10.4 Topography, Contour Lines, Slope Calculations, and Plan Amendments

Free CESSWI Certified Erosion, Sediment and Stormwater Inspector Study Guide 2026 Exam

Track your progress as you read

Finished sections get a check mark.

1 Chapter 1: CESSWI Program Overview, Scope of Practice & Professional Ethics

1.1 CESSWI Scope of Practice, Eligibility, and Exam Structure 1.2 Certification Renewal, PDH Requirements, and Audit Policies 1.3 EnviroCert Code of Ethics and Professional Conduct

2 Chapter 2: Federal, State, and Local Stormwater Regulations

2.1 Federal Water-Pollution History and Stormwater Phases 2.2 CWA Sections, Water Quality, and Related Federal Programs 2.3 EPA Construction Permit Coverage and Operational Clocks 2.4 Industrial MSGP and Municipal MS4 Programs 2.5 Regulatory Compliance, Enforcement Mechanisms, and Penalties

3 Chapter 3: Soil Mechanics, Erosion Processes, and Climatic Factors

3.1 Soil Formation, Horizons, and Geomorphology 3.2 Soil Texture, Mechanics, and Revegetation 3.3 Splash, Sheet, Rill, Gully, Channel Erosion, and Slope Movement 3.4 Wind Erosion, Sediment Transport, Climatic Erosivity, and Resource Impacts

4 Chapter 4: Hydrology, Runoff Characteristics, and Drainage Principles

4.1 The Hydrologic Cycle, Watershed Drainage Planning, and Precipitation 4.2 Hydrologic Soil Groups, Disturbed Profiles, and Time Parameters 4.3 Hydrograph Characteristics, Curve Numbers, and Runoff Estimation Equations

5 Chapter 5: Inspection Fundamentals, Duties, and Field Procedures

5.1 Inspector Roles, Scope of Authority, and Core Professional Skills 5.2 Pre-Inspection Document Review and Inspector Support Equipment 5.3 Systematic Field Inspection Sequence, Post-Inspection Meetings, and Follow-Through

6 Chapter 6: Inspection Elements for Active Construction Sites

6.1 Pre-Construction Meetings, Entrance Posting, and On-Site Document Inspections 6.2 Inspecting Active Construction Controls and Diagnosing BMP Failure Modes 6.3 Final Stabilization Verification, Final Inspections, and Notice of Termination

7 Chapter 7: Stormwater Monitoring, Field Sampling, and Chain of Custody

7.1 Permit Monitoring Triggers and Water-Quality Indicators 7.2 Sampling Preparation and Analytical Parameters 7.3 Sampling Locations, Collection Methods, and Field Meter Calibration 7.4 Sample Preservation, Data Recording, Shipping, and Chain of Custody

8 Chapter 8: Inspection Documentation, Reporting, and Map Management

8.1 Inspection Notes and Evidence Procedures 8.2 Objective Findings and Photographic Evidence 8.3 Proper Reporting Techniques and Corrective Action Log Management 8.4 Site Drawing (Map) Management, Compliance Resolution, and Enforcement Records

9 Chapter 9: Professional Communication and Site Safety for Inspectors

9.1 Communication Protocols in Pre-Construction, Post-Inspection, and O&M Meetings 9.2 Dealing with Difficult People, Problematic Sites, and Unpleasant Findings 9.3 Site Hazard Recognition: Physical, Biological, Trenching, and Confined Spaces 9.4 Hazardous Substances, Safety Data Sheets (SDS), Spill Response, and PPE

10 Chapter 10: Stormwater Plan Reading, Map Interpretation, and Site Calculations

10.1 Stormwater Plan Types, Credentials, and Authority 10.2 SWPPP Components and Permit Notifications 10.3 Civil Plan Sets, Legends, Phased Sequencing, and Living Site Maps 10.4 Topography, Contour Lines, Slope Calculations, and Plan Amendments

11 Chapter 11: BMP Framework, Site Planning, and Erosion Control Practices

11.1 Six Functional BMP Categories, Preservation of Vegetation, Phasing, and Tree Protection 11.2 Seeding and Sod Establishment 11.3 Hydroseeding and Hydromulching Inspection 11.4 Mulch and Rolled Erosion-Control Products 11.5 Tackifiers, Soil Binders, Roughening, and Temporary Cover

