AUTOMATED PROCESS FOR MONITORING GROUND - WATER QUALITY USING ESTABLISHED MANUAL SAMPLING PROTOCOLS
SITE AND EQUIPMENT
A prototype was installed to test the technology at the U.S. Geological Survey Toxic Substances Hydrology Program Research Site near a sewage-treatment plant on the Massachusetts Military Reservation, Cape Cod, Massachusetts
(fig.1) Map showing the study area
The wells for the prototype were drilled in a study site on a sand infiltration bed used for the disposal of sewage effluent from a treatment plant in the process of being decommissioned. Two large pulses of partially treated sewage effluent would be applied to the infiltration bed during the study period as a result of the decommissioning of the sewage plant. Two test wells and an equipment shelter housing the electronics, instrumentation, equipment, and hardware for the prototype
(fig. 2) Photo of the study site looking North
were emplaced in a sand infiltration bed about 20 feet downgradient of an impoundment constructed to form a line source of ponded infiltrating-water for the study.
(fig. 3) Photo of the study site looking South
A semi-elliptical overflow area in the bed behind the impoundment was flooded when flow rates from the discharge pipe exceeded the infiltration capacity of soils in the impoundment. Two 2-inch diameter polyvinyl-chloride wells were emplaced, one screened from about 5 feet above to 5 feet below the water table (about 24 feet below land surface), and another screened from about 5 to 10 feet below the water table (USGS wells SDW 479-0028 and SDW 479-0033, respectively). The system ran autonomously under independent control, power, and communications. A data logger controlled the process and stored data in a solid-state storage device.
(fig 4) Photo of the prototype system used at the test site
Power for instruments and the pumps was provided by batteries recharged by solar panels (fig. 2) and nitrogen gas, respectively.
A telephone modem was used for communication and remote control.
(fig. 5) Photo of the prototype system as installed in the equipment shelter
A hand-operated three-way valve was placed near the beginning of the flow train to divert water for manual collection of samples (fig 4). The system monitored and recorded the water level in the water- table well with a pressure transducer and the flow rate of ground- water pumped through the system during purge and recording cycles with an in-line flow sensor (fig 4). A multiprobe with a flow cell was used as a control module for the water temperature, pH, specific conductance, dissolved oxygen, and dissolved ammonium probes under data logger control (fig. 4) and (fig. 5). Other instruments were used to monitor the pressure in the nitrogen tanks as well as shelter air temperature and other system parameters.
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