Our full guide to the Geoceptor product

Turtle’s integrated approach to stormwater management and Sustainable Drainage Systems (SuDS) includes protecting our watercourses from surface water contaminants such as hydrocarbons and silt. Surface water runoff contaminated with hydrocarbons (petrol, diesel, and engine oil) poses a significant threat to the environment and watercourses.

UK law requires any site where there is a risk of surface water contamination by hydrocarbons, including oils, to implement environmental pollution prevention measures. Hydrocarbon/oil separators must be installed on sites where there is a risk of accidental oil spills or leaks from vehicles, plants, and machinery. There are two types of separators, full retention and bypass. 

Bypass separators are installed and used when it is considered acceptable to not provide full treatment for extremely high flows, such as when the risk of a large spillage and heavy rainfall occurring at the same time is low.

Introducing the Geoceptor range

Our brand-new Geoceptor bypass separator range has a unique design that has been tested and proven to remove hydrocarbons, oils, silts, and solids from low-flow surface runoffs, thereby preventing the contamination of the surrounding environment.

There are four models in the range, designed to treat the runoff from drainage areas of up to 22,220m².

These models are: 

• GNSB6: nominal size 6, 1260mm diameter
• GNSB16: nominal size 15, 1260mm diameter
• GNSB20: nominal size 20, 1560mm diameter 
• GNSB40: nominal size 40, 2150mm diameter 

Applications of these separators include: 

• Car parks with 50 or more car parking spaces larger than 800m²
• Smaller car parks discharging to environmentally sensitive areas
• Highways and roads
• Light industrial yards

Each model has an inverted depth of 550mm and features a robust HDPE body with a patented vertical separation system, which is designed for rainfall intensities of up to 6.5mm per hour. 

How do they work?

Our Geoceptor products use a two-stage process to remove hydrocarbons, oils, silts, and solids from low-flow surface runoffs. 

• Stage 1: The initial runoff 

The initial flush or runoff of surface water from a storm is typically the most contaminated with hydrocarbons and silt. 

During the early stages of a runoff event, surface water flows into the primary chamber, suspending any oils and hydrocarbons. As oils and hydrocarbons have a lower density than water, they rise to the surface and can be syphoned away into the base chamber using the skim pipe.

Any silts in the suspension will also be skimmed into the base chamber. Over time, settled silt and solids that are not skimmed will build up in the top chamber until they reach the skim pipe and are syphoned down into the base chamber. 

• Stage 2: Bypass overflow

As the runoff from the first storm event reaches its peak, the levels of incoming hydrocarbon and silt sharply decrease, and the flow into the primary chamber begins to exceed the skim pipe’s maximum flow velocity, causing the water level in the primary chamber to rise rapidly. 

As the flow increases, the level in the primary separation chamber quickly rises to the top level, where it bypasses the main flow path via the overflow ports at the top of the unit. 

How to choose the correct size separator

Geoceptor bypass separators should be sized according to the guidance of the Pollution Prevention Guidance 3 (PPG3). The size of the separator is determined by applying a standard formula to the surface area being treated and rounding it to the nearest size.

The nominal size (NS) is the flow rate in litres per second that the unit processes to meet the specified standard. The nominal size of a bypass separator (NSB) for a catchment of area A (m2) is obtained using the following formula:

NSB = 0.0018 x A

For example, assume you have a car park of 3000m². This area is A in the calculation. So to calculate the correct size, you would make the equation:

NSB = 0.0018 x 3000

This gives a result of 5.4, meaning that the bypass separator required for this application is our GNSB6. 

Installation process

Once you’ve purchased the correct size and are ready to install the separator, you will find the major cost saving within the range, the vertical installation. 

The Geoceptor can be installed inside a standard manhole box (3.5m x 3.5m),  this allows a significant cost saving compared to horizontal designs which require sheet pile and frames due to the larger length of horizontal chambers.

Through investigations with consultants,  a like-for-like model of a Geoceptor versus a leading manufacturers horizontal model,  the Geoceptor provided a cost saving of over 60%!

For pricing and purchase options, or more in-depth information on this product, contact the Turtle team today.