Stormwater Monitoring

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Credit: Beckley Sanitary Board
The most dramatic and identifying characteristic of water is that it is always moving. Even so-called standing water is never completely static; it’s either being drawn by gravity to seep down into the earth or being agitated by warmth at the surface to rise into the air as a vapor. Water finds its way into every space available and into plants and animals, which help it move about across the land, sea, and into the air. It finds its way into the full gamut of human activities as well, sluicing off in various directions, carrying a complement of whatever impurities or enhancements might have been imparted by the people who used it. The complex cycle circulates from the clouds to the sea and back again in a never-ending circle. Along the way, various obstacles, impediments, and conveyances influence its movement and each, in its own way, can have a considerable effect on water quality. Understanding the dynamics of water as it moves across surfaces impacted by commerce, industry, and habitation becomes a powerful and necessary step in managing these effects.

An Information Gold Mine
Tom Killingbeck notes that water quality for mining sites in Ontario (ON), Canada, where BluMetric Environmental is headquartered, is heavily regulated. As a hydrogeologist for the firm, Killingbeck finds himself working on water-quality monitoring and management programs for more than 100 sites at any given time. “The big thing is the chemistry of the water,” he says. “Under regulations, the mining companies are required to make sure the chemistry of the water leaving their sites is as good as the environment. You have to release it cleaner than what it was when it came in.”

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The province operates “a huge sampling program,” he says. “If they find any spots where water doesn’t meet standards, they’re required to collect all of that water and treat it.” However, he says regulators are equally concerned with hydrology in areas affected by mining activities. “They want to make sure that if you’re doing a lot of dewatering that you’re not drying out the entire area. They also want to make sure that you’re not adding extra water to the environment,” which occurs through the excess treated water used in mining processes.

BlueMetric Environmental plays a key role by “collecting volume data for discharges and providing monitoring for an area.” On some projects, rather than focusing on the level of contamination, it’s the precise level of the water flowing across, through, or from a site that becomes the target for in-depth analysis.

Killingbeck says he recently worked on an active diamond mining project, monitoring dewatering operations to evaluate potential impacts on nearby creeks and the local environment. Dewatering involves potential risks from inadvertently siphoning out the water table from below while pumping out excess water from the working face of the mine shaft.

In cases where the level of contamination is already well understood, he says, the question of how much affected water is flowing from the site becomes predominant. It’s a question that often arises when evaluating historic and legacy mining sites that have ceased active operations. He says many such sites can be found in the US and Canada.

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Sometimes the land surrounding these mines has been impacted by ore residues or remnants of process chemicals and, if sufficiently mobilized by stormwater, they can eventually discharge into receiving waters, leading to environmental degradation. The question facing managers is how much of a risk they pose. Answering that question requires precise, high-quality data.

Killingbeck says he relies on ­Greyline Instruments’ Stingray Level-Velocity Loggers. “We’ve been using them since 2000. We’ve had good luck with them. I get data back at 0.1% accuracy,” he says.

“I worked on an open-pit mine that was discharging water that was high in iron. The government wanted data on the historic location, and they wanted to know how far away they were contaminating. They were looking for the volume, and then they could then run the contamination tables,” in order to evaluate which areas might be at environmental risk from the escaping ore.

Killingbeck says he typically deploys the loggers at strategic points on creek beds. “It gives you two readings together—the velocity and the depth. The only other requirement is to obtain a cross-section of the stream [at the site of the reading].” With that information, he can perform a simple calculation revealing water volume passing through the location at any point in time.

“It’s a relatively low-profile probe, measuring just 1 centimeter, so it doesn’t perturb the flow while taking a reading. When I mount that to the bottom of anything, it’s not interfering with the flow.” To further ensure comparable data across sites, when possible, Killingbeck prefers to situate the loggers within infrastructure with a known dimension and flat base. When no such structure exists at the measurement site, he often constructs a portable steel sluice to embed in the stream. After securing the logger to the base, he lowers it to the streambed, sandbagging the perimeter up to the streambank on both sides to ensure the full volume of water passes through the homemade culvert.

In areas where the stream is too wide and too deep to install a temporary sluice, says Killingbeck, he takes advantage of bridge pylons and trestles to provide a uniform base for taking velocity measurements. On rivers too large or unwieldy for any of these strategies, after taking a cross-section from aboard a small craft, he simply positions the boat mid-channel, mounts the logger to a steel plate, and lowers the assembly to the bottom, ready to transmit flow-volume data via cable to the data collection logger housed in a rugged case on shore.

“If I didn’t have the Stingrays, we’d have to manually go out with a flow meter and get a flow curve,” a prospect he says risks introducing various human errors into the raw data. With the Stingray, the only onsite staff needed is for making the initial placement of the device, periodic visits to download readings from the data logger, and performing basic maintenance such as battery replacement or modifying the data collection frequency. “I prefer to set them at 15-minute intervals,” he notes. “It has enough battery power, but to save battery power, I could set it to a different frequency.”

