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Section 9 BMP Construction <br /> A. Total Nitrogen Removal Rates <br /> Each BMP receives an assigned TN(total nitrogen)removal rate. <br /> BMP Type TN Removal Rate Appropriate Design Standards <br /> Wet detention ponds 25% NC and MD Design Manuals <br /> Constructed wetlands 40% NC and MD Design Manuals <br /> Open channel practices 30% NC and MD Design Manuals <br /> Riparian buffers 30% Orange Co.Buffer Standards <br /> Vegetated buffer strips with 20% NC and MD Design Manuals <br /> level spreader <br /> Bioretention 25% NC and MD Design Manuals <br /> Sand filters 35% NC and MD Design Manuals <br /> Other BMP's varies subject to Orange County and <br /> NCDENR-DWQ approval <br /> 1. If more than one BMP is installed in series on a development,then the <br /> removal rate shall be determined through SERIAL rather than additive <br /> calculations. <br /> a) Example: <br /> If a wet detention pond discharges through a riparian buffer,then <br /> the TN removal rate would be 47.5%. This number is reached by <br /> assuming that the pond removes 25% of the TN and discharges <br /> 75%into the riparian buffer. The buffer then removes 30%of the <br /> nitrogen discharged by the pond,which is 22.5%. This totals <br /> 47.5%(25%+22.5%=47.5%). <br /> The removal rate is NOT 25%plus 30%. <br /> B. Surety <br /> The financially responsible party may be required to file with Orange County an <br /> improvement security,performance bond or letter of credit in the form of an <br /> escrow account or other instruments satisfactory to the County attorney in the <br /> amount deemed sufficient by the County to cover all costs of repairing or <br /> installing the required Permanent BMP's according to requirements of this <br /> Ordinance, and the approved Stormwater Management Plans. The amount of such <br /> surety requirement shall be determined by the County. Such surety shall be valid <br /> until the work is completed in accordance with the Stormwater Management Plan <br /> and until same is released by the County.Applicable surety shall be forfeited <br /> upon violation of this Ordinance and shall be used to establish protective cover on <br /> the site,to control the velocity of runoff, and/or prevent off-site nitrogen export. <br /> Any monies in excess of the cost of providing protective measures shall be <br /> refunded to the applicant. Surety shall be released when the County has certified <br /> that the requirements of this Ordinance has been met. Surety amounts will be <br /> 27 <br />