydrodynamic field, hydrochemistry field

Formation and Evolvement of Groundwater System of Taiyuan Basin in Shanxi

1Formation and evolvement of hydrogeologic structure of taiyuan basin in shanxi

1.1 Basic tectonic framework of taiyuan basin

1.1.1 Basic feature of Yanshan deformation structure

Yanshan deformation structure mainly formed in Mesozoic Yanshan period (Upper Jurassic), which establishes the basic tectonic framework of this basin. In Mesozoic, a formation sight alternating anticlinorium and synclinorium appeared in Northwest-Southeast extrusion stress field of Shanxi plot because Kula-Pacific Ocean plate swooped down to Asia continent. Meanwhile deformation structure had the characteristic of right-rotary cut. Because of the effect of central Lishi–Yangquan West-East structure belt, there was mainly Northeast anticlinorium in the North and there was mainly north-north-east synclinorium. Primary zones of fracture were as follows, which formed the boundary of groundwater system of Taiyuan basin (Figure 1).

Xizhou mountain Northeast zone of fracture is developed in the north of Xizhou mountain. It tends towards N45ºE and its length is 100km. Because a series of approximately parallel inverted faultages are developed in this zone, terrane is vertical or inverted and terrane is slick between layers. This formation is the most developed at the bottom of Cambrian. The group piezotropy faultage was changed to normal faultage. Two sides of the faultage was slick between layers and it formed the separated water faultage.

Shilingguan-Kangjiahui latitudinal zone of fracture is the first latitudinal formation zone. It is conjugate with Xizhoushan faultage and longitudinal faultage in Shilingguan. There is metamorphic rock in the north which dives to south and Cambrian-Ordovician single tilted stratum in the south. Minitype folds and fractures are developed in Cambrian shale and marlite nearby zone of fracture and they glide between layers. So this faultage group forms the separated water boundary in the north of Taiyuan basin groundwater system.

Liukefu-zhouhong mountain zone of fracture is one part of southeast zone of fracture of Jingle syncline. Steep stratum and mutual incised faultage makes the terrane in the whole lower Palaeozoic outcrop between 1 and 3km. This is normal faultage gliding between layers. Terrane on the zone of fracture breaks up and it is attenuated. So this faultage group is considered the separated water boundary in the northwest of Taiyuan basin groundwater system.

Shentanggou-Xishe longitudinal zone of fracture in the north of Tunlan river forms the separated water boundary in the west of Taiyuan city groundwater system. There is mainly approximately south-north faultage and concomitant east-west faultage. The middle of it becomes very complex because alkali mixed terrane in Huyanshan intrudes. The whole zone assumes a westering bulgy arc and peripheral lower Paleozoic forms a vault. Arc zone of fracture gliding along the layer is developed in the east, south and west of the intruded terrane.

Shijiaping-Zhangjia river northeast zone of fracture is located at southeast of Xiyan basin in the southeast of Taiyuan. It is composed of diagonal piezotropy faultage and concomitant intruded diorite. The southeast of this faultage rises to between +1601 meters and 1741 meters so that it is higher than Aohui water table and forms the separated water terrane. The middle part is disturbed by latitudinal faultage and there are small developed northwest faultage. Zone of fracture is bounded on the southeast by ShouYang concave and the northwest O₁¹ dolomie of the fault directly contacts southeast fragment（C₂—P₁）. Aohui flow field at the two sides is different and it is considered the separated water boundary in the northwest of Taiyuan basin groundwater system.

Shanglancun-Donglingjing latitudinal zone of fracture intermittently emerges nearby north latitude 38 degrees, which is the second latitudinal faultage in this area. The east is developed in the zone of Huangling-Pingtou and the middle passes through the north of the Dongshan. The east-west positive faultage is developed in the zone of Houcun coal measures and the distance of some faultages reaches 350 meters.

There are three latitudinal zones of fracture near Guanjiayu in the south of Dongshan. Its structural feature is mainly closed parallel piezotropy normal faultage and interphase fold in the east-west direction and it has a tiled gradient descent in the south, which makes the depth of burial of Majiagou limestone descending to the direction of Yuci. The latitudinal structure extends to Shouyang and Niangziguan in the east, which is the permeable passage for karst water’s run-off to the deep of Niangziguan spring.

Pudong is from east-northeast fold strap and extends to the northwest of Qinshui and the east of Taiyuan basin periphery. The fold strap is very complex from Tianzhongshan and Banyu in Jiexiu to Pudong and Shicheng in Pingyao. The main fold is broad anticline and close syncline in N70-80oE direction. The fracture is in the same direction with the fold axis and it appears in the syncline trough in a dense group and in the form of rift valley. These zones of fracture have the characteristic of normal faultage, but faultage mud is developed in the zones and forms lens. There are concomitant sub folds having the characteristic of slick surface and score and they form pressed structure and extrusion strap.

1.1.2 Basic feature of himalayas period deformation structure

India plate moves to north and collides with Eurasia plate after Himalayas movement. The region of Shanxi is affected by south-south-west to north-north-east extrusion because India plate continually moves to north. The plot in the boundary of Eerduosi and Shanxi plot, the zone has the characteristic of right-rotated cut in the north-northeast direction and has tensile stress in each direction because of the rigidity of Eerduosi plot. The stress field has resulted from inverted development of Mesozoic stress field.

