Penhesgyn Landfill – Closure, Monitoring and Aftercare
Download the full case study PDF for the complete project overview.
The Challenge
Penhesgyn is a long-standing closed landfill site on Anglesey. When Isle of Anglesey County Council needed to move the site towards aftercare and long-term environmental protection, they faced a set of compounding challenges.
Historic engineering documentation was incomplete. The absence of basal drawings created genuine uncertainty around the site’s original construction – and how it was behaving environmentally in the present day.
At the same time, leachate levels were rising and there was a risk of gas migration. Both issues required timely, expert attention to protect groundwater, surface water, and the sensitive habitats surrounding the site – including adjacent fen and wetland areas.
The Council also needed to rebuild a productive working relationship with Natural Resources Wales (NRW), which had stalled, and establish a credible pathway toward closure and permit surrender.
They needed a consultant with deep landfill experience, strong regulatory knowledge, and the ability to provide practical answers – fast.
That’s where Egniol came in.
What Egniol Delivered
Egniol provided end-to-end project coordination from day one, taking responsibility for health and safety oversight and contractor engagement throughout.
The team delivered a detailed programme of environmental investigation and assessment, including:
- Leachate review – assessing current levels and the condition of existing leachate and gas systems
- Groundwater investigation – examining groundwater interaction and the potential for basal heave
- Gas migration assessment – evaluating perimeter boreholes to understand the extent and risk of gas migration
- Construction Quality Assurance (CQA) – ensuring all excavation and investigative works were carried out without compromising the site’s engineering integrity
Alongside the technical work, Egniol played a key role in re-engaging constructively with NRW on the Council’s behalf. By presenting robust, evidence-led assessments and providing clear technical interpretation, Egniol helped unlock progress on a regulatory relationship that had become difficult to move forward.
This engagement contributed directly to the development of a closure plan addendum – a formal document providing a clear pathway toward aftercare and, ultimately, permit surrender.
The project remains an active management programme, with monitoring and evaluation continuing over a 12–24 month horizon to build the evidence needed for full compliance.
Outcomes and Benefits
Egniol’s involvement has delivered measurable results across four areas:
Cost Savings
Rationalised monitoring reduced the number of boreholes required, cutting unnecessary testing and maintenance spend without compromising compliance or environmental oversight.
Regulatory Compliance
Clear, evidence-based reporting gave the Council the confidence to demonstrate compliance with NRW’s requirements – turning a difficult regulatory relationship into a constructive one.
Environmental Protection
Proactive measures to manage gas migration and potential groundwater impacts have helped protect the sensitive habitats adjacent to the site, including fen and wetland areas, while maintaining its strong environmental performance record.
Strategic Guidance
Egniol’s broader industry expertise supported wider due diligence, helping the Council think through long-term infrastructure and asset management options with greater clarity.
The longer-term goal is permit surrender – which would substantially reduce the Council’s ongoing operational costs and liabilities, and enable the land to transition towards re-wilding and ecological recovery.
What the Client Said
“Working with Egniol on the Penhesgyn landfill site on Anglesey has been a genuine partnership. Together we’ve addressed both long-term and immediate challenges on site, from groundwater and gas monitoring to ongoing compliance with NRW. The Egniol team’s expertise in landfill management has been invaluable – guiding us through testing, trials and practical solutions that ensure the site continues to operate safely and sustainably.”Bob Parry, Principal Waste Management Officer, Penhesgyn Waste Site, Isle of Anglesey County Council
An Ongoing Relationship
The Council has described Egniol as their first point of contact for technical support – able to provide fast, authoritative answers where regulators or other contractors could not.
Three qualities stand out in the way the relationship has developed:
| Responsiveness “When we call, we get answers the same day, not in two weeks.” | Trust Egniol’s expertise has enabled the Council to engage confidently with NRW, overcoming barriers that had previously blocked progress. | Reliability Practical, solution-focused advice has been central to unlocking movement on a site that had long been stalled. |
The Council has since recommended Egniol to other local authorities, including Gwynedd Council, where Egniol has gone on to secure further landfill projects.
Download the full case study PDF for the complete project overview.
Could Your Site Benefit from the Same Approach?
Whether you’re managing a legacy landfill, reviewing your monitoring plan, or looking to build a credible path toward permit surrender, Egniol provides experienced, practical support across the full landfill lifecycle.
Get in touch for a no-obligation review of your site
Or contact Michelle Moran directly:
Email: [email protected]
Telephone: 01248 355996
Related resource: Egniol’s Practical NRW Guide for Landfill Compliance, Cost Control & Closure – a free guide covering monitoring frameworks, leachate and gas strategies, and a step-by-step closure pathway aligned to Welsh policy.
