Don’t Get Sunk: Everything You Need to Know About Sinkholes (Part Two)

Sinkhole in Frederick, Maryland. Credit: Randall Orndorff, U.S. Geological Survey. Public domain.

Sinkholes can be quite terrifying. We see them on the news, on television and in movies seemingly appearing out of nowhere, swallowing up cars and creating calamity in towns across the world. In this two-part blog series, our experts uncover the mystery around sinkholes and arm you with the facts you need to make them less scary.

In part one of the blog series, we discuss what a sinkhole is, three different types of sinkholes, and what causes them to form. In this second part, we explore how to detect sinkholes, what to do if you detect a sinkhole, and the steps taken to repair them.

WELCOME TO PART TWO: DON’T GET SUNK: EVERYTHING YOU NEED TO KNOW ABOUT SINKHOLES
How to Detect a Sinkhole:

Cover-collapse sinkholes (outlined in red) in eastern Bullitt County Kentucky. Photo by Bart Davidson, Kentucky Geological Survey.Not all sinkholes are Hollywood-style monstrosities capable of swallowing your whole house. But even a much smaller, less noticeable sinkhole can do its fair share of harm, compromising your foundation and damaging utilities.

Although sinkholes can be scary to think about, you can take comfort in knowing there are ways to detect them, both visually and experimentally. Often, you can spot the effects of a developing sinkhole before you can spot the hole itself. If you live in an area with characteristics common to sinkhole formation (i.e. “karst terrain,” or types of rocks that can easily be dissolved by groundwater), there are some things you can do to check your property for signs of potential sinkhole formation.

According to the American Society of Home Inspectors, there are key signs you should be on the lookout for in and around your home:

Inside:

  • structural cracks in walls and floors;
  • muddy or cloudy well water;
  • interrupted plumbing or electrical service to a building or neighborhood due to damaged utility lines; and
  • doors and windows that don’t close properly, which may be the result of movement of the building’s foundation.

Outside:

  • previously buried items, such as foundations, fence posts, and trees becoming exposed as the ground sinks;
  • localized subsidence or depression anywhere on the property; in other words, an area that has dropped down relative to the surrounding land;
  • gullies and areas of bare soil, which are formed as soil is carried towards the sinkhole;
  • a circular pattern of ground cracks around the sinking area;
  • localized, gradual ground settling;
  • formation of small ponds, as rainfall accumulates in new areas;
  • slumping or falling trees or fence posts; and
  • sudden ground openings or ground settlement, keeping in mind that sudden earth cracking should be interpreted as a very serious risk of sinkhole or earth collapse.
Actions to Take if You Believe You’ve Detected a Sinkhole:

If you spot any of the signs listed above, or you suspect that you have a sinkhole on or near your property, you should contact your township, public works, or the local engineering firm that represents your municipality right away. If you have discovered a sinkhole that is threatening your house or another structure, be sure to get out immediately to avoid a potentially dangerous situation.

Also, it is highly recommended that:

  • Credit: USGSIf a sinkhole expert can’t get to the area relatively quickly, you ensure that kids and animals keep away, fence/rope-off the area while maintaining a far distance away from the actual sinkhole, keeping in mind that doing so requires extreme caution and is always best left to the experts when possible;
  • Notify your neighbors, local Water Management District, and HOA;
  • Take photos to document the site;
  • Remove trash and debris from around the suspected area in order; and
  • Keep detailed records of all the actions you took.

If you’re trying to determine whether or not you have a sinkhole on your property, there are a few physical tests that can be conducted to determine the best course of action.

In Australia, a courtyard formed a sinkhole. Credit: Earth-Chronicles.comElectro-resistivity testing: This extremely technical test can best be summed up by saying it uses electrodes to determine the conductivity of the soil. Since electricity can’t pass through air, this test shows any pockets where the current didn’t pass through. This is a fairly accurate way to determine if there is a sinkhole and where it is.

Micro-gravity testing: Another incredibly technical method, this test uses sensors that detect the measure of gravity. Since the gravitational pull in a given area should be the same, you can see if there are minute differences in the measurement. If there is a difference, then it’s likely that you have a sinkhole in that area.

If you are still unsure whether or not you live in a sinkhole risk area, you can check with your local, territorial, or national government offices; review geological surveys such as the United States Geological Survey (USGS); and contact an expert.

How a Sinkhole is Repaired?

There are three main techniques experts utilize to repair sinkholes. The type of sinkhole and landowner’s aesthetic preferences determine the methodology used to repair the sinkhole.

The three common methods are:

  1. Inject grout with a drill rig: This uses a piece of large drilling equipment that pierces the ground and goes down into the sinkhole, injecting it with grout/concrete. This method stops the filling of the carbonate crack with sediment since concrete and grout do not break down into such small particles (no piping).
  2. Inverted cone: With this method, the construction crew digs down and finds the bowl-shaped opening. They then open up the surface so that the entire sinkhole area is exposed. To stop the draining of sediment into the crack in the carbonate rock, they fill the hole with bigger rocks first, then gradually fill in the seams with smaller rocks until the sinkhole is plugged.
  3. Filling it with concrete/grout from the surface: This is a combination of the prior two methods. The construction crew opens the surface all the way up so the entire hole is exposed. Then, they bring in a big concrete pourer and fill the sinkhole with concrete.

Missouri Dept of Natural Resources, Inverted cone repair sinkhole mitigation diagram

Our engineers regularly go out in the field to oversee and inspect sinkhole repairs. If you detect a sinkhole, or what might be a sinkhole, on your property, our experts strongly advise immediate actions be taken. Ignoring a sinkhole will only cause it to get larger and more dangerous as time passes, and putting topsoil over a sinkhole will only exacerbate the symptoms.

What Can You Do to Prepare for a Sinkhole?

While there’s really no way to prevent a sinkhole, you can never be too prepared! Here are three easy steps you can take to determine if you live in or around a sinkhole-prone area and what to do in the event of a surprise sinkhole:

  1. Find out whether or not you’re living in one of the sinkhole-prone states, which includes Pennsylvania, Texas, Florida, Alabama, Tennessee, and Missouri. You can do so by visiting USGS.com and searching for Bedrock Geology maps of your area. If your town is underlain by carbonate rocks, you are likely in a sink-hole prone area.
  2. Contact an engineer who’s certified to deal with sinkholes to determine if your property is at-risk.
  3. Develop a plan for what to do in the event of a sinkhole. Do you grab your family, pets, and leave immediately? Do you have a safe zone somewhere near (but not too near) your property? Do you have the appropriate emergency contact numbers in your phone? Does your car have a safety kit? These are some of the things to consider when making your emergency plan.
  4. Speak with your insurance company to see if they have sinkhole coverage, especially if you live in an area where they’re known to occur.

