Tag: Stormwater

5 Facts About Sustainable Stormwater Practices

In urban and densely populated suburban areas where the highest concentration of impervious surfaces are found, stormwater runoff can be a significant contributor to water pollution. As rain falls in outlying rural areas, the water is absorbed and filtered by the natural vegetation and soil. The impervious surfaces, including roofs, sidewalks, paved parking areas and wide city streets, do not allow the ground to absorb the water and instead is collected in closed drainage systems and often time discharged into nearby surface waters without filtration.

Here we review 5 Facts About Sustainable Stormwater Practices to help communities and agencies that may be planning to develop new “green” infrastructure.

  1. Regulatory Compliance: Stormwater is regulated at the federal level by the Environmental Protection Agency (EPA) under the Clean Water Act (CWA). The CWA “establishes the basic structure for regulating discharges of pollutants into the waters of the United States and regulating quality standards for surface waters.” Thus making it “unlawful to discharge any pollutant from a point source into navigable waters, unless a permit was obtained.” State Environmental Agencies often apply additional requirements beyond EPA minimum standards to further protect impaired state waters. On a local level, some communities have developed Stormwater Management Plans to assist managing discharge from both private and public properties. Local Ordinances are crafted by community officials as an integral part of subdivision and site plan development review and approval processes. New stormwater regulations often require implementation of sustainable stormwater management practices.
  2. Green Materials: “Green” or sustainable stormwater best management practices treat stormwater as a resource to be preserved and maintained, taking advantage of natural processes to clean and filter stormwater runoff.  Vegetation and soil filtration highlight the obvious green materials used, but some methods growing in popularity include permeable pavement, down spout disconnection, rainwater harvesting, rain gardens, planter boxes, tree filters, green roofs, bioswales, as well as land conservation. With the incorporation of one or more of these design features, urban spaces are able to reduce the percentage of impervious surfaces thus reducing the volume of stormwater runoff.
  3. Public-Private Partnerships: State and local governments collaborating with developers on properties within different regions to incorporate Green Infrastructure into the design/redesign will in turn save money via stormwater diversion and treatment by the agencies. Offering tax credits or incentives to the developers is intended to accelerate the adoption of these improved stormwater management practices leading to more extensive implementation statewide.
  4. Funding Availability: Many funding options are available through federal and state agencies including EPA, Departments of Transportation, US Economic Development Administration (EDA), Department of Housing and Urban Development (HUD), National Oceanic and Atmospheric Administration (NOAA), as well as the Departments of Agriculture, Energy and Treasury. Grants available through these agencies will help offset the cost for municipal and private entities to invest in sustainable stormwater collection, filtration and treatment upgrades to existing or redeveloping sites.
  5. Benefits: Environmental – Improperly managing stormwater runoff into surface waters can contain pollutants from the surfaces it is diverted from, potentially causing damage to aquatic vegetation and wildlife. Uncontrolled stormwater runoff can also cause physical damage such as erosion and flooding.  With the implementation of green infrastructure practices, contaminants can be reduced in the receiving water bodies and create healthier environments. Social – Incorporating sustainable stormwater management practices can improve water quality, quantity and aesthetics, thereby enhancing the livability of a community, creating multifunctional landscapes and green spaces, encouraging revitalization, and providing educational opportunities. Economic – The use of green infrastructure may provide incentives to attract investment; reinvigorate neighborhoods; inspire redevelopment; or provide new recreational opportunities.

To find out more about community stormwater management practices, the EPA has issued resources outlining practices to assist while achieving other environmental, social and economic benefits.

Celebrating St. Patrick’s Day with a Focus on Green (Infrastructure)

Stormwater Detention Pond Construction

To celebrate St. Patrick’s Day this year, we wanted to highlight some the ways we embrace green infrastructure. Sometimes our projects are naturally geared towards sustainability out of necessity (i.e. so we don’t disturb wildlife or certain plant species), while other projects may not have a need for sustainability but we see a way to incorporate it (i.e. better stormwater management).

