Stable water isotopes as a tool for assessing groundwater infiltration in sewage networks in cold climate conditions

Abstract Effective identification and quantification of groundwater (GW) infiltration into sewage collection networks represents an important step towards sustainable urban water management. In many countries, including northern regions, sewage networks are aging to the point where renovation is needed. This study focused on the utilization of stable water isotopes as tracer substances for GW infiltration detection. The main objectives were to investigate the validity of the method for quantifying GW infiltration in cold climate conditions and to test the robustness of this method under assumed low GW infiltration rates. In general, the stable water isotopes (δ¹⁸O) produced reliable results regarding origin identification and quantification of GW infiltration rates in winter conditions (continuous below zero temperatures and snow accumulation during preceding months). The 1.6‰ distinction between the δ¹⁸O isotope composition signals of the two water sources (drinking water from river and groundwater) in the studied network was sufficient to allow source separation. However, a larger distinction would reduce the uncertainties connected to GW-fraction identification in situations where low GW infiltration rates (<8%) are expected. Due to the climate conditions (no surface water inflow), GW infiltration to the network branch monitored represented the totality of I/I (infiltration/surface inflow) flows and was estimated to reach a maximum daily rate of 6.5%. This being substantially lower than the 29% yearly average I/I rate of ca 29% reported for the city’s network. Overall, our study tested the stable water isotope method for GW infiltration detection in sewage networks successfully and proved the suitability of this method for network assessment in cold climate conditions. Isotope sampling could be part of frequent monitoring campaigns revealing potential infiltration and, consequently, the need for renovation

Long-term results of a prospective randomized trial comparing tension-free vaginal tape versus transobturator tape in stress urinary incontinence

Abstract Introduction and hypothesis: This study was aimed at investigating the long-term effectiveness of minimally invasive mid-urethral sling (MUS) surgery and at comparing the outcomes between retropubic (tension-free vaginal tape, TVT) and transobturator tape (TOT) methods in the treatment of stress urinary incontinence (SUI) and mixed urinary incontinence (MUI) with a predominant stress component in a long-term follow-up of a randomized controlled trial. Methods: This work is a long-term follow-up study of a previous prospective randomized trial conducted in the Department of Obstetrics and Gynecology at Oulu University Hospital between January 2004 and November 2006. The original 100 patients were randomized into the TVT (n=50) or TOT (n=50) group. The median follow-up time was 16 years, and the subjective outcomes were evaluated using internationally standardized and validated questionnaires. Results: Long-term follow-up data were obtained from 34 TVT patients and 38 TOT patients. At 16 years after MUS surgery, the UISS significantly decreased from a preoperative score in the TVT (11.88 vs 5.00, p<0.001) and TOT (11.05 vs 4.95, p<0.001) groups, showing a good long-term success of the MUS surgery in both groups. In comparing the TVT and TOT procedures, the subjective cure rates did not differ significantly between the study groups in long-term follow-up according to validated questionnaires. Conclusion: Midurethral sling surgery had good long-term outcomes in the treatment of SUI and MUI with a predominant stress component. The subjective outcomes of the TVT and TOT procedures were similar after a 16-year follow-up