Introduction and Opening Remarks. The key points of our discussion today include a brief overview of the statewide general construction permit with a focus on sediment risk determination; We will also discuss the permit requirements in regards to Risk 3 sites, as well as the areas in San Diego County where these sites are most likely to be located; This will be followed by a discussion of the procedures and results of our BMP assessment using the RUSLE2 program; And finally, our conclusions from this study as well as tips on how to stay in compliance with the permit and what to expect for your upcoming projects.
General Permit Overview The new statewide general construction permit uses a risk-based permitting approach that is based on the project sediment risk and the receiving water risk. The focus of our study is on sites in San Diego County that have a risk category of 3…meaning the project site generates high rates of sediment, and is tributary to a receiving body of water that is impaired for sediment or designated with sediment sensitive beneficial uses (Cold, Spawn).
Summary of Risk 3 Category Requirements The general permit has several base and category specific requirements applicable for Risk 3 sites. However, this study looks at the potential for a construction project to match pre development sediment delivery rates by utilizing traditional erosion and sediment control best management practices. This determination was done by using the RUSLE2 software application. According to the general permit, if project soil loss is greater than pre-construction levels, then the project is not in compliance. The permit recommends the potential use of Advanced Treatment Systems (ATS) as an acceptable action to achieve compliance.
Summarize Different Types of Advanced Treatment Systems. Discuss Factors influencing cost. There are primarily three techniques available on the market today for advanced treatment: Most of the discussion around ATS has centered around Coagulant Enhanced Filtration…the most commonly mentioned coagulant is. Chitosan has a strong positive ionic charge, which acts as a flocculant and binds to the negatively charged clay and silt particles. It is produced from recycled crustacean shells. Each of these treatment methods requires trained operators who are knowledgeable in the evaluation of the physical, chemical and regulatory limitations of your project. The costs of these treatment systems will depend on factors that are difficult to predict, such as total rainfall, rainfall intensity, and the effectiveness of your site BMPs throughout the duration of the project. All these factors must be considered in the budget.
Animated Slide Sediment Production of 75 Tons Per Acre, coupled with receiving water risk, will trigger Risk Category 3 Requirements. The map shown here shows combined Risk Factors for soil erodibility (K), slope (S), and length (L) that were developed by the US EPA. Isoerodent (“R” in RUSLE Equation) information to account for varying intensity of precipitation is also shown. For a one year duration, the combination of isoerodent value with sediment risk factors will produce a minimum 75 tons per acre. The communities included in this area include eastern Camp Pendleton/Fallbrook and unincorporated areas near Pala Reservation, east of Escondido. Advance Slide. For a 2 year duration, the necessary isorodent value drops in half, dramatically increasing the areas that produce minimum 75 tons per acre. All of the areas shown here are tributary to a water body either impaired for sediment, or defined as having a beneficial use of “Cold” or “Spawn.”
Tina, A series of one year models were conducted in RUSLE2 software. Our models considered these 3 basic soil types, and varying combinations of length and slope.
Predevelopment ground cover was assumed as “Bahia” grass. Post development conditions were simulated for a series of standard erosion and sediment control BMPs…in some cases acting individually, or in others working as part of a management train.
This slide shows the overall relationship of natural conditions (grass cover) versus bare ground, once the site has been stripped. Advance slide to produce circle area…
This close in area shows a better view of the typical results…. In all cases, the stripped site produces sediment at a substantial order of magnitude (7 to 15 times) the predevelopment condition. Sites with silt or silty loams produced the most sediment, followed by clays, then sand.
The modeling runs used to simulate BMP performance rely on a series of cover “C” and practice “P” factors that are applied to the RUSLE Equation. Note the limited applicability of mulch to flow lengths of 300’. RUSLE2 calculated sediment production at a factor of 1.0 when a groundcover of tackified mulch is applied. However a study by Wischmeier and Smith (who? When?) indicates that a value of 0.08 is appropriate for lengths less than 300 feet.
This graph shows the ability of various BMP scenarios to reduce sediment from the construction site back to predevelopment levels. The analysis is specific to sites with sandy soils. Notice also the highly limited effectiveness of Mulch (and similar practices) to lengths 300’ or less. Published research has shown that mulched areas will tend to channelize when flow lengths exceed several hundred feet. Advance animation to see blow up area.
This is a blow up area for a flow length of 300’, and a slope of 10%. Notice the high level of effectiveness in reaching predevelopment sediment levels through just the use of silt fence. This result was typical of all the model runs for sandy sites.
This is a similar range of results for our various combination of erosion and sediment control measures…..this time for silty sites. Advance animation to show blow up area.
This blow up area shows results for a slope of 10%, and a flow path length of 300’. The general relationships shown here a representative of the other modeling runs for silty sites. Notice the overall ineffectiveness of silt fence, even when combined with the use of mulch for erosion control. Use of a sediment basin and complete coverage with hydroseed would be necessary to reduce sediment levels to the predevelopment value. This approach would not be realistic to maintain in an active construction site, since hydroseed can only be used in areas already brought to rough grade. The reality is, some sort of Advanced Treatment System would be necessary to meet the requirements of the General Permit for these silty sites.
