Real Time, High Resolution Monitoring of Discharges from Southend Airport and the Impact on the Eastwood Brook October 2012-March 2013

Matthew Loewenthal and June Jones

National Water Quality Instrumentation Service

Summary

Two real time Automatic Water Quality Monitoring Systems (AWQMS) were deployed in the East Wood Brook and Foxtrot Manhole in close proximity to Southend Airport over the winter of 2012/13.

High resolution measurements were collected for conductivity, ammonium, dissolved oxygen, pH and turbidity.

These parameters were examined to determine whether the effects of de-icing (using potassium derived products) undertaken at the airport, could clearly be identified at the Foxtrot Manhole site and in addition if discharges, containing de icing products, from this point source, impacted upon water quality in the receiving water course; the East Wood Brook.

Ammonium measurements were of significant interest during this investigation as the ammonium sensors used during this investigation are subject to predicable and distinct interferences from both potassium and sodium. For example; two solutions possessing the same conductivity but at concentrations of 23mg/l of potassium and 821mg/l of sodium ion respectively would both produce an apparent reading of 1mg/l of ammonium on the sensor. Reference to be provided 1. Potassium ions are in fact thirty five times more interfering to the ammonium sensor than sodium.

This interference Data from the ammonium sensor, used in combination with measurements of conductivity has been analysed to determine the specific ionic content of samples from both sites at ultra high resolution.

The presence of potassium derived de-icing materials at the Foxtrot Manhole site is confirmed by analysis of interference data. However the same technique has been used to clearly demonstrate: that observed changes in water chemistry within the East Wood Brook are caused by inputs unrelated to discharges from within the airport and are in fact correlated to the introduction of sodium salts to the watercourse as a result of gritting and de-icing of highways by third parties.

Introduction

The Eastwood Brook runs along the northern boundary of Southend airport. Two real time Automatic Water Quality Monitoring Systems (AWQMS) were deployed in the East Wood Brook and Foxtrot Manhole in close proximity to Southend Airport over the winter of 2012/13.

Figure 1 is a map of the deployment area.

Figure 1: Deployment sites of real time monitoring equipment at Southend airport

Method

Automatic Water Quality Monitoring Systems (AWQMS) were deployed at two sites close to the perimeter of Southend airport.

Ammonium, conductivity, temperature, dissolved oxygen; pH and turbidity were measured at thirty minute intervals using a YSI 6600 multi parameter sonde.

Ammonium is measured using an ion selective electrode. In combination with an Ag/AgCl reference. Conductivity is reported as specific to 25 degree c in µS/cm and was calibrated using a solution of potassium chloride (KCl). Dissolved oxygen is measured as % Saturation using an optical sensor. Turbidity is measured using a light scattering technique and is reported in NephelometericTurbidity Units ( NTU’s). pH is measured using a combination electrode.2

The sonde software measures and automatically compensates for the effects of temperature using a thermister of sintered metal oxide.

In order to guarantee the accuracy of these readings, the sensors are calibrated on a monthly basis. Methods are fully described in Water Quality Monitoring system laboratory procedures. 3

The sensors produce electrical signals proportional to the concentration or value of the chemical or physical parameter being measured. This data is then communicated to a radio telemetry system on behalf of the Environment Agency

Results

Separate graphs were made for each site representing each month of deployment. Figures 2, 4 and 6 represent Foxtrot Manhole and Figures 3, 5 and 7 Eastwood Brook. These are found in Appendix I.

Southend Airport has provided the quantities of de-icer used in January 2013.

Figures 8, 9 and 10 represent de-icer usage and graphs of water quality data at Foxtrot Manhole and Eastwood Brook over the same time period.

Figure 11 is a plot of de-icer used in the airport and river flow on the Eastwood brook measured at a gauging station, TQ85856 88875 which is upstream of the real time monitoring equipment. These four graphs can be found in Appendix II.

Time period 19/12/12-19/01/13

Foxtrot Manhole, Figure 2 On deployment conductivity read 849µS/cm, ammonium 0.29mg/l and dissolved oxygen concentration 78.3%. There was an input on the 20th which increased the conductivity to 915µS/cm and ammonium to 15mg/l. Dissolved oxygen remained fairly constant at 76.9%. From the 22nd-28th a series of events caused drops in conductivity with corresponding increases in dissolved oxygen saturation and small increases in ammonium.

From the 28/12/12 until the 8/01/13 a failure of the pumping system was identified.

