Wet-Weather Flow Characterization for the Rock Creek through Monitoring and Modeling

Transcription

1 Wet-Weathe Flow Chaacteization fo the Rock Ceek though Monitoing and Modeling Pogess Repot Pepaed fo DC Wate Resouces Reseach Institute Univesity of the Distict of Columbia Washington DC Pepaed by Padeep K Behea, Ph.D., P.E. and Segun Adebayo, Ph.D. Depatment of Engineeing, Achitectue, & Aeospace Technology School of Engineeing and Applied Sciences Univesity of the Distict of Columbia June 2007

2 Acknowledgement This eseach study would not have possible without the geneous suppot of the following oganizations: DC Wate Resouces Reseach Institute U.S. Geological Suvey though US Depatment of Inteio School of Engineeing and Applied Sciences, UDC 2

3 Table of Contents Intoduction...4 Distict of Columbia Dainage System...5 Chaacteization of Uban Runoff Quality...6 Souces of Pollutants...7 Uban Runoff Quality Constituents...10 Monitoing Runoff Quality at the Rock Ceek...16 Modeling of Uban Stomwate Management...21 Analytical Pobabilistic Stomwate Models...24 Modeling Appoach...28 Example - Development of an Analytical Pobabilistic Model...29 Conclusions...33 Refeences

4 Intoduction In spite of massive public investments in sewage and dainage infastuctue, pollution loading fom wet-weathe flows continues to have significant impacts on eceiving wates. Tends in ubanizations, inceased quantities of uban wet-weathe flows and coesponding incease in pollution loadings dischaged to eceiving wates demand that wet-weathe flow contol systems be planned and engineeed to effect highe levels of wate quality contol. Fo futue investments in dainage infastuctue to be costeffective, decisions in wet-weathe flow contol systems planning must be made within a igoous, compehensive and systematic famewok. Simila to many olde cities in the nation, the sewe system in the Distict of Columbia is compised of both combined and sepaate sewe systems. It has ecognized that these systems contibute significant pollution to the Anacostia and Potomac Rives and Rock Ceek though Combined Sewe Oveflows (CSOs) and Stom Sewe dischages duing wet-weathe (i.e., ainfall and snowmelt) events. These oveflows and associated pollutant loads can advesely impact the quality of the eceiving wates. As pe the Distict of Columbia wate quality standads, the designated use of the Anacostia Rive, Potomac Rive and Rock Ceek is Class A o suitable fo pimay contact eceation. Because the wate quality in the eceiving wates cuently does not meet these standads much of the time, the actual use of the wate body is Class B o suitable fo seconday contact eceation and aquatic enjoyment. As a esult, the Distict law pohibits pimay contact eceation such as swimming in each of the eceiving wates (DC WASA, 2002). To addess these poblems, the Distict of Columbia Wate and Sewe Authoity (WASA) has developed a Long Tem Contol Plan (LTCP) that povides the altenative solutions and thei implementation costs. In ode to suppot LTCP a continuous monitoing and modeling of the wateshed and dainage system is necessay not only to povide technical assessment but also to develop a cost-effective solution. In this egad, a long-tem eseach pogam has been poposed at the Univesity of the Distict of Columbia. The eseach pogam include capacity building fo envionmental eseach such as development of envionmental simulation and modeling laboatoy and wate quality testing laboatoy and student taining in the field of envionmental science and engineeing. As a pat of this pogam, it is envisioned that envisioned that a numbe of wate quality paametes that include suspended solids, nutients, heavy metals and othe toxins, will be monitoed and monitoed data will be used fo the development of models which ultimately suppot in developing effective solutions. The pupose of the poposed study is to collect infomation on the Distict dainage system, chaacteize unoff quality constituents, and field monitoing of unoff quality paametes and development of uban stomwate modeling systems. The modeling of uban stomwate system is developed using analytical pobabilistic appoach. 4

5 Distict of Columbia Dainage System The seweage system of the Distict of Columbia is the esult of both andom gowth and planned development. Stating about 1810, sewe and culvets wee built to dain steets and these scatteed sewes gadually become linked togethe to fom a system intended to cay stom and gound wate (ASCE, 1982). Cuently, the Distict of Columbia sewe system compised of both combined and sepaate sanitay sewes. A combined sewe caies both sanitay sewage and unoff fom wet weathe events (i.e., ainfall and snowmelt). The combined system was built ealy 1900 s exists in the oldest pat of the city and moden pactice is to build sepaate sewes fo sewage and stomwate. Appoximately one-thid of the Distict (12,478 aces) is seved by combined sewes (DCWASA, 2002). In the combined sewe system, sewage fom esidential, institutional and commecial aeas duing dy weathe conditions is conveyed to the Distict of Columbia Wastewate Teatment Plant at the Blue Plains, which is located in the southwesten pat of the Distict on the east bank of Potomac Rive. The Blue Plain teatment plant was put into opeation in At the teatment plant, the wastewate is teated to emoved hamful pollutants befoe being dischaged to the Potomac Rive. Duing wet weathe events, when the capacity of combined sewe is exceeded, the excess flow, which is mixtue of unoff and sewage, is dischaged to the Anacostia and Potomac Rives, Rock Ceek and tibutay wates though the sewe outfalls. The excess flow is called as Combined Sewe Oveflow (CSOs). Thee ae a total of 60 CSO outfalls in the combined sewe system listed in the National Pollutant Dischage Elimination System (NPDES) pemit issued by the Envionmental Potection Agency to WASA. The dischages fom the sepaated stom sewe system geneally diects to the ive systems without any teatments. The CSOs and stomwate dischages known as uban wet weathe flow o uban unoff can advesely impact the quality of the eceiving wates. The pollutants in uban unoff include visible matte, suspended solids, oxygen demanding mateials, nutients, pathogenic micooganisms and toxicants such as heavy metals, pesticides and hydocabons. These pollutants impose consideable physical, chemical and biological stesses on the eceiving wates that affect aquatic life and human health [Field et al., 1998] and impai the designated uses of wate esouces. Typical uban stomwate-elated eceiving wate quality poblems include the degadation of aquatic habitats, degadation in wate quality duing and afte wet weathe events, beach closues, and acceleated ates of eutophication in lakes and estuaies, and themal pollution [WEF, 1998]. The pimay pupose of the LTCP is to contol CSOs such that wate quality standads ae met. In ode to assess the existing condition, WASA conducted study that developed the compute model of combined sewe systems, sepaate stom wate 5

