TECHNICAL MEMORANDUM #11 TO: Applicants and Designers for

TECHNICAL MEMORANDUM #11

TO: Applicants and Designers for State and Federal Projects

FROM: Sediment and Stormwater Plan Review Division, Water and Science Administration

DATE: July 17, 2018

SUBJECT: Stormwater Management Spreadsheets – Instructions and Definitions of Terms

The Sediment and Stormwater Plan Review Division has developed computational spreadsheets for

State and federal applicants and their designers to calculate a project’s stormwater management

requirements. These spreadsheets follow the process presented in Technical Memorandum #10

Stormwater Management Overview. The purpose of the spreadsheets is to reduce the time and

money spent by both designers and reviewers assessing a project’s requirements and to “get

everyone on the same page.” Every attempt was made to simplify the process while adhering to

regulatory requirements. Unfortunately, the very issues that have given cause for question and

resulted in varying interpretations of the stormwater regulations have also produced multifaceted

computations, which upon first glance, may appear overly complicated. Please understand that

many of the nuances addressed by the spreadsheets will not apply to the majority of projects and are

easily skipped over, but the steps and computations are built-in regardless, for use with the

complicated projects – the ones with dozens of points of investigation, shifts in drainage areas,

existing management, loss of existing water quality, partial waivers, etc.

All projects, except those exclusively eligible for a waiver in accordance with Section 3.3.A of the

Guidelines, will be required to use these spreadsheets. Projects that are exclusively MS4 restoration

only need to use the Provided Treatment Summary. Projects that are exclusively demolition only

need to use the Water Quality Summary Sheet. There will be a three month grandfathering

period for this requirement from issuance of this memorandum. Electronic copies of the

spreadsheets are available on MDE’s website at

http://mde.maryland.gov/programs/water/StormwaterManagementProgram/Pages/PlanReviewforStat

eandFederalProjects.aspx

Instructions and definitions of terms are provided herein for four spreadsheets:

I. Stormwater Management (SWM) Calculator…………………………………pages 2 - 9

II. Environmental Site Design Summary Sheet (ESDSS)………………….......pages 10 - 14

III. Water Quality Summary Sheet (WQSS)……………………………………pages 15 - 19

IV. Provided Treatment: Achieved P

, Treated ESDv, and Treated Re

…...…...…page 20

For reference,

BMP is best management practice.

ESD is environmental site design.

ESDv is ESD volume.

IART is impervious area requiring treatment.

LOD is limit of disturbance.

POI is point of investigation/ LOI is line of investigation.

SWM is stormwater management.

July 2018 Technical Memo #11 Page 2 of 21

I. SWM Calculator – Instructions and Definitions of Terms

The SWM Calculator is to be completed for each point of investigation (POI), line of investigation,

or sub-drainage area identified in the SWM report (i.e. one spreadsheet per POI/LOI). Print outs

should be included in the concept design report and then updated for the final design report.

This spreadsheet was made compatible for Microsoft Excel 97-2003 and newer. It was created in

Microsoft Excel 2016 and tested in multiple versions. It utilizes macros to eliminate the need for

repetitive calculations and formatting by the user. When opening the file, a message will appear

below the tool bar that reads “Security Warning Macros have been disabled. Options…” Click on

“Options” and then “Enable this content.”

The SWM Calculator has two sheets: the Development Category Sheet and the ESDv Sheet. The

development category needs to be determined first. Depending on level of existing imperviousness,

the point of investigation will be categorized as either “redevelopment” or “new development”. This

classification affects the level of management required for reconstruction activities and decides

which set of calculations will be used by the ESDv Sheet to determine the stormwater management

requirements. It is important to note that a both sheets need to be completed for each POI and that

care be taken not to skip the Development Category Sheet.

A. Development Category Sheet (establishes development classification)

1. The turquoise cells in the Development Category Sheet serve as a user guide by providing

instructions and defining terms used within the sheet. These cells, along with the “Clear Input

Cells” and “Re/New Development ESDv” button, will not print. The yellow cells are input

cells to be completed by the designer. To clear all input cells, click the “Clear Input Cells”

button.

2. “Project Description”, “Point of Investigation”, “Job #”, “Contract #”, “Date”, and “Designed

by” are to be completed by the designer.

3. “MDE #” will be assigned by the MDE reviewer. After the initial submittal this number

should be typed in by the designer following the 00-SF-0000 format.

4. “Reviewed by” is written in by the MDE reviewer.

5. The entries for “Project Description”, “Point of Investigation”, “Job #”, “Contract #”, “Date”,

“Designed by”, “MDE #”, and “Reviewed by” will automatically carry over to the ESDv

sheet.

6. “County” is chosen from the drop down provided. This data is for informational purpose and

does not affect calculations.

7. “SWM Study Area, A

” is the boundary area for determining the development classification.

It typically corresponds to the LOD draining to the point of investigation under existing

conditions but could also be the property area, the site area, or the right-of-way. Refer to

Technical Memorandum #10 for a detailed discussion on the SWM Study Area.

8. “Existing Impervious Surface Area, A

EXi

” is the pre-development impervious area within

the corresponding SWM Study Area.

9. “Percent Existing Imperviousness, %I” is calculated by the spreadsheet. This percentage

is used to asses on which side of the 40% threshold the POI falls. If I>40%, then the

reconstructed areas are considered “redevelopment.” If I≤40%, then the reconstructed areas

are considered “new development” and need to be managed accordingly. “Development

Classification for Reconstruction” will auto populate based on the %I, and the reconstruction

will be classified as either “re-development” or “new development.” Record this value in

July 2018 Technical Memo #11 Page 3 of 21

Column D of the Water Quality Summary Sheet (WQSS).

10. Once data is input on this sheet, proceed to the ESDv Sheet by clicking the purple “Re/New

Development ESD

” button located on the right. Make sure that the development

classification is determined before clicking the button. The spreadsheet will then navigate to

the calculations for the respective development category. If revisions are made to the

Development Category Sheet after the ESDv Sheet has been completed, steps 1-10 of the

ESDv Sheet will update accordingly. It is possible to toggle between sheets without losing

the input.

B. ESDv Sheet (calculates the IART and the ESDv requirements for the POI)

The entries for “Project Description”, “Point of Investigation”, “Job #”, “Contract #”, “Date”,

“Designed by”, “MDE #”, and “Reviewed by” will automatically carry over to the ESDv sheet.

