Introduction
Mineral resources were crucial for human development, reproduction, and survival. However, human activities including coal burning, metal smelting, mining for minerals, and sewage irrigation were significant sources of heavy metal pollution [1]. Pollution and environmental issues could arise when mining mineral resources. The continual expansion of scale brought about by the quick development of mineral resource mining had resulted in a significant accumulation in tailings [2]. The majority of mine tailings were kept in natural stacks and ponds, which might take up a lot of space and could seriously pollute the environment. The main causes of heavy metal migration during the extraction of heavy mineral resources were natural hydrological and atmospheric processes. The primary elements that could provide possible risks to the mining environment were the weathering and leaching of the ore and discharged industrial waste, which were significant sources of heavy metal pollution in soil [3].
There were various degrees of heavy metal contamination in the soil, surface water, and groundwater in the mining area as a result of the waste residues produced during mining, beneficiation, and smelting operations migrating and spreading to the surrounding areas through rainfall and dustfall processes [4]. Heavy metals are persistent, accumulate, and degrade slowly, making them some of the most prevalent soil environmental contaminants. Once heavy metals enter the soil, they could not be biodegraded due to the lack of effective export routes. Because heavy metals were present in the soil for a long time, they continue to accumulate [5]. This process, which also could reduce the yield and quality of agricultural products, could affect the nature and function of the soil [6]. Additionally, heavy metals could be accumulated in crops and infiltrate the food chain, posing a health concern to the local resident [7].
The non-degradable nature of heavy metals could result in the accumulation of pollutants in the substrate of water bodies, sites, and soil in some areas [8]. The potential pollution risk was more serious due to the prolonged duration of pollution, outdated treatment technology, and poor supervision and management [9]. Therefore, the pilot project to address historical legacy issues about ailing ponds, waste storage sites, agricultural land contaminated by heavy metals, landfill surroundings, and ecological damage in mining areas was explicitly listed as one of the key projects in the national ‘Comprehensive Prevention and Control Plan for Heavy Metal Pollution’ [10]. The state of heavy metal contamination in a pyrite mining location with historical residues was examined in this study and the remediation strategies that could serve as a model for similar operations were provided.
Material and Methods
Study Area
This sulfur iron mine, which was shut down in 1988 and is now abandoned, was mined in 1972 and was situated in Liaoyang County, Liaoyang City, Liaoning Province. A source of waste contamination upstream of the Tanghe reservoir was created by the mine’s abandoned waste residue dumps. The nearby soil environment, surface water environment, groundwater environment and the nearby rural environment were seriously polluted by the toxic and harmful substances contained in the waste residue, which also posed a threat to the Tanghe Reservoir. Over time, the mining waste rocks have been haphazardly piled up naked, producing yellow acidic wastewater. The project was surrounded by 135hm2 of farmland. The waste residue from the contaminated site would be washed away by rainwater, which was very likely to cause the continuous spread of pollution and would continue to cause more serious pollution and damage to the neighboring farmland [11]. Also, the water quality of the Tanghe Reservoir's drinking water sources were affected by the pollutants in the waste residue. Contamination of the drinking water source water quality of the Tonghe Reservoir, as well as agricultural soils, could affect the health and safety of local residents. This was because the waste residue was located upstream of the Tanghe reservoir. Therefore, the ecological restoration of the abandoned waste residue piles was essential.
The cause of site pollution was mainly due to the accumulation of waste residue in this project area [12]. The exudate of waste residue had a high content of iron and manganese. Pyrite ions in the waste residue were oxidized by oxygen in the air to form iron hydroxide precipitation. This could lead to reddish and yellowish seepage and the formation of "sulfur water". Thus, a layer of yellowish-brown sediment had settled at the bottom of the river over time. Also, the acid water generated in the project area was in the pH range of 3-5, and the water was strongly acidic.
Site Status
The project’s scope was illustrated in the Fig. 1. The project's total solid waste treatment area was approximately 34,800 m2. In the north and south portions of the iron sulfide mine during mining, there were two abandoned waste residue stockpiles. 6080.44 m2 was the size of the north area, and 28680.4m2 was the size of the south area. The storage capacity of waste residue was 208565.04 m3.
