RESULTS OF PUMPING TESTS - esperance.wa.gov.au

PLANNED LANDFILL SITE,

ESPERANCE

RESULTS OF PUMPING TESTS

REPORT FOR

SHIRE OF ESPERANCE

AUGUST 2018

Report No 419-0/18/01a

Planned Landfill Site, Esperance Results of Pumping Tests

Rockwater I:\419-0\Report\18-01a_Pumping Test Results.docx

TABLE OF CONTENTS

1. INTRODUCTION 1

2. HYDROGEOLOGICAL SETTING 1

3. DRILLING AND BORE CONSTRUCTION 1

4. PUMPING TESTS 2

4.1. Method 2

4.2. Results 2Nth Production 34.2.1.

Sth Production 34.2.2.

5. GROUNDWATER FLOW VELOCITY 4

5.1. Nth Production 4

5.2. Sth Production 4

6. ASSESSMENT OF OTHER WORK ITEMS 4

6.1. Potential to Recovery Leachate 4

6.2. Need for an EM Survey 5

6.3. Bore into the Werillup Formation 5

6.4. Need for Additional Monitoring Bores to Determine Flow Directions 5

7. CONCLUSIONS 6

REFERENCES 6

Table

Table 1: Details of Test and Monitoring Bores 2

Figures

1 Bore Locations

2 Nth Production Pumping Test at 1.62 L/s, Drawdowns in Pumped and Monitoring Bores

3 Sth Production Pumping Test at 1.6 L/s, Drawdowns in Pumped and Monitoring Bores

4 Calculated Drawdowns after One Year Pumping Recovery Bore at 120 m3/d, and Flow-Paths

REVISION AUTHOR REVIEW AUTHORISED ISSUED

0 PHW JRP 14/8/18

1 PHW JRP 23/8/18

Planned Landfill Site, Esperance Results of Pumping Tests Page 1


1. INTRODUCTION

The Shire of Esperance is planning a new landfill at Lot 12 Kirwan Road, located about 16.5 km north-east

of Esperance.

A detailed hydrogeological investigation of the site was completed by Talis Consultants (2017) that

included the drilling of cored holes at 18 sites and completing them as monitoring bores; geological

logging of the cores; conducting falling-head permeability tests; monitoring groundwater levels on several

occasions and determining groundwater levels and flow velocities; and monitoring groundwater quality.

The investigations were reviewed by Pennington Scott (2018), who recommended that additional work be

carried out, including the following:

Conduct a surface EM geophysical survey;

Construct at least two bores into the spongolite aquifer for test-pumping;

Drill an optional hole into the Werillup aquifer and complete as a monitoring bore; and

Drill additional bores to determine whether there is any flow to Lake Warden.

Rockwater was engaged to plan the drilling and construction of two test bores and associated monitoring

bores into the spongolite aquifer, to supervise the test-pumping of the bores, and analyse the results to

determine groundwater flow velocity.

In a second stage, Rockwater was asked to assess whether the additional work items recommended by

Pennington Scott should be completed; and whether the values of hydraulic conductivity determined from

the pumping tests would allow time to recover leachate, should a leak from the landfill occur.

This report presents the results of the pumping tests, and an assessment of whether the additional work

items should be completed, and whether any leachate from the landfill could be recovered.

2. HYDROGEOLOGICAL SETTING

The geological logs and core photographs included in the Talis Consultants report show that the water

table is about 11 m deep at the two test bore sites (near bores GW12 and GW17), below which there is

predominantly fossiliferous, vuggy and jointed siliceous siltstone with clayey interbeds to about 25 m

depth, overlying siltstone and clays. The siliceous siltstone is interpreted to be the spongolite member of

the Pallinup Siltstone, that can be moderately permeable.

Falling-head permeability tests indicated hydraulic conductivities of the spongolite of 0.1 to 0.4 m/d (Talis

Consultants (2017). That report also shows that the groundwater flows to the south-south-west under a

hydraulic gradient of about 0.0055.

3. DRILLING AND BORE CONSTRUCTION

The test bore sites were selected near monitoring bores GW12 and GW17 to be along the groundwater

flow-path between the planned landfill and the southern boundary of the property. They were located

about 30 m along flow direction from bores GW12 and GW17; and an additional monitoring bore was

constructed at each site across-flow direction, about 30 m north-west of the production bores.



The test bores, named Nth Pumped and Sth Pumped (Fig. 1) were drilled by Kent’s Water Boring using a

Gemco drilling rig and hollow-flight augers with water circulation. They were drilled at 200 mm diameter,

and completed with 100 mm Class 9 uPVC casing, machine-slotted below the water table to 29 m or 30 m

depth with 1.3 mm-wide slots. The annuli were gravel-packed (3 mm to 6 mm gravel) to 1 m above the

slots, then sealed above with cement to the surface.

