2 Renmark to border LAP area assessment - EPA - Sa.gov.au

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River Murray and Lower Lakes catchment risk assessment for water quality: Results and management options Nutrients A significant number of very high-risk nutrient hazards were identified in flood-irrigation discharges from the Lower Murray Reclaimed Irrigation Area (LMRIA). The irrigation areas given a very high risk ranking were those with a high proportion of area still in dairy farming—Monteith, Woods Point, Jervois (Woods Point and Wellington end9 ), Long Island, Long Flat, Pompoota, Cowirra, Mypolonga, Neeta and Wall Flat. Areas with a smaller proportion in dairying (eg Toora, Baseby, Glen Lossie) or beef/pasture production (Riverglen, Burdett, Thiele, Wellington south) were also given a high risk ranking. The large volume discharges (several megalitres per day) in the LMRIA during the irrigation season (October–April), contain high concentrations of bacteria, organic matter and nutrients from runoff of animal faecal matter and fertilisers (Eco Management Services 2003). A major ($30 million) government and irrigator funded rehabilitation project is underway in the LMRIA which should significantly reduce these risks within the next few years. Improvements in water delivery infrastructure (metering and channel improvement) and construction of runoff recycling systems are mandatory as part of this project. The EPA has also implemented Environment Improvement and Management Programs (EIMPs) on every farm with additional requirements (eg bridge bunding, laneway runoff diversion, record keeping). Despite the reduced (compared to irrigation runoff) likelihood of rainfall events resulting in runoff from the LMRIA, most of this area was given a high risk ranking for event discharges. Large rainfall events typically see runoff of high volumes of pollutants from adjacent highland (including dairy yards, milking sheds) areas (EPA current monitoring project unpublished data). The EPA audits dairy effluent milking sheds to ensure sustainable disposal or reuse of effluent. Event discharge from Rocky Gully creek/wetland outflow was rated as a high nutrient risk. This creek receives urban and rural runoff, including potential runoff from an abattoir and associated wastewater disposal areas on the highland (Dry Creek subcatchment). A number of moderate-risk nutrient hazards were attributed to several urban stormwater discharges, predominantly from the townships of Murray Bridge, Mannum and Tailem Bend. Most of the stormwater discharges direct into the river. Most of these nutrients are in organic form (plant and detrital material) and not immediately bioavailable (likely to result in algal blooms). The risk mitigation of some discharges by gross pollutants traps is limited because they are designed to trap large organic debris only. The pond near the mill in Murray Bridge receives stormwater from the mill surrounds (though not from the mill itself) and was considered a moderate nutrient risk. This pond is built on a disused dumpsite; a clear consensus on other contaminants within the pond water is yet to be reached. The risk from the large sewage retention ponds for the Murray Bridge and Mannum Wastewater Treatment Plant (WWTP) was rated as high. These ponds are located below the 1956 flood level and are immediately adjacent to the river (
River Murray and Lower Lakes catchment risk assessment for water quality: Results and management options Marinas (eg Long Island and Riverglen) and other vessel mooring areas (eg several moorings in Mannum) were identified as a moderate nutrient risk due to the risk of greywater, and to a lesser extent blackwater, discharges in a localised area. The river vessel waste disposal stations also received a moderate risk ranking. Although this risk is unlikely to occur regularly, the potential consequences of a sewage spill contributed to a moderate ranking. No public river vessel waste disposal stations are present between Murray Bridge and Goolwa (only private pump-outs at some marinas) but there are not many live-aboard vessels on the Lower Lakes. The entire east side of Murray Bridge township is on septic tank systems and was considered a high nutrient (nitrate) risk, although there was some uncertainty due to a lack of quantitative data. Septic tanks in several shack, small township and recreation areas were considered a moderate risk to river water quality due to the likelihood of nutrients (in particular nitrate) leaching into groundwater (SADHS 2004). The age of the septic tanks, irregular auditing and location of soakage trenches on the floodplain contribute to this level of risk. Two of these locations were identified in 2002 (SAMDB NRMB unpublished data) for implementation of STEDS but are yet to be upgraded. Riverglades wetland, where residences on the floodplain surrounding the wetland are all on septic tank systems with soakage trenches for waste disposal, was also classified as a moderate risk although there was some uncertainty about its impact on river water quality. Horticultural areas (eg Monteith, Woodlane, Pompoota) received a moderate nutrient risk ranking as they are relatively small areas. Several permanent and ephemeral wetlands also received a moderate risk ranking (although the certainty value for this was low, indicating the need for further research). Organic matter As noted above, the entire east side of Murray Bridge township is on septic tank systems and was considered a high organic matter risk, although there is some uncertainty due to a lack of quantitative data. Flood irrigation dairy runoff discharges had high-very high risks for the reasons noted above for the nutrient stressor. The impact and fate of the high levels of organic matter discharged to the river from these sources is somewhat uncertain and worthy of further investigation. The Murray Bridge and Mannum WWTP effluent ponds received a high risk ranking for the reasons noted above. Moderate organic matter risks included marinas and river vessel mooring locations (greywater contains high organic levels from detergents), horticultural area leakage to groundwater, stormwater and septic tank discharges, and the pipeline under the river from the Murray Bridge WWTP. Salinity A number of high salinity risks were identified, including discharges from the LMRIA and wetland areas. It should be noted that the drainage channels in the LMRIA receive regional groundwater inputs that are highly saline (eg DWLBC 2003a; Eco Management Services 2003). This is diluted during the irrigation season and rainfall events but concentrations can be greater than 10,000 EC units during winter periods (the river is typically less than 500 EC units in this area). 159
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E N V I R O N M E N T P R O T E C T
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The River Murray and Lower Lakes ca
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6 Mannum to Wellington LAP area ass
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Table 6.5 Frequency of risk to recr
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Figure 7.2 Example of hazard to wat
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Roz Becker, Riverland Tourism Assoc
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Abbreviations 10 ADWG Australian Dr
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Executive Summary The River Murray
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River Murray and Lower Lakes catchm
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