Ecosol Drop Trap

The unit is installed either in-line, or at the end of the stormwater line, where there is a drop between the upstream invert, and downstream obvert, level of at least 600mm, and preferably more, so that the structure can house an adequately-sized basket.


Key Features

The EcosolTM Drop Trap is designed to remove and retain solid pollutants in stormwater flows on a range of pipelines and consists of a pre-cast concrete pit containing a capture basket and overflow by-pass flaps. The unit is installed either in-line, or at the end of the stormwater line, where there is a drop between the upstream invert and downstream obvert levels of at least 450mm, and preferably more.

This drop is needed so that the structure can house an adequately-sized basket. Solid pollutants conveyed in flows from the upstream pipe are filtered through the basket positioned directly below the upstream pipe invert. The filtered stormwater then passes through the unit to the downstream outlet pipe and into the drainage network without any head/hydraulic loss through the unit. As the basket approaches 90% full, the by-pass flaps begin to open in response to the incoming flow. Once the basket is 100% full the pressure of the incoming flow forces open the by-pass flaps, allowing the excess flow, to enter the drainage system through the by-pass openings. This effectively eliminates the likelihood of flooding, a common fault with other systems. Even when in by-pass, the captured pollutants are not remobilised and are retained in the basket.

When the flow ceases, the flaps return to their normal position (see opposite for a graphical representation of the unit in operation). In the unlikely event that the spring mechanism fails, or debris lodges in the by-pass flaps, they will be in the open position and will not obstruct the flow or cause flooding.

The patented overflow by-pass minimises any hydraulic headloss on the drainage network under a worst-case scenario, which is defined as a full design flow and a full capture basket.

The EcosolTM Drop Trap separates, collects, and retains more than 97% of solid pollutants greater than 3mm in size, 15% of TSS and TP and 4% of TN.

The EcosolTM Drop Trap has many key features and benefits some of which are listed below.

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Key Dimensions

As the EcosolTM Drop Trap is generally designed to suit site specific conditions the table below provides some indicative key dimensions and holding capacities for the system.


  1. Depth indicated is the overall external pit depth based on the drop indicated between the upstream inlet pipe invert level and downstream outlet pipe obvert level inclusive of a 150mm base slab thickness and nominal 1.0m depth to inlet invert.
    E.g. EcosolTM Drop Trap 1200 with a 300mm inlet and outlet. 1000mm depth to inlet invert + a further 450mm (drop) to outlet obvert + 300mm outlet pipe + 150mm base slab thickness = 1,900mm over all depth from finished surface level to the underside of the base slab.
  2. Drop as shown is the drop indicated between the upstream inlet pipe invert level and downstream outlet pipe obvert level
  3. Pollutant storage capacities are largely determined by the available drop in the system.
  4. Weights indicated are an indicative guide only and will vary depending on the depth to inlet invert and the available drop between the inlet and outlet pipes.

Ecosol-Drop-Trap-Pit-Base-InstallationOutlet/Pit base installation

Ecosol-Drop-Trap-Inlet-Pit-InstallationInlet pit installation Ecosol-Drop-Trap-Filtration-Basket-InstallationFiltration basket installation Ecosol-Drop-Trap-Access-CoverAccess cover installation  

Life Expectancy
The EcosolTM Drop Trap is designed to meet the strictest engineering guidelines. The reinforced concrete has an expected life span of 50 years while the internal filtration components, comprised of 304 or 316-grade stainless steel, have a life expectancy of 25 years.

All EcosolTM Drop Traps are covered by a twelve-month warranty provided the unit is maintained and cleaned with the frequency, and using the method recommended in our operation and maintenance manual.

Unit Design Basis
The units design based on Exposure Classifications A2 for external surfaces in contact with the ground and for installations in nonaggressive soils. Where the conditions are outside the design limits of the standard EcosolTM Drop Trap, EcosolTM must be notified so that the product is designed specific to these site conditions. This includes instances where the unit is to be installed in aggressive soils, or below any permanent, or transient water table, or if the unit is to be installed in close proximity to a building or other structure


Collection Efficiencies

Particle Size Distribution Collection Efficiency

Field Testing Particle Size Distribution Data
The EcosolTM Drop Trap has been subject to a range of field-based tests where it has demonstrated effective performance in retention of stormwater pollutants, hydraulic capacity and durability for the environment in which it operates. The below Particle Size Distribution graph confirms how efficient the product is at retaining particulates conveyed in stormwater surface runoff.



Figure 3 - Field testing particle size distribution data for three separate product installations.

In recent years modern Water Sensitive Urban Design (WSUD) objectives and principles now applied to most urban development’s require more onerous water quality objectives (WQOs) specifically targeting the removal of suspended solids, nitrogen, phosphorus and heavy metals. The EcosolTM Drop Trap is an integral part of the treatment train providing essential pre-screening of stormwater flows, and when used in conjunction with other treatment measures such as swales or sand filters will achieve target water quality objectives.


