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From page 56... ... 56 8.1 Methodology Options A variety of methods may be used to assess the efficiency and effectiveness of a given BMP, but it is important to understand the constraints and assumptions of any method before selecting it. For example, many effectiveness models measure efficiency on a storm-by-storm, pollutant-load basis, which assumes that for any given storm, the influent and effluent volumes are equal, and the outflow is directly related to the inflow. Read the entire page →
From page 57... ... 57 an event may vary greatly from the calculated EMC, but use of the EMC ensures that the relative mass of pollutant in a system during a storm is accurately represented (Huber 1993) Read the entire page →
From page 58... ... Parameter Name BMP Category Data Solids, Total Suspended Cu, Dissolved Cu, Total Zn, Dissolved Zn, Total Pb, Dissolved Pb, Total Cd, Dissolved Cd, Total P Total Nitrate Nitrogen, Total Nitrogen, Ammonia Total Nitrogen, Kjeldahl, Total Nitrogen, Total Biofilter Count of Inflow n 17 11 14 11 17 11 17 7 8 18 15 1 12 4 Count of Outflow n 17 11 14 11 17 11 17 7 8 18 15 1 12 4 Detention Basin Count of Inflow n 11 6 12 6 13 6 12 4 7 10 7 6 4 Count of Outflow n 11 6 12 6 13 6 12 4 7 10 7 6 4 Hydrodynamic Device Count of Inflow n 13 6 9 6 11 6 8 4 5 9 2 4 3 1 Count of Outflow n 13 6 9 6 11 6 8 4 5 9 2 4 3 1 Media Filter Count of Inflow n 18 16 18 16 18 16 18 8 9 17 16 8 15 Count of Outflow n 18 16 18 16 18 16 18 8 9 17 16 8 15 Retention Pond Count of Inflow n 21 4 13 4 17 5 16 1 10 20 4 9 12 6 Count of Outflow n 21 4 13 4 17 5 16 1 10 20 4 9 12 6 Wetland Basin Count of Inflow n 12 1 2 2 7 3 6 1 2 13 6 8 6 10 Count of Outflow n 12 1 2 2 7 3 6 1 2 13 6 8 6 10 Source: International BMP Database (http://www.bmpdatabase.org/) April 2004. Read the entire page →
From page 59... ... 59 Generally, there were two primary issues affecting the usability of the data for the International BMP Database. First, several of the studies had sparse data or large sections of absent data for certain water-quality constituents and/or certain monitored runoff events. Read the entire page →
From page 60... ... DUST Marsh System C WC Urban Stormwater Treatment at Coyote Hills Marsh ABAG 1986 7 pH, EC, TDS, TSS, BOD, oil/grease, NH4, NO3, KN, Ortho-P, TP, Cd, Cr, Cu, Pb, Mn, Ni, Zn general urban (Fremont, CA) Yes Yes Yes No Barton Creek Square Shopping Center Pond DB Effects of Runoff Controls on the Quantity and Quality of Urban Runoff at Two Locations in Austin, Texas Welborn and Veenhis 1987 6 COD, BOD, fecal coliform strep, DS (180 degC) Read the entire page →
From page 61... ... 61 Barton Creek Square Shopping Center Pond WQ and discharge data collected immediately upstream and downstream of pond. Manning X System Level Transmitter and Recorder was used at the inflow and outflow stations to measure stage. Read the entire page →
From page 62... ... 62 the Greenville site were evaluated by Brown (2003) , whose study may be consulted for more detail. Read the entire page →
From page 63... ... 63 y = 0.7148x 0 20 40 60 80 100 120 140 160 0 50 100 150 200 EMCin, mg/L EM Co ut , m g/ L 1) Read the entire page →
From page 64... ... 64 be characterized by a frequency distribution, as exemplified by the effluent probability method (EPM) (see Section 8.5.3) Read the entire page →
From page 65... ... 65 statistical tests can be applied, such as the t-test, chi-square test, and analysis of variance. Statistical tests used to compare data sets typically require normality in the data sets, and some also require the data sets to have equal variances. Read the entire page →
From page 66... ... 66 y = 12.452e0.9935x R2 = 0.8969 y = 96.658e1.1569x R2 = 0.9545 1 10 100 1000 -2.00 -1.75 -1.50 -1.25 -1.00 -0.75 -0.50 -0.25 0.00 0.25 0.50 0.75 1.00 1.25 1.50 1.75 2.00 Standard Normal Variate (z) TS S EM C, m g/ L Influent Effluent 25% 50% 75% Figure 8-6. Read the entire page →
From page 67... ... 67 same event) can be shown on scatter diagrams. Read the entire page →
From page 68... ... 68 The notches encompass the 95% confidence interval of the median and provide a nonparametric means of assessing the difference between the centers of multiple distributions. A logarithmic scale was determined to be best suited for plotting most data. Read the entire page →
From page 69... ... 69 data. Hence, box plots are used to concisely compare performance among BMPs in terms of effluent EMCs in the Guidelines Manual, Appendix A Read the entire page →
From page 70... ... 70 As shown in Table 8-7, the hypothesis that the data are normally distributed is confirmed for nitrate influent and effluent EMCs and for TSS influent EMCs. In order to use parametric tests to assess the difference between the means of two samples (influent and effluent) Read the entire page →
From page 71... ... 71 the potential loss of power of parametric tests when distributional requirements are not met. The parametric test employed for the statistical analysis of the log-transformed data is the one-tailed t-test for unequal variance. Read the entire page →
From page 72... ... 72 simulation of BMP quality treatment in SWMM and how this method might be adapted to produce frequency distributions similar to those observed earlier for the U.S. 183 filter strip. Read the entire page →
From page 73... ... 73 impacts (see Section 10.2.3) Read the entire page →
From page 74... ... 74 in a runoff volume equivalent to the storage design volume of a detention basin. The runoff volume for the tributary area is a function of the watershed size and runoff coefficient; the runoff coefficient is a function of the impervious fraction and soil type(s) Read the entire page →
From page 75... ... 75 do not significantly deviate from typical stormwater. Welldesigned treatment systems that incorporate wet pools and wetland vegetation typically exhibit good effluent quality for suspended solids. Read the entire page →
From page 76... ... 76 have been shown to provide considerable reduction in effluent volume (up to 30%) , which may translate into lower total mass loading of TSS downstream. Read the entire page →
From page 77... ... 77 Simulation models also allow one to evaluate a long-term rainfall record to assess how much stormwater is treated by the BMP and how much is bypassed or processed by the BMP at the lower, water-quality design flow rate, and the higher, flood control rate at which higher flows (and resulting short detention times) will result in minimal or ineffective treatment. Read the entire page →

From page 56...

... 56 8.1 Methodology Options A variety of methods may be used to assess the efficiency and effectiveness of a given BMP, but it is important to understand the constraints and assumptions of any method before selecting it. For example, many effectiveness models measure efficiency on a storm-by-storm, pollutant-load basis, which assumes that for any given storm, the influent and effluent volumes are equal, and the outflow is directly related to the inflow.