Storm Water - Low Impact Development (LID) Recommended Practices and Details
PARTICULATE FILTRATION SYSTEMS
Particulate filtration devices allow stormwater to pass through filter media which are designed to reduce specific stormwater pollutants, but primarily solids, nutrients, and oils. Pollutants are captured physically or through absorption onto the filter media. Filters may be inserts that are retrofitted into existing catch basins or manholes, stand alone proprietary units supplied by a manufacturer, or individually designed and constructed units. Typically suited for locations where infiltration is not an option.
Ideal Conditions for Installation
Precipitation: (typically designed for 90% storm or storms up to 2 year event)
Soils: (Sandy, silty or clayey soils)
Groundwater: (1-3 feet below the bottom of filter system)
Ultra Urban: Yes
- With pretreatement: 4-5 years
- With no pretreatment: annually
Type: Vac. Truck, Filter media replacement, Jetting, Filter media back washing
Monitoring: Inspected annually
Permit Renewal: Varies by permit
Total Suspended Solids (TSS): High
Chloride: Medium/High depending on media
Total Nitrogen (TN): Low/Medium/High depending on media
Metals: Low/Medium/High depending on media
Oils and Grease: Medium
Pathogens: Low/Medium/High depending on oxygen in filter media
Pretreatment is recommended to remove sediments and floatables.
1. Follow the manufacturer recommended requirements for installation, operation and maintenance.
2. Include inspection and maintenance ports to make it easy to inspect and maintain the filtration device.
3. Select filter material designed to drain within 24 hours.
4. Filter cloth should be woven geotextile with a hydraulic flow rate of at least 100 gpm/ft^2.
5. Liner material should be a minimum of 20 ml poly.
6. Gravel should be clean/washed with no more than 5% fines.
7. Limestone aggregate is not acceptable.
1. Install pretreatment device.
2. Install liner if contaminated soils underlying the site.
3. Install main structure (if proprietary) and then filter media.
4. Install initial base course of gravel or filter media.
5. Install pipe network of chambers and interconnecting pipes.
6. Install remaining gravel and filter media.
7. Cover entire area with filter cloth.
8. Install necessary ground cover (pavement, top soil and seed)