In this section
Boulder Spring main view
Boulder Spring is a fifth-magnitude spring. The spring head is a small pool in an area of limerock outcrop, with large limestone boulders in the spring pool and run. Water flows from vents at the base of the hillside and in sand boils in the spring run as it flows about 0.3 mile toward the northwest to Sulphur Run.
Boulder Spring run
Discharge at Boulder Spring was measured by St. Johns River Water Management District in 2003, 2005, and 2008. The mean and median discharge was 0.23 and 0.32 cubic feet per second.
Boulder Spring was sampled once in 2004 by Lake County and once in 2005 by the district. Summary statistics of the water quality data for selected variables are shown in the table below.
Summary statistics of water quality and discharge at Boulder Spring
|Alkalinity, total, mg/L as CaCO3||120.0||120.5||120.5||121.0||2||2004−2005|
|Calcium, total, mg/L as Ca||98.8||98.8||98.8||98.8||1||2005|
|Chloride, total, mg/L as Cl||110.0||114.5||114.5||119.0||2||2004−2005|
|Magnesium, total, mg/L as Mg||25.4||25.7||25.7||26.0||2||2004−2005|
|Nitrate + nitrite, total, mg/L as N||0.07||0.08||0.08||0.10||2||2004−2005|
|Orthophosphate, total, mg/L as P||0.06||0.06||0.06||0.06||1||2005|
|Phosphorus, total, mg/L as P||0.18||0.18||0.18||0.18||1||2005|
|Potassium, total, mg/L as K||2.4||2.7||2.7||2.9||2||2004−2005|
|Sodium, total, mg/L as Na||63.3||64.5||64.5||65.7||2||2004−2005|
|Specific conductance, field, µmhos/cm at 25°C||989||1015||1015||1041||2||2004−2005|
|Specific conductance, lab, µmhos/cm at 25°C||1041||1041||1041||1041||1||2005|
|Sulfate, total, mg/L as SO4||216.0||216.2||216.2||216.4||2||2004−2005|
|Total dissolved solids, mg/L||619||675||675||730||2||2004−2005|
|Water temperature, °C||22.7||22.9||22.9||23.0||2||2004−2005|
mg/L = milligrams per liter
cfs = cubic feet per second
Age of discharge water
The age of water discharging from Boulder Springs was determined by measuring the concentration of tritium, carbon-14, and carbon-13 in the spring discharge, which was measured in March 2005. Boulder Springs had a tritium concentration of 0.51 tritium units, a carbon-14 concentration of 29 percent modern carbon, and a delta carbon-13 value of −9.78 parts per thousand. The tritium concentration suggests that the water is between 40 and 70 years old. The carbon-14 concentration of 29% modern carbon can result from the reaction of rainfall with calcite, dolomite, and soil organic matter and from the mixing with Lower Floridan water.