We’ve worked closely with a lot of stormwater site maps and have seen the good, the bad and the ugly along the way. A site map is not only a requirement of the California industrial stormwater permit – it is actually a valuable tool to help you understand and coordinate your site’s stormwater pollution prevention plan (SWPPP). In fact, a good site map not only will guide the development and implementation of your SWPPP, but also can guide your facility's operations.
While the California State Water Resources Control Board (SWRCB)'s industrial stormwater permit provides the basic requirements for a site map, we know that many industrial facilities still need help with the details. Here’s our insider tips on how to develop a good site map:
It may seem obvious, but the site boundary is a critical first step that paves the way for the rest of the site map. The site boundary delineates your site from the surrounding area. Outside of that boundary, you need to show what drainage areas are contributing stormwater runoff ("run-on") to your site. Typically, you want to keep those flows separate from the flows generated on site so that you can manage smaller volumes and the known potential pollutants from your site. By eliminating run-on, you only have to deal with your stormwater, not someone else's stormwater discharges. Within the site, drainage areas need to be properly delineated and directional flow lines need to show where run-off is going and where the discharge locations should be depicted. Based on the permit requirement of sampling from each drainage area, these discharge locations are usually are also the sampling location for your stormwater team.
Surface flow, depicted through the use of flow direction arrows, should be directed to the stormwater infrastructure (e.g. pipes, drain inlets). All stormwater control measures or structural Best Management Practices (BMPs) located on the site or tied into the infrastructure all needs to be drawn and labeled on the map too. The map also needs to show where the different industrial activities are occurring and where industrial materials are located. These generally can be described as potential pollutant sources on the site map. Their locations and proximity to the structural BMPs will influence the types, frequency, and level of non-structural BMPs needed on your site.
The last parts of a good site map are the required, but often forgotten, legend and North arrow.
A site map is Bad if it is missing that required information or if it is inconsistent with information in the text of the SWPPP. Labeling consistency is one of the biggest problems we see in maps and SWPPPs. In addition, inconsistent labeling makes it much more difficult to communicate on a project. What I may be calling "DI-1" may appear as "Drain-11" on a site map due to outdated information or changes since the map was created. Samples collected with the label DI-1 and DI-11 may cause problems, especially if there are exceedances and BMPs need to be evaluated, but the site maps don't match the activities occurring.
That brings up another common trend with bad site maps, outdated information. With the new industrial stormwater permit requiring updates and re-submissions within 30 days of significant changes, an outdated site map is not only a headache for internal staff, but also could get a facility in trouble with the SWRCB. The SWPPP and the site map are living documents that need to be quickly updated with changes in operations.
While the information on a site map is critical to permit compliance and internal facility operations, you can have too much info. We sometimes come across a site map, just one sheet mind you, covered with 20, 30, or 40+ different features and labels, that often are overlapping each other or way too small to read the text. Site maps with superfluous information are as ineffective as site maps with incorrect information. Sometimes it makes sense to have a set of maps rather than just one map. The information on the map should be the key, permit-required features - so don't include the kitchen sink (unless it is a non-stormwater discharge).
If a site map isn’t showing the whole picture of the potential pollutant sources on your site and where stormwater is being discharged, then things could get Ugly. The map could be used against you in court as an example of why you were not in compliance with the permit or worse, trying to deceive the public and the SWRCB. An ugly map can definitely make the case for the plaintiff when talking about non-compliance, which is very costly.
Developing a site map all boils down to showing how stormwater is flowing across your site, the potential pollutant sources for stormwater discharges, and what is being done to manage it all. The key to making a good site map (or set of maps) is to provide the permit required information while keeping it well organized, accurate, and up to date.
Mapistry makes creating site maps simple. Our software leads you through a checklist of exactly what the permit requires. Click here to learn more about the specific IGP requirements for site maps.
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