Design, supply and maintenance of a package sewage treatment plant serving a busy petrol station, retail premises and cafe, discharging to a Site of Special Scientific Interest

10th May 2018

Mike Perris, MD and owner of Britican Master Builders of Windermere, Cumbria, knew immediately that wastewater treatment would be a challenge when he won the design-and-build contract to develop a cafe and planned "go-to" retail destination attached to the existing service station at Ings, between Kendal and Windermere. The site is the former home of a very popular Little Chef so its potential to attract custom was known, and tourists and locals alike often stop to fill up with fuel and a few last-minute groceries as they near their destinations in the southern Lake District.

The site was originally served by a Clearwater trickling filter package sewage treatment plant, installed in the late 1980s or early 1990s. It had since failed and latterly was being used only to store the raw sewage generated on the site, rather than to treat it and discharge it.

Since there had been no discharge, the originalEnvironment Agency consent had lapsed- the annual "subsistence fee" not having been paid -and a new permit was therefore required, to current regulations and standards. Or might it be possible to pump the crude sewage to United Utilities' sewage treatment works in nearby Staveley?

Mike had previously installed a WPL Diamond package sewage treatment plant for a smaller commercial development at St-Johns-in-the-Vale, near Keswick and, pleased with the plants ease-of-installation and build-quality, he approached WPL for guidance. When Mike explained the nature of the project WPL recommended Hutchinson Environmental Solutions to oversee the design of the wastewater treatment solution. WPL's Technical Manager, Dominic Hamblin: "We know that Hutchinson staff have the skills and experience to ask the right questions to identify all sources of wastewater to be treated and from which the hydraulic loads and organic flows - or the amount and strength of the sewage - are calculated. Their familiarity with the location - Hutchinsonhad some years ago designed, supplied and installed a large WPL HiPAF system at The Watermill pub and micro-brewery only 200m away from the service station- and the local support available from Technical Manager Paul Usher, working from Lancaster into Cumbria, made Hutchinson an obvious choice."

Any good installers first step is to establish how many people visit a site, and for what purpose. Data was available on how often the treatment plant, being used as a cess pit, i.e. for storage only, was emptied, and how much wastewater was taken away, but it didn't show peaks and troughs in flows and loads, essential for the good design of a package sewage treatment plant. So, Simon Hockings, MD of AUK Investments, the site's owner, asked his service station staff to count the number of customers who used the toilets. Since the survey was done out-of-season the collected data was extrapolated and correlated to high season usage by comparing monthly turnover and average transaction values from low- and high season. That the potable water consumption figures didn't match the figures for the size of plant that Hutchinson quoted to supply caused eyebrows to be raised until it was explained that the sewage was particularly strong in ammonia due to the disproportionate volume of urine it contained - lots of customers visiting the toilets - and it was this parameter, not the daily water consumption, that was driving the treatment capacity of the plant.

The total volume of the discharge came to less than the 5m3 per day to surface waters that requires an application to be made to the Environment Agency for a Permit to Discharge. (Surface waters are commonly a stream or river that flows throughout the year, as opposed to groundwater, quite literally water that sits below the ground surface level; discharges to ground are almost always via a constructed drainage field.) However, since the discharge point was not just within 500m of an aquatic Site of Special Scientific Interest (SSSI) but was, in fact, directly into the SSSI itself, the River Gowan, a permit was necessary. Simon instructed Hutchinson to prepare, submit and manage the application to the Environment Agency. During the 13 weeks it takes for the EA to assess a permit application it was agreed that the costs of installing a package pump station and rising main to pump to the main sewer would be looked as an alternative solution to deal with the wastewater.

In the meantime, Hutchinson asked WPL to price treatment plants for two different qualities of treated effluent for budgeting purposes as it was thought that a similarly tight, or demanding, numerical consent would be required for the new development as had been for the nearby Watermill. Proving that it's always unwise to try to second-guess the Environment Agency, the permit that was issued was not numerical, i.e. absolute and measureable in terms of the required quality parameters of the secondary treated effluent to be discharged, but descriptive. The descriptive permit in this case said that nopollution, nor the effects of any pollution, should ever be noticeable upon inspection of the river downstream of the discharge point. In many ways such a requirement is more onerous than a demanding numerical consent because a judgement has to be made as to how good the treatment process must be in order to comply. For example, treating the sewage to the same purity as bottled water would guarantee compliance but would be tremendously expensive: doing as little as was necessary would have been the least expensive but wouldn't have offered any peace-of-mind or "wiggle room" in the event of a particularly busy summer holiday period. Hutchinson discussed different choices with Simon and explained their implications, flows and loads were checked again, and it was eventually agreed to increase the size of the treatment plant to allow a greater margin of safety.

As for the package pump station, although even high quality products from Flygt and TT Pumps were far less expensive that the treatment plant, and requiring a utility provider to treat your wastewater is always a first choice rather than a last resort, the cost of laying nearly 1.6km of rising main pipework either across third party land or in the roadside verge proved much more expensive than the whole on-site treatment solution.

Fresh food and hot drinks were to be prepared in the new cafe so anunder-sink GreaseShield grease removal unit was also proposed. The removal of FOG (fats, oils and grease) from wastewater produced by a FSE (food service establishment) is not only a requirement of Building Regulations but absolutely essential for the successful and effective treatment of the wastewater in a downstream package sewage treatment plant. FOG removal also protects other valuable assets such as pump stations.

On placing his order, Simon wrote: "We have been convinced by your knowledge and determination to arrive at the necessary data required to size the appropriate package sewage treatment plant and together with good references we are happy to award the supply contract to your company. We look forward to a rewarding working relationship in terms of maintenance and service requirements of the system in the coming years."

The HiPAF plant was delivered to site on a dedicated HIAB crane-equipped vehicle on Britican's chosen date and time of early morning on Friday 4 December 2016, the day before Storm Desmond hit Cumbria and the north of England in general. The 3.5m deep excavation was even then already making water at an alarming rate so discretion prevailed over valour and Mike sensibly postponed his company's first installation of a large plant until the New Year when water levels had fallen to more manageable levels. He admits to driving past the site several times over the Christmas period to make sure that the plant hadn't floated away from where it was "moored"!

When asked what was important to him about how Hutchinson had approached the project, Mike explained:

"Hutchinson offered a very professional wastewater treatment system design service from the outset with an unbiased approach. On this scheme, I met with representatives from some of the leading manufacturers who were focussed only on selling one of their own systems rather than providing a long term solution which was carefully calculated and considered.

In the past, we have engaged independent drainage consultants but quickly felt like Hutchinson provided more independent and expert advice and could supply whatever we needed, and then commission and maintain it, at great value and with peace of mind.

And it was a real pleasure working with them at Ings I feel like we have been working in partnership a lot longer than just the one project."

The "go-to" retail outlet was revealed to be the new, specialist road-, women's- and children's bike branch of long-established and very successful Ambleside bike shop, Biketreks, now part of AUK Investments stable of companies. That is indeed the same Biketreks that was voted as "one of the world's 7 coolest bike shops" by Esquire magazine, for being "The best mountain bike shop (that's handily next to some mountains)." Incidentally, in the same article, Pave in Barcelona was voted "The best bike shop that's more like an art gallery", a title that could be stolen by Biketreks new outlet, as could "The best bike shop to get a coffee in" category, with Biketreks' adjacent Cafe Ambio. Well worth a visit!


Britican Master Builders


Cafe Ambio


Esquire magazine:

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