Well Water Testing in Miami, FL

Local Soil Conditions: Miami-Dade's soils are thin skins of marl and gravelly loam over porous Miami Limestone, and the depth to that rock is usually the whole story. The Biscayne series is very poorly drained with bedrock at roughly 15 inches and a water table within 10 inches of the surface for four to six months of the year, receding only to about 20 inches in dry spells. The Perrine marly silt loam is also very poorly drained, with a seasonal high water table at 0 to 6 inches and moderately high to high conductivity through the marl but effectively none into the rock beneath it. Krome very gravelly marly loam, on the low rises of the Miami Rock Ridge, is the better card: moderately well drained, limestone at about seven inches, water held in the bedrock at 40 inches or more. Tamiami muck and Udorthents-urban land fill out the map. Across most of the urbanised county the hydrologic soil group is C or D — slow to very slow infiltration — with A and B only where sand or rockfill has been brought in.

Water Table: USGS monitoring wells in the Biscayne aquifer put the water table generally two to six feet below land surface across Miami-Dade, with medians near four feet in the central county and under three feet in the south, and wet-season minimums that come within a few inches of the ground. Florida requires 24 inches of unsaturated soil between the bottom of a drain field and the seasonal high water table for a new system. Because a typical drain field bottom sits 18 inches down, the county's own vulnerability work treats a system as compromised once wet-season groundwater comes within 42 inches of the surface — a threshold much of Miami-Dade already crosses in an ordinary summer.

Climate Impact: Miami's climate is tropical to humid subtropical, with a mean annual temperature around 77-78°F and roughly 60 inches of rain a year, the large majority of it falling in a wet season that runs May through October. Dry-season months often stay under three inches while late-summer months average eight to ten. That distribution matters more than the annual total: a septic system here is not asked to handle 60 inches evenly, it is asked to keep working through months when the ground is already saturated and the water table is at its seasonal peak. Add a hurricane season that regularly pushes storm surge and days of standing water across low-lying neighbourhoods, and the design problem is drainage under saturation rather than drainage overall.