Suitability of reclaimed asphalt pavement and recycled

crushed brick as filter media in bioretention applications

Abstract: Bioretention systems are increasingly being used in urban stormwater management systems which enable
stormwater to get treated by infiltration through filter media before draining to the drainage system. Bioretention
systems also substantially reduce runoff volumes and peak flows. Typically quarry materials are used as the filter
media; however the use of quarry materials will reduce valuable natural resources. The main objective of this research
is to evaluate suitability of Reclaimed Asphalt Pavement (RAP) and Crushed Brick (CB) as filter media in bioretention
systems. Such a novel approach of using recycled waste materials will significantly conserve valuable natural
resources. A series of laboratory tests was undertaken to investigate the suitability of these recycled materials. The
laboratory tests include particle size distribution, organic content, pH, specific gravity, flakiness index and hydraulic
conductivity. Among the pollutants, total suspended solid (TSS), total phosphorus (TP) and total nitrogen (TN) were
selected. An earlier calibrated mathematical model (MUSIC) for permeable pavements was converted to a bioretention
system model whilst retaining the filter material properties. A model for bioretention system was simulated to
investigate the effectiveness of RAP and CB materials in trapping selected pollutants. In terms of physical and
chemical properties, RAP and CB were found to meet the stringent requirements of various environmental protection
authorities. This research further indicates that recycled waste materials can be reused viably as alternative materials in
bioretention systems.

Keywords: Recycled material, construction and demolition, bioretention system, hydraulic conductivity, pollutant

Introduction
Stormwater runoff in urban areas is one of the major leading sources of decreasing water quality in various water bodies (EPA U.S.,
2004). However, stream ecosystems are also being degraded in various ways which are very difficult to distinguish, such as decrease
groundwater levels, increase frequency and intensity of flood flows, increase loads of pollutants and increase stream bank erosion with
multiple impacts on aquatic ecosystems (Novotny and Olem, 1994; Paul and Meyer, 2001). Increases of imperviousness in urban areas
also results in increase in flood flows, decrease groundwater levels, increase erosion and pollutants due to uncontrolled stormwater
(Novotny and Olem, 1994). Such uncontrolled stormwater discharges are very harmful for receiving water in urban waterways. It is
therefore required to manage the quality and quantity of urban runoff to protect and restore the ecological health of urban waterways.
The negative impacts of urban stormwater management are widely recognized among various end-users, and as such, two important
goals being maintaining stormwater quantity and quality are essential for its proper management (Meyer et al., 2005). A number of
treatment technologies such as stormwater wetlands, sedimentation ponds, sand filters and infiltration systems have been previously
developed (Davis, 2005). Bioretention systems (also known as rain gardens and biofilters) is a filtration technique used to infiltrate
stormwater through filter media prior to discharge stormwater runoff from impervious surfaces such as roads, parking lots and roofs to
the drainage system. These bioretention systems also control pollutants by filtering distracted stormwater runoff through vegetation
followed by vertical filtration into filter media. A schematic diagram of the bioretention system is shown in Fig. 1. The treatment
process is obtained through different systems such as sedimentation, sorption fine filtration and biological uptake (PGC, 2002). The
water is then discharged through the under-drains of the filter media to the drainage system or waterways. If the filter media is not

