Green Infrastructure Plan
A hybrid approach that blends the best of gray and green infrastructure controls.
2016 Consent Decree Modification
On January 14, 2016, DC Water, in conjunction with the United States Environmental Protection Agency (EPA), United States Department of Justice, and the District of Columbia executed a modification to the 2005 Long Term Control Plan (LTCP) Consent Decree to include innovative green infrastructure (GI) practices to achieve the reduction of combined sewer overflow (CSO) volume by 96 percent system-wide (for the Anacostia and Potomac rivers and Rock Creek) and offer additional community triple bottom line benefits. In addition to tunnels for the Anacostia River sewershed and portions of the Potomac River sewershed, the modification proposed managing 1.2 inches of rain over 365 impervious acres in the Rock Creek sewershed and 1.2 inches of rain over 133 impervious acres in the Potomac River sewershed with GI and targeted sewer separation. The 2016 Amended Consent Decree requires DC Water to submit Practicability Assessments to EPA after the construction of the first green infrastructure projects in each sewershed.
The DC Clean Rivers Map below, shows the two Green Infrastructure Program areas for Rock Creek and Potomac River Sewersheds in the Amended Consent Decree:
Practicability Assessment and a Proposed Path Forward
The Practicability Assessments consider constructability, operability, public acceptability, efficacy, and cost effectiveness of the first set of GI projects within each sewershed. DC Water has submitted the Practicability Assessments for both the Rock Creek GI and Potomac River GI projects and those assessments are found in the resources section of this website. A determination for the recommended approach is pending EPA review. Per the terms of the Consent Decree, EPA has 180 days to review each Practicability Assessment.
Potomac River Practicability Assessment
DC Water completed the Practicability Assessment in August 2020 and determined that implementation of GI to manage the required 133 impervious acres in the Potomac River sewershed (CSOs 027, 028 and 029) is not practicable from a constructability, public acceptability, and cost to ratepayers’ perspective. Per the terms of the Consent Decree, DC Water will instead plan, design, and construct the Potomac River Storage/Conveyance Tunnel with a total storage volume of not less than 40 million gallons.
Rock Creek Practicability Assessment
The experience implementing the first project in the Rock Creek sewershed, as well as other DC Water GI initiatives, informed the Practicability Assessment. While GI in the Rock Creek sewershed was found to be practicable for the constructability, operability, public acceptability, and efficacy criteria, high costs to implement all 365 acres of GI coupled with ongoing costs associated with operations and maintenance resulted in the determination that GI to manage the required 365 impervious acres in the Rock Creek sewershed is impracticable. As compared to the all gray alternative outlined in the Amended Consent Decree, a full GI build-out in the Rock Creek sewershed is nearly twice as expensive over a 30-year period when operations and maintenance are taken into consideration. An alternative “hybrid” approach for Rock Creek has been submitted to the EPA that would blend the best of gray and green technologies. This approach provides the same degree of control as the all gray alternative, lowers capital costs below the “all gray” or “all green” alternatives, and would be implemented by 2030, the same deadline in the Consent Decree. This hybrid approach is accountable to District ratepayers and delivers additional triple bottom line benefits such as more green space, habitat creation for birds and pollinators, and more local green jobs as compared to the all gray option.
DC Water’s Hybrid Plan proposes the best features of both green and gray controls in an effective and financially responsible manner.
The DC Water Hybrid Plan offers many advantages to District ratepayers and residents and is recommended by DC Water for the following principal reasons:
- Best Mix of Green and Gray to Achieve Same 9.5 Million Gallons Storage. The hybrid approach achieves the same volume equivalence of 9.5 million gallons of storage as the all gray alternative by integrating the best features of green and gray for an optimized solution.
- Maintains DC Water’s Commitment to the Success of GI in the District of Columbia. DC Water’s leadership and stewardship in GI will continue under the Hybrid Plan to achieve economic, social, and environmental benefits for District residents.
- Equivalent Level of Performance. Modeling demonstrates that the Hybrid Plan will achieve the same degree of CSO control as required by the LTCP. There is no change in DC Water’s commitment to the degree of CSO control.
- Same Technologies. The Hybrid Plan uses the same technologies as the LTCP – storage and GI to achieve CSO reductions. There are no unproven or new technologies that may jeopardize CSO performance objectives.
- Certain CSO Performance. The Hybrid Plan includes gray storage which has been proven reliable and effective on the Anacostia River in achieving CSO reductions, even during 2018, the wettest year on record in the District of Columbia.
- Fiscally Responsible. The Hybrid Plan is the most cost effective on a capital cost basis and is comparable to the gray alternative on a net present value basis. This maintains DC Water’s accountability to ratepayers who fund the majority of the project.
- Same Schedule. The Hybrid Plan will be implemented with the same schedule deadline in the Amended Consent Decree – by March 23, 2030.
What is Green Infrastructure?
GI is an approach to managing stormwater runoff that takes advantage of natural processes such as infiltration and evapotranspiration, to slow down, clean and in some cases reuse stormwater to keep it from overwhelming sewer systems and polluting waterways. The goal of GI is to mimic the natural environment through the use of plants, trees and other measures.
Types of GI include:
- Roof Top Collection Practices: rain barrels, cisterns, green roofs, blue roofs
- Permeable Pavements: porous asphalt, pervious concrete, permeable pavers
- Bioretention: tree boxes, rain gardens, vegetated filter strips, bioswales
See the figure below to see how these processes work.
In addition to the control of stormwater, GI technologies like permeable pavement and bioretention provide other benefits to the community.
Site Level Stormwater Management. GI provides water quality benefits as soon as installation begins. The GI and other improvements have allowed the District to enjoy water quality and environmental and social benefits beginning in 2017.
Triple Bottom Line Benefits. GI offers environmental, social, and economic benefits that would not be realized under the previous plan. GI can increase property values, beautify neighborhoods, cool extreme summer temperatures, support natural habitats, enhance public space and support local green jobs.
Jobs. DC Water has established an ambitious local jobs program that includes training and certification opportunities for District residents interested in GI construction, inspection and maintenance jobs. The National Green Infrastructure Certification Program (NGICP.org) has trained and certified the first group of individuals. DC Water has established a goal to have 51% of new jobs created by the GI project to be filled by District residents. DC Water has also engaged professional service firms and contractors based in the District to perform work associated with GI.