Well Forensics

Solid material sediment analysis leading to well development procedures.

Difficult well problems may require a more detailed approach of investigation.

By Roger Miller

Forensic science is considered a careful and detailed search and examination beyond what is considered common or normal.

And while all well assessment activities are investigative in nature, periodically we encounter an issue not easily identified through common assessment practices and requiring a more detailed process. A review of the more common problems in a well and how they are evaluated will emphasize how the more difficult problems require the detailed efforts of well forensics.

Common Well Problems

Well fouling can cover a multitude of problems involving any change that impacts operation or water quality. The most common problems encountered in groundwater wells are scale accumulation, biomass buildup, sediment infiltration, corrosion, and coliform occurrences.

In the assessment of common types of potential mineral deposits, water sample analysis can identify chemical concentrations that can point to precipitation. These carbonate, sulfate, and oxide scales can easily foul the well, blocking flow and reducing capacity.

Carbon-base material built up on well screen.

Additionally, the oxidation potential of the system water can identify the potential for system corrosion along with the buildup of metal oxides into the scale mass. This information is beneficial not only for structuring a rehabilitation process for the effective removal of these deposits, but can potentially identify the source of corrosion that may allow for some change to prevent corrosion damage to the system.

Biomass, referring to the accumulation of biofilm in a well, can cause quality declines, capacity losses, corrosion damage, and of course, unsafe water conditions. Not only the bacteria themselves, but the exopolymer slime they secrete, can cause quality issues along with capacity losses as the biofilm mass can block flow in conjunction with dislodging into the flowing water and provide organic masses creating taste and odor issues.

Oily type materials taken from well components.

Specific bacteria, identifiable through laboratory analysis, can be the cause of microbial influenced corrosion, and the bacterial load of the sample analyzed can evaluate the severity of the biofilm buildup, guiding the selection of the proper resolution process.

Formation materials can block flow if not effectively developed during well construction or if the well is operated improperly, creating turbulent flow and mobilizing them into the well, plugging flow paths. Microscopic analysis of system water can identify common formation materials such as sands, silts, and clays.

Formation clays can also be separated from processed clays (drilling muds) under the microscope to determine if ineffective development is the potential problem or if the natural clays from the formation are potentially being mobilized into the well by improper operation.

Water well corrosion can come from a multitude of sources. Water chemistry is the first step in an evaluation process, generally looking at the calculation of the Langelier Saturation Index developed through a series of water chemistry parameters.

The results of the LSI will indicate if the water itself is corrosive. In 2016, the U.S. Geological Survey reported the corrosion potential of U.S. groundwater sources was higher than expected, with most of the country having moderately aggressive groundwater.

One of the most common types of corrosion in groundwater supplies is “concentration cell”—also referred to as “under deposit” corrosion. The typical electrochemical corrosion biofilm buildup, on the metal surfaces. This type of corrosion is the leading cause of well component degradation within the groundwater industry.

Additionally, microbial influenced corrosion is common as many types of bacteria in groundwater either produce acids or enzymes that will pit metal or they are natural iron-oxidizing species that oxidize and degrade iron in their metabolic process.

The bacterial issue in groundwater of greatest concern, and one which is controlled by regulatory rules, is the presence of pathogens, predominantly the coliform group.

Although many members of the coliform group are not pathogens, the presence of any member raises the potential. Therefore, the regulations require periodic testing and required actions if various levels are found.

Most of the coliform group are anaerobic bacteria and through monitoring the anaerobic activity within the well, we can predict the increased potential of a positive total coliform test result. This information can guide us in problem identification and resolution even prior to required reaction of regulatory controls, avoiding emergency conditions.

Difficult Well Problems

As stated earlier, all well assessment activities are investigative in nature and the investigator operates at various levels of detail in the process of problem identification and resolution.

An emulsified oily substance deposited on well casing and screen.

The investigation is often dependent on the customer, the role the well plays, and the level of failure or impaction occurring. For example, a single well supplying a home will require a simplified and faster response to return service, while a well that is part of a larger wellfield may offer time for a more academic approach.

The following projects are examples where the common assessment steps have been taken without satisfactory resolution to the particular problem. Therefore, the investigator has gone beyond, and in some cases considerably beyond, the normal steps in order to identify the source of the problem and effectively develop a resolution to the particular issue.

The following examples of well forensics will involve a well construction-related issue, water quality issues, deposited materials not responding to conventional treatments, and operational issues within the water chemistry realm.

Case Study I

In the northern United States, a dual-rotary drilled well was not responding to standard well development procedures using both physical and chemical processes.

A sample of what was presumed to be plugging the screened interval of the well was secured and sent to our laboratory. The material was noted to be a “mud-like substance” and when observed under the microscope, was predominantly clay particulate.

As clays can be from either processed drilling muds or natural-formation materials and react differently to various chemical reactions, further assessments were performed to make this determination.

Closer observation under the microscope showed the particles to be of random structure with sharp defined edges. This pointed to the source being natural-formation clays as processed drilling muds are more uniform and rounded.

Additionally, a settling study was performed as the processed clays will settle slower than natural-formation clays. This test again pointed toward the source being formation material.

Based on this determination and the knowledge that normal well development chemistry (phosphates) provides the reaction of sequestration, the formation of a more water-soluble complex, it was apparent the phosphates were not effectively sequestering the natural-formation clays.

From these factors, the investigator looked into the uncommon chemical reaction for well development of dispersion chemistry. The dispersion chemical reaction actually interferes with the positively charged particles, destabilizing the clay structures and breaking up the bonding, allowing them to be washed from the well.

