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What are TMDLs and why are they relevant?

Total maximum daily loads, or TMDLs, establishes a maximum amount of a pollutant allowed in a waterbody. It differs from other pollution management efforts because it requires loads from all pollution sources within an impaired watershed to be allocated instead of from just a few sources, including industrial facilities. In short, TMDLs are utilized as a planning tool for restoring water bodies that fall short of its water quality standards and mobilizes all sources of pollution to make an effort in improving these standards. TMDLs may represent a single waterbody/pollutant combination. However, there are also cases where a single TMDL represents multiple waterbody/pollutant combinations within a watershed or multiple watersheds.

The California Water Board has recently passed the 2018 Industrial General Permit amendments that include the update of 26 new TMDLs within Los Angeles, 3 in the San Francisco Bay Area, 1 in Santa Ana, and 7 in San Diego. So when will these TMDLs be imposed on industrial facilities? Well, it was originally proposed to be June 2019 (I can hear your jaws dropping), but thanks to the industrial community taking a stand and pushing back on the feasibility of implementing the structural Best Management Practices (BMPs) needed to meet these new standards, the board decided to push the implementation date back to until July 1, 2020 (phew – sigh of relief)! Although the effective date for this amendment is not for another year and a half, now is the time to properly inform yourself on TMDLs, establish whether or not they will affect your state of compliance, and if they do apply, take action in preparing your facility to meet the new limits.

How are TMDLs developed?

According to EPA regulations, States are responsible for developing TMDLs and submitting them for approval or disapproval. In the event that the EPA disapproves, the EPA must then develop a replacement TMDL.

That being said, there are 5 steps to producing a TMDL:

Step 1: Stakeholder Involvement – The public and/or other private groups become involved in bringing a water body of concern to the water boards’ attention and may continue to participate in the development of the TMDL (i.e. providing data, commenting on drafts)

Step 2: Water Body Assessment – Selection of pollutants to consider, estimation of waterbody’s loading capacity, estimation of the pollutant load and determination of needed reductions to meet water quality standards

Step 3: Allocation Development – Based on data, pollutant loads are allocated for each source while water quality standards are still met. A TMDL can be expressed through this equation:

TMDL =∑WLA + ∑LA +MOS, where WLA is the sum of waste load allocations (point sources), LA is the sum of load allocations (nonpoint sources and background) and MOS is the margin of safety. Not a mathematician? Basically, add up all the pollutants that can enter a waterbody without exceeding the quality standards sprinkle in a safety factor, and boom, a TMDL is born!

Step 4: Implementation Plan Development – A plan is developed to specify what actions must be taken in order to meet allocations

Step 5: Basin Plan Amendment – A Basin Plan is amended so that TMDLs are incorporated and approved by the appropriate Regional Board, State Water Resources Control Board, the Office of Administrative Law, and U.S. EPA Region 9. Public hearings are utilized in this step to complete the processes

Complying with TMDL-specific permit requirements: Defining a responsible discharger and what TMDLs pertain to you

First off, if you are a discharger with NEC coverage or a facility that is complying with the NONA criteria, these TMDL specific permit requirements do not apply to you. However, if you are a discharger with NOI coverage, and you discharge stormwater directly or through an MS4 directly to an impaired water body, then you are a responsible discharger subject to these TMDL specific permit requirements.

Now to correctly read the amendment’s table E.2, there are 3 questions about your site you need to know the answers to:

  1. Which impaired waterbody and/or tributary of impaired waterbody does your site directly discharge to?
  2. What watershed is your site located in?
  3. What pollutants does your site discharge?

Now for an example, let’s say you have defined yourself as a responsible discharger. You also successfully answered the questions above and identified your site directly discharges to Ballona Creek and your watershed is Ballona Watershed. From your pollutant source assessment, copper is a pollutant of concern at your facility through your industrial activities. In the past your facility has averaged around 0.0102 mg/L for copper samples. You are now ready to tackle Table E.2 of IGP with 4 easy steps:

Step 1: Under the 2nd column, look for both of your impaired waterbody and watershed (Ballona Creek and Ballona Watershed) because the scales of water bodies vary in this column. Note that more than 1 TMDL may fall under your water body or watershed

Step 2: Look for the pollutants (copper) that correlate with your pollutant source assessment in the 3rd column

Step 3: The 4th column will inform you whether or not there is an additional TMDL Numeric Action Level (TNAL) or Numeric Effluent Limitation (NEL) and the 5th column informs you on any actions you are required to take. In this case, total Copper has an NEL of 0.01237mg/L and Qualifying Storm Event (QSE) sampling and reporting has to be conducted to compare them to the TMDL NEL.

