4S Ranch Park Biofiltration Project

Water Quality Improvement Project | Completed October 2025

This project added a biofiltration basin (rain garden) at 4S Ranch Sports Park to treat runoff from the parking lot.

Before This Project

Stormwater runoff from rain events picked up pollutants as it flowed over hard surfaces, like the parking lot, carrying them into the storm drain system.

This untreated runoff discharged into nearby waterways, such as the San Dieguito River.

After This Project

Stormwater runoff from the parking lot flows to a new biofiltration basin (rain garden) within the park.

Native plants and soils in the basin filter pollutants.

Cleaner water then leaves the system.

Project Details

This project is located in the San Dieguito Watershed.

The San Dieguito Watershed is affected by bacteria. Learn more on Project Clean Water.

Cleaner waterways & healthier communities

A biofiltration basin with native plants and soil cleans stormwater by filtering out pollutants. The benefits reach all the way to the Pacific Ocean!

Native plants

The biofiltration basin is planted with native plants, which has a positive impact on local biodiversity.

Educational sign

An educational sign informs park visitors on the importance of stormwater and how green infrastructure is used to improve water quality.

Project Photos

The new biofiltration basin, also known as a rain garden.

When the basin is full, an overflow drain directs excess water to the storm drain system, reducing flood risk.

This project won the 2026 APWA San Diego and Imperial Counties Chapter Project of the Year, Sustainable/Green Cateogry for Projects less than $2 Million