NC0001422_8-HydrogeologicInvestigationsPolicy-20070531_20150805

Michael F. Easley, Governor
William G. Ross Jr., Secretary
North Carolina Department of Environment and Natural Resources
Alan W. Klimek, P.E. Director
Division of Water Quality
May 31, 2007
MEMORANDUM
To: Aquifer Protection Section Central Office
Aquifer Protection Section Regional Supervisors
Construction Grants and Loans Section
Interested Parties
From: Ted L. Bush, Jr., Chief
Aquifer Protection Section
Subject: Hydrogeologic Investigati n and Reporting Policy
In response to the need for consistent evaluation of land based utilization and disposal sites as
well as other subsurface investigations, the Aquifer Protection Section has adopted the subject
policy dated May 31, 2007, to be utilized by both consultants preparing applications and
Division review staff. The subject policy reflects recent changes in the non -discharge rules with
the adoption of Subchapter 02T. This policy provides additional detail to the requirements in
Subchapter 02T. In addition this policy will assist with the preparation and review of other
subsurface investigations needed for reports submitted for Division review.
All permit applications and other site reports shall be reviewed in accordance with the attached
document for any Mplication received on or after August 1 2007. For any application received
prior to that time, staff should review the application for adherence to the policy and discuss with
the applicant and/or their consultants to encourage consistency with the policy.
Aquifer Protection Section 1636 Mail Service Center
Internet: www.ncwatMuality.org Location: 2728 Capital Boulevard
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Hydrogeologic Investigation and Reporting Policy
May 31, 2007
Table of Contents
page
Introduction and Purpose of the Policy...........................................................................................2
Elements of a Hydrogeologic Investigation....................................................................................2
(1) Define study objectives ........................................................................................................2
(2) Collect required data to prepare a hydrogeologic description..............................................3
(3) Develop hydrogeologic conceptual model ...........................................................................4
(4) Merge hydrogeologic conceptual model into a groundwater predictive model ...................6
(5) Report hydrogeologic investigation results ..........................................................................6
References .......................................................................................................................................6

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Introduction and Purpose of the Policy
Hydrogeologic investigations are often required in conjunction with the design of non-discharge
waste treatment and disposal systems pursuant to Subchapter 15A NCAC 02T as well as
investigations related to groundwater quality under the Division of Water Quality’s (Division)
regulatory purview. This policy is intended to supplement those and other Division rules when
conducting hydrogeologic investigations. This policy does not supersede Division rules.
The purpose of this policy is to improve the quality of hydrogeologic investigations submitted to
the Division, to better define the criteria used to evaluate proposed systems, and thereby better
protect the waters of the State. Past permit applications have revealed the need for consistent
Division policy, and this policy is intended to provide direction for all permit applications and/or
hydrogeologic investigations required by the Division. Adherence to this policy is mandatory,
and not following it may result in prolonged review, further site characterization, and/or
additional analysis.
Elements of a Hydrogeologic Investigation
The hydrogeologic investigation process involves five steps that are discussed individually in the
following paragraphs. Documentation of the investigation process and report preparation is
outlined in the next section.
In general, the hydrogeologic investigation should disclose sufficient site information to
characterize the geologic and hydrogeologic character of the area of interest, and, where
appropriate, lead directly to the proper construction of a groundwater flow and transport model.
The data required by the groundwater modeling process should be acquired in the hydrogeologic
investigation and documented in the hydrogeologic report. The following are the five steps that
should be included in the formulation of professional hydrogeologic reports:
(1) Define study objectives
(2) Collect required data to prepare a hydrogeologic description
(3) Develop hydrogeologic conceptual model
(4) Merge hydrogeologic conceptual model into a groundwater predictive model
(5) Report hydrogeologic investigation results
(1) Define study objectives
In this critical first step, complete and detailed objectives of the hydrogeologic investigation
should be specified. These objectives will dictate the level of detail necessary in the
investigation. These objectives should:
(a) Adequately address the regulatory requirements regarding documentation
required in the non-discharge permit application, and
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(b) Adequately address the regulatory requirements regarding the minimum design
requirements for the non-discharge wastewater treatment and disposal system
which, in general, address the following concerns:
(i.) ensure that the groundwater quality standards will be maintained at the
facility’s compliance boundary or at the point of discharge for systems
with no compliance boundary,
(ii.) estimate the zone of influence around an infiltration gallery/injection well
to ensure that the system does not result in a violation of the groundwater
quality standards beyond the compliance boundary or affected area; and
(iii.) ensure that the one foot water table separation will be maintained during
system operation.
(iv.) document areas of groundwater discharge to surface waters.
By defining the objectives in this manner, the professional should know whether or not minimum
design requirements can be met.
