Management and Prevention of Stormwater Benchmark Exceedances

The prevention of stormwater contamination is a major concern that does not discriminate between, and is applicable to, all types of industry. Stormwater can be defined as storm water runoff (e.g. rain flow), snow melt runoff, and drainage. All industrial facilities have some form of stormwater discharge which has the potential to be impacted by pollutants from different types of industrial activities, such as pallets stored outside, forklift traffic between buildings, outdoor parts storage, etc. Due to this potential, all industrial facilities in the United States are required to comply with National Pollutant Discharge Elimination System (NPDES) Industrial Stormwater Regulations. Noncompliance with any of the Industrial Stormwater Regulations, such as the discharge of stormwater mixed with pollutants from processes or other industrial activity, is a violation of the Clean Water Act, which regulates the discharge of pollutants to waters of the United States.

Facilities are required to ensure that any stormwater discharging from their property is free from contaminants by conducting analytical sampling. Analytical sample results are then submitted to prove that their stormwater discharges do not exceed benchmark monitoring requirements for parameters such as heavy metals, total suspended solids, and chemical oxygen demand, among many others. The parameters that a facility must sample for are determined based on the facility’s Standard Industrial Classification (SIC) or North American Industry Classification System (NAICS) Codes. If the facility exceeds the benchmark monitoring requirements for any parameter, then the facility must take corrective action. The level of this corrective action is mainly determined by which state the facility is located in, because in addition to the federal level requirements, each state can, and oftentimes does, impose a stricter level of stormwater requirements.

For example, the Georgia Industrial Stormwater Permit GAR050000 requires facilities to review their Stormwater Pollution Prevention Plan (SWPPP) and the selection, design, installation, and implementation of control measures to determine if modifications are necessary to meet the benchmark limits in the permit. Facilities are required to take corrective action to minimize or prevent the discharge of pollutants within 30 calendar days of discovery. Documentation is required if this time frame is infeasible, and a schedule for completion of the corrective action must be prepared by the facility. If the corrective action cannot be completed within 90 calendar days, then the facility must notify the Georgia Environmental Protection Division (EPD) and explain the rationale for the extension.

In order to avoid benchmark exceedances and the issues that accompany them, facilities have several different options, ranging from inexpensive to costly, temporary to permanent, and requiring a low or high level of maintenance, and everything in between. There is no one size fits all approach to benchmark exceedance prevention as the parameters and site layout can widely vary from facility to facility. The first step to management of benchmark exceedances is to determine which parameter(s) are exceeding the benchmark. The facility should then identify which outfalls, the locations where stormwater leaves a facility, have parameters with benchmark exceedances. This knowledge will allow the facility to research possible sources for that particular parameter and concentrate its focus to the drainage area serving that specific outfall. Identification of possible sources of the parameter is paramount in determining how to best minimize the potential of the source to contaminate stormwater.

The most effective method for benchmark exceedance prevention is elimination of the potential for the source of contamination. Common sources of stormwater contamination can include scrap metal and old equipment storage, tire storage, leaking dumpsters, poor housekeeping, improper chemical and petroleum product storage, equipment wash water, equipment maintenance, air pollution control devices such as baghouses, erosion, lack of best management practices, and process wastewater. For example if you have elevated levels of Zinc, you may want to minimize the amount of galvanized material stored outside. The facility should examine the drainage area(s) serving the outfall(s) and relocate rusty scrap metal, old equipment, and tires away from drainage leading to the outfall preferably under cover if possible. This will prevent further degradation of the metal, equipment, and tires which can contribute to heavy metals contamination such as iron, copper, zinc, and aluminum.

Dumpsters can also contribute to increased metals contamination as they are oftentimes delivered to a facility with holes and are sometimes not well maintained while they are on site. You should ensure that dumpsters are stored away from drainage areas and placed under cover. Additionally, you can refuse to accept dumpsters that are heavily damaged. If dumpsters are used at your facility to store materials that have the potential to contribute to benchmark exceedances, such as wastewater sludge, it is in your benefit to ensure they do not leak too much and are in good working condition.

