Plans to create a wetland have been approved amid fears it could contaminate drinking water supply.

The scheme for the “engineered” landscape in Chilham would help address issues relating to pollution in the River Stour catchment caused by wastewater from housing.

But while water bosses felt the design of the landscaped wetland might harm the supply, Ashford Borough Council planning officers and councillors believed there are enough safeguards in place to prevent that.

The site near the junction of Ashford Road and Branch Road is next to the Great Stour and about 330 metres from South East Water’s drinking water treatment works.

Emma Goddard, head of environment for South East Water, told a meeting of ABC’s planning committee on September 11: “We have serious concerns about this application in its current form due to the risk of contamination posed to the local water supply.

“The proposed wetland is inappropriately positioned in a groundwater protection zone highlighting the vulnerability of a critical public source supplying more than 13 million litres of drinking water every day to the Ashford area.

“We remain concerned about firstly the long-term effectiveness of the proposed wetland design and the risk due to its proximity combined with the transmissivity rate to our abstractions.”

Miss Goddard explained that water abstracted in Chilham is naturally filtered through an aquifer and is currently good quality so very little treatment is required.

She said the only protection of this source from potential contamination from this wetland is a liner. She said if that failed it would lead to an “unacceptable consequence” and ultimately additional cost to customers.

Water abstraction means taking it from a natural source such as a river, lake spring or groundwater.

The demand for wetlands stems from the pollution of Stodmarh Nature reserve near Canterbury and has led to delays for some new housing projects.

ABC believes the Chilham wetlands scheme would help unlock 470 homes proposed for the area.

Kent Mitigation Ltd asked for full planning permission for the wetland which will be designed to receive and treat wastewater effluent from the Southern Water-operated Chilham Wastewater Treatment Works.

The applicant says the wetland would be lined with a geosynthetic clay liner to prevent any infiltration into the ground and is expected to last more than 100 years.

A leak detection system is also planned to be installed as a further safeguard.

But despite the concerns raised by South East Water, 11 members of the authority’s planning committee voted it through and there was one abstention.

Councillors were told the wetland would not need water to be abstracted from adjacent watercourses, including the Great Stour.

Its purpose is to provide additional treatment for sewage effluent from the Chilham wastewater works.

ABC planning officers recommended approval of the scheme, saying risks could also be dealt with through planning conditions.

Their report to councillors said: “Subject to securing conditions the development would comply with relevant policies designed to protect groundwater from pollution.

“In summary the development would improve the quality of the river water whilst protecting the groundwater below.”

Conditions would include a groundwater contamination mitigation strategy and reporting of unexpected contamination.

Cllr Linda Harman (Ash Ind, Saxon Shore) commented: “I think the risk is small - the risk to the aquifer and drinking water being damaged by this development.”

Cllr Ray McGeever (Ash Ind, Kingsnorth and Bridgefield) said: “The risk to the aquifer is minimal, it doesn’t carry any danger.”

The Environment Agency raised no objection subject to the appropriate conditions being imposed and neither did groups such as Natural England.

A total 17 letters of objection from residents were sent to the council planning portal, with locals fearing pollution and harm to wildlife.

Vivien Potter wrote: “I cannot understand why an application for engineered wetlands should benefit the river in any way. I am totally against the scheme.

“This area in itself is a wetland (not an engineered one) that is full of unusual insects butterflies, coots and many other species that should in my mind be left alone.

“I have seen other parts of the river completely ruined by interference from outside sources so I cannot see that what is proposed will be of any benefit.”

Find out about planning applications that affect you by visiting the Public Notice Portal.

Guy Beech wrote: “Over 25 years the river has been seriously degraded by abstraction, sewage outfall and agricultural pollution. The proposed scheme is a further risk to this fragile and rare ecosystem.

“There is no evidence that it will not damage the ecosystem. There is a significant risk of high temperature treated water entering the river causing significant damage to fauna.”

The Stodmarsh is a protected beauty spot and has been affected by wastewater run-off from developments across east Kent causing high levels of harmful nitrate and phosphate nutrients.

As a result, Natural England rules insist developers must ensure all schemes in the River Stour catchment area - stretching between Ashford, Canterbury and Hawkinge - are “nutrient neutral.”

This means developers must either install an on-site water treatment facility or offset the impact by providing mitigation measures elsewhere, such as wetlands.