Distribution of responsibilities – Distributed acceptable loads and required…

Distribution of responsibilities – Distributed acceptable loads and required treatment between stakeholders within the catchment

Distributed acceptable load for stormwater between different stakeholders within the catchment
It is possible in StormTac Web to distribute the acceptable load and the required treatment of the receiving water between different stakeholders by creating different sub catchment areas (A1, A2, …).
One can input agricultural land in one area, the Transport Administration’s roads in another, urban areas in a third and you can also add land uses for one municipality in one area and for another municipality in another. StormTac Web then calculates a distributed acceptable load for each stakeholder, you get a division of responsibilities.
This gives an interesting basis regarding for example how the required treatment (kg/year) can be distributed between different municipalities whose stormwater loads the recipient.

Distributed acceptable load for point flows between different stakeholders
In addition to stakeholders that contribute to stormwater loads, there may be other actors connected to a recipient, calculated as point flows in the StormTac Web model. It can be wastewater treatment plants, pumping stations that overflow (CSO’s) or point flows from upstream receiving waters.
Such point flows may not be the responsibility of the municipality/municipalities (within the catchment area) to treat. It could make unreasonable and unfair demands. The municipalities located upstream the receiving water that gives a point flow to the receiving water, the pumping stations and wastewater treatment plants that add loads to the recipient also need to be responsible for their part of the treatment need and get an acceptable load to relate to.
As an example, a wastewater treatment plant that gives a certain load to the recipient gets an assigned treatment need (kg/year) and an acceptable load (kg/year) that can be led out to the recipient (a watercourse, a lake or a sea).
The model can be used to simulate an expansion of the plant and see what change it entails in terms of treatment needs and acceptable load. The plant can be designed according to this, as well as any subsequent wetlands or the like.

Updated irreducible concentrations in StormTac database and in StormTac…

Updated irreducible concentrations in StormTac database and in StormTac Web

The values affect the maximum treatment effect that can be achieved by stopping the treatment when these minimum concentrations are reached. The difficulty in achieving lower concentrations is due to e.g. the decomposition of plants, sedimentation due to high flows and that vegetation beds (soil) and filters contain materials that can leak nutrients and pollutants. You can test different facilities and combinations of facilities with different irreducible concentrations if lower outlet concentrations are required.

The update is a result of a comprehensive investigation and literature review with new outlet concentrations and a comparative analysis of minimum outlet concentrations from similar types of facilities.

Completed database with updated stormwater concentrations during different seasons…

Completed database with updated stormwater concentrations during different seasons and months

The sheet “Monthly and seasonal conc” already presents 5 case studies with flow-weighted sampled concentrations every month for a year, which is considered unique. These have now been adjusted with additions for total concentrations and an introductory table that presents calculated average percentages of total annual concentrations that a month or season gives.

Examples of use:

A stormwater sampling has taken place during the summer and it is desired to get an estimate of which annual average concentrations this corresponds to, taking into account whether there are higher or lower concentrations during the summer than the annual average. Based on the percentages in the table (e.g. 117% of P during the summer compared with the annual average), it is possible to roughly (!) calculate which annual average concentration the sampled concentrations are deemed equivalent, e.g. which annual average concentration of the sampled concentration 120 ug/l P corresponds to as annual average value.

These recalculated annual average concentrations, e.g. 120 / 1.17 = 103 ug/l, can then e.g. be used in StormTac Web to replace estimated values ​​from the area where sampling took place. Then these can be used to calculate pollutant loads, design treatment facilities, etc., taking into account the site-specific conditions. This presupposes that the sampling took place in proportion to the flow with a sufficient number of collected samples (we recommend at least 7 samples).

Updated database regarding new references, stormwater concentrations, reduction efficiencies…

Updated database regarding new references, stormwater concentrations, reduction efficiencies and concentrations for overflow water

There is now an updated version of StormTac’s database with a lot of new data from a large number of new references. Several sheets have been updated with new data, which means a larger basis for the development of new typical concentrations for stormwater, treatment effects and concentrations for overflow water. The work of producing new typical concentrations and treatment effects from this data is in progress. Recently, the typical concentrations of TBT and the treatment effect of phosphorus (P) from ponds were changed. More changes are planned in the near future, first regarding irreducible (minimum possible outlet) concentrations and typical concentrations for different land uses.

