Module 2 of 4 Stormwater Management Design Review

Stormwater Management Design ReviewNJ DEP Division of Watershed Protection and Restoration

October 7, 2021

Module 2 of 4

2

Agenda

Module 2No. Subject Duration

1 Stormwater Calculations (xx minutes)Goal 1: Understand the calculation methods allowed

Goal 2: Use the CN equation to calculate runoff volume

Goal 3: Calculate time of concentration

Goal 4: Use the NJDEP Two-Step Method for unconnected impervious

surface to calculate runoff volume

Goal 5: Learn when exfiltration may be used in stormwater routing

calculations

Goal 6: Size an MTD using the Rational Method with the correct rainfall

intensity

2 Soil Testing (xx minutes)

Goal 1: Understand the various reasons soil testing data is needed

Goal 2: Understand the requirements of soil testing procedures

3 Manufactured Treatment Devices (xx minutes)

- Quiz 2 and Review (xx minutes)

Anthony Robalik/ Lisa Schaefer

NJDEP Division of Watershed Protection

and Restoration

SWMDR Training Module 2

October 7, 2021

STORMWATER

CALCULATIONS:NJDEP BMP MANUALChapter 5

3

Presentation Goals

• Understand the Calculation Methods Allowed per N.J.A.C. 7:8

• Use the NRCS Runoff Equation to Calculate the Volume of Runoff Produced

• Calculate the Time of Concentration (Tc)

• Use the NJDEP Two-Step Method for an Unconnected Impervious Surface to Calculate the Runoff Volume for a Site

• Conditions for using exfiltration in runoff calculations

• Size an MTD using the rational method with the correct rainfall intensity

4

5

ALLOWED METHODS

ii. The Rational Method for peak flow rates and the Modified Rational Method for hydrograph computations

- The Rational Method and Modified Rational Method can be used in a single drainage area measuring 20 acres or less

http://www.nj.gov/agriculture/divisions/anr/pdf/2014NJSoilErosionControlStandardsComplete.pdf

6

N.J.A.C. 7:8-5.7(a)1: Stormwater runoff shall be calculated in accordance with the following:

Allowed Methods of Calculating Stormwater Runoff

http://www.nj.gov/agriculture/divisions/anr/pdf/2014NJSoilErosionControlStandardsComplete.pdf

i. NRCS Methodology

- Section 4, National Engineering Handbook (2002)

- Technical Release 55, “TR-55” (1986) - superseded

- NEH, Part 630 – Hydrologyhttps://directives.sc.egov.usda.gov/viewerFS.aspx?hid=21422

7

N.J.A.C. 7:8-5.7(a)1: Stormwater runoff shall be calculated in accordance with the following:

Allowed Methods of Calculating Stormwater Runoff

https://directives.sc.egov.usda.gov/viewerFS.aspx?hid=21422

8

Intro. to the NRCS

Methodology

NRCS Methodology

9

(𝑃 − 𝐼𝑎)2

𝑃 − 𝐼𝑎 + 𝑆

𝑄 = depth of runoff

𝑃 = rainfall depth (in)

𝐼𝑎 = initial abstraction (in), losses before runoff begins, where 𝐼𝑎 = 0.2𝑆

𝑆 = potential maximum retention after

runoff begins, where 𝑆 = 1000

𝐶𝑁− 10

Simplified,

𝑪𝑵 Runoff Equation:

𝑄 (in) =

(𝑃 − 0.2𝑆)2

𝑃 + 0.8𝑆𝑄 (in) =

NRCS Methodology

10

Curve Numbers (𝑪𝑵):

• Hydrologic Soil Group (HSG)

o ‘A’ = Low runoff and high infiltration

o ‘B’ = Moderately low runoff and infiltration

o ‘C’ = Moderately high runoff and low infiltration

o ‘D’ = High runoff and very low infiltration

• Different Land Covers have different CN values

11

Curve Number (CN )N.J.A.C. 7:8-5.6(a)2: Presume that the pre-construction condition of a site or portion thereof is a wooded land use with good hydrologic condition

Take note that the cover types for streets and roads, urban districts and residential districts by average lot size in Table 9-5, of Chapter 9, NEH Part 630 are intended for modeling large watershed on a watershed-wide scale.

Average 𝐶𝑁 vs. Separate 𝐶𝑁

12

• N.J.A.C. 7:8-5.6(a)4: In computing stormwater runoff from all design storms, the design engineer shall consider the relative stormwater runoff rates and/or volumes of pervious and impervious surfaces separately to accurately compute the rates and volume of stormwater runoff from the site.