The majority of the sulfur and iron waste residue was piled up in a dispersed manner due to the early mining methods, and the available land resources were occupied. Acidic wastewater was generated under the action of air oxidation, rainwater drenching, and surface runoff, and the nearby soil and water environment was polluted by the acidic wastewater. Tanghe Reservoir was located 2,000 meters downstream of the Lan River. Therefore, Tanghe Reservoir's water quality was also affected by the acid water. In addition, soil and nearby vegetation might also be polluted by the two waste residue piles in different degrees. Therefore, the two waste residue piles posed a possible threat to the surrounding environment.
(1) The present state of waste residue pile in the region of the north
There are no environmental protection facilities for waste residue piles in the north, such as waste residue retaining walls or flood drains around the waste residue accumulation area. The surface area of the waste residue pile in the north area was 6080.44 m2, with a height of 22 m, and the estimated volume was 36,482.64 m3. The waste residue pile in the north was piled in the open, and the exposed waste residue was blade-like after natural weathering, with a loose structure, and the overall shape of the regional slope was irregular. The surface layer of the slope body was covered with thin loose accumulation, which was primarily small-grained gravel falling blocks during the early mining process, and the slope was steeper. The subsequent mining process resulted in a more uneven shape. The pile could easily slide downstream into the river, which would have a negative impact on the surrounding area. The pile might continue to slide to the foot of the slope. One mining cave with a 1 x 1.5 m shaft size was located in the project's northern region. The pollution status was shown in Fig. 2.
(2) Waste residue pile’s southern section
The surface area of the south section’s waste residue pile is 28680.4 m2. The volume of waste residue was estimated to be 172,082.4 m3. The waste residue pile in the southern area was covered with planting soil, shrubs, and grass. Also, drainage ditch had been built. However, there was no isolation and anti-permeation measure above the waste residue pile. As a result, under rainfall conditions, acidic wastewater could seep out of the waste residue pile in the southern zone and sink into the drainage ditch in the southern zone.
(3) The condition of the drainage ditches around the project site
On the project site, there were four drainage ditches. The site survey revealed that there were exposed waste materials and loose construction in the project site ditches. With surface water infiltration and rainfall erosion, acidic wastewater from the project site could seep out of the drainage ditches and was discharged into the Lan River with the on-site ditches. Agricultural land was located downstream of the project site, and both the waste residue and the agricultural land were in the same watershed. The leachate was generated by precipitation drenching and could enter the project site ditch with surface runoff, which in turn could pose a threat to farmland.
Sampling
Waste Residue Sampling
The site's waste residue samples were examined. Five profile waste residue samples (0-600 cm) were collected using a stainless-steel auger in May 2023 [1]. And two soil control was collected in the farmland area upstream of the waste site and the bottom of the hill, respectively. The location of the collected samples were shown in the Fig. 3 and recorded using Global Positioning System (GPS, Garmin 72).
All the samples were collected using a plastic shovel and put in the polyethylene bags, labeled and transported to the laboratory [13]. Samples were homogenized, air-dried, and crushed manually. Samples were ground to pass through a < 0.149 mm sieve and analyzed for their heavy metal contents and tested for leaching toxicity (water leaching test) [14].
Soil Sampling
Ten profile soil samples (0-100 cm) were collected using a stainless-steel auger in May 2023 [15]. The sample point map was displayed in Fig. 3, and sampling depth and details about the sampling points was listed in the following table.
All the samples were collected using a plastic shovel and put in the polyethylene bags, labeled and transported to the laboratory [16]. Soil material was homogenized, air-dried, and crushed manually. Samples were ground to pass through a <0.149 mm sieve and analyzed for their heavy metal contents [17].
Surface Water Sampling
The Lan Rive could play a critical role in the Tang River Reservoir, which was located about 500 m downstream of the waste residue. The sampling points were shown in the table below. Four unfiltered surface water samples were collected from the center of the river for pH, arsenic, suspended particles, and sulfides analyses. The samples were then transferred into acid cleaned 100 mL polypropylene bottles. One mL of ultrapure nitric acid was added in each polypropylene bottle to achieve a pH of 1 [18].
Groundwater Sampling
One groundwater monitoring site was established in a groundwater well in the community downriver of the waste residue site to examine the effect of waste residue on groundwater pollution. The Groundwater Quality Standard (GB/T 14848-2017) III standard limits were used to analyze the groundwater test findings.
Sample Analysis
Waste Residue Analysis
All the chemicals used in our study were of analytical grade and aqueous solutions were prepared with deionized water [1]. The contents of the heavy metal for waste residue was determined according to the Solid Waste-Determination of metals - Inductively coupled plasma mass spectrometry (ICP-MS, HJ766- 2015) [19].
