Sebastian Leschik

Micropollutant Loads in the Urban Water Cycle

The assessment of micropollutants in the urban aquatic environment is a challenging task since both the water balance and the contaminant concentrations are characterized by a pronounced variability in time and space. In this study the water balance of a central European urban drainage catchment is quantified for a period of one year. On the basis of a concentration monitoring of several micropollutants, a contaminant mass balance for the study areas wastewater, surface water, and groundwater is derived. The release of micropollutants from the catchment was mainly driven by the discharge of the wastewater treatment plant. However, combined sewer overflows (CSO) released significant loads of caffeine, bisphenol A, and technical 4-nonylphenol. Since an estimated fraction of 9.9-13.0% of the wastewaters dry weather flow was lost as sewer leakages to the groundwater, considerable loads of bisphenol A and technical 4-nonylphenol were also released by the groundwater pathway. The different temporal dynamics of release loads by CSO as an intermittent source and groundwater as well as treated wastewater as continuous pathways may induce acute as well as chronic effects on the receiving aquatic ecosystem. This study points out the importance of the pollution pathway CSO and groundwater for the contamination assessments of urban water resources.

Investigation of sewer exfiltration using integral pumping tests and wastewater indicators.

Leaky sewers affect urban groundwater by the exfiltration of untreated wastewater. However, the impact of sewer exfiltration on the groundwater is poorly understood. Most studies on sewer exfiltration focus on water exfiltration, but not on the impact on groundwater quality. In this paper we present a new monitoring approach to estimate mass flow rates M(ex) of different wastewater indicators (WWIs) from leaky sewers by applying integral pumping tests (IPTs). The problem of detecting and assessing heterogeneous concentrations in the vicinity of leaky sewers can be overcome with the IPT approach by the investigation of large groundwater volumes up- and downstream of leaky sewers. The increase in concentrations downstream of a leaky sewer section can be used to calculate M(ex) with a numerical groundwater model. The new monitoring approach was first applied using four IPT wells in Leipzig (Germany). Over a pumping period of five days we sampled five inorganic WWIs: B , Cl(-), K+, NO3(-), NH4+ and three xenobiotics: bisphenol-a, caffeine and tonalide. The resulting concentration-time series indicated an influence of wastewater at one IPT well downstream of the leaky sewer. We defined ranges of M(ex) by implementing the uncertainty of chemical analyses. The results showed a M(ex) of 0-10.9 g m(-1) d(-1). The combination of M(ex) with wastewater concentrations from the target sewer yielded an exfiltration rate Q(ex) of 28.0-63.9 Lm(-1)d(-1) for the conservative ion Cl(-). Most non-conservative WWIs showed reduced mass flow rates in the groundwater downstream of the leaky sewer that indicate a mass depletion during their passage from the sewer to the pumping well. Application of the IPT methodology at other field sites is possible. The IPT monitoring approach provides reliable M(ex) values that can help to assess the impact of leaky sewers on groundwater.

Evaluation of xenobiotic impact on urban receiving waters by means of statistical methods

Xenobiotics in urban receiving waters are an emerging problem. A sound knowledge of xenobiotic input, distribution and fate in the aquatic environment is a prerequisite for risk assessments. Methods to assess the impact of xenobiotics on urban receiving waters should address the diverse characteristics of the target compounds and the spatiotemporal variability of concentrations. Here, we present results from a one-year-monitoring program concerning concentrations of pharmaceuticals, additives from personal care products and industrial chemicals in an urban drainage catchment in untreated and treated wastewater, surface water and groundwater. Univariate and multivariate statistical methods were applied to characterize the xenobiotic concentrations. Correlation and principal component analysis revealed a pronounced pattern of xenobiotics in the surface water samples. The concentrations of several xenobiotics were characterized by a negative proportionality to the water temperature. Therefore, seasonal attenuation is assumed to be a major process influencing the measured concentrations. Moreover, dilution of xenobiotics the surface water was found to significantly influence the concentrations. These two processes control more the xenobiotic occurrence in the surface water than the less pronounced concentration pattern in the wastewater sources. For the groundwater samples, we assume that foremost attenuation processes lead to the found differentiation of xenobiotics.

Towards optimal sampling schedules for integral pumping tests

Conventional point sampling may miss plumes in groundwater due to an insufficient density of sampling locations. The integral pumping test (IPT) method overcomes this problem by increasing the sampled volume. One or more wells are pumped for a long duration (several days) and samples are taken during pumping. The obtained concentration-time series are used for the estimation of average aquifer concentrations C(av) and mass flow rates M(CP). Although the IPT method is a well accepted approach for the characterization of contaminated sites, no substantiated guideline for the design of IPT sampling schedules (optimal number of samples and optimal sampling times) is available. This study provides a first step towards optimal IPT sampling schedules by a detailed investigation of 30 high-frequency concentration-time series. Different sampling schedules were tested by modifying the original concentration-time series. The results reveal that the relative error in the C(av) estimation increases with a reduced number of samples and higher variability of the investigated concentration-time series. Maximum errors of up to 22% were observed for sampling schedules with the lowest number of samples of three. The sampling scheme that relies on constant time intervals ∆t between different samples yielded the lowest errors.

Transport and Fate of Xenobiotics in the Urban Water Cycle: Studies in Halle/Saale and Leipzig (Germany)

This chapter on urban water in large population centres like Halle/Saale and Leipzig (Germany) focuses on the source, distribution and transport behaviour of xenobiotics as indicator substances for anthropogenic impacts on urban water systems. The xenobiotics reported here are micropollutants including pharmaceuticals, personal care products (collectively known as PPCPs) and industrial chemicals, which show low concentrations in urban waters. Such chemicals can be endocrine disrupters or are otherwise eco-toxic. The concepts presented herein required a new methodology for assessing the impact of human activities on the urban water system and processes in urban watersheds. To this end, we used different approaches in relation to the hydrogeological and hydrodynamic settings of the cities of Halle and Leipzig. For the Halle urban area, a conceptual flow and transport model was developed based on interaction between the river Saale and groundwater, and mass fluxes were computed, based on water balance calculations. For Leipzig, as a first approach, we established a monitoring program that involved various urban land use types and investigated their influence on the urban water system. Multivariate statistics and integral pumping tests were applied to account for the spatially highly heterogeneous conditions and time-varying concentrations. At both sites, we demonstrated the use of indicators consisting of physico-chemical parameters, ions, isotopes and compound-specific patterns of xenobiotics. The chosen indicators of pH, temperature, electrical conductivity, redox conditions, nitrate, sulphate, chloride, boron, the isotopes of hydrogen, nitrogen, oxygen, sulphur and boron, as well as bisphenol A, carbamazepine, technical 4-nonylphenol (t-nonylphenol), galaxolide, tonalide, and gadolinium, helped to balance urban substance fluxes and assess urban effects on surface water quality. From our current quantification, it is clear that predicting contaminant behaviour in urban areas demands a detailed process understanding which cannot be derived from laboratory experiments or phenomenological analyses at the catchment scale. Through an installation of measuring equipment at the interfaces between the unsaturated and saturated zone as well as between ground- and surface water, in situ contaminant transport and fate can be quantified from the cm- up to the m-range.