He adds, “Getting humans to mine sites is costly.” Compared to the limited number of periodic or seasonal readings that a human technician could provide, he says, “I get readings every 15 minutes—that’s the big difference.”

BluMetric Environmental has had such success with the Stingray model that the company has decided to augment its stable of velocity-level loggers to include Greyline’s new Manta Ray Portable Area-Velocity Flow Meter, which Killingbeck expects to begin deploying at future monitoring sites to provide wireless data collection capability.

The biggest problem he has encountered in the field, he says, “is that for some reason, people like to steal the Pelican case that houses the controls and the data loggers,” but overall he has had few problems with the product. “Greyline has always been very responsive. They have excellent technical support. If we have a problem and we can’t troubleshoot in the field, they send a replacement.”

Accurate readings, Killingbeck believes, will allow managers to predict where a plume might emerge, or whether the volume of water coming onto or going off a landscape represents an anomaly that requires closer inspection of mining operations in the watershed. “When you set up any monitoring situation, you need to make sure the quality of the data is good and that your initial setup is good.” He feels the diversity of situations encountered during water-quality monitoring projects—and having the tools that can handle them—are part of “what makes the work fun.”

Credit: Beckley Sanitary Board
Beckley Sanitary Board

Mining History
While the Beckley, WV, region has been influenced historically by coal mining, with the gradual decline of the fossil fuel economy the Ohio Valley town has begun to reemerge as a blossoming retail and service sector hub for area residents. In spite of its recent migration into the digital age, the city nonetheless boasts one last coal mine. It is an exposition and educational mine serving as a tribute to regional history. Open to the public as a tourist attraction, along with the scenic mountainous landscapes and the nearby New River Gorge National River, the mine represents just one of the city’s expanding list of drawing cards. Together they contribute to an average of 25,000 vehicles per day that flow through the city’s major avenue. Unfortunately, cars are not the only things that have been known to flow along the street. Storms cresting the Appalachian Mountains drop precipitation on the hills and glades surrounding Beckley, and runoff pouring over the roadways frequently comes between motorists and their destinations all over the region.

Home to a population of 200,000 residents, the regional community surrounding Beckley is regulated as a Phase II NPDES permit holder, with its stormwater management services managed by the Beckley Sanitary Board.

“We’re a mountainous state, and Beckley reflects that; the terrain creates challenges for stormwater,” says Matt Huffman of the Beckley Sanitary Board. As the thunderstorms come across the Ohio Valley, it’s common to have brief periods of intense rainfall. West Virginia has regularly occurring flash floods across many jurisdictions, he says. Although Beckley is spared for the most part the worst of the flash flooding, during even moderate rainfall events, an existing stormwater conveyance had been known to overflow frequently, causing nuisance flooding to an area of local road four or five lanes wide.

Huffman says the problem has existed “since long before the town’s 2004 permit.” With the increased traffic generated by a renewed interest in the region, the board took up a search for a solution.

“It was not so much about private property damage. It was more about the safety concerns,” says Jeremiah Johnson, general manager of the Beckley Sanitary Board. “We’ve always had water-quality concerns. We had a bacteria TMDL [total maximum daily load], and there was an iron TMDL from when the streambanks erode.”

The board, in consultation with the Department of Highways and the local Soil and Water Conservation District, considered expanding the local stormwater conveyance. Based on the hydrology, Johnson says, that solution would have required reconfiguring existing utility infrastructure to fit a new box culvert into a roadway with a narrow right of way. The projected cost of a conveyance modification was estimated at $10 million, far more than what was available in the board’s stormwater management budget. Moreover, an expanded culvert would likely result in a more forceful flow downstream, serving only to exacerbate erosion and the related iron and suspended solids concerns, thus working counter to the community’s goal of TMDL compliance.

Johnson notes, however, that a stormwater utility funding mechanism provided some resources to address the issue. The board began looking at city-owned properties higher up in the watershed as possible sites for building retention facilities and in 2012 completed construction of a multistage passive outlet retention structure. “The design was of some benefit, but not maximal benefit,” says Johnson. “It was better than what we had.”

It was possible to improve the situation, however. “We became aware of Opti and felt the pond we built would be a great place to implement the real-time control technology,” he says. The board installed OptiRTC’s interactive software, connected flow controls, and sensors to the internet via CMAC (continuous monitoring and adaptive control) and gave the structure the moniker iPond to help residents understand its function as an interactive retention structure designed to reduce the risk of flooding.

Designed to provide 24-hour connectivity 365 days a year, the iPond incorporates decision-support tools such as the flow hydrograph, baseflow conditions, and rainfall forecasts. A dashboard interface places readout and control of the retention and discharge valves on the desktop.

