Water Quality Sampling

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:

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:

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.