The Mangrove Mountain landfill is owned and operated by Verde Terra Pty Ltd (Verde Terra). In October 1998, Gosford City Council, now Central Coast Council, granted development consent permitting the remodelling of the Mangrove Mountain Memorial Golf Club, and landfilling activities at the site.
In November 2001, we issued an Environment Protection Licence to authorise landfilling activities at the premises. In May 2014, landfilling activities at this site ceased due to legal actions commenced by Gosford City Council. Acceptance of further waste can only proceed once we vary the Environment Protection Licence to allow the landfill to recommence operations.
In August 2018, Verde Terra applied to us to vary the Environment Protection Licence for the site. The grant of the application would regulate the operation of the facility for a 10-year period and involve disposal of waste on the site, the volume of which would not exceed the volume required to fill approximately 1.318 million m³ of space. The application also involved substantial additional earthworks dealing with materials already on the site. The proposed ultimate land use of the site was as an 18 hole golf course.
We refused the application. Verde Terra has appealed to the Land and Environment Court against the refusal. There are also other legal actions between Central Coast Council, Verde Terra and the EPA that are ongoing.
Investigations until now have not found any impact to water quality from landfill operations
We conduct announced and unannounced inspections of the landfill to assess the management of water and leachate, including after periods of high or intensive rainfall.
Staff from the EPA and DPE Science, Economics and Insights (SEI) have conducted sampling of Ourimbah Creek and its tributaries over several years and have not found any impact to water quality from landfill operations. The most recent sampling was conducted by the EPA and DPE-SEI in April and May 2022.
Summary of results
- Overall water quality was good except for elevated total nitrogen concentrations in Stringybark Creek, and elevated oxidised nitrogen in Hallards Creek (refer to comments below).
- No semi‐volatile organic compounds were detected in any of the water samples.
- Dissolved metal concentrations were below recommended water quality guideline levels except for aluminium in both Hallards Creek and Stringybark Creek.
- Concentrations of ammonia and reactive phosphorus were below default trigger values for south‐east Australian slightly disturbed lowland rivers (ANZECC/ARMCANZ 2000) at all sites.
- Concentrations of oxidised (NOx‐N) nitrogen and total nitrogen well exceeded the trigger values (ANZECC/ARMCANZ 2000) for south‐east Australian slightly disturbed lowland rivers and NSW and Victorian east flowing coastal rivers (respectively) at all sites for both sampling events.
Catchment nitrogen load
There are likely multiple sources of runoff influencing the nitrogen load in the Ourimbah Catchment, such as the landfill, golf course, agriculture and a number of local unsewered rural residential properties. Elevated nitrogen was evident across all sample locations including the point upstream of the Stringybark Creek / Ourimbah Creek confluence. Investigation of water quality further upstream in the catchment is needed before source/s can be determined with any confidence.
Sample results
Physico-chemical properties of the water samples collected from Hallards Creek, Ourimbah Creek and three locations in Stringybark Creek on 12th April and 10th May 2022.
