Appendix B: Proposed trigger levels for groundwater quality and Response to Breach of Trigger Levels

Transcription

1 Appendix B: Proposed trigger levels for groundwater quality and Response to Breach of Trigger Levels Trigger levels Miners Road and Selwyn McLeans Island Suite 1 - All wells ph field measurement <6.0 or >8.5 <6.0 or >8.5 Conductivity, ms/m Calcium, dissolved, mg/l Magnesium, dissolved, mg/l Hardness, mg/l as CaCO Alkalinity, mg/l as CaCO Sodium, dissolved, mg/l Chloride, dissolved, mg/l Sulphate, dissolved, mg/l E. coli, MPN/100 ml * Suite 2 - Downgradient monitoring wells Ammoniacal nitrogen, mg/l as N Aluminium, dissolved, mg/l* Arsenic, dissolved, mg/l Boron, dissolved, mg/l Cadmium, dissolved, mg/l Chromium, dissolved, mg/l Copper, dissolved, mg/l 1 1 Lead, dissolved, mg/l Nickel, dissolved, mg/l Manganese, dissolved, mg/l * Iron, dissolved, mg/l * Zinc, dissolved, mg/l Benzene, mg/l <0.005 <0.005 Ethlybenzene, mg/l <0.005 <0.005 Toluene, mg/l <0.005 <0.005 Xylenes (o, m+p, total), mg/l <0.005 <0.005 tes: *Specific comments on the concentrations recorded for these parameters relative to the NZ Drinking Water Standards and the likely cause of any elevated concentrations are to be documented in the annual monitoring report for each site. The reason for this is that no specific trigger levels have been set due to the potential occurrence of elevated concentrations above the water standards for reasons other than the quarries.

2 Derivation of trigger levels from Miners Road data Table 1 Trigger UG Max ph <6.0 or >8.5 DG 95 th %ile DG 98 th %ile DG Max Exceedence,% Trigger based on 8.2 3% Upper limit = NZDWS, lower limit 2 nd percentile Conductivity % approx 3 x UG maximum Calcium % Hardness is the issue, so no trigger required Magnesium % Hardness is the issue, so no trigger required Hardness % GV NZDWS 2008 (from concrete slurry?) Alkalinity % approx 3 x UG maximum Sodium % approx 3 x UG maximum Chloride % approx 3 x UG maximum Sulphate % 1/2 x GV NZDWS, exceeded once (from GIB?) E. coli % E. coli can be frequently present in rural environment Table 2 Ammoniacal % GV, NZDWS 2008, converted to ammonia as N N 1.2 Aluminium % Elevated concentrations may occur naturally, so no trigger Arsenic % 1/2 x MAV, NZDWS 2008 Boron % 1/2 x MAV, NZDWS 2008 Cadmium < < < % 1/2 x MAV, NZDWS 2008 Chromium % 1/2 x MAV, NZDWS 2008 Copper % 1/2 x MAV, NZDWS 2008 Lead % 1/2 x MAV, NZDWS 2008 Nickel % 1/2 x MAV, NZDWS 2008 Manganese % MAV NZDWS 2008 because lower concentrations may occur naturally 0.4 in sediment Iron % Elevated concentrations may occur naturally, so no trigger Zinc % GV NZDWS 2008

3 Benzene < < < < < % t naturally present in groundwater Ethlybenzene < < < < < % t naturally present in groundwater Toluene < < < < < % t naturally present in groundwater Xylenes (total) < < < < < % t naturally present in groundwater Derivation of trigger levels from McLeans Island data Table 1 Trigger UG Max DG 95 th %ile DG 98 th %ile DG Max Trigger based on ph <6.0 or > Upper limit = NZDWS, lower limit for natural ph is outside NZDWS range Conductivity Approx 1/2 x Miners Rd limit - adjusted for lower background near river Calcium Hardness is the issue, so no trigger required Magnesium Hardness is the issue, so no trigger required Hardness Approx 1/2 x Miners Rd limit Alkalinity Approx 1/2 x Miners Rd limit Sodium Approx 1/2 x Miners Rd limit Chloride Approx 1/2 x Miners Rd limit Sulphate Approx 5 x UG maximum (no GIB at McLeans Island) E. coli < E. coli can be frequently present in rural environment Table 2 Ammoniacal N 1.2 < GV, NZDWS 2008, converted to ammonia as N Aluminium Elevated concentrations may occur naturally, so no trigger Arsenic < /2 x MAV, NZDWS 2008 Boron /2 x MAV, NZDWS 2008 Cadmium < /2 x MAV, NZDWS 2008

4 Chromium < /2 x MAV, NZDWS 2008 Copper 1 < /2 x MAV, NZDWS 2008 Lead < /2 x MAV, NZDWS 2008 Nickel 0.04 < /2 x MAV, NZDWS 2008 Manganese 0.4 MAV NZDWS 2008, because lower concentrations may occur naturally in < sediment Iron 0.10 Elevated concentrations may occur naturally, so no trigger Zinc GV NZDWS 2008 Benzene < no data t naturally present in groundwater Ethlybenzene < no data t naturally present in groundwater Toluene < no data t naturally present in groundwater Xylenes (total) < no data t naturally present in groundwater UG = upgradient DG = downgradient

5 Response to Breach of Trigger Level Breach of Trigger, assessed on an individual parameter basis. Criteria must be met in at least 1 well from each of the 3 groups for the response to be required Bores to be Sampled Parameters to be Analysed Action to be taken Upgradient Monitoring Bore Downgradient Monitoring Bore Downgradient Water Supply Well Quarterly monitoring in at least one upgradient monitoring bore, two downgradient monitoring bores and at least 3 downgradient water supply wells within 1 km of the downgradient quarry boundary (subject to availability and land owner approval) Suite 1 in all bores at each sampling round. Suite 2 in downgradient monitoring bores once per year at the spring sampling round additional actions required As above As above, with parameters that breach triggers added to water supply well analyses additional actions required Add in quarterly monitoring of all water supply wells within 1 km downgradient of the quarry boundary (subject to availability and land owner approval) As above with parameters that breach triggers added to all water supply bore analyses Investigate cause of trigger level exceedance in water supply wells and report to ECan and neighbouring well owners Discuss water supply mitigation strategy (management of water use, treatment or alternative supply) with well owners and ECan and prepare for its implementation

6 Samples fail water standards due to quarry activities Samples greater than 90% of water MAV or GV due to quarry activities from 2 consecutive monthly samples 1 Continue sampling as above. Add in monthly sampling of the parameters that threaten the water standards. As above Confirm quarries are the likely cause and advise well owners Samples fail water standards due to quarry activities Samples fail water MAV or GV due to quarry activities from 2 consecutive monthly samples Continue sampling as above. Add in monthly sampling of the parameters that threaten the water standards. As above Confirm quarries are the likely cause Implement mitigation measures tes: 1. This category does not apply to Hardness, Ammoniacal-N, Aluminium, Manganese or Zinc, which have their trigger levels set at either MAV or GV levels