This was an in-situ remediation project at a pharmaceutical plant in Shanghai with BTEX contamination. The main contaminant of concern was toluene, which is a LNAPL. The investigation results using membrane interface probe (MIP) indicated that the contamination was mainly within 5m below ground surface. This project was completed between 2010 and 2011. Dual phase extraction (DPE) and in-situ chemical oxidation (ISCO) were used for the in-situ remediation. DPE was used to recover the free phase toluene. Hydrogen peroxide was used in ISCO to destroy the residual toluene in dissolved phase. Within 25 days, a total of 720 L of liquids was extracted from 9 wells by the DPE system. The total amount of toluene removed was approximately 125kg. The thickness of LNAPL in all extraction wells decreased significantly after 25 days of extraction. No LNAPL could be found in wells located near the periphery of the LNAPL plume after 25 days of extraction. During the process of ISCO treatment, 49 injection wells were installed and two rounds of injection were conducted. Approximately 10,355 liters of 5% sulfuric acid and 22,565 liters of 8% hydrogen peroxide were injected into the ground within a half month in the first round. An average of 200 liters of sulfuric acid and 400 liter of hydrogen peroxide were injected into each well. In the second round, approximately 15,816 liters of 5% sulfuric acid and 38,850 liters of 8% hydrogen peroxide were injected. The subsequent monitoring results showed that the concentration of toluene in the treatment area was significantly reduced and the desired remediation goal was achieved.
This was a soil and groundwater remediation project at a site in Shanghai with contamination of chlorinated hydrocarbons. The contaminants of concern included vinyl chloride, dichloroethane, trichloroethane (TCA), trichloroethylene (TCE) and dioxane. Contamination was found in seven areas of the site with a total volume of approximately 80,000 m3 of contaminated soil. TCA was the main contaminants of concern. Its density is higher than water so it is a dense non-aqueous phase liquid (DNAPL). Based on the results of previous investigations, the extent of groundwater contamination was approximately 2,000m2. Approximately 100 tonnes of TCA was estimated to be present as DNAPL between 6m to 8m below ground surface. The total volume of contaminated soil in this area was approximately 12,000m3. DNAPL was mainly located above the top of the aquitard beneath the phreatic aquifer, which consists of sandy silt. The first stage of remediation was to enhance the recovery of DNAPL using multi-phase extraction (MPE). Dual pumps were used in the MPE system. The extracted liquids included mobile DNAPL and groundwater, which were directly extracted to the ground using a submersible pump in the extraction well. Meanwhile, a vacuum pump system was set up on the ground to create a vacuum at the head space of each extraction well so that the DNAPL recovery can be enhanced and part of residual DNAPL can also be removed by extraction of soil vapor. This project is still ongoing and the remediation system has been operating effectively to date. The other two areas were relatively less significantly contaminated, with no DNAPL present. In-situ chemical reduction was used to treat the groundwater contamination, which was approximately 3,500m2 with depth ranging between 7 to 9 m. Chemical re agents were injected using direct push methods from 1.5 m to 9 m below ground surface at intervals of 0.5 m. The reagent used was a patented EHC product, composed of zero-valent iron and a slow-release carbon source for enhanced reductive dechlorination by biological activities. Three hundred injection points were used across the entire treatment area to inject a total of 100 tonnes of the EHC reagent. The results of subsequent monitoring indicated that the concentrations of contaminants decreased significantly after treatment and the expected remediation goal was achieved.