6 systems. The compute models wee calibated based on the histoical data and 9 to 12 months of monitoed data collected in the eceiving wates, combined and sepaated sewe systems. Table 1 pesents annual CSO oveflow pedictions fo existing conditions (WASA, 2002). Table 1: Existing Condition Annual Aveage CSO Oveflow Volume and Oveflows Desciption Anacostia Rive Potomac Rive Rock Ceek Total System CSO Oveflow Volume (million gallons/y) No Phase I Contols (pio to 1991) With Phase I Contol (afte 1991) 2,142 1,485 1, ,254 2,490 Numbe of Oveflow/y No Phase I Contols (pio to 1991) With Phase I Contol (afte 1991) Chaacteization of Uban Runoff Quality Assessments of uban unoff pollution poblems ae aely well pescibed. Stomwate unoff fom uban watesheds contains constituents that can, in some cases, occu with damaging pollutant levels. These situations and the uban aeas that poduce such unoff quality levels need to be identified. While infomation fom the liteatue might be adequate to undestand cetain geneal issues, site-elated data ae often collected and analyzed to chaacteize the unoff pollution poblem. Uban stomwate management fom a unoff quality pespective is geneally elated to the magnitude and fequency of pollutant mass dischages fom combined sewe oveflows (CSOs), stomwate dischages and unoff-induced sanitay sewe oveflows to eceiving wates. These dischages ae intemittent in natue and often difficult to quantify. Nonetheless, documentation and chaacteization of site-specific unoff quality ae impotant in developing effective stomwate management pogams fo the uban aeas. Such a chaacteization includes assessment of the existing unoff pollution condition and its contibution to local wate quality poblems, and is followed by an analysis of futue pollution conditions and the development of management options. In addition, chaacteization is equied by many juisdictions in the U.S. fo compliance of new egulatoy equiements (WEF, 1998). Theefoe, most Noth Ameican cities ae investing significant esouces in assembling and analyzing infomation on uban unoff in an effot to develop plans to meet the new egulatoy equiements. 6

7 Runoff quality data collection and analysis ae the most expensive component of an uban stomwate management study. Thus, thee is a need to maximize the use of existing data so that the need fo new unoff quality data can be minimized. In such cases, the infomation deived fom the existing data is elatively moe impotant. In many instances, the availability of continuous unoff quality data (e.g., on an event basis) is not long enough to pefom easonable statistical evaluations. Theefoe, wheneve a continuous data set of longe peiod is available, the statistical chaacteistics should be obtained which is useful fo modeling and management of uban unoff pollution. To assess and addess uban unoff pollution poblems, the chaacteization of unoff quality is necessay. The tem chaacteization efes to the evaluation of statistical chaacteistics of measuable pollution causing vaiables (i.e., pollutant concentations). Fom the quality pespective, uban unoff pollution is pimaily influenced by the type of sewe system (i.e., sepaated stomwate and combined sewe systems). Accodingly, the chaacteization of unoff quality developed in this chapte is based on types of catchments, sepaated and combined systems. Souces of Pollutants Numeous studies on uban unoff quality conducted in diffeent pats of the wold ove ecent decades have poved that unoff caies elatively high concentations of a vaiety of pollutants. These pollutants oiginate fom divese souces, both natual and anthopogenic, categoized by vaious bounday inputs, pollution pocesses and human activities that occu on the uban catchment. In addition, pollutant-geneating activities ae consideed to be moe pevalent on impevious aeas than on pevious aeas. The undestanding of pollution souces is impotant fo both the pediction and the contol of pollutant loads. Common souces of uban unoff pollution include dy and wet atmospheic deposition; accumulation of steet efuse including litte, steet dit, and oganic esidues, vehicula taffic emissions; vegetation; accidental spills; uban aea eosion; and oad deicing chemicals. One of the pincipal souces of pollutant accumulation in uban aeas is dy and wet atmospheic deposition, which is consideed as a bounday input caused by local o distant ai pollution souces. In most cities, the deposition ate of atmospheic paticulate matte is highe in the congested downtown coe and industial aeas than ates in esidential and sububan aeas. Wet and dy fallout ates ange fom 7 to moe than 30 tonnes/km 2 -month (Novotny and Olem, 1994). Dy deposition esults fom the tubulent and gavitational tansfe of pollutants fom the ai to the undelying suface, unaccompanied by atmospheic pecipitation (Hicks, 1997). A study of the chemical composition of paticulate matte and aeosols ove Edmonton, Albeta (Klemm and Gey, 1982) concluded that industial emissions and tanspot ae the majo souces of dy deposition fom the atmosphee. Atmospheic paticulate 7