On the 9th and 15th of January there were inputs which dropped the conductivity readings , the largest was from 860µS/cm to 450µS/cm this was accompanied by an initial increase in dissolved oxygen from 83-90%. Ammonium increased from 0.5 to 4.5mg/l correlated to a drop in dissolved oxygen to 70%. Temperature range over this time was 6-9.5oC.

During this period dissolved oxygen ranged from 70 to 95%

Eastwood Brook, Figure 3 At the start of this time period the conductivity was 1117µS/cm, ammonium 0.4mg/ and dissolved oxygen saturation 113%. Subsequently there were a series of events which resulted in a decrease in conductivity and ammonium readings, the largest of which occurred on the 22nd December when conductivity was 250µs/cm and ammonium 0.2mg/l. There was a corresponding increase in dissolved oxygen during these events.

From the 20/12/12 until the 10/01/13 the temperature ranged from 6.5-9.5oC, after this time the temperature dropped to between 4-6.5oC. On the 15th and 16th of January inputs significantly increased the ionic concentration of the river water. Conductivity was increased in a series of three events and peaked at 2800µS/cm. Ammonium readings and patterns were closely correlated reaching a peak of 1.4mg/l. Over the month dissolved oxygen ranged from 78 to100%.

Time period 20/01/13-19/02/13

Foxtrot Manhole, Figure 4 A series of events from the 22nd to the 28th were represented by an increase in conductivity closely correlated with elevated ammonium levels. Conductivity and ammonium peaks were observed at 2300µS/cm and 28mg/l respectively. Dissolved oxygen did not show significant correlated drops.

There was a pump failure due to the cold weather for a period of 24hours on the 25-26th.

A series of five events from the 30th January to the 14th February decreased the conductivity from around 850µS/cm to 500µS/cm. At these times there were correlated increases in ammonium from 1mg/l to 13mg/l.

Dissolved oxygen saturation also fell on these occasions the lowest level was recorded on the 1st February, 35%, recovering to 80% in under thirty six hours. Temperature ranged from 6-9.5oC and monthly range of dissolved oxygen saturation was observed to be 35 to 95%.

Eastwood Brook, Figure 5 On the 21st there was a large increase in conductivity from 1250µS/cm to 4330µS/cm with closely correlated small increases in ammonium from 0.6mg/l to 1.6mg/l.

Dissolved oxygen saturation remained constant at 83%. Four small inputs from the 24th-26th caused a small but correlated increase in conductivity and ammonium levels. In the first week of this time period temperature ranged from 3-6oC, this then increased to 5-9oC over the second part of the deployment. The increase in temperature coincided with five events which caused a decrease in conductivity and ammonium, the lowest of these occurred on the 1st February, the conductivity was 335µS/cm, ammonium 0.24mg/l and dissolved oxygen 99.7%. There were a series of small increases in conductivity and ammonium on the 5th, 10th,

11th and 14th, the largest of which occurred on the 10th, conductivity 1700µS/cm and ammonium 0.85mg/l.

Time period 20/02/13-6/03/13

Foxtrot Manhole, Figure 6 Over this time conductivity remained very constant 860-900µS/cm, there was very little variation in the dissolved oxygen saturation 100-109% and the temperature ranged from 7-9oC. Ammonium readings ranged from 0.6-1.18mg/l and were erratic in nature.

Eastwood Brook, Figure 7 There were three small increases in conductivity, the largest of these occurred on the 27th when conductivity increased from 1124-1309µS/cm, ammonium increased from 0.53-0.6mg/l. A diurnal pattern in dissolved oxygen saturation was seen throughout this period with a range of 81-113%. The daily fluctuation of dissolved oxygen increased with increasing temperature. In the later part of February temperature ranged from 4-6.5oC, during early March temperatures increased to a maximum of 8.5oC.

Interference

The ammonium sensors used during this investigation are subject to predicable and distinct interferences from both potassium and sodium. For example; two solutions possessing the same conductivity but at concentrations of 23mg/l of potassium and 821mg/l of sodium ion respectively would both produce an apparent reading of 1mg/l of ammonium on the sensor. In practice potassium ions are approximately thirty five times more interfering to the ammonium sensor than sodium ions.

De-icer usage and Flow

The largest usage of de-icer was during the 14th -22nd of January and ranged from 500-2500litres. The highest flows occurred on the 19th and 28th of December and levels peaked at 0.751m3/sec. There were two other increases in flow, on the 1st and 11th of February with a resultant flow of 0.242m3/sec and 0.317m3/sec respectively.