Poor housekeeping can have a surprisingly significant impact on analytical results as well. Facilities should ensure that garbage, dust, and debris is regularly removed from the exterior areas of the facility. If these types of materials are allowed to regularly wash into drainage channels, they can adversely impact the amount of total suspended solids that are discharged from the facility’s outfalls. Requiring employees to regularly contribute to the cleanliness of the facility will eliminate this potential issue. Regular and routine housekeeping can help prevent exceedances and other environmental impacts that can be costly and inconvenient to say the least. This will also maintain a positive site appearance which will discourage heavily scrutinizing inspections.

Improper chemical, oil, and petroleum product storage is an obvious source for stormwater pollution but can be sometimes overlooked. Facilities should examine the Safety Data Sheets (SDSs) for all of the chemicals stored outside to determine if the chemicals are a potential source of a particular contaminant. Oil and petroleum products can heavily impact chemical oxygen demand and Oil & Grease. Even if it is determined that the chemicals are not a potential source, the facility’s chemical, oil, and petroleum products should be provided with secondary containment and placed under cover to eliminate the risk of a spill mixing with stormwater. Common forms of secondary containment include spill pallets, portable berms, and concrete dikes which should be sized to contain 100% of the contents of the largest storage container (110% if the secondary containment is not under cover).

Equipment and vehicle wash water and maintenance can increase the level of metals, total suspended solids, and chemical oxygen demand. Wash water is a non-allowable stormwater discharge as it can be contaminated with oil and other fluids used to operate the equipment. Equipment washing should always take place in containment and the wash water should be collected and properly disposed of or sent to wastewater treatment. Equipment maintenance should also be conducted in a covered designated area to ensure that oils and other fluids can be properly captured without the potential for mixing with stormwater. This is one specific pollutant source that some state agencies, like the GA EPD, are scrutinizing during facility inspections and report submission reviews.

Air pollution control devices like baghouses can be another easily overlooked contributor to stormwater pollution. These types of devices pull particulate matter and dust out of the air inside facilities. This dust can sometimes be contaminated with metals or other pollutants and is typically collected in a 55-gallon drum. These devices must be regularly emptied. During this process the collected dust oftentimes is spilled onto the ground where it can mix with stormwater and contribute to contamination issues. These unloading areas should be regularly cleaned, and work instructions should be developed for the unloading process to ensure that the potential for spillage is minimized.

Erosion can be a significant contributor of total suspended solids. Facilities should regularly inspect the property, including drainage ditches and Outfall locations, for areas of erosion. Best management practices (BMPs) are the optimal method of combating contamination originating from erosion. Any exposed soil or actively eroding areas should be stabilized through seeding, regrading, implementation of silt fences, or the introduction of gravel or rip rap. Erosion is an issue that regulatory agencies are focusing on at an increased rate and should be addressed as soon as it is discovered on site. BMPs should be employed in any areas that carry a risk of heavy flow of stormwater. A combination of the BMPs listed above can be used to redirect flow and disperse the energy of the flow to discourage the possibility of further erosion.

Process wastewater is typically the easiest potential contamination contributor to identify, but it can also be the most detrimental. Process wastewater is a non-allowable stormwater discharge as it has the potential to be contaminated with any number of pollutants depending on the process producing it. A facility should regularly conduct inspections of the property in order to identify any process changes that may have taken place which could result in a discharge of process wastewater. Any process wastewater generated by the facility should be collected and properly disposed of or sent to wastewater treatment.

The sources that can contribute to contamination of the stormwater discharged from a facility can vary widely depending on the particular parameter in question and the type of industrial activity performed at the facility. However, if the facility takes a measured approach examining the impacted outfalls, layout of the site, and the specific parameter, the scope of the problem can be reduced which can, in turn, make the optimal solution more apparent and attainable.

If you have any questions regarding management of your facility’s stormwater permits and practices, or if you would like CTI’s help in determining your facility’s compliance with your state and the federal stormwater regulations, please contact Conversion Technology Inc. at (770) 263-6330 or visit our website at

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