Dagvattnet från Märsta är belastat med bland annat tungmetaller och näringsämnen. Vattnet hamnar i Märstaån och transporteras vidare ut till Mälaren. Steningedalens våtmark är ett dammsystem som renar och fördröjer en del av Märstaåns flöde före transport ut mot Mälaren.   Syftet med detta självständiga arbete på kandidatnivå har varit att undersöka anläggningens reningsfunktion med hjälp av sedimentprovtagning. Sedimentprover har tagits vid in- och utloppet och en kemisk analys av dessa har utförts i ett ackrediterat laboratorium. Resultaten från in- och utloppet har jämförts för att se om det sker en minskning av föroreningar genom systemet. Fem sedimentfällor har placerats ut i delar av dammsystemet för att undersöka sedimentfördelningen och muddringsbehovet i anläggningen. Resultatet av studien visade att dammsystemet har en god vattenreningsfunktion med avseende på tungmetallerna bly, nickel, kadmium, krom, koppar och zink samt näringsämnet fosfor. Anläggningen har bedömts att vara i behov av muddring. / In Märsta, the storm water is contaminated with heavy metals and nutrients (nitrogen and phosphorus) among other pollutants. The water emits to the river Märstaån and further to the lake Mälaren. The wetland of Steningedalen is a pond system that delays part of the stream in Märstaån and purifies the water on its way through the system. This independent project is based on investigation of the purification functioning at Steningedalen wetland. The investigation has been done by sediment sampling and analysis. The samples were taken from the inlet and the outlet of the pond system. Chemical analysis has been made on these samples in an accredited laboratory. The results were compared in order to see if there is a trend through the system. Five sediment traps were placed in parts of the system to study the distribution of the sediment and the need of dredging. The results of the study have concluded that the stormwater pond system has a good water purification function with regard to heavy metals lead, nickel, cadmium, chromium, copper and and zinc aswell as the nutrient phosphorous. The study has also shown that the system is in need of dredging.

<p>Stormwater run-off from surfaces such as roads or rooftops is often polluted with heavy metals and nutrients. Many of these substances can cause great damage in biota if they end up in the recipient. In Sweden constructed wetlands and ponds for treatment of stormwater are frequently used, since research has shown that these treatment ponds are reducing stormwater pollution considerably to a low cost. The knowledge of these pollutant removal mechanisms and how follow-up and assessment of the ponds should be performed is still limited.</p><p>To determine the pollutant removal efficiency of the stormwater ponds it is recommended that flow-weighted water samples are collected from both the inflow and the outflow of the pond. This method demands considerable resources of time and money for installations and analysis. Alternative methods for assessing pollutant removal are requested, methods with lower costs but relevant results. This thesis is investigating whether sediment sampling could be such an alternative.</p><p>Sediment core samples were taken in four stormwater ponds where flow-weighted water sampling has been performed as well. This makes it possible to compare the two methods. A method of sampling recently sedimented material was also tried out by constructing and placing sediment traps on the pond floor. Analysis of concentration of six heavy metals (Cd, Cr, Cu, Ni, Pb and Zn) and phosphorus were carried out.</p><p>The results show i.e. that the concentrations of heavy metals and phosphorus in the pond sediments decrease as the distance from the pond inlet increase. Comparing the two methods shows that the results from the sediment sampling are in the same order of magnitude as the results from the water sampling. Consequently, the conclusion states that a well executed sediment sampling may be an alternative to flow-weighted water sampling.</p> / NOS dagvatten

Stormwater run-off from surfaces such as roads or rooftops is often polluted with heavy metals and nutrients. Many of these substances can cause great damage in biota if they end up in the recipient. In Sweden constructed wetlands and ponds for treatment of stormwater are frequently used, since research has shown that these treatment ponds are reducing stormwater pollution considerably to a low cost. The knowledge of these pollutant removal mechanisms and how follow-up and assessment of the ponds should be performed is still limited. To determine the pollutant removal efficiency of the stormwater ponds it is recommended that flow-weighted water samples are collected from both the inflow and the outflow of the pond. This method demands considerable resources of time and money for installations and analysis. Alternative methods for assessing pollutant removal are requested, methods with lower costs but relevant results. This thesis is investigating whether sediment sampling could be such an alternative. Sediment core samples were taken in four stormwater ponds where flow-weighted water sampling has been performed as well. This makes it possible to compare the two methods. A method of sampling recently sedimented material was also tried out by constructing and placing sediment traps on the pond floor. Analysis of concentration of six heavy metals (Cd, Cr, Cu, Ni, Pb and Zn) and phosphorus were carried out. The results show i.e. that the concentrations of heavy metals and phosphorus in the pond sediments decrease as the distance from the pond inlet increase. Comparing the two methods shows that the results from the sediment sampling are in the same order of magnitude as the results from the water sampling. Consequently, the conclusion states that a well executed sediment sampling may be an alternative to flow-weighted water sampling. / NOS dagvatten

