Discussion: View Thread

CSOs & Green Infrastructure - Targeting Solutions?

  • 1.  CSOs & Green Infrastructure - Targeting Solutions?

    Posted 09-11-2018 10:16 AM
    Edited by Tirza Austin 09-11-2018 10:15 AM
    Green infrastructure (GI) solutions are on the rise for addressing combined sewer overflows (CSOs), but are we strategically targeting the "right" source areas for controls? Using Hoboken, NJ as an example (high density development with ~95% build out and almost the only "permeable" spaces in pocket parks), I've measured that roofs occupy 57% of all the impervious area. I suggest we start targeting GI towards roof runoff. What do you think?

    I'll be sharing more thoughts on the topic in a live TEDx on Wed. Sept 12 at 4 pm EDT. You're welcome to tune in livestream.

    Elizabeth Fassman-Beck, Ph.D., M.ASCE
    ASCE-NJ Educator of the Year, 2018

  • 2.  RE: CSOs & Green Infrastructure - Targeting Solutions?

    Posted 09-12-2018 11:29 AM
    Edited by Tirza Austin 09-12-2018 11:28 AM
    It is a right concern. It varies according to the project and site conditions. As a very general concept, I believe the sooner the runoff is captured the better.

    Cesar Simon A.M.ASCE
    Civil Environmental Engr.
    Cosmos Technologies, Inc.
    Pittsburgh PA

  • 3.  RE: CSOs & Green Infrastructure - Targeting Solutions?

    Posted 09-12-2018 11:30 AM
    Edited by Tirza Austin 09-12-2018 11:29 AM
    ​Additional consideration in support of this: infiltration infrastructure geared toward roads in northern climates also is a source for infiltrating roadway deicing salt into groundwater supplies, a rapidly increasing problem. Roof runoff will not be a major source for this contaminant.

    John Zollers EIT, A.M.ASCE
    Philadelphia PA

  • 4.  RE: CSOs & Green Infrastructure - Targeting Solutions?

    Posted 09-12-2018 02:44 PM
    Edited by Tirza Austin 09-12-2018 02:43 PM
    In most instances, the roof drains connect to the site drainage system which may have a holding pond for runoff control.  However, in some cases as in Noblesville, IN, the city had a combined sewer system and was challenged to limit discharge from a new city hall and parking facility during rain events. Their solution was to construct a holding basin under the parking lot thereby controlling the rate of discharge to the combined system. Their Long Term Control Plan includes a new storm system eventually and their city hall roof and parking lot is already prepared for connection as well as rate of discharge control.

    Harold Dungan P.E., M.ASCE
    PRESIDENT-H2Oaks Consulting LLC
    H2Oaks Consulting LLC
    Maxwell IN

  • 5.  RE: CSOs & Green Infrastructure - Targeting Solutions?

    Posted 09-13-2018 09:58 AM
    Edited by Tirza Austin 09-13-2018 09:58 AM
    I missed the TEDx, but yes, roofs can be an easy place to start.  The BMPs I've seen utilized are green roofs, cisterns, rain barrels, downspout disconnection, pervious concrete, pervious asphalt, permeable pavers, pervious sidewalks, underground detention and tree planters that will infiltrate more water.

    Barrett Fisher A.M.ASCE
    Plans Reviewer
    Hamilton County Water Quality Program
    Chattanooga TN
    (423) 693-9253

  • 6.  RE: CSOs & Green Infrastructure - Targeting Solutions?

    Posted 09-13-2018 04:43 PM
    Edited by Tirza Austin 09-13-2018 04:42 PM
    Chattanooga, TN faces a similar situation in the CSO, which is primarily the downtown/urban area.  We've also discussed UG tanks, but have space constraints, a large number of basements, dense utility corridors, and topographic challenges.  GI poses a concern as the majority of the buildings have basements (some of which are already subject to flooding).  Roof disconnection tends to yield in an inter-basin transfer as it reenters the system via curb inlet, etc.

    Green Roofs are not economically feasible as these are older buildings & may need a bit of structural reinforcement to allow for the additional loading.  Along those lines, as there are very few green roofs in town, maintenance is an issue.  Developer buy-in is also lacking.

    Stone storage under perm pavers (or similar) in the ROW has been one successful avenue, but is also not without challenges.

    Maria Price P.E., M.ASCE
    Engineering Manager
    Chattanooga, TN
    (423) 643-5961

  • 7.  RE: CSOs & Green Infrastructure - Targeting Solutions?

    Posted 09-14-2018 09:59 AM
    Edited by Tirza Austin 09-14-2018 09:59 AM
    In a highly developed city, the concern are basements and underground utilities.  I believe that LID improvements will be limited to alleys (pervious pavements) and green space (multi-use areas) inside the city.  Because maintenance funding and crews are limited, central facilities outside the city will provide the greatest bang for the buck.

