Nine Nationwide Nonpoint Solutions

When it comes to managing stormwater, U.S. communities nationwide face many different regulatory frameworks and paths to achieving clean water. While some communities are building green infrastructure to reduce combined sewer overflows, others are installing stormwater controls as part of total maximum daily loads, while still others are implementing minimum control measures for municipal separate storm sewer system permits. From industrial to agricultural to ultra-urban settings, the arenas for stormwater management vary greatly. Stormwater is a variable force, so the solutions must be equally adaptive. With such tools as manufactured treatment devices, nonstructural controls, green and gray infrastructure, and agricultural conservation practices, stormwater professionals can be better equipped to handle new challenges.

The following nine case studies share how some are developing the tools to overcome stormwater challenges. These solutions will be presented at the 2015 Stormwater Congress, a spotlight event at WEFTEC 2015, which will be held Sept. 26 – 30 at McCormick Place in Chicago.

1. Stormwater Solutions for TMDLs

Many cities face stormwater requirements for combined and separate storm sewers and may have the added challenge of addressing impaired waters through total maximum daily loads (TMDL). While TMDLs specify the maximum amount of a pollutant that a waterbody can receive and still meet water quality standards, it does not address how sources should treat or reduce those pollutant loads.

To meet a TMDL for total phosphorus and pathogens in the Charles River Watershed, the Boston Water and Sewer Commission is developing a best management practice (BMP) recommendation plan. To prioritize potential BMP implementation, Dingfang Liu — formerly a senior technical consultant with CH2M Hill and now a principal engineer at Kleinfelder — and other CH2M consultants, developed a quantitative, geographic-information-system-based ranking process. The rankings account for both the physical suitability of sites — which includes such factors as site conditions or whether the location is a pollutant hot spot — as well as the likelihood of implementation, which accounts for social and economic conditions. Before this analysis, Liu and others also screened BMPs for their effectiveness at removing total phosphorus and pathogens.

2. Non-Structural Stormwater Solutions

The City of San Diego has developed a first-of-its-kind methodology for quantifying the effects of dozens of nonstructural stormwater strategies, including outreach and education programs.

Within its stormwater permit and as part of a TMDL, San Diego must identify BMPs and the effects of those BMPs on various pollutants as well as anticipated water quality changes. To quantify the effects of non-structural controls, the analysis included the level of control the city has over the strategy as well as constructs affected by outreach campaigns, such as guilt and social norms.

A percent removal range was developed for each of the pollutants removed by various BMPs. The removal range could be as low as 2% for a minor pollutant that is only partially affected by a certain BMP up to 72% for a major pollutant where the city has significant control over the management strategy.

3. Agricultural Stormwater Solutions

Lake Champlain in Vermont — the sixth largest freshwater lake in the U.S. — is considered impaired by phosphorus, and EPA is expected to issue a TMDL for the lake this summer. The agency’s modeling efforts show that runoff from agricultural lands is responsible for almost 40% of the lake’s annual phosphorus load. While agricultural landowners have made significant investments in BMPs, these efforts have not yet yielded desired water quality results nor have site-specific benefits of the BMPs been quantified. However in 2012, the Vermont Agency of Agriculture, Food & Markets, in partnership with the U.S. Department of Agriculture’s Natural Resource Conservation Service, the Vermont Agency of Natural Resources, and the Lake Champlain Basin Program, initiated the Agricultural Practice Monitoring and Evaluation Program

BMP performance data and accurate pollutant reduction estimates will help to inform the TMDL process and have led to unexpected insights about managing agricultural runoff. “Our expectation was that most of the phosphorus leaving farm fields would be in particulate form and attached to soils,” said Julie Moore, water resources group leader with Stone Environmental Inc. and principal investigator for the study. “It was unexpected to see how much of the phosphorus being lost in runoff was in the dissolved fraction as compared to the particulate fraction.” Because particulate phosphorus has been the target of most conservation measures promoted to date, BMPs have relied on reducing soil loss to achieve phosphorus reductions.

4. Stormwater Solutions in Dense Urban Areas

The San Francisco Public Utilities Commission (SFPUC) is implementing green infrastructure as part of a 20-year, multi-billion dollar effort to upgrade the city’s aging sewer infrastructure, which is 90% combined. Initially, the city will construct and monitor eight Early Implementation Projects — ranging from creek daylighting to green street projects — one in each of San Francisco’s urban watersheds. This pilot will inform citywide implementation of green infrastructure as part of the Sewer System Improvement Program.

However, integrating stormwater management into the city’s already heavily utilized and many-times constrained streetscape right-of-ways requires careful planning, public outreach, and innovative design responses. When implementing such surface improvements as green infrastructure into a city as dense as San Francisco, it is critical to integrate with other planned projects to achieve multiple community priorities, said Kerry Rubin, an ecological engineer and green infrastructure specialist with AECOM and SFPUC’s program management consultant for sewer infrastructure. The concept of placemaking is a multi-faceted planning and design approach that capitalizes on community assets to create public spaces that promote people’s well-being. Integrating stormwater management and placemaking provides an important opportunity to create functional urban landscapes while providing greater community value through traffic calming and community greening and by providing wildlife habitat, gathering spaces, and other improvements. Crucial to placemaking in dense urban environments is public outreach. SFPUC informed and engaged stakeholders, but also used public outreach to gain an understanding of local issues and preferences to build better projects while meeting community needs.

