Review of reports and monitoring data related to environmental

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					Report to WA Department of Environment

 Monitoring environmental impacts on surface water and groundwater
from disposal of wastes at the South Cardup landfill: Recommendations
                       for additional monitoring

1. Background and project brief

Two independent reviews of monitoring data related to the South Cardup landfill were
carried out by CSIRO (Dr Greg Davis) and Stass Environmental in March 2004 (referred
to later as Stass). These reviews related particularly to conclusions drawn in a consultant
report (GHD, 2004), and identified information gaps and overall on impacts of the
landfill. An internal DoE review of consultant reports was also carried out (Angeloni,
September 2003). Recommendations were made in all these reviews on data
interpretation and the scope for further monitoring at the site.

DoE requested that recommendations within the review reports be assessed, and these be
collated and re-assessed through additional review of key data from the South Cardup site
given in various consultant reports and other data provided by DoE. In this study, a
summary review of all these reports was to be carried out and recommendations made for
additional work and monitoring to allow better understanding of impacts of the landfill
on surface water and groundwater.

2. Local situation and perceived impacts of the landfill

2.1 Geology and Hydrogeology
The landfill is in a geologically and hydrogeologically complex area immediately to the
east of the Darling fault. The regional geology would seem to be reasonably well known,
with fractured and weathered Archean granitic/gneissic rocks in the east of the area
largely underlying the Stage 1 landfill. Fractured sandstones (Neerigen Formation) and
Armadale Shales of the Cardup Group are present in the mid section of the site beneath
the Stage 2 landfill, and Quaternary alluvial/colluvial sediments (gravelly clays and
sands) to the west of the landfill. The local (as opposed to regional) geology beneath the
site has surprisingly not been considered in any detail in the consultants reports, except
for geotechnical investigation of the Stage 1 landfill area which focused on identification
of suitable clays for the landfill liner from the weathered, lateritic granite and gneiss
(AGC Woodward Clyde, 1993). Drillers logs from bores drilled for the monitoring
program, and other geotechnical information from excavations for the landfill would be
useful in better defining the local geology and assessing the validity of the various
boundaries identified on regional geological interpretations and maps provided in the
consultants reports.

A fault has been identified running northwest-southeast across the site laterally displacing
outcrops of the Neerigen Formation and Armadale Shales. The position of the fault
coincides with the natural drainage line (an ephemeral creek), which has now been
diverted around the landfill. As suggested in several reports and the reviews, it is likely
that this fault zone is hydrogeologically more conductive (i.e., more fractured) than
elsewhere in the area, which has given rise to increased weathering and juxtaposition of

Prepared by Chris Barber and Greg Davis – May 2004
Report to WA Department of Environment

the creek and faultline. This clearly will impact on local groundwater flow conditions,
and needs to be taken into account in further monitoring.

2.2 Landfill Site and Monitoring Data
The site is lined and has leachate collection and disposal systems, although some leachate
overflow has occurred over the edge of the landfill in July 2000. This was thought to
have entered the underdrain below the HDPE/clay liner, and had also entered the surface
water diversion drains and associated ponds. The latter recovered quickly following the
overflow event, although it was considered by GHD that low concentrations of typical
leachate “markers” (mainly ammonium-nitrogen) in the underdrain water at locations U1
to U4 were more persistent and resulted from more prolonged flushing of leachate from
the underdrain following the overflow. In their review, CSIRO suggested that this low
level of ammonium nitrogen could also be indicative of some leakage through the liner,
and they and GHD recommended further monitoring of the discharge to determine
longer-term trends. Clearly, the underdrain monitoring at U1 to U4 are critical monitoring
points for the landfill, as shallow groundwater seems likely to discharge to the drains at
least seasonally (i.e., following winter when groundwater levels are highest) and any
leachate discharge from whatever source would appear first in the underdrains rather than
in monitoring bores downgradient of the landfill (e.g., in bores SL8 and SL9). This was
recognized in the GHD (2004) report.

