Archive for the ‘Abstracts’ Category

First Steps in Inter-Basin Coordination for SGMA: Basin Boundary Modification Requests in Santa Cruz County

Friday, September 30th, 2016

Cameron Tana, Sean Culkin, and Nick Byler presented this poster at the Groundwater Resources Association of California Annual Conference in Concord this week. Download this poster here. DWR has draft approved these basin boundary modifications.

First Steps in Inter-Basin Coordination for SGMA: Basin Boundary Modification Requests in Santa Cruz County
Cameron Tana, Sean Culkin, Nick Byler, and Derrik Williams, HydroMetrics Water Resources Inc.

The Sustainable Groundwater Management Act (SGMA) uses Department Water Resources (DWR) Bulletin 118 (2003) to define the groundwater basins to be managed. SGMA also provides local agencies the opportunity to request basin boundary modifications. DWR issued regulations for modification requests and accepted modification requests from January-March 2016.

Three eligible agencies in Santa Cruz County submitted basin boundary modification requests to DWR during this period. The requests varied in the types of modifications requested but shared the goal of defining each basin as the groundwater resource providing supply for each agency. In conjunction with re-prioritization of some of the basins involved , the modifications will allow each agency to focus its management efforts on its groundwater supply resource and therefore improve management of groundwater resources in the region.

1) Scotts Valley Water District (SVWD) requested expansion of its basin defined by Bulletin 118 based on surficial alluvium with a new name of the Santa Margarita Basin to represent the series of underlying stacked aquifers that provide the groundwater resource for the area.
2) The Santa Cruz Mid-County Groundwater Agency (MGA) requested consolidation of all or parts of four basins defined by Bulletin 118 based on separate areas of surficial alluvium as the Santa Cruz Mid-County Basin to represent the series of stacked aquifers that represent the shared groundwater resource for MGA.
3) Pajaro Valley Water Management Agency (PVWMA) requested jurisdictional modifications to internal boundaries of the Pajaro Valley Basin (3-2) to be consistent with PVWMA being named the exclusive Groundwater Sustainability Agency (GSA) for its jurisdiction.

These modifications involved shared boundaries between the proposed basins. SVWD and MGA had to coordinate on the scientific justification for their shared boundary while accounting for their jurisdictional areas. In addition, the two agencies had to respond to a private water company objection to the initial shared boundary. MGA had to understand PVWMA’s plans to be the exclusive GSA for its jurisdiction in proposing their shared boundary. The basin boundary modifications have the advantage of removing the need for intra-basin coordination agreements between the agencies, but inter-basin coordination will still be necessary for these connected basins. Working through the issues for modifications of the shared basin boundaries in these requests were good first steps for future inter-basin coordination to achieve groundwater sustainability in Santa Cruz County.

Using Cross-Sectional Models to Develop Measurable Objectives for Saltwater Intrusion

Tuesday, April 12th, 2016

Sean Culkin gave this presentation at the California Water and Environmental Modeling Forum 2016 Annual Meeting is a session called Managing Groundwater According to SGMA – Developing Approaches moderated by Rob Gailey. Download the presentation here.

Using Cross-Sectional Models to Develop Measurable Objectives for Saltwater Intrusion
Sean Culkin, Cameron Tana and Derrik Williams, HydroMetrics Water Resources Inc.

The Sustainable Groundwater Management Act defines saltwater intrusion as an undesirable result that must be avoided to achieve basin sustainability. Groundwater Sustainability Plans need to define measurable objectives that prevent undesirable results such as saltwater intrusion. A water quality standard for salt concentrations is certainly necessary as a measurable objective, but measurable objectives based on groundwater elevations can also facilitate management of the basin to prevent saltwater intrusion for two main reasons:

1. If the saltwater/freshwater interface is offshore, water quality may not indicate risk of saltwater intrusion resulting from depressed groundwater levels until the interface comes onshore. Measurable objectives based on groundwater elevations can be designed to prevent intrusion over the long term.
2. If a groundwater model is used to manage a basin, modeling the density dependent flow of the saltwater/freshwater interface can be numerically intensive and may produce errant results without a fine vertical model grid. By developing measurable objectives based on groundwater elevations, basinwide models do not need to model density dependent flow and groundwater elevation results from the basinwide models can be used for comparison to measurable objectives when evaluating groundwater management alternatives.