Cuttings samples were taken at 1 m intervals, although at Nth Pumped there were no cuttings returned

below 8 m depth (all drilling water was lost to the formation).

The new monitoring bores were drilled at 150 mm diameter and completed with 50 mm Class 18 uPVC,

slotted over much the same intervals as the test bores, with annuli gravel-packed, and sealed with

cement. The bores were developed by bailing.

Bore details are summarised in Table 1.

Table 1: Details of Test and Monitoring Bores

4. PUMPING TESTS

4.1. METHOD

The pumping tests were conducted by Kent’s Water Boring under Rockwater supervision, using an electric

submersible pump with a gate valve and a pressure gauge at the borehead to control and monitor flow

rate. The flow rate was measured by timing the flow into a graduated 25 litre bucket. Water was piped

about 100 m from the borehead to minimise the risk of re-circulation.

Each test comprised an eight-hour constant rate test; this is a suitable duration for determining values of

hydraulic conductivity. The tests were to be extended if boundary effects were detected, evidenced by

changes in the rate of water-level drawdown.

Water levels were monitored manually in the pumped bore using a graduated electric probe, and by

pressure transducers coupled to a data logger in the monitoring bores, with manual measurements as a

check. The frequency of measurements ranged from 0.5 minute (start) to 30 minutes in the later stages of

each test. On completion of each test, recovery measurements were made until at least 95 percent water-

level recovery had been achieved.

4.2. RESULTS

Similar results were observed in both tests:

Drawdowns in the production bores followed straight-line trends on semi-logarithmic scale after 8 to 10

minutes of pumping, typical of a laterally extensive aquifer (Figs. 2 and 3). The steeper drawdown trends

Bore mE mNDist. From

Prod. Bore

Depth

Drilled

Casing

Diam.Casing Type Ht Casing Slots SWL

(m) (m) (mm) (magl) (m bgl) (m btc)

Nth Pumped 412836 6261237 0 29 100 Cl. 9 uPVC 0.48 11-29 11.48

Sth Pumped 412670 6260435 0 30 100 Cl. 9 uPVC 0.70 12-30 12.00

N-W Obs 412803 6261255 37 29 50 Cl. 18 uPVC 0.37 11-29 11.68

S-W Obs 412646 6260456 31 31 50 Cl. 18 uPVC 0.64 10-31 11.69

(GPS)



at the start of each test are attributed to additional head losses due to turbulent flow through the casing

slots.

The pressure transducer data had to be corrected for the effects of a marked decrease in air pressure

during 31 July and early part of 1 August before the passage of a significant frontal system. Before

correction, the drawdowns were up to 0.1 m larger than those indicated by the (accurate) manual

measurements.

At the end of each pumping test, water levels in the pumped bores reached 95 % recovery in less than 10

minutes.

Drawdowns in the monitoring bores were all significantly smaller than would be expected from their

distance from the pumped bore, indicating incomplete hydraulic connection with the pumped bores (due

to discontinuities in the joints and vugs in the aquifer). In an ideal aquifer, the slopes of drawdown-time

curves for the monitoring bores would be the same as for the production bore, on semi-log scale.

NTH PRODUCTION 4.2.1.

Nth Production bore was test-pumped at 1.62 L/s (140 m3/d) for eight hours from 0900 hrs on 31 July

2018. Drawdowns measured in the pumped and monitoring bores are shown in Fig. 2. The maximum

drawdown was 7.3 m in the pumped bore, but only 0.11 m in N-W Obs and 0.08 m in GW12.

Only the data for the pumped bore are suitable for determining aquifer transmissivity and average

hydraulic conductivity. The Jacob’s straight-line method was used (Cooper and Jacob, 1946), where:

T = 2.3Q/4πΔs

T = Transmissivity (m2/d),

Q = Pumping rate (m3/d)

Δs = Drawdown in one log cycle, on semi-log drawdown-time plot.

Using the straight-line section of the drawdown-time plot for the pumped bore in Fig. 2:

T = 36 m2/d, and assuming an aquifer thickness (b) = 14 m, average hydraulic conductivity (KH) = T/b = 2.6

m/d.

STH PRODUCTION 4.2.2.

Sth Production bore was test-pumped at 1.6 L/s (138 m3/d) for eight hours from 0815 hrs on 1 August

2018. Drawdowns measured in the pumped and monitoring bores are shown in Fig. 3. The maximum

drawdown was 9.0 m in the pumped bore, but only 0.14 m in S-W Obs and 0.10 m in GW17.

