FLOOD04935

• County: Statewide
• Basin: Statewide
• Title: Storm Water Management for Constructed Activities
• Date: 9/1/1992
• Prepared By: EPA
• Floodplain - Doc Type: Educational/Technical/Reference Information

Chapter 2-Storm Water Pollution Prevention Plan

SITE EVALUATION AND oeSIG~' DEVELOPMENT i
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2.2 ASSESSMENT

ASSESSMENT

After the charactelristics of the site and the
construction have been, defined, the next phase in
developing a Storm Wa11er Pollution Prevention Plan
is to measure the size 'Jf the land disturbance and
estimate the impact tho project will have on storm
water runoff from the site from the information
developed in phase 1. There are three tasks which
should be done to aslOess the project, they are:
measure site area. measure drainage areas. and
calculate runoff coefficient.

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. Measur. the Slt.area
. Oe'ermllle lhe drainage ar.as
. Calculat. the runolt coel'flclent

CONTROL SElECT10f\4lPLAN DESIGN

CERTIFICATION AND NOTIFICATION

CONSTRUCnONlIMPLEr.4ENTATlON

FINAL STABlUZATlONITEAM1NATlON

2.2.1 Measure Site Area

Typically, NPDES storm water permits may require that you indicate in t~e Storm Water Pollution
Prevention Plan estimates of the total site area and the area which wHI bo disturbed. You will need
the Storm Water Pollution Prevention Plan site map which clearly shows the site boundary and the
limit of disturbance. T~e area of the site can usually be found on the deod of sale for the property,
the record plat, site survey, or the site plan. The amount of area to be disturbed is sometimes
noted on a site plan, or grading plan. If the Information is not available from one of these sources
you may measure using the grid method or by using a planimeter.

The most accurate method to measure area from t~e site map is with a planimeter. A planimeter is
a device whic~ can measure the area on a drawing by tracing its outline. Planimeters are available
from Engineering and Surveyor Supply Stores.

If you do not have access to a planimeter and do not wish to buy one, the grid method is an easy
method for estimating the size of an area which only requires transparent graph or grid paper. The
steps are as follows:

1. Place graph or grid paper over the scale drawing and trace the outline of the entire property.

2. Count the total number of complete squares within the site area, (:ount every two partial
squares along the edges of the site as one square.

3. Divide the total number of squares by the number of squares in, orle square inch of graph!
grid paper. This results in an estimate of the number of square im:hes contained in the
outline of the site.

4. Multiply t~e result of Step 3 by the number of square feet in a onEI inch square based on the
scale of the drawing. This results in an estimate of the number of square feet on the site.

2-8

September 1992

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