Excess nutrients, particularly phosphorus (P), significantly contribute to anthropogenic eutrophication, which negatively impacts ecosystems, human health, and the economy. Traditional Best Management Practices (BMPs) such as wet retention ponds prevent eutrophication by acting as a sink for nutrients, but can become a source of pollutants if not properly monitored and maintained. A proposed solution is a standalone, multi-stage filter system that can attach to BMPs with standing water for targeted removal of excess nutrients and with the potential to recycle the filter media. The studies in this dissertation seek to address the feasibility of this solution through the following tasks: 1.) develop a tool that can identify ponds and locations within ponds with high total phosphorus (TP) concentrations, 2.) evaluate filter media that can remove P and can be recycled along with captured P, and 3.) develop a filter system that can remove pollutants in separate stages for the option to recycle certain pollutants. The studies focused primarily on P because the nutrient has the potential to be recycled if captured within the filter. Models developed in the first task showed that TP concentrations in the water were correlated with the pond outlet, pH of the water, and iron concentrations. TP concentrations in the sediment were correlated with the pond's length-to-width ratio and the concentration of aluminum and copper. For the second task, a batch experiment and measurements of physicochemical properties were conducted on four biochars (corn stover pyrolized at 400°C , corn stover pyrolized at 600°C, mixed hardwood, and rice husk). Results indicated that mixed hardwood biochar could sorb dissolved phosphorus (DP) above a solution concentration of 2.9 mg P/L. The properties that could allow this biochar to sorb DP were a smaller negative surface charge, high surface area, smaller concentration of elemental P, and more water-extractable cations. A laboratory-scale test of a three-stage filter system was performed as part of the third task. The filter effectively separated nitrogen and P in different stages, but did not separate lead from P. Median water quality parameters (pH, conductivity, temperature, turbidity, dissolved oxygen, carbon, iron) met U.S. EPA recommended limits, but some parameters violated the recommended limits at a few time points. These studies demonstrate that excessive pollutant concentrations exist in current BMPs, which can benefit from a filter system. The filter system has the potential to collect pollutants separately provided that the correct media mix and configuration is identified such that P can be more completely isolated and water quality parameters are met. / PHD

Denna studie syftar till att ta fram lösningsförslag som kan komplettera Hemlingbys befintliga avvattningssystem som består av VA-ledningar och dammar. Lösningsförslagen som presenteras i rapporten har tagits fram med hänsyn till nulägesanalysering samt bedömning av nollalternativ. Studien omfattar en kartläggning av dagvattenhantering inom distriktet, via en sådan undersökning har författarna lokaliserat två problem områden som bör ses över. Dessa är Hemlingbybäcken och Kryddstigen. Recipienten tillstånd d.v.s. Hemlingbybäcken påverkas av mänskliga aktiviteter. Föroreningar som drabbar bäcken utgörs av tungmetaller såsom koppar, bly och zink. Brist på dagvattenmagasiner har medfört att bäcken innehar kapacitetsproblem med dagvatteninflöde från närliggande fastigheter och industriområden. Kryddstigen är ett område där det bedrivs företag inom teknik och handel, dessa aktiviteter bidrar med föroreningar som försämrar grundvattnets och recipientens tillstånd. Norra delen av Hemlingby utgörs till största del av hårdgjorda ytor, vilket reducerar möjligheten för en naturlig infiltration och avvattning av nederbördsvatten, detta har i sin tur orsakat att översvämningsrisken ökat i distriktet. Gävle kommun har via tidigare utredningar identifierat problemet och försökt förebygga dessa genom att implementera fördröjningsdammar, våtmarksdammar och rondelldammar. Uppföljningsarbete har gjorts som konstaterar att dammarna har ett större avrinningsområde än tidigare beräknat, vilket påverkar verkningsgraden negativt. Kapacitetsproblem har därför uppkommit t.ex. våtmarksdammarna är dimensionerade att omhänderta ett 10-årsregn från ett avrinningsområde på 19 hektar. För tillfället klarar våtmarksdammarna endast av att hantera 2-årsregn för ett avrinningsområde på 2400m3. Studien presenterar öppen dagvattenhantering som lösningsalternativ för dessa områden, detta görs med hänsyn till befintliga VA-ledningar och dammar. Öppna dagvattenlösningar tillämpas oftast i urbana miljöer för att fördröja, lokalt omhänderta samt för att få en samlad fördröjning av dagvatten. Detta sker med hjälp av växtligheter som gör