The effects of waste disposal on groundwater quality in Tasmania The effects of waste disposal on groundwater quality in Tasmania Tasmanian Geological Survey Record 2002/09 NHT Funded Project NLP 13188 Stieglitz sewage lagoons MINERAL RESOURCES TASMANIA DEPARTMENT INFRASTRUCTURE, ENERGY RESOURCES of and Tasmania Natural Heritage Trust Helping Communities Helping Australia
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The effects of wastedisposal on groundwater
quality in Tasmania
The effects of wastedisposal on groundwater
quality in Tasmania
Tasmanian Geological
Survey Record 2002/09
NHT Funded Project
NLP 13188
Stieglitzsewagelagoons
MINERAL RESOURCESTASMANIA
DEPARTMENTINFRASTRUCTURE,
ENERGY RESOURCES
of
and
Tasmania
NaturalHeritage
TrustHelp in g Comm uni t i e s
He lp ing A us t ra l i a
While every care has been taken in the preparation of this report, no warranty is given as to the correctness of the
information and no liability is accepted for any statement or opinion or for any error or omission. No reader
should act or fail to act on the basis of any material contained herein. Readers should consult professional
advisers. As a result the Crown in Right of the State of Tasmania and its employees, contractors and agents
expressly disclaim all and any liability (including all liability from or attributable to any negligent or wrongful
act or omission) to any persons whatsoever in respect of anything done or omitted to be done by any such
person in reliance whether in whole or in part upon any of the material in this report.
INTRODUCTION
Mineral Resources Tasmania (MRT) initiated a projectto investigate the effects of waste disposal ongroundwater quality in Tasmania. The project wasfunded by MRT and the Natural Heritage Trust (NHT)and included a number of sites for detailed study. Thesewage lagoons at Stieglitz were one of these sites.
The objectives of the investigations at the Stieglitzsewage lagoons were to:
� Determine the geological nature of the hostmaterials;
� Identify the depth of the water table;
� Examine the quality of the groundwater;
� Determine the permeability of the host materials;and
� Identify if a potential hydraulic connection existsbetween the lagoons and the local groundwatersystem.
SITE DESCRIPTION
The township of Stieglitz is located on the east coast ofTasmania, bordering Georges Bay about fourkilometres east of St Helens. The Stieglitz sewagelagoons are located approximately 500 metressoutheast of Stieglitz (609 200 mE, 5 423 700 mN)(fig. 1). The lagoons, which have been in operationsince about 1983, are currently licensed by theDepartment of Primary Industries, Water andEnvironment (DPIWE) while the Break O’Day Councilis responsible for maintenance. Engineering
consultants Sinclair Knight Merz have supervisedadditional engineering works undertaken since theinitial construction of the lagoons.
During construction both lagoons had a one metrecement wave wall constructed at surface level toprevent wave erosion damage. Post construction, thesouthern lagoon was lined with geo-fabric materialsprayed with bitumen. This liner has since lifted fromthe base of the lagoon and can been seen floating at thesurface (Plate 1). Both lagoons are located in gravellysand.
Tasmanian Geological Survey Record 2002/09 1
Groundwater quality investigationsat the Stieglitz sewage lagoons
A. R. Ezzy
DEPARTMENTINFRASTRUCTURE,
ENERGY RESOURCES
of
and
Tasmania
Mineral Resources Tasmania
Tasmanian Geological Survey
Record 2002/09
NaturalHeritage
TrustH elp in g Commu n i t i e s
H e l p ing Aus t r a l i a
Abstract
Groundwater was investigated in the area of the Stieglitz sewage lagoons to determine if the lagoons were
affecting groundwater quality. The lagoons are situated close to perched shallow water tables. Further
investigations are required to refine the hydrogeological model of the site and preferred pathways of flow
Geo-fabric liner sprayed with bitumenfloating in the southern lagoon.
Figure 2
Extract from the St Helens geological map (McClenaghan et al., 1987) of the local area and related geology.
Plate 2
Drainage line west of the sewagelagoons with bore hole SZSL2001/2
in the foreground.
Geology
The Tasmania Department of Mines 1:50 000 scalegeological map of the St Helens area (McClenaghan etal., 1987) indicates that the geology of the lagoonfootprints comprises Tertiary-aged conglomerate,gravel and sand (fig. 2). Quaternary-aged alluvial,swamp and marsh deposits are indicated to the east ofthe lagoons.
Geological mapping during the current studyindicated that the site is dominated by gravel and sanddeposits within 80 m of the lagoons in all directions.Occasional small pods of high plasticity white claywere observed in the area of an old landfill southwestof the lagoons. Dark brown hard pans of iron-enrichedmaterial were also observed in the area.
