Storm Water Phase II

Final Rule

Fact Sheet Series

Overview

1.0 – Storm Water Phase II

Proposed Rule Overview

Small MS4 Program

2.0 – Small MS4 Storm Water

Program Overview

2.1 – Who’s Covered? Designation

and Waivers of Regulated Small

MS4s

2.2 – Urbanized Areas: Definition

and Description

Minimum Control Measures

2.3 – Public Education and

Outreach

2.4 – Public Participation/

Involvement

2.5 – Illicit Discharge Detection

and Elimination

2.6 – Construction Site Runoff

Control

2.7 – Post-Construction Runoff

Control

2.8 – Pollution Prevention/Good

Housekeeping

2.9 – Permitting and Reporting:

The Process and Requirements

2.10 – Federal and StateOperated MS4s: Program

Implementation

Construction Program

3.0 – Construction Program

Overview

3.1 – Construction Rainfall

Erosivity Waiver

Industrial “No Exposure”

4.0 – Conditional No Exposure

Exclusion for Industrial Activity

United States Office of Water EPA 833-F-00-014

Environmental Protection (4203) January 2001

Agency Fact Sheet 3.1

Storm Water Phase II

Final Rule

Construction Rainfall Erosivity

Waiver

T

he 1972 amendments to the Federal Water Pollution Control Act, later referred to as the Clean

Water Act (CWA), prohibit the discharge of any pollutant to navigable waters of the United States

unless the discharge is authorized by a National Pollutant Discharge Elimination System (NPDES)

permit. Because construction site storm water runoff can contribute significantly to water quality

problems, the Phase I Storm Water Rule imposed a requirement that all construction sites with a

planned land disturbance of 5 acres or more obtain an NPDES permit and implement storm water

runoff control plans. Phase II extends the requirements of the storm water program to sites of

between 1 and 5 acres. The Rainfall erosivity waiver, along with the water quality waiver, allows

permitting authorities to waive those sites that do not have adverse water quality impacts. 

What is Erosivity?

E

rosivity is the term used to describe the potential for soil to wash off disturbed, devegetated earth

into waterways during storms. The potential for erosion is in part determined by the soil type

and geology of the site. For instance, dense, clay-like soils on a glacial plain will erode less readily

when it rains than will sandy soils on the side of a hill. Another important factor is the amount and

force of precipitation expected during the time the earth will be exposed. While it is impossible to

predict the weather several months in advance of construction, for many areas of the country, there

are definite optimal periods, such as a dry season when rain tends to fall less frequently and with less

force. When feasible, this is the time to disturb the earth, so that the site is stabilized by the time the

seasonal wet weather returns. There are many other important factors to consider in determining

erosivity, such as freeze/thaw cycles and snow pack.

How Is Site Erosivity Determined?

T

he method for determining if a site qualifies for the erosivity waiver is based on the Universal Soil

Loss Equation (USLE) developed by the U.S. Department of Agriculture (USDA) in the 1950s to

help farmers conserve their valuable topsoil. The USLE has been updated to the Revised USLE

(RUSLE). Using a computer model supported by decades worth of soil and rainfall data, USDA

established estimates of annual erosivity values (R) for sites throughout the country. These R factors

are used as surrogate measures of the impact that rainfall had on erosion from a particular site. They

have been mapped using isoerodent contours, as shown in Figures 2 through 5. 

USDA developed the Erosivity Index Table (EI Table, provided here in Table 1), to show how the

annual erosivity factor is distributed throughout the year in two-week increments. Table 1 is based on

120 rainfall distribution zones for the continental U.S. Detailed instructions for calculating a project

R Factor are provided later in this fact sheet.

The Storm Water Phase II rule allows permitting authorities to waive NPDES requirements for small

construction sites if the value of the rainfall erosivity factor is less than 5 during the period of

construction activity (see § 122.26(b)(15)(i)(A)). Note that the permitting authority has the option to

not allow waivers for small construction activity. If the permitting authority in a State chooses to use

the rainfall erosivity waiver, it will not become effective until permits are required from small

construction activity.
Fact Sheet 3.1 - Construction Rainfall Erosivity Waiver Page 2

If the R Factor for the period of construction calculates to 5 or

lower, and the permitting authority allows the use of the waiver,

the site owner may apply for a waiver under the low rainfall

erosivity provision of the applicable NPDES Construction

General Permit. When applying, owners are encouraged to

consider other site-specific factors, such as proximity to water

resources and the sensitivity of receiving waters to sedimentation

impacts. The small construction operator must certify to the

permitting authority that the construction activity will take place

during a period when the rainfall erosivity factor is less than 5. 

The start and end dates used for the construction activity will be

the initial date of disturbance and the anticipated date when the

site will have achieved final stabilization as defined by the

permit. If the construction continues beyond this period, the

operator will need to recalculate the EI for the site based on this

new ending date (but keeping the old start date) and either

resubmit the certification form or apply for NPDES permit

coverage.

What Other Factors Can Affect Waiver Availability

and Eligibility?

E

PA has established the R Factor of 5 or lower as the criteria

for determining waiver eligibility. However, since the intent

is to waive only those construction activities that will not

adversely impact water quality, State and Tribal permitting

authorities have considerable discretion in determining where,

when, and how to offer it. They can establish an R Factor

threshold lower than 5, or they can suspend the waiver within an

area where watersheds are known to be heavily impacted by, or

sensitive to, sedimentation. They can also suspend the waiver

during certain periods of the year. They may opt not to offer the

waiver at all. NOTE: This waiver is not available to sites that

will disturb more than 5 acres of land (large construction).