The yellow cells are input cells to be completed by the designer. To clear all input cells, click the

“Clear Input Cells” button on the Development Category Sheet. Calculations that do not apply

for the respective development category are made inactive, struck through, or printed with a

result of 0. All Steps within this tab will print.

Step 1 – Site/ Drainage Area Data. The user inputs the data as follows:

• Existing Condition Drainage Area - A

: the area that comprises the total drainage

area to the POI in pre-development conditions. This data is for informational

purposes and does not affect calculations.

• Proposed Condition Drainage Area - A

: the area that comprises the total drainage

area to the POI in post-development conditions. This data is for informational

purposes and does not affect calculations.

• Existing Impervious Area within LOD - A

: the pre-development impervious area

within the LOD within the existing drainage area to the POI. This includes all

pavement and roof-top including maintenance and access areas in A

. Record this

value in Column B of the WQSS.

• Proposed Impervious Area within LOD - A

: the post-development impervious

area within the LOD within the proposed drainage area to the POI. This includes all

pavement and roof-top including maintenance and access areas in A

. Alternative

surfaces should be included in this value. They will also need to be listed as

treatment practices. This way they can be tracked. Record this value in Column C of

the WQSS.

Note: A

is based on the existing drainage area, and A

is based on the proposed

drainage area. This will allow a correct assessment of management requirements

should the drainage area divide shift from existing to proposed conditions. However,

if the drainage area shift involves impervious area outside the LOD, it needs to be

accounted for in A

SHIFT

below.

• Area for which WQ is Not Required (i.e. 3.3.A Waiver) - A

: any impervious

surface within the LOD for which management is not required. This includes existing

impervious areas that are considered maintenance or that qualify for a 3.3.A waiver.

It may also include impervious surfaces shown within the LOD that are part of the

work area but are being left intact or are generally not considered to be a disturbance.

Examples of this include milling/resurfacing areas as well as taxiways, roads, or

parking lots being traversed for access or used for staging. Any area included in this

July 2018 Technical Memo #11 Page 4 of 21

column must also be included in A

and A

. Record this value in Column E of the

WQSS.

• Loss of Existing Water Quality (Area) - A

: the existing impervious area that is

losing water quality benefits due to the removal of an existing water quality BMP or

other water quality feature, such as an alternative surface or non-structural practice,

previously approved by MDE or due to the removal of an existing pond with water

quality features as described in Chapter 5 of the 2000 Maryland Stormwater Design

Manual. Lost water quality must be re-cooped. Therefore, this deficit is added to the

IART. Record this value in Column F of the WQSS.

Notes:

(1) If the treated P

is less than 1.0 inch, this value must be pro-rated to reflect the

effective treatment area. For example, a BMP that treats 0.5 acres of impervious for a

of 0.7 inch has an effective impervious treatment area of 0.35 acre.

(2) If previously treated impervious area is removed along with the water quality

feature, the result is considered a “wash”. If previously treated impervious area is

removed, but the water quality feature or BMP is not physically being removed, the

result is also considered a “wash” because the treatment is effectively lost since there

is no impervious area to be treated. These equivalent scenarios can be reflected by

recording the impervious area that was previously treated and is now being removed

in both A

and A

RECi

• Loss of Existing ESD

(Volume) - ESD

V Loss

: the ESD volume lost due to the

removal of an existing water quality BMP, alternative surface, or non-structural

practice previously approved by MDE or the removal of a pond that provides water

quality features as described in Chapter 5 of the 2000 Maryland Stormwater Design

Manual. If the previously treated impervious area is removed along with the water

quality feature, there is no loss of existing ESDv. The designer needs to provide

separate computations supporting this volume.

• Loss of Existing Recharge

(Volume) - Re

Loss

: the recharge volume lost due to the

removal of an existing water quality BMP, alternative surface, or non-structural

practice previously approved by MDE or the removal of a pond that provides water

quality features as described in Chapter 5 of the 2000 Maryland Stormwater Design

Manual. If the previously treated impervious area is removed along with the water

quality feature, there is no loss of existing Re

. The designer needs to provide

separate computations supporting this volume.

• Reconstructed Impervious Area Already Treated

(Area) - A

RECi

: the existing

impervious area within the LOD that in existing conditions drains to a functioning

water quality practice. A value in this box indicates that the treatment practice will

remain operative and will continue to treat the specified amount impervious area after

the area has been reconstructed. The entered value reflects the full treated acreage

without any adjustments for redevelopment. The IART is reduced by either 50% or

100% of this value depending on whether the development is classified as

redevelopment or new development. Record this value in Column G of the WQSS.

Notes:

(1) If previously treated impervious areas are being removed, those areas need to be

included in A

RECi

as well A

(2) If the treated P

is less than 1.0 inch, this value must be pro-rated to reflect the

effective treatment area. For example, a BMP that treats 0.5 acres of impervious for a

of 0.7 inch has an effective impervious treatment area of 0.35 acre.

July 2018 Technical Memo #11 Page 5 of 21

(3) There is a potential for overlapping areas in A

and A

RECi

. If maintenance or

utility work is being performed on an existing impervious surface that already has

water quality treatment, include this area only in A

• Existing Impervious Area outside of LOD Shifted in/out of POI - A

SHIFT

: the

impervious area outside of the LOD that is shifted into or out of the POI from existing

to proposed conditions. This can occur when a storm drain system that collects

runoff from outside the LOD is modified as a result of the proposed project. A

positive number indicates impervious area shifted into the POI from existing to

proposed conditions, and a negative number indicates impervious area shifted out of

the POI from existing to proposed conditions.

• Will POI Qualify for Cp

Waiver under Section 3.3.B of the Guidelines? - Cp

This is a YES/NO input. It is set to a default value of “NO” and requires user input to

change the field if the POI qualifies for a 3.3.B waiver. ESD volume requirements

are reduced to a P

of 1.0 inch when the POI qualifies for a 3.3.B waiver. “YES”

should also be selected if a variance from Cpv has been requested and granted by

MDE. For POIs that are classified as redevelopment and have ΔA

≤ 0, this box is

irrelevant.

Step 2 – Determine the Impervious Area Requiring Treatment (IART):

This step calculates the IART based on the development classification and the input

from Step 1. Many projects involve a combination of redevelopment and new

development. The portion of IART that comes from redevelopment and the portion

that comes from new development are calculated and then totaled.

IART from Redevelopment (IART

RE-DEV’L

When the POI is classified as redevelopment, IART

RE-DEV’L

is calculated based on the

equation shown and the input from Step 1.