det möjligt att uppnå en naturlig infiltration. Allmänheten kan dra nyttja av att implementera öppna dagvattenlösningar. Det kan förvandla en tråkig stadsmiljö till en livlig sådan genom att omhänderta dagvatten ovanpå ytan. Det blir fördelaktigt för allmänheten eftersom öppna dagvattenlösningarna bidrar med en estetisk tilltalande miljö samt ökad biologiskmångfald. Alternativen redogörs på följande sätt: Gröna tak – LOD för privat mark, Permeabla markytor – Fördröjning nära källan & LOD, Svackdiken med makadammagsin – Trög avledning & Samlad fördröjning, Biofilteranläggning i form av Regnbäddar – samlad fördröjning. Lösningsförslagen har sedan bedömts ihop med nollalternativet utifrån inre och yttre aspekter som berör omhändertagande av dagvatten. Yttre aspekter omfattar lagstiftning och dagvattenpolicy, inre aspekter tar hänsyn till faktorer som ekonomiska, tekniska, sociala och miljömässiga förhållanden. Bedömningsmetoden som presenteras i studien syftar till att utvärdera och ta fram underlag som är relevanta vid beslutsfattning och framtagning av tekniska lösningar. Värderingsmetoden är inspirerad av PESTEL-analys modellen. I denna undersökning har denna metod anpassats för att bedöma dagvattenlösningar. Övergripande beskrivning av vad en PESTEL-analys är ges i rapporten samt tolkning och tillämpning av bedömningsmetoden. Bedömningsresultateten för enskilt alternativ presenteras och diskuteras med hänsyn till nollalternativet samt tillämpningsområde i rapporten. / The aim of this study is to propose appropriate solutions that can complete Hemlingbys existing stormwater treatment systems. The solutions presented in this study has been developed with regards to the current situation, which includes water drainage systems and ponds. The study includes a survey of the current stormwater management within the district, as a result, the authors have localized two problem areas that should be investigated, i.e. are Hemlingbybäcken and Kryddstigen. The stormwater recipient i.e. Hemlingbybäcken is affected by human activities. Contaminates that affect the stream consist mainly of copper, lead and zinc. Due to the lack of stormwater storage capacity problems associated with stormwater flooding occurred from nearby buildings and industrial areas. Kryddstigen is an area in the district where business in technology and trade are located, these activities contribute to pollution that degrades groundwater and recipient conditions. The northern part of Hemlingby consist mostly of hard surfaces, which reduces the possibility of a natural infiltration of rain water, this in turn has caused an increased risk of flooding in the area. Gävle municipality have through earlier investigations identified some of the problems and tried to prevent them by implementing ponds that can delay incoming stormwater. Follow-up works proves that the ponds serve a larger catchment area than previously estimated, which adverse the ponds efficiency. Capacity problems have therefore arisen, for instance wetland ponds are sized to handle 10-yearsrain from a catchment area of 19 hectares. However, the existing wetland ponds can only handle a 2-yearsrain from a catchment area of 2400m3. This study presents open stormwater management as alternative solution, this has been proposed based on existing sewerage systems and ponds. Open stormwater solutions are applied mostly in urban environment to delay and locally dispose stormwater. This is done by vegetation which makes it possible to achieve a natural infiltration. The public can also take use of open stormwater solutions by turning an unattractive city to a beautiful one. It can also be beneficial to the community because open stormwater solutions contribute with an aesthetically pleasing environment and increasing biodiversity. The alternatives are described as follows: Green roofs, permeable ground surfaces, ditch with macadam basin and, rain gardens. These solutions are then assessed together with the existing solutions based on internal and external aspects concerning stormwater management. External aspects include legislation and stormwater policy, internal aspects take into account factors such as economy, technology, social and environment conditions. Assessment methodology that are presented in this study aims to evaluate and prepare documentation that is relevant for decision- making and the development of technical solutions based on the current situation. The evaluation method used in this study is inspired by PESTEL- analysis model. This method has been adapted to assess stormwater solutions. An overall description of what a PESTEL- analysis is given in this study as well as the interpretation and application of the assessment method. The result for single alternatives is presented and discussed with respect to existing solutions in the area of this study.

