Construction & Demolition

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Construction & Demolition

There are three key water pollutants associated with sites where excavation, tunneling and demolition is required. These pollutants are:

Silt and suspended solids

Alkaline pH from cement

Fuel & oils, chemicals

key water pollutants 1

Silt and suspended solids

Problem

Excavation and the movement of large vehicles over bare soil can release turbid, cloudy, silt-laden water into water courses following rainfall. Fine-grained sediment may settle to the bed of the waterway destroying vital habitats. The simple act of turning a water course cloudy may cause fish gills to become blocked, alter the natural penetration of light, cause a reduction in oxygen levels and increase the temperature of the water body. Silt is often very visual, easily traceable and therefore can cause reputational damage and lead to prosecution.

Technical Solutions

Lamella Clarifiers – simple & effective, robust, no power required, easily transported, small footprint. Can treat volumes of up to 300m/hr3.

Chemical Dosing – use of dosing systems to introduce coagulants, flocculants and pH regulators. Effective and reliable, often used in conjunction with other technologies, but requires power and knowledge regarding the correct use of chemicals.

key water pollutants 2

Cement, concrete,

hydro demolition – Alkaline pH

Problem

The hydration of cement to make it set causes a dramatic increase in the pH of any water that comes into contact with curing concrete e.g. wash water, run-off from recently poured areas of concrete.

Similarly, the use of hydro-demolition to cut concrete will cause a similar increase in the pH of the blast water.

Frequently, the pH of concrete wash water, hydro-demolition water and run-off from fresh concrete surfaces will be in the region of pH12 to 13, a similar pH to oven cleaner. The pH of inland waters is between pH 6 to 9; discharge to foul sewers is typically in the range pH 5 to 10. The aquatic environment is very sensitive to pH, and even small changes can have widespread impact on bio-diversity.

Technical Solutions

Concrete Washout Units – available in a variety of sizes depending on the capacity required, this technology uses CO2 to neutralise the alkaline effluent; this is safe, effective and simple to use.

key water pollutants 3

Oils and Chemicals

Problem

Fuels (petrol, diesel, kerosene) and oils (lubricating oil, engine oil) are present on nearly all construction sites. Other organic compounds e.g. chlorinated solvents, creosote and tar may be present as a result of particular industrial activities which have been undertaken on a construction or demolition site.

Organic compounds may be present as a separate liquid phase or may be dissolved within the water.

They principally pose a hazard to the environment as a result of either: their toxicity; their ability to coat surfaces; biodegradation consuming oxygen dissolved within the water.

Technical Solutions

Oil Water Separators – there are several different Oil Water Separators types available, therefore the specific type must be carefully chosen taking into account the parameters in question, such as water volume and flow rate, concentration of pollutant and required discharge concentration. These are highly effective but can vary in complexity, from a simple non-powered flotation system to dissolved air flotations systems (DAF’s).

Support services

we can provide the construction and demolition industries:

Pre-construction – development of water management plans, permitting support, optioneering, training

Construction phase – installation, operation, maintenance of equipment; compliance support

Post-construction – demobilisation, environmental reporting

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