Taiyuan fault basin was formed under the northwest-southeast tensile stress. The basin structure is unilateral concave like a dustpan which is deep in the west and shallow in the east. The two sides of the basin are normal faultage and one side of the bottom is controlled by the fringe shovel fracture. There are concomitant sub reverse normal faultage whose direction is parallel with the basin in the basin and have the character of unilateral incline.

The fringe shovel fracture in the fault basin is concomitant with Mesozoic overturned faultage so that it cuts parts of overturned body, such as Xizhou mountain fracture. Another one is tensile shear faultage. It is along the former Mesozoic piezotropy fracture and forms tensility in Cenozoic, such as Qingxu-Jiaocheng fracture.

Taiyuan fault basin is a new fault basin and it is superposed on Mesozoic tectonic setting.

Taiyuan fault basin is one of Cenozoic fault zone in Shanxi platform is situated in middle part of platform and middle part of Fenwei fault zone. It is inserted in the north of Qinshui synclinorium in the northeast direction. The west of it is north-south Luliang anticlinorium and the north is northeast Wutai anticlinorium and the east is north-south Taihang anticlinorium.

Taiyuan basin becomes fault basin being on the base of large synclinorium and it is a new tectonics subregion. So its sedimentary layer is thick and the buried depth of former Zhendan metamorphic rock is large and the foundation is new. Large numbers of boreholes show that underTaiyuan fault basin Cenozoic，it is carboniferous Permian in the horst of Fenyang, Xiaoyi and Taiyuan and it is trias lower Liujiagou group. In addition, it is mainly trias upper Yanchang group in the vast of the area and it is Jurassic Heifeng group under the well of Hucun in Taigu. It is metaseiment containing volcano fragment under late Cenozoic stratum in number 3 well nearby Qixian. Monzonite intrudes under the metaseiment and its absolute age is between 136 and 140 million years. It is supposed that the monzonite belongs to Mesozoic.

Wanjin period controlling fractures in Taiyuan fault basin are all normal faultage. The fractures in different direction trace each other but not incise each other. So the faultage should be the result of new tectonic movement. The former tectonic system acts as bound condition of fault or tectonic setting in Wanjin period. As stated above, new tectonic movement in fault basin has the character of inheritance. Tectonic feature from tertiary to quaternary period is approximately consistent. The fracture movement, especially fringe fracture is active up to now and the fracture in the basin mostly signed off in middle Pleistocene.

North-northeast, east-northeast and north-northwest fractures in fault basin are very developed and become tectonic setting of Taiyuan fault basin. They form tectonic frame which is hunchy faultage and downcast fault in northeast direction. The hunchy faultage forms mountain and downcast fault forms basin.

1.2 Geologic time of formation of Taiyuan basin

Lithosphere of the area rose before middle Jurassic and the whole suffered denudation. Vertical reverse wring of Yanshan movement and vertical extrusion stress became fiercely activated at the end of Jurassic, so that the platform of Shanxi formed anticlinorium and synclinorium and a new Huaxia fracture system with concomitant monzonite intrusion. Until early tertiary the area was in the long-term

Figure1 structure outline map of fault basin in and around Taiyuan

1.Precambrian System ⒉ Cambrian System, Ordovician system 3.Carboniferous System, Permian System 4.Triassic System，

Jurassic system 5.Cenozoic Erathem 6.Yanshanian structure 7.Himalayan structure 8.dorsally syncline 9.normal fault，reversed

fault 10. measured and conjectured structure 11.hot-water spot

denudation stage, so the stratum from Lower Jurassic to Lower Tertiary was absent and Middle Jurassic suffered denudation.At the end of Lower Tertiary, Himalayas movement became fiercely activated and regional stress field changed reversely from Yanshan reverse wring to normal wring. Under the control of new stress field, the original northeast, north-northeast and east-northeast fracture was traced and translated into tensile fracture. At the early of Upper Tertiary north-south normal wring was suddenly enhanced so that superpower northwest-southeast tensile stress was induced. The northeast, north-northeast and east-northeast fracture was further tensed and some faultage sank along the fracture. From then on upper Cenozoic started aggrading and Taiyuan fault entered mature stage.

Fault subsidence mainly goes through two stages which are Pliocene overstep and Quaternary Period drape during its own development process. Fault subsidence continuously sank under tensile stress in Pliocene. Wangwuzu and Chengzizu were filled sediment on the early sediment stage. At that time the range of water area was small and the deeper concave accepted coarser red sediment which was mainly river phase. Wangwuzu had the character of conglomerate.

Hucunzu sediment accepted almost coarser red sediment which was mainly river phase because the water area extended.The middle period Pliocene which was from Xiguzu to Shijiashezu sediment stage was lake basin heyday and Taiyaun fault sank steadily in this period. At that time the lake was widely distributing. Not only Taiyuan fault became a major lakeland ,but also a series of upper Cenozoic fault basin on Shanxi platform which was from north Sangganhe fault to south Weihe fault all went through lakebuilding stages. There was laky basin in Getaiyueshan of Yushe, Wuxiang, Qinxian and Tunliu.At that time the biology was thriving because of moist climate of Taiyuan fault and alternate cold and warm.The deep of laky phase sediment exceeded one thousand meters and the deep in fringe area was about one hundred meters. At the end of Pliocene, the lake shoaled and Yianzu stratum became coarse and contained gypsum crystal. The sediment was mainly river phase in the fringe area. There was also Hongyazu laterite phase sediment because the climate was damp and hot and Lithosphere moved frequently and sediment was weathered. But there was laky phase marlite and shale in Dagouzu. This showed that lake water often pervaded to the fringe of basin. Strong tectinization took place after Pliocene and lake basin in Pliocene almost disappeared. The stratum in the middle of Shanxi also suffered different denudation In Quaternary fault completely started sinking; hence all convexity and fault of Taiyuan faultt draped Fenhe group. Taiyuan basin in the south of Taiyuan city sank to be lake in upper Pleistocene and accepted the lake sediment whose deep was 200 to 300 meters. At the early of Pleistocene, the lithosphere rose and Fenhe cut through laky basin. Fluvial sediment and hilly diluvial deposits started aggrading and the current physiognomy of Taiyuan fault basin was formed until Holocene.

