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What is the Purpose of Stormwater Testing and When is it Required?

Stormwater is rain or melting snow that is unable to soak quickly into the ground. This is usually because soil is already saturated or because storms dump unusually large amounts of rain. Most stormwater runoff is from impervious surfaces like rooftops, paved streets, highways, and parking lots. In the process of flowing over these surfaces, the water collects pollutants like oil, fertilizers, pesticides, soil, trash and animal manure. Most stormwater does not get treated, even when it goes into a street drain. Instead, it flows directly into lakes, streams, rivers and marine waters. Stormwater runoff is a leading threat to our urban waters, streambeds, banks and habitats.

What is Stormwater Testing?

The rapid expansion of our cities and suburban areas has created dramatically greater risks and dangers from stormwater runoff pollution. As a result, most states have mandated stormwater testing, monitoring and remediation to deal with the problem. The purpose of mandating regular stormwater testing is to identify, remove and reduce contaminants, pollutants, fertilizers and debris that previously flowed freely into surface waters (lakes, rivers, oceans) and groundwater.

Regular stormwater inspection is required in many states and involves setting up a system for identified buildings, parking lots, roads, farms, etc., that need to do regular stormwater sampling. Samples are taken from multiple locations on a property. Then these collected samples are sent to an environmental testing laboratory for testing. The intention here is to identify whether contaminants and pollutants are entering into stormwater runoff from that property. This requires many different tests to be performed so the specific pollutants can be identified, and then the potential sources of contamination can be located and removed or remediation methods can be devised.

Why is Stormwater Testing Important?

Testing and monitoring stormwater is important because it is the best means to accomplish the goal of stormwater pollution prevention. In addition, it reduces erosion, flooding and many other environmental and health concerns, when stormwater inspections are regularly performed. Because of the many benefits, urban stormwater monitoring efforts have been implemented to provide a unified approach that continually improves stormwater pollution prevention.

Additionally, communities have increased their efforts to develop effective ways of working with rainfall, runoff, inflow, outflow and infiltration. The idea is to devise new green infrastructure practices and mitigation efforts that will benefit waters that receive this runoff, such as lakes, reservoirs, major rivers, oceans and groundwater sources (including wells).

When Should You Do Stormwater Testing?

A growing number of states, led by California, require two tests a year during a qualifying storm event. This means that stormwater sampling kits must be put in place within the specified periods of time and before a storm takes place. Immediately after a storm, these samples must be collected and sent for testing. Stormwater inspections may occur in order to identify the best places to take samples and to ensure that proper sampling procedures are in place. It is always in your best interest to follow the best practices and procedures in order to ensure that your testing results are accurate.

Who Performs Stormwater Tests and What Should You Expect?

Environmental laboratories perform stormwater sample tests. They also help with the sampling kits. Local EPA or other authorities will walk property owners through the necessary steps for where to place sampling kits, how many samples must be collected, when the two annual testing windows occur and will answer any questions. Most laboratories provide containers for collection and the packaging necessary for shipping collected samples to their laboratory.

Not only do many of these laboratories work with communities and industries to offer excellent stormwater runoff analysis, in order to provide stormwater pollution prevention, but they also help identify the sources of these pollutants. Labs cooperate with the municipal, regional, state and federal regulatory agencies, and their stringent regulatory requirements for industrial wastewater, landfills, highways, parking lots and other land uses. Quality labs follow very specifically defined stormwater testing procedures to identify a long list of regulated pollutants. This list includes specific pollutants in certain regions and states that have been identified for more specific regulation because of their potentially high concentrations.

Following testing, the lab report identifies the presence of all specific pollutants as well as their detected amounts. At this point, regulatory agencies will work with property owners to identify where the pollutants are coming from, remove the problems, make a plan for stormwater treatment on the property and help owners do whatever is necessary to reach compliance. The good news is that recommendations for remediation and control of these pollutants have helped many communities to greatly improve their water quality and their marine and/or freshwater environments.


Concerted efforts in many communities are turning stormwater into a resource. Communities are using green infrastructure and new low impact development practices, they are creating plans to capture stormwater runoff, clean it and use it for landscape and agricultural irrigation and/or groundwater recharge. Torrent Laboratory works with communities and industries to offer excellent stormwater runoff testing and analysis for stormwater pollution prevention.