12 Chapter 12: Perimeter, Linear, and In-Water Sediment Control Practices

12.1 Perimeter & Sheet-Flow Sediment Barriers: Silt Fence, Fiber Rolls, Straw Bales, and Filter Dikes 12.2 Access & Roadside Sediment/Runoff Controls: Stabilized Entrances, Cut-Back Curbs, and Ditch Checks 12.3 In-Water & Dewatering Controls: Temporary Stream Crossings, Turbidity Curtains, and Sediment Bags

13 Chapter 13: Sediment Basins, Traps, and Runoff Conveyance Controls

13.1 Sediment Basins and Traps 13.2 Porous Baffles and Surface Skimmers 13.3 Runoff Conveyances: Diversions, Swales, Pipe Slope Drains, and Rock Check Dams 13.4 Riprap and Gabion Inspection 13.5 Retaining Walls, Outlet Protection, and Wet Ponds

14 Chapter 14: Storm Drain Inlet Protection and Good Housekeeping BMPs

14.1 Storm Drain Inlet Protection: At-Grade, Curb, Block & Gravel, Excavated, Fabric Drop, Gravel Bag, Stone Collar, and Pre-Manufactured 14.2 Good Housekeeping Part 1: Concrete Washout, Equipment Maintenance, Materials Management, and Secondary Containment 14.3 Good Housekeeping Part 2: Stockpiles, Dust Control, Wind Fence, Street Cleaning, Sanitary Waste, and Trash

15 Chapter 15: Post-Construction Stormwater Management BMPs

15.1 Vegetative & Structural Dispersion BMPs: Final Ground Cover, Headwalls, Level Spreaders, Filter Strips, and Riparian Buffers 15.2 Permeable Surfaces and Construction Protection 15.3 Infiltration, Bioretention, and Media Filters 15.4 Detention, Retention & Proprietary BMPs: Dry/Wet Basins, Wetlands, Inline Storage, Catch Basin Inserts, Vaults, and Manufactured Devices

10.4 Topography, Contour Lines, Slope Calculations, and Plan Amendments

Key Takeaways Explain This Topic AI

Under the 7 fundamental contour rules, closely spaced contours indicate steep slopes, widely spaced contours indicate gentle slopes, hachured concentric loops indicate depressions/basins, and the Rule of V's dictates that contour 'V' shapes point upstream/upslope in valleys and swales (with water flowing perpendicular to contours out of the open mouth of the V) and point downslope along ridges.

Candidates must memorize the slope formula ( Slope = Rise / Run and % Slope = (Rise / Run) × 100 ): a 15-foot vertical rise over a 45-foot horizontal run equals a 0.333 decimal slope, a 33.3% grade, or a 3H:1V slope ratio ( 2H:1V = 50% , 4H:1V = 25% , 1H:1V = 100% ).

Check dam center-to-center spacing ( L = H / S ) ensures the upstream check dam toe sits at the exact elevation of the downstream check dam crest (e.g., a 2-ft weir height on a 4% [0.04] swale requires 50-ft spacing), while Pure Live Seed math ( % PLS = [% Purity × % Germination] / 100 ; Bulk Rate = PLS Rate / decimal PLS ) governs vegetative seeding.

Changes that alter site hydrology, drainage divides, disturbed acreage outside the LOD, or structural BMP sizing require a formal SWPPP amendment (and legally authorized designer design certification) within 7 calendar days, whereas minor operational adjustments within the design envelope (such as adding a check dam or extending silt fence) are recorded as dated, initialed field red-lines on the living site map.

Last updated: October 2026

Reading Topographic Maps and the Seven Fundamental Contour Rules

Important

SAOP 10 Core Competency: Topographic contour interpretation and slope math appear throughout Part B of the CESSWI examination. You must be able to look at a contour map, immediately identify whether a feature is a valley swale or a ridge divide, trace the 90 ∘ 90^\circ 9 0 ∘ overland flow path, and calculate slope steepness, check dam spacing, and Pure Live Seed rates.

