Attachment G - Stormwater Quality Management plan

 

Bioretention System Specification
1. Referenced documents.

The following documents are incorporated into this specification by reference:
1.1. Standards
1.1.1. AS 1289 - Methods of Testing Soils for Engineering Purposes
1.1.2. AS 1289.5.4.1-2007- Soil Compaction and Density Tests--Compaction
Control Test--Dry Density Ratio, Moisture Variation and Moisture Ratio
1.1.3. AS 1289.5.7.1-2006 - Soil Compaction and Density Tests--Compaction
Control Test--Hilf Density Ratio and Hilf Moisture Variation (rapid method)
1.1.4. AS 2758 - Aggregates and Rock for Engineering Purposes
1.1.5. AS 4419 - Soils for Landscaping and Garden Use
1.1.6. 1.1.6 AS 4454 - Composts, Soil Conditioners and Mulches
1.2. Other publications
1.2.1. Guidelines for Soil Filter Media in Bioretention Systems (FAWB) - the
current version of the guideline can be found at
http://www.monash.edu.au/FAWB/
1.2.2. Construction and Establishment Guidelines - Swales, Bioretention systems
and Wetlands (Water by Design) http:/waterbydesign.com.au/ceguide/
1.2.3. Transferring Ownership of Vegetated Stormwater Assets (Water by
Design) http://waterbydesign.com.au/transferguide/
1.2.4. Transferring Ownership of Vegetated Stormwater Assets (Water by
Design) http://waterbydesign.com.au/transferguide/
1.2.5. Bioretention Technical Design Guidelines (Water by Design)
http://waterbydesign.com.au/techguide/
1.2.6. Water Sensitive Urban Design Field Guide (Water by Design)
2. Abbreviations and definitions

2.1, The bioretention system specification consists of the following abbreviations
and definitions:

2.2. Filter: soil layer which acts as a pollutant filter and supports plant growth.

2.3. Impermeable liners: the liner that prevents water movement between the filter
and the surrounding soils and defines the edge of the system.

2.4. Transition layer: layer to separate filter layer from the drainage layer to avoid
migration of soils from the filter to the drainage layer

2.5. Drainage layer: relatively free draining layer to convey infiltrated water to the
underdrainage.

2.6.  Under-drains: slotted drains collect treated stormwater from the drainage layer
at the base of the bioretention system.

3. Test methods and standards

3.1. The following test methods and standards are to be used as specified in the
above guidelines when conducting tests associated with this specification

3.2. The hydraulic conductivity of potential filter media shall be measured using the
ASTM F1815-11 method

3.3. Particle size distribution: AS1289.3.6.1 - 1995

3.4. Soils for landscaping and garden use: AS4419 - 2003.

4. Materials

4.1. Materials shall meet the required specifications detailed in Section 8 Filter
media, Section 9 Transition layer, Section 10 Drainage layer, Section 11
Under drainage, Section 12 Permeable liner, Section 13 impermeable liner
and Section 14 Landscaping of this document.

4.2. All materials must be certified by the supplier with certification and delivery
supply dockets shall be provided on request to certify the material delivered is
the material tested.

5. Timing and erosion and sediment control

5.1. The timing of civil and landscape works for bioretention systems must be
carefully planned to ensure that both the bioretention system and the
downstream waterways, are not impacted by stormwater and sediment (e.g.
through best practice erosion and sediment control). In particular, the drainage
layer, transition layer and filter media must not be placed until the risk of high
sediment loading from upstream construction activities has been mitigated.
The construction sequence must be approved by the superintendent.

5.2. _ Erosion and sediment control during construction must be delivered in
accordance with all legislative requirements including, where required, the
preparation of site-specific ESC plan/s in accordance with current Best
Practice Erosion and Sediment Control (e.g. IECA 2008, or later version).

6. Earthworks and hydraulic structures

6.1 The construction of hydraulic structures must ensure the design levels are
achieved. Bunds/ embankments surrounding the system shall be at correct
levels. The below table summarises the construction tolerances for each
element of a typical bioretention system.