properly designed, the trapping objectives to capture various pollutants and heavy metals will not be achieved. Therefore, it is required
to the design filter media accurately which can reduce pollutants and heavy metals.
Laboratory studies on the reduction of heavy metals, phosphorus, ammonium and other pollutants have been conducted previously
(Davis et al. 2006 and Fletcher et al. 2007). Hatt et al. (2006) also investigated the leaching characterises of nitrogen and phosphorus
through non-vegetated filter media. Henderson et al. (2007) investigated the performance of three different filter media (gravel, sand
and sandy loam) in vegetated and non-vegetated columns, whereas vegetated columns removed more nitrogen and phosphorus than
non-vegetated columns. In addition to water quality benefits, bioretention systems also help to reduce flood peak and volume (Hunt,
2003).
With rapid industrialization and population growth, large amounts of land are being used in various infrastructures such as roads,
footpaths and parking lots in both urban and rural areas. These days, it is also important to also design and manage the surrounding
areas of these infrastructures in such a way that it can reduce runoff, as well as pollutants that are transported during storm events.
Urban runoff is one of the main causes of pollution and hence stormwater management is an increasing priority worldwide. Melbourne
is the capital of the state of Victoria, Australia. The Victorian state government has put into effect a zero-waste policy directive in
which all wastes, regardless of quantity, should be diverted from landfill. Challenges of low-carbon economies and resource depletion
are major factors in pushing toward reuse of construction and demolition (C&D) materials in roadwork applications (DSEWPC, 2012).
The extensive amount of waste generated by various industries and human activities has made a major problem for the disposal of
solids waste in Victoria, as well as around the world. In Australia, approximately 8.7 million tons of demolition concrete, 1.3 million
tons of demolition brick, 3.3 million tons of waste excavation rock, 1.0 million tons of waste glass and 1.2 million tons of reclaimed
asphalt pavements are stockpiled annually and these stockpiles are growing radically (Sustainability Victoria 2010; Arulrajah et al.
2013a). A similar trend exists around the world in all developed and developing countries.
The state road and water authorities in Australia are currently exploring the potential reuse option for C&D materials in various civil
engineering applications (EPA Victoria, 2009; VicRoads, 2007). The sustainable usages of waste materials in stormwater and
geotechnical engineering applications have considerable social and economic benefits to industrialized and developing nations.
Simultaneously, shortages of natural mineral resources and increasing waste disposal costs have brought added significance to the
recycling and reusing of C&D wastes in recent years (Landris 2007; Arulrajah et al. 2014; Rahman et al. 2014a, 2014b). The
engineering properties of various waste aggregates used as alternative construction materials in various developed and developing
countries have also been reported by several authors (Kartam et al. 2004; Arulrajah et al. 2012a, 2013a). Other waste materials that
have generated recent interests in various geotechnical applications include waste glass (Imteaz et al. 2012), municipal solid waste
(Zekkos et al., 2010), waste excavation rock in pavement subbase applications (Tsang et al. 2005; Arulrajah et al. 2012b) and biosolids
(Arulrajah et al. 2013b). These considerations suggest that reusing C&D waste in most cases will be a cost-effective solution compared
to using natural virgin aggregate (DSEWPC, 2012). In addition to potential cost savings, there are also significant carbon savings in the
usage of recycled materials in civil engineering applications. A comparison of the properties of the C&D materials is required for uses
in bioretention systems as this will be of importance to consultants, contractors, designers, local councils, state water authorities,
operators, and end-users alike in their potential usage in water engineering applications.
An attempt has been made in this research to encourage reuse of C&D materials as bioretention filter media in urban storm water
management systems. Bioretention system is a useful technique of urban stormwater management which can help to prevent flooding
and control pollution. The hydrologic and pollutant removal performance of stormwater bioretention systems in urban catchment areas
has been established by Hatt et al. (2009). The hydraulic behaviour of C&D materials in bioretention systems has however not yet been
established to date and furthermore, there is also a lack of information on the treatment performance of C&D materials in bioretention

systems. The present study investigates the hydraulic performance and pollutants removal efficiency of bioretention systems using
C&D materials, RAP and CB. Another attempt has also been made in this research to compare evaluated properties of RAP and CB
with various physical, geotechnical and hydraulic properties recommended by different regulatory authorities in regards to bioretention
system.

