STORM WATER QUALITY IN THE CASCINA SCALA (PAVIA, ITALY) EXPERIMENTAL CATCHMENT

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1 New Trends in Water and Environmental Engineering for Safety and Life: Ecocompatible Solutions for Aquatic Environments Capri (Italy), June, 00 STORM WATER QUALITY IN THE CASCINA SCALA (PAVIA, ITALY) EXPERIMENTAL CATCHMENT C. Ciaponi*, M. Mutti**, S. Papiri*** * Dipartimento di Ingegneria Idraulica, Università degli Studi di Pavia, Via Ferrata,, 700 Pavia, Italy, Tel (+9) 0, Fax (+9) 09, ciaponi@unipv.it ** Dipartimento di Ingegneria Idraulica, Università degli Studi di Pavia, Via Ferrata,, 700 Pavia, Italy Tel (+9) 076, Fax (+9) 09, matteo.mutti@unipv.it *** Dipartimento di Ingegneria Idraulica, Università degli Studi di Pavia, Via Ferrata,, 700 Pavia, Italy Tel (+9) 0, Fax (+9) 09, papiri@unipv.it KEYWORDS: experimental catchment, storm water, water quality SUMMARY This paper aims at presenting the first results of an experimental research taking place in the Cascina Scala (Pavia, Italy) experimental catchment. The purpose of the research consists in leading to a better knowledge of the phenomena ruling the pollutant dynamics during storm water runoff from urban areas. The results of two experimental campaigns, concerning both quantity and quality aspects of storm water discharges during meteorological events, have been reported. Quality analyses have been carried out for each of the 6 collected samples, thus making available the values of the following constituents: specific conductivity, COD, BOD, suspended solids, settleable solids, total nitrogen, ammonium nitrogen, phosphorus, lead, zinc and hydrocarbons. Moreover, information on the characteristics of dry weather flows in the sewer network has been provided by samples which have been collected at different times during a dry day. Storm Water Quality in the Cascina Scala (Pavia, Italy) Experimental Catchment Page

2 New Trends in Water and Environmental Engineering for Safety and Life: Ecocompatible Solutions for Aquatic Environments Capri (Italy), June, 00 INTRODUCTION Several studies (Weibel et al., 96; De Filippi and Shih, 97; Sartor et al., 97; Wanielista et al., 977; Lindholm and Balmèr, 97; Novotny and Chester, 9; Reinertsen, 9; Berndtsson et al., 990; Bujon and Herremans, 990) have stated that urban storm waters must be considered a major source of pollution for receiving waters due to the presence of both conventional (suspended solids, COD, BOD, NH, PO, etc.) and toxic contaminants (Pb, Cu, Zn, hydrocarbons, etc.). Experimental researches aiming at a better definition of wastewater and rainwater characteristics have been carried out in Italy as well. Nonetheless so far published results (Veltri, 9; La Loggia and Viviani, 99; Artina et al., 997) are scarce and certainly not fully representative of the different climatic, urban, social and economical Italian situations. At the present time, the design and the construction of urban stormwater management systems in Italy are planned according to technical criteria based on the experience of other countries where the meteorological and urban features may be quite different. It is therefore evident that data on sewer system flow rates and waste water quality, under both dry weather and wet weather conditions for the Italian situations, can contribute to a better solution of many technical problems. With these aims, systematic investigations to collect storm water quality data in the Cascina Scala (Pavia, Italy) experimental catchment started in June 000. The first results are presented in this paper. THE EXPERIMENTAL CATCHMENT OF CASCINA SCALA (PAVIA) The Cascina Scala experimental catchment is a residential district situated on the northern outskirts of Pavia. The total contributing area adds up to m. 6% of the total area is impervious (.% roofs and.% streets and paved surfaces) while % of the total area is pervious and not connected to the sewer system. The combined sewerage network has a total length of 0 m; the slope of the sewer pipes ranges between 0.% and.0% with an average value weighted on the length of 0.%. All the sewers are made of standard concrete pipes. Research activities on the hydrologic and hydraulic behaviour of the basin have been started in 99 (Papiri, 99). More details on the physical characteristics of the basin and the drainage system are reported in another paper (Ciaponi and Papiri, 99). The rainfall on the basin is measured with two SIAP tipping bucket rain gauges with a 0. mm accuracy and a UM 70 precipitation sensor. The distance between the two rain gauges is 0 m, therefore the spatial uniformity of the precipitation can be checked and the meteorological volume can be evaluated accurately. Storm water runoff in the final reach of the sewer network is measured using a Venturi flume and a ISCO 0 bubbler flow meter. Temperature and conductivity in the final reach of the sewer network are measured on site with a YSI 0 multiparameter sonde ( measurement every minutes), while storm water Storm Water Quality in the Cascina Scala (Pavia, Italy) Experimental Catchment Page