A topographic map depicts three-dimensional terrain on a flat two-dimensional sheet using contour lines (isolines connecting points of equal elevation). As detailed in the CESSWI General Principles Review Manual (Chapter 11, Sections 11.6–11.8), seven fundamental rules govern contour interpretation:

Rule 1 — Equal Elevation Along a Contour: Every point along a single continuous contour line sits at the exact same vertical elevation above the benchmark datum. Therefore, a BMP installed strictly along a single contour line (such as a level perimeter silt fence or contour wattling) has a 0 % 0\% 0% longitudinal grade along its length, preventing runoff from flowing laterally along the barrier.

Rule 2 — Contour Interval ( CI ) and Index Contours: The Contour Interval ( CI ) is the constant vertical elevation difference between any two adjacent contour lines on a given map (typically 1 ft 1\text{ ft} 1 ft or 2 ft 2\text{ ft} 2 ft on civil site grading plans, and 5 ft , 10 ft , or 20 ft 5\text{ ft}, 10\text{ ft},\text{ or }20\text{ ft} 5 ft , 10 ft , or 20 ft on regional USGS maps). Every fifth contour line is printed bolder and labeled with its numerical elevation as an index contour . To find an unlabeled contour interval between two adjacent index contours (for example, index contours labeled 200 and 210 with 4 4 4 intermediate lines—which form 5 5 5 vertical spaces—between them), divide the elevation difference by the number of spaces: Contour Interval (CI) = 210 ft − 200 ft 5 spaces = 2 ft per contour \text{Contour Interval (CI)} = \frac{210\text{ ft} - 200\text{ ft}}{5\text{ spaces}} = 2\text{ ft per contour} Contour Interval (CI) = 5 spaces 210 ft − 200 ft ​ = 2 ft per contour

Rule 3 — Spacing Indicates Slope Steepness and Profile Geometry:

Closely Spaced Contours: Indicate a steep slope where elevation changes rapidly over a short horizontal distance, producing high runoff velocities and severe rill/gully erosion risk.

Widely Spaced Contours: Indicate a gentle or flat slope where runoff moves slowly and sediment settles.

Uniformly (Evenly) Spaced Contours: Indicate a uniform planar slope of constant gradient.

Closer at the Top (Crest) and Wider at the Bottom (Toe): Indicate a concave slope . Because the gradient flattens near the bottom, runoff decelerates at the toe—making concave slopes the most stable profile against erosion.

Wider at the Top (Crest) and Closer at the Bottom (Toe): Indicate a convex slope . Because the slope steepens sharply toward the bottom, runoff accelerates as it approaches the toe, creating high shear stress and severe toe scour.

Rule 4 — The Rule of V's (Valleys/Swales vs. Ridges/Noses):

Valleys, Swales, Gullies, and Streams ( V Points UPSTREAM / UPSLOPE): Whenever contour lines cross a drainage swale, ditch, valley, or stream channel, they bend into V or U shapes whose apex points upstream / upslope toward higher elevation . Because gravity pulls surface water downhill perpendicular ( 90 ∘ 90^\circ 9 0 ∘ ) to contour lines , overland runoff converges into the center of the swale and flows downstream out of the open mouth of the V .

Ridges, Spurs, Noses, and Divides ( V Points DOWNSLOPE): Whenever contour lines cross a ridge crest or nose, they form V or U shapes whose apex points downslope toward lower elevation . Surface water diverges (splits away) from the ridge centerline toward adjacent watersheds.

Rule 5 — Closed Concentric Loops (Hills/Stockpiles vs. Depressions/Basins):

Concentric Closed Loops with Increasing Elevation Toward the Center: Represent a hill, knoll, summit, or soil stockpile ; runoff sheds radially outward ( 360 ∘ 360^\circ 36 0 ∘ ) away from the center.

Concentric Closed Loops with Short Inward Tick Marks (Hachures / Depression Contours): Represent an enclosed depression, sinkhole, sump, or excavated sediment basin/trap ; runoff flows radially inward toward the bottom.

Rule 6 — Continuity and Non-Intersection: Contour lines never cross, split, or fork (except at a vertical retaining wall or overhanging cliff) and always form closed loops—either closing on the plan sheet or extending beyond the neatline border of the drawing.