Although scary, sinkholes are a manageable threat if you’re informed and prepared. After all, it is possible to do something about sinkholes – if they can be detected in time.

Special thanks to Princeton Hydro Staff Engineer Stephen Duda, Geologist Marshall Thomas, and Communications Intern Rebecca Burrell for their assistance in developing this blog series.

Revisit Part One of this blog series in which we provide a detailed look at what a sinkhole is, three different types of sinkholes, and what causes them to form:

Don’t Get Sunk: Everything You Need to Know About Sinkholes (Part One)

Laura Wildman Awarded for “Bringing the Presumpscot River Back to Life”

Photo provided by the Friends of the Presumpscot River

The Friends of the Presumpscot River (The Friends) Board of Trustees awarded Laura Wildman, P.E., Princeton Hydro’s New England Regional Office Director and Water Resources and Fisheries Engineer, with its “Chief Polin Award.” The award recognizes Laura for her accomplishments and efforts in bringing life back to the Presumpscot River and rivers across the nation. The award was presented at The Friends’ Three Sisters Harvest Dinner & Annual Celebration.

The Chief Polin Award recognizes those who are making significant efforts to restore fish passage, improve water quality and bring back the natural character of the Presumpscot river.During her acceptance speech, Laura thanked The Friends for its continued dedication to restoring fish passage and revitalizing the river. “I am so proud to be part of the ‘river warriors’ team,” Laura said. “Our collective efforts to protect and restore the river have resulted in invaluable benefits to fish, aquatic organisms, wildlife, and the surrounding communities.”

The award is named after local Abanaki tribe leader Chief Polin, who led the first documented dam protest in New England during the mid-1700s, advocating for fish passage, which had been compromised by the first dams built along the river. The award recognizes those who are making significant efforts to restore fish passage, improve water quality, and bring back the natural character of the Presumpscot River. Sean Mahoney from the Conservation Law Foundation also received the Chief Polin Award during the Annual Celebration.

Map provided by The Friends of the Presumpscot RiverLocated in Cumberland County, Maine, the Presumpscot is a 25.8-mile-long river and the largest freshwater input into Casco Bay. The river has long been recognized for its vast quantity of fish. According to The Friends, when Europeans first arrived, they reported that “the entire surface of the river, for a foot deep, was all fish.”

In the 1730s, however, the construction of dams halted the passage of fish up the river. As more dams sprung up in the following centuries, the ecological vitality of the river steadily declined.

For more than 250 years, people have advocated for the unobstructed passage of fish up the Presumpscot River. Over the last 50 years, the river has undergone profound transformation due to the enactment of the Clean Water Act, the removal of a few dams, and the installation of fish passages on existing dams. Fish passage at Cumberland Mills Dam, which was completed in 2013, restored critical habitat to sea run fish such as shad, American eel, and river herring, and allowed them to move upstream again.

Saccarappa Falls dam removal in actionIn July, work began to restore a large reach of the river through Westbrook, Maine. The project involves the removal of two dam spillways from the upper Saccarappa Falls and the construction of a fishway around the lower falls. The project, which was three years in the making, was finally approved to move forward once the City of Westbrook, Sappi Fine Paper, the U.S. Fish and Wildlife Service, the Maine Department of Marine Resources, and the nonprofits, Friends of the Presumpscot River and Conservation Law Foundation, were able to reach a ground breaking settlement. The Saccarappa Falls project is a major step in restoring the river and was a focal point of the Three Sisters Harvest Dinner, celebrating decades of effort on the parts of the Friends of the Presumpscot along with their numerous project partners, including Princeton Hydro.

About the Friends of the Presumpscot River: A nonprofit organization founded in 1992, supported primarily by membership dues and small donations. Its mission is to protect and improve the water quality, indigenous fisheries, recreational opportunities and natural character of the Presumpscot River.
Learn more: presumpscotriver.org

About Princeton Hydro: Princeton Hydro has designed, permitted, and overseen the removal of dozens of small and large dams along the East Coast. To learn more about our fish passage and dam removal engineering services, visit: bit.ly/DamBarrier.

Sediment Testing on the St. Lawrence Seaway

Way up in Northern New York, the St. Lawrence River splits the state’s North Country region and Canada, historically acting as an incredibly important resource for navigation, trade, and  recreation. Along the St. Lawrence River is the St. Lawrence Seaway, a system of locks, canals, and channels in both Canada and the U.S. that allows oceangoing vessels to travel from the Atlantic Ocean all the way to the Great Lakes.

Recently, the St. Lawrence Seaway Development Corporation (SLSDC) contracted Princeton Hydro to conduct analytical and geotechnical sampling on material they plan to dredge out of the Wiley-Dondero Canal. Before dredging, sediment and soils have to be tested to ensure their content is suitable for beneficial reuse of dredged material. In August, our Geologist, Marshall Thomas and Environmental Scientist, Pat Rose, took a trip up north to conduct soil sampling and testing at two different sites within the canal near Massena and the Eisenhower Lock, which were designated by the SLSDC. The first site was at the SLSDC Marine Base, which is a tug/mooring area directly southwest of Snell Lock. The second location was directly northeast of the Eisenhower Lock, which is also used as a mooring area. Both of these sites require dredging in order to maintain mooring access for boat traffic navigating the channel.

During this two-day sampling event, our team, which also included two licensed drillers from Atlantic Testing Laboratories, used a variety of equipment to extract the necessary samples from the riverbed. Some of the sampling equipment included:

  • Vibracoring equipment: this sampling apparatus was assembled on Atlantic Testing’s pontoon boat. To set up the vibracore, a long metal casing tube was mounted on the boat more than 10 feet in the air. The steel casing was lowered through the water approximately 17-20 feet down to the mudline. From there, the vibracore was then vibrated through the sediment for an additional 4-6 feet. For this project, vibracore samples were taken at 4 feet in 10 different locations, and at 6 feet in 3 different locations.

