Wet Weather Sampling

Many pollutants, including solids, nutrients, metals, bacteria, and others, are washed into nearby streams during rainstorms. To better understand the conditions in the County’s streams, it is necessary to characterize the pollutant loadings that occur during wet weather. In 1999, the County established automated sampling at five locations to monitor stream conditions during and immediately after periods of rain.

The five sampling stations are strategically located in watersheds representing various land uses. One station was located west of Williamsburg on Kain Run, which receives runoff from agricultural fields, this station was removed in 2009 because of ODOT construction.  Stations are also located on Shayler Creek and Hall Run, two principally residential/commercial tributaries to the East Fork, located in the lower section of the watershed.  The remaining two samples are located on Stonelick Creek, the largest tributary to the East Fork, and on the East Fork itself at Williamsburg.

Each sampling station includes several pieces of monitoring and sampling equipment, including:

  1. a water quality probe that measures and records stream temperature, pH, conductivity and dissolved oxygen concentrations at 15-minute intervals throughout the year
  2. a flow meter that records stream depth at 15-minute intervals
  3. a sampling unit that is programmed to collect water quality samples when the stream rises above a certain level

After periods of rain, if the streams exceed a pre-determined level, the sampling unit will pump water from the stream and fill sample bottles that have been placed in a refrigerated unit. After the event, field crews visit each sampler to collect the bottles and transport them to the lab for analysis. These units allow OEQ to collect the data necessary to calculate pollutant loadings during periods of rain when most pollutants are being washed into the streams. The results from each station can then be used to predict conditions in other watersheds with similar land uses.