It appears that the majority of the effects on stormwater quantity and quality can be tracked either explicitly or implicitly through the measurement of the percentage of impervious area on a zoning parcel of land.  In reviewing literature and studies done in this regard, a few observations may prove useful in the ordinance rewrite.

• Total Impervious Area (TIA) is often distinguished from Effective Impervious Area (EIA) when tracking impacts.  EIA is the portion of the TIA that has improved drainage area.  It is similar to concepts like “Directly connected Impervious Area” found in TR-55.  Unfortunately, it takes quite a bit of investigation to separate EIA from TIA on a project parcel, and often generalized ratios dependent on description of the land use are used rather than direct measurement.
• An on-going challenge in stormwater Ordinance language is finding language for and descriptions of “Development” that make meaningful distinctions technically, practically and administratively.  One potential way out of this on-going problem is to use the % impervious of a project as a threshold trigger for certain mitigation requirements.  Here is an example:
  • Define any project that is less than 10% TIA as not requiring a site runoff storage facility.
  • Define projects that increase the % impervious area of a project site as requiring a site runoff storage facility to mitigate the change, if the TIA is greater than 10%.
  • If a project can be shown to significantly reduce the EIA,  then a site runoff storage facility may not be required.
  • These are only examples, but consider something like the holdings of the Forest Preserve District, or the trend toward Low Impact Design.
  • The overwhelming majority of studies show that percent impervious can be correlated with the “health” of streams,  with nearly all studies beginning to register stream impairments as low as 10% impervious.  While that is the “bad news”, it also tells us what is and is not likely to further degrade water quality.  Many studies site the percent impervious threshold for characterization of land use as rural/undeveloped less than 10% impervious,  suburban as up to 50% impervious and urban as greater than 50% impervious.  Is a site that has been urban for a number of years, likely to degrade or improve conditions if a new project on the site is approved as an urban land use but at a reduced percent impervious?  Certainly a trend toward a watershed scale reduction in impervious surfaces has already been recognized as a goal by the EPA and as a valid approach to meeting NPDES requirements.
  • What about flooding?  Don’t all developments, of any kind, increase flooding?  The answer is: not necessarily if one considers that the drainage of an existing land use has often been accomplished by existing drainage infrastructure for years.   Consider many of our older “downtown” areas.  While localized drainage problems may exist,  drainage infrastructure out of the downtown area is usually “mature” at this stage, and a new outlet or modification of the existing outlet into a stream is probably not proposed.  If an urban project is discharging to the same storm sewer as the previous urban land-use, is not causing its neighbors additional damages, and has actually reduced the volume of pollutants and runoff volume, doesn’t that embody the trend we desire?  Considering the current push towards denser and more intense downtown land use,  Does a pond or an underground tank really sound like wise use of infrastructure dollars?

Where is this discussion going?  I am wondering if we can’t eliminate the often confusing pages and pages of ordinance language with something more direct, like percent impervious, that is not only more universally recognizable but more directly associated with the impacts we wish to continue regulating.  Can we replace the references to single family residential, multifamily, commercial, industrial, institutional land use with thresholds of percent impervious?  Is that an improvement, or just a new complication?  What do you think?

Welcome to the first “official” post on the Stormwater Update blog.  “We” are a team of Consultants, The County Staff, and representatives of the Municipalities within DuPage County.   We are beginning a process, in which we will be looking at and potentially modifying stormwater regulation in DuPage County.    The objective is to retool the Countywide Stormwater and Floodplain Ordinance so that it better reflects DuPage County in 2009 and going forward.  The County places a very high value on the quality of life in the county,  and the current Ordinance reflects this in its’ “Purposes”.   Stormwater Quantity, Quality, and valuable environmental resources fall under the current regulation.  

We want to look at “what we do now”, and “what we should be doing”  from as many perspectives as we can.  Above all,  the commitment to the health, safety and welfare of those who live, work, find recreation, own property, and own and operate businesses in DuPage County cannot be compromised.   That statement though is too broad,  and to be effective the Stormwater Regulations must ask:  What is the “right” level of regulation?   How can the timelines for the processes of permitting be made reflective of and appropriate to the differing levels of complexity that Stormwater regulation implies?  What about new state/Federal mandates?  These are some of the questions that will drive the next 15-months of work. 

We highly value your input and feedback as we move forward.  You will see that each of the posts will be available for comment by representatives of every community that has a role in implementing these regulations.  Just as importantly, all who view this website are invited to comment by clicking on “Provide Us Your Comments” located on this webpage just to the left of this box.   All of the documents that are in their final form will be made available to read through this website, and our goal is to be open and transparent about where this process is headed and what it is intended to achieve. 

We will be reaching out to many stakeholder groups, soliciting comment, and anticipate a lively discussion on many issues.  That is why such a long period has been set aside for this effort.  Like any process,  we have to make sure that the right people are fully engaged at the right time. 

Please follow along with us as we take the first real steps toward shaping Stormwater Management in DuPage County for the future.