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AECOM Australia Pty LtdLevel 10, Tower Two727 Collins StreetMelbourne VIC 3008Australiawww.aecom.com

+61 3 9653 1234 tel+61 3 9654 7117 faxABN 20 093 846 925

Ref: 60557772

21 June 2019

Ray CakebreadProject SupervisorThales AustraliaBayly StreetMulwala NSW 2647

Dear Ray

MUL018 - Mulwala Groundwater Management and Remediation Program 2017 - 2020 -Groundwater Modelling Event, October 2018AECOM Australia Pty Ltd (AECOM) has been commissioned by Thales Australia Limited (Thales)through the Department of Defence (Defence) Directorate of Contamination Assessment, Remediationand Management (DCARM) to undertake works associated with ongoing assessment andmanagement activities required for Phase 2 of the Remediation Implementation Plan (HLA, 2007)developed for the Mulwala Explosives and Chemical Manufacturing Facility located at Bayly Street,Mulwala (the Site).Historic Site operations and waste management practices associated with explosives and chemicalmanufacturing have resulted in soil and groundwater contamination. The primary contaminants ofconcern include nitrate and sulphate.

Ongoing management of the off-Site dissolved phase plume is being undertaken through a four-phased Remediation Implementation Plan developed for the Site. Hydraulic containment has beenidentified as a potentially effective groundwater management mechanism to reduce rates andtimeframes associated with the off-Site migration of contaminated groundwater at concentrations thatcurrently preclude off-Site beneficial uses of groundwater.

The Shepparton Formation Aquifer East Hydraulic Containment System (HCS) was commissioned forongoing operation on 24 October 2016 to mitigate the off-Site migration of groundwater passingthrough Source Zone A (SZA), located in the eastern portion of the Shepparton Formation Aquifer(refer to Figure F1). The HCS comprises of five extraction wells; namely, EBS2 and EBS4 – EBS7).Ongoing groundwater modelling is considered to be one aspect in assessing the efficacy of the HCS inthe Shepparton Formation Aquifer East area.

As part of the current project, MUL018 – Mulwala Contaminated Groundwater Management andRemediation Program 2017 -2020, five Groundwater Modelling Events are to be completed to assist inthe assessment of the efficacy of the HCS.

The purpose of this correspondence is to provide an overview of the second modelling event for thisproject, namely; Groundwater Modelling Event, October 2018.

1.0 Groundwater Modelling ObjectivesThe objectives of the Groundwater Modelling Events are to:

· Simulate groundwater capture zones and assess/verify appropriate locations of extraction wells.

· Verify groundwater pumping rates and water levels against modelled groundwater flowcharacteristics during operation of the HCS.

· Assess the effectiveness of plume capture in the Shepparton Formation Aquifer East area.

2.0 Scope of WorkThe scope of works for Groundwater Modelling Event, October 2018 included:

· Assessment of:

- Rainfall and standing water levels (SWLs) [refer to Section 5.1]

- SWLs measured in groundwater wells against the predicted (modelled) SWLs (refer toSection 5.4 and 5.5)

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- Hydraulic capture based on simulated operation of the HCS (refer to Section 5.6).

3.0 Overview of Previous ModellingGroundwater Modelling Event, March 2018 (AECOM, 2019) was completed following the operation ofthe HCS to 26 March 2018 with data obtained during the extraction of groundwater from up to fivewells; namely EBS2; 0.1 L/s; EBS4; 0.5 L/s; EBS5; 0.2 L/s; EBS6: 0.4 L/s and EBS7; 0.3 L/s(approximate flow rates only). In addition, modelling was undertaken to simulate extraction from EBS1,located between EBS2 and EBS4The March 2018 groundwater modelling event noted:

· The Shepparton and Calivil Formation aquifers both showed a good correlation between SWLsand rainfall which may indicate the aquifers have a similar recharge source and/ or have a degreeof interconnectivity. This is consistent with previous conclusions made regarding the ConceptualSite Model (CSM).

· The automatic model calibration further improved the calibration with the % root mean square(RMS) decreasing from 7.3 to 4.5 and mRMS decreasing from 0.36 to 0.31. The continuedimprovement in the model calibration provides further confidence in the robustness of the model.

· As reflected in the CSM, the water balance indicated there is a high degree of interaction betweenthe Shepparton Formation Aquifer, Lower Shepparton Clays and Calivil Formation Aquifer.

· Based on the HCS extraction scenario (EBS2, 0.1 L/s; EBS4, 0.5 L/s; EBS5, 0.2 L/s; EBS6, 0.4L/s; and EBS7, 0.3 L/s), the groundwater model predicted that a portion of groundwater flowbetween EBS2 and EBS4 was not being captured by the HCS. The groundwater that is notcaptured between EBS2 and EBS4 is predicted to migrate to the Calivil Formation.

· It is estimated that approximately 42% of the nitrate plume emanating from SZA is escapingcapture between EBS2 and EBS4.

· The addition of extraction well EBS1 into the HCS configuration, which is located between EBS2and EBS4, appears to intercept the majority of groundwater flow that is not intercepted by EBS2and EBS4. Based on the model, a small portion of flow is not intercepted by EBS1. An increase inthe extraction rate at EBS1 (e.g. 0.3 L/s) may intercept the groundwater flow that the modelpredicts is not intercepted at an extraction rate of 0.2 L/s.

· The groundwater model predicted that groundwater flow emanating from the eastern boundary ofSZA is descending from the Shepparton Formation to the Calivil Formation over the 3.5 yearmodelling period. Due to the modelling duration, it is not known if the groundwater ascends backto the Shepparton Formation.

4.0 Operations OverviewThe HCS commenced operation in 2015 and operated intermittently until November 2017. SinceNovember 2017, the HCS has increased operational up-time when compared to previous operationalperiods.

It is noted that the existing extraction scenario was modified from the previously recommendedextraction scenario (EBS2, EBS4, and EBS7 at 0.2 L/s, EBS6 at 0.3 L/s and EBS5 at 0.1 L/s; AECOM,2017b) based on a request from Thales to increase discharge to the Effluent Management Facility(EMF) for operational purposes in November 2017.

Since the March 2018 groundwater modelling event, the HCS has typically continued to operate as perthe following scenario:

· EBS2 – 0.1 L/s

· EBS4 – 0.5 L/s

· EBS5 – 0.2 L/s

· EBS6 – 0.5 L/s

· EBS7 – 0.4 L/s.

