Supplemental Guide II-Delineations

Transcription

1 Supplemental Guide II-Delineations Contents Source Water Protection Area Delineation... 1 Delineation Criteria for Systems Using Groundwater Sources... 2 Time of Travel... 4 Flow Boundaries... 4 Delineation of Community Water Systems... 6 Delineation of Non-Community Non-Transient and Transient Water Systems... 6 Delineation Criteria for Systems Using Surface Water... 7 Watershed Delineation Area... 7 Zone of Critical Concern... 9 Zone of Peripheral Concern Ohio River Delineation Conjunctive Delineations for GWUDIs Source Water Protection Area Delineation Delineation is the process used to identify and map the recharge area that supplies water to the well or spring, or the drainage basin that supplies water to a surface water intake. This area is referred to as the Source Water Protection Area (SWPA). The size and shape of the SWPA depends on the characteristics of the aquifer, the well, and/or the watershed. It is within the SWPA that potential releases of contaminants could end up in the community's water supply. (Supplemental Guide III provides guidance for preparing a potential sources of significant contamination (PSSC) inventory.) Several methodologies exist for delineating a SWPA. The appropriate methodology for any system depends on the area geology, water source, water demand, and available resources such as data or funding. The WV Source Water Assessment and Protection (SWAP) Program has prepared SWPA delineations for most community water systems in the state. In general the delineations prepared by SWAP Program were intended for use in source water protection planning. The following provides details on SWPA delineation. A planning 1

2 team may decide that an enhanced delineation is needed for a specific system and may also refer to these methodologies. Delineation Criteria for Systems Using Groundwater Sources The main purposes for delineating a ground water Wellhead Protection Area (WHPA) are to provide a well field management area in which all PSSC can be identified and to reduce or eliminate the risk of contamination of public drinking water supplies posed by these sources. The delineation area provides protection for the area that supplies water to the well and distinguishes which areas warrant special protection (Figure 1). The shape of the delineated area varies depending on flow boundaries and gradient of the water table. The Environmental Engineering Division (EED) has assumed the responsibility to define the protection areas for each public water supply. The SWAP program is using the delineation techniques developed under the Wellhead Protection Program (WHPP) with the modification of adding fixed radius as a delineation technique. Techniques used to generate the WHPP were specially developed to fit the complexity of the State s geology, which includes unique features like as abandoned coal mine sources. No remote recharge areas are known in West Virginia. Due to the fact that West Virginia extends across six hydrogeologic environments, each with its own varied hydrogeologic settings, the selection of methods and criteria for delineating WHPA s in the state is complex. A map showing the six hydrogeologic environments found in West Virginia is shown in Figure 2 and is discussed below: Figure 1. WHPA Delineation Using Hydrogeologic Mapping 2

3 Alluvial Valleys Areas -consisting of geologically recent flood plains of the larger rivers. These flood plains contain unconfined, fine to coarse grained, slightly silty alluvium. Appalachian Plateau Province - consisting of nearly horizontal shales, sandstones and coals. The aquifers may be porous or slightly fractured. Folded Plateau Area - consisting of faulted blocks that contain either localizedconfined or localized unconfined aquifers, or lack of aquifers. The aquifers may be porous media or fractured rock. Karst Areas - consisting of water-soluble rocks such as Figure 2. Geologic Setting for Public Water Supplies of West Virginia limestone or dolostone with subterranean drainage underlying an area. A very complex regime. Valley and Ridge Province - consisting of complex faulted blocks that contain either localized-confined or localized unconfined aquifers, or lack of aquifers. The aquifers may be porous media or fractured rock. Coal Mine Areas - consisting of areas where deep coal mining has occurred. This practice has been extensive in parts of West Virginia, and underground mines can act as a ground water drain for all permeable rocks above them. Therefore, mines may store a large quantity of water or may deplete surrounding ground water for an entire area if the mine is draining freely. The first step in the delineation process is to determine the appropriate method(s) of delineations for each of the hydrogeologic environments. The following delineation criteria will be used in the development of the delineation zones for use in West Virginia s six hydrologic environments. 3

4 Time of Travel The minimum time of travel (TOT) to be applied for each water supply is five (5) years for all geologic settings. The five-year TOT, in some cases, will yield WHPA s with extremely large areas due to geologic anomalies, for example, karst areas involving major faults. In such cases, flow boundaries will be employed as the alternate criterion to delineate the WHPA. Flow Boundaries Flow boundaries are based on determining the locations of ground water divides and/or other physical/hydrologic features that control ground water flow. Flow boundaries are used to delineate the maximum potential zone of contribution to a well. The flow boundaries that will be used are topographic and local ground water divides for smaller aquifers, and regional ground water divides for large aquifers. The following EPA recommended delineation methods were selected to be used in the SWAP process. These delineation methods into three main types; fix-radius method, computer models, and hydrogeologic mapping. Figure 3. Computer Model and Fixed Radius for a WHPA Fixed Radius Method - This delineation method involves a circle of a specified radius drawn around a well or well field (Figure 3). The fixed radius is generally calculated based on volumetric flow (or well pumping rate), porosity of the aquifer, and well construction. Depending upon available data, certain constants can be used for these variables. This is an easy, fast and inexpensive way to determine the distance boundary. This type of delineation will only be used on the smaller systems consisting of the non-community non-transient and noncommunity transient systems in West Virginia on an interim basis Computer Models - There are many types of computer generated flow models for delineating SWAP areas. These models are based on mathematical assumption that an aquifer is a granular, porous material, like sand and gravel. Figure 3 is an example of a computer model for a delineated WHPA/SWAP area. 4

