Current through August 26, 2024
(1) COMBINED WASTE STREAMS. In the event that
waste streams from various subcategories or segments of subcategories in this
chapter 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 may 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 may not exceed the volume that could
have been discharged had each waste stream been treated separately.
(2) STORM EXEMPTION FOR FACILITIES PERMITTED
TO DISCHARGE. If, as a result of precipitation or snowmelt, a source with an
allowable discharge under this chapter has an overflow or excess discharge of
effluent which does not meet the limitations of this chapter, the source may
qualify for an exemption from such limitations with respect to such discharge
if the following conditions are met:
(a) 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 shall 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.
(b) The
facility takes all reasonable steps to maintain treatment of the wastewater and
minimize the amount of overflow.
(c) The facility complies with the
notification requirements of
40
CFR 122.41(m) and (n). 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 conditions have been met.
(3) 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 this chapter, has
an overflow or discharge which violates the limitations of this chapter, the
source may qualify for an exemption from such limitations with respect to such
discharge if the following conditions are met:
(a) 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 shall 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.
(b) The facility takes all
reasonable steps to minimize the overflow or excess discharge.
(c) The facility complies with the
notification requirements of
40
CFR 122.41(m) and (n). 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 conditions have been met.
(4) PH ADJUSTMENT.
(a) 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 6.0 to 9.0, 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.
(b) 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 may a pH limitation below 5.0
be permitted.
(5)
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 department 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.
