To meet the County’s near-term water needs of up to an additional 7.5 MGD, O’Brien & Gere was retained by Stafford County to design the expansion/upgrade of the Smith Lake Water Treatment Plant (WTP) from 7.5 MGD to 15 MGD. Under the preliminary engineering phase of this project, O’Brien & Gere performed bench-scale testing for DBP formation, kinetic testing, manganese removal, and alum dose optimization. This testing was used to optimize process performance and sludge generation, and to confirm the feasibility of bypassing the raw water contact tank to achieve the 15 MGD expanded capacity. A future membrane filtration upgrade was also evaluated. Upon completion of these studies/tests, the treatment process and chemical system design criteria were finalized, and preliminary layouts and a basis of design report were prepared. O’Brien & Gere also designed the new sodium hypochlorite ammonia storage and feed facilities for the County’s two water treatment facilites, the 15 MGD Smith Lake WTP and 6 MGD Abel Lake WTP. The chloramine systems were required to meet Stage 2 D/DBP limits. The aqueous ammonia reacts with free-chlorine to form chloramines that control formation of disinfection by-products.