G. Metal Mining (Ore Mining and Dressing)

1. Authorized Stormwater Discharges

The requirements in Sector G apply to stormwater discharges associated with industrial activity from metal mining facilities as identified by the industrial activity code specified in Table 5 of Appendix D, including mines abandoned on Public lands on or after August 25, 1980, discharges from inactive facilities, and mining sites undergoing reclamation. Coverage is required for metal mining facilities that discharge stormwater contaminated by contact with, or that has come in contact with, any overburden, raw material, intermediate product, finished product, byproduct, or waste product located on the site of the operation.

Discharges from the following areas are authorized for active and temporarily inactive facilities:

a. Discharges from waste rock and overburden piles if composed entirely of stormwater and not combining with mine drainage.

b. Topsoil piles.

c. Off-site haul and access roads.

d. On-site haul and access roads constructed of waste rock, overburden, or spent ore if discharge is composed entirely of stormwater and not combined with mine drainage.

e. On-site haul and access roads not constructed of waste rock, overburden, or spent ore except if mine drainage is used for dust control.

f. Runoff from tailings dams or dikes when not constructed of waste rock or tailings and no process fluids are present.

g. Runoff from tailings dams or dikes when constructed of waste rock or tailings and no process fluids are present, if composed entirely of stormwater and not combined with mine drainage.

h. Concentration building if no contact with material piles.

i. Mill site if no contact with material piles.

j. Office or administrative building and housing if mixed with stormwater from industrial area.

k. Chemical storage area.

l. Docking facility if no excessive contact with waste product that would otherwise constitute mine drainage.

m. Explosive storage.

n. Fuel storage.

o. Vehicle and equipment maintenance area and building.

p. Power plant.

q. Truck wash areas if no excessive contact with waste product that would otherwise constitute mine drainage.

r. Unreclaimed, disturbed areas outside of active mining area.

s. Partially or inadequately reclaimed areas or areas not released from reclamation requirements.

2. Industrial Activities Authorized by Sector G Permittees under Sector G are primarily engaged in the following types of activities:

a. Mining of ores.

b. Ore dressing and beneficiating, whether performed at co-located, dedicated mills, or at separate (e.g. custom) mills.

c. Reclamation of mining sites.

3. Limitations on Authorization Discharges not authorized by this permit:

a. Discharges from active metal mining facilities that are subject to effluent limitation guidelines for the Ore Mining and Dressing Point Source Category (40 CFR pt. 440). Discharges that come in contact with overburden or waste rock are subject to 40 CFR pt. 440, and are therefore not authorized under this permit, provided that the discharges drain to a point source (either naturally or as a result of intentional diversion) and they combine with “mine drainage” that is otherwise regulated under the Part 440 regulations. Discharges from overburden or waste rock can be covered under this permit if they are composed entirely of stormwater, do not combine with sources of mine drainage that are subject to 40 CFR pt. 440, and meet other eligibility criteria contained in Part I.A.

b. Discharges from exploration sites and land disturbance activities that are conducted to determine the viability of ore extraction and the construction of infrastructure prior to ore extraction, including the building of site access roads and removal of overburden and waste rock, and are not covered by an active mining permit issued by the applicable State or Federal agency. These discharges do not require an NPDES/SDS industrial stormwater permit. Discharges from these areas which disturb greater than one acre are covered by the General Stormwater Permit for Construction Activity.

c. Acid drainage and contaminated springs or seeps. Contaminated seeps and springs discharging from waste rock dumps that do not directly result from precipitation events are not authorized by this permit (see also the standard Limitations on Authorization in Part I.B).

d. Closed or abandoned mine sites where disturbances associated with extraction, beneficiation, or processing of mined materials took place prior to August 25, 1980, and where extraction, beneficiation or processing activities have not taken place after August 25, 1980, are not considered either active or inactive mining facilities and do not require an NPDES/SDS industrial stormwater permit.

e. Sites where mining claims are being maintained prior to disturbances associated with extraction, beneficiation, or processing of mined materials and sites where minimal activities are undertaken for the sole purpose of maintaining a mining claim are not considered either active or inactive mining facilities and do not require an NPDES industrial stormwater permit.

4. Sector-Specific Definitions

The following definitions do not supersede the definitions of active and inactive mining facilities established by 40 CFR 122.26(b)(14)(iii):

a. Reclamation - activities undertaken, in compliance with applicable mined land reclamation requirements, following cessation of the activities associated with extraction through production of a salable product, intended to return the land to an appropriate post-mining land use in order to meet applicable Federal and State reclamation requirements.

b. Active metal mining facility -a place where work or other activity related to the extraction, removal, or recovery of metal ore is being conducted. For surface mines, this definition does not include any land where grading has returned the earth to a desired contour and reclamation has begun. This definition is derived from the definition of “active mining area” found at 40 CFR pt. 440.132(a).

c. Inactive metal mining facility -a site or portion of a site where metal mining and/or milling occurred in the past but is not an active facility as defined above, and where the inactive portion is not covered by an active mining permit issued by the applicable State or Federal agency. An inactive metal mining facility has an identifiable Owner/Operator.

d. Temporarily inactive metal mining facility -a site or portion of a site where metal mining and/or milling occurred in the past but currently are not being actively undertaken, and the facility is covered by an active mining permit issued by the applicable State or Federal agency.