What if My Site Is Not Eligible?

I

f your site is not eligible for a waiver, you must submit a Notice

of Intent under the NPDES General Permit, and comply with

its requirements. These requirements are described in more

detail in Storm Water Phase II Fact Sheet 3.0. 

How Do I Compute the R Factor for My Project?

1. Estimate the construction start date. This is the day you

expect to begin disturbing soils, including grubbing,

stockpiling, excavating, and grading activities. Pick the 15-

day period for your start date (e.g., June 1-15.)

2. Estimate the day you expect to have a permanent vegetative

cover of at least 70%, or as defined by your permitting

authority, over all previous disturbed areas. Round to the

nearest 15-day period.

3. Refer to Figure 1 to find your Erosivity Index (EI) Zone

based on your geographic location.

4. Refer to Table 1, the Erosivity Index (EI) Table. Find the

number of your EI Zone in the left column. Locate the EI

values for the 15-day periods that correspond to the project

start and end periods you identified in Steps 1 and 2.

Subtract the start value from the end value to find the % EI

for your site. The maximum annual EI value for a project is

100%. 

5. Refer to the appropriate Isoerodent Map (Figures 2 through

5). Interpolate the annual isoerodent value for your area. 

This is the annual R Factor for your site.

6. Multiply the percent value obtained in Step 4 by the annual

isoerodent value obtained in Step 5. This is the R Factor for

your scheduled project.

Examples

1. Construction started and completed in one

calendar year.

Find the R value of a construction site in Denver, Colorado. 

Assume the site will be disturbed from March 1 to May 15. 

The EI distribution zone is 84 (Figure 1). Referring to Table 1,

the project period will span from March 1 to May 15. The

difference in values between these two periods is 4.7 % (4.9-0.2

=4.7). Since the annual erosion index for this location is about

45 (interpolated from Figure 2), the R Factor for the scheduled

construction project is 4.7% of 45, or 2.1.

Because 2.1 is less than 5, the operator of this site would be

able to seek a waiver under the low rainfall erosivity provision.

2. Construction spanning two calendar years.

Find the R value for a construction site in Pittsburgh,

Pennsylvania. Assume the site will be disturbed from August 1

to April 15.

The EI distribution zone is 111 (Figure 1). Referring to Table

1, the project will span from August 1 to April 15. The

difference in values between August 1 and December 30 is 35%

(100- 65.0 = 35.0). The difference between January 1 and April

15 is 8%. The total percentage EI for this project is 43% (35 +

8). Since the annual erosion index for this location is 112

(interpolated from Figure 2), the R Factor for the scheduled

construction is 43% of 112, or 48. 

Since 48 is greater than 5, the operator of this site would not be

able to seek a waiver under the low rainfall erosivity provision.
Fact Sheet 3.1 - Construction Rainfall Erosivity Waiver Page 3

Can I Use A Personal Computer to Calculate the R

Factor?

T

he computer program used by USDA to develop the current R

Factor maps and table is called the Revised Universal Soil

Loss Equation, or RUSLE. The current version of RUSLE (v.

1.60) will calculate the R factor for the entire year for a limited

number of cities in the U.S., but does not allow the R factor to be

easily adjusted based on a shorter period of construction. If you

are interested in using RUSLE; Version 1.06 for Mined Lands,

Construction Sites, and Reclaimed Lands, is downloadable free of

charge from the Internet at http://www.sedlab.olemiss.edu/rusle.

Where Can I Get Help?

” A copy of “Chapter 2, Rainfall-Runoff Erosivity Factor (R)”

from the USDA Handbook 703 - Predicting Soil Erosion by

Water: A Guide to Conservation Planning With the Revised

Universal Soil Loss Equation (RUSLE), January 1997, is

available on EPA’s web site at http://www.epa.gov/npdes/stormwater.

” Your local soil conservation district office can provide

assistance with R Factors and other conservation-related

issues. To find the office nearest you, look in the

government section of the phone book under soil

conservation district, conservation district, natural resource

conservation district, etc.

For Additional Information

Reference Documents

L Storm Water Phase II Final Rule Fact Sheet Series

• Internet: cfpub.epa.gov/npdes/stormwater/swfinal.cfm

L Storm Water Phase II Final Rule(64 FR 68722)

• Internet: www.epa.gov/npdes/regulations/phase2.pdf

• Contact the U.S. EPA Water Resource Center

• Phone: (202) 564-9545

L Agricultural Handbook Number 703, Predicting Soil

Erosion by Water: A Guide to Conservation Planning

With the Revised Universal Soil Loss Equation

(RUSLE), Chapter 2, pp. 21-64, January 1997.

• Internet: www.epa.gov/npdes/pubs/ruslech2.pdf
Fact Sheet 3.1 - Construction Rainfall Erosivity Waiver Page 4

Figure 1. Erosivity Index Zone Map
Fact Sheet 3.1 - Construction Rainfall Erosivity Waiver Page 5

Figure 2. Isoerodent Map of the Eastern U.S.

