Effective Stormwater Discharge Monitoring: Best Practices and Compliance

Stormwater monitoring is a way for facilities, construction sites, and municipal sewer systems to limit the release of pollutants into waterways keeping them clean and safe. Those subject to developing stormwater monitoring plans must identify sources of pollutants and best practices to limit their release. Being able to effectively monitor stormwater discharge will give insight as to how successful their plans are so adjustments can be made. Let’s review the importance of stormwater monitoring that protects our water and wetlands. 

Understand Regulations 

Stormwater discharge monitoring requirements came into effect with the Clean Water Act (CWA). The CWA established the National Pollutant Discharge Elimination System (NPDES) permit program in 1972 aimed at regulating point sources to decrease water pollution.¹ Stormwater is a major source of water pollution as runoff is collected in stormwater drainage systems and often released via point sources to neighboring waterbodies. Stormwater remains untreated, unless the stormwater is connected to a combined stormwater sewer system, meaning the harmful pollutants get discharged to the waterbodies.  

While the CWA and establishment of the NPDES permit program are enacted at the federal level, most states are in charge of implementing the program. States developed plans to implement the regulation which then must be approved by the EPA. States are then responsible for administering permits, reviewing management plans and monitoring reports, and delivering penalties. With each state overseeing implementation, permitting and monitoring requirements vary between jurisdictions so it’s important that facilities are aware of the specific state-level requirements.² 

Pollution Means Permits 

The NPDES permit program requires permits for construction activities that disrupt soil, municipal sewer systems, and certain industrial activities. Permits set forth limits on the amount of pollutants (e.g., grease, oil, pesticides, nutrients) that can be discharged. Limits are based on technology to control pollutants and the quality of the waterbodies where stormwater is discharged to.³ 

Facilities submit a Notice of Intent (NOI) if they have the potential to discharge regulated pollutants or a No Exposure Certification which indicates that the facility has reviewed their stormwater management system and confirmed that industrial activities are covered and aren’t exposed to stormwater runoff. In some states, public notice is required prior to NOI approval, meaning you must publish in a newspaper notification that your facility is seeking NPEDS permit coverage. While issued permits are good for five years, it’s important to review your state’s requirements upon renewal.   

Pollution Prevention Plan 

When required to obtain a stormwater discharge permit, facilities must also develop a Stormwater Pollution Prevention Plan (SWPPP). A SWPPP should cover all industrial activities and materials that have the potential to release pollutants into stormwater runoff. The purpose of the plan is for facilities to identify ways to limit and control the release of pollutants. The plan also includes procedures for monitoring stormwater discharge, which may vary by state. The SWPPP needs to be kept onsite and available for inspections, and any updates should be documented accordingly. As part of the permitting process, some jurisdictions may require you to submit your SWPPP with your NOI application.⁴

For industrial facilities, a SWPPP includes facility contact information, a site map, sediment and erosion controls, good housekeeping practices, and monitoring procedures. Let’s dive into some of these key components and best management practices. 

Maintain Drainage System

When developing your site map, you must identify potential pollutant sources and areas where industrial activities (e.g., oil containing equipment, maintenance areas, chemical storage areas, loading/unloading areas, dumpsters) occur as well as features of the site’s stormwater drainage system. This includes identifying features such as stormwater drains and inlets, retention and detention ponds, swales, impermeable areas, and underground piping. The map should also identify outfalls, the flow of water into drainage features, and drainage areas, which are important for determining monitoring locations.  

An important part of good housekeeping is ensuring the drainage system is maintained. This includes removing trash and debris from inlets and outfalls, sweeping of paved areas, cleaning any filters, maintaining landscaping and green infrastructure, and ensuring retention and detention ponds are free of trash and debris, there is good water flow, and there are no signs of bank erosion. Facilities should assign responsibility and keep a maintenance log to track inspections and any repairs or corrective actions that occur. The log should be kept as an appendix to the site’s SWPPP for record keeping purposes. Regularly inspecting and maintaining your facilities drainage system helps keep pollutants out of stormwater and ensures proper capture and discharge of stormwater to keep your facility in optimal condition.  

Proper Material Storage

Some facilities may store materials in tanks, drums, or containers outside in designated areas. Fuel tanks associated with equipment such as generators and fire pumps, and transformers containing insulating oil, can also be located outside. Leaks in the storage containers and tanks or spills during refilling or refueling can be carried away in runoff so it’s important to properly store materials. Some practices include storing containers on raised surfaces such as pallets or concrete pads. Concrete containing walls can also be built around areas that store materials to contain any spills. Secondary containment systems can also be used, and are generally required for fuel tanks, to prevent the accumulation of substances that can pollute stormwater. Designated storage areas can also be covered by structures to limit contact with precipitation. In some instances, salt is stored onsite for deicing in the winter. Proper coverings, such as tarps, are important for preventing it from mixing with runoff and precipitation. Inspections to check for damage to containers and ensuring they are sealed appropriately is an important step for preventing the release of chemicals to stormwater runoff. 