5. Stormwater Controls

a. Employee Training.

The Permittee shall conduct training at active and temporarily inactive sites. All training regardless of site type shall be documented in the facility’s SWPPP.

b. Erosion and Sedimentation Controls (No additional requirements).

c. Good Housekeeping (No additional requirements).

d. Inspections.

The Permittee shall conduct site inspections in accordance with Part III.G, of the permit. If the facility is inactive and unstaffed, temporarily inactive and unstaffed as defined above, or is a site undergoing reclamation, the Permittee is waived from the requirement to conduct monthly facility inspections in Part III.G.1. The Permittee shall inspect the site when the Permittee has reason to believe that severe weather or natural disasters may have damaged stormwater control measures or increased discharges.

If circumstances change and the facility becomes active and/or staffed, this exception no longer applies and compliance with monthly inspection requirements in accordance with Part III.G.1 shall begin immediately.

The Agency retains the authority to revoke this waiver where it is determined that the discharge causes, has a reasonable potential to cause, or contributes to an in-stream excursion above an applicable water quality standard, including designated uses.

e. Preventive Maintenance (No additional requirements).

f. Spills and Leaks (No additional requirements).

g. Management of Runoff.

If treatment of stormwater (e.g. chemical or physical systems, oil and water separators, artificial wetlands) is necessary to protect water quality, describe the type and location of treatment used. Passive and/or active treatment of stormwater runoff is encouraged where practicable. Treated runoff may be discharged as a stormwater source regulated under this permit provided the discharge is not combined with discharges subject to effluent limitation guidelines for the Ore Mining and Dressing Point Source Category (40 CFR pt. 440).

h. Other Industry specific Controls Measures.

When capping is necessary to minimize pollutant discharges in stormwater, identify the source being capped and the material used to construct the cap.

6. SWPPP Requirements

In addition to the requirements of Part IV, the Permittee shall also comply with the following:

a. Facility Map.

The Permittee shall document in the SWPPP the locations of the following (as appropriate):

1. Mining or milling site boundaries.

2. Access and haul roads.

3. Outline of the drainage areas of each monitoring location within the facility with indications of the types of discharges from the drainage areas.

4. Location(s) of all permitted discharges covered under an individual NPDES/SDS permit, outdoor equipment storage, fueling, and maintenance areas.

5. Materials handling areas.

6. Outdoor manufacturing, outdoor storage, and material disposal areas.

7. Outdoor chemicals and explosives storage areas.

8. Overburden, materials, soils, or waste storage areas.

9. Location of mine drainage (where water leaves mine) or other process water.

10. Tailings piles and ponds (including those proposed).

11. Heap leach pads.

12. Off-site points of discharge for mine drainage and process water.

13. Surface waters.

14. Boundary of tributary areas that are subject to effluent limitations guidelines.

15. Location(s) of sites undergoing reclamation and reclaimed areas.

b. Inventory of Exposed Materials.

The Permittee shall document in the SWPPP the mining and associated activities that can potentially affect stormwater, including a general description of the location of the site relative to major transportation routes and communities.

c. Potential Pollutant Sources.

For each area of the mine or mill site where stormwater discharges associated with industrial activities occur, the Permittee shall identify the types of pollutants (e.g. heavy metals, sediment) likely to be present in significant amounts. The Permittee shall consider the following factors:

1. The mineralogy of the ore and waste rock (e.g. acid forming).

2. Toxicity and quantity of chemicals used, produced, or discharged.

3. The likelihood of contact with stormwater.

4. Vegetation of site (if any).

5. History of significant leaks or spills of toxic or hazardous pollutants. Also include a summary of any existing ore or waste rock or overburden characterization data and test results for potential generation of acid rock. If any new data is acquired due to changes in ore type being mined, the Permittee shall update the SWPPP with this information.

d. Description of Stormwater Controls.

The Permittee shall document all control measures that are implemented consistent with Part 5. If control measures are implemented or planned but are not listed in Part 5, above, the Permittee shall include descriptions of these controls in the SWPPP.

7. Monitoring and Reporting Requirements

a. Monitoring and reporting requirements in this part do not apply to unstaffed inactive and temporarily inactive facilities or sites undergoing reclamation.

b. In accordance with the benchmark monitoring requirements of Part V, the Permittee shall monitor the applicable parameters in Table G-1, below.

Sector-Specific Benchmark Values and Effluent Limitations: Sector - G-1. Discharges may be subject to requirements for more than one sector or subsector.
Link to this table

Subsector Parameter Benchmark Values
G1 Active Copper Ore Mining, Dressing Facilities Solids, Total Suspended (TSS) 100 mg/L 3
Nitrite Plus Nitrate-Nitrogen, Total (as N) 0.68 mg/L
COD (Chemical Oxygen Demand) 120 mg/L


c. In accordance with the monitoring requirements of Part V, the Permittee shall monitor the applicable parameters in Table G-2. The Permittee may be notified by the Agency that additional monitoring must be conducted to accurately characterize the quality and quantity of pollutants discharged from waste rock and overburden piles.

