ID#3110 made on
SSc6.2 - Stormwater design - quality control
LEED BD+C: New Construction, LEED BD+C: Schools, LEED BD+C: Core and Shell
The intent of Credit SS-6.2, as we interpret from the stated Credit Intent and subsequent CIRs, is to minimize the disruption and pollution of natural water bodies by contaminated stormwater. To meet...
The intent of Credit SS-6.2, as we interpret from the stated Credit Intent and subsequent CIRs, is to minimize the disruption and pollution of natural water bodies by contaminated stormwater. To meet the Credit Intent, the Credit Requirements specify active TP and TSS treatment of stormwater, using BMPs that reduce the percentage of contaminants in the runoff. A subsequent Credit Interpretation Ruling (dated 2/28/02) has allowed projects to achieve partial credit equivalency through preventative means (using low-phosphorus cleaning agents and minimizing fertilization of plantings) rather than active treatment of stormwater. Our project, an urban convention center that covers 97 percent of its site, proposes credit equivalency for demonstrating that the absolute levels of TSS and TP in the runoff meet strict municipal and state standards for "clean" stormwater, and therefore qualify for the credit with minimal active treatment.
The common contaminants for stormwater include dirt, oil, salt, garbage, fertilizers, pesticides, and animal excrement picked up from roads, parking lots and lawns. Roof runoff, by comparison, can be free of many of these contaminants. Roof runoff can therefore obtain the same level of water purity, with little or no treatment, that would be achieved by actively removing TSS and TP from full site runoff.
Since an absolute threshold of TSS/gallon or TP/gallon has not been developed for the LEED program, we submit that the approvals our project received to discharge runoff from our roof directly into Lake Michigan constitute a definition of "clean" runoff. Water quality tests were taken from the roof of the existing convention center building to which our project will be an expansion. These tests were submitted to several municipal and state agencies to confirm that any contaminants in the water were at or below the levels defined in the applicable regulatory standards (results of the water tests can be submitted with the credit application). The Chicago Department of Water Management and Chicago Department of Environment approved the roof runoff as safe for discharge directly into Lake Michigan. As a result, our project is building a 3100 ft long tunnel from the site to the Lake to enable this direct discharge (the tunnel separates the stormwater from the city's combined sewer system, and prevents transport of existing contaminants in the site's soil).
For the remaining non-roof site runoff (3% of site), the City of Chicago has determined that first-flush treatment is to be provided. First flush treatment, which is a common method of reducing TSS and TP, works by storing or diverting an initial volume of runoff, with the remaining runoff allowed to flow unimpeded to its discharge point. The first flush washes up to the 85th percentile of pollutants from a site, leaving the remaining runoff clean. For this project, first flush, as determined by the City of Chicago Department of Water Management, is a volume of water equivalent to the detention volume for a 1 year storm event, with a release rate determined appropriate to the project site. This method has been employed for the recently completed Soldier Field project, to the Lake Michigan Federations satisfaction. The first flush will be stored in an underground pipe, with the stored volume discharged to the existing City combined sewer system. The remaining runoff volume will be directed to the new "clean stormwater" tunnel that discharges in Lake Michigan.
In conclusion, we propose the following actions undertaken by this project constitute credit equivalency: 1) water quality testing of stormwater on existing facility roof; 2) approval by municipal and state agencies for direct discharge to accepting water body, based on water quality tests; and 3) development of stormwater infrastructure to take clean runoff directly from the roof and site (after first-flush diversion) to the accepting water body.
Although the proposed strategies are laudable, they do not satisfy the requirements of the credit. SSc6.2 requires the treatment of stormwater runoff, therefore a direct discharge to Lake Michigan, even in this specialized case, does not satisfy the credit requirements.
Combined sewer overflows (CSOs) represent a major water quality problem in many parts of the U.S., including Chicago. Strategies that disconnect stormwater runoff from the CSS, thereby reducing the potential for overflows, should be encouraged. By separating clean roof runoff from the CSS and properly treating the first flush from the non-roof areas the project can make a significant improvement to local waterbodies.
Since CSO reduction is not adequately addressed in the framework of the stormwater management credits, the project team could pursue an innovation credit in this regard. Applicable Internationally.
Related Addenda (Corrections & Interpretations)