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calculate solids removal efficiency.The relative removal efficiency analyzed using standard method "Gradation ASTM 0-422 at each operating rate is added to produce a net annual pollutant with Hydrometer'by a certified laboratory. UF Sediment is a removal efficiency estimate. mixture of three different U.S. Silica Sand products referred as: "Sil-Ca Sil 106", "#1 DRY"and"20/40 Oil Frac". Particle Probabalistic Rational Method size distribution analysis shows that the UF Sediment has a very Ihe Probabalistic Rational Method is a sizing program CON I ECH fine gradation (d50 = 20 to 30 gm)covering a wide size range developed to estimate a net annual sediment load reduction for (uniform coefficient Cu averaged at 10.6). In comparison with a particular CDS model based on site size, site runoff coefficient, the hypothetical TSS gradation specified in the NJDEP(New Jersey regional rainfall intensity distribution, and anticipated pollutant Department of Environmental Protection)and'MCAT(New Jersey characteristics. Corporation for Advanced Technology)protocol for lab testing. the UF Sediment covers a similar range of particle size but with a The Probabilistic rational method is an extension of the rational finer d50(d50 for NIDEP is approximately 50 pm) (NJDEP, 2003). method used to estimate peak discharge rates generated by The OK-110 silica sand is a commercial product of U.S. Silica storm events of varying statistical return frequencies(i.e.: 2 year Sand, The particle size distribution analysis of this material,also storm event). Under this method,an adjustment factor is used included in Figure 1, shows that 99.9%of the OK-110 sand is to adjust the runoff coefficient estimated for the 10-year event, finer than 250 microns,with a mean particle size(d50)of 106 correlating a known hydrologic parameter with the target storm microns. The PSDs for the test material are shown in Figure 1. vent. The rainfall intensities vary depending on the return frequency of the storm event under consideration,In general, these two frequency dependent parameters increase as the return 0.0 - Seeirrient("ma) frequency increases while the drainage area remains constant. BOO O110( ) -- :1 • These intensities,along with the total drainage area and runoff coefficient for each specific site;are translated into flow rates using the Rational Method. Since most sites are relatively small and highly impervious,the Rational Method is appropriate. Based • on the runoff flow rates calculated for each intensity, operating rates within a proposed CDS are determined. Performance efficiency curve on defined sediment PSDs is applied to calculate tads removal efficiency. The relative removal efficiency at each 1 10 100 10(X) operating rate is added to produce a net annual pollutant Pankla Sto(Pm) removal efficiency estimate. Treatment Flow Rate Figure 1. Particle size distributions for the test materials, as The inlet throat area is sized to ensure that the WOO passes compared to the NJCAT/NJDEP theoretical distribution. through the separation chamber at a water surface elevation Tests were conducted to quantify the CDS unit(1.1 cfs(31.3-b/s) equal to the crest of the diversion weir.The diversion weir design capacity)performance at various flow rates, ranging from bypasses excessive flows around the separation chamber,thus 1%up to 125%of the design capacity of the unit, using the helping to prevent re-suspension or re-entrainment of previously 2400 micron screen. All tests were conducted with controlled captured particles. influent concentrations approximately 200 mg/L. Effluent Hydraulic Capacity samples were taken at equal time intervals across the entire duration of each test run. These samples were then processed CDS hydraulic capacity is determined by the length and height with a Dekaport Cone sample spliffer to obtain representative of the diversion weir and by the maximum allowable head in sub-samples for Suspended Sediment Concentration(SSC—ASTM The system.Typical configurations allow hydraulic capacities of Standard Method D3977-97)and particle size distribution up to ten times the treatment flow rate.As needed,the crest of analysis. the diversion weir may be lowered and the inlet throat may be widened to increase the capacity of the system at a given water Results and Modeling surface elevation.The unit is designed to meet project specific hydraulics. Based on the testing data from the University of Florida, a performance model was developed for the CDS system. A Performance regression analysis was used to develop a fitting curve for the scattered data points at various design flow rates. This model, Full-Scale Laboratory Test Results which demonstrated good agreement with the laboratory data, A full-scale CDS unit(Model CDS2020-5B)was tested at the can then be used to predict COS system performance with facility of University of Florida, Gainesville,FL This full-scale CDS respect to SSC removal for any particle size gradation assuming unit was evaluated under controlled laboratory conditions of sandy-silt type of inorganic components of SSC. Figure 2 pumped influent and the controlled addition of sediment. shows CDS predictive performance for two typical particle size Two different gradations of silica sand material(UF Sediment gradations(NJCAT gradation and OK-110 sand), &OK-110)were used in the CDS performance evaluation. The particle size distributions(P50)of the test materials were 3