Land and Water Magazine: Reducing Turbidity, ELG’s, and Compost-Based BMPs
Summary
The final rule for the US EPA Effluent Limitation Guideline for the Construction and Development Industry (40 CFR Part 450 of the Federal Register) went into effect in February 2010. The new rule creates storm water quality performance standards for soil disturbance on construction sites 10 acres or greater. The land owner will be required to monitor and report the daily average nephelometric turbidity (NTU) from waters discharged from the construction site. The turbidity standard (numerical limit) to trigger a violation was originally 280 NTUs.
Under the current rule, the US EPA will begin enforcement on construction sites with a total active soil disturbance of 20 acres of 20 acres or greater as of August 2011. Sites that disturb 10 acres or greater will undergo active enforcement starting February 2014. For large developments this includes the sum total area of disturbance at any given time, including small sections under the acre limit.
Effluent Limitation Guideline (ELG) states the permitted party must report the daily average turbidity from all site storm water discharge areas. A violation will only occur if the daily average exceeds the NTU threshold, whereas, one reading in breach of the NTU limit does not constitute a violation. Also, if the 2yr 24hr storm event is surpassed for the local area where the construction site is located, the turbidity standard will not be enforced.
Storm water sampling frequency, number of daily samples required, sampling methodology, sampling equipment, method of measurement, and reporting method is up to the local permitting authority. Although, the US EPA will likely release a guidance document which will likely steer the permitting authorities.
The Final Rule does not dictate what type of best management practices can be used as the US EPA does not want to limit strategies that may help permitted parties comply with the new rule. They estimate that full enforcement and compliance with the new rule will encompass 73% of construction site soil disturbance nationally and should reduce annual sediment discharges from construction sites by 77%
For those with sites of 20 acres or greater, this rule will be effecting you very soon. The new standards have been described as strict and depending on the site type may be difficult to comply with. Remember that the owner is in-charge of reporting the daily average NTU, and should also be considering ways to reduce the turbidity level to keep it under limitations. The link below gives an article which includes suggestions for reducing turbidity levels: http://viewer.zmags.com/publication/f15cb27c#/f15cb27c/24
