4.5 Reading the Site: Weather, Terrain, Drainage, Soil, and Surrounding Communities

The Standard Behind the Habit

Most environmental training teaches hazards one at a time: drift here, leaching there, pollinators somewhere else. ATCP 29.30(4)(b) asks for something integrative — knowledge of "how environmental hazards may be affected by factors such as weather, terrain, drainage patterns, soil types, hydrogeologic conditions, and the nature of surrounding biological communities."

That is a site assessment. Done properly it takes about five minutes and produces one of three outputs: go, modify (rate, nozzle, buffer, timing), or postpone.

1. Weather

The counterintuitive entry is dead calm. New applicators treat 0–2 mph as ideal spraying weather. It is often the opposite: calm conditions at sunrise and sunset commonly accompany a temperature inversion, in which cool dense air near the ground is capped by warmer air above. Fine droplets released into an inversion do not disperse upward; they concentrate in a shallow layer and can move a considerable distance intact once a light breeze develops. A steady 3–7 mph breeze in a safe direction is a better condition than dead calm.

2. Terrain

Slope changes both runoff and drift.

• Slope percentage drives runoff velocity, which drives both dissolved and sediment-bound transport. Steeper ground means less infiltration time and more erosion.
• Slope aspect and position determine where water concentrates. Concave positions, swales, and field edges below the slope accumulate both water and chemical.
• Downhill neighbors matter as much as downwind neighbors. A drift plan that only considers wind direction misses half the risk on rolling Wisconsin ground.
• Air movement follows terrain. Cold air drains downhill at night, so an inversion in a valley bottom can move spray along the valley rather than across it.

3. Drainage Patterns

Wisconsin fields are full of engineered shortcuts to water:

• Surface tile inlets accept water directly into a subsurface drain that discharges to a stream — a direct conduit that bypasses the soil profile entirely.
• Tile drainage shortens the path from root zone to surface water and can carry a pulse of soluble chemical within hours of a rain.
• Grassed waterways are designed concentration points; they carry water, so they carry chemical.
• Sinkholes and closed depressions in the karst regions of eastern and southwestern Wisconsin route surface water into fractured dolomite with almost no filtration.
• Road ditches frequently connect to surface water even though they look like dry ground.

Mark these features before you spray, not after. A tile inlet in the middle of a field is the reason a "300 feet from the stream" mental buffer can be worthless.

4. Soil Types

Soil is the variable Wisconsin regulates by number. ATCP 30.32 caps atrazine by surface soil texture:

Where a rescue treatment is involved, ATCP 30.32(3) caps the annual total at 1.5 lb ai/acre on coarse soils and 2.0 lb ai/acre on medium and fine soils. Note the structure: on coarse soils, prior-year use does not change the cap, because the cap is already at its floor.

Beyond the atrazine rule, three soil properties drive fate:

• Texture. Coarse sands have large pores, low water-holding capacity, and low adsorptive surface area — the Central Sands leaching profile.
• Organic matter. Higher organic matter increases adsorption and feeds the microbial population that degrades most pesticides, so it reduces both leaching and persistence.
• pH. Soil pH controls the ionization state of many active ingredients. Some sulfonylurea herbicides persist much longer and stay more mobile in high-pH soils, producing carryover injury to a rotational crop.

5. Hydrogeologic Conditions

The two Wisconsin landscapes from section 4.1 reappear here as decision inputs: the Central Sands, with permeable outwash sand and a shallow water table, and the karst country over fractured dolomite, where water can move through solution channels for miles with essentially no attenuation. Depth to groundwater, presence of a confining layer, and well density all belong in the assessment. The 100-foot mixing and loading setback in ATCP 29.45 applies statewide, but on karst or sand it is a minimum rather than a comfortable margin.

6. Surrounding Biological Communities

The last variable is about neighbors — biological and human.

• Registered apiaries. Under ATCP 29.51(1), a beekeeper with a colony within 1.5 miles of your site may file a written request for notice, and you must then give at least 24 hours advance notice before applying a product labeled "Highly Toxic to Bees" or containing methomyl.
• Sensitive crops. Grapes, tomatoes, cucurbits, tobacco, and organic operations are exquisitely sensitive to growth-regulator herbicides. Wisconsin's cranberry marshes and orchards add their own constraints.
• Endangered species habitat. Where a label directs you to Bulletins Live! Two, the county-and-month bulletin becomes enforceable labeling.
• Registered residents. The DATCP Landscape Pesticide Registry under ATCP 29.56(7) requires 12 hours advance notice to enrolled residents on adjacent parcels.
• Schools, day cares, health care facilities, and public recreation areas. Under ATCP 29.52(1)(a), warning signs are required when a dual notice agricultural pesticide is applied within 300 feet of a residence, migrant labor camp, school, playground, day care facility, health care facility, commercial or industrial facility, public recreation area, or other nonagricultural area — a public road excepted — where people are likely to be present during the REI.

Putting It Together

Run the assessment in this order, because each step can stop the job before you spend time on the next:

1. Weather now and forecast — inversion, wind, rain. Stop or postpone conditions.
2. Terrain and drainage — where does water go from here, and how fast.
3. Soil texture and hydrogeology — does this site force a rate reduction or a product change.
4. Neighbors — apiaries, sensitive crops, registry residents, ESA bulletins, 300-foot facilities.
5. Decide — go, modify, or postpone, and write down what you decided and why.

That last step is not required by rule, but a dated site note is the most useful document an applicator can hold when a drift complaint arrives three weeks later.