The City of San Marcos hired Plummer to design its new surface water treatment plant. Plummer performed a site selection evaluation, process evaluation, preliminary design, detailed design, construction representation, and startup for the new 6-mgd water treatment plant. The site was master planned for a total of 24 mgd. The initial study included an evaluation of water quality compatibility and the integration of a water treatment plant into the system, as the City was previously solely dependent on the Edwards Aquifer for its water supply needs.

The design project included in-line rapid mix, a solids contact clarifier with tube settlers, four dual media filters, a 1-mg baffled clearwell, high service and backwash pumps, and chemical storage and feed systems, as well as backwash and sludge lagoons with decant capability. The clearwell was designed for base bid using glass-lined steel with aluminum dome roof and alternate bids for prestressed concrete tanks.