This site was a former automobile accessory factory in Nanjing. The factory had been relocated in 2013. The site will be redeveloped. Organic contamination in soil and groundwater in some areas of the site was found during the investigation. The main contaminants of concern were chlorinated hydrocarbons and petroleum hydrocarbons with a total contamination area of approximately 5000m2 and the maximum contamination depth of 10 meters. Light non-aqueous phase fluids (LNAPLs) were found in some areas. Greenment was entrusted to develop the groundwater remediation scheme. Based on the significant differences in different contaminated areas, the site was divided into three contaminated zones and different remediation technologies were proposed. 1）For the TPH (mainly C10~C14 compounds) zone, in-situ chemical oxidation was proposed. The recommended oxidation reagent was proprietary persulfate; 2）For the LNAPL zone, the most effective approach was direct recovery of LNAPL. Therefore, multi-phase extraction was proposed; 3）For the complex contamination zone, multi-phase extraction combined with in-situ chemical reduction was proposed. The recommended reagent for in-situ chemical reduction remediation was patented EHC.
The phase II project for a hazardous waste landfill in Shanghai was classified as a Class I construction project, which could potentially cause groundwater contamination. The EIA level for groundwater was Class I. Greenment applied a numerical model to evaluate the potential impact on the groundwater environment. The main potential groundwater contamination in this project was the leakage of landfill leachate to the surrounding groundwater in the phreatic layer. The assessment factors were identified to be mercury, arsenic and cadmium based on the analysis of contaminants in the leachate. Considering the operation time of the landfill site, continuous leakage over15 years was simulated to evaluate the impact on groundwater quality. Visual MODFLOW was used for the groundwater modeling. The area was horizontally subdivided into 10-meter grids (2.5-meter grids in the source area). Two layers were used to represent the unsaturated zone and unconfined aquifer consisting of fill and silty clay, respectively. The input parameters were obtained from the results of geotechnical tests and empirical values, and were calibrated by the software or manually. The simulated groundwater contour was consistent with the monitoring results of groundwater level and flow direction. Solute transport was simulated based on the groundwater flow model. The migration of contamination in fill/silty clay layer and sandy silty layer at different times could be obtained from these simulations. The Class IV limits of “Groundwater Quality Standard” (GB/T14848-93) were used to represent the leading front of the plume. The following figures show the migration of the mercury plume in fill/silty clay layer in 5, 15, 50 and 100 years after the leakage. Based on the simulation results, it is estimated that the furthest extent of contamination caused by leachate leakage in the fill/silty clay layer was 33.7 m down gradient from the landfill site and the longest duration of impact was 250 years. In the sandy silt layer, the furthest extent of contamination and longest duration of impact were 222.8 m and 500 years, respectively. The extent of contamination could not reach the nearest surface water in the down gradient. Therefore, the impact of this project to groundwater quality was minimum and the risk to the groundwater environment was acceptable.
A new commercial district will be developed at the site in Shanghai. Environmental investigation and human health risk assessment were required to be conducted at the site by a qualified organization according to national and local regulations. Greenment was entrusted to conduct the preliminary investigation and detailed investigation in August and November 2012, respectively. The investigation results indicated that the concentrations of antimony, trivalent chromium, hexavalent chromium, copper, nickel, lead and arsenic in the soil in some areas of the site were higher than screening values. In early 2013, Greenment was entrusted by the owner to conduct a human health risk assessment to determine the contaminants of concern in soil, to systemically evaluate the sensitive receptors and exposure characteristics at the site, to quantitatively estimate the risks to sensitive receptors from exposure to soil contamination at the site, and to develop the risk-based target values for soil remediation. Ø Assessment protocol:“Technical Guidelines for Risk Assessment of Contaminated Sites” (HJ25.3-2014); Ø Assessment procedure：hazards identification, exposure assessment, toxicity assessment, risk characterization and calculation of risk control values; Ø Target level of carcinogenic risk for a single contaminant: 10-5; Ø Target level of non-carcinogenic hazards for a single contaminant: 1. Potential contaminants of concern in soil were first screened based on the results of site investigation. Sensitive receptors included commercial workers, construction workers and local residents. Primary exposure pathways included oral intake, dermal contact, inhalation of indoor and outdoor particulate matters from surface soil, and inhalation of indoor and outdoor vapor from surface and subsurface soil. Future construction workers will mainly be exposed to contaminants in surface and subsurface soil. Future commercial workers and local residents will mainly be exposed to contaminants in surface soil. The health risks of contaminants of concern were quantitatively calculated based on the exposure models and parameters in “Technical Guidelines for Risk Assessment of Contaminated Sites” (HJ25.3-2014) and toxicological parameters in commonly used databases. The results indicated that for hexavalent chromium, nickel, antimony and arsenic in soil in some areas of the site, the carcinogenic risks were higher than 10-5, or the non-carcinogenic hazards were higher than 1. The calculated target values for hexavalent chromium, nickel, antimony, lead and arsenic in soil were 17.7mg/kg, 418mg/kg, 47.4mg/kg, 800mg/kg and 20mg/kg, respectively.
