HCT UNIVERSITY · EDUCATION
Biofilm is the limiting factor in well rehabilitation.
In most declining water wells, performance loss isn’t just mineral scale. The primary culprit is biofilm — structured organic matrices that colonize screens, gravel packs and the near-wellbore formation. Unless they are chemically disrupted, rehabilitation produces only temporary gains.
NSF/ANSI/CAN 60 listed · corrosion-inhibited chemistry · 1,000+ wells assessed · biodegrades to O₂ + H₂O
WHAT BIOFILM DEPOSITS DO
A permeability problem, not debris.
Biofilm forms cohesive organic matrices along every well component. From an engineering perspective, what follows is permeability impairment — not simple debris accumulation.
Encapsulate
Scale and fines get trapped
Mineral scale and fine sediments are bound inside the polysaccharide sheeting.
Restrict
Screen open area shrinks
Effective open area falls as colonies grow across slots, louvers and wire wrap.
Reduce
Hydraulic conductivity drops
Near-wellbore porosity declines, so the same pumping rate needs more drawdown.
Accelerate
Fouling cycles repeat faster
Residual matrix seeds regrowth, so each cycle recovers less for a shorter time.
BIOFILM SCIENCE
How biofilms impair well performance.
Iron-reducing bacteria (IRB) and sulfate-reducing bacteria (SRB) generate extracellular polymeric substances (EPS) — a polysaccharide matrix that is both a home and a shield for the colony. This is the root mechanism behind most well decline, and it works in four ways.
01
Diffusion barrier
The EPS matrix keeps treatment chemistry from reaching the bacteria embedded inside the biofilm structure, so surface contact alone never finishes the job.
02
Mineral entrapment
Iron oxides, carbonates and fines are trapped within the polysaccharide sheeting, creating composite deposits that are far harder to remove than either alone.
03
Porosity reduction
As colonies grow, near-wellbore porosity drops. The effective flow area shrinks and drawdown rises at the same pumping rate.
04
Increased drawdown
With flow paths restricted, the well needs more energy to produce the same volume — higher operating cost and faster pump wear.
IRB
Iron-reducing bacteria
Less aggressive to steel, but the primary builder of the slime that traps iron and manganese.
SRB
Sulfate-reducing bacteria
Produce hydrogen sulfide and, in HCT's field experience, can degrade casing on the order of ¼ inch in 10 years.
EPS
Extracellular polymeric substance
The polysaccharide matrix itself — the thing that must be chemically broken before anything else works.
THE MECHANICAL PROBLEM
Why mechanical methods alone are insufficient.
Sonar jetting, air blasting, high-pressure jetting and brushing can dislodge loose debris. They cannot chemically degrade the polysaccharide matrix that binds biofilm and mineral deposits to well surfaces. The result is temporary improvement followed by rapid decline.
Fracture
Force doesn’t dissolve
Force may fracture sections of biofilm, but it does not dissolve or depolymerize the matrix responsible for adhesion.
Surface
Deep deposits stay put
Jetting and air affect exposed surfaces. Scale embedded in the gravel pack and formation interface — what restricts flow most — remains.
Regrowth
Fragments seed recolonization
Residual biofilm acts as nucleation sites, so each mechanical-only cycle yields less recovery over a shorter duration.
Engineers
Supplemental, not standalone
Biofilm shields carbonate, iron and manganese scale from chemical contact. Agitation mobilizes material but does not convert bound deposits to soluble form.
WHAT YOU ARE ACTUALLY FIGHTING
The matrix is both a home and a shield.
Look at a pulled pump column and you will see iron, scale and sediment — but the glue holding it to the steel is organic. The polysaccharide matrix binds those minerals into a composite deposit and protects the bacteria living underneath it from disinfectants, acids and mechanical force.
That is why the sequence matters: break the biofilm first, then dissolve the scale it was protecting, then flush everything out. Treat scale alone and the colony simply rebuilds on the same surfaces.
Fouled pump column and casing — iron and scale bound together by biofilm.
