Demonstrating Natural Background in Stormwater

Date / Time:
Wednesday, Sep 27 9:10am to 9:40am
Convention Center Hall D
Track / Session:
Industrial Track / Demonstrating Compliance Through the ERA Process


This presentation will explain how to help determine if Natural Background concentrations may be a contributor to, or causing Numeric Action Levels (NALs) exceedances in stormwater at a site.  Exceeding NALs is not a violation of the California Industrial Stormwater Permit (Industrial Permit) if the exceedances are caused by naturally occurring chemicals in the environment.  Furthermore, implementing advanced BMPs for industrial activities when NAL exceedances may actually be from naturally occurring sources is unnecessary, expensive and often ineffective.  This session will be informed by recent findings from in-depth natural background studies the presenters have conducted at the Lawrence Livermore National Laboratory (LLNL), and at industrial stormwater litigation and monitoring sites throughout California.


The Industrial Permit lists several general items to include in a Natural Background Pollutant Source Demonstration, such as summarizing past data and soil sampling, but no details on what to look for in past data, such as relationships between total suspended sediment and metals or between different metals, or where to sample soil and at what depths.  This presentation will help fill in the blanks on what to look for, describe the most likely indications of natural background contribution, and discuss the importance of pursuing multiple lines of evidence in a natural background evaluation.  The presentation will discuss additional lines of evidence not mentioned in the Industrial Permit, such as evaluating total and dissolved concentrations, using naturally occurring elements, such as europium in the LLNL study, as tracer compounds from natural sources, and considering other natural background contributors such as chemicals in precipitation and aerial deposition. 


Certain chemicals are much more likely than others to be from natural background sources, and a matrix will be provided of common stormwater pollutants and their relative likelihood that they could be from natural background sources.  Links to reference sources on local and regional soil background concentrations, regulatory agency guidance documents and other references with more details than the session can cover will also be provided.




Take aways from this presentation include:


  • A better understanding of natural background contributions in stormwater;

  • Information on the most likely chemicals that contribute to natural background;

  • Research tested tools and  techniques to use in a natural background study;

  • An understanding of how to conduct a natural background study for an industrial stormwater site; and

  • References for natural background studies, regulatory guidance, where to find soil background concentrations, current chemical in precipitation data, etc.


Primary Speaker:
David Dixon, Roux Associates, Inc.
Supporting Speaker 1:
Craig Fish, Lawrence Livermore National Laboratory
Primary Speaker Biography: 


Mr. Dixon is a Principal Geologist with Roux Associates and has twenty-eight years of experience managing and conducting complex characterization and remediation projects, determining background concentrations, NPDES permitting and evaluations, Industrial stormwater evaluations and SWPPP preparation and implementation, and litigation support and expert testimony on Clean Water Act (CWA) cases.  He is currently managing the stormwater compliance at multiple industrial sites and providing litigation support for CWA stormwater  cases.  He is a member of the CASQA industrial and aerial deposition subcommittees, and has presented at national and regional venues on CWA stormwater issues.

Supporting Speakers Biographies: 

Craig Fish is an Environmental Analyst and Stormwater Program Lead for surface and groundwater compliance at Lawrence Livermore National Laboratory, where he developed a storm water plan to comply with the new State Industrial permit.  He is a Member of the CASQA industrial and aerial deposition subcommittees.  He has a Master of Arts, in Geology from Boston University and a Bachelor of Arts, in Geology from Earlham College in Richmond, Indiana.  Craig has 29 years of experience as an environmental professional. His other experience includes preparing Notices of Intent, annual reports and Storm Water Pollution Prevention Plans.