Note: Units for all maps on this page are are hundreds ftCtonfCin(acChCyr)-1
Fact Sheet 3.1 - Construction Rainfall Erosivity Waiver Page 6

Figure 3. Isoerodent Map of the Western U.S.

Note: Units for all maps on this page are are hundreds ftCtonfCin(acChCyr)-1
Fact Sheet 3.1 - Construction Rainfall Erosivity Waiver Page 7

Note: Units for all maps on this page are are hundreds ftCtonfCin(acChCyr)-1

Figure 4. Isoerodent Map of California
Fact Sheet 3.1 - Construction Rainfall Erosivity Waiver Page 8

Note: Units for all maps on this page are are hundreds ftCtonfCin(acChCyr)-1

Figure 5. Isoerodent Map of Oregon and Washington
Table 1. Erosivity Index Table

EI as a percentage of Average Annual R Value Computed for Geographic Areas Shown in Figure 1

Jan Jan Feb Feb Mar Mar Apr Apr May May Jun Jun Jul Jul Aug Aug Sep Sep Oct Oct Nov Nov Dec Dec

EI# 1-15 16-31 1-15 16-29 1-15 16-31 1-15 16-30 1-15 16-31 1-15 16-30 1-15 16-31 1-15 16-31 1-15 16-31 1-15 16-31 1-15 16-31 1-15 16-31

1 0.0 4.3 8.3 12.8 17.3 21.6 25.1 28.0 30.9 34.9 39.1 42.6 45.4 48.2 50.8 53.0 56.0 60.8 66.8 71.0 75.7 82.0 89.1 95.2 

2 0.0 4.3 8.3 12.8 17.3 21.6 25.1 28.0 30.9 34.9 39.1 42.6 45.4 48.2 50.8 53.0 56.0 60.8 66.8 71.0 75.7 82.0 89.1 95.2 

3 0.0 7.4 13.8 20.9 26.5 31.8 35.3 38.5 40.2 41.6 42.5 43.6 44.5 45.1 45.7 46.4 47.7 49.4 52.8 57.0 64.5 73.1 83.3 92.3 

4 0.0 3.9 7.9 12.6 17.4 21.6 25.2 28.7 31.9 35.1 38.2 42.0 44.9 46.7 48.2 50.1 53.1 56.6 62.2 67.9 75.2 83.5 90.5 96.0 

5 0.0 2.3 3.6 4.7 6.0 7.7 10.7 13.9 17.8 21.2 24.5 28.1 31.1 33.1 35.3 38.2 43.2 48.7 57.3 67.8 77.9 86.0 91.3 96.9 

6 0.0 0.0 0.0 0.5 2.0 4.1 8.1 12.6 17.6 21.6 25.5 29.6 34.5 40.0 45.7 50.7 55.6 60.2 66.5 75.5 85.6 95.9 99.5 99.9 

7 0.0 0.0 0.0 0.0 0.0 1.2 4.9 8.5 13.9 19.0 26.1 35.4 43.9 48.8 53.9 64.5 73.4 77.5 80.4 84.8 89.9 96.6 99.2 99.7 

8 0.0 0.0 0.0 0.0 0.0 0.9 3.6 7.8 15.0 20.2 27.4 38.1 49.8 57.9 65.0 75.6 82.7 86.8 89.4 93.4 96.3 99.1 100.0 100.0 

9 0.0 0.8 3.1 4.7 7.4 11.7 17.8 22.5 27.0 31.4 36.0 41.6 46.4 50.1 53.4 57.4 61.7 64.9 69.7 79.0 89.6 97.4 100.0 100.0 

10 0.0 0.3 0.5 0.9 2.0 4.3 9.2 13.1 18.0 22.7 29.2 39.5 46.3 48.8 51.1 57.2 64.4 67.7 71.1 77.2 85.1 92.5 96.5 99.0 

11 0.0 5.4 11.3 18.8 26.3 33.2 37.4 40.7 42.5 44.3 45.4 46.5 47.1 47.4 47.8 48.3 49.4 50.7 53.6 57.5 65.5 76.2 87.4 94.8 

12 0.0 3.5 7.8 14.0 21.1 27.4 31.5 35.0 37.3 39.8 41.9 44.3 45.6 46.3 46.8 47.9 50.0 52.9 57.9 62.3 69.3 81.3 91.5 96.7 

13 0.0 0.0 0.0 1.8 7.2 11.9 16.7 19.7 24.0 31.2 42.4 55.0 60.0 60.8 61.2 62.6 65.3 67.6 71.6 76.1 83.1 93.3 98.2 99.6 

14 0.0 0.7 1.8 3.3 6.9 16.5 26.6 29.9 32.0 35.4 40.2 45.1 51.9 61.1 67.5 70.7 72.8 75.4 78.6 81.9 86.4 93.6 97.7 99.3 

15 0.0 0.0 0.0 0.5 2.0 4.4 8.7 12.0 16.6 21.4 29.7 44.5 56.0 60.8 63.9 69.1 74.5 79.1 83.1 87.0 90.9 96.6 99.1 99.8 

16 0.0 0.0 0.0 0.5 2.0 5.5 12.3 16.2 20.9 26.4 35.2 48.1 58.1 63.1 66.5 71.9 77.0 81.6 85.1 88.4 91.5 96.3 98.7 99.6 

