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ENGINEERING DIVISION

Other:

August"4, 1988

Mr. Stephen A. Alfred Town Manager Town of South Kingstown P. 0. Box 31 Wakefield, RI 02880-0031

Re: Rose Hill Landfill Environmental Protection Agency Ranking

Dear Mr. Alfred:

At your request, YWC, Inc. has reviewed the Hazard Ranking System (HRS) ranking conducted by the United States Environmental Protection Agency (EPA> of the Rose Hill Landfill located in South Kingstown, Rhode Island.

We are particularly concerned with the EPA's ranking of potential migration by the groundwater route which has resulted in an EPA proposed rule to place the Rose Hill Landfill on the National Priorities List (NPL). The proposed rule was published by the EPA in the Federal Register on June 24, 1988 (Volume 53, No. 122).

The major objective of the HRS, which was used to propose Rose H i l l for the NPL, is to determine the potential harm from sites on human health and the environment. One of the highest priorities is to determine the potential for contamination of drinking water supplies within a three mile radius of the site. YWC believes that the EPA has made an egregious error in its ranking of the relative potential harm from the Rose Hill Landfill by the groundwater route.

In fact, there appears to be no potential for contamination of the aquifers where public supply wells are located, and minimal potential for the contamination of the water supply of private dwellings. The EPA has totally ignored the hydrogeology of the area, and the fact that there are significant geologic barriers which isolate and protect those public water supplies provided by aquifers within the three mile radius of the Rose Hill Landfill. The remainder of this report describes the rationale for the conclusion of no potential for groundwater contamination of public supply well fields and most private wells, and recommendations as to how the HRS score should be revised. The following hydrogeological evaluation was developed by Dr. James C. Hall of the YWC Engineering Division staff.

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The conclusions of this investigation are based upon an analysis of the local and regional hydrogeology, which has identified both physical and hydraulic barriers to the transport of any potential contaminants from the Rose Hill Landfill to public water supply aquifers. As the following analysis will indicate, these barriers preclude the movement of contaminated groundwater towards the water supply well fields within the EPA-specified three mile radius.

LOCATION OF PUBLIC WATER SUPPLY WELLS

There are two groups of water supply wells located within three miles of the Rose Hill Landfill, and a third slightly beyond this range. Drawing 1 indicates the location of the well fields, aquifers, and groundwater divides. The University of Rhode Island wells are located almost three miles northwest of the landfill near Thirty Acre Pond.

The Kingstown Fire District wells are locatec about one half mile south, roughly half way between Thirty Acre Pcr:d and Larkin Pond. The Tuckertown Well Field (Wakefield Water Company) is located slightly more than three miles to the southwest in a swamp area.

GROUNDWATER FLOW CONSIDERATIONS - I

An examination of the existing and potential groundwater flow patterns is critical to the determination of contaminant transport pathways. These flow patterns have been examined with respect to:

• local groundwater flow patterns; • regional static groundwater hydraulics; and • regional, worst case groundwater hydraulics.

Figure 1 (Figure 4 from the 1985 NUS Inspection Report) provides a graphical presentation of the direction of local groundwater flow. This information indicates that groundwater in the surficial deposits flows "primarily southeasterly with some southwesterly flow" (NUS, 1985). Although some local "mounding" effects may be associated in the close proximity of the landfill, the general flow of groundwater appears to follow the surface drainage patterns (i.e., southeasterly to Mitchell Brook and southwesterly to the unnamed tributary of the Saugatucket River).

Next, it should be noted that all three of the referenced well fields are located at elevations greater than the elevation of the top of the landfill, and considerably greater than the elevation of the land and groundwater surrounding the landfill. The University of Rhode Island Well Field is located very close to Thirty Acre Pond, which has an elevation of 97 feet above mean sea level (msl). Presumably, the elevation of the groundwater in the vicinity is within a few feet of this elevation. The North Kingstown Fire District wells are at a somewhat higher elevation, but the elevation of the groundwater in the area is about 96 feet above msl, as these wells are very close to the Chipuxet River at that elevation. The static water level in the Tuckertown wells is at an elevation of about 100 feet above msl, as is shown by the proximity of a portion of the Great Swamp. The groundwater in

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the landfill is found at an elevation of about 58 to 60 feet above msl at its maximum elevation (NUS, 1985). Thus, it is impossible under static conditions, that water can flow from the vicinity of the landfill to any of the well fields.

