4 Insufficient infiltration documentation –No testing performed, not enough tests performed, test field logs not provided, –Unacceptable testing techniques utilized Testing not performed at location(s) or elevation(s) of proposed system(s) Avoid using the “perc” test Use infiltration test that determines hydraulic conductivity. –No geotechnical information provided –Reduction factors not used
5 Common Mistakes Runoff from impervious surfaces are conveyed directly to infiltration systems –Pretreatment should be provided for stormwater runoff prior to entering a subsurface infiltration system. Clogging from sediment and debris→Failure Off-Site Discharges –Discharges are not going to well defined drainage features –Not identified in the Notice Of Intent (NOI)
6 Off site discharge (Section C) Becoming a common problem.
7 Off Site Discharges –Easements (Legal Issue) Fact Sheet Follow bulleted items –Analysis of discharge Discharges to non-surfaces waters need to demonstrate that the discharge will not cause erosion or damage –Discharge to Non-Surface Water: Level Spreader Conveyance Inflow h Y X Level Spreader Undisturbed Ground Profile View N.T.S. Plunge Pool Outflow Suitable rigid measures and protective geofabric (TRM)- min. 3 ft. or as needed. Optional Drain. 2” ductile iron Driven horizontally
8 Common Mistake Modified Rational Method used for Runoff Volume calculations. –National Resources Conservation Service (NRCS) methods must be used for Volume calculations. –The Modified Rational Method is not acceptable. Potential Pollutants/Contamination –Not identified on the NOI –Contamination documentation not provided –For Site Specific Standard or Non-residential Statewide Health Standards proper Erosion and sediment (E&S) not utilized
9 Common Mistake Not requesting a Pre-application meeting –Projects of complex nature or varying from PA Stormwater Best Management Practices (BMP) Manual should request pre-application meeting. –Conservation District and/or DEP Inconsistencies between plans, details, and calculations –Inconsistent submittals will cause confusion and increase review time.
10 Common Mistakes Structural/Non-Structural (NS) BMP Volume Credit –Volume reduction credit can only be taken for runoff reaching the proposed BMP during the 2-yr 24 hour storm or a smaller event –No more than 25% of required volume reduction achieved through NS –Can not claim volume credits on Worksheet 5 for extended detention
11 Non Structural Credits from WS 3 Other credits for Non-Struct. BMPs are listed in Chapter 8 of BMP Manual such as: BMP 5.4.3 Protect/Utilize Natural Flow Paths Credit = ¼” x Area BMP 5.6.3 (pt. 2) Revegetate/Reforest Credit = 6 cf/tree Deciduous or Credit = 10 cf/tree Evergreen
12 Checklist: Criteria and Credits for Non Structural BMPs Checklists are found in Ch. 8 (Section 8.8) Checklists are required when seeking NS Volume Credit To receive credit, each box should be checked.
15 Worksheets Worksheets 1 thru 5 and 10, should be completed for each point of interest.
16 Nitrates Compliance Worksheet 10 can be misleading. Only use when can meet Volume Control Guidance (CG-1). –If not, complete WS 11 to 13 Should control runoff from at least 90% of the disturbed area. –If not, also need WS 12 & 13. –WS 12 – Pollutant Loading –WS 13 – Pollutant Reduction
18 Standard Notes Ownership, Operations, and Maintenance Procedures (Must be included on drawings) –Applicant or entity (association, company, agency, etc.) listed as responsible party Provide Quality Control of Materials. As with all BMPs, the final product is only as good as the materials and workmanship that went into it. The designer is encouraged to review and approve materials and workmanship, especially as related to aggregates, geotextiles, soil and topsoil, and vegetative materials.
19 Standard Notes Do not compact soil infiltration beds during construction. Prohibit all heavy equipment from the infiltration area and minimize all other traffic. Equipment should be limited to vehicles that will cause the least compaction, such as tracked vehicles. Protect the infiltration area from sediment until the surrounding site is completely stabilized. Methods to prevent sediment from washing into BMPs should be clearly shown on plans. Where geo-textile is used as a bed bottom liner, this should be extended several feet beyond the bed and folded over the edge to protect from sediment wash into the bed during construction, and then trimmed. Runoff from construction areas should never be allowed to drain to infiltration BMPs. This can usually be accomplished by diversion berms and immediate vegetative stabilization. If an infiltration area is also to be utilized as a temporary sediment basin, excavation should be limited to within 1 foot of the final bottom invert of the infiltration BMP to prevent clogging and compacting the soil horizon, and final grade removed when the contributing site is fully stabilized. All infiltration BMPs should be finalized at the end of the construction process, when upstream soil areas have a dense vegetative cover.
20 PCSM Notes & Permit Special Conditions 1. A Notice of Termination (NOT) will be required to be submitted following approval of the final as-built plans. Prior to accepting the NOT, the Department and/or Conservation District will perform final inspection to ensure site stabilization and verify adequate installation and function of stomwater best management practices (BMPs) 2. As-built plans for the stomwater BMPs for each project phase shall be provided within six months following the completion of each phase. The as- built plans shall be signed and sealed by a PA Registered Professional Engineer. 3. The Permittee shall provide engineering construction oversight for the proposed stormwater BMPs. Additional soil testing may be required prior to the installation of infiltration BMPs to ensure proper location and function. 4. The permittee shall provide for engineering construction oversight for the proposed stormwater best management practices (BMPs). A licensed professional engineer knowledgeable in the design and construction of stormwater BMPs, preferably the design engineer, shall conduct oversight.
22 Stormwater BMP Info Chart 5.B Why is this needed? –A condensing of the calculations for proposed BMP’s –Highlights common mistakes Supporting calculation/documentation should be included in Stormwater Report
29 Stormwater BMP Info Chart 5.B Foot notes reference Appendix C of the PA BMP Manual under Site conditions and constraints and Design consideration
30 2-year 24-hour storm only Similar to WS 4 but limited to drainage to indiv. BMP (Post Dev)
31 Section C – E&S and PCSM Stormwater BMP Chart 5B should match the summary table in section C.2 of the NPDES application. Both should match Stormwater Report
32 How to expedite the review Submit a complete application Follow the application instructions and BMP Manual. Provide volume control for difference in 2-year w/o any voodoo hydrology. Utilize Worksheets and supporting checklists. (for each point of interest) Request a preapplication meeting with CD and/or DEP. Communicate with reviewer to better understand outstanding issues and find viable solution
33 Timeframes* for NPDES Approval: Varies among by region and county. PAG-2: –45 to 100 days Individual Permit: –3 to 6 months Add another 60 days if a public hearing is required. Each deficiency letter allows 60 days to provide a complete response *Timeframes above assume a reasonably quick turnaround by designers to comments.
34 Stormwater BMP Highlights Chapter 3- Principles & Control Guidance Chapter 5- Non-structural BMPs Chapter 6- Structural BMPs Chapter 8- Methods & Worksheets Appendix C – Site Evaluation & Soil testing NOI checklist & instruction
35 FIN Questions? Contact Info: Aneca Y. Crews Stormwater Section PA DEP - SERO 484-250-5129 firstname.lastname@example.org
36 Checklists Criteria and Credits for Non-Structural BMPs. –Plan requirements –Required for most submittals requesting NS Credits.