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on June 30, 2005

Cleaning and product performance report on The Ecosol RSF 100 At-Source Solid Pollutant Filters for Tauranga City Council Prepared by Ecosol (NZ) Wastewater Filtration Systems Ltd Nicholas Watson June 2005


Tauranga is a seaside city located in the Bay of Plenty region on the east coast of New Zealand.

Tauranga City Council (TCC) is one of the smallest districts in terms of land area, with only 12,742 hectares. However, Tauranga City has a population of over 100,000 people, making it the sixth most densely populated city in New Zealand. This figure is set to increase over the next 5 years as demonstrated by the 2001 census, which showed a 19.3% growth in the number of new dwellings in Tauranga.

The area is known for its beautiful weather, having about 2,200 hours of sunshine per year. The average rainfall for the city is 1,349mm and the average temperature is 14.2 degrees. The city swells with holidaymakers in summertime, many make the 206km journey from Auckland every year to enjoy the aquatic lifestyle, beaches, and many marinas.

With this activity comes added strain on services, one being Tauranga’s stormwater drainage network. TCC currently manages approximately 6,000 cesspits and is required by the Regional Council to lower discharges from the CBD area into the harbour. One of TCC’s initiatives is the installation of stormwater filters at selected locations to reduce the level of pollutants entering the drainage network.

In June 2002 TCC engaged Ecosol (NZ) to install three RSF 100 units as part of a trial. After two years of monitoring, TCC decided to install further units as part of ongoing redevelopment works. Ecosol, after the success of the trial, won the tender to install a further 22 units baskets in the CBD area and also at a major suburban intersection. These units were installed in December 2004.

All of the RSF 100 units were fitted with 200 micron mesh.

This report summarises the results of the first clean of all 25 installed units.

Testing Methodology

Ecosol, in conjunction with TCC, randomly selected four of the 25 RSF 100 units to be independently tested by SGS Food Environment Laboratories. The units selected for testing were:

Table 1 Cesspit One Cesspit Two Cesspit Four Cesspit Five
Locations CNR Cameron Road and State Highway 2 Elizabeth Street CBD Spring Street Mall CBD Cnr The Strand and Commercial Road CBD
Catchments Traffic, residential Commercial Commercial Traffic, Parklands


As Ecosol’s RSF 100 units can be cleaned either manually or by eductor truck, the four test units were cleaned manually while the remainder was cleaned using an eductor truck supplied by Tankman Waste Disposal Services, for City Care, TCC’s maintenance contractors. The total time taken for the clean, including travelling time and disposal, four hours.

Tankman’s group operation manager, with assistance from Ecosol’s representative, conducted the sampling. The samples taken consisted of the complete contents of each basket, which was then weighed using City Care’s electronic scales. The four samples were then transported to SGS Food and Environment Laboratories in Penrose, Auckland and tested for pollutant content, including heavy metals and hydrocarbons. SGS also carried out a sieve analysis to determine the capture efficiency of the RSF 100 mesh.


Attachment 1 contains a summary of the test results provided to TCC and Ecosol by SGS Food and Environment Laboratories.

The weight of captured pollutants for the four units tested ranged from 16kg to 44kg, which was consistent with the amount of pollutants captured by the other 21 units. The composition of the samples consisted predominantly of fine and coarse sediments and a mixture of vegetation (leaf an grass matter) with some human-contributed pollutants (such as cigarette butts, glass bottles and aluminium cans).

SGS’s sieve analysis showed a capture efficiency of between 86% and 94% of particles down to 200 micron and between 6% and 14% for particles of 53 microns and below.

The weights collected by each unit are shown the opposite. Cesspit 2 had the most of the four units owing to it being the main cesspit in Elizabeth Street.

The composition of pollutants captured is shown on the next page of this report. As expected, large amounts of lead and hydrocarbons were captured by the unit located on State Highway 2. These hydrocarbons and heavy metals are then picked up in the stormwater runoff and attach to heavier objects such as sediment.

AS New Zealand now has a smoke-free policy in clubs and pubs many of RSF 100 units in the CBD area contained large amounts of cigarette butts mainly because patrons now have to smoke outside. There was also a large quantity of alcohol cans and bottles, possibly caused by the liquor ban in Tauranga’s CBD area causing many patrons to discard their empty bottles down the drain.

The required frequency of cleaning will be dictated by litter loadings and weather patterns. One month after this clean the baskets required a further clean due to Tauranga having a one-in 100 year storm event.

TCC will inspect the units monthly and, based on the results of this first cleaning report, will need to be cleaned approximately every three months.

All 25 baskets were found to be in good working order with no remedial work necessary.


Overall, in just four months, more than 600kg of pollutants was captured by the 25 RSF 100 units baskets. It is clear that the 200 micron mesh used in the RSF 100 units results in a significant level of pollutant capture. It should be noted though that the use of this finer mesh will increase the frequency of cleaning required.

Ecosol will continue to monitor these baskets and work with TCC to ensure that they continue to operate as specified and help prevent the discharge of pollutants into Tauranga’s waterways.

For further Information – please contact Urban Asset Solutions on P: 1300 706 624

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