Since March 2018, the HCS was shut down between:

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· 8 to 10 October 2018

· 17 to 20 October 2018.

It is noted that groundwater modelling was undertaken using data collected to 20 October 2018.

Since October 2018, the HCS has been operating as per the following scenario:

· EBS2 – 0.1 L/s

· EBS4 – 0.5 L/s

· EBS5 – 0.2 L/s

· EBS6 – 0.2 L/s

· EBS7 – 0.2 L/s.

5.0 Groundwater Modelling OutcomesThe existing transient groundwater model was run using data from 1 January 2012 to 20 October 2018including:

· Groundwater SWLs

· Rainfall

· Evapotranspiration

· Groundwater extraction rates.

Details of the quantitative groundwater modelling undertaken by Hydrosimulations (MulwalaGroundwater Modelling – Re-calibration and Scenario Analysis [HS, 2019]) are provided inAttachment A and a summary of the findings is provided in the following sections.

5.1 Rainfall AssessmentThe groundwater model was updated to include rainfall and evapotranspiration data from 8 February2017 to 4 April 2018. The following is noted with regard to the model response to rainfall:

· Below average rainfall was noted since March 2017 which is illustrated by the rainfall massresidual (refer to Attachment A, Figure 3).

· The SWL of select groundwater wells has been measured from 2016 to October 2018 usingdown-hole pressure transducers. The groundwater wells monitored include BH12, BH38, BH106,BH107A BH108A, BH130A, BH135 and BH138A, screened within the Shepparton FormationAquifer, and BH104, BH107B, BH108B, BH109, BH112 and BH138B, screened with the CalivilFormation Aquifer. All locations showed a good correlation between SWL and periods of aboveand below average rainfall (i.e. increasing and decreasing SWLs; refer to Attachment A, Figure5 and Figure 6). This indicates that the aquifer has a strong response to rainfall events (i.e.recharge).

· Similar to previous modelling events, the response duration and the magnitude of SWL changesto rainfall (i.e. decreasing SWL as a response decreased rainfall since April 2018) was similar inthe Shepparton and Calivil Formation aquifers. This indicates the aquifers likely have a have adegree of interconnectivity.

5.2 Modell CalibrationDuring the March 2018 modelling event, the transient model was calibrated automatically usingParameter Estimation (PEST) software. The automatic model calibration resulted in an improvementof the overall model calibration which was demonstrated by

- %RMS decrease from 7.5 to 4.5

- mRMS decrease from 0.36 to 0.31.

The groundwater model was re-run with the same model parameters and new rainfall,evapotranspiration, and SWL data, and extraction volumes. The calibration statistics improved for both

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%RMS (3.5%) and mRMS (0.22). The improvement in the model statistics provides further confidencethat the groundwater model is robust and continues to predict groundwater fluctuations associatedwith temporal variations and groundwater extraction.

5.3 Water BalanceAn assessment of the water balance between the different layers in the model domain, which is basedon the model data at the end of the modelling period (20 October 2018), was undertaken to assess themodelled interaction between the different layers (i.e. formations). It is noted that as temporalvariations occur (e.g. changes in rainfall), this water balance will continue to change. The waterbalance is illustrated in Attachment A, Figure 11 (simulated at 20 October 2018), and the following isnoted:

· The dominant recharge sources into the model are Lake Mulwala (13%), the Murray River (49%)and rainfall (38%). An increase in rainfall infiltration from 0.11 ML/day to 0.68 ML/day isassociated with temporal variations, most notably the ~20 mm of rainfall recorded in the weekprior to the water balance date.

· Flow between the Shepparton and Calivil Formations (i.e. vertical flow) is consistent with the 20March 2018 water balance, which is likely to be related to natural groundwater flow conditionsand not associated with the HCS.

· The water balance indicates that there is a high degree of interaction between the differentformations beneath the Site. This further supports the CSM, and rationale for the migration ofnitrate and sulphate impacts from the Shepparton Formation to the Calivil Formation over time.

5.4 Extraction Well ResponseTable 1 below provides a summary of the groundwater response compared to the predicted responseduring pumping at EBS2 and EBS4 – EBS7.Table 1 Summary of Extraction Well Reponses

Well ID ExtractionRate1 Comments

EBS2 0.1 L/s Consistent with previous modelling events, during operational periods themodel under predicted the magnitude of the drawdown by approximately2 m. This may suggest extraction well inefficiency, or may be associatedwith variable hydraulic properties in the immediate vicinity of EBS2.

EBS4 0.5 L/s There is good correlation between the modelled and observed SWLs.

EBS5 0.2 L/s Consistent with previous modelling events, during periods where the HCSwas operational, the model tended to under predict the magnitude of thedrawdown. Overtime, and with ongoing extraction, the difference betweenthe modelled and measured SWL has decreased and the modelled SWL isnearing the measured SWL.

EBS6 0.5 L/s There is good correlation between the modelled and observed SWLs duringperiods where the HCS was and was not operational, however the modelpredicts approximately 0.5 m more drawdown than is observed.

EBS7 0.4 L/s The model over predicts drawdown by approximately 1 m. This is likely tobe associated with lithological differences at EBS7 when compared to theother locations such as porosity.

Note: 1. Typical extraction rate between November 2017 and March 2018

5.5 Observation Well ResponseAn assessment of modelled and observed SWLs was undertaken using model residuals (i.e. theaverage difference between the predicted and measured SWLs). The distribution of the averagemodel residuals is shown in Figure F1 in the Figures section. No distinct clustered high/ low SWL

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residuals were noted within the groundwater model that may indicate the failure to capture localvariability in hydrogeological parameters.

5.6 Hydraulic CaptureBased on the outcomes of the March 2018 groundwater modelling event, hydraulic escape wasidentified between EBS2 and EBS4. Given the model parameters used in March 2018 were not alteredduring this modelling event and the calibration statistics remained strong, the modelling event focusedon assessing the efficacy of EBS1 in mitigating the previously identified hydraulic escape. Given themodelling parameters were not altered, the outcomes of the March 2018 modelling (i.e. identifyingescape between EBS2 and EBS4) are unlikely to change.