2. The evolution of hydrodynamical field of quaternary groundwater system in taiyuan basin

As far as the Quaternary pore water in Taiyuan basin is concerned, its hydrodynamical field is mainly controlled by physical factor [1] in natual state, pore-space phreatic water is recharged by atmospheric precipitation, surface water and lateral runoff alongside of the basin and its main discharge method is manual exploitation and Evaporation .and its main discharge method is manual exploitation and Evaporation. Before the 1970s, confined water in middle or deeper layer recharged the shallow phreatic water by virtue of upswing leakage because the mining quantity of confined water was so small that confined level is higher than phreatic water level. Since the 1970s, the mining quantity of quaternary pore water in taiyuan basin has been on the increase; in successive years, substantial overmining of ground water has lead to a substantial descent of water level both in area and quantity while the range of drawdown cone has been enlarging,which has resulted a radical change of hydrodynamical field of quaternary groundwater system in the basin. Because of the substantial overming of confined pore water in middle or deeper layer, confined level has been 3-16m widely lower than shallow pore water and confined pore water in middle or deeper layer is recharged by shallow phreatic pore-space water by virtue of downward leakage .confined pore-space water has become the main discharge method of phreatic water in the basin.. For the groundwater system of Taiyuan basin, the discharge quantity is larger than recharge quantity in a normal year, and the water Level of ground water has been declined year by year and exploition and utilization of groundwater by man has become a main discharge method of quaternary pore water in taiyuan basin. Human activities has changed the hydrodynamic field of groundwater system in taiyuan basin and so the system has become a interactional multiplexed system of nature and human activities from a simple natural system. See figures of underground flow field of the basin in different times. (Figure 2-5).

Pore water in loose rock distributes over loess undulating area of the basin, intermontane valley and plain which is the main area.

Containing-water System in the basin has a single tectonics, and grades into a multiple structure in the middle; therefor, ground water gradually grows to shallow phreatic pore-space water and confined pore water in middle or deeper layer from phreatic water .and the basin has gradually lowered toward the central section from the relatively higher sides of constituented by hills and dip plain, and thus formed an open and even landform. Ground water lies in the porous medium and it is characteristic of vertically alternating and horizontal translation. At the upper part of the Bianshan proluvial fan and dip plain, the water-bearing media is made up of sandy gravel and grit, which has a single hierarchy and a great thickness .The ground water has a great depth of burial as well as a great hydraulic gradient .The ground water gives priority to horizontal transmission and is primarily recharged by lateral runoff from bedrock while the vertical transmission is primarily recharged by vertical influent seepage from precipitation. At the lower part of the dip plain and the central section of the basin, the radient of the landform becomes small and the component of the water-bearing media gets fine. The aquifer grades into multiple structure from a single structure, whose monolayer thickness gets thin and whose hierarchies increase in number .The aquitard among the monolayer increases in number and thickness, and the depth of burial of groundwater level get shallow from deep, and the hydraulic gradient gets small from big, and runoff condition weakens .The changs of a series of hydrogeologic factors stated above result in the changes of the movement mode of the groundwater. The movement of groundwater gives priority to vertical alternating movement from horizontal movement .In the extensive and even alluvial plain, horizontal runoff of ground water is considerably feeble and the movement of groundwater gives priority to vertical alternating movement in shallow and middle layer because the hydraulic gradient is quite small. As far as aeration zone and fluctuation belt of water table in plain is concerned, the lithology gives priority to sand loam and grainsize is coarse and soil texture is loose and the depth of burial is shallow .The recharge by precipitation, irrigation and surface water translates into uninterrupted underground flow through the store adjustment of the shallow pore water system. Part of the precipitation infiltrate in the form of leakage crossing the aquitard and recharges the confined pore water in the middle layer below and another part of

Figure2 measured underground flow field of Taiyuan zone in 1965.

Figure3 measured underground flow field of Taiyuan zone in 2002.

Figure4 measured underground flow field of Taiyuan zone in 1989.

Fig 5 measured underground flow field of Taiyuan zone in 2003.

precipitation is consumed in evaporation. The fundamental movement mode of groundwater is vertical alternating movement of ground water..

2.1 Dynamic performance of shallow pore water in taiyuan basin.

The dynamic performance of shallow pore water in Taiyuan basin is mostly affected by atmospheric precipitation, manual exploitation and lateral runoff etc, which is a result of combined influence of multi factors and thus behaves as the cyclical changes of water level with season and weather. Generally, the low flow season begins in March and April each year and the precipitation is scarce during the season and so it is necessary to exploit a great quantity of shallow groundwater to meet the command of agricultural irrigation, which makes the water level fall rapidly until June or July; the rain season usually begins in July and the exploitation of groundwater decreases to a certain extent and precipitation infiltrates acutly which makes the water level rise again sharply. Because of the lag of recharge by precipitation inleakage and recharge of lateral runoff, the high groundwater level lasts until January or February of new Year and the top water level in a year appears.. The dynamic types in this area can be summarized to several types below..