In order to confirm this process and formulate the proper dosage, a bench test study was performed using multiple chemical combinations. From this study a final dispersion chemistry was selected to match specific mechanical efforts and sent to the field for application. The final results of these forensic efforts were an effective removal of the formation clays and an acceptable production capacity for the well.

Case Study II

A finding of an oily film and black deposits forming in the well was reported to our laboratory.

Samples were requested and received of both the deposited material and water from the well. Laboratory analysis identified the oily material to be a form of coal tar. Coal tar is a complicated hydrocarbon derived from the thermal destruction of coal with hundreds of potential chemical structures.

One of the more common coal tar structures is creosote, used as a sealer in road construction, and to a lesser known structure with analgesic properties used in acetaminophen or Tylenol.

The end result of this assessment was we were dealing with a complicated hydrocarbon and would need an effective degreaser chemical to remove it from the well. Further complicating these efforts, most effective degreasers for this type of hydrocarbon material are petroleum distillates with strong butyl or alkali components, which are toxic and not acceptable for potable water use.

However, previous work had been performed in our laboratory on similar material from the oil industry with success, using a citrus-based chemical known as D’Limonene. This chemical is nontoxic, biodegradable, and currently carries NSF certification for several formulas.

After identifying the most appropriate D’Limonene formula for the water chemistry of the particular aquifer, the product was recommended for rehabilitating the well using standard chemical procedures. The project resulted in an effective cleanup of the well with no signs of oil film or deposits.

Note: The actual source of the coal tar material was never identified by the client.

Case Study III

Although this case was not directly related to the source water well, it is an excellent reference to the delicacies of water chemistry and deposit formation that can adversely affect well operation.

Heavy scale formation was reported within the piping and storage system adjacent to a client’s water treatment plant facility. A site visit was performed and samples of the scale material were secured and taken to our lab for analysis. Laboratory results indicated the material to be 99% calcium carbonate, a common water mineral precipitate.

From the review of operations during the site visit, there was noted an intermittent discoloration in the finished water, and a consultant had recommended an adjustment of the finished water pH value to a maximum of 9.0 to alleviate the corrosion potential.

Further evaluating the information provided, we noted the majority of the piping system was constructed of PVC material and only a few valves were of metal components. We also observed 30% of the raw well water bypassed the treatment plant and went directly into the distribution system.

From this information we analyzed the raw well water and found moderate levels of iron. Based on the operational information and the seasonal relationship to the water color issues, we concluded the iron in the raw bypass water was oxidizing and settling out in low areas of the distribution piping during low-usage periods and being mobilized during high-usage periods, creating the intermittent colored water issues.

Therefore, without the corrosion potential to consider, we calculated the LSI and established the proper pH value for a balanced water. The consultants recommended pH adjustment was driving the development of carbonate scale within the system. Based on our evaluations, we recommended the scale be cleaned from the piping and storage system and the plant operator establish a finished water pH value of 8.0–8.2, significantly reducing the potential for calcium carbonate deposition.

This case study shows how delicate water chemistry can be. Only a slight change in one parameter without considering all the other parameters that may come into play can be detrimental to the overall operation of the water system.

Case Study IV

Our laboratory was contacted regarding a black particulate appearing in the rinse water within a food processing plant in Texas. The water source was a 3000-foot-deep well with multiple screened intervals.

From submitted information, a previous lab had identified the particulate as containing 85% iron. However, in our analysis of the water we did not find high concentrations of iron and therefore pursued other potential sources.

The more difficult issues require a more detailed search and examination—well forensics.

From our research into the geology of the area in which the well was located, we observed stringers of coal throughout the subsurface. In our literature search into carbon compounds we found lignite, a form of soft coal, exhibited ion exchange with calcium. Additionally, the exchange is facilitated by chloride solutions, and soft coals such as lignite generally exhibited high total organic carbon levels in water environments.

Correlating this information with our water analysis, we found no calcium in the sample. However, we found high levels of sodium and chlorides and the total organic carbon levels well above what would be considered normal for groundwater. All of these factors pointed us toward the material being carbon-based and most likely coal.

After a thorough system inspection of the processing plant and collection of the black material in bag filters throughout the facility, we received a large enough sample to perform a material analysis. The results of those tests showed a carbon concentration of 71% by weight. This was exactly within the carbon content range of lignite for the region.

With knowing the local geology contained some coal formations and the black precipitate in the rinse water contained carbon levels common to lignite coal, we requested all the geological logs and construction data associated with the well. From our review of this information, we noted that in the state licensing report showing the formation materials and screen interval locations, a well screen had been constructed 72 feet into a lignite formation.

As the resolution to this problem, we had the well cleaned and disinfected as our analysis did indicate a heavy biofilm buildup. Additionally, we had the well redeveloped to remove the residual lignite particulate that may still be present in the formation and gravel pack. Finally, we had the subject screen interval sealed off with the installation of a packer.

Operation of this well for the past two years has resulted in no black particulate noted by the client.

_________________________

Most well problems can be somewhat easily assessed and resolved using common testing and evaluation practices. However, the more difficult issues require a more detailed search and examination—well forensics.


Roger Miller is a senior consultant at Water Systems Engineering, specializing in water chemistry. He has worked over the past 40 years in research and development, analytical procedures, site assessment, and project oversight in the groundwater and water treatment industries. He can be reached at rdmiller@h2osystems.com.

 

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