The focus of the modelling event was to identify if the existing extraction well located between EBS2and EBS4 (i.e. EBS1) could intercept the hydraulic escape. The incorporation of EBS1 into the HCSwas modelled using four scenarios are summarised in Table 2 below and shown as Figure 15a,Figure 15b, Figure 16a and Figure 16b in Attachment A.Table 2 Modelling Scenarios

Run Figure1ModelDuration(yr)

EffectivePorosity(%)

Extraction Rates (L/S)EBS1 EBS2 EBS4 EBS5 EBS6 EBS7 Total

1 15a 0.5 3 0.2 0.1 0.2 0.1 0.2 0.1 0.9

2 15b 0.3 0.1 0.3 0.1 0.2 0.1 1.1

3 16a 5.5 2 0.2 0.1 0.2 0.1 0.2 0.1 0.9

4 16b 0.3 0.1 0.3 0.1 0.2 0.1 1.1Note: 1. Figures provided in Attachment A

Based on the groundwater modelling, the following is noted:

· Both Model Runs 1 and 2 suggest that groundwater emanating from SZA is captured by the HCS,including the portion of groundwater flow between EBS2 and EBS4. This suggests that theinclusion of EBS1 in the HCS at the extraction rates noted in Table 2 would likely minimisehydraulic loss.

· Model Runs 3 and 4, which were run with a lower effective porosity, which typically increases thevelocity of groundwater flow, suggests that a small portion of groundwater flow between EBS1and EBS4 escapes when EBS1 and EBS4 operate at 0.2 L/s. When the extraction rate isincreased to 0.3 L/s for EBS1 and EBS4, all groundwater flow emanating from SZA is captured.

· All modelling scenarios suggest that EBS2 and EBS5 are not effective in interceptinggroundwater sourced from SZA and do not contribute to hydraulic capture. However, theoperation of both wells results in approximately 5,500 kg of nitrate mass removal per year fromthe Shepparton Formation, which is almost half of the total 11,500 kg of nitrate estimated to beremoved by the HCS per year (assuming constant operation of the HCS). EBS2 and EBS5contribute to approximately 25% of the total groundwater volume extracted by the HCS per year.

· Consistent with the March 2018 groundwater modelling, groundwater from the eastern portion ofSZA descends from the Shepparton Formation Aquifer, to the Calivil Formation Aquifer beforeascending back to the Shepparton Clays.

6.0 ConclusionsBased on the Groundwater Modelling Event, October 2018, the following conclusions are made:

· Consistent with previous groundwater modelling, the groundwater model shows good correlationbetween SWLs and rainfall data for both the Shepparton and Calivil Formations. This maysuggest a degree of interconnectivity between the two aquifers. This is supported by the waterbalance that indicates vertical groundwater flow between the two aquifer units.

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· While further model calibration was not undertaken, the modelling statistics improved with theaddition of new monitoring data with %RMS decreasing from 4.5 to 3.5% and mRMS 0.31 to 0.22.Given new modelling data has been used and the overall modelling statistics have improved, itsuggests the parameters currently used by the model are sound and the overall model issufficiently robust.

· With the current extraction well network (EBS2 and EBS4 – EBS7), groundwater flow emanatingfrom SZA is not captured sufficiently between EBS2 and EBS4. Groundwater modelling suggeststhat the inclusion of an extraction pump in the previously installed extraction well (EBS1) into theHCS could aid in the intercept of hydraulic escape. The modelling consisted of two extractionscenarios (i.e. two different extraction rates) at two different effective porosities. The extractionscenario that intercepted groundwater flow at the differing effective porosity values comprised ofEBS1 and EBS4 at 0.3 L/s, EBS6 at 0.2 L/s and EBS1 at 0.1 L/s (excluding EBS2 and EBS5which do not intercept groundwater emanating from SZA).

· While EBS2 and EBS5 do not appear to contribute to the hydraulic capture of groundwateremanating from SZA, they contribute to almost 50% of the total nitrate mass removal from theShepparton Formation by the HCS, but only contribute to 25% of the total groundwater extracted(i.e. mass removal is dominated by EBS2 and EBS5). This indicates that while EBS2 and EBS5may not be actively intercepting groundwater from SZA, they both contribute to significant massremoval overtime.

7.0 RecommendationsBased on the outcomes of the Groundwater Modelling Event, October 2018, the followingrecommendations are provided:

· Ongoing operation of the HCS should continue in order to demonstrate that the HCS caneffectively mitigate the off-Site migration of impacted groundwater from SZA in the SheppartonFormation Aquifer East area.

· EBS1 should be integrated into the HCS to supplement groundwater capture between EBS2 andEBS4.

· Table 3 provides an updated recommended extraction scenario based on the outcomes of thegroundwater modelling. A comparison against the current extraction scenario is also provided.Table 3 Current and Recommended Extraction Scenario

ExtractionWell ID

Current ExtractionRates

RecommendedExtraction Rate

L/s kL/d L/s kL/dEBS1 0.0 0.0 0.3 25.9

EBS2 0.1 8.6 0.1 8.6

EBS4 0.5 43.2 0.3 25.9

EBS5 0.2 17.3 0.1 8.6

EBS6 0.2 17.3 0.2 17.3

EBS7 0.2 17.3 0.1 8.6

Total 1.2 103.7 1.1 95.0

· Groundwater modelling should continue to be undertaken on a biannual basis to assess theefficacy of the HCS, and further refine the model.

· Where possible, planned shutdown periods should not extend longer than one week.

· If a reduced extraction rate is required (e.g. if the Thales EMF requires a lower volume for a shortduration), priority should be given to maintaining operation of EBS1 (if integrated with the HCS),EBS4 and EBS6.

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· While the model suggests EBS2 and EBS5 do not contribute to hydraulic capture of groundwateremanating from SZA, given the mass removal achieved through extraction from both wells, theiroperation should continue to reduce the off-Site migration of impacted groundwater.

· Additional lines of evidence supporting the conclusions of this groundwater modelling event (e.g.groundwater contours and contaminant concentration trends) should continue to be assessedduring biannual groundwater monitoring events.

Should you have any questions regarding the information provided, please do not hesitate to contactthe undersigned.

Yours sincerely

Matthew Johnson Paul CarstairsPrincipal Environmental Engineer Technical [email protected] [email protected]

Mobile: +61 429 141 091 Mobile: +61 427 575 123Direct Dial: +61 3 9653 8053 Direct Dial: +61 3 9653 8059Direct Fax: +61 3 9654 7117 Direct Fax: +61 3 9654 7117encl: Figures

Attachment Acc: Karen Hansen (Defence)

© AECOM Australia Pty Ltd (AECOM). All rights reserved.