Before we get into some of the specific green infrastructure examples, it is important to establish some background. First, green infrastructure is not just a marketing term; it is defined by the US Environmental Protection Agency (EPA) as “the range of measures that use plant or soil systems, permeable pavement or other permeable surfaces or substrates, stormwater harvest and reuse, or landscaping to store, infiltrate, or evapotranspirate stormwater and reduce flows to sewer systems or to surface waters.”

In other words, green infrastructure is using natural means to move water rather than building more infrastructure like pipes or drains. These projects are highlights of our recent green stormwater infrastructure.

Green Methodology

As part of a consultant team, we have developed a methodology for the Vermont Department of Environmental Conservation (VTDEC) to prepare cost estimates for the implementation, and operation and maintenance of stormwater projects for all land use sectors (agricultural, wetlands, river/streams, lakeshore, forest roads/trails, roads, urban, etc.), as well as developed an O&M standards manual for continued operation of these practices. The final product was recently submitted to the State of Vermont and will outline how stormwater projects are planned, implemented and maintained throughout the State.

Green Bioretention

Bioretention

One project I worked on was to conduct an Engineering Feasibility Analysis for the City of South Burlington Municipal Office complex which had been identified as a location to evaluate and implement stormwater management improvements. The analysis resulted in the implementation of Low Impact Development (LID) measures. The designed stormwater management improvements included a bioretention facility, vegetated swale, and underground storage system.

The bioretention facility works to collect and absorb runoff from rooftops, sidewalks, and paved surfaces.  Bioretention practices mimic natural hydrology by infiltrating and evaporating and transpiring stormwater runoff.

Green Gravel Wetlands

This project addressed collected stormwater flowing into Bartlett Brook, crossing beneath Route 7 and ultimately into Shelburne Bay in Vermont. The design concept that had been developed by others through the Bartlett Brook Flow Restoration Plan process included capturing collected stormwater runoff from the neighborhood and conveying this stormwater to a City-owned parcel on the west and downgradient side of the neighborhood to allow for underground infiltration. Upon further investigation, site soil conditions were found to be unfavorable for stormwater infiltration. As a result, the Hoyle, Tanner Team designed a gravel wetland at the City-owned site to provide for flow detention and phosphorus removal of the collected stormwater runoff from the contributing residential drainage area.

Green Plans

Finally, but not least in importance, is planning for green infrastructure’s future. As part of a large integrated water quality planning effort for the City of Burlington, green stormwater infrastructure (GSI) projects were included as an important means to reduce stormwater flows and phosphorus loading to the combined sewer system in Burlington.

As part of meeting requirements for different Clean Water Act programs, Burlington’s Integrated Plan is intended to identify and prioritize water quality opportunities that result in a cost-effective program to achieve water quality goals. Tasks included the development of a comprehensive clean water alternatives analysis, including identification of enhanced phosphorus optimization at wastewater treatment facilities; identification of City-wide runoff (stormwater and wet-weather) opportunities; planning concepts for high-priority runoff mitigation projects; financial capability analysis; facilitation of public outreach; and development of an Integrated Plan with an implementation schedule. Burlington’s Integrated Plan development is currently in progress with an anticipated submission to State regulators later this year.

Stormwater runoff is a major cause of water pollution in urban areas, carrying trash, bacteria, phosphorus, and other pollutants from the urban landscape into our waterways.  Implementation of green infrastructure can help mitigate stormwater runoff by providing natural areas within the urban landscape that provide habitat, flood protection, and cleaner water. At Hoyle, Tanner, we look for ways to incorporate green infrastructure into our planning and design concepts to maximize the environmental benefits they can provide.

Part 1: Why & How 2D Hydraulic Modeling is Enhancing Bridge Engineering

Image of colorful 2D hydraulic modeling image with arrows indicating which way water flows

A bridge, culvert, the road nearby or above, the banks, and the surrounding ecosystem are affected by water’s flow. It is no surprise, then, that studying hydraulics and hydrology when designing bridges is paramount for safety, road users, and engineers.

The purpose of hydrology is to study water itself with respect to the land, whereas hydraulics studies what the water is doing within a channel or pipe. So, when engineers develop 2D hydraulic models, they are looking at how water behaves in a given area, and ultimately use that information to build safer bridges. This type of modeling tells engineers not only where the water is going, but where it wants to be.

