County’s aging stormwater system faces climate change stresses

Although the Charles County government has been working aggressively in recent years to upgrade the county’s stormwater drainage network, its aging infrastructure is straining under the combined loads of increasingly severe weather and the construction of ever more acres of impervious surface. As the county commissioners consider legislation that would accelerate the approval of new subdivisions, will the stormwater system be able to handle the additional runoff?

Earlier this month, the county’s Department of Public Works announced the start of a 10-month sewer rehabilitation project in the Pinefield neighborhood of Waldorf, which has been inundated with severe flooding for years. According to an official announcement on Facebook, the project’s purpose is to “reduce the amount of unwanted groundwater and rainwater infiltrating the sewer system through leaking joints, connections, and manholes to reduce the amount of sewer volunteer that reaches the Mattawoman Wastewater Treatment Plant.”

It is one of several projects currently underway or planned in the coming years. In September 2018, the county began a similar rehabilitation program for sewer lines and manholes along Old Washington Road, Western Parkway, U.S. 301, and Route 5. For years, county budgets have included hikes in residents’ stormwater remediation fees to help pay for these and other critically important upgrades.

During the record-shattering rains of 2018, some Pinefield residents reported that the flooding reached the hoods of their cars. Residents in Acton Village, further south along Western Parkway and along the Mattawoman Creek watershed, have also been hard hit with flooding.

Excessive rainwater entering the county’s sewer system through heavy rains and hurricanes — which sanitation engineers call inflow and infiltration, or I&I — can overload the county’s six wastewater treatment facilities, causing the lines leading to the treatment plants to back up and discharge raw sewage into the watershed. Two years ago, a combination of unprecedentedly heavy rains and the unavailability of three out of four pumps resulted in nearly six million gallons of raw sewage overflowing from the main trunk line leading into the Mattawoman Wastewater Treatment Plant near Mason Springs and spilling into Mattawoman Creek and the surrounding watershed.

In an effort to prevent that from happening again, the Board of Charles County Commissioners allocated additional funding to DPW to replace the station’s aging pumps with larger-capacity ones, construct a 10-million gallon storage tank to absorb surges caused by heavy I&I, replace old and damaged drainage pipes around the county, and reinforce the main drainage line that supplies the treatment plant to allow it to hold nearly double the amount of water pressure.

The county has also sought to address a lack of clarity about who is responsible for maintaining stormwater systems in various communities: the county, the homeowners’ associations, or the property owners. Depending on the community, the location of the drainage system, and modifications to adjacent properties, it can be a confusing — and costly — conundrum.

Three years ago, a drainage culvert in the Greenmont subdivision off Berry Road collapsed due to a combination of age, excessive runoff from storms, and possibly also an inadequately maintained drainage pond, threatening to undermine the foundations of a house and collapse the owners’ in-ground pool. Over the next eight weeks, the sinkhole continued to grow while the HOA and the county wrangled over responsibility. Ultimately, the county decided to front the costs of the repair though it argued that the HOA’s covenant made it clear that it really had been the HOA’s problem to solve.

To forestall similar situations from developing in the future, not long after that high-profile incident the county’s Department of Planning and Growth Management rolled out a series of proposed changes to the county planning ordinances that would clarify responsibilities for the various components of the county’s storm drainage and stormwater management systems.

Developers must now locate storm drainage systems — curbs, gutters, and pipes that drain water from road surfaces — and stormwater management systems — drainage channels and settling ponds that allow water soak back into the ground — only in public right-of-ways. HOAs are now responsible for maintaining storm drainage and stormwater management easements in developments that have private roads and open spaces.

Counties Seek Alternatives to Reducing Impervious Surfaces

During the building boom of the 1990s, many neighborhoods were constructed with storm drains and stormwater management systems that were sized to handle runoff from the impervious surfaces — roads, sidewalks, driveways, and roofs — in their immediate neighborhood. But over the last 30 years, as new subdivisions have been constructed on adjacent parcels and roads have been widened to accommodate the increased traffic, the amount of impervious surface preventing water from soaking back into the ground has increased, resulting in greater amounts of water pouring into those existing — and aging — drains and culverts.

The Maryland Department of the Environment helps limit the proliferation of impervious surface area by requiring county governments to reduce existing impervious surfaces by 20% in order to continue to qualify for state-issued stormwater management system permits, which are reviewed and updated every five years. When Charles County’s permit came up for review last year, the planning and growth management department asked for permission to engage in “nutrient trading” — reducing the amount of nitrogen and phosphorous in water runoff — instead of reducing the amount of existing impervious surface.

It’s a trade that many other counties have sought and been granted; in the past two years, MDE has also approved nutrient trades for Frederick, Harford, Prince George’s, Anne Arundel, and Baltimore counties — every county whose permit was up for renewal, in fact — as well as for the Maryland Highway Administration, which oversees tens of thousands of miles of impervious-surface roadway throughout the state. Howard County, where stormwater runoff has been implicated in two catastrophic flooding events in Ellicott City, is up for permit renewal next year.

The county’s recently released draft Climate Resilience Action Strategy identifies roads and their associated stormwater management facilities as among the high priority infrastructure requiring fortification against sea-level rise and flooding. The strategies being proposed include “improving drainage/stormwater management in the public right-of-way” and “improving drainage/stormwater management in flood-prone areas.” The plan calls for half of all stormwater runoff generated by susceptible roads to be managed on-site by 2030, and the other half by 2050.

The plan also addresses stormwater infrastructure not associated with road runoff, calling for the improvement of 10% of stormwater management facilities in flood-prone areas to be fortified by 2030, 25% a decade later, and half of them by 2050.

The draft action strategy document does not address the potential costs of such infrastructure improvements; the cost estimating phase comes later in the process. But to give some sense of the costs involved, the county’s most recent quarterly review of capital improvement expenses lists maintenance and improvements to the county’s stormwater infrastructure as already budgeted at over $2.5 million.

Two-thirds of the county’s households are connected to the county’s wastewater systems, which are in turn served by six county-owned wastewater treatment plants. The county’s 2016 Comprehensive Plan states that “[a]ll of the County’s public sewer systems have adequate capacity to serve the majority of projected development through 2040.” Should the Board of Charles County Commissioners vote to pass legislation reducing the wait time for new developments based on school seat allocations, and as more residents telecommute during and after the COVID-19 pandemic, and as the effects of climate change portend more record-setting rainy seasons in the years ahead, it’s important that Charles County residents know whether that conclusion, made four years ago, is still accurate.

illustration: Charles County Government