Bairds Malt News

Title: A silk purse from a sow's ear

Authors: Dr Richard Broadbent (Bairds Malt) & Dr Phil Ham (Envireau Water)

This article was published in the December issue Brewer & Distiller International.

Introduction

As one of the UK's largest Maltsters and Scotland's leading malt producer, Bairds Malt operates five malting plants in the UK with a total output of 250,000t tonnes per year.  Their water consumption is substantial, with approximately 4.5m3 of water required to steep every tonne of barley, meaning their average annual consumption tops 960 million litres.  This equates to a major cost for Bairdsas the majority of the water used for steeping is sourced from mains suppliers. 

The high cost of purchasing mains water means that Bairds are keen to find ways of developing independent groundwater supplies, in order to deliver a significant reduction in the unit cost of water consumed and so give them a major competitive advantage.

The Background to Water Supply at Arbroath Maltings

Bairds' state of the art malting plant at Arbroath was opened an additional 57,000t of annual productionin 2010 and is now capable of producing over 80,000 tonnes of malt per annum and requires water equivalent to 260 million litres per year.

Recognising the advantages to be gained by using an independent water supply, Bairds have made various attempts in the past to supply water from the Old Devonian sandstone aquifer that underlies the site. This aquifer provides an important source of supply for agricultural and industrial operators along the northeast coast of Scotland. In 1993, four boreholes were constructed to target the sandstone, which were drilled to various depths of between 60 and 120m. One of these was brought into production but had to be abandoned after only two years on account of diminished rates of abstraction through biofouling. Another attempt involved the investigation of seven or more shallow boreholes across the site to provide water from shallow deposits above the sandstone, again without success.

Hydrogeological Investigation – What had gone wrong?

The past experience with boreholes at Arbroath led Bairds Malt to the conclusion that they didn't work effectively and when they did, the microbiological quality was poor. Consequently, water has been provided solely from mains water, which has steadily increased in cost, with unit costs essentially doubling over the last 15 years.

In early 2012, Bairds' commitment to reduce production costs led to a more strategic review of water supply at Arbroath. Specialist water resource consultants Envireau Water were requested to carry out a hydrogeological review to investigate whether there was any possibility of securing a sustainable groundwater supply at the site and if so, why previous attempts had failed. This was combined with a review of the existing boreholes, of which only one was still accessible.

The hydrogeological report concluded that there was a good chance of securing a yield of between 35,000 l/hour (35m3/hour) or more from a single borehole at the Arbroath Maltings. A borehole condition survey comprising geophysics and CCTV carried out on the only remaining borehole demonstrated that the majority of inflow horizons within the sandstone were in the top 30m of bedrock. Most importantly, the condition survey also suggested that the issues relating to water quality were most likely related to the poor installation of surface casing, which in this case was very poorly grouted, and completed in the soils overlying the sandstone rather than in competent bedrock. This meant that microbiologically poor quality surface water, high in nutrients on account of the surrounding agricultural land use, could be easily drawn into the borehole.

Envireau Water's conclusions from the investigation were firstly that it should be possible to develop a reliable groundwater supply at Bairds Malt's Arbroath site but there was unlikely to be any significant benefit of drilling boreholes beyond 40m in depth.  Secondly, the water quality issues, which had previously been experienced, could probably be controlled through properly installed casing into competent rock to prevent the ingress of shallow waters.

A Trial Hole to Test the Theory

A practical approach was taken to test the theory. Specialist water well contractors were contracted and the existing borehole was modified by backfilling the bottom section of the existing borehole to a depth of 40mbgl and installing a 150mm diameter uPVC well screen, casing string and grout seal to seal off water in the shallow deposits. The trial borehole was developed using airlifting to maximise hydraulic efficiency and then sanitised on completion to ensure the borehole was microbiologically 'clean'.