6.2. _ Bioretention systems tolerances

  

 

Bioretention element Tolerance (unless specified otherwise)

 

Hydraulic structures + /- 25 mm (+/- 15 mm for streetscape

 

 

 

 

systems)
Earthworks + 7-50 mm
Under-drainage +-25 mm
Drainage and transition layers [+ 25mm
Surface level +/- 25mm

+/-40 mm for filter media >300 m?
provided the average extended detention
requirement is within 25 mm of the design
requirement.

-25 mm, + 50 mm

 

 

 

 

Embankments and bunds

 

7. Maintenance access.
Maintenance access is provided in accordance with the design drawings.

8. Filter media
8.1. Materials

A fundamental part of bioretention systems is the filter media. The main role of the
filter media is to support vegetation and remove pollutants. Filter media should be
loamy sand that has high permeability when compacted. It should not contain any
rubbish or deleterious material. The loamy sand should contain some organic matter
to improve water-holding capacity and plant health, but it should be low in nutrient
content. The filter media must be compliant with AS4419 - Soils for Landscaping and
Garden Use, and meet the following requirements

 

Test method in
accordance with

Parameter Requirement

 

Saturated hydraulic ASTM (1815-11

conductivity

50 - 500 mm/hr (200 preferred)

 

 

 

 

 

pH AS 4419 55-75
Electrical conductivity AS 4419 <1,2 dSim
Nitrogen content ‘AS 4419 <800 mg/kg
Phosphorus content AS 4419 <40 mg/kg
‘Organic content AS 4419 3% - 10%

Where organic content is below
this threshold, the filter media
may be ameliorated by adding 50
mm of compost and tining it into
the top 150 mm of filter media.

 

 

Particle size distribution AS 1289.3.6.1- 1995 [Clay & silt 3 - 6% (<0.05 mm)
Very fine sand 5 - 30% (0.05 -
0.15 mm)

Fine sand 10- 30% (0.15 - 0.25
mm)

Medium to coarse sand 40-60%
(0.25 - 1,0 mm)

Coarse sand 7 - 10% (1.0 - 2.0
mm)

Fine gravel <3% (2.0 - 3.4%)

 

 

 

 

Source: Guidelines for Soil Filter Media in Bioretention Systems (FAWB) and
Bioretention Technical Design Guidelines (Water by Design)

Filter media must be free of weeds and propagates. Other characteristics of the filter
media required for plant growth should be confirmed with a soil analysis or confirmed
with a horticulturist/iandscape architect.

8.2. Testing frequency

Suitable filter media can be delivered to site or imported sand can be ameliorated

to meet the above specification. In either case, the media shall be tested against

the above parameters at one sample per 500 m3 of filter media. For soil supplied
to site, testing must be undertaken on the actual material to be delivered to the
bioretention system. The supplier and contractor will be responsible for ensuring
the filter media meets the specification and the correct material is delivered to site
prior to installation.

8.3. _ Installation and compaction

When installing, the following specifications shall be applied:

8.3.1. Filter media shall be installed and compacted in two lifts for depths of over
500 mm. Compaction shall be light and even across the surface.

8.3.2. The top surface of the drainage layer, transition layer and the filter media
layer shall be level and free from localised depressions to ensure even
distribution of stormwater flows across the surface and prevent localised
ponding.

8.3.3. Filter fabric must not be used between drainage layer, transition layer and
the filter media layers or wrapped around the under-drainage

9. Transition layer
9.1. Transition layers prevent filter media migrating into the drainage layer.
9.1.1, Materials

9.1.1.1. Transition layer shall be minimum thickness of 100 mm coarse sand
unless otherwise specified (typically 1mm particle size diameter) with
<2% fines.

9.1.1.2. A particle size distribution for the sand shall be obtained to ensure
that it meets the following criteria (VicRoads).

9.1.1.3. D15 (transition layer) < 5 x D865 (filter media)
9.2. Testing

A sample of the proposed transition layer is to be provided to the superintendent
for approval prior to installation. The superintendent may require the transition
layer to be tested to ensure its particle size.