Hydrology
The lagoons are located within 100 m of a drainage lineto the west that discharges into Chimneys Lagoon(Plate 2). Windmill Lagoon is located approximately250 m to the east of the lagoons. Australian Bureau ofMeteorology rainfall station 092033 (St Helens PostOffice) is the closest rainfall station to the site. The chartof average monthly recorded rainfall (fig. 3) shows thatthe average annual rainfall of 774.6 mm is evenlydistributed over the year. The average annual rainfallis low when regarded in a statewide perspective.
INVESTIGATION METHODS
Borehole drilling and installation
Five 120 mm diameter monitoring bores were augerdrilled on 8 March 2001 for this project (fig. 4). All bores(except SZSL2001/4) were drilled to the maximumdepth capacity of the drilling rig. Fifty millimetre PVCcasing and slotted screens with bentonite seals wereinstalled in each hole. All bores were logged inaccordance with AS 1726-1993; engineering logs arepresented in Appendix 1.
Groundwater was encountered between 3.2 m(SZSL2001/4) and 7.1 m (SZSL2001/3) depth below
ground level across the site. Flow during drillingindicated that the groundwater in all boreholes wasunconfined. Recorded yields of bores ranged between0.012 to 0.033 l/s. Figure 5 shows a cross-section andthe standing water level on 19 August 2001.
Both the unsaturated and saturated zones mainlyconsist of heterogenous layers of clay, fine tocoarse-grained sand and gravel. Layers of low tomedium plasticity clay were intercepted in boreholesSZSL2001/2 and SZSL2001/3. A strong organic odourwas observed on the returns of SZSL2001/1 between2.3 and 8.3 metres. Rounded quartzite pebbles wereintercepted in bore SZSL2001/4 and indicatereworking and imported material in this area.
SZSL2001/4 was drilled as a potential up-gradientbackground bore. Several months after the installationof the bores, the Break O’Day Council undertookearthworks to control surface water run off in thevicinity of the southwest corner of the southernlagoon. Hole SZSL2001/4 failed to make water afterthese earthworks were undertaken.
Engineering logs of the boreholes indicate that thebund walls overlying the Tertiary sediments consist ofreworked clayey sandy gravelly material.
In situ permeability testing
A slug extraction test on bore SZSL2001/3 was carriedout on 17 August 2001. Data collected during this test ispresented in Appendix 2.
The slug extraction test data was analysed in thesoftware package AquiferWin32 (Version 2.17,Environmental Simulations Inc.). The Bouwer andRice (1976, Unconfined Aquifer) solution was used tocalculate the hydraulic conductivity value forSZSL2001/3 (fig. 6). This method was selected as themost appropriate available within the softwarepackage.
Tasmanian Geological Survey Record 2002/09 3
56.154.6
76.2
66.762.9
65.0
70.967.3
60.8
67.4
59.3
67.1
Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec0
20
10
40
30
50
60
70
80
90
Mo
nth
lyR
ain
fall
(mm
)
Figure 3
Average monthly rainfall for AustralianBureau of Meteorology rainfall station
092033, St Helens Post Office.
Tasmanian Geological Survey Record 2002/09 4
60
00
88
mE 90
92
94
96
98
542 0028 mN
30
32
34
36
38
61
00
00
mE
OLD LANDFILLFOOTPRINT
(APPROX. ONLY)
SZSL2001/3
SZSL2001/2
SZSL2001/1
SZSL2001/4
SZSL2001/5
Windmill
Lagoon
Figure 4
Locations of environmental monitoring bores installed at the Stieglitz sewage lagoons.
Environmental Simulations Inc.),Bouwer and Rice (1976 Unconfined
Aquifer) solution.
HYDROLOGICAL MODEL
Constraints related to the drilling contractor’s depthcapacity did not allow for a complete groundwaterflow-regime investigation. Iron pans within thesediments appear to be producing perched watertables. The drying up of borehole SZSL2001/4 (refusalon iron pan) after surface drainage control workssupports this comment.
Some of the gravel is clay bound (also demonstrated bylow yields), implying the main groundwater storagecapacity occurs within the sandy zones. Perched wateris also most likely occurring above the clay-enrichedlayers/lens. It is expected that holes drilled to greaterdepth would intercept additional groundwater andallow for a more complete interpretation of thegroundwater flow regime in the area of the lagoons.
An interpretation of the piezometric surface (based onsurveyed heights and groundwater depths of theboreholes in the limited area of the lagoons) is shownin Figure 7. The water table appears to slope towardsthe northwest and a groundwater mounding effect isalso indicated close to and beneath the lagoons.