Rule 7 — Underground Pipe Invert Elevations ( INV ): When stormwater enters an underground storm sewer pipe or culvert, surface contours no longer govern flow direction; instead, gravity flow inside the pipe always travels from the higher pipe invert elevation ( INV up \text{INV}_{\text{up}} INV up ​ ) to the lower pipe invert elevation ( INV down \text{INV}_{\text{down}} INV down ​ ) , with pipe slope calculated as: Pipe Slope ( S ) = INV up − INV down Pipe Length ( L ) \text{Pipe Slope } (S) = \frac{\text{INV}_{\text{up}} - \text{INV}_{\text{down}}}{\text{Pipe Length } (L)} Pipe Slope ( S ) = Pipe Length ( L ) INV up ​ − INV down ​ ​

Core CESSWI Exam Calculations and Step-by-Step Worked Examples

Tip

Memorization Rule for CESSWI Part B: EnviroCert International's official exam guidance states that candidates must memorize the Slope Formula ( Rise / Run = Slope \text{Rise} / \text{Run} = \text{Slope} Rise / Run = Slope ) . All other equations (Pure Live Seed, area/volume formulas, flow rate Q = V × A Q = V \times A Q = V × A ) and unit conversion factors are provided on the exam screen.

1. Slope Calculations: Decimal, Percentage, and Horizontal-to-Vertical ( H : V H:V H : V ) Ratio

Slope measures the vertical change in elevation ( Rise , V V V ) divided by the horizontal map distance ( Run , H H H ) measured perpendicular to the contour lines: Decimal Slope ( S ) = Rise Run = Elev 2 − Elev 1 Horizontal Distance ( L ) (ft/ft) \text{Decimal Slope } (S) = \frac{\text{Rise}}{\text{Run}} = \frac{\text{Elev}_2 - \text{Elev}_1}{\text{Horizontal Distance } (L)}\text{ (ft/ft)} Decimal Slope ( S ) = Run Rise ​ = Horizontal Distance ( L ) Elev 2 ​ − Elev 1 ​ ​ (ft/ft) Percent Slope ( % Slope ) = Rise Run × 100 \text{Percent Slope } (\%\text{Slope}) = \frac{\text{Rise}}{\text{Run}} \times 100 Percent Slope ( % Slope ) = Run Rise ​ × 100 Horizontal-to-Vertical Ratio ( H : V ) = Run Rise : 1 = 100 % Slope : 1 \text{Horizontal-to-Vertical Ratio } (H:V) = \frac{\text{Run}}{\text{Rise}}:1 = \frac{100}{\%\text{Slope}}:1 Horizontal-to-Vertical Ratio ( H : V ) = Rise Run ​ : 1 = % Slope 100 ​ : 1

Conversely, if you know the horizontal distance ( Run \text{Run} Run ) and decimal slope ( S S S ), or if you know the vertical change ( Rise \text{Rise} Rise ) and decimal slope ( S S S ), rearrange the equation: Rise = Run × S and Run = Rise S \text{Rise} = \text{Run} \times S \qquad \text{and} \qquad \text{Run} = \frac{\text{Rise}}{S} Rise = Run × S and Run = S Rise ​

Slope Ratio ( H : V H:V H : V ) Vertical Rise per Horizontal Run Decimal Slope ( S S S , ft/ft \text{ft/ft} ft/ft ) Percent Slope ( % Slope \%\text{Slope} % Slope ) Field Engineering & Inspection Context

1 H : 1 V 1\text{H}:1\text{V} 1 H : 1 V 1 ft 1\text{ ft} 1 ft rise per 1 ft 1\text{ ft} 1 ft run ( 45 ∘ 45^\circ 4 5 ∘ ) 1.000 ft/ft 1.000\text{ ft/ft} 1.000 ft/ft 100.0 % 100.0\% 100.0% Extremely steep cut/fill; requires retaining wall, cellular confinement, or heavy riprap

2 H : 1 V 2\text{H}:1\text{V} 2 H : 1 V 1 ft 1\text{ ft} 1 ft rise per 2 ft 2\text{ ft} 2 ft run 0.500 ft/ft 0.500\text{ ft/ft} 0.500 ft/ft 50.0 % 50.0\% 50.0% Steep embankment; typically requires RECP/TRM blankets or bonded fiber matrix (BFM)

