(4) Hydrogeological conditions in the downstream reservoir area of underground reservoir in Yongfu Park, Dagujia River.

The downstream reservoir area of Yongfuyuan underground reservoir, namely the emergency water supply area of Gongjiadao Waterworks, is located in the west of Zhifu District and the east of Fushan District in Yantai City. The scope of investigation is from Yushu Village of Waijiahe below Tushan to Yangshan in Hebei Province to the dam line of Yongfuyuan-Gongjiadao underground reservoir, with emphasis on the coastal areas south of Xiaoshaba Village of Waijiahe and north of Hebei Pass to above the dam of underground reservoir.

1. Spatial distribution and water abundance of water-bearing sand layers

The overburden in this area is mostly of three-layer structure, the upper part is about 3m medium fine sand, the middle part is about 12m cohesive soil layer, and the lower part is 15 ~ 28m thick sandy pebble layer with strong water permeability and permeability coefficient of100 ~ 200m/d.

Plane distribution law of (1) water-bearing sand layer

The area with large sediment thickness of water-bearing sand layer in this area is Beitushan-Nanshangfang-Gongjiadao Waterworks; Near Dongguan-Xiaoshabu; Luanjiatuan West-Puwan Village South; The dam of the underground reservoir clamps the west bank of the river. The thickness of water-bearing sand layer is generally 15 ~ 28m. The sand layer in this area has good continuity, coarse particles and large thickness. The aquifer is divided into two layers: the upper phreatic aquifer and the lower confined aquifer. To the south of Gongjia Island, the relative water-resisting layer in the middle is missing, forming a "skylight". From the contour map of water-bearing sand layer thickness, it can be seen that there are mainly two runoff zones in this area, which are near the intersection of Beitushan-Nanshangfang-Jiahe and south of Luanjiatuan-Puwan Village. The sedimentary law of water-bearing sand layer is consistent with the distribution law of Quaternary, the cutting depth of the ancient river channel basement is large, and the Quaternary sediments on both sides become thinner from thick.

(2) Vertical distribution law of water-bearing sand layer

According to the existing drilling data, the water-bearing sand layers in the upper reaches of Weijiatuan Waijia River and the west of Beitushan-Zhiyang in this area are of binary structure, with few sand layers, generally 1 ~ 3 layers, and the thickness of sand layer is 5 ~ 15m, and the particles become coarse from top to bottom, from medium coarse sand to gravel. The buried depth of the roof of medium-coarse sand layer is generally 5 ~17 ~ 20m; Gravel roof is generally17 ~ 20m. In most other areas of this area, the water-bearing sand layer is of ternary structure, and the number of upper sand layers is relatively small, generally 1 ~ 2 layers, with a thickness of 2 ~ 5m. The particles become coarse from top to bottom, and gradually change from medium fine sand to gravel sand, and the buried depth of the sand layer is 7 ~ 10m. The middle sandy layer is generally 2-3 layers with a thickness of 5-20m. The particles become coarse from top to bottom, and gradually change from medium coarse sand to gravel. The buried depth of the sand layer roof is generally 10 ~ 18m, with gravel layer at the lower part and clay lens at the local part.

(3) Water abundance of water-bearing sand layer

According to the drilling and pumping test data, the water-bearing sand layer in this area is closely related to the thickness, particle size and sorting of sand layer. Its water-rich characteristics are: the unit water inflow of drilling holes with large sand layer thickness is large, the better the sorting property is, and the coarser the particle size is, the stronger the water-rich property is.

The section with water-bearing sand layer thickness greater than 15m in this area has the best water yield, the permeability coefficient is 70 ~ 100 m/d, and the single well water inflow can be greater than 2000m3/d, which is mainly distributed in the vicinity of Dongguan-Xiaoshaba and Beitushan-Nanshangfang-Gongjiadao Waterworks, as well as the downstream of the dam line of underground reservoirs and the west bank of rivers. It is a favorable location for arranging water pipelines. There is a water-bearing sand layer with a thickness of 10 ~ 15m around it, and the water inflow of a single well is between 1000 ~ 2000m3/d, while the water inflow of other sections is relatively poor, and the water inflow of a single well is generally less than1000m3/d. ..

