RFI - Attachment F - Engineering Report

The StormFilter® system described in the report by Contech (2012) consisted of
eight cartridge StormFilter® preceded by a detention tank designed to capture 75%
of the runoff volume from the 25.4 mm storm event. The carpark catchment area was
0.437 ha, with an equivalent impervious area of 0.297 ha i.e. 68% impervious.
The equipment and sampling techniques used for this study were in accordance with
the Project Plan (Contech, 2010) developed by Contech in consultation with local
government organisation. Qualified Contech personnel were responsible for the
installation, operation, and maintenance of the sampling equipment. Water sample
processing and analysis was performed by Pace and Test America. It should be
noted that Pace and Test America are accredited laboratories in accordance with the
National Environmental Laboratory Accreditation Conference (NELAC) and all
samples were tested in accordance with their nationally approved testing protocols
as reported by Contech (2010).
Both the influent and effluent samples were collected using twelve, one litre sample
bottles. The collection of flow proportional samples commenced when the flow rate
exceeded 0.32 L/s. The sample strainers intakes and flow measurement equipment
were secured to the invert of the influent and effluent pipes, which biases the
samples towards the larger fraction of the suspended solids (Contech, 2010).
Testing of the StormFilter® system was conducted to assess the effectiveness of this
device to remove Total Suspended Solids (TSS), Suspended Sediment
Concentration (SSC), Total Volatile Suspended Solids (TVSS), Total Phosphorus
(TP), Dissolved Phosphorus (Diss. P), Ortho-phosphate (Ortho-P), Particulate
Phosphorus (PP), Ammonia (NH3+), Total Kjeldahl Nitrogen (TKN), Nitrate plus
Nitrite (NO2- plus NO3-), Total Nitrogen (TN), and Organic Nitrogen (ON) in
accordance with the approved Project Plan, (Contech, 2010) as well as the
conditions outlined in the North Carolina Department of Environment and Natural
Resources (NCDENR) Division of Water Quality (DWQ) Preliminary Evaluation
Period (PEP) program, (NCDENR, 2007).
Results from the twenty month study, that represented a total of 13 storm events and
70.4 mm of precipitation, showed that the StormFilter® system tested was effective
in removing solid and nutrient pollutants from stormwater runoff. The study was
completed using the recommended design criteria of a maximum cartridge specific
flow rate of 1gpm/ft2, a coated perlite media, and a volume based design
methodology. The StormFilter® system was designed to capture and treat the 25
mm water quality volume, typical for the Piedmont region of North Carolina. The
StormFilter system was also designed on a mass-loading basis to meet the annual
pollutant loading requirements of the site with a minimum expected interval between
maintenance of 1 year (Contech, 2012). Significant reductions for solid and nutrient
pollutants were observed in the testing between influent and effluent sampling
locations using the Efficiency Ratio (ER) calculation (TSS 90.4%, TP 86.1%, and TN
55.9%) and Summation of Load (SOL) efficiency calculation methods (TSS 90.9%,
TP 87.1%, and TN 50.2 %) (Contech, 2012).
The study concluded that the StormFilter® system successfully treated stormwater
runoff with respect to removal of solid and nutrient pollutants and was able to meet
North Carolina’s 85% TSS pollutant removal requirement, and provided excellent



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