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Case Study

Phase I Hazard Identification and Assessment P & B Ltd.

Phase I Hazard Identification and Assessment P & B Ltd.

Geotechnology recommends a phased approach tosite investigations in accordance with guidanceproduced by the NHBC and the EnvironmentAgency. Phase I should comprise HazardIdentification and Assessment. This initial Phaseinvolves desk study review and a site walkover.These activities enable a Conceptual Site Model(CSM) and Preliminary Risk Assessment (PRA) tobe completed and the scope of any intrusive siteinvestigations or further work to be determined. Ifrequired, the additional work activities are taken forward for Phase II Risk Estimation and Evaluationwhere the identified risks are evaluated in greaterdetail. Geotechnology has extensive experience ofconducting Phase I and Phase II studies for clientsas part of the planning process, to complement due diligence during site acquisition or as standaloneprojects. Proposals for a residential development comprisingtwenty houses on a 1.4 Ha site were prepared forsubmittal to the Local Authority for Outline PlanningPermission. Pre-application discussions with theLocal Authority revealed that the Application wouldneed to be accompanied by a Phase I study. The overall objective of the Phase I study was toidentify and asses hazards potentially present atthe site. To achieve this site history needed to bepieced together, potential contamination sourcesidentified and the sensitivity of the site within itsenvironmental setting determined. To assess eachof these aspects information was obtained fromseveral third parties, supplemented by informationalready held by Geotechnology. In some cases thisinformation was freely available but in others a feewas paid to secure the information. Based on a review of historical ordnance surveymaps and geological base plans the site was foundto be located in an area of historic mining andindustrial activity. Review of The Coal AuthorityMining Report and mine abandonment plans

Phase I Hazard Identification and Assessment P & B Ltd.

indicated several mine entrances to be present atthe site and that parts of the site were under-mined. In addition to the previous mining activity,the review of the historical ordnance plansindicated that a Chemical Works was once locatedadjacent to the site and that several rail sidingspassed in close proximity. Records held by the EAalso indicated that inert, industrial and householdwastes had been deposited at the site untilrelatively recently. Geological base plans revealed the site to beunderlain by Coal Measures bedrock overlain by anunknown thickness of superficial deposits. Nomajor faults were mapped as crossing the site butone coal seam was indicated to traverse the site.Careful scrutiny of the vertical log of the geologicalplan indicated that additional coal seams may

outcrop on the site although these were not marked on the geological plan. According to information provided by the EA, the site was considered to be located over a minor aquifer and outside of any groundwater protection zones. A controlled watercourse was however found to be located within 250m. Chemical and biological monitoring of this watercourse by the EA indicated the water quality to be good. No protected sites were found within the vicinity of the site. Review of radon potential maps and flood maps indicated that the site did not lie within an area requiring protection. Based upon the information gathered a

Phase I Hazard Identification and Assessment P & B Ltd.

diagrammatic and tabulated Conceptual Site Model(CSM) was developed. The aim of the CSM was toclearly define potential exposure pathwaysconnecting hazards and receptors, on site and offsite. The key hazards identified from the desk studywere ground instability and contaminationassociated with the previous mining activities,contamination related to the adjacent chemicalworks and waste activities, and ground gas fromthe mine workings and degradation of the relativelyrecent waste deposits. Receptors considered to beat risk were site development workers, future siteoccupants / visitors, infrastructure and controlledwater. Within the tabulated CSM each identified exposurepathway was subjected to a Preliminary RiskAssessment (PRA). This process enabledGeotechnology to screen out potential risks that didnot require further evaluation. The outcome was aclearer understanding of potential exposurepathways that required further evaluation. The final step in the Phase I study was todetermine the additional investigations andassessment required in Phase II. Geotechnologyrecommended that the potential presence of arange of contaminants at the site associated withthe historical land use needed to be evaluatedthrough a statistically sound ground investigationinitially comprising trial pits set out on a regulargrid. This data would enable the level ofcontamination to be directly investigated andhuman health and environmental risk assessmentsto be initiated. To investigate the presence ofshallow mine workings a phased approach wassuggested with the preliminary intrusiveinvestigation comprising trial pitting around themine entrances and rotary drilling of the shallowcoal seams. To enable the assessment of risksfrom ground gas the installation of permanent gaswells was also recommended.