WorldWide Drilling Resource

Notes from The Groundwater Guy by Thomas E. Ballard, PG, CHG Southeast Hydrogeology, PLLC WWDR welcomes Thomas E. Ballard as a contributing writer. Thomas E. Ballard, PG, CHG, aka The Groundwater Guy, is principal hydrogeologist at Southeast Hydrogeology, PLLC, a groundwater re- sources consulting firm with offices in Murfreesboro, Tennessee; and Sacramento, California. He is a reg- istered professional geologist in California and Tennessee, and certified hydrogeologist in California. His work focuses mainly on water resources development and well troubleshooting for small water districts. The Importance of a Proper Well Seal The annular seal, also known as a sanitary seal, is an important component of a water well which protects the well from surface water contamination and provides protection for the upper part of the well. The seal consists of a mixture of cement, bentonite, and sand which is placed to make a watertight seal in the annular space between the casing and the borehole wall. The materials allowed for the seal can vary by state requirements and geologic conditions. Most state well regulations contain a requirement for a minimum annular seal depth and thickness. These regulations often contain requirements for a minimum seal depth for different classes of wells. In California, for instance, a public water supply system well is required to have a minimum seal depth of 50 feet; while in Tennessee, requirements include a minimum of 19 feet of casing and 10 feet of seal. Minimum seal depths specified in the regulations are just that - a minimum depth. It is important to take the geology of the borehole into consideration when determining the actual depth of the seal. Fractures in bedrock and wells screened across multiple aquifers can result in an inadequate seal, even if it technically meets regulatory re- quirements. Many water quality issues impacting water supply wells often have a surface water component - especially in cases of nitrates and E. coli. Often, the surface water intru- sion can be traced to an inadequate seal which, while it meets the minimum regulatory standards, does not seal the well against surface water intrusion based on a number of geologic factors. For instance, we were consulted on an E. Coli contamination issue in several community water system wells in a volcanic bedrock and, after examining the well logs, determined the 50-foot seals to be inadequate due to shallow lost circulation zones encountered during drilling which were not adequately sealed off. This allowed intrusion of surface water containing E. coli from surrounding properties with septic/leach field systems. In another case, nitrates impacted a well drilled into a fractured granite, and a review of the well logs again revealed a seal which met minimum regulatory requirements, but did not address shallow fracture zones which extended to 70 feet below the ground surface and allowed intrusion of nitrate-impacted surface water into the well. In either of these cases, an adequate seal could have been installed based on geologic information available at the time of drilling, but a decision was made to not use the available information and just to install the minimally acceptable seal according to regulations. An inadequate seal resul t ing in impacts to well water quality can be very expensive in terms of required treatment of the impacted water or dri l l ing of a new, properly constructed well. Our phi- losophy is: It is best to construct the well properly in the first place. This usually means to have both an adequate geo- logic log of the borehole and a geophys- ical log, as well. Tom Tom Ballard may be contacted via e-mail to michele@ worldwidedrillingresource.com We have stainless steel and metal valves, as well as plastic cycle valves! For more info call: (800) 364-2124 or visit us online: www.barrettsupply.com Proudly made in the USA Sales rep territories available. 37 WorldWide Drilling Resource ® OCTOBER 2017 Thank you for all you and your team do, Michele, in putting your magazine together. Dave Denver, Colorado