• Due to the non-linear character of the equation and the presence ofinitial abstraction, averaging pervious and impervious CN can result inerrors

• For the Water Quality Design Storm, 1 acre impervious with 𝐶𝑁 = 98 plus 2 acres grass lawn with 𝐶𝑁 = 65

= 1,089 cf, when CNs are

averaged in calculation

• Basin is undersized

• Design does not

merit the presumed

TSS removal rate

= 3,811 cf, when

calculated separately &

then added

• Basin is sized for the

WQDS

• Design merits the TSS

removal rate*

} generates runoff volumes as follows:

% Difference

= (3,811 cf – 1,089 cf)

(3,811 cf)

= 71.4%


13

A portion of a major development consists of a 200 ft wide, 25 ft long impervious surface and a 200 ft wide, 75 ft long grass lawn area that are separated by a grass swale. The soil is identified as HSG ‘A.’ The 2-year design storm produces 3.5 in of rain over 24 hours. The slopes of the impervious surface and the grass lawn are each 1%. Compute the volume of runoff that is produced.

Example 5-4

25 ft Impervious

AreaSheet Flow

Grass Swale

75 ft Pervious Area

Sheet Flow

CN = 98 CN = 39

200 ft


14

Example 5-4 (cont’d.)

25 ft Impervious

AreaSheet Flow

Grass Swale

75 ft Pervious Area

Sheet Flow

CN = 98 CN = 39

200 ft

Using a Composite CN:

Grass:

S = 1000

𝐶𝑁−10 =

1000

39−10 = 15.64

𝑄= 3.5 − 0.2 𝑥 15.64 2

(3.5 + 0.8 𝑥 15.64)= 0.009 in

Volume = 0.009 𝑖𝑛 𝑥1 𝑓𝑡

12 𝑖𝑛𝑥 200 𝑓𝑡 𝑥 75 𝑓𝑡 = 10.8 cf

Impervious:

S = 1000

𝐶𝑁−10 =

1000

98−10 = 0.204

𝑄= 3.5 − 0.2 𝑥 0.204 2

(3.5 + 0.8 𝑥 0.204)= 3.27 in


12 𝑖𝑛𝑥 200 𝑓𝑡 𝑥 25 𝑓𝑡 = 1,362.5 cf

Total Volume = 1,373.3 cf

Computing Separately:

𝐶𝑁 = 98 𝑥 200 𝑓𝑡 𝑥 25 𝑓𝑡 + 39 𝑥 (200 𝑓𝑡 𝑥 75 𝑓𝑡)

(200 𝑓𝑡 𝑥 25 𝑓𝑡) + (200 𝑓𝑡 𝑥 75 𝑓𝑡)= 53.75

S = 1000

𝐶𝑁−10 =

1000

53.75−10 = 8.60

𝑄= 3.5 − 0.2 𝑥 8.60 2

(3.5 + 0.8 𝑥 8.60)= 0.305 in


12 𝑖𝑛𝑥 200 𝑓𝑡 𝑥 100 𝑓𝑡

= 508 cf This method does not comply with the rules!

15

Calculate the

Time of

Concentration (Tc)

16

Drainage Area

Time of Concentration (Tc)

Includes all the land that

drains into a point of

analysis.

Point of

Analysis


• Surface Roughness

• Channel shape and flow patterns

• Slope

17

What Affects the Tc?


1. Sheet Flow,

2. Shallow Concentrated Flow,

3. Channel Flow or

A combination of these

18

Runoff moves through a watershed as:

19

Sheet FlowShallow

Concentrated Flow Channel Flow


Depth: about <0.1 ft Depth: 0.1 to 0.5 ft Visible on Maps


20

Velocity Method:

Tc =

𝑖=1

𝑛

(Tt−sheet flow𝑖) + ( ]Tt−channel flow𝑖

Tt−shallow conc flow𝑖) + ([ )

• There is no longer a minimum or default value that may

be used for the time of concentration. Tc for pre- and

post-construction conditions must be calculated.

21

Maximum Sheet Flow Length


• For the pre-construction condition, assume sheet

flow occurs for 100 ft unless physical constraint is

present that prevents sheet flow from occurring

o i.e., swale, curb or inlet

o depth of flow > 0.1 ft

o applies to both pervious and impervious surfaces

22

Maximum Sheet Flow Length


• For the post-construction condition, the maximum

distance, L, over which sheet flow occurs is 100 ft

• L must be calculated using the McCuen-Spiess

limitation, as follows:

L = 100 𝑆

𝑛

where 𝑆 is the slope, in ft/ft, and 𝑛 is the Manning’s roughness coefficient for sheet flow.


Tt = travel time (hr)

L = length of sheet flow (≤ 100 ft in length)

𝑛 = Manning’s roughness coefficient

P2 = 2-year, 24-hour rainfall (NJ Depth: 3.2 – 3.5 in)

s = slope of hydraulic grade line (ft/ft)

23

Tt =0.007 (𝑛𝐿)0.8

(𝑃2)0.5𝑠0.4

Sheet Flow:


• The values for the Manning’s roughness coefficient can also be found in Table 15-1 in Chapter 15 of NEH, Part 630.

• Values for Manning’s roughness coefficient must be selected in accordance with the land surface condition.

• The maximum value that can be used for woods, in New Jersey, is 0.40.

