The Norfolk District believes it beneficial to the public
to provide seasonal Public Notices (PNs) regarding preceding precipitation
conditions for shallow groundwater well monitoring associated with wetland
determinations. The purpose of this PN
is to inform the public of relevant parts of our process, and our
interpretation and findings regarding current precipitation conditions in
portions of southeastern Virginia for the 2015 monitoring season. This is accomplished by our analysis of
several rainfall recording stations and our use of hydrology monitoring wells distributed
across the Hampton Roads region. For the upcoming monitoring season,
precipitation for Suffolk (Lake Kilby data) and Williamsburg have been within normal ranges as of
the end of March 2015. Given the current
and antecedent conditions at this time, the public has the option to
submit well data to the Corps for
consideration in its wetland determinations for the Suffolk (in proximity to Lake
Kilby) and Williamsburg, provided they comply with the guidance and standards
noted herein. However, for the Norfolk
area (Norfolk International Airport data) and Peninsula (Hampton [Joint Base
Langley-Eustis]) data) precipitation has been below or near the 30th
percentile (below normal range) for the timeframe of January through March, 2015.
Given the current and antecedent
conditions at this time, we conclude that groundwater well data alone may be
unreliable for wetland determinations in these areas this year.
Background
Wetlands are defined as "those areas that are inundated or
saturated by surface or groundwater at a frequency and duration sufficient to
support, and that under normal
circumstances do support, a prevalence of vegetation typically adapted for
life in saturated soil conditions"
(33 CFR 328.3(b)(emphasis added). Wetland
determinations typically entail observation of field indicators of wetland
vegetation, hydric (wetland) soils, and wetland hydrology.
Occasionally, property owners or their agents may elect
to install and monitor shallow groundwater wells for the late winter and spring
seasons to gather data about the levels and duration of groundwater (i.e.
saturated soil conditions) for particular areas to attempt to clarify the
limits of wetlands. There is no
requirement that well data be submitted to obtain confirmations of wetland delineations.
However, the Corps does consider
groundwater well data in its determinations if such data are collected in
accordance with proper well installation and monitoring standards and during
periods consistent with "normal circumstances" prior to and during
the monitoring period.
Any monitoring wells used to facilitate wetland hydrology
determinations should be installed and monitored in accordance with the guidelines
in Technical Standard for Water-Table
Monitoring of Potential Wetland Sites, ERDC-TN-WRAP-05-2.
Before we will consider well data for a specified site,
we require submittal and approval of a well monitoring plan, which includes a
review of the location and installation of the monitoring wells. In
addition, during the monitoring season (typically February through April), the
Corps' staff must be allowed periodic access to the particular sites and wells
without any prior notice to provide proper quality assurance.
When reviewing shallow groundwater well data in order to
determine whether normal circumstances for wetland hydrology are present, we
consider the amount and distribution of precipitation prior to the start of the
growing season (after leaf drop in the fall) and during the early growing
season. The U.S. Department of
Agriculture’s Natural Resource Conservation Service (NRCS) National Water and
Climate Center calculates normal precipitation ranges for each month (defined
as between the 30th and 70th percentiles of monthly precipitation totals) for NOAA’s
National Weather Service (NWS) stations throughout the United States. The information for Virginia is published in WETS tables
available from the NRCS.
2015 Precipitation
Methods to evaluate precipitation trends for wetland
delineation purposes are described in Accessing
and Using Meteorological Data to Evaluate Wetland Hydrology, ERDC TR-WRAP-00-1. Short-term
water-table monitoring data (i.e., <10 years) must be evaluated with
consideration of the amount and distribution of precipitation that fell prior
to the beginning of the growing season (but after leaf drop in the fall), which
is the groundwater recharge period. Although
we analyze all months after leaf drop, this timeframe is generally at least 3
months prior to the beginning of the growing season each year. Precipitation monthly totals for the 3 months
preceding this PN for Lake Kilby
and Williamsburg have been within normal ranges. However, precipitation monthly totals for
Norfolk and Langley have been
below the 30th percentile (below normal range) (summary data
attached). As with PNs on this topic issued for previous
years, this assessment only analyzes whether precipitation amounts for the
prior three months fall within the 30th to 70th percentiles for the start of
the growing season. As the growing
season progresses rainfall conditions will be similarly analyzed until full
leaf-out, generally around mid- to late April. Dry wells in a drier-than-typical rainfall
period and wet wells in a wetter-than-typical rainfall period are of limited
value in making definitive determinations regarding wetland hydrology.
This analysis is based on evaluation of precipitation
data for four WETS stations in southeastern Virginia (Norfolk, Lake Kilby, Langley
& Williamsburg). Rainfall trends
(e.g., percent of normal for different time periods) for the entire
Commonwealth are available from NWS’s Advanced Hydrologic Prediction Service, and
they correspond well with our more detailed analysis for Tidewater, Virginia. Lastly, water levels at shallow groundwater
reference well sites in southeastern Virginia that have been monitored for
several years are consistent with our interpretation of precipitation trends
detailed above. While groundwater levels
have risen to within 12 inches of the soil surface for most of the reference
wells as of early March, we cannot predict how long this condition will
continue. Precipitation trends control
this.
Regardless of precipitation conditions, we will continue
to make wetland determinations based on the field indicators of vegetation,
soils, and wetland hydrology described in the Regional Supplement to the Corps of
Engineers Wetland Delineation Manual: Atlantic
and Gulf Coastal Plain Region (version 2.0), the
Regional Supplement to the Corps of Engineers
Wetland Delineation Manual: Eastern Mountains and Piedmont Region (version 2.0), including use of Chapter 5 when appropriate, and
portions of the Corps of Engineers Wetlands Delineation
Manual (1987) that were not replaced
by the regional supplements.
Growing Season
Beginning and ending dates of the growing season are
needed in the event water-table monitoring data must be analyzed for wetland
hydrology determinations. The Regional Supplements
state that the growing season has begun and is ongoing in a given year when two
or more different non-evergreen vascular plant species growing on the site or
surrounding areas exhibit certain indicators of biological activity, or when
soil temperature measured at the 12-in. (30-cm) depth is 41 °F (5 °C) or
higher.
Soil temperature and plant activity are
both surrogates for estimating soil microbial activity which produces anaerobic
conditions in the soil that are characteristic of wetlands.
Several of
the indicators of plant biological activity signaling the start of the growing
season as described in the Regional Supplements were observed broadly across southeastern
Virginia by late February 2015.
A graph of soil temperature data collected at reference
sites in southeastern Virginia (Virginia Beach, Chesapeake, Hampton, York
County and Isle of Wight County) from mid-December 2014 to mid-March 2015 is attached. The data collected to date indicates soil
temperatures remained above 41 °F for the monitoring period except for a 23-day
period between 13 Feb and 08 March 2015 when 5 reference sites dropped below 41 °F for different amounts of
time (Virginia Beach [Back Bay] for 23 days, Isle of Wight [Wellington Park]
for 16 days, Virginia Beach [Stumpy Lake] for 15 days and Chesapeake [Oak Grove
& Su] for 10 days).
This PN does not relieve those that have constructed
wetland mitigation projects from monitoring hydrologic conditions. Monitoring should be conducted in accordance
with the associated permit, approved plan, or mitigation banking instrument. Credits will be released from mitigation banks
for those areas meeting all applicable performance standards, including hydrologic
criteria.
William T. Walker
Chief,
Regulatory Branch