2.1.1 Weather runoff -type.

It mostly appears in loess undulating area and upper part of dip plain and isn't influenced directly by precipitation .And the source of replenishment is mainly underground runoff from mountain area .Ground water lags behind recharge of precipitation. The lowest water level appears during June to September each year. After the flood season, water level rises slowly until the highest water level appears in January_ March next year. Water level begins to fall slowly in March .The dynamical drift of shallow pore water in this area essentially keeps natural state. See the dynamic performance graph of shallow seated groundwater level at Yingxin Street in taiyuan city.

2.1.2 exploitation-weather type. It distributes over the lower part of dip plain and zone of exploitation is the main zone of exploitation of ground water, which has a shallow depth of burial on an average of 4-20m .The source of replenishment of groundwater is mostly underground runoff and precipitation inleakage. Dynamic performance of Groundwater level is greatly affected by exploitation. Secondly, water level is obviously affected by precipitation because of a shallow depth of burial .during the exploitation, there occurs a great drawdown in water level and the low water level generally appears in June-July .with the arrival of flood season, the exploitation quantity decreases and begins to rise due to precipitation and the highest water level in a year appears in October and November. See the dynamic performance graph of shallow seated groundwater level at Yingxin Street in taiyuan city.

2.1.3 Exploitation-hydrology type.

It Mostly distributes over irrigated area in alluvial plain .water depth of burial in Fenhe River alluvial plain is 2 to 10m, whose range of stage is great and often appears in indentation .the variation in water level is affected by surface water irrigation, precipitation inleakage and groundwater mining etc. Because of surface water inleakage caused by spring irrigation, groundwater level rise acutely and the highest water level usually appears in Aprial and May; afterwards ,the Ground water level falls rapidly and then begins to rise again because of precipitation inleakage recharge or ceasing exploitation .See dynamic performance graph of observational well at Zhao village ,Wenshui. The range of water level in a year is 2 to 3m and the range of water level between years is 2 to 5m. 2.1.4 Exploitation-runoff type

It mostly distributes over zone of hopper caused by drawdown in deep layer. The exploitation of water head site resulted in recession of level in deep underground water and caused a widened hydraulic gradient and thus shallow seated groundwater recharged the deep zone water through leaking recharge and the shallow seated groundwater level gradually decreased ,for example, the shallow seated groundwater in Xizhang and Beiying etc gradually run dry and got Discarded.

2.2 Dynamic performance of pore water in deep zone of taiyuan basin.

Deep zone pore water level is restricted by lateral runoff, leaking recharge of shallow seated

groundwater and manual exploitation .the water level presents a downtrend because of a great quantity of exploitation of deep zone pore water. The dynamic performance type may be divided into three sub-types exploitation drop type, runoff -exploitation type and

weather runoff type.

2.2.1 Exploitation-drop type.

This type Distributes over most of alluvial plain and the lower part of dip plain.the water level is mainly dominated by exploitation quantity and physical factor has a feeble effect on Groundwater level .groundwater mining has been increasing rapidly since April and dropped and the water level dropped to lowest point .afterwards precipitation grows in number and exploitation Quantity decreases and thus water level rises again. See the dynamic performance graph of exploitation- drop type in deep zone at Xiaodian.

2.2.2 Runoff- exploitation type.

It distributes over the upper part of alluvial-proluvial fan and spacious Dip plain, which is the main exploitation zone of ground water. Groundwater regime is affected by runoff and exploitation and Groundwater level totally presents a downtrend .during the exploitation, there is a great decreasing amplitude in water level and dynamical drift curve of water level over the years presents a funnel form .Lowest water level in a year appears in March –June. Generally water level begins to rise lagged behind the rain season about one month, which reflects that groundwater movement gives priority to horizontal runoff and that range of water level in a year is 3 to 20m and that range of water level over the years is great. See the dynamic performance graph at Wenshui Kaishan.

2.2.3 Weather-runoff type.

It mostly distributes over hilly ground and Yangqu County where the exploitation quantity is

lesser and range of water level in a year is small and smooth. It is a dull season of water utilization during January to March, and underground runoff underground runoff and recharge are intense while the

variation in water level is smooth .exploitation quantity gradually increases from April and thus water level has a slight drawdown .water level rises again after July because precipitation increases and exploitation quantity decreases.

2.3 Dynamic comparison between shallow layer and middle or deeper layer pore water.

Compare the dynamical drift curve of pore water over the years in shallow layer and middle or deeper layer and it is observed that the curve of shallow layer is relatively steady while the curve of middle or deeper layer has an obvious downtrend. See the dynamic performance graph over the years at Changguankong, Xiaoyi in the basin.

2.4 Forming and evolution of ground water drawdown cone in taiyuan basin.

In recent years ,on the one hand there is a reductive tendency in precipitation in Taiyuan basin, which makes the phreatic recharge decrease; on the other hand the phreatic exploitation quantity is on the increase with the economical development of town and country ,and excessive groundwater abstraction makes underground water resources miss efficient

The dynamic performance graph over the years at Changguankong,Xiaoyi county.

recharge and recovering, and thereby local ground

water level continually drop down and extensive

drawdown cones come into being in urban area and county seat.（See form 1 ）

The deep water zone of hopper in Taiyuan was earliest found in 1965, which centers in Caiyuan water factory and the depth of burial is 16.15 m and water level elevation is 767.0m.closed area of 770m water table contour is about 11.2 km².At the same time, there is a local drawdown cone in Beiying with an area of about 5 km².