The manufacturing facility was mainly engaged in the design, research and development, manufacturing and after-sales service of automobile exhaust decorative pipes in Ningbo City, Zhejiang Province. In February 2013, a fire occurred at this facility. Due to concerns for potential contamination to soil and groundwater by electroplating wastewater leaked from the electroplating workshop and the wastewater treatment facility through the landscaping area in the facility and cracks on the workshop floor, the client hired two consulting companies to conduct preliminary investigation with sampling and analysis in September and December, 2013, respectively. Greenment conducted detailed and supplementary investigations in January and March, 2014, respectively, based on the results of previous investigations, to obtain a comprehensive understanding of soil and groundwater contamination at the site. A total of 13 deep boreholes and 27 shallow boreholes were installed during the detailed and supplementary investigations. The maximum depth of the deep boreholes was ten meters below the ground surface (bgs) and the maximum depth of the shallow boreholes was five meters bgs. In addition, ten groundwater monitoring wells were also installed across the site. A total of 165 soil samples and 15 groundwater samples were sent to laboratory for chemical analysis. The boreholes and groundwater monitoring wells were installed using hand augers and Powerprobe systems. Based on the land use, presence of sensitive receptors, exposure scenarios, pathways and parameters and toxicological properties of contaminants, Greenment characterized the risk, and calculated the risk control values of contaminants of concern. Ø Assessment protocol:“Technical Guidelines for Risk Assessment of Contaminated Sites” (HJ25.3-2014) and “Technical Guidelines for Risk Assessment of Contaminated Sites in Zhejiang (DB 33/T 892-2013)”; Ø Assessment procedure：hazards identification, exposure assessment, toxicity assessment, risk characterization and calculation of risk control values; Ø Target level of carcinogenic risk for a single contaminant：10-6; Ø Target level of non-carcinogenic hazards for a single contaminant: 1. The land use type of the site was industrial. The main exposure pathways included oral intake, dermal contact and inhalation of indoor and outdoor particulate matter from surface soil. There was no obvious exposure pathway from groundwater contamination. The main sensitive receptors were site workers. The Class IV limits of “Groundwater Quality Standard” (GB/T14848-93) were used as the target values for groundwater remediation. Based on the risk assessment results, the soil and groundwater in some parts of the site had been contaminated by heavy metals, resulting in unacceptable risks to human health. Greenment determined the remediation target values and contamination extent based on the results of site investigation and risk assessment. The area of soil contamination in the electroplating workshop was approximately 1500m2, with the depth of 1.2~2.4m and a total volume of approximately 2100m3. The contaminant of concern in soil was nickel with the maximum concentration of 5,955 mg/kg and the remediation target value of 476 mg/kg. The area of contaminated groundwater was approximately 5000m2 with the depth of approximately 4.5m.The contaminants of concern in groundwater include nickel and Cr(VI) with their maximum concentrations of 3.75mg/L and 0.698mg/L, respectively. Their remediation target values were both 0.1mg/L. Greenment evaluated multiple candidate remediation technologies and selected a remedy best suitable for the soil and groundwater contamination at the site. Excavation and ex-situ disposal as hazardous waste or reuse was selected for contaminated soil. Pump and treat was selected for groundwater remediation. Extracted groundwater was treated to acceptable standards before discharge.