Updated database with a large number of new volume-weighted…

Updated database with a large number of new volume-weighted land-use specific concentration data and BMP reduction efficiencies

Introduction
StormTac’s database has been updated with a large number of new volume-weighted concentrations (ug/l) and treatment effects (%) from various references (case studies), not least from all data that is considered to be reliable from the recognized International Stormwater BMP Database, http: // www.bmpdatabase.org/. Many other reference data have also been entered after an extensive literature study focused on finding data for substances and land uses as well as types of treatment facilities where there was previously a lack of data in StormTac’s database.

Only flow-weighted data has been entered, thus excluding grab sample data. Concentration data from base flow from different land uses have also been added to StormTac’s database, after volume weighting from obtained raw data from various case studies.

The references for runoff coefficients have also been updated and more clearly divided between volume runoff coefficients and design runoff coefficients. A large number of new case studies with data of irreducible concentrations (outlet concentrations) has been added.

For the case studies with data from treatment facilities, various site-specific parameters that affect the treatment effect have also been compiled, e.g. data on filter material and hydraulic conductivity for biofilters.

This data should now be used to update the typical land-use specific concentrations and calculated treatment effects in StormTac Web.

Data from BMP Database
Data from hundreds of stormwater treatment facilities (BMPs) from the International Stormwater BMP Database of a wide variety of types have been processed by transferring them from Access to Excel and by performing a volume-weighted calculation of both inlet and outlet concentrations from all runoff events, after which volume-weighted treatment effects were calculated for a large number of substances and types of stormwater facilities. To our knowledge, this calculation has not been performed and compiled in any other database or documentation. A quality assurance has been carried out by studying extreme values whereby uncertain data were marked or removed. In cases where the inlet concentrations come from areas with single land uses, these data are used as typical land-use specific concentrations, which are added to the database.

Examples of interesting new data are that treatment effects from Storm drainage filter (catch basin inserts) were expanded from 5 to 10 case studies and data from underground retention filter basins were expanded from 5 to 16 case studies. This provides a much more secure basis for calculating the treatment effects in StormTac Web. Facility types that you may not have previously dared to use in a project due to uncertain data, may now be able to start using as more data is available which shows the treatment effect that can be achieved for different types of treatment facilities.

Site-specific parameters
For the case studies with data from treatment facilities, various site-specific parameters affecting the treatment effect have also been compiled for further updating of the treatment effect calculations in StormTac Web. Examples of such parameters are permanent water surface, the catchment area and runoff coefficient, water depth for different facilities of different types as well as information on filter material and hydraulic conductivity for biofilters.

Update of typical land-use specific concentrations
For the many added typical concentrations per land use, this will provide a base for continued update of typical concentrations for different land uses, after an analysis and comparison of data from different similar land uses.

Availability
The many added typical concentrations from different land uses are available to everyone, but data in the form of baseflow concentrations, runoff coefficients and treatment effects (%) from different types of stormwater facilities are only available to those licensed on StormTac Web.

Extent
Through this update, StormTac’s database includes all relevant compiled and volume-weighted data from the large international databases NSQD and BMP database for concentrations and treatment effects for stormwater and stormwater facilities, respectively. The aforementioned databases contain all raw data from all rain events, but StormTac’s database is now probably the most comprehensive database of calculated volume-weighted compiled data per land use and facility type. The other databases contain only raw data, while these raw data are volume weighted and compiled into StormTac’s database, broken down by substance, land use and facility type.

Continued evaluation of data and updating of the database
The data can already be used to further study uncertainties by substance, land use and type of treatment facility, where these concentrations and treatment effects are used in projects. During the fall of 2020, StormTac will use this data to update the land-use specific typical concentrations of stormwater and baseflow per land use. StormTac will also, based on added data and site-specific parameters, update the calculations of treatment effects for all types of treatment facilities, taking into account more site-specific parameters, such as hydraulic conductivity and material in biofilters, for the parameters and substances where sufficient data is available.

