Risk to the River Itchen and Drinking Water

• The development proposes a new on-site wastewater treatment works to deal with sewage from the site.
   
• Treated water would be infiltrated into the chalk aquifer beneath the site.
   
• The area sits within a drinking water Source Protection Zone, meaning pollution could quickly reach water supplies.
   
• The site is also within the River Itchen catchment, one of the most important chalk stream ecosystems in Europe.
   
• The River Itchen is a Special Area of Conservation (SAC) because of its rare chalk stream habitats.
   
• These ecosystems are extremely sensitive to pollution, especially nutrients such as nitrogen and phosphorus.
   
• Even small increases in pollution can cause:
   
  • algal growth
     
  • loss of wildlife
     
  • damage to the river ecosystem.
     
• The development could increase pollution through:
   
  • wastewater discharge into the aquifer
     
  • increased runoff from roads and buildings.
     
• Under the Conservation of Habitats and Species Regulations 2017, planning permission can only be granted if it is certain that the development will not harm the River Itchen SAC.
   
• The law requires this to be proven beyond reasonable scientific doubt.
   
• If uncertainty remains, the precautionary principle applies, meaning permission should not be granted until risks are resolved.
   
• Development in the River Itchen catchment must show nutrient neutrality, meaning it does not increase pollution entering the river.
   
• The current proposal relies on assumptions about building occupancy and wastewater treatment performance, which introduce uncertainty into the calculations.
   
• The scheme also removes some previously proposed mitigation measures, increasing concern about surface water pollution risks.
   
• The site sits above the Seaford Chalk aquifer, which allows water to move quickly through underground fissures.
   
• Infiltration systems in such areas can allow pollutants to bypass natural soil filtration and move rapidly into groundwater.
   
• Environment Agency guidance generally discourages infiltration systems in the most sensitive protection zones unless risks can be clearly ruled out.
   

The development introduces new risks to groundwater and the River Itchen, one of the UK’s most protected river systems.  Because of the strict legal protections for the river and local drinking water supplies, the council must be certain that the scheme will not cause pollution or ecological harm before granting permission.