MEMO TO: MGG
RE: SWFWMD (R)
Establishment of Mean Low Level for Ground Water
FROM: LMB
January 16, 1970
Yesterday I met with Garald Parker and Dr. Joseph Rosenschein,
HydrologistinCharge, U. S. Geological Service, Tampa, for
discussing the procedures for establishing the mean low level
for ground water at given points in connection with the new
St. Petersburg well field. This is authorized by Section
373.081(10), Florida Statutes.
This Section 373.081 is the definition section but states:
"When required for the purpose of this law,
the Division shall determine and establish
the mean of low level for ground water at
a given point. The mean low level...shall
be the level...below which the lowering of
the ground water level will cause irreparable
damage to adjacent land owners or contamination
of the water source...." (Emphasis added.)
After lengthy discussion it was agreed that the Chief
Hydrologist will do the following:
1. Determine the extent of each proposed well field
and plot the location of proposed production wells in relation
ship to the perimeter of the property.
2. Plot locations for proposed observation wells along
the perimeter of the property at points nearest the location
of proposed production wells.
3. Require that these proposed observation wells be
constructed in such manner as to penetrate the strata of
aquifer as the nearest production well.
4. Plot a crosssection profile to show the typical
draw down cone of depression for the particular well field area.
5. Recommend to the Board the amount of draw down to
be allowed at the perimeter of the well field. (This could
remain a constant figure adopted by the Regulatory Board
and applied to each of the respective well fields.)
6. Calculate a reference base by selecting three or
four wells to be identified as key base wells. These should be
existing wells which are being monitored by USGS. They should
be of sufficient distance from the well field so as not to be
materially affected by the draw down of the proposed well field.
If necessary, an adjustment factor should be established to ad
just differences between the proposed well field and the key
base wells.
7. The adjusted reference base is then recalculated each
month by finding the average of the lows for each of the key
base wells for the last day of the preceding month. A pre
determined adjustment factor is then applied to determine the
adjusted reference base for the current month.
8. The allowable perimeter drawdown is then subtracted
from the monthly adjusted reference base to determine the
calculated mean low level at the point of the observation well.
9. Each observation well must be monitored so as to
determine the actual mean low level of each observation well.
This is calculated by averaging the monthly lows of the
observation well.
10. If the actual mean low level for an observation
well is lower than the calculated mean low level, pumping for
the following month would have to be curtailed.
When these steps have been completed the mean low level
of the ground water at the point of each observation well could
be established by adoption of a formula. Use of this formula
would then give flexibility to allow for times of flooding and
times of drouth.
Calculations:
For example, on the first day of each month the Chief
Hydrologist would determine the average of the lows for the
key base wells for the last day of the preceding month.
Example:
Key Well No. 1 low for 12/31 14.8' m.s.l.
Key Well No. 2 low for 12/31 14.6' m.s.l.
Key Well No. 3 low for 12/31 14.2' m.s.l.
Key Well No. 4 low for 12/31 14.4' m.s.l.
4)5Tg
Reference Base Average T14.5' m.s.l.
Plus the adjustment
factor necessary to
determine reference
base for well field,
say + 0.4
Adjusted Reference Base 14.9' m.s.l.
Less the drawdown
allowable at peri
meter, say 3.0'
Calculated mean low
level of P.S. at point
of observation well 11.9' m.s.1.
The monthly lows for the observation well will then be averaged
to determine the actual mean low level for the observation well.
If the actual mean low level for the month is lower than the
calculated mean low level, pumping would be ordered curtailed
for the following month.
LMB:cs