Basically, 2D modeling determines and depicts water flowing back and forth (on a horizontal plane) instead of horizontally and vertically (3D modeling). The modeling is presented as a dynamic graphic that shows the flow of the river or water body. With a bridge in the model, engineers can determine how the water will move around piers and abutments (the bridge foundation), what could happen with scour and decide how to design for it, and predict the bridge’s impact on the environment (and the environment’s impact on the bridge) for years to come.

2D hydraulic image of black water on a map with white, moving lines showing water flow direction
2D hydraulic model

First things First

When a bridge engineer designs a bridge or culvert associated with water, hydraulic modeling isn’t an afterthought; it’s one of the first things that gets done when a project starts. Structural engineers already have data about the area and usually the existing bridge. Still, they often need more specific information to understand the entire project better – for example, data points on the lowest part of the bridge and how the structure is situated in relation to the water below.

2D hydraulic modeling at the beginning of the project gathers that information and helps the engineers better plan for the project, and is welcomed by this engineer as a preferred alternative to the conventional 1D modeling. It’s not just a benefit to engineers who want to know a system’s details, though. Clients, municipalities, and everyday citizens benefit from engineers using 2D hydraulic modeling – because it helps convey to them what’s happening with the water and helps the engineers better protect the infrastructure we use every day.

When it Rains, it Pours

When you think back to the Mother’s Day floods in 2006 or any other time flooding threatened New England, you probably don’t think much about the bridges you drive unless the water pools over the road. What few people think about is what’s happening under and over the bridge; with faster rushing waters and more force, there’s the potential for three big events: scour, rising water carrying debris, and pressure on the bridge caused by flooding water.

Scour is what happens when sediment around the bridge foundation (or along the roadway) erodes and starts washing downstream, leaving the potential for the material under the bridge to become unstable. In some cases, sediment from upstream of the bridge will wash downstream and fill in these holes during the storm before anyone realizes how big of a scour hole actually developed. We use 2D hydraulic modeling to help better predict the scour that might occur during these events even though we may not see it.

Image of a flooding truss bridge in Ludlow, VT during a large storm

This erosion can also occur beside and/or below the roadways leading up to the bridge if the water flows over the roadway. The 2D model enables us to see how much of the water is going over the roadway as well as provides us with the depth and velocity of this water. We can use this information to determine if the sides of the roadway might be in danger of washing away with the water. If the embankments might erode, we can properly armor them and keep them protected.

Part of our job is looking out for this erosion – if we determine that scour might be a potential issue during a storm, we can get ahead of it. One way of doing this to help prevent it under the bridge is by putting riprap (larger stones) in front of and around the bridge foundation to help keep the natural, finer sediment of the streambed and below the foundation in place. Another way is potentially changing the foundation type: if the anticipated scour is deep, we might change from a shallow foundation to a deep foundation. Scour is just one of the dangers associated with large storms, and 2D hydraulic modeling gives engineers the insight they need to help prevent dangerous situations.

Rising water is another danger to bridges, not just because it could potentially overtop (flow over) the bridge, but because the rushing waters can carry debris (say, a fallen tree) that could hit the bridge and cause damage. When we plug in potential flooding scenarios into the 2D hydraulic models, we use the models to predict how high the water could potentially get during a storm. That way, we can plan to build a new bridge or raise an existing bridge above the water level, reducing the chance for the bridge to be damaged.

2D hydraulic image showing velocity and water flooding on top of bridge

The third big concern with large storms is the power of flooding waters pushing on the bridge. This pressure could be going into and on top of the bridge, but also could come from under the bridge (buoyant forces trying to lift the bridge up). For this scenario, 2D hydraulic modeling allows us to see where the water would want to go during a flood and determine how much of it is going under the bridge, over the bridge, and around the bridge. This allows us to evaluate what an existing bridge might experience, and to design a new bridge to eliminate these forces (locate the deck above the water) and to resist the forces that can’t be eliminated for a certain storm event.

Garbage in, Garbage Out

The more data we can put into the model and the more accurate that data is, the more confident we can be with the results. That means that for the most part, 2D hydraulic modeling provides valuable information that we had to assume or make educated guesses about 30 years ago. While 2D hydraulic modeling doesn’t solve every problem, it gets us closer to understanding the hydraulics of the bridge. In the event that a solution doesn’t quite make sense, it could be because we need more or better data to put into the 2D hydraulic model.