  • A track mounted drill rig: this rig was positioned along the shoreline to allow advancement of a standard geotechnical test boring close to existing sheet piling. Advancement of the boring was done by way of a 6-inch hollow stem auger. As the auger was advanced, it resembled a giant screw getting twisted into the ground. This drilling method allows the drilling crew to collect soil samples using a split spoon sampler, which is a 2-foot long tubular sample collection device that is split down the middle. The samplers were collected by driving the split spoon into the soil using a 140 lb drop hammer.

For our team, conducting sampling work on the St. Lawrence Seaway was a new experience, given most of our projects occur further east in the Mid-Atlantic region. The most notable difference was the hardness of the sediment. Because the St. Lawrence River sediments contain poorly sorted, dense glacial till, augering into it took a little more elbow grease than typical sediments further south do.  The St. Lawrence River is situated within a geological depression that was once occupied by glaciers. As the glaciers retreated, they were eventually replaced by the Champlain Sea, which flooded the area between 13,000 and 9,500 years ago. Later on, the continent underwent a slight uplift, ultimately creating a riverlike watercourse that we now deem the St. Lawrence River. Because it was once occupied by a glacier, this region is full of glacial deposits.

For this project, our team was tasked with collecting both geotechnical and analytical samples for physical and analytical testing. Physical testing included grain size analysis, moisture content, and Atterberg limit testing. Grain size analysis helps determine the distribution of particle sizes of the sample in order to classify the material, moisture content testing determines exactly that — how moist the sediment is, and Atterberg limits help to classify the fines content of the materials as either silt or clay. Analytical testing included heavy metals, pesticides, volatile organic compounds, and dioxins.

Our scientists were responsible for logging, testing, and providing a thorough analysis of fourteen sampling locations. The samples collected from the vibracore tubes filled with sediment were logged and spilt on-shore. In order to maintain a high level of safety due to the possible presence of contaminants, all of the sampling equipment was decontaminated. This process involves washing everything with a soapy water mixture, a methanol solution, and 10% nitric acid solution.

The samples collected at each vibrocore location were split into multiple jars for both analytical and physical testing. The physical test samples were placed into air and moisture tight glass sample jars and brought to our AASHTO accredited soils laboratory in Sicklerville, New Jersey for testing. The analytical samples were placed into airtight glass sample jars with Teflon-lined caps. These samples were then placed into an ice-filled cooler and sent to Alpha Analytical Laboratories for the necessary analytical testing.

Once all the laboratory testing was completed, a summary report was developed and presented to the client. This report was made to inform the SLSDC of the physical properties of each sediment sample tested and whether contaminants exceeded threshold concentrations as outlined in the New York State Department of Environmental Conservation (NYSDEC) Technical & Operation Guidance Series (TOGS) 5.1.9. This data will ultimately be used by the SLSDC to determine the proper method for dredging of the material and how to properly dispose of the material.

Princeton Hydro provides soil, geologic, and construction materials testing to both complement its water resources and ecological restoration projects and as a stand-alone service to clients. Our state-of-the-art Soils Testing Laboratory is AASHTO-accredited to complete a full suite of soil, rock, and construction material testing for all types of projects. For more information, go here: http://bit.ly/2IwqYfG 

Don’t Get Sunk: Everything You Need to Know About Sinkholes (Part One)

Photo by Steven Reilly/New Jersey Herald

Sinkholes are a phenomenon that tend to baffle and frighten most people. How is it possible that the ground beneath our feet could just drop? How do we know if we’re nearby a sinkhole? What should we do if we see one? How are sinkholes fixed? The mystery of the unknown around sinkholes can be quite unnerving.

Have no fear, we’ve got answers to all of those questions and more! In this two-part blog series, our experts share their knowledge and provide important information about this scary occurrence. In part one, we provide a detailed look at what a sinkhole is, three different types of sinkholes, and what causes them to form. In part two, we explore how to detect sinkholes and the steps taken to repair them.

What is a Sinkhole?

Sinkholes are a common phenomenon around the world. They result from both man-made and natural causes. Marshall Thomas, a Princeton Hydro geologist, describes sinkholes as “depressions observed from the surface, caused by dissolution of carbonate rocks.” In other words, sinkholes form when the rock below the land surface gets dissolved by water that penetrates the surface and continues to move downward, further into the subsurface.

Most common in areas with “karst terrain,” or types of rocks that can easily be dissolved by groundwater, sinkholes can go undetected for years until the space underneath the surface gets too big or enough of the surface soil is washed away. Sometimes the holes are small, measuring a few feet wide and ten feet deep. Sometimes the holes are hundreds of miles wide and deep. However, all of them can be dangerous.

Sinkholes are found throughout the world. States like Pennsylvania, Texas, Florida, Alabama, Tennessee, and Missouri are at higher risk for sinkholes because they tend to have more soluble rocks like salt beds and domes, gypsum, limestone, and other carbonate rocks. People living in these states are recommended to have professionals look at any property they intend to buy to make sure it isn’t in an area above soluble rock.

Types of Sinkholes

Not all sinkholes are the scary, earth-falling-out-from-underneath-your-feet events. Some occur slowly over time and are very evident from the surface. Geologists classify sinkholes in three major types. Their formation is determined by the same geological processes, barring a few differences. Let’s dive in!

1. Dissolution Sinkholes

Illustration by USGSDissolution sinkholes start to form when limestone or dolomite is very close to the soil surface, usually covered by a thin layer of soil and permeable sand which washes away or is eroded. Rain and stormwater runoff gradually percolate through crevices in the rock, dissolving it. Consequently, a bowl-shaped depression slowly forms.

Sometimes, dissolution sinkholes become ponds when the depression gets lined with debris, which traps water inside. Dissolution sinkholes develop gradually and are normally not dangerous. However, the ones that become ponds can drain abruptly if water breaks through the protective bottom layer.

Fun fact: Most of Florida’s lakes are actually just large sinkholes that filled up with water!

2. Cover-Subsidence Sinkholes

Illustration by USGSThis type of sinkhole, which starts with the dissolution of the underlying carbonate bedrock, occurs where the covering sediment is permeable (water can pass through it) and contains sand. First, small pieces of sediment split into smaller pieces and fall into openings in the carbonate rock underneath the surface. With time, in a process called piping, the small particles settle into the open spaces. This continues, eventually forming a dip in the surface ranging from one inch to several feet in depth and diameter. Again, these aren’t the sinkholes movies are made about.