17 0.0 0.0 0.0 0.7 2.8 6.1 10.7 12.9 16.1 21.9 32.8 45.9 55.5 60.3 64.0 71.2 77.2 80.3 83.1 87.7 92.6 97.2 99.1 99.8 

18 0.0 0.0 0.0 0.6 2.5 6.2 12.4 16.4 20.2 23.9 29.3 37.7 45.6 49.8 53.3 58.4 64.3 69.0 75.0 86.6 93.9 96.6 98.0 100.0 

19 0.0 1.0 2.6 7.4 16.4 23.5 28.0 31.0 33.5 37.0 41.7 48.1 51.1 52.0 52.5 53.6 55.7 57.6 61.1 65.8 74.7 88.0 95.8 98.7 

20 0.0 9.8 18.5 25.4 30.2 35.6 38.9 41.5 42.9 44.0 45.2 48.2 50.8 51.7 52.5 54.6 57.4 58.5 60.1 63.2 69.6 76.7 85.4 92.4 

21 0.0 7.5 13.6 18.1 21.1 24.4 27.0 29.4 31.7 34.6 37.3 39.6 41.6 43.4 45.4 48.1 51.3 53.3 56.6 62.4 72.4 81.3 88.9 94.7 

22 0.0 1.2 1.6 1.6 1.6 1.6 1.6 2.2 3.9 4.6 6.4 14.2 32.8 47.2 58.8 69.1 76.0 82.0 87.1 96.7 99.9 99.9 99.9 99.9 

23 0.0 7.9 15.0 20.9 25.7 31.1 35.7 40.2 43.2 46.2 47.7 48.8 49.4 49.9 50.7 51.8 54.1 57.7 62.8 65.9 70.1 77.3 86.8 93.5 

24 0.0 12.2 23.6 33.0 39.7 47.1 51.7 55.9 57.7 58.6 58.9 59.1 59.1 59.2 59.2 59.3 59.5 60.0 61.4 63.0 66.5 71.8 81.3 89.6 

25 0.0 9.8 20.8 30.2 37.6 45.8 50.6 54.4 56.0 56.8 57.1 57.1 57.2 57.6 58.5 59.8 62.2 65.3 67.5 68.2 69.4 74.8 86.6 93.0 

26 0.0 2.0 5.4 9.8 15.6 21.5 24.7 26.6 27.4 28.0 28.7 29.8 32.5 36.6 44.9 55.4 65.7 72.6 77.8 84.4 89.5 93.9 96.5 98.4 

27 0.0 0.0 0.0 1.0 4.0 5.9 8.0 11.1 13.0 14.0 14.6 15.3 17.0 23.2 39.1 60.0 76.3 86.1 89.7 90.4 90.9 93.1 96.6 99.1 

28 0.0 0.0 0.0 0.0 0.2 0.5 1.5 3.3 7.2 11.9 17.7 21.4 27.0 37.1 51.4 62.3 70.6 78.8 84.6 90.6 94.4 97.9 99.3 100.0 

29 0.0 0.6 0.7 0.7 0.7 1.5 3.9 6.0 10.5 17.9 28.8 36.6 43.8 51.5 59.3 68.0 74.8 80.3 84.3 88.8 92.7 98.0 99.8 99.9 

30 0.0 0.0 0.0 0.0 0.0 0.2 0.8 2.8 7.9 14.2 24.7 35.6 45.4 52.2 58.7 68.5 77.6 84.5 88.9 93.7 96.2 97.6 98.3 99.6 

Fact Sheet 3.1 - Construction Rainfall Erosivity Waiver Page 9
Table 1. Erosivity Index Table (cont.)

Jan Jan Feb Feb Mar Mar Apr Apr May May Jun Jun Jul Jul Aug Aug Sep Sep Oct Oct Nov Nov Dec Dec

EI# 1-15 16-31 1-15 16-29 1-15 16-31 1-15 16-30 1-15 16-31 1-15 16-30 1-15 16-31 1-15 16-31 1-15 16-31 1-15 16-31 1-15 16-31 1-15 16-31

31 0 0 0 0 0 0.2 1 3.5 9.9 15.7 26.4 47.2 61.4 65.9 69 77.2 86 91.6 94.8 98.7 100 100 100 100 

32 0 0.1 0.1 0.1 0.1 0.6 2.2 4.3 9 14.2 23.3 34.6 46.3 54.2 61.7 72.9 82.5 89.6 93.7 98.2 99.7 99.9 99.9 99.9 

33 0 0 0 0 0 0.6 2.3 4.2 8.8 16.1 30 46.9 57.9 62.8 66.2 72.1 79.1 85.9 91.1 97 98.9 98.9 98.9 98.9 

34 0 0 0 0 0 1.8 7.3 10.7 15.5 22 29.9 35.9 42 48.5 56.9 67 76.9 85.8 91.2 95.7 97.8 99.6 100 100 

35 0 0 0 0 0 2.5 10.2 15.9 22.2 27.9 34.7 43.9 51.9 56.9 61.3 67.3 73.9 80.1 85.1 89.6 93.2 98.2 99.8 99.8 

36 0 0 0 0 0 0.9 3.4 6.7 12.7 18.5 26.6 36.3 46 53.5 60.2 68.3 75.8 82.6 88.3 96.3 99.3 99.9 100 100 

