Shallow Wells in Riparian Zone Impacted by Surface Water Indicators and Horsehair Worms (Nematodes)

Brian Oram, Licensed Professional Geologist
Photo by Ian Sutton

The KnowYourH2O Team has been contacted by residents in Western Pennsylvania regarding a problem with Nematodes in their Well Water.  With respect to the location of these wells, I am just going to say they are in the Allegheny River Basin located in the riparian zone for the Allegheny River and reportedly in wells that are 75 to < 100 feet deep. During my discussion with the well owners, the following seem to be the common threads:

1. They did not know how the wells were constructed.

2. They did not know if the wells were in the unconsolidated (sand and gravel aquifer) or bedrock.

3. The wells were not fitted with Sanitary Well Caps and the well casings were not 18 inches above grade.

4. The wells have never been evaluated to determine if the well is under the direct or indirect influence of surface water.  (For more info, visit our page Groundwater Under the Influence)

5.  The wells appear to be located in the floodplain.

The Facts

It was suggested that the worms were “horsehair worms.”  The following are some of the “Facts” related to “Horsehair Worms” that we have been able to compile.

1. Horsehair worms are long, measuring from several inches to over 14 inches.

2. The worms are quite thin, ranging from 1/25 inch to 1/16 inch wide (1 mm to 1.5 mm) and are uniform in diameter from front to back.

3. The worms vary in color from whitish to yellow/tan to brown/black.

4. Horsehair worms are found on the ground or on plants, especially near water.

5. Horsehair worm eggs range in size from 40 microns wide  to 50  microns long. Note: 40 microns is 0.001574803 inches ( Maybe visible to the naked eye).

6. The number of eggs produced per female is 27 million.

7. In general, the worms are considered non-pathogenic to humans and more pathogenic or disease-causing to: grasshoppers, crickets, beetles, katydids, caddisflies, millipedes, centipedes, spiders, crustaceans, leeches, snails, slugs, and other invertebrates (One reason to keep insects out of your well water).

8. “There are four stages in the life of a horsehair worm: the egg, the preparasitic larva that hatches from the egg, the parasitic larva that develops within an invertebrate (its host), and the free-living aquatic adult. The worms spend the winter in water. After mating in spring, the female worm deposits a string of eggs 12 to 24 inches long in the water. About three weeks to one month later, minute immature larvae hatch.”

9. “Domestic water supply systems should be filtered, chemically treated, and inspected for necessary repairs, especially when the homeowner discovers horsehair worms in wash water, bathtubs, or sinks. Moreover, it isn't unusual to find horsehair worms in the home in such places as shower stalls or toilets where crickets may die and worms emerge into the water. Prevent nuisance insects such as crickets, which are known hosts, from entering the home by caulking or sealing entryways.”

10. Case of Human Infection - “Two gordiid worms were collected in the vomit and excreta of an 80-year-old woman in November 2009 in Kyoto city, and in the mouth of a 1-year-old boy in December 2009 in Nara city, Japan, respectively. Both worms were males having bifurcated posterior ends and male gonads in cross sectional specimens. They were identified as Parachordodes sp. (Nematomorpha: Chordodidae) based on the characteristic morphologies of cross sections and areoles in the cuticle.(View Article)

11.So yes, horsehair worms can end up in humans, but they do not gestate or mature in humans, nor do they burst out of humans. They do not migrate out of the digestive tract in humans, and, as the best medical knowledge at the time of writing this indicates, they do not produce any indirect symptoms, only the symptoms associated with something unpleasant in the digestive tract.”

The KnowYou H2O Team Comments

1. Shallow wells near surface water are vulnerable to surface water impacts that may include the presence of disease-causing agents, pathogens, and viruses.

2. For a water well, we typically suggest a camera inspection of the well to make sure there are not structural problems or deficiencies.  We also recommend the well not be over-pumped, the casing be at least 18 inches above grade, surface water is diverted away from the source, the well should not be in a pit, and the well should be fitted with a sanitary well cap and maybe even a Well Seal.