Together with Luleå Technological University (LTU), the quantification of uncertainty of calculated concentrations and quantities of pollutants and treatment effects will be improved and performed specifically per substance based on compiling relative standard errors from all reference data. A second international scientific paper on quantification of uncertainty has been started in collaboration with LTU for scientific review of the calculations and used data.

During the summer and autumn 2020, the database will be converted to a web application available from the website and fully integrated into StormTac Web.

Updated method description

Updated method description

General method description for StormTac Web has been updated on this homepage and more detailed in the guide to the application, incl. addition of a new introductory chapter.

The description of quantified uncertainty has been updated incl. added equations in the guide.

Description of the recipient model has been updated, incl. a section on calculating new distributed acceptable load and on how to calculate acceptable load for e.g. urban areas and agricultural land, which provides the opportunity to distribute the treatment needs to several actors (the Transport Administration, municipalities, operators, etc.). The distribution of the treatment needs is based on the amount of pollutant load the individual operator contributes to in the catchment area.

Improved function for calculating distributed acceptable load on receiving…

Improved function for calculating distributed acceptable load on receiving waters

Previous method in StormTac Web of producing distributed acceptable load (kg/ha/year), for the watershed to the recipient, has meant that the recipient’s acceptable load (kg/year) has been distributed over the total area (ha) of the watershed area. The new method is based on the fact that the distributed acceptable load is instead based on the recipient’s treatment needs (kg/year), the total load on the recipient (kg/year) and the area of the watershed area (ha).

It is the pollution load via the drainage (such as stormwater and baseflow) that stormwater measures refer to and therefore the new calculation of distributed acceptable load (kg/ha/year) is based on the total load via only stormwater and baseflow from the watershed area, and does not include the part that comes as direct atmospheric deposition on the recipient surface and not as the part of the groundwater that flows directly into the recipient.

The improved function and description in the guide provides the opportunity to distribute the treatment needs to several actors (the Transport Administration, municipalities, operators, etc.). The distribution of the treatment needs is based on the amount of pollutant load the individual operator contributes to in the catchment area.

 

Improved functions for quantification of uncertainties after scientific review

Improved functions for quantification of uncertainties after scientific review

The revised and improved functions are the result of ongoing work in collaboration with Luleå Technical University with a scientifically reviewed publication on quantification of uncertainties in the StormTac Web application (Wu et al., 2020). The features use a method based on The Law of Propagation of Uncertainties (Taylor, 1994), where absolute uncertainties are calculated from relative uncertainties. This is described in the guide, with reference to the publication (Wu et al., 2020) for more detailed description.

The improvement uses a new function when different values are summed, which reduces uncertainty, while a multiplication gives increased uncertainty, according to a scientifically reviewed paper by Hedbrant and Sörme (2001). This new breakdown using different equations gives changed resulting relative uncertainties for total flow, total load and total concentration before and after treatment, respectively, with consequent changes in calculated absolute uncertainty.

As before, various absolute uncertainties for different substances are obtained, but based so far on assumed relative general uncertainties for concentrations and runoff coefficients from literature values. However, there is a continued collaboration with Luleå Technical University to develop specific uncertainties that take into account the uncertainty in concentrations for each substance and land use from StormTac’s database, as well as for runoff coefficients per land use. That work will be described in a new paper that will also be scientifically reviewed. Implementation of this more advanced uncertainty model is expected to take place within a few months.

18th of March, at the conference VAK2020 Jönköping

18th of March, at the conference VAK2020 Jönköping

Come and meet four of us, on the 18th of March, at the conference VAK2020 (Vatten avlopp kretslopp) in Jönköping, Sweden. There you get the opportunity to ask us questions about StormTac Web and see us show the application live. We will be in Monter 35. Hope to see you there!

/StormTac Team