Detecting oil, hydrocarbons and pollution in river water

Introduction

In this study, we are going to look at how the MS1200 Oil in Water/VOC/Hydrocarbon analyzer has been used by municipal water companies in the UK. Specifically, we will show how the instrument has been used to monitor spillages and contamination events affecting source water, and how this detection has been beneficial to the water companies concerned.

We will also look at some graphs that show what kind of response can be expected during different kinds of events, and we will also briefly discuss what subsequent measures the water companies can take and some technical details relating to this application.

Case Study – Protecting a Water Intake from a Kerosene Spill

The water intake feeds a water treatment plant which is located 300m away.

It is located in a rural area with issues of high Ammonia levels from surface water run off (fertilizer and livestock). The water has wide ranging levels of turbidity dependent upon rainfall. Ambient temperature and flow levels also vary widely due to the geography.

The river is in a steep valley and a major road runs parallel to the river for a long distance, with a high probability that accidents will cause a pollution incident.

The lack of mains supply of gas also means that there are many farms and houses using and storing kerosene for heating, as well as diesel fuel for agricultural vehicles. Environmental contamination from these sources is frequent and usually goes unreported.

The intake is also vulnerable to illegal dumping of petroleum based products.

Unfortunately, the water supply from this site is key to the water company due to the geography of the local area and the lack of an alternative water supply in the event that the treatment works be affected by a pollution incident.

The water company installed a VOC Analyzer supplied by Multisensor Systems in 2013 as part of a suite of instruments to protect the intake. It had previously used Multisensor’s products successfully as part of a response to a major spill of kerosene, which threatened the aquifer elsewhere in their region.

The lack of sensitivity to changes in the turbidity of the river water was a key factor in selecting Multisensor’s technology against others, such as optically based systems which are inherently susceptible to false readings and to equipment failure in turbid water.

After a number of months the analyzer saw an event which closed the site. The plot from this can be seen below. This event was slow to clear and was due to a spill of kerosene heating oil. The rise in concentration can be seen to the point where the pumps were turned off to prevent damage to the plant. Once the incident had passed the pumps were turned back on and normal operation resumed.

Installation of the instrument was completed without any issues and integration to the customer’s SCADA system via the 4-20mA connection was trouble free once correctly scaled.

The only issue which has been experienced at the site was the cleanliness of the feed to the sample tank, which is required to be cleaned once a month in this application. This was cured by increasing the pressure of the feed to the sample tank, the removal of redundant ancillary components and updating of internal procedures to include the cleaning process.

The instrument has continued to work without interruption since the event and its subsequent planned service.

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Case Study – Monitoring in a Borehole

The borehole is located in an urban area in the South of England and it supplies water to customers in the locality.

The borehole has been sunk into strata which causes the water to have a high Iron content, increasing the turbidity of the incoming raw water. Additionally, there is the issue of contamination from spills of Hydrocarbons , particularly one from a local fuel retailer. As a result the location was deemed to be high risk and VOC Monitoring was specified.

The Multisensor MS1200 was successful in this application because of its non-contact measurement technique and immunity from the condition of the water being tested.

Initially an instrument using UV fluorescence as the VOC sensing technique was used. It soon became clear that this kind of system could not cope with the high iron content of the water, which caused iron oxide to be deposited on the optical components, resulting in failure of the instrument within days. The local water company had repeatedly had the instrument re-setup and calibrated, but it always failed again very quickly.

After some time the UV fluorescence system was abandoned in favor of the Multisensor Systems MS1200. This was in early 2015. The MS1200 was installed and commissioned and then challenged with varying concentrations of Diesel in solution in the water under test up to 20ppb. This testing was successfully passed.

Since installation the MS1200 at the site has not been out of action for any time at all.

The lack of sensitivity to changes in the turbidity of the water was a key factor in selecting Multisensor’s technology against others, such as other optically based systems, which are inherently susceptible to false readings and equipment failure in turbid water. Multisensor’s use of “e-nose” technology makes their products immune to turbidity and highly reliable.