For example, we’re working on a project right now that is analyzing an existing bridge in a river. Using 2D hydraulic modeling, we noticed that the water isn’t flowing as expected. We looked upstream and noticed old bridge abutments causing a constriction in the water flow. This slight constriction causing the river to backwater and holding part of the flow back is a great example of how limited data can affect the hydraulic modeling, or what I like to call “garbage in, garbage out.” If we didn’t have the data that depicted this constriction, we might have missed how it influences the river and the flow at our crossing.

Another project currently underway involves an upgrade and analysis of two culverts, with a third culvert right upstream, that have all been causing water constriction. The 2D hydraulic model shows us how these constrictions are causing backwater and increased flooding. The 2D hydraulic analysis also allows us to see what happens when we change the structures in the water. With some tweaks to the 2D model, we’re able to see that if we replace the two downstream culverts with a wide open structure that spans the bankfull width, the flooding is significantly reduced in the model. Meaning that if we replace these culverts with this other bridge system we designed, the next huge rainstorm won’t cause so much issue.

Want to know more about 2D hydraulic modeling?

We’re only as good as our data and our engineers’ analysis of that data. 2D hydraulic modeling has helped us foresee challenges to certain bridge structures while advocating for others to serve an area better. It replaces 1D hydraulic modeling at a time when computers now have the bandwidth to handle the massive programs required to use.

If you have any further questions, reach out to me and stay tuned for the follow-up blog on the different programs and math needed for this undertaking!

The New Great Bay Total Nitrogen General Permit

Pink and purple sunset image over water with tree skyline of Great Bay Estuary

What is the Great Bay Total Nitrogen General Permit & why does it matter?

The US Environmental Protection Agency (EPA) issued the final Great Bay Total Nitrogen General Permit (GBTNGP) on November 24, 2020. The GBTNGP is aimed at reducing the overall nitrogen loading into Great Bay, a unique coastal marine estuary. The GBTNGP covers discharges of nitrogen from the 13 communities that own/operate wastewater treatment facilities in the watershed: Dover, Durham, Epping, Exeter, Milton, Newfields, Newington, Newmarket, Pease Tradeport, Portsmouth, Rochester, Rollinsford and Somersworth. The permit allows for an adaptive management approach to monitoring and reducing nitrogen discharges. Each community has the option of being included for coverage under the GBTNGP or not (opt in or opt out). If a community decides to be included for coverage under the permit it must file a Notice of Intent with the EPA, Region 1, by April 2, 2021. The alternative to opting in to the GBTNGP will be that the community will receive a new/revised individual NPDES permit to govern its WWTF discharge. Key dates for actions to be taken pursuant to the GBTNGP are as follows:

  • February 1, 2021 – Effective date of the Great Bay Total Nitrogen General Permit.
  • March 31, 2021 – Deadline for finalizing an Intermunicipal Agreement to develop the Adaptive Management Plan.
  • April 2, 2021 – Deadline for sending EPA the Notice of Intent to Opt-In to the TN General Permit.
  • July 31, 2021 – Deadline for submittal to EPA of the Part 3 Adaptive Management Plan.

How can an Adaptive Management Approach help?

The GBTNGP allows for an adaptive management approach to be taken for monitoring and controlling nitrogen discharges and allows for the communities to develop the Adaptive Management Plan. Adaptive management is a key aspect of watershed management and restoration. Elements of adaptive management included in GBTNGP involve ambient monitoring, pollution tracking, reduction planning, and review. Adaptive Management is, by definition, a structured iterative process of robust decision making in the face of uncertainty, with an aim to reducing uncertainty over time via ongoing system monitoring. In this way, decision making simultaneously meets one or more resource management objectives and, either passively or actively, accrues information needed to improve future management and decision-making. Adaptive management is a tool which can be used not only to change a system, but also to learn about the system (Holling 1978). Because adaptive management is based on a learning process, it improves long-term management outcomes. The challenge in using the adaptive management approach lies in finding the correct balance between gaining knowledge to improve management in the future and achieving the best short-term outcomes based on current knowledge (Allan & Stankey 2009).

