An overhead view of the project, with the area South of Second St. where crews will mix cement with soil in a solidification process to trap and contain contaminants shaded. Landscapes have a way of changing over the decades, where it occurs naturally or by redevelopment, urban renewal, land reclamation or whatever else you want to call it. But like a bad breakup, the past has a particularly nasty habit of leaving pieces of itself behind, little archeological clues that An especially toxic relationship existed at the block-sized parcel of land immediately South of Second St. between Hilton Ave. and Franklin Ave. A manufactured gas plant operated on the site from the early 1900’s to the 1950’s, converting both coal and oil into a liquid gas used to heat homes. There were once thousands of similar plants across United States until after WWII when natural gas became popular following the installation of pipelines. During the plant’s 50-plus years of operation, a series leaks, spills, etc. contaminated the surrounding ground, which now falls to National Grid to clean up the area.

In a back corner room on the campus of Hofstra University last Thursday night, National Grid engineers and representatives had set up easels with diagrams detailing the extent of the contamination as well as the lengthy cleanup process. The cleanup is divided into two parts: cementing closed a large area where tar-like residue is below the surface, and installing two lines of wells to provide oxygen to a groundwater plume. With a total estimated cost of the cleanup is $46 million, the scale of the cleanup is comparable to a site in Bayshore which has multiple groundwater plumes. An overhead map of the Second St. site shaded in yellow shows that the soil area most contaminated that stretches from the interior of the large parcel South of Second St. in Garden City, across Wydler Place and Intersection St. in Hempstead, and comes to a point at the intersection of Wendell and Smith streets. This triangular area runs approximately 600-ft. in length North to South at it’s longest point. It is this area which will be entombed using cement.

Described as “a tar-like oily substance; basically an oily residue,” by National Grid project manager Patrick Van Rossem, the contamination lies 25-30 ft. below ground level and contains “the same kinds of compounds that you see from service stations, gasoline stations, and other fuel spills; similar type materials.” Known as polycyclic aromatic hydrocarbons, the petroleum byproducts include benzine, toluene, ethel benzene and xylene. When questioned about the potential health hazards these chemicals produce, and considering the proximity to residences, Van Rossem said that the contaminants were at “such a favorable depth” below the surface that there was no health risk as the Dept. of Health determined that there was no exposure pathways for chemicals to come to the surface.

In order to seal the area - basically entombing the soil in cement - it would have to undergo a solidification process called “deep soil mixing” where an auger drills into the ground, injecting a “grout” or fluid cement and mixes it with the soil. The auger would work in a honeycomb layout, carving column that would overlap each other to create a solid mass once the cement hardens. Crews would first excavate the surface down to eight feet, disposing of the soil at appropriate land fills. From the depth of eight ft. the deep soil mixing process is utilized. Engineers noted that some contaminated material is as deep as 60 ft. Following the cement hardening, crews would come back and place clean fill and sod on top of the area. A parking lot at the at the Southern edge of the site on Medical Place would also be dug up, but rebuilt after the cleanup process. A temporary parking lot would be created for workers in the area. Temporary cement batch plants would be built on the site to supply the auger with cement, as well as temporary construction trailers for offices.

National Grid previously excavated two sites just South of Second St. where the soil was dug up and trucked offsite for thermal treatment; a process that “cooks off” the contaminants with a catalytic incinerator and leaves clean soil. Van Rossem said that National Grid conducted an investigation into the size and shape of contaminated area during 2009, and began work on the groundwater testing and system design. Design for the deep soil mixing would be completed in 2010 with field work starting in 2011.

Unfortunately, the chemicals that have contaminated the soil have bled off, creating a groundwater plume that stretches South from the site just past the intersection of Cathedral Ave. and Fulton Ave. in Hempstead. “Once this is encapsulated here then you remove the source and then this starts to go away on its own,” said Van Rossem, pointing to the plume. National Grid’s plan is to install two oxygenation systems to speed up the process where oxygen is reintroduced to the soil and bacteria clean up the contaminates by feeding on them. “There’s a lack of oxygen because the contaminates basically deplete the natural oxygen. So this is just replacing Mother Nature’s supply of oxygen,” Van Rossem explained. The process calls for drilling a series of wells about 15. ft. apart, with each well has its own pipe with its own oxygen supply. The oxygenation systems would be installed in 2010, and depending on access agreements, crews would break ground sometime in March or April.

The first system runs from Smith St. and Sealey Ave. across to Wendell St., down to Atlantic Ave. and back up Hilton Ave. A second line of wells would run across Mirschel Park to Hilton Ave., then up, across and down Kensington Court. A drilling machine would dig the individual wells, but trenches are required for pipes. The trenches would be the size of a normal utility trench. A shed housing the oxygen generation equipment would also be built on the Long Island Railroad’s right of way at end of Wendell St.

Even though the plume stretches well beyond the second line of oxygen wells, Van Rossem said that no third line because “these two zones are going to treat the most contaminated areas.” He added that National Grid did look to install third line but “we just couldn’t find the private properties to allow us to do it.” The oxygenation wells would be removed once cleanup is completed, which would take between five to 10 years.