There's a lot of excitement in the Environmental Industry about Geoprobe® Prepacked Well Screens designed for setting small diameter groundwater monitoring wells. Prepacked screens consist of a standard, slotted PVC well screen pipe surrounded by a stainless steel mesh. Sand is packed between the slotted PVC and the stainless steel mesh. Since the sand is packed around the slotted PVC before the well screen is installed, using prepacks guarantees sand will be located directly around the well screen. This makes groundwater monitoring well installation quicker and more efficient than traditional methods.
The 2-inch slim prepack uses a standard, 2 in. Schedule 40 slotted screen with a sand pack and 2.8 in. diameter stainless steel mesh screen on the outside. The 2.8 in. outside diameter can be used with 3.75 in. probe rods for an efficient combination of tooling for easy prepack installation.
Geoprobe® Small Diameter Groundwater Monitoring Well Benefits include:
To install a groundwater monitoring well with these prepacks, probe rods are first driven to depth with a Geoprobe® probing machine. The well assembly is then lowered into the probe rod string with threaded PVC riser pipe. The 3.4 in. OD prepacked well assembly uses 2.0-inch Schedule 40 PVC riser pipe and is installed with 4.25-inch OD probe rods or through hollow stem augers. The 2.5-inch OD prepack well assembly uses 1.0-inch Schedule 40 PVC riser pipe and is installed with 3.25-inch OD probe rods. The smaller diameter prepacked well screen assembly uses 0.5-inch Schedule 80 PVC riser pipe and is installed with 2.25-inch OD probe rods.
Once the well assembly is lowered to the bottom of the probe rod string, the probe rods are retracted to a point above the screen. A sand barrier, installed directly above the well screen, prevents grout from entering the screens. This barrier can be created either by natural formation collapse (occurring during the initial probe rod retraction) or by gravity installation of fine-grade sand through the rod annulus. With the barrier in place, granular bentonite or bentonite slurry is then installed in the annulus to form a well seal.
Prepacked Screen Monitoring Wells from Geoprobe Systems® have been installed in various types of soil compositions including alluvial sediments consisting of clays, silts, and sands with fine to medium gravels at depths exceeding 60 feet. The time required for installation and grouting one of these wells varies from approximately one to four hours depending on the depth, site specific conditions, and experience of the operators.
Several steps can be followed to facilitate prepacked screen installation. Get your copy of one of the Monitoring Well SOPs for a detailed installation guide.
Prepack installation breaks down into these steps:
A conductivity log shows distinctive clay layers within saturated sands at a research project in Central Kansas. These are alluvial deposits. A thin, distinct sand lens is indicated at 20 feet with confining clays at 40 to 42 feet (12.2 to 12.8 m) and at 45 to 47 feet (13.7 to 14.3 m). Prior to setting the prepacked screen groundwater monitoring wells, a LB soil sample was taken from 45 to 47 feet bgs. The sample consisted of a dark, gray-black clay at the 45- to 47-foot interval correlating exactly with the conductivity log.
2.0 in. ID x 3.4 in. OD Prepacked Screen | ||||
Slotted Pipe / Min. ID | Sand Pack | Length | Rod Size OD | Rod Size ID |
2.0 in. Sch. 40 PVC | 20/40 mesh sand | 60 in. | 4.5 in. | 3.75 in. |
0.010 in slots | factory packed | 1.5 m | 114 mm | 95 mm |
1.5 in. ID x 2.5 in. OD Prepacked Screen | ||||
Slotted Pipe / Min. ID | Sand Pack | Length | Rod Size OD | Rod Size ID |
1.5 in. Sch. 40 PVC | 20/40 mesh sand | 60 in. | 3.25 in. | 2.625 in. |
0.010 in. slots | factory packed | 1.5 m | 82.5 mm | 66.7 mm |
1.0 in. ID x 2.5 in. OD Prepacked Screen | ||||
Slotted Pipe / Min. ID | Sand Pack | Length | Rod Size OD | Rod Size ID |
1.0 in. Sch. 40 PVC | 20/40 mesh sand | 60 in. | 3.25 in. | 2.625 in. |
0.010 in. slots | factory packed | 1.5 m | 82.5 mm | 66.7 mm |
1.0 in. Sch. 40 PVC | field packed | 60 in. | 3.25 in. | 2.625 in. |
0.010 in. slots | 1.5 m | 82.5 mm | 66.7 mm | |
0.75 in. ID x 1.4 in. OD Prepacked Screen | ||||
Slotted Pipe / Min. ID | Sand Pack | Length | Rod Size OD | Rod Size ID |
0.75 in. Sch.40 PVC | 20/40 mesh sand | 36 in. | 2.25 in. | 1.5 in. |
0.010 in. slots | factory packed | 1 m | 57 mm | 38 mm |
0.75 in. Sch.40 PVC | 20/40 mesh sand | 60 in. 1.5 m | 2.25 in. | 1.5 in. |
0.010 in. slots | factory packed | 57 mm | 38 mm |
Many state regulatory agencies have approved the use of prepacked screen wells installed by direct push methods, and more states are joining this movement on an almost daily basis. Likewise, many federal agencies have specified the installation of direct push prepacked screen wells for their permanent groundwater monitoring needs.
