Assessing the Practical Feasibility of Stormwater Capture for both Potable and Non-potable use in Commercial Structures
January 01, 2013 at 3:21 PM
- Project Featured in New York Water Environment Association's National Publication Clear Waters
- Author: Kyle E. Thomas, P.E., LEED® APBC+C is the Principal of Natural Systems Engineering, PLLC, , Syracuse, NY, and may be reached at: email@example.com.
Onondaga Commons, a nationally recognized health and human servcies park in Central Upstate New York, has been approved for funding through Onondaga County’s ”Save the Rain” program for implementation of a rainwater harvesting system in association with the Gar Building development project located at 414-416 West Onondaga Street, Syracuse, New York. The project is a component of the broader Onondaga Commons Comprehensive Green Expansion & Jobs Creation Initiative, a project of Syracuse development firm Short Enterprises. The proposed rainwater harvesting system would recover rainwater for both potable and non-potable uses in the new facility. Although common in more arid climates, rainwater harvesting for potable uses is uncommon in humid climates of the United States. This study was undertaken to evaluate potential health implications associated with harvesting rainwater for potable use in Central New York or the northeastern US in general.
Rainwater harvesting is defined as "the gathering and storage of water running off surfaces on which rain has directly fallen" (Pacey and Cullis, 1986). The most common approach is to collect water from rooftops immediately following a rain event. This provides a source of water that can be used when groundwater is scarce, which is especially useful in arid climates. The water source is located close to the point of use, reducing the need for complex distribution systems and the associated utility bills. In wetter climates, rainwater harvesting acts as a stormwater mitigation technique, reducing the stormwater volume, thereby lessening downstream erosion and decreasing the load on storm sewers (Krishna, 2005).
The quality of harvested rainwater depends primarily on both air quality and the cleanliness of the rooftop catchment. Vehicles through which contamination of harvested rainwater occur are the dry deposition of airborne contaminants, dry weather accumulations of contaminants such as bird and other animal feces, and leachates from rooftop materials (Macomber, 2001). Contaminants known to be associated with roof rainwater include metals such as aluminum, manganese, copper, zinc and lead, as well as microbiological pathogens such as E. coli,Cryptosporidium, Giardia lamblia, total coliforms, legionella, and fecal coliforms (Krishna, 2005; Lye, 2002; Lye, 2009). The quality of rainwater collected from rooftops is often not sufficient to meet drinking water standards primarily due to the presence of bacteria and pathogens (Li et al., 2010;Mwenge Kahinda et al., 2007;Mwenge Kahinda et al., 2007).
Consistent with stormwater pollution from impervious surfaces in general, higher contaminant levels have been shown to be associated with the “first flush” (1‐2 mm) of runoff from roof systems compared with the runoff that follows (Vasudevan et al., 2001), and research has shown that contamination of rainwater increases as the duration between rainfall events increases. Rainfall acts as a cleansing mechanism for the rainwater catchment with removal efficiency increasing with the intensity of the rainfall event (Yaziz et al., 1989). Therefore, it follows that the length of dry periods between rain events will affect the quality of the first flush volume. Because dry periods in the Northeast are relatively short, the typical first flush volume should be smaller than would be found in more arid climates.
Metallic contaminants in harvested rainwater such as lead and copper usually occur as a result of leaching from roof substrate and piping, and can largely be controlled through system design and construction. In industrial and urban areas, particulate matter and increased acidity from fuel combustion may be of concern (Krishna, 2005). However, the primary contaminants of concern in the northeast are likely to be biological contaminants from animal, especially bird, feces. Pathogens of greatest concern are those associated with birds such as pigeons, gulls, sparrows, starlings, etc., which are known to inhabit urban areas in the northeast (National Audubon Society, 2010). Tsiodras et al. (Tsiodras et al., 2008) identify biological pathogens associated with birds worldwide. Based on this work, enteric biological contaminants associated with birds that might be expected to inhabit an urban area in northeast US, such as Syracuse, New York, have been identified and are presented in Table 1.
Standard rainwater harvesting designs routinely incorporate a first flush diverter to prevent collection of these contaminants in rainwater to be reused. Where rainwater is also to be used for potable purposes subsequent treatment systems also have included chlorination, solar sterilization, sand filtration and solar pasteurization (Krishna, 2005; Li et/ al., 2010; Mwenge Kahinda et al., 2007). More sophisticated treatment methods such as carbon filtration combined with ultraviolet (UV) sterilization have been used in Europe since the early 1900s and more recently in the United States and have been demonstrated to be capable of achieving potable use standards (Krishna, 2005). While some research regarding the quality of harvested rainwater with respect to microbiological contamination has been done in more arid regions of the US, especially Texas, it appears that little research to characterize or quantify the nature or degree of contamination of rooftop runoff has been performed in more humid climates, particularly the Northeast.
While it is possible to test for pathogenic microorganisms such as Cryptospridium and Giardia lambia, the tests are usually costly. Thus, tests for total coliforms or fecal coliforms, or both, are often used as indicators of biological contamination for conventional drinking water sources such as groundwater or surface waters. Little research appears to have been performed in the area of fecal coliforms as indicators of pathogenic contamination in rainwater. However, tests for fecal coliforms appear to represent a satisfactory surrogate for other fecal pathogens much as they similarly serve as such indicators for conventional potable water sources (USEPA, 2010).
The Public Version 1.0 of the International Green Construction Code™ (IGCC) was published for public comment in March 2010. The document has been undertaken to meet the need for a mandatory baseline of codes addressing green commercial construction, providing a framework linking sustainability with safety and performance through model code regulations that promote safe and sustainable construction in an integrated fashion with the ICC Family of Codes. The Code, which will reportedly be relied upon by New York State for establishing acceptable practices for rainwater harvesting, states that accumulated rainwater shall be tested for Echerichia coli, total coliform (TC), heterotrophic bacteria and cryptosporidium. The Code stipulates that the tests shall be performed prior to connection to a potable rainwater distribution system and annually thereafter.
Turbidity, suspended solids, and pH tests are simple and relatively inexpensive, and may be useful for evaluating general water quality. While not likely to be significant, testing for levels of potentially harmful metals such as aluminum, manganese, copper, zinc and lead may also be useful. Further investigation into the effectiveness of carbon filtration and UV sterilization as treatment options may also be important to support rainwater harvesting designs for potable use.
- For a link to the full article at the New York Water Environment Association's website, click here.