When rainfall probabilities surpass 50%, the iPond gears up for action, interacting in a complex fashion with the storm as it traverses the area. As rainfall approaches, the actuated butterfly valve closes to sequester the subwatershed’s stormwater output, storing it in the iPond. The system is designed to provide 48-hour retention, with the discharge valve controls programmed for a 12-hour drawdown to match the drainage capacity of a highly impervious area.

Credit: Beckley Sanitary Board
Building the pond

The pressure transducer is right next to the butterfly valve and is triggered by water level and predicted rainfall. System logic also takes into account static hydrological factors in the watershed to set the appropriate level of discharge to minimize the risk of flooding, says Johnson.

“By knowing the forecasted precipitation, if more rain is expected than the pond can hold, the valve can be adjusted” to regulate the proportion of rainwater retained over the course of the event, keeping water levels within reasonable bounds downstream. “It’s a heck of a lot more control than if we had a passive system,” says Huffman.

“I like to tell the staff here that rainfall events have personalities,” says Huffman. “They are like people; no one is exactly the same. With the old approach, using the passive system, you’d have to, on the front end, do some simulated hydrographs and design something to store [runoff], but at the end of the day there is only a limited amount of events that you could design your structure to accommodate.” The Opti system, he says, “allows you to handle a lot more diversity in terms of the number of events. For a lot of events, we’re basically able to catch all anticipated runoff and store it with no discharge until 48 hours after the event. Other events, if they are such an intensity that you can’t capture everything, you capture what you can and you start discharging before the 48 hours, but the rate of discharge will be regulated, and it varies.”

The control panel sends and receives information on water level and the rate of discharge. “The nice thing about the dashboard being cloud-based is that you can log in and see what’s going on with the pond from anywhere, as long as you have a secure login,” says Johnson.

“There’s a good deal of peace of mind that comes with it,” adds Huffman. “I’ve been doing stormwater for 15 years. I’d be home at night and the rain would be hitting my roof. I’d be wondering if I got problems.” Now, he says, the iPond combined with OptiRTC takes away the worry. “Back in October we had 3/4 inches of rain in 15 minutes—that would have been a scenario that would have caused the road to flood, but we followed up afterward and found there were not any calls or any complaints.”

Huffman says he enjoyed working with specialists from Opti throughout the process. “They’re a startup company. They’ve been a good solution partner. They came out and got a good understanding of what we were facing—they’re getting as many takeaways from the project as we are,” he notes.

Water Everywhere
Contrary to the sound of it, the Hampton Roads region of Virginia is not named for a highway but for a body of water. Hampton Roadstead at the mouth of the James River on the Chesapeake Bay is considered one of the largest natural harbors in the world. It is home to a major US Naval station, but that’s not all. Describing his hometown, Danny Barker, environmental scientist with the Hampton Roads Sanitation District, says, “There’s a big oyster population down here. They are harvested for commercial purposes.” The area is also a big recreational destination, making water quality a focal point for residents and visitors. “People are interested in making sure the water they swim in is clean,” says Barker.

Aaron Porter, US Geological Survey project chief for the Hampton Roads Regional Water Quality Monitoring Program, can see the attraction. “A big draw of being down in that region is that it’s so beautiful because there is water everywhere.”

On the Atlantic Coastal Plain, adjacent to the Chesapeake Bay, along with numerous beaches and shorefront areas, the Tidewater region boasts natural wonders like the Great Dismal Swamp. It is also experiencing increasing urban development in a number of areas, including Norfolk. According to Barker, Norfolk, “very influenced by the tides,” has the distinction of being, next to New Orleans, the US city most vulnerable to sea level rise. Both landmarks serve as a testament to the region’s mild topographical relief. “It’s flat,” laughs Barker.

The flat terrain raises some ­challenges for stormwater managers. Propelled by tides, water sometimes flows upstream. During certain high tides, low-lying storm outfalls can function more like intakes as brackish water pushes its way into the area’s dense maze of stormwater pipes.

With its fast-growing urbanized areas, increasing ­impervious surfaces, and changing hydrology due to soil compaction and other impacts, developments in the ­Tidewater region have a significant potential to influence to Chesapeake Bay’s water quality.

TMDLs already in place, with particular emphasis on control of nutrients and sediments, span the Chesapeake Bay watershed including the Hampton Roads region. However, many of the guidelines designed to promote a healthy bay ecology by reducing the deposition of sediment and accumulation of nutrients in receiving waters are based on data derived much farther inland, over the piedmont area of the state. Porter believes the coastal plain has been underrepresented in data used to determine TMDL allocations. He says there is a question whether nutrients and sediments behave the same over the coastal plains as they do between the coasts and the foothills.

