Module 1: Construction Site Erosion Control

Transcription

1 Module 1: Construction Site Erosion Control Problems and Regulations Robert Pitt Department of Civil and Environmental Engineering University of Alabama Tuscaloosa, AL Problems Associated with Erosion of Construction Sites Construction site erosion rates in the US range from about 20 to more than 200 tons per acre per year. These rates are about 3 to more than 100 times greater than erosion rates from croplands. Construction site erosion rates vary depending on local rain energy, soil, and topographic conditions, plus the use of effective erosion controls. Increased Construction Site Erosion Causes Many Problems: Highly turbid receiving waters adversely affects aquatic life (gill abrasion, decreased light penetration, can t see predators or prey, etc.). Stream sedimentation destroys habitat (smothers food sources, destroys spawning areas, etc.). Decreased aesthetics along linear parks (highly turbid waters can persist for several days after a rain). Damage to construction sites require re-grading. Decreases real estate sales opportunities in affected areas. Causes ill-will in surrounding areas that are adversely affected. WI DNR photo 1

2 Regulations Affecting Construction Site Erosion Control Many local and regional agencies in the US have implemented erosion control regulations for several decades (Virginia is a prime example). The 1987 Stormwater Permit Program of the National Pollutant Discharge Elimination System (NPDES) required local erosion control programs for construction sites 5 acres, or greater, for more than 10 years. Phase II of this program now requires erosion control for sites as small as 1 acre, or less. Some Features of Phase II of Stormwater Permit Program Rule became final on Dec 8, Small construction site permit applications are due, starting from March 10, Applicable to all construction sites from 1 to 5 acres (Phase I covered larger sites). Smaller sites may be covered if part of larger common plan, or if designated as a significant water pollutant contributor. Waivers Available for Small Construction Sites Low predicted rainfall erosion potential (NRCS rainfall erosivity factor, R, less than 5 for period of construction activity; not expected to be applicable for Alabama conditions), or Determination that controls are not necessary based on TMDL analysis or equivalent (considering proximity to water resources and sensitivity of receiving waters). Phase II Construction Program Requirements (EPA Guidance) EPA recommends the use of existing Phase I general permits as a guide for developing Phase II small construction permits. Three general requirements: - Notice of Intent (NOI) - Stormwater Pollution Prevention Plan (SWPPP) - Notice of Termination (NOT) 2

3 Notice of Intent Contains general information (location, timing, nearby water resources, etc.) Contains certification that the activity will not impact endangered or threatened species (for the EPA s NOI, not commonly included in delegated state s NOIs) Stormwater Pollution Prevention Plan (SWPPP) Lists and describes construction site erosion controls that will minimize the discharge of pollutants from the site Technology-based standards (Best Available Technology, or BAT) Professional judgment of permit writer (Best Conventional Technology, or BCT) Notice of Termination This is submitted when the final stabilization of the site has been achieved. Problems Associated with Construction Site Erosion Real estate sales adversely affected Receiving water sedimentation Destroyed aquatic life habitat Increased turbidity concentrations Decreased conveyance capacity and increased flooding Fugitive dust and traffic hazards 3

4 Adversely Affects Real Estate Sales Damages Property Bad Publicity and Ill-Will of Neighbors Increased Stream Turbidity 4

5 Stream Sedimentation Clogged Culverts and Increased Flooding Fugitive Dust and Associated Traffic Safety Problems Sediment Sources WI DNR photos 5

6 Major Sediment Sources at Construction Sites Eroded slopes and channels Long-term exposed/bare soil Improper site activities and waste disposal practices Unprotected storage piles Construction activity near roadways Construction in streams Birmingham Construction Site Erosion Runoff Characteristics (Nelson 1996) Suspended solids, mg/l Particle size (median), µm Low intensity rains (<0.25 in/hr) Moderate intensity rains (about 0.25 in/hr) 2,000 5 High intensity rains (>1 in/hr) 25,

7 Eroded Slopes and Channels WI DNR photo 7

8 Long-Term Exposed/Bare Soil WI DNR photo 8

9 Heavy Sediment Loadings on Streets in Construction Areas Soil Compaction During Site Activities Working Near Streets Storage Piles 9

