AST works on a wide variety of water supply and geophysical projects.  The following list presents a few of our recent projects:

Well Siting Projects   AST is currently working with a number of southeastern Wisconsin communities to site new wells. These well siting projects typically consist of geologic reconnaissance studies followed by seismic refraction and electromagnetic induction or electrical resistivity surveys to find promising test drilling sites. The following communities are in various phases of this process:

• City of Pewaukee
• Village of Pewaukee
• Village of Germantown
• City of Brookfield
• Village of Mukwonago
• Village of Slinger
• City of Waukesha
• Village of North Prairie
• City of Marshfield
• City of Antigo
• Village of Hartland
• City of Oconomowoc
• City of Muskego

Water Supply - Rio Dulce, California

AST is conducting a geophysical survey to site a water supply well for a new subdivision in the Santa Barbara Mountains in California. Using a Magneto Telluric (MT) survey, AST mapped the top of a granite aquifer and mapped the fault system and fracture patterns on a mountainous site neat the San Andras Fault. AST identified several promising location for site that will supply 200 new homes. The well will be drilled to a depth of between 1,000 and 1,500 feet.

Geophysical Survey to Map Saline Plume in Los Angeles County, California

AST conducted a Time Domain Electromagnetic Induction (TEM) and high-resolution dipole-dipole electrical resistivity survey in the City of Torrance, California for the Water Replenishment District of Southern California (WRD). The survey was conducted as a field demonstration project to determine if surface geophysical methods could image a plume of brackish water present in the Silverado aquifer at depths of about 400 to 800 feet. Over pumping in the early 20th century caused salt water to intrude into the groundwater for the West Coast Basin of Los Angeles County. An injection well barrier system installed in the 1950s through 1970s halted further saltwater intrusion but stranded pockets of saline and brackish water inland from the barrier wells. Past efforts by WRD to map the position of the saline plume with monitoring wells were limited by the cost of drilling and the limited land available for monitoring wells.

WRD wanted to evaluate geophysical methods for mapping the distribution of brackish to saline groundwater in the basin. The area is highly developed with very limited open land and abundant sources of cultural interference that made the application of most geophysical methods difficult or impossible. AST worked with WRD to find a baseball field, drainage channel, and city park with enough open area to conduct field trials. The resistivity survey provided high-resolution images of the composition of the upper 200 feet of the basin fill deposits. The TEM method was used with customized multiple turn transmitter loops with a smaller footprint to provide greater penetration on a smaller site and reduce cultural interference from nearby development. The TEM data was able to map brackish water in the aquifer and image the base of the saline zone at depths of over 500 feet. The results of the survey were used to design a larger basin-wide survey that will be conducted by AST in early 2008.

Geophysical Mapping of Regional Ground Water Flow System, Death Valley National Park, California

AST conducted a series of gravity, magnetic, and Time Domain Electromagnetic Induction surveys in Death Valley National Park to map subsurface geology between Yucca Mountain and Death Valley and determine the geologic factors controlling the location of several major springs along the eastern side of Death Valley. A total of 85 TEM soundings, 91 miles of gravity data, 19 miles of magnetic data, 5 magnetotelluric profile lines, 3 component TEM profile lines and 10 high resolution electrical resistivity lines were collected over 8 field seasons. The surveys were conducted to support a regional ground water flow model being conducted by the Hydrodynamics Group for Inyo County, California. The study is attempting to document the continuity of a carbonate aquifer system from Yucca Mountain to Death Valley and map the fracture system supporting Devil’s Hole.

Our geophysical work indicated that the springs are related to faults supplied by a regional flow system. Our interpretation has been independently supported by aeromagnetic data from the USGS and geochemical analysis of the spring water by the Hydrodynamics Group.

Two deep monitoring wells have been drilled on the basis of our geophysical surveys to measure the head and water quality in the carbonate aquifer in the western Amargosa Valley. Based on our geophysical work, the carbonate aquifer was found at depths of less than 4,000 feet, as opposed to 8,000 feet, which is more typical for the Valley. Several additional monitoring wells will be drilled over the next two to three years.

Geophysical Survey of the Ames, Means, and Johnson Valleys, Mojave Water Agency

Aquifer Science & Technology designed and implemented a geophysical investigation to define the basin geometry and valley fill stratigraphy of the Ames, Means, and Johnson Valleys near Yucca Valley, California for the Mojave Water Agency (MWA) as part of a feasibility study for an artificial recharge project. Two electrical methods were used, a high-resolution electrical resistivity survey to map the lateral and vertical grain size distribution of the upper 300 to 400 feet, and a time domain electromagnetic induction (TEM) survey to determine the grain size distribution to depths of up to approximately 1,000 feet. The resistivity survey was designed to provide the greatest resolution of the distribution of coarse-grained and fine-grained sediments above the water table, which will most significantly affect the ability of water to quickly infiltrate. The TEM survey was designed to determine the grain size distribution of the lower unsaturated zone and the saturated aquifer material above bedrock.

