Land Use Interpretation for a Proposed Housing Development

The soil properties indicate significant limitations for the proposed development. Basements: The seasonal high water table at 45 cm is a major constraint. Basements typically require excavation to at least 2-2.5 m, which would be below the water table for much of the year. This would require extensive dewatering during construction and a permanent waterproofing and drainage system. The somewhat poorly drained nature and occasional ponding increase the risk of water damage and structural issues. The soil's low available water capacity (0.18 cm/cm) is not directly relevant to basements, but the wetness is. Septic systems: Septic systems require adequate depth to a limiting layer (water table, bedrock) and suitable soil permeability for treatment. The water table at 45 cm is too shallow for a conventional septic system, which typically requires at least 60-90 cm of unsaturated soil below the drainfield. The occasional ponding could also saturate the drainfield. A mound system or alternative treatment may be necessary, increasing costs. The soil texture (silt loam) has moderate permeability, but the wetness is the limiting factor. Stormwater infiltration: Infiltration basins require soils with good drainage and a deep water table to prevent standing water and contamination. The seasonal high water table at 45 cm and somewhat poor drainage mean that infiltration basins would likely fail or function poorly, especially during wet periods. The low available water capacity (0.18 cm/cm) means the soil holds little water, but the shallow water table limits the depth for infiltration. The occasional ponding indicates that water already ponds on the site, so adding more water could exacerbate problems. Prime farmland argument: The developer claims the land is not prime farmland because it is Class III. However, prime farmland is defined by the USDA based on soil properties, not just capability class. The Honeywood silt loam may still qualify as prime farmland if it has adequate moisture, temperature, and pH, and is not excessively eroded or wet for too long. The land capability class IIIw indicates wetness limitations, but prime farmland can include soils with moderate limitations if they are managed. The soil survey may list this map unit as 'prime farmland if drained' or 'farmland of statewide importance.' The developer's argument is an oversimplification. The county's comprehensive plan prioritizes preserving prime farmland, so the planning commission should verify the prime farmland designation using the soil survey's farmland classification. Even if not prime, the land may be of statewide importance. The adjacent wetland and impaired stream add environmental concerns: increased stormwater runoff and nutrients from the development could worsen the impairment. The site's wetness and ponding also make it unsuitable for infiltration-based stormwater management, which could lead to more runoff. Overall, the soil limitations are severe for the proposed use, and the developer's argument is not sufficient to override the plan's farmland preservation goal.

I recommend that the planning commission deny the rezoning as proposed, or approve it only with stringent conditions that address the soil limitations and environmental concerns. The soil survey data show severe limitations: the seasonal high water table at 45 cm, occasional ponding, and somewhat poor drainage make conventional development with basements and septic systems risky and costly. Stormwater infiltration is not feasible due to the shallow water table. The site is adjacent to a wetland and an impaired stream, so increased runoff and nutrient loads would conflict with water quality goals. The comprehensive plan prioritizes preserving prime farmland and directing growth to areas with infrastructure. The developer's claim that the land is not prime farmland is not supported by the soil survey; the map unit may still be prime farmland if drained or farmland of statewide importance. Even if not prime, the plan's intent is to avoid converting agricultural land when alternatives exist. Conditions for approval could include: (1) Requiring a site-specific engineering study to design foundations and septic systems that account for the water table, such as mounding or connection to a centralized sewer. (2) Prohibiting basements or requiring waterproofing and sump pumps. (3) Using stormwater management that does not rely on infiltration, such as detention ponds with liners or constructed wetlands, and treating runoff to reduce nutrients before discharge. (4) Preserving a buffer along the wetland and stream. (5) Clustering housing on the less wet portions of the site (if any) and dedicating the rest as open space or restoration. (6) Requiring a nutrient management plan for the development. However, given the plan's priorities, a better alternative would be to direct the development to an area with existing infrastructure and less sensitive soils. The commission should request an alternative site analysis from the developer. If the developer insists, the commission could approve a lower-density cluster development with the above conditions, but the burden is on the developer to demonstrate that the limitations can be overcome without environmental harm. The decision should be based on the soil survey's limitations and the plan's goals, not just the capability class.