Township engineers raise concerns after pollutant models overstate suspended solids

Township civil engineer John reported that recent public reporting of pollutant loads — drawing on modeled estimates — appears to substantially overestimate suspended solids compared with live monitoring data linked from USGS and county pages.

"On just on the suspended solids, it was, like, 10 times the value," John said, describing the discrepancy between model output and monitored concentrations. He told the board that the goal across consortium communities has been a 10% reduction in loading, but that model error could misstate compliance needs and policy triggers.

John and other supervisors discussed how older cities upstream contribute to nutrient and solids loads and how the township has invested in erosion control during development. Diana, the township environmental engineer, added that the model differences extend to nitrogen and phosphorus as well: "Phosphorus and nitrogen as well were way off," she said.

Board members suggested caution in relying on uncalibrated models when agencies prepare stricter stormwater and erosion control rules. Supervisors noted that while monitoring shows improvement in water quality over the past two decades, significant contributions from upstream municipalities and legacy infrastructure still matter for regional water quality.

The board did not adopt new policy at the meeting but asked staff to monitor developments and bring technical updates as regulators consider rule changes. Staff noted modeling and permitting implications will affect potential future ordinances and accounting for impervious surface assessments.