CSLB C-27 Landscaping ContractorSite Preparation and DrainageHard
A landscape contractor is designing a bioretention area (rain garden) to manage stormwater runoff. To ensure effective pollutant removal and infiltration, what is the most critical characteristic of the engineered soil media used in the bioretention cell?
- ASpecific infiltration rate and water holding capacity.
- BHigh compaction to prevent settling of plants.
- CHigh clay content for water retention.
- DLow organic matter content to prevent nutrient leaching.
Show answer & explanationAnswer & explanation
Correct answer: A. Specific infiltration rate and water holding capacity.
The engineered soil media in a bioretention area is specifically designed to have a balance of infiltration rate (to allow water to soak in) and water holding capacity (to support plant life and allow for pollutant breakdown). These properties are critical for both stormwater management and ecological function.
Why the other options are wrong
- B. The soil media should be loosely placed, not highly compacted, to ensure good infiltration. Compaction would hinder its function.
- C. High clay content would impede infiltration, defeating the primary purpose of a bioretention area.
- D. Organic matter is crucial for the biological processes that break down pollutants and support plant growth in a bioretention area.
Bioretention Soil Media
A precisely engineered mixture of sand, compost, and sometimes topsoil, designed to filter stormwater runoff, promote infiltration, and support specific vegetation in bioretention facilities.
- Balanced infiltration and water holding capacity.
- Filters pollutants from stormwater.
- Supports specialized plant life.
Memory trick: Soil's dual role, water's control, for plants to thrive, and pollutants not to strive.