striving to make stormwater green pcsm plans common mistakes, notes, etc. presented by aneca y....

STRIVING TO MAKE STORMWATER GREEN

PCSM PlansCommon Mistakes, Notes, etc.

Presented by

Aneca Y. CrewsPADEP-SERO

2

Agenda

• Common Mistakes

• PCSM Plan Notes

• Stormwater BMP Information Chart 5B

3

Common Mistakes

4

Common Mistakes

• 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

UndisturbedGround

Profile ViewN.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.

13

NPDES Application (rev. 12/2009)

14

Updated Worksheet 5

NEW OLD

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

17

Standard Notes

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.

21

STORMWATER BMP INFORMATION CHART 5B

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

23


Measured Infiltration

RateFactor of

Safety

Design Infiltration

RateDewatering

Time*

Elevation Soils, Water

Table, Rock**

Total Drainage Area to BMP

Total Impervious Drainage

Area to BMP

Infiltration BMP

Surface Area

Total Drainage

Area Loading

Ratio

Impervious Area Loading

Ratio

Infil. Elevation

Top of Bed/

Basin***

Infil. Elevation Bottom of

Bed/ Basin***

Elevation Infiltration Test****

Elevation E & S

Sediment Basin

Bottom (if applies)

Volume to be Infiltrated or Permanently removed*****

in./hr. 2 min. in./hr. hrs. sq. ft sq. ft. sq. ft. 8:1 Max 5:1 Max cf

BMP 6.4.1 Pervious Pvmnt w. Infilt. Bed

BMP 6.4.2 Infiltration Basin

BMP 6.4.3 Subsurface Infiltration Bed

BMP 6.4.4 Infiltration Trench

BMP 6.4.5 Rain Garden/Bioretention

BMP 6.4.6 Dry Well / Seepage Pit

BMP 6.4.7 Constructed FilterBMP 6.4.8 Vegetated SwaleBMP 6.4.9 Vegetated Filter StripBMP 6.4.10 Infilt. Berm & Ret. Grading

All information to be based on the 2-year 24-hour storm only.Provide page numbers from the stormwater narrative identifying the location of the above information.* Include active infiltration time, maximum 6 hrs.** Depth to limiting zones must be >2 ft below infiltration testing elevation/proposed infiltration elevation.***If greater than 2 feet of Hydraulic head then a soil scientist justification is required.****Provide supporting field notes/documenation.*****Permanently Removed Volume includes water that is captured and not released. (reused or reduced by evapotranspiration.)

BMP Information

Stormwater BMP Information Chart 5.B 11-20-08

Proposed Infiltration BMP(s) (site specific)

Drainage InformationInfiltration Information

24

Infiltration Information


RateFactor of

Safety

Design Infiltration

RateDewatering

Time*


Table, Rock**









BMP 6.4.7 Constructed FilterBMP 6.4.8BMP 6.4.9




25



RateFactor of

Safety

Design Infiltration

RateDewatering

Time*


Table, Rock**



Area to BMP

Infiltration BMP

Surface Area

Total Drainage

Area Loading

Ratio


Ratio

Infil. Elevation

Top of Bed/

Basin***


Bed/ Basin***


Elevation E & S

Sediment Basin

Bottom (if applies)











BMP Information




26

Drainage Information


Table, Rock**



Area to BMP

Infiltration BMP

Surface Area

Total Drainage

Area Loading

Ratio


Ratio

Infil. Elevation

Top of Bed/

Basin***










BMP InformationDrainage InformationInfiltration Information

27



RateFactor of

Safety

Design Infiltration

RateDewatering

Time*


Table, Rock**



Area to BMP

Infiltration BMP

Surface Area

Total Drainage

Area Loading

Ratio


Ratio

Infil. Elevation

Top of Bed/

Basin***


Bed/ Basin***


Elevation E & S

Sediment Basin

Bottom (if applies)











BMP Information




28

BMP Information


Ratio

Infil. Elevation

Top of Bed/

Basin***


Bed/ Basin***


Elevation E & S

Sediment Basin

Bottom (if applies)











BMP InformationDrainage Information

29



RateFactor of

Safety

Design Infiltration

RateDewatering

Time*


Table, Rock**



Area to BMP

Infiltration BMP

Surface Area

Total Drainage

Area Loading

Ratio


Ratio

Infil. Elevation

Top of Bed/

Basin***


Bed/ Basin***


Elevation E & S

Sediment Basin

Bottom (if applies)











BMP Information




•Foot notes reference Appendix C of the PA BMP Manual under Site conditions and constraints and Design consideration

30

2-year 24-hour storm onlySimilar 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

[email protected]

36

Checklists

• Criteria and Credits for Non-Structural BMPs.– Plan requirements– Required for most

submittals requesting NS Credits.

striving to make stormwater green pcsm plans common mistakes, notes, etc. presented by aneca y....

Documents

b slide

common mistakes runoff

ns volume credit

volume credits

cftree evergreen slide

extended detention slide

runoff volume calculations

proposed bmp