3. We recommend some baseline assessment before any cleaning

a.  Test the water from the well for Total Coliform, E. coli, and standard plate count (Use an enumeration method – check with a local certified laboratory). The cost should be no more than $ 150 per sample.

Other Items if your budget permits:

b. Additional testing – Total Microbiological Assessment - about $350.00 per sample

 c.  MPA (Microscopic Particulate Analysis) – this requires filtering 1000 gallons of water through a special 1 micron filter – the cost for the analysis is about $600 to $ 700. This tells us how vulnerable the source is to surface water influence and provides some load analysis. (Description of the MPA Test )

Cleaning Well / Household Piping/ Inspection  (Hire a Professional)

 1. First get Baseline Water Quality Testing completed and a well camera survey and inspection.  Recommend you hire a professional.

2. Cleaning – Step 1:  DO this Twice – Use Well Safe to shock-disinfect well and delivery line to house. (DO NOT use Bleach)

a. How to Shock Chlorination, Shock Disinfect Your Private Water Supply, or Water Well Shock Chlorinate - Procedure and Chemical

b. Shock Disinfection of a Private Well Video

3. Cleaning House Water Piping – Repeat the Shock Disinfection of the well but focus on the indoor plumbing (cold water lines) – make sure to remove or bypass inline filters, any other filters, and aeration devices. Afterward, install new filters.

4. Pasteurize the hot water lines.

Treatment and Other Action

1. It is critical to know the type of worm and the size of eggs they produce. To be microbiological sanitary, the final filtration system has to filter to less than 0.2 microns in size. The worms mentioned above have an egg size of about 40 microns wide to 50 microns long. Note: 40 microns is 0.001574803 inches (Maybe visible to the naked eye) .

2. Since the well water is likely under the direct influence of surface water and experiencing intermittent problems with elevated levels of heterotrophic bacteria, Total Coliform, sediment, Turbidity, and/or E.Coli, it appears clear that a  standard Class B UV system (Residential System)  would not be an adequate barrier top protect the health / safety and welfare of your family.

At a minimum, the system needs a physical barrier and we would recommend you consider a 5 micron prefilter followed by a 1 micron absolute filter on the raw water and then a 0.2 micron filter on all drinking water taps. Please note: this level of filtration may cause a significant reduction in the pressure of the system and may require the user to upgrade pump, add a booster pump, or add additional pressure tanks. 

Because  of the concern about other Waterborne Pathogens or Viruses in the untreated well water, a disinfection barrier may be necessary. If a disinfection barrier is required, it would need to be a Class A UV disinfection system with the proper pretreatment that considers the raw water quality of the well water.  A Class A  UV disinfection system is a commercial system that meets NSF 55 or you may want to consider installing a chlorination or ozone based system sized to provide  a 4 -log reduction, i.e.,  99.99% reduction, in the target pathogen, typically viruses. These commercial systems need to be designed and sized by a Professional and the system sizing and design requires additional water quality testing of well water.

Chlorination or Ozone Based Systems

Commercial UV Systems (Class A)

3. If your water may have other problems or issues – like Iron – this would need to be known and documented. We recommend one of these test:

Water Well Testing Kits (At least the Basic – about $190)

4.  It may be necessary to repair the well or line the casing of an existing well to seal off or line the zone that is vulnerable to surface water impact. (Hire a Professional – a Licensed Well Driller).

Resource Links

Horsehair Worms - University of Minnesota

Horsehair Worms in People (Nematomorpha Infestation in Humans)

Horsehair Worms - Pests of Homes, Structures, People, and Pets

Two Human Cases Infected by the Horsehair Worm, Parachordodes sp. (Nematomorpha: Chordodidae), in Japan

Horsehair Worms, Hairworms, Gordian Worms, Nematomorphs

Other Topics

Questions about Methane, Natural Gas, and Baseline Testing, Methane in Well Water

Well by Well Review of Dimock, PA (Only the facts)

Baseline Testing

Drinking Water Guide for Well Water and City Water