Stormwater Management Fact Sheet: Visual Inspection

Visual inspection is a Best Management Practice (BMP) in which members of a Stormwater Pollution Prevention Team visually examine material storage and outdoor processing areas, the stormwater discharges from such areas, and the environment in the vicinity of the discharges, to identify contaminated runoff and its possible sources.

In a visual inspection, stormwater runoff may be examined for the presence of floating and suspended materials, oil and grease, discoloration, turbidity, odor or foam; and storage areas may be inspected for leaks from containers, discolorations on the storage area floor, or other indications of a potential for pollutants to contaminate stormwater runoff.

Visual inspections may indicate the need to modify a facility to reduce the risk of contaminating runoff.


EPA has recognized visual inspection as a baseline BMP for over 10 years. Its implementation, however, has been sporadic. Implementation may increase as more facilities develop Stormwater Pollution Prevention Plans. Implementation may also increase as facility management recognizes visual inspection to be effective both in protecting water quality and in reducing costs.

Advantages And Disadvantages

Visual inspections are an effective way to identify a variety of problems. Correcting these problems can improve the water quality of the receiving water.

Limitations associated with visual inspections include the following:

  • Visual inspections are effective only for those areas clearly visible to the human eye.
  • The inspections need to be performed by qualified personnel.
  • To be effective, inspections must be carried out routinely. This requires a corporate commitment to implementing them.
  • Inspectors need to be properly motivated to perform a thorough visual inspection.

Key Program Components

Visual inspections for signs of stormwater contamination should be performed routinely. Flows should be observed during dry periods to determine the presence of any stains, sludge, odors, and other abnormal conditions.

Visual inspections should also be made at all stormwater discharge outlet locations during the first hour of a storm event, once runoff has reached its maximum flow rate. Inspectors should examine the discharge for the presence of floating and suspended materials, oil and grease, discoloration, turbidity, foam, or odor.

Inspection frequency interval may be determined by the stormwater discharge permit, by storm frequency, or by the potential risk from the site. Inspections should be made at least once a month in areas with frequent storms; inspections may be less frequent where storms are less frequent. Finally, inspection frequency may be based in part on the history of previous spills and leaks. Experienced personnel should evaluate the causes of previous accidents, assess the risks for future accidents, and determine an inspection schedule based on these risks.

Proper records of inspection results must be kept. The record for each inspection should include the date of the inspection, the names of the personnel who performed the inspection, and their observations.

Visual inspections of a facility should focus on the following key areas:

  • Storage facilities.
  • Transfer pipelines.
  • Loading and unloading areas.
  • Pipes, pumps, valves, and fittings.
  • Tanks (including internal and external inspection of the tank for corrosion and inspection of its support or foundation for deterioration).
  • Primary or secondary containment facilities.
  • Shipping containers.

In addition, a visual inspection should include assessing the integrity of the stormwater collection system; checking for leaks, seepage, and overflows from sludge and waste disposal sites; and ensuring that dry chemicals and dust from industrial areas is not exposed to wind or other elements that may move them into the runoff.


A visual inspection BMP program should be incorporated into every stormwater discharger's record keeping and internal reporting structure. Outfall flow rates and the presence of oil sheens, floatables, coarse solids, color, and odors will probably be the most useful indicators of potential problems. Specific parameters to look for in completing a visual inspection include the following:

  • Odor: Discharge odors can vary widely. Some may indicate the source of contamination. Industrial discharges may smell like a particular spoiled product, oil, gasoline, a specific chemical, or a solvent. For example, the decomposition of organic wastes in a discharge will release sulfide compounds, creating an intense smell of rotten eggs. Significant sanitary wastewater contributions also will cause pronounced and distinctive odors.
  • Color: Color may indicate inappropriate discharges, especially from industrial sources. Industrial discharges may be any color. Dark colors, such as brown, gray, or black, are most common. For instance, flow contaminated by meat processing industries is usually a deep reddish-brown. Paper mill wastes (plating-mill wastes) are often yellow. Wash water from cement and stone working plants can cause cloudy discharges. Contamination from industrial areas may come from process waters (slug or continuous discharges); from equipment and work area wash water discharged to floor drains; or from spills washed into storm drains.
  • Turbidity: Turbidity is often affected by the degree of gross contamination. Industrial flows can be cloudy (moderately turbid) or opaque (highly turbid). Undiluted industrial discharges, such as those coming from continual flow sources or intermittent spills, are often highly turbid. Sanitary wastewater also is often cloudy in nature.
  • Floatable matter: A contaminated flow may also contain floatable solids or liquids. Identifying floatables can aid in finding the source of the contamination, because these substances are usually direct products or byproducts of the manufacturing process or the sanitary system. Examples of floatables of industrial origin are animal fats, spoiled food products, oils, plant parts, solvents, sawdust, foams, packing materials and fuel.
  • Deposits and Stains: Deposits and stains (residues) are any type of coating that remains after a non-stormwater discharge has ceased. Deposits or stains usually are of a dark color and usually cover the area surrounding the stormwater discharge. They often contain fragments of floatable substances, and, at times, take the form of a crystalline or amorphous powder. For example, contamination from leather tanneries often produces grayish-black deposits containing fragments of animal flesh and hair. Another characteristic example is the coating of white crystalline powder formed on sewer outfalls by nitrogenous fertilizer wastes.
  • Vegetation: Stormwater discharges often affect surrounding vegetation. Industrial pollutants often cause a substantial alteration in the chemical composition and pH of the discharge water, which can affect plant growth even when the source of contamination is intermittent. For example, nutrients from various food product wastes increase plant growth. In contrast, the discharge of chemical dyes and inorganic pigments from textile mills may decrease vegetation, as these discharges are often very acidic. In either case, even when the pollution source is gone, the vegetation surrounding the discharge will continue to show the effects of the contamination. In order to accurately judge if the vegetation surrounding a discharge is normal, the observer must take into account recent weather conditions, as well as the time of year. Increased or inhibited plant growth near stormwater discharges, as well as dead and decaying plants, is often a sign of pollution. However, it is important to distinguish whether plant damage is caused by contamination or by the physical effects of increased flows, such as scour. This can be done by chemically analyzing the flow or by confirming its source through additional visual inspections.
  • Structural Damage: Structural damage also is a sign of industrial discharge contamination. Cracked or deteriorated concrete or peeling surface paint at an outfall usually indicates the presence of severely contaminated discharges. Contaminants causing this type of damage are usually very acidic or basic and are usually of industrial origin. For instance, discharges from primary metal industries may cause structural damage because their batch dumps are highly acidic.

The effectiveness visual inspections in reducing stormwater runoff contamination is highly variable and dependent upon site-specific parameters. These factors include inspectors' motivation level, the types of industrial activity occurring at the facility, and the facility's maintenance procedures. Because familiarity with facility operations is essential in performing effective visual inspections, the inspections should be assigned to qualified staff such as maintenance personnel or environmental engineers.


Costs for performing the visual inspection BMP are minimal and consist of direct labor and overhead costs for staff hours spent on training, planning inspections, inspecting, and completing follow-up activities.

Fact sheet from EPA. EPA's Stormwater Program:

This article originally appeared in the 09/01/2005 issue of Environmental Protection.

Featured Webinar