Eurobodalla Integrated Water Cycle Management Strategy

Eurobodalla Integrated Water Cycle Management Strategy
Table 9-9 Current and Future Peak Day Demands for Batemans Bay
Sewerage
Current KL/d 2032 KL/d
Long Beach 1 224 2 242
Lilli Pilli 758 919
Surf Beach 1 717 1 522
Catalina 2 9 750 12 377
Batemans Bay 406 523
TOTAL 13 855 17 583
The Batemans Bay sewage treatment plant has a nominal biological capacity of 15 000 EP
(equivalent persons) but has been assessed to have the capability to treat double this
biological load with minor modification. This is due to past conservativeness in design and
improved process designs. However, the plant’s hydraulic capacity is inadequate to meet
current peak loads, particularly when it coincides with a storm event in peak holiday
periods. It is an accepted practice under these circumstances to by-pass secondary
treatment but not disinfection as the strength of the sewage is very weak. In addition to
requiring an upgrade due to inadequate hydraulic capacity, the STP also needs works to
meet current OH&S requirements.
In recent years there have been incidences of sewage overflows from the sewer network
particularly during and after power failure on rainy days. Investigations undertaken by
Council and as part of this study show that these overflows occurs due to a combination of
unreliable power supply to some critical pumping stations, inadequate coverage and
limitation on the existing telemetry system, high storm inflows and inadequate storm
storage capacity. Council has commenced a monitoring program of the pump stations to
determine those pump catchments suffering from inflow and infiltration. A preliminary
analysis of the data shows that the catchments prone to storm inflows include Denhams
Beach (SPS BB38) and Malua Bay (SPS BB44). Analysis also shows that a rainfall event
greater than approximately 6 mm will impact on sewage flows due to storm inflow.
A preliminary pumping and storage capacity analysis of the sewage transport system
indicated that there is inadequate storage capacity in most of the system under current load
conditions to comply with the agreed service levels. The analysis also indicated that the
major and oldest transfer main in the foreshores of central Batemans Bay is most at risk,
with inadequate transfer and storage capacity. Continued strong growth will exacerbate this
problem, potentially resulting in major sewage spills when a power failure coincides with a
peak load and rainfall event. Analysis has also indicated that not all pumping facilities are
controlled by the shire telemetry system and that some of the critical pumping facilities do
not have reliable external power supply and/or provision to connect to an emergency diesel
generator. Council’s operator indicated that pressurisation of the sewer pipeline between
Batehaven and Surf Beach is occurring and that some pump stations do not meet OH&S
requirements. Council has undertaken a comprehensive risk analysis to prioritise the
facilities needing immediate attention and is now in the process of undertaking a
comprehensive review of the transport network for capacity and storage.
The NSW Environment Protection Authority has indicated that there may be less than ideal
mixing of effluent at the current ocean discharge point, and that this may potentially lead to
an environmental health risk.
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