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31 4 UXc ASO SES£??VCM MANAaSMEJn’. VCLUMS » <br />I <br />PHOSPHORUS REMOVAL BY URBAN RUNOFF DETENTION BASINS <br />V/illiam W.-Walker, Jr. <br />Environmental Engineer <br />Concord, Massachusetts <br />ABSTRACT <br />An •mpineai mods< prBvieualy ammiaomd for prodictiaQ <br />pnespnorut rotonOen in rooorvoin lo Mtod againit M <br />ufOon loKB/ettomion pond dmtM tot Dotomion pond <br />cnfnm Ooviopod undor tho EPA't Nooomwdt <br />Urton Ajnoff Progrmm (NUBP) iro ovmlu«od ytinp tno <br />modol. For tommor proeipiuoon and njneir quatity typi­ <br />cal ef St Paul. MinnaaoUk a baain doaipnod aooording to <br />NUAP entana ia aatimatad to hova a tong-tarm-avoraQa <br />pnetpnorua ramoval atfibancy of paroant For a <br />Qrvan loading ragima. pnoapnorua ramovai ia shown to <br />Pa mora tantitva to pond daptn than to aurtaea araa. <br />Spacifie datjgn faaturaa for anhanang phoaphonja <br />rtmovaJ (daapaning, promeong infiltration, promoong <br />plug flow, and chamicai traatmant) ara diaeuaaad. Tha <br />mathodoiogy can Oa uaad to avaluata wat datanoon <br />pond dasign entana m othar ragtont. with aupsttution of <br />appropnata practpitauon artd runoff quality cnaractana- <br />tica. <br />INTRODUCTION <br />Caus*—effect relationships linking urban watershed <br />development to lake and reseniroif eutrophication <br />are well esublished. Urban watersheds typically ex-. <br />port 5 to 20 times as much phosphonjs per unS area i <br />per year, as compared with undeveloped waters <br />sheds In a given region (Reckhow et al. 1980; <br />Athayde et al. 1S83: Dennis. 1985). Summaries of <br />urban runoff data collected under the ERA'S Nation­ <br />wide Urban Runoff Program (NURP) indicate mean _ <br />concentrations of 420 ppb total phosphorus and 150 <br />ppb dissolved phosphorus (Athavde et aL 1983). In <br />^rr.ntrast lakes with total Phosphorus concentrations <br />exceeding 20-30 cDb rnay expenence nuisangg <br />algal growths (Vcllenweider. 1976). NURP con ­ <br />cluded that “lakes for which the contributions of <br />urban runoff are significant in relation to other non­ <br />point sources (even in the absence of point source <br />discharges) are indicated to be highly susceptible to <br />eutrophication and that urban runoff controls may <br />be warranted in such situations" (Athayde et al. <br />1982). <br />A relationship between urban land use and phos­ <br />phorus export for watersheds in the Minneapolis/St. <br />Paul area is shown in Figure 1 (Walker. 198Sa). In­ <br />creases In phosphorus export associated with urban <br />watershed development primarily reflect increases in <br />impervious area and surface runoff. Runoff tends to <br />have much highar concentrations of total and dis­ <br />saved phosphorus compared with base flows that <br />are fBtered through the sofl column before reaching <br />stream chann els or lakes. SpeeflSe urban sources <br />(lawn.Wtlizera. leaf faU. pets) and s^eambank <br />sroaion isaifliln(J from higner peak flows also con- <br />tributt to urban phosphorus loadings. <br />Physical, economic, and Institutional constraints <br />make eontral of nonpoint phosphonjs export from <br />watersheds i difficult problem. While the con ­ <br />cept of "source control* is attractive, the sources are <br />generally too dlvarse to permit control of a major <br />fraction of the total loading by targeting one or more <br />specific components. Devices and management <br />practices such as catch basins and street sweeping <br />are generally irWfective at controlling the export of <br />fine particulates and soluble nutrients which have <br />the greatest poterttial for stimulating lake eutrophica- <br />tioa Performance monitoring conducted urxjer <br />NURP (Athayde et al. 1983; U.S. Environ. Prot. <br />Agency. 19a . has shown that detention ponds, <br />which intercept, store, and treat runoff before releas­ <br />ing It to receiving streams or lakes, can be designed <br />to provide significant removals of many urban runoff <br />poHutarUa. inctuding phosphorus. <br />This paper compiles arid analyzes data on phos­ <br />phorus removal by runoff detention basins and <br />urban lakes reported in the literature. It describes <br />the basin design criteria for suspended solids <br />removal developed under NURP. An empirical <br />model for predicting phosphorus removal efficiency <br />as a function of watershed characteristics, basin <br />morphometry, arxl dimatologic (actors is described <br />and tested. The model is employed to evaluate the <br />NURP design criteria from a phosphorus removal <br />perspective under Minnesota dimatologic condi- <br />tjons. Specific design features which may enhance <br />phosphorus removal are discussed. <br />NURP DESIGN CRITERIA FOR <br />SUSPENDED SOUDS REMOVAL <br />Athayde et al. (1983) eonduded that wet detention <br />basins, in which permanent water pools are main­ <br />tained. are potentiaily effective for reducing loadings <br />of suspended solids, heavy metals, arxj nutrients <br />I