The water leaching test for waste residue was performed according to the Solid waste-Extraction procedure for leaching toxicity-Horizontal vibration method (HJ557-2009) [20]. Distilled water was used to extract samples. The samples were extracted at a liquid to solid (L/S) ratio of 10 in a capped polypropylene bottle on a rotary tumbler at 110 rpm for different time at room temperature. After the extraction, the final pH of the leachate was measured. The liquid was separated by filtration through a 15 µm paper filter and the concentrations of the Cd, Cu, Ni, Hg, As, Zn, Cr and Pb was analyzed. The test results of water leaching were calculated using the maximum allowable emission limits for pollutants of Class I standards of the Integrated Sewage Discharge Standards (GB8978-1996) [8]. The results could allow researchers to better understand the properties of heavy metal scrap in the area.
Soil Sample Analysis
The soil samples were digested according to USEPA Method 3051A [21] for total heavy metal concentrations analysis with minor modifications by digesting 0.200 g soil sample with 15 mL of tri-acidic mixture (HNO3, HCl, HCIO4) in a volume ratio of 1:3:1.The concentrations of Cd, Cu, Ni, Pb and Zn in digested samples were determined using atomic absorption spectrophotometry [22]. Detection limits for Cd, Cu, Ni, Pb, and Zn were 1.8, 2.3, 6.8.27.3, and 1.6 g L-1, respectively.
The concentrations of Cd, Pb, mercury (Hg), arsenic (As), Zn, copper (Cu), nickel (Ni), and chromium (Cr) were determined [23]. Briefly, soil samples (0.5 g) were digested with a mixture of HNO3, HCl, HF, and HClO4 using an Automated Sample Digestion System (Thomas Cain Inc., Mequon, WI, USA). The total concentration of Hg was determined using a Hydra-C atomic absorption spectrophotometer (Leeman, USA). The total concentration of As was determined using an atomic fluorescence spectrometer (JiTian, Bejing, China). An inductively coupled plasma atomic emission spectrometer (Leeman, USA) was used to detect the total concentrations of Pb and Zn. The total concentrations of Cd, Cu, Ni, and Cr were measured using inductively coupled plasma-mass spectrometer (Agilent, Japan) [24].
Soil pH were measured in this study [23]. A digital pH meter (ORION5 STAR, thermo scientific) was used for measuring the pH of the extraction solution (1:10, w/v sample: distilled water) after extraction by shaking for 2 h at 150 rpm [25].
Water Analysis
The surface water and underground water sampling bottles were rinsed with distilled water in order to eliminate any primary contamination [26]. The pH of samples was set to lower two by the nitric acids (65% Merch, Germany) to reduce HMs absorption [27]. The samples were sampled in 2-L polypropylene bottles and transported to the lab at 4ºC. Based on the guidelines, the time between collecting the samples and delivering them to the laboratory was about 5-6 h. In all the analysis, double-distilled water was used. The standard solution of all metals was produced by diluting 1000 mg/L predetermined amount of standard solutions. Inductively coupled plasma mass spectrometry is the method for measuring the contents of heavy metal of surface water and underground water [28].
Results and Discussion
Nature of Waste Residue
After the solid waste was subjected to toxic leaching experiments, the concentration of any one pollutant in the leachate obtained from the solid waste did not exceed the maximum allowable discharge concentration specified in the "Comprehensive Sewage Discharge Standard" (GB8978-1996), and the pH value of the leachate was within the range of 6~9 [29]. This industrial solid waste was the first category of general industrial solid waste according to the "General Industrial Solid Waste Storage and Disposal Site Pollution Control Standards" (GB18599-2001). Leachate obtained from industrial solid waste on the toxic leaching experiments had one or more pollutant concentrations exceeding the maximum allowable discharge concentration specified in the “Integrated Sewage Discharge Standard” (GB8978- 1996), or the pH value of the leachate was outside the range of 6 to 9 [30]. This industrial solid waste was the second category of general industrial solid waste.
Although the number of pollutants in the waste sludge in the north and south areas did not exceed the maximum allowable discharge concentration specified in the “Integrated Sewage Discharge Standards (GB8978-1996)”, the pH of the leaching solution for the waste sludge was less than 6. Therefore, the wastes in the north and south districts were classified as Class II general industrial solid wastes.