Methodology
Recycled C&D materials (RAP and CB) were collected from a recycling site in the state of Victoria, Australia. The samples were first
oven dried and subsequently different laboratory tests were undertaken on the recycled aggregates targeting their usage as alternative
filter materials in urban stormwater bioretention systems. Physical, geotechnical and hydraulic properties were subsequently analysed
in this research.
2.1 Physical Properties Testing
Particle size distribution tests of the C&D materials were conducted according to ASTM D422-63 (2007). The particle size distribution
targeted between lower and upper bound reference lines for aggregates in backfilling, filter media, subbase and other civil engineering
applications. Initially the samples were washed with distilled water through a sieve size of 75 m. The retained samples were taken and
dried for 24 hours before further sieve analysis tests. Specific gravity and water absorption tests of coarse aggregate (retained on 4.75
mm sieve) and fine aggregate (passed through 4.75 mm sieve) were undertaken according to ASTM C127 (2007).
The pH tests were performed in accordance with BS 1377 (1990). About 30 g of dry sample, which passed through a 200 m sieve,
was taken and 75 ml of distilled water was added to the sample and stirred for a few minutes before suspension was left standing
overnight. The suspension was stirred immediately before testing. The pH value of the suspension was measured by a digital device.
The loss of ignition method was used to determine the organic content of the aggregates (ASTM D2974, 2007). To determine the
maximum dry density and optimum moisture content, modified compaction tests were performed on the recycled materials (ASTMD1557, 2009). Flaky characteristics of the materials were determined using flakiness index test according to BS 812-105.1 (BSI, 2000).
2.2 Permeability Testing
A laboratory test setup of constant head permeability testing apparatus was used in this research for determining the coefficient of
hydraulic conductivity of the C&D materials. A schematic diagram of the hydraulic conductivity testing apparatus is shown in Fig. 2.
The main cylinder of the hydraulic conductivity testing apparatus had an internal diameter of 152 mm and a height of 132 mm.
Coustumer et al. (2008) used a cylinder having 100 mm diameter and 85 mm height for their laboratory tests. The C&D materials were
selected between the lower and upper bound limits as per the state water and road authoritys requirements to allow sufficient
infiltration through the media. The hydraulic conductivity tests were performed for coarse grained C&D materials in accordance with
ASTM D2434-68 (2006). For the determination of hydraulic conductivity, the constant head method was used for granular C&D
materials used in this research.
The influent solutions were prepared in the laboratory by adding pollutants with distilled water to achieve a Total Suspended Solids
(TSS) concentration of approximately 250 mg/L as worst case scenario. This is slightly higher than the average TSS concentrations in
stormwater runoff events occurring in urban areas (Kim and Sansalone, 2008; Li and Davis, 2008). Several researchers (i.e. Hatt et al.
2005; Clark and Pitt, 2009) have investigated reductions in sediment concentrations through various filter media such as sand, carbon
sand, peat sand and composed sand.. In this research, water samples were collected at the inflow and outflow of the C&D filter media.
Subsequently, the water samples were analysed for TSS, Total Nitrogen (TN) and Total Phosphorus (TP) using standard methods
(Standard Methods, 1998). Only these three pollutants (TSS, TN and TP) were selected as the mathematical model (MUSIC) which
was developed to simulate pollutants trapping efficiencies can calculate only for these three pollutants in addition to gross pollutants.

