ALOJZY SZYMAŃSKI, ZBIGNIEW LECHOWICZ, KAZIMIERZ GARBULEWSKI Department of Geotechnical Engineering, Warsaw Agricultural University SGGW, Poland Geoenvironmental impact assessment of a landfill for solid chemical wastes Introduction Across Europe there are many thousands of impoundments and landfills containing both liquid and solid chemical wastes, including old landfills where remediation works and protection against progressive environmental damage are required. This paper presents a case study of the environmental impact assessment of a large landfill located in northern Poland. The landfill covers an area of over hectares, consisting of four adjacent basins connected by a concrete outlet boxes to the drainage ditch. The landfill had been in service since 98 and contains over million m of ferrous sulphate wastes from the Chemical Plant (fig. ). High-polluted leachate from the landfill is a major problem for the surrounding environment. The influence of selected environmental factors on transfer of pollution from the landfill to the groundwater is discussed in the paper. Characteristics of the site The landfill of ferrous sulphate wastes consisting of four in series situated basins was located in southern region of the Chemical Plant (fig. ). Basins marked with Nos, and cover an area of approximately hectares each, while the basin No. has been under construction and at present covers an area of. ha. Total area of landfill together with surrounding green strip is ha. The drainage and sewerage systems to outflow of landfill leakage were situated in north and south of all basins (fig. ). The basins were rounded with the earthen embankments, generally m in height, constructed of local sandy and loam materials. The width of embankment crest with the access unpaved roads were 6 m, slope of embankment from :.5 to :, depending on the soil type. The test results from light soundings indicated (Technical Report, 998) that the soils in the bottom part of embankments should be considered as medium or even loose (density index I D Geoenvironmental impact assessment of a landfill for solid chemical wastes
Chemical plant Canal Odra River Landfill FIGURE. Location of the test site in range of..), while in the upper part as dense (I D =.6.). The above I D values were determined assuming that embankment fill was composed of the granular soils only. In reality, the embankments were constructed from a wide range of materials including silt and clay and therefore the I D values obtained can not be proper to assess of compaction state. Landfill liners both for bottom and side of all basins were constructed using two layers of geomembranes,.5 mm propylene type for the basins Nos, and, and.5 mm HDPE for the basin No.. The exploitation of the basin No. was begin in 995. However, it should be noted that no liner system, even if perfectly designed and constructed, will result in zero seepage losses. To collect x G No. No. No. No. x G 6 5 6 8 9 x W x W 5 x G boreholes, SL soundings, CTU CPT sondings, test BAT BAT soundings, test - piezometers, xg soil sampling, xw water sampling FIGURE. Layout of landfill with location of field tests. x W Alojzy Szymański, Zbigniew Lechowicz, Kazimierz Garbulewski
FIGURE. View of the basin No. (under construction) any leakage passing through, a secondary geomembrane liner was placed beneath the underdrain system, currently recommended for hazardous waste landfills. Underdrain system contains layer of granular materials with perforated PCV collection pipes with diameter of 6 mm. In case of the basin No., to collect and outflow landfill leakage only one drainage layer was installed above the geomembrane liner. The main source of leachate generation in the landfill bottom is rain and snowfall, which cause infiltration of water into the landfilled chemical wastes. Determination of the amount of water infiltrating a landfill wastes can be made from the hydrological balance, paying attention to precipitation, surface run-off, evapotranspiration and changes in moisture content of the chemical wastes. The major environmental concern associated with the landfill of chemical wastes is related to discharge of leachate into the environment and groundwater. Climate conditions for the area of the Chemical Plant studied are given in Tables and. TABLE. Number of days with precipitation (normal values) Average number of days With precipitation. mm. mm. mm with snowfall. mm Months Jan. Feb. March Apr May June July Aug. Sept Oct. Nov. Dec.. 8.. 9.,6,9, 8,.8.. 6..6 8..8.8.9.5...8 8.,5 -... -... -. 8.. -.6 9....6 8....9 9..5 6.9 Year 6..6. 5. Geoenvironmental impact assessment of a landfill for solid chemical wastes 5
