Guidance

Engineering construction proposals for deposit for recovery

Updated 29 June 2023

Applies to England

This guide will help you find out what borehole monitoring infrastructure and attenuation layer information you must include in your construction proposals.

Risk assessment

If you apply for a bespoke deposit for recovery activity permit, you must understand and describe your site. You will need do a risk assessment to support your application.

Where your site is in a sensitive groundwater setting, you will need to carry out a hydrogeological risk assessment. Find out what you must include in your hydrogeological risk assessment

Your risk assessments may show that you need to install infrastructure to:

• protect the environment from your activity
• monitor changes to the environment to show that your activity is not causing pollution

Construction proposals

Depending on the waste you intend to deposit and the sensitivity of the site, you may need to build an attenuation layer across the base and sides of the site to protect soil and water. You may also need to install site infrastructure such as boreholes to monitor soil gas, or around the site to monitor groundwater. You may also need to manage surface water at your site.

Your need to agree your construction proposals with your local Environment Agency office before you start work. The Environment Agency will normally accept a single set of construction proposals to cover an attenuation layer for the whole site. You will normally only need to provide construction proposals for groundwater monitoring, soil gas monitoring or the surface water drainage system once.

If the Environment Agency grants a permit, the conditions will tell you when you must send them detailed construction proposals and a construction quality assurance (CQA) plan.

All personnel involved in the CQA plan and its procedures must be appropriately qualified. They must be independent of the permit holder and construction contractor.

Construction quality assurance plan contents

Your CQA plan must specify which codes of practice and guidance you plan to follow.

It must also show how you will make sure that you use suitable materials to construct the attenuation layer or site infrastructure.

Information you must include in your CQA plan

Your CQA plan must include:

• the design of the engineered attenuation layer or site infrastructure
• a method statement for the construction and placement of the attenuation layer or site infrastructure
• criteria you will use for rejecting any materials that are not suitable for the attenuation layer or site infrastructure
• how you will assess specific design criteria with clearly defined acceptable limits

Your CQA plan must include details of:

• records you will keep and methods of reporting
• the surface water drainage system
• groundwater monitoring boreholes
• gas monitoring boreholes
• permeability testing the CQA engineer will do on the attenuation layer (at least 4 tests per hectare) – you must agree the method you will use to determine permeability with the Environment Agency
• your field trial to verify the suitability of the construction method – show that you will achieve thickness and permeability standards in the attenuation layer

You must only use cohesive material to construct your attenuation layer. It must achieve the permeability and attenuation standards identified from your risk assessment.

You must consider the Environment Agency guidance on monitoring landfill leachate, groundwater and surface water if you need to install groundwater monitoring boreholes.

You must consider the Environment Agency guidance on drilling into waste on landfill sites if you need to drill into waste.

Your CQA plan must show how you will:

• achieve and check the properties of materials you will use
• achieve and check the shape and size of the structure you are building
• train site staff on the requirements of your CQA plan, including record keeping and procedures for selecting material
• record compliance with the construction method so that the CQA engineer or inspector can audit the records
• use CQA procedures to make sure that any material you use in the attenuation layer is physically and chemically suitable

Using waste in your attenuation layer

You must only use materials that can achieve the permeability and attenuation standards identified in your risk assessment.

If you are going to use waste in your attenuation layer, you must confirm that it is chemically and physically suitable by:

• making sure that the waste is from a single source or waste type
• making sure it meets the definition of inert waste
• making sure the waste has a pollution potential less than, or equal to, the natural quality of the surrounding geology and water
• using suitable cohesive material in the attenuation layer (you must test this waste as part of your material assessment)
• confirming that the attenuation material will not leach non-hazardous pollutants into groundwater
• including evidence that the material contains no hazardous substances at sites over a principal aquifer or below the water table

Using waste beneath groundwater level

Where you need to construct the sub-grade or attenuation layer beneath groundwater level, you must include details of how you will do this in your application.

Where your risk assessment requires your attenuation layer to provide a continuous barrier to the base and sides of your site, you must be able to construct this to the required thickness and permeability.

For more information see the guidance on depositing inert waste into water.

The design must demonstrate the stability of any sidewall attenuation layer above and below the water level.

Construction quality assurance supervision

The Environment Agency requires different levels of CQA supervision depending on the location of your site relative to a secondary or principal aquifer.

You must provide full time CQA supervision when you construct groundwater monitoring or soil gas monitoring infrastructure.

Secondary B Aquifer site

The CQA engineer must carry out 1 visit per 10,000 cubic metres of attenuation material laid, or 1 visit for each 2 weeks of engineering works.

Secondary A or principal aquifer site

The CQA engineer must carry out 1 visit per 5,000 cubic metres of attenuation material laid, or 1 visit for each week of engineering works.

The CQA engineer must be appropriately qualified and have at least 6 months’ experience of earthworks on landfill or recovery sites or the method of constructing the site infrastructure.

An appropriate qualification is a formal qualification in science or engineering. For example, an OND, ONC or higher in:

• civil engineering
• mining engineering
• engineering geology
• geology
• building or quantity surveying
• science with training in soil mechanics

The engineer must be supervised by a chartered engineer or geologist with more than 5 years’ experience.

Site records

You must keep records of all construction activities at the site or at a location agreed in writing with your local Environment Agency office. Include all of the following:

• photographs of the works
• a site diary maintained by site staff showing works carried out, CQA visits, non-conformance and remedial actions
• the identity (source, quantity and dates of delivery) of all material used in the attenuation layer or site infrastructure
• the results of any geotechnical or chemical testing on the attenuation layer material
• the results of any testing on the materials used for the site infrastructure
• dates and times when the attenuation layer or site infrastructure was constructed
• details of any unsuitable materials, including source of material, reasons it was considered unsuitable and action taken
• the progressive construction of the attenuation layer, marked on a plan
• the progressive construction of the groundwater or landfill gas monitoring boreholes
• thickness of the layer as placed, either by records of the location and depth of trial pits or isopachyte survey plans

Validation report

The validation report confirms that your construction method has produced an attenuation layer, or other infrastructure, that complies with your CQA plan.

Your validation report must include:

• details of how you have complied with your CQA plan
• justifications for any changes or deviations from the agreed plan
• all design calculations or, if these have been included in the CQA plan, reference to the relevant sections of the CQA plan
• as-built plans and cross-sections of the attenuation layer and site infrastructure
• copies of the site engineer’s daily records
• records of any problems or non-compliance and the solution
• any other relevant site-specific information to prove the integrity of the construction
• all test results

Test results include:

• all records showing compliance with the specification
• records of any failed tests with a written explanation
• details of the remedial action you took
• references to the appropriate secondary post-remediation testing
• plans showing the location of all tests

A chartered civil engineer or geologist must sign the validation report.

Send the validation report to your local Environment Agency office when the work is complete.