3 H : 1 V 3\text{H}:1\text{V} 3 H : 1 V 1 ft 1\text{ ft} 1 ft rise per 3 ft 3\text{ ft} 3 ft run 0.333 ft/ft 0.333\text{ ft/ft} 0.333 ft/ft 33.3 % 33.3\% 33.3% Steep slope requiring equipment-specific mowing assessment ( Rise = 15 ft , Run = 45 ft \text{Rise}=15\text{ ft}, \text{Run}=45\text{ ft} Rise = 15 ft , Run = 45 ft )

4 H : 1 V 4\text{H}:1\text{V} 4 H : 1 V 1 ft 1\text{ ft} 1 ft rise per 4 ft 4\text{ ft} 4 ft run 0.250 ft/ft 0.250\text{ ft/ft} 0.250 ft/ft 25.0 % 25.0\% 25.0% Moderate slope; readily stabilized with conventional seed and anchored straw mulch

5 H : 1 V 5\text{H}:1\text{V} 5 H : 1 V 1 ft 1\text{ ft} 1 ft rise per 5 ft 5\text{ ft} 5 ft run 0.200 ft/ft 0.200\text{ ft/ft} 0.200 ft/ft 20.0 % 20.0\% 20.0% Gentle slope; low rill erosion risk

Worked Example 1: Calculating Slope from Map Contours and Scale

Problem: On a grading plan with a scale of 1" = 50' and a contour interval of CI = 2 ft \text{CI} = 2\text{ ft} CI = 2 ft , a fill embankment drops across 8 8 8 contour intervals from the top of the pad at elevation 426.0 ft 426.0\text{ ft} 426.0 ft to the toe at elevation 410.0 ft 410.0\text{ ft} 410.0 ft . Using an engineer's scale perpendicular to the contours, the horizontal width of the slope on the paper is 1.28 inches 1.28\text{ inches} 1.28 inches . Calculate the Rise, Run, Decimal Slope, Percent Slope, and H : V H:V H : V ratio.

Step-by-Step Solution:

Calculate Vertical Rise: Rise = 426.0 ft − 410.0 ft = 16.0 ft ( or 8 intervals × 2 ft/interval = 16.0 ft ) \text{Rise} = 426.0\text{ ft} - 410.0\text{ ft} = 16.0\text{ ft}\quad (\text{or } 8\text{ intervals} \times 2\text{ ft/interval} = 16.0\text{ ft}) Rise = 426.0 ft − 410.0 ft = 16.0 ft ( or 8 intervals × 2 ft/interval = 16.0 ft )

Calculate Horizontal Run from Map Scale ( 1" = 50' ): Run = 1.28 in × 50 ft/in = 64.0 ft \text{Run} = 1.28\text{ in} \times 50\text{ ft/in} = 64.0\text{ ft} Run = 1.28 in × 50 ft/in = 64.0 ft

Calculate Decimal Slope, Percent Slope, and H : V H:V H : V Ratio: S = 16.0 ft 64.0 ft = 0.25 ft/ft ⟹ % Slope = 0.25 × 100 = 25.0 % ⟹ H : V = 64.0 16.0 : 1 = 4 H : 1 V S = \frac{16.0\text{ ft}}{64.0\text{ ft}} = \mathbf{0.25\text{ ft/ft}} \implies \%\text{Slope} = 0.25 \times 100 = \mathbf{25.0\%} \implies H:V = \frac{64.0}{16.0}:1 = \mathbf{4\text{H}:1\text{V}} S = 64.0 ft 16.0 ft ​ = 0.25 ft/ft ⟹ % Slope = 0.25 × 100 = 25.0% ⟹ H : V = 16.0 64.0 ​ : 1 = 4 H : 1 V

2. Check Dam Spacing Formula ( L = H / S L = H / S L = H / S )

When rock, wattle, or aggregate-bag check dams are installed in a conveyance swale or roadside ditch, they must be spaced close enough so that the toe of the upstream check dam sits at the exact same elevation as the center overflow weir crest of the downstream check dam . This creates a series of low-velocity ponding steps that prevent supercritical channel bed scour between structures. L = H S L = \frac{H}{S} L = S H ​

where:

L L L = maximum center-to-center spacing between check dams along the channel ( ft \text{ft} ft );

H H H = effective center weir height of the downstream check dam ( ft \text{ft} ft ) (measured at the depressed center notch, not the higher outer wing edges keyed into the channel banks!);

S S S = longitudinal channel slope expressed as a decimal ( ft/ft \text{ft/ft} ft/ft ).

