Summary of Existing Environmental Data for Foxton Wastewater Treatment Plant
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Summary of Existing Environmental Data For Foxton Wastewater Treatment Plant (LEI, 2014:B1) Prepared for Horowhenua District Council Prepared by August 2014 Summary of Existing Environmental Data For Foxton Wastewater Treatment Plant (LEI, 2014:B1) Horowhenua District Council This report has been prepared for the Horowhenua District Council by Lowe Environmental Impact (LEI). No liability is accepted by this company or any employee or sub-consultant of this company with respect to its use by any other parties. Quality Assurance Statement Task Responsibility Signature Project Manager: Hamish Lowe Prepared by: Philip Lake Reviewed by: Hamish Lowe Approved for Issue by: Hamish Lowe Status: Final Prepared by : Lowe Environmental Impact Ref: Foxton_WWTP_B1 - P O Box 4467 Existing_environmental_data-FINAL Palmerston North 4462 Job No.: 10 172 | T | [+64] 6 359 3099 | E | [email protected] Date: August 2014 | W| www.lei.co.nz TABLE OF CONTENTS 1 EXECUTIVE SUMMARY ..................................................................................... 1 2 INTRODUCTION ............................................................................................... 4 2.1 Purpose ................................................................................................................................. 4 2.2 Background ........................................................................................................................... 4 2.3 Scope .................................................................................................................................... 4 3 ENVIRONMENTAL DATA SOURCES AND DESCRIPTIONS ................................. 6 3.1 Environmental Data Sources ................................................................................................... 6 3.2 Environmental Data Descriptions ............................................................................................. 6 3.3 Completeness of Datasets....................................................................................................... 7 4 ENVIRONMENTAL DATA SUMMARIES .............................................................. 8 4.1 Merging and Correlation of Data ............................................................................................. 8 4.2 Manawatu River Flow and Level Data ...................................................................................... 8 4.3 Rainfall and Evapotranspiration Data for Moutoa and Levin ..................................................... 10 4.4 Water Quality Changes and River Flow Effects at Whirokino ................................................... 13 4.5 Water Quality Changes and River Flow Effects in Foxton Loop Near Foxton WWTP .................. 21 4.6 Comparison of Whirokino and Foxton Loop Water Quality Data ............................................... 26 4.7 Cawthron Institute Assimilative Capacity Report ..................................................................... 27 5 CONCLUSIONS ............................................................................................... 30 5.1 Manawatu River Flow and Level Data .................................................................................... 30 5.2 Water Quality Changes and River Flow Effects at Whirokino ................................................... 30 5.3 Water Quality Changes and River Flow Effects in Foxton Loop ................................................ 31 5.4 Comparison of Whirokino and Foxton Loop Water Quality Data ............................................... 31 5.5 Cawthron Institute Assimilative Capacity Report ..................................................................... 32 6 RECOMMENDATIONS ..................................................................................... 33 7 REFERENCES .................................................................................................. 34 1 EXECUTIVE SUMMARY Horowhenua District Council (HDC) operate the Foxton wastewater treatment plant (WWTP) which is currently located on land known as Matakarapa Island. This land is located south-west of the Foxton township and surrounded by the Foxton Loop, which is a former meander of the main Manawatu River channel that was bypassed with a new channel directly to the final reach into the Tasman Sea in 1943. The WWTP consists of three oxidation ponds in series, with the effluent discharging into an open drain that leads to the western arm of the Foxton Loop about 1 km upstream of its confluence with the Manawatu River and its estuary. The discharges of treated wastewater from the Foxton WWTP into the Foxton Loop require re- consenting by Horizons Regional Council (HRC) upon