10. Drainage layer

Drainage layers convey infiltrated water into the slotted under-drainage pipes.
10.1. Materials

10.1.1.Drainage layer shall be comprised of fine gravel (nominal 2-5 mm) with
<2% fines and a minimum saturated hydraulic conductivity of 400 mm/hr.
The depth of the drainage layer shall ensure at least 50 mm of aggregate
cover over all perforated under-drainage pipes.

10.1.2. A particle size distribution for the gravel shall be obtained to ensure that it
meets the following bridging criteria (VicRoads): D15 (drainage layer) < 5 x
D85 (transition layer)

10.2. Testing

A sample of the proposed drainage layer is to be provided to the
superintendent for approval prior to installation. The superintendent may
require the drainage layer to be tested to ensure its particle size

11. Under-drainage
11.1. Materials

Either slotted rigid pipe (HDPE or similar) or ag-pipe can be used for
under-drainage as specified in the construction drawings. When installing, the
following specifications shall be considered:

11.1.1. Typically 100 mm-slotted HDPE pipe is the preferred type of rigid pipe.

11.1.2. The slots in the pipe shall not allow the drainage layer aggregate to freely
enter the pipe (under-drainage with slot width of 2 mm or smaller is
preferred).

11.1.3. Under-drainage pipes must not be surrounded by any geofabric or sock.
11.2. Installation

11.2.1. The maximum spacing of under-drains for bio-retention systems <100 m2
is 1.5 m from centre to centre. For bioretention systems >100 m2 the
maximum spacing can be increased to 2.0 - 2.5 m if specified in the
construction drawings

11.2.2. The under-drains shall be sloped towards the outlet pit (min. 0.5%
longitudinal grade) and the base of filtration trench shall be free from
localised depressions, For bioretention systems with a saturated zone a
0% pipe grade is acceptable.

11.2.3. All junctions and connections shall be appropriately sealed
11.2.4. Under-drainage pipes shall be sealed into the overflow pit.

11.2.5. All under drainage pipes to have raised clean out points constructed from
non-slotted pipes which extend to 150 mm above filter media surface

12, Permeable liner (where specified)

12.1. A permeable geotextile liner fabric must be used to line the outside of the
bioretention system

12.2. The liner must extend at least 500 mm beyond the top of the sides and must
be keyed into batter and covered by at least 200 mm of topsoil.

12.3. The liner must be resistant to all soil acids and alkalis, resistant to
microorganisms and comply with the requirements of AS3706.12 and
AS3706.13.

13. Impermeable liner (where specified)
13.1. Materials

Liner options include clay, geosynthetic bentonite clay liners or high-density
poly ethylene (HDPE) liners. Refer to the project drawings for liner details.

13.2. Installation

Installation must be in accordance with manufacturers specifications and
design drawings and achieve the following

13.2.1. The liners shall be keyed into the batters and to the embankments.
13.2.2. Liners must be sealed around protrusions such as outlet pipes.
13.2.3 Must achieve a maximum permeability of 1x10°m/s
14. Landscaping
14.0. Refer to landscape design drawings

14.1. Batter slopes must have min 200 mm topsoil which must be tested by a
NATA-accredited laboratory in accordance with AS 4419.

14.2. Subsoils to be cultivated to 150 mm prior to placing topsoil on batter slopes.

14.3. Planting densities and species must be consistent with the landscape design
drawings. No substitutions should be made unless approved by the
superintendent

14.4, Plants supplied to site must
14.4.1. be grown in clean, weed- and pest-free conditions;

14.4.2. be well developed, sun-hardened and contain a fully established root ball
that does not crumble when removed from its container.

14.4.3. be at least 200 mm high.