24


• 3.2 – 3.5 in. in NJ

• NOAA’s National Weather Service

o Precipitation Frequency Data Server (PFDS)

• NRCS County Rainfall

25

P2 = 2-year, 24-hour rainfall


Tt = travel time (hr)

L = flow length (ft)

V = estimated velocity (ft/sec)

26

Tt (hr)

Shallow Concentrated Flow:

=𝐿

𝑉 ∗ 3600

Figure 15-4:

Velocity versus slope for shallow concentrated flow

27



𝑛 = roughness coefficient for open channel flow

L = length (ft)

R = hydraulic radius of channel (ft)

= a

pw, where a = cross sectional flow area (sf)

pw = wetted perimeter (ft)

s = channel slope (ft/ft)

28

Tt(hr) =

Channel Flow: 𝐿 𝑛

3600(1.49𝑅23𝑠0.5)

Example Project

For the post-construction condition, stormwater runoff

flows through a wooded drainage area along a flow

path, measuring 1,000 ft in length, consisting of sheet flow

over an area with a 0.5% slope and shallow concentrated

flow over an area of 1% slope. Calculate the time of

concentration for the post-construction condition.

29

Example 5-1: Calculate Time of Concentration

Example Project

Step 1: In this example, there are only 2 different segments of flow. Travel time under sheet flow is calculated as follows:

Tt =0.007(𝑛𝐿)0.8

(𝑃2)0.5𝑠0.4

where:Tt = travel time, hr

𝑠 = slope of land surface, ft/ft = 0.005 ft/ft

𝑛 = Manning’s roughness coefficient for sheet flow = 0.40

𝐿 = sheet flow length, ft =100 𝑆

𝑛=100 0.005

0.4= 17.68 ft

𝑃2 = 2-year, 24-hour rainfall, in = 3.33 in

Tt =0.007[ 0.40 17.68 ]0.8

(3.33)0.5(0.005)0.4= 0.153 hr = 9.18 min

30


Example Project

Step 2: Travel time under shallowconcentrated flow iscalculated as follows:

Tt =𝑆ℎ𝑎𝑙𝑙𝑜𝑤 𝐶𝑜𝑛𝑐𝑒𝑛𝑡𝑟𝑎𝑡𝑒𝑑 𝐹𝑙𝑜𝑤 𝐿𝑒𝑛𝑔𝑡ℎ

𝑉 𝑥 3600

where:Tt = travel time, hr𝑉 = flow velocity, ft/s = 0.25 ft/s

Tt =982.32

0.25 𝑥 3600= 65.5 min

31


Example Project

Step 3: Since no channel flow is specified in the example, the time of concentration for the post-construction condition is the sum of the travel times under sheet flow and shallow concentrated flow

Tc= 9.18 + 65.5 = 74.7 min

32


Time of Concentration

33

Questions?

You may also submit questions on this topic by email to

[email protected]

mailto:[email protected]

34

NRCS Methodology Hydrographs & Rainfall Distributions

Dimensionless Unit Hydrograph

35

Synthetic Hydrographs:

• Developed for determining runoff hydrograph for ungauged watersheds

• Based on an average of natural watersheds with different sizes and geographic locations

• 2 commonly usedo SCSo Delmarva

SCS Dimensionless Unit Hydrograph

36

Dimensionless curvilinear unit hydrograph and

equivalent triangular hydrograph

TcTc

DelMarVa Dimensionless Unit Hydrograph

• Particularly suited for the flat, coastal areas in Delaware, Maryland, Virginia and New Jersey

• Must be used in all areas of the coastal plain unless

• the design engineer proves that those conditions are in no way present onsite• Completed pavement, average steep slope ≥10%

• In the sizing of an MTD

37

• SCSo 484 peaking factoro 48.4% of runoff

discharged before peak

• Delmarvao 284 peaking factoro 28.45% runoff

discharged before peak

38

Unit Hydrograph Info:Dimensionless Unit Hydrograph

SCS

DelMarVa

DelMarVa Dimensionless Unit Hydrographhttps://www.nj.gov/dep/stormwater/rainfalldata.htm

• Conditions for use

o Watershed slope ≤ 5%

o Coastal Plain physiography

• Use the same UH for pre- and post-development

39

Physiographic

Provinces of

New Jersey

Imagery modified from New Jersey Geological Survey Information Circular, Physiographic Provinces of New Jersey, 2006

https://www.nj.gov/dep/stormwater/rainfalldata.htm

DelMarVa Dimensionless Unit Hydrographhttps://www.nj.gov/dep/gis/digidownload/metadata/html/Geol_province.html

40

Physiographic

Provinces of

New Jersey


https://gisdata-njdep.opendata.arcgis.com/datasets/physiographic-provinces-of-new-jersey

https://www.nj.gov/dep/gis/digidownload/metadata/html/Geol_province.html


NRCS Rainfall Distributions for Stormwater Runoff Quantity Control Design Storms

41

• Typically bell-shaped

• The NRCS rainfall distributions were grouped into four types

according to the applicable regions or geographic situations.