3. Cover-Collapse Sinkholes

Illustration by USGSThis type of sinkhole is the one making headlines and causing fear. In order for cover-collapse sinkholes to happen, the covering soil has to be cohesive, contain a lot of clay and the bedrock has to be carbonate. Similar to the cover-subsidence sinkholes, the cohesive soil erodes into a cavity in the bedrock. The difference with this is that the clay-filled top surface appears to remain intact from above. However, underneath, a hollowed out, upside down bowl shape forms. That hollowing gets bigger and bigger over time until eventually, the cavity reaches the ground surface, causing the sudden and dramatic collapse of the ground. Just like that, poof, we have a sinkhole that appears to be surprising and abrupt but really has been brewing for many years.

What Causes a Sinkhole?

Sinkholes can be natural or man-made. The most common causes of a sinkhole are changes in groundwater levels or a sudden increase in surface water.

Intensive rain events can increase the likelihood of a sinkhole collapse. Alternatively, drought, which  causes groundwater levels to significantly decrease, can also lead to a greater risk of collapse of the ground above. In a world with a greater variability in rainfall and drought events due to climate change, sinkholes may become a more common occurrence around the world.

Humans are also responsible for the formation of sinkholes. Activities like drilling, mining, construction, broken water or drain pipes, improperly compacted soil after excavation work, or even significantly heavy traffic (heavy weight on soft soil) can result in small to large sinkholes. Water from broken pipes can penetrate through mud and rocks and erode the ground underneath and cause sinkholes.

Most commonly, human-caused sinkholes are the result of:

  • Land-use practices like groundwater pumping, construction, and development
  • Changing of natural water-drainage patterns
  • Development of new water-diversion systems
  • Major land surface changes, causing substantial weight changes

In some cases, human-induced sinkholes occur when an already forming sinkhole is encountered during construction processes such as excavation for stormwater basins and foundations. Dissolution of bedrock generally occurs in geologic time-frames (thousands of years). In these cases, the excavation process has removed the covering soils, decreasing the distance between the top of the void and the ground surface.  

In other cases, voids in the bedrock are generated due to rock removal processes such as hammering and blasting. Hammering and blasting can generate fractures or cracks in the bedrock that soil can then erode into. A void in the bedrock may already exist, however, the process of removing the bedrock by hammering and/or blasting can speed up the meeting of the upside-down bowl and the surface that much quicker. One site where this happened has experienced over 35 sinkholes in 4 years.

Overall, it’s generally not a good idea to pump groundwater or do major excavation in areas that are prone to sinkholes. According to the USGS, over the last 15 years sinkhole damages have cost on average at least $300 million per year. Because there is no national tracking of sinkhole damage costs, this estimate is probably much lower than the actual cost. Being more mindful about the subsurface around us and our actions could help lower the average yearly cost in damages and even save lives.

Photo by Barbara Miller PennLive Patriot News

Stay tuned for Part Two of this blog series in which we explore we explore how to detect sinkholes and the steps taken to repair them! For more information about Princeton Hydro’s Geotechnical Engineering services, go here: http://bit.ly/PHGeotech

Special thanks to Princeton Hydro Staff Engineer Stephen Duda, Geologist Marshall Thomas, and Communications Intern Rebecca Burrell for their assistance in developing this blog series.

Sources:

A Day in the Life of a Construction Oversight Engineer

Have you ever wondered what it actually means to conduct construction oversight on a project? Our engineers regularly do so to ensure design plans are being implemented correctly. But, construction oversight requires a lot more than just the ability to oversee. Our engineers have to understand the ins and outs of the plans, be adaptable, fast-thinking, and incredibly capable of communicating with and coordinating various parties.

Let’s walk through a day in the life of one of our construction oversight engineers, Casey Schrading, EIT, and outline the key components of his job:

SAFETY. When it comes to construction sites, safety always comes first. It is important to have the proper health and safety training before entering an active construction zone. On an active construction site, there could be many different hazards that workers encounter. Before heading to the site, Casey makes sure he has all his necessary safety equipment and protection gear. Personal Protection Equipment (PPE) usually includes a neon safety vest (visibility), hard hat (head protection), long pants (protective clothing), safety glasses (eye protection), and steel-toed boots (foot protection). In some cases, on construction sites with more risk factors, higher levels of PPE may be required including hearing protection, gloves, respiratory masks, fall protection equipment, and disposable Tyvek coveralls.

COORDINATION.  For most construction projects, the day starts early. Upon arrival, Casey checks the site out to see if anything has changed from the day before and takes pictures of the site. He then checks in with the contractor to discuss the plan for the day and any outstanding items from the day prior.

Most of the day consists of a back and forth process between watching the construction workers implement the design and then monitoring and checking the design plans. In order for the contractor to properly implement the design, the oversight engineer must direct the workers during the installation process; for many designs, there are critical angles, locations, heights, and widths that features must be installed at. It is imperative for the oversight engineer to direct and work hand-in-hand with the contractor so those features are installed correctly for effective design implementation.

ON-SITE MONITORING.  For certain projects, the day-to-day construction oversight tasks may get a little more involved. For instance, when conducting construction oversight for our Columbia Dam Removal project, Casey was tasked with taking turbidity samples every three hours at two locations along the Paulins Kill — one upstream of the site to collect baseline data and one downstream of the site to quantify the site’s effect on turbidity. If the turbidity readings downstream of the site came out too high, Casey would then have to determine how those high levels were affecting the turbidity in the Delaware River, which the Paulins Kill discharges into less than a quarter mile downstream of the site. If flooding in the Delaware River wasn’t enough to pose safety concerns, Casey would then take readings at two additional locations upstream and downstream of the Delaware River-Paulins Kill confluence. Again, the upstream reading served as a baseline reading for turbidity while the downstream reading showed the effects of the Paulins Kill on the Delaware River.

These turbidity samples were necessary because this project involved passive sediment transport, meaning the sediment that had built up behind the dam for over a century was going to slowly work its way downstream as the dam was notched out piece by piece, as opposed to it being dredged out before the barrier removal. It’s important to monitor turbidity in a case like this to make sure levels remain stable. The need for monitoring at construction sites further emphasizes the need for construction oversight engineers to be multifaceted.