5. Green and Grey Stormwater Solutions

In addition to being part of a holistic solution for addressing combined sewer overflows and flooding, gray infrastructure — such as pipe networks, curb and gutters, and inlet and outlet structures — also plays a role in collecting and conveying stormwater to green infrastructure systems.

While there may be a great open space to create green infrastructure, the system will not work unless stormwater can get to it, said Brenda Macke, water resources engineer with CDM Smith and an expert at designing conveyance systems and green infrastructure for separate and combined sewer systems.

Between overland flow and pipe systems, designers must consider the amount of water green infrastructure systems are receiving and understand what the system can handle. For instance, an upstream pipe system may be able to convey flows from a 10-year storm, but the green infrastructures systems may be designed to treat smaller, more frequent storm events. Determining the thresholds for each piece and considering how green infrastructure systems receive water from and overflow back to the gray pipe system enables communities to optimize both systems.

6. Industrial Stormwater Solutions

The Port of Tacoma in Washington State is a leader in industrial stormwater treatment innovation. The port’s industrial general stormwater permit contains some of the most stringent requirements in the nation. The port recently installed three different types of proprietary stormwater treatment equipment to reduce zinc concentrations in runoff at three unique but linked industrial sites. Looking to increase the number of tools in its stormwater management toolbox, the port is exploring the effectiveness of various treatment devices the port environment. Two of the installations represent the first ever application of the technologies at an industrial facility.

Ross Dunning, stormwater practice leader with Kennedy/Jenks Consultants, helped the Port of Tacoma evaluate options for the three facilities — all of which are flat, completely paved, and subject to extremely heavy equipment traffic. The site’s conditions and stormwater runoff characteristics as well as the design and treatment capabilities of the individual approaches played key roles in their selection. An additional consideration was system flexibility. “One of the unique challenges ports face is that stormwater characteristics can change based on what commodities the port is handling.” Dunning said.

While product cost often is a deciding factor, designing proper system hydraulics affects costs more, said Dunning. Accordingly, he said he uses hydraulic modeling to select gravity-based solutions whenever possible. If electricity was needed to pump stormwater to the systems at these three sites, project costs would have doubled at two sites and tripled at the third, he said.

7. Stormwater Solutions for Groundwater Recharge

The trend in stormwater permits is to encourage infiltration to reduce stormwater pollution. In light of water supply issues, groundwater augmentation also is becoming increasingly important. “We should be collecting the rare water we have and making good use of it,” said Martin Spongberg, a senior engineer with Amec Foster Wheeler.

However, some water quality experts have questioned whether infiltration-based practices could degrade groundwater quality. The Los Angeles Basin Water Augmentation Study, led by the Council for Watershed Health — a Los Angeles-based nonprofit  — in partnership with eight local, state, and federal agencies, sought to answer that question with long-term, comprehensive subsurface monitoring at six southern California infiltration sites.

Over the long-term, researchers saw no negative effects on groundwater quality. In some cases, infiltration even decreased the concentration of groundwater pollutants due to dilution and filtration by soil media. “There is a really low potential for augmentation to negatively impact groundwater quality,” said Spongberg, who has been the consultant program manager since 2003. However, areas with recalcitrant pollutant loads, such as salts or nitrates, or areas with very shallow groundwater may not be suitable for infiltration, he said.

8. Solutions for Stormwater Volume Reduction

Transportation systems present unique stormwater management challenges in that they cross many variable conditions, basins, and infrastructure. A 2008 National Academies of Sciences report identified roads and parking lots as the most significant land use with respect to stormwater pollution, as they constitute as much as 70% of total impervious areas in ultra-urban settings and typically export more pollutants than other impervious land covers. According to the report, maintaining predevelopment conditions is essential to managing stormwater discharges. Capturing stormwater volume and preventing runoff not only reduces the amount of pollutants flowing into surface waters but also reduces the water’s energy in downstream channels.

Eric Strecker, a principal water resources engineer with Geosyntec Consultants and one of the highway report authors, said transportation agencies should ask the following four questions. First, can the water be infiltrated? For instance, are the soil conditions and groundwater depths appropriate? Second, should the water be infiltrated? For instance, will infiltration cause slope stability issues or introduce pollutants into the groundwater? Third, how should water be infiltrated? And, fourth, how much should be infiltrated?

9. Technology as a Stormwater Solution

Curtiss Field Park in City of Falcon Heights, Minn., is a first-ring suburb of St. Paul. The park contains a small, landlocked stormwater pond that receives runoff from approximately 15 ha (38 ac). With a history of flooding, the pond presented a safety concern until the implementation of an innovative technology solution.

The Capitol Region Watershed District installed a large underground detention and infiltration facility under an adjacent sports field. The system includes 119 m (390 ft) of large-diameter perforated pipe that stores and infiltrates floodwater from the pond. An optimized, real-time controller draws the pond down half a meter (2 ft) in advance of a predicted storm. This automated inlet technology added 58% more capacity to the system. With the real-time controller, the system achieves the same level of flood protection at half the cost of a second storage pipe alternative, which was estimated to cost $140,000 dollars.

Through its connection to the internet, the controller monitors national weather service information, and begins to draw down the pond when a particular size rain event is predicted at a predetermined percent probability. The draw-down thresholds can be changed as the district collects more data. At any time, staff can remotely login to the system to monitor performance and modify programming.