AECOM has prepared this document for the sole use of the Client and for a specific purpose, each as expressly stated in the document. No otherparty should rely on this document without the prior written consent of AECOM. AECOM undertakes no duty, nor accepts any responsibility, to anythird party who may rely upon or use this document. This document has been prepared based on the Client’s description of its requirements andAECOM’s experience, having regard to assumptions that AECOM can reasonably be expected to make in accordance with sound professionalprinciples. AECOM may also have relied upon information provided by the Client and other third parties to prepare this document, some of whichmay not have been verified. Subject to the above conditions, this document may be transmitted, reproduced or disseminated only in its entirety.

ReferencesAECOM (2011), Hydraulic Containment Trial

AECOM (2014), Groundwater Modelling Update – Shepparton Formation Aquifer East

AECOM (2017a), Groundwater Modelling Event, February 2017

AECOM (2017b), Groundwater Monitoring Event, February 2017

HS (2018) Mulwala Groundwater Modelling – Re-calibration and Scenario Analysis

HS (2019) Mulwala Groundwater Modelling – Re-calibration and Scenario Analysis

LimitationsThe purpose for which the works were performed by AECOM Australia Pty Ltd (AECOM) on behalf ofThales Australia Limited (Thales) is set out in Section 1.0 of this report (Groundwater ModellingObjectives). The report must not be used or relied upon for any purpose other than the Purpose andsubject to the limitations set out in this section.

The report has been prepared for Thales in accordance with the scope, and subject to the time andbudget constraints, disclaimers, limitations, assumptions, qualifications and exclusions set out in the

JohnsonML

Matt Johnson

JohnsonML

Paul Carstairs

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report, as agreed with Thales. The report is strictly limited to the matters contained within it and doesnot extend by implication or otherwise to any other purpose or matter.

The scope of works to be performed by AECOM and described in this report is in accordance with anagreement dated 25 October 2017 between AECOM and Thales, (Agreement) and is subject to allrights, obligations and limitations stated in the Agreement including AECOM’s limitation of liability. Adescription of work performed by AECOM is set out in the report.

This report is prepared based on field work undertaken by AECOM between 1 January 2012 and 20October 2018 and is based on the conditions encountered and information reviewed at the time ofpreparation of the report and AECOM has no obligation, of any kind or nature, to update the report, orto confirm the continued validity of any information contained within it, beyond the validity date(s)nominated in the report (and to the extent none is nominated, the date of the report). The analyses,evaluations, opinions and conclusions presented in this report are applicable as at the date of thisreport.

Any conclusions, results or assumptions reached or determined by AECOM from field work it hasundertaken are an expression of opinion based on representative samples or locations at the site.This report accordingly is not operating as a guarantee, or warranty that the condition of the site couldnot be different at intermediate points between sampling locations or at different parts of the site. Dueto the inherent variability in natural soils and subsurface conditions, it is unlikely that the results,assumptions and conclusions set out in this report represent the extremes of conditions at any locationremoved in time and/or place from the specific points of sampling.

Where this report indicates that information has been provided to AECOM by Thales or by thirdparties, AECOM has made no independent verification of this information nor checked suchinformation for accuracy, adequacy or completeness except as expressly stated in the report. Noresponsibility is assumed by AECOM for inaccuracies in reporting by the providers of such informationincluding, without limitation, inaccuracies in any other data source whether provided in writing or orallyused in preparing or presenting this report.

AECOM does not make any representation or warranty that the analyses, evaluations, opinions orconclusions in the report can be extrapolated or modified for future use as there may be changes inthe condition of the site, applicable legislation or law and other factors that are beyond AECOM’scontrol and which would affect the analyses, evaluations, opinions or conclusions contained in thisreport. AECOM may not be held responsible or liable for such circumstances or events and specificallydisclaims any responsibility therefore.

The report must be read in full and no excerpts, extracts or summaries are to be taken asrepresentative of the analyses, evaluations, opinions or conclusions of AECOM. This report may betransmitted, reproduced or disseminated only in its entirety.

This report and the works have been performed by AECOM with due care, skill and diligence expectedof an environmental consultant performing the same or similar services as those set out in thePurchase Order.

This report has been prepared on the instruction of Thales and may only be used and relied on byThales and the Department of Defence. AECOM undertakes no duty to, nor accepts any responsibilityto, any third party who may use or rely upon this report.

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www.aecom.com

PROJECT ID

LAST MODIFIEDCREATED BY

60521473DJBDJB 29 MAR 2019

DATUM AMG 1994, PROJECTION MGA ZONE 55

Bayly Street, Mulwala, NSW

Notes:Groundwater modelling residuals (measured - modelled water level)All results are expressed as metres

Map Document: (O:\Spatial_Data\Large_Client\Defence\Mulwala\4.99_GIS\02_Maps\2019\03\F1_Average_GW_Modelling_Residuals.mxd)

F1Figure

Thales Australia Limited

AVERAGE GROUNDWATERMODELLING RESIDUALS

LEGEND&< Calivil&< Shepparton

?

? Aquitard AbsentSite BoundaryWestern Site BoundarySite PlanExtent of Source Zone ASource Zone A - Hot Spot AreasSource Zone BSource Zone C/D2/D3Source Zone D1Source Zone E

Groundwater Modelling Event,October 2018

Bore IDGroundwater Modelling Residuals (m)

BH1160.07

Observed SWL higher than predicted SWLObserved SWL lower than predicted SWL

Attachment AGroundwater Modelling

Report

HS2019-09 Mulwala Groundwater Modelling March2019.docx 1

NPM Technical Pty Ltd ●ABN 52 613 099 540 ●T/A HydroSimulations PO Box 241, Gerringong NSW 2534. Phone: (+61 2) 4234 3802 [email protected]

DATE: 28 March 2019 TO: Matthew Johnson

Project Environmental Engineer AECOM Australia Pty Ltd 727 Collins Street Melbourne VIC 3008

FROM: Dr Noel Merrick and Ms Tingting Liu

RE: Mulwala Groundwater Modelling – Re-calibration and Scenario Analysis

OUR REF: HS2019/09 [AEC010]

Introduction

HydroSimulations (HS) has been engaged by AECOM to undertake the next phase of groundwater modelling to assess the efficiency of the hydraulic containment system (HCS) at the Thales facility at Mulwala, situated on the northern bank of the Murray River about 85km west of Albury (NSW). The HCS has been designed as a pump-and-treat mechanism to contain a nitrate/sulphate plume emanating from several identified contaminant source areas.

