575'? Gary, you're killin' me!
Are you sure they didn't hit salt water????
Hey Rob, the bad part about it though, once they connect another 20' extension. . you bought the whole nine yards so to speak. . meaning, even if you hit water within the first several feet after adding the new extension you pay for 20'x $whatever per foot. Hoowah!
Champ, thanks for the stats. At 1 GPM is 350 gallons of storage enough? you may want to check with your insurance company (that's assuming there is no city water in the vicinity thus, no fire hydrants... see what I'm getting at?). In my county, if there is no city water present, your well must produce to a certain level otherwise a DEDICATED storage system must be installed. NOTE: this is ALSO assuming the ingress (road and driveway) to your property is NOT up to stringent county and Fire district codes, which would also necessitate the installation of a sprinkler system thus, the DEDICATED storage tank (for the fire suppression system).
(which in the case of our county would have to be designed and installed by a State approved/licensed company. $$$$) Fortunately, we just squeeked through the system unscathed.
Unfortunately, the septic system that was designed for our property was the absolute state of the art... septic tank, pump tank, sand filter (in ground mound) and finally, a full blown mound system. The real unfortunate part was the cost
about $20k including design, as built fees, health permit, recording fees, variance mitigation and of course, the construction of the project. Certified sand (with a documentable paper trail was required for this project). He!!, the way things were going I thought they were going to tell me they had to fly sand in from the Kona coast. . first class under armed guard no less!
Two pumps and and a "mile" of wiring later, it was complete! I was told by the septic system designer and health inspector that once the effluent was processed through the entire system we have it is just about drinkable. BTW, the reason for the elaborate septic system is due to the sandstone out where we live. Here's the real bite, my neighbor two properties away lives down, almost on the plateau "valley floor"; they were able to have a reasonably simple pressure feed system installed... around $3500. (installed about 9-12 months before our system was installed). This was due to soil conditions etc. Don't ya just love it?
..... builds character
Attention: TDR Forum Junkies 
Champane flight, congrats on the h2o,you are doing great so far,I was the construction business for years and I can tell you that you are right on witn the concrete septic tank and infiltrator system,never put in a plastic tank as it will colapse on you,you must fill it with h2o before backfilling the dirt
what does that tell you,a little flimsey eh? the only other thing I can suggest is buying risors for the top of the tank,the company that sells the tank will have them,they are 16" round and come in various lengths,simply pull the lids off the tank and add the risors then put your lids on the risors,then when time to call the honey wagon for a pump job you just pull the lids with no digging 
