Page 149 - California Stormwater Workshop Handouts

Industrial General Permit Fact Sheet

action or additional benchmark monitoring providing that the other 2008
MSGP requirements are met. The 2008 MSGP Fact Sheet requires
Dischargers to include in the following in the SWPPP: 1) map(s) showing the
reference site location, facility, available land cover information, reference site
and test site elevation, available geology and soil information for reference
and test sites, photographs showing site vegetation, site reconnaissance
survey data and records. This General Permit requires this information to be
included in the Natural Background Pollutant Source Demonstration in
Section XII.D.2.c.

The Natural Background Pollutant Source Demonstration in this General
Permit is for a Discharger that can demonstrate that pollutants causing the
NAL exceedances are not related to industrial activities conducted at the
facility, and are solely attributable to the presence of those pollutants in
natural background. The pollutant may also be present due to industrial
activities, in which case the Discharger must demonstrate that the pollutant
contribution from the industrial activities by itself does not result in an NAL
exceedance. Natural background pollutants include those substances that
are naturally occurring in soils or groundwater that have not been disturbed
by industrial activities. Natural background pollutants do not include legacy
pollutants from earlier activity on a site, or pollutants in run-on from
neighboring sources which are not naturally occurring. Dischargers are not
required to reduce concentrations for pollutants in the effluent caused by
natural background sources if these pollutants concentrations are not
increased by industrial activity.

The 2008 MSGP Fact Sheet states that the background concentration of a
pollutant in runoff from a non-human impacted reference site in the same
watershed must be determined by evaluation of ambient monitoring data or
by using information from a peer-reviewed publication or a local, state, or
federal government publication specific to runoff or storm water in the
immediate region. Studies that are in other geographic areas, or are clearly
based on different topographies or soils, are not sufficient to meet this
requirement. When such data is not available, and there are no known
sources of the pollutant, the background concentration should be assumed to
be zero.
In cases where historic monitoring data from a site are used for generating a
natural background concentration, and the site is no longer accessible or able
to meet reference site acceptability criteria, the Discharger must submit
documentation (e.g., historic land use maps) indicating the site did meet
reference site criteria (such as indicating the absence of human activity)
during the time data collection occurred.

Once the Level 2 ERA Technical Report, including a Natural Background
Demonstration meeting the conditions in Section XII.D.2.c of this General
Permit is certified and submitted via SMARTS, the Discharger is no longer
responsible for the identified background parameters(s) in the corresponding
drainage area(s). A Discharger that submits this type of demonstration will

Order 2014-0057-DWQ 65