Calculator Inputs
Example Data Table
| Scenario | Method | Inputs | Runoff (m3) | Untreated (kg) | Efficiency | Treated (kg) |
|---|---|---|---|---|---|---|
| Small pad | Rainfall + Area | 0.5 acre, 20 mm, C=0.65, 600 mg/L | 26.305 | 15.783 | 40% | 9.470 |
| Road widening | Rainfall + Area | 2 ha, 15 mm, C=0.50, 450 mg/L | 150.000 | 67.500 | 60% | 27.000 |
| Measured discharge | Known Volume | 800 m3, 1,000 mg/L | 800.000 | 800.000 | 70% | 240.000 |
These examples are illustrative. Replace with site-specific monitoring or approved design values.
Formula Used
1) Runoff volume (rainfall method)
V (m3) = A (m2) × P (mm ÷ 1000) × C
2) TSS mass load
Load (kg) = Concentration (mg/L) × V (m3) ÷ 1000
Because 1 m3 = 1000 L and 1 kg = 1,000,000 mg.
3) Treated load (using removal efficiency)
Treated (kg) = Load (kg) × (1 − Efficiency ÷ 100)
How to Use This Calculator
- Select a calculation method based on available data.
- Enter TSS concentration as event mean concentration (EMC).
- If using rainfall, provide area, rainfall depth, and runoff coefficient.
- If using known volume, enter the measured runoff volume and unit.
- Enter removal efficiency for sediment controls or treatment.
- Optionally set events per year for annualized load estimates.
- Click Calculate to show results above the form.
- Use Download CSV or Download PDF for reporting.
For compliance submittals, use approved local guidance for EMCs, runoff factors, and credited treatment performance.
Practical Notes on TSS Load Estimation
Total Suspended Solids (TSS) is a widely used indicator of sediment leaving a construction site. Earthworks, hauling routes, stockpiles, and unprotected slopes can release fine particles that move with runoff. Many stormwater permits and erosion and sediment control plans use TSS because it links to turbidity, habitat stress, and downstream dredging or cleaning costs. A load estimate (mass per event or per year) gives teams a consistent way to compare phases, justify controls, and document expected performance.
This calculator supports two practical workflows. The rainfall + area method estimates runoff volume from contributing area, rainfall depth, and a runoff coefficient (C). It is helpful during planning when monitoring data is not available. Choose C to reflect surface condition and compaction; stabilized soils tend to have lower runoff than paved or heavily compacted areas. The known volume method uses a measured or modeled runoff volume and is ideal for flowmeter records, pump totals, detention drawdowns, or dewatering activities.
The mass balance relationship is commonly used for screening-level estimates: Load (kg) = Concentration (mg/L) x Volume (m3) / 1000. The division by 1000 comes from unit conversions because 1 m3 = 1000 L and 1 kg = 1,000,000 mg. If treatment is applied, the calculator reduces the untreated mass by the specified removal efficiency to estimate treated discharge. When multiple controls are installed, apply conservative combined performance unless your permit guidance provides a specific treatment-train method.
Use monitoring to calibrate assumptions after the first few storms.
Example dataset (rainfall workflow): contributing area 1.5 acre, rainfall depth 25 mm, runoff coefficient C = 0.70, event mean concentration 800 mg/L, and removal efficiency 50%. The runoff volume is 106.230 m3. The untreated load is 84.984 kg (about 187.358 lb). After treatment, the estimated discharge is 42.492 kg. If you expect 30 similar runoff-producing events per year, annualized loads are 2549.514 kg/yr untreated and 1274.757 kg/yr treated.
For professional documentation, focus on traceability and consistency. Record the source of concentration values, the basis for the runoff coefficient, and what control configuration the efficiency represents. Where uncertainty exists, run low, typical, and high scenarios to show sensitivity and reduce the chance of underestimating loads. Recalculate when the disturbed area changes, when stabilization improves, or when controls are reconfigured. Use the Notes field to capture key assumptions so exported CSV and PDF files remain defensible over the project lifecycle.
FAQs
1) What TSS concentration should I use?
Use values from local manuals, monitoring reports, or project sampling. If unsure, run several scenarios (low, typical, high) to understand sensitivity and support conservative planning.
2) Why does the rainfall method use a runoff coefficient?
The coefficient represents losses to infiltration and storage. Compacted soils, bare subgrades, and paved areas usually have higher runoff. Choose a value aligned with surface condition and drainage connectivity.
3) Can I calculate loads for dewatering or wash water?
Yes. Use the known-volume method with measured discharge volume and a representative concentration from sampling. This works well for pump logs, tank records, or treatment system flow totals.
4) How should I choose removal efficiency?
Use credited performance from permits, validated monitoring, or manufacturer testing accepted by your authority. Avoid overly optimistic assumptions. For treatment trains, apply conservative combined performance unless guidance provides a method.
5) Why are results shown in both kg and lb?
Different projects and agencies prefer different units. Showing both supports consistent reporting and cross-checking. The values are directly converted from the same calculated mass load.
6) What does “events per year” represent?
It is the number of runoff-producing events expected annually. Multiplying event load by this value gives an annualized estimate for reporting or for comparing control strategies.
7) What are common mistakes to avoid?
Unit mix-ups are most common. Confirm area unit, rainfall depth, and volume unit. Also record sources for concentration and efficiency, and update calculations when site phases or controls change.