B08_Attach_6_Geologic_Survey___Drilling_Approach.pdf

B

Geologic Survey and Redundant Well

Drilling Approach

Memorandum

Date: 10/29/2021

Project No.: 20694B

To: Ed Whatley, PE; Vik N. Desai, PE

From: Greg Smith

Subject: Geologic Survey and Redundant Well Drilling Approach - Sandy Hook, NJ

Project Summary The Gateway National Recreation Area (PWS ID# NJ1331001), operated by the National Parks Service (NPS) is a public drinking water system permitting by New Jersey Department of Environmental Protection (DEP) and serving the Sandy Hook Unit in Highlands, New Jersey (the water system). The water system is currently served by one drinking water well, identified as well 5A. Well 5A was constructed in 1970 approximately 30 feet from Well 5 which was constructed in 1942 and is considered by DEP to be decommissioned. Well 5 and 5A Well Record

Drawings are found in Attachment A. Historically the water system was served by several other wells that have been either taken offline or decommissioned. The goal of the project is to provide system upgrades and to decommission existing abandoned Well No 4 and construct a redundant/backup well for Well No. 5A in accordance with DEP regulations.

Geology of Sandy Hook, NJ The known geology of Sandy Hook (shown below) consists of younger beach and estuarian soil deposits (Qbs-Qpg) underlain by a thin layer of older glaciofluvial gravel (~10-12,000 years old) in some areas. Beneath these sediments are Cretaceous age coastal plain sediments (Kns-Kmg) deposited 66 to 145 million years ago. Well 5A is located at the Pump Station (shown below) and is screened in the coastal plain sediment complex.

Johnson et al. 2018. The role of sediment compaction and groundwater withdrawal in local sea-level rise, Sandy Hook, New Jersey, USA – Quaternary Science Reviews 181 (2018) 30-42.

Memo: Geologic Survey and Redundant Well Drilling Approach - Sandy Hook, NJ

The aquifer that well 5A is screened in is confined underlying significant clay layers (Attachment A). Given the elevation at the site, and assuming that the maximum elevation of the groundwater table in the area is 10 feet above mean sea level (amsl) based on contours and wetlands present at the site, the depth to salt water can be estimated using the Ghyben-Herzberg Relation:

z = 40h

• z is the depth to the salt water/freshwater interface

• 40 is derived from (df/ds-df) where df = density of fresh water and ds = density of salt water

• h is the freshwater groundwater table above sea level.

Given this equation and the estimated groundwater table, the saltwater interface (z) is approximately 400 feet below amsl. This indicates that well 5A is screened more than two times deeper than the salt-water interface. Well logs indicate that significant clay layers are present at the site and that the well is screened below two significant clay confining layers.

This indicates that the confined aquifer must be expansive, and the confining layers competent over a large area to not have saltwater intrusion occur after operating for almost 80 years. The confining clay may extend continuously onto land in the west where recharge to the well is occurring. This hypothesis is supported by the presence of the

Cretaceous coastal plain complex mapped on the mainland to the southwest in Middletown NJ as shown on the published 1964 USGS Geologic Map and Cross section of the Sandy Hook Quadrangle, Monmouth County, New

Jersey (Attachment B).

Decommission Well No.4 Well No. 4 is located in a vaulted concrete structure approximately 4 feet below ground surface. An access hatch in the roof used for maintenance, or the bulkhead located at ground surface to decommission the well. This configuration is not anticipated to result in additional costs for decommissioning the well. Well No. 4 was drilled in

1941 and is reported to be ~481 feet deep below ground surface (bgs) at the time of drilling. The well log is included in Attachment C. The total well depth is likely less than reported (~4 feet less) due to the vaulted structure and possibly due to grading during structure construction.

The well was constructed with 12-inch diameter casing to 227 feet bgs. 8-inch diameter casing was installed inside the 12-inch diameter casing from 188 feet bgs to ~321 feet bgs. 155 feet of undetermined well screen type or slot-size was installed below the 8-inch diameter casing to approximately 481 feet bgs. The diagram appears to show that the well screen is completed with a lead packer, however the diameter of the well screen is not reported.

Generally, the most important parameters for well decommissioning are the length and diameter of casing and screen. This is used to precisely estimate the time and materials to decommission the well. Given that the well screen dimeter is undetermined may result in questions from bidders. The actual volume range for materials is dependent on well screen diameter and ranges from 0.5 to 2.0 cubic yards, respectively for 4-inch and 8-inch diameter well screens. However, this is not likely to result in significant variability in cost but should be adequately addressed in the bid-specifications to avoid change orders.

Typically, well screens are backfilled with gravel, graded to fine sand above the well screen and grouted. This is to avoid grout loss to the formation. A licensed well driller is required to perform the work in accordance with N.J.A.C

7:9D. The driller must hold a Master Drilling License in the state of New Jersey. The driller will be required to submit a proposed decommissioning plan for approval based on the following requirements:

1. The well casing reportedly broke per 7:9D (j) 5.

2. Well 4A is a “multiple cased well” 7:9D (j) 6.

Steven Reya is the contact for well decommissioning at the NJ DEP (Steven.Reya@dep.nj.gov).