5 Analytical Modeling - This modeling technique solves ground water flow equations through simple, calculus-based mathematics, generating an exact mathematical solution for the unknown variable. Hydraulic head is usually the unknown at a given location. Analytical modeling simplifies the equation by assuming the aquifer is homogeneous and isotropic, and that flow is one or two dimensions. Results may be questionable when applied to a heterogeneous aquifer. Numerical Modeling -This technique can be used for modeling layered aquifers, partial penetrating wells and boundaries, variations of transmissivity and recharge, and a number of other scenarios that cannot be addressed by the analytical models. Numerical modeling capabilities are only relevant if the data is available. Hydrogeologic Mapping -This delineation method involves determining the flow boundaries for the area of interest and designating those boundaries as the SWAP area. An example would be the karst areas within Jefferson and Berkeley Counties, West Virginia. The karst areas are very vulnerable to contamination, because surface water enters the aquifer directly through numerous sinkholes. Since ground water travel times in area are fast, the flow direction is difficult to predict, and the aquifer is vulnerable, a regional delineation approach that encompasses the entire surficial and near surface karst is the most conservative and cost effective method. Figure 4 and Figure 5 are examples of Figure 4. WHPA Terminology: Karst using hydrogeologic mapping using flow boundaries to determine WHP/SWAP areas for karst and fractured zones. 5

6 Delineation of Community Water Systems In general community water systems will be delineated by one of the following WHPP methods. In some instances, such as for small community water systems, a fixed radius methodology may be used. Bedrock Wells - Hydrogeologic Mapping Karst Areas - Hydrogeologic Mapping Mine Areas - Hydrogeologic Mapping Alluvial Wells - Numerical or Analytical Mapping Delineation of Non-Community Non- Transient and Transient Water Systems Delineations will be performed by using an interim fixed radius for all Non-Community Non-Transient and Transient Public Water Systems. The radius will be determined based on a sliding scale (see below) based on pumping or estimated pumping capacity and Figure 5. WHPA Terminology: Fractured Rock other relevant information available. The WHPA s may be redone using a computer model later, if the necessary information is available or special needs for these systems arise. Table 1 presents the used to determine the distance of the radius: The reason that the interim fixed radius for the Non-Community Non-Transient and Transient systems is used is due to the general lack of information on the PWSS and well(s). Some systems may not have a well log or even know when the well was drilled or production rates. Pumpage from these systems is generally during a short period of the day with usually low rates. The analytical modeling method assumes a uniform 24-hour pumping period that results in a reduction of the size of the cone of depression. This draws more of the water from up gradient, thereby reducing the protection area and ultimately under-protecting the system. Therefore, a SWAP using the fixed radius approach may be more accurate and protective. Also, the EED budget and time constraints are issues that may not allow computer or hydrogeologic modeling delineations by the federal deadline. 6

7 Table 1: Scale used to delineate fix radius protection areas for non-community water systems. Pumping Capacity (Gallons per Day) Fixed Radius (Feet) <2,500 gpd 500 2,500 gpd - 5,000 gpd 750 5,000 gpd - 10,000 gpd ,000 gpd - 25,000 gpd 1500 >25,000 gpd Use Hydrogeologic and/or Analytical Mapping Delineation Note: In Karst or Flooded mine systems the interim fixed radius will be 2,000 feet for all pumping capacities; even equal to or less than 25,000 gpd. Delineation Criteria for Systems Using Surface Water The West Virginia SWAP program will utilize two types of delineations for West Virginia s intrastate waterways. These will consist of a broad Watershed Delineation Area (WSDA) and the detailed Zone of Critical Concern (ZCC) delineation. ORSANCO will conduct the delineations for the public water systems (PWS) along the Ohio River. Watershed Delineation Area The WSDA includes the entire watershed area upstream of the PWS s intake structure, up to the boundary of the state borders or a topographic boundary, and is the perimeter of the catchment that provides water to the water supply intake (Figure 6). This delineation will use the eight-digit and/or ten digit hydrologic cataloging units (HUC) based on the watershed network established by the United States Figure 6. Boundary of the Watershed Area Contributing to a WSDA and ZCC Geological Survey (USGS). An eightdigit HUC number is assigned to each of approximately 32 hydrologic units, known as watersheds, which make 7

8 up West Virginia (Figure 7). A smaller network within the eight-digit HUCs are the ten-digit HUCs, which are shown in Figure 8. A total of 344 hydrologic units make up the ten-digit HUCs in West Virginia. Some modification of the HUCs may be required due to the fact that the HUCs were not developed for SWAP and extend well downstream of the supply intakes. Figure 7. 8 Digit Hydrologic Units in West Virginia 8