TABELE. Month and year average of evaporation potential in mm Months Year Jan. Feb. March Apr. May June July Aug. Sept. Oct. Nov. Dec.. *.. 55. 9.**.8.. 55.9 9..9. 558.9 * Min year value; ** Max year value Subsurface conditions At the site discussed in this paper, no uniform stratified deposit was recognized. In general, the cohesionless soil layers consisting primarily of alluwial and fluwioglacial sands overlie cohesive soil deposit which is composed of silty clays and clayey sands. The layer of cohesive soil is one of the essential element in protection of groundwater environment in the landfill vicinity. Moreover, the organic soils consisting peat, mud and gyttja are also discovered in subsoil profile of the landfill. At the western part of the landfill, between basins Nos and fine and medium sand and gravel were recognized directly from the surface of site. Similar conditions were distinguished in southen-east part of the landfill, between the basins Nos and, where so called hydrogeological window was recognized. Sandy soils between the basins Nos and, where observational well - piezometer No. 9 was installed, exist up to the depth of.5 m. The thickness of sandy layer decreases in direction of the southern part of the basins Nos and and in the northern part of the basin No., were directly from the ground surface cohesive soils were deposited. At the northern parts of the basins Nos and, besides Holocene sands, glacial deposit containing fine sands interbedded by clayey sands was also present. The CPT tests (fig. ), documented in the Technical Report from 998, indicate the fine sand deposit containing many thin layers of sandy clay to the depth of.6 m between the basins Nos and, near pezometer No. 9. In the deeper part of subsurface, two layers exist: m layer of clayey sand and.5 m layer of fine sand. Based on the classified ranking for density index of sands, the sandy soils in the basin No. foundation can be considered as medium dense (I D =..65). The values of the CPT cone resistances (fig. ) obtained for sounding near piezometer No. 9 (q c = MPa) indicate that the angles of internal friction are for sands in the range of - 5. The liquidity index (I L ) values of sandy clays discovered in sandy deposits as lenses varies from. to., however for sandy clays beneath sandy layer I L values are in the range from to. (semi solid state). A recognition of the hydraulic conductivity in cohesive soils which might possibly serve as a geologic barrier in the landfill basement was carried out using the BAT system 6 Alojzy Szymański, Zbigniew Lechowicz, Kazimierz Garbulewski
Sandy clay Fine sand Cone resistance, q c [MPa] Sleave friction, f s [MPa] 5 5,,,6,8,,,6,8 Density index, I D,,,6,8 Clayey sand Clayey sand & Sandy clay Depth [m] 5 6 8 9 Depth [m] 5 6 8 9 Depth [m] 5 6 8 9 ID IL IL FIGURE. Results of CPT test near piezometer No. 9,,,6,8 Liquidity index, I L (Torstensson, 98) near piezometer No. 9 at the depth of.5 m in clayey sands. Additionally, BAT tests were conducted in sandy clays, interbedded with clayey and fine-grained sand near piezometer No. at the depth of. m. Test conducted near piezometer No. 9 shows that the clayey sands at.5 m are characterized by the hydraulic conductivity k = -9 m/s (fig. 5). In turn, sandy clays with sandy interbeddings in piezometer No are characterized by the hydraulic conductivity k = -6 m/s (fig. 5). The recognition of the hydraulic properties of cohesive soils indicates that they are low permeable soils. However, due to numerous sandy interbeddings, they may have a considerably high permeability, with the hydraulic conductivity k > -9 m/s. Hydraulic conductivity k [x -9 m/s] Hydraulic conductivity k [x - m/s] a) b) k= -9 m/s 6 8 Time [s] k= k= -6-6 m/s / / 5 5 5 5 Time [s] FIGURE 5. Results of BAT test: a) near piezometer No. 9, depth of.5m b) near piezometer No., depth of.m Geoenvironmental impact assessment of a landfill for solid chemical wastes
Taking into account the geological setting, state of soils in the basement and the groundwater level, it is not possible to exclude the connection between the I and II aquifer horizons. In order to determine the hydrogeological condition, a wider range of analyses is essential. Nevertheless, it should be stated that the hydrogeological system in the basement induces the risk of creating filtration deformations. This fact should be taken into account when designing projects for renovation of the particular landfill appliances. Geochemical tests Based on the monitoring of the water chemistry presented in the available compilations, it is possible to state that in the vicinity of the sulphate wastes landfill, groundwater pollution occurs in the I and II aquifer horizons. Its level is extremely variable. The most polluted is water in piezometer No. 9 between basins No. and, with the content of sulphates reaching above, and of Fe mg/l. The water reaction is very acidic, with ph between.5 and.65. Smaller, but equally high pollution particularly by sulphates occurs in water from piezometers Nos, 5, 5b, and - (SO content between - mg/l). The reaction of water from piezometers Nos 5 and is very acidic (ph ), and neutral in the remaining. Slight sulphate pollution is noted in water from piezometers Nos,, 6b, and, where the content of sulphates reaches 5 mg/l. The water reaction in this case is neutral (ph