MNA can be a sustainable risk management strategy for a wide range of groundwater contaminants where environmental data are collected and assessed that demonstrate  natural attenuation will protect receptors from pollution or harm. Understanding natural attenuation and performing MNA requires evolution of an advanced conceptual site model describing relevant processes and associated risks, overlapping with requirements of hydrogeological risk assessment for land contamination.

Despite this, characterisation, monitoring and predictive modelling approaches and technologies developed for MNA, are not routinely considered for hydrogeological risk assessment. 
Since the Environment Agency originally published technical guidance for MNA in 2000, significant scientific advances have been made that more ably provide convergent lines of evidence for plume mass or concentration reduction than were previously possible. These methods are captured in recent technical guidance about MNA published by CL:AIRE. An overview of the updated guidance will be presented, highlighting applications of newer MNA methods to better understand risks to groundwater dependent receptors.

A case study presentation of the use of the SoBRA AiSHHRA toolbox as part of expert evidence given in conjoined environmental permit appeals for two soil treatment facilities in England.  The presentation will cover the use of the AiSHHRA toolbox in evaluating the potential fugitive airborne fibre release from the STF operational activities and the consequent off-site exposure risk to identified receptors.

A case study will be presented for a former colliery and coking works site in the UK, which was subsequently redeveloped into a residential estate comprising approximately 200 houses. The Site was being assessed under Part 2A, with arsenic identified during initial investigations as one of the primary contaminants of concern.

The driving pathway in relation to arsenic exposure in a residential setting is the direct soil and dust ingestion pathways. Modification of model input parameters associated with this exposure pathway can be challenging, as these parameters are justified based on national or international studies which evaluate population behaviours. However, the relative bioavailability of arsenic adopted in modelling is often considered conservative. As such, a multiple lines of evidence approach was adopted for the assessment of arsenic exposure in soils, which included detailed soil characterisation, bioaccessibility testing, derivation of Site-specific criteria and statistical analysis. The methodology employed and the results of the bioaccessiblity testing and statistical analysis will be shared from the case study to demonstrate how this impacted upon decision-making at the site.

RBKC and AECOM carried out a Part 2A site investigation at a residential housing development where earlier sampling had identified high lead concentrations. Investigation was carried out to evaluate the risk to site residents in accordance with Part 2A.  

235 soil samples were collected and analysed for lead from 90 hand pit locations at varying depth intervals, including 0-5cm, 10-20cm, 30-40cm and 60-70cm.  After screening soil concentrations against GAC, the DQRA for lead was completed in two steps.  Step 1 involved calculating SSAC using site-specific information that would be considered to meet the definition of Category 4 land.  Key changes for the Step 1 SSAC derivation included adjustment of the exposure frequency, occupancy period and exposure duration, and reduction of the soil ingestion rate (SIR) based on USEPA 2017 guidance.  Site specific bioaccessibility results were also adopted. A Step 1 SSAC of 1,060mg/kg was derived for child residents, and 2,150mg/kg for adult residents. There was also detailed consideration of normal background concentrations.

Step 2 involved calculation of an SSAC for child residents at which SPOSH might exist i.e. Category 2 land.  For Step 2, additional modelling changes included increasing the toxicological threshold (from 3.5ug/dL to 5ug/dL), further reduction of the SIR based on USEPA 2017 guidance, and a reduction in the assumed contribution to indoor dust from garden soil.  These further changes resulted in a Step 2 SSAC for child residents of 4,530mg/kg.  Ultimately comparison of the site soil concentrations with the Step 2 SSAC resulted in the conclusion that the land would fall into Category 3 in accordance with Part 2A. Subsequently a detailed modelling exercise considering of exposure frequency and occupancy period was undertaken and confirmed the model assumptions.

RBKC and AECOM now intend to use this approach to produce refined Category 4 screening levels within RBKC.

To date the most highly exposed populations to PFAS remain those commercial industrial worker populations associated with manufacture or high-volume use along the product supply chain.  Contrary to our preoccupation with PFAS in drinking water, these worker population exposures are not driven by ingestion exposures but rather by inhalation (particulate, aerosol, and volatile components).  Despite this, there are very few inhalation exposure studies which can be used to assess current or future potential exposures.  Where ambient or indoor air screening levels do exist, they are predicated on ingestion-based toxicity criteria through simple route to route extrapolation, rather than expressly designed inhalation studies.  This discussion will address PFAS inhalation exposure assessment options, inclusive of volatility and vapor intrusion potential, along with toxicity criteria attendant uncertainty, for use in assessing particulate, aerosol, and volatile components under residential and commercial/industrial land uses.

Numerous per- and polyfluoroalkyl substances (PFAS) are detected in environmental media at hazardous waste (e.g., Brownfield) sites. However, there are limited PFAS regulatory toxicity values for assessing human health risk. The need to address toxicity and risk of all PFAS detected at a site is reflected in regulatory guidance and policies. Jacobs is conducting the environmental investigation, human health risk assessment, and remedial design for a PFAS investigation and cleanup at a site in Ontario, Canada. 

This presentation will provide an overview of the project and summarize the approach used to assess human health site-specific risks of PFAS with and without regulatory toxicity values. It is recognized that alternatives to animal and human studies are needed to understand the potential toxicity of the many PFAS. There has been exponential growth over the last ~20+ years in the development and application, by academic, regulatory, and industry scientists, of innovative New Approach Methods (NAMs) that provide toxicity information without using animals.  NAMs can reduce animal testing, scientific uncertainties, and facilitate more defensible risk assessments. The innovative generalized read-across (GenRA) computational toxicology NAMs tool for assessing relative toxicity to chemicals without regulatory toxicity criteria was incorporated into this case study’s quantitative human health risk assessment. 

An overview of the risk assessment methods and results will be provided, including how GenRA NAMs were utilized. The relevant strengths, limitations, and challenges will be summarized.  The lessons learned and relevance of the methods/conclusions for conducing PFAS risk assessments in the UK will also be discussed. 

In this presentation, Lucy will introduce the “wicked problem” of Antimicrobial Resistance, its relevance to the environment and how it is applicable to contaminated land practitioners both now and in the future. Lucy aims to present both the potentially devastating impacts AMR could have but also the positive steps that are being taken and why she believes that land contamination practitioners are well suited to using their skills to tackle this global threat.

A case study will be presented of the additional site characterisation and visualisation undertaken by AECOM to inform and communicate the conceptual site model for the Shawfield Masterplan area of southeast Glasgow. The Masterplan area is affected by a legacy of hexavalent chromium impact to soil, groundwater and surface water resulting from 150 years of chromate production. The evolution of the conceptual site model has also driven a review of the risks posed to the adjacent River Clyde. Groundwater discharge to the River Clyde across five geological strata was calculated and used to compare to observed chromium impacts within the River. Using the calculated discharge a revised site-specific assessment criteria for groundwater protective of surface water quality within the River was calculated, taking account of potential future climate change.