I need to determine the recharge rate of a well to be sure that it has the capasity I need. The well is 50 yr old with 30" concrete pipe casing . It is 30 feet deep with 16' of water. I tried to find a smaller pump with 25 GPM with no luck. The smallest I can find is 4000 GPH. If I pump it down and then time how long it takes to refill will that give me an accurate flow rate? Do I need to do it several times to be accurate?