GROUNDWATER CHEMISTRY
All bores were sampled in accordance withAustralian/New Zealand Standard AS/NZS5667.11:1998 on 15 May 2001. Bore SZSL2001/4contained no water and therefore was not sampled.Laboratory testing of samples of groundwaterextracted form the boreholes was carried out byAnalytical Services Tasmania, in accordance with
relevant Australian and international standards(Appendix 3). Values for pH ranged between 5.0 and5.5. Conductivity values ranged between 430 and 656
�S/cm. Analytical results are presented on site maps inAppendix 4. Figure 8 is a cation Ternary plot for theresults of the groundwater analyses. Tables 1 and 2compare the analytical results against internationalstandards where a guideline/emission value is statedby the relevant standard.
Tasmanian Geological Survey Record 2002/09 5
SZSL2001/2 SZSL2001/1 SZSL2001/5
A’A
GC
GC
SP
SC
SM
SP
CL
CL
CL
SM
SP
SP
GC
SC
SM
GC
DTW — 19 August 2001 V:H = 10:1
23
22
21
20
19
18
17
16
15
14
23
22
21
20
19
18
17
16
15
14
Figure 5
Cross-sections and related standing water levels on 19 August 2001 for bores SZSL 2000/2, 1 and 5 [A-A’].
90
92
94
36
38
SZSL2001/3
SZSL2001/2
SZSL2001/1
SZSL2001/4 SZSL2001/5
15.5 m
16.0 m
15.0 m
Figure 7
Interpretation of the piezometric surface based onsurveyed heights and groundwater depths of the boreholes
(RL water surface contours).
For the water parameters analysed, the groundwaterchemistry shows little variation in the area of thelagoons. Groundwater that was interpreted asdown-gradient of the lagoons (SZSL2001/2 and 5) hadsome slightly elevated chemical results for sulphate,magnesium, and iron. The water chemistry ofSZSL2001/3 and 5 is dominated by sodium andpotassium cations (fig. 8), with the other two borescontaining higher levels of magnesium and calciumcations. SZSL2001/3 and 5 are both screenedpredominantly in clayey gravel, which may accountfor these differences.
CONTAMINATION ASSESSMENT
The combination of in situ permeability testing, thecross section (fig. 5) and piezometric surface map(fig. 7) demonstrate that the Tertiary unconsolidatedsedimentary aquifer may potentially transport anyleakage from the sewage lagoons. There is a highpotential for significant migration of effluent andconsequent effects in the coastal sediments and theTertiary plain area. Transport velocities, based on slugtest data, may be as high as one metre per day. This
implies that leakage from the sewage lagoons couldreach Chimneys Lagoon or Windmill Lagoon inapproximately one year.
There are currently no known users of groundwater inthe area.
PRINCIPAL CONCLUSIONS
Layers and/or lens of clayey gravel, clay and iron pans(acting as aquitards) control perched groundwater.Migration of effluent water from the lagoons mayfollow preferred pathways to a deeper, unconfinedunconsolidated aquifer. This aquifer most likely hashydraulic connection to Chimneys and Windmilllagoons. Investigations of groundwater quality in thearea should consider potential impacts of the unlinedold landfill to the west.
FURTHER WORK
Because of the clay content within the gravel,geophysical investigations may not detect a distinctgroundwater plume at the site. A ground conductivitysurvey may identify potential sand/gravel channelsand therefore preferred pathways of flow within thesediments. Any identified channels/pathways mayrepresent future drilling targets.
The drilling of a background bore some distance fromthe lagoons would enable the determination of localTDS levels. A comparison of background TDScombined with the installation of strategically placedadditional bores may indicate the degree of recharge togroundwater from the lagoons.
Future monitoring of microbiological water qualityparameters may help to confirm the extent of thedegradation of groundwater quality in the local areaand the processes associated with potential naturalattenuation at the site. Effluent water chemistry fromthe lagoons should be considered as part of thisassessment.
REFERENCE
MCCLENAGHAN, M. P.; TURNER, N. J.; WILLIAMS, P. R. 1987.Geological Atlas 1:50 000 Series. Sheet 41 (8515S). St Helens.Department of Mines Tasmania.
[30 May 2002]
Tasmanian Geological Survey Record 2002/09 6
Mg
80
60
40
20
0
Ca
20
0100
40
60
80
80100 60 40 20 0100
Na + K
3
2
5
4
1
Figure 8
Cation ternary plot for groundwater bores at the Stieglitzsewage lagoons. 1 — SZSL2001/1; 2 — SZSL2001/2;
3 — SZSL2001/3; 4 — SZSL2001/5; 5 — average of allMRT groundwater records for Quaternary coastal sands.
