The direct push ground method is a rapid and economical procedure for installing ground water monitoring wells to obtain representative ground water samples and location-specific hydrogeologic measurements. Direct push installations may offer an advantage over conventional rotary drilled monitoring wells (Practice D5092) for ground water investigations in unconsolidated formations because they reduce disturbance to the formation, and eliminate or minimize drill cuttings. At facilities where contaminated soils are present, this can reduce hazard exposure for operators, local personnel, and the environment, and can reduce investigative derived wastes. Additionally, smaller equipment can be used for installation, providing better access to constricted locations.
Direct push monitoring wells generally do not extend to depths attainable by drilling. They are also typically smaller in diameter than drilled wells, thereby reducing purge water volumes, sampling time, and investigative derived wastes. Practice D5092 monitoring wells are used when larger diameters and/or sample volumes are required, or at depths to which it is difficult to install direct push wells. Direct push monitoring wells should be viable for monitoring for many years.
Prior to construction and installation of a direct push well or any other type of ground water well the reader should consult appropriate local and state agencies regarding regulatory requirements for well construction in the state. A regulatory variance may be required for installation of direct push monitoring wells in some states.
To date, published comparison studies between drilled monitoring wells and direct push monitoring wells have shown comparability (1, 2, 3, 4, 5). However, selection of direct push monitoring wells over conventional rotary drilled wells should be based on several criteria, such as site accessibility and penetrability, stratigraphic structure, depth to groundwater, and aquifer transmissivity.
Typical penetration depths for installation of ground water monitoring wells with direct push equipment depend on many variables. Some of the variables are the size and type of the driving system, diameter of the drive rods and monitoring well, and the resistance of the earth materials being penetrated. Some direct push systems are capable of installing ground water monitoring wells to depths in excess of 100 feet, and larger direct push equipment, such as the vibratory sonic type drill (Guide D6286) are capable of reaching much greater depths, sometimes in excess of 400 ft. However, installation depths of 10 to 50 feet are most common. Direct push methods cannot be used to install monitoring wells in consolidated bedrock (for example, granite, limestone, gneiss), but are intended for installation in unconsolidated materials such as clays, silts, sands, and some gravels. Additionally, deposits containing significant cobbles and boulders (for example, some glacial deposits), or strongly cemented materials (for example, caliche) are likely to hinder or prevent penetration to the desired monitoring depth.
For direct push methods to provide accurate ground water monitoring results, precautions must be taken to ensure that cross-contamination by “smearing” or “drag-down” (that is, driving shallow contamination to deeper levels) does not occur, and that hydraulic connections between otherwise isolated water bearing strata are not created. Similar precautions as those applied during conventional..........
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