HCT’S ENGINEERED APPROACH
Chemistry that targets the root cause.
HCT remediation chemistry addresses biofilm fouling at the molecular level — disrupting the EPS structure, dissolving the mineral deposits it protects, and doing so without damaging well infrastructure.
01
Biofilm disruption
Formulations penetrate the EPS structure, break adhesive bonding and expose the underlying scale. Without this first step, descaling chemistry can’t reach the deposits it needs to dissolve.
02
Scale dissolution
Targeted chemistry then dissolves calcium carbonate, iron and manganese oxides and mixed mineral deposits — converting them to soluble or dispersible form for complete removal during development.
03
Controlled reactivity
Unlike aggressive acids or oxidizers, HCT solutions react in a controlled way with reduced corrosion risk — formulated for use with steel, stainless and PVC, and handled under protocol and SDS precautions.
04
Lasting results
With both the biological matrix and the embedded scale removed: higher specific capacity, restored screen open area, better gravel pack permeability, longer intervals between rehabs.
COMMON ALTERNATIVE · CHLORINE
Disinfectant, not a bioremediation agent
Chlorine is a disinfectant with legitimate uses in wells — shock chlorination and final disinfection among them. On its own it does not remove an established biofilm matrix, and at the doses used for aggressive disinfection it is corrosive to casings, screens and 416 stainless bowl shafts.
COMMON ALTERNATIVE · PEROXIDE
Oxidizer that reacts with everything
Standard hydrogen peroxide can reduce bacteria, but it reacts with nearly everything it touches and raises corrosion risk at the rates deep fouling requires.
HCT · WATERSOLV™ BC
Inhibited, catalyzed peroxide
An organically inhibited, catalyzed peroxide solution engineered to be corrosion-inhibited and targeted at the biofilm — and it biodegrades to oxygen and water.
RECOLONIZATION SCIENCE
Bacterial cleaning and recolonization.
The more bacteria you remove, the longer it takes for the well to be recolonized. Stagnant water greatly accelerates growth and restricts flow, and the two kinds of bacteria involved behave differently.
Aerobic
Attach in low-flow zones first
Aerobic bacteria settle at welds and perforations where water barely moves, then expand into higher-flow zones as the biofilm develops. They need oxygen and are the first colonizers during idle periods.
Anaerobic
Produce H₂S — toxic and corrosive
Anaerobic bacteria are usually easier to remove but generate hydrogen sulfide, which is toxic and corrosive to metal alloys. In HCT's field experience SRB can degrade casing on the order of ¼ inch in 10 years and cost you the filter pack.
2–3 wks
Lay-up chemistry
A well left stagnant beyond two to three weeks should be flooded with sodium bicarbonate and water so microbes cannot recolonize it while idle. Turn your pool off and watch what happens.
FOR ENGINEERS & SPECIFIERS
Specification considerations.
For bid documents and rehabilitation planning, these four principles should guide the scope of work.
1
Mechanical is supplemental
In biofilm-dominated wells, agitation supports the chemistry — it is never the standalone method.
2
Degrade the matrix
Effective rehabilitation requires chemical degradation of the polysaccharide matrix, not just surface disruption.
3
Document the metrics
Pre- and post-treatment pumping tests should be specified to verify specific-capacity recovery.
4
Compatibility and disposal
Chemistry must be compatible with well materials and meet regulatory disposal requirements.
RESOURCES
“Go deeper on biofilm and well rehabilitation.”
NEXT TOPIC
Scale dissolution
Once the biofilm is broken, carbonate, iron and silicate scale still has to be dissolved. Learn how Well-Klean© Descaler does it downhole.
Topic 01
HCT University · water wells
TAKE THE NEXT STEP
Ready to address the root cause?
Whether you are writing bid specifications or managing well assets, HCT can help you evaluate the right chemistry for biofilm-dominated decline — starting with the data from your well.
KEEP LEARNING
HCT, LLC · HCT University · Biofilms & Polysaccharide Scale