Water Well Journal
Issue link: http://read.dmtmag.com/i/543740
H ave you ever had to explain or represent something you did without any proof and only your word? It can be difficult. Once we have fin- ished installing a well and the cuttings are removed, covered over, or hauled off—there is little evidence to support any claim as to the assembly of the subsurface formations. That is the basis of some issues we encounter as groundwater professionals when fielding well completion ques- tions. My dad always says, "Once you get below the ground surface and be- yond an arm's reach, it's anybody's guess." Case Study I had the opportunity to review a hy- drogeological report for a groundwater production permit application. One of the requirements for the production per- mit was to perform a valid pumping test for aquifer characterization. On this particular application, a test production well had to be installed to produce the anticipated amount of water. A drilling contractor was selected to install the production well, and after the well was completed, the contractor submitted their log for the report. During the course of the drilling process, there was no geologist on-site to collect any representative samples of the formation or log the drilling process. It was left up to the discretion of the contractor to provide the sole record of the formational information, which is not abnormal. But in this case, discrepancies were found while reviewing the drilling log. Based on the driller's description, it appeared the contractor may have inad- vertently commingled two aquifers. The well successfully produced a sig- nificant amount of water, much to the pleasure of the landowner, contractor, and hydrogeologist assembling the re- port. The only problem was the potential of commingling the aquifers. Notwithstanding that commingling aquifers is against most state laws, the permitting agency did not want to per- mit water production from one aquifer and have withdrawals from another. This led to speculation as to the true nature of the formation material. In the area the well was drilled, the formation and aquifer contacts are not that well defined and the formational contacts are sometimes not distinct. In order to provide an answer to the problem, a geologic consultant was hired to go to the well site and try to determine if the well was completed into two different aquifers. The consultant found evidence by re- trieving samples from the now covered- over drilling pit. In his interpretation of the cuttings, he supported the theory the well was completed into only one aquifer. Based on a successful pumping test and the completed hydrogeological report supporting the production for the permit, the application was approved. Because of the case, the permitting agency—wanting to avoid any future problems associated with a lack of veri- fiable proof from the drilling process— enacted the requirement to collect and retain drill cutting samples of all water production wells drilled within their jurisdiction. Sample Retention It is not out of the ordinary for con- trolling or permitting agencies to require sample retention practices. Several states require the retention of samples for public water supply wells, compli- cated wells, or wells in areas of limited geologic data. An example of these poli- cies are presented by the following state rules. North Carolina requires the retention of samples in a specific way as listed in an excerpt from its state rules: 15A NCAc 02c .0114 DATA AND RECORDS REQUIRED (a) Well Cuttings. (1) The well contractor shall collect and furnish samples of formation cuttings to the Division from a well the well contractor has drilled when such samples are requested by the Division prior to completion of the drilling or boring activities. (2) The well contractor shall obtain samples or representative cuttings for depth intervals not exceeding 10 feet. The well contractor shall also collect representative cuttings at depths of each change in formation. (3) The well contractor shall place samples of cuttings in containers furnished by the Division and such containers shall be filled, sealed, and labeled with indelible‑type markers, showing the well owner, well number if applicable, and depth interval the sample represents. (The State of North Carolina n.d.) The New Mexico Office of the State Engineer is not as specific. Its rules leave a lot of discretion to the individual districts as to the requirements of sam- ple retention: Geologic formation samples: When requested by the state engineer, the well driller shall furnish lithologic samples ("drill cuttings") of the geo- logic units penetrated during drilling operations. The method of sampling, interval of sampling, and the quanti- ties required will be specified by the state engineer. Lithologic samples shall be placed in sample bags supplied by the state engineer. (The State of New Mexico n.d.) There are a variety of options for retaining samples. FIELD NOTES continues on page 34 WWJ August 2015 33 Twitter @WaterWellJournl FIELD NOTES Retaining Geologic Samples By Raymond L. Straub Jr., PG