Again, only the data for the pumped bore are suitable for determining aquifer transmissivity and average

hydraulic conductivity:

Using the straight-line section of the drawdown-time plot for the pumped bore in Fig. 3:

T = 21.4 m2/d, and assuming an aquifer thickness (b) = 13 m, average hydraulic conductivity (KH) = 1.65

m/d. This lower value (compared to Nth Production) is in accordance with the steeper hydraulic gradient

in the southern area shown by the groundwater-level contour plans in Talis Consultants (2017).



5. GROUNDWATER FLOW VELOCITY

Groundwater flow velocity is given by a form of the Darcy Equation:

V = KH x i/n, where:

V = Velocity (m/d);

KH = horizontal hydraulic conductivity (m/d);

i = hydraulic gradient; and

n = effective porosity (i.e. the portion of the rock volume comprising interconnected pores that enable

groundwater flow).

Whereas total porosity might be 0.3 (30% of rock volume) the effective porosity is likely to be about 0.1.

This assumed value is used in the calculations below.

5.1. NTH PRODUCTION

At Nth Production, KH = 2.6 m/d, i = 0.0041 (March 2017 groundwater level contours, Talis Consultants,

2017).

Therefore, V = 2.6 x 0.0041/0.1 = 0.107 m/d or 39 m/yr. With a distance of 1.6 km from the planned

landfill to the southern property boundary, the travel time would be about 41 years.

5.2. STH PRODUCTION

At Sth Production, KH = 1.65 m/d, i = 0.0065 (March 2017 groundwater level contours, Talis Consultants,

2017).

Therefore, V = 1.65 x 0.0065/0.1 = 0.107 m/d or 39 m/yr (as at Nth Production). Again, the travel time

from the planned landfill to the southern property boundary would be about 41 years.

6. ASSESSMENT OF OTHER WORK ITEMS

6.1. POTENTIAL TO RECOVERY LEACHATE

The pumping test results have shown that the Pallinup Siltstone underlying the site is moderately

permeable and suitable for the construction of leachate recovery bores, should they be needed. With a

natural groundwater flow velocity of 39 m/yr, there would be time to construct a bore, say 100 m down-

gradient, to intercept any leachate.

A simple numerical groundwater model was constructed using the average KH value obtained from the

pumping tests, to assess whether there would be sufficient time to recover leachate. The model consists

of:

A rectangular grid of 20 m x 20 m cells centred on the landfill site, extending over a 1 km x 1 km

area, and aligned with the groundwater flow direction (to the south-west);

An unconfined aquifer thickness of 13 m;



A hydraulic gradient of about 0.005 m/m;

KH = 2.1 m/d, and specific yield 0.1;

Constant-head boundaries in the north-east and south-west to simulate flow into and out of the

model area.

The model utilises Processing Modflow Pro and Modflow-96, finite-difference groundwater modelling

software designed by the U.S. Geological Survey (McDonald and Harbaugh, 1988) to simulate pumping

from a point about 100 m south of a landfill cell, at a rate of 120 m3/d for about one year. Modpath

(Pollock, 19898) was then used to determine flow paths from a 40 m width (of landfill) to the bore.

The results of this indicative modelling using an uncalibrated model suggest that groundwater-level

drawdowns around the bore after one year would extend at least 100 m radially, and that the bore would

capture all of the flow from a 40 m front after about 14 months (Fig. 4). In reality, the aquifer is likely to be

semi-confined rather than unconfined, and so drawdowns (and the capture zone) would be greater.

6.2. NEED FOR AN EM SURVEY

An electromagnetic (EM) survey can delineate variations in ground conductance, and so may be able to

delineate areas of shallow granitic bedrock. However, other factors such as variations in groundwater

salinity, variations in clay content and the presence of carbonaceous sediments can also result in EM

anomalies. There is insufficient information in the Baddock (1995) report to show whether shallow

bedrock was detected using the method in a nearby area.

As stated in the Pennington Scott (2018) review, any sub-surface granitic ridge is likely to be parallel to the

groundwater flow direction, and so would have little impact on the flow. The groundwater flow direction

indicated by groundwater-level contour plans, such as Fig. 19 of the Talis (2017) report give no indications

of any impact from such a ridge, if it exists.

Consequently, an EM survey is considered to be unnecessary.

6.3. BORE INTO THE WERILLUP FORMATION

The Werillup Formation is the main, or one of, the main aquifers in the region, and so a drillhole is

recommended to determine whether that formation occurs (at one location) beneath the site, and its

local characteristics.

The hole should be completed as a monitoring bore so that groundwater quality in the Werillup Formation

can be monitored. Although the Pallinup Siltstone would restrict the vertical movement of groundwater,

some flow down to the Werillup Formation could occur.

A suitable site would be between GW02 and GW17, in the western part of the southern boundary of the

property, down-gradient of the planned landfill.

