volumes 11 days from 6 days from volumes are in small gaps Over the

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1 Greytown Wastewater Treatment Plant Effluent Quantity and Quality Review Wastewater flow volumes The existing discharge consent allows for an average discharge volume of 1,350 m 3 per day ( annual mean) and a maximum flow of 6,600 m 3 per day too the Papawai Stream. Influent and effluent flow volumes are monitored continuously by the operator 1. Flow volumes recorded between b January 2009 and June 2014 are presented below 2. Figure 1 Pond Influent and Effluent Flow volumes between Jan 2009 andd Jun 2014 Over the years theree have been several malfunctions of the outlet meter m that have resulted in small gaps in data or potentially erroneous data. Thesee have been documentedd to have occurred for: Fault detected in January 2011 and the meter was replaced in March Data recorded over this period is considered suspect and has been removed. The issue was nott immediately noticed, during this period a number of spikes in data were recorded.. 11 days from the 16 th 26 th of December 2011, 5 days from 14 th 18 th off January days from the 26 th 311 st of March Considering individual years, the compliancee with discharge limits is shown in thee following table: t 1 Effluent inflows were not measured following equipment failure in late 2011 and which w has been replaced by outflow monitoring. 2 An outlier reading of almost 12,000m 3 from August 2011 has been removed for presentation purposes. The result was due to a pump malfunction and skewed results. Refer below for additional detail. Page 1

2 Table 1 GWWTP Annual Flow monitoring statistics for years Average Maximum Compliance * Yes No Yes Yes Yes Notes: * As noted above there was a fault noted with the outlet meter in early 2011 that resulted r in the replacement of the meter. During this faulty period a number of high readings were made and we note that this faulty period may have in fact commenced earlier than initially thought andd may have started late Across the period presented the flow monitoring records indicate the following: Table 2 GWWTP Flow monitoring data statistics from January 2009 to June 2014 Actual Consent limit Compliance achieved? Averagee daily discharge* Median Daily Discharge Max daily discharge Summer daily average Winter daily averagee 772m (728m ) 656 m 3 (648m ) 7, 018 m 3 (6,670m )* 703 m 3 (605m ) 847 m 3 (847m ) 1,350m 3 6,600m 3 Yes No Notes: count = 1914, * again it may be argued that this peak may have beenn related to the faulty outflow meter. It has been determined that a reasonablee portion of inflow andd thus outflow from the GWWTP is contributed to by inflow and infiltration (I/ I) within the network. Based B on theoretical calculations it is understood that up to 42% of the t average daily flow entering the plant and up to 61% off wet weather flows may be attributable to I/ /I. This is not an uncommon problem in agingg networks, however, the average per capita flows in Greytown (394 L/per/d) are at the higher end of the range considered reasonable for typical domestic wastewater schemes ( L/per/d) 3. Wastewater Quality Condition 20 of the consent outlines the effluent quality requirements, prior to discharge to the Papawai Stream. The measurement of compliance is based on a running geometric mean and 90 th percentile based on 40 consecutive samples collected on monthly as prescribed in Condition 18. Table 2 presents the compliance results against Condition 20.. Table 2 Flow monitoring data of discharge quantities from GWWTP Junee 2009 June 2014 Year Standard TSS Geomean %ile BOD Geomean %ile Notes: * Running Geometric mean and 90 th percentile is based on 40 consecutive samples collected monthly. This table presents the average of thesee results for each monitoring year FC Geomean 90%ile R. P. a. B.. Ellwood, Chapter 1: Sewage Effluent Characteristics, in New Zealand Guidelines for f Utilisation of Sewage Effluent,, Rotorua, NZ Land Treatment Collective, 2000, pp Page 2

3 Non compliance with the geomean BOD hass occurred during the monitoring period We note that SWDC have been collecting effluent quality data more m frequently than monthly, and a summary of the full set of effluent quality data collected from January 2009 to June 2014 is also presented at the end of this document. Thee following sections assess more closely the different effluent quality parameters. Total Suspended solids (TSS) Monitoring data assessed from January 2009 for TSS concentrations indicates the pond effluent ranges from 8 292mg/l with an average of 63mg/L. There is no trend shown of increasing or decreasing TSS over this period, although some seasonal variation is shown with increases during summer months likely to be attributable to increased algae growth during the warmer months. m TSSS concentrations have not altered markedly from the original Assessment of Environmental Effects (AEE) prepared by BECA (1998) 4 with only a slight increase in average concentrations observed, which is likely to be correlated to sludge build up in the ponds, discussed in the Opuss sludge assessment report. Figure 2 Suspended sediment concentrations (mg/l) from GWWTP; January 2009 to June 2014(fulll dataset) 4 BECA, Assessment of Effects on the Environment, Effluent Discharge from Greytown Sewage Ponds to Papawai Stream, September Opus, Sludge Survey Report Greytown WWTP, May Page 3