Discussion

The interference data from the ammonium sensor, used in combination with measurements of conductivity has been analysed to inform this discussion and determine the specific ionic content of samples from both monitoring sites.

There were a number of occasions when conductivity and ammonium readings increased at Foxtrot manhole due to inputs with high ionic strengths These occurred on the 20th December, the 22nd, 27th and 28th January.

Six thousand litres of de-icer were used at the airport on the 11th December. Analysis of data was indicative of a rainfall event on the 20th which washed de-icer into the drain increasing the conductivity to 915µS/cm and causing an ammonium interference of 15mg/l. No large correlated drop in dissolved oxygen was observed.

Time correlated data clearly demonstrates no impact on water quality in the Eastwood Brook with peaks in conductivity and ammonium reaching 1117µS/cm and 0.6mg/l respectively.

On the 15th January there were two sharp drops in conductivity at Foxtrot manhole which decreased the conductivity to 300µS/cm from 850µS/cm, with a correlated increase in ammonium to 4mg/l. Flows on the Eastwood Brook increased at this time, indicative of storm events. De-icing activities had occurred on this and the days preceding these events.

Time correlated readings on the Eastwood Brook show conductivity increased from 800-2750µS/cm and ammonium from 0.5mg/l to 1.4mg/l. The size, pattern and relative increases in conductivity and ammonium interference and the absence of significant drops in dissolved oxygen readings are strongly indicative of the presence of road run off containing sodium salts.

Very significant increases ammonium readings correlated to moderate increases in conductivity were observed at the Foxtrot manhole site 22nd, 26th and 27th of January. Conductivity peaked at 1750µS/cm, closely correlated with high very high ammonium readings of 37mg/l on the 22nd. Time correlated readings at Eastwood Brook for both conductivity and ammonium were 4250µS/cm and1.6mg/l respectively.

De-icing activities had ceased on the 22nd January, there was a slight increase in flow arod this time as measured on the Eastwood brook, 0.03m3/sec to 0.05m3/sec.

On the 11th February there was a rain event with an increased flow in the Eastwood Brook from 0.06-0.31m3/sec at the Foxtrot site conductivity dropped and ammonium increased. At Eastwood Brook both conductivity and ammonium increased.

The patterns of conductivity and ammonium levels suggests that the discharge from the drain is not impacting on the Eastwood Brook but it is upstream wash off from gritted roads/discharges which is having the over-riding impact on the in stream chemistry.

Conclusion

This interference data from the ammonium sensor, used in combination with measurements of conductivity has been analysed to determine the specific ionic content of samples from both sites at ultra high resolution.

The presence of potassium derived de-icing materials at the Foxtrot Manhole site is confirmed by analysis of interference data. In addition the same technique has been used to clearly demonstrate: that observed changes in water chemistry within the Eastwood Brook are caused by inputs unrelated to discharges from within the airport and are in fact correlated to the introduction of sodium salts to the watercourse as a result of gritting and de-icing of highways by third parties.

References

1.2. Loewenthal, M, Water Quality Monitoring system laboratory procedures3. YSI, 6 Series, Multiparameter Water quality sondes, User manual, September 2009

Appendix I

Figure 2: Foxtrot manhole 19/12/12-19/01/2013

Figure 3: Eastwood Brook 19/12/12-19/01/2013

Figure 4: Foxtrot Manhole 20/01/13-19/02/13

Figure 5: Eastwood Brook 20/01/13-19/02/13

Figure 6: Foxtrot Manhole 20/02/13-

Figure 7: Eastwood Brook 20/02/13-

Appendix II

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0

500

1000

1500

2000

2500

3000

Volume of de-icer used at Southend Airport

De-icer (litres)

Figure 8: Amount of de-icer used at Southend Airport, January 2013-03-07

Figure 9: Foxtrot manhole 13-23/1/13

Figure 10: Eastwood Brook 13-23/1/13

01/12/2012

06/12/2012

11/12/2012

16/12/2012

21/12/2012

26/12/2012

31/12/2012

05/01/2013

10/01/2013

15/01/2013

20/01/2013

25/01/2013

30/01/2013

04/02/2013

09/02/2013

14/02/2013

19/02/2013

24/02/2013

01/03/20130

1000

2000

3000

4000

5000

6000

7000

8000

0

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0.8

De-icer (litres)FQ [m3/s]

Figure 11: Eastwood Brook flow at Eastwood gauging station and de-icer usage at Southend Airport