Soil Contamination Results
Their test results were shown in Table 8, and the Soil Soil Environmental Quality Risk Control Standards for Soil Contamination on Agricultural Land (GB15618- 2018 )were used for assessment (Table 4).
The soil in the project area was basically acidic. This result could be due to acidic soil caused by the acidic water generated at the project site. The arsenic contents of soil in the exceeded the screening value of the "Soil Environmental Quality Risk Control Standard for Soil Contamination on Agricultural Land" (GB15618-2018). The contents of cadmium and copper in the farmland soil exceeded the screening value of "Soil Environmental Quality Standards for Soil Contamination Risk Control on Agricultural Land" (GB15618-2018). The soil exceeded the standard to some extent. Therefore, it was determined that the migration of arsenic, cadmium and copper in the waste residue with rainwater caused some pollution to the downstream soil.
Surface Water Pollution Results
The result of the surface water was listed in Table 9. The surface water on the south, west and east side of the drainage canal and the entrance to Lanhe River was acidic, and the pH was lower than the standard limit of category III of the "Surface Water Environmental Quality Standard" (GB3838-2002). The surface water at the mouth of the Lanhe River and the east, south, and west drains all contained more arsenic than was permitted. The arsenic concentration in the west drains reached 1.31 mg/L, which could exceed the standard limit of category III of the "Surface Water Environmental Quality Standard" (0.05 mg/L) and exceed the standard by 25.2 times.
Table 1.
Statistical table of waste residue sampling points.
Table 2.
Evaluation criteria for waste residues.
| Number | Category | Pollution factor | Concentration limit value (mg/L) | Implementation standard |
|---|---|---|---|---|
| 1 | Water leaching | pH | 6-9 | Integrated Sewage Discharge Standards (GB 8978-1996) |
| 2 | Pb | 1.0 | ||
| 3 | Cd | 0.1 | ||
| 4 | As | 0.5 | ||
| 5 | Zn | 2.0 |
Table 3.
Statistical table of soil sampling points.
Table 4.
Soil evaluation criteria.
Table 5.
Surface water sampling point statistics.
Table 6.
Groundwater sampling points.
| Test category | Sampling number | Sampling points | Sampling coordinates | |
|---|---|---|---|---|
| Groundwater | GW1 | Groundwater wells in the village downstream of the waste residue | 123.405631° | 41.044632° |
The arsenic content of the south side drain was 0.137 mg/L, which was 1.74 times higher than the 0.05 mg/L limit set by the standard limit of category III of Surface Water Environmental Quality Standard (GB3838-2002). The pH of surface water decreased significantly after the waste residue, while the arsenic content in water increased significantly. This demonstrated the arsenic in the waste was continuously migrating to the surrounding soil and downstream farmland with rainwater. As a result, the surface water was affected by the acidic effluent from this operation.
Groundwater Contamination Results
The groundwater of the project was not polluted and the concentration of the groundwater could meet the standard of "Groundwater Environmental Quality Standard" (GB/T14848-2017) for Class III. It was obvious that the waste residue in the project might pose little effect on the groundwater.
Conclusion and Discussion
Waste Residue Risk Assessment
Based on the result, the waste residue could be determined as the second general industrial solid waste. The exposed pile of waste residue layer was vulnerable to rainfall erosion or drenching. Meanwhile, the site was located in the higher mountainous terrain. During spring and summer rainy seasons, heavy rainfall directly washed the waste residue pile in the site, which could cause waste migration [31]. In addition, rainwater leaching could cause the heavy metals in the waste residue to infiltrate the lower layer and the surrounding area, leading to the spread of heavy metal pollution in the soil below and around the site.
Risk Assessment for Soil Pollution
The total amount of heavy metals arsenic, cadmium and copper of the waste residue within the site area could exceed the standard, and the plants within the site area were sparse, with soil erosion and bare ground state. The waste residue has caused serious pollution to the soil in this area. The waste residue and its contaminated soil distributed within the site had become an important source of pollution [32]. According to the site investigation results, the site residue was distributed along the mountain road. Therefore the waste residue was washed by rainwater, which was very susceptible to the continuous spread of pollution. The waste residue would continue to cause more serious pollution and damage to the surrounding soil and ecological environment [33].