The resistivity data also produced high-resolution images of several significant faults that formed hydraulic barriers in the basin. The TEM data mapped the valley fill stratigraphy to depths of over 1,000 feet and mapped the truncation of geologic units at depth due to faulting. This data was used to construct a conceptual model of the basins and will be used by the Mojave Water Agency to determine the most suitable locations for artificial recharge and water banking. Similar geophysical surveys were also conducted by AST for MWA in the Antelope Wash and Greentree areas.

Geophysical Survey of the Oro Grande Wash, Mojave Water Agency

Aquifer Science & Technology designed and implemented a geophysical investigation to define the subsurface characteristics and hydraulic properties of the aquifer system in the Oro Grande Wash area near Victorville, California for the Mojave Water Agency (MWA) as part of a feasibility study for an artificial recharge project. Two electrical methods used high-resolution electrical resistivity survey to map the lateral and vertical grain size distribution of the upper 300 to 400 feet, and a time domain electromagnetic induction (TEM) survey to determine the grain size distribution to depths of up to approximately 1,000 feet. The resistivity survey was designed to provide the greatest resolution of the distribution of coarse-grained and fine-grained sediments above the water table, which will most significantly affect the ability of water to quickly infiltrate. The TEM survey was designed to determine the grain size distribution of the lower unsaturated zone and the saturated aquifer material above bedrock.

The geophysical surveys showed that a thin, fine-grained material is present at the surface overlying a thick sequence of coarse-grained material. Beneath this layer lies an extensive sequence of low-permeability clay. The modeled TEM resistivity data was utilized to construct maps of the elevation of the top of the lower clay formation. The elevation of the clay layer estimated from the TEM data was confirmed by subsequent test drilling. This data will be used by the Mojave Water Agency to determine the most suitable locations for artificial recharge and water banking. Similar geophysical surveys were also conducted by AST for MWA in the Antelope Wash and Greentree areas.

TEM Soundings of the Sandstone Aquifer in Eastern Wisconsin, Mapping Saline Zones in Aquifers

The deep sandstone aquifer of eastern Wisconsin has been the primary aquifer for municipal and industrial demand for decades. The aquifer has always been a reliable source of good quality water. However, over the last several years, salinity levels have doubled or tripled in several wells in a suburb of Milwaukee and new wells have hit unexpectedly high salinity in southeastern and east-central Wisconsin. Salinity levels are approaching usable limits in several wells, creating concerns about the long-term viability of the aquifer.

AST conducted time domain electromagnetic induction (TEM) surveys in eastern Wisconsin to determine the distribution of the saline water in the aquifer. The TEM method can measure subsurface conductivity to depths of over two thousand feet. The data can be used to map the thickness of the aquifer and identify pockets of saline water.

Individual surveys were conducted to site high capacity municipal wells in the sandstone aquifer for the following Wisconsin communities.

1. Waukesha Water Utility
2. City of Brookfield, Wisconsin
3. City of Oakfield, Wisconsin

In addition, AST teamed with the University of Wisconsin-Milwaukee to obtain research grants from the UW-Extension Groundwater Coordinating Council to conduct regional TEM surveys in two parts of eastern Wisconsin. In 2000, 69 soundings were conducted in Waukesha and Milwaukee counties to map the distribution of saline water in the sandstone aquifer. In 2002, 55 soundings were conducted in Fond du Lac, Winnebago, Outagamie and Calumet counties to map the distribution of saline water and the presence of Precambrian mounds on the base of the aquifer. The results of both projects were released as reports of the Groundwater Coordinating Council (UW-WRI # 00-HDG-8 and DNR Project #173).

The TEM sounding identified pockets of saline water at depths of over 1,000 feet in the aquifer. Several faults and buried mounds of pre-Cambrian igneous rock projecting into the aquifer were discovered.

Magnetotelluric Survey to Site a Community Well, near Santa Clarita, California

AST completed a magnetotelluric (MT) survey to site a high capacity well to supply a planned development in the San Gabriel Mountains near Santa Clarita, California. The MT survey consisted of 28 soundings on a 1,100-acre site that consists of up to 2,000 feet of dense sandstone over a fractured igneous basement. The survey mapped the structure of the igneous aquifer at depth of between 1,000 and 2,000 feet. The data also identified a major transform fault system bisecting the site. The results of the survey identified several drilling targets at depths of 1,000 to 2,000 feet where major fracture zones are expected to be present within a favorable stress field based on the mapped structure of the fault system.

