Download Stormwater Pollution: Sources, Impacts, and Solutions and more Slides Water and Wastewater Engineering in PDF only on Docsity! • Most of the contaminated water reaching our beaches and coastal waters is through stormwater discharges. ➔ Crosses yards, roof tops, parking lots and freeways on its way to the ocean. • Lawns and gardens release nutrients and pesticides, streets release hydrocarbons, oil and grease and heavy metals associated with motor vehicles. Stormwater 33 Docsity.com • Ballona Creek stormwater is elevated in many pollutants, such as heavy metals (zinc, lead, copper, and nickel). • Another problem with storm drains is dry weather flow ➔ natural drainage ➔ Excessive irrigation of lawns, leakage, car washing, hosing down of streets and sidewalks, and other small sources. 34 Docsity.com • Stormwater flow = (rainfall)(surface area)(runoff coeff.) ➔ The runoff coefficient depends on the land surface permeability. –Open areas, with vegetation have low runoff coefficients (< 20–30% of the rain flows to the storm drain)—most of the water percolates into the soil. –Paved areas have higher runoff coeficients. Source of Stormwater 37 Docsity.com –In West LA, 60% of rainfall becomes runoff. –In greater LA, 5% of rainfall once ran into the ocean; now about 50% does. –Currently we allow $100 million/year of water we could use to recharge our aquifers just flow into the ocean. 38 Docsity.com Where does the stormwater go? • Stormwater makes its way from the street in front of your house or your roof drains directly to the ocean through a series of increasingly larger pipes, channels, creeks and rivers. • Stormwater reaches the ocean untreated. 39 Docsity.com Beach Water Quality • Beach water quality is improving. ➔ Upgrades of the Hyperion Treatment Plant and replace aging sewers are resulting in far fewer sewage leaks. • Beaches are posted or closed when the indicator organism count exceeds a specific threshold. Beaches next to a stormdrain are permanently posted. ➔ Swim when it hasn’t rained recently! 42 Docsity.com Possible Solutions • Can’t use treatment plants ➔ One large rainfall, creates more stormwater flow to Santa Monica Bay than our new Hyperion treatment plant treats in a month. • Porous Pavement ➔ Porous pavement results in more infiltration and less stormwater flow. 43 Docsity.com • Biomass Injection ➔ Stormwater is often directed towards a drain and not to the green space. Green space can actually provide treatment for some of the pollutants. • Wetlands, Ponds and Detention Basins ➔ Useful where there is space, which there is little of, here. • Trash Screens and Racks ➔ These new technologies may be able to remove trash and gross solids without excessive maintenance or flood control risks. 44 Docsity.com