Under pumping conditions, the best available information indicates that the various wells in question have maximum operating drawdowns of approximately 30 feet. Thus, at maximum operating drawdown, the minimum elevation of the water in the wells is expected to be on the order of 60 feet above msl. This is still slightly greater than the elevation of the groundwater in the vicinity of the landfill. Under the most reasonable extreme assumptions (absolutely no recharge, all of the pumped water coming from storage in a uniform circle around the wells), some 250 billion gallons of water would have to be pumped to lower the groundwater table to the point where it was level between the wells and the landfill. Given a user population of 15,000, the amount of water available is adequate for approximately 750 years prior to this condition being reached. It is concluded on the basis of groundwater hydrology alone that none of the well fields could be contaminated by the Rose Hill Landfill. This conclusion is in concurrence with that formulated by others (NUS, 1985), where it was noted that "The supply wells for the University of Rhode Island and the Kingstown Water Supply District are not likely to be impacted by this site due to their upgradientfr location." Thus, the location of the public water supply aquifers is such that an hydraulic barrier exists between them and any contaminant plumes from the Rose H i l l Landfill. Hence, their use in computation of "affected water supply source" cannot be justified.

The question of private water supply systems which may be affected by the leachate plume from the landfill must be addressed by examining the aquifers which are tapped by these wells. The following discussions examine these aquifers.

DESCRIPTION OF AQUIFERS

The aquifers in this region may be divided into four principle groups: the stratified drift in the vicinity of the landfill, the stratified drift in the Great Swamp/Worden Pond area in which the wells are located, the tills, and the bedrock.

The bedrock in this vicinity is a granite gneiss. While this formation locally produces small amounts of water for domestic wells, it is best characterized as being relatively impermeable and non-porous. The bedrock configuration in the area of interest consists of two pre-glacial valleys separated by a pre-glacial ridge (Kaye, 1960; Shafer, 1961a and 1961b), the approximate location of which is shown in Drawing 1. The valleys' floors are believed to be below sea level at the shoreline, and may be below sea level for a considerable distance inland, although not, apparently, in the gravel pit prior to landfilling) or the wells. The intervening bedrock ridge rises to over 200 feet above sea level in the vicinity of North Kingstown, sloping gently and more or less uniformly southward to the ocean. The lowest point in the area of concern appears to be on the divide east of the Tuckertown Wells at an elevation of 142 feet above msl. There are no known bedrock valleys crossing the ridge below the level of the stratified drift on either side anywhere in this vicinity.

The predominant till 1n this area is light colored till derived from the metamorphic rocks of the New England Uplands to the north and west, although there are small amounts of a dark till derived from the Pennsylvanian rocks of the Narragansett Basin found in the eastern part of the region. Morphogenetically, the tills may be divided into two groups: a lodgement till, with a thin layer of ablation till, commonly referred to as ground moraine, which mantles the bedrock in most places, particularly on the bedrock ridge (Tills A and B on Drawing 1), and ablation tills, which are found primarily in the Charlestown Moraine to the south of the Great Swamp region and the Point Judith Moraine found in the eastern part of the region (Till C on Drawing 1). The lodgement till is dense to extremely dense in places, and is "essentially impermeable" (Kaye, 1960). In places, this till is very nearly as hard as rock (ibid.) due to overcompaction by over riding ice, and may be expected to have extremely low permeabilities. Although it is possible that some recharge of the bedrock will occur through the t i l l , the rate would be extremely small. The till in the moraines is an ablation till, partly water washed, and can be expected to have a permeability probably two orders of magnitude greater than that of the ground moraine. Even so, the permeability of the Charlestown Moraine is small enough to support a natural hydrogeologic gradient approaching 100 feet per mile. The Charlestown Moraine diverts essentially all of the drainage in the Pawcatuck Valley (Great Swamp and tributaries) towards the west over a bedrock sill at afl t elevation of 84 feet, thus controlling the water levels in this basin to that elevation or greater. The Point Judith Moraine is so oriented that it is crossed by several streams reaching the sea, particularly the Saugatucket, and thus water levels and groundwater levels on the eastern side of the bedrock ridge are controlled by these streams and are considerably lower than the levels in the Great Swamp area.