Well No.5A Backup Well Well 5A was drilled in 1970 and reported to be 878 feet deep with 40 feet of 10-inch diameter stainless steel 8-slot shutter/louver type well screen. A larger diameter well casing was drilled to facilitate a surface seal, likely 36-inch diameter to 140 feet bgs. The well was drilled to 826 feet bgs using 24-inch diameter casing, with 140 feet of 24” diameter well casing left in place (LIP). 16-inch diameter casing was drilled to a total depth of 911 feet bgs. The well was backfilled to 878 feet where 40 feet of 10-inch diameter stainless steel shutter/louver well screen was exposed. 20 feet of stainless steel, with ~98 feet of black steel riser extends into the 16-inch diameter well casing to approximately 720 feet bgs. A total of 16-inch diameter steel casing was left in place. The annulus between the 24-inch and 16-inch diameter casing was grouted. The well log is included in Attachment A.

The following are some key points for developing specifications for drilling the backup well:

• To be considered a backup source (synonymous with replacement well) and not a new source, the well would need to be located within 100 feet of the existing well and constructed in the same aquifer to meet DEP Minor

Allocation Permit requirements. Significant permitting and testing required if the well is drilled at a distance greater than 100 feet.

• We recommend primary and secondary drilling locations. The first well will be drilled with a pilot bore. The suitability of the well location will be assessed using soil sieve analysis and borehole geophysics of the piolet bore.

• The aquifer is confined underlying a significant clay layer, the well seal was likely extended down to this layer to prevent salt water intrusion. Given the elevation at the site, we assume that the maximum elevation of the groundwater table in the area is 10 feet above mean sea level based on contours and wetlands present at the site.

• The well seal was extended down through the lowest confining layer (clay to 826 feet bgs or as encountered in the well bore) to prevent salt-water intrusion from occurring in Well 5A, which is screened twice as deep as the freshwater/saltwater interface. A competent well seal through the deepest clay layer above the well screen and care during drilling is critical to ensure water quality of the new backup well and will be a critical component of drilling and constructing the new well. Driller’s experience with similar conditions on other deep wells is required.

• One driller (Unitech) was identified with the capability to perform this work, however at least one other driller was identified by NJ DEP (A.C. Schultz) capable of drilling wells of this size and depth. Over a dozen drilling companies were contacted. Estimated project cost was provided based on constructing the well with identical parameters. However, others may be able to complete the work that may not have been identified. As such, to provide the possibility for competitive bidding, careful thought needs to be put into the drilling and well construction specifications to provide a quality well but allow for variability in design or approach that would be equivalent.

• Drilling is to be completed using mud rotary with reverse circulation in the productive formation. Reverse circulation will be an important part of the specifications to prevent ‘clogging’ the productive formation with drilling mud.

• Prior to drilling the well, a Permit to Construct is required under a Minor Modification Application. This has a 30 to 60-day lead time for approval for this permit. However, NJDEP has a 90-day review period. The Permit to

Construct is valid for 5 years.

• A 6-8 hour step test is to be performed to assess specific capacity once the well is constructed to confirm yield.

• A 24-hour pump test at a rate of 120% of the well yield or a 72-hour pump test at 100% of the well yield is required by DEP Bureau of Water System Engineering.

• Pump testing would require setting a temporary pump, drop pipe, discharge and approved flow measurement equipment. We recommend using a generator as a power source to allow the existing power system to run well

5A and ensure an uninterrupted pump test. The DB Contractor will be required to submit a pump testing plan for NPS and engineer review.

• A full suite of water quality samples is required at the end of the pump test. NJ DEP will also collect a set of water quality samples from the well.

• A final report summarizing well construction, well performance and water quality is to be submitted following testing.

The contacts at DEP who will be involved in this project are:

• Nasir Butt Bureau of Water System Engineering Nasir.Butt@dep.nj.gov

• James McDonald, Bureau of Water Allocation and Well Permitting James.MacDonald@dep.nj.gov

• Jennifer Myers Bureau of Water Allocation and Well Permitting Jennifer.Myers@dep.nj.gov

• Steven Reya Bureau of Water Allocation and Well Permitting Steven.Reya@dep.nj.gov

• Barbara Ware Bureau of Water Allocation and Well Permitting Barbara.Ware@dep.nj.gov

Final Well Infrastructure Following the successful drilling and permitting of the well, the final pump, level transducer and well head should be completed. There is some risk associated with completing this work in advance of receiving a final permit and the responsibility will be assigned to the contractor. Pump depth setting and design should be based on actual head conditions.

mailto:Nasir.Butt@dep.nj.gov mailto:James.MacDonald@dep.nj.gov mailto:Jennifer.Myers@dep.nj.gov mailto:Steven.Reya@dep.nj.gov mailto:Barbara.Ware@dep.nj.gov

Attachment A

Well 5A and 5 Record Drawings

Attachment B

1964 USGS Geologic Map and Cross section of the Sandy Hook Quadrangle

Attachment C

Well 4 Well Log