Stormwater runoff from construction sites has been identified by the US EPA as a major source of pollution in rivers and streams. Construction sites immediately on or adjacent to rivers are especially scrutinized. In these cases, the contractor may be required to monitoring water quality above and below the construction site to insure the company is following best practices. In many instances the regulating agency only requires the construction company to measure and record turbidity. At other, more high-profile sites construction companies may be required to measure and record a suite of water quality parameters.
Frontier Precision recently cooperated on a high-profile project to provide and install water quality monitoring stations at a small hydro-electric dam that was being refurbished. The dam is one of three on a scenic river very popular for fishing and camping. The project requirements called for water quality monitoring stations upstream and downstream of the construction site with near real-time access to measurements and alarm notification if parameters exceeded thresholds.
The specific requirements of the project were for the following parameters to be measured: water temperature, pH, conductivity, dissolved oxygen, depth and turbidity. The objective was to maintain US EPA criteria for Class 3A (R317-2) waters. Accordingly, downstream water temperature could be no more than 2 degrees C different from the upstream site, downstream conductivity could not be greater than 50% of the upstream conductivity or no higher than 1275 uS/cm. Downstream pH had to be within the band of 6.5 to 9.0 pH units. Downstream dissolved oxygen could not be less than 8 mg/l and downstream turbidity could not be more than 10 NTU’s greater than the upstream turbidity. Any exceedance of these values would trigger an alarm condition resulting in a text message and e-mail to approximately 10 people including construction personnel, private consultants, state and federal land management and regulatory agencies. A valid alarm also meant that construction activities would cease until corrective action was taken.
The challenges with working in a narrow canyon included no power at the monitoring sites, no cellular reception, very little sunlight in the winter months to charge batteries and securing the equipment on public land to prevent vandalism and theft. There was also some concern with radio signal strength through thick riparian vegetation and not having good line-of-site. With these projects there is also the challenge of positioning the probes at a location in the river suitable to make representative measurements while still protecting the probes and making them accessible for periodic cleaning and calibration.
Monitoring stations were constructed at bridge crossings approximately 300 meters above the construction site and 500 meters below the site. Large steel enclosures were attached to the outside of bridge railings, sized to support a 12 VDC deep-cycle marine battery, excess antenna and water quality probe cable, and a small fiberglass enclosure for the electronics. A perforated deployment tube was secured for each probe and a 10’ mast installed to support a solar panel and radio antenna. For the water quality measurements, two In-Situ AquaTroll 500 multi-parameter transmitters were selected. The multi-parameter transmitters has a central wiper that is programmed to clean the sensors every hour to reduce biological and sediment fouling.
For datalogging and remote communication, Campbell Scientific (CSI) CR300 dataloggers with model RF451, 1-watt, spread spectrum radios were selected. Water quality is measured every minute and every 5-minutes that data from both monitoring sites is polled by a CSI CR310 data logger with an ethernet connection, installed at a small power-house building adjacent to the dam. The CR310 is running a program that compares that data from the upstream and downstream sites and e-mails the list of recipients if an alarm condition exists. The people also receive a text message by sending an e-mail with the recipients phone number to their cell phone provider who forwards the e-mail as a text message. The datalogger program creates separate data tables for the individual sites for hourly and 24-hour data, and also creates a Differences Table that simply shows the difference between the upstream and downstream sites.
The data is also made available to parties on a mobile app called LoggerLink. With this, staff can view real-time data for each station as well as the custom differences table. The status of the station including battery voltage, alarm condition and ambient temperature is also available on the app.
This method of on-site, automated data comparison and alarm notification combined with remote telemetry has proved to be extremely reliable and efficient.
Through Frontier Precision representation of market leaders in water resource instrumentation and our many years of experience providing and installing remote monitoring stations we are well equipped to satisfy environmental monitoring requirements faced by our customers.
A PDF version of a PowerPoint of this project is available at: Construction Site Water Quality