Conditions That Hold Up: Noise, Generators, Water, Light and Bonds

Approval of a data center almost always comes with a list of conditions. The list can run twenty pages. Some conditions do real work, and some are decoration. The difference is whether anyone can measure the thing the condition promises, at a set place and time, and whether someone has the duty and the money to check.

Idaho's enabling law gives counties and cities room here. Idaho Code 67-6512 lets a special use permit carry conditions that minimize adverse impact, control the timing and duration of development, fix the exact location of buildings and equipment, require on-site or off-site public facilities, and set standards stricter than the ordinance usually requires. It also warns that conditions a landowner finds unacceptable may face a regulatory takings analysis. So conditions need a clear link to an actual impact.

Noise: what the number actually limits

"55 decibels" at a hearing sounds precise. It means little until you know the weighting, the metric, the location, the hours and the baseline.

Question	Why it matters	What good conditions say
Which weighting?	dBA discounts the low hum that carries farthest and annoys most. dBC counts more of it.	A dBA limit plus a dBC limit or octave-band limits
Which metric?	Leq averages over a period. Lmax is the loudest moment. A 1-hour Leq can hide short spikes.	Leq over a stated period, plus an Lmax cap
Where?	The property line of the data center, the property line of the nearest home, or the home itself give very different numbers	At the nearest residential property line, and at named sensitive sites
When?	Night is quieter, so the same equipment is more noticeable	Separate day and night limits with clock hours
Compared to what?	A rural night can sit near 30 dBA; a 45 dBA hum there is a big change	Baseline survey (often reported as L90) before construction

A large gap between C-weighted and A-weighted readings of the same sound is a sign of strong low-frequency content. That gap is the measurement version of what neighbors describe as a hum they feel more than hear. The land, noise and air lesson in the impacts module explains why A-weighted limits miss it.

Real examples, as of October 2026. Kent County, Delaware's ordinance caps sound at 55 decibels at the data center property line and requires testing before construction and after opening with all equipment running together. Lancaster, Pennsylvania's community benefits agreement sets a different kind of limit: operations may not exceed existing ambient noise at nearby homes and parks, with testing before and after. Fairfax County, Virginia requires pre- and post-construction noise studies against its existing noise ordinance. The ambient standard is the strictest in a quiet place and the hardest to verify.

Generators: federal floor, local options

Federal rules set the floor. Under 40 CFR 60.4202, new emergency stationary diesel engines from 50 up to 3,000 horsepower are certified to Tier 2 or Tier 3 nonroad standards, and larger ones (many data center units are larger) to Tier 2. Non-emergency stationary engines must meet the current nonroad standards under 60.4201, which for most sizes means Tier 4. And 40 CFR 60.4211(f) caps an emergency engine's maintenance and testing at 100 hours a year, with up to 50 of those allowed for limited non-emergency use. Emergency hours are unlimited.

So a data center with emergency generators can legally use Tier 2 engines. A county or the state air permit can ask for more:

• Tier 4 engines or aftertreatment. Selective catalytic reduction cuts nitrogen oxides; particulate filters cut soot. They add cost and need maintenance logs to prove they work.
• Testing windows. Kent County limits routine testing to weekdays, 10 a.m. to 4 p.m. Lancaster allows daytime testing only, never on Sundays or federal holidays.
• One engine at a time. Simultaneous tests create a local spike in noise and exhaust.
• No demand response. A condition can bar running generators to sell power or shave peaks, even the limited non-emergency hours federal rules allow.
• Reporting. Monthly run logs filed with the county, not just kept on site.

Water, light, screening, roads

Water source and cooling design. Kent County requires written confirmation of water utility capacity where a utility serves the site, and generally bans open-loop or once-through cooling unless reclaimed water is used. Lancaster caps municipal water use at 20,000 gallons a day per campus and requires closed-loop cooling without added chemicals. Lesson 5 covers the water supply side.

Lighting. Security lighting runs all night. Useful conditions require fully shielded fixtures aimed down, no uplighting of facades, motion controls where security allows, warm color temperatures and a photometric plan showing light levels at the property line.

Screening. Kent County requires exterior mechanical equipment next to homes to be enclosed on all four sides by an acoustical barrier, and two staggered rows of evergreens at least six feet tall at planting along roads and residential districts. Fairfax requires equipment to be enclosed or screened by a wall.

Roads. Construction brings concrete trucks, steel and oversize transformer loads for a year or more per building. A road use agreement should name haul routes, require a recorded condition survey (often video) before construction, set the repair standard, and require a bond or letter of credit for damage. The county road agency or highway district signs it, not the planning commission, so ask whether it exists before the land-use vote.

Decommissioning

Data centers are new enough that few large campuses have been abandoned. Counties write decommissioning conditions anyway, because a shell with transformers, fuel tanks and batteries is expensive to clear. Kent County requires financial assurance covering 100 percent of expected cleanup and restoration cost, reviewed at least every five years. A facility closed for one continuous year may be presumed abandoned and must be removed within 180 days.

Enforceable or decorative

Decorative	Enforceable
Noise will be minimized	45 dBA Leq (1-hour) at any residential property line, 10 p.m. to 7 a.m.; 55 dBC Leq; verified by a county-selected consultant at the owner's expense within 90 days of each building opening and every 3 years
Generators will be tested responsibly	Testing weekdays 10 a.m. to 4 p.m., one engine at a time, logs filed with the county monthly
Water use will be efficient	Potable water not to exceed 50,000 gallons per day averaged monthly, metered, reported quarterly
Lighting will be appropriate	Fully shielded fixtures; photometric plan approved before building permit; no more than 0.1 foot-candle at residential property lines

Every enforceable condition answers: what number, measured how, where, when, by whom, paid by whom, and what happens if it fails. If the condition doesn't name a consequence, the consequence is a code enforcement case, which a small county may not have staff to bring.