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Land Contamination Study

Cork City Council appointed Consultants in 2005 to undertake a study of possible land contamination in Docklands, given its industrial use since the turn of the 20th Century. The objectives of this Study were:

  • to quantify the extent of land contamination by various substances within the South Docks Area;
  • to identify potential strategies and solutions which comply with legislation and best international practice; and to estimate potential costs of necessary remedial works.

The Study also fed into the preparation of the South Docks Local Area Plan guiding such issues as potential land uses.

T.J. O’Connor/D.H.V. Consulting Engineers were appointed in August 2005 to undertake the study in two phases:

  • Phase 1: a desk study based on the historical uses of the sites since they began in the early 1900s.
  • Phase 2: a detailed site investigation to determine the extent and level of contamination with a report on the potential solutions and options with associated costs.

Phase 1 of the Study was completed in January 2006 and Phase 2 was completed in 2007.

The summary of the Phase 2 study is as follows:

Stata

A clay layer forms the upper natural layer in the South Docks.  The area has been raised since the 19th century, first with sludge/dredging material from the River Lee and also with waste and rubble after industrialisation in the beginning of the 19th century.

In general the strata in the South Docks are as follows:

  • Pavement 0.2 m;
  • Fill, a mixture of rubble and clay, 0.5 up to 4 m;
  • Clay until 3 – 5 mbgl, in the Showgrounds until 6.5 mbgl;
  • Gravel aquifer, with a depth of more than 25 m in the central part of the South Docks.  

Hydrology

Tidal fluctuations in the aquifer result in a 1.5 m difference in groundwater level between high and low tide. Average groundwater flow is perpendicular on the River Lee, dropping around 0.5 m from the southern border down to the River. A hydrogeological model has been prepared which may serve as a basis or tool for several activities including remedial action design, urban water management plans and abstraction calculations for construction works.  

Fill

The fill layer throughout the South Docks was found to contain contaminants in varying concentrations, often above DIV. This is partly due to the use of contaminated materials for level raising and the industrial history of the area (car and tyre manufacturing, electricity production, fuel storage and transhipment). Contaminants that have been detected above DIV include lead, copper, zinc, arsenic, cadmium, mercury, polcyclic aromatics (PAH), and mineral oil. Lead and high PAH concentrations may involve health risks where humans have direct contact with the fill (e.g. gardens).

The most cost-effective method to treat this contamination is to cover the soil with 1 m clean soil, as full cleaning of the fill will be expensive due to its mixed structure). Removal of the fill down to 1 m and its replacement with clean material is also acceptable.  

Oil

Seven zones (in total 8 hectares) in the South Docks are considerably contaminated with oil, mainly in the fill layer. The total polluted volume is estimated to be 105,000m3. The contamination in these zones is generally related to (bulk) fuel storage and transhipment activities. Although oil polluted groundwater was found locally, the aquifer is not significantly affected, as it is isolated from the pollution by a (generally) thick clay layer.

Where this clay layer is thin or absent, adequate measures should be taken. Excavation of the entire polluted fill layer in this instance and its replacement by clean clay of at least 1m is recommended. The clay layer must be repaired where it has been perforated. 

Volatile chlorinated hydrocarbons (VCH)

Four spots with elevated concentrations (>DIV) of dichloroethene and/or vinyl chloride have been identified. Generally concentrations of these substances above DIV involve health risks in buildings with ground floors, unless ground membranes are introduced in the floor slabs. Likely significant contaminant sources are present in the soil (fill and clay).

Biodegradation assessment and groundwater modelling indicate that where no action is taken, vinyl chloride concentrations in the aquifer would drop below DIV within 21 years. In the clay layer vinyl chloride would still exceed DIV after 30 years. Excavation of the pollution source would accelerate sufficient breakdown in the aquifer to 8 years (combined with biological stimulation, breakdown may be reduced to 1 year). A cost efficient method to reduce breakdown time is to ‘pump and treat (in combination with excavation of the source), which would lead to a drop below DIV within 2 years. 

Principle Recommendations

VCH contamination is identified as the most hazardous element, demanding further investigation. Attention should be paid to possible VCH contamination below existing buildings and below vulnerable parts in the sewerage system. It may not be necessary or cost effective to remediate all contamination. The preparation of a land management plan is recommended to ensure optimum remediation solutions are identified and implemented.