DeKalb committee hears Arcadis master plan: inventory, risk scoring and pond review; committee defers vote

DeKalb County received a detailed briefing on a draft stormwater master plan, including an inventory of assets, a risk-based prioritization methodology and early results from watershed-level assessments such as Snap Finger Creek. Commissioners asked for more granular cost estimates and prioritized capital projects and voted to hold the master-plan item in committee for two weeks.

Arcadis consultant Rich Grewell and county staff described a county inventory of roughly 52,000 stormwater pipe segments (about 700 miles of pipe), tens of thousands of inlets and approximately 1,000 detention ponds. Grewell said the team applied a risk score combining probability of failure and consequence of failure to prioritize assets. "As we move higher probability failure and higher consequence failure, those are the ones we really want to get ahead of the curve on," Grewell said, summarizing the approach.

The presentation highlighted corrugated metal pipe as a major source of long-term risk. Grewell said corrugated metal is inexpensive and quick to install but corrodes over decades, and that many of the county's high-risk pipes are corrugated metal segments often located under roadways. He described rehabilitation approaches that can extend life and avoid road closures, including in-situ lining that can add decades of service life without full replacement.

The consultants also presented a watershed-level example from Snap Finger Creek. In that watershed the team identified 218 county-owned detention ponds; staff flagged 64 ponds as potential candidates for retrofit or decommissioning because they appear to provide little flood-control benefit for their watershed and may draw county maintenance resources without delivering commensurate value. Grewell cautioned that field surveying and hydrologic analysis are needed before final decisions: decommissioning or resizing a pond can shift flows downstream and create new problems if not done with a downstream analysis.

On funding, the Arcadis team provided a desktop estimate that a large portion of the countys renewal and replacement need could be on the order of hundreds of millions of dollars. Grewell said earlier, lower-end desktop estimates suggested roughly $500 million for a mix of lining and replacement; he emphasized the number is approximate and sensitive to inflation and field findings. The team noted the county has used borrowing (a JIFA loan) and federal grant programs in some places; Grewell also pointed to a $2,000,000 federal grant award tied to one subdivision pipeline project as an example of external funding the county pursued.

Commissioners asked technical and process questions during the presentation. Commissioner Robert Patrick and Commissioner Shakira Johnson pressed for how the utility will prioritize assets, what funding tools are available (rate adjustments, loans, grants), and how the county will resolve ambiguity around whether infrastructure within easements outside rights-of-way is the countys responsibility. A county attorney (Matt) explained that ownership and maintenance of off-right-of-way pipes is a case-by-case legal determination that requires review of recorded plats, dedication language and historical county actions; the county is developing policies to address shared-responsibility situations.

After discussion commissioners agreed to hold the master-plan item in committee for two weeks so staff and Arcadis can return with more detail on prioritization criteria, project-level cost estimates, hydrant spacing and routine operational metrics such as work-ticket throughput and pothole repair counts. The committee emphasized the goal of moving from a reactive posture to proactive, prioritized renewal and replacement.

Ending: Staff will continue watershed-level assessments (starting with Snap Finger Creek and similar basins), refine the risk-based CIP and return to the committee with project-level costs and funding options within two weeks.