County engineer details watershed protections, impervious limits and pending state rule changes

Christopher Sonton, Orange County—s county engineer, walked commissioners through the county—s watershed map and the UDO provisions that govern water‑supply protection overlays, impervious surface limits and density limits on Sept. 9.

Sonton said Orange County contains 18 watersheds, 13 of which are protected as water‑supply watershed overlay areas that carry both maximum impervious‑surface allowances and residential density limits. "We do have 18 individual watersheds in Orange County," Sonton told the board. He described a color‑coded set of protections on the county map: dark blue or dark green areas near reservoirs carry the strictest limits; lighter blue or green areas are less restrictive; and some portions of the county are outside water‑supply protection overlays.

Why it matters: Watershed overlay rules affect what property owners can build in areas that drain to public reservoirs. Limits on density and impervious cover determine feasible lot sizes, septic and water options, and the cost and design of new development.

Key technical limits and requirements cited by staff

- Impervious surface caps: Staff said the county enforces impervious limits that vary by watershed: the most restrictive areas have a 6% maximum impervious allowance; the state general requirement is commonly 12% in many jurisdictions. Sonton and planning staff explained that owners may increase impervious area in some watersheds by up to an additional 3 percentage points if they install approved stormwater control measures that treat the added runoff.

- Residential density: In critical‑area watersheds such as University Lake, the maximum residential density cited by staff is as restrictive as one dwelling unit per five acres; other protected watershed areas carry different, lower‑intensity density allowances (for example, 1 du per 2 acres in some overlay zones). Nonresidential projects are controlled by different measures (floor‑area ratios and nonresidential impervious limits).

- Septic and setback rules: Staff summarized setback requirements for septic systems in water‑supply watersheds: a general 100‑foot setback from reservoirs or streams for septic tanks, with larger setbacks in critical areas (University Lake critical area was cited as 300 feet for tanks and fields in staff remarks).

- Permit triggers and stormwater matrix: Commissioners were shown a stormwater/erosion control matrix that defines the earth‑disturbance thresholds that trigger an erosion‑control or stormwater permit. Critical areas have very low disturbance thresholds (for example, 10,000 square feet in some critical reservoirs), meaning most development in those zones requires formal permits and stormwater treatment plans.

Pending or recent state legislation

Staff identified several state law changes that already affect local implementation and one proposed change they were tracking: House Bill 218 (2021) clarified treatment of preexisting development in watershed rules; House Bill 600 (2023) further limited regulation of existing impervious surfaces and reinforced that new development remains subject to modern stormwater requirements; and staff said a 2025 regulatory‑reform measure in the General Assembly (described in staff slides as the "regulatory reform act of 2025") would, if enacted as then drafted, exempt residential land disturbances under 1 acre from local stormwater treatment requirements. Planning and engineering staff said they are monitoring the bill and would adjust local requirements if and when state law changes.

Commissioner concerns and clarifications

Commissioners and staff discussed the practical consequences for homeowners and small projects: several commissioners noted that a 6% impervious cap can make routine improvements (driveways, decks) difficult on small lots. Staff acknowledged the hardship and pointed to two pathways: (1) applicants may rely on the fact that impervious installed before specified effective dates (set out in staff materials) generally are not counted under some state rules; and (2) property owners may pursue stormwater control measures to qualify for incremental impervious increases under the UDO.

What was decided and next steps

No regulatory changes were adopted; staff told the board they will continue to track state legislation and bring proposed UDO amendments or guidance back to the board if statutory changes require local adjustments. Sonton and planning staff said they will provide clearer explanatory handouts for residents and developers about preexisting development dates, permit triggers and how to request site‑specific permits.

Ending

The board received the technical briefing and asked staff to return with materials that explain the practical consequences of impervious and density limits for small properties and how recent and pending state laws alter local authority to require stormwater treatment.