RFI - Attachment F - Engineering Report

        into the StormFilter® rather than the relationship between catchment rainfall and
        runoff;
       The small catchment area and high impervious nature of the carpark could be
        expected to result in a “first flush” effect with a high initial EMC in the influent
        concentrations as demonstrated by Morison P (2001). Consequently treating the first
        1 inch (25.4 mm) of runoff from the catchment should result in the majority of pollutants
        being washed from the surface of the carpark into the system. Morison P (2001) was
        only treating the first 10 mm of runoff and was observing a marked reduction in
        pollutant loads after 10 minutes;
       It would appear from the information provided in the Contech Product Evaluation
        Report that by-pass of the system did not occur during the course of the study (John
        Pedrick pers com) and as a result was not able to be included in the ER determination.
        In general Australian requirements, for issuing approvals for specific stormwater
        treatment systems, are based on an ER determined through the use of Average
        Annual Rainfall and the total volume of runoff from the catchment. Consequently any
        assessment of the pollutant removal by a system should include all of the runoff from
        the catchment i.e. the influent volume and EMC as well as any by-pass volume and its
        corresponding EMC;
       For modelling purposes, in Australia, Suspended Solid (SS) loads have generally been
        defined as that fraction of the Particle Size Distribution (PSD) that is ≤ 125 µm (Brodie
        & Rosewell, 2008, Hunter G, 2008). The Contech Product Evaluation Report does not
        include a PSD breakdown of the SS load and only refers to the < 2000 µm fraction and
        the < 500 µm fraction. Pace and TestAmerica referred to the texture of the suspended
        solids sampled as Loamy Sand (John Pedrick pers com), refer to Figures 1 & 2.
        However, additional sieve analyses of the sediment, captured within the system,
        undertaken by GeoTesting Express on 5 September 2014, has determined that in
        excess of 80% of the sediment was < 75 µm in diameter (refer to Figure 3);
       Both TSS and SSC testing (Kayhanian M, et al 2005) was undertaken to determine
        ERs for the < 2000 µm and < 500 µm fractions of Suspended Solids. The results for
        both testing procedures returned ERs in excess of 90%. The Suspended Solids EMC
        recorded in the influent was significantly less than that recorded in the Australian
        literature and consequently achieving an ER in excess of 90% demonstrates that the
        system can achieve very high pollutant reductions from runoff containing lower than
        expected levels of Suspended Solids contamination;
       The detention tank and StormFilter® system is designed to drain completely within a
        short period of time after completion of a rainfall/runoff event. Consequently the
        captured solids are retained in a dry/semi-dry condition intended to maintain them in a
        solid state, thereby minimising the opportunity for anaerobic decomposition and their
        re-suspension in the effluent in a dissolved form (refer to Figure 4);
       The intake to the automatic samplers, being located in the invert of the influent and
        effluent pipes could bias the samples towards the larger fraction of suspended solids.
        However, the sieve analysis, undertaken by GeoTesting Express on 5 September
        2014 (refer Figure 3) suggests that the majority of the sediment retained within the
        system was < 75 µm and was removed prior to the location of the effluent sampling
        intake. Consequently the relationship between the influent and effluent EMCs for SS
        indicate a significant reduction in the finer fraction of the Suspended Solids.



HES – StormFilter® System Peer Review                                                       Page 5