Slug Testing with the SP15 or SP16 Groundwater Samplers

Assembly and Driving
The SP15 or SP16 sampler is assembled with fresh O-rings to provide a sealed system while advancing the tool string. An O-ring kit is available for these tools and details of assembly are provided in the standard operating procedure (request Technical Bulletin 951500). After each rod is driven, an O-ring is placed on the rod before the next rod is added. All rod joints must be sealed to prevent air leaks and allow for pneumatic slug testing. Additional probe rods are added to the tool string and driven until the end of the screen is at the desired depth.

Deployment
Once the screen is at the desired depth, extension rods with a screen push adapter (GW1535) are inserted through the bore of the rods. While holding down on the extension rod handle, the probe rods and screen sheath are retracted with the rod grip system to expose the screen to the formation. Knowing the exact length of screen exposed to the formation is critical for calculating the hydraulic conductivity. Determine beforehand the length of screen to be exposed and mark this on the extension rod above the top probe rod. Be sure to add 2 in. to the screen length to account for the shaft of the expendable drive point and blank section at base of screen (see inset).

Screen Development
Development is a key step required to make an accurate determination of the hydraulic conductivity of the screened formation. Development is needed to reestablish natural flow from the formation into the screen (ASTM 5521). Even in “clean” sand aquifers, slug tests conducted before development routinely yield determinations of hydraulic conductivity 3 to 5 times less than slug tests after development (Butler et al. 2002). Development in sandy formations may be completed using the tubing check valve system. Oscillating and purging through the screen interval with the check valve is effective.

Slug Testing Fine Grained Formations
So you need to conduct a slug test in a fine grained formation.  Yet you know that driving the SP15/16 groundwater samplers or advancing the DT22 rod system into the formation will cause compression and bias your test results.  Your best option... drive the 2.25 in. dual tube rods down to the top of the interval you want to slug test.  Retract the inner 1 in. rods and attach the Soil Precore Drive head and sample tube.  Lower the sampler to depth and core the soil below the DT21 Profiler screen.  You may want to "brush" the cored formation before installing the screen with the BU600 brush to relieve smearing.  Now you are ready to slug test in the fine grained low-K formation.

A free SOP with complete operating instructions and additional transducer and data logger specifications is available from Geoprobe® Systems, 1-800-436-7762. Or download now: Pneumatic Slug Test SOP (640 KB PDF).