1. Assessing Metaldehyde Concentrations in Surface Water Catchments and Implications for Drinking Water Abstraction
Alemayehu Asfaw, PhD student - University of Sheffield
James Shucksmith, Senior Lecturer – University of Sheffield
Andrea Smith, Process Engineer, Severn Trent Water Ltd
Katherine Cherry, Catchment Management Advisor, Severn Trent Water Ltd
April 16, 2015
Vienna

2. Outline Background Metaldehyde in surface water Managing mataldehyde
Grab sampling
Managing mataldehyde
Catchment management
Abstraction management
Auto-sampler data collection
Catchment characteristics Vs metaldehyde
Conclusions and Future work
Why? What? How? What are the benefits to the business?

3. Background Metaldehyde, active ingredient in slug control
Heavily used in agriculture (6000 – tons every year in UK)
Application period between September – December
Following periods of heavy rainfall, reaches water sources
Can not be removed by existing treatment process

4. Metaldehyde in Surface Water
Grab sampling
Why Sampling?
Understanding where and when high levels of metaldehyde occur in the catchment
Identify high risk areas and target catchment management work
R. Leam
R. Itchen
R. Rains Brook
R. Radford Brook
- Grab sampling Points
- Used for catchment management practices
When and where are samples taken?
Sample locations are chosen to capture the influence of different tributaries
Samples are taken on a monthly basis increasing frequency at high risk times

5. Metaldehyde in Surface Water
R Leam source to conf Rains Brook
R Leam conf Rains Brook to conf R Itchen
R. Leam
R. Itchen
R. Rains Brook
R. Radford Brook
- Grab sampling Points
Willes Meadow Bridge
Grab sampling data
- Used for catchment management practices

6. Metaldehyde in Surface Water
General trend of metaldehyde application generated from grab sampling data
Week numbers starting from first week of September
Rainfall event at each week causes different rate of metaldehyde flux in to water bodies.
- Used for catchment management practices

7. Managing Metaldehyde Effective catchment management strategies.
Identify high risk areas
Target catchment management work and engage with stakeholders
Drinking water abstraction management to reduce the amount of metaldehyde finding its way into drinking water systems.
understand which hydro-meteorological characteristics of the catchment trigger the peak migration of metaldehyde to surface waters
assess the relationship between measured metaldehyde levels and catchment characteristics
Fine scale datasets required to link rainfall events to fate and transport of metaldehyde
such as land use, topographic index, proximity to water bodies and runoff generation area

8. Data Collection Auto-sampler locations in the River Leam catchment
R. Itchen
R. Rains Brook
R. Radford Brook
such as land use, topographic index, proximity to water bodies and runoff generation area

9. Auto-sampler data Triggered when there is rainfall
24 slots - Hourly samples
Five events (3 and 5 day)
EU limit in drinking water
EU limit in drinking water
EU limit in drinking water
Peak metaldehyde flux is related with high rainfall intensity
Delay of
- such as land use, topographic index, proximity to water bodies and runoff generation area

10. Flow Vs Metaldehyde
Flow variation triggered mainly by direct runoff has shown some correlation with metaldehyde concentration
Rate of runoff generations from different parts of the catchment impacts flow Vs metaldehyde correlation

11. (1 Km2 and 5 minute resolution)
Rainfall Variability
Assess the impact of rainfall variability on Metaldehyde generation
Metaldehyde risk map
Rainfall
Radar rainfall
(1 Km2 and 5 minute resolution)
River
High risk area
Auto-sampler location
High risk Area
Most of the past studies have primarily focused on the assessment of the influence of spatial rainfall variability on hydrologic responses, such as runoff volume, time to peak runoff, and peak runoff rate. Information on the effect of spatial rainfall variability on pollutant transport is limited.
Low risk Area

12. Rainfall Variability
Comparison of rainfall on high risk areas to low risk areas
Significant rainfall variability has not been observed during data collection events. However, rainfall variability needs to be considered in the development of prediction model.

13. Rainfall Vs Metaldehyde
36 hours
36 hours

14. Conclusions Conventional grab sampling data is highly variable
Doesn’t provide full understanding of the occurrence of metaldehyde in the water environment
Can mislead on the prediction of potential risk of exposure
Grab sampling routines need to be guided by initial assessments using high resolution data and risk map assessments (information on when and where to take samples).
Surface water abstraction can be managed to avoid the entrance of peak metaldehyde concentrations into drinking water system with no significant impact on abstraction volumes
Future work
Auto-sampler starting time
Use detailed weather prediction data
Turbidity data
Use in-catchment grab sampling data, land use map, and recommended metaldehyde application and application information to predict application dose
Develop prediction model to inform abstraction decisions based on
Rainfall intensity/duration
Direct runoff
Duration between rainfall events
Pesticide application

15. Thank you