The MS1200 is reading 0 – 30 ppb levels typically and is used to control the pump so that in the event of elevated levels of VOCs in the water the pumps can be automatically turned off. The MS1200 has provided trouble free operation for more than one year, needing only to be serviced every six months. The water company has also begun rolling out the MS1200 in other locations, in both ground water and surface water applications.

Case Study – River Intake Protection

This intake is located in the East Midlands. The intake feeds a WTW which is located 1 km away. The intake is licensed to extract 60 M liters annually.

The River has wide ranging levels of turbidity dependent upon rainfall.

The river is used by light marine vessels for pleasure and is crossed by roads. It is also vulnerable to illegal dumping of petroleum based products.

The local water company has installed two VOC Analyzer supplied by Multisensor Systems after exhaustive testing in 2011. This was an upgrade from a previous system, also provided by Multisensor Systems. The lack of sensitivity to changes in the turbidity of the river were a key factor in selecting Multisensor’s technology against others such as optically based systems which are inherently susceptible to false readings and equipment failure in turbid water.

The River has seen few significant events with the recorded levels of hydrocarbons up to 5ppb.

The main issues have been the cleanliness of the sample tank, which is required to be cleaned once a month in this application. An event in 2016 is shown below. Here can be seen a clear peak in VOCs in the water. The event was not sufficiently high to automatically close the treatment works, but demonstrates the sensitivity of the equipment to any event, in this case an event which was short term and passed quickly.

What to do in case of an alarm?

The Multisensor VOC Analyzer

As we have seen in the previous case studies, once an analyzer is set up and running, it’s very likely that at some point during the operation it will detect a contamination event. So what are the options available to water treatment plant once the analyzer detects an event? Below you can find a non-exhaustive list

1. Protect the water treatment plant
   The first step will be obviously to automatically shut down the water intake and stop the water from reaching the water treatment plant. This is usually done by stopping the water abstraction pumps and/or diverting the contaminated water via a valve to a retention tank or back into the river if no other options are available
2. Investigate the event
   The second step is usually to promptly start an investigation to determine the source of the pollution event (sometimes it’s a real accident, sometimes it can be a malicious act). Fast action is needed in order to identify potential culprits like an illegal discharge from a factory or from private individuals
3. Clean-up operations
   In the case of a substantial spill that might affect ,for example, an aquifer, clean-up operations might involve digging up the contaminated soil, putting in place some underground barriers (in the form of a wall) and so forth
4. Risk Assessment
   Once the emergency has been dealt with an the full picture emerges, it’s now time to make a risk assessment and define the likelihood of a similar event to happen again in the same area or in other areas of interest for the water supply
5. Risk Management and Reduction
   Finally a number of steps can be taken in order to reduce the risk (exclusion zones, controlled areas) and to manage the risk by, for example, adding additional monitoring points upstream and/or downstream

Since water companies operate in an ever changing environment the risk assessment should be a reiterative process and part of an ongoing improvement program.

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Unexpected Results with a VOC Analyzer

Very often customers who install a VOC analyzer start from the assumption that they are abstracting water from a relatively clean body of water that need to be protected from unexpected pollution events. However, our experience on hundreds of sites shows that, whilst in most cases this is true, there are some cases where there was already a relatively high level of background contamination which the customer wasn’t aware of.

This usually happens when the contamination is due to some exotic contaminants which are not detected during routine analysis. In fact, routine tests will usually look for a number of widely used VOCs such as benzene, toluene, total xylene, trichloroethylene etc.. and these tests usually are in the region of hundreds of pounds. On the other hand, if it is required to know everything that is present in the water then a full chemical analysis should be carried out, which takes some time and above all, is much more expensive (£1000-£2000).

Conclusions

Our MS1200 Total VOC monitor is a wide-spectrum detection monitor, which enables water companies to not only detect pollution events and spills, but also to get a better understanding of their water abstraction points.

Use of monitoring mitigates risk ,and whilst not every abstraction point is susceptible to spills, many are and the costs of such an event are very high.

Using this technology in conjunction with risk assessment procedures and risk management plans, can help water companies to protect their water reserves and avoid problems due to interruption of supply, contamination of assets, financial penalties and damage to the water company’s reputation.

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