Routine Dry Weather Sampling

Under base flow (dry-weather) conditions, CWD staff members collect water samples and measure streamflow and in situ parameters (dissolved oxygen, specific conductance, temperature, oxidation-reduction potential, and pH) throughout the watershed.  Base flow sampling, conducted in regular intervals on days with no more than 0.10 in of rain 72 hours prior, provides a representative measurement without the influence of stormwater.  Sampling is conducted at 8 reservoir, 12 primary tributary, and 4 secondary tributary monitoring stations.

 

Reservoir Sampling Process Overview

The Hobbs Brook, Stony Brook, and Fresh Pond Reservoirs are all sampled regularly using USGS clean-sampling protocols.  Each reservoir is sampled for nutrients, metals, chlorophyll-a, bacteria and in-situ parameters.  During summer months, when the water column is thermally stratified, additional water samples are pumped from below the thermocline (the point of maximum rate of change in water temperature with depth) at the deepest point of the reservoirs with a peristaltic pump through pre-cleaned Tygon tubing.  Studies conducted by the USGS have shown that under most conditions, water quality data collected in depth profiles at these stations are indicative of conditions throughout the reservoirs.

Samples are analyzed at the CWD laboratory for volatile organic compounds, total organic carbon, color, alkalinity, nitrates/nitrites, turbidity, bacteria, concentrations of major ions (sodium, calcium, chloride, and sulfate), and selected metals (aluminum, iron, and manganese) using standard methods.  Nutrients (ammonia nitrogen, total Kjeldahl nitrogen, and total phosphorus) and chlorophyll-a are analyzed at contracted laboratories.

 

Routine Tributary Monitoring Process Overview

Water entering the reservoirs is monitored at 12 primary and 4 secondary tributary monitoring stations.  Primary monitoring stations are sampled 4 - 8 times a year.  Specific conductance, pH, water temperature, and dissolved oxygen concentrations are measured in situ and water samples are collected at the stream channel center in accordance with clean-sampling protocols.  The samples are analyzed at both CWD and contracted laboratories for the same suite of parameters as the reservoir samples except for chlorophyll-a.

The four secondary stream monitoring stations are monitored 1 - 2 times a year, usually during base flow conditions.  These stations are located higher up in the drainage basin on smaller tributaries that feed into larger tributaries that have primary monitoring stations.  The secondary stations are sampled for the same constituents as the primary stations to provide indicators of potential changes in water quality or of base flow conditions.

 

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