Pervious pavements in car parks and driveways reduce peak discharge and the volume of runoff flowing in to urban drains and improve the water quality by trapping the sediments in the infiltrated water. This reduces the risk of pollutants such as suspended solids and particle bound chemicals such as phosphorous, nitrogen, heavy metals and oils and hydrocarbons entering receiving waters. The key objectives of the study are to establish relationships between rainfall and pervious pavement runoff and quantify improvements to infiltrated stormwater quality through the pervious pavement. The field experimental results were used to calibrate the PCSWMMPP model and to develop water flow and quality improvement transfer functions of the MUSIC model for concrete block and turf cell pavements. The research reported herein has demonstrated that pervious pavements can be introduced as a sustainable stormwater management initiative and as a key Water Sensitive Urban Design feature to deliver numerous benefits to the environment. The outcomes from the study will be useful in designing environmentally friendly car parks, pedestrian paths, light traffic drive ways, sporting grounds and public areas in the future. Land developers and local government authorities will be major beneficiaries of the study which has increased the understanding of the use of pervious pavements and explored a number of issues that previously inhibited the wider use of pervious pavements in practice.

Urban runoff is generated by precipitation of rain and snowmelt on impervious surfaces.  The increasing demand of urbanization causes contaminants to accumulate on roads,  roofs and pathways. In turn, as runoff wash off these surfaces, contaminants such as heavy metals, particles and organic pollutants end up in the stormwater. Urban stormwater ponds improve water quality of runoff by facilitating contaminants in form of particles. To preserve the function of a stormwater pond accumulated sediment must periodically be removed.Therefore, upland disposal alternatives should be evaluated. This study examined stormwater sediment and outlet stormwater quality in seven and four ponds respectively in the vicinity of Halmstad. 7 heavy metals and 24 organic contaminants were analysed in both sediments and stormwater. Results showed metal and organic contaminant concentrations in stormwater pond discharge and sediment exceeding concentrations reported in guideline values. From the analysed heavy metals, Zn and Pb was considered the most critical contaminants. Heavier organic compounds were more frequently quantified than lighter ones, where 42 % of the analysed organic contaminants were quantified in at least one sample. Variability between inlets and outlets, between ponds and between sampling occasions was observed. The observed variability suggests that the contamination level is influenced by catchment area characteristics and activities. Significant correlation from Spearman’s rank correlation was found between the individual heavy metals (Cu, Cr, Ni, Pb and Zn), which suggest they originate from similar sources

Green roofs are increasingly being used in the United States to mitigate the negative effects of impervious surfaces on aquatic ecosystems. Though performance of these systems varies with climate, little research has been conducted in the Southeastern U.S., and no prior research has been conducted in Mississippi. An experiment was conducted to determine the effect of soil depth and roof slope on the stormwater retention of green roofs in Mississippi’s hot, humid climate. Simulated roof platforms were constructed to investigate two soil depths and two slopes, each replicated three times and planted with four species of Sedum. The green roof platforms significantly reduced runoff depth when compared with total rainfall depth. Soil depth and slope both significantly affected retention, with higher retention seen with increasing soil depth and lower retention seen with increasing slope. These results indicate that green roofs can be an effective tool to reduce runoff in Mississippi.

