Chemical Storage Facility in Houston, Texas
Engineering Case Study
Chemical Storage Facility in Houston, Texas
Scenario
A Tier-2 hazardous chemical storage facility is being constructed at an industrial park near the Houston Ship Channel. The site is subject to EPA 40 CFR §264.193 and TCEQ regulations requiring secondary containment for bulk liquid storage. Key constraints include limited footprint (due to adjacent rail access), high local rainfall intensity from Gulf Coast thunderstorms, and aggressive corrosion potential from stored sodium hydroxide (50% w/w) and sulfuric acid.
Given Data
- Volume of the largest tank: 2,850 m³ (single vertical cylindrical tank storing caustic soda)
- Projected area of the containment sump: 320 m² (determined by pad layout and 1.5× tank footprint envelope)
- Local rainfall intensity: 92 mm/hour (based on NOAA Atlas 14, 100-year 6-hour storm for Harris County)
- Design storm duration: 6 hours
Calculation
The required secondary containment volume is computed as:
Secondary Containment Volume = Volume of largest tank + (Rainfall intensity × Duration × Sump area)
Convert rainfall intensity to meters/hour: 92 mm/hour = 0.092 m/hour
Rainwater accumulation = 0.092 m/h × 6 h × 320 m² = 176.64 m³
Total required volume = 2,850 m³ + 176.64 m³ = 3,026.64 m³
Rounded to two decimal places per tool specification: 3,026.64 m³
Result and Decision
The design team selected a reinforced concrete sump with integral epoxy-lined walls and floor (ASTM C1582 Class II), sized to 3,030 m³ (providing 3.36 m³ safety margin). A dual-slope floor (0.5% toward central sump pit) and submersible level sensors with SCADA integration were incorporated. The sump was elevated 0.3 m above grade to prevent flood ingress during storm surge events.
Lesson
Rainwater contribution can exceed 6% of total containment volume in high-intensity rainfall zones — always validate local IDF curves against regulatory design storms (e.g., 100-year/6-hour), not just historical averages. Ignoring this led to a non-compliant sump retrofit at a nearby facility in 2022 after TCEQ enforcement action.