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2015 National IDDE Program Assessment Summary

posted Dec 28, 2016, 4:05 PM by Lori Lilly

Illicit discharge elimination is an under-utilized yet effective tool for water quality improvement efforts. Finding and fixing these ubiquitous and oftentimes egregious point sources of pollution is, to me, a relatively easy win for our environment. I say “relatively” because illicit discharge elimination can be as easy as turning off a faucet, sometime requires significantly more detective work and occasionally seems impossible… However, the benefits are generally quite obvious, particularly compared to other restoration activities such as stormwater management where effectiveness is more difficult to determine, based on assumptions from scientific literature and studies, assumes proper installation and maintenance over time and the specifications of which seem to be continuously changing. Finding a sewer pipe that has been illicitly connected to a storm drain and properly re-connecting it is pretty straightforward, is 100% efficient and does not require the same level of follow-up monitoring, maintenance and performance verification as, for example, a bioretention facility.

In 2004, the Center for Watershed Protection (the Center) published the primary guidance manual for Illicit Discharge Detection and Elimination (IDDE) program development and implementation with support from the Environmental Protection Agency (EPA). Development of the Brown et al (2004) guidance manual consisted of a national survey of Phase I Municipal Separate Storm Sewer System (MS4) permittees. Given that this guidance is over 10 years old now, I was curious what folks were doing currently in the IDDE world. I conducted an informal survey of MS4 IDDE program managers and present some of these results below.

Data from this survey was collected through voluntary contributions from primarily local governments (80% of respondents). Solicitation to complete the survey was conducted via two listserves in late April, 2015 – the national NPSInfo listserve and the Chesapeake Network listserve. Of the 29 respondents, 69% were Phase I representatives and 31% were Phase II representatives. 35% of the respondents were from EPA Region 3, 10% from Regions 4, 5, 9 & 10 and the remaining were from the other regions or did not know which Region they were in (uh oh!). I was happy to see that roughly 60% of respondents conducted water quality monitoring with their IDDE programs – although many illicit discharges are visually obvious, many are not quite so due to dilution and can only be detected with actual water quality monitoring. Respondents measured a wide variety of parameters with their programs as shown below.


Most respondents report including temperature as one of their IDDE parameters of choice. Although temperature may be an important parameter for assessing biological conditions, it is not an ideal illicit discharge source indicator. I was pleased to see that 44% of respondents were using ammonia and 41% were using detergents as an indicator – these two indicators were determined in Brown et al (2004) to be excellent illicit discharge indicators. A few communities are still using phenols and copper in their IDDE programs – these parameters are likely relics of the industrial permitting program and are not very good indicators of MS4 illicit discharges (again, see Brown et al).

In the survey conducted for development of the Brown et al IDDE manual, communities reported that outfall screening was not always the most effective means of finding illicit discharges. The original survey suggested that communities felt the use of discharge tracers as “challenging and sometimes fruitless, because of false or ambiguous results and complex or hazardous analytical methods.” Communities wanted accurate, cost-effective, and safe monitoring. In the survey that I conducted, 56% of respondents found outfall screening to be one of the most helpful means for finding illicit discharges – perhaps this is a result of the Brown et al guidance being put to good use? The majority also (74%) stated that staff reporting from other department was the most effective means of finding illicit discharges, pointing to the value of cross-departmental training for illicit discharge detection program efforts.

At the Center, we thought that communities were largely sampling only outfalls >36” in diameter. My colleague Paul Sturm and I led a study in Baltimore in 2010 that pointed to the value of sampling all outfalls, regardless of size ( I was pleased to see in this recent survey that almost half of all respondents do sample all outfalls and not just the large ones. Although communities seem to be having more success at implementing effective outfall screening programs, 66% still report of having complaint-driven programs. However, a healthy 41% are using GIS-based desktop assessments and 28% use water quality monitoring to target their programs.

Another happy surprise that I found was that 31% of communities partner with non-profit, watershed group or citizen monitoring programs to supplement their IDDE efforts. Citizen monitoring groups and watershed associations can be very valuable partners in such efforts. These entities can serve as excellent eyes, ears and advocates and, when properly trained, can also supplement actual local government monitoring efforts. Some of these citizen-based programs are listed on my IDDE Knowledge Bank web-page (more will be added):

With the ever-increasing regulation of nutrients in the Bay watershed, governments are seeking out every tool possible in order to obtain nutrient reduction credits. An important game-changer as related to this has come into play in the Chesapeake Bay region recently. Since the end of 2014, illicit discharge elimination is now creditable for nutrient reduction through the mechanism of Discovered Nutrient Discharges from Grey Infrastructure (DNDGI; When I first started working at the Center in 2003, we began to employ nutrient screening during regular outfall screening and found the nutrient load from illicit discharges to be quite significant. With this current survey that I conducted, I was also curious whether Bay MS4s were aware of DNDGI credit and, if so, whether they were planning to utilize it.

40% of respondents were located in the Chesapeake Bay watershed. 58% of those in the Bay watershed were aware of the new DNDGI credit but 67% did not know whether they yet planned to use the credit for meeting their Chesapeake Bay Watershed Implementation Plan requirements. This is understandable – I think it’s going to take a few brave communities to pave the way in this endeavor with their States. In addition, the Option 1 credit for implementing an Advanced Nutrient Discovery program is likely not going to be worth the program modification efforts for most communities. In a recent IDDE program audit that I recently conducted, this was the case; simply gearing up for the Option 2 credit will potentially have much more benefit.

If your community is interested in an IDDE program audit, assistance with IDDE program development, or IDDE training, please feel free to drop me a line!