Environment-friendly groundwater recharge and source supplementation technical method for northern karst water system supplementation area

Abstract

The invention provides a northern karst water system supply area underground water environment-friendly recharge source supplementing technical method, and relates to the technical field of hydrogeology. According to the method, urban construction engineering and recharge engineering in northern karst areas are combined, rainwater collection, treatment and recharge are achieved, downstream water quality deterioration caused by underground water recharge can be avoided, it is ensured that the recharge source supplementing process is safe and environmentally friendly, and organic combination of source supplementing and water protecting is achieved. The method breaks through the limitation of a traditional sponge city rainwater infiltration project, urban rainwater can be efficiently collected, accurate and efficient recharge of a specific karst aquifer can be achieved according to the geological characteristics of the northern karst area and the distribution characteristics of the karst aquifer, karst groundwater reserve is supplemented from the source, and the construction period is shortened. The stable runoff of karst spring water is effectively maintained, the risk of spring water depletion and cutoff is fundamentally reduced, and the core target of groundwater recharge source supplementation is achieved.

Description

Technical Field

[0001] This invention relates to the field of hydrogeology, specifically to a method for environmentally friendly groundwater recharge in the northern karst water system recharge area. Background Technology

[0002] Water resources are a fundamental natural resource and a strategic economic resource that is crucial to the national economy and people's livelihood. Therefore, rainwater harvesting is valued both domestically and internationally. Urban rainwater harvesting can not only reduce urban flood disasters and reduce the pressure on municipal pipe networks, but also mitigate non-point source pollution from rainwater, improve the urban water environment, and realize the resource utilization of rainfall.

[0003] However, current rainwater harvesting and infiltration projects all adopt sponge city technology, which uses specialized infiltration modules to infiltrate treated rainwater into the ground to reduce runoff. The purpose is to prevent urban flooding and waterlogging. In other words, current rainwater harvesting and infiltration projects do not consider the target aquifer for recharge and cannot achieve the purpose of recharge and replenishment. Summary of the Invention

[0004] In response to the problem of poor recharge effect of current rainwater harvesting and infiltration projects, the environmentally friendly recharge technology for groundwater in the northern karst water system recharge area provided in this application can effectively collect rainwater and achieve the purpose of recharge.

[0005] The technical solution adopted by this invention to solve its technical problem is: The environmentally friendly groundwater recharge technology for the karst water system recharge area in northern China includes the following steps. S1, determine the direction of groundwater flow in the area where the surface water collection zone is located, and calculate the hydraulic gradient; S2, based on the identified groundwater flow direction, deploy observation wells downstream of the surface water collection area; S3, construct the observation well and calculate the permeability coefficient k of the area where the surface water collection zone is located; S4. Determine the location of the recharge well based on the location of the observation well and the permeability coefficient of the area where the surface water collection zone is located; S5, Recharge Well Construction: Determine the type and characteristics of the recharge aquifer, and calculate the recharge volume per well based on the type of recharge aquifer. S6, Set up water purification tanks and water storage tanks according to the site conditions of the surface water collection area; S7, Verify the reinjection volume of the reinjection well and determine the standard single-well reinjection volume of the reinjection well; S8, Recharge Monitoring.

[0006] Further, step S3 includes the following steps: 3.1 Drilling and core drilling, and calculating the karst fracture rate of the core samples in segments; 3.2 Pump water to flush the well until the water is clear and the sand is clean; 3.3 The permeability coefficient k of the surface water collection area was calculated through pumping tests.

[0007] Furthermore, the pumping test adopts steady-flow pumping, and the water level stabilization time is not less than 8 hours.

[0008] Furthermore, when calculating the permeability coefficient k, 3.3.1 The karst strata in the area where the surface water collection area is located are relatively thin, and the area is a karst phreatic zone. Furthermore, there are no observation wells around the observation well. The formula for calculating the permeability coefficient k is... ; 3.3.2 The karst strata in the area where the surface water collection area is located are relatively thin. The area is a karst phreatic zone, and there are observation wells around the observation wells. The formula for calculating the permeability coefficient k is: ; 3.3.3 The karst strata in the area where the surface water collection area is located are relatively thin. The area is a confined karst water zone with overburden, and there are no observation wells around the observation well. The formula for calculating the permeability coefficient k is: ; 3.3.4 The karst strata in the area where the surface water collection area is located are relatively thin. The area is a confined karst water zone with overburden, and there are observation wells around the observation wells. The formula for calculating the permeability coefficient k is: ; 3.3.5 Given the relatively thick karst strata in the surface water collection area, and the relatively uniform development of karst fissures, incomplete wells are used for observation. The formula for calculating the permeability coefficient k is: ; 3.3.6 Given the significant thickness of the karst strata in the surface water collection area, and the presence of fractured karst formations in the central part of the karst strata, incomplete wells are used for observation. The formula for calculating the permeability coefficient k is: ; 3.3.7 The karst strata in the area where the surface water collection area is located are thick and the water level is deep. The karst strata are relatively uniformly developed with fissures. Therefore, the observation wells are non-complete wells, and the permeability coefficient k of the karst section above the water level is calculated through water injection tests.

[0009] Furthermore, if there is an observable well around the observation well, then that well is selected as the observation well; if there are multiple observable wells around the observation well, then the well closest to the observation well is selected as the observation well.

[0010] Furthermore, according to the groundwater flow direction, the recharge well is located upstream of the observation well, and the distance between the recharge well and the observation well is greater than or equal to 6m. If there is a water source protection target downstream of the recharge well, then the recharge well is located outside the boundary of the recharge area of ​​the recharge well.

[0011] Furthermore, in step S5, For recharge wells in unconfined aquifers, the formula for calculating the recharge volume per well is as follows: ； For recharge wells in confined aquifers, the formula for calculating the recharge volume per well is as follows: 。

[0012] Further, step S7 includes the following steps: 7.1 Calculate the single-well verification recharge volume. The formula for calculating the single-well verification recharge volume is as follows: ； 7.2 Verify the reinjection volume of a single well With single well reinjection volume Compare; like Then This refers to the standard single-well recharge volume of the recharge well; like Then and The smaller value in the equation is the standard reinjection volume of the reinjection well.

[0013] Furthermore, the purification tank is provided with a horizontal reverse filter layer, which includes, in sequence along the water flow direction, a homogeneous medium sand layer, a homogeneous coarse sand layer, and a homogeneous gravel layer.

[0014] Furthermore, the reinjection well is located within the reservoir, and a steel pipe filter is fixedly installed at the inlet of the reinjection well, the porosity of which is 30-35%.

[0015] The beneficial effects of this invention are: 1. The groundwater environmental protection recharge technology for the northern karst water system recharge area provided in this application overcomes the limitations of traditional sponge city rainwater infiltration projects. It not only efficiently collects urban rainwater but also, based on the geological characteristics and distribution features of karst aquifers in northern karst regions, achieves precise and efficient recharge of specific karst aquifers, replenishing karst groundwater reserves from the source, effectively maintaining stable runoff of karst springs, and fundamentally reducing the risk of spring depletion and flow interruption, thus achieving the core objective of groundwater recharge. Simultaneously, this technology retains the original advantages of rainwater harvesting and utilization, effectively reducing urban surface runoff, lowering the risk of urban stormwater disasters and the pressure on municipal drainage networks, realizing the resource utilization of rainwater resources, and taking into account multiple benefits such as ecological protection, flood control and drainage, and water resource supply, thus meeting the development needs of northern karst regions.

[0016] 2. The environmentally friendly groundwater recharge technology for the northern karst water system recharge area provided in this application clarifies the integration path between urban construction projects and recharge projects. The project structure is clear, and the implementation process is standardized, providing a solid guarantee for the successful implementation of recharge projects. For example, recharge projects can be planned and constructed simultaneously with various urban construction projects such as residential communities and industrial parks, achieving integrated operation of rainwater collection, treatment, and recharge. This decentralized and routine recharge model can effectively expand the recharge coverage, improve recharge efficiency, and ensure the continuous and stable technical effect of recharge. It avoids the drawbacks of centralized recharge projects, such as high implementation difficulty and limited coverage, and is easier to promote and apply in urban construction.

[0017] 3. The groundwater environmental protection recharge technology and method for the northern karst water system recharge area provided in this application has a monitoring program built for the water source protection target. It can effectively avoid the deterioration of downstream water quality caused by groundwater recharge, ensure the safety and environmental protection of the recharge process, realize the organic combination of "recharge" and "water protection", and provide strong support for the ecological protection of the northern karst water system. Attached Figure Description

[0018] Figure 1 This refers to the water level contour map of karst water level drawn in step S1; Figure 2 A schematic diagram illustrating the classification of permeability coefficient calculation methods in step S3; Figure 3 A schematic diagram for calculating the permeability coefficient when the karst strata are relatively thick and uniformly developed. Figure 4 A schematic diagram for calculating the permeability coefficient when the karst strata are thick and the developed section is in the middle; Figure 5 This is a schematic diagram of the purification tank. Figure 6 Schematic diagram of the layout of the diversion pool, purification pool, storage pool, reinjection well, and observation well. Figure 1 ; Figure 7 Schematic diagram of the layout of the diversion pool, purification pool, storage pool, reinjection well, and observation well. Figure 2 . Detailed Implementation

[0019] To enable those skilled in the art to better understand the technical solutions in this application, the technical solutions in the embodiments of this application will be described in detail below with reference to the accompanying drawings. The described embodiments are merely a part of the embodiments of this application, and not all of them. All other embodiments obtained by those skilled in the art based on the embodiments of this application without creative effort should fall within the protection scope of this application.