Worked Example 2: Check Dam Spacing in a Graded Swale

Problem: A 300 -foot 300\text{-foot} 300 -foot long trapezoidal drainage swale is graded at a longitudinal slope of 4 % 4\% 4% ( S = 0.04 ft/ft S = 0.04\text{ ft/ft} S = 0.04 ft/ft ). The standard detail sheet specifies rock check dams with a 2.0 -foot 2.0\text{-foot} 2.0 -foot high center weir crest ( H = 2.0 ft H = 2.0\text{ ft} H = 2.0 ft ) and 3.0 -foot 3.0\text{-foot} 3.0 -foot outer bank wings. What is the maximum center-to-center spacing ( L L L ) between check dams, and how many check dams are required for the 300 -foot 300\text{-foot} 300 -foot swale?

Step-by-Step Solution:

Use the Center Weir Height ( H = 2.0 ft H = 2.0\text{ ft} H = 2.0 ft , NOT the 3.0 -ft 3.0\text{-ft} 3.0 -ft wing height): L = H S = 2.0 ft 0.04 ft/ft = 50 feet on center L = \frac{H}{S} = \frac{2.0\text{ ft}}{0.04\text{ ft/ft}} = \mathbf{50\text{ feet on center}} L = S H ​ = 0.04 ft/ft 2.0 ft ​ = 50 feet on center

Determine Total Check Dams Required: Number of Check Dams = 300 ft 50 ft/dam = 6 check dams \text{Number of Check Dams} = \frac{300\text{ ft}}{50\text{ ft/dam}} = \mathbf{6\text{ check dams}} Number of Check Dams = 50 ft/dam 300 ft ​ = 6 check dams

3. Pure Live Seed ( PLS \text{PLS} PLS ) and Bulk Seeding / Fertilizer Application Math

Commercial seed bags contain inert chaff, stems, and a fraction of dormant or non-germinating seeds. Therefore, SWPPP revegetation specifications state seeding rates in pounds of Pure Live Seed ( PLS \text{PLS} PLS ) per acre . Before hydroseeding or drill-seeding begins, the CESSWI inspects the certified seed bag tags to verify that the contractor applies enough bulk seed to deliver the specified PLS \text{PLS} PLS weight: % PLS = % Purity × % Germination 100 ( or Decimal PLS = Decimal Purity × Decimal Germination ) \%\text{PLS} = \frac{\%\text{Purity} \times \%\text{Germination}}{100} \qquad (\text{or Decimal PLS} = \text{Decimal Purity} \times \text{Decimal Germination}) % PLS = 100 % Purity × % Germination ​ ( or Decimal PLS = Decimal Purity × Decimal Germination ) Bulk Seed Rate (lb/acre) = Specified PLS Rate (lb/acre) % PLS / 100 \text{Bulk Seed Rate (lb/acre)} = \frac{\text{Specified PLS Rate (lb/acre)}}{\%\text{PLS} / 100} Bulk Seed Rate (lb/acre) = % PLS /100 Specified PLS Rate (lb/acre) ​

Worked Example 3: Pure Live Seed ( PLS \text{PLS} PLS ) and Bulk Fertilizer N-P-K Math

Problem A (Bulk Seed): The SWPPP requires applying 40 lb PLS/acre 40\text{ lb PLS/acre} 40 lb PLS/acre of perennial tall fescue across a 3.5 -acre 3.5\text{-acre} 3.5 -acre disturbed slope. The certified seed tag on the contractor's pallets lists 90 % Purity 90\%\text{ Purity} 90% Purity and 80 % Germination 80\%\text{ Germination} 80% Germination . How many total pounds of bulk seed must the crew apply across the 3.5 -acre 3.5\text{-acre} 3.5 -acre slope?

