Chart of Suspended Sediment in Rivers and Lakes Area of ​​Hon Gai Coal Mine Cluster in 2005 2009

Coal sorting plant I, using screening technology to separate dry coal dust, manually selecting large lump coal and the remaining coal using inclined washing troughs, recovering peat using a system of tower settling tanks and natural settling pits. Water from the screening process arises as follows: water in the industrial cleaning process, water overflowing tanks, discharge bottoms, and peat reservoirs. The water sources generated at this stage are mainly mixed with coal dust. If not treated promptly, it will affect the receiving environment.

Coal Entrainment Plant III uses advanced technology so it does not generate wastewater during the production process. Wastewater used in watering and dust suppression process.

Wastewater from screening activities contains coal dust and a large amount of suspended solids, thus affecting the surface water environment in the area. Causes sedimentation of water bodies around the project due to solid waste generated. During the exploitation process, it will cause fluctuations in the hydrological network. According to the results of research on the surface water environment in the surrounding area, it shows that most of the surface water environment around the study area is acidic, the amount of CO2 in the water is high, so it has the ability to corrode metals and concrete . . The hardness of water is high, due to the dissolution of mine waste. In addition, when wastewater flows through the drainage system, it carries organic matter, garbage, animal and plant remains, oil and grease...

b. Hon Gai Coal Selection Company

Wastewater generated from screening activities contains many pollutants, with increased levels of organic substances and heavy metals. Source of pollution

Contamination is from waste rock and dust during the screening process. All water there is recovered and reused to the maximum level, to minimize impact on the environment. Through the research and evaluation of the facilities we have.

Hon Gai). Currently, Hon Gai Coal Processing Company has invested in a peat flotation system combined with a pressurized filter press system. The products after screening and filtering are bran 3 and waste rock. These products all have a moisture content of W≤20%, this technology ensures maximum recovery of circulating water.

3.2.2. Wastewater from underground mining

Because the furnaces are dug straight along the seam, the slope of the furnace road changes up and down. There are sections where the furnace is sunken between the two slope tops, so water cannot flow. These areas are forced to be drained using local pumps.

surface water quality of the area. The level of this impact is not large, because the mine already has mine wastewater treatment systems, oil and grease treatment and domestic wastewater treatment that meet allowed standards.

The total amount of water supplied for daily use when the project comes into stable operation is 200m 3 /day and night. Therefore, the amount of domestic wastewater generated is calculated as 80% of the water supply, respectively:

treated in septic tanks built underground under toilets. After storing the water here, it will be sucked up and treated by the Environmental Sanitation Company. Therefore, only 3/4 of the amount of domestic wastewater passing through temporary manholes and not being thoroughly treated will have an impact on surface water quality.

Table 3.12. The content of pollutants in wastewater discharged into streams (when there are no mitigation measures) according to standard 20 TCN-51-84

According to Table 3.12, the quality of domestic wastewater is forecast to be polluted with the parameters TSS, BOD, total Nitrogen, total Phosphorus, and Coliform. Therefore, domestic wastewater will be treated by the company to meet QCCP standards before being discharged into the receiving source, Ha Tu stream.

The total industrial production area of ​​the mine according to the project's calculations is: 45,500 m 2 . The average annual rainfall of the Hon Gai area is about 1,619 mm/year, the highest rainfall in a day in the area is: rainwater runoff on the ground only accounts for about 2% of the amount of rainwater falling on the ground.

Rainwater that flows over the surface of the production area often has high solid content (from 100 - 1500 mg/l), and also contains oil and grease. If the estimated solid content washed away by rainwater running over the Nui Beo coal mine production site is 1,500 mg/l, the total amount of solids brought into Ha Tu stream per year is 220,994 tons/year.