8 matte is composed of aeosols and lage paticles in the fom of dust, soot, ash, fibe and pollen. The Edmonton study epoted that the wate soluble potion of collected uban ai samples of total suspended paticulates contained pollutants such as lead, nickel, chomium, cadmium, zinc, sulfate, nitate and ammonium. The oigin of atmospheic pollutants is attibuted to souces such as constuction sites, paved and unpaved aeas, oads, landfills, tailing piles, industial souces, fuel combustion fom stationay and tanspotation souces, waste incineation, etc. A study (Hilbon and Still, 1990) of U.S. data indicated that the amounts and souces of toxic ai pollutants can vay geogaphically fom city to city and fom neighbohood to neighbohood. Moeove, toxic ai pollution is stongly influenced by local widespead souces, such as moto vehicles, wood stoves, combustion of oil and gas, metallugical industies, chemical poduction and manufactuing, gasoline maketing, solvent use and waste oil disposal. Wet deposition is a esult of cloud pocesses that scavenge pollutants fom the ai at cloud altitudes and deposit them in falling ain, snow, and so on (Hicks, 1997). Studies on pollutant mass loading in pecipitation and unoff have concluded that most of the atmospheic contaminants ae washed out duing the ealy stages of a ainfall event (Randall et al., 1982). Futhemoe, the washout of atmospheic pollutants by ainfall doplets is effective and may contibute to a fist-flush effect, indicating that pollutant concentations in the ealie pat of a pecipitation event ae highe than in the latte ainfall (Novotny et al., 1985). Uban ainfall is geneally acidic in natue with ph values less than 5, which can cause damage to stuctues such as pavements, sewes and buildings. The atmospheic deposition of nitogen compounds, tace metals, and oganic compounds has caused substantial effects on wate quality in the Chespeake Bay aea (Hicks, 1997). An example of typical atmospheic loadings in uban catchments is pesented in Table 1 in the fom of epoted mean values. Table 1: Atmospheic loading in uban catchments Pollutant Total suspended solids Total Deposition Rate (g / m 2 -y) Wet Deposition Concentation (mg/l) 5 70 Snowmelt Concentation (mg/l) Contibution to Runoff (%) Chemical oxygen demand Sulfates Phosphous (sic) Nitate-nitogen Lead Zinc Souce: Afte Ellis (1986) 8

9 Steet efuse accumulation is chaacteized by locally geneated paticles of vaious sizes on the steet sufaces. Typically, the faction of steet efuse passing a 3mm (1/8- inch) sieve is efeed as dust and dit. In geneal, most of the accumulation of steet efuse occus within one mete of the cub, and hence the accumulation is often expessed as mass pe unit of cub length. Paticle sizes geate than dust and dit ae consideed as litte deposits. The geneal litte deposits in uban aeas include debis, solid wastes deposited on sufaces, pape and plastic poducts, building mateials, vegetation, dead animals, and animal exceta, so on. The steet dit paticles include disintegated pats of lage litte paticles, pavement deteioation paticles, soil paticles and small oganisms. Vegetation inputs including fallen leaves, seeds, gass clippings, and othe vegetation esidues contibute significant quantities of dust and dit in uban aeas. The ate of vegetation input inceases substantially duing the fall season depending on the density of vegetation. A study conducted in Etobicoke, in the Geate Toonto Aea (GTA), showed that a significant amount of oganic load oiginates fom autumn leaves in an uban aea (James and Boegowda, 1986). The pesence of phosphous in unoff is commonly attibuted to its leaching fom vegetation in addition to plant fetilizes. Fo example, the potential phosphous content of tee leaves and seeds is epoted to ange fom 1.6 to 11 mg/g (Walle and Hat, 1986). Vehicula taffic constitutes a majo souce of pollutants in uban aeas. It contibutes to solids (including fine paticles) and many chemicals including heavy metals, polycyclic aomatic hydocabons (PAHs) and deicing salts (Thomson et al., 1997). These pollutants oiginate fom vehicle exhaust pipe emissions, vehicle opeation, tie wea, solids caied on ties and vehicle bodies, and the abasion and coosion of highway stuctues. The moe impotant souces of PAHs ae fom oil leakage of vehicle cankcases and exhaust pipe emissions. Futhemoe, pavement conditions also have an effect on pollutant loads. Sato et al. (1974), epoted that steets paved with asphalt could have a loading about 80% highe than steets paved with concete. A study (Bebee et al., 1999) on the chaacteization of highway unoff in the Nethelands indicated that the concentation of pollutants in unoff fom impevious asphalt is significantly highe than in unoff fom pevious asphalt. In snow-belt aeas, deicing salts and sand ae applied to oad sufaces and side walks to povide safe diving and walking conditions duing the winte season. The applied salt potentially inceases the chloide content of the unoff. As an example, the citywide salt application ates in Halifax, Nova Scotia contibute to an annual aveage chloide loading in unoff at the ode of 3,000 kg/ha-y. The median chloide concentation in winte gab samples of unoff inceased to as much as 786 mg/l, while the mean summe concentation in unoff is epoted at 14 mg/l, which is highe than the concentation of 4.6 mg/l ecoded in total atmospheic deposition at Halifax (Walle and Hat, 1986). 9

10 Pevious uban aeas ae geneally consideed to be well potected by vegetation and they contibute pollutants such as pesticides and hebicides duing lage ainfall events. Howeve, eosion of soil fom constuction sites, vacant lands and sububan agicultual lands may contibute significant amount of solids and sediments, which futhe degade the unoff quality. Uban Runoff Quality Constituents The quality constituents of typical concen in uban unoff ae visible matte, suspended solids, oxygen-demanding mateials, nutients, pathogenic micooganisms, and toxicants such as heavy metals, pesticides, and petoleum hydocabons (Field et al., 1998). These constituents can cause substantial impacts in tems of physical, chemical and biological stesses on eceiving wates, esulting in ecological and envionmental imbalance (Ellis and Hvitved-Jacobsen, 1996; Field et al., 1998; and Masalek, 1998). Moeove, these impacts depend on the chaacteistics of both the catchment poducing such dischages (in tems of unoff quantity and quality) and those of eceiving wates. Hence, to potect the eceiving wate, the actual impacts should be evaluated in tems of specific chaacteistics of each site, including physical habitat altenation (e.g., change in mophology), wate quality changes (e.g., dissolved oxygen depletion, and eutophication), sediment and toxic pollutant impacts, impacts on biological communities, and gound wate impacts (Ellis and Hvitved-Jacobsen, 1996). To assess these impacts of stomwate dischages on eceiving wate quality, it is necessay to undestand the effects of classes of pollutants independently as well as the combined effects of vaious pollutants. In the fome case, the effects ae undestood to a easonable extent; howeve, in the latte case, the combined effect of the entie ange of diffeent classes of pollutants is not well undestood. To estoe, maintain and enhance the physical, chemical and biological quality of eceiving wates, the pemise of uban unoff quality contol analysis should focus on undestanding the souces, types of pollutants fom stomwate dischages and combined sewe oveflows, thei potential effects on eceiving wate bodies, and thei contol altenatives. The souces o oigins of vaious pollutants found in uban unoff ae descibed in the pevious section, while the following section focuses on the types of pollutants and thei effect on eceiving wate bodies. Solids The most common pollutants in stomwate ae oganic and inoganic solids in the fom of paticulate o colloidal matte. These solids ae eithe eoded fom pevious sufaces o washed off the paved sufaces by stomwate. In addition, dainage systems supply a significant amount of solids, which ae accumulated on the bottom of sewes, and fom 10