This slide shows the overall performance of all the BMP combinations on the moderately active clay sites. Advance slide to show blow up area.
This blow up of the results for the 10%, 300’ flow length are representative of the other clay site runs. Again, sediment levels cannot be reduced to predevelopment levels without the unrealistic assumption of total hydroseed coverage. However, the use of silt fence in combination with mulch and a traditional sediment basin can get reasonably close for shorter flow lengths.
This chart summarizes the compliance findings of all the RUSLE2 model runs, considering soil type, length, slope, and application of best management practices. It can be used as a quick reference for projects in San Diego County to determine basic effectiveness of BMPs to match predevelopment sediment production rates.
Rich, To summarize our study, The requirements in the new general permit include a risk determination requirement for each project site. All risk category 3 sites are required to either match or lower pre development sediment delivery rates or use advance treatment systems. By combining the K*LS risk category map from the Regional board and the R factors from the California isoerodent map, we were able to determine the areas in San Diego County where projects will most likely be risk category 3. Finally, we used RUSLE2 to assess the performance of traditional construction BMPs in regards to controlling project sediment loss.
The results from this study show that locations of risk 3 sites is fairly limited in San Diego county when construction duration is one year or less. However, if the project extends 2 years or greater, the occurrence of risk 3 sites greatly increases dramatically and could potentially encompass much of San Diego County. The RUSLE2 results show that sediment control (by itself without the aide or erosion control practices) is fairly ineffective except when used on sandy sites. The RUSLE2 results also show that traditional BMPs are most ineffective in terms of matching predevelopment sediment production when used with silty soils. Therefore, sites with silt soils will most likely require advanced treatment systems to comply with the current regulations in the Statewide General Permit. The same situation is true, but to a lesser extent, on sites with clay soils.
Assessment of CGP Risk Level 3 Sites
Numeric Assessment of Best Management Practices for Risk Level 3 Projects <ul><li>Richard Lucera, PE, CFM, CPESC </li></ul><ul><li>Tina Fransson </li></ul>
Introduction <ul><li>Today’s Discussion </li></ul><ul><ul><li>General Permit Overview / Risk Determination </li></ul></ul><ul><ul><li>Risk Category 3 Site Requirements </li></ul></ul><ul><ul><li>San Diego County Trouble Spots </li></ul></ul><ul><ul><li>Assessment of BMP Performance (RUSLE 2) </li></ul></ul><ul><ul><li>Conclusions and Tips </li></ul></ul>
Statewide General Permit Overview <ul><li>Effective July 1, 2010 </li></ul><ul><li>Requires Risk Based Categorization </li></ul><ul><ul><li>Erosion Risk </li></ul></ul><ul><ul><li>Receiving Water Risk </li></ul></ul><ul><li>Specific Requirements Vary Based Upon Risk Category </li></ul><ul><li>Today’s Focus is on Category 3 </li></ul>
Risk 3 Sites – Permit Requirements <ul><li>Base Requirements </li></ul><ul><ul><li>Initial Risk Determination </li></ul></ul><ul><ul><li>Numeric Action Levels (NALs) </li></ul></ul><ul><ul><li>Extensive Inspection, Monitoring, Sampling and Reporting </li></ul></ul><ul><ul><li>Record Keeping </li></ul></ul><ul><li>Risk 3 “Category Specific” Requirements </li></ul><ul><li>Numeric Effluent Limitations (NELs) </li></ul><ul><li>Potential In Stream Monitoring </li></ul><ul><li>Bio-assessment </li></ul><ul><li>Match Pre Development Sediment Delivery Rates – Advance Treatment Systems (ATS) </li></ul>
Advanced Treatment Systems <ul><li>Requires Chemical Enhancement </li></ul><ul><ul><li>Cartridge Filtration </li></ul></ul><ul><ul><li>Electro Coagulation </li></ul></ul><ul><ul><li>Coagulant Enhanced Sand Filtration </li></ul></ul><ul><li>Trained Operators </li></ul><ul><li>Potentially Wide Ranging Cost Considerations </li></ul>Image by Clearwater Compliance Services, 2005
Risk 3 Trouble Spots in San Diego County Duration of Construction: 1 Year Duration of Construction: 2 Years
Compliance Summary Silt Sites – San Diego County
Summary <ul><li>Today We Have Discussed </li></ul><ul><ul><li>General Permit Overview / Risk Determination </li></ul></ul><ul><ul><li>Risk Category 3 Site Requirements </li></ul></ul><ul><ul><li>San Diego County Trouble Spots </li></ul></ul><ul><ul><li>Assessment of BMP Performance (RUSLE 2) </li></ul></ul>
Conclusions <ul><li>Occurrence of Risk 3 Sites – Highly Limited for 1 Year Projects. Two Year or Longer Projects Much More Prevalent </li></ul><ul><li>Sediment Control - Little to No Effectiveness When Used Alone, Except on Sandy Sites </li></ul><ul><li>Silt and Silty Loam Sites Will Invariably Require Use of Advanced Treatment Measures to Comply with Permit </li></ul><ul><li>Advanced Treatment Also Likely on Most (If Not All) Clay Sites </li></ul>