ADAPTATION.  In all construction projects, the goal is to have everything installed or constructed according to plan, but, with so many environmental factors at play, that rarely happens. Because of the ever-changing nature of most of our projects, it is essential that our construction oversight engineers have the keen ability to adapt and to do so quickly. Casey has experienced a range of changes in plan while conducting construction oversight. He says the skills he relies on most is communication. When something changes, it’s imperative that the onsite engineer knows exactly who to contact to work out a solution. Sometimes that might be Princeton Hydro’s internal project manager, or sometimes it might be a regulatory official from NJDEP.

WEEKLY MEETINGS.  Another critical part of construction oversight is facilitating weekly coordination meetings. The weekly meeting is usually attended by the contractor, the engineering firm, and the client.  The parties will discuss what has happened thus far at the site and what still needs to happen, allowing them to establish action items. Occasionally, other entities like organizations that provided funding for a project or regulatory agencies, will also be involved in those conversations. The weekly meetings are designed to keep everybody on task and help to ensure every party’s goals and needs are being met.

DOCUMENTATION.  Anytime field work is being conducted, it is essential to document the happenings and the progress made. This documentation usually comes in the form of a Daily Field Report (DFR). A DFR includes information about the work performed on a given day, such as measurements, quantities of structures installed, and how that installation process went. Also included in the DFRs are clear and descriptive photographs.

COMMUNICATION.  Working on any project, it’s important to make sure all involved parties understand the reason behind each installation. It is often easier for a construction team to implement plans correctly if they know and understand why each part of it is important and included in the project. Explaining why a task needs to be completed also helps relieve tension that could potentially arise between the engineer and the contractor. It is essential to make sure every person on the project team is on the same page.

PUBLIC OUTREACH.  Another critical aspect of construction oversight is having the ability to successfully communicate with the public. Members of the community surrounding a site need to be kept apprised of the goings on so they can remain safe during the construction period and understand the goals of the project. When citizens understand the purpose and goals of a project, they are more likely to support and respect it.

REGULATORY COMPLIANCE.  Understanding the permitting surrounding a project is also essential to success as a construction oversight engineer. The engineer has to understand the ins and outs of the permitting and regulations in order to be able to make decisions about changes in the plan and to be able to successfully point the contractor in the correct and compliant direction.

Construction oversight is a tedious and incredibly important job, yet I really enjoy it because it gives me a new and better understanding of the engineering design process,” explains Casey. He feels it gives him a much more practical understanding of engineering design, as he has seen what kinds of plans are actually implementable and what that process looks like. “Watching a design plan get implemented brings the project full circle and allows me to take that knowledge and experience back to the office and back into the design process.

Princeton Hydro provides construction oversight services to private, public, and nonprofit clients for a variety of ecosystem restoration, water resource, and geotechnical projects across the Northeast.  Learn more.

Casey graduated from Virginia Tech in 2018 with a degree in Biological Systems Engineering and now works as a staff engineer for the firm with a focus in water resources engineering. He has experience in ecological restoration, flood management, water quality analysis, and best management practices. His experience also includes construction oversight for dam removal and restoration projects as well as design, technical writing, and drafting for a wide variety of water resources engineering projects. In his free time Casey very much enjoys travelling, hiking, skiing, and camping.

If you enjoyed this blog, check out another one from our “Day in the Life” series, and stay tuned for more:

A Day in the Life of a Stormwater Inspector

A Day in the Life of a Stormwater Inspector

Walking through a park isn’t always a walk in the park when it comes to conducting stormwater inspections. Our team routinely spots issues in need of attention when inspecting stormwater infrastructure; that’s why inspections are so important.

Princeton Hydro has been conducting stormwater infrastructure inspections for a variety of municipalities in the Mid-Atlantic region for a decade, including the City of Philadelphia. We are in our seventh year of inspections and assessments of stormwater management practices (SMPs) for the Philadelphia Water Department. These SMPs are constructed on both public and private properties throughout the city and our inspections focus on areas served by combined sewers. 

Our water resource engineers are responsible for construction oversight, erosion and sediment control, stormwater facilities maintenance inspections, and overall inspection of various types of stormwater infrastructure installation (also known as “Best Management Practices” or BMPs).

The throat of a sinkhole observed by one of our engineers while on site.

Our knowledgeable team members inspect various sites regularly, and for some municipalities, we perform inspections on a weekly basis. Here’s a glimpse into what a day of stormwater inspection looks like:

The inspector starts by making sure they have all their necessary safety equipment and protection. For the purposes of a simple stormwater inspection the Personal Protection Equipment (PPE) required includes a neon safety vest, hard hat, eye protection, long pants, and boots. Depending on the type of inspection, our team may also have to add additional safety gear such as work gloves or ear plugs. It is recommended that inspectors hold CPR/First Aid and OSHA 10 Hour Construction Safety training certificates. 

Once they have their gear, our inspection team heads to the site and makes contact with the site superintendent. It’s important to let the superintendent know they’re there so that 1) they aren’t wondering why a random person is perusing their construction site, and 2) in case of an emergency, the superintendent needs to be aware of every person present on the site.

Once they arrive, our team starts by walking the perimeter of the inspection site, making sure that no sediment is leaving the project area. The team is well-versed in the standards of agencies such as the Pennsylvania Department of Environmental Protection, the Pennsylvania Department of Transportation, the New Jersey Department of Environmental Protection, and local County Soil Conservation Districts, among others. These standards and regulations dictate which practices are and are not compliant on the construction site.

After walking the perimeter, the inspection team moves inward, taking notes and photos throughout the walk. They take a detailed look at the infrastructure that has been installed since the last time they inspected, making sure it was correctly installed according to the engineering plans (also called site plans or drainage and utility plans). They also check to see how many inlets were built, how many feet of stormwater pipe were installed, etc.

If something doesn’t look quite right or needs amending, our staff makes recommendations to the municipality regarding BMPs/SMPs and provides suggestions for implementation.

One example of an issue spotted at one of the sites was a stormwater inlet consistently being inundated by sediment. The inlet is directly connected o the subsurface infiltration basin. When sediment falls through the inlet, it goes into the subsurface infiltration bed, which percolates directly into the groundwater. This sediment is extremely difficult to clean out of the subsurface bed, and once it is in the bed, it breaks down and becomes silt, hindering the function of the stormwater basin.