37 0 0 0 0 0 0 0 1 3.9 9.1 19.1 26.7 36.3 47.9 61.4 75.1 84.5 92.3 96 99.1 100 100 100 100 

38 0 0 0 1.1 4.3 7.2 11 13.9 17.9 22.3 30.3 43.1 55.1 61.3 65.7 72.1 77.9 82.6 86.3 90.3 93.8 98.4 100 100 

39 0 0 0 0 0 1.6 6.5 11 17.8 24.7 33.1 42.8 50.3 54.9 59.7 68.9 78.1 83.6 87.5 93 96.5 99.2 100 100 

40 0 0 0 0 0 1.5 6.2 10.1 16.3 23.3 32.5 42.2 50.1 55.6 60.5 67.5 74.3 79.4 84.1 91.1 95.8 99.1 100 100 

41 0 0.1 0.2 0.2 0.2 0.2 0.2 0.4 1.1 6.8 22.9 40.1 54.9 63.8 70.7 81.5 89.8 96.3 98.7 99.2 99.3 99.4 99.4 99.7 

42 0 0 0 0 0 0 0 0.2 0.9 5.2 17.3 33.8 53.2 66.5 75.9 87.6 93.7 97.5 99 99.7 100 100 100 100 

43 0 0 0 0 0 0 0 0.1 0.4 2.7 9.5 21.9 42.7 58.6 71.1 84.6 91.9 97.1 99 99.8 100 100 100 100 

44 0 1.7 2.3 2.4 2.4 2.4 2.4 2.7 3.5 7.6 18.5 34.3 52.5 64 72.3 83.3 90 95.1 97.3 98.5 98.9 98.9 98.9 99.2 

45 0 0.2 0.2 0.3 0.3 0.4 0.6 0.8 1.4 3.7 10.2 22.6 41.8 54 64.5 78.7 88.4 96 98.7 99.4 99.7 99.7 99.8 99.9 

46 0 0 0 0 0 0 0 0.6 2.6 7.5 19.6 32.9 48.9 63 73.5 83.3 89.5 95.6 98.3 99.6 100 100 100 100 

47 0 0 0 0 0 0 0 0.4 1.6 5.8 17 33 52.5 66.4 75.7 85.5 91.3 96.5 98.8 100 100 100 100 100 

48 0 0 0 0 0 0 0 0 0 2 8.1 15.4 27.8 40.7 52.6 61.1 69.3 82.6 92 98 100 100 100 100 

49 0 0 0 0 0 0 0 0.7 2.7 8.3 20 27.5 35.6 44.6 56 70.2 81.3 89.2 93.6 98.5 100 100 100 100 

50 0 0 0 0 0 0.1 0.4 2.4 8.2 13.7 23.8 38.8 55.1 66.1 73.6 81.8 87.7 93.8 97 99.4 100 100 100 100 

51 0 0 0 0 0 0.3 1 3.1 8.7 18.8 35.8 49.6 60.4 70.2 77 84 88.8 93.8 96.6 99.1 100 100 100 100 

52 0 0 0 0 0 0 0 0.6 2.5 6.8 17.5 29.8 46.1 60.5 72.7 86 92.8 96.8 98.4 99.7 100 100 100 100 

53 0 0 0 0 0 0 0 0.8 3 9.5 24.2 35.3 48 63.1 76.1 87.7 93.5 97.2 98.6 99.5 99.8 99.9 100 100 

54 0 0 0 0 0 0.2 0.7 2.4 7.2 14.7 27.2 37.2 47.3 58.8 67.6 74 79.2 86.7 92.6 97.9 99.8 99.9 100 100 

55 0 0 0 0 0 0 0 1.3 5.4 13.3 25.5 31.6 38.8 52.5 66.8 75.5 81.2 87.9 92.8 98.3 100 100 100 100 

56 0 0 0 0 0 0 0 1.3 5.1 11.4 22.3 29.5 38.5 51.1 65.2 77.8 85.6 91.7 95 98.7 100 100 100 100 

57 0 0 0 0 0 0 0.1 1 3.5 9.2 21.5 31 43.5 60.4 75.1 86.1 91.6 96.2 98.1 99.4 99.9 99.9 100 100 

58 0 0 0 0 0 0.2 0.9 2.9 8 13.2 21 29.1 38 45.9 54.5 65.4 74.8 82.1 87.5 95.4 98.8 99.7 100 100 

59 0 0 0 0 0 0 0 2.2 8.9 15.6 24.2 31.1 38.3 46 54.9 64.2 73.2 81.9 88.5 95.7 98.6 99.4 99.7 99.7 

60 0 0 0 0 0 0 0 0.4 1.5 4 9.5 13.3 20.5 33.6 52.8 66.5 76.7 88.1 94.2 98.6 100 100 100 100 

Fact Sheet 3.1 - Construction Rainfall Erosivity Waiver Page 10
Table 1. Erosivity Index Table (cont.)

