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Groundwater Resource Evaluations

For two consecutive years, PES was awarded contracts to perform water resource evaluations at six properties along the middle reach of the Russian River in Sonoma County. The evaluations comprised the design and implementation of hydrogeologic studies to assess the suitability of new locations for the development of additional groundwater resources to meet water supply demands in Sonoma and Marin counties. The evaluations were performed to characterize the site-specific hydrogeologic conditions associated with the shallow alluvial aquifer, further advance the understanding of the river/alluvial aquifer interaction at these properties, and provide data to enhance the MODFLOW groundwater flow model developed by PES to simulate groundwater flow conditions and groundwater production scenarios along the middle reach of the Russian River.

Highlights of these projects, which demonstrate PES’ technical capabilities include:

  • Siting, design, and providing construction oversight services for high capacity test wells at three properties with groundwater production capacities ranging from approximately 1,100 to 2,500 gallons per minute (gpm);
  • Design and analysis of surface geophysical surveys (using seismic refraction techniques) to assess the thickness and distribution of alluvial deposits; depth to bedrock; presence of previously unidentified faults; and occurrence and potential water-bearing characteristics of deeper water-bearing formations;
  • Design, performance, and analysis of complex aquifer testing programs, which involved the design and installation of a comprehensive network of approximately 30 observation wells, and 20 riverbed piezometers, to characterize hydrogeologic properties and surface water/groundwater interactions at each property;
  • Evaluation and assessment of surface water recharge characteristics to the shallow alluvial aquifer using heat tracing techniques; and
  • Modification, extension, and calibration of an existing MODFLOW groundwater flow model for a seven mile-long segment of the shallow aquifer system along the Russian River. The objectives of the modeling activities were to assess steady-state and transient groundwater-surface water interactions and estimate the steady-state groundwater production rate for a major water supply well with both a conventional and enhanced horizontal lateral system.



Project-Specific Hydrogeologic Evaluations
PES has provided technical assistance to a Central California Health Department to evaluate hydrogeologic and water quality aspects of development projects under County review and for use in completing initial studies for CEQA purposes. As part of our services, PES has assessed water-supply and water quality issues for numerous proposed development projects throughout the County, including: (1) the availability of long-term groundwater supply; (2) potential effects on the local and basin-wide water balance; (3) potential effects on nearby wells due to increases or changes in groundwater production; (4) potential effects on groundwater quality from increased septic system recharge; and (5) potential cumulative effects on the underlying aquifer in terms of groundwater quantity and quality. As part of these projects, PES has coordinated closely with numerous public and private stakeholders.

In performing the groundwater supply evaluations, PES has routinely applied the following hydrogeologic techniques:

  • Detailed analyses of geologic and hydrogeologic conditions, including: (1) evaluating the source capacity of water-supply wells; (2) evaluating lithologic and geophysical well log data; (3) evaluating and analyzing aquifer test and pump test data to estimate hydraulic properties of local aquifers; and (4) reviewing local and regional groundwater level trends;
  • Calculating local and regional water balances, which incorporated estimates of groundwater recharge, evapotranspiration, surface water runoff and streamflows, soil moisture demands, and groundwater demand;
  • Assessing the potential effects to the local nitrate balance using mass balance calculations;
  • Developing analytical groundwater flow models based on project-specific hydrogeologic data to analyze potential hydraulic interferences to neighboring water-wells; and
  • Developed potential mitigation measures that could be implemented to minimize effects of additional demands placed on groundwater resources resulting from the proposed development, including recommendations for water conservation measures, enhanced groundwater recharge programs, properly siting water-supply wells, and properly siting septic systems.



Drinking Water Supply and Treatment
For three school districts in the Sonoma County, PES has provided a variety of services to provide a safe and reliable source of drinking water.

Services have included:

Alternative Groundwater Supply Assessment:

  • Previous drinking water supplies within two school districts contained high levels of iron and manganese. PES assisted the School District in siting and designing two new water-supply wells to provide higher quality drinking water. PES prepared well construction and drilling specifications and provided construction management services during the installation and testing of two approximately 500-foot deep wells. Services provided by PES included the review and evaluation of borehole geophysical logs and drill cutting samples to determine design criteria for the water wells, including the selection of appropriate well-screen intervals and filterpack gradation and placement.

Arsenic Assessment in Groundwater Supply Well:

  • PES performed a hydrogeologic and geochemical investigation of the occurrence of naturally occurring arsenic in groundwater extracted from a 300-foot deep well which provided the sole source of drinking water for the school. PES evaluated local and regional geologic and geochemical data (pH, iron chemistry, and oxidation/reduction conditions) and developed a conceptual model for the arsenic occurrence. Based on this conceptual model, it was determined that the arsenic was a natural constituent of the aquifer formation and was very mobile under the reducing conditions present in the deep well;
  • PES evaluated several engineering alternatives to treat the groundwater and/or provide an alternate source of water. Based on the results of the evaluation, PES assisted the school district in siting, designing, and constructing a new water-supply well to avoid the arsenic-bearing zone of the aquifer and to provide a sufficient quantity of groundwater that achieved state and federal drinking water standards. PES established excellent working relationships with Department of Health Services, Drinking Water Field Operations Branch personnel to gain regulatory acceptance and approval of the selected alternative; and
  • PES also conducted an evaluation of district compliance with State of California Title 22 and Title 17 drinking water regulations and made recommendations to improve compliance and provided training to district staff.

Treatment System Modification to Improve Water Quality:

  • Elevated levels of iron, manganese, and turbidity were present in drinking water supplied by a water-supply well. PES evaluated the characteristics of the water supply and treatment system, determined the necessary system improvements, and selected an ion-exchange/ozonation/tank storage system as the most cost-effective solution to improve water quality and storage. PES prepared a preliminary engineering design, developed costs and assisted with acquisition of State funding.

Lead, Manganese and Odor Reduction:

  • Lead, manganese, and odor were present in drinking water in excess of drinking water standards. PES evaluated the source of these constituents in the water, assessed corrosion control/treatment alternatives and selected ozonation/polyphosphate corrosion inhibitor/tank storage as the preferred alternative. PES developed cost estimates, assisted with the acquisition of state funding and provided construction management oversight.

Services & Projects

Environmental Site Assessments and Investigations

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Regulatory Compliance

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Environmental Management of Building Systems

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Engineering and Remediation Services

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Water Resources

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Litigation Support and Expert Witness Testimony

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