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Thursday, July 05, 2012

Design Memo Outlines Plans for Civic Center Wastewater Disposal

• 500,000 Gallons Per Day to Be Injected

                                 BY BILL KOENEKER

Plans for a proposed Civic Center wastewater treatment plant have hit a stumbling block or a delay in the city’s timetable because of the method selected for disposal of the treated effluent, according to city officials.
Groundwater injection has become the preferred method, but feasibility tests to confirm the viability of groundwater injection of the treated effluent in the Civic Center area, and the estimated groundwater injection capacity in that area, have yet to be done.
The city council last week held off on spending its own money, $1.5 million for the study, to wait and see if the proposed Community Facilities District could come up with the cash to finance the rest of the study and other work including an Environmental Impact Report.
In a scope of work prepared by RMC Water and Environment, the design firm indicates there are three phases of the feasibility study that need to be carried out so the “intent is that the results of each phase need to indicate that injection of meaningful quantities of treated effluent is viable before the subsequent phase of work is undertaken.”
The tests are to determine if up to 500,000 gallons of effluent can be injected on a daily basis.
The first goal of the study is to determine the extent and hydraulic properties of what are called the Civic Center gravels. “The intent of this work is to assess if the hydraulic properties of this unit are adequate to meet project needs. Three exploratory test wells will be installed to bedrock for this purpose. Pumping tests will be conducted to each of the wells to measure local aquifer hydraulic properties. If these tests show that the Civic Center gravels are reasonably transmissive, more in-depth investigative work, Phase 2, may be conducted,” a RMC document states.
The design firm notes it is believed the test wells, created by using the sonic drilling method, will be drilled to a depth of 150 to 200 feet where it is assumed the bedrock is located.
Water sampling tests will be taken along with other water testing and analysis will be done including an assessment for the potential for adverse geochemical reactions that could occur with groundwater injection of treated wastewater. Aquifer properties will be measured and other related water sample tests undertaken.
Phase 2 would be to determine if the Civic Center gravels could receive and transmit the planned quantities of up to approximately 500,000 gallons per day of injected water “without adverse consequences.”
The planned work of the second phase includes geophysical surveys to estimate the off-shore extent of the gravels and groundwater modeling to estimate effects on local water levels, the ultimate fate of injected water, and the potential for adverse geochemical reactions. If the findings of the work are favorable, meetings will be held with regulatory agencies to present and discuss project findings and the scope of work and cost estimate for the next phase of work.
Other tasks include producing high-resolution subbottom profiling records of the near-surface geological layering with a 1-square mile survey area.
Many other tests are included in Phase 2 besides geophysical and geotechnical assessments, including conducting a geotechnical evaluation of the allowable pressurization of the system during injection, preliminary modeling simulations and geochemistry assessment.
Phase 3 consists of conducting a full scale testing, confirming feasibility and finalizing the basis of design. A full-size well will be drilled, and the installation of deep multi-level monitoring wells will take place with the installation of full-scale test wells.
Some of the last tasks include final model simulations, meeting with regulators and preparation of a basis of design report.
“RMC will prepare a brief report that discusses and illustrates proposed injection facilities, including facility requirements, layout, system connections and operations and maintenance considerations. An order of magnitude cost estimate for the final facility arrangement will be prepared.”

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