222 W MARINE VIEW DR 2016-01-01 MF Import

TERNATIVES FOR WqTER OUALITY i af design settling velocity, which is from Q x 3600 �'o •age—discharge relationship for the cun ends on the diffetence between the in� rate is baud on a specific rainfall vo�m d characteristics. if average precipihl : overflow rate and detention time wi� :ause the mean is greater than the me� rtal impact on fishing bed areas requu n diameter be removed from stortnw�i ea is 240 acres with a runoff coefficient ) ft deep.'1't�e rainfall intensity associat 0.4 in./h, (Data for intensiry are given ographic areas in the United States.) e settling velocity is 0.00019 ft/s. 3,560 ft2Jacres)(1 ft/12 in.)(1 h/3600 utflow rate equals runoff rate: s/h) g 152,632 ft= or 3.5 acres !.0 acre-ft. With this volume, check ons 7.6 and 7.7. 609,840 ft' 3600(29) ' S.84 h 0.68 ft/h = 0.00019 ft/s ; with faster rates (0.00019 ft/s) 90`1u 7.8 REMOVAL OF DISSOLVED CC>JTAMINANTS IN STORMWATER 237 The flow rate through a pond is rarely mnstant znd usually follows a hdrograph form. Also, the size/weight composition of particles vary. Thus dctention time, storm efficiencies, and overflow rate vary. 7.6 REMOVAL OF DISSOLVED CONTAMINANTS IN STORMWATER Some organics and metals are dissolved in solution but can be removed by �dsorption. Adsorption is the process whereby an adsorbate (some organics �nd metals) moves from thc solution phase to the surface of an adsorbent, nc�rc it is held by attractive forces. These forces of attraction may be ph>sical, chemical, electrical, or a combination of the three. Some soils and arbon are excellent for adsorption. Soils high in silt content may remove �wne impurities. Heavy metals from highway runoff were greatly attentuated m the soils and most heavy metals in stormwater ponds were associated with �Ae bottom sediments (Yousi ` 1984). Mazimum contact with soils was wggested, which leads to a sign using swales, selected soil filtration material, or activared carbon. !her altematives for removino dissolved cdemicals in stormwater are the aadition of a chemical to induce coagulation, �nd biological uptake. 7.6.1 Activated Cerbon Commercial carbons can be prepared from a variety of raw materials, mcluding wood, lignite, coal, bor.e, petroleum, and nut shells. After prepara• tion, the carbons are termed activated carbon and in a granular (orm are alled granular activated carbon. Activated carbons are carbonaceous materi- ds that are subjected to selective oxidation to produce a highly porous suucture. The high porosiry and surface area gives activated carbon its �dwrptive properties. In wacer treatment activated carbon is used to remove comp�unds that ause objectionablc taste, odor, or color. Recently, suspect catcinogens have bean partly removed. In industrial wastewater and stormwater treatment it is mainly used to adsurb to�tic, organic compounds, and metals. Three of the major considerations in the application of activated carbon ue the form o( the activated carbon, the carbon capaciry, and the rate of �dsorption. The capacity and rate of adsorption are in8uenced by the nature �nd concentration of the activated carbon, and nature and concentration of �� impurities present, the nature of the sofvent, and the environmental and aPerating conditions. The equilibrium adsorptive capacity may be detertnined from simple �solhermal batch tests. Various dosages of acticated carbon are added to different containers of the stormwater to be treared, and the amount of organics removed calculated by the expression X = (Co — C�)V (7.10)