Remediation recommendations: 1006, Road, Condong, 2484 Australian Research Council Linkage Project LP110100480

Prepared by

Jackie Stroud and Richard Collins

UNSW Water Research Centre School of Civil and Environmental Engineering University of

July 2013

DOCUMENT STATUS RECORD

Project Title: ARC Linkage Project LP110100480 “Exploiting natural processes to effectively remediate acidified coastal environments”. Clients: Council, New South Wales Sugar Milling Co-operative Ltd and New South Wales Cane Growers’ Association Inc. Document Title: Remediation Recommendations Document Number: 2013/2 File Name: RemediationRecommendations

Issue Signatures Date of Issue Description No. Authors Checked Approved 1 28/6/2013 Draft (for JS, RC RC JS comment)

Notes

Disclaimer:

1. The Water Research Centre has taken all reasonable steps to ensure that the information contained within this report is accurate at the time of production. In some cases, we have relied upon the information supplied by the client. 2. This report has been prepared in accordance with good professional practice. No other warranty expressed or implied is made as to the professional advice given in this report. 3. The Water Research Centre maintains no responsibility for the misrepresentation of results due to incorrect usage of the information contained within this report. 4. This report should remain together and be read as a whole. 5. This report has been prepared solely for the benefit of the clients listed above. No liability is accepted by the Water Research Centre with respect to the use of this report by third parties without prior written approval.

Contact Details:

Water Research Centre Name: Dr Richard N Collins School of Civil and Environmental Engineering Email: [email protected] University of New South Wales Name: Dr Jackie Stroud Physical: Email: [email protected] Building H22, Vallentine Annexe Botany Street Gate 11 Kensington.

Postal: UNSW, Sydney, 2052

Telephone: (02) 9385 5017 Fax: (02) 9313 8624

© Water Research Centre Table of Contents

Table of Contents ...... 3 Executive Summary ...... 4 Introduction & Background ...... 4 Remediation aims and strategies ...... 5 Site assessment...... 6 Area ...... 6 Land capability ...... 6 Geomorphology and elevation ...... 6 Land use ...... 7 Drainage history ...... 7 Number, length and volumes of drains ...... 7 Current drainage control structures ...... 7 Drain water quality ...... 8 Soil properties ...... 8 Area of acid scald ...... 9 Vegetation characteristics ...... 9 Site assessment summary ...... 10 Working with the landholders ...... 10 Remediation for a wet pasture: ...... 10 Remediation outline ...... 11 Remediation costing estimate...... 12 Remediation targets: ...... 13 Monitoring programme ...... 13 Acknowledgements: ...... 13 References: ...... 13

Executive Summary

Site 1006, Clothiers Creek Road, Condong, 2484 is principally implicated in acid and metal rain-induced discharge impacting Nature Reserve. Site geomorphology (low lying back swamp), soil chemistry (surficial acid sulfate soil layer), the Grazing and Dairy Industries in Acid Sulfate Soil Guidelines and the Acid Sulfate Soils Remediation Guidelines for Coastal Floodplains in NSW identify that wet pastures are the best agricultural practise for this farm. This contradicts the land owners’ dry pasture farming philosophy and land owner engagement is difficult as the farm is currently for sale. Management and remediation options are presented, namely to comprehensively re-design water management on the farm to establish a wet pasture, and monitoring requirements are also outlined.

Introduction & Background

Cudgen lake is a shallow (<2 m), tidal back barrier lake (160 ha). Reserve and Clothiers creeks (combined catchment of 33 km2) discharge into the lake from the west, and have been implicated in the characteristic poor water quality of Cudgen lake (Tulau, 1999). The lake has a low buffering capacity with low flushing/dilution factors and reported very small tidal range (3 cm). Remediation activities are a priority because the lake is part of the Cudgen Nature Reserve with significant conservation value. The acid sulfate soil management objective is to maintain agricultural productivity whilst restoring the ecology of the Cudgen Nature Reserve.