Calculate % PLS \%\text{PLS} % PLS : % PLS = 90 × 80 100 = 72 % ( Decimal PLS = 0.72 ) \%\text{PLS} = \frac{90 \times 80}{100} = 72\%\quad (\text{Decimal PLS} = 0.72) % PLS = 100 90 × 80 ​ = 72% ( Decimal PLS = 0.72 )

Calculate Required Bulk Seed Rate per Acre: Bulk Seed Rate = 40 lb PLS/acre 0.72 = 55.56 lb bulk seed/acre \text{Bulk Seed Rate} = \frac{40\text{ lb PLS/acre}}{0.72} = 55.56\text{ lb bulk seed/acre} Bulk Seed Rate = 0.72 40 lb PLS/acre ​ = 55.56 lb bulk seed/acre

Multiply by Disturbed Acreage ( 3.5 acres 3.5\text{ acres} 3.5 acres ): Total Bulk Seed Required = 55.56 lb/acre × 3.5 acres = 194.4 lb of bulk seed \text{Total Bulk Seed Required} = 55.56\text{ lb/acre} \times 3.5\text{ acres} = \mathbf{194.4\text{ lb of bulk seed}} Total Bulk Seed Required = 55.56 lb/acre × 3.5 acres = 194.4 lb of bulk seed

Problem B (N-P-K Fertilizer): Commercial fertilizer bags display a three-number guarantee ( N-P-K , such as 10 - 20 - 10 10\text{-}20\text{-}10 10 - 20 - 10 ), representing the weight percentages of elemental Nitrogen ( N \text{N} N ) , available Phosphate ( P 2 O 5 \text{P}_2\text{O}_5 P 2 ​ O 5 ​ ) , and soluble Potash ( K 2 O \text{K}_2\text{O} K 2 ​ O ) . If the SWPPP specifies applying 40 lb 40\text{ lb} 40 lb of actual Nitrogen per acre using 10 - 20 - 10 10\text{-}20\text{-}10 10 - 20 - 10 bulk fertilizer ( 10 % N = 0.10 10\%\text{ N} = 0.10 10% N = 0.10 ), the required bulk fertilizer rate per acre is: Bulk Fertilizer Rate = 40 lb N/acre 0.10 = 400 lb/acre of 10 - 20 - 10 bulk fertilizer \text{Bulk Fertilizer Rate} = \frac{40\text{ lb N/acre}}{0.10} = \mathbf{400\text{ lb/acre of } 10\text{-}20\text{-}10\text{ bulk fertilizer}} Bulk Fertilizer Rate = 0.10 40 lb N/acre ​ = 400 lb/acre of 10 - 20 - 10 bulk fertilizer

4. Area, Volume, RECP Blanket Rolls, and Sediment Basin Storage Math

CESSWI inspectors routinely verify surface areas for Rolled Erosion Control Products ( RECPs ) and excavation volumes for temporary sediment traps and basins using standard civil unit conversions:

1 acre = 43 , 560 ft 2 1\text{ acre} = 43,560\text{ ft}^2 1 acre = 43 , 560 ft 2 ; 1 square yard (yd 2 ) = 9 ft 2 1\text{ square yard (yd}^2\text{)} = 9\text{ ft}^2 1 square yard (yd 2 ) = 9 ft 2

1 cubic yard (yd 3 ) = 27 ft 3 1\text{ cubic yard (yd}^3\text{)} = 27\text{ ft}^3 1 cubic yard (yd 3 ) = 27 ft 3 ; 1 acre-foot = 43 , 560 ft 3 1\text{ acre-foot} = 43,560\text{ ft}^3 1 acre-foot = 43 , 560 ft 3

