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Calcimator

Stormwater Permit Compliance Calculator

Estimate NPDES stormwater permit compliance costs including SWPPP preparation, BMP installation, post-construction management, and ongoing monitoring.

Inputs

%

Results

First-year total cost ($)

$22,000.00

≈ 11 gaming PCs

SWPPP preparation ($)$2,500.00
BMP installation ($)$6,000.00
Post-construction BMPs ($)$8,400.00
Annual monitoring ($)$4,300.00
Total lifecycle cost ($)$30,600.00
Detention volume (gallons)32,585
Impervious area (acres)1.2
How to Use This Calculator
  1. Enter Total Site Acreage and Impervious Coverage (%).
  2. Select Project Type (land development, industrial, municipal, etc.) and MS4 Tier (1 or 2).
  3. Set Monitoring Period (years) for the permit term.
  4. Review First-Year Total Cost and SWPPP Preparation cost.
  5. Use this estimate to budget stormwater compliance as part of the project's soft costs.

How the result changes with Total site acreage

Total site acreageFirst-year total cost ($)
500$3,681,850.00
1,750$12,869,350.00
3,250$23,894,350.00
4,500$33,081,850.00

What each input means

Total site acreage
Total project site area in acres.
Impervious coverage (%)
Percentage of site covered by impervious surfaces (roofs, pavement, etc.).
Project type
0 = New construction, 1 = Redevelopment, 2 = Industrial facility.
MS4 tier (1-2)
1 = Phase II (small MS4), 2 = Phase I (medium/large MS4, stricter requirements).
Monitoring period (years)
Number of years of post-construction monitoring.

What each result means

First-year total cost ($)
Complete first-year compliance cost including installation.
SWPPP preparation ($)
Stormwater Pollution Prevention Plan development cost.
BMP installation ($)
Construction-phase Best Management Practices installation.
Post-construction BMPs ($)
Permanent stormwater management infrastructure.
Annual monitoring ($)
Yearly inspection, sampling, and reporting costs.
Total lifecycle cost ($)
All costs over the full monitoring period.
Detention volume (gallons)
Required stormwater detention capacity for 1-inch design storm.
Impervious area (acres)
Calculated impervious surface area.

How this is calculated

Worked example, using the default values

  1. Identify Input Parameters
    4 parameters
    Total site acreage = 2, Impervious coverage (%) = 60, Project type = 0, MS4 tier (1-2) = 1 = 5 input(s) provided
  2. Calculate First-year total cost
    First-year total cost = swpppCost + permitFee + bmpInstallCost + postConstructionCost + annualMonitor...
    22000 = $22,000
  3. Calculate SWPPP preparation
    SWPPP preparation = swpppBase + swpppAcreAdder
    2500 = $2,500
  4. Calculate BMP installation
    BMP installation = imperviousAcres * bmpRatePerAcre * bmpComplexityMult
    6000 = $6,000

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