“When you have hills and mountains and you have water rushing down them, you have more energy to move sediment,” he says. “If you have a flat area, you might suppose that the energy would not be there to move as much sediment. So you wouldn’t necessarily want to compute the amount of sediment coming out of a region based on data collected in an area that is much different.” For that reason, he says, a fresh set of local data would be needed to serve as a basis for TMDL allocations for the Hampton Roads region.

Together, Barker and Porter lead a project coordinating the efforts of six municipalities to collect the data on the transport of nutrients and sediments on the low-lying coastal plain of Virginia. The cities of Hampton, Newport News, Chesapeake, Portsmouth, Norfolk, and Virginia Beach joined forces with the USGS, the Hampton Roads Sanitation District (HRSD), and the Hampton Roads Planning District to build an understanding of how sediments and nutrients behave in the coastal zone.

In 2014, they began installing a series of monitors, samplers, and sondes in stormwater pipes at various sites in the region’s stormwater infrastructure. “We have Wi-Fi multiparameter sondes collecting water temperature, specific conductance, and turbidity at a five-minute interval,” says Porter. “We’re using ISCO and SonTek equipment to quantify the discharge coming through. We’re also collecting storm samples at discrete points in time. We have ISCO refrigerated samplers; I have written an algorithm to have them turn on automatically and collect samples during storm conditions. Then HRSD crew will collect those samples for analysis in the lab. That gives us these slices of time when we know what the nitrate and phosphorus and sediment concentrations are.”

Porter explains how these two modes of data collection, with a little math added in, generate a picture of nutrient and sediment flow in the watershed. Researchers, he says, will build a regression model, taking the continuous data on the discharge, turbidity, conductance, and water temperature collected by the sondes, and collate these continuous measurements with the storm sampling data. It is then possible to “compute the concentration for all those times when we’re not actually taking samples,” he says. “Then we can aggregate that over a certain time period and assign a load. We can do a monthly load or an annual load for nitrates, for instance.”

The goal is to characterize conditions during different types of storms and during different seasons with distinct data from commercial/industrial, high-density residential, and single-family residential land uses. Barker says that because of the area’s “highly engineered drainage infrastructure,” with various types of land uses evolving over time and cojoined via drainpipe, one of the challenges was finding subwatersheds appropriate for monitoring that would reflect the highly homogenous land use required for the study. To get background load, they also selected sites where BMPs were generally absent.

Whittling down the pool of potential monitoring sites to just a dozen, the project deployed YSI 600OMS sondes at selected points within targeted storm drains. The YSI 600 was a good choice, Porter explains, because “it is very small and we were working with really low water levels, so we needed something that could stay submerged at all times.”

The 12 sampling sites were further equipped with ISCO refrigerated samplers with a target of collecting 40 to 60 stormwater runoff samples annually from each location. It’s a “very high-resolution” sampling protocol, says Barker, amounting to “sampling virtually every event that provided enough precipitation to capture a sample.”

To capture continuous flow data, the researchers installed either the ISCO TIENet 350 area velocity sensor or the ISCO TIENet 360 LaserFlow velocity sensor, which is a non-contact laser meter, says Porter.

Barker has found the ISCO samplers reliable and durable. “We use them in the wastewater industry, and they are very suitable in that environment, which is not a very hospitable environment.” As a testament to its durability when it counted most, Barker recalls one site that flooded during Hurricane Matthew. “The water covered halfway up the sampler and it’s still running today,” he says.

Having a sampler that can operate during extreme weather is essential to the protocols for the study, says Porter. “If you don’t capture the load from the biggest event during the year, your load estimate might be off by 50%.”

Porter hopes the study has many imitators. “The method employed here is tried and true. We have other networks that we have been doing for quite some time, and this has been a huge success. The big issue in Chesapeake Bay watershed is nutrients and sediments; this program is designed to quantify loads of nutrients and sediments. This type of approach can easily be altered to do any type of water-quality monitoring research, whether that be bacteria, heavy metals, emerging contaminants—this type of setup can be used for whatever question they may have.”

Barker advises patience for future teams that might want to undertake similar studies. “Take the time to really understand each site before installing monitoring equipment,” he counsels. “It might be necessary to preliminarily install your equipment to make sure you don’t have any surprises. The last thing you want is to go through the expense of installing your site and then to find out that some weird anomaly is occurring that would cause the location not to be representative; in our case, tidal influence can be one of those things that cause problems. If you already have your equipment, a lot of times they can be put in temporary enclosures, just to measure things like flow.” It can help eliminate sites from consideration “that would probably not be very representative of what you would be looking for.”

In addition to using GIS data for guidance, says Porter, “We had folks walk through and put equipment out at sites to see if there was tidal influence. We wanted to know what was coming off the land.” SW_bug_web

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