[0020] The environmentally friendly groundwater recharge technology for the northern karst water system recharge area includes the following steps: S1, determine the direction of groundwater flow in the area where the surface water collection zone is located, and calculate the hydraulic gradient.

[0021] 1.1 Select no fewer than 3 karst water wells and use RTK (Real-Time Dynamic Carrier Phase Differential) measurement equipment to measure the wellhead elevation Li of the karst water wells; 1.2 Determine the depth Di from the wellhead of the karst water well to the groundwater surface inside the well, then the water level elevation of the karst water well is Ci = Li - Di; 1.3 Based on the water level elevation Ci of each karst water well measured in step 1.2, draw the karst water level elevation contour map using interpolation and calculate the hydraulic gradient I.

[0022] As a specific implementation method, this embodiment selects three karst water wells, and the measured water level elevations are 59.714m, 59.131m, and 58.599m, respectively. Based on these elevations, a karst water level contour map is drawn as follows: Figure 1 As shown.

[0023] S2. Based on the groundwater flow direction identified in step S1, set up observation wells downstream of the surface water collection area.

[0024] Furthermore, when there is a river near the surface water collection area, the observation wells should be placed as far away from the river as possible; when there are multiple layers of karst media in the surface water collection area, the observation wells should only be placed in the uppermost layer of karst media.

[0025] S3, construct the well at the location determined in step S2, and calculate the permeability coefficient k.

[0026] 3.1 Rotary drilling method shall be used for drilling and core drilling, and the karst fracture ratio of the core shall be calculated in segments. The core sampling rate of sandy soil shall not be less than 40%, and the core sampling rate of rock shall not be less than 75%.

[0027] Furthermore, the depth of the observation well should be below the historical lowest water level during the dry season, and it should expose a karst development section.

[0028] Furthermore, the final borehole diameter should be no less than 168 mm to meet the requirements of pumping, sampling, and monitoring. That is, when the borehole reaches the designed depth, its final borehole wall diameter should be greater than or equal to 168 mm. The purpose of setting this rigid dimensional specification is to ensure that after well completion, the borehole has sufficient space (to smoothly lower the water pump, sampler, and monitoring probe), thereby enabling high-quality completion of subsequent pumping tests, water quality sampling, and long-term water level and quality monitoring tasks.

[0029] Furthermore, to prevent borehole collapse, wall spalling, and siltation in the upper soil layer during construction and use, a 219mm diameter retaining pipe is inserted into the borehole. The bottom end of the retaining pipe is driven into unweathered limestone, and the annular gap between the retaining pipe and the borehole wall is filled with cement. By injecting cement grout into the annular gap between the retaining pipe and the borehole wall, the external channel can be completely sealed, preventing surface sewage from seeping down the pipe wall and polluting groundwater. It also prevents water from the upper loose layer (or water from different aquifers) from mixing into the borehole through the external gap, ensuring that the groundwater monitored is from the target stratum.

[0030] If the limestone is directly exposed on the surface without a loose soil cover, the length of the retaining pipe should be 3-5m. Because the limestone is exposed, the shallow limestone is often strongly weathered, with well-developed fissures and even small solution channels. Lowering a 3-5 meter long retaining pipe ensures that the bottom of the retaining pipe is driven into the unweathered limestone.

[0031] If a layer of Quaternary cohesive soil (such as silty clay, clay, etc.) covers the limestone, the lower end of the retaining pipe must penetrate the Quaternary cohesive soil layer and be inserted into the limestone below to prevent the observation well from being clogged with mud and sand. Although Quaternary cohesive soil itself has a certain degree of stability, it is prone to disintegration and softening after drilling disturbance, resulting in "diameter reduction" or collapse. If the retaining pipe does not penetrate this soil layer but only stops in the soil layer, then soil particles (mud and sand) will slowly fall into the borehole along the joint between the bottom end of the retaining pipe and the limestone during pumping or long-term monitoring, leading to siltation.

[0032] 3.2 After the observation well is completed, pump water to flush the well until the water is clear and the sand is clean.