Cudgen Lake (Clothiers & Reserve Cks) has been the subject of previous research and remediation studies (e.g. LP0219475 & NSW Environmental Trust ASS Hot Spot Remediation Program 2000‐2004). Cudgen Lake has been subjected to poor water quality over many years, linked to the construction of an adjacent golf course and residential development that was abandoned before its completion. This resulted in major fish kills in 1991 and 1998, and an overall degradation of aquatic life. Research from LP0219475 has shown that the problem is mainly due to rain‐induced discharges from oxidising ASS in the catchment (Macdonald et al. 2004). The Hot Spot Remediation Program resulted in approximately 6 km of drains being filled and almost 11,000 m2 of severely degraded ‘acid scald’ being remediated. Despite these measures, large fish kills continue to occur within Cudgen Lake and adjoining waterways (Perkins 2010).

An area designated Management Unit 1 (1006, Clothiers Creek Road, Condong, 2484) was previously identified as a remediation priority as part of the NSW Environmental Trust ASS Hot Spot Remediation Program 2000‐2004 (Tweed Shire Council, 2004). The 70 ha grazing site contained 30 – 37 tonnes per hectare acidity, is situated approximately 3.3 km from Cudgen Lake and was heavily drained with 38 drains totalling 12 km. Part of this unit (N of the Highway) was remediated (800 m2 scald treatment and 150 m drains in-filled) and sold following the subsequent highway development that divided the management unit in two. The N site has since undergone further remediation involving extensive drain infilling (S.Garcia-Cuenca, pers comm.). Plans for the rest of the unit (S of the Highway) included levee treatment and drain infilling. However, no work was carried out due to landholder concerns (desire to maintain a dry pasture) and availability of funding. The major issues for the land owner included productivity of the land, drainage, minor scalding, water quality, weed introduction and fire potential. The main acid discharge mechanisms are groundwater from the drain banks, event-based surface flows and surface acid accumulation in scalded areas. The impacts of acid discharge are degradation of ecology of Cudgen Lake, impact of water quality downstream, scalding and land subsidence.

The final stage of the Australian Research Council Linkage Project LP110100480; 2011 – 2014 was to monitor and remediate Reserve and Clothiers Creeks within the Cudgen Lake catchment (2012 – 2014). One year of water quality monitoring (2012 Annual Progress Report for the Australian Research Council Linkage Project LP110100480) identified that the lowland paddocks (ca. 40 hectares) within former Management Unit 1 - S of the Highway were principally responsible for acid discharge and elevated Al concentration during rain- induced discharge events. Discussions with the landholder in 2013 revealed her dry pasture farming philosophy, providing a considerable barrier to discussing remediation activities. Further, the $2.5 million site is for sale (http://www.realestate.com.au/property-other-nsw- tweed+heads-7344851), thus remediation activities are not a priority to the landholder.

The aim of this report is to identify the required remediation activities, water quality monitoring requirements and remediation targets suitable for this site based on the Acid Sulfate Soils Remediation guidelines for Coastal Floodplains in NSW.

Remediation aims and strategies Using the Acid Sulfate Remediation and Floodplain Management for Coastal Floodplains in NSW (Tulau, 2007); the aims of remediation are to: (a) minimise the production of acid and other oxidation products and (b) reduce the export of existing acid and oxidation product discharges.

The guidelines state this (a) is achieved via water table management to maintain water above the ASS layer and (b) is achieved via containing, neutralising, diluting or chemically reducing these products.

The guidelines outline four remediation strategies for coastal floodplains, floodgate management/modification; restoration of estuarine areas; dry acid containment, and wet acid containment strategies. The limited tidal influence (floodgate management), limited neutralising/buffering capacity of receiving waters (estuarine area strategy) and inability to control the water table (dry acid containment), mean that the wet acid containment strategy is the most appropriate to manage this site.

The objective of a wet acid containment strategy is the restoration of a freshwater wetland/ wet grazing area in order to:

- Prevent further oxidation and contain oxidation products by raising groundwater levels - Reduce oxidation products by increasing organic matter over time - Provide a grazing resource Agronomic advantages include protection from fire (one of landholder concerns), but other issues include snail and fluke management, mosquito risks, botulism, providing a new drinking water source for cattle (dammed water is currently piped to troughs), medium term stock exclusion, and resultant surface water quality.

Site assessment

Area The whole site (including house and farm buildings) is ca. 123 hectares with 40 hectares of lowland dry pasture. The proposed area for remediation (40 hectares) is marked in red (Fig. 1).

Figure 1:. Aerial view of the remediation site: 1006, Clothiers Creek Road, Condong, 2484 (delineated in red).

