EXHIBIT 14-E

 

                   MONTEREY PENINSULA WATER MANAGEMENT DISTRICT

 

 

                                                           MEMORANDUM

 

Date:               August 6, 2012

To:                  David Stoldt, General Manager

From:             Joe Oliver, Water Resources Division Manager

Subject:          Response Comments to Technical Items in August 1, 2012 Appeal Letter from Judy and David Beech, re:  Flores and Pisenti Water Distribution System (WDS) Applications

 

·         Page 2, Background.  Regarding the pumping tests of the Flores/Pisenti Wells #1 and 2 that were conducted in October 2010, it is important to note that these tests were conducted simultaneously for 72 hours at constant pumping rates that were 5 to 6 times the dry-season demand rates for these WDSs[1].  Accordingly, drawdown effects from this testing would have been commensurately greater than under the anticipated operating conditions for these WDSs.

 

·         Page 3, Failure to Comply with Documentation of Drawdown and Recovery.  The discussion states recovery measurements were not continued until 95% recovery was achieved.  MPWMD concurs that the wording in the “Documentation of Drawdown and Recovery” section of the Procedures document does not clearly convey the intended requirement.  The intention of the statement in question is clarified by the highlighted additional phrase as follows:

Water-level recovery data shall be measured until the recovering water level in the pumping well reaches 95% of the pre-test static water level or two times the pumping period has elapsed, whichever occurs first.

It was not the intention that water-level recovery measurements must be made for an indefinite period of time until the recovering water level reaches 95% of pre-test level, as in practice this could require a considerably longer period than twice the pumping period and be difficult to achieve in some instances for reasons that would not affect the validity of the pumping test calculations (e.g., existence of other documented or undocumented pumping affecting the well’s recovery measurements, natural seasonal water-level declines of the groundwater system superimposed on the recovery curve).  It is important to note that there is no certainty that a given well’s recovery rate (fast or slow) is directly relatable to the sustainability of the well’s yield.  For example, it can be argued through hydraulic theory that a well tapping a relatively small effective storage system of a fractured-rock network could achieve a higher post-test recovery rate due to the faster refilling rate of this smaller volume system, compared to another well tapping into a relatively large effective storage system that achieves a slower post-test recovery rate due to the larger storage volume in that system.  Which of these two wells is more reliable in terms of a sustainable supply?  Regardless of this uncertainty as to whether a well’s recovery rate is a valid and appropriate gauge of a well’s sustainability, MPWMD has opted for consideration of reducing the calculated well yield in cases where 95% recovery has not been achieved after two times the pumping period, as an additional conservative measure to hedge against this uncertainty.  It should also be noted that the precise role that post-test recovery data should play in evaluating a well’s yield is not well defined and agreed upon in the professional hydrogeologic community.  MPWMD plans to continue research and explore refinement of this aspect of well source assessments as part of future planned updating of the Procedures.  As part of this update, the language associated with the time period during which recovery measurements must be made will also be clarified.

 

·            Page 4, Relief Requested.  Item 3 requests 95% recovery within 6 days shall be demonstrated by actual measurements for Well #1 and 2 with no use of estimates.  See Page 3 response comment above.  Also, it should be noted that the relative efficiency of water-level recovery after pumping only affects the well-yield calculation; it does not affect the calculation of predicted drawdowns (i.e., offsite water-level effects) in the vicinity of the pumping well.

 

·         Page 5, Relief Requested.  Item 4 requests that “well capacity shall be determined by the actual pumping rates chosen for tests, with no use of estimates”.  This request does not conform to standard hydrogeologic practice and may reflect a misunderstanding of well hydraulics and aquifer analysis.  It is the principle purpose of aquifer testing to utilize actual pumping test derived data (pumping rate, water-level drawdown, specific capacity) to calculate hydraulic characteristics of the aquifer (transmissivity, hydraulic conductivity, storativity) in order to determine well yield and predict drawdowns from well operations[2].  By its nature, this is an estimating process in that actual pumping test data are utilized to determine (i.e., estimate) well yield and time and distance drawdown relationships.  Setting a well yield equal to the rate that was achieved during a short-term pumping test is not standard hydrogeologic practice and can result in erroneous well-yield determinations that could be greater than the recommended well yield based on calculations from the pumping test data.

 

·         Page 6, Detailed Grounds for Appeal.  The exercise provided under “Failure to comply with Documentation of Drawdown and Recovery” ignores important hydrogeologic considerations.  The example calculations on Page 6 show changing percent recovery, but this example does not consider that other hydrogeologic parameters used to calculate well yield would be expected to change as the percentage recovery declines.  Both Specific Capacity and the late-time to early-time transmissivity ratio (affected by the steepening slope of the drawdown curve) would be expected to decline under such circumstances, and would result in lower calculated well yields.  In other words, it is incorrect and misleading to hold the calculated well yield “static” while reducing the percentage recovery, as the parameters used to calculate well yield would not be expected to remain static under changing recovery conditions, such as is assumed in the example provided.

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[1] Well #1 test pumping rate = 8.1 gpm, 6.6 times dry-season demand rate of 1.23 gpm; Well #2 test pumping rate = 6.3 gpm, 5.4 times dry-season demand rate of 1.16 gpm.

[2] Suggested reference sources for well hydraulic theory and pumping test applications include:

Sterrett, Robert J., 2007.  Groundwater and Wells, 3rd Edition; see page 179.

Kruseman, G.P. and N.A. de Ridder, 1994.  Analysis and Evaluation of Pumping Test Data, 2nd Edition; see page 27.