Jacquelyn Martin/AP Photo

With a potential stalemate on Capitol Hill over defunding Obamacare and the clock ticking down to Sept. 30, the country is inching closer and closer to a possible shutdown of the federal government.

The last time that happened was in 1996 when the federal government was shuttered for 21 days between Dec. 15, 1995, and Jan. 6, 1996. Before that, a five-day shutdown occurred from Nov. 13 through Nov. 19, 1995. According to the Congressional Research Service, 800,000 federal employees were furloughed during that period.

After the 1996 fiscal year shutdowns, the Office of Budget and Management estimated the cost of the shutdown to be $1.4 billion.

A government shutdown does not mean the lights will go out on Capitol Hill, in the White House and in every government department and agency. Many agencies and government functions would be exempt from a shutdown. All government agencies that are not funded through annual congressional appropriations will not be affected. In addition, there are certain functions deemed "excepted" by the federal government that may continue in an absence of appropriations. Such functions include those necessary for emergencies involving "the safety of human life or the protection of property," and those necessary for activities essential to national security, including the conduct of foreign affairs essential to national security.

With the threat of a shutdown looming once again, ABC News is compiling an ongoing list of what agencies, departments and people would be affected - and those that wouldn't:

WHO WOULD BE AFFECTED?

1. Dirty in D.C.

Earlier this week, Washington, D.C. Mayor Vincent C. Gray said a government shutdown would mean a much dirtier city - as least temporarily. "Trash collection will not start until one week after shutdown. Street sweeping will be suspended," a city press release noted. The release also said all Department of Motor Vehicles locations would be closed as well as all of the city's public libraries. Washington's Department of Transportation "will be operating with a skeletal crew, so routine maintenance and repairs will cease." Other departments, including police, fire and public schools, will remain open. "We regret that we even have to consider the possibility that the District of Columbia would fall victim to a partisan standoff on Capitol Hill," Gray said in a statement. However, in an attempt to avoid this mess, on Wednesday Gray decided to declare all District government operations essential in the event of a government shutdown. In a press release, Gray explained the reasoning behind his decision. "It is ridiculous that a city of 632,000 people - a city where we have balanced our budget for 18 consecutive years and have a rainy-day fund of well over a billion dollars - cannot spend its residents' own local tax dollars to provide them the services they've paid for without congressional approval. Congress can't even get its own fiscal house in order; they should be taking lessons from us rather than imposing needless suffering on us. I will not allow the safety and well-being of District residents to be compromised by Congress' dysfunction."

2. E.P.A. M.I.A.

Environmental Protection Agency Administrator Gina McCarthy recently told the Associated Press that the agency would "effectively shut down" if the federal government shuts down. According to the AP: "[The] agency won't be able to pay employees. She says only a core group of people will remain on duty in case the EPA has to respond to a 'significant emergency.' The vast majority of employees will stay home. That means that most of EPA's functions, like drafting regulations and enforcing laws to protect the environment, will likely remain stalled until government operations fully resume."

3. Access Denied to United States' Landmarks

A statement released on the National Park Service page cautions visitors of the potential effects a government shutdown would have on national parks, wildlife refuges and other public lands. In the event of a government shutdown, "the National Park Service, Fish and Wildlife Service and Bureau of Land Management will close and secure park, refuge and visitor facilities on public lands." That means that access to popular United States' landmarks like the Statue of Liberty and Ellis Island, Independence Hall, Alcatraz, and the Washington Monument will be denied to all visitors. In addition, many administrative offices will be minimally staffed, and many will be entirely closed. Overall, "ordinary business of these bureaus will be extremely curtailed," if a government shutdown takes place.

4. Pay Difficulties at the DOD

ABC's Pentagon reporter, Louis Martinez, notes that it will not be business as usual at the Department of Defense if a government shutdown occurs. Specifically, military and civilian employees' pay could be delayed. But, as long as a DOD appropriations bill is passed, military employees will be paid retroactively. Second, civilian employees who are "excepted" from the shutdown, like military employees, will also qualify for retroactive pay. But, the last group of DOD employees, civilian employees not designated as "excepted" will be furloughed and not qualify for retroactive pay. According to Martinez, about 50 percnet of DOD employees will fall into the "excepted" category, leaving the other half of employees falling into the furloughed, unpaid category.

5. Passport Offices Closed

According to the State Department 'Guidance in the Absence of Appropriations' memo published in 2011, in the event of a government shutdown, Passport offices will be closed for business. So if your passport is about to expire, make sure to get it renewed by Sept. 30, the day the federal budget is set to expire if Congress doesn't act, or your international travel will be grounded until the government shutdown is resolved.

WHO WOULDN'T BE AFFECTED?

1. Paging the President

In case you were wondering, President Obama will not be out of a job if the federal government shuts down. Nor will members of his cabinet or other presidential appointees. The Congressional Research Service analyzed the Executive branch, the branch of government with the largest number of personnel and the largest budget. According to the report, "several types of executive branch officials and employees are not subject to furlough. These include the president, presidential appointees and federal employees deemed excepted by the OPM." But, even though excepted employees are not subject to furloughs, according to the CRS report, excepted employees who are normally paid from annual appropriations would not receive pay during the shutdown period.

2. Signed, Sealed, Delivered

The United States Postal Service, will remain open and operational during a government shutdown. The agency, not unfamiliar with budget woes, is exempt from the federal government shutdown because it does not receive it's budget from annual appropriations from Congress. According to USA Today, all federal agencies that do not receive their operating budgets from annual congressional appropriations "will continue to operate normally." In addition to the USPS, the Patent and Trademark Office and the Federal Highway Administration will remain operational.

3. Meteorologists Continue Forecasting

According to the Department of Commerce's contingency plan published in 2011, weather forecasts and alerts will remain functioning during a government shutdown. Weather forecasts would continue to be issued by meteorologists at the National Weather Service, because they "provide the nation with weather, water and air quality forecasts and warnings to imminent threats to protect life and property."

FOR MORE INFORMATION

For a full list of government agencies contingency plans, please visit the White House Office of Management and Budget webpage. There you can find links to contingency plans for agencies across the Federal Government, from 2011. The page will be updated as more plans are posted. To read the full CRS Report, "Shutdown of the Federal Government: Causes, Processes, and Effects," click here.