11 the slime gowth on the walls of the sewes duing dy peiods (Novotny and Olem, 1994). The solids content in unoff is measued as total solids, suspended solids, dissolved solids, and volatile solids as well as by tubidity [definitions of which may be found in Standad Methods, (Clescei, et al., 1998)]. Suspended solids cause a numbe of diect and indiect envionmental impacts such as inceased tubidity, abasion of fish gills and othe sensitive tissues, eduction of visibility, tanspot of pollutants, loss of ipaian vegetation with the concomitant loss of shade and efuge, decease in sunlight penetation (intefeence with photosynthesis), and degadation of spawning aeas. Suspended solids usually cay consideable quantities of othe pollutants sobed to thei sufaces (Randall et al., 1986). Pollutants that ae believed to have a paticulaly high affinity of adsoption on suspended solids include phosphous, metals, and petoleum based oganics. The effective means of emoving suspended solids fom stomwate ae sedimentation and othe foms of physical sepaation. In addition, the emoval of suspended solids fom stomwate may significantly impove the wate quality because of simultaneous emoval of the othe pollutants with suspended solids. Typically, combined sewe oveflows contain a highe suspended solids concentation than stomwate dischages (Moffa, 1990). Nutients Uban unoff may contain significant concentations of nitogen, phosphous and cabon compounds which acceleate the nutient enichment and eutophication of eceiving wates. These substances ae essential fo the gowth of aquatic plants and ae egaded as biostimulants. The souce of nutients is attibuted to leaching of vegetation, agicultual fetilizes in unoff and municipal wastewate dischages. Nitogen in the fom of ammonia and nitates and phosphous occuing as othophosphates ae eadily available fo plant gowth, possibly leading to algal blooms and excessive macophytic gowth and causing depletion of dissolved oxygen upon death and decay. Common measues of nutients ae total nitogen, nitates, ammonia, total Kjeldahl nitogen (TKN), total phosphous, total oganic cabon, and indiectly, alga mass and chloophyll a. (Wanielista and Yousef, 1993). Oxygen Demanding Matte Sufficient levels of dissolved oxygen (DO) in the wate column ae necessay to maintain aeobic conditions to suppot aquatic life. The influx of stomwate containing oganic and othe oxidizable matte may exet substantial oxygen demand on the wate column impaiing the wate quality by depleting DO level. These impacts ae estimated eithe by diect measuement of DO o by the indiect measues of biochemical oxygen demand (BOD), chemical oxygen demand (COD) and total oganic cabon (TOC). Typically CSOs contain highe levels of oxygen demanding substances elative to stom dischages. 11

12 Micobiological Pollutants Both CSOs and stomwate dischages can be significant souces of micobiological pollution in eceiving wates. Micobiological pollutants ae typically descibed by oganism counts pe unit volume of wate and include indicato bacteia, such as Escheichia coli, fecal colifoms, fecal steptococci and specific pathogens such as Shigella, Salmonella and Clostidium. These pollutants ente the dainage system fom the washoff of animal feces and oganic matte fom catchment sufaces. Bacteia may also ente the dainage system though illegal sanitay sewe connections. Concentations of indicato bacteia, such as E. coli and fecal colifoms, in CSOs and stomwate ae often found in magnitudes well exceeding eceational wate quality guidelines. Thus, eceational beaches in uban aeas ae fequently closed duing and immediately afte ainfall events because of fecal bacteia contamination caused by stomwate and CSOs. By definition, pathogenic bacteia and viuses may seiously affect human health. The emoval of such micobiological pollutants is achieved pimaily though the pocesses of biological decay, ultaviolet adiation and atificial disinfection whee pacticed. Toxic Constituents and Pioity Pollutants Studies in the United States, Canada and Euope indicate that heavy metals ae the most pevalent toxic contaminant found in uban unoff (U.S. EPA, 1983a, Masalek et al., 1997). Commonly found heavy metals ae asenic, cadmium, coppe, ion, mecuy, lead, selenium and zinc. The pimay souces of heavy metals ae taffic-elated activities and atmospheic fall out. Unlike some oganic compounds, heavy metals ae not degaded in the envionment and ae toxic when pesent beyond a theshold concentation. Deteioation of eceiving wate quality is also caused by the pesence of elevated levels of toxic constituents in uban unoff commonly known as pioity pollutants. The pioity pollutants ae a goup of 129 toxic chemicals o classes of chemicals identified as substances of seious concen in the Clean Wate Act of U.S. (Testiep et al., 1986). The pollutants fall into ten goups: pesticides, metals and inoganic, PCBs (polychloinated biphenyls), halogeneted aliphatics, ethes, monocyclic aomatics, phenols and ceosols, phthalate estes, PAHs, nitosamines and nitogen-containing compounds. Compehensive investigations of toxic constituents and pioity pollutants wee conducted unde the U.S. Nationwide Uban Runoff Pogam (NURP) (U.S. EPA, 1983a). Futhe studies conducted in the U.S. and Canada indicate that these pioity pollutants ae fequently detected in highway unoff (Sansalone and Buchbege, 1997; Masalek et al., 1997). The impacts of pioity pollutants ae evaluated on the basis of toxicity effects. Toxic pollutants have been chaacteized by acute o chonic effects on the envionment (U.S. EPA, 1983b; Haemoes, 1988). Acute effects ae chaacteized by elatively high 12