14.4.4. show no sign of pest and disease

14.4.5. show no signs of nutrient deficiency

14.4.6. be free from weeds

14.4.7. be clearly labelled

14.4.8. be supplied in a container that is at least: 90 mm high x 50 mm wide
14.5. Preparing Filter media: Unless specified otherwise, each plant must receive

These drawings have been developed in consultation between the participating Councils.
BEFORE USE, the user shall confirm that the drawing has been adopted by the appropriate Council.

at least 10 g of slow-release native fertilizer in granular or tablet form.
Pre-hydrated water crystals may be applied at 1-2% by weight.

14.6. Mulch must be applied in accordance with the design drawings, be applied

prior to planting, provide coverage of the soil and not exceed 75 mm
thickness, and be kept 50 mm clear of plant stems. Unless otherwise
specified, mulch should be fine sugar cane mulch secured in place by a loose
weave jute net pinned at 500 mm centres.

14.7. Filter media surface and plant stock are to be watered immediately prior to

planting. Unless otherwise specified, plants should be planted in clumps of the
same species, and large monocultures avoided

14.8. Plant method must minimise soil compaction and ensure that all roots are

covered by at least 10 - 20 mm of soil, avoid covering plant crowns.

14.9. Unless specified otherwise, the following irrigation schedule applies during

plant establishment (at 2.5 - 5 L per plant per week)

- Week 1-5 Five waterings per week
- Week 6-10 Three waterings per week

-Week 11-15 Two waterings per week

- Thereafter As required to sustain plants until successful establishment

14.10. Replanting must occur during the establishment period if less than 90% of

plants survive.

14.11. Successful plant establishment in bioretention systems is considered when

the plants are robust and self-sustaining, and meet the following criteria.

- Vegetation must cover at least 90% of the bioretention surface with mulch
covering the remainder (< 10% mulch visible from above)

- Average groundcover plant height must be greater than 500 mm.
- Plants must be healthy and free from disease.
- No weeds or litter to be present.

. Certification and chain of custody
15.1, The following certification and the chain of custody applies to bioretention

media;

15.1.1. The supplier and contractor are responsible for ensuring the bioretention
media meets the specifications outlined in these guidelines and that the
correct material is delivered to site. The supplier must arrange for testing
of the filter media by a soil laboratory certified for the methods in
accordance with the requirements listed above. On the basis of the testing,
the soil laboratory and supplier must certify the material meets these
specifications. The supplier must provide the certification and laboratory
test results to the contractor with the supply docket.

15.1.2. The contractor provides a copy of the supplier's certification, test results
and supply docket to the site superintendent or bioretention designer for
review.

15.1.3. Following review of the certification, test results and the supply docket, the
site superintendent or bioretention designer approves installation of the
bioretention media.

15.1.4. The relevant sections of the bioretention media sign-off form as per the
Construction and Establishment Guidelines (Water by Design) should be
completed and signed. This sign-off form is provided as part of the
construction certification by the site superintendent or bioretention
designer.

16. Hold points

16.1. The following hold points must be observed in accordance with the most

recent Water by Design construction checklists and superintendent approval is
required for works to proceed:

16.1.1.Prestart meeting
16.1.2. Completion of hydraulic structures and under-drainage

16.1.3 Prior to placing filter media

16.1.4. After placement of filter media (prior to applying mulch and planting)

17. Compliance testing (for on-maintenance or off-maintenance)

17.1. Compliance testing must be in accordance with chapter 5 of Transferring

Ownership of Vegetated Stormwater Assets (Water by Design). Checklists
must be completed and signed by the superintendent.

Disclaimer: it is the responsibility of the certifying registered professional engineer to
ensure these standard notes are adapted to the specific needs of the project. It is
expected that additional drawing notes would be required to cover other important
project issues (e.g. Workplace Health and Safety, Environmental Protection, Erosion and
Sediment Control, etc). Healthy Waterways, IPWEA and all contributors to this
document accept no liability for the use, misuse or any omission or inaccuracy in this
document.

 

 

 

 

 

 

 

 

 

DATE

February, 2016 REVISIONS _ Original Issue

 

 

 

 

INSTITUTE OF PUBLIC WORKS ENGINEERING AUSTRALASIA
STANDARD DRAWINGS

 

BIORETENTION

STANDARD NOTES

DS—078