HomeMy WebLinkAboutHEARTHFIRE PUD, 1ST FILING - FINAL - 31-95D - SUBMITTAL DOCUMENTS - ROUND 1 - STORMWATER-RELATED DOCUMENTSRichards Lake. While Vegetated filter strips can improve water
quality by removing nutrients, sediment, suspended solids, and
pesticides,they are most effective in he removal of sediment and
other suspended solids.
Upland vegetated filter strips will help, coupled with ponds and
wetland vegetation in controlling pollutant loadings into Richards
Lake. Grading and level spreaders can be used to create a uniformly
area that distributes runoff evenly across •the filter strip.
Excessive use of pesticides, fertilizers, and other chemical usage
should be avoided in vegetated filter strip areas.
Wetlands and Ponds
Wetlands can treat and contain surface water runoff pollutants and
decrease loadings to Richards Lake.
Wetlands are an ecotone - an edge habitat, a transition zone
between dry land and water, an environment that is neither clearly
terrestrial and clearly aquatic.
Wetlands may have various functions, one of the more important
functions is water quality improvement. Wetlands provide effective,
free treatment for many types of water pollution. Wetlands can
effectively remove or convert large quantities of pollutants from
such nonpoint sources such as urban runoff.
The existing ponds (existing on -site and created ponds adjacent to
the access road) will maintain a permanent pool of water and
temporarily store urban runoff until it is released at a controlled
rate. Suspended solids and various pollutants such as hydrocarbons
and heavy metals will settle out in the pond
Constructed wetlands (adjacent to the access road and 0.03 acres of
wetlands on the south edge of on exiting pond)) will stimulate
water quality improvement functions of existing wetlands to treat
and contain surface water runoff pollutants and decrease loadings
to Richards Lake.
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5.0 HEARTHFIRE PUD MITIGATION
Introduction
The Hearthfire mitigation measures were selected for the following
factors:
(1) Removal of a high percentage of total suspended solids (TSS) is
assumed to control heavy metals, phosphorus, and other
pollutants; and
(2) Analysis has shown that wetlands, ponds, and other infiltration
devices, can remove of a high percentage of TSS, provided that
they are designed and maintained properly (as discussed in
Section 4.0).
Practices
The following practices are described for the urban runoff from the
Hearthfire PUD.
The majority of the runoff from the Hearthfire PUD will be through
a complex of upland/wetland vegetated filter strips and an existing
pond, before the urban runoff enters Richards Lake. There will be
several outfall area from the Hearthfire PUD that will enter
directly into Richards Lake, that will be diffused by sand filters.
Upland Vegetated Filter Strips
Upland vegetated strips (such as lawns and vegetated open areas)
are effective for overland sheet flow, they do not provide
treatment for concentrated flows.
The purpose of upland vegetated filter strips is to remove sediment
and other pollutants from urban stormwater runoff by filtration,
deposition, infiltration, absorption, decomposition, and
volitization, thereby reducing the amount of pollutants entering
into wetlands and the associated on -site pond and into
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4.0 URBAN RUNOFF MANAGEMENT
Sound urban runoff management requires both structural and
nonstructural measures to be employed to mitigate potential adverse
impacts to adjacent water bodies.
Management measures which may accomplish such mitigation include:
(1) decrease the erosive potential of increased runoff volumes and
velocities associated with development -induced changes in
hydrology; and
(2) remove suspended solids and associated pollutants by entrained
by vegetation filter strips (upland lawns and open spaces and
wetland vegetation) and open water bodies such as ponds.
Adequate maintenance of vegetation filter strips and ponds during
construction, and after construction should be required.
Typical maintenance include:
(1) Inspection of the on -site ponds and adjacent water bodies (such
as Richards Lake) after every major storm event for during
construction activities (until the developments completed);
(2) Maintaining outfall areas in emergent vegetation (keeping woody
vegetation from invading);
(3) Removal of litter in outfall areas;
(4) Revegetation of eroded or killed vegetation areas;
(5) Periodic removal and replacement of filter media from
infiltration areas (infiltration trenches or ponds);
(6) Frequent jet -hosing or vacuuming of porous pavements or
concrete pavements;
(7) Periodic removal of accumulated sediments in outflow/inflow
devices to prevent failure due to clogging.
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Nutrients
The problems resulting from elevated levels of nutrients of
phosphorus and nitrogen (lawn fertilizers) are eutrophication and
depressed dissolved oxygen (DO) levels due to elevated
phytoplankton populations. Eutrophication- induced hypoxia and
anoxia may result in fish kills and destruction of benthic habitat
destruction. Surface algal scum, water discoloration, and releases
of toxins from sediments may also occur.
Road Salts
Road salts can be a major pollutant. Snow runoff may produce high
salt/chlorine concentrations at the bottom of ponds and lakes. This
condition is toxic to benthic organisms, and may prevent crucial
vertical spring mixing in Richards Lake.
Hydrocarbons
Petroleum hydrocarbons are derived from oil products, and the
source of most of such pollutants found in urban runoff is vehicle
engines that oil drip. Concentrations of petroleum -based
hydrocarbons are often high enough to cause mortalities in aquatic
organisms.
Heavy Metals
Heavy metals are typically found in urban runoff. Heavy metals may
consist of such metals as cadmium, chromium, lead, and zinc.
Heavy metals are of concern because of toxic effects on aquatic
life and potential groundwater contamination. High metal
concentrations may bioaccumulate in fish.
