Mohawk Late Receipt Prebid Questions for Relief Wells.docx

Mohawk Late Receipt Prebid Questions – Geotechnical Responses

· Is it permissible to use a tight wrap (0 slot) well screen for those wells that have a blank section of screen specified?

If 0 slot well screens provide adequate strength and would not allow clay and silt size particles into the well, they could be considered. However, a submittal would be required for review prior to construction.

· Because the slot size of the screen is specified by the USACOE, will the contractor be compensated on an hourly basis for extra development time if the wells make sand or otherwise do not clean up in a timely manner?

Additional surging and pumping development time have been added to items 26 and 27 of the bid sheet. Development surging and pumping time will be compensated on an hourly basis at the negotiated contract rates. The Contractor will still need to notify the COR when it is anticipated that the quantities of development time are expected to be exceeded, in advance to exceeding the contract quantities.

· With respect to drilling fluids, Section 3.1.6 states that “Drilling fluids are not permitted until sand heave occurs …” With the cable-toll drilling method, the only fluid we will use is water. However, we may wish to use water when drilling in shallow clays above the water table. Is this permissible?

The use of water above the groundwater table in the well drilling would be permissible.

· Section 3.4 DEVELOPMENT of the specifications states that “The Contracting Officer may order that wells which continue to show no significant improvement after 48 hours of development be abandoned in accordance with the Paragraph “BACKFILLING OF ABANDONED WELL HOLE.” However, items 26 and 27 of the bid sheet – Development Surging, and Development Pumping – list estimated quantities of 30 hours and 60 hours, respectively. Do the 30 and 60 hours refer to the total amount of development time for the entire project, or is this a per-well estimate? If it is a total amount, how does this reconcile with the 48 hours of development time referenced in 3.4 DEVELOPMENT?

The 48 hours of development is in reference to total surging and pumping per individual well. The previous hours for surging and pumping did not agree and have been increased. Total surging and pumping development time has been increased to 160 and 320 hours, respectively. This is cumulative time for all new wells.

· We did not see information on the quantity of chemicals that are required. Is this specified?

The quantity of chemicals is not specified. It shall be included in the development unit prices.

· Section 3.4.1 Chemicals refers repeatedly to “chemicals” as a plural, however, only one type of chemical is specified – “a commercial liquid polymer phosphate free dispersant”. Are other types of chemicals specified? If so, in what quantity?

No other chemicals are specified. No quantities are specified. Chemicals was stated as plural in the case it was deemed necessary by the driller that additional chemicals are necessary. All proposed chemicals will still need to be described in the well installation plan as described in Section 1.3.1 of the Relief Wells Specification and reviewed by USACE prior to construction.

· In general, we are having difficulty interpreting the intent of section 3.4.1 Chemicals. At a bare minimum, we must add the chemical, wait 24 hours, and then agitate for a minimum of two eight-hour intervals. This requires a minimum of 16 hours of surging per well, or 160 total hours of agitation for the project. In Section 3.4.2 Surging and Pumping, additional surging is specified. How much surging time will be required per well, assuming that the well clears up in a timely manner? How much pumping time is required per well, again assuming the well clears up in a timely manner?

As previously stated, well development surging and pumping times have been increased for items 26 and 27 in the bid sheet.

· A 36-inch permanent casing is referenced in section 3.5 CONCRETE BACKFILLING. Is this a typographical error? Should this read “30-inch”?

The permanent casing should read “30-inch”.

· What criterion will be used to determine when “static water levels shall have completely recovered”, as referenced in the third paragraph of 3.6.1 Step-Drawdown Pump Test?

Static water level would be whenever water within the pumped well has returned to within 0.2 ft. of prior to pumping condition (expected within 15 minutes based on results from well pump testing performed at other glacial outwash projects in the Muskingum Area).

· Similarly, what criterion will be used to determine when the drawdown has stabilized for each step?

Drawdown will be considered to have stabilized whenever the drawdown rate is equal to or less than 0.1 feet/10 minute interval. In the specification, it is anticipated that a minimum of 1 to 1.5 hours per step should be used.

· Section 3.6.1 Step Drawdown Pump Test, states that “Pump tests and data analyses shall be conducted using established accepted procedures.” Will only the step test require an evaluation, or will the nine specific capacity tests also require evaluation beyond just calculating the specific capacity?

Only the step test will require an evaluation. The nine specific capacity tests will only require a specific capacity evaluation.

· Who will specify the pumping rate at which the nine Specific Capacity Pump Test are to be run?

It is anticipated that the maximum 1,800 gpm flow rate referenced in 3.6.2 will be used for the specific capacity pump test. The COR will have the final say for the specific capacity pump test.

· What is meant by the “end of each intermittent pumping” in the first line of 3.6.3 Sand Test?

Intermittent pumping would be a case where a well would have to be incrementally pumped to produce the desired flow (to simulate high pool loading flows) in a lower permeability aquifer. This was standard specification language and is not expected to be the case at Mohawk.

· Is the pumping in 3.6.3 Sand Test separate from the Specific Capacity Pump Test, or can they be combined?

The sand test can be combined with the specific capacity pump test.

· Given that many vendors are working from home during the COVID-19 pandemic and timely responses to questions and requests are difficult, will the USACOE consider extending the bid date?

Due to time and schedule constraints, the bid opening will remain at 2:00 p.m., June 4, 2020.

Pre-Bid Atendees