Green stormwater management for brownfield

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    Stormwater management is an increasingly challenging aspect of brownfield redevelopment, particularly in today’s sustainably minded business environment.

    In the competitive real estate market with high energy costs, brownfield developers are seeking to differentiate themselves in the marketplace by meeting Leadership in Energy and Environmental Design (LEED) scoring incentives to keep stormwater onsite. These incentives include the use of green infrastructure management approaches and technologies to infiltrate, evapotranspire, capture, and reuse stormwater to maintain or restore natural hydrologies.

    Yet, sustainable approaches are often not in line with agreed-on, risk-based engineering controls that are used to cleanup brownfields, some of which can pose challenges to stormwater quality and quantity. To bring these two seemingly disparate strategies together, we as an industry must reshape and redefine conventional best practices to deliver sustainable brownfield redevelopment solutions.

    Going green
    To earn a stormwater management LEED credit according to the LEED guidelines, the owner/developer must implement and sustain a stormwater management plan that infiltrates, collects, and reuses runoff or evapotranpirates runoff from at least 15 percent of the precipitation falling on the entire project site both for an average weather year and for the two-year, 24-hour design storm. The suggested strategies for achieving the LEED point include landscape irrigation, toilet and urinal flushing, and custodial uses.

    Another LEED credit can be earned by increasing onsite infiltration, reducing or eliminating pollution from stormwater runoff, and eliminating contaminants. In this case, the owner would have to ensure that a) existing site imperviousness is less than or equal to 50 percent or b) greater than 50 percent and then must reduce volume by 25 percent using the two-year, 24-hour design storm.

    The quality control LEED credit requires the owner to implement a stormwater management plan with best management practices that treats and captures 90 percent of average annual rainfall and best management practices to reduce 80 percent of the post-development average annual total suspended solids (TSS).

    With this in mind, it’s up to engineers to combine these green strategies (e.g. surface-to-groundwater infiltration, bio-swale, and green filter buffers) to meet onsite stormwater management and quality control LEED credits with prescribed engineering controls.

    Enter AULs
    One of the most common methods of facilitating a cost-effective, risk-based cleanup is the use of Activity and Use Limitation (AUL) property restrictions. AULs protect onsite workers and the public from exposure to contaminants that exist or remain on a brownfield redevelopment property.

    The EPA estimates that 90 percent of brownfield redevelopment projects across the country use some form of AUL property restriction to comply with risk and regulatory requirements. Federal, state, and local governments have pushed for legislation, developed policy, and embraced the use of AULs in lieu of requiring unrestricted site cleanups in non-residential end-use exposure risk scenarios.

    The use of AULs permits restricted-use developments, such as brownfields, to proceed in a cost-effective manner, while still addressing the potential human and environmental exposure risks posed by residual contamination left on a site. As long as a comprehensive, long-term management plan is put in place to maintain the contamination controls, these non-permanent AUL remedies are effective.

    Implementing engineering controls will significantly reduce options for the design of best practice sustainable stormwater management strategies and could pose adverse impacts on stormwater quantity and quality.

    Therefore, special care is necessary to stay consistent with the intent of new stormwater regulations, within defined engineering controls, and achieve voluntary sustainable site redevelopment goals outlined by the LEED guidelines.

    Environmental synergy
    AULs often consist of engineering controls that might include impermeable caps over soil contamination, pavements and hardscaping, fencing to prevent access, slurry walls to control groundwater flow, groundwater pump-and-treat systems to treat and/or control groundwater, and other physical controls.

    One of the more popular engineered controls is to use impervious caps to create a barrier to potential soil or vapor exposure scenarios from contamination left behind. These two types of AULs work best if they are applied together.

    For example, a parking lot in combination with a new building foundation may be used to cap (engineering control) a contaminated site and a deed notice or declaration of environmental restriction is placed in title documents to alert future owners of site cap maintenance requirements.

    The EPA dictates stormwater best management practices through the NPDES programs. In turn, states certify that their approach to stormwater management meets or exceeds the practices developed by the EPA.

    For example, a manufacturing facility in New Jersey is required to maintain a New Jersey Pollutant Discharge Elimination System (NJPDES) permit to monitor stormwater quality from an asphalt parking area draining to a catch basin connected to a storm sewer system. This asphalt parking area serves to cap some residual low-level soil contamination. The permit holder is required to monitor TSS semi-annually during storm events. To maintain compliance with the low-level TSS threshold values, the permitee must perform monthly sweeping of the parking lot to remove sediment and other particles that might elevate TSS values above the permit threshold.

    The AUL engineered control cap in the above case example overrides the ability to implement stormwater best management practices that would remove the need for a NJPDES permit. In this way, the subsequent engineering solution would direct stormwater runoff to an onsite infiltration gallery or green design swale, thus using accepted engineering controls to address the potential human and environmental exposure risks posed by residual contamination and improving the stormwater quantity and quality.

    Best runoff strategies
    There are a number of best practices that owners and developers can put in place on every project to achieve sustainable brownfield redevelopment.

    The first is to develop and implement comprehensive operation and maintenance plans for a sustainable stormwater drainage system. The pubic must have confidence first and foremost in the adequacy of the engineered control. Even partial reduction (say by 25 percent) of stormwater runoff through sustainable best management practices is a significant step in the right direction.

    Next, anticipate the potential desire to achieve LEED building and site certification early in the brownfield redevelopment process. Anyone involved in the process of selecting best management practices to manage stormwater should consider a wide variety of factors, including pollutant removal potential, stormwater volume reduction, installation considerations (soils, slopes, and climate and rainfall patterns), capital costs, maintenance costs, and other factors.

    Finally, attempt to incorporate brownfield cleanup strategies with stormwater best management practices by demonstrating risks and rewards to the regulators early in the process. For example, try to avoid conventional impermeable cap engineering controls over soil contamination. Also, attempt to better characterize the nature and extent of the soil contamination and seek ways to facilitate stormwater infiltration onsite.

    Clearly, more innovative thinking is needed to develop stormwater management practices on brownfield sites. Organizations such as the Interstate Technical and Regulatory Commission (ITRC) are in a unique position to develop approaches that meet regulatory requirements. ITRC is currently entertaining a proposal to initiate research with the objective of developing sustainable solutions to this challenge.

    Donald W. Richardson, C.P.G., R.B.P., is the current chairman of the board of the Institute for Brownfi eld Professionals. He can be reached at Don@terradex.com. Daniel L. Harpstead, P.E., is a technical discipline lead for engineering with Kleinfelder, a professional services fi rm in the natural and built environments. He can be reached at dharpstead@kleinfelder.com.