LIMESTONE/KARST AREAS IN THE NEW JERSEY
HIGHLANDS
David Peifer
Project Director
Association of
(973)539-7547
10/26/06
Problem:
Substantial areas of the New Jersey Highlands area are underlain by what are known to geologists as carbonate rocks. These rock formations, consisting primarily of limestone, dolomite, and marble have unique characteristics that require responses from the Council at both the policy level and in specific technical guidance to municipalities.
Widespread Presence in the
According to NJDEP, (appendix
A, RSIS Standards), 59 of the 88 municipalities within the
Subsidence and Sinkhole Formation
Areas underlain by carbonate
rock may contain surface depressions and open drainage passages making such
areas unstable and susceptible to subsidence and surface collapse. As a result, the alteration of drainage
patterns, placement of impervious coverage, grade changes or increased loads
can result in land subsidence and sinkhole formation.
Groundwater Concerns
Fractures and solution
openings in these formations result in the rapid downward flow of surface water
to aquifers. In carbonate rock areas
this condition can lead to rapid and extensive pollution of groundwater.
Additionally, due to the
voids and solution channels present in these formations, there may be a large amount
of groundwater present in a rapidly
moving aquifer. Groundwater flows through these underground channels as if
were in pipes. In situations where the
carbonate rock is overlain by permeable materials, such as glacial sands and
gravels, high yielding aquifers may be present.
Examples if these conditions are present at the Allamatong Wellfield and
the Flanders Valley Wellfield (Morris County MUA). These prolific aquifers have extraordinary
significance as water supplies and are extremely vulnerable to contamination.
Surface Water Inter-relationships
These aquifers contribute
large quantities of base flow vital to water supply during drought. These flows are significant for ecologic
reasons. In particular, these flows
contribute to the maintenance of stream temperatures within the proper range
for trout reproduction and maintenance.
Scenic Qualities
In addition, carbonate rock
areas often contain specialized scenic developments with unique topographic
features and offer opportunities for outdoor recreation. More commonly, they occupy valley bottoms,
producing dramatic contrasts in relief and valuable scenic vistas, especially
when viewed from the higher elevations of the ridges.
Known Problems
Lack of understanding of the
location, character and values of these formations has lead to serious
consequences worldwide and within the
·
Collapse or
subsidence of structures, including buildings, roadways and underground
utilities.
·
Contamination of
groundwater from agricultural operations.
·
Contamination of
groundwater from septic systems.
·
Contamination of
groundwater from hazardous materials.
II. Policy
Issues
Steep Slope Avoidance
Because carbonate rocks
weather more rapidly that the older, precambrian rock that underlies the ridges
of the
·
Traditional
environmental planning practices of avoiding steep slopes tends to favor
development in carbonate rock areas .
Wetland and Surface Water Avoidance
Because groundwater recharge
is relatively rapid, in many cases few surface waters or wetlands are present
in carbonate rock areas. Although large
amounts of groundwater are present, little is visible on the surface.
·
Applying
environmental planning that avoids wetlands and surface waters tends to favor
development in carbonate rock areas.
Application of the Nitrate Dilution
Model
Application of a nitrate
dilution model usually results in smaller lot sizes in carbonate areas since
because the dilution equations favor smaller lots where more groundwater is
present. This has the potential to
“load” the best aquifers in a region with more development. Development of these aquifers today will
compromise their utility as water supplies in the future
·
Application of
nitrate dilution model policies tends to favor the most intensive development
(using septic systems) on the valuable carbonate aquifers
Farmland/Agriculture
Highly productive
agricultural soils (Class II or Class III) often overly carbonate rock, having
weathered from the parent material in place.
Protection of “prime farmland” as a policy objective will favor farming
as a use in these areas. While preserving the land is a desirable goal, the
agricultural practices employed should recognize the critical nature of the
underlying geology.
·
Agricultural
activities, favored by “prime farmland” preservation approaches, do have the potential
to contaminate the underlying groundwater, rapidly entering the groundwater
through sinkholes and solution channels.
Transportation Criteria
Due to the gentle topography
and low relief typical of carbonate areas, transportation systems, especially
roadways and railroads historically tended tend to follow the gentler
topography of the carbonate rock formations.
In the
·
Planning
policies that favor proximity to transport as a desirable condition for growth
may select for carbonate geology.
Stormwater Management
Concentrating stormwater
run-off on carbonate rock areas can induce “sink-holing” and subsidence. Attempting to induce recharge without an
understanding of the constraints of the sub-surface geology can have negative
impacts on water quality. Current stormwater policies that favor induced
recharge can have disastrous consequences in carbonate areas.
·
Stormwater
recharge approaches should be carefully screened and selected prior to approval.
RSIS Inadequacy
RSIS regulations 5:21-1.6
(Development Over Limestone Geologic Formations) recognizes the importance of
proper planning and standards. However,
the RSIS defers specific ordinance development to each municipality. Specific ordinances “shall be referred to the
technical committee and recommended to the Site Improvement Advisory Board for
approval”. This approach is cumbersome
and will result in case by case decision making and differing and possibly
incompatible approaches throughout the region.
·
The council
should prepare a model carbonate geology ordinance using existing work and
require adoption during the conformance process in the 59 towns that contain
carbonate rock.
Policy Summary
In sum, traditional
“critical areas” planning has the potential to select carbonate rock areas as
“suitable or desirable” for development.
Without a clear policy recognition of the critical value of these
resources future water supplies and important ecological values will likely be
compromised. From a regulatory
perspective all surface activities have at least some potential to harm the
resource and, if improperly conducted, may result in severe impacts on private
and public property such as buildings, underground utilities and roads, scenic character and water
quality. Other land uses, such as
agriculture, conducted without consideration of the resource, will also risk
contamination.
III.
Suggestions for the Council
·
Establish a policy statement in the RMP that
recognizes the critical nature of carbonate rock formations, including, at a
minimum, their values as:
o
Water supplies
o
Agricultural lands
o
Scenic resources
o
Ecological
values and:
Recognizes the critical nature of
these areas, including;
o
Sensitivity to subsidence and collapse.
o
Sensitivity to contamination from all surface
activities
o
Contribution of base flow
·
Map carbonate rock areas (and areas that contribute
water to them) on the Land Capability Map and classify them as “critical
areas”.
·
Prepare a model carbonate rock ordinance and require
its adoption as part of plan conformance based on the model developed by NRCS
(attached)
