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r GROUNDWATER TECHNOLOGY <br /> STANDARD OPERATING PROCEDURE <br /> CONCERNING GROUNDWATER MONITORING <br /> SOP 8 <br /> Groundwater monitoring of wells at the site shall be <br /> conducted using an ORS Interface Probe and Surface <br /> Sampler. The Interface Probe is a hand held, battery <br /> operated device for measuring depth to petroleum product <br /> and depth to water as measured from an established datum <br /> (i.e. , top of the well casing which has been surveyed) . <br /> Product thickness is then calculated by subtracting the <br /> depth to product from the depth to water. In addition, <br /> water elevations are adjusted for the .presence of fuel <br /> with the following calculation: <br /> (Product Thickness) ( .8)+(Water Elevation) <br /> Corrected Water Elevation <br /> Note: The factor of 0.8 accounts for the density <br /> difference between water and petroleum <br /> hydrocarbons, <br /> The Interface Probe consists of a dual sensing probe <br /> utilizing an optical liquid sensor and electrical con- <br /> ductivity to distinguish between water and petroleum <br /> products. A coated steel measuring tape transmits the <br /> sensor's signals to the reel assembly, where an audible <br /> alarm sounds a continuous tone when the sensor is <br /> immersed in petroleum product and an oscillating tone <br /> when immersed in water. The Interface Probe is accurate <br /> to 1/16-inch. <br /> A Surface Sampler shall be used for visual inspection of <br /> the groundwater to note sheens (difficult to detect with <br /> the Interface Probe) , odors, microbial action, etc. <br /> The Surface Sampler used consists of a ' 12-inch long cast <br /> acrylic tube with a Delrin ball which closes onto a <br /> conical surface creating a seal as the sampler is pulled <br /> up. The sampler is calibrated in inches and centimeters <br /> for visual inspection of product thickness. <br /> To reduce the potential for cross contamination between <br /> wells the monitorings shall take place in order from the <br /> least to most contaminated wells . Wells containing free <br /> product should be monitored last. Between each monitoring <br /> the equipment shall be washed with laboratory grade <br /> detergent and double rinsed with distilled water. <br />