9.2 Groundwater & Surface Water Protection

9.2 Groundwater & Surface Water Protection

Quick Answer: Groundwater protection is one of the highest regulatory priorities in New Hampshire because over 46% of the state's population depends on private domestic wells for drinking water, while municipal systems draw from permeable stratified-drift sand and gravel aquifers. New Hampshire's hydrogeology features shallow, acidic glacial till over fractured crystalline bedrock; contaminants that leach through coarse topsoils enter open rock fractures where they travel hundreds of feet without filtration. New Hampshire's protective distances are set by rule: 400 feet from gravel packed public water supply wells and 250 feet from other public supply wells (Pes 502.05), 250 feet from the reference line of a public water supply surface water within 5 miles of the intake (Pes 502.04), 75 feet for mixing and loading near surface water or a private well (Pes 805.01), and 25 feet from the reference line of surface waters not covered by RSA 483-B (Pes 1001.01). Furthermore, applicators must prevent back-siphonage during tank filling by maintaining an unbroken physical air gap (twice the hose diameter, never under 1 inch) or installing a Reduced Pressure Zone (RPZ) backflow preventer.

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New Hampshire Hydrogeology: Glacial Till, Stratified Drift & Fractured Bedrock

Protecting water resources requires an applicator to understand the subterranean geology of the Granite State. Unlike regions with deep, uniform silt or clay soils that provide extensive physical filtration and chemical adsorption, New Hampshire's geological profile offers minimal protection against mobile contaminants.

1. Glacial Till

Most upland terrain across New Hampshire is mantled by glacial till—an unsorted, unstratified mixture of clay, silt, sand, gravel, cobbles, and boulders deposited directly beneath retreating glaciers during the last ice age:

• Depth Constraints: In many upland areas, glacial till forms an extremely thin veneer, frequently measuring less than 2 to 6 feet in depth over solid bedrock.
• Low Sorptive Capacity: These soils are naturally acidic (pH 4.5 to 5.5) and coarse-textured, with low clay fractions. Their capacity to adsorb mobile pesticide molecules is severely constrained.

2. Stratified Drift Aquifers

In river valleys and lowlands (such as the Merrimack, Connecticut, Saco, and Piscataqua basins), melting glacial meltwater deposited washed, highly sorted layers of sand and gravel known as stratified drift aquifers:

• High Hydraulic Conductivity: Stratified drift deposits are exceptionally permeable. Water infiltrates through these sandy formations at rates exceeding several feet per day.
• Municipal Water Sources: The vast majority of high-yield commercial and municipal public water supply wells in New Hampshire are gravel-packed wells completed in stratified drift deposits.

3. Fractured Crystalline Bedrock

Beneath the surficial glacial sediments lies ancient, crystalline metamorphic and igneous bedrock (granite, schist, gneiss):

• Secondary Porosity: Solid crystalline rock has near-zero primary porosity—water cannot penetrate the rock matrix itself. Instead, groundwater moves entirely through secondary porosity: an intricate, unpredictable network of stress fractures, cooling joints, and fault lines.
• Preferential Flow Channels: Once a soluble, mobile pesticide leaches past the thin soil horizon into bedrock fractures, it enters high-velocity preferential conduits. Contaminated water can travel hundreds of feet horizontally in days with zero microbial degradation or soil adsorption.

Contaminant Leaching Dynamics & Preferential Macropore Flow

Pesticides move downward through soil toward groundwater via two distinct physical hydrologic regimes: uniform matrix flow and preferential macropore flow.

Uniform Matrix Flow vs. Macropore Flow

• Uniform Matrix Flow: Water and dissolved solutes move slowly and uniformly through the microscopic pore spaces between individual sand, silt, and clay particles. This slow percolation maximizes contact time with soil organic matter and active microbial communities, enabling significant sorption and biodegradation.
• Preferential Macropore Flow: Water bypasses the dense soil matrix entirely, traveling rapidly downward through macroscopic continuous channels:
  • Decaying Root Channels: Tubular cavities left behind when deep tree or crop roots die and decay.
  • Earthworm and Insect Burrows: Unobstructed structural biopores.
  • Desiccation Cracks & Structural Fissures: Deep cracks formed in clay-rich or compacted soils during dry periods.
• The Risk: During intense New England rainstorms, dissolved pesticides wash directly into macropores, descending 3 to 6 feet in minutes without interacting with the sorptive soil matrix.