2. Dynamic characteristics of groundwater

The main factors affecting the dynamic change of groundwater in this area are mining, precipitation and surface water bodies. There are two types of groundwater in this area: phreatic water and confined water. Because of the obvious difference in water-bearing characteristics, the groundwater dynamics are also obviously different.

(1) diving

The groundwater aquifer in this area is directly recharged by atmospheric precipitation and surface water infiltration, and its dynamics are obviously affected by precipitation. Generally, May-June is the dry season, with scarce precipitation and the lowest groundwater level in the whole year. July to September is the rainy season, with increased and concentrated precipitation, and the groundwater level is the highest in the whole year. Due to the construction of many dams on Jiahe River, the rivers in the area basically store water all the year round and directly replenish the phreatic aquifer, which makes the groundwater dynamics of most phreatic aquifers change little, with an annual change of 1 ~ 2m.

(2) Confined water

The dynamic change of confined water in this area is mainly influenced by artificial mining, atmospheric precipitation and surface water. Artificial mining is the main way of groundwater discharge in this area, while atmospheric precipitation and surface water bodies are directly replenished to the confined aquifer through the overflow and air leakage holes of the aquifer. The dynamic change of groundwater level is obviously related to artificial mining, atmospheric precipitation and surface water bodies. In the dry season, the exploitation amount increases, the recharge amount decreases, the groundwater level continues to drop, the recharge amount of groundwater increases in the wet season, and the water level rises slowly. Due to the layer-by-layer water storage in the area, the river channel basically keeps water all the year round, which plays a great role in maintaining the groundwater level, and the groundwater level in the area changes by 2 ~ 5m every year.

3. Groundwater hydrochemical characteristics

Influenced by topography, stratum lithology, runoff conditions, human activities and distance from the sea, the hydrochemical characteristics of groundwater in this area have obvious zoning. From south to north, from the piedmont to the lower reaches of both banks of the river, the groundwater quality gradually becomes salty and worse. TDS of groundwater increases from about 0.5g/L to 1 ~ 2g/L at the dam line of underground reservoir, and increases to 7.0g/L at the place where rivers enter the sea. The Cl- content in Jiahe Estuary increased from less than 100mg/L to 3600 mg/L.. Hydrochemical types range from simple to complex, from Cl-

S

O-Ca2+Na+Mg2+ water →Cl-Ca2+Na+Mg2+ water →Cl-Ca2+Na+Mg2+ water →Cl+-Na+ water, which reflects the law that the content of soluble salts gradually increases in the process of groundwater runoff from upstream to downstream in this area, and seawater intrusion is caused by artificial exploitation in offshore areas.

4. Present situation of groundwater development and utilization

The groundwater in the area is highly utilized, and Gongjiadao Water Plant (formerly the Second Water Plant), Ximou Water Plant and Yantai Power Plant have been built successively. In addition, Foshan has its own industrial water sources and water for agricultural exploitation. According to statistics, the actual exploitation of groundwater in the survey area is about 27,000m3/d at present.

5. Groundwater quality in the downstream area of Yongfuyuan underground reservoir

According to groundwater monitoring data, the water quality in the downstream reservoir area of Yongfuyuan underground reservoir is poor. In the area of about 5km2 along the Jiahe River near the dam line, due to the influence of seawater immersion in front of the dam, the Cl- content is mostly above 200 ~ 250mg/L, and locally exceeds 500mg/L near the dam line, which exceeds the sanitary standard for drinking water (the upper limit is 250mg/L).

Due to the large amount of seawater infiltration before the completion of the reservoir, the groundwater in this area can not meet the hygienic standard of drinking water. Therefore, it is necessary to replace the water bodies in this area, extract brackish water for light supplement, and recharge with Jiahe surface water and abandoned water from menlou reservoir construction to meet the water quality requirements of urban water supply.