(2) Collect required data to prepare a hydrogeologic description
Hydrogeologic descriptions are required under portions of several sets of rules, including the
15A NCAC 02T rules that address wastewater irrigation systems (e.g., 15A NCAC 02T .0504
(e)), reclaimed water systems (e.g., 15A NCAC 02T .0905(e)), residuals management systems
(e.g., 15A NCAC 02T .1104 (e)(4)), groundwater remediation systems (e.g., 15A NCAC 02T
.1604 (c)), and certain types of injection wells (15A NCAC 2C .0211(d)). Depending on site
specifics, data collection could include the following:
(a) Published reports describing the regional geology and hydrogeology, reports on
local hydrogeologic investigations performed by consultants and government
agencies;
(b) Background information about the site, identification of the nature and extent of
all contaminants, identification of possible receptors in the surrounding area,
characterization of the geologic, hydrologic, and meteorological settings, first-
hand field observations supported by aerial photography, detailed county soils
maps, 1:24,000 USGS topographic map, and any other project maps to regionally
locate the site and designate contaminant and receptor locations (required),
rainfall data from nearby weather stations obtained to determine the nature of
rainfall patterns and estimate groundwater recharge, streamflow records from
nearby gauging stations to determine variability in flow if the risk to a stream is
being modeled;
(c) Sufficient number of bore holes drilled at the site to characterize site stratigraphy,
existing lithologies, and depth to bedrock or confining layers
[Note: The maximum depth of subsurface investigation is the maximum depth that
can be used in any predictive calculations or groundwater model for the purposes
of calculating groundwater mound height and for calculating contaminant
transport. For example, if a hydrogeologic investigation terminates its subsurface
investigation at a depth of 20 feet, the groundwater predictive model can only use
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a maximum subsurface depth of 20 feet also.] (See the http://www.ncwater.org/
website for regional stratigraphic information in the Coastal Plain);
(d) Sufficient number of wells or piezometers installed to determine prevailing
hydraulic gradients in the area, both horizontal and vertical, and an assessment as
to how these gradients may vary seasonally and over time (required); determine
the hydraulic properties of the aquifer(s) and aquitard(s) including the
transmissive and storage characteristics of the aquifer system, such as
transmissivity, hydraulic conductivity, storativity, and specific yield. An
assessment of heterogeneity and anisotropy over the aquifer domain for each
property should be made, particularly in the Piedmont and Mountain regions of
the State. Include one or more aquifer tests of 24-hour minimum duration with
sufficient observation wells to characterize horizontal and vertical isotropy for
determining aquifer parameters. Depending on the nature of the contaminants and
investigation objectives, slug tests or other such methods may be adequate to
estimate aquifer parameters;
(e) The depth to the seasonal high water table;
(f) An inventory of groundwater recharge sources (precipitation infiltration areas,
influent (“losing”) streams, surface water bodies, etc.) and groundwater discharge
mechanisms (wells, springs, groundwater discharge areas, effluent (“gaining”)
streams, etc.) within the area, and records obtained from any major sources
withdrawing water from modeled aquifers (site specific);
(g) Sufficient testing of the contaminants to characterize the nature of each pollutant,
concentrations at the source, and current migration patterns within the aquifer.
Such data for contaminant transport simulations should include:
(i) The horizontal and vertical extent of the contaminant plume(s).
(ii) Organic carbon content of soil or sediment.
(iii) History and mass loading or removal rates for contaminant sources and
sinks.
(iv) The presence of all known and potential receptors in the model domain.
(3) Develop hydrogeologic conceptual model
A hydrogeologic conceptual model is an interpretation or working description of the
characteristics and dynamics of the physical hydrogeologic system. Developing this conceptual
model is a critical step in the groundwater modeling process, for if the investigator incorrectly
conceptualizes the hydrogeologic environment, then groundwater model results will likewise be
incorrect and will produce invalid predictions.
The purpose of the hydrogeologic conceptual model is to consolidate site and regional geologic,
hydrogeologic and hydrologic data into a set of assumptions and concepts that can be evaluated
quantitatively. The components of the conceptual model, as described below, can be illustrated
using contour maps, cross sections, block diagrams, and channel networks. It is essential that the
uncertainty associated with each property or component of the conceptual model be
quantitatively estimated. (See LeGrand, 2004 for a more detailed description of the development
of a conceptual model for sites in the piedmont and mountain regions of North Carolina.)
(a) Geologic/Soil Framework
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The geologic framework describes the distribution, configuration, and physical structure
of underlying aquifers and confining units. Important factors to consider are the
thickness and continuity of aquifer/confining units, representative lithologies within
units, and the unit's geologic structure. The soil framework describes the various soils at
the particular site that overlay and merge into the geologic framework. For many types
of land application systems, the restrictive soil horizons (e.g., B soil horizon, a hard-pan
horizon) are equally important to document as the underlying geologic units.