To remedy this issue, our inspection team suggested they install stone around the perimeter of the inlet on three sides. Although this wasn’t in the original plan, the stones will help to catch sediment before entering the inlet, greatly reducing the threat of basin failure.

Once they’ve thoroughly inspected the site, our team debriefs the site superintendent with their findings. They inform the municipality of any issues they found, any inconsistencies with the construction plans, and recommendations on how to alleviate problems. The inspector will also prepare a Daily Field Report, summarizing the findings of the day, supplemented with photos.

In order to conduct these inspections, one must have a keen eye and extensive stormwater background knowledge. Not only do they need to know and understand the engineering behind these infrastructure implementations, they need to also be intimately familiar with the laws and regulations governing them. Without these routine inspections, mistakes in the construction and maintenance of essential stormwater infrastructure would go unnoticed. Even the smallest overlook can have dangerous effects, which is why our inspections team works diligently to make sure that will not happen.

Our team conducts inspections for municipalities and private entities throughout the Northeast. Visit our website to learn more about our engineering and stormwater management services.

 

Part Two: Damned If You Do, Dammed If You Don’t: Making Decisions and Resolving Conflicts on Dam Removal

Credit: FWRA.org

In this two part blog series piece we take a look at addressing and preventing potential conflicts and the key factors involved in dam removal decision-making – to remove or not to remove.

What to Do About Dams

Typically, the decision to remove a dam is made by varying entities, depending on the regulatory oversight of the dam. In most cases, the dam owner itself is the decision-maker, often deciding that the costs of continuing to operate and maintain the dam are more than removing the dam. State dam safety offices can sometimes order a dam to be removed or lowered if there are major safety concerns. State fish and wildlife offices and environmental organizations are also often involved in the decision-making, particularly when the goals of the project include restoration of habitat for migratory and resident aquatic species. If the dam in question is a hydropower facility, the Federal Energy Regulatory Commission also has the power to order a hydropower dam under their jurisdiction to be removed for both environmental and safety reasons.

Laura Wildman, P.E., dam removal and river restoration expert and Director of Princeton Hydro’s New England Regional Office, says, “Identifying key barriers early on and understanding which of those barriers might have potential solutions versus remain an impediment, is critical to prioritizing limited ecological restoration resources.”

The careful formulation and communication of the benefits for dam removal specific to each project, adequate education of the public, and stakeholder involvement are incredibly important components to dam removal conflict resolution. As is an understanding that not all dams will or should be removed, and that the local community and stakeholders needs/concerns should be fully integrated into the decision-making process.

Key facets of stakeholder involvement, include:

  • Initial Stakeholder Discussions: Gather information and input from all stakeholders involved
  • Field Work & Initial Assessment: Know the project site inside and out, conduct an in-person inspection, and gather all of the initial data needed to have an informed discussion
  • Report Back with Results, without Judgement: Share the current state of the dam with stakeholders & regulators, without implying any solution or recommendation
  • Detailed Analysis, Feasibility & Alternatives Assessment: Collaboratively select alternative options, and include for a discussion of the alternative analysis process in the pre-application regulatory and stakeholder meetings
  • Formal Regulatory Review w/ Public Meetings: Present solution and/or submit engineering design and permit applications to regulators, and host public meetings to inform the community about the timeline and status.  Some public meetings are required as part of the regulatory process, however, it is important to keep the stakeholders involved in the process. So, additional meetings or presentations are recommend for true engagement.
  • Implementation: If the solution is to remove or repair the dam, continue to update the community about the status and timeline of construction. Local residents, elected officials, and nonprofit groups could be your best allies in keeping everyone informed.

It’s crucial to keep stakeholders and general public informed throughout the process via regular social media and traditional media outreach. Successful projects are based on a transparent process that integrates the local community.  It is the local community that then becomes the environmental stewards of the restored river system.

Celebrating the start of the Columbia Dam removal with the New Jersey Nature Conservancy, American Rivers, Princeton Hydro, USFWS, NJDEP, the local community, and other stakeholders.

 

Analyzing Dams for Removal

There are few “easy” dam removal decisions. Most dams have both positive and negative impacts. The challenge in making a sound decision about whether or not to remove a dam is to identify all of the costs and benefits of keeping (and eventually repairing or replacing) that particular structure, as well as the costs and benefits of removing it, and balance the findings to determine the best option. It is important to ensure that the full range of costs and benefits are identified.

Working through the many issues involved in deciding to keep or remove a dam can offer surprising conclusions that can lead to a reasoned approach – reducing subjectivity and increasing objectivity. The key issues typically investigated include:

  • Impounded sediment
  • Infrastructure/utility impacts
  • Current use (& economic value of dam)
  • Environmental concerns & benefits
  • Geomorphic equilibrium
  • Public health & safety
  • Flooding & hydrologic impacts
  • Aesthetic & sentimental value
  • Historic/archeological
  • Community concerns
  • Sensitive or invasive species
  • Water rights
  • Cost & funding availability

When making a final decision, it’s important to critically examine all factors to understand the influences on the decision. No matter the final outcome, at least it will be a well-informed process, and the information and understanding gained can help shape future decisions.

Although each dam removal project is unique, we developed a standard process that we follow:

While there is often no definitive answer to a question about whether a particular dam should be removed, there is a right and wrong way to go about making a dam removal decision. A good dam removal/retention decision is one that is based on an assessment of all the facts, collaboration with all stakeholders, and objective criteria.

Princeton Hydro has designed, permitted, and overseen the reconstruction, repair, and removal of dozens of dams throughout the Northeast.  To contact us and learn more about our fish passage and dam removal engineering services, visit: bit.ly/DamBarrier.

Revisit part-one of this blog series:

Part One: Damned If You Do, Dammed If You Don’t: Making Decisions and Resolving Conflicts on Dam Removal

Part One: Damned If You Do, Dammed If You Don’t: Making Decisions and Resolving Conflicts on Dam Removal

People have been building dams since prerecorded history for a wide variety of economically valuable purposes including water supply, flood control, and hydroelectric power. Back in the 1950s and 60s, the U.S. saw a boom in infrastructure development, and dams were being built with little regard to their impacts on rivers and the environment. By the 1970s, the rapid progression of dam building in the U.S. led researchers to start investigating the ecological impacts of dams. Results from these early studies eventually fueled the start of proactive dam removal activities throughout the U.S.