• TYPE III was previously used for nearly two decades.

• The State was divided into Regions C & D in 2012 and a new rainfall distribution replaced the TYPE III distribution in each region

o Use NOAA_C in Region C: Sussex, Warren, Hunterdon, Somerset, Mercer, Burlington, Camden, Gloucester, Atlantic, Salem, Cumberland and Cape May Counties.

o Use NOAA_D in Region D: Bergen, Hudson, Essex, Passaic, Morris, Union, Middlesex, Monmouth and Ocean Counties.

o Note that the C & D distributions will yield higher peak flow rates than Type III

NRCS Rainfall Distributions for Stormwater Runoff Quantity Control Design Storms

42

NOAA_C and NOAA_D rainfall

distributions, are available online, in

text format, at:

https://www.nrcs.usda.gov/wps/portal/nrcs/main/nj/technical/engineering/

NOAA_C and NOAA_D rainfall

precipitation distributions and

rainfall intensity will also be

available, in Excel format, from the

Department’s website

https://www.nrcs.usda.gov/wps/portal/nrcs/main/nj/technical/engineering/

43

Unconnected Impervious Cover


• We can consider an impervious surface to be unconnected if flow can travel as sheet flow onto an adjacent pervious area and meet other requirements

• By providing the right conditions to encourage infiltration, some of the runoff will provide groundwater recharge, address water quality and reduce the volume of runoff requiring treatment by a down-gradient BMP

44

How and Why

ImperviousSurface

Sheet Flow Directed to Down-gradient Grass Swale

Sheet Flow Directed to Down-gradient Stream


An impervious area can be considered to be an unconnected

impervious surface only when meeting all of the following 5

conditions:

45

5 Conditions:

a. Upon entering the down-gradient pervious area, all runoffmust remain as sheet flow

b. Flow from the impervious surface must enter the down-gradient pervious area as sheet flow or, in the case of roofs,from one or more downspouts, each equipped with a splashpad, level spreader or dispersion trench that reduces flowvelocity and induces sheet flow in the down-gradientpervious area


An impervious area can be considered to be an unconnected

impervious surface only when meeting all of the following 5

conditions:

46

5 Conditions (cont’d.):

c. All discharges onto the down-gradient pervious surfaces must bestable and non-erosive

d. The shape, slope and vegetated cover in the down-gradientpervious area must be sufficient to maintain sheet flowthroughout its length

e. The maximum slope of the down-gradient pervious area is 8%


47

Additional Requirements:Two methods are available for computation of the resultant runoff,

provided the following requirements are met:

a. Only the portions of the impervious surface and the down-gradient pervious surface on which sheet flow occurs can beconsidered as an unconnected surface in the calculation. Thearea beyond the maximum sheet flow path length cannot beconsidered in the calculation

b. The maximum sheet flow path length across the unconnectedimpervious surface is 100 ft

c. The minimum sheet flow length across the down-gradientpervious surface is 25 ft in order to maintain the required sheetflow state of the runoff


48

2 Methods Allowed for computation of the resultant runoff :

• The NRCS composite CN with unconnected impervious method from Chapter 9, NEH, Part 630

o This method can be used only when the total impervious

surface is less than 30 percent of the receiving down-gradient

pervious surface because absorptive capacity of the pervious

surface will not be sufficient to affect the overall runoff

significantly

• The NJDEP Two-Step Method

Example 5-3: The NJDEP Two-Step Method

49

Calculate the runoff volume. Assume the soils are HSG ‘A’ and the depth of rainfall, P = 3.5 in

Grass Swale

75 ft Pervious Area

Sheet Flow

CN = 98 CN = 39

200 ft

25 ft Impervious

AreaSheet Flow

Step 1: Calculate the Runoff from the Impervious Area

S = 1000

𝐶𝑁−10 =

1000

98−10 = 0.204

𝑄 = 3.5 − 0.2 𝑥 0.204 2

(3.5 + 0.8 𝑥 0.204)= 3.27 in


12 𝑖𝑛𝑥 200 𝑓𝑡 𝑥 25 𝑓𝑡 = 1,362.5 cf

Step 2: Convert the Runoff from the Impervious Surface to a Hypothetical Rainfall on the Pervious Area

P2 = (1,362.5 𝑐𝑓 𝑥 (12 𝑖𝑛)/(1 𝑓𝑡))

(200 𝑓𝑡 𝑥 75 𝑓𝑡)= 1.09 in

P2 = 3.5 in + 1.09 in = 4.59 in

S = 1000

𝐶𝑁−10 =

1000

39−10 = 15.64

𝑄 = 4.59 − 0.2 𝑥 15.64 2

(4.59 + 0.8 𝑥 15.64)= 0.125 in

Total Effective Volume

= 0.125 𝑖𝑛 𝑥1 𝑓𝑡

12 𝑖𝑛𝑥 200 𝑓𝑡 𝑥 75 𝑓𝑡 = 156 cf

Example 5-3: The NJDEP Two-Step Method

50

Grass Swale

75 ft Pervious Area

Sheet Flow

CN = 98 CN = 39

200 ft

25 ft Impervious

AreaSheet Flow

I

I + P

Calculate the runoff volume. Assume the soils are HSG ‘A’ and the depth of rainfall, P2 = 3.5 in

NJDEP Two-Step Method

51

Questions?

