A listing of SC Earth Day events can be found at http://www.earthday.org/events/search/state/SC

EPA has set up a website with Earth Day information (http://www.epa.gov/earthday/) , including a "PICK 5 " program to choose 5 actions you can take to use less resources, reduce pollution, recycle, and more.

Southeastern regional activities are listed at http://www.epa.gov/region4/earthday/

South Carolina's activities include:

Charleston County Recycling's 2010 Earth Day Festival
Charleston County Recycling's 2010 Earth Day Festival will be held on April 17, from 11:00 a.m. to 3:00 p.m. in North Charleston's beautiful Park Circle. The purpose of the Earth Day Festival is to increase awareness about the Lowcountry's environmental issues, while celebrating Charleston's environmental community and highlighting our challenges and successes.
Location: Park Circle, North Charleston, South Carolina
Date and time: Saturday, April 17 – 11:00 a.m. – 3:00 p.m.
Contact: (843) 720-7111, publicinfo@charlestoncounty.org
Learn more about the event 

Celebrate Aiken! Earth Day
Performances by the Community Playhouse Youth Wing coincide with the city's annual Earth Day Celebration.
Location: Hopelands Gardens, Aiken, South Carolina
Date and time: Friday, April 23 – 9:00 a.m. – 1:00 p.m
Learn more about the event 

DHEC's web offering is rather bland: http://www.scdhec.gov/environment/earthday/GetInvolved/

The Kiawah Island Golf Resort  has some interesting activities all week (from Sun Apr 18-Sat Apr 24),  special workshops, tours and volunteer opportunities. http://www.kiawahresort.com/recreation/kiawah-earth-day.php

On the other hand, a search of Earth Day activities on the SC.gov website turns up the following:

"Your search returned no results."  (http://sc.gov/Pages/Search.aspx?q=earth%20day)

Another proud moment.