Worked Example 4A: Rolled Erosion Control Blanket (RECP) Roll Quantity

Problem: A graded embankment measures 150 ft 150\text{ ft} 150 ft long by 60 ft 60\text{ ft} 60 ft wide. The contractor is installing double-net straw erosion control blankets where each roll measures 8 ft × 112.5 ft 8\text{ ft} \times 112.5\text{ ft} 8 ft × 112.5 ft ( 900 ft 2 = 100 yd 2 900\text{ ft}^2 = 100\text{ yd}^2 900 ft 2 = 100 yd 2 per roll). Including a standard 10 % 10\% 10% waste/overlap allowance for crest anchor trenching and adjacent roll overlaps, how many rolls must be staged on site? Slope Area = 150 ft × 60 ft = 9 , 000 ft 2 ⟹ Area with 10 % Overlap = 9 , 000 ft 2 × 1.10 = 9 , 900 ft 2 \text{Slope Area} = 150\text{ ft} \times 60\text{ ft} = 9,000\text{ ft}^2 \implies \text{Area with } 10\%\text{ Overlap} = 9,000\text{ ft}^2 \times 1.10 = 9,900\text{ ft}^2 Slope Area = 150 ft × 60 ft = 9 , 000 ft 2 ⟹ Area with 10% Overlap = 9 , 000 ft 2 × 1.10 = 9 , 900 ft 2 Required Rolls = 9 , 900 ft 2 900 ft 2 / roll = 11 rolls \text{Required Rolls} = \frac{9,900\text{ ft}^2}{900\text{ ft}^2/\text{roll}} = \mathbf{11\text{ rolls}} Required Rolls = 900 ft 2 / roll 9 , 900 ft 2 ​ = 11 rolls

Worked Example 4B: Temporary Sediment Basin Storage Volume

Problem: Under the standard NPDES CGP volumetric sizing rule requiring 3 , 600 ft 3 3,600\text{ ft}^3 3 , 600 ft 3 of storage per acre drained ( 134 yd 3 / acre 134\text{ yd}^3/\text{acre} 134 yd 3 / acre ), what minimum storage volume (in both cubic feet and cubic yards) must be excavated for a temporary sediment basin serving a 10 -acre 10\text{-acre} 10 -acre disturbed watershed? Required Storage Volume = 10 acres × 3 , 600 ft 3 / acre = 36 , 000 ft 3 = 36 , 000 ft 3 27 ft 3 / yd 3 = 1 , 333.3 yd 3 \text{Required Storage Volume} = 10\text{ acres} \times 3,600\text{ ft}^3/\text{acre} = \mathbf{36,000\text{ ft}^3} = \frac{36,000\text{ ft}^3}{27\text{ ft}^3/\text{yd}^3} = \mathbf{1,333.3\text{ yd}^3} Required Storage Volume = 10 acres × 3 , 600 ft 3 / acre = 36 , 000 ft 3 = 27 ft 3 / yd 3 36 , 000 ft 3 ​ = 1 , 333.3 yd 3

SWPPP Plan Amendments vs. Minor Field Red-Lines

As construction progresses, field conditions inevitably diverge from the original baseline drawings. Under SAOP 10 Test Objective 8, a CESSWI must distinguish between major engineering changes that trigger a formal SWPPP Plan Amendment (within 7 calendar days ) and routine operational adjustments that are documented as minor field red-line markups on the on-site living map:

Modification Type Field Examples Triggering This Category Required Administrative & Engineering Action Mandatory Timeline & Signatory

Formal SWPPP Plan Amendment (Major Engineering / Hydrologic Change) Expanding earthwork outside the approved Limits of Disturbance ( LOD ) ; altering drainage divides or outfall locations; resizing or relocating a sediment basin ; changing a spillway riser, orifice, or culvert diameter; replacing a structural BMP with a different engineered system Must be engineered and recalculated by a qualified designer ( legally authorized designer ); formal revision to SWPPP narrative, hydrologic calculations, and plan sheets Completed within 7 calendar days 7\text{ calendar days} 7 calendar days ; must be formally certified by the primary executive signatory ( 40 CFR § 122.22(a) ) or authorized delegate

Minor Field Red-Line Markup (Operational Adjustment Within Design Envelope) Adding an extra rock check dam inside an existing swale; extending a perimeter silt fence run by 30 ft 30\text{ ft} 30 ft to prevent end-around bypass; adding secondary gravel bags around an existing drop inlet; shifting a portable toilet, dumpster, or concrete washout within an already approved staging pad Marked neatly in red ink directly on the on-site living SWPPP site map (and logged in the inspection / maintenance record) without needing new hydrologic modeling Updated immediately / during the inspection cycle with the date, description of change, and initials of the inspector or site superintendent