[0033] 3.3 After the observation wells are completed, the permeability coefficient k of the surface water collection area is calculated through pumping tests. The pumping tests use steady-flow pumping, with a water level stabilization time of no less than 8 hours, and the steady-flow output Q of the observation wells is recorded. 出 And stable descent depth s.

[0034] The calculation method for permeability coefficient k varies depending on the geological structure. For example... Figure 2 As shown, the specific situations include the following: 3.3.1 If the karst strata thickness in the surface water collection area is relatively small (usually referring to karst strata thickness less than or equal to 100 meters), and the surface water collection area is a karst groundwater zone with no observation wells around the observation well, then the formula for calculating the permeability coefficient k is:

[0035] In the formula, Q 出 To ensure a stable water output from the observation well; s represents the stable drawdown depth of the observation well; H represents the water level of the observation well; r is the radius of the observation well; R is the radius of influence of the observation well.

[0036] 3.3.2 If the karst strata thickness in the surface water collection area is relatively small (usually referring to karst strata thickness less than or equal to 100 meters), and the surface water collection area is a karst groundwater zone with observation wells around the observation wells, then the formula for calculating the permeability coefficient k is:

[0037] In the formula, Q 出 To ensure a stable water output from the observation well; s represents the stable drawdown depth of the observation well; H represents the water level of the observation well; r is the radius of the observation well; r1 is the straight-line distance between the observation well and the observation well; s1 represents the stable drawdown of the observation well.

[0038] If there is one observable well around the observation well, then that well is selected as the observation well, and the straight-line distance r1 between the observation wells and the steady drawdown s1 of the observation well are recorded. If there are multiple observable wells around the observation well, then the well closest to the observation well is selected as the observation well, and the straight-line distance r1 between the observation wells and the steady drawdown s1 of the observation wells are recorded.

[0039] 3.3.3 If the karst strata thickness in the surface water collection area is relatively small (usually referring to karst strata thickness less than or equal to 100 meters), and the surface water collection area is a covered karst water confined zone with no surrounding observation wells, then the formula for calculating the permeability coefficient k is:

[0040] In the formula, Q 出 To ensure a stable water output from the observation well; s represents the stable drawdown depth of the observation well; M is the thickness of the confined aquifer; r is the radius of the observation well; R is the radius of influence of the observation well.

[0041] 3.3.4 If the karst strata thickness in the surface water collection area is relatively small (usually referring to karst strata thickness less than or equal to 100 meters), and the surface water collection area is a covered karst water confined zone, and there are observation wells around the observation wells, then the formula for calculating the permeability coefficient k is:

[0042] In the formula, Q出 To ensure a stable water output from the observation well; s represents the stable drawdown depth of the observation well; M is the thickness of the confined aquifer; r is the radius of the observation well; r1 is the straight-line distance between the observation well and the observation well; s1 represents the stable drawdown of the observation well.

[0043] If there is one observable well around the observation well, then that well is selected as the observation well, and the straight-line distance r1 between the observation wells and the steady drawdown s1 of the observation well are recorded. If there are multiple observable wells around the observation well, then the well closest to the observation well is selected as the observation well, and the straight-line distance r1 between the observation wells and the steady drawdown s1 of the observation wells are recorded.

[0044] For the four cases described in 3.3.1, 3.3.2, 3.3.3, and 3.3.4 (i.e., when the karst strata thickness in the area where the surface water collection zone is located is relatively small), the observation well should preferably be a complete well, meaning that the bottom of the observation well reaches the water-resistant bottom plate.

[0045] 3.3.5 If the karst strata in the surface water collection area are relatively thick (usually greater than 100 meters) and the karst fissures are relatively uniformly developed, then incomplete wells should be used for observation, meaning the observation well depth does not reach the impermeable bottom plate. Figure 3 As shown, the formula for calculating the permeability coefficient k is:

[0046] In the formula, Q 出 To ensure a stable water output from the observation well; s represents the stable drawdown depth of the observation well; r is the radius of the observation well; R is the radius of influence of the observation well; l To determine the length of the remaining intake section after the well water level stabilizes, the pumping test was conducted by controlling... l <0.3H, where H is the water level of the observation well.

[0047] 3.3.6 If the karst strata in the surface water collection area are thick (usually greater than 100 meters), and the fractured karst development section is in the middle of the karst strata, then the observation wells should be incomplete wells, meaning the observation well depth does not reach the aquitard. Figure 4 As shown, the formula for calculating the permeability coefficient k is:

[0048] In the formula, Q 出 To ensure a stable water output from the observation well; s represents the stable drawdown depth of the observation well; r is the radius of the observation well; l To determine the length of the remaining intake section after the well water level stabilizes, the pumping test was conducted by controlling... l <0.3H, where H is the water level of the observation well.