Despite the proven benefits of dam removal, conflicts are a prevalent part of any dam removal project. Dam removal, like any other social decision-making process, brings up tensions around economics and the distribution of real and perceived gains and losses. In this two part blog series, we take a look at addressing and preventing potential conflicts and the key factors involved in dam removal decision-making – to remove or not to remove.

Why We Remove Dams

The primary reasons we remove dams are safety, economics, ecology, and regulatory. There has been a growing movement to remove dams where the costs – including environmental, safety, and socio-cultural impacts – outweigh the benefits of the dam or where the dam no longer serves any useful purpose. In some cases, it’s more beneficial economically to remove a dam than to keep it, even if it still produces revenue. Sometimes the estimated cost of inspection, repair, and maintenance can significantly exceed the cost of removal, rendering generated projected revenue insignificant.

Safety reasons are also vital, especially for cases in which dams are aging, yet still holding large amounts of water or impounded sediment. As dams age and decay, they can become public safety hazards, presenting a failure risk and flooding danger. According to American Rivers, “more than 90,000 dams in the country are no longer serving the purpose that they were built to provide decades or centuries ago.” Dam removal has increasingly become the best option for property owners who can no longer afford the rising cost of maintenance and repair work required to maintain these complex structures.

The goal of removal can be multi-faceted, including saving taxpayer money; restoring flows for migrating fish, other aquatic organisms, and wildlife; reinstating the natural sediment and nutrient flow; eliminating safety risks; and restoring opportunities for riverine recreation.

Moosup River

Common Obstacles to Dam Removal

Dam removal efforts are often subjected to a number of different obstacles that can postpone or even halt the process altogether. Reasons for retaining dams often involve: aesthetics and reservoir recreation; water intakes/diversions; hydroelectric; quantity/quality of sediment; funding issues; cultural/historic values of manmade structures; owner buy-in; sensitive species; and community politics.

Of those common restoration obstacles, one of the more frequently encountered challenges is cost and funding. Determining who pays for the removal of a dam is often a complex issue. Sometimes, removal can be financed by the dam owner, local, state, and federal governments, and in some cases agreements are made whereby multiple stakeholders contribute to cover the costs. Funding for dam removal projects can be difficult to obtain because it typically has to come from a variety of sources.

Anecdotally, opposition also stems from fear of change and fear of the unknown. Bruce Babbitt, the United States Secretary of the Interior from 1993 through 2001 and dam removal advocate, said in an article he wrote, titled A River Runs Against It: America’s Evolving View of Dams, “I always wonder what is it about the sound of a sledgehammer on concrete that evokes such a reaction? We routinely demolish buildings that have served their purpose or when there is a better use for the land. Why not dams? For whatever reason, we view dams as akin to the pyramids of Egypt—a permanent part of the landscape, timeless monuments to our civilization and technology.”

Negative public perceptions of dam removal and its consequences can seriously impede removal projects. Although there are many reasons for the resistance to dam removal, it is important that each be understood and addressed in order to find solutions that fulfill both the needs of the environment and the local communities.

Stay tuned for Part Two of this blog series in which we explore strategies for analyzing dams and what goes into deciding if a dam should remain or be removed.

Study Data Leads to Healthier Wreck Pond Ecosystem

Wreck Pond is a tidal pond located on the coast of the Atlantic Ocean in southern Monmouth County, New Jersey. The 73-acre pond, which was originally connected to the sea by a small and shifting inlet, got its name in the 1800s due to the numerous shipwrecks that occurred at the mouth of the inlet. The Sea Girt Lighthouse was built to prevent such accidents. In the 1930s, the inlet was filled in and an outfall pipe was installed, thus creating Wreck Pond. The outfall pipe allowed limited tidal exchange between Wreck Pond and the Atlantic Ocean.

In the 1960s, Wreck Pond flourished with wildlife and was a popular destination for recreational activities with tourists coming to the area mainly from New York City and western New Jersey. In the early spring, hundreds of river herring would migrate into Wreck Pond, travelling up its tributaries — Wreck Pond Brook, Hurleys Pond Brook and Hannabrand Brook — to spawn. During the summer, the pond was bustling with recreational activities like swimming, fishing, and sailing.

Over time, however, the combination of restricted tidal flow and pollution, attributable to increased development of the watershed, led to a number of environmental issues within the watershed, including impaired water quality, reduced fish populations, and flooding.

Throughout the Wreck Pond watershed, high stream velocities during flood conditions have caused the destabilization and erosion of stream banks, which has resulted in the loss of riparian vegetation and filling of wetlands. Discharge from Wreck Pond during heavy rains conveys nonpoint source pollutants that negatively impact nearby Spring Lake and Sea Girt beaches resulting in beach closings due to elevated bacteria counts. Watershed erosion and sediment transported with stormwater runoff has also contributed to excessive amounts of sedimentation and accumulations of settled sediment, not only within Wreck Pond, but at the outfall pipe as well. This sediment further impeded tidal flushing and the passage of anadromous fish into and out of Wreck Pond.

In 2012, Hurricane Sandy caused wide-spread destruction throughout New Jersey and the entire eastern seaboard. The storm event also caused a major breach of the Wreck Pond watershed’s dune beach system and failure of the outfall pipe. The breach formed a natural inlet next to the outfall pipe, recreating the connection to the Atlantic Ocean that once existed. This was the first time the inlet had been open since the 1930s, and the reopening cast a new light on the benefits of additional flow between the pond and the ocean.

Hurricane Sandy sparked a renewed interest in reducing flooding impacts throughout the watershed, including efforts to restore the water quality and ecology of Wreck Pond. The breach caused by Hurricane Sandy was not stable, and the inlet began to rapidly close due to the deposition of beach sand and the discharge of sediment from Wreck Pond and its watershed.

