Lewisville, Idaho

The city of Lewisville, in rural Jefferson County, Idaho, was established in 1882. This small farming community still exists within much the same geographic footprint as it was platted out, with an area of about 0.6 square miles. Lewisville’s nearest neighbors include Menan, about two miles to the north, founded three years earlier, and Rigby, the county seat, about 4 miles to the west and established in 1884.

Lewisville, named in honor of the Lewis and Clark expedition nearly 80 years earlier, was established by settlers branching out from the Salt Lake Valley. The Elsworth family, encouraged by a brother-in-law, Spencer Raymond, who founded Menan in 1879, came 200 miles north to escape the crowded Salt Lake Valley to the open land and fertile soil near the Snake River.

In 2023, the population of Lewisville has been estimated at 503 in about 160 households and has remained within about 20 percent of this current number of residents for most of the last century. At the same time, the population of Jefferson County has more than doubled since 1990, a 34 percent growth in the previous decade. Most of that growth has occurred in the surrounding county and nearby cities of Menan and, primarily, Rigby. While Jefferson County and Lewisville are known for potatoes and potato processing, more of the farmland surrounding Lewisville, Menan, and Rigby is being cultivated for houses instead of potatoes each year. Many of these new houses are in subdivisions with 1-5 acre lots located within the county, as opposed to established cities.

Census information indicates about 160 housing units are present within the boundaries of Lewisville. These homes include a mix of old and new construction, and all supplied drinking water and wastewater services are from individual wells and septic systems (septics). Likewise, the associated wells and septics include a similar mix of recent construction, with wells and septic systems meeting current standards and older wells built to less protective standards and septic systems and cesspools. Additionally, some lots within Lewisville lack sufficient space for the addition of a replacement drain field should the original drain field need to be replaced.

Groundwater in the Lewisville area is shallow, generally less than 25 ft. below the land surface. Depths to groundwater tend to increase from the northeast to the southwest with some variation due to slight changes in the topography. The thin, sandy-loamy soils with sandy gravels encountered in most wells tend to lack lower-permeability soil layers, making groundwater vulnerable to surface impacts. Additionally, groundwater levels vary throughout the year, responding to seasonal high flows in the nearby Snake River and irrigation and flow in irrigation canals. Potential surface impacts include nitrates from agriculture as well as septic systems. Many older homes are served by shallow wells less than 40 ft. deep, with some older wells constructed as “sand points” (well casing driven into the sandy soil deep enough to produce water). The seasonal increase in groundwater levels can also impact the effectiveness of septic systems and worsen the effects of failed septics, drain fields, and old cesspools.

The City of Lewisville expressed concerns regarding the possible combination of old, failing septic systems and the fact that some older homes rely on shallow wells not built to current construction standards. This could result in a water supply vulnerable to contamination, which could be a detriment to current sustainability and the future growth of the community.

This concern for the potential of water quality impacts due to failed onsite wastewater treatment (septics) and shallow drinking water wells prompted the city of Lewisville to commission a Wastewater Facilities Planning Study. Funding for this study, completed in 2023, was provided primarily by a grant from the Idaho Department of Environmental Quality, with the balance of the funding contributed by the City of Lewisville. The planning study considered environmental conditions and population growth projections and included alternatives for constructing a city wastewater treatment system or connecting to Menan’s wastewater treatment plant. The resulting cost estimate for the least expensive alternative was over $23 million over 20 years of operation. Greater than $9 million of that cost would be the construction of the system to collect wastes for any treatment option considered for the estimated 208 connections required over that same 20-year planning period, or more than $50,000 per connection with an estimated $185 monthly sewer bill unless loan unless grants or loan forgiveness could be obtained.

In response to the outcome of this wastewater study feasibility study, the Lewisville residents formed a community association and Facebook group, “Lewisville Idaho Fans,” as a communication forum, with the primary goal of providing the community with information regarding assessments of drinking water and assistance to aid in protecting their individual domestic wells, and information regarding proper care and maintenance of private septic systems.  For both these concerns – private wells and septics - the community would investigate options for loans, grants, and other financial assistance.

