10 State Standards Wastewater Weir Overflow Rates Calculation

function calculateWOR() { var flow = parseFloat(document.getElementById('flowRate').value); var length = parseFloat(document.getElementById('weirLength').value); var resultDiv = document.getElementById('worResult'); if (isNaN(flow) || isNaN(length) || length <= 0 || flow < 0) { resultDiv.style.display = 'block'; resultDiv.style.backgroundColor = '#f8d7da'; resultDiv.style.color = '#721c24'; resultDiv.innerHTML = 'Error: Please enter valid positive numbers for Flow Rate and Weir Length.'; return; } var wor = flow / length; var statusMessage = ""; var statusColor = ""; // 10 State Standards Guidelines: // For plants 1.0 MGD: 15,000 to 20,000 gpd/ft if (wor <= 10000) { statusMessage = "Excellent. This meets the most stringent 10 State Standards for small plants."; statusColor = "#d4edda"; } else if (wor 1 MGD)."; statusColor = "#fff3cd"; } else if (wor <= 30000) { statusMessage = "Warning: Exceeds standard average limits. May be acceptable for peak hourly flow in some jurisdictions."; statusColor = "#ffeeba"; } else { statusMessage = "High Overflow Rate: Exceeds recommended 10 State Standards. Risk of solids carryover."; statusColor = "#f8d7da"; } resultDiv.style.display = 'block'; resultDiv.style.backgroundColor = statusColor; resultDiv.style.color = '#333'; resultDiv.style.border = '1px solid #ccc'; resultDiv.innerHTML = '

' + wor.toLocaleString(undefined, {maximumFractionDigits: 2}) + ' GPD/ft

' + '

' + statusMessage + '

' + '

Note: Calculated as Total Flow / Total Weir Length.

'; }

Understanding Wastewater Weir Overflow Rates (WOR)

In wastewater treatment, the Weir Overflow Rate (WOR) is a critical hydraulic loading parameter used to design clarifiers (sedimentation tanks). It measures the volume of effluent passing over each foot of the weir per day. According to the "Recommended Standards for Wastewater Facilities" (often referred to as the 10 State Standards or GLUMRB), controlling this rate is essential to prevent high velocities near the weir that could pull settled solids out of the tank.

The WOR Formula

The calculation is straightforward but vital for engineering compliance:

WOR = Q / L
Where:

• Q: Total Flow Rate (Gallons per Day)
• L: Total Effluent Weir Length (Feet)

10 State Standards Guidelines

The 10 State Standards provide specific design criteria to ensure effective solids separation:

• Small Plants (< 1.0 MGD): Weir loading should generally not exceed 10,000 gallons per day per linear foot (gpd/ft) at average design flow.
• Large Plants (> 1.0 MGD): Loading can increase up to 15,000 to 20,000 gpd/ft at average design flow.
• Peak Hourly Flow: For peak conditions, many jurisdictions allow rates up to 30,000 gpd/ft, though higher rates increase the risk of "density currents" and solids carryover.

Example Calculation

Suppose a treatment plant has a design average flow of 2,500,000 GPD (2.5 MGD) and a circular clarifier with a peripheral weir that is 150 feet in length.

1. Flow (Q): 2,500,000 GPD
2. Length (L): 150 ft
3. Calculation: 2,500,000 / 150 = 16,666.67 GPD/ft

In this case, the rate is roughly 16,667 GPD/ft. Since the plant is over 1.0 MGD, this meets the standard 10 State Standards guideline of staying below 20,000 GPD/ft.

Why Weir Loading Matters

If the Weir Overflow Rate is too high, the upward velocity of the water near the effluent launder exceeds the settling velocity of the flocculent particles. This causes "pin floc" or suspended solids to be pulled over the weir and into the final effluent, potentially leading to permit violations for Total Suspended Solids (TSS) and Biochemical Oxygen Demand (BOD).

Frequently Asked Questions

How can I reduce my WOR?

If your WOR is too high, you can increase the weir length by adding "serpentine" or "finger" weirs, or by installing a double-sided launder. This increases the total linear feet (L) without needing a larger tank diameter.

Do these standards apply to both primary and secondary clarifiers?

Yes, though the specific allowable rates may vary slightly depending on the settling characteristics of the solids (e.g., primary sludge vs. activated sludge). Always check your specific state's adaptation of the GLUMRB standards.