The modelling is based on a groundwater model developed by REN Consulting (2016). Minor re-calibration of the model was undertaken by HS (2017) after extension of the monitoring and pumping records from March 2016 to February 2017. A full re-calibration of the model was undertaken by HS (2018) using Parameter ESTimation (PEST) software to improve model calibration performance for the period from 1st January 2012 to 4th April 2018. In the current study, there are no model parameter changes, but the evaluation period has been extended to 20 October 2018.

The project location is shown in Table 1 with the model extent in Figure 2. The model is defined by three stratigraphic layers: the upper and lower Shepparton Formations, and the Calivil Formation.


Figure 1 Location plan [after REN Consulting, 2014]

Figure 2 Groundwater model extent and boundary conditions [REN Consulting, 2014]

Lake Mulwala

Murray River


Climate data

In this study climate data has been sourced from SILO. SILO (Scientific Information for Land Owners) is a database of Australian climate data from 1889, hosted by the Science Division of the Queensland Government's Department of Environment and Science (DES). SILO provides:

Point datasets - continuous daily time series of data at either recording stations (BOM, missing data interpolated) or grid points across Australia (interpolated)

Gridded datasets - gridded daily climate surfaces which have been derived either by splining or kriging the observational data:

The nearest BoM climate station to the project site is located at Mulwala Post Office (station 74081). The point data for station 74081 from 1 January 1889 to 6 January 2019 was downloaded and is shown on Figure 3, along with the rainfall residual mass curve (RMC).

Drier conditions have prevailed during the current reporting period since March 2017, as evidenced by the declining RMC during the first half of 2017, average conditions for the second half of 2017, and declining RMC from December 2016 to October 2018 (Figure 3).

Figure 3 Daily rainfall data for the SILO 74081 PPD and residual rainfall

Groundwater level data

Contaminant source areas and bore networks are shown in Figure 4.

There are on-site and off-site groundwater monitoring bores at 73 locations in the Shepparton Formation and at 43 locations in the Calivil Formation. Table 1 provides groundwater level monitoring bore locations.


Pressure transducers have been used to record continuous groundwater level fluctuations at nine locations, seven in the Shepparton Formation and two in the Calivil Formation. However, two of the Shepparton bores no longer have installed pressure transducers: BH113 and BH124.

Figure 5 and Figure 6 show the continuous water level measurements compared with the rainfall RMC in the Shepparton and Calivil Formations respectively. Shifts in the reference elevations around May 2015 in BH38, BH106, BH107A and BH113 have been noted. From February 2015, a correction has been applied to all data for BH106 following resurveying of the site; the Top of Casing reference elevation was raised by 0.31 m.

Every site actively monitored by a pressure transducer, in the Shepparton and Calivil formations shows strong correlation with the RMC during the wet period since May 2016 and the drier period since December 2016. This indicates a strong response to recharge events and associated recession during periods between major recharge episodes.


Figure 4 Contaminant source areas and bore networks


Table 1 Groundwater level monitoring bores

Bore ID Easting Northing

Formation Bore ID Easting Northing

Formation m MGA Zone 55 m MGA Zone 55

BH08 408512.01 6016447.53 Shepparton BH39 408667.00 6017029.48 Shepparton BH09 408139.77 6016664.48 Shepparton BH85 408529.00 6016805.47 Shepparton BH104A 408291.90 6016684.62 Shepparton BH86 408657.00 6016826.47 Shepparton

BH105 408232.08 6016866.89 Shepparton BH88 408810.50 6016860.97 Shepparton BH106 408356.98 6016778.96 Shepparton BH89 406634.25 6017271.39 Shepparton

BH107A 408436.89 6016729.78 Shepparton BH93A 408534.90 6016839.57 Shepparton BH108A 408513.84 6016704.22 Shepparton BH94A 408688.00 6016916.67 Shepparton

BH11 408369.56 6016727.85 Shepparton BH95A 408766.80 6016888.47 Shepparton

BH111A 408622.07 6016780.09 Shepparton EBS1 408473.05 6016759.19 Shepparton BH113 408532.81 6016815.33 Shepparton EBS2 408451.06 6016770.99 Shepparton

BH114 408613.59 6016825.90 Shepparton EBS3 408434.33 6016830.42 Shepparton


BH118 408790.47 6016847.07 Shepparton EBS5 408358.36 6016724.52 Shepparton BH119 408620.62 6016855.32 Shepparton EBS6 408562.48 6016691.29 Shepparton


BH120 408490.77 6016894.84 Shepparton BH100 408151.95 6016300.69 Calivil BH121A 408485.66 6016862.41 Shepparton BH101 408238.72 6016426.98 Calivil

BH122 408454.78 6016877.35 Shepparton BH102 408281.85 6016413.09 Calivil BH123 408429.59 6016807.60 Shepparton BH103 408329.37 6016423.38 Calivil

BH124 408461.66 6016769.94 Shepparton BH107B 408447.60 6016727.16 Calivil BH125 408439.47 6016815.10 Shepparton BH108B 408514.75 6016704.08 Calivil BH128 408188.90 6017126.04 Shepparton BH109 408476.52 6016771.35 Calivil

BH128A 408189.40 6017123.52 Shepparton BH110 408728.60 6016733.07 Calivil

BH129A 408462.33 6016650.93 Shepparton BH111B 408623.31 6016779.06 Calivil

BH130A 408488.20 6016797.81 Shepparton BH112 408385.40 6016846.77 Calivil BH133 408408.81 6016851.10 Shepparton BH115 408787.70 6016779.27 Calivil

BH135 408358.13 6016720.86 Shepparton BH117 408811.60 6016800.47 Calivil

BH136 408558.04 6016691.39 Shepparton BH121B 408486.63 6016861.97 Calivil BH137 408630.44 6016677.99 Shepparton BH126 408497.61 6016735.84 Calivil

BH138A 408384.68 6016670.02 Shepparton BH129B 408465.13 6016649.17 Calivil BH15 407824.98 6016893.43 Shepparton BH131 408223.58 6016849.45 Calivil

