[Code of Federal Regulations]
[Title 40, Volume 27]
[Revised as ofJuly 1, 2003]
From the U.S. Government Printing Office via GPO Access
[CITE: 40CFR440.131]

[Page 432-433]
 
                   TITLE 40--PROTECTION OF ENVIRONMENT
 
         CHAPTER I--ENVIRONMENTAL PROTECTION AGENCY (CONTINUED)
 
PART 440--ORE MINING AND DRESSING POINT SOURCE CATEGORY--Table of Contents
 
              Subpart L--General Provisions and Definitions
 
Sec. 440.131  General provisions.

    (a) Combined waste streams. In the event that waste streams from 
various subparts or segments of subparts in part 440 are combined for 
treatment and discharge, the quantity and concentration of each 
pollutant or pollutant property in the combined discharge that is 
subject to effluent limitations shall not exceed the quantity and 
concentration of each pollutant or pollutant property that could have 
been discharged had each waste stream been treated separately. In 
addition, the discharge flow from the combined discharge shall not 
exceed the volume that could have been discharged had each waste stream 
been treated separately.
    (b) Storm exemption for facilities permitted to discharge. If, as a 
result of precipitation or snowmelt, a source with an allowable 
discharge under 40 CFR part 440 has an overflow or excess discharge of 
effluent which does not meet the limitations of 40 CFR part 440, the 
source may qualify for an exemption from such limitations with respect 
to such discharge if the following conditions are met:
    (1) The facility is designed, constructed and maintained to contain 
the maximum volume of wastewater which would be generated by the 
facility during a 24-hour period without an increase in volume from 
precipitation and the maximum volume of wastewater resulting from a 10-
year, 24-hour precipitation event or treat the maximum flow associated 
with these volumes. In computing the maximum volume of wastewater which 
would result from a 10-year, 24-hour precipitation event, the facility 
must include the volume which would result from all areas contributing 
runoff to the individual treatment facility, i.e., all runoff that is 
not diverted from the active mining area and runoff which is not 
diverted from the mill area.
    (2) The facility takes all reasonable steps to maintain treatment of 
the wastewater and minimize the amount of overflow.

[[Page 433]]

    (3) The facility complies with the notification requirements of 
Sec. 122.60 (g) and (h). The storm exemption is designed to provide an 
affirmative defense to an enforcement action. Therefore, the operator 
has the burden of demonstrating to the appropriate authority that the 
above conditions have been met.
    (c) Storm exemption for facilities not permitted to discharge. If, 
as a result of precipitation (rainfall or snowmelt), a source which is 
not permitted to discharge under 40 CFR part 440, has an overflow or 
discharge which violates the limitations of 40 CFR part 440, the source 
may qualify for an exemption from such limitations with respect to such 
discharge if the following conditions are met:
    (1) The facility is designed, constructed, and maintained to contain 
the maximum volume of wastewater stored and contained by the facility 
during normal operating conditions without an increase in volume from 
precipitation and the maximum volume of wastewater resulting from a 10-
year, 24-hour precipitation event. In computing the maximum volume of 
wastewater which would result from a 10-year, 24-hour precipitation 
event, the facility must include the volume which would result from all 
areas contributing runoff to the individual treatment facility, i.e., 
all runoff that is not diverted from the area or process subject to zero 
discharge, and other runoff that is allowed to commingle with the 
influent to the treatment system.
    (2) The facility takes all reasonable steps to minimize the overflow 
or excess discharge.
    (3) The facility complies with the notification requirements of 
Sec. 122.60(g) and (h). The storm exemption is designed to provide an 
affirmative defense to an enforcement action. Therefore, the operator 
has the burden of demonstrating to the appropriate authority that the 
above conditions have been met.
    (d) pH adjustment. (1) Where the application of neutralization and 
sedimentation technology to comply with relevant metal limitations 
results in an inability to comply with the pH range of 6 to 9, the 
permit issuer may allow the pH level in the final effluent to slightly 
exceed 9.0 so that the copper, lead, zinc, mercury, and cadmium 
limitations will be achieved.
    (2) In the case of a discharge into natural receiving waters for 
which the pH, if unaltered by human activities, is or would be less than 
6.0 and approved water quality standards authorize such lower pH, the pH 
limitations for the discharge may be adjusted downward to the pH water 
quality criterion for the receiving waters provided the other effluent 
limitations for the discharge are met. In no case shall a pH limitation 
below 5.0 be permitted.
    (e) Groundwater infiltration provision. In the event a new source 
subject to a no discharge requirement can demonstrate that groundwater 
infiltration contributes a substantial amount of water to the tailing 
impoundment or wastewater holding facility, the permitting authority may 
allow the discharge of a volume of water equivalent to the amount of 
groundwater infiltration. This discharge shall be subject to the 
limitations for mine drainage applicable to the new source subcategory.