Jan Jan Feb Feb Mar Mar Apr Apr May May Jun Jun Jul Jul Aug Aug Sep Sep Oct Oct Nov Nov Dec Dec

EI# 1-15 16-31 1-15 16-29 1-15 16-31 1-15 16-30 1-15 16-31 1-15 16-30 1-15 16-31 1-15 16-31 1-15 16-31 1-15 16-31 1-15 16-31 1-15 16-31

61 0 0 0 0 0 0 0 1.3 5 8.5 15.5 29.8 41.8 46 49.2 56 65.1 71.6 78.6 91.1 97.3 99.3 100 100 

62 0 0 0 0.1 0.3 0.8 2.1 3.6 6.5 9.7 13.7 16.5 20.8 27.3 40.1 56.9 72.6 83.4 89.4 95.5 98.1 99.6 100 100 

63 0 0 0 0 0 0 0 0.9 3.7 7.8 13.3 15.8 19.9 29 46.8 64.7 78.3 88.8 93.9 98.5 100 100 100 100 

64 0 0 0 0.7 2.8 7.4 12.4 14.4 15.6 17.3 19.4 21 24.4 32.3 48 61.4 72.1 81.9 87 90.1 92.4 98.1 100 100 

65 0 3.6 7 9.6 11.4 13 14.4 16.3 17.7 18.4 19.3 20.5 23.6 32 50 66.2 77.2 85.4 88.8 90.4 91.3 92.7 94.8 97 

66 0 0 0 0 0 0.1 0.5 1.1 2.2 3.6 6 7.6 11.1 19.8 38.9 59.7 74.4 83.2 88.1 94.6 97.7 99.4 100 100 

67 0 0 0 0 0 0.1 0.4 0.9 1.6 1.9 2.4 5 12.1 24.8 48.3 73.6 86.5 92 94.3 96.6 97.9 99.5 100 100 

68 0 2.3 4.5 7.8 10.4 12 13.3 16.3 17.7 18.1 18.2 18.3 18.4 19.9 24.5 35 54.4 69.4 78.6 85.7 89.2 91.9 93.9 97 

69 0 2 3.7 5.7 7.8 10.5 12.4 13.7 14.3 14.7 15.1 15.7 17.1 22.7 36.7 50.4 63.6 75 81.8 87.8 90.8 93.2 94.9 97.5 

70 0 0.5 0.7 1 1.3 1.7 2.2 2.8 3.4 3.9 4.7 5.4 7.4 15.7 36.5 55.8 70.3 80.9 86.4 90.9 93.4 96.4 98.1 99.4 

71 0 0.7 1.2 1.6 2.1 2.8 3.3 3.6 4 4.5 5.6 6.5 9.1 18.5 40.6 59.7 74 86.3 91.7 94.7 96 96.7 97.3 98.8 

72 0 0 0 0 0 0 0.1 0.2 0.7 0.8 1.3 3.5 9.9 24.7 51.4 71.5 83.6 93.8 97.7 99.2 99.8 99.9 99.9 100 

73 0 0 0.1 0.1 0.2 0.2 0.3 0.6 1.3 4.1 11.5 18.1 28.3 40.2 54.1 67 77.2 87.7 93.3 97.5 99.1 99.6 99.8 100 

74 0 0 0 0 0 0.1 0.2 0.5 1.2 2.7 6.4 10.2 18.4 31 50.7 68.7 81.2 91.6 96.1 98.4 99.2 99.8 100 100 

75 0 0.1 0.1 0.1 0.2 0.5 1.3 1.9 3 4.1 6.6 10 17.6 28.3 44.7 59.4 71.6 83.9 90.3 94.7 96.7 98.8 99.6 99.9 

76 0 0 0 0 0 0.1 0.2 0.6 1.3 2 3.5 4.9 8.4 17.4 37.3 57.5 72.9 83.7 89.5 95.8 98.4 99.6 100 100 

77 0 0.2 0.3 0.3 0.4 0.8 1.5 2 2.8 3.9 5.9 7.2 10.3 21.5 46.5 66.3 78.3 86.5 90.8 96 98.2 99.1 99.5 99.8 

78 0 0 0 0 0 0 0.2 0.5 1.6 3.8 8.9 13.2 21.8 35.8 56.6 75.4 86 92.9 95.9 98.2 99.2 99.8 100 100 

79 0 0 0 0 0 0.2 0.7 1.3 2.7 5.8 12.7 18.8 28.8 41.6 58.4 75.7 86.5 94.2 97.3 98.9 99.5 99.9 100 100 

80 0 0.6 1.2 1.6 2.1 2.5 3.3 4.5 6.9 10.1 15.5 19.7 26.6 36.4 51.7 67.5 79.4 88.8 93.2 96.1 97.3 98.2 98.7 99.3 

81 0 0.1 0.1 0.2 0.4 0.5 0.8 0.9 1.5 3.9 9.9 12.8 18.2 30.7 54.1 77.1 89 94.9 97.2 98.7 99.3 99.6 99.7 99.9 

82 0 0 0.1 0.1 0.2 0.2 0.5 1.2 3.1 6.7 14.4 20.1 29.8 44.5 64.2 83.1 92.2 96.4 98.1 99.3 99.7 99.8 99.8 99.9 

83 0 0 0.1 0.1 0.1 0.3 0.9 1.6 3.5 8.3 19.4 30 44 59.2 72.4 84.6 91.2 96.5 98.6 99.5 99.8 99.9 100 100 

84 0 0 0.1 0.1 0.2 0.3 0.6 1.7 4.9 9.9 19.5 27.2 38.3 52.8 68.8 83.9 91.6 96.4 98.2 99.2 99.6 99.8 99.8 99.9 

