Evaluation of hydrogeologic conditions was based on updating an existing three-dimensional groundwater model developed as part of the preliminary design of the dewatering operations. The updated groundwater flow model was used to simulate groundwater conditions with and without the dewatering pumping to quantify the impact of the dewatering pumping on flow gradients near the marina site. The model was also used to evaluate the effectiveness of positioning a recharge trench between the MTBE plume and the dewatering wells as a way to overcome the influence of dewatering well operations on plume migration and to establish a hydraulic barrier to groundwater flow and MTBE plume migration.
A triangular network of monitoring wells was installed to establish a baseline groundwater gradient near the contaminated area before dewatering began. Baseline conditions also exhibited variation due to natural tidal influences from the nearby river. The rate of flow into the recharge trench was adjusted to maintain the groundwater gradients within an acceptable range based on the baseline conditions. Real-time modeling was used to confirm both dewatering and recharge system performance and to validate changes in recharge rates. The monitoring results indicated the recharge trench was effective in mitigating the impact on plume migration during dewatering operations.
| Bill Fernandez, PE , CDM Smith | |
| Bill Fernandez is a water resources engineer with 12 years of experience in water resources system analysis and planning. He has extensive experience in performing modeling and analysis for simulation of groundwater flow and contaminant transport, optimization of water supply systems including supply wells, reservoirs, and raw water systems. Fernandez has developed a number of dewatering designs to address sensitive locations including dewatering in support of the excavation and construction of an earthen dam, dewatering next to sensitive wetlands, and dewatering control during pipeline construction in the vicinity of an active groundwater contaminant plume. | |
| John P. Nyznyk, PE, BCEE, LEEDAP , CDM Smith | |
| Mr. Nyznyk has over 26 years of experience in environmental engineering with a focus in site investigation and environmental remediation. Mr. Nyznyk currently serves as the manager of the Environmental Remediation Division for CDM Smith in Northern California. His project work encompasses a broad range of engineering disciplines, including solid waste and hazardous waste management; planning, permitting, and design associated with remediation systems; hazardous waste site assessments; and environmental management program compliance. | |
| Robert P. Schreiber, PE, BCEE, D.WRE , CDM Smith | |
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Robert P. Schreiber has more than 36 years of experience in water resources engineering and computerized engineering analysis. He is a senior technical leader specializing in groundwater flow and contaminant studies, and serves as a company-wide resource in this area. He currently serves as ASCE representative to the federal Advisory Committee on Water Information, and co-chair of ACWI's Subcommittee on Groundwater, which is spearheading the design, piloting, and implementation of the National Ground Water Monitoring Network in the United States. Schreiber is also serving as vice chair on the board of NGWA's Scientists and Engineers Division. |
