Client: Developer Location: Lake Winnipesaukee, Laconia, New Hampshire Cease and Desist Order Issued Following Repeated Water Quality Violations When the New Hampshire Department of Environmental Services (NHDES) and the City of Laconia (the City) issued Cease and Desist orders following repeated water quality violations, the developer retained GeoInsight, Inc. (GeoInsight) to provide storm water and erosion control expertise, allowing our client to achieve compliance objectives and keep the project moving forward. GeoInsight’s roll included: • assessing existing storm water control system (including culvert sizes, flow velocities, headwalls, and basins); • observing the construction of temporary and permanent storm water control structures; and • interfacing with City and NHDES personnel regarding storm water quality improvements. Site and Violation Specifics The Site is an approximately 80-acre residential development located adjacent to Lake Winnipesaukee near Weirs Beach. The Cease and Desist orders were issued in response to repeated water quality violations resulting from elevated suspended solids discharging at a beach area.

Colloidal Material Poses a Unique Challenge Discharge violations were largely the result of colloidal material present in the storm water resulting from natural glacial till soils existing at the site. Colloids are very fine soil particles that are practically water soluble, mixing evenly within the water column and remaining suspended for extremely long time periods. Colloids are typically untreatable with conventional erosion control Best Management Practices. Although our client had made significant efforts to implement standard storm water quality controls, the colloidal materials proved to be a significant challenge to

achieving a water quality discharge criteria of 10 nephelometric turbidity units.

Engineering a Unique Solution GeoInsight assisted our client with sequencing of operations, engineering new components of the project’s erosion control plan. Based upon results of storm water flow analyses in the subdivision’s drainage areas (three of which had their own separate detention basins), GeoInsight engineered and permitted the use of flocculants in a contact channel, designed as a supplement to the final detention basin. This removed the colloids from the site runoff and prevented further water quality violations.

On-going Monitoring GeoInsight performed weekly visual monitoring of the erosion controls, inspections, sampling and testing of surface runoff, and provided documentation of activities and performance reports to the City and the NHDES. This design solution was enabled by close working relationships with the City and the NHDES, and active coordination with a local beachfront group.

EROSION CONTROL AND STORM WATER COMPLIANCE Residential Development

Case History No. 1