By Christopher S. Johnson, PG, CHg
The meetings are done, everyone has read the specifications, the pilot hole is almost finished, and it’s time to start building a well. So begins the hard work.
This is going to be more of a list of things to do and think about rather than a philosophical discussion. For field geologists, hydrogeologists, geohydrologists or engineers tasked with observing the compliance of a drilling contractor with specifications related to the construction of a new water well, you need to engage is some basic to advanced practices to hold up your end of the bargain.
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- Safety first: Drilling is dangerous enough as it is, but when well construction begins the risks increase rapidly. Have a plan, follow the plan, stay out of the way!
- Drilling fluid management: Managed through the pilot hole, keep a close eye on the drilling fluid which may be modified to facilitate well construction.
- Materials management, drilling fluid: Make sure you know how much drilling fluid products went into the pilot hole (and reamed hole if that happened) so you have an idea of how much fluid needs to be recovered during development. This is also applicable to how much water was used during drilling, as ideally all the water and drilling fluid should be recovered during development.
- Materials management, well materials, inventory: Probably, the best place to start is simply making sure you have “all the parts” at the job site. Too often it’s the smallest parts that get left behind and stops the construction of the well. Sometimes it’s just for hours, but other times can be for days. This is where having a good design drawing with all the parts clearly labelled is helpful. Pretty basic, but so often overlooked.
- Materials management, shipping and handling: Ideally, you’ll be onsite when the casing/screen is delivered. Depending on the size and weight of casing and screen, it may be trucked onsite, and if so, it might be strapped or chained down. Before the material is offloaded, look carefully at the casing and screen. Look for obvious damage, but more importantly, look for evidence of the pipe being bent or bowed because of the method with which it was secured. Even a 1% decrease in the ellipticity (roundness) of the pipe will reduce the ability of the pipe to resist collapse pressures in the ground.
- Materials management, well materials, dimension check: You will also want to make certain the correct lengths, thicknesses, weights, and diameters of the well casing and screen/intake structures are present. Measure twice, cut once as the saying goes. Check for correct collar alignment, correct lengths, and casing roundness. Measure and number each piece but keep a separate tally of the casing (by number) lengths. Compare this to the drilling contractor’s own tally.
- Materials management, filter pack: Tally how much gravel you have, either in bags or Super Sacks, and make sure you’ve got all you need and then some. Collect samples of the pack material, randomly from the bags, both before and during the placement. Save it!
- Gravel pack tally: Using the caliper log from the open borehole, and the planned outside dimension of the well, you should be able to calculate the approximate cubic feet per foot of the annulus between the casing and borehole wall. This is a quantitative guide, so that as you fill the annulus with filter pack, you can track how much should go in versus how much has gone in. This is important because if the tally is short it suggests that there may be a bridging condition. Bridges are a hiatus or gap in the consistent placement of the gravel pack. This can lead to formation materials entering the well, potentially creating a “sanding” condition (i.e. sand in the pumped water), which is an abrasive (worn pump impellers) or plugging agent. It truly is important to have a schedule of how much filter pack per foot is required so that you can accurately track the installation of the filter pack. A drilling contractor will usually measure every so often (e.g. each Super Sack, every 30 bags of sand, etc.), which is also know as “tagging the gravel pack” to estimate how far up the annulus the gravel pack rose with the incremental addition of the sand. Rule of thumb: Needing more sand is better then not using what you were scheduled to use.
- Annular seal, quality and quantity: Verify the concrete, concrete/grout, or grout mixture either delivered or mixed on site is of the right blend (Portland cement to sand to water, etc.) and type. Additionally, when using concrete trucks, be advised a truck sitting idle poses a hydration risk to the concrete batch. If the truck sits longer than 20 to 30 minutes (depending on mix, outside temperature, and humidity) then it might hydrate its water content and should not be pumped down the tremie tubes. Pumping “dry” concrete will plug up your tremie lines! Rule of thumb: Right mix, right amount, keep it wet.
These are the highlights for preparing for and observing well construction. Following this list will go a long way to ensuring a quality water well is delivered to the customer.
Christopher S. Johnson, PG, CHg, is the president and principal hydrogeologist at Aegis Groundwater Consulting LLC in Fresno, California. Johnson works with well owners and operators on a variety groundwater-related projects, including locating new water resources, well design and construction management, aquifer testing, and well rehabilitation. He can be reached at firstname.lastname@example.org.