A holistic & cost-effective approach.

The objective of an adaptive management approach is to take a broad holistic and more cost-effective approach to implementing water quality restoration and management measures that will achieve better overall results in improving water quality goals in less time and at less cost than the traditional regulate-react approach by applying limited resources where they will have the greatest effect. In fact, the GBTNGP encourages sharing of resources and costs among the participating communities. The adaptive management approach allows for planning, implementation, monitoring and refinement in order to maximize the results with limited resources (resource optimization). The idea behind an adaptive management approach is for communities to become proactive rather than reactive in restoring water quality within the watershed. A successful adaptive management approach will require extensive collaboration and cooperation between municipalities, regulators, agencies, volunteer groups and other watershed stakeholders.

Our experience.

Hoyle, Tanner’s Northeast Municipal Engineering services Group (NEME) employs 20 engineers whose primary focus is water quality engineering – wastewater, stormwater and drinking water. Our depth and breadth of experience includes working with communities to assist them with compliance with permits such as NPDES (wastewater and stormwater), MS4 (stormwater and non-point) and a host of other regulatory and environmental permits. We have been working with communities under regulatory constraints to monitor and reduce the amount of total nitrogen discharged to local water bodies and helping them to achieve water quality goals. Jennie Auster, one of our wastewater process engineers, has been working with communities affected by the Long Island Sound Total Maximum Daily Load (TMDL) for Nitrogen for over six years including completing biological nutrient removal analysis for several facilities. Jennie completed nitrogen removal optimization plans for six communities and has presented at the Green Mountain Water Environment Association Technical Sessions on her experience with low-cost nitrogen optimization plans (presentation available upon request). We are assisting several communities on compliance with the 2017 MS4 permit which includes nutrient reduction in stormwater and non-point sources. We are also working with many communities on asset management for their wastewater, stormwater and drinking water systems, the goal of which is resource optimization to improve decision-making and maximize the life of the infrastructure.

Let us help!

Our team has a history of developing creative and innovative solutions to help clients achieve their goals in cost-effective ways while optimizing the use of limited resources. For more information please visit our website at: www.hoyletanner.com or contact Michael Trainque or Joseph Ducharme.

I am a Senior Environmental Engineer and Vice President at Hoyle, Tanner, and chairman of the Board of Directors of the Southeast Watershed Alliance (SWA). The SWA is a non-profit watershed organization for which enabling legislation was enacted by the NH State Legislature in 2009 encompassing the 42 communities in the NH coastal watershed. I have been following the development of this permit on behalf of clients.

MS4 Timeline: The Second Annual Report & What’s Next

MS4 timeline with relevant dates

September 2020 marks another year for MS4 permitting in New Hampshire. Since MS4 rules were updated in 2017, we have continued to help communities regulate their stormwater discharges to meet these new requirements. This month on the MS4 timeline, communities should be aware that Second Annual Reports are due.

First, let’s back-track and recall that MS4 permitting refers to regulations in place to manage stormwater in a community. Stormwater outfalls from an MS4 area must be located, mapped, and assigned a unique identification number. Then, inspections and condition assessments must be completed for each outfall based on priority ranking. We have a detailed post about what happens if you observe flow during dry weather and different outfall rankings based on testing samples. We also identified a timeline  following the initial mapping, focusing on what happens after the first annual report. With September’s deadline quickly approaching, here is what communities can expect with the next steps.

The Second Annual Report

Communities should be submitting their second annual reports to EPA by September 28, 2020.

EPA has provided a partially filled-in report template to permitees; EPA has provided a partially filled-in report template to permitees; however, the New Hampshire stormwater coalitions have modified the template to be more user-friendly. The updated template can be found as part of the Coalition blog site here: NH Stormwater Coalition Annual Report for Year 2 Template.