13 concentations of pollutants within a elatively shot time causing immediate physiological impacts such as in the ingestion of heavy metal laden wate, while chonic effects ae chaacteized by the cumulative impact of gadual exposue to elatively low concentations of pollutants that accumulate in the tissues of oganisms ove long peiods of time. To evaluate the ecological impacts of these constituents in stomwate, wate quality standads ae defined in tems of thei degee of toxicity. The pemissible fequency and duation of exposue to conventional and pioity pollutants (wate quality standads) as suggested by the U.S. EPA ae (Novotny, 1997): Acute toxicity citeia: 1-h aveage concentation (essentially a daily gab sample) not to be exceeded moe than once in thee yeas on an aveage. Chonic toxicity citeia: 4-day aveage concentation, not to be exceeded moe than once in thee yeas on an aveage. It is geneally ecognized that a lage pecentage of heavy metals and toxic contaminants have a high affinity fo the suspended sediments pesent in unoff. This association is fotuitous in tems of contol and teatment of unoff since it is elatively easy to sepaate suspended solids and the pollutants attached to them. Othe Paametes In listing the unoff quality paametes of concen, physical paametes such as goss solids, tubidity, tempeatue, ph and electical conductivity ae also consideed. The pesence of dispesed and floatable mateials along the shoes of beaches o embankments deteioates the aesthetic value of wate bodies. Tempeatue is an impotant paamete because uban sufaces may incease the tempeatue of unoff by as much as 100C compaed to unoff fom undeveloped aeas (Masalek, 1998). This themal enichment can influence the physiological pocesses of aquatic oganisms such that oiginal cold-wate fisheies may become wam-wate fisheies ove time. The incease in tempeatue also deceases the wate s capacity to dissolve oxygen. In addition, the ise in tempeatue inceases the ate at which nutients attached to solid paticles ae conveted into eadily available soluble foms (Hall, 1984). Uban unoff also conveys lage amounts of chloides oiginating fom oad salting duing winte. The pimay physical envionmental effects of elevated chloides ae high dischages of dissolved solids and the establishment of density gadients in eceiving wates, especially lakes (Walle and Hat, 1986). The pesence and amount of chloide ions is measued by the electical conductivity of the sample. 13

14 Chaacteistics of Runoff Quality Constituents The analysis of uban stomwate quality poblems equies an undestanding of the chaacteistics of unoff pollutants and the natue of eceiving wates. As descibed in the pevious section, diffeent types of pollutants have diffeent types of impacts on eceiving wates, and they opeate on diffeent tempoal and spatial scales. The time scale of the pollutant effects on the eceiving wate is influenced by the chaacteistics of vaious pollutants. The time scale of concen anges fom a few hous to a few yeas. Figue 1 illustates the time scale of diffeent categoies of unoff pollutants. Fo example, wate-bone pathogens may die away elatively quickly in eceiving wates; thus, the time scale of inteest in this case is elatively shot (e.g., on the ode of seveal hous o days). In this case, inteest would lie in the low fequency oveflow events, causing high concentations of pathogens. Shot-tem effects ae associated with bacteia, biodegadable oganic matte and hydaulic effects. In contast, plant nutients such as phosphous influence long-tem effects elated to eutophication, causing inteest in elatively long time scales (e.g., on the ode of seveal yeas). Inteest would lie moe in the aveage annual mass dischages to the eceive. Long-tem effects tend to be associated with suspended solids, nutients and heavy metals. In still othe cases, such as cetain type of hazadous contaminants, both the long and shot time scales would be of concen. Typically, the shot time scale poblem of acute toxicity and long time scale poblem of toxic contaminant accumulation and chonic toxicity would cause inteest in both the low fequency, high concentation oveflow events and the aveage annual mass dischages to the eceiving wates. 14

15 SECONDS Flotables Bacteia Dissolved Oxygen Suspended Solids Nutients Dissolved Solids ACUTE TOXIC EFFECTS LONG TERM TOXIC EFFECTS HOUR DAY WEEK MONTH SEASON YEAR DECADE Figue 1: Time scale effects of unoff quality constituents (afte U.S. EPA, 1979) The spatial scale anges fom the localized eceiving wate to wates that ae hundeds of kilometes fom the souces. Fo instance, bacteial contamination geneally occus in a localized aea (e.g., beach closues), while some toxic substances such as pesticides, pesistent oganics and heavy metals, which ae viewed on the longe time scale, tend to be pesistent (i.e., they do not eadily decay in envionment) ove hunded of miles (U.S. EPA, 1979). The elevancy of chaacteistics of pollutants found in uban unoff is an impotant consideation in eceiving wate analysis. To effectively addess the wate quality poblems aising fom uban unoff, the quantitative aspects of unoff quality, in paticula the acquisition of data and analysis of 15

