Integrated Water Resource Management Plan

Stormwater Data Collection and Nutrient Load Modeling

Weston & Sampson was hired by the Town of Truro to develop an Integrated Water Resource Management Plan (IWRMP). Part of this plan required the analysis of stormwater and its impacts on water resources. The effort to control stormwater is connected to water supply protection and water resource impairment due to runoff. The most common problem for municipalities is identifying areas of concern and then prioritizing future actions.

Stormwater efforts generally are divided into both point and non-point sources of pollution. In areas where porous, permeable deposits exist, stormwater systems have not evolved in a systematic or planned fashion. Instead, run off from impervious surfaces is routed locally where it either infiltrates or is discharged directly into a surface water body. In Truro, large stormwater detention or treatment systems have not been developed and extensive local regulatory control has not, as yet, been needed.

Based on pollutant load modeling and stormwater management techniques undertaken in Plymouth, Weston & Sampson developed a data collection methodology linking powerful GIS tools with state-of-the-art electronic field data acquisition methods for use in Truro, MA. This technique provides the most cost-effective method of determining critical areas of concern within a community, such as critical surface water bodies, near shore environments, or protected drinking water sources.

In Truro, land use patterns, stormwater features, and impervious surfaces were mapped using geospatial data available from MassGIS. This effort was combined with current Truro parcel mapping. Recharge areas were developed for the town and visual interpretation and implementation of pollutant load modeling of this data resulted in loading rates for each recharge area.

Weston & Sampson then employed iDataCollect methods to field survey and verify MassGIS data, fill in data gaps, and refine areas of concern using software developed for the iPad and geospatial orientation using a Trimble, high accuracy GPS unit. Field verification included collecting data on land use patterns and practices, including impervious surfaces, stormwater infrastructure, and lawn application of fertilizers. These efforts were extremely useful in refining pollutant load values, determining potential impacts to groundwater and surface water quality, and for use in developing reasonable mitigation options.

Field results were automatically linked to GIS maps through a database built and designed for this specific. This refined data was then used to refine pollutant load models for each of 17 sub basins. Sites with the highest potential pollutant load, critical habitat, proximity to sensitive receptors, and favorable soil types were then compared and ranked. The resultant summary map identified target areas for stormwater improvements. Following this effort, the town plans on implementing long-term solutions that will include modification of local regulatory controls, public education and municipal practices.

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