6.4. NEED FOR ADDITIONAL MONITORING BORES TO DETERMINE FLOW DIRECTIONS

Pennington Scott (2018) suggested that additional monitoring bores might be needed to show that

groundwater flow from the site is not towards Lake Warden, north of Esperance and some 15 km west of

the site.



Groundwater-level contour plans, such as Fig. 19 of the Talis (2017) report show that the groundwater

flow is to the south-west towards an ancient shoreline (escarpment) 1.4 km away. Groundwater beneath

the landfill property eventually discharges to seeps and springs on and below the escarpment, and to

small lakes and wetlands further towards the coast.

There is no need for additional bores to define the groundwater flow direction. Monitoring of bores on

the landfill property will be required to show there is no groundwater contamination, irrespective of the

groundwater discharge area.

7. CONCLUSIONS

The results of two pumping tests on bores constructed along the groundwater flow-path from the planned

landfill site to the southern boundary of the property indicate that the Pallinup Siltstone (probably

Spongolite Member) from the water table to about 25 m depth is moderately permeable, with hydraulic

conductivity values of 2.6 and 1.65 m/d determined. These values coincide with lower and higher

hydraulic gradients, respectively, and calculations indicate the same groundwater flow velocity of 0.107

m/d or 39 m/yr for both test locations.

The nature of the siltstone at both locations is similar, although there appear to be more vugs at Nth

Production (and GW12) than at Sth Production (and GW17). There are no indications from either the test

results or the groundwater-level contours that there are any zones of preferred groundwater flow

beneath the site that would result from, for example, a major karstic feature such as a solution pipe.

In the event of leachate reaching groundwater beneath the landfill, the Pallinup Siltstone down-gradient

will be a suitable aquifer for a recovery bore or bores, should they be needed.

Neither an EM geophysical survey to delineate shallow granite, nor additional bores to define

groundwater flow directions, are considered necessary. However, a hole is recommended to see whether

the Werillup Formation occurs beneath the Pallinup Siltstone, and if so the hole should be completed as a

monitoring bore.

Dated: 23 August 2018 Rockwater Pty Ltd

P H Wharton Principal

REFERENCES

Baddock, L.J., 1995, Coramup – Bandy Creek Esperance groundwater investigation. Geological Survey of

Western Australia Hydrogeology report 1995/13.



Cooper, H.H. & Jacob, C.E., 1946, A generalised Graphical Method for Evaluating Formation Constants and

Summarising Well Field History. Transactions of the American Geophysics Union, Vol. 27, pp. 526-

534.

McDonald, M.G., and A.W. Harbaugh, 1988, A Modular Three-Dimensional Finite-Difference

Ground-Water Flow Model. Book 6, Chapter A1, Techniques of Water Resources Investigations.

U.S. Geol. Surv., Washington, DC. (A:3980).

Pennington Scott, 2018, Independent technical review of Esperance waste management facility Env

Referral. Report to Shire of Esperance.

Pollock, D.W., 1989, Documentation of computer programs to compute and display pathlines using results

from the U.S. Geological Survey modular three-dimensional finite-difference groundwater flow

model. U.S. Geol. Surv. Open-File Report 89-381, 199p.

Talis Consultants, 2017, Phase I – hydrogeological investigation, Lot 12 Kirwan Road. Report to Shire of

Esperance.


FIGURES

Nth Pumped

N-W Obs

Sth PumpedS-W Obs

GW17

411000 411500 412000 412500 413000 413500 414000

6260000

6260500

6261000

6261500

6262000

6262500

6263000

Landfill Site

Base Map from Talis Consultants, 2017

0.1 1 10 100 1000Time (Mins)

10

8

6

4

2

0

Dra

wdow

n (m

)

Drawdown Pumped Bore

Manual DD N-W Obs

Logger DD N-W Obs

Logger DD GW12

Manual DD GW12

Clie

nt: S

hire

of E

sp

era

nce

Pro

ject: L

an

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ite G

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nth

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d

0.1 1 10 100 1000Time (Mins)

10

8

6

4

2

0

Dra

wdow

n (m

)

Drawdown Pumped Bore

Manual DD S-W Obs

Logger DD S-W Obs

Logger DD GW17

Manual DD GW17

Clie

nt: S

hire

of E

sp

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Pro

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sth

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d n

ew

0.2

0.2

0.2

0.4

0.6

412350 412400 412450 412500 412550 412600 412650 412700 412750 412800

6261000

6261050

6261100

6261150

6261200

6261250

6261300

6261350

6261400

6261450

6261500

Each Arrow-Head Represents Two Months Flow

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RESULTS OF PUMPING TESTS - esperance.wa.gov.au