Measurable objectives based on groundwater elevations can be developed using density dependent cross-sectional models. The use of these models accounts for basin-specific geology as opposed to using more generalized approaches like the Ghyben-Herzberg relationship. Cross-sectional models were developed for the critically overdrafted Santa Cruz Mid-County Basin and the adjudicated Seaside Basin on the central coast of California. The cross-sectional models extend offshore to identify onshore groundwater elevations that allow the interface to equilibrate at a known location offshore, regardless of the interface’s current position. This approach is a time independent approach that has the advantage of not requiring time series model inputs. Model layers were extended offshore based on understood geology and the aquifer parameters were varied based on a Monte Carlo approach. Results from the Monte Carlo approach were used to assess the probability that a protective groundwater elevation will prevent saltwater intrusion. Based on these probabilities, measurable objectives for groundwater levels were established for coastal locations. These measurable objectives can be compared to groundwater elevation data to assess whether the basin will avoid the undesirable result of saltwater intrusion over the long term. Groundwater flow model results can also be compared to the measurable objectives to evaluate groundwater management alternatives.

Evaluating Water Quality with Data from Dynamic Dye Tracer and Sampling Techniques Used in Production Wells

Wednesday, March 26th, 2014

Cameron Tana is giving a talk today at the CA-NV AWWA Spring Conference in Anaheim. The talk is at 2:45 PM in the Water Well Technology committee’s session. Here is the abstract:

Evaluating Water Quality with Data from Dynamic Dye Tracer and Sampling Techniques Used in Production Wells

Cameron Tana1, Nicholas Byler1, Haleemah Qureshi1, David Van Brocklin2, and Derrik Williams1

1 HydroMetrics Water Resources Inc., Oakland, CA
2 Perth, Western Australia

The U.S. Geological Survey (USGS) has developed a technique for characterizing depth dependent flow in water supply wells (Izbicki et al. 1999) that is commonly used to evaluate well water quality issues. The technique involves injecting a dye tracer at various depths in the well and using travel times to estimate velocity and cumulative flow at various intervals in the well. To evaluate well water quality, depth-discrete samples are collected in conjunction with the dye tracer study. Sample concentrations and flow data from the dye tracer technique are used to estimate contaminant mass flux and aquifer concentrations over depth. These estimates often inform plans for well modification or other strategies to improve water quality produced by the well.

However, the resolution of the data obtained from the dye tracer technique is limited since the technique only provides average velocities and flows over depth intervals in the wells. If the data’s resolution limitations are not addressed, flows and therefore contaminant mass fluxes and chemical concentrations may be assigned to the wrong depth interval without acknowledging the potential error.

Data interpretation should address the resolution limits of the technique by fitting estimated travel times and well concentrations to the raw data. One approach is to calculate a mass balance that fits the obtained data (Halford et al., 2010). A second approach is to use an axi-symmetric model based on Langevin (2008) such as AnalyzeHOLE (Halford 2009) and calibrating to the obtained data. We will present case studies of wells affected by Chromium VI that show how plans to address well water quality can change when using a data interpretation approach that addresses the data’s resolution limits.

We also recommend two field strategies for improving the resolution of using the dye tracer technique with depth-discrete sampling: 1) injecting the dye tracer at different depths within blank casings between screens, as flows should be uniform within the blank and 2) sampling at different depths than the dye injection depths to increase spatial resolution of obtained data. We will use the case studies to present an evaluation of these strategies.

