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Starting at the top to prevent soil erosion

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“Treat soil as a resource not a pollutant,” said Mike Harding, CPESC, CESSWI of Geosyntec Consultants. It takes 10,000 years for nature to make an inch of topsoil. Behind population growth, the World Bank has recognized that conserving topsoil is the second biggest global challenge.

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Harding explained, “Vegetation is the skin of the earth, and when vegetation is removed, the earth bleeds. That’s what we call erosion.” Harding offered a workshop at the International Erosion Control Association Northeast Chapter’s annual Conference and Trade Show “Changing Paradigms: Engineering for the Future” in Warwick, RI. The program included three days of seminars on climate change, low-Impact development and storm water regulations.

Harding offered these key points to complying with storm water regulations:

  • Control water, beginning at the top of the slope
  • Prevent erosion by limiting the amount of area disturbed
  • Minimize erosion on all slopes
  • Silt fences and other sediment control devices do not prevent erosion; they contain runoff and sedimentation before it can move offsite or pollute waterways.

More Benign Planning (MBP)

Harding recommends designers, engineers and operators plan for erosion control before applying for permits, delivering equipment to sites and planting the first shovel in the ground. He believes proper planning can eliminate 90 to 95% of construction site erosion.

Like all erosion control professionals, Harding recommends projects be scheduled and implemented in phases, to minimize the amount of exposed, bare soil. Other recommendations for stormwater pollution prevention include:

  • Separate and preserve topsoil and subsoil for re-application after final grading
  • Leave a rough surface with ridges or tracks across the slope to slow down runoff, increase infiltration and reduce erosion
  • Provide temporary erosion control on inactive topsoil stockpiles to prevent erosion and dust
  • Use straw mulch, hydraulic mulch, compost or erosion control blankets until permanent vegetation is re-established

Harding advocated “Aboriginality,” or utilizing any resource(s) available on-site. “Sometimes a simple, locally-derived solution works just as well or better than an expensive, high tech solution,” he said.

At mine reclamation sites, Harding recommended teams transplant seedlings from nearby ecosystems to control erosion and re-vegetate sites. He pioneered techniques to revegetate abandoned coalmine slurry ponds. Teams applied lime, seeded with pioneering plants and spread thick mulch. Thirty years later, sites host dense pine forests.

Harding advises all sites have emergency spill kits allowing fast action. Some states mandate sites have 120% of permitted BMP materials.

Starting at the Top

“The top of a slope is the most cost-effective place to start controlling erosion,” Harding said. “The velocities and volumes of water are lowest, and erosion is at its lowest potential.” He recommended retaining as much vegetation as possible

“The cost of preventing erosion is always lower than the costs for reworking the site and paying fines for off-site pollution,” Harding insisted. Implement erosion control measures as soon as possible after soil disturbance to reduce the amount of time and money spent on repair of rills and gullies and maintenance of sediment control devices.”

Treatment Trains

A combination of drainage, erosion and sediment control BMPs (known as a “treatment train”) should be in place before winter or the rainy season. Examples include:

  • Temporary down drains to safely convey water from the top of a slope to the bottom
  • Trackwalked slope to slow down surface runoff and settle out sediment
  • Fiber rolls (straw wattles) placed on the contour to break up slope length
  • Erosion control blankets, straw mulch or hydraulically-applied mulches to break up rainfall impact and reduce soil erosion
  • Silt fence, straw wattles or compost-filled socks placed a at 20’ intervals across slopes and a few feet away from slope toes (bottoms)
  • Inlet and storm water drain protection devices

Contractors should seek effective BMP applications and installations. “If you can see the soil, so can a raindrop. All mulches should provide a high percentage of surface cover. Erosion control blankets provide 90-100% cover when installed with enough staples to hold them firmly to the ground,” Harding advised. He urged everyone to follow manufacturers’ installation instructions.

“Hydraulic applications and compost blankets should be applied so that there is no soil exposed. Over rough ground, apply hydraulic mulch from multiple directions to eliminate shadowing. Compost blankets should be applied at least one inch deep.”

Sediment Control

“Muddy or turbid water is a visual hint of a water quality problem,” said Harding and “Dissolved pollutants attach to soil particles.” Water that passes through a silt fence may not meet water quality standards for turbidity or dissolved pollutants. “Although silt fence can be effective in a treatment train, the focus should always be on erosion control upslope,” he added. Harding stressed that all sediment control devices requires routine inspection and maintenance.

Site Boundaries & Entrances

Harding recommended clearly marking construction limits on the Storm Water Pollution Prevention Plan (SWPPP) map and at work sites. Restrict access to environmentally sensitive areas (ESAs). Protect tree root from soil compaction by installing orange hazard or snow fence, not silt fence, around tree drip lines.

Mud tracked off-site indicates other site issues are likely,” Harding said. Metal shaker plates combined with 4” to 6” rock pads will loosen mud or silt from tires and equipment on their way offsite. Construction vehicle exits should be at least 50’ long with side barriers to prevent drivers from bypassing bumpy exits. Stone should be refreshed as it fills with sediment. Each site exit/entrance should have a back-up plan and equipment to remove mud from adjacent streets. (i.e. a vacuum sweeper, shovels and wheelbarrows)

Sediment must not enter storm drains on or off sites. Effective upslope BMP options may include prefabricated geotextiles, gravel-filled burlap bags, compost socks and straw wattles.

Inspections & Maintenance

Monitor sites and erosion control measures weekly, during and after every rainstorm and per construction permits. In dry states like California, contractors must monitor National Oceanic and Atmospheric Administration (NOAA) forecasts. If NOAA predicts a 50% or greater chance of ½” of rain or more, water quality monitoring and BMP inspections are required.

Repair damaged control measures promptly. Make minor repairs immediately or within 24 hours. Make major repairs per permit schedule requirements. Remove and properly dispose of accumulated sediment trapped behind control devices when it reaches one third of the barrier height.

Records of all inspections, monitoring and repairs should be kept for three years or as required by project permits.

Training & Education

“We won’t change attitudes with regulations, we’ll change them with education,” said Harding.

Many states require formal stormwater management training and certification for designers, engineers and operators. Many states use an international certification program by Envirocert International. (See www.envirocert.org). Envirocert offers training, testing and certification for Certified Professionals in Erosion and Sediment Control (CPESC) and Certified Erosion, Sediment and Stormwater Inspectors (CESSWI) and other certifications.

Institutional Accounting Practices (IAP)

California is the leader in stormwater management transparency. Permits, inspection records and violations are available on public websites here. Harding expects other states to follow this model soon.

Learn More

Learn more about Mike Harding and Geosyntec here. Contact Mike at mharding@geosyntec.com or call at 619-810-4004. Learn about the International Erosion Control Association here. See the 2013 Northeast Chapter’s Conference agenda here.

A similar story ran in the February 2014 edition of Hard Hat News.

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