The above calculation shows that if there are no mitigation measures, solids will be introduced into the stream bed, causing sedimentation of the stream bed, while reducing the self-assimilation ability of the stream, increasing the possibility of causing pollution in stream water. . In addition, rainwater runoff also introduces many other pollutants into streams. The Ha Tu stream flowing through is the place that receives most of the solids and oils from rainwater flowing over the total mine area.

3.2.3. Rainwater flows over the field

The amount of wastewater from the mine depends on the coal mining output each year. Based on data declaring and paying environmental protection fees for industrial wastewater of units in the coal industry, the total amount of wastewater from the mine (in 2009) was 38,914,075m 3 . Two typical parameters affecting the environment of mine wastewater are pH and suspended sediment, heavy metals (iron, manganese). In which the pH ranges from 3.1 to 6.5, the suspended solids content is 1.7 to 2.4 times higher than the allowed threshold. Therefore, wastewater from mines causes many impacts on river systems,

streams and lakes in coastal areas - causing sedimentation, loss of aquatic resources, and deterioration of water quality. In particular, pollution in the mining area is cumulative pollution, combined with the impact of illegal coal mining over a long period of time, leading to a situation where some lakes and ponds in the Cam Pha area have become acidified, affecting the water quality for agriculture.

Results of wastewater analysis in 2010 at some mines in Quang Ninh province show that wastewater from mines often contains high color and low pH. Wastewater at Coc Sau, Cao Son, Mong Duong mines... all have suspended matter content higher than allowed standards. Almost all wastewater from coal mines is contaminated with manganese, exceeding allowable standards.

The impact of mine wastewater has caused the quality of surface water in rivers, streams, and lakes in the vicinity of coal mines to decline. In particular, surface water quality in Quang Ninh shows signs of severe pollution.

- The acidity of mine wastewater varies seasonally and depends on the sulfur content. However, the wastewater from Nui Beo mine is quite strongly acidic in the dry season, pH=5.5. [28]

Table 3.13. The amount of water drained from the seams

3.2.4. Rainwater flows through coal warehouses

Most of the locations of workshops and coal warehouses have not changed, so the impact of rainwater runoff through these premises has been evaluated. Rainwater in coal warehouses often brings in solids and dust, affecting the surface water environment of the area. Most coal warehouses do not have roofs, so rainwater easily washes away coal and dirt. The pH of mine wastewater always ranges from 3.1 - 6.5. Suspended residue content often exceeds QCVN by 2-3 times. According to an assessment by a unit in the group, wastewater from coal mines is causing many negative impacts on the environment of rivers, streams, and coastal areas such as causing sedimentation, loss of aquatic resources, and deterioration of water quality. ...

In Hon Gai and Cam Pha areas, water quality has changed fundamentally, rich in sulfate ions, reduced in bicarbonate ions, and acidic. Water resources are reduced in both quality and reserve.

3.2.5. Rainwater overflows through the coal port

Table 3.14. Rainwater flows over some coal ports

At coal ports, the situation of transporting and loading coal in the "absolute protection zone" still exists. Many large tonnage ships coming to receive coal cannot enter the port and have to use transshipment methods, so a large amount of coal is scattered into Ha Long Bay. Report on the current state of the environment in Ha Long Bay in 2010 said: in coastal areas of Ha Long Bay, there have been signs of local pollution due to increased amount of suspended solids (TSS), decreased amount of dissolved oxygen (DO). ); Nitririte and Coliform disease-causing bacteria at the southern coastal coal port of Cau Trang... have caused turbidity to approximate or exceed allowable standards.

The quality of coastal sea water at some coal loading ports of coal processing plants and coal loading docks at coal ports of companies is also polluted or beginning to be polluted due to suspended sediment and although it tends to decrease gradually, still higher than the allowable limit. There were times when monitoring in the Hon Gai - Cam Pha area (Quang Ninh) determined that ammonium exceeded the limit in aquaculture and aquatic conservation areas. Particularly, coastal oil and grease in Quang Ninh has been polluted from mild to severe levels,