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Paso Robles, CA 93446
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Public Works

WATER QUALITY STRATEGY REPORT

Water Quality Strategy Report
4-15-03 Staff Report
4-15-04 Presentation Slides

The City Council established goals for the 2003-2004 in a series of public goal-setting sessions in early 2003. The top priority for the City is to diversify water resource reliability, stated as:

Develop New Source(s) of Water

In addition to providing added reliability by diversify the sources, the City also intends to address other water issues facing the community, including demands for higher quality source water, and lower salts (or TDS) concentrations in wastewater effluent, and the need for added water resource quantities.

Background

The City, with help from experts in the water/wastewater engineering firm, Malcolm Pirnie, investigated and studied the relationship between wastewater discharge and source water quality. The study focused on meeting wastewater discharge limitations for total dissolved solids (TDS or “salts”), as well as individual salt ions such as sulfate, chloride, and sodium.

The Water and Wastewater Quality Concerns Study identifies alternatives for resolving the wastewater salt concentration by:

  • examining salt removal alternatives,
  • finding a better (lower TDS or less salty) source

Summary Results

The study used a primary requirement - to reduce wastewater effluent salinity and river discharge – on a pass/fail basis. If the alternative passed this test, it was graded numerically, based upon benefits to water supply, cost, time and other impacts. The recommended results from the study, for action, are:

  • Control Industrial and Commercial Discharge Quality
  • Partially Desalinate Effluent
  • Import Lake Nacimiento Water

Control Industrial and Commercial Discharge Quality

The report recommends comprehensive sampling and monitoring to determine the extent of industrial and/or commercial discharge TDS contribution. The City’s water supply, before use, typically averages 510 mg/L TDS. Raw wastewater at the treatment plant averages near the current Municipal Code sewer discharge limit for TDS (limit is 1000 mg/L, current average is 992 mg/L). Industrial and/or commercial discharges may be contributing to the increase in TDS during water usage, resulting in the increase from 510 mg/L to 992 mg/L during the usage phase of the cycle.

Desalinate Effluent

The City anticipates significant challenges in reliably and consistently meeting the NPDES effluent TDS limit of 1100 mg/L. The fine for violating the limit is at least $3000 per day for each day the NPDES limit is exceeded. While desalinating wastewater is expensive, it is a viable alternative, provides more certainty, and greater potential benefits than industrial controls. The most tangible community benefit from desalinating wastewater is to meet NPDES TDS limits, thus avoiding fines (or other more onerous requirements).

Import Lake Nacimiento

Water Participating in the Nacimiento Water Project provides the most viable alternative for resolving wastewater salinity (TDS). The study clearly indicates that importing Lake Nacimiento water, which contains much lower TDS concentrations than the City’s current water resources, is the most prudent course to resolve community water quality issues (including wastewater discharge compliance) over the next twenty years.

 


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