P1.1.4.2 Take account of the Water quality Insufficient Review gallery range of possible raw before and difference design and Poor water qualities when after the between modify if infiltration designing the gallery. gallery: turbidities of necessary. gallery design. turbidity and raw water and Consider suspended gallery outlet. alternative solids. abstraction/ pretreatment system. Slow abstraction rate to reduce filtration velocities through the gravel packs. Clean gravel packs with compressed air lances. Event: INFILTRATION GALLERY PRODUCES LESS WATER THAN IT WAS DESIGNED TO Possible hazards: Germs and chemicals that get into the water because of low system pressure; hazards associated with poor hygiene. Level of risk: Low–high4 P1.1.5.1 Turn off the gallery Flows. Reduction in Scarify the under extreme flow. gravel or Clogged Regular conditions to clean with gravel packs checks on raw Abstraction minimise drawing compressed in the water quality. pump sediment deep into air lances. infiltration cavitation. the gravel packs. gallery. Staining in Regular programme stream bed to scarify gravel pack gravels. with tractor mounted Determinands unit. (NB: If gallery is of concern in the stream bed a found in resource consent will gallery filtered be required.) water. Regular programme of cleaning gravel packs using compressed air lances. P1.1.5.2 Regular programme In the raw Langelier Review extent of cleaning gravel water: Saturation of problem Gravel packs packs using Index is zero and consider and/or screen compressed air or positive. alternative to slots calcified lances pre-treatment calculate or clogged Elevated options. the with oxidised Use raw water quality levels of iron Langelier iron or data when planning and Scarify the Saturation manganese. the abstraction manganese. gravel packs, Index process to help or clean with (hardness, decide whether a compressed pH, gallery is appropriate air lances. alkalinity) given the quality of water. iron and manganese turbidity/ suspended solids.
P1.1.4.2 Poor infiltration gallery design. Take account of the range of possible raw water qualities when designing the gallery. Water quality before and after the gallery: turbidity and suspended solids. Insufficient difference between turbidities of raw water and gallery outlet. Review gallery design and modify if necessary. Consider alternative abstraction/ pretreatment system. Slow abstraction rate to reduce filtration velocities through the gravel packs. Clean gravel packs with compressed air lances. Event: INFILTRATION GALLERY PRODUCES LESS WATER THAN IT WAS DESIGNED TO Possible hazards: Germs and chemicals that get into the water because of low system pressure; hazards associated with poor hygiene. Level of risk: Low–high4 P1.1.5.1 Clogged gravel packs in the infiltration gallery. Turn off the gallery under extreme conditions to minimise drawing sediment deep into the gravel packs. Regular programme to scarify gravel pack with tractor mounted unit. (NB: If gallery is in the stream bed a resource consent will be required.) Regular programme of cleaning gravel packs using compressed air lances. Flows. Regular checks on raw water quality. Reduction in flow. Abstraction pump cavitation. Staining in stream bed gravels. Determinands of concern found in gallery filtered water. Scarify the gravel or clean with compressed air lances. P1.1.5.2 Gravel packs and/or screen slots calcified or clogged with oxidised iron or manganese. Regular programme of cleaning gravel packs using compressed air lances Use raw water quality data when planning the abstraction process to help decide whether a gallery is appropriate given the quality of water. In the raw water: to calculate the Langelier Saturation Index (hardness, pH, alkalinity) iron and manganese turbidity/ suspended solids. Langelier Saturation Index is zero or positive. Elevated levels of iron and manganese. Review extent of problem and consider alternative pre-treatment options. Scarify the gravel packs, or clean with compressed air lances.