This document provides an overview of managing construction site water runoff. It discusses evaluating projects based on discharge location, permits required, site characteristics like soil type and rainfall, and selecting best management practices (BMPs). Passive BMPs like detention ponds are effective for larger particle sizes, while active treatment systems can remove particles down to 0.01 microns. A case study example demonstrates initially using detention and sand filtration, but achieving compliance only with electrocoagulation active treatment due to small particle sizes. The document emphasizes properly planning projects based on regulatory requirements and site specifics to treat turbidity and contaminants.
11. 11
Discharge to Surface Water
NPDES (aka Construction Stormwater General Permit or CSWGP)
• Applicability
• Construction Sites disturbing ≥ 1 acre and will discharge stormwater
offsite
• Sites under an acre that are part of a common plan (residential)
• Other sites that may discharge to sensitive areas or have contamination
• Requirements
• Must comply with permit limits for Turbidity (<25) and pH (6.5‐8.5)
• Must have a site‐specific Stormwater Pollution Prevention Plan (SWPPP)
• Must have a CESCL perform site inspection weekly and take water
quality readings
• Additional sampling/treatment required if site has contaminants
PROPOSED UPDATES for JAN 1st:
• More information required for Contaminated sites
• Contaminated sites will use AKART – Active Treatment
• Drilled shaft water (no drilling fluids) can be infiltrated
• SWPPP Elements (preserving topsoil/LID)
12. 12
Discharge to Sanitary Sewer/CSO
King County Industrial Waste Discharge Authorization and/or Local Approval
• Applicability
• Sites discharging to a Combined Sewer
• Construction Sites disturbing < 1 acre and will discharge stormwater offsite
• Alternate discharge for sites that may discharge to sensitive areas or have
contamination
• Requirements
• Must comply with permit limits for Maximum Daily Volume, Settleable Solids
(<7mg/L) and pH (5.5‐12)
• Must take Field Measurements (min Flow/Volume, Settleable Solids, pH)
every day that discharge occurs
• Additional sampling/treatment required if site has contaminants
• Must submit monthly reports and pay per gallon fee.
Current review time for KCIW permit is at least 4 weeks, double if complex
or contaminated site.
City of Seattle may hold grading permit until SSPTD is obtained.
13. 13
Local Authority
• Local Jurisdictions (City/County)
– May require specific plans for work during the wet season
• Review SWPPP, site plans, geotech, may have formal application pkg
– May have more stringent discharge requirements than the State
– Allow time for review and approval (4 weeks min)
– Administrative fees associated with some approvals
City of Redmond – Wet Weather Plan
City of Bellevue – Turbidity Monitoring Plan
City of Seattle – Drainage Side Sewer Permit $, Dry Season Grading Extension
City of Tacoma – Special Authorization to Discharge (SAD) $
King County – Wet Season Plan
Snohomish – Enhanced TESC Review
14. 14
• Surface Water
– Turbidity
• 25 ntu benchmark
• 250 enforcement level
– pH
• 6.5 – 8.5
– Other as receiving water or
past site activity dictates
• Sanitary Sewer/CSO
– Settleable Solids
• <7 mg/L
– pH
• 5.0 – 11.0
– Other as receiving water or
past site activity dictates
Discharge Limits
2000 1000 500 100 5
20. 20
Chitosan Enhanced Sand
Filtration (CESF)
Electrocoagulation (EC)
Approval Level GULD GULD
Consumable Liquid Chitosan EC Cells
Labor
On‐Site Labor When
Operating
Automated Operator with
Alerts
Contaminants Turbidity Only
Turbidity, Metals, Emulsified
Oils
Active pH Range 7 to 8 5 to 12
Active NTU Range 0 to 600 0 to 4,000+
Rental Cost (300 gpm) $195 to 225 / day $250 to 310 / day
Active Treatment BMPs
