Background Image

PollutionEngineering May 2012 : Page 26

COAL TAR CONTAMINATION REMEDIATION An MGP coal tar contaminated site was remediated in fi ve months and the land can now have a library and ranger station erected. C oal tar contamination was successfully destroyed at a former roofing products manufacturing site in New York City using a surfac-tant-enhanced in situ chemical oxidation (S-ISCO) system. The urban site, surrounded by dense residential and commercial development along the shores of the East River, was contami-nated with repurposed coal tar from a nearby Manufactured Gas Plant (MGP) for the roofing manufacturing process. The supplier con-ducted five months of S-ISCO injections that destroyed greater than 90 percent of coal tar-related contaminants including benzene, toluene, ethylbenzene, and total 26 Pollution Engineering MAY 2012 xylenes (BTEX), and polycyclic aromatic hydrocarbons (PAHs) and naphthalene in the targeted interval. The treatment consist-ed of injections of a patented plant-based surfactant and co-solvent mixture, and an alkaline-activated sodium persulfate that redevelopment of the Brownfield site as a public library and park ranger sta-tion. The New York State Department of Environmental Conservation (NYSDEC) has issued a Certificate of Completion to confirm the success of the cleanup. The successful destruction of MGP-related coal tar at the urban Brownfield site demonstrates the effectiveness of S-ISCO as a remedy for MGP-related contamination. Site background were augmented by pressure-pulsing injec-tion enhancement technology that is often used to maximize oil recovery operations. S-ISCO was an integral part of the remedial implementation that will enable Located on a bank of the East River in a densely developed residential and com-mercial area, this 0.73-acre parcel is part of an urban revitalization project and will be redeveloped as a public library

