NATO/CCMS Pilot Study Evaluation of Demonstrated and ... - CLU-IN

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NATO/CCMS Pilot Project on Contaminated Land and Groundwater (Phase III) January 2001 2. BACKGROUND/SITE DESCRIPTION From 1952 to 1985, a chemical factory was located on an area of about 10,000 m² in a city in the Ruhr area. Mostly solvents, like hydrocarbons, volatile chlorinated hydrocarbons, PAHs, petroleum, turpentine oil substitute, ketones, monoethyleneglycol, and alcohols were handled, stored, and processed. Today, a residential building is left on the site while underground and above ground tanks are demolished. The ground was filled up 2.0 m over silty soil (approx. 4 to 11 m thick). Below the silt, a layer of sand and gravel (0.8 to 7.4 m) and marly sands (7.0 to 16.3 m below the top) have been detected. The marly sands are the first waterproof layer. The first aquifer is about 1.0 to 3.2 m thick and the flow velocity is very slow (kf = 6.6 ⋅ 10 -6 m/s). The concentrations of main contaminants in groundwater are petrol hydrocarbons 23.6 mg/l to 164.0 mg/l, volatile chlorinated hydrocarbons 27.0 mg/l and aromatic hydrocarbons 153.0 mg/l. Furthermore, higher concentrations of manganese and iron are present. The project is funded by the city of Essen and the state; Nordrhein-Westfalen, the former owner, went bankrupt. 3. DESCRIPTION OF THE PROCESS The pilot plant was fed with groundwater, which was pumped directly from the aquifer into the front column. Two dosing pumps located behind a gravel bed in the front column fed groundwater into columns 1 and 2. The gravel filter served to hold back sediments as well as to eliminate iron and manganese. • Column 1 contained: - 45 cm gravel filter (size: 2 to 3.15 mm) - 5 cm activated carbon ROW 0.08 supra - 5 cm gravel filter (gravel size: 2 to 3.15 mm) - 65 cm activated carbon ROW 0.08 supra The thickness of the activated carbon bed in Column 1 corresponded to the recommended thickness of the activated carbon bed of the adsorbent wall in the feasibility study. • Column 2 contained: - 100 cm activated carbon ROW 0.08 supra The treated water was led via an overflow into a trough located outside the container. Groundwater analyses were based on the contamination at the site; their scope was determined by the feasibility study to install an adsorbent wall. The analyses covered field parameters, general parameters and parameters to quantify BTEX and volatile CHC contamination. The analyzed general parameters included sum parameters for organic compounds as well as the parameters iron and manganese. A sum parameter for organic compounds was used in order to study whether it could serve as a substitute for analyses of individual substances. Moreover, the sum parameters were also used to check whether the results of individual analyses were plausible. Iron and manganese contents were determined in order to check whether precipitation of these substances would block the adsorbent wall. Separate analyses were carried out for BTEX and volatile CHC. The number of analyzed parameters (16) was deliberately large so as to also cover important decomposition products such as vinyl chloride. Contaminant retention by the activated carbon was determined in two ways. First, contaminant concentrations were continuously monitored at the inlet, in the columns, and at the column outlets. 21
NATO/CCMS Pilot Project on Contaminated Land and Groundwater (Phase III) January 2001 Secondly, following the conclusion of tests, the columns were disassembled and individual partitions of carbon samples were analyzed for contaminant content. Tests were carried out to determine whether iron and manganese precipitation or microbial activity in the activated carbon could block the adsorbent wall. Water samples collected on 11 days were tested for numerous parameters; on the whole, over 1,600 individual results were obtained for water samples taken during pilot operation. The determined concentrations for dissolved organic carbons (DOC) ranged between 80 and 160 mg/l at the inlet. The DOC values correlate well with the CSB and TOC concentrations. No contaminant breakthrough was detected in samples from the outlets of the two columns over a period of almost half a year. The pilot tests with Columns 1 and 2 confirm that putting up an adsorbent wall is feasible. With respect to contaminant retention, results of the pilot tests indicate that the long-term effectiveness would be much higher than the estimated period of 30 years in the feasibility study. 4. RESULTS AND EVALUATION The pilot tests confirm the findings of the feasibility study, to the effect that the site is suited to put up an adsorbent wall. The following statements can be made with respect to the present tests: • The pilot tests show good contaminant retention in the activated carbon, in fact much higher than what was assessed in the feasibility study. Contaminant breakthrough for toluene and trichloroethylene was determined at sampling point S2P50 (i.e., after flow through 50 cm), Column 2, only at the end of the 5-month pilot test operation. By this time, throughput had reached 600 times the bed volume. • The pilot tests indicate that the durability of the wall given a 70 cm-thick activated carbon layer would be much higher than the 30 years estimated in the feasibility study. The thickness of the carbon layer should therefore be reduced when the wall is put up. • The DOC concentrations established during the pilot tests can almost entirely be traced to the contaminants detected at the site. It is therefore to be expected that the adsorbing potential of the activated carbon will not be impaired by natural organic compounds, such as humin. • Data pertaining to the contaminant breakthrough suggest that the depletion of the adsorbing capacity of the activated carbon is accompanied by a sharp peak in the concentration of volatile substances. A suitable monitoring system should therefore be set up when the adsorbent wall is erected. • The fact that the activated carbon could be regenerated after disassembling the plant suggests economic operation of the adsorbent wall. • Laboratory analyses of the water and activated carbon samples indicate that iron and manganese precipitation will be insignificant and will not block the adsorbent wall. • Microbial activity could not be detected in the gravel filter or in the activated carbon; it may be concluded that under the given site conditions, the build-up of bacterial film does not pose a risk. • Preliminary laboratory tests to determine the choice of activated carbon as well as pilot tests must be carried out in all cases prior to setting up an adsorbent wall given the variance in site conditions. 5. COSTS The costs for conducting the field tests have been EURO 50.000,--. The overall costs to erect the wall system and then fill it with activated carbon are estimated to be EURO 750.000,--. Included are additional costs for monitoring the water quality for 30 years, which is as long as the minimum performance time of one single filling will be. In comparison with traditional pump-and-treat groundwater remediation costs, the proposed permeable reactive barrier system will be at least 25% less expensive. 22
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