A uniform system for classifying water well boreholes would advance the groundwater industry.
By Thomas M. Hanna, RPG
The water well industry has not adopted a universal classification system for the logging of water well boreholes. This has resulted in inconsistent and incomplete records that are not correlative or, in many cases, unusable to identify aquifers, formations, confining layers, or significant waterproduction zones.
A standard classification system is needed to provide structure and uniformity for the logging of these water well boreholes.
The actions of drilling have a significant effect on the quality of the samples that are collected and described. Each drilling method has a different level of disturbance to the samples whose description must reflect, as much as possible, the undisturbed nature of the materials.
Water well boreholes can be drilled for production or hydrogeologic investigations. Contractors, hydrogeologists, and engineers—all who have varying backgrounds and training in describing hydrogeologic systems—are tasked with producing borehole logs that are incorporated into the permanent hydrogeologic record. The result, though, is on occasion borehole logs that are not of value when important hydrogeologic data could have been collected.
The Hydrogeologic Classification System for Water-Well Boreholes (HCSWB) was developed in 2006 as a means of recording the pertinent hydrogeologic information in a succinct approach to provide accurate and correlative borehole logs. As part of a product sold by the National Ground Water Association, it has been used by many groundwater professionals around the world with much success.
However, the groundwater industry would benefit from its further use.
The two main parts of the HCSWB are a classification system and a Field Guide allowing fast identification of materials in the field. Figure 1 presents a flow chart with the logging procedures and categories of the classification system. Figure 2 is a plastic Field Guide that can be used to standardize descriptions, an important element in creating consistent descriptions. Figure 3 is an example of a hypothetical log that was created using a spreadsheet with simple drop-down menus.
The HCSWB provides a concise menu-driven format that ensures basic information is recorded. At the same time, it allows enough flexibility for describing unique hydrogeologic features.
It will help document unconsolidated sediments so the relative hydraulic conductivities can be accessed based on grain size and location of significant water-producing zones that are observed during drilling. The HCSWB accommodates for general lithologic description of consolidated formations and water production from fracture zones.
It incorporates important aspects of geologic description for distinguishing formation/aquifer characteristics and documents important hydrologic characteristics that control groundwater flow.
The level of detail in the description is appropriate for the level of information gained from a water well borehole, which quite often is poor as drill cuttings are small and have different amounts of damage depending on the drilling method.
It is important to identify and properly describe the attributes of water-bearing strata that control the flow of water. The capacity of a formation to transmit water can vary greatly. Unconsolidated formations consisting of clay and silt, and bedrock formations such as granite, yield little water and form barriers to flow.
On the other hand, unconsolidated earth materials consisting of coarse sand and gravel, and cavernous limestone, can be prolific aquifers. The HCSWB was created to describe the water-transmitting capacity of the water-bearing formations.
The HCSWB includes observations of water production often omitted in water well borehole logs. The descriptors are based on hydrogeology as most logs present geologic data but rarely hydrogeologic data. The use of the HCSWB and Field Guide provides a standard logging technique to create hydrogeologic logs that can be correlated with all logs completed using the HCSWB.
The HCSWB defines a minimum standard for logging water well boreholes and a system that can be taught to those involved in the recording of hydrologic data. These data include important observations as to the potential transmitting capacity of the formation, location of the water-bearing/producing zones, and a framework to provide consistent borehole logs.
The HCSWB also provides the basis for storing and sorting data in a digital format because the descriptions and identifiers are uniform and can be digitized so that records can be sorted by the descriptors.
As more borehole logs are being recorded online, a menudriven system of recording data is desired to aid in standardization, which the HCSWB achieves. Several states and provinces have already adopted the HCSWB or major portions of it as their standard to create better borehole logs.
By incorporating this methodology as a minimum standard, the logging of water well boreholes can be uniform and data generated will be able to be interpreted by all groundwater professionals. In addition, the uniformity is an important aspect for incorporation into electronic databases being used today.
Thomas M. Hanna, RPG, is a technical director of water well products/hydrogeologist for Johnson Screens where he works in areas of well design, development, and well rehabilitation. He is a registered professional geologist in Arizona, Kentucky, and Wyoming and has worked for several groundwater consulting firms.