Wong et al. (2002) developed the Model for Urban Stormwater Improvement Conceptualisation (MUSIC). MUSIC provides the ability
to simulate both quantity and quality of runoff from urban and rural areas. One of the great strengths of MUSIC is the ability to model
the treatment processes that occur with stormwater treatment devices (Wong et al., 2006). MUSIC enables users to evaluate conceptual
design of stormwater management systems to ensure they are appropriate for their catchments and are expected to achieve specified
water quality objectives. MUSICs simulations can be based on event or continuous basis, which allows rigorous analysis and
comparisons between short-term and long-term benefits of any stormwater treatment system. MUSIC Version 3.0 can simulate
treatment efficiencies for Buffer strip, Vegetated swale, Bio-retention system, Wetland, Infiltration system, Pond, Sedimentation basin,
Rainwater tank and Gross Pollutant Traps. MUSIC is currently one of the most popular models used by Australian industries in
predicting the performance outcomes for various WSUD techniques. MUSIC has been used in some other countries as well. Imteaz et
al. (2013) tested MUSIC for different treatment systems in Brisbane, Melbourne, Sweden, Auckland and Scotland. Their findings were
quite varying; in some cases it is found to overestimate the stormwater treatment systems capacity and on the other hand in some other
cases it underestimates the treatment capacity. In general, MUSICs predictions for flow and TSS removals were close to
measurements, whereas in some cases predictions of TP and TN removals were overestimated.
In terms of bioretention applications, initially the MUSIC software was validated for porous pavement system, which uses filter
media only without biological actions (i.e. without plants/shrubs). The validated model was then converted to bioretention model
keeping the individual filter media properties of each C&D material. Different C&D materials are represented by their relevant
hydraulic conductivity values (obtained thorough laboratory experiments) in MUSIC program. Developed MUSIC models simulated
various treatment efficiencies through bioretention systems in regards to TSS, TN and TP. As MUSIC requires rainfall data; a random
6 minutes interval recorded rainfall series from the year 1959 was selected for this purpose. The MUSICs default parameters regarding
inflow pollutants concentrations were adjusted to generate the same influent pollutants concentrations used in the experiments.

Results and Discussions

The physical, geotechnical, hydraulic and chemical properties of the C&D materials in urban bioretention applications and comparison
with typical specified requirements are presented in the following sections.
3.1 Physical properties
Physical properties of the C&D materials were conducted from three replicate samples for each test to maintain consistency of the
results. Specific gravity values of CB and RAP were found to meet typical requirements specified by state water and road authorities.
The specific gravity for RAP was however found to be slightly lower than CB materials. The specific gravity results for the C&D
materials indicate that they can be considered high quality aggregates. It can also be seen from Table 1 that the specific gravity values
of coarse aggregates are slightly higher than those of the fine aggregates for all the tested materials used in this research. The organic
content of the C&D materials was found to be low except for RAP, which was also found in the acceptable ranges. Several researchers
have found that the typical organic content values of biofilter filter media are between 0-10% as shown in Table 2 (Woods-Ballart et
al. 2007; FAWB, 2009).
The pH value of the C&D materials indicated those materials were slightly alkaline, though within expected limits of 6-11. The pH
value for natural soils and soil blends that can be used as biofilter media is 5.5-7.5, according to FAWB (2009) requirements. The
flakiness index value was within the upper limit of 35; typically specified for backfilling, bioretention filter media and permeable
pavement subbase materials. Table 1 also shows the results of modified compaction tests conducted on the recycled C&D materials.
The modified compaction results indicated that CB had the highest MDD, while RAP had the lowest due to the presence of bitumen