    John Wood P.E., M.ASCE
    Project Engineer
    Pittsburgh PA

  • 8.  RE: CSOs & Green Infrastructure - Targeting Solutions?

    Posted 09-14-2018 09:59 AM
    many valid concerns and ideas along the GI discussion. Columbus, OH has used some GI filters for separation bmps and for peak flow delay. New York with roofs and disconnection. Los Angles is getting into it with urban pocket parks and thoroughfares. With an ultra urban environment I would hesitate to infiltrate without a very intense underground infrastructure evaluation and if installed, aggressive structure and infrastructure monitoring program. The older the area, the greater the risk of abandoned or unknown underground conduits that increase the risk of potential voids and/or sinkholes even away from the GI itself. If you can't separate completely, use of GI may be able to hold various levels of your storms until capacity (without overflow) is available within the system, gets a little more hydraulically complicated, but various levels of automation may be helpful, especially in the downstream flow monitoring arena. The more interconnected you can make your GI, the greater area wide attenuation and storage you can achieve. In my humble opinion, don't discount the distributed storage capability and capacity of anything you may be thinking about. On the other side of the coin, maintenance and simplicity is key. If landowners aren't buying in and municipality isn't equipped and trained, and if everyone isn't educated on the whole concept, it will lead to failure. If staying above ground, such as bump ins or bump outs (See Indianapolis Cultural Trail) get the landscape architects to provide a very manicured landscape look, as the urbanites tend to discount the prairie look as a weed-fest. Its my experience the more native and natural you go, the more you will need highly trained maintenance so they don't pull your expensive plants. May even be able to get in involved in the pollinator and Monarch programs for urban participation. GI in urban setting is a good tool in the CSO abatement toolbox, but without an "all in" attitude on everyone's part (check out Philadelphia, PA CSO program) it will continue to be an uphill battle. All said and done, go for it.

    Brian Neilson P.E., M.ASCE
    HWC Engineering, Inc.
    Indianapolis IN

  • 9.  RE: CSOs & Green Infrastructure - Targeting Solutions?

    Posted 09-17-2018 09:58 AM
    Edited by Tirza Austin 09-17-2018 09:57 AM

    GI presents numerous opportunities and challenges in an urban setting. Green roofs are effective in capturing perhaps the first inch of rainfall on one of the largest impervious areas by percentage in a city. They are, however, expensive, relative to other options and are not always possible due to structural issues. Infiltrating street and driveway runoff is very effective and, as shown in Philadelphia, can often handle even relatively large storms of 2 to 3 inches. The complication there is that maintenance costs are relatively high in relation to initial capital costs, and must be permanently  funded. We have found that, if GI is placed at least 10 feet from the nearest building or basement, that basement flooding is usually not an issue. There will be, however, some cases where a buried conduit will lead to basement flooding even with separations of more than 10 feet, and this will have to be one of the risks that are prepared for.  Finally, if a large scale GI program is contemplated, it is important to do some groundwater modeling to assess the cumulative effects of moving from a low infiltration situation to one of relatively high infiltration. There may be a general increase in the groundwater table.

    Despite all this, GI is an attractive option when compared to pure storage options like tunnels and tanks if the additional benefits of greening are considered in making a decision to pursue GI as part of a CSO reduction program.

    Mark Maimone PhD, P.E., D.WRE, BCEE
    SR VP
    CDM Smith
    Woodbury NY
    (631) 385-0373

  • 10.  RE: CSOs & Green Infrastructure - Targeting Solutions?

    Posted 09-18-2018 10:15 AM
    Edited by Tirza Austin 09-18-2018 10:14 AM
    ​I want to caveat again - infiltrating water at the ground level and including runoff from streets and sidewalks in northern climates risks infiltrating deicing salts into groundwater. I believe this issue requires more consideration in project planning than it currently receives.  Rooftop water is generally free of this hazard.

    Some papers on this issue: http://www.jstor.org/stable/pdf/3376665.pdf and https://pubs.acs.org/doi/pdfplus/10.1021/acs.est.6b00679

    John Zollers EIT, A.M.ASCE
    Philadelphia PA

  • 11.  RE: CSOs & Green Infrastructure - Targeting Solutions?

    Posted 09-19-2018 08:00 AM
    Edited by Tirza Austin 09-19-2018 07:59 AM
    The point of contaminating groundwater with salts actually is a much broader consideration during design for all pollutants that are expected to run off the area of interest. There are means and design methods, even for salts and other soluble pollutants, to remove these before the infiltration stage, however it requires pretreatment and with any treatment train design, the capability to provide direct maintenance to remove the pollutants and dispose of properly. It probably takes more room/space as well. Green Infrastructure is just a smaller version of a wastewater treatment plant and needs the design attention on the same level and consideration of pollutant identification, pollutant removal and disposal and operational maintenance. It is very unwise to believe that the pollutants in the storm runoff "disappear" as you utilize infiltration or even evapotranspiration. Even in the cleanest of areas, there will be a break point at some level of pollutant, perhaps even thermal (think roof) that needs to be designed for such that the GI element doesn't move one issue from one medium to another medium to what can become actually a higher environmental and economic impact than no GI at all.

