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CASE STUDY
The Challenge
Located in the Chesapeake Bay Watershed and borderingWashington, DC, Montgomery County is one of the first Phase 1 MS4snationwide to implement a stormwater management program in 1972.Faced with decades of urbanization with the pressures of higherrunoff volumes, outdated infrastructure and water quality challenges,the County needed an innovative approach to tackle its 20%impervious area restoration goal, including EPA’s Chesapeake BayTMDL requirement to restore over 3,700 impervious acres to reducenutrients and sediment. The County also needed to minimize cost andcommunity disruption.
The Solution
Montgomery County innovated its approach to stormwatermanagement by retrofitting existing ponds with Opti’s digital solutionsplatform, continuous monitoring and adaptive control (CMAC). Opti’sCMAC predicts and responds to the weather forecast, enabling thesystem to maximize storage capacity and retention time.
By using predictive analytics and real-time data, Opti’s platformprovides substantial cost savings and pollutant removal to enhanceefficiencies and effectiveness compared to other solutions.
At a Glance
95% cost savings over otherwater quality projects;
Total pollutant removalaveraged: 80% TSS, 29%TP and 29% TN;
“Opti's CMAC is as anadvantageous andcost-effective tool toattain multipleenvironmentalobjectives and helpmeet MS4 permitrequirements”
Leying Zhang, P.E., PhDSenior Engineer,Montgomery County, MD
ECONOMICAL
95% Savings
$22k vs. $200k per acre
RESILIENT
86% Wet WeatherCapture
Wet pond performance
PEACE OF MIND
Regulatory Compliance
Achieve MS4 nutrient andsediment goals
Results
To date, Montgomery County has retrofitted four ponds withOpti’s CMAC and, in May 2024, extended the program for tenadditional years to reduce stormwater pollution and improvewater quality.
One large regional wet pond (440 acres of area) wasretrofitted and now controls over 12 acre-feet of storage,which generated 123 Impervious Area Credits (IACs) and hasreduced wet weather outflow by 86%. The cost per creditwas only $976.
Retrofitting three small extended detention dry ponds thatpreviously provided no water quality treatment resulted inadditional IACs averaging $21,645/credit. Total pollutantremovals averaged 80% for TSS, 29% for TP, and 29% for TN.
Together, these four ponds generate 151.6 IACs towardChesapeake Bay TMDL requirements, achieving over 95%cost savings compared to other water quality projects.CMAC is now an integral part of the County’s stormwatermanagement action plan, including its Clean WaterMontgomery initiative for restoration of local waters andlong-term resilience.
Opti’s tool helps you make preliminary assessments ofexisting facilities to determine suitability and potential benefitsof a CMAC dry or wet pond retrofit. Learn more at optirtc.com.
In 2016, National Fish and Wildlife Foundation selected aregional wet pond in Montgomery County to evaluateCMAC efficacy for sediment and nutrient reduction.Success led to the Maryland Department of Environment(MDE) approving Opti’s CMAC for wet pond retrofits tomeet MS4 permit water quality restoration requirements.Results also led to the Chesapeake Bay Program’s UrbanStormwater Group Expert Panel unanimous endorsementof the use of CMAC retrofits for pollutant removal credits.
Through a national program sponsored by WaterEnvironment Federation and Water Environment ResearchFoundation, the County then identified 10 stormwaterponds for potential retrofit and secured funding for fourprojects. Results provided evidence for MDE’s approval ofCMAC for dry pond retrofits to meet MS4 water qualityrestoration requirements. The County continues to expandand model pond retrofits using CMAC technology, whoseefficacy it helped demonstrate for regulators. Read aboutOpti’s approvals at optirtc.com.
University Blvd Wet Pond
Randolph Dry Pond
Bethesda Dry Pond
Broadmore Dry Pond
Opti,an Aliaxis company, is the leading provider of digital adaptive stormwater control solutions.With over 300 deployments to date, Opti empowers customers and partners to address theimpacts of climate change, aging infrastructure, urbanization, and water pollution, enabling themto secure the sustainability of our communities and natural resources. Opti’s cloud-basedplatform optimizes stormwater asset performance through instant actionable insights to provideeconomic savings, resilient solutions, and peace of mind. With our commitment to innovation, weare driving a resilient and brighter future for all.