The eastern stratified drift aquifer (Rose Hill Aquifer on Drawing 1) in which the landfill is located is defined more or less by the Point Judith Moraine to the east, the ocean to the south, gently rising ground moraines to the north, and the bedrock ridge noted earlier to the west. This aquifer is composed mostly (Shafer, 1961a) of kames, kame terraces, kame deltas, and similar water laid deposits, although there are some lake bottom sediments present as well. In general, the permeabilities are rather high. Water levels in this aquifer are controlled by the outlets to the sea and are in the range of 50 to 60 feet in the vicinity of the landfill, sloping with the rivers to the sea.

The Great Swamp aquifer consists mostly of fine sands, with some coarser materials locally, deposited in Glacial Lake Worden. This glacial lake was created by the impoundment of water between the bedrock ridge to the east, ice and bedrock ridges to the north and west, and the Charlestown Moraine to the south. The lake level was controlled throughout most of its existence by the bedrock spillway noted earlier at 84 feet above msl, although there may have been at least one higher outlet (Kaye, 1960), as there is some evidence of lake laid ice contact stratified drift at higher elevations. The lake was essentially filled with fine sand. The present higher elevations in the Great Swamp/Worden Pond area, and particularly those northward along the influent streams, arise from continued outwash over the lake sediments after lake filling, with more recent, coarser alluvial materials over that, establishing the stream gradients in the area. Isotatic rebound is also likely to have contributed to the present higher elevations. Very

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little material finer than fine sand has been reported in the area, except for the swamp deposits themselves. These are normally up to 10 feet thick, although rarely they may reach 25 feet. Worden Pond and the other ponds and various streams generally have bottoms directly on the fine sand of the body aquifer. The majority of the area, excepting only the area actually covered by swamps, has sand slightly coarsening upwards continuously to the surface (Kaye, 1960, personal observation 1981, 1982, 1983) with no vertical barriers to infiltration. The aquifer is believed to be highly homogeneous, with very sharp boundaries. Due to the very low surface gradients, it is likely that the vast majority of the precipitation infiltrates directly into the ground. This is also supported by the relative absence and disorganization of surface drainage over much of the area.

DESCRIPTION OF HYDROGEOLOGY

The hydrogeology of the region may be divided in much the same way as the aquifers. It should be noted that there is a natural bedrock ridge barrier between the Great Swamp aquifer and the Rose Hill Landfill which prevents the migration of groundwater from the landfill to the aquifer.

The groundwater in the bedrock/ground moraine region may be expected to follow the slope of the land surface in a general way. The source is locilfr infiltration, the flow amounts are small, and the discharge is predominantly to the east or west to the two stratified drift aquifers. There does not appear to be any possibility of cross flow through or under the bedrock ridge. Drawing 2 presents a cross section of the surficial geology in the landfill area.

The groundwater in the ablation moraines (Till C) flows slowly from the stratified drift aquifers behind them, particularly for the Charlestown Moraine, towards the ocean with a gradient in the case of the Charlestown Moraine of approximately 100 feet per mile. This is supported by the general decrease in elevation of the various kettle ponds within the moraine area as one progresses south. The amounts of flow are rather small, in spite of the gradient, due to the impermeability of the material. The dominant source of water is the stratified drift aquifers, with minor contributions from local infiltration, and the discharge is to the ocean to the south.

The groundwater flow in the eastern stratified drift aquifer, as evidenced by water levels in streams and ponds in the region, as well as by observations in the monitoring wells around the landfill (NUS, 1985), is to the south. There appears to be some disturbance of flow direction due to gravel mining operations adjacent to the landfill in the immediate vicinity of the landfill (NUS, 1985), but it seems unlikely that these disturbances extend more than 1,000 feet in any direction. The source of water for this aquifer is predominantly from local infiltration, with minor amounts from interflow and stream flow from the bedrock ridge to the west. The primary sink is the various streams crossing the Point Judith Moraine, with small amounts passing through the moraine itself. Water levels may reach as high as 70 feet in the northwest where this aquifer meets the bedrock ridge in the vicinity of North Kingstown.