    Brian Neilson P.E.
    HWC Engineering, Inc.
    Indianapolis IN

  • 12.  RE: CSOs & Green Infrastructure - Targeting Solutions?

    Posted 09-18-2018 06:43 PM
    Edited by Tirza Austin 09-18-2018 06:43 PM
    Are you looking to simply reduce CSOs or improve water quality?

    It can't hurt to look at GI to improve water quality but TBL/ancillary benefits should be accounted for as well for a more accurate comparison. Philadelphia has done a good job with this. Depending on your ultimate goals (what % reduction of CSOs?), GI will provide some benefits and should be considered, but may not get you all the way to your final goal. For CSOs, Philly took a GI-first approach and may be considering tunnels. Chicago took a grey infrastructure (Tunnel and Reservoir) Plan-first approach, and has since supplemented with GI (roofs, alleys, etc.). DC took a grey (tunnel) approach and later amended the Consent Decree to use GI to offset tunnels (currently under construction).

    If you want to really improve water quality, I would guess that just looking at GI in the urban core will not get you there. We've taken centuries to adversely impact our rivers and streams, and it will take us a long time to significantly improve urban water quality. You need to take a long-term, watershed-scale approach to improving water quality holistically and to equitably distribute the burden as well.

    Matthew Ries
    PhD, P.E., M.ASCE
    Chief, Water Quality and Watershed Management
    DC Water

  • 13.  RE: CSOs & Green Infrastructure - Targeting Solutions?

    Posted 09-20-2018 10:04 AM
    Edited by Tirza Austin 09-20-2018 10:03 AM
    Matthew - I would be curious to hear more about what you are doing in D.C.  You gave examples in other cities, but how is DC Water focusing their green infrastructure plan.  I know you are working on a couple P3's, but to what extent have you engaged the private sector in maintaining GI installations.  I am working for several clients in the Northeast that are looking to install GI as only a part of their LTCP implementation, but the consistent problem has been not the installation, but the maintenance of such installations (often they need to be weeded, mowed, etc.).  I would be interested in speaking with you further, if you have a couple minutes next week (Week of 9/24)?


    Angela Hintz P.E., M.ASCE
    Senior Environmental Engineer
    Arcadis US, Inc.
    Buffalo NY

  • 14.  RE: CSOs & Green Infrastructure - Targeting Solutions?

    Posted 09-19-2018 10:12 AM
    Edited by Tirza Austin 09-19-2018 10:12 AM
    I may be just repeating what others have already stated, but the consistent theme in this thread is that GI is a tool in the suite of solutions to be considered and depending on your definition of green may or may not get you to your goal alone.  The definition is highly variable by locality where geometry (shallow) or function (infiltration) may be a limiting factor in the descriptor.  Therefore a holistic solution with end in mind should be the starting point and see where green adds value depending on the site constraints, stated goals and the owners maintenance resources.

    Morgan Byars P.E., M.ASCE
    Managing Engineer
    Austin TX

  • 15.  RE: CSOs & Green Infrastructure - Targeting Solutions?

    Posted 09-20-2018 03:26 PM
    Edited by Tirza Austin 09-20-2018 03:26 PM
    In the ultra-urban setting, such as Philly, NYC, Baltimore, etc., we know that the sweet spot for having a meaningful impact on CSO's is managing ~50-55% of the impervious surface areas within the area tributary to an outfall. We also know that only ~25% of that area is area available in the public ROW, and a lot of those areas are challenging in and of themselves due to utilities, topography, etc.

    A successful CSO-reduction program dependent on GI needs to look "Beyond the Streets" and into other areas such as triangle parks, vacant lots, school yards, etc. Partnership with private property owners is also critical, and finding a way to incentive managing public runoff on private property is going to be a hot topic of discussion in the coming years. 

    Shameless plus....I just did a presentation on this very topic at the LID Conference, and we will continue the discussion at SWS in November.


    Michael D. Devuono P.E., M.ASCE
    Senior Water Engineer
    Arcadis U.S.
    Philadelphia PA

  • 16.  RE: CSOs & Green Infrastructure - Targeting Solutions?

    Posted 09-25-2018 03:23 PM
    Edited by Tirza Austin 09-25-2018 03:22 PM
    Hello All,

    If you have time, please watch Elizabeth Fassman-Beck, an ASCE-Stormwater Leader and professor at Stevens Institute of Technology, give a TEDx Talk on Green Infrastructure For Runoff.

    Nicole Erdelyi
    EWRI Conference Coordinator
    American Society of Civil Engineers
    Reston VA
    (703)295-6158 EXT 6370