In 1972, the closed area of 770m water table contour is up to 74 km² and depth of burial at the center is 33m and water level elevation is 750m .the area of hopper zone extends to 17 km². The depth of burial at the center is 23 m and water level elevation is 755 m.

In 1976, the hopper at Beiying joined with the urban hopper centered in the zoo and Caiyuan water factory. The center of urban hopper transfers southwester because the exploitation degree exploitation degree of Xiaowang village water factory and chemical water factory was increasing. The depth of burial at the center is 46.0 m and water level elevation is 737.80 m.

The depth and area of hopper zone rapidly increased in 1981.The drawdown at the Zoo water factory is largest and depth of burial is 67 m and water level elevation is 716 m. The 770 m water table contour is 25- km long in north and south, 11 km wide in east and west and the closed area is 275 km².

In 1984, the hopper form was relatively steady except that the northern area, and the depth of burial at the center was 71m and the water level elevation was 712m. After 1980 the speed of descent at Beiying hopper sped up and the burial depth of highest hydrostatic level was beyond 90m and the water level elevation was 707.86m. And annual rate of descent was 4.7m. rate of descent of Wusu hopper was as intense as that of Beiying since it was found in 1981 .the depth of burial at the center of Wusu hopper 65.6 m and 128.34m in 2001 with a water level elevation of 654.06m; compared with that of 1984, the rate of descent in 17 years was 3.69 m; depth of burial in 2003 was 128.27 m and water level elevation was 654.13 m..

In 1982, the deep water drawdown cone in Xizhang zone firstly appeared Beigunian village in 1982 and then appeared in Xizhang village. The Lowest water level elevation was 776.91 m and the closed area of 780m water table contour was 15 km2 in 1982 and extended to 48.2 km² in 1984 with a water level elevation of 768.74 m at the center.

Depth of burial at the center of Xizhang hopper was 44.4m in 1990 and water level elevation was 754.76m, and the closed area of water table contour was 57.21km². The hopper in the urban area was 29.2 km long in south and north and 15.5 km wide in east and west; the closed area of 740 m water table contour was 248 km², including 3 dropdown center all together, of which the biggest dropdown center was in urban area with a lowest depth of burial at center of 87.65 m and a water level elevation of 695.24 m. The depth of burial at the center of Xizhang in 1996 was 65m with an open bottom and the closed area of 770 m water table contour was 72 km². The variation of the hopper in urban area was bigger. The range of the Hopper shrunk ,while the single depth increased ;the Hopper was 25km long in south and north and was 12km wide ;the closed area of 740m water table contour was 213km² including 3dropdown center of which the depth of burial of Dama-Qinxian Hopper was deepest (101.4m deep with an elevation of 683.64m)..

Because the drawdown cone in Xizhang was restricted by Geographic conditions ,In 2000 , the closed area of 760m water table contour dropped to 60 km² and depth of burial at the center dropped down to 52.80 and water level elevation dropped down to 749.70- 742.49 m and the 770 m water table contour was linked together with the urban area. The Hopper in Urban area joined with the Hopper in Beiying and thus a tremendous Hopper zone covered the whole urban area of Taiyuan city was formed which distributed between the north of Beiying and the south of Sangei.

In 2003, the depth of burial of the centre of drawdown cone in Xizhang was 63.66 m, and water level elevation was 743.03 m and the closed area of 760mwater table contour was 55 km². The variation of the hopper in urban area was bigger. The 740 m water table contours joined together in the basin including 3 dropdown centers.（see 2003 water level contour map）. The depth of burial of dropdown center in Beiying was 175.06 m and water level elevation was 627.94 m, and the closed area of 700m water table contour was 14 km2. The depth of burial of dropdown center in Wujiabu was 98.45 m and water level elevation was 676.55 m, and the closed area of 730 m water table contour was 55 km2. The depth of burial of dropdown center in Wujiabu was 98.45 m and water level elevation was 676.55 m, and the closed area of 730 m water table contour was 55 km².

The center of drawdown cone in middle or deeper layer in Jiexiu lay around Songgu,Jiexiu. In 1977, the depth of burial of center of Hopper was 41 m and the closed area of 71 m water table contour was 103 km². In 1984, the depth of burial of center of Hopper was 50.47m which was 9.47 m lower than that in 1977 with an Average rate of 1.35 m and the closed area of 720 m water table contour extended to 130 km2. In 2003, the depth of burial of Hopper was 66.22m and the total descent was 64.21m, and the Average rate of descent over the years was 1.78m and the closed area of 720m water table contour was 287km².

The depth of burial of drawdown cone in Bianshan, Wenshui was 64m in 1987 and became 170m in 2003 with a drawdown of 106m, and the Average rate of descent over the years was 6.62m; and the closed area of 730m water table contour was about 104km². The depth of burial of drawdown cone in Bianshan, Wenshui was 64m in 1987 and became 170m in 2003 There are two drawdown cone altogether in Fenyang: one lies in Xinghua town, Fenyang city and the other lies in Tian village, Fenyang city. The drawdown cone in Xinghua town was earliest Found in 1985 and the depth of burial was 18.15m then and became 112.61m in 2003, and the closed area of 730m water table contour was 18km². The drawdown cone in Tian village lay in the west of Fenyang city and was earliest Found in 1987and the depth of burial was about 64m then and became 164.80m in 2003 with a drawdown of 100.8m, and the Average rate of descent over the years was 6.3m, and the closed area of 720m water table contour was 16km².