You may also submit questions on this topic by email to

[email protected]

mailto:[email protected]

52

Other Recent Updates toChapter 5

Using Exfiltration in Routing Computations

• See Pages 7 and 8 of Chapter 5

• All soil testing must be fully compliant with Chapter 12: Soil Testing Criteria

• The design of the BMP must comply with all of the design criteria within the respective subchapter of Chapter 9

• Pretreatment, in the form of a forebay or any of the other BMPs found in the BMP Manual, must be incorporated into the BMP design, unless specifically stated otherwiseo For BMPs whose contributory drainage area ≤1 acre, pre-treatment

is not required

(cont’d. after next slide)53

Pretreatment Requirement

• Roof runoff that directly discharges into the stormwater BMP can be pretreated by leaf screens, first flush diverters or roof washers. For details of these pretreatment measures, see Pages 5 and 6 of Chapter 9.1: Cisterns

54

Pretreatment Requirement (cont’d.)

• This pretreatment requirement for roof runoff can be waived by the review agency if the building in question has no potential for debris and other vegetative material to be present in the roof runoff

• Pretreatment for non-roof runoff, or roof runoff comingled with stormwater from other surfaces, must be in accordance with the respective BMP Manual chaptero Pretreatment for subsurface infiltration basins must be consistent

with Chapter 5 and remove 80% TSS, for which any of the BMPs in the BMP Manual may be used

o For small-scale bioretention systems designed to infiltrate, where inflow that is in the form of sheet or overland flow, a 5 foot wide gravel or stone filter strip, with a slope of no greater than 10 percent, can be substituted for the required pretreatment when exfiltration is used in the routing calculations

55

Using Exfiltration in Routing Computations (cont’d.)

• Exfiltration cannot be used in any BMP designed with an underdrain system

• Infiltration of the entire 2-, 10- or 100-year storm is allowed only when:

a. existing site conditions are such that no runoff leaves the site for the pre-construction condition scenario, thereby constraining the design to infiltrate 100% of the volume produced by the post-construction condition for the same design storm. In this case, the maximum storm that can be entirely infiltrated is the largest storm event with no runoff leaving the site in pre-construction conditions, or

b. the volume of stormwater runoff to be fully infiltrated is required by law or rule implemented by the Pinelands Commission, Highlands Council, or any other stormwater review agency with jurisdiction over the project.

(cont’d.) 56


• The analysis of groundwater hydrology and the hydraulic impact due to the exfiltration, required pursuant to N.J.A.C. 7:8-5.2(h), must be conducted in conjunction with the design using exfiltration.

a. The design vertical hydraulic conductivity of the most hydraulically restrictive soil horizon below an infiltration type BMP may be used as the exfiltration rate in the routing calculations only when the soil is tested strictly in accordance with Chapter 12

b. This analysis must be performed using the method outlined in Chapter 13: Groundwater Table Hydraulic Impact Assessments for Infiltration BMPs

(cont’d.)

57


• The runoff volume discarded as exfiltration and the design vertical hydraulic conductivity of the most hydraulically restrictive soil horizon below an infiltration BMP must be used, in the initial model, to calculate the duration of

infiltration period in the groundwater mounding analysis.

a. When the groundwater mounding reaches the bottom of the BMP, the hydraulic gradient is reduced, thereby reducing the exfiltration rate

b. To reflect the impact on the hydraulic gradient, the reduced exfiltration rate must also be used to re-run the routing calculation(s) to check the peak flow rate(s) produced for the respective design storm(s) through the proposed outlet structure of the infiltration BMP used to meet the Stormwater Runoff Quantity Standards

c. If adverse impacts cannot be avoided, the infiltration BMP cannot be used.

58

59

Using the Rational Method

Rational Method

• Rainfall intensity is uniform over the drainage basin during the duration of the rainfall

• Maximum runoff rate occurs when the rainfall lasts as long or longer than the time of concentration

• The frequency for rainfall and runoff are equal

60

Assumptions:

Rational Method

• Used for relatively small drainage areas with uniform surface cover (≤20 acres)

• Used for urban areas

• Not applicable if areas of ponding occur

• Used only to estimate the peak runoff rate

61

General Use:

Rational Method

62

𝑄 = 𝑐𝑖𝐴Equation:

Q = peak flow(cfs)

c = rational runoff coefficient (dimensionless)

𝑖 = average rainfall intensity (in/hr)

A = drainage area basin (acres)