Syfte: Klimatförändringarna bidrar till att Sverige kommer att få ett förändrat regnmönster. Vilket leder till att större krav ställs på dagvattenhaneringen och dess funktion. När grönytor bebyggs ökar risken för översvämningar vid stora skyfall. Det är därför viktigt att anpassa städerna efter de framtida skyfallen samt att dagvattenhanteringen utvecklas och inte nedprioriteras. Syftet med studien är att ge svar på vilka lösningar som används mest och är framgångsrika i kommunerna, vilka faktorer som påverkar kommunernas beslut vid val av dagvattenlösning och hur kommunerna tar hänsyn till klimatförändringarna när det väljer dagvattenlösning.  Metod: Litteraturstudien har gett rapporten forskningsfronten inom ämnet och en bra vetenskaplig grund att baseras på. Sex olika interjuver har utförts med respondenter från VA- och samhällsbyggnadsavdelningen på tre kommuner i Skaraborg. Studiens deltagande kommuner är Lidköpings kommun, Skövde kommun och Falköpings kommun. Intervjuerna var indelade i olika huvudkategorier för att kunna besvara studiens frågeställningar. En dokumentanalys har gjorts utifrån ritningar och dokument på nyexploaterade bostadsområden från kommunernas hemsidor. Resultat: Den dagvattenhantering som används mest i kommunerna är öppna dagvattenlösningar så som öppna diken, fördröjningsytor och dammar. Vilket gör lösningarna till de mest framgångsrikaste. Genom öppna dagvattenlösningar säkras samhället från översvämningar då lösningen kan reglera vatten. Faktorer som påverkar kommuners val av lösning är kunskap om dagvatten, samarbetet mellan avdelningarna, teknisk funktion, tid, kapital, lagar och rekommendationer. Utformning av vägar, vattenvägar och höjdsättning i nyexploaterade bostadsområden är viktiga faktorer som kommunerna tar hänsyn till för att klara av de pågående klimatförändringarna. Konsekvenser: Slutsatser som kan tas av studien är att öppna dagvattenlösningar är det som kommunerna strävar efter att använda. Dessutom är lösningen bäst tillämpningsbar för att klara av klimatförändringarna. Genom att använda öppna dagvattenlösningar behöver inte avkall på funktion göras för att använda den billigaste lösningen. Bostadsområdena utformas med vattenvägar, strategiska utlopp och utefter klimatfaktorn. För att uppnå bra dagvattenhantering är personalens kunskapsläge och samarbete mellan avdelningar en viktig del. Rekommendationer som kommunerna kan arbeta vidare med för att få en bättre hållbar dagvattenhantering är utöka kunskap bland de anställda, förbättra samarbetet, granska konsulternas arbete och öka tillsyn samt uppföljningen i produktionen.  Begränsningar: Studien har avgränsats till tre kommuner med samma geografiska läge i Sverige. Det går att generalisera studien för att det finns städer i Sverige som har liknande antal invånare. / Purpose: The climate changes contribute to Sweden’s future change in rain pattern. This leads to a higher demand on the stormwater management and its function. When green areas are built upon the risk for flooding increase when heavy rains occur. It is therefore important to adapt the cities according to future heavy rains and the stormwater management should not be downgraded. The goal of this study is to answer what solutions are used the most and are successful in the municipalities, what factors that affect the municipalities choice of stormwater solution and how the municipalities account for climate changes when choosing stormwater solutions. Method: The literature review has given the report the research front within the subject and a good scientific base to be based upon. Six different interviews have been held with respondents from the water and plant-department and the community building department withing three municipalities in Skaraborg. The participating municipalities are Lidköpings municipality, Skövdes municipality and Falköpings municipality. The interviews are split into different main categories to answer the questions at issue. A document analysis has been done based upon blueprints and document of newly exploited residential areas from the municipalities’ websites. Findings: The stormwater management solution that is used the most in the municipalities are open stormwater solutions, such as trenches, delay surfaces and ponds. This makes these solutions the most successful. Through open stormwater solutions the society is secured from flooding since the solution can regulate the water. Factors that affect the municipalities choice of solution are knowledge of stormwater, the cooperation between departments, technical function, time, money, laws, and recommendations. The design of roads, waterways, and elevation in newly exploited residential areas are important factors that the municipalities consider, in order to manage the ongoing climate changes. Implications: Conclusions that can be drawn from the study is that open stormwater solutions are what the municipalities strive towards using. In addition, the solution is best suited to manage the climate changes. Through using open stormwater solutions, a need to waiver on function is not needed to use the cheapest solution. The residentials areas are designed with waterways, strategic outlets and along the climate factor. To achieve good stormwater management the level of knowledge within the staff and the cooperation between departments are important. Recommendations that the municipalities could continue to work with to get a more sustainable stormwater management is to expand the knowledge between the staff, improve the cooperation, review the consultants work, increase supervision and to follow up in production. Limitations: The study has been delimited to three municipalities with the same geographic location in Sweden. It is possible to generalize the study since there are cities in Sweden with similar a amount of residents.

