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Using Advanced Odor Control
Municipalities and developers that reclaim pre-existing industrial sites for urban renewal projects must perform an abundance of environmental tests due to the likelihood that there is some form of contamination left over from prior activities. However, it is nearly impossible to predict the full impact from those activities until the ground is broken and work has commenced. And unfortunately, mid-project issues more often than not increase budgets, expand scope and stress timelines.
That was the case for an urban renewal project by the Worcester Regional Transit Authority (WRTA) in Central Massachusetts involving an 11-acre site of an old manufactured gas plant that operated on the property from 1870 to 1969. WRTA received a $39 million federal grant to construct a 156,000-square-foot maintenance and operations facility with a 7-acre paved lot. Upon testing, TRC Companies (TRC), an environmental consulting company based in Massachusetts, found coal tar waste from the gas manufacturing process had leached into the soil. This raised the cost of the project by nearly $15 million and increased the scope significantly, adding tension to the schedule because of the firm completion date.
Manufactured gas uses a heat and filtration process to extract gaseous fuel for use in homes as a supplement to natural gas reserves. To create it, the previous owners used coal carbonization, carbureted water gas (water gas passed through a heated and oiled retort to boost the caloric value) and oil. Residual waste products of the process include contaminated water and coal tar, so from the 1930s until the 1950s, the property was also used for tar distillation. Over the century of operation, some of the waste from the process was mishandled and leached deep into the soil. After demolition of the structures in the late 1960s, rather than perform a proper cleanup, the site was merely covered in a 3-foot layer of topsoil, surrounded by a fence, and left unused.
A Tight Work Schedule
Over time, single family and multi-family housing units grew up around the site, with a large park built across the street. Residents considered it a blighted area and an eyesore. This was until WRTA proposed to use the site to house and maintain its fleet of 52 buses and 16 vans. The organization had been operating out of an old trolley barn from the 1920s that was converted to a bus facility after World War II. Over time, the small and outdated site fell into disrepair.
The new property is conveniently located only a short distance from the transit authority's main bus hub at Union Station, which allows for more efficient operations. "Before the general contractor broke ground, the WRTA gave us a hard end date for the project, due to the tight transitional timeline between old and new maintenance facilities," said Chris McDermott, senior project manager for TRC. "Any delays in remediation or construction would cause the entire region to suffer a transit service interruption, affecting thousands of residents who depend on the system for transportation everyday. Needless to say, if we ran into any obstacles, we required a fast solution."
Naphthalene Odor Emissions
As the Licensed Site Professional (LSP) on the project, TRC takes the lead in permitting, oversight, and compliance. This role also puts the company in charge of creating environmental remediation plans, along with working closely with the Massachusetts Department of Environmental Protection (DEP) and the local conservation commission. After TRC's remediation plan was approved, project managers gave the green light for work to begin. "Because we detected traces of naphthalene in the soil, we included an odor control plan into the remediation strategy, but the odor emission levels are unpredictable," said McDermott.
Naphthalene is a volatile organic compound (VOC) composed of carbon, hydrogen, and multiple aromatic benzene rings (the cause of the odor). It is a derivative of the coal tar distillation process, which removes moisture and impurities using heat. Coal tar can contain of up to 50 percent naphthalene. Commonly used in mothballs, when the VOC is refined it becomes a white chalky substance with a unique aroma that repels household pests. The smell is described as acrid, bitter and chemical -- similar to the odor emitted by roofing tar -- and can be detected by humans in concentrations as small as 0.08 parts per million (ppm). In large quantities, the smell can become overwhelming and disruptive to people with existing respiratory issues or sensitivity to smell.
As part of the odor control plan, excavators worked in sections, stripping the site's topsoil cover layer and exposing the contaminated subsoil. Tests had revealed that the contamination penetrated between 10 feet and 15 feet deep across the entire site. The estimated 85,000 tons (77,110 metric tons) of soil extracted from the site was piled into storage mounds approximately 30-40 feet high. Front loaders filled trucks and train cars that were covered to mitigate fugitive dust and odor emissions. The material was then transported to a landfill in upstate New York.
"The deeper we dug and the more soil we exposed, the worse the odor became," explained Brian Burk, field technician for TRC. "When summer temperatures heated the soil, complaints from neighbors started coming in, so we immediately implemented our odor strategy."