• Rational method runoff coefficient (c ) is a function of the soil typeand drainage basin slope

• See Table 5-3 for runoff coefficients

Rational Method

63

Table 5-3:c , Runoff Coefficients

New Jersey Department of Environmental Protection, Land Use Management Program. 1988. Technical Manual for Land Use Regulation Program, Bureau of Inland and Coastal Regulations, NJDEP Flood Hazard Area Permits

Rational Method Equation

64

NOAA’s National Weather Service

Precipitation Frequency Data Server (PFDS)

𝒊 = rainfall intensity

Rational Method EquationIDF Curve

65

𝒊=

ra

infa

ll in

ten

sity

66

NJDEP 1.25-Inch/2-Hour WQDS Intensity-Duration Curve

Minimum Time of Concentration = 10 minutes when using the Rational Method

3.2

Any Questions?

Stormwater Management UnitBureau of Flood Hazard and Stormwater Engineering

Watershed Engineering ElementDivision of Watershed Protection and Restoration

401 East State Street

PO Box 420, Mail Code 401-2B

Trenton, NJ 08625-420

Tel: 609-633-7021

www.njstormwater.org

Anthony [email protected]

Lisa [email protected]

67

http://www.njstormwater.org/

Changi Wu

NJDEP Division of Watershed Protection and Restoration

SWMDR Training Module 2

October 7, 2021

SOIL

TESTING

Soil Testing

• Not only infiltration BMPs need soil test

• Soil Testing is used to determine:

o Hydrologic Soil Group (HSG)

o Seasonal High Water Table (SHWT)

o Saturated soil hydraulic conductivity for BMP calculations and groundwater mounding analysis

o Soil series for groundwater recharge (annual recharge spreadsheet)

2

Soil Testing – What?

Soil Testing for HSG

1. NRCS Web Soil Survey

2. Default Method

3. HSG Testing Method

3

Methods to Identify HSGs:

In coastal plain:

Pre-developed: HSG A

Post-developed: HSG D

Outside coastal plain:

Pre-developed: HSG B

Post-developed: HSG D

1b: Default Hydrologic Soil Groups:Default Method for Identifying HSG

• NJDEP BMP Manual Chapter 12:

8

Physiographic Provinces of

New Jersey




Soil Testing for Determining HSG

• Soil testing can be used to determine HSG

• HSG depends on:

o Saturated hydraulic conductivity (Ksat)

o Depth to impermeable layer

o Depth to seasonal high water table

9

Ch. 12 Subsection 1c: HSG Testing Procedures


• Number of required soil tests depends on

size of soil mapping unit:

10

HSG Testing Procedures (cont’d.)

Soil Mapping

Unit Size (Acres) # of Soil Profile Pits # of Soil Borings

X < 0.5 1 1

0.5 ≤ X ≤ 2 1 4

X > 21 + (1 per each add’l.

2 Acres)

4 + (2 per each add’l.

2 Acres)


11


Example: Soil Profile Pits and Soil Boring Locations

(2 Acres)

(2 Acres)

(2 Acres)

Soil Mapping UnitOf Unknown Soil #1

(2 acres)

(2 acres)

Soil Mapping Unit Of Unknown Soil #2 (6 acres)

(2 acres) (2 acres)


• Required profile pit and boring depths:

o At least 40 inches below existing grade, except when the SHWT is at a depth of 24 inches or less

o If SHWT is at a depth of 24 inches or less, the exploration may be terminated before excavation to the depth of 40 inches below existing grade and the soils are classified as HSG ‘D’

12


Source: NRCS


• Perform test for saturated hydraulic conductivity of the most restrictive soil layer above the impermeable soil layer

• Determine the depth to the seasonal high water table

13


Source: NRCS

14


NRCS National Engineering

Handbook, Part 630 –

Hydrology (NEH), Chapter 7

Hydrologic Soil Groups,

January 2009, available at:

https://www.wcc.nrcs.usda.gov/ftpref/w

ntsc/H&H/NEHhydrology/ch7.pdf

https://www.wcc.nrcs.usda.gov/ftpref/wntsc/H&H/NEHhydrology/ch7.pdf


15

Soil Testing Depth

Source: NRCS


Sample Soil Log

Soil Testing for Infiltration BMPs

• For infiltration BMPs

o Minimum of two soil profile pits within the infiltration area of any proposed BMP and

o One additional profile pit for every additional 10,000 sf

16

Number and Location

What soil information is required for infiltration BMPs

• Saturated hydraulic conductivity

• Depth to seasonal high water table


17

Soil Profile Pit Locations for Infiltration BMPs

100 ft

100 ft 100 ft 50 ft


• One or multiple infiltration BMPs including small-scale GI BMPs or dry wellso One soil profile pit for each soil mapping unit where

the multiple BMPs are located, plus

• Each equal to or less than 500 sfo One soil boring at each BMP

• Each greater than 500 sfo Two soil borings at each BMP

• Small-scale GI BMPs located linearlyo One soil boring at each BMP ando One soil profile pit for every 2000 ft

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Number and Location (cont’d.)