Step 4: The 6th column states the effective compliance due date for that specific TMDL. In other words, your copper sample values must meet the NEL values by this date

From reading the chart, you know that your TMDL is a Numeric Effluent Limitation and that you are meeting them. Yay! But what exactly do the terms TNAL and NEL mean? What would it mean if your values were to exceed?

In the proposed amendment, the TNALs and NELs are defined as instantaneous maximums rather than annual averages. This means that one reported value above either TNAL or NEL will automatically deem you in exceedance. As dictated in Section XII of the IGP, the exceedance of TNALs is not a direct violation of the General Permit and it will trigger the same Exceedance Response Action process that would be required if a Numeric Action Level (NAL) was exceeded. On the other hand, if there is an exceedance of a NEL, the responsible discharger will be in direct violation of the General Permit and as a result, subject to Water Quality Based Corrective Actions. Although this may sound like a daunting state to be in, there is a way back to baseline! Beginning to reassess your site, improving non-structural BMPs and implementing structural BMPs would be a great start to bring your values down.

Keeping up with TMDLs not your cup of tea?

The waterboard has also approved two (2) compliance options in Attachment I that, if implemented with all criteria met, automatically deems you in compliance of the General Permit and makes any Level 1 or Level 2 status you previously had no longer applicable. Crazy right?!

The On-site Compliance Option states that a responsible discharger may implement on-site BMPs for the capture and use, infiltration, and/or evapotranspiration of stormwater. They may also instead include BMPs they capture and divert the required stormwater runoff volumes to a publicly -owned sanitary sewer treatment without discharging into a municipal sewer system or receiving surface water body. These structural BMPs have to meet the following criteria:

  • Effectively capture, infiltrate and/or evapotranspire the volume of runoff produced up to and during the 85th percentile 24-hour precipitation.
  • Designed to work for all areas associated with industrial activities and water sources  (i.e. stormwater, run-on)
  • Be designed by a California licensed civil engineer with the ability to empty within 24 hours or with additional storage capacity beyond the standard to offset longer drawdown time
  • Properly inspect and maintain the BMP
  • Include a shut-off mechanism
  • Meet Maximum Contaminant Level (MCL) criteria from Table A (as seen below) for industrial pollutants at the facility in order to protect the groundwater. Currently, there are no repercussions if MCLs are exceeded, but keep in mind this may change in the future!

Aside from developing the BMPs, there a few more steps to ensure proper reporting and monitoring. If you were to select this option, you would need to report the type of BMP with a description of its pretreatment system, a map with the BMP’s location along with its latitude and longitude, and bypass mechanisms. You are also required to sample the influent entering the infiltration BMP(s) at least two times within the first half of the Reporting Year (July 1 – December 31), two times within the second half of the Reporting Year (January 1 – June 30), and report them to SMARTS within 30 days. In addition, stormwater pollution prevention plans (SWPPPs) need to be updated with proper documentation and photographs.

The Off-site Compliance Option states that a responsible discharger may form a partnership, approved by the applicable Regional Water Board Executive Officer, with a local jurisdiction or another discharger to implement an off-site stormwater capture and/or infiltration BMP. This option requires the following criteria:

  1. Effectively capture, infiltrate and/or evapotranspire the volume of runoff produced up to and during the 85th percentile 24-hour precipitation.
  2. Authorized non-stormwater and industrial stormwater is not discharged to a water of the United States or reaches a water body of the state before reaching the BMP

If you were to select this option, you would still need to comply with the same monitoring and records requirement of the on-site compliance option and update your SWPPP to include proper documentation of the BMP.

I know this is A LOT of essential information to get through, but by getting through this blog you have a basic grasp on the new TMDLs and Compliance Options. Congratulations! Now by thoroughly looking through Table E.2, with your own facility’s information, you will be able to identify which, if any, TMDLs pertain to you and begin implementing new BMPs your site may need to stay in compliance by July 1, 2020.

Where to get started?

Mapistry has experts standing by from our stormwater services team to help guide you through these amendments. Whether you need help understanding the new stormwater permit amendments or answering specific questions about your situation, set up a consultation with one of our experts.


  • Full Attachment E of IGP: mnamend_igp_e.pdf
  • Full Attachment I of IGP:

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