16 data is impotant. Recent advances in wate quantity and quality monitoing technologies gadually povide cost-effective means of collecting lage amounts of infomation fo complex wate quality poblems. Technological advances in wate quality data analysis, howeve, have lagged, paticulaly fo conveting aw data into infomation, which can suppot decision-making on a egula basis (Hughes and Kummle, 1998). Theefoe, intelligent decisions about the unoff quality management can be made easie when the appopiate data analysis methodologies ae developed to deive infomation in suitable foms that would be useful. Monitoing Runoff Quality at the Rock Ceek Monitoing and modeling ae two essential components of implementing CSO Contol policy (EPA, 1999). A planned development and implementation of a monitoing and modeling effot will suppot the selection and implementation of cost-effective CSO contols and an assessment of thei impovements on eceiving wate quality. Rock Ceek, a tibutay of the Potomac Rive is pimaily an uban steam. The wateshed fo the ceek coves pat of Montgomey County (appoximately 60 mi 2 ) and pat of the Distict of Columbia (appoximately 16 mi 2 ). The total length of the Rock Ceek (in Mayland and Washington DC) is appoximately 33 mi of meandeing steam. The Ceek flows fom its souce nea Laytonsville, Mayland to the Potomac Rive in Washington DC. Wate quality in Rock Ceek is impotant to biotic life in and nea the ceek, and in the Potomac Rive Basin and the Chesapeake Bay (USGS, 2000). The wate quality of the Rock Ceek has been affected by ubanization and agicultual gowth in the wateshed. In the long-tem monitoing pogam, it is envisioned that a numbe of wate quality paametes that include suspended solids, nutients, heavy metals and othe toxins, will be monitoed. Total Suspended Solids (TSS) has been consideed as an indicato pollutant and typically used fo stomwate modeling. It is also envisioned that TSS will be continuously monitoed at vaious epesentative sites of Anacostia and Potomac Rives and Rock Ceek and the monitoed data will be used fo the development of integated dainage system and eceiving wate system models. The monitoed data will be analyzed in the envionmental laboatoy of the Univesity. The scope of this pesent eseach is limited to field monitoing of Dissolved Oxygen at seveal locations within the Rock Ceek neae to Univesity of the Distict of Columbia. The data pesented in this epot wee collected fom thee locations along the Rock Ceek in the fall and sping season of The monitoing was conducted in Novembe 2006 to epesent fall season and in Mach 2007 to epesent sping season. Figues 2 pesents the location of thee sampling stations along the Rock Ceek within the Washing DC. 16

17 Figue 2: Locations of DO sampling stations Dissolved Oxygen was measued at the thee locations using a calibated Oakton RS232 Dissolved Oxygen mete. Two undegaduate engineeing student intens wee tained to take the field measuements. The thee locations include at the upsteam of Militay Road bidge cossing, neae to police head quate and thid location is 0.5 miles south of Militay Road bidge cossing. Figues 2 to 4 pesents the location of thee sampling stations. 17

18 Figue 2: Station 1 Located nea to Police Head Quate Figue 3: Station 2 Located upsteam of a Militay Road bidge cossing 18

19 Figue 4: Station 3 Located south of Militay Road bidge cossing Table 2 though 4 pesent the measued DO data fo thee locations fo fall and sping seasons. Table 2 - Station 1: Nea Police Head Quate Season Date Tempeatue Dissolved Oxygen ( o C) (mg/l) 11/1/ Fall 11/13/ /15/ /20/ /27/ /1/ /5/ /6/ /9/ /12/ /13/ Sping 3/15/ /19/ /20/ /23/ /26/ /27/ /29/

20 Table 2 - Station 2: Upsteam of a Militay Road bidge cossing Season Fall Sping Date Tempeatue Dissolved Oxygen ( o C) (mg/l) 11/1/ /13/ /20/ /27/ /1/ /5/ /6/ /9/ /12/ /13/ /15/ /19/ /20/ /23/ /26/ /27/ /29/ Table 3 - Station 1: 0.5 mile south of Militay Road bidge cossing Season Date Tempeatue ( o C) Fall Sping Dissolved Oxygen (mg/l) 11/1/ /13/ /20/ /27/ /1/ /5/ /6/ /9/ /12/ /13/ /15/ /19/ /20/ /23/ /26/ /27/ /29/

21 The aveage tempeatue fo the fall 2006 was 11.4 o C and fo the sping 2007 was 12 o C. Table 5 pesents the mean and standad deviation of DO at the thee locations. Table 5: Mean and Standad Deviation of DO at thee locations Season Station 1 Station 2 Station 3 Mean Std. Dev. Mean Std. Dev. Mean Std. Dev. Fall Sping The measuement of Dissolved Oxygen at the Rock Ceek eveals that thee is no evidence of low dissolved oxygen poblems aound the measued locations. The steam is natually aeated by tubulence as it flows ove the iegula channel bottom. It is feeflowing steam which povides elatively shot esidence time to wet weathe pollution. Modeling of Uban Stomwate Management The analysis of uban catchment systems is peequisite to the planning and design of stomwate management, which not only allows the assessment of existing conditions but also helps to undestand the behavio of the system unde vaious design conditions. In addition, the analysis with economic functions assists in detemining appopiate costeffective contol measues. Uban catchment systems ae subjected to ainfall input - a andom phenomenon. Theefoe, the hydologic, hydaulic and pollutant pocesses that goven the system ae complex in natue. The system vaiables and pocess paametes also vay tempoally and spatially and, as a esult, the analysis of such systems is geneally pefomed on simplified epesentations based on vaious assumptions that may o may not sufficiently epesent the undelying pocesses fo planning puposes. Often these epesentations use mathematical elationships intended to imitate the petinent pocesses. Because these epesentations ae not pefect, veification and validation is equied fo thei egula use in simila situations. Veification is the adjustment of model paametes to eplicate the measued condition and validation is confimation of veification fo a wide ange of conditions. The model can be used to undestand the system behavio (i.e., how the model output changes ealistically as input to the model is vaied). A ange of stomwate models, fom simple to compehensive, exists fo the analysis of uban catchment systems. Models that povide geate levels of accuacy ae complex, compehensive models and include a heavy computational buden. Theefoe, while selecting a model fo the analysis, a balance must be stuck between the accuacy and simplicity of the model, wheein this balance is dependent on the analysis objectives of the equied model (Adams and Papa, 2000). 21

