Apache with prefork model using 1000 MB memory per process

I am currently working on a site which uses Apache running on the prefork memory model. The following is the configuration from httpd.conf

 
  StartServers            30
  MinSpareServers         15
  MaxSpareServers         30
  MaxClients              96 
  ServerLimit             512
  MaxRequestsPerChild     0

The following is a sample line from top

PID USER      PR  NI  VIRT  RES  SHR S %CPU %MEM    TIME+  COMMAND           
29261 apache    15   0 1003m 231m  53m S 16.3  2.9   1:47.68 httpd              

The following are the loaded apache modules

core prefork http_core mod_so mod_auth_basic mod_authn_file 

mod_authz_host mod_authz_user mod_include mod_log_config 
mod_logio mod_env mod_ext_filter mod_mime_magic mod_expires 
mod_deflate mod_headers mod_usertrack mod_setenvif mod_mime 
mod_status mod_autoindex mod_info mod_vhost_alias mod_negotiation 
mod_dir mod_actions mod_alias mod_rewrite mod_cgi mod_version 
mod_realip2 mod_php5 mod_ssl

I am not sure if all of these modules are used.

The following are the php extensions loaded

date, libxml, openssl, pcre, zlib, bz2, calendar, ctype, 
curl, hash, filter, ftp, gettext, gmp, session, iconv, 
posix, Reflection, standard, shmop, SimpleXML, SPL, sockets, 
exif, sysvmsg, sysvsem, sysvshm, tokenizer, wddx, xml, 
apache2handler, memcache, uploadprogress, dbase, dom, 
eAccelerator, gd, json, mbstring, mcrypt, memcached, mongo, 
mysql, mysqli, newrelic, PDO, pdo_mysql, pdo_sqlite, xmlreader, 
xmlwriter, xsl, zip

Why would apache be using so much memory per process? Is ti because of these modules? If so are there memoryhogs in there which I can start looking at to see if they are being used? Or could it be because of the php extensions? Any memoryhogs in there?

The php memory limit is set to 256MB.

Eaccelerator is configured with 512MB memory.

The server is not able to handle even slightly above average loads as swap usage starts as soon as traffic increases making the system unresponsive. The server has a total of 8GB of RAM and it is a dedicated quad core server.

Thanks in advance for any help in solving this problem.