3 New Trends in Water and Environmental Engineering for Safety and Life: Ecocompatible Solutions for Aquatic Environments Capri (Italy), June, 00 runoff sampling is collected by means of a ISCO 6700 SR refrigerated sampler equipped with bottles. The samples are collected according to programmable enable controls and laboratory analyses are then carried out. EXPERIMENTAL DATA Quantity and quality data concerning the drainage flows in the sewer network during wet weather have been recorded in the period JuneJuly 000 and MarchApril 00. The data collection refers to meteorological events during which 6 samples have been collected and analysed. The main characteristics of the events are reported in Table. The number of samples is strongly variable for each event, since the sampler enable condition has been programmed so as to depend on a fixed minimum water level in the final reach of the sewer network, therefore an adequate number of samples has been gathered only for events with a certain precipitation intensity. In addition, during the first period of the June 000 campaign there have been some problems in programming the sampling sequence, since the equipment had to be regulated. The results of the analyses for each sample are reported in Table and the range and the mean value of the constituents are reported in Table. Aiming at the characterisation of the dry weather flows, in February 00, samples have been collected ( sample every hours), so as to cover a whole day. The results obtained for the analysed samples are reported in Table and the range and the mean value of the constituents are reported in Table. Comparing the values reported in Table and in Table, it can be observed that the fluctuations of the values of suspended solids, COD and BOD during wet weather are more noticeable than during dry weather. The maximum values of the constituents during wet weather are greater than during dry weather. A list of symbols and abbreviations is reported in Table 6. Many attempts have been made to establish correlation relationships between the concentrations of different constituents. Correlation relationships have been searched particularly between suspended solids and the other contaminants, since suspended solids are assumed as a reference parameter in many mathematical models simulating the pollutant dynamics during storm water runoff. Comparing the results of the two sampling campaigns (JuneJuly 000 and MarchApril 00), the connection between the concentration of COD and BOD and the concentration of suspended solids appears to be markedly evident, thus justifying the assumptions made in many simulation models. However, it must be outlined that the correlation relationships are quite different for the samples of the two campaigns. The difference of statistical behaviour for the two series of experimental data can be essentially explained considering the role played by the temperature in the degradation kinetics of the BOD associated to the suspended solids. Storm Water Quality in the Cascina Scala (Pavia, Italy) Experimental Catchment Page

4 New Trends in Water and Environmental Engineering for Safety and Life: Ecocompatible Solutions for Aquatic Environments Capri (Italy), June, 00 The correlation relationships between the other constituents and the importance of the temperature will be extensively analysed in a still unpublished paper. ACKNOWLEDGEMENTS This research has been financed by MIUR 000. Special thanks are due to Paola Boriani for the contribution given to this research while working on her degree s thesis. Table. Characteristics of the events. Event Date Rainfall Rainfall Maximum Measured Number of Dry Time Length Depth Flow Rate Volume Collected day min mm l/s m³ Samples 0/06/ (*) 6 (*). /06/ (*) 6 (*) 0. /06/ /06/ /06/ /06/ /07/ /07/ /07/ /0/ /0/ /0/ /0/ /0/ (*) The value has been evaluated through numerical simulation because the sewer reaches pressure flow conditions. Table. Results of the quality analyses for the samples collected in the combined sewer system during storms. Storm Water Quality in the Cascina Scala (Pavia, Italy) Experimental Catchment Page