22 As is noted, the models ae based on simplifications, and cannot povide a pecise epesentation of physical eality unde all conditions; howeve, they should povide easonable solutions fo the intended poblems. Theefoe, the system analyst should be awae of the assumptions on which the model is fomulated and the limitations of the modeling execise. Beyond these limitations, models povide the analyst an economical advantage ove thei pototypes because models ende pefomance analysis of the system fo the full ange of conditions to which the pototype might be subjected. In uban stomwate quantity and quality analysis, only monitoing theoetically can povide the ideal long-tem infomation equied fo planning and design of systems (Nix et al., 1983). But, being cost pohibitive, monitoing ove a ealistic limited time fame cannot diectly povide, a pioi, the infomation needed to chaacteize the long-tem behavio of a wide ange of futue designs. Theefoe, it is essential to have popely fomulated and validated models which can pedict system behavio fo analysis and design. Uban stomwate models ae developed in a mathematically desciptive mode to simulate the system o in a pedictive mode to evaluate contol pefomance befoe implementing the expensive measues in the field. These models and thei mathematical equations - ae defined by: System input such as ainfall and tempeatue; System output such as unoff volume, infiltation, unoff ate and pollutant load; System paametes of the uban catchment system such as unoff coefficient, depession stoage, pollutant buildup and washoff coefficients; The contol o decision vaiables such as design stoage volumes and outflow ates. Models descibing stomwate management systems ae classified in many ways, including the level of detail they povide, the type of appoach they adopt and the time fame of analysis. Geneally, based on thei analysis timefame, models fall into two categoies: (i) event-based models and (ii) continuous simulation models. Each type of model has advantages and disadvantages. Taditionally, unoff quantity contol poblems have been dominant in the uban stomwate management, and the design of quantity contol systems was accomplished with event-based models. In this appoach, an analysis is pefomed to select a design stom of a specified duation and fequency fom a histoical ainfall ecod o fom synthetically geneated ainfall pattens, and used to estimate unoff peaks and volumes. A commonly used event-based model is, fo instance, the ational method. This appoach ignoes the effects of successive events on the analysis; theefoe, it is not 22

23 suitable fo estimating the aveage long-tem pefomance of the system. This appoach is not suitable fo unoff quality analysis, which is stongly influenced by moe fequent and smalle ainfall events and which equies long-tem analysis. In addition, a fundamental assumption of assigning a unique fequency to a natual hydologic event and assigning this same fequency to both input and system output ae questionable (Adams and Papa, 2000). Although event-based appoaches have been employed in uban unoff contol planning fo many yeas, the cuent diection is towads the application of continuous simulation and pobabilistic models fo the long-tem pefomance analysis of uban systems. Continuous simulation modeling is cuently consideed to be the most sophisticated appoach to stomwate modeling. It is a fom of deteministic modeling of the physical system that not only consides the popeties of a stom but also evaluates the impacts of closely-spaced successive stoms. This appoach is consideed continuous because it uses long-tem ainfall ecods as inputs to poduce a continuous time seies of output vaiables and continuously updates soil moistue etc. The statistics of the time seies of output vaiables ae then used fo pedicting the pefomance of the system. Continuous simulation can povide additional infomation such as the quality of unoff and pollutant loads as they can tack the antecedent conditions, peceding pollutant buildup and stoage conditions. Howeve, these models ae both data computation, and esouce intensive and equie elaboate calibations. They ae usually pefeed in the detailed design analysis phase of engineeing studies. In tems of igo of the modeling appoach, some ae less intensive, such as STORM (U.S. Amy Cops of Enginees, 1974) and the HSPF (Hydologic Simulation Pogam- FORTRAN) (Johanson et al., 1984). The moe igoous and compehensive continuous simulation models include the U.S. EPA s Stom Wate Management Model, SWMM (Hube and Dickinson, 1988), and the Quantity-Quality Simulato, o QQS, (Geige and Dosch, 1980). An altenative to continuous simulation is to model the system by the analytical pobabilistic modeling appoach. The basic pemise fo both the continuous simulation and analytical modeling appoach emains same - long-tem meteoology is the input to the model. Continuous simulation attempts to pedict the system esponse of the output vaiable (i.e., dependent vaiable) time seies in the sequence that would occu fom the input time seies (histoical o synthetically deived ainfall), and post-pocessed statistical analysis povides the aveage, and/o long-tem pefomance of an output vaiable. The analytical pobabilistic appoach fits pobability distibutions to the ainfall chaacteistics (e.g., ainfall event volume, duations, intensity and inteevent times) detemined fom the same ainfall ecod othewise used fo continuous simulation. These fitted pobability distibution functions (PDFs) ae used to epesent the independent vaiables and the paametes of the PDFs constitute the input to the model. The deteministic functional elationships (e.g., hydologic and hydaulic pocesses) between the independent and dependent vaiables of continuous simulation models 23

24 constitute the tansfomation function of the analytical pobabilistic models, albeit, in a simplified manne. Using deived pobability distibution theoy (Benjamin and Conell, 1970), the PDFs of the dependent vaiables ae deived fom those of the independent vaiables and the tansfomation functions. Often closed-fom solutions of the dependent vaiable PDFs, which depict the system pefomance measues in tems of the independent vaiables, ae obtained. The elative modeling ageement between the analytical and the continuous simulation appoaches may be attibuted to how well the PDFs of the input vaiables ae hypothesized and the tansfomation functions ae simplified and othe things. Since the PDFs of meteoological inputs ae deived fom the statistical analysis of longtem ainfall ecods, the mathematically deived PDFs of system outputs eflect the long-tem pefomance of the dainage system unde analysis (Papa et al., 1998). This method is intended to appoximate continuous simulation modeling and is ecommended fo peliminay planning and design because of its computational efficiency. Futhemoe, the closed-fom mathematical equations can be easily incopoated into an optimization famewok fo system analysis. A ecognized limitation of this appoach is the simplified epesentation of uban dainage systems. In the last decade, eseaches have been developing a family of analytical pobabilistic models and planning methodologies fo analyzing the vaious aspects of uban stomwate management planning. These models ae based on diffeent hydological epesentations, which ange fom simple such as STORM-type hydology to complex such as SWMM-type hydology. As an added contibution, analytical pobabilistic models and planning methodologies developed in this thesis ae intended fo analyzing and contolling unoff pollution in uban catchments. The models poposed in this eseach ae intended to be used fo sceening and planning level analysis to povide immediate insight into the magnitude of stomwate quality poblems and to povide peliminay cost-effective designs of quality contol altenatives. In the following section, a bief eview of existing analytical pobabilistic uban stomwate models is pesented. Analytical Pobabilistic Stomwate Models Benjamin and Conell (1970) outlined the deived distibution theoy and its applications to civil engineeing poblems in thei classic textbook Pobability, Statistics and Decisions fo Civil Enginees. The theoy pemits the deivation of the pobabilistic chaacteistics of a system output fom the pobabilistic chaacteistics of system input(s) and the knowledge of elationship between system input and output. As descibed in the pevious section, the application of this theoy to hydological and uban wate esouces poblems has culminated with the development of a set of analytical pobabilistic models fo uban stomwate management planning which can be used eithe as a paallel 24

