Reviewed August 2026 against Illinois EPA’s Source Water Assessment Program (SWAP) and USGS Scientific Investigations Report 2022-5110.

Jump to the calculator →

Farmer City, Illinois draws its public water supply from aquifer code 0101 — the sand and gravel classification used throughout the Illinois EPA’s Source Water Assessment Program. Four of the city’s wells (Wells #2, #9, #10, #11) are listed in the Illinois EPA SWAP factsheet as susceptible to inorganic, volatile organic, and synthetic organic contamination, with eight documented hazard sources mapped near the wellheads. This article walks through what aquifer code 0101 means, what the Illinois EPA SWAP factsheet says about Farmer City specifically, and how sand-and-gravel aquifers compare across the state on contamination risk.

Table of Contents

What Aquifer Code 0101 Means

Illinois EPA’s Source Water Assessment Program assigns a numeric aquifer code to every well serving a public water supply, and code 0101 designates sand and gravel aquifers — unconsolidated glacial deposits that sit close to the surface across central and northern Illinois. Per Illinois EPA SWAP data, the top of a sand and gravel (0101) aquifer typically begins around 300 feet below the surface, though the figure varies by well and by the local glacial deposit sequence. Farmer City’s public wells fall into this classification, which is why searches pairing “Farmer City” with “aquifer code” return Illinois EPA SWAP material rather than a bedrock or sandstone designation.

Sand and gravel aquifers behave differently from Illinois’ deeper bedrock aquifers (such as the Cambrian-Ordovician or Silurian dolomite systems used elsewhere in the state). Because they sit shallower and are more permeable, they recharge faster from precipitation — but that same permeability means surface contaminants reach the water table faster too. That single fact drives most of what the SWAP factsheet flags for Farmer City.

Farmer City’s SWAP Factsheet: Wells and Hazards

The Illinois EPA SWAP factsheet for Farmer City identifies four wells — Wells #2, #9, #10, and #11 — as susceptible to inorganic chemical (IOC), volatile organic chemical (VOC), and synthetic organic chemical (SOC) contamination. Susceptibility in SWAP terminology means a well’s aquifer type and surrounding land use combine to create elevated contamination potential; it does not by itself mean a contaminant has been detected in the water leaving the treatment plant. Actual compliance results are reported separately in the city’s annual Consumer Confidence Report.

The same factsheet inventories eight documented hazard sources near Farmer City’s wellheads: a salvage yard, fuel storage facilities, grain elevators, an auto repair shop, a hazardous waste facility, and a generator/substation. These are proximity-based risk factors — their presence near a wellhead protection area is what elevates the SWAP susceptibility rating, not confirmed contamination events. The factsheet does not, in the material reviewed for this piece, specify current remediation status or well-replacement plans for the four susceptible wells; that level of detail would require a direct records request to Illinois EPA or a review of recent Farmer City council minutes, neither of which is published in the SWAP dataset itself.

For residents specifically searching the Illinois EPA SWAP fact sheet language tied to “Farmer City” and “water supply” and “sand and gravel,” this factsheet is the primary document: it is issued per community system, listing well counts, aquifer codes, and hazard proximity together in one place.

Sand and Gravel Aquifers Across Illinois

Farmer City is not an outlier in relying on code 0101. Illinois EPA SWAP data covering 3,272 active wells statewide shows 46% draw from sand and gravel aquifers — a total of 1,513 Community Water Supply wells on this classification. Illinois EPA further reports that roughly 60% of the state’s rural water supply depends on groundwater from aquifers including the code 0101 sand-and-gravel type, and that more than 1,700 community water supplies statewide require SWAP assessment, serving an estimated 12 million Illinois residents on public drinking water systems.

That scale matters for interpreting Farmer City’s own numbers: a shallow, sand-and-gravel-fed system with hazard sources nearby is a common profile across the state, not a unique vulnerability specific to one town. What differs from system to system is the density and type of nearby land use — industrial, agricultural, or residential — which is exactly what the SWAP hazard inventory is designed to capture on a per-community basis.