When the POI is classified as new development, IART

RE-DEV’L

will be inactive and set

to a value of zero.

Record this value in Column 1 of the ESDSS. This value should match Column I of the

WQSS.

IART from New Development (IART

NEW

When the POI is classified as redevelopment, IART

NEW

is calculated based on the

equation shown and the input from Step 1.

When the POI is classified as new development, IART

NEW

is calculated based on the

equation shown and the input from Step 1.

Record this value in Column 3 of the ESDSS. This value should match Column J of the

WQSS.

Total IART:

The total IART is the sum of IART

RE-DEV’L

and IART

NEW

and A

This value should match Column K of the WQSS.

July 2018 Technical Memo #11 Page 6 of 21

Steps 3 through 8 calculate the required ESDv. There is an ESDv requirement for the project

and an ESDv requirement for the POI. The ESDv for the project is calculated by the ESDSS

based the SWM Calculator’s step-by-step breakdown of each POI. The required ESDv for the

project is the sum of the ESDv from redevelopment and the ESDv from new development with

adjustments made as necessary for 3.3.B waivers, shifts in drainage areas, and loss of existing

water quality.

When the reconstruction is classified as redevelopment (Redevelopment POI) and there is a

decrease in impervious area (ΔAi<0), the computational structure is as follows:

When the reconstruction is classified as redevelopment (Redevelopment POI) and there is an

increase in impervious area (ΔAi≥0), the computational structure is as follows:

When the reconstruction is classified as new development (New Development POI), the

computational structure is as follows:

The required ESDv for the POI is a function of the amount of new development proposed within

the respective POI only. The Regulations require that new development be managed for channel

protection volume (Cpv), and channel projection volume, like other forms of quantity

management, can only be managed within the impacted drainage area and POI. The required

ESDv for the POI also takes into consideration whether the POI qualifies for a 3.3.B waiver, has

a shift in drainage area from outside the LOD, or experiences a loss of existing water quality.

Step-by-step instructions continue below:

PROJECT

ESD

VRE-DEV’L

based on

IART

RE-DEV’l

and P

=1.0 in

(step 3)

ESD

VNEW

based on

IART

NEW

and P

=1.0 in

*negative number

(step 4)

ESDv for

impervious

area shifted

into/out of

POI from

outside the

LOD

(step 6)

ESDv from

loss of

existing

water

quality

(step 7)

PROJECT

ESD

VRE-DEV’L

based on

IART

RE-DEV’l

and P

=1.0 in

(step 3)

ESD

VNEW

based on

IART

NEW

and P

=2.0 to

2.6 in or in case

of 3.3.B waiver

=1.0 in

(step 5)

ESDv for

impervious

area shifted

into/out of

POI from

outside the

LOD

(step 6)

ESDv

from loss

of existing

water

quality

(step 7)

PROJECT

ESD

VNEW

based on

IART

NEW

and P

=2.0 to

2.6 in or in case

of 3.3.B waiver

=1.0 in

(step 5)

ESDv for

impervious

area shifted

into/out of

POI from

outside the

LOD

(step 6)

ESDv from

loss of

existing

water

quality

(step 7)

July 2018 Technical Memo #11 Page 7 of 21

Step 3 – Determine the Required Environmental Site Design Volume for treating

Redevelopment (ESD

VRE-DEV’L

This step calculates the portion of the required ESDv that is attributed to the

redevelopment portion of the proposed development. The rainfall depth, P

, required to

be treated for redevelopment is 1.0 inch. The required area to be treated is the IART

RE-

DEV’L

. Because IART

RE-DEV’L

is 100% impervious, Rv is always 0.95.

When the POI is classified as new development, ESDv

RE-DEV’L

will be inactive and set

to a value of zero.

Record this value in Column 3 of the ESDSS.

Step 4 – Determine the Environmental Site Design Volume Reduction from Decreasing

Impervious Area (ESDv

reducedAi

) for Redevelopment Classification when ΔA

< 0):

This step is active only when the POI is classified as redevelopment and there is a

reduction of impervious area from existing to proposed conditions (Ai<0). This

volume (which is equivalent to a negative IART

NEW

and ESDv

NEW

) is calculated

separately to illustrate the ESDv reduction that results from removing impervious area

as well as to allow appropriate assessment of the ESDv required at the POI. For POIs

that experience strictly impervious reduction, there is no ESDv requirement at the POI.

However, impervious reduction within the LOD can be accompanied by a shift in

drainage area from outside the LOD and/or a loss of existing water quality. The

reduction in impervious area can be used to offset the ESDv required from a shifted

drainage area or a loss of existing water quality. Therefore, the reduction, based on a

of 2.6 inches, represents the maximum offset available from the impervious

reduction. To simplify calculations and eliminate debates between designers and

reviewers, 2.6 inches is being used regardless of soil type.

Step 4.1 - Determine the ESD

V reduced Ai

Applied to Project:

This step calculates the ESD volume reduction based on 1.0 inch of P

and Ai

(IART

NEW

). This is always a negative volume and is credited towards the ESD volume

requirement at the project level. Record this value in Column 4a of the ESDSS.

Step 4.2 - Determine the ESD

V reduced Ai

Applied to POI:

This step calculates the ESD volume reduction based on 2.6 inch of P

and Ai

(IART

NEW

). This is always a negative volume and is credited towards the ESD volume

requirement at the POI level. Record this value in Column 4b of the ESDSS.

Step 5 – Determine the Required Environmental Site Design Volume for treating New

Development (ESD

V NEW

) for POI:

This step calculates the portion of the required ESDv that is attributed to the new

development portion of the proposed development. The rainfall depth, P

, required to

be treated for new development ranges from 2.0 to 2.6 inches depending on the soils.

The required area to be treated is the IART

NEW

. Because IART

NEW

is 100%

impervious, Rv is always 0.95. For POIs that qualify for a 3.3.B waiver, the required

is reduced to 1.0 inch.

Step 5.1 - Determine the ESD

V NEW

for 3.3.B Waiver:

This step is active only when the POI qualifies for a 3.3.B waiver and a value of “YES”

is selected for “Cp

” in Step 1. This step calculates the required ESD

V NEW

for a 3.3B

waiver based on the IART

NEW

and a P

= 1.0 inch. This value contributes to project

level ESDv requirements.

July 2018 Technical Memo #11 Page 8 of 21

If this step is active then Steps 5.2 and 5.3 will be inactive. Record this value in Column

5.a of the ESDSS.