5 New Trends in Water and Environmental Engineering for Safety and Life: Ecocompatible Solutions for Aquatic Environments Capri (Italy), June, 00 Sample SC µs/cm COD mg/l BOD mg/l HC mg/l SS mg/l Set S ml/l TN mg/l AN mg/l P mg/l Pb mg/l Zn mg/l EVENT : 0/06/ EVENT : /06/ EVENT : /06/ EVENT : /06/ EVENT : /06/ < Storm Water Quality in the Cascina Scala (Pavia, Italy) Experimental Catchment Page

6 New Trends in Water and Environmental Engineering for Safety and Life: Ecocompatible Solutions for Aquatic Environments Capri (Italy), June, 00 EVENT 6: /06/ EVENT 7: 0/07/ EVENT : 0/07/ Storm Water Quality in the Cascina Scala (Pavia, Italy) Experimental Catchment Page 6

7 New Trends in Water and Environmental Engineering for Safety and Life: Ecocompatible Solutions for Aquatic Environments Capri (Italy), June, 00 EVENT 9: /07/ EVENT 0: /0/ EVENT : 7/0/ Storm Water Quality in the Cascina Scala (Pavia, Italy) Experimental Catchment Page 7

8 New Trends in Water and Environmental Engineering for Safety and Life: Ecocompatible Solutions for Aquatic Environments Capri (Italy), June, < < < < < EVENT : /0/ EVENT : 0/0/ Storm Water Quality in the Cascina Scala (Pavia, Italy) Experimental Catchment Page

9 New Trends in Water and Environmental Engineering for Safety and Life: Ecocompatible Solutions for Aquatic Environments Capri (Italy), June, 00 Storm Water Quality in the Cascina Scala (Pavia, Italy) Experimental Catchment Page EVENT : 0/0/

10 New Trends in Water and Environmental Engineering for Safety and Life: Ecocompatible Solutions for Aquatic Environments Capri (Italy), June, 00 Table. Range and mean values of the quality constituents for the 6 samples collected during storms. Constituent Unit of Mean Minimum Maximum Measure Value Value Value Specific Conductivity µs/cm COD mg/l BOD mg/l 7 Hydrocarbons mg/l Suspended Solids mg/l 0 0 Settleable Solids ml/l Total Nitrogen mg/l.. 6. Ammonium Nitrogen mg/l Phosphorus mg/l Lead mg/l Zinc mg/l Table. Results of the quality analyses for the samples collected during dry weather ( February 00). Hour SC COD BOD HC SS Set S TN AN P Pb Zn µs/cm mg/l mg/l mg/l mg/l ml/l mg/l mg/l mg/l mg/l mg/l < < < Storm Water Quality in the Cascina Scala (Pavia, Italy) Experimental Catchment Page 0

11 New Trends in Water and Environmental Engineering for Safety and Life: Ecocompatible Solutions for Aquatic Environments Capri (Italy), June, 00 Table. Range and mean values of the quality constituents for the samples collected during dry weather. Constituent Unit of Mean Minimum Maximum Measure Value Value Value Specific Conductivity µs/cm COD mg/l 6 07 BOD mg/l 6 70 Hydrocarbons mg/l Suspended Solids mg/l Settleable Solids ml/l.0 < Total Nitrogen mg/l Ammonium Nitrogen mg/l Phosphorus mg/l Lead mg/l Zinc mg/l Table 6. List of symbols and abbreviations. LEGEND SC COD BOD HC SS Set S TN AN P Pb Zn Specific Conductivity Chemical Oxygen Demand Biochemical Oxygen Demand Hydrocarbons Suspended Solids Settleable Solids Total Nitrogen Ammonium Nitrogen Phosphorus Lead Zinc Storm Water Quality in the Cascina Scala (Pavia, Italy) Experimental Catchment Page

12 New Trends in Water and Environmental Engineering for Safety and Life: Ecocompatible Solutions for Aquatic Environments Capri (Italy), June, 00 Figure. Hyetograph, hydrograph and samples for event. Figure. Hyetograph, hydrograph and samples for event. Storm Water Quality in the Cascina Scala (Pavia, Italy) Experimental Catchment Page

14 New Trends in Water and Environmental Engineering for Safety and Life: Ecocompatible Solutions for Aquatic Environments Capri (Italy), June, 00 Figure. Hyetograph, hydrograph and samples for event. Figure 6. Hyetograph, hydrograph and samples for event 6. Storm Water Quality in the Cascina Scala (Pavia, Italy) Experimental Catchment Page

