March
3, 2010
Wetland Hydrology Determinations for the 2010
Monitoring Season
The Norfolk District believes it beneficial to the public to
provide seasonal notices regarding preceding precipitation conditions for
shallow ground water well monitoring associated with wetland
determinations. The purpose of this
notice is to inform the public of relevant parts of our process, and our
interpretation and findings regarding current precipitation conditions for the
2010 monitoring season.
From 2006-2009,
due to drier-than-typical precipitation leading into the growing season, we concluded
that groundwater well data alone were unreliable for wetland determinations. For this monitoring season, precipitation
for most of
Wetlands are defined as ''those areas that are inundated or
saturated by surface or ground water 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). 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 ground water (i.e. soil
saturation) for particular areas to attempt to clarify the limits of
wetlands. There is no requirement that
well data be submitted to obtain 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.
When
reviewing shallow ground water 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-Natural Resource Conservation Service National Water and
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.
Although we analyze all months after leaf fall, this timeframe is
generally at least 3 months prior to the beginning of the growing season
each year. Precipitation for the 3
months preceding this notice for most of
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 Interim Regional
Supplement to the Corps of Engineers Wetland Delineation Manual: Atlantic and Gulf Coastal Plain Region
(October 2008) (Regional Supplement)
for the Virginia Coastal Plain and the Corps of Engineers
Wetlands Delineation Manual (1987) (1987
Manual)
and appropriate regional supplements for the remainder of the state.
The publication
entitled Technical
Standard/or Water-Table Monitoring of Potential Wetland Sites (USACE 2005)
notes: "For many wetlands, water tables in a
given year may be affected by precipitation
that occurred in previous years, especially if monitoring occurs after an
extended period of drought or precipitation excess. After a series of dry years, for example, it
may take several years of normal or
above-normal rainfall to recharge groundwater and return water tables to normal
levels. Therefore, in
evaluating wetland hydrology based on short-term monitoring, it is necessary to
consider the normality of rainfall over a period of years
prior to the groundwater study. …".
The previous years (2006-2009) were determined by Norfolk District to
have drier-than-typical early growing seasons based
on similar analyses. The precipitation
that occurred in the late fall and winter of this season most likely have
recharged groundwater levels which decreased during the drier-than-typical conditions of 2006-2009.
Any monitoring
wells used to facilitate wetland hydrology determinations should be installed
in accordance with the guidelines in Technical
Standard for Water-Table Monitoring of Potential Wetland Sites, ERDC-TN-WRAP-05-2, U.S. Army Research and
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 late February through April), the Corps
must be allowed reasonable periodic checks without notice to provide proper
quality assurance.
This notice
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.
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 Supplement
states that the growing season has begun and is ongoing in a given year when
two or more different non-evergreen vascular plant species growing in the
wetland 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. Observations of soil temperatures and plant biological activity consistent with
the Regional Supplement at several sites in the Hampton Roads area indicate
that the growing season for this region of the state began this year during the
last week of February.
J.
Robert Hume, III
Chief, Regulatory Office