Matters agreed upon
8 We had discussions about the questions provided in the Brief. We had regard to the available evidence outlined in the Brief as to the condition of the receiving waters. We had made estimations on the condition of the receiving water Prospect Creek, which are presented in Annexure C. Paragraphs [9] ‑ [15] below are the matters we agreed upon.
9 There is some degree of uncertainty as to what is 'typical' condition of Prospect Creek waters, due to the limited amount of data that is available. As such, baseline conditions were estimated at best. The creek has a large, developed catchment with many secondary sources of potential impact, such as industry and urban development. It has a history reflecting this, with sediments likely to be polluted and holding a variety of contaminants. Despite this it is certain that the sewage discharged during the Incident, including the discharge from the Pumping station, had altered the condition of Prospect Creek waters around the discharge area.
10 Prior to the discharge from the Pumping station from 11:59 pm on 15 January 2019, the estimates on the condition of Prospect Creek waters based on bacterial concentrations given in Annexure C(1) at Table C‑2, show that the waters around the discharge area was heavily contaminated with sewage.
11 The added discharge of untreated sewage from the Pumping station resulted in making worse the condition of Prospect Creek waters in the following at least 6 days, until the rain event recorded on 22 January 2019. See details at Annexure C(2) of the approach taken in estimating the likely harm caused by the discharge from the Pumping station. In brief, we estimate that the discharge from the Pumping station contributed around 26% of the observed impacts at Prospect Creek. The estimated 26% is derived from the discharge volume from the Pumping station to the total volume of sewage discharged into the creek during the Incident. We note that this estimated 26% contribution to the observed impacts from the discharge at the Pumping station is conservative, given that the 282 kL discharge volume from the Pumping station occurred at the last 1½ hours within the 31¾ hours of the 821 kL discharge from the Rising main.
12 The discharge from the Pumping station had likely caused additional actual harm to the environment. The actual harm took the form of direct alteration of the biological, physical and chemical characteristics of Prospect Creek waters. This had the effect of degrading for at least 6 days, of up to 4.9 km length of Prospect Creek: from approximately 1.3 km upstream (due to tidal influence), to approximately 3.6 km downstream of the Pumping station discharge point or the Reference pt (see Site location in Annexure B Table B‑1 and Figure B‑1).
13 The direct alterations that were likely caused to the characteristics of Prospect Creek waters were:
a. reduced DO levels, sewage odour and water turbidity;
b. increased concentrations of indicator organism faecal coliforms exceeding the ANZECC 2000 recreational water quality guideline by up to >2,000 times (as shown in Annexure C Table C‑3);
c. increased concentrations of indicator organism Enterococci exceeding the ANZECC 2000 recreational water quality guideline by approximately 315 times (as shown in Annexure C Table C‑4);
d. addition to the ammonia levels particularly in the area where discharge occurred (as shown in Annexure C Tables C‑5 and C‑6).
14 The discharge from the Pumping station would have also contributed to the:
a. potential acute harm to aquatic organisms as summarised in Table 10 and discussed in paragraphs [113] to [117] of Pablo's Affidavit;
b. possible potential risks to amenity for members of the community in the vicinity of Carrawood Reserve to Knights St Lansvale who complained of odour of sewage‑ contaminated water in Prospect Creek (see paragraphs [53] to [56] of Pablo's Affidavit).
15 We acknowledge that Sydney Water Corporation had implemented the following actions to mitigate the overall impacts of the discharge of untreated sewage into Prospect Creek.
a. Impacts were being offset, at least partially, through aeration of the waterway using a variety of techniques. Aeration had primarily increased the amount of dissolved oxygen in water as well as provided numerous other benefits including increasing the amount of gas exchange to breakdown nutrient and other chemical pollutants and ultimately lowering bacterial loads.
b. The introduction of clean water from the drinking (potable) water system using multiple standpipes, diluted the sewage contamination. This action introduced something in the vicinity of 36 kL per hour per standpipe running. Two to three standpipes were running at least 8 to 12 hours per day during and following the Incident. A total volume of 864 kL to 1,296 kL were discharged, adding to the dilution of the sewage and reducing the impacts and harm caused.
c. Dechlorination using sodium ascorbate in accordance with Sydney Water's procedures was used to avoid potential impacts from chlorine during flushing. This eliminated the risk of harm from the chlorine in the drinking water entering the waterway.
Matters not agreed upon
16 There were no matters that we disagreed on.