10 Improper Site Activities Fuel Spillage Improper On-Site Waste Disposal 10

11 Working Near Streams and in Channels Stream erosion first season after new outfall for subdivision expansion Alabama has areas that Experience some of the Highest Erosion Rates in the Nation: Rainfall energy (Alabama has the highest in the US). Soil erodibility (northern part of the state has fine-grained, highly erosive soils). Site topography (many areas have steep hills undergoing development). Surface cover (prior forested cover usually totally removed during initial site grading on hilly construction sites). Common Components of Many Erosion Control Regulations 1) divert upslope water around disturbed areas, or pass it through the site along a protected channel, 2) expose disturbed areas for the shortest possible time (typically 14 day limit), either through better scheduling or by using temporary or permanent mulching or other cover, 3) treat any runoff before it leaves the site (perimeter filter fencing and downslope fencing or sediment pond, depending on size of site). 11

12 Other Typically Required Erosion Control Elements: Construction wastes must be properly stored and disposed. Sediment tracking controlled using graveled driveways, roads, and construction entrances. Protect storm drain inlets. Storage piles properly located and protected from erosion. Have an effective inspection and repair program. A local construction site erosion control program would qualify and meet federal requirements of the phase 2 stormwater permit program if it met the following five principles: 1) good site planning 2) minimize soil movement 3) capture sediment 4) good housekeeping practices 5) mitigation of post-construction stormwater discharges and the following eight elements: 1) program description 2) coordination mechanism 3) requirements for nonstructural and structural BMPs 4) priorities for site inspections 5) education and training 6) exemption of some activities due to limited impacts 7) incentives, awards, and streamlining mechanisms 8) description of staff and resources States are already addressing these key requirements of the initially proposed Federal effluent guidelines: Stormwater Pollution Prevention Plans All 50 states require site managers to prepare a stormwater pollution prevention plan, erosion and sediment control plan, or an equivalent document. Inspections by Construction Site Operator All 50 states require construction site operators to inspect their sites on a regular basis. 12

13 Erosion and Sediment Control All 50 states require site managers to implement a combination of erosion and sediment controls to prevent soil erosion and to manage construction site runoff. The EPA s proposed effluent guideline would have mandated sediment basins of a particular size across the country. Currently, states base their technical requirements for basins or other erosion control techniques on local rainfall patterns and other considerations. Stabilization of Soils After Construction All 50 states require stabilization of soils after construction activities have temporarily or permanently ceased. The EPA s proposed effluent guidelines would have mandated this step within 14 days. States currently set their own requirements based on local conditions. In dry areas, for instance, 14 days may not be necessary because of low rainfall. It may also be impractical due to slow growth of vegetation. Existing Local Programs Many local governments have long-standing programs in place to control sediment and erosion from construction sites within their jurisdiction. EPA s stormwater regulations (Phase I and Phase II) set minimum requirements for these programs. Approximately, 6,000 municipalities are covered by these regulations. Many of the approximately 5,000 communities covered by Phase II are just now developing or upgrading their programs to meet these requirements. Some of the minimum requirements for these local programs include: Ordinances or other regulatory mechanisms requiring the implementation of proper erosion and sediment controls Review of site plans to ensure proper design and installation of sediment and erosion controls Site inspections and enforcement of control measures Sanctions to ensure compliance Procedures for public review and comment 13

14 Review of Site Plans The NPDES regulations require that municipalities set up procedures for review of site plans to ensure proper implementation of sediment and erosion controls. The EPA s proposed effluent guideline would have required certification of the design and installation of sediment and erosion controls by a qualified professional (generally a third-party). States and communities are working together to define and develop effective programs. Communities have until 2008 to fully implement these requirements. The problem is lack of resources (and will) to enforce regulations, improper sizing and design of controls (let alone maintenance), and application of inappropriate controls for local conditions. This book and course are intended to help the engineer in proper application and use of erosion and sediment controls. Module 1 Homework Problem Value of continuing education and engineering registration - Search the internet (and/or other resources) for available continuing education classes in a technical discipline of interest to you (not necessarily construction erosion control!) - Prepare a summary of the types of workshops available and how they would supplement material you have learned during your forma university education - Also prepare a summary of the job opportunities available to a person having an FE and a PE license. What work activities would you not be allowed to do if you are not registered as a professional engineer. 14