Stormwater runoff is a primary culprit of degraded waterbodies nationwide. To protect and improve water resources, EPA, state, and tribal agencies administer the National Pollutant Discharge Elimination Program (NPDES), under which they regulate stormwater discharges from construction sites, industrial activities, and municipal separate storm sewer systems (MS4s). Our firm’s thorough understanding of permit requirements, and the science behind them gives us unique insights into the challenges and opportunities of an effective stormwater program. We offer numerous services to help our clients develop comprehensive planning strategies to not only achieve stormwater compliance but also build sustainable and resilient management programs.

HW is a leader in the fields of stormwater and watershed planning, including innovative nutrient management, emerging contaminants, regulation revisions, pollution prevention plans, and GSI retrofit inventories and design. Our staff has decades of experience with a wide range of stormwater management and compliance projects. These often include adapting stormwater designs for unique sites and a changing climate as well as completing code audits to identify local opportunities and barriers to green infrastructure. Our engineers, landscape architects and designers, planners, licensed site professionals, and scientists collaborate with state and federal agencies, watershed groups, municipalities, and other partners to ensure stormwater programs are not only meeting compliance requirements, but also advancing local goals, such as improved water quality, resiliency, public health, social equity, open space, and public access to waterbodies.

Our Stormwater Compliance services are:

  • Program Planning
  • Public Education & Outreach
  • Illicit Discharge Detection & Elimination Plans (IDDE)
  • Water Quality Sampling & Field Investigations
  • Oil & Hazardous Material Remediation
  • Erosion & Sediment Control Plans
  • Stormwater By-laws and Regulations
  • Code Audits
  • Green Stormwater Infrastructure (GSI) Retrofits
  • Prioritization & Planning
  • Stormwater Pollution Prevention Plans (SWPPPs)
  • Spill Prevention, Control, & Countermeasure Plans (SPCCPs)
  • Operations and Maintenance Plans (O&M)
  • Nutrient Source Identification Reports
  • Nutrient Contral Plans
  • Multi-Sector Permits
  • Training, Reporting, Documentation

 Contact us  if you have a project you would like to discuss.

Watershed Management & Nutrient Control Plans

Watershed-based plans are critical to understanding key watershed issues and developing effective implementation strategies, including prioritized restoration actions. Specific nutrient control plans may be required for regulated MS4s with waterbodies that have a total maximum daily load (TMDL) for phosphorus or nitrogen. These plans outline nutrient sources, load analyses and modeling, retrofit opportunities, implementation schedule, long-term operations and maintenance concerns, and on-going evaluations. We have completed over 100 watershed planning and implementation projects, including nitrogen and phosphorus control plans.

GSI Retrofits

MS4 permits typically require municipalities to identify and prioritize GSI retrofits. HW has 30+ years of experience providing retrofit inventories and identifying opportunities for improving water quality, restoring critical habitats, creating green spaces, and building resilience. We have had great success in siting, ground truthing, and designing realistic and targeted GSI projects. We work closely with communities and stakeholders to develop ranking criteria based on watershed goals and local constraints to ensure priority projects are impactful and ultimately constructible.

IDDE Services

IDDE programs aim to prevent, identify, and eliminate illicit discharges to MS4s. We have assisted several municipalities and non-traditional MS4s with GIS mapping of drainage systems and outfall catchments. We have also conducted dry-weather outfall inspections and sampling, and we are helping clients prepare for upcoming catchment investigations and wet-weather sampling.

Education and Training

Public education, outreach, and trainings are key components of the MS4 permit, as well as critical elements for any effective stormwater program. HW has written technical guidance manuals and conducted extensive trainings on low impact development strategies, erosion and sediment control, GSI designs, watershed planning, retrofitting, emergency response, advanced zoning techniques, and climate change preparation. We work with non-profit and community groups to engage diverse stakeholders, and frequently underrepresented populations, to ensure that they are included in the decisions, policies and actions emerging from the process.

Municipal Code Audits & Stormwater Regulations

Municipal by-laws, ordinances, codes, and regulations dictate the form and density of development, which has an impact on the quality and quantity of stormwater runoff and receiving waters. Reviews of local codes can determine barriers and opportunities to implement nature-based solutions, like reducing impervious cover, installing GSI, and restoring resource areas. HW is well-versed in “green” code audits, as we have promoted these smart growth techniques for decades. Our staff not only help communities meet their permit requirements but explore meaningful code changes to enhance climate resiliency, social equity, and quality of life specific to their town or city.


SWPPPs are required for multi-sector permittees, municipal maintenance yards, and waste handling facilities, as well as for construction activities that disturb greater than 1 acre of land. SWPPPs describe sources of stormwater pollution and best practices to reduce it at these sites. We have supported numerous municipalities and private clients in preparing effective SWPPPs. Under federal regulations, a SPCCP is required when a facility has large aboveground oil storage tanks (>1,320 gallons) and containers with a capacity of 55 gallons or more. Our staff provides hands-on training and assists with required inspections and monitoring as needed.

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