expiry of the current resource consents on 1 December 2014. HDC has committed to investigate changing the treated effluent discharge method prior to the expiry of the resource consents. An upgrade of the treatment system may also be required. The consenting and upgrade requirements will be influenced by understanding the existing environment among other factors such as the Manawatu River Accord which HDC and HRC are signatories to. This Accord requires all parties to avoid discharges of wastewater into the Manawatu River during periods of low flows (less than half median flow rate). The purpose of this report is to identify and summarise the existing available information about the environment surrounding the Foxton WWTP and in particular the Manawatu River and Foxton Loop. The specific types of data sought and summarised are river levels, river flow rates, tidal impacts on river levels and flow rates, river and estuary water quality, and climate data (ie. rainfall and evapotranspiration). The WWTP treatment performance and resource consent compliance data were not assessed in this report, as these aspects are assessed in other reports. The following environmental data was obtained by LEI: • River level data on an hourly basis at Teachers’ College in Palmerston North, Moutoa, and Foxton from 1 January 2008 to 31 December 2013 was obtained from HRC. • River flow rate data on an hourly average basis at Teachers’ College in Palmerston North and calculated on an hourly basis at Moutoa due to tidal influences on flows at Moutoa from 1 January 2008 to 31 December 2013 was obtained from HRC. • Daily total rainfall data and soil moisture deficit at Moutoa covering 1 January 1980 to 1 May 2012 was obtained from NIWA, and daily total rainfall data at Moutoa covering 2 January 2009 to 31 December 2013 was obtained from HRC. • Daily total rainfall data, soil moisture deficit, and various evapotranspiration data at Levin covering 1 January 1993 to 31 December 2013 was obtained from NIWA. • Water quality data at Whirokino about 3 km upstream of the Foxton WWTP discharge covering January 1990 to December 2013 and data for Foxton Loop Wharf covering July 2000 to June 2008 and for Foxton Wharf (adjacent to Manawatu Marine Boating Club on Hartley Street, Foxton Beach) for January 2010 to June 2014 was obtained from Aquanet and HRC. • Water quality data for the Foxton WWTP effluent and within Foxton Loop 200 m upstream and downstream of the Foxton WWTP discharge covering November 2009 to December 2013 was obtained from Beca on behalf of HDC. The monitoring frequency was weekly during summer months (November to March) and monthly during the remainder of each year. | Horowhenua District Council – Summary of Existing Environmental Data for Foxton WWTP |P a g e | 1 | This environmental data was supplemented by a report by Cawthron Institute that assessed the assimilative capacity of the Manawatu Estuary for contaminant loads. The river level data was able to be used by LEI to assess the nature of the tidal cycle occurring during most of the sampling times at Whirokino and within the Foxton Loop between 1 January 2008 and July 2012. The river flow data was able to be used to assess whether the Manawatu River was in flood or at very low flows during each of the sampling times at Whirokino and within the Foxton Loop between 1 January 2008 and July 2012. A very small number of samples were collected on the same day since 2009 by HRC at Whirokino and by HDC in the Foxton Loop which allowed an assessment of the degree of connection between the water quality of the main Manawatu River, its estuary, and Foxton Loop. A larger number of samples were collected on the same day by HRC at Whirokino and at Foxton Loop Wharf on Harbour Street, Foxton, during 2000-08. A comparison of these datasets showed no relationship between the water quality of the two sites. A number of Foxton WWTP effluent samples were collected at times similar to the Foxton Loop samples, and these were analysed for a range of parameters ranging from only E. coli to a total of eight parameters. Comparisons of the effluent results with the Foxton Loop results were possible on these occasions to determine whether the Foxton WWTP effluent was the likely cause of the water quality changes in the Foxton Loop and the potential maximum extent of any changes that could be attributed to the effluent discharge. Overall, the data indicated that the Manawatu River water quality within the estuary and Foxton Loop is primarily influenced by upstream sources, flooding, and tidal restrictions on river flow rates through the estuary into the Tasman Sea. The water quality within Foxton Loop appeared to be independent of the water quality measured at Whirokino, and this indicated that the Foxton Loop is likely to be subjected to other sources of contaminants,