Water quality assessment is complicated by the presence of low concentrations of nitrate-
nitrogen (in surface water on the southern edge of the site at SW2) and ammonium-
nitrogen in groundwater downgradient of the landfill (SL9S) prior to commencement of
landfill operations. These indicate some source of nitrogenous contamination other than
landfilled wastes, as indicated in the GHD (2004) report. These have persisted since
landfilling began in 1999, although the low concentrations of ammonium-N in
groundwater in bores SL9S did decrease to very low levels over 2001 and 2002, but
showed some increase again in late 2002/ 2003. These have persisted into the latest
monitoring in November 2003 (reported in GHD (2004). Some higher concentrations of
ammonium-N were found in bore SL4A in mid 2003. It seems prudent to continue
monitoring all observation bores around the site to determine long-term trends in
groundwater quality, although there are key areas where additional information would be
valuable, for example to assess groundwater quality within the Quaternary alluvium (as
suggested by Angeloni, 2003) and to better define background groundwater quality (as
suggested by CSIRO). These are considered below in recommendations for further

2.3 Groundwater Dynamics
Groundwater level contouring of the presumed water table, shown in GHD (2004)
suggest a reasonable hydraulic connectivity between the various geological formations
around the landfill. As indicated in the reviews, primary porosity in granite/gneiss,
sandstone and shale are negligible, and groundwater storage and flow would be largely in
fractures within these formations. Indicated groundwater gradients are high in these hard
rocks, which suggests a relatively low level of fracturing and consequently a low
hydraulic conductivity. The indicated gradients in the Quaternary Formation of gravelly

Prepared by Chris Barber and Greg Davis – May 2004
Report to WA Department of Environment

clay and sand are somewhat lower generally, suggesting relatively higher hydraulic
conductivity compared with the fractured rocks to the east. It seems likely that
groundwater in the fractured shales discharges into the Quaternary alluvial sediments,
which indicates a need to monitor groundwater quality within these sediments. Although
any impacts may be small (there seems to be no direct discharge of leachate into these
sediments), it is prudent to determine any impacts as the Quaternary sediments as these
are considered to flow westwards across the Darling fault (Angeloni, 2003).

As pointed out in all the reviews, although the regional direction of groundwater flow is
westwards, there is local variability that would likely define flow paths for any leachate
contaminated groundwater. The ephemeral creek and juxtaposed fault line has a local
impact on groundwater level contours shown by GHD (2003). All the reviews also record
that bores SL8 and SL9 show hydraulic gradients vertically upwards, indicative of
groundwater discharge conditions (i.e., to the stream) in these areas. These bores are also
reported to be artesian at times (GHD, 2004). In contrast, as noted by CSIRO, at bore
SL11 hydraulic gradients are vertically downwards which indicates this is in an area of
local recharge. Clearly, groundwater – surface water interaction is important at the South
Cardup landfill.

In terms of flow downgradient of the Stage 1 landfill, this would likely be somewhat
north of west towards the creek line for northerly parts of the site if the contours are
indeed correct, and any leachate-contaminated groundwater encompassed by these
flowlines would be likely to be discharged to the creek or at least migrate subsurface to
the northwest along the creek line. In contrast, groundwater flow for southern parts of
Stage 1 area and from the Stage 2 landfill which is mostly to the south of the creek line
would be westwards, following the regional gradient.

Thus the existing monitoring bores could reasonably account for downgradient flows
towards the stream from the Stage 1 area (SL8 and SL9), although there is a more sparse
coverage elsewhere, particularly in the mid section between bores SL9 and SL10. In the
latter case, some monitoring of ponded water in the base of the shale pit could be
considered, as CSIRO have noted that this persists in summer and is thus likely to be
groundwater seepage. This pond was mislabeled as SW5 in Figure 2 in the URS (2003)
report, although this is identified in the text of the report as “groundwater relief outlet
sump” and is clearly part of the underdrain monitoring system. The latter discharge has
the same characteristics of low levels of leachate contamination as the underdrain
samples UD1-4, reported in the URS (2003) report. However, monitoring of the SW5
underdrain monitoring point was discontinued when an access road was re-routed over
this point (Ian Watkins (WALS), pers. Comm.). In any case, the apparent pond in the
shale pit would provide a useful additional monitoring point for groundwater seepage if
indeed seepage continues over time – which seems to be the case. Also, the level of this
pond should be evaluated relative to that of regional water table in the area.