substances with RAP. The OMC of the C&D materials indicated that RAP had the lowest OMC of 8.30%, while CB had the highest of
12.75%.
The gradation curves of the C&D materials are shown in Fig. 3, and compared with the state road and water authorities specifications
for the usage of quarried materials in urban stormwater management systems. Soil classification symbols from the Australian Soil
Classification System (ASCS), the Unified Soil Classification System (USCS) and AAHOTO systems are also presented in Table 1.
According to the ASCS, the C&D materials have approximately equal amounts of sand and gravel sized fractions, enabling them to be
classified as well-graded gravel (GW). Based on the gradation curves, the grain size distribution parameters including D90, D10, Cu and
Cc are summarised in Table 3. The comparison between C&D materials and drainage applications requirements is also shown in Table
3 (Drainage Factsheet, 2000). The soil classification results show all those parameters were satisfied with the drainage filter media
requirements. Therefore, the C&D materials used in this research are suitable for bioretention filter media in stormwater management
systems. The results show that the tested RAP and CB aggregates were consistent with the requirements of typical aggregates for civil
engineering applications such as bioretention filter materials, permeable pavement subbases, footpaths and back filling purposes
(Arulrajah et al. 2014).
3.2 Permeability Results Analysis
Constant head permeability testing of the C&D materials was undertaken in this research. Table 4 shows the hydraulic behaviour of
the C&D materials used in this research. Among the tested C&D materials, hydraulic conductivity is higher for RAP compared to CB.
The hydraulic conductivity values were found to be within the range of those specified for the usage of aggregates in bioretention filter
media and permeable pavement subbase applications in urban stormwater management system (Melbourne Water, 2005). Table 4 also
shows the comparison of hydraulic conductivities between present study and published guidelines (CASQA, 2003; City of Austin,
2011; EPA, U.S. 2004; FAWB, 2009; PGC, 2007; Woods-Ballart et al. 2007; Hunt and Lord, 2006). The permeability results obtained
from present study satisfied the requirements to use in bioretention filter media according to mentioned guidelines. Therefore, authors
recommend that the particular RAP and CB materials used in this research can be used as filter materials in stormwater management
systems.
3.3 Nutrients Removal Efficiency
Nutrients removal efficiencies of the C&D materials were assessed in this research to investigate the suitability of these materials as
filter media in bioretention systems. The laboratory results and MUSIC modelling were compared with the previous guidelines and
case studies. The influent suspension was prepared in the laboratory using 250 mg/L sediments. Although this concentration level is
slightly higher than the average concentration generated from urban areas, that was selected as a worst case scenario (Kim and
Sansalone, 2008; Li and Davis, 2008). Kaolinite fine solid particles and distilled water were used to prepare influent suspension.
Chemical tests of the inflow and outflow samples were carried out in an accredited commercial environmental laboratory, Australian
Laboratory Services (http:// www.alsglobal.com/). Series of laboratory experiments were conducted to assess pollutants removal
efficiencies of permeable pavement systems using C&D materials. Later MUSIC models were developed and calibrated with the
experimental results. Three different water quality parameters such as TSS, TN and TP were assessed and compared in this research, as
among fine and chemical pollutants, MUSIC can simulate only these parameters. Rahman et al. (2014c) provided details of comparison
with experimental results and calibration of MUSIC models. In general MUSIC models simulations were reasonable.
Bioretention system uses same filter media as permeable pavements, having some specific shrubs in it. Root system of the grown
shrubs provides additional treatment. As such, in regards to pollutants removal efficiency, bioretention system is better than the
permeable pavement system having same filter media. Calibrated MUSIC models for permeable pavements systems were converted to
bioretention models retaining filter media data same as for permeable pavements. All other required data was kept as default provided