(b) Hydrologic Framework
The hydrologic framework describes the movement of water and other fluids within the
geologic/soil framework. Factors to consider are:
(i) whether flow is primarily through porous media, fractures, or solution
cavities;
(ii) what hydraulic boundaries exist within the flow domain;
(iii) the horizontal and vertical hydraulic gradients within the system;
(iv) how the fluid potential or head is distributed and how it varies over time
(seasonally or otherwise);
(v) the rate and direction of predominant groundwater flow;
(vi) the locations of groundwater recharge and discharge areas;
(vii) the configuration of the groundwater flow lines and their tendency to
change over time;
(viii) the existence and stability of groundwater divides within the area;
(ix) the existence of a restrictive soil horizon that will impact the overall
vertical infiltration to the surficial groundwater table; and
(x) the existence of a semi-confined aquifer below the surficial aquifer that is
having a pronounced affect on the overall water movement, such as
vertical leakage into the semi-confined aquifer.
In the Piedmont and Mountain regions of the state, care should be given to how the
hydrologic framework is conceptualized and modeled because of the difficulties in
modeling fractured rock media. Typically, the subsurface may be conceptualized as a
shallow soil medium overlying a saprolite (decomposed bedrock) zone, followed by a
highly fractured bedrock transition zone, with an underlying less fractured bedrock zone.
The groundwater table may lie in any of these zones (or fluctuate between them)
depending on the site (See LeGrand, 2004; Daniel et al., 1997; and Harned and Daniel,
1992.). Special attention should be given to known underlying discrete faults, diabase
dikes, and other distinct geologic features that potentially have hydrologic significance.
(c) Hydraulic Properties
Hydraulic properties include the transmission and storage characteristics of the aquifer
system, such as transmissivity, hydraulic conductivity, storativity, and specific yield.
Field and laboratory measurements of these properties should be documented (along with
their uncertainties) and compared to accepted ranges for the medium under investigation.
An assessment of heterogeneity and anisotropy over the aquifer domain for each property
should be made, particularly in the Piedmont and Mountain regions of the state. The
Division’s document entitled Performance and Analysis of Aquifer Slug Tests and
Pumping Tests Policy should be referred to regarding the performance and analysis of
aquifer tests.
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(4) Merge hydrogeologic conceptual model into a groundwater predictive model
The hydrogeologic conceptual model should lead the investigator into selecting an appropriate
groundwater flow and/or transport model for demonstrating (through model prediction)
compliance with the seasonal high water table separation rules, any discharge areas to surface
waters, and with the groundwater standards (15A NCAC 02L .0202) at the compliance boundary
or receptor area. The modeling method selected may be simple to complex, depending on the
complexity of the hydrogeologic and soil framework. The Division’s document entitled
Groundwater Modeling Policy should be referred to regarding modeling details.
(5) Report hydrogeologic investigation results
All hydrogeologic investigation data should be clearly documented. Maps should clearly present
the layout of the site, showing all features including surface water bodies, property lines,
compliance boundaries, review boundaries, structures, subsurface borings, pumping and
observation wells. The general geologic setting should be described, as well as information
describing the current utilization of groundwater resources in the immediate area. All drilling
logs for exploratory borings should be provided, in addition to the available construction details
of any nearby wells. Geologic and hydrogeologic cross sections should be provided. Predictive
calculations for groundwater mounding and/or hydaulic breakout should be performed.
Descriptions of all aquifer testing data (elapsed time and concurrent drawdown measurements)
and analyses should be provided (see Performance and Analysis of Aquifer Slug Tests and
Pumping Tests Policy). Any information obtained from the US Geological Survey or other
agencies should be accurately referenced. The hydrogeologic investigation report must lead
smoothly and directly into the predictive calculations or modeling documentation, where the
appropriate conclusions are drawn regarding the regulatory minimum design requirements.
References
Daniel, C.C., III, Smith, D.G., and Eimers, J.L., Hydrogeology and Simulation of Ground-Water
Flow in the Thick Regolith-Fractured Crystalline Rock Aquifer System of Indian Creek Basin,
North Carolina, in Ground-water resources of the Piedmont-Blue Ridge Provinces of North
Carolina: U.S. Geological Survey Water-Supply Paper 2341–C, 1997.
Driscoll, Fletcher G., Groundwater and Wells, 2ndEdition, Johnson Division, St. Paul, MN, 1986.
Fetter, C.W., Contaminant Hydrogeology, Macmillan Publishing Co., New York, 1993.
Freeze, R. Allen and Cherry, John A., Groundwater, Prentice-Hall, Inc., Englewood Cliffs, New
Jersey, 1979.
Harned, D.A., and Daniel, C.C., III, The Transition Zone between Bedrock and Regolith:
Conduit for Contamination?, in Daniel, C.C., III, White, R.K., and Stone, P. A., eds., Ground
water in the Piedmont, Proceedings of a Conference on Ground Water in the Piedmont of the
Eastern United States, Charlotte, N.C., Oct. 16–18, 1989: Clemson, S.C., Clemson University, p.
336–348, 1992.
LeGrand, H.E. Sr., 2004, A Master Conceptual Model for Hydrogeologic Site Characterization
in the Piedmont and Mountain Region of North Carolina, NCDENR, Division of Water Quality,
Groundwater Section.

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