References:
Halford, K., 2009. AnalyzeHOLE-An integrated wellbore flow analysis tool, U.S. Geological Survey Techniques and Methods 4-F2.
Halford, K.J., Stamos, C.L., Nishikawa, T., and P. Martin, 2010. Arsenic management through well modification and simulation, 48, no. 4. 526-537
Izbicki, J.A., 2004. A small diameter sample pump for collection of depth-dependent samples from production wells under pumping conditions, U.S. Geological Survey Fact Sheet FS 2004-3096, September.
Izbicki, J.A., Christensen, A.H., and R.T. Hanson, 1999. U.S. Geological Survey combined well-bore flow and depth-dependent water sampler, U.S. Geological Survey Fact Sheet FS 196-99, October.
Langevin, C.D., 2008. Modeling axisymmetric flow and transport, Ground Water, 46, no. 4, 579-590.

Evaluation of Stream Depletion from Groundwater Pumping Using the Time-Series Thermal Method

Tuesday, March 25th, 2014

Derrik Williams is giving a talk tomorrow at the CA-NV AWWA Spring Conference in Anaheim. The talk is at 8:30 AM in the Water Management and Efficiency committee’s joint session with the Water Well Technology committee. Here is the abstract

Evaluation of Stream Depletion from Groundwater Pumping Using the Time-Series Thermal Method

Derrik Williams, Stephen Hundt, and Georgina King

A recent study (Hydrometrics, 2013) was undertaken to estimate the impacts that a municipal supply well has on the streamflow in a nearby stream. Aquifer and streambed properties were collected from a combination of traditional and novel field techniques, including aquifer tests and the time-series thermal method of Hatch (1999). The hydraulic properties derived from these analyses were used with the analytical solution of Hunt (1999) to estimate the streamflow depletion that occurs due to the operation of a nearby pump.

The Hunt (1999) solution computes the streamflow depletion that occurs when a nearby well pumps from an unconfined aquifer that is connected to the stream through a semipervious streambed layer. The analytical solution gives an easy and flexible way of estimating the impact that a single well has on a stream – provided that appropriate values of streambed conductance and aquifer transmissivity can be found and that the assumed hydrologic conditions and field conditions closely match. All field measurements were collected from locations near the pumping well of concern, and data collection and analysis techniques were chosen that measure the aquifer and streambed parameters used by the Hunt solution as directly as possible. Streambed conductance was estimated by combining streambed seepage rates found with the time-series thermal method and vertical gradients captured from vertically separated piezometers. Aquifer transmissivity was estimated from an aquifer test that was carried out during the same period in which streambed measurements were collected. Pumping was drawn from the well of concern. A second pumping test helped corroborate the match of the hydraulic conditions with those assumed by the Hunt solution by revealing the impact of additional boundaries. The insight gain through the analytical solution, and the defensibility of the techniques used to support it, provide a valuable tool in managing for the dual goals of water supply and ecosystem protection.

References:

Hatch, C.E., A.T. Fisher, J.S. Revenaugh, J. Constantz, and C. Ruehl, C. 2005, Quantifying Surface Water – Ground Water Interactions Using Time Series Analysis of Streambed Thermal Records: Method Development, Water. Resour. Res., 42(10): 10.1029/2005WR004787.

Hunt, B. 1999. Unsteady stream depletion from ground water pumping. Ground Water, 37(1), 98-102.

HydroMetrics Water Resources Inc. 2013. Task 4.1: Technical memorandum on seasonal creek/aquifer interactions. Prepared for Squaw Creek Public Service District.