85 0 0 0 0 0 0 1 2 3 6 11 23 36 49 63 77 90 95 98 99 100 100 100 100 

86 0 0 0 0 0 0 1 2 3 6 11 23 36 49 63 77 90 95 98 99 100 100 100 100 

87 0 0 0 0 1 1 2 3 6 10 17 29 43 55 67 77 85 91 96 98 99 100 100 100 

88 0 0 0 0 1 1 2 3 6 13 23 37 51 61 69 78 85 91 94 96 98 99 99 100 

89 0 0 1 1 2 3 4 7 12 18 27 38 48 55 62 69 76 83 90 94 97 98 99 100 

90 0 1 2 3 4 6 8 13 21 29 37 46 54 60 65 69 74 81 87 92 95 97 98 99 

Fact Sheet 3.1 - Construction Rainfall Erosivity Waiver Page 11
Table 1. Erosivity Index Table (cont.)

Jan Jan Feb Feb Mar Mar Apr Apr May May Jun Jun Jul Jul Aug Aug Sep Sep Oct Oct Nov Nov Dec Dec

EI# 1-15 16-31 1-15 16-29 1-15 16-31 1-15 16-30 1-15 16-31 1-15 16-30 1-15 16-31 1-15 16-31 1-15 16-31 1-15 16-31 1-15 16-31 1-15 16-31

91 0 0 0 0 1 1 1 2 6 16 29 39 46 53 60 67 74 81 88 95 99 99 100 100 

92 0 0 0 0 1 1 1 2 6 16 29 39 46 53 60 67 74 81 88 95 99 99 100 100 

93 0 1 1 2 3 4 6 8 13 25 40 49 56 62 67 72 76 80 85 91 97 98 99 99 

94 0 1 2 4 6 8 10 15 21 29 38 47 53 57 61 65 70 76 83 88 91 94 96 98 

95 0 1 3 5 7 9 11 14 18 27 35 41 46 51 57 62 68 73 79 84 89 93 96 98 

96 0 2 4 6 9 12 17 23 30 37 43 49 54 58 62 66 70 74 78 82 86 90 94 97 

97 0 1 3 5 7 10 14 20 28 37 48 56 61 64 68 72 77 81 86 89 92 95 98 99 

98 0 1 2 4 6 8 10 13 19 26 34 42 50 58 63 68 74 79 84 89 93 95 97 99 

99 0 0 0 1 1 2 3 5 7 12 19 33 48 57 65 72 82 88 93 96 98 99 100 100 

100 0 0 0 0 1 1 2 3 5 9 15 27 38 50 62 74 84 91 95 97 98 99 99 100 

101 0 0 0 1 2 3 4 6 9 14 20 28 39 52 63 72 80 87 91 94 97 98 99 100 

102 0 0 1 2 3 4 6 8 11 15 22 31 40 49 59 69 78 85 91 94 96 98 99 100 

103 0 1 2 3 4 6 8 10 14 18 25 34 45 56 64 72 79 84 89 92 95 97 98 99 

104 0 2 3 5 7 10 13 16 19 23 27 34 44 54 63 72 80 85 89 91 93 95 96 98 

105 0 1 3 6 9 12 16 21 26 31 37 43 50 57 64 71 77 81 85 88 91 93 95 97 

106 0 3 6 9 13 17 21 27 33 38 44 49 55 61 67 71 75 78 81 84 86 90 94 97 

107 0 3 5 7 10 14 18 23 27 31 35 39 45 53 60 67 74 80 84 86 88 90 93 95 

108 0 3 6 9 12 16 20 24 28 33 38 43 50 59 69 75 80 84 87 90 92 94 96 98 

109 0 3 6 10 13 16 19 23 26 29 33 39 47 58 68 75 80 83 86 88 90 92 95 97 

110 0 1 3 5 7 9 12 15 18 21 25 29 36 45 56 68 77 83 88 91 93 95 97 99 

111 0 1 2 3 4 5 6 8 11 15 20 28 41 54 65 74 82 87 92 94 96 97 98 99 

112 0 0 0 1 2 3 4 5 7 12 17 24 33 42 55 67 76 83 89 92 94 96 98 99 

113 0 1 2 3 4 5 6 8 10 12 17 22 31 42 52 60 68 75 80 85 89 92 96 98 

114 0 1 2 4 6 8 11 13 11 13 21 26 32 38 46 55 64 71 77 81 85 89 93 97 

115 0 1 2 3 4 5 6 8 10 14 19 26 34 45 56 66 76 82 86 90 93 95 97 99 

116 0 1 3 5 7 9 12 15 18 21 25 29 36 45 56 68 77 83 88 91 93 95 97 99 

117 0 1 2 3 4 5 7 9 11 14 17 22 31 42 54 65 74 83 89 92 95 97 98 99 

118 0 2 4 6 8 12 16 20 25 30 35 41 47 56 67 75 81 85 87 89 91 93 95 97 

119 0 1 2 4 6 7 9 12 15 18 23 31 40 48 57 63 72 78 88 92 96 97 98 99 

120 0 8 16 25 33 41 46 50 53 54 55 56 56.5 57 57.75 58 58.75 60 61 63 66.5 72 80 90 

Fact Sheet 3.1 - Construction Rainfall Erosivity Waiver Page 12
Table 1. Erosivity Index Table (cont.)

