Reducing Flood Risk to Key Wastewater Infrastructure in New York City

The New York City Department of Environmental Protection (DEP) owns and operates one of the largest wastewater collection and treatment systems in the world, with 96 pumping stations conveying sewage from across the City's five boroughs to 14 wastewater treatment plants. Many of the city's wastewater treatment plants and pumping stations are located within close proximity to waterfronts and shorelines. As such, they are vulnerable to flooding when surrounding waters rise. This vulnerability was plainly evident during Hurricane Sandy. When Sandy surge caused damage to wastewater facilities resulting in millions of gallons of untreated and partially treated wastewater spilling into the harbor, DEP quickly reacted to repair the damage and to develop resiliency measures to ensure the highest level protection from future storms.Since 2008, long before Hurricane Sandy, DEP has been an active leader in climate risk planning and investigating the impacts of climate change on its infrastructure not only for wastewater facilities, but also for drinking water supply and stormwater management facilities. In 2013, DEP completed the City-Wide Risk Assessment and Adaptation Study which presents a comprehensive assessment of facilities at-risk from future storms, potential costs for adaptation, and suggested measures to protect critical equipment and reduce the risk of damage and loss of services. It follows the recent release of Mayor Bloomberg's A Stronger More Resilient New York, which committed the City to harden its wastewater treatment plants and pumping stations. Through the study, DEP developed a set of recommended design standards and cost-effective protective measures that are tailored to each facility to improve resiliency in the face of future flood events. In determining potential costs, DEP considered not only the value of wastewater assets but also potential impacts to the population and critical facilities and beaches.The study used a consistent and flexible framework to assess flood risk and identify appropriate protective measures. This framework can be applied as prototype to protect a wide range of vital City infrastructure beyond wastewater facilities. The framework is comprised of 3 major modules: Climate Analysis, Vulnerability Analysis and Adaptation Analysis. The Climate Analysis investigated the question “What to adapt to?”. The FEMA 100-year flood event was selected as the maximum surge assessed in this study. An additional 30 inches of flooding was also added to account for future sea level rise by the 2050s, the high end of the projections from the NYC Panel on Climate Change. Vulnerability Analysis identified which infrastructure will be affected in flood events through site visits, analysis of facility blueprints and interviews with facility personnel. The elevations of flood pathways and infrastructure compared to the flood elevation defined in the climate analysis to determine the infrastructure at risk. Cost estimates for replacement of at-risk equipment under emergency conditions, cleaning of facilities, and temporary power and pumping were developed, and then used as a metric to inform the prioritization of vulnerabilities. Adaptation Analysis identified what can be done to protect vulnerable infrastructure from surges and how much it will cost. DEP performed an extensive literature review of strategies being considered around the globe to protect against climate change and narrowed the list down to six measures that would work best for the NYC's infrastructure. These protective measures were then evaluated for use at each wastewater facility and recommendations were based on feasibility, effectiveness, and cost.Prioritizing investments for capital improvements is an important aspect of planning since the required economic funding needs are greater than the available resources. In order to aid with prioritization, a number of criteria were applied including operational, environmental, social and financial metrics. These metrics included historical flooding frequency at each pumping station, proximity to beaches and sensitive water bodies, population served, number of critical facilities served (eg. hospitals, nursing homes, fire and police stations), and whether the particular asset is scheduled for upgrades in DEPs' 10 year capital plan for improvements. Based on these criteria the top five priority at risk pumping stations are identified as Van Brunt, Howard Beach, Throgs Neck, Nautilus Creek and 40th Road pumping stations. DEP has also selected wastewater treatment plants that can affect bathing beaches as high priority for implementing protective measures. These plants include 26th Ward, Coney Island, Hunts Point, Jamaica, Oakwood Beach, and Rockaway.Study results indicated that all 14 wastewater treatment plants and 60% of pumping stations (58 out of 96) are at risk of flood damage. In fact, of the almost 47,700 total assets at these facilities, about 4,000 that are necessary for primary treatment and 10,600 other facility assets were shown to be vulnerable. The study estimates that more than a billion dollars' worth of equipment are at risk and require additional protection. The recommended protective measures, totaling $317 million in improvements, are costly, but critical and could avoid almost 90 percent of risk citywide to wastewater treatment plants and ensure continuous service at pumping stations. Increased resiliency not only reduces damage costs during a flood event, but also enables rapid recovery of full-service following a flood event, prevents sewage backup into homes, and reduces the likelihood of the release of untreated sewage into the environment.