Kemira Oyj/Kemira M&I ABSTRACT Vesa Kettunen ... - Svenskt Vatten

Title: A GIS based environmental risk assessment of wastewater pumping station overflows
Name of author: Leena Sänkiaho, M.Sc(Eng.)
Name of the institution: Pöyry Finland Oy, Jaakonkatu 3, 01621 Vantaa, Finland
E-­‐mail address to the author: leena.sankiaho@poyry.com
Platform presentation
Language of the platform presentation: English
The Helsinki Region Environmental Services Authority (HSY) operates nearly 500 wastewater
pumping stations around the Helsinki metropolitan area. As HSY is currently renewing its
environmental permit, they are obliged by the environmental authority to conduct an environmental
risk assessment, which reviews the wastewater pumping station overflows. Similar studies have not
been conducted before, hence there are no common guidelines or previous examples of how the study
should be carried out.
To go through all 500 pumping stations individually would have been time consuming and inefficient.
This led to the development of a new geographic information system (GIS) based method. The
presentation will include a description of the method used and how the results can be utilized.
In Finland the Finnish Environment Institute and The National Land Survey of Finland publish free GIS
data. For instance all groundwater areas, lakes, rivers, sea shore and nature reserves are available in
GIS formats. In addition the metropolitan area cities have conducted surveys that map the ecologically
valuable small streams. Beaches can be mapped according to the address details available. HSY
supplied the coordinates of the fresh water intakes. All these data was used as separate risk layers in
the GIS analysis. The layers were rated according to the severity and consequence a sewer overflow
may pose. The rating method has been modified from the rating method used in Water Safety Plans
(WSP) (Bartramet al. 2009).
HSY provided the pumping station coordinates and capacities. The GIS analysis is based on an overlay
operation. If a pumping station overlaps a risk layer, the pumping station will be awarded with the risk
rating.
There are three ways to utilize the results: risk layers, risk sums or risk scores.
Risk layers:
This method detects the pumping stations which are located on certain risk layer. For instance
pumping stations which are located less than 500 m from a beach can be listed and certain risk
prevention methods can be applied to these stations or beaches.
Risk sums:
A risk sum is the aggregated risk rate for each pumping station. It is assumed that a pumping station
will have a higher environmental risk if it is located on more than one risk layer. The values range
from 0 to 6. For instance, the highest risk sum was allocated to a pumping station that is located on a
groundwater area, it is also on the buffer zone of a groundwater well (< 500 m) and less than 100 m
radius from an ecologically valuable small stream.
Risk scores:
It is assumed that the overall risk is also related to the pumping station capacity as the pumping
station capacities vary from 3 l/s up to 2000 l/s. Therefore the risk sums were weighted by the