(a) To
establish the alternative effluent limitations of Group B or C in §
89.52(c)
(relating to water quality standards, effluent limitations and best management
practices), a permittee shall demonstrate to the Department's satisfaction that
a precipitation event has occurred, under the procedures in this section.
(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 specified in §
89.52, unless the permit specifies
a more stringent water quality based effluent limitation, in which case no
exemption is 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 of Group C
in §
89.52 (c).
(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 § 89.52, unless
the permit specifies a more stringent water quality based effluent limitation,
in which case no exemption is 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 of Group B in §
89.52(c).
(b) The
10-year, 24-hour rainfall events 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 event has for the mine area been exceeded, or that dry weather
flow conditions did not exist, the permittee shall comply with one of the
following:
(1) The permittee shall comply with
subparagraphs (i) and (ii).
(i) Collect
24-hour rainfall information from official United States Weather Bureau
Stations within a 25-mile distance-radius-of the site.
(ii) By appropriate interpolation of the data
collected under subparagraph (i), calculate the estimated rainfall event for
the site. Appropriate interpolation shall be accomplished by:
(A) Construction of an isohyetal map in
accordance with the guidelines established by the Department.
(B) Linear interpolation between the
isohytes.
(2)
The permittee shall comply with the following:
(i) 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 secured to prevent tampering and acts of third
parties.
(ii) 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 rainfall event specified for the
mine area.
(3) Develop
alternative documentation or data concerning the rainfall event. The method or
system for developing the documentation or data shall be approved in writing
prior to the occurrence of the rainfall event for which the exemption is being
sought, and shall guarantee the integrity of the information
collected.
(d) When 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
rainfall.
(e) The
permittee is not entitled to claim a greater than 10-year, 24-hour
precipitation event storm exemption unless the permittee has fully complied
with subsections (c) and (d).
(f)
Nothing in this section authorizes the Department to grant an exemption for a
discharge which the Department finds may have caused or contributed to a
violation of general or specific water quality criteria in Chapter 93 (relating
to water quality standards).