Coal Tar Contamination Remediation

An MGP coal tar contaminated site was remediated in five months and the land can now have a library and ranger station erected.<br /> <br /> Coal tar contamination was successfully destroyed at a former roofing products manufacturing site in New York City using a surfactant- enhanced in situ chemical oxidation (S-ISCO) system. The urban site, surrounded by dense residential and commercial development along the shores of the East River, was contaminated with repurposed coal tar from a nearby Manufactured Gas Plant (MGP) for the roofing manufacturing process. The supplier conducted five months of S-ISCO injections that destroyed greater than 90 percent of coal tar-related contaminants including benzene, toluene, ethylbenzene, and total xylenes (BTEX), and polycyclic aromatic hydrocarbons (PAHs) and naphthalene in the targeted interval. The treatment consisted of injections of a patented plant-based surfactant and co-solvent mixture, and an alkaline-activated sodium persulfate that were augmented by pressure-pulsing injection enhancement technology that is often used to maximize oil recovery operations.<br /> <br /> S-ISCO was an integral part of the remedial implementation that will enable redevelopment of the Brownfield site as a public library and park ranger station. The New York State Department of Environmental Conservation (NYSDEC) has issued a Certificate of Completion to confirm the success of the cleanup. The successful destruction of MGP-related coal tar at the urban Brownfield site demonstrates the effectiveness of S-ISCO as a remedy for MGPrelated contamination.<br /> <br /> Site background <br /> <br /> Located on a bank of the East River in a densely developed residential and commercial area, this 0.73-acre parcel is part of an urban revitalization project and will be redeveloped as a public library and park ranger station. As part of the history of roofing products manufacture at the parcel, MGP coal tar that was brought onto the site leaked into the subsurface, contaminating the soil and groundwater with BTEX, naphthalene, and PAHs. Contaminant concentrations in the soil and groundwater exceeded the NYSDEC regulatory limits, including in a number of groundwater locations by orders of magnitude. The majority of contamination was present as residual non-aqueous phase liquid (NAPL) held within the pore spaces of the predominately sandy and silty soil that also included lenses of silt and silty clay. Traditionally these NAPL droplets, especially in fine soils such as the silts and clays present at this site, present a challenge to in-situ treatments.<br /> <br /> The S-ISCO technology was approved as part of the Brownfield cleanup strategy for the site after the results of benchscale treatability tests and pilot-scale field implementation demonstrated that S-ISCO could effectively contact and destroy contamination at the site, including sorbed NAPL. The laboratory and field-scale testing indicated that an S-ISCO treatment composed of a proprietary solution from VeruTEK and an alkaline-activated sodium persulfate was the optimal remedy for site contaminants. The pilot test also indicated that the incorporation of a pressure-pulsing technology with the S-ISCO injections enhanced the radius of influence and uniformity of dispersion for the injected chemistry.<br /> <br /> Implementation<br /> <br /> S-ISCO implementation took place between Oct. 2010 and March 2011, and consisted of injections of teh approved solution and sodium hydroxide [1] into 34 wells that were located in the areas with the greatest contamination had been identified [2]. These wells were variably screened across 6- to 7-foot intervals between 10 and 22 feet below ground surface (bgs) in order to target approximately 64,000 pounds of contamination. Injections took place at an average rate of eight gallons per minute (gpm) per well to four wells at a time (32 gpm overall), and were augmented by the pressure-pulsing tool. Table 1 summarizes the injection parameters.<br /> <br /> Monitoring <br /> <br /> Monitoring was conducted before, during and after S-ISCO injections to track the progress and performance of the injected chemistry in the subsurface and to confirm that the treatment was not negatively impacting sensitive receptors, such as the adjacent river. Monitoring included: continuous tracking of water quality parameters using in-situ data loggers; collection of groundwater samples for analysis in an on-site laboratory; observation of all wells on and off-site for indications of NAPL; and collection of soil and groundwater samples for contaminant analysis.<br /> <br /> Contamination destruction <br /> <br /> Approximately five months after the completion of injections, when the results of groundwater monitoring indicated that the sodium persulfate reactions had subsided, the injections had largely degraded and the pH conditions were approaching pre-injection levels. A total of 114 soil grab samples were collected from the treatment area and analyzed for total VOCs and SVOCs [3]. These results were used to calculate the mass of contamination remaining and were compared to the mass calculated before treatment. This analysis indicated that the S-ISCO treatment destroyed 90. 3 percent of the mass of total VOCs and SVOCs present before treatment, including more than 95 percent of the naphthalene present. Naphthalene, a principal component of coal tar, was one of the primary SVOCs affecting the site soils and groundwater; it accounted for almost 65 percent of the total pretreatment contaminant mass. Table 2 shows additional reductions for priority contaminants, including BTEX.