Application of integral pumping tests to investigate the influence of a losing stream on groundwater quality

Abstract. Losing streams that are influenced by wastewater treatment plant effluents and combined sewer overflows (CSOs) can be a source of groundwater contamination. Released micropollutants such as pharmaceuticals, endocrine disrupters and other ecotoxicologically relevant substances as well as inorganic wastewater constituents can reach the groundwater, where they may deteriorate groundwater quality. This paper presents a method to quantify exfiltration mass flow rates per stream length unit M_ex of wastewater constituents from losing streams by the operation of integral pumping tests (IPTs) up- and downstream of a target section. Due to the large sampled water volume during IPTs the results are more reliable than those from conventional point sampling. We applied the method at a test site in Leipzig (Germany). Wastewater constituents K⁺ and NO₃⁻ showed M_ex values of 1241 to 4315 and 749 to 924 mg m_stream⁻¹ d⁻¹, respectively, while Cl⁻ (16.8 to 47.3 g m_stream⁻¹ d⁻¹) and SO₄²⁻ (20.3 to 32.2 g m_stream⁻¹ d⁻¹) revealed the highest observed M_ex values at the test site. The micropollutants caffeine and technical-nonylphenol were dominated by elimination processes in the groundwater between upstream and downstream wells. Additional concentration measurements in the stream and a connected sewer at the test site were performed to identify relevant processes that influence the concentrations at the IPT wells.