TENDER 0517 – RETENTION STORAGE SYSTEM
Question
1. Can Council release the hydraulic model prepared for the Aurecon
Clarification
Yes the hydraulic model can be released.
preliminary design? This would allow us to determine whether
there are alternative approaches to storage volumes and
conveying bypass flows.
2. Is the area set aside for retention storage within the Moonah
Primary School fixed? Would the School consider an area of
1000 m2 in the northwest corner in lieu of the linear retention
tank shown on the preliminary design?
3. The preliminary design suggests a 2.1m pipe from HLO-07 in
Derwent Park Road to carry 13.4 m3/s. The existing pipe work is
a 1.5m pipe which presumably has a much lower capacity with
the balance of the water arriving as surface flows. Detail 2
shows a proposed grated pit as the inlet for these surface flows.
Can Council provide any information on flood depths and surface
flow rates on Derwent Park Road that could be used to design the
inlet?
4. The linear retention storage is a structure that is generally quite
deep (~5m). Is there any reason why such a structure has to be
sealed against groundwater flows given its nature as a retention
storage?
Page 1
It is council preference not to expand the retention storage within the
school grounds, But this option maybe considered.
There are actually two 1.5m diameter pipes: one along Derwent Park
Rd, and one coming into it from Chesterman St.
Section 2.4.7, p19 of Part D specifies the grate on the inlet pit shall be
designed to accommodate a flow rate of 2.4 m3/s. This is incorrect.
The grate shall be designed to accommodate a flow rate of 1 m3/s.
The flood depth is not defined, however, please assume 200 mm.
The structure is to be sealed against groundwater flows due to
environmental requirements: if a spill occurs in the roadway,
contaminants are to remain in the storage structure rather than being
diffused into the groundwater as it travels along the structure.
Question
5. PS1 – on page 5 of the scope of works (1.6) it mentions 1 pump,
Clarification
A single pump was deemed sufficient for the purpose of the project.
similarily the drawing W-216 only depicts 1 pump. However on
page 11 of the overall design philosophy (4.2.1) it asks for duty
and standby pumps. What do we allow for?
6. At the site meeting you mentioned that there was UV at the
school site in addition to the 10 um filtration. I can’t seem to find
any reference to this UV system anywhere – is it missing, am I
blind or is it not required?
7. Section 2.1, Performance Requirements, I am wondering if it could
be clarified as to what percentage removal of TSS down to 10
microns is required? Do you need 100% or is something like 8590% OK?
8. With many design elements needing time and cooperation, an
extension to the due tender date would enable us to produce
better detail and quality, thus the projects pricing estimations
overall will be of a higher accuracy. We are requesting an
extension to the due tender date of one week which will also
subsequently push back the projects time line by the same
amount. If the tender date isn’t extended then most likely various
parts will not be fully designed by the due date leaving unknown
aspects to the project and attributed vague pricings. The
construction period is also worrying with 14 weeks specified
leaving a tight schedule, we see that 6 weeks of this period would
easily be taken up by investigations, design (there will be some,
tender date extension or not), documentation and compiling and
waiting for approvals. Leaving 8 weeks to construct and finish the
Page 2
- The school will use harvested water exclusively for drip irrigation
purposes, and therefore does not require UV treatment.
- injection to the ASR bores does not require UV treatment.
Filtration required prior to ASR injection, the allowable upper limit is
10mg/l
Council notify tenderers that an extension of time for construction has
been granted from 14 weeks to 20 weeks.
Question
job; an insufficient amount of time for these projects. Allowance
for the previously mentioned items into the construction period
should be considered, we see this needing an extension of 8-10
weeks to accommodate appropriately for both projects on offer
at this present time.
9. What is the invert level of the existing 1800dia pipes?
10. From the long section it seems the invert level of the proposed
overflow culvert is 1.50m, is this correct?
11. If the new overflow culvert is set higher than the existing 1800dia
pipes, wont Gepp Road still be inundated in the event the 1800’s
capacity is exceeded?
12. A request for an extension to the current closing date of the
tender. Our preferred tender closing date being Wednesday 15th
February 2012. We request this extension due to the timing of
the tender period coinciding with the Christmas/New Year period
in which a number of key potential suppliers and subcontractors
are unavailable to provide pricing or design alternatives. An
extension of time would also facilitate the opportunity to explore
design options and optimisations to ensure that we can be in a
position to offer a quality design combined with a competitive
price structure.
13. Could you please confirm that GCC will accept at no charge to the
Contractor all surplus and/or contaminated fill material at the
Glenorchy Waste Centre. The Contractor being essentially
responsible for including in our tender price the site handling,
loading and cartage of such material to the GCC Waste Centre for
disposal.
Page 3
Clarification
Approx. 1L 0.5m AHD. Please see pickup drawing within the tender
documents Gepp Parade 29/4/96 sheet 1.
This is correct
The invert of the new culvert is set slightly above the centreline of the
existing DN1800 to accommodate excess flow prior to the DN1800
pipes capacity being exceeded.
Notified of extension of time.
Been answered previously.
Question
14. I have been having a look at the provided documentation and
there is very little detail on what happens at SF001/04 which is
the large pit on the Brooker Highway. There are some indicative
line drawings from Council’s GIS showing the alignment of the
stormwater pipes but these do not show pipe sizes or invert
levels and the only other detail plan is a copy of the DPW plan of
the twin 1800 pipes under the highway which is in imperial units
to presumably an imperial datum. Can you provide me with some
details of the pipe configuration at the Brooker Highway to the
same datum please?
Page 4
Clarification
Invert level of existing DN1800 diameter pipes is approx 0.5m AHD.
Other dimensions/levels should be determined from the provided
drawings
Question
15. What I have done here is prepare a DRAIN model of the line to see
what variations in overflow culvert are possible whilst still
meeting the maximum water level limits for the 1 year and 20
year flows.
16. Table 3, section 2.3.2 of part D – Specification, specifies the design
flow rate through the culvert as 8,880 l/s (1 year ARI) and 22,500
l/s (20 year ARI). Can you please confirm if these flow rates are
for the new culvert only, or for the combined new culvert/existing
dual pipe system?
17. Are details of the existing dual DN1800 pipe system and outlet
structure available please? Design/construction drawings
including RL’s would be of assistance.
Page 5
Clarification
No answer required.
New culvert only
Additional information drawings are available, will be distributed to
all tenders by 20/01/2012