The Great Swamp/Worden Pond aquifer is a highly uniform unit defined by the bedrock ridge to the east, bedrock hills to the north and west, and the Charlestown Moratne to the south. The general slope of the water table, as evidenced by streams, swamps, and ponds, is very gently to the west, with some southerly component near the Charlestown Moraine and in the northeast, following the gradient of the Chipuxet River. The surface drainage is entirely to the west; there is no surface flow across the Charlestown Moraine or the bedrock ridge. The predominant source of water for this aquifer is local infiltration, with minor amounts attributed to interflow and stream flow from the bedrock ridge to the east and streams from the north and west. The predominant outflow is to the Pawcatuck and thence to the west, with minor amounts passing through the Charlestown Moraine directly to the ocean. The elevation of the water in the aquifer ranges from about 84 feet near the outlet to greater than 100 feet on the eastern edge near the bedrock ridge.

CONCLUSIONS BASED ON STUDY OF THE GEOLOGY AND PUBLIC WATER SUPPLY WELLS

Based upon the review of the geology and hydrogeology in the region near the Rose H i l l Landfill, it was concluded that:

• the water levels in the public drinking water supply wells i-s higher than the groundwater in the vicinity of the landfill, even under maximum anticipated pumping conditions;

• the groundwater levels in the bedrock ridge separating the source aquifer from the aquifer in which the landfill is located are considerably higher than the levels in either the wells or the top of the landfill;

t the permeability of the bedrock/ground moraine system separating the two aquifers is several (perhaps as much as six) orders of magnitude less than the permeability of the aquifers themselves, resulting in an essentially impermeable barrier to groundwater flow regardless of gradient;

• the bedrock/ground moraine barrier is continuous from wells north of the study area to the ocean, and is higher than the stratified drift aquifers to either side at all points;

-• it would be virtually impossible for the public supply wells to be contaminated by the Rose Hill Landfill; and

t the HRS developed by the EPA should be revised to reflect the true potential for contamination by the groundwater route.

PRIVATE WATER SUPPLY WELLS

In addition to public supply wells, YWC reviewed the potential for contamination of private wells. The Town of South Kingstown located all of the houses in South Kingstown that are not served by public water supply. Figures 2A and 2B illustrate the locations of these houses in the northern and southern halves within a three mile radius of the landfill. The locations of the1private wells were categorized as follows:

• Wells to the west of Great Swamp Divide - 97. • Wells to the east of Rose H i l l Divide - 95. • Wells upgradient of Rose H i l l Landfill - 134. • Wells potentially down gradient of Rose H i l l Landfill - 5.

It is our opinion that only the down gradient wells could be impacted because of the bedrock divides or the location of upgradient wells. Further, it is not entirely clear that these wells are, indeed, down gradient of the landfill. However, because such a situation could exist under worst-case conditions, these wells were considered to be sited down gradient from the landfill.

PROPOSED RANKING OF ROSE HILL LANDFILL

YWC believes that the EPA HRS ranking should be changed to reflect the true potential for contaminant migration by the groundwater route. Attachment A includes copies of two of the significant HRS Work Sheets completed by the EPA (Figure 2 - Groundwater Route Work Sheet and Figure 10 - Work Sheet for Computing Sm).

Attachment B contains the same work sheets which were completed by YWC tofr reflect the true potential for contamination. With regard to the Groundwater Route Worksheet, YWC agrees with the^Qbserved Release_Score_of _4_5, the Waste Characteristic.s Scores..jQf_-To.xlcity/PersLsAence - 18. Hazardous Waste Quantity - 1, and the Target Score for Groundwater Use of 3. However, it is believed that the Target Score for Distance/Population should have been scored as 10, not 35, to reflect the true potential for contamination. The values for the distance to the nearest well (page 25 of HRS ranking in Attachment B) would be 4 as per the EPA ranking, but the population served score should have been 1. The score of 1 corresponds to a population range of 1 - 100. The EPA had given a score of 4,, corresponding to a population range of 3,001 - 10,000. The population estimated by the EPA was calculated as follows:

Population

• University of Rhode Island (URI) Wells = 4,350 • Kingstown District Supply Wells = 2,500 • Private Wells = 1,178

8,028

It is our opinion that the populations served by the URI and Kingstown Well Fields should not be included because there is no potential for contamination of these well fields as discussed earlier. We also believe that the total population should be reduced to five households or 19 people (5 x 3.8 = 19). The reduction in the population results in a Groundwater Route Score (Sqw) of 28.34 and a Migration Score (Sm) of 16.78. The Surface Water and Air Route Scores were not changed from the EPA scores.