[0049] Furthermore, if the karst strata in the surface water collection area are relatively thick (usually referring to karst strata thickness greater than 100 meters), and the fractured karst development section is located in the middle of the karst strata, then in step 3.1, during drilling, the bottom end of the retaining pipe should be positioned at the top of the fractured karst development section. By sealing off the upper undeveloped section (or weakly developed section) with the retaining pipe, water can be allowed to enter only the middle karst development section, ensuring the water intake section... l It is located entirely within the fractured karst development section, thus only capturing the permeability of the central development section. Preferably, the length of the retaining pipe is 0.3H-0.4H.

[0050] 3.3.7 If the karst strata in the area where the surface water collection area is located are thick (usually referring to karst strata thickness greater than 100 meters), the water level is deep (usually referring to water level greater than 100 meters), and the karst strata fissures are relatively uniformly developed, then the observation wells are non-complete wells (i.e. the depth of the observation wells does not reach the water-resistant bottom plate), and the permeability coefficient k of the karst section above the water level is calculated through water injection tests.

[0051] The water injection test was conducted in accordance with the industry standard "NB / T 35104-2017 Water Injection Test Procedure for Drilling in Hydropower Engineering". The permeability coefficient k was calculated according to the industry standard "NB / T 35104-2017 Water Injection Test Procedure for Drilling in Hydropower Engineering". The specific process will not be described here.

[0052] Preferably, in step S3, the groundwater level H of the observation well is calculated from the top surface of the non-karstified strata (i.e., the top surface of the impermeable base). When calculating the groundwater level H of the observation well, the ground surface or any arbitrary point is not used as the zero point. Instead, the upper surface of the stable impermeable base (i.e., the non-karstified strata, such as shale or mudstone) at the bottom of the uppermost karst aquifer exposed by the well is used as the reference surface for calculation. This can eliminate the error caused by the irregularity of the bottom of the karst strata, accurately calculate the actual thickness of the aquifer and the effective drawdown during pumping, and ensure the reliability of hydrogeological parameters.

[0053] S4. Based on the location of the observation well and the permeability coefficient of the surface water collection area calculated in step S3, determine the location of the recharge well. The specific requirements for the location of the recharge well include the following aspects: 4.1 According to the groundwater flow direction, the recharge well should be located upstream of the observation well, and the distance between the recharge well and the observation well should be greater than or equal to 6m. Preferably, the distance between the recharge well and the observation well should be greater than 15m.

[0054] 4.2 If there is a water source protection target (such as a drinking water source well) downstream of the recharge well, then the recharge well is located outside the boundary of its recharge area. The boundary of the recharge area of ​​the recharge well is calculated using an empirical formula, the specific formula being:

[0055] In the formula, α is the coefficient of variation, α≥1, dimensionless, and usually taken as 2; k is the permeability coefficient (m / d) of the area where the surface water collection zone is located; T represents the migration time of groundwater particles (d); n e The effective porosity of the aquifer is dimensionless and can be replaced by the karst fracture ratio obtained in step 3.1. I represents the hydraulic gradient calculated in step S1, which is dimensionless.

[0056] Preferably, the boundary of the recharge zone is defined by the area centered on the recharge well and the distance traveled by solute particles over 100 days. That is, the groundwater particle migration time T is taken as 100 days.

[0057] S5, Recharge Well Construction: Determine the type and characteristics of the recharge aquifer, and calculate the recharge volume per well based on the type of recharge aquifer.

[0058] like Figure 6 As shown, the formula for calculating the recharge volume of a single well in a recharge well for unconfined aquifers is:

[0059] In the formula, k is the permeability coefficient of the area where the surface water collection zone is located, which has been calculated in step S3; h w This refers to the water level in the recharge well after recharge. h0 is the static water level of the recharge well before recharge; R' is the radius of influence of the reinjection well, which is replaced by the radius of influence R of the observation well obtained in step S3; r w The radius of the recharge well.

[0060] like Figure 7 As shown, for recharge wells in confined aquifers, the formula for calculating the recharge volume of a single well is:

[0061] In the formula, k is the permeability coefficient of the area where the surface water collection zone is located, which has been calculated in step S3; M is the thickness of the confined aquifer; h w This refers to the water level in the recharge well after recharge. h0 is the static water level of the recharge well before recharge; R' is the radius of influence of the reinjection well, which is replaced by the radius of influence R of the observation well obtained in step S3; r w The radius of the recharge well.

