Type of Samples Needed

According to 40 CFR 122.21(g)(7) and 40 CFR Part 136 , industrial facilities must collect samples by either grab sampling or composite sampling methods to comply with stormwater application requirements.

Grab Samples

A grab sample is a single sample “grabbed” by filling up a container, either by hand or with the container attached to a pole. It is the simplest method to collect samples. Grab samples must be collected during the first 30 minutes of the discharge. Enough water sample (at least 100 milliliters) needs to be collected to perform required analysis. Water samples must be collected a t least 15 minutes apart. To prevent the tendency of water parameters changing concentration or characteristics, grab samples must be used for the following parameters analysis:

• pH

• Temperature

• Cyanide

• Total phenols

• Residual chlorine

• Oil and grease

• Fecal coliform

• Fecal streptococcus

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Composite Samples

Composite samples consist of a number of subsamples of specific volumes collected at specified time intervals rather than a single grab sample. Composite samples can be flow-weighted or time-weighted. For all stormwater permit applicants taking flow-weighted composites, quantitative data must be reported for all pollutants specified in 40 CFR 122.26 except pH, temperature, cyanide, total phenols, residual chlorine, oil and grease, fecal coliform, and fecal streptococcus which can only be collected by grab sampling method.

For stormwater monitoring a flow-weighted composite shall be taken for either the entire discharge or for the first three hours of the discharge. The flow-weighted composite sample for a stormwater discharge may be taken with a continuous sampler or as a combination of a minimum of three sample aliquots taken in each hour of discharge for the entire discharge or for the first three hours of the discharge. Each sample should be at least fifteen minutes apart. For a flow-weighted composite sample, only one analysis of the composite of aliquots is required. A minimum of one grab sample may be taken for stormwater discharges from holding ponds or other impoundments with a retention period greater than 24 hours.

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Copyright @ January,2005 Prepared by Transportation Environmental Resource Center (TERC)