Per soil mapping unit

# of

Soil Pit(s) Soil Boring

First 500 feet 1 -------

Additional 2000 feet 1 1 boring per 500 linear feet

19

Soil Tests for Linear Infiltration BMPs

• Infiltration area length to width ratio ≥ 4:1,

• Bottom width is 25 feet or less, and

• Top width is 40 feet or less


20

Figure 12-4: Soil Exploration Locations for Linear Infiltration BMPs


21

Soil Hydraulic Conductivity Tests –

No Soil Replacement

• Perform the test on the most hydraulically restrictive soil layer below BMP and above SHWT or bedrock:

o To the greater of:

• 8 feet below lowest point of basin or

• 2 times the maximum water depth


22

Soil Hydraulic Conductivity Tests –

Soil Replacement

• Perform the test on the most hydraulically restrictive soil layer below the depth of soil replacement and above SHWT or bedrock:

o To the greater of:

• 8 feet below lowest point of basin or

• 2 times the maximum water depth

Soil Testing for Determining Soil Hydraulic Conductivity

• Tube Permeameter Test

• Percolation Test

• Cased borehole infiltration test

• Single ring infiltration test

• Basin flooding test (for bedrock)

• ASTM D 3385 Double-Ring infiltrometer

• USBR 7300-89 Well permeameter

• Soil hydraulic conductivity tests that utilize in-situ conditions and are accompanied by a recognized published source reference

23

Acceptable hydraulic conductivity tests:

Soil Testing for Determining Saturated Soil Hydraulic Conductivity

24

Acceptable hydraulic conductivity tests:

• When performing a soil boring during the soil exploration, the soil borings must be performed and reported in accordance with ASTM D 1452 -Practice for Soil Investigation and Sampling Auger Borings and ASTM D 1586 - Test Method for Penetration Test and Split-Barrel Sampling of Soils

• Sampling must be continuous for the entire depth of the soil boring to fully characterize the soil profile

Hydraulic Conductivity Testing

25

Test procedures available in BMP Manual Ch. 12

Hydraulic Conductivity Testing

26

The field measured hydraulic conductivity value shall be calculated as follows:

Percolation Test

Although the test step 4b in the test procedure for a percolation test in Chapter 12 requires water be filled to a depth of 7 inches, the time recording shall be started at when the water level drops to 6 inches and stopped when the water in the hole has emptied

where:

pm is the percolation rate (min/in),

𝑑 is the diameter of the test hole (in)

𝑎 is calculated as shown in Table 12-9

Soil Testing for Seasonal High Water Table

• Observation of redoximorphic features of soil mottling

o Any season of the year

• Direct observation of SHWT

o January – April oro From the NRCS Web Soil Survey, provided that the soil

series present at the site is identified based upon a comparison of the soil profile morphology observed within a soil profile pit and the soil profile description provided for the soil series in question within the NRCS Web Soil Survey.

27

N.J.A.C. 7:9A-5.8 Criteria for recognition of zones of saturation

Soil Testing

• Constructiono Pre-construction meetingo Minimize compactiono Testing each layer where hydraulic conductivity is critical

before adding a new layer

• Post-Constructiono Number of tests same as pre-construction testo Hydraulic conductivity test on the bottom of the

excavation of the BMP before sand or soil bed is placedo Only single ring, double ring, basin flooding test are

allowed

28

Chapter 12 Construction and Post-Construction

Soil Testing

• Web soil survey showing HSG

• Location of the soil profiles and/or soil borings

• Soil test logso Date of performing soil profile or boringo Elevation of existing ground levelo Depth of the soil profile or boringo Soil classifications and descriptionso Depth of the soil where the saturated soil hydraulic

conductivity test is performedo Observation of soil mottling showing redoximorphic features

or groundwater observation showing SHWT

• Hydraulic conductivity testing records

29

What should be submitted?

More Information:

30

Stormwater Management UnitBureau of Flood Hazard and Stormwater Engineering

Watershed Engineering ElementDivision of Watershed Protection and Restoration

401 East State Street

PO Box 420, Mail Code 401-2B

Trenton, NJ 08625-420

Tel: 609-633-7021

www.njstormwater.org

Changi [email protected]

http://www.njstormwater.org/

The New Jersey Corporation for

Advanced Technology (NJCAT)

Stormwater Manufactured Treatment Device (MTD) Verification/Certification

Program: An NJCAT/NJDEP Partnership

Dick Magee

NJCAT

P.L. 1999-Chapter 400

⚫ P.L. 1999-Chapter 400 is a public law approved on

January 18, 2000 to support the development and

promotion of innovative energy and environmental

technologies (IEETs) in New Jersey. The law, commonly

referred to as the Energy and Environmental Technology

Verification (EETV) Act, outlines the roles and

responsibilities of:

⚫ The State of New Jersey

⚫ NJDEP

⚫ NJCAT

Performance Partnership Agreement

⚫ A PPA between the NJDEP and NJCAT was adoptedon June 6, 2000. Some of the applicable directivesrelevant to the stormwater program are as follows:⚫ Allows for a process to achieve clarification of any NJDEP and

NJCAT interpretations of laws, rules, and regulations relatingto the review, selection and verification of a technology for theNJCAT verification program.