[0062] Furthermore, the recharge well is constructed using rotary drilling and core sampling to facilitate observation of the formation lithology, determine the well structure of the recharge well, and identify the type of recharge aquifer based on the degree of development of karst fissures in the lithology.

[0063] Furthermore, the drilling process for the recharge well adopts water drilling, and after drilling to the designed depth, the rock powder at the bottom of the hole is removed, and the inclination of the recharge well should be less than 1%.

[0064] S6. Based on the site conditions of the surface water collection area, select a suitable location within the surface water collection area to set up a water purification tank and a water storage tank.

[0065] The aforementioned water purification tank is used to filter and purify the collected surface water, and the aforementioned water storage tank is used to store the purified reinjection water. The water purification tank and the water storage tank are connected, and the purified water in the purification tank is pumped into the water storage tank by a water pump. The water storage tank is connected to a reinjection well, and the clean reinjection water stored in the water storage tank is injected into the underground aquifer through the reinjection well to replenish groundwater resources.

[0066] 6.1 About the water purification tank like Figure 5 As shown, the purification tank is equipped with a horizontal reverse filter layer, which, along the water flow direction, sequentially comprises a homogeneous medium sand layer, a homogeneous coarse sand layer, and a homogeneous gravel layer. The permeability coefficient of the homogeneous medium sand layer is 35-50 m / d, the permeability coefficient of the homogeneous coarse sand layer is 60-75 m / d, and the permeability coefficient of the homogeneous gravel layer is 50-100 m / d. The thickness of each of the homogeneous medium sand layer, homogeneous coarse sand layer, and homogeneous gravel layer is not less than 30 cm, meaning the runoff length of the water in the purification tank is not less than 0.9 meters, to ensure effective filtration.

[0067] In one specific embodiment, the water purification tank in this example has a width of 2m, a height of 3m, and a length of 3.1m. A homogeneous medium sand layer, a homogeneous coarse sand layer, and a homogeneous gravel layer are sequentially arranged along the length of the water purification tank. The homogeneous medium sand layer has a thickness of 1.1m and is divided into four layers with thicknesses of 20cm, 30cm, 30cm, and 30cm respectively along the water flow direction. The homogeneous coarse sand layer has a thickness of 0.9m and is divided into three equal layers, each with a thickness of 30cm. The homogeneous gravel layer has a thickness of 1.1m and is divided into four layers with thicknesses of 30cm, 30cm, 30cm, and 20cm respectively along the water flow direction.

[0068] The three layers of homogeneous medium sand, homogeneous coarse sand, and homogeneous gravel act as a filter, effectively removing suspended solids, organic matter, colloidal particles, and gravel from the water, ultimately reducing turbidity and purifying the water. When the permeability of the homogeneous medium sand, coarse sand, and gravel layers decreases, they can be removed, cleaned, and then backfilled for reuse.

[0069] In addition, when the surface water collection area is large, more purification ponds can be set up, and the specifications of the purification ponds can be deepened and widened to increase the treatment capacity.

[0070] 6.2 Regarding the water storage tank, its volume is calculated as follows: 6.2.1 Calculate the estimated maximum single-event catchment volume based on historical rainfall data of the area where the surface water collection zone is located. The specific calculation formula is as follows:

[0071] In the formula, ψ is the runoff coefficient. According to the "Code for Design of Building Water Supply and Drainage" GB50015-2019, the design runoff coefficient Ψ for concrete and asphalt pavement is taken as 0.90. p represents the design rainfall corresponding to an annual runoff volume control rate of 75%, with historical data for at least 10 years; A represents the collection area of ​​the surface water collection zone.

[0072] 6.2.2 Calculate the volume of the reservoir based on the estimated maximum single-well water collection volume and the single-well recharge volume. The specific calculation formula is as follows:

[0073] In the formula, W is the estimated maximum water collection volume per cycle; Q 回 This represents the amount of water injected into a single well.

[0074] Furthermore, based on the site conditions of the surface water collection area, a diversion pond is selected at a suitable location within the area. This diversion pond is used to collect and discard initial rainfall with high pollutant concentrations. The diversion pond is equipped with a level sensor to detect the water level. During rainfall, the collected rainwater is first discharged into the diversion pond for disposal. Once the water level in the diversion pond reaches a preset height, the collected rainwater is then discharged into a purification pond for purification and reinjection. The water in the diversion pond can be used for greening irrigation.

[0075] The collected rainwater mainly includes two aspects: rooftop rainwater collection and surface runoff formed by the hardening of large areas of ground by non-polluting enterprises.