The U.S. Environmental Protection Agency has recommended the use of prepacked screens in their guidance document, "Expedited Site Assessment Tools for Underground Storage Tank Site, " (EPA, 1997). Geoprobe® brand prepacks meet the requirements of ASTM Standards for the installation of prepacked screen monitoring wells (ASTM D6725-01).
Current standards are available from ASTM (610-832-9500 or www.astm.org).
Conventional Method: Stripping the cuttings from the auger and removing cuttings to a waste container. Multiple barrels may be filled with cuttings by this method.
Geoprobe® Method: No cuttings generated; no disposal costs incurred. Probe rods are used to set the prepacked screen monitoring wells. Saves time and labor costs.
Why rely on Geoprobe® brand Prepacks?
Geoprobe® Prepacked Screen Monitoring Wells are the most cost-effective method for installing permanent monitoring wells. Why?
Prepacked screen groundwater monitoring wells can be sampled by several available methods (peristaltic pump, mini-bailer, tubing check valve, mechanical bladder pump, etc.) to obtain high-integrity water quality samples. These wells also provide accurate water level measurements and can be used as observation wells during aquifer pump tests.
Find out more about the Mechanical Bladder Pump.
For SOP's, technical papers, and other info about Geoprobe® Prepacked Screens click here.
So, why is groundwater monitoring important you ask? And what does 'direct push' have to do with it? And for that matter, what is 'direct push'?
ID: 5267 | Date: 2019-02-12
With an inside diameter of 3.0 in., the 3.75 in. Probe Rods have an optimal casing combining ease of use for 2.0-in. Slim Prepack monitoring well installation,
ID: 5257 | Date: 2016-01-11
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PVC Screen .75 x 60 in. x .01 Slot
MN: 203101
MN: 201813
PREPACK 0.75 X 1.4 X 60 W/ SAND
MN: 203095
MN: 202059
TOP CAP BLACK VINYL 0.75 in. RISER
MN: 600148
WELL PLUG 0.75 in. RISER NON-LOCKING
MN: 601079
WELL PLUG 0.75 in. RISER LOCKING
MN: 601078
MN: 214070
MN: 213788
MN: 202136
PREPACK 1.0 X 2.5 X 60 W/O SAND
MN: 201807
PREPACK 1.0 X 2.5 X 60 W/ SAND
MN: 203096
MN: 202137
MN: 601071
WELL DEVELOPMENT TOOL 1.0 in. PVC
MN: 207276
WELL DEVELOPMENT WIPER 1.0 PVC RED
MN: 104674
MN: 114968
MN: 102256
MN: 213798
MN: 208504
MN: 203081
PREPACK 1.5 X 2.5 X 60 W/ SAND
MN: 203079
MN: 203082
WELL PLUG 1.5 in. RISER LOCKING
MN: 601072
WELL DEVELOPMENT TOOL 1.5 in. PVC
MN: 207012
WELL DEVELOPMENT WIPER 1.5 in. PVC GRN
MN: 600522
MN: 102881
MN: 213798
MN: 208504
MN: 104378
PREPACK 2.0 X 3.4 X 60 W/ SAND
MN: 206644
MN: 104397
MN: 601073
WELL DEVELOPMENT TOOL 2 in. PVC
MN: 205636
Well Development Wiper Red 2 in.
MN: 104411
MN: 207735
PVC Screen .75 x 60 in. x .01 Slot
MN: 203101
MN: 201813
PREPACK 0.75 X 1.4 X 60 W/ SAND
MN: 203095
MN: 202059
TOP CAP BLACK VINYL 0.75 in. RISER
MN: 600148
WELL PLUG 0.75 in. RISER NON-LOCKING
MN: 601079
WELL PLUG 0.75 in. RISER LOCKING
MN: 601078
MN: 214070
MN: 213788
MN: 202136
PREPACK 1.0 X 2.5 X 60 W/O SAND
MN: 201807
PREPACK 1.0 X 2.5 X 60 W/ SAND
MN: 203096
MN: 202137
MN: 601071
WELL DEVELOPMENT TOOL 1.0 in. PVC
MN: 207276
WELL DEVELOPMENT WIPER 1.0 PVC RED
MN: 104674
MN: 114968
MN: 102256
MN: 213798
MN: 208504
MN: 203081
PREPACK 1.5 X 2.5 X 60 W/ SAND
MN: 203079
MN: 203082
WELL PLUG 1.5 in. RISER LOCKING
MN: 601072
WELL DEVELOPMENT TOOL 1.5 in. PVC
MN: 207012
WELL DEVELOPMENT WIPER 1.5 in. PVC GRN
MN: 600522
MN: 102881
MN: 213798
MN: 208504
MN: 104378
PREPACK 2.0 X 3.4 X 60 W/ SAND
MN: 206644
MN: 104397
MN: 601073
WELL DEVELOPMENT TOOL 2 in. PVC
MN: 205636
Well Development Wiper Red 2 in.
MN: 104411
MN: 207735