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Best Management Practices for Chemical Treatment Systems for Construction Stormwater and Dewatering

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4. Stormwater Treatment (Use of CTS)

• 4.1 Inspection and Maintenance
• 4.2 Discharge Compliance
• 4.3 Operator Training
• 4.4 Standard BMPs

4.1 Inspection and Maintenance

Chemical treatment systems must be operated and maintained by individuals with expertise in their use. Chemical treatment systems should be monitored continuously while in use. Test results must be recorded in a daily log kept on site, and all records turned over to the contracting agency at completion of CTS operation and upon request of the local permitting authority. Th e following monitoring should be conducted:

1. Monitoring - Minimal operational daily logs will include the following:
   1. pH conductivity (as a surrogate for alkalinity), turbidity, and temperature of the untreated stormwater.
   2. Rainfall (start of treatment shift).
   3. Total volume treated and discharged (for active CTS, not feasible for passive systems).
   4. Discharge time duration and flow rate.
   5. Type and amount of chemical used for pH adjustment.
   6. Amount of polymer used for treatment.
   7. Settling time (applies to batch treatments).
2. Compliance Monitoring - The following should:
   1. pH and turbidity of the treated stormwater.
   2. pH and turbidity of the receiving water.

4.2 Discharge Compliance

Treated stormwater must be sampled and tested for compliance with pH and turbidity limits. The sampling frequency may be established by the water quality standards or a site-specific discharge permit. Sampling and testing for other pollutants may also be necessary at some sites. Generally, the following apply:

1. Turbidity must be no more than 5 NTUs (Nephelometric Turbidity Unit), a nationwide multi-sector standard, above background turbidity. Background is measured in the receiving water, upstream from the treatment process discharge point.
2. pH must be within applicable water quality standards and not cause a change in the pH of the receiving water of more than 0.2 standard units. It is often possible to discharge treated stormwater that has a lower turbidity than the receiving water and that matches the pH. Treated stormwater samples and measurements should be taken from the discharge pipe or another location representative of the nature of the treated stormwater discharge. Samples used for determining compliance with the water quality standards in the receiving water should not be taken from the treatment pond for decanting. Compliance with the water quality standards is determined in the receiving water.

4.3 Operator Training

Each contractor who intends to use chemical treatment should be trained by an experienced system operator.

4.4 Standard BMPs

Erosion and sediment control BMPs should be implemented throughout the site to prevent erosion and discharge of sediment.

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