Page 134 - California Stormwater Workshop Handouts

Industrial General Permit Fact Sheet

requirements have been revised. Section XI.B.4 of this General Permit requires
Dischargers to collect samples from all discharge locations regardless of whether
the discharges are substantially similar or not. Dischargers may analyze each
sample collected, or may analyze a combined sample consisting of equal
volumes, collected from as many as four (4) substantially similar discharge
locations. A minimum of one combined sample shall be analyzed for every one
(1) to four (4) discharge locations, and the samples shall be combined in the lab
in accordance with Section XI.C.5 of this General Permit.

Representative sampling is only allowed for sheet flow discharges or discharges
from drainage areas with multiple discharge locations. Dischargers shall select
the appropriate location(s) to be sampled and intervals necessary to obtain
samples representative of storm water associated with industrial activities
generated within the corresponding drainage area. Dischargers are not required
to sample discharge locations that have no exposure of industrial activities or
materials as defined in Section XVII of this General Permit within the
corresponding drainage area. However, Dischargers are required to conduct the
monthly visual observations regardless of the selected locations to be sampled.

This General Permit defines a QSE as a precipitation event that produces a
discharge from any drainage area that is preceded by 48 consecutive hours
without a discharge from any drainage area. The previous permit did not include
a QSE definition; instead, it utilized a different approach to defining the storm
events that were required to be sampled. Under the previous permit, eligible
storm events were storm events that occurred after three consecutive working
days of dry weather. The three consecutive working days of dry weather
definition in the previous permit led Dischargers to miss many opportunities to
sample. Some Dischargers were unable to collect samples from two storm
events in certain years under the previous definition. To resolve this difficulty,
this General Permit increases the sampling requirements to four (4) QSEs per
year, while decreasing the number of days without a discharge, resulting in
additional opportunities for Dischargers to sample. Additionally, by eliminating
the previous permit’s reference to “dry weather,” this General Permit allows some
precipitation to occur between QSEs so long as there is no discharge from any
drainage area. This change will result in more QSE sampling opportunities.

To improve clarity and consistency, the definitions contained in other storm water
permits were considered with the goal of developing a standard definition for ‘dry
weather’ for this General Permit. The 2008 MSGP sets a “measurable storm
event” as one that produces at least 0.1 inches of precipitation and results in an
actual discharge after 72 hours (three days) of dry weather. The State of
Washington defines a “qualifying storm event” as a storm with at least 0.1 inches
of precipitation preceded by at least 24 hours of no measurable precipitation,
mirroring the definition found in the previous MSGP (2000 version). The State of
Oregon requires that samples be taken in the first 12 hours of discharge and no
less than 14 days apart. Review of other permits concludes that there is not a
single commonly used approach to triggering sampling in industrial general
permits. Therefore an enforceable sampling trigger is included in this General

Order 2014-0057-DWQ 50