11We couple current findings of pesticides in surface and groundwater to the history of pesticide usage, 12 focusing on the potential contribution of legacy pesticides to the predicted ecotoxicological impact on 13 benthic macroinvertebrates in headwater streams. Results suggest that groundwater, in addition to 14 precipitation and surface runoff, is an important source of pesticides (particularly legacy herbicides) 15 entering surface water. In addition to current-use active ingredients, legacy pesticides, metabolites and 16 impurities are important for explaining the estimated total toxicity attributable to pesticides. Sediment-17 bound insecticides were identified as the primary source for predicted ecotoxicity. Our results support 18 recent studies indicating that highly sorbing chemicals contribute and even drive impacts on aquatic 19 ecosystems. They further indicate that groundwater contaminated by legacy and contemporary 20 pesticides may impact adjoining streams. Stream observations of soluble and sediment-bound 21 pesticides are valuable for understanding the long-term fate of pesticides in aquifers, and should be 22 included in stream monitoring programs. 23Capsule: Legacy pesticides, particularly sediment-bound insecticides were identified as the primary 24 source for predicted ecotoxicity impacting benthic macroinvertebrates in headwater streams. 25 2

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This paper presents a novel modeling analysis of a 40-year-long dataset to examine the impact of urbanization, with widespread stormwater infiltration, on groundwater levels and the water balance of a watershed. A dataset on the hydrologic impact of urbanization with extensive stormwater infiltration is not widely available, and is important because many municipalities are considering infiltration as an alternative to traditional stormwater systems. This study analyzes groundwater level observations from an urban catchment located in Perth, Western Australia. The groundwater observation data cover approximately a 40-year-long period where land use changes (particularly due to urbanization) occurred; moreover, the monitored area contains both undeveloped and urbanized areas where stormwater infiltration is common practice via soakwells (shallow vertical infiltration wells). The data is analyzed using a distributed and dynamic hydrological model to simulate the groundwater response. The model explicitly couples a soakwell model with a groundwater model so that the performance of the soakwells is reduced by the increase of groundwater levels. The groundwater observation data is used to setup, calibrate and validate a coupled MIKE SHE-MIKE URBAN groundwater model and the model is used to quantify the extent of groundwater rise as a result of the urbanization process. The modeled urbanization processes included the irrigation of new established private and public gardens, the reduction of evapotranspiration due to a decrease in green areas, and the development of artificial stormwater infiltration. The study demonstrates that urbanization with stormwater infiltration affects the whole catchment water balance, increasing recharge and decreasing evapotranspiration. These changes lead to a rise in the groundwater table and an increase in the probability of groundwater seepage above terrain. Highlights  Monitoring data and model used to analyze the hydrologic impact of urbanization  Groundwater observations used to calibrate a model of urban stormwater infiltration  Local stormwater infiltration increases groundwater levels throughout a catchment  Urbanization reduces evapotranspiration from shallow aquifers  Urbanization alters the water balance and can lead to increased groundwater levels View publication stats View publication stats

16Infiltration trenches are widely used in stormwater management, but their capacity decreases when 17 installed in areas with shallow groundwater where infiltration is limited by groundwater drainage. 18Here the hydrological performance of single infiltration trenches in areas with shallow water tables

Contaminated sites pose a significant threat to groundwater resources. The resources that can be allocated by water regulators for site investigation and cleanup are limited compared to the large number of contaminated sites. Numerical transport models of individual sites require large amounts of data and are labor intensive to set up, and thus they are likely to be too expensive to be useful in the management of thousands of contaminated sites. Therefore, simple tools based on analytical solutions of contaminant transport models are widely used to assess (at an early stage) whether a site might pose a threat to groundwater. We present a tool consisting of five different models, representing common geological settings, contaminant pathways, and transport processes. The tool employs a simplified approach for preliminary, conservative, fast and inexpensive estimation of the contamination levels of aquifers. This is useful for risk assessment applications or to select and prioritize the sites, which should be targeted for further investigation. The tool is based on steady-state semi-analytical models simulating different contaminant transport scenarios from the source to downstream groundwater, and includes both unsaturated and saturated transport processes. The models combine existing analytical solutions from the literature for vertical (from the source to the top of the aquifer) and horizontal (within the aquifer) transport. The effect of net recharge causing a downward migration and an increase of vertical dispersion and dilution of the plume is also considered. Finally, we illustrate the application of the tool for a preliminary assessment of two contaminated sites in Denmark and compare the model results with field data. The comparison shows that a first preliminary assessment with conservative, and often non-site specific parameter selection, is qualitatively consistent with broad trends in observations and provides a conservative estimate of contamination.