Management | Planning | Design | Implementation

Terraphase provides comprehensive stormwater management planning, design and implementation, Clean Water Act/NPDES compliance/permitting  support, erosion and sediment control planning/design, as well as watershed management and analysis services. Terraphase routinely works with public and private sector clients to prepare Stormwater Pollution Prevention Plans (SWPPPs), stormwater management plans (SWMPs), watershed management plans and drainage/stormwater treatment infrastructure designs. Our hydrologists and civil/water resource engineers have collaborated to address our clients’ stormwater issues during both construction and operations of their developments and facilities. Terraphase stormwater consulting, engineering, watershed analysis and associated permitting services include:

• Civil/Site Engineering Design
• Hydrologic and Hydraulic Modeling
• GIS Analysis and Mapping
• Flood Assessments
• Drainage Studies and Design
• Pollutant Loading and TMDL Assessments
• Stormwater Pollution Prevention Plans (SWPPP)
• Stormwater Management Plans
• Erosion and Sedimentation Control Plans
• Biotechnical Erosion Control Design
• Stormwater Best Management Practices (BMPs)
• Low Impact Development (LID)
• Municipal (MS4) Stormwater Compliance
• NPDES Stormwater Permitting and Compliance
• Stormwater Sampling
• Stormwater Systems and BMP Operation and Maintenance Plans
• Site/watershed soil stabilization planning and design

Innovative Approaches to Stormwater Control
Terraphase has considerable experience evaluating and implementing Low Impact Development (LID) measures and stormwater flow-control and water quality enhancement BMPs as well as in supporting watershed stabilization efforts. We have designed and implemented numerous innovative stormwater solutions in accordance with stringent NPDES permit requirements. Many of these alternative stormwater treatment and LID designs have included water quality treatment using infiltration basins/trenches, bioretention systems, rain gardens, constructed wetlands, landscape/soil stabilization measures, proprietary units, porous pavement features, and engineered treatment systems. Terraphase has also assisted with design and evaluation of non-structural controls including ordinances and by-laws, public outreach programs, and stormwater utilities.

Stormwater/Watershed Analysis & Modeling
We have conducted dozens of comprehensive stormwater evaluations and watershed assessments. These assessments have involved project-specific stormwater analysis and modeling including:

• Runoff Volume Calculations
• Sizing and Design of Stormwater Conveyance and Treatment Structures
• Dry and Wet Weather Sampling
• Hydrologic and Hydraulic Load Modeling
• Pollutant Loading Assessments
• Effluent Discharge Monitoring
• Receiving Water Sampling
• Stormwater Monitoring and Sampling
• Assessment of physical watershed processes such as mass wasting, soil erosion, hydrology, and channel geomorphology
• Development of effective planning documents that can be used by foresters to guide land management decisions
• Analysis of hillslope and channel sensitivity to resource management
• Evaluation of road/forest management impacts on sedimentation and hydrology
• Channel stability and sediment transport evaluations
• Integration of long-term land/resource management planning and fish/wildlife needs
• Analysis of cumulative watershed effects
• Assessment of point and non-point source pollution
• Drainage litigation expert witness services

Stormwater Permitting & Compliance
Terraphase has developed stormwater designs and permit applications that have supported our clients in obtaining stormwater discharge permits associated with industrial facilities, land management projects, Municipal Separate Stormwater Systems (MS4), and construction sites. Our stormwater permitting experience has ranged from stormwater retrofits and BMP implementation to finding solutions at contaminated sites and large industrial and institutional facilities. We have effectively navigated the complex CWA and NPDES regulations to satisfy federal and state stormwater management policies as well as local ordinances.