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 Worcester, 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 Cos., a national environmental consulting company based in Lowell, Massachusetts, found coal tar waste from the gas manufacturing process had leeched into the soil. This raised the cost of the project by nearly $15 million dollars 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 and oil. The property was also used for tar distillation from the 1930s until the 1950s, so residual waste products of the process include contaminated water and coal tar.
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 three-foot layer of topsoil, surrounded by a fence and left unused.
A TIGHT WORK SCHEDULE
Over time, single-family and multifamily 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 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,” says Chris McDermott, senior project manager for TRC.
NAPHTHALENE ODOR EMISSIONS
As the licensed site professional 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 (MassDEP) and the local conservation commission.
“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,” says McDermott.
Naphthalene is a volatile organic compound (VOC), deriving from the coal tar distillation process. Coal tar can contain of up to 50 percent naphthalene.
When the VOC is refined, it becomes a white chalky substance with a unique aroma, described as acrid, bitter and chemical, 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 85,000 tons of soil extracted from the site were piled into storage mounds 30 to 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.
“The deeper we dug and the more soil we exposed, the worse the odor became,” says 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.”
ODOR MANAGEMENT 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. Higher temperatures increased the intensity of the smell, and westerly wind carried 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. Surface suppression was the primary method of odor control.
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 respray.
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.
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 says. “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.”
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 for TRC.
After a few frustrating days of downtime, TRC site managers discovered Dust Control Technology (DCT), Peoria, Illinois. Offering industrial-scale airborne odor suppression over a large area, the units employ proprietary environmentally safe chemicals delivered by an atomized misting technology.
“They delivered a unit to us on-site within days,” McDermott says. “We were very relieved.”
A WORKING SOLUTION
The two previous methods TRC used were unsuccessful because neither approach actually eliminated the odor.
Instead, the OB-60G introduces an engineered mist of the OdorBoss air treatment agent solution. 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.
Since VOCs 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 time, further treating the lingering odor molecules.
At a 1000:1 water-to-chemical ratio, the 500-gallon tank and 5-gallon OdorBoss 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.
An open-cylinder cannon design is mounted with the large water tank on a towable trailer The 25 horsepower fan generates 30,000 cubic feet per minute of air flow, which propels a long cone of vapor that provides expansive coverage when using the standard 180 degree built-in electric oscillator with a vertical angle adjustment of 0 to 50 degrees.
Since adding the OB-60G into TRC’s odor control plan, the site has not experienced downtime due to odor. With work back on schedule, site managers are anticipating no disruptions in service.
“Before we implemented this solution, every morning there would be at least one odor complaint on my voicemail, but from the moment we turned the OdorBoss on, they stopped completely,” McDermott says. “We are extremely happy with the results and the service DCT provided, and will definitely use this solution on other projects.”