B09_40571653_AM02_Questions_and_Responses_0002.pdf

140P1322Q0008

Attachment 4

CAVE Geophysical Survey Services

140P1322Q0009

Questions and Responses

1. The use of GPR in evaporites and in areas of interbedded shales may result in limited depth of investigation due to the radio wave signal being absorbed or changed to heat.

Since the depth of the GPR investigation may be potentially compromised should ER be considered in paved areas?

There will be no evaporites within the survey area. All of the bedrock is limestone with very shallow soils. GPR should be used in paved areas.

2. Conducting ER in paved areas requires ½ inch holes to be drilled into the pavement a minimum of 6 in and preferably deeper. The holes are typically filled with an asphalt caulk sealer after removal of the stakes. Is this acceptable.

No ER will be used in paved areas, only GPR.

3. Holes may need to be drilled outside of paved areas in potentially sensitive areas as well due to the caliche in the area, will this be an issue?

There is no caliche in the area of the survey. Stakes will have to be inserted in all non-paved areas.

4. If limestone is encountered at the surface the use of alternate methods to direct current into the subsurface, such as bentonite slurry or similar materials may need to be employed. Is this a problem?

Potentially. Should this occur during work, the contractor shall alert the CO and the COR prior to proceeding.

5. During the use of ER at least 8 to 12 trips of potentially 3 personnel are required along the ER line to lay out tapes, set stakes and drive stakes, deploy cables, hook cables to stakes, apply water to the area around the stake (to reduce contact resistance) potentially several times, determine elevations and locate lines with DGPS. The process is then reversed to remove equipment. These steps can cause soils, flora and fauna to be trampled. Will damage to soils, flora and fauna along the ER lines need to be repaired?

The contractor shall work around larger plants and not damage them, as well as minimize trails and trampling. It is expected that if there are large areas of damage created, the contractor would make the required repairs. Please refer to FAR 52.237-2 in the RFQ, which will also be in any contract resulting from this RFQ.

6. In order to obtain good contact resistance for collection of acceptable data the area around the stakes must remain moist during data acquisition. This will require sufficient water to keep the area moist and a means of transport to the ER lines and a means of deployment to the stakes. May a UTV (side by side) be used to transport a water tank adjacent (as close as possible) to the lines? Will water be available in sufficient quantities at the park? Will water being applied in the areas be a problem?

Water will be available from sources close to the areas being surveyed. Most all areas can be approached from nearby roads, parking lots, or trails. UTVs are not allowed off of these established routes (see Prohibition of All Terrain Vehicles in the RFQ). Short hauls will be necessary. Water could be hauled using backpacks or large, soft-wheeled non-motorized vehicles (Note - there are lots of cactus and yuccas in the area).

7. In order to detect a void 50 feet in diameter at depth lines need to be less than 50 feet apart so at least one line crosses the void. If ER is not used in the parking lots and GPR depth is limited will the inability to detect deep voids in parking areas be an issue?

Typically, if a subsurface void is detected in multiple ER lines on either side of the parking lot it can be inferred that the void continues across the area. With the dominate fracture patterns and cave passage development being rather obvious, would this be an acceptable inference? Are cave maps available in KMZ format? This allows better orientation of the ER lines to intersect dominate passages at perpendicular angles.

KMZ files are available upon request. The NPS anticipated GPR would be used in the parking lots, and the contractor wouldn't be able to achieve the same depths below those paved surfaces.

8. In the ER method non-uniqueness is a problem that allows for two or more solutions to a model. A dry competent limestone can have the same properties as a dry air-filled cave as both define resistive conditions. In areas of high humidity, the air moisture will condense on the side of the cave and make them mostly conductive. However, in the dry desert environment caves can and do appear very resistive. The problem of non-uniqueness is resolved by collecting differing physical parameters such as density resolved with gravity

(expensive) or surface wave velocity resolved with ReMi or MASW (less expensive).

Should solutions to potential non-uniqueness be a consideration?

The contractor shall determine their method for performing the work in accordance with the SOW.

9. In order to prepare an extreme (hot or cold) weather safety plan what time period do you foresee the project starting?

Work shall be completed each day by 5:30 PM during the bat flight seasons (April-

October). If coordinated, work may begin as early as 6:00 AM. Temperatures and bat issues would be greatly reduced outside of the bat flight season dates. However, this project will most likely be during the summer, fall and is expected to be substantially complete before winter.

10. We use a wheeled garden cart to transport the ER equipment from line to line. Is this acceptable?

Yes, if the wheels are large, soft rubber wheels (Note - there are lots of cactus and yuccas in the area).

11. If ER lines are required to cross walkways and roads, we typically use cable protectors requiring vehicle traffic to drive very slowly over the protectors. Is this an issue?

Not for sidewalks. There is no requirement to survey below roads.

12. Current conductive utilities can cause noise in the ER system. Will utilities be marked?

The NPS can provide the best knowledge of utilities annotated on maps. There are park owned utilities, so the local utility companies do not have records of everything on site.