We have worked with a half dozen small communities in New Hampshire to prepare them for their annual reports. In some communities, this means we mapped, visited, and screened their outfalls, and provided training. For others, we helped coordinate stormwater team meetings and activities, or just provided reassurance. After working with several communities, we’ve found that the same hurdles present themselves and have gathered a few tips to help the process move smoothly:

  • Do not omit information. When filling out the second annual report, be sure to take credit for everything that had progress between July 1, 2019 and June 30, 2020.
  • Take time now to review the requirements for the next report. Some required activities or tasks are more easily performed during specific times of the year; now is a good time to plan how to keep up with your Stormwater Management Program activities.
  • Be conscious of the timeframe.  Any efforts begun, but not completed in the Year 2 timeframe, cannot be marked complete. Any progress should be mentioned in the comments section.

What Next?

The most important thing to keep in mind is that as each year of the permit term passes, the stringency of the requirements increases. There is no time for rest or relaxation – pull out that Stormwater Management Program and see what elements (written program updates, outfall screenings, training, regulatory review and updates, stormwater management device Inspection, etc.) are required to be completed when the complete outfall ranking (based on dry-weather samplings) is due – June 30, 2021. Reviewing the required elements ahead of time will help with early coordination of next year’s report.

Not every MS4 community will encounter the same challenges. Meeting these deadlines and documenting all stormwater sources can be time consuming and difficult. Our stormwater experts are here to help and are fully prepared to help with unique challenges and stormwater setbacks. Reach out to our experts Heidi Marshall, PE or Michael Trainque, PE with stormwater inquiries!

*This post was co-written by Catie Hall, marketing coordinator. MS4 Expert Michael Trainque, PE also contributed to this post.

MS4 Regulations in New Hampshire Communities: How to Deal with Stormwater

Storm Drain Photo

Whew!! You got that Notice of Intent form submitted (hopefully) to EPA on or before October 1. Now what? Grab a cold one, sit back, relax? Wishful thinking. Now the real fun begins.

Stormwater Sampling For those communities that have not already done so, stormwater outfalls from the MS4 area must be located, mapped and assigned a unique identification number. Then an inspection and condition assessment must be done for each outfall. If you were an MS4 community subject to the 2003 permit, you would have (or at least should have) completed this. However, you are not finished. Mapping completed pursuant to the 2003 MS4 permit must be updated with significantly more detail added per the 2017 MS4 permit. You have 2 years to complete the update. If you are a new MS4 community subject to the 2017 MS4 permit, you need to start this process and complete it within 3 years. For all MS4s, the stormwater mapping must be updated annually; and catch basins, catchment areas, manholes, and other features must be added. You must also complete an outfall inventory and ranking. The ranking is based on potential for illicit discharges and sanitary sewer overflows. Are we having fun yet??

If flow is observed from any outfalls during dry weather, it will be necessary to conduct dry-weather sampling and testing of each outfall in which dry-weather flow was observed in order to determine if there are potentially illicit discharges in the outfall. Outfalls must be ranked as “Problem”, “High-Priority”, “Low-Priority”, or “Excluded” based on known or suspected illicit discharges or sewer system overflows. This is all part of the required Illicit Discharge Detection and Elimination Program (IDDE). Did I mention you need to complete a written IDDE program within one year (by June 30, 2019)?

A number of New Hampshire communities are specifically listed in the 2017 MS4 permit based on discharges to waters with an approved Total Maximum Daily Load (TMDL) and/or based on discharges to certain water quality limited (impaired) waters without an approved TMDL. Approved TMDLs include chlorides, bacteria or pathogens, and phosphorus.

How is your Phosphorus Reduction Plan coming along?
Impairments to waters without an approved TMDL include: nitrogen, phosphorus, bacteria or pathogens, chloride, total suspended solids, metals, and oil and grease. Did you know that leaf litter contributes phosphorus and nitrogen to stormwater runoff?

How is your Chloride Reduction Plan coming along?
The written Plan has to be completed within 1 year (on or before June 30, 2019). There are also specific requirements for public education and outreach as well as public participation including messages and outreach to target audiences.

How are your stormwater regulations?
MS4 communities need to update their stormwater regulations and ordinances (if you already have them) or develop and implement regulations for managing stormwater (if you do not have them).

By the way, did I mention that all of the foregoing has to be addressed in your Stormwater Management Plan? The Hoyle, Tanner team of experts is available to assist you as needed with MS4 permit compliance. If you have questions, please contact me or Heidi Marshall for assistance.