Page 140 - California Stormwater Workshop Handouts

Industrial General Permit Fact Sheet

are required in response to an exceedance, have been identified as a problem by
the Water Boards, industry and environmental stakeholders.

This General Permit contains two (2) types of NALs. Annual NALs function similarly
to, and are based upon, the values provided in the 2008 MSGP. Instantaneous
maximum NALs target hot spots or episodic discharges of pollutants and are
established based on California industrial storm water discharge monitoring data.
When a Discharger exceeds an NAL it is required to perform ERAs. The ERAs are
divided into two levels of responses and can generally be differentiated by the
number of years in which a facility’s discharge exceeds an NAL trigger. These two
levels are explained further in Section XII of this General Permit. This ERA process
provides Dischargers with an adaptive management-based process to develop and
implement cost-effective BMPs that are protective of water quality and compliant
with this General Permit. This process is also designed to provide Dischargers with
a more defined pathway towards full compliance.

The ERA requirements in this General Permit were developed using best
professional judgment and Water Board experience with the shortcomings of the
previous permit’s compliance procedures. Public comments received during State
Water Board hearings on the 2002, 2005, 2011, 2012 and 2013 draft permits, and
NPDES industrial storm water discharge permits from other states with well-defined
ERA requirements were also considered by the State Water Board.

The State Water Board presumes that one single NAL exceedance for a particular
parameter is not a clear indicator that a facility’s discharge is out of compliance with
the technology-based effluent limitations or receiving water limitations. This
presumption recognizes the highly variable nature of storm water discharge and the
limited value of a single quarterly grab sample to represent the quality of a facility’s
storm water discharge for an entire storm event and all other non-sampled storm
events. With this presumption, the State Water Board is addressing costly
monitoring requirements that do not bring forth valuable compliance and/or water
quality information.

2. NALs and NAL Exceedances

a. This General Permit contains two types of NAL exceedances as follows:

Annual NAL exceedance - the Discharger is required to calculate the
average annual concentration for each parameter using the results of all
sampling and analytical results for the entire facility for the reporting year
(i.e., all "effluent" data), and compare the annual average concentration to
the corresponding Annual NAL values in Table 2 of this General Permit. An
annual NAL exceedance occurs when the annual average of all the sampling
results for a parameter taken within a reporting year exceeds the annual NAL
value for that parameter listed in Table 2 of this General Permit.

For the purposes of calculating the annual average concentration for each
parameter, this General Permit considers any sampling result that are a
“non-detect” or less than the method detection limit as a zero (0) value. The
reason to use zero (0) values instead of the detected but not quantifiable

Order 2014-0057-DWQ 56