Development of cities, new buildings and other impervious surfaces entails increased stormwater flows, volumes and pollutant loads. Heavy metals, nutrients, sediments and salt are common pollutants in stormwater. The conventional way to manage stormwater, which is by discharge to the receiving water body via a sewage network, will not be sufficient for mitigating high flows, flood risks and pollution export. Thus, Low Impact Development (LID) stormwater facilities, such as stormwater biofilters, are built in an increasing rate in Sweden and worldwide. The main function of a stormwater biofilter is water quality treatment, which is achieved when stormwater percolates through a vegetated filter media. Sometimes a pre-treatment facility is installed before the biofilter to reduce the sediment load on the biofilter and extend its life-length. However, there are knowledge gaps regarding pollutant removal in biofilters and the role of associated pre-treatment facilities. In this study the impact of a pre-treatment facility, calcium carbonate as amendment in the filter media and vegetation was investigated regarding treatment of heavy metals (Cd (cadmium), Cu (copper), Pb (lead) and Zn (zinc)), phosphorus and total suspended solids. To do this, influent and effluent stormwater samples from an existing biofilter in Sundsvall were analysed and evaluated regarding removal performance of the above-mentioned pollutants.  In general, the stormwater biofilter facility (including pre-treatment) removed total metals well while the removal of the dissolved fraction showed higher variations. Influent concentrations of TP were always higher than effluent concentrations. Leaching of phosphate repeatedly occurred from the filter sections. The mean removal of TSS was high (96.9%). CaCO3 as amendment in the filter material had a beneficial effect on the overall metal removal of the stormwater facility. Although leaching of phosphate occurred from all filter sections, the leaching was lowest from the section with CaCO3,indicating possible benefits of CaCO3 as amendment. CaCO3 did not seem to affect the mean total phosphorus removal significantly. Removal of total metals seemed to be improved by vegetation, but the removal of dissolved metals, total phosphorus and phosphate did not seem to be enhanced by vegetation. The filter section with vegetation and without CaCO3 amendment contributed with the highest effluent concentrations of total phosphorus and phosphate (leaching), considering that vegetation released more phosphate that it captured. The main treatment of the stormwater pollutants occurred within the biofilter and both positive and negative removal of all pollutants was observed by the pre-treatment facility. The result showed that the pre-treatment facility was most beneficial for removal of dissolved metals. / Utvecklingen av städer, nya byggnader och andra hårdgjorda ytor ökar både mängden dagvatten och föroreningshalterna. Vanligt förekommande föroreningar i dagvatten är tungmetaller, näringsämnen, sediment och salt. Det traditionella sättet att hantera dagvatten är genom avledning via avloppsnätet till närliggande recipient, men med den förändrade kvalitén och kvantitet på dagvatten blir kapaciteten i det befintliga ledningsnätet otillräckligt för de ökade flödena och föroreningsinnehållet. Därför byggs bland annat dagvattenbiofilter, som är en typ av Low Impact Development (LID), i en ökande takt i Sverige och globalt. Huvudsyftet med dagvattenbiofilter är dagvattenrening, vilket uppnås när dagvattnet filtreras genom en filterbädd med växter. För att minska (sediment)belastningen och förlänga livslängden på biofiltret kan ibland en förbehandlingsanläggning placeras i före biofiltret. Dock finns det fortfarande kunskapsluckor om reningspotentialen i biofilter och betydelsen av en förbehandlingsanläggning. I den här studien undersöktes betydelsen av en förbehandlingsanläggning, kalciumkarbonat som tillsats i filter materialet och växter på biofiltret för reningen av tungmetaller (Cd (kadmium), Cu (koppar), Pb (bly) och Zn (zink)), fosfor och totalt suspenderat material. För att undersöka detta analyserades och utvärderades dagvattenprover på inkommande och utgående vatten från ett biofilter i Sundsvall, med avseende på reningsprestation av ovan nämnda föroreningar. Resultatet visade att biofiltret (med förbehandlingsanläggningen inkluderad), renade totala metaller bra medan reningen av lösta metaller varierade mer. Inkommande koncentrationer av totalfosfor var alltid högre än utgående koncentrationer och fosfat lakades kontinuerligt ut från filtersektionerna. Den genomsnittliga reningen av TSS var hög (96,9%). CaCO3 som tillsats i filtermaterialet hade en positiv effekt på reningen av totala och lösta metaller i biofiltret. Fosfat lakades ut från alla filtersektioner, men urlakningen var lägst från filtersektionen med CaCO3, vilket tyder på möjliga positiva effekter det som tillsats i filtermaterialet. CaCO3 verkade inte öka genomsnittliga reningen av totalfosfor signifikant. Vegetationen verkade öka reningen av totala metaller men inte reningen av lösta metaller, totalfosfor eller fosfat. Filtersektionen med vegetation men utan CaCO3 genererade de högsta utgående koncentrationerna av totalfosfor och fosfat (urlakning), vilket tyder på att vegetation avgav mer fosfor än den tog upp. Den dominerande reningen av dagvattenföroreningarna skedde inuti biofiltret och både högre och lägre koncentrationer av samtliga föroreningar observerades efter förbehandlingsanläggningen. Resultatet visade att förbehandlingsanläggningen var mest effektiv för reningen av lösta metaller.

