Remediation recommendations: 1006, Clothiers Creek 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 New South Wales July 2013 DOCUMENT STATUS RECORD Project Title: ARC Linkage Project LP110100480 “Exploiting natural processes to effectively remediate acidified coastal environments”. Clients: Tweed Shire 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 Cudgen 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