RFI - Attachment F - Engineering Report

The City is considering the use of CFS devices to treat road runoff primarily in the central business district
which combine high traffic volumes and limited space to employ other treatment devices.

CFS units are a relatively new method of stormwater treatment aimed at capturing stormwater pollutants close
to their source. Being a relatively new treatment method, limited information was available on the operation and
sediment removal performance of CFS. Previous performance investigations on some products has shown it is
very difficult to carry out conclusive field testing. The City sought to identify CFS products that met their
performance targets before progressing to large scale installation of CFS.

A study was carried out to compare the performance and the effectiveness of four different CFS. The four
suppliers of the four different CFS all took part in the study on a voluntary basis.

The study consisted of
© A Field Trial

e Laboratory Testing

2 FIELD TRIAL

The aim of the field trial was to compare the operational performance of the four different CFS by observing
their installation, operational performance and maintenance requirements.

The field trial was a comparative investigation of the four CFS based on qualitative observations of their
operational performance under similar weather conditions. The individual catchpits or contributing catchments
were not identical, requiring observations to take account of the differing characteristics, The field trial looked
at the qualitative performance of the CFS under conditions that the laboratory testing could not simulate.

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The field trial was tindertaken by Tonkin & Taylor (T&T) in the Newmarket/Grafton area of Auckland city from
21 March to 20 August 2002.

2.1 FIELD TRIAL METHODOLOGY

CFS product suppliers were invited to install two CFS units in two trial catchpits identified by Auckland Ci
Prior to the installation of CFS, all catchpits were cleaned and downstream pipes were checked for blockages.

 
  
 
 
 
 
 
 
 
 
 
  
 
 
  

During the trial period, suppliers were responsible for deciding when any maintenance (including clea
the CFS was required. Suppliers were also requested to meet with Auckland City's maintenance contractor,
discuss suppliers’ maintenance/cleaning requirements. Suppliers were encouraged to be present during
maintenance operations so they could direct the maintenance contractors, :

Operational performance observations for each CFS product were undertaken every fortnight and during and.
after significant rain events. Inspections were carried out by the same two T&T staff members throughout the
trial to ensure consistency of observations and records. .

The performance of each of the CFS was compared on a number of attributes, as described below.

(a) Ability of the CFS to capture and retain sediment
(b) CFS maintenance characteristics

(c) CFS physical fit within the catchpits

(d) Rigidity and strength of CFS

(e) CFS ability to catch road runoff

(f) Effect of litter and organics on the CFS performance

The information from the field observations was then used to summarise the operational perfc
each of the above performance criteria. These results were then used to focus selection for:
testing of the CFS products.