<br /> <br /> Groundwater controlled desorption & destruction process <br /> <br /> The results of groundwater analysis for S-ISCO performance parameters [4], as well as regular inspection of all on and offsite wells for the presence of either NAPL or the injected chemistry, confirmed that the S-ISCO desorption and destruction process proceeded in a safe, controlled and effective manner. Specifically, while the injected solution desorbed and emulsified the NAPL and sorbed contaminants, these contaminants were subsequently destroyed by the coeluted persulfate oxidant. Figure 3 shows the coelution process at a shallow well in the treatment area. The coelution process is explained in greater detail in the sidebar.<br /> <br /> In addition, at no time during injections was any indication of either the injected chemistry or the targeted contamination, including NAPL, solubilized NAPL, odors or sheen, observed in off-site groundwater.<br /> <br /> Contaminant reductions <br /> <br /> Groundwater samples from the nine onsite monitoring wells screened across the treatment interval (10 to 22 feet bgs) were analyzed before and after treatment. This data indicated that the treatment achieved significant VOCs reductions, including 92 percent for xylenes, 87 percent for benzene, the most toxic and mobile VOC at the site, 90 percent for ethylbenzene, and 91 percent for BTEX.<br /> <br /> Soil vapor samples collected from three areas adjacent to the site were analyzed before (Oct. 2010) and after (April 2011) injections [5]. Because regular measurement of soil gas pressure [6] indicated that the injected oxidant was not causing measurable increase in pressure, additional rounds of vapor sampling during injections were deemed unnecessary. Reductions in soil gas concentrations are summarized in Table 3 and shown in 4, and included 100 percent for benzene, ethylbenzene, naphthalene and TCE. Improvement in soil gas contamination included reductions at a sampling location more than 100 feet from the southeastern corner of the injection area, indicating that the effects of the treatment extended far beyond the immediate injection area.<br /> <br /> Conclusions <br /> <br /> The successful destruction of MGPrelated coal tar at this urban Brownfield site demonstrates a clear success for S-ISCO and its safety and effectiveness as a remedy for MGP-related contamination. The five-month S-ISCO treatment successfully contacted, desorbed and destroyed NAPL contaminants and reduced soil vapor contamination in a controlled process without impacting the adjacent water body (the East River) or the local community.<br /> <br /> For more information, call John Collins, Ph.D. and founder of Verutek Technologies Inc. at (860) 242-9800 or send him an e-mail at jcollins@ verutek.com.<br /> <br /> References<br /> <br /> 1. Sodium hydroxide was injected to create alkaline conditions to activate the sodium persulfate.<br /> <br /> 2. Additional wells were installed when interim soil sampling revealed a previously unidentified area of contamination.<br /> <br /> 3. TCL SVOCs (Method 8270) and TCL VOCs (Method 8260).<br /> <br /> 4. S-ISCO performance parameters include interfacial tension (IFT), an indication of VeruSOL, electrolytic conductivity, and concentrations of sodium persulfate and total petroleum hydrocarbons (TPH).<br /> <br /> 5. Samples were collected from the 4 to 6 feet bgs interval and analyzed using Method TO-15 plus naphthalene.<br /> <br /> 6. 4,440 soil gas readings were taken throughout the injection process.<br /> <br /> Tracking Coelution<br /> <br /> Implementations of S-ISCO include comprehensive groundwater monitoring programs designed to track the progress and performance of the injected chemistry and ensure the success of the coelution process. This monitoring includes laboratory analysis of groundwater samples for parameters including interfacial tension (IFT), conductivity and concentrations of oxidant (such as persulfate and peroxide) and TPH.<br /> <br /> • Increased oxidant concentrations indicate effective transport and sufficient dosage of the oxidant.<br /> <br /> • Increased conductivity measurements indicate the presence of oxidative reactions, and also that the oxidant has been successfully activated and is entering into reactions with contaminants.<br /> <br /> • Reductions in IFT indicate the presence and effective solution transport.<br /> <br /> • Accompanied by increases in TPH concentration, decreases in IFT indicate that the active solution has desorbed and solubilized immiscible contaminants.<br /> <br /> • Subsequent decreases in TPH, in the presence of elevated conductivity, indicate that the desorbed contaminants have been oxidized.<br /> <br /> Figure 3 (right) shows the results of groundwater monitoring conducted during S-ISCO treatment. This shallow well, screened from 11 to 22 feet bgs, was down-gradient to four injection wells into which the proprietary chemicals and the alkaline-activated sodium persulfate were injected during the period from October 2010 to the end of February 2011.<br /> <br /> At the start of injections, the persulfate (blue) and conductivity (red) fronts arrive, indicating the presence of the injected oxidant (persulfate) and its entrance into reactions with dissolved contaminants present. The activity of the persulfate also indicates its successful activation. The solution front (green) follows as shown by the drop in IFT in early January. The rise in TPH that accompanies this decrease in IFT indicates that the treatment is successfully desorbing and solubilizing contamination into the aqueous phase. The corresponding spike in conductivity and subsequent reduction in TPH indicates that the solubilized TPH is reacting with the activated persulfate. The IFT remains low as the injections continue and the surfactant continues to desorb and emulsify additional TPH contaminants. As injections end, the persulfate remains in the subsurface but its reactions with the dissolved contamination slow as the alkaline conditions used for its activation become more acidic. Nevertheless, continued elevations in conductivity as well as continued decreases in TPH indicate that oxidative reactions are ocontinuing.

Previous Page  Next Page


Publication List
Using a screen reader? Click Here