Addressing Resolution Limitations of the Dynamic Dye Tracer and Sampling Techniques Used in Production Wells

Tuesday, June 18th, 2013

We are presenting a poster at GRA’s Symposium on High Resolution Tools and Techniques for Optimizing Groundwater Extraction for Water Supply.  Here is our abstract:

Addressing Resolution Limitations of the Dynamic Dye Tracer and Sampling Techniques Used in Production Wells

Cameron Tana1, Nicholas Byler2 (presenting),  David Van Brocklin3, and Derrik Williams2

1 HydroMetrics Water Resources Inc., Potomac, MD

2 HydroMetrics Water Resources Inc., Oakland, CA

3 Perth, Western Australia

The U.S. Geological Survey (USGS) has developed a commonly used technique for characterizing depth dependent flow in water supply wells (Izbicki et al. 1999).  The technique involves injecting a dye tracer at various depths in the well and measuring the time elapsed for the tracer to reach the well head.  Differences in travel times are used to estimate velocity and cumulative flow in the well between two depths.  However, the resolution of the obtained data is limited since the technique only provides average velocities and flows over depth intervals in the wells.  If the data’s resolution limitations are not addressed, important flows or chemical concentrations may be assigned to the wrong depth interval without acknowledging the potential error.

We recommend two field strategies for improving the resolution of the dye tracer and sampling techniques: 1) injecting the dye tracer at different depths within blank casings between screens, as flows should be uniform within the blank and 2) sampling at different depths than the dye injection depths to increase spatial resolution of obtained data.

Data interpretation should address the resolution limits of the techniques by fitting estimated travel times and well concentrations to the raw data.  One approach is to calculate a mass balance that fits the obtained data (Halford et al., 2010).  We will present an example of this approach modified to use data obtained with the two recommended field strategies.  A second approach is to use an axi-symmetric model such as AnalyzeHOLE (Halford 2009) and calibrating to the obtained data.  We will also present an example of calibration for an axi-symmetric model developed based on Langevin (2008).

Halford, K., 2009.  AnalyzeHOLE-An integrated wellbore flow analysis tool, U.S. Geological Survey Techniques and Methods 4-F2.

Halford, K.J., Stamos, C.L., Nishikawa, T., and P. Martin, 2010.  Arsenic management through well modification and simulation, 48, no. 4. 526-537

Izbicki, J.A., Christensen, A.H., and R.T. Hanson, 1999. U.S. Geological Survey combined well-bore flow and depth-dependent water sampler, U.S. Geological Survey Fact Sheet FS 196-99, October.

Langevin, C.D., 2008.  Modeling axisymmetric flow and transport, Ground Water, 46, no. 4, 579-590.

Considerations for Developing Effective Groundwater Recharge Policies

Monday, June 17th, 2013

Derrik Williams gave this talk to Groundwater Association of California’s San Francisco Branch meeting June 17, 2013.

Mapping and quantifying natural groundwater recharge is arguably one of the most important factors in successful groundwater management. Unfortunately, recharge is often very difficult to measure directly. Recharge estimates are therefore often based on assumptions: some which are valid and some which are questionable. These assumptions can lead to, and have led to, land use policies that can be counterproductive to groundwater managers. A clear discussion of recharge mechanisms, physical factors limiting recharge, groundwater quality impacts from recharge, and ecological/habitat impacts from enhancing recharge must precede any land use decisions.

Because groundwater recharge is often viewed in the context of providing urban supplies, we will focus on recharge in urban areas – and land use policies that can enhance this recharge. This talk reviews the current understanding of the influences of urbanization on groundwater recharge from both a quantity and quality perspective. We will compare what is known about recharge with existing policies and recently passed legislation requiring mapping of recharge zones. Based on our understanding of recharge mechanisms, we can outline what hydrogeologists should consider when negotiating with land use planners, and how they should be influencing land use policy.

Monitoring Private Wells as an EIR Mitigation Measure for Municipal Wells

Thursday, October 11th, 2012

Cameron Tana presented this at the CA-NV AWWA Annual Fall Conference October 11, 2012

Monitoring Private Wells as an EIR Mitigation Measure for Municipal Wells

Cameron Tana1, Georgina King2 , Kelly White3, and Taj Dufour4

1 HydroMetrics Water Resources Inc., Potomac, MD
2 HydroMetrics Water Resources Inc., Oakland, CA
3 Environmental Science Associates, San Francisco, CA
4 Soquel Creek Water District, Soquel, CA

In order to meet requirements of the California Environmental Quality Act (CEQA), Soquel Creek Water District (SqCWD) assessed potential impacts from operating up to five proposed production wells in its Well Master Plan Environmental Impact Report (EIR). One of the impacts assessed was the potential for pumping from the proposed wells to negatively affect nearby non-SqCWD wells, including private wells.