⚫ The NJDEP is required to consult and work with NJCAT todevelop performance evaluation and verification procedures,processes, and protocols for the purposes of:⚫ Determining the application and use of certain IEETs;

⚫ Studying, evaluating, and verifying the benefits of IEETs; and

⚫ Identifying beneficial and innovative technologies requiringassistance with regulatory pathways.

⚫ NJCAT is required to promote awareness of the EETVprogram to entities with technologies that are likely to beeligible for performance evaluation and verification.

USEPA Stormwater Compliance

⚫ States have adopted strategies and stormwater

management rules to directly address the adverse

impacts of stormwater runoff and to meet EPA

regulations.

⚫ Low Impact Development (LID) strategies seek to reduce

and/or prevent adverse runoff impacts through sound

site planning and both nonstructural and structural

stormwater management measures that are a subset of

practices and facilities known as Best Management

Practices or BMPs.

Best Management Practices

⚫ Manufactured treatment devices (MTDs) are a subset of

BMPs.

⚫ MTDs are proprietary, pre-fabricated stormwater treatment

systems that rely upon a variety of mechanisms to remove

pollutants from stormwater runoff.

⚫ MTDs utilize settling, filtration (organic/inorganic media),

absorptive/adsorptive materials, vortex separation, vegetative

components, and/or other appropriate technology to remove

pollutants from stormwater runoff.

New Jersey Stormwater

Management Rules at N.J.A.C. 7:8⚫ Require “major development” projects to remove 80% of

the project’s TSS runoff on an annual basis.

⚫ N.J.A.C. 7:8 requires use of Green Infrastructure (GI)BMPs, that manages stormwater close to its source by:⚫ Treating stormwater runoff through infiltration into the subsoil;

⚫ Treating stormwater runoff through filtration by vegetation or soil;or

⚫ Storing stormwater runoff for reuse.

⚫ N.J.A.C. 7:8 provides approved TSS removal rates forboth BMPs and MTDs.

⚫ TSS removal rates for manufactured treatment devices(MTDs) are verified by NJCAT and certified by NJDEP.

Technology Verification Program

⚫ NJCAT conducts an independent, third party evaluation program toverify the performance claims of IEET.

⚫ Program has strong national and international recognition.

⚫ Stormwater MTDs are evaluated against NJDEP Protocols:⚫ Hydrodynamic Separators (January 1, 2021). TSS removal-50%

⚫ Filtration Treatment Devices (January 25, 2013). TSS removal-80%

⚫ Stormwater MTDs NJCAT verified and NJDEP certified are the onlyMTDs that can be used to satisfy the requirements of the Stormwater Management rules (N.J.A.C. 7:8) for major developments.⚫ Hydrodynamic Separators – 18 (all have sunset dates)

⚫ Filtration Devices – 11

⚫ Green Infrastructure – 7

http://www.njstormwater.org/treatment.html

http://www.njstormwater.org/treatment.html

Debris Separating Baffle Box

Contech Filterra HC

Bio Clean SciClone

Misuse of Certifications

⚫ Not all NJCAT verified stormwater technologies are NJDEP

certified (different sediment PSD - larger D50).

⚫ This occurs primarily with HDS separators. Allows for a smaller unit.

All certified MTDs have been tested with the NJDEP sediment PSD.

⚫ Only 25% certified stormwater technologies are GI certified.

⚫ Only the HDS MTD configuration that was tested has been

NJDEP certified. Manufacturers will frequently offer other

configurations claiming certification. These include:

⚫ Inlet/outlet configuration that is not 180 degrees apart

⚫ Multiple inlet pipes, e.g.,two

⚫ Grate inlet

Misuse of Certifications

⚫ An MTD cannot be used in series with another MTD or a

media filter (such as a sand filter) to achieve an enhanced

removal rate for total suspended solids (TSS) removal

under N.J.A.C. 7:8-5.5.

Program Moving Forward

⚫ Implementation of the new HDS Protocol⚫ Based on sediment capture in the MTD. No longer will the

technology be credited with sediment deposited in the inlet pipe.

⚫ Manage the sunset of 7 technologies by 6/30/22.

⚫ All HDS technologies already certified or undergoing testingunder the 1/25/13 protocol will be required to undergo retestingwith the new protocol by 1/1/25.

⚫ New Filtration Protocol in 2021.

⚫ Role of Stormwater Testing and Evaluation for Productsand Practices (STEPP) initiative.

QUESTIONS

Module 2 of 4 Stormwater Management Design Review

Documents

Transcript of Module 2 of 4 Stormwater Management Design Review