Spill Cleanup Protocol

Being prepared for spills is another way to prevent water pollution from your facility. Spill kits and other supplies should be located in close proximity to where substances are stored and used. Training employees on how to properly clean up spills is important, both for the safety of employees and the environment. Spill cleanup procedures need to be documented in the site’s SWPPP. Facility inspections should include checking that spill kits are fully stocked and contain the necessary equipment for the materials present onsite. Preparing for potential spills is necessary for proper stormwater management and reduces a site’s risk of exceeding pollutant thresholds. 

Organized Trash Area

Even for companies that don’t store materials and equipment outside, dumpsters can pose a potential problem regarding water pollution and maintaining the storm drainage system. Dumpster lids need to be kept closed at all times and trash should never be left on the ground. Fencing surrounding dumpster locations will also prevent trash from blowing away in cases of overflow and protect it from animals. Employees should frequently inspect dumpster areas to maintain proper conditions. This will prevent trash from blocking storm inlets and outfalls and polluting water runoff. 

Erosion and Sediment Control

Many sites are not comprised of entirely impermeable surface areas and surrounding land areas have the potential to erode. Sediment control measures are important for reducing the amount of sediment in discharged stormwater and for proper functioning stormwater drainage systems. Measures can include landscaping or mulching to prevent soil from dislodging from permeable areas of the site. For slopes and hills, seeding, sodding, and slope drains can help prevent erosion as water flows down the gradient. Consulting with civil engineers can help determine susceptible areas and the best control measures to implement.  

Stormwater Monitoring and Corrective Actions

Testing stormwater discharges from your facility will help determine if your control measures are effective and discharge is in compliance with limits set out by your permit. Again, each receiving waterbody will have their own benchmarks for the type and amount of pollutants that can be discharged. Monitoring frequencies will vary depending on the state but will generally include both visual and analytical monitoring.  

When developing your SWPPP, sampling points should be identified and are usually at the outfalls where stormwater exits the site. Sampling points should capture all types of industrial activities or pollutant sources. In some cases, certain outfalls will be substantially identical so only one outfall needs to be sampled. Samples must be collected after a measurable storm event. Visual inspections will collect qualitative data such as stormwater odor, color, clarity, oil sheens, and presence of solids. Stormwater samples from sheet flow, drains, or pipes must be sent to a laboratory to test for pollutant concentrations. All monitoring procedures and results should be documented in the SWPPP appendices. Leveraging trained professionals to do conduct the monitoring can lead to better samples and safety outcomes.  

Based on monitoring results, corrective actions should then be identified, implemented, and documented. Quality monitoring procedures coupled with good maintenance of your site and proper oversight of industrial activities and materials can help keep your facility in regulatory compliance and limit its impact on the environment. ⁵ 

How EHS Insight Can Help 

EHS Insight provides a software solution for many environmental, health, and safety challenges, including stormwater monitoring. Our platform allows you to record stormwater monitoring events and results of analytical testing. For each event, you can record details of the event and for each outfall, information on the sample itself along with the results. The platform has the ability to add attachments, such as pictures or complete laboratory results for additional record keeping. As each location will have different parameters and benchmarks, EHS Insight allows you to input specific benchmarks for each location and enables you to determine if the monitoring results exceed the established benchmarks. The platform goes one step further and allows you to assign corrective actions and ensure completion for occurrences where discharge exceeds benchmarks or is continuously increasing. EHS Insight’s document library allows you to upload your SWPPP so that it is always accessible by necessary personnel on their computers, phones, and tablets. Additionally, our offline sync enables employees to complete stormwater monitoring forms from the field without the use of internet connection.  

If your facility is subject to stormwater monitoring, reach out to an EHS Insight representative today to learn how we can help simplify your monitoring process! 

¹ National Pollutant Discharge Elimination System (NPDES), U.S Environmental Protection Agency, 29 October 2024, https://www.epa.gov/npdes 

² NPDES Permit Basics, U.S Environmental Protection Agency, 26 November 2024, https://www.epa.gov/npdes/npdes-permit-basics  

³ NPDES Permit Limits, U.S Environmental Protection Agency, 16 September 2024, https://www.epa.gov/npdes/npdes-permit-limits 

⁴ Developing Your Stormwater Pollution Prevention Plan: A Guide for Industrial Operators, U.S Environmental Protection Agency, February 2009, https://www3.epa.gov/npdes/pubs/industrial_swppp_guide.pdf  

⁵ Industrial Stormwater Monitoring and Sampling Guide, U.S Environmental Protection Agency, March 2009, https://www3.epa.gov/npdes/pubs/msgp_monitoring_guide.pdf