## Facts

- A developer owned a 60-acre parcel in Derry, New Hampshire, and proposed an age-restricted independent adult community consisting of 36 detached single-family residences, a private road, and substantial open space.
- The proposal included six community septic systems using four-inch collection pipes and 36 individual wells.
- The New Hampshire Department of Environmental Services (DES) reviewed and approved the sewage disposal system under state regulations.
- During site plan review, the Town’s Department of Public Works urged use of sewer-division design preferences (including larger pipe diameters) that were not adopted in the Town’s site-plan or septic regulations for this type of private system.
- The Planning Board acknowledged DES compliance but denied final site plan approval based largely on concerns about pipe size, private-road width, and potential impacts on downgradient neighboring wells if the system failed.
- The Town had not adopted site-plan or septic standards more stringent than DES rules governing subsurface sewage disposal.

## Issues

1. Whether a planning board may deny site plan approval for a DES-approved septic design when the municipality has not adopted more stringent local standards and the denial is not supported by substantial evidence of an actual threat to water supplies or public health.
2. Whether generalized concerns, preferences for unwritten standards, and speculation about possible failures constitute a lawful basis to deny site plan approval.

## Decision

- The New Hampshire Supreme Court reversed the superior court and held that the Planning Board unreasonably and unlawfully denied the site plan application.
- The court concluded that DES approval, combined with the absence of duly adopted stricter municipal standards and the lack of record evidence that the system would not protect water supplies, made the denial improper.
- The case was remanded for further proceedings consistent with the court’s ruling.

## Legal Principles

- A planning board’s site plan decision must be grounded in properly adopted regulations and supported by substantial evidence in the record.
- When DES has approved a septic system and the municipality has not enacted more stringent standards applicable to the proposal, DES approval is strong evidence that the system is adequate.
- A municipality may not impose ad hoc requirements or enforce agency or departmental preferences that are not incorporated into applicable ordinances or site-plan regulations.
- Generalized fears, anecdotal references to unrelated failures, and speculative health-and-safety concerns do not satisfy the substantial-evidence requirement, particularly where the relevant state agency has approved the design.

## Conclusion

The court held that the Planning Board exceeded its lawful discretion by denying site plan approval based on speculative concerns and unwritten design preferences, where DES had approved the septic system, the Town had not adopted stricter local standards, and the record lacked substantial evidence of a concrete risk to water supplies or public health.


Derry Senior Dev. LLC v. Town of Derry, 157 N.H. 441, 951 A.2d 170 (N.H. 2008)