9 Figure Digit Hydrologic Units in West Virginia Zone of Critical Concern The ZCC is a corridor along the stream, lake, or reservoir within the WSDA that warrants a more detailed inventory and management strategy due to its proximity to the source water and its susceptibility to potential contaminants. ZCC delineations will consist of the following: Free flowing streams within the WSDA will use the following configuration (Figure 6): -A width of 1000 feet on each bank of the principal stream and 500 feet on each bank of the tributaries draining into the principal stream. -A length along the source stream determined by a 5-hour time of travel (TOT) at an estimated 90 percent high flow rate, or up to the next upstream intake where it is available. If high flow rate data is not available to calculate the flow time then a 5-MPH flow rate will be used. The TOT approach facilitates advanced management of those stream reaches which are most critical to protecting 9

10 drinking water intakes from PSSC. This method also enhances delineations of surface water SWPAs by facilitating spill and other emergency response activities. This method calculates the TOT for flow in a stream between a drinking water intake and a point of PSSC upstream. It is the stream-flow TOT between these two points that provides the opportunity for managers to enhance protection from long-term PSSCs and to respond to a contamination event. The ZCC will also extend ¼ mile below the intake. Reservoirs or lakes within the WSDA will use the following standards: -A width of 1000 feet on each bank of the reservoir and 500 feet on each bank of the tributaries draining into the reservoir or lake. -Length along source stream - The free flowing stream segment will be delineated following the free flow stream procedure. If a lake or reservoir is encountered within the five-hour time of travel, the following delineation will be used. If the length of the lake/reservoir is less than or equal to the five hour calculated time of travel distance from the intake then the entire water body will be included. If the length of the lake/reservoir is greater than the calculated five-hour time of travel distance from the intake then the section of water body within the five-hour time of travel distance will be used to establish the ZCC Zone. This method was adapted from the EPA State Source Water Assessment and Protection Final Guidance, Zone of Peripheral Concern The ZPC for a public surface water supply source and for a public surface water influenced groundwater supply source is a corridor along streams within a watershed that warrants scrutiny due to its proximity to the surface water intake and the intake s susceptibility to potential contaminants within that corridor. The ZPC is determined using a mathematical model that accounts for stream flows, gradient and area topography. ZPC delineations will consist of the following: -A width of 1000 feet on each bank of the principal stream and 500 feet on each bank of the tributaries draining into the principal stream. The length of the zone of peripheral concern is based on an additional five-hour time-of-travel of water in the streams beyond the perimeter of the ZCC, which creates a protection zone of ten hours above the water intake (Figure 9). 10

11 Figure 9: Zone of Peripheral Concern extends beyond Zone of Critical Concern for a 10 hour time of travel. Ohio River Delineation ORSANCO will delineate the Ohio River and will use a tiered delineation system consisting of three protection zones for each Ohio River surface intake consisting of the following: Zone 1 - Zone of Critical Concern - The area adjacent to the Ohio River from 1/4 mile downstream of the intake to a distance of 25 miles (equivalent to a 5-hour time of travel) upstream or the next upstream intake. The lateral extent of this zone extends 1/4 mile on both sides of the river and major tributaries. Zone 2 - Zone of High Concern - All 14 digit hydrologic units adjacent to the Ohio River from a distance of 1/4 mile downstream of the intake up to a distance of 1/4 mile below the next upstream intake and all 14 digit hydrologic units adjacent to the major Ohio River tributaries a distance of 25 miles upstream or to the next upstream intake. At the time of development West Virginia did not have the 14 digit hydrologic units completed, therefore these zones were not be completed within West Virginia. Zone 3 - Source Water - The entire portion of the Ohio River Basin upstream of the surface intake. This is equivalent to the West Virginia WSDA for the intrastate waterways. 11

12 This method would be of greatest importance for drinking water utilities tapping rivers that receive municipal and industrial wastewater discharges. Water-quality flow models provide a means through which specific hydrologic, geographic, and water quality parameters can be used to estimate the travel time for a contaminant to reach a drinking-water intake and to estimate the level of contamination at that intake. Conjunctive Delineations for GWUDIs (Ground Water Under the Direct Influence of Surface Water) GWUDI wells are those that tap into a ground water source that is hydraulically connected to a surface water body. The SWAP guidance requires the watershed that contains the surface water that is impacting the well(s) to have a surface water delineation performed. In West Virginia, the State is in the process of determining PWS wells that are under the direct influence of surface water according to the Surface Water Treatment Rule. The state will make this determination by comparing selected physical parameters of water found in the wells with those of surface water in nearby streams. Using this information, West Virginia has developed a statewide standard for the GWUDI designation. If a PWS has been determined to be under the direct influence of surface water and its WHPA intersects a surface water body, that system will be required to do a surface delineation in addition to the ground water delineation (Figure 10). Figure 10. Conjunctive Delineation 12