BH20A 408606.40 6016675.31 Shepparton BH132 407904.63 6016772.89 Calivil BH21A 408143.60 6016749.46 Shepparton BH134 408552.58 6016791.83 Calivil

BH22a 408097.79 6016320.25 Shepparton BH138B 408385.45 6016669.88 Calivil BH23 408872.67 6016635.33 Shepparton BH20B 408602.75 6016676.11 Calivil

BH28 407712.00 6017137.49 Shepparton BH22b 408093.49 6016319.68 Calivil

BH28R 407688.00 6017140.99 Shepparton BH45 407780.00 6015921.46 Calivil BH34 407658.00 6016114.46 Shepparton BH47B 407661.52 6016200.00 Calivil

BH37 408819.00 6016776.47 Shepparton BH48B 408102.05 6016392.16 Calivil

BH38 408674.00 6016742.47 Shepparton BH50B 408396.97 6016328.43 Calivil


Bore ID Easting Northing

Formation Bore ID Easting Northing

Formation m MGA Zone 55 m MGA Zone 55

BH41 408405.00 6017062.48 Shepparton BH53B 407211.90 6016584.53 Calivil BH42 407482.01 6017390.50 Shepparton BH54B 407102.87 6016195.52 Calivil

BH44 409011.00 6016833.47 Shepparton BH55B 407246.92 6016019.65 Calivil BH46 406988.02 6018956.56 Shepparton BH56B 407503.10 6015916.33 Calivil

BH48A 408101.17 6016387.61 Shepparton BH58 408353.85 6016722.43 Calivil

BH50A 408395.71 6016325.29 Shepparton BH63 408011.48 6015855.92 Calivil BH52 407261.08 6017015.54 Shepparton BH68B 406609.33 6016196.56 Calivil

BH54A 407104.93 6016197.33 Shepparton BH70B 406507.85 6016582.88 Calivil

BH55A 407246.92 6016021.78 Shepparton BH73A 406824.67 6016867.83 Calivil BH56A 407497.30 6015920.54 Shepparton BH74B 407425.47 6016831.60 Calivil

BH57 408223.84 6016751.36 Shepparton BH90 406784.28 6017116.84 Calivil BH61 406951.78 6016957.76 Shepparton BH91B 406633.70 6017107.08 Calivil

BH62 407668.94 6016539.93 Shepparton BH93B 408533.10 6016839.97 Calivil BH72C 406623.61 6016868.34 Shepparton BH94B 408687.70 6016914.97 Calivil

BH74A 407428.68 6016831.14 Shepparton BH95B 408767.10 6016889.97 Calivil BH75 407973.74 6016753.54 Shepparton BH97B 408300.80 6016964.78 Calivil

BH83 408286.45 6016737.51 Shepparton BH99 408129.13 6016309.59 Calivil

BH49A 408069.48 6016202.59 Shepparton EBC1 408483.10 6016735.62 Calivil BH49B 408074.59 6016211.57 Calivil BH21B 408139.72 6016749.33 Calivil

BH104 408289.99 6016688.03 Calivil


Figure 5 Continuous water level measurements - Shepparton Formation


Groundwater extraction

The Shepparton Formation East HCS consists of five active extraction bores (EBS2, EBS4, EBS5, EBS6 and EBS7) at locations shown in Figure 4.

Figure 7 shows the average daily extraction volumes for the extraction events from 2015 to October 2018 along with the monitoring water levels at the HCS bores.

The extraction system has not been operating continuously, as evidenced by the periods of shutdown listed in Table 2. From 29 March 2016 to 20 October 2018, the system has been operating on 59 percent of days. The longest non-pumping period started from 29 April 2017 for about half year and turned on since 30 October 2017. Taking non-pumping days into account, the average extraction rates

Figure 6 Continuous water level measurements – Calivil Formation


over the past approximately two and half years are recorded in Table 3. EBS6 is the highest yielding bore, followed by EBS4.

Table 2 Periods of system shutdown since 28 March 2016

Event Start Date End Date Number of Days

1 2 April 2016 5 April 2016 4

2 3 May 2016 4 May 2016 2

3 13 May 2016 13 May 2016 1

4 1 July 2016 25 October 2016 117

5 20 December 2016 13 January 2017 25

6 24 January 2017 25 January 2017 2

7 15 February 2017 15 February 2017 1

8 5 March 2017 5 March 2017 1

9 29 April 2017 29 October 2017 184

10 17 November 2017 20 November 2017 4

11 7 December 2017 10 December 2017 4

12 14 January 2018 17 January 2018 4

13 26 January 2018 30 January 2018 16

14 30 March 2018 9 April 2018 11

15 11 April 2018 16 April 2018 6

16 19 April 2018 19 April 2018 1

17 5 August 2018 5 August 2018 1

18 18 October 2018 18 October 2018 1

Table 3 Average extraction rates from 29 March 2016 to 20 October 2018

BORE: EBS2 EBS4 EBS5 EBS6 EBS7

Rate (kL/day) 5.9 16.5 7.9 17.0 11.5


Figure 7 Average daily water extraction volumes and continuous water level measurements at HCS bores


Transient groundwater model simulation

As reported in HS (2018), HydroSimulations 2017 groundwater model was converted from MODFLOW-SURFACT to MODFLOW-USG through the Groundwater Vistas platform, to allow re-calibration of the transient model. In the current reporting period, the model was updated to extend in time to 20th October 2018 in weekly simulation steps.

The model also been updated with:

rainfall and evapotranspiration data from SILO;

water levels from five pressure transducers;

measured water levels from up to 97 observation wells;

water levels from five extraction wells; and

weekly extraction data from five extraction wells.

Model parameters such as permeability and storage have been kept the same as those used in the previous calibrated model.

Transient model calibration

Based on the previously calibrated model (Calb09, HS 2018), model Calb10 has been developed with timing extended from 2,275 to 2,485 days (to 20th October 2018) in 355 stress periods. This model uses the same deepdd value to update the rainfall recharge and evapotranspiration data using the same soil moisture water balance model (wethyd.f90) as developed by REN (2014). Compared with Calb09, data from 4 monitoring bores have been added into the Calb10 model.

With weighted targets the model performance statistics are 3.5 %RMS and 0.22 mRMS. This compares favourably with 4.5 %RMS and 0.31 mRMS for the previous Calb09 model.

