Great Oak Subdivision, MO
Lead detected, under the action levels
Latest 90th-percentile lead: 1.4 ppb (monitoring period 2025-2025). The federal action level is 15 ppb today and drops to 10 ppb in Nov 2027; EPA's health goal is 0. Lead was measured in sampled homes but the 90th percentile is under both action levels. EPA's health goal for lead is zero, so test your own tap if your home was built before 1986 or anyone in it is pregnant or a young child.
About Great Oak Subdivision
Great Oak Subdivision serves about 30 people through 12 service connections, which makes it a very small system under EPA's size classes. It is privately owned and draws groundwater, in Warren County, Missouri. EPA system ID: MO6036386; phone on file: 636-235-2910. Call that number and ask whether your address has a lead, galvanized or unknown service line.
Lead results over time
That is up 1.4 ppb from 0 ppb in the period ending 2025. The highest 90th-percentile result EPA holds for Great Oak Subdivision is 1.4 ppb across 2 monitoring periods, none of them over 15 ppb.
| Period ending | 90th-percentile lead |
|---|---|
| 2025 | 1.4 ppb |
| 2025 | 0 (not detected) |
Against other Missouri systems
Of the 1,674 Missouri systems with a lead result, the median latest reading is 1.04 ppb; 2 are over 15 ppb right now and 74 have gone over at some point. Great Oak Subdivision's 1.4 ppb sits at the 58th percentile in Missouri and the 61st nationally (higher means more lead).
Neighbouring systems
15 other systems share Warren County; 4 of them have a higher latest lead result than Great Oak Subdivision. If you are unsure which one supplies your house, the name on your water bill decides it.
| System | People | Latest lead |
|---|---|---|
| Warrenton Pws | 8,208 | 0 (not detected) |
| St Charles Co Pwsd #2 Wright City | 3,550 | 1.14 ppb |
| Marthasville Pws | 1,200 | 0 (not detected) |
| St Charles County Pwsd 2 Warren | 1,192 | 1.22 ppb |
| Lake Sherwood Subd | 1,100 | 3.83 ppb |
| Truesdale Pws | 853 | 0 (not detected) |
| Innsbrook | 810 | 0 (not detected) |
| St Charles County Pwsd 2 North Oak Dr | 660 | 1.26 ppb |
| St Charles County Pwsd 2 Dutzow | 400 | 3.92 ppb |
| Pleasant Oak Mhp | 150 | 0.56 ppb |
What to do in your house
Test your own tap with a certified lab first-draw sample; Wright City, MO may offer free or low-cost kits through the utility. If your own line is lead, replacing the private side runs about $1,200-$12,300 (EPA average about $4,700). Ask Great Oak Subdivision whether it covers that cost before hiring anyone - many utilities now do.
These figures describe homes the utility sampled, not your tap. Only your service line record or a test of your own water answers the question for your house. What a 90th-percentile result does and does not tell you: how to read a lead result. Size matters more than most people expect: small vs large water systems.