Step 5.2 Determine Weighted P

This step is active when IART

NEW

> 0 and a 3.3.B waiver does not apply. This step

calculates the weighted P

to be used in Step 5.3. Input by the user is required in the

IART

NEW

column of the Weighted P

table. IART

NEW

entries should be representative

of the predominant Hydrologic Soil Group (HSG) within the LOD or the actual soil

breakup within the LOD. Where selection between two HSGs is required, use the more

conservative option. The user should enter the area on the respective row or rows. The

total IART

NEW

must equal the IART

NEW

calculated in Step 2.

Step 5.3 Determine the ESD

V NEW

for No Waiver or No Impervious Reduction

(∆A

≥ 0):

This step is active when IART

NEW

> 0 and a 3.3.B waiver does not apply. This step

calculates the ESD volume requirement based on the IART

NEW

and the weighted P

from Step 5.2. This value contributes to both the project and POI level ESDv

requirements. Record this value in Column 5.b of the ESDSS.

Note: If “?????” is shown in the ESD

V NEW

box, return to Step 5.2 to correct the

inconsistency in IART

NEW

between Step 5.2 and Step 2.

Step 6 - Determine the Required Environmental Site Design Volume for the Shifted

Impervious Area (ESD

V SHIFT

) in/out of POI:

This volume can be a positive or negative value. A positive number reflects the

required ESDv for the impervious area shifted into the POI from outside the LOD. A

negative number reflects the ESDv off-set for the impervious area shifted out of the

POI from outside the LOD. This value contributes to the ESDv requirements at both

the POI level and the project level. At the POI level, a positive value reflects the

required ESDv. At the project level, the required ESDv is





 

for all the

POIs. If an equivalent amount of impervious area is shifted both in and out for the

project, there will be no overall ESD

V SHIFT

requirement for the project.

If a POI has shifted impervious area into the POI, but the POI qualifies for a Cpv

waiver (despite the shift), the ESD

V SHIFT

is also waived, and this step will be inactive.

Record this value in Column 6 of the ESDSS.

Note: The net contribution of the ESD

V SHIFT

from all the POIs should be zero at the

project level if there are no Cpv waivers at any POI.

Step 7 - Determine the Required Environmental Site Design Volume from Loss of Existing

SWM (ESD

V Loss

No calculations are performed in this step. The value shown here is the ESD

V Loss

reported in Step 1 and based on separate computations by the designer supporting this

volume. It is a positive number and reflects the ESDv requirement due to the loss of an

existing water quality BMP or water quality feature. This value contributes to both the

project and POI level ESDv requirements. This step is always active. If there was no

input to the ESD

Loss

field in Step 1, this step

will report a value of zero. Record this

value in Column 7 of the ESDSS.

July 2018 Technical Memo #11 Page 9 of 21

Step 8 - Determine the Required Environmental Site Design Volume for the POI

(ESD

VPOI

This step calculates the total ESDv requirement for the POI. This spreadsheet only

calculates the required ESDv; treated ESDv is recorded on the ESDSS. This step is

always active. Record this value in Column 8 of the ESDSS.

Notes:

(1) This SWM Calculator only considers impervious area when calculating ESDv

requirements. Therefore, when there is an increase in the overall drainage area to the

POI from existing to proposed conditions, MDE will also require that the 1-year

discharge rate for proposed conditions not exceed the rate for existing conditions. This

will not be in an issue for minor increases in drainage area, but in the case of shifted

drainage area divides could necessitate additional management. When A

> A

, an

advisory message is given that reads, If “(A

-A

) > 0, provide separate calculations

demonstrating that the Proposed Condition 1-Year Discharge Rate (Q

) <= the

Existing Condition 1-Year Discharge Rate (Q

)”

(2) Apart from the requirements of this SWM Calculator for ESDv, the user is

reminded that the overbank and extreme flood protection management requirements

must also be met at the POI, namely 2-year, 10-year, and 100-year management as set

forth by the local approval authority. The necessary calculations are to be included in

the SWM report.

(3) A negative value results when there is a decrease in impervious area. When the

results of the SWM Calculator are entered into the ESDSS, Column 8 will re-calculate

the required ESDv for the POI and, if negative, will show value as zero.

Step 9 - Determine the Required Recharge Volume (Re

This step calculates the recharge volume requirement based on the Soil Specific

Recharge Factor and the IART

NEW

as well as any loss in existing recharge. This

recharge volume shall be satisfied at the project level.

Step 9.1 – Determine Weighted Soil Specific Recharge Factor (S):

The Weighted Soil Specific Recharge Factor Table will populate based on entries to the

Weighted P

Table in Step 5.2. This step is active when IART

NEW

> 0.

Step 9.2 – Determine the Required Recharge Volume (Re

V NEW

) for New

Development:

This step calculates the recharge volume requirement based on the Soil Specific

Recharge Factor from step 9.1 and the IART

NEW

. This step is active when IART

NEW

Step 9.3 – Determine Loss of Existing Recharge Volume (Re

V Loss

This step calculates the recharge volume requirement due to the loss of existing

recharge volume. This step is always active. If there was no input to the Re

v Loss

field in

Step 1, this step

will report a value of 0.0.

Step 9.4 – Determine Total Recharge Volume (Re

This step calculates the total recharge volume requirement that shall be satisfied at the

project level. This step is always active. If Steps 9.1 and 9.2 are inactive, and Re

v Loss

0, Re

will report a value of 0.0. Record this value in Column 10 of the ESDSS.

July 2018 Technical Memo #11 Page 10 of 21

Step 10 – Designer’s Notes:

This step is for any designer’s notes, including assumptions or descriptions of unusual

design circumstances. The maximum character limit is 600 characters.

Last Step – SAVE FILE!

The standard format of the SWM Calculator requires a separate file for each POI.

Avoid data loss by saving the Excel file under a name with POI number before entering

data for succeeding POIs. The condensed format spreadsheet records data for more

than one POI.

The SWM Calculator is available in standard format and condensed format. Both spreadsheets are

available on MDE’s website. The standard format is recommended for designers unfamiliar with the

SWM Calculator or for projects with only a few POIs. The condensed format uses the same process,

but rather than entering data from top to bottom through explained steps, data is entered from left to

right in a tabular format, resulting in a single sheet of data for multiple POIs.

