A construction project requires 3,200 cubic yards of concrete. The NPDES permit requires pH monitoring of stormwater discharge. Concrete washout water has a pH of 11.5. What is the maximum allowable pH for discharge under NPDES permits?
Correct Answer
B) 9.0
NPDES permits typically limit stormwater discharge pH to between 6.0 and 9.0. The concrete washout water at pH 11.5 exceeds allowable limits and must be treated or properly disposed of to prevent environmental violations.
Why This Is the Correct Answer
Under NPDES (National Pollutant Discharge Elimination System) permits, stormwater discharge pH must be maintained between 6.0 and 9.0 to protect aquatic ecosystems and comply with Clean Water Act requirements. The maximum allowable pH of 9.0 ensures that discharged water remains within acceptable alkalinity levels that won't harm receiving waters or violate federal environmental regulations.
Why the Other Options Are Wrong
Option A: 8.5
8.5 is below the actual maximum allowable pH limit under NPDES permits. While this would be environmentally safe, it's not the regulatory maximum threshold established by EPA guidelines for stormwater discharge.
Option C: 10.0
10.0 exceeds the NPDES permit limits for stormwater discharge pH. This level of alkalinity would violate Clean Water Act requirements and could cause environmental damage to receiving waters and aquatic life.
Option D: 9.5
9.5 is above the maximum allowable pH limit of 9.0 established by NPDES permits. This would constitute a permit violation and could result in enforcement actions and environmental penalties.
Memory Technique
Remember 'NPDES Nine' - the maximum pH of 9.0 for stormwater discharge. Think 'Nine is Fine' for NPDES compliance.
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