What Water Quality Testing Actually Finds

The most detailed public dataset on sand-and-gravel aquifer water chemistry in Illinois comes from a 2020 USGS study of McHenry County — a different sand-and-gravel-fed county from Farmer City’s, but the same aquifer code, and the only county-level dataset with published exceedance rates broken out by contaminant. The USGS Scientific Investigations Report on sand and gravel aquifer water quality in McHenry County tested wells against federal and state health-based and aesthetic benchmarks, with these results from 2020 monitoring:

• 24% of sampled wells exceeded health-based benchmarks for arsenic
• 40% exceeded health-based benchmarks for sodium
• 87% exceeded aesthetic (non-health) benchmarks for iron
• 29% exceeded aesthetic benchmarks for dissolved solids
• Jump to the calculator

These figures are specific to McHenry County’s 2020 sampling round and should not be read as Farmer City’s own water chemistry — no equivalent contaminant-by-contaminant breakdown for Farmer City’s wells was located in the sources reviewed for this piece. What the McHenry County study does establish is a documented benchmark-exceedance range for the same aquifer classification (code 0101) elsewhere in Illinois, useful as context for what “susceptible” can translate to once a well is actually sampled. Iron and dissolved solids are aesthetic issues (taste, staining, scale) rather than health hazards; arsenic and sodium are the two the USGS study flagged against health-based limits.

For Farmer City’s own tested results — as opposed to susceptibility ratings — the authoritative document is the city’s Consumer Confidence Report, published annually before July 1 under Illinois EPA’s Drinking Water program rules.

Comparison Table: Farmer City vs. Statewide Sand-and-Gravel Systems

The table below lines up what is actually documented for Farmer City against the statewide sand-and-gravel picture, so it’s clear which figures are Farmer City-specific and which are drawn from the wider Illinois EPA SWAP dataset or the McHenry County study.

Well Vulnerability Scoring Tool

Use the inputs below to score relative wellhead vulnerability the way a SWAP-style review weighs it: aquifer depth, number of nearby hazard sources, and distance to the closest one.

This tool produces a relative index for comparing wellhead scenarios, not an official Illinois EPA SWAP susceptibility rating. It excludes actual contaminant sampling results, aquifer transmissivity, and site-specific hydrogeology — for a well’s real susceptibility rating, request the current Illinois EPA SWAP factsheet for that community system.

How to Check the Current SWAP Status Yourself

Because well susceptibility ratings, hazard inventories, and testing results all update on different schedules, the figures in this article carry a shelf life. Here is how to pull the current version of each:

• Illinois EPA SWAP Factsheet (Farmer City-specific): Illinois EPA updates community-level SWAP assessments and factsheets periodically. Visit Illinois EPA’s Source Water Assessment Program page and request the current Farmer City factsheet for the latest well evaluations and hazard inventory.
• USGS sand-and-gravel water quality studies: These county-level studies are periodic, roughly every 5 to 10 years per county based on publication history. Check USGS’s publication listing for newer Illinois sand-and-gravel aquifer studies, or subscribe to USGS Illinois Water Science Center releases.
• Farmer City’s own tested water quality: The city’s Consumer Confidence Report is published annually before July 1, per Illinois EPA Drinking Water program requirements. Check Farmer City’s Consumer Confidence Report page for the current year’s edition, which lists tested results, not just susceptibility ratings.
• Statewide aquifer mapping: The Illinois State Geological Survey maintains statewide sand-and-gravel aquifer extent and depth mapping, useful for comparing Farmer City’s local geology against neighboring counties.

This four-source check — SWAP factsheet, USGS study, local CCR, and ISGS mapping — is the durable method behind this article: it doesn’t expire when any single figure updates, because it tells you where to re-pull each number.

Frequently Asked Questions

Related: Mineral & Land Monitoring Resources

Farmonaut’s satellite monitoring work spans beyond water infrastructure into mineral exploration and land-use mapping across North America. For readers researching critical mineral supply — including tungsten deposits tied to Canadian sources such as the Cantung and Mactung mines and broader tungsten ore market trends — Farmonaut’s satellite-based mineral detection platform applies the same remote-sensing approach used for land and water monitoring to mineral prospectivity. A sample satellite-driven 3D mineral prospectivity map shows the output format.