The Well Master Plan EIR considered pumping impacts on private wells to be significant if:

1. Drawdown from the proposed production wells would be expected to lower groundwater levels below the top of the private well screen, thereby increasing the risk of physical damage to the well; or
2. Drawdown from the proposed production wells would be expected to cause a loss of yield in the nearby private well such that its water quantity or quality is rendered incapable of meeting its historically measured production levels.

An analytical model indicated that the proposed production wells would not drop water levels below the average top-of-screen depth of nearby private well screens and would not cause a significant decline in well yield of the average nearby pumping well. The average top-of-screen depth is an appropriate benchmark for the analysis because it would be unreasonable for the shallowest well or a marginally performing well to constrain the use of basin supply by all users. However, to account for the possibility of adverse impacts to shallower non-average private wells, or to private wells for which information is not available, the EIR conservatively determined pumping impacts to nearby private wells to be potentially significant. To reduce these potential impacts to a less than significant level, SqCWD is implementing a voluntary monitoring and mitigation program for private well owners.

The program involves installing flow meters and groundwater level loggers in the private wells of owners that enroll in the program. The equipment is installed at least 6 months prior to the planned start-up of the nearby proposed production well to collect baseline data. Data collected after the proposed production well is online is used to evaluate whether pumping of the District well has had a restrictive effect on the private well.

SqCWD developed a waiver agreement for private well owners defining the terms and conditions of the program. SqCWD has completed enrollment and equipment installation for 13 private wells near the first of the proposed production wells that will come online. Once enrollment was completed, a field inspection of the private wellhead was completed to measure groundwater levels and collect information to plan installation of equipment. Installation of flow meters was typically straightforward. However, well seals with access ports too small to accommodate the groundwater level loggers were replaced and PVC pipes to protect the loggers were installed. The private wells were disinfected and dechlorinated before returning the wells to service. The loggers were installed at a later date. The presentation will outline information useful for the private well monitoring program, describe and show examples of implementation challenges and summarize lessons for improving the program.

Applications of Precipitation-Runoff Modeling System (PRMS) in Groundwater Studies

Thursday, October 4th, 2012

Georgina King gave this presentation at the Groundwater Resources Association of California 21st Annual Conference and Meeting October 4, 2012.

Applications of Precipitation-Runoff Modeling System (PRMS) in Groundwater Studies

Georgina King, PG, CHg, and Cameron Tana, PE

Water purveyors in the Soquel-Aptos basin, Santa Cruz County, California need recharge estimates to assist them making groundwater management decisions. Specific decisions are related to pumping curtailments during low rainfall periods, planning for recharge impacts due to future land use changes, and effects of shifting pumping closer to recharge areas. The USGS’s Precipitation-Runoff Modeling System (PRMS) was selected as the tool to determine the rainfall-recharge relationship for the basin, and thus be used to estimate the amount of recharge likely from available rainfall data. The model can also be used to identify or map areas of recharge.

PRMS simulates streamflow from precipitation, after evapotranspiration, and groundwater recharge are accounted for. Model input is daily climatic data: precipitation and temperature. Hydrologic and physical characteristics are assigned to the model area. Calibration using average monthly solar radiation, potential evapotranspiration, and daily streamflow as targets improved model credibility.

The deep recharge results from the PRMS model are also being used as the recharge input to a MODFLOW model for Central Water District, which pumps from the Aromas area of the Soquel-Aptos basin. The MODFLOW model will be used to evaluate shifting pumping inland closer to recharge areas in order to address water quality issues. MODFLOW estimates of stream percolation will be used to evaluate the uncertainty introduced by using PRMS and MODFLOW in sequence as opposed to coupling PRMS and MODFLOW in a GSFLOW model.