Stormwater Filtration Performance for the Ecosol Storm Pit (Class 2): Statistical Analysis of Field Data

Abstract

An independent field performance evaluation for a secondary stormwater filtration device, named the Ecosol Strom Pit (Class 2), was performed between May 2017 and July 2019 in an urban catchment in Queensland, Australia. During the testing period, a total of 37 rainfall events were recorded, of which between 15 and 21 events were evaluated as qualifying for the purposes of characterizing the removal efficiency performance of the device. A statistical analysis of the event mean concentrations (EMCs) of the flow streams through the device indicate a statistically significant difference between the influent and effluent streams. A variety of pollutant removal evaluation metrics, including concentration-based and total load-based metrics, were utilized in this study to characterise the efficacy of the device. Two new approaches are proposed for facilitation the analysis: a nonlinear regression approach to more effectively deal with nonlinear patterns in the influent and effluent data and the regression of concentration (ROC), which is an added concentration-based metrics. In summary, the removal efficiencies of the Ecosol Storm Pit (Class 2) were evaluated to be 72–74% for total suspended solids (TSS), 45–50% for total phosphorus (TP), 41–45% for total nitrogen (TN), 27–32% for total heavy metals (THM), 79–85% for total petroleum hydrocarbons (TPH), and 80–88% for total recoverable hydrocarbons (TRH).

Statistical Analysis of Field-Based Stormwater Filtration Performance for the Ecosol Litter Basket

“…The two key criteria for accepting a rainfall event as a qualifying event are based on the hydraulic properties of the run-off (i.e., duration, and the interval between events) and the input pollutant concentration values (i.e., concentrations within an acceptable band) [1]. These are comprehensively discussed in [18].…”

“…The locations of the sampling for influent and effluent streams are shown in Figure 4. The adopted sampling methodology was selected based on the methodology discussed in [18]. Grab samples (a maximum of four samples at 2 min intervals at the start of each event) were used to evaluate event mean concentration (EMC) for total petroleum hydrocarbons (TPH) and total recoverable hydrocarbons (TRH).…”

“…The removal efficiency metrics (suggested by [1]) that are generally used for evaluating the performance of a stormwater filtration device along with regression metrics are comprehensively discussed in [18] and are summarized in Table 1. The results of these two metric categories (efficiency and regression metrics) are presented and will be compared in Section 3.…”

“…As observed in this figure, all data are highly skewed towards the lower concentrations. Overlapping confidence intervals between the influent and effluent box plots indicate that the central tendency of the data may not be significantly different [18]. A significant difference in the central tendency of the influent and effluent streams (with the effluent being the lesser of the two) is a key indicator that the filtration device is effective in reducing pollutant concentrations.…”

“…Regression metrics include the regression of loads (ROL) and the regression of concentrations (ROC), as shown in Table 1 and comprehensively discussed in [18]. The best regression curves, along with their functions ( f (x)) for all pollutants loads, are shown in Figure 8.…”