Appendix D – Groundwater Monitoring Event March 2013 · Carrick Waste-Water Treatment Plant Effluent Re-use Scheme, December 2010 (DP&EMP). This report indicates that the Carrick

GHD | Report for TasWater - Carrick STP New Discharge Pipeline and Outfall , 32/17413

Appendix D – Groundwater Monitoring Event March 2013

PN: 102690

CLIENT:

Ben Lomond Water.

©The concepts and information contained in this report are the Copyright of Sloane Geoscience Pty. Ltd. Without the written permission of Sloane Geoscience Pty. Ltd., the copying of all or parts

of this report by whatever means is an infringement of Copyright

SGEO PN 102690

GROUNDWATER MONITORING PLAN:

CARRICK RECYCLED WATER SCHEME.

‘THE MOAT’, MEANDER VALLEY ROAD, CARRICK.

Carrick RWS GMP – Ben Lomond Water PN: 102690

© Sloane Geoscience Pty. Ltd. 102690 Carrick RWS GMP.doc 1

1 INTRODUCTION Sloane Geoscience Pty. Ltd. (SGEO) was engaged by Ben Lomond Water (BLW) to prepare a Groundwater Monitoring Plan (GMP) for the Carrick Recycled Water Scheme (RWS) on ‘The Moat’ property at Meander Valley Road, Carrick. The need for a RWS GMP is a requirement of the Tasmanian Environment Protection Authority (EPA). The monitoring of groundwater quality in the vicinity of the Carrick RWS site is to ensure that contamination does not occur from any RWS irrigation infiltration. Groundwater monitoring, involving two existing monitoring bores, is currently undertaken at the Carrick Wastewater Treatment Plant (WWTP) site on the SW side of ‘The Moat’. SGEO conducts GMP assessments with reference to:

• National Environment Protection (Assessment of Site Contamination) Measure, 1999. Schedule B(6) Guideline on Risk Based Assessment of Groundwater Contamination.

2 BACKGROUND 2.1 PREVIOUS REPORTS This GMP has been prepared with reference to the Ben Lomond Water:

• Development Proposal and Environmental Management Plan. Carrick Waste-Water Treatment Plant Effluent Re-use Scheme, December 2010 (DP&EMP).

This report indicates that the Carrick WWTP processes about 0.5-0.6 ML/day of wastewater which has previously been discharged to the north, along a drain to the Liffey River. There is a 30ML recycled water storage dam on the NE side of this site. The Carrick RWS proposal primarily involves partial irrigation of a 70ha centre pivot area on ‘The Moat’. Emergency irrigation of about 16 ML/year was applied to the ‘West Boundary’ emergency irrigation area on the western side of the centre pivot during March-May 2012 (BLW, J. Bush, pers. comm., 13/12/12). According to the BLW DP&EMP, the median (50 percentile) quality of the recycled water is expected to be about 8.0 mg/L Total N, 4.5 mg/L Total P, thermotolerant coliforms 800 cfu/100 mL, and 11.2 mg/L BOD. Therefore, the expected median Total N and Total P content of the wastewater is relatively low. A GMP for the Carrick WWTP site was prepared by SGEO and reported to BLW as:

• SGEO PN 99445-2. Groundwater Monitoring Plan: Carrick WWTP, Meander Valley Road, Carrick. (December 2011).

In this report, SGEO recommended installing three additional groundwater monitoring bores at the WWTP to supplement the two existing bores. Existing and proposed bore locations are shown in Figure 1.

2.2 TOPOGRAPHY ‘The Moat’ property has a total area of about 167 ha and is bordered by the Liffey River on the NW side and by the Meander River on the NE side. The primary RWS irrigation area consists of a centre pivot with radius of about 500 m and an irrigable area of about 70 ha. The site is located on a broad river terrace level at an altitude approximately within the range 130-135 m AHD and with a very low overall slope of about half a degree to the NE. The WWTP is located on the southern side of the RWS centre pivot, at the base of a small, approximately 10 m, escarpment slope which defines the NE edge of a higher, Carrick Township, terrace level with an altitude of about 145 m AHD.



The ‘West Boundary’ emergency irrigation area is located on the higher, Carrick Township, terrace level and is bordered on the northern, NW and NE sides by escarpment slopes ranging from about 12 degrees to the NE to about 6 degrees to the NW. A surface drain, which drains to the Meander River, is present on the SE side of the RWS centre pivot and a shallow drainage line is present on the western side, along which WWTP effluent drains to the north, to the Liffey River. The site is shown in Figure 1, with background satellite imagery courtesy of Google Earth.

Figure 1: Carrick RWS Proposed Monitoring Bore Locations.