25 appoach to continuous simulation modeling, o as a complementay aid to continuous simulation. In this eseach, the models developed on the basis of the deived pobability distibution appoach ae efeed as analytical pobabilistic models, o analytical models, o deived pobability models. The emainde of this section biefly eviews the development and application of analytical models in uban stomwate analyses. Eagleson (1972) fist applied the deived pobability distibution theoy to wate esouces engineeing though hydological poblems. Eagleson (1972) deived the fequency of peak steamflow ates fom a catchment fom the exponential PDFs of climatic vaiables that included ainfall event aveage intensity, event duation and inteevent time. The deived elationship between dependent and independent vaiables established the theoetical basis fo estimating peak flood flow fequency in the absence of steamflow ecods and povided the insight of the effects of land use and climatic changes on flood fequency. Howad (1976) applied the deived pobability distibution theoy to analyze the contol pefomance of stoage-teatment systems; which not only intoduced the theoy of stoage in the analysis of uban dainage systems but also paved the way fo futhe eseach. The pobability distibution of spill volumes fom a stoage esevoi was deived fom the joint PDFs of ainfall event volume and inteevent time assuming that the esevoi is full at the end of the pevious ainfall event. In the deivation, it is assumed that the ainfall events occu instantaneously. Following the pioneeing wok of Howad, a numbe of eseach studies wee conducted at the Univesity of Toonto, which impoved substantially on the initial development. Smith (1980) impoved the Howad model by incopoating the steady-state pobability distibution of esevoi contents at the end of the last stom. The deivation was based on the joint PDFs of thee ainfall chaacteistics - event volume, duation and inteevent time. The PDFs of ainfall chaacteistics wee assumed to be independent and exponentially distibuted and the joint PDFs wee fomulated as a poduct of thei maginal distibutions. The pobability distibution of stoage level afte a stom event was detemined numeically using a tansitional matix. The analysis of a single catchment with a stoage esevoi by Howad s and Smith s method was extended to a seies of catchments in cascade by Schwaz (1980) and Schwaz and Adams (1981). Each catchment was descibed by a catchment aea, hydological and meteoological paametes, a esevoi stoage volume and a contolled outflow ate. Models wee developed fo both conditions of spill outed to downsteam catchments and spills outed out of the system to a eceiving wate. Adams and Bontje (1984) simplified Howad s single catchment model by consideing the two extemities of esevoi conditions such as esevoi full and esevoi empty at 25

26 the end of the last ainfall event and also deived many othe pefomance chaacteistics which include annual numbe of spills and aveage annual unoff volume contol. These theoetical developments wee incopoated into a softwae package called the Statistical Uban Dainage Simulato (SUDS) by Bontje et al. (1984). In ode to elax and/o veify the assumption of statistical independence of ainfall chaacteistics, Seto (1984) exploed seveal altenative deivations of Howad s model incopoating the statistical dependence between ainfall chaacteistics. The deived models wee compaed to that of Howad (1976) and to STORM simulations. The closed-fom analytical pobabilistic models that wee developed on the basis of statistical independence of ainfall chaacteistics compaed favoably with continuous simulation models; howeve, the Howad model maintained the closest ageement to the simulation model. Wate quality aspects of stomwate dainage wee addessed by Flatt and Howad (1978). They initiated the investigation of pollution contol effectiveness of stoageteatment systems assuming constant, unifom pollutant concentations in unoff and unifom teatment efficiencies. Zukovs (1983) developed a methodology to pedict the quality behavio of uban unoff. The models wee developed to pedict unoff volume and pollutant loads fom uban catchments, to evaluate the effectiveness of souce contol measues and to evaluate the pollution contol effectiveness of downsteam stoage-teatment systems. Deivation of analytical models was based on linea pollutant buildup and washoff pocesses. Stoage analysis consideed both batch and detention mode opeation and pollutant emoval was descibed by eithe fist ode decay o sedimentation. Although the mathematical fomulations of the above wee developed, thei closed-fom solutions wee not obtained. In addition, the models wee compaed neithe with simulation models no with field data. DiToo and Small (1979) deived pobability distibutions of stomwate oveflows to evaluate the pefomance analysis of stoage-intecepto teatment devices. They assumed a gamma distibution of unoff chaacteistics such as unoff flow, duation, and inteevent time as opposed to ainfall chaacteistics, and the flow was assumed to be unifom ove the duation. Seveal of the deived expessions did not have analytical solutions and equied numeical evaluation. The analytical contol isoquants, which could achieve the same faction of unoff load contol by diffeent combinations of stoage-intecepto devices, wee compaed with those pedicted by continuous simulation STORM model. It was found that these contol isoquants wee in good ageement with those simulated by STORM model. Employing log-nomal pobability distibutions of stomwate oveflows and those of upsteam flow ates and pollutant concentation, DiToo (1984) deived the pobability distibution of in-steam pollutant concentation. This methodology was successfully applied to seveal wate pollutants fo seveal ives in the U.S. Loganathan and Delleu (1984) and Loganathan et al. 26