As consulting engineers to the City of South Lyon, Hubbell, Roth & Clark, Inc. (HRC) provided design, bid phase, construction administration and observation services for expansion of the South Lyon Water Treatment Plant (WTP).  The existing South Lyon WTP is an iron removal facility utilizing induced draft aeration and detention to convert soluble ferrous iron to insoluble ferric iron followed by pressure filtration to remove insoluble iron.  The WTP iron removal system, originally constructed in 1970, had undergone two previous expansions – the last of which was designed by HRC in 1995.  

Due to increasing water demand during the mid to late 1990s, HRC provided design services for the addition of Well House No. 5 to increase on-site well production capacity.  In November 1999, HRC completed an iron removal study for the WTP which concluded that the existing iron removal filters, although rated at a capacity of 3.5 MGD, were not providing adequate iron removal during peak demand conditions due to media age in the oldest filters.  Furthermore, expected future growth would cause water demand to exceed the rated treatment capacity.  HRC recommended plant expansion to increase treatment capacity from 3.5 MGD to 5.5 MGD and replacement of four of the oldest of six filters with newer filters using the latest in media backwash technology.

In addition to the new filter and aeration equipment, the WTP expansion involved increasing the size of the wet well to allow for 20 minutes of aerated water detention, expansion of the low service pump building, construction of a backwash surge tank and new chemical feed/storage building, revision of the plant piping and chemical feed systems, and electrical and instrumentation revisions to allow for full automation of the entire facility.

Based on plans and specifications developed by HRC, the City of South Lyon pre-purchased four new, larger, dual-cell horizontal pressure filters (HPFs) and a new induced draft aerator installed under the WTP expansion project.  The new HPFs utilize a simultaneous air and water backwash system to completely agitate and remove solids and reduce backwash volume.

Furthermore, the expansion required that additional raw water be made available to the treatment plant as demand increases during future years.   HRC accomplished this task by designing an automatic flow control/pressure reducing valve (FCV/PRV) facility to allow a controlled interconnection between on-site WTP well system and two off-site well houses.  Control modifications, pump upgrades, replacement of a liquid drive system with a variable frequency drive unit, and ventilation system upgrades completed the necessary revisions at the off-site well houses.  During demand conditions that exceed the WTP on-site well capacity, the new FCV/PRV automatically opens to allow controlled supplemental water flow from the off-site well houses to the WTP.

Construction of the WTP expansion required creative project sequencing and coordination to ensure continued water production throughout the duration of the project.   The overall success of the project is evidenced by the reduction of 3.2 ppm of iron in the raw water to 0.1 ppm of iron in the filter effluent while maintaining minimum filter run lengths of 72 hours as well as the ease of plant operation.