2.3 GEOLOGY The Mineral Resources Tasmania Digital Geology 1:25000 information indicates that the majority of the alluvial terrace level RWS site is underlain by Quaternary age sediments described as ‘Low (<5 m above present stream) alluvial terraces of sand, silt and clay’. Northwestern and northern fringe areas are described as underlain by ‘Stream alluvium, swamp and marsh deposits’. Sediments underlying the higher, Carrick Township, terrace level to the SW and higher ground on which ‘The Moat’ farmhouse is situated to the SE are described as ‘Siliceous pebble gravel and sand with little or no dolerite (part of ‘Brickendon soil association’)’.

SC10

Scale 100 m

SC11

Liffey River

Meander River

N

Existing monitoring bore WWTP GMP proposed monitoring bore Proposed monitoring bore

Centre Pivot Primary RWS Irrigation Area

West Boundary Emergency Irrigation Area

Small escarpment approx. 10m

Liffey frontage area

Drain

Drain



2.4 GROUNDWATER The Department of Primary Industries, Parks, Water and Environment (DPIPWE) Groundwater Information Access Portal (GIAP) information indicates that records are only available for two bores within about a 1.5 kilometre radius of the Carrick WWTP and RWS sites. The closest bore (40568) is located about 1.0 km to the SW and the other bore (3768) is about 1.5 km to the ENE of the WWTP. Bore 40568 encountered groundwater in quartz gravel sediments from 6.0-15.0 m. Bore 3768 encountered groundwater in basalt from 12.2 to the termination depth of 19.8 m with a cumulative yield of 1.77 L/sec and a total dissolved solids (TDS) value of 730 mg/L, indicating that the groundwater is possibly suitable for drinking water. Both bores are reported as functioning. Bore locations and a GIAP summary report are presented in the Appendix. Two existing groundwater monitoring bores (SC10 and SC11) are present at the Carrick WWTP but there are apparently no drill logs or installation details available for these bores. The Meander Valley Council (MVC) conducted groundwater monitoring events (GMEs) for these bores in December 2005, January 2006 and April 2006. In October 2008 SGEO developed the bores to remove sediment or drilling disturbance and conducted a GME. SGEO collated and assessed all historical GME results and prepared an assessment of groundwater quality. This was reported to the MVC as:

• SGEO PN 85282: MVC Sewage Lagoons Groundwater Monitoring Project: Monitoring Bore Development & October 2008 GME.

A GME was subsequently conducted by SGEO in June 2009 with results reported to the MVC as:

• SGEO PN 88112: Meander Valley Council Sewage Lagoons Groundwater Monitoring Event, June 2009.

An additional GME was conducted in March 2012 with results reported to BLW as:

• SGEO PN 100309: Deloraine, Westbury, Carrick & Prospect WWTPs: March 2012 Groundwater Monitoring Event.

SGEO previously reported that monitoring bore SC10 has a very low yield and is located on the upper edge of the fill embankment on the SE side of the WWTP. The fill embankment appears to overlie an alluvial terrace level and the monitoring bore probably penetrates fill before intersecting an aquifer in the underlying sediments. In contrast, bore SC11 is located on the ‘The Moat’ alluvial terrace level at the foot of the sewage lagoon fill embankment on the NE side. Judging from the depth of SC11 (3.76 m) and the standing water level (SWL) of about 0.4 m, a relatively shallow and possibly unconfined but low-yielding (approx. 35 L/hr) aquifer is present at this site. SGEO also previously reported that the groundwater salinity in WWTP monitoring bores was low, with TDS levels indicating that it was potentially suitable for drinking water. The similarity in field-test results for the two bores suggested that they intersect the same aquifer. Low to very low nutrient levels were evident from GME results and assessment indicated that there was no noticeable evidence to indicate that groundwater quality was affected by the Carrick WWTP site. Monitoring bore SC11 could not be found during the March 2012 GME as the site was overgrown with reedy vegetation and after a comprehensive search the bore was assumed to have been possibly destroyed during erection of an electric fence in the area. However, SGEO subsequently found the bore after brush-cutting the site during a visit on 21 November 2012.



3 CONCLUSION & RECOMMENDATIONS 3.1 CONCLUSIONS Based on the existing groundwater monitoring bore data in the vicinity of the Carrick WWTP, the conceptual site model (CSM) suggests that a shallow, low yielding and possibly unconfined, aquifer with groundwater of drinking water quality occurs at a depth of less than 4.0 m below the alluvial terrace level on the lower, NW side of the WWTP site. Judging from this CSM, as well as site topography and geology information, a relatively shallow aquifer or aquifers may occur in sandy or gravelly alluvial sediment horizons or lenses below the primary RWS site. Note that the RWS site extends 700-900 m to the north and NE of the WWTP and aquifer variations, including presence as well as condition, are likely to occur within the alluvial sediments. We suggest that, in relation to environmental risk, the potential for any deleterious effects on groundwater quality from RWS irrigation infiltration is likely to be very low. This assessment is based on consideration of the following conditions which are expected to occur:

• Low groundwater gradient(s) and flow rate due to the extremely low surface gradient of the alluvial terrace level.

