#SSR1017 Stormwater Sampling Requirements

The Construction General Permit requires effluent stormwater samples be taken each day during a qualifying rain event (when a rain event produces 0.5” or more of precipitation) for Risk Level 2 and 3 sites. Sampling is conducted to ensure water discharging from your site is in compliance, and to determine the effectiveness of your BMPs. Visual monitoring of stormwater discharges is also required for all sites, regardless of Risk Level.

Stormwater runoff must meet Numeric Action Levels (NALs) for pH and turbidity in order to be in compliance. pH measures how acidic or alkaline a sample is, while turbidity measures a sample’s cloudiness. If either of these NALs are exceeded, then you must take action to improve your water quality, or you could receive a violation.

  • Acceptable pH range: 6.5 – 8.5 pH units
  • Turbidity: under 250 NTUs

In the event of an exceedance, dischargers must:

  • Take corrective actions to ensure runoff is within acceptable range
  • Change or implement additional BMPs
  • Electronically submit sampling results to State Water Board within 10 days
  • Certify each NAL Exceedance Report
  • Retain a copy of each NAL Exceedance Report for at least 3 years

Exceedances can be caused by stormwater runoff coming into contact with construction materials such as freshly poured concrete or asphalt, mulch, and uncovered stockpiles. Failure to clean chemical spills promptly and maintain BMPs can also contribute to exceedances.

In order to reduce turbidity, you can:

  • Deploy chevrons/check dams prior to rain events
  • Protect storm drains with appropriate BMPs
  • Maintain perimeter and sediment controls

In order to improve pH, you can:

  • Schedule activities accordingly – don’t pour cement or apply mulch, etc within 48 hours of a rain event
  • Clean spills in a timely manner – see our website (http://scottenvironmental.com/spill-kits) for information on spill kits and cleanup