Water Well Journal
Issue link: http://read.dmtmag.com/i/451364
WWJ February 2015 23 This article is the fourth in a six-part series that will detail each of the 11 sections of the ANSI/NGWA Water Well Construction Standard. I had the pleasure of serving on the Plumbness and Alignment Task Group and the Well Development Task Group for the ANSI/NGWA-01-14 Water Well Construction Standard. The groups consisted of dedicated volunteers including hydrogeologists, professional engineers, contractors, suppliers, manufacturers, and National Ground Water Association staff. The standard represents the efforts of numer- ous volunteers and NGWA staff over a period of about six years. I have been a hydrogeologist for more than 25 years and spent most of the first decade of my career chasing around various drilling rigs and pump rigs. I've worked with numerous color- ful characters on wells ranging from shallow monitoring wells to large- capacity water wells completed to depths of thousands of feet. The best thing about working with numerous different contractors, aside from the entertainment value provided by a huge cast of characters, is I learned about the industry firsthand. The on-the- job education I received provided me with a plethora of methods and proce- dures that should be followed, and those that should not be followed. Plumbness and Alignment Plumbness and alignment are impor- tant for the proper installation of annular materials, pump installation to the de- sired depth, and to prevent excessive wear on line-shaft turbine pumps. In the field, people usually don't refer to plumbness and alignment, but instead combine the two into the single word—"crooked." I've met quite a number of drilling contractors who "have never drilled a crooked hole." These folks are the best drillers in the world or have a different definition of plumbness and alignment than the rest of us. Generally, boreholes that are not straight or plumb are drilled in the absence of plumbness and alignment specifications. A crooked borehole can result in the screen or blank casing lying against the side of the borehole, thereby preventing filter gravel and annular seals from being placed around the entire casing. Improper installation of filter gravel can result in wells that produce sand during pumping. Improper installation of annu- lar seals can allow contaminants to more readily enter the annulus from near or at the ground surface, or allow comingling of water from various portions of the aquifer into or out of the desired pro- duction interval. I have seen a number of instances where wells were so crooked the desired pumping rates could not be obtained. This was because either the pump (pump/motor) of the required diameter could not be installed and a smaller pump had to be used, or the pump could not be run to the required depth and had to be set at a shallower depth. Hopefully those of us involved with wells that will be equipped with line- shaft turbine pumps know if a well is straight and plumb—the shafts, bear- ings, and pump will last a long time. However, this may not have always been the case. About 20 years ago, a colleague gave me an undated letter regarding "Water Well Straightness Requirements" written on letterhead from a company that is a major supplier of line-shaft turbine pumps. Interestingly enough, the letter indi- cated decreased life of the pumps had been experienced "if a well is too crooked" and "if a well is too straight." The letter went on to suggest a small de- viation from vertical was helpful but no "doglegs" or "kinks" could be tolerated. Some simple steps can be taken to prevent problems with plumbness and alignment: • Checking and correcting the rig level several times a shift • Using an appropriate number of drill collars for the depth and diameter being drilled • Maintaining reasonable weight on the bit • Using equipment and methods that allow good circulation rates. Last, and maybe most important, don't drill too fast. Fast drilling gener- ally equals a crooked borehole. I have been involved with many projects where the upper 80% of the borehole was drilled straight and plumb, and the lower 20% was neither straight nor plumb. Review of the penetration rate data indicated, in the majority of cases, the driller began to drill faster as he got closer to finishing the borehole. Deviation surveys performed as part of the geophysical logging suite of the final borehole clearly showed the borehole curving out of specification at the bottom—a curve we call "the impatience curve." Well Development By now, the majority of professionals in our industry dealing with water sup- ply or injection wells understand the need to perform thorough well develop- ment. Part of my field education, fortu- nately from only a small number of drilling contractors, has made me refer to well development as the "Why do we need to do this? We finished the well and have another to drill!" process. But the reality is proper well devel- opment is crucial in making an efficient well. A poorly developed well will have low efficiency that in turn will result in lower production rates and increased pumping costs. In the case of boreholes drilled using direct or reverse mud-rotary methods, Go to the NGWA Bookstore to purchase your copy of the ANSI/NGWA-01-14 Water Well Construction Standard. It encompasses municipal, residential, agricultural, monitoring, and industrial water production wells. Topics covered include: well site selection; casing and casing installation; well screens, filter pack, and formation stabilizer; grouting; plumbness and alignment; well development; testing for performance; data recording; disinfection with chlorine; water sampling and analysis; and permanent well and test-hole decommissioning. Go to the bookstore at www.NGWA.org. Twitter @WaterWellJournl STANDARD continues on page 24