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3.0 URBANIZATION AND ITS IMPACTS
During the Hearthfire PUD urbanization process, previous vegetated
spaces will be converted to a land use that will increase areas of
impervious surface, that will result in increased runoff volumes
and pollutants loadings. Urbanization will result in changes to the
physical, chemical, and biological characteristics of the Richards
Lake watershed.
As the Hearthfire PUD development occurs, there will be changes to
the natural hydrology. Hydrologic and hydraulic changes will occur
in response to site clearing, grading, and the addition of
impervious surfaces and maintained landscapes. Most problematic
will be the greatly increased runoff volumes and the potential
sediment loadings to Richards Lake.
Hydrological changes to Richards Lake may be magnified after the
Hearthfire PUD construction is completed. Impervious surfaces, such
as roads, sidewalks, and rooftops, will result in an increased
runoff.
Urban development also causes an increase in pollutants. The
pollutants in urban areas vary widely, from common organic material
to highly toxic metals. Some pollutants, such as insecticides, road
salts, and fertilizers, are intentionally placed in an urban
environment. Other pollutants, including lead from automobile
exhaust and oil drippings from trucks and cars, are the indirect
result of urban activities.
The following discussion identifies the principal types of
pollutants found in urban runoff.
Sediment
Suspended sediments constitute the largest mass of pollutant
loadings to surface waters. Among the immediate adverse impacts of
high concentrations of increased sediment are increased turbidity,
reduced light penetration and decreases in submerged aquatic
vegetation, and impaired respiration of fish and aquatic
invertebrates. Heavy sediment deposition in low -velocity surface
waters may result in ,smothered benthic communities, changes in the
composition of bottom substrate, and degradation of aesthetic
value.
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2.0 MANAGEMENT MEASURES FOR THE HEARTHFIRE PUD
In the context of the Hearthf ire PUD "Management Measures" they
are defined as economically achievable measures to control the
addition of pollutants to Richards Lake. They reflect the greatest
degree of pollutant reduction achievable through the application of
the best available "nonpoint" pollution control practices,
technologies, processes, siting criteria, operating methods, or
other alternatives.
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HEARTHFIRE P.U.D.
RUNOFF
FIGURE 2
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DOTTED LINES REPRESENT 5-FOOT CONTOURS
NATIONAL GEODETIC VERTICAL DATUM OF 1929
THIS MAP COMPLIES WITH NATIONAL MAP ACCURACY STANDARDS
FOR SALE BY U. S. GEOLOGICAL SURVEY, DENVER, COLORADO 80225, OR RESTON, VIRGINIA 22092
A FOLDER DESCRIBING TOPOGRAPHIC MAPS AND SYMBOLS IS AVAILABLE ON REOUEST
VICINITY MAP
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II
URBAN RUNOFF MITIGATION
HEARTHFIRE VUD
FORT COLLINS, COLORADO
1.0 INTRODUCTION
The Hearthfire PUD is adjacent to Richards Lake in north Fort
Collins. It is located in the northwest corner of Section 30,
Township 8 North, Range 68 West (105 03108" west, longitude 40 38"
00" north). The City of Ft. Collins is concerned with the effects
of urban runoff into on -site wetlands and ultimately into Richards
Lake (Figure 1).
The purpose of this study is to discuss the effects urban runoff
from the Hearthfire PUD on Richards Lake and its associated
wetlands. Because impacts from the Hearthfire PUD to Richards Lake,
the structure of the mitigation is toward minimizing impacts, and
not catastrophic events, which the Hearthfire PUD would only be one
factor.
This document addresses urban runoff into on -site wetlands and/or
water quality of water into Richards Lake. A mitigation plan to
deal with negative impacts of urban runoff to the wetlands and
Richards Lake is provided.
Mitigation is first through impact avoidance, then impact
minimization, and finally through replication of the impacted area.
The Hearthfire realizes that avoidance is not realistic, and that
replication is impossible. Therefore the approach is through impact
minimization, and possibly, enhancement to Richards Lake through
its mitigation plan.
Most of the Hearthfire PUD runoff will be through an existing pond
and associated wetlands, and across fringing wetlands along
Richards Lake. There are several minor runoff points from the
Hearthfire PUD directly into Richards Lake (Figure 2).
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P
Mitiaation Plan For Upland Vegetated Filter Strips, Wetland and
Ponds
The Hearthfire PUD mitigation plan for upland vegetated filter
strips, wetlands, and ponds is as follows:
Urban runoff will be diffused, to some degree, across lawns and
vegetated open spaces, before it is then diffused across wetlands
into the on -site pond (Figure ). Runoff from the pond will, in -
turn, be diffused across another wetland before runoff enters into
Richards Lake (Figure ). Diffusion of runoff will act like
sheetflow runoff, therefore reducing flood flows and velocity of
runoff, which reduces erosion and increases sedimentation; and
modifies pollutants carried in urban runoff.
Sand Filters/Filtration Basins
There will be approximately to minor outfall sources from the
Hearthfire PUD into Richards Lake. Due to the outfall discharge for
each point it is proposed that sand filters or filtration basins be
placed at each outfall site.
Sand filters are a self-contained bed of sand to which the first
flush of runoff water is diverted. The runoff percolates through
the sand, where colloidal and particulate materials are strained
out by the cake of solids that forms, or is placed, on the surface
of the media. Water leaving the filter is collected in an
underground pipe, and is discharged into Richards Lake.A layer of
topsoil may be added to improve removal efficiency.
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