Measure 3d:  Implement illicit discharge detection

“Implement an inspection program to detect dry weather flows at system outfalls.  Establish procedures for tracing the sources of illicit discharges and for removing the sources. Develop procedures for identification of priority areas likely to have illicit discharges. Continue to identify, locate and update map of drainage system components on a priority basis per approved Illicit Discharge Program.”

Picture3d1.jpgOutfall inspection is one of the most commonly used methods for identifying illicit discharges.

Outfall inspections are easy and inexpensive to implement and you can verify and update your storm sewer base map as you conduct them. The disadvantage of outfall inspections is that illicit discharges occur periodically and can be hard to find unless you are at the right place at the right time. (That is why your permit also requires you to have a public reporting mechanism so that your citizens can help find the illicit discharges as they occur.)

There are four steps to completing the outfall detection requirement:

  • Prioritize areas for inspection.
  • Design an outfall tracking system.
  • Conduct outfall inspections.
  • Trace and remove illicit discharges.

Step 1: Prioritize areas for inspection

Each year, select a portion of your jurisdiction’s area for dry weather inspection, starting with the highest priority areas and moving to lower priority areas. Check your Stormwater Plan to see if you agreed to inspect a certain percentage of your jurisdiction's area each year.

As you prioritize areas within your jurisdiction, bear in mind the most common source of illicit discharges are:

  • Illegal dumping  
  • Floor drains improperly connected to the storm sewer
  • Broken sanitary sewer line
  • Cross-connections with sewer line               
  • Sanitary sewer overflows
  • Straight pipe sewer discharge 
  • Failing septic system

Potential high priority areas are older sections of town, commercial or mixed use areas, high density areas, etc. Each year, you should document your basis for selecting the high priority area.

Step 2: Design an outfall tracking system

You will also need to develop a tracking system to report illicit discharges, suspect outfalls, citizen complaints, enforcement actions and corrective measures. The Center for Watershed Protection has developed an Outfall Reconnaissance Inventory / Sample Collection Field Sheet to assist the Phase II’s as they inspect their outfalls.

Step 3: Conduct outfall inspections

Picture3d2.jpgAt least two staff members should work together to conduct the inspections. The most common approach to outfall inspection is to complete a visual inspection of the outfall and a qualitative assessment of any flow present, including observation of water color, odor, turbidity, floatables and sediment (Zielinski and Brown 2001). In some cases, if the flow is suspected to be inappropriate, a follow-up grab sample is taken for quantitative assessment. Some local governments bypass the quantitative tests and immediately move upstream to find the source of the discharge. 

Step 4: Trace and remove illicit discharges

If you find an illicit discharge in the field, you should try to identify the source of the discharge. Investigation of suspicious discharges will be made by visual inspection and/or testing of discharges within the storm drainage system upstream of the suspicious discharge. Letters may be sent to residents and businesses alerting them to the problem that is under investigation to solicit their assistance in finding the source. A building-by-building evaluation may also be used in areas where a problem has been isolated to a small area. 

Once you have identified the source of the illicit discharge, your staff should notify the responsible party verbally if possible and follow-up with written notification. The written notice will provide contact information as well as a schedule for the responsible party to remove the illegal discharge. If the responsible party does not comply with the schedule or receive approval for a revised schedule, you will need to take enforcement action as defined in your ordinance.

EPA has developed guidance for removing the following common sources of illicit discharges: