MWSD Tracer Study

Client

Montara Water and Sanitary District

Location

MONTARA, CA

Project Description

SRT performed a tracer study to evaluate whether treated groundwater and surface water entering a tank that Montara Water and Sanitary District (MWSD) uses as clearwell at its Alta Vista Water Treatment Plant was compromising disinfection in drinking water.

The study was initiated in response to a State Division of Drinking Water request that MWSD either utilize the tank solely for contact time (CT) compliance purposes or demonstrate that there is no adverse effect on CT compliance based on all possible system configurations. SRT evaluated the overall hydraulic conditions of the tank under normal system configurations during peak demand season and whether the tank meets the disinfection credit requirement under maximum demand and presence of groundwater during normal operations.

The actual CT was estimated to be 23 times higher than the CT required for the tank. The tracer study found introduction of treated groundwater and surface water from the distribution system improved mixing, resulting in better disinfection.

Unique Challenges

The Alta Vista Tank’s suitability for operation was in question. With no existing standardized equipment for the necessary testing and analysis, SRT designed a custom field station and confirmed the tank’s viability. We sampled data and created the report that allowed the tank to operate.

Value Added By SRT

SRT provided technical and local expertise to measure and document conditions, enabling the plant to ensure safe continued operations. The tracer study designed and led by SRT allowed the client to save millions of dollars in capital expenditures that would have been otherwise required by DDW.