Two areas of operation on the work site were identified as the primary sources of the smell: the exhumed zones and the storage piles. As excavators and front loaders disrupted material in the ground or stored in piles, the odor was released and immediately carried on air currents. Higher temperatures increased the intensity of the smell, and westerly wind extended the travel distance, carrying the odor for several blocks toward the most densely populated residential area near the site. With operating hours of 7 a.m. to 5 p.m., strategies were implemented to address both active and dormant periods. The primary method of odor control was surface suppression. As excavated zones were uncovered, workers sprayed environmentally safe chemical foam over the exposed areas. The foam acted as a barrier between the contaminated soil and the open air, but did not neutralize the odor, so if the area was disrupted, the smell would return and workers would have to re-spray.
A combination of urethane sheeting and foam was employed in the storage pile area. Piles that were not in the process of loading onto train cars were wrapped in urethane sheets to provide an extra layer of protection, a labor-intensive task that took time away from other productive activities on the site. According to Burk, operators also placed individually timed misting units containing perfume spray canisters at the site's western fence line. These were intended to mask any fugitive odor emissions leaving the site. He explained that the units offered inadequate coverage, only changed the smell slightly and required labor to monitor and maintain on a regular basis.
"The first summer had its issues, but our strategy worked for the most part," Burk said. "But as excavation continued in colder weather, we realized that as we exposed more of the area and the storage piles grew, we may require a new strategy for the next summer."
Choosing an Odor Control Solution
When warmer weather returned, TRC worked closely with the local community and DEP officials. Managers agreed to halt operations, cover all exposed material with foam and/or plastic sheeting and seek another, more sustainable odor solution. However, the firm transition date between facilities was swiftly closing in, and excessive downtime was not an option. "Everyone involved in the project was extremely concerned about the odor's impact on the local community and the workers on the site," McDermott said. "We needed a solution quickly that could deliver odor control on an industrial scale. Technology that was mobile, environmentally safe and – most of all – worked."
A few frustrating days of downtime had already passed when TRC site managers discovered Dust Control Technology®, manufacturer of the OdorBoss® line of odor suppression systems. Offering industrial-scale airborne odor suppression over a large area, the units employ proprietary environmentally-safe chemicals delivered by an innovative atomized misting technology. "They delivered a unit to us on site within days," McDermott said. "We were very relieved."
The two methods TRC used, trapping the smell or masking it with perfumes, were unsuccessful because neither approach actually eliminated the odor. Containing it under foam merely held it in as it became more concentrated, so once the substance was disrupted by machinery, the odor escaped. In addition, many industries have discovered that perfumes like those placed on the site’s perimeter fence only add to the smell rather than mask it, with minimal benefit in most cases. Instead, the OB-60G introduces an engineered mist of the OdorBoss air treatment agent solution, comprised of millions of tiny droplets as small as 15 microns in diameter (approximately the size of airborne plant spores). Biodegrading in just 36 hours and safe for humans, animals, and plants, this chemical travels on air currents with the odor-causing molecules. It attaches to molecules and alters their composition, eliminating the component that causes the smell.
The process applies to a host of other odor-causing elements, such as sulfides, mercaptans, ammonia and amines. Since VOCs -- like naphthalene -- are particularly volatile during hot periods, the water droplets are merely used as a delivery system to introduce the chemical over a large area. Once the droplets evaporate, the chemical remains airborne for a period of time, further treating lingering odor molecules.
At a 1000:1 water-to-chemical ratio, the 500-gallon tank and 5-gallon additive container provide a full day of odor suppression at a volume of about 0.5 gallons of solution per minute. At that rate, the tank delivers about 16 hours of run time between refills, depending on the level of activity.
Creating an Area of Odor Control
To be effective, the air treatment agent must be delivered in the finest mist possible, said DCT President Laura Stiverson. "That's why the unit features a single air atomizer, a very specialized nozzle that transforms pressurized liquid into tiny droplets." The unit uses a large, ducted fan to propel the solution into the air, covering large areas with an odor-neutralizing mist.
The special open-cylinder cannon design is mounted with the large water tank on a towable trailer with foam-filled tires. Just 8.8 feet wide, the unit can be quickly positioned anywhere on the WRTA site by a single worker using a pickup truck or other towing vehicle. And since adding it to TRC's odor control plan, the site has not experienced any downtime due to odor. With work back on schedule to wrap up by the date of WRTA's transition from the old facility to the new one, site managers are anticipating no disruptions in service for public transit customers.
Complaints about odors stopped completely as a result, McDermott said. "We are extremely happy with the results and the service DCT provided and will definitely use this solution on other projects."