Risk Assessment for Agricultural Pollution
According to the site study, agricultural land was located downstream of the project site. And both the waste residue and the agricultural land were located within the same watershed. Leachate was generated from the waste residue under the effect of precipitation leaching, which might enter the ditch of the project site with surface runoff, and then could threaten the farmland [34]. As shown in the table below, the pH of the waste leachate in the south and north areas does not meet the irrigation water quality standard (GB 5084-2021). Therefore, the acidic wastewater could have an impact on farmland.
Pollution of Surface Waters Risk Assessment
About 500 m downstream of the contaminated site was surface water of Lanhe River was about 500 m downstream of the waste residue. There was acidic wastewater with a yellow color and a certain degree of pollution at the project site according to the survey. As shown in the result of the surface water, the arsenic and pH content of the drainage canal and the estuary into Lanhe River could exceed the water quality standard of Class III of the Surface Water Environmental Quality Standard (GB3838-2002). And the acidic wastewater produced by the waste residue could flow into the river, polluting the surface water quality [35]. Therefore, the acidic wastewater produced by the waste residue flowed into the river and caused pollution to the surface water quality.
Table 7.
Leaching test results of waste residue (mg/L) (water leaching).
Table 8.
Heavy metal content in the waste residue (mg/kg).
Groundwater Pollution Risk Assessment
The main source of groundwater recharge was precipitation in the atmosphere [36]. Due to the large slope of the surface topography, most of the precipitation gathered on the surface of the mountainous area was rapidly collected in the low-lying valley areas, thus forming surface streams [37]. Additionally, the project site was located in a mountainous area with high terrain, and thus the groundwater of the site was buried deep. Therefore, the impact of waste residue on groundwater is minimal, as shown by the monitoring data from groundwater wells.
Risk from the Geological Environment
A large amount of waste residue was piled up in the project area. The piling of waste residue along the slope was susceptible to geological hazards such as landslides and mudslides [38]. No landslide and mudslide geological hazards were found during the investigation. However, the waste residue in the project area was exposed and no protective measures had been laid, which was prone to landslides and mudslides under special circumstances such as heavy precipitation [39].
Comprehensive Management Strategies
Solution Comparison
The treatment technology of this project mainly consisted of off-site landfill and in-situ storage.
Table 9.
Heavy metal contents in the farmland soil (mg/kg).
(l) In-situ storage
By disposing of the waste residue in-situ, the contaminated soil was sealed off from the surrounding area, preventing pollutants from migrating with rain or groundwater and contaminating the neighborhood, and harming human health [40]. In-situ storage of waste residue could be sealed based on not destroying the original structure of the waste residue piles. The area of the waste residue pile could be effectively protected by constructing a retaining wall under the waste residue pile and interception and diversion channels around the waste residue pile. Through the upper sealing and ecological restoration measures, the cost of excavation and transportation of waste residue pile could be effectively reduced.
Table 10.
Surface water monitoring results.
Table 11.
Groundwater monitoring results.
| Sampling number | Testing factor | Concentration | Groundwater Environmental Quality Standard (GB/T14848-2017) for Class III water bodies |
|---|---|---|---|
| GW1 | pH | 7.2 | 6.5~8.5 |
| Sulfide (mg/L) | <0.003 | 0.02 | |
| As (mg/L) | 0.001 | 0.01 |
(2) Off-site landfill
Off-site landfill disposal was to select a special waste residue disposal site within the perimeter of the waste residue area, and then transport waste residue to the disposal site for landfill disposal. After the completion of landfilling, the disposal site was sealed and greened. The disposal of waste residue by landfill could isolate the contact between waste residue and human and animals, to ensure the safety of personal property and the health of regional residents. Off-site landfill disposal technology was a relatively more thorough treatment technology. However, it could require relocation and disturbance of the waste residue, the waste residue transfer process might bring risks, and the vegetation restoration area was large, and the corresponding investment cost could be increased [41].
Although off-site landfill disposal technology could have a better treatment effect, the volume of waste residue in this project was large. The relocation of large disturbed areas of waste materials was not only expensive but also difficult to find another suitable site for a new landfill [42]. In the process of waste residue relocation and transfer, the waste residue was exposed to the air, which might cause serious pollution [43]. Also the construction period was risky, and the amount of handling work was enormous, and thus the consequences were numerous. The in-situ disposal project was small in volume, short in duration, and the cost of in-situ disposal was small. In-situ disposal could also effectively solve the pollution problem of waste residue [44]. Therefore, in-situ sequestration for waste residue was chosen in this study. The desired purpose could be achieved by retaining surface water and controlling the leaching effect of surface water on the waste residue, thus reducing the generation of acidic wastewater.