2.4 Water Quality Analysis
The range of analytes determined in water quality samples is large, and the reasons for
monitoring some of these for assessment of landfill leachate impacts is questionable, but

Prepared by Chris Barber and Greg Davis – May 2004
Report to WA Department of Environment

their inclusion is perhaps understandable and probably most are a license condition. The
number of organic compounds determined is particularly excessive and in our view this is
unnecessary when key leachate indicators (e.g., ammonium-N) are present in very low
concentrations. Sampling and analysis for exotics like pesticides, and hydrocarbons is by
no means trivial and false positives and negatives are common. The detection of the
BTEX compounds in background and downgradient groundwater in earlier sampling at
the site would seem to be an artifact (false positive), which reinforces this. However, later
sampling (GHD, 2004) suggests that there are low concentrations of BTEX in leachate
(mostly xylene isomers) and lower concentrations have been found in samples from
underdrains (GHD, 2004) but not in any groundwater samples. We agree with GHD that
these concentrations in leachate are not unusual and detection in underdrains indicates
low levels of leachate contamination. Thus analysis for BTEX compounds seems
justifiable in those samples showing evidence of low levels of leachate contamination.

The range of metals determined is similarly quite large and we question whether this is
warranted. Some review of the extent and range of monitoring seems necessary, for
example to focus the full analytical program on those samples showing possible evidence
of contamination, or on key sampling points.

3. Recommendations for additional work and monitoring to better define impacts on
surface water and groundwater

3.1 More Holistic Interpretation of Local Hydrogeology
The CSIRO review recommends integration of geology, hydrogeology and water
chemistry to allow a more holistic interpretation of the workings of the local surface
water–groundwater system. The Stass review similarly recommends that surface water /
groundwater interaction could be better evaluated using water quality variability,
specifically using Piper diagrams for analysis of water quality distribution. In the
Angeloni review, investigation of groundwater flow and anomalous groundwater
chemistry (in background bores) is suggested, and in this study, it is argued that there is a
need for better definition of local geology using drillers logs and the results of
geotechnical investigation, as well as better definition of surface water-groundwater
interaction. In particular it would be essential to relate topographic levels in underdrains
and in other surface water discharges (e.g., the pond in the shale pit) with the regional
groundwater levels to identify whether the surface discharges are in fact groundwater
discharges, or whether these are evidence of throughflow discharges from perched
aquifers beneath the site. The following is therefore recommended:

Recommendation 1: That DoE consider additional work being carried out to verify the
local geology, and to evaluate both level and quality data from both surface water and
groundwater systems to provide a holistic analysis of the local hydrology, hydrogeology
and water quality to provide a more robust basis for evaluation of impacts of the landfill
on water resources.

3.2 Monitoring of Underdrain Flow

Prepared by Chris Barber and Greg Davis – May 2004
Report to WA Department of Environment

As argued above, any leachate discharge (whether through overspillage as has occurred
from time to time or from leakage through the landfill liner) is likely to show first in the
underdrain flow at UD1-UD4, which would largely represent discharge of shallow
groundwater or throughflow from development of perched aquifers beneath the lined

These surface discharges are regarded in this review as critical monitoring points, which
should be regularly monitored when underdrain flows and other discharges occur (also
recommended in the GHD (2004) report). It is unclear why previous consultants reports
show little data from these, although this may reflect irregularity of flows.