in MUSIC. Table 5 show the results of TSS removal efficiencies from the present study and comparison with other studies and
guidelines (Hsieh and Davis, 2005; UNHSC, 2006; Davis et al. 2007; Hunt et al. 2008; Carpenter and Hallam, 2010). From the
presented comparison, as the simulated nutrients removal efficiencies of the C&D materials are higher than typical requirements, it can
be used as filter materials in bioretention systems.
Table 6 show total nitrogen removal efficiency from the present study and comparison with previous studies and guidelines
(Hsieh and Davis, 2005; UNHSC, 2006; Davis et al. 2007; Hunt et al. 2006, 2008; Carpenter and Hallam, 2010). They reported wide
ranges (30~99%) of total nitrogen removal efficiencies, whereas present study found 59-72% total nitrogen removal efficiencies. Table
7 show TP removal efficiencies obtained from different studies and guidelines (Davis et al. 2007; Hsieh et al. 2007; Hunt et al. 2008;
Sharkey, 2006) and comparison with the present study. Again, wide range (32~99%) of TP removal efficiencies were reported;
whereas present study found 62~77% total phosphorus removal efficiencies. In some cases, the pollutants removal performances for
phosphorus are not significant. This may be attributed to the fact that some bound pollutants (especially phosphorus) are mainly
associated with smaller particles and trapping of such smaller particles is not achievable through tested filter media. However, for a
longer period of such sediment accumulation, the filter media is expected to become clogged and eventually would be able to trap
smaller particles (Hatt et al. 2005). However, previous researchers also investigated the TP removal efficiency from different filter
media.
In reality, 100% pollutants removal efficiency is achievable in many cases, however with the compromise of reducing hydraulic
conductivity, which is not recommended with the consideration of urban flooding. As such, there should be always a balance of target
pollutants removal efficiency and acceptable hydraulic conductivity. The nutrients removal efficiency can also be increased using
larger depth and/or area of filter media, which will cause increase in cost. As such a proper cost optimisation is necessary for the
decision making of optimum size of bioretention system. Imteaz and Ahsan (2014) presented detailed cost optimisation of three
different systems including bioretention using MUSIC. Also, in many cases 100% removal of nutrients is not necessary or overoptimistic. Australian best management practice guideline recommends achieving captures of 80% TSS, 45% TN and 45% TP
(Melbourne Water, 2005). From the above-mentioned results, it is found that the tested RAP and CB materials can be used as filter
media in bioretention systems and will be able to provide expected water quality treatment standards.
3.4 Bioretention Filter Media Depth
Filter media is one of the major components of bioretention systems in urban stormwater management. Appropriate filter media depth
is required for successful removal of TSS, TN and TP. Table 8 show effects of filter media depth in achieving 100% pollutants removal
efficiencies. Diblasi et al. (2009) suggested that minimum 300 mm bioretention media depth is required to remove 100% TSS from
stormwater. However, in this study the authors suggest that minimum 200-300 mm filter media depth is required to remove 100% TSS
from stormwater for these particular C&D materials. Several researchers found that 100% TP can be removed from stormwater runoff
using appropriate filter media depths between 600 mm to 900 mm (Hsieh et al. 2007; Passeport et al. 2009; Hatt et al. 2009). This
research suggests filter media depth of 300-1100 mm is required depending on the materials used to remove 100% TN.
The comparison shows that the minimum required depth for C&D materials is also quite similar with previous guidelines. TN removal
efficiency from stormwater runoff has been investigated by Passeport et al. (2009). Based on their research it can be concluded that
minimum media depth of 900 mm is required for natural soils to remove 100% TN. Current study also suggests that minimum filter
media depth of 300-900 mm (depending on the filter material) is essential for RAP and CB as filter media to reduce 100% TN through
bioretention systems.

Conclusion
Physical and hydraulic properties of the RAP and CB materials were assessed in this research to investigate the suitability of these
materials as filter media in bioretention systems. Comparisons were also made between laboratory results and previous guidelines to
investigate whether it can satisfy or not with various regulatory authorities requirements for urban stormwater management systems.
Thorough comparison and analysis were performed in this study, which indicate that selected RAP and CB materials satisfy the criteria
for use as filter materials in bioretention systems.
The pH values of the materials indicated the materials to be slightly alkaline, though still within expected limits. The compaction
characteristics of the tested RAP and CB materials were found to be in a consistent range and equivalent to those expected of a
quarried material. The specific gravity values of the RAP and CB materials were found to meet specified requirements and these
indicate that they can be considered high quality aggregates. The organic contents of the recycled C&D materials were found to be low,
except for RAP for which the organic content was also found in the acceptable ranges. The flakiness index of CB is observed to be
lower than that of RAP. The hydraulic conductivity of the recycled materials can be described as low for CB and high for RAP
aggregate.
Among the tested C&D materials, the lower pollutant removal and the higher hydraulic conductivity were obtained from RAP. It is
also noted that the permeability values achieved from C&D materials used in this research are within the acceptable limits as filter
materials in filter media applications. In general the hydraulic conductivity values of CB and RAP are higher than that of natural
aggregate. The hydraulic conductivity values were found to be within the range of those specified for the usage of aggregates as
biofilter media in urban stormwater management systems. The permeability values obtained from RAP and CB materials ranges
between 44 mm/h and 121 mm/h, whereas the minimum requirement is 12.7 mm/h.
For 100% removal of nutrients, bioretention filter media depth is a salient feature. Through MUSICs simulations required filter media
depth was calculated for 100% removal of nutrients. It was found that filter media depth between 300 mm to 1100 mm is required for
complete removal of nutrients using selected C&D materials as bioretention filter media. This finding is quite similar to the findings by
other researchers and/or available guidelines.
This research highlights the fact that C&D (RAP and CB) materials traditionally destined for landfill can be used in a sustainable
manner as an alternative materials in filter media for bioretention systems. The presented results would provide the reader with an
indication of the testing methodology, physical properties, chemical properties and performance of these traditionally waste materials
in bioretention applications. In terms of entire life cycle of filter materials it is necessary to make sure that groundwater should not be
contaminated when C&D materials are reused. Based on the extensive suite of geotechnical and chemical tests, it can be concluded that
the RAP and CB materials used in this research are suitable alternative materials for bioretention filter media in stormwater
management systems.