General Technical Route
There were two waste residue pile regions in the project. The north area was currently exposed and was a steep slope platform. Due to the previously built interception and drainage ditches, the southern section was covered in bushes and grasses. Different restoration technology alternatives were therefore presented in accordance with the divergent conditions of the north and south areas.
The mine cave in the north area should be closed off. By constructing a retaining wall, the waste residue pile could be prevented from producing landslides. And the stability of the waste residue pile could be guaranteed by cutting and shaping the slope of the pile. The construction of interception and drainage facilities on the periphery of the remediated waste residue pile to reduce surface water infiltration and surface runoff into the waste residue pile. The surface impermeability of the north area was carried out with artificial composite materials to achieve the purpose of blocking the transmission pathway and controlling the environmental risk. The treated waste residue pile area was covered with planting soil and soil fertilization to improve the soil structure and reach the purpose of controlling the acidification of the slag pile area from the source. Vegetation was also planted to restore the ecological environment of the pile-up area.
Artificial composite surface impermeability was employed in the south to achieve the purpose of blocking the transmission pathway and controlling the environmental risk [45]. To restore the biological environment of the waste residue pile area, the waste pile area was covered with planting soil, and vegetation was also planted.
Three primary methods for treating acidic wastewater were source control, process interception, and final treatment [46]. Source control is mainly to establish interception drains to collect acidic wastewater in the waste residue pile area to reduce surface runoff. Process interception was mainly to establish ecological ditches to adsorb acidic wastewater pollution by improving the existing drainage channels with in-situ substrate and adding microbial bacterial agents and carbon sources. The final treatment was mainly to treat the acidic wastewater generated by using mobile wastewater treatment equipment [47].
Specific Treatment Programs
(1) North area.
In the northern area of the waste residue area, the first step was to block the mine cave. One mine cave was sealed to reduce the generation of acidic wastewater at the source. The second step was to protect the slope of the waste residue pile. The intercepting ditch was set at the bottom of the waste residue retaining wall and at the top of the slope. Meanwhile, drainage ditches were set up on each side of the waste residue pile to reduce the infiltration of surface water on the periphery and reduce surface runoff into the waste residue pile. The third step was to build the physical isolation layer. A physical isolation layer was used to limit environmental threats and to create an impermeable surface. This layer was made of artificial composite material. The fourth step was to perform soil fertilization. Soil fertilization could improve the soil's structure and increase the soil's capacity to store water and retain fertilizer. Finally, ecological restoration was performed in this waste residue pile by planting.
(2) South area
The first step was to clear vegetation and topsoil in the southern area. And then artificial composite materials were utilized to create an impermeable surface, to block the course of transmission and to limit environmental concerns. Through soil fertilization, the capacity of soil to store water and retain nutrients could be improved. Lastly, vegetation was planted in the waste residue pile area to restore the ecological environment of the pile area.
(3) Acidic wastewater treatment
Acidic wastewater treatment was performed by source control, process interception, and final treatment. The major method of source control was to install intercepting drains in the vicinity of the waste residue stockpile to collect acidic wastewater and lessen surface runoff. The major goal of process interception was to create ecological ditches and absorb acidic wastewater pollution by enhancing the current drainage channels with in-situ substrate and microbial bacterium. mobile sewage treatment technology was used in the final treatment to treat the produced acidic wastewater.
Conclusion
Due to the primitive mining techniques used in the early days, the majority of the sulfur and iron waste residue was piled up in a dispersed manner, taking up some of the available land resources. The waste residue produced acidic wastewater under the action of air oxidation, rainwater drenching, and surface runoff, polluting the surrounding soil and water environment. The acidic wastewater directly entered the river channel of Lanhe River through surface runoff and the reservoir of Tanghe River. The water quality of Tanghe Reservoir was affected. Furthermore, to varying degrees, the waste residue in the north area and southern areas of this study could pollute the soil and harm the nearby vegetation and biological landscape, which would pose a possible threat to the environment.
Controlling the migration of heavy metals to the outside world and reducing the heavy metal pollution in the mining area of the watershed through remediation would significantly enhance the ecological environment of the region and safeguard the health of downstream inhabitants. The local economy, community, and environment might all develop sustainably at the same time. The management precautions and strategies suggested in this study could serve as technical guidelines for projects of a similar nature. The management strategies put forward in this paper could serve as technical references for projects of a similar nature.