Form 1 Statistical list of drawdown hopper in middle or deeper layer in Taiyuan basin in 2003

Compare the two maps of flow field measured in August, 2003 and May, 1989 and it is observed that the variation of flow field of shallow pore water isn't great for the entire basin, on the one hand, it is related with the abandon of the shallow well and the reduction of exploitation quantity of shallow seated groundwater, on the other Hand ,it is related with the good adjusting capability and that of shallow seated groundwater is easy to recover. However, the variation of pore water flow field in middle or deeper layer was relatively great. In 1989,only obvious Hoppers appeared in Urban area of Taiyuan city ,Pingyao county, Jiexiu county etc; and groundwater drawdown Hoppers appeared at nearly all of nearly all of county seats such as Taiyuan , Bianshan Jiao cheng City, Wenshui, Fenyang , Xiaoyi, Jiexiu , Pingyao etc.The local water lowering and human activities caused a tremendous Change of Ground water hydrodynamic field. Among others, the recession of level of Hopper in the neighbourhood of Wenshui, Fenyang was up to 5 to 6m/a.

3.The Characteristic and Space Time Evolvement of Hydrochemistry Field in the Basin

3.1 Hydrochemistry characteristic of the basin

3.1.1 Hydrochemistry characteristic of shallow pore water

Shallow pore water in the middle and upper part of clinoplain in the north, east and southwest of the basin is strongly alternate. The degree of mineralization is smaller than 0.5g/l and the type of hydrochemistry is HCO3—Ca.Mg or HCO3—Ca.Na. The type of hydrochemistry is HCO3·SO4—Ca.Mg and the degree of mineralization is 0.5 to 1.0 g/l in the west and northeast of the basin and Bianshan because of the influence of coal stratum in Carboniferous.

The type of shallow pore water of diluvial clinoplain is all HCO3·SO4 or SO4·HCO3, except that the type of water is HCO3 in partial area. The groundwater of this area directly accept side replenishment of Bianshan groundwater and inleakage replenishment of precipitation. The degree of mineralization is higher and it is 3165 mg/l because of finer particle, shallower water table, slower velocity of flow and stronger evaporation. The degree of mineralization is greater than 3 g/l and the type of hydrochemistry is S—M·C. For example, the degree of mineralization is 5.26 g/l and total hardness is 3165 mg/l in Jinyuan, Taiyuan.

Because the content of sulfate ion is generally higher in western area, the type of hydrochemistry in diluvial clinoplain is SO4·HCO3. The distance of flowthrough is short and the particle of unconsolidated sediment is big, so cation exchange adsorption is insufficient and cation is still Ca·Mg. The terrain of the east is very flat and the thickeness of unconsolidated sediment is very big. The type of hydrochemistry in the east is HCO3·SO4 and the type of hydrochemistry in partial area is HCO3 because of finer particle and stronger evaporation. Exchange adsorption of cation takes place in the soil and Na+ exchanges Ca²⁺ and Mg²⁺. The concentration of Na⁺ in the water heightens clearly and the type is HCO3—Na.Ca.

The type of hydrochemistry in alluvial plain is complicated because the buried depth of watertable is shallow and it is affected by human. The type is SO4·Cl or HCO3·Cl and the degree of mineralization is generally 3 to 5g/l. Water in alluvial plain of Taiyuan city is diluted by the water of Fenhe, so the water quality along the Fenhe is very good. The type in Lancun, Zhaozhuang and Xizhai is HCO₃—Ca.Mg and the degree of mineralization is smaller than 1g/l. But the type in the else area is SO₄·HCO₃, SO₄·Cl and HCO₃·Cl.

The type of water in the middle of the basin is NaCl water and the degree of mineralization is 3 to 5 g/l,such as Xiaodian, Beige, Wangda, Nanbaijiazhuang, Ninggu and Yanwu. The ground water discharge in middle of the basin is mainly vertical evaporation and salinity is continuously enriched. Mobility of Cl is very strong, so HCO₃ and SO₄² in the groudwater becomes saturated and starts chemical precipitation. Meanwhile, domestic sewage discharge of basin occupant and wastewater irrigation to farmland creats mobility condition to Cl.

In the last tens years, with a great deal of groundwater exploitation in industry and agriculture, the groundwater table in basin descends year by year. The large area salted earth distributed in qingxu, jiaocheng, wenshui and fenyang is under control generally. The degree of mineralization, total hardness and the content of every ion descend.

The TDS of Shallow pore water in the basin gets higher from north to south and from mountainside to basin center. It is noticeable that TDS chorogram and watertable buried depth figure of shallow pore water is analogical. For example, minima watertable buried area (watertable buried depth<4m) which is located in xiaodianqu(taiyuan), qingxu and xiaoyi,pingyao in south and pore water’s two TDS maxima area(TDS>2000mg/L) just right are inosculated. Evaporation-discharge is one of the upmost discharging manner of this basin shallow pore water. In the area of shallow water table, the water table is related to evaporation and concentration of the groundwater.

3.1.2 Hydrochemistry characteristic of pore water in semideep stratum

Water quality of pore water in semideep stratum is superior to shallow pore water. The hydrochemistry type of basin pore water accords with its hydrodynamic condition.The replenishment area of basin pore water is situated at the north, west and east of Bianshan. The fall of phreatic water surface in this area is big and the velocity of groundwater is quick, so its hydrochemistry type is mainly weight carbonic acid and weight carbonic-sulfuric acid. Runoff area is situated in the middle to south part of the basin and topograph is smooth and the fall of water table is small. The velocity of groundwater is very slow, so the hydrochemistry type is mainly weight carbonic acid-sulfuric acid-chloride whose degree of mineralization is higher. Discharge area is situated in the south of the basin.The hydrochemistry type turns into hypersalinity carbonic acid-chloride and sulfuric acid-chloride because the velocity of groundwater in the area is almost stagnant.

