Tank Replacement Program – Stockstill
Background: The Inverness Public Utility District (District) has 11 tanks in the system of which eight are redwood and three are steel. There is a total storage capacity of 425,000 gallons that can supply 4 to 6 days of typical system demand for domestic potable use. The problems specific to the redwood tanks are: 1) Seismically unsafe; 2) Leaking; 3) Producing higher chlorine demand loads; and, 4) Vulnerable to fire hazards. The District identified in November 2016 the replacement of the most vulnerable tanks. The two existing 20,000 gallon redwood tanks (referred to as Stockstill Tanks 1 and 2) are identified as the most vulnerable in the District. They were installed as used tanks in 1955 (age unknown), leak, have deteriorated tank bands and are on a support system that is in poor condition. Besides being in overall poor condition, the redwood tanks exert a high chlorine demand. The State Water Resources Control Board (SWRCB) inspection of the Stockstill Tanks (performed in 2011) documented the leaking tanks at the Stockstill site. The District is proposing to eventually replace all redwood tanks in the system.
Project Description: The existing Stockstill water storage system is critical for the domestic drinking and life safety aspect as a fire water supply for the Seahaven (Third Valley) neighborhood of Inverness. It is proposed to replace the two redwood Stockstill tanks with a single steel tank designed to current seismic criteria from the American Society of Civil Engineers-7 (ASCE-7) and the American Water Works Association (AWWA). This requires a volume to allow for “sloshing” of water in the tank in a seismic event. The tank has been positioned (see story poles) to be roughly the same height by lowering into the ground. It is proposed to install a single bolted steel tank with an operating volume of 40,000 gallons (56,000 operating fire volume and 75,000 dry volume). Projected installation date is mid-to late 2017. It is anticipated that a 4’ x 8’ building wooden structure will be constructed for the chlorine pump and to house equipment for tank and water distribution operations. Color will be similar to the Seahaven Tank located at 231 Via de La Vista.
Environmental Review: The project is being considered as being categorically exempt under CEQA Article 19 Categorical Exemption, 15301(b)-Existing Facilities. This Project undertakes no expansion of use by IPUD in providing domestic drinking water for the Seahaven neighborhood of Inverness. The project is also expected to be exempt under the California Environmental Quality Act (CEQA) Guidelines Section 15061(b)(3). The activity is covered by the general rule that CEQA applies only to projects, which have the potential for causing a significant effect on the environment.
Stockstill Tank Replacement Public Notification