Low impact development sand filter media replacement: Costs and effect on pollutant removal efficiencies

Area of Science:

• Environmental Engineering
• Water Resource Management
• Stormwater Management

Background:

• Sand filter basins are crucial Best Management Practices (BMPs) for stormwater mitigation in Texas.
• Effective operation relies heavily on regular inspections and maintenance procedures.
• Basins in Bexar County, TX, over the Edwards Aquifer recharge zone were examined.

Purpose of the Study:

• To evaluate the impact of sand filter media maintenance on contaminant removal efficiency.
• To analyze cost variations associated with sand filter maintenance activities.
• To identify maintenance-related issues from inspection records (2017-2022).

Main Methods:

• Assessed contaminant removal performance before and after sand media maintenance.
• Analyzed inspection records for sand filter and sedimentation basins.
• Documented costs for media replacement by private and government entities.

Main Results:

• Minimal change in suspended solids removal post-top media layer replacement.
• Observed decreased removal of total coliforms, total nickel, and total lead, likely due to biofilm disruption.
• Average media replacement cost was $18,462 ± $6325, including removal, replacement, and disposal.

Conclusions:

• Sand filter media replacement has a limited effect on suspended solids removal but can negatively impact pathogen and heavy metal removal.
• Biofilm disruption (schmutzdecke) during maintenance is a key factor affecting performance.
• Media replacement is a necessary but costly component of maintaining sand filter BMPs to meet regulatory standards.