In response to the lack of current water quality information, residents John Walker and brother Doug Walker began developing plans for a community domestic well sampling event. Doug contacted a former coworker and recently retired regional hydrogeologist from the Idaho Department of Environmental Quality (IDEQ), Idaho Falls Regional Office, L. Flint Hall, to aid in the design. Mr. Hall is a registered professional geologist whose primary role with IDEQ has been regional groundwater monitoring to assess nitrate impacts on groundwater quality.

In a May 2024 community meeting, Mr. Hall presented information concerning regional groundwater quality based on the IDEQ water quality monitoring, sources of potential water quality impacts, rules regarding domestic wells and septic systems in Idaho, and a review of water quality sampling approaches to understand sources. From that meeting and follow-up discussions, a plan for sampling to address the concerns presented by the group was developed.

John Walker and Doug Walker worked with Mr. Hall to develop a plan for sampling and assessing groundwater quality data to identify local areas impacted by failed septics. The plan was based on individual well owners collecting samples for bacteria and nitrate, with the option of samples from selected sites to undergo further analysis to identify likely sources for bacteria and nitrates. As many wells in the Lewisville area were completed before the Idaho Department of Water Resources regularly maintained records, information concerning well construction and septic age and maintenance would also be requested.

Planning included coordination with a local drinking water analytical laboratory concerning the samples to be collected and the recommended analyses. Samples collected by the individual well owners were for total coliforms and e. Coli (presence/absence) and for nitrate as N (by ion chromatography, method EPA 300.0). Total coliforms are naturally occurring bacteria present in soil and surface water. e. Coli are a family of bacteria present in surface water and associated with fecal matter. The analytical method selected for nitrate allowed for chloride and sulfate to be analyzed from the same sample and for results to be calculated after nitrates were reported. The well owner also agreed to cover the cost of analysis ($35 for bacteria analysis and $20 for nitrate, with an additional $20 each for chloride and sulfate, if requested) to review for evidence of the possible source of bacteria and nitrates in each sample.

Sampling kits (a Ziploc bag with the instruction/ permission/information form) were made available at the Lewisville Community Center on Saturday, June 15th. The kits instructed that samples be collected and returned to the Center on Monday, June 17th. The planning team received samples and confirmed the information, with John Walker delivering samples to the laboratory the next day. Questions concerning sampling and what the results received might mean were addressed.

Total coliform was reported positive for ten samples, with two of the ten also reported positive for e. Coli. Nitrate as N was reported as less than the 1 mg/L reporting level for 10 sites, with a maximum value of 2.7 milligrams per liter (mg/L) reported. The mean and median values were 1.30 and 1.34 mg/L. A review of regional nitrate levels suggests that results greater than values as low as ~1.25 mg/L represent low nitrate impact from human (anthropogenic) activities. For all of the samples collected in the sampling event, nitrate results were much less than the 10 mg/L drinking water limit set by EPA.

Sites with total coliform detections were closely located (clustered) with those having nitrates greater than 1.25 mg/L in two different locations within Lewisville, while other clusters of sites with nitrates greater than 1.25 mg/L did not yield bacteria detections. The two sites with e. Coli detections included one clustered with another nearby site with a total coliform detection.  These specific sites yielded nitrate at or less than 1 mg/L. Overall, there was not a consistent correlation between bacteria detections and nitrate levels.

After this initial review of results, the laboratory was requested to report values for chloride and sulfate for nine sites to determine if the observed chloride and sulfate values likely represented surface water, waste, or fertilizer impacts based on the concentrations and relative proportions of these indicators. Sites within the identified clusters and individual locations with higher nitrate values were included. Sulfate and chloride were requested for one site with the initial sampling.

The ten sites' sulfate and chloride results were compared to those of a similar sampling conducted by IDEQ for the Ashton, Idaho area, about 40 miles north of Lewisville, in 2023, and to water quality for surface water representative of Eastern Idaho groundwater  (Click to connect to IDEQ groundwater quality data  ). The comparison suggested that sulfate and chloride concentrations reflect a mixture of values found in the surface water from the South Fork of the Snake River and Henry's Fork of the Snake River, which does not suggest a significant fertilizer or waste influence. The one site from 30 miles north returned a similar sulfate value to the nearby Henry's Fork of the Snake River with a proportionally greater chloride concentration. This site may reflect a possible waste influence.