Some consideration could also be given to monitoring underdrain discharges for leachate
constituents which are more demonstrably associated with subsurface discharge from the
landfill, such as dissolved methane, rather than from infiltration of a surface leachate
discharge to underdrains where volatilization of methane would be expected to be
significant. Dissolved methane analysis could be carried out simply and cheaply on site
using headspace analysis with methane detection using a hydrocarbon sensor, and tested
initially using leachate itself.

Recommendation 2. Regular monitoring of the quality of underdrain flow and other
discharges (e.g., at the shale pit) should be carried out as a priority, recording “no flow”
when this is observed, as a first indicator of any leachate discharge which can then be
evaluated further. Simple on-site analysis of discharges for dissolved methane could be
tested as a rapid indicator of leachate leakage directly into the underdrain.

3.3 Better Definition of Aquifer Properties
There has been no reported evaluation of hydraulic conductivities of the various
formations beneath the landfill, or of groundwater flow velocities. This has been
recommended in most previous reviews, and some pump tests should at least be
attempted for observation bores in the Armadale shale close to the creek and fault line
(bores SL8S and SL9S) and remote from the creek (SL10 or SL11), and in the
Quaternary sediments (SL4A). Pump testing of any new observation bores which are
emplaced for monitoring could provide useful additional information, particularly if these
are drilled into formations not previously investigated (e.g., Quaternary sands, gravelly
clayey sands). As suggested by CSIRO, pumping of shallow bores and monitoring level
response in deeper bores at the same location (e.g., SL8 and SL9) would provide useful
information on vertical connectivity within the local formation. Continuous water level
measurements in selected bores (as suggested previously by CSIRO) would provide
further information on hydraulic conductivities through response to rainfall events.

Recommendation 3. Limited, short-term pumping tests be carried out on selected
observation bores to determine local formation hydraulic conductivities and allow
estimates to be made of groundwater transit times from the landfill to monitoring or
discharge points. Vertical connectivity within aquifers could also be determined during
pump tests as indicated above. Some consideration could also be given to monitoring

Prepared by Chris Barber and Greg Davis – May 2004
Report to WA Department of Environment

bore response to rainfall events, which would provide additional data on hydraulic

3.4 Additional Observation Bores.
The earlier reviews and memos within DoE have called for a variety of additional drilling
of observation wells, for a variety of reasons. These are summarized in Table 1. There are
clearly merits in all these proposed additional works, but (as stated in Stass’s review) it is
arguably better to carry out a further comprehensive review of the local hydrogeology
(Recommendation 1) and then base proposals for additional drilling on this more detailed
analysis. However, the following is recommended:

Source            Recommendation                     Reason
Angelino #1       Deepen well SL3                    Frequently dry, in key position
                                                     downgradient of Stage 2 and leachate
Angelino #2       Install bore between SL4A and      Provide additional monitoring of
                  SL9                                groundwater associated with the creek
                                                     and fault line, within the alluvials
Stass #1          Carry out further
                  hydrogeological appraisal (see
                  Recommendation 1) prior to
                  siting further observation wells
CSIRO #1          Bore on the northeastern edge      Assess upstream (background)
                  of the Stage 1 area                groundwater quality
CSIRO #2          Bore located downgradient of       Provide additional monitoring close to
                  Stage 1 area near, but south of    the fault line and creek
                  the drainage line (see Angelino
DoE Memo          Proposed new bores SL12 and        Monitoring immediately downgradient of
                  SL13                               the Stage 2 area
This study        Bores in Quaternary sediments      Impacts likely low, but flow possible
                  downgradient of Stage 2            westwards beyond the Darling fault
                                                     within these formations.

Table 1. Recommendations from various reviews for further drilling of observation bores.