15 New Trends in Water and Environmental Engineering for Safety and Life: Ecocompatible Solutions for Aquatic Environments Capri (Italy), June, 00 Figure 7. Hyetograph, hydrograph and samples for event 7. Figure. Hyetograph, hydrograph and samples for event. Storm Water Quality in the Cascina Scala (Pavia, Italy) Experimental Catchment Page

16 New Trends in Water and Environmental Engineering for Safety and Life: Ecocompatible Solutions for Aquatic Environments Capri (Italy), June, 00 Figure 9. Hyetograph, hydrograph and samples for event 9. Figure 0. Hyetograph, hydrograph and samples for event 0. Storm Water Quality in the Cascina Scala (Pavia, Italy) Experimental Catchment Page 6

17 New Trends in Water and Environmental Engineering for Safety and Life: Ecocompatible Solutions for Aquatic Environments Capri (Italy), June, 00 Figure. Hyetograph, hydrograph and samples for event. Figure. Hyetograph, hydrograph and samples for event. Storm Water Quality in the Cascina Scala (Pavia, Italy) Experimental Catchment Page 7

19 New Trends in Water and Environmental Engineering for Safety and Life: Ecocompatible Solutions for Aquatic Environments Capri (Italy), June, 00 REFERENCES Artina S., Maglionico M., Marinelli A. (997). Le misure di qualità nel bacino urbano Fossolo. Modelli qualiquantitativi del drenaggio urbano, p. 7, Centro Studi Deflussi Urbani, Milan. Berndtsson R., Hogland W., Larson M. (990). Field measurements and mathematical modelling of pollution buildup and pipedeposit washout in combined sewers. Proceedings of the Fifth International Conference on Urban Storm Drainage, Osaka, Japan, p.. Bujon G., Herremans L. (990). FLUPOL Modèle de prévision des débits et des flux polluants en réseaux d assainissement par temps de pluie: calage et validation. La Houille Blanche, n.. Ciaponi C., Papiri S. (99). Bacino di Cascina Scala Codice IT0. Le misure di pioggia e di portata nei bacini sperimentali urbani in Italia, p. 7, Centro Studi Deflussi Urbani, Milan. De Filippi J.A., Shih C.S. (97). Characteristics of separated storm and combined sewer flows. Journal of Water Pollution Control Federation, vol.. La Loggia G., Viviani G. (99). Misure delle caratteristiche di qualità delle acque di pioggia nel bacino di Parco D Orleans. Analisi dei primi risultati. Atti del III Seminario sui Sistemi di Drenaggio Urbano, Ancona, Italy. Lindholm O., Balmér P. (97). Pollution in storm runoff and combined sewer overflows. Proceedings of the First International Conference on Urban Storm Drainage, Southampton, Great Britain, p. 7. Novotny V., Chester G. (9). Handbook of nonpoint pollution: sources and management. Van Nostrand Reinhold Co., New York. Papiri, S. (99). Precipitazioni e deflussi nel bacino urbano sperimentale di Cascina Scala (Pavia). Pubblicazione del Dipartimento di Ingegneria Idraulica e Ambientale, Università di Pavia, n. 66. Veltri P. (9). La qualità delle acque nelle fognature urbane. Tecniche per la difesa dall inquinamento; Atti del Corso di Aggiornamento, p. 79, BIOS, Cosenza. Reinertsen T.R. (9). Quality of stormwater runoff from streets. Proceedings of the First International Conference on Urban Storm Drainage, Southampton, Great Britain, p. 07. Sartor J.D., Boyd G.B., Agardy F.J. (97). Water pollution aspects of street surface contaminants. Journal of Water Pollution Control Federation, vol. 6. Wanielista M.P., Yousef Y.A., McLellon W.M. (977). Nonpoint sources effects on water quality. Journal of Water Pollution Control Federation, vol. 9. Weibel S.R., Anderson R.J., Woodward H.L. (96). Urban land runoff as a factor in stream pollution. Journal of Water Pollution Control Federation, vol. 6. Storm Water Quality in the Cascina Scala (Pavia, Italy) Experimental Catchment Page 9