ca. ), and the content of Fe does not exceed mg/l. Water from the remaining piezometers (Nos, 6, 8 and ) is considered as non-polluted with a natural content of sulphates not exceeding mg/l and of Fe generally not exceeding mg/l. The water reaction in this case is also neutral (ph 6.5.5). Water collected from borehole No. from the depths of.8 and m is also polluted by ferrous sulphate; the content of sulphates in both samples exceeds mg/l and of Fe 5 mg/l. The water reaction at.8 m is strongly acidic (ph.6), and at m slightly acidic (ph 6.). The results of analyses carried on water samples collected in September 998 are presented in Table. The comparison of results presented in Table confirms the high pollution of water in piezometer No. 9, where the Fe content exceeds mg/l at a very acidic reaction. This indicates that this piezometer is directly supplied by the acidified effluents from the neighbouring landfills of ferrous sulphate. Water from piezometer No. 8 (W), similarly as in the monitoring results, does not show pollution by ferrous sulphate. The content of iron and sulphates is within their natural values. Similarly, water from the irrigation ditch B (W), dewatering the area southwards from the landfill does not indicate pollution by ferrous sulphate. In turn, water from the collecting ditch (W) after connection with ditch B and pipeline A indicates high pollution by sulphates. 8 Alojzy Szymański, Zbigniew Lechowicz, Kazimierz Garbulewski
TABLE. Results of water analyses No. of Sampling site ph mg/l sample Fe total - SO. W piezometer No. 9. 9. W ditch B 8.... W piezometer No. 8.. 96.. W collecting ditch 6..8 96. The iron content exceeds here mg/l, and sulphates reach almost mg/l at a slightly acidic reaction (ph 6.). This pollution comes from the ditch of pipeline A dewatering the area northwards from the landfill. The source of this pollution should be unquestionably located and removed, because the collecting ditch carries water towards the Odra River. Conclusions and recommendations The geological condition of the landfill basement indicates that down to - m there is no continuous bed of cohesive deposits acting as a geological barrier for the transfer of pollution from the landfill. This is testified by the pollution of groundwater. The analysis of the chemistry of water in piezometers indicates a high content of sulphates in the groundwater, particularly in the vicinity of basin No., what suggests the lack of tightness of the geomembranes and the ineffective activity of the drainage bed. In this case the work of the system dewatering the area and carrying the pollutants to the Local Sewage Plant is crucial. The dewatering system should secure the groundwater flow towards the landfill site, restricting the transfer of pollution outwards. To secure the proper technical condition of the landfill and its safe exploitation, additional activities should be conducted in order to: installing measurement overflows in the buffer zones of basins Nos and to determine the volume of effluents; work out a project of protecting the neighbouring area against pollutants migration from basin No. comprising a system of underground dewatering (i.e. by wells) of the second aquifer horizon and directing the effluents to the Local Sewage Plant; work out a project of covering the non-exploited ferrous sulphate wasteheaps and carry out the analysis of the stability of all waste-heaps, if required smoothing down the escarpments and their protection against erosion. References Technical Report. (998). Assesment of technical condition of the landfill for solid chemical wastes at Police. Department of Geotechnical Engineering. Warsaw Agricultural University (in Polish). Torstensson, B. A. (98). A new system for Groundwater Monitoring. Groundwater Monitoring Review, -8. Geoenvironmental impact assessment of a landfill for solid chemical wastes 9
Summary In order to characterise the site and determine soil and water parameters in the subsoil of landfill of chemical wastes, field and laboratory investigations were carried out. The field investigation included CPT sounding and BAT testing for identification of the soil profile and the general groundwater flow direction in the aquifer as well as the hydraulic conductivity of the subsoil in the vicinity of the landfill. In laboratory, besides the index properties of soils and groundwater, geochemical analyses including measurements of the contents of the prevailing ions (Fe +, Fe +, SO - ) were performed. The results of investigation allow to conclude that the existing geological barrier on the site is not continuous and therefore a leachate drainage system should be designed to avoid pollution of the surface water and ground water. Author s address: A. Szymański, Z. Lechowicz, K. Garbulewski Department of Geotechnical Engineering Faculty of Engineering and Environmental Science, Warsaw Agricultural University - SGGW -6 Warszawa, 59 Nowoursynowska St. Poland Alojzy Szymański, Zbigniew Lechowicz, Kazimierz Garbulewski