Members of the Northwest U.S. Highway 93 Corridor Area Plan Committee got a quick lesson in hydrological studies and roadwork Tuesday night.
David Anning from the US Geological Survey gave the group a description of where the department was in its timeline to finish its surveys of the Detrital, Hualapai and Sacramento Valley aquifers in Mohave County.
The department is currently about halfway through its survey of the three basins and expects to complete the survey and start publishing its findings in September 2009. The final comprehensive report on the three basins will be finished in September 2010.
Anning explained how the aquifers in Mohave County work. Each aquifer has a water budget. Just like a checkbook, the aquifer has a deposit and outflow system.
Water is withdrawn from the system through pumping from wells or by the natural flow of water underground toward a larger body of water, Anning said. The Detrital and Hualapai Valley aquifers naturally drain toward Lake Mead. The Sacramento Valley Aquifer drains into the Colorado River.
Water is also deposited into the aquifers through recharge. Recharge can come from natural sources such as rainwater, he said. It can take millions of years for recharge water to percolate through silt and sediment to reach an aquifer.
It can take several million more years for the water to move north toward Lake Mead, Anning said.
The USGS currently has between eight and 10 people working on the study of the aquifers in Mohave County, he said. The department has also been using special equipment in the air and on the ground to penetrate the soil and give the department an idea of what kinds of sediments make up the aquifers and how deep the aquifers are, he said.
The department also uses soil logs from local well drillers to determine the different types of soil in an aquifer, he said.
The group is not only studying the amount of available water in the ground but also the quality of the water, he said. The department can run a number of tests that will list the levels of specific minerals and chemicals in the water.
The department can also determine the age of the water by testing the different carbon isotopes in the water, Anning said.
The department has already released some preliminary information about the water levels in the aquifers. By testing the levels in more than 40 index wells throughout the county over a number of years, the department was able to get an idea of how water levels have fluctuated over the years, he said.
The preliminary information from those wells indicate a slight increase in the amount of water available in the aquifer, Anning said. However, that increase may only be occurring near the index well and may not be occurring elsewhere in the aquifer.
It also takes a number of years for the department to see a pattern in the water levels in a well, he said.
One resident asked if the department could determine the effects of the current drought on the aquifers.
Anning said it depended on where and when the department tested the levels in the aquifer.
In some areas, water levels rise and fall more quickly, such as along ridgelines or over bedrock areas, he said. This is because runoff from rain moves more quickly in these areas.
In the middle of an aquifer basin, water moves more slowly because it must make its way through several layers of silt and sediment, Anning said.
This is why it is important for the department to test many different wells in an area, he said.
Once the department gathers all the information, it will be able to create models that show the depth and quantity of water in the aquifers, Anning said.
More information on the USGS and its studies can be found at the USGS Web site, www.az.water.usgs.gov.
Also on hand to answer questions at the meeting was Engineer Steve Latoski from the County Public Works Department.
Latoski explained how most of the department's funding came from the state Highway User Revenue Fund, which is collected through a sales tax on gasoline and diesel.
The county also has a five-year road maintenance program, which is updated by the County Transportation Commission in April or May every year.
The department also gets some grant funding from the Western Arizona Council of Governments, he said.
Latoski also explained the two different levels that the county maintains roads at in the county.
The first level is regular maintenance. These roads are sometimes paved and connect into a county or state highway. The roads have also been dedicated to the county and meet specific right of way and engineering standards for the county, he said. The second level of maintenance is a tertiary road. These roads are usually dirt roads and do not meet all of the county's engineering and right of way standards, Latoski said.
There are a number of roads in the county that do not meet the county standards and are maintained by private developers or residents, he said.
Residents can petition the Public Works Department to have a road accepted into the county's maintenance program, Latoski said.
In order to have a road accepted into the county's regular maintenance program, the road must be brought up to and meet all county road engineering standards, without any expense to the county. This can be expensive, he said.
The requirement to get a road on the county's tertiary plan is a little easier, he said. The road must be at least 28 feet wide with ditches on either side, connect to a county road, have a 30 foot right of way on either side and be passable by a two-wheeled vehicle. All of this needs to be done without expense to the county, he said. The Public Works Department also contains a Traffic Control Department, which makes all the road signs for the county and the Engineering Department, which designs the roads and handles traffic counts.
More information on the department can be found on the county's Web site, www.co.mohave.az.us.
The committee set its next meeting for 5:30 p.m. on March 18 at Black Mountain Elementary School in Golden Valley.