[0076] The formula for calculating the volume of the wastewater is as follows:

[0077] In the formula, ψ is the runoff coefficient. According to the "Code for Design of Building Water Supply and Drainage" GB50015-2019, the design runoff coefficient Ψ for concrete and asphalt pavement is taken as 0.90. q represents the thickness of the overflow, which is generally taken as 3-5 mm; A represents the collection area of ​​the surface water collection zone.

[0078] Because initial rainfall is collected in a diversion basin and then discharged, the estimated maximum single-time water collection capacity of the reservoir will change after adding the diversion basin. The formula for calculating the estimated maximum single-time water collection capacity of the reservoir after adding the diversion basin is as follows:

[0079] In the formula, ψ is the runoff coefficient. According to the "Code for Design of Building Water Supply and Drainage" GB50015-2019, the design runoff coefficient Ψ for concrete and asphalt pavement is taken as 0.90. p represents the design rainfall corresponding to an annual runoff volume control rate of 75%. q represents the thickness of the overflow, which is generally taken as 3-5 mm; A represents the collection area of ​​the surface water collection zone.

[0080] Furthermore, such as Figure 6 and Figure 7 As shown, the reinjection well is located within the reservoir, and a filter is fixedly installed at the inlet of the reinjection well. Preferably, the filter is a steel pipe filter, and the upper end of the steel pipe filter extends above the water surface in the reservoir. Preferably, the depth of the reservoir is greater than or equal to 1.5m to ensure that the reinjection well is equipped with a steel pipe filter of not less than 1 meter, and the porosity of the steel pipe filter is 30-35%.

[0081] Furthermore, the bottom of the reservoir is not treated with anti-seepage measures to improve the infiltration guarantee of the reinjection water.

[0082] S7, Verify the reinjection volume of the reinjection well and determine the standard single-well reinjection volume of the reinjection well; 7.1 Calculate the verification recharge volume for a single well. The specific formula is as follows:

[0083] In the formula, R' is the radius of influence of the recharge well; α is a correction factor, which is selected based on local experience. If there is no experience, take 0.15-0.3. s w This refers to the rise in water level in the recharge well; H' is the water level of the recharge well; β is a correction factor, which is selected based on local experience. If there is no experience, take 0.2-0.3. k is the permeability coefficient; h w This refers to the water level in the recharge well after recharge. h0 is the static water level of the recharge well before recharge; r w The radius of the recharge well.

[0084] 7.2 The single-well verification reinjection volume calculated in step 7.1 is used. The single-well reinjection volume calculated in step S5 Compare; like Then This refers to the standard single-well recharge volume of the recharge well; like Then and The smaller value in the equation is the standard reinjection volume of the reinjection well.

[0085] S8, Recharge Monitoring 8.1 If there is no downstream water source protection target, groundwater quality should be sampled and tested once a year after the rainy season. If there is a downstream water source protection target, sampling and testing should be conducted monthly during the rainy season. When conducting water quality monitoring, the monitoring and analysis items can be comprehensively determined based on the environmental conditions and pollution source characteristics of the surface water collection area.

[0086] 8.2 When abnormal exceedances of water quality indicators are detected during water quality monitoring, recharge should be stopped immediately, and the cause of pollution should be analyzed to determine if it is related to recharge. Water quality analysis can ensure that groundwater recharge does not cause downstream water quality deterioration, thus achieving the goal of protecting karst water.

[0087] 8.3 After the recharge begins, the water level in the observation well should be monitored daily until the recharge is completed. If any abnormal water level is detected, the cause should be analyzed promptly. Water level monitoring can demonstrate the effectiveness of recharge in replenishing karst water.

[0088] Other embodiments obtained by those skilled in the art based on the embodiments provided in this application by combining, splitting, or reorganizing the embodiments of this application do not exceed the protection scope of this application.

[0089] The above detailed embodiments have provided a detailed explanation of the purpose, technical solutions, and beneficial effects of the embodiments of this application. The above are merely specific embodiments of the embodiments of this application and are not intended to limit the protection scope of the embodiments of this application. That is, any modifications, equivalent substitutions, improvements, etc., made on the basis of the embodiments of this application should be included within the protection scope of the embodiments of this application.

Claims

1. A method for environmentally friendly groundwater recharge in the recharge area of ​​the northern karst water system, characterized by: Includes the following steps, S1, determine the direction of groundwater flow in the area where the surface water collection zone is located, and calculate the hydraulic gradient; S2, based on the identified groundwater flow direction, deploy observation wells downstream of the surface water collection area; S3, construct the observation well and calculate the permeability coefficient k of the area where the surface water collection zone is located; S4. Determine the location of the recharge well based on the location of the observation well and the permeability coefficient of the area where the surface water collection zone is located; S5, Recharge Well Construction: Determine the type and characteristics of the recharge aquifer, and calculate the recharge volume per well based on the type of recharge aquifer. S6, Set up water purification tanks and water storage tanks according to the site conditions of the surface water collection area; S7, Verify the reinjection volume of the reinjection well and determine the standard single-well reinjection volume of the reinjection well; S8, Recharge Monitoring.