Dagvatten kallas det regn- och smältvatten som rinner av från hårdgjorda ytor i stadsmiljön. Detta vatten för ofta med sig stora mängder av föroreningar som tungmetaller, näringsämnen och oljerelaterade ämnen, vilka kan göra stor skada om de når recipienter. För att rena dagvattnet och därmed minska föroreningsbelastningen byggs det allt fler öppna dagvattensystem som t.ex. våtmarker och dammar. Studier har visat att dessa system har hög reningseffekt och dessutom är de kostnadseffektiva. Kunskapen om hur avskiljningen i dessa system fungerar och om hur de bäst utvärderas är dock begränsad. Kungsängsdammen utanför Uppsala är en nybyggd dagvattenanläggning som är avsedd att rena och fördröja dagvattnet från industri- och handelsområdet Boländerna. Detta examensarbete syftar till att utreda reningsfunktionen av anläggningen. Framför allt genomfördes flödesproportionell provtagning vid inlopp och utlopp under 8 veckor. Ämnen som analyserades var näringsämnena P och N, suspenderat material, tungmetallerna As, Cd, Co, Cr, Cu, Mo, Ni, Pb, V, Zn och oljekolväten. Vid några tillfällen analyserades också de oljerelaterade organiska föreningarna PAH:er, oktyl- och nonylfenoler samt tributyltenn. Flödesproportionell provtagning rekommenderas för att säkert avgöra avskiljningseffektiviteten av en damm, men nackdelen är att den tar mycket tid och stora resurser i anspråk. Utöver denna metod genomfördes kompletterande mätningar med sedimentfällor samt en beräkning av föroreningsbelastning vid inloppet med programmet StormTac. Den flödesproportionella provtagningen visade att Kungsängsdammen fungerar väl som avskiljningsanläggning för föroreningar. Suspenderat material, näringsämnen och tungmetaller avskiljs effektivt och utloppshalterna understiger föreslagna riktvärden för dagvatten. Detta trots att både zink, koppar, kväve och suspenderat material hade inloppshalter som låg över riktvärdena. Flödesberäkningar visade att andelen av flödet som bräddas i bypass-diket förbi dammen är viktig vid bedömning av avskiljningseffektiviteten. För organiska föreningar uppmättes tributyltenn i halter över miljökvalitetsnormen för ytvatten både vid inlopp och vid utlopp. Inloppskoncentrationer framräknade i StormTac gav överensstämmande resultat med den flödesproportionella provtagningen för tungmetaller och näringsämnen. Vidare visade undersökningen av sediment att sedimentationen sker främst i fördiket och i inloppet till dammen. Fördiket är i stort behov av rensning, då sediment riskerar att spolas bort vid höga flöden. / Stormwater is the name for rainwater and snowmelt runoff from impervious surfaces in the urban environment. This water often carries large amounts of pollutants such as heavy metals, nutrients, and oil-related substances, which can cause great damage if they reach the receiving waters. To clean the storm water and thus reduce the pollution load, more and more open storm water systems are being built, such as wetlands and ponds. Studies have shown that these systems have high pollutant removal efficiency and are cost effective. Knowledge of how these systems work and how they best are evaluated is limited. “Kungsängsdammen” near Uppsala is a newly constructed stormwater facility that is designed to clean and retard stormwater from the industrial and commercial area Boländerna. This thesis aims to investigate the purification function of the facility. Flow proportional sampling was carried out at the inlet and outlet for 8 weeks. Substances that were analyzed were nutrients P and N, suspended solids, heavy metals As, Cd, Co, Cr, Cu, Mo, Ni, Pb, V, Zn and petroleum hydrocarbons. On some occasions, the petroleum-related organic parameters PAHs, octyl and nonylphenols and tributyltin were analyzed. Flow proportional sampling is recommended to determine the efficiency of a stormwater pond, but the problem is that it takes much time and considerable resources. In addition to this method, additional measurements were carried out with sediment traps, and a calculation of pollution load at the inlet with the program StormTac. The flow proportional sampling showed that the “Kungsängsdammen” pond-, functions well as a treatment facility for pollutions. Suspended solids, nutrients and heavy metals are separated effectively and the outlet concentrations for these substances were below proposed guideline values. This is observed, despite the fact that zinc, copper, nitrogen and suspended solids had intake concentrations above the guideline values. Flow calculations showed that the bypass flow is important when estimating the pollutant removal efficiency. For organic compounds, tributyltin was measured at concentrations above the Environmental Quality Standards (EQS) for surface water both at the inlet and outlet. The inlet concentrations that were calculated in StormTac were consistent with the results of the flow proportional sampling for heavy metals and nutrients. Moreover, the investigation of sediments showed that sedimentation occurs mainly in the ditch before the pond and at the inlet to the pond. The ditch is in need of cleansing, because of the risk of sediment being washed away during high flows. The flow proportional sampling showed that the “Kungsängsdammen” pond-, functions wellas a treatment facility for pollutions. Suspended solids, nutrients and heavy metals are separated effectively and the outlet concentrations for these substances were below proposedguideline values. This is observed, despite the fact that zinc, copper, nitrogen and suspended solids had intake concentrations above the guideline values. Flow calculations showed that the bypass flow is important when estimating the pollutant removal efficiency. For organiccompounds, tributyltin was measured at concentrations above the Environmental Quality Standards (EQS) for surface water both at the inlet and outlet. The inlet concentrations that were calculated in StormTac were consistent with the results of the flow proportional sampling for heavy metals and nutrients. Moreover, the investigation of sediments showedthat sedimentation occurs mainly in the ditch before the pond and at the inlet to the pond. The ditch is in need of cleansing, because of the risk of sediment being washed away during high flows.