Assessing Metaldehyde Concentrations in Surface Water Catchments and Implications for

Drinking Water Abstraction

Alemayehu Asfaw, PhD student - University of SheffieldJames Shucksmith, Senior Lecturer – University of Sheffield Andrea Smith, Process Engineer, Severn Trent Water LtdKatherine Cherry, Catchment Management Advisor, Severn Trent Water Ltd

April 16, 2015Vienna

Outline

• Background• Metaldehyde in surface water

– Grab sampling• Managing mataldehyde

– Catchment management– Abstraction management

• Auto-sampler data collection• Catchment characteristics Vs metaldehyde• Conclusions and Future work

Background

• Metaldehyde, active ingredient in slug control• Heavily used in agriculture (6000 – 10000 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

Metaldehyde in Surface Water

R.

Leam

R. Leam

R.

Leam

R. Itche

n

R. Rains

Brook

R. R

adford

Brook

- Grab sampling Points

Grab sampling

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

Why Sampling?• Understanding where and when high

levels of metaldehyde occur in the catchment

• Identify high risk areas and target catchment management work

Metaldehyde in Surface Water

Grab sampling data

R.

Leam

R. Leam

R.

Leam

R. Itche

n

R. Rains

Brook

R. R

adford

Brook

- Grab sampling Points

Willes Meadow Bridge

R Leam conf Rains Brook to conf R Itchen R Leam source to conf Rains Brook

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.

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

Data Collection

• Auto-sampler locations in the River Leam catchment

R.

Leam

R. Leam

R.

Leam

R. Itche

n

R. Rains

Brook

R. R

adford

Brook

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 waterEU limit in drinking water

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

Rainfall Variability

• Assess the impact of rainfall variability on Metaldehyde generation

Metaldehyde risk map

RiverHigh risk areaAuto-sampler location

Radar rainfall (1 Km2 and 5 minute resolution) High risk Area

Low risk Area

Rainfall

Rainfall Variability

• Significant rainfall variability has not been observed during data collection events. However, rainfall variability needs to be considered in the development of prediction model.

Comparison of rainfall on high risk areas to low risk areas

36 hours

36 hours

Rainfall Vs Metaldehyde

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

Thank you