Use of Small-Diameter Bladder Pumps in Direct-Push Ground Water Monitoring Wells at the CRREL Site

Abstract : Several different small-diameter (1/2-inch and 3/4-inch) bladder pumps (from different manufacturers) were tested in 1/2-inch and 3/4-inch direct-push (DP) monitoring wells at the CRREL site in Hanover, New Hampshire. Obtaining a sample at this site has been challenging because the depth to ground water is over 100 feet and thus substantial lift is required to bring the water to the surface. Although the different brands of pumps fit into the small-diameter wells, all of them hung up in some of the wells when attempting to install them at the sampling depth. However, it was found that machining a few thousandths of an inch off the diameter of the pumps was all that was necessary to get them to the desired depth. Three brands of 3/4-inch bladder pumps were tested in the site's DP wells and delivered between 25 and 315 mL/min. Two brands of 1/2-inch bladder pumps were tested and delivered between 20 and 100 mL/min. Concentrations of TCE obtained using two different brands of a 3/4-inch diameter pump were compared and statistically significant differences were found. The same was true when the same two brands of 1/2- inch diameter pumps were compared, although the differences in this case were slight. It is believed that differences in the previous conditioning the pumps received in the wells (i.e., equilibration times for the materials with the well water) were responsible for much of these differences.