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Storm Drainage Credits Policy cont. <br />2. Volume of pond below outlet elevation. <br />b. When treatment facility not a pond, applicant to <br />furnish sufficient documentation to ascertain the <br />effectiveness of the facilitiy in removing suspended <br />solids. <br />3. Calculation procedure for wet ponds: <br />a. Divide site into areas draining to each outlet or <br />facility. <br />b. Calculate the average annual runoff for each area <br />using the following equations; <br />Dr=P (.75 TMf.15}-5:234 (.25-.1875 TM} <br />where Dr=annual runoff depth <br />P=annual rainfall=29 inches <br />TM=$ improved, expressed as a decimal. <br />c. Calculate annual runoff volume (V annual} = DR X <br />12 <br />area acreage. <br />d. Calculate or verify pond volume- in acre-feet below <br />outlet elevation. <br />e. Calculate, capacity-inflow ration (CTR) <br />CTR=pond volume~V annual <br />f. Read sediment removal efficiency from Brune's Trap <br />Efficiency Curve. (See policy) <br />g. Calculate total site efficiency by proportioning the <br />efficiency of each area, and adding together. <br />h. Calculate credit: <br />Credit=site efficiency~2 X RGII value X current <br />rate. <br />4. Exceptions <br />a. Off-site water drains to treatment area-- <br />Tgnore effects of off-site water in calculating <br />pond efficiency. <br />b. Parcel shares ponding facility. <br />Tf parcel has water normally ponded on site, <br />calculate volume of pond on that site below <br />outfall. Then calculate credit per normal <br />procedure. <br />Other Credits: <br />Where, in the opinion of the staff, the above procedures do <br />not result in an appropriate storm drainage charge, the Public <br />Works Director has the authority to make adjustments consistant <br />with the intent of the storm drainage utility. <br />