Table 4 summarises the median layer thickness and the median hydraulic and storage properties for each model layer after transient calibration.

Figure 8 provides the layer water balances at the end of the transient calibration period (20 October 2018). This indicates that the Murray River accounts for about 22% of recharge to the groundwater system (by leakage), and about 10% of losses from the groundwater system by discharge (baseflow) to the river. Supplemented by rainfall recharge at 17% Lake Mulwala provides a further 6% recharge, with boundary inflows of 4% and total upflow at 51%. Most of the loss from the upper Shepparton Formation occurs via downwards flow (49%), with boundary outflows of 39% and HCS extraction at about 2%. At the time simulated, there was a storage loss of about 0.17 ML/day. The net downflow to the Calivil Formation of 0.84 ML/day balances the flow through the model boundaries.

Table 4 Calibrated Horizontal and Vertical Hydraulic Conductivities, Storage Coefficient and Specific Yield


Layer Lithology Median Thickness (m) Kh (m/d) Kv (m/d) S Sy 1 Shepparton Formation 12 12.8 1.01 N/A 0.07 2 Lower Shepparton Clay 3 0.23 0.023 0.0001 0.0045 3 Calivil Formation 13 2.3 0.44 0.001 0.0045

Figure 8 Layer water balances at the end of simulation (20 October 2018) (ML/day)

Comparison of simulated water levels with observed water levels

While the scattergrams in Figure 9. give an overall impression of model performance, local performance is best shown in the form of hydrographs. Individual comparisons of simulated and observed water levels at key monitoring bores are shown in the following figures:

Figure 10 – Simulated water levels at HCS extraction bores

Figure 11 – Simulated water levels at Shepparton Formation monitoring bores with pressure transducers

Figure 12 – Simulated water levels at Calivil Formation monitoring bores with pressure transducers

Figure 13 – Simulated water levels at Shepparton Formation monitoring bores measured manually, BH108A and BH135 measured with pressure transducers after November 2017

Figure 14 – Simulated water levels at Calivil Formation monitoring bores measured manually and after November 2017 with pressure transducers


Figure 9 Comparison of modelled and observed water levels: (a) without weighted targets; (b) with weighted targets

(a)

(b)


Figure 10 Simulated water levels at HCS bores


Figure 11 Simulated water levels in Shepparton Formation monitoring bores with pressure transducers


Figure 12 Simulated water levels in Calivil Formation monitoring bores with pressure transducers

Figure 13 Simulated water levels in Shepparton Formation monitoring bores measured manually, BH108A and BH135 measured with pressure transducers after November 2017


Figure 14 Simulated water levels in Calivil Formation monitoring bores measured manually and after November

2017 with pressure transducers

Discussion on model calibration

The target water levels have been increased to 8,759 with the model period extension. These targets were distributed throughout the model layers in the form of 97 groundwater hydrographs.

The agreement between simulated and observed hydrographs (Figure 10 to Figure 14) is very good, and much improved from the previous modelling. The model is now able to replicate the rising water levels that occurred during the very wet episode from May 2016 to October 2016. The model also captures the response in the dry period from November 2017 to October 2018 with decreasing water levels as observed (see plots).

Table 5 provides an analysis of the spatial performance of the model through a list of the average residuals at each site (defined as observed minus modelled water level).


Table 5 Average residual (m) at each monitoring bore

Bore ID Residual Bore ID Residual Bore ID Residual Bore ID Residual

BH91B -2.15 BH12 -0.24 BH107A -0.11 EBS4 0.05

BH21B -1.26 BH23 -0.22 BH38 -0.10 BH118 0.05

BH138B -1.03 BH111B -0.21 BH96B -0.10 BH94B 0.07

BH99 -0.90 BH105 -0.21 BH133 -0.09 BH131 0.08

BH100 -0.87 BH102 -0.20 BH106 -0.09 EBS7 0.09

BH91C -0.74 BH121B -0.20 BH39 -0.08 BH110 0.11

BH57 -0.64 BH107B -0.20 BH93A -0.08 BH136 0.15

BH50A -0.58 BH134 -0.19 BH49A -0.08 BH135 0.18

BH47B -0.58 EBS5 -0.18 BH109 -0.08 BH122 0.20

BH58 -0.57 BH115 -0.18 BH95B -0.07 BH137 0.20

BH90 -0.50 BH88 -0.18 BH128 -0.04 BH138A 0.25

BH116 -0.43 BH120 -0.17 BH101 -0.04 BH129A 0.26

BH62 -0.41 BH112 -0.16 BH111A -0.04 BH83 0.28

BH21A -0.39 BH108B -0.16 BH125 -0.03 BH08 0.32

BH22A -0.36 BH103 -0.16 BH123 -0.03 BH108A 0.34

BH37 -0.34 BH126 -0.16 BH124 -0.02 BH104A 0.38

BH22B -0.32 BH113 -0.16 BH132 -0.01 BH74A 0.53

BH20B -0.31 BH94A -0.15 BH117 0.02 BH52 0.56

BH44 -0.30 BH114 -0.14 BH11 0.03 BH61 0.91

BH48B -0.29 BH121A -0.14 BH09 0.03 BH15 0.95

BH48A -0.27 EBS2 -0.14 EBS6 0.03 BH34 1.02

BH75 -0.25 BH130A -0.12 BH119 0.04

BH93B -0.25 BH95A -0.12 BH128A 0.04

BH129B -0.24 BH49B -0.11 BH20A 0.04

Plume capture

The mod-PATH3DU Version 1.1 particle tracking post-processing package, developed by S. S. Papadopulos and Associates, Inc., has been used in this study to compute and display three-dimensional pathlines based on groundwater flow outputs from MODFLOW-USG. There are two different calculating algorithms in mod-PATH3DU, the Waterloo method and the SSP&A method (SSP&A, 2016). The Waterloo method has been used by default in this study.

A 6-month (182-days, 26 stress periods) transient MODFLOW-USG model was been built with time


from 22nd April 2018 to 20th October 2018, during which forward tracking has been simulated from the southern boundary of Source Zone A towards six extraction bores (EBS1, EBS2, EBS4, EBS5, EBS6 and EBS7, Figure 4) assuming a uniform effective porosity of 0.03 (3%). The assumed extraction at EBS1 follows the same pattern as EBS4 (as stipulated by AECOM).