Princeton Hydro and HDR generated the data used to support the goals of the feasibility study through a USACE-approved model of Wreck Pond that examined the dynamics of Wreck Pond along with the water bodies directly upland, the watershed, and the offshore waters in the immediate vicinity of the ocean outfall. The model was calibrated and verified using available “normalized” tide data. Neighboring Deal Lake, which is also tidally connected to the ocean by a similar outfall pipe, was used as the “reference” waterbody. The Wreck Pond System model evaluated the hydraulic characteristics of Wreck Pond with and without the modified outfall pipe, computed pollutant inputs from the surrounding watershed, and predicted Wreck Pond’s water quality and ecological response. The calibrated model was also used to investigate the effects and longevity of dredging and other waterway feature modifications.

As part of the study, Princeton Hydro and HDR completed hazardous, toxic, and radioactive waste (HTRW) and geotechnical investigations of Wreck Pond’s sediment to assess potential flood damage reduction and ecological restoration efforts of the waterbody. The investigation included the progression of 10 sediment borings conducted within the main body of Wreck Pond, as well as primary tributaries to the pond. The borings, conducted under the supervision of our geotechnical staff, were progressed through the surgical accumulated sediment, not the underlying parent material. Samples were collected for analysis by Princeton Hydro’s AMRL-accredited (AASHTO Materials Reference Library) and USACE-certified laboratory. In accordance with NJDEP requirements, sediment samples were also forwarded to a subcontracted analytical laboratory for analysis of potential nonpoint source pollutants.

In the geotechnical laboratory, the samples were subjected to geotechnical indexing tests, including grain size, organic content, moisture content, and plasticity/liquid limits. For soil strength parameters, the in-field Standard Penetration Test (SPT), as well as laboratory unconfined compression tests, were performed on a clay sample to provide parameters for slope stability modeling.

The culvert construction and sediment dredging were completed at the end of 2016. Continued restoration efforts, informed and directed by the data developed through Princeton Hydro’s feasibility study, are helping to reduce the risk of flooding to surrounding Wreck Pond communities, increase connectivity between the pond and ocean, and improve water quality. The overall result is a healthier, more diverse, and more resilient Wreck Pond ecosystem.

During the time of the progression of study by the USACE, the American Littoral Society and the towns of Spring Lake and Sea Girt were also progressing their own restoration effort and completed the implementation of an additional culvert to the Atlantic Ocean.  The American Littoral Society was able to utilize the data, analysis, and modeling results developed by the USACE to ensure the additional culvert would increase tidal flushing and look to future restoration projects within Wreck Pond.

American Littoral Society

 

To learn more about our geotechnical engineering services, click here.

Fish Passage Restored on the Paulins Kill

A view of where the Columbia Lake Dam used to reside. February 19, 2019. Photo courtesy of Casey Schrading, Staff Engineer, Princeton Hydro

On the Paulins Kill, the 100-year old Columbia Lake Dam has almost been completely removed, and fish passage has been restored!  Since the first cut was executed on the main dam in August, many exciting advances have been made towards restoring the Paulins Kill back to its natural state. Check out the video below, courtesy of the New Jersey Nature Conservancy Volunteer Drone Team. 

Piece by piece, the dam was notched out throughout the fall season and is now completely removed with the exception of the dam apron, the horizontal concrete structure that sits downstream of the dam, and the section of the dam that sits below the riverbed. The part of the dam in the riverbed is now being removed all the way down  to three feet under the ground. The full removal is estimated to be complete by mid-March. In mid-August, the first cut was widened to 80 feet, allowing for better management of high flows during storm events, which had been posing a challenge immediately following the first cut.

In late August, the installation of rock vanes at the Brugler Road Bridge began. Rock vanes are engineered, in-stream structures that help to stabilize a channel while enhancing aquatic habitat and movement.

A generic schematic example of cross vanes, this is not the exact engineering plan for this specific project. Photo courtesy of North Carolina Cooperative Extension.

The rock vanes installed at the Brugler Road Bridge site are cross vanes. Cross vanes consist of a set of boulders angled upstream on a river, with another section of smaller rocks placed upstream. The taller sections of the cross vanes deflect the streamflow away from the banks, decreasing scouring effects. Instead, the flow travels over the rock walls and concentrates down the center of the channel, creating a deep and elongated pool in the middle of the stream.  

Velocities between the notches in the rock vanes were evaluated using a velocity meter in accordance with the design specifications originally proposed. Based on the U.S. Fish and Wildlife Service fish passage design criteria, velocities in the notches could not be greater than 8.25 feet per second. All of the velocity measurements in this rock vane were below the maximum thresholds, ensuring no blockage of fish passage is made through the vanes.

Since the removal of the dam began, vegetative growth from the natural seedbed of the upper impoundment has been observed (see photo below).

In October, scour protection installation commenced at the Warrington Road Bridge site. After the team conducted geotechnical test pits, they discovered that a concrete scour wall that slopes out to the Paulins Kill was present and deep enough to be able to install rock at the necessary depth. They also found that the existing gabions, caged baskets filled with rock or concrete often used to protect against erosion, were intact and could be left in place. The team installed four (4) feet of riprap under and around the bridge in the riverbed and tied it into the existing grade of the banks.

The original notch in the dam was lowered one foot per day starting in mid-December, reducing water surface elevations down to the apron elevation during the month of January.

To accommodate NJ Fish and Wildlife’s request for animal passage under the I-80 bridges, an area of the previously installed riprap on the northwest abutment wall was flattened out and filled in with river cobble. This path will promote wildlife movement under the bridge as opposed to through the existing tunnel.

Currently, rock vanes are being installed under the I-80 bridges specifically to enhance fish passage. These structures vary slightly from the rock vanes at the Brugler Road Bridge site, as they are designed to slow river flow, helping migrating fish travel upstream and traverse a 5-foot elevation difference in the streambed, much like a fish ladder

These rock vanes are more than halfway completed and are on track to be finished in time for fish populations to make full use of them.  The next steps are to finish the demolition of the dam and the construction of the fish passage rock vanes under the I-80 bridges, plant vegetation throughout the upper impoundment, create a recreational trail through the upper impoundment, and plan for fishing and boating access! Stay tuned for more exciting developments on this incredible project.

Thank you to our project partners: The Nature Conservancy, American Rivers, U.S. Fish and Wildlife Service, and NJDEP Division of Fish and Wildlife Service.

Princeton Hydro has designed, permitted, and overseen the reconstruction, repair, and removal of a dozens of small and large dams in the Northeast. To learn more about our fish passage and dam removal engineering services, visitbit.ly/DamBarrier.