In the north, east and southwest of Taiyuan basin and In the loess hills ,loess 台塬, skirt of proluvial fan and part of Dip plain, and in the both sides of Fenhe River Fenhe River from Lanbun to Sangei and from Xizhai to Sunjiazhai ,the mineralization of water was less than 1 g/l and the water quality was passable and the Type of water chemistry HCO -Ca. Mg or HCO₃-Ca. Na because of the recharge of precipitation and fresh water from bedrock at Bianshan and and a short avenue of runoff and fluvial diluting effect. Affected by upper shallow pore water, the content of Na + is on the high side and the Type of water chemistry is HCO3Na .Ca or HCO₃—Na. In the area from the south of Sangei village, taiyuan to the proluvial fan skirt in the north of Qingxu,from the Yangqu Dashuping to Hou village ,from Taigu Fan village Wenshui Kaishan to Qi county Shangbadong Yipantuo,Xiaoyi Baibiguan and Zhao village etc,the Type of water chemistry is HCO₃. SO₄ or SO₄·. HCO₃. This is caused by recharge of ground water in the coal-bearing rock of Carboniferous System in the upper part of the mountain area which is high in SO4^2-..

From part of the lower part of the dip plain to the alluvial plain , the type of water chemistry is HCO₃ SO₄,mineralization of water is 0.4—1.26g/l;in some area ,the Type of water chemistry is SO₄Cl· HCO₃ or Cl· SO₄ or SO₄ ,for example, the type of water chemistry is SO4Cl· HCO₃ --Mg·Na(Na) and the mineralization of water 1.37—2.43g/l and the total hardness 650—700mg/l in Taiyuan Wusu,Qingxu Echi,and the type of water chemistry is Cl·SO₄--HCO₃ --Ca·Na (Na) and the mineralization of water 1.25-2.91g/l and the total hardness 518-- 2139mg/l in Taiyuan Wujiazhuang,Nanheiyao.and the type of water chemistry is SO₄-- Ca·(Na) and the mineralization of water 1.25-1.54g/l and the total hardness 843.2 --851mg/l and the water quality is bad in Dongzhuang district Taiyuan Jinyuan and Wu Village Qingxu. In these area such as the middle part of the basin,Xiaodian,Wangda,Xigu,south of Baijiazhuang village, Hongshan,Dujiazhuang village, Yanwu,Yanguotou etc,Sealed-in water and the mineralization of water is 1—3g/l.. This is because the pore water in the middle or deeper layer has the character of confined water and semi-confined water and the pore water in this layer is recharged by surface runoff and part of part of atmospheric precipitation just at the top of the Bianshan proluvial fan and basin around. The ground water recharged runs off toward centre of the basin and dissolves out a large quantity of salt during its flow process because the ground water flows particularly slowly.. At the bottom of the basin ,because artesian head is high;besides, the runoff is slow;there is a vertical alternating movement as well.and the precipitation is mainly consumed in land evaporation and there is only a little inleakage particularly in the dry season because the temperature in the basin is higher .Moreover ,because it is affected by human factor and the discharge of industrial sewage and domestic sewage and sewage irrigation and mixed exploitation of pore water in shallow and middle or deeper layer and the leaking recharge of shallow seated groundwater to pore water in middle or deeper layer. All these reasons stated above cause the complication of types of ground water.

3.2 Formative factor analysis of quality of groundwater

The formation and variation of phreatic chemical composition is constrained by many factors which can mainly be summarized as properties of water-bearing media (rock composition), conditions of recharge, runoff and discharge of ground-water, evaporative concentration and human factors.

3.2.1 The effect of water-bearing media character

Groundwater exists and translates in water-bearing media which is pore and cranny. Groundwater dissolves the dissolved salt in the rock and becomes the solution that comprises of ion、molecule、colloform、air and so on. For example, the stratum of Cambrian Ordovician comprises of limestone and contains higher salt of calcium and magnesium, so the kind of groundwater contains higher ions of calcium and magnesium. Coal stratum of carboniferous system contains higher sulfide, so the cranny water in the stratum of clastic rock and carbonate rock form the sulfuric acid water of weight carbonic or the weight carbonic acid water of sulfuric. The sandrock of clastic rock are feldspar quarta sandstone and contain more plagioclase, so the ions of calcium and natrium are higher in the fissured water of clastic rock. Also, the limestone of Fengfengzu in Ordovician contains mass gypsum interlayer. When Fengfengzu lies under the groundwater, dissolution of gypsous makes the quality of karst water deteriorate, and water turns from the weight carbonic acid water to the weight carbonic acid water of sulfuric or the sulfuric acid water of weight carbonic.