To enhance the product capture efficiencies other filter medias can be incorporated into the design.

  • Hydrocarbon booms installed within the EcosolTM Drop Trap will provide additional protection against oil or fuel spills in wet conditions.
  • Reactive filtration media pillows installed at the base of the basket will provide improved capture efficiencies for heavy metals, Total Nitrogen, Total Phosphorous, Turbidity and Suspended Solids.

Quoted Capture Efficiency (CE) values are intended as a general guide only, please consult with your Ecosol representative for site specific product sizing and modelling.


Hydraulic Specification

Treatable Flow Rate, By-pass Capacity and Headloss
The EcosolTM Drop Trap is designed to treat 100% of the incoming flow and operates with little or no impact on the hydraulic performance of the upstream pipe. Utilising the drop between the upstream pipe invert and the downstream pipe obvert to accommodate the capture basket ensures there is no obstruction to the flow through the drainage line of the outlet pipe.

According to the report prepared independently by the University of South Australia the unit provides minimal Hydraulic Grade Line increases within the drainage design. In most cases, even with a full capture basket, the water level within the pit does not exceed the obvert level of the upstream pipe under full-flow conditions. In this state the maximum flow for each pipe size is shown in the table below.

Consult your EcosolTM representative if the flows are likely to exceed these figures.


  1. Treatable Flow Rate (TFR) is the maximum flow the unit can treat without by-pass in a surcharged pit based on outlet pipe gradients up to 5%. It is important to note that the TFR will decline as the basket fills with pollutants.
  2. By-pass capacity is the maximum flow that can by-pass through a surcharged unit based on a minimum drop of from inlet invert to outlet obvert of 450mm.
  3. Headloss figures quoted refers to the head above the upstream pipe invert level in a surcharged environment with full impermeable basket and full pipe flow (worst case scenario).


The EcosolTM Drop Trap should be cleaned regularly. The cleaning frequency and the cost depend heavily on the surrounding environment, the unit’s proximity to a waste facility, the number of units, their location, and the type of pollution collected. The figures in the table below give a broad guideline about the optimal catchment size and the number of cleans required annually based on typical expected pollutant loads.

Initially EcosolTM recommends that regular monitoring is undertaken monthly. Once the unit has been in operation for an extended period of time (say, 12 months) the monitoring schedule can be adjusted to reflect the actual operating conditions specific to the catchment. It is also recommended that the unit is inspected after every major storm event.

One of the key advantages of the EcosolTM Drop Trap is that it can be cleaned by either vacuum method using street-sweeping vehicles or by crane truck. Both methods are safe and cost efficient.



Ecosol-Drop-Trap-Maintenance1 Cleaning frequency is based on typical gross pollutant loads anticipated for standard commercial, residential and light industrial catchments. Gross pollutants in this instance includes vegetation as well as anthropogenic litter, however excludes sediment. Cleaning frequencies may vary based on local catchment conditions and rainfall.

EcosolTM has a very competitive cleaning service. After each clean we provide a report detailing the volume and type of pollutants removed. We believe that it is in your best interests for Ecosol staff to clean and maintain the unit, not only because we are specialists, but also because proper monitoring and maintenance enhances the unit life significantly.

Should you use another company to clean the unit, or undertake this work yourself, we request that it be conducted according to Ecosol'sTM specifications. Otherwise, you may invalidate your warranty, as damage caused by inappropriate cleaning procedures is not covered. The advantages of using EcosolTM to clean and maintain your unit are that you get:

  • regular inspections of your unit
  • a comprehensive cleaning service with removal and disposal of all captured pollutants
  • a detailed report provided on completion of each clean
  • trained and experienced staff; and remedial work completed, if required.


The EcosolTM Drop Trap operates in-line or end-of-line on stormwater pipes. The pre-cast EcosolTM Drop Trap modular unit can be fitted to conduits equivalent to a 600mm diameter pipe, either within the drainage network (as a junction pit drop structure) or end-of-line. A customised basket to fit existing concrete drop structures is also available.

The compact pre-cast unit can be fitted at any point within a drainage network where there is at least a 450mm drop between the inlet pipe invert and outlet pipe obvert levels. The basket can be retro fitted to most existing pits, provided the pit meets the required dimensions and construction tolerances.

The unit has a range of applications including:

  • Industrial and commercial sites such as car parks and shopping centres
  • Residential developments
  • Freeways and civil construction projects and
  • Stormwater discharge points to wetlands, shorelines, creeks and rivers.





Ecosol Drop Trap Technical Specifications

EcosolTM Drop Trap - Technical Specifications

Ecosol Drop Trap Installation Guide

EcosolTM Drop Trap - Installation Guide

Ecosol Drop Trap Maintenance Guide

EcosolTM Drop Trap - Maintenance Guide

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