(a) To
establish the alternative effluent limitations of Group B or C in §
87.102(a)
(relating to hydrologic balance: effluent standards), a permittee shall
demonstrate to the Department's satisfaction that, under this section, a
precipitation event has occurred.
(1) The
occurrence of a precipitation event greater than a 10-year, 24-hour
precipitation event may be demonstrated by meeting the requirements of
subsections (b)-(d) for each discharge that exceeds the effluent limits in
§
87.102, unless the permit
specifies a more stringent water quality based effluent limitation, in which
case no exemption will be available under this section. If the permittee
demonstrates to the Department's satisfaction that a greater than 10-year,
24-hour precipitation event has occurred, the permittee shall meet the effluent
limitation enumerated as Group C in §
87.102 (a).
(2) The occurrence of a precipitation event
equal to or less than a 10-year, 24-hour precipitation event may be
demonstrated by meeting the requirements of subsections (c) and (d) for each
discharge that exceeds the effluent limits specified in § 87.102, unless
the permit specifies a more stringent water quality based effluent limitation,
in which case no exemption will be available under this section. If the
permittee demonstrates to the Department's satisfaction that a precipitation
event equal to or less than a 10-year, 24-hour precipitation event has
occurred, the permittee shall meet the effluent limitations enumerated as Group
B in § 87.102(a).
(b) The 10-year, 24-hour precipitation event
for specific areas in this Commonwealth shall be determined by reference to
data provided by the National Oceanic and Atmospheric Administration or
equivalent resources.
(c) For the
permittee to demonstrate that the 10-year, 24-hour precipitation event has for
the permittee's mine area been exceeded or that dry weather flow conditions did
not exist, the permittee shall do one of the following:
(1) Collect 24-hour rainfall information from
all official United States Weather Bureau Stations within a 25-mile distance
(radius) of the site; by appropriate interpolation of the data collected,
calculate the estimated rainfall event for the site. Appropriate interpolation
shall be accomplished by the following:
(i)
Construction of an isohyetal map in accordance with the guidelines established
by the Department.
(ii) Linear
interpolation between the isohytes.
(2) Prepare a verified copy of the chart or
readout from a Department approved flow measuring device which continuously
records the influent to the permitted treatment facility. The device shall be
approved by the Department in writing prior to the rainfall event for which the
exemption is sought and shall be secure to prevent tampering and acts of third
parties.
(3) Prepare an analysis
identifying the runoff area tributary to the treatment facility, and compare
the actual runoff as measured and depicted by the flow measuring device with
the runoff expected from the 10-year, 24-hour precipitation event specified for
the mine area.
(4) Develop
alternative documentation or data concerning the precipitation event. The
method or system for developing the documentation or data shall be approved in
writing prior to the occurrence of the event for which the exemption is being
sought, and shall guarantee the integrity of the information
collected.
(d) If the
discharge from the site exceeds an effluent limit in the permit, the permittee
shall notify the Department within 5 days of the occurrence of the event that
he is applying for an exemption from that limit and shall within 30 days
thereafter provide to the Department:
(1) The
data required by subsection (c).
(2) A showing that the facility from which
the discharge occurred was designed, maintained and operated during and prior
to the event to accommodate or treat a 10-year, 24-hour precipitation event.
(e) The permittee will
not be entitled to claim a greater than 10-year, 24-hour precipitation event
storm exemption unless the permittee has fully complied with the requirements
of subsections (c) and (d).
(f)
Nothing in this section shall be construed as authorizing the Department to
grant an exemption for a discharge which the Department finds may have caused
or contributed to a violation of a general or specific water quality criteria
in Chapter 93 (relating to water quality standards).