July 2018 Technical Memo #11 Page 11 of 21

II. Environmental Site Design Summary Sheet (ESDSS) – Instructions

One ESDSS is to be completed per project or per 6-digit watershed in the case of projects that span

multiple watersheds. A print out should be included in the concept design report and then updated

for the final design report. The ESDSS is a compilation of the stormwater management

requirements for all the POIs based on the results of the SWM Calculator and is used to calculate the

overall ESDv requirement for the project. Additionally, it presents a summary of the proposed

BMPs.

This spreadsheet was made compatible for Microsoft Excel 97-2003 and newer. It was created in

Microsoft Excel 2016 and tested in multiple versions. It utilizes macros to eliminate the need for

repetitive calculations and formatting by the user. When opening the file, a message will appear

below the tool bar that reads “Security Warning Macros have been disabled. Options…” Click on

“Options” and then “Enable this content.”

User Instructions:

1. A maximum of twenty POI entries are permissible in the spreadsheet. If the project consists

of more than twenty POIs, please contact the Plan Review Division for an appended

spreadsheet. Calculations are performed at the top of the spreadsheet so for projects having

fewer POIs, set the print area to exclude the blank POI fields. The spreadsheet is set up with

five rows per POI for water quality practices, but BMP rows can be deleted or added as

necessary by moving cursor to left hand column with row numbers and right clicking.

2. All user entries must be entered sequentially, working from the left to the right of the

spreadsheet.

3. All yellow cells in the spreadsheet are the input cells. Cells will turn grey when they do not

apply.

4. Data validations are present within this spreadsheet. If data entry is not consistent with data

entry provided in the spreadsheet, an error message will appear and alert the user about the

inconsistency is causing the error.

ESDVSS Column Descriptions and Instructions

Required ESD Management

Point of Investigation

Enter the number associated with the POI, LOI, or sub-drainage area in the SWM report. A

given POI will require more than one row if there are multiple treatment practices in the

associated drainage area.

Column 1 - IART

RE-DEV’L

Enter the IART from Redevelopment as computed in Step 2 of the SWM Calculator. The

spreadsheet calculates the total IART

RE-DEV’L

for the project at the top of the column.

Column 2 - IART

NEW

July 2018 Technical Memo #11 Page 12 of 21

Enter the IART from New Development as computed in Step 2 of the SWM Calculator.

Note that if IART

NEW

> 0, then column 4a and 4b will be grayed out and unavailable for

input. The spreadsheet calculates the total IART

NEW

for the project at the top of the column.

Column 3 - ESD

V RE-DEV’L

= 1.0 in)

Enter the Required ESD Volume for Treating Redevelopment as computed in Step 3 of the

SWM Calculator. This value is based on 1.0 inch of P

and IART

RE-DEV’L

. The spreadsheet

calculates the total Required ESDv

RE-DEV’L

for the project at the top of the column.

Column 4a - ESD

V reducedAi

Reduction Applied to Project (P

= 1.0 in)

Enter the ESDv Reduction Applied to the Project from Decreasing Impervious Area as

computed in Step 4.1 of the SWM Calculator. This value represents the ESD volume

reduction based on 1.0 inch of P

and Ai (IART

NEW

). It is always a negative number and is

credited towards the ESD volume requirement at the project level. The spreadsheet

calculates the total ESD

V reducedAi

Reduction for the project at the top of the column.

Column 4b - ESD

V reducedAi

Reduction Applied to POI (P

= 2.6 in)

Enter the ESDv Reduction Applied to the POI from Decreasing Impervious Area as

computed in Step 4.2 of the SWM Calculator. This value represents the ESD volume

reduction based on 2.6 inch of P

and Ai (IART

NEW

). It is always a negative number and is

credited towards the ESD volume requirement at the POI level.

Column 5a - ESD

V NEW

for 3.3.B Waiver (P

= 1.0 in)

Enter the Required ESDv for Treating New Development when the POI qualifies for a 3.3.B

Waiver as computed in Step 5.1 of the SWM Calculator. This value is based on 1.0 inch of

and IART

NEW

. This value contributes to the required ESDv at the project level. Note that

if there is an entry in this field then there cannot be an entry in Column 5b. The spreadsheet

calculates the total required ESD

V NEW

for 3.3.B waivers for the project at the top of the

column.

Column 5b - ESD

V NEW

= 2.0 to 2.6 in)

Enter the Required ESDv for Treating New Development when there is No Waiver or No

Impervious Reduction as computed in Step 5.3 of the SWM Calculator. This value is based

on a weighted P

ranging from 2.0 inches to 2.6 inches and IART

NEW

. This value contributes

to the required ESDv at the POI level. Note that for there to be an entry in this field, Column

2 must be greater than zero and Column 5a cannot have an entry. The spreadsheet calculates

the total required ESD

V NEW

for the project at the top of the column.

Column 6 - ESD

V SHIFT

= 2.6 in)

Enter the ESD Volume for the Shifted Impervious Area in/out of POI from outside the LOD

as computed in Step 6 of the SWM Calculator. This value is based on the impervious area

shifted into or out of the drainage area to the POI and a P

of 2.6 inches. A positive number

reflects existing impervious shifted into the POI, a negative value reflects existing

impervious shifted out of POI. This value contributes to the required ESDv at both the POI

and project levels. The spreadsheet calculates the total ESD

V SHIFT

for the project at the top

of the column.

Column 7 - ESD

V Loss

Enter ESD Volume from Loss of Existing SWM as computed in Step 7 of the SWM

Calculator. It is a positive number and contributes to the required ESDv at both the POI and

project levels. The spreadsheet calculates the total ESD

V Loss

for the project at the top of the

column.

July 2018 Technical Memo #11 Page 13 of 21

Column 8 – Required ESD

for POI

This column is calculated by the spreadsheet and is the sum of the corresponding fields in

Columns 4b, 5b, 6, and 7. It should be the same value as the Required ESDv for the POI as

computed in Step 8 of the SWM Calculator. If the result of Step 8 is a negative value, there

is no POI level requirement and zero will be recorded. If the values do not match Step 8 of

the SWM Calculator, check for input errors in the ESDSS.

Column 9 – Required ESD

for the Project

This field is calculated by the spreadsheet and is the sum of Columns 3, 4a, 5a, 5b, 6, and 7.

This is the total ESD volume requirement for the project resulting from the work proposed in

all the POIs collectively. The project requirement will govern the needed level of

management when quality management is provided outside the POI for POIs that have no

quantity management requirements because there is redevelopment or a 3.3.B waiver.