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List of Tables
Table 1: Physical and geotechnical properties of C&D materials
Table 2: Comparisons between present study and previous guidelines of bioretention filter materials properties
Table 3: Typical requirements and comparisons for well graded filter materials
Table 4: Comparisons between present study and previous guidelines of hydraulic conductivity for bioretention filter materials
Table 5: Comparisons of total suspended solid removal efficiencies for bioretention systems between present study and previous
guidelines
Table 6: Comparisons of total nitrogen removal efficiencies for bioretention filter materials between present study and previous
guidelines
Table 7: Comparisons of total phosphorus removal efficiencies for bioretention filter materials between present study and previous
guidelines
Table 8: Required filter media depths for specific nutrients removal in bioretention systems
List of Figures
Fig. 1: Schematic diagram of a typical bioretention system
Fig. 2: Schematic diagram of laboratory testing setup for permeability testing
Fig. 3: Particle size distribution and comparisons of the C&D materials

Table 1: Physical and geotechnical properties of C&D materials

Physical properties
Specific gravity - Coarse
Specific gravity - Fine
Organic content (%)
pH
Compaction (Modified): MDD (kN/m3)
Compaction (Modified): OMC (%)
USCS classification
ASCS classification
AASHTO classification

CB

RAP

Typical requirements

2.41
2.48
2.02
9.50
20.40
12.75
GW
GP-GM
A-1-a

2.34
2.33
4.03
7.20
19.40
8.30
GW
GP
A-1-a

>2.0
>2.0
<5.0
6-11
>17.50
8-15
GW/SW
GW/SW
A-1-a

Table 2: Comparisons between present study and previous guidelines of bioretention filter materials
properties
Guideline

Aggregate

Organic content

Remarks

Present study

Sand-gravel (38-56%)

2-4%

ARC (2003)

Sandy loam (35-60%)

Not specified

2-9% Fine content

Clay content
<25%

35-60% sand

20-30% well aged

leaf compost

Clay content <5%

35-60% sand
30-50% silt

0-4% organic
content

10-25% clay
content

Washed, well graded

sand with specified
PSD band

3-10% organic
content

Clay content <3%

85-88% washed
medium sand

3-5% organic
content

8-12% silt and

clay

70-80% concrete sand

20-30% screened
bulk topsoil

3-10% clay
content

PGC, Meryland
(2007)
The SUDS manual
(Woods-Ballart et al.
2007)
Facility for advance
water biofiltration
(FAWB, 2009)
North Carolina
cooperative
extension service
(Hunt and Lord, 2006
City of Austin (2011)

Table 3: Typical requirements and comparisons for well graded filter materials
Properties