Sector-Specific Benchmark Values and Effluent Limitations: Sector - G-2. Discharges may be subject to requirements for more than one sector or subsector.
Link to this table

Subsector Parameter Benchmark Values
G2 Active Metal Mining Facilitiess Solids, Total Suspended (TSS) 100 mg/L 3
pH 4 6.0-9.0 SU
Hardness, Calcium & Magnesium, Calculated (as CaCO3)1 no benchmark value
Antimony, Total (as Sb) 0.18 mg/L
Arsenic, Total (as As) 0.680 mg/L
Cadmium, Total (as Cd) 1 0.0078 mg/L 2
Copper, Total (as Cu) 1 0.028 mg/L 2
Iron, Total (as Fe) 1.0 mg/L
Lead, Total (as Pb) 1 0.164 mg/L 2
Nickel, Total (as Ni) 1 0.938 mg/L 2
Selenium, Total (as Se) 0.040 mg/L
Silver, Total (as Ag) 1 0.0041 mg/L 2
Zinc, Total (as Zn) 1 0.234 mg/L 2

1The benchmark values of some metals are dependent on water hardness. For these parameters, the Permittee shall determine the hardness of the receiving water to identify the applicable ‘hardness range’ for determining their benchmark value. See Table 4 of Appendix B for hardness dependent benchmark values in accordance with Minn. R. 7050.0222 and Minn. R. 7052.0100.
2Values given are for total hardness of 100 mg/L only.
3If the Permittee is required to comply with Appendix A, part F.1, the benchmark value for Solids, Total Suspended (TSS) is 65 mg/L, instead of 100 mg/L.
4For purposes of benchmark pH monitoring, the Permittee is required to report instantaneous results only, and not a calculation of pH averages. pH measurements are logarithmic, and the Agency will be performing a logarithmic average for this parameter using the instantaneous results submitted.


Sector-Specific Benchmark Values and Effluent Limitations: Sector - G-3. Discharges may be subject to requirements for more than one sector or subsector.
Link to this table

Discharge/Source of Discharge Note/Comment
Piles
Waste rock/overburden If composed entirely of stormwater and not combining with mine drainage. See note below.
Topsoil No additional comments
Roads constructed of waste rock or spent ore
On-site haul roads If composed entirely of stormwater and not combining with mine drainage. See note below.
Off-site haul and access roads No additional comments
Roads not constructed of waste rock or spent ore
On-site haul roads Except if mine drainage is used for dust control
Off-site haul and access roads No additional comments
Ore Processing/Plant Site
Runoff from tailings dams and dikes when constructed of waste rock/tailings Except if process fluids are present and only if composed entirely of stormwater and not combining with mine drainage. See note below.
Runoff from tailings dams/dikes when not constructed of waste rock and tailings Except if process fluids are present
Concentration building If stormwater only and no contact with piles
Mill site/pellet plant If stormwater only and no contact with piles
Ancillary areas
Office and administrative building and housing If mixed with stormwater from the industrial area
Chemical storage area No additional comments
Docking facility Except if excessive contact with waste product that would otherwise constitute mine drainage
Explosive storage No additional comments
Fuel storage (oil tanks/coal piles) No additional comments
Vehicle and equipment maintenance area/building No additional comments
Parking areas But coverage unnecessary if only employee and visitor-type parking
Power plant
Truck wash area Except when excessive contact with waste product that would otherwise constitute mine drainage
Reclamation-related areas
Any disturbed area (unreclaimed) Any disturbed area (unreclaimed)
Partially/inadequately reclaimed areas or areas not released from reclamation requirements No additional comments

Note: Stormwater runoff from these sources is subject to the NPDES program for stormwater unless mixed with discharges subject to 40 CFR pt. 440 that are regulated by another permit prior to mixing. Non-stormwater discharges from these sources are subject to NPDES/SDS permitting and may be subject to the effluent limitation guidelines under 40 CFR pt. 440. Discharges from overburden/waste rock and overburden/waste rock-related areas are not subject to 40 CFR pt. 440 unless: (1) it drains naturally (or is intentionally diverted) to a point source; and (2) combines with “mine drainage” that is otherwise regulated under the Part 440 regulations. For such sources, coverage under this permit would be available if the discharge composed entirely of stormwater does not combine with other sources of mine drainage that are not subject to 40 CFR pt. 440, as well as meeting other eligibility criteria contained in Part I of the permit. Permit applicants bear the initial responsibility for determining the applicable technology-based standard for such discharges.


8. Use of Infiltration Devices and/or Industrial Stormwater Ponds for Stormwater Treatment and Disposal

Sector G industrial facilities are authorized to use designed infiltration devices or industrial stormwater ponds for stormwater management.

9. Termination of Permit Coverage

A site or a portion of a site that has been released from applicable state or federal reclamation requirements on or after August 25, 1980, is no longer required to maintain coverage under this permit, provided that the covered stormwater discharges do not have the potential to cause or contribute to violations of state water quality standards.

This page was last edited on 30 April 2015, at 15:56.