Column 10 – Required Re

Enter the Required Recharge Volume as computed in Step 9.4 of the SWM Calculator. This

is a positive number and is a function of IART

NEW

and any loss of existing Re

. The

spreadsheet calculates the total Required Re

for the project at the top of the column.

Provided ESD Management

Column 11 – Type of Practice

From the fly down, select the type of SWM practice being proposed. This can include

alternative surfaces, non-structural practices, and micro-scale practices from Chapter 5 of the

SWM Manual as well as various types of Chapter 3 practices and innovative technologies as

allowed by MDE. A given POI/LOI will require more than one row if multiple treatment

practices are being proposed within the associated drainage area. The spreadsheet is set up

with five rows per POI for water quality practices, but BMP rows can be deleted or added

as necessary.

Column 12 – BMP number

Enter the BMP identification number as assigned by the designer or the applicant.

Column 13 – P

Treated by Practice

Enter the amount of rainfall (P

) treated by the practice listed in Column 11. This value

should be calculated using MDE’s spreadsheet “Provided Treatment: Achieved P

and

Treated ESDv” or an equivalent. Any value other than 1.0 inch will automatically update to

a text color of red. This value is limited to the rainfall level for the 1-year storm in the

respective county and the spreadsheet will not accept a value larger than 3.0 inches.

Column 14 – Provided ESD

Enter the ESD volume that the respective practice is treating. This value should be

calculated using MDE’s template spreadsheet “Provided Treatment: Achieved P

and

Treated ESDv” or an equivalent. This value is governed by either the drainage area to the

facility or the physical storage provided within the facility, whichever is more limiting. For

ESD filtering practices that are required to store only 75% of the ESDv, the treated ESDv is

the provided surface storage divided by 0.75 (assuming physical storage, not drainage area, is

the limiting parameter). The spreadsheet calculates the total Provided ESD

for the project at

the top of the column.

Note that if it is not practicable to provide the entire ESD volume in ESD practices and

instead structural practices are used to provide Cpv (i.e. for P

above 1 inch), the designer

July 2018 Technical Memo #11 Page 14 of 21

needs to demonstrate how Cpv management is being met. If the structural practice is a

Chapter 3 water quality enhancing practice, the practice can use the remaining required ESD

volume as the design water quality volume. If the proposed structural practice is without

water quality features (i.e. dry extended detention), the designer must demonstrate through

separate calculations that Cpv management is being met in accordance with Appendix D.11

of the SWM Manual.

Column 15 – ESDv from WQ Bank Debit

For projects that are satisfying water quality and IART by debiting the Water Quality Bank,

the associated ESDv may be credited towards meeting the ESDv requirement at the project

level. The WQ Bank may not be used to meet ESDv requirement at the POI level. This

entry requires that the WQSS first be completed. If a debit is not being made to the WQ

Bank, input either zero or leave cell blank. Otherwise, calculate the input value as ESDv

BANK

= (1.0 in)(0.95)(debit in acres)(43,560 sf/ac)/12 in/ft.

Column 16 – Provided Re

Enter the recharge volume that the respective practice is providing. The spreadsheet

calculates the total Provided Re

for the project at the top of the column.

ESD

and Re

Requirements

ESDv Project Requirement and Provided ESD

Check

This check is calculated by the spreadsheet. If the ESD

provided at the project level > the

ESD

required at the project level, a “CHECK: OK” will print. If the ESD

provided at the

project level < the ESD

required at the project level, a “CHECK: FAIL” will print and a red

ALERT will be given that additional management is necessary. If a variance is being granted

by MDE for the POI or project due to exceptional circumstances, additional management

may not be necessary.

Project Requirement and Provided Re

Check

This check is calculated by the spreadsheet. If the Re

provided at the project level > the Re

required at the project level, a “CHECK: OK” will print. If the Re

provided at the project

level < the Re

required at the project level, a “CHECK: FAIL” will print and a red ALERT

will be given that additional management is necessary. If a variance is being granted by

MDE for the POI or project due to exceptional circumstances, additional management may

not be necessary.

Is the POI Requirement met?

This check is calculated by the spreadsheet. If the ESD

provided at the POI level > the

ESD

required at the POI level, a “Provided ESD

at POI x cf >= y cf” and “YES” will

populate this field. If the ESD

provided at the POI level < the ESD

required at the POI

level, a “Provided ESD

at POI x cf < y cf” and “NO” will populate this field. Also, a red

ALERT will be given if additional management at the POI is necessary. If a variance is being

granted by MDE for the POI due to exceptional circumstances, additional management may

not be necessary.

July 2018 Technical Memo #11 Page 15 of 21

III. Water Quality Summary Sheet (WQSS) – Instructions

The WQSS was originally developed as an accounting ledger for the Water Quality Bank and was

previously only required for projects that were crediting or debiting the Bank.

As part of this new

initiative, every project (except 3.3.A waivers and MS4 restoration projects) will need to complete a

WQSS. One WQSS is to be completed per project or per 6-digit watershed in the case of projects

that span multiple watersheds. Note that for applicants with multiple banks based on watershed, a

separate water quality summary sheet is required for each watershed affected by the project. A print

out should be included in the concept design report and then updated for the final design report.

The WQSS is a compilation of the water quality requirements for all the POIs based on the results of

the SWM Calculator and is used to calculate the overall IART requirement for the project (or

watershed). Additionally, it presents a summary of the proposed BMPs.

This spreadsheet was created in Microsoft Excel 2007 and tested in multiple versions. It utilizes

macros to eliminate the need for repetitive calculations and formatting by the user. When opening

the file, a message will appear below the tool bar that reads “Security Warning Macros have been

disabled. Options…” Click on “Options” and then “Enable this content.”

The yellow cells are input cells to be completed by the designer. To clear all input cells, click the

“Clear Input Cells” button. All Steps within this tab will print.

User Instructions:

1. The spreadsheet is configured for a maximum of eighty rows of data. Please use multiple

spreadsheets if the project requires more than eighty rows. Entry rows can be shown or

hidden by clicking on the (+) or (-) along the left hand column. Calculations are performed

at the top of the spreadsheet so for projects using fewer rows, set the print area to exclude the

blank rows.

2. Either POI data or BMP data can be entered on a row. The POI entry should be the top row

with the BMPs listed below the respective POI. The first BMP in the group can be entered

on the same row as the POI data. Repeat this for all the POIs. The format should mirror the

ESDSS.

3. All user entries must be entered sequentially, working from the left to the right of the

spreadsheet.

