The York Water Company serves a large area in York and Adams Counties. Planning studies have projected significantly increasing demand with a rise to more than 42 MGD within 20 years.
To meet the increased demand, York Water embarked on a project to increase the capacity of its Grantley Road Filter Plant to 42 MGD. BH assisted with design of the project, and fast-tracked the design for Phase I and the project was out to bid within five months of the Notice-to-Proceed. Construction of Phase I was completed in less than nine months, before the summer increase in water demand occurred.
Phase I involved the upgrade of a sedimentation basin and the addition of a new residuals handling facility. The basin upgrade included adding inclined plate settlers and a telescoping sludge collection system in one of the existing 1950s sedimentation basins. Thirty-six plate cartridges were added to the basin. Each plate cartridge measures approximately 5 feet by 8 feet by 22 feet and holds 83 plates. In total, nearly 3,000 plates were installed.
The plate settlers improved the sedimentation efficiency by introducing substantially more settling area to the basin and shortening the solids settling distance from more than 10 feet to just a few inches. The plates added an equivalent settling area of approximately 73,000 SF to the basin, significantly increasing sedimentation efficiency without the need to increase the basin size.
New influent and effluent gates and a large effluent flume were added to handle the increased flow to and from the basin. An influent baffle wall was also installed to eliminate short-circuiting and create conditions conducive to settling along nearly the entire length of the basins. The influent baffle wall incorporated an innovative weighted swinging door that closes at low flows and opens as flows increase, thus providing good flow distribution in low flow conditions and low head losses at high flow conditions. The plate cartridges, flumes, and baffle wall were constructed of stainless steel and should have an exceptionally long service life.
A telescoping sediment collection system was also installed on the floor of the basin. The collection headers telescope to cover the entire length of the basin. The collected sediment flows by gravity to a pump station constructed in a corner of the existing basin. The operator can adjust rate at which sediment is allowed to flow, the rate at which the telescoping arms move across the floor, and the frequency of sediment collection. A density meter installed in the piping also reports the solids concentration leaving the basin. The density data and the operational flexibility described above allow the operator to control the solids concentration in the sediments collected and to use the storage capacity available in the basin to the greatest extent possible.
Sediment collected from the basin is pumped to a new residuals handling facility that houses three 16 feet by 24 feet batch thickeners and an advanced dewatering system called volute dehydrators. The sediment is thickened from about 1% solids to about 4% solids before being fed to the volute dehydrators. A volute dehydrator was pilot tested at the York Water facility and was shown to produce a material of approximately 25% solids. The dewatered material is loaded by conveyor into roll-off containers, and is classified as a co-product and used off-site as a soil supplement.
York Water pre-purchased most of the major equipment for this project. BH assisted with specifying the equipment and negotiating with the suppliers as well as providing construction documents for the equipment installation.