0 Jan Jan Feb Feb Mar Mar Apr Apr May May Jun Jun Jul Jul Aug Aug Sep Sep Oct Oct Nov Nov Dec Dec

EI# 1-15 16-31 1-15 16-29 1-15 16-31 1-15 16-30 1-15 16-31 1-15 16-30 1-15 16-31 1-15 16-31 1-15 16-31 1-15 16-31 1-15 16-31 1-15 16-31

121 0 7 14 20 25.5 33.5 38 43 46 50 52.5 54.5 56 58 59 60 61.5 63 65 68 72 79 86 93 

122 0 4 8 12 17 23 29 34 38 44 49 53 56 59 62 65 69 72 75 79 83 88 93 96 

123 0 4 9 15 23 29 34 40 44 48 50 51 52 53 55 57 60 62 64 67 72 80 88 95 

124 0 7 12 17 24 30 39 45 50 53 55 56 57 58 59 61 62 63 64 66 70 77 84 92 

125 0 9 16 23 30 37 43 47 50 52 54 55 56 57 58 59 60 62 64 67 71 77 86 93 

126 0 8 15 22 28 33 38 42 46 50 52 53 53 53 53 54 55 57 59 63 68 75 83 92 

127 0 8 15 22 29 34 40 45 48 51 54 57 59 62 63 64 65 66 67 69 72 76 83 91 

128 0 9 16 22 27 32 37 41 45 48 51 53 55 56 57 57 58 59 61 64 68 73 79 89 

129 0 10 20 28 35 41 46 49 51 53 55 56 56 57 58 59 60 61 62 65 69 74 81 90 

130 0 8 15 22 28 33 38 41 44 47 49 51 53 55 56 58 59 60 63 65 69 75 84 92 

131 0 10 18 25 29 33 36 39 41 42 44 45 46 47 48 49 51 53 56 59 64 70 80 90 

132 0 8 16 24 32 40 46 51 54 56 57 58 58 59 59 60 60 61 62 64 68 74 83 91 

133 0 12 22 31 39 45 49 52 54 55 56 56 56 56 57 57 57 57 58 59 62 68 77 88 

134 0 7 15 22 30 37 43 49 53 55 57 58 59 60 61 62 63 65 67 70 74 79 85 92 

135 0 11 21 29 37 44 50 55 57 59 60 60 60 60 61 61 61 62 63 64 67 71 78 89 

136 0 10 18 25 30 39 46 51 54 57 58 59 59 60 60 60 61 62 63 64 67 72 80 90 

137 0 11 22 31 39 46 52 56 58 59 60 61 61 61 61 62 62 62 63 64 66 71 78 89 

138 0 8 14 20 25 32 37 42 47 50 53 55 56 58 59 61 63 64 66 68 71 76 85 93 

139 0 10.6 21.2 28.6 36 41.4 46.8 49.3 51.8 52.5 53.2 53.5 53.7 53.9 54 54.3 54.7 55.7 56.8 61.6 65.3 73.9 82.5 91.2 

140 0 0.2 0.3 0.3 0.3 0.3 0.3 0.8 1.3 5.3 9.3 30.1 50.8 56.8 62.9 67.5 72.2 75.8 79.4 85.6 91.7 95.9 100 100 

141 0 10.7 21.4 28.7 36 41.7 47.3 50.3 53.2 54.5 55.7 56.2 56.7 56.9 57 57.4 57.8 59 60.2 64.1 67.9 76.1 84.2 92.1 

142 0 2.7 5.5 5.7 5.9 7.1 8.4 10 11.7 15.3 19 22.6 26.1 29 31.9 36.6 41.2 46 50.7 62.3 73.9 83.5 93.1 96.6 

143 0 8.7 17.5 25.2 33 39.9 46.7 50.8 54.8 56.2 57.6 58 58.4 58.9 59.4 60.8 62.3 64.1 65.9 68.8 71.7 78.6 85.5 92.7 

144 0 4.3 8.6 9.3 10.1 11.1 12 15.3 18.6 22.7 26.7 28.7 30.7 31.3 32 34 36 44.4 52.9 60.1 67.3 78.2 89.2 94.6 

145 0 11.7 23.3 33.5 43.7 50.7 57.6 60.3 63 63.5 64.1 64.2 64.2 64.5 64.8 66.1 67.3 68.6 69.8 70.7 71.6 79.2 86.7 93.4 

146 0 4.8 9.6 13.1 16.5 22.6 28.7 30.8 32.8 33.3 33.8 34 34.2 36.4 38.6 43 47.5 56 64.5 66.2 67.9 77.9 88 94 

147 0 0 4.7 9.4 10.8 12.2 13.2 14.3 14.9 15.5 24.2 32.8 45.5 58.2 67.9 77.6 86.3 95.1 95.6 96.1 98 100 100 100 

148 0 5.5 11 19.2 27.5 36.6 45.7 47.8 50 50.9 51.7 52.1 52.5 54.2 55.9 60.1 64.4 70.5 76.7 81.2 85.7 90.4 101 97.6 

149 0 2.4 4.9 7.4 9.9 11.7 13.6 14.6 15.6 16.2 16.8 17.2 17.7 24.7 31.7 46.9 62.1 67 72 80.7 89.3 92.3 95.3 97.7 

Fact Sheet 3.1 - Construction Rainfall Erosivity Waiver Page 13