Brownish or Dirty water is a common occurrence after earthquakes. An earthquake can cause water wells to become turbid, which is when the water is cloudy or more commonly dirty looking, and well water quality have become degraded as a result of earthquakes. Earthquakes can affect the water level in your well. To see if your well has been impacted, you will have to empty your pressure tank and see what pumps out of the well. Turbidity could move through the system and pass in a short period or not depending on the specific geology, soil type and hydro geology. Aquifers are water-bearing subsurface soil and rock formations that can be effected by seismic activity. In bedrock formations, for instance, the well will be drilled until it hits a fracture or crevice that holds water. Earthquake shocks can increase the permeability of the aquifer rocks and cause the water level to fall with gravity through the more permeable materials and the water will fall to a lower level leaving the well dry. http://pubs.usgs.gov/fs/fs-096-03/
There are also plumbing problems that can cause brownish water and do not forget that earthquakes can cause the fittings to the septic tank to fail and a well could become impacted by a leaking septic tank (or several leaking tanks in the neighborhood). First, check your plumbing, check the screens and aerators in your sinks and then verify that both the hot water and cold water are both discolored. If the hot water only is discolored then the problem might be with rust the hot water heater that was shaken loose, simply drain it. After determining that the brown water is coming from the cold water tap also, it is still possible that there is rust in the plumbing fixtures or the piping, but it would typically manifest in only one sink or tub and not uniformly throughout the house (unless the rust is in the main water pipe from the well).
After rust in the household fixtures there are four likely causes for well water to be brown or brownish, surface infiltration, soil fines having shaken loose are being pulled into the well, water level dropping or iron (and/or manganese) in the water. Earthquakes can cause a change in water, either by loosening fine grains of silt and soil, loosening minerals or lowering the water level. According the US Geological Survey there is no rhyme or reason to which wells will be impacted by an earthquake, but time might restore your well. Run your well thought your hoses to the yard for a couple of hours. Let the well rest for a couple of hours and then run the hoses again. See if there is sediment or only color with the water. If no sediment appears, you probably are only pumping fines and the well should clear after several rounds of pumping and rest. If you are pumping sediment, it might be a loss of water level. Wait and see if the well recovers. According to David Helms of the US Geological Survey in Richmond, who is still analyzing the data, USGS monitoring wells have shown significant impact. The example he gave me was the Reston well which experienced a sudden drop in groundwater level yesterday and though it recovered by this morning, the water level was lower than the pre-event level. It is unknown if the groundwater level will recover fully and a lowering of the water in a well can cause the well to basically pump mud.
Surface infiltration of water is due to impaired pump and casing system, but is unlikely to be the cause of sudden brownish water after an earthquake. A leaking septic system could also impact water quality. Testing the well for bacteria would determine if the water were safe to drink. A bacteria test checks for the presence of total coliform bacteria and fecal coliform bacteria. These bacteria are not normally present in deeper groundwater sources. They are associated with warm-blooded animals, so they are normally found in surface water and in shallow groundwater(less than 20-40 feet deep). Most bacteria (with the exception of fecal and e-coli) are not harmful to humans, but are used as indicators of the safety of the water. An inspection of the well and pump system might visually locate any obvious flaws but the presence of coliform surface bacteria would certainly identify where to begin looking. The most likely source of brown water after the earthquake is from the well itself. It is typical in Virginia not to have well casing beyond 40-50 feet deep. The Balls Bluff Siltstone and red clay common to this area does not typically need a casing. The most common modern well installation is to have a pump that installed in the well and looks a little like an outboard motor on a stick. While the most common source of brown water is soil fines shaken loose in the earthquake, there can be other causes. Changes in water level or supply could result in the pump pulling up a bit of mud or the pump could have wracked a bit and is hitting the side of the well hole. So that water that suddenly turns brown may indicate a problem with the well structure or water level. Turn on your hoses and put your hands on the well cap, if you feel any vibrations or hear a sound you probably have a pump problem. Also listen at the well pipe into the house.
The final source of brown water is iron (and/or manganese) in the water. As rain falls or snow melts on the land surface, and water seeps through iron-bearing soil and rock, iron can be dissolved into the water. In some cases, iron can also result from corrosion of iron or steel well casing or water pipes. Iron can occur in water in a number of different forms. Iron is harmless, but can affect taste and use of water. The earthquake might have shaken loose minerals or rust in your system. This source of brownish color might pass through the system like soil fines, but could require a greensand filter.