4 Figure 3 GWWTP Suspended sediment concentration compliance (mg/l); June 2009 too June 2014 Total BOD 5 Monitoring data assessed from January 2009 for BOD 5 concentrations indicates a decreasing trend in effluent BOD 5 over the past five and a halff years. Pond effluent BODB 5 concentrations range from mg/ l with an average of 42mg/L (summer average of 48mg/L andd winter average of 33mg/L). However when compared against the BECA (1998) assessment, there t appears to have been a slight performance declinee in BOD 5 effluent concentration from the ponds. This is likely to be attributable to increased sludge accumulation and hence reduced hydraulic retention time inn the ponds (Opus, 2013). Similarly to TSS, there is some seasonal s variability in BOD 5, again most m likely due to algae growth during the warmer months and dilution during winter as a result of inflow and a infiltration. Figure 4 BOD concentrations (mg/l) from GWWTP; January 2009 to Junee 2014(total dataset) Page 4

5 Figure 5 GWWTP BOD concentration compliance (mg/l); June 2009 to June 2014 Opus (2013) 6 have undertaken a theoretical assessment of the BOD loading to the Greytown Ponds, in the absencee of influent monitoring data, and concluded that the average loading off Pond 1 is approximate ely 97.5kg/ha/d 7. Under cooler winter temperatures, Opus advises thatt the existingg BOD load on the primary pond may exceed design guidelines, although does not account for the aerationn provided by the diffused aeration system. Thus it is considered that following desludging thee ponds are unlikely to be overloaded, and further influent monitoring can be undertaken to confirm this. Faecal Coliforms Monitoring data assessed from January 2009 for Faecal coliform numbers indicate a slight decline in pathogen removal performancee over the past five and a half years. Pond effluent pathogen numbers range from 8 33,000 (no./100ml) with an average of 2,317 and median of This decline in pathogen removal is likely to be attributable to increased sludge accumulation and hence reduced hydraulic retention time in the ponds (Opus, 2013). Compared against the BECA (1998) assessment, there t appears to have been a slight improvement in faecall counts from the ponds,, although the log reduction is similar. There is seasonal variability in pathogen removal, with improvements seen over summer months when natural UV disinfection is at its highest. 6 Opus, Sludge Survey Report Greytown WWTP, May Mott MacDonald have adjusted the calculations in light of new Census data.. Page 5

6 Figure 6 Faecal Coliform count from GWWTP; January 2009 to June 2014(total dataset) Recent monitoring results for Faecal counts indicate compliance withh the consent standards both in terms of geomean (583 MPN) and 90 th percentile performancee (3,240 MPN). As part of this consent application, SWDC are proposing to install a UV disinfection plant on the outlet of the ponds to further improve pathogen removal prior to discharge to water and land. Figure 7 Faecal Coliform Compliance from GWWTP; June 2009 to June 2014 Other Parameters South Wairarapa District Council have also sampled a number of other parameters which are not required by the consent and analysis of these results is presented below. Page 6

7 Total Nitrogen (TN) Monitoring data assessed from January 2009 for TN concentrations indicate relatively little change has occurred in effluent TN over the past five and a half years. Pond effluent TN concentrations range from (mg/l) with an average of 20mg/L (summer average of 16.5mg/ /L and winter average of 23.3mg/ /L). There has also been little change in TN effluent concentrations when compared against the BECA (1998) assessment. There is seasonal variability in TN concentrations, with improvements seen over summer months most likely due to enhanced ammonia stripping in summer months due to higher ph in the ponds caused by algae growth, andd nitrogen uptake by thee pond s biomass. Figure 8 Total Nitrogen concentrations (mg/l)) from GWWTP; January 2009 to June 2014(total dataset) Ammoniacal Nitrogen (NH 4 N) The response in Ammoniacal Nitrogen in the effluent mimics TN concentratioc ons with obvious seasonal trends with improving nitrogen removal in summer compared with winter as expected in pond systems. Monitoring data assessed from January 2009 for effluent NH4 N 4 concentrations indicate a slight improvement has occurred in effluent quality over the past five and a half years.. This may be attributable to the long dry sunny spells we have experienced in 2012/2013 and 2013/2014 which is likely to have resulted in some improvement in ammoniaa stripping. Pond effluent NH 4 N concentrations range from (mg/l) with an average of 11.53mg/L (summer average of 6.5mg/ g/l and winter average of 16.1mg/ /L). There has also been little change in NH 4 N effluent concentrationss when compared against the BECA (1998) assessment. Page 7