CONCLUSIONS

In summary, we conclude that the Rose Hill Landfill has been ranked improperly because there is no potential for contamination of all public supply wells and most private wells within a three mile radius. This conclusion is based upon both the presence of significant groundwater barriers between the landfill and many of the wells, and the location of wells hydraulically upgradient of the landfill (even under pumping conditions). We believe that the Groundwater Route Score (Sqw) should be revised to 28.34, and that the Migration Score (Sm) should be revised to 16.78. The Rose Hill Landfill should not be proposed for placement on the NPL because the score as revised would be less than 28.5.

We would strongly urge that you submit this report to the EPA during the 60 day comment period. If you have any comments, please do not hesitate to contact me.

Very truly yours,

Keith E. Warner, P.E. Manager of Engineering

KEWrcgk

Attachments

cc: J. C. Hall, Ph.D., P.E. S. R. Kellogg, P.E. R. 0. Drake, Ph.D.

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ATTACHMENT A EPA GROUNDWATER ROUTE WORK SHEET EPA WORK SHEET FOR COMPUTING SM

Site Name: Rose Hill Regional Lanar'.lL Date: 9/15/87

Grouno water flout* wonc sneet

Auigned value MUIO* Rating factor Score .Circle Onei oner Score .S*̂ ,,

Q Ooaer»eo fl«i*aa« 0 @ i 45 3.1 «

if ooserved rateaae ia given • »cor* of 43. procoo to line Q. if ooaerved reteea* i* given a score of 0. sxoceoc to tine Q

31 flout* Cnaraet*nattea - 3.2 Ototn to Aquifer of 0 1 2 3 2 9 Concern

N*t Pr«cioitatton 0 1 2 3 1 3 Permeaoillty of tn* 0 1 2 3 1 3 Unaaturawd Zon*

Pnyaical Stat* 0 1 2 3 1 3 ' ^

Total flout* ChariKt*fiadca Score; 19

til Containment 0 1 2 3 1 3 3.3

ED Waat* Cnaract*nadca 3.4 Toxictty/P*r*iat*nc* 0 3 « 9 12 13(T§) 1 18 11 Hazareoua waat* 0 ( T ) 2 3 4 5 i 7 l i i 1 Quantity .

Tow Waat* CnaracMrtadea SCOT* 19 2t

3.3 Ground Water Ua« 0 1 2 (T) 3 9 1 Olatane* to N**r« 4 a i 10 1 35 40 ) 012 it n a24 30 32 (S) 40

Total Target* Scora 44 «•

G3 ifiln* Q i«4«, muittoiy Q] » Q « QJ 3 7 . 6 2 C if un« Q .« 0. muJttcly Qj * (2 « Q « OH 37.330 .

UJ Ol«id*un* (T) oy 37.330 and multHMy Oy 100 3gw« 65.62

F1QURI2 ' QROUNO WATER ROUTt WORK SHIIT

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Sice Name: Rose Hill Regional Land: Dace: 9/15/87

O/oun4v*tw Rout* Soor* 65.62 4305.98

Aeut* SCOT* (Stw) 6.30 3*}.

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FIQUM 10 WORKSHEET FOR COMPUTING 3M

ATTACHMENT B REVISED GROUNDWATER ROUTE WORK SHEET REVISED WORK SHEET FOR COMPUTING SM

G'OUi.c! .Vjiu.' Rouie

Ground water Route Score (Sgw)

Surface Water Route Soore (Ssw) £.10

Air Route Score (Sa) 0 0

gw

l/S2 + S2 + S2 * gw s^ Ja Z7.03

FIGURE 10 WORKSHEET FOR COMPUTING SM