• Relatively low nutrient levels in the recycled water (median Total N 8.0 mg/L and Total P 4.5 mg/L).

• Efficient application of recycled water using centre pivot irrigation.

• Very low infiltration rates for clayey alluvial terrace soils due to the nature of the soil, the use of soil moisture sensors for irrigation control and the likelihood of optimum irrigation practices. Excessive irrigation resulting in the possibility of deep infiltration is extremely unlikely as crop yields would be affected by over watering.

• The apparent absence of any significant, high quality aquifers below the site.

• The unlikely contribution of any significant amount of nutrient rich groundwater from the RWS site as base flow to the Liffey and Meander Rivers.

Considering the known and likely site conditions the greatest environmental risk undoubtedly relates to potential effects on river water quality from WWTP discharge to the Liffey River, rather than RWS effects on groundwater quality.

3.2 RECOMMENDATIONS Considering the above site assessment and the extent of the Carrick RWS site, we recommend the following: • Drilling five investigation holes with an initial maximum target depth of about

8.0 m. Holes should be drilled using 150 mm diameter hollow augers with a combination of auger-pull and split-tube sampling used for investigation. Each hole should be converted to a 50 mm diameter groundwater monitoring bore if groundwater is encountered. Indicative hole locations are shown in Figure 1 and final locations will be determined in consultation with the manager of ‘The Moat’, to ensure that monitoring bores are in locations that do not interfere with farm operations. Holes should preferably be drilled in association with the three previously recommended for the Carrick WWTP site.

• Investigations should be preferably conducted at some time during the January-

March 2013 period, when ground conditions are likely to be dry enough for drill rig access. Investigation holes should be logged and, if conditions are suitable,



monitoring bore installations should be designed and supervised by a suitably experienced and qualified hydrogeologist.

• After installation, groundwater monitoring bores should be developed by pumping to

remove drilling disturbance. The standing water level (SWL) in the bores should be recorded prior to development and parameters such as electrical conductivity (EC), TDS, pH, temperature and dissolved oxygen should be field tested and recorded at the end of development.

• An initial groundwater monitoring event (GME) should be conducted by purging and

sampling new monitoring bores, together with any new bores for the WWTP site and the existing monitoring bore SC11, no earlier than about one week after development, to allow groundwater parameters to stabilise. Sampling should be conducted in accordance with relevant guidelines with SWL measured and recorded prior to sampling. Groundwater parameters such as EC, TDS, pH, temperature and dissolved oxygen should be field tested and recorded at the end of sampling.

• Groundwater samples should be initially analysed for parameters specified in the

EPN. To characterise groundwater quality and geochemistry, as well as quantify principal parameters that are potentially indicative of sewage lagoon leakage or RWS infiltration, the minimum requirements for initial analysis should include: EC, TDS, Total Nitrogen (N), ammonia N, nitrite N and nitrate N, Total P, dissolved reactive P, anions, cations, carbonate and bicarbonate.

• GMEs should be conducted at six-monthly intervals for the first year. Groundwater

analysis parameters should be reviewed after the initial GME and the monitoring frequency reviewed after one year.

• Standards and guidelines to be referenced in relation to conducting site investigations

and installation of groundwater monitoring bores, as well as conducting and assessing subsequent GMEs, should include: o Minimum construction requirements for water bores in Australia, Edition 2, S19.0

Monitoring Bores. Land and Water Biodiversity Committee, September 2003. o AS 5667.1:1998: Water Quality-Sampling. Part 1. Guidance on the design of

sampling programs, sampling techniques, and the preservation and handling of samples. Standards Australia.

o AS 5667.112-1998: Water Quality-Sampling, Part II: Guidance on the sampling of groundwater. Standards Australia 1998.

o Groundwater Sampling Guidelines. Publication 669, EPA Victoria, April 2000. o Hydrogeological Assessment (Groundwater Quality) Guidelines. Publication 668,

EPA Victoria, September 2006. • GME assessment should be undertaken by a suitably experienced and qualified

hydrogeologist. D.J. Sloane BSc (Hons) [16 December 2012]

© Sloane Geoscience Pty. Ltd. 102690 Carrick RWS GMP.doc

APPENDIX Groundwater Information Access Portal Bore Location Map & Summary Report

Documents

Appendix D – Groundwater Monitoring Event March 2013 · Carrick Waste-Water Treatment Plant Effluent Re-use Scheme, December 2010 (DP&EMP). This report indicates that the Carrick