4. All yellow cells in the spreadsheet are the input cells.

In the early 1990s, the Plan Review Division developed a banking system for the State Highway

Administration in which the currency was impervious area. In the decade that followed, banks were

established for other State and federal applicants through a formal Memorandum of Agreement.

Additionally, MDE has been operating informal banks with some applicants. At present twelve

federal installations and twelve state institutions have water quality banks. For more information on

the Water Quality Bank and the terms of the banking agreement, contact Amanda Malcolm

[email protected] .

July 2018 Technical Memo #11 Page 16 of 21

WQSS Column Instructions and Descriptions

Column A – POI

Enter the number associated with the POI, LOI, or sub-drainage area in the SWM report.

A given POI will require more than one row if there are multiple treatment practices in the

associated drainage area.

Column B - Existing Impervious Area within LOD (acres), A

Enter A

from Step 1 of the SWM Calculator. This value includes all pavement and roof-

top including maintenance and access areas recorded in Column E as A

Column C - Proposed Impervious Area (acres) within LOD, A

Enter A

from Step 1 of the SWM Calculator. This value includes all pavement and roof-

top including maintenance and access areas recorded in Column E as A

. Alternative

surfaces need to be included in this column and also listed as treatment practices in Columns

L - R.

Column D – Existing Imperviousness within SWM Study Area (0 to 100), %I

Enter %I from the Development Category Sheet of the SWM Calculator. This value ranges

from 0 to 100. It is not the same %I used to determine the P

Column E - Area for which WQ is Not Required (acres), A

Enter A

from Step 1 of the SWM Calculator. Any area included in this column must also

be included in Columns B and C.

Column F - Loss of Existing Water Quality (acres), A

Enter A

from Step 1 of the SWM Calculator. This value represents the effective

impervious area previously treated and is pro-rated for partial treatment. (A treated P

≥1.0

inch is considered full treatment. A treated P

< 1.0 is pro-rated linearly. For example, P

0.1 inch is considered 10% treatment.)

Notes: If previously treated impervious area is removed along with the water quality feature,

the result is considered a “wash”. If previously treated impervious area is removed, but the

water quality feature or BMP is not physically being removed, the result is also considered a

“wash” because the treatment is effectively lost since there is no impervious area to be

treated. These equivalent scenarios can be reflected by entering the impervious area that was

previously treated and is now being removed in both Columns F and G.

Column G – Reconstructed Impervious Area Already Treated (acres), A

RECi

Enter A

RECi

from Step 1 of the SWM Calculator. This value represents the effective

impervious area previously treated and is pro-rated for partial treatment. (A treated P

≥1.0

inch is considered full treatment. A treated P

< 1.0 is pro-rated linearly. For example, P

0.1 inch is considered 10% treatment.)

Note: If previously treated impervious areas are being removed, those areas need to be

included in this column as well as Column F. There is a potential for overlapping areas in

Column E and G. If maintenance or utility work is being performed on an existing

impervious surface that already has water quality treatment, include this area only in Column

July 2018 Technical Memo #11 Page 17 of 21

Water Quality Required

Column H - Net Increase in Impervious (acres), ∆Ai

This column is calculated by the spreadsheet and equals the net change in impervious area

from existing to proposed conditions. H = C-B. A positive number reflects an increase in

impervious area, and a negative number reflects a decrease in impervious area.

Column I - IART from Redevelopment (acres), IART

RE-DEV’L

This column is calculated by the spreadsheet and equals the portion of the proposed

development that must meet redevelopment requirements (i.e. 50% management). For POIs

where the existing impervious area exceeds 40%, this equals fifty percent of the existing

impervious area less the maintenance areas and the already treated impervious areas within

the LOD. For POIs where the existing impervious area is less than or equal to 40%, this

value is zero because the existing impervious must meet new development requirements and

as such is accounted for in Column J. If D > 40%, then I = 0.5(B-E-G). If D ≤ 40%, then

I = 0.

This value should be the same value as the IART

RE-DEV’L

as computed in Step 2 of the SWM

Calculator. If the values do not match, check both the SWM Calculator and the WQSS

for input errors. The spreadsheet calculates the total IART

RE-DEV’L

for the project at the top

of the column.

Column J - IART from New Development (acres), IART

NEW

This column is calculated by the spreadsheet and equals the portion of the proposed

development that must meet new development requirements (i.e. 100% management). For

POIs where the existing impervious area exceeds 40%, this equals the net increase in

impervious area. For POIs where the existing impervious area is less than or equal to 40%,

the entire LOD must meet the new development requirements (i.e. 100% management) and

this equals the proposed impervious area, less the maintenance areas and the already treated

impervious areas. If D > 40%, then J = H. If D ≤ 40%, then J = C-E-G.

This value should be the same value as the IART

NEW

as computed in Step 2 of the SWM

Calculator. If the values do not match, check both the SWM Calculator and the WQSS

for input errors. The spreadsheet calculates the total IART

NEW

for the project at the top of

the column.

Column K - TOTAL IART (acres), IART

This column is calculated by the spreadsheet and equals the impervious area requiring water

quality treatment for a P

of 1 inch. The total IART equals the IART from redevelopment

plus the IART from new development. Any loss of existing water quality recorded in

Column F is added to the IART. K = I+J=F. The spreadsheet calculates the total IART for

the project at the top of the column.

Water Quality Provided

Column L - Type of Treatment

List all proposed water quality practices located within the drainage area to the respective

POI. This includes the various types of alternative surfaces, non-structural practices, and

micro-scale practices from Chapter 5 of the SWM Manual as well as Chapter 3 practices and

innovative technologies proscribed in the Banking Terms or otherwise accepted by MDE. A

given POI/LOI will require more than one row if multiple treatment practices are being

proposed within the associated drainage area.

July 2018 Technical Memo #11 Page 18 of 21

Column M - BMP Tracking Number or Practice ID

List the unique number assigned by the applicant/designer to the stormwater treatment

practice.

Column N – Treatment Already Provided by Existing BMP (acres)

Enter the reconstructed impervious area already treated. This will be the same value reported

in Column G if the treated area is also in the LOD. This value represents the effective

impervious area treated and before entering needs to be pro-rated for partial treatment. (A

treated P

≥1.0 inch is considered full treatment. A treated P

< 1.0 is pro-rated linearly. For

example, P

= 0.1 inch is considered 10% treatment.) This column is not used by

spreadsheet to calculate the Impervious Area Treated; its purpose is to help distinguish

between existing treatment and proposed treatment within an existing/retrofit BMP.

