County staff says Aspen Creek infiltration basins likely can handle about 500,000 gallons per day; NDEP requests more review

Lyon County staff and the county's engineer presented updated field testing, groundwater monitoring and preliminary modeling for the Aspen Creek rapid infiltration basins on May 15, reporting a best current estimate of roughly 500,000 gallons per day of effluent disposal capacity.

The presentation, led by county wastewater staff and engineer representatives from Dowell, summarized months of slug tests, constant-head tests, noninvasive seismic (REMI) surveys, excavation observations and installation of additional piezometers and monitoring wells. Dowell told the board its review of the expanded dataset produced a preliminary capacity estimate materially higher than an earlier engineering estimate but lower than initial design targets.

County presenter David Brickhead (wastewater operations) and Dowell's consultants described key findings: groundwater mounding under the basins is more pronounced at the north end of the cells, tests produced a wide range of hydraulic conductivity values (which drive disposal capacity calculations), and trenches and a donated 14-inch pipe installation to move water toward the south side produced limited improvement. Field excavation found variable groundwater depths across the…