| Australian Drinking Water Guidelinea
|
Water Quality Default Guideline Valueb
|
Hallards Creek | Ourimbah Creek (OB 1) | Stringybark Creek (SB 1) | Stringybark Creek - North (SB 2) | Stringybark Creek - South (SB 3) | ||||
|---|---|---|---|---|---|---|---|---|---|---|
| 10 May | 12 Apr | 10 May | 12 Apr | 12 Apr | 10 May | 12 Apr | 10 May | |||
| Temperature °C | ‐ | ‐ | 14.1 | 17.7 | 13.3 | 17.8 | 17.7 | 14.1 | 17.8 | 14.2 |
| pH | ‐ | 6.5‐8.0c | 6.9 | 6.7 | 6.9 | 6.9 | 6.9 | 7.1 | 7.0 | 7.1 |
| Conductivity (µS/cm) | ‐ | 125‐2200c | 140 | 130 | 140 | 150 | 170 | 200 | 140 | 160 |
| Turbidity (FNU) | ‐ | 6‐50c,d | 5 | 7 | 3 | 26 | 41 | 34 | 10 | 5 |
| Dissolved oxygen (% Sat) | ‐ | ‐ | 99 | 96 | 99 | 98 | 98 | 97 | 98 | 99 |
| Alkalinity (mg/L CaCO3) | ‐ | ‐ | ‐ | 9 | ‐ | 11 | 10 | ‐ | 12 | ‐ |
| Total suspended solids (mg/L) | ‐ | ‐ | ‐ | ‐ | ‐ | ‐ | ‐ | ‐ | ‐ | ‐ |
| Metalse (μg/L) | ||||||||||
| Aluminium | ‐ | 55 | 90 | 240 | 90 | 320 | 300 | 160 | 340 | 140 |
| Arsenic | 10 | 13 | < 1 | < 1 | < 1 | < 1 | < 1 | < 1 | < 1 | < 1 |
| Boron | 4000 | 940 | < 100 | < 100 | < 100 | < 100 | < 100 | < 100 | < 100 | < 100 |
| Cadmium | 2 | 0.2 | < 0.1 | < 0.1 | < 0.1 | < 0.1 | < 0.1 | < 0.1 | < 0.1 | < 0.1 |
| Chromium | 50 | 1 | < 1 | < 1 | < 1 | 1 | 1 | < 1 | 1 | < 1 |
| Copper | 2000 | 1.4 | < 0.5 | 1.5 | 0.6 | 1.1 | 0.9 | 0.7 | 1.9 | 0.9 |
| Lead | 10 | 3.4 | 0.1 | 0.2 | 0.1 | 0.4 | 0.4 | 0.3 | 0.4 | 0.2 |
| Manganese | 500 | 1900 | 8 | 10 | 7 | 9 | 8 | 8 | 11 | 8 |
| Nickel | 20 | 11 | 0.6 | 1.4 | 0.6 | 1.4 | 1.3 | 1 | 1.6 | 0.8 |
| Selenium (total acid extractable) | ‐ | 5f | < 5 | < 5 | < 5 | < 5 | < 5 | < 5 | < 5 | < 5 |
| Silver | 100 | 0.05 | < 0.1 | < 0.1 | < 0.1 | < 0.1 | < 0.1 | < 0.1 | < 0.1 | < 0.1 |
| Zinc | ‐ | 8 | 2 | 3 | 2 | 2 | 2 | 1 | 6 | 2 |
| External Nutrients (μg/L) | ||||||||||
| Ammonia as Ammonia Nitrogen | ‐ | 20c | < 10 | < 10 | < 10 | 10 | < 10 | 20 | < 10 | < 10 |
| Oxidised nitrogen NOx‐N | ‐ | 40c | 650* | 590* | 1150* | 560* | 190* | 330* | 150* | 280* |
| Reactive Phosphorus as P | ‐ | 20c | < 10 | < 10 | < 10 | < 10 | < 10 | < 10 | < 10 | < 10 |
| Total Phosphorus as P | ‐ | 25g | 20 | 40 | 40 | 30 | 40 | 40 | 50 | 20 |
| Total Nitrogen as N | ‐ | 350g | 900 | 1100 | 1700 | 800 | 1200 | 800 | 700 | 700 |
a Health-based guideline values (NHMRC 2022)
b Freshwater default guideline values for toxicants, for 95% species protection unless otherwise stated (ANZG 2018)
c Default trigger value for south-east Australian lowland rivers (ANZECC/ARMCANZ 2000)
d The units for the default trigger value for turbidity are NTU. This range can be directly compared to results reported in FNU despite the unit difference
e Dissolved metal (<0.45 mm filtered) levels reported unless otherwise stated
f To account for the bioaccumulating nature of this toxicant, it is recommended that the 99% species protection level default guideline value is used for moderately disturbed systems
g Default trigger value for NSW and Vic east flowing coastal rivers (ANZECC/ARMCANZ 2000)
*Oxidised nitrogen NOx-N (also referred to as Nitrite+Nitrate as N) was measured in both filtered and unfiltered portions for some samples. The unfiltered measurement has been used to calculate total nitrogen. The filtered/dissolved measurement has been reported above.