One Rain Event, Multiple Samples

Aug. 20, 2008

About the author: Rhett Farrell is president of EcoServe Environmental Consulting Corp. Farrell can be reached at 832.422.2425 or by e-mail at [email protected].

Have you ever been challenged with sampling more than one location during a single qualifying rain event? Would you like to clone yourself or your sampling technicians in order to sample more than one location at the same time to reduce mileage, time and the overall cost associated with making several trips to facilities to take grab samples over long periods of time? If so, a storm water mounting bracket and sampler may be the answer.

Permit Compliance

World Environmental LLC, an environmental consulting firm in The Woodlands, Texas, provides storm water sampling in accordance with the Texas Pollution Discharge Elimination System Multi-Sector General Permit (TPDES-MSGP) TXR050000, which is similar to the National Pollutant Discharge Elimination System permit for the state. One method used for sample collection is a bracket and sampler—enormous aids in gathering samples for more than one location during qualifying storm events.

The TPDES-MSGP sets sampling guidelines which must be met to obtain a compliant sample in accordance with the permit. The guidelines in the TPDES are to collect a sample during the first 30 minutes of discharge during a rainfall of 0.1 in. or more following a 72-hour dry-weather period. When installed correctly, a bracket and sampler system can meet all these guidelines.

World has installed the Nalgene storm water mounting bracket and sampler system in various locations and at facilities with multiple outfalls. The components can be installed directly in the ground or in a water-filled drainage ditch, or hung in a municipal-type side-of-road storm drain.

How a System Works

The bracket is a plastic cylinder with a lid and hollow core accommodating insertion of a sampler bottle. To stay within requirements, a sampler should be inserted into the bracket just prior to a rain event following a 72-hour dry-weather period. The bracket has three pop-out buttons to which a wire harness can be attached so that it can be hung in a storm water drain.

Knowing the characteristic flow at an outfall is necessary so that the installation depth of a bracket can be estimated to ensure a grab sample is obtained within the first 30 minutes of flow. The bracket must be installed to a level where inlets will allow storm water to enter a sampler during this discharge period.

A screen in the bottom allows a sampler to note any trapped materials such as vegetative matter and trash. The lid has a stopper to prevent rainfall from directly entering the top of the system. When the bracket is installed into a drain, however, this stopper can be removed to allow for the draining water to enter the sampler through the top of the bracket.

Nalgene’s sampler bottle is a 1,000-mL sterile plastic bottle with a floating ball valve that enables the sampler to receive a sample and then close within the first couple of minutes that storm water runoff has reached the inlets on the bracket. When the bottle is full, the ball floats to the top, closing off the sampler and containing the grab sample inside.

The fact that an entire system can be submerged after a heavy rainfall but a grab sample will be preserved inside increases efficiency and helps minimize project budgets.

Download: Here

About the Author

Rhett Farrell