3.2.2 The condition of replenishment, flowthrough and drainage and the influence of evaporation and concentration

The condition of replenishment, flowthrough and drainage of groundwater has effect on the accumulation of salinity in the groundwater and transformation of hydrochemistry type. The groundwater in mountainous area commonly has much bicarbonate (carboniferous coal bed exception). The quality of cranny water in drossy terrane is worse than the one in regolith. In the loessial hill and middle-top area of diluvian pie slice, the quality of the groundwater is better because water table is imbedded deeply and the formation of groundwater is mainly dissolving and filtration. In the center of basin or diluvian connect billabong area ,the grain of hydrated bed is thin,and the route of flowthrough is longer, water table is imbedded shallowly,and the condition of flowthrough is bad,so evaporation and concentration have much effect and the quality of water is worse. Middle and deep bed water in basin mainly accept mountainous's groundwater's side replenishment, and accept shallow groundwater across replenishment , so mountain side basin terrane groundwater's quality and shallow groundwater's quality have much effect on middle-deep groundwater's quality.

3.2.3 The influence of the factitious factors

The influence is mainly three wastes, domestic sewage and sewage irrigation. They not only pollute the groundwater but also deteriorate water quality, so fresh water resource reduces. They have the bad effect on the people’s life and they are important factors affecting the water quality of shallow groundwater.

3.3 The space time evolvement of geochemistry surrounding of basin groundwater

3.3.1 Shallow pore water

The quality of shallow pore water in basin is chiefly controlled by water-bearing media’s property, depositional environment, climate and patch track exhaustion, so it offer visibie diapason variation regular pattern. From basin margin to basin center, the degree of mineralization increases and water quality deteriorates.

In basin north, hill and mountainside limon rolling country, the quality of shallow pore water is accepted by human factor faintly and water quality is relative steady. For example, in xiangyangdian, beixiawen(taiyuan), water quality datum indicate that total hardness, degree of mineralization variate smally. In some area water quality have obvious variation, for instance, in xizhang spung drpression (taiyuan), 11 year’s water quality moniroring roven water quality is running down, degree of mineralization, chloridion, sulfate ion present escalation inclination, from 1993 to now, degree of mineralization buidup 164 mg/L, chloridion and sulfate ion for each buidup 28.3 mg/L and 58.2 mg/L. In the alluvial-proluvial plain,, major ion content, total hardness and degree of mineralization in shallow pore water (except some area) of large area of basin all rises. For example, taiyuan chemical industry water head site, water quality is deteriorating, especially the content of five poison is high. From 1993 to 2000, except a little reduction of sulphate acid ion, the reat all have in favour of buidup, catch sight of diag 10. In wujiazhuang which located in chemical industry zone, water quality changed muchly, chloridion, sulfate ion, total hardness and degree of mineralization rise muchly Among them, chloridion content rised from 316 mg/L 1994 to 1613 mg/L 2003, reach 510% range. This show that chemical industry water head site is contaminated muchly by chemical industry. In nulli suffer contaminative area, shallow pore water quality change to good direction because exploitation rising, water table descend, evaporation slack. In case of dacun, vary ion concentration degrdn, cation integrate descend from 514mg/L to 196 mg/L, cation integrate descend from 1542 mg/L to 581.2 mg/L. total hardness descend from 1021 mg/L to 318 mg/L, degree of mineralization descend from 1670 mg/L to 568 mg/L. 3.3.2 Pore water of semideep stratum

Variation regularity of pore water quality in semideep stratum is similar to shallow pore water. In other words, pore water quality in semideep stratum changes regularly from basin margin to basin centre. Water quality of basin margin is superior to the one of basin centre and water quality of the north is superior to the one of the south. Water quality is consistent with the direction of groundwater flow. Figure 11 shows that the direction of groundwater flowthrough in the south of the basin isLuoyangcun-Guxianzhen–Xiashen –Nangufeng. Along this direction, TDS of water, total hardness, SO42- and Cl- gradually increases. Variance of hydrochemistry ingredient reflects the direction of groundwater flow.

Figure10 Change chart of mineralization of water, total hardness and content of chloride ion in the water head site of chemical plant

Figure11 tendency chart of groundwater ingredients with spatial variation

The hydrochemistry type of semideep stratum pore water is more steadier than the one of shallow pore water and the variation of the type is small. Especially in the alluvial fan area and clinoplain area, the condition of groundwater runoff is preferable and the hydrochemistry type is steady for many years, such as the north of Xincheng,Taiyuan and the east of Yuanwo-Beitian, Yuci and Guoli-Houcun-Wenshuiyier,Taigu. On the other hand, the major ion, total hardness and the degree of

mineralization increases slowly because local area suffers pollution from shallow pore water, such as Wujiazhuang in Taiyuan chemical industry zone and Zhaojiazhuang in Xiaoyi. Water quality of alluvial plain area and howe between fans is looking Up. The content of major ion, the degree of mineralization and total hardness in water obviously decreases. For example, the content of Cl- in Duancun,Jiaocheng decreased from 1572.2mg/l in 1994 to 189mg/l in 2003 and total hardness decreased from 698.1mg/l to 181mg/l. The degree of mineralization decreased from 10529.4mg/l to 1219mg/l. The content also decreased in Wuxiu,Taiyuan.

By contrasting the variety hydrochemistry field of basin in 1983 with 2003, it is found that hydrochemistry type of semideep pore water trends to be simple, especially in the middle of basin the variety is obvious. At present the type is H.S and H.C, but in 1983 it is H.S、H.C、S、S.H、S.C、C.S、C.H and so on.

The area in which TDS is 1 to 3 g/L is 1657 km2 and the area in which TDS is 3 to 5g/L is 40 km2 in 1983. The area is 895 km2 in 2003 and TDS is smaller than 3g/L.

It shows that exploition and utilization of groundwater resources in Taiyuan basin accelerates the recycle of groundwater and watertable declines in the middle part of basin. Evaporation and salinisation becomes weaker and brackish water area obviously reduces.