Clues to detect contaminated sites

Identification of potentially contaminated sites as a preliminary step before performing a detailed site investigation refers to a study, which usually is known as Level I Environmental Site Assessment. This phase includes site examination and recompilation of relevant information regarding present or past sources of contamination in order to understand the historical development and current use of the site in terms of possible risk for the sight to be contaminated.

The examination of a site and review of interesting information may include:

  • Performance of onsite visits in order to check present site conditions (visual inspection):

    • Identification of site location; within industrial, agricultural, residential, reserved area, etc. Risk to be polluted is much higher for the sites located within industrial areas.
    • Assessment of any chemical substances or contamination spots. An inventory of hazardous substances stored (if present) or used on site shall be performed.
    • Unpleasant soil odor
    • Examination and observation of any already existing monitoring well
    • Inspection of colour and odor of existing nearby surface water

    • Vegetation dieback

  • Inspection of present or past installations and review of relevant documentation (industrial sites)

    • Historical and current site layout plans with indicated storage areas, storage tank locations, production buildings, wastewater treatment plants (WWTP), transformer stations, drainage systems, on site pumping well locations, etc.
    • Inventory of materials handled, stored and used in production process including raw materials both hazardous and nonhazardous
    • Inventory of wastes produced from all processes and operations, stored and disposed on/off site (including solid, liquid, hazardous and nonhazardous)
    • Physical state and presentation form of waste
    • Presence of aboveground storage areas or tanks as well as underground tanks. The following data should be reviewed:

Aboveground open-air storage Aboveground storage tanks Underground tanks
Age of the installations Age of the installations Age of the installations
Total surface and volume Number of tanks and capacity (m3) Number of tanks and capacity (m3)
State of usage (in use or out of use) State of usage (in use or out of use) State of usage (in use or out of use)
Landfill cap (percentage and condition) Presence of spillage retention tank Tightness test. Last performance
Presence of drainage system Leakage collection system Leak identification and retention system
Presence of security procedure and equipment Type of construction material Type of construction material
Waste type Waste type Waste type

    • Current and past production process flow diagrams
    • Existing Control and Emergency Systems
    • Monitoring data for wastewater discharge including sampling and analysis protocols
    • Written procedure for inspection and maintenance of onsite drainage system, sumps and interceptors

  • Historic study of potentially contaminated site. This study refers to the examination and assessment of past industrial, agricultural or commercial activities which have been developed at the site and which could have contaminated the site due to production or management of hazardous substances (POPs):

    • Review of historical and recent aerial photographs of the site and surrounding areas
    • Interview of persons knowledgeable in relation to property history: past and/or present owners or tenants, neighbours, etc..
    • Existing studies (health impact studies or statistics, environmental impact studies, previous environmental audits, geotechnical reports, subsurface information such as borehole logs, etc.)
    • Consultation of Air emission inventory reports
    • Consultation of the Property Registry
    • Consultation of Potentially Contaminated Site Inventories. Some countries have an inventory including contaminated sites. This document can be a very important and useful instrument in order to decide whether a site is contaminated or not.
    • Examination of prior land usage and granted permits (city archives)
    • Any environmental incident reports (spillages, leakages, etc.)

  • Assessment of risks of neighbour properties upon the selected study site. It is important to keep in mind that the current surrounding land use can also impact the subsurface of the subject site in terms of potential soil and ground water contamination. For this reason it is recommended to perform some investigation in the nearby in order to:

    • Look for existing or ancient industries that could cause soil or groundwater contamination in your site (see table below)
    • Evaluate potential impact or to make sure that such impact is absent or negligible

    This investigation can include:

    • Review of readily available webbased public records and any other applicable documentation and reports if available
    • Walkover or driveby of the vicinity of the subject site (approximately 1 km or 0.5 mile radius from the site) to understand the immediate surrounding site operations and potential offsite source of contamination. Special attention has to be paid on existing landfills, uncontrolled waste dumps, storage tanks, etc..

With all the data obtained during site visits and recompilation of relevant information a Preliminary Situation Report is usually prepared in order to assess the potential contamination of a site. Once the preliminary investigation has been fulfilled and the soil is considered as potentially contaminated a Phase II Site Assessment has to be performed. The following figure shows the process and indicators that help to assess whether a soil might be contaminated or not.

Surface Water

Related Documents

  • Preliminary Site Investigation

    Download table (PDF, 129 KB)


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