Durham seeks site for algal flowway to reduce nutrient loads under Falls Lake rules

Durham Public Works and staff presented a contract proposal to identify and evaluate sites in Durham County for an algal flowway, an engineered treatment system that uses algae to remove nitrogen and phosphorus from water.

John Baker of the Public Works Department said an algal flowway pumps water across a large vegetated pad where algae grow and absorb excess nutrients; the algae are harvested every one to two weeks and can be composted or otherwise disposed of. Baker said the city has studied the technology since 2013, ran a pilot, and concluded a full-scale flowway can be more time- and cost-effective than numerous smaller stormwater control measures (SCMs) for complying with Falls Lake nutrient rules.

The proposed professional services contract would pay a consultant (Gradient) to run a detailed site search within Durham County inside the Falls Lake watershed, conduct field assessments, analyze engineering and permitting constraints, estimate construction costs and complete community engagement. Staff presented an optional task set that would add a 30% site plan, evaluate solar power potential, and allow a dual-site evaluation if 1 large contiguous site is not found. Staff put the total contract cost with optional tasks and a 15% contingency at $1,203,332 and said the optional additional site evaluation task would add about $320,000.

Council members asked detailed questions about externalities, environmental justice and reuse of algal biomass. Council Member Cook raised environmental-justice concerns, asking about odors and nuisance impacts near neighborhoods; Baker said he had visited a full-scale site in Florida and did not observe a significant nuisance odor and that piles of harvested algae dry and are usually moved off-site or composted. Baker estimated a 10 million-gallon-per-day facility could produce about 21 to 28 truckloads of harvested material per year (roughly one to two truckloads every two weeks, on average).

Council members asked about the possibility of amenitizing the site (trails, greenspace), integrating solar power and the prospect of locating multiple smaller sites rather than a single large flowway to spread impacts and avoid concentrating environmental burdens. Council Member Caballero and others encouraged exploring opportunities to combine the flowway with other city-owned sites and to keep solar evaluation as a priority where feasible.

Council members also pressed staff on site acquisition logistics: staff said the present contract does not include land acquisition authority and that permission from property owners would be needed for field assessments; council asked whether the city could secure options or other protections to avoid losing a desirable parcel to private buyers during the study period. Staff said those acquisition and negotiation details would be handled later and would require separate authority.

Michelle Wolfolk, water quality manager, said earlier cost estimates for compliance under the Falls Lake rules (from about 2010) had been in the order of hundreds of millions to a billion dollars for various agencies and noted inflation and changing rule status; staff said they expect the final design and site to be a key element in the city's ability to meet the revised Phase 2 nutrient targets.

No formal council vote to approve construction or to acquire property was recorded during the presentation; the item was presented for council review and questions. Staff said the contract and site-search work are included in the current capital improvement program budget and that additional approvals, permitting and any acquisitions would come back to council.

Ending: Council members endorsed aggressive community engagement and asked staff to evaluate options that avoid concentrating impacts in a single neighborhood; staff will return with more detailed analysis and any required acquisition proposals for council action.