Present study

Maximum size

19 mm

Typical requirements
(Drainage Factsheet, 2000)
38 mm

D90

12-15 mm

19 mm

D10

0.19-0.85 mm

0.25 mm

Cu

7.8-71.0

Gravel, Cu > 6; Sand > 4

Cc

1.80-2.80

1 Cc 3

Table 4: Comparisons between present study and previous guidelines of hydraulic conductivity for
bioretention filter materials
Guideline
Present study
California bioretention TC-32 (CASQA, 2003)
City of Austin (2011)
EPA, U.S (2004)
FAWB (2009)
PGC, Meryland (2007)
The SUDS manual (Woods-Ballart et al. 2007)
North Carolina cooperative extension service
(Hunt and Lord, 2006)

Hydraulic conductivity (mm/h)

47-124
12.50
50.80
12.70
50-300
12.70
12.60
25.4 (for nitrogen removal)
50.80 (for phosphorus, metal and other
pollutant removal)

Table 5: Comparisons of total suspended solid removal efficiencies for bioretention systems between
present study and previous guidelines
Influent
concentration
(mg/L)

Effluent
concentration
(mg/L)

Load
reduction (%)

Study cases

250

21-45

82-92

Present study

150

107

27

34

18

59

Charlotte, N.C.

49.5

20

60

Durham, N.H.

--

--

97

Field study

--

--

79-97

Site name
MUSIC
modelling
Laboratory
columns
College Park

Hsieh and
Davis, (2005)
Davis et al.
(2007)
Hunt et al.
(2008)
UNHSC,
(2006)
Carpenter and
Hallam,
(2010)

Table 6: Comparisons of total nitrogen removal efficiencies for bioretention filter materials between
present study and previous guidelines
Site name
MUSIC
modelling
Laboratory
columns
Greensboro,
N.C.
Louisburg, N.C.
Pilot boxes
Haddam, Conn.

Influent
concentration
(mg/L)

Effluent
concentration
(mg/L)

Load
reduction (%)

Study cases

2.8

0.78-1.15

59-72

Present study

2.1

0.1-3

95

1.35

4.38

40

1.70

1.25

65

1.6-6.0

1.1-2.8

30-99

1.2

0.8-1.0

32

Kim et al.
(2003)
Hunt et al.
(2006)
Sharkey
(2006)
Davis et al.
(2006)
Dietz and
Clausen
(2006)

Table 7: Comparisons of total phosphorus removal efficiencies for bioretention filter materials
between present study and previous guidelines
Influent
concentration
(mg/L)

Effluent
concentration
(mg/L)

Load
reduction (%)

Study cases

2.24

0.52-0.85

62-77

Present study

3.0

0.05-1.6

63-85

0.29

0.18

69

0.28-0.88

0.06-0.15

52-99

Charlotte, N.C.

0.19

0.13

32

College, Park

0.61

0.15

79

Site name
MUSIC
Modelling
Laboratory
columns
Louisburg,
N.C.
Pilot boxes

Hsieh et al.
(2007)
Sharkey,
(2006)
Davis et al.
(2007)
Hunt et al.
(2008)
Davis, (2007)

Table 8: Required filter media depths for specific nutrients removal in bioretention systems
Previous study
Gross pollutants
Total suspended
solids
Total
phosphorus
Total nitrogen

Study cases
Diblasi et al. (2009)
Hsieh et al. (2007),
Passeport et al. (2009),
Hatt et al. (2009)
Passeport et al. (2009)

Present study

Typical depth
(mm)

Recommended
depth (mm)

300

200-300

600-900

300-1100

900

300-900

Pipe connected
to roof drains

Overflow system
Runoff
Ponding area

Filter

Transition Layer
Drainage Layer
Perforated Drainage Pipe
Figure 1

Mixer

Influent suspension
Control valve
Constant head
water jar
Overflow tube

132 mm

Inlet tube

C&D filter media

152 mm
Outlet tube
Sampling bottle

Figure 2

Head loss tube

Figure 3