Wells 23 & 24; Marshfield Electric and Water Utility, City of Marshfield, Wisconsin

Geophysical surveys were conducted on two sites to site two new wells in the sand and gravel aquifer. The geophysical surveys consisted of electrical resistivity profiles and seismic refraction soundings. The geophysical surveys were used to direct a test boring and water sampling program. Test wells were drilled on both sites.

As a result of the survey results, a new well, Well 23, is on line on the first side with a design capacity of 400 gpm. Well 23 will replace two existing wells in the immediate area that have a combined capacity of less than 200 gpm. A production well was under construction on the second site, Well 24, with a capacity of 500 gpm. AST is currently exploring several additional sites to develop new higher capacity wells to allow the utility to abandon several old low capacity wells that have exceeded their service life.

Wells 9 and 13; City of Muskego, Wisconsin

As part of a municipal well siting study, AST conducted a geologic reconnaissance study was conducted followed by a geophysical survey consisting of Time Domain Electromagnetic Induction soundings, electrical resistivity profiles, and seismic refraction on four sites for the City of Muskego, Wisconsin. AST conducted geophysical survey, test drilling, pumping tests and water sampling followed the reconnaissance study.

The study identified three well sites in a sand and gravel bedrock valley aquifer with production capacities of from 700 gpm to over 1,000 gpm. Production wells have been constructed on two sites with capacities of 700 gpm and 1200 gpm. During the construction of one well, the drilling contractor experienced a casing failure and damaged the formation. AST conducted several step draw down tests to document the efficiency of the well. These tests were crucial in holding the contractor responsible for fixing their mistakes and resulted in the City receiving a well that produced a significantly higher yield than the contractor alleged was possible from the aquifer. The third well site has been banked for future needs. AST is currently evaluating several additional sites for additional wells to meet the long-term future needs of the City.

Wells 5 and 6; Village of Mukwonago, Wisconsin

A geologic reconnaissance study was completed to find sand and gravel well sites. The Village needed to provide low radium water to blend with two existing sandstone aquifer wells that exceed the radium standard. The reconnaissance study was followed by a geophysical survey using electromagnetic induction, seismic refraction and electrical resistivity profiles. The geophysical survey let to several test borings that identified two new municipal well sites for the Village of Mukwonago, Wisconsin.

Two sand and gravel wells were constructed on the basis of the exploration project. One well has a capacity of approximately 1,200 gpm. The second well produces about 4,00 gpm. A controlled pumping test was conducted to document the capacity of the wells and demonstrate that they will not adversely affect a spring supporting a calcareous fen approximately 1,500 feet from the higher capacity well. The capacity of the sand and gravel wells is adequate to blend with the sandstone aquifer wells and meet the radium standard for the system.

Well 6; Village of Hartland, Wisconsin

A geologic reconnaissance study was conducted, followed by a geophysical survey consisting of time domain electromagnetic induction soundings and seismic refraction on four sites to identify municipal well sites for the Village of Hartland, Wisconsin. Test drilling, pumping tests and water sampling followed the reconnaissance study.

A well site has been constructed in a sand and gravel bedrock valley aquifer with a capacity of over 2,000 gpm. A pumping test was conducted that successfully proved to a concerned lake management association and their consultant that operation of the well would not adversely impact nearby Beaver Lake. An additional future well site with an estimated capacity of over 1,000 gpm was identified near the same site.

City of Antigo, Wisconsin

A geologic reconnaissance study was conducted to identify promising exploration areas for new municipal well sites for the City of Antigo, Wisconsin, to replace five very shallow wells impacted by biological contamination in the aquifer. The project included a wellhead protection plan to identify the capture zone of the existing well fields, DNA fingerprint analysis to identify the source of fecal coliform contamination in the major well field, and an evaluation of nitrate contamination in the north well field.

The source of the fecal coliform bacteria has been linked to non-human sources and shown to be endemic in the portion of the aquifer around the well field. Several promising exploration areas were identified that were away from sources of high agricultural chemical use and are expected to provide safe water from the sand and gravel aquifer. A nitrate management plan was developed to reverse the trend of rising nitrates in the north well field by encouraging local farmers to reduce nitrogen use in the capture zone of the well field. Subsequent geophysical exploration identified several promising test boring sites in deeper sand and gravel deposits in areas less prone to contamination. Two production wells were drilled with capacities of 600 and 700 gpm. The wellhead protection plan was modified to cover the two new wells.