Land capability To date, the land is used beyond its capability. There is no water table control, significant ASS discharge; some 90 % of drains intersect the ASS layer, extensive scalds are present and soil , groundwater and surface water have pH values <4.

Geomorphology and elevation The paddocks identified for targeted remediation are a characteristic back swamp, with a low elevation (Fig. 2).

Figure 2: Contour map of the area showing that the remediation site (circled) is one of the lowest areas of the catchment (< 1 m).

Land use The current landholders have been at the site since 1974 (S. Streatfield, pers comm). The area is used for cattle grazing.

Drainage history The site drainage was carried out by the current land holders whose aim is to maintain a dry grazing pasture.

Number, length and volumes of drains Drainage is strategic but not uniform, with mixed depth, width and direction.

Three main drains adjacent to Reserve creek are up to 1.4 m in depth, 3 m wide and range in length from 219 - 375 m, totalling 875 m (Fig.1).

There are 16 main field drains that run parallel to Reserve creek (Fig.1). The field drains range in depth from 0.3 m – 1.4 m undulating in depth along the field surface to the main drains (Fig. 3). Width varies from 0.6 m to 4 m, varying along the field surface. Length varies from 93 m – 312 m, with a cumulative length of ca. 4300 m.

Figure 3: Mixed field drainage designs (channel on left is wide and shallow; channel on right is narrow and deep). Other channels follow a more natural water course.

Current drainage control structures Natural drainage has been heavily altered at this site. The proposed paddock for remediation is downstream from 7 spring and rainwater fed dams (with an additional 30, 000 gallons of rainwater storage on the high land at the house) and an extensive 1 – 3 m high artificial levee surrounding serves to minimise inflow from Reserve Ck during flooding. Two flood gate structures are embedded in the levee adjacent to Reserve Ck (Fig. 4) and are approximately 0.5 m above the ground surface in the paddock. As a result, flow into Reserve Ck will only occur when surface water levels in the paddock are > 0.5 m.

Figure 4: Water control structures embedded in the levee at the lower end (east) of the paddock adjacent to Reserve Ck.

Spring and rainwater is dammed around this dry lowland pasture (Fig. 5), has good water quality (pH 6) and is piped for cattle drinking pools.

Figure 5: Dammed spring water and rainfall upstream from the acidified paddocks. The levee diverts runoff around the lower acidified paddock and also serves as a source of stock water.

Drain water quality Drain water and surface standing water is circa pH 2.5 – 3.5 on the lower pasture, with elevated aluminium (2 - 11 mg/l) concentrations, average 8 mg/l. The spring water is pH 6 – 7, with no elevated metal concentrations. For the protection of aquaculture species the trigger concentration is 0.01 mg/l Aluminium at pH <6.5 (ANZECC Water Quality Guidelines, 2000).

Soil properties The acid sulfate soil layer is very close to the soil surface, ranging from 20 – 45 cm from the surface and is enriched with jarosite – an oxidation product of acid sulfate soils. The soil chemistry was analysed a decade ago, and contained 30 – 37 tonnes of acidity per hectare. Samples are awaiting analysis at EAL, Lismore to confirm these previous analyses (June 2013).

Area of acid scald There are two areas of scalding (Fig. 6), with a total area of ca. 0.6 hectares. They are at the lowest lying areas of the floodplain, adjacent and extending from the levee outlets indicating that this is caused by overlying flood water therefore drain infilling will largely incorporate these areas.

Figure 6: Areas of scalding adjacent to the levee at the lower end (east) of the paddock adjacent to Reserve Ck.

Vegetation characteristics Vegetation cover is ca. 85 % of lower pasture land area, with grasses, sedges, reeds, mushrooms and trees at paddock borders. Areas on the paddocks without vegetation are associated with scalding (discussed above) and/or overlying Pleistocene material, presumably sourced from the onsite quarry, which is also used for levee maintenance (Fig. 7).

Figure 7: Mixed vegetation cover of pastures with presumed quarry fill in the background on the levee. Site assessment summary The former back swamp is isolated from all water sources (except direct rainfall) and has an extensive network of drains in order to maintain a dry pasture. The land use and drainage design was carried out before the problems of acid sulfate soils were known (1970’s).