For example, a new inflow pipe is being added to an existing BMP that provides water

quality for 1 acre in existing conditions. The BMP is being enlarged and will provide water

quality for 3 acres in proposed conditions. Column N will be 1 acre, and Column O will be 2

acres.

Column O - Treated Impervious Area from on-site or inside the ROW (acres)

Enter the amount of on-site impervious area within the drainage area to the treatment facility.

If the BMP is existing or a retrofit of an existing BMP, the previously treated impervious

area from Columns G and N is not included here. “On-site” refers to area that is within the

applicant’s property. Whether this area is located inside or outside the project’s LOD is

irrelevant. The IART does not have to be treated in the POI for which it was generated; it

can be treated anywhere in the defined Watershed.

Column P - Treated Impervious Area from off-site or outside the ROW (acres)

Enter the amount of off-site impervious area within the drainage area to the treatment

facility. If the BMP is existing or a retrofit of an existing BMP, the previously treated

impervious area from Columns G and N is not included here. “Off-site” refers to area owned

by an entity other than the applicant. Whether this area is located inside or outside the

project’s LOD is irrelevant. A 50% efficiency rate is applied to this area to compensate for

the applicant’s lack of control over property owned by others.

Column Q - P

Treated by Practice (inches)

Enter the total amount of rainfall (P

) treated by the water quality practice listed in Column

L. This value should be calculated using MDE’s spreadsheet “Provided Treatment:

Achieved P

and Treated ESDv” or an equivalent. For water quality banking purposes, the

required treatment is P

= 1 inch for the 1-year storm. One inch corresponds to the “first

flush” and is the water quality component of the target P

. Any treatment provided in excess

of 1.0 inch (for meeting ESDv) will not receive additional water quality credit. Water quality

credit is limited to 1.0 inch. Partial credit will be given for practices that provide less than

1.0 inch of treatment. Enter the total P

treated by the practice for the 1-year storm; Column

P will automatically limit the effective P

to 1.0 inch.

Column R - Effective Impervious Area Treated (acres)

This column is calculated by the spreadsheet and represents the equivalent amount of

impervious area receiving full treatment by pro-rating partial treatment (i.e. P

<1 inch) and

discounting off-site treatment areas by 50%. If P

≥ 1.0 inch, R = O+ 0.5P. If P

< 1.0

inch, R = (Q/1 inch)(O + 0.5P). The spreadsheet calculates the total Effective Impervious

Area Treated for the project at the top of the column.

July 2018 Technical Memo #11 Page 19 of 21

Column S - Water Quality Summary Excess/Deficit (acres)

The box at the top of this column is calculated by the spreadsheet and summarizes the

resulting water quality required or provided for a given POI and/or treatment practice. S =

ΣR – ΣK. A positive number indicates excess treatment, and a negative number indicates a

deficit in treatment. The spreadsheet calculates the total excess/deficit water quality for the

project at the top of the column. A positive number indicates an excess/credit, and a negative

number indicates a deficit/debit. If there is a deficit, additional water quality treatment needs

to be provided or the scope needs to be modified to be commensurate with the proposed

treatment. Alternatively, for applicants having a Water Quality Bank with MDE, a debit may

be withdrawn from the bank, subject to the approval of the applicant’s bank keeper. For

projects resulting in a debit to the Water Quality Bank, the amount of the debit needs to be

entered in Column 15 of the ESDVSS.

Excess water quality will be credited to the Water Quality Bank for the respective watershed.

MDE “charges” a 15% banking fee. The banking fee is the price the applicant pays for

having the latitude to provide WQv management at a selective location outside the project

limits. The fee is applied to credits before they are deposited in the bank. However, no fee is

applied to credits, or portions thereof, that result from impervious removal. Also, a fee is not

applied when the applicant has an approved institutional management plan (e.g. BWI,

UMBC). A banking fee is not applied to debits.

If ΣS > 0, there is a credit and the banking fee = 15% (ΣR)*

* The banking fee is only applied to excess treatment and not to any impervious removal.

If ΣS = 0, there is a “wash” and the banking fee = 0

If ΣS < 0, there is a debit and the banking fee = 0

July 2018 Technical Memo #11 Page 20 of 21

IV. Provided Treatment: Achieved P

, Treated ESDv, and Treated Re

The previous three spreadsheets focus on SWM design requirements. This spreadsheet, on the other

hand, calculates the SWM treatment provided by the proposed BMPs. It is unprotected and intended

to be used as a template for correctly calculating the provided ESDv, achieved P

, and provided Re

If the user edits the formatting, please assure that the printed version include the SWM report shows

the equations used in the calculations as well as an explanation.

Questions about this information or other items relating to sediment and stormwater plans for State

and federal projects can be directed to Amanda Malcolm amanda.malcolm@maryland.gov

July 2018 Technical Memo #11 Page 21 of 21

SIX TRICKY SCENARIOS

(Note this is a simplistic representation using 1.0 acre for all values in order to illustrate the

principal.)

SCENARIO

exist.

prop.

loss of

already

treated

RECi

RESULT

Previously untreated

impervious area is being

removed.

1.0 ac 1.0 ac >40% 0 0 0.5 ac credit

Previously treated

impervious area is being

reconstructed, and BMP

remains.

1.0 ac 1.0 ac

>40%

≤40%

0 1.0 ac

(requirement met)

Previously treated

impervious area and

BMP are being removed.

1.0 ac 0

40%

≤40%

1.0 ac 1.0 ac*

(wash)

Previously treated

impervious area is being

removed, and BMP

remains (to possibly be

used in future or not).

1.0 ac 0

>40%

≤40%

1.0 ac* 1.0 ac*

(wash)

Previously treated

impervious area is being

reconstructed, and BMP

is being removed.

1.0 ac 1.0 ac

>40%

≤40%

1.0 ac 1.0 ac*

IART = 1.0

(treatment needs to

be re-cooped for A

)

New impervious area is

added in drainage area to

BMP with available WQ

treatment capacity.

0 1.0 ac

>40%

≤40%

0 0

1.0 ac of treatment

required and 1.0

acre of treatment

provided by

indicating

previously unused

capacity as new

treatment in Column

O or P.

* Need to enter it this way to get the correct result.

Note that removal of treated impervious area does not result in a WQ credit regardless of whether

corresponding BMP is left in the ground or removed. From a SWM development regulatory

standpoint, impervious area treated by a BMP is considered to be equivalent with undeveloped

pervious area (although in reality the best BMP is pavement removal).