Stormwater May 2012 : Page 12
Surface Drains for Sediment Basins x PVC skimmer floats on the surface, releasing the cleanest water x Drains from the basin’s SURFACE instead of the bottom x Improves basin performance x Simple, automatic, gravity operation x Works in basins with risers or sediment traps with spillway F aircloth Skimmer® Patent #5,820,751 x Replaces perforated risers and stone outlets as the basin’s drain x Convenient for using a detention basin as a temporary sediment basin during construction x 8 sizes available x Inlet orifice easily adjusted for drawdown requirements Sizes, flow rates, prices, illustrations, instructions and SIZING CALCULATOR online at www.FairclothSkimmer.com J W Faircloth & Son Inc. Hillsborough, NC 27278 (919) 732-1244 (919) 732-1266 Fax Offering A Proven Solution to Stormwater Runoff for Over 20 Years ECO-OPTILOC ® ECO-PRIORA ® ECO-STONE ® Sustainable, Durable, Beautiful and Economical. UNI ECO-STONE ® FAMILY OF PERMEABLE INTERLOCKING CONCRETE PAVERS • Manages runoff through on-site infiltration -accommodates a variety of stormwater management objectives • Can save money by combining parking AND detention in one cost-effective system • Allows better land-use planning, especially in high-density areas and reduces impacts on combined storm/sewer systems for cost savings • Mitigates runoff volumes and peak flows, reduces pollutants, addresses water quality/quantity • EPA-recommended BMP and qualifies for LEED ® and other green building accreditation • Superior durability under traffic loading -withstands turning movements without surface degredation or raveling, can be installed in any season, and can be used immediately • Call 1-800-872-1864 or visit www.uni-groupusa.org for our free Lockpave Pro software ECOLOC ® are about 0.39, and 0.15, respective-ly, for the discount rate of 10%. Present value: • Initial cost = $125,000 • Constant stream of maintenance costs = 8.51 x $3,000 = $25,530 • Periodic costs = 0.39 x $10,000 + 0.15 x $10,000 = $5,400 • Total = $155,930 The analysis shows that the effect of future periodic costs is modest, again because of the dramatic ef-fect of the discount rate. If the dis-count rate is taken as 5%, the effect of future periodic costs is much more signifi cant. In the case above, the present value of the periodic costs becomes about $12,200. Still, in the example shown, the fu-ture cost of $30,000 is relatively mod-est in present value and may have a modest impact on the decision. But again, the regulator conduct-ing such an analysis must take into consideration that the future periodic cost will be very real, in present val-ue so to speak, when it is required, which may profoundly affect the owner’s willingness to do the mainte-nance. How does the regulator take this into consideration? Perhaps the regulator could re-duce the discount rate. It could be argued that since in the mind of the owner there is no value in put-ting the money into some invest-ment as viewed by the economist, the discount rate should only refl ect infl ation. Given uncertainties, the analysis can consider different values for the useful life of the facility and different discount rates to ascertain if the out-come is sensitive to judgments with either input. Example of Calculating Annualized Cost Analysis An alternative method is to calculate the annualized cost. To make this calculation, the engineer annualizes the initial cost—that is, spreads that cost over the selected facility life. Added to this annualized initial cost are the annual maintenance costs. Again, the analysis can be done for a system with a constant annual cost or one that also has periodic addi-UNI-GROUP U.S.A. MANUFACTURING PERMEABLE PAVERS SINCE 1989 12 May 2012 www.stormh2o.com