Tasmanian Geological Survey Record 2002/09 7
Table 1
Comparison of analytical results against water quality standards(guideline value listed when stated by a relevant standard)
Lead (mg/L) <0.005 <0.005 <0.005 <0.005 0.05* (mg/L)
Zinc (mg/L) <0.001 0.005 0.003 0.003 5.0* (mg/L)
* Environment Protection (Water Pollution) Regulations 1974, emission into inland water.** Australian Water Quality Guidelines for Fresh and Marine Waters 1992.
N/A— no emission limit available.
Table 2
Comparison of analytical results against the Australian and New Zealand Guidelinesfor Fresh and Marine Water Quality 2000
Shaded areas indicate values above relevant guideline levelsNotes: ** set to limit potential for corrosion and fouling of pumping, irrigation and stock watering systems.
*** Chromium (VI)(1) Suitability depends on salt tolerance of crop & calculation of ECse, the average root zone salinity.
ECse depends on soil type & average root zone leaching fraction.(2) Depending on animal type, within this salinity range may be reluctance to drink or may be some
scouring but stock should adapt without loss of production.(3) ES = Suits extremely sensitive crops
MT = Suits moderately tolerant cropsMR = Medium risk of increasing crop cadmium concentrations
STV — Short term trigger value for contaminant in irrigation water (<20 years) useLTV — Long term trigger value for contaminant in irrigation water (100 years) use
Tasmanian Geological Survey Record 2002/09 8
Appendix 1
Engineering logs of boreholes
Tasmanian Geological Survey Record 2002/09 9
EXPLANATION SHEET FOR ENGINEERING LOGS
Borehole and excavation log
Cored borehole log
No resistance
ranging to
refusal
1 2 3
Penetration Water
22 Jan, 80 Water level
Water inflow
Water outflow
on date shown
Notes — samples and tests
U50 Undisturbed sample50 mm diameter
Disturbed sampleD
Standard penetrometerblow count for 300 mm
N
SPT + SampleN*
Material classification
Based on Unified SoilClassification System.
In Graphic Log materials arerepresented by clear contrastingsymbols consistent for each project.
Moisture content
D Dry, looks and feels dry
Moist, no free water on handMwhen remoulding
when remouldingWet, free water on handW
Liquid limitLL
PL Plastic limit
PI Plasticity index
e.g. M>PL — Moist, moisture content
greater than the plastic limit
Hard
Very stiff
Firm
Soft
Very soft
Consistency
F
VSt
H
St
S
VS
Stiff
: hand penetrometer
Fb Friable
50 100–
200 400–
>400
100 200–
25 – 50
<25 (kPa)
Notes: X on log is test result
is range of results
%
Density index
VD
D
MD
L
VL
Very dense
Dense
Very loose
Medium dense
Loose 15 35–
35 65–
85 100–
65 85–
0 15–
Smooth irregular
Smooth planar
Rough irregular
Rough planar
Fracture description
SL
SP
RP
RL
Lugeons
Lugeon units (uL) are a measure
of rock mass permeability. For a
46 to 74 mm diameter borehole
1 Lugeon is defined as a rate of
loss of 1 litre per metre per minute.
1 Lugeon is roughly equivalent to
a permeability of 1 x 10 mm / sec.-4
Casing used
Barrel withdrawn
Case - lift Fluid loss
No loss
100% loss
50% loss
Graphic log
No core
Rock substances represented
by clear, contrasting symbols
consistent for each project.
Fresh
Slightly weathered
Highly weathered
Extremely weathered
Fr
SW
HW
EW
Weathering
Notes: X on log is test result.
index 1 (MPa)
Strength
EH
VH
H
M
L
VL
EL
Extremely high
Very high
High
Medium
Extremely low
Low
Very low 0.03 0.1–
3 10–
0.1 0.3–
1 3–
0.3 1–
< 0.03
>10
point load strength Significant defects
Significant defects shown graphically
Joint
Sheared zone
Crushed seam
Infill seam
Extremely weathered seam
-4
5 (50)
Tasmanian Geological Survey Record 2002/09 10
MINERAL RESOURCES TASMANIA
ENGINEERING LOG - BOREHOLEProject
Co-ordinates Drill type
Drill method
Drill fluid
Hole commenced
Hole completed
Drilled by
Logged by
supp
ort
R.L
.
dept
h
grap
hic
log
materialsoil type: plasticity or particle characteristics,colour, secondary and minor components.
notes metres
Borehole no.
Sheet of
wat
er samples,tests
moi
stur
eco
nditi
on
cons
iste
ncy
dens
ity in
dex
structure, geology
Location
R.L.InclinationBearing
clas
sific
atio
nsy
mbo
l
pene
trat
ion
1 2 3
0°0°
Stieglitz sewage lagoons St Helens Point Road, Stieglitz