Thirty-six participants provided information regarding their wells and or septic systems. About half were familiar with the age or construction of their wells, while more, 32, were aware of the status of their septic systems. Five indicated that their septics were new, less than five years old, fifteen indicated they had pumped or otherwise maintained theirs within the last five years, and nine indicated maintenance within as many as 30 years ago. Another three indicated their status as "good," suggesting some inspection or maintenance within their memory.

• A common source may impact small groups of wells. Slightly elevated nitrates and bacteria detections for multiple groups of wells within Lewisville may reflect a minor but common source of impact for those wells, such as irrigation from surface water. The observed nitrate concentrations are slightly distinguishable from ambient conditions and much less than the 10 milligram/liter EPA limit for nitrates in drinking water.
• Individual wells are likely impacted by conditions local to those wells. Wells with e. Coli detections and isolated wells with higher nitrates (above about 2 milligrams/liter) likely reflect impacts from conditions local to those individual wells. These impacts are a combination of ambient conditions and minor influence from fertilizer-related nitrates rather than from significant septic impacts.
• The impact from surface water is more likely than from failed septics. Comparing sulfate and chloride concentrations for the ten sites with regional water quality and surface water suggests that irrigation-related surface water has a more significant impact than wastewater from septics.

• While failed septics may contribute to water quality issues, shallow drinking water wells, and corresponding high groundwater vulnerability are likely the dominant factors contributing to impacted groundwater quality. Addressing sources of anthropogenic impact, including agricultural practices and septics, and addressing vulnerability to contamination at private wells would be among the first steps to protecting water quality for Lewisville residents.

All domestic well and septic owners should remember that, just like all other aspects of their homes, these systems require regular maintenance. This sampling and follow-up emphasize that there are times when steps are needed to protect private drinking water sources, and homeowners should realize the impact their actions or inactions can have on their neighbors. This can be accomplished by:

• Regularly inspecting well heads, ensuring that well sanitary seals are intact, surface water or irrigation water runs away from the well, and that sources of contamination are not stored next to the well.
• Testing private well water regularly, annually for bacteria and nitrates, or after a potential change in water quality - cloudy water, a smell, or flooding around the wellhead.  
• Regularly maintain your septic system by having it inspected at least every three years and pumped every three to five years. Flush only “septic-safe” materials.

Based on information gained by this sampling:

• The City of Lewisville may consider implementing ordinances requiring regular pumping and inspection of septics.

• The City may consider applying for grants or establishing a fund to help offset the costs of this regular inspection and maintenance of septics for low-income residents.

• Likewise, the City may consider investigating funding sources to aid residents in replacing old, shallow wells.

• The City may encourage the County to require community water and wastewater systems for any new developments adjacent to the Lewisville townsite.

•  Well evaluation checklist  - A summary of factors that the private well owner should be aware of and actions they can take to protect their drinking water source.
•  Septic maintenance checklist  - Information concerning how septic systems work and recommended regular maintenance.

• National Groundwater Association: Water well basics, well maintenance, and water quality.  Wellowner.org 

• Illinois State Water Survey: Webinars on well maintenance and septic systems.  The Private well class.org 

• EPA Private drinking water and septic information: General information regarding private wells and septics, along with rules, definitions, and state programs.  EPA drinking water wells   EPA Septic system information 

• Centers for Disease Control: Private well information focusing on health - diseases and contamination concerns.  CDC Drinking Water, Private Water Systems 

Idaho Department of Health and Welfare (IDHW) Idaho Groundwater quality: Idaho Private Well Water Project with information for specific contaminants and water quality data from private wells in Idaho.   Drinking water/Idaho Private Well Projec t

What if sampling indicates bacteria in my well? Instructions for chlorine shock treating a well. Cleanwaterstore.com /how-to-shock-chlorinate-a-well-to-kill-bacteria/ 

Idaho State Revolving Fund- household septic program: - Administered through the Rural Community Assistance Corporation (RCAC) - Low-interest loan/grant program to refurbish/replace individual septics  Idaho SRF Household septic system program 

RCAC – Household water Well and septic loan/grant program: Low-interest loan/grant program to refurbish/replace household wells or septics.    Household  water well and septic system loan/grant program

USDA Rural Development Low-income repair Loan and grant programs: Low-interest loans and grants for rural homes and businesses.  Rural Development Water & Waste Disposal Loan & Grant Program in Idaho