The Groundwater Ubiquity Score (GUS Index)

Toxicologists synthesize chemical mobility ($K_{oc}$) and environmental persistence ($DT_{50}$) into the Groundwater Ubiquity Score (GUS) to rank leaching potential:

$\text{GUS} = \log_{10}(DT_{50}) \times \left(4 - \log_{10}(K_{oc})\right)$

• GUS > 2.8: The compound is classified as a Confirmed Leacher. Active ingredients such as atrazine, picloram, and clopyralid fall into this category and carry strict groundwater advisory warnings.
• GUS between 1.8 and 2.8: Marginal or transition leacher.
• GUS < 1.8: Non-leacher. Chemical exhibits high sorption, short half-life, or both.

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Wellhead Protection Areas & Private Well Safeguards

In New Hampshire, safe drinking water oversight involves a stark public-versus-private divide that applicators must navigate responsibly.

The Vulnerability of Private Domestic Wells

Approximately 46% of New Hampshire residents obtain their drinking water from private domestic wells drilled 150 to 800 feet into fractured bedrock or dug into shallow water tables:

• No Federal Oversight: Private wells are completely exempt from the federal Safe Drinking Water Act. Property owners are not required to test their water for synthetic organic chemicals or pesticides.
• Direct Infiltration Risk: Many older domestic bedrock wells possess short, poorly grouted steel casings that allow surface runoff and shallow leachate to channel directly down the borehole annulus into the home's drinking water intake.

Public Water Systems (PWS) and Wellhead Protection Areas (WHPAs)

Municipal utilities and community water systems operate under strict state oversight administered by the New Hampshire Department of Environmental Services (NHDES) Drinking Water and Groundwater Bureau:

• Wellhead Protection Area (WHPA): A scientifically delineated surface and subsurface recharge area surrounding a public well through which groundwater contaminants are reasonably likely to move toward the well intake within a specified time horizon.
• Sanitary Protective Radius: A non-disturb outer protection zone (typically 75 to 400 feet in radius depending on well pumping capacity) where chemical applications and pollutant storage are strictly restricted.

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The New Hampshire Water-Protection Distances

New Hampshire does not use one universal buffer. It uses different distances for different activities, set by different rules. Memorize the activity along with the number.

Two points are worth restating because they are the ones most often gotten backwards.

The gravel packed well gets the larger number. Pes 502.05 sets 400 feet for gravel packed wells used for public water supply and 250 feet for other wells so used. A gravel packed well is screened in permeable stratified drift and draws a wide, fast cone of influence, so it needs the wider protective radius.

There is no general application setback from a private well. New Hampshire protects private wells through the mixing and loading rule: Pes 805.01(c) forbids mixing or loading within 75 feet of surface water or private water wells. Product labels frequently impose their own well setbacks, and those are independently enforceable under Pes 502.01.

Aquatic applications. Any pesticide purposefully applied to standing or running water is governed by Chapter Pes 600, which requires a special permit from the Division, issued after an application process that can include public hearings, agency recommendations, and treatment conditions. Category D is the corresponding commercial certification category. Pes 502.01(e) is the only route to a below-label rate, and it must be proposed in the permit application and approved.

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Backflow Prevention: Tank-Filling Engineering Safeguards

One of the most immediate routes of acute groundwater and drinking supply contamination is back-siphonage during spray tank filling. If an applicator places a fill hose directly inside a spray tank below the fluid level and a sudden drop in water supply pressure occurs (e.g., a well pump failure, water main break, or neighboring hydrant usage), the resulting negative suction pressure will instantly draw hundreds of gallons of concentrated pesticide mix backward into the drinking water system.

1. Physical Air Gap (The Gold Standard)

A physical air gap is an unobstructed vertical physical separation through free atmosphere between the lowest end of the water supply discharge pipe and the highest overflow rim (flood level) of the spray tank:

• Regulatory Specification: The vertical distance must be at least twice the effective inside diameter of the water supply pipe (2D), and in no case may it measure less than one full inch (25 mm).
• Unbreakable Separation: Because air cannot transmit hydraulic suction, an air gap provides absolute, foolproof mechanical protection against back-siphonage.

2. Reduced Pressure Zone (RPZ) Backflow Preventers

When a physical air gap cannot be maintained (such as during closed-system pressurized tank injection), applicators must install an approved mechanical Reduced Pressure Zone (RPZ) backflow preventer:

• Mechanism: Contains two independently operating spring-loaded check valves separated by an intermediate, hydraulically operated differential pressure relief valve. If either check valve leaks or back-siphonage occurs, the relief valve vents the water directly to the atmosphere, preventing any reverse flow into the potable supply.
• Inspection: RPZ assemblies must be tested and certified annually by a certified backflow device inspector.

Strict Applicator Prohibition: Applicators must NEVER submerge the end of a fill hose into a pesticide mixture, nor rest a hose on the rim of an unshielded spray tank opening.