A total of 95% drains cut through the actual acid sulfate layer (which is <0.5 m below the ground surface) providing a groundwater source of acidity into the shallow drains and possibly through the soil surface during flooding, and this water is trapped onsite via a levee design leading to extensive scalding near levee outlets (the water outlets in the levees are currently 0.5 m above the ground surface). All drains and surface water are permanently (10 months of monitoring) acidic with elevated levels of aluminium.

NSW Department of Trade and Industries Grazing and Dairy best management practices (1998) state when acid sulfate layers are <0.5 m, all drainage should be avoided and wet pasture grazing is required.

Thus, the NSW government remediation guidelines and NSW government grazing best management practices coupled to the site assessment identify a need for wet farming practices, and the establishment of a wet pasture at 1006, Clothiers Creek Road, Condong, 2484.

However, this clashes with the landholders farming philosophy to maintain a dry pasture and secondly the site has been for sale for 10 months indicating the current landholders are not in a position to establish a wet pasture.

Working with the landholders The landholders have been very co-operative in the collection of water and soil samples from their paddocks over the past decade. However, they do not wish to participate in remediation activities.

Therefore, there are three strategies open:

- Develop a short-term management plan while the site is for sale in order to stop acute pollution events (specifically liming drain waters entering Reserve Ck during discharge (i.e. rainfall) events). - Land acquisition ($2.5 million), followed by remediation into a wetland (removal of levee and dams) as current agricultural activity is inappropriate for site characteristics. - Develop a wet pasture remediation recommendation in preparation for new landholders.

Remediation for a wet pasture: Based on the ‘fix and forget’ principle, the modification of the dams and levees are the preferred engineering solution at this time to maximise the success of establishing a wet pasture. Natural drainage channels could not be identified, land grading cannot be justified for a low gross margin per hectare site, and site geomorphology indicates that removing the levee would potentially take the land out of agricultural productivity through increased flooding from Reserve Ck negating the acid sulfate soil management objective, if the current hydrology of the wider catchment is maintained. It is noted, however, that efforts are underway to improve water flow through Reserve Ck to Cudgen lake by removal of tree debris that is currently impeding flow to the lake. Bearing this in mind, water management structures are key to establishing and maintaining a wet pasture. Modification of the existing dams and levees to allow spring water and runoff to irrigate lower paddocks is central to establishing a wet pasture.

The remediation activities recommended include a comprehensive re-design (or removal) of the current, and largely ineffective, drainage system at the site in order to create a wet pasture (surface water inundated) on the problem paddocks, briefly:

- Temporary stock exclusion of ca. 40 ha arable paddocks - Filling-in extensive (ca. 5.2 km) network of drains (main source of acidity) - Dam modification to allow the spring water and runoff to shallow flood (ca. <15 - 20 cm) 19 ha of priority remediation paddocks (this level of shallow flooding is needed to support wet grazing plant species) - Planting the paddocks with suitable grazing species, e.g. water couch (Paspalum distichum) to improve organic matter levels and evaporation, and potentially provide a wet pasture grazing source. - Following surface water quality monitoring and establishment of vegetation, re- evaluate stock exclusion status.

Remediation outline (Fig. 8):

Figure 8: Recommended remediation activities

1) Exclude stock from areas marked in Red.

2) Drainage is not recommended at this site and all drains should be in-filled. Priority drains for infilling are highlighted in pink. The priority drains are up to 1.4 m in depth, 3 m in width and 1200 m in length, and based on the successful drain infilling within the catchment (containing 30 - 40 tonnes acidity per hectare) a liming rate of 20 kg per tonne of soil is suggested, and so the total priority fill required is 5040 tonnes (assuming a bulk density of 1 tonne/m3), made up of 108 tonnes lime and 4932 tonnes fill.

The essential drains (highlighted in purple) total 4000 m in length and require an average of 0.6 m in depth and 1 m in width of fill in order raise the average depth above the actual acid sulfate soil layer. Therefore, at a liming rate of 20 kg per tonne of soil, the total fill required is 2400 tonnes (assuming a bulk density of 1 tonne/m3), made up of 48 tonnes lime and 2352 tonnes fill.

There is an onsite quarry which may provide a useful source of Pleistocene fill, although up to a 30 cm depth (1560 tonnes) of topsoil is required to facilitate vegetation establishment.

Therefore, a total of:

156 tonnes lime

7284 tonnes fill (with a minimum of 1560 tonnes of topsoil is required).