A temporary pump was installed into the trial borehole and a short duration test pumping exercise was carried out to test the yield of the borehole and the resulting water quality during pumping. The results revealed that despite the modifications, the yield from the borehole was excellent, delivering around 15m3/hour for only a minimal drawdown in water levels. Whilst the borehole could probably deliver higher yields, the rate of abstraction was now controlled by the smaller diameter of the modified trial hole; in effect limiting the size of the submersible borehole pump that could be physically installed.

The next important measure related to the quality of the water. Laboratory analysis of water samples showed that the raw water obtained from the borehole was essentially of potable quality, with no microbiological loading and requiring no treatment prior to use in the malting process.

The trial borehole had demonstrated that by spending somewhere in the region of £10,000, Bairds Malt was able to turn a forgotten problem into a valuable asset, which is capable of supplying around a quarter to a third of the site's water demand.

From Theory to Full Production

Buoyed by the results of the trial hole, Bairds Malt asked Envireau Water to help them develop and licence a new, properly designed production borehole, with a view to realising the full water requirement at the site, which equated to a design yield of 55m3/hour.

An application was made to the Scottish Environmental Protection Agency (SEPA) to construct and test the new borehole. SEPA raised concerns about the potential impact the proposed abstraction could have on nearby, existing groundwater abstractors and other sensitive water dependent features (streams and rivers). In addition, the proximity of the Arbroath Maltings to the coast meant there was a risk the borehole could induce saline intrusion.

Envireau Water carried out a detailed desk-based risk assessment of the potential impacts supported by field verification to address these concerns. They then negotiated with SEPA to specify practical and appropriate monitoring conditions which could be incorporated into a programme of hydraulic testing, to be carried out following the construction phase of the borehole project.

The new borehole was constructed in November 2012 and comprised a 200mm finished diameter borehole to a depth of 40m with the top 14m cased using mild steel, grouted into place. A programme of testing was carried out in the following December and January, and demonstrated that the new borehole could deliver 35m3/hour sustainably with no impact to any nearby abstractors or other features.

This yield was significantly short of Bairds' requirement, but additional testing proved that a total of 45m3/hour could be delivered by pumping both the new and the trial borehole together.  A further prolonged period of test pumping using this combined strategy, proved that there was no observable impact at any of the nearby water features. The water quality of the yield from both holes remained excellent, showing no microbiological contamination with the boreholes consistently yielding water fit for the intended purpose.

Based on the results of the test pumping, an application was made to SEPA for a full abstraction licence and the final licence, granted in July 2013, was the first in over 20 years in the region.

The Final Installation

With the licence granted, Bairds Malt has now completed both boreholes with permanent submersible pumping equipment installed on a ZSM stainless steel rising main. The ZSM riser was chosen because it is robust and facilitates easy and efficient removal during pump changes or other routine down-hole maintenance.

At the surface, both boreholes have been completed with full stainless steel headworks and pipework leading back to a simple manifold. The combined flow then runs through a UV filtration unit, which has been installed as a failsafe and provides a 'belt and braces' approach to ensuring water quality, though there is no requirement to treat the water. The combined flow then runs into a 15m high storage tank, providing around 219m3 of water storage prior to distribution.

Abstraction, groundwater level, and electrical conductivity monitoring equipment are installed at both boreholes and have been fully integrated into the site's energy management system. The data will be reviewed frequently to monitor the performance of the borehole over time, which will enable a programme of preventive maintenance to be carried out; maximising hydraulic efficiency and significantly reducing the risk of pump and other failures.

Was It All Worth It?

The total borehole project cost is close to >£250,000 but will provide a return on investment in less than 2 years based on  current mains water costs. Even though the capital expenditure is high, the return on investment is clearly good.

The most startling element to the project is perhaps the trial borehole, which, with a very modest investment, was capable of delivering useful quantities of good quality water. This highlights the need for large water abstractors, particularly within the brewing and distilling industry, to revisit old or unused boreholes and investigate whether they can be re-engineered to provide a beneficial commercial asset. And if it can, then it may be worth looking at what else can be achieved at the site to deliver cost savings and competitive advantage.


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