Recommendation 4: On the basis of information to hand, there seems to be strong
reasons for extending existing bore SL3 (if indeed this is feasible), and for emplacement
of an observation bore within the alluvial sediments close to the creek and fault line,
between bores SL4A and SL9 (Angelino#2 and CSIRO #2 in Table 1). Additional bores
downgradient of the Stage 2 landfill could well be considered later following the re-
appraisal of the local hydrogeology of the site e.g., between SL9 and SL10 as indicated

3.5 Targeted Groundwater Quality Monitoring
As indicated above, monitoring of a wide range of inorganic and organic analytes in
samples of groundwater from the site is excessive, and given the difficulties in sampling
for trace levels of these and the extensive series of non-detects reported by consultants for

Prepared by Chris Barber and Greg Davis – May 2004
Report to WA Department of Environment

both major leachate constituents (e.g., ammonium-N) and trace ions and compounds, it
seems preferable to be more selective on requirements for the range of analytes to be
determined at specific locations. Thus it is recommended that DoE consider the
following, if necessary amending the license conditions for the landfill:

Recommendation 5: It is recommended that DoE consider the need for the full suite of
inorganic and organic analytes to be determined in all samples of surface water and
groundwater, and recommend that this only be carried out in key monitoring locations
(e.g., bore SL9S, underdrain monitoring point UD1-4 when available) or in those bores
where major leachate constituents have been detected (e.g., in Bore SL4A if ammonium-
N concentrations continue to be detected) as well as in one or more background bores for
comparative purposes. Further, DoE consider the need for this wide range of analytes,
and where these have consistently shown non-detects or very low concentrations, that
these not be required to be included in the suite of analyses for the key bores.

Recommendation 6: It is recommended that monitoring of groundwater levels and
quality in all bores continue as at present, but restrict the range of analytes (except the
key bores described above) to common leachate and general water quality indicators,
particularly ammonium-N, chloride, TDS, COD or TOC, dissolved oxygen, pH, iron,
manganese, potassium and zinc.

3.6 Other Recommendations Raised by Reviewers
Both Stass and Angelino suggest using resistivity-based geophysical surveying
techniques to assess leakage from the liner and possible leachate plumes in groundwater.
Various electrical resistivity and electromagnetic surveying has been successfully used in
uniform aquifer conditions (e.g., shallow sand aquifers on the Swan Coastal Plain) but the
complexity of electrical signals from wastes and the highly variable rock and sediment
types beneath and around the landfill in our view would give too high a background
signal variability for detection of leachate.

Recommendation 7: It is not recommended that a geophysical survey be conducted at
the site due to naturally high variability in electrical signal from rocks, sediment and

The Stass review recommended a tracer test be conducted to attempt to prove a hydraulic
connection between the area of leachate overflow on the southern perimeter of the site
and the underdrainage system beneath the liners, and it is understood this is currently
being carried out. The results of the testing could be usefully considered in the
hydrogeological/hydrological review (Recommendation 1).

Recommendation 8: The results of the tracer test to identify a hydraulic connection
between the area of surface overflow of leachate and the underdrainage system be
considered in the proposed review of geology, hydrology and hydrogeology.

4. Cited References

Prepared by Chris Barber and Greg Davis – May 2004
Report to WA Department of Environment

CSIRO, 2004. Review of monitoring data related to the South Cardup landfill. Report to
the Department of Environment, March 2004.

Stass Environmental, 2004. Cardup landfill site – review of monitoring data. Report to
the Department of Environment, March 2004.

Angeloni, J, 2003. Review of consultants reports on South Cardup landfill project 1993-
2003. Land and Water Quality Branch, DoE, September 2003.

GHD, 2004. West Australian Landfill Services : South Cardup landfill, Cardup. Surface
and Groundwater Monitoring, November 2003. Report to the Department of the

URS, 2003. Letter report to WALS, 13 June 2003. Six monthly surface and groundwater
sampl;ing, May 2003, South Cardup landfill.

West Australian Landfill Services (WALS), 2004. Fax from Ian Watkins to DoE (Monika
Siwiack), Leachate and Underdrain Results, 11 March 2004.

Prepared by Chris Barber and Greg Davis – May 2004

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