3) Hydrological assessment to modify water control structures (dams and levee) onsite to enable spring waters and runoff to irrigate the lower pastures and maintain water levels.

4) Seed the site (ca. 19 ha to the North of the priority drain infilling) with water couch to facilitate rapid vegetation establishment.

6) Develop a monitoring programme including surface water quality, depth, soil properties and vegetation cover.

7) Re-evaluate stock exclusion status during monitoring programme to include (a) fenced off sensitive areas (soil properties), (b) good surface water quality (acidity and metals), (c) established vegetation cover and (d) source of drinking water.

Remediation costing estimate:

Labour and tractor at 180 hours @ $150 = $27 000

Topsoil @ 7284 tonnes @ $50/tonne = $364 200

Lime @ 156 tonnes @ $60/tonne = $9360

Seed at $115 per 0.025 hectares = $87 400

Hydrological assessment by WRC = $30 000

24-months quarterly monitoring by WRC = $20 000

Total estimate cost: $ 537 960 The best case scenario, with 80 % landholder participation, all except topsoil (1560 t) fill coming from onsite (quarry); and assuming the presence of a seed bank, the total estimated cost is $142 760.

Remediation targets: - To engage the landholder - In-fill 1.2 km priority drains and shallow 4 km remaining drains - Modify drainage control structures (dam and levee) to flood an area ca. 19 - 34 ha in order to establish a wet pasture - Water quality monitoring at Clothiers Creek Road Roundabout site to improve from the long durations of pH 2 – 3.5 following rainfall discharge events, to shorter duration (<2 days) and improved water quality (pH >4.5).

Monitoring programme:

The outcomes from the Australian Research Council Linkage Project LP110100480 included the establishment of four water quality monitoring stations at Reserve Ck in order to monitor improvements in water quality before and after remediation activities (in place June 2013).

Following remediation, monitoring onsite should include:

- Capacitance probe installation for surface water levels monitoring - Soil monitoring for surficial pyrite formation - Vegetation establishment monitoring - Surface water chemistry

Acknowledgements: This work could not be completed without the assistance of Tweed Shire Council Officers Sebastian Garcia-Cuenca (Sustainable Agriculture Programme Leader) and Hamish Brace (Sustainable Agriculture Officer). Sincere thanks to the landholders who enabled the environmental monitoring to be carried out at Reserve Creek, including Shirley Streatfield, Harry Boyd, Ian Taggert, Reg Carter and Robert Quirk.

References: ANZECC (2000). Australian and New Zealand guidelines for fresh and marine water quality. Volume 2:Aquatic Ecosystems. Australian and New Zealand Environment and Conservation Council, Agriculture and Resource Management Council of Australia and New Zealand, Canberra, Australia.

Establishing a Wet Pasture System (2008), Floodplain Grazing Project Information Sheet, NSW Department of Primary Industries.

Feed Quality of Coastal Wet Pastures (2008), Floodplain Grazing Project Information Sheet, NSW Department of Primary Industries. Grazing and Dairy Industries in Acid Sulfate Soil (1998). Grazing and Dairy Industry Guidelines, ASSMAC.

Grazing the Coastal Floodplain (2008): Meet the graziers who are farming the floodplain sustainably, Floodplain Grazing Project Information Sheet, NSW Department of Primary Industries.

Macdonald BCT, J Smith, AF Keene, M Tunks, A Kinsela and I White (2004). Impacts of runoff from sulfuric soils on sediment chemistry in an estuarine lake. Science of the Total Environment 329:115‐130.

Perkins J (2010). Fish kill occurs in Cudgen Creek. Tweed Daily News (12th April 2010)..

Tulau M.J. 1999. Acid Sulfate Soil Management Priority Areas in the Lower Tweed Floodplains.

Tulau, M.J. Acid Sulfate Soils Remediation Guidelines for Coastal Floodplains in NSW. Department of Environment and Climate Change.

Tweed Shire Council (2004) Cudgen Lake Acid Sulfate Soil Hotspot Remediation Programme: Final Report. Tweed Shire Council & Department of Infrastructure, Planning and Natural Resources.

Water Couch, (2008)Floodplain Grazing Project Information Sheet, NSW Department of Primary Industries.

Maps:

Taken from Google.com and Tweed Shire Council (2004)

Photographs: by Jackie Stroud