Master of Science / Department of Biological & Agricultural Engineering / Stacy L. Hutchinson / To understand the region-specific effects of biota on function of bioretention cells, a lysimeter study was conducted at Kansas State University to determine how earthworms and native Kansas grasses impact runoff treatment and hydraulic function of a bioretention cell. This study also employed the Comprehensive Bioretention Cell (BRC) model to demonstrate how three seasons of growth could impact bioretention cell function. The model results of the first season of growth were then compared to field data. Results indicate that the interaction of plant roots and soil macrofauna over one growing season improved several aspects of bioretention cell function. The greatest increase in saturated hydraulic conductivity was in the treatment that included both plants and macrofauna. The presence of vegetation reduced ponding effects and increased water storage. Earthworm treatments had a lesser ability to store water. All treatments were effective in reducing the concentration of P in effluent. A large amount of N was released during all events from all treatments probably because of a high initial N content of the bioretention media. No treatment performed significantly better in improving water quality, indicating that macropore flow in the earthworm treatments did not induce a higher rate of pollutant transport.

Recently, the Texas Department of Transportation began using Permeable Friction Course (PFC), a 5 cm overlay of porous pavement that is applied over conventional pavement. PFC was initially developed because it allows water to drain off the surface of roads much more rapidly, thus reducing visual impairment due to splash and spray as well as reducing the risk of hydroplaning. While investigating the water quality of stormwater runoff, researchers at the University of Texas discovered that PFC caused a reduction in many common stormwater pollutant concentrations. Monitoring of stormwater at one site has been ongoing for 5 years without any indication of a decline in water quality. A second location provided paired samples to analyze the particle size distribution. Results show a significant reduction in the mass of particles commonly associated with heavy metals and nutrient loads. A third location was chosen based on tests indicating it to have a lower hydraulic conductivity relative to other locations. The paired samples provided a comparison of runoff quality at a site believed to be heavily clogged. The results show PFC continues to produce significantly lower runoff pollutant concentrations despite the decreased hydraulic conductivity. / text

Management of urban stormwater is becoming increasingly difficult due to an anticipated increase in precipitation and extreme storm events that are expected under climate change. The goal of this research is to develop an approach that effectively accounts for the uncertain conditions that may occur under climate change and to develop best management practices to manage stormwater in urban areas. This presentation focuses on management of stormwater and combined sewage in Worcester, MA, where approximately four square miles of the downtown area is serviced by a combined sewer system. The EPA Stormwater Management Model was used to determine the impacts of storms on the urban environment for future conditions. This model was used to simulate discharges of selected design storms associated with a range of climate change scenarios. Various design storms were simulated in SWMM for 2010, 2040, and 2070 under high, moderate, and low climate change scenarios. Alternative best management practices were assessed in terms of specific metrics that included flood volumes and combined sewer overflow volumes through the Worcester sewer system. Cost evaluations were used to identify appropriate best management strategies for managing the combined sewer system under future scenarios. A design cost approach and net benefits approach were used to analyze different options for managing stormwater under climate change. Both of these approaches utilize the concept of risk analyze to determine expected values of both costs and benefits for different options under different climate change scenarios. Results for the design cost approach indicate that providing upstream underground storage in select locations throughout the Worcester combined sewer system is the most cost-effective strategy. In addition, increased pumping capacity at the Quinsigamond Avenue Combined Sewer Overflow Storage and Treatment Facility (QCSOSTF) should be included for this option. However, it was determined that only select upstream storage is the most beneficial option under the net benefits approach as increased pumping capacity at the QCSOSTF was determined to be too costly due to the additional costs of CSO treatment required at the facility. The Worcester case study provides an ideal context for assessing the relative advantages of full treatment at the wastewater treatment facility, limited treatment at a centralized CSO treatment facility, decentralized storage options, and low impact stormwater controls. It also allows for an assessment of decision making methods for controlling flows and loads from the Worcester system. Comparisons between Worcester and other case studies provide a foundation for understanding how stormwater and combined sewer systems can be managed given climate change uncertainty.