Figure 15 and Figure 16 summarise the particle tracking results for four model runs with the following conditions:

Table 6 Particle tracking model run extraction rates

Run Time Porosity % Bore extraction rates, kL/d ‖ L/s

EBS1 EBS2 EBS4 EBS5 EBS6 EBS7 1 182 d 3 17 ‖ 0.2 9 ‖ 0.1 17 ‖ 0.2 9 ‖ 0.1 17 ‖ 0.2 9 ‖ 0.1 2 182 d 3 26 ‖ 0.3 “ 26 ‖ 0.3 “ “ “

3 + 5 yrs 2 17 ‖ 0.2 9 ‖ 0.1 17 ‖ 0.2 9 ‖ 0.1 17 ‖ 0.2 9 ‖ 0.1 4 + 5 yrs 2 26 ‖ 0.3 “ 26 ‖ 0.3 “ “ “

The 182-days average pumping rates shown in Table 6 are approximately 28% (approximately 7 to 9) and 58% (approximately 17 to 26) higher than the rates in Table 3 averaged over the past two years, respectively. Although weekly average rates (from AECOM) are shown as an indicator of bore strength, real time-varying rates are applied during the simulation according to the actual patterns in Figure 7.

Arrows are placed on the pathlines in Figure 15 and Figure 16 every 60 days. Orange pathlines present particle tracking in model layer 1, green pathlines present particle tracking in model layer 2and blue pathlines present particle tracking in model layer 3. Traces with less than three arrows indicate that plume particles are fully captured within the six-month window of examination.

Figure 15(a) shows that Source Zone A was completely captured by three extraction bores (EBS1, EBS4, EBS6) after about 30 days, 85 days and a little more than 180 days, respectively with the extraction conditions of run 1. Figure 15(b) shows that with increased extraction rates on bores EBS1 and EBS4 (run 2), all particles are captured after about 25 days and 80 days by those bores respectively, and 180 days by extraction bore EBS6.

Due to the redefinition of permeability fields, the particles along the eastern third of the source zone now travel westerly before heading south towards the HCS bores, whereas in the previous model the particles travelled south-westerly. The particles are still captured by EBS6.

Bores EBS2, EBS5 and EBS7 appear redundant for contaminants emanating from Source Zone A.

Run 3 has a reduced porosity of 0.02, the same extraction rates as for model run 1, and an extended simulation period (182-days plus 5 years). Except for one particle missing, Source Zone A was captured by four extraction bores EBS1, EBS4, EBS6 and EBS7 after about 30 days, as shown on Figure 16(a).

Run 4, also with reduced porosity, had the same extraction rate as model run 3. Source Zone A was


also fully captured in this run Figure 16(b).

Figure 15 Simulated particle tracks (porosity 3%) over a period of 182 days from April 2018 to October 2018, model particle tracking runs 1 (a) and 2 (b)

Particles along the eastern edge of Source Zone A move westerly and descend to Layer 2 shortly before the end of the 6-months simulation period, and then descend naturally into the Calivil Formation. The 5.5 year simulation is too short to determine the ultimate fate of these particles, whether or not they are drawn upwards into the HCS bores eventually. However, particles along the south-eastern edge initially descend to Layer 2 and then move upwards to Layer 1 for capture by EBS7, as shown on Figure 16 (a & b). Bores EBS1, EBS4, EBS6 and EBS7 continue to capture all the flow that emanates from Source Zone A. One particle to the west of the source zone descends immediately to the Calivil Formation due to locally high vertical permeability at that site. Some neighbouring particles to the west of the source zone appear to stagnate after descending to Layer 2, but most continue downwards into the Calivil Formation. This is natural groundwater behaviour and is unrelated to HCS extraction.

(a)

(b)

Source zone A

Source zone A

‘Lines’ of arrows show 60-day time intervals

60

120

180


Figure 16 Simulated particle tracks (porosity 2%) over a period of 182 days plus another 5 years from April 2018 to October 2023, model particle tracking runs 3 (a) and 4 (b)

Figure 15(b), particle tracking run 2 and Figure 16(b), particle tracking run 4, have the same extraction rates but different porosities of 3% and 2% respectively, and higher extraction rate (0.3 L/s) on bores EBS1 and EBS4.

For 3% porosity, all Source Zone A was captured, which means both rates of extraction are optimal, the rates could be reduced if the bores are maintained in more continuous operation.

For 2% porosity, the capture efficiency is similar. However, there is one new escape between EBS1 and EBS4 with lower extraction rate.

(a)

(b)

Source zone A

Source zone A


CONCLUSION

Despite periods of borefield shutdown, it is evident that the HCS bores are capturing all of the contaminants emanating from Source Zone A.

The particle tracks simulated in transient mode, with time-varying borefield extraction, are more robust than those previously reported for steady-state pumping at pump design rates as illustrated in REN Consulting (2016). The permeability fields are now defined better, following successful re-calibration.

The efficiency of capture is similar to that reported in HS (2018) when the pumping strengths were about 28% lower. For an experiment in which pumping rates were artificially increased by a factor of about 58% overall, some improvement of capture efficiency was recorded, particularly between EBS1 and EBS4. This suggests that the current average rates of extraction are close to optimal and should not be reduced much. However, the rates could be reduced if the bores are maintained in more continuous operation.

Adding bore EBS1 in this study improves capture efficiency substantially between EBS1 and EBS4, where escape pathways in HS (2018) are currently simulated.

References

Merrick, D. P. (2017) AlgoCompute: Large-Scale Calibration and Uncertainty Analysis Made Easy in the Cloud. MODFLOW and More 2017 Conference Proceedings, Integrated GroundWater Modeling Center, Golden Colorado.

REN Consulting (2014) Mulwala – Hydraulic Containment Optimisation Project : Groundwater Modelling. Report GW-14-12-REP-001, Rev 0, December 2014.

REN Consulting (2016) Mulwala – Groundwater Modelling. Letter Report GW-16-03, 12 April 2016.

HydroSimulations (2017) Mulwala – Groundwater Modelling. Report HS2017/11 [AEC006], 25 April 2017.

HydroSimulations (2018) Mulwala – Groundwater Modelling. Report HS2018/40b [AEC010], 16 August 2018.S.S.Papadopulos & Associates, Inc.(SSP&A) – User’s Guide for mod-PATH3DU. Mod-PATH3DU version 1.1.0, September 2016.

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