8 Figure 9 Ammoniacal Nitrogen concentrationss (mg/l) from GWWTP; January 2009 too June 2014(total dataset) Total Phosphorus (TP) Monitoring data assessed from January J for effluent TP concentrations indicate a slight improvement has occurred in effluent quality over the past five and a half years. Pond P effluent TP concentrations range from (mg/l) with an average of 5.16mg/L (summer average of 5.6mg/L and winter average of 4.8mg/L). The plot below illustrates a seasonal variation in TP concentrations with a decline in effluent quality in the later summer months, likely due to increase algae growth in the discharge during this time (algae uptakes nutrients). There has also been little change in TP effluent concentrations when compared against the BECA (1998) assessment. Figure 10 Total Phosphorus concentrations (mg/l) from GWWTP; January 2009 to June 2014(total dataset) Page 8

9 Dissolved Reactive Phosphorus (DRP) The response in DRP in the effluent mimics TP concentrations with obvious seasonal trendss of improving DRP concentrations in late winter as would be expected in pond systems. Monitoring data assessed from January 2009 for effluent DRP concentratioc ons indicate a marked improvementt has occurred in effluent quality over the past five and a half years. Pond effluent DRP concentrations range from (mg/l) with an average of 4.32mg/L (summer average of 4.9 mg/l and winter average of 3.5 mg/l). Figure 111 DRP concentrations (mg/l) from GWWTP; January 2009 to June 2014(total dataset) Temperature Figure 12 Temperature from GWWTP; Januaryy 2009 to June 2014(total dataset) d Page 9

10 Conductivity Figure 13 Conductivity from GWWTP; January 2009 to June 2014(total dataset) Dissolved Oxygen Figure 14 Dissolved Oxygen from GWWTP; January 2009 to June 2014(total dataset) Page 10

11 ph (laboratory) Figure 15 ph from GWWTP; January 2009 to June 2014(total dataset) Oil and Grease (TOG) Figure 16 Total Oil and Grease from GWWTP; July 2009 November 2013 (total dataset) In regards to Temperature, Conductivity, Dissolved Oxygen, ph and Oil and Grease results, these have been plotted in Figures above. Little change has occurred in temperature and ph results when compared against the Beca (1998) assessment. Temperature, DO and a TOG all appear to have improved over the past 5.5 years, whilst there has been no change observedd with pondd effluent ph, and a slight decline in conductivity. Page 11

12 The following tables present a summary s of all effluent quantity andd quality data that has been reviewed including a calculation of mass loads. Summary Overall the Greytown ponds are operating reasonably well, with little decline in performance since the Beca 1998 assessment. The installation of the proposed inlett screen, UVV disinfection plant and desludging over the next four years is expected to result in improvements in TSS and BOD 5 effluent concentrations and significant improvements to pathogen removal. No major treatment process changes have been proposed as it is understood the land application schemee will not be nutrient limited, and thus nutrientt removal at the treatment plant has not been proposed as part of the replacement consent application. Page 12

13 GREYTOWN WWTP EFFLUENT DATA SUMMARY All Year S.S. Total Solids BOD5 Total BOD Soluble NH3-N TP DRP TN F.C. E.Coli ph Temp Conductivity DO TOG Outflow mg/l No./100mL mg/l mg/l mg/l m3/d Minimum Average %ile Median %ile %ile Maximum Count Summer (Nov - Apr) S.S. Total Solids BOD5 Total BOD Soluble NH3-N TP DRP TN F.C. E.Coli ph Temp Conductivity DO TOG Outflow TRUE mg/l No./100mL m3/d Average %ile Median %ile %ile Count Winter (May - Oct) S.S. Total Solids BOD5 Total BOD Soluble NH3-N TP DRP TN F.C. E.Coli ph Temp Conductivity DO TOG Outflow FALSE mg/l No./100mL m3/d Average %ile Median %ile %ile Count Notes: Only data from 2009 onwards has been used We have deleted all F.C. and E.Coli values <=10 because these results seemed unrealistic. Approximately 6.5 years of overlapping quality and flow data from March 2005 June 2013 TP effluent quality data prior to May 2009 has been excluded as looks eroneous GREYTOWN MASS LOADS SS BOD TN NH4 N TP DRP Annual Mass Load kg/yr Daily Mass Load kg/d Summer Mass Load kg/summer Summer Daily Load kg/d Winter Mass Load kg/winter Winter Daily Load kg/d The above mass load information has been based on average effluent concentrations and average flow rather than a detailed analysis of daily loads.