What is the pH range and turbidity limit for Risk Level 2 & 3?

What is the pH range and turbidity limit for Risk Level 2 & 3?

• A. pH 6.0-8.0; Turbidity 200 NTU
• B. pH 6.5-8.5; Turbidity 250 NTU
• C. pH 5.5-8.0; Turbidity 300 NTU
• D. pH 7.0-8.0; Turbidity 50 NTU

Answer: (B)

This question tests the acceptable water quality parameters used for Risk Levels 2 and 3, focusing on the pH range and a turbidity limit. The correct pair sets pH between 6.5 and 8.5 and limits turbidity to 250 NTU. The pH range of 6.5 to 8.5 keeps discharges within a moderate, natural-like range that is generally safe for aquatic life and downstream treatments. Extremely acidic or very alkaline water can stress or injure organisms and can affect how disinfectants work downstream, so having a balanced range helps protect receiving waters while allowing typical site runoff. Turbidity is measured in NTU (nephelometric turbidity units) and reflects how clear the water is—the higher the turbidity, the more suspended solids and sediment are present. A limit of 250 NTU provides a practical, attainable ceiling for construction runoff at these risk levels, balancing environmental protection with the realities of rainfall events and site disturbances. Lower limits like 50 NTU would be too stringent for many sites, while higher or looser limits could permit sediment loads that harm aquatic life and downstream water quality. The other options either tighten the pH range to less practical values or set turbidity limits that are either too restrictive or too permissive for Risk Levels 2 & 3, making them less consistent with typical regulatory expectations for these levels.

This question tests the acceptable water quality parameters used for Risk Levels 2 and 3, focusing on the pH range and a turbidity limit. The correct pair sets pH between 6.5 and 8.5 and limits turbidity to 250 NTU.

The pH range of 6.5 to 8.5 keeps discharges within a moderate, natural-like range that is generally safe for aquatic life and downstream treatments. Extremely acidic or very alkaline water can stress or injure organisms and can affect how disinfectants work downstream, so having a balanced range helps protect receiving waters while allowing typical site runoff.

Turbidity is measured in NTU (nephelometric turbidity units) and reflects how clear the water is—the higher the turbidity, the more suspended solids and sediment are present. A limit of 250 NTU provides a practical, attainable ceiling for construction runoff at these risk levels, balancing environmental protection with the realities of rainfall events and site disturbances. Lower limits like 50 NTU would be too stringent for many sites, while higher or looser limits could permit sediment loads that harm aquatic life and downstream water quality.

The other options either tighten the pH range to less practical values or set turbidity limits that are either too restrictive or too permissive for Risk Levels 2 & 3, making them less consistent with typical regulatory expectations for these levels.