Equipment and sampling needs vary among monitoring levels. At the lowest level, hydrology is usually the only aspect monitored. At a moderate level, quality tends to be coupled with hydrology monitoring. Quality is important in protecting wildlife and vegetation on site and downstream.
Surface samples are representative of runoff and direct precipitation. They are important in evaluating the contaminants found on nearby impervious surfaces. Surface samples include:
First Flush Samplers- is a sample consisting of the is the amount of runoff resulting from 90% of the storm. A sampler is set up prior to storm and collected at end for analysis.
When: Collected until filled during a storm event.
Where: In a location that leads into the SCM. Typically near an inlet source.
Grab Samples- are samples collected by hand from an area of ponded depth or continuous flow. Samples are collected at user defined intervals for analysis.
When: Periodically throughout the storm.
Where: At a source of continuous flow or ponded depth.
Automated Samplers- a unit capable of taking several discrete or a single composite sample. Samples are collected by a tube that extends out of the sampler and into the streaming or ponded water. Sampler programmed prior to storm and collected at end for analysis.
When: Collected at user defined intervals throughout the storm.
Where: At a source of continuous flow or ponded water.
Grab samples and automated samplers can be a means of collecting overflow. This can help determine the amount of pollutants being removed by the SCM.
Subsurface samples collect infiltrated pore water from the soil strata. The equipment used is:
Lysimeters-a ceramic cup to which a vacuum pressure is placed on after a storm has initialized. During the storm, the pressure exceeds that of the soil suction within capillary spaces causing water to flow into the sampler.
When: Setup during a storm event while the moisture front is moving through the vadose zone. Extracted
via suction 12-24 hours after pressure.
Where: Various depths beneath the soil strata.
At varying depths, a record of contaminant removal can be recorded as recharge moves through the vadose zone.