2. The environmentally friendly groundwater recharge technology for the northern karst water system recharge area as described in claim 1, characterized in that: Step S3 includes the following steps: 3.1 Drilling and core drilling, and calculating the karst fracture rate of the core samples in segments; 3.2 Pump water to flush the well until the water is clear and the sand is clean; 3.3 The permeability coefficient k of the surface water collection area was calculated through pumping tests.

3. The environmentally friendly groundwater recharge technology for the northern karst water system recharge area according to claim 2, characterized in that: The pumping test uses steady flow pumping, and the water level stabilizes for no less than 8 hours.

4. The environmentally friendly groundwater recharge technology for the northern karst water system recharge area according to claim 2, characterized in that: When calculating the permeability coefficient k, 3.3.1 The karst strata in the area where the surface water collection area is located are relatively thin, and the area is a karst phreatic zone. Furthermore, there are no observation wells around the observation well. The formula for calculating the permeability coefficient k is... ; 3.3.2 The karst strata in the area where the surface water collection area is located are relatively thin. The area is a karst phreatic zone, and there are observation wells around the observation wells. The formula for calculating the permeability coefficient k is: ; 3.3.3 The karst strata in the area where the surface water collection area is located are relatively thin. The area is a confined karst water zone with overburden, and there are no observation wells around the observation well. The formula for calculating the permeability coefficient k is: ; 3.3.4 The karst strata in the area where the surface water collection area is located are relatively thin. The area is a confined karst water zone with overburden, and there are observation wells around the observation wells. The formula for calculating the permeability coefficient k is: ; 3.3.5 Given the relatively thick karst strata in the surface water collection area, and the relatively uniform development of karst fissures, incomplete wells are used for observation. The formula for calculating the permeability coefficient k is: ; 3.3.6 Given the significant thickness of the karst strata in the surface water collection area, and the presence of fractured karst formations in the central part of the karst strata, incomplete wells are used for observation. The formula for calculating the permeability coefficient k is: ; 3.3.7 The karst strata in the area where the surface water collection area is located are thick and the water level is deep. The karst strata are relatively uniformly developed with fissures. Therefore, the observation wells are non-complete wells, and the permeability coefficient k of the karst section above the water level is calculated through water injection tests.

5. The environmentally friendly groundwater recharge technology for the northern karst water system recharge area according to claim 4, characterized in that: If there is one observable well around the observation well, then that well will be used as the observation well. If there are multiple observable wells around the observation well, then the well closest to the observation well will be selected as the observation well.

6. The environmentally friendly groundwater recharge technology for the northern karst water system recharge area according to claim 1, characterized in that: The recharge well is located upstream of the observation well, and the distance between the recharge well and the observation well is greater than or equal to 6m. If there is a water source protection target downstream of the recharge well, then the recharge well is located outside the boundary of the recharge area of ​​the recharge well.

7. The environmentally friendly groundwater recharge technology for the northern karst water system recharge area according to claim 1, characterized in that: In step S5, For recharge wells in unconfined aquifers, the formula for calculating the recharge volume per well is as follows: ； For recharge wells in confined aquifers, the formula for calculating the recharge volume per well is as follows: .

8. The environmentally friendly groundwater recharge technology for the northern karst water system recharge area according to claim 7, characterized in that: Step S7 includes the following steps: 7.1 Calculate the single-well verification recharge volume. The formula for calculating the single-well verification recharge volume is as follows: ； 7.2 Verify the reinjection volume of a single well With single well reinjection volume Compare; like Then This refers to the standard single-well recharge volume of the recharge well; like Then and The smaller value in the equation is the standard reinjection volume of the reinjection well.

9. The environmentally friendly groundwater recharge technology for the northern karst water system recharge area according to claim 1, characterized in that: The purification tank is equipped with a horizontal reverse filter layer, which includes a homogeneous medium sand layer, a homogeneous coarse sand layer and a homogeneous gravel layer in sequence along the water flow direction.

10. The environmentally friendly groundwater recharge technology for the northern